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Abstract

Cardiac fibrosis is a pivotal cardiovascular disease (CVD) process and represents a notable health concern worldwide. While the complex mechanisms underlying CVD have been widely investigated, recent research has highlighted microRNA-21’s (miR-21) role in cardiac fibrosis pathogenesis. In this narrative review, we explore the molecular interactions, focusing on the role of miR-21 in contributing to cardiac fibrosis. Various signaling pathways, such as the RAAS, TGF-β, IL-6, IL-1, ERK, PI3K-Akt, and PTEN pathways, besides dysregulation in fibroblast activity, matrix metalloproteinases (MMPs), and tissue inhibitors of MMPs cause cardiac fibrosis. Besides, miR-21 in growth factor secretion, apoptosis, and endothelial-to-mesenchymal transition play crucial roles. miR-21 capacity regulatory function presents promising insights for cardiac fibrosis. Moreover, this review discusses numerous approaches to control miR-21 expression, including antisense oligonucleotides, anti-miR-21 compounds, and Notch signaling modulation, all novel methods of cardiac fibrosis inhibition. In summary, this narrative review aims to assess the molecular mechanisms of cardiac fibrosis and its essential miR-21 function.

Plain language summary

Unraveling cardiac fibrosis: insights into microRNA-21’s key role and promising approaches for control

Cardiac fibrosis poses a significant global health threat and plays a central role in cardiovascular diseases. This examination delves into recent research revealing the participation of microRNA-21 (MiR-21) in the progression of cardiac fibrosis, providing insight into its critical function in this process. The investigation explores diverse molecular interactions, underscoring MiR-21’s contribution to the development of cardiac fibrosis. Various signaling pathways, including the Renin-Angiotensin-Aldosterone System, TGF-β, IL-6, IL-1, ERK, PI3K-Akt, and PTEN pathways, coupled with disturbances in fibroblast activity, matrix metalloproteinases (MMPs), and tissue inhibitors of MMPs (TIMPs), contribute to cardiac fibrosis. MiR-21’s influence on growth factor secretion, apoptosis, and endothelial-to-mesenchymal transition further emphasizes its crucial role. What adds promise to MiR-21 is its capacity for regulation, providing potential insights into controlling cardiac fibrosis. The review also investigates various methods to modulate MiR-21 expression, such as antisense oligonucleotides, anti-miR-21 compounds, and Notch signaling modulation – innovative approaches showing potential in inhibiting cardiac fibrosis. In summary, this narrative review aims to dissect the complex molecular mechanisms behind cardiac fibrosis, explicitly emphasizing the indispensable role of MiR-21. By comprehending these mechanisms, researchers can lay the groundwork for inventive interventions and therapeutic strategies to hinder cardiac fibrosis, ultimately contributing to advancing cardiovascular health.

Keywords

cardiac fibrosis cardiovascular disease microRNA microRNA-21 miR-21 signaling pathways

Introduction

MicroRNAs (miRs) are non-coding RNAs pivotal in the regulation of gene expression by modulating target messenger RNAs’ (mRNAs) translational efficiency or stability.¹ miRs influence varied cellular processes and the tissue- and temporal-specific expression of miRs contributes significantly to protein synthesis,¹ while aberrant miR expression correlates with the pathogenesis of numerous diseases.^2–4 The miR-21, in comparison to other miRs, exhibits high expression levels and is the subject of extensive research.⁵ miR-21 is encoded within the 17q23.2 human genome locus, spanning 3433 nucleotides. miR-21 possesses its promoter sequence and is actively transcribed by RNA polymerase II despite residing within an intron. It is present extracellularly and intracellularly and can be detected across various body fluids associated with diverse molecular components.⁶

miRs exhibit a conserved pathway, with miR-21 function initially reported in 2004.⁷ All cells express miR-21 and play a role in crucial mediating processes. Research has shown that fluids are often identified as biomarkers for various diseases, such as heart disease and neoplasms.⁸ It has been demonstrated that miR-21 contributes to both oncogenic and non-oncogenic diseases through its interactions with several targets, such as programmed cell death 4 (PDCD4), tropomyosin 1 (TPM1), and phosphatase and tensin homolog (PTEN) being three notable targets of miR-21.^9–12

miR-21 exerts various effects in diverse diseases; its downregulation has been linked to increased cell death.⁸ In malignancies, miR-21 enhances cell migration, while among its inflammatory functions, it is notable for the upregulation of cytokine expression. Furthermore, in cardiovascular disease (CVD), miR-21 has been implicated in exacerbating cardiac fibrosis and hypertrophy.¹³ As a result of its crucial biological roles in oncogenic and non-oncogenic pathologies, miR-21 has been the subject of extensive therapeutic research.¹⁴ Corroboratively, miR-21’s involvement in CVD pathogenesis has been involved by mediating downstream target genes.¹⁵

CVD, encompassing pathologies such as ischemic heart disease, hypertensive heart disease, and hereditary cardiomyopathies, critically affects the cardiovascular system or heart. It is responsible for approximately 31% of all global mortality, standing as the leading cause of death worldwide, and is a significant inducer of cardiac fibrosis.^16–19 Endomyocardial fibrosis and ischemic heart disease are principal etiologies in the progression to advanced heart failure (HF).²⁰ Fibrosis is acknowledged as a contributing factor to both mortality and morbidity.¹⁶ Notably, fibrotic scars in the cardiac muscle happen post-myocardial infarction (MI), yet various conditions, including idiopathic dilated cardiomyopathy, diabetic cardiomyopathy, and hypertensive heart disease, enhance the risk of cardiac fibrosis.^21,22 Following cardiac injury, a considerable number of cardiomyocytes are lost due to necrosis, autophagy, or apoptosis.²³ The removal of necrotic and damaged cardiomyocytes occurs with monocyte recruitment, finally reducing cardiac muscle mass, resulting in HF and an associated increased risk of mortality and severe arrhythmia.²⁴ On the other hand, excessive left ventricle wall scarring is attributed to extensive fibroblast proliferation, which exacerbates cardiomyocyte remodeling following cardiac injury. miRs play significant roles in HF and left ventricular (LV) remodeling post-cardiac damage, primarily derived from fibroblast activity. Notably, there is a critical interaction between anti-fibrotic miRs, such as miR-19a, miR-19b, and miR-22, and pro-fibrotic miRs, including miR-9, miR-15, and miR-21.^24,25

Cardiac fibrosis in the myocardium, characterized as a scarring process, is distinguished by increased deposition of type I collagen and the differentiation and activation of cardiac fibroblasts (CF) into myofibroblasts.²² After cardiac injury, such as MI, fibrotic replacement occurs, with type I collagen predominantly resulting in scar tissue.^22,26 The fibrotic myocardium displays miR-21 overexpression, correlating with the severity of HF, and myofibroblast proliferation is reduced by miR-21 inhibition.^27,28 Hence, this article aims to describe the role of miR-21 in cardiac fibrosis and explore its therapeutic potential.

Regulatory mechanisms of miR-21

The human MIR21 gene encodes miR-21. Within the nucleus, it is transcribed by RNA polymerase II to produce the primary miR-21 transcript (pri-miR-21), which subsequently undergoes a precise two-step processing sequence to yield the mature miR-21. Initially, pri-miR-21 is cleaved into the approximately 72-nucleotide-long precursor miR-21 (pre-miR-21) in a stem-loop formation by the Drosha enzyme, integral to the RNA polymerase III complex.²⁹ The pre-miR-21 is then transported from the nucleus to the cytoplasm by Exportin-5, where it is further processed by another RNA polymerase III-associated enzyme, Dicer, generating a miR duplex. This duplex, characterized by considerable stability, is typically resistant to unwinding, leading to its degradation. On the other hand, the less stable miR strand can be unwound and, subsequently, incorporated into the RNA-induced silencing complex (RISC), culminating in the formation of an active miRISC complex. This complex is then implicated in modulating mRNA expression.^30,31

The miR-21 gene is immediately downstream of the vacuole membrane protein-1 (VMP1) gene, located within exon 10.³² The transcriptional modulation of miR-21 expression potentially involves an array of transcription factors, including signal transducer and activator of transcription 3 (STAT3), p53, serum response factor, nuclear factor I, CCAAT/enhancer-binding protein α (C/EBPα), Ets/PU.1, and activator protein 1 (AP-1), each of which may exert diverse influences.^33–36 Intriguingly, miR-21 expression is impacted by many regulatory signaling pathways, with distinct transcription factors. For example, AP-1-induced stimulation within 293FT cells can trigger miR-21 transcriptional activation, engaging PU.1 in this process. Conversely, C/EBPα and NFIB interaction appears to inhibit miR-21 expression, negatively influencing the interaction between Nuclear Factor I B (NFIB) and miR-21.³⁷

Moreover, the regulation of miR-21 expression is multifaceted, subject to modulation at both the transcriptional and post-transcriptional stages. Key regulatory agents such as bone morphogenetic protein 4 (BMP4) and transforming growth factor-β (TGF-β) serve to elevate miR-21 expression by facilitating the enhanced processing of pri-miR-21 transcripts through the action of the Drosha enzyme, underscoring a sophisticated layer of gene expression control.³⁸

Mechanism of cardiac fibrosis

Molecular mechanisms involved in cardiac fibrosis

Signaling pathways, including the renin-angiotensin-aldosterone system (RAAS), TGF-β, interleukins IL-6 and IL-1, extracellular signal-regulated kinases (ERK), phosphoinositide 3-kinases-Akt (PI3K-Akt), Smads, and PTEN, participate intricately in the progression of cardiac fibrosis, underscoring the complexity of this pathological process, which we discuss in this section.

Cardiac fibrosis is a multifaceted process containing a variety of components, notably CFs, myoblasts, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs).³⁹ CFs are predominantly implicated in synthesizing the extracellular matrix (ECM),⁴⁰ which increases myocardial thickening and consequently diminishes cardiac performance.⁴¹ MMPs, a critical enzyme, act in the degradation and subsequent remodeling of the ECM. TIMPs, as endogenous antagonists, increase MMP activity to reduce their activity; this interaction is crucial for the regulation of MMP function and for preserving the balance between ECM formation and its breakdown.³⁹ A dysregulated balance between TIMPs and MMPs leads to aberrant proteolytic activity, which not only disturbs ECM remodeling but is also associated with the progression and instability of atherosclerotic plaques within coronary arteries, in addition to resulting in post-MI and HF.⁴²

TGF-β signaling axis is essential in the fibrotic process in diverse tissues, including the myocardium.⁴³ Activating the TGF-β receptor results in the phosphorylation of Smad2 and 3 transcription factors, which then transmit the signal to the nucleus, consequently increasing gene transcription. In addition, TGF-β has the potential to initiate non-canonical signaling pathways, ultimately enhancing the transformation of fibroblasts into myofibroblasts.⁴⁴ Besides, TGF-β provokes the transdifferentiation of fibroblasts into myofibroblasts, which are notably proficient in ECM synthesis. Concurrently, TGF-β suppresses ECM formation and promotes fibroblast proliferation. About cardiac fibrosis, aberrant TGF-β signaling depositions increased collagen accumulation and fibrotic tissue remodeling. Furthermore, TGF-β potentiates the upregulation of type 1 angiotensin II (Ang II) receptors.⁴⁵ The TGF-β interaction between the RAAS, IL-6, and Smads is explained further.

Smad2 and 3 function as transcription factors downstream in the TGF-β signaling pathway, presenting similar amino acid sequences and structural but diverse roles in fibrosis and tissue repair.⁴⁴ Smad3 is a pivotal TGF-β signaling effector in tissue fibrosis and ECM synthesis, reducing Smad3’s downstream correlates with cardiac fibrosis mitigation, protecting diabetic mice from cardiac fibrosis, and increasing myocardial compliance.^46,47 Moreover, Smad3’s capacity to activate fibroblasts reduces myocardial collagen deposition within the heart, forming ECM.⁴⁸ Conversely, a deficiency in Smad3 may exacerbate the progression of cardiac fibrosis.⁴⁹ Moreover, evidence indicates that in fibroblasts, a Smad3-specific decrease, as opposed to Smad2, within the infarcted myocardium can markedly inhibit cardiac fibrosis development.⁵⁰ By contrast, activation of Smad2 occurs in TGF-β-stimulated myofibroblasts and fibroblasts within the infarcted myocardium, and a targeted Smad2 ablation in myofibroblasts may confer a temporary reduction in post-infarction remodeling.⁵⁰

Smad7 is a negative modulator of Smad2 and 3 activations, indicating its antagonistic role in TGF-β signaling, manifesting anti-fibrotic properties.⁵¹ In diabetic cardiomyopathy models, notably in rats, there is a noted decrease in Smad7 levels, and high glucose conditions exacerbate cardiac fibrosis, which can be reduced by elevated expression of Smad7.⁵² Correspondingly, reduced Smad7 expression correlated with upregulated TGF-β1 levels characterizes hypertensive rats with fibrotic tissue manifestations. However, Smad7 upregulation can block the progression of human CFs to myofibroblasts, diminishing cardiac fibrosis.⁵³ Moreover, the overexpression of Smad7 is observable in fibroblasts following MI, with the transition to myofibroblasts upon interactions with Smad3 signaling. Highlighted Smad7 expression can decrease the myofibroblast transformation and downregulate fibronectin and collagen type I synthesis, yet it does not affect collagen type III expression.⁵⁴

RAAS exacerbates cardiac fibrosis via Ang II, a vasoconstrictor known to provoke inflammation, oxidative stress, and subsequent activation of fibroblasts.⁵⁵ This peptide hormone is pivotal in initiating fibroblast proliferation and elevated collagen synthesis,⁵⁶ contributing to ECM formation within the myocardial tissue.⁵⁷ Furthermore, Ang II, akin to TGF-β, can induce cardiac hypertrophy and fibrosis; it also plays a role in stimulating the generation of TGF-β,⁵⁸ which includes facilitating Smad2 and Smad3 phosphorylation and, eventually, the translocation of the Smad complex into the cell nucleus. Ang II further amplifies the association of Smad2 and Smad3 with DNA upon mediation.⁵⁹

The RAAS pathway is necessary for mediating cardiac fibrosis, primarily through the TGFβ, a critical downstream signaling molecule of the Ang II/Angiotensin II receptor type 1 (AT1R) pathway. This pathway functions in paracrine or autocrine, consistently leading to fibrotic outcomes.⁶⁰ Upon binding to its receptors TGF-β receptor I and TGF-β receptor II, TGF-β promotes the activation of the Smad2/3 pathway, thus elevating the progression of cardiac fibrosis.⁶¹ The interaction of Ang II with AT1R results in fibrosis development. In addition, TGF-β activates CFs, contributing to cardiac remodeling and provoking alterations in the cardiac ECM, which are precursors to the development of HF.⁶²

IL-6 and IL-1 are pro-inflammatory cytokines essential to the pathogenesis of cardiac fibrosis.^63,64 These cytokines stimulate fibroblast activation, causing inflammation, ECM formation, and collagen deposition.^65,66 The interaction between the TGF-β pathway and IL-6 prompts a self-amplifying loop. TGF activity and expression can be increased by IL-6, which, reciprocally, can enhance IL-6 synthesis.⁶⁷ This synergistic interaction promotes fibrotic activities, thereby activating ECM synthesis and fibroblast activation. In addition, research has demonstrated increased IL-6 expression following Ang II infusion in murine cardiac models.⁶⁸

The ERK signaling pathway, a critical component of the mitogen-activated protein kinase (MAPK) pathway, involves many cellular processes, including fibrosis. ERK pathway upregulation in cardiac fibrosis elevates fibroblast activity, ECM formation, and myofibroblast activation. It also provokes inflammation and oxidative stress, exacerbating fibrosis.⁶⁹ Glycogen synthase kinase-3 alpha (GSK-3α) may influence the ERK pathway in fibroblasts. Investigations have revealed that GSK-3α regulates mitogen-activated protein kinase (MEK)-ERK activation, an essential profibrotic signaling pathway that interacts with the dysregulation of myocardium’s TGF-β1/Smad3 pathway. Downregulation of GSK-3α in cardiac injury maintains myocardial function and dimension fibrotic remodeling, with a noted particularity in fibroblasts.⁷⁰

The PI3K/Akt signaling pathway affects cellular proliferation, fibrosis, and survival.⁷¹ Activation of PI3K catalyzes Akt, which, in turn, modulates a spectrum of downstream effectors pivotal in fibrosis, including the key enzymes such as the mammalian target of rapamycin (mTOR)⁷² and GSK-3β, then impacts Smad3 stability, thereby controlling TGF-β pathway.⁷³ This signaling pathway is integrally associated with fibroblast activation, ECM production, and fibrotic tissue remodeling.^74,75 The TGF-β1 necessarily mediated the activation of ERK 1 and 2, Akt, and Smad3 to modulate factor Forkhead box protein O3a (FoxO3a), which acts as an inhibitor of cardiac myofibroblast transformation.⁷⁶ The tumor suppressor gene PTEN plays a functional role in cardiac fibrosis.⁷⁷ As a negative regulator of the PI3K-Akt pathway, PTEN contributes to tissue growth and preservation. Diminished PTEN expression or functionality can increase Akt activity, thus promoting fibroblast proliferation and ECM buildup and effectively serving as a catalyst for fibrotic progression.⁷⁸

In summary, cardiac fibrosis is produced by a complex network of molecular pathways, such as RAAS, TGF-β, interleukins, ERK, PI3K-Akt, Smads, and PTEN. These pathways collectively activate fibroblasts, stimulate ECM synthesis, and regulate MMP and TIMP balance, leading to myocardial stiffening and impaired function. Intervention in these pathways presents promising therapeutic strategies to treat HF progression and cardiac fibrosis (Figure 1).

Figure 1.

Molecular mechanisms involved in cardiac fibrosis.

Role of miR-21 in cardiac fibrosis

TGF-β pathway

TGF-β targets miR-21, leading to the transition of endothelial cells to mesenchymal cells (EndMT), a process delineated as occurring via the miR-21-mediated signaling pathway.^79,80 Elevated miR-21 expression under anoxic conditions through activating the TGF-β1/Smad-3 signaling pathway leads to the progression of cardiac fibrosis.⁸¹

TGF-β receptor III (TGFβRIII) exhibits a protective role against cardiac fibrosis.⁸² Investigations reveal a feedback loop involving TGFβRIII and miR-21; raised miR-21 levels prompt a decrease in TGFβRIII, which releases TGF-β1, thereby provoking miR-21 expression levels and maintaining fibrosis. This feedback mechanism drives collagen formation and ECM protein production, enhancing fibrotic changes. It concurrently elevates resistance to apoptosis and activation of fibroblasts during MI, whereas increased TGFβRIII expression mitigates collagen deposition by reducing Smad3 and TGF-β1 activities.⁸³

In the context of peritoneal macrophages, miR-21 levels increase post-phagocytosis of apoptotic cells, affecting inflammation.⁸⁴ Nanoparticle-facilitated delivery of miR-21 mimics to cardiac macrophages enhances myocardial remodeling post-MI through angiogenesis and an elevation in anti-inflammatory gene expression. Furthermore, in mice treated with miR-21, an increase in TGF-β activity and activation of caspase-3, alongside a reduction in collagen, was observed in the LV posterior wall myocardium, suggesting that increasing miR-21 expression in cardiac macrophages in the initial 3 days post-MI at the infarct site substantially affects disease progression, particularly in the remote myocardium, potentially enhancing an inflammatory macrophage phenotype switch at the site.⁸⁵ Besides, in human cardiomyocytes, in vitro, miR-21 upregulation induces a downregulation in cellular damage markers, as revealed by the decrease in TGF-β, catalase, phospho-NF-κB, Bax, and PDCD4. By contrast, the inhibition of miR-21 function prompts the initiation of inflammation and apoptosis.⁸⁶ The dose and timing-dependent nature of TGF-β’s damaging and reparative properties is noteworthy.⁸⁷

Furthermore, growth differentiation factor 15 (Gdf15), belonging to the TGF-β superfamily,⁸⁸ exercises an anti-hypertrophic regulatory function in the cardiac context, potentially via Smad2 and 3 enhancing, showing anti-hypertrophic effects. Nonetheless, the anti-hypertrophic effects of Gdf15 are reversed under conditions of Smad7 overexpression, implicating that miR-21 upregulation post-irradiation, by targeting and downregulating Smad7, prompts hypertrophy in cardiac tissues, thereby counteracting the Gdf15-driven opposition to hypertrophic responses.⁸⁹

CADM pathway

Post-MI, miR-21 exhibits elevated levels, with marked alternations in its expression within the infarcted zone.⁹⁰ miR-21 promotes cardiac fibrosis and fibroblast proliferation through the cell adhesion molecule (CADM) 1-STAT3 pathway. A pivotal role is attributed to both CADM1 and miR-21 in cardiac fibrosis. Moreover, miR-21 can drive CF proliferation via the regulatory mechanisms of the CADM1-STAT3 pathway, a process mediated by miR-21 through targeting of CADM1. The overexpression of miR-21 via the STAT3 signaling pathway increases cardiac fibrosis by reducing CADM1 expression. In addition, miR-21 can modulate CADM1 levels; a study showed the suppressive effect miR-21 on CADM1, thereby leading to the upregulation of STAT3 expression.²⁸

Notch pathway

The role of miR-21 is crucial in the Notch signaling pathways with TGF-b1 and overseeing the transformation of CFs to myofibroblasts (CMT).⁹¹ It is implicated in various diseases, including cardiac fibrosis, which features tissue fibrosis.^92,93 Notch signaling inhibition diminishes CMT while exacerbating myocardial fibrosis.⁹⁴ TGF-b1, under the influence of miR-21 and targeting Jagged1, declines its expression and activates the Notch signaling pathway. The effects of miR-21-mediated TGF-b1 include upregulation of CMT and increased invasion and proliferation of CFs. Likewise, in rat models, miR-21 targets Jagged1, which results in the augmentation of myocardial fibrosis !!!!⁹¹

Spry pathway

The Sprouty (Spry) family represents a negative fibroblast growth factor regulatory function.⁹⁵ Spry1 is a gene that inhibits the Ras/MEK/ERK pathway.⁹⁶ miR-21 targets Spry1 and, through its upregulation, inhibits Spry1, subsequently suppressing ERK-MAPKactivity.⁹⁷ This modulation significantly influences the secretion of growth factors, underlining fibroblast growth and TGF-β1 survival mechanisms. Overexpressed TGF-β1 decreases Spry1 expression levels, thereby enhancing both cardiac hypertrophy and interstitial fibrosis.⁹⁸ Moreover, miR-21, by targeting Spry1, provokes the Ang II-induced ERK activation feedback loop, which, in turn, increases TGF-β/Smad2/Smad3 activation. This process could elevate the maturation of miR-21, causing a positive regulatory loop.⁹⁵

PTEN pathway

PTEN functions as a phosphatase, dephosphorylating the secondary messenger generated by PI3K, thereby disrupting the downregulation of Akt activation as part of the critically regulated PTEN/PI3K/Akt process.⁹⁹ PTEN is acknowledged as one of the targets of miR-21,¹¹ but it is found that its activity is blocked by ischemic-reperfusion (IR)-induced miR-21. This blockage leads to Akt pathway activation and a concomitant increase in MMP-2 expression within the CFs of the infracted zone in IR-affected hearts.¹⁰⁰ Also, through the PTEN/MMP-2 signaling pathway, specific long noncoding RNAs (lncRNAs) have been identified that target miR-21, contributing to CF activation and fibrosis, causing cardiac fibrosis.¹⁰¹ miR-21, via the PTEN/Akt-dependent route, is implicated in TGF-β-stimulated endothelial-to-mesenchymal transition, facilitating an increase in fibrogenic transdifferentiation.¹⁰²

PDCD4 pathway

The tumor suppressor gene PDCD4, recognized as a miR-21 target, is essential in inhibiting tumorigenesis.^103,104 Its significant pro-inflammatory and apoptotic characteristics are revealed.^105,106 In cardiomyocytes subjected to oxidative stress, miR-21 exerts a negative regulatory control over PDCD4 expression, elucidating miR-21’s roles in anti-apoptosis and cellular protection.¹⁰⁷ In a negatively related process, miR-21-dependent targeting of Spry1 and PDCD4 is notable, particularly during the fibrogenic epithelial-to-mesenchymal transition of epicardial mesothelial cells, contributing to the development of fibroblast.¹⁰⁸ Furthermore, the lncRNA growth arrest-specific 5 (GAS5) has been identified as targeting miR-21, which mediates the PDCD4 levels, thereby playing a role in the apoptosis of cardiomyocytes induced by MI. By targeting PDCD4, miR-21 may lead to a direct downregulation of its level, modulating PTEN activity and inhibiting the PI3K/Akt signaling pathway.¹⁰⁹

Oncogene Bcl-2 pathway

Bcl-2, a target of miR-21,¹¹⁰ is assumed to be one of the main pathways of apoptosis regulation, and it is a potent suppressor of apoptosis in various types of cells, including CFs, vascular endothelial cells, and tumor cells.¹¹¹ In heart failure with preserved ejection fraction (HFpEF) rat models, MiR-21 enhances cardiac fibrosis by increasing the anti-apoptotic Bcl-2 in vitro and in vivo. MiR-21 diminishes the CF apoptosis, resulting in myocardial fibrosis and cardiac hypertrophy.¹¹²

Ajuba/Isl1 pathway

miR-21 is found to be targeting Ajuba and negatively regulating its expression in bone marrow mesenchymal stem cells (BMSCs).¹¹³ Therefore, miRNA-21 upregulation inhibits target Ajuba expression and enhances Isl1 expression to promote BMSC differentiation to cardiomyocyte-like cells. Ajuba also participates in establishing and maintaining cell–cell connections and supports cell division and migration. Cardiac Isl1-interacting protein via direct interaction with Isl1 represses its transcriptional activity¹¹⁴ and can inhibit the transition from cardiac hypertrophy to HF and cardiac fibrosis.¹¹⁵

Peroxisome proliferator-activated receptor alpha

MiR-21 directly targets and downregulates peroxisome proliferator-activated receptor alpha (PPARα) in LV cardiac tissue.¹¹⁶ Cardiomyocyte PPARα is critical for myocardial energy metabolism and homeostasis, and a deficit of cardiomyocyte PPARα is shown to hasten transverse aortic constriction-induced cardiac remodeling and contractile dysfunction. Moreover, both interstitial and myocardial fibrosis were escalated in transverse aortic constriction (TAC)-induced mice, in agreement with the elevated amount of collagen type I and III (Table 1; Figure 2).¹¹⁷

Table 1.

MiR-21 targets in cardiac fibrosis.

Author/year	Target	Regulation	Study type	Study sample	Effect	References
Zhang et al./2022	TGF-β1/Smad-3	Up	In vitro and in vivo	Acute myocardial infarction patients, H9C2 cells	miR-21 regulates TGF-β1/Smad3 expression	81
Guo et al./2020	Grem1, Clu, Gdf15, Ccl7, and Cxcl1	Up	In vitro	Irradiated rat CFs	miR-21 promotes fibrosis and G2/M blockade	89
Tao et al./2018	WWP-1	Down	In vivo	Atrial tissue, CFs	miR-21 and WWP-1 participate in the AF pathogenesis	118
Yang et al./2018	KBTBD7	Down	In vivo	Wild-type C57BL/6 mice	miR-21 inhibits inflammatory responses in the early phase of MI by targeting KBTBD7 and impairing MKK3/6 activation in immune cells	119
Zhou et al./2018	Jagged1	Down	In vivo	SD rats CFs	Cardiac fibroblast-to-myofibroblast transformation promotion	91
Pan et al./2018	TLR4	Down	In vitro	Ventricles of male SD rats	miR-21 inhibits the TLR4/NF-κB pathway	120
Yuan et al./2017	Smad7	Down	In vitro and in vivo	SD rats primary CFs, male C57BL/6 mice	Suppression of Smad7/Smad2/3 signaling pathway	90
Cao et al./2017	CADM1/STAT3	Down	In vitro	SD rats CFs, AF patients’ atrial tissue	miR-21 enhances cardiac fibrotic remodeling and fibroblast proliferation via CADM1/STAT3 pathway	92
Dong et al./2014	Bcl-2	Up	In vitro and in vivo	Adult male SD rats	Inhibiting the apoptosis of fibroblasts	112
Liu et al./2014	DUSP8	Down	In vitro	Male SD rats	miR-21-3p exaggerates STZ-induced diabetic cardiac fibrosis	121
Brønnum et al./2013	PDCD4	Down	In vitro	SD rats	Fibrogenic epithelial-to-mesenchymal transition promotion	108
Liang et al./2012	TGFβRIII	Down	In vitro	Male C57BL6 mice cardiac fibroblasts	Deposition of collagen and other ECM proteins involved in fibrosis	83
Roy et al./2009	PTEN	Down	In vivo	Male C57BL/6 mice, IR-insulted cardiac tissue	IR-induced miR-21 restricts PTEN function and triggers Akt pathway activation and MMP-2 expression increase in CFs of the infarct region of the IR heart.	100
Thum et al./2008	Spry1	Down	In vitro	Male C57/BL6 mice	Activation of ERK-MAPK activity utilizing SPRY1, which positively regulates cardiac fibroblast survival, leading to fibrosis, hypertrophy, and cardiac dysfunction	97

CADM1, cell adhesion molecule 1; CF, cardiac fibroblast; ECM, extracellular matrix; ERK, extracellular signal-regulated kinases; IR, ischemic-reperfusion; MAPK, mitogen-activated protein kinase; MI, myocardial infarction; miR-21, microRNA-21; PDCD4, programmed cell death 4; PTEN, phosphatase and tensin homolog; SD, Sprague-Dawley; STAT3, signal transducer and activator of transcription 3; TGF-β, transforming growth factor-β; TGFβRIII, TGF-β receptor III.

Figure 2.

Interplay between miR-21 and molecular pathways in cardiac fibrosis development.

Therapeutic implications

Potential use of miR-21 as a therapeutic target

MiR-21: A versatile therapeutic target in cardiac and pulmonary fibrosis

miR-21 has been investigated in cardiopulmonary diseases, including MI, pulmonary, and cardiac fibrosis. miR-21 has appeared as a potent pharmacological and genetic modification target in several diseases.¹¹⁴ Mouse and human research on cardiac fibrosis for miR-21 role organ fibrosis, which they discuss later, contains more direct data.

Lung fibrosis induced by bleomycin has shown a remarkable role of miR-21 in organ fibrosis. miR-21 substantially increases in idiopathic pulmonary fibrosis cases and mice with bleomycin-induced lung fibrosis.¹⁴ In fibrotic lungs, miR-21 is dominated by myofibroblasts. Also, fibroblasts around cancer tissues and colorectal cancer cells presented further miR-21.¹¹⁵

In 2008, the first research on miR-21 showed the potential impacts of miR-21 on HF therapeutic inhibition.⁹⁶ More studies have revealed overexpression of miR-21 in the CFs, mainly failing heart fibroblasts.^96,116–118 miR-21 blocking induces an apoptotic response in CFs, which is affected by RK-MAPK signaling. Also, miR-21 overexpression notably elevated the activation of ERK-MAPK, suggesting that miR-21 plays an essential role in the signaling mediator, vital for fibroblast activation and survival.¹¹⁹ A high level of miR-21 expression, by inhibiting Spry1, increased ERK-MAPK activity in HF fibroblasts. This process mediates the progress of cardiac hypertrophy and interstitial fibrosis. These data support the miR-21 function in the fibrotic process as a regulator in aortic stenosis cases in response to pressure excess and mention the miR-21 implication as a myocardial fibrosis biomarker.^96,120 In addition, Liu et al.¹²¹ have illustrated that the plasma level of miR-21 is significantly associated with LA fibrosis quantity by utilizing delayed enhancement MRI.

In conclusion, miR-21 is a potent therapeutic agent in cardiopulmonary diseases, such as fibrotic lung diseases and MI. Many studies have mentioned miR-21’s roles in fibrosis, especially in CFs, which are vital in signaling pathways. It has a promising function for controlling fibrosis due to many triggers, like cancer and pressure excess. Moreover, fibrosis severity is associated with miR-21 concentration, which suggests a promising biomarker.

MiR-21 is a promising diagnostic and therapeutic player in cardiac fibrosis and HF

Another investigation into the rats with cardiac overexpression of Rac1 showed an elevation in miR-21 expression in rats with spontaneous atrial fibrosis and AF, while Spry1 had decreased. Ang II activates Rac1, leading to lysyl and CTGF-oxidase-mediated miR-21 overexpression, which regulates structural atrial myocardium remodeling.¹²²

A study found that miR-21 is negatively associated with cardiac function in CHF patients compared to healthy controls and favorably related to myocardial remodeling. This information indicates that during CHF development, the miR-21 level may have a role in inflammation, suggesting its uses in management, severity assessment, and diagnosis.¹²³ Besides, AF has been revealed to be correlated with structural remodeling, like miR-21, lysyl oxidase, and connective tissue growth factor.^122,124 In addition, another study presents a positive correlation between AF recurrence and a high amount of miR-21.¹²⁵

An investigation explored HF prognosis and diagnosis in 80 HF cases and 40 healthy subjects by assessing circulating miR-21. The research showed that patients with HF presented a higher amount of miR-21, associated with prognosis, diagnosis, re-hospitalization rate, and HF severity. Moreover, the miR-21 level is related to brain natriuretic peptide levels and ejection fraction. Significantly, miR-21 effectively predicts HF re-hospitalization in the coronary sinus, indicating a potential cardiac failure biomarker.¹²⁶ Also, another study of cases of hypertensive heart disease revealed a correlation between the miR-21/PDCD4/AP-1 signaling pathway and TGF-1 synthesis. This study showed that higher miR-21 levels are associated with myocardial fibrosis positively.¹²⁷ These findings confirm miR’s therapeutic roles and prognostic effectiveness in CVD and support miR-21 as a disease target in HF and cardiac fibrosis.

To conclude, HF and cardiac fibrosis investigations showed various miR-21 roles. miR-21 is correlated with cardiac function, inflammation, and remodeling. miR-21 expression has illustrated potency in diagnosing and severity evaluation. miR-21 affects the essential signaling pathways, indicating its therapeutic potential in managing cardiac fibrosis (Tables 2 and 3).

Table 2.

Current cardiac fibrosis treatments.

Therapeutic strategy	Target pathway	Mechanism of action	Drugs (examples)	Advantages	Limitations/adverse effects	Study
Anti-fibrotic agents	TGF-β	TGF-β receptor blockers	Losartan, telmisartan, tranilast	Specific targeting, reduction of fibrosis, prevention of collagen deposition, reduction of inflammation	- Hypotension, renal dysfunction, hyperkalemia (in ACE inhibitors)	86, 128 –130
		Smad3 inhibitors	SB-431542, SIS3	Reduction of fibrosis, combination therapy, potential for reversibility	- Off-target effects on other TGF-β signaling pathways	131, 132
		Downregulating the production of growth factors and procollagens I and II	Pirfenidone	Reduction of fibrosis, reduction of inflammation, tolerability, combination therapy	- Nausea, rash, fatigue, gastrointestinal disturbances	133
	CTGF	CTGF-neutralizing antibodies	FG-3019	Specific targeting, reduction of fibrosis, combination therapy, potential for reversibility, reduction of inflammation	- Limited efficacy in advanced fibrosis	134
	MMPi	TIMP1	GM6001, Marimastat	Fibrosis regulation, reduction of scar formation, endogenous regulation, combination therapy, tolerability	- Off-target effects on other MMPs	44, 62, 135
		Promoted TIMP-1/2/3 and inhibited MMP-13 expression	Traditional Chinese medicine (Shenlijia)		NA	136
		Inhibiting p38 activation and MMP-9 expression	Lycopene		NA	137
		Attenuating titin proteolysis, myofilament lysis, and interstitial fibrosis	ONO-4817, Doxy		NA	138
Anti-inflammatory agents	NF-κB	NF-κB inhibitors	BAY 11-7082, TPCA-1	Reduction of inflammation, combination therapy, inhibition of fibrotic signaling	- Impaired host defense against infections (general immunosuppression)	139
		Steroidal anti-inflammatory drugs	Prednisone, dexamethasone	Reduction of inflammation, prevention of fibrosis progression, adjunct therapy	- Long-term use may lead to side effects like weight gain, osteoporosis	140
Epigenetics-based therapies	DNA methylation	DNA methyltransferase inhibitors	Azacytidine, decitabine	Epigenetic regulation, inhibition of fibrotic signaling, reduction of myofibroblast activation, reduction of inflammation, combination therapy	- Off-target DNA methylation changes, bone marrow suppression (in high doses)	141, 142
	Histone deacetylase (HDAC)	HDAC inhibitors	Mocetinostat, vorinostat, trichostatin A		- Non-selective inhibition may affect other cellular processes	143, 144
RAAS Inhibitors	Renin	Renin inhibitors	Aliskiren	Attenuation of fibrotic signaling, reduction of myocardial hypertrophy, combination therapy, reduction of inflammation	NA	145
	ACE	ACE inhibitors	Enalapril, lisinopril, captopril		- Cough, angioedema, hyperkalemia, hypotension	44, 146
	Angiotensin II receptor	ARB	Losartan, valsartan		- Hyperkalemia, hypotension, renal dysfunction	147 –149
	Aldosterone	Aldosterone antagonist	Spironolactone, eplerenone		- Hyperkalemia, gynecomastia (in spironolactone), menstrual irregularities (in spironolactone)	124, 150
Beta-blockers	Beta-adrenergic receptor	Beta-adrenergic receptor blocker	Carvedilol, metoprolol	Inhibition of fibrotic signaling, reduction of myocardial hypertrophy, anti-arrhythmic effects, reduction of sympathetic tone	- Bradycardia, hypotension, bronchospasm (in non-selective blockers)	151
Biomaterials	Porcine decellularized myocardial matrix hydrogel	Myocardial matrix hydrogel	Porcine decellularized, alginate, polyester-VEG	Delivery of therapeutic agents, promotion of tissue repair and regeneration, reduction of inflammation, customization		152 –156
Cell transplantation	Mesenchymal stem/stromal cells		MSCs	Regeneration of cardiac tissue, angiogenesis, personalized medicine	- Risk of uncontrolled cell differentiation, potential tumorigenicity	157 –159
Immunotherapy	CAR-T cell therapy		CAR-T cells	Targeted cell depletion, reduction of inflammation, synergistic effects with anti-fibrotic therapies, personalized medicine	- Cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome (ICANS)	160, 161

CAR-T cell, chimeric antigen receptor T cell; Doxy, doxycycline; MMP, matrix metalloproteinase; MMPi, matrix metalloproteinase inhibitor; MSC, mesenchymal stem cell; RAAS, renin–angiotensin–aldosterone system; TGF-β, transforming growth factor-β; TIMP, tissue inhibitors of metalloproteinase.

Table 3.

miR-21 associated anti-fibrosis treatment strategies.

Study	Study sample	Potential therapeutic agent	Mechanism of action	Outcome
He et al.¹⁴²	Male New Zealand rabbits	miR-21 inhibitor lentiviral vectors	Inhibition of miR-21 expression	Inhibit myocardial fibrosis by upregulating Smad7 expression
Cheng et al.¹⁴³	Male Kunming mice, cultured cardiac fibroblasts	Celastrol	Inhibition of miR-21/ERK activation by downregulating the TGF-β1 signaling pathway	Amelioration of myocardial fibrosis and cardiac dysfunction
Rana et al.¹²⁵	Male SD rats	AST-120	Modulating the expression of miR-21 and miR-29b, through inhibition of the angiotensin and TGF-β1 pathway	Attenuating cardiac fibrosis in MI rats with CKD
Nonaka et al.⁸⁰	Male C57BL/6 mice, human serum sample	LNA-anti-miR-21	Not mentioned	Reduction of cardiac fibrosis and inflammatory response in chronic Chagas cardiomyopathy
Li et al.¹⁷²	Type 2 diabetic mouse model, rat cardiac myoblast H9c2 cells	Vildagliptin	Inhibiting the expression of miR-21 and activating the SPRY1/ERK/mTOR pathway	Enhancing cardiac function by restoring autophagy and alleviating fibrosis
Tao et al.¹⁰¹	Adult male SD rats	LncRNA GAS5	Regulating the miR-21 leads to altered MMP-2 expression by influencing PTEN pathway	Suppress cardiac fibrosis via negative regulation of miR-21
Zhang et al.²⁰⁵	Male SD rats	Doxycycline	Altering PTEN/PI3K signaling pathway by reducing miR-21 expression	Attenuating CIH-induced atrial fibrosis
Dong et al.²⁰¹	Male Kunming mice	UA	Inhibiting miR-21/ERK signaling pathways	Inhibiting myocardial fibrosis both in vitro and in vivo
Huang et al.²⁰³	Male SD rats	S3I-201	Inhibition of miR-21 leads to decreased STAT3 activation	Ameliorating atrial fibrosis and preventing inducible AF

No limitations or adverse effects have been reported to date, as the available studies primarily consist of animal experiments or in vitro investigations.

ERK, extracellular signal-regulated kinases; GAS5, growth arrest-specific 5; MMP, matrix metalloproteinase; mTOR, mammalian target of rapamycin; MI, myocardial infarction; miR-21, microRNA-21; PI3K, phosphoinositide 3-kinases; PTEN, phosphatase and tensin homolog; SD, Sprague-Dawley; STAT3, signal transducer and activator of transcription 3; TGF-β, transforming growth factor-β.

Strategies to Regulate miR-21 Expression

miR-21 dysregulation is crucial in cardiac fibrosis and is associated with excessive ECM deposition and fibroblast activation. Targeting miR-21 is a practical approach to reduce cardiac fibrosis, and its associated complications have generated considerable interest. Several methods for modulating miR-21 expression levels have been explored, including inhibiting its function, promoting its downregulation, and emulating its suppression.^80,162–168 This section discusses the diverse methods examined to regulate miR-21 expression and their potential implications in cardiac fibrosis.

LncRNA-MiR interplay in controlling miR-21: Potential therapeutic strategies

Current research has illustrated that lncRNAs bind to miRs and control their role as molecular sponges, suggesting an inverse relation between miR and lncRNA expression.^169,170 Cardiac damage is not prevented by therapy with the 8-mer anti-miR-21 in the LV pressure overload mouse model. For long-term miR-21 suppression, it may be better to utilize lengthier anti-miRs due to treatment duration and potency in vivo. Short 8-mer LNA-modified oligonucleotides have no benefits in management and are less effective against miR-21. 15- and 22-nucleotide-long anti-miR-21 oligonucleotides are predominately specific for preventing pulmonary and cardiac fibrosis.^14,171

Innovative approaches for miR-21 regulation

GAS5 has been recognized in many cancers as a tumor suppressor and has even been related to fibrosis disease.¹⁷² Complementary region of GAS5 with miR-21 in the RISC may block miR-21 expression.¹⁷³ Furthermore, another investigation showed that in cardiac fibrosis and fibroblasts, miR-21 expression was elevated while GAS5 expression was decreased. CF activation is inhibited by GAS5 upregulation; however, GAS5-4 silencing enhances CF proliferation. Their research suggests that GAS5 may function by regulating miR-21 in cardiac fibrosis progression.¹⁰⁰

Isoflurane saves many organs from I/R harm. miR-21 and emulsified isoflurane (EI) were found to play roles in myocardial I/R damage. In mice, treatment with EI by suppressing fibrosis and prompting cardiac function diminished myocardial I/R damage. EI impact on the miR-21 and inhibit it. Besides, in mice, myocardial I/R damage is improved by EI therapy by targeting miR-21 with phosphoprotein-1. This study may show a novel treatment of myocardial I/R injury.¹⁷⁴

Ursolic acid (UA), a TGF-1 inhibitor in human fibroblasts, inhibits the formation of collagen.¹⁷⁵ In myocardial fibroblasts, management with UA showed that the dose-dependent decrease in P-ERK/ERK and miR-21 was relative to the healthy control in vitro and in vivo. The UA impact on cardiac fibrosis can be due to the capacity to block miR-21/ERK signaling pathways.¹⁶⁶ miR-21/ERK signaling process to prevent myocardial fibrosis may illustrate a potential treatment approach. Celastrol alleviates cardiac dysfunction and fibrosis, which in vitro and in vivo are probably correlated with miR-21/ERK signaling. Celastrol inhibits CF fibrosis and proliferation by inhibiting miR-21 expression and MAPK/ERK signaling. These data indicate that celastrol is a prospective therapy approach to prevent cardiac fibrosis.^176–180

Overall, miR-21 approaches for modulating avenues for addressing cardiac fibrosis. GAS5, as a miR-21 regulator, proposes a prevention mechanism for cardiac fibrosis advance. Besides, by targeting miR-21, EI illustrated functions in mitigating myocardial I/R injury. UA may inhibit miR-21/ERK signaling, leading to stopping cardiac fibrosis. Furthermore, another prospective therapy, celastrol, plays a role in inhibiting MAPK/ERK signaling and miR-21 expression.

Innovative miR-21 control methods

AST-120, an oral intestinal sorbent, decreases miR-21 expression, cardiac fibrosis, and serum uremic toxins. Another also showed therapy with AST-120 and miR-21 antisense oligonucleotides revealed that miR-21 is a potent therapy for cardiorenal syndrome.^117,168 Kolling et al.¹⁴⁹ illustrated that in diabetic nephropathy-affected rats, blocking miR-21 impacts various functional and structural variables. In renal fibrosis management, anti-miR-21 compounds can suggest practical applications in treating other organ fibrosis like heart. Moreover, a study by Zhou et al.⁹¹ utilized a miR-21 sponge to stop TGF-1’s suppression of Jagged1 mRNA, inhibit rat CF transformation into myofibroblasts, and eliminate protein expression. Furthermore, on rat cerebrospinal fluid, miR-21 sponges’ impacts were reversed by small interfering RNA-mediated Jagged1 suppression. In MI model rodents, cardiac fibrosis and heart dysfunction are ameliorated partially by the miR-21 sponge in vivo, while Jagged1 knockdown worsens these circumstances.

Notch signaling pathways such as scleroderma, cardiac, liver, kidney, and pulmonary are related to tissue fibrosis in some diseases. Jagged1, a Notch ligand in malignant breast cells, is a direct miR-21 ligand.^28,91,92,178. Dey et al.¹⁴⁷ revealed that TGF-β-stimulated collagen and fibronectin are prevented by miR-21 Sponge. Mammalian target of rapamycin complex 1 (mTORC) expression, constitutively active Akt kinase, and PTEN suppression reversed miR-21 contributed TGFβ inhibition, which induced collagen and fibronectin expression. To initiate a non-canonical signaling circuit by targeting PTEN, TGF-β interferes with miR-21. Akt/mTORC1 for this process leads to matrix protein production and mesangial cell hypertrophy.

In summary, miR-21 regulation strategies hold the potential to prevent cardiac fibrosis. AST-120 and miR-21 antisense oligonucleotides in addressing cardiorenal syndrome reveal effective therapeutic outcomes. Anti-miR-21 suggests valuable applications for fibrosis treatment in diverse organs, like the heart. Notch signaling and miR-21 sponges, particularly Jagged1, present a promising capacity for therapy. These methods indicate more potent management against cardiac fibrosis.

Targeting MiR-21 in cardiac fibrosis: Multifaceted signaling pathways

A study found that miR-21 suppression blocks cardiac remodeling induced by hypertrophic stimulation with contributing TGF, AP-1, and PDCD4 signaling pathways. One of the main MiR-21 targets is PDCD4, whose expression level is remarkably TAC and Ang II-infused mice comparable to the control group. Also, the transcriptional TGF-1 and AP-1 transcriptional expression levels downregulated PDCD4 targets and were elevated in TAC and Ang II-infused mice. In addition, a miR-21 inhibitor diminished PDCD4 downregulation induced by Ang II in vitro in neonatal rat cardiomyocytes, which play a role in the AP-1/TGF-1 signaling pathway inactivation.¹²⁷

miR-21 can induce inflammation-related atrial fibrosis by activating the STAT3 pathway. Using an antagomiR to block miR-21 in rodents diminished phosphorylation fibrosis-related gene expression. Besides, in AF cases, a second signaling pathway implicates the Smad7 downregulation, a TGF-1 pathway inhibitor. miR-21 blocking reduced collagen type I and III and raised Smad7 (a direct miR-21 target) production in vivo.^125,162 Furthermore, a STAT3 inhibitor downregulates miR-21, which decreases atrial fibrillation vulnerability, atrial fibrosis, atrial conduction inhomogeneity, α-smooth muscle actin, and collagen type 1 and 3. AntagomiR-21 diminishes atrial fibrillation, atrial remodeling, sterile pericarditis-induced inhomogeneous conduction, and STAT3 phosphorylation. Also, antagomiR-21 decreases STAT3 phosphorylation and activation of CFs by IL-6.¹⁶⁷ Also, to block cardiac remodeling by decreasing miR-21 expression may block contained TGF-1, AP-1, and PDCD4 signaling pathways.¹²⁷

To summarize, strategies to regulate miR-21 expression offer promise in stopping cardiac fibrosis. miR-21 downregulation, such as PDCD4, AP-1, and TGF-1 signaling pathways, may block the process and cardiac remodeling. In addition, in decreasing inflammation-related atrial fibrosis, miR-21 inhibition has been demonstrated via the STAT3 pathway. It shows the prospect of mitigating AF and related structural alternations. These data highlight the efficacy of miR-21 in cardiac fibrosis.

Discussion

The involvement of miR-21 in cardiac fibrosis has attracted considerable interest owing to its control over fibroblast activation and excessive deposition of ECM. It looks like targeting miR-21 expression could be a good way to treat heart fibrosis and the problems that come with it, but putting these ideas into practice in the real world is complicated. This discussion explores the therapeutic possibilities of modulating miR-21, namely by employing antagomiR-21, and addresses the accompanying constraints.

As mentioned before, numerous studies have demonstrated that miR-21 suppression may reduce heart fibrosis, reducing pathological remodeling. In contrast with other studies, Schneider et al.²⁰⁴ and Yuan and Fu¹⁹⁹ found greater miR-21 levels and better cardiac function and damage outcomes. These contrasting findings highlight miR-21’s intricacy in cardiac pathophysiology and the need to understand its context-dependent effects. More study is needed to explain these contradictory findings and determine miR-21’s role in cardiac fibrosis, enabling more focused therapies.^174,180

However, antagomiR-21, developed to block the function of miR-21, is being considered a promising treatment for addressing cardiac fibrosis. AntagomiR-21 disrupts profibrotic signaling pathways by antagonizing miR-21, leading to decreased fibroblast activation and reduced collagen deposition in the myocardium.^96,181 Although there have been advancements in the research and therapeutic potential of antagomir medicines, there are still several problems that need to be addressed.

A difficulty is to minimize the possible off-target effects of antagomirs while still controlling any undesirable on-target effects that might be problematic. For instance, miR-21 exhibits non-specificity toward organs or cell types and performs varied roles based on the specific organ or condition.¹⁸² Despite targeting miR-21 in the kidney may have unintended effects in one organ, such as the heart. AntagomiR-21 therapy may benefit cardiomyocytes but harm endothelial cells in the same organ. Careful dose-regulation studies must establish the ideal dosage to prevent off-target effects.^168,183 However, translating antagomiR-21 treatment from preclinical to clinical trials is difficult. One important worry is that antagomiR-21 may interact with unanticipated molecular targets, causing unexpected biological effects.

Hepatotoxicity is another major safety issue linked to the systemic use of antagomiR-21.^184–186 Due to its role in drug metabolism and clearance, the liver is very vulnerable to the buildup of antagomiR-21 molecules, leading to hepatotoxic consequences.¹⁸⁷ Hepatotoxicity can be reduced by finding the best dosing schedules, using delivery methods that are designed to work with the liver, and keeping an eye on liver function measures during clinical studies.

Another important factor to consider is the possible effect of antagomiR-21 treatment on other miRs and cellular functions. AntagomiR-21 is meant to target miR-21 but may also impact the expression or function of other miRs in the cell, causing off-target effects and undesired biological outcomes. It is crucial to comprehend the wider impacts of antagomiR-21 treatment on the miR profile to anticipate and reduce any off-target interactions.^188,189

Moreover, the effectiveness of antagomiR-21 in therapy may differ across various patient groups, underscoring the need for customized medicine methods and patient stratification techniques. Differences in patient factors, including age, genetic background, and comorbidities, may impact how individuals respond to antagomiR-21 medication and make some people more susceptible to experiencing adverse effects.^190–193

Exosomes and extracellular vesicles (EVs) are miR-21 sources, complicating treatment. Delivery tactics must be carefully considered since delivery vehicles vary in efficacy and safety. AntagomiR-21 treatment delivered via EVs may improve cellular absorption and lessen off-target effects compared to systemic dosing.¹⁹⁴ EVs from certain cell types or designed to express specific surface molecules may also preferentially target cardiac fibrosis-related tissues or diseased locations. This tailored delivery method may improve antagomiR-21 treatment while reducing systemic exposure and negative effects.¹⁹⁵

Enriching antagomiR-21 in EVs may enhance cardiac fibrosis treatment’s pharmacokinetics, biodistribution, and efficacy.¹⁹⁵ EV-based delivery systems need more preclinical and clinical research to improve and assess safety and effectiveness.¹⁹⁶

For the intended impact in the ultimate target cell, numerous obstacles must be solved, including safe blood transit, organ targeting, and fine-tuned doses. miR-based treatments might be administered ex vivo to blood cells to circumvent these issues.^197–205

In conclusion, antagomiR-21 may treat cardiac fibrosis, but its clinical translation must consider its drawbacks. Off-target effects, hepatotoxicity, and treatment response variability must be addressed to maximize antagomiR-21 therapy in clinical practice. Future study should optimize delivery techniques, understand antagomiR-21’s impacts on cellular processes, and undertake thorough clinical studies to assess its safety and efficacy in cardiac fibrosis patients. AntagomiR-21 treatment may improve cardiac fibrosis management and patient outcomes if it overcomes these difficulties.

Limitations

We investigated miR-21’s function in cardiac fibrosis and its therapeutic potential in this work. Our study’s limitations must be acknowledged, but our findings help explain miR-21-mediated heart disease and prospective therapeutic approaches. First, our assessment focuses on literature and data accessible at the time of publishing, so it may not include the latest advances in this quickly growing-subject. As with any review, biases and study quality affect interpretation and results. Even with these limitations, we believe our study sheds light on miR-21’s complex involvement in cardiac fibrosis and lays the groundwork for future research and clinical trials.

Conclusion

In this study, the miR-21 role in cardiac fibrosis has been discussed, and we have revealed molecular interactions in cardiac fibrosis pathogenesis, a leading cause of global concern.

miR-21 has a notable expression in cardiac cells and has a prominent role in this study. Its activities in controlling downregulations of target genes and following interaction in various pathways are associated with fibrosis, inflammation, and apoptosis in cardiac health and disease.

Cardiac fibrosis presents in many conditions, including hypertensive heart disease, diabetic cardiomyopathy, and MI. In this process, CFs and several signaling pathways like TIMPs and MMPs are linked to cardiac fibrosis formation. Our research showed that other signaling pathways with fibrosis function are PTEN, PI3K-Akt, ERK, IL-1/6, TGF-β, and RAAS. Moreover, the miR-21 role in this review has been investigated.

miR-21 regulation is controlled by crucial targets such as PDCD4, Bcl-2, and DUSP8, which considerably impact cardiac fibrosis. While its inhibition of PDCD4 shows anti-apoptotic and cell-protective effects, it can also contribute to fibrogenic transitions through alternate routes. Furthermore, our discussion has emphasized potential therapeutic approaches targeting miR-21, such as antisense oligonucleotides, anti-miR-21 compounds, modulation of Notch signaling, and various other strategies for regulating miR-21 expression. These methods hold the potential to alleviate cardiac fibrosis and its associated complications. To sum up, this narrative review has furnished a comprehensive overview of the complex molecular mechanisms underlying cardiac fibrosis, explicitly focusing on the crucial role played by miR-21.

Footnotes

Acknowledgements

None.

Declarations

ORCID iD

Amirreza Khalaji

References

Ambros

. The functions of animal microRNAs. Nature 2004; 431: 350–355.

Slack

Weidhaas

. MicroRNA in cancer prognosis. N Engl J Med 2008; 359: 2720–2722.

Visone

Croce

. MiRNAs and cancer. Am J Pathol 2009; 174: 1131–1138.

Mirnezami

Pickard

Zhang

, et al. MicroRNAs: key players in carcinogenesis and novel therapeutic targets. Eur J Surg Oncol 2009; 35: 339–347.

Kawai

Akira

. Signaling to NF-kappaB by toll-like receptors. Trends Mol Med 2007; 13: 460–469.

Krzywińska

Bracha

Jeanniere

, et al. Meta-analysis of the potential role of miRNA-21 in cardiovascular system function monitoring. Biomed Res Int 2020; 2020: 4525410.

Cai

Hagedorn

Cullen

. Human microRNAs are processed from capped, polyadenylated transcripts that can also function as mRNAs. RNA 2004; 10: 1957–1966.

Jenike

Halushka

. miR-21: a non-specific biomarker of all maladies. Biomark Res 2021; 9: 18.

Zhu

, et al. MicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1). J Biol Chem 2007; 282: 14328–14336.

10.

Zhang

Wang

Zhao

, et al. MicroRNA-21 (miR-21) represses tumor suppressor PTEN and promotes growth and invasion in non-small cell lung cancer (NSCLC). Clin Chim Acta 2010; 411: 846–852.

11.

Meng

Henson

Wehbe-Janek

, et al. MicroRNA-21 regulates expression of the PTEN tumor suppressor gene in human hepatocellular cancer. Gastroenterology 2007; 133: 647–658.

12.

Zhu

Wang

, et al. miR-21 promotes migration and invasion by the miR-21-PDCD4-AP-1 feedback loop in human hepatocellular carcinoma. Oncol Rep 2012;27(5):1660–1668.

13.

Liu

Friggeri

Yang

, et al. miR-21 mediates fibrogenic activation of pulmonary fibroblasts and lung fibrosis. J Exp Med 2010; 207: 1589–1597.

14.

Liang

Zhu

Ali

, et al. Engineered exosomes for targeted co-delivery of miR-21 inhibitor and chemotherapeutics to reverse drug resistance in colon cancer. J Nanobiotechnol 2020; 18: 10.

15.

Surina

Fontanella

Scisciola

, et al. miR-21 in human cardiomyopathies. Front Cardiovasc Med 2021; 8: 767064.

16.

Murtha

Schuliga

Mabotuwana

, et al. The processes and mechanisms of cardiac and pulmonary fibrosis. Front Physiol 2017; 8: 777.

17.

Frangogiannis

. Cardiac fibrosis. Cardiovasc Res 2021; 117: 1450–1488.

18.

Jiang

Xiong

, et al. Cardiac fibrosis: cellular effectors, molecular pathways, and exosomal roles. Front Cardiovasc Med 2021; 8: 715258.

19.

Tian

Niu

. Myocardial fibrosis in congenital and pediatric heart disease. Exp Ther Med 2017; 13: 1660–1664.

20.

Mozaffarian

Benjamin

, et al. Heart disease and stroke statistics – 2016 update. Circulation 2016; 133: e38–e360.

21.

Jellis

Martin

Narula

, et al. Assessment of nonischemic myocardial fibrosis. J Am Coll Cardiol 2010; 56: 89–97.

22.

Disertori

Masè

Ravelli

. Myocardial fibrosis predicts ventricular tachyarrhythmias. Trends Cardiovasc Med 2017; 27: 363–372.

23.

Ouyang

Wei

. miRNA in cardiac development and regeneration. Cell Regen 2021; 10: 14.

24.

Kabłak-Ziembicka

Badacz

Okarski

, et al. Cardiac microRNAs: diagnostic and therapeutic potential. Arch Med Sci 2023; 19: 1360–1381.

25.

Varzideh

Kansakar

Donkor

, et al. Cardiac Remodeling after myocardial infarction: functional contribution of microRNAs to inflammation and fibrosis. Front Cardiovasc Med 2022; 9: 863238.

26.

Graham-Brown

MPM

Patel

Stensel

, et al. Imaging of Myocardial fibrosis in patients with end-stage renal disease: current limitations and future possibilities. BioMed Res Int 2017; 2017: 5453606.

27.

Cao

Shi

. miR-21 enhances cardiac fibrotic remodeling and fibroblast proliferation via CADM1/STAT3 pathway. BMC Cardiovasc Disord 2017; 17: 88.

28.

Cavarretta

Condorelli

. miR-21 and cardiac fibrosis: another brick in the wall? Eur Heart J 2015; 36: 2139–2141.

29.

Davis

Hilyard

Lagna

, et al. SMAD proteins control DROSHA-mediated microRNA maturation. Nature 2008; 454: 56–61.

30.

Borchert

Lanier

Davidson

. RNA polymerase III transcribes human microRNAs. Nat Struct Mol Biol 2006; 13: 1097–1101.

31.

Koo

Kobiyama

Shen

, et al. RNA polymerase III regulates cytosolic RNA:DNA hybrids and intracellular microRNA expression. J Biol Chem 2015; 290: 7463–7473.

32.

Ribas

Castanares

, et al. A novel source for miR-21 expression through the alternative polyadenylation of VMP1 gene transcripts. Nucleic Acids Res 2012; 40: 6821–6833.

33.

Lee

Kim

. Mulberry fruit extract ameliorates adipogenesis via increasing AMPK activity and downregulating microRNA-21/143 in 3T3-L1 adipocytes. J Med Food 2020; 23: 266–272.

34.

Collins

Hess

. Deregulation of the HOXA9/MEIS1 axis in acute leukemia. Curr Opin Hematol 2016; 23: 354–361.

35.

McClure

Brudecki

Ferguson

, et al. MicroRNA 21 (miR-21) and miR-181b couple with NFI-A to generate myeloid-derived suppressor cells and promote immunosuppression in late sepsis. Infect Immun 2014; 82: 3816–3825.

36.

Misawa

Katayama

Koike

, et al. AP-1-Dependent miR-21 expression contributes to chemoresistance in cancer stem cell-like SP cells. Oncol Res 2010; 19: 23–33.

37.

Fujita

Ito

Mizutani

, et al. miR-21 Gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism. J Mol Biol 2008; 378: 492–504.

38.

Ribas

Lupold

. The transcriptional regulation of miR-21, its multiple transcripts, and their implication in prostate cancer. Cell Cycle 2010; 9: 923–929.

39.

Kremastiotis

Handa

Jackson

, et al. Disparate effects of MMP and TIMP modulation on coronary atherosclerosis and associated myocardial fibrosis. Sci Rep 2021; 11: 23081.

40.

Sohns

Marrouche

. Atrial fibrillation and cardiac fibrosis. Eur Heart J 2020; 41: 1123–1131.

41.

Brown

Ambler

Mitchell

, et al. The cardiac fibroblast: therapeutic target in myocardial remodeling and failure. Annu Rev Pharmacol Toxicol 2005; 45: 657–687.

42.

Spinale

Villarreal

. Targeting matrix metalloproteinases in heart disease: lessons from endogenous inhibitors. Biochem Pharmacol 2014; 90: 7–15.

43.

Meng

Nikolic-Paterson

Lan

. TGF-β: the master regulator of fibrosis. Nat Rev Nephrol 2016; 12: 325–338.

44.

Saadat

Noureddini

Mahjoubin-Tehran

, et al. Pivotal role of TGF-β/Smad signaling in cardiac fibrosis: non-coding RNAs as effectual players. Front Cardiovasc Med 2020; 7: 588347.

45.

Ehanire

Ren

Bond

, et al. Angiotensin II stimulates canonical TGF-β signaling pathway through angiotensin type 1 receptor to induce granulation tissue contraction. J Mol Med (Berl) 2015; 93: 289–302.

46.

Tuleta

Frangogiannis

. Diabetic fibrosis. Biochim Biophys Acta Mol Basis Dis 2021; 1867: 166044.

47.

Dong

, et al. Deletion of Smad3 protects against diabetic myocardiopathy in db/db mice. J Cell Mol Med 2021; 25: 4860–4869.

48.

Khalil

Kanisicak

Prasad

, et al. Fibroblast-specific TGF-β-Smad2/3 signaling underlies cardiac fibrosis. J Clin Invest 2017; 127: 3770–3783.

49.

Song

, et al. MicroRNA-663 prevents monocrotaline-induced pulmonary arterial hypertension by targeting TGF-β1/smad2/3 signaling. J Mol Cell Cardiol 2021; 161: 9–22.

50.

Huang

Chen

, et al. Distinct roles of myofibroblast-specific Smad2 and Smad3 signaling in repair and remodeling of the infarcted heart. J Mol Cell Cardiol 2019; 132: 84–97.

51.

Shi

Liu

, et al. TIEG1 represses Smad7-mediated activation of TGF-β1/Smad signaling in keloid pathogenesis. J Invest Dermatol 2017; 137: 1051–1059.

52.

Meng

Yang

Wang

, et al. Silymarin ameliorates diabetic cardiomyopathy via inhibiting TGF-β1/Smad signaling. Cell Biol Int 2019; 43: 65–72.

53.

Xiao

Yang

, et al. Interference of TGF-β1/Smad7 signal pathway affects myocardial fibrosis in hypertension. Pak J Pharm Sci 2020; 33: 2625–2631.

54.

Humeres

Shinde

Hanna

, et al. Smad7 effects on TGF-β and ErbB2 restrain myofibroblast activation and protect from postinfarction heart failure. J Clin Invest 2022; 132: e146926.

55.

Weber

Sun

Bhattacharya

Ahokas

Gerling

. Myofibroblast-mediated mechanisms of pathological remodelling of the heart. Nat Rev Cardiol. 2013;10(1):15–26.

56.

Schorb

Booz

Dostal

, et al. Angiotensin II is mitogenic in neonatal rat cardiac fibroblasts. Circ Res 1993; 72: 1245–1254.

57.

Barallobre-Barreiro

Radovits

, et al. Extracellular matrix in heart failure: role of ADAMTS5 in proteoglycan remodeling. Circulation 2021; 144: 2021–2034.

58.

Border

Noble

. Interactions of transforming growth factor-beta and angiotensin II in renal fibrosis. Hypertension 1998; 31: 181–188.

59.

Rodríguez-Vita

Sánchez-López

Esteban

, et al. Angiotensin II activates the Smad pathway in vascular smooth muscle cells by a transforming growth factor-beta-independent mechanism. Circulation 2005; 111: 2509–2517.

60.

AlQudah

Hale

Czubryt

. Targeting the renin-angiotensin-aldosterone system in fibrosis. Matrix Biol 2020; 91–92: 92–108.

61.

Yuan

, et al. Cardiac fibrosis: new insights into the pathogenesis. Int J Biol Sci 2018; 14: 1645–1657.

62.

Parichatikanond

Luangmonkong

Mangmool

, et al. Therapeutic targets for the treatment of cardiac fibrosis and cancer: focusing on TGF-β signaling. Front Cardiovasc Med 2020; 7: 34.

63.

Bujak

Dobaczewski

Chatila

, et al. Interleukin-1 receptor type I signaling critically regulates infarct healing and cardiac remodeling. Am J Pathol 2008; 173: 57–67.

64.

Meléndez

McLarty

Levick

, et al. Interleukin 6 mediates myocardial fibrosis, concentric hypertrophy, and diastolic dysfunction in rats. Hypertension 2010; 56: 225–231.

65.

Huang

Yang

Xiang

, et al. Role of interleukin-6 in regulation of immune responses to remodeling after myocardial infarction. Heart Fail Rev 2015; 20: 25–38.

66.

Kaden

Dempfle

Grobholz

, et al. Interleukin-1 beta promotes matrix metalloproteinase expression and cell proliferation in calcific aortic valve stenosis. Atherosclerosis 2003; 170: 205–211.

67.

Seong

Hong

Jung

, et al. TGF-beta-induced interleukin-6 participates in transdifferentiation of human Tenon’s fibroblasts to myofibroblasts. Mol Vis 2009; 15: 2123–2128.

68.

Jia

Han

, et al. Macrophage-stimulated cardiac fibroblast production of IL-6 is essential for TGF-β/Smad activation and cardiac fibrosis induced by angiotensin II. PLoS One 2012; 7: e35144.

69.

Turner

Blythe

. Cardiac fibroblast p38 MAPK: a critical regulator of myocardial remodeling. J Cardiovasc Dev Dis 2019; 6: 27.

70.

Umbarkar

Tousif

Singh

, et al. Fibroblast GSK-3α promotes fibrosis via RAF-MEK-ERK pathway in the injured heart. Circ Res 2022; 131: 620–636.

71.

Qin

Cao

Massey

. Role of PI3K/Akt signaling pathway in cardiac fibrosis. Mol Cell Biochem 2021; 476: 4045–4059.

72.

Shioi

McMullen

Tarnavski

, et al. Rapamycin attenuates load-induced cardiac hypertrophy in mice. Circulation 2003;107: 1664–1670.

73.

Guo

Ramirez

Waddell

, et al. Axin and GSK3- control Smad3 protein stability and modulate TGF-signaling. Genes Dev 2008; 22: 106–120.

74.

Matsui

Rosenzweig

. Convergent signal transduction pathways controlling cardiomyocyte survival and function: the role of PI 3-kinase and Akt. J Mol Cell Cardiol 2005; 38: 63–71.

75.

Bernardo

Weeks

Pretorius

, et al. Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies. Pharmacol Ther 2010; 128: 191–227.

76.

Vivar

Humeres

Anfossi

, et al. Role of FoxO3a as a negative regulator of the cardiac myofibroblast conversion induced by TGF-β1. Biochim Biophys Acta Mol Cell Res 2020; 1867: 118695.

77.

Schwartzbauer

Robbins

. The tumor suppressor gene PTEN can regulate cardiac hypertrophy and survival. J Biol Chem 2001; 276: 35786–35793.

78.

Crackower

Oudit

Kozieradzki

, et al. Regulation of myocardial contractility and cell size by distinct PI3K-PTEN signaling pathways. Cell 2002; 110: 737–749.

79.

Zhu

Tang

Ren

, et al. Downregulation of microRNA-21 contributes to decreased collagen expression in venous malformations via transforming growth factor-β/Smad3/microRNA-21 signaling feedback loop. J Vasc Surg Venous Lymphat Disord 2022; 10: 469–481.e2.

80.

Nonaka

CKV

Sampaio

Silva

, et al. Therapeutic miR-21 silencing reduces cardiac fibrosis and modulates inflammatory response in chronic chagas disease. Int J Mol Sci 2021; 22: 3307.

81.

Zhang

Yuan

, et al. MiR-208b/miR-21 promotes the progression of cardiac fibrosis through the activation of the TGF-β1/Smad-3 signaling pathway: an in vitro and in vivo study. Front Cardiovasc Med 2022; 9: 924629.

82.

Hermida

López

González

, et al. A synthetic peptide from transforming growth factor-beta1 type III receptor prevents myocardial fibrosis in spontaneously hypertensive rats. Cardiovasc Res 2009; 81: 601–609.

83.

Liang

Zhang

Ban

, et al. A novel reciprocal loop between microRNA-21 and TGFβRIII is involved in cardiac fibrosis. Int J Biochem Cell Biol 2012; 44: 2152–2160.

84.

Sheedy

. Turning 21: induction of miR-21 as a key switch in the inflammatory response. Front Immunol 2015; 6: 19.

85.

Bejerano

Etzion

Elyagon

, et al. Nanoparticle delivery of miRNA-21 mimic to cardiac macrophages improves myocardial remodeling after myocardial infarction. Nano Lett 2018; 18: 5885–5891.

86.

Scisciola

Benedetti

Chianese

, et al. The pivotal role of miRNA-21 in myocardial metabolic flexibility in response to short- and long-term high glucose treatment: evidence in human cardiomyocyte cell line. Diabetes Res Clin Pract 2022; 191: 110066.

87.

Bujak

Frangogiannis

. The role of TGF-beta signaling in myocardial infarction and cardiac remodeling. Cardiovasc Res 2007; 74: 184–195.

88.

Hedman

ÅK

Enroth

, et al. Genome-wide DNA methylation study identifies genes associated with the cardiovascular biomarker GDF-15. Hum Mol Genet 2016; 25: 817–827.

89.

Guo

Zhao

, et al. miR-21 is upregulated, promoting fibrosis and blocking G2/M in irradiated rat cardiac fibroblasts. PeerJ 2020; 8: e10502.

90.

Yuan

Chen

, et al. Mir-21 promotes cardiac fibrosis after myocardial infarction via targeting Smad7. Cell Physiol Biochem 2017; 42: 2207–2219.

91.

Zhou

Liu

, et al. miR-21 promotes cardiac fibroblast-to-myofibroblast transformation and myocardial fibrosis by targeting Jagged1. J Cell Mol Med 2018; 22: 3816–3824.

92.

Zhou

Liu

. Role of Notch signaling in the mammalian heart. Braz J Med Biol Res 2014; 47: 1–10.

93.

Phan

. Notch in fibrosis and as a target of anti-fibrotic therapy. Pharmacol Res 2016; 108: 57–64.

94.

Nemir

Metrich

Plaisance

, et al. The Notch pathway controls fibrotic and regenerative repair in the adult heart. Eur Heart J 2014; 35: 2174–2185.

95.

Mao

Zhou

, et al. MicroRNA-21 Mediates a positive feedback on angiotensin II-induced myofibroblast transformation. J Inflamm Res 2020; 13: 1007–1020.

96.

Hanafusa

Torii

Yasunaga

, et al. Sprouty1 and Sprouty2 provide a control mechanism for the Ras/MAPK signalling pathway. Nat Cell Biol 2002; 4: 850–858.

97.

Thum

Gross

Fiedler

, et al. MicroRNA-21 contributes to myocardial disease by stimulating MAP kinase signalling in fibroblasts. Nature 2008; 456: 980–984.

98.

Qiao

Xia

Cheng

, et al. Role of Sprouty1 (Spry1) in the pathogenesis of atrial fibrosis. Pathol Res Pract 2018; 214: 308–313.

99.

Carnero

Blanco-Aparicio

Renner

, et al. The PTEN/PI3K/AKT signalling pathway in cancer, therapeutic implications. Curr Cancer Drug Targets 2008; 8: 187–198.

100.

Roy

Khanna

Hussain

, et al. MicroRNA expression in response to murine myocardial infarction: miR-21 regulates fibroblast metalloprotease-2 via phosphatase and tensin homologue. Cardiovasc Res 2009; 82: 21–29.

101.

Tao

Zhang

Qin

, et al. LncRNA GAS5 controls cardiac fibroblast activation and fibrosis by targeting miR-21 via PTEN/MMP-2 signaling pathway. Toxicology 2017; 386: 11–18.

102.

Kumarswamy

Volkmann

Jazbutyte

, et al. Transforming growth factor-β-induced endothelial-to-mesenchymal transition is partly mediated by microRNA-21. Arterioscler Thromb Vasc Biol 2012; 32: 361–369.

103.

Cheng

Liu

Zhang

, et al. MicroRNA-21 protects against the H(2)O(2)-induced injury on cardiac myocytes via its target gene PDCD4. J Mol Cell Cardiol 2009; 47: 5–14.

104.

Allgayer

. Pdcd4, a colon cancer prognostic that is regulated by a microRNA. Crit Rev Oncol Hematol 2010; 73: 185–191.

105.

Merline

Moreth

Beckmann

, et al. Signaling by the matrix proteoglycan decorin controls inflammation and cancer through PDCD4 and microRNA-21. Sci Signal 2011; 4: ra75.

106.

Eto

Goto

Nakashima

, et al. Loss of programmed cell death 4 induces apoptosis by promoting the translation of procaspase-3 mRNA. Cell Death Differ 2012; 19: 573–581.

107.

Xiao

Pan

, et al. Cardiac progenitor cell-derived exosomes prevent cardiomyocytes apoptosis through exosomal miR-21 by targeting PDCD4. Cell Death Dis 2016; 7: e2277.

108.

Brønnum

Andersen

Schneider

, et al. miR-21 promotes fibrogenic epithelial-to-mesenchymal transition of epicardial mesothelial cells involving Programmed Cell Death 4 and Sprouty-1. PLoS One 2013; 8: e56280.

109.

Zhou

Chai

Bai

, et al. LncRNA-GAS5 regulates PDCD4 expression and mediates myocardial infarction-induced cardiomyocytes apoptosis via targeting MiR-21. Cell Cycle 2020; 19: 1363–1377.

110.

Sims

Lakhter

Anderson-Baucum

, et al. MicroRNA 21 targets BCL2 mRNA to increase apoptosis in rat and human beta cells. Diabetologia 2017; 60: 1057–1065.

111.

Elmore

. Apoptosis: a review of programmed cell death. Toxicol Pathol 2007; 35: 495–516.

112.

Dong

Hao

, et al. microRNA-21 promotes cardiac fibrosis and development of heart failure with preserved left ventricular ejection fraction by up-regulating Bcl-2. Int J Clin Exp Pathol 2014; 7: 565–574.

113.

Yang

Zhao

Xue

, et al. MiRNA-21 promotes differentiation of bone marrow mesenchymal stem cells into cardiomyocyte-like cells by regulating the Ajuba/Isl1 axis pathway. Arch Med Sci 2022; 18: 1672–1677.

114.

Huang

Young Seok

Zhou

, et al. CIP, a cardiac Isl1-interacting protein, represses cardiomyocyte hypertrophy. Circ Res 2012; 110: 818–830.

115.

Yan

Long

, et al. Cardiac ISL1-interacting protein, a cardioprotective factor, inhibits the transition from cardiac hypertrophy to heart failure. Front Cardiovasc Med 2022; 9: 857049.

116.

Chuppa

Liang

Liu

, et al. MicroRNA-21 regulates peroxisome proliferator-activated receptor alpha, a molecular mechanism of cardiac pathology in Cardiorenal Syndrome Type 4. Kidney Int 2018; 93: 375–389.

117.

Wang

Zhu

Jiao

, et al. Cardiomyocyte peroxisome proliferator-activated receptor alpha is essential for energy metabolism and extracellular matrix homeostasis during pressure overload-induced cardiac remodeling. Acta Pharmacol Sin 2022; 43: 1231–1242.

118.

Tao

Zhang

Yang

, et al. MicroRNA-21 via dysregulation of WW domain-containing protein 1 regulate atrial fibrosis in atrial fibrillation. Heart Lung Circ 2018; 27: 104–113.

119.

Yang

Wang

Zhou

, et al. MicroRNA-21 prevents excessive inflammation and cardiac dysfunction after myocardial infarction through targeting KBTBD7. Cell Death Dis 2018; 9: 769.

120.

Pan

, et al. Effect of miR-21/TLR4/NF-κB pathway on myocardial apoptosis in rats with myocardial ischemia-reperfusion. Eur Rev Med Pharmacol Sci 2018; 22: 7928–7237.

121.

Liu

, et al. Micro-RNA 21Targets dual specific phosphatase 8 to promote collagen synthesis in high glucose-treated primary cardiac fibroblasts. Can J Cardiol 2014; 30: 1689–1699.

122.

Kumarswamy

Volkmann

Thum

. Regulation and function of miRNA-21 in health and disease. RNA Biol 2011; 8: 706–713.

123.

Nielsen

Jørgensen

Fog

, et al. High levels of microRNA-21 in the stroma of colorectal cancers predict short disease-free survival in stage II colon cancer patients. Clin Exp Metastasis 2011; 28: 27–38.

124.

Zhang

Liu

, et al. Plasma microRNA-21 is a potential diagnostic biomarker of acute myocardial infarction. Eur Rev Med Pharmacol Sci 2016; 20: 323–329.

125.

Rana

Kompa

Skommer

, et al. Contribution of microRNA to pathological fibrosis in cardio-renal syndrome: impact of uremic toxins. Physiol Rep 2015; 3: e12371.

126.

Tian

Yan

, et al. Diagnostic and prognostic value of miR-486-5p, miR-451a, miR-21-5p and monocyte to high-density lipoprotein cholesterol ratio in patients with acute myocardial infarction. Heart Vessels 2023; 38: 318–331.

127.

Kim

Choi

. Pathological roles of MAPK signaling pathways in human diseases. Biochim Biophys Acta 2010; 1802: 396–405.

128.

Villar

García

Merino

, et al. Myocardial and circulating levels of microRNA-21 reflect left ventricular fibrosis in aortic stenosis patients. Int J Cardiol 2013; 167:2875–2881.

129.

Chen

Zhang

, et al. Relationship between circulating miRNA-21, atrial fibrosis, and atrial fibrillation in patients with atrial enlargement. Ann Palliat Med 2021; 10: 12742–12749.

130.

Adam

Löhfelm

Thum

, et al. Role of miR-21 in the pathogenesis of atrial fibrosis. Basic Res Cardiol 2012; 107: 278.

131.

Jiang

, et al. Correlation between serum levels of microRNA-21 and inflammatory factors in patients with chronic heart failure. Medicine (Baltimore) 2022; 101: e30596.

132.

Lavall

Selzer

Schuster

, et al. The mineralocorticoid receptor promotes fibrotic remodeling in atrial fibrillation. J Biol Chem 2014; 289: 6656–6668.

133.

Zhou

Maleck

von Ungern-Sternberg

SNI

, et al. Circulating microRNA-21 correlates with left atrial low-voltage areas and is associated with procedure outcome in patients undergoing atrial fibrillation ablation. Circ Arrhythm Electrophysiol 2018; 11: e006242.

134.

Zhang

Xing

Zhou

, et al. Circulating miRNA-21 is a promising biomarker for heart failure. Mol Med Rep 2017; 16: 7766–7774.

135.

Watanabe

Narumi

Watanabe

, et al. The association between microRNA-21 and hypertension-induced cardiac remodeling. PLoS One 2020; 15: e0226053.

136.

Darakhshan

Pour

. Tranilast: a review of its therapeutic applications. Pharmacol Res 2015; 91: 15–28.

137.

Hanna

Humeres

Frangogiannis

. The role of Smad signaling cascades in cardiac fibrosis. Cell Signal 2021; 77: 109826.

138.

Xiao

Feng

, et al. Metformin attenuates cardiac fibrosis by inhibiting the TGFbeta1-Smad3 signalling pathway. Cardiovasc Res 2010; 87: 504–513.

139.

Vainio

Szabó

Lin

, et al. Connective tissue growth factor inhibition enhances cardiac repair and limits fibrosis after myocardial infarction. JACC Basic Transl Sci 2019; 4: 83–94.

140.

Peterson

Wang

Shettigar

, et al. NF-κB inhibition rescues cardiac function by remodeling calcium genes in a Duchenne muscular dystrophy model. Nat Commun 2018; 9: 3431.

141.

Wang

Bertucci

, et al. Celecoxib, but not rofecoxib or naproxen, attenuates cardiac hypertrophy and fibrosis induced in vitro by angiotensin and aldosterone. Clin Exp Pharmacol Physiol 2010; 37: 912–918.

142.

Zhang

Gao

, et al. Rapid atrial pacing induces myocardial fibrosis by down-regulating Smad7 via microRNA-21 in rabbit. Heart Vessels 2016; 31: 1696–1708.

143.

Cheng

Song

, et al. Celastrol-induced suppression of the MiR-21/ERK signalling pathway attenuates cardiac fibrosis and dysfunction. Cell Physiol Biochem 2016; 38: 1928–1938.

144.

Cardin

Guasch

Luo

, et al. Role for microRNA-21 in atrial profibrillatory fibrotic remodeling associated with experimental postinfarction heart failure. Circ Arrhythm Electrophysiol 2012; 5: 1027–1035.

145.

Gomez

MacKenna

Johnson

, et al. Anti-microRNA-21 oligonucleotides prevent Alport nephropathy progression by stimulating metabolic pathways. J Clin Invest 2015; 125: 141–156.

146.

Fan

Ren

Chen

, et al. Celastrol relieves myocardial infarction-induced cardiac fibrosis by inhibiting NLRP3 inflammasomes in rats. Int Immunopharmacol 2023; 121: 110511.

147.

Dey

Ghosh-Choudhury

Kasinath

, et al. TGFβ-stimulated microRNA-21 utilizes PTEN to orchestrate AKT/mTORC1 signaling for mesangial cell hypertrophy and matrix expansion. PLoS One 2012; 7: e42316.

148.

Patrick

Montgomery

, et al. Stress-dependent cardiac remodeling occurs in the absence of microRNA-21 in mice. J Clin Invest 2010; 120: 3912–3916.

149.

Kölling

Kaucsar

Schauerte

, et al. Therapeutic miR-21 silencing ameliorates diabetic kidney disease in mice. Mol Ther 2017; 25: 165–180.

150.

Wang

Ruan

, et al. MicroRNA-132 attenuated cardiac fibrosis in myocardial infarction-induced heart failure rats. Biosci Rep 2020; 40: BSR20201696.

151.

Micheletti

Plaisance

Abraham

, et al. The long noncoding RNA Wisper controls cardiac fibrosis and remodeling. Sci Transl Med 2017; 9: eaai9118.

152.

Shu

Gao

Sun

Luo

, et al. MIAT is a pro-fibrotic long non-coding RNA governing cardiac fibrosis in post-infarct myocardium. Sci Rep 2017; 7: 42657.

153.

Park

Nguyen

Pezhouman

, et al. Cardiac fibrosis: potential therapeutic targets. Transl Res 2019;2 09: 121–137.

154.

Felisbino

McKinsey

. Epigenetics in cardiac fibrosis: emphasis on inflammation and fibroblast activation. JACC Basic Transl Sci 2018; 3:eaai9118 704–715.

155.

Shao

Liu

Zuo

. Roles of epigenetics in cardiac fibroblast activation and fibrosis. Cells 2022; 11: 2347.

156.

Nural-Guvener

Zakharova

Nimlos

, et al. HDAC class I inhibitor, Mocetinostat, reverses cardiac fibrosis in heart failure and diminishes CD90+ cardiac myofibroblast activation. Fibrogenesis Tissue Repair 2014; 7: 10.

157.

Yoon

Eom

. HDAC and HDAC inhibitor: from cancer to cardiovascular diseases. Chonnam Med J 2016; 52: 1–11.

158.

Staessen

Richart

. Oral renin inhibitors. Lancet 2006; 368: 1449–1456.

159.

Simon

Bocan

TMA

, et al. MMP/TIMP expression in spontaneously hypertensive heart failure rats: the effect of ACE- and MMP-inhibition. Cardiovasc Res 2000; 46: 298–306.

160.

Brooks

Bing

Robinson

, et al. Effect of angiotensin-converting enzyme inhibition on myocardial fibrosis and function in hypertrophied and failing myocardium from the spontaneously hypertensive rat. Circulation 1997; 96: 4002–4010.

161.

Iwai

Nakagami

, et al. Effect of angiotensin II type 1 receptor blockade on cardiac remodeling in angiotensin II type 2 receptor null mice. Arterioscler Thromb Vasc Biol 2002; 22: 49–54.

162.

De Carvalho Frimm

Sun

Weber

. Angiotensin II receptor blockade and myocardial fibrosis of the infarcted rat heart. J Lab Clin Med 1997; 129: 439–446.

163.

Teymouri

Mesbah

Navabian

SMH

, et al. ECG frequency changes in potassium disorders: a narrative review. Am J Cardiovasc Dis 2022; 12: 112–124.

164.

Desai

Liu

Pfeffer

, et al. Incident hyperkalemia, hypokalemia, and clinical outcomes during spironolactone treatment of heart failure with preserved ejection fraction: analysis of the TOPCAT trial. J Card Fail 2018; 24: 313–320.

165.

Dang

Zhang

, et al. Blockade of β-adrenergic signaling suppresses inflammasome and alleviates cardiac fibrosis. Ann Transl Med 2020; 8: 127.

166.

Iyer

Gurujeyalakshmi

Giri

. Effects of pirfenidone on transforming growth factor-beta gene expression at the transcriptional level in bleomycin hamster model of lung fibrosis. J Pharmacol Exp Ther 1999; 291: 367–373.

167.

Kamisah

Che Hassan

. Therapeutic use and molecular aspects of ivabradine in cardiac remodeling: a review. Int J Mol Sci 2023; 24: 2801.

168.

Shao

Zhang

Gong

, et al. Ivabradine ameliorates cardiac function in heart failure with preserved and reduced ejection fraction via upregulation of miR-133a. Oxid Med Cell Longev 2021; 2021: 1257283.

169.

Ertl

Frantz

. Healing after myocardial infarction. Cardiovasc Res 2005; 66: 22–32.

170.

Mozaffarian

. Omega-3 fatty acids and cardiovascular disease: effects on risk factors, molecular pathways, and clinical events. J Am Coll Cardiol 2011; 58: 2047–2067.

171.

Zhang

Wang

, et al. Effect of doxycycline on chronic intermittent hypoxia-induced atrial remodeling in rats. Herz 2020; 45: 668–675.

172.

Meng

Han

, et al. Vildagliptin attenuates myocardial dysfunction and restores autophagy via miR-21/SPRY1/ERK in diabetic mice heart. Front Pharmacol 2021; 12: 634365.

173.

Zhou

Yang

Yuan

, et al. Paeoniflorin attenuates pressure overload-induced cardiac remodeling via inhibition of TGFβ/Smads and NF-κB pathways. J Mol Histol 2013; 44: 357–367.

174.

Yamagami

Oka

Wang

, et al. Pirfenidone exhibits cardioprotective effects by regulating myocardial fibrosis and vascular permeability in pressure-overloaded hearts. Am J Physiol Heart Circ Physiol 2015; 309: H512–H522.

175.

de Melo

Vieira

Antônio

, et al. Exercise training attenuates right ventricular remodeling in rats with pulmonary arterial stenosis. Front Physiol 2016; 7: 541.

176.

Wang

Christman

. Decellularized myocardial matrix hydrogels: in basic research and preclinical studies. Adv Drug Del Rev 2016; 96: 77–82.

177.

Hinderer

Schenke-Layland

. Cardiac fibrosis – a short review of causes and therapeutic strategies. Adv Drug Del Rev 2019; 146: 77–82.

178.

Leor

Tuvia

Guetta

, et al. Intracoronary injection of in situ forming alginate hydrogel reverses left ventricular remodeling after myocardial infarction in Swine. J Am Coll Cardiol 2009; 54: 1014–1023.

179.

Zeng

Huang

, et al. Infarct stabilization and cardiac repair with a VEGF-conjugated, injectable hydrogel. Biomaterials 2011; 32: 579–586.

180.

Singelyn

Sundaramurthy

Johnson

, et al. Catheter-deliverable hydrogel derived from decellularized ventricular extracellular matrix increases endogenous cardiomyocytes and preserves cardiac function post-myocardial infarction. J Am Coll Cardiol 2012; 59: 751–763.

181.

Takawale

Zhang

Patel

, et al. Tissue inhibitor of matrix metalloproteinase-1 promotes myocardial fibrosis by mediating CD63–integrin β1 interaction. Hypertension 2017; 69: 1092–1103.

182.

DeLeon-Pennell

Meschiari

Jung

, et al. Matrix metalloproteinases in myocardial infarction and heart failure. Prog Mol Biol Transl Sci 2017; 147: 75–100.

183.

Sun

Song

Xie

, et al. Shenlijia attenuates doxorubicin-induced chronic heart failure by inhibiting cardiac fibrosis. Evid Based Complement Alternat Med 2021; 2021: 6659676.

184.

Wang

, et al. Protective effect of lycopene on cardiac function and myocardial fibrosis after acute myocardial infarction in rats via the modulation of p38 and MMP-9. J Mol Histol 2014; 45: 113–120.

185.

Chan

Roczkowsky

Cho

, et al. MMP inhibitors attenuate doxorubicin cardiotoxicity by preventing intracellular and extracellular matrix remodelling. Cardiovasc Res 2021;117: 188–200.

186.

Wang

. Mesenchymal stem/stromal cells in progressive fibrogenic involvement and anti-fibrosis therapeutic properties. Front Cell Dev Biol 2022; 10: 902677.

187.

Wang

L-T

Ting

C-H

Yen

M-L

, et al. Human mesenchymal stem cells (MSCs) for treatment towards immune- and inflammation-mediated diseases: review of current clinical trials. J Biomed Sci 2016; 23: 76.

188.

Behfar

Faustino

Arrell

, et al. Guided stem cell cardiopoiesis: discovery and translation. J Mol Cell Cardiol 2008; 45: 523–529.

189.

Wang

Fang

Chen

, et al. Recombinant adeno-associated virus-mediated delivery of microRNA-21-3p lowers hypertension. Mol Ther Nucleic Acids 2018; 11: 354–366.

190.

Mathison

Singh

Chiuchiolo

, et al. In situ reprogramming to transdifferentiate fibroblasts into cardiomyocytes using adenoviral vectors: implications for clinical myocardial regeneration. J Thorac Cardiovasc Surg 2017; 153: 329–339.e3.

191.

Morfino

Aimo

Castiglione

, et al. Treatment of cardiac fibrosis: from neuro-hormonal inhibitors to CAR-T cell therapy. Heart Fail Rev 2023; 28: 555–569.

192.

Aghajanian

Kimura

Rurik

, et al. Targeting cardiac fibrosis with engineered T cells. Nature 2019; 573: 430–433.

193.

Huang

Bär

Thum

. miR-21, mediator, and potential therapeutic target in the cardiorenal syndrome. Front Pharmacol 2020; 11: 726.

194.

Wang

, et al. Mechanisms of circRNA/lncRNA-miRNA interactions and applications in disease and drug research. Biomed Pharmacother 2023; 162: 114672.

195.

Han

Wang

Zhang

. Functional interactions between lncRNAs/circRNAs and miRNAs: insights into rheumatoid arthritis. Front Immunol 2022; 13: 810317.

196.

Thum

Chau

Bhat

, et al. Comparison of different miR-21 inhibitor chemistries in a cardiac disease model. J Clin Invest 2011; 121: 461–462.

197.

Zheng

Mao

, et al. Long non-coding RNA growth arrest-specific transcript 5 (GAS5) inhibits liver fibrogenesis through a mechanism of competing endogenous RNA. J Biol Chem 2015; 290: 28286–28298.

198.

Zhang

Zhu

Watabe

, et al. Negative regulation of lncRNA GAS5 by miR-21. Cell Death Differ 2013; 20: 1558–1568.

199.

Yuan

. MicroRNA-21 mediates the protective role of emulsified isoflurane against myocardial ischemia/reperfusion injury in mice by targeting SPP1. Cell Signal 2021; 86: 110086.

200.

Murakami

Takashima

Sato-Watanabe

, et al. Ursolic acid, an antagonist for transforming growth factor (TGF)-beta1. FEBS Lett 2004; 566: 55–59.

201.

Dong

Liu

Zhang

, et al. Downregulation of miR-21 is involved in direct actions of ursolic acid on the heart: implications for cardiac fibrosis and hypertrophy. Cardiovasc Ther 2015; 33: 161–167.

202.

Selcuklu

Donoghue

Kerin

, et al. Regulatory interplay between miR-21, JAG1 and 17beta-estradiol (E2) in breast cancer cells. Biochem Biophys Res Commun 2012; 423: 234–239.

203.

Huang

Chen

Qian

, et al. Signal transducer and activator of transcription 3/microRNA-21 feedback loop contributes to atrial fibrillation by promoting atrial fibrosis in a rat sterile pericarditis model. Circ Arrhythm Electrophysiol 2016; 9: e003396.

204.

Schneider

SIdR

Silvello

Martinelli

, et al. Plasma levels of microRNA-21,-126 and-423-5p alter during clinical improvement and are associated with the prognosis of acute heart failure. Mol Med Rep 2018; 17: 4736–4746.

205.

Zhang

Zhao

, et al. Doxycycline Attenuates atrial remodeling by interfering with microRNA-21 and downstream phosphatase and tensin homolog (PTEN)/phosphoinositide 3-kinase (PI3K) signaling pathway. Med Sci Monit 2018; 24: 5580–5587.

Inhibitory effect of microRNA-21 on pathways and mechanisms involved in cardiac fibrosis development

Abstract

Plain language summary

Keywords

Introduction

Regulatory mechanisms of miR-21

Mechanism of cardiac fibrosis

Molecular mechanisms involved in cardiac fibrosis

Role of miR-21 in cardiac fibrosis

TGF-β pathway

CADM pathway

Notch pathway

Spry pathway

PTEN pathway

PDCD4 pathway

Oncogene Bcl-2 pathway

Ajuba/Isl1 pathway

Peroxisome proliferator-activated receptor alpha

Therapeutic implications

Potential use of miR-21 as a therapeutic target

MiR-21: A versatile therapeutic target in cardiac and pulmonary fibrosis

MiR-21 is a promising diagnostic and therapeutic player in cardiac fibrosis and HF

Strategies to Regulate miR-21 Expression

LncRNA-MiR interplay in controlling miR-21: Potential therapeutic strategies

Innovative approaches for miR-21 regulation

Innovative miR-21 control methods

Targeting MiR-21 in cardiac fibrosis: Multifaceted signaling pathways

Discussion

Limitations

Conclusion

Footnotes

Acknowledgements

Declarations

ORCID iD

References