Sage Journals: Discover world-class research

Abstract

Macrophages are involved in every cardiovascular disease and are an attractive therapeutic target. Macrophage activation is complex and can be either beneficial or deleterious, depending upon its mode of action, its timing, and its duration. An important macrophage characteristic is its plasticity, which enables it to switch from one subset to another. Macrophages, which regulate healing and repair after myocardial infarction, have become a major target for both treatment and diagnosis (theranostic). The aim of the present review is to describe the recent discoveries related to targeting and modulating of macrophage function to improve infarct repair. We will briefly review macrophage polarization, plasticity, heterogeneity, their role in infarct repair, regeneration, and cross talk with mesenchymal cells. Particularly, we will focus on the potential of macrophage targeting in situ by liposomes. The ability to modulate macrophage function could delineate pathways to reactivate the endogenous programs of myocardial regeneration. This will eventually lead to development of small molecules or biologics to enhance the endogenous programs of regeneration and repair.

Keywords

heart liposomes macrophage monocyte myocardial infarction nanomedicine theranostic

Introduction

The inability of the human heart to regenerate efficiently represents one of the greatest hurdles in cardiovascular medicine. Despite improvements in interventional and pharmacological therapy, cardiovascular disease is the leading cause of death in Europe, accounting for 4.1 million deaths annually, 46% of the total number of deaths per year.¹ Thus, there is a clear and immediate need for new effective therapies.

The adult heart responds to injury with inflammation, scar formation, and fibrosis, with minimal regeneration.² The inflammatory response to myocardial injury is an essential component of infarct healing.^3,4 However, inflammation may continue beyond the early period of healing and also spread into the remote myocardium,^5,6 resulting in adverse ventricular remodeling and heart failure. This inflammatory reaction has emerged as a therapeutic target. Although, encouraging results have been obtained in animal models, the results of clinical trials targeting the inflammatory response have been disappointing.^7,8

Regenerative cardiovascular medicine holds immense promise for treating damaged and diseased hearts.^9,10 The term regeneration defines the healing process that rebuilds damaged tissue to its normal structure and function.¹¹ The term repair defines the healing process that replaces the damaged tissue with a scar.¹¹ A potential therapeutic strategy is to augment endogenous regenerative mechanisms and to stimulate regeneration—a growth of new heart muscle from the milieu of cardiac progenitors and cardiomyocytes, spared by injury.¹²

The most common cause of acute heart injury is acute myocardial infarction (MI).¹³ Macrophages are the dominant cells in the infarcted myocardium, controlling the initiation, maintenance, and resolution of the inflammatory response (Figure 1).^14,15 They facilitate the healing process by removing dead cells, as well as by secreting trophic, angiogenic, and profibrotic cytokines, chemokines, and proteases.^15,17 These healing properties are attributed to distinct monocyte and macrophage subsets.^{14,16,18–20} Thus, control of macrophage function could be a major therapeutic target in directing the process of infarct repair.^21,22

Figure 1.

Macrophages as the dominant cell type in the infarcted myocardium.^14–16

The aim of our review is to describe recent discoveries related to targeting and modulating macrophage function to improve infarct repair. The pivotal role of monocytes and macrophages in other cardiovascular diseases, such as atherosclerosis and heart failure, is beyond the scope of this review and has been extensively described elsewhere.^23,24 We will focus on macrophage polarization, plasticity and heterogeneity, their role in infarct repair, and bidirectional interaction with stem cells, particularly mesenchymal cells. Specifically, we will focus on the potential of macrophage targeting and modulation in situ by drug carriers, particularly liposomes. The ability to improve infarct healing and repair by macrophage modulation could advance the field of cardiovascular regenerative medicine, particularly in elderly and sick individuals who have an impaired and uncontrolled immune system and reparative capability.

Macrophages are Characterized by Plasticity and Heterogeneity

Macrophages are versatile cells that embrace diverse activation states in response to stimuli. Macrophages play an important role in many features of human health: from development and homeostasis to regulation of inflammation, angiogenesis, healing, regeneration, and repair.^16,25
–27 An important macrophage characteristic is its plasticity, which enables it to switch from one phenotype to another.²⁷ However, attempts to define and classify monocyte and macrophage subsets, particularly in vivo, are complex and have created confusion.

Monocytes, macrophage precursors, comprise around 10% of leukocytes in humans and 4% in mice. The old classical dogma dictated that tissue macrophages develop from hematopoietic stem cells (HSCs) in bone marrow via blood monocyte intermediates. However, new data show that some adult tissue-resident macrophages develop from embryonic progenitors independent of HSCs and can self-renew.^28

–31 The number of resident macrophages in normal adult tissue varies: they are abundant in the spleen, liver, and lung while barely detectable in the heart. However, following injury, monocytes migrate to the damaged heart and convert to macrophages. The ability of cardiac macrophages to proliferate in response to injury has been an enigma until lately.

Most recently, Epelman et al have shown by genetic fate mapping that most subsets of resident cardiac macrophages originate from yolk sac and fetal monocyte progenitors (Table 1).²⁸ During normal hemostasis, resident macrophages are maintained through local proliferation. However, after macrophage depletion, or during inflammation, circulating-Ly6C^hi monocytes (M1 like) infiltrate the heart and dominant cardiac macrophages. In parallel, in response to injury or inflammation, resident macrophages also proliferate and expand. Expression of C-C chemokine receptor type 2 (CCR2) distinguished cardiac macrophages of adult monocytes from those of embryonic origin. These findings revealed the presence of multiple macrophage subsets in the heart, with different functions and origins (Table 1).²⁸

Table 1.

Origins and Function of Resident Macrophage Subsets in the Adult Heart.^28,32

Surface Markers	Origin	Phenotype Activity
CCR2⁻Ly6C⁻MHCII^hi	Yolk sac	Efficient presentation of antigens to T cells
CCR2⁻Ly6C⁻MHCII^lo	Yolk sac	Enhanced phagocytic ability of apoptotic cells and cell debris
CCR2⁻Ly6C⁺	Hematopoiesis
CCR2⁺Ly6C⁺	Hematopoiesis	Role in inflammation initiation by secreting IL-1β, for example

Abbreviations: IL, interleukin.

The heterogeneity of macrophages is dictated by different environmental signals from different tissues that undergo changes during injury, healing, and repair. A detailed discussion of the different classifications of monocytes and macrophages by their surface marker expression profiles is beyond the scope of this review and has been presented in Tables 2 and 3. In brief, monocyte/macrophage subsets are categorized by their chemokine receptors, surface markers, and function (Tables 2 and 3). Most of the studies on monocyte subsets have been performed in mice, which have a different distribution of mononuclear cells. For example, circulating “classic” monocytes in mice, such as Ly6C^hi, account for 50% of blood monocytes compared with 90% cluster of differentiation (CD) 14^hi CD16^lo “classic” monocytes in humans.³³ Several monocyte/macrophage classifications using various markers have been suggested, without consensus, due to the fact that such classifications vary among mice, rats, and humans (Table 2). Probably, the most popular is the M1/M2 classification based on classic (interferon or lipopolysaccharide [LPS]) and alternative (interleukin [IL] 4 and IL-13) activation (Tables 2 and 3). Although this might represent an over simplification of a complex and heterogeneous condition, the M1 and M2 classification is used to simplify the wide spectrum of macrophage activation and polarization.

Table 2.

Monocyte/Macrophage Characteristics.

	Macrophages as General Population	M1 Proinflammatory	Intermediate Monocytes/Macrophages (a Little Bit of Both M1 and M2)	M2 Anti-Inflammatory Reparative	References
Monocytes
Mouse	CD11b^hi CD64⁺ macrosialin (CD68)^hi	Ly-6C (Gr-1⁺)^hi CCR2^hiCX3 CR1⁺ CD43^lo	Ly-6C (Gr-1)⁺⁺ CD43⁻	Ly-6C(GR-1)^lo CCR2⁺CX3CR1^hi CD43^hi	^{14,16,19,33 –39}
Rat		CCR2^hi CD43^lo		CCR2^lo CD43^hi	^40,41
Human	CD68⁺CD64⁺	CD14^hiCD16^lo CCR2⁺CD62L⁺	CD14^hiCD16⁺	CD14⁺CD16^hiCD163⁺ CD32⁺mannose receptor (CD206)⁺	^{14,33,34,38,39,42,43}
Macrophages
Mouse	F4/80^hi CD64⁺Macrosialin (CD68)^hi	CD86^hi CD80^hi MHC class II^hi iNOS^hi		CD206⁺CD163⁺ RELMα⁺ Dectin⁺ Ym-1⁺ arginase-1^hi	^19,44 –47
Rat	ED-1 (CD68)⁺	CD80⁺ CCR7⁺ iNOS^hi		arginase-1 ^hi CD163⁺	^48,50
Biological function	Immune cells aimed to maintain organism steady state phagocytes	“Killers” fighting against pathogens or stress conditions	Biomarkers of inflammatory process and pathology at its initiation	“Healers” aimed to rehabilitate and repair the injured tissue

Abbreviations: CD, cluster of differentiation; MHC, major histocompatibility complex; iNOS, inducible nitric oxide synthase; RELM, resistin-like molecule α.

Table 3.

Mouse Macrophage Subsets.

Macrophage Subset	Activation State	Stimuli	Surface Markers	Cytokine Profile	Phenotype Activity
M1	Classical activation⁵¹				Damaged tissue destruction and digestion T-helper 1 response Proteolysis Inflammation amplification^{37,52 –56}
M1a		IFNγ, LPS, TLR	CD80, CD86, MHC class II, IL-1R	IL-1, IL-12, IL-23, TNF-α, ROS, iNOS, IL-6	Immediate and local host defense against pathogens ^19,33,57 Injury of endothelium and tissue damage Damaged tissue destruction and digestion T-helper 1 response Proteolysis^{7,14,16,20–22,58}
M1b		PAMPs such as LPS, HMGB1, ATP, and iron	CD80, CD86, MHC class II, IL-1R	IL-1, IL-23, TNF-α, ROS, iNOS, IL-6 Low levels of IL-12	Not as enhanced phagocytosis as M1a Innate macrophages^59–61
M2	Alternative activation⁵¹				Tissue healing and repair^{16,18,19,35,37,46 –48,62 –65}
M2a	Wound healing macrophages	IL-4, IL-13^19,48	Scavenger receptors, CD163, CD206	Fibronectin, arginase 1, IL-6, TNF-α	Promotes tissue granulation and proliferation Th2 responses
M2b		Immune complexes, TLR^19,48	MHC class II, CD86	IL-10, TNF-α, IL-1, IL-6, low IL-12	Microbicidal activity Phagocytosis T-helper 2 response Immunoregulation
M2c	Regulatory macrophages; type II activated	IL-10, TGF-β, glucocorticoids^19,48	CD150, CD163, CD206	IL-10, IL-1β, IL-6, TGF-β	Inflammation resolution Immunosuppressive Promotes wound repair angiogenesis Fibrosis and tissue remodeling Matrix deposition

Abbreviations: IFNγ, interferon γ; LPS, lipopolysaccharide; TLR, toll-like receptor; CD, cluster of differentiation; MHC, major histocompatibility complex; IL, interleukin; TNF, tumor necrosis factor; ROS, reactive oxygen species; iNOS, inducible nitric oxide synthase; PAMPs, pathogen-associated molecular patterns; HMGB, high-mobility group box; ATP, adenosine triphosphate; TGF, transforming growth factor.

In response to local triggers, macrophages are “reeducated” and polarize into either an M1 (proinflammatory) or an M2 (anti-inflammatory and reparative) phenotype.^19,62,66,67 M1 macrophages are proinflammatory^65,68 and have been linked to the development of atherosclerosis^69,70 as well as to acute inflammation after skeletal muscle injury and MI.^14,16 On the other hand, M2 macrophages are anti-inflammatory and reparative⁶⁵ and are implicated in the advanced stages of atherosclerosis,³⁴ MI healing,^14,16 fibrosis, and the development of pulmonary hypertension.⁷¹ Thus, modulating macrophage polarization could lead to a therapeutic strategy to prevent and treat these disorders.

There is evidence that the ability to modulate macrophage function relies on local signals, cell contact-dependent mechanisms, paracrine effects through the release of soluble factors, and epigenetic changes (reviewed by Krampera, Doorn, Delaroasa, and Galli).^57,72
–74 It has been suggested that a broad panel of molecular pathways could affect macrophage polarization.

Additionally, M2 macrophages contribute to the pathogenesis of cancer. Solid tumors induce M2 macrophage activation, the so-called tumor-associated macrophages, which then stimulate angiogenesis and tumor growth.⁷⁵ In summary, caution is recommended when classifying infarct macrophages. Due to the complexity that arises from the mixed phenotypes in vivo, some investigators classify macrophages based on their function: host defense, wound healing, or immune regulation (Table 2).^51,68

Macrophages in Acute MI

Because the adult mammalian heart lacks significant regenerative power, repair of the infarcted myocardium is dependent upon the coordinated process of inflammation and scar formation.⁴ During MI, cardiomyocyte death triggers inflammation that is essential to clean the debris and subsequently induce scar formation.⁷⁶ However, disproportionate activation of inflammatory monocytes and M1 macrophages could propagate tissue damage and worsen post-MI remodeling.^4,77,78

Macrophages are the central immune cells in the infarcted myocardium, controlling the progression and resolution of inflammation.¹⁶ Early depletion of monocytes or macrophages,^16,79

–82 as well as inhibition of macrophage migration,⁸³ worsen healing and provoke adverse left ventricular (LV) remodeling after MI. On the other hand, controlled activation of macrophages^21,84 improves myocardial healing and repair, thus subsequently improving remodeling and function. These findings were reproduced in a mouse model of kidney disease when ex vivo-activated macrophages reduced the severity of chronic renal disease and fibrosis.⁸⁵ Additionally, selective mineralocorticoid receptor blockade with eplerenone, immediately after MI, accelerates macrophage infiltration and switches to M2 activation during infarct healing, leading to improved tissue repair, angiogenesis, and remodeling.⁸⁶

Nahrendorf et al¹⁶ were the first to show that 2 distinct subsets of monocytes, precursors of tissue macrophages, participate in healing after MI in a sequential manner. CD11b^high/Ly-6C^high cells, exhibiting phagocytic and proinflammatory functions, accumulate during phase I (1-3 days post-MI), while CD11b^high/Ly-6C^low cells, attenuating the inflammatory response and expressing vascular endothelial growth factors (VEGFs), are present during phase II (4-7 days post-MI).¹⁶ Rapid monocyte turnover in the infarcted myocardium has been reported. Although the Ly-6C^high monocytes infiltrate the infarct in large numbers,^16,87 many of them depart or die within an average of 20 hours.⁸⁷ Macrophages derived from infiltrating monocytes acquire M1-proinflammatory characteristics. This rapid monocyte turnover in the infarcted heart could be significant for future monocyte/macrophage targeting. Nevertheless, as inflammation gives way to resolution, other Ly-6Cint/^low monocytes, equivalent to M2, emerge and contribute to infarct healing and repair.^16,87 These pioneering studies on sequential monocyte and macrophage subset dynamics in the infarcted myocardium have been confirmed by us and others.^26,81,82 Thus, control of macrophage function could be a major therapeutic target in optimizing the process of infarct repair.

Macrophages and Myocardial Regeneration

Due to their plasticity, macrophages coordinate and influence tissue remodeling, regeneration, and repair.^88

–93 Macrophages are abundant in the embryonic heart and are essential in cardiac morphogenesis. Subsequently, macrophage depletion leads to cardiac malformation.⁹⁴ Macrophages secrete a variety of trophic mediators including platelet-derived growth factors, transforming growth factors, insulin-like growth factor 1, Wnts ligands, and thymosin β4 (Table 4). Macrophage-derived factors dictate cell fate decisions and promote regeneration of neurons,⁹⁵ nerves,⁹⁶ skeletal myocytes,^88,92 and hepatocytes.⁹⁷ Thus, macrophage activation is a critical process contributing to healing and repair.

Table 4.

Cytokines Secreted by Macrophages.

Cytokine	Biological function	References
Proinflammatory cytokines
IL-12	Induces production of IFNγ	⁹⁸
IFNγ	Activating signal for M1, stimulates macrophages toward proinflammatory phenotype	⁹⁹
IL-1	High levels predict atherosclerotic heart disease Crucial for activation of inflammation pathways after MI Enhances neutrophil infiltration followed by monocyte arrival to the injured area and their differentiation to macrophages within the tissue The major ligands of IL-1 are IL-1α and IL-1β. IL-1β is a stronger inflammation inducer than IL-1α, mainly because most of the secreted IL-1α is cell associated	¹⁰⁰ ³ ^101–103 ¹⁰⁴
IL-8	Important regulator of neutrophil influx in inflammatory process	^105,106
IL-17	Stimulates cytokine expression to recruit neutrophils or monocytes Induces IL-1β and TNF-α in macrophages	¹⁰⁷
Anti-inflammatory cytokines
Thymosin β4	Angiogenic factor; elevating VEGF levels Induces metalloproteinases and chemotaxis to enhance cell migration Antioxidant and antimicrobial factor Limits inflammation in various pathways such as suppressing NF-κB and enhancing vasodilation to enable cell recruitment Myocardial regeneration	^108 –111
IL-10	Anti-inflammatory cytokine Inhibits Th1 responses by inhibition of IL-2 and IFN-γ Promotes Th2 responses for inflammation resolution Inhibits production of proinflammatory cytokines (IL1, IL-6, IL-8, and TNF-α) by classical activated macrophages	¹¹²
TGF-β	Initiates together with IL-10 healing pathways Decreases leukocytes adhesion, enhances fibroblast proliferation and myofibroblast differentiation Inducer of fibrosis and extracellular matrix production	¹¹³ ⁴⁶ ¹¹⁴
VEGF	Angiogenic factor: induces migration and proliferation mainly of endothelial cells Regulates cell survival and function of nonendothelial cells	^115,116
bFGF	Mediates proliferation, migration, and differentiation of variety of cells, such as fibroblast, epithelial, endothelial, etc Enhances angiogenesis by induction of endothelial cell proliferation and migration	^116,117
Dual function: pro- and anti-inflammatory cytokines
TNF-α	Cytokine activation is time-dependent and may act as a pro- or anti-inflammatory cytokine	^118–120
TNF-α	Mediates production of other proinflammatory cytokines, such as IL-12, activates neutrophils, triggers inflammation onset together with IL-1, resulting in tissue destruction (proinflammatory) Helps limit inflammation duration by inducing apoptosis of activated antigen-specific lymphocytes and by reducing proinflammatory cytokines, such as IL-12 and IL-23 (anti-inflammatory)	^118–120
IL-6	Involved in the regulation of immune responses and in the production of most of the acute phase proteins Plays a role in regulation of cell survival, growth, and differentiation May also enhance anti-inflammatory activities in the initial stages of healing and repair by induction of IL-1 receptor antagonist and TNF antagonists	¹²¹ ¹²² ^123,124
Oncostatin M	Belongs to the interleukin 6 (IL-6) family Induces dedifferentiation of cardiomyocytes as an initial step before cardiomyocyte proliferation

Abbreviations: IFNγ, interferon γ; TGF, transforming growth factor; VEGF, Vascular endothelial growth factor; bFGF, basic fibroblast growth factor; TNF, tumor necrosis factor; MI, myocardial infarction; Th1, T-helper 1; Th2, T-helper 2.

The neonatal heart of rat and mouse maintains certain regenerative mechanisms, but the window of regeneration is limited and disappears soon after birth.^2,125,126 We noticed a massive transient accumulation of monocytes and macrophages at the site of myocardial resection and subsequent regeneration in the neonatal heart of mouse (Konfino T, MSc, unpublished data).¹²⁷

Indeed, most recently, Aurora et al have identified macrophages as mediators of neonatal heart regeneration.¹²⁸ Following MI and monocyte and macrophage depletion in newborn (day 1) mice, they found that monocytes and macrophages are essential for neonatal heart regeneration, particularly myocardial angiogenesis. Comparison between the immune reaction after MI between mice at day 1 after birth (regenerative phase) and at day 14 (nonregenerative phase) revealed differences in phenotype and function of cardiac monocytes and macrophages. Macrophages derived from newborn mouse represent a unique population that does not match the classical characteristics of M1 or M2 macrophages. Thus, the monocytes/macrophages from newborn mice might have regenerative functions different from those of the profibrotic activities of adult macrophages.¹²⁸ Understanding the role of macrophages in cardiac regeneration may lead to the development of novel therapies that could improve cardiac function after MI.¹²⁹

Macrophages have been suggested to interact with stem cells, progenitor cells, and myocytes and play a critical role during skeletal muscle regeneration.^{88,92,130,131} Furthermore, a most recent study has suggested that macrophages are essential for limb regeneration in salamander.¹³² Systemic macrophage depletion during limb amputation resulted in failure of limb regeneration and fibrosis. Significantly, full regenerative capacity was restored by reamputation once endogenous macrophage populations had been replenished. Together, these studies suggest that identification of macrophage-derived therapeutic molecules may promote myocardial regeneration.¹³²

Although myocardial regeneration in the adult heart is scarce, its mechanism is unclear. It may originate from resident cardiac stem cells,^133,134 cardiomyocyte dedifferentiation and proliferation,^125,135 or both.¹³⁶ Macrophages might play a role in myocardial regeneration. For example, zebra fish have an amazing ability to regenerate their hearts.¹³⁷ However, treatment with an anti-inflammatory glucocorticoid inhibits myocardial regeneration in the zebra fish.¹³⁷ Thus, manipulating its immune response could regulate zebra fish cardiac repair.

During acute MI in mouse, macrophages in the infarcted tissue and border zone express high levels of oncostatin M (OSM).¹³⁸ Oncostatin M is a member of the IL-6 family. It exerts several unique effects, such as stimulation of cardiomyocyte dedifferentiation. Dedifferentiation of adult cardiomyocytes has been suggested to be the initial step before cardiomyocyte proliferation.^125,135 Thus, it is tempting to speculate that macrophage OSM can promote cardiomyocyte proliferation and myocardial regeneration. However, it should be noted that sustained dedifferentiation, cardiac remodeling, and heart failure characterize continuous uncontrolled stimulation with OSM.¹³⁸ Together, these studies on the potential role of macrophages in myocardial repair and regeneration suggest that future research is necessary to understand how modulation of macrophage response to cardiac injury can influence heart regeneration and functional outcomes.¹²⁹

Interaction of Macrophages with Mesenchymal Stem/Stromal Cells

A relatively simple and feasible approach to target and modulate macrophage function in situ is to use mesenchymal stromal cell (MSC) therapy. Mesenchymal stromal cells are nonhematopoietic, multipotent, progenitor cells found in various adult tissues, particularly bone marrow and adipose tissue.¹³⁹ They are characterized by their paracrine reparative and immunomodulatory properties. Mesenchymal stromal cells ameliorate infarct healing and repair,¹⁴⁰ but their mechanism of action is not entirely clear.

In the last few years, it has been recognized that MSCs are modulators of immune response¹⁴¹ and can attenuate a systemic inflammatory response in animal models of lung injury and sepsis.¹⁴² These protective effects could be mediated by macrophages.²² Recent reports have shown that MSCs act via macrophages, switching them from M1 to M2 (reparative) phenotype, in vitro^143

–146 and in vivo (Table 5).^81,82

Table 5.

Mesenchymal Stromal Cells Switch Macrophages From M1 to M2 Subset.

MΦ	Manipulation	Result	MΦ Subset	Reference
Circulating or cardiac mouse MΦ after MI	In vivo infusion of human BM-MSCs or human umbilical cord perivascular cells to immune-deficient mice	Anti-inflammatory M2 in circulation and heart	Reduced overall macrophage number CD206⁺⁺, IL-1β^lo, IL-6^lo, IL-10^hi	⁸¹
Mouse macrophages after MI	Local injection of mouse BM-MSCs	Anti-inflammatory and reparative M2	CD206+, IL-10^hi, IL-5^hi and granulocyte–macrophage colony-stimulating factor^hi	⁸²
Human MΦ from circulating mononuclear cells of healthy donors	In vitro coculture with human MSCs isolated from bone marrow	MSC-educated MΦ	IL-10^hi, IL-12^lo, IL-6^hi, TNF^lo, CD206⁺⁺, higher level of phagocytic activity	¹⁴⁵
Mouse peritoneal MΦ	In vitro coculture with MSCs isolated from mouse bone marrow	Anti-inflammatory M2	TNFα^lo, IL-6^lo, IL-12p70^lo, IFNγ^lo, IL-10^hi	¹⁴⁴
Mouse MΦ infiltration in response to glass cylinder implantation	In vivo inoculation of MSCs from mouse bone marrow inside the cylinders	Anti-inflammatory M2	CD86^lo, IL-12p70^lo, IL-10^hi, IL12p40^hi	¹⁴⁴
Human circulating mononuclear cells	In vitro coculture with MSCs isolated from human gingival (GMSC)	Anti-inflammatory M2	CD206^hi, IL-10^hi, IL-6^hi, TNFα^lo	¹⁴³
Mouse MΦ in a wound healing model	In vivo infusion of GMSC	Anti-inflammatory M2	TNFα^lo, IL-6^lo, IL-10^hi	¹⁴³
Human MΦ from circulating mononuclear cells of healthy donors	Adipose tissue-derived MSCs	Anti-inflammatory M2	CD206⁺⁺, CD163⁺⁺, CD16⁺⁺, IL-4^hi IL-13^hi, IL-10^hi, low phagocytic capacity	¹⁴⁶

Abbreviations: MΦ, macrophages; MI, myocardial infarction; BM-MSCs, bone marrow-derived mesenchymal stromal cells; CD, cluster of differentiation; IL, interleukin; TNF, tumor necrosis factor; IFNγ, interferon γ; GMSC, gingiva-derived mesenchymal stem cells.

Mesenchymal stromal cell-based macrophage reprogramming is associated with increased secretion of M2 cytokines such as IL-10 and VEGFs.¹⁴⁶ Concomitantly, MSCs decrease secretion of inflammatory cytokines such as IL-1α, tumor necrosis factor α (TNF-α), IL-12, and IL-17 from macrophages.¹⁴⁶ Significantly, this interaction is bidirectional, and macrophages also stimulate MSCs to secrete cytokines such as IL-4 and IL-13, which are M2 inducers.¹⁴⁶

We have recently shown that MSC therapy significantly increased the percentage of reparative M2 macrophages (F4/80⁺CD206⁺) in the infarcted myocardium of mice, 3 and 4 days after MI.⁸² Macrophage cytokine secretion, relevant to infarct healing and repair, was significantly increased after MSC therapy or incubation with MSCs or an MSC supernatant. Notably, with or without MSC therapy, transient, early macrophage depletion increased mortality after MI and produced the greatest negative effect on infarct size, LV remodeling, and function as well as a significant incidence of LV thrombus formation. These adverse effects were attenuated with macrophage restoration and MSC therapy.⁸²

Dayan et al⁸¹ investigated the effect of human MSCs in an MI model of immune-deficient mice. Human bone marrow-derived MSCs and human perivascular cells from umbilical cord were infused 48 hours after MI. Mesenchymal stromal cells reduced the number of macrophage/monocytes, while the proportion of M2 macrophages was increased in the circulation and the heart, 24 hours after treatment. Moreover, LV contractility was improved 2 weeks after cell infusion but was similar to controls 16 weeks after MI.

Taken together, some of the protective effects of MSCs on infarct repair are mediated by macrophages, which are essential for early healing and repair. Thus, targeting macrophages by MSCs could be a novel strategy to improve infarct healing and repair.

Targeting Macrophages with Liposomes

Carrier-mediated drug targeting provides several advantages that improve the pharmacokinetics and bioavailability of therapeutic and imaging agents. Drug targeting by a carrier requires recognition and high-affinity binding between 2 partners: (1) a receptor (in its broadest definition) sufficiently unique to, and/or overexpressed at, the target cell membrane and (2) a targeting agent that constitutes an integral part of the carrier (with 1 macrophage-linked exception that will be discussed later), thus assuring that it will not dissociate in vivo causing carrier-targeting ability loss. Recognition and high-affinity binding operate at short range, and conditions have to be created or met in a living system in order to bring the targeted carrier close enough to its target for it to produce the desired effect. The in vivo conditions required to bring the 2 targeting partners close enough have been discussed elsewhere.¹⁴⁷ In the present section, we will focus on macrophages.

Targeting particular drug carriers to macrophages that are part of the reticuloendothelial system (RES) warrants special attention. One of the physiological roles of macrophages, that is, its ability to bind and internalize foreign microparticles (whether made from natural or synthetic materials) was recognized in the world of liposomes and has led to the terms active and passive targeting.^148

–151 Passive targeting is when the RES is the therapeutic target, and active targeting is when the therapeutic target is outside the RES avoiding both the RES and transferring the carrier to its target. We wish to point out that the term passive targeting (for drug carriers) is also used in another context—the enhanced retention and permeability in tumor therapy. In this review, dedicated to macrophages and infarct repair, the use of the term passive targeting will be applied only to the RES as the therapeutic target.

The case of passive liposome targeting to macrophages is the exception to the need for both partners. Macrophages possess unique scavenger receptors that recognize and bind liposomes, negating the need for a second partner (ie, the targeting agent) since the macrophages recognize and bind regular (conventional) liposomes as they are.^148

–151 Using liposomes as macrophage-targeted drug carriers has been applied for several different therapeutic goals, usually utilizing passive targeting.¹⁵² Two veteran objectives were in the fields of cancer and Leishmania. For cancer therapy, the goal was to render macrophages tumoricidal by liposome-formulated muramil tripeptide.^148,151,153 The parasite causing Leishmania resides within the macrophages and was eradicated using antimonial drugs formulated in liposomes.¹⁵⁴ In the field of cancer therapy, the need for active tumor targeting was recognized early on, and extensive efforts have been successfully invested for more than 2 decades in identifying and establishing liposome requirements for RES avoidance or uptake.¹⁵⁵ Consequently, it is to the older literature one frequently has to go for the fundamental work done on liposome-mediated drug targeting to the RES.

We recently studied macrophage interactions with 4 liposome types. Two were regular (conventional) nano- and microsized liposomes denoted regular unilamellar (RL-ULV) and regular multilamellar (RL-MLV), respectively, and 2 were veteran developments by our team, nano- and microsized liposomes, surface-modified by covalent anchoring of hyaluronan, denoted HA-ULV and HA-MLV, respectively.¹⁵⁵ The macrophages bound all liposome types, with the affinity sequence of HA-MLV > HA-ULV > RL-MLV > RL-ULV, but only the RL-MLVs were internalized.¹⁵⁵ The HA-MLVs and RL-MLVs emerged as the favored candidates for drug delivery to macrophages. The finding that, despite being microparticles, HA-MLVs are not internalized by macrophages, yet bind to them with high affinity (the highest), is a manifestation of their binding to hyaluronan-specific receptors (the CD44 family) harbored by macrophage membranes rather than to scavenger receptors.¹⁵⁵ Although CD44 receptors are expressed in the majority of tissues, the one expressed on normal tissues is usually CD44s (also named CD44H), whereas in cancer and in inflammatory diseases those expressed are usually the CD44 splice variants (CD44v).¹⁵⁶ It is well known that the affinity of hyaluronan to the latter is significantly higher than to CD44s.¹⁵⁶

Testing HA-MLV targeting to infarct macrophages in mouse (intravenous [IV] tail vein injection, 3 days after MI), we found a high accumulation of these liposomes in the infarcted heart, but none in the liver, spleen, or lungs. There was also no HA-MLV accumulation in the healthy hearts of the control mice. Taken together, these results are in vivo proof of the concept that HA-MLVs actively target macrophages, which are pivotal cells in the inflammatory process.

Bearing in mind that the goal is to target the drug to its site of action, the targeted carrier being a means to this end, it is not enough to have the carrier preferentially accumulate at the target. Getting the drug to its molecular target also requires consideration of the pathways for drug supply from the carrier to the cell. Contrary to a prominently held assumption, carrier internalization is not a critical requirement for small-molecular-weight drugs that operate inside the cell, such as steroids and nonsteroidal anti-inflammatory drugs (NSAIDs) applied for the treatment of inflammations and infections. One of the advantages of carrier-mediated drug delivery is the potential to perform as slow-release drug depots for the many cases that such release profiles benefit the therapy. For example, half-lives of drug release for anti-inflammatory liposomal formulations of diclofenac, dexamethasone, or their combination are in the range of 1 to 3 days.¹⁵⁷ The following scenario can be envisioned for liposome-mediated drug supply to the macrophage cytosol: the RL-MLVs undergo internalization—a fairly fast process that can take under an hour and is considered complete within a few hours.^151,155,158 Once the liposome is disrupted in the course of release from the endosome, the cytosol is exposed at once to the whole drug load. Whether this is beneficial or detrimental may be drug species dependent, but clearly drug supply to the cytosol will be dominated by the endocytotic process rather than by the slow-release property of the liposomal formulation. For the HA-MLVs that stay as high-affinity bound drug depots at the macrophage membrane, it is reasonable to assume that their slow-release property will dominate drug supply to the cytosol, the drug diffusing out of the liposome across the cell membrane and into the cell. Thus, it may well be that in such cases carrier internalization is not necessary and may actually be less effective than a membrane-adhering drug depot.

In conclusion, 2 types of microsized liposomes are strong candidates for drug targeting to macrophages: regular liposomes that are bound and internalized and surface-modified liposomes, bearing a ligand directed against a receptor on the macrophage membrane, that remain bound without internalization, as exemplified earlier for hyaluronan and CD44. In vitro studies on liposomes and macrophages yield data on binding thermodynamics and cellular localizations and also shed light on whether internalization does or does not take place. With a given drug, in vitro studies in established or primary macrophages can also provide insight into pathways of drug supply to the cells. However, in vivo studies with animal models of the designated pathology are required to obtain proof of concept for liposome-mediated drug targeting to macrophages for infarct repair.

An original approach to improve infarct repair is based on the delivery of apoptotic-mimicking particles, such as phosphatidylserine-presenting liposomes.¹⁵⁹ The rational for this approach is based on the observation that macrophages recognize apoptotic cells by exposed phosphatidylserine.¹⁶⁰ Phagocytosis of apoptotic cells by macrophages inhibit secretion of proinflammatory cytokines, stimulate secretion of anti-inflammatory cytokines, and thereby resolve inflammation.¹⁶⁰ Indeed, reprogramming of infarct macrophages by IV delivery of phosphatidylserine-presenting liposomes improved angiogenesis and prevented adverse cardiac remodeling in rat after MI.¹⁵⁹

Modulating Macrophage Function by Other Approaches

Short interfering RNAs (siRNAs) are an emerging technology aimed at silencing specific gene targets.¹⁶¹ Unlike small molecule drugs, siRNAs are highly specific toward their target sequence and have little off-target effects, making them a useful tool in basic research and a potential new approach to treat different gene-related diseases. Several siRNAs are already in clinical trials for different diseases^162,163 including age-related macular degeneration (ClinicalTrials.gov Identifier: NCT00259753), solid tumors (ClinicalTrials.gov Identifier: 00689065), acute kidney injury after cardiac bypass surgery (ClinicalTrials.gov Identifier: NCT00554359), and more.¹⁶⁴ However, a major impediment for siRNA treatment still remains: that of safe and efficacious delivery to target cells. Short interfering RNA delivery faces many obstacles when administered in vivo, such as degradation by serum nucleases, immune cell phagocytosis, and renal excretion. Lately, scientists have developed new strategies to improve stability and specificity of siRNA by use of nanoparticle-mediated delivery (ie, liposomes and polymers) and conjugation to ligands.^163,165 These modifications have made siRNAs both target specific and less toxic, making them much more relevant for clinical use.

Macrophages are an appealing candidate for siRNA delivery, not only because they play roles in various diseases^166,167 but also because they are easy to target due to their phagocytic capability. As previously mentioned, macrophages are essential for the healing of infarcted myocardium.^16,82 Hence, modulation of macrophage function with siRNAs could be a novel method to treat cardiovascular disease. Several studies have begun investigating the effects of different siRNAs targeted to macrophages. In a study by Leuschner et al, silencing monocyte chemokine receptor CCR2 by nanoparticle-mediated siRNA delivery has shown to diminish the migration of inflammatory monocytes to the heart after MI and shift the balance toward an M2 anti-inflammatory subset.¹⁶⁸ This anti-inflammatory environment helped attenuate infarct size as well as reduce lesion size in a mouse model of atherosclerosis. Inhibition of macrophage-induced inflammation has also proven useful in a model of murine arthritis, where TNF-α siRNA nanoparticles targeted to peritoneal macrophages, lowered systemic inflammation, and joint swelling.¹⁶⁹ Another example of the beneficial use of macrophage-targeted siRNAs is the work of Aouadi et al, where macrophage administration of Map4k4-siRNA reduced cytokine toxicity in a mouse model of LPS-induced systemic inflammation by inhibiting TNF-α and IL-1β production.¹⁷⁰ In summary, it seems that the application of siRNAs for macrophage gene silencing could be used for these and many more targets involved in macrophage migration, cytokine secretion, and even polarization.

Another approach that can both reduce the number of inflammatory macrophages and switch their function to reparative phenotype after MI is administration of thymosin β4 sulfoxide.¹⁰⁸ Administration of thymosin β4 sulfoxide in mouse after MI improves healing and limits fibrosis.¹⁰⁸ Finally, another potential method to modulate macrophage function is by targeting heme oxygenase 1 (HO-1). Heme oxygenase 1, also known as heat shock protein 32, has long been known for its anti-inflammatory properties. Heme oxygenase 1 exerts its protective effects through the degradation of heme and the subsequent production of anti-inflammatory, antiapoptotic, and antioxidative molecules.¹⁷¹ Hemin is an iron-containing porphyrin that potently upregulates the expression of HO-1 in macrophages.^172,173 Heme oxygenase 1 decreases macrophage inflammatory cytokine levels, such as TNF-α, through an IL-10-mediated pathway,^173,174 making macrophage HO-1 a potential therapeutic target, especially in diseases associated with prolonged inflammation. Indeed, several studies have shown that administration of hemin alleviates various pathologies in murine models of cardiovascular disease, NSAID-induced intestinal injury, graft transplantation, and others. For example, in a rat model of ischemia reperfusion injury, hemin preconditioned hearts had improved postischemic cardiac function compared with control rats.¹⁷⁵ Jadhav et al¹⁷⁶ recently showed that the anti-inflammatory and antioxidative influence of hemin-ameliorated cardiac function restored normoglycemia and reduced blood pressure in a rat model of diabetic cardiomypoathy. Furthermore, they also showed that hemin administration decreased macrophage infiltration and enhanced the anti-inflammatory type 2 macrophage phenotype, while decreasing levels of inflammatory M1 macrophages.¹⁷⁶

This finding is in agreement with a previous study describing the role of HO-1 in macrophage polarization¹⁷⁷ and the study of Yoriki et al, which showed that upregulation of HO-1 in macrophages induces M2 characteristics.¹⁷⁸ These findings shed more light on the many mechanisms through which hemin exerts its beneficial effects and demonstrates new ways to polarize macrophages toward a cytoprotective, reparative phenotype. Hemin-based macrophage polarization may be of particular interest due to its translational possibilities, since it is already an administered drug against porphyria.¹⁷⁹

Summary and Future Directions

Macrophages play a critical role in the pathobiology of MI and are attractive therapeutic targets. Macrophage function can be stimulated or inhibited to improve healing, repair, and regeneration. Potential therapeutic approaches include reducing proinflammatory macrophage infiltration or the induction of a reparative and antifibrotic phenotype to guide repair and regeneration. The principles and strategies described here could be applicable to other cardiovascular diseases associated with macrophages, such as atherosclerosis, myocarditis, and pulmonary hypertension.

As this review highlights the actions of macrophages are complex and can be either beneficial or deleterious. Further research needs to be carried out to increase our understanding of the processes that control human macrophage activation during the various stages of acute and chronic myocardial disease. Better understanding of macrophage regulatory action could lead to the development of specific macrophage-based theranostic, which could improve infarct repair and recovery of patients after MI.

Footnotes

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was supported by grants from the Israel Ministry of Science, Culture, and Sport (JL and RM) and the Israeli National Nanotechnology Initiative and Helmsley Charitable Trust for a focal technology area on Nanomedicines for Personalized Theranostics (JL and RM).

References

Nichols

Townsend

Scarborough

Rayner

. Cardiovascular disease in Europe: epidemiological update. Eur Heart J. 2013;34:3028–3034.

Xin

Olson

Bassel-Duby

. Mending broken hearts: cardiac development as a basis for adult heart regeneration and repair. Nature reviews Molecular cell biology. 2013;14:529–41.

Frantz

Bauersachs

Ertl

. Post-infarct remodelling: contribution of wound healing and inflammation. Cardiovascular research. 2009;81:474–81.

Kong

Christia

Frangogiannis

. The pathogenesis of cardiac fibrosis. Cell Mol Life Sci. 2014;71:549–574.

Lee

Marinelli

van der Laan

Sena

Gorbatov

Leuschner

Dutta

Iwamoto

Ueno

Begieneman

Niessen

Piek

Vinegoni

Pittet

Swirski

Tawakol

Di Carli

Weissleder

Nahrendorf

. PET/MRI of inflammation in myocardial infarction. Journal of the American College of Cardiology. 2012;59:153–63.

Varda-Bloom

Leor

Ohad

Hasin

Amar

Fixler

Battler

Eldar

Hasin

. Cytotoxic T lymphocytes are activated following myocardial infarction and can recognize and kill healthy myocytes in vitro. Journal of molecular and cellular cardiology. 2000;32:2141–9.

Bonvini

Hendiri

Camenzind

. Inflammatory response post-myocardial infarction and reperfusion: a new therapeutic target? European Heart Journal Supplements. 2005;7:I27–I36.

Heymans

Hirsch

Anker

Aukrust

Balligand

J-L

Cohen-Tervaert

Drexler

Filippatos

Felix

Gullestad

Hilfiker-Kleiner

Janssens

Latini

Neubauer

Paulus

Pieske

Ponikowski

Schroen

Schultheiss

H-P

Tschöpe

Van Bilsen

Zannad

McMurray

Shah

. Inflammation as a therapeutic target in heart failure? A scientific statement from the Translational Research Committee of the Heart Failure Association of the European Society of Cardiology. European Journal of Heart Failure. 2009;11:119–129.

Braunwald

. Cardiovascular science: opportunities for translating research into improved care. The Journal of clinical investigation. 2013;123:6–10.

10.

Olson

Eric

. Interview by Hannah Stower. Nature reviews Genetics. 2013;14:371.

11.

Krafts

. Tissue repair: The hidden drama. Organogenesis. 2010;6:225–33.

12.

Zebrowski

Engel

. The cardiomyocyte cell cycle in hypertrophy, tissue homeostasis, and regeneration. Reviews of physiology, biochemistry and pharmacology. 2013;165:67–96.

13.

Lozano

Naghavi

Foreman

Lim

Shibuya

Aboyans

Abraham

Adair

Aggarwal

Ahn

Alvarado

Anderson

Andrews

Atkinson

Baddour

Barker-Collo

Bartels

Bell

Benjamin

Bennett

Bhalla

Bikbov

Bin Abdulhak

Birbeck

Blyth

Bolliger

Boufous

Bucello

Burch

Burney

Carapetis

Chen

Chou

Chugh

Coffeng

Colan

Colquhoun

Colson

Condon

Connor

Cooper

Corriere

Cortinovis

de Vaccaro

Couser

Cowie

Criqui

Cross

Dabhadkar

Dahodwala

De Leo

Degenhardt

Delossantos

Denenberg

Des Jarlais

Dharmaratne

Dorsey

Driscoll

Duber

Ebel

Erwin

Espindola

Ezzati

Feigin

Flaxman

Forouzanfar

Fowkes

Franklin

Fransen

Freeman

Gabriel

Gakidou

Gaspari

Gillum

Gonzalez-Medina

Halasa

Haring

Harrison

Havmoeller

Hay

Hoen

Hotez

Hoy

Jacobsen

James

Jasrasaria

Jayaraman

Johns

Karthikeyan

Kassebaum

Keren

Khoo

Knowlton

Kobusingye

Koranteng

Krishnamurthi

Lipnick

Lipshultz

Ohno

Mabweijano

MacIntyre

Mallinger

March

Marks

Matsumori

Matzopoulos

Mayosi

McAnulty

McDermott

McGrath

Mensah

Merriman

Michaud

Miller

Mock

Mocumbi

Mokdad

Moran

Mulholland

Nair

Naldi

Narayan

Nasseri

Norman

O’Donnell

Omer

Ortblad

Osborne

Ozgediz

Pahari

Pandian

Rivero

Padilla

Perez-Ruiz

Perico

Phillips

Pierce

Pope

3rd Porrini

Pourmalek

Raju

Ranganathan

Rehm

Rein

Remuzzi

Rivara

Roberts

De Leon

Rosenfeld

Rushton

Sacco

Salomon

Sampson

Sanman

Schwebel

Segui-Gomez

Shepard

Singh

Singleton

Sliwa

Smith

Steer

Taylor

Thomas

Tleyjeh

Towbin

Truelsen

Undurraga

Venketasubramanian

Vijayakumar

Vos

Wagner

Wang

Watt

Weinstock

Weintraub

Wilkinson

Woolf

Wulf

Yeh

Yip

Zabetian

Zheng

Lopez

Murray

AlMazroa

Memish

. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet. 2012;380:2095–128.

14.

Nahrendorf

Pittet

Swirski

. Monocytes: Protagonists of Infarct Inflammation and Repair After Myocardial Infarction. Circulation. 2010;121:2437–2445.

15.

Lambert

Lopez

Lindsey

. Macrophage roles following myocardial infarction. International journal of cardiology. 2008;130:147–58.

16.

Nahrendorf

Swirski

Aikawa

Stangenberg

Wurdinger

Figueiredo

Libby

Weissleder

Pittet

. The healing myocardium sequentially mobilizes two monocyte subsets with divergent and complementary functions. The Journal of experimental medicine. 2007;204:3037–47.

17.

Cardilo-Reis

Witztum

Binder

. When Monocytes Come (Too) Close to Our Hearts. Journal of the American College of Cardiology. 2010;55:1639–1641.

18.

Gordon

Taylor

. Monocyte and macrophage heterogeneity. Nat Rev Immunol. 2005;5:953–64.

19.

Mantovani

Sica

Sozzani

Allavena

Vecchi

Locati

. The chemokine system in diverse forms of macrophage activation and polarization. Trends Immunol. 2004;25:677–86.

20.

Gordon

Martinez

. Alternative Activation of Macrophages: Mechanism and Functions. Immunity. 2010;32:593–604.

21.

Leor

Rozen

Zuloff-Shani

Feinberg

Amsalem

Barbash

Kachel

Holbova

Mardor

Daniels

Ocherashvilli

Orenstein

Danon

. Ex vivo activated human macrophages improve healing, remodeling, and function of the infarcted heart. Circulation. 2006;114:I94–100.

22.

Amsalem

Mardor

Feinberg

Landa

Miller

Daniels

Ocherashvilli

Holbova

Yosef

Barbash

Leor

. Iron-oxide labeling and outcome of transplanted mesenchymal stem cells in the infarcted myocardium. Circulation. 2007;116:I38–45.

23.

Apostolakis

Lip

Shantsila

. Monocytes in heart failure: relationship to a deteriorating immune overreaction or a desperate attempt for tissue repair? Cardiovascular research. 2010;85:649–60.

24.

Swirski

Nahrendorf

. Leukocyte behavior in atherosclerosis, myocardial infarction, and heart failure. Science. 2013;339:161–6.

25.

Yano

Miura

Whittaker

Miki

Sakamoto

Nakamura

Ichikawa

Ikeda

Kobayashi

Ohori

Shimamoto

. Macrophage colony-stimulating factor treatment after myocardial infarction attenuates left ventricular dysfunction by accelerating infarct repair. Journal of the American College of Cardiology. 2006;47:626–34.

26.

Troidl

Mollmann

Nef

Masseli

Voss

Szardien

Willmer

Rolf

Rixe

Troidl

Kostin

Hamm

Elsasser

. Classically and alternatively activated macrophages contribute to tissue remodelling after myocardial infarction. J Cell Mol Med. 2009;13:3485–96.

27.

Wynn

Chawla

Pollard

. Macrophage biology in development, homeostasis and disease. Nature. 2013;496:445–55.

28.

Epelman

Lavine

Beaudin

Sojka

Carrero

Calderon

Brija

Gautier

Ivanov

Satpathy

Schilling

Schwendener

Sergin

Razani

Forsberg

Yokoyama

Unanue

Colonna

Randolph

Mann

. Embryonic and Adult-Derived Resident Cardiac Macrophages Are Maintained through Distinct Mechanisms at Steady State and during Inflammation. Immunity. 2014;40:91–104.

29.

Gautier

Shay

Miller

Greter

Jakubzick

Ivanov

Helft

Chow

Elpek

Gordonov

Mazloom

Ma’ayan

Chua

Hansen

Turley

Merad

Randolph

. Gene-expression profiles and transcriptional regulatory pathways that underlie the identity and diversity of mouse tissue macrophages. Nature immunology. 2012;13:1118–28.

30.

Sieweke

Allen

. Beyond stem cells: self-renewal of differentiated macrophages. Science. 2013;342:1242974.

31.

Yona

Kim

Wolf

Mildner

Varol

Breker

Strauss-Ayali

Viukov

Guilliams

Misharin

Hume

Perlman

Malissen

Zelzer

Jung

. Fate mapping reveals origins and dynamics of monocytes and tissue macrophages under homeostasis. Immunity. 2013;38:79–91.

32.

Cohen

Mosser

. Cardiac macrophages: how to mend a broken heart. Immunity. 2014;40:3–5.

33.

Lech

Anders

. Macrophages and fibrosis: How resident and infiltrating mononuclear phagocytes orchestrate all phases of tissue injury and repair. Biochimica et biophysica acta. 2013;1832:989–97.

34.

Mantovani

Garlanda

Locati

. Macrophage diversity and polarization in atherosclerosis: a question of balance. Arterioscler Thromb Vasc Biol. 2009;29:1419–23.

35.

Arnold

Henry

Poron

Baba-Amer

van Rooijen

Plonquet

Gherardi

Chazaud

. Inflammatory monocytes recruited after skeletal muscle injury switch into antiinflammatory macrophages to support myogenesis. The Journal of experimental medicine. 2007;204:1057–69.

36.

Ziegler-Heitbrock

Ancuta

Crowe

Dalod

Grau

Hart

Leenen

Liu

MacPherson

Randolph

Scherberich

Schmitz

Shortman

Sozzani

Strobl

Zembala

Austyn

Lutz

. Nomenclature of monocytes and dendritic cells in blood. Blood. 2010;116:e74–80.

37.

Geissmann

Jung

Littman

. Blood monocytes consist of two principal subsets with distinct migratory properties. Immunity. 2003;19:71–82.

38.

Ancuta

Rao

Moses

Mehle

Shaw

Luscinskas

Gabuzda

. Fractalkine preferentially mediates arrest and migration of CD16+ monocytes. The Journal of experimental medicine. 2003;197:1701–7.

39.

Ancuta

Liu

Misra

Wacleche

Gosselin

Zhou

Gabuzda

. Transcriptional profiling reveals developmental relationship and distinct biological functions of CD16+ and CD16- monocyte subsets. BMC Genomics. 2009;10:403.

40.

Strauss-Ayali

Conrad

Mosser

. Monocyte subpopulations and their differentiation patterns during infection. J Leukoc Biol. 2007;82:244–52.

41.

Yrlid

Jenkins

MacPherson

. Relationships between distinct blood monocyte subsets and migrating intestinal lymph dendritic cells in vivo under steady-state conditions. J Immunol. 2006;176:4155–62.

42.

Tallone

Turconi

Soldati

Pedrazzini

Moccetti

Vassalli

. Heterogeneity of human monocytes: an optimized four-color flow cytometry protocol for analysis of monocyte subsets. J Cardiovasc Transl Res. 2011;4:211–9.

43.

Zeyda

Stulnig

. Adipose tissue macrophages. Immunol Lett. 2007;112:61–7.

44.

Devaraj

Jialal

. C-reactive protein polarizes human macrophages to an M1 phenotype and inhibits transformation to the M2 phenotype. Arterioscler Thromb Vasc Biol. 2011;31:1397–402.

45.

Lee

Huen

Nishio

Lee

Choi

Ruhrberg

Cantley

. Distinct macrophage phenotypes contribute to kidney injury and repair. J Am Soc Nephrol. 2011;22:317–26.

46.

Ricardo

van Goor

Eddy

. Macrophage diversity in renal injury and repair. J Clin Invest. 2008;118:3522–30.

47.

Tugal

Liao

Jain

. Transcriptional control of macrophage polarization. Arterioscler Thromb Vasc Biol. 2013;33:1135–44.

48.

Kou

Babensee

. Macrophage and dendritic cell phenotypic diversity in the context of biomaterials. J Biomed Mater Res A. 2010;96:239–60.

49.

Badylak

Valentin

Ravindra

McCabe

Stewart-Akers

. Macrophage phenotype as a determinant of biologic scaffold remodeling. Tissue Eng Part A. 2008;14:1835–42.

50.

Brown

Valentin

Stewart-Akers

McCabe

Badylak

. Macrophage phenotype and remodeling outcomes in response to biologic scaffolds with and without a cellular component. Biomaterials. 2009;30:1482–91.

51.

Mosser

Edwards

. Exploring the full spectrum of macrophage activation. Nat Rev Immunol. 2008;8:958–69.

52.

Wang

Tang

Yago

McDaniel

McGee

Huo

Xia

. P-selectin glycoprotein ligand-1 is highly expressed on Ly-6Chi monocytes and a major determinant for Ly-6Chi monocyte recruitment to sites of atherosclerosis in mice. Circulation. 2008;117:3227–37.

53.

Mildner

Schmidt

Nitsche

Merkler

Hanisch

Mack

Heikenwalder

Bruck

Priller

Prinz

. Microglia in the adult brain arise from Ly-6ChiCCR2+ monocytes only under defined host conditions. Nat Neurosci. 2007;10:1544–53.

54.

Noel

Osterburg

Wang

Guo

Byrum

Schwemberger

Goetzman

Caldwell

Ogle

. Thermal injury elevates the inflammatory monocyte subpopulation in multiple compartments. Shock. 2007;28:684–93.

55.

Robben

LaRegina

Kuziel

Sibley

. Recruitment of Gr-1+ monocytes is essential for control of acute toxoplasmosis. The Journal of experimental medicine. 2005;201:1761–9.

56.

Sunderkotter

Nikolic

Dillon

Van Rooijen

Stehling

Drevets

Leenen

. Subpopulations of mouse blood monocytes differ in maturation stage and inflammatory response. J Immunol. 2004;172:4410–7.

57.

Galli

Borregaard

Wynn

. Phenotypic and functional plasticity of cells of innate immunity: macrophages, mast cells and neutrophils. Nature immunology. 2011;12:1035–44.

58.

Martinez

Sica

Mantovani

Locati

. Macrophage activation and polarization. Front Biosci. 2008;13:453–61.

59.

Janeway

Jr Medzhitov

. Innate immune recognition. Annual review of immunology. 2002;20:197–216.

60.

Mukhopadhyay

Gordon

. The role of scavenger receptors in pathogen recognition and innate immunity. Immunobiology. 2004;209:39–49.

61.

Wilson

. Macrophages heterogeneity in atherosclerosis - implications for therapy. J Cell Mol Med. 2010;14:2055–65.

62.

Gordon

. Alternative activation of macrophages. Nat Rev Immunol. 2003;3:23–35.

63.

Rodero

Khosrotehrani

. Skin wound healing modulation by macrophages. Int J Clin Exp Pathol. 2010;3:643–53.

64.

Hall

Banks

Chamberlain

Olwin

. Prevention of muscle aging by myofiber-associated satellite cell transplantation. Sci Transl Med. 2010;2:57ra83.

65.

Laskin

. Macrophages and Inflammatory Mediators in Chemical Toxicity: A Battle of Forces. Chem Res Toxicol. 2009.

66.

Sica

Mantovani

. Macrophage plasticity and polarization: in vivo veritas. The Journal of clinical investigation. 2012;122:787–95.

67.

Lech

Grobmayr

Weidenbusch

Anders

. Tissues use resident dendritic cells and macrophages to maintain homeostasis and to regain homeostasis upon tissue injury: the immunoregulatory role of changing tissue environments. Mediators of inflammation. 2012;2012:951390.

68.

Mosser

. The many faces of macrophage activation. J Leukoc Biol. 2003;73:209–12.

69.

Libby

Ridker

Hansson

. Progress and challenges in translating the biology of atherosclerosis. Nature. 2011;473:317–25.

70.

Swirski

Weissleder

Pittet

. Heterogeneous in vivo behavior of monocyte subsets in atherosclerosis. Arteriosclerosis, thrombosis, and vascular biology. 2009;29:1424–32.

71.

Vergadi

Chang

Lee

Liang

Liu

Fernandez-Gonzalez

Mitsialis

Kourembanas

. Early macrophage recruitment and alternative activation are critical for the later development of hypoxia-induced pulmonary hypertension. Circulation. 2011;123:1986–95.

72.

Delarosa

Dalemans

Lombardo

. Toll-like receptors as modulators of mesenchymal stem cells. Frontiers in immunology. 2012;3:182.

73.

Doorn

Moll

Le Blanc

van Blitterswijk

de Boer

. Therapeutic applications of mesenchymal stromal cells: paracrine effects and potential improvements. Tissue engineering Part B, Reviews. 2012;18:101–15.

74.

Krampera

. Mesenchymal stromal cell ‘licensing’: a multistep process. Leukemia. 2011;25:1408–14.

75.

Solinas

Germano

Mantovani

Allavena

. Tumor-associated macrophages (TAM) as major players of the cancer-related inflammation. J Leukoc Biol. 2009;86:1065–73.

76.

Ismahil

Prabhu

. Cardiac immune cell remodeling after myocardial infarction. J Mol Cell Cardiol. 2013;62:142–3.

77.

Tsujioka

Imanishi

Ikejima

Kuroi

Takarada

Tanimoto

Kitabata

Okochi

Arita

Ishibashi

Komukai

Kataiwa

Nakamura

Hirata

Tanaka

Akasaka

. Impact of heterogeneity of human peripheral blood monocyte subsets on myocardial salvage in patients with primary acute myocardial infarction. Journal of the American College of Cardiology. 2009;54:130–8.

78.

Panizzi

Swirski

Figueiredo

Waterman

Sosnovik

Aikawa

Libby

Pittet

Weissleder

Nahrendorf

. Impaired infarct healing in atherosclerotic mice with Ly-6C(hi) monocytosis. Journal of the American College of Cardiology. 2010;55:1629–38.

79.

van Amerongen

Harmsen

van Rooijen

Petersen

van Luyn

. Macrophage depletion impairs wound healing and increases left ventricular remodeling after myocardial injury in mice. The American journal of pathology. 2007;170:818–29.

80.

Frantz

Hofmann

Fraccarollo

Schafer

Kranepuhl

Hagedorn

Nieswandt

Nahrendorf

Wagner

Bayer

Pachel

Schon

Kneitz

Bobinger

Weidemann

Ertl

Bauersachs

. Monocytes/macrophages prevent healing defects and left ventricular thrombus formation after myocardial infarction. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 2012.

81.

Dayan

Yannarelli

Billia

Filomeno

Wang

Davies

Keating

. Mesenchymal stromal cells mediate a switch to alternatively activated monocytes/macrophages after acute myocardial infarction. Basic research in cardiology. 2011;106:1299–310.

82.

Ben-Mordechai

Holbova

Landa-Rouben

Harel-Adar

Feinberg

Elrahman

Blum

Epstein

Silman

Cohen

Leor

. Macrophage Subpopulations are Essential for Infarct Repair with and without Stem Cell Therapy. Journal of the American College of Cardiology. 2013;62:1890–1901.

83.

Frangogiannis

Dewald

Xia

Ren

Haudek

Leucker

Kraemer

Taffet

Rollins

Entman

. Critical role of monocyte chemoattractant protein-1/CC chemokine ligand 2 in the pathogenesis of ischemic cardiomyopathy. Circulation. 2007;115:584–92.

84.

Morimoto

Takahashi

Izawa

Ise

Hongo

Kolattukudy

Ikeda

. Cardiac overexpression of monocyte chemoattractant protein-1 in transgenic mice prevents cardiac dysfunction and remodeling after myocardial infarction. Circulation research. 2006;99:891–9.

85.

Alikhan

Ricardo

. Mononuclear phagocyte system in kidney disease and repair. Nephrology (Carlton). 2013;18:81–91.

86.

Fraccarollo

Galuppo

Schraut

Kneitz

van Rooijen

Ertl

Bauersachs

. Immediate mineralocorticoid receptor blockade improves myocardial infarct healing by modulation of the inflammatory response. Hypertension. 2008;51:905–14.

87.

Leuschner

Rauch

Ueno

Gorbatov

Marinelli

Lee

Dutta

Wei

Robbins

Iwamoto

Sena

Chudnovskiy

Panizzi

Keliher

Higgins

Libby

Moskowitz

Pittet

Swirski

Weissleder

Nahrendorf

. Rapid monocyte kinetics in acute myocardial infarction are sustained by extramedullary monocytopoiesis. The Journal of experimental medicine. 2012;209:123–37.

88.

Kharraz

Guerra

Mann

Serrano

Munoz-Canoves

. Macrophage plasticity and the role of inflammation in skeletal muscle repair. Mediators of inflammation. 2013;2013:491497.

89.

Chazaud

. Macrophages: Supportive cells for tissue repair and regeneration. Immunobiology. 2013.

90.

Stefater

3rd Ren

Lang

Duffield

. Metchnikoff’s policemen: macrophages in development, homeostasis and regeneration. Trends in molecular medicine. 2011;17:743–52.

91.

van den Akker

Deddens

Doevendans

Sluijter

. Cardiac stem cell therapy to modulate inflammation upon myocardial infarction. Biochimica et biophysica acta. 2013;1830:2449–58.

92.

Saclier

Yacoub-Youssef

Mackey

Arnold

Ardjoune

Magnan

Sailhan

Chelly

Pavlath

Mounier

Kjaer

Chazaud

. Differentially activated macrophages orchestrate myogenic precursor cell fate during human skeletal muscle regeneration. Stem Cells. 2013;31:384–96.

93.

Swirski

Nahrendorf

. Macrophage-stem cell crosstalk after myocardial infarction. Journal of the American College of Cardiology. 2013;62:1902–4.

94.

Jones

Roicardo

. Macrophage and CSF-1: implications for development and beyond. Organogenesis. 2013;9:1–12.

95.

London

Cohen

Schwartz

. Microglia and monocyte-derived macrophages: functionally distinct populations that act in concert in CNS plasticity and repair. Frontiers in cellular neuroscience. 2013;7:34.

96.

Kigerl

Gensel

Ankeny

Alexander

Donnelly

Popovich

. Identification of two distinct macrophage subsets with divergent effects causing either neurotoxicity or regeneration in the injured mouse spinal cord. The Journal of neuroscience : the official journal of the Society for Neuroscience. 2009;29:13435–44.

97.

Boulter

Govaere

Bird

Radulescu

Ramachandran

Pellicoro

Ridgway

Seo

Spee

Van Rooijen

Sansom

Iredale

Lowell

Roskams

Forbes

. Macrophage-derived Wnt opposes Notch signaling to specify hepatic progenitor cell fate in chronic liver disease. Nature medicine. 2012;18:572–9.

98.

Trinchieri

. Interleukin-12 and the regulation of innate resistance and adaptive immunity. Nat Rev Immunol. 2003;3:133–46.

99.

Chen

Mandelin

Ceponis

Miller

Hukkanen

Konttinen

. Regulation of macrophage activation. Cellular and molecular life sciences : CMLS. 2003;60:2334–46.

100.

Frangogiannis

. The immune system and cardiac repair. Pharmacol Res. 2008;58:88–111.

101.

Hasdai

Scheinowitz

Leibovitz

Sclarovsky

Eldar

Barak

. Increased serum concentrations of interleukin-1 beta in patients with coronary artery disease. Heart. 1996;76:24–8.

102.

Guillen

Blanes

Gomez-Lechon

Castell

. Cytokine signaling during myocardial infarction: sequential appearance of IL-1 beta and IL-6. Am J Physiol. 1995;269:R229–35.

103.

Han

Ray

Baughman

Feldman

. Detection of interleukin and interleukin-receptor mRNA in human heart by polymerase chain reaction. Biochem Biophys Res Commun. 1991;181:520–3.

104.

Carmi

Voronov

Dotan

Lahat

Rahat

Fogel

Huszar

White

Dinarello

Apte

. The role of macrophage-derived IL-1 in induction and maintenance of angiogenesis. J Immunol. 2009;183:4705–14.

105.

Frangogiannis

. The mechanistic basis of infarct healing. Antioxid Redox Signal. 2006;8:1907–39.

106.

Boyle

Jr Kovacich

Hebert

Canty

Jr Chi

Morgan

Pohlman

Verrier

. Inhibition of interleukin-8 blocks myocardial ischemia-reperfusion injury. J Thorac Cardiovasc Surg. 1998;116:114–21.

107.

Witowski

Ksiazek

Jorres

. Interleukin-17: a mediator of inflammatory responses. Cellular and molecular life sciences : CMLS. 2004;61:567–79.

108.

Evans

Smart

Dube

Bollini

Clark

Evans

Taams

Richardson

Levesque

Martin

Mills

Riegler

Price

Lythgoe

Riley

. Thymosin beta4-sulfoxide attenuates inflammatory cell infiltration and promotes cardiac wound healing. Nature communications. 2013;4:2081.

109.

Smart

Rossdeutsch

Riley

. Thymosin beta4 and angiogenesis: modes of action and therapeutic potential. Angiogenesis. 2007;10:229–41.

110.

Huff

Muller

Otto

Netzker

Hannappel

. beta-Thymosins, small acidic peptides with multiple functions. Int J Biochem Cell Biol. 2001;33:205–20.

111.

Sosne

Qiu

Christopherson

Wheater

. Thymosin beta 4 suppression of corneal NFkappaB: a potential anti-inflammatory pathway. Exp Eye Res. 2007;84:663–9.

112.

Opal

DePalo

. Anti-inflammatory cytokines. Chest. 2000;117:1162–72.

113.

Desmouliere

Geinoz

Gabbiani

. Transforming growth factor-beta 1 induces alpha-smooth muscle actin expression in granulation tissue myofibroblasts and in quiescent and growing cultured fibroblasts. J Cell Biol. 1993;122:103–11.

114.

Rosenkranz

. TGF-beta1 and angiotensin networking in cardiac remodeling. Cardiovascular research. 2004;63:423–32.

115.

Breen

. VEGF in biological control. J Cell Biochem. 2007;102:1358–67.

116.

Cross

Claesson-Welsh

. FGF and VEGF function in angiogenesis: signalling pathways, biological responses and therapeutic inhibition. Trends Pharmacol Sci. 2001;22:201–7.

117.

Yun

Won

Jeon

Lee

Kang

Jang

Shin

Kim

. Fibroblast growth factors: biology, function, and application for tissue regeneration. J Tissue Eng. 2010;2010:218142.

118.

Dunlay

Weston

Redfield

Killian

Roger

. Tumor necrosis factor-alpha and mortality in heart failure: a community study. Circulation. 2008;118:625–31.

119.

Tanno

Gorog

Bellahcene

Cao

Quinlan

Marber

. Tumor necrosis factor-induced protection of the murine heart is independent of p38-MAPK activation. J Mol Cell Cardiol. 2003;35:1523–7.

120.

Dinarello

. Proinflammatory cytokines. Chest. 2000;118:503–8.

121.

Dawn

Guo

Rezazadeh

Wang

Stein

Hunt

Varma

Xuan

Tan

Zhu

Bolli

. Tumor necrosis factor-alpha does not modulate ischemia/reperfusion injury in naive myocardium but is essential for the development of late preconditioning. J Mol Cell Cardiol. 2004;37:51–61.

122.

Kamimura

Ishihara

Hirano

. IL-6 signal transduction and its physiological roles: the signal orchestration model. Rev Physiol Biochem Pharmacol. 2003;149:1–38.

123.

Gabay

. Interleukin-6 and chronic inflammation. Arthritis Res Ther. 2006;8 Suppl 2:S3.

124.

Tilg

Trehu

Atkins

Dinarello

Mier

. Interleukin-6 (IL-6) as an anti-inflammatory cytokine: induction of circulating IL-1 receptor antagonist and soluble tumor necrosis factor receptor p55. Blood. 1994;83:113–8.

125.

Porrello

Mahmoud

Simpson

Hill

Richardson

Olson

Sadek

. Transient regenerative potential of the neonatal mouse heart. Science. 2011;331:1078–80.

126.

Robledo

. Myocardial regeneration in young rats. The American journal of pathology. 1956;32:1215–39.

127.

Konfino

Landa-Rouben

Leor

. Mode of Injury Affects the Course of Regeneration and Repair in Neonatal and Adult Mouse Heart. Circulation research. 2013;113:(abstract).

128.

Aurora

Porrello

Tan

Mahmoud

Hill

Bassel-Duby

Sadek

Olson

. Macrophages are required for neonatal heart regeneration. The Journal of clinical investigation. 2014;124:1382–92.

129.

Christoffels

. Developing insights into cardiac regeneration. Development. 2013;140:3933–3937.

130.

Tidball

. Mechanisms of muscle injury, repair, and regeneration. Comprehensive Physiology. 2011;1:2029–62.

131.

Saclier

Cuvellier

Magnan

Mounier

Chazaud

. Monocyte/macrophage interactions with myogenic precursor cells during skeletal muscle regeneration. The FEBS journal. 2013.

132.

Godwin

Pinto

Rosenthal

. Macrophages are required for adult salamander limb regeneration. Proc Natl Acad Sci U S A. 2013;110:9415–20.

133.

Beltrami

Barlucchi

Torella

Baker

Limana

Chimenti

Kasahara

Rota

Musso

Urbanek

Leri

Kajstura

Nadal-Ginard

Anversa

. Adult cardiac stem cells are multipotent and support myocardial regeneration. Cell. 2003;114:763–76.

134.

Orlic

Kajstura

Chimenti

Jakoniuk

Anderson

Pickel

McKay

Nadal-Ginard

Bodine

Leri

Anversa

. Bone marrow cells regenerate infarcted myocardium. Nature. 2001;410:701–5.

135.

Senyo

Steinhauser

Pizzimenti

Yang

Cai

Wang

Guerquin-Kern

Lechene

Lee

. Mammalian heart renewal by pre-existing cardiomyocytes. Nature. 2013;493:433–6.

136.

Malliaras

Zhang

Seinfeld

Galang

Tseliou

Cheng

Sun

Aminzadeh

Marban

. Cardiomyocyte proliferation and progenitor cell recruitment underlie therapeutic regeneration after myocardial infarction in the adult mouse heart. EMBO molecular medicine. 2013;5:191–209.

137.

Huang

Yang

Chen

Liu

Chang

Chuang

. Treatment of Glucocorticoids Inhibited Early Immune Responses and Impaired Cardiac Repair in Adult Zebrafish. PloS one. 2013;8:e66613.

138.

Kubin

Poling

Kostin

Gajawada

Hein

Rees

Wietelmann

Tanaka

Lorchner

Schimanski

Szibor

Warnecke

Braun

. Oncostatin M is a major mediator of cardiomyocyte dedifferentiation and remodeling. Cell stem cell. 2011;9:420–32.

139.

Uccelli

Moretta

Pistoia

. Mesenchymal stem cells in health and disease. Nat Rev Immunol. 2008;9:726–36.

140.

Segers

Lee

. Stem-cell therapy for cardiac disease. Nature. 2008;451:937–42.

141.

Prockop

. Repair of tissues by adult stem/progenitor cells (MSCs): controversies, myths, and changing paradigms. Mol Ther. 2009;17:939–46.

142.

Nemeth

Leelahavanichkul

Yuen

Mayer

Parmelee

Doi

Robey

Leelahavanichkul

Koller

Brown

Jelinek

Star

Mezey

. Bone marrow stromal cells attenuate sepsis via prostaglandin E(2)-dependent reprogramming of host macrophages to increase their interleukin-10 production. Nature medicine. 2009;15:42–9.

143.

Zhang

Shi

Wilder-Smith

Xiang

Wong

Nguyen

Kwon

. Human gingiva-derived mesenchymal stem cells elicit polarization of m2 macrophages and enhance cutaneous wound healing. Stem Cells. 2010;28:1856–68.

144.

Maggini

Mirkin

Bognanni

Holmberg

Piazzon

Nepomnaschy

Costa

Canones

Raiden

Vermeulen

Geffner

. Mouse bone marrow-derived mesenchymal stromal cells turn activated macrophages into a regulatory-like profile. PloS one. 2010;5:e9252.

145.

Kim

Hematti

. Mesenchymal stem cell-educated macrophages: a novel type of alternatively activated macrophages. Experimental hematology. 2009;37:1445–53.

146.

Adutler-Lieber

Ben-Mordechai

Naftali-Shani

Asher

Loberman

Raanani

Leor

. Human macrophage regulation via interaction with cardiac adipose tissue-derived mesenchymal stromal cells. Journal of cardiovascular pharmacology and therapeutics. 2013;18:78–86.

147.

Margalit

. Biomaterial-Based Particulate Drug Carriers. In: Peer

, ed. Handbook of Harnessing Biomaterials in Nanomedicine Singapore: Pan Stanford Publishing Pte. Ltd. ; 2012: 1–16.

148.

Fidler

Raz

Fogler

Hoyer

Poste

. The role of plasma membrane receptors and the kinetics of macrophage activation by lymphokines encapsulated in liposomes. Cancer Res. 1981;41:495–504.

149.

Gregoriadis

Senior

Wolff

Kirby

. Fate of liposomes in vivo: control leading to targeting Receptor-mediated targeting of drugs New York: Plenum Press; 1984: 243–266.

150.

Rahman

Cerny

Patel

Lau

Wright

. Differential uptake of liposomes varying in size and lipid composition by parenchymal and kupffer cells of mouse liver. Life Sci. 1982;31:2061–71.

151.

Raz

Bucana

Fogler

Poste

Fidler

. Biochemical, morphological, and ultrastructural studies on the uptake of liposomes by murine macrophages. Cancer Res. 1981;41:487–94.

152.

Kelly

Jefferies

Cryan

. Targeted liposomal drug delivery to monocytes and macrophages. Journal of drug delivery. 2011;2011:727241.

153.

Nardin

Lefebvre

Labroquere

Faure

Abastado

. Liposomal muramyl tripeptide phosphatidylethanolamine: Targeting and activating macrophages for adjuvant treatment of osteosarcoma. Curr Cancer Drug Targets. 2006;6:123–33.

154.

Alving

Steck

Chapman

Jr Waits

Hendricks

Swartz

Jr Hanson

. Therapy of leishmaniasis: superior efficacies of liposome-encapsulated drugs. Proc Natl Acad Sci U S A. 1978;75:2959–63.

155.

Glucksam-Galnoy

Zor

Margalit

. Hyaluronan-modified and regular multilamellar liposomes provide sub-cellular targeting to macrophages, without eliciting a pro-inflammatory response. Journal of controlled release : official journal of the Controlled Release Society. 2012;160:388–93.

156.

Pure

Cuff

. A crucial role for CD44 in inflammation. Trends in molecular medicine. 2001;7:213–21.

157.

Elron-Gross

Glucksam

Margalit

. Liposomal dexamethasone-diclofenac combinations for local osteoarthritis treatment. Int J Pharm. 2009;376:84–91.

158.

Daleke

Hong

Papahadjopoulos

. Endocytosis of liposomes by macrophages: binding, acidification and leakage of liposomes monitored by a new fluorescence assay. Biochimica et biophysica acta. 1990;1024:352–66.

159.

Harel-Adar

Ben Mordechai

Amsalem

Feinberg

Leor

Cohen

. Modulation of cardiac macrophages by phosphatidylserine-presenting liposomes improves infarct repair. Proc Natl Acad Sci U S A. 2011;108:1827–32.

160.

Huynh

Fadok

Henson

. Phosphatidylserine-dependent ingestion of apoptotic cells promotes TGF-beta1 secretion and the resolution of inflammation. The Journal of clinical investigation. 2002;109:41–50.

161.

Fire

Montgomery

Kostas

Driver

Mello

. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature. 1998;391:806–11.

162.

Castanotto

Rossi

. The promises and pitfalls of RNA-interference-based therapeutics. Nature. 2009;457:426–33.

163.

Whitehead

Langer

Anderson

. Knocking down barriers: advances in siRNA delivery. Nat Rev Drug Discov. 2009;8:129–38.

164.

ClinicalTrials.gov (2014). siRNA. Available at: http://clinicaltrial.gov/ct2/results?term=siRNA&Search=Search (Accessed: 14th June 2014).

165.

Lee

Yang

Kao

Pierce

Murthy

. Solid polymeric microparticles enhance the delivery of siRNA to macrophages in vivo. Nucleic Acids Res. 2009;37:e145.

166.

Duffield

. The inflammatory macrophage: a story of Jekyll and Hyde. Clin Sci (Lond). 2003;104:27–38.

167.

Lameijer

Tang

Nahrendorf

Beelen

Mulder

. Monocytes and macrophages as nanomedicinal targets for improved diagnosis and treatment of disease. Expert review of molecular diagnostics. 2013;13:567–80.

168.

Leuschner

Dutta

Gorbatov

Novobrantseva

Donahoe

Courties

Lee

Kim

Markmann

Marinelli

Panizzi

Lee

Iwamoto

Milstein

Epstein-Barash

Cantley

Wong

Cortez-Retamozo

Newton

Love

Libby

Pittet

Swirski

Koteliansky

Langer

Weissleder

Anderson

Nahrendorf

. Therapeutic siRNA silencing in inflammatory monocytes in mice. Nature biotechnology. 2011;29:1005–10.

169.

Howard

Paludan

Behlke

Besenbacher

Deleuran

Kjems

. Chitosan/siRNA nanoparticle-mediated TNF-alpha knockdown in peritoneal macrophages for anti-inflammatory treatment in a murine arthritis model. Mol Ther. 2009;17:162–8.

170.

Aouadi

Tesz

Nicoloro

Wang

Chouinard

Soto

Ostroff

Czech

. Orally delivered siRNA targeting macrophage Map4k4 suppresses systemic inflammation. Nature. 2009;458:1180–4.

171.

Otterbein

Soares

Yamashita

Bach

. Heme oxygenase-1: unleashing the protective properties of heme. Trends Immunol. 2003;24:449–55.

172.

Habtezion

Kwan

Yang

Morgan

Akhtar

Wanaski

Collins

Butcher

Kamal

Omary

. Heme oxygenase-1 is induced in peripheral blood mononuclear cells of patients with acute pancreatitis: a potential therapeutic target. Am J Physiol Gastrointest Liver Physiol. 2010;300:G12–20.

173.

Yin

Antonini

Castranova

. Roles of reactive oxygen species and heme oxygenase-1 in modulation of alveolar macrophage-mediated pulmonary immune responses to Listeria monocytogenes by diesel exhaust particles. Toxicol Sci. 2004;82:143–53.

174.

Lee

Chau

. Heme oxygenase-1 mediates the anti-inflammatory effect of interleukin-10 in mice. Nature medicine. 2002;8:240–6.

175.

Lakkisto

Csonka

Fodor

Bencsik

Voipio-Pulkki

Ferdinandy

Pulkki

. The heme oxygenase inducer hemin protects against cardiac dysfunction and ventricular fibrillation in ischaemic/reperfused rat hearts: role of connexin 43. Scand J Clin Lab Invest. 2009;69:209–18.

176.

Jadhav

Tiwari

Lee

Ndisang

. The heme oxygenase system selectively enhances the anti-inflammatory macrophage-M2 phenotype, reduces pericardial adiposity, and ameliorated cardiac injury in diabetic cardiomyopathy in Zucker diabetic fatty rats. J Pharmacol Exp Ther. 2013;345:239–49.

177.

Weis

Weigert

von Knethen

Brune

. Heme oxygenase-1 contributes to an alternative macrophage activation profile induced by apoptotic cell supernatants. Mol Biol Cell. 2009;20:1280–8.

178.

Yoriki

Naito

Takagi

Mizusima

Hirai

Harusato

Yamada

Tsuji

Kugai

Fukui

Higashimura

Katada

Kamada

Uchiyama

Handa

Yagi

Ichikawa

Yosikawa

. Hemin ameliorates indomethacin-induced small intestinal injury in mice through the induction of heme oxygenase-1. Journal of gastroenterology and hepatology. 2013;28:632–8.

179.

Anderson

Collins

. Open-label study of hemin for acute porphyria: clinical practice implications. Am J Med. 2006;119:801 e19–24.

Targeting Macrophage Subsets for Infarct Repair

Abstract

Keywords

Introduction

Macrophages are Characterized by Plasticity and Heterogeneity

Macrophages in Acute MI

Macrophages and Myocardial Regeneration

Interaction of Macrophages with Mesenchymal Stem/Stromal Cells

Targeting Macrophages with Liposomes

Modulating Macrophage Function by Other Approaches

Summary and Future Directions

Footnotes

Declaration of Conflicting Interests

Funding

References