GATM-ALDH2-Mediated mitophagy orchestrates macrophage polarization and efferocytosis to suppress AKI-to-CKD progression

Abstract

Objective

The transition from acute kidney injury (AKI) to chronic kidney disease (CKD) remains a critical unsolved clinical problem. Mitochondrial homeostasis and macrophage function are pivotal in this process. This study aimed to investigate whether glycine amidinotransferase (GATM), a key enzyme in creatine biosynthesis, mediates mitophagy and macrophage function to participate in AKI-to-CKD progression.

Methods

A renal ischemia-reperfusion (I/R) model was established in myeloid-specific GATM knockout (LysM-cre⁺/GATM^fl/fl) and control (LysM-cre⁺/GATM^+/+) mice (n = 3 per group, 3 independent replicates). Renal pathological injury and fibrosis were evaluated by hematoxylin-eosin (HE) and Masson staining. Serum creatinine (Cr), blood urea nitrogen (BUN), and renal biomarkers (Kim-1, NGAL, creatine, IL-1β, TNF-α) were quantified via ELISA. Gene and protein expressions of GATM, Collagen I, α-SMA, and mitophagy-related molecules were assessed by RT-qPCR and immunohistochemistry/western blot. Macrophage polarization, mitochondrial ROS levels, and efferocytosis efficiency were analyzed by flow cytometry. In vitro, bone marrow-derived macrophages (BMDMs) were differentiated with macrophage colony-stimulating factor (m-CSF), and polymorphonuclear neutrophils (PMNs) were induced to apoptosis by serum-free starvation. Functional rescue experiments were performed using ALDH2 overexpression plasmids. Statistical analyses were conducted with t-test and one-way ANOVA.

Results

GATM deficiency significantly exacerbated the pathological damage induced by AKI and promoted the AKI-to-CKD progression, as evidenced by elevated serum creatinine and blood urea nitrogen levels, along with increased expression of Kim-1, NGAL, and fibrotic markers (Collagen I, α-SMA). The absence of GATM led to a reduction in creatine levels within BMDMs, downregulation of ALDH2 expression, inhibition of mitophagy, and an elevation of ROS in mitochondria. Concurrently, there was an enhanced polarization of BMDMs towards the M1 phenotype, accompanied by a diminished efferocytic capacity. Notably, in vitro overexpression of ALDH2 partially revived mitophagy activity, reset the polarization balance of BMDMs, and rejuvenated their efferocytic function.

Conclusion

Data suggest that GATM may regulate ALDH2-linked mitophagy via creatine, influencing macrophage polarization and efferocytosis during AKI-to-CKD transition. Targeting the GATM-ALDH2 pathway represents a promising novel therapeutic strategy for mitigating CKD development after acute kidney injury.