ACSL4 Exacerbates Tubulointerstitial Inflammatory Injury in Diabetic Nephropathy by Regulating Mitochondrial Dynamics via AKAP1-DRP1 Axis

Background: Diabetic nephropathy (DN), which is characterized by progressive inflammation and fibrosis, is the leading cause of end-stage renal disease. Although mitochondrial fragmentation in DN renal tubular cells exacerbates oxidative stress and inflammatory injury, the underlying mechanisms remain unclear. Methods: This study used transcriptomics, machine learning, and single-cell transcriptomics to identify key molecules in the renal tubules of DN patients and validated their clinical significance through kidney biopsy specimens and clinical data from patients with DN. For in vivo experiments, a DN mouse model was established using tubule-specific Acsl4 knockout mice combined with high-fat diet and streptozotocin induction. HK-2 cells exposed to high glucose and palmitic acid were utilized in vitro in conjunction with gene knockdown/overexpression, co-immunoprecipitation, and immunofluorescence techniques to verify the role and mechanism of Acsl4 in mitochondrial dynamics. Results: Bioinformatic analysis indicated that ACSL4 was significantly upregulated in the tubulointerstitium of patients with DN and was involved in immune cell infiltration and inflammatory regulation via chemokine pathways, such as chemokine (C-X-C motif) ligand (CXCL) and chemokine (C-X3-C motif) (CX3C). In renal biopsies from patients with DN, the expression of ACSL4 was upregulated in tubular cells, negatively correlated with eGFR (r = -0.833, p= 6.555e-5), and positively correlated with the degree of interstitial fibrosis/tubular atrophy (r = 0.83, p= 1.7253e-5). In vivo, knockout of Acsl4 specifically in proximal tubular epithelial cells resulted in enhanced expression of Akap1 and increased phosphorylation of DRP1 at Ser637, preserving mitochondrial morphology and attenuating tubulointerstitial inflammatory injury and renal fibrosis in DN mice. In vitro experiments demonstrated that ACSL4 bound to AKAP1 and promoted its ubiquitin-dependent degradation, leading to DRP1 Ser637 dephosphorylation, exacerbated mitochondrial fission and elevated mitochondrial oxidative stress. Conclusion: In DN, ACSL4 could bind to AKAP1 and promote its ubiquitin-mediated degradation, leading to DRP1 Ser637 dephosphorylation and mitochondrial fragmentation, ultimately resulting in inflammatory injury and interstitial fibrosis in DN renal tissues. Funding: Government Support – Non-U.S.