HMGCS2 Drives Mitochondrial Reprogramming and Histone β-Hydroxybutyrylation in Diabetic Nephropathy

Background: Accumulating evidence implicates mitochondrial dysfunction and epigenetic dysregulation in the progression of diabetic nephropathy (DN). 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), a rate-limiting enzyme in ketogenesis, plays a pivotal role in mitochondrial metabolism. However, its involvement in regulating histone post-translational modifications, particularly β-hydroxybutyrylation (Kbhb), in the context of DN remains to be elucidated. Methods: Quantitative real-time PCR and immunohistochemical analyses were performed to assess HMGCS2 expression in renal biopsy specimens from patients with established DN (n=32) and age-matched healthy controls (n=20). In vitro studies utilized human renal proximal tubular epithelial cells (HK-2) cultured under high glucose conditions (30 mM) with genetic modulation of HMGCS2 expression. Mitochondrial bioenergetics were evaluated using extracellular flux analysis, while liquid chromatography-mass spectrometry (LC-MS) was employed for metabolomic profiling. ChIP-seq and transcriptomic analysis (RNA-seq) were conducted to identify Kbhb-modified genomic loci and associated transcriptional networks. In vivo validation was performed using a streptozotocin-induced murine model of diabetes with conditional tubule-specific Hmgcs2 knockout. Results: Renal tissues from DN patients exhibited significant upregulation of HMGCS2 expression (p<0.01), which positively correlated with histopathological indices of glomerulosclerosis and tubulointerstitial fibrosis. High glucose-stimulated HMGCS2 overexpression resulted in elevated intracellular β-hydroxybutyrate (β-OHB) concentrations, concomitant with mitochondrial fragmentation and increased reactive oxygen species production. Genome-wide mapping revealed HMGCS2-dependent enrichment of Kbhb marks at regulatory regions of pro-fibrotic genes, including TGF-β1 and COL4A1, with consequent transcriptional activation. Genetic ablation of HMGCS2 ameliorated renal Kbhb modification and attenuated DN progression, effects that were reversed by exogenous β-OHB administration. Conclusion: This study delineates a novel pathogenic mechanism in DN wherein HMGCS2-driven mitochondrial metabolic remodeling facilitates histone β-hydroxybutyrylation, thereby exacerbating renal fibrogenesis. Therapeutic targeting of the HMGCS2/β-OHB/Kbhb axis may represent a promising strategy for DN intervention.