SIRT1-regulated mitophagy mitigates lipotoxicity-induced ferroptosis in diabetic kidney disease.

Diabetic kidney disease (DKD) is characterized by renal lipid deposition, andlipotoxicity-induced ferroptosis plays a pivotal role in its progression. This study aimed to elucidate the regulatory mechanism of silent information regulator 1 (SIRT1) in lipotoxicity-induced ferroptosis in DKD using clinical samples, animal models, and cellular experiments. Renal tissues from DKD patients and non-diabetic controls were collected for pathological and molecular analyses. DKD mouse model was established by combining a high-fat diet (HFD) with streptozotocin (STZ) injection. Human renal proximal tubular epithelial cells (HK-2) were exposed to palmitic acid/high glucose (PA/HG) to mimic lipotoxic sress. SIRT1 overexpression or knockdown was achieved using lentiviral vectors. Mitophagy was evaluated by Western blot, qPCR, and immunohistochemistry (IHC), and transmission electron microscopy (TEM), focusing on the expression of PINK1, Parkin, LC3B, and P62. Ferroptosis was assessed by detecting the expression of glutathione peroxidase 4 (GPX4), xCT, Ferritin, as well as the levels of malondialdehyde (MDA), and reactive oxygen species (ROS), alongside TEM observations of ferroptotic mitochondrial alterations. The mitophagy inhibitor Mdivi-1 and ferroptosis inhibitor Ferrostatin-1 (Fer-1) were used for mechanistic validation. In renal tubules of DKD patients and HFD/STZ-induced DKD mice, lipid droplet membrane protein (Perilipin-2) expression and lipid deposition were markedly elevated, while SIRT1 expression was significantly reduced and negatively correlated with lipid deposition (P < 0.05). PA/HG treated HK-2 cells reproduced these features. SIRT1 deficiency impaired mitophagy, as evidenced by reduced expression of PINK1, Parkin, and LC3B, increased P62 levels (P < 0.05), and TEM revealed mitochondrial swelling with decreased autophagosomes. Furthermore, SIRT1 knockdown exacerbated ferroptosis, characterized by reduced GPX4, xCT, and Ferritin expression, increased MDA and ROS levels (P < 0.05), and mitochondrial pyknosis with loss of cristae. Conversely, SIRT1 overexpression restored mitophagy activity and alleviated ferroptosis (P < 0.05). The protective effect of SIRT1 overexpression against PA-induced ferroptosis was abolished by Mdivi-1, while Fer-1 partially rescued SIRT1 downregulation-induced renal fibrosis (P < 0.05). SIRT1 attenuates lipotoxicity-induced ferroptosis in renal tubular epithelial cells by promoting mitophagy, thereby mitigating DKD progression. These findings suggest that SIRT1-mediated mitophagy may represent a potential therapeutic target for DKD.