#5453 lipid nephrotoxicity induced by hif-1α activation accelerates interstitial injury in diabetic nephropathy

Abstract Background and Aims Our previous study demonstrated lipid accumulation contributes to tubulointerstitial injury in diabetic nephropathy. However, the exact mechanism of which accelerate lipid accumulation in tubulointerstitium has not been completely elucidated. Increasing studies suggest that chronic hypoxia plays an important pathophysiologic role in diabetic nephropathy. This study aimed to investigate the effect of hypoxia inducible factor-1α (HIF-1α) activation induced by chronic hypoxia on lipid accumulation in diabetic kidney and to explore its potential mechanism. Method Human proximal tubular cell line HK-2 was incubated with or without cobalt chloride (CoCl2, 100 μM) which stimulates hypoxic condition in the presence or absence of glucose (30 mM) for 24 h. Specific siRNA was transfected in cells to knock down HIF-1α expression. Type 1 diabetic rats model were induced by STZ injection, and Lificiguat (YC-1) was used as HIF-1α inhibitor by intraperitoneal injection. Immunofluorescence staining and Western blot were used to determine the cellular localization and expression of HIF-1α. Periodic Acid-Schiff (PAS) staining was used to observe basic structure and pathological changes of kidney. The expression of carnitine palmitoyl transferase 1A (CPT1A), tissue growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF) were measured by immunohistochemical staining and Western blot. Lipid accumulation was detected by oil red O staining and cellular triglyceride quantification assay. Results In in vitro study, CoCl2 effectively increased the expression of HIF-1α and its translocation from cytoplasm to nucleus. Meanwhile, HIF-1α activation induced by CoCl2 significantly increased lipid accumulation in HK-2 cells. Moreover, CoCl2 treatment increased TGF- β and CTGF expression in HK-2 cells. The presence of glucose (30mM) made no significant difference to HK-2 cells incubated with CoCl2. HIF-1α siRNA treatment significantly reduced lipid deposition in HK-2 cells incubated with CoCl2. In vivo study showed YC-1 treatment decreased the expression of HIF-1α in renal tubules of diabetic rats, which was accompanied by less lipid accumulation compared with the diabetes mellitus (DM) group. PAS staining showed the desquamation and necrosis of tubular epithelial cells in the YC-1 group were alleviated compared with the DM group. YC-1 treatment did not affect the ratio of kidney weight to body weight, whereas decreased the levels of blood glucose, urine albumin creatinine ratio and NAG creatinine ratio in diabetic rats. The expressions of fibrosis factor TGF- β and CTGF were decreased in the YC-1 group compared with the DM group. Furthermore, the protein expression of CPT1A, the key enzyme of fatty acid oxidation, which was decreased in the DM group compared with the controls, was regained by YC-1 treatment. Conclusion Our findings demonstrated that HIF-1α activation contributed to interstitial injury in diabetic nephropathy by inducing lipid accumulation. HIF-1α activation might contribute to lipid nephrotoxicity by downregulating fatty acid oxidation.