HIF-1α activation induces cholesterol homeostasis dysfunction to accelerate progression of diabetic nephropathy in rats

Abstract

To investigate the effect of hypoxia inducible factor-1α (HIF-1α) activation on cholesterol homeostasis dysfunction in diabetic nephropathy (DN). Rat models of type 1 diabetes established by intraperitoneal STZ injection were treated with intraperitoneal injection of Lificiguat (YC-1, a HIF-1α inhibitor). Human proximal tubular cell line HK-2 was incubated with cobalt chloride (CoCl2, 100 μmol/L) in the presence or absence of 30 mmol/L glucose for 24 h. Renal injury of the rats was assessed by measuring 24-h urinary total protein level and PAS staining of the renal tubules. Cholesterol deposition in rat kidneys and HK-2 cells were observed using a quantitative assay of total cholesterol and Filipin staining, and HIF-1α protein expression was detected using Western blotting, immunohistochemistry or immunofluorescence assay; the expressions of cholesterol metabolism-related proteins HMGCR, LDLr, CXCL16 and profibrogenic factors including TGF-β1 and CTGF were also analyzed. The diabetic rats showed significantly increased 24-h urinary protein level (P<0.001), obvious renal tubular injury, and increased renal cholesterol content (P<0.05) with significantly increased HIF-1α expression in the renal tubular (P<0.01). YC-1 treatment significantly ameliorated tubulointerstitial injury in the diabetic rats as shown by decreased 24-h urinary total protein (P<0.05) and reduced damage area of the tubules, and effectively decreased renal cholesterol levels and renal expression of HIF-1α (P<0.05). In HK-2 cells, CoCl2 stimulation in the presence of high glucose effectively activated HIF-1α expression (P<0.0001), aggravated cholesterol accumulation (P<0.05), and increased the expressions of HMGCR, LDLr, CXCL16, TGF-β1, and CTGF (P<0.05 or 0.01). Consistent with the in vitro study, YC-1 treatment also significantly decreased the expressions of cholesterol metabolism-related proteins and the profibrogenic factors in the renal tubules of the diabetic rats. HIF-1α activation induces cholesterol homeostasis dysregulation possibly by upregulating the de novo synthesis and uptake of cholesterol, thereby aggravating tubulointerstitial injury in DN.