Active vitamin D3 plays a protective role in podocytes of diabetic rats by regulating autophagy activity

Abstract

Objective To investigate the protective effect and mechanism of active vitamin D3 on podocyte injury in type 1 diabetic rats. Methods Animals were randomly divided into normal control group (NC group), diabetic nephropathy group (DN group), diabetes nephropathy plus active vitamin D3 group (DN+ VD group). Random tail vein blood glucose was measured and 24 hours of urine was collected every 3 weeks to observe the dynamic changes of blood glucose and 24-hour urine volume and urinary albumin. Rats were sacrificed at the end of 18th week, the kidney weight to body weight ratio, serum creatinine, blood urea nitrogen, serum calcium, and serum phosphorus levels were measured. Pathological in glomeruli were observed by PAS staining. Immunohistochemistry and Western blotting were used to observe the expression of slit diaphragms proteins including Nephrin, Podocin, and vitamin D receptor protein VDR. The mRNA level of autophagy-related protein P62 was detected by realtime quantitative PCR, and expression of autophagy-related protein including LC3B/A, Beclin1, and P62 were detected by Western blotting. Ultrastructure of podocytes and autophagosomes in podocytes were observed by electron microscopy. Results Levels of serum creatinine, blood urea nitrogen, and blood glucose in diabetic rats were higher than those in NC group (P 0.05). Compared with the DN group, the urinary protein and kidney weight to body weight ratio in the DN+ VD group were significantly lower (P<0.05). Mesangial matrix hyperplasia and basement membrane thickening were improved, and podocyte fusion and shedding were partially reversed. The expressions of Nephrin, Podocin, VDR, LC3B/A and Beclin1 were increased, and P62 mRNA and protein were down-regulated (P<0.05). The number of autophagosomes in podocytes increased. Besides, positive correlations were found between Nephrin and Beclin1 (r=0.939 8, P<0.05), as well as Nephrin and VDR (r=0.948 3, P<0.05), and Beclin1 and VDR (r=0.909 3, P<0.05). Conclusion Active vitamin D3 inhibits the injury of diabetic nephropathy podocytes by up-regulating VDR expression and enhancing autophagy activity, thereby reducing proteinuria and delaying the development of diabetic nephropathy. Key words: Active vitamin D3; Diabetic nephropathy; Podocytes; Autophagy