PODOCYTE INJURY IS SUPPRESSED BY 1,25-DIHYDROXYVITAMIN D3 VIA MODULATION OF TRANSFORMING GROWTH FACTOR-β1/BONE MORPHOGENETIC PROTEIN-7 SIGNALLING IN PUROMYCIN AMINONUCLEOSIDE NEPHROPATHY RATS

P>Accumulating evidence suggests that vitamin D and its analogues are renoprotective. However, the precise mechanisms and the molecular targets by which active vitamin D exerts its beneficial effects remain obscure. The objective of the present study was to evaluate the effect of active vitamin D on rats with puromycin aminonucleoside (PAN) nephropathy, a model that is characterized by predominant podocyte injury. The PAN nephropathy rats were created by a single intravenous injection of 100 mg/kg PAN. Changes in renal pathology and podocyte numbers were observed. Real-time polymerase chain reaction (PCR) was performed to examine mRNA expression of nephrin, transforming growth factor (TGF)-beta 1 and bone morphogenetic protein (BMP)-7. Protein expression of nephrin, TGF-beta 1, BMP-7 and p-Smad2/3 and p-Smad1/5/8 was examined by immunofluorescence, immunohistochemistry and western blotting, respectively. Rats were treated with 1,25(OH)(2)D-3 by gastric gavage at a dose of 2.5 mu g/kg per day, starting 2 days before PAN injection and continuing throughout the experiment. A single injection of PAN induced massive proteinuria and elevated serum creatinine on Day 7, both of which were significantly suppressed by 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3). Immunofluorescence and real-time PCR of the podocyte-associated protein nephrin revealed reduced and discontinuous staining and this change was reversed by 1,25(OH)(2)D-3. In PAN nephropathy rats, TGF-beta 1 and p-Smad2/3 expression was upregulated, whereas that of BMP-7 and p-Smad1/5/8 was downregulated. Treatment with 1,25(OH)(2)D-3 significantly restored BMP-7/Smad signalling while suppressing TGF-beta 1/Smad signalling. In conclusion, 1,25(OH)(2)D-3 can ameliorate podocyte damage and proteinuria induced by PAN. The beneficial effects of 1,25(OH)(2)D-3 on podocytes may be attributable, in part, to direct modulation of TGF-beta 1/BMP-7 signalling.