Role of down-regulated expression of vitamin D receptor mediated by fibroblast growth factor 23 and bone morphogenetic protein 7 in rats with type 2 diabetes and osteoporosis

Objective To investigate the expression and significance of Vitamin D receptor (VDR),fibroblast growth factor(FGF) 23 and bone morphogenetic protein(BMP) 7 in the kidney and bone tissues in rats with type 2 diabetes and osteoporosis.Methods Female Wistar rats were randomly divided into four groups:sham control group (NS group),ovariectomy group (NOVX group),type 2 diabetes sham surgery group (DS group) and type 2 diabetic rats undergoing ovariectomy group (DOVX group).In diabetes groups,rats were administrated with high-sugar-fat diet and intraperitoneal injection of small dose of streptozotocin so as to establish type 2 diabetes models (T2DMs).After the models were successfully established,the ovariectomy groups received ovariectomy and were randomly sacrificed at the end of week 4,8 and 12 after ovariectomy in batches.The mRNA expression levels of VDR,FGF23 and BMP7 in kidney and bone tissues in each group were observed by RT-PCR and the protein expression levels of VDR,FGF23 and BMP7 in kidney tissues by Western blot.Results The models of type 2 diabetes with osteoporosis were successfully established.Both mRNA expression levcls of VDR and BMP7 in kidney and bone tissues and the protein expression levels of VDR and BMP7 in kidney tissues of DS and DOVX groups were lower than those of NS and NOVX groups along with time (P＜0.05).DS and DOVX groups had significantly lower mRNA expression of FGF23 in bone tissues as compared with NS and NOVX groups(0.566±0.059,0.452±0.057 vs 1.008±0.068,0.520±0.049,P＜0.05),but the mRNA and protein expression of FGF23 in kidney tissues of DS and DOVX groups was significantly higher than that of NS and NOVX groups (protein:1.034±0.071,1.136±0.112 vs 0.919±0.086,0.952±0.143),with expression level in DOVX group being the highest(P＜ 0.05).Conclusion The expression of vitamin D receptor(VDR) mediated by both FGF23 and BMP7 may not exert effects on rats of type 2 diabetes with osteoporosis. Key words: Diabetes mellitus,type 2; Osteoporosis; Receptors,calcitriol; Fibroblast growth factor 23; Bone morphogenetic protein 7