Mice lacking the renal epithelial Ca2+ channel TRPV5 (TRPV5-/-) display impaired renal Ca2+ reabsorption, hypercalciuria, and intestinal Ca2+ hyperabsorption, due to secondary hypervitaminosis D. Using these mice, we previously demonstrated that ZK191784 acts as an intestine-specific 1,25(OH)2D3 antagonist without affecting serum calcium levels. On the other hand, it acted as an agonist in the kidney and the effects of ZK191784 on bone were ambiguous. The present study was undertaken to further evaluate the effect of the vitamin D receptor antagonist on murine bone in mice lacking TRPV5. Eight-week-old female Trpv5+/+ and Trpv5-/- mice were treated for 4 weeks with or without 50μg/kg/day ZK191784. Quantitative backscattered electron imaging showed that the reduced bone matrix mineralization found in femoral bones of Trpv5-/- mice was partially but significantly restored upon ZK191784 treatment, just as we observed for trabecular bone thickness. This supports the significance of 1,25(OH)2D3 and optimal control of Ca2+ homeostasis for bone formation and matrix mineralization. Restoration also took place at the bone gene expression level, where 1α-hydroxylase (Cyp27b1) mRNA in femurs from ZK-treated Trpv5-/- mice was upregulated compared to control levels. The downregulated 24-hydroxylase (Cyp24a1) gene expression in femoral bone indicated local vitamin D resistance in the mice treated with ZK191784. Phosphate homeostasis was unaffected between the groups as shown by unaltered serum and fibroblast growth factor (FGF) 23 as well as Fgf23 mRNA expression in bone. In conclusion, circulating 1,25(OH)2D3 is important for optimal control of Ca2+ homeostasis but also for controlled bone formation and matrix mineralization.

doi.org/10.1002/jcp.24144, hdl.handle.net/1765/58168
Journal of Cellular Physiology
Department of Internal Medicine

van der Eerden, B., Fratzl-Zelman, N., Nijenhuis, T., Roschger, P., Zügel, U., Steinmeyer, A., … van Leeuwen, H. (2013). The vitamin D analog ZK191784 normalizes decreased bone matrix mineralization in mice lacking the calcium channel TRPV5. Journal of Cellular Physiology, 228(2), 402–407. doi:10.1002/jcp.24144