Megalin mediates 25-hydroxyvitamin D3 actions in human mesenchymal stem cells.

Osteoblast differentiation of human mesenchymal stem cells (hMSCs) is stimulated by 1α,25-dihydroxycholecalciferol [1α,25(OH)2D3] and 25-hydroxycholecalciferol [25(OH)D3]; the latter's effects require intracellular hydroxylation to 1α,25(OH)2D3. Thus, hMSCs are both a source of and target for 1α,25(OH)2D3. Megalin is a transmembrane receptor for serum d-binding protein (DBP) in kidney cells and is required for uptake of the 25(OH)D3-DBP complex. We tested the hypothesis that megalin is required for D actions in hMSCs with cells from surgically discarded marrow for RT-PCR, for effects of 25(OH)D3 and 1α,25(OH)2D3, for 1α,25(OH)2D3 biosynthesis, for osteoblastogenesis, and for small interfering RNA for megalin (si-Meg) and control (si-Ctr). In hMSCs with high constitutive megalin expression, both 1α,25(OH)2D3 and 25(OH)D3 stimulated osteoblastogenesis (P < 0.05), but only 1α,25(OH)2D3 did so in hMSCs with lower megalin (lo-Meg, P < 0.001) or in si-Meg cells (P < 0.05). In addition, 1α,25(OH)2D3 biosynthesis was significantly lower in lo-Meg (46%, P = 0.034) and in si-Meg (23%, P < 0.001) than each control. Leptin significantly stimulated megalin expression 2.1-fold in lo-Meg cells (P < 0.01). These studies show that megalin is expressed in hMSCs and is required for the biosynthesis of 1α,25(OH)2D3 and for the 25(OH)D3/DBP complex to stimulate vitamin D receptor targets and osteoblastogenesis.-Gao, Y., Zhou, S., Luu, S., Glowacki, J. Megalin mediates 25-hydroxyvitamin D3 actions in human mesenchymal stem cells.