Megalin mediates 25‐hydroxyvitamin D 3 actions in human mesenchymal stem cells

Osteoblast differentiation of human mesenchymal stem cells (hMSCs) is stimulated by 1α,25‐dihydroxycholecalciferol [1α,25(OH) 2 D 3 ] and 25‐hydroxycholecalciferol [25(OH)D 3 ]; the latter's effects require intracellular hydroxylation to 1α,25(OH) 2 D 3 . Thus, hMSCs are both a source of and target for 1α,25(OH) 2 D 3 . Megalin is a transmembrane receptor for serum d ‐binding protein (DBP) in kidney cells and is required for uptake of the 25(OH)D 3 ‐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)D 3 and 1α,25(OH) 2 D 3 , for 1α,25(OH) 2 D 3 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) 2 D 3 and 25(OH)D 3 stimulated osteoblastogenesis ( P < 0.05), but only 1α,25(OH) 2 D 3 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) 2 D 3 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) 2 D 3 and for the 25(OH)D 3 /DBP complex to stimulate vitamin D receptor targets and osteoblastogenesis.—Gao, Y., Zhou, S., Luu, S., Glowacki, J. Megalin mediates 25‐hydroxyvitamin D 3 actions in human mesenchymal stem cells. FASEB J. 33, 7684–7693 (2019). www.fasebj.org