Age-related decline in osteoblastogenesis and 1α-hydroxylase/CYP27B1 in human mesenchymal stem cells: stimulation by parathyroid hormone.

With aging, there is a decline in bone mass and in osteoblast differentiation of human mesenchymal stem cells (hMSCs) in vitro. Osteoblastogenesis can be stimulated with 1,25-dihydroxyvitamin D(3) [1,25(OH)(2) D(3) ] and, in some hMSCs, by the precursor 25-hydroxyvitamin D(3) (25OHD(3) ). CYP27B1/1α-hydroxylase activates 25OHD(3) and, to a variable degree, hMSCs express CYP27B1. In this study, we tested the hypotheses (i) that age affects responsiveness to 25OHD(3) and expression/activity of CYP27B1 in hMSCs and (ii) that parathyroid hormone (PTH) upregulates CYP27B1 in hMSCs, as it does in renal cells. There were age-related declines in osteoblastogenesis (n=8, P=0.0286) and in CYP27B1 gene expression (n=27, r= -0.498; P=0.008) in hMSCs. Unlike hMSCs from young subjects (≤50 years), hMSCs from older subjects (≥55 years) were resistant to 25OHD(3) stimulation of osteoblastogenesis. PTH1-34 (100 nm) provided hMSCs with responsiveness to 25OHD(3) (P=0.0313, Wilcoxon matched pairs test) and with two episodes of increased 1,25(OH)(2) D(3) synthesis, of cAMP response element binding protein (CREB) activation, and of CYP27B1 upregulation. Both increases in CYP27B1 expression by PTH were obliterated by CREB-siRNA or KG-501 (which specifically inhibits the downstream binding of activated CREB). Only the second period of CREB signaling was diminished by AG1024, an inhibitor of insulin-like growth factor-I receptor kinase. Thus, PTH stimulated hMSCs from elders with responsiveness to 25OHD(3) by upregulating expression/activity of CYP27B1 and did so through CREB and IGF-I pathways.