Endogenous bone morphogenetic proteins mediate 1α, 25‐dihydroxyvitamin D 3 ‐induced expression of osteoblast differentiation markers in human dermal fibroblasts

Human dermal fibroblasts are generally considered to be restricted to a fibroblastic lineage. Although dermal fibroblasts do not typically express markers of osteoblastic differentiation, they have previously been shown to undergo osteoinduction when stimulated with bone morphogenetic proteins (BMPs) or vitamin D 3 . However, involvement of BMP signaling in vitamin D 3 ‐mediated osteoinduction has not been reported. In this study, human dermal fibroblasts were cultured in chemically defined medium containing vitamin D 3 , in the presence of the BMP antagonist noggin or neutralizing antibodies specific for BMP‐4 or BMP‐6, and characterized for markers of osteoblastic differentiation. Treatment of dermal fibroblasts with vitamin D 3 induced expression of BMP‐4 (1.2 ± 0.2, 1.7 ± 0.2, and 1.8 ± 0.2 relative fold increase) and BMP‐6 (9.1 ± 0.3, 23.3 ± 2.1, and 30.4 ± 3.0 relative fold increase) at 3, 14, and 21 days, respectively. Vitamin D 3 was also shown to induce the expression of the osteoblast‐specific markers, alkaline phosphatase and osteocalcin, in a dose‐dependent manner in human dermal fibroblasts. Addition of noggin, BMP‐4 antibodies, and BMP‐6 antibodies resulted in a downregulation of alkaline phosphatase activity (by 42%, 22%, and 20%, respectively) and secreted osteocalcin (by 20%, 31%, and 49%, respectively) after 21 days in culture. However, blocking BMP signaling did not result in complete recovery of a fibroblastic phenotype. Taken together, these results suggest that BMP signaling plays a role in the induction of an osteoblastic phenotype in human dermal fibroblasts in response to vitamin D 3 stimulation. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:162–168, 2009