Stimulation of B7-H3 (CD276) directs the differentiation of human marrow stromal cells to osteoblasts

Previous studies showed that B7-H3 (CD276), a cytokine involved in the activation of T lymphocytes, regulates murine bone formation. However, the role of B7-H3 in bone formation is barely understood. Herewith, we report, that stimulation of B7-H3 promotes the differentiation of human marrow stromal cells (hMSCs) to osteoblasts. With 4H7, a new monoclonal antibody against human B7-H3, we have identified B7-H3 is located on the surface of human marrow stromal cells. Evermore, we have found that increase of B7-H3 levels are correlated with the differentiation course of hMSCs. Stimulation of B7-H3 with 4H7 antibody considerably increases the numbers of osteoblasts generated from the hMSCs in the presence of inducing medium containing dexamethasone, sodium β-glycerophosphate and l-ascorbic acid. 4H7 treatments significantly increase osteoblast markers including alkaline phosphatase (ALP), and osteocalcin (OC) after day 7 and day 14 of the inducing hMSCs differentiation. The numbers of mineralized nodules of osteoblasts have been remarkly increased after 21 days of induced differentiation of hMSCs. However, stimulation effects of 4H7 antibody on membrane B7-H3 has been eliminated by addition of B7-H3Fc fusion protein. These results indicate 4H7 antibody specifically stimulates the membrane B7-H3 and directs the differentiation of hMSCs. Furthermore, our study also shows that stimulation of B7-H3 increases the expression of osteoprotein (OPG), and decreases the expression of its cognate ligand, the receptor activator of nuclear factor kappaB ligand (RANKL).