Pluripotent mesenchymal stem cells can undergo lineage‐specific differentiation in adult organisms. However, understanding of the factors and mechanisms that drive this differentiation is limited. We show the novel ability of specific oxysterols to regulate lineage‐specific differentiation of mesenchymal stem cells into osteogenic cells while inhibiting their adipogenic differentiation. Such effects may have important implications for intervention with osteoporosis.

Introduction: Oxysterols are products of cholesterol oxidation and are formed in vivo by a variety of cells including osteoblasts. Novel pro‐osteogenic and anti‐adipogenic effects of specific oxysterols on pluripotent mesenchymal cells are demonstrated in this report. Aging and osteoporosis are associated with a decrease in the number and activity of osteoblastic cells and a parallel increase in the number of adipocytic cells.

Materials and Methods: The M2–10B4 pluripotent marrow stromal cell line, as well as several other mesenchymal cell lines and primary marrow stromal cells, was used to assess the effects of oxysterols. All results were analyzed for statistical significance using ANOVA.

Results and Conclusion: Pro‐osteogenic and anti‐adipogenic effects of specific oxysterols were assessed by the increase in early and late markers of osteogenic differentiation, including alkaline phosphatase activity, osteocalcin mRNA expression and mineralization, and the decrease in markers of adipogenic differentiation including lipoprotein lipase and adipocyte P2 mRNA expression and adipocyte formation. Complete osteogenic differentiation of M2 cells into cells expressing early and late markers of differentiation was achieved only when using combinations of specific oxysterols, whereas inhibition of adipogenesis could be achieved with individual oxysterols. Oxysterol effects were in part mediated by extracellular signal‐regulated kinase and enzymes in the arachidonic acid metabolic pathway, i.e., cyclo‐oxygenase and phospholipase A₂. Furthermore, we show that these specific oxysterols act in synergy with bone morphogenetic protein 2 in inducing osteogenic differentiation. These findings suggest that oxysterols may play an important role in the differentiation of mesenchymal stem cells and may have significant, previously unrecognized, importance in stem cell biology and potential therapeutic interventions.