Discovering small molecules that inhibit adipogenesis and promote osteoblastogenesis: unique screening and Oncostatin M-like activity.

Oncostatin M (OSM), one of the IL-6 family cytokines, inhibits adipogenic differentiation and stimulates osteoblastogenic differentiation from human bone marrow mesenchymal stem cells (hBMSCs). This functional study of OSM enabled us to develop a two-dimensional small-molecule screen that shifts hBMSC differentiation from adipocyte to osteoblast. Several structurally related compounds (isoxazoles) inhibited the accumulation of intracellular lipid droplets, whereas they promoted alkaline phosphatase activity and extracellular matrix calcification. Isoxazoles also reduced the expression of adipogenic transcription factor PPARγ and increased the levels of osteogenic transcription factors Runx2 and Osterix. They also induced the expression of the Wnt/β-catenin downstream gene and TOPflash reporter; however, the dephosphorylated β-catenin-active form was not significantly increased. Interestingly, the slight modification of the active compound led to a complete reversion of the dual differentiation activities. In summary, we have identified isoxazoles with anti-adipogenic and pro-osteogenic activities that provide a potential new tool for exploring the lineage commitment of mesenchymal stem cells and a possible lead for therapeutic intervention in osteopenia and osteoporosis.