Bone marrow mesenchymal stromal cells (BMSC) can differentiate into multiple tissutal lineages such as osteoblasts, chondrocytes and adipocytes. During the differentiative process BMSCs undergo considerable changes, above all the shift from anaerobic to aerobic metabolism and an increase in mitochondrial activity. Various factors regulate the BMSC differentiation in vivo, among others glucocorticoides. Osteogenic media used in vitro to induce differentiation contain Dexamethasone, a synthetic glucocorticoide which at physiological concentrations (<100 nM) enhances the BMSCs proliferation, differentiation and consequently the new bone matrix deposition. Instead, at the higher concentrations (100 M) or under continuous exposition, this substance produces osteoporotic effects. In the osteoporotic phenotype, the cell proliferative activity decreases with augmented reactive oxygen species (ROS) levels, demonstrating a massive involvement of mitochondria. Mitochondria present a decline in the respiratory chain functionality and an increase in the Mt DNA copy number and mutations, such as aged mitochondria; furthermore the apoptotic cell number increases. The aim of our study was to investigate the effects of osteogenic medium, with two Dexamethasone concentrations (100 nM and 100 M) during the osteogenic differentiation of human BMSC (hBMSC); in particular, we examined the mitochondria morphology, their cell localization, the transmembrane potential (Δψm), the ATP amount and the intracellular ROS levels, .referring to undifferentiated hBMSC. The Dexamethasone effects on proliferation (MTT), cell differentiation (ALP and mineralization) and mitochondrial activity depend on the concentration given. The Dexamethasone100 M altered the mittochondrial functionality and the MtDNA through oxidative stress, in a way similar to that which occurred in osteoporotic osteoblasts.
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