Tungsten inhibits osteogenesis of MSCs in vitro. MSC cultures were transitioned to OM medium and were either left untreated (OM) or treated with 15 μg/ml tungsten (OM +W) throughout osteoblast differentiation. A, RNA expression analysis of osteoblast gene markers (Runx2, Sp7, and Bglap) were analyzed by qRT-PCR at day 10 of differentiation. Graph shows the mean fold change in gene expression ± SEM, normalized to naïve gene expression for each gene. Data normalized to housekeeping gene Rn18s. ***P ≤ .001 1-way ANOVA. Graph is a representative experiment of 3 biological replicates each performed in four technical replicates. B, ALP activity was measured in MSC cultures on day 12 of differentiation. Graph shows the mean level of ALP activity (absorbance) ± SEM for naïve, OM, and OM +W samples. ***P ≤ .001 1-way ANOVA. Graph is a representative experiment of 3 biological replicates each performed in triplicate. C, Calcium mineralization was measured by Alizarin Red staining in MSC cultures at day 12 of differentiation. Graph shows the mean level of Alizarin Red dye (absorbance) ± SEM for naïve, OM, and OM +W samples. Graph is a representative experiment of 3 biological replicates each performed in triplicate. ***P ≤ .001 1-way ANOVA.