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Supplementary Material for: Antagonistic Effects of Insulin and TGF-β3 during Chondrogenic Differentiation of Human BMSCs under a Minimal Amount of Factors

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posted on 12.02.2016, 00:00 by Hara E.S., Ono M., Yoshioka Y., Ueda J., Hazehara Y., Pham H.T., Matsumoto T., Kuboki T.
Growth factors are crucial regulators of cell differentiation towards tissue and organ development. Insulin and transforming growth factor-β (TGF-β) have been used as the major factors for chondrogenesis in vitro, by activating the AKT and Smad signaling pathways. Previous reports demonstrated that AKT and Smad3 have a direct interaction that results in the inhibition of TGF-β-mediated cellular responses. However, the result of this interaction between AKT and Smad3 during the chondrogenesis of human bone marrow-derived stem/progenitor cells (hBMSCs) is unknown. In this study, we performed functional analyses by inducing hBMSCs into chondrogenesis with insulin, TGF-β3 or in combination, and found that TGF-β3, when applied concomitantly with insulin, significantly decreases an insulin-induced increase in mRNA levels of the master regulator of chondrogenesis, SOX9, as well as the regulators of the 2 major chondrocyte markers, ACAN and COL2A1. Similarly, the insulin/TGF-β3-treated group presented a significant decrease in the deposition of cartilage matrix as detected by safranin O staining of histological sections of hBMSC micromass cultures when compared to the group stimulated with insulin alone. Intracellular analysis revealed that insulin-induced activation of AKT suppressed Smad3 activation in a dose-dependent manner. Accordingly, insulin/TGF-β3 significantly decreased the TGF-β3-induced increase in mRNA levels of the direct downstream factor of TGF-β/Smad3, CCN2/CGTF, compared to the group stimulated with TGF-β3 alone. On the other hand, insulin/TGF-β3 stimulation did not suppress insulin-induced expression of the downstream targets TSC2 and DDIT4/REDD1. In summary, insulin and TGF-β3 have antagonistic effects when applied concomitantly, with a minimal number of factors. The application of an insulin/TGF-β3 combination without further supplementation should be used with caution in the chondrogenic differentiation of hBMSCs.