Hypoxia inhibition of adipocytogenesis in human bone marrow stromal cells requires transforming growth factor-β/Smad3 signaling

Abstract

Although hypoxia and transforming growth factor-β (TGF-β) inhibit differentiation of adipocytes from preadipocytes and bone marrow-derived cells in several species, the relationship between hypoxia and TGF-β signaling in adipocytogenesis is unknown. In this study, we evaluated the mechanisms of inhibition of adipocyte differentiation by hypoxia and TGF-β in human and murine marrow stromal cells (MSCs) and the role of TGF-β/Smad signaling in the inhibition of adipocytogenesis by hypoxia. Both hypoxia-mimetic deferoxamine mesylate (DFO) and TGF-β1 inhibited adipocyte differentiation (1.0% versus the control at 15 μM DFO and 1.4% versus the control at 1 ng/ml TGF-β1) and adipocyte gene expression (peroxisome proliferator-activated receptor-γ2 and lipoprotein lipase) in human MSCs after 21 days of treatment. Hypoxia (2% O2) and DFO (but not TGF-β1) increased hypoxia-inducible factor-1α as shown by Western blotting. Macroarrays and Western and Northern blot analyses showed that hypoxia activated the TGF-β/Smad signaling pathway and that both hypoxia and TGF-β1 modulated adipocyte differentiation pathways such as the insulin-, peroxisome proliferator-activated receptor-γ, phosphatidylinositol 3-kinase-, and MAPK-associated signaling pathways. Studies with mouse marrow stromal cell lines derived from Smad3+/+ or Smad3-/- mice revealed that the TGF-β type I receptor (ALK-5) and its intracellular signaling molecule Smad3 were necessary for the inhibition of adipocyte differentiation by both TGF-β and hypoxia-mimetic DFO. Thus, the TGF-β/Smad signaling pathway is required for hypoxia-mediated inhibition of adipocyte differentiation in MSCs. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.