Hypoxia Suppresses TGF-B1-Induced Cardiac Myocyte Myofibroblast Transformation by Inhibiting Smad2/3 and Rhoa Signaling Pathways

Background/Aims: Hypoxia modulation of transforming growth factor (TGF)-beta-induced signaling during myofibroblast transformation is dependent on the specific cell type. The purpose of this study was to explore the effects of hypoxia on myofibroblast transformation of TGF-beta 1-induced cardiomyocyte H9c2 cells. Methods: H9c2 cells were cultured for intermittent hypoxia treatment and TGF-beta 1 treatment. alpha-Smooth muscle actin (alpha-SMA) expression was examined by western blotting and immunofluorescence after treatment. To further explore the possible mechanism for this effect, the effects of hypoxia on three early TGF-beta-dependent signaling pathways, i.e. the Smad2/3, RhoA and mitogen-activated protein kinase (MAPK) pathways, were screened by western blotting. Results: Intermittent hypoxia induced TGF-beta 1 expression, but had no effect on alpha-SMA expression. Exogenous TGF-beta 1 alone upregulated alpha-SMA expression in H9c2 cells in a concentration-and time-dependent manner. alpha-SMA expression declined with the duration of hypoxia after intermittent hypoxia and exogenous TGF-beta 1 cotreatment. Phospho-JNK and phospho-p38 levels were not significantly altered after TGF-beta 1 and hypoxia treatment. However, levels of phospho-ERK increased after TGF-beta 1 treatment and continued to increase after hypoxia co-treatment. The activation of phospho-Smad2/3 and phospho-RhoA induced by TGF beta 1 was significantly reduced after hypoxia co-treatment. Conclusion: Hypoxia can inhibit TGF-beta 1-induced H9c2 myofibroblast transformation, based on inhibition of alpha-SMA expression by suppressing signaling downstream of TGF-beta 1, Smad2/3 and RhoA. It suggested that TGF-beta-mediated cardiomyocyte transformation is not involved in hypoxia-mediated fibrosis. (C) 2018 The Author(s) Published by S. Karger AG, Basel