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

ABSTRACT

BACKGROUND/AIMS: Hypoxia modulation of transforming growth factor (TGF)- ß-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-ß1-induced cardiomyocyte H9c2 cells. METHODS: H9c2 cells were cultured for intermittent hypoxia treatment and TGF-ß1 treatment. α-Smooth muscle actin (α-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-ß-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-ß1 expression, but had no effect on α-SMA expression. Exogenous TGF-ß1 alone upregulated α-SMA expression in H9c2 cells in a concentration- and time-dependent manner. α-SMA expression declined with the duration of hypoxia after intermittent hypoxia and exogenous TGF-ß1 co-treatment. Phospho-JNK and phospho-p38 levels were not significantly altered after TGF-ß1 and hypoxia treatment. However, levels of phospho-ERK increased after TGF-ß1 treatment and continued to increase after hypoxia co-treatment. The activation of phospho-Smad2/3 and phospho-RhoA induced by TGFß1 was significantly reduced after hypoxia co-treatment. CONCLUSION: Hypoxia can inhibit TGF-ß1-induced H9c2 myofibroblast transformation, based on inhibition of α-SMA expression by suppressing signaling downstream of TGF-ß1, Smad2/3 and RhoA. It suggested that TGF-ß-mediated cardiomyocyte transformation is not involved in hypoxia-mediated fibrosis.