Extracellular Superoxide Dismutase (EC-SOD) Regulates Gene Methylation and Cardiac Fibrosis During Chronic Hypoxic Stress.

Abstract

BackgroundChronic hypoxic stress induces epigenetic modifications in cardiac fibroblasts, such as inactivation of tumor suppressor genes (RASSF1A), and activation of kinases (ERK1/2). The effects of the antioxidant enzyme, extracellular superoxide dismutase (EC-SOD), on these epigenetic changes has not been fully explored. ObjectivesTo define the effect of EC-SOD overexpression on cardiac fibrosis induced by chronic hypoxia. MethodsWild type C57B6 male mice (WT) and transgenic males with an extra copy of human hEC-SOD (TG) were housed in hypoxia (10% O2) for 21 days. Right ventricular tissue was studied for cardiac fibrosis markers using RT-PCR and Western Blot analyses. Downstream effects were studied, for both RASSF-1 expression and methylation and its relation to ERK1/2, using in-vivo & in-vitro models ResultsThere were significant increases in markers of cardiac fibrosis : Collagen 1, Alpha Smooth Muscle Actin (ASMA) and SNAIL, in the WT hypoxic animals as compared to the TG hypoxic group (p< 0.05). Expression of DNA methylation enzymes (DNMT 1,2) was significantly increased in the WT hypoxic mice as compared to the hypoxic TG mice (p<0.001). RASSF1A expression was significantly lower and ERK1/2 was significantly higher in hypoxia WT compared to the hypoxic TG group (p<0.05). Use of SiRNA to block RASSF1A gene expression in murine cardiac fibroblast tissue culture led to increased fibroblast proliferation (p<0.05). Methylation of RASSF1A promoter region showed a significant reduction in the TG hypoxic group compared to the WT hypoxic group (0.59 vs 0.75 respectively). ConclusionsEC-SOD significantly attenuates RASSF1A gene methylation, and plays a pivotal role cardiac fibrosis induced by hypoxia.