Mechanosensitive TRPV4 channels mediate cardiac fibroblast differentitation to myofibroblasts

Abstract

Cardiac fibroblasts play critical role in cardiac remodeling and during development. Cardiac remodeling following myocardial infarction involves the migration, proliferation and differentiation of cardiac fibroblasts to hypersecretory myofibroblasts. Myofibroblasts facilitate wound repair in the myocardium by secreting and organizing extra cellular matrix (ECM) and fibrosis. However, the molecular mechanisms involved in myofibroblast differentiation are not well known. Because the infarcted/ischemic myocardium is known to undergo mechanical stretch and the muscle phenotypic modulator TGF‐β is also increased in ischemia, we hypothesized the mechanotransduction and TGF‐β signaling pathway play active role in the differentiation of cardiac fibroblasts to myofibroblasts. Here, we show that the mechanosensitve ion channel TRPV4 is required for TGF‐β‐induced differentiation of cardiac fibroblasts to myofibroblasts. We found that cardiac fibroblasts functionally express TRPV4 channels and the TRPV4‐specific antagonist, AB159908 significantly inhibited TGFβ‐induced differentiation as measured by incorporation of α‐SMA into actin stress fibers (p < 0.05). Importantly, we demonstrate that TGF‐β‐induced myofibroblast differentiation is regulated by the variations in ECM elasticity in a TRPV4 dependent manner. Further, we found that TGF‐β treatment increased the expression of TRPV4. Finally, calcium imaging experiments with Fluo‐4 revealed that TGF‐β treated fibroblasts exhibit enhanced TRPV4‐dependent calcium influx compared to untreated controls ( p< 0.05). Taken together these results suggest, for the first time, that a mechanosensitive ion channel, TRPV4 regulates cardiac fibroblast differentiation to myofibroblasts which could be used as a novel therapeutic target for the treatment of ischemia and myocardial infarction.