Abstract 223: Yap and Its Homolog Wwtr1 Are Regulators of Myofibroblast Activation Following Ischemic Injury

Introduction: Following ischemic injury in adult mammals, cardiac fibroblasts differentiate into myofibroblasts and promote secretion of matrix fibers. Myofibroblast activation is critical for initial scar formation and preventing heart rupture, however, extended activity can lead to heart failure progression. Thus, there is a need to identify the mechanisms mediating persistent activation of myofibroblasts to prevent excessive fibrosis and adverse cardiac remodeling. Here we demonstrate that Hippo-Yap pathway offers a target for modulating myofibroblast activation and thus the fibrotic response. Methods and Results: We tested the hypothesis that Yap and its homolog Wwtr1 (known as ‘Taz’) are regulators of myofibroblast activation following ischemic injury. We implemented a Cre-lox system whereby Yap alone or both Yap and Wwrt1 were depleted using an inducible Cre expressed under a myofibroblast specific promoter ( Postn MCM ). Following permeant ligation of the left anterior descending artery in adult mice, we found that myofibroblast depletion of Yap alone resulted in a significant reduction in left ventricular dilation 28 days post injury (dpi) and decreased proliferation of scar associated cells. Strikingly, myofibroblast specific depletion of Yap and one copy of Wwrt1 resulted in further attenuation of left ventricular dilation as well as improved fractional shortening and ejection fraction at 28 and 60 dpi. Histological assessment revealed that depletion of both Yap and Wwrt1 resulted in greater than 50% reduction in scar size (by midline) at 60 dpi. RNAseq of whole hearts collected at 4 dpi suggested that Hippo-Yap pathway expression specifically in myofibroblasts facilitates immune cell recruitment in the heart. Collectively These data illustrate a role for Hippo-Yap signaling mediating myofibroblast activity and immune cell coordination following injury and therefore cardiac fibrosis and remodeling. Conclusions: Our data demonstrate that endogenous Yap and Wwrt1 deletion in myofibroblasts suppresses the fibrotic response, mediates inflammation, and improves cardiac function after ischemic injury. These results therefore offer a regulatory pathway that can be targeted therapeutically to prevent progressive heart failure.