Loss of Yap/taz in cardiac fibroblasts attenuates adverse remodeling and improves cardiac function.

AIMS: Fibrosis is associated with all forms of adult cardiac diseases including myocardial infarction (MI). In response to MI, the heart undergoes ventricular remodeling that leads to fibrotic scar due to excessive deposition of extracellular matrix mostly produced by myofibroblasts. The structural and mechanical properties of the fibrotic scar are critical determinants of heart function. Yes-associated protein (Yap) and transcriptional coactivator with PDZ-binding motif (Taz) are the key effectors of the Hippo signaling pathway and are crucial for cardiomyocyte proliferation during cardiac development and regeneration. However, their role in cardiac fibroblasts, regulating post-MI fibrotic and fibroinflammatory response is not well established.

METHODS AND RESULTS: Using mouse model, we demonstrate that Yap/Taz are activated in cardiac fibroblasts after MI and fibroblasts-specific deletion of Yap/Taz using Col1a2Cre(ER)T mice reduces post-MI fibrotic and fibroinflammatory response and improves cardiac function. Consistently, Yap overexpression elevated post-MI fibrotic response. Gene expression profiling shows significant downregulation of several cytokines involved in post-MI cardiac remodeling. Furthermore, Yap/Taz directly regulate the promoter activity of pro-fibrotic cytokine interleukin-33 (IL33) in cardiac fibroblasts. Blocking of IL33 receptor ST2 using the neutralizing antibody abrogates the Yap-induced pro-fibrotic response in cardiac fibroblasts. We demonstrate that the altered fibroinflammatory program not only affects the nature of cardiac fibroblasts but also the polarization as well as infiltration of macrophages in the infarcted hearts. Furthermore, we demonstrate that Yap/Taz act downstream of both Wnt and TGFβ signaling pathways in regulating cardiac fibroblasts activation and fibroinflammatory response.

CONCLUSIONS: We demonstrate that Yap/Taz play an important role in controlling MI-induced cardiac fibrosis by modulating fibroblasts proliferation, transdifferentiation into myofibroblasts, and fibroinflammatory program.

TRANSLATIONAL PERSPECTIVE: Cardiac fibroblasts are the most prevalent cell type in the heart and play an important role in regulating post-myocardial infarction (MI) cardiac fibrosis. Excessive cardiac fibrosis causes ventricular stiffness leading to systolic/diastolic cardiac dysfunction and heart failure. Therefore, understanding the molecular mechanism of cardiac fibroblasts activation will help to modulate the post-MI fibrotic response and improve cardiac function. In our study, we show that Yap/Taz play an important role in controlling MI-induced cardiac fibrosis by modulating fibroblasts proliferation, transdifferentiation into myofibroblasts, and fibroinflammatory program.