Shear and hydrostatic stress regulate fetal heart valve remodeling through YAP-mediated mechanotransduction

Abstract

Clinically serious congenital heart valve defects arise from improper growth and remodeling of endocardial cushions into leaflets. Genetic mutations have been extensively studied but explain less than 20% of cases. Mechanical forces generated by beating hearts drive valve development, but how these forces collectively determine valve growth and remodeling remains incompletely understood. Here we decouple the influence of those forces on valve size and shape, and study the role of YAP pathway in determining the size and shape. The low oscillatory shear stress promotes YAP nuclear translocation in valvular endothelial cells (VEC), while the high unidirectional shear stress restricts YAP in cytoplasm. The hydrostatic compressive stress activated YAP in valvular interstitial cells (VIC), whereas the tensile stress deactivated YAP. YAP activation by small molecules promoted VIC proliferation and increased valve size. Whereas YAP inhibition enhanced the expression of cell-cell adhesions in VEC and affected valve shape. Finally, left atrial ligation was performed in chick embryonic hearts to manipulate the shear and hydrostatic stress in-vivo. The restricted flow in the left ventricle induced a globular and hypoplastic left atrioventricular (AV) valves with an inhibited YAP expression. By contrast, the right AV valves with sustained YAP expression grew and elongated normally. This study establishes a simple yet elegant mechanobiological system by which transduction of local stresses regulates valve growth and remodeling. This system guides leaflets to grow into proper sizes and shapes with the ventricular development, without the need of a genetically prescribed timing mechanism.

Yap is a Nutrient Sensor Sensitive to the Amino Acid L-Isoleucine and Regulates Expression of Ctgf in Cardiomyocytes

“…Yap signalling and methods of regulation have been extensively studied in diverse cell types and disease conditions, but the specific molecular mechanisms underlying the effects of Yap activation after myocardial infarction (MI) are not fully understood. While mechanical stress is considered the primary driver of cardiac Yap signalling [25][26][27] this study reveals that cardiac metabolic stress can also be a major driver of altered Yap-signalling. The role of Yap-signalling in metabolism has been shown in predominantly cancer metabolism as a regulator of cellular proliferation and substrate utilization [28].…”

egr3 is a mechanosensitive transcription factor gene required for cardiac valve morphogenesis

“…S6A), suggesting that it is independent of VEGF/ERK signaling. Given the fundamental role of mechanical signaling in cardiac valve formation ( 10 , 23 , 26 ), we then decided to test whether egr3 expression was downstream of mechanical forces. We simulated a no-flow/no-contraction condition in vivo by taking advantage of the zebrafish embryo’s ability to withstand severe cardiac dysfunction ( 59 ).…”

“…1C). Notably, egr3 expression appears more enriched in the valve EdCs when compared with other established valve transcription factor genes (16,18,23,35), including klf2a/b (29) and nfatc1 (14) (fig. S1, B and C).…”

“…Extensive work in vertebrates has shown that perturbation of mechanical forces in the heart severely affects valve formation (10,(22)(23)(24)(25). In particular, the zebrafish model allows for the observation and manipulation of intracardiac mechanical forces while imaging valve morphogenesis at single-cell resolution.…”

Differential Development of the Chordae Tendineae and Anterior Leaflet of the Bovine Mitral Valve

“…These cell types contribute differently to the different AV leaflets, where the anterior mitral valve leaflet is said to be derived from predominantly endocardial cells whereas the posterior leaflet is derived from epicardial cells [19]. The endocardial cushions protrude into the lumen and change blood flow from oscillatory to unidirectional pulsatile flow [20,21], increasing shear stress and activating mechanotransduction pathways [21]. The mechanotransduction pathways have been extensively documented in the literature [13,[20][21][22], particularly in zebrafish models [14,[23][24][25].…”