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. YAP inhibition suppressed the VIC proliferation and reduced valve size, but enhanced cell-cell adhesions between VEC thus maintaining an elongated 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.

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

“…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).…”

“…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 ).…”

Feeder-free generation and characterization of endocardial and cardiac valve cells from human pluripotent stem cells

“… 64 Notably, the function of Vgll4 has recently been explored in mice, where knockout of Vgll4 led to semilunar valve thickening—a phenotype that was rescued with partial knockout of Yap . 65 As YAP also responds differentially to changes in mechanical force and regulates valve growth and remodeling, 66 it would be worth investigating the influence of VGLL3 on these processes and how its function in this context differs from VGLL4.…”

Feeder-Free Generation of Endocardial and Cardiac Valve Cells from Human Pluripotent Stem Cells

“…49 Notably, the function of Vgll4 has recently been explored in mice, where knockout of Vgll4 led to semilunar valve thickening—a phenotype that was rescued with partial knockout of Yap . 50 As YAP also responds differentially to changes in mechanical force and regulates valve growth and remodeling, 51 it would be worth investigating the influence of VGLL3 on these processes and how its function differs from VGLL4.…”