Hemodynamic forces such as shear stress are intimately linked with cardiac morphogenesis. Mutations in Notch signaling components result in congenital heart defects in humans and mice. During heart development, the trabeculae form a network of branching outgrowths from the ventricular wall, and both trabeculation and compaction are essential for normal cardiac contractile function. Hemodynamic shear stress induces vascular endothelial Notch signaling, and Notch pathway mediates differentiation and proliferation of trabecular myocytes. However, the mechanotransduction mechanisms underlying endocardial shear stress (ESS) and the initiation of trabeculation remain elusive. Our multi-disciplinary approach has demonstrated that peristaltic contraction of the embryonic heart tube produces time-varying shear stress (??/?t) and pressure gradients (?P) across the atrioventricular (AV) canal in a zebrafish model of cardiac development. The advent of zebrafish genetic system has enabled the application of fli1 promoter to drive expression of enhanced green fluorescent protein (EGFP) in all vasculature throughout embryogenesis (Tg(fli1a:EGFP)y1); thereby, allowing for 3-D visualization of the moving boundary conditions (2D + time) for computational fluid dynamics (CFD) simulation. However, 4-D (3-D + time) imaging to recapitulate the endocardium throughout the cardiac cycle requires fast tissue scanning and deep axial penetration. In this context, we seek to develop fluorescent Super-Resolution Light-Sheet Microscopy (SRLSM) to capture the 4-D endocardial trabecular network. We hypothesize that spatial (??/?x) and temporal ??/?t) variations in shear stress differentially modulate endocardial Notch signaling to initiate trabeculation. To test our hypothesis, we propose the following three aims.
In Aim 1, we will develop a fast 4-D cardiac imaging technique for moving boundary conditions. Our goal is to image endocardiac morphogenesis throughout the cardiac cycle.
In Aim 2, we will establish a link between shear stress and endocardial trabeculation. Our goal is to determine the effects of temporal (??/?t) and spatial (??/?x) variations in endocadial shear stress on the initiation of trabeculation from 20 to 120 hours post fertilization.
In Aim 3, e will elucidate the mechanotransduction mechanisms underlying trabeculation via Notch signaling. Our goal is to demonstrate that the shear stress-mediated endocardial Notch signaling pathway initiates differentiation and proliferation of cardiac trabeculation. Overall, ou team approach aims to establish a fundamental direction at the interface of hemodynamic forces and cardiac development with pathophysiological significance to non- compaction cardiomopathy.
Non-compaction (LVNC) is the third most common cardiomyopathy with an estimated prevalence from 4.5 to 26 per 10,000 adult patients referred for echocardiographic diagnosis. While most clinical studies are based on the anatomical feature of LVNC, there remains a poor genotype-phenotype association in LVNC patients, and a paucity of knowledge regarding the mechanotransduction mechanisms of trabeculation and compaction. For these reason, our multi-disciplinary team seeks to embrace hemodynamic forces and laser light-sheets to elucidate endocardiac development with clinical relevance to pediatric and adult cardiovascular diseases. .
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