Valve related congenital heart defects (CHD) are a major cause of preterm and infant death. Despite considerable research progress uncovering important genetic regulators of cardiac morphogenesis, translation to clinical benefit has been hampered by a lack of understanding of how these pathways coordinate to drive valve formation and remodeling. The embryonic valves are exposed to an increasingly demanding mechanical environment as they grow and mature, but the functional consequences of these forces are far less understood. Valvulogenesis can alternatively be considered an engineering process rather than a purely genetic program. Uncovering these new governing relationships is therefore essential but has been challenging because of the lack of analytical tools and experimental approaches that can isolate and quantify mechanical effects in live embryonic valves. First, we have developed unique biomechanical testing devices that can quantify embryonic cushion and valve biomechanics. Second, we have created a novel speckle tracking algorithm in conjunction with high frequency ultrasound that can non-invasively quantify dynamic tissue strains within the embryonic valves. Third, we developed a unique finite element simulation strategy that iterates with in vivo measurements to map local biomechanical parameters in anatomically precise geometries. Fourth, we have created the first experimental strategy to create locally isolated intracardiac defects in live avian embryos non-invasively through femtosecond laser photoablation (FLP). Using these enabling technologies, our objective for this proposal is to identify and characterize mechano-genetic relationships that guide the formation of the embryonic valves. Our overall hypothesis is that mechanical signaling orchestrates the sculpting and strengthening of the embryonic valves through simultaneous regulation of multiple valvulogenic signaling pathways. We will first quantify the changing in vivo mechanical environments surrounding the valves and their biomechanical adaptation (Aim 1). We will next determine how the network of known molecular regulators of valvulogenesis is modulated by mechanical stimulation in vitro (Aim 2). Then we test the mechano-genetic mechanisms suggested by the previous experiments in vivo using locally controlled photoablations to avian embryonic valves (Aim 3). This proposal will generate significant quantitative detail of the in vivo biomechanical environment during embryonic valvulogenesis and how this regulates local gene expression to promote valve formation and maturation. This novel information will complement existing datasets from genetic manipulation studies and guide new interpretations of these results. A better understanding of the mechanobiological relationships guiding valve formation and remodeling significantly broadens the array of mechanisms to explain the pathogenesis of CHD and tools to enable new clinical strategies to prevent or repair CHD.
This proposal will implement new technologies to quantify the biomechanical environment surrounding developing embryonic heart valves. We will then determine how specific mechanical forces simultaneously regulate multiple genes to control heart valve formation and remodeling. By confirming these relationships in vivo, we will uncover a natural heart valve engineering paradigm that can inform new regenerative strategies for heart valve disease.
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