Decreased smooth muscle cell force generation contributes to thoracic aortic disease via altered focal adhesion dynamics, composition, and signaling

Yale University, New Haven CT

Investigators

Abstract

PROJECT SUMMARY – PROJECT 1 The majority of genes with pathogenic variants that confer a highly penetrant risk for heritable thoracic aortic disease (HTAD) lead to aberrant smooth muscle cell (SMC) - extracellular matrix (ECM) interactions and are predicted to compromise SMC homeostatic force generation. By contrast, we hypothesize that the normal structure of the aortic medial layer allows the SMCs to generate basal levels of tension across elastic-contractile units (ECUs) to maintain a homeostatic state such that normal mechanosensing focal adhesions (FAs) are not activated (i.e., they are quiescent at basal levels). Pathogenic variants in HTAD genes that decrease SMC contractile force generation activate FA kinase (FAK) signaling through altered FA-ECM composition and dynamics, thus triggering distinct downstream pathways, with Rho/ROCK signaling and hypercontractile actinomyosin motors allowing aneurysm formation and the addition of mTOR signaling driving progression to dissection. We will initially determine, in collaboration with Project 3, how the loss of force generation in Acta2-/- SMCs alters the composition and dynamics of FA-ECM interactions and alters downstream signaling pathways. Altered ECM composition, along with manipulation of FAs and downstream signaling pathways, will rigorously test how altered FA-ECM interactions drive specific downstream signaling. We will also assess changes FA- ECM composition and FAK-driven signaling in Prkg1R177Q/+ mice associated with slowly enlarging aneurysms versus acute dissections, including a hypertensive challenge to complement Projects 4-5. Specific FA-driven pathogenic or protective pathways will be targeted with drugs or genetic manipulation to confirm their role in disease progression. Finally, the role of developmental or chronic versus acute changes in FA-ECM composition in triggering dissection will be assessed by varying timing of conditional knock-in of Prkg1R177Q/+ variant in SMCs, thus complementing work in Project 2. Thus, this Project will address a critical knowledge gap of the role of SMC mechanosensing in thoracic aortic disease by focusing on FA-ECM dynamics and structure, along with downstream signaling, when force generation across FAs is disrupted by variants in genes encoding proteins involved in SMC contraction. Since FAK activation of Rho/ROCK may be an adaptive change that maintains SMC homeostasis (e.g., mean wall stress, see Overall Project) while allowing aneurysm growth and delaying ascending dissections, it will be contrasted with FAK activation of mTOR signaling, which augments TAD progression to dissection. In this way, we will complement studies in Projects 2-5 to collectively identify new therapeutic targets, including FA-driven signaling pathways to prevent dissections.