Exploring the mechanism by which defects in the PIX signaling pathway result in cardiomyopathy - Project Summary Integrin adhesion complexes (IACs) play a critical role in cardiomyocyte attachment to the extracellular matrix and in force transduction—both essential processes required for effective blood pumping. Mutations in several genes encoding IAC proteins are associated with cardiomyopathies, conditions with 50% lethality rate within five years of diagnosis. Notably, nearly half of known cardiomyopathy cases lack an identifiable genetic mutation, underscoring an urgent need to discover additional genes linked to the disease. To address this gap, we translated our findings from C. elegans to a mammalian model by generating a cardiomyocyte-specific knockout of β-PIX (β-PIX-cKO) in mice. In C. elegans, we identified PIX-1 (the β-PIX ortholog) as a guanine nucleotide exchange factor that regulates IAC assembly in muscle cells. β-PIX-cKO mice develop dilated cardiomyopathy by 8-months of age and exhibit premature lethality between 9- and 11-months. Additionally, I localized β-PIX to three key cardiomyocyte structures where IACs are present: costameres, intercalated disks, and Z-disks. Our research aims to identify the specific small GTPase and GAP involved in the PIX pathway in mouse cardiomyocytes. To this end, we will establish an overexpression model of two candidate GAP proteins, allowing us to conduct parallel studies with β-PIX-cKO mice. Using these murine models, we will examine how PIX pathway disruptions affect IAC protein localization, expression levels, and the functional adhesion strength of cardiomyocytes. These experiments will shed light on the mechanisms by which β-PIX deficiency leads to cardiomyopathy. Furthermore, our findings could support the inclusion of PIX pathway genes in genetic screens for cardiomyopathy, potentially enabling earlier diagnosis and more targeted treatments. While mutations in several IAC proteins are linked to cardiomyopathy, the mechanisms driving disease onset remain largely unknown; our model system may also offer broader insights into cardiomyopathy that develops from mutations in many other proteins.
