FAK signaling in cardiac growth and hypertrophy

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DESCRIPTION (provided by applicant): Recent genetic evidence indicates that the integrin class of fibronectin-binding adhesion receptors (5E1 and others) can regulate both the form and function of the heart. Integrin ligation drives recruitment of a number of structural and signaling molecules to the ventral plasma membrane collectively termed a "focal adhesion" which serves to link the force-generating actin cytoskeleton inside the cell to the extracellular matrix (ECM), and to coordinate activation of downstream signaling pathways. The non-receptor tyrosine kinase, Focal Adhesion Kinase (FAK) is strongly activated by both integrins and growth factors, and is a likely candidate to integrate downstream signals from these diverse pathways during growth and development. Indeed, germline deletion of FAK results in mesodermal defects and embryonic lethality between E7.5-10 similar to the phenotype observed in both fibronectin-, and D5-null mice. Although a direct role for FAK in cardiac development has yet to be examined, hearts from FAK-null embryos revealed a lack of separate mesocardial and endocardial layers, indicative of a defect in cardiomyocyte maturation. Interestingly, recent work by our group and others clearly indicate that FAK is activated in cultured cardiomyocytes by a variety of hypertrophic stimuli including, phenylephrine (PE), endothelin I (ET-1), angiotensin II (AII), and hypo-osmotic stress, and that increased cardiac FAK activity is observed in vivo in hypertrophic hearts. The idea that FAK activation plays a direct role in the development of cardiomyocyte hypertrophy is evident from our seminal findings that the activation of FAK is required for PE-stimulated hypertrophy of cultured cells and similar findings from others that FAK is required for maximal ET-1 and stretch-induced hypertrophy in vitro. The experimental goals of this proposal are to test the hypothesis that FAK regulates cardiac development and pathological hypertrophy in vivo and to identify the FAK-dependent signaling pathways involved in these processes. We will generate genetically modified mice in which FAK will be deleted in a temporal and cardiac-restricted fashion using Cre/LoxP technology to examine a functional role for FAK in cardiac growth. We will also establish a cardiac cell culture model to identify FAK-dependent signals and target genes that are differentially regulated by hypertrophic stimuli.