Abstract P2030: Regulation Of Pathologic Cardiac Signaling Via Rac1 Palmitoylation

Abstract

Development of more effective therapies to prevent maladaptive cardiac remodeling and heart failure would be greatly aided by the identification of novel signaling pathways that regulate cardiac hypertrophy. Cysteine palmitoylation is a reversible post-translational lipid modification that dynamically regulates intracellular trafficking and subcellular compartmentalization of signaling proteins. Previous work from our group identified that mice with cardiomyocyte (CM)-specific overexpression of zDHHC3, a Golgi-localized S-acyltransferase, develop lethal dilated cardiomyopathy. S-acyl-proteomics revealed Cys-178 of Rac1, a small GTPase, as a palmitoylation site modified by zDHHC3 and hearts from zDHHC3-overexpressing mice display elevated levels of palmitoylated, active, and total Rac1, suggesting Rac1 palmitoylation promotes its activation and may drive pathologic cardiac remodeling. Rac1-dependent activation of NADPH oxidase 2 (Nox2) in CMs is required for angiotensin II (AngII)-induced cardiac hypertrophy and myocardial oxidative stress, suggesting inhibition of Rac1/Nox2 signaling could potentially ameliorate adverse cardiac remodeling. We found Rac1 palmitoylation at Cys-178 to be required for hypertrophy and oxidative stress in neonatal rat CMs as reactive oxygen species production and hypertrophy elicited by expression of a constitutively active Rac1 mutant were attenuated by mutation of the Cys-178 palmitoylation site, suggesting palmitoylation targets Rac1 to the Nox2 complex to promote myocardial oxidative stress. Notably, Rac1 palmitoylation and oxidative stress were also enhanced in hearts of mice subjected to AngII infusion and transgenic mice with CM-specific overexpression of the angiotensin II receptor type I (AT1R), suggesting a role for Rac1 palmitoylation in AngII-induced maladaptive cardiac signaling. To further elucidate the role of Rac1 palmitoylation in cardiac pathology, we developed a CM-specific knock-in mouse model in which Cys-178 of Rac1 is mutated to serine. Ongoing work utilizing this model will investigate mechanisms by which palmitoylated and depalmitoylated Rac1 differentially regulate signaling, oxidative stress, and hypertrophy in CMs in response to pathologic stimuli.