The role of redox regulation of SERCA in cardiomyocyte hypertrophy
Morgan, Robert Joseph
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Cardiac hypertrophy is a fundamental response to an increased workload on the heart characterized by cardiac myocyte (CM) growth and left ventricular (LV) wall thickening. In a model of hypertension, e.g. chronic pressure overload, this process may become maladaptive, initially leading to impaired myocardial relaxation and LV filling, and subsequently to LV dilation, wall thinning, and contractile failure. Hemodynamic overload activates Gαq-mediated signaling responsible for transcriptional reactivation of fetal growth programs, activation of the mitogen-activated protein kinase (MAPK) cascade, and oxidative stress. The precise mechanism by which MAPK is activated in pressure overload, and the role oxidative stress plays in mediating this hypertrophic signaling are still under investigation. In CMs, the sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) maintains calcium stores, and thus may regulate calcium-dependent MAPK signaling. Our laboratory showed that SERCA is activated in CMs by reversible oxidative post-translational modification (OPTM) of its most reactive cysteine site (C674). We hypothesized that OPTMs mediate the effects of hypertrophic stimuli in CMs via reversible oxidation of SERCA at C674. To test this hypothesis, we employed a reductionist model: isolated adult rat ventricular myocytes (ARVM) overexpressing wild-type (WT) or mutant SERCA, in which C674 is substituted with a redox-insensitive serine (C674S). Using alpha-adrenergic receptor (αAR) stimulation as a model of Gq-mediated hypertrophy, we found that C674S expression decreased both CM growth and MAPK activation. Furthermore, biotin switch revealed that αAR stimulation induced a reversible OPTM of SERCA at C674. We generated a transgenic mouse expressing a single-allele C674S SERCA2 knock-in mutation (SKI) to explore this mechanism further in the setting of pressure overload, a disease model of Gq-activation in vivo. SKI mice subjected to ascending aortic constriction (AAC) had decreased hypertrophy compared to WT. Ventricular myocytes isolated from adult SKI mice also had diminished MAPK activation in response to hypertrophic stimulation in vitro and decreased SERCA function at baseline. These findings led us to the conclusion that redox-activation of SERCA via reversible modification of C674 is critical for the complete transduction of hypertrophic stimuli to MAPK signaling and CM hypertrophy.