Kv4.3 expression abrogates and reverses norepinephrine-induced myocyte hypertrophy by CaMKII inhibition.

BACKGROUND:Down-regulation of Kv4.3 protein is a general feature of cardiac hypertrophy. Based on our recent studies, we propose that Kv4.3 reduction may be a hypertrophic stimulator. OBJECTIVE:We tested whether Kv4.3 expression can prevent or reverse cardiac hypertrophy induced by norepinephrine (NE). METHODS AND RESULTS:Incubation of 20 μM NE in cultured neonatal rat ventricular myocytes (NRVMs) for 48 h and 96 h induced myocyte hypertrophy in a time-dependent manner, characterized by progressive increase in cell size, protein/DNA ratio, ANP and BNP, along with an progressive increase in the activity of CaMKII and calcineurin and reduction of Kv4.3 mRNA and proteins. Interestingly, phosphorylation of phospholamban (PLB) at Ser16 was increased at 48 h but reduced to the basal level at 96 h NE incubation. CaMKII inhibitors KN93 and AIP blunted NE-induced hypertrophic response and caused regression of hypertrophy, which is associated with a reduction of CaMKII activity and calcineurin expression. Kv4.3 expression completely suppressed the development of NE-induced hypertrophy and led to a regression in the hypertrophic myocytes. These effects were accompanied by a reduction in CaMKII autophosphorylation, PLB phosphorylation at Thr-17 without changing PLB phosphorylation at Ser-16. NFATc3 was also reduced by Kv4.3 expression. CONCLUSIONS:Our results demonstrated that Kv4.3 reduction is an important mediator in cardiac hypertrophy development via excessive CaMKII activation and that Kv4.3 expression is likely a potential therapeutic strategy for prevention and reversion of adrenergic stress-induced cardiac hypertrophy.

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