Abstract 3602: Genetic Ablation and Inhibition of the Plasma Membrane Calcium/Calmodulin-Dependent ATPase 4 (PMCA4) With a Newly Identified Compound Reduce Pressure-Overload Hypertrophy
We have recently shown that PMCA4 is involved in signaling in the heart by modulating the function of nNOS, which is also calcium/calmodulin dependent, via a PDZ-domain interaction. Here we investigated whether genetic ablation or specific pharmacological inhibition of PMCA4 in mice modifies the development of cardiac hypertrophy. We subjected our PMCA4 knock out (KO) mice to transverse aortic constriction (TAC) for 5 weeks. PMCA4 KO mice displayed a significantly reduced hypertrophic response compared to wild type (WT)(12% increase of heart weight/tibia length in KO vs 46% increase in WT, P10 in each group). Echocardiography and hemodynamic analyses revealed that PMCA4 ablation protected the heart from abnormal left ventricular remodeling and contractile dysfunction after TAC. In neonatal rat cardiomyocytes PMCA4 gene silencing using an adenoviral shRNA system significantly reduced phenylephrine-induced hypertrophy as indicated by cell size (1.4 fold increase of cell size in PMCA4 knock down vs 1.8 fold in control cells, P<0.05). Nitric oxide levels generated from nNOS were increased and Akt activity decreased in cardiomyocytes lacking PMCA4 suggesting that this signaling pathway is regulated by PMCA4. As a first step to identify specific PMCA4 inhibitors, we screened a medically optimised chemical library and successfully identified a novel PMCA4 inhibitor (AP4) with an IC50 of 150 nM for PMCA4. Treatment of WT mice with AP4 for 2 weeks (5mg/kg body weight, BW) reversed the pre-established advanced hypertrophy in the setting of pressure overload (16% decrease of LVmass/BW in AP4 treated mice vs 11% increase of LVmass/BW in control group, P<0.05). Likewise, phenylephrine-induced hypertrophy in isolated cardiomyocytes was significantly reduced after treatment with AP4. In conclusion, our data shows that PMCA4 is a key regulator of pressure overload induced hypertrophy. Specific inhibition of PMCA4 ameliorates pre-existing hypertrophy in mice suggesting PMCA4 as a candidate target for the treatment of cardiac hypertrophy and failure.