Rationale Previously, we demonstrated that a deoxycorticosterone acetate (DOCA)-salt hypertensive mouse model produces cardiac oxidative stress and diastolic dysfunction with preserved systolic function. Oxidative stress has been shown to increase late inward sodium current (INa), reducing the net cytosolic Ca2+ efflux. Objective Oxidative stress in the DOCA-salt model may increase late INa resulting in diastolic dysfunction amenable to treatment with ranolazine. Methods and Results Echocardiography detected evidence of diastolic dysfunction in hypertensive mice that improved after treatment with ranolazine (E/E′, sham 31.9 ± 2.8, sham+ranolazine 30.2 ± 1.9, DOCA-salt 41.8 ± 2.6, and DOCA-salt+ranolazine 31.9 ± 2.6, p = 0.018). The end diastolic pressure volume relationship slope was elevated in DOCA-salt mice, improving to sham levels with treatment (sham 0.16 ± 0.01 vs. sham+ranolazine 0.18 ± 0.01 vs. DOCA-salt 0.23 ± 0.2 vs. DOCA-salt+ranolazine 0.17 ± 0.01 mm Hg/L, p < 0.005). DOCA-salt myocytes demonstrated impaired relaxation, τ, improving with ranolazine (DOCA-salt 0.18 ± 0.02, DOCA-salt + ranolazine 0.13 ± 0.01, Sham 0.11 ± 0.01, Sham + ranolazine 0.09 ± 0.02 s, p = 0.0004). Neither late INa nor the Ca2+ transients were different from sham myocytes. Detergent extracted fiber bundles from DOCA-salt hearts demonstrated increased myofilament response to Ca2+ with glutathionylation of myosin binding protein C. Treatment with ranolazine ameliorated the Ca2+ response and cross-bridge kinetics. Conclusions Therefore, diastolic dysfunction could be reversed by ranolazine, likely resulting from a direct effect on myofilaments, indicating that cardiac oxidative stress may mediate diastolic dysfunction through altering the contractile apparatus.

Background Stress-induced hypertrophic remodeling is a critical pathogenetic process leading to heart failure. While many signal transduction cascades are demonstrated as important regulators to facilitate the induction of cardiac hypertrophy, the signaling pathways for suppressing hypertrophic remodeling remain largely unexplored. In this study, we identified p21-activated kinase 1 (Pak1) as a novel signaling regulator which antagonizes cardiac hypertrophy. Methods and Results Hypertrophic stress applied to primary neonatal rat cardiomyocytes (NRCMs), or murine hearts caused the activation of Pak1. Analysis of NRCMs expressing constitutively active Pak1 or in which Pak1 was silenced disclosed that Pak1 played an anti-hypertrophic role. To investigate the in vivo role of Pak1 in the heart, we generated mice with a cardiomyocyte-specific deletion of Pak1 (Pak1cko). When subject to 2 weeks of pressure overload, Pak1cko mice compared to controls, developed greater cardiac hypertrophy with attendant blunting of JNK activation, and these knockout mice underwent the transition into heart failure when prolonged stress was applied. In addition, chronic angiotensin II infusion also caused increased cardiac hypertrophy in Pak1cko mice. Moreover, we discovered that the Pak1 activator FTY720, a sphingosine-like analogue, was able to prevent pressure overload-induced hypertrophy in wild-type mice, without compromising their cardiac functions. Meanwhile FTY720 failed to exert such an effect on Pak1cko mice, suggesting that the anti-hypertrophic effect of FTY720 likely acts through Pak1 activation. Conclusions These results, for the first time, establish Pak1 as a novel anti-hypertrophic regulator and suggest that it may be a potential therapeutic target for the treatment of cardiac hypertrophy and heart failure.