Abstract 361: Loss of Cardiac Retinoic Acid Receptor Alpha Promotes Diastolic Heart Failure With Preserved Ejection Fraction

Objectives: We have previously demonstrated that the expression/activation of retinoic acid receptor (RAR) is inhibited in diabetic hearts, and that activation of RARα prevents diabetes-induced diastolic heart failure, suggesting that impairment of RARα signaling may be a critical mechanism in heart failure. Methods and Results: Cardiac RARα gene deletion (KO) was achieved by tamoxifen injection at 6-weeks old RARαfl/fl α-MHC-MerCreMer mice, RARαfl/fl mice were used as control (WT). Heart function was monitored by echocardiograph for 64 wks. Mice were sacrificed at 20 or 64 wks post gene deletion, respectively. A significant decrease in E/A ratio and TDI E’ and increase in IVRT (isovolumic relaxation time) and DT (deceleration time) suggested diastolic dysfunction after 16 wks of gene deletion in KO mice, which was confirmed by cardiac catheterization (decreased dP/dtmin and increased tau). Concentric hypertrophy developed in KO mice after 56 wks of gene deletion, as confirmed by increased thickness of left ventricular wall and interventricular septum and elevated heart weight/tibia length ratio. However, no significant difference was observed in LVEF (LV ejection fraction), FS (fraction shortening) and dP/dtmax between KO and WT mice. Significantly increased gene expression of NOX2 (NADPH oxidase 2) and NOX4, decreased SOD1 and SOD2 levels and increased intracellular reactive oxygen species (ROS) were observed in KO mouse hearts, along with a significantly decreased protein expression of SERCA2a and CaMKIIδ, decreased phosphorylation of PLB, Akt and CaMKIIδ. Overexpression of RARα in cardiomyocytes rescued RARα deletion-induced changes in SERCA2a, PLB, Akt and CaMKIIδ. Deletion of RARα in cardiomyocytes impaired intracellular calcium reuptake into SR and cardiomyocyte relaxation. Inhibition of ROS by N-acetyl cysteine abolished RARα deletion-induced calcium mishandling and cardiomyocyte relaxation. Conclusion: Cardiac specific deletion of RARα induces diastolic heart failure with preserved ejection fraction (HFpEF), by promoting intracellular ROS and disrupting SERCA2a-mediated calcium reuptake and cardiomyocyte relaxation. Our study suggests that deficiency in RARα signaling is a novel mechanism leading to HFpEF.