Abstract MP140: Epigenetic Silencing of SERCA2a by Long Noncoding RNA Lnc-SYNPO Contributes to Impaired Ca 2+ Homeostasis and Contractility in the Failing Heart

Abstract

Abnormal sarcolemmal Ca 2+ handling and impaired contractile function owing to sarcoplasmic reticulum/endoplasmic reticulum ATPase 2a (SERCA2a, encoded by ATP2A2 ) downregulation and/or dysfunction are pathognomonic hallmarks of heart failure (HF). There is, however, no clinically proven HF therapy that targets SERCA2a/ ATP2A2 dysregulation directly. Exploiting gene co-expression network analysis using an RNA sequencing dataset generated from human failing and non-failing left ventricular (LV) tissues, we identified long noncoding RNA lnc-SYNPO , transcribed from the 3’ untranslated region of SYNPO2 , as a potential regulator of SERCA2a/ ATP2A2 . Myocardial lnc-SYNPO was markedly upregulated during HF and its expression level showed a strong negative correlation (Pearson correlation coefficient=-0.60) with that of SERCA2a/ ATP2A2 in both mouse and human LV. Knockdown of lnc-SYNPO in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) increased, whereas overexpression of lnc-SYNPO reduced, SERCA2a/ ATP2A2 expression. In addition, lnc-SYNPO knockdown reversed endothelin-1 (ET-1) treatment-induced SERCA2a/ ATP2A2 downregulation, impaired Ca 2+ homeostasis and contractile dysfunction in hiPSC-CM. Mechanistically, the depletion of lnc-SYNPO, a chromatin-associated nuclear lncRNA, led to increased H3K4me3 and reduced H3K27me3 occupancy at SERCA2a/ ATP2A2 promoter. Chromatin isolation by RNA purification showed direct physical binding between lnc-SYNPO and the promoter of SERCA2a/ ATP2A2 . In addition, RNA pull-down assays showed that lnc-SYNPO binds to EZH2 and SUZ12, two core components of the polycomb repressor complex 2 (PRC2), suggesting that lnc-SYNPO represses SERCA2a/ ATP2A2 expression by recruiting PRC2 complex to the promoter of SERCA2a/ ATP2A2 , leading to epigenetic silencing of SERCA2a/ ATP2A2 . Taken together, these results unveiled a previously undiscovered epigenetic regulatory mechanism of SERCA2a/ ATP2A2 by lnc-SYNPO , contributing to impaired myocardial Ca 2+ homeostasis and contractile dysfunction observed with HF. Targeting lnc-SYNPO , therefore, could be a novel therapeutic approach to improve Ca 2+ homeostasis and contractile function in the failing human heart.