Abstract 894: Inhibition of Long Noncoding RNA lncExACT1 Induces Physiological Cardiac Hypertrophy and Protects Against Pathological Hypertrophy

Abstract

Long noncoding-RNAs (lncRNAs) are critical regulators of cardiac development as well as pathological hypertrophy and heart failure (HF). However, their roles in exercise-induced physiological hypertrophy are unclear. Here, we used RNAseq to identify a novel class of cardiac lncRNAs that are dynamically regulated by exercise. We call these l ong n on c oding Ex ercise A ssociated C ardiac T ranscripts (lncExACTs). Among them, lncExACT1, a highly conserved lncRNA, is down-regulated in exercised hearts but upregulated in transverse aortic constriction (TAC)-induced pathological hypertrophy and HF. In primary neonatal cardiomyocytes (CMs), transfection of LNA antisense oligonucleotide complementary to lncExACT1 (GapmeR) was sufficient to inhibit lncExACT1 expression and increase CM size with a gene expression pattern consistent with physiological hypertrophy (increased PCG1α and α/βMHC ratio, all p <0.05 vs . control). In contrast, lentiviral overexpression of lncExACT1 in primary CMs induced a pathological gene expression pattern (decreased PCG1α and β/αMHC ratio, with increased ANP and BNP, all p <0.05 vs . control). In vivo, GapmeR treatment for two weeks reduced cardiac lncExACT1 expression (0.5-fold at 2 weeks), increased ventricular wall thickness and fractional shortening (FS, p =0.034 vs . control), increased heart weight to tibial length ratio (HW/TL) and α/βMHC. In contrast, injection of AAV9-lncExACT1 increased cardiac lncExACT1 (6-fold at 5 weeks) increased HW/TL as well as βMHC and ANP. Further, lncExACT1 acted as a sponge for microRNA-222 (a microRNA we previously reported is necessary for physiological cardiac growth) thereby increasing expression of microRNA-222 targets, including p27, a cell cycle inhibitor protein. Moreover, GapmeR injection reduced TAC-induced increase of interventricular septal end diastole (IVSd) and left Ventricular Posterior Wall Dimensions (LVPWd) without affecting FS. We conclude that inhibition of lncExACT1 is sufficient to induce physiological hypertrophy and protect against pathological hypertrophy, while induction of lncExACT1 promotes pathological hypertrophy. lncExACT1 appears to mediate these effects, at least in part, by acting as competing endogenous RNA for microRNA-222.