Antihypertrophic Memory after Regression of Exercise-induced Physiological Myocardial Hypertrophy

Background: Exercise can induce physiological myocardial hypertrophy (PMH), and former athletes can live 5-6 years longer than nonathletic controls, suggesting a benefit after regression of PMH. We previously reported that regression of pathological myocardial hypertrophy has antihypertrophic effects. Accordingly, we hypothesized that antihypertrophic memory exists even after PMH has regressed, increasing myocardial resistance to subsequent pathological hypertrophic stress. Methods and Results: C57BL/6 mice were submitted to 21 days of swimming training to develop PMH. After termination of exercise, PMH regressed within 1 week. PMH regression mice (hypertrophic preconditioning group, EHP) and sedentary mice (control group) then underwent transverse aortic constriction (TAC) or a sham operation. At 1 and 4 weeks after TAC, the EHP group showed less increase in myocardial hypertrophy and lower expression of the Nppa and Myh7 genes than the sedentary group. At 4 weeks after TAC, EHP mice had less pulmonary congestion, smaller left ventricular dimensions and end-diastolic pressure, and a larger left ventricular ejection fraction and maximum pressure change rate than sedentary mice. Quantitative polymerase chain reaction (qPCR) revealed that the long noncoding myosin heavy chain associated RNA transcript Mhrt779 was one of the markedly upregulated long noncoding RNAs in the EHP group. Silencing of Mhrt779 attenuated the antihypertrophic effect of EHP in mice with TAC and in cultured cardiomyocytes treated with angiotensin II, and overexpression enhanced the antihypertrophic effect. By chromatin immunoprecipitation assay and qPCR, we found that EHP increased histone 3 trimethylation (H3K4me3 and H3K36me3) at a4 promoter of Mhrt779. Comprehensive identification of RNA-binding proteins by mass spectrometry and Western blot showed that Mhrt779 can bind Brg1 to upregulate Hdac2 and inhibit phosphorylation of Akt and GSK3β. Conclusions: Myocardial hypertrophy preconditioning evoked by exercise increases resistance to pathological stress via an antihypertrophic effect mediated by a signal pathway of Mhrt779 /Hdac2/p-Akt/p-GSK3β. lnc RNA sequencing analysis of exercise prehypertrophic preconditioning(EHP) and sedentary mouse hearts