Long-term epigenetic and metabolomic changes in the mouse ventricular myocardium after exertional heat stroke

Evidence from human epidemiological studies suggests that exertional heat stroke (EHS) results in elevated risk of long-term cardiovascular and systemic disease. Previous results using a preclinical mouse model of EHS demonstrated a severe metabolic imbalance in the ventricular myocardium developing at 9-14 d of recovery. Whether this resolves over time is unknown. We hypothesized that long-term effects of EHS on the heart reflect a maladaptive epigenetic response. In this study, we determined the DNA methylation and the metabolomic profiles of the left ventricular myocardium in female C57BL/6 mice 30 d after EHS (exercise in 37.5C; n = 7-8) and compared to sham exercise controls. EHS mice ran to apparent loss of consciousness, reaching a core temperature of 42.4 0.2C. All mice recovered quickly and after 30 d the left ventricles were rapidly frozen for DNA methyl sequencing and untargeted metabolomics. Within promoter regions, ventricular DNA from EHS mice revealed >6,000 differentially methylated cytosines (DMCs) and >900 differentially methylated regions (DMRs; 5 DMCs within 300 base pairs). Pathway analysis revealed alterations in genes regulating basic cell functions, DNA binding, transcription and metabolism. Metabolomics revealed a relative return to metabolic homeostasis, but with a few remaining disturbances such as reduced alpha-ketoglutarate and elevated lipid metabolic intermediates. We conclude that EHS results in a sustained DNA methylation memory that lasts through 30 d of recovery, while heart metabolism recovers to a relative homeostasis. Such long-lasting alterations to the DNA methylation landscape could alter responsiveness to subsequent environmental or pathological challenges to the myocardium later in life.