Long‐term myocardial DNA methylation and metabolomic responses to exertional heat stroke in mice

Abstract

Epidemiological studies indicate that exposure to exertional heat stroke (EHS) can increase the risk of all‐cause cardiovascular and systemic disease and promote early mortality. Using a preclinical mouse model of EHS, we previously characterized profound DNA methylation changes in immune cells at 30 d of recovery and severe cardiometabolic disturbances in the ventricular myocardium (VM) at 9‐14 d. These observations indicate that a single exposure to EHS can result in long‐term epigenetic and metabolic alterations. However, whether a long‐term epigenetic responses occur in the VM and or whether cardiometabolic perturbations persist is unknown.PURPOSETo determine if long‐term alterations to (1) DNA methylation and (2) the metabolome occur within the VM after 30 d of recovery from EHS and (3) whether epigenetic alterations predict imbalances within the metabolome.METHODSSixteen C57BL6 female mice underwent a standardized EHS protocol using a forced running wheel (environmental temp: 37.5°C, 40% humidity) or a matched exercise control trial (EXC) (22.5°C). The EHS mice achieved peak core temps of ~42.4°C, accompanied by transient loss of consciousness. Mice were sacrificed after 30 d of recovery; left ventricles were isolated and frozen in liquid nitrogen for DNA methylation sequencing and untargeted metabolomics.RESULTSFollowing 30 d of recovery from EHS, more than 6,000 differentially methylated cytosines (DMCs) were observed within promoter regions; 900 differentially methylated regions (DMRs) were also observed (i.e ≥ 5 differentially DMCs within 300 base pairs) at (Q < 0.05) compared to EXC. Pathway analysis of promoter DMRs indicated changes in genes that modulate basic cell functions, DNA binding, transcription, and metabolism. Cardiometabolic perturbations were found to largely resolve compared to observations at 9‐14 d. Some metabolic disturbances remained, e.g. reductions in α‐ketoglutarate and increases in several lipid intermediates. These remnant alterations are known to be common in early onset heart failure and chronic kidney disease. Repressive DMCs (P < 0.05) were observed within transcriptional regulatory regions of enzymes that regulate α‐ketoglutarate, e.g. isocitrate dehydrogenase 1 & 2 (IDH1 & IDH2), suggesting a potential link with metabolomic findings.CONCLUSIONSA single EHS episode results in a robust epigenetic response in VM when observed at 30 d of recovery, whereas all but a subset of metabolites within the VM had fully recovered. These long‐term molecular changes may induce altered or maladaptive physiological outcomes in response to future environmental or medical challenges.