Epigenetic responses to exertional heat stroke in mice: a potential link to long term Ca2+ dysregulation in skeletal muscle

Abstract

Exposure to extreme environments can induce a long‐term epigenetic memory of stress that is stored as altered DNA‐methylation and/or histone posttranslational modifications. These ultimately affect gene and protein expression as well as cellular functions. Exertional heat stroke (EHS) is a life‐threatening stress, but whether it induces epigenetic changes is unknown. Previous studies have suggested long‐term complications of EHS that could be mediated by epigenetics, including greater vulnerability to disease, heat stress susceptibility and disordered muscle Ca2+ signaling; the latter characterized as a malignant‐hyperthermia‐type muscle phenotype, based on the in vitro contracture test (IVCT).PURPOSETo determine whether a single exposure to EHS using a preclinical mouse model induces significant changes in DNA methylation and altered skeletal muscle Ca2+ regulation.METHODSMice were either subjected to a standardized EHS protocol using a forced running wheel at 37.5°C or a matched exercise control trial (22.5 °C), N=4/group. The EHS mice achieved peak core temps of ~42.2 °C, accompanied by transient loss of consciousness. Mice were euthanized after 4 or 30 days. At day 4, cells of a monocyte lineage were isolated from bone marrow, and DNA was extracted and tested using bisulfite DNA sequencing. At 30 days, soleus muscles were excised (N=5/group) and tested for a Ca2+ response to caffeine and halothane (IVCT test).RESULTS>3,000 genes from monocytes were significantly hyper‐ or hypomethylated in EHS mice compared to matched controls. Some genes of physiological interest included Ryr1&2, Cacna1s&c (DHPR isoforms), Orai1 (store operated calcium channel), Camk2d, Pde4d (cAMP signaling), Atp2a1/2, Sod2, Nox4, Nos1&2 isoforms, Hsp72, a number of K+ channels, and isoforms of Mir669a‐1 (inhibitors of skeletal muscle myogenesis). The IVCT displayed an abnormal response in solei from EHS mice (3/5) vs. control (0/5) (p=0.031; adjusted Wald Chi‐Square test). Two mice showed an abnormal response to caffeine; one displayed abnormal responses to both caffeine and halothane.CONCLUSIONSThe data demonstrates that EHS induces striking alterations in the epigenome at 4 days. Most biological and behavioral responses return to normal by this time. DNA methylation profiles from accessible blood cell populations may prove to be a useful biomarker for severity of EHS exposures. The IVCT findings mirror the incidence in military EHS populations. Coupled with the epigenetic changes observed in Ca2+‐related genes, studying skeletal muscle Ca2+ regulation may prove a promising target for future discovery.Support or Funding InformationBK and Betty Stevens Endowment and DOD Grant W81XWH‐15‐2‐0038. Disclaimers: Research was conducted in compliance with the Animal Welfare Act, and all other Federal requirements. The views expressed are those of the authors and do not constitute endorsement by the U.S. Army.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.