Malignant Hyperthermia‐associated Mutation of RyR1 Induces Mitochondrial Damages and Cellular Oxidation in the Heart

Abstract

Human pedigrees carrying the ryanodine receptor type 1 (RyR1) mutations frequently show skeletal muscle (SM) disorders including malignant hyperthermia (MH). There are also case reports describing sudden cardiac death (SCD) in MH patients in the conscious condition without anesthesia. These observations cannot be explained as a secondary effect of their SM dysfunction; however, the molecular mechanism underlying cardiac phenotypes in MH is still unknown. We previously reported that a low level of RyR1 is expressed in the mitochondria (termed as mitochondrial RyR1: mRyR1), but not in the sarcoplasmic reticulum (SR) in the cardiomyocytes and serves as an important mitochondrial Ca2+ influx pathway in addition to the mitochondrial Ca2+ uniporter in cardiomyocytes. We also reported, using knock‐in mice carrying a MH‐related RyR1 mutation Y522S (YS) that YS hearts exhibit disrupted mitochondrial morphology as well as compromised mitochondrial functions with a high cellular oxidative state, which can account for cardiac phenotypes in MH. In addition, YS heart developed multiple ventricular extrasystoles by β‐adrenergic stimulation. Therefore, we hypothesize that YS‐RyR1s form “leaky channel” at mitochondria and induce mitochondrial Ca2+ overload, which alters the cellular Ca2+ handling in cardiomyocyte. Using isolated mitochondria or isolated cardiomyocytes under confocal microscope, we found that YS cardiomyocytes have higher basal mitochondrial Ca2+ concentration, depolarized mitochondrial membrane potential and slower cytosolic Ca2+ clearance as compared to WT. Moreover, pretreatment of RyR1 blocker dantrolene prevented these changes in YS cardiomyocytes and normalized their Ca2+ handling profiles similar to those in WT. In conclusion, these results indicate that chronic mitochondrial Ca2+ overload via leaky mutant mRyR1 damages cardiac mitochondrial functions/structures, reduces cytosolic Ca2+ buffering capacity and induces cellular oxidation, which may increase arrhythmogenic events in MH.Support or Funding InformationThis work was partly supported by American Heart Association (AHA) grant (14BGIA18830032 to J.O.‐U.), Medical Research Grant from W.W. Smith Charitable Trust (H1403 to J.O.‐U.) and NIH grants (2R01HL093671 and 1R01HL122124 to SSS).