Phosphorylation of RYR1 at Ser 2902 decreases Ca 2+ leak in skeletal muscle and susceptibility to malignant hyperthermia and heat stroke

Ryanodine receptor 1 (RYR1) is the sarcoplasmic reticulum (SR) Ca 2+ release channel required for both skeletal muscle contraction and Ca 2+ leak. Mutations in RYR1 cause malignant hyperthermia susceptibility (MHS) and enhanced sensitivity to heat stroke (ESHS), which can result in death due to excessive skeletal muscle thermogenesis upon exposure to volatile anesthetics or heat. Here, we investigated the molecular and physiological functions of phosphorylation of RYR1 at Ser 2902 by the kinase striated muscle preferentially expressed protein (SPEG). Muscle from SPEG-deficient mice expressing RYR1 with a Ser 2902 →Asp 2902 (S2902D) point mutation to mimic phosphorylation by SPEG showed decreased SR Ca 2+ sparks. Muscle from mice homozygous for the S2902D point mutation had reduced SR Ca 2+ transients and small changes in force generation but overall mild phenotypic changes. YS mice, which are heterozygous for a Tyr 524 →Ser 524 point mutation in RYR1, show increased Ca 2+ leak and are a model of MHS and ESHS. Crossing YS mice with S2902D mice led to decreased SR Ca 2+ leak and desensitized the mice to both volatile anesthetics and heat. Thus, SPEG inhibits SR Ca 2+ leak in skeletal muscle by phosphorylating Ser 2902 on RYR1, and mutation of Ser 2902 to Asp 2902 to mimic this phosphorylation event rescues YS mice from heat-induced death.