The disorders of the calcium release unit of skeletal muscles: what have we learned from mouse models?

Calcium storage, release, and reuptake are essential for normal physiological function of muscle. Several human skeletal muscle disorders can arise from dysfunction in the control and coordination of these three critical processes. The release from the Sarcoplasmic Reticulum stores (SR) is handled by a multiprotein complex called Calcium Release Unit and composed of DiHydroPyridine Receptor or DHPR, Ryanodine Receptor or RYR, Calsequestrin or CASQ, junctin, Triadin, Junctophilin and Mitsugumin 29. Malignant hyperthermia (MH), Central Core Disease (CCD), Exertional/environmental Heat Stroke (EHS) and Multiminicore disease (MmD) are inherited disorders of calcium homeostasis in skeletal muscles directly related to mutations of genes coding for proteins of the CRU, primarily ryanodine receptor (RYR1). To understand the pathophysiology of MH and CCD, four murine lines carrying point mutations of human RYR1 have been developed: Y524S, R163C, I4898T and T4826I. Mice carrying those mutations show a phenotype with the traits of MH and/or CCD. Interestingly, also ablation of skeletal muscle calsequestrin (CASQ1) leads to a phenotype with MH-like lethal episodes in response to halothane and heat stress and development of central cores. In this review, we aim to describe the murine lines with RYR mutations or CASQ ablation, which show a phenotype similar to human MH or CCD, to underline their specific phenotypes and their differences and to discuss their contribution to the understanding of the pathophysiology of the disorders and the development of therapeutic strategies.