Human disease variants in the ryanodine receptor have effects in vivo for Caenorhabditis elegans neuromuscular function

The ryanodine receptor is a key intracellular calcium ion channel in nerve and muscle cells. A number of links have been made between the ryanodine receptor and age- related muscular and neurodegeneration. Variants of the RYR1 gene are associated with malignant hyperthermia, which is a hypermetabolic reaction to inhalational anaesthetics. I used eight genome-edited Caenorhabditis elegans strains expressing ryanodine receptors with modifications equivalent to known RYR1 disease variants to characterise the consequences of these variants on neuromuscular function in vivo. Animals expressing variant ryanodine receptors exhibited increased sensitivity to halothane when both homozygous and heterozygous for the variants. This mirrors the situation in humans where malignant hyperthermia is inherited in an autosomal dominant pattern. Novel, subtle, locomotion defects were found in animals expressing variant ryanodine receptors even in the absence of halothane. In-depth analysis of crawling suggested that these variant channels release excessive calcium, resulting in increased muscle contraction. Exaggerated age-related degeneration of locomotion was observed in variant strains, which may be a result of excessive calcium release via variant ryanodine receptors throughout the lifespan resulting in cellular damage. Cholinergic pharmacological agents were used to characterise if the consequences of the variants were pre and/ or post-synaptic. A range of complex phenotypes were found, reflecting the complexity of regulatory inputs to the ryanodine receptor. The altered properties of variant ryanodine receptors and effects of long-term calcium mishandling found here are anticipated to have consequences for human carriers, which may be in the nerve cells. Assessment of these phenotypes in a whole organism was important to fully appreciate the significant effects of variant ryanodine receptors.