RYR1-related myopathies (RYR1-RM) are a group of heterogeneous diseases that involve proximal skeletal muscle weakness, malignant hyperthermia susceptibility and respiratory involvement, and ophthalmoplegia in some severe cases. The ryanodine receptor 1 (RYR1) gene encodes the major calcium (Ca2+) release channel in skeletal muscle, RyR1. Pathogenic variants in the RYR1 gene lead to malformations in the RyR1 protein that disrupt normal Ca2+ flow from the sarcoplasmic reticulum (SR) into muscle cell cytosol, which can result in reduced or excessive Ca2+ leak into the cytosol. This can significantly impair excitation-contraction coupling, resulting in muscle weakness. This Ca2+ dysfunction also increases oxidative stress, especially in the mitochondria, that can lead to post-translational modifications of the RyR1 channel.
In this experiment, we are investigating a potential method of alleviating this oxidative stress by using nicotinamide riboside (NR) to supplement NAD+. NR has been shown to increase NAD+ and therefore improve oxidative metabolism in mammalian cells and mouse tissue. Control and RYR1-RM patient myotubes were treated with NR by testing for an acute duration or for a longer period of 24 or 48 hours. Mitochondrial respiration was measured using Seahorse Cell Mito Stress Test assays. NAD+ content will also be measured after dosing with NR. This project aims to determine the feasibility of using nicotinamide riboside to reduce oxidative stress and improve cell respiration in individuals affected with RYR1-RM. RYR1-RM does not have a cure, which creates a significant health and economic inequities for patients and their families. The exploration of this potential treatment will hopefully lead to the alleviation of some of this burden on patients.