Authors: Chang Seok Lee, Amy D. Hanna, Hui Wang, Adan Dagnino-Acosta, Aditya D. Joshi, Mark Knoblauch, Yan Xia, Dimitra K. Georgiou, Jianjun Xu, Cheng Long, Hisayuki Amano, Corey Reynolds, Keke Dong, John C. Martin, William R. Lagor, George G. Rodney, Ergun Sahin, Caroline Sewry & Susan L. Hamilton
Mutations in the RYR1 gene cause severe myopathies. Mice with an I4895T mutation in the type 1 ryanodine receptor/Ca2þ release channel (RyR1) display muscle weakness and atrophy, but the underlying mechanisms are unclear. Here we show that the I4895T mutation in RyR1 decreases the amplitude of the sarcoplasmic reticulum (SR) Ca2þ transient, resting cytosolic Ca2þ levels, muscle triadin content and calsequestrin (CSQ) localization to the junctional SR, and increases endoplasmic reticulum (ER) stress/unfolded protein response (UPR) and mitochondrial ROS production. Treatment of mice carrying the I4895T mutation with a chemical chaperone, sodium 4-phenylbutyrate (4PBA), reduces ER stress/UPR and improves muscle function, but does not restore SR Ca2þ transients in I4895T fibres to wild type levels, suggesting that decreased SR Ca2þ release is not the major driver of the myopathy. These findings suggest that 4PBA, an FDA-approved drug, has potential as a therapeutic intervention for RyR1 myopathies that are associated with ER stress.