Differently from S165F, Y141H Mutation of Junctophilin-2 affects Calcium Signaling in Skeletal Muscle

Abstract

Junctophilins (JPs) play an important role in the formation of junctional membrane complexes in muscle cells by physically linking the transverse-tubule and sarcoplasmic reticulum (SR) membranes. In humans with hypertrophic cardiomyopathy (HCM), mutations in JP2 are associated to altered Ca2+ signaling in cardiomyocytes. One of the HCM-related JP2 mutants, S165F also induces both hypertrophy and altered intracellular Ca2+ signaling in skeletal myotubes. Here, we tried to identify the dominant negative role of another HCM-related JP2 mutation, Y141H, in primary mouse skeletal myotubes in order to examine the effects of Y141H on skeletal muscle function. Consistent with S165F-expressing skeletal myotubes, over-expression of Y141H led to a significant increase in myotube diameter and resting cytosolic Ca2+ concentration. Immunoblot assays suggested that the increased resting cytosolic Ca2+ concentration is possibly due to the increased expression level of an extracellular Ca2+-entry channel, Orai1. Unlike S165F, single myotube Ca2+ imaging experiments with Y141H-expressing myotubes showed a reduction in the gain of excitation-contraction coupling without an alteration in both ryanodine receptor1-mediated Ca2+ release from the SR and the amount of SR Ca2+. Therefore, the hypertrophy in the Y141H-expressing skeletal myotubes would be differently progressed from that in the S165F-expressing skeletal myotubes.