Congenital myopathy results from misregulation of a muscle Ca²⁺channel by mutant Stac3

Abstract

Skeletal muscle contractions are initiated by an increase in Ca 2+ released during excitation-contraction (EC) coupling, and defects in EC coupling are associated with human myopathies. EC coupling requires communication between voltage-sensing dihydropyridine receptors (DHPRs) in transverse tubule membrane and Ca 2+ release channel ryanodine receptor 1 (RyR1) in the sarcoplasmic reticulum (SR). Stac3 protein (SH3 and cysteine-rich domain 3) is an essential component of the EC coupling apparatus and a mutation in human STAC3 causes the debilitating Native American myopathy (NAM), but the nature of how Stac3 acts on the DHPR and/or RyR1 is unknown. Using electron microscopy, electrophysiology, and dynamic imaging of zebrafish muscle fibers, we find significantly reduced DHPR levels, functionality, and stability in stac3 mutants. Furthermore, stac3NAM myofibers exhibited increased caffeine-induced Ca 2+ release across a wide range of concentrations in the absence of altered caffeine sensitivity as well as increased Ca 2+ in internal stores, which is consistent with increased SR luminal Ca 2+ . These findings define critical roles for Stac3 in EC coupling and human disease.zebrafish | skeletal muscle | excitation-contraction coupling | dihydropyridine receptor | Native American myopathy

STAC3variants cause a congenital myopathy with distinctive dysmorphic features and malignant hyperthermia susceptibility

“…The functional data strongly support the notion that the STAC3 variants lead to impaired ECC. Indeed, application of KCl caused a small release of sarcoplasmic reticulum Ca 2+ , a result consistent with previous observations in animal models (Cong, Doering, Grange, & Jiang, ; Linsley, Hsu, Groom, et al., ; Nelson et al., ; Polster et al., ). Our results, however, are not fully supportive of previously published data on Ca 2+ release mediated by direct RyR1 activators.…”

“…As STAC3 has been shown to be a part of the DHPR complex and to stably interact with Ca V 1.1 (Campiglio & Flucher, ; Horstick et al., ; Linsley, Hsu, Groom, et al., ), we hypothesized that the defective ECC in STAC3 patients was a result of impaired binding to Ca V 1.1. Nevertheless, co‐immunoprecipitation of STAC3 with Ca V 1.1 in patient and control muscle samples pulled down STAC3 to equal extent and demonstrated that the protein interaction between STAC3 and Ca V 1.1 was not significantly affected by the STAC3 variants.…”

STAC Proteins Associate to the IQ Domain of CaV1.2 and Inhibit Calcium-Dependent Inactivation

“…Expression of STAC3 is restricted to skeletal muscle, where STAC3 associates with the voltage-gated calcium channel Ca V 1.1 and is involved in mediating voltage-induced calcium release from the sarcoplasmic reticulum (3,4). In nonmuscle cells, STAC3 was shown to facilitate functional membrane expression of Ca V 1.1 and alter the current properties of Ca V 1.2 (5), suggesting a role of STAC proteins as an L-type calcium channel (Ca V 1) regulator.…”

“…We previously demonstrated that the stable association of STAC3 to the Ca V 1 channel complex in the triads of skeletal muscle relies on the C1 domain (7). In contrast, the NAM mutation, which impairs EC coupling and is located in the SH3-1 domain of STAC3 (2)(3)(4), did not abolish the interaction with the calcium channel (2,4,7). We therefore proposed that STAC3 establishes multiple interactions: one through the C1 domain, responsible for the stable anchoring of STAC3 to the channel, and another one through the SH3-1 domain, involved in EC coupling (7).…”

How the expression of green fluorescent protein and human cardiac actin in the heart influences cardiac function and aerobic performance in zebrafish Danio rerio

“…This species is amenable to genetic manipulation and there is significant conservation in gene sequence and protein function between humans and D. rerio . As a result, human mutant genes are being incorporated into the genomic DNA of D. rerio to examine the molecular basis of disease dysfunction (Ha et al ., ; Buhrdel et al ., ; Bragato et al ., ; Linsley et al ., ). To rapidly screen for the expression of non‐native proteins in the transparent D. rerio embryo, the complementary (c)DNA for green fluorescent protein (GFP) driven by an expression promoter is co‐injected into cells (Long et al ., ; Brion et al ., ).…”