Structural Basis for the Modulation of Ryanodine Receptors.

Historically, ryanodine receptors (RyRs) have presented unique challenges for high-resolution structural determination despite long-standing interest in their role in excitation-contraction coupling. Owing to their large size (nearly 2.2 MDa), high-resolution structures remained elusive until the advent of cryogenic electron microscopy (cryo-EM) techniques. In recent years, structures for both RyR1 and RyR2 have been solved at near-atomic resolution. Furthermore, recent reports have delved into their more complex structural associations with key modulators - proteins such as the dihydropyridine receptor (DHPR), FKBP12/12.6, and calmodulin (CaM), as well as ions and small molecules including Ca2+, ATP, caffeine, and PCB95. This review addresses the modulation of RyR1 and RyR2, in addition to the impact of such discoveries on intracellular Ca2+ dynamics and biophysical properties.

Comparison of literature mining tools for variant classification: Through the lens of 50 RYR1 variants.

PURPOSE: The American College of Medical Genetics and Genomics and the Association for Molecular Pathology have outlined a schema that allows for systematic classification of variant pathogenicity. Although gnomAD is generally accepted as a reliable source of population frequency data and ClinGen has provided guidance on the utility of specific bioinformatic predictors, there is no consensus source for identifying publications relevant to a variant. Multiple tools are available to aid in the identification of relevant variant literature, including manually curated databases and literature search engines. We set out to determine the utility of 4 literature mining tools used for ascertainment to inform the discussion of the use of these tools. METHODS: Four literature mining tools including the Human Gene Mutation Database, Mastermind, ClinVar, and LitVar 2.0 were used to identify relevant variant literature for 50 RYR1 variants. Sensitivity and precision were determined for each tool. RESULTS: Sensitivity among the 4 tools ranged from 0.332 to 0.687. Precision ranged from 0.389 to 0.906. No single tool retrieved all relevant publications. CONCLUSION: At the current time, the use of multiple tools is necessary to completely identify the literature relevant to curate a variant.

Structural changes and contractility in muscle assessed by magnetic resonance imaging in individuals with ryanodine receptor 1-related rhabdomyolysis or myalgia.

INTRODUCTION/AIMS: Ryanodine receptor 1 (RYR1)-related myopathies associated with variants in the RYR1 gene present with a wide range of symptoms and severity. Two of the milder phenotypes associated with dominant pathogenic variants in RYR1 are rhabdomyolysis and myalgia. Only a few studies have investigated the muscle function and structure of individuals with RYR1-related rhabdomyolysis/myalgia objectively, showing inconsistent results. This study aimed to describe structural changes and contractility of muscles in individuals with RYR1-related rhabdomyolysis/myalgia. METHODS: We investigated 15 individuals with dominant variants in the RYR1-gene and compared them with 15 age-, sex-, and body mass index (BMI)-matched controls using MRI, stationary isokinetic dynamometry, and comprehensive clinical evaluation. RESULTS: No significant differences were found between individuals with RYR1-related rhabdomyolysis/myalgia and healthy controls in peak torque, fat fraction, cross-sectional area, contractile cross-sectional area, or contractility (p > .05) in muscles of the lower back (MRI data only), thigh, or calf. On clinical examination, three individuals exhibited weakness in hip or back extension on the Medical Research Council (MRC) test and eight had muscle hypertrophy. Individuals with weakness were not hypertrophic. DISCUSSION: Most individuals with RYR1-related rhabdomyolysis/myalgia have close to normal strength, and normal fat fraction and contractility of muscles, and therefore constitute a mild phenotype of RYR1-related myopathies.

Unusual cause of muscle weakness, type II respiratory failure and pulmonary hypertension: a case report of ryanodine receptor type 1(RYR1)-related myopathy.

BACKGROUND: Patients with congenital myopathies may experience respiratory involvement, resulting in restrictive ventilatory dysfunction and respiratory failure. Pulmonary hypertension (PH) associated with this condition has never been reported in congenital ryanodine receptor type 1(RYR1)-related myopathy. CASE PRESENTATION: A 47-year-old woman was admitted with progressively exacerbated chest tightness and difficulty in neck flexion. She was born prematurely at week 28. Her bilateral lower extremities were edematous and muscle strength was grade IV-. Arterial blood gas analysis revealed hypoventilation syndrome and type II respiratory failure, while lung function test showed restrictive ventilation dysfunction, which were both worse in the supine position. PH was confirmed by right heart catheterization (RHC), without evidence of left heart disease, congenital heart disease, or pulmonary artery obstruction. Polysomnography indicated nocturnal hypoventilation. The ultrasound revealed reduced mobility of bilateral diaphragm. The level of creatine kinase was mildly elevated. Magnetic resonance imaging showed myositis of bilateral thigh muscle. Muscle biopsy of the left biceps brachii suggested muscle malnutrition and congenital muscle disease. Gene testing revealed a missense mutation in the RYR1 gene (exon33 c.C4816T). Finally, she was diagnosed with RYR1-related myopathy and received long-term non-invasive ventilation (NIV) treatment. Her symptoms and cardiopulmonary function have been greatly improved after 10 months. CONCLUSIONS: We report a case of RYR1-related myopathy exhibiting hypoventilation syndrome, type II respiratory failure and PH associated with restrictive ventilator dysfunction. Pulmonologists should keep congenital myopathies in mind in the differential diagnosis of type II respiratory failure, especially in patients with short stature and muscle weakness.

Defective cerebellar ryanodine receptor type 1 and endoplasmic reticulum calcium 'leak' in tremor pathophysiology.

Essential Tremor (ET) is a prevalent neurological disease characterized by an 8-10 Hz action tremor. Molecular mechanisms of ET remain poorly understood. Clinical data suggest the importance of the cerebellum in disease pathophysiology, and pathological studies indicate Purkinje Cells (PCs) incur damage. Our recent cerebellar cortex and PC-specific transcriptome studies identified alterations in calcium (Ca2+) signaling pathways that included ryanodine receptor type 1 (RyR1) in ET. RyR1 is an intracellular Ca2+ release channel located on the Endoplasmic Reticulum (ER), and in cerebellum is predominantly expressed in PCs. Under stress conditions, RyR1 undergoes several post-translational modifications (protein kinase A [PKA] phosphorylation, oxidation, nitrosylation), coupled with depletion of the channel-stabilizing binding partner calstabin1, which collectively characterize a "leaky channel" biochemical signature. In this study, we found markedly increased PKA phosphorylation at the RyR1-S2844 site, increased RyR1 oxidation and nitrosylation, and calstabin1 depletion from the RyR1 complex in postmortem ET cerebellum. Decreased calstabin1-RyR1-binding affinity correlated with loss of PCs and climbing fiber-PC synapses in ET. This 'leaky' RyR1 signature was not seen in control or Parkinson's disease cerebellum. Microsomes from postmortem cerebellum demonstrated excessive ER Ca2+ leak in ET vs. controls, attenuated by channel stabilization. We further studied the role of RyR1 in tremor using a mouse model harboring a RyR1 point mutation that mimics constitutive site-specific PKA phosphorylation (RyR1-S2844D). RyR1-S2844D homozygous mice develop a 10 Hz action tremor and robust abnormal oscillatory activity in cerebellar physiological recordings. Intra-cerebellar microinfusion of RyR1 agonist or antagonist, respectively, increased or decreased tremor amplitude in RyR1-S2844D mice, supporting a direct role of cerebellar RyR1 leakiness for tremor generation. Treating RyR1-S2844D mice with a novel RyR1 channel-stabilizing compound, Rycal, effectively dampened cerebellar oscillatory activity, suppressed tremor, and normalized cerebellar RyR1-calstabin1 binding. These data collectively support that stress-associated ER Ca2+ leak via RyR1 may contribute to tremor pathophysiology.

The RyR1 P3528S Substitution Alters Mouse Skeletal Muscle Contractile Properties and RyR1 Ion Channel Gating.

The recessive Ryanodine Receptor Type 1 (RyR1) P3527S mutation causes mild muscle weakness in patients and increased resting cytoplasmic [Ca2+] in transformed lymphoblastoid cells. In the present study, we explored the cellular/molecular effects of this mutation in a mouse model of the mutation (RyR1 P3528S). The results were obtained from 73 wild type (WT/WT), 82 heterozygous (WT/MUT) and 66 homozygous (MUT/MUT) mice with different numbers of observations in individual data sets depending on the experimental protocol. The results showed that WT/MUT and MUT/MUT mouse strength was less than that of WT/WT mice, but there was no difference between genotypes in appearance, weight, mobility or longevity. The force frequency response of extensor digitorum longus (EDL) and soleus (SOL) muscles from WT/MUT and MUT/MUT mice was shifter to higher frequencies. The specific force of EDL muscles was reduced and Ca2+ activation of skinned fibres shifted to a lower [Ca2+], with an increase in type I fibres in EDL muscles and in mixed type I/II fibres in SOL muscles. The relative activity of RyR1 channels exposed to 1 µM cytoplasmic Ca2+ was greater in WT/MUT and MUT/MUT mice than in WT/WT mice. We suggest the altered RyR1 activity due to the P2328S substitution could increase resting [Ca2+] in muscle fibres, leading to changes in fibre type and contractile properties.

Genetic characterization of domestic pigs in the core zone of swine production of Argentina.

Argentina is a small player in the global pork market, contributing only 0.7% of the total production. With increasing global demand for meat, there is an opportunity for countries with an agricultural profile to grow their pork production. However, there is a need to understand the current state of the pork production sector in all aspects to inform decision-making. The aim of this study was to genetically characterize pig herds from different production strata in the primary region for pork production in the country. For this purpose, phylogenetic and genetic variability analyses were performed using the mitochondrial control region marker (n=95 pig samples). Moreover, genotyping of ryr1 and PRKAG3 genes (n=108 pig samples) were performed to evaluate the frequency of deleterious alleles for meat quality traits in the region. The results showed high levels of genetic variability in the pig herds (Hd= 0.840 ± 0.031 and π= 0.010 ± 0.001), with a creole sow and Iberian lineage standing out in the phylogeny. The genotyping of the ryr1 marker revealed the presence of the deleterious t allele in all analyzed strata. However, the RN-allele of the PRKAG3 gene was detected only in the two lower strata. This study represents the first analysis of the phylogenetic relationships among domestic pigs from Argentina and provides an initial assessment of genetic variability in the region. Additionally, the results present, for the first time, the frequency of deleterious alleles for pig production in the productive core area, demonstrating their prevalence.

Congenital myopathies in adults: A diagnosis not to overlook.

BACKGROUND: Congenital myopathies (CM) were traditionally classified according to the muscle histopathological features, but in recent years, molecular diagnosis has become increasingly important. CM may present a wide phenotype variability, and while adult-onset CM have been increasingly recognized, substantial diagnostic delays are still reported. OBJECTIVES: To describe a cohort of adult CM patients, including clinical, genetic, and histopathological features, and further characterize the subgroup of adult-diagnosed patients. MATERIALS AND METHODS: We performed a retrospective observational cohort study to characterize the CM patients evaluated in our adult Neuromuscular outpatient clinic, including the subgroup of adult-diagnosed patients. RESULTS: We identified 19 CM patients with compatible molecular and/or histological diagnoses, of which 14 were diagnosed in adulthood. Eleven adult-diagnosed patients had symptoms since childhood and 9 had a family history of myopathy. The median age of symptoms' onset was 4 years old and the median age at diagnosis was 37 years old. The most common causative gene was RYR1, followed by TTN and MYH7. Three patients had non-specific features on muscle biopsy, all diagnosed during adulthood. CONCLUSIONS: In our cohort, the majority of CM were diagnosed in adulthood, despite most having pediatric-onset symptoms and positive family history. The diagnostic delay may be associated with mild presentation, slow course, atypical muscle histology, and lack of awareness of adult-onset CM. Studies with larger populations are needed.

The reduced contraction capacity of palatopharyngeal muscle in OSAHS is related to the decreased intra-cellular [Ca2+] mediated by low RyR1 and DHPRα1s expression.

PURPOSE: To aim of the study was to explore the possible mechanisms for the decreased contraction capacity of the palatopharyngeal muscle in cases with obstructive sleep apnea hypopnea syndrome (OSAHS). METHODS: Palatopharyngeal muscle specimens from patients with OSAHS were taken as the case group. Palatopharyngeal muscle tissue by surgical removal of oropharyngeal malignant tumors was used as a control cohort. The palatopharyngeal muscle contraction capacity was measured by assessing diaphragm peak-twitching force / cross-sectional area (Pt/CSA), fatigue index (FI) twitch tension, and force per cross-sectional area (Force/CSA). Myofibril and sarcoplasmic reticulum (SR) ultra-structures were observed by electron microscopy. The intra-cellular calcium concentration was measured by fluorescence spectrophotometry. DHPRα1s and RyR1 expression profiles were probed through RT-qPCR and Western blot, and the colocalization of them was determined by immunofluorescence. RESULTS: In comparison with the control cohort, the OSAHS cohort demonstrated decreased Pt/CSA (P < 0.01), FI twitch tension (P < 0.01), together with contraction capacity (P < 0.01). This cohort also had lower intra-cellular [Ca2+] of palatopharyngeal muscle cells with abnormal ultrastructure of sarcoplasmic reticulum (SR) (P < 0.01). In addition, transcriptomic (P < 0.01) and proteomic expression (P < 0.01) for RyR1 and DHPRα1s were markedly reduced within OSAHS cohort, although the degree of colocalization of them was not altered. CONCLUSION: RyR1 and DHPRα1s downregulation may disrupt intra-cellular [Ca2+] homeostasis and subsequently decrease the palatopharyngeal muscle contraction capacity in patients with OSAHS, thus providing a novel insight into the pathogenesis of OSAHS.

Clinical, genetic, and histological features of centronuclear myopathy in the Netherlands.

Centronuclear myopathy (CNM) is a genetically heterogeneous congenital myopathy characterized by muscle weakness, atrophy, and variable degrees of cardiorespiratory involvement. The clinical severity is largely explained by genotype (DNM2, MTM1, RYR1, BIN1, TTN, and other rarer genetic backgrounds), specific mutation(s), and age of the patient. The histopathological hallmark of CNM is the presence of internal centralized nuclei on muscle biopsy. Information on the phenotypical spectrum, subtype prevalence, and phenotype-genotype correlations is limited. To characterize CNM more comprehensively, we retrospectively assessed a national cohort of 48 CNM patients (mean age = 32 ± 24 years, range 0-80, 54% males) from the Netherlands clinically, histologically, and genetically. All information was extracted from entries in the patient's medical records, between 2000 and 2020. Frequent clinical features in addition to muscle weakness and hypotonia were fatigue and exercise intolerance in more mildly affected cases. Genetic analysis showed variants in four genes (18 DNM2, 14 MTM1, 9 RYR1, and 7 BIN1), including 16 novel variants. In addition to central nuclei, histologic examination revealed a large variability of myopathic features in the different genotypes. The identification and characterization of these patients contribute to trial readiness.

Design, synthesis, and biological activity of novel semicarbazones as potent Ryanodine receptor1 inhibitors of Alzheimer's disease.

Ryanodine receptors (RyRs) are important ligand-gated Ca2+ channels; their excessive activation leads to Ca2+ leakage in the sarcoplasmic reticulum that may cause neurological diseases. In this study, three series of novel potent RyR1 inhibitors based on dantrolene and bearing semicarbazone and imidazolyl moieties were designed and synthesized, and their biological activity was evaluated. Using a single-cell calcium imaging method, the calcium overload inhibitory activities of 26 target compounds were tested in the R614C cell line, using dantrolene as a positive control. The preliminary investigation showed that compound 12a suppressed Ca2+ release as evidenced by store overload-induced Ca2+release (SOICR) (31.5 ± 0.1%, 77.2 ± 0.1%, 93.7 ± 0.2%) at 0.1 µM, 3 µM and 10 µM, respectively. Docking simulation results showed that compound 12a could bind at the active site of the RyR1 protein. The Morris water-maze test showed that compound 12a significantly improved the cognitive behavior of AD-model mice. Further studies on the structural optimization of this series of derivatives are currently underway in our laboratory.

Luminal Ca2+ regulation of RyR1 Ca2+ channel leak activation and inactivation in sarcoplasmic reticulum membrane vesicles.

In this study, we tested the hypothesis that the RyR1 Ca2+ channel closure is sensitive to outward trans-SR membrane Ca2+ gradients established by SERCA1 pumping. To perform these studies, we employed stopped-flow rapid-kinetic fluorescence methods to measure and assess how variation in trans-SR membrane Ca2+ distribution affects evolution of RyR1 Ca2+ leaks in RyR1/ CASQ1/SERCA1-rich membrane vesicles. Our studies showed that rapid filling of a Mag-Fura-2-sensitive free Ca2+ pool during SERCA1-mediated Ca2+ sequestration appears to be a crucial condition allowing RyR1 Ca2+ channels to close once reloading of luminal Ca2+ stores is complete. Disruption in the filling of this pool caused activation of Ruthenium Red inhibitable RyR1 Ca2+ leaks, suggesting that SERCA1 pump formation of outward Ca2+ gradients is an important aspect of Ca2+ flux control channel opening and closing. In addition, our observed ryanodine-induced shift in luminal Ca2+ from free to a CTC-Ca+-sensitive, CASQ1-associated bound compartment underscores the complex organization and regulation of SR luminal Ca2+. Our study provides strong evidence that RyR1 functional states directly and indirectly influence the compartmentation of luminal Ca2+. This, in turn, is influenced by the activity of SERCA1 pumps to fill luminal pools while synchronously reducing Ca2+ levels on the cytosolic face of RyR1 channels.

Whole-exome sequencing in patients with protein aggregate myopathies reveals causative mutations associated with novel atypical phenotypes.

BACKGROUND: Myofibrillar myopathies (MFM) are a subgroup of protein aggregate myopathies (PAM) characterized by a common histological picture of myofibrillar dissolution, Z-disk disintegration, and accumulation of degradation products into inclusions. Mutations in genes encoding components of the Z-disk or Z-disk-associated proteins occur in some patients whereas in most of the cases, the causative gene defect is still unknown. We aimed to search for pathogenic mutations in genes not previously associated with MFM phenotype. METHODS: We performed whole-exome sequencing in four patients from three unrelated families who were diagnosed with PAM without aberrations in causative genes for MFM. RESULTS: In the first patient and her affected daughter, we identified a heterozygous p.(Arg89Cys) missense mutation in LMNA gene which has not been linked with PAM pathology before. In the second patient, a heterozygous p.(Asn4807Phe) mutation in RYR1 not previously described in PAM represents a novel, candidate gene with a possible causative role in the disease. Finally, in the third patient and his symptomatic daughter, we found a previously reported heterozygous p.(Cys30071Arg) mutation in TTN gene that was clinically associated with cardiac involvement. CONCLUSIONS: Our study identifies a new genetic background in PAM pathology and expands the clinical phenotype of known pathogenic mutations.

Next-generation sequencing and bioinformatics to identify genetic causes of malignant hyperthermia.

BACKGROUND/PURPOSE: Malignant hyperthermia (MH) is a life-threatening pharmacogenetic disease with only two known causative genes, RYR1 and CACNA1S. Both are huge genes containing numerous exons, and they reportedly only account for 50-70% of known MH patients. Next-generation sequencing (NGS) technology and bioinformatics could help delineate the genetic diagnosis of MH and several MH-like clinical presentations. METHODS: We established a capture-based targeted NGS sequencing framework to examine the whole genomic regions of RYR1, CACNA1S and the 16.6 Kb mitochondrial genome, as well as 12 other genes related to excitation-contraction coupling and/or skeletal muscle calcium homeostasis. We applied bioinformatics analyses to the variants identified in this study and also to the 48 documented RYR1 pathogenic variants. RESULTS: The causative variants were identified in seven of the eight (87.5%) MH families, but in none of the 10 individuals classified as either normal controls (N = 2) or patients displaying MH-like clinical features later found to be caused by other etiologies (N = 8). We showed that RYR1 c.1565A>G (p.Tyr522Cys)(rs118192162) could be a genetic hot spot in the Taiwanese population. Bioinformatics analyses demonstrated low population frequencies and predicted damaging effects from all known pathogenic RYR1 variants. We estimated that more than one in 1149 individuals worldwide carry MH pathogenic variants at RYR1. CONCLUSION: NGS and bioinformatics are sensitive and specific tools to examine RYR1 and CACNA1S for the genetic diagnosis of MH. Pathogenic variants in RYR1 can be found in the majority of MH patients in Taiwan.

Malignant hyperthermia in a 16-day-old infant with congenital diaphragmatic hernia: a case report.

Malignant hyperthermia (MH) is a severe hypermetabolic disorder associated with dysregulation of calcium homeostasis and is triggered by inhalational anesthetics (isoflurane, sevoflurane, desflurane) and a depolarizing muscle relaxant (succinylcholine). We report the case of a 16-day-old infant undergoing laparoscopic surgery. The patient developed hyperthermia and hypercarbia with muscle rigidity. After the diagnosis of MH, dantrolene was administered with sufficient hydration. The patient was transferred to the pediatric intensive care unit for monitoring and treatment of acute renal injury due to myoglobinuria. Subsequently, two variants of the ryanodine receptor 1 (RYR1) gene were identified in the patient as the mutation point at c.1589G > A p.Arg530His and c.1841G > T p.Arg614Leu, which are known to be associated with MH. This was a rare case of MH in a 16-day-old infant that might be related to two RYR1 mutations inherited from the parents.

Intracellular calcium leak as a therapeutic target for RYR1-related myopathies.

RYR1 encodes the type 1 ryanodine receptor, an intracellular calcium release channel (RyR1) on the skeletal muscle sarcoplasmic reticulum (SR). Pathogenic RYR1 variations can destabilize RyR1 leading to calcium leak causing oxidative overload and myopathy. However, the effect of RyR1 leak has not been established in individuals with RYR1-related myopathies (RYR1-RM), a broad spectrum of rare neuromuscular disorders. We sought to determine whether RYR1-RM affected individuals exhibit pathologic, leaky RyR1 and whether variant location in the channel structure can predict pathogenicity. Skeletal muscle biopsies were obtained from 17 individuals with RYR1-RM. Mutant RyR1 from these individuals exhibited pathologic SR calcium leak and increased activity of calcium-activated proteases. The increased calcium leak and protease activity were normalized by ex-vivo treatment with S107, a RyR stabilizing Rycal molecule. Using the cryo-EM structure of RyR1 and a new dataset of > 2200 suspected RYR1-RM affected individuals we developed a method for assigning pathogenicity probabilities to RYR1 variants based on 3D co-localization of known pathogenic variants. This study provides the rationale for a clinical trial testing Rycals in RYR1-RM affected individuals and introduces a predictive tool for investigating the pathogenicity of RYR1 variants of uncertain significance.

A multi-dimensional analysis of genotype-phenotype discordance in malignant hyperthermia susceptibility.

BACKGROUND: Malignant hyperthermia (MH) susceptibility is an inherited condition, diagnosed either by the presence of a pathogenic genetic variant or by in vitro caffeine-halothane contracture testing. Through a multi-dimensional approach, we describe the implications of discordance between genetic and in vitro test results in a patient with a family history of possible MH. METHODS: The patient, whose brother had a possible MH reaction, underwent the caffeine-halothane contracture test (CHCT) according to the North American MH Group protocol. Screening of the complete RYR1 and CACNA1S transcripts was done using Sanger sequencing. Additional functional analyses included skinned myofibre calcium-induced calcium release sensitivity, calcium signalling assays in cultured myotubes, and in silico evaluation of the effect of any genetic variants on their chemical environment. RESULTS: The patient's CHCT result was negative but she carried an RYR1 variant c.1209C>G, p.Ile403Met, that is listed as pathogenic by the European Malignant Hyperthermia Group. Functional tests indicated a gain-of-function effect with a weak impact, and the variant was predicted to affect the folding stability of the 3D structure of the RyR1 protein. Based on American College of Medical Genetics and Genomics/Association of Molecular Pathology guidelines, this variant would be characterised as a variant of uncertain significance. CONCLUSIONS: Available data do not confirm or exclude an increased risk of MH for this patient. Further research is needed to correlate RyR1 functional assays, including the current gold standard testing for MH susceptibility, with clinical phenotypes. The pathogenicity of genetic variants associated with MH susceptibility should be re-evaluated.

A novel homozygous variant of RYR1 p.Ala3072Asp in a neonate with dusty core disease: A new entity with clinicopathological implications.

Dusty core disease (DuCD) is a recently described form of congenital myopathy with clinicopathological implications. The presence of "dusty core fibers" is the defining myopathological feature of DuCD. Most cases have a recessive inheritance and harbor RYR1 mutations. I hereby describe a novel homozygous variant of RYR1 p.Ala3072Asp clinicopathologically compatible with DuCD. To the best of my knowledge, this is the first documented case of DuCD from India.

De novo reconstitution reveals the proteins required for skeletal muscle voltage-induced Ca2+ release.

Skeletal muscle contraction is triggered by Ca2+ release from the sarcoplasmic reticulum (SR) in response to plasma membrane (PM) excitation. In vertebrates, this depends on activation of the RyR1 Ca2+ pore in the SR, under control of conformational changes of CaV1.1, located ∼12 nm away in the PM. Over the last ∼30 y, gene knockouts have revealed that CaV1.1/RyR1 coupling requires additional proteins, but leave open the possibility that currently untested proteins are also necessary. Here, we demonstrate the reconstitution of conformational coupling in tsA201 cells by expression of CaV1.1, ß1a, Stac3, RyR1, and junctophilin2. As in muscle, depolarization evokes Ca2+ transients independent of external Ca2+ entry and having amplitude with a saturating dependence on voltage. Moreover, freeze-fracture electron microscopy indicates that the five identified proteins are sufficient to establish physical links between CaV1.1 and RyR1. Thus, these proteins constitute the key elements essential for excitation-contraction coupling in skeletal muscle.

iNOS is not responsible for RyR1 S-nitrosylation in mdx mice with truncated dystrophin.

BACKGROUND: Previous research indicated that nitric oxide synthase (NOS) is the key molecule for S-nitrosylation of ryanodine receptor 1 (RyR1) in DMD model mice (mdx mice) and that both neuronal NOS (nNOS) and inducible NOS (iNOS) might contribute to the reaction because nNOS is mislocalized in the cytoplasm and iNOS expression is higher in mdx mice. We investigated the effect of iNOS on RyR1 S-nitrosylation in mdx mice and whether transgenic expression of truncated dystrophin reduced iNOS expression in mdx mice or not. METHODS: Three- to 4-month-old C57BL/6 J, mdx, and transgenic mdx mice expressing exon 45-55-deleted human dystrophin (Tg/mdx mice) were used. We also generated two double mutant mice, mdx iNOS KO and Tg/mdx iNOS KO to reveal the iNOS contribution to RyR1 S-nitrosylation. nNOS and iNOS expression levels in skeletal muscle of these mice were assessed by immunohistochemistry (IHC), qRT-PCR, and Western blotting. Total NOS activity was measured by a citrulline assay. A biotin-switch method was used for detection of RyR1 S-nitrosylation. Statistical differences were assessed by one-way ANOVA with Tukey-Kramer post-hoc analysis. RESULTS: mdx and mdx iNOS KO mice showed the same level of RyR1 S-nitrosylation. Total NOS activity was not changed in mdx iNOS KO mice compared with mdx mice. iNOS expression was undetectable in Tg/mdx mice expressing exon 45-55-deleted human dystrophin, but the level of RyR1 S-nitrosylation was the same in mdx and Tg/mdx mice. CONCLUSION: Similar levels of RyR1 S-nitrosylation and total NOS activity in mdx and mdx iNOS KO demonstrated that the proportion of iNOS in total NOS activity was low, even in mdx mice. Exon 45-55-deleted dystrophin reduced the expression level of iNOS, but it did not correct the RyR1 S-nitrosylation. These results indicate that iNOS was not involved in RyR1 S-nitrosylation in mdx and Tg/mdx mice muscles.