Calsequestrin as a risk factor in Graves’ hyperthyroidism and Graves’ ophthalmopathy patients

Background: The pathogenesis of Graves’ ophthalmopathy (GO), Graves’ hyperthyroidism (GH) and the mechanisms for its link to thyroid autoimmunity are poorly understood. Our research focuses on the role of the skeletal muscle calcium binding protein calsequestrin (CASQ1) in thyroid. We measured the concentration of the CASQ1 protein correlating levels with parameters of the eye signs, CASQ1 antibody levels and CASQ1 gene polymorphism rs3838284. Methods: CASQ1 protein was measured by quantitative Western Blotting. The protein concentrations were expressed as pmol/mg total protein by reference to CASQ1 standards. Results: Western blot analysis showed the presence of two forms of CASQ1 in the thyroid. The mean concentration of CASQ1 protein was significantly reduced in patients with Graves’ disease, compared to thyroid from control subjects with multi-nodular goitre or thyroid cancer. Although in patients with GO it was lower than that, compared with patients with GH this difference was not significant. Reduced CASQ1 in Graves’ thyroid correlated with the homozygous genotype of the rs3838284 CASQ1 polymorphism. Conclusions: Decreased CASQ1 in the thyroid of patients with Graves’ disease compared to thyroid from control subjects is not explained but may reflect consumption of the protein during an autoimmune reaction against CASQ1 in the thyroid

Calsequestrin as a risk factor in Graves’ hyperthyroidism and Graves’ ophthalmopathy patients

Background: The pathogenesis of Graves’ ophthalmopathy (GO), Graves’ hyperthyroidism (GH) and the mechanisms for its link to thyroid autoimmunity are poorly understood. Our research focuses on the role of the skeletal muscle calcium binding protein calsequestrin (CASQ1) in thyroid. We measured the concentration of the CASQ1 protein correlating levels with parameters of the eye signs, CASQ1 antibody levels and CASQ1 gene polymorphism rs3838284. Methods: CASQ1 protein was measured by quantitative Western Blotting. The protein concentrations were expressed as pmol/mg total protein by reference to CASQ1 standards. Results: Western blot analysis showed the presence of two forms of CASQ1 in the thyroid. The mean concentration of CASQ1 protein was significantly reduced in patients with Graves’ disease, compared to thyroid from control subjects with multi-nodular goitre or thyroid cancer. Although in patients with GO it was lower than that, compared with patients with GH this difference was not significant. Reduced CASQ1 in Graves’ thyroid correlated with the homozygous genotype of the rs3838284 CASQ1 polymorphism. Conclusions: Decreased CASQ1 in the thyroid of patients with Graves’ disease compared to thyroid from control subjects is not explained but may reflect consumption of the protein during an autoimmune reaction against CASQ1 in the thyroid

Ablation of Calsequestrin-1, Ca2+ unbalance, and susceptibility to heat stroke

Introduction: Ca2+ levels in adult skeletal muscle fibers are mainly controlled by excitation-contraction (EC) coupling, a mechanism that translates action potentials in release of Ca2+ from the sarcoplasmic reticulum (SR) release channels, i.e. the ryanodine receptors type-1 (RyR1). Calsequestrin (Casq) is a protein that binds large amounts of Ca2+ in the lumen of the SR terminal cisternae, near sites of Ca2+ release. There is general agreement that Casq is not only important for the SR ability to store Ca2+, but also for modulating the opening probability of the RyR Ca2+ release channels. The initial studies: About 20 years ago we generated a mouse model lacking Casq1 (Casq1-null mice), the isoform predominantly expressed in adult fast twitch skeletal muscle. While the knockout was not lethal as expected, lack of Casq1 caused a striking remodeling of membranes of SR and of transverse tubules (TTs), and mitochondrial damage. Functionally, CASQ1-knockout resulted in reduced SR Ca2+ content, smaller Ca2+ transients, and severe SR depletion during repetitive stimulation. The myopathic phenotype of Casq1-null mice: After the initial studies, we discovered that Casq1-null mice were prone to sudden death when exposed to halogenated anaesthetics, heat and even strenuous exercise. These syndromes are similar to human malignant hyperthermia susceptibility (MHS) and environmental-exertional heat stroke (HS). We learned that mechanisms underlying these syndromes involved excessive SR Ca2+ leak and excessive production of oxidative species: indeed, mortality and mitochondrial damage were significantly prevented by administration of antioxidants and reduction of oxidative stress. Though, how Casq1-null mice could survive without the most important SR Ca2+ binding protein was a puzzling issue that was not solved. Unravelling the mystery: The mystery was finally solved in 2020, when we discovered that in Casq1-null mice the SR undergoes adaptations that result in constitutively active store-operated Ca2+ entry (SOCE). SOCE is a mechanism that allows skeletal fibers to use external Ca2+ when SR stores are depleted. The post-natal compensatory mechanism that allows Casq1-null mice to survive involves the assembly of new SR-TT junctions (named Ca2+ entry units) containing Stim1 and Orai1, the two proteins that mediate SOCE

Investigating myopathic causes of rhabdomyolysis

Rhabdomyolysis is an acute, and frequently severe, pathological event, characterized by rapid necrosis and destruction of striated muscle tissue. It is clinically characterized by muscle pain, weakness and emission of dark urine. The mechanisms that lead to rhabdomyolysis are various and different, and share common alterations such as dysfunction of the pumps Na + / K + and Ca2 + ATPase, and rupture of the sarcolemma, which in turn determine calcium homeostasis alterations, mitochondrial dysfunction, proteases activation, reduced availability of ATP and, overall, cell apoptosis and rhabdomyolysis. Several causes can initiate this vicious circle, both acquired and genetic. When facing an episode of rhabdomyolysis, the identification of the etiological cause can be extremely complex, long, and costly. Nevertheless, the correct identification of the underlying cause is of utmost importance for the correct information regarding prognosis (risk of recurrence) and for the family genetic counselling. Despite the application of extended diagnostic work up frequently it is not easy to distinguish if the rhabdomyolysis episode is due to a genetic disorder or whether it is the result of an abnormal effort, of an infectious episode or effect of a toxic. The main objective of this study is the evaluation of the diagnostic process of rhabdomyolysis, and to propose an updated, comprehensive, rational and cost effective protocol based on the latest information and techniques. We first studied the diagnostic process currently in use for rhabdomyolysis in a large retrospective study including 208 patients (aim 1). We characterized the clinical, molecular and radiological features of a new genetic cause of rhabdomyolysis, the CASQ1-related myopathy (aim 2). We determined the clinical spectrum of limb-girdle muscular dystrophy 2E (LGMD2E), investigating the risk of rhabdomyolysis of this disease (aim 3). We demostrated the role of EMG with provocative test (Long Exercise Test) as a sensitive and specific diagnostic test in the work up of rhabdomyolysis, especially in Glycogenosis type V (aim 4). We proposed a multi gene panel that should be studied by Next Generation Sequencing (NGS) in patients presenting rhabdomyolysis (aim 5) In conclusion, the results of this study suggest a new diagnostic algorithm for rhabdomyolysis. In this algorithm, the clinical features and few first-line tests (blood tests, EMG, acylcarnitines, grip test) exclude the most frequent causes or the treatable ones. The subsequent muscle biopsy will identify certain myopathies and guide toward the use of specific genetic panels for metabolic myopathies, muscular dystrophies or mitochondrial diseases that should be studied by NGS. The diagnostic algorithm that we propose will allow cost reduction and time optimization, and hopefully will increase the rate of etiological diagnosis of rhabdomyolysis, a serious event with major impact on patients' lives that, to date, remains poorly diagnosed

Round Table on Malignant Hyperthermia in Physically Active Populations: Meeting Proceedings

Context: Recent case reports on malignant hyperthermia (MH)-like syndrome in physically active populations indicate potential associations among MH, exertional heat stroke (EHS), and exertional rhabdomyolysis (ER). However, an expert consensus for clinicians working with these populations is lacking. Objective: To provide current expert consensus on the (1) definition of MH; (2) history, etiology, and pathophysiology of MH; (3) epidemiology of MH; (4) association of MH with EHS and ER; (5) identification of an MH-like syndrome; (6) recommendations for acute management of an MH-like syndrome; (7) special considerations for physically active populations; and (8) future directions for research. Setting: An interassociation task force was formed by experts in athletic training, exercise science, anesthesiology, and emergency medicine. The “Round Table on Malignant Hyperthermia in Physically Active Populations” was convened at the University of Connecticut, Storrs, September 17–18, 2015. Conclusions: Clinicians should consider an MH-like syndrome when a diagnosis of EHS or ER cannot be fully explained by clinical signs and symptoms presented by a patient or when recurrent episodes of EHS or ER (or both) are unexplained. Further research is required to elucidate the genetic and pathophysiological links among MH, EHS, and ER

Mechanistic models for muscle diseases and disorders originating in the sarcoplasmic reticulum

AbstractThis review focuses on muscle disorders and diseases caused by defects in the Ca2+ release channels of the sarcoplasmic reticulum, the ryanodine receptors, and in the luminal, low affinity, high capacity Ca2+-binding proteins, calsequestrins. It provides a time line over the past half century of the highlights of research on malignant hyperthermia (MH), central core disease (CCD) and catecholaminergic polymorphic ventricular tachycardia (CPVT), that resulted in the identification of the ryanodine receptor (RYR), calsequestrin (CASQ) and dihydropyridine receptor (CACNA1S) genes as sites of disease-causing mutations. This is followed by a description of approaches to functional analysis of the effects of disease-causing mutations on protein function, focusing on studies of how mutations affect spontaneous (store overload-induced) Ca2+-release from the sarcoplasmic reticulum, the underlying cause of MH and CPVT. Subsequent sections describe results obtained by analysis of knockin mouse lines carrying MH- and CCD-causing mutations, including a Casq1 knockout. The review concludes with the presentation of two mechanistic models. The first shows how dysregulation of Ca2+ homeostasis can lead to muscle diseases involving both RyR and Casq proteins. The second describes a theory of central core formation wherein non-uniformity of Ca2+ release, resulting in non-uniformity of muscle contraction, is presented as an intrinsic property of the specific tertiary structure of mutant heterotetrameric ryanodine receptors and as the underlying cause of core formation in skeletal muscle. This article is part of a Special Issue entitled: 11th European Symposium on Calcium

Mutations in proteins involved in E-C coupling and SOCE and congenital myopathies

In skeletal muscle, Ca2+ necessary for muscle contraction is stored and released from the sarcoplasmic reticulum (SR), a specialized form of endoplasmic reticulum through the mechanism known as excitation-contraction (E-C) coupling. Following activation of skeletal muscle contraction by the E-C coupling mechanism, replenishment of intracellular stores requires reuptake of cytosolic Ca2+ into the SR by the activity of SR Ca2+-ATPases, but also Ca2+ entry from the extracellular space, through a mechanism called store-operated calcium entry (SOCE). The fine orchestration of these processes requires several proteins, including Ca2+ channels, Ca2+ sensors, and Ca2+ buffers, as well as the active involvement of mitochondria. Mutations in genes coding for proteins participating in E-C coupling and SOCE are causative of several myopathies characterized by a wide spectrum of clinical phenotypes, a variety of histological features, and alterations in intracellular Ca2+ balance. This review summarizes current knowledge on these myopathies and discusses available knowledge on the pathogenic mechanisms of disease

Muscle energetics and ageing in the context of RYR1 variants.

In aged muscle, from humans and mice, the ryanodine receptor (RyR1) is leaky, leading to increased levels of resting Ca2+ in the myoplasm. This is also a feature of skeletal muscle disorders caused by variants in RyR1 such as malignant hyperthermia (MH), central core disease (CCD), exertional heat illness (EHI) and late-onset axial myopathy (LOAM). Elevated Ca2+ is damaging to mitochondria, leading to production of reactive oxygen and nitrogen species associated with MH susceptibility to inhalational anaesthetics. Mice with Ryr1 variants show premature muscle ageing and highlight the cycle of inefficient calcium handling and oxidative damage to mitochondria that impairs skeletal muscle energetics. Caenorhabditis elegans models of MH CCD EHI and LOAM variants, both homozygous and heterozygous forms, showed increased sensitivity to halothane. Altered caffeine sensitivity was evident in MH and CCD models, and at very high concentrations in EHI models. Strains with RyR1 variants exhibit age-related accelerated myosin disorganisation. Whole genome Affymetrix arrays revealed genes and pathways correlated with skeletal muscle ageing and MH. Of additional genes of interest investigated UNC13, CASQ1, ORAI1, MCU and MICU1 showed altered expression with age. Array data from blood has been used to identify a signature for MH susceptibility. There is loss of mitochondrial membrane integrity and alteration in mitochondrial number in MH. New apparatus, capable of quantifying heat produced during muscle contraction, has enabled calculation of skeletal muscle efficiency. Preliminary data indicates that there was loss of skeletal muscle efficiency in aged muscle from wild type mice. This work provides new information on the role of RYR1 variants in skeletal muscle ageing and the importance of calcium handling in muscle energetics

Cored in the act: The use of models to understand core myopathies

The core myopathies are a group of congenital myopathies with variable clinical expression - ranging from early-onset skeletal-muscle weakness to later-onset disease of variable severity - that are identified by characteristic 'core-like' lesions in myofibers and the presence of hypothonia and slowly or rather non-progressive muscle weakness. The genetic causes are diverse; central core disease is most often caused by mutations in ryanodine receptor 1 (RYR1), whereas multi-minicore disease is linked to pathogenic variants of several genes, including selenoprotein N (SELENON), RYR1 and titin (TTN). Understanding the mechanisms that drive core development and muscle weakness remains challenging due to the diversity of the excitation-contraction coupling (ECC) proteins involved and the differential effects of mutations across proteins. Because of this, the use of representative models expressing a mature ECC apparatus is crucial. Animal models have facilitated the identification of disease progression mechanisms for some mutations and have provided evidence to help explain genotype-phenotype correlations. However, many unanswered questions remain about the common and divergent pathological mechanisms that drive disease progression, and these mechanisms need to be understood in order to identify therapeutic targets. Several new transgenic animals have been described recently, expanding the spectrum of core myopathy models, including mice with patient-specific mutations. Furthermore, recent developments in 3D tissue engineering are expected to enable the study of core myopathy disease progression and the effects of potential therapeutic interventions in the context of human cells. In this Review, we summarize the current landscape of core myopathy models, and assess the hurdles and opportunities of future modeling strategies