Gain of function in the immune system caused by a ryanodine receptor 1 mutation

Modulation of Ryanodine Receptors Activity Alters the Course of Experimental Autoimmune Encephalomyelitis in Mice

Ryanodine receptors (RyRs), the intracellular Ca²⁺ release channels, are expressed in T lymphocytes and other types of immune cells. Modulation of RyRs has been shown to affect T cell functions in vitro and immune responses in vivo. The effects of modulation of RyRs on the development of autoimmune diseases have not been investigated. Here we studied how modulation of RyRs through administration of RyR inhibitor dantrolene or introducing a gain-of-function RYR1-p.R163C mutation affects clinical progression of experimental autoimmune encephalomyelitis (EAE) in mice, a T cell-mediated autoimmune neuroinflammatory disease. We found that daily intraperitoneal administration of 5 or 10 mg/kg dantrolene beginning at the time of EAE induction significantly reduced the severity of EAE clinical symptoms and dampened inflammation in the spinal cord. The protective effect of dantrolene on EAE was reversible. Dantrolene administration elicited dose-dependent skeletal muscle weakness: mice that received 10 mg/kg dose developed a waddling gait, while 5 mg/kg dantrolene dose administration produced a reduction in four-limb holding impulse values. Mice bearing the gain-of-function RYR1-p.R163C mutation developed the EAE clinical symptoms faster and more severely than wild-type mice. This study demonstrates that RyRs play a significant role in EAE pathogenesis and suggests that inhibition of RyRs with low doses of dantrolene may have a protective effect against autoimmunity and inflammation in humans.

A case of dermatomyositis in a patient with central core disease: unusual association with autoimmunity and genetic muscle disease

BACKGROUND

Dermatomyositis is an inflammatory muscle disease caused by immune-mediated muscle injury, and central core disease (CCD) is a congenital myopathy associated with disturbed intracellular calcium homeostasis and excitation-contraction coupling. To date, CCD has not been reported to have autoantibodies or coexist with inflammatory myopathy.

CASE PRESENTATION

Here, we described the case of a 25-year-old woman who had progressive proximal muscle weakness, myalgia, pruritic macular rash, skin ulcers, and calcinosis. Dermatomyositis was initially suspected based on the clinical symptoms accompanied by elevated muscle enzyme levels, electromyography abnormalities, and a positive antinuclear antibody test. However, the patient's muscle biopsy revealed the characteristic findings of both dermatomyositis and CCD, suggesting that dermatomyositis occurred in this patient with previously asymptomatic CCD. The patient did not have any pathogenic gene mutations associated with congenital myopathy, including RYR1 and SEPN1 in targeted next-generation sequencing. She received high-dose glucocorticoid therapy and azathioprine with a significant improvement in muscle strength.

CONCLUSIONS

We present a case of rare coexistence of dermatomyositis and CCD. Clinicians should be aware that patients with CCD may have inflammatory myopathy that responds well to immunosuppressive therapy.

The Cycling of Intracellular Calcium Released in Response to Fluid Shear Stress Is Critical for Migration-Associated Actin Reorganization in Eosinophils

The magnitude of eosinophil mobilization into respiratory tissues drives the severity of inflammation in several airway diseases. In classical models of leukocyte extravasation, surface integrins undergo conformational switches to high-affinity states via chemokine binding activation. Recently, we learned that eosinophil integrins possess mechanosensitive properties that detect fluid shear stress, which alone was sufficient to induce activation. This mechanical stimulus triggered intracellular calcium release and hallmark migration-associated cytoskeletal reorganization including flattening for increased cell–substratum contact area and pseudopodia formation. The present study utilized confocal fluorescence microscopy to investigate the effects of pharmacological inhibitors to calcium signaling and actin polymerization pathways on shear stress-induced migration in vitro. Morphological changes (cell elongation, membrane protrusions) succeeded the calcium flux in untreated eosinophils within 2 min, suggesting that calcium signaling was upstream of actin cytoskeleton rearrangement. The inhibition of ryanodine receptors and endomembrane Ca²⁺-ATPases corroborated this idea, indicated by a significant increase in time between the calcium spike and actin polymerization. The impact of the temporal link is evident as the capacity of treated eosinophils to move across fibronectin-coated surfaces was significantly hampered relative to untreated eosinophils. Furthermore, we determined that the nature of cellular motility in response to fluid shear stress was nondirectional.

T lymphocytes from malignant hyperthermia-susceptible mice display aberrations in intracellular calcium signaling and mitochondrial function

Gain-of-function RyR1-p.R163C mutation in ryanodine receptors type 1 (RyR1) deregulates Ca²⁺ signaling and mitochondrial function in skeletal muscle and causes malignant hyperthermia in humans and mice under triggering conditions. We investigated whether T lymphocytes from heterozygous RyR1-p.R163C knock-in mutant mice (HET T cells) display measurable aberrations in resting cytosolic Ca²⁺ concentration ([Ca²⁺]_i), Ca²⁺ release from the store, store-operated Ca²⁺ entry (SOCE), and mitochondrial inner membrane potential (ΔΨ_m) compared with T lymphocytes from wild-type mice (WT T cells). We explored whether these variables can be used to distinguish between T cells with normal and altered RyR1 genotype. HET and WT T cells were isolated from spleen and lymph nodes and activated in vitro using phytohemagglutinin P. [Ca²⁺]_i and ΔΨ_m dynamics were examined using Fura 2 and tetramethylrhodamine methyl ester fluorescent dyes, respectively. Activated HET T cells displayed elevated resting [Ca²⁺]_i, diminished responses to Ca²⁺ mobilization with thapsigargin, and decreased rate of [Ca²⁺]_i elevation in response to SOCE compared with WT T cells. Pretreatment of HET T cells with ryanodine or dantrolene sodium reduced disparities in the resting [Ca²⁺]_i and ability of thapsigargin to mobilize Ca²⁺ between HET and WT T cells. While SOCE elicited dissipation of the ΔΨ_m in WT T cells, it produced ΔΨ_m hyperpolarization in HET T cells. When used as the classification variable, the amplitude of thapsigargin-induced Ca²⁺ transient showed the best promise in predicting the presence of RyR1-p.R163C mutation. Other significant variables identified by machine learning analysis were the ratio of resting cytosolic Ca²⁺ level to the amplitude of thapsigargin-induced Ca²⁺ transient and an integral of changes in ΔΨ_m in response to SOCE. Our study demonstrated that gain-of-function mutation in RyR1 significantly affects Ca²⁺ signaling and mitochondrial fiction in T lymphocytes, which suggests that this mutation may cause altered immune responses in its carrier. Our data link the RyR1-p.R163C mutation, which causes inherited skeletal muscle diseases, to deregulation of Ca²⁺ signaling and mitochondrial function in immune T cells and establish proof-of-principle for in vitro T cell-based diagnostic assay for hereditary RyR1 hyperfunction.

The influence of sex, genotype, and dose on serum and hippocampal cytokine levels in juvenile mice developmentally exposed to a human-relevant mixture of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are pervasive environmental contaminants implicated as risk factors for neurodevelopmental disorders (NDDs). Immune dysregulation is another NDD risk factor, and developmental PCB exposures are associated with early life immune dysregulation. Studies of the immunomodulatory effects of PCBs have focused on the higher-chlorinated congeners found in legacy commercial mixtures. Comparatively little is known about the immune effects of contemporary, lower-chlorinated PCBs. This is a critical data gap given recent reports that lower-chlorinated congeners comprise >70% of the total PCB burden in serum of pregnant women enrolled in the MARBLES study who are at increased risk for having a child with an NDD. To examine the influence of PCBs, sex, and genotype on cytokine levels, mice were exposed throughout gestation and lactation to a PCB mixture in the maternal diet, which was based on the 12 most abundant PCBs in sera from MARBLES subjects. Using multiplex array, cytokines were quantified in the serum and hippocampus of weanling mice expressing either a human gain-of-function mutation in ryanodine receptor 1 (T4826I mice), a human CGG premutation repeat expansion in the fragile X mental retardation gene 1 (CGG mice), or both mutations (DM mice). Congenic wildtype (WT) mice were used as controls. There were dose-dependent effects of PCB exposure on cytokine concentrations in the serum but not hippocampus. Differential effects of genotype were observed in the serum and hippocampus. Hippocampal cytokines were consistently elevated in T4826I mice and also in WT animals for some cytokines compared to CGG and DM mice, while serum cytokines were usually elevated in the mutant genotypes compared to the WT group. Males had elevated levels of 19 cytokines in the serum and 4 in the hippocampus compared to females, but there were also interactions between sex and genotype for 7 hippocampal cytokines. Only the chemokine CCL5 in the serum showed an interaction between PCB dose, genotype, and sex. Collectively, these findings indicate differential influences of PCB exposure and genotype on cytokine levels in serum and hippocampal tissue of weanling mice. These results suggest that developmental PCB exposure has chronic effects on baseline serum, but not hippocampal, cytokine levels in juvenile mice.

Genomic Mapping Identifies Mutations in RYR2 and AHNAK as Associated with Favorable Outcome in Basal-Like Breast Tumors Expressing PD1/PD-L1

Treatment with anti-PD-L1 antibodies has shown efficacy in basal-like breast cancer. In this context, identification of pre-activated immune tumors is a main goal. Here we explore mutations in PD1 and PD-L1 high-expressing tumors to identify genomic correlates associated with outcome. To do so, RNA-seq and mutation data from 971 breast cancer patients from the TCGA dataset were used to identify most prevalent mutations in patients with high levels of PD1 and PD-L1. Transcriptomic signatures associated with the selected mutations were identified and analyzed in terms of outcome and immune cell infiltration. We identified co-occurrent mutations in RYR2 and AHNAK in 8% and 5% of basal-like tumors respectively, which conferred good prognosis in patients with high expression of PD1 and PD-L1 genes. The transcriptomic signature associated with these mutations, composed of CXCL9, GBP5, C1QA, IL2RG, CSF2RB, IDO1 and LAG3 genes, also conferred good prognosis and correlated with immune infiltrations within the tumors. The joint signature classified patients with favorable relapse-free survival (HR: 0.28; CI: 0.2–0.38; p = 1.7 × 10⁻¹⁶) and overall survival (HR: 0.18; CI: 0.09–0.34; p = 6.8 × 10⁻⁹), showing a stronger prediction capacity than previous reported signatures. In conclusion, we describe two novel mutations and their transcriptomic signature, both associated with a favorable outcome and immune infiltrates in PD1 and PD-L1 high-expressing basal-like tumors.

Preclinical model systems of ryanodine receptor 1-related myopathies and malignant hyperthermia: a comprehensive scoping review of works published 1990-2019

BACKGROUND

Pathogenic variations in the gene encoding the skeletal muscle ryanodine receptor (RyR1) are associated with malignant hyperthermia (MH) susceptibility, a life-threatening hypermetabolic condition and RYR1-related myopathies (RYR1-RM), a spectrum of rare neuromuscular disorders. In RYR1-RM, intracellular calcium dysregulation, post-translational modifications, and decreased protein expression lead to a heterogenous clinical presentation including proximal muscle weakness, contractures, scoliosis, respiratory insufficiency, and ophthalmoplegia. Preclinical model systems of RYR1-RM and MH have been developed to better understand underlying pathomechanisms and test potential therapeutics.

METHODS

We conducted a comprehensive scoping review of scientific literature pertaining to RYR1-RM and MH preclinical model systems in accordance with the PRISMA Scoping Reviews Checklist and the framework proposed by Arksey and O'Malley. Two major electronic databases (PubMed and EMBASE) were searched without language restriction for articles and abstracts published between January 1, 1990 and July 3, 2019.

RESULTS

Our search yielded 5049 publications from which 262 were included in this review. A majority of variants tested in RYR1 preclinical models were localized to established MH/central core disease (MH/CCD) hot spots. A total of 250 unique RYR1 variations were reported in human/rodent/porcine models with 95% being missense substitutions. The most frequently reported RYR1 variant was R614C/R615C (human/porcine total n = 39), followed by Y523S/Y524S (rabbit/mouse total n = 30), I4898T/I4897T/I4895T (human/rabbit/mouse total n = 20), and R163C/R165C (human/mouse total n = 18). The dyspedic mouse was utilized by 47% of publications in the rodent category and its RyR1-null (1B5) myotubes were transfected in 23% of publications in the cellular model category. In studies of transfected HEK-293 cells, 57% of RYR1 variations affected the RyR1 channel and activation core domain. A total of 15 RYR1 mutant mouse strains were identified of which ten were heterozygous, three were compound heterozygous, and a further two were knockout. Porcine, avian, zebrafish, C. elegans, canine, equine, and drosophila model systems were also reported.

CONCLUSIONS

Over the past 30 years, there were 262 publications on MH and RYR1-RM preclinical model systems featuring more than 200 unique RYR1 variations tested in a broad range of species. Findings from these studies have set the foundation for therapeutic development for MH and RYR1-RM.

Comparative Proteomic Analysis of Murine Cutaneous Lesions Induced by Leishmania amazonensis or Leishmania major

Cutaneous leishmaniasisis is the most common clinical form of leishmaniasis and one of the most relevant neglected diseases. It is known that the progress of the disease is species specific and the host's immune response plays an important role in its outcome. However, the pathways that lead to parasite clearance or survival remain unknown. In this work, skin tissue from mice experimentally infected with L. amazonensis, one of the causative agents of cutaneous leishmaniasis in the Amazon region, L. major, another causative agent of cutaneous leishmaniasis in Africa, the Middle East, China, and India, or lipopolysaccharides from Escherichia coli as an inflammation model were investigated using label-free proteomics to unveil Leishmania-specific protein alterations. Proteomics is a powerful tool to investigate host-pathogen relationships to address biological questions. In this work, proteins from mice skin biopsies were identified and quantified using nano-LC coupled with tandem mass spectrometry analyses. Integrated Proteomics Pipeline was used for peptide/protein identification and quantification. Western blot was used for validation of protein quantification by mass spectrometry, and protein pathways were predicted using Ingenuity Pathway Analysis. In this proteomics study, several proteins were pointed out as hypothetical targets to guide future studies on Leishmania-specific modulation of proteins in the host. We identified hundreds of exclusively modulated proteins after Leishmania spp. infection and 17 proteins that were differentially modulated in the host after L. amazonensis or L. major infection.

An RYR1 mutation associated with malignant hyperthermia is also associated with bleeding abnormalities

Malignant hyperthermia is a potentially fatal hypermetabolic disorder triggered by halogenated anesthetics and the myorelaxant succinylcholine in genetically predisposed individuals. About 50% of susceptible individuals carry dominant, gain-of-function mutations in RYR1 [which encodes ryanodine receptor type 1 (RyR1)], though they have normal muscle function and no overt clinical symptoms. RyR1 is predominantly found in skeletal muscle but also at lower amounts in immune and smooth muscle cells, suggesting that RYR1 mutations may have a wider range of effects than previously suspected. Mild bleeding abnormalities have been described in patients with malignant hyperthermia carrying gain-of-function RYR1 mutations. We sought to determine the frequency and molecular basis for this symptom. We found that some patients with specific RYR1 mutations had abnormally high bleeding scores, whereas their healthy relatives did not. Knock-in mice with the malignant hyperthermia susceptibility RYR1 mutation Y522S (MHS RYR1Y522S) had longer bleeding times than their wild-type littermates. Primary vascular smooth muscle cells from RYR1Y522S knock-in mice exhibited a higher frequency of subplasmalemmal Ca(2+) sparks, leading to a more negative resting membrane potential. The bleeding defect of RYR1Y522S mice and of one patient was reversed by treatment with the RYR1 antagonist dantrolene, and Ca(2+) sparks in primary vascular smooth muscle cells from the MHS RYR1Y522S mice were blocked by ryanodine or dantrolene. Thus, RYR1 mutations may lead to prolonged bleeding by altering vascular smooth muscle cell function. The reversibility of the bleeding phenotype emphasizes the potential therapeutic value of dantrolene in the treatment of such bleeding disorders.

Functional characterization of orbicularis oculi and extraocular muscles

Facial muscles are skeletal muscles that control facial expression. Sekulic-Jablanovic et al. characterize orbicularis oculi and extraocular muscles and find divergence in the expression of key molecules for muscle function between facial, extraocular, and quadriceps muscles.

The orbicularis oculi are the sphincter muscles of the eyelids and are involved in modulating facial expression. They differ from both limb and extraocular muscles (EOMs) in their histology and biochemistry. Weakness of the orbicularis oculi muscles is a feature of neuromuscular disorders affecting the neuromuscular junction, and weakness of facial muscles and ptosis have also been described in patients with mutations in the ryanodine receptor gene. Here, we investigate human orbicularis oculi muscles and find that they are functionally more similar to quadriceps than to EOMs in terms of excitation–contraction coupling components. In particular, they do not express the cardiac isoform of the dihydropyridine receptor, which we find to be highly expressed in EOMs where it is likely responsible for the large depolarization-induced calcium influx. We further show that human orbicularis oculi and EOMs express high levels of utrophin and low levels of dystrophin, whereas quadriceps express dystrophin and low levels of utrophin. The results of this study highlight the notion that myotubes obtained by explanting satellite cells from different muscles are not functionally identical and retain the physiological characteristics of their muscle of origin. Furthermore, our results indicate that sparing of facial and EOMs in patients with Duchenne muscular dystrophy is the result of the higher levels of utrophin expression.

Signature Channels of Excitability no More: L-Type Channels in Immune Cells

Although the concept of Ca(2+) as a universal messenger is well established, it was assumed that the regulatory mechanisms of Ca(2+)-signaling were divided along the line of electric excitability. Recent advances in molecular biology and genomics have, however, provided evidence that non-excitable cells such as immunocytes also express a wide and diverse pool of ion channels that does not differ as significantly from that of excitable cells as originally assumed. Ion channels and transporters are involved in virtually all aspects of immune response regulation, from cell differentiation and development to activation, and effector functions such as migration, antibody-secretion, phagosomal maturation, or vesicular delivery of bactericidal agents. This comprises TRP channel family members, voltage- and Ca(2+)-gated K(+)- and Na(+)-channels, as well as unexpectedly, components of the CaV1-subfamily of voltage-gated L-type Ca(2+)-channels, originally thought to be signature molecules of excitability. This article provides an overview of recent observations made in the field of CaV1 L-type channel function in the immune context, as well as presents results we obtained studying these channels in B-lymphocytes.

Characterization of excitation–contraction coupling components in human extraocular muscles

We show that the expression level of RyR1 in human extraocular muscles (EOMs) is low and that these muscles express different levels of proteins involved in excitation–contraction coupling (ECC) compared with leg muscles (LMs).