RYR1 Mutations Research Articles

FastD: Fast detection of insecticide target-site mutations and overexpressed detoxification genes in insect populations from RNA-Seq data.

Target‐site mutations and detoxification gene overexpression are two major mechanisms conferring insecticide resistance. Molecular assays applied to detect these resistance genetic markers are time‐consuming and with high false‐positive rates. RNA‐Seq data contains information on the variations within expressed genomic regions and expression of detoxification genes. However, there is no corresponding method to detect resistance markers at present. Here, we collected 66 reported resistance mutations of four insecticide targets (AChE, VGSC, RyR, and nAChR) from 82 insect species. Next, we obtained 403 sequences of the four target genes and 12,665 sequences of three kinds of detoxification genes including P450s, GSTs, and CCEs. Then, we developed a Perl program, FastD, to detect target‐site mutations and overexpressed detoxification genes from RNA‐Seq data and constructed a web server for FastD (http://www.insect-genome.com/fastd). The estimation of FastD on simulated RNA‐Seq data showed high sensitivity and specificity. We applied FastD to detect resistant markers in 15 populations of six insects, Plutella xylostella, Aphis gossypii, Anopheles arabiensis, Musca domestica, Leptinotarsa decemlineata and Apis mellifera. Results showed that 11 RyR mutations in P. xylostella, one nAChR mutation in A. gossypii, one VGSC mutation in A. arabiensis and five VGSC mutations in M. domestica were found to be with frequency difference >40% between resistant and susceptible populations including previously confirmed mutations G4946E in RyR, R81T in nAChR and L1014F in VGSC. And 49 detoxification genes were found to be overexpressed in resistant populations compared with susceptible populations including previously confirmed detoxification genes CYP6BG1, CYP6CY22, CYP6CY13, CYP6P3, CYP6M2, CYP6P4 and CYP4G16. The candidate target‐site mutations and detoxification genes were worth further validation. Resistance estimates according to confirmed markers were consistent with population phenotypes, confirming the reliability of this program in predicting population resistance at omics‐level.

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

BackgroundMyofibrillar 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.MethodsWe performed whole-exome sequencing in four patients from three unrelated families who were diagnosed with PAM without aberrations in causative genes for MFM.ResultsIn 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.ConclusionsOur study identifies a new genetic background in PAM pathology and expands the clinical phenotype of known pathogenic mutations.

Bioenergetic defects in muscle fibers of RYR1 mutant knock-in mice associated with malignant hyperthermia

Mutations in the skeletal muscle ryanodine receptor gene (RYR1) can cause susceptibility to malignant hyperthermia (MH), a potentially lethal genetic condition triggered by volatile anesthetics. MH is associated with hypermetabolism, which has directed research interest into oxidative phosphorylation and muscle bioenergetics. The most common cause of MH in the United Kingdom is the c.7300G>A RYR1 variant, which is present in ∼16% of MH families. Our study focuses on the MH susceptible G2435R-RYR1 knock-in mouse model, which is the murine equivalent of the human c.7300G>A genotype. Using a combination of transcriptomics, protein expression, and functional analysis, we investigated adult muscle fiber bioenergetics in this mouse model. RNA-Seq data showed reduced expression of genes associated with mitochondria and fatty acid oxidation in RYR1 mutants when compared with WT controls. Mitochondrial function was assessed by measuring oxygen consumption rates in permeabilized muscle fibers. Comparisons between WT and homozygous G2435R-RYR1 mitochondria showed a significant increase in complex I-facilitated oxidative phosphorylation in mutant muscle. Furthermore, we observed a gene-dose-specific increase in reactive oxygen species production in G2435R-RYR1 muscle fibers. Collectively, these findings provide evidence of metabolic defects in G2435R-RYR1 knock-in mouse muscle under basal conditions. Differences in metabolic profile could be the result of differential gene expression in metabolic pathways, in conjunction with mitochondrial damage accumulated from chronic exposure to increased oxidative stress.

The central domain of cardiac ryanodine receptor governs channel activation, regulation, and stability

Structural analyses identified the central domain of ryanodine receptor (RyR) as a transducer converting conformational changes in the cytoplasmic platform to the RyR gate. The central domain is also a regulatory hub encompassing the Ca2+-, ATP-, and caffeine-binding sites. However, the role of the central domain in RyR activation and regulation has yet to be defined. Here, we mutated five residues that form the Ca2+ activation site and 10 residues with negatively charged or oxygen-containing side chains near the Ca2+ activation site. We also generated eight disease-associated mutations within the central domain of RyR2. We determined the effect of these mutations on Ca2+, ATP, and caffeine activation and Mg2+ inhibition of RyR2. Mutating the Ca2+ activation site markedly reduced the sensitivity of RyR2 to Ca2+ and caffeine activation. Unexpectedly, Ca2+ activation site mutation E3848A substantially enhanced the Ca2+-independent basal activity of RyR2, suggesting that E3848A may also affect the stability of the closed state of RyR2. Mutations in the Ca2+ activation site also abolished the effect of ATP/caffeine on the Ca2+-independent basal activity, suggesting that the Ca2+ activation site is also a critical determinant of ATP/caffeine action. Mutating residues with negatively charged or oxygen-containing side chains near the Ca2+ activation site significantly altered Ca2+ and caffeine activation and reduced Mg2+ inhibition. Furthermore, disease-associated RyR2 mutations within the central domain significantly enhanced Ca2+ and caffeine activation and reduced Mg2+ inhibition. Our data demonstrate that the central domain plays an important role in channel activation, channel regulation, and closed state stability.

Adaptive thermogenesis enhances the life-threatening response to heat in mice with an Ryr1 mutation

Mutations in the skeletal muscle Ca2+ release channel, the type 1 ryanodine receptor (RYR1), cause malignant hyperthermia susceptibility (MHS) and a life-threatening sensitivity to heat, which is most severe in children. Mice with an MHS-associated mutation in Ryr1 (Y524S, YS) display lethal muscle contractures in response to heat. Here we show that the heat response in the YS mice is exacerbated by brown fat adaptive thermogenesis. In addition, the YS mice have more brown adipose tissue thermogenic capacity than their littermate controls. Blood lactate levels are elevated in both heat-sensitive MHS patients with RYR1 mutations and YS mice due to Ca2+ driven increases in muscle metabolism. Lactate increases brown adipogenesis in both mouse and human brown preadipocytes. This study suggests that simple lifestyle modifications such as avoiding extreme temperatures and maintaining thermoneutrality could decrease the risk of life-threatening responses to heat and exercise in individuals with RYR1 pathogenic variants.

NEW GENES IN NEUROMUSCULAR DISEASES: O.03 Dominant mutations in the junctin gene are related to malignant hyperthermia and exertional heat stroke

Malignant hyperthermia (MH) and Exertional Heat Stroke (EHS) present hypermetabolic states leading to rhabdomyolysis and muscle rigidity with progressive hyperthermia; MH is triggered by volatile inhaled anesthetics, while EHS is triggered by exercise in hot/humid environment. Given the similarity of clinical features and the fact that a portion of EHS cases were diagnosed as MH susceptible by the in vitro contracture test, MH and EHS are believed to share common etiology. Mutations in RYR1 and CACNA1S have been found to be associated with MH; however the genetic cause remains to be identified in approximately 30% of MH cases.

CONGENITAL MYOPATHIES 2: P.103 Congenital neuromuscular disease with uniform type 1 fibers due to RYR1 mutation is a de facto core myopathy

Typical central core disease (CCD) is characterized pathologically by the presence of a ``core'' which is devoid of oxidative enzyme activity in the central region of myofibers, and is typically accompanied by a strong type 1 fiber predominance (> 99%), referred to as type 1 fiber uniformity. Congenital neuromuscular disease with uniform type 1 fibers (CNMDU1) is characterized pathologically by the presence of essentially identical type 1 fiber uniformity but without the abnormal structural changes in muscle fibers.

Sever Rhabdomyolysis With Normal Renal Function Test in a 29-Year Old Who is Known to have RYR1 Mutation

Ryanodine receptor gene (RYR-1) is a gene encode calcium release channel in skeletal muscle , mutation in this gene lead to rare type of inherited congenital myopathy which is associated with rhabdomyolysis and fatal malignant hyperthermia . We report a case of a 29 year old male known to have sporadic RYR-1 mutation who presented with myalgia and fatigue post upper respiratory tract infection symptoms during COVID19 pandemic .His Creatine Kinase was markedly elevated without evidence of acute kidney injury which is usually uncommon. We also discuss in this case importance of checking CK during COVID19 pandemic .There is no cure for RYR-1 mutation but proper genetic counselling and patient’s education about precipitating factor for malignant hyperthermia will prevent serious complication which can lead to death.

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.

Dietary Caffeine Synergizes Adverse Peripheral and Central Responses to Anesthesia in Malignant Hyperthermia Susceptible Mice.

Ryanodine receptor (RYR) mutations confer stress-triggered malignant hyperthermia (MH) susceptibility. Dietary caffeine (CAF) is the most commonly consumed psychoactive compound by humans. CAF-triggered Ca2+ release and its influences on skeletal muscle contractility are widely used as experimental tools to study RYR function/dysfunction and diagnose MH susceptibility. We hypothesize that dietary CAF achieving blood levels measured in human plasma exacerbates the penetrance of RYR1 MH susceptibility mutations triggered by gaseous anesthetic, affecting both central and peripheral adverse responses. Heterozygous R163C-RYR1 (HET) MH susceptible mice are used to investigate the influences of dietary CAF on both peripheral and central responses before and after induction of halothane (HAL) maintenance anesthesia under experimental conditions that maintain normal core body temperature. HET mice receiving CAF (plasma CAF 893 ng/ml) have significantly shorter times to respiratory arrest compared with wild type, without altering blood chemistry or displaying hyperthermia or muscle rigor. Intraperitoneal bolus dantrolene before HAL prolongs time to respiratory arrest. A pilot electrographic study using subcutaneous electrodes reveals that dietary CAF does not alter baseline electroencephalogram (EEG) total power, but significantly shortens delay to isoelectric EEG, which precedes respiratory and cardiac arrest. CAF ± HAL are studied on RYR1 single-channel currents and HET myotubes to define molecular mechanisms of gene-by-environment synergism. Strong pharmacological synergism between CAF and HAL is demonstrated in both single-channel and myotube preparations. Central and peripheral nervous systems mediate adverse responses to HAL in a HET model of MH susceptibility exposed to dietary CAF, a modifiable lifestyle factor that may mitigate risks of acute and chronic diseases associated with RYR1 mutations. SIGNIFICANCE STATEMENT: Dietary caffeine at a human-relevant dose synergizes adverse peripheral and central responses to anesthesia in malignant hyperthermia susceptible mice. Synergism of these drugs can be attributed to their actions at ryanodine receptors.

Structural mechanism of two gain-of-function cardiac and skeletal RyR mutations at an equivalent site by cryo-EM.

Mutations in ryanodine receptors (RyRs), intracellular Ca2+ channels, are associated with deadly disorders. Despite abundant functional studies, the molecular mechanism of RyR malfunction remains elusive. We studied two single-point mutations at an equivalent site in the skeletal (RyR1 R164C) and cardiac (RyR2 R176Q) isoforms using ryanodine binding, Ca2+ imaging, and cryo-electron microscopy (cryo-EM) of the full-length protein. Loss of the positive charge had greater effect on the skeletal isoform, mediated via distortion of a salt bridge network, a molecular latch inducing rotation of a cytoplasmic domain, and partial progression to open-state traits of the large cytoplasmic assembly accompanied by alteration of the Ca2+ binding site, which concur with the major "hyperactive" feature of the mutated channel. Our cryo-EM studies demonstrated the allosteric effect of a mutation situated ~85 Å away from the pore and identified an isoform-specific structural effect.

Targeted next-generation sequencing identifies the disruption of the SHANK3 and RYR2 genes in a patient carrying a de novo t(1;22)(q43;q13.3) associated with signs of Phelan-McDermid syndrome

BackgroundIt has been known for more than 30 years that balanced translocations, especially if de novo, can associate with congenital malformations and / or neurodevelopmental disorders, following the disruption of a disease gene or its cis-regulatory elements at one or both breakpoints.Case presentationWe describe a 10-year-old girl with a non-specific neurodevelopmental disorder characterized by moderate intellectual disability (ID), gross motor clumsiness, social and communication deficits. She carries a de novo reciprocal translocation between chromosomes 1q43 and 22q13.3, the latter suggesting the involvement of SHANK3. Indeed, its haploinsufficiency associates with Phelan-McDermid Syndrome, whose main symptoms are characterized by global developmental delay and absent or severely delayed expressive speech. A deep molecular approach, including next-generation sequencing of SHANK3 locus, allowed demonstrating the breakage of RYR2 and SHANK3 on the derivative chromosomes 1 and 22 respectively, and the formation of two fusion genes SHANK3-RYR2 and RYR2-SHANK3 with concomitant cryptic deletion of 3.6 and 4.1 kilobases at translocation junction of both derivatives chromosomes 22 and 1, respectively.ConclusionsAlthough the interruption of SHANK3 accounts for the patient’s psychomotor retardation and autism-like behavior, we do not exclude that the interruption of RYR2 may also have a role on her disorder, or result in further pathogenicity in the future. Indeed, RYR2 that has a well-established role in the etiology of two autosomal dominant adulthood cardiac disorders (#600996 and #604772) is also expressed in the brain (cerebellum, hippocampus, and cerebral cortex) and about half of RYR2 mutation carriers present late onset primary generalized epilepsy without cardiac arrhythmogenic disorders. Moreover, RYR2 variants have also been sporadically reported in individuals with early onset schizophrenia or ID, and its constraint values suggest intolerance to loss-of-function. This study not only confirms the usefulness of the molecular mapping of de novo balanced rearrangements in symptomatic individuals, but also underscores the need for long-term clinical evaluation of the patients, for better evaluating the pathogenicity of the chromosomal breakpoints.

Managing pregnancy and anaesthetics in patients with skeletal muscle channelopathies

The skeletal muscle channelopathies are a group of rare diseases and include non-dystrophic myotonia and periodic paralysis. Given their rarity, little has been published on the management of anaesthesia and pregnancy in this cohort despite being important aspects of care. We have conducted a large study of over 70 patients who underwent anaesthesia and 87 pregnancies to investigate the problems encountered following anaesthesia or during pregnancy. This was performed via patient surveys sent out to genetically confirmed channelopathy patients seen at the National Hospital for Neurology and Neurosurgery. Most significantly in our cohort, patients frequently experienced a worsening or precipitation of symptoms during pregnancy (75%) or following anaesthetic (31%). None of our patients developed malignant hyperthermia, although there are confirmed reports of this in patients with periodic paralysis and mutations in RYR1. There was a significantly higher number of miscarriages compared to the normal population. There was no significant difference in antenatal or delivery complications compared to the general population. However, three neonates did have complications, all of whom were found to carry mutations in SCN4A. This study highlights the importance of counselling patients and clinicians for the possibility of worsening symptoms during pregnancy or anaesthesia and the careful management of neonates following delivery.

Genomic mapping to identify mutations in RYR2 and AHNAK in basal-like breast tumors expressing PD-L1.

1027 Background: Basal-like breast cancer is a specific subtype of breast tumors with limited therapeutic options. Although treatment with the anti-PD-L1 antibody atezolizumab has recently shown clinical activity in this setting, not all patients do respond even expressing high levels of PD-L1. In the present article we explored the presence of mutations in breast cancer tumors with high expression of PD1 and PD-L1 with the aim to identify molecular correlates associated with outcome. Methods: We used RNA-seq and mutational data from 971 breast cancer patients using the TCGA dataset, to identify mutations in patients with high levels of PD1 and PD-L1. Data analysis was performed using DESeq R and MAFTools Bioconductor packages. Transcriptomic signatures from the identified mutations were associated with outcome using the Kapplan-Meyer Plotter tool. We correlated the identified transcripts with immune populations using TIMER online tool and correlation between genes with Cancertool online platform. Results: We identified co-occurrent mutations in RYR2 and AHNAK in 8% and 5% of basal like tumors, respectively, in patients with high levels of PD1 and PD-1. The transcriptomic signature of these mutations conferred good prognosis for relapse free survival (RFS) and overall survival (OS). CXCL9 for RYR2 and GBP5, C1QA, IL2RG, CSF2RB and IDO1 for AHNAK were the most relevant genes identified in these signatures. Expression of CXCL9, GBP5, IL2RG and IDO1 correlated with the presence of immune cell populations mainly dendritic cells. This signature, including CXCL9, GBP5, C1QA, IL2RG, CSF2RB and IDO1 classified patients with favorable RFS (HR 0.27 CI 0.2-0.30; p = 1.1e-16) and OS (HR 0.18 CI 0.09-0.34; p = 6.8e-9). This signature showed a stronger prediction capacity compared with already described immunologic signatures. Finally we identify that LAG3 was the only gene commonly present in both signatures and correlated positively with the expression of PD1 and PD-L1. Conclusions: We describe two novel mutations which transcriptomic signatures associated with favorable outcome in basal-like tumors that express elevated levels of PD1 and PD-L1. Future studies should be performed to confirm the role of these mutations and signatures in relation with clinical activity of PD1/PD-L1 inhibitors.

Molecular basis of impaired extraocular muscle function in a mouse model of congenital myopathy due to compound heterozygous Ryr1 mutations.

Mutations in the RYR1 gene are the most common cause of human congenital myopathies, and patients with recessive mutations are severely affected and often display ptosis and/or ophthalmoplegia. In order to gain insight into the mechanism leading to extraocular muscle (EOM) involvement, we investigated the biochemical, structural and physiological properties of eye muscles from mouse models we created knocked-in for Ryr1 mutations. Ex vivo force production in EOMs from compound heterozygous RyR1p.Q1970fsX16+p.A4329D mutant mice was significantly reduced compared with that observed in wild-type, single heterozygous mutant carriers or homozygous RyR1p.A4329D mice. The decrease in muscle force was also accompanied by approximately a 40% reduction in RyR1 protein content, a decrease in electrically evoked calcium transients, disorganization of the muscle ultrastructure and a decrease in the number of calcium release units. Unexpectedly, the superfast and ocular-muscle-specific myosin heavy chain-EO isoform was almost undetectable in RyR1p.Q1970fsX16+p.A4329D mutant mice. The results of this study show for the first time that the EOM phenotype caused by the RyR1p.Q1970fsX16+p.A4329D compound heterozygous Ryr1 mutations is complex and due to a combination of modifications including a direct effect on the macromolecular complex involved in calcium release and indirect effects on the expression of myosin heavy chain isoforms.

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 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.

Abstract P4-09-02: Somatic tumor profiles of breast cancer in Latinas

Abstract Background: Latinos represent the largest and fastest-growing minority population in the US; breast cancer is the most common cancer and causes the most cancer deaths in this population. Precision medicine is being applied increasingly to guide breast cancer treatment decisions. However, the ability to apply precision medicine for prognosis and targeted treatments for breast cancer in Latinas is limited by insufficient data on somatic mutation and gene expression profiles in available tumor mutation datasets. In The Cancer Genome Atlas (TCGA), one of the largest publicly available tumor mutation datasets, only 31 of ~1100 total breast cancers are Latina. Therefore, we performed whole exome sequencing on matched tumor/normal pairs in 146 tumors from 142 women reporting here on their somatic mutational profile compared to non-Latino women of European ancestry from TCGA. Methods: We enrolled 142 Latinas with invasive breast cancer and obtained blood and tumor tissue (formalin-fixed paraffin embedded). After whole exome sequencing of 146 pairs of tumor (somatic) and normal (germline) samples, high quality data were available for 142 tumor-normal pairs for analysis. Target coverage for normal was ~30X and for tumor was ~100X. Sequence data were aligned using Burrows-Wheeler Aligner, genotype calls were made using GATK and Mutect2 was used to call somatic mutations including base substitutions and small insertions and deletions. We estimated genetic ancestry from the germline genotype data using ADMIXTURE. Results: Age at diagnosis ranged from 31 to 75 years with a median age of 48 years. Histologically, 83% were estrogen-receptor positive, 71 % were progesterone-receptor positive, and 17% were human epidermal growth factor receptor positive; 87% were Stage 1 or 2 at diagnosis. The mean genetic ancestry in our sample was 52.3% European, 41.6% Indigenous American, and 6.2% African. We compared the 30 genes most commonly mutated in breast cancers (e.g., PIK3CA, TP53, MAP3K1, MLL3) in non-Latina Whites in TCGA to our data both overall and by subtype and searched for additional recurrently mutated genes not commonly observed in other populations. Similar to non-Latinos, PIK3CA and TP53 were the most commonly mutated genes; mutations in PIK3CA, GATA3, MAP3K1, and RYR2 were significantly more frequent in Latinas (p-value range from 0.001-0.002). Summary: In general, breast tumors from Latinas have similar rates of somatic mutations in most of the top commonly observed genes in European-ancestry women. Citation Format: Susan Neuhausen, Daniel Schmolze, Linda Steele, Shu Tao, Aaron Adamson, Charleen Adams, Donglei Hu, Scott Huntsman, Jung Byun, Kevin Gardner, Eliseo Perez-Stable, Anna Napoles, Jeffrey Weitzel, Elad Ziv. Somatic tumor profiles of breast cancer in Latinas [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-09-02.

SERCA Stimulation Triggers Arrhythmogenic Ca2+ Events in Mouse Cardiomyocytes Harboring the RyR2R420Q+/- Mutation

Mutations of the RyR2 are channelopathies that can predispose to life threatening catecholaminergic polymorphic ventricular tachycardias (CPVTs) during exercise or stress. However, the cellular mechanisms that are causal downstream of the ß-adrenergic receptor (ß-AR) activation are not defined. They may be specific and different for each particular RyR2 mutation. Obvious possibilities are the phosphorylation of the mutated RyR2s or the stimulation of the SR Ca2+ pump (SERCA), which could increase SR Ca2+ loading. Potentially arrhythmogenic Ca2+ signals, such as Ca2+ waves, were recorded and analyzed from WT and RyR2R420Q+/- mouse cardiomyocytes with confocal microscopy after field stimulation at 1Hz. In RyR2R420Q+/- cardiomyocytes we found a higher occurrence and frequency of Ca2+ waves, particularly upon ß-AR stimulation with Isoproterenol. This was accompanied by a shorter latency to the first spontaneous wave. Wave velocity, amplitude and decay time (tau) analyzed in de-skewed waves were comparable in both cell types. When determining the SR Ca2+ threshold for wave generation by simultaneously measuring the cytosolic and SR Ca2+ concentration in permeabilized cells, we found a significantly lower threshold for Ca2+ waves in the RyR2R420Q+/- cells. To obtain further insight into the role of the SERCA we specifically stimulated SERCA using Fab fragments of a PLB antibody (2D12). The Fab fragments increased wave frequency, which was more pronounced in the R420Q+/- cardiomyocytes. Spark-to-spark recovery analysis suggested a remarkably higher RyR2R420Q+/- Ca2+ sensitivity, both in control and upon ß-AR stimulation. Together with the lowered SR Ca2+ wave threshold and the arrhythmogenicity of isolated SERCA stimulation, these findings are consistent with a higher intra-SR Ca2+ sensitivity of the RyR2R420Q+/-. In this CPVT mouse model harboring a RyR2 gain of function mutation, the lower wave threshold may lead to SR Ca2+ imbalance during SERCA stimulation.

Molecular Dynamics and Ca2+ Imaging of Mutant Type 1 Ryanodine Receptor

In skeletal muscle cells, membrane depolarization is translated into intracellular Ca2+ signals, and type 1 ryanodine receptors (RyR1), located in the sarcoplasmic reticulum membrane, play a key role in intracellular Ca2+ release. Mutations in the RYR1 gene cause severe muscle diseases, such as malignant hyperthermia (MH), which is a disorder of Ca2+-induced Ca2+ release via RyR1 in the skeletal muscle. Thus far, more than 300 mutations have been reported in RYR1 in patients with MH, and most of those mutations have been found in three “hotspot” regions of RYR1. However, due to a lack of comprehensive analysis of the structure-function relationship of mutant RyR1, the mechanism remains largely unknown. Here, we combined functional studies and molecular dynamics (MD) simulation of RyR1 bearing disease-associated mutations at the N-terminal region. When expressed in HEK293 cells, the mutant RyR1 caused abnormalities in Ca2+ homeostasis. MD simulations of wildtype (WT) and mutants were performed using crystal structure of the NTD monomer of RyR1. In WT, we found that the B(R283)-A(D61)-C(R402)-A(E40)-C(S406) hydrogen bonds/salt bridges network (B-A-C-A-C network) around R402. MD simulation of the mutant of R402 revealed that alterations of hydrogen bonds/salt bridges between NTD, consisting of A, B and C domains. Furthermore, to verify the role of the B-A-C-A-C network, we have newly created alanine mutants of E40 and D61, and measurements of Ca2+ transient and calculations of MD simulations of these mutants were performed. Although the calculation could not detect any effect of the mutations located around subunit interfaces, the mutations located around inter-domain region of the three domains of the NTD revealed that alterations in hydrogen bonds/salt bridges between NTDs strongly correlate with the channel function of RyR1.