RESUMO
Junctin is a transmembrane protein of striated muscles, located at the junctional sarcoplasmic reticulum (SR). It is characterized by a luminal C-terminal tail, through which it functionally interacts with calsequestrin and the ryanodine receptor (RyR). Interaction with calsequestrin was ascribed to the presence of stretches of charged amino acids (aa). However, the regions able to bind calsequestrin have not been defined in detail. We report here that, in non-muscle cells, junctin and calsequestrin assemble in long linear regions within the endoplasmic reticulum, mirroring the formation of calsequestrin polymers. In differentiating myotubes, the two proteins colocalize at triads, where they assemble with other proteins of the junctional SR. By performing GST pull-down assays with distinct regions of the junctin tail, we identified two KEKE motifs that can bind calsequestrin. In addition, stretches of charged aa downstream these motifs were found to also bind calsequestrin and the RyR. Deletion of even one of these regions impaired the ability of junctin to localize at the junctional SR, suggesting that interaction with other proteins at this site represents a key element in junctin targeting.
Assuntos
Proteínas de Ligação ao Cálcio , Calsequestrina , Cálcio/metabolismo , Proteínas de Ligação ao Cálcio/genética , Calsequestrina/genética , Oxigenases de Função Mista/metabolismo , Músculo Esquelético/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Retículo Sarcoplasmático/metabolismoRESUMO
Tubular aggregate myopathy (TAM) is a rare myopathy characterized by muscle weakness and myalgia. Muscle fibers from TAM patients show characteristic accumulation of membrane tubules that contain proteins from the sarcoplasmic reticulum (SR). Gain-of-function mutations in STIM1 and ORAI1, the key proteins participating in the Store-Operated Ca2+ Entry (SOCE) mechanism, were identified in patients with TAM. Recently, the CASQ1 gene was also found to be mutated in patients with TAM. CASQ1 is the main Ca2+ buffer of the SR and a negative regulator of SOCE. Previous characterization of CASQ1 mutants in non-muscle cells revealed that they display altered Ca2+dependent polymerization, reduced Ca2+storage capacity and alteration in SOCE inhibition. We thus aimed to assess how mutations in CASQ1 affect calcium regulation in skeletal muscles, where CASQ1 is naturally expressed. We thus expressed CASQ1 mutants in muscle fibers from Casq1 knockout mice, which provide a valuable model for studying the Ca2+ storage capacity of TAM-associated mutants. Moreover, since Casq1 knockout mice display a constitutively active SOCE, the effect of CASQ1 mutants on SOCE inhibition can be also properly examined in fibers from these mice. Analysis of intracellular Ca2+ confirmed that CASQ1 mutants have impaired ability to store Ca2+and lose their ability to inhibit skeletal muscle SOCE; this is in agreement with the evidence that alterations in Ca2+entry due to mutations in either STIM1, ORAI1 or CASQ1 represents a hallmark of TAM.
RESUMO
Two likely causative mutations in the RYR1 gene were identified in two patients with myopathy with tubular aggregates, but no evidence of cores or core-like pathology on muscle biopsy. These patients were clinically evaluated and underwent routine laboratory investigations, electrophysiologic tests, muscle biopsy and muscle magnetic resonance imaging (MRI). They reported stiffness of the muscles following sustained activity or cold exposure and had serum creatine kinase elevation. The identified RYR1 mutations (p.Thr2206Met or p.Gly2434Arg, in patient 1 and patient 2, respectively) were previously identified in individuals with malignant hyperthermia susceptibility and are reported as causative according to the European Malignant Hyperthermia Group rules. To our knowledge, these data represent the first identification of causative mutations in the RYR1 gene in patients with tubular aggregate myopathy and extend the spectrum of histological alterations caused by mutation in the RYR1 gene.
Assuntos
Hipertermia Maligna , Miopatias Congênitas Estruturais , Humanos , Hipertermia Maligna/genética , Hipertermia Maligna/patologia , Músculo Esquelético/patologia , Mutação/genética , Miopatias Congênitas Estruturais/genética , Miopatias Congênitas Estruturais/patologia , Canal de Liberação de Cálcio do Receptor de Rianodina/genéticaRESUMO
In adult skeletal muscles, 2 junctophilin isoforms (JPH1 and JPH2) tether the sarcoplasmic reticulum (SR) to transverse tubule (T-tubule) membranes, generating stable membrane contact sites known as triads. JPHs are anchored to the membrane of the SR by a C-terminal transmembrane domain (TMD) and bind the T-tubule membrane through their cytosolic N-terminal region, which contains 8 lipid-binding (MORN) motifs. By combining expression of GFP-JPH1 deletion mutants in skeletal muscle fibers with in vitro biochemical experiments, we investigated the molecular determinants of JPH1 recruitment at triads in adult skeletal muscle fibers. We found that MORN motifs bind PI(4,5)P2 in the sarcolemma, but do not mediate the selective localization of JPH1 at the T-tubule compartment of triads. On the contrary, fusion proteins containing only the TMD of JPH1 were able to localize at the junctional SR compartment of the triad. Bimolecular fluorescence complementation experiments indicated that the TMD of JPH1 can form dimers, suggesting that the observed localization at triads may result from dimerization with the TMDs of resident JPH1. A second domain, capable of mediating homo- and heterodimeric interactions between JPH1 and JPH2 was identified in the cytosolic region. FRAP experiments revealed that removal of either one of these 2 domains in JPH1 decreases the association of the resulting mutant proteins with triads. Altogether, these results suggest that the ability to establish homo- and heterodimeric interactions with resident JPHs may support the recruitment and stability of newly synthesized JPHs at triads in adult skeletal muscle fibers.
Assuntos
Proteínas de Membrana/metabolismo , Fibras Musculares Esqueléticas/metabolismo , Proteínas Musculares/metabolismo , Sarcolema/metabolismo , Motivos de Aminoácidos , Animais , Humanos , Proteínas de Membrana/genética , Camundongos , Proteínas Musculares/genética , Mutação , Domínios Proteicos , Ratos , Ratos Sprague-Dawley , Sarcolema/genéticaRESUMO
Obscurin is a giant sarcomeric protein expressed in striated muscles known to establish several interactions with other proteins of the sarcomere, but also with proteins of the sarcoplasmic reticulum and costameres. Here, we report experiments aiming to better understand the contribution of obscurin to skeletal muscle fibers, starting with a detailed characterization of the diaphragm muscle function, which we previously reported to be the most affected muscle in obscurin (Obscn) KO mice. Twitch and tetanus tension were not significantly different in the diaphragm of WT and Obscn KO mice, while the time to peak (TTP) and half relaxation time (HRT) were prolonged. Differences in force-frequency and force-velocity relationships and an enhanced fatigability are observed in an Obscn KO diaphragm with respect to WT controls. Voltage clamp experiments show that a sarcoplasmic reticulum's Ca2+ release and SERCA reuptake rates were decreased in muscle fibers from Obscn KO mice, suggesting that an impairment in intracellular Ca2+ dynamics could explain the observed differences in the TTP and HRT in the diaphragm. In partial contrast with previous observations, Obscn KO mice show a normal exercise tolerance, but fiber damage, the altered sarcomere ultrastructure and M-band disarray are still observed after intense exercise.
Assuntos
Cálcio/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Fatores de Troca de Nucleotídeo Guanina Rho/metabolismo , Sarcômeros/metabolismo , Animais , Anquirinas/metabolismo , Conectina/metabolismo , Conectina/fisiologia , Masculino , Camundongos , Camundongos Knockout , Contração Muscular/fisiologia , Fibras Musculares Esqueléticas/metabolismo , Proteínas Musculares/metabolismo , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiologia , Condicionamento Físico Animal , Proteínas Serina-Treonina Quinases/genética , Fatores de Troca de Nucleotídeo Guanina Rho/genética , Sarcômeros/fisiologia , Retículo Sarcoplasmático/metabolismo , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismoRESUMO
Calsequestrin (CASQ) is the most abundant Ca2+ binding protein localized in the sarcoplasmic reticulum (SR) of skeletal and cardiac muscle. The genome of vertebrates contains two genes, CASQ1 and CASQ2. CASQ1 and CASQ2 have a high level of homology, but show specific patterns of expression. Fast-twitch skeletal muscle fibers express only CASQ1, both CASQ1 and CASQ2 are present in slow-twitch skeletal muscle fibers, while CASQ2 is the only protein present in cardiomyocytes. Depending on the intraluminal SR Ca2+ levels, CASQ monomers assemble to form large polymers, which increase their Ca2+ binding ability. CASQ interacts with triadin and junctin, two additional SR proteins which contribute to localize CASQ to the junctional region of the SR (j-SR) and also modulate CASQ ability to polymerize into large macromolecular complexes. In addition to its ability to bind Ca2+ in the SR, CASQ appears also to be able to contribute to regulation of Ca2+ homeostasis in muscle cells. Both CASQ1 and CASQ2 are able to either activate and inhibit the ryanodine receptors (RyRs) calcium release channels, likely through their interactions with junctin and triadin. Additional evidence indicates that CASQ1 contributes to regulate the mechanism of store operated calcium entry in skeletal muscle via a direct interaction with the Stromal Interaction Molecule 1 (STIM1). Mutations in CASQ2 and CASQ1 have been identified, respectively, in patients with catecholamine-induced polymorphic ventricular tachycardia and in patients with some forms of myopathy. This review will highlight recent developments in understanding CASQ1 and CASQ2 in health and diseases.
Assuntos
Cálcio , Calsequestrina , Animais , Cálcio/metabolismo , Proteínas de Ligação ao Cálcio , Calsequestrina/genética , Humanos , Músculo Esquelético/metabolismo , Canal de Liberação de Cálcio do Receptor de Rianodina , Retículo Sarcoplasmático/metabolismoRESUMO
Small Ankyrins (sAnk1) are muscle-specific isoforms generated by the Ank1 gene that participate in the organization of the sarcoplasmic reticulum (SR) of striated muscles. Accordingly, the volume of SR tubules localized around the myofibrils is strongly reduced in skeletal muscle fibers of 4- and 10-month-old sAnk1 knockout (KO) mice, while additional structural alterations only develop with aging. To verify whether the lack of sAnk1 also alters intracellular Ca2+ handling, cytosolic Ca2+ levels were analyzed in stimulated skeletal muscle fibers from 4- and 10-month-old sAnk1 KO mice. The SR Ca2+ content was reduced in sAnk1 KO mice regardless of age. The amplitude of the Ca2+ transients induced by depolarizing pulses was decreased in myofibers of sAnk1 KO with respect to wild type (WT) fibers, while their voltage dependence was not affected. Furthermore, analysis of spontaneous Ca2+ release events (sparks) on saponin-permeabilized muscle fibers indicated that the frequency of sparks was significantly lower in fibers from 4-month-old KO mice compared to WT. Furthermore, both the amplitude and spatial spread of sparks were significantly smaller in muscle fibers from both 4- and 10-month-old KO mice compared to WT. These data suggest that the absence of sAnk1 results in an impairment of SR Ca2+ release, likely as a consequence of a decreased Ca2+ store due to the reduction of the SR volume in sAnk1 KO muscle fibers.
Assuntos
Anquirinas/metabolismo , Cálcio/metabolismo , Músculo Esquelético/metabolismo , Retículo Sarcoplasmático/metabolismo , Animais , Anquirinas/genética , Masculino , Camundongos , Camundongos Knockout , Fibras Musculares Esqueléticas/metabolismo , Retículo Sarcoplasmático/genéticaRESUMO
Here, we report the identification of three novel missense mutations in the calsequestrin-1 (CASQ1) gene in four patients with tubular aggregate myopathy. These CASQ1 mutations affect conserved amino acids in position 44 (p.(Asp44Asn)), 103 (p.(Gly103Asp)), and 385 (p.(Ile385Thr)). Functional studies, based on turbidity and dynamic light scattering measurements at increasing Ca2+ concentrations, showed a reduced Ca2+ -dependent aggregation for the CASQ1 protein containing p.Asp44Asn and p.Gly103Asp mutations and a slight increase in Ca2+ -dependent aggregation for the p.Ile385Thr. Accordingly, limited trypsin proteolysis assay showed that p.Asp44Asn and p.Gly103Asp were more susceptible to trypsin cleavage in the presence of Ca2+ in comparison with WT and p.Ile385Thr. Analysis of single muscle fibers of a patient carrying the p.Gly103Asp mutation showed a significant reduction in response to caffeine stimulation, compared with normal control fibers. Expression of CASQ1 mutations in eukaryotic cells revealed a reduced ability of all these CASQ1 mutants to store Ca2+ and a reduced inhibitory effect of p.Ile385Thr and p.Asp44Asn on store operated Ca2+ entry. These results widen the spectrum of skeletal muscle diseases associated with CASQ1 and indicate that these mutations affect properties critical for correct Ca2+ handling in skeletal muscle fibers.
Assuntos
Proteínas de Ligação ao Cálcio/genética , Cálcio/metabolismo , Variação Genética , Proteínas Mitocondriais/genética , Miopatias Congênitas Estruturais/genética , Adulto , Idoso , Sequência de Aminoácidos , Substituição de Aminoácidos , Proteínas de Ligação ao Cálcio/metabolismo , Calsequestrina , Linhagem Celular Tumoral , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Proteínas Mitocondriais/metabolismo , Modelos Moleculares , Músculo Esquelético/metabolismo , Mutação de Sentido Incorreto , Multimerização Proteica , Proteólise , Proteínas Recombinantes , Alinhamento de Sequência , Imagem com Lapso de Tempo , Sequenciamento Completo do GenomaRESUMO
Ca2+ release, which is necessary for muscle contraction, occurs at the j-SR (junctional domain of the sarcoplasmic reticulum). It requires the assembly of a large multiprotein complex containing the RyR (ryanodine receptor) and additional proteins, including triadin and calsequestrin. The signals which drive these proteins to the j-SR and how they assemble to form this multiprotein complex are poorly understood. To address aspects of these questions we studied the localization, dynamic properties and molecular interactions of triadin. We identified three regions, named TR1 (targeting region 1), TR2 and TR3, that contribute to the localization of triadin at the j-SR. FRAP experiments showed that triadin is stably associated with the j-SR and that this association is mediated by TR3. Protein pull-down experiments indicated that TR3 contains binding sites for calsequestrin-1 and that triadin clustering can be enhanced by binding to calsequestrin-1. These findings were confirmed by FRET experiments. Interestingly, the stable association of triadin to the j-SR was significantly decreased in myotubes from calsequestrin-1 knockout mice. Taken together, these results identify three regions in triadin that mediate targeting to the j-SR and reveal a role for calsequestrin-1 in promoting the stable association of triadin to the multiprotein complex associated with RyR.
Assuntos
Proteínas de Transporte/metabolismo , Proteínas Musculares/metabolismo , Retículo Sarcoplasmático/metabolismo , Animais , Sinalização do Cálcio/fisiologia , Compartimento Celular/fisiologia , Células Cultivadas , Sistemas de Liberação de Medicamentos , Células HEK293 , Humanos , Camundongos , Camundongos Knockout , Microssomos/química , Microssomos/metabolismo , Células NIH 3T3 , Mapeamento de Interação de Proteínas/métodos , Estrutura Terciária de Proteína/fisiologia , Ratos , Ratos Sprague-Dawley , Canal de Liberação de Cálcio do Receptor de Rianodina/química , Retículo Sarcoplasmático/químicaRESUMO
A missense mutation in the calsequestrin-1 gene (CASQ1) was found in a group of patients with a myopathy characterized by weakness, fatigue, and the presence of large vacuoles containing characteristic inclusions resulting from the aggregation of sarcoplasmic reticulum (SR) proteins. The mutation affects a conserved aspartic acid in position 244 (p.Asp244Gly) located in one of the high-affinity Ca(2+) -binding sites of CASQ1 and alters the kinetics of Ca(2+) release in muscle fibers. Expression of the mutated CASQ1 protein in COS-7 cells showed a markedly reduced ability in forming elongated polymers, whereas both in cultured myotubes and in in vivo mouse fibers induced the formation of electron-dense SR vacuoles containing aggregates of the mutant CASQ1 protein that resemble those observed in muscle biopsies of patients. Altogether, these results support the view that a single missense mutation in the CASQ1 gene causes the formation of abnormal SR vacuoles containing aggregates of CASQ1, and other SR proteins, results in altered Ca(2+) release in skeletal muscle fibers, and, hence, is responsible for the clinical phenotype observed in these patients.
Assuntos
Proteínas de Ligação ao Cálcio/genética , Doenças por Armazenamento dos Lisossomos/metabolismo , Proteínas Mitocondriais/genética , Doenças Musculares/metabolismo , Mutação de Sentido Incorreto , Agregação Patológica de Proteínas/genética , Adulto , Animais , Células COS , Cálcio/metabolismo , Proteínas de Ligação ao Cálcio/química , Proteínas de Ligação ao Cálcio/metabolismo , Calsequestrina , Chlorocebus aethiops , Feminino , Humanos , Doenças por Armazenamento dos Lisossomos/genética , Doenças por Armazenamento dos Lisossomos/patologia , Masculino , Camundongos , Pessoa de Meia-Idade , Proteínas Mitocondriais/química , Proteínas Mitocondriais/metabolismo , Fibras Musculares Esqueléticas/ultraestrutura , Doenças Musculares/genética , Doenças Musculares/patologia , Linhagem , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Retículo Sarcoplasmático/metabolismo , Retículo Sarcoplasmático/ultraestrutura , Vacúolos/metabolismo , Vacúolos/ultraestrutura , Adulto JovemRESUMO
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.
Assuntos
Cálcio , Doenças Musculares , Cálcio/metabolismo , Sinalização do Cálcio , Acoplamento Excitação-Contração/fisiologia , Humanos , Doenças Musculares/genética , Doenças Musculares/metabolismo , Mutação , Retículo Sarcoplasmático/metabolismoRESUMO
Autosomal dominant mutations in sarcomere proteins such as the cardiac troponin T (TNNT2) are the main genetic causes of human hypertrophic cardiomyopathy and dilated cardiomyopathy. Allele-specific silencing by RNA interference (ASP-RNAi) holds promise as a therapeutic strategy for downregulating a single mutant allele with minimal suppression of the corresponding wild-type allele. Here, we propose ASP-RNAi as a possible strategy to specifically knockdown mutant alleles coding for R92Q and R173W mutant TNNT2 proteins, identified in hypertrophic and dilated cardiomyopathy, respectively. Different siRNAs were designed and validated by luciferase reporter assay and following analysis in HEK293T cells expressing either the wild-type or mutant TNNT2 alleles. This study is the first exploration of ASP-RNAi on TNNT2-R173W and TNNT2-R92Q mutations in vitro and gives a base for further application of allele silencing as a therapeutic treatment for TNNT2-mutation-associated cardiomyopathies.
Assuntos
Cardiomiopatia Dilatada , Cardiomiopatia Hipertrófica , Alelos , Cardiomiopatia Dilatada/genética , Cardiomiopatia Hipertrófica/genética , Cardiomiopatia Hipertrófica/metabolismo , Células HEK293 , Humanos , Mutação , Interferência de RNA , Troponina T/genética , Troponina T/metabolismoRESUMO
The sarcoplasmic reticulum of skeletal muscle cells is a highly ordered structure consisting of an intricate network of tubules and cisternae specialized for regulating Ca2+ homeostasis in the context of muscle contraction. The sarcoplasmic reticulum contains several proteins, some of which support Ca2+ storage and release, while others regulate the formation and maintenance of this highly convoluted organelle and mediate the interaction with other components of the muscle fiber. In this review, some of the main issues concerning the biology of the sarcoplasmic reticulum will be described and discussed; particular attention will be addressed to the structure and function of the two domains of the sarcoplasmic reticulum supporting the excitation-contraction coupling and Ca2+-uptake mechanisms.
Assuntos
Cálcio , Retículo Sarcoplasmático , Cálcio/metabolismo , Contração Muscular/fisiologia , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/metabolismo , Organelas , Retículo Sarcoplasmático/metabolismoRESUMO
Mesenchymal stem cells (MSCs) from human adult adipose tissue (A-MSCs) have a better differentiative ability than MSCs derived from the derma (D-MSCs). To test whether this difference is associated with differences in the content of multi-potent progenitors in A-MSCs, the number and the differentiative properties of multi-potent progenitors have been analyzed in various preparations of A-MSCs and D-MSCs. Adipogenic and osteogenic differentiation performed on colony-forming units have revealed that adipogenic and osteogenic progenitors are similar in the two populations, with only a slighty better performance of A-MSCs over D-MSCs from passages p0 to p15. An analysis of the presence of tri-, bi-, uni- and nulli-potent progenitors isolated immediately after isolation from tissues (p0) has shown comparable numbers of tri-potent and bi-potent progenitors in MSCs from the two tissues, whereas a higher content in uni-potent cells committed to adipocytes and a lower content in nulli-potent cells has been observed in A-MSCs. Furthermore, we have characterized the progenitors present in A-MSCs after six passages in vitro to verify the way in which in vitro culture can affect content in progenitor cells. We have observed that the percentage of tri-potent cells in A-MSCs at p6 remains similar to that observed at p0, although bi-potent and uni-potent progenitors committed to osteogenic differentiation increase at p6, whereas nulli-potent cells decrease at p6. These data indicate that the greater differentiative ability of A-MSC populations does not correlate directly with the number of multi-potent progenitors, suggesting that other factors influence the differentiation of bulk populations of A-MSCs.
Assuntos
Tecido Adiposo/citologia , Derme/citologia , Células-Tronco Mesenquimais/citologia , Células-Tronco/citologia , Adipogenia , Técnicas de Cultura de Células , Separação Celular , Células Cultivadas , Humanos , OsteogêneseRESUMO
Neurotrophins and their receptors are known to play a role in the proliferation and survival of many different cell types of neuronal and non-neuronal lineages. In addition, there is much evidence in the literature showing that the p75 neurotrophin receptor (p75(NTR)), alone or in association with members of the family of Trk receptors, is expressed in a wide variety of stem cells, although its role in such cells has not been completely elucidated. In the present work we have investigated the expression of p75(NTR) and Trks in totipotent and pluripotent cells, the mouse pre-implantation embryo and embryonic stem and germ cells (ES and EG cells). p75(NTR) and TrkA can be first detected in the blastocyst from which ES cell lines are derived. Mouse ES cells retain p75(NTR)/TrkA expression. Nerve growth factor is the only neurotrophin able to stimulate ES cell growth in culture, without affecting the expression of stem cell markers, alkaline phosphatase, Oct4 and Nanog. Such proliferation effect was blocked by antagonizing either p75(NTR) or TrkA. Interestingly, immunoreactivity to anti-p75(NTR) antibodies is lost upon ES cell differentiation. The expression pattern of neurotrophin receptors in murine ES cells differs from human ES cells, that only express TrkB and C, and do not respond to NGF. In this paper we also show that, while primordial germ cells (PGC) do not express p75(NTR), when they are made to revert to an ES-like phenotype, becoming EG cells, expression of p75(NTR) is turned on.
Assuntos
Células-Tronco Embrionárias/metabolismo , Receptor de Fator de Crescimento Neural/metabolismo , Receptor trkA/metabolismo , Fosfatase Alcalina/metabolismo , Animais , Apoptose/efeitos dos fármacos , Apoptose/fisiologia , Linhagem Celular , Proliferação de Células/efeitos dos fármacos , Fragmentação do DNA/efeitos dos fármacos , Células-Tronco Embrionárias/citologia , Células-Tronco Embrionárias/efeitos dos fármacos , Proteínas de Homeodomínio/metabolismo , Camundongos , Proteína Homeobox Nanog , Fator de Crescimento Neural/farmacologia , Fator 3 de Transcrição de Octâmero/metabolismo , Receptor de Fator de Crescimento Neural/efeitos dos fármacos , Receptor trkA/efeitos dos fármacosRESUMO
BACKGROUND: Triadin is a protein expressed in cardiac and skeletal muscle that has an essential role in the structure and functional regulation of calcium release units and excitation-contraction coupling. Mutations in the triadin gene (TRDN) have been described in different forms of human arrhythmia syndromes with early onset and severe arrhythmogenic phenotype, including triadin knockout syndrome. OBJECTIVE: The purpose of this study was to characterize the pathogenetic mechanism underlying a case of severe pediatric malignant arrhythmia associated with a defect in the TRDN gene. METHODS: We used a trio whole exome sequencing approach to identify the genetic defect in a 2-year-old boy who had been resuscitated from sudden cardiac arrest and had frequent episodes of ventricular fibrillation and a family history positive for sudden death. We then performed in vitro functional analysis to investigate possible pathogenic mechanisms underlying this severe phenotype. RESULTS: We identified a novel homozygous missense variant (p.L56P) in the TRDN gene in the proband that was inherited from the heterozygous unaffected parents. Expression of a green fluorescent protein (GFP)-tagged mutant human cardiac triadin isoform (TRISK32-L56P-GFP) in heterologous systems revealed that the mutation alters protein dynamics. Furthermore, when co-expressed with the type 2 ryanodine receptor, caffeine-induced calcium release from TRISK32-L56P-GFP was relatively lower compared to that observed with the wild-type construct. CONCLUSION: The results of this study allowed us to hypothesize a pathogenic mechanism underlying this rare arrhythmogenic recessive form, suggesting that the mutant protein potentially can trigger arrhythmias by altering calcium homeostasis.
Assuntos
Proteínas de Transporte/genética , DNA/genética , Proteínas Musculares/genética , Mutação , Taquicardia Ventricular/genética , Proteínas de Transporte/metabolismo , Pré-Escolar , Análise Mutacional de DNA , Homozigoto , Humanos , Masculino , Proteínas Musculares/metabolismo , Linhagem , Índice de Gravidade de Doença , Taquicardia Ventricular/metabolismoRESUMO
Central Core Disease (CCD) is a congenital myopathy characterized by presence of amorphous central areas (or cores) lacking glycolytic/oxidative enzymes and mitochondria in skeletal muscle fibers. Most CCD families are linked to mutations in ryanodine receptor type-1 (RYR1), the gene encoding for the sarcoplasmic reticulum (SR) Ca2+ release channel of skeletal muscle. As no treatments are available for CCD, currently management of patients is essentially based on a physiotherapic approaches. Functional electrical stimulation (FES) is a technique used to deliver low energy electrical impulses to artificially stimulate selected skeletal muscle groups. Here we tested the efficacy of FES in counteracting muscle loss and improve function in the lower extremities of a 55-year-old female patient which was diagnosed with CCD at the age of 44. Genetic screening of the RyR1 gene identified a missense mutation (c.7354C>T) in exon 46 resulting in an amino acid substitution (p.R2452W) and a duplication (c.12853_12864dup12) in exon 91. The patient was treated with FES for 26 months and subjected before, during, and after training to a series of functional and structural assessments: measurement of maximum isometric force of leg extensor muscles, magnetic resonance imaging, a complete set of functional tests to assess mobility in activities of daily living, and analysis of muscle biopsies by histology and electron microscopy. All results point to an improvement in muscle structure and function induced by FES suggesting that this approach could be considered as an additional supportive measure to maintain/improve muscle function (and possibly reduce muscle loss) in CCD patients.
RESUMO
Biological roles of obscurin and its close homolog Obsl1 (obscurin-like 1) have been enigmatic. While obscurin is highly expressed in striated muscles, Obsl1 is found ubiquitously. Accordingly, obscurin mutations have been linked to myopathies, whereas mutations in Obsl1 result in 3M-growth syndrome. To further study unique and redundant functions of these closely related proteins, we generated and characterized Obsl1 knockouts. Global Obsl1 knockouts are embryonically lethal. In contrast, skeletal muscle-specific Obsl1 knockouts show a benign phenotype similar to obscurin knockouts. Only deletion of both proteins and removal of their functional redundancy revealed their roles for sarcolemmal stability and sarcoplasmic reticulum organization. To gain unbiased insights into changes to the muscle proteome, we analyzed tibialis anterior and soleus muscles by mass spectrometry, uncovering additional changes to the muscle metabolism. Our analyses suggest that all obscurin protein family members play functions for muscle membrane systems.
Assuntos
Proteínas do Citoesqueleto/metabolismo , Músculo Esquelético/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Fatores de Troca de Nucleotídeo Guanina Rho/metabolismo , Animais , Proteínas do Citoesqueleto/deficiência , Proteínas do Citoesqueleto/genética , Feminino , Humanos , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Knockout , Desenvolvimento Muscular/genética , Desenvolvimento Muscular/fisiologia , Músculo Esquelético/crescimento & desenvolvimento , Proteínas Serina-Treonina Quinases/genética , Proteoma/metabolismo , Fatores de Troca de Nucleotídeo Guanina Rho/genética , Sarcoglicanas/metabolismo , Sarcolema/metabolismo , Retículo Sarcoplasmático/metabolismoRESUMO
Adult stem cells represent a fundamental biological system that has fascinated scientists over the last decades, and are currently the subject of a large number of studies aimed at better defining the properties of these cells, with a prominent focus on improving their application in regenerative medicine. One of the most used adult stem cells in clinical trials are mesenchymal stem cells (MSCs), which are multipotent cells able to differentiate into mature cells of mesodermal lineages. Following the initial studies on MSCs isolated from bone marrow, similar cells were also isolated from a variety of fetal and adult human tissues. Initially considered as identical and equipotent, MSCs from tissues other than bone marrow actually display differences in terms of their plastic abilities, which can be ascribed to the tissue of origin and/or to the procedures used for their isolation. Moreover, results from additional studies suggest that cultured MSCs represent the in vitro version of a subset of in vivo resident cells localized in the perivascular environment. In this review, we will focus our attention on MSCs from tissues other than bone marrow, their in vivo localization and their current applications in clinics.
Assuntos
Células-Tronco Adultas/citologia , Células-Tronco Mesenquimais/citologia , Medicina Regenerativa/métodos , Animais , Humanos , Engenharia Tecidual/métodosRESUMO
INTRODUCTION: Obscurin, a giant protein of striated muscles, is emerging as an important player in a wide range of processes including myofibril assembly and maintenance, muscle protein degradation and intracellular signaling. Accordingly, obscurin participates to the mechanisms by which muscles adapt to physiological requirements or to pathological cues associated with cardiac and skeletal muscle diseases. Areas covered: The structure of the different obscurin isoforms identified so far, their tissue distribution and the most recent findings on obscurin in invertebrates and mammals will be reviewed. We will provide a synopsis of known molecular interactions between obscurin and other proteins and the biological relevance of these interactions for striated muscle function. The involvement of obscurin in protein degradation mechanisms and intracellular signaling will be also discussed along with initial evidence of a role of obscurin in the pathophysiology of human diseases. Expert opinion: Although still much remains to be discovered about the role of obscurin either as a structural component of the sarcomere or as a mediator of signaling pathways within muscle cells, it can be envisioned that this protein represents an interesting novel pharmacological target for the prevention and treatment of cardiac and skeletal muscle diseases.