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Braun JL, Fajardo VA. Spaceflight increases sarcoplasmic reticulum Ca 2+ leak and this cannot be counteracted with BuOE treatment. NPJ Microgravity 2024; 10:78. [PMID: 39030182 DOI: 10.1038/s41526-024-00419-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Accepted: 07/11/2024] [Indexed: 07/21/2024] Open
Abstract
Spending time in a microgravity environment is known to cause significant skeletal muscle atrophy and weakness via muscle unloading, which can be partly attributed to Ca2+ dysregulation. The sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) pump is responsible for bringing Ca2+ from the cytosol into its storage site, the sarcoplasmic reticulum (SR), at the expense of ATP. We have recently demonstrated that, in the soleus of space-flown mice, the Ca2+ uptake ability of the SERCA pump is severely impaired and this may be attributed to increases in reactive oxygen/nitrogen species (RONS), to which SERCA is highly susceptible. The purpose of this study was therefore to investigate whether treatment with the antioxidant, Manganese(III) meso-tetrakis(N-n-butoxyethylpyridinium-2-yl)porphyrin, MnTnBuOE-2-PyP5+ (BuOE), could attenuate muscle atrophy and SERCA dysfunction. We received soleus muscles from the rodent research 18 mission which had male mice housed on the international space station for 35 days and treated with either saline or BuOE. Spaceflight significantly reduced the soleus:body mass ratio and significantly increased SERCA's ionophore ratio, a measure of SR Ca2+ leak, and 4-HNE content (marker of RONS), none of which could be rescued by BuOE treatment. In conclusion, we find that spaceflight induces significant soleus muscle atrophy and SR Ca2+ leak that cannot be counteracted with BuOE treatment. Future work should investigate alternative therapeutics that are specifically aimed at increasing SERCA activation or reducing Ca2+ leak.
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Affiliation(s)
- Jessica L Braun
- Department of Kinesiology, Brock University, St. Catharines, ON, Canada
- Centre for Bone and Muscle Health, Brock University, St. Catharines, ON, Canada
| | - Val A Fajardo
- Department of Kinesiology, Brock University, St. Catharines, ON, Canada.
- Centre for Bone and Muscle Health, Brock University, St. Catharines, ON, Canada.
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2
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Protasi F, Girolami B, Roccabianca S, Rossi D. Store-operated calcium entry: From physiology to tubular aggregate myopathy. Curr Opin Pharmacol 2023; 68:102347. [PMID: 36608411 DOI: 10.1016/j.coph.2022.102347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 11/30/2022] [Accepted: 12/04/2022] [Indexed: 01/06/2023]
Abstract
Store-Operated Ca2+ entry (SOCE) is recognized as a key mechanism in muscle physiology necessary to refill intracellular Ca2+ stores during sustained muscle activity. For many years the cell structures expected to mediate SOCE in skeletal muscle fibres remained unknown. Recently, the identification of Ca2+ Entry Units (CEUs) in exercised muscle fibres opened new insights into the role of extracellular Ca2+ in muscle contraction and, more generally, in intracellular Ca2+ homeostasis. Accordingly, intracellular Ca2+ unbalance due to alterations in SOCE strictly correlates with muscle disfunction and disease. Mutations in proteins involved in SOCE (STIM1, ORAI1, and CASQ1) have been linked to tubular aggregate myopathy (TAM), a disease that causes muscle weakness and myalgia and is characterized by a typical accumulation of highly ordered and packed membrane tubules originated from the sarcoplasmic reticulum (SR). Achieving a full understanding of the molecular pathways activated by alterations in Ca2+ entry mechanisms is a necessary step to design effective therapies for human SOCE-related disorders.
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Affiliation(s)
- Feliciano Protasi
- CAST, Center for Advanced Studies and Technology; University G. d'Annunzio of Chieti-Pescara, I-66100, Italy; DMSI, Department of Medicine and Aging Sciences; University G. d'Annunzio of Chieti-Pescara, I-66100, Italy
| | - Barbara Girolami
- CAST, Center for Advanced Studies and Technology; University G. d'Annunzio of Chieti-Pescara, I-66100, Italy; DMSI, Department of Medicine and Aging Sciences; University G. d'Annunzio of Chieti-Pescara, I-66100, Italy
| | - Sara Roccabianca
- DMMS, Department of Molecular and Developmental Medicine; University of Siena, I-53100, Siena Italy
| | - Daniela Rossi
- DMMS, Department of Molecular and Developmental Medicine; University of Siena, I-53100, Siena Italy.
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3
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Chan S, Kueh SLL, Morley JW, Head SI. Sarcoplasmic reticulum calcium handling in unbranched, immediately post-necrotic fast-twitch mdx fibres is similar to wild-type littermates. Exp Physiol 2022; 107:601-614. [PMID: 35471703 DOI: 10.1113/ep090057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 04/19/2022] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS Central question: What are the early effects of dystrophin deficiency on SR Ca2+ handling in the mdx mouse? MAIN FINDING In the mdx mouse, Ca2+ handling by the SR is little affected by the absence of dystrophin when looking at fibres without branches that have just regenerated following massive myonecrosis. This has important implications for our understanding of Ca2+ pathology in the mdx mouse. ABSTRACT There is a variety of results in the literature regarding the effects of dystrophin deficiency on the Ca2+ -handling properties of the SR in mdx mice, an animal model of Duchenne muscular dystrophy. One possible source of variation is the presence of branched fibres. Fibre branching, a consequence of degenerative-regenerative processes such as muscular dystrophy, has in itself a significant influence on the function of the SR. In our present study we attempt to detect early effects of dystrophin deficiency on SR Ca2+ handling by using unbranched fibres from the immediate post-necrotic stage in mdx mice (just regenerated following massive necrosis). Using kinetically-corrected Fura-2 fluorescence signals measured during twitch and tetanus, we analysed the amplitude, rise time and decay time of Δ[Ca2+ ]i in unfatigued and fatigued fibres. Decay was also resolved into SR pump and SR leak components. Fibres from mdx mice were similar in all respects to fibres from wt littermates apart from: (i) a smaller amplitude of the initial spike of Δ[Ca2+ ]i during a tetanus; and (ii) a mitigation of the fall in Δ[Ca2+ ]i amplitude during the course of fatigue. Our findings suggest that the early effects of a loss of dystrophin on SR Ca2+ handling in mdx mice are subtle, and emphasise the importance of distinguishing between Ca2+ pathology that is due to lack of dystrophin and Ca2+ pathology that is due to muscle degeneration. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Stephen Chan
- School of Medicine, Western Sydney University, Campbelltown, New South Wales, Australia.,Department of Physiology, Faculty of Science, Mahidol University, Ratchatewi, Bangkok, Thailand
| | - Sindy L L Kueh
- School of Medicine, Western Sydney University, Campbelltown, New South Wales, Australia
| | - John W Morley
- School of Medicine, Western Sydney University, Campbelltown, New South Wales, Australia
| | - Stewart I Head
- School of Medicine, Western Sydney University, Campbelltown, New South Wales, Australia
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4
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Uchimura T, Sakurai H. Orai1-STIM1 Regulates Increased Ca 2+ Mobilization, Leading to Contractile Duchenne Muscular Dystrophy Phenotypes in Patient-Derived Induced Pluripotent Stem Cells. Biomedicines 2021; 9:biomedicines9111589. [PMID: 34829817 PMCID: PMC8615222 DOI: 10.3390/biomedicines9111589] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 10/24/2021] [Accepted: 10/26/2021] [Indexed: 11/21/2022] Open
Abstract
Ca2+ overload is one of the factors leading to Duchenne muscular dystrophy (DMD) pathogenesis. However, the molecular targets of dystrophin deficiency-dependent Ca2+ overload and the correlation between Ca2+ overload and contractile DMD phenotypes in in vitro human models remain largely elusive. In this study, we utilized DMD patient-derived induced pluripotent stem cells (iPSCs) to differentiate myotubes using doxycycline-inducible MyoD overexpression, and searched for a target molecule that mediates dystrophin deficiency-dependent Ca2+ overload using commercially available chemicals and siRNAs. We found that several store-operated Ca2+ channel (SOC) inhibitors effectively prevented Ca2+ overload and identified that STIM1–Orai1 is a molecular target of SOCs. These findings were further confirmed by demonstrating that STIM1–Orai1 inhibitors, CM4620, AnCoA4, and GSK797A, prevented Ca2+ overload in dystrophic myotubes. Finally, we evaluated CM4620, AnCoA4, and GSK7975A activities using a previously reported model recapitulating a muscle fatigue-like decline in contractile performance in DMD. All three chemicals ameliorated the decline in contractile performance, indicating that modulating STIM1–Orai1-mediated Ca2+ overload is effective in rescuing contractile phenotypes. In conclusion, SOCs are major contributors to dystrophin deficiency-dependent Ca2+ overload through STIM1–Orai1 as molecular mediators. Modulating STIM1–Orai1 activity was effective in ameliorating the decline in contractile performance in DMD.
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Affiliation(s)
- Tomoya Uchimura
- Center for iPSC Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
- Takeda-CiRA Joint Program, Fujisawa 251-8555, Japan
- Correspondence: (T.U.); (H.S.)
| | - Hidetoshi Sakurai
- Center for iPSC Cell Research and Application (CiRA), Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
- Takeda-CiRA Joint Program, Fujisawa 251-8555, Japan
- Correspondence: (T.U.); (H.S.)
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5
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Zabłocka B, Górecki DC, Zabłocki K. Disrupted Calcium Homeostasis in Duchenne Muscular Dystrophy: A Common Mechanism behind Diverse Consequences. Int J Mol Sci 2021; 22:11040. [PMID: 34681707 PMCID: PMC8537421 DOI: 10.3390/ijms222011040] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Revised: 09/30/2021] [Accepted: 10/09/2021] [Indexed: 12/12/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) leads to disability and death in young men. This disease is caused by mutations in the DMD gene encoding diverse isoforms of dystrophin. Loss of full-length dystrophins is both necessary and sufficient for causing degeneration and wasting of striated muscles, neuropsychological impairment, and bone deformities. Among this spectrum of defects, abnormalities of calcium homeostasis are the common dystrophic feature. Given the fundamental role of Ca2+ in all cells, this biochemical alteration might be underlying all the DMD abnormalities. However, its mechanism is not completely understood. While abnormally elevated resting cytosolic Ca2+ concentration is found in all dystrophic cells, the aberrant mechanisms leading to that outcome have cell-specific components. We probe the diverse aspects of calcium response in various affected tissues. In skeletal muscles, cardiomyocytes, and neurons, dystrophin appears to serve as a scaffold for proteins engaged in calcium homeostasis, while its interactions with actin cytoskeleton influence endoplasmic reticulum organisation and motility. However, in myoblasts, lymphocytes, endotheliocytes, and mesenchymal and myogenic cells, calcium abnormalities cannot be clearly attributed to the loss of interaction between dystrophin and the calcium toolbox proteins. Nevertheless, DMD gene mutations in these cells lead to significant defects and the calcium anomalies are a symptom of the early developmental phase of this pathology. As the impaired calcium homeostasis appears to underpin multiple DMD abnormalities, understanding this alteration may lead to the development of new therapies. In fact, it appears possible to mitigate the impact of the abnormal calcium homeostasis and the dystrophic phenotype in the total absence of dystrophin. This opens new treatment avenues for this incurable disease.
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Affiliation(s)
- Barbara Zabłocka
- Molecular Biology Unit, Mossakowski Medical Research Institute Polish Academy of Sciences, 02-106 Warsaw, Poland;
| | - Dariusz C. Górecki
- School of Pharmacy and Biomedical Sciences, University of Portsmouth, St Michael’s Building, White Swan Road, Portsmouth PO1 2DT, UK
- Military Institute of Hygiene and Epidemiology, 01-163 Warsaw, Poland
| | - Krzysztof Zabłocki
- Laboratory of Cellular Metabolism, Nencki Institute of Experimental Biology Polish Academy of Sciences, 02-093 Warsaw, Poland
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6
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Watanabe D, Wada M. Orthograde signal of dihydropyridine receptor increases Ca 2+ leakage after repeated contractions in rat fast-twitch muscles in vivo. Am J Physiol Cell Physiol 2021; 320:C806-C821. [PMID: 33596151 DOI: 10.1152/ajpcell.00364.2020] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 02/10/2021] [Indexed: 11/22/2022]
Abstract
The purpose of this study was to investigate the mechanism underlying sarcoplasmic reticulum (SR) Ca2+ leakage after in vivo contractions. Rat gastrocnemius muscles were electrically stimulated in vivo, and then mechanically skinned fibers and SR microsomes were prepared from the muscles excised 30 min after repeated high-intensity contractions. The mechanically skinned fibers maintained the interaction between dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs), whereas the SR microsomes did not. Interestingly, skinned fibers from the stimulated muscles showed increased SR Ca2+ leakage, whereas Ca2+ leakage decreased in SR microsomes from the stimulated muscles. To enhance the orthograde signal of DHPRs, SR Ca2+ leakage in the skinned fiber was measured 1) under a continuously depolarized condition and 2) in the presence of nifedipine. As a result, in either of the two conditions, SR Ca2+ leakage in the rested fibers reached a level similar to that in the stimulated fibers. Furthermore, the increased SR Ca2+ leakage from the stimulated fibers was alleviated by treatment with 1 mM tetracaine (Tet) but not by treatment with 3 mM free Mg2+ (3 Mg). Tet exerted a greater inhibitory effect on the DHPR signal to RyR than 3 Mg, although their inhibitory effects on RyR were almost similar. These results suggest that the increased Ca2+ leakage after muscle contractions is mainly caused by the orthograde signal of DHPRs to RyRs.
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Affiliation(s)
- Daiki Watanabe
- Graduate School of Humanities and Social Sciences, Hiroshima University, Hiroshima, Japan
| | - Masanobu Wada
- Graduate School of Humanities and Social Sciences, Hiroshima University, Hiroshima, Japan
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7
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Mareedu S, Million ED, Duan D, Babu GJ. Abnormal Calcium Handling in Duchenne Muscular Dystrophy: Mechanisms and Potential Therapies. Front Physiol 2021; 12:647010. [PMID: 33897454 PMCID: PMC8063049 DOI: 10.3389/fphys.2021.647010] [Citation(s) in RCA: 54] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 03/02/2021] [Indexed: 12/18/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked muscle-wasting disease caused by the loss of dystrophin. DMD is associated with muscle degeneration, necrosis, inflammation, fatty replacement, and fibrosis, resulting in muscle weakness, respiratory and cardiac failure, and premature death. There is no curative treatment. Investigations on disease-causing mechanisms offer an opportunity to identify new therapeutic targets to treat DMD. An abnormal elevation of the intracellular calcium (Cai2+) concentration in the dystrophin-deficient muscle is a major secondary event, which contributes to disease progression in DMD. Emerging studies have suggested that targeting Ca2+-handling proteins and/or mechanisms could be a promising therapeutic strategy for DMD. Here, we provide an updated overview of the mechanistic roles the sarcolemma, sarcoplasmic/endoplasmic reticulum, and mitochondria play in the abnormal and sustained elevation of Cai2+ levels and their involvement in DMD pathogenesis. We also discuss current approaches aimed at restoring Ca2+ homeostasis as potential therapies for DMD.
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Affiliation(s)
- Satvik Mareedu
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, Rutgers University, Newark, NJ, United States
| | - Emily D Million
- Department of Molecular Microbiology and Immunology, The University of Missouri, Columbia, MO, United States
| | - Dongsheng Duan
- Department of Molecular Microbiology and Immunology, The University of Missouri, Columbia, MO, United States.,Department of Biomedical, Biological & Chemical Engineering, The University of Missouri, Columbia, MO, United States
| | - Gopal J Babu
- Department of Cell Biology and Molecular Medicine, New Jersey Medical School, Rutgers University, Newark, NJ, United States
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8
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Ruggieri S, Viggiano L, Annese T, Rubolino C, Gerbino A, De Zio R, Corsi P, Tamma R, Ribatti D, Errede M, Operto F, Margari L, Resta N, Di Tommaso S, Rosati J, Trojano M, Nico B. DP71 and SERCA2 alteration in human neurons of a Duchenne muscular dystrophy patient. Stem Cell Res Ther 2019; 10:29. [PMID: 30646960 PMCID: PMC6334379 DOI: 10.1186/s13287-018-1125-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2018] [Revised: 11/27/2018] [Accepted: 12/25/2018] [Indexed: 01/16/2023] Open
Abstract
Cognitive deficit has been identified in one third of patients affected by Duchenne Muscular Dystrophy, primarily attributed to loss of the short Dp71 dystrophin, the major brain dystrophin isoform. In this study, we investigated for the first time the Dp71 and Dp71-associated proteins cellular localization and expression in human neurons obtained by differentiation from induced pluripotent stem cell line of a patient affected by cognitive impairment. We found structural and molecular alterations in both pluripotent stem cell and derived neurons, reduced Dp71 expression, and a Ca2+ cytoplasmic overload in neurons coupled with increased expression of the SERCA2 pump in the dystrophic neurons. These results suggest that the reduction of Dp71 protein in the Duchenne muscular dystrophy neurons leads to alterations in SERCA2 and to elevated cytosolic Ca2+ concentration with consequent potential disruption of the dystrophin proteins and Dp71-associated proteins.
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Affiliation(s)
- Simona Ruggieri
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | | | - Tiziana Annese
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | | | - Andrea Gerbino
- Department of Bioscience, Biotechnology and Biopharmaceutics, University of Bari, Bari, Italy
| | - Roberta De Zio
- Department of Bioscience, Biotechnology and Biopharmaceutics, University of Bari, Bari, Italy
| | - Patrizia Corsi
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Roberto Tamma
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Domenico Ribatti
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Mariella Errede
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Francesca Operto
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Lucia Margari
- Department of Biomedical Sciences and Human Oncology, Unit of Internal Medicine "Guido Baccelli", University of Bari Medical School, Bari, Italy
| | - Nicoletta Resta
- Division of Medical Genetics, Department of Biomedical Sciences and Human Oncology (DIMO), University of Bari Medical School, Bari, Italy
| | - Silvia Di Tommaso
- Division of Medical Genetics, Department of Biomedical Sciences and Human Oncology (DIMO), University of Bari Medical School, Bari, Italy
| | - Jessica Rosati
- Cellular Reprogramming Unit, IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy
| | - Maria Trojano
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy
| | - Beatrice Nico
- Department of Basic Medical Sciences, Neurosciences and Sensory Organs, University of Bari Medical School, Bari, Italy.
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10
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A study of the mechanisms of excitation–contraction coupling in frog skeletal muscle based on measurements of [Ca2+] transients inside the sarcoplasmic reticulum. J Muscle Res Cell Motil 2018; 39:41-60. [DOI: 10.1007/s10974-018-9497-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 08/16/2018] [Indexed: 10/28/2022]
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11
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Allard B. From excitation to intracellular Ca 2+ movements in skeletal muscle: Basic aspects and related clinical disorders. Neuromuscul Disord 2018; 28:394-401. [DOI: 10.1016/j.nmd.2018.03.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Revised: 02/19/2018] [Accepted: 03/05/2018] [Indexed: 01/18/2023]
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12
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Pauly M, Angebault-Prouteau C, Dridi H, Notarnicola C, Scheuermann V, Lacampagne A, Matecki S, Fauconnier J. ER stress disturbs SR/ER-mitochondria Ca 2+ transfer: Implications in Duchenne muscular dystrophy. Biochim Biophys Acta Mol Basis Dis 2017. [PMID: 28625916 DOI: 10.1016/j.bbadis.2017.06.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Besides its role in calcium (Ca2+) homeostasis, the sarco-endoplamic reticulum (SR/ER) controls protein folding and is tethered to mitochondria. Under pathophysiological conditions the unfolded protein response (UPR) is associated with disturbance in SR/ER-mitochondria crosstalk. Here, we investigated whether ER stress altered SR/ER-mitochondria links, Ca2+ handling and muscle damage in WT (Wild Type) and mdx mice, the murine model of Duchenne Muscular Dystrophy (DMD). In WT mice, the SR/ER-mitochondria links were decreased in isolated FDB muscle fibers after injection of ER stress activator tunicamycin (TM). Ca2+ imaging revealed an increase of cytosolic Ca2+ transient and a decrease of mitochondrial Ca2+ uptake. The force generating capacity of muscle dropped after TM. This impaired contractile function was accompanied by an increase in autophagy markers and calpain-1 activation. Conversely, ER stress inhibitors restored SR/ER-mitochondria links, mitochondrial Ca2+ uptake and improved diaphragm contractility in mdx mice. Our findings demonstrated that ER stress-altered SR/ER-mitochondria links, disturbed Ca2+ handling and muscle function in WT and mdx mice. Thus, ER stress may open up a prospect of new therapeutic targets in DMD.
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Affiliation(s)
- Marion Pauly
- Inserm U1055, Hypoxie et Physiopathologies, Université Grenoble Alpes, Grenoble, France; Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | | | - Haikel Dridi
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | - Cécile Notarnicola
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | - Valérie Scheuermann
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | - Alain Lacampagne
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | - Stefan Matecki
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France
| | - Jérémy Fauconnier
- Inserm U1046, UMR CNRS 9214, Université Montpellier, CHRU Montpellier, Montpellier, France.
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13
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Abstract
The role of cytosolic Ca(2+) on the kinetics of Inositol 1,4,5-triphosphate receptors (IP3Rs) and on the dynamics of IP3R-mediated Ca(2+) signals has been studied at large both experimentally and by modeling. The role of luminal Ca(2+) has not been investigated with that much detail although it has been found that it is relevant for signal termination in the case of Ca(2+) release through ryanodine receptors. In this work we present the results of observing the dynamics of luminal and cytosolic Ca(2+) simultaneously in Xenopus laevis oocytes. Combining observations and modeling we conclude that there is a rapid mechanism that guarantees the availability of free Ca(2+) in the lumen even when a relatively large Ca(2+) release is evoked. Comparing the dynamics of cytosolic and luminal Ca(2+) during a release, we estimate that they are consistent with a 80% of luminal Ca(2+) being buffered. The rapid availability of free luminal Ca(2+) correlates with the observation that the lumen occupies a considerable volume in several regions across the images.
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14
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Allen DG, Whitehead NP, Froehner SC. Absence of Dystrophin Disrupts Skeletal Muscle Signaling: Roles of Ca2+, Reactive Oxygen Species, and Nitric Oxide in the Development of Muscular Dystrophy. Physiol Rev 2016; 96:253-305. [PMID: 26676145 DOI: 10.1152/physrev.00007.2015] [Citation(s) in RCA: 272] [Impact Index Per Article: 34.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Dystrophin is a long rod-shaped protein that connects the subsarcolemmal cytoskeleton to a complex of proteins in the surface membrane (dystrophin protein complex, DPC), with further connections via laminin to other extracellular matrix proteins. Initially considered a structural complex that protected the sarcolemma from mechanical damage, the DPC is now known to serve as a scaffold for numerous signaling proteins. Absence or reduced expression of dystrophin or many of the DPC components cause the muscular dystrophies, a group of inherited diseases in which repeated bouts of muscle damage lead to atrophy and fibrosis, and eventually muscle degeneration. The normal function of dystrophin is poorly defined. In its absence a complex series of changes occur with multiple muscle proteins showing reduced or increased expression or being modified in various ways. In this review, we will consider the various proteins whose expression and function is changed in muscular dystrophies, focusing on Ca(2+)-permeable channels, nitric oxide synthase, NADPH oxidase, and caveolins. Excessive Ca(2+) entry, increased membrane permeability, disordered caveolar function, and increased levels of reactive oxygen species are early changes in the disease, and the hypotheses for these phenomena will be critically considered. The aim of the review is to define the early damage pathways in muscular dystrophy which might be appropriate targets for therapy designed to minimize the muscle degeneration and slow the progression of the disease.
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Affiliation(s)
- David G Allen
- Sydney Medical School & Bosch Institute, University of Sydney, New South Wales, Australia; and Department of Physiology & Biophysics, University of Washington, Seattle, Washington
| | - Nicholas P Whitehead
- Sydney Medical School & Bosch Institute, University of Sydney, New South Wales, Australia; and Department of Physiology & Biophysics, University of Washington, Seattle, Washington
| | - Stanley C Froehner
- Sydney Medical School & Bosch Institute, University of Sydney, New South Wales, Australia; and Department of Physiology & Biophysics, University of Washington, Seattle, Washington
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15
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Robin G, Allard B. Voltage-gated Ca(2+) influx through L-type channels contributes to sarcoplasmic reticulum Ca(2+) loading in skeletal muscle. J Physiol 2015; 593:4781-97. [PMID: 26383921 DOI: 10.1113/jp270252] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 09/08/2015] [Indexed: 12/15/2022] Open
Abstract
Muscle contraction is triggered by Ca(2+) ions released from the sarcoplasmic reticulum (SR) in response to depolarization of skeletal muscle fibres. Muscle activation is also associated with a voltage-activated trans-sarcolemmal Ca(2+) influx early identified as a current flowing through L-type Ca(2+) channels. Because removal of external Ca(2+) does not impede fibres from contracting, a negligible role was given to this voltage-activated Ca(2+) entry, although the decline of Ca(2+) release is more pronounced in the absence of Ca(2+) during long-lasting activation. Furthermore, it is not clearly established whether Ca(2+) exclusively flows through L-type channels or in addition through a parallel voltage-activated pathway distinct from L-type channels. Here, by monitoring the quenching of fura-2 fluorescence resulting from Mn(2+) influx in voltage-controlled mouse and zebrafish isolated muscle fibres, we show that the L-type current is the only contributor to Ca(2+) influx during long-lasting depolarizations in skeletal muscle. Calibration of the Mn(2+) quenching signal allowed us to estimate a mean Mn(2+) current of 0.31 ± 0.06 A F(-1) flowing through L-type channels during a train of action potentials. Measurements of SR Ca(2+) changes with fluo-5N in response to depolarization revealed that an elevated voltage-activated Ca(2+) current potentiated SR Ca(2+) loading and addition of external Mn(2+) produced quenching of fluo-5N in the SR, indicating that voltage-activated Ca(2+) /Mn(2+) influx contributes to SR Ca(2+) /Mn(2+) loading.
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Affiliation(s)
- Gaëlle Robin
- Université de Lyon, Université Lyon 1, CNRS UMR 5534, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Villeurbanne, France
| | - Bruno Allard
- Université de Lyon, Université Lyon 1, CNRS UMR 5534, Centre de Génétique et de Physiologie Moléculaire et Cellulaire, Villeurbanne, France
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16
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Blat Y, Blat S. Drug Discovery of Therapies for Duchenne Muscular Dystrophy. ACTA ACUST UNITED AC 2015; 20:1189-203. [PMID: 25975656 DOI: 10.1177/1087057115586535] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 04/21/2015] [Indexed: 01/16/2023]
Abstract
Duchenne muscular dystrophy (DMD) is a genetic, lethal, muscle disorder caused by the loss of the muscle protein, dystrophin, leading to progressive loss of muscle fibers and muscle weakness. Drug discovery efforts targeting DMD have used two main approaches: (1) the restoration of dystrophin expression or the expression of a compensatory protein, and (2) the mitigation of downstream pathological mechanisms, including dysregulated calcium homeostasis, oxidative stress, inflammation, fibrosis, and muscle ischemia. The aim of this review is to introduce the disease, its pathophysiology, and the available research tools to a drug discovery audience. This review will also detail the most promising therapies that are currently being tested in clinical trials or in advanced preclinical models.
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Affiliation(s)
| | - Shachar Blat
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA
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17
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Abstract
Muscular dystrophies are a group of diseases characterised by the primary wasting of skeletal muscle, which compromises patient mobility and in the most severe cases originate a complete paralysis and premature death. Existing evidence implicates calcium dysregulation as an underlying crucial event in the pathophysiology of several muscular dystrophies, such as dystrophinopathies, calpainopathies or myotonic dystrophy among others. Duchenne muscular dystrophy is the most frequent myopathy in childhood, and calpainopathy or LGMD2A is the most common form of limb-girdle muscular dystrophy, whereas myotonic dystrophy is the most frequent inherited muscle disease worldwide. In this review, we summarise recent advances in our understanding of calcium ion cycling through the sarcolemma, the sarcoplasmic reticulum and mitochondria, and its involvement in the pathogenesis of these dystrophies. We also discuss some of the clinical implications of recent findings regarding Ca2+ handling as well as novel approaches to treat muscular dystrophies targeting Ca2+ regulatory proteins.
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18
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Brault JJ, Pizzimenti NM, Dentel JN, Wiseman RW. Selective inhibition of ATPase activity during contraction alters the activation of p38 MAP kinase isoforms in skeletal muscle. J Cell Biochem 2014; 114:1445-55. [PMID: 23296747 DOI: 10.1002/jcb.24486] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Accepted: 12/18/2012] [Indexed: 11/10/2022]
Abstract
Muscle contractions strongly activate p38 MAP kinases, but the precise contraction-associated sarcoplasmic event(s) (e.g., force production, energetic demands, and/or calcium cycling) that activate these kinases are still unclear. We tested the hypothesis that during contraction the phosphorylation of p38 isoforms is sensitive to the increase in ATP demand relative to ATP supply. Energetic demands were inhibited using N-benzyl-p-toluene sulphonamide (BTS, type II actomyosin) and cyclopiazonic acid (CPA, SERCA). Extensor digitorum longus muscles from Swiss Webster mice were incubated in Ringer's solution (37°C) with or without inhibitors and then stimulated at 10 Hz for 15 min. Muscles were immediately freeze-clamped for metabolite and Western blot analysis. BTS and BTS + CPA treatment decreased force production by 85%, as measured by the tension time integral, while CPA alone potentiated force by 310%. In control muscles, contractions resulted in a 73% loss of ATP content and a concomitant sevenfold increase in IMP content, a measure of sustained energetic imbalance. BTS or CPA treatment lessened the loss of ATP, but BTS + CPA treatment completely eliminated the energetic imbalance since ATP and IMP levels were nearly equal to those of non-stimulated muscles. The independent inhibition of cytosolic ATPase activities had no effect on contraction-induced p38 MAPK phosphorylation, but combined treatment prevented the increase in phosphorylation of the γ isoform while the α/β isoforms unaffected. These observations suggest that an energetic signal may trigger phosphorylation of the p38γ isoform and also may explain how contractions differentially activate signaling pathways.
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Affiliation(s)
- Jeffrey J Brault
- Department of Kinesiology, East Carolina University, Greenville, North Carolina, USA
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19
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Robin G, Allard B. Major contribution of sarcoplasmic reticulum Ca(2+) depletion during long-lasting activation of skeletal muscle. ACTA ACUST UNITED AC 2014; 141:557-65. [PMID: 23630339 PMCID: PMC3639577 DOI: 10.1085/jgp.201310957] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Depolarization of skeletal muscle fibers induces sarcoplasmic reticulum (SR) Ca2+ release and contraction that progressively decline while depolarization is maintained. Voltage-dependent inactivation of SR Ca2+ release channels and SR Ca2+ depletion are the two processes proposed to explain the decline of SR Ca2+ release during long-lasting depolarizations. However, the relative contribution of these processes, especially under physiological conditions of activation, is not clearly established. Using Fura-2 and Fluo-5N to monitor cytosolic and SR Ca2+ changes, respectively, in voltage-controlled mouse muscle fibers, we show that 2-min conditioning depolarizations reduce voltage-activated cytosolic Ca2+ signals with a V1/2 of −53 mV but also induce SR Ca2+ depletion that decreased the releasable pool of Ca2+ with the same voltage sensitivity. In contrast, measurement of SR Ca2+ changes indicated that SR Ca2+ release channels were inactivated after SR had been depleted and in response to much higher depolarizations with a V1/2 of −13 mV. In response to trains of action potentials, cytosolic Ca2+ signals decayed with time, whereas SR Ca2+ changes remained stable over 1-min stimulation, demonstrating that SR Ca2+ depletion is exclusively responsible for the decline of SR Ca2+ release under physiological conditions of excitation. These results suggest that previous studies using steady-state inactivation protocols to investigate the voltage dependence of Ca2+ release inactivation in fact probed the voltage dependence of SR Ca2+ depletion, and that SR Ca2+ depletion is the only process that leads to Ca2+ release decline during continuous stimulation of skeletal muscle.
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Affiliation(s)
- Gaëlle Robin
- Centre National de la Recherche Scientifique UMR 5534, Centre de Génétique et de Physiologie Moléculaires et Cellulaires, Université Lyon 1, 69622 Villeurbanne, France
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20
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Melzer W. Skeletal muscle fibers: Inactivated or depleted after long depolarizations? ACTA ACUST UNITED AC 2014; 141:517-20. [PMID: 23630336 PMCID: PMC3639573 DOI: 10.1085/jgp.201310997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Werner Melzer
- Institute of Applied Physiology, Ulm University, D-89081 Ulm, Germany.
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Ramadasan-Nair R, Gayathri N, Mishra S, Sunitha B, Mythri RB, Nalini A, Subbannayya Y, Harsha HC, Kolthur-Seetharam U, Srinivas Bharath MM. Mitochondrial alterations and oxidative stress in an acute transient mouse model of muscle degeneration: implications for muscular dystrophy and related muscle pathologies. J Biol Chem 2013; 289:485-509. [PMID: 24220031 DOI: 10.1074/jbc.m113.493270] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Muscular dystrophies (MDs) and inflammatory myopathies (IMs) are debilitating skeletal muscle disorders characterized by common pathological events including myodegeneration and inflammation. However, an experimental model representing both muscle pathologies and displaying most of the distinctive markers has not been characterized. We investigated the cardiotoxin (CTX)-mediated transient acute mouse model of muscle degeneration and compared the cardinal features with human MDs and IMs. The CTX model displayed degeneration, apoptosis, inflammation, loss of sarcolemmal complexes, sarcolemmal disruption, and ultrastructural changes characteristic of human MDs and IMs. Cell death caused by CTX involved calcium influx and mitochondrial damage both in murine C2C12 muscle cells and in mice. Mitochondrial proteomic analysis at the initial phase of degeneration in the model detected lowered expression of 80 mitochondrial proteins including subunits of respiratory complexes, ATP machinery, fatty acid metabolism, and Krebs cycle, which further decreased in expression during the peak degenerative phase. The mass spectrometry (MS) data were supported by enzyme assays, Western blot, and histochemistry. The CTX model also displayed markers of oxidative stress and a lowered glutathione reduced/oxidized ratio (GSH/GSSG) similar to MDs, human myopathies, and neurogenic atrophies. MS analysis identified 6 unique oxidized proteins from Duchenne muscular dystrophy samples (n = 6) (versus controls; n = 6), including two mitochondrial proteins. Interestingly, these mitochondrial proteins were down-regulated in the CTX model thereby linking oxidative stress and mitochondrial dysfunction. We conclude that mitochondrial alterations and oxidative damage significantly contribute to CTX-mediated muscle pathology with implications for human muscle diseases.
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Cully TR, Launikonis BS. Store-operated Ca²⁺ entry is not required for store refilling in skeletal muscle. Clin Exp Pharmacol Physiol 2013; 40:338-44. [PMID: 23517302 DOI: 10.1111/1440-1681.12078] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Revised: 02/27/2013] [Accepted: 03/03/2013] [Indexed: 11/28/2022]
Abstract
The present review describes store-operated Ca²⁺ entry (SOCE) in skeletal muscle. Fundamental discoveries in the field of skeletal muscle SOCE are described and the techniques that were used to make these. The advantages and limitations in these techniques are discussed to provide a means of questioning and determining the physiological role(s) of SOCE in skeletal muscle. It is concluded that SOCE has little or no role in the filling of the sarcoplasmic reticulum with Ca²⁺ at rest or during a single contracture. It is likely that SOCE is activated during fatigue, although direct measurements of SOCE are lacking and the physiological significance remains uncertain.
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Affiliation(s)
- Tanya R Cully
- School of Biomedical Sciences, The University of Queensland, Brisbane, Qld, Australia
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23
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Schneider JS, Shanmugam M, Gonzalez JP, Lopez H, Gordan R, Fraidenraich D, Babu GJ. Increased sarcolipin expression and decreased sarco(endo)plasmic reticulum Ca2+ uptake in skeletal muscles of mouse models of Duchenne muscular dystrophy. J Muscle Res Cell Motil 2013; 34:349-56. [DOI: 10.1007/s10974-013-9350-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2013] [Accepted: 05/27/2013] [Indexed: 02/02/2023]
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Manno C, Sztretye M, Figueroa L, Allen PD, Ríos E. Dynamic measurement of the calcium buffering properties of the sarcoplasmic reticulum in mouse skeletal muscle. J Physiol 2013; 591:423-42. [PMID: 23148320 PMCID: PMC3577525 DOI: 10.1113/jphysiol.2012.243444] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Accepted: 11/06/2012] [Indexed: 12/25/2022] Open
Abstract
The buffering power, B, of the sarcoplasmic reticulum (SR), ratio of the changes in total and free [Ca(2+)], was determined in fast-twitch mouse muscle cells subjected to depleting membrane depolarization. Changes in total SR [Ca(2+)] were measured integrating Ca(2+) release flux, determined with a cytosolic [Ca(2+)] monitor. Free [Ca(2+)](SR) was measured using the cameleon D4cpv-Casq1. In 34 wild-type (WT) cells average B during the depolarization (ON phase) was 157 (SEM 26), implying that of 157 ions released, 156 were bound inside the SR. B was significantly greater when BAPTA, which increases release flux, was present in the cytosol. B was greater early in the pulse - when flux was greatest - than at its end, and greater in the ON than in the OFF. In 29 Casq1-null cells, B was 40 (3.6). The difference suggests that 75% of the releasable calcium is normally bound to calsequestrin. In the nulls the difference in B between ON and OFF was less than in the WT but still significant. This difference and the associated decay in B during the ON were not artifacts of a slow SR monitor, as they were also found in the WT when [Ca(2+)](SR) was tracked with the fast dye fluo-5N. The calcium buffering power, binding capacity and non-linear binding properties of the SR measured here could be accounted for by calsequestrin at the concentration present in mammalian muscle, provided that its properties were substantially different from those found in solution. Its affinity should be higher, or K(D) lower than the conventionally accepted 1 mm; its cooperativity (n in a Hill fit) should be higher and the stoichiometry of binding should be at the higher end of the values derived in solution. The reduction in B during release might reflect changes in calsequestrin conformation upon calcium loss.
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Affiliation(s)
- Carlo Manno
- Section of Cellular Signaling Department of Molecular Biophysics and Physiology, Rush University School of Medicine, 1750 W. Harrison St, Chicago, IL 60612, USA
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25
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Abstract
There is substantial evidence indicating that disruption of Ca2+ homeostasis and activation of cytosolic proteases play a key role in the pathogenesis and progression of Duchenne Muscular Dystrophy (DMD). However, the exact nature of the Ca2+ deregulation and the Ca2+ signaling pathways that are altered in dystrophic muscles have not yet been resolved. Here we examined the contribution of the store-operated Ca2+ entry (SOCE) for the pathogenesis of DMD. RT-PCR and Western blot found that the expression level of Orai1, the pore-forming unit of SOCE, was significantly elevated in the dystrophic muscles, while parallel increases in SOCE activity and SR Ca2+ storage were detected in adult mdx muscles using Fura-2 fluorescence measurements. High-efficient shRNA probes against Orai1 were delivered into the flexor digitorum brevis muscle in live mice and knockdown of Orai1 eliminated the differences in SOCE activity and SR Ca2+ storage between the mdx and wild type muscle fibers. SOCE activity was repressed by intraperitoneal injection of BTP-2, an Orai1 inhibitor, and cytosolic calpain1 activity in single muscle fibers was measured by a membrane-permeable calpain substrate. We found that BTP-2 injection for 2 weeks significantly reduced the cytosolic calpain1 activity in mdx muscle fibers. Additionally, ultrastructural changes were observed by EM as an increase in the number of triad junctions was identified in dystrophic muscles. Compensatory changes in protein levels of SERCA1, TRP and NCX3 appeared in the mdx muscles, suggesting that comprehensive adaptations occur following altered Ca2+ homeostasis in mdx muscles. Our data indicates that upregulation of the Orai1-mediated SOCE pathway and an overloaded SR Ca2+ store contributes to the disrupted Ca2+ homeostasis in mdx muscles and is linked to elevated proteolytic activity, suggesting that targeting Orai1 activity may be a promising therapeutic approach for the prevention and treatment of muscular dystrophy.
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Affiliation(s)
- Xiaoli Zhao
- Department of Physiology and Biophysics, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
- Division of Pharmacology, College of Pharmacy, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail: (XZ); (NW)
| | - Joseph G. Moloughney
- Department of Physiology and Biophysics, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Sai Zhang
- Department of Physiology and Biophysics, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
| | - Shinji Komazaki
- Department of Anatomy, Saitama Medical University, Saitama, Japan
| | - Noah Weisleder
- Department of Physiology and Biophysics, Robert Wood Johnson Medical School, Piscataway, New Jersey, United States of America
- Department of Physiology & Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail: (XZ); (NW)
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Robin G, Allard B. Dihydropyridine receptors actively control gating of ryanodine receptors in resting mouse skeletal muscle fibres. J Physiol 2012; 590:6027-36. [PMID: 23006480 DOI: 10.1113/jphysiol.2012.237321] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Contraction of skeletal muscle is triggered by the release of Ca(2+) from the sarcoplasmic reticulum (SR) in response to depolarization of the muscle membrane. Depolarization is known to elicit a conformational change of the dihydropyridine receptor (DHPR) in the tubular membrane that controls in a time- and voltage-dependent manner the opening of the ryanodine receptor (RyR), the SR Ca(2+) release channel. At rest, it is assumed that RyRs are kept in a closed state imposed by the repressive action of DHPRs; however, a direct control of the RyR gating by the DHPR has up to now never been demonstrated in resting adult muscle. In this study, we monitored slow changes in SR Ca(2+) content using the Ca(2+) indicator fluo-5N loaded in the SR of voltage-clamped mouse muscle fibres. We first show that external Ca(2+) removal induced a reversible SR Ca(2+) efflux at -80 mV and prevented SR Ca(2+) refilling following depolarization-evoked SR Ca(2+) depletion. The dihydropyridine compound nifedipine induced similar effects. The rate of SR Ca(2+) efflux was also shown to be controlled in a time- and voltage-dependent manner within a membrane potential range more negative than -50 mV. Finally, intracellular addition of ryanodine produced an irreversible SR Ca(2+) efflux and kept the SR in a highly depleted state following depolarization-evoked SR Ca(2+) depletion. The fact that resting SR Ca(2+) efflux is modulated by conformational changes of DHPRs induced by external Ca(2+), nifedipine and voltage demonstrates that DHPRs exert an active control on gating of RyRs in resting skeletal muscle.
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Affiliation(s)
- Gaëlle Robin
- Université Lyon 1, CNRS UMR 5534, Centre de Génétique et de Physiologie Moléculaires et Cellulaires, 43 boulevard du 11 novembre 1918, 69622 Villeurbanne cedex, France
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27
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Altamirano F, López JR, Henríquez C, Molinski T, Allen PD, Jaimovich E. Increased resting intracellular calcium modulates NF-κB-dependent inducible nitric-oxide synthase gene expression in dystrophic mdx skeletal myotubes. J Biol Chem 2012; 287:20876-87. [PMID: 22549782 DOI: 10.1074/jbc.m112.344929] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is a genetic disorder caused by dystrophin mutations, characterized by chronic inflammation and severe muscle wasting. Dystrophic muscles exhibit activated immune cell infiltrates, up-regulated inflammatory gene expression, and increased NF-κB activity, but the contribution of the skeletal muscle cell to this process has been unclear. The aim of this work was to study the pathways that contribute to the increased resting calcium ([Ca(2+)](rest)) observed in mdx myotubes and its possible link with up-regulation of NF-κB and pro-inflammatory gene expression in dystrophic muscle cells. [Ca(2+)](rest) was higher in mdx than in WT myotubes (308 ± 6 versus 113 ± 2 nm, p < 0.001). In mdx myotubes, both the inhibition of Ca(2+) entry (low Ca(2+) solution, Ca(2+)-free solution, and Gd(3+)) and blockade of either ryanodine receptors or inositol 1,4,5-trisphosphate receptors reduced [Ca(2+)](rest). Basal activity of NF-κB was significantly up-regulated in mdx versus WT myotubes. There was an increased transcriptional activity and p65 nuclear localization, which could be reversed when [Ca(2+)](rest) was reduced. Levels of mRNA for TNFα, IL-1β, and IL-6 were similar in WT and mdx myotubes, whereas inducible nitric-oxide synthase (iNOS) expression was increased 5-fold. Reducing [Ca(2+)](rest) using different strategies reduced iNOS gene expression presumably as a result of decreased activation of NF-κB. We propose that NF-κB, modulated by increased [Ca(2+)](rest), is constitutively active in mdx myotubes, and this mechanism can account for iNOS overexpression and the increase in reactive nitrogen species that promote damage in dystrophic skeletal muscle cells.
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Affiliation(s)
- Francisco Altamirano
- From the Centro de Estudios Moleculares de la Célula, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago 8389100, Chile
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