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Guo A, Hall D, Zhang C, Peng T, Miller JD, Kutschke W, Grueter CE, Johnson FL, Lin RZ, Song LS. Molecular Determinants of Calpain-dependent Cleavage of Junctophilin-2 Protein in Cardiomyocytes. J Biol Chem 2015; 290:17946-17955. [PMID: 26063807 DOI: 10.1074/jbc.m115.652396] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2015] [Indexed: 12/29/2022] Open
Abstract
Junctophilin-2 (JP2), a membrane-binding protein that provides a structural bridge between the plasmalemma and sarcoplasmic reticulum, is essential for precise Ca(2+)-induced Ca(2+) release during excitation-contraction coupling in cardiomyocytes. In animal and human failing hearts, expression of JP2 is decreased markedly, but the molecular mechanisms underlying JP2 down-regulation remain incompletely defined. In mouse hearts, ischemia/reperfusion injury resulted in acute JP2 down-regulation, which was attenuated by pretreatment with the calpain inhibitor MDL-28170 or by transgenic overexpression of calpastatin, an endogenous calpain inhibitor. Using a combination of computational analysis to predict calpain cleavage sites and in vitro calpain proteolysis reactions, we identified four putative calpain cleavage sites within JP2 with three N-terminal and one C-terminal cleavage sites. Mutagenesis defined the C-terminal region of JP2 as the predominant calpain cleavage site. Exogenous expression of putative JP2 cleavage fragments was not sufficient to rescue Ca(2+) handling in JP2-deficient cardiomyocytes, indicating that cleaved JP2 is non-functional for normal Ca(2+)-induced Ca(2+) release. These data provide new molecular insights into the posttranslational regulatory mechanisms of JP2 in cardiac diseases.
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Affiliation(s)
- Ang Guo
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Duane Hall
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Caimei Zhang
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Tianqing Peng
- Departments of Medicine and Pathology, University of Western Ontario, London, Ontario N6A 4G5, Canada
| | - Jordan D Miller
- Division of Cardiovascular Surgery, Mayo Clinic, Rochester, Minnesota 55905
| | - William Kutschke
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Chad E Grueter
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Frances L Johnson
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242
| | - Richard Z Lin
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York 11794
| | - Long-Sheng Song
- Division of Cardiovascular Medicine, Department of Internal Medicine and François M. Abboud Cardiovascular Research Center, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242.
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Takeshima H, Hoshijima M, Song LS. Ca²⁺ microdomains organized by junctophilins. Cell Calcium 2015; 58:349-56. [PMID: 25659516 PMCID: PMC5159448 DOI: 10.1016/j.ceca.2015.01.007] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 01/15/2015] [Accepted: 01/16/2015] [Indexed: 11/21/2022]
Abstract
Excitable cells typically possess junctional membrane complexes (JMCs) constructed by the plasma membrane and the endo/sarcoplasmic reticulum (ER/SR) for channel crosstalk. These JMCs are termed triads in skeletal muscle, dyads in cardiac muscle, peripheral couplings in smooth and developing striated muscles, and subsurface cisterns in neurons. Junctophilin subtypes contribute to the formation and maintenance of JMCs by serving as a physical bridge between the plasma membrane and ER/SR membrane in different cell types. In muscle cells, junctophilin deficiency prevents JMC formation and functional crosstalk between cell-surface Ca2+ channels and ER/SR Ca2+ release channels. Human genetic mutations in junctophilin subtypes are linked to congenital hypertrophic cardiomyopathy and neurodegenerative diseases. Furthermore, growing evidence suggests that dysregulation of junctophilins induces pathological alterations in skeletal and cardiac muscle.
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Affiliation(s)
- Hiroshi Takeshima
- Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8501, Japan.
| | - Masahiko Hoshijima
- Department of Medicine and Center for Research in Biological Systems, University of California, San Diego, CA 92093, USA.
| | - Long-Sheng Song
- Department of Internal Medicine, University of Iowa Carver College of Medicine, Iowa City, IA 52242, USA.
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Ca2+-dependent regulations and signaling in skeletal muscle: from electro-mechanical coupling to adaptation. Int J Mol Sci 2015; 16:1066-95. [PMID: 25569087 PMCID: PMC4307291 DOI: 10.3390/ijms16011066] [Citation(s) in RCA: 110] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2014] [Accepted: 12/22/2014] [Indexed: 01/07/2023] Open
Abstract
Calcium (Ca2+) plays a pivotal role in almost all cellular processes and ensures the functionality of an organism. In skeletal muscle fibers, Ca(2+) is critically involved in the innervation of skeletal muscle fibers that results in the exertion of an action potential along the muscle fiber membrane, the prerequisite for skeletal muscle contraction. Furthermore and among others, Ca(2+) regulates also intracellular processes, such as myosin-actin cross bridging, protein synthesis, protein degradation and fiber type shifting by the control of Ca(2+)-sensitive proteases and transcription factors, as well as mitochondrial adaptations, plasticity and respiration. These data highlight the overwhelming significance of Ca(2+) ions for the integrity of skeletal muscle tissue. In this review, we address the major functions of Ca(2+) ions in adult muscle but also highlight recent findings of critical Ca(2+)-dependent mechanisms essential for skeletal muscle-regulation and maintenance.
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Casas M, Buvinic S, Jaimovich E. ATP signaling in skeletal muscle: from fiber plasticity to regulation of metabolism. Exerc Sport Sci Rev 2014; 42:110-6. [PMID: 24949845 DOI: 10.1249/jes.0000000000000017] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Tetanic electrical stimulation releases adenosine triphosphate (ATP) from muscle fibers through pannexin-1 channels in a frequency-dependent manner; extracellular ATP activates signals that ultimately regulate gene expression and is able to increase glucose transport through activation of P2Y receptors, phosphatidylinositol 3-kinase, Akt, and AS160. We hypothesize that this mechanism is an important link between exercise and the regulation of muscle fiber plasticity and metabolism.
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Affiliation(s)
- Mariana Casas
- 1Center for Molecular Studies of the Cell, Biomedical Sciences Institute, Faculty of Medicine, Universidad de Chile; and 2Institute for Research in Dental Sciences, Faculty of Dentistry, Universidad de Chile, Santiago, Chile
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Nakada T, Yamada M. Molecular mechanism of junctional membrane-targeting of cardiac and skeletal muscle L-type calcium channels. Nihon Yakurigaku Zasshi 2014; 144:217-21. [PMID: 25381890 DOI: 10.1254/fpj.144.217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Baumann CW, Rogers RG, Gahlot N, Ingalls CP. Eccentric contractions disrupt FKBP12 content in mouse skeletal muscle. Physiol Rep 2014; 2:2/7/e12081. [PMID: 25347864 PMCID: PMC4187567 DOI: 10.14814/phy2.12081] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Strength deficits associated with eccentric contraction‐induced muscle injury stem, in part, from impaired voltage‐gated sarcoplasmic reticulum (SR) Ca2+ release. FKBP12 is a 12‐kD immunophilin known to bind to the SR Ca2+ release channel (ryanodine receptor, RyR1) and plays an important role in excitation‐contraction coupling. To assess the effects of eccentric contractions on FKBP12 content, we measured anterior crural muscle (tibialis anterior [TA], extensor digitorum longus [EDL], extensor hallucis longus muscles) strength and FKBP12 content in pellet and supernatant fractions after centrifugation via immunoblotting from mice before and after a single bout of either 150 eccentric or concentric contractions. There were no changes in peak isometric torque or FKBP12 content in TA muscles after concentric contractions. However, FKBP12 content was reduced in the pelleted fraction immediately after eccentric contractions, and increased in the soluble protein fraction 3 day after injury induction. FKBP12 content was correlated (P = 0.025; R2= 0.38) to strength deficits immediately after injury induction. In summary, eccentric contraction‐induced muscle injury is associated with significant alterations in FKBP12 content after injury, and is correlated with changes in peak isometric torque. Eccentric contraction‐induced muscle injury is associated with immediate and prolonged strength deficits that stem in part from impaired sarcoplasmic reticulum (SR) calcium release. The content of FKBP12, a 12‐kD immunophilin known to bind to the SR calcium release channel and influence SR calcium release, is reduced in mouse skeletal muscle immediately after injury induction and is significantly associated with strength deficits.
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Affiliation(s)
- Cory W Baumann
- Department of Kinesiology and Health, Muscle Biology Laboratory, Georgia State University, Atlanta, 30302, Georgia
| | - Russell G Rogers
- Department of Kinesiology and Health, Muscle Biology Laboratory, Georgia State University, Atlanta, 30302, Georgia
| | - Nidhi Gahlot
- Department of Kinesiology and Health, Muscle Biology Laboratory, Georgia State University, Atlanta, 30302, Georgia
| | - Christopher P Ingalls
- Department of Kinesiology and Health, Muscle Biology Laboratory, Georgia State University, Atlanta, 30302, Georgia
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Beavers DL, Landstrom AP, Chiang DY, Wehrens XHT. Emerging roles of junctophilin-2 in the heart and implications for cardiac diseases. Cardiovasc Res 2014; 103:198-205. [PMID: 24935431 DOI: 10.1093/cvr/cvu151] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cardiomyocytes rely on a highly specialized subcellular architecture to maintain normal cardiac function. In a little over a decade, junctophilin-2 (JPH2) has become recognized as a cardiac structural protein critical in forming junctional membrane complexes (JMCs), which are subcellular domains essential for excitation-contraction coupling within the heart. While initial studies described the structure of JPH2 and its role in anchoring junctional sarcoplasmic reticulum and transverse-tubule (T-tubule) membrane invaginations, recent research has an expanded role of JPH2 in JMC structure and function. For example, JPH2 is necessary for the development of postnatal T-tubule in mammals. It is also critical for the maintenance of the complex JMC architecture and stabilization of local ion channels in mature cardiomyocytes. Loss of this function by mutations or down-regulation of protein expression has been linked to hypertrophic cardiomyopathy, arrhythmias, and progression of disease in failing hearts. In this review, we summarize current views on the roles of JPH2 within the heart and how JPH2 dysregulation may contribute to a variety of cardiac diseases.
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Affiliation(s)
- David L Beavers
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Translational Biology and Molecular Medicine Program, Baylor College of Medicine, Houston, TX, USA
| | - Andrew P Landstrom
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Pediatrics, Baylor College of Medicine, Houston, TX, USA
| | - David Y Chiang
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Translational Biology and Molecular Medicine Program, Baylor College of Medicine, Houston, TX, USA
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX, USA Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA Deptartment of Medicine (Cardiology), Baylor College of Medicine, Houston, TX, USA
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Landstrom AP, Beavers DL, Wehrens XHT. The junctophilin family of proteins: from bench to bedside. Trends Mol Med 2014; 20:353-62. [PMID: 24636942 PMCID: PMC4041816 DOI: 10.1016/j.molmed.2014.02.004] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Revised: 02/10/2014] [Accepted: 02/14/2014] [Indexed: 12/25/2022]
Abstract
Excitable tissues rely on junctional membrane complexes to couple cell surface signals to intracellular channels. The junctophilins have emerged as a family of proteins critical in coordinating the maturation and maintenance of this cellular ultrastructure. Within skeletal and cardiac muscle, junctophilin 1 and junctophilin 2, respectively, couple sarcolemmal and intracellular calcium channels. In neuronal tissue, junctophilin 3 and junctophilin 4 may have an emerging role in coupling membrane neurotransmitter receptors and intracellular calcium channels. These important physiological roles are highlighted by the pathophysiology which results when these proteins are perturbed, and a growing body of literature has associated junctophilins with the pathogenesis of human disease.
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Affiliation(s)
- Andrew P Landstrom
- Department of Pediatrics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX 77030, USA
| | - David L Beavers
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX 77030, USA
| | - Xander H T Wehrens
- Department of Molecular Physiology and Biophysics, Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX 77030, USA; Department of Medicine (Cardiology), Cardiovascular Research Institute, Baylor College of Medicine, Houston, TX 77030, USA.
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Rebbeck RT, Karunasekara Y, Board PG, Beard NA, Casarotto MG, Dulhunty AF. Skeletal muscle excitation–contraction coupling: Who are the dancing partners? Int J Biochem Cell Biol 2014; 48:28-38. [DOI: 10.1016/j.biocel.2013.12.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2013] [Revised: 11/29/2013] [Accepted: 12/04/2013] [Indexed: 01/15/2023]
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Toral-Ojeda I, Aldanondo G, Vallejo-Illarramendi A. Junctophilins and μ-calpain: partners in excitation-contraction uncoupling. J Physiol 2014; 591:3679-80. [PMID: 23908410 DOI: 10.1113/jphysiol.2013.258574] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Affiliation(s)
- I Toral-Ojeda
- Neuroscience Area, Instituto Biodonostia, San Sebastian, Spain.
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61
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Distinct regions of triadin are required for targeting and retention at the junctional domain of the sarcoplasmic reticulum. Biochem J 2014; 458:407-17. [DOI: 10.1042/bj20130719] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Three regions contribute to triadin localization to the junctional sarcoplasmic reticulum. Dynamics studies revealed that TR3 mediates triadin stability at junctional sites. The stable association of triadin at the junctional sites is facilitated by interactions with calsequestrin-1.
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62
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Vesicular transport system in myotubes: ultrastructural study and signposting with vesicle-associated membrane proteins. Histochem Cell Biol 2013; 141:441-54. [PMID: 24263617 DOI: 10.1007/s00418-013-1164-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/06/2013] [Indexed: 10/26/2022]
Abstract
Myofibers have characteristic membrane compartments in their cytoplasm and sarcolemma, such as the sarcoplasmic reticulum, T-tubules, neuromuscular junction, and myotendinous junction. Little is known about the vesicular transport that is believed to mediate the development of these membrane compartments. We determined the locations of organelles in differentiating myotubes. Electron microscopic observation of a whole myotube revealed the arrangement of Golgi apparatus, rough endoplasmic reticulum, autolysosomes, mitochondria, and smooth endoplasmic reticulum from the perinuclear region toward the end of myotubes and the existence of a large number of vesicles near the ends of myotubes. Vesicles in myotubes were further characterized using immunofluorescence microscopy to analyze expression and localization of vesicle-associated membrane proteins (VAMPs). VAMPs are a family of seven proteins that regulate post-Golgi vesicular transport via the fusion of vesicles to the target membranes. Myotubes express five VAMPs in total. Vesicles with VAMP2, VAMP3, or VAMP5 were found near the ends of the myotubes. Some of these vesicles are also positive for caveolin-3, suggesting their participation in the development of T-tubules. Our morphological analyses revealed the characteristic arrangement of organelles in myotubes and the existence of transport vesicles near the ends of the myotubes.
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63
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Beavers DL, Wang W, Ather S, Voigt N, Garbino A, Dixit SS, Landstrom AP, Li N, Wang Q, Olivotto I, Dobrev D, Ackerman MJ, Wehrens XHT. Mutation E169K in junctophilin-2 causes atrial fibrillation due to impaired RyR2 stabilization. J Am Coll Cardiol 2013; 62:2010-9. [PMID: 23973696 DOI: 10.1016/j.jacc.2013.06.052] [Citation(s) in RCA: 148] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Revised: 05/24/2013] [Accepted: 06/05/2013] [Indexed: 02/07/2023]
Abstract
OBJECTIVES This study sought to study the role of junctophilin-2 (JPH2) in atrial fibrillation (AF). BACKGROUND JPH2 is believed to have an important role in sarcoplasmic reticulum (SR) Ca(2+) handling and modulation of ryanodine receptor Ca(2+) channels (RyR2). Whereas defective RyR2-mediated Ca(2+) release contributes to the pathogenesis of AF, nothing is known about the potential role of JPH2 in atrial arrhythmias. METHODS Screening 203 unrelated hypertrophic cardiomyopathy patients uncovered a novel JPH2 missense mutation (E169K) in 2 patients with juvenile-onset paroxysmal AF (pAF). Pseudoknock-in (PKI) mouse models were generated to determine the molecular defects underlying the development of AF caused by this JPH2 mutation. RESULTS PKI mice expressing E169K mutant JPH2 exhibited a higher incidence of inducible AF than wild type (WT)-PKI mice, whereas A399S-PKI mice expressing a hypertrophic cardiomyopathy-linked JPH2 mutation not associated with atrial arrhythmias were not significantly different from WT-PKI. E169K-PKI but not A399A-PKI atrial cardiomyocytes showed an increased incidence of abnormal SR Ca(2+) release events. These changes were attributed to reduced binding of E169K-JPH2 to RyR2. Atrial JPH2 levels in WT-JPH2 transgenic, nontransgenic, and JPH2 knockdown mice correlated negatively with the incidence of pacing-induced AF. Ca(2+) spark frequency in atrial myocytes and the open probability of single RyR2 channels from JPH2 knockdown mice was significantly reduced by a small JPH2-mimicking oligopeptide. Moreover, patients with pAF had reduced atrial JPH2 levels per RyR2 channel compared to sinus rhythm patients and an increased frequency of spontaneous Ca(2+) release events. CONCLUSIONS Our data suggest a novel mechanism by which reduced JPH2-mediated stabilization of RyR2 due to loss-of-function mutation or reduced JPH2/RyR2 ratios can promote SR Ca(2+) leak and atrial arrhythmias, representing a potential novel therapeutic target for AF.
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Affiliation(s)
- David L Beavers
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Wei Wang
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Sameer Ather
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Niels Voigt
- Institute of Pharmacology, Faculty of Medicine, University of Duisburg-Essen, Essen, Germany
| | - Alejandro Garbino
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Sayali S Dixit
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Andrew P Landstrom
- Depts of Medicine, Pediatrics, and Molecular Pharmacology & Experimental Therapeutics/Divisions of Cardiovascular Diseases and Pediatric Cardiology; Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN
| | - Na Li
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Qiongling Wang
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
| | - Iacopo Olivotto
- Careggi University Hospital, University of Florence, Florence, Italy
| | - Dobromir Dobrev
- Institute of Pharmacology, Faculty of Medicine, University of Duisburg-Essen, Essen, Germany
| | - Michael J Ackerman
- Depts of Medicine, Pediatrics, and Molecular Pharmacology & Experimental Therapeutics/Divisions of Cardiovascular Diseases and Pediatric Cardiology; Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, MN
| | - Xander H T Wehrens
- Cardiovascular Research Institute, Dept of Molecular Physiology & Biophysics and Medicine (Cardiology), Baylor College of Medicine, Houston, TX
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Interaction of membrane/lipid rafts with the cytoskeleton: impact on signaling and function: membrane/lipid rafts, mediators of cytoskeletal arrangement and cell signaling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:532-45. [PMID: 23899502 DOI: 10.1016/j.bbamem.2013.07.018] [Citation(s) in RCA: 378] [Impact Index Per Article: 34.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 05/14/2013] [Accepted: 07/16/2013] [Indexed: 12/14/2022]
Abstract
The plasma membrane in eukaryotic cells contains microdomains that are enriched in certain glycosphingolipids, gangliosides, and sterols (such as cholesterol) to form membrane/lipid rafts (MLR). These regions exist as caveolae, morphologically observable flask-like invaginations, or as a less easily detectable planar form. MLR are scaffolds for many molecular entities, including signaling receptors and ion channels that communicate extracellular stimuli to the intracellular milieu. Much evidence indicates that this organization and/or the clustering of MLR into more active signaling platforms depends upon interactions with and dynamic rearrangement of the cytoskeleton. Several cytoskeletal components and binding partners, as well as enzymes that regulate the cytoskeleton, localize to MLR and help regulate lateral diffusion of membrane proteins and lipids in response to extracellular events (e.g., receptor activation, shear stress, electrical conductance, and nutrient demand). MLR regulate cellular polarity, adherence to the extracellular matrix, signaling events (including ones that affect growth and migration), and are sites of cellular entry of certain pathogens, toxins and nanoparticles. The dynamic interaction between MLR and the underlying cytoskeleton thus regulates many facets of the function of eukaryotic cells and their adaptation to changing environments. Here, we review general features of MLR and caveolae and their role in several aspects of cellular function, including polarity of endothelial and epithelial cells, cell migration, mechanotransduction, lymphocyte activation, neuronal growth and signaling, and a variety of disease settings. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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Abstract
RATIONALE Fibroblast growth factor (FGF) homologous factors (FHFs; FGF11-14) are intracellular modulators of voltage-gated Na+ channels, but their cellular distribution in cardiomyocytes indicated that they performed other functions. OBJECTIVE We aimed to uncover novel roles for FHFs in cardiomyocytes, starting with a proteomic approach to identify novel interacting proteins. METHODS AND RESULTS Affinity purification of FGF13 from rodent ventricular lysates followed by mass spectroscopy revealed an interaction with junctophilin-2, a protein that organizes the close apposition of the L-type Ca2+ channel CaV1.2 and the ryanodine receptor 2 in the dyad. Immunocytochemical analysis revealed that overall T-tubule structure and localization of ryanodine receptor 2 were unaffected by FGF13 knockdown in adult ventricular cardiomyocytes but localization of CaV1.2 was affected. FGF13 knockdown decreased CaV1.2 current density and reduced the amount of CaV1.2 at the surface as a result of aberrant localization of the channels. CaV1.2 current density and channel localization were rescued by expression of an shRNA-insensitive FGF13, indicating a specific role for FGF13. Consistent with these newly discovered effects on CaV1.2, we demonstrated that FGF13 also regulated Ca(2+)-induced Ca2+ release, indicated by a smaller Ca2+ transient after FGF13 knockdown. Furthermore, FGF13 knockdown caused a profound decrease in the cardiac action potential half-width. CONCLUSIONS This study demonstrates that FHFs not only are potent modulators of voltage-gated Na+ channels but also affect Ca2+ channels and their function. We predict that FHF loss-of-function mutations would adversely affect currents through both Na+ and Ca2+ channels, suggesting that FHFs may be arrhythmogenic loci, leading to arrhythmias through a novel, dual-ion channel mechanism.
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Affiliation(s)
- Jessica A Hennessey
- Department of Medicine/Cardiology, Duke University Medical Center, Durham, NC 27710, USA
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67
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Sorrentino V. A proteolytic cleavage to separate the sarcolemma/T-tubule from the sarcoplasmic reticulum. J Physiol 2013; 591:601. [DOI: 10.1113/jphysiol.2012.249029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Murphy RM, Dutka TL, Horvath D, Bell JR, Delbridge LM, Lamb GD. Ca2+-dependent proteolysis of junctophilin-1 and junctophilin-2 in skeletal and cardiac muscle. J Physiol 2012; 591:719-29. [PMID: 23148318 DOI: 10.1113/jphysiol.2012.243279] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Excessive increases in intracellular [Ca(2+)] in skeletal muscle fibres cause failure of excitation-contraction coupling by disrupting communication between the dihydropyridine receptors in the transverse tubular system and the Ca(2+) release channels (RyRs) in the sarcoplasmic reticulum (SR), but the exact mechanism is unknown. Previous work suggested a possible role of Ca(2+)-dependent proteolysis in this uncoupling process but found no proteolysis of the dihydropyridine receptors, RyRs or triadin. Junctophilin-1 (JP1; ∼90 kDa) stabilizes close apposition of the transverse tubular system and SR membranes in adult skeletal muscle; its C-terminal end is embedded in the SR and its N-terminal associates with the transverse tubular system membrane. Exposure of skeletal muscle homogenates to precisely set [Ca(2+)] revealed that JP1 undergoes Ca(2+)-dependent proteolysis over the physiological [Ca(2+)] range in tandem with autolytic activation of endogenous μ-calpain. Cleavage of JP1 occurs close to the C-terminal, yielding a ∼75 kDa diffusible fragment and a fixed ∼15 kDa fragment. Depolarization-induced force responses in rat skinned fibres were abolished following 1 min exposure to 40 μm Ca(2+), with accompanying loss of full-length JP1. Supraphysiological stimulation of rat skeletal muscle in vitro by repeated tetanic stimulation in 30 mm caffeine also produced marked proteolysis of JP1 (and not RyR1). In dystrophic mdx mice, JP1 proteolysis is seen in limb muscles at 4 and not at 10 weeks of age. Junctophilin-2 in cardiac and skeletal muscle also undergoes Ca(2+)-dependent proteolysis, and junctophilin-2 levels are reduced following cardiac ischaemia-reperfusion. Junctophilin proteolysis may contribute to skeletal muscle weakness and cardiac dysfunction in a range of circumstances.
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Affiliation(s)
- R M Murphy
- Department of Zoology, La Trobe University, Melbourne, Victoria 3086, Australia
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Criswell TL, Corona BT, Wang Z, Zhou Y, Niu G, Xu Y, Christ GJ, Soker S. The role of endothelial cells in myofiber differentiation and the vascularization and innervation of bioengineered muscle tissue in vivo. Biomaterials 2012; 34:140-9. [PMID: 23059002 DOI: 10.1016/j.biomaterials.2012.09.045] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2012] [Accepted: 09/20/2012] [Indexed: 12/25/2022]
Abstract
Musculoskeletal disorders are a major cause of disability and effective treatments are currently lacking. Tissue engineering affords the possibility of new therapies utilizing cells and biomaterials for the recovery of muscle volume and function. A major consideration in skeletal muscle engineering is the integration of a functional vasculature within the regenerating tissue. In this study we employed fluorescent cell labels to track the location and differentiation of co-cultured cells in vivo and in vitro. We first utilized a co-culture of fluorescently labeled endothelial cells (ECs) and muscle progenitor cells (MPCs) to investigate the ability of ECs to enhance muscle tissue formation and vascularization in an in vivo model of bioengineered muscle. Scaffolds that had been seeded with both MPCs and ECs showed significantly greater vascularization, tissue formation and enhanced innervation as compared to scaffolds seeded with MPCs alone. Subsequently, we performed in vitro experiments using a 3-cell type system (ECs, MPCs, and pericytes (PCs)) to demonstrate the utility of fluorescent cell labeling for monitoring cell growth and differentiation. The growth and differentiation of individual cell types was determined using live cell fluorescent microscopy demonstrating the utility of fluorescent labels to monitor tissue organization in real time.
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Affiliation(s)
- Tracy L Criswell
- Wake Forest Institute for Regenerative Medicine, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157, USA
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