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Andersson D.C.,Columbia University | Andersson D.C.,Karolinska Institutet | Meli A.C.,Columbia University | Meli A.C.,Masaryk University | And 7 more authors.
Skeletal Muscle | Year: 2012

Background: Disruption of the sarcolemma-associated dystrophin-glycoprotein complex underlies multiple forms of muscular dystrophy, including Duchenne muscular dystrophy and sarcoglycanopathies. A hallmark of these disorders is muscle weakness. In a murine model of Duchenne muscular dystrophy, mdx mice, cysteine-nitrosylation of the calcium release channel/ryanodine receptor type 1 (RyR1) on the skeletal muscle sarcoplasmic reticulum causes depletion of the stabilizing subunit calstabin1 (FKBP12) from the RyR1 macromolecular complex. This results in a sarcoplasmic reticular calcium leak via defective RyR1 channels. This pathological intracellular calcium leak contributes to reduced calcium release and decreased muscle force production. It is unknown whether RyR1 dysfunction occurs also in other muscular dystrophies. Methods: To test this we used a murine model of Limb-Girdle muscular dystrophy, deficient in β-sarcoglycan (Sgcb-/-). Results: Skeletal muscle RyR1 from Sgcb-/- deficient mice were oxidized, nitrosylated, and depleted of the stabilizing subunit calstabin1, which was associated with increased open probability of the RyR1 channels. Sgcb-/- deficient mice exhibited decreased muscle specific force and calcium transients, and displayed reduced exercise capacity. Treating Sgcb-/- mice with the RyR stabilizing compound S107 improved muscle specific force, calcium transients, and exercise capacity. We have previously reported similar findings in mdx mice, a murine model of Duchenne muscular dystrophy. Conclusions: Our data suggest that leaky RyR1 channels may underlie multiple forms of muscular dystrophy linked to mutations in genes encoding components of the dystrophin-glycoprotein complex. A common underlying abnormality in calcium handling indicates that pharmacological targeting of dysfunctional RyR1 could be a novel therapeutic approach to improve muscle function in Limb-Girdle and Duchenne muscular dystrophies. © 2012 Andersson et al; licensee BioMed Central Ltd. Source

Kushnir A.,Clyde and Helen Wu Center for Molecular Cardiology | Betzenhauser M.J.,Clyde and Helen Wu Center for Molecular Cardiology | Marks A.R.,Clyde and Helen Wu Center for Molecular Cardiology | Marks A.R.,Columbia University
FEBS Letters | Year: 2010

Ryanodine receptors (RyR) regulate intracellular Ca2+ release in many cell types and have been implicated in a number of inherited human diseases. Over the past 15years genetically engineered mouse models have been developed to elucidate the role that RyRs play in physiology and pathophysiology. To date these models have implicated RyRs in fundamental biological processes including excitation-contraction coupling and long term plasticity as well as diseases including malignant hyperthermia, cardiac arrhythmias, heart failure, and seizures. In this review we summarize the RyR mouse models and how they have enhanced our understanding of the RyR channels and their roles in cellular physiology and disease. © 2010 Federation of European Biochemical Societies. Source

Shan J.,Clyde and Helen Wu Center for Molecular Cardiology | Xie W.,Clyde and Helen Wu Center for Molecular Cardiology | Betzenhauser M.,Clyde and Helen Wu Center for Molecular Cardiology | Reiken S.,Clyde and Helen Wu Center for Molecular Cardiology | And 3 more authors.
Circulation Research | Year: 2012

Rationale: Atrial fibrillation (AF) is the most common cardiac arrhythmia, however the mechanism(s) causing AF remain poorly understood and therapy is suboptimal. The ryanodine receptor (RyR2) is the major calcium (Ca) release channel on the sarcoplasmic reticulum (SR) required for excitation-contraction coupling in cardiac muscle. Objective: In the present study, we sought to determine whether intracellular diastolic SR Ca leak via RyR2 plays a role in triggering AF and whether inhibiting this leak can prevent AF. Methods and Results: We generated 3 knock-in mice with mutations introduced into RyR2 that result in leaky channels and cause exercise induced polymorphic ventricular tachycardia in humans [catecholaminergic polymorphic ventricular tachycardia (CPVT)]. We examined AF susceptibility in these three CPVT mouse models harboring RyR2 mutations to explore the role of diastolic SR Ca leak in AF. AF was stimulated with an intra-esophageal burst pacing protocol in the 3 CPVT mouse models (RyR2-R2474S, 70%; RyR2-N2386I, 60%; RyR2-L433P, 35.71%) but not in wild-type (WT) mice (P<0.05). Consistent with these in vivo results, there was a significant diastolic SR Ca leak in atrial myocytes isolated from the CPVT mouse models. Calstabin2 (FKBP12.6) is an RyR2 subunit that stabilizes the closed state of RyR2 and prevents a Ca leak through the channel. Atrial RyR2 from RyR2-R2474S mice were oxidized, and the RyR2 macromolecular complex was depleted of calstabin2. The Rycal drug S107 stabilizes the closed state of RyR2 by inhibiting the oxidation/phosphorylation induced dissociation of calstabin2 from the channel. S107 reduced the diastolic SR Ca leak in atrial myocytes and decreased burst pacing-induced AF in vivo. S107 did not reduce the increased prevalence of burst pacing-induced AF in calstabin2-deficient mice, confirming that calstabin2 is required for the mechanism of action of the drug. Conclusions: The present study demonstrates that RyR2-mediated diastolic SR Ca leak in atrial myocytes is associated with AF in CPVT mice. Moreover, the Rycal S107 inhibited diastolic SR Ca leak through RyR2 and pacing-induced AF associated with CPVT mutations. © 2012 American Heart Association, Inc. Source

Andersson D.C.,Clyde and Helen Wu Center for Molecular Cardiology | Betzenhauser M.J.,Clyde and Helen Wu Center for Molecular Cardiology | Reiken S.,Clyde and Helen Wu Center for Molecular Cardiology | Umanskaya A.,Clyde and Helen Wu Center for Molecular Cardiology | And 3 more authors.
Journal of Physiology | Year: 2012

Enhancement of contractile force (inotropy) occurs in skeletal muscle following neuroendocrine release of catecholamines and activation of muscle β-adrenergic receptors. Despite extensive study, the molecular mechanism underlying the inotropic response in skeletal muscle is not well understood. Here we show that phosphorylation of a single serine residue (S2844) in the sarcoplasmic reticulum (SR) Ca2+ release channel/ryanodine receptor type 1 (RyR1) by protein kinase A (PKA) is critical for skeletal muscle inotropy. Treating fast twitch skeletal muscle from wild-type mice with the β-receptor agonist isoproterenol (isoprenaline) increased RyR1 PKA phosphorylation, twitch Ca2+ and force generation. In contrast, the enhanced muscle Ca2+, force and in vivo muscle strength responses following isoproterenol stimulation were abrogated in RyR1-S2844A mice in which the serine in the PKA site in RyR1 was replaced with alanine. These data suggest that the molecular mechanism underlying skeletal muscle inotropy requires enhanced SR Ca2+ release due to PKA phosphorylation of S2844 in RyR1. © 2012 The Physiological Society. Source

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