Calpain-1-dependent degradation of troponin I mutants found in familial hypertrophic cardiomyopathy

Barta, Judit; Tóth, Attila; Jaquet, Kornélia; Redlich, Alexander; Édes, István; Papp, Zoltán

doi:10.1007/978-1-4419-9238-3_12

Cited by 5 publications

(5 citation statements)

References 17 publications

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“…This is consistent with the observation in fusing myoblasts that muscle-derived calpain is exteriorized and acts on extracellular matrix components, such as fibronectin (33). Last, the ultrastructural and immunoblot studies also point to some protection by calpain inhibition of myofibrillar structural proteins, recognized targets of calpains, indicating the action and potential role of this enzyme in muscle disease (41)(42)(43).…”

Section: Discussionsupporting

confidence: 85%

Calpain activation impairs neuromuscular transmission in a mouse model of the slow-channel myasthenic syndrome

et al. 2007

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The slow-channel myasthenic syndrome (SCS) is a hereditary disorder of the acetylcholine receptor (AChR) of the neuromuscular junction (NMJ) that leads to prolonged AChR channel opening, Ca 2+ overload, and degeneration of the NMJ. We used an SCS transgenic mouse model to investigate the role of the calcium-activated protease calpain in the pathogenesis of synaptic dysfunction in SCS. Cleavage of a fluorogenic calpain substrate was increased at the NMJ of dissociated muscle fibers. Inhibition of calpain using a calpastatin (CS) transgene improved strength and neuromuscular transmission. CS caused a 2-fold increase in the frequency of miniature endplate currents (MEPCs) and an increase in NMJ size, but MEPC amplitudes remained reduced. Persistent degeneration of the NMJ was associated with localized activation of the non-calpain protease caspase-3. This study suggests that calpain may act presynaptically to impair NMJ function in SCS but further reveals a role for other cysteine proteases whose inhibition may be of additional therapeutic benefit in SCS and other excitotoxic disorders. IntroductionThe slow-channel congenital myasthenic syndrome (SCS) is a dominantly inherited neuromuscular disorder characterized by impaired neuromuscular transmission and degeneration of the neuromuscular junction (NMJ) (1-3). Patients with SCS manifest fatigability and progressive weakness of the skeletal muscles, with symptoms ranging from eye muscle and mild limb weakness to severe incapacitation and respiratory failure. Ultrastructural study of muscle in SCS reveals a focal degenerative and remodeling process selectively localized to the NMJ termed endplate myopathy. This progressive, purely synaptic disease process, in which the cleft is widened and nerve terminals are shrunken, is characterized by expansion and degeneration of postsynaptic folds as well as degeneration of subsynaptic nuclei, mitochondria, and myofibrils (1-4).The SCS is caused by missense mutations within the genes encoding nicotinic acetylcholine receptor (AChR) subunits. The mutations alter the AChR channel gating function, causing prolonged activation events, persistent synaptic currents, and localized calcium overload at the NMJ, amplified by calcium release from intracellular stores (1, 3, 5-10). These changes lead to weakness and impaired neuromuscular transmission through an effect on both pre- and postsynaptic determinants of synaptic transmission, including quantal release, synaptic cleft anatomy, and the

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Section: Discussionsupporting

confidence: 85%

Calpain activation impairs neuromuscular transmission in a mouse model of the slow-channel myasthenic syndrome

et al. 2007

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“…44 Moreover, phosphorylation of TnI has been shown to protect TnI from degradation. 31,45 Therefore, the decreased TnI phosphorylation observed in remodeled myocardium ( Figure 5G) might render TnI more susceptible to degradation.…”

Section: Reduced Force-generating Capacitymentioning

confidence: 99%

Alterations in Myofilament Function Contribute to Left Ventricular Dysfunction in Pigs Early After Myocardial Infarction

Velden

Merkus

James

et al. 2004

Circulation Research

113

131

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Myocardial infarction (MI) initiates cardiac remodeling, depresses pump function, and predisposes to heart failure. This study was designed to identify early alterations in Ca2+ handling and myofilament proteins, which may contribute to contractile dysfunction and reduced beta-adrenergic responsiveness in postinfarct remodeled myocardium. Protein composition and contractile function of skinned cardiomyocytes were studied in remote, noninfarcted left ventricular (LV) subendocardium from pigs 3 weeks after MI caused by permanent left circumflex artery (LCx) ligation and in sham-operated pigs. LCx ligation induced a 19% increase in LV weight, a 69% increase in LV end-diastolic area, and a decrease in ejection fraction from 54+/-5% to 35+/-4% (all P<0.05), whereas cardiac responsiveness to exercise-induced increases in circulating noradrenaline levels was blunted. Endogenous protein kinase A (PKA) was significantly reduced in remote myocardium of MI animals, and a negative correlation (R=0.62; P<0.05) was found between cAMP levels and LV weight-to-body weight ratio. Furthermore, SERCA2a expression was 23% lower after MI compared with sham. Maximal isometric force generated by isolated skinned myocytes was significantly lower after MI than in sham (15.4+/-1.5 versus 19.2+/-0.9 kN/m2; P<0.05), which might be attributable to a small degree of troponin I (TnI) degradation observed in remodeled postinfarct myocardium. An increase in Ca2+ sensitivity of force (pCa50) was observed after MI compared with sham (DeltapCa50=0.17), which was abolished by incubating myocytes with exogenous PKA, indicating that the increased Ca2+ sensitivity resulted from reduced TnI phosphorylation. In conclusion, remodeling of noninfarcted pig myocardium is associated with decreased SERCA2a and myofilament function, which may contribute to depressed LV function. The full text of this article is available online at http://circres.ahajournals.org.

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“…In parallel, the loading was visualized by silver staining [23], as described previously [24]. Following the electrophoresis step, myofibrillar proteins were transferred to nitrocellulose membranes, which were subsequently incubated with 5% non-fat dry milk and thereafter with primary antibodies (monoclonal anti-nitrotyrosine (Cayman Chemicals, Ann Arbor, MI, USA), dilution 1 : 5000; polyclonal anti-nitrotyrosine (Upstate, Charlottesville, VA, USA), dilution 1 : 7500; and anti-a-actinin (clone EA-53, Sigma, St. Louis, MO, USA), dilution 1 : 5000).…”

Section: Western Immunoblotmentioning

confidence: 99%

Peroxynitrite-induced α-actinin nitration and contractile alterations in isolated human myocardial cells

Borbély

Tóth

Édes

et al. 2005

Cardiovascular Research

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Objective: Peroxynitrite-mediated myocardial protein nitration has been associated with a depressed cardiac pump function. In the present study, an attempt was made to elucidate the molecular background of peroxynitrite-evoked alterations in the human myocardium. Methods: Isometric force generation was measured in permeabilized human ventricular myocytes and biochemical methods were employed to identify the proteins affected by peroxynitrite-induced nitrotyrosine formation. Results: The maximal Ca 2+ -activated isometric force (pCa = 4.75) decreased to zero with increasing concentrations of peroxynitrite in a concentration-dependent manner (IC 50 : 55T 4 AM; based on a total of 75 myocytes). However, there were no differences before and after the application of 50 AM peroxynitrite in the Ca 2+ -sensitivity of force production (pCa 50 : 5.89 T 0.02 and 5.86 T 0.04), in the steepness of the Ca 2+ -force relationship (nHill: 2.22 T 0.11 and 2.42 T 0.25), and in the actin -myosin turnover kinetics (k tr at saturating [Ca 2+ ]: 1.14 T 0.03 1/s and 1.05 T 0.07 1/s) ( P > 0.05). Nevertheless, 50 AM peroxynitrite greatly deteriorated the cross-striation pattern and induced a slight, but significant, increase in the passive force component (from 2.1 T 0.1 to 2.5 T 0.2 kN/m 2 ; n = 57 cells), reflecting ultrastructural alterations. Western immunoblots revealed that 50 AM peroxynitrite selectively induced the nitration of a protein with an apparent molecular mass of about 100 kDa. Subsequent immunoprecipitation assays identified this nitrated protein as a-actinin, a major Z-line protein.Conclusions: These results suggest a-actinin as a novel target for peroxynitrite in the human myocardium; its nitration induces a contractile dysfunction, presumably by decreasing the longitudinal transmission of force between adjacent sarcomeres.

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Calpain-1-dependent degradation of troponin I mutants found in familial hypertrophic cardiomyopathy

Cited by 5 publications

References 17 publications

Calpain activation impairs neuromuscular transmission in a mouse model of the slow-channel myasthenic syndrome

Calpain activation impairs neuromuscular transmission in a mouse model of the slow-channel myasthenic syndrome

Alterations in Myofilament Function Contribute to Left Ventricular Dysfunction in Pigs Early After Myocardial Infarction

Peroxynitrite-induced α-actinin nitration and contractile alterations in isolated human myocardial cells

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