Lamin A/C–mediated neuromuscular junction defects in Emery-Dreifuss muscular dystrophy

The LMNA gene encodes lamins A and C, two intermediate filament-type proteins that are important determinants of interphase nuclear architecture. Mutations in LMNA lead to a wide spectrum of human diseases including autosomal dominant Emery-Dreifuss muscular dystrophy (AD-EDMD), which affects skeletal and cardiac muscle. The cellular mechanisms by which mutations in LMNA cause disease have been elusive. Here, we demonstrate that defects in neuromuscular junctions (NMJs) are part of the disease mechanism in AD-EDMD. Two AD-EDMD mouse models show innervation defects including misexpression of electrical activity–dependent genes and altered epigenetic chromatin modifications. Synaptic nuclei are not properly recruited to the NMJ because of mislocalization of nuclear envelope components. AD-EDMD patients with LMNA mutations show the same cellular defects as the AD-EDMD mouse models. These results suggest that lamin A/C–mediated NMJ defects contribute to the AD-EDMD disease phenotype and provide insights into the cellular and molecular mechanisms for the muscle-specific phenotype of AD-EDMD

Repetitive stimulation of skeletal muscle: effect of adrenaline and intracellular pH regulation

Thèse de doctorat en sciences biomédicales (FYMU) -- UCL, 200

Effect of adrenaline on the post-tetanic potentiation in mouse skeletal muscle.

We report the influence of adrenergic stimulation on the amplitude and time course of post-tetanic potentiation of twitch contraction. This was complemented by measurements of the peak of [Ca2+]i transients in twitches and of the level of myosin light chain 2 (LC2) phosphorylation, before, 20 and 300 s after the conditioning tetanus. Soon after the tetanus, twitch potentiation and increases of LC2 phosphorylation and of [Ca2+]i peak were similar in control conditions and in the presence of adrenaline. In control conditions, twitch potentiation, LC2 phosphorylation and [Ca2+]i peak returned to, or close to, pre-tetanic values in 300 s. On the contrary, in the presence of adrenaline, twitch potentiation and LC2 phosphorylation were partially or fully maintained respectively, while the increase of [Ca2+]i peak was not. This situation allowed us to analyse the relative contributions of elevated LC2 phosphorylation and [Ca2+]i peak in the twitch post-tetanic potentiation phenomenon. Moreover, it was shown that the increase of LC2 phosphorylation (up to 0.5 mol P/mol LC2) affected neither the kinetic parameters of the twitch nor the maximal velocity of shortening. It is proposed that the maintenance of LC2 phosphorylation in the presence of adrenaline results from the inhibition of myosin light chain phosphatase. This could be achieved through the production of the active, phosphorylated form of the inhibitor-1, an endogenous inhibitor, which binds to the catalytic sub-units common to class 1 protein phosphatases

Altered cross-bridge properties in skeletal muscle dystrophies

International audience† Co-first authors. Force and motion generated by skeletal muscle ultimately depends on the cyclical interaction of actin with myosin. This mechanical process is regulated by intracellular Ca 2+ through the thin filament-associated regulatory proteins i.e.; troponins and tropomyosin. Muscular dystrophies are a group of heterogeneous genetic affections characterized by progressive degeneration and weakness of the skeletal muscle as a consequence of loss of muscle tissue which directly reduces the number of potential myosin cross-bridges involved in force production. Mutations in genes responsible for skeletal muscle dystrophies (MDs) have been shown to modify the function of contractile proteins and cross-bridge interactions. Altered gene expression or RNA splicing or post-translational modifications of contractile proteins such as those related to oxidative stress, may affect cross-bridge function by modifying key proteins of the excitation-contraction coupling. Micro-architectural change in myofilament is another mechanism of altered cross-bridge performance. In this review, we provide an overview about changes in cross-bridge performance in skeletal MDs and discuss their ultimate impacts on striated muscle function

Lamin A/C mutants disturb sumo1 localization and sumoylation in vitro and in vivo.

A-type lamins A and C are nuclear intermediate filament proteins in which mutations have been implicated in multiple disease phenotypes commonly known as laminopathies. A few studies have implicated sumoylation in the regulation of A-type lamins. Sumoylation is a post-translational protein modification that regulates a wide range of cellular processes through the attachment of small ubiquitin-related modifier (sumo) to various substrates. Here we showed that laminopathy mutants result in the mislocalization of sumo1 both in vitro (C2C12 cells overexpressing mutant lamins A and C) and in vivo (primary myoblasts and myopathic muscle tissue from the Lmna(H222P/H222P) mouse model). In C2C12 cells, we showed that the trapping of sumo1 in p.Asp192Gly, p.Gln353Lys, and p.Arg386Lys aggregates of lamin A/C correlated with an increased steady-state level of sumoylation. However, lamin A and C did not appear to be modified by sumo1. Our results suggest that mutant lamin A/C alters the dynamics of sumo1 and thus misregulation of sumoylation may be contributing to disease progression in laminopathies

N-acetyl cysteine alleviates oxidative stress and protects mice from dilated cardiomyopathy caused by mutations in nuclear A-type lamins gene

International audienceCardiomyopathy caused by lamin A/C gene (LMNA) mutations (hereafter referred as LMNA cardiomyopathy) is an anatomic and pathologic condition associated with muscular and electrical dysfunction of the heart, often leading to heart failure-related disability. There is currently no specific therapy available for patients that target the molecular pathophysiology of LMNA cardiomyopathy. We showed here an increase in oxidative stress levels in the hearts of mice carrying LMNA mutation, associated with a decrease of the key cellular antioxidant glutathione (GHS). Oral administration of N-acetyl cysteine, a GHS precursor, led to a marked improvement of GHS content, a decrease in oxidative stress markers including protein carbonyls and an improvement of left ventricular structure and function in a model of LMNA cardiomyopathy. Collectively, our novel results provide therapeutic insights into LMNA cardiomyopathy

Quantification of skeletal muscle strength in laminopathies

Valérei Decostre : Speaker invitéeInternational audienc

French recommendations for the management of glycogen storage disease type III

Abstract The aim of the Protocole National De Diagnostic et de Soins/French National Protocol for Diagnosis and Healthcare (PNDS) is to provide advice for health professionals on the optimum care provision and pathway for patients with glycogen storage disease type III (GSD III).The protocol aims at providing tools that make the diagnosis, defining the severity and different damages of the disease by detailing tests and explorations required for monitoring and diagnosis, better understanding the different aspects of the treatment, defining the modalities and organisation of the monitoring. This is a practical tool, to which health care professionals can refer. PNDS cannot, however, predict all specific cases, comorbidities, therapeutic particularities or hospital care protocols, and does not seek to serve as a substitute for the individual responsibility of the physician in front of his/her patient