Atrophy of type II fibres in myasthenia gravis muscle in thymectomized patients: steroid-induced change with prognostic impact

Rituximab for myasthenia gravis

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

To assess:

the safety and efficacy, as assessed by the effect on disease severity or functional ability and the burden of alternative treatment, of rituximab (including biosimilar variants) for the treatment of myasthenia gravis in adults; and

outcomes and adverse effects between different patient subgroups, and treatment strategies, in order to aid treatment choice for individuals, and to inform policymakers about those most likely to benefit. 

Muscle satellite cells are functionally impaired in myasthenia gravis: consequences on muscle regeneration

Myasthenia gravis (MG) is a neuromuscular disease caused in most cases by anti-acetyl-choline receptor (AChR) autoantibodies that impair neuromuscular signal transmission and affect skeletal muscle homeostasis. Myogenesis is carried out by muscle stem cells called satellite cells (SCs). However, myogenesis in MG had never been explored. The aim of this study was to characterise the functional properties of myasthenic SCs as well as their abilities in muscle regeneration. SCs were isolated from muscle biopsies of MG patients and age-matched controls. We first showed that the number of Pax7+ SCs was increased in muscle sections from MG and its experimental autoimmune myasthenia gravis (EAMG) mouse model. Myoblasts isolated from MG muscles proliferate and differentiate more actively than myoblasts from control muscles. MyoD and MyoG were expressed at a higher level in MG myoblasts as well as in MG muscle biopsies compared to controls. We found that treatment of control myoblasts with MG sera or monoclonal anti-AChR antibodies increased the differentiation and MyoG mRNA expression compared to control sera. To investigate the functional ability of SCs from MG muscle to regenerate, we induced muscle regeneration using acute cardiotoxin injury in the EAMG mouse model. We observed a delay in maturation evidenced by a decrease in fibre size and MyoG mRNA expression as well as an increase in fibre number and embryonic myosin heavy-chain mRNA expression. These findings demonstrate for the first time the altered function of SCs from MG compared to control muscles. These alterations could be due to the anti-AChR antibodies via the modulation of myogenic markers resulting in muscle regeneration impairment. In conclusion, the autoimmune attack in MG appears to have unsuspected pathogenic effects on SCs and muscle regeneration, with potential consequences on myogenic signalling pathways, and subsequently on clinical outcome, especially in the case of muscle stress.

IL-6 and Akt are involved in muscular pathogenesis in myasthenia gravis

Introduction

Anti-acetylcholine receptor (AChR) autoantibodies target muscles in spontaneous human myasthenia gravis (MG) and its induced experimental autoimmune model MG (EAMG). The aim of this study was to identify novel functional mechanisms occurring in the muscle pathology of myasthenia.

Results

A transcriptome analysis performed on muscle tissue from MG patients (compared with healthy controls) and from EAMG rats (compared with control rats) revealed a deregulation of genes associated with the Interleukin-6 (IL-6) and Insulin-Like Growth Factor 1 (IGF-1) pathways in both humans and rats. The expression of IL-6 and its receptor IL-6R transcripts was found to be altered in muscles of EAMG rats and mice compared with control animals. In muscle biopsies from MG patients, IL-6 protein level was higher than in control muscles. Using cultures of human muscle cells, we evaluated the effects of anti-AChR antibodies on IL-6 production and on the phosphorylation of Protein Kinase B (PKB/Akt). Most MG sera and some monoclonal anti-AChR antibodies induced a significant increase in IL-6 production by human muscle cells. Furthermore, Akt phosphorylation in response to insulin was decreased in the presence of monoclonal anti-AChR antibodies.

Conclusions

Anti-AChR antibodies alter IL-6 production by muscle cells, suggesting a putative novel functional mechanism of action for the anti-AChR antibodies. IL-6 is a myokine with known effects on signaling pathways such as Akt/mTOR (mammalian Target of Rapamycin). Since Akt plays a key role in multiple cellular processes, the reduced phosphorylation of Akt by the anti-AChR antibodies may have a significant impact on the muscle fatigability observed in MG patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0179-6) contains supplementary material, which is available to authorized users.

Proteomic analysis of rat tibialis anterior muscles at different stages of experimental autoimmune myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease in which autoantibodies, most commonly directed against the acetylcholine receptor (AChR), impair neuromuscular transmission and cause muscle weakness. In this study, we utilized two-dimensional difference in-gel electrophoresis (2D-DIGE) to analyze the muscle's proteomic profile at different stages of experimental autoimmune myasthenia gravis (EAMG). We identified twenty-two differentially expressed proteins, mainly related to metabolic and stress-response pathways. Interestingly, these identified proteins have also been associated with other contraction-impairing muscle pathologies (e.g. inclusion body myositis), suggesting a similar response of the muscle to such conditions.