Autoimmune inflammatory myopathies

Activation of the wnt/β-Catenin Signaling Pathway in Polymyositis, Dermatomyositis and Duchenne Muscular Dystrophy

BACKGROUND AND PURPOSE

The wnt/β-catenin signaling pathway plays a critical role in embryonic development and adult-tissue homeostasis. Recent investigations implicate the importance of wnt/β-catenin signaling in normal wound healing and its sustained activation being associated with fibrogenesis. We investigated the immunolocalization and activation of wnt/β-catenin in polymyositis (PM), dermatomyositis (DM), and Duchenne muscular dystrophy (DMD).

METHODS

Immunofluorescence staining and Western blot analysis of β-catenin were performed in muscle specimens from 6 PM, 8 DM, and 6 DMD subjects. The β-catenin/Tcf4 DNA-binding activity in muscle was studied using an electrophoretic mobility shift assay (EMSA), and serum wnt/β-catenin/Tcf transcriptional activity was measured using a luciferase reporter gene assay.

RESULTS

Immunoreactivity for β-catenin was found in the cytoplasm and nuclei of muscle fibers in PM, DM, and DMD. The protein level of β-catenin was elevated, and EMSA analysis confirmed the activation of wnt/β-catenin signaling. The transcriptional activities of β-catenin/Tcf in the circulation were increased in patients with PM, DM, and DMD, especially in those with interstitial lung disease, and these transcriptional activities decreased when PM or DM patients exhibited obvious clinical improvements.

CONCLUSIONS

Our findings indicate that wnt/β-catenin signaling is activated in PM, DM, and DMD. Its activation in muscle tissue and the circulation may play a role in modulating muscle regeneration and be at least partly involved in the process of muscle and pulmonary fibrosis.

An unusual case of inflammatory necrotizing myopathy and neuropathy with pipestem capillaries

Necrotizing myopathy with pipestem capillaries is a form of chronic inflammatory myopathy, with histopathology showing necrotizing myopathy, minimal cellular infiltration, and microangiopathy. A 30-year-old female presented with progressive limb weakness of 6 months, with skin pigmentation and Raynaud's phenomenon. Serum creatine phosphokinase was 3990 u/L. Muscle biopsy showed necrotic fibers, focal sparse perivascular inflammation/perifascicular atrophy, endomysial/epimysial vessel wall thickening with luminal narrowing. The features were of inflammatory necrotizing myopathy and neuropathy with pipestem capillaries/microangiopathy. She was pulsed with intravenous immunoglobulin, methylprednisolone, and cyclophosphamide and showed a good improvement. In the absence of widespread inflammatory response and classical histopathology findings, it is important to diagnose this condition as it shows a good response to aggressive and prolonged immunotherapy.

Beneficial role of rapamycin in experimental autoimmune myositis

INTRODUCTION

We developed an experimental autoimmune myositis (EAM) mouse model of polymyositis where we outlined the role of regulatory T (Treg) cells. Rapamycin, this immunosuppressant drug used to prevent rejection in organ transplantation, is known to spare Treg. Our aim was to test the efficacy of rapamycin in vivo in this EAM model and to investigate the effects of the drug on different immune cell sub-populations.

METHODS

EAM is induced by 3 injections of myosin emulsified in CFA. Mice received rapamycin during 25 days starting one day before myosin immunization (preventive treatment), or during 10 days following the last myosin immunization (curative treatment).

RESULTS

Under preventive or curative treatment, an increase of muscle strength was observed with a parallel decrease of muscle inflammation, both being well correlated (R(2) = -0.645, p<0.0001). Rapamycin induced a general decrease in muscle of CD4 and CD8 T cells in lymphoid tissues, but spared B cells. Among T cells, the frequency of Treg was increased in rapamycin treated mice in draining lymph nodes (16.9 ± 2.2% vs. 9.3 ± 1.4%, p<0.001), which were mostly activated regulatory T cells (CD62L(low)CD44(high): 58.1 ± 5.78% vs. 33.1 ± 7%, treated vs. untreated, p<0.001). In rapamycin treated mice, inhibition of proliferation (Ki-67(+)) is more important in effector T cells compared to Tregs cells (p<0.05). Furthermore, during preventive treatment, rapamycin increased the levels of KLF2 transcript in CD44(low) CD62L(high) naive T cell and in CD62L(low) CD44(high) activated T cell.

CONCLUSIONS

Rapamycin showed efficacy both as curative and preventive treatment in our murine model of experimental myositis, in which it induced an increase of muscle strength with a parallel decrease in muscle inflammation. Rapamycin administration was also associated with a decrease in the frequency of effector T cells, an increase in Tregs, and, when administered as preventive treatment, an upregulation of KFL2 in naive and activated T cells.

Clinical presentation and evaluation of dermatomyositis

Dermatomyositis (DM) is a chronic inflammatory disorder of the skin and muscles. Evidence supports that DM is an immune-mediated disease and 50–70% of patients have circulating myositis-specific auto-antibodies. Gene expression microarrays have demonstrated upregulation of interferon signaling in the muscle, blood, and skin of DM patients. Patients with classic DM typically present with symmetric, proximal muscle weakness, and skin lesions that demonstrate interface dermatitis on histopathology. Evaluation for muscle inflammation can include muscle enzymes, electromyogram, magnetic resonance imaging, and/or muscle biopsy. Classic skin manifestations of DM include the heliotrope rash, Gottron's papules, Gottron's sign, the V-sign, and shawl sign. Additional cutaneous lesions frequently observed in DM patients include periungual telangiectasias, cuticular overgrowth, “mechanic's hands”, palmar papules overlying joint creases, poikiloderma, and calcinosis. Clinically amyopathic DM is a term used to describe patients who have classic cutaneous manifestations for more than 6 months, but no muscle weakness or elevation in muscle enzymes. Interstitial lung disease can affect 35–40% of patients with inflammatory myopathies and is often associated with the presence of an antisynthetase antibody. Other clinical manifestations that can occur in patients with DM include dysphagia, dysphonia, myalgias, Raynaud phenomenon, fevers, weight loss, fatigue, and a nonerosive inflammatory polyarthritis. Patients with DM have a three to eight times increased risk for developing an associated malignancy compared with the general population, and therefore all patients with DM should be evaluated at the time of diagnosis for the presence of an associated malignancy. This review summarizes the immunopathogenesis, clinical manifestations, and evaluation of patients with DM.