Article
Proteasome immunosubunits in the pathogenesis of myopathies
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Authors
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Salyan Bhattarai
- Charité - Universitätsmedizin Berlin, Department of Rheumatology and Clinical Immunology, Berlin, Germany
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Khetam Ghannam
- Charité - Universitätsmedizin Berlin, Department of Rheumatology and Clinical Immunology, Berlin, Germany
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Werner Stenzel
- Charité - Universitätsmedizin Berlin, Institut für Neuropathologie, Berlin, Germany
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Lorena Gamboa Martinez
- Charité - Universitätsmedizin Berlin, Department of Rheumatology and Clinical Immunology, Berlin, Germany
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Simone Spuler
- Charité - Universitätsmedizin Berlin, Muscle Research Unit, Experimental and Clinical Research Center, Berlin, Germany
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Olivier Benveniste
- La Pitié-Salpêtrière Hospital, Internal Medicine Department, Paris, France
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Eugen Feist
- Charité - Universitätsmedizin Berlin, Department of Rheumatology and Clinical Immunology, Berlin, Germany
| Published: | August 25, 2015 |
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Outline
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Introduction: Idiopathic inflammatory myopathies (IIM) are characterized by infiltration of immune cells into muscle and upregulation of MHC-I molecule. Previously, we found mRNA of that IFN-γ inducible proteasome subunits (β1i and β5i) significantly increased in IIM muscle biopsies showing its possible role in diseases pathogenesis.
Objectives: We aim to investigate the functional role of immunoproteasome subunit in the pathogenesis of IIM.
Materials & methods: Cryosections of muscle biopsies from Inclusion body myositis (IBM) (n=7), Immune-mediate necrotizing myopathy (IMNM) (n=6), Dermatomyositis (DM) (n=6) patients and healthy controls (n=2) were examined for proteasome subunits and cellular infiltrates by western blot and dual immunofluorescence. Effect of cytokines in the induction of immunoproteasome in skeletal muscle was studied in vitro. Furthermore, in experimental autoimmune myositis (EAM) mice model, the proteasome expression in skeletal muscle was analyzed by immunoblot. The disease activity in this model was correlated by measuring proteasomal activity of skeletal muscle.
Results: Western blot of muscle biopsies from IBM (n=3), IMNM (n=3), DM (n=3) patients showed upregulation of β1i and β5i only in diseased condition. Dual immunofluorescence detected immunosubunits β1i and β5i in the infiltrated muscle fiber in all studied disease conditions, whereas healthy muscle fiber showed no staining of β1i and β5i. Muscle fiber expressing MHC-I showed increased expression of immunosubunits. Among the infiltrating cells, staining of immunosubunits was lowest in CD8+ T cells. In contrast, CD68+ and CD14+ cells showed strong staining of these subunits. Similarly, human myoblast showed increased immunosubunit expression under the influence of IFN-γ in correlation with the expression of MHC-I. In addition to enhanced chymotrypsin-like (CTL) activity of muscle proteasome, immunoblot showed a significant increase in immunosubunit expression in muscle of EAM compared to wild type. Treatment with Rapamycin caused significant decreased in CTL activity of proteasome as well as improvement of myositis in EAM.
Conclusion: These results suggest direct involvement of IFN-γ induced immunosubunits in the pathogenesis of myopathies through enhanced upregulation of MHC-I.
