Expression of retinoic acid-I nducible gene I in the muscle tissues of idiopathic inflammatory myopathies

Abstract

To investigate the expression of retinoic acid-I inducible gene I (RIG-I) in the muscle tissues from patients with idiopathic inflammatory myopathies (IIMs), and to speculate the possible role of RIG-I in the immunopathogenesis of IIMs. Muscle specimens were obtained from 20 dermatomyositis (DM) and 20 polymyositis (PM) patients who underwent muscle biopsies from February 2010 to April 2014 at Qilu hospital affiliated to Shandong University. Besides, 4 facioscapulohumeral muscular dystrophy (FSHD), and 4 non-myopathic patients were taken as control group. All the biopsy specimens were processed with hematoxylin-eosin and immunohistochemical (Mouse anti human RIG-I antibodies) staining. We also examined the co-localization of RIG-I and CD303, which is the specific surface marker of plasmacytoid dendridic cells (pDCs), by means of double immunofluorescence staining. Western blot was performed for quantitative analysis. There was strong expression of RIG-I protein in DM/PM muscle tissues while in normal controls was virtually absent. RIG-I was specifically expressed in inflammatory cells and vessel endothelium, and nonspecifically expressed in regenerating and necrotic fibers. Besides, strong positive expression was observed in the perimysial perifascicular fibers of DM. In FSHD muscle tissues, only a few regenerating and necrotic fibers was stained nonspecifically for RIG-I. However, co-expression of RIG-I and CD303 was not detected in DM/PM muscles. The mean grey value of RIG-I observed in DM (0.901 ± 0.470) and PM (0.630 ± 0.444) group was significantly higher than in control group including Normal (0.003 ± 0.003) and FSHD (0.019 ± 0.013) groups (P < 0.05). RIG-I may operate as a mediator in Th1 cytokine-I induced chemokine expression, so it is involved in the pathogenesis of IIMs. But RIG-I may not play a major role in innate immune reaction mediated by type I interferon.