Myeloid related protein induces muscle derived inflammatory mediators in juvenile dermatomyositis
- Equal contributors
1 Rheumatology Unit, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK
2 Institute of Immunology and Interdisciplinary Centre for Clinical Research IZKF, University of Muenster, Muenster, Germany
3 Department of General Pediatrics, University Children’s Hospital Muenster, Muenster, Germany
4 Department of Pediatrics and Adolescent Medicine, First Faculty of Medicine, Charles University in Prague and General University Hospital in Prague, Ke Karlovu 2, 12000 Prague 2, Czech Republic
5 Thérapie des maladies du muscle strié, Institut de Myologie, UM76, UPMC Université Paris 6/U974 - Inserm/UMR7215 – CNRS, 47, bld de l’hôpital - G.H. Pitié-Salpétrière - Bâtiment Babinski, 75651 Paris, cedex 13, France
Arthritis Research & Therapy 2013, 15:R131 doi:10.1186/ar4311Published: 23 September 2013
The aetiopathogenesis of juvenile dermatomyositis (JDM) remains poorly understood. In particular the contribution of monocytes or macrophages, which are frequently observed to be an infiltrate within muscle tissue very early in the disease process, is unknown. We hypothesised that these cells secrete the pro-inflammatory myeloid related protein (MRP) 8/14 which may then contribute to muscle pathology in JDM.
In this study of 56 JDM patients, serum MRP8/14 levels were compared with clinical measures of disease activity. Muscle biopsies taken early in disease were assessed by immunohistochemistry to determine the frequency and identity of MRP-expressing cells. The effects of MRP stimulation and endoplasmic reticulum (ER) stress on muscle were tested in vitro. Serum or supernatant levels of cytokines were analyzed by multiplex immunoassay.
Serum MRP8/14 correlated with physician’s global assessment of disease activity in JDM (R = 0.65, p = 0.0003) and muscle strength/endurance, childhood myositis assessment score (CMAS, R = −0.55, p = 0.004). MRP8/14 was widely expressed by CD68+ macrophages in JDM muscle tissue. When cultured with human myoblasts, MRP8 led to the secretion of MCP-1 and IL-6, which was enhanced by ER stress. Both inflammatory mediators were detected in significantly higher levels in the serum of JDM patients compared to healthy controls.
This study is the first to identify serum MRP8/14 as a potential biomarker for disease activity in JDM. We propose that tissue infiltrating macrophages secreting MRP8/14 may contribute to myositis, by driving the local production of cytokines directly from muscle.