Myo-endothelial repair in inflammatory myopathies

Autoimmune inflammatory myopathies (IM) are a large group of acquired and potentially treatable muscle diseases. Based on distinct clinical, histopathological and immunological features three major subtypes, dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM), have been delineated. IBM is now recognized as the most common IM associated with ageing characterized by the co-existence of chronic inflammation and a degenerative process related to protein misfolding and deposition of ß-amyloid causing a poor response to conventional immunosuppressive therapies in most patients with IBM. The regenerative capacity of inflamed muscle after treatment is the limiting factor for functional recovery of muscle strength, which might be impaired in patients un-responsive to currently available immunomodulatory therapies. The main source for muscle repair following injury in postnatal individuals are considered tissue specific myogenic stem cells, called "satellite cells". Based on recent experimental studies, however, incorporation of circulating hematopoietic progenitor cells (HPCs) into damaged skeletal muscle has been proposed as a novel mechanism of tissue repair complementary to satellite cell dependent regeneration. In a pilot study we were able to demonstrate HPCs in human skeletal muscle in IM by immunohistochemistry and RT-PCR and provided evidence for in-situ myo-endothelial differentiation of HPCs by confocal laser scanning microscopy. The aim of the proposed study is to characterize patterns of muscle regeneration in relation to different pathogenic mechanisms - complement and antibody associated capillary changes versus T cell-mediated myocytotoxicity - in a large cohort of patients. In Cooperation with the reference center for neuromuscular diseases at the Institute de Myologie, Hopital Pitié-Salpetrière, we will be able to investigate > 300 of myositis patients and corresponding muscle biopsies. Using a broad panel of antibodies we will immunohistochemically analyze and quantify the expression of endothelial (CD31, vWF, VEGFR-2), hematopoietic (CD34, CD133, CD45, CD14) and myogenic (Pax7, Myf5, MRF4, MyoD, and myogenin) markers attempting to delineate pathways of myo- and vasculogenesis in response to inflammation. Co-expression patterns of individual cells will be studied by confocal laser scanning microscopy to determine their origin. The proposed study may extend our understanding of the pathophysiology of inflammatory myopathies and form the basis for the definition of prognostic factors, evaluation of the effects of various immunomodulatory treatments on muscle repair, and possibly the development of strategies to support regeneration.