Icos gene disruption in non‐obese diabetic mice elicits myositis associated with anti‐troponin T3 autoantibodies

Abstract

Aims: Idiopathic inflammatory myopathies (IIM) are autoimmune inflammatory disorders leading to skeletal muscle weakness and disability. The pathophysiology of IIM is poorly understood due to the scarcity of animal disease models. Genetic deletion of Icos or Icosl (inducible T cell co-stimulator/ligand) in non-obese diabetic (NOD) mice leads to muscle disease. Our aim was to characterise Icos À/À NOD myopathy and to search for novel autoantibodies (aAbs) in this model.Methods: Diabetes, weight, myopathy incidence/clinical score and grip strength were assessed over time. Locomotor activity was analysed with the Catwalk XT gait analysis system. Muscle histology was evaluated in haematoxylin/eosin and Sirius red-stained sections, and immune infiltrates were characterised by immunofluorescence and flow cytometry. 2D gel electrophoresis of muscle protein extracts and mass spectrometry were used to identify novel aAbs. NOD mice were immunised with troponin T3 (TNNT3) in incomplete Freund's adjuvant (IFA) and R848. An addressable laser bead immunoassay (ALBIA) was developed to measure aAb IgG serum levels.Results: Icos À/À NOD mice did not exhibit diabetes but developed spontaneous progressive myositis with decreased muscle strength and altered locomotor activity. Muscle from these mice exhibited myofibre necrosis, myophagocytosis, central nuclei, fibrosis and perimysial and endomysial cell infiltrates with macrophages and T cells. We identified anti-TNNT3 aAbs in diseased mice. Immunisation of NOD mice with murine TNNT3 protein led to myositis development, supporting its pathophysiological role.

IFNγ causes mitochondrial dysfunction and oxidative stress in myositis

“…Experimental autoimmune myositis (EAM) models based on immunization with muscle homogenates, myosin, or C-protein may be useful to unravel certain aspects of the disease, but their specific immunogen-driven nature may not reflect the complexity of IIMs mechanisms 16 . We previously reported the occurrence of severe spontaneous muscle autoimmune disease in Non-Obese Diabetic (NOD) mice with a constitutive deletion of the costimulatory molecule ICOS or its ligand ( Icos -/- NOD or Icosl -/- NOD mice) 17 – 19 . Whereas NOD mice constitute a classical model of spontaneous type 1 diabetes, Icos -/- NOD and Icosl -/- NOD mice exhibit progressive and chronic muscle inflammation with Th1-infiltrating cells, while being protected from diabetes development.…”