Background/Purpose: Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of autoimmune disorders targeting muscle as well as extra-muscular organs. Among the most common autoantibodies associated with IIM is anti-histidyl-tRNA synthetase (HRS; Jo-1), which defines a distinct subset of IIM. Although pathogenic mechanisms of the anti-synthetase syndrome are incompletely understood, administration of recombinant HRS in mice has been shown to recapitulate histopathological features and robust anti-HRS antibody responses that are characteristic of human disease. In this study, we used an established murine model of HRS-induced myositis to evaluate the role of membranopathy in IIM pathogenesis and to investigate the therapeutic potential of regulatory T cells (Tregs).

Methods: BALB/C-Tg(NF-κB-RE-luc)-Xen mice harboring a firefly luciferase cDNA reporter gene under the regulation of κB-responsive binding sites or synaptotagmin VII (Syt VII) knockout (KO) mice (B6.129S1-Syt7tm1Nan/J) were injected intramuscularly with a recombinant amino-terminal fragment of murine HRS (mHRS). In NF-κB-RE-luc mice, bioluminescent signals were measured longitudinally. To evaluate suppression of disease pathology, Tregs isolated from wild-type (WT) mice were co-administered with mHRS injections. At experimental endpoints, histopathology of muscle tissue was analyzed and serum was collected to measure autoantibody production. In addition, nuclear extracts of muscle tissue cells were evaluated via EMSA to measure NF-κB activation. Sarcolemmal membrane repair capacity in skeletal muscle was assessed ex vivo by laser injury assays.

Results: NF-κB-RE-luc mice stimulated with mHRS developed an acute inflammatory response consisting primarily of lymphocytes and monocytes/macrophages, which correlated with NF-κB-associated bioluminescence and enhanced nuclear NF-κB binding activity in injected muscles. Despite a reduction in NF-kB activity at later time points, histopathology of mHRS-injected muscle tissue revealed persistent endomysial inflammatory infiltrates consisting of both lymphocytes (CD4+ and CD8+ T cells) and macrophages. Similar mHRS-induced muscle tissue pathology and anti-Jo-1 autoantibody production was observed in mice with a different genetic background (C57BL/6); inflammatory pathology was further amplified in SytVII KO mice that are characterized by inherent sarcolemmal membrane instability, but was ameliorated with concurrent adoptive transfer of WT Tregs. Moreover, WT C57BL/6 mice with mHRS-induced myositis demonstrated significantly compromised cell membrane repair ex vivo.

Conclusion: In summary, these data indicate that the initial inflammatory response in mHRS-induced myositis is NF-κB-regulated and exacerbated by membranopathy, suggesting that aberrant exposure of intracellular antigens, including HRS, can augment autoimmune-mediated pathogenesis. However, myositis pathology is suppressed by adoptive transfer of Tregs from healthy mice. Therefore, strategies engaging the immunosuppressive capacity of Tregs and/or sarcolemmal membrane stabilization represent novel areas of future therapeutic development for the treatment of IIM.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/myositis-induced-by-histidyl-transfer-trna-synthetase-is-exacerbated-by-membranopathy-and-suppressed-by-regulatory-t-cells/