Background/Purpose: Antisynthetase syndrome (AS) is type of myositis characterized by autoantibodies targeting aminoacyl-transfer tRNA synthetases (aaRSs), the enzymes responsible for loading the appropriate amino acid onto its corresponding tRNA. We recently showed that myositis autoantibodies are internalized into muscle fibers where they have functional effects on their protein targets. This study aimed to determine whether AS autoantibodies impair the normal function of their target aaRS.

Methods: Bulk RNA sequencing was conducted on 669 frozen human muscle biopsies from patients with different AS autoantibodies (37 anti-Jo1, 12 anti-PL7, 12 anti-PL12, 3 anti-EJ, 1 anti-OJ), other inflammatory myopathies, and healthy controls. Cultured human skeletal muscle myoblasts (HSMM) were electroporated to internalize AS autoantibodies or treated with histidinol, an inhibitor of histidyl-tRNA synthetase (i.e., Jo1). Transcriptomic profiles were compared between AS muscle biopsies and human HSMM after antibody internalization and inhibition of histidyl-tRNA synthetase. Specific gene sets were defined by intersecting differentially overexpressed genes (q-value < 0.01) between groups.

Results: An AS-specific gene set including CAMK1G, EGR4, PROK2, ALOXE3, and CXCL8 was uniquely overexpressed in AS muscle biopsies. This gene set was expressed at highest levels in anti-Jo1-positive patients followed by anti-PL7-positive and then anti-PL12-positive patients. The expression of the AS-specific gene set was correlated with the expression of genes related to disease activity. Internalization of purified immunoglobulin from anti-Jo1 patients into HSMM induced overexpression of the AS-specific gene set identified in the muscle biopsies from AS patients. In addition, these cells exhibited NFKB pathway activation and increased expression of IL1 and CXCL8 (IL8) genes. Histidinol treatment also activated the NFKB pathway and increased IL1 and IL8 expression. Comparing cells electroporated with antibodies from anti-Jo1-positive patients to histidinol-treated cells, 54% of differentially expressed genes overlapped, suggesting a common mechanism. Furthermore, a significant association was observed between genes expressed in both experiments and those in human muscle biopsies.

Conclusion: We identified a set of genes that are only upregulated in muscle biopsies from patients with AS. The expression of these genes correlated with transcriptomic markers of disease activity. In cultured myoblasts, internalization of antibodies from anti-Jo1-positive patients and histidinol treatment replicated transcriptomic changes observed in muscle biopsies from anti-Jo1-positive patients. Taken together, these findings demonstrate that anti-Jo1 autoantibodies, and perhaps other AS autoantibodies, inhibit its target aminoacyl-tRNA synthetase and activate the NFKB pathway.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/antisynthetase-autoantibodies-disrupt-the-function-of-their-target-aminoacyl-trna-synthetases-in-muscle-cells/