Meletakos, T. | Search bioRxiv

bioRxiv2023

Cyld aborts hyperactivation of synovial fibroblasts in inflammatory arthritis by regulating the TAK1/IKK2 signaling axis

TNF is a potent cytokine known for its involvement in physiology and pathology. In Rheumatoid Arthritis (RA), persistent TNF signals cause aberrant activation of synovial fibroblasts (SFs), the resident cells crucially involved in the inflammatory and destructive responses of the affected synovial membrane. However, the molecular switches that control the pathogenic activation of SFs remain poorly defined. Cyld is a major component of deubiquitination (DUB) machinery regulating the signaling responses towards survival/inflammation and programmed necrosis that induced by cytokines, growth factors and microbial products. Here we follow functional genetic approaches to understand how Cyld affects arthritogenic TNF signaling in SFs. We demonstrate that in spontaneous and induced RA models, SF-Cyld DUB deficiency deteriorates arthritic phenotypes due to increased levels of chemokines, adhesion receptors and bone-degrading enzymes generated by mutant SFs. Mechanistically, Cyld serves to restrict the TNF-induced hyperactivation of SFs by limiting Tak1-mediated signaling, and, therefore, leading to supervised NFkB and JNK activity. However, Cyld is not critically involved in the regulation of TNF-induced death of SFs. Our results identify SF-Cyld as a regulator of TNF-mediated arthritis and inform the signaling landscape underpinning the SF responses.

immunology↗

bioRxiv2022

miR-221/222 drive synovial fibroblast expansion and pathogenesis of TNF-mediated arthritis

MicroRNAs (miRNAs) constitute fine tuners of gene expression and are implicated in a variety of diseases spanning from inflammation to cancer. miRNA expression is deregulated in rheumatoid arthritis (RA), however, their specific role in key arthritogenic cells such as the synovial fibroblast (SF) remains elusive. We have shown in the past that the expression of the miR-221/222 cluster is upregulated in RA SFs. Here, we demonstrate that miR-221/222 activation is downstream of major inflammatory cytokines, such as TNF and IL-1{beta}, which promote miR-221/222 expression independently. miR-221/222 expression in SFs from the huTNFtg mouse model of arthritis correlates with disease progression. Targeted transgenic overexpression of miR-221/222 in SFs of the huTNFtg mouse model led to further expansion of synovial fibroblasts and disease exacerbation. miR-221/222 overexpression altered the transcriptional profile of SFs igniting pathways involved in cell cycle progression and ECM regulation. Validated targets of miR-221/222 included p27 and p57 cell cycle inhibitors, as well as Smarca1 (a chromatin remodeling component). In contrast, complete genetic ablation of miR-221/222 in arthritic mice led to decreased proliferation of fibroblasts, reduced synovial expansion and attenuated disease. scATAC-seq data analysis revealed increased miR-221/222 gene activity in the pathogenic and activated clusters of the intermediate and lining compartment. Taken together, our results establish an SF-specific pathogenic role of the miR-221/222 cluster in arthritis and suggest that its therapeutic targeting in specific subpopulations should inform the design of novel fibroblast-targeted therapies for human disease.

cell biology↗