Citrullinated Inhibitor of DNA Binding 1 Is a Novel Autoantigen in Rheumatoid Arthritis

The Role of Extracellular Vesicles in the Pathogenesis and Treatment of Rheumatoid Arthritis and Osteoarthritis

Cells can communicate with each other through extracellular vesicles (EVs), which are membrane-bound structures that transport proteins, lipids and nucleic acids. These structures have been found to mediate cellular differentiation and proliferation apoptosis, as well as inflammatory responses and senescence, among others. The cargo of these vesicles may include immunomodulatory molecules, which can then contribute to the pathogenesis of various diseases. By contrast, EVs secreted by mesenchymal stem cells (MSCs) have shown important immunosuppressive and regenerative properties. Moreover, EVs can be modified and used as drug carriers to precisely deliver therapeutic agents. In this review, we aim to summarize the current evidence on the roles of EVs in the progression and treatment of rheumatoid arthritis (RA) and osteoarthritis (OA), which are important and prevalent joint diseases with a significant global burden.

Role and mechanism of fibroblast-activated protein-α expression on the surface of fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-activated protein-α (FAP) is a type II integrated serine protease expressed by activated fibroblasts during fibrosis or inflammation. Fibroblast-like synoviocytes (FLSs) in rheumatoid arthritis (RA) synovial sites abundantly and stably overexpress FAP and play important roles in regulating the cellular immune, inflammatory, invasion, migration, proliferation, and angiogenesis responses in the synovial region. Overexpression of FAP is regulated by the initial inflammatory microenvironment of the disease and epigenetic signaling, which promotes RA development by regulating FLSs or affecting the signaling cross-linking FLSs with other cells at the local synovium and inflammatory stimulation. At present, several treatment options targeting FAP are in the process of development. This review discusses the basic features of FAP expressed on the surface of FLSs and its role in RA pathophysiology and advances in targeted therapies.

MiR-326 regulates cell proliferation and apoptosis in fibroblast-like synoviocytes in rheumatoid arthritis

The dysregulation of microRNAs plays a critical role in the development of rheumatoid arthritis (RA). This study aims to explore the functional significance of miR-326 in RA. The RT-qPCR results showed that miR-326 was downregulated in synovial tissues of RA patients and RA fibroblast-like synoviocytes (RA-FLS). We found that miR-326 could target and reduce the expression of inhibitor of DNA binding 1 (Id1). MTT assay and flow cytometry were conducted to explore the biological function of miR-326. Our data revealed that the upregulation of miR-326 suppressed cell proliferation and induced apoptosis in RA-FLS. In collagen-induced arthritis mice, intraarticular injection of lentivirus carrying miR-326 overexpression vectors could reduce the arthritis score and attenuate synovial inflammation and cartilage destruction. We also found that long non-coding RNA-Ewing sarcoma-associated transcript 1 (lncRNA-EWSAT1) was significantly increased in RA synovial tissues and RA-FLS. The RNA immunoprecipitation and RNA pull-down assay indicated that lncRNA-EWSAT1 directly bound and negatively regulated the expression of miR-326. Knockdown of lncRNA-EWSAT1 could upregulate miR-326 expression and attenuate its proliferation inhibition and apoptosis induction effect in RA-FLS.  In conclusion, the lncRNA-EWSAT1/miR-326 axis might provide a novel therapeutic target in the treatment of RA.

Targeting fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-like synoviocytes (FLS) are mesenchymal-derived cells that play an important role in the physiology of the synovium by producing certain components of the synovial fluid and articular cartilage. In rheumatoid arthritis (RA), however, fibroblasts become a key driver of synovial inflammation and joint damage. Because of this, there has been recent interest in FLS as a therapeutic target in RA to avoid side effects such as systemic immune suppression associated with many existing RA treatments. In this review, we describe how approved treatments for RA affect FLS signaling and function and discuss the effects of investigational FLS-targeted drugs for RA.