RA and OA are two common types of arthritis with an inflammatory component, but have distinct etiologies, clinical trajectories and treatment. The pathogenesis and manifestations of these two diseases are complex, with clinical heterogeneity in presentation and disease course. Distinguishing between these two arthritic conditions is critically important for early diagnosis, appropriate treatment and elucidates the underlying pathophysiology of these disorders. Studies have demonstrated that synovial tissue plays an important role in the occurrence and development of both RA and OA. Our study performed second-generation sequencing on the synovial tissue of these two diseases, thereby enabling the identification of DEGs, analysis of the functions and pathways from DEGs enrichment results, and subsequently verified the hub DEGs by RT-qPCR.
In previous studies, the data sets in the GEO database were used for bioinformatics analysis of RA synovial tissue, such as GSE55235, GSE12021, etc. These studies are based on previous chip information, with different data sets and different genes identified[24, 25]. To further investigate the biomarkers of synovial tissue in RA synovial tissue. In order to further analyze the transcriptome of RA synovial tissue derived from patients in a clinical setting, we collected synovial tissue from patients with RA and OA within a single rheumatology hospital, performed RNA-seq, and investigated the pathways, gene networks and hub genes to further arthritis transcriptome studies.
In this study, a total of 17736 genes were detected. The GSEA was sensitive to detect genes with relatively smaller fold change . We found that in curated gene sets, the significant enriched gene sets positively correlated with RA group were CD40 signaling up, Th1 cytotoxic module. The CD40 signaling is associated with the production of human rheumatoid factor  and the CD40/NF-kB signaling pathway play an important role in RA pathogenesis.The Th1 cytotoxic module has not been reported to be related to RA, but the Th1 cytotoxic is reportedly associated with tumor microenvironment. In ontology gene sets, the significant enriched gene sets positively correlated with RA group were activation of immune response, adaptive immune response. The RA is an autoimmune disease involved in innate and adaptive immunity. In immunologic signature gene sets, the significant enriched gene sets positively correlated with RA group was the up-regulation of the gene set of effective versus memory CD8 T cell; The down-regulation of gene set of naïve versus effective CD8 T cell.
-The CD8 + T cells are involved in the pathogenesis of many autoimmune diseases mainly due to their self-reactive cytotoxic inflammatory behavior. Effective CD8 + T cells have proliferation and cytotoxic properties, and induce the death of infected cells and effective memory CD8 + T cells have a lower ability to induce cytotoxicity than effective CD8 + T cells[31, 32].
In our study, a total of 651 DEGs were identified, of which 403 were up-regulated genes and 248 were down-regulated genes. GO functional enrichment analysis demonstrated that the DEGs were enriched in signal transduction, immune response and inflammatory response in BP term, enriched in calcium ion binding, receptor binding and chemokine activity in MF term, enriched in plasma membrane, integral component of membrane and extracellular region in CC term. The KEGG pathway analysis showed that the DEGs were enriched in the cytokine-cytokine receptor interaction, chemokine signaling pathway, systemic lupus erythematosus, T cell receptor signaling pathway and rheumatoid arthritis. The DEGs was mainly concentrated in immune and inflammation-related pathways.
A total of 10 DEGs were distinguished as hub genes by MCODE and cytoHubba plugin of Cytoscape. According to the ROC analysis, and qRT-PCR validation, for the synovial tissue ,the expression of CXCL13, CXCL6, CCR5, CXCR5, CCR2, CXCL3, CXCL10 in RA were higher than OA,but the expression of SSTR1 in OA was higher than RA. The expression of CCR7 and SSTR3 showed no difference between RA and OA synovial tissue. CXCL13, CXCL10, CXCL6 and CXCL3 are the main members of the CXC chemokine subfamily. C-X-C motif chemokine ligand 13 (CXCL13), a B cell chemokine, interacting with its receptor C-X-C motif chemokine receptor 5 (CXCR5) promotes the migration and aggregation of B lymphocytes . The expression level of CXCL13 with the serum of RA patients are positively correlated with the level of rheumatoid factor, and is also correlated with the disease activity and treatment response of early rheumatoid arthritis [34–36]. C-X-C motif chemokine ligand 10 (CXCL10) is a ligand for the receptor C-X-C motif chemokine receptor 3 (CXCR3), which may stimulate the migration of monocytes, natural killer and T-cell migration . The expression of CXCL10 was detected in serum, synovial fluid and synovial tissue of RA patients [38, 39]. CXCL10 may be a disease activity marker in early RA because of its high circulating level in plasma of untreated early RA and its association with clinical disease activity. Our study confirmed the high expression of CXCL10 in RA synovial tissue, and identified that CXCL10 expression level in RA synovial tissue was higher than that in OA synovial tissue, and the difference was statistically significant. C-X-C motif chemokine ligand 3 (CXCL3) was reported to be associated with the invasion and metastasis of various cancer[41–43]. CXCL3 and CXCL6 are related to the invasion and migration of a variety of cancers [44–46]. The differential expression of CXCL3 and CXCL6 between RA and OA synovial tissue has not been reported. CCR7, CCR5, CCR2 are typical chemokine receptors. C-C motif chemokine receptor 5 (CCR5) is reportedly expressed in the RA synovial tissue and T helper-cell type 1 inflammatory infiltrates. The CCR5 ( the Delta32 allelic variant) has previously been reported as having a protective effect on RA susceptibility , however, the effect of CCR5 inhibitors on RA is still controversial[48–50]. C-C motif chemokine receptor 2 (CCR2) has been widely considered as a potential therapeutic target for RA and the CCR2 blocking agents have been developed. The monocyte chemoattractantprotein (MCP)-1 (CCL2) and its high-affinity receptor, CCR2, are central to the development of pain associated with knee osteoarthritis. CCR2 plays an important role in both RA and OA. our study found the expression of CCR2 in RA and OA synovial tissue was different, may further identify its differential function between RA and OA. Somatostatins can regulate diverse cellular functions such as neurotransmission, cell proliferation. The somatostatin receptor 1 (SSTR1) was reportedly associated with various cancer, such as prostate cancer and gastric cancer . The role of SSTR1 in RA and OA has not been studied, our study may provide a basis for future arthritis research.