Osteoarthritis (OA) is a group of states associated with defective articular cartilage and changes in the underlying bone.OA is divided into erosive or non-erosive. Erosive OA is more abrupt and commonly exhibits subchondral bone erosions (1). Pathological changes in articular cartilage and subchondral bone result from chondrocyte imbalance in the extracellular matrix. Although numerous studies have reported probable chemical or mechanical causes of cartilage destruction (2,3), this area of research requires more detailed investigation.

Rheumatoid arthritis (RA) is a complex, chronic multisystemic autoimmune disease, which affects the synovial membranes of multiple joints, cartilage and bone as well as bursa and tendon sheaths (4). RA is a prevalent chronic inflammatory joint disease affecting 0.5–1% of the world’s population (5). RA leads to severe morbidity and disability if incorrectly treated, imposing a substantial economic burden on the affected individuals and society. The inflammatory process associated with RA is primarily observed in the synovial tissue. Synovial hyperplasia results from synovial outgrowths or synovial villi, comprised of macrophages, synovial lining cells, lymphocytes and blood vessels (6). Joint destruction occurs when the synovial pannus produces enzymes resulting in cartilage penetration, cartilage damage and joint erosion (7).

Although RA and OA share similar symptoms, it has been demonstrated that RA follows an alternative inflammatory pathway of pathogenesis to OA. Diagnosis and assessment of RA and OA is largely based on semi-quantitative methods of diagnosis, including symptoms, joint damage and physical function (8). At present, no cure exists for RA and OA and the management of these diseases depends upon early detection and aggressive treatment. Therefore, it is increasingly important to explore the molecular mechanisms of these diseases and analyze the associated signaling pathways, in order to uncover an effective therapeutic approach. In this study, we analyzed gene expression profiles of OA and RA cells to determine differentially expressed genes (DEGs) in the two forms of arthritis. Furthermore, through comparison we determined changed metabolic and non-metabolic pathways, small bioactive molecules and SNP corresponding genes associated with RA and OA.

During the development of OA and RA, significant changes in gene expression occur. The present study demonstrated that more than 320 genes changed in OA and RA. Study of these common DEGs may help identify potential broad-spectrum anti-arthritis drugs. Furthermore, only 196 DEGs were identified between OA and RA, including interleukin 3 receptor α (IL3RA), transforming growth factor β receptor III and CRYAB, indicating that the two diseases are correlated and drugs that simultaneously treat these diseases may exist.

Cluster analysis of DEGs demonstrated several common pathways associated with these diseases, including the classic mitogen-activated protein kinase (MAPK) signaling pathway and the insulin signaling pathway. The signaling pathways leading to MAPK activation have been linked to various catabolic responses in diseases, including arthritis (16,17). Two immune pathways, antigen processing and presentation and intestinal immune network for IgA production, were also activated in the arthritic tissues, indicating that the immune response is involved in these diseases. Inflammation and cytokines play significant roles in RA and in certain cases of OA (17). Furthermore, changes of several cell adhesion molecules, including integrin β2 (ITGB2) (18) and protein tyrosine phosphatase receptor type c (PTPRC) (19) and lysosome-related molecules, including phospholipase A2 group XV (PLA2G15) (20) and adaptor-related protein complex 1β (AP1B1) (21) in OA and RA cells demonstrated that the two diseases altered their microenvironment and removed the exogenous substances by the lysosome. In addition, graft-versus-host (22) and autoimmune thyroid disease-related pathways were also activated in OA and RA (23). Further investigation of these pathways is likely to be shed light the network of signal pathways under OA and RA. More studies on the DEGs between OA and RA may provide useful information to differentiate the molecular mechanisms associated with OA and RA.

Based on the DEGs and data from the CMap database, we acquired a series of small molecules. Two of these small molecules, parthenolide and alsterpaullone, demonstrated significant similarity in OA and RA tissues (P<0.05) and required additional analysis to determine their suitability as broad spectrum anti-arthritis drugs.

Parthenolide is a sesquiterpene lactone of the germacranolide class which occurs naturally in the plant feverfew (Tanacetum parthenium). Parthenolide modulates the NF-κB-mediated inflammatory responses in experimental atherosclerosis (24) and blocks lipopolysaccharide-induced osteolysis through suppression of NF-κB activity (25). Parthenolide induces apoptosis in acute myelogenous leukemia cells, leaving normal bone marrow cells relatively unscathed (26). Pharthenolide also exhibits microtubule-interfering activity (27), anti-inflammatory and anti-hyperalgesic effects (28) and activity against the parasite Leishmania amazonensis(29). Since numerous cases of OA and RA result from the interruption of immune responses, including inflammation, it is probable that parthenolide is a suitable therapeutic for these ailments.

Alsterpaullone is a potent, ATP-competitive inhibitor of the cell cycle regulating cyclin-dependent kinases CDK1/cyclin B (IC₅₀ = 0.035 μM) and an inhibitor of GSK-3β and the neuronal CDK5/p25 (30). In addition, alsterpaullone induces apoptosis by activation of caspase-8 and -9 followed by disruption of mitochondrial potential (31).

Through analysis of RA- and OA-related SNPs, we identified that three osteoporosis-related SNP corresponding genes (IGF1, COL1A2 and SATB2) were differentially expressed. Insulin-like growth factor 1 (IGF-1), also called somatomedin C, is a protein encoded by the IGF1 gene in humans (32,33). IGF-1 is expressed and produced by chondrocytes and is one of the anabolic growth factors associated with cartilage (34) and thus is involved in arthritis. Collagen α2(I) chain is a protein encoded by the COL1A2 gene in humans (35,36). Mutations in this gene are associated with osteogenesis imperfecta, Ehlers-Danlos syndrome, idiopathic osteoporosis and atypical Marfan syndrome. Special AT-rich sequence-binding protein 2 (SATB2), also known as DNA-binding protein SATB2, is a human protein encoded by the SATB2 gene (37). SATB2 has been identified to be disrupted in two unrelated cases with de novo apparently balanced chromosome translocations associated with cleft palate and Pierre Robin Sequence (38). The present study also demonstrated that these DEGs were often mutated under arthritis and thereby more studies should focus on their roles in OA and RA.

The present findings shed new light on the molecular mechanisms of OA and RA. Results revealed more than 320 DEGs in both diseases which may be involved in OA and RA development via MAPK and insulin signaling pathways, antigen processing and presentation, intestinal immune network, graft-versus-host disease and autoimmune thyroid disease-related pathways. Notably, parthenolide and alsterpaullone were identified as important small molecules involved in the induction of anti-inflammatory and apoptosis-related gene expression and thus we suggest that these molecules may be suitable anti-arthritis drugs for OA and RA. Furthermore, mutations of IGF1, COL1A2 and SATB2 genes were critical for the pathogenesis of OA and RA. However, there are specific limitations in our study. The pathway enrichment was only based on the connection between genes and therefore genes without strong neighbors are likely to be excluded from the analysis (13). In addition, further experimental analysis is required to confirm the conclusions of the present study.