Phosphoproteomic investigation of pathological molecules in rheumatoid arthritis

Objective: To survey synoviocyte-related pathological molecules in rheumatoid arthritis (RA) of a representative inflammatory polyarthritis, we investigated phosphoproteome of synoviocytes of patients with RA, in comparison with that of osteoarthritis (OA). Materials and Methods: Proteins extracted from cultured synoviocytes of 5 RA and 5 OA patients were respectively separated by 2-dimentional electrophoresis and phosphorylation levels of the protein spots were compared between the RA and OA samples. Some of the protein spots which were phosphorylated at higher levels in RA than in OA were identified by mass spectrometry. Further, the gene for one of the identified protein was introduced to mice to investigate its arthritogenicity. Results: We detected 56 protein spots whose phosphorylation levels were more than two-fold higher in RA than in OA. One of the identified protein spots was annexin 7. Up-regulation of annexin 7 expression in synoviocytes was confirmed and the section of synovium in RA. Further, the gene for annexin 7 was introduced into B6 mice, which were resistant to collagen-induced arthritis (CIA). As a result, the annexin 7-transgened B6 mice became sensitive to CIA. Conclusion: The phosphoproteome profiles of synoviocytes in RA were distinct from those in OA. One of the highly phosphorylated proteins in RA, annexin 7, was found to have potential to alter CIA-resistant mice to sensitive ones. This indicates that annexin 7, strongly involved in the pathogenesis of RA, may be a new therapeutic target of RA.