Expression of ID family genes in the synovia from patients with rheumatoidarthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized b y aggressive proliferation of synovial tissue leading to destruction of car tilage and bone. To identify molecules which play a crucial role for the pa thogenesis, we compared mRNA expression pattern of RA synovium with that of osteoarthritis (OA), using the differential display. From the panel of dif ferentially expressed genes, ID1 (inhibitor of differentiation 1) was consi dered to be particularly relevant to the pathogenesis of RA, because Id fam ily genes have been shown to play a role in cell proliferation and angiogen esis. To examine whether the upregulation of these genes is consistently ob served in the patients with RA, mRNA levels of ID1 and ID3 in the synovial tissues from 13 patients with RA and 6 patients with OA were semi-quantitat ively analyzed by RT-PCR. Mean mRNA levels of ID1 and ID3 were significantl y elevated in RA synovia compared with OA by 8.6-fold (P = 0.0044) and 3.3- fold (P = 0.0085), respectively. Immunohistochemistry revealed striking sta ining of Idl and Id3 in the endothelial cells, suggesting a possible role o f Id in severe angiogenesis observed in RA. The expression of Id family gen es in the synovium constitutes a new finding of particular interest. Their functional role as well as their contribution to the genetic susceptibility to RA requires further investigation. (C) 2001 Academic Press.