We will test a novel hypothesis of rheumatoid arthritis (RA) pathogenesis; namely that abnormalities in the p53 tumor suppressor protein result in dysregulation of synoviocyte function. In this model, immunologic inflammatory processes lead to the accumulation of cytokines, reactive oxygen species (ROS), and nitric oxide (NO) in the joint, which in turn induce DNA damage, p53 activation, and apoptosis in synoviocytes. We propose that either by spontaneous mutation or due to mutagenesis triggered by ROS or NO, somatic defects in p53 arise such that some cells either fail to undergo apoptosis, gain a growth advantage, or express genes that contribute to tissue destruction. This hypothesis does not exclude a role for immune-mediated damage in RA, but rather attempts to explain the nonimmunologic processes responsible for progression of this disease. Three studies lay the foundation for this hypothesis. The first study documented extensive DNA fragmentation in the RA synovial intimal lining without a commensurate increase in morphologic evidence of apoptosis. Second, our investigation of the proteins involved in he regulation of apoptosis demonstrated overexpression of the p53 tumor suppressor gene in the rheumatoid synovium and in cultured RA fibroblast- like synoviocytes (FLS). This degree of expression is unprecedented in a non-neoplastic disease and suggests abnormalities in p53 structure or function. Finally, we have demonstrated that somatic mutations are frequent in freshly isolated synovial tissue and cultured FLS of RA patients. Over 40% of p53 cDNA clones isolated from RA synovium exhibit point mutations, many of which have been previously identified in neoplastic diseases. What is not known, however, is how these mutations alter the function of synoviocytes. This project is designed to extend and confirm these findings by determining the distribution and timing of somatic mutations in RA synovium as well as investigating the occurrence of mutations in other inflammatory and non-inflammatory arthropathies. Second, the function of wild type and mutant p53 in RA synoviocytes will be determined. Finally, the ability of chronic inflammation to induce p53 mutations in an animal model of arthritis will be tested. A p53-targeted therapeutic approach using a defective adenoviral vector lacking the E1B 55 kD protein will be tested in vivo and in vitro.
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