Citation

Most forms of arthritis, have a distinctive topographical pattern of joint involvement. Beyond these differences among diseases, there are also differences in phenotype and response to treatment between joints of the same type of arthritis, suggesting that molecular mechanisms may differ depending on joint location. Here we show that there are joint-specific molecular and tissue changes in the synovium and in local stromal cells (synovial fibroblasts;SF). The long non-coding RNA HOTAIR, expressed only in lower extremities SF, regulates much of this site-specific gene expression in SF. Downregulation of HOTAIR after TNF stimulation regulated relevant inflammatory pathways by epigenetic and transcriptional mechanisms and modified the migratory function of SF, decreased SF-mediated osteoclastogenesis, and increased the attraction of B cells by SF. Since site-specific expression of HOTAIR was also measured in the skin, spine and gastrointestinal tract, we propose HOTAIR as important epigenetic factor that modulates site-specific phenotypes of chronic inflammation.