The α7 Nicotinic Acetylcholine Receptor on Fibroblast-like Synoviocytes and in Synovial Tissue From Rheumatoid Arthritis Patients A Possible Role for a Key Neurotransmitter in Synovial Inflammation

Objective. Recent studies have suggested an important role for neurotransmitters as modulators of inflammation. Therefore, we undertook this study to investigate the expression of the alpha 7 subunit of the nicotinic acetylcholine receptor (alpha 7nAChR) and its function in rheumatoid arthritis (RA). Methods. The potential role of the alpha 7nAChR in modulating proinflammatory cytokine expression in fibroblast-like synoviocytes (FLS) was identified by screening an adenoviral short hairpin RNA (Ad.shRNA) library. An alpha 7-specific antibody was used for immunohistochemistry, and fluorescein isothiocyanate-labeled alpha-bungarotoxin, which binds specifically to the alpha 7nAChR, was used for immunofluorescence. Gene expression in FLS was determined by quantitative polymerase chain reaction with primers specific for the alpha 7nAChR. In addition, we analyzed messenger RNA (mRNA) expression of dup alpha 7, a variant alpha 7 transcript. Next, we studied the functional role of the alpha 7nAChR in RA FLS by examining the effects of alpha 7-specific agonists on the production of interleukin-6 (IL-6) and IL-8 by activated FLS. Results. A screen using an Ad.shRNA library against 807 transcripts revealed that a specific alpha 7nAChR shRNA potently modulated IL-8 and matrix metalloproteinase expression in FLS. The alpha 7nAChR was expressed in the inflamed synovium from RA patients, predominantly in the intimal lining layer. We found alpha 7nAChR expression at both the mRNA and protein level in cultured RA FLS. FLS also constitutively expressed dup alpha 7 mRNA. Specific alpha 7nAChR agonists reduced tumor necrosis factor alpha-induced IL-6 and IL-8 production by FLS. Conclusion. The alpha 7nAChR and its dup alpha 7 variant are expressed in RA synovium, where they may play a critical role in regulating inflammation. Targeting the alpha 7nAChR could provide a novel antiinflammatory approach to the treatment of RA.