Recent studies have suggested an important role for neurotransmitters as modulators of inflammation. Therefore, we undertook this study to investigate the expression of the alpha7 subunit of the nicotinic acetylcholine receptor (alpha7nAChR) and its function in rheumatoid arthritis (RA).
The potential role of the alpha7nAChR in modulating proinflammatory cytokine expression in fibroblast-like synoviocytes (FLS) was identified by screening an adenoviral short hairpin RNA (Ad.shRNA) library. An alpha7-specific antibody was used for immunohistochemistry, and fluorescein isothiocyanate-labeled alpha-bungarotoxin, which binds specifically to the alpha7nAChR, was used for immunofluorescence. Gene expression in FLS was determined by quantitative polymerase chain reaction with primers specific for the alpha7nAChR. In addition, we analyzed messenger RNA (mRNA) expression of dupalpha7, a variant alpha7 transcript. Next, we studied the functional role of the alpha7nAChR in RA FLS by examining the effects of alpha7-specific agonists on the production of interleukin-6 (IL-6) and IL-8 by activated FLS.
A screen using an Ad.shRNA library against 807 transcripts revealed that a specific alpha7nAChR shRNA potently modulated IL-8 and matrix metalloproteinase expression in FLS. The alpha7nAChR was expressed in the inflamed synovium from RA patients, predominantly in the intimal lining layer. We found alpha7nAChR expression at both the mRNA and protein level in cultured RA FLS. FLS also constitutively expressed dupalpha7 mRNA. Specific alpha7nAChR agonists reduced tumor necrosis factor alpha-induced IL-6 and IL-8 production by FLS.
The alpha7nAChR and its dupalpha7 variant are expressed in RA synovium, where they may play a critical role in regulating inflammation. Targeting the alpha7nAChR could provide a novel antiinflammatory approach to the treatment of RA.