The Modulatory Role of Neuronal Nicotinic Receptors on Peripheral Inflammation

This dissertation examines the relationship between inflammatory cytokines and nicotinic acetylcholine receptors (nAChR). WT and nAChRa7 null mice were exposed to 4.8kJ/m2 of UVB on a standardized area of back skin. This dose of UVB caused the skin to be visibly inflamed 48 hours after exposure; at this point the back skin was removed and analyzed for inflammatory cytokines. Production of IL-lp and IL-6, but not TNFa was significantly increased in a 7 null mice. Further, H&E stained skin sections revealed greater edema in mice lacking a7. Production of SOCS3, a negative regulator of cytokines, was decreased in inflamed skin from a7 null mice, suggesting a potential mechanism by which a7 could regulate cytokine production. The induction of IL-1(3 and IL-6 in skin by UVB was inhibited in mice first exposed to y-irradiation, suggesting that rapidly dividing cells that infiltrate the inflamed skin were responsible for the measured cytokine production. To further identify the types of cells infiltrating the skin following an inflammatory stimulus, croton oil was applied to mouse ears and infiltrating cells were isolated following the separation of dorsal and ventral ear flaps. Mice lacking a7 had a significant increase in the total number of recruited cells as well as increased expression of IL-lp, IL-6 and TNFa by infiltrating cells. The cells infiltrating the inflamed site were determined to be CD1 lb+ Ly6g+ neutrophils and CD1 lb+ F4/80+ macrophages by FACS analysis. Further, it was determined that chemokines which recruit neutrophils and macrophages, such as CXCL2, CXCL5 and CCL3 were all also increased in a7 null mice. Inhibiting the p38 MAP Kinase signaling pathway in WT and a 7 null primary macrophage cultures decreased the LPS induced expression of cytokines and chemokines. The reciprocal effect of cytokines on nicotinic receptors was also investigated. It was determined that treatment of transfected HEK293 cells with TNFa induces enhanced upregulation of the high affinity nicotine binding receptor a4p2. Treatment of these cells with a p38 MAP Kinase inhibitor blocks the TNFa enhanced upregulation. Collectively, these data demonstrate a relationship between nicotinic receptors and inflammatory cytokines and the involvement of the p38 MAP Kinase pathway.