Acetylcholine released by efferent vagus nerves inhibits macrophage activation. Here we show that the anti-inflammatory action of nicotinic receptor activation in peritoneal macrophages was associated with activation of the transcription factor STAT3. STAT3 was phosphorylated by the tyrosine kinase Jak2 that was recruited to the alpha7 subunit of the nicotinic acetylcholine receptor. The anti-inflammatory effect of nicotine required the ability of phosphorylated STAT3 to bind and transactivate its DNA response elements. In a mouse model of intestinal manipulation, stimulation of the vagus nerve ameliorated surgery-induced inflammation and postoperative ileus by activating STAT3 in intestinal macrophages. We conclude that the vagal anti-inflammatory pathway acts by alpha7 subunit-mediated Jak2-STAT3 activation.

The cholinergic nervous system attenuates the production of pro-inflammatory cytokines and inhibits inflammatory processes. Hence, in animal models of intestinal inflammation, such as postoperative ileus and dextran sulfate sodium-induced colitis, vagus nerve stimulation ameliorates disease activity. On the other hand, in infectious models of microbial peritonitis, vagus nerve activation seemingly acts counteractive; it impairs bacterial clearance and increases mortality. It is originally indicated that the key mediator of the cholinergic anti-inflammatory pathway, acetylcholine (ACh), inhibits cytokine release directly via the alpha7 nicotinic ACh receptor (nAChR) expressed on macrophages. However, more recent data also point towards the vagus nerve as an indirect modulator of innate inflammatory processes, exerting its anti-inflammatory effects via postganglionic modulation of immune cells in primary immune organs. This review discusses advances in the possible mechanisms by which the vagus nerve can mediate the immune response, and the role of nAChR activation and signalling on macrophages and other immune cells.

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The role of STAT3 in infectious diseases remains undetermined, in part because unphosphorylated STAT3 has been considered an inactive protein. Here, we report that unphosphorylated STAT3 contributes to cholinergic anti-inflammation, prevents systemic inflammation, and improves survival in sepsis. Bacterial endotoxin induced STAT3 tyrosine phosphorylation in macrophages. Both alpha7 nicotinic receptor (alpha7nAChR) activation and inhibition of JAK2 blunt STAT3 phosphorylation. Inhibition of STAT3 phosphorylation mimicked the alpha7nAChR signaling, inhibiting NF-κB and cytokine production in macrophages. Transfection of macrophages with the dominant-negative mutant STAT3F, to prevent its tyrosine phosphorylation, reduced TNF production but did not prevent the alpha7nAChR signaling. However, inhibition of STAT3 protein expression enhanced cytokine production and abrogated alpha7nAChR signaling. Alpha7nAChR controls TNF production in macrophages through a mechanism that requires STAT3 protein expression, but not its tyrosine phosphorylation. In vivo, inhibition of STAT3 tyrosine phosphorylation by stattic prevented systemic inflammation and improved survival in experimental sepsis. Stattic also prevented the production of late mediators of sepsis and improved survival in established sepsis. These results reveal the immunological implications of tyrosine-unphosphorylated STAT3 in infectious diseases.

Background and purpose:In various models vagus nerve activation has been shown to ameliorate intestinal inflammation, via nicotinic acetylcholine receptors (nAChRs) expressed on immune cells. As the a7 nAChR has been put forward to mediate this effect, we studied the effect of nicotine and two selective a7 nAChR agonists (AR-R17779, (-)-spiro[1-azabicyclo[2.2.2] octane-3,5′-oxazolidin-2′-one and GSK1345038A) on disease severity in two mouse models of experimental colitis. Experimental approach: Colitis was induced by administration of 1.5% dextran sodium sulphate (DSS) in drinking water or 2 mg 2,4,6-trinitrobenzene sulphonic acid (TNBS) intrarectally. Nicotine (0.25 and 2.50 mmol·kg -1

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 ␣7 subunit of the nicotinic acetylcholine receptor (␣7nAChR) and its function in rheumatoid arthritis (RA).Methods. The potential role of the ␣7nAChR in modulating proinflammatory cytokine expression in fibroblast-like synoviocytes (FLS) was identified by screening an adenoviral short hairpin RNA (Ad.shRNA) library. An ␣7-specific antibody was used for immunohistochemistry, and fluorescein isothiocyanate-labeled ␣-bungarotoxin, which binds specifically to the ␣7nAChR, was used for immunofluorescence. Gene expression in FLS was determined by quantitative polymerase chain reaction with primers specific for the ␣7nAChR. In addition, we analyzed messenger RNA (mRNA) expression of dup␣7, a variant ␣7 transcript. Next, we studied the functional role of the ␣7nAChR in RA FLS by examining the effects of ␣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 ␣7nAChR shRNA potently modulated IL-8 and matrix metalloproteinase expression in FLS. The ␣7nAChR was expressed in the inflamed synovium from RA patients, predominantly in the intimal lining layer. We found ␣7nAChR expression at both the mRNA and protein level in cultured RA FLS. FLS also constitutively expressed dup␣7 mRNA. Specific ␣7nAChR agonists reduced tumor necrosis factor ␣-induced IL-6 and IL-8 production by FLS.

<i>Objective:</i> Smoking is generally accepted as a factor that affects the disease course in inflammatory bowel disease patients. Whether these effects can be contributed to the immunomodulatory effects of nicotine via nicotinic acetylcholine receptor (nAChR) activation is unclear. As previous data suggest that the α7 nicotinic acetylcholine receptor <i>(CHRNA7)</i> and its duplicated variant <i>CHRFAM7A</i> may specifically participate in the inflammatory response of monocytes, we evaluated whether repeated nicotine exposure or smoking affects monocyte <i>CHRNA7 </i>and<i> CHRFAM7A</i> expression and cholinergic immunomodulation. <i>Methods:</i> The human monocyte cell line THP-I was incubated with nicotine for different time points before endotoxin exposure. In a pilot volunteer study using smoking (n = 4) and nonsmoking (n = 7) individuals, vagal output was stimulated by olive oil administration after which monocytes were analyzed for nicotinic receptor expression. Serum tumor necrosis factor (TNF) levels were determined using ELISA and expression levels of the nAChR subunits <i>CHRNA7</i>, <i>CHRNB2</i> or <i>CHRFAM7A </i>were analyzed using QPCR. <i>Results:</i> Repeated nicotine exposure upregulated <i>CHRNA7</i> expression on THP-I monocytes and led to an enhanced potential of α7 nAChR agonist GSK1345038A to reduce TNF levels. Furthermore, <i>CHRNA7</i> was only detectable in isolated blood monocytes of smokers. On the other hand, the expression of <i>CHRFAM7A</i> and <i>CHRNB2</i> was not affected by nicotine exposure. Lipopolysaccharides-induced TNF secretion was inhibited by nicotinic receptor activation in THP-I monocytes, but this response was not consistently seen in blood monocytes from smoking individuals. <i>Conclusions:</i> We conclude that <i>CHRNA7 </i>expression on blood monocytes is upregulated in smoking individuals, which may contribute to cholinergic immunomodulation.

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