Nicotinic Acetylcholine Receptor Expression and Susceptibility to Cholinergic Immunomodulation in Human Monocytes of Smoking Individuals

Abstract

<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.

Nicotinic Receptor Alpha7 Expression Identifies a Novel Hematopoietic Progenitor Lineage

“…We and others have found that the α7 KO mouse has an enhanced pro-inflammatory response, demonstrated most often by an increase in TNFα release [13], [14], [34]. We find here that the α7 lin+ cells are those that are most responsive to stimulation with LPS and contribute substantially to the expression of certain cytokines (IL-12/23(p40)) while having little impact on the total expression of TNFα.…”

CHRFAM7A: a human‐specific α7‐nicotinic acetylcholine receptor gene shows differential responsiveness of human intestinal epithelial cells to LPS

“…Very little is known regarding the regulation of CHRFAM7A gene expression, but at least 2 groups have reported that LPS inhibits both CHRNA7 and CHRFAM7A in undifferentiated human THP1 cells and human macrophages (31,32,43). In contrast, surprisingly little is published on the effects of LPS treatment in gut epithelial cells, presumably because these cells are constitutively exposed to LPS in vivo.…”

“…In leukocyte cell lines like THP1 cells and in normal human monocytes, CHRFAM7A gene expression is reported to parallel that of CHRNA7 (31,32,43). Unfortunately, primer crosshybridization and antibody crossreactivities have confounded several studies that purport to measure CHRFAM7A gene expression or CHRFAM7A protein in cell lysates (31).…”

Expression of CHRFAM7A and CHRNA7 in neuronal cells and postmortem brain of HIV-infected patients: considerations for HIV-associated neurocognitive disorder

“…For instance, the ratio of CHRNA7 : CHRFAM7A mRNA levels is different in bipolar subjects when compared to unaffected controls (De Luca et al 2006). Moreover, in vitro studies have demonstrated that two pro-inflammatory mediators characteristic of HIV-I infection, LPS and IL-1β, decrease CHRFAM7A expression leading to the suggestion that chronic pro-inflammatory responses might change the CHRFAM7A : CHRNA7 expression ratio (Benfante et al 2011; van der Zanden et al 2012). gp120 IIIB is unable to promote CHRNA7:CHRFAM7A alterations in the presence of AMD3100, an antagonist of CXCR4, suggesting that the gp120 IIIB -induced CHRNA7:CHRFAM7A dysregulation is CXCR4-dependent.…”