Immunomodulatory effects of nicotine on interleukin 1ß activated human astrocytes and the role of cyclooxygenase 2 in the underlying mechanism.

BACKGROUND: The cholinergic anti-inflammatory pathway (CAP) primarily functions through acetylcholine (ACh)-alpha7 nicotinic acetylcholine receptor (α7nAChR) interaction on macrophages to control peripheral inflammation. Interestingly, ACh can also bind α7nAChRs on microglia resulting in neuroprotective effects. However, ACh effects on astrocytes remain elusive. Here, we investigated the effects of nicotine, an ACh receptor agonist, on the cytokine and cholinesterase production of immunocompetent human astrocytes stimulated with interleukin 1ß (IL-1ß) in vitro. In addition, the potential involvement of prostaglandins as mediators of nicotine was studied using cyclooxygenase 2 (COX-2) inhibition. METHODS: Cultured human fetal astrocytes were stimulated with human recombinant IL-1ß and treated simultaneously with nicotine at different concentrations (1, 10, and 100 µM). Cell supernatants were collected for cytokine and cholinesterase profiling using ELISA and MesoScale multiplex assay. α7nAChR expression on activated human astrocytes was studied using immunofluorescence. For the COX-2 inhibition studies, enzyme activity was inhibited using NS-398. One-way ANOVA was used to perform statistical analyses. RESULTS: Nicotine treatment dose dependently limits the production of critical proinflammatory cytokines such as IL-6 (60.5 ± 3.3, %inhibition), IL-1ß (42.4 ± 1.7, %inhibition), and TNF-α (68.9 ± 7.7, %inhibition) by activated human astrocytes. Interestingly, it also inhibits IL-8 chemokine (31.4 ± 8.5, %inhibition), IL-13 (34.243 ± 4.9, %inhibition), and butyrylcholinesterase (20.8 ± 2.8, %inhibition) production at 100 µM. Expression of α7nAChR was detected on the activated human astrocytes. Importantly, nicotine's inhibitory effect on IL-6 production was reversed with the specific COX-2 inhibitor NS-398. CONCLUSIONS: Activation of the cholinergic system through α7nAChR agonists has been known to suppress inflammation both in the CNS and periphery. In the CNS, earlier experimental data shows that cholinergic activation through nicotine inhibits microglial activation and proinflammatory cytokine release. Here, we report similar anti-inflammatory effects of cholinergic activation on human astrocytes, at least partly mediated through the COX-2 pathway. These results confirm the potential for cholinergic neuroprotection, which is looked upon as a promising therapy for neuroinflammation as well as neurodegenerative diseases and stroke. Our data implicates an important role for the prostaglandin system in cholinergic regulatory effects.

Impaired vagus-mediated immunosuppression in microsomal prostaglandin E synthase-1 deficient mice.

The cholinergic anti-inflammatory pathway controls innate immune responses and inflammation. The prostaglandin (PG) system is involved in several neuro-processes and associated with inflammatory activation of cells in vagal nuclei. Here we aimed to investigate the potential role of PG in cholinergic neuro-regulation. The effect of vagus nerve stimulation (VNS) has been evaluated in microsomal prostaglandin E synthase-1 (mPGES-1) knockout (-/-) and wild-type (+/+) mice regarding cytokine and PG levels after lipopolysaccharides (LPS) challenge. As expected, VNS decreased the release of pro-inflammatory cytokines both in serum and spleen extracts of mPGES-1 (+/+)animals. However, the immune suppressive effect of VNS was completely abolished in mPGES-1 (-/-) mice. The PG content was not affected by VNS in the spleen of mPGES-1 (+/+) and mPGES-1 (-/-) mice but interestingly, acetylcholine (ACh) release in spleen induced by VNS confirmed an intact cholinergic pathway in mPGES-1 (+/+) whereas no VNS-induced ACh release was found in mPGES-1 (-/-) animals. Our data show that mPGES-1 and consequently PGE2 are crucial in the cholinergic anti-inflammatory pathway. Moreover, the mechanisms involved do not affect PG content in the spleen, but lack of mPGES-1 was found to strongly affect cholinergic mechanisms in the inflamed spleen. These findings illustrate previously unrecognized associations between the cholinergic and prostaglandin systems, and may be of importance for further development of therapeutic strategies directed at modulation of the inflammatory reflex, and immunosuppression in chronic inflammatory diseases.

Correction: Microsomal prostaglandin E synthase-1 gene deletion impairs neuro-immune circuitry of the cholinergic anti-inflammatory pathway in endotoxaemic mouse spleen.

[This corrects the article DOI: 10.1371/journal.pone.0193210.].

Microsomal prostaglandin E synthase-1 gene deletion impairs neuro-immune circuitry of the cholinergic anti-inflammatory pathway in endotoxaemic mouse spleen.

The cholinergic anti-inflammatory pathway (CAP) is an innate neural reflex where parasympathetic and sympathetic nerves work jointly to control inflammation. Activation of CAP by vagus nerve stimulation (VNS) has paved way for novel therapeutic strategies in treating inflammatory diseases. Recently, we discovered that VNS mediated splenic acetylcholine (ACh) release and subsequent immunosuppression in response to LPS associated inflammation is impaired in mice lacking microsomal prostaglandin E synthase-1 (mPGES-1) expression, a key enzyme responsible for prostaglandin E2 synthesis. Here, we have further investigated the consequences of mPGES-1 deficiency on various molecular/cellular events in the spleen which is critical for the optimal functioning of VNS in endotoxaemic mice. First, VNS induced splenic norepinephrine (NE) release in both mPGES-1 (+/+) and (-/-) mice. Compared to mPGES-1 (+/+), immunomodulatory effects of NE on cytokines were strongly compromised in mPGES-1 (-/-) splenocytes. Interestingly, while LPS increased choline acetyltransferase (ChAT) protein level in mPGES-1 (+/+) splenocytes, it failed to exert similar effects in mPGES-1 (-/-) splenocytes despite unaltered ß2 AR protein expression. In addition, nicotine inhibited TNFα release by LPS activated mPGES-1 (+/+) splenocytes in vitro. However, such immunosuppressive effects of nicotine were reversed both in mPGES-1 (-/-) mouse splenocytes and human PBMC treated with mPGES-1 inhibitor. In summary, our data implicate PGE2 as an important mediator of ACh synthesis and noradrenergic/cholinergic molecular events in the spleen that constitute a crucial part of the CAP immune regulation. Our results suggest a possible link between cholinergic and PG system of CAP that may be of clinical significance in VNS treatment.

Increased Recovery Time and Decreased LPS Administration to Study the Vagus Nerve Stimulation Mechanisms in Limited Inflammatory Responses.

Inflammation is a local response to infection and tissue damage mediated by activated macrophages, monocytes, and other immune cells that release cytokines and other mediators of inflammation. For a long time, humoral and cellular mechanisms have been studied for their role in regulating the immune response, but recent advances in the field of immunology and neuroscience have also unraveled specific neural mechanisms with interesting therapeutic potential. The so-called cholinergic anti-inflammatory pathway (CAP) has been described to control innate immune responses and inflammation in a very potent manner. In the early 2000s, Tracey and collaborators developed a technique that stimulates the vagus nerve and mimics the effect of the pathway. The methodology is based on the electrical stimulation of the vagus nerve at low voltage and frequency, in order to avoid any side effects of overstimulation, such as deregulation of heart rate variability. Electrical devices for stimulation are now available, making it easy to set up the methodology in the laboratory. The goal of this research was to investigate the potential involvement of prostaglandins in the CAP. Unfortunately, based on earlier attempts, we failed to use the original protocol, as the induced inflammatory response either was too high or was not suitable for enzymatic metabolism properties. The different settings of the original surgery protocol remained mostly unchanged, but the conditions regarding inflammatory induction and the time point before sacrifice were improved to fit our purposes (i.e., to investigate the involvement of the CAP in more limited inflammatory responses). The modified version of the original protocol, presented here, includes a longer time range between vagus nerve stimulation and analysis, which is associated with a lower induction of inflammatory responses. Additionally, while decreasing the level of lipopolysaccharides (LPS) to inject, we also came across new observations regarding mechanistic properties in the spleen.

Biochemical studies of poly-T variants in the Alzheimer's disease associated TOMM40 gene.

The apolipoprotein E (APOE) gene remains the most strongly established risk factor for late onset Alzheimer's disease (LOAD). Recently the gene, TOMM40, which is in linkage disequilibrium with APOE, was identified to be associated with LOAD in genome-wide association studies. One of the identified polymorphisms in TOMM40 is rs10524523, which is located in intron 6 and composed of thymidine repeats varying between 14 to 36 base-pairs in length. Reported results are contradictory in regard to the very long poly-T variant that has been associated with both increased and decreased risk of LOAD. Our study aimed to elucidate the functional implication of rs10524523 in an in vitro model of human fibroblast cells obtained from cognitively healthy APOE ε3/ε4 carriers harboring very long or short poly-T variants coupled to their APOE ε3 allele. We have studied (i) expression levels of TOM40 protein and mRNA, (ii) TOM40 mRNA splicing, and (iii) mitochondrial function and morphology; and we have found no significant differences in regards to very long or short poly-T variant.