α7 nicotinic acetylcholine receptors are involved in suppression of the antibody immune response

Alpha 7 nicotinic acetylcholine receptors signaling boosts cell-cell interactions in macrophages effecting anti-inflammatory and organ protection

Activation of the cholinergic anti-inflammatory pathway (CAP) via vagus nerve stimulation has been shown to improve acute kidney injury in rodent models. While alpha 7 nicotinic acetylcholine receptor (α7nAChR) positive macrophages are thought to play a crucial role in this pathway, their in vivo significance has not been fully understood. In this study, we used macrophage-specific α7nAChR-deficient mice to confirm the direct activation of α7nAChRs in macrophages. Our findings indicate that the administration of GTS-21, an α7nAChR-specific agonist, protects injured kidneys in wild-type mice but not in macrophage-specific α7nAChR-deficient mice. To investigate the signal changes or cell reconstructions induced by α7nAChR activation in splenocytes, we conducted single-cell RNA-sequencing of the spleen. Ligand-receptor analysis revealed an increase in macrophage-macrophage interactions. Using macrophage-derived cell lines, we demonstrated that GTS-21 increases cell contact, and that the contact between macrophages receiving α7nAChR signals leads to a reduction in TNF-α. Our results suggest that α7nAChR signaling increases macrophage-macrophage interactions in the spleen and has a protective effect on the kidneys.

The controversial effect of smoking and nicotine in SARS-CoV-2 infection

The effects of nicotine and cigarette smoke in many diseases, notably COVID-19 infection, are being debated more frequently. The current basic data for COVID-19 is increasing and indicating the higher risk of COVID-19 infections in smokers due to the overexpression of corresponding host receptors to viral entry. However, current multi-national epidemiological reports indicate a lower incidence of COVID-19 disease in smokers. Current data indicates that smokers are more susceptible to some diseases and more protective of some other. Interestingly, nicotine is also reported to play a dual role, being both inflammatory and anti-inflammatory. In the present study, we tried to investigate the effect of pure nicotine on various cells involved in COVID-19 infection. We followed an organ-based systematic approach to decipher the effect of nicotine in damaged organs corresponding to COVID-19 pathogenesis (12 related diseases). Considering that the effects of nicotine and cigarette smoke are different from each other, it is necessary to be careful in generalizing the effects of nicotine and cigarette to each other in the conducted researches. The generalization and the undifferentiation of nicotine from smoke is a significant bias. Moreover, different doses of nicotine stimulate different effects (dose-dependent response). In addition to further assessing the role of nicotine in COVID-19 infection and any other cases, a clever assessment of underlying diseases should also be considered to achieve a guideline for health providers and a personalized approach to treatment.

α7- and α9-Containing Nicotinic Acetylcholine Receptors in the Functioning of Immune System and in Pain

Nicotinic acetylcholine receptors (nAChRs) present as many different subtypes in the nervous and immune systems, muscles and on the cells of other organs. In the immune system, inflammation is regulated via the vagus nerve through the activation of the non-neuronal α7 nAChR subtype, affecting the production of cytokines. The analgesic properties of α7 nAChR-selective compounds are mostly based on the activation of the cholinergic anti-inflammatory pathway. The molecular mechanism of neuropathic pain relief mediated by the inhibition of α9-containing nAChRs is not fully understood yet, but the role of immune factors in this process is becoming evident. To obtain appropriate drugs, a search of selective agonists, antagonists and modulators of α7- and α9-containing nAChRs is underway. The naturally occurring three-finger snake α-neurotoxins and mammalian Ly6/uPAR proteins, as well as neurotoxic peptides α-conotoxins, are not only sophisticated tools in research on nAChRs but are also considered as potential medicines. In particular, the inhibition of the α9-containing nAChRs by α-conotoxins may be a pathway to alleviate neuropathic pain. nAChRs are involved in the inflammation processes during AIDS and other viral infections; thus they can also be means used in drug design. In this review, we discuss the role of α7- and α9-containing nAChRs in the immune processes and in pain.

Cholinergic dysfunction in COVID-19: frantic search and hoping for the best

A novel coronavirus known as severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is a potential cause of acute respiratory infection called coronavirus disease 2019 (COVID-19). The binding of SARS-CoV-2 with angiotensin-converting enzyme 2 (ACE2) induces a series of inflammatory cellular events with cytopathic effects leading to cell injury and hyperinflammation. Severe SARS-CoV-2 infection may lead to dysautonomia and sympathetic storm due to dysfunction of the autonomic nervous system (ANS). Therefore, this review aimed to elucidate the critical role of the cholinergic system (CS) in SARS-CoV-2 infection. The CS forms a multi-faceted network performing diverse functions in the body due to its distribution in the neuronal and non-neuronal cells. Acetylcholine (ACh) acts on two main types of receptors which are nicotinic receptors (NRs) and muscarinic receptors (MRs). NRs induce T cell anergy with impairment of antigen-mediated signal transduction. Nicotine through activation of T cell NRs inhibits the expression and release of the pro-inflammatory cytokines. NRs play important anti-inflammatory effects while MRs promote inflammation by inducing the release of pro-inflammatory cytokines. SARS-CoV-2 infection can affect the morphological and functional stability of CS through the disruption of cholinergic receptors. SARS-CoV-2 spike protein is similar to neurotoxins, which can bind to nicotinic acetylcholine receptors (nAChR) in the ANS and brain. Therefore, cholinergic receptors mainly nAChR and related cholinergic agonists may affect the pathogenesis of SARS-CoV-2 infection. Cholinergic dysfunction in COVID-19 is due to dysregulation of nAChR by SARS-CoV-2 promoting the central sympathetic drive with the development of the sympathetic storm. As well, nAChR activators through interaction with diverse signaling pathways can reduce the risk of inflammatory disorders in COVID-19. In addition, nAChR activators may mitigate endothelial dysfunction (ED), oxidative stress (OS), and associated coagulopathy in COVID-19. Similarly, nAChR activators may improve OS, inflammatory changes, and cytokine storm in COVID-19. Therefore, nAChR activators like varenicline in virtue of its anti-inflammatory and anti-oxidant effects with direct anti-SARS-CoV-2 effect could be effective in the management of COVID-19.

Dequalinium chloride is an antagonists of α7 nicotinic acetylcholine receptors

Dequalinium chloride has been used primarily as antiseptic compounds, but recently has been investigated for its effects on specific targets, including muscarinic acetylcholine receptors. Here we investigated dequalinium chloride as an antagonist to α7 nicotinic acetylcholine receptors. The pharmacological properties of dequalinium were established using cell lines stably co-transfected with the calcium-permeable human α7 nicotinic acetylcholine receptors and its chaperone NACHO, calcium dye fluorescent measurements or a calcium-sensitive protein reporter, and patch clamp recording of ionic currents. Using calcium dye fluorescence plate reader measurements, we find dequalinium chloride is an antagonist of α7 nicotinic acetylcholine receptors with an IC₅₀ of 672 nM in response to activation with 500 μM acetylcholine chloride and positive allosteric modulator PNU-120596. However, using a membrane-tethered GCAMP7s calcium reporter allowed detection of α7-mediated calcium flux in the absence of PNU-120596. Using this approach revealed an IC₅₀ of 157 nM for dequalinium on 300 μM acetylcholine-evoked currents. Using patch clamp recordings with 300 μM acetylcholine chloride and 10 μM PNU-120596, we find lower concentrations are sufficient to block ionic currents, with IC₅₀ of 120 nM for dequalinium chloride and 54 nM for the related UCL 1684 compound. In summary, we find that dequalinium chloride and UCL1684, which are generally used to block SK-type potassium channels, are also highly effective antagonists of α7 nicotinic acetylcholine receptors. This finding, in combination with previous studies of muscarinic acetylcholine receptors, clearly establishes dequalinium compounds within the class of general anti-cholinergic antagonists.

Universal nature of cholinergic regulation demonstrated with nicotinic acetylcholine receptors

Mammalian nicotinic acetylcholine receptors (nAChRs) were initially discovered as ligand-gated ion channels mediating fast synaptic transmission in the neuro-muscular junctions and autonomic ganglia. They were further found to be involved in a wide range of basic biological processes within the brain and in non-excitable tissues. The present review summarizes the data obtained in our laboratory during last two decades. Investigation of autonomic ganglia with the nAChR subunit-specific antibodies was followed by identification of nAChRs in B lymphocytes, discovery of mitochondrial nAChRs and their role in mitochondrial apoptosis pathway, and revealing the role of α7 nAChRs and α7-specific antibodies in neuroinflammation-related Alzheimer disease and COVID-19. The data obtained demonstrate the involvement of nAChRs in cell survival, proliferation, cell-to-cell communication and inflammatory reaction. Together with the ability of nAChRs to function in both ionotropic and metabotropic way, these data illustrate the universal nature of cholinergic regulation mediated by nAChRs.

Cholinergic System and Its Therapeutic Importance in Inflammation and Autoimmunity

Neurological and immunological signals constitute an extensive regulatory network in our body that maintains physiology and homeostasis. The cholinergic system plays a significant role in neuroimmune communication, transmitting information regarding the peripheral immune status to the central nervous system (CNS) and vice versa. The cholinergic system includes the neurotransmitter\ molecule, acetylcholine (ACh), cholinergic receptors (AChRs), choline acetyltransferase (ChAT) enzyme, and acetylcholinesterase (AChE) enzyme. These molecules are involved in regulating immune response and playing a crucial role in maintaining homeostasis. Most innate and adaptive immune cells respond to neuronal inputs by releasing or expressing these molecules on their surfaces. Dysregulation of this neuroimmune communication may lead to several inflammatory and autoimmune diseases. Several agonists, antagonists, and inhibitors have been developed to target the cholinergic system to control inflammation in different tissues. This review discusses how various molecules of the neuronal and non-neuronal cholinergic system (NNCS) interact with the immune cells. What are the agonists and antagonists that alter the cholinergic system, and how are these molecules modulate inflammation and immunity. Understanding the various functions of pharmacological molecules could help in designing better strategies to control inflammation and autoimmunity.

Cholinergic modulation of the immune system - A novel therapeutic target for myocardial inflammation

The immune system and the nervous system depend on each other for their fine tuning and working, thus cooperating to maintain physiological homeostasis and prevent infections. The cholinergic system regulates the mobilization, differentiation, secretion, and antigen presentation of adaptive and innate immune cells mainly through α7 nicotinic acetylcholine receptors (α7nAChRs). The neuro-immune interactions are established and maintained by the following mechanisms: colocalization of immune and neuronal cells at defined anatomical sites, expression of the non-neuronal cholinergic system by immune cells, and the acetylcholine receptor-mediated activation of intracellular signaling pathways. Based on these immunological mechanisms, the protective effects of cholinergic system in animal models of diseases were summarized in this paper, such as myocardial infarction/ischemia-reperfusion, viral myocarditis, and endotoxin-induced myocardial damage. In addition to maintaining hemodynamic stability and improving the energy metabolism of the heart, both non-neuronal acetylcholine and neuronal acetylcholine in the heart can alleviate myocardial inflammation and remodeling to exert a significant cardioprotective effect. The new findings on the role of cholinergic agonists and vagus nerve stimulation in immune regulation are updated, so as to develop improved approaches to treat inflammatory heart disease.

Augmented autophagy suppresses thymocytes development via Bcl10/p-p65 pathway in prenatal nicotine exposed fetal mice

Tobacco smoke is a common global environmental pollutant. Maternal tobacco smoke/nicotine exposure has long-term toxic effects on immune organs. We previously found that prenatal nicotine exposure (PNE)-induced programmed immune diseases caused by fetal thymic hypoplasia, but the mechanism still unknown. Autophagy has important functions in maintaining thymopoiesis, whether autophagy was involved in PNE-inhibited fetal thymocytes development is also obscure. Therefore, this study aimed to investigate how nicotine changed the development of fetal thymocytes from the perspective of autophagy in vivo and in vitro. PNE model was established by 3 mg/kg nicotine administration in Balb/c mice from gestational day 9 to 18. The results showed that PNE reduced the percentage and absolute number of CD69^-CD4⁺SP cells, suggesting a block of fetal thymocytes mature. PNE promoted autophagosome formation, autophagy related proteins (Beclin1, LC3I/II) expression, and upregulated α7 nAChR as well as AMPK phosphorylation in fetal thymus. Moreover, PNE promoted Bcl10 degradation via autophagy-mediated proteolysis and inhibited p65 activation, blocking the transition of thymocytes between the DP to SP stage. Further, primary thymocytes were treated with nicotine in vitro and showed induced autophagy in a dose- and time-dependent manner. In addition, nicotine-inhibited CD69^-CD4⁺SP cells and the Bcl10/p-p65 pathway have been reversed by an autophagy inhibitor. The α7 nAChR specific antagonist abrogated nicotine-induced AMPK phosphorylation and autophagy initiation. In conclusion, our findings showed that PNE repressed the Bcl10/p-p65 development pathway of CD4⁺SP cells by triggering autophagy, and illuminated the developmental origin mechanism of programmed immune diseases in PNE offspring.

Smoking and COVID-19: Similar bronchial ACE2 and TMPRSS2 expression and higher TMPRSS4 expression in current versus never smokers

Uncertainties remain concerning the pathophysiology, epidemiology, and potential therapeutics for COVID-19. Among unsettled controversies is whether tobacco smoking increases or protects from severe COVID-19. Several epidemiological studies reported reduced COVID-19 hospitalizations among smokers, while other studies reported the opposite trend. Some authors assumed that smokers have elevated airway expression of ACE2, the cell recognition site of the SARS-Cov-2 spike protein, but this suggestion remains unverified. We therefore performed data mining of two independent NCBI GEO genome-wide RNA expression files (GSE7894 and GSE994) and report that in both data sets, current smokers and never smokers have, on average, closely similar bronchial epithelial cell mRNA levels of ACE2, as well as TMPRSS2, coding for a serine protease priming SARS-Cov-2 for cell entry, and ADAM17, coding for a protease implicated in ACE2 membrane shedding. In contrast, the expression levels of TMPRSS4, coding for a protease that primes SARS-CoV-2 for cell entry similarly to TMPRSS2, were elevated in bronchial epithelial cells from current smokers compared with never smokers, suggesting that higher bronchial TMPRSS4 levels in smokers might put them at higher SARS-Cov-2 infection risk. The effects of smoking on COVID-19 severity need clarification with larger studies. Additionally, the postulated protective effects of nicotine and nitric oxide, which may presumably reduce the risk of a "cytokine storm" in infected individuals, deserve assessment by controlled clinical trials.

Berberine Ameliorates Spatial Learning Memory Impairment and Modulates Cholinergic Anti-Inflammatory Pathway in Diabetic Rats

Background: Cognitive impairment caused by diabetes has been recognized. Berberine is well known for its resistance to peripheral lesions, but it is rarely used for the treatment of spatial learning and memory caused by diabetes. This study explored the mechanism of berberine to alleviate cognitive impairment via the cholinergic anti-inflammatory and insulin signaling pathways.

Methods: Morris water maze was used to appraise spatial learning and memory. Positron-emission tomography (PET) imaging was adopted to detect the transport of glucose, and blood/cerebrospinal fluid (CSF) glucose was checked using commercial blood glucose meter. Insulin level was measured by ELISA kit and β-Amyloid (Aβ) formation was observed by Congo red staining. Western-blot was performed to appraise protein expression.

Results: We found that berberine rectified some aberrant changes in signal molecules concerning inflammation, and cholinergic and insulin signaling pathways in the hippocampus. Furthermore, CSF/blood glucose, inflammatory response or acetyl cholinesterase enzyme (AChE) activity were reduced by berberine. Additionally, acetylcholine levels were enhanced after berberine treatment in diabetic rats. Finally, Aβ formation in diabetic hippocampus was inhibited and spatial learning memory was ameliorated by berberine.

Discussion: In conclusion, berberine clears Aβ deposit and consequently ameliorates spatial learning memory impairment via the activation of the cholinergic anti-inflammatory and insulin signaling pathways in diabetic rats.

Distinct Roles of α7 nAChRs in Antigen-Presenting Cells and CD4+ T Cells in the Regulation of T Cell Differentiation

It is now apparent that immune cells express a functional cholinergic system and that α7 nicotinic acetylcholine receptors (α7 nAChRs) are involved in regulating T cell differentiation and the synthesis of antigen-specific antibodies and proinflammatory cytokines. Here, we investigated the specific function α7 nAChRs on T cells and antigen presenting cells (APCs) by testing the effect of GTS-21, a selective α7 nAChR agonist, on differentiation of CD4⁺ T cells from ovalbumin (OVA)-specific TCR transgenic DO11.10 mice activated with OVA or OVA peptide_323−339 (OVAp). GTS-21 suppressed OVA-induced antigen processing-dependent development of CD4⁺ regulatory T cells (Tregs) and effector T cells (Th1, Th2, and Th17). By contrast, GTS-21 up-regulated OVAp-induced antigen processing-independent development of CD4⁺ Tregs and effector T cells. GTS-21 also suppressed production of IL-2, IFN-γ, IL-4, IL-17, and IL-6 during OVA-induced activation but, with the exception IL-2, enhanced their production during OVAp-induced activation. In addition, during antigen-nonspecific, APC-independent anti-CD3/CD28 antibody-induced CD4⁺ polyclonal T cell activation in the presence of respective polarizing cytokines, GTS-21 promoted development of all lineages, which indicates that GTS-21 also acts via α7 nAChRs on T cells. These results suggest 1) that α7 nAChRs on APCs suppress CD4⁺ T cell activation by interfering with antigen presentation through inhibition of antigen processing; 2) that α7 nAChRs on CD4⁺ T cells up-regulate development of Tregs and effector T cells; and that α7 nAChR agonists and antagonists could be potentially useful agents for immune response modulation and enhancement.

Downregulation of α7 nicotinic acetylcholine receptors in peripheral blood monocytes is associated with enhanced inflammation in preeclampsia

Background

Preeclampsia is associated with chronic inflammation. The cholinergic anti-inflammatory pathway regulates systemic inflammation through activating α7 nicotinic acetylcholine receptors (α7nAChR) expressed in monocytes/macrophages. This study aimed to investigate the role of α7nAChR in peripheral blood monocytes in preeclampsia.

Methods

Peripheral blood monocytes were isolated from 30 nonpregnant (NP), 32 normotensive pregnant (NT), and 35 preeclamptic (PE) women.

Results

We found that both protein and mRNA expression levels of α7nAChR in monocytes from the PE women were significantly lower than those of the NP and NT women (both p < 0.01). α7nAChR protein expression levels in monocytes were negatively correlated with levels of systolic blood pressure (r = − 0.40, p = 0.04), proteinuria (r = − 0.54, p < 0.01), tumor necrosis factor-alpha (TNF-α, r = − 0.42, p = 0.01), and interleukin (IL)-1β (r = − 0.56, p < 0.01), while positively correlated with IL-10 levels (r = 0.43, p = 0.01) in the PE women. Both baseline and lipopolysaccharides (LPS)-induced increase of TNF-α, IL-1β, and IL-6 levels from monocytes were higher in the PE group than the NP and NT groups (all p < 0.01), but IL-10 levels in the PE group was lower than that of the NP and NT groups (p < 0.01). In addition, the NF-κB activity in monocytes from the PE women was higher than the NP and NT women (p < 0.01). Importantly, activation of α7nAChR with its agonist PNU-282987 inhibited NF-κB, decreased TNF-α, IL-1β, and IL-6 release, and increased IL-10 release in monocytes from the PE women (all p < 0.01).

Conclusion

In conclusion, these findings suggest that downregulation of α7nAChR may be associated with the development of preeclampsia through increasing pro-inflammatory and decreasing anti-inflammatory cytokine release via the NF-κB pathway.