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

α7 nicotinic acetylcholine receptor agonist attenuates allergen-induced immediate nasal response in murine model of allergic rhinitis

The expression of nicotinic acetylcholine receptor (nAChR) subunits on various immune cells suggests their involvement in allergic rhinitis. However, how exactly they contribute to this pathogenesis is not yet confirmed. Our present study examined the therapeutic potential of GTS-21, an α7 nAChR agonist, for treating allergic rhinitis by employing its mouse models. GTS-21 treatment reduced allergen-induced immediate nasal response in ovalbumin (OVA)-sensitized model. However, nasal hyperresponsiveness or eosinophil infiltration elicited in either the OVA-sensitized or T helper 2 cell-transplanted model was not affected by GTS-21. GTS-21 did not alter allergen-induced passive cutaneous anaphylaxis response in anti-dinitrophenyl IgE-sensitized mice. This evidence implies GTS-21's potential to alleviate allergic rhinitis without perturbing T cells or mast cells.

Contributions of Non-Neuronal Cholinergic Systems to the Regulation of Immune Cell Function, Highlighting the Role of α7 Nicotinic Acetylcholine Receptors

Loewi's discovery of acetylcholine (ACh) release from the frog vagus nerve and the discovery by Dale and Dudley of ACh in ox spleen led to the demonstration of chemical transmission of nerve impulses. ACh is now well-known to function as a neurotransmitter. However, advances in the techniques for ACh detection have led to its discovery in many lifeforms lacking a nervous system, including eubacteria, archaea, fungi, and plants. Notably, mRNAs encoding choline acetyltransferase and muscarinic and nicotinic ACh receptors (nAChRs) have been found in uninnervated mammalian cells, including immune cells, keratinocytes, vascular endothelial cells, cardiac myocytes, respiratory, and digestive epithelial cells. It thus appears that non-neuronal cholinergic systems are expressed in a variety of mammalian cells, and that ACh should now be recognized not only as a neurotransmitter, but also as a local regulator of non-neuronal cholinergic systems. Here, we discuss the role of non-neuronal cholinergic systems, with a focus on immune cells. A current focus of much research on non-neuronal cholinergic systems in immune cells is α7 nAChRs, as these receptors expressed on macrophages and T cells are involved in regulating inflammatory and immune responses. This makes α7 nAChRs an attractive potential therapeutic target.

Effect of clothianidin exposure at the no-observed-adverse-effect level (NOAEL) in a mouse model of atopic dermatitis

The effects of exposure to clothianidin (CLO), a neonicotinoid pesticide (NN), on the thymus and intestinal microbiota were recently revealed. Immune cells express nicotinic acetylcholine receptors (nAChRs), an NN target, suggesting CLO may disrupt the immune system. However, the relationship between CLO and atopic dermatitis (AD) is unknown. We administered a no-adverse-effect-level (NOAEL) dose of CLO to male NC/Nga mice with induced AD and measured, at three time points, key AD symptom indicators: epidermal thickening, mast cell number, total plasma IgE, and histamine levels. CLO increased total plasma IgE levels but reduced epidermal thickening, mast cell number, and plasma histamine levels in the early stages of AD. This demonstrates for the first time that CLO exposure inhibits AD's early symptoms.

Nicotinic receptors in airway disease

With continued smoking of tobacco products and expanded use of nicotine delivery devices worldwide, understanding the impact of smoking and vaping on respiratory health remains a major global unmet need. Although multiple studies have shown a strong association between smoking and asthma, there is a relative paucity of mechanistic understanding of how elements in cigarette smoke impact the airway. Recognizing that nicotine is a major component in both smoking and vaping products, it is critical to understand the mechanisms by which nicotine impacts airways and promotes lung diseases such as asthma. There is now increasing evidence that α7 nicotinic acetylcholine receptors (α7nAChRs) are critical players in nicotine effects on airways, but the mechanisms by which α7nAChR influences different airway cell types have not been widely explored. In this review, we highlight and integrate the current state of knowledge regarding nicotine and α7nAChR in the context of asthma and identify potential approaches to alleviate the impact of smoking and vaping on the lungs.

Selective targeting of α7 nicotinic acetylcholine receptor by synthetic peptide mimicking loop I of human SLURP-1 provides efficient and prolonged therapy of epidermoid carcinoma in vivo

α7-Type nicotinic acetylcholine receptor (α7-nAChR) promotes the growth and metastasis of solid tumors. Secreted Ly6/uPAR-Related Protein 1 (SLURP-1) is a specific negative modulator of α7-nAChR produced by epithelial cells. Here, we investigated mechanisms of antiproliferative activity of recombinant SLURP-1 in epidermoid carcinoma A431 cells and activity of SLURP-1 and synthetic 21 a.a. peptide mimicking its loop I (Oncotag) in a xenograft mice model of epidermoid carcinoma. SLURP-1 inhibited the mitogenic pathways and transcription factors in A431 cells, and its antiproliferative activity depended on α7-nAChR. Intravenous treatment of mice with SLURP-1 or Oncotag for 10 days suppressed the tumor growth and metastasis and induced sustained changes in gene and microRNA expression in the tumors. Both SLURP-1 and Oncotag demonstrated no acute toxicity. Surprisingly, Oncotag led to a longer suppression of pro-oncogenic signaling and downregulated expression of pro-oncogenic miR-221 and upregulated expression of KLF4 protein responsible for control of cell differentiation. Affinity purification revealed SLURP-1 interactions with both α7-nAChR and EGFR and selective Oncotag interaction with α7-nAChR. Thus, the selective inhibition of α7-nAChRs by drugs based on Oncotag may be a promising strategy for cancer therapy.

GTS-21 Enhances Regulatory T Cell Development from T Cell Receptor-Activated Human CD4+ T Cells Exhibiting Varied Levels of CHRNA7 and CHRFAM7A Expression

Immune cells such as T cells and macrophages express α7 nicotinic acetylcholine receptors (α7 nAChRs), which contribute to the regulation of immune and inflammatory responses. Earlier findings suggest α7 nAChR activation promotes the development of regulatory T cells (Tregs) in mice. Using human CD4+ T cells, we investigated the mRNA expression of the α7 subunit and the human-specific dupα7 nAChR subunit, which functions as a dominant-negative regulator of ion channel function, under resting conditions and T cell receptor (TCR)-activation. We then explored the effects of the selective α7 nAChR agonist GTS-21 on proliferation of TCR-activated T cells and Treg development. Varied levels of mRNA for both the α7 and dupα7 nAChR subunits were detected in resting human CD4+ T cells. mRNA expression of the α7 nAChR subunit was profoundly suppressed on days 4 and 7 of TCR-activation as compared to day 1, whereas mRNA expression of the dupα7 nAChR subunit remained nearly constant. GTS-21 did not alter CD4+ T cell proliferation but significantly promoted Treg development. These results suggest the potential ex vivo utility of GTS-21 for preparing Tregs for adoptive immunotherapy, even with high expression of the dupα7 subunit.

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.

Noninvasive ultrasound stimulation to treat myocarditis through splenic neuro-immune regulation

BACKGROUND

The cholinergic anti-inflammatory pathway (CAP) has been widely studied to modulate the immune response. Current stimulating strategies are invasive or imprecise. Noninvasive low-intensity pulsed ultrasound (LIPUS) has become increasingly appreciated for targeted neuronal modulation. However, its mechanisms and physiological role on myocarditis remain poorly defined.

METHODS

The mouse model of experimental autoimmune myocarditis was established. Low-intensity pulsed ultrasound was targeted at the spleen to stimulate the spleen nerve. Under different ultrasound parameters, histological tests and molecular biology were performed to observe inflammatory lesions and changes in immune cell subsets in the spleen and heart. In addition, we evaluated the dependence of the spleen nerve and cholinergic anti-inflammatory pathway of low-intensity pulsed ultrasound in treating autoimmune myocarditis in mice through different control groups.

RESULTS

The echocardiography and flow cytometry of splenic or heart infiltrating immune cells revealed that splenic ultrasound could alleviate the immune response, regulate the proportion and function of CD4+ Treg and macrophages by activating cholinergic anti-inflammatory pathway, and finally reduce heart inflammatory injury and improve cardiac remodeling, which is as effective as an acetylcholine receptor agonists GTS-21. Transcriptome sequencing showed significant differential expressed genes due to ultrasound modulation.

CONCLUSIONS

It is worth noting that the ultrasound therapeutic efficacy depends greatly on acoustic pressure and exposure duration, and the effective targeting organ was the spleen but not the heart. This study provides novel insight into the therapeutic potentials of LIPUS, which are essential for its future application.

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.

Schizophrenia Hypothesis: Autonomic Nervous System Dysregulation of Fetal and Adult Immune Tolerance

The autonomic nervous system can control immune cell activation via both sympathetic adrenergic and parasympathetic cholinergic nerve release of norepinephrine and acetylcholine. The hypothesis put forward in this paper suggests that autonomic nervous system dysfunction leads to dysregulation of immune tolerance mechanisms in brain-resident and peripheral immune cells leading to excessive production of pro-inflammatory cytokines such as Tumor Necrosis Factor alpha (TNF-α). Inactivation of Glycogen Synthase Kinase-3β (GSK3β) is a process that takes place in macrophages and microglia when a toll-like receptor 4 (TLR4) ligand binds to the TLR4 receptor. When Damage-Associated Molecular Patterns (DAMPS) and Pathogen-Associated Molecular Patterns (PAMPS) bind to TLR4s, the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway should be activated, leading to inactivation of GSK3β. This switches the macrophage from producing pro-inflammatory cytokines to anti-inflammatory cytokines. Acetylcholine activation of the α7 subunit of the nicotinic acetylcholine receptor (α7 nAChR) on the cell surface of immune cells leads to PI3K/Akt pathway activation and can control immune cell polarization. Dysregulation of this pathway due to dysfunction of the prenatal autonomic nervous system could lead to impaired fetal immune tolerance mechanisms and a greater vulnerability to Maternal Immune Activation (MIA) resulting in neurodevelopmental abnormalities. It could also lead to the adult schizophrenia patient’s immune system being more vulnerable to chronic stress-induced DAMP release. If a schizophrenia patient experiences chronic stress, an increased production of pro-inflammatory cytokines such as TNF-α could cause significant damage. TNF-α could increase the permeability of the intestinal and blood brain barrier, resulting in lipopolysaccharide (LPS) and TNF-α translocation to the brain and consequent increases in glutamate release. MIA has been found to reduce Glutamic Acid Decarboxylase mRNA expression, resulting in reduced Gamma-aminobutyric acid (GABA) synthesis, which combined with an increase of glutamate release could result in an imbalance of glutamate and GABA neurotransmitters. Schizophrenia could be a “two-hit” illness comprised of a genetic “hit” of autonomic nervous system dysfunction and an environmental hit of MIA. This combination of factors could lead to neurotransmitter imbalance and the development of psychotic symptoms.

Interactions between the Autonomic Nervous System and the Immune System after Stroke

Acute stroke is one of the leading causes of morbidity and mortality worldwide. Stroke-induced immune-inflammatory response occurs in the perilesion areas and the periphery. Although stroke-induced immunosuppression may alleviate brain injury, it hinders brain repair as the immune-inflammatory response plays a bidirectional role after acute stroke. Furthermore, suppression of the systemic immune-inflammatory response increases the risk of life-threatening systemic bacterial infections after acute stroke. Therefore, it is essential to explore the mechanisms that underlie the stroke-induced immune-inflammatory response. Autonomic nervous system (ANS) activation is critical for regulating the local and systemic immune-inflammatory responses and may influence the prognosis of acute stroke. We review the changes in the sympathetic and parasympathetic nervous systems and their influence on the immune-inflammatory response after stroke. Importantly, this article summarizes the mechanisms on how ANS regulates the immune-inflammatory response through neurotransmitters and their receptors in immunocytes and immune organs after stroke. To facilitate translational research, we also discuss the promising therapeutic approaches modulating the activation of the ANS or the immune-inflammatory response to promote neurologic recovery after stroke. © 2022 American Physiological Society. Compr Physiol 12:3665-3704, 2022.

Neuroimmune Regulation in Sepsis-Associated Encephalopathy: The Interaction Between the Brain and Peripheral Immunity

Sepsis-associated encephalopathy (SAE), the most popular cause of coma in the intensive care unit (ICU), is the diffuse cerebral damage caused by the septic challenge. SAE is closely related to high mortality and extended cognitive impairment in patients in septic shock. At present, many studies have demonstrated that SAE might be mainly associated with blood–brain barrier damage, abnormal neurotransmitter secretion, oxidative stress, and neuroimmune dysfunction. Nevertheless, the precise mechanism which initiates SAE and contributes to the long-term cognitive impairment remains largely unknown. Recently, a growing body of evidence has indicated that there is close crosstalk between SAE and peripheral immunity. The excessive migration of peripheral immune cells to the brain, the activation of glia, and resulting dysfunction of the central immune system are the main causes of septic nerve damage. This study reviews the update on the pathogenesis of septic encephalopathy, focusing on the over-activation of immune cells in the central nervous system (CNS) and the “neurocentral–endocrine–immune” networks in the development of SAE, aiming to further understand the potential mechanism of SAE and provide new targets for diagnosis and management of septic complications.

Non-neuronal Cholinergic Muscarinic Acetylcholine Receptors in the Regulation of Immune Function

Immune cells such as T and B cells, monocytes and macrophages all express most of the cholinergic components of the nervous system, including acetylcholine (ACh), choline acetyltransferase (ChAT), high affinity choline transporter, muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively), and acetylcholinesterase (AChE). Because of its efficient cleavage by AChE, ACh synthesized and released from immune cells acts only locally in an autocrine and/or paracrine fashion at mAChRs and nAChRs on themselves and other immune cells located in close proximity, leading to modification of immune function. Immune cells generally express all five mAChR subtypes (M₁-M₅) and neuron type nAChR subunits α2-α7, α9, α10, β2-β4. The expression pattern and levels of mAChR subtypes and nAChR subunits vary depending on the tissue involved and its immunological status. Immunological activation of T cells via T-cell receptor-mediated pathways and cell adhesion molecules upregulates ChAT expression, which facilitates the synthesis and release of ACh. At present, α7 nAChRs expressed in macrophages are receiving much attention because they play a central role in anti-inflammatory cholinergic pathways. However, it now appears that through modification of cytokine synthesis, G_q/11-coupled mAChRs play a prominent role in regulation of T cell proliferation and differentiation and B cell immunoglobulin class switching. It is anticipated that greater understanding of G_q/11-coupled mAChRs on immune cells will provide an opportunity to develop new and effective treatments for immunological disorders.

The α7 Nicotinic Acetylcholine Receptor Agonist GTS-21 Improves Bacterial Clearance via Regulation of Monocyte Recruitment and Activity in Polymicrobial Septic Peritonitis

The cholinergic anti-inflammatory pathway has been identified as an effective pathway to modify inflammatory responses. Here, we verified that delayed administration with a selective α7nAChR agonist GTS-21 enables a more efficient elimination of the offending pathogens, diminished inflammatory response and organ injury, and improved survival rates in the polymicrobial septic peritonitis model. We illustrated that the improved bacterial clearance upon GTS-21 stimulation was accompanied by enhanced recruitment of monocytes into the peritoneal cavity and simultaneously increased phagocytic activity and iNOS expression of these recruited monocytes. Mechanically, splenectomy prior to administration of GTS-21 attenuated the recruitment of monocytes into the peritoneal cavity and abolished the protective benefits of GTS-21 treatment. Meanwhile, GTS-21 administration accelerates the deployment of splenic monocytes during septic peritonitis. Collectively, these data suggested that appropriate selective pharmacological α7nAChR activation promotes monocytes trafficking in a spleen-dependent manner and upregulates the antibacterial activity of recruited monocytes during septic peritonitis, which may be utilized as a promising therapeutic modality for patients suffering from septic peritonitis.

The Effect of α7nAChR Signaling on T Cells and Macrophages and Their Clinical Implication in the Treatment of Rheumatic Diseases

Rheumatoid arthritis (RA) is one of the most common autoimmune disease and until now, the etiology and pathogenesis of RA is not fully understood, although dysregulation of immune cells is one of the leading cause of RA-related pathological changes. Based on current understanding, the priority of anti-rheumatic treatments is to restore immune homeostasis. There are several anti-rheumatic drugs with immunomodulatory effects available nowadays, but most of them have obvious safety or efficacy shortcomings. Therefore, the development of novel anti-rheumatic drugs is still in urgently needed. Cholinergic anti-inflammatory pathway (CAP) has been identified as an important aspect of the so-called neuro-immune regulation feedback, and the interaction between acetylcholine and alpha 7 nicotinic acetylcholine receptor (α7nAChR) serves as the foundation for this signaling. Consistent to its immunomodulatory functions, α7nAChR is extensively expressed by immune cells. Accordingly, CAP activation greatly affects the differentiation and function of α7nAChR-expressing immune cells. As a result, targeting α7nAChR will bring profound therapeutic impacts on the treatment of inflammatory diseases like RA. RA is widely recognized as a CD4+ T cells-driven disease. As a major component of innate immunity, macrophages also significantly contribute to RA-related immune abnormalities. Theoretically, manipulation of CAP in immune cells is a feasible way to treat RA. In this review, we summarized the roles of different T cells and macrophages subsets in the occurrence and progression of RA, and highlighted the immune consequences of CAP activation in these cells under RA circumstances. The in-depth discussion is supposed to inspire the development of novel cell-specific CAP-targeting anti-rheumatic regimens.

Toxic mechanisms of cigarette smoke and heat-not-burn tobacco vapor inhalation on rheumatoid arthritis

Tobacco combustion exposure worsens rheumatoid arthritis (RA). Non-combustible tobacco devices, as heat-not-burn tobacco (HNBT), are emerging as harm reduction to smokers by releasing nicotine and lower combustible tobacco products. Nevertheless, HNBT toxicity remains unclear. Hence, here we investigated the impacts of the tobacco combustible product (cigarette smoke; CS) or HNBT vapor exposures on antigen-induced arthritis (AIA) in C57BL/6 mice. Animals were exposed to airflow, HNBT vapor, or CS during 1 h/twice a day, under the Health Canada Intense (HCI) smoking regime, between days 14 to 20 after the first immunization. At day 21, 16 h after the last exposures, mice were i.a. challenged and the AIA effects were evaluated 24 h later. CS- or HNBT-exposed mice presented equivalent blood nicotine levels. CS exposure worsened articular symptoms, pulmonary inflammation, and expression of lung metallothioneins. Nevertheless, CS or HNBT exposures reduced lymphoid organs' cellularity, splenocyte proliferation and IL-2 secretion. Additional in vitro CS or HNBT exposures confirmed the harmful effects on splenocytes, which were partially mediated by the activation of nicotine/α7nAchR pathway. Associated, data demonstrate the toxic mechanisms of CS or HNBT inhalation at HCI regime on RA, and highlight that further investigations are fundamental to assure the toxicity of emerging tobacco products on the immune system during specific challenges.

Expression and Function of Nicotinic Acetylcholine Receptors in Induced Regulatory T Cells

A contribution of the cholinergic system to immune cell function has been suggested, though the role of nicotine and its receptors in T cells, especially regulatory T (Treg) cells, is unclear. We herein investigated the expression and function of nicotinic acetylcholine receptors (nAChRs) in murine-induced Treg (iTreg) cells. Upon differentiation of naive BALB/c T cells into iTreg cells and other T-cell subsets, the effect of nicotine on cytokine production and proliferation of iTreg cells was examined. The expression of nAChRs and its regulatory mechanisms were comparatively analyzed among T-cell subsets. Stimulation-induced transforming growth factor-β1 (TGF-β1) production of iTreg cells was suppressed by nicotine, whereas interleukin (IL)-10 production and proliferation was not affected. α2-, α5-, α9-, and β2-nAChRs were differentially expressed in naive, Th1, Th2, Th9, Th17, and iTreg cells. Among these cell types, the α9-nAChR was particularly upregulated in iTreg cells via its gene promoter, but not through tri-methylation at the 4th lysine residue of the histone H3-dependent mechanisms. We conclude that the immunoregulatory role of Treg cells is modified by the cholinergic system, probably through the characteristic expression of nAChRs.

Neuroinflammation Modulation via α7 Nicotinic Acetylcholine Receptor and Its Chaperone, RIC-3

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in or on various cell types and have diverse functions. In immune cells nAChRs regulate proliferation, differentiation and cytokine release. Specifically, activation of the α7 nAChR reduces inflammation as part of the cholinergic anti-inflammatory pathway. Here we review numerous effects of α7 nAChR activation on immune cell function and differentiation. Further, we also describe evidence implicating this receptor and its chaperone RIC-3 in diseases of the central nervous system and in neuroinflammation, focusing on multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). Deregulated neuroinflammation due to dysfunction of α7 nAChR provides one explanation for involvement of this receptor and of RIC-3 in neurodegenerative diseases. In this review, we also provide evidence implicating α7 nAChRs and RIC-3 in neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD) involving neuroinflammation. Besides, we will describe the therapeutic implications of activating the cholinergic anti-inflammatory pathway for diseases involving neuroinflammation.

Regulators of cholinergic signaling in disorders of the central nervous system

Cholinergic signaling is crucial in cognitive processes, and degenerating cholinergic projections are a pathological hallmark in dementia. Use of cholinesterase inhibitors is currently the main treatment option to alleviate symptoms of Alzheimer's disease and has been postulated as a therapeutic strategy in acute brain damage (stroke and traumatic brain injury). However, the benefits of this treatment are still not clear. Importantly, cholinergic receptors are expressed both by neurons and by astrocytes and microglia, and binding of acetylcholine to the α7 nicotinic receptor in glial cells results in anti-inflammatory response. Similarly, the brain fine-tunes the peripheral immune response over the cholinergic anti-inflammatory axis. All of these processes are of importance for the outcome of acute and chronic neurological disease. Here, we summarize the main findings about the role of cholinergic signaling in brain disorders and provide insights into the complexity of molecular regulators of cholinergic responses, such as microRNAs and transfer RNA fragments, both of which may fine-tune the orchestra of cholinergic mRNAs. The available data suggest that these small noncoding RNA regulators may include promising biomarkers for predicting disease course and assessing treatment responses and might also serve as drug targets to attenuate signaling cascades during overwhelming inflammation and to ameliorate regenerative capacities of neuroinflammation.

Muscarinic Acetylcholine Receptors Modulate Interleukin-6 Production and Immunoglobulin Class Switching in Daudi Cells

B cells express muscarinic and nicotinic acetylcholine receptors (mAChRs and nAChRs, respectively). Following immunization with ovalbumin, serum immunoglobulin G (IgG) and interleukin (IL)-6 levels were lower in M₁ and M₅ mAChR double-deficient mice and higher in α7 nAChR-deficient mice than in wild-type mice. This suggests mAChRs participate in the cytokine production involved in B cell differentiation into plasma cells, which induces immunoglobulin class switching from IgM to IgG. However, because these results were obtained with conventional knockout mice, in which all cells in the body were affected, the specific roles of these receptors expressed in B cells remains unclear. In the present study, Daudi B lymphoblast cells were used to investigate the specific roles of mAChRs and nAChR in B cells. Stimulating Daudi cells using Pansorbin cells (heat-killed, formalin-fixed Staphylococcus aureus coated with protein A) upregulated expression of M₁-M₄ mAChRs and the α4 nAChR subunit. Under these conditions, mAChRs, but not nAChRs, mediated immunoglobulin class switching to IgG. This effect was blocked by scopolamine, a non-selective mAChR antagonist, and 4-diphenylacetoxy-N-methyl-piperidine methiodide (4-DAMP), a G_q/11-coupled M₁, M₃, M₅ antagonist. In addition, IL-6 secretion was further enhanced following mAChR activation. Thus, G_q/11-coupled mAChRs expressed in B cells thus appear to contribute to IL-6 production and B cell maturation into IgG-producing plasma cells.

Regulation of Immune Functions by Non-Neuronal Acetylcholine (ACh) via Muscarinic and Nicotinic ACh Receptors

Acetylcholine (ACh) is the classical neurotransmitter in the cholinergic nervous system. However, ACh is now known to regulate various immune cell functions. In fact, T cells, B cells, and macrophages all express components of the cholinergic system, including ACh, muscarinic, and nicotinic ACh receptors (mAChRs and nAChRs), choline acetyltransferase, acetylcholinesterase, and choline transporters. In this review, we will discuss the actions of ACh in the immune system. We will first briefly describe the mechanisms by which ACh is stored in and released from immune cells. We will then address Ca²⁺ signaling pathways activated via mAChRs and nAChRs on T cells and B cells, highlighting the importance of ACh for the function of T cells, B cells, and macrophages, as well as its impact on innate and acquired (cellular and humoral) immunity. Lastly, we will discuss the effects of two peptide ligands, secreted lymphocyte antigen-6/urokinase-type plasminogen activator receptor-related peptide-1 (SLURP-1) and hippocampal cholinergic neurostimulating peptide (HCNP), on cholinergic activity in T cells. Overall, we stress the fact that ACh does not function only as a neurotransmitter; it impacts immunity by exerting diverse effects on immune cells via mAChRs and 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.

Nicotine: Regulatory roles and mechanisms in atherosclerosis progression

Smoking is an independent risk factor for atherosclerosis. The smoke produced by tobacco burning contains more than 7000 chemicals, among which nicotine is closely related to the occurrence and development of atherosclerosis. Nicotine, a selective cholinergic agonist, accelerates the formation of atherosclerosis by stimulating nicotinic acetylcholine receptors (nAChRs) located in neuronal and non-neuronal tissues. This review introduces the pathogenesis of atherosclerosis and the mechanisms involving nicotine and its receptors. Herein, we focus on the various roles of nicotine in atherosclerosis, such as upregulation of growth factors, inflammation, and the dysfunction of endothelial cells, vascular smooth muscle cells (VSMC) as well as macrophages. In addition, nicotine can stimulate the generation of reactive oxygen species, cause abnormal lipid metabolism, and activate immune cells leading to the onset and progression of atherosclerosis. Exosomes, are currently a research hotspot, due to their important connections with macrophages and the VSMC, and may represent a novel application into future preventive treatment to promote the prevention of smoking-related atherosclerosis. In this review, we will elaborate on the regulatory mechanism of nicotine on atherosclerosis, as well as the effects of interference with nicotine receptors and the use of exosomes to prevent atherosclerosis development.

Therapeutic efficacy of α7 ligands after acute ischaemic stroke is linked to conductive states of α7 nicotinic ACh receptors

BACKGROUND AND PURPOSE

Targeting α7 nicotinic ACh receptors (nAChRs) in neuroinflammatory disorders including acute ischaemic stroke holds significant therapeutic promise. However, therapeutically relevant signalling mechanisms remain unidentified. Activation of neuronal α7 nAChRs triggers ionotropic signalling, but there is limited evidence for it in immunoglial tissues. The α7 ligands which are effective in reducing acute ischaemic stroke damage promote α7 ionotropic activity, suggesting a link between their therapeutic effects for treating acute ischaemic stroke and activation of α7 conductive states.

EXPERIMENTAL APPROACH

This hypothesis was tested using a transient middle cerebral artery occlusion (MCAO) model of acute ischaemic stroke, NS6740, a known selective non-ionotropic agonist of α7 nAChRs and 4OH-GTS-21, a partial α7 agonist. NS6740-like ligands exhibiting low efficacy/potency for ionotropic activity will be referred to as non-ionotropic agonists or "metagonists".

KEY RESULTS

4OH-GTS-21, used as a positive control, significantly reduced neurological deficits and brain injury after MCAO as compared to vehicle and NS6740. By contrast, NS6740 was ineffective in identical assays and reversed the effects of 4OH-GTS-21 when these compounds were co-applied. Electrophysiological recordings from acute hippocampal slices obtained from NS6740-injected animals demonstrated its remarkable brain availability and protracted effects on α7 nAChRs as evidenced by sustained (>8 h) alterations in α7 ionotropic responsiveness.

CONCLUSION AND IMPLICATIONS

These results suggest that α7 ionotropic activity may be obligatory for therapeutic efficacy of α7 ligands after acute ischaemic stroke yet, highlight the potential for selective application of α7 ligands to disease states based on their mode of receptor activation.

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.

Vagus nerve plays a pivotal role in CD4+ T cell differentiation during CVB3-induced murine acute myocarditis

Abnormalities in CD4⁺ T cell (Th cell) differentiation play an important role in the pathogenesis of viral myocarditis (VMC). Our previous studies demonstrated that activation of the cholinergic anti-inflammatory pathway (CAP) alleviated the inflammatory response. In addition, we observed that right cervical vagotomy aggravates VMC by inhibiting CAP. However, the vagus nerve’s effect on differentiation of CD4⁺ T cells has not been studied in VMC mice to date. In this study, we investigated the effects of cervical vagotomy and the α7nAChR agonist pnu282987 on CD4⁺ T cell differentiation in a murine myocarditis model (BALB/c) infected with coxsackievirus B3 (CVB3). Splenic CD4⁺ T cells from CVB3-induced mice obtained and cultured to investigate the potential mechanism of CD4⁺ T cell differentiation. Each Th cell subset was analyzed by flow cytometry. Our results showed that right cervical vagotomy increased proportions of Th1 and Th17 cells and decreased proportions of Th2 and Treg cells in the spleen. Vagotomy-induced upregulation of T-bet, Ror-γ, IFN-γ, and IL-17 expression while downregulating the expression of Gata3, Foxp3, and IL-4 in the heart. In addition, we observed upregulated levels of proinflammatory cytokines, aggravated myocardial lesions and cellular infiltration, and worsened cardiac function in VMC mice. Pnu282987 administration reversed these outcomes. Furthermore, vagotomy inhibited JAK2-STAT3 activation and enhanced NF-κB activation in splenic CD4⁺ T cells. The CD4⁺ T cell differentiation was related to JAK2-STAT3 and NF-κB signal pathways. In conclusion, vagus nerve modulates the inflammatory response by regulating CD4⁺ T cell differentiation in response to VMC.

Role of the α7 Nicotinic Acetylcholine Receptor in the Pathophysiology of Atherosclerosis

Atherosclerosis constitutes a major risk factor for cardiovascular diseases, the leading cause of morbidity and mortality worldwide. This slowly progressing, chronic inflammatory disorder of large- and medium-sized arteries involves complex recruitment of immune cells, lipid accumulation, and vascular structural remodeling. The α7 nicotinic acetylcholine receptor (α7nAChR) is expressed in several cell types involved in the genesis and progression of atherosclerosis, including macrophages, dendritic cells, T and B cells, vascular endothelial and smooth muscle cells (VSMCs). Recently, the α7nAChR has been described as an essential regulator of inflammation as this receptor mediates the inhibition of cytokine synthesis through the cholinergic anti-inflammatory pathway, a mechanism involved in the attenuation of atherosclerotic disease. Aside from the neuronal cholinergic control of inflammation, the non-neuronal cholinergic system similarly regulates the immune function. Acetylcholine released from T cells acts in an autocrine/paracrine fashion at the α7nAChR of various immune cells to modulate immune function. This mechanism additionally has potential implications in reducing atherosclerotic plaque formation. In contrast, the activation of α7nAChR is linked to the induction of angiogenesis and VSMC proliferation, which may contribute to the progression of atherosclerosis. Therefore, both atheroprotective and pro-atherogenic roles are attributed to the stimulation of α7nAChRs, and their role in the genesis and progression of atheromatous plaque is still under debate. This minireview highlights the current knowledge on the involvement of the α7nAChR in the pathophysiology of atherosclerosis.

[Dual Roles of α7 Nicotinic Acetylcholine Receptors Expressed in Immune Cells in T Cell Differentiation -α7 nAChRs Exert Different Actions between Antigen-presenting Cells and CD4+ T Cells]

Immune cells such as T cells, macrophages and dendritic cells express various cholinergic system components, including muscarinic and nicotinic acetylcholine receptors (mAChRs and nAChRs, respectively) and choline acetyltransferase (ChAT), depending on the status of the immune system. The cholinergic system which these components comprise has important effects on the regulation of immune and inflammatory responses. α7 nAChR is a neuronal-type nAChR composed of a homopentamer of the α7 subunit and is characterized by high permeability to Ca²⁺. It is also expressed in immune cells. For example, α7 nAChRs expressed in B cells suppress IgG production by suppressing B cell maturation into plasma cells. In addition, α7 nAChRs expressed in macrophages suppress production and release of tumor necrosis factor (TNF)-α in a mouse lipopolysaccharide (LPS)-induced sepsis model, thereby protecting the mice from lethal shock. In this review, we summarize the functions of α7 nAChRs expressed in CD4⁺ helper T (Th) cells and antigen-presenting cells (APCs), such as dendritic cells and macrophages. We focus in particular on their role in Th cell differentiation. α7 nAChRs on APCs interfere with antigen presentation, which leads to suppression of Th cell differentiation. By contrast, α7 nAChRs on naïve Th cells enhance their differentiation. These distinct roles of α7 nAChRs expressed in APCs and Th cells could be useful for development of drugs and therapeutic strategies for the treatment of immune- and inflammation-related diseases and cancers.

Endogenous neurotoxin-like protein Ly6H inhibits alpha7 nicotinic acetylcholine receptor currents at the plasma membrane

α7 nicotinic acetylcholine receptors (nAChRs) are widely expressed in the central nervous system and regarded as potential therapeutic targets for neurodegenerative conditions, such as Alzheimer's disease and schizophrenia. Yet, despite the assumed pathophysiological importance of the α7 nAChR, molecular physiological characterization remains poorly advanced because α7 nAChR cannot be properly folded and sorted to the plasma membranes in most mammalian cell lines, thus preventing the analyses in heterologous expression system. Recently, ER-resident membrane protein NACHO was discovered as a strong chaperone for the functional expression of α7 nAChR in non-permissive cells. Ly6H, a brain-enriched GPI-anchored neurotoxin-like protein, was reported as a novel modulator regulating intracellular trafficking of α7 nAChR. In this study, we established cell lines that stably and robustly express surface α7 nAChR by introducing α7 nAChR, Ric-3, and NACHO cDNA into HEK293 cells (Triple α7 nAChR/RIC-3/NACHO cells; TARO cells), and re-evaluated the function of Ly6H. We report here that Ly6H binds with α7 nAChRs on the cell membrane and modulates the channel activity without affecting intracellular trafficking of α7 nAChR.

A historic perspective on the current progress in elucidation of the biologic significance of non-neuronal acetylcholine

The "5th International Symposium on Non-neuronal Acetylcholine: from bench to bedside" was held on September 27-29, 2019 in Hyatt Regency, Long Beach, CA, USA. Approximately 50 scientists from 11 countries over 6 continents participated in this meeting. The major topics included an overall biologic significance of non-neuronal acetylcholine (ACh) and the roles of the non-neuronal cholinergic systems in mucocutaneous, respiratory, digestive, immunologic, endocrine, cardiovascular, musculoskeletal and kidney diseases, and cancer. This meeting facilitated continued work to advance the fundamental science and translational aspects of the interdisciplinary studies on non-neuronal ACh. The progress made has opened a new chapter in the field of cholinergic pharmacology, and advanced our knowledge beyond regulation of individual cell- and tissue-types, defining a new paradigm of selective pharmacological regulation of vital function of practically all types of non-neuronal cells. It is now clear that the autocrine and paracrine control of non-neuronal cells by non-neuronal ACh is implemented through synergistic, additive, and reciprocal effects triggered by two different cholinergic receptor classes. Each biologic effect of ACh is determined by a unique combination of cholinergic receptors subtype expressed at each stage of cell development and differentiation. The plasticity of the non-neuronal cholinergic system helps adjust homeostasis to new environmental conditions.

Cholinergic signaling controls immune functions and promotes homeostasis

Acetylcholine (ACh) was created by nature as one of the first signaling molecules, expressed already in procaryotes. Based on the positively charged nitrogen, ACh could initially mediate signaling in the absence of receptors. When evolution established more and more complex organisms the new emerging organs systems, like the smooth and skeletal muscle systems, energy-generating systems, sexual reproductive system, immune system and the nervous system have further optimized the cholinergic signaling machinery. Thus, it is not surprising that ACh and the cholinergic system are expressed in the vast majority of cells. Consequently, multiple common interfaces exist, for example, between the nervous and the immune system. Research of the last 20 years has unmasked these multiple regulating mechanisms mediated by cholinergic signaling and thus, the biological role of ACh has been revised. The present article summarizes new findings and describes the role of both non-neuronal and neuronal ACh in protecting the organism from external and internal health threats, in providing energy for the whole organism and for the individual cell, controling immune functions to prevent inflammatory dysbalance, and finally, the involvement in critical brain functions, such as learning and memory. All these capacities of ACh enable the organism to attain and maintain homeostasis under changing external conditions. However, the existence of identical interfaces between all these different organ systems complicates the research for new therapeutic interventions, making it essential that every effort should be undertaken to find out more specific targets to modulate cholinergic signaling in different diseases.

Minireview: Divergent roles of α7 nicotinic acetylcholine receptors expressed on antigen-presenting cells and CD4+ T cells in the regulation of T cell differentiation

α7 nAChRs expressed on immune cells regulate antigen-specific antibody and proinflammatory cytokine production. Using spleen cells from ovalbumin (OVA)-specific T cell receptor transgenic DO11.10 mice and the α7 nAChR agonist GTS-21, investigation of (1) antigen processing-dependent and (2) -independent, antigen presenting cell (APC)-dependent, naïve CD4+ T cell differentiation, as well as (3) non-specific APC-independent, anti-CD3/CD28 mAbs-induced CD4+ T cell differentiation, revealed the differential roles of α7 nAChRs expressed on T cells and APCs in the regulation of CD4+ T cell differentiation. GTS-21 suppressed OVA-induced antigen processing- and APC-dependent differentiation into regulatory T cells (Tregs) and effector T cells (Th1, Th2 and Th17) without affecting OVA uptake or cell viability. By contrast, GTS-21 upregulated OVA peptide-induced antigen processing-independent T cell differentiation into all lineages. During anti-CD3/CD28 mAbs-induced T cell differentiation in the presence of polarizing cytokines, GTS-21 promoted wild-type T cell differentiation into all lineages, but did not affect α7 nAChR-deficient T cell differentiation. These results demonstrate (1) that α7 nAChRs on APCs downregulate T cell differentiation by inhibiting antigen processing and thereby interfering with antigen presentation; and (2) that α7 nAChRs on T cells upregulate differentiation into Tregs and effector T cells. Thus, the divergent roles of α7 nAChRs on APCs and T cells likely regulate the intensity of immune responses. These findings suggest the possibility of using α7 nAChR agonists to harvest greater numbers of Tregs and Th1 and Th2 cells for adoptive immune therapies for treatment of autoimmune diseases and cancers.

α7 nAChRs expressed on antigen presenting cells are insensitive to the conventional antagonists α-bungarotoxin and methyllycaconitine

Expression of α7 nicotinic acetylcholine receptors (nAChRs) on antigen presenting cells (APCs), such as macrophages and dendritic cells, is now well established. We have shown that GTS-21, a selective α7 nAChR agonist, downregulates APC-dependent CD4⁺ T cell differentiation into regulatory T cells (Tregs) and effector Th1, Th2 and Th17 cells by inhibiting antigen processing, thereby interfering with antigen presentation. α7 nAChRs on Jurkat human leukemic T cells require functional T cell receptors (TCRs)/CD3 and leukocyte-specific tyrosine kinase to mediate nicotine-induced Ca²⁺-signaling via Ca²⁺ release from intracellular stores, and are insensitive to two conventional α7 nAChR antagonists, α-bungarotoxin (α-BTX) and methyllycaconitine (MLA). We investigated the effects of GTS-21, α-BTX and MLA on ovalbumin (OVA)-induced Th cytokine release from spleen cells isolated from OVA-specific TCR transgenic DO11.10 mice. We found that: (1) GTS-21 dose-dependently suppresses OVA-induced IFN-γ, IL-4 and IL-17 release, but neither α-BTX nor MLA alone affected the OVA-induced cytokine release. (2) Neither α-BTX nor MLA abolished the suppressive effects of GTS-21 on IFN-γ and IL-17 release from OVA-activated DO11.10 spleen cells. (3) GTS-21 significantly suppressed OVA-induced APC-dependent CD4⁺ T cell differentiation into Tregs. Neither MLA nor mecamylamine, a non-specific nAChR antagonist, abolished the suppressive effect of GTS-21 on Treg differentiation. These results suggest that α7 nAChRs on APCs involved in cytokine synthesis and T cell differentiation are insensitive to the conventional α7 nAChR antagonists, α-BTX and MLA, and that α7 nAChRs on APCs differ pharmacologically from those in neurons.

Immunotoxicity evaluation by subchronic oral administration of clothianidin in Sprague-Dawley rats

Neonicotinoid pesticides (NNs) act as agonists on nicotinic acetylcholine receptors (nAChRs) of insects, and there have been concerns about the effects of NNs on the health of mammals. Since nAChRs are expressed in immune cells, it is possible that NNs disturb the immune system. However, few reports have examined the immunotoxicity of clothianidin (CLO), a widely-used NN. Here, we report the effects of CLO on immune organs and type IV allergic reactions in ear auricles. We orally administered CLO at 0, 30 and 300 mg/kg/day (CLO-0, 30 and 300) to Sprague-Dawley rats for 28 days. The effects were evaluated by organ and body weights, histopathology, and immunohistochemistry (TCRαβ, CD4, CD8, CD11b, CD68, CD103). In addition, some cecal contents were subjected to preliminary gut microbiota analysis, because microbiota contribute to host homeostasis, including the immunity. Our results showed loose stool, suppression of body weight gain, significant changes in organ weights (thymus: decreased; liver: increased) and changes of the gut microbiota in the CLO-300 group. There were no obvious histopathological changes in immune organs. Granulomas of the ear auricles were found in one rat of each of the CLO-30 and 300 groups, but CLO had no apparent effect on the thickness or immunohistochemistry in the ear auricles. We present new evidence that CLO affects the thymus and intestine, and might enhance the local inflammatory response. These findings should contribute to the appropriate evaluation of the safety of NNs in the future.