T and B cells express most cholinergic system components-e.g., acetylcholine (ACh), choline acetyltransferase (ChAT), acetylcholinesterase, and both muscarinic and nicotinic ACh receptors (mAChRs and ...nAChRs, respectively). Using ChAT
-eGFP transgenic mice, ChAT expression has been confirmed in T and B cells, dendritic cells, and macrophages. Moreover, T cell activation
T-cell receptor/CD3-mediated pathways upregulates ChAT mRNA expression and ACh synthesis, suggesting that this lymphocytic cholinergic system contributes to the regulation of immune function. Immune cells express all five mAChRs (M
-M
). Combined M
/M
mAChR-deficient (M
/M
KO) mice produce less antigen-specific antibody than wild-type (WT) mice. Furthermore, spleen cells in M
/M
-KO mice produce less tumor necrosis factor (TNF)-α and interleukin (IL)-6, suggesting M
/M
mAChRs are involved in regulating pro-inflammatory cytokine and antibody production. Immune cells also frequently express the α2, α5, α6, α7, α9, and α10 nAChR subunits. α7 nAChR-deficient (α7-KO) mice produce more antigen-specific antibody than WT mice, and spleen cells from α7-KO mice produce more TNF-α and IL-6 than WT cells. This suggests that α7 nAChRs are involved in regulating cytokine production and thus modulate antibody production. Evidence also indicates that nicotine modulates immune responses by altering cytokine production and that α7 nAChR signaling contributes to immunomodulation through modification of T cell differentiation. Together, these findings suggest the involvement of both mAChRs and nAChRs in the regulation of immune function. The observation that vagus nerve stimulation protects mice from lethal endotoxin shock led to the notion of a cholinergic anti-inflammatory reflex pathway, and the spleen is an essential component of this anti-inflammatory reflex. Because the spleen lacks direct vagus innervation, it has been postulated that ACh synthesized by a subset of CD4
T cells relays vagal nerve signals to α7 nAChRs on splenic macrophages, which downregulates TNF-α synthesis and release, thereby modulating inflammatory responses. However, because the spleen is innervated solely by the noradrenergic splenic nerve, confirmation of an anti-inflammatory reflex pathway involving the spleen requires several more hypotheses to be addressed. We will review and discuss these issues in the context of the cholinergic system in immune cells.
T and B cells, macrophages and dendritic cells (DCs) all express most of the components necessary for a functional cholinergic system. This includes choline acetyltransferase (ChAT), muscarinic and ...nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs, respectively) and acetylcholinesterase (AChE). Immunological activation of T cells up-regulates cholinergic activity, including ChAT and AChE expression. Moreover, toll-like receptor agonists induce ChAT expression in DCs and macrophages, suggesting cholinergic involvement in the regulation of immune function. Immune cells express all five M1–M5 mAChR subtypes and several nAChR subtypes, including α7. Modulation of antigen-specific antibody and pro-inflammatory cytokine production in M1/M5 mAChR gene-knockout (KO) and α7 nAChR-KO mice further support the idea of a non-neuronal cholinergic system contributing to the regulation of immune function. Evidence also suggests that α7 nAChRs are involved in suppressing DC and macrophage activity, leading to suppression of T cell differentiation into effector T cells. These findings suggest the possibility that immune function could be modulated by manipulating immune cell cholinergic activity using specific agonists and antagonists. Therefore, a fuller understanding of the immune cell cholinergic system should be useful for the development of drugs and therapeutic strategies for the treatment of inflammation-related diseases and cancers.
Lymphocytes express both muscarinic and nicotinic acetylcholine (ACh) receptors (mAChRs and nAChRs, respectively), and stimulation of mAChRs and nAChRs produces various biochemical and functional ...changes. Although it has been postulated that parasympathetic cholinergic nerves directly innervate immune cells, no evidence has supported this hypothesis. We measured ACh in the blood of various animal species and determined its localization in T cells using a sensitive and specific radioimmunoassay. Furthermore, we showed that T cells express choline acetyltransferase (ChAT), an ACh synthesizing enzyme. Immunological T cell activation enhances ACh synthesis through the up-regulation of ChAT expression, suggesting lymphocytic cholinergic activity is related to immunological activity. Most immune cells such as T cells, B cells, and monocytes express all five subtypes of mAChRs (M1–M5), and various subunits of the nAChR, such as α3, α5, α7, α9, and α10. Studies on serum antibody production in M1 and M5 combined mAChR gene knockout (KO) mice immunized with ovalbumin (OVA) revealed that M1/M5 mAChRs up-regulate TNF-α, IFN-γ and IL-6 production in spleen cells, leading to an elevation of serum anti-OVA specific IgG1. In contrast, studies of nAChR α7 subunit gene KO mice immunized with OVA show that α7 nAChRs down-regulate these proinflammatory cytokines, thereby leading to a reduction of anti-OVA specific IgG1. Taken together, these findings demonstrate that both mAChRs and nAChRs modulate production of cytokines, such as TNF-α, resulting in a modification of antibody production. These findings support the notion that a non-neuronal cholinergic system is involved in the regulation of immune cell function.
Regulation of proinflammatory cytokine production through mAChRs and nAChRs by ACh derived from CD4+ T cells during antigen presentation. Display omitted
Diabetic kidney disease (DKD) is the most common cause of chronic kidney disease (CKD), leading end-stage renal disease. Thus, DKD is one of the most important diabetic complications. Incretin-based ...therapeutic agents, such as glucagon-like peptide-1 (GLP-1) receptor agonizts and dipeptidyl peptidase-4 (DPP-4) inhibitors have been reported to elicit vasotropic actions, suggesting a potential for effecting reduction in DKD. Glucose-dependent insulinotropic polypeptide (GIP) is also classified as an incretin. However, the insulin action after GIP secretion is known to be drastically reduced in patients with type 2 diabetes. Therefore, GIP has been formally considered unsuitable as a treatment for type 2 diabetes in the past. This concept is changing as it has been reported that resistance to GIP can be reversed and its effect restored with improved glycemic control. The development of novel dual- or triple- receptor agonizts that can bind to the receptors, not only for GLP-1 but also to GIP and glucagon receptors, is intended to simultaneously address several metabolic pathways including protein, lipid, and carbohydrate metabolism. These led to the development of GIP receptor agonist-based drugs for type 2 diabetes. The possibility of combined GIP/GLP-1 receptor agonist was also explored. The novel dual GIP and GLP-1 receptor agonist tirzepatide has recently been launched (Mounjaro®, Lilly). We have revealed precise mechanisms of the renoprotective effect of GLP-1 receptor agonizts or DPP-4 inhibitors, while the long-term effect of tirzepatide will need to be determined and its potential effects on kidneys should be properly tested.
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•Glucagon-like peptide-1 (GLP-1) receptor agonizts and dipeptidyl peptidase-4 (DPP-4) inhibitors are known to elicit vasotropic actions, and they could potentially be used for improving diabetic kidney disease (DKD).•The dual GIP/GLP-1 receptor agonist tirzepatide was shown to significantly reduce the risk of kidney-specific composite outcome and worsening albuminuria.•Tirzepatide may become the first-choice incretin-based therapeutic agent for the treating DKD.
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.
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.
Hippocampal cholinergic neurostimulating peptide (HCNP) is a secreted undecapeptide produced through proteolytic cleavage of its precursor protein, HCNPpp. Within hippocampal neurons, HCNP increases ...gene expression of choline acetyltransferase (ChAT), which catalyzes acetylcholine (ACh) synthesis, thereby modulating neural activity. HCNPpp also appears to be expressed in various immune cells. In the present study, we observed that HCNPpp is expressed in U937 human macrophage-like cells and that HCNP exposure suppresses lipopolysaccharide (LPS)-induced gene expression of ChAT. The opposite action is also seen in T lymphocytes, which suggest that HCNP appear to suppress cholinergic system in immune cells. In addition, HCNP suppresses LPS-induced gene expression of inflammatory enzymes including cyclooxygenase 2 (COX2) and inducible nitric oxide (NO) synthase (iNOS). The suppressive effect of HCNP may reflect suppression of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling activated by LPS. Thus, HCNP may have therapeutic potential as an anti-inflammatory drug.
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, Gq/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 Gq/11-coupled mAChRs on immune cells will provide an opportunity to develop new and effective treatments for immunological disorders.
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 Gq/11-coupled M1, M3, M5 antagonist. In addition, IL-6 secretion was further enhanced following mAChR activation. Thus, Gq/11-coupled mAChRs expressed in B cells thus appear to contribute to IL-6 production and B cell maturation into IgG-producing plasma cells.
Acetylcholine (ACh) is a phylogenetically ancient molecule involved in cell-to-cell signaling in almost all life-forms on earth. Cholinergic components, including ACh, choline acetyltransferase, ...acetylcholinesterase, and muscarinic and nicotinic ACh receptors (mAChRs and nAChRs, respectively) have been identified in numerous non-neuronal cells and tissues, including keratinocytes, cancer cells, immune cells, urinary bladder, airway epithelial cells, vascular endothelial cells, and reproductive organs, among many others. Stimulation of the mAChRs and nAChRs elicits cell-specific functional and biochemical effects. These findings support the notion that non-neuronal cholinergic systems are expressed in certain cells and tissues and are involved in the regulation of their function and that cholinergic dysfunction is related to the pathophysiology of certain diseases. They also provide clues for development of drugs with novel mechanisms of action.
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