Non-neuronal functions of the m2 muscarinic acetylcholine receptor

Screening of neurotransmitter receptor modulators reveals novel inhibitors of influenza virus replication

Influenza presents a significant public health threat, as severe cases can lead to excessive inflammation and complications such as pneumonia or acute respiratory distress syndrome. Current antiviral agents targeting viral proteins may lead to the development of resistance, highlighting the need for new agents targeting host factors. Neurotransmitter receptors are vital for cellular signaling and cell cycle modulation, making them promising antiviral therapeutic targets. Recent research has demonstrated that screening libraries of compounds aimed at these receptors can help identify inhibitors that prevent the replication of various viruses, including filoviruses and SARS-CoV-2. We screened a neurotransmitter receptor modulator library in influenza-infected U937 cells and found that many adrenergic, histamine, dopamine, and serotonin receptor agonists and antagonists exhibit antiviral activity. We identified 20 candidate compounds with IC50 values below 20 μM, suggesting a critical role for these receptors in influenza replication. Three representative compounds (isoxsuprine, ciproxifan, and rotigotine) inhibited H1N1 replication in a dose-dependent manner in multiple cell lines, and were effective against H1N1, oseltamivir-resistant H1N1, H3N2, and influenza B strains. Mechanistic studies indicated that these compounds affect virus internalization during the early infection stages. In a mouse model of lethal influenza, isoxsuprine significantly decreased lung viral titers, mitigated pulmonary inflammation, and enhanced survival rates. These findings highlight neurotransmitter receptors as potential targets for developing novel anti-influenza agents, providing a foundation for further optimization of the identified compounds as potential therapeutic agents.

Anti-carcinogenic effects of arecaidine but-2-ynyl ester tosylate on breast cancer: proliferation inhibition and activation of apoptosis

BACKGROUND

Breast cancer (BC) is the most prevalent cancer among women globally and is notoriously difficult to treat due to its heterogeneous nature and the lack of an effective treatment. Muscarinic receptors (MRs), which serve as key regulators in the parasympathetic nervous system, exhibit significant regulatory functions in non-neural cells. Recent studies suggest that modulating MR activity can elicit anti-carcinogenic effects across various malignancies, stimulating interest in their oncological implications. To investigate this further, we explored the anti-carcinogenic effects of arecaidine but-2-ynyl ester tosylate (ABET), a potential M2 receptor activator, in BC cells using several cellular and molecular assays.

METHODS AND RESULTS

Molecular docking assays were employed to confirm the binding affinity of ABET to M2/M4 receptors. Subsequently, we evaluated the impact of ABET on cell viability, proliferation, clonogenicity, and migration in MDA-MB-231 and MCF-7 BC cell lines. Computational analysis revealed preferential binding of ABET to M2 and M4 receptors. In-vitro experiments demonstrated that ABET markedly inhibits viability, growth, clonogenicity, and migration in BC cells. Notably, ABET induced cell cycle arrest in MDA-MB-231 cells and promoted apoptotic cell death in MCF-7 cells. Furthermore, ABET downregulated key proliferation- and cell cycle-associated genes, including CCND1, CDK6, and MKI67.

CONCLUSIONS

Our findings underscore ABET as a promising therapeutic candidate for BC treatment, capable of suppressing cell growth, survival, and migration. Additional in-vivo studies are necessary to validate ABET's anti-neoplastic efficacy and evaluate its feasibility as novel therapeutic agent in BC management.

Mitochondrial morphology and energy metabolism in reprogrammed porcine expanded potential stem cells

OBJECTIVE

Expanded potential stem cells (EPSCs) are stem cells that can differentiate into embryonic and extraembryonic lineages, including extraembryonic endoderm and trophoblast lineages. Therefore, EPSCs have great potential in advancing regenerative medicine, elucidating disease mechanisms, and exploring early embryonic development. However, the generation and characterization of EPSCs in pigs have not been thoroughly explored. In this study, we successfully generated porcine EPSCs (pEPSCs).

METHODS

We reprogrammed porcine fetal fibroblasts (PFFs) using an integration-free method with Sendai virus vectors.

RESULTS

The resulting pEPSCs expressed key pluripotency markers and demonstrated the ability to differentiate between embryonic and extraembryonic lineages. Notably, reprogramming into pEPSCs was associated with a transformation of mitochondrial morphology from the elongated form observed in PFFs to a globular shape, reflecting potential alterations in energy metabolism. We observed significant remodeling of mitochondrial morphology and a subsequent shift towards glycolytic energy dependence during the reprogramming of PFFs into pEPSCs.

CONCLUSION

Our findings provide valuable insights into the characteristics of EPSCs in pigs and highlight their potential applications in regenerative medicine, disease modeling, and emerging fields such as cell-based meat production.

[Role and place of ipidacrine in the therapy of diseases of the peripheral nervous system. The resolution of the expert council]

The resolution of the expert council is devoted to discussing aspects of the use of ipidacrine for the treatment of mononeuropathies, polyneuropathies and radiculopathies of various etiologies. Specialists prepared recommendations for ipidacrine's application in treating peripheral nervous system disorders.

Stimulation of the muscarinic receptor M4 regulates neural precursor cell proliferation and promotes adult hippocampal neurogenesis

Cholinergic signaling plays a crucial role in the regulation of adult hippocampal neurogenesis; however, the mechanisms by which acetylcholine mediates neurogenic effects are not completely understood. Here, we report the expression of muscarinic acetylcholine receptor subtype M4 (M4 mAChR) on a subpopulation of neural precursor cells (NPCs) in the adult mouse hippocampus, and demonstrate that its pharmacological stimulation promotes their proliferation, thereby enhancing the production of new neurons in vivo. Using a targeted ablation approach, we also show that medial septum (MS) and the diagonal band of Broca (DBB) cholinergic neurons support both the survival and morphological maturation of adult-born neurons in the mouse hippocampus. Although the systemic administration of an M4-selective allosteric potentiator fails to fully rescue the MS/DBB cholinergic lesion-induced decrease in hippocampal neurogenesis, it further exacerbates the impairment in the morphological maturation of adult-born neurons. Collectively, these findings reveal stage-specific roles of M4 mAChRs in regulating adult hippocampal neurogenesis, uncoupling their positive role in enhancing the production of new neurons from the M4-induced inhibition of their morphological maturation, at least in the context of cholinergic signaling dysfunction.

Establishment of bovine trophoblast stem cells

Here, we report that a chemical cocktail (LCDM: leukemia inhibitory factor [LIF], CHIR99021, dimethinedene maleate [DiM], minocycline hydrochloride), previously developed for extended pluripotent stem cells (EPSCs) in mice and humans, enables de novo derivation and long-term culture of bovine trophoblast stem cells (TSCs). Bovine TSCs retain developmental potency to differentiate into mature trophoblast cells and exhibit transcriptomic and epigenetic (chromatin accessibility and DNA methylome) features characteristic of trophectoderm cells from early bovine embryos. The bovine TSCs established in this study will provide a model to study bovine placentation and early pregnancy failure.

Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

RC-4BC cells express nicotinic and muscarinic acetylcholine receptors

Acetylcholine is one of the most important endogenous neurotransmitters in a range of organisms spanning different animal phyla. Within pituitary gland it acts as autocrine and paracrine signal. In a current study we assessed expression profile of the different subunits of nicotinic as well as muscarinic acetylcholine receptors in RC-4BC cells, which are derived from rat pituitary gland tumor. Our findings indicate that β2, δ, and M2 subunits are expressed by the cells with the lowest Ct values compared to other tested subunits. The detected Ct values were 26.6±0.16, 27.95±0.5, and 28.8±0.25 for β2, δ, and M2 subunits, respectively.

Differential Actions of Muscarinic Receptor Subtypes in Gastric, Pancreatic, and Colon Cancer

Cancers arising from gastrointestinal epithelial cells are common, aggressive, and difficult to treat. Progress in this area resulted from recognizing that the biological behavior of these cancers is highly dependent on bioactive molecules released by neurocrine, paracrine, and autocrine mechanisms within the tumor microenvironment. For many decades after its discovery as a neurotransmitter, acetylcholine was thought to be synthesized and released uniquely from neurons and considered the sole physiological ligand for muscarinic receptor subtypes, which were believed to have similar or redundant actions. In the intervening years, we learned this former dogma is not tenable. (1) Acetylcholine is not produced and released only by neurons. The cellular machinery required to synthesize and release acetylcholine is present in immune, cancer, and other cells, as well as in lower organisms (e.g., bacteria) that inhabit the gut. (2) Acetylcholine is not the sole physiological activator of muscarinic receptors. For example, selected bile acids can modulate muscarinic receptor function. (3) Muscarinic receptor subtypes anticipated to have overlapping functions based on similar G protein coupling and downstream signaling may have unexpectedly diverse actions. Here, we review the relevant research findings supporting these conclusions and discuss how the complexity of muscarinic receptor biology impacts health and disease, focusing on their role in the initiation and progression of gastric, pancreatic, and colon cancers.

Cyclic Adenosine Monophosphate, Inositol 1,4,5-trisphosphate, Calcium, and Phosphorylated Myosin Light Chain Regulation Through M2 and M3 Muscarinic Receptors of Scleral Fibroblast Cells in Rat Myopia Model

AIM: This study aims to investigate the concentration of cyclic adenosine monophosphate (cAMP), inositol 1,4,5-trisphosphate (IP3), calcium (Ca2+), and the expression phosphorylated myosin light chain (MLC) in Rattus norvegicus scleral fibroblast cells. METHODOLOGY: This study utilized an in vitro experimental study by applying Rattus norvegicus scleral fibroblast cell culture. The cultured cells were divided into control and lens-induced myopia (LIM) groups. The control and LIM culture groups were each divided into five groups, namely, negative control, 0.1 μM acetylcholine, 0.1 μM himbacine, 0.1 μM methoctramine, and 0.1 μM 4-DAMP group. The cAMP, IP3, and Ca2+ concentration were analyzed in the 0th, 5th, 10th, 20th, and 30th. The phosphorylated MLC expression was analyzed using confocal microscope. RESULTS: In the LIM group, the highest cAMP concentration is visible at the 10th min on the himbacine group (0.304 ± 0; p = 0.043) and on the 4-DAMP group (0.346 ± 0; p = 0.043). The highest IP3 concentration is found on the LIM group at the 20th min in comparison to the control group (2503.6 ± 11 vs. 2039.2 ± 2.1; p = 0.046). The highest Ca2+ concentration belongs to the 4-DAMP treatment group from the 5th to the 30th min. The highest average phosphorylated MLC expression value in the LIM group is shown by the 0.1μM 4-DAMP treatment (184.2 ± 37.9c au). CONCLUSION: The regulation of cAMP, IP3, Ca2+, and phosphorylated MLC on the M2 and M3 muscarinic receptor of the scleral fibroblast cells of myopia animal models differs from normal animal models which may be due to interactions of M2 and M3 muscarinic receptor as compensation reaction or crosstalk on myopia induction.

The role of potassium and host calcium signaling in Toxoplasma gondii egress

Toxoplasma gondii is an obligate intracellular parasite and replicates inside a parasitophorous vacuole (PV) within the host cell. The membrane of the PV (PVM) contains pores that permits for equilibration of ions and small molecules between the host cytosol and the PV lumen. Ca²⁺ signaling is universal and both T. gondii and its mammalian host cell utilize Ca²⁺ signals to stimulate diverse cellular functions. Egress of T. gondii from host cells is an essential step for the infection cycle of T. gondii, and a cytosolic Ca²⁺ increase initiates a Ca²⁺ signaling cascade that culminates in the stimulation of motility and egress. In this work we demonstrate that intracellular T. gondii tachyzoites are able to take up Ca²⁺ from the host cytoplasm during host cell signaling events. Both intracellular and extracellular Ca²⁺ sources are important in reaching a threshold of parasite cytosolic Ca²⁺ needed for successful egress. Two peaks of Ca²⁺ were observed in egressing single parasites with the second peak resulting from Ca²⁺ entry. We patched infected host cells to allow the delivery of precise concentrations of Ca²⁺ for the stimulation of motility and egress. Using this approach of patching infected host cells, allowed us to determine that increasing the host cytosolic Ca²⁺ to a specific concentration can trigger egress, which is further accelerated by diminishing the concentration of potassium (K⁺).

Impairment of agonist-induced M2 muscarinic receptor activation by autoantibodies from chagasic patients with cardiovascular dysautonomia

Previous studies showed that circulating autoantibodies against M₂ muscarinic receptors (anti-M₂R Ab) are associated with decreased cardiac parasympathetic modulation in patients with chronic Chagas disease (CD). Here we investigated whether the exposure of M₂R to such antibodies could impair agonist-induced receptor activation, leading to the inhibition of associated signaling pathways. Preincubation of M₂R-expressing HEK 293T cells with serum IgG fractions from chagasic patients with cardiovascular dysautonomia, followed by the addition of carbachol, resulted in the attenuation of agonist-induced G_i protein activation and arrestin-2 recruitment. These effects were not mimicked by the corresponding Fab fractions, suggesting that they occur through receptor crosslinking. IgG autoantibodies did not enhance M₂R/arrestin interaction or promote M₂R internalization, suggesting that their inhibitory effects are not likely a result of short-term receptor regulation. Rather, these immunoglobulins could function as negative allosteric modulators of acetylcholine-mediated responses, thereby contributing to the development of parasympathetic dysfunction in patients with CD.

Severe Hypoglycemia-Induced Fatal Cardiac Arrhythmias Are Mediated by the Parasympathetic Nervous System in Rats

The contribution of the sympathetic nervous system (SNS) versus the parasympathetic nervous system (PSNS) in mediating fatal cardiac arrhythmias during insulin-induced severe hypoglycemia is not well understood. Therefore, experimental protocols were performed in nondiabetic Sprague-Dawley rats to test the SNS with 1) adrenal demedullation and 2) chemical sympathectomy, and to test the PSNS with 3) surgical vagotomy, 4) nicotinic receptor (mecamylamine) and muscarinic receptor (AQ-RA 741) blockade, and 5) ex vivo heart perfusions with normal or low glucose, acetylcholine (ACh), and/or mecamylamine. In protocols 1-4, 3-h hyperinsulinemic (0.2 units/kg/min) and hypoglycemic (10-15 mg/dL) clamps were performed. Adrenal demedullation and chemical sympathectomy had no effect on mortality or arrhythmias during severe hypoglycemia compared with controls. Vagotomy led to a 6.9-fold decrease in mortality; reduced first- and second-degree heart block 4.6- and 4-fold, respectively; and prevented third-degree heart block compared with controls. Pharmacological blockade of nicotinic receptors, but not muscarinic receptors, prevented heart block and mortality versus controls. Ex vivo heart perfusions demonstrated that neither low glucose nor ACh alone caused arrhythmias, but their combination induced heart block that could be abrogated by nicotinic receptor blockade. Taken together, ACh activation of nicotinic receptors via the vagus nerve is the primary mediator of severe hypoglycemia-induced fatal cardiac arrhythmias.

Role of Muscarinic Acetylcholine Signaling in Gastrointestinal Cancers

In the tumor microenvironment, various stromal and immune cells accumulate and interact with cancer cells to contribute to tumor progression. Among stromal players, nerves have recently been recognized as key regulators of tumor growth. More neurotransmitters, such as catecholamines and acetylcholine (ACh), are present in tumors, as the cells that secrete neurotransmitters accumulate by the release of neurotrophic factors from cancer cells. In this short review, we focus on the role of nerve signaling in gastrointestinal (GI) cancers. Given that muscarinic acetylcholine receptor signaling seems to be a dominant regulator of GI stem cells and cancers, we review the function and mechanism of the muscarinic ACh pathway as a regulator of GI cancer progression. Accumulating evidence suggests that ACh, which is secreted from nerves and tuft cells, stimulates GI epithelial stem cells and contributes to cancer progression via muscarinic receptors.

Acetylcholine-treated murine dendritic cells promote inflammatory lung injury

In recent years a non-neuronal cholinergic system has been described in immune cells, which is often usually activated during the course of inflammatory processes. To date, it is known that Acetylcholine (ACh), a neurotransmitter extensively expressed in the airways, not only induces bronchoconstriction, but also promotes a set of changes usually associated with the induction of allergic/Th2 responses. We have previously demonstrated that ACh polarizes human dendritic cells (DC) toward a Th2-promoting profile through the activation of muscarinic acetylcholine receptors (mAChR). Here, we showed that ACh promotes the acquisition of an inflammatory profile by murine DC, with the increased MHC II IA^d expression and production of two cytokines strongly associated with inflammatory infiltrate and tissue damage, namely TNF-α and MCP-1, which was prevented by blocking mAChR. Moreover, we showed that ACh induces the up-regulation of M3 mAChR expression and the blocking of this receptor with tiotropium bromide prevents the increase of MHC II IAd expression and TNF-α production induced by ACh on DC, suggesting that M3 is the main receptor involved in ACh-induced activation of DC. Then, using a short-term experimental murine model of ovalbumin-induced lung inflammation, we revealed that the intranasal administration of ACh-treated DC, at early stages of the inflammatory response, might be able to exacerbate the recruitment of inflammatory mononuclear cells, promoting profound structural changes in the lung parenchyma characteristic of chronic inflammation and evidenced by elevated systemic levels of inflammatory marker, TNF-α. These results suggest a potential role for ACh in the modulation of immune mechanisms underlying pulmonary inflammatory processes.

Derivation of Pluripotent Stem Cells with In Vivo Embryonic and Extraembryonic Potency

Of all known cultured stem cell types, pluripotent stem cells (PSCs) sit atop the landscape of developmental potency and are characterized by their ability to generate all cell types of an adult organism. However, PSCs show limited contribution to the extraembryonic placental tissues in vivo. Here, we show that a chemical cocktail enables the derivation of stem cells with unique functional and molecular features from mice and humans, designated as extended pluripotent stem (EPS) cells, which are capable of chimerizing both embryonic and extraembryonic tissues. Notably, a single mouse EPS cell shows widespread chimeric contribution to both embryonic and extraembryonic lineages in vivo and permits generating single-EPS-cell-derived mice by tetraploid complementation. Furthermore, human EPS cells exhibit interspecies chimeric competency in mouse conceptuses. Our findings constitute a first step toward capturing pluripotent stem cells with extraembryonic developmental potentials in culture and open new avenues for basic and translational research. VIDEO ABSTRACT.

Revisiting the endocytosis of the m2 muscarinic acetylcholine receptor

The agonist-induced endocytosis of the muscarinic acetylcholine receptor M2 is different from that of the other members of the muscarinic receptor family. The uptake of the M2 receptor involves the adapter proteins of the β-arrestin family and the small GTPase ADP-ribosylation factor 6. However, it has remained inconclusive if M2 endocytosis is dependent on clathrin or the large GTPase dynamin. We here show by means of knocking down the clathrin heavy chain that M2 uptake upon agonist stimulation requires clathrin. The expression of various dominant-negative dynamin-2 mutants and the use of chemical inhibitors of dynamin function revealed that dynamin expression and membrane localization as such appear to be necessary for M2 endocytosis, whereas dynamin GTPase activity is not required for this process. Based on the data from the present and from previous studies, we propose that M2 endocytosis takes place by means of an atypical clathrin-mediated pathway that may involve a specific subset of clathrin-coated pits/vesicles.

Modified expression of peripheral blood lymphocyte muscarinic cholinergic receptors in asthmatic children

Lymphocytes possess an independent cholinergic system. We assessed the expression of muscarinic cholinergic receptors in lymphocytes from 49 asthmatic children and 10 age matched controls using Western blot. We demonstrated that CD4+ and CD8+ T cells expressed M2 and M4 muscarinic receptors which density were significantly increased in asthmatic children in comparison with controls. M2 and M4 receptor increase was strictly related with IgE and fraction of exhaled nitric oxide (FeNO) measurements and with impairment in objective measurements of airway obstruction. Increased lymphocyte muscarinic cholinergic receptor expression may concur with lung cholinergic dysfunction and with inflammatory molecular framework in asthma.

Cholinergic transactivation of the EGFR in HaCaT keratinocytes stimulates a flotillin-1 dependent MAPK-mediated transcriptional response

Acetylcholine and its receptors regulate numerous cellular processes in keratinocytes and other non-neuronal cells. Muscarinic acetylcholine receptors are capable of transactivating the epidermal growth factor receptor (EGFR) and, downstream thereof, the mitogen-activated protein kinase (MAPK) cascade, which in turn regulates transcription of genes involved in cell proliferation and migration. We here show that cholinergic stimulation of human HaCaT keratinocytes results in increased transcription of matrix metalloproteinase MMP-3 as well as several ligands of the epidermal growth factor family. Since both metalloproteinases and the said ligands are involved in the transactivation of the EGFR, this transcriptional upregulation may provide a positive feed-forward loop for EGFR/MAPK activation. We here also show that the cholinergic EGFR and MAPK activation and the upregulation of MMP-3 and EGF-like ligands are dependent on the expression of flotillin-1 which we have previously shown to be a regulator of MAPK signaling.

Muscarine-like compounds derived from a pyrolysis product of cellulose

Starting from a hydroxylactone anhydrosugar available from catalytic cellulose pyrolysis, five new muscarine-like compounds have been synthesized and studied for their binding affinity to human subtype muscarine receptors, obtaining results supported by docking calculation.

A spatial simulation approach to account for protein structure when identifying non-random somatic mutations

Background

Current research suggests that a small set of “driver” mutations are responsible for tumorigenesis while a larger body of “passenger” mutations occur in the tumor but do not progress the disease. Due to recent pharmacological successes in treating cancers caused by driver mutations, a variety of methodologies that attempt to identify such mutations have been developed. Based on the hypothesis that driver mutations tend to cluster in key regions of the protein, the development of cluster identification algorithms has become critical.

Results

We have developed a novel methodology, SpacePAC (Spatial Protein Amino acid Clustering), that identifies mutational clustering by considering the protein tertiary structure directly in 3D space. By combining the mutational data in the Catalogue of Somatic Mutations in Cancer (COSMIC) and the spatial information in the Protein Data Bank (PDB), SpacePAC is able to identify novel mutation clusters in many proteins such as FGFR3 and CHRM2. In addition, SpacePAC is better able to localize the most significant mutational hotspots as demonstrated in the cases of BRAF and ALK. The R package is available on Bioconductor at: http://www.bioconductor.org/packages/release/bioc/html/SpacePAC.html.

Conclusion

SpacePAC adds a valuable tool to the identification of mutational clusters while considering protein tertiary structure.