Molecular function of α7 nicotinic receptors as drug targets

Novel interplay between agonist and calcium binding sites modulates drug potentiation of α7 acetylcholine receptor

Drug modulation of the α7 acetylcholine receptor has emerged as a therapeutic strategy for neurological, neurodegenerative, and inflammatory disorders. α7 is a homo-pentamer containing topographically distinct sites for agonists, calcium, and drug modulators with each type of site present in five copies. However, functional relationships between agonist, calcium, and drug modulator sites remain poorly understood. To investigate these relationships, we manipulated the number of agonist binding sites, and monitored potentiation of ACh-elicited single-channel currents through α7 receptors by PNU-120596 (PNU) both in the presence and absence of calcium. When ACh is present alone, it elicits brief, sub-millisecond channel openings, however when ACh is present with PNU it elicits long clusters of potentiated openings. In receptors harboring five agonist binding sites, PNU potentiates regardless of the presence or absence of calcium, whereas in receptors harboring one agonist binding site, PNU potentiates in the presence but not the absence of calcium. By varying the numbers of agonist and calcium binding sites we show that PNU potentiation of α7 depends on a balance between agonist occupancy of the orthosteric sites and calcium occupancy of the allosteric sites. The findings suggest that in the local cellular environment, fluctuations in the concentrations of neurotransmitter and calcium may alter this balance and modulate the ability of PNU to potentiate α7.

The role of nicotinic acetylcholine receptors in the pathophysiology and pharmacotherapy of autism spectrum disorder: Focus on α7 nicotinic receptors

Postmortem studies have revealed that brains of individuals with autism spectrum disorder (ASD) exhibit abnormalities in various components of the cholinergic system including cholinergic receptors, projections, and nuclei. Deletions in the 15q13.3 region which encompasses CHRNA7, the gene that encodes the α7-nACh receptor, have been linked to various neurodevelopmental disorders, including ASD. In addition, the involvement of α7-nACh receptors in biological phenomena known to play a role in the pathophysiology of ASD such as cognitive functions, learning, memory, neuroinflammation, and oxidative stress, as well as the excitation-inhibition balance in neuronal circuits and maternal immune activation have been reported in previous studies. Furthermore, evolving preclinical and clinical literature supports the potential therapeutic benefits of using selectively acting cholinergic compounds, particularly those targeting the α7-nACh receptor subtype, in the treatment of ASD. This study reviews the previous literature on the involvement of nACh receptors in the pathophysiology of ASD and focuses on the α7-nACh receptor as a potential therapeutic target.

The human-specific nicotinic receptor subunit CHRFAM7A reduces α7 receptor function in human induced pluripotent stem cells-derived and transgenic mouse neurons

We investigated the impact of the human-specific gene CHRFAM7A on the function of α7 nicotinic acetylcholine receptors (α7 nAChRs) in two different types of neurons: human-induced pluripotent stem cell (hiPSC)-derived cortical neurons, and superior cervical ganglion (SCG) neurons, taken from transgenic mice expressing CHRFAM7A. dupα7, the gene product of CHRFAM7A, which lacks a major part of the extracellular N-terminal ligand-binding domain, co-assembles with α7, the gene product of CHRNA7. We assessed the receptor function in hiPSC-derived cortical and SCG neurons with Fura-2 calcium imaging and three different α7-specific ligands: PNU282987, choline, and 4BP-TQS. Given the short-lived open state of α7 receptors, we combined the two orthosteric agonists PNU282987 and choline with the type-2 positive allosteric modulator (PAM II) PNU120596. In line with different cellular models used previously, we demonstrate that CHRFAM7A has a major impact on nicotinic α7 nAChRs by reducing calcium transients in response to all three agonists.

The complexities of ligand/receptor interactions: Exploring the role of molecular vibrations and quantum tunnelling

Molecular vibrations and quantum tunneling may link ligand binding to the function of pharmacological receptors. The well-established lock-and-key model explains a ligand's binding and recognition by a receptor; however, a general mechanism by which receptors translate binding into activation, inactivation, or modulation remains elusive. The Vibration Theory of Olfaction was proposed in the 1930s to explain this subset of receptor-mediated phenomena by correlating odorant molecular vibrations to smell, but a mechanism was lacking. In the 1990s, inelastic electron tunneling was proposed as a plausible mechanism for translating molecular vibration to odorant physiology. More recently, studies of ligands' vibrational spectra and the use of deuterated ligand analogs have provided helpful information to study this admittedly controversial hypothesis in metabotropic receptors other than olfactory receptors. In the present work, based in part on published experiments from our laboratory using planarians as an experimental organism, I will present a rationale and possible experimental approach for extending this idea to ligand-gated ion channels.

Apigenin Alleviates Autistic-like Stereotyped Repetitive Behaviors and Mitigates Brain Oxidative Stress in Mice

Studying the involvement of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in neuropsychiatric brain disorders such as autism spectrum disorder (ASD) has gained a growing interest. The flavonoid apigenin (APG) has been confirmed in its pharmacological action as a positive allosteric modulator of α7-nAChRs. However, there is no research describing the pharmacological potential of APG in ASD. The aim of this study was to evaluate the effects of the subchronic systemic treatment of APG (10-30 mg/kg) on ASD-like repetitive and compulsive-like behaviors and oxidative stress status in the hippocampus and cerebellum in BTBR mice, utilizing the reference drug aripiprazole (ARP, 1 mg/kg, i.p.). BTBR mice pretreated with APG (20 mg/kg) or ARP (1 mg/g, i.p.) displayed significant improvements in the marble-burying test (MBT), cotton-shredding test (CST), and self-grooming test (SGT) (all p < 0.05). However, a lower dose of APG (10 mg/kg, i.p.) failed to modulate behaviors in the MBT or SGT, but significantly attenuated the increased shredding behaviors in the CST of tested mice. Moreover, APG (10-30 mg/kg, i.p.) and ARP (1 mg/kg) moderated the disturbed levels of oxidative stress by mitigating the levels of catalase (CAT) and superoxide dismutase (SOD) in the hippocampus and cerebellum of treated BTBR mice. In patch clamp studies in hippocampal slices, the potency of choline (a selective agonist of α7-nAChRs) in activating fast inward currents was significantly potentiated following incubation with APG. Moreover, APG markedly potentiated the choline-induced enhancement of spontaneous inhibitory postsynaptic currents. The observed results propose the potential therapeutic use of APG in the management of ASD. However, further preclinical investigations in additional models and different rodent species are still needed to confirm the potential relevance of the therapeutic use of APG in ASD.

Structural mechanisms of α7 nicotinic receptor allosteric modulation and activation

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that plays an important role in cholinergic signaling throughout the nervous system. Its unique physiological characteristics and implications in neurological disorders and inflammation make it a promising but challenging therapeutic target. Positive allosteric modulators overcome limitations of traditional α7 agonists, but their potentiation mechanisms remain unclear. Here, we present high-resolution structures of α7-modulator complexes, revealing partially overlapping binding sites but varying conformational states. Structure-guided functional and computational tests suggest that differences in modulator activity arise from the stable rotation of a channel gating residue out of the pore. We extend the study using a time-resolved cryoelectron microscopy (cryo-EM) approach to reveal asymmetric state transitions for this homomeric channel and also find that a modulator with allosteric agonist activity exploits a distinct channel-gating mechanism. These results define mechanisms of α7 allosteric modulation and activation with implications across the pentameric receptor superfamily.

New Alpha9 nAChR Ligands Based on a 5-(Quinuclidin-3-ylmethyl)-1,2,4-oxadiazole Scaffold

Several lines of evidence have indicated that nicotinic acetylcholine receptors (nAChR) that contain α9 subunits, probably in combination with α10 subunits, may be valuable targets for the management of pain associated with inflammatory diseases through a cholinergic anti-inflammatory system (CAS), which has also been associated with α7 nAChR. Both α7- and α9-containing neuronal nAChR can be pharmacologically distinguished from the high-affinity nicotinic receptors of the brain by their sensitivity to α-bungarotoxin, but in other ways, they have quite distinct pharmacological profiles. The early association of α7 with CAS led to the development of numerous new ligands, variously characterized as α7 agonists, partial agonists, or silent agonists that desensitized α7 receptors without activation. Subsequent reinvestigation of one such family of α7 ligands based on an N,N-diethyl-N'-phenylpiperazine scaffold led to the identification of potent agonists and antagonists for α9. In this paper, we characterize the α9/α10 activity of a series of compounds based on a 5-(quinuclidin-3-ylmethyl)-1,2,4-oxadiazole (QMO) scaffold and identify two new potent ligands of α9, QMO-28, an agonist, and QMO-17, an antagonist. We separated the stereoisomers of these compounds to identify the most potent agonist and discovered that only the 3R isomer of QMO-17 was an α9 antagonist, permitting an in silico model of α9 antagonism to be developed. The α9 activity of these compounds was confirmed to be potentially useful for CAS management of inflammatory pain in cell-based assays of cytokine release.

Molecular Docking Analysis at the Human α7-nAChR and Proliferative and Evoked-Calcium Changes in SH-SY5Y Cells by Imidacloprid and Acetamiprid Insecticides

Acetamiprid (ACE) and Imidacloprid (IMI) are widely-used neonicotinoid insecticides (NNIs) with functional activity at human acetylcholine nicotinic receptors and, therefore, with putative toxic effects. The objective of this study was the evaluation of the interactions between NNIs and α7-nAChR, as this receptor keeps intracellular Ca2+ ([Ca2+]i) to an optimum for an adequate neuronal functioning. Possible interactions between NNIs and the cryo-EM structure of the human α-7 nAChR were identified by molecular docking. Additionally, NNI effects were analyzed in neuroblastoma SH-SY5Y cells, as they naturally express α-7 nAChRs. Functional studies included proliferative/cytotoxic effects (MTT test) in undifferentiated SH-SY-5Y cells and indirect measurements of [Ca2+]i transients in retinoic acid-differentiated SH-SY-5Y cells loaded with Fluo-4 AM. Docking analysis showed that the binding of IMI and ACE occurred at the same aromatic cage that the specific α-7 nAChR agonist EVP-6124. IMI showed a better docking strength than ACE. According to the MTT assays, low doses (10-50 µM) of IMI better than ACE stimulated neuroblastoma cell proliferation. At higher doses (250-500 µM), IMI also prevailed over ACE and dose-dependently triggered more abrupt fluorescence changes due to [Ca2+]i mobilization in differentiated SH-SY5Y neurons. Indeed, only IMI blunted nicotine-evoked intracellular fluorescence stimulation (i.e., nicotine cross-desensitization). Summarizing, IMI demonstrated a superior docking strength and more robust cellular responses compared to ACE, which were likely associated with a stronger activity at α-7nAChRs. Through the interaction with α-7nAChRs, IMI would demonstrate its high neurotoxic potential for humans. More research is needed for investigating the proliferative effects of IMI in neuroblastoma cells.

α7nAChR Activation Combined with Endothelial Progenitor Cell Transplantation Attenuates Lung Injury in Diabetic Rats with Sepsis through the NF-κB Pathway

Chronic diabetes mellitus compromises the vascular system, which causes organ injury, including in the lung. Due to the strong compensatory ability of the lung, patients always exhibit subclinical symptoms. Once sepsis occurs, the degree of lung injury is more severe under hyperglycemic conditions. The α7 nicotinic acetylcholine receptor (α7nAChR) plays an important role in regulating inflammation and metabolism and can improve endothelial progenitor cell (EPC) functions. In the present study, lung injury caused by sepsis was compared between diabetic rats and normal rats. We also examined whether α7nAChR activation combined with EPC transplantation could ameliorate lung injury in diabetic sepsis rats. A type 2 diabetic model was induced in rats via a high-fat diet and streptozotocin. Then, a rat model of septic lung injury was established by intraperitoneal injection combined with endotracheal instillation of LPS. The oxygenation indices, wet-to-dry ratios, and histopathological scores of the lungs were tested after PNU282987 treatment and EPC transplantation. IL-6, IL-8, TNF-α, and IL-10 levels were measured. Caspase-3, Bax, Bcl-2, and phosphorylated NF-κB (p-NF-κB) levels were determined by blotting. Sepsis causes obvious lung injury, which is exacerbated by diabetic conditions. α7nAChR activation and endothelial progenitor cell transplantation reduced lung injury in diabetic sepsis rats, alleviating inflammation and decreasing apoptosis. This treatment was more effective when PNU282987 and endothelial progenitor cells were administered together. p-NF-κB levels decreased following treatment with PNU282987 and EPCs. In conclusion, α7nAChR activation combined with EPC transplantation can alleviate lung injury in diabetic sepsis rats through the NF-κB signaling pathway.

Pharmacological profiles and anti-inflammatory activity of pCN-diEPP and mCN-diEPP, new alpha9alpha10 nicotinic receptor ligands

Pain due to inflammation can be reduced by targeting the noncanonical nicotinic receptors (NCNR) in cells of the immune system that regulate the synthesis and release of pro- and anti-inflammatory cytokines. Although NCNR do not generate ion channel currents, the pharmacology of ion-channel forms of the receptors can predict drugs which may be effective regulators of the cholinergic anti-inflammatory system (CAS). Agonists of α7 type receptors have been definitively associated with CAS. Receptors containing α9 and α10 subunits have also been implicated. We have recently characterized two small molecules, pCN-diEPP and mCN-diEPP, as selective α9α10 agonists and antagonists, respectively. We used these drugs, along with nicotine, an α7 agonist and α9α10 antagonist, to probe the mixed populations of receptors that are formed when α7, α9, and α10 are all expressed together in Xenopus oocytes. We also evaluated the effects of the CN-diEPP compounds on regulating the ATP-induced release of interleukin-1β from monocytic THP-1 cells, which express NCNR. The compounds successfully identified separate populations of receptors when all three subunits were co-expressed, including a potential population of homomeric α10 receptors. The α9α10 agonist pCN-diEPP was the more effective regulator of interleukin-1β release in THP-1 cells. pCN-diEPP was also fully effective in a mouse model of inflammatory pain, while mCN-diEPP had only partial effects, requiring a higher dosage. The analgetic effects of pCN-diEPP and mCN-diEPP were retained in α7 knockout mice. Taken together, our results suggest that drugs that selectively activate α9α10 receptors may useful to reduce inflammatory pain through the CAS.

Ionotropic and metabotropic responses by alpha 7 nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) belong to a superfamily of cys-loop receptors characterized by the assembly of five subunits into a multi-protein channel complex. Ligand binding to nAChRs activates rapid allosteric transitions of the receptor leading to channel opening and ion flux in neuronal and non-neuronal cell. Thus, while ionotropic properties of nAChRs are well recognized, less is known about ligand-mediated intracellular metabotropic signaling responses. Studies in neural and non-neural cells confirm ionotropic and metabotropic channel responses following ligand binding. In this review we summarize evidence on the existence of ionotropic and metabotropic signaling responses by homopentameric α7 nAChRs in various cell types. We explore how coordinated calcium entry through the ion channel and calcium release from nearby stores gives rise to signaling important for the modulation of cytoskeletal motility and cell growth. Amino acid residues for intracellular protein binding within the α7 nAChR support engagement in metabotropic responses including signaling through heterotrimeric G proteins in neural and immune cells. Understanding the dual properties of ionotropic and metabotropic nAChR responses is essential in advancing drug development for the treatment of various human disease.

Positive allosteric modulators of the α7 nicotinic acetylcholine receptor: SAR investigation around PNU-120596

The α7 nicotinic acetylcholine receptor is a calcium permeable, ligand-gated ion channel that modulates synaptic transmission in the hippocampus, thalamus, and cerebral cortex. Previously disclosed work described PNU-120596 that acts as a powerful positive allosteric modulator of the α7 nicotinic acetylcholine receptor. The initial structure-activity relationships around PNU-120596 were gleaned from screening a large thiazole library. Independent systematic examination of the aryl and heteroaryl groups resulted in compounds with enhanced potency and improved physico-chemical properties culminating in the identification of 16 (PHA-758454). In the presence of acetylcholine, 16 enhanced evoked currents in rat hippocampal neurons. In a rat model of impaired sensory gating, treatment with 16 led to a reversal of the gating deficit in a dose-dependent manner. These results demonstrate that aryl heteroaryl ureas, like compound 16, may be useful tools for continued exploration of the unique biology of the α7 nicotinic acetylcholine receptor.

Review of triazole scaffolds for treatment and diagnosis of Alzheimer's disease

Triazole scaffolds, a series of 5-membered heterocycles, are well known for their high efficacy, low toxicity, and superior pharmacokinetics. Alzheimer's disease (AD) is the first neurodegenerative disorder with complex pathological mechanisms. Triazole, as an aromatic group with three nitrogen atoms, forms polar and non-polar interactions with diverse key residues in the receptor-ligand binding procedure, and has been widely used in the molecular design in the development of anti-AD agents. Moreover, considering the simple synthesis approaches, triazole scaffolds are commonly used to link two pharmacodynamic groups in one chemical molecule, forming multi-target directed ligands (MTDLs). Furthermore, the click reaction between azide- and cyano-modified enzyme and ligand provides feasibility for the new modulator discovery, compound tissue distribution evaluation, enzyme localization, and pharmacological mechanism study, promoting the diagnosis of AD course.

Side Groups Convert the α7 Nicotinic Receptor Agonist Ether Quinuclidine into a Type I Positive Allosteric Modulator

The quinuclidine scaffold has been extensively used for the development of nicotinic acetylcholine receptor (nAChR) agonists, with hydrophobic substituents at position 3 of the quinuclidine framework providing selectivity for α7 nAChRs. In this study, six new ligands (4-9) containing a 3-(pyridin-3-yloxy)quinuclidine moiety (ether quinuclidine) were synthesized to gain a better understanding of the structural-functional properties of ether quinuclidines. To evaluate the pharmacological activity of these ligands, two-electrode voltage-clamp and single-channel recordings were performed. Only ligand 4 activated α7 nAChR. Ligands 5 and 7 had no effects on α7 nAChR, but ligands 6, 8, and 9 potentiated the currents evoked by ACh. Ligand 6 was the most potent and efficacious of the potentiating ligands, with an estimated EC50 for potentiation of 12.6 ± 3.32 μM and a maximal potentiation of EC20 ACh responses of 850 ± 120%. Ligand 6 increased the maximal ACh responses without changing the kinetics of the current responses. At the single-channel level, the potentiation exerted by ligand 6 was evidenced in the low micromolar concentration range by the appearance of prolonged bursts of channel openings. Furthermore, computational studies revealed the preference of ligand 6 for an intersubunit site in the transmembrane domain and highlighted some putative key interactions that explain the different profiles of the synthesized ligands. Notably, Met276 in the 15' position of the transmembrane domain 2 almost abolished the effects of ligand 6 when mutated to Leu. We conclude that ligand 6 is a novel type I positive allosteric modulator (PAM-I) of α7 nAChR.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy. Cholinergic dysfunction is associated with inflammatory processes mainly through the involvement of α7 nAChRs expressed in brain and in peripheral immune cells. Evidence suggests that these neuroinflammatory processes trigger and aggravate pathological states. We discuss the preclinical evidence demonstrating the therapeutic potential of nAChR ligands in Alzheimer disease, Parkinson disease, schizophrenia spectrum disorders, and in autosomal dominant sleep-related hypermotor epilepsy. PubMed and Google Scholar bibliographic databases were searched with the keywords indicated below.

Noradrenergic and cholinergic systems take centre stage in neuropsychiatric diseases of ageing

Noradrenergic and cholinergic systems are among the most vulnerable brain systems in neuropsychiatric diseases of ageing, including Alzheimer's disease, Parkinson's disease, Lewy body dementia, and progressive supranuclear palsy. As these systems fail, they contribute directly to many of the characteristic cognitive and psychiatric symptoms. However, their contribution to symptoms is not sufficiently understood, and pharmacological interventions targeting noradrenergic and cholinergic systems have met with mixed success. Part of the challenge is the complex neurobiology of these systems, operating across multiple timescales, and with non-linear changes across the adult lifespan and disease course. We address these challenges in a detailed review of the noradrenergic and cholinergic systems, outlining their roles in cognition and behaviour, and how they influence neuropsychiatric symptoms in disease. By bridging across levels of analysis, we highlight opportunities for improving drug therapies and for pursuing personalised medicine strategies.

Generation of nanobodies acting as silent and positive allosteric modulators of the α7 nicotinic acetylcholine receptor

The α7 nicotinic acetylcholine receptor (nAChR), a potential drug target for treating cognitive disorders, mediates communication between neuronal and non-neuronal cells. Although many competitive antagonists, agonists, and partial-agonists have been found and synthesized, they have not led to effective therapeutic treatments. In this context, small molecules acting as positive allosteric modulators binding outside the orthosteric, acetylcholine, site have attracted considerable interest. Two single-domain antibody fragments, C4 and E3, against the extracellular domain of the human α7-nAChR were generated through alpaca immunization with cells expressing a human α7-nAChR/mouse 5-HT₃A chimera, and are herein described. They bind to the α7-nAChR but not to the other major nAChR subtypes, α4β2 and α3β4. E3 acts as a slowly associating positive allosteric modulator, strongly potentiating the acetylcholine-elicited currents, while not precluding the desensitization of the receptor. An E3-E3 bivalent construct shows similar potentiating properties but displays very slow dissociation kinetics conferring quasi-irreversible properties. Whereas, C4 does not alter the receptor function, but fully inhibits the E3-evoked potentiation, showing it is a silent allosteric modulator competing with E3 binding. Both nanobodies do not compete with α-bungarotoxin, localizing at an allosteric extracellular binding site away from the orthosteric site. The functional differences of each nanobody, as well as the alteration of functional properties through nanobody modifications indicate the importance of this extracellular site. The nanobodies will be useful for pharmacological and structural investigations; moreover, they, along with the extracellular site, have a direct potential for clinical applications.

Small molecule ligands for α9* and α7 nicotinic receptors: a survey and an update, respectively

The α9- and α7-containing nicotinic acetylcholine receptors (nAChRs) mediate numerous physiological and pathological processes by complex mechanisms that are currently the subject of intensive study and debate. In this regard, selective ligands serve as invaluable investigative tools and, in many cases, potential therapeutics for the treatment of various CNS disfunctions and diseases, neuropathic pain, inflammation, and cancer. However, the present scenario differs significantly between the two aforementioned nicotinic subtypes. Over the past few decades, a large number of selective α7-nAChR ligands, including full, partial and silent agonists, antagonists, and allosteric modulators, have been described and reviewed. Conversely, reports on selective α9-containing nAChR ligands are relatively scarce, also due to a more recent characterization of this receptor subtype, and hardly any focusing on small molecules. In this review, we focus on the latter, providing a comprehensive overview, while providing only an update over the last five years for α7-nAChR ligands.

Nicotinic acetylcholine receptors in neurological and psychiatric diseases

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are widely distributed both pre- and post-synaptically in the mammalian brain. By modulating cation flux across cell membranes, neuronal nAChRs regulate neuronal excitability and the release of a variety of neurotransmitters to influence multiple physiologic and behavioral processes including synaptic plasticity, motor function, attention, learning and memory. Abnormalities of neuronal nAChRs have been implicated in the pathophysiology of neurologic disorders including Alzheimer's disease, Parkinson's disease, epilepsy, and Tourette´s syndrome, as well as psychiatric disorders including schizophrenia, depression, and anxiety. The potential role of nAChRs in a particular illness may be indicated by alterations in the expression of nAChRs in relevant brain regions, genetic variability in the genes encoding for nAChR subunit proteins, and/or clinical or preclinical observations where specific ligands showed a therapeutic effect. Over the past 25 years, extensive preclinical and some early clinical evidence suggested that ligands at nAChRs might have therapeutic potential for neurologic and psychiatric disorders. However, to date the only approved indications for nAChR ligands are smoking cessation and the treatment of dry eye disease. It has been argued that progress in nAChR drug discovery has been limited by translational gaps between the preclinical models and the human disease as well as unresolved questions regarding the pharmacological goal (i.e., agonism, antagonism or receptor desensitization) depending on the disease.

Maternal Inflammation with Elevated Kynurenine Metabolites Is Related to the Risk of Abnormal Brain Development and Behavioral Changes in Autism Spectrum Disorder

Several studies show that genetic and environmental factors contribute to the onset and progression of neurodevelopmental disorders. Maternal immune activation (MIA) during gestation is considered one of the major environmental factors driving this process. The kynurenine pathway (KP) is a major route of the essential amino acid L-tryptophan (Trp) catabolism in mammalian cells. Activation of the KP following neuro-inflammation can generate various endogenous neuroactive metabolites that may impact brain functions and behaviors. Additionally, neurotoxic metabolites and excitotoxicity cause long-term changes in the trophic support, glutamatergic system, and synaptic function following KP activation. Therefore, investigating the role of KP metabolites during neurodevelopment will likely promote further understanding of additional pathophysiology of neurodevelopmental disorders, including autism spectrum disorder (ASD). In this review, we describe the changes in KP metabolism in the brain during pregnancy and represent how maternal inflammation and genetic factors influence the KP during development. We overview the patients with ASD clinical data and animal models designed to verify the role of perinatal KP elevation in long-lasting biochemical, neuropathological, and behavioral deficits later in life. Our review will help shed light on new therapeutic strategies and interventions targeting the KP for neurodevelopmental disorders.

Nicotinic acetylcholine receptors: Therapeutic targets for novel ligands to treat pain and inflammation

Nicotinic acetylcholine receptors (nAChRs) have been historically defined as ligand-gated ion channels and function as such in the central and peripheral nervous systems. Recently, however, non-ionic signaling mechanisms via nAChRs have been demonstrated in immune cells. Furthermore, the signaling pathways where nAChRs are expressed can be activated by endogenous ligands other than the canonical agonists acetylcholine and choline. In this review, we discuss the involvement of a subset of nAChRs containing α7, α9, and/or α10 subunits in the modulation of pain and inflammation via the cholinergic anti-inflammatory pathway. Additionally, we review the most recent advances in the development of novel ligands and their potential as therapeutics.

Regulation of nicotinic acetylcholine receptors by post-translational modifications

Nicotinic acetylcholine receptors (nAChRs) comprise a family of pentameric ligand-gated ion channels widely distributed in the central and peripheric nervous system and in non-neuronal cells. nAChRs are involved in chemical synapses and are key actors in vital physiological processes throughout the animal kingdom. They mediate skeletal muscle contraction, autonomic responses, contribute to cognitive processes, and regulate behaviors. Dysregulation of nAChRs is associated with neurological, neurodegenerative, inflammatory and motor disorders. In spite of the great advances in the elucidation of nAChR structure and function, our knowledge about the impact of post-translational modifications (PTMs) on nAChR functional activity and cholinergic signaling has lagged behind. PTMs occur at different steps of protein life cycle, modulating in time and space protein folding, localization, function, and protein-protein interactions, and allow fine-tuned responses to changes in the environment. A large body of evidence demonstrates that PTMs regulate all levels of nAChR life cycle, with key roles in receptor expression, membrane stability and function. However, our knowledge is still limited, restricted to a few PTMs, and many important aspects remain largely unknown. There is thus a long way to go to decipher the association of aberrant PTMs with disorders of cholinergic signaling and to target PTM regulation for novel therapeutic interventions. In this review we provide a comprehensive overview of what is known about how different PTMs regulate nAChR.

Action of the Purinergic and Cholinergic Anti-inflammatory Pathways on Oxidative Stress in Patients with Alzheimer's Disease in the Context of the COVID-19 Pandemic

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of the 2019 coronavirus disease (COVID-19), has affected more than 20 million people in Brazil and caused a global health emergency. This virus has the potential to affect various parts of the body and compromise metabolic functions. The virus-mediated neural inflammation of the nervous system is due to a storm of cytokines and oxidative stress, which are the clinical features of Alzheimer's disease (AD). This neurodegenerative disease is aggravated in cases involving SARS-CoV-2 and its inflammatory biomarkers, accelerating accumulation of β-amyloid peptide, hyperphosphorylation of tau protein, and production of reactive oxygen species, which lead to homeostasis imbalance. The cholinergic system, through neurons and the neurotransmitter acetylcholine (ACh), modulates various physiological pathways, such as the response to stress, sleep and wakefulness, sensory information, and the cognitive system. Patients with AD have low concentrations of ACh; hence, therapeutic methods are aimed at adjusting the ACh titers available to the body for maintaining functionality. Herein, we focused on acetylcholinesterase inhibitors, responsible for the degradation of ACh in the synaptic cleft, and muscarinic and nicotinic receptor agonists of the cholinergic system owing to the therapeutic potential of the cholinergic anti-inflammatory pathway in AD associated with SARS-CoV-2 infection.

Differential Activation and Desensitization States Promoted by Noncanonical α7 Nicotinic Acetylcholine Receptor Agonists

A series of dipicolyl amine pyrimidines (DPPs) were previously identified as potential α7 agonists by means of a calcium influx assay in the presence of the positive allosteric modulator (PAM) 1-(5-chloro-2,4-dimethoxy-phenyl)-3-(5-methyl-isoxazol-3-yl)-urea (PNU-120596). The compounds lack the quaternary or strongly basic nitrogens of typical nicotinic agonists. Although differing in structure from typical nicotinic agonists, based on crystallographic data with the acetylcholine binding protein, they appeared to engage the site shared by such typical orthosteric agonists. Using oocytes expressing human α7 receptors, we found that the DPPs were efficacious activators of the receptor, with currents showing rapid desensitization characteristic of α7 receptors. However, we note that the rate of recovery from this desensitization depends strongly on structural features within the DPP family. Although the activation of receptors by DPP was blocked by the competitive antagonist methyllycaconitine (MLA), MLA had no effect on the DPP-induced desensitization, suggesting multiple modes of DPP binding. As expected, the desensitized conformational states could be reactivated by PAMs. Mutants made insensitive to acetylcholine by the C190A mutation in the agonist binding site were weakly activated by DPPs. The observation that activation of C190A mutants by the DPP compounds was resistant to the allosteric antagonist (-)cis-trans-4-(2,3,5,6-tetramethylphenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide supports the hypothesis that the activity of these noncanonical agonists in the orthosteric binding sites was not entirely dependent on the classic epitopes controlling activation by typical agonists and that perhaps they may access alternative modes for promoting the conformational changes associated with activation and desensitization. SIGNIFICANCE STATEMENT: This study reports a family of nicotinic acetylcholine receptor agonists that break the rules about what the structure of a nicotinic acetylcholine receptor agonist should be. It shows that the activity of these noncanonical agonists in the orthosteric binding sites is not dependent on the classical epitopes controlling activation by typical agonists and that through different binding poses, they promote unique conformational changes associated with receptor activation and desensitization.

Differential interactions of resting, activated, and desensitized states of the α7 nicotinic acetylcholine receptor with lipidic modulators

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that modulates neuronal excitability, largely by allowing Ca2+ permeation. Agonist binding promotes transition from a resting state to an activated state, and then rapidly to a desensitized state. Recently, cryogenic electron microscopy (cryo-EM) structures of the human α7 receptor in nanodiscs were reported in multiple conformations. These were selectively stabilized by inhibitory, activating, or potentiating compounds. However, the functional annotation of these structures and their differential interactions with unresolved lipids and ligands remain incomplete. Here, we characterized their ion permeation, membrane interactions, and ligand binding using computational electrophysiology, free-energy calculations, and coarse-grained molecular dynamics. In contrast to nonconductive structures in apparent resting and desensitized states, the structure determined in the presence of the potentiator PNU-120596 was consistent with an activated state permeable to Ca2+. Transition to this state was associated with compression and rearrangement of the membrane, particularly in the vicinity of the peripheral MX helix. An intersubunit transmembrane site was implicated in selective binding of either PNU-120596 in the activated state or cholesterol in the desensitized state. This substantiates functional assignment of all three lipid-embedded α7-receptor structures with ion-permeation simulations. It also proposes testable models of their state-dependent interactions with lipophilic ligands, including a mechanism for allosteric modulation at the transmembrane subunit interface.

A Functional Interaction Between Y674-R685 Region of the SARS-CoV-2 Spike Protein and the Human α7 Nicotinic Receptor

The α7 nicotinic acetylcholine receptor (nAChR) is present in neuronal and non-neuronal cells and has anti-inflammatory actions. Molecular dynamics simulations suggested that α7 nAChR interacts with a region of the SARS-CoV-2 spike protein (S), and a potential contribution of nAChRs to COVID-19 pathophysiology has been proposed. We applied whole-cell and single-channel recordings to determine whether a peptide corresponding to the Y674-R685 region of the S protein can directly affect α7 nAChR function. The S fragment exerts a dual effect on α7. It activates α7 nAChRs in the presence of positive allosteric modulators, in line with our previous molecular dynamics simulations showing favourable binding of this accessible region of the S protein to the nAChR agonist binding site. The S fragment also exerts a negative modulation of α7, which is evidenced by a profound concentration-dependent decrease in the durations of openings and activation episodes of potentiated channels and in the amplitude of macroscopic responses elicited by ACh. Our study identifies a potential functional interaction between α7 nAChR and a region of the S protein, thus providing molecular foundations for further exploring the involvement of nAChRs in COVID-19 pathophysiology.

Recent advance on carbamate-based cholinesterase inhibitors as potential multifunctional agents against Alzheimer's disease

Alzheimer's disease (AD), as the fourth leading cause of death among the elderly worldwide, has brought enormous challenge to the society. Due to its extremely complex pathogeneses, the development of multi-target directed ligands (MTDLs) becomes the major strategy for combating AD. Carbamate moiety, as an essential building block in the development of MTDLs, exhibits structural similarity to neurotransmitter acetylcholine (ACh) and has piqued extensive attention in discovering multifunctional cholinesterase inhibitors. To date, numerous preclinical studies demonstrate that carbamate-based cholinesterase inhibitors can prominently increase the level of ACh and improve cognition impairments and behavioral deficits, providing a privileged strategy for the treatment of AD. Based on the recent research focus on the novel cholinesterase inhibitors with multiple biofunctions, this review aims at summarizing and discussing the most recent studies excavating the potential carbamate-based MTDLs with cholinesterase inhibition efficacy, to accelerate the pace of pleiotropic cholinesterase inhibitors for coping AD.

Ameliorating potential of curcumin and its analogue in central nervous system disorders and related conditions: A review of molecular pathways

Curcumin, isolated from turmeric (Curcuma longa L.) is one of the broadly studied phytomolecule owing to its strong antioxidant and anti-inflammatory potential and has been considered a promising therapeutic candidate in a wide range of disorders. Considering, its low bioavailability, different curcumin analogs have been developed to afford desired pharmacokinetic profile and therapeutic outcome in varied pathological states. Several preclinical and clinical studies have indicated that curcumin ameliorates mitochondrial dysfunction, inflammation, oxidative stress apoptosis-mediated neural cell degeneration and could effectively be utilized in the treatment of different neurodegenerative diseases. Hence, in this review, we have summarized key findings of experimental and clinical studies conducted on curcumin and its analogues with special emphasis on molecular pathways, viz. NF-kB, Nrf2-ARE, glial activation, apoptosis, angiogenesis, SOCS/JAK/STAT, PI3K/Akt, ERK1/2 /MyD88 /p38 MAPK, JNK, iNOS/NO, and MMP pathways involved in imparting ameliorative effects in the therapy of neurodegenerative disorders and associated conditions.

CCDC88A Post-Transcriptionally Regulates VEGF via miR-101 and Subsequently Regulates Hepatocellular Carcinoma

Background

miR-101 is one of the most abundantly expressed microRNA (miRNA) and exerst a critical role in hepatocellular carcinoma (HCC) by targeting to 3’ -untranslated region (UTR) of Girders of actin filaments (CCDC88A) and Vascular endothelial growth factor (VEGF) mRNA, but the underlying molecular mechanism remains to be elucidated. This study aimed to investigate the potential role of CCDC88A on malignancies and stemness by regulating VEGF via miR-101 in HCC.

Methods

Gene Expression Profiling Interactive Analysis (GEPIA) was employed to analyze the relevance of CCDC88A expression with prognosis in HCC. Tissue slides were performed to confirm the protein level of CCDC88A in HCC. Correlation between CCDC88A and VEGF was transcriptionally and post-transcriptionally detected, followed by evaluation of malignancies.

Results

By employing Immunohistochemistry, we found CCDC88A protein was upregulated in HCC tissues, which is closely correlated to poor prognosis and survival rate. Employment of GEPIA revealed the positive correlation between CCDC88A and VEGF in HCC, but not in liver tissue. Silencing of CCDC88A in Huh-7 and SK-HEP-1 cells significantly decreased proliferation, cell cycle phases, migration, invasion, colony formation, and tumor formation. Introduction of miR-101 mimics specifically targeting CCDC88A and VEGF decreased protein levels of both CCDC88A and VEGFA. Notably, inhibition of miR-101 reversed the correlation between CCDC88A and VEGFA protein levels, indicating that CCDC88A and VEGF may exert as a miR-101 sponge. The addition of SKLB1002, a VEGFR2 inhibitor inhibited malignant behaviors, which was further inhibited by the introduction of miR-101 mimics, indicating that CCDC88A regulates malignant behaviors partially via regulating VEGF. Moreover, CCDC88A also promotes the stemness of cancer stem-like cells derived from HCC cells depending on VEGF modification.

Conclusion

Taken together, our findings suggested that the miR-101/CCDC88A/VEGF axis could be a potential therapeutic target of HCC treatment.

CHRNA5 Contributes to Hepatocellular Carcinoma Progression by Regulating YAP Activity

Hepatocellular carcinoma (HCC) is a major health concern worldwide. A better understanding of the mechanisms underlying the malignant phenotype is necessary for developing novel therapeutic strategies for HCC. Signaling pathways initiated by neurotransmitter receptors, such as α5-nicotinic acetylcholine receptor (CHRNA5), have been reported to be implicated in tumor progression. However, the functional mechanism of CHRNA5 in HCC remains unclear. In this study, we explored the role of CHRNA5 in HCC and found that CHRNA5 expression was increased in human HCC tissues and positively correlated with the T stage (p < 0.05) and AJCC phase (p < 0.05). The KM plotter database showed that the high expression level of CHRNA5 was strongly associated with worse survival in HCC patients. Both in vitro and in vivo assays showed that CHRNA5 regulates the proliferation ability of HCC by regulating YAP activity. In addition, CHRNA5 promotes the stemness of HCC by regulating stemness-associated genes, such as Nanog, Sox2 and OCT4. Cell migration and invasion assays demonstrated that CHRNA5 significantly enhanced the metastasis of HCC by regulating epithelial–mesenchymal transition (EMT)-associated genes. Furthermore, we found that CHRNA5 regulates the sensitivity of sorafenib in HCC. Our findings suggest that CHRNA5 plays a key role in the progression and drug resistance of HCC, and targeting CHRNA5 may be a strategy for the treatment of HCC.

Computational methods and theory for ion channel research

Ion channels are fundamental biological devices that act as gates in order to ensure selective ion transport across cellular membranes; their operation constitutes the molecular mechanism through which basic biological functions, such as nerve signal transmission and muscle contraction, are carried out. Here, we review recent results in the field of computational research on ion channels, covering theoretical advances, state-of-the-art simulation approaches, and frontline modeling techniques. We also report on few selected applications of continuum and atomistic methods to characterize the mechanisms of permeation, selectivity, and gating in biological and model channels.

Potassium channels as molecular targets of endocannabinoids

Endocannabinoids are a group of endogenous mediators derived from membrane lipids, which are implicated in a wide variety of physiological functions such as blood pressure regulation, immunity, pain, memory, reward, perception, reproduction, and sleep. N-Arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG) represent two major endocannabinoids in the human body and they exert many of their cellular and organ system effects by activating the Gi/o protein-coupled, cannabinoid type 1 (CB1) and type 2 (CB2) receptors. However, not all effects of cannabinoids are ascribable to their interaction with CB1 and CB2 receptors; indeed, macromolecules like other types of receptors, ion channels, transcription factors, enzymes, transporters, and cellular structure have been suggested to mediate the functional effects of cannabinoids. Among the proposed molecular targets of endocannabinoids, potassium channels constitute an intriguing group, because these channels not only are crucial in shaping action potentials and controlling the membrane potential and cell excitability, thereby regulating a wide array of physiological processes, but also serve as potential therapeutic targets for the treatment of cancer and metabolic, neurological and cardiovascular disorders. This review sought to survey evidence pertaining to the CB1 and CB2 receptor-independent actions of endocannabinoids on ion channels, with an emphasis on AEA and potassium channels. To better understand the functional roles as well as potential medicinal uses of cannabinoids in human health and disease, further mechanistic studies to delineate interactions between various types of cannabinoids and ion channels, including members in the potassium channel superfamily, are warranted.

Discovery and functional characterization of N-(thiazol-2-yl)-benzamide analogs as the first class of selective antagonists of the Zinc-Activated Channel (ZAC)

The Zinc-Activated Channel (ZAC) is an atypical member of the Cys-loop receptor (CLR) superfamily of pentameric ligand-gated ion channels, with its very different endogenous agonists and signalling properties. In this study, a compound library screening at ZAC resulted in the identification of 2-(5-bromo-2-chlorobenzamido)-4-methylthiazole-5-methyl ester (1) as a novel ZAC antagonist. The structural determinants for ZAC activity in 1 were investigated by functional characterization of 61 analogs at ZAC expressed in Xenopus oocytes by two-electrode voltage clamp electrophysiology, and couple of analogs exerting more potent ZAC inhibition than 1 were identified (IC₅₀ values: 1-3 μM). 1 and N-(4-(tert-butyl)thiazol-2-yl)-3-fluorobenzamide (5a, TTFB) were next applied in studies of the functional properties and the mode of action of this novel class of ZAC antagonists. TTFB was a roughly equipotent antagonist of Zn⁺- and H⁺-evoked ZAC signaling and of spontaneous ZAC activity, and the slow on-set of its channel block suggested that its ZAC inhibition is state-dependent. TTFB was found to be a selective ZAC antagonist, exhibiting no significant agonist, antagonist or modulatory activity at 5-HT₃A, α₃β₄ nicotinic acetylcholine, α₁β₂γ_2S GABA_A or α₁ glycine receptors at 30 μM. 1 displayed largely non-competitive antagonism of Zn²⁺-induced ZAC signalling, and TTFB was demonstrated to target the transmembrane and/or intracellular domains of the receptor, which collectively suggests that the N-(thiazol-2-yl)-benzamide analog acts a negative allosteric modulator of ZAC. We propose that this first class of selective ZAC antagonists could constitute useful pharmacological tools in future explorations of the presently poorly elucidated physiological functions governed by this CLR.

Chromosomal Microarray Analysis as First-Tier Genetic Test for Schizophrenia

Schizophrenia is a chronic, devastating mental disorder with complex genetic components. Given the advancements in the molecular genetic research of schizophrenia in recent years, there is still a lack of genetic tests that can be used in clinical settings. Chromosomal microarray analysis (CMA) has been used as first-tier genetic testing for congenital abnormalities, developmental delay, and autism spectrum disorders. This study attempted to gain some experience in applying chromosomal microarray analysis as a first-tier genetic test for patients with schizophrenia. We consecutively enrolled patients with schizophrenia spectrum disorder from a clinical setting and conducted genome-wide copy number variation (CNV) analysis using a chromosomal microarray platform. We followed the 2020 “Technical Standards for the interpretation and reporting of constitutional copy-number variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics (ACMG) and the Clinical Genome Resource (ClinGen)” to interpret the clinical significance of CNVs detected from patients. We recruited a total of 60 patients (36 females and 24 males) into this study. We detected three pathogenic CNVs and one likely pathogenic CNV in four patients, respectively. The detection rate was 6.7% (4/60, 95% CI: 0.004–0.13), comparable with previous studies in the literature. Also, we detected thirteen CNVs classified as uncertain clinical significance in nine patients. Detecting these CNVs can help establish the molecular genetic diagnosis of schizophrenia patients and provide helpful information for genetic counseling and clinical management. Also, it can increase our understanding of the pathogenesis of schizophrenia. Hence, we suggest CMA is a valuable genetic tool and considered first-tier genetic testing for schizophrenia spectrum disorders in clinical settings.

Modulation of preeclampsia by the cholinergic anti-inflammatory pathway: Therapeutic perspectives

The cholinergic anti-inflammatory pathway (CAP) is vital for the orchestration of the immune and inflammatory responses under normal and challenged conditions. Over the past two decades, peripheral and central circuits of CAP have been shown to be critically involved in dampening the inflammatory reaction in a wide array of inflammatory disorders. Additionally, emerging evidence supports a key role for CAP in the regulation of the female reproductive system during gestation as well as in the advent of serious pregnancy-related inflammatory insults such as preeclampsia (PE). Within this framework, the modulatory action of CAP encompasses the perinatal maternal and fetal adverse consequences that surface due to antenatal PE programming. Albeit, a considerable gap still exists in our knowledge of the precise cellular and molecular underpinnings of PE/CAP interaction, which hampered global efforts in safeguarding effective preventive or therapeutic measures against PE complications. Here, we summarize reports in the literature regarding the roles of peripheral and reflex cholinergic neuroinflammatory pathways of nicotinic acetylcholine receptors (nAChRs) in reprogramming PE complications in mothers and their progenies. The possible contributions of α7-nAChRs, cholinesterases, immune cells, adhesion molecules, angiogenesis, and endothelial dysfunction to the interaction have also been reviewed.

Curcumin Potentiates α7 Nicotinic Acetylcholine Receptors and Alleviates Autistic-Like Social Deficits and Brain Oxidative Stress Status in Mice

Autistic spectrum disorder (ASD) refers to a group of neurodevelopmental disorders characterized by impaired social interaction and cognitive deficit, restricted repetitive behaviors, altered immune responses, and imbalanced oxidative stress status. In recent years, there has been a growing interest in studying the role of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in the CNS. Influence of agonists for α7-nAChRs on the cognitive behavior, learning, and memory formation has been demonstrated in neuro-pathological condition such as ASD and attention-deficit hyperactivity disorder (ADHD). Curcumin (CUR), the active compound of the spice turmeric, has been shown to act as a positive allosteric modulator of α7-nAChRs. Here we hypothesize that CUR, acting through α7-nAChRs, influences the neuropathology of ASD. In patch clamp studies, fast inward currents activated by choline, a selective agonist of α7-nAChRs, were significantly potentiated by CUR. Moreover, choline induced enhancement of spontaneous inhibitory postsynaptic currents was markedly increased in the presence of CUR. Furthermore, CUR (25, 50, and 100 mg/kg, i.p.) ameliorated dose-dependent social deficits without affecting locomotor activity or anxiety-like behaviors of tested male Black and Tan BRachyury (BTBR) mice. In addition, CUR (50 and 100 mg/kg, i.p.) mitigated oxidative stress status by restoring the decreased levels of superoxide dismutase (SOD) and catalase (CAT) in the hippocampus and the cerebellum of treated mice. Collectively, the observed results indicate that CUR potentiates α7-nAChRs in native central nervous system neurons, mitigates disturbed oxidative stress, and alleviates ASD-like features in BTBR mice used as an idiopathic rodent model of ASD, and may represent a promising novel pharmacological strategy for ASD treatment.

Activation of α7 nicotinic acetylcholine receptor ameliorates HIV-associated neurology and neuropathology

HIV-associated neurocognitive disorders (HAND) in the era of combination antiretroviral therapy are primarily manifested as impaired behaviours, glial activation/neuroinflammation and compromised neuronal integrity, for which there are no effective treatments currently available.

In the current study, we used doxycycline-inducible astrocyte-specific HIV Tat transgenic mice (iTat), a surrogate HAND model, and determined effects of PNU-125096, a positive allosteric modulator of α7 nicotinic acetylcholine receptor (α7 nAChR) on Tat-induced behavioural impairments and neuropathologies.

We showed that PNU-125096 treatment significantly improved locomotor, learning and memory deficits of iTat mice while inhibited glial activation and increased PSD-95 expression in the cortex and hippocampus of iTat mice. Using α7 nAChR knockout mice, we showed that α7 nAChR knockout eliminated the protective effects of PNU-125096 on iTat mice. In addition, we showed that inhibition of p38 phosphorylation by SB239063, a p38 MAPK-specific inhibitor exacerbated Tat neurotoxicity in iTat mice. Last, we used primary mouse cortical individual cultures and neuron-astrocytes co-cultures and in vivo staining of iTat mouse brain tissues and showed that glial activation was directly involved in the interplay among Tat neurotoxicity, α7 nAChR activation and the p38 MAPK signalling pathway.

Taken together, these findings demonstrated for the first time that α7 nAChR activation led to protection against HAND and suggested that α7 nAChR modulator PNU-125096 holds significant promise for development of therapeutics for HAND.

N1H- and N1-Substituted Phenylguanidines as α7 Nicotinic Acetylcholine (nACh) Receptor Antagonists: Structure-Activity Relationship Studies

We previously reported that N-(3-chlorophenyl)guanidine (1) represents a novel α7 nicotinic ACh (nACh) receptor antagonist chemotype. In the present study, a small series of compounds was synthesized with the intent to investigate the structure-activity relationship (SAR). Preliminary data suggested that the N-methyl analog of 1, 2, was several times more potent. Therefore, the chloro group at the aryl 3-position of 1 and its N₁-methyl counterpart 2 were replaced with a number of substituents considering the electronic, lipophilic, and steric nature of the substituents. The potencies of the compounds to inhibit acetylcholine (ACh)-induced responses were obtained in Xenopus laevis oocytes expressing human α7 nicotinic ACh receptors (nAChRs) using a two-electrode voltage-clamp assay. We found that the nature of the 3-position substituents had relatively little (i.e., <10-fold) effect on potency, and the presence of an N₁-isopropyl substituent was tolerated. Here, we report the first SAR investigation of this novel α7 nAChR antagonist chemotype.

Tyrosine phosphorylation differentially fine-tunes ionotropic and metabotropic responses of human α7 nicotinic acetylcholine receptor

The α7 nicotinic acetylcholine receptor is involved in neurological, neurodegenerative, and inflammatory disorders. It operates both as a ligand-gated cationic channel and as a metabotropic receptor in neuronal and non-neuronal cells. As protein phosphorylation is an important cell function regulatory mechanism, deciphering how tyrosine phosphorylation modulates α7 dual ionotropic/metabotropic molecular function is required for understanding its integral role in physiological and pathological processes. α7 single-channel activity elicited by ACh appears as brief isolated openings and less often as episodes of few openings in quick succession. The reduction of phosphorylation by tyrosine kinase inhibition increases the duration and frequency of activation episodes, whereas the inhibition of phosphatases has the opposite effect. Removal of two tyrosine residues at the α7 intracellular domain recapitulates the effects mediated by tyrosine kinase inhibition. The tyrosine-free mutant receptor shows longer duration-activation episodes, reduced desensitization rate and significantly faster recovery from desensitization, indicating that phosphorylation decreases α7 channel activity by favoring the desensitized state. However, the mutant receptor is incapable of triggering ERK1/2 phosphorylation in response to the α7-agonist. Thus, while tyrosine phosphorylation is absolutely required for α7-triggered ERK pathway, it negatively modulates α7 ionotropic activity. Overall, phosphorylation/dephosphorylation events fine-tune the integrated cell response mediated by α7 activation, thus having a broad impact on α7 cholinergic signaling.

A subset of DN1p neurons integrates thermosensory inputs to promote wakefulness via CNMa signaling

Sleep is an essential and evolutionarily conserved behavior that is modulated by many environmental factors. Ambient temperature shifting usually occurs during climatic or seasonal change or travel from high-latitude area to low-latitude area that affects animal physiology. Increasing ambient temperature modulates sleep in both humans and Drosophila. Although several thermosensory molecules and neurons have been identified, the neural mechanisms that integrate temperature sensation into the sleep neural circuit remain poorly understood. Here, we reveal that prolonged increasing of ambient temperature induces a reversible sleep reduction and impaired sleep consolidation in Drosophila via activating the internal thermosensory anterior cells (ACs). ACs form synaptic contacts with a subset of posterior dorsal neuron 1 (DN1p) neurons and release acetylcholine to promote wakefulness. Furthermore, we identify that this subset of DN1ps promotes wakefulness by releasing CNMamide (CNMa) neuropeptides to inhibit the Dh44-positive pars intercerebralis (PI) neurons through CNMa receptors. Our study demonstrates that the AC-DN1p-PI neural circuit is responsible for integrating thermosensory inputs into the sleep neural circuit. Moreover, we identify the CNMa signaling pathway as a newly recognized wakefulness-promoting DN1 pathway.

Apigenin and Structurally Related Flavonoids Allosterically Potentiate the Function of Human α7-Nicotinic Acetylcholine Receptors Expressed in SH-EP1 Cells

Phytochemicals, such as monoterpenes, polyphenols, curcuminoids, and flavonoids, are known to have anti-inflammatory, antioxidant, neuroprotective, and procognitive effects. In this study, the effects of several polyhydroxy flavonoids, as derivatives of differently substituted 5,7-dihydroxy-4H-chromen-4-one including apigenin, genistein, luteolin, kaempferol, quercetin, gossypetin, and phloretin with different lipophilicities (cLogP), as well as topological polar surface area (TPSA), were tested for induction of Ca²⁺ transients by α7 human nicotinic acetylcholine (α7 nACh) receptors expressed in SH-EP1 cells. Apigenin (10 μM) caused a significant potentiation of ACh (30 μM)-induced Ca²⁺ transients, but did not affect Ca²⁺ transients induced by high K⁺ (60 mM) containing solutions. Co-application of apigenin with ACh was equally effective as apigenin preincubation. However, the effect of apigenin significantly diminished by increasing ACh concentrations. The flavonoids tested also potentiated α₇ nACh mediated Ca²⁺ transients with descending potency (highest to lowest) by genistein, gossypetin, kaempferol, luteolin, phloretin, quercetin, and apigenin. The specific binding of α7 nACh receptor antagonist [¹²⁵I]-bungarotoxin remained unchanged in the presence of any of the tested polyhydroxy flavonoids, suggesting that these compounds act as positive allosteric modulators of the α7-nACh receptor in SH-EP1 cells. These findings suggest a clinical potential for these phytochemicals in the treatment of various human diseases from pain to inflammation and neural disease.

Natural Polyhydroxy Flavonoids, Curcuminoids, and Synthetic Curcumin Analogs as α7 nAChRs Positive Allosteric Modulators

The α7 nicotinic acetylcholine receptor (α7 nAChR) is a ligand-gated ion channel that is involved in cognition disorders, schizophrenia, pain, and inflammation. Allosteric modulation of this receptor might be advantageous to reduce the toxicity in comparison with full agonists. Our previous results obtained with some hydroxy-chalcones, which were identified as positive allosteric modulators (PAMs) of α7 nAChR, prompted us to evaluate the potential of some structurally related naturally occurring flavonoids and curcuminoids and some synthetic curcumin analogues, with the aim of identifying new allosteric modulators of the α7 nAChR. Biological evaluation showed that phloretin, demethoxycurcumin, and bis-demethoxicurcuming behave as PAMs of α7 nAChR. In addition, some new curcumin derivatives were able to enhance the signal evoked by ACh; the activity values found for the tetrahydrocurcuminoid analog 23 were especially promising.

The Role of α7nAChR-Mediated Cholinergic Anti-inflammatory Pathway in Immune Cells

Alpha 7 nicotinic acetylcholine receptor (α7nAChR) is widely distributed in the nervous and non-cholinergic immune systems. It is necessary for the cholinergic transmitter to participate in the regulation of inflammatory response and is the key element of cholinergic anti-inflammatory pathway (CAP). Because of the profound impact of CAP on the immune system, α7nAChR is considered as a potential therapeutic target for the treatment of inflammatory diseases. Available evidences confirmed that manipulation of CAP by activating α7nAChR with either endogenous acetylcholine (ACh) or cholinergic agonists can substantially alleviate inflammatory responses both in vivo and in vitro. However, the mechanism through which CAP curbs the excessive pro-inflammatory responses and maintains immune homeostasis is not fully understood. Obtained clues suggest that the crosstalk between CAP and classical inflammatory pathways is the key to elucidate the anti-inflammatory mechanism, and the impacts of CAP activation in α7nAChR-expressing immune cells are the foundation of the immunoregulatory property. In this article, we review and update the knowledge concerning the progresses of α7nAChR-based CAP, including α7nAChR properties, signal transductions, interactions with classic immune pathways, and immunoregulatory functions in different immune cells. Certain critical issues to be addressed are also highlighted. By providing a panoramic view of α7nAChR, the summarized evidences will pave the way for the development of novel anti-inflammatory reagents and strategy and inspire further researches.

Vitamin D3 reduces hippocampal NR2A and anxiety in nicotine withdrawal mice

Nicotine withdrawal symptoms, mainly anxiety, cause high level of relapse rate after quitting smoking. Vitamin D supplementation has shown its potential for the prevention and treatment of anxiety disorders; however, neurobiological studies about the effect of vitamin D on nicotine withdrawal-induced anxiety are limited. To investigate the effect and molecular mechanism of vitamin D3 supplement by dietary on anxiety-like behavior during nicotine withdrawal, male C57/BL6 mice were divided into four groups: vehicle, nicotine only, vitamin D3 only, and nicotine plus vitamin D3. Mice were administrated with nicotine in drinking water (200 µg/mL), and vitamin D3 in feed for 6 weeks. During nicotine withdrawal, vitamin D3-treated mice showed significantly less anxiety-like behavior by an open-field test and marble buried test that performed an increase in the duration of the central zone and a decrease buried marble, respectively. Moreover, vitamin D3 supplementation attenuated the hippocampal NR2A expression on both protein and mRNA levels in nicotine and vitamin D3-treated mice. Our data showed that dietary supplementation with vitamin D3 ameliorated nicotine withdrawal-induced anxiety, which may be related to downregulation of NR2A expression in hippocampus. Vitamin D3 may provide a new dietary intervention with the easy access for smoking cessation.

α9α10 nicotinic acetylcholine receptors regulate murine bone marrow granulocyte functions

Polymorphonuclear neutrophilic granulocytes (PMNs) are extremely important in defense of the organism against infections and in inflammatory processes including neuroinflammation and pain sensation. Different subtypes of nicotinic acetylcholine receptors (nAChRs) are involved in modulation of PMN activities. Earlier we determined expression of α2-7, α9, β3, β4 subunits and regulatory role of α7 and α3β2 nAChR subtypes in functions of inflammatory PMNs. Other authors detected mRNA of α9 subunit in bone marrow neutrophils (BM-PMNs). Murine BM-PMNs coming out from the bone marrow, where they develop, to blood were characterized as mature. There was no data for α10 and for the presence of functionally active α9α10 nAChRs in BM-PMNs. Here we detected for the first time mRNA expression of the α10 nAChR subunit in BM-PMNs and confirmed the expression of mRNA for α9 nAChR. With the help of α-conotoxins RgIA and Vc1.1, highly selective antagonists of α9α10 nAChRs, we have revealed participation of α9 and/or α9α10 nAChRs in regulation of cytosolic Ca²⁺ concentration, cell adhesion, and in generation of reactive oxygen species (ROS). Nicotine, choline, RgIA, and Vc1.1 induced Ca²⁺ transients in BM-PMNs, enhanced cell adhesiveness and decreased production of ROS indicating involvement of α9, possibly co-assembled with α10, nAChRs in the BM-PMN activity for recruitment and cytotoxicity.

Neurotransmitter and neuropeptide regulation of mast cell function: a systematic review

The existence of the neural control of mast cell functions has long been proposed. Mast cells (MCs) are localized in association with the peripheral nervous system (PNS) and the brain, where they are closely aligned, anatomically and functionally, with neurons and neuronal processes throughout the body. They express receptors for and are regulated by various neurotransmitters, neuropeptides, and other neuromodulators. Consequently, modulation provided by these neurotransmitters and neuromodulators allows neural control of MC functions and involvement in the pathogenesis of mast cell–related disease states. Recently, the roles of individual neurotransmitters and neuropeptides in regulating mast cell actions have been investigated extensively. This review offers a systematic review of recent advances in our understanding of the contributions of neurotransmitters and neuropeptides to mast cell activation and the pathological implications of this regulation on mast cell–related disease states, though the full extent to which such control influences health and disease is still unclear, and a complete understanding of the mechanisms underlying the control is lacking. Future validation of animal and in vitro models also is needed, which incorporates the integration of microenvironment-specific influences and the complex, multifaceted cross-talk between mast cells and various neural signals. Moreover, new biological agents directed against neurotransmitter receptors on mast cells that can be used for therapeutic intervention need to be more specific, which will reduce their ability to support inflammatory responses and enhance their potential roles in protecting against mast cell–related pathogenesis.

Design, Synthesis, and Functional Evaluation of a Novel Series of Phosphonate-Functionalized 1,2,3-Triazoles as Positive Allosteric Modulators of α7 Nicotinic Acetylcholine Receptors

The α7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel widely distributed in the central nervous system, mainly in the hippocampus and cortex. The enhancement of its activity by positive allosteric modulators (PAMs) is a promising therapeutic strategy for cognitive deficits and neurodegenerative disorders. With the aim of developing novel scaffolds with PAM activity, we designed and synthesized a series of phosphonate-functionalized 1,4-disubstituted 1,2,3-triazoles using supported copper nanoparticles as the cycloaddition reaction catalyst and evaluated their activity on α7 receptors by single-channel and whole-cell recordings. We identified several triazole derivatives that displayed PAM activity, with the compound functionalized with the methyl phosphonate group being the most efficacious one. At the macroscopic level, α7 potentiation was evidenced as an increase of the maximal currents elicited by acetylcholine with minimal effects on desensitization, recapitulating the actions of type I PAMs. At the single-channel level, the active compounds did not affect channel amplitude but significantly increased the duration of channel openings and activation episodes. By using chimeric and mutant α7 receptors, we demonstrated that the new α7 PAMs share transmembrane structural determinants of potentiation with other chemically nonrelated PAMs. To gain further insight into the chemical basis of potentiation, we applied structure-activity relationship strategies involving modification of the chain length, inversion of substituent positions in the triazole ring, and changes in the aromatic nucleus. Our findings revealed that the phosphonate-functionalized 1,4-disubstituted 1,2,3-triazole is a novel pharmacophore for the development of therapeutic agents for neurological and neurodegenerative disorders associated with cholinergic dysfunction.