The Nicotinic Acetylcholine Receptor and Its Pentameric Homologs: Toward an Allosteric Mechanism of Signal Transduction at the Atomic Level.

The nicotinic acetylcholine receptor has served, since its biochemical identification in the 1970s, as a model of an allosteric ligand-gated ion channel mediating signal transition at the synapse. In recent years, the application of X-ray crystallography and high-resolution cryo-electron microscopy, together with molecular dynamic simulations of nicotinic receptors and homologs, have opened a new era in the understanding of channel gating by the neurotransmitter. They reveal, at atomic resolution, the diversity and flexibility of the multiple ligand-binding sites, including recently discovered allosteric modulatory sites distinct from the neurotransmitter orthosteric site, and the conformational dynamics of the activation process as a molecular switch linking these multiple sites. The model emerging from these studies paves the way for a new pharmacology based, first, upon the occurrence of an original mode of indirect allosteric modulation, distinct from a steric competition for a single and rigid binding site, and second, the design of drugs that specifically interact with privileged conformations of the receptor such as agonists, antagonists, and desensitizers. Research on nicotinic receptors is still at the forefront of understanding the mode of action of drugs on the nervous system.

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.

Structure and gating mechanism of the α7 nicotinic acetylcholine receptor.

The α7 nicotinic acetylcholine receptor plays critical roles in the central nervous system and in the cholinergic inflammatory pathway. This ligand-gated ion channel assembles as a homopentamer, is exceptionally permeable to Ca2+, and desensitizes faster than any other Cys-loop receptor. The α7 receptor has served as a prototype for the Cys-loop superfamily yet has proven refractory to structural analysis. We present cryo-EM structures of the human α7 nicotinic receptor in a lipidic environment in resting, activated, and desensitized states, illuminating the principal steps in the gating cycle. The structures also reveal elements that contribute to its function, including a C-terminal latch that is permissive for channel opening, and an anionic ring in the extracellular vestibule that contributes to its high conductance and calcium permeability. Comparisons among the α7 structures provide a foundation for mapping the gating cycle and reveal divergence in gating mechanisms in the Cys-loop receptor superfamily.

Ion transport in muscle acetylcholine receptor maintained by conserved salt bridges between the pore and lipid membrane.

Pores through ion channels rapidly transport small inorganic ions along their electrochemical gradients. Here, applying single-channel electrophysiology and mutagenesis to the archetypal muscle nicotinic acetylcholine receptor (AChR) channel, we show that a conserved pore-peripheral salt bridge partners with those in the other subunits to regulate ion transport. Disrupting the salt bridges in all five receptor subunits greatly decreases the amplitude of the unitary current and increases its fluctuations. However, disrupting individual salt bridges has unequal effects that depend on the structural status of the other salt bridges. The AChR ε- and δ-subunits are structurally unique in harboring a putative palmitoylation site near each salt bridge and bordering the lipid membrane. The effects of disrupting the palmitoylation sites mirror those of disrupting the salt bridges, but the effect of disrupting either of these structures depends on the structural status of the other. Thus, rapid ion transport through the AChR channel is maintained by functionally interdependent salt bridges linking the pore to the lipid membrane.

MafB-dependent neurotransmitter signaling promotes ß cell migration in the developing pancreas.

Hormone secretion from pancreatic islets is essential for glucose homeostasis, and loss or dysfunction of islet cells is a hallmark of type 2 diabetes. Maf transcription factors are crucial for establishing and maintaining adult endocrine cell function. However, during pancreas development, MafB is not only expressed in insulin- and glucagon-producing cells, but also in Neurog3+ endocrine progenitor cells, suggesting additional functions in cell differentiation and islet formation. Here, we report that MafB deficiency impairs ß cell clustering and islet formation, but also coincides with loss of neurotransmitter and axon guidance receptor gene expression. Moreover, the observed loss of nicotinic receptor gene expression in human and mouse ß cells implied that signaling through these receptors contributes to islet cell migration/formation. Inhibition of nicotinic receptor activity resulted in reduced ß cell migration towards autonomic nerves and impaired ß cell clustering. These findings highlight a novel function of MafB in controlling neuronal-directed signaling events required for islet formation.

Cholinergic-Sensitive Theta Oscillations in Memory Encoding in Mice.

Cholinergic regulation of hippocampal theta oscillations has long been proposed to be a potential mechanism underlying hippocampus-dependent memory encoding processes. However, cholinergic transmission has been traditionally associated with type II theta under urethane anesthesia. The mechanisms and behavioral significance of cholinergic regulation of type I theta in freely exploring animals is much less clear. In this study, we examined the potential behavioral significance of cholinergic regulation of theta oscillations in the object location task in male mice that involves training and testing trials and provides an ideal behavioral task to study the underlying memory encoding and retrieval processes, respectively. Cholinergic regulation of hippocampal theta oscillations and the behavioral outcomes was examined by either intrahippocampal infusion of cholinergic receptor antagonists or knocking out cholinergic receptors in excitatory neurons or interneurons. We found that both muscarinic acetylcholine receptors (mAChRs) and α7 nicotinic AChRs (α7 nAChRs) regulated memory encoding by engaging excitatory neurons and interneurons, respectively. There is a transient upregulated theta oscillation at the beginning of individual object exploration events that only occurred in the training trials, but not in the testing trials. This transient upregulated theta is also the only theta component that significantly differed between training and testing trials and was sensitive to mAChR and α7 nAChR antagonists. Thus, our study has revealed a transient cholinergic-sensitive theta component that is specifically associated with memory encoding, but not memory retrieval, in the object location task, providing direct experimental evidence supporting a role for cholinergic-regulated theta oscillations in hippocampus-dependent memory encoding processes.

Pathogenic residue insertion in neuronal nicotinic receptor alters intra- and inter-subunit interactions that tune channel gating.

We describe molecular-level functional changes in the α4ß2 nicotinic acetylcholine receptor by a leucine residue insertion in the M2 transmembrane domain of the α4 subunit associated with sleep-related hyperkinetic epilepsy. Measurements of agonist-elicited single-channel currents reveal the primary effect is to stabilize the open channel state, while the secondary effect is to promote reopening of the channel. These dual effects prolong the durations of bursts of channel openings equally for the two major stoichiometric forms of the receptor, (α4)2(ß2)3 and (α4)3(ß2)2, indicating the functional impact is independent of mutant copy number per receptor. Altering the location of the residue insertion within M2 shows that functionally pivotal structures are confined to a half turn of the M2 α-helix. Residue substitutions within M2 and surrounding α-helices reveal that both intrasubunit and intersubunit interactions mediate the increase in burst duration. These interactions impacting burst duration depend linearly on the size and hydrophobicity of the substituting residue. Together, the results reveal a novel structural region of the α4ß2 nicotinic acetylcholine receptor in which interhelical interactions tune the stability of the open channel state.

Analogs of α-conotoxin PnIC selectively inhibit α7ß2- over α7-only subtype nicotinic acetylcholine receptors via a novel allosteric mechanism.

This study was undertaken to identify and characterize the first ligands capable of selectively identifying nicotinic acetylcholine receptors containing α7 and ß2 subunits (α7ß2-nAChR subtype). Basal forebrain cholinergic neurons express α7ß2-nAChR. Here, they appear to mediate neuronal dysfunction induced by the elevated levels of oligomeric amyloid-ß associated with early Alzheimer's disease. Additional work indicates that α7ß2-nAChR are expressed across several further critically important cholinergic and GABAergic neuronal circuits within the central nervous system. Further studies, however, are significantly hindered by the inability of currently available ligands to distinguish heteromeric α7ß2-nAChR from the closely related and more widespread homomeric α7-only-nAChR subtype. Functional screening using two-electrode voltage-clamp electrophysiology identified a family of α7ß2-nAChR-selective analogs of α-conotoxin PnIC (α-CtxPnIC). A combined electrophysiology, functional kinetics, site-directed mutagenesis, and molecular dynamics approach was used to further characterize the α7ß2-nAChR selectivity and site of action of these α-CtxPnIC analogs. We determined that α7ß2-nAChR selectivity of α-CtxPnIC analogs arises from interactions at a site distinct from the orthosteric agonist-binding site shared between α7ß2- and α7-only-nAChR. As numerous previously identified α-Ctx ligands are competitive antagonists of orthosteric agonist-binding sites, this study profoundly expands the scope of use of α-Ctx ligands (which have already provided important nAChR research and translational breakthroughs). More immediately, analogs of α-CtxPnIC promise to enable, for the first time, both comprehensive mapping of the distribution of α7ß2-nAChR and detailed investigations of their physiological roles.

VNS-mediated α7nAChR signaling promotes SPM synthesis via regulation of netrin-1 expression during LPS-induced ALI.

The α7 nicotinic acetylcholine receptor (α7nAChR) plays a crucial role in the cholinergic anti-inflammatory pathway (CAP) during sepsis-associated acute lung injury (ALI). Increasing evidence suggests that specialized pro-resolving mediators (SPMs) are important in resolving α7nAChR-mediated ALI resolution. Our study aims to elucidate the pivotal role of α7nAChR in the CAP during LPS-associated acute lung injury (ALI). By employing vagus nerve stimulation (VNS), we identified α7nAChR as the key CAP subunit in ALI mice, effectively reducing lung permeability and the release of inflammatory cytokines. We further investigated the alterations in SPMs regulated by α7nAChR, revealing a predominant synthesis of lipoxin A4 (LXA4). The significance of α7nAChR-netrin-1 pathway in governing SPM synthesis was confirmed through the use of netrin-1 knockout mice and siRNA-transfected macrophages. Additionally, our evaluation identified a synchronous alteration of LXA4 synthesis in the α7nAChR-netrin-1 pathway accompanied by 5-lipoxygenase (5-LOX), thereby confirming an ameliorative effect of LXA4 on lung injury and macrophage inflammatory response. Concurrently, inhibiting the function of LXA4 annulled the lung-protective effect of VNS. As a result, our findings reveal a novel anti-inflammatory pathway wherein VNS modulates netrin-1 expression via α7nAChR, ultimately leading to LXA4 synthesis and subsequent lung protection.

Unraveling the molecular interactions between α7 nicotinic receptor and a RIC3 variant associated with backward speech.

Recent work putatively linked a rare genetic variant of the chaperone Resistant to Inhibitors of acetylcholinesterase (RIC3) (NM_024557.4:c.262G > A, NP_078833.3:p.G88R) to a unique ability to speak backwards, a language skill that is associated with exceptional working memory capacity. RIC3 is important for the folding, maturation, and functional expression of α7 nicotinic acetylcholine receptors (nAChR). We compared and contrasted the effects of RIC3G88R on assembly, cell surface expression, and function of human α7 receptors using fluorescent protein tagged α7 nAChR and Förster resonance energy transfer (FRET) microscopy imaging in combination with functional assays and 125I-α-bungarotoxin binding. As expected, the wild-type RIC3 protein was found to increase both cell surface and functional expression of α7 receptors. In contrast, the variant form of RIC3 decreased both. FRET analysis showed that RICG88R increased the interactions between RIC3 and α7 protein in the endoplasmic reticulum. These results provide interesting and novel data to show that a RIC3 variant alters the interaction of RIC3 and α7, which translates to decreased cell surface and functional expression of α7 nAChR.

Key role of the TM2-TM3 loop in calcium potentiation of the α9α10 nicotinic acetylcholine receptor.

The α9α10 nicotinic cholinergic receptor (nAChR) is a ligand-gated pentameric cation-permeable ion channel that mediates synaptic transmission between descending efferent neurons and mechanosensory inner ear hair cells. When expressed in heterologous systems, α9 and α10 subunits can assemble into functional homomeric α9 and heteromeric α9α10 receptors. One of the differential properties between these nAChRs is the modulation of their ACh-evoked responses by extracellular calcium (Ca2+). While α9 nAChRs responses are blocked by Ca2+, ACh-evoked currents through α9α10 nAChRs are potentiated by Ca2+ in the micromolar range and blocked at millimolar concentrations. Using chimeric and mutant subunits, together with electrophysiological recordings under two-electrode voltage-clamp, we show that the TM2-TM3 loop of the rat α10 subunit contains key structural determinants responsible for the potentiation of the α9α10 nAChR by extracellular Ca2+. Moreover, molecular dynamics simulations reveal that the TM2-TM3 loop of α10 does not contribute to the Ca2+ potentiation phenotype through the formation of novel Ca2+ binding sites not present in the α9 receptor. These results suggest that the TM2-TM3 loop of α10 might act as a control element that facilitates the intramolecular rearrangements that follow ACh-evoked α9α10 nAChRs gating in response to local and transient changes of extracellular Ca2+ concentration. This finding might pave the way for the future rational design of drugs that target α9α10 nAChRs as otoprotectants.

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.

An experimental test of the nicotinic hypothesis of COVID-19.

The pathophysiological mechanisms underlying the constellation of symptoms that characterize COVID-19 are only incompletely understood. In an effort to fill these gaps, a "nicotinic hypothesis," which posits that nicotinic acetylcholine receptors (AChRs) act as additional severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptors, has recently been put forth. A key feature of the proposal (with potential clinical ramifications) is the suggested competition between the virus' spike protein and small-molecule cholinergic ligands for the receptor's orthosteric binding sites. This notion is reminiscent of the well-established role of the muscle AChR during rabies virus infection. To address this hypothesis directly, we performed equilibrium-type ligand-binding competition assays using the homomeric human α7-AChR (expressed on intact cells) as the receptor, and radio-labeled α-bungarotoxin (α-BgTx) as the orthosteric-site competing ligand. We tested different SARS-CoV-2 spike protein peptides, the S1 domain, and the entire S1-S2 ectodomain, and found that none of them appreciably outcompete [125I]-α-BgTx in a specific manner. Furthermore, patch-clamp recordings showed no clear effect of the S1 domain on α7-AChR-mediated currents. We conclude that the binding of the SARS-CoV-2 spike protein to the human α7-AChR's orthosteric sites-and thus, its competition with ACh, choline, or nicotine-is unlikely to be a relevant aspect of this complex disease.

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.

Proteome profile of the cerebellum from α7 nicotinic acetylcholine receptor deficient mice.

The alpha7 nicotinic acetylcholine receptor (α7 nAChR; CHRNA7) is expressed in the nervous system and in non-neuronal tissues. Within the central nervous system, it is involved in various cognitive and sensory processes such as learning, attention, and memory. It is also expressed in the cerebellum, where its roles are; however, not as well understood as in the other brain regions. To investigate the consequences of absence of CHRNA7 on the cerebellum proteome, we performed a quantitative nano-LC-MS/MS analysis of samples from CHRNA7 knockout (KO) mice and corresponding wild type (WT) controls. Liver, an organ which does not express this receptor, was analyzed, in comparison. While the liver proteome remained relatively unaltered (three proteins more abundant in KOs), 90 more and 20 less abundant proteins were detected in the cerebellum proteome of the KO mice. The gene ontology analysis of the differentially abundant proteins indicates that the absence of CHRNA7 leads to alterations in the glutamatergic system and myelin sheath in the cerebellum. In conclusion, our dataset provides new insights in the role of CHRNA7 in the cerebellum, which may serve as a basis for future in depth-investigations.

Differential Regulation of Prelimbic and Thalamic Transmission to the Basolateral Amygdala by Acetylcholine Receptors.

The amygdalar anterior basolateral nucleus (BLa) plays a vital role in emotional behaviors. This region receives dense cholinergic projections from basal forebrain which are critical in regulating neuronal activity in BLa. Cholinergic signaling in BLa has also been shown to modulate afferent glutamatergic inputs to this region. However, these studies, which have used cholinergic agonists or prolonged optogenetic stimulation of cholinergic fibers, may not reflect the effect of physiological acetylcholine release in the BLa. To better understand these effects of acetylcholine, we have used electrophysiology and optogenetics in male and female mouse brain slices to examine cholinergic regulation of afferent BLa input from cortex and midline thalamic nuclei. Phasic ACh release evoked by single pulse stimulation of cholinergic terminals had a biphasic effect on transmission at cortical input, producing rapid nicotinic receptor-mediated facilitation followed by slower mAChR-mediated depression. In contrast, at this same input, sustained ACh elevation through application of the cholinesterase inhibitor physostigmine suppressed glutamatergic transmission through mAChRs only. This suppression was not observed at midline thalamic nuclei inputs to BLa. In agreement with this pathway specificity, the mAChR agonist, muscarine more potently suppressed transmission at inputs from prelimbic cortex than thalamus. Muscarinic inhibition at prelimbic cortex input required presynaptic M4 mAChRs, while at thalamic input it depended on M3 mAChR-mediated stimulation of retrograde endocannabinoid signaling. Muscarinic inhibition at both pathways was frequency-dependent, allowing only high-frequency activity to pass. These findings demonstrate complex cholinergic regulation of afferent input to BLa that is pathway-specific and frequency-dependent.SIGNIFICANCE STATEMENT Cholinergic modulation of the basolateral amygdala regulates formation of emotional memories, but the underlying mechanisms are not well understood. Here, we show, using mouse brain slices, that ACh differentially regulates afferent transmission to the BLa from cortex and midline thalamic nuclei. Fast, phasic ACh release from a single optical stimulation biphasically regulates glutamatergic transmission at cortical inputs through nicotinic and muscarinic receptors, suggesting that cholinergic neuromodulation can serve precise, computational roles in the BLa. In contrast, sustained ACh elevation regulates cortical input through muscarinic receptors only. This muscarinic regulation is pathway-specific with cortical input inhibited more strongly than midline thalamic nuclei input. Specific targeting of these cholinergic receptors may thus provide a therapeutic strategy to bias amygdalar processing and regulate emotional memory.

Chemical Flavorants in Vaping Products Alter Neurobiology in a Sex-Dependent Manner to Promote Vaping-Related Behaviors.

Electronic nicotine delivery systems (ENDS) are distinctly different from combustible cigarettes because of the availability of flavor options. Subjective measures have been used to demonstrate that adults and adolescents prefer flavors for various reasons; (1) they are pleasing and (2) they mask the harshness of nicotine. Despite this, there have been few investigations into the molecular interactions that connect chemical flavorants to smoking or vaping-related behaviors. Here, we investigated the effects of three chemical flavorants (hexyl acetate, ethyl acetate, and methylbutyl acetate) that are found in green apple (GA) ENDS e-liquids but are also found in other flavor categories. We used a translationally relevant vapor self-administration mouse model and observed that adult male and female mice self-administered GA flavorants in the absence of nicotine. Using α4-mCherryα6-GFP nicotinic acetylcholine receptor (nAChR) mice, we observed that mice exposed to GA flavorants exhibited a sex-specific increase (upregulation) of nAChRs that was also brain-region specific. Electrophysiology revealed that mice exposed to GA flavorants exhibited enhanced firing of ventral tegmental area dopamine neurons. Fast-scan cyclic voltammetry revealed that electrically stimulated dopamine release in the nucleus accumbens core is increased in mice that are exposed to GA flavorants. These effects were similarly observed in the medial habenula. Overall, these findings demonstrate that ENDS flavors alone change neurobiology and may promote vaping-dependent behaviors in the absence of nicotine. Furthermore, the flavorant-induced changes in neurobiology parallel those caused by nicotine, which highlights the fact that nonmenthol flavorants may contribute to or enhance nicotine reward and reinforcement.SIGNIFICANCE STATEMENT The impact of flavors on vaping is a hotly debated topic; however, few investigations have examined this in a model that is relevant to vaping. Although a full understanding of the exact mechanism remains undetermined, our observations reveal that chemical flavorants in the absence of nicotine alter brain circuits relevant to vaping-related behavior. The fact that the flavorants investigated here exist in multiple flavor categories of vaping products highlights the fact that a multitude of flavored vaping products may pose a risk toward vaping-dependent behaviors even without the impact of nicotine. Furthermore, as the neurobiological changes have an impact on neurons of the reward system, there exists the possibility that nonmenthol flavorants may enhance nicotine reward and reinforcement.

SARS-CoV-2 spike ectodomain targets α7 nicotinic acetylcholine receptors.

Virus entry into animal cells is initiated by attachment to target macromolecules located on host cells. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) trimeric spike glycoprotein targets host angiotensin converting enzyme 2 to gain cellular access. The SARS-CoV-2 glycoprotein contains a neurotoxin-like region that has sequence similarities to the rabies virus and the HIV glycoproteins, as well as to snake neurotoxins, which interact with nicotinic acetylcholine receptor (nAChR) subtypes via this region. Using a peptide of the neurotoxin-like region of SARS-CoV-2 (SARS-CoV-2 glycoprotein peptide [SCoV2P]), we identified that this area moderately inhibits α3ß2, α3ß4, and α4ß2 subtypes, while potentiating and inhibiting α7 nAChRs. These nAChR subtypes are found in target tissues including the nose, lung, central nervous system, and immune cells. Importantly, SCoV2P potentiates and inhibits ACh-induced α7 nAChR responses by an allosteric mechanism, with nicotine enhancing these effects. Live-cell confocal microscopy was used to confirm that SCoV2P interacts with α7 nAChRs in transfected neuronal-like N2a and human embryonic kidney 293 cells. The SARS-CoV-2 ectodomain functionally potentiates and inhibits the α7 subtype with nanomolar potency. Our functional findings identify that the α7 nAChR is a target for the SARS-CoV-2 glycoprotein, providing a new aspect to our understanding of SARS-CoV-2 and host cell interactions, in addition to disease pathogenesis.

Nicotinic receptors in airway disease.

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

The calcium-calmodulin-dependent protein kinase kinase inhibitor, STO-609, inhibits nicotine-induced currents and intracellular calcium increase in insect neurosecretory cells.

Insect neuronal nicotinic acetylcholine receptors (nAChRs) are transmembrane receptors that play a key role in the development and synaptic plasticity of both vertebrates and invertebrates and are considered to be major targets of neonicotinoid insecticides. We used dorsal unpaired median (DUM) neurons, which are insect neurosecretory cells, in order to explore the intracellular mechanisms leading to the regulation of insect neuronal nAChRs in more detail. Using whole-cell patch-clamp and fura-2AM calcium imaging techniques, we found that a novel CaMKK/AMPK pathway could be involved in the intracellular regulation of DUM neuron nAChRs. The CaMKK selective inhibitor, STO, reduced nicotinic current amplitudes, and strongly when co-applied with α-Bgt. Interestingly, intracellular application of the AMPK activator, A-76, prevented the reduction in nicotine-induced currents observed in the presence of the AMPK inhibitor, dorsomorphin. STO prevented the increase in intracellular calcium induced by nicotine, which was not dependent on α-Bgt. Currents induced by 1 mM LMA, a selective activator of nAChR2, were reduced under bath application of STO, and mecamylamine, which blocked nAChR2 subtype, inhibited the increase in intracellular calcium induced by LMA. These findings provide insight into potential complex mechanisms linked to the modulation of the DUM neuron nAChRs and CaMKK pathway.