Homomeric and Heteromeric α7 Nicotinic Acetylcholine Receptors in Health and Some Central Nervous System Diseases

α7 nicotinic acetylcholine receptor in memory processing

Information storage in the brain involves different memory types and stages that are processed by several brain regions. Cholinergic pathways through acetylcholine receptors actively participate on memory modulation, and their disfunction is associated with cognitive decline in several neurological disorders. During the last decade, the role of α7 subtype of nicotinic acetylcholine receptors in different memory stages has been studied. However, the information about their role in memory processing is still scarce. In this review, we attempt to identify brain areas where α7 nicotinic receptors have an essential role in different memory types and stages. In addition, we discuss recent work implicating-or not-α7 nicotinic receptors as promising pharmacological targets for memory impairment associated with neurological disorders.

Human restricted CHRFAM7A gene increases brain efficiency

Introduction

CHRFAM7A, a uniquely human fusion gene, has been associated with neuropsychiatric disorders including Alzheimer's disease, schizophrenia, anxiety, and attention deficit disorder. Understanding the physiological function of CHRFAM7A in the human brain is the first step to uncovering its role in disease. CHRFAM7A was identified as a potent modulator of intracellular calcium and an upstream regulator of Rac1 leading to actin cytoskeleton reorganization and a switch from filopodia to lamellipodia implicating a more efficient neuronal structure. We performed a neurocognitive-MRI correlation exploratory study on 46 normal human subjects to explore the effect of CHRFAM7A on human brain.

Methods

Dual locus specific genotyping of CHRFAM7A was performed on genomic DNA to determine copy number (TaqMan assay) and orientation (capillary sequencing) of the CHRFAM7A alleles. As only the direct allele is expressed at the protein level and affects α7 nAChR function, direct allele carriers and non-carriers are compared for neuropsychological and MRI measures. Subjects underwent neuropsychological testing to measure motor (Timed 25-foot walk test, 9-hole peg test), cognitive processing speed (Symbol Digit Modalities Test), Learning and memory (California Verbal Learning Test immediate and delayed recall, Brief Visuospatial Memory Test-Revised immediate and delayed recall) and Beck Depression Inventory-Fast Screen, Fatigue Severity Scale. All subjects underwent MRI scanning on the same 3 T GE scanner using the same protocol. Global and tissue-specific volumes were determined using validated cross-sectional algorithms including FSL's Structural Image Evaluation, using Normalization, of Atrophy (SIENAX) and FSL's Integrated Registration and Segmentation Tool (FIRST) on lesion-inpainted images. The cognitive tests were age and years of education-adjusted using analysis of covariance (ANCOVA). Age-adjusted analysis of covariance (ANCOVA) was performed on the MRI data.

Results

CHRFAM7A direct allele carrier and non-carrier groups included 33 and 13 individuals, respectively. Demographic variables (age and years of education) were comparable. CHRFAM7A direct allele carriers demonstrated an upward shift in cognitive performance including cognitive processing speed, learning and memory, reaching statistical significance in visual immediate recall (FDR corrected p = 0.018). The shift in cognitive performance was associated with smaller whole brain volume (uncorrected p = 0.046) and lower connectivity by resting state functional MRI in the visual network (FDR corrected p = 0.027) accentuating the cognitive findings.

Conclusion

These data suggest that direct allele carriers harbor a more efficient brain consistent with the cellular biology of actin cytoskeleton and synaptic gain of function. Further larger human studies of cognitive measures correlated with MRI and functional imaging are needed to decipher the impact of CHRFAM7A on brain function.

CHRFAM7A diversifies human immune adaption through Ca2+ signalling and actin cytoskeleton reorganization

BACKGROUND

Human restricted genes contribute to human specific traits in the immune system. CHRFAM7A, a uniquely human fusion gene, is a negative regulator of the α7 nicotinic acetylcholine receptor (α7 nAChR), the highest Ca2+ conductor of the ACh receptors implicated in innate immunity. Understanding the mechanism of how CHRFAM7A affects the immune system remains unexplored.

METHODS

Two model systems are used, human induced pluripotent stem cells (iPSC) and human primary monocytes, to characterize α7 nAChR function, Ca2+ dynamics and decoders to elucidate the pathway from receptor to phenotype.

FINDINGS

CHRFAM7A/α7 nAChR is identified as a hypomorphic receptor with mitigated Ca2+ influx and prolonged channel closed state. This shifts the Ca2+ reservoir from the extracellular space to the endoplasmic reticulum (ER) leading to Ca2+ dynamic changes. Ca2+ decoder small GTPase Rac1 is then activated, reorganizing the actin cytoskeleton. Observed actin mediated phenotypes include cellular adhesion, motility, phagocytosis and tissue mechanosensation.

INTERPRETATION

CHRFAM7A introduces an additional, human specific, layer to Ca2+ regulation leading to an innate immune gain of function. Through the actin cytoskeleton it drives adaptation to the mechanical properties of the tissue environment leading to an ability to invade previously immune restricted niches. Human genetic diversity predicts profound translational significance as its understanding builds the foundation for successful treatments for infectious diseases, sepsis, and cancer metastasis.

FUNDING

This work is supported in part by the Community Foundation for Greater Buffalo (Kinga Szigeti) and in part by NIH grant R01HL163168 (Yongho Bae).

Translational implications of CHRFAM7A, an elusive human-restricted fusion gene

Genes restricted to humans may contribute to human-specific traits and provide a different context for diseases. CHRFAM7A is a uniquely human fusion gene and a negative regulator of the α7 nicotinic acetylcholine receptor (α7 nAChR). The α7 nAChR has been a promising target for diseases affecting cognition and higher cortical functions, however, the treatment effect observed in animal models failed to translate into human clinical trials. As CHRFAM7A was not accounted for in preclinical drug screens it may have contributed to the translational gap. Understanding the complex genetic architecture of the locus, deciphering the functional impact of CHRFAM7A on α7 nAChR neurobiology and utilizing human-relevant models may offer novel approaches to explore α7 nAChR as a drug target.

The Sobering Sting: Oleoyl Serotonin Is a Novel Stephanoconus Snail Venom-Derived Antagonist of Cannabinoid Receptors That Counteracts Learning and Memory Deficits

Cannabinoid receptors (CB1 and CB2) are promising targets for a better understanding of neurological diseases. Nevertheless, only a few ligands of CB have reached clinical application so far. Venoms are considered as interesting sources of novel biologically active compounds. Here, we describe an endocannabinoid-like molecule, oleoyl serotonin (OS), present in the venom of Stephanoconus snails. Using electrophysiological assays, it was shown that OS inhibits CB1 and CB2. Structure-activity relationship studies using a chimeric CB1/2 revealed that the domain encompassing the transmembrane helix V (TMHV)- intracellular loop 3 (ICL3)-TMHVI of the CB2 is critical for the binding and function of OS. We concluded that OS binds to sites of the CB2 that are different from the binding sites of the non-selective CB agonist WIN55,212-2. Behavioral assays in mice showed that OS counteracted learning and memory deficits caused by WIN55,212-2. Furthermore, a selectivity screening of OS showed high selectivity for CB over various ion channels and receptors. Overall, OS may represent a new approach to the prevention and treatment of learning and memory cognition impairment in neurological diseases.

Regulation of Inflammation by IRAK-M Pathway Can Be Associated with nAchRalpha7 Activation and COVID-19

In spite of the vaccine development and its importance, the SARS-CoV-2 pandemic is still impacting the world. It is known that the COVID-19 severity is related to the cytokine storm phenomenon, being inflammation a common disease feature. The nicotinic cholinergic system has been widely associated with COVID-19 since it plays a protective role in inflammation via nicotinic receptor alpha 7 (nAchRalpha7). In addition, SARS-CoV-2 spike protein (Spro) subunits can interact with nAchRalpha7. Moreover, Spro causes toll-like receptor (TLR) activation, leading to pro- and anti-inflammatory pathways. The increase and maturation of the IL-1 receptor-associated kinase (IRAK) family are mediated by activation of membrane receptors, such as TLRs. IRAK-M, a member of this family, is responsible for negatively regulating the activity of other active IRAKs. In addition, IRAK-M can regulate microglia phenotype by specific protein expression. Furthermore, there exists an antagonist influence of SARS-CoV-2 Spro and the cholinergic system action on the IRAK-M pathway and microglia phenotype. We discuss the overexpression and suppression of IRAK-M in inflammatory cell response to inflammation in SARS-CoV-2 infection when the cholinergic system is constantly activated via nAchRalpha7.

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.

Modulation of a rapid neurotransmitter receptor-ion channel by membrane lipids

Membrane lipids modulate the proteins embedded in the bilayer matrix by two non-exclusive mechanisms: direct or indirect. The latter comprise those effects mediated by the physicochemical state of the membrane bilayer, whereas direct modulation entails the more specific regulatory effects transduced via recognition sites on the target membrane protein. The nicotinic acetylcholine receptor (nAChR), the paradigm member of the pentameric ligand-gated ion channel (pLGIC) superfamily of rapid neurotransmitter receptors, is modulated by both mechanisms. Reciprocally, the nAChR protein exerts influence on its surrounding interstitial lipids. Folding, conformational equilibria, ligand binding, ion permeation, topography, and diffusion of the nAChR are modulated by membrane lipids. The knowledge gained from biophysical studies of this prototypic membrane protein can be applied to other neurotransmitter receptors and most other integral membrane proteins.

Nicotinic acetylcholine receptors in cancer: Limitations and prospects

Nicotinic acetylcholine receptors (nAChRs) have long been considered to solely mediate neurotransmission. However, their widespread distribution in the human body suggests a more diverse physiological role. Additionally, the expression of nAChRs is increased in certain cancers, such as lung cancer, and has been associated with cell proliferation, epithelial-to-mesenchymal cell transition, angiogenesis and apoptosis prevention. Several compounds that interact with these receptors have been identified as potential therapeutic agents. They have been tested as drugs for treating nicotine addiction, alcoholism, depression, pain and Alzheimer's disease. This review focuses on nAChR-mediated signalling in cancer, presenting opportunities for the development of innovative nAChR-based anticancer drugs. It displays the differences in expression of each nAChR subunit between normal and cancer cells for selected cancer types, highlighting their possible involvement in specific cases. Antagonists of nAChRs that could complement existing cancer therapies are summarised and critically discussed. We hope that this review will stimulate further research on the role of nAChRs in cancer potentially leading to innovative cancer therapies.

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.

Therapeutic Strategies Aimed at Improving Neuroplasticity in Alzheimer Disease

Alzheimer disease (AD) is the most prevalent form of dementia among elderly people. Owing to its varied and multicausal etiopathology, intervention strategies have been highly diverse. Despite ongoing advances in the field, efficient therapies to mitigate AD symptoms or delay their progression are still of limited scope. Neuroplasticity, in broad terms the ability of the brain to modify its structure in response to external stimulation or damage, has received growing attention as a possible therapeutic target, since the disruption of plastic mechanisms in the brain appear to correlate with various forms of cognitive impairment present in AD patients. Several pre-clinical and clinical studies have attempted to enhance neuroplasticity via different mechanisms, for example, regulating glucose or lipid metabolism, targeting the activity of neurotransmitter systems, or addressing neuroinflammation. In this review, we first describe several structural and functional aspects of neuroplasticity. We then focus on the current status of pharmacological approaches to AD stemming from clinical trials targeting neuroplastic mechanisms in AD patients. This is followed by an analysis of analogous pharmacological interventions in animal models, according to their mechanisms of action.

Analogs of 6-Bromohypaphorine with Increased Agonist Potency for α7 Nicotinic Receptor as Anti-Inflammatory Analgesic Agents

Hypaphorines, tryptophan derivatives, have anti-inflammatory activity, but their mechanism of action was largely unknown. Marine alkaloid L-6-bromohypaphorine with EC₅₀ of 80 μM acts as an agonist of α7 nicotinic acetylcholine receptor (nAChR) involved in anti-inflammatory regulation. We designed the 6-substituted hypaphorine analogs with increased potency using virtual screening of their binding to the α7 nAChR molecular model. Fourteen designed analogs were synthesized and tested in vitro by calcium fluorescence assay on the α7 nAChR expressed in neuro 2a cells, methoxy ester of D-6-iodohypaphorine (6ID) showing the highest potency (EC₅₀ 610 nM), being almost inactive toward α9α10 nAChR. The macrophages cytometry revealed an anti-inflammatory activity, decreasing the expression of TLR4 and increasing CD86, similarly to the action of PNU282987, a selective α7 nAChR agonist. 6ID administration in doses 0.1 and 0.5 mg/kg decreased carrageenan-induced allodynia and hyperalgesia in rodents, in accord with its anti-inflammatory action. Methoxy ester of D-6-nitrohypaphorine demonstrated anti-oedemic and analgesic effects in arthritis rat model at i.p. doses 0.05-0.26 mg/kg. Tested compounds showed excellent tolerability with no acute in vivo toxicity in dosages up to 100 mg/kg i.p. Thus, combining molecular modelling and natural product-inspired drug design improved the desired activity of the chosen nAChR ligand.

Deletion induced splicing in RIC3 drives nicotinic acetylcholine receptor regulation with implications for endoplasmic reticulum stress in human astrocytes

Nicotinic acetylcholine receptor (nAChR) dysregulation in astrocytes is reported in neurodegenerative disorders. Modulation of nAChRs through agonists confers protection to astrocytes from stress but regulation of chaperones involved in proteostasis with pathological implications is unclear. Resistance to inhibitors of cholinesterase 3 (RIC3), a potential chaperone of nAChRs is poorly studied in humans. We characterized RIC3 in astrocytes derived from an isogenic wild-type and Cas9 edited "del" human iPSC line harboring a 25 bp homozygous deletion in exon2. Altered RIC3 transcript ratio due to deletion induced splicing and an unexpected gain of α7nAChR expression were observed in "del" astrocytes. Transcriptome analysis showed higher expression of neurotransmitter/G-protein coupled receptors mediated by cAMP and calcium/calmodulin-dependent kinase signaling with increased cytokines/glutamate secretion. Functional implications examined using tunicamycin induced ER stress in wild-type astrocyte stress model showed cell cycle arrest, RIC3 upregulation, reduction in α7nAChR membrane levels but increased α4nAChR membrane expression. Conversely, tunicamycin-treated "del" astrocytes showed a comparatively higher α4nAChR membrane expression and upsurged cAMP signaling. Furthermore, reduced expression of stress markers CHOP, phospho-PERK and lowered XBP1 splicing in western blot and qPCR, validated by proteome-based pathway analysis indicated lowered disease severity. Findings indicate (i) a complex RNA regulatory mechanism via exonic deletion induced splicing; (ii) RIC-3 as a disordered protein having contrasting effects on co-expressed nAChR subtypes under basal/stress conditions; and (iii) RIC3 as a potential drug target against ER stress in astrocytes for neurodegenerative/nicotine-related brain disorders. Cellular rescue mechanism through deletion induced exon skipping may encourage ASO-based therapies for tauopathies.

Synthesis and Antagonist Activity of Methyllycaconitine Analogues on Human α7 Nicotinic Acetylcholine Receptors

Methyllycaconitine (MLA), 1, is a naturally occurring norditerpenoid alkaloid that is a highly potent (IC₅₀ = 2 nM) selective antagonist of α7 nicotinic acetylcholine receptors (nAChRs). Several structural factors affect its activity such as the neopentyl ester side-chain and the piperidine ring N-side-chain. The synthesis of simplified AE-bicyclic analogues 14-21 possessing different ester and nitrogen side-chains was achieved in three steps. The antagonist effects of synthetic analogues were examined on human α7 nAChRs and compared to that of MLA 1. The most efficacious analogue (16) reduced α7 nAChR agonist responses [1 nM acetylcholine (ACh)] to 53.2 ± 1.9% compared to 3.4 ± 0.2% for MLA 1. This demonstrates that simpler analogues of MLA 1 possess antagonist effects on human α7 nAChRs but also indicates that further optimization may be possible to achieve antagonist activity comparable to that of MLA 1.

Structure and function meet at the nicotinic acetylcholine receptor-lipid interface

The nicotinic acetylcholine receptor (nAChR) is a transmembrane protein that mediates fast intercellular communication in response to the endogenous neurotransmitter acetylcholine. It is the best characterized and archetypal molecule in the superfamily of pentameric ligand-gated ion channels (pLGICs). As a typical transmembrane macromolecule, it interacts extensively with its vicinal lipid microenvironment. Experimental evidence provides a wealth of information on receptor-lipid crosstalk: the nAChR exerts influence on its immediate membrane environment and conversely, the lipid moiety modulates ligand binding, affinity state transitions and gating of ion translocation functions of the receptor protein. Recent cryogenic electron microscopy (cryo-EM) studies have unveiled the occurrence of sites for phospholipids and cholesterol on the lipid-exposed regions of neuronal and electroplax nAChRs, confirming early spectroscopic and affinity labeling studies demonstrating the close contact of lipid molecules with the receptor transmembrane segments. This new data provides structural support to the postulated "lipid sensor" ability displayed by the outer ring of M4 transmembrane domains and their modulatory role on nAChR function, as we postulated a decade ago. Borrowing from the best characterized nAChR, the electroplax (muscle-type) receptor, and exploiting new structural information on the neuronal nAChR, it is now possible to achieve an improved depiction of these sites. In combination with site-directed mutagenesis, single-channel electrophysiology, and molecular dynamics studies, the new structural information delivers a more comprehensive portrayal of these lipid-sensitive loci, providing mechanistic explanations for their ability to modulate nAChR properties and raising the possibility of targetting them in disease.

Cyclodextrin-Based Nanoparticles for Delivery of Antisense Oligonucleotides Targeting Huntingtin

Huntington's disease (HD) is a progressive inherited neurodegenerative disease caused by a CAG repeat expansion in the huntingtin gene, which is translated into the pathologic mutant huntingtin (mHTT) protein. Despite the great potential of HTT lowering strategies and the numerous antisense oligonucleotides (ASOs) in pre- and clinical trials, sustained silencing of mHTT has not been achieved. As a strategy to improve ASO delivery, cyclodextrin-based nanoparticles (CDs) offer a promising approach. Here, three CDs with distinct chemical structures were designed and their efficacies were compared as potential platforms for the delivery of ASO targeting HTT. Results using striatal neurons and HD patient-derived fibroblasts indicate that modified γ-CDs exhibited the best uptake efficiency and successfully downregulated mHTT at protein and allele levels. The incorporation of the brain-targeting peptide RVG into the modified γ-CDs showed greater downregulation of mHTT protein and HD-causing allele SNP1 than untargeted ones in an in vitro blood-brain barrier model. Although the ASO sequence was designed as a nonallele-specific therapeutic approach, our strategy gives an additional benefit of some mHTT selectivity. Overall, this study demonstrated the CD platform's feasibility for delivering ASO-based therapeutics for HD treatment.

Central α7 and α4β2 nicotinic acetylcholine receptors offset arterial baroreceptor dysfunction in endotoxic rats

Cardiac autonomic neuropathy is a prominent feature of endotoxemia. Given the defensive role of the cholinergic pathway in inflammation, we assessed the roles of central homomeric α7 and heteromeric α4β2 nAChRs in arterial baroreceptor dysfunction caused by endotoxemia in rats. Endotoxemia was induced by i.v. administration of lipopolysaccharides (LPS, 10 mg/kg), and baroreflex activity was measured by the vasoactive method, which assesses reflex chronotropic responses to increments (phenylephrine, PE) or decrements (sodium nitroprusside, SNP) in blood pressure. Shifts caused by LPS in PE/SNP baroreflex curves and associated decreases in baroreflex sensitivity (BRS) were dose-dependently reversed by nicotine (25-100 μg/kg, i.v.). The nicotine effect disappeared after intracisternal administration of methyllycaconitine (MLA) or dihydro-β-erythroidine (DHβE), selective blockers of α7 and α4β2 receptors, respectively. The advantageous effect of nicotine on BRSPE was replicated in rats treated with PHA-543613 (α7-nAChR agonist) or 5-iodo-A-85380 (5IA, α4β2-nAChRs agonist) in dose-dependent fashions. Conversely, the depressed BRSSNP of endotoxic rats was improved after combined, but not individual, treatments with PHA and 5IA. Central α7 and α4β2 nAChR activation underlies the nicotine counteraction of arterial baroreflex dysfunction induced by endotoxemia. Moreover, the contribution of these receptors depends on the nature of the reflex chronotropic response (bradycardia vs. tachycardia).

Effects of cannabinoids on ligand-gated ion channels

Phytocannabinoids such as Δ⁹-tetrahydrocannabinol and cannabidiol, endocannabinoids such as N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol, and synthetic cannabinoids such as CP47,497 and JWH-018 constitute major groups of structurally diverse cannabinoids. Along with these cannabinoids, CB1 and CB2 cannabinoid receptors and enzymes involved in synthesis and degradation of endocannabinoids comprise the major components of the cannabinoid system. Although, cannabinoid receptors are known to be involved in anti-convulsant, anti-nociceptive, anti-psychotic, anti-emetic, and anti-oxidant effects of cannabinoids, in recent years, an increasing number of studies suggest that, at pharmacologically relevant concentrations, these compounds interact with several molecular targets including G-protein coupled receptors, ion channels, and enzymes in a cannabinoid-receptor independent manner. In this report, the direct actions of endo-, phyto-, and synthetic cannabinoids on the functional properties of ligand-gated ion channels and the plausible mechanisms mediating these effects were reviewed and discussed.

Predictors of response to acetylcholinesterase inhibitors in dementia: A systematic review

Background

The mainstay of therapy for many neurodegenerative dementias still relies on acetylcholinesterase inhibitors (AChEI); however, there is debate on various aspects of such treatment. A huge body of literature exists on possible predictors of response, but a comprehensive review is lacking. Therefore, our aim is to perform a systematic review of the predictors of response to AChEI in neurodegenerative dementias, providing a categorization and interpretation of the results.

Methods

We conducted a systematic review of the literature up to December 31st, 2021, searching five different databases and registers, including studies on rivastigmine, donepezil, and galantamine, with clearly defined criteria for the diagnosis of dementia and the response to AChEI therapy. Records were identified through the string: predict * AND respon * AND (acetylcholinesterase inhibitors OR donepezil OR rivastigmine OR galantamine). The results were presented narratively.

Results

We identified 1,994 records in five different databases; after exclusion of duplicates, title and abstract screening, and full-text retrieval, 122 studies were finally included.

Discussion

The studies show high heterogeneity in duration, response definition, drug dosage, and diagnostic criteria. Response to AChEI seems associated with correlates of cholinergic deficit (hallucinations, fluctuating cognition, substantia innominate atrophy) and preserved cholinergic neurons (faster alpha on REM sleep EEG, increased anterior frontal and parietal lobe perfusion after donepezil); white matter hyperintensities in the cholinergic pathways have shown inconsistent results. The K-variant of butyrylcholinesterase may correlate with better response in late stages of disease, while the role of polymorphisms in other genes involved in the cholinergic system is controversial. Factors related to drug availability may influence response; in particular, low serum albumin (for donepezil), CYP2D6 variants associated with reduced enzymatic activity and higher drug doses are the most consistent predictors, while AChEI concentration influence on clinical outcomes is debatable. Other predictors of response include faster disease progression, lower serum cholesterol, preserved medial temporal lobes, apathy, absence of concomitant diseases, and absence of antipsychotics. Short-term response may predict subsequent cognitive response, while higher education might correlate with short-term good response (months), and long-term poor response (years). Age, gender, baseline cognitive and functional levels, and APOE relationship with treatment outcome is controversial.

Speculation on How RIC-3 and Other Chaperones Facilitate α7 Nicotinic Receptor Folding and Assembly

The process of how multimeric transmembrane proteins fold and assemble in the endoplasmic reticulum is not well understood. The alpha7 nicotinic receptor (α7 nAChR) is a good model for multimeric protein assembly since it has at least two independent and specialized chaperones: Resistance to Inhibitors of Cholinesterase 3 (RIC-3) and Nicotinic Acetylcholine Receptor Regulator (NACHO). Recent cryo-EM and NMR data revealed structural features of α7 nAChRs. A ser-ala-pro (SAP) motif precedes a structurally important but unique "latch" helix in α7 nAChRs. A sampling of α7 sequences suggests the SAP motif is conserved from C. elegans to humans, but the latch sequence is only conserved in vertebrates. How RIC-3 and NACHO facilitate receptor subunits folding into their final pentameric configuration is not known. The artificial intelligence program AlphaFold2 recently predicted structures for NACHO and RIC-3. NACHO is highly conserved in sequence and structure across species, but RIC-3 is not. This review ponders how different intrinsically disordered RIC-3 isoforms from C. elegans to humans interact with α7 nAChR subunits despite having little sequence homology across RIC-3 species. Two models from the literature about how RIC-3 assists α7 nAChR assembly are evaluated considering recent structural information about the receptor and its chaperones.

α9-Containing Nicotinic Receptors in Cancer

Neuronal nicotinic acetylcholine receptors containing the α9 or the α9 and α10 subunits are expressed in various extra-neuronal tissues. Moreover, most cancer cells and tissues highly express α9-containing receptors, and a number of studies have shown that they are powerful regulators of responses that stimulate cancer processes such as proliferation, inhibition of apoptosis, and metastasis. It has also emerged that their modulation is a promising target for drug development. The aim of this review is to summarize recent data showing the involvement of these receptors in controlling the downstream signaling cascades involved in the promotion of cancer.