Increased alpha 7 nicotinic acetylcholine receptor protein levels in Alzheimer's disease patients

Role of Alpha-7-Nicotinic Acetylcholine Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder affecting millions worldwide. One of the leading hypotheses for the underlying cause of AD is a reduction in nicotinic receptor levels in the brain. Among the nicotinic receptors, the alpha-7-nicotinic acetylcholine receptor (α7nAChR) has received particular attention due to its involvement in cognitive function.α7nAChR is a ligand-gated ion channel that is primarily found in the hippocampus and prefrontal cortex, areas of the brain responsible for learning, memory, and attention. Studies have shown that α7nAChR dysfunction is a key contributor to the pathogenesis of AD. The receptor is involved in regulating amyloidbeta (Aβ) production, a hallmark of AD pathology. Many drugs have been investigated as α7nAChR agonists or allosteric modulators to improve cognitive deficits in AD. Clinical studies have shown promising results with α7nAChR agonists, including improved memory and cognitive function. Although several studies have shown the significance of the α7 nAChR in AD, little is known about its function in AD pathogenesis. As a result, in this review, we have outlined the basic information of the α7 nAChR's structure, functions, cellular responses to its activation, and its role in AD's pathogenesis.

The role of astrocytic α7 nicotinic acetylcholine receptors in Alzheimer disease

The ongoing search for therapeutic interventions in Alzheimer disease (AD) has highlighted the complexity of this condition and the need for additional biomarkers, beyond amyloid-β (Aβ) and tau, to improve clinical assessment. Astrocytes are brain cells that control metabolic and redox homeostasis, among other functions, and are emerging as an important focus of AD research owing to their swift response to brain pathology in the initial stages of the disease. Reactive astrogliosis - the morphological, molecular and functional transformation of astrocytes during disease - has been implicated in AD progression, and the definition of new astrocytic biomarkers could help to deepen our understanding of reactive astrogliosis along the AD continuum. As we highlight in this Review, one promising biomarker candidate is the astrocytic α7 nicotinic acetylcholine receptor (α7nAChR), upregulation of which correlates with Aβ pathology in the brain of individuals with AD. We revisit the past two decades of research into astrocytic α7nAChRs to shed light on their roles in the context of AD pathology and biomarkers. We discuss the involvement of astrocytic α7nAChRs in the instigation and potentiation of early Aβ pathology and explore their potential as a target for future reactive astrocyte-based therapeutics and imaging biomarkers in AD.

Acetylcholinesterase inhibitors targeting the cholinergic anti-inflammatory pathway: a new therapeutic perspective in aging-related disorders

Neuroinflammation and cholinergic dysfunction, leading to cognitive impairment, are hallmarks of aging and neurodegenerative disorders, including Alzheimer's disease (AD). Acetylcholinesterase inhibitors (AChEI), the symptomatic therapy in AD, attenuate and delay the cognitive deficit by enhancing cholinergic synapses. The α7 nicotinic acetylcholine (ACh) receptor has shown a double-edged sword feature, as it binds with high affinity Aβ_1-42, promoting intracellular accumulation and Aβ-induced tau phosphorylation, but also exerts neuroprotection by stimulating anti-apoptotic pathways. Moreover, it mediates peripheral and central anti-inflammatory response, being the effector player of the activation of the cholinergic anti-inflammatory pathway (CAIP), that, by decreasing the release of TNF-α, IL-1β, and IL-6, it may have a role in improving cognition. The finding in preclinical models that, in addition to their major function (choline esterase inhibition) AChEIs have neuroprotective properties mediated via α7nAChR and modulate innate immunity, possibly as a result of the increased availability of acetylcholine activating the CAIP, pave the way for new pharmacological intervention in AD and other neurological disorders that are characterized by neuroinflammation. CHRFAM7A is a human-specific gene acting as a dominant negative inhibitor of α7nAChR function, also suggesting a role in affecting human cognition and memory by altering α7nAChR activities in the central nervous system (CNS). This review will summarize the current knowledge on the cholinergic anti-inflammatory pathway in aging-related disorders, and will argue that the presence of the human-restricted CHRFAM7A gene might play a fundamental role in the regulation of CAIP and in the response to AChEI.

The Cholinergic System, the Adrenergic System and the Neuropathology of Alzheimer's Disease

Neurodegenerative diseases are a major public health problem worldwide with a wide spectrum of symptoms and physiological effects. It has been long reported that the dysregulation of the cholinergic system and the adrenergic system are linked to the etiology of Alzheimer’s disease. Cholinergic neurons are widely distributed in brain regions that play a role in cognitive functions and normal cholinergic signaling related to learning and memory is dependent on acetylcholine. The Locus Coeruleus norepinephrine (LC-NE) is the main noradrenergic nucleus that projects and supplies norepinephrine to different brain regions. Norepinephrine has been shown to be neuroprotective against neurodegeneration and plays a role in behavior and cognition. Cholinergic and adrenergic signaling are dysregulated in Alzheimer’s disease. The degeneration of cholinergic neurons in nucleus basalis of Meynert in the basal forebrain and the degeneration of LC-NE neurons were reported in Alzheimer’s disease. The aim of this review is to describe current literature on the role of the cholinergic system and the adrenergic system (LC-NE) in the pathology of Alzheimer’s disease and potential therapeutic implications.

Crosstalk between the M1 muscarinic acetylcholine receptor and the endocannabinoid system: A relevance for Alzheimer's disease?

Alzheimer's disease (AD) is a neurodegenerative disorder which accounts for 60-70% of the 50 million worldwide cases of dementia and is characterised by cognitive impairments, many of which have long been associated with dysfunction of the cholinergic system. Although the M1 muscarinic acetylcholine receptor (mAChR) is considered a promising drug target for AD, ligands targeting this receptor have so far been unsuccessful in clinical trials. As modulatory receptors to cholinergic transmission, the endocannabinoid system may be a promising drug target to allow fine tuning of the cholinergic system. Furthermore, disease-related changes have been found in the endocannabinoid system during AD progression and indeed targeting the endocannabinoid system at specific disease stages alleviates cognitive symptoms in numerous mouse models of AD. Here we review the role of the endocannabinoid system in AD, and its crosstalk with mAChRs as a potential drug target for cholinergic dysfunction.

Nicotinic Acetylcholine Receptor Agonists for the Treatment of Alzheimer's Dementia: An Update

A significant portion of the clinical phenotype observed in Alzheimer's disease (AD) occurs through nicotinic acetylcholine receptors (nAChRs). Degeneration of cholinergic neurons, combined with aberrant nAChR expression and activation partially through amyloid-beta peptide (Aβ)-nAChR leads to upregulation of pro-inflammatory pathways and subsequently the progressive cognitive decline of AD. Interestingly, the cholinergic anti-inflammatory pathway is also mediated through nAChR particularly α7 nAChR. Thus, agonists of these receptors will likely exert pro-cognitive benefits through multiple mechanisms including stimulating the cholinergic pathway, modulating inflammation, and buffering the effects of amyloid. Despite this promising theoretical use, trials thus far have been complicated by adverse effects or minimal improvement. This review will provide an update on several pharmacological nAChR agonists tested in clinical trials and reasons that further investigation of nAChR agonists is merited.

IMPLICATIONS

nAChRs have consistently presented a promising theoretical use in the treatment of AD; however, trials thus far have been complicated by adverse effects or minimal improvement. This review will provide an update on several pharmacological nAChR agonists trialed and reasons that further investigation of nAChR agonists is merited.

Multivariate Platelet Analysis Differentiates Between Patients with Alzheimer's Disease and Healthy Controls at First Clinical Diagnosis

BACKGROUND

Early diagnosis of Alzheimer's disease (AD) is challenging, and easily accessible biomarkers are an unmet need. Blood platelets frequently serve as peripheral model for studying AD pathogenesis and might represent a reasonable biomarker source.

OBJECTIVE

In the present study, we investigated the potential to differentiate AD patients from healthy controls (HC) based on blood count, platelet morphology, and function as well as molecular markers at the time of first clinical diagnosis.

METHODS

Blood samples from 40 AD patients and 29 age-matched HC were included for determination of 78 parameter by blood counting, platelet morphometry, aggregometry, flow cytometry (CD62P, CD63, activated fibrinogen receptor), protein quantification of nicotinic acetylcholine receptor α7 (nAChRα7) and caveolin-1 (CAV-1), and miRNA quantification (miR-26b, miR-199a, miR-335). Group comparison between patients and controls was performed in univariate and multivariate statistical analyses.

RESULTS

AD patients showed significantly lower aggregation response to ADP and arachidonic acid and significantly decreased CD62P and CD63 surface expression induced by ADP and U46619 compared to HC. Relative nAChRα7 and CAV-1 expression was significantly higher AD platelets than in HC. Multivariate analysis of 63 parameter revealed significant differences between AD patients and healthy controls. The best performing feature model revealed a sensitivity of 96.6%, a specificity of 80.0%, and a positive predictive value of 89.3%. No grouping could be achieved by using single parameter groups.

CONCLUSION

Significant differences between platelet characteristics from AD patients and HC at the time of first clinical diagnosis were observed. The best performing parameter can be used as a blood-based biomarker for AD diagnosis in a multivariate model in addition to the standardized mental tests.

Increased Aβ42-α7-like nicotinic acetylcholine receptor complex level in lymphocytes is associated with apolipoprotein E4-driven Alzheimer's disease pathogenesis

BACKGROUND

The apolipoprotein E ε4 (APOE4) genotype is a prominent late-onset Alzheimer's disease (AD) risk factor. ApoE4 disrupts memory function in rodents and may contribute to both plaque and tangle formation.

METHODS

Coimmunoprecipitation and Western blot detection were used to determine: 1) the effects of select fragments from the apoE low-density lipoprotein (LDL) binding domain and recombinant apoE subtypes on amyloid beta (Aβ)₄₂-α7 nicotinic acetylcholine receptor (α7nAChR) interaction and tau phosphorylation in rodent brain synaptosomes; and 2) the level of Aβ₄₂-α7nAChR complexes in matched controls and patients with mild cognitive impairment (MCI) and dementia due to AD with known APOE genotypes.

RESULTS

In an ex vivo study using rodent synaptosomes, apoE_141-148 of the apoE promotes Aβ₄₂-α7nAChR association and Aβ₄₂-induced α7nAChR-dependent tau phosphorylation. In a single-blind study, we examined lymphocytes isolated from control subjects, patients with MCI and dementia due to AD with known APOE genotypes, sampled at two time points (1 year apart). APOE ε4 genotype was closely correlated with heightened Aβ₄₂-α7nAChR complex levels and with blunted exogenous Aβ₄₂ effects in lymphocytes derived from AD and MCI due to AD cases. Similarly, plasma from APOE ε4 carriers enhanced the Aβ₄₂-induced Aβ₄₂-α7nAChR association in rat cortical synaptosomes. The progression of cognitive decline in APOE ε4 carriers correlated with higher levels of Aβ₄₂-α7nAChR complexes in lymphocytes and greater enhancement by their plasma of Aβ₄₂-induced Aβ₄₂-α7nAChR association in rat cortical synaptosomes.

CONCLUSIONS

Our data suggest that increased lymphocyte Aβ₄₂-α7nAChR-like complexes may indicate the presence of AD pathology especially in APOE ε4 carriers. We show that apoE, especially apoE4, promotes Aβ₄₂-α7nAChR interaction and Aβ₄₂-induced α7nAChR-dependent tau phosphorylation via its apoE_141-148 domain_. These apoE-mediated effects may contribute to the APOE ε4-driven neurodysfunction and AD pathologies.

Retinal changes in the Tg-SwDI mouse model of Alzheimer's disease

Alzheimer's disease (AD), a debilitating neurodegenerative illness, is characterized by neuronal cell loss, mental deficits, and abnormalities in several neurotransmitter and protein systems. AD is also associated with visual disturbances, but their causes remain unidentified. We hypothesize that the visual disturbances stem from retinal changes, particularly changes in the retinal cholinergic system, and that the etiology in the retina parallels the etiology in the rest of the brain. To test our hypothesis, quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) were employed to assess changes in acetylcholine receptor (AChR) gene expression, number of retinal cells, and astrocytic gliosis in the Transgenic Swedish, Dutch and Iowa (Tg-SwDI) mouse model as compared to age-matched wild-type (WT). We observed that Tg-SwDI mice showed an initial upregulation of AChR gene expression early on (young adults and middle-aged adults), but a downregulation later on (old adults). Furthermore, transgenic animals displayed significant cell loss in the photoreceptor layer and inner retina of the young adult animals, as well as specific cholinergic cell loss, and increased astrocytic gliosis in the middle-aged adult and old adult groups. Our results suggest that the changes observed in AD cerebrum are also present in the retina and may be, at least in part, responsible for the visual deficits associated with the disease.

Alpha-7 nicotinic agonists for cognitive deficits in neuropsychiatric disorders: A translational meta-analysis of rodent and human studies

Cognitive dysfunction in schizophrenia (SCZ) and Alzheimer's disease (AD) is a major driver of functional disability but is largely unresponsive to current therapeutics. Animal models of cognitive dysfunction relevant to both disorders suggest the α7 nicotinic acetylcholine receptor (nAChR) may be a promising drug development target, with multiple clinical trials subsequently testing this hypothesis in individuals with SCZ and AD. However, the translational value of rodent cognitive tasks for predicting the overall efficacy of this therapeutic target in clinical trials is unknown. To compare effect sizes between rodent and human studies, we searched PubMed and the Cochrane Library for all randomized, placebo-controlled trials of compounds with pharmacological activity at the α7 nAChR for treatment of cognitive dysfunction in SCZ and AD and identified 18 studies comprising 2670 subjects treated with eight different compounds acting as full or partial agonists. Cognitive outcomes were standardized, and random-effects meta-analyses revealed no statistically significant effects of α7 nAChR agonists on overall cognition or any of eight cognitive subdomains when all doses were included (Range of all cognitive outcomes: Cohen's d=-0.077 to 0.12, negative favoring drug). In contrast, analysis of 29 rodent studies testing the same α7 agonists revealed large effect sizes in multiple commonly used preclinical behavioral tests of cognition (Range: d=-1.18 to - 0.73). Our results suggest that targeting the α7 nAChR with agonists is not a robust treatment for cognitive dysfunction in SCZ or AD and necessitate a better understanding of the translational gap for therapeutics targeting the α7 nAChR.

Genetic Polymorphisms in Estrogen Metabolic Pathway Associated with Risks of Alzheimer's Disease: Evidence from a Southern Chinese Population

OBJECTIVES

To investigate whether genetic variations on the estrogen metabolic pathway would be associated with risk of Alzheimer's disease (AD).

DESIGN

Cross-sectional study.

SETTING

Individuals were recruited at the Memory Clinic, Queen Mary Hospital, Hong Kong.

PARTICIPANTS

Chinese individuals with (n = 426) and without (n = 350) AD.

MEASUREMENTS

All subjects underwent a standardized cognitive assessment and genotyping of four candidate genes on the estrogen metabolic pathway (estrogen receptor α gene (ESR1), estrogen receptor β gene (ESR2), cytochrome P450 19A1 gene (CYP19A1), cytochrome P450 11A1 gene (CYP11A1)).

RESULTS

Apart from consistent results showing an association between apolipoprotein (APO)E and AD, strong evidence of disease associations were found for polymorphisms in ESR2 and CYP11A1 based on the entire data set. For ESR2, significant protective effects were found for A alleles of rs4986938 (permuted P = .02) and rs867443 (permuted P = .02). For CYP11A1, significant risk effects were found for G alleles of rs11638442 (permuted P = .03) and rs11632698 (permuted P = .03). Stratifying subjects according to APOE ε4 status, their genetic effects continued to be significant in the APOE ε4-negative subgroup. Associations between CYP11A1 polymorphisms (rs2279357, rs2073475) and risk of AD were detected in women but not men. Further gene-level analysis confirmed the above association between ESR2 and CYP11A1, and pathway-level analysis highlighted the genetic effect of the estrogen metabolic pathway on disease susceptibility (permuted pathway-level P = .03).

CONCLUSION

Consistent with previous biological findings for sex steroid hormones in the central nervous system, genetic alterations on the estrogen metabolic pathway were revealed in the Chinese population. Confirmation of these present findings in an independent population is warranted to elucidate disease pathogenesis and to explore the potential of hormone therapy in the treatment of AD.

Donepezil modulates the endogenous immune response: implications for Alzheimer's disease

OBJECTIVE

Donepezil (DNPZ) is a drug commonly used for Alzheimer's disease (AD) that may favour a T helper 2 phenotype leading to increased naturally occurring auto-antibodies (NAb) against beta-amyloid (Aβ). We hypothesized the involvement of the cholinergic receptors [α7-nicotnic acetylcholine receptor (α7nAChR)] expressed on peripheral blood mononuclear cells (PBMC).

METHODS

Fifty patients with mild-to-moderate AD, DNPZ treated (DNPZ+, n = 25) or not (DNPZ-, n = 25), and 25 matched controls were enrolled and PBMC extracted for both in vitro cultures, and real-time polymerase chain reaction and chromatin immunoprecipitation assay. Plasma samples were also obtained for Aβ and NAb determination.

RESULTS

Donepezil increased in vitro the expression of the transcription factor GATA binding protein 3 (GATA3) through α7nAChR, because prevented by the specific antagonist methyllycaconitine. Ex vivo PBMC α7nAChR mRNA expression was increased in both AD groups, while GATA3 expression was not. A significant increase in the GATA3/interleukin 5 promoter association was found in DNPZ+ patients. Finally, DNPZ+ patients showed both significantly higher plasma levels of anti-Aβ NAb with respect to DNPZ- patients and Aβ 1-42 with respect to normal controls.

CONCLUSIONS

Donepezil might modulate a T helper 2 bias via α7nAChR leading to increased expression of NAb. Further studies on the role of the modulation of the immune response against Aβ may pave the way to innovative therapeutic strategies for AD. Copyright © 2016 John Wiley & Sons, Ltd.

(I) Pharmacological profiling of a novel modulator of the α7 nicotinic receptor: Blockade of a toxic acetylcholinesterase-derived peptide increased in Alzheimer brains

The primary cause of Alzheimer's disease is unlikely to be the much studied markers amyloid beta or tau. Their widespread distribution throughout the brain does not account for the specific identity and deep subcortical location of the primarily vulnerable neurons. Moreover an unusual and intriguing feature of these neurons is that, despite their diverse transmitters, they all contain acetylcholinesterase. Here we show for the first time that (1) a peptide derived from acetylcholinesterase, with independent trophic functions that turn toxic in maturity, is significantly raised in the Alzheimer midbrain and cerebrospinal fluid; (2) a synthetic version of this peptide enhances calcium influx and eventual production of amyloid beta and tau phosphorylation via an allosteric site on the α7 nicotinic receptor; (3) a synthetic cyclic version of this peptide is neuroprotective against the toxicity not only of its linear counterpart but also of amyloid beta, thereby opening up the prospect of a novel therapeutic approach.

Nicotinic ACh receptors as therapeutic targets in CNS disorders

The neurotransmitter acetylcholine (ACh) can regulate neuronal excitability by acting on the cys-loop cation-conducting ligand-gated nicotinic ACh receptor (nAChR) channels. These receptors are widely distributed throughout the central nervous system (CNS), being expressed on neurons and non-neuronal cells, where they participate in a variety of physiological responses such as anxiety, the central processing of pain, food intake, nicotine seeking behavior, and cognitive functions. In the mammalian brain, nine different subunits have been found thus far, which assemble into pentameric complexes with much subunit diversity; however, the α7 and α4β2 subtypes predominate in the CNS. Neuronal nAChR dysfunction is involved in the pathophysiology of many neurological disorders. Here we will briefly discuss the functional makeup and expression of the nAChRs in mammalian brain, and their role as targets in neurodegenerative diseases (in particular Alzheimer's disease, AD), neurodevelopmental disorders (in particular autism and schizophrenia), and neuropathic pain.

Phase II crossover trial of varenicline in mild-to-moderate Alzheimer's disease

BACKGROUND

Evidence supports a role of α4β2 receptors in Alzheimer's disease (AD).

METHODS

This Korean, multicenter, double-blind, two-period (6 weeks each), crossover study randomized participants to the order in which they received varenicline (1 mg twice daily) and placebo. Assessments included AD Assessment Scale-Cognitive Subscale (ADAS-Cog) 75, Neuropsychiatric Inventory (NPI), adverse events (AEs) and Columbia-Suicide Severity Rating Scale (C-SSRS).

RESULTS

For varenicline versus placebo (n = 66 randomized), there was no significant difference in the week 6 least square (LS) mean ADAS-Cog 75 total score (primary endpoint; 18.07 vs. 18.49; p = 0.3873) and a slight worsening in the week 6 LS mean NPI (3.82 vs. 2.55; p = 0.0468), primarily driven by decreased appetite/eating. Common treatment-related AEs were nausea (23.3; 3.4%), vomiting (15.0%; 0) and decreased appetite (15.0; 6.8%).

CONCLUSIONS

Varenicline did not improve cognition, behavior or global change in this population. The most frequent varenicline-associated AEs were gastrointestinal; psychiatric AEs were rare and similar between the groups.

A novel nicotinic mechanism underlies β-amyloid-induced neuronal hyperexcitation

There is a significantly elevated incidence of epilepsy in Alzheimer's disease (AD). Moreover, there is neural hyperexcitation/synchronization in transgenic mice expressing abnormal levels or forms of amyloid precursor protein and its presumed, etiopathogenic product, amyloid-β1-42 (Aβ). However, the underlying mechanisms of how Aβ causes neuronal hyperexcitation remain unclear. Here, we report that exposure to pathologically relevant levels of Aβ induces Aβ form-dependent, concentration-dependent, and time-dependent neuronal hyperexcitation in primary cultures of mouse hippocampal neurons. Similarly, Aβ exposure increases levels of nicotinic acetylcholine receptor (nAChR) α7 subunit protein on the cell surface and α7-nAChR function, but not α7 subunit mRNA, suggesting post-translational upregulation of functional α7-nAChRs. These effects are prevented upon coexposure to brefeldin A, an inhibitor of endoplasmic reticulum-to-Golgi protein transport, consistent with an effect on trafficking of α7 subunits and assembled α7-nAChRs to the cell surface. Aβ exposure-induced α7-nAChR functional upregulation occurs before there is expression of neuronal hyperexcitation. Pharmacological inhibition using an α7-nAChR antagonist or genetic deletion of nAChR α7 subunits prevents induction and expression of neuronal hyperexcitation. Collectively, these results, confirmed in studies using slice cultures, indicate that functional activity and perhaps functional upregulation of α7-nAChRs are necessary for production of Aβ-induced neuronal hyperexcitation and possibly AD pathogenesis. This novel mechanism involving α7-nAChRs in mediation of Aβ effects provides potentially new therapeutic targets for treatment of AD.

Optimizing cholinergic tone through lynx modulators of nicotinic receptors: implications for plasticity and nicotine addiction

The cholinergic system underlies both adaptive (learning and memory) and nonadaptive (addiction and dependency) behavioral changes through its ability to shape and regulate plasticity. Protein modulators such as lynx family members can fine tune the activity of the cholinergic system and contribute to the graded response of the cholinergic system, stabilizing neural circuitry through direct interaction with nicotinic receptors. Release of this molecular brake can unmask cholinergic-dependent mechanisms in the brain. Lynx proteins have the potential to provide top-down control over plasticity mechanisms, including addictive propensity. If this is indeed the case, then, what regulates the regulator? Transcriptional changes of lynx genes in response to pharmacological, physiological, and pathological alterations are explored in this review.

Alpha7 nicotinic acetylcholine receptor is a target in pharmacology and toxicology

Alpha7 nicotinic acetylcholine receptor (α7 nAChR) is an important part of the cholinergic nerve system in the brain. Moreover, it is associated with a cholinergic anti-inflammatory pathway in the termination of the parasympathetic nervous system. Antagonists of α7 nAChR are a wide group represented by conotoxin and bungarotoxin. Even Alzheimer's disease drug memantine acting as an antagonist in its side pathway belongs in this group. Agonists of α7 nAChR are suitable for treatment of multiple cognitive dysfunctions such as Alzheimer's disease or schizophrenia. Inflammation or even sepsis can be ameliorated by the agonistic acting compounds. Preparations RG3487, SEN34625/WYE-103914, SEN12333, ABT-107, Clozapine, GTS-21, CNI-1493, and AR-R17779 are representative examples of the novel compounds with affinity toward the α7 nAChR. Pharmacological, toxicological, and medicinal significance of α7 nAChR are discussed throughout this paper.

Upregulation of alpha7 Nicotinic Receptors by Acetylcholinesterase C-Terminal Peptides

Background

The alpha-7 nicotinic acetylcholine receptor (α7-nAChR) is well known as a potent calcium ionophore that, in the brain, has been implicated in excitotoxicity and hence in the underlying mechanisms of neurodegenerative disorders such as Alzheimer's disease. Previous research implied that the activity of this receptor may be modified by exposure to a peptide fragment derived from the C-terminal region of the enzyme acetylcholinesterase. This investigation was undertaken to determine if the functional changes observed could be attributed to peptide binding interaction with the α7-nAChR, or peptide modulation of receptor expression.

Methodology/Principal Findings

This study provides evidence that two peptides derived from the C-terminus of acetylcholinesterase, not only selectively displace specific bungarotoxin binding at the α7-nAChR, but also alter receptor binding properties for its familiar ligands, including the alternative endogenous agonist choline. Of more long-term significance, these peptides also induce upregulation of α7-nAChR mRNA and protein expression, as well as enhancing receptor trafficking to the plasma membrane.

Conclusions/Significance

The results reported here demonstrate a hitherto unknown relationship between the α7-nAChR and the non-enzymatic functions of acetylcholinesterase, mediated independently by its C-terminal domain. Such an interaction may prove valuable as a pharmacological tool, prompting new approaches for understanding, and combating, the process of neurodegeneration.

Cholinergic system during the progression of Alzheimer's disease: therapeutic implications

Alzheimer's disease (AD) is characterized by a progressive phenotypic downregulation of markers within cholinergic basal forebrain (CBF) neurons, frank CBF cell loss and reduced cortical choline acetyltransferase activity associated with cognitive decline. Delaying CBF neurodegeneration or minimizing its consequences is the mechanism of action for most currently available drug treatments for cognitive dysfunction in AD. Growing evidence suggests that imbalances in the expression of NGF, its precursor proNGF and the high (TrkA) and low (p75(NTR)) affinity NGF receptors are crucial factors underlying CBF dysfunction in AD. Drugs that maintain a homeostatic balance between TrkA and p75(NTR) may slow the onset of AD. A NGF gene therapy trial reduced cognitive decline and stimulated cholinergic fiber growth in humans with mild AD. Drugs treating the multiple pathologies and clinical symptoms in AD (e.g., M1 cholinoceptor and/or galaninergic drugs) should be considered for a more comprehensive treatment approach for cholinergic dysfunction.

A novel intronic polymorphism of ABCA1 gene reveals risk for sporadic Alzheimer's disease in Chinese

Recent genetic studies have shown that variants of the ATP-binding cassette transporter A1, ABCA1, may be implicated in the pathogenesis of Alzheimer's disease (AD). In this case-control study, a panel of 19 single nucleotide polymorphisms (SNP) (including three amino-acid-coding SNPs used for replication of previous work, and 16 newly selected intronic tag SNPs) was genotyped. Nominally significant single marker P-values were observed in four SNPs, with the highest score of 0.003 for rs2297404 (OR = 1.88, 95%CI 1.23-2.87). In addition, six distinct linkage disequilibrium (LD) blocks were detected. LD block1 harbored three nominally significant SNPs (rs2297404, rs2230808, and rs2020927), and showed a different haplotype structure in the affected and unaffected groups. Of the four haplotypes identified, haplotype2 (CAC) was more prevalent in the disease group (0.323 in AD vs. 0.202 in control); while haplotype1 (TGG) was over-represented in the healthy controls (0.595 in control vs. 0.493 in AD), indicating disease risk conferring possibility of haplotype2. After doubling the sample size, the three nominally significant SNPs were still significantly associated with AD. Although coding SNP (rs2230808) was confirmed to have a significant association with AD, prediction of the effects of an amino acid substitution SNP rs2230808 (R1587K) on the three-dimensional structure and function of the ABCA1 protein using PolyPhen program revealed that it is unlikely to be functionally significant. However, the adjacent rs2297404 in the same LD block is potentially functionally significant because of its position in the immediate vicinity of a splicing branch site. Further functional analysis of this polymorphism should be a high priority.

Alpha7 nicotinic acetylcholine receptor expression in Alzheimer's disease: receptor densities in brain regions of the APP(SWE) mouse model and in human peripheral blood lymphocytes

The brains of people with Alzheimer's disease (AD) display several characteristic pathological features, including deposits (plaques) of beta-amyloid 1-42 (Abeta1-42), intraneuronal accumulations (tangles) of hyperphosphorylated tau, degeneration of the basal forebrain cholinergic pathway, and gliosis. Abeta1-42 plaques develop in specific brain regions, including hippocampus and cortex, as well as in the vasculature. Abeta1-42 might promote neurodegeneration through the induction of free radicals and disruption of Ca2+ homeostasis, giving rise to the symptoms of AD. Abeta1-42 interacts with the alpha7 subtype of the nicotinic acetylcholine receptor (alpha7 nAChR), which is widely expressed throughout the central and peripheral nervous systems, as well as in several nonneuronal loci, such as epithelial cells, lymphoid tissues, and peripheral blood lymphocytes. Western blot and autoradiographic analyses indicate that the alpha7 nAChR subunit protein is up-regulated in human brain samples from Alzheimer patients, as well as in animal models of AD (Dineley et al., 2001; Bednar et al., 2002), and might be involved in nicotine-mediated reduction of Abeta1-42 deposition (Hellstrom et al., 2004), although the nature of this relationship remains ill-defined. We have undertaken a semiquantitative histological evaluation of alpha7 nAChR expression in a mouse model of AD pathology, as well as a comparison of alpha7 nAChR levels in lymphocytes from AD patients and control subjects.

Intron 2 (T/C) CYP46 polymorphism is associated with Alzheimer's disease in Chinese patients

BACKGROUND

Cholesterol metabolism has been implicated in the pathophysiology of Alzheimer's disease (AD), and cholesterol-related genes are plausible candidate genes for AD. Genetic association of CYP46A1 polymorphisms with AD had been under extensive investigations; however, observations on intron 2 T-->C (rs754203) generated inconclusive results.

OBJECTIVE

To analyse an independent data set in a Chinese population to see whether the polymorphic site rs754203 of the CYP46A1 gene is associated with AD.

METHODS

We analysed 130 sporadic AD patients and 110 healthy controls of the Southern Chinese origin.

RESULTS

An association between the genotype frequency and AD was suggested in the general population (p = 0.047, odds ratio, OR = 1. 61, 95% confidence interval, CI = 0.96-2.70), while the association was most significant in the apolipoprotein E (ApoE) epsilon4-negative group (p = 0.004, OR = 2.54, 95% CI =1.31-4.95). Linkage disequilibrium block prediction results also favoured this association. Consistent with previous reports, intron 3 C-->T (rs4900442) polymorphism did not show any evidence of association; in our data set ApoEepsilon4 was confirmed to be a genetic risk factor for AD (p = 0.0016, OR = 2.76, 95% CI = 1.50-5.11).

acr-16 encodes an essential subunit of the levamisole-resistant nicotinic receptor at the Caenorhabditis elegans neuromuscular junction

The Caenorhabditis elegans neuromuscular junction (NMJ) contains three pharmacologically distinct ionotropic receptors: gamma-aminobutyric acid receptors, levamisole-sensitive nicotinic receptors, and levamisole-insensitive nicotinic receptors. The subunit compositions of the gamma-aminobutyric acid- and levamisole-sensitive receptors have been elucidated, but the levamisole-insensitive acetylcholine receptor is uncharacterized. To determine which of the approximately 40 putative nicotinic receptor subunit genes in the C. elegans genome encodes the levamisole-resistant receptor, we utilized MAPCeL, a microarray profiling strategy. Of seven nicotinic receptor subunit transcripts found to be enriched in muscle, five encode the levamisole receptor subunits, leaving two candidates for the levamisole-insensitive receptor: acr-8 and acr-16. Electrophysiological analysis of the acr-16 deletion mutant showed that the levamisole-insensitive muscle acetylcholine current was eliminated, whereas deletion of acr-8 had no effect. These data suggest that ACR-16, like its closest vertebrate homolog, the nicotinic receptor alpha7-subunit, may form homomeric receptors in vivo. Genetic ablation of both the levamisole-sensitive receptor and acr-16 abolished all cholinergic synaptic currents at the NMJ and severely impaired C. elegans locomotion. Therefore, ACR-16-containing receptors account for all non-levamisole-sensitive nicotinic synaptic signaling at the C. elegans NMJ. The determination of subunit composition for all three C. elegans body wall muscle ionotropic receptors provides a critical foundation for future research at this tractable model synapse.