Neuronal overexpression of "readthrough" acetylcholinesterase is associated with antisense-suppressible behavioral impairments

Evaluating the chronic effect of two varroacides using multiple biomarkers and an integrated biological response index

There is mounting evidence that acaricides are among the most prevalent medicinal compounds in honey bee hive matrices worldwide. According to OCDE guideline No. 245 chronic lethal concentration of tau-fluvalinate (at concentrations ranging from 77.5 to 523.18 ppm), coumaphos (59.8 ppm) and dimethoate (0.7 ppm) were determined. The activity of the biomarkers acetylcholinesterase (AChE), carboxylesterase (CbE), glutathione S-transferase (GST), catalase (CAT) and malondialdehyde (MDA) was analysed and as they are implicated in neurotoxicity, biotransformation and antioxidant defences, these values were combined into an integrated biomarker response (IBR). There was enhanced AChE, CAT and GST activity in honey bees exposed to tau-fluvalinate, while dimethoate inhibited AChE activity. Both dimethoate and coumaphos inhibited CbE activity but they enhanced CAT activity and MDA formation. Our results highlight how these biomarkers may serve to reveal honey bee exposure to commonly used acaricides.

Integrative Transcriptomics Reveals Sexually Dimorphic Control of the Cholinergic/Neurokine Interface in Schizophrenia and Bipolar Disorder

RNA sequencing analyses are often limited to identifying lowest p value transcripts, which does not address polygenic phenomena. To overcome this limitation, we developed an integrative approach that combines large-scale transcriptomic meta-analysis of patient brain tissues with single-cell sequencing data of CNS neurons, short RNA sequencing of human male- and female-originating cell lines, and connectomics of transcription factor and microRNA interactions with perturbed transcripts. We used this pipeline to analyze cortical transcripts of schizophrenia and bipolar disorder patients. Although these pathologies show massive transcriptional parallels, their clinically well-known sexual dimorphisms remain unexplained. Our method reveals the differences between afflicted men and women and identifies disease-affected pathways of cholinergic transmission and gp130-family neurokine controllers of immune function interlinked by microRNAs. This approach may open additional perspectives for seeking biomarkers and therapeutic targets in other transmitter systems and diseases.

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Single-cell transcriptomes reveal a unique profile of cortical cholinergic neurons

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Female- and male-derived cells show distinct neurokine-induced miRNA responses

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Differentially enriched microRNA families constitute a self-organizing network

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Integrative analysis identifies mir-10/mir-199 regulators of cholinergic function

Cholinergic Stress Signals Accompany MicroRNA-Associated Stereotypic Behavior and Glutamatergic Neuromodulation in the Prefrontal Cortex

Stereotypic behavior (SB) is common in emotional stress-involved psychiatric disorders and is often attributed to glutamatergic impairments, but the underlying molecular mechanisms are unknown. Given the neuro-modulatory role of acetylcholine, we sought behavioral-transcriptomic links in SB using TgR transgenic mice with impaired cholinergic transmission due to over-expression of the stress-inducible soluble 'readthrough' acetylcholinesterase-R splice variant AChE-R. TgR mice showed impaired organization of behavior, performance errors in a serial maze test, escape-like locomotion, intensified reaction to pilocarpine and reduced rearing in unfamiliar situations. Small-RNA sequencing revealed 36 differentially expressed (DE) microRNAs in TgR mice hippocampi, 8 of which target more than 5 cholinergic transcripts. Moreover, compared to FVB/N mice, TgR prefrontal cortices displayed individually variable changes in over 400 DE mRNA transcripts, primarily acetylcholine and glutamate-related. Furthermore, TgR brains presented c-fos over-expression in motor behavior-regulating brain regions and immune-labeled AChE-R excess in the basal ganglia, limbic brain nuclei and the brain stem, indicating a link with the observed behavioral phenotypes. Our findings demonstrate association of stress-induced SB to previously unknown microRNA-mediated perturbations of cholinergic/glutamatergic networks and underscore new therapeutic strategies for correcting stereotypic behaviors.

Differential expression of acetylcholinesterase 1 in response to various stress factors in honey bee workers

The honey bee acetylcholinesterase 1 (AmAChE1) has been suggested to be related to stress response as judged from its elevated expression level under brood rearing-suppressed conditions. To further investigate the involvement of AmAChE1 expression in the stress response and its physiological functions, we analyzed altered expression profiles of AmAChE1 induced by diverse stress factors. In addition, transcription profiles of several heat shock protein (Hsp) genes (hsps) and the vitellogenin (Vg) gene (vg) known as general stress markers were investigated as positive references. Among the tested stress conditions, AmAChE1 expression was induced under the brood rearing-suppressed, crowding and heat shock conditions. The hsps, particularly hsp70 and hsp90, responded to seven of nine stress conditions tested, confirming that hsp expression profiles can serve as a general stress marker. Taken together, AmAChE1 expression is not suitable for using as a stress marker due to its limited response. Nevertheless, AmAChE1 expression appears to be connected, at least in part, to heat shock response and other pathways. Considering that AmAChE1 likely regulates the ACh titer particularly in non-neuronal tissues, thereby modulating the signal cascades mediated by mAChR, the AmAChE1 expression profile under different conditions likely provides important information on its physiological roles in honey bees.

Increased Active OMI/HTRA2 Serine Protease Displays a Positive Correlation with Cholinergic Alterations in the Alzheimer's Disease Brain

OMI/HTRA2 (high-temperature requirement serine protease A2) is a mitochondrial serine protease involved in several cellular processes, including autophagy, chaperone activity, and apoptosis. Few studies on the role of OMI/HTRA2 in Alzheimer's disease (AD) are available, but none on its relationship with the cholinergic system and neurotrophic factors as well as other AD-related proteins. In this study, immunohistochemical analyses revealed that AD patients had a higher cytosolic distribution of OMI/HTRA2 protein compared to controls. Quantitative analyses on brain extracts indicated a significant increase in the active form of OMI/HTRA2 in the AD brain. Activated OMI/HTRA2 protein positively correlated with stress-associated read-through acetylcholinesterase activity. In addition, α7 nicotinic acetylcholine receptor gene expression, a receptor also known to be localized on the outer membrane of mitochondria, showed a strong correlation with OMI/HTRA2 gene expression in three different brain regions. Interestingly, the activated OMI/HTRA2 levels also correlated with the activity of the acetylcholine-biosynthesizing enzyme, choline acetyltransferase (ChAT); with levels of the neurotrophic factors, NGF and BDNF; with levels of the soluble fragments of amyloid precursor protein (APP); and with gene expression of the microtubule-associated protein tau in the examined brain regions. Overall, the results demonstrate increased levels of the mitochondrial serine protease OMI/HTRA2, and a coherent pattern of association between the activated form of OMI/HTRA2 and several key proteins involved in AD pathology. In this paper, we propose a new hypothetical model to highlight the importance and needs of further investigation on the role of OMI/HTRA2 in the mitochondrial function and AD.

PRMT8 as a phospholipase regulates Purkinje cell dendritic arborization and motor coordination

The development of vertebrate neurons requires a change in membrane phosphatidylcholine (PC) metabolism. Although PC hydrolysis is essential for enhanced axonal outgrowth mediated by phospholipase D (PLD), less is known about the determinants of PC metabolism on dendritic arborization. We show that protein arginine methyltransferase 8 (PRMT8) acts as a phospholipase that directly hydrolyzes PC, generating choline and phosphatidic acid. We found that PRMT8 knockout mice (prmt8 (-/-)) displayed abnormal motor behaviors, including hindlimb clasping and hyperactivity. Moreover, prmt8 (-/-) mice and TALEN-induced zebrafish prmt8 mutants and morphants showed abnormal phenotypes, including the development of dendritic trees in Purkinje cells and altered cerebellar structure. Choline and acetylcholine levels were significantly decreased, whereas PC levels were increased, in the cerebellum of prmt8 (-/-) mice. Our findings suggest that PRMT8 acts both as an arginine methyltransferase and as a PC-hydrolyzing PLD that is essential for proper neurological functions.

Subchronic treatment of donepezil rescues impaired social, hyperactive, and stereotypic behavior in valproic acid-induced animal model of autism

Autism spectrum disorder (ASD) is a group of pervasive developmental disorders with core symptoms such as sociability deficit, language impairment, and repetitive/restricted behaviors. Although worldwide prevalence of ASD has been increased continuously, therapeutic agents to ameliorate the core symptoms especially social deficits, are very limited. In this study, we investigated therapeutic potential of donepezil for ASD using valproic acid-induced autistic animal model (VPA animal model). We found that prenatal exposure of valproic acid (VPA) induced dysregulation of cholinergic neuronal development, most notably the up-regulation of acetylcholinesterase (AChE) in the prefrontal cortex of affected rat and mouse offspring. Similarly, differentiating cortical neural progenitor cell in culture treated with VPA showed increased expression of AChE in vitro. Chromatin precipitation experiments revealed that acetylation of histone H3 bound to AChE promoter region was increased by VPA. In addition, other histone deacetyalse inhibitors (HDACIs) such as trichostatin A and sodium butyrate also increased the expression of AChE in differentiating neural progenitor cells suggesting the essential role of HDACIs in the regulation of AChE expression. For behavioral analysis, we injected PBS or donepezil (0.3 mg/kg) intraperitoneally to control and VPA mice once daily from postnatal day 14 all throughout the experiment. Subchronic treatment of donepezil improved sociability and prevented repetitive behavior and hyperactivity of VPA-treated mice offspring. Taken together, these results provide evidence that dysregulation of ACh system represented by the up-regulation of AChE may serve as an effective pharmacological therapeutic target against autistic behaviors in VPA animal model of ASD, which should be subjected for further investigation to verify the clinical relevance.

Neuronal AChE splice variants and their non-hydrolytic functions: redefining a target of AChE inhibitors?

AChE enzymatic inhibition is a core focus of pharmacological intervention in Alzheimer's disease (AD). Yet, AChE has also been ascribed non-hydrolytic functions, which seem related to its appearance in various isoforms. Neuronal AChE presents as a tailed form (AChE-T) predominantly found on the neuronal synapse, and a facultatively expressed readthough form (AChE-R), which exerts short to medium-term protective effects. Notably, this latter form is also found in the periphery. While these non-hydrolytic functions of AChE are most controversially discussed, there is evidence for them being additional targets of AChE inhibitors. This review aims to provide clarification as to the role of these AChE splice variants and their interplay with other cholinergic parameters and their being targets of AChE inhibition: AChE-R is particularly involved in the mediation of (anti-)apoptotic events in cholinergic cells, involving adaptation of various cholinergic parameters and a time-dependent link to the expression of neuroprotective factors. The AChE-T C-terminus is central to AChE activity regulation, while isolated AChE-T C-terminal fragments mediate toxic effects via the α7 nicotinic acetylcholine receptor. There is direct evidence for roles of AChE-T and AChE-R in neurodegeneration and neuroprotection, with these roles involving AChE as a key modulator of the cholinergic system: in vivo data further encourages the use of AChE inhibitors in the treatment of neurodegenerative conditions such as AD since effects on both enzymatic activity and the enzyme's non-hydrolytic functions can be postulated. It also suggests that novel AChE inhibitors should enhance protective AChE-R, while avoiding the concomitant up-regulation of AChE-T.

Predicted overlapping microRNA regulators of acetylcholine packaging and degradation in neuroinflammation-related disorders

MicroRNAs (miRNAs) can notably control many targets each and regulate entire cellular pathways, but whether miRNAs can regulate complete neurotransmission processes is largely unknown. Here, we report that miRNAs with complementary sequence motifs to the key genes involved in acetylcholine (ACh) synthesis and/or packaging show massive overlap with those regulating ACh degradation. To address this topic, we first searched for miRNAs that could target the 3′-untranslated regions of the choline acetyltransferase (ChAT) gene that controls ACh synthesis; the vesicular ACh transporter (VAChT), encoded from an intron in the ChAT gene and the ACh hydrolyzing genes acetyl- and/or butyrylcholinesterase (AChE, BChE). Intriguingly, we found that many of the miRNAs targeting these genes are primate-specific, and that changes in their levels associate with inflammation, anxiety, brain damage, cardiac, neurodegenerative, or pain-related syndromes. To validate the in vivo relevance of this dual interaction, we selected the evolutionarily conserved miR-186, which targets both the stress-inducible soluble “readthrough” variant AChE-R and the major peripheral cholinesterase BChE. We exposed mice to predator scent stress and searched for potential associations between consequent changes in their miR-186, AChE-R, and BChE levels. Both intestinal miR-186 as well as BChE and AChE-R activities were conspicuously elevated 1 week post-exposure, highlighting the previously unknown involvement of miR-186 and BChE in psychological stress responses. Overlapping miRNA regulation emerges from our findings as a recently evolved surveillance mechanism over cholinergic neurotransmission in health and disease; and the corresponding miRNA details and disease relevance may serve as a useful resource for studying the molecular mechanisms underlying this surveillance.

Chronic dietary exposure to chlorpyrifos causes behavioral impairments, low activity of brain membrane-bound acetylcholinesterase, and increased brain acetylcholinesterase-R mRNA

Chlorpyrifos (CPF) is an organophosphate (OP) insecticide that is metabolically activated to the highly toxic chlorpyrifos oxon. Dietary exposure is the main route of intoxication for non-occupational exposures. However, only limited behavioral effects of chronic dietary exposure have been investigated. Therefore, male Wistar rats were fed a dose of 5mg/kg/day of CPF for thirty-one weeks. Animals were evaluated in spatial learning and impulsivity tasks after 21 weeks of CPF dietary exposure and one week after exposure ended, respectively. In addition, the degree of inhibition of brain acetylcholinesterase (AChE) was evaluated for both the soluble and particulate forms of the enzyme, as well as AChE gene expression. Also, brain acylpeptide hydrolase (APH) was investigated as an alternative target for OP-mediated effects. All variables were evaluated at various time points in response to CPF diet and after exposure ended. Results from behavioral procedures suggest cognitive and emotional disorders. Moreover, low levels of activity representing membrane-bound oligomeric forms (tetramers) were also observed. In addition, increased brain AChE-R mRNA levels were detected after four weeks of CPF dietary exposure. However, no changes in levels of brain APH were observed among groups. In conclusion, our data point to a relationship between cognitive impairments and changes in AChE forms, specifically to a high inhibition of the particulate form and a modification of alternative splicing of mRNA during CPF dietary exposure.

Readthrough acetylcholinesterase is increased in human liver cirrhosis

Background & Aims

There have been many studies on plasma butyrylcholinesterase in liver dysfunction. However, no data is available about acetylcholinesterase in human cirrhosis, although profound changes have been described in cirrhotic rat models.

Methods

Human serum and liver acetylcholinesterase and its molecular forms were determined enzymatically, after butyrylcholinesterase immunodepletion. The distinct species of acetylcholinesterase, with a distinct C-terminus, were determined by western blotting, and the level of liver transcripts by real-time PCR. Liver acetylcholinesterase was also evaluated by immunocytochemistry.

Results

In patients with liver cirrhosis, the activity of plasma acetylcholinesterase (rich in light species), appeared to be apparently unaffected. However, the levels of the soluble readthrough (R) acetylcholinesterase form, an acetylcholinesterase species usually associated with stress and pathology, was increased compared to controls. Human liver acetylcholinesterase activity levels were also unchanged, but protein levels of the acetylcholinesterase-R and other acetylcholinesterase subunit species were increased in the cirrhotic liver. This increase in acetylcholinesterase protein expression in the cirrhotic liver was confirmed by PCR analysis. Immunohistological examination confirmed that acetylcholinesterase immunoreactivity is increased in parenchymal cells of the cirrhotic liver.

Conclusions

We demonstrate significant changes in acetylcholinesterase at the protein and mRNA levels in liver cirrhosis, with no difference in enzymatic activity. The altered expression of acetylcholinesterase protein may reflect changes in its pathophysiological role.

miR-212/132 expression and functions: within and beyond the neuronal compartment

During the last two decades, microRNAs (miRNAs) emerged as critical regulators of gene expression. By modulating the expression of numerous target mRNAs mainly at the post-transcriptional level, these small non-coding RNAs have been involved in most, if not all, biological processes as well as in the pathogenesis of a number of diseases. miR-132 and miR-212 are tandem miRNAs whose expression is necessary for the proper development, maturation and function of neurons and whose deregulation is associated with several neurological disorders, such as Alzheimer's disease and tauopathies (neurodegenerative diseases resulting from the pathological aggregation of tau protein in the human brain). Although their involvement in neuronal functions is the most described, evidences point towards a role of these miRNAs in many other biological processes, including inflammation and immune functions. Incidentally, miR-132 was recently classified as a ‘neurimmiR’, a class of miRNAs operating within and between the neural and immune compartments. In this review, we propose an outline of the current knowledge about miR-132 and miR-212 functions in neurons and immune cells, by describing the signalling pathways and transcription factors regulating their expression as well as their putative or demonstrated roles and validated mRNA targets.

Hippocampal microRNA-132 mediates stress-inducible cognitive deficits through its acetylcholinesterase target

Diverse stress stimuli induce long-lasting cognitive deficits, but the underlying molecular mechanisms are still incompletely understood. Here, we report three different stress models demonstrating that stress-inducible increases in microRNA-132 (miR-132) and consequent decreases in its acetylcholinesterase (AChE) target are causally involved. In a mild model of predator scent-induced anxiety, we demonstrate long-lasting hippocampal elevation of miR-132, accompanied by and associated with reduced AChE activity. Using lentiviral-mediated suppression of "synaptic" AChE-S mRNA, we quantified footshock stress-inducible changes in miR-132 and AChE and its corresponding cognitive damages. Stressed mice showed long-lasting impairments in the Morris water maze. In contrast, pre-stress injected AChE-suppressing lentivirus, but not a control virus, reduced hippocampal levels of both miR-132 and AChE and maintained similar cognitive performance to that of naïve, non-stressed mice. To dissociate between miR-132 and synaptic AChE-S as potential causes for stress-inducible cognitive deficits, we further used engineered TgR mice with enforced over-expression of the soluble "readthrough" AChE-R variant without the 3'-untranslated region binding site for miR-132. TgR mice displayed excess AChE-R in hippocampal neurons, enhanced c-fos labeling and correspondingly intensified reaction to the cholinergic agonist pilocarpine. They further showed excessive hippocampal expression of miR-132, accompanied by reduced host AChE-S mRNA and the GTPase activator p250GAP target of miR-132. At the behavioral level, TgR mice showed abnormal nocturnal locomotion patterns and serial maze mal-performance in spite of their reduced AChE-S levels. Our findings attribute stress-inducible cognitive impairments to cholinergic-mediated induction of miR-132 and consequently suppressed ACHE-S, opening venues for intercepting these miR-132-mediated damages.

Davunetide (NAP) as a preventative treatment for central nervous system complications in a diabetes rat model

AIMS

Central nervous system complications including cognitive impairment are an early manifestation of diabetes mellitus, also evident in animal models. NAP (generic name, davunetide), a neuroprotective peptide was tested here for its ability to prevent diabetes-related brain pathologies in the streptozotocin injected diabetes rat model.

METHODS

Diabetes was induced by an intraperitoneal streptozotocin injection (55 mg/kg). Intranasal NAP or vehicle was administered daily starting on the day following streptozotocin injection. Cognitive assessment was performed 12 weeks after diabetes induction, using the Morris water maze paradigm. Brain structural integrity was assessed on the 15th week of diabetes by magnetic resonance T2 scan. Characterization of cellular populations, apoptosis and synaptic density was performed 16 weeks after diabetes induction, using immunohistochemical markers and quantified in the prefrontal cortex, the cerebral cortex and the hippocampus of both hemispheres.

RESULTS

Impaired spatial memory of the diabetic rats was observed in the water maze by attenuated learning curve and worsened performance in the probe memory test. NAP treatment significantly improved both measurements. T2 magnetic resonance imaging revealed atrophy in the prefrontal cortex of the diabetes rat group, which was prevented by NAP treatment. Immunohistochemical analysis showed that NAP treatment protected against major loss of the synaptic marker synaptophysin and astrocytic apoptosis, resulting from streptozotocin treatment.

CONCLUSIONS

Our results show for the first time protective effects for NAP (davuentide) in a diabetes rat model at the behavioral and structural levels against one of the most severe complications of diabetes.

Acetylcholinesterase readthrough peptide shares sequence similarity to the 28-53 peptide sequence of the acetylcholinesterase adhesion-mediating site and competes for ligand binding in vitro

It has been reported that unlike the more commonly expressed splice variants, the embryonic and stress-associated readthrough form of acetylcholinesterase (AChE-R) is unable to promote cell adhesion and neurite outgrowth. We investigated the possibility that the unique AChE-R C-terminal peptide (ARP) might be responsible for this difference, either by binding to AChE itself and inactivating the adhesion-mediating site or by competing with AChE for ligand binding. Synthetic peptides representing the ARP, a scrambled version of the ARP, and sequences of the previously identified adhesion-mediating site on AChE were used in in vitro binding and neuroblastoma cell-spreading assays. It was observed that the ARP was able to bind to laminin-1, identified previously as an in vitro AChE ligand and, to a lesser extent, to collagen IV and to AChE itself. ARP-AChE binding was, however, of very low affinity and was not significantly affected by peripheral site inhibitors, suggesting that inactivation of the AChE adhesion site is not the reason for AChE-R's antiadhesive character. On the other hand, the ARP competed with AChE and the adhesion site peptides for binding to laminin in vitro, and the ARP was observed to inhibit cell spreading in neuroblastoma cells grown on laminin. Monoclonal antibodies recognizing the known AChE adhesion site reacted with the ARP, suggesting structural similarities. These were borne out by an examination of sequence alignments of the ARP and the 28-53 AChE sequence. The ARP contains part of the PPxxxxRFxPPEP motif seen in AChEs and cholinesterase-domain proteins, and both it and the 37-53 sequence bear some resemblance to collagen and collagen-like proteins. It therefore appears likely that the ARP's structural similarity to the AChE adhesion-mediating site is the basis for the observed competition for ligand binding and might account for the antiadhesive characteristics of AChE-R.

Comparative developmental neurotoxicity of organophosphates in vivo: transcriptional responses of pathways for brain cell development, cell signaling, cytotoxicity and neurotransmitter systems

Organophosphates affect mammalian brain development through a variety of mechanisms beyond their shared property of cholinesterase inhibition. We used microarrays to characterize similarities and differences in transcriptional responses to chlorpyrifos and diazinon, assessing defined gene groupings for the pathways known to be associated with the mechanisms and/or outcomes of chlorpyrifos-induced developmental neurotoxicity. We exposed neonatal rats to daily doses of chlorpyrifos (1mg/kg) or diazinon (1 or 2mg/kg) on postnatal days 1-4 and evaluated gene expression profiles in brainstem and forebrain on day 5; these doses produce little or no cholinesterase inhibition. We evaluated pathways for general neural cell development, cell signaling, cytotoxicity and neurotransmitter systems, and identified significant differences for >60% of 252 genes. Chlorpyrifos elicited major transcriptional changes in genes involved in neural cell growth, development of glia and myelin, transcriptional factors involved in neural cell differentiation, cAMP-related cell signaling, apoptosis, oxidative stress, excitotoxicity, and development of neurotransmitter synthesis, storage and receptors for acetylcholine, serotonin, norepinephrine and dopamine. Diazinon had similar effects on many of the same processes but also showed major differences from chlorpyrifos. Our results buttress the idea that different organophosphates target multiple pathways involved in neural cell development but also that they deviate in key aspects that may contribute to disparate neurodevelopmental outcomes. Equally important, these pathways are compromised at exposures that are unrelated to biologically significant cholinesterase inhibition and its associated signs of systemic toxicity. The approach used here demonstrates how planned comparisons with microarrays can be used to screen for developmental neurotoxicity.

Impaired hippocampal plasticity and errors in cognitive performance in mice with maladaptive AChE splice site selection

Neuronal splice site selection events control multiple brain functions. Here, we report their involvement in stress-modulated hippocampal plasticity and errors of cognitive performance. Under stress, alternative splicing changes priority from synaptic acetylcholinesterase (AChE-S) to the normally rare, soluble and monomeric AChE-R variant, which facilitates hippocampal long-term potentiation (LTP) and intensifies fear-motivated learning. To explore the adaptive value of changes in AChE splicing, we compared hippocampal plasticity and errors of executive function in TgS and TgR transgenic mice overexpressing AChE-S or AChE-R, respectively. Hippocampal slices from TgS and TgR mice presented delayed and facilitated transition to LTP maintenance, respectively, compared with strain-matched FVB/N controls. TgS slices further showed failed recruitment of both the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate and N-methyl-D-aspartate components of LTP, refractory response to cholinergic enhancement and suppressed protein kinase C (PKC) levels. Stable LTP could, however, be rescued by phorbol ester priming, attributing the TgS deficits to disrupted signal transduction. In serial maze tests, TgS mice displayed more errors of conflict and executive function than did FVB/N controls, reflecting maladaptive performance under chronic AChE-S overexpression. In contrast, TgR mice displayed enhanced serial maze performance, suggesting that chronic AChE-R overexpression facilitates adaptive reactions. Our findings are compatible with the notion that changes in the alternative splicing of AChE pre-mRNA and consequent alterations in PKC signalling are causally involved in modulating hippocampal plasticity and cognitive performance.

Adaptive changes in acetylcholinesterase gene expression as mediators of recovery from chemical and biological insults

Both organophosphate (OP) exposure and bacterial infection notably induce short- and long-term cholinergic responses. These span the central and peripheral nervous system, neuromuscular pathway and hematopoietic cells and involve over-expression of the "readthrough" variant of acetylcholinesterase, AChE-R, and its naturally cleavable C-terminal peptide ARP. However, the causal involvement of these changes with post-exposure recovery as opposed to apoptotic events remained to be demonstrated. Here, we report the establishment of stably transfected cell lines expressing catalytically active human "synaptic" AChE-S or AChE-R which are fully viable and non-apoptotic. In addition, intraperitoneally injected synthetic mouse ARP (mARP) elevated serum AChE levels post-paraoxon exposure. Moreover, mARP treatment ameliorated post-exposure increases in corticosterone and decreases in AChE gene expression and facilitated earlier retrieval of motor activity following both paraoxon and lipopolysaccharide (LPS) exposures. Our findings suggest a potential physiological role for overproduction of AChE-R and the ARP peptide following exposure to both chemical warfare agents and bacterial LPS.

Neuromuscular therapeutics by RNA-targeted suppression of ACHE gene expression

RNA-targeted therapeutics offers inherent advantages over small molecule drugs wherever one out of several splice variant enzymes should be inhibited. Here, we report the use of Monarsen, a 20-mer acetylcholinesterase-targeted antisense agent with three 3'-2'o-methyl-protected nucleotides, for selectively attenuating the stress-induced accumulation of the normally rare, soluble "readthrough" acetylcholinesterase variant AChE-R. Acetylcholine hydrolysis by AChE-R may cause muscle fatigue and moreover, limit the cholinergic anti-inflammatory blockade, yielding inflammation-associated pathology. Specific AChE-R targeting by Monarsen was achieved in cultured cells, experimental animals, and patient volunteers. In rats with experimental autoimmune myasthenia gravis, oral delivery of Monarsen improved muscle action potential in a lower dose regimen (nanomolar versus micromolar), rapid and prolonged manner (up to 72 h versus 2-4 h) as compared with the currently used small molecule anticholinesterases. In central nervous system neurons of both rats and cynomolgus monkeys, systematic Monarsen treatment further suppressed the levels of the proinflammatory cytokines interleukin-1 (IL-1) and IL-6. Toxicology testing and ongoing clinical trials support the notion that Monarsen treatment would offer considerable advantages over conventional cholinesterase inhibitors with respect to dosing, specificity, side effects profile, and duration of efficacy, while raising some open questions regarding its detailed mechanism of action.

Cerebrospinal fluid acetylcholinesterase changes after treatment with donepezil in patients with Alzheimer's disease

We analyzed whether donepezil differently influences acetylcholinesterase (AChE) variants from cerebrospinal fluid (CSF) in patients with Alzheimer's disease (AD) after long-term treatment. Overall CSF-AChE activity in AD patients before treatment was not different from controls, but the ratio between the major tetrameric form, G(4), and the smaller G(1) and G(2) species was significantly lower. AChE levels at study outset were found to correlate positively with beta-amyloid (1-42) (Abeta42). When patients were re-examined after 12 months treatment with donepezil, there was a remarkable increase in both the G(4) and the lighter species of CSF AChE. As compared with placebo, donepezil caused decreases in the percentage of AChE that failed to bind to the lectin concanavalin A and the antibody AE1. These non-binding species comprised primarily a small subset of G(1) and G(2) forms. In treated patients, these light variants were the only subset of CSF AChE that correlated with CSF-Abeta42 levels. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that a 77-kDa band, attributed in part to inactive AChE, was lower in AD patients than in controls. Unlike enzyme activity, the intensity of this band did not increase after donepezil treatment. The varying responses of different AChE species to ChE-I treatment suggest different modes of regulation, which may have therapeutic implications.

Nonenzymatic functions of acetylcholinesterase splice variants in the developmental neurotoxicity of organophosphates: chlorpyrifos, chlorpyrifos oxon, and diazinon

BACKGROUND

Organophosphate pesticides affect mammalian brain development through mechanisms separable from the inhibition of acetylcholinesterase (AChE) enzymatic activity and resultant cholinergic hyperstimulation. In the brain, AChE has two catalytically similar splice variants with distinct functions in development and repair. The rare, read-through isoform, AChE-R, is preferentially induced by injury and appears to promote repair and protect against neurodegeneration. Overexpression of the more abundant, synaptic isoform, AChE-S, enhances neurotoxicity.

OBJECTIVES

We exposed differentiating PC12 cells, a model for developing neurons, to 30 microM chlorpyrifos (CPF) or diazinon (DZN), or CPF oxon, the active metabolite that irreversibly inhibits AChE enzymatic activity, in order to determine whether they differentially induce the formation of AChE-S as a mechanistic predictor of developmental neurotoxicity. We then administered CPF or DZN to neonatal rats on postnatal days 1-4 using daily doses spanning the threshold for AChE inhibition (0-20%); we then evaluated AChE gene expression in forebrain and brainstem on post-natal day 5.

RESULTS

In PC12 cells, after 48 hr of exposure, CPF, CPF oxon, and DZN enhanced gene expression for AChE-R by about 20%, whereas CPF and DZN, but not CPF oxon, increased AChE-S expression by 20-40%. Thus, despite the fact that CPF oxon is a much more potent AChE inhibitor, it is the native compound (CPF) that induces expression of the neurotoxic AChE-S isoform. For in vivo exposures, 1 mg/kg CPF had little or no effect, but 0.5 or 2 mg/kg DZN induced both AChE-R and AChE-S, with a greater effect in males.

CONCLUSIONS

Our results indicate that nonenzymatic functions of AChE variants may participate in and be predictive of the relative developmental neurotoxicity of organophosphates, and that the various organophosphates differ in the degree to which they activate this mechanism.

RNA-targeted suppression of stress-induced allostasis in primate spinal cord neurons

Peripheral acetylcholine levels notably control the synthesis in macrophages of pro-inflammatory cytokines; however, it remains unclear whether this peripheral regulatory pathway affects central nervous system neurons. To explore the interrelationship between neuronal cholinergic homeostasis and peripheral inflammatory responses in primates, we used spinal cord sections from cynomolgus monkeys after 7 days oral or intravenous treatment with Monarsen oligonucleotide. Monarsen is an antisense oligonucleotide 3'-protected by 2'-oxymethylation, which was proved to induce selective destruction of the stress-induced acetylcholinesterase splice variant AChE-R mRNA. Handling stress predictably suppressed neuronal choline acetyl transferase (ChAT) and the vesicular acetylcholine transporter (VAChT) in all treated monkeys. In Monarsen-treated animals, we further observed suppression of stress-induced increases in plasma AChE activities. Corresponding decreases in AChE-R mRNA were seen in spinal cord neurons, associated with parallel decline patterns in the mRNA encoding for the splice factor SC35 (the levels of which co-increase with those of AChE-R) as well as in the neuronal pro-inflammatory interleukins IL-1beta and IL-6. The antisense effects showed direct dose dependence and were inversely associated with neuronal cell size. These findings suggest a causal association between neuronal cholinergic allostasis and inflammatory reactions in primates and support the peripheral use of RNA-targeted intervention with AChE-R accumulation for the management of both stress and inflammatory responses.

Acetylcholinesterase modulates stress-induced motor responses through catalytic and noncatalytic properties

BACKGROUND

Cholinergic neurotransmission notably participates in stress-induced motor responses. Here we report the contribution of alternative splicing of acetylcholinesterase (AChE) pre-mRNA to modulate these responses. More specifically, we induced stress-associated hypofunction of dopaminergic, mainly D2 dopamine receptor-mediated neurotransmission by haloperidol and explored stress induced hyperlocomotion and catalepsy, an extreme form of immobility, induced in mice with AChE deficiencies.

METHODS

Conditional transgenic (Tet/AS) mice were created with tetracycline-induced antisense suppression of AChE gene expression. Locomotion and catalepsy times were measured in Tet/AS and strain-matched control mice, under open-field exposure threat and under home-cage safety.

RESULTS

In vitro, NGF-treated PC12 cells failed to extend neurites upon Tet/AS suppression. In vivo, Tet/AS but not control mice showed stress-associated hippocampal deposits of heat-shock protein 70 and GRP78 (BiP), predicting posttranscriptional changes in neuronal reactions. Supporting this notion, their striatal cholinergic neurons demonstrated facilitated capacity for neurite extension, attributing these in vivo changes in neurite extension to network interactions. Tet/AS mice presented stress-induced hyperlocomotion. Moreover, the dopamine antagonist haloperidol induced longer catalepsy in threatened Tet/AS than in control mice. When returned to home-cage safety, Tet/AS mice showed retarded release from catalepsy.

CONCLUSIONS

Acetylcholinesterase modulates stress-induced motor responses and facilitates resumption of normal motor behavior following stress through both catalytic and noncatalytic features.

Virtues and woes of AChE alternative splicing in stress-related neuropathologies

The ACh hydrolyzing enzyme acetylcholinesterase (AChE) is a combinatorial series of proteins with variant N and C termini generated from alternate promoter usage and 3' alternative splicing. Neuronal AChE variants show indistinguishable enzymatic activity yet differ in their expression, multimeric assembly and membrane-association patterns. Differentially induced under stress, they show distinct non-hydrolytic properties and interact with different protein partners. Recent findings suggest that transcriptional and post-transcriptional regulation of AChE pre-mRNA is a neuroprotection strategy but might involve long-term damage. Specifically, variant-specific causal involvement of AChE in the progression of both neurodegenerative diseases (e.g. Alzheimer's and Parkinson's diseases) and neuromuscular syndromes (e.g. myasthenia gravis) raises the possibility that future therapeutic drugs might target specific AChE variant(s) or the corresponding RNA transcripts.

Chronic cholinergic imbalances promote brain diffusion and transport abnormalities

Cholinergic imbalances occur after traumatic effects and in the initial stages of neurodegenerative diseases, but their long-lasting effects remained largely unexplained. To address this, we used TgS transgenic mice constitutively overexpressing synaptic acetylcholinesterase (AChE-S) and presenting a complex phenotype of progressive neurodeterioration. T1- and T2-weighted magnetic resonance (MR) brain images appeared similar. However, diffusion-weighted MRI showed decreased baseline water apparent diffusion coefficient in the brains of TgS animals. Furthermore, contrast-enhanced MRI after gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) injection demonstrated slower recovery of normal signals in the TgS brains than with controls. Perfusion MR imaging and difference T1 maps calculated from pre- postcontrast T1-weighted MR images indicated accumulation of more Gd-DTPA molecules in the TgS brains than in the parent strain, reflecting impaired blood-brain barrier (BBB) functioning in these transgenic mice. To explore the molecular mechanism(s) underlying these global phenotypes, we performed microarray analysis in the stress-controlling prefrontal cortex of TgS vs. strain-matched wild-type animals. Profound overexpression of numerous ion channels, transporters, and adhesion genes was confirmed by real time RT-PCR tests. Immunohistochemical and immunoblot analyses revealed corresponding increases in the level and cellular distributions of the chloride channel CLCN3 and the water channel AQP4, both of which contribute to BBB maintenance. Our study attributes to balanced cholinergic neurotransmission, a central role in the brain's maintenance of water diffusion and ion transport, and indicates that chronic impairments in this maintenance facilitate neurodeterioration through interference with BBB function.

Mouse intestinal cryptdins exhibit circadian oscillation

The innate immunity utilizes a plethora of antibacterial polypeptides, known as defensins, to combat ingested bacteria. Mouse enteric defensins (cryptdins) are produced and secreted constitutively but are overexpressed in instances of infection and/or inflammation. Our objective was to determine whether the biological clock plays a role in cryptdin expression under healthy conditions. Analysis of cryptdin 1 and cryptdin 4 expression in the ileum and jejunum of the small intestine of FVB/N mice around the circadian cycle revealed oscillation that peaked at the end of the dark phase. To eliminate the possibility that cryptdin oscillation stems from food intake, we analyzed cryptdin expression under fasting conditions and found oscillation but with a 3 h phase-shift. Comparison of cryptdin expression in two mouse strains (C57BL/6 vs. FVB/N) revealed higher levels in C57BL/6, a mouse strain that is highly susceptible to enteric infection, due, most likely, to impaired cryptdin maturation. The results of this study indicate the involvement of the biological clock in regulating cryptdin expression in the small intestine and reinforce the capacity of food to act as a zeitgeber (synchronizer). With the assumption of similar control in humans, our results may imply that defensin expression peaks during the day.

The readthrough variant of acetylcholinesterase remains very minor after heat shock, organophosphate inhibition and stress, in cell culture and in vivo

Acetylcholinesterase (AChE) exists in various molecular forms, depending on alternative splicing of its transcripts and association with structural proteins. Tetramers of the 'tailed' variant (AChE(T)), which are anchored in the cell membrane of neurons by the PRiMA (Proline Rich Membrane Anchor) protein, constitute the main form of AChE in the mammalian brain. In the mouse brain, stress and anticholinesterase inhibitors have been reported to induce expression of the unspliced 'readthrough' variant (AChE(R)) mRNA which produces a monomeric form. To generalize this observation, we attempted to quantify AChE(R) and AChE(T) after organophosphate intoxication in the mouse brain and compared the observed effects with those of stress induced by swimming or immobilization; we also analyzed the effects of heat shock and AChE inhibition on neuroblastoma cells. Active AChE molecular forms were characterized by sedimentation and non-denaturing electrophoresis, and AChE transcripts were quantified by real-time PCR. We observed a moderate increase of the AChE(R) transcript in some cases, both in the mouse brain and in neuroblastoma cultures, but we did not detect any increase of the corresponding active enzyme.

Acetylcholinesterase inhibitors reduce brain and blood interleukin-1beta production

Overproduction of interleukin-1 within the brain is associated with Alzheimer's disease and other neurological conditions. We report that peripheral administration of the acetylcholinesterase inhibitors tacrine, rivastigmine, neostigmine, or EN101 (an antisense oligonucleotide directed at acetylcholinesterase messenger RNA) to mice significantly attenuated the production of interleukin-1beta in the hippocampus and blood, concomitantly with the reduction in acetylcholinesterase activity. These findings demonstrate that cholinergic enhancement produces central and peripheral antiinflammatory effects and suggest a novel therapeutic mechanism for acetylcholinesterase inhibitors.

Acetylcholinesterase interaction with Alzheimer amyloid beta

Acetylcholinesterase (AChE) is an enzyme involved in cholinergic and non-cholinergic functions in both the central and peripheral nervous system, most of the AChE is found as a tetrameric form bound to neuronal membranes. Early cytochemical studies have demonstrated that the AChE associated with senile plaques differs enzymatically from the AChE associated with neurons in several respects. Biochemical studies indicated that AChE induces amyloid fibril formation and form highly toxic AChE-Abeta complexes. A 3.5 kDa peptide containing a tryptophan of the enzyme peripheral binding site (PAS) mimics the effect of the whole enzyme on amyloid formation. The neurotoxicity induced by AChE-Abeta complexes indicated that they trigger more neurodegeneration than those of the Abeta peptide alone, both in vitro (hippocampal neurons) and in vivo (rats injected in the dorsal hippocampus as a model of Alzheimer). The fact that AChE is able to accelerate amyloid formation and that such effect is sensitive to drugs that block PAS of the enzyme, suggests that specific and new AChE inhibitors may well provide an attractive possibility for treating Alzheimer's disease.

Cholinesterase inhibitors used in the treatment of Alzheimer's disease: the relationship between pharmacological effects and clinical efficacy

The deficiency in cholinergic neurotransmission in Alzheimer's disease has led to the development of cholinesterase inhibitors as the first-line treatment for symptoms of this disease. The clinical benefits of these agents include improvements, stabilisation or less than expected decline in cognition, function and behaviour. The common mechanism of action underlying this class of agents is an increase in available acetylcholine through inhibition of the catabolic enzyme, acetylcholinesterase. There is substantial evidence that the cholinesterase inhibitors, including donepezil, galantamine and rivastigmine, decrease acetylcholinesterase activity in a number of brain regions in patients with Alzheimer's disease. There is also a significant correlation between acetylcholinesterase inhibition and observed cognitive improvement. However, the cholinesterase inhibitors are reported to have additional pharmacological actions. Rivastigmine inhibits butyrylcholinesterase with a similar affinity to acetylcholinesterase, although it is not clear whether the inhibition of butyrylcholinesterase contributes to the therapeutic effect of rivastigmine. Based on data from preclinical studies, it has been proposed that galantamine also potentiates the action of acetylcholine on nicotinic receptors via allosteric modulation; however, the effects appear to be highly dependent on the concentrations of agonist and galantamine. It is not yet clear whether these concentrations are related to those achieved in the brain of patients with Alzheimer's disease within therapeutic dose ranges. Preclinical studies have shown that donepezil and galantamine also significantly increase nicotinic receptor density, and increased receptor density may be associated with enhanced synaptic strengthening through long-term potentiation, which is related to cognitive function. Despite these differences in pharmacology, a review of clinical data, including head-to-head studies, has not demonstrated differences in efficacy, although they may have an impact on tolerability. It seems clear that whatever the subsidiary modes of action, clinical evidence supporting acetylcholinesterase inhibition as the mechanism by which cholinesterase inhibitors treat the symptoms of Alzheimer's disease is accumulating. Certainly, as a class, the currently approved cholinesterase inhibitors (donepezil, galantamine, rivastigmine and tacrine) provide important benefits in patients with Alzheimer's disease and these drugs offer a significant advance in the management of dementia.

From brain to blood: alternative splicing evidence for the cholinergic basis of Mammalian stress responses

Three principal features of mammalian stress responses are that they span peripheral and CNS changes, modify blood cell composition and activities, and cover inter-related alterations in a large number of gene products. The finely tuned spatiotemporal regulation of these multiple events suggests the hierarchic involvement of modulatory neurotransmitters and modified process(es) in the pathway of gene expression that together would enable widely diverse stress responses. We report evidence supporting the notion that acetylcholine (ACh) acts as a stress-response-regulating transmitter and that altered ACh levels are variously associated with changes in the alternative splicing of pre-mRNA transcripts in brain neurons and peripheral blood cells. We used acetylcholinesterase (AChE) gene expression as a case study and developed distinct probes for its alternative splice variants at the mRNA and protein levels. In laboratory animals and human-derived cells, we found stress-induced changes in the alternative splicing patterns of AChE pre-mRNA, which attributes to this gene and its different protein products diverse stress responsive functions that are associated with the enzymatic and noncatalytic properties of AChE. Together, these approaches provide a conceptually unified view of the studied pathways for controlling stress responses in brain and blood.

Acetylcholinesterase and Its Inhibition in Alzheimer Disease

Until recently, the only established function of acetylcholinesterase (AChE) was the termination of cholinergic neurotransmission. Therefore, the use of AChE inhibitors to treat symptoms caused by cholinergic imbalances in Alzheimer disease (AD) represented a rational approach. However, it is now clear that AChE and the cholinergic system may have broader effects in AD. Of particular interest may be signal transduction pathways mediated through cholinergic receptors that promote nonamyloidogenic amyloid precursor protein processing and decrease tau phosphorylation, and the role of AChE in the aggregation of beta-amyloid (Abeta) peptide. In addition, the neuronal and nonneuronal cholinergic systems have important roles in the modulation of regional cerebral blood flow. These findings may modify the overly simplistic cholinergic hypothesis in AD that is limited to symptomatic treatment and ignores the potential of cholinergic therapies as disease-modifying agents. Chronic increases in AChE activity may exacerbate neurodegenerative processes, make clinically relevant levels of AChE inhibition more difficult to achieve, and cause the therapeutic value of cholinesterase inhibitors (ChE-Is) to be limited and temporary. Rapidly reversible ChE-Is appear to increase AChE activity over the longer term whereas, remarkably, irreversible or very slowly reversible ChE-Is do not seem to have this effect. If such differences between ChE-Is are shown to have clinical correlates, this may prompt reconsideration of the rationale and expectations of some agents in the long-term management of AD.

Long-lasting acetylcholinesterase splice variations in anticholinesterase-treated Alzheimer's disease patients

Protein levels of different acetylcholinesterase (AChE) splice variants were explored by a combination of immunoblot techniques, using two different antibodies, directed against the C-terminus of the AChE-R splice variant or the core domain common to all variants. Both AChE-R and AChE-S splice variants as well as several heavier AChE complexes were detected in brain homogenates from the parietal cortex of patients with or without Alzheimer's disease (AD) as well as the cerebrospinal fluid (CSF) of AD patients, compatible with the assumption that CSF AChEs might originate from CNS neurons. Long-term changes in the composition of CSF AChE variants were further pursued in AD patients treated with rivastigmine (n = 11) or tacrine (n = 17) in comparison to untreated AD patients (n = 5). In untreated patients, AChE-R was markedly reduced as compared with the baseline level (37%), whereas the medium size AChE-S complex was increased by 32%. Intriguingly, tacrine produced a general and profound up-regulation of all detected AChE variants (up to 117%), whereas rivastigmine treatment caused a mild and selective up-regulation of AChE-R ( approximately 10%, p < 0.05). Moreover, the change in the ratio of AChE-R to AChE-S (R/S-ratio) strongly and positively correlated with sustained cognition at 12 months (p < 0.0001). Thus, evaluation of changes in the composition of CSF AChE variants may yield important information referring to the therapeutic efficacy and/or development of drug tolerance in AD patients treated with anti-cholinesterases.

Stress-induced alternative splicing of acetylcholinesterase results in enhanced fear memory and long-term potentiation

Stress insults intensify fear memory; however, the mechanism(s) facilitating this physiological response is still unclear. Here, we report the molecular, neurophysiological and behavioral findings attributing much of this effect to alternative splicing of the acetylcholinesterase (AChE) gene in hippocampal neurons. As a case study, we explored immobilization-stressed mice with intensified fear memory and enhanced long-term potentiation (LTP), in which alternative splicing was found to induce overproduction of neuronal 'readthrough' AChE-R (AChE-R). Selective downregulation of AChE-R mRNA and protein by antisense oligonucleotides abolished the stress-associated increase in AChE-R, the elevation of contextual fear and LTP in the hippocampal CA1 region. Reciprocally, we intrahippocampally injected a synthetic peptide representing the C-terminal sequence unique to AChE-R. The injected peptide, which has been earlier found to exhibit no enzymatic activity, was incorporated into cortical, hippocampal and basal nuclei neurons by endocytosis and retrograde transport and enhanced contextual fear. Compatible with this hypothesis, inherited AChE-R overexpression in transgenic mice resulted in perikaryal clusters enriched with PKCbetaII, accompanied by PKC-augmented LTP enhancement. Our findings demonstrate a primary role for stress-induced alternative splicing of the AChE gene to elevated contextual fear and synaptic plasticity, and attribute to the AChE-R splice variant a major role in this process.

Acetylcholinesterase induces neuronal cell loss, astrocyte hypertrophy and behavioral deficits in mammalian hippocampus

Previous studies have demonstrated that acetylcholinesterase (AChE) promotes the assembly of amyloid-beta-peptides into neurotoxic amyloid fibrils and is toxic for chick retina neuronal cultures and neuroblastoma cells. Moreover, AChE is present in senile plaques in Alzheimer's disease (AD) brains. Here we have studied the effect of AChE on astrocytes and hippocampal neurons in vivo. Morphological as well as behavioral disturbances were analyzed after intrahippocampal injection of AChE. Rats were trained in the Morris water maze and assayed for behavioral parameters. Neuronal cell loss was found in the upper leaf of the dentate gyrus in rats injected with AChE in comparison with control animals. Glial fibrillary acidic protein immunoreactivity showed astrocytic hypertrophy and the magnitude of the response was associated with neuronal cell loss. Behavioral results show that injection of AChE produces cognitive impairment demonstrated by an altered water maze performance including (i) a higher escape latency score, (ii) a decreased spatial acuity and (iii) a shorter time of swimming in the platform quadrant. These findings indicate that a local increment in neuronal AChE concentration at the mammalian hippocampus, such as those present in amyloid deposits, may play a role in triggering neuropathological and behavioral changes such as those observed in AD brains.

Interaction of "readthrough" acetylcholinesterase with RACK1 and PKCbeta II correlates with intensified fear-induced conflict behavior

Behavioral reactions to stress are altered in numerous psychiatric and neurodegenerative syndromes, but the corresponding molecular processes and signal transduction pathways are yet unknown. Here, we report that, in mice, the stress-induced splice variant of acetylcholinesterase, AChE-R, interacts intraneuronally with the scaffold protein RACK1 and through it, with its target, protein kinase CbetaII (PKCbetaII), which is known to be involved in fear conditioning. In stress-responsive brain regions of normal FVBN mice, the mild stress of i.p. injection increased AChE and PKCbetaII levels in a manner suppressible by antisense prevention of AChE-R accumulation. Injection stress also prolonged conflict between escape and hiding in the emergence into an open field test. Moreover, transgenic FVBN mice overexpressing AChE-R displayed prolonged delay to emerge into another field (fear-induced behavioral inhibition), associated with chronically intensified neuronal colabeling of RACK1 and PKCbetaII in stress-responsive brain regions. These findings are consistent with the hypothesis that stress-associated changes in cholinergic gene expression regulate neuronal PKCbetaII functioning, promoting fear-induced conflict behavior after stress.

Chronic acetylcholinesterase overexpression induces multilevelled aberrations in mouse neuromuscular physiology

Chronic overexpression of the acetylcholine-hydrolysing enzyme acetylcholinesterase (AChE) is a notable consequence of exposure to anticholinesterase drugs or poisons. However, the physiological consequences for the resultant neuromuscular disfunction have not yet been carefully analysed. Here we report detailed dissection of the different components of neuromuscular function in transgenic mice previously shown to display motor fatigue and altered muscle morphology as a consequence of neuronal overexpression of AChE-S, the synaptic AChE variant. Transgenic diaphragm muscle presented exaggerated fatigue as a combined consequence of neurotransmission fading and muscle mechanical malfunctioning. In a tetanic stimulation protocol, transgenic muscles rapidly fatigued to a larger extent than wild-type muscles, when stimulated either directly or via the phrenic nerve. AChE overexpression involved moderate but significant aberrations of synaptic transmission with higher quantal content (measured at 0.2 mM Ca(2+), 2.3 mM Mg(2+)). Furthermore, treatment with the anti-cholinesterase physostigmine revealed a higher amplitude and half-decay time of the transgenic quantal postsynaptic response. Our observations imply that elevated levels of neuronal AChE-S are expected to cause muscle exhaustion due to a combination of modest, multilevelled aberrations in synaptic transmission, muscle function and morphology.