Acetylcholinesterase enhances neurite growth and synapse development through alternative contributions of its hydrolytic capacity, core protein, and variable C termini

Acetylcholinesterase modulates neurite outgrowth on fibronectin

Acetylcholinesterase (AChE) has been reported to be involved in the modulation of neurite outgrowth. To understand the role played by different domains, we transfected neuroblastoma cells with three constructs containing the invariant region of AChE, differing in the exon encoding the C-terminus and therefore in AChE cellular fate and localization. All isoforms increased neurite extension, suggesting the involvement of the invariant domain [A. De Jaco, G. Augusti-Tocco, S. Biagioni, Alternative AChE molecular forms exhibit similar ability to induce neurite outgrowth, J. Neurosci. Res. 70 (2002) 756-765]. The peripheral anionic site (PAS) is encoded by invariant exons and represents the domain involved in non-cholinergic functions of AChE. Masking of PAS with fasciculin results in a significant decrease of neurite outgrowth in all clones overexpressing AChE. A strong reduction was also observed when clones were cultured on fibronectin. Treatment of clones with fasciculin, therefore masking PAS, abolished the fibronectin-induced reduction. The inhibition of the catalytic site cannot revert the fibronectin effect. Finally, when clones were cultured on fibronectin in the presence of heparin, a ligand of fibronectin, the inhibitory effect was completely reversed. Our results indicate that PAS could directly or indirectly mediate AChE/fibronectin interactions.

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.

Regulation of a transcript encoding the proline-rich membrane anchor of globular muscle acetylcholinesterase. The suppressive roles of myogenesis and innervating nerves

The transcriptional regulation of proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), was revealed in muscle during myogenic differentiation under the influence of innervation. During myotube formation of C2C12 cells, the expression of AChE(T) protein and the enzymatic activity were dramatically increased, but the level of G(4) AChE was relatively decreased. This G(4) AChE in C2C12 cells was specifically recognized by anti-PRiMA antibody, suggesting the association of this enzyme with PRiMA. Reverse transcription-PCR analysis revealed that the level of PRiMA mRNA was reduced during the myogenic differentiation of C2C12 cells. Overexpression of PRiMA in C2C12 myotubes significantly increased the production of G(4) AChE. The oligomerization of G(4) AChE, however, did not require the intracellular cytoplasmic tail of PRiMA. After overexpressing the muscle regulatory factors, myogenin and MyoD, the expressions of PRiMA and G(4) AChE in cultured myotubes were markedly reduced. In addition, calcitonin gene-related peptide, a known motor neuron-derived factor, and muscular activity were able to suppress PRiMA expression in muscle; the suppression was mediated by the phosphorylation of a cAMP-responsive element-binding protein. In accordance with the in vitro results, sciatic nerve denervation transiently increased the expression of PRiMA mRNA and decreased the phosphorylation of cAMP-responsive element-binding protein as well as its activator calcium/calmodulin-dependent protein kinase II in muscles. Our results suggest that the expression of PRiMA, as well as PRiMA-associated G(4) AChE, in muscle is suppressed by muscle regulatory factors, muscular activity, and nerve-derived trophic factor(s).

The thymic theme of acetylcholinesterase splice variants in myasthenia gravis

Cholinergic signaling and acetylcholinesterase (AChE) influence immune response and inflammation. Autoimmune myasthenia gravis (MG) is mediated by antibodies to the acetylcholine receptor and current therapy is based on anti-AChE drugs. MG is associated with thymic hyperplasia, showing signs of inflammation. The objectives of this study were to analyze the involvement of AChE variants in thymic hyperplasia. We found lower hydrolytic activities in the MG thymus compared with adult controls, accompanied by translocation of AChE-R from the cytoplasm to the membrane and increased expression of the signaling protein kinase PKC-betaII. To explore possible causal association of AChE-R changes with thymic composition and function, we used an AChE-R transgenic model and showed smaller thymic medulla compared with strain-matched controls, indicating that AChE-R overexpression interferes with thymic differentiation mechanisms. Interestingly, AChE-R transgenic mice showed increased numbers of CD4(+)CD8(+) cells that were considerably more resistant in vitro to apoptosis than normal thymocytes, suggesting possibly altered positive selection. We further analyzed microarray data of MG thymic hyperplasia compared with healthy controls and found continuous and discrete changes in AChE-annotated GO categories. Together, these findings show that modified AChE gene expression and properties are causally involved in thymic function and development.

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.

Acetylcholinesterase genes within the Diptera: takeover and loss in true flies

It has recently been reported that the synaptic acetylcholinesterase (AChE) in mosquitoes is encoded by the ace-1 gene, distinct and divergent from the ace-2 gene, which performs this function in Drosophila. This is an unprecedented situation within the Diptera order because both ace genes derive from an old duplication and are present in most insects and arthropods. Nevertheless, Drosophila possesses only the ace-2 gene. Thus, a secondary loss occurred during the evolution of Diptera, implying a vital function switch from one gene (ace-1) to the other (ace-2). We sampled 78 species, representing 50 families (27% of the Dipteran families) spread over all major subdivisions of the Diptera, and looked for ace-1 and ace-2 by systematic PCR screening to determine which taxonomic groups within the Diptera have this gene change. We show that this loss probably extends to all true flies (or Cyclorrhapha), a large monophyletic group of the Diptera. We also show that ace-2 plays a non-detectable role in the synaptic AChE in a lower Diptera species, suggesting that it has non-synaptic functions. A relative molecular evolution rate test showed that the intensity of purifying selection on ace-2 sequences is constant across the Diptera, irrespective of the presence or absence of ace-1, confirming the evolutionary importance of non-synaptic functions for this gene. We discuss the evolutionary scenarios for the takeover of ace-2 and the loss of ace-1, taking into account our limited knowledge of non-synaptic functions of ace genes and some specific adaptations of true flies.

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.

Molecular, biochemical and histochemical characterization of two acetylcholinesterase cDNAs from the German cockroach Blattella germanica

Full length cDNAs encoding two acetylcholinesterases (AChEs; Bgace1 and Bgace2) were cloned and characterized from the German cockroach, Blattella germanica. Sequence analyses showed that both genes possess all the typical features of ace, and that Bgace1 is orthologous to the insect ace1 whereas Bgace2 is to the insect ace2. Transcript level of Bgace1 was significantly higher (c. 10 fold) than that of Bgace2 in all 11 tissues examined, suggesting that Bgace1 likely encodes a predominant AChE. Multiple AChE bands were identified by native polyacrylamide gel electrophoresis and isoelectricfocusing from various tissue preparations, among which ganglia produced distinct two major and two minor AChE bands, indicative of the presence of at least two active AChEs. B. germanica AChEs appeared to be mainly localized in the central nervous system as demonstrated by histochemical activity staining, together with quantitative analysis of Bgace transcripts. Fluorescence in situ hybridization of the 1st thoracic ganglion confirmed that Bgace1 is predominantly transcribed and further showed that its transcript is found in almost entire region of inter or motor neurones including the cell bodies and axonal/dendritic branches. Bgace2 transcript is found only in the subset of neurones, particularly in the cell body. In addition, certain neurones were observed to express Bgace1 only.

Termination and beyond: acetylcholinesterase as a modulator of synaptic transmission

Termination of synaptic transmission by neurotransmitter hydrolysis is a substantial characteristic of cholinergic synapses. This unique termination mechanism makes acetylcholinesterase (AChE), the enzyme in charge of executing acetylcholine breakdown, a key component of cholinergic signaling. AChE is now known to exist not as a single entity, but rather as a combinatorial complex of protein products. The diverse AChE molecular forms are generated by a single gene that produces over ten different transcripts by alternative splicing and alternative promoter choices. These transcripts are translated into six different protein subunits. Mature AChE proteins are found as soluble monomers, amphipatic dimers, or tetramers of these subunits and become associated to the cellular membrane by specialized anchoring molecules or members of other heteromeric structural components. A substantial increasing body of research indicates that AChE functions in the central nervous system go far beyond the termination of synaptic transmission. The non-enzymatic neuromodulatory functions of AChE affect neurite outgrowth and synaptogenesis and play a major role in memory formation and stress responses. The structural homology between AChE and cell adhesion proteins, together with the recently discovered protein partners of AChE, predict the future unraveling of the molecular pathways underlying these multileveled functions.

Stress-induced cholinergic signaling promotes inflammation-associated thrombopoiesis

To study the role of the stress-induced “readthrough” acetylcholinesterase splice variant, AChE-R, in thrombopoiesis, we used transgenic mice overexpressing human AChE-R (TgR). Increased AChE hydrolytic activity in the peripheral blood of TgR mice was associated with increased thrombopoietin levels and platelet counts. Bone marrow (BM) progenitor cells from TgR mice presented an elevated capacity to produce mixed (GEMM) and megakaryocyte (Mk) colonies, which showed intensified labeling of AChE-R and its interacting proteins RACK1 and PKC. When injected with bacterial lipopolysaccharide (LPS), parent strain FVB/N mice, but not TgR mice, showed reduced platelet counts. Therefore, we primed human CD34+ cells with the synthetic ARP26 peptide, derived from the cleavable C-terminus of AChE-R prior to transplantation, into sublethally irradiated NOD/SCID mice. Engraftment of human cells (both CD45+ and CD41+ Mk) was significantly increased in mice that received ARP26-primed CD34+ human cells versus mice that received fresh nonprimed CD34+ human cells. Moreover, ARP26 induced polyploidization and proplatelet shedding in human MEG-01 promegakaryotic cells, and human platelet engraftment increased following ex vivo expansion of ARP26-treated CD34+ cells as compared to cells expanded with thrombopoietin and stem cell factor. Our findings implicate AChE-R in thrombopoietic recovery, suggesting new therapeutic modalities for supporting platelet production.

Localization, specific activity, and molecular forms of acetylcholinesterase in developmental stages of the cestode Mesocestoides corti

The nervous system of flatworms is quite simple although there is increasing evidence indicating that it is chemically complex. Studies of the nervous system in these animals have only been performed in the larval stage or in the adult worms, which are easy to obtain in nature, while the description of the nervous system in developing stages of these organisms is missing. Mesocestoides corti is a parasitic platyhelminth whose larvae can be induced in vitro to develop to adult, sexually mature worms, opening the possibility of studying the nervous system of a flatworm in different stages of development. Here, we describe the presence, activity, location, and molecular forms of acetylcholinesterase (AChE) in different stages of development of M. corti, from the larvae to adult forms of this endoparasite, obtained in in vitro cultures after induction of the larval stage with trypsin. Our results point to AChE as a molecular marker of the nervous system in platyhelminthes. The change in molecular forms of this enzyme and the increase in its activity during development from larvae to adult worm may reflect the presence of a more complex nervous system, necessary to adjust and coordinate the movement of a much bigger structure. A relationship between the development of the reproductive apparatus in segmented and adult worms with a more complex nervous system in these stages is also apparent. Finally, our study opens the possibility of applying anti-AChE as more effective therapeutic strategies against cestode parasites.

Hydrolytic and nonenzymatic functions of acetylcholinesterase comodulate hemopoietic stress responses

Glucocorticoid-initiated granulocytosis, excessive proliferation of granulocytes, persists after cortisol levels are lowered, suggesting the involvement of additional stress mediator(s). In this study, we report that the stress-induced acetylcholinesterase variant, AChE-R, and its cleavable, cell-penetrating C-terminal peptide, ARP, facilitate granulocytosis. In postdelivery patients, AChE-R-expressing granulocyte counts increased concomitantly with serum cortisol and AChE activity levels, yet persisted after cortisol had declined. Ex vivo, mononuclear cells of adult peripheral blood responded to synthetic ARP26 by overproduction of hemopoietically active proinflammatory cytokines (e.g., IL-6, IL-10, and TNF-alpha). Physiologically relevant ARP26)levels promoted AChE gene expression and induced the expansion of cultured CD34+ progenitors and granulocyte maturation more effectively than cortisol, suggesting autoregulatory prolongation of ARP effects. In vivo, transgenic mice overexpressing human AChE-R, unlike matched controls, showed enhanced expression of the myelopoietic transcription factor PU.1 and maintained a stable granulocytic state following bacterial LPS exposure. AChE-R accumulation and the consequent inflammatory consequences can thus modulate immune responses to stress stimuli.

In utero exposure to nicotine and chlorpyrifos alone, and in combination produces persistent sensorimotor deficits and Purkinje neuron loss in the cerebellum of adult offspring rats

This study was carried out to investigate the effect of in utero exposure to the cholinotoxicants, nicotine and chlorpyrifos, alone or in combination on neurobehavioral alterations and neuronal morphology latter in adult age. In the present study, 90 days old (corresponding to a human adult age) male and female offspring rats were evaluated for neurobehavioral, and neuropathological alterations following maternal, gestational exposure to nicotine and chlorpyrifos (O,O-diethyl-O-3,5,6-trichloro-2-pyridinyl phosphorothioate), alone and in combination. Female Sprague-Dawley rats (300-350 g) with timed-pregnancy were treated with nicotine (3.3 mg/kg/day, in bacteriostatic water via s.c. implantation of mini osmotic pump), chlorpyrifos (1.0 mg/kg, daily, dermal, in 75% ethanol, 1.0 ml/kg) or a combination of both chemicals, on gestational days (GD) 4-20. Control animals received bacteriostatic water via s.c. implantation of mini osmotic pump and dermal application of 70% ethanol. The offspring at postnatal day (PND) 90 were evaluated for neurobehavioral performance, changes in the activity of plasma butyrylcholinesterase (BChE) and acetylcholinesterase (AChE), and neuropathological alterations in the brain. Neurobehavioral evaluations included beam-walk score, beam-walk time, incline plane performance and forepaw grip time. Male and female offspring from mothers treated with nicotine and CPF, alone or in combination showed impairments in the performance of neurobehavioral tests, indicating sensorimotor deficits. Female offspring from mothers treated with a combination of nicotine and chlorpyrifos showed significant increase in plasma BChE activity. Brain regional AChE activity showed differential increases in male and female offspring. Brainstem and cerebellum of female offspring from mothers treated with nicotine or chlorpyrifos, alone or in combination showed increased AChE activity, whereas brainstem of male offspring from mothers treated with nicotine alone or a combination of nicotine and chlorpyrifos showed increase in AChE activity. Also, male offspring exposed in utero to nicotine exhibited increased AChE activity. Histopathological evaluations using cresyl violet staining showed a decrease in surviving Purkinje neurons in the cerebellum in offspring of all treatments groups. An increase in glial fibrillary acidic protein (GFAP) immuno-staining was observed in cerebellum white matter as well as granular cell layer (GCL) of cerebellum following all exposures. These results indicate that in utero exposure to nicotine and chlorpyrifos, alone and in combination produced significant sensorimotor deficits in male and female offspring, differential increase in brain AChE activity, a decrease in the surviving neurons and an increased expression of GFAP in cerebellum in adult offspring rats at a corresponding human adult age. Collectively, this study demonstrates that maternal exposure to environmental neurotoxic chemicals, i.e., nicotine and chlorpyrifos leads to developmental abnormalities in the offspring that persist latter into adulthood.

Concentration-Dependent Kinetics of Acetylcholinesterase Inhibition by the Organophosphate Paraoxon

For decades the interaction of the anticholinesterase organophosphorus compounds with acetylcholinesterase has been characterized as a straightforward phosphylation of the active site serine (Ser-203) which can be described kinetically by the inhibitory rate constant k(i). However, more recently certain kinetic complexities in the inhibition of acetylcholinesterase by organophosphates such as paraoxon (O,O-diethyl O-(p-nitrophenyl) phosphate) and chlorpyrifos oxon (O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphate) have raised questions regarding the adequacy of the kinetic scheme on which k(i) is based. The present article documents conditions in which the inhibitory capacity of paraoxon towards human recombinant acetylcholinesterase appears to change as a function of oxon concentration (as evidenced by a changing k(i)), with the inhibitory capacity of individual oxon molecules increasing at lower oxon concentrations. Optimization of a computer model based on an Ordered Uni Bi kinetic mechanism for phosphylation of acetylcholinesterse determined k(1) to be 0.5 nM(-1)h(-1), and k(-1) to be 169.5 h(-1). These values were used in a comparison of the Ordered Uni Bi model versus a k(i) model in order to assess the capacity of k(i) to describe accurately the inhibition of acetylcholinesterase by paraoxon. Interestingly, the k(i) model was accurate only at equilibrium (or near equilibrium), and when the inhibitor concentration was well below its K(d) (pseudo first order conditions). Comparisons of the Ordered Uni Bi and k(i) models demonstrate the changing k(i) as a function of inhibitor concentrations is not an artifact resulting from inappropriate inhibitor concentrations.

Diisopropylfluorophosphate administration in the pre-weanling period induces long-term changes in anxiety behavior and passive avoidance in adult mice

The developing brain may be particularly vulnerable to exposure to acetylcholinesterase (AChE) inhibitors because of the role of AChE on neuronal development and the effects of cholinergic pathways in mediating behavioral and hormonal responses to stress. C57BL/65 mice of both sexes were injected with 1 mg/kg s.c. diisopropylfluorophosphate (DFP) or saline in three separate experiments, on postnatal days (PNDs) 4-10, 14-20, or 30-36. Anxiety and conditioned avoidance were assessed on the elevated-plus maze (EPM) and step-down passive avoidance (PA) paradigms, respectively, at age 4-5 months. In addition, locomotion and reactivity to pain on the hot plate were assessed. Mice treated on PNDs 4-10 or PNDs 14-20 spent relatively more time and made more entries to the open arms on the first, but not second, exposure to the EPM. Females, but not males, treated with DFP showed deficits in PA retention after 24 h when treated on PNDs 4-10 and on PNDs 14-20. Mice treated on PNDs 30-36 were not impaired in either behavior. Administration of DFP in the preweanling period did not affect locomotor activity or pain reactivity. The results suggest that preweanling exposure to DFP results in anxiolysis in novel conflict situations but exacerbated context-enhanced anxiety.

On the multifunctionality of cholinesterases

Here we present novel information on non-classical functions of cholinesterases and on a cross-talk linking the two enzymes AChE and BChE. The first part of the article is focussed on the regulation of ChEs and the effects acquired when one of the proteins is knocked down (siRNA for BChE, AChE knock-out mouse). In the second part evidence is presented showing that AChE may exert adhesive properties through its binding to laminin, thus being involved in cell-matrix or cell-cell communication.

The C-terminal peptides of acetylcholinesterase: Cellular trafficking, oligomerization and functional anchoring

In vertebrates, the catalytic domain of acetylcholinesterase (AChE) may be associated with several C-terminal peptides generated by alternative splicing in the 3' region of transcripts. The "readthrough" (R) variant results from a lack of splicing after the last exon encoding the catalytic domain. Such a variant has been observed in Torpedo and in mammals; its C-terminal r peptide, also called "AChE Related Peptide" (ARP), is poorly conserved between rodents and humans. In rodents, it is significantly expressed in embryonic tissues and at a very low level in the brain of adult mice; it may be increased under various stress conditions, but remains very low. The "hydrophobic" (H) variant generates glycolipid (GPI)-anchored dimers, which are expressed in muscles of Torpedo, and in blood cells of mammals; H variants exist in Torpedo and in mammals, but apparently not in other vertebrate classes, suggesting that they were lost during evolution of early vertebrates and re-appeared independently in mammals. The "tailed" (T) variant exists in all vertebrate cholinesterases and their C-terminal t peptides are strongly conserved; in mammals, AChE(T) subunits represent the major type of acetylcholinesterase in cholinergic tissues. They produce a wide variety of oligomeric forms, ranging from monomers to heteromeric assemblies containing the anchoring proteins ColQ (collagen-tailed forms) and PRiMA (membrane-bound tetramers), which constitute the major functional enzyme species in mammalian muscles and brain, respectively. The oligomerization of AChE(T) subunits depends largely on the properties of their C-terminal t peptide. These peptides contain seven conserved aromatic residues, including three tryptophans, and are organized in an amphiphilic alpha helix in which these residues form a hydrophobic cluster. The presence of a cysteine is required for dimerization, while aromatic residues are necessary for tetramerization. In the collagen-tailed molecules, four t peptides form a coiled coil around a proline-rich motif (PRAD) located in the N-terminal region of ColQ. The t peptide also strongly influences the folding and cellular trafficking of AChE(T) subunits: the presence of hydrophobic residues induces partial misfolding leading to inactive protein, while aromatic residues, organized or not in an amphiphilic helix, induce intracellular degradation through the "Endoplasmic Reticulum Associated Degradation" (ERAD) pathway, rather than secretion. It has been proposed that the r and t C-terminal peptides, or fragments of these peptides, may exert independent, non cholinergic biological functions: this interesting possibility still needs to be documented, especially in view of their various degrees of evolutionary conservation.

Pharmacology and toxicology of cholinesterase inhibitors: uses and misuses of a common mechanism of action

Cholinesterase inhibitors have been used in the treatment of human diseases, the control of insect pests, and more notoriously as chemical warfare agents and weapons of terrorism. Most uses of cholinesterase inhibitors are based on a common mechanism of action initiated by inhibition of acetylcholinesterase (AChE). Extensive inhibition of this enzyme leads to accumulation of the neurotransmitter acetylcholine and enhanced stimulation of postsynaptic cholinergic receptors. This action is beneficial in cases where a reduction in cholinergic transmission contributes to clinical symptoms, e.g., low muscle tone in the autoimmune disorder myasthenia gravis due to loss of nicotinic receptors. Under normal conditions, however, extensive inhibition of AChE leads to excess synaptic acetylcholine levels, over-stimulation of cholinergic receptors, alteration of postsynaptic cell function and consequent signs of cholinergic toxicity. This biochemical cascade forms the basis for the use of anticholinesterase insecticides in pest control as well as for nerve agents in chemical warfare. Paradoxically, the short-acting cholinesterase inhibitor pyridostigmine, an important therapeutic agent in the treatment of myasthenia gravis, was used during the Persian Gulf War to prevent the long-term clinical consequences of possible organophosphate nerve agent exposure. As shown in the attacks in Matsumoto and Tokyo, these same nerve agents can be effectively used to inflict urban terror. Cholinesterase inhibitors thus share a common mechanism of pharmacological or toxicological action, ultimately modifying cholinergic signaling through disruption of acetylcholine degradation. While the use of cholinesterase inhibitors relies on their interaction with AChE, a variety of reports indicate that a number of cholinesterase inhibitors have additional sites of action that may have pharmacologic or toxicologic relevance. A variety of esterase and non-esterase enzymes, neurotransmitter receptors and elements of cell signaling pathways are targeted by some anticholinesterases. In some cases, these actions may occur at concentrations/dosages below those affecting cholinergic transmission. Studies of interactive toxicity of binary mixtures of common organophosphorus insecticides indicate that non-cholinesterase targets may be important in cumulative toxicity. Exposure to multiple anticholinesterases having selective effects on other macromolecules could confound the assumption of additivity in cumulative risk assessment. Knowledge of such selective additional targets may aid, however, in the optimization of strategies for poisoning therapy and in the further elucidation of mechanisms of toxicity for this class of compounds.

Acetylcholinesterase in Hirschsprung's disease

The association between the congenital absence of colonic ganglion cells and an increased acetylcholinesterase (AChE) expression in the affected tissue is of diagnostic importance in Hirschsprung's disease (HSCR). Investigation of AChE's function in development may also help unravel some of the complex pathophysiology in HSCR. Normal nerves do not stain for AChE, but increased AChE expression is associated with the hypertrophied extrinsic nerve fibres of the aganglionic segment in HSCR. Although a high degree of histochemical diagnostic accuracy exists, results are not always uniform, and false positives and false negatives are reported. False negative results are primarily related to age, and an absence of AChE reaction does not exclude HSCR in neonates within the first 3 weeks after birth. AChE staining results may lack uniformity, resulting in a number of technical modifications that have been made to improve standardization of AChE staining. At least two distinct histological patterns are described, types A and B. The interpretation of increased AChE staining patterns in ganglionated bowel at the time of surgical pull-through remains a problem in patients with HSCR. The development of rapid staining techniques has helped to identify normal ganglionated bowel with greater certainty. The presence of fine AChE neurofibrils in the ganglionated segment has contributed to the debate surrounding intestinal neuronal dysplasia. Quantitative assay of cholinesterase activity confirms the pattern of histochemical staining. AChE is particularly increased in relation to butrylcholinesterase, with one molecular form, the G4 tetrameric form, predominating. It is likely that the raised levels of AChE in aganglionic tissue are the transcriptional consequence of the abnormalities in signalling molecules that characterize HSCR. Evidence suggests that this AChE is functioning in a nonenzymatic capacity to promote cell adhesion and differentiation and that the hypertrophied nerves and neurofibrils may be the result of this increased AChE expression.

A preclinical view of cholinesterase inhibitors in neuroprotection: do they provide more than symptomatic benefits in Alzheimer's disease?

The prevalence of Alzheimer's disease (AD), a neurodegenerative condition whose greatest risk factor is old age, is expected to rise dramatically during the next five decades, along with the trend for increased longevity. Early diagnosis and intervention with therapies that halt or slow disease progress are likely to represent an important component of effective treatment. Although much progress has been made in this area, there are currently no clinically approved interventions for AD that are classed as disease modifying or neuroprotective. Cholinesterase inhibitors are a drug class used for the symptomatic treatment of AD. Recent evidence from preclinical studies indicates that these agents can attenuate neuronal damage and death from cytotoxic insults, and therefore might affect AD pathogenesis. The mechanisms by which these actions are mediated might or might not be directly related to their primary mode of action.

Characterization of acetylcholinesterase expression and secretion during osteoblast differentiation

Although best known for its role in cholinergic signalling, a substantial body of evidence suggests that acetylcholinesterase (AChE) has multiple biological functions. Previously, we and others identified AChE expression in areas of bone that lacked expression of other neuronal proteins. More specifically, we identified AChE expression at sites of new bone formation suggesting a role for AChE as a bone matrix protein. We have now characterised AChE expression, secretion and adhesive function in osteoblasts. Using Western blot analysis, we identified expression of two AChE species in osteoblastic cells, a major species of 68 kDa and less abundant species of approximately 55 kDa. AChE colocalised with the Golgi apparatus in osteoblastic cells and was identified in osteoblast-conditioned medium. Further analyses revealed differentiation-dependent secretion by osteoblasts, with AChE secretion levels corresponding with alkaline phosphatase activity. AChE expression by osteoblastic cells was also found to be regulated by mechanical strain both in vitro and in vivo. Finally, we investigated the possibility of a functional role for AChE in osteoblast adhesion. Using specific inhibitors, blockade of sites thought to be responsible for AChE adhesive properties caused a concentration-dependent decrease in osteoblastic cell adhesion, suggesting that AChE is involved in regulating cell-matrix interactions in bone.

Mouse acetylcholinesterase interacts in yeast with the extracellular matrix component laminin-1β

Acetylcholinesterase (AChE) is likely to have roles other than the hydrolysis of acetylcholine, e.g., related to developmental processes like neurite outgrowth, differentiation and adhesion. Here, we investigated whether AChE can function as a heterophilic cell adhesion molecule and searched for proteins interacting with it. Using the yeast two-hybrid method and a mouse brain cDNA library, we have identified an interaction between a partial cDNA encoding the globular domain IV of laminin chain beta1 and the amino acids 240-503 of mouse AChE. Biochemical co-immunoprecipitation assays confirmed the genetic results. We suggest that AChE, by interacting with laminin-1, is able to exert changes in adhesion signaling pathways.

Acetylcholinesterase function is dispensable for sensory neurite growth but is critical for neuromuscular synapse stability

The enzyme acetylcholinesterase (AChE) terminates synaptic transmission at cholinergic synapses by hydrolyzing the neurotransmitter acetylcholine. In addition, AChE is thought to play several 'non-classical' roles that do not require catalytic function. Most prominent among these is facilitation of neurite growth. Here, we report that the zebrafish zieharmonika (zim) locus encodes AChE. We show that one mutant zim allele is caused by a pre-mature stop codon, resulting in a truncated protein that lacks both the catalytic site and the carboxy-terminal neuritogenic domain. To explore the 'non-classical' role of AChE, we examined embryos mutant for this allele. In contrast to previous results using a catalytic-inactive allele, our analysis demonstrates that AChE is dispensable for muscle fiber development and Rohon-Beard sensory neuron growth and survival. Moreover, we show that in the absence of AChE, acetylcholine receptor clusters at neuromuscular junctions initially assemble, but that these clusters are not maintained. Taken together, our results demonstrate that AChE is dispensable for its proposed non-classical roles in muscle fiber formation and sensory neuron development, but is crucial for regulating the stability of neuromuscular synapses.

Bioactivity of a peptide derived from acetylcholinesterase: involvement of an ivermectin-sensitive site on the alpha 7 nicotinic receptor

A peptide fragment of 14 amino acids, derived from the C-terminus of acetylcholinesterase (AChE), might underlie the now well-established noncholinergic effects of the enzyme. This peptide is bioactive in a variety of systems including acute (brain slices) and chronic (organotypic culture) preparations of hippocampus, a pivotal area in Alzheimer's disease (AD); invariably, the action of the peptide is mediated specifically via an as yet unknown receptor. In this study, the allosteric alpha 7 agent, ivermectin (IVM), had a modest inhibitory effect, whilst that of the peptide was significantly more marked. However, ivermectin rendered ineffective the toxicity of high doses of the peptide, that is, when the two were co-applied, only the smaller effects of ivermectin were seen. Ivermectin, therefore, is presumably acting at a site that is identical to, or at least strongly interactive with, the normal binding site for AChE-peptide. This observation could have important implications for eventual therapeutic targeting of the action of AChE-peptide, in neurodegeneration.

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.

Neurological deficits induced by malathion, DEET, and permethrin, alone or in combination in adult rats

Malathion (O,O-dimethyl-S-[1,2-carbethoxyethyl]phosphorodithionate), DEET (N,N-diethyl-m-toluamide), and permethrin [(+/-)-cis/trans-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane carboxylic acid (3-phenoxyphenyl) methyl ester] are commonly used pesticides. To determine the effects of the dermal application of these chemicals, alone or in combination, the sensorimotor behavior, central cholinergic system, and histopathological alterations were studied in adult male Sprague-Dawley rats following a daily dermal dose of 44.4 mg/kg malathion, 40 mg/kg DEET, and 0.13 mg/kg permethrin, alone and in combination for 30 d. Neurobehavioral evaluations of sensorimotor functions included beam-walking score, beam walk time, inclined plane, and grip response assessments. Twenty-four hours after the last treatment with each chemical alone or in combination all behavioral measures were impaired. The combination of DEET and permethrin, malathion and permethrin, or the three chemicals together resulted in greater impairments in inclined performance than permethrin alone. Only animals treated with a combination of DEET and malathion or with DEET and permethrin exhibited significant increases in plasma butyrlcholinesterase (BChE) activity. Treatment with DEET or permethrin alone, malathion and permethrin, or DEET and permethrin produced significant increases in cortical acetylcholinesterase (AChE) activity. Combinations of malathion and permethrin or of DEET and permethrin produced significant decreases in midbrain AChE activity. Animals treated with DEET alone exhibited a significant increase in cortical m2 muscarinic ACh receptor binding. Quantification of neuron density in the dentate gyrus, CA1 and CA3 subfields of the hippocampus, midbrain, brainstem, and cerebellum revealed significant reductions in the density of surviving neurons with various treatments. These results suggest that exposure to real-life doses of malathion, DEET, and permethrin, alone or in combination, produce no overt signs of neurotoxicity but induce significant neurobehavioral deficits and neuronal degeneration in brain.

Signal transduction cascades underlying de novo protein synthesis required for neuronal morphogenesis in differentiating neurons

Differentiating neurons must acquire many unique morphological and functional characteristics in creating the precise neural circuits of the mature nervous system. The phenomenon of 'neuronal differentiation' includes a special set of simple, separate processes, that is, neuritogenesis, neurite outgrowth, pathfinding, targeting and synaptogenesis. All of these processes are critically dependent on the reorganization of actin cytoskeleton by many actin-binding proteins that function downstream of Rho-family GTPases. Furthermore, de novo synthesis of key proteins are critically involved in the reorganization of actin cytoskeleton during neuronal differentiation. In this article, we review recent progresses in the general mechanisms that control actin dynamics by various actin-binding proteins in differentiating neurons, including a series of recent studies from our laboratory on de novo synthesis of several key proteins that are essential for actin reorganization induced by second messengers. We demonstrated that dual regulation of cyclic AMP and Ca2+ determines cofilin (an actin-binding protein) phosphorylation states and LIM kinase 1 (a cofilin kinase) expression level during neuritogenesis.

A paradigm for single nucleotide polymorphism analysis: The case of the acetylcholinesterase gene

Acetylcholinesterase (AChE) plays a crucial physiological role in termination of impulse transmission at cholinergic synapses through rapid hydrolysis of acetylcholine. It is a highly conserved molecule, and only a few naturally occurring genetic polymorphisms have been reported in the human gene. The goal of the present study was to make a systematic effort to identify natural single nucleotide polymorphisms (SNPs) in the human ACHE gene. To this end, the genomic coding sequences for acetylcholinesterase of 96 unrelated control individuals from three distinct ethnic groups were analyzed. A total of 13 ACHE SNPs were identified, 10 of which are newly described, and five that should produce amino acid substitutions [c.101G>A (p.Arg34Gln), c.169G>A (p.Gly57Arg), c.1031A>G (p.Glu344Gly), c.1057C>A (p.His353Asn), and c.1775C>G (p.Pro592Arg)]. Population frequencies of 11 of the 13 SNPs were established in four different populations: African Americans, Ashkenazi Jews, Sephardic Jews, and Israeli Arabs; 15 haplotypes and five ethnospecific alleles were identified. The low number of SNPs identified until now in the ACHE gene is ascribed to technical hurdles arising from the high GC content and the presence of numerous repeat sequences, and does not reflect its intrinsic heterozygosity. Among the SNPs resulting in an amino acid substitution, three are within the mature protein, mapping on its external surface: they are thus unlikely to affect its catalytic properties, yet could have antigenic consequences or affect putative protein-protein interactions. Furthermore, the newly identified SNPs open the door to a study of the possible association of AChE with deleterious phenotypes-such as adverse drug responses to AChE inhibitors employed in treatment of Alzheimer patients and hypersensitivity to pesticides.

Functional idiotypic mimicry of an adhesion- and differentiation-promoting site on acetylcholinesterase

Acetylcholinesterase mediates cell adhesion and neurite outgrowth through a site associated with the peripheral anionic site (PAS). Monoclonal antibodies raised to this site block cell adhesion. We have raised anti-idiotypic antibodies to one of these antibodies. The anti-idiotypic antibodies recognized the immunogenic antibody and non-specific mouse IgG, but not acetylcholinesterase. Five antibodies (out of 143 clones, an incidence of 3.5%) were able to promote neurite outgrowth in human neuroblastoma cells in vitro in a similar manner to acetylcholinesterase itself, suggesting that these antibodies carry an internal image of the neuritogenic site. Two of the antibodies were significantly more effective (P < 0.01) than acetylcholinesterase in this regard. The antibodies also bound specifically to mouse laminin-1 and human collagen IV, as does acetylcholinesterase. This binding was displaced by unlabelled antibody, as well as by acetylcholinesterase itself, indicating competition with acetylcholinesterase. We have also investigated the development of anti-anti-idiotypic antibodies in mice in vivo, and have observed that four of these (out of 318 clones, an incidence of 1.26%) mimic the idiotypic antibody and abrogate adhesion in neuroblastoma cells. We have thus demonstrated functional mimicry of the neuritogenic site on acetylcholinesterase in anti-idiotypic antibodies, enhancement of this activity in one antibody, and mimicry of the idiotypic antibody site in anti-anti-idiotypic antibodies. Implications of these findings for differentiation-promoting cancer therapy are discussed.

Muscle induces neuronal expression of acetylcholinesterase in neuron-muscle co-culture: transcriptional regulation mediated by cAMP-dependent signaling

Presynaptic motor neuron synthesizes and secretes acetylcholinesterase (AChE) at vertebrate neuromuscular junctions. In order to determine the retrograde role of muscle in regulating the expression of AChE in motor neuron, a chimeric co-culture of NG108-15 cell, a cholinergic cell line that resembles motor neuron, with chick myotube was established to mimic the neuromuscular contact in vitro. A DNA construct of human AChE promoter tagged with luciferase (pAChE-Luc) was stably transfected into NG108-15 cells. The co-culture with myotubes robustly stimulated the promoter activity as well as the endogenous expression of AChE in pAChE-Luc stably transfected NG108-15 cells. Muscle extract derived from chick embryos when applied onto pAChE-Luc-expressing NG108-15 cells induced expressions of AChE promoter and endogenous AChE. The cAMP-responsive element mutation on human AChE promoter blocked the muscle-induced AChE transcriptional activity in cultured NG108-15 cells either in co-culturing with myotube or in applying muscle extract. The accumulation of intracellular cAMP and the phosphorylation of cAMP-responsive element-binding protein in cultured NG108-15 cells were stimulated by applied muscle extract. Part of the muscle-induced signaling was mimicked by application of calcitonin gene-related peptide in cultured NG108-15 cells. These results suggest the muscle-induced neuronal AChE expression in the co-culture is mediated by a cAMP-dependent signaling.

Making connections: cholinesterase-domain proteins in the CNS

Recent studies have highlighted novel functions of a group of cell adhesion molecules during nervous system development. Members of this protein family are characterized by an extracellular domain with sequence homology to cholinesterases and include the neuroligins, synaptic cell adhesion molecules recently implicated in autism, and neurotactin, a cell surface receptor involved in axonal pathfinding. Although these proteins have a structural organization similar to the enzyme acetylcholinesterase, the cholinesterase domain lacks enzymatic activity and functions as a protein-protein interaction motif. This protein family provides a striking example of how the function of a catalytically active domain has evolved to mediate receptor-ligand interactions that regulate morphogenetic processes during development of the nervous system.

Acetylcholinesterase level and molecular isoforms are altered in brain of Reelin Orleans mutant mice

In this study we examined changes in acetylcholinesterase (AChE) pattern in the brain of adult Reelin Orleans (RelnOrl) homozygous mutant mice. The AChE histochemistry firstly revealed an abnormal distribution of AChE-positive cells in several areas of the reeler brain, including cortices; the strongest labelling was observed in cerebellum and hippocampus when compared with controls. Biochemical determinations demonstrated an increase of 80-90% in AChE specific activity from cerebellar and hippocampal extracts. We also report that the AChE tetrameric form (G4) was selectively increased in the RelnOrl brain. The relationship between AChE and Reelin and suggested morphogenetic functions are also discussed.

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.

Acetylcholinesterase promotes neurite elongation, synapse formation, and surface expression of AMPA receptors in hippocampal neurones

Here we show that chronic application of low concentrations (0.01-0.05 U/ml) or a single application of 1-5 U/ml acetylcholinesterase (AChE) promotes the extension of neuronal processes, synapse formation, and alpha-amino-3-hydroxy-5-methylisoxazolepropionate receptor (AMPAR) surface expression in both embryonic and postnatal hippocampal cultures. The total number of AMPARs was unchanged but the proportion of receptors that were surface-expressed, predominantly at synapses, was approximately doubled following AChE treatment. Blockade of the peripheral anionic site of endogenous AChE in the cultures dramatically reduced neurite outgrowth but did not alter the appearance of synaptic markers SV2a and PSD95. These results indicate that AChE is necessary for normal dendrite and axon formation in hippocampal neurones and suggest that it may also play a role in excitatory synapse development, plasticity, and remodelling.

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

Molecular origin(s) of the diverse behavioral responses to anticholinesterases were explored in behaviorally impaired transgenic (Tg) FVB/N mice expressing synaptic human acetylcholinesterase (hAChE-S). Untreated hAChE-S Tg, unlike naïve FVB/N mice, presented variably intense neuronal overexpression of the alternatively spliced, stress-induced mouse "readthrough" mAChE-R mRNA. Both strains displayed similar diurnal patterns of locomotor activity that were impaired 3 days after a day-to-night switch. However, hAChE-S Tg, but not FVB/N mice responded to the circadian switch with irregular, diverse bursts of increased locomotor activity. In social recognition tests, controls displayed short-term recognition, reflected by decreased exploration of a familiar, compared to a novel juvenile conspecific as well as inverse correlation between social recognition and cortical and hippocampal AChE specific activities. In contrast, transgenics presented poor recognition, retrievable by tetrahydroaminoacridine (tacrine, 1.5 mg kg(-1)). Tacrine's effect was short-lived (24 h) suppression of the abnormal social recognition pattern in transgenics. Efficacy of antisense treatment was directly correlated with AChE-R levels and the severity of the impaired phenotype, being most apparent in transgenics presenting highly abnormal pre-treatment behavior. These findings demonstrate that neuronal AChE-R overproduction is involved in various behavioral impairments and anticholinesterase responses, and point to the antisense strategy as a potential approach for re-establishing cholinergic balance.

Post-transcriptional regulation of acetylcholinesterase mRNAs in nerve growth factor-treated PC12 cells by the RNA-binding protein HuD

Expression of acetylcholinesterase (AChE) is greatly enhanced during neuronal differentiation, but the nature of the molecular mechanisms remains to be fully defined. In this study, we observed that nerve growth factor treatment of PC12 cells leads to a progressive increase in the expression of AChE transcripts, reaching approximately 3.5-fold by 72 h. Given that the AChE 3'-untranslated region (UTR) contains an AU-rich element, we focused on the potential role of the RNA-binding protein HuD in mediating the increase in AChE mRNA seen in differentiating neurons. Using PC12 cells engineered to stably express HuD or an antisense to HuD, our studies indicate that HuD can regulate the abundance of AChE transcripts in neuronal cells. Furthermore, transfection of a reporter construct containing the AChE 3'-UTR showed that this 3'-UTR can increase expression of the reporter gene product in cells expressing HuD but not in cells expressing the antisense. RNA gel shifts and Northwestern blots revealed an increase in the binding of several protein complexes in differentiated neurons. Immunoprecipitation experiments demonstrated that HuD can bind directly AChE transcripts. These results show the importance of post-transcriptional mechanisms in regulating AChE expression in differentiating neurons and implicate HuD as a key trans-acting factor in these events.

The role of readthrough acetylcholinesterase in the pathophysiology of myasthenia gravis

Alternative splicing induces, under abnormal cholinergic neurotransmission, overproduction of the rare "readthrough" acetylcholinesterase variant AChE-R. We explored the pathophysiological relevance of this phenomenon in patients with myasthenia gravis (MG) and rats with experimental autoimmune MG (EAMG), neuromuscular junction diseases with depleted acetylcholine receptors. In MG and EAMG, we detected serum AChE-R accumulation. In EAMG, we alleviated electromyographic abnormalities by nanomolar doses of EN101, an antisense oligonucleotide that selectively lowers AChE-R in blood and muscle yet leaves unaffected the synaptic variant AChE-S. Whereas animals treated with placebo or conventional anticholinesterases continued to deteriorate, a 4 wk daily oral administration of EN101 improved survival, neuromuscular strength and clinical status in moribund EAMG rats. The efficacy of targeting only one AChE splicing variant highlights potential advantages of mRNA-targeted therapeutics for chronic cholinergic malfunctioning.

Pyridostigmine enhances glutamatergic transmission in hippocampal CA1 neurons

Pyridostigmine, a carbamate acetylcholinesterase (AChE) inhibitor, is routinely employed in the treatment of the autoimmune disease myasthenia gravis. Due to its positively charged ammonium group, under normal conditions pyridostigmine cannot cross the blood-brain barrier (BBB) and penetrate the brain. However, several studies have suggested that under conditions in which the BBB is disrupted, pyridostigmine enters the brain, changes cortical excitability, and leads to long-lasting alterations in gene expression. The aim of this study was to characterize the mechanisms underlying pyridostigmine-induced changes in the excitability of central neurons. Using whole cell intracellular recordings in hippocampal neurons we show that pyridostigmine decreases repetitive firing adaptation and increases the appearance of excitatory postsynaptic potentials. In voltage clamp recordings, both pyridostigmine and acetylcholine (ACh) increased the frequency but not the amplitude of excitatory postsynaptic currents. These effects were reversible upon the administration of the muscarinic receptor antagonist, atropine, and were not blocked by tetrodotoxin. We conclude that pyridostigmine, by increasing free ACh levels, causes muscarinic-dependent enhancement of excitatory transmission. This mechanism may explain central side effects previously attributed to this drug as well as the potency of AChE inhibitors, including nerve-gas agents and organophosphate pesticides, in the initiation of cortical synchronization, epileptic discharge, and excitotoxic damage.

AMPA receptor potentiation by acetylcholinesterase is age-dependently upregulated at synaptogenesis sites of the rat brain

We have used radioligand binding to synaptic membranes from distinct rat brain regions and quantitative autoradiography to investigate the postnatal evolution of acetylcholinesterase (AChE)-evoked up-regulation of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors in CNS areas undergoing synaptogenesis. Incubation of synaptosomal membranes or brain sections with purified AChE caused a developmentally modulated enhancement in the binding of [3H]-(S)-AMPA and the specific AMPA receptor ligand [3H]-(S)-5-fluorowillardiine, but did not modify binding to kainate neither N-methyl-D-aspartate receptors. In all postnatal ages investigated (4, 7, 14, 20, 27, 40 days-old and adult rats), AChE effect on binding was concentration-dependent and blocked by propidium, BW 284c51, diisopropylfluorophosphonate and eserine, therefore requiring indemnity of both peripheral and active sites of the enzyme. AChE-mediated enhancement of [3H]-fluorowillardiine binding was measurable in all major CNS areas, but displayed remarkable anatomical selectivity and developmental regulation. Autoradiograph densitometry exhibited distinct temporal profiles and peaks of treated/control binding ratios for different cortices, cortical layers, and nuclei. Within the parietal, occipital and temporal neocortices, hippocampal CA1 field and cerebellum, AChE-potentiated binding ratios peaked in chronological correspondence with synaptogenesis periods of the respective AMPA-receptor containing targets. This modulation of AMPA receptors by AChE is a molecular mechanism able to transduce localized neural activity into durable modifications of synaptic molecular structure and function. It might also contribute to AChE-mediated neurotoxicity, as postulated in Alzheimer's disease and other CNS disorders.

Development of human antibody fragments directed towards synaptic acetylcholinesterase using a semi-synthetic phage display library

Current Alzheimer's disease therapies suppress acetylcholine hydrolysis by inhibiting acetylcholinesterase (AChE) at cholinergic synapses. However, anticholinesterases promote alternative splicing changing the composition of brain AChE variants. To study this phenomenon we developed monoclonal antibodies to acetylcholinesterase synaptic peptide (ASP), a synthetic peptide with the C-terminal sequence unique to the human synaptic variant AChE-S. Screening of a phage display human antibody library allowed the isolation of single-chain Fv (scFv) antibodies that were highly specific for ASP, and displayed closely related third complementarity determining regions of the variable heavy chain domain (V(H)-CDR3). BIAcore analysis demonstrated dissociation constants at the micromolar range: 1.6 x 10(-6) and 2.0 x 10(-6) M for ASP and the complete AChE-S protein, respectively. The anti-ASP antibodies provide a novel tool for studying the synaptic AChE-S variant, the expression of which is altered in ageing and dementia.

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.

Alternative acetylcholinesterase molecular forms exhibit similar ability to induce neurite outgrowth

Several groups have reported that acetylcholinesterase (AChE), through a mechanism not involving its catalytic activity, may have a role in fiber elongation. These observations were performed on experimental systems in which acetylcholine synthesis was active. Because neurite outgrowth can be modulated by neurotransmitters, we used the N18TG2 neuroblastoma line, which is defective for neurotransmitter production, to evaluate whether AChE may modulate neurite sprouting in nonenzymatic ways. To avoid the possibility that differences between transfected and mock-transfected clones may be due to the selection procedure, N18TG2 cells were previously subcloned, and the FB5 subclone was used for transfections. We performed transfections of FB5 cells with three distinct constructs encoding for the glycosylphosphoinositol-anchored AChE form, the tetrameric AChE form, and a soluble monomeric AChE form truncated in its C-terminus. A morphometric analysis of retinoic acid-differentiated clones was also undertaken. The results revealed that higher AChE expression following transfection brings about a greater ability of the clones to grow fibers with respect to nontransfected or mock-transfected cells irrespective of the used construct. Having observed no differences between the morphology of the transfected clones, we tested the possibility that the culture substrate can affect the capability of the clones to extend fibers. Also in this case we revealed no differences between the clones cultured on uncoated or collagen-pretreated dishes. These data indicate that alternative AChE molecular forms that differ in their C-teminal region exhibit similar ability to induce fiber outgrowth and suggest that the protein region responsible for this role is located in the invariant portion of the AChE molecule.

Prevalence of fetal exposure to environmental toxins as determined by meconium analysis

OBJECTIVE

The primary objective was to determine whether environmental pollutants, specifically lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As) and organochlorine and organophosphate pesticides can be detected in meconium.

STUDY DESIGN

Prospective, cohort study. Infants were randomly recruited from the nurseries of five hospitals in Manila, Philippines. Their stools (meconium) were collected and analyzed for heavy metals by atomic absorption spectrophotometry and for pesticides by gas chromatography/mass spectrometry (GCMS).

RESULTS

A total of 426 infants were studied. The exposure rate (based on meconium analysis) and the median concentration of the pollutants in the positive samples were as follows: lead (26.5%; 35.77 microg/ml), cadmium (8.5%; 13.37 microg/ml), mercury (83.9%; 3.17 ng/ml), chlordane (12.7%; 22.48 microg/ml), chlorpyrifos (11.0%; 8.26 microg/ml), diazinon (34.3%; 12.96 microg/ml), DDT (26.5%; 12.56 microg/ml), lindane (73.5%; 2.0 microg/ml), malathion (53.0; 6.80 microg/ml), parathion (32.0%; 2.30 microg/ml) and pentachlorphenol (16.1%; 90.00 microg/ml). Some maternal and neonatal factors that were significantly associated with the presence of environmental toxins in meconium included multi-gravidity, multiparity, multiple gestation, meconium stained fluid, smoking, gestational age, low birth weight and infant gender.

CONCLUSION

Meconium analysis is a new and sensitive tool to detect fetal exposure to environmental toxins and its clinical use awaits further investigation.

A non-cholinergic, trophic action of acetylcholinesterase on hippocampal neurones in vitro: molecular mechanisms

In this study neurite outgrowth from cultured hippocampal neurones was increased by addition of acetylcholinesterase acting in a non-cholinergic manner. Only monomeric acetylcholinesterase, a form of acetylcholinesterase dominant in development, increased neurite outgrowth (3-10 U/ml); moreover this effect was not blocked by active site blockers (echothiophate and galanthamine) but was sensitive to the addition of peripheral site blockers (fasciculin and BW284c51). It appears therefore that acetylcholinesterase has alternative, non-cholinergic functions, one of which could be in development, via a peripheral site. The possibility of a causal relationship between neurite outgrowth and calcium influx was explored using a spectrum of acetylcholinesterase variants, inhibitors and calcium channel blockers. Acetylcholinesterase regulation of outgrowth was shown to depend on an influx of extracellular calcium specifically via the L-type voltage-gated calcium channel. In summary, we propose that, independent of its catalytic activity, a selective form of acetylcholinesterase has a role in the development of hippocampal neurones via a selective voltage-gated calcium channel.

Uranyl acetate-induced sensorimotor deficit and increased nitric oxide generation in the central nervous system in rats

We investigated the effects of uranyl acetate on sensorimotor behavior, generation of nitric oxide and the central cholinergic system of rats. Male Sprague-Dawley rats were treated with intramuscular injection of 0.1 and 1 mg/kg uranyl acetate in water, daily for 7 days. Control animals received equivalent amount of water. The treatment was stopped after the seventh injection because the animals in the 1-mg/kg group appeared lethargic. The animals were maintained for an additional observation period of 30 days. The study was initiated as a dose-finding study that covered doses of 10 and 100 mg/kg, as well. However, all the animals in the 100-mg/kg treatment group died after the third and fourth injections, and all animals given 10 mg/kg died after the fifth and sixth injections. On Day 30 following the cessation of treatment, the sensorimotor functions of the animals in the 0.1- and 1-mg/kg treatment groups were evaluated using a battery of tests that included measurements of postural reflexes, limb placing, orientation to vibrissae touch, grip time, beam walking and inclined plane performance. The animals were sacrificed the same day and the cerebral cortex, brainstem, cerebellum and midbrain were dissected. The levels of nitric oxide as marker for increased oxidative stress, and the integrity of the cholinergic system as reflected in acetylcholinesterase (AChE) activity and m2 muscarinic acetylcholine receptors ligand binding, were determined. The data from behavioral observations show that there was a dose-related deficit at the 0.1- and 1-mg/kg treatment groups for inclined plane performance. Both doses reduced grip time, but there was no significant difference between the two doses. Similarly, both beam-walk score and beam-walk time were impaired at both doses as compared with the controls. A significant increase in nitric oxide was seen at 0.1 mg/kg dose in cortex and midbrain, whereas brainstem and cerebellum showed an insignificant decrease at both the doses. Similarly, there was no significant change in nitric oxide levels in kidneys and liver of the treated animals as compared with the controls. There was a significant increase in AChE activity in the cortex of the animals treated with 1 mg/kg uranyl acetate, but not in other brain regions. Ligand binding densities for the m2 muscarinic receptor did not show any change. These results show that low-dose, multiple exposure to uranyl acetate caused prolonged neurobehavioral deficits after the initial exposure has ceased.

Concordance across species in the reproductive and developmental toxicity of tetrachloroethylene

Reproductive and developmental toxicities resulting from exposure to tetrachloroethylene include delayed or impaired conception, sperm quality, death during development, developmental neurotoxicity, and growth retardation. In most cases there was concordance between rodents and humans. The risk assessments indicated that neurotoxicity was the most sensitive endpoint for inhalation, whereas growth retardation was the most sensitive endpoint when exposure was by the oral route. The reference concentration (RfC) of 0.01 ppm was based on neurotoxicity among human subjects. The reference dose (RfD) of 0.0006 mg/kg per day was based on small for gestation age infants. In both cases, studies in rodents supported the credibility of these assessments. For the RfD, similar findings for other trihalomethanes have been reported. The latter part of pregnancy and early life may constitute a susceptible period for alterations leading to behavioral deficits. During this period, the capacity to metabolize tetrachloroethylene is reduced and may further contribute to the sensitivity during this phase of development. Studies suggest that an effect on dopamine metabolism is a plausible mode of action for some types of neurotoxicity. In addition, it has been suggested that this alteration may affect reproductive integrity by influencing prolactin levels.

Acetylcholinesterase is required for neuronal and muscular development in the zebrafish embryo

The neurotransmitter acetylcholine (ACh) has a crucial role in central and neuromuscular synapses of the cholinergic system. After release into the synaptic cleft, ACh is rapidly degraded by acetylcholinesterase (AChE). We have identified a mutation in the ache gene of the zebrafish, which abolishes ACh hydrolysis in homozygous animals completely. Embryos are initially motile but subsequently develop paralysis. Mutant embryos show defects in muscle fiber formation and innervation, and primary sensory neurons die prematurely. The neuromuscular phenotype in ache mutants is suppressed by a homozygous loss-of-function allele of the alpha-subunit of the nicotinic acetylcholine receptor (nAChR), indicating that the impairment of neuromuscular development is mediated by activation of nAChR in the mutant. Here we provide genetic evidence for non-classical functions of AChE in vertebrate development.

Identification of hybrid cholinesterase forms consisting of acetyl- and butyrylcholinesterase subunits in human glioma

Brain and non-brain tumors contain acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) transcripts and enzyme activity. AChE and BuChE occur in tissues as a set of molecular components, whose distribution in a cyst fluid from a human astrocytoma we investigated. The fluid displayed high BuChE and low AChE activities. Three types of cholinesterase (ChE) tetramers were identified in the fluid by means of sedimentation analyses and assays with specific inhibitors, and their sedimentation coefficients were 11.7S (ChE-I), 11.1S (ChE-II), and 10.5S (ChE-III). ChE-I was unretained, ChE-II was weakly retained and ChE-III was adsorbed to edrophonium-agarose, confirming the AChE nature of the latter. ChE-I and ChE-II tetramers contained BuChE subunits as shown by their binding with an antiserum against BuChE. The ChE activity of the immunocomplexes made with ChE-II and anti-BuChE antibodies decreased with the AChE inhibitor BW284c51, revealing that ChE-II was made of AChE and BuChE subunits, in contrast to ChE-I, which only contained BuChE subunits. The binding of an anti-AChE antibody (AE1) to ChE-II and ChE-III, but not to ChE-I, demonstrated the hybrid composition of ChE-II. A substantial fraction of the AChE tetramers and dimers of astrocytomas and oligodendrogliomas bound both to anti-AChE and anti-BuChE antibodies, which revealed a mixed composition of AChE and BuChE subunits in them. The AChE components of brain, meningiomas and neurinomas were only recognized by AE1. In conclusion, our results demonstrate that aberrant ChE oligomers consisting of AChE and BuChE subunits are generated in astrocytomatous cyst and gliomas but not in brain, meningiomas or neurinomas.