Induction of a 55 kDa acetylcholinesterase protein during apoptosis and its negative regulation by the Akt pathway

Restraint Stress Exacerbates Apoptosis in a 6-OHDA Animal Model of Parkinson Disease

Activation of the apoptotic pathway has been associated with promoting neuronal cell death in the pathophysiology of Parkinson disease (PD). Nonetheless, the mechanisms by which it may occur remain unclear. It has been suggested that stress-induced oxidation and potential apoptosis may play a major role in the progression of PD. Thus, in this study, we aimed to investigate the effect of subchronic restraint stress on striatal dopaminergic activity, iron, p53, caspase-3, and plasmatic acetylcholinesterase (AChE) levels in male Wistar rat model of PD induced by administration of 6-hydroxydopamine (6-OHDA) in the medial forebrain bundle (MFB). The obtained results showed that restraint stress exacerbates motor coordination deficits and anxiety in animals treated with 6-OHDA in comparison to animals receiving saline, and it had no effect on object recognition memory. On another hand, 6-OHDA decreased dopamine (DA) levels, increased iron accumulation, and induced overexpression of the pro-apoptotic factors caspase-3, p53, and AChE. More interestingly, post-lesion restraint stress exacerbated the expression of caspase-3 and AChE without affecting p53 expression. These findings suggest that subchronic stress may accentuate apoptosis and may contribute to DA neuronal loss in the striatal regions and possibly exacerbate the progression of PD.

Protection of insect neurons by erythropoietin/CRLF3-mediated regulation of pro-apoptotic acetylcholinesterase

Cytokine receptor-like factor 3 (CRLF3) is a conserved but largely uncharacterized orphan cytokine receptor of eumetazoan animals. CRLF3-mediated neuroprotection in insects can be stimulated with human erythropoietin. To identify mechanisms of CRLF3-mediated neuroprotection we studied the expression and proapoptotic function of acetylcholinesterase in insect neurons. We exposed primary brain neurons from Tribolium castaneum to apoptogenic stimuli and dsRNA to interfere with acetylcholinesterase gene expression and compared survival and acetylcholinesterase expression in the presence or absence of the CRLF3 ligand erythropoietin. Hypoxia increased apoptotic cell death and expression of both acetylcholinesterase-coding genes ace-1 and ace-2. Both ace genes give rise to single transcripts in normal and apoptogenic conditions. Pharmacological inhibition of acetylcholinesterases and RNAi-mediated knockdown of either ace-1 or ace-2 expression prevented hypoxia-induced apoptosis. Activation of CRLF3 with protective concentrations of erythropoietin prevented the increased expression of acetylcholinesterase with larger impact on ace-1 than on ace-2. In contrast, high concentrations of erythropoietin that cause neuronal death induced ace-1 expression and hence promoted apoptosis. Our study confirms the general proapoptotic function of AChE, assigns a role of both ace-1 and ace-2 in the regulation of apoptotic death and identifies the erythropoietin/CRLF3-mediated prevention of enhanced acetylcholinesterase expression under apoptogenic conditions as neuroprotective mechanism.

Acetylcholinesterase Inhibitors in the Treatment of Neurodegenerative Diseases and the Role of Acetylcholinesterase in their Pathogenesis

Acetylcholinesterase (AChE) plays an important role in the pathogenesis of neurodegenerative diseases by influencing the inflammatory response, apoptosis, oxidative stress and aggregation of pathological proteins. There is a search for new compounds that can prevent the occurrence of neurodegenerative diseases and slow down their course. The aim of this review is to present the role of AChE in the pathomechanism of neurodegenerative diseases. In addition, this review aims to reveal the benefits of using AChE inhibitors to treat these diseases. The selected new AChE inhibitors were also assessed in terms of their potential use in the described disease entities. Designing and searching for new drugs targeting AChE may in the future allow the discovery of therapies that will be effective in the treatment of neurodegenerative diseases.

Acetylcholinesterase promotes apoptosis in insect neurons

Apoptosis plays a major role in development, tissue renewal and the progression of degenerative diseases. Studies on various types of mammalian cells reported a pro-apoptotic function of acetylcholinesterase (AChE), particularly in the formation of the apoptosome and the degradation of nuclear DNA. While three AChE splice variants are present in mammals, invertebrates typically express two ache genes that code for a synaptically located protein and a protein with non-synaptic functions respectively. In order to investigate a potential contribution of AChE to apoptosis in insects, we selected the migratory locust Locusta migratoria. We established primary neuronal cultures of locust brains and characterized apoptosis progression in vitro. Dying neurons displayed typical characteristics of apoptosis, including caspase-activation, nuclear condensation and DNA fragmentation visualized by TUNEL staining. Addition of the AChE inhibitors neostigmine and territrem B reduced apoptotic cell death under normal culture conditions. Moreover, both inhibitors completely suppressed hypoxia-induced neuronal cell death. Exposure of live animals to severe hypoxia moderately increased the expression of ace-1 in locust brains in vivo. Our results indicate a previously unreported role of AChE in insect apoptosis that parallels the pro-apoptotic role in mammalian cells. This similarity adds to the list of apoptotic mechanisms shared by mammals and insects, supporting the hypothesized existence of an ancient, complex apoptosis regulatory network present in common ancestors of vertebrates and insects.

Acetylcholinesterase and human cancers

The enzyme acetylcholinesterase (AChE) is a serine hydrolase whose primary function is to degrade acetylcholine (ACh) and terminate neurotransmission. Apart from its role in synaptic transmission, AChE has several "non-classical" functions in non-neuronal cells. AChE is involved in cellular growth, apoptosis, drug resistance pathways, response to stress signals and inflammation. The observation that the functional activity of AChE is altered in human tumors (relative to adjacent matched normal tissue) has raised several intriguing questions about its role in the pathophysiology of human cancers. Published reports show that AChE is a vital regulator of oncogenic signaling pathways involving proliferation, differentiation, cell-cell adhesion, migration, invasion and metastasis of primary tumors. The objective of this book chapter is to provide a comprehensive overview of the contributions of the AChE-signaling pathway in the growth of progression of human cancers. The AChE isoforms, AChE-T, AChE-R and AChE-S are robustly expressed in human cancer cell lines as well in human tumors (isolated from patients). Traditionally, AChE-modulators have been used in the clinic for treatment of neurodegenerative disorders. Emerging studies reveal that these drugs could be repurposed for the treatment of human cancers. The discovery of potent, selective AChE ligands will provide new knowledge about AChE-regulatory pathways in human cancers and foster the hope of novel therapies for this disease.

Acetylcholinesterase inhibition ameliorates retinal neovascularization and glial activation in oxygen-induced retinopathy

AIM

To investigate whether inhibition of acetylcholinesterase (AChE) by donepezil ameliorate aberrant retinal neovascularization (RNV) and abnormal glial activation in oxygen-induced retinopathy (OIR).

METHODS

A mouse model of RNV was induced in postnatal day 7 (P7) mice by exposure to 75% oxygen. Donepezil was administrated to P12 mice by intraperitoneal injection. Expression and localization of AChE in mouse retinas were determined by immunofluorescence. RNV was evaluated by paraffin sectioning and hematoxylin and eosin (HE) staining. Activation of retinal Müller glial cells were examined by immunoblot of glial fibrillary acidic protein (GFAP). rMC-1, a retinal Müller cell line, was used for in vitro study. Expression of hypoxia-induced factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) were determined by Western-blot analysis, enzyme-linked immunosorbent assay (ELISA) or immunostaining.

RESULTS

Aberrant RNV and glial activation was observed after OIR. Of note, retinal AChE was mainly expressed by retinal Müller glial cells and markedly increased in OIR mice. Systemic administration of donepezil significantly reduced RNV and abnormal glial activation in mice with OIR. Moreover, ischemia-induced HIF-1α accumulation and VEGF upregulation in OIR mouse retinas and cultured rMC-1 were significantly inhibited by donepezil intervention.

CONCLUSION

AchE is implicated in RNV with OIR. Inhibition of AChE by donepeizl is likely to be a potential therapeutic approach for retinal neovascular diseases.

Characterisation of cholinesterases in mucous secretions and their localisation in epidermis of Labeo rohita and Cirrhinus mrigala

Cholinesterases are multifunctional enzymes and have been associated with diverse physiological functions in addition to their classical role at synapses. In the present study, cholinesterase (ChE) isozymes have been characterised in mucous secretions and their activity has been localised in the epidermis of Labeo rohita and Cirrhinus mrigala. Zymography using specific substrates and inhibitors revealed the presence of two ChE isozymes-ChE-1 and ChE-2. The isozyme ChE-1 was characterised as an atypical butyrylcholinesterase and ChE-2 as a typical acetylcholinesterase in skin mucous secretions of both the fish species. Enzyme histochemical analysis demonstrated the presence of ChE activity in the epidermis of the fish species investigated. In both the fish species, strong ChE activity was observed in the outer-layer epithelial cells, taste buds and neuromasts. The middle and basal layer epithelial cells showed moderate to weak ChE activity. Club cells and mucous goblet cells showed the absence of ChE activity. Characterisation with specific inhibitors indicates that acetylcholinesterase (AChE) was the major cholinesterase type expressed in the epidermis of the two fish species investigated. Immunohistochemical localisation of apoptotic and cell proliferation markers, in addition, revealed high expression of active caspase 3 in the outer-layer epithelial cells, and proliferating cell nuclear antigen (PCNA) in the middle and basal layer epithelial cells. High ChE activity in caspase 3-positive cells in the outer layer of the epidermis and low in PCNA-positive cells in middle and basal layers could point towards the possible involvement of ChEs in cell death and their final extrusion from skin surface.

Bisphenol A Exposure and Sperm ACHE Hydroxymethylation in Men

Exposure to bisphenol A (BPA) has been shown to impact human sperm quality. The epigenetic mechanisms underlying the effect remain unknown. The acetylcholinesterase (ACHE) gene is a sperm-expressed gene encoding the acetylcholine hydrolyzing enzyme acetylcholinesterase and participates in the apoptosis of cells, including sperm. This study aimed to examine whether BPA exposure is associated with the hydroxymethylation level of the sperm ACHE gene. A total of 157 male factory workers were studied, among whom 74 had BPA exposure in the workplace (BPA exposure group) and 83 had no BPA exposure in the workplace (control group). Urine samples were collected for BPA measurement and semen samples were collected to assay for ACHE hydroxymethylation. Sperm ACHE hydroxymethylation level was higher in the BPA exposure group (p = 0.041) compared to the control group. When subjects were categorized according to tertiles of detected BPA level, higher ACHE hydroxymethylation levels were observed for the lowest, middle, and top tertiles compared to those with BPA below the limit of detection (LOD). In a linear regression analysis adjusted for confounders, a positive linear association between urine BPA concentration and 5-hydroxymethylcytosine (5hmC) rate of the sperm ACHE gene was observed, although the association did not reach statistical significance in all categories after being stratified by the BPA tertile. In conclusion, 5hmC of the sperm ACHE gene was positively associated with BPA exposure, which may provide supportive evidence for BPA’s effects on male fertility or other health endpoints.

Proteolytic cleavage is required for functional neuroligin 2 maturation and trafficking in Drosophila

Neuroligins (Nlgs) are transmembrane cell adhesion molecules playing essential roles in synapse development and function. Genetic mutations in neuroligin genes have been linked with some neurodevelopmental disorders such as autism. These mutated Nlgs are mostly retained in the endoplasmic reticulum (ER). However, the mechanisms underlying normal Nlg maturation and trafficking have remained largely unknown. Here, we found that Drosophila neuroligin 2 (DNlg2) undergoes proteolytic cleavage in the ER in a variety of Drosophila tissues throughout developmental stages. A region encompassing Y642-T698 is required for this process. The immature non-cleavable DNlg2 is retained in the ER and non-functional. The C-terminal fragment of DNlg2 instead of the full-length or non-cleavable DNlg2 is able to rescue neuromuscular junction defects and GluRIIB reduction induced by dnlg2 deletion. Intriguingly, the autism-associated R598C mutation in DNlg2 leads to similar marked defects in DNlg2 proteolytic process and ER export, revealing a potential role of the improper Nlg cleavage in autism pathogenesis. Collectively, our findings uncover a specific mechanism that controls DNlg2 maturation and trafficking via proteolytic cleavage in the ER, suggesting that the perturbed proteolytic cleavage of Nlgs likely contributes to autism disorder.

Hydrogen peroxide modifies both activity and isoforms of acetylcholinesterase in human neuroblastoma SH-SY5Y cells

The involvement of cholinergic system and the reactive oxygen species (ROS) in the pathogenesis of some degenerative diseases has been widely reported; however, the specific impact of hydrogen peroxide (H₂O₂) on the acetylcholinesterase (AChE) activity as well as AChE isoform levels has not been clearly established. Hence, the purpose of present study is to clarify whether H₂O₂ alters these parameters.

Human neuroblastoma SH-SY5Y cells were treated with H₂O₂ (1–1000 µM) for 24 h and AChE activity and AChE and cytochrome c levels were evaluated. AChE activity was strongly increased from 1 µM to 1000 µM of H₂O_2. The results of the kinetic study showed that H₂O₂ affected Vmax but not Km; and also that H₂O₂ changed the sigmoid kinetic observed in control samples to hyperbolic kinetic. Thus, results suggest that H₂O₂ acts as an allosteric activators. In addition, H₂O₂, (100–1000 µM) reduced the total AChE content and modified its isoform profile (mainly 50-, 70-, and 132-kDa)·H₂O₂ from 100 µM to 1000 µM induced cytochrome c release confirming cell death by apoptosis. All these results together suggest: a) the involvement of oxidative stress in the imbalance of AChE; and b) treatment with antioxidant agents may be a suitable strategy to protect cholinergic system alterations promoted by oxidative stress.

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H₂O₂ impact on AChE structure from SH-SY5Y cells, acting as an allosteric effector.

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H₂O₂ decreased AChE levels and changed AChE isoform profile from SH-SY5Y cells.

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Oxidative stress could promote disturbances in cholinergic system.

Endochondral Ossification Is Accelerated in Cholinesterase-Deficient Mice and in Avian Mesenchymal Micromass Cultures

Most components of the cholinergic system are detected in skeletogenic cell types in vitro, yet the function of this system in skeletogenesis remains unclear. Here, we analyzed endochondral ossification in mutant murine fetuses, in which genes of the rate-limiting cholinergic enzymes acetyl- (AChE), or butyrylcholinesterase (BChE), or both were deleted (called here A-B+, A+B-, A-B-, respectively). In all mutant embryos bone growth and cartilage remodeling into mineralizing bone were accelerated, as revealed by Alcian blue (A-blu) and Alizarin red (A-red) staining. In A+B- and A-B- onset of mineralization was observed before E13.5, about 2 days earlier than in wild type and A-B+ mice. In all mutants between E18.5 to birth A-blu staining disappeared from epiphyses prematurely. Instead, A-blu+ cells were dislocated into diaphyses, most pronounced so in A-B- mutants, indicating additive effects of both missing ChEs in A-B- mutant mice. The remodeling effects were supported by in situ hybridization (ISH) experiments performed on cryosections from A-B- mice, in which Ihh, Runx2, MMP-13, ALP, Col-II and Col-X were considerably decreased, or had disappeared between E18.5 and P0. With a second approach, we applied an improved in vitro micromass model from chicken limb buds that allowed histological distinction between areas of cartilage, apoptosis and mineralization. When treated with the AChE inhibitor BW284c51, or with nicotine, there was decrease in cartilage and accelerated mineralization, suggesting that these effects were mediated through nicotinic receptors (α7-nAChR). We conclude that due to absence of either one or both cholinesterases in KO mice, or inhibition of AChE in chicken micromass cultures, there is increase in cholinergic signalling, which leads to increased chondroblast production and premature mineralization, at the expense of incomplete chondrogenic differentiation. This emphasizes the importance of cholinergic signalling in cartilage and bone formation.

Acetylcholinesterase Regulates Skeletal In Ovo Development of Chicken Limbs by ACh-Dependent and -Independent Mechanisms

Formation of the vertebrate limb presents an excellent model to analyze a non-neuronal cholinergic system (NNCS). Here, we first analyzed the expression of acetylcholinesterase (AChE) by IHC and of choline acetyltransferase (ChAT) by ISH in developing embryonic chicken limbs (stages HH17-37). AChE outlined formation of bones, being strongest at their distal tips, and later also marked areas of cell death. At onset, AChE and ChAT were elevated in two organizing centers of the limb anlage, the apical ectodermal ridge (AER) and zone of polarizing activity (ZPA), respectively. Thereby ChAT was expressed shortly after AChE, thus strongly supporting a leading role of AChE in limb formation. Then, we conducted loss-of-function studies via unilateral implantation of beads into chicken limb anlagen, which were soaked in cholinergic components. After varying periods, the formation of cartilage matrix and of mineralizing bones was followed by Alcian blue (AB) and Alizarin red (AR) stainings, respectively. Both acetylcholine (ACh)- and ChAT-soaked beads accelerated bone formation in ovo. Notably, inhibition of AChE by BW284c51, or by the monoclonal antibody MAB304 delayed cartilage formation. Since bead inhibition of BChE was mostly ineffective, an ACh-independent action during BW284c51 and MAB304 inhibition was indicated, which possibly could be due to an enzymatic side activity of AChE. In conclusion, skeletogenesis in chick is regulated by an ACh-dependent cholinergic system, but to some extent also by an ACh-independent aspect of the AChE protein.

Cholinergic system and cell proliferation

The cholinergic system, comprising acetylcholine, the proteins responsible for acetylcholine synthesis and release, acetylcholine receptors and cholinesterases, is expressed by most human cell types. Acetylcholine is a neurotransmitter, but also a local signalling molecule which regulates basic cell functions, and cholinergic responses are involved in cell proliferation and apoptosis. So, activation of nicotinic and muscarinic receptors has a proliferative and anti-apoptotic effect in many cells. The content of choline acetyltransferase, acetylcholine receptors and cholinesterases is altered in many tumours, and cholinesterase content correlates with patient survival in some cancers. During apoptosis, acetylcholinesterase is induced and appears in the nuclei. Acetylcholinesterase participates in the regulation of cell proliferation and apoptosis through hydrolysis of acetylcholine and by other catalytic and non catalytic mechanisms, in a variant-specific manner. This review gathers information on the role of cholinergic system and specially acetylcholinesterase in cell proliferation and apoptosis.

Linking Pesticide Exposure with Pediatric Leukemia: Potential Underlying Mechanisms

Leukemia is the most common cancer in children, representing 30% of all childhood cancers. The disease arises from recurrent genetic insults that block differentiation of hematopoietic stem and/or progenitor cells (HSPCs) and drives uncontrolled proliferation and survival of the differentiation-blocked clone. Pediatric leukemia is phenotypically and genetically heterogeneous with an obscure etiology. The interaction between genetic factors and environmental agents represents a potential etiological driver. Although information is limited, the principal toxic mechanisms of potential leukemogenic agents (e.g., etoposide, benzene metabolites, bioflavonoids and some pesticides) include topoisomerase II inhibition and/or excessive generation of free radicals, which may induce DNA single- and double-strand breaks (DNA-DSBs) in early HSPCs. Chromosomal rearrangements (duplications, deletions and translocations) may occur if these lesions are not properly repaired. The initiating hit usually occurs in utero and commonly leads to the expression of oncogenic fusion proteins. Subsequent cooperating hits define the disease latency and occur after birth and may be of a genetic, epigenetic or immune nature (i.e., delayed infection-mediated immune deregulation). Here, we review the available experimental and epidemiological evidence linking pesticide exposure to infant and childhood leukemia and provide a mechanistic basis to support the association, focusing on early initiating molecular events.

A novel role for synaptic acetylcholinesterase as an apoptotic deoxyribonuclease

In addition to terminating neurotransmission by hydrolyzing acetylcholine, synaptic acetylcholinesterase (AChES) has been found to have a pro-apoptotic role. However, the underlying mechanism has rarely been investigated. Here, we report a nuclear translocation-dependent role for AChES as an apoptotic deoxyribonuclease (DNase). AChES polypeptide binds to and cleaves naked DNA at physiological pH in a Ca(2+)-Mg(2+)-dependent manner. It also cleaves chromosomal DNA both in pre-fixed and in apoptotic cells. In the presence of a pan-caspase inhibitor, the cleavage still occurred after nuclear translocation of AChES, implying that AChES-DNase acts in a CAD- and EndoG-independent manner. AChE gene knockout impairs apoptotic DNA cleavage; this impairment is rescued by overexpression of the wild-type but not (aa 32-138)-deleted AChES. Furthermore, in comparison with the nuclear-localized wild-type AChES, (aa 32-138)-deleted AChES loses the capacity to initiate apoptosis. These observations confirm that AChES mediates apoptosis via its DNase activity.

Identification and Expression of Acetylcholinesterase in Octopus vulgaris Arm Development and Regeneration: a Conserved Role for ACHE?

Acetylcholinesterase (ACHE) is a glycoprotein with a key role in terminating synaptic transmission in cholinergic neurons of both vertebrates and invertebrates. ACHE is also involved in the regulation of cell growth and morphogenesis during embryogenesis and regeneration acting through its non-cholinergic sites. The mollusk Octopus vulgaris provides a powerful model for investigating the mechanisms underlying tissue morphogenesis due to its high regenerative power. Here, we performed a comparative investigation of arm morphogenesis during adult arm regeneration and embryonic arm development which may provide insights on the conserved ACHE pathways. In this study, we cloned and characterized O. vulgaris ACHE, finding a single highly conserved ACHE hydrophobic variant, characterized by prototypical catalytic sites and a putative consensus region for a glycosylphosphatidylinositol (GPI)-anchor attachment at the COOH-terminus. We then show that its expression level is correlated to the stage of morphogenesis in both adult and embryonic arm. In particular, ACHE is localized in typical neuronal sites when adult-like arm morphology is established and in differentiating cell locations during the early stages of arm morphogenesis. This possibility is also supported by the presence in the ACHE sequence and model structure of both cholinergic and non-cholinergic sites. This study provides insights into ACHE conserved roles during processes of arm morphogenesis. In addition, our modeling study offers a solid basis for predicting the interaction of the ACHE domains with pharmacological blockers for in vivo investigations. We therefore suggest ACHE as a target for the regulation of tissue morphogenesis.

Acetylcholinesterase function in apoptotic retina pigment epithelial cells induced by H2O2

AIM

To investigate the acetylcholinesterase (AChE) expression involved in retina pigment epithelial (RPE) apoptosis induced by higher concentrations H2O2.

METHODS

The human retinal pigment epithelium cell line ARPE-19 was from ATCC (Rockville, MD). Cultured ARPE-19 cells were treated with H2O2 at 0, 250, 500, 1 000, 2 000µmol/L and cell viability was measured with MTT assay. AChE expression and DNA fragments were analyzed by immunocytochemistry, TUNEL and PARP-1 Western blotting.

RESULTS

Immunofluorescence detected AChE exist in the normal human retinal tissue. When H2O2 >500µmol/L, AChE expression showed an increase after 2h, and this concentration was selected for the present study. RPE cell was induced with 1 000µmol/L H2O2 for 2h, compared to the control group, cell activity decline detected by MTT, AChE and PARP-1 protein expression was significantly increased detected by Western blotting. AChE immunofluorescence staining was positive in RPE cell after H2O2 incubate 2h. In addition, pretreatment with 100µmol/L epigallocatechin gallate (EGCG), cell viability increased from 31.20%±3.90% to 70.23%±12.96%.

CONCLUSION

AChE is weakly expressed in normal human RPE cells. Stimulation with H2O2 caused the stable increase of AChE expression in RPE cells, which may indicate that AChE may be an important role in AMD.

Hsa-miR-132 regulates apoptosis in non-small cell lung cancer independent of acetylcholinesterase

MiR-132 is enriched in the central nerve system and is thought to be involved in neuronal development, maturation and function, and to be associated with several neurological disorders including Alzheimer's disease. In addition to its documented neuronal functions, an emerging role for miR-132 in tumorigenesis has been suggested. Recently, hsa-miR-132 was shown to be modulated in different tumor types. However, its role in non-small cell lung cancer (NSCLC) remains unclear. Here, we show that hsa-miR-132 can initiate apoptosis in NSCLC cells to dramatically attenuate tumor formation in nude mice independent of its effect on the proliferation/apoptosis-associated gene, acetylcholinesterase (AChE). Interestingly, hsa-miR-132 has no pro-apoptotic effect in normal pulmonary trachea epithelium. Taken together, these results suggest that hsa-miR-132 represses NSCLC growth by inducing apoptosis independent of AChE.

Adult hippocampal neurogenesis and mRNA expression are altered by perinatal arsenic exposure in mice and restored by brief exposure to enrichment

Arsenic is a common and pervasive environmental contaminant found in drinking water in varying concentrations depending on region. Exposure to arsenic induces behavioral and cognitive deficits in both human populations and in rodent models. The Environmental Protection Agency (EPA) standard for the allotment of arsenic in drinking water is in the parts-per-billion range, yet our lab has shown that 50 ppb arsenic exposure during development can have far-reaching consequences into adulthood, including deficits in learning and memory, which have been linked to altered adult neurogenesis. Given that the morphological impact of developmental arsenic exposure on the hippocampus is unknown, we sought to evaluate proliferation and differentiation of adult neural progenitor cells in the dentate gyrus after 50 ppb arsenic exposure throughout the perinatal period of development in mice (equivalent to all three trimesters in humans) using a BrdU pulse-chase assay. Proliferation of the neural progenitor population was decreased by 13% in arsenic-exposed mice, but was not significant. However, the number of differentiated cells was significantly decreased by 41% in arsenic-exposed mice compared to controls. Brief, daily exposure to environmental enrichment significantly increased proliferation and differentiation in both control and arsenic-exposed animals. Expression levels of 31% of neurogenesis-related genes including those involved in Alzheimer's disease, apoptosis, axonogenesis, growth, Notch signaling, and transcription factors were altered after arsenic exposure and restored after enrichment. Using a concentration previously considered safe by the EPA, perinatal arsenic exposure altered hippocampal morphology and gene expression, but did not inhibit the cellular neurogenic response to enrichment. It is possible that behavioral deficits observed during adulthood in animals exposed to arsenic during development derive from the lack of differentiated neural progenitor cells necessary for hippocampal-dependent learning. This study is the first to determine the impact of arsenic exposure during development on adult hippocampal neurogenesis and related gene expression.

Synaptic acetylcholinesterase targeted by microRNA-212 functions as a tumor suppressor in non-small cell lung cancer

Acetylcholinesterase expression is modulated in various types of tumor, which suggests it is associated with tumor development; however, the mechanism of acetylcholinesterase gene regulation in tumors remains unclear. Here, we report that acetylcholinesterase is aberrantly expressed in non-small cell lung cancer and is an evolutionarily conserved functional target of miR-212. Acetylcholinesterase expression was negatively regulated by miR-212 in vitro and was inversely correlated with miR-212 expression in vivo. In addition, acetylcholinesterase levels were increased, and miR-212 levels decreased, in non-small cell lung cancer cells during cisplatin-induced apoptosis. We further determined that acetylcholinesterase acted as a pro-apoptotic gene in non-small cell lung cells; and attenuated the growth of xenografts in nude mice when upregulated. In contrast, elevated miR-212 levels preserved the protective effect of acetylcholinesterase silencing by RNA interference against cisplatin-induced apoptosis, whereas restoration of miR-212-resistant synaptic acetylcholinesterase expression inhibited the miR-212 anti-apoptotic function. The results demonstrated that miR-212 exerted an anti-apoptotic effect through direct repression of synaptic acetylcholinesterase expression in non-small cell lung cancer cells. Taken together, our study revealed that synaptic acetylcholinesterase may be a tumor suppressor and is modulated by miR-212 in non-small cell lung cancer.

Acetylcholinesterase deficiency decreases apoptosis in dopaminergic neurons in the neurotoxin model of Parkinson's disease

The apoptosis pathway has been proposed to be involved in causing neuronal cell death in the pathogenesis of Parkinson's disease. However, the details of this pathway are poorly understood. Previous research has shown increased acetylcholinesterase expression during apoptosis in various cell types, which suggests that acetylcholinesterase has a potential role in neuronal cell death. In this study, we found that acetylcholinesterase protein expression increased and caspase-3 was activated in PC12 cells treated with 1-methyl-4-phenylpyridinium. Furthermore, the genetic or pharmacological inhibition of acetylcholinesterase was shown to protect PC12 cells from MPP+ induced apoptotic cell death. To study the function of acetylcholinesterase as a mechanism of neuronal cell death in vivo, we subsequently established a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine Parkinson's disease mouse model utilizing acetylcholinesterase-deficient mice. Studies in these mice revealed reduced dopaminergic neuron loss and lower expression levels of apoptotic proteins in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated heterozygous mice compared to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated wild-type mice. We conclude that it is highly probable that acetylcholinesterase is involved in the pathogenesis of the neurotoxin model of Parkinson's disease via apoptosis. Specifically, a deficiency or inhibition of acetylcholinesterase can decrease apoptosis and protect dopaminergic neurons in the neurotoxin model of Parkinson's disease.

Cholinesterases in development: AChE as a firewall to inhibit cell proliferation and support differentiation

Acetylcholinesterase (AChE) is a most remarkable protein, not only because it is one of the fastest enzymes in nature, but also since it appears in many molecular forms and is regulated by elaborate genetic networks. AChE is expressed in many tissues during development and in mature organisms, as well as in healthy and diseased states. In search for alternative, "non-classical" functions of cholinesterases (ChEs), AChE could either work within the frame of classic cholinergic systems, but in non-neural tissues ("non-synaptic function"), or act non-enzymatically. Here, we review briefly some of the major ideas and advances of this field, and report on some recent progress from our own experimental work, e.g. that (i) non-neural ChEs have pronounced, predominantly enzymatic effects on early embryonic (limb) development in chick and mouse, that (ii) retinal R28 cells of the rat overexpressing synaptic AChE present a significantly decreased cell proliferation, and that (iii) in developing chick retina ACh-synthesizing and ACh-degrading cells originate from the same postmitotic precursor cells, which later form two locally opposing cell populations. We suggest that such distinct distributions of ChAT(+) vs. AChE(+) cells in the inner half retina provide graded distributions of ACh, which can direct cell differentiation and network formation. Thus, as corroborated by works from many labs, AChE can be considered a highly co-opting protein, which can combine enzymatic and non-enzymatic functions within one molecule.

A mechanistic overview of health associated effects of low levels of organochlorine and organophosphorous pesticides

Organochlorine and organophosphate pesticides are compounds that can be detected in human populations as a result of occupational or residential exposure. Despite their occurrence in considerably low levels in humans, their biological effects are hazardous since they interact with a plethora of enzymes, proteins, receptors and transcription factors. In this review we summarize the cell and molecular effects of organochlorine and organophosphate pesticides with respect to their toxicity, with particular emphasis on glucose and lipid metabolism, their interaction with some members of the nuclear receptor family of ligand-activated transcription factors, including the steroid and peroxisome proliferator activated receptors that changes the expression of genes involved in lipid metabolism and xenobiotic detoxification. More importantly, evidence regarding the metabolic degradation of pesticides and their accumulation in tissues is presented. Potential non-cholinergic mechanisms after long-term low-dose organophosphate exposure resulting in neurodevelopmental outcomes and neurodegeneration are also addressed. We conclude that the mechanism of pesticide-mediated toxicity is a combination of various enzyme-inhibitory, metabolic and transcriptional events acting at the cellular and molecular level.

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.

Lithium treatment induces proteasomal degradation of over-expressed acetylcholinesterase (AChE-S) and inhibit GSK3β

Lithium is one of the most widely used mood-stabilizing agents for the treatment of bipolar disorder. Lithium is also a potent inhibitor of glycogen synthase kinase-3β (GSK3β) activity, which is linked to Alzheimer's disease (AD). In experiments with cultured HEK293T cells, we show here that GSK3β stabilizes synaptic acetylcholinesterase (AChE-S), a critical component of AD development. Cells treated with lithium exhibited rapid proteasomal degradation of AChE-S. Furthermore treatment of the cells with MG132, an inhibitor of the 26S proteasome, prevented the destabilizing effect of lithium on AChE-S. Taken together, these findings suggest that regulation of AChE-S protein stability may be an important biological target of lithium therapy.

Acetylcholinesterase involvement in apoptosis

To date, more than 40 different types of cells from primary cultures or cell lines have shown AChE expression during apoptosis and after the induction apoptosis by different stimuli. It has been well-established that increased AChE expression or activity is detected in apoptotic cells after apoptotic stimuli in vitro and in vivo, and AChE could be therefore used as a marker of apoptosis. AChE is not an apoptosis initiator, but the cells in which AChE is overexpressed undergo apoptosis more easily than controls. Interestingly, cells with downregulated levels of AChE are not sensitive to apoptosis induction and AChE deficiency can protect against apoptosis. Some tumor cells do not express AChE, but when AChE is introduced into a tumor cell, the cells cease to proliferate and undergo apoptosis more readily. Therefore, AChE can be classified as a tumor suppressor gene. AChE plays a pivotal role in apoptosome formation, and silencing of the AChE gene prevents caspase-9 activation, with consequent decreased cell viability, nuclear condensation, and poly (adenosine diphosphate-ribose) polymerase cleavage. AChE is translocated into the nucleus, which may be an important event during apoptosis. Several questions still need to be addressed, and further studies that address the non-classical function of AChE in apoptosis are needed.