Targeting of acetylcholinesterase in neurons in vivo: a dual processing function for the proline-rich membrane anchor subunit and the attachment domain on the catalytic subunit

Cardiac acetylcholinesterase and butyrylcholinesterase have distinct localization and function

Cholinesterase (ChE) inhibitors are under consideration for use in the treatment of cardiovascular pathologies. A prerequisite to advancing ChE inhibitors into the clinic is their thorough characterization in the heart. The aim here was to provide a detailed analysis of cardiac ChE to understand their molecular composition, localization, and physiological functions. A battery of biochemical, microscopic, and physiological experiments was used to analyze two known ChE, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), in hearts of mutant mice lacking different ChE molecular forms. Overall, AChE activity was exceeded by BChE, while it was localized mainly in the atria and the ventricular epicardium of the heart base. AChE was anchored by collagen Q (ColQ) in the basal lamina or by PRiMA at the plasma membrane and co-localized with the neuronal marker TUJ1. In the absence of anchored AChE, the heart rate was unresponsive to a ChE inhibitor. BChE, the major ChE in the heart, was detected predominantly in ventricles, presumably as a precursor (soluble monomers/dimers). Mice lacking BChE were more sensitive to a ChE inhibitor. Nevertheless, the overall impact on heart physiology was subtle, showing mainly a role in cholinergic antagonism to the positive inotropic effect of β-adrenergic stimulation. Our results help to unravel the mechanisms of ChE in cardiovascular pathologies and provide a foundation to facilitate the design of novel, more effective pharmacotherapies, which may reduce morbidity and mortality of patients with various heart diseases.NEW & NOTEWORTHY Inhibition of cholinesterases has therapeutic potential in cardiovascular pathologies. Both acetylcholinesterase and butyrylcholinesterase are present in the heart. Each cholinesterase has distinct localization patterns in the heart and functions in cardiac physiology. Selective inhibition of acetylcholinesterase or butyrylcholinesterase may be used to alter specific cardiac functions. Butyrylcholinesterase polymorphism may have an impact on the outcome of the cholinesterase inhibitor treatment.

The activation of inflammatory responses in the brain is potentiated by over-expressing acetylcholinesterase in myeloid lineage of transgenic mice

Acetylcholinesterase (AChE) has functions in neuroinflammation, beyond its classical role in neurotransmission. Understanding the role of AChE in neuroinflammation is of great significance, as it highlights the potential therapeutic targets for the treatment of neurodegenerative diseases. In an in vitro study, the expression of AChE was up-regulated in lipopolysaccharide (LPS)-induced microglia/macrophage and contrarily potentiated the inflammatory responses via disturbing the cholinergic anti-inflammatory pathway (CAP). However, the regulation of AChE in neuroinflammation has not been revealed in vivo yet. Here, we aim to uncover the inflammatory roles of microglial AChE in LPS-induced neuroinflammation by using the conditional AChE over-expression mouse model. AChE was specifically over-expressed in the myeloid cell linkage of mouse by applying CRISPR/cas9 combined with Cre-LoxP system. LPS was intraperitoneally injected into the mice to induce inflammation. The results showed that the inflammation, induced by LPS, was aggravated in the brain of transgenic mice having over-expression of AChE in microglia. The expressions of pro-inflammatory cytokines were robustly up-regulated in the brains of LPS-treated transgenic mice, as compared to the LPS-treated wildtypes. In parallel, the activations of microglia and astrocytes in hippocampus were enhanced significantly in AChE transgenic mice. Transcriptomics analysis further confirmed the severer inflammation in the transgenic mice than the wildtype after LPS administration. These findings shed light on the regulation of microglial AChE in neuroinflammation in vivo for the first time, presenting another angle to understand the role of AChE in neurodegenerative diseases.

α7 nicotinic receptors play a role in regulation of cardiac hemodynamics

The α7 nicotinic receptors (NR) have been confirmed in the heart but their role in cardiac functions has been contradictory. To address these contradictory findings, we analyzed cardiac functions in α7 NR knockout mice (α7-/-) in vivo and ex vivo in isolated hearts. A standard limb leads electrocardiogram was used, and the pressure curves were recorded in vivo, in Arteria carotis and in the left ventricle, or ex vivo, in the left ventricle of the spontaneously beating isolated hearts perfused following Langedorff's method. Experiments were performed under basic conditions, hypercholinergic conditions, and adrenergic stress. The relative expression levels of α and β NR subunits, muscarinic receptors, β1 adrenergic receptors, and acetylcholine life cycle markers were determined using RT-qPCR. Our results revealed a prolonged QT interval in α7-/- mice. All in vivo hemodynamic parameters were preserved under all studied conditions. The only difference in ex vivo heart rate between genotypes was the loss of bradycardia in prolonged incubation of isoproterenol-pretreated hearts with high doses of acetylcholine. In contrast, left ventricular systolic pressure was lower under basal conditions and showed a significantly higher increase during adrenergic stimulation. No changes in mRNA expression were observed. In conclusion, α7 NR has no major effect on heart rate, except when stressed hearts are exposed to a prolonged hypercholinergic state, suggesting a role in acetylcholine spillover control. In the absence of extracardiac regulatory mechanisms, left ventricular systolic impairment is revealed.

Molecular Analysis of a Congenital Myasthenic Syndrome Due to a Pathogenic Variant Affecting the C-Terminus of ColQ

Congenital Myasthenic Syndromes (CMSs) are rare inherited diseases of the neuromuscular junction characterized by muscle weakness. CMSs with acetylcholinesterase deficiency are due to pathogenic variants in COLQ, a collagen that anchors the enzyme at the synapse. The two COLQ N-terminal domains have been characterized as being biochemical and functional. They are responsible for the structure of the protein in the triple helix and the association of COLQ with acetylcholinesterase. To deepen the analysis of the distal C-terminal peptide properties and understand the CMSs associated to pathogenic variants in this domain, we have analyzed the case of a 32 year old male patient bearing a homozygote splice site variant c.1281 C > T that changes the sequence of the last 28 aa in COLQ. Using COS cell and mouse muscle cell expression, we show that the COLQ variant does not impair the formation of the collagen triple helix in these cells, nor its association with acetylcholinesterase, and that the hetero-oligomers are secreted. However, the interaction of COLQ variant with LRP4, a signaling hub at the neuromuscular junction, is decreased by 44% as demonstrated by in vitro biochemical methods. In addition, an increase in all acetylcholine receptor subunit mRNA levels is observed in muscle cells derived from the patient iPSC. All these approaches point to pathophysiological mechanisms essentially characterized by a decrease in signaling and the presence of immature acetylcholine receptors.

Interactions with amyloid beta peptide and acetylcholinesterase increase alkaline phosphatase activity

Multiple studies have shown that the activity of alkaline phosphatase (AP) increases during Alzheimer's disease (AD). In this paper, using UV-Visible spectroscopy, we show that this increase in activity is due to its interaction with key components of AD such as amyloid β peptide and acetylcholinesterase. Activity increase also occurs due to high concentrations of acetylcholine and choline. These conditions are present in AD or could occur due to drugs used for treating AD.

The collagen ColQ binds to LRP4 and regulates the activation of the Muscle-Specific Kinase-LRP4 receptor complex by agrin at the neuromuscular junction

Collagen Q (ColQ) is a nonfibrillar collagen that plays a crucial role at the vertebrate neuromuscular junction (NMJ) by anchoring acetylcholinesterase to the synapse. ColQ also functions in signaling, as it regulates acetylcholine receptor clustering and synaptic gene expression, in a manner dependent on muscle-specific kinase (MuSK), a key protein in NMJ formation and maintenance. MuSK forms a complex with low-density lipoprotein receptor-related protein 4 (LRP4), its coreceptor for the proteoglycan agrin at the NMJ. Previous studies suggested that ColQ also interacts with MuSK. However, the molecular mechanisms underlying ColQ functions and ColQ-MuSK interaction have not been fully elucidated. Here, we investigated whether ColQ binds directly to MuSK and/or LRP4 and whether it modulates agrin-mediated MuSK-LRP4 activation. Using coimmunoprecipitation, pull-down, plate-binding assays, and surface plasmon resonance, we show that ColQ binds directly to LRP4 but not to MuSK and that ColQ interacts indirectly with MuSK through LRP4. In addition, we show that the LRP4 N-terminal region, which contains the agrin-binding sites, is also crucial for ColQ binding to LRP4. Moreover, ColQ-LRP4 interaction was reduced in the presence of agrin, suggesting that agrin and ColQ compete for binding to LRP4. Strikingly, we reveal ColQ has two opposing effects on agrin-induced MuSK-LRP4 signaling: it constitutively reduces MuSK phosphorylation levels in agrin-stimulated myotubes but concomitantly increases MuSK accumulation at the muscle cell surface. Our results identify LRP4 as a major receptor of ColQ and provide new insights into mechanisms of ColQ signaling and acetylcholinesterase anchoring at the NMJ.

Striatal Cholinergic Signaling in Time and Space

The cholinergic interneurons of the striatum account for a small fraction of all striatal cell types but due to their extensive axonal arborization give the striatum the highest content of acetylcholine of almost any nucleus in the brain. The prevailing theory of striatal cholinergic interneuron signaling is that the numerous varicosities on the axon produce an extrasynaptic, volume-transmitted signal rather than mediating rapid point-to-point synaptic transmission. We review the evidence for this theory and use a mathematical model to integrate the measurements reported in the literature, from which we estimate the temporospatial distribution of acetylcholine after release from a synaptic vesicle and from multiple vesicles during tonic firing and pauses. Our calculations, together with recent data from genetically encoded sensors, indicate that the temporospatial distribution of acetylcholine is both short-range and short-lived, and dominated by diffusion. These considerations suggest that acetylcholine signaling by cholinergic interneurons is consistent with point-to-point transmission within a steep concentration gradient, marked by transient peaks of acetylcholine concentration adjacent to release sites, with potential for faithful transmission of spike timing, both bursts and pauses, to the postsynaptic cell. Release from multiple sites at greater distance contributes to the ambient concentration without interference with the short-range signaling. We indicate several missing pieces of evidence that are needed for a better understanding of the nature of synaptic transmission by the cholinergic interneurons of the striatum.

Cholinesterases in Tripartite Neuromuscular Synapse

The neuromuscular junction (NMJ) is a tripartite synapse in which not only presynaptic and post-synaptic cells participate in synaptic transmission, but also terminal Schwann cells (TSC). Acetylcholine (ACh) is the neurotransmitter that mediates the signal between the motor neuron and the muscle but also between the motor neuron and TSC. ACh action is terminated by acetylcholinesterase (AChE), anchored by collagen Q (ColQ) in the basal lamina of NMJs. AChE is also anchored by a proline-rich membrane anchor (PRiMA) to the surface of the nerve terminal. Butyrylcholinesterase (BChE), a second cholinesterase, is abundant on TSC and anchored by PRiMA to its plasma membrane. Genetic studies in mice have revealed different regulations of synaptic transmission that depend on ACh spillover. One of the strongest is a depression of ACh release that depends on the activation of α7 nicotinic acetylcholine receptors (nAChR). Partial AChE deficiency has been described in many pathologies or during treatment with cholinesterase inhibitors. In addition to changing the activation of muscle nAChR, AChE deficiency results in an ACh spillover that changes TSC signaling. In this mini-review, we will first briefly outline the organization of the NMJ. This will be followed by a look at the role of TSC in synaptic transmission. Finally, we will review the pathological conditions where there is evidence of decreased AChE activity.

Evaluation of radiolabeled acetylcholine synthesis and release in rat striatum

Cholinergic transmission underlies higher brain functions such as cognition and movement. To elucidate the process whereby acetylcholine (ACh) release is maintained and regulated in the central nervous system, uptake of [³ H]choline and subsequent synthesis and release of [³ H]ACh were investigated in rat striatal segments. Incubation with [³ H]choline elicited efficient uptake via high-affinity choline transporter-1, resulting in accumulation of [³ H]choline and [³ H]ACh. However, following inhibition of ACh esterase (AChE), incubation with [³ H]choline led predominantly to the accumulation of [³ H]ACh. Electrical stimulation and KCl depolarization selectively released [³ H]ACh but not [³ H]choline. [³ H]ACh release gradually declined upon repetitive stimulation, whereas the release was reproducible under inhibition of AChE. [³ H]ACh release was abolished after treatment with vesamicol, an inhibitor of vesicular ACh transporter. These results suggest that releasable ACh is continually replenished from the cytosol to releasable pools of cholinergic vesicles to maintain cholinergic transmission. [³ H]ACh release evoked by electrical stimulation was abolished by tetrodotoxin, but that induced by KCl was largely resistant. ACh release was Ca²⁺ dependent and exhibited slightly different sensitivities to N- and P-type Ca²⁺ channel toxins (ω-conotoxin GVIA and ω-agatoxin IVA, respectively) between both stimuli. [³ H]ACh release was negatively regulated by M2 muscarinic and D2 dopaminergic receptors. The present results suggest that inhibition of AChE within cholinergic neurons and of presynaptic negative regulation of ACh release contributes to maintenance and facilitation of cholinergic transmission, providing a potentially useful clue for the development of therapies for cholinergic dysfunction-associated disorders, in addition to inhibition of synaptic cleft AChE.

Characterization of Human Genes Modulated by Porphyromonas gingivalis Highlights the Ribosome, Hypothalamus, and Cholinergic Neurons

Porphyromonas gingivalis, a bacterium associated with periodontal disease, is a suspected cause of Alzheimer's disease. This bacterium is reliant on gingipain proteases, which cleave host proteins after arginine and lysine residues. To characterize gingipain susceptibility, we performed enrichment analyses of arginine and lysine proportion proteome-wide. Genes differentially expressed in brain samples with detected P. gingivalis reads were also examined. Genes from these analyses were tested for functional enrichment and specific neuroanatomical expression patterns. Proteins in the SRP-dependent cotranslational protein targeting to membrane pathway were enriched for these residues and previously associated with periodontal and Alzheimer's disease. These ribosomal genes are up-regulated in prefrontal cortex samples with detected P. gingivalis sequences. Other differentially expressed genes have been previously associated with dementia (ITM2B, MAPT, ZNF267, and DHX37). For an anatomical perspective, we characterized the expression of the P. gingivalis associated genes in the mouse and human brain. This analysis highlighted the hypothalamus, cholinergic neurons, and the basal forebrain. Our results suggest markers of neural P. gingivalis infection and link the cholinergic and gingipain hypotheses of Alzheimer's disease.

Forebrain Cholinergic Signaling: Wired and Phasic, Not Tonic, and Causing Behavior

Conceptualizations of cholinergic signaling as primarily spatially diffuse and slow-acting are based largely on measures of extracellular brain ACh levels that require several minutes to generate a single data point. In addition, most such studies inhibited the highly potent catalytic enzyme for ACh, AChE, to facilitate measurement of ACh. Absent such inhibition, AChE limits the presence of ambient ACh and thus renders it unlikely that ACh influences target regions via slow changes in extracellular ACh concentrations. We describe an alternative view by which forebrain signaling in cortex driving cognition is largely phasic (milliseconds to perhaps seconds), and unlikely to be volume-transmitted. This alternative is supported by new evidence from real-time amperometric recordings of cholinergic signaling indicating a specific function of rapid, phasic, transient cholinergic signaling in attentional contexts. Previous neurochemical evidence may be reinterpreted in terms of integrated phasic cholinergic activity that mediates specific behavioral and cognitive operations; this reinterpretation fits well with recent computational models. Optogenetic studies support a causal relationship between cholinergic transients and behavior. This occurs in part via transient-evoked muscarinic receptor-mediated high-frequency oscillations in cortical regions. Such oscillations outlast cholinergic transients and thus link transient ACh signaling with more sustained postsynaptic activity patterns to support relatively persistent attentional biases. Reconceptualizing cholinergic function as spatially specific, phasic, and modulating specific cognitive operations is theoretically powerful and may lead to pharmacologic treatments more effective than those based on traditional views.Dual Perspectives Companion Paper: Diverse Spatiotemporal Scales of Cholinergic Signaling in the Neocortex, by Anita A. Disney and Michael J. Higley.

Expression of cholinesterases and their anchoring proteins in rat heart

Acetylcholine (ACh)-mediated vagal transmission as well as nonneuronal ACh release are considered cardioprotective in pathological situations with increased sympathetic drive such as ischemia–reperfusion and cardiac remodeling. ACh action is terminated by hydrolysis by the cholinesterases (ChEs), acetylcholinesterase, and butyrylcholinesterase. Both ChEs exist in multiple molecular variants either soluble or anchored by specific anchoring proteins like collagen Q (ColQ) anchoring protein and proline-rich membrane anchoring protein (PRiMA). Here we assessed the expression of specific ChE molecular forms in different heart compartments using RT-qPCR. We show that both ChEs are expressed in all heart compartments but display different expression patterns. The acetylcholinesterase-T variant together with PRiMA and ColQ is predominantly expressed in rat atria. Butylcholinesterase is found in all heart compartments and is accompanied by both PRiMA and ColQ anchors. Its expression in the ventricular system suggests involvement in the nonneuronal cholinergic system. Additionally, two PRiMA variants are detected throughout the rat heart.

Targeted sequencing of linkage region in Dominican families implicates PRIMA1 and the SPATA7-PTPN21-ZC3H14-EML5-TTC8 locus in carotid-intima media thickness and atherosclerotic events

Carotid intima-media thickness (cIMT) is a subclinical marker for atherosclerosis. Previously, we reported a quantitative trait locus (QTL) for total cIMT on chromosome 14q and identified PRiMA1, FOXN3 and CCDC88C as candidate genes using a common variants (CVs)-based approach. Herein, we further evaluated the genetic contribution of the QTL to cIMT by resequencing. We sequenced all exons within the QTL and genomic regions of PRiMA1, FOXN3 and CCDC88C in Dominican families with evidence for linkage to the QTL. Unrelated Dominicans from the Northern Manhattan Study (NOMAS) were used for validation. Single-variant-based and gene-based analyses were performed for CVs and rare variants (RVs). The strongest evidence for association with CVs was found in PRiMA1 (p = 8.2 × 10⁻⁵ in families, p = 0.01 in NOMAS at rs12587586), and in the five-gene cluster SPATA7-PTPN21-ZC3H14-EML5-TTC8 locus (p = 1.3 × 10⁻⁴ in families, p = 0.01 in NOMAS at rs2274736). No evidence for association with RVs was found in PRiMA1. The top marker from previous study in PRiMA1 (rs7152362) was associated with fewer atherosclerotic events (OR = 0.67; p = 0.02 in NOMAS) and smaller cIMT (β = −0.58, p = 2.8 × 10⁻⁴ in Family). Within the five-gene cluster, evidence for association was found for exonic RVs (p = 0.02 in families, p = 0.28 in NOMAS), which was enriched among RVs with higher functional potentials (p = 0.05 in NOMAS for RVs in the top functional tertile). In summary, targeted resequencing provided validation and novel insights into the genetic architecture of cIMT, suggesting stronger effects for RVs with higher functional potentials. Furthermore, our data support the clinical relevance of CVs associated with subclinical atherosclerosis.

Respiratory failure triggered by cholinesterase inhibitors may involve activation of a reflex sensory pathway by acetylcholine spillover

Respiration failure during exposure by cholinesterase inhibitors has been widely assumed to be due to inhibition of cholinesterase in the brain. Using a double chamber plethysmograph to measure various respiratory parameters, we observed long "end inspiratory pauses" (EIP) during most exposure that depressed breathing. Surprisingly, Colq KO mice that have a normal level of acetylcholinesterase (AChE) in the brain but a severe deficit in muscles and other peripheral tissues do not pause the breathing by long EIP. In mice, long EIP can be triggered by a nasal irritant. Eucalyptol, an agonist of cold receptor (TRPM8) acting on afferent sensory neurons and known to reduce the EIP triggered by such irritants, strongly reduced the EIP induced by cholinesterase inhibitor. These results suggest that acetylcholine (ACh) spillover from the neuromuscular junction, which is unchanged in Colq KO mice, may activate afferent sensory systems and trigger sensory reflexes, as reversed by eucalyptol. Indeed, the role of AChE at the cholinergic synapses is not only to accurately control the synaptic transmission but also to prevent the spillover of ACh. In the peripheral tissues, the ACh flood induced by cholinesterase inhibition may be very toxic due to interaction with non-neuronal cells that use ACh at low levels to communicate with afferent sensory neurons.

Optogenetic augmentation of the hypercholinergic endophenotype in DYT1 knock-in mice induced erratic hyperactive movements but not dystonia

BACKGROUND

The most prevalent inherited form of generalized dystonia is caused by a mutation in torsinA (DYT1, ∆GAG) with incomplete penetrance. Rodent models with mutated torsinA do not develop dystonic symptoms, but previous ex vivo studies indicated abnormal excitation of cholinergic interneurons (ChI) and increased striatal acetylcholine.

METHODS

We used in vivo optogenetics to exacerbate this endophenotype in order to determine its capacity to trigger dystonic symptoms in freely behaving mice. Tor1a^+/Δgag DYT1 mice and wildtype littermates expressing channelrhodopsin2 under the Chat promotor were implanted bilaterally with optical LED cannulae and stimulated with blue light pulses of varied durations.

FINDINGS

Six months old DYT1 KI mice but not wildtype controls responded with hyperactivity to blue light specifically at 25 ms pulse duration, 10 Hz frequency. Neuronal activity (c-Fos) in cholinergic interneurons was increased immediately after light stimulation and persisted only in DYT1 KI over 15 min. Substance P was increased specifically in striosome compartments in naïve DYT1 KI mice compared to wildtype. Under optogenetic stimulation substance P increased in wildtype to match levels in Dyt1 KI, and acetylcholinesterase was elevated in the striatum of stimulated DYT1 KI. No signs of dystonic movements were observed under stimulation of up to one hour in both genotypes and age groups, and the sensorimotor deficit previously observed in 6 months old DYT1 KI mice persisted under stimulation.

INTERPRETATION

Overall this supports an endophenotype of dysregulated cholinergic activity in DYT1 dystonia, but depolarizing cholinergic interneurons was not sufficient to induce overt dystonia in DYT1 KI mice.

Electro-behavioral phenotype and cell injury following exposure to paraoxon-ethyl in mice: Effect of the genetic background

Organophosphorus compounds (OP) are irreversible inhibitors of both central and peripheral cholinesterases (ChE). They still represent a major health issue in some countries as well as a terrorist and military threat. In order to design appropriate medical counter-measures, a better understanding of the pathophysiology of the poisoning is needed. Little to nothing is known regarding the impact of the genetic background on OP-induced seizures and seizure-related cell injury. Using two different mouse strains, Swiss and C57BL/6J, exposed to a convulsing dose of the OP pesticide paraoxon-ethyl (POX), our study focused on seizure susceptibility, especially the occurrence of SE and related mortality. We also evaluated the initial neuropathological response and SE-induced cell injury. Following the administration of 2.4 mg/kg POX, more Swiss mice experienced SE than C57BL/6J (55.6% versus 17.2%) but the duration of their SE, based on EEG recordings, was shorter (64.3 ± 19.5 min versus 180.8 ± 36.8 min). No significant difference was observed between strains regarding mortality (33% versus 14%). In both strains limited cell injury was observed in the medial temporal cortex, the dentate gyrus and the CA3 field without inter-strain differences (Fluorojade C-positive cells/mm²). Conversely, only C57BL/6J mice showed cell injury in the CA1 field. There was no obvious correlation between the number of Fluorojade C-positive cells and the duration of the EEG discharges. Our work suggests some differences between Swiss and C57BL/6J mice and lay ground to further studies on the impact of strains in the development of central nervous system toxicity of OP.

Increased Expression of Readthrough Acetylcholinesterase Variants in the Brains of Alzheimer's Disease Patients

Alzheimer's disease (AD) is characterized by a decrease in the enzymatic activity of the enzyme acetylcholinesterase (AChE). AChE is expressed as multiple splice variants, which may serve both cholinergic degradative functions and non-cholinergic functions unrelated with their capacity to hydrolyze acetylcholine. We have recently demonstrated that a prominent pool of enzymatically inactive AChE protein exists in the AD brain. In this study, we analyzed protein and transcript levels of individual AChE variants in human frontal cortex from AD patients by western blot analysis using specific anti-AChE antibodies and by quantitative real-time PCR (qRT-PCR). We found similar protein and mRNA levels of the major cholinergic "tailed"-variant (AChE-T) and the anchoring subunit, proline-rich membrane anchor (PRiMA-1) in frontal cortex obtained from AD patients and non-demented controls. Interestingly, we found an increase in the protein and transcript levels of the non-cholinergic "readthrough" AChE (AChE-R) variants in AD patients compared to controls. Similar increases were detected by western blot using an antibody raised against the specific N-terminal domain, exclusive of alternative N-extended variants of AChE (N-AChE). In accordance with a subset of AChE-R monomers that display amphiphilic properties that are upregulated in the AD brain, we demonstrate that the increase of N-AChE species is due, at least in part, to N-AChE-R variants. In conclusion, we demonstrate selective alterations in specific AChE variants in AD cortex, with no correlation in enzymatic activity. Therefore, differential expression of AChE variants in AD may reflect changes in the pathophysiological role of AChE, independent of cholinergic impairment or its role in degrading acetylcholine.

Colorectal adenoma and cancer detection based on altered methylation pattern of SFRP1, SFRP2, SDC2, and PRIMA1 in plasma samples

Aberrant methylation is one of the most frequent epigenetic alterations that can contribute to tumor formation. Cell-free DNA can originate from tumor tissue; therefore, the evaluation of methylation markers in cell-free DNA can be a promising method for cancer screening. Our aim was to develop a panel of biomarkers with altered methylation along the colorectal adenoma-carcinoma sequence in both colonic tissue and plasma. Methylation of selected CpG sites in healthy colonic (n = 15), adenoma (n = 15), and colorectal cancer (n = 15) tissues was analyzed by pyrosequencing. MethyLight PCR was applied to study the DNA methylation of SFRP1, SFRP2, SDC2, and PRIMA1 gene promoters in 121 plasma and 32 biopsy samples. The effect of altered promoter methylation on protein expression was examined by immunohistochemistry. Significantly higher (P < 0.05) DNA methylation levels were detected in the promoter regions of all 4 markers, both in CRC and adenoma tissues compared with healthy controls. Methylation of SFRP1, SFRP2, SDC2, and PRIMA1 promoter sequences was observed in 85.1%, 72.3%, 89.4%, and 80.9% of plasma samples from patients with CRC and 89.2%, 83.8%, 81.1% and 70.3% from adenoma patients, respectively. When applied as a panel, CRC patients could be distinguished from controls with 91.5% sensitivity and 97.3% specificity [area under the curve (AUC) = 0.978], while adenoma samples could be differentiated with 89.2% sensitivity and 86.5% specificity (AUC = 0.937). Immunohistochemical analysis indicated decreasing protein levels of all 4 markers along the colorectal adenoma-carcinoma sequence. Our findings suggest that this methylation biomarker panel allows non-invasive detection of colorectal adenoma and cancer from plasma samples.

In Vitro Innervation as an Experimental Model to Study the Expression and Functions of Acetylcholinesterase and Agrin in Human Skeletal Muscle

Acetylcholinesterase (AChE) and agrin, a heparan-sulfate proteoglycan, reside in the basal lamina of the neuromuscular junction (NMJ) and play key roles in cholinergic transmission and synaptogenesis. Unlike most NMJ components, AChE and agrin are expressed in skeletal muscle and α-motor neurons. AChE and agrin are also expressed in various other types of cells, where they have important alternative functions that are not related to their classical roles in NMJ. In this review, we first focus on co-cultures of embryonic rat spinal cord explants with human skeletal muscle cells as an experimental model to study functional innervation in vitro. We describe how this heterologous rat-human model, which enables experimentation on highly developed contracting human myotubes, offers unique opportunities for AChE and agrin research. We then highlight innovative approaches that were used to address salient questions regarding expression and alternative functions of AChE and agrin in developing human skeletal muscle. Results obtained in co-cultures are compared with those obtained in other models in the context of general advances in the field of AChE and agrin neurobiology.

Ultrafast and Slow Cholinergic Transmission. Different Involvement of Acetylcholinesterase Molecular Forms

Acetylcholine (ACh), an ubiquitous mediator substance broadly expressed in nature, acts as neurotransmitter in cholinergic synapses, generating specific communications with different time-courses. (1) Ultrafast transmission. Vertebrate neuromuscular junctions (NMJs) and nerve-electroplaque junctions (NEJs) are the fastest cholinergic synapses; able to transmit brief impulses (1-4 ms) at high frequencies. The collagen-tailed A12 acetylcholinesterase is concentrated in the synaptic cleft of NMJs and NEJs, were it curtails the postsynaptic response by ultrafast ACh hydrolysis. Here, additional processes contribute to make transmission so rapid. (2) Rapid transmission. At peripheral and central cholinergic neuro-neuronal synapses, transmission involves an initial, relatively rapid (10-50 ms) nicotinic response, followed by various muscarinic or nicotinic effects. Acetylcholinesterase (AChE) being not concentrated within these synapses, it does not curtail the initial rapid response. In contrast, the late responses are controlled by a globular form of AChE (mainly G4-AChE), which is membrane-bound and/or secreted. (3) SlowAChsignalling. In non-neuronal systems, in muscarinic domains, and in most regions of the central nervous system (CNS), many ACh-releasing structures (cells, axon terminals, varicosities, boutons) do not form true synaptic contacts, most muscarinic and also part of nicotinic receptors are extra-synaptic, often situated relatively far from ACh releasing spots. A12-AChE being virtually absent in CNS, G4-AChE is the most abundant form, whose function appears to modulate the "volume" transmission, keeping ACh concentration within limits in time and space.

Low Plasma Cholinesterase Activities are Associated with Deficits in Spatial Orientation, Reduced Ability to Perform Basic Activities of Daily Living, and Low Body Mass Index in Patients with Progressed Alzheimer's Disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder characterized by a central cholinergic deficit. Non-neuronal cholinergic changes are, however, described as well. Here we focused on possible changes in the activity of the plasma cholinesterases, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), in hospitalized AD patients. We analyzed plasma AChE and BChE activities with regards to age, gender, body mass index (BMI), cognitive functions, and ability to perform activities of daily living in AD patients in comparison to healthy subjects. We observed lower AChE activity and trend toward lower BChE activity in AD patients, which both correlated with low BMI. AD patients unable to perform basic activities of daily living (feeding, bathing, dressing, and grooming) showed reduced plasma AChE activities, while worse spatial orientation was linked to lower BChE activities. Three out of four AD patients with the lowest BChE activities died within one year. In conclusion, progressed AD was accompanied by lower plasma AChE activity and trend toward lower BChE activity, which correlated with BMI and deficits in different components of the AD.

What do phasic cholinergic signals do?

In addition to the neuromodulatory role of cholinergic systems, brief, temporally discrete cholinergic release events, or "transients", have been associated with the detection of cues in attention tasks. Here we review four main findings about cholinergic transients during cognitive processing. Cholinergic transients are: (1) associated with the detection of a cue and influenced by cognitive state; (2) not dependent on reward outcome, although the timing of the transient peak co-varies with the temporal relationship between detection and reward delivery; (3) correlated with the mobilization of the cue-evoked response; (4) causal mediators of shifts from monitoring to cue detection. We next discuss some of the key questions concerning the timing and occurrence of transients within the framework of available evidence including: (1) Why does the shift from monitoring to cue detection require a transient? (2) What determines whether a cholinergic transient will be generated? (3) How can cognitive state influence transient occurrence? (4) Why do cholinergic transients peak at around the time of reward delivery? (5) Is there evidence of cholinergic transients in humans? We conclude by outlining future research studies necessary to more fully understand the role of cholinergic transients in mediating cue detection.

Aberrant DNA Methylation of rDNA and PRIMA1 in Borderline Personality Disorder

Borderline personality disorder (BPD) is a serious psychic disease with a high risk for suicide. DNA methylation is a hallmark for aberrant epigenetic regulation and could be involved in the etiology of BPD. Previously, it has been reported that increased DNA methylation of neuropsychiatric genes is found in the blood of patients with BPD compared to healthy controls. Here, we analyzed DNA methylation patterns of the ribosomal RNA gene (rDNA promoter region and 5′-external transcribed spacer/5′ETS) and the promoter of the proline rich membrane anchor 1 gene (PRIMA1) in peripheral blood samples of 24 female patients (mean age (33 ± 11) years) diagnosed with DSM-IV BPD and in 11 female controls (mean age (32 ± 7) years). A significant aberrant methylation of rDNA and PRIMA1 was revealed for BPD patients using pyrosequencing. For the promoter of PRIMA1, the average methylation of six CpG sites was 1.6-fold higher in BPD patients compared to controls. In contrast, the methylation levels of the rDNA promoter region and the 5′ETS were significantly lower (0.9-fold) in patients with BPD compared to controls. Thus, for nine CpGs located in the rDNA promoter region and for four CpGs at the 5′ETS decreased methylation was found in peripheral blood of patients compared to controls. Our results suggest that aberrant methylation of rDNA and PRIMA1 is associated with the pathogenesis of BPD.

A selective and sensitive near-infrared fluorescent probe for acetylcholinesterase imaging

HupNIR2 is the first NIR fluorescent probe for acetylcholinesterase imaging in tissues. This probe penetrates easily and deeply into the tissue, and directly labels AChE.

Hepatoprotective Effect of Citrus limon Fruit Extract against Carbofuran Induced Toxicity in Wistar Rats

Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranol methylcarbamate), is known to induce oxidative stress and to cause inhibition of acetylcholinesterase activity. The present work was envisaged to evaluate the effect of carbofuran on redox indices and its interactions with hepatic markers in rat. The ameliorating effect of Citrus limon fruit extract on carbofuran induced toxicity was also monitored. The results indicated that carbofuran treatment caused significant alterations in the levels of activities of AST, ALT, and LDH in liver tissues and serum. The levels of enzymatic oxidative stress markers such as SOD and catalase and nonenzymatic redox molecules such as total thiol, GSH, and protein thiol also showed significant perturbations in rat liver due to carbofuran treatment. The administration of Citrus limon fruit extract, however, was able to markedly ameliorate the toxicity of carbofuran by protecting the levels of aforesaid biomarkers to near normal levels. The ameliorative effect of Citrus limon fruit extract may be due to the presence of different antioxidants in it which may neutralize the ROS and RNS generated in the body tissue due to pesticide stress. These results suggested that Citrus limon fruit extract may be utilized as a potential supplement in proper management of pesticide intoxication in association with relevant therapeutics.

Dysfunctional Presynaptic M2 Receptors in the Presence of Chronically High Acetylcholine Levels: Data from the PRiMA Knockout Mouse

The muscarinic M2 receptor (M2R) acts as a negative feedback regulator in central cholinergic systems. Activation of the M2 receptor limits acetylcholine (ACh) release, especially when ACh levels are increased because acetylcholinesterase (AChE) activity is acutely inhibited. Chronically high ACh levels in the extracellular space, however, were reported to down-regulate M2R to various degrees. In the present study, we used the PRiMA knockout mouse which develops severely reduced AChE activity postnatally to investigate ACh release, and we used microdialysis to investigate whether the function of M2R to reduce ACh release in vivo was impaired in adult PRiMA knockout mice. We first show that striatal and hippocampal ACh levels, while strongly increased, still respond to AChE inhibitors. Infusion or injection of oxotremorine, a muscarinic M2 agonist, reduced ACh levels in wild-type mice but did not significantly affect ACh levels in PRiMA knockout mice or in wild-type mice in which ACh levels were artificially increased by infusion of neostigmine. Scopolamine, a muscarinic antagonist, increased ACh levels in wild-type mice receiving neostigmine, but not in wild-type mice or in PRiMA knockout mice. These results demonstrate that M2R are dysfunctional and do not affect ACh levels in PRiMA knockout mice, likely because of down-regulation and/or loss of receptor-effector coupling. Remarkably, this loss of function does not affect cognitive functions in PRiMA knockout mice. Our results are discussed in the context of AChE inhibitor therapy as used in dementia.

PRIMA1 mutation: a new cause of nocturnal frontal lobe epilepsy

Objective

Nocturnal frontal lobe epilepsy (NFLE) can be sporadic or autosomal dominant; some families have nicotinic acetylcholine receptor subunit mutations. We report a novel autosomal recessive phenotype in a single family and identify the causative gene.

Methods

Whole exome sequencing data was used to map the family, thereby narrowing exome search space, and then to identify the mutation.

Results

Linkage analysis using exome sequence data from two affected and two unaffected subjects showed homozygous linkage peaks on chromosomes 7, 8, 13, and 14 with maximum LOD scores between 1.5 and 1.93. Exome variant filtering under these peaks revealed that the affected siblings were homozygous for a novel splice site mutation (c.93+2T>C) in the PRIMA1 gene on chromosome 14. No additional PRIMA1 mutations were found in 300 other NFLE cases. The c.93+2T>C mutation was shown to lead to skipping of the first coding exon of the PRIMA1 mRNA using a minigene system.

Interpretation

PRIMA1 is a transmembrane protein that anchors acetylcholinesterase (AChE), an enzyme hydrolyzing acetycholine, to membrane rafts of neurons. PRiMA knockout mice have reduction of AChE and accumulation of acetylcholine at the synapse; our minigene analysis suggests that the c.93+2T>C mutation leads to knockout of PRIMA1. Mutations with gain of function effects in acetylcholine receptor subunits cause autosomal dominant NFLE. Thus, enhanced cholinergic responses are the likely cause of the severe NFLE and intellectual disability segregating in this family, representing the first recessive case to be reported and the first PRIMA1 mutation implicated in disease.

Schwann cells sense and control acetylcholine spillover at the neuromuscular junction by α7 nicotinic receptors and butyrylcholinesterase

Terminal Schwann cells (TSCs) are key components of the mammalian neuromuscular junction (NMJ). How the TSCs sense the synaptic activity in physiological conditions remains unclear. We have taken advantage of the distinct localization of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) at the NMJ to bring out the function of different ACh receptors (AChRs). AChE is clustered by the collagen Q in the synaptic cleft and prevents the repetitive activation of muscle nicotinic AChRs. We found that BChE is anchored at the TSC by a proline-rich membrane anchor, the small transmembrane protein anchor of brain AChE. When BChE was specifically inhibited, ACh release was significant depressed through the activation of α7 nAChRs localized on the TSC and activated by the spillover of ACh. When both AChE and BChE were inhibited, the spillover increased and induced a dramatic reduction of ACh release that compromised the muscle twitch triggered by the nerve stimulation. α7 nAChRs at the TSC may act as a sensor for spillover of ACh adjusted by BChE and may represent an extrasynaptic sensor for homeostasis at the NMJ. In myasthenic rats, selective inhibition of AChE is more effective in rescuing muscle function than the simultaneous inhibition of AChE and BChE because the concomitant inhibition of BChE counteracts the positive action of AChE inhibition. These results show that inhibition of BChE should be avoided during the treatment of myasthenia and the pharmacological reversal of residual curarization after anesthesia.

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

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

Optimal detection of cholinesterase activity in biological samples: modifications to the standard Ellman's assay

Ellman's assay is the most commonly used method to measure cholinesterase activity. It is cheap, fast, and reliable, but it has limitations when used for biological samples. The problems arise from 5,5-dithiobis(2-nitrobenzoic acid) (DTNB), which is unstable, interacts with free sulfhydryl groups in the sample, and may affect cholinesterase activity. We report that DTNB is more stable in 0.09 M Hepes with 0.05 M sodium phosphate buffer than in 0.1M sodium phosphate buffer, thereby notably reducing background. Using enzyme-linked immunosorbent assay (ELISA) to enrich tissue homogenates for cholinesterase while depleting the sample of sulfhydryl groups eliminates unwanted interactions with DTNB, making it possible to measure low cholinesterase activity in biological samples. To eliminate possible interference of DTNB with enzyme hydrolysis, we introduce a modification of the standard Ellman's assay. First, thioesters are hydrolyzed by cholinesterase to produce thiocholine in the absence of DTNB. Then, the reaction is stopped by a cholinesterase inhibitor and the produced thiocholine is revealed by DTNB and quantified at 412 nm. Indeed, this modification of Ellman's method increases butyrylcholinesterase activity by 20 to 25%. Moreover, high stability of thiocholine enables separation of the two reactions of the Ellman's method into two successive steps that may be convenient for some applications.

Presenilin-1 influences processing of the acetylcholinesterase membrane anchor PRiMA

Presenilin-1 (PS1) is the catalytic component of the γ-secretase complex. In this study, we explore if PS1 participates in the processing of the cholinergic acetylcholinesterase (AChE). The major AChE variant expressed in the brain is a tetramer (G(4)) bound to a proline-rich membrane anchor (PRiMA). Overexpression of the transmembrane PRiMA protein in Chinese hamster ovary cells expressing AChE and treated with the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester have enabled us to study whether, through its γ-secretase activity, PS1 participates in the processing of PRiMA-linked AChE. γ-Secretase inhibition led to a notable increase in the level of PRiMA-linked AChE, suggesting that γ-secretase is involved in the cleavage of PRiMA. We demonstrate that cleavage of PRiMA by γ-secretase results in a C-terminal PRiMA fragment. Immunofluorescence labeling allowed us to identify this PRiMA fragment in the nucleus. Moreover, we have determined changes in the proportion of the raft-residing AChE-PRiMA in a PS1 conditional knockout mouse. Our results are of interest as both enzymes have therapeutic relevance for Alzheimer's disease.

Proteomic screening of glutamatergic mouse brain synaptosomes isolated by fluorescence activated sorting

For decades, neuroscientists have used enriched preparations of synaptic particles called synaptosomes to study synapse function. However, the interpretation of corresponding data is problematic as synaptosome preparations contain multiple types of synapses and non-synaptic neuronal and glial contaminants. We established a novel Fluorescence Activated Synaptosome Sorting (FASS) method that substantially improves conventional synaptosome enrichment protocols and enables high-resolution biochemical analyses of specific synapse subpopulations. Employing knock-in mice with fluorescent glutamatergic synapses, we show that FASS isolates intact ultrapure synaptosomes composed of a resealed presynaptic terminal and a postsynaptic density as assessed by light and electron microscopy. FASS synaptosomes contain bona fide glutamatergic synapse proteins but are almost devoid of other synapse types and extrasynaptic or glial contaminants. We identified 163 enriched proteins in FASS samples, of which FXYD6 and Tpd52 were validated as new synaptic proteins. FASS purification thus enables high-resolution biochemical analyses of specific synapse subpopulations in health and disease.

Zebrafish locomotor capacity and brain acetylcholinesterase activity is altered by Aphanizomenon flos-aquae DC-1 aphantoxins

Aphanizomenon flos-aquae (A. flos-aquae) is a source of neurotoxins known as aphantoxins or paralytic shellfish poisons (PSPs) that present a major threat to the environment and to human health. Generally, altered neurological function is reflected in behavior. Although the molecular mechanism of action of PSPs is well known, its neurobehavioral effects on adult zebrafish and its relationship with altered neurological functions are poorly understood. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed by HPLC. The major analogs found in the toxins were the gonyautoxins 1 and 5 (GTX1 and GTX5; 34.04% and 21.28%, respectively) and the neosaxitoxin (neoSTX, 12.77%). Zebrafish (Danio rerio) were intraperitoneally injected with 5.3 and 7.61 μg STXeq/kg (low and high dose, respectively) of A. flos-aquae DC-1 aphantoxins. The swimming activity was investigated by observation combined with video at 6 timepoints from 1 to 24 h post-exposure. Both aphantoxin doses were associated with delayed touch responses, reduced head-tail locomotory abilities, inflexible turning of head, and a tailward-shifted center of gravity. The normal S-pattern (or undulating) locomotor trajectory was replaced by a mechanical motor pattern of swinging the head after wagging the tail. Finally, these fish principally distributed at the top and/or bottom water of the aquarium, and showed a clear polarized distribution pattern at 12 h post-exposure. Further analysis of neurological function demonstrated that both aphantoxin doses inhibited brain acetylcholinesterase activity. All these changes were dose- and time-dependent. These results demonstrate that aphantoxins can alter locomotor capacity, touch responses and distribution patterns by damaging the cholinergic system of zebrafish, and suggest that zebrafish locomotor behavior and acetylcholinesterase can be used as indicators for investigating aphantoxins and blooms in nature.

Developmental adaptation of central nervous system to extremely high acetylcholine levels

Acetylcholinesterase (AChE) is a key enzyme in termination of fast cholinergic transmission. In brain, acetylcholine (ACh) is produced by cholinergic neurons and released in extracellular space where it is cleaved by AChE anchored by protein PRiMA. Recently, we showed that the lack of AChE in brain of PRiMA knock-out (KO) mouse increased ACh levels 200-300 times. The PRiMA KO mice adapt nearly completely by the reduction of muscarinic receptor (MR) density. Here we investigated changes in MR density, AChE, butyrylcholinesterase (BChE) activity in brain in order to determine developmental period responsible for such adaptation. Brains were studied at embryonal day 18.5 and postnatal days (pd) 0, 9, 30, 120, and 425. We found that the AChE activity in PRiMA KO mice remained very low at all studied ages while in wild type (WT) mice it gradually increased till pd120. BChE activity in WT mice gradually decreased until pd9 and then increased by pd120, it continually decreased in KO mice till pd30 and remained unchanged thereafter. MR number increased in WT mice till pd120 and then became stable. Similarly, MR increased in PRiMA KO mice till pd30 and then remained stable, but the maximal level reached is approximately 50% of WT mice. Therefore, we provide the evidence that adaptive changes in MR happen up to pd30. This is new phenomenon that could contribute to the explanation of survival and nearly unchanged phenotype of PRiMA KO mice.

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.

Near-complete adaptation of the PRiMA knockout to the lack of central acetylcholinesterase

Acetylcholinesterase (AChE) rapidly hydrolyzes acetylcholine. At the neuromuscular junction, AChE is mainly anchored in the extracellular matrix by the collagen Q, whereas in the brain, AChE is tethered by the proline-rich membrane anchor (PRiMA). The AChE-deficient mice, in which AChE has been deleted from all tissues, have severe handicaps. Surprisingly, PRiMA KO mice in which AChE is mostly eliminated from the brain show very few deficits. We now report that most of the changes observed in the brain of AChE-deficient mice, and in particular the high levels of ambient extracellular acetylcholine and the massive decrease of muscarinic receptors, are also observed in the brain of PRiMA KO. However, the two groups of mutants differ in their responses to AChE inhibitors. Since PRiMA-KO mice and AChE-deficient mice have similar low AChE concentrations in the brain but differ in the AChE content of the peripheral nervous system, these results suggest that peripheral nervous system AChE is a major target of AChE inhibitors, and that its absence in AChE- deficient mice is the main cause of the slow development and vulnerability of these mice. At the level of the brain, the adaptation to the absence of AChE is nearly complete.

N-linked glycosylation of proline-rich membrane anchor (PRiMA) is not required for assembly and trafficking of globular tetrameric acetylcholinesterase

Acetylcholinesterase (AChE) is organized into globular tetramers (G(4)) by a structural protein called proline-rich membrane anchor (PRiMA), anchoring it into the cell membrane of neurons in the brain. The assembly of AChE tetramers with PRiMA requires the presence of a C-terminal "t-peptide" in the AChE catalytic subunit (AChE(T)). The glycosylation of AChE(T) is known to be required for its proper assembly and trafficking; however, the role of PRiMA glycosylation in the oligomer assembly has not been revealed. PRiMA is a glycoprotein containing two putative N-linked glycosylation sites. By using site-directed mutagenesis, the asparagine-43 was identified to be the N-linked glycosylation site of PRiMA. Abolishing glycosylation on mouse PRiMA appeared not to affect its assembly with AChE(T), the enzymatic properties of AChE, and the membrane trafficking of PRiMA-linked AChE tetramers. This result is contrary to the reports that glycosylation is essential for conformation and trafficking of membrane glycoproteins.

Genome-wide DNA methylation scan in major depressive disorder

While genome-wide association studies are ongoing to identify sequence variation influencing susceptibility to major depressive disorder (MDD), epigenetic marks, such as DNA methylation, which can be influenced by environment, might also play a role. Here we present the first genome-wide DNA methylation (DNAm) scan in MDD. We compared 39 postmortem frontal cortex MDD samples to 26 controls. DNA was hybridized to our Comprehensive High-throughput Arrays for Relative Methylation (CHARM) platform, covering 3.5 million CpGs. CHARM identified 224 candidate regions with DNAm differences >10%. These regions are highly enriched for neuronal growth and development genes. Ten of 17 regions for which validation was attempted showed true DNAm differences; the greatest were in PRIMA1, with 12-15% increased DNAm in MDD (p = 0.0002-0.0003), and a concomitant decrease in gene expression. These results must be considered pilot data, however, as we could only test replication in a small number of additional brain samples (n = 16), which showed no significant difference in PRIMA1. Because PRIMA1 anchors acetylcholinesterase in neuronal membranes, decreased expression could result in decreased enzyme function and increased cholinergic transmission, consistent with a role in MDD. We observed decreased immunoreactivity for acetylcholinesterase in MDD brain with increased PRIMA1 DNAm, non-significant at p = 0.08.While we cannot draw firm conclusions about PRIMA1 DNAm in MDD, the involvement of neuronal development genes across the set showing differential methylation suggests a role for epigenetics in the illness. Further studies using limbic system brain regions might shed additional light on this role.

Fine mapping study reveals novel candidate genes for carotid intima-media thickness in Dominican Republican families

BACKGROUND

Carotid intima-media thickness (CIMT) is a subclinical measure for atherosclerosis. Previously, we have mapped quantitative trait loci (QTLs) for CIMT to chromosomes 7p (maximum logarithm of odds=3.1) and to 14q (maximum logarithm of odds=2.3). We sought to identify the underlying genetic variants within those QTLs.

METHODS AND RESULTS

Using the 100 extended Dominican Republican (DR) families (N=1312) used in the original linkage study, we fine mapped the QTLs with 2031 tagging single nucleotide polymorphisms (SNPs). Promising SNPs in the family data set were examined in an independent population-based subcohort comprised of DR individuals (N=553) from the Northern Manhattan Study. Among the families, evidence for association (P<0.001) was found in multiple genes (ANLN, AOAH, FOXN3, CCDC88C, PRiMA1, and an intergenic SNP rs1667498), with the strongest association at PRiMA1 (P=0.00007, corrected P=0.047). Additional analyses revealed that the association at these loci, except PRiMA1, was highly significant (P=0.00004≈0.00092) in families with evidence for linkage, but not in the rest of families (P=0.13≈0.80) and the population-based cohort, suggesting the genetic effects at these SNPs are limited to a subgroup of families. In contrast, the association at PRiMA1 was significant in both families with and without evidence for linkage (P=0.002 and 0.019, respectively) and the population-based subcohort (P=0.047), supporting a robust association.

CONCLUSIONS

We identified several candidate genes for CIMT in DR families. Some of the genes manifest genetic effects within a specific subgroup and others were generalized to all groups. Future studies are needed to further evaluate the contribution of these genes to atherosclerosis.

A tetrameric acetylcholinesterase from the parasitic nematode Dictyocaulus viviparus associates with the vertebrate tail proteins PRiMA and ColQ

Dictyocaulus viviparus causes a serious lung disease of cattle. Similar to other parasitic nematodes, D. viviparus possesses several acetylcholinesterase (AChE) genes, one of which encodes a putative neuromuscular AChE, which contains a tryptophan (W) amphiphilic tetramerization (WAT) domain at its C-terminus. In the current study, we describe the biochemical characterization of a recombinant version of this WAT domain-containing AChE. To assess if the WAT domain is biologically functional, we investigated the association of the recombinant enzyme with the vertebrate tail proteins, proline-rich membrane anchor (PRiMA) and collagen Q (ColQ), as well as the synthetic polypeptide poly-l-proline. The results indicate that the recombinant enzyme hydrolyzes acetylthiocholine preferentially and exhibits inhibition by excess substrate, a characteristic of AChEs but not butyrylcholinesterases (BChEs). The enzyme is inhibited by the AChE inhibitor, BW284c51, but not by the BChE inhibitors, ethopropazine or iso-OMPA. The enzyme is able to assemble into monomeric (G(1)), dimeric (G(2)), and tetrameric (G(4)) globular forms and can also associate with PRiMA and ColQ, which contain proline-rich attachment domains (PRADs). This interaction is likely to be mediated via WAT-PRAD interactions, as the enzyme also assembles into tetramers with the synthetic polypeptide poly-l-proline. These interactions are typical of AChE(T) subunits. This is the first demonstration of an AChE(T) from a parasitic nematode that can assemble into heterologous forms with vertebrate proteins that anchor the enzyme in cholinergic synapses. We discuss the implications of our results for this particular host/parasite system and for the evolution of AChE.

Different sensitivities of rat skeletal muscles and brain to novel anti-cholinesterase agents, alkylammonium derivatives of 6-methyluracil (ADEMS)

BACKGROUND AND PURPOSE

The rat respiratory muscle diaphragm has markedly lower sensitivity than the locomotor muscle extensor digitorum longus (EDL) to the new acetylcholinesterase (AChE) inhibitors, alkylammonium derivatives of 6-methyluracil (ADEMS). This study evaluated several possible reasons for differing sensitivity between the diaphragm and limb muscles and between the muscles and the brain.

EXPERIMENTAL APPROACH

Increased amplitude and prolonged decay time of miniature endplate currents were used to assess anti-cholinesterase activity in muscles. In hippocampal slices, induction of synchronous network activity was used to follow cholinesterase inhibition. The inhibitor sensitivities of purified AChE from the EDL and brain were also estimated.

KEY RESULTS

The intermuscular difference in sensitivity to ADEMS is partly explained caused by a higher level of mRNA and activity of 1,3-bis[5(diethyl-o-nitrobenzylammonium)pentyl]-6-methyluracildibromide (C-547)-resistant BuChE in the diaphragm. Moreover, diaphragm AChE was more than 20 times less sensitive to C-547 than that from the EDL. Sensitivity of the EDL to C-547 dramatically decreased after treadmill exercises that increased the amount of PRiMA AChE(G4), but not ColQ AChE(A12) molecular forms. The A12 form present in muscles appeared more sensitive to C-547. The main form of AChE in brain, PRiMA AChE(G4), was apparently less sensitive because brain cholinesterase activity was almost three orders of magnitude more resistant to C-547 than that of the EDL.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that ADEMS compounds could be used for the selective inhibition of AChEs and as potential therapeutic tools.

The assembly of proline-rich membrane anchor (PRiMA)-linked acetylcholinesterase enzyme: glycosylation is required for enzymatic activity but not for oligomerization

Acetylcholinesterase (AChE) anchors onto cell membranes by a transmembrane protein PRiMA (proline-rich membrane anchor) as a tetrameric form in vertebrate brain. The assembly of AChE tetramer with PRiMA requires the C-terminal "t-peptide" in AChE catalytic subunit (AChE(T)). Although mature AChE is well known N-glycosylated, the role of glycosylation in forming the physiologically active PRiMA-linked AChE tetramer has not been studied. Here, several lines of evidence indicate that the N-linked glycosylation of AChE(T) plays a major role for acquisition of AChE full enzymatic activity but does not affect its oligomerization. The expression of the AChE(T) mutant, in which all N-glycosylation sites were deleted, together with PRiMA in HEK293T cells produced a glycan-depleted PRiMA-linked AChE tetramer but with a much higher K(m) value as compared with the wild type. This glycan-depleted enzyme was assembled in endoplasmic reticulum but was not transported to Golgi apparatus or plasma membrane.

Naturally occurring variations in the human cholinesterase genes: heritability and association with cardiovascular and metabolic traits

Cholinergic neurotransmission in the central and autonomic nervous systems regulates immediate variations in and longer-term maintenance of cardiovascular function with acetylcholinesterase (AChE) activity that is critical to temporal responsiveness. Butyrylcholinesterase (BChE), largely confined to the liver and plasma, subserves metabolic functions. AChE and BChE are found in hematopoietic cells and plasma, enabling one to correlate enzyme levels in whole blood with hereditary traits in twins. Using both twin and unrelated subjects, we found certain single nucleotide polymorphisms (SNPs) in the ACHE gene correlated with catalytic properties and general cardiovascular functions. SNP discovery from ACHE resequencing identified 19 SNPs: 7 coding SNPs (cSNPs), of which 4 are nonsynonymous, and 12 SNPs in untranslated regions, of which 3 are in a conserved sequence of an upstream intron. Both AChE and BChE activity traits in blood were heritable: AChE at 48.8 ± 6.1% and BChE at 81.4 ± 2.8%. Allelic and haplotype variations in the ACHE and BCHE genes were associated with changes in blood AChE and BChE activities. AChE activity was associated with BP status and SBP, whereas BChE activity was associated with features of the metabolic syndrome (especially body weight and BMI). Gene products from cDNAs with nonsynonymous cSNPs were expressed and purified. Protein expression of ACHE nonsynonymous variant D134H (SNP6) is impaired: this variant shows compromised stability and altered rates of organophosphate inhibition and oxime-assisted reactivation. A substantial fraction of the D134H instability could be reversed in the D134H/R136Q mutant. Hence, common genetic variations at ACHE and BCHE loci were associated with changes in corresponding enzymatic activities in blood.

Altered expression of brain acetylcholinesterase in FTDP-17 human tau transgenic mice

Pathological hyperphosphorylation and aggregation of the tau protein is associated with dementia and can be the central cause of neurodegeneration. Here, we examined potential alterations in the level of the cholinergic enzyme acetylcholinesterase (AChE) in the brain of transgenic mice (Tg-VLW) expressing human tau mutations. Overexpression of mutant hyperphosphorylated tau (P-tau) led to an increase in the activity of AChE in the brain of Tg-VLW mice, paralleled by an increase in AChE protein and transcripts; whereas the levels of the enzyme choline acetyltransferase remained unaffected. VLW tau overexpression in SH-SY5Y cells also increased AChE activity levels. All major molecular forms of AChE were increased in the Tg-VLW mice, including tetrameric AChE, which is the major species involved in hydrolysis of acetylcholine in the brain. Colocalization of human P-tau and AChE supports the conclusion that P-tau can act to increase AChE. This study is the first direct evidence of a modulatory effect of P-tau on brain AChE expression.

Distinct localization of collagen Q and PRiMA forms of acetylcholinesterase at the neuromuscular junction

Acetylcholinesterase (AChE) terminates the action of acetylcholine at cholinergic synapses thereby preventing rebinding of acetylcholine to nicotinic postsynaptic receptors at the neuromuscular junction. Here we show that AChE is not localized close to these receptors on the postsynaptic surface, but is instead clustered along the presynaptic membrane and deep in the postsynaptic folds. Because AChE is anchored by ColQ in the basal lamina and is linked to the plasma membrane by a transmembrane subunit (PRiMA), we used a genetic approach to evaluate the respective contribution of each anchoring oligomer. By visualization and quantification of AChE in mouse strains devoid of ColQ, PRiMA or AChE, specifically in the muscle, we found that along the nerve terminus the vast majority of AChE is anchored by ColQ that is only produced by the muscle, whereas very minor amounts of AChE are anchored by PRiMA that is produced by motoneurons. In its synaptic location, AChE is therefore positioned to scavenge ACh that effluxes from the nerve by non-quantal release. AChE-PRiMA, produced by the muscle, is diffusely distributed along the muscle in extrajunctional regions.

From Split to Sibenik: the tortuous pathway in the cholinesterase field

The interim between the first and tenth International Cholinesterase Meetings has seen remarkable advances associated with the applications of structural biology and recombinant DNA methodology to our field. The cloning of the cholinesterase genes led to the identification of a new super family of proteins, termed the alpha,beta-hydrolase fold; members of this family possess a four helix bundle capable of linking structural subunits to the functioning globular protein. Sequence comparisons and three-dimensional structural studies revealed unexpected cousins possessing this fold that, in turn, revealed three distinct functions for the alpha,beta-hydrolase proteins. These encompass: (1) a capacity for hydrolytic cleavage of a great variety of substrates, (2) a heterophilic adhesion function that results in trans-synaptic associations in linked neurons, (3) a chaperone function leading to stabilization of nascent protein and its trafficking to an extracellular or secretory storage location. The analysis and modification of structure may go beyond understanding mechanism, since it may be possible to convert the cholinesterases to efficient detoxifying agents of organophosphatases assisted by added oximes. Also, the study of the relationship between the alpha,beta-hydrolase fold proteins and their biosynthesis may yield means by which aberrant trafficking may be corrected, enhancing expression of mutant proteins. Those engaged in cholinesterase research should take great pride in our accomplishments punctuated by the series of ten meetings. The momentum established and initial studies with related proteins all hold great promise for the future.