Respective roles of the catalytic domains and C-terminal tail peptides in the oligomerization and secretory trafficking of human acetylcholinesterase and butyrylcholinesterase

Protective role of acetylcholine and the cholinergic system in the injured heart

This review explores the roles of the cholinergic system in the heart, comprising the neuronal and non-neuronal cholinergic systems. Both systems are essential for maintaining cardiac homeostasis by regulating the release of acetylcholine (ACh). A reduction in ACh release is associated with the early onset of cardiovascular diseases (CVDs), and increasing evidence supports the protective roles of ACh against CVD. We address the challenges and limitations of current strategies to elevate ACh levels, including vagus nerve stimulation and pharmacological interventions such as cholinesterase inhibitors. Additionally, we introduce alternative strategies to increase ACh in the heart, such as stem cell therapy, gene therapy, microRNAs, and nanoparticle drug delivery methods. These findings offer new insights into advanced treatments for regenerating the injured human heart.

Synthesis and characterization of new inhibitors of cholinesterases based on N-phenylcarbamates: In vitro study of inhibitory effect, type of inhibition, lipophilicity and molecular docking

Based on current treatment of Alzheimer's disease, where the carbamate inhibitor Rivastigmine is used, two series of carbamate derivatives were prepared: (i) N-phenylcarbamates with additional carbamate group (1-12) and (ii) N-phenylcarbamates with monosaccharide moiety (13-24). All compounds were tested for the inhibitory effect on both of the cholinesterases, electric eel acetylcholinesterase (eeAChE) and butyrylcholinesterase from equine serum (eqBChE) and the inhibitory activity (expressed as IC₅₀ values) was compared with that of the established drugs Galanthamine and Rivastigmine. The compounds with two carbamate groups 1-12 revealed higher inhibitory efficiency on both cholinesterases in compared with monosaccharide derived carbamates 13-24 and with Rivastigmine. The significant decrease of inhibitory efficiency on eqBChE (also for eeAChE but in less manner) was observed after deacetalization of monosaccharide. Moreover, the type of inhibitory mechanism of five chosen compounds was studied. It was found, that compounds with two carbamate groups act presumably via a mixed inhibitory mechanism and the compounds with monosaccharide moiety act as non-competitive inhibitors. The lipophilicity of tested compounds was determined using partition coefficient. Specific positions of the inhibitors in the binding sites of cholinesterases were determined using molecular modeling and the results indicate the importance of phenylcarbamate orientation in the catalytic gorges of both enzymes.

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.

Early appearance and possible functions of non-neuromuscular cholinesterase activities

The biological function of the cholinesterase (ChE) enzymes has been studied since the beginning of the twentieth century. Acetylcholinesterase plays a key role in the modulation of neuromuscular impulse transmission in vertebrates, while in invertebrates pseudo cholinesterases are preeminently represented. During the last 40 years, awareness of the role of ChEs role in regulating non-neuromuscular cell-to-cell interactions has been increasing such as the ones occurring during gamete interaction and embryonic development. Moreover, ChE activities are responsible for other relevant biological events, including regulation of the balance between cell proliferation and cell death, as well as the modulation of cell adhesion and cell migration. Understanding the mechanisms of the regulation of these events can help us foresee the possible impact of neurotoxic substances on the environmental and human health.

Molecular Assembly and Biosynthesis of Acetylcholinesterase in Brain and Muscle: the Roles of t-peptide, FHB Domain, and N-linked Glycosylation

Acetylcholinesterase (AChE) is responsible for the hydrolysis of the neurotransmitter, acetylcholine, in the nervous system. The functional localization and oligomerization of AChE T variant are depending primarily on the association of their anchoring partners, either collagen tail (ColQ) or proline-rich membrane anchor (PRiMA). Complexes with ColQ represent the asymmetric forms (A(12)) in muscle, while complexes with PRiMA represent tetrameric globular forms (G(4)) mainly found in brain and muscle. Apart from these traditional molecular forms, a ColQ-linked asymmetric form and a PRiMA-linked globular form of hybrid cholinesterases (ChEs), having both AChE and BChE catalytic subunits, were revealed in chicken brain and muscle. The similarity of various molecular forms of AChE and BChE raises interesting question regarding to their possible relationship in enzyme assembly and localization. The focus of this review is to provide current findings about the biosynthesis of different forms of ChEs together with their anchoring proteins.

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.

The PRiMA-linked cholinesterase tetramers are assembled from homodimers: hybrid molecules composed of acetylcholinesterase and butyrylcholinesterase dimers are up-regulated during development of chicken brain

Acetylcholinesterase (AChE) is anchored onto cell membranes by the transmembrane protein PRiMA (proline-rich membrane anchor) as a tetrameric globular form that is prominently expressed in vertebrate brain. In parallel, the PRiMA-linked tetrameric butyrylcholinesterase (BChE) is also found in the brain. A single type of AChE-BChE hybrid tetramer was formed in cell cultures by co-transfection of cDNAs encoding AChE(T) and BChE(T) with proline-rich attachment domain-containing proteins, PRiMA I, PRiMA II, or a fragment of ColQ having a C-terminal GPI addition signal (Q(N-GPI)). Using AChE and BChE mutants, we showed that AChE-BChE hybrids linked with PRiMA or Q(N-GPI) always consist of AChE(T) and BChE(T) homodimers. The dimer formation of AChE(T) and BChE(T) depends on the catalytic domains, and the assembly of tetramers with a proline-rich attachment domain-containing protein requires the presence of C-terminal "t-peptides" in cholinesterase subunits. Our results indicate that PRiMA- or ColQ-linked cholinesterase tetramers are assembled from AChE(T) or BChE(T) homodimers. Moreover, the PRiMA-linked AChE-BChE hybrids occur naturally in chicken brain, and their expression increases during development, suggesting that they might play a role in cholinergic neurotransmission.

Emerging hypotheses regarding the influences of butyrylcholinesterase-K variant, APOE epsilon 4, and hyperhomocysteinemia in neurodegenerative dementias

Non-enzymatic functions of butyrylcholinesterase (BuChE) include prevention of the aggregation of amyloid-beta peptide (A beta) in a concentration-dependent manner. This is mediated by the C-terminus of the protein, distal from the enzymatic site. The BuChE-K variant polymorphism lowers expression of BuChE protein and/or alters C-terminal activity. In combination with factors that increase production or reduce elimination of A beta, and/or increase susceptibility to A beta toxicity - such as the apolipoprotein E (APOE) epsilon 4 allele and/or hyperhomocysteinemia - BuChE-K may accelerate cholinergic synaptic and neuronal damage and cognitive decline. A beta-mediated damage to ascending cholinergic pathways may be further accentuated by Lewy body and/or cerebrovascular disease. As the disease advances and functioning cholinergic synapses disappear, both the rapid cognitive decline and response to cholinesterase inhibitor therapy in individuals with these factors may diminish. Non-enzymatic functions of the BuChE protein, APOE epsilon 4 status and hyperhomocysteinemia influence the progression of pathology, symptom expression, and response to cholinesterase inhibition in a stage-specific manner in neurodegenerative disorders associated with Alzheimer, Lewy body and vascular pathology.