Erythropoietin regulates the expression of dimeric form of acetylcholinesterase during differentiation of erythroblast

Design, Synthesis, and Biological Evaluation of Novel Tetrahydroacridin Hybrids with Sulfur-Inserted Linkers as Potential Multitarget Agents for Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative disease that can lead to the loss of cognitive function. The progression of AD is regulated by multiple signaling pathways and their associated targets. Therefore, multitarget strategies theoretically have greater potential for treating AD. In this work, a series of new hybrids were designed and synthesized by the hybridization of tacrine (4, AChE: IC50 = 0.223 μM) with pyrimidone compound 5 (GSK-3β: IC50 = 3 μM) using the cysteamine or cystamine group as the connector. The biological evaluation results demonstrated that most of the compounds exhibited moderate to good inhibitory activities against acetylcholinesterase (AChE) and glycogen synthase kinase 3β (GSK-3β). The optimal compound 18a possessed potent dual AChE/GSK-3β inhibition (AChE: IC50 = 0.047 ± 0.002 μM, GSK-3β: IC50 = 0.930 ± 0.080 μM). Further molecular docking and enzymatic kinetic studies revealed that this compound could occupy both the catalytic anionic site and the peripheral anionic site of AChE. The results also showed a lack of toxicity to SH-SY5Y neuroblastoma cells at concentrations of up to 25 μM. Collectively, this work explored the structure-activity relationships of novel tetrahydroacridin hybrids with sulfur-inserted linkers, providing a reference for the further research and development of new multitarget anti-AD drugs.

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.

Tacrine Induces Endoplasmic Reticulum-Stressed Apoptosis via Disrupting the Proper Assembly of Oligomeric Acetylcholinesterase in Cultured Neuronal Cells

Acetylcholinesterase inhibitors (AChEIs), the most developed treatment strategies for Alzheimer's disease (AD), will be used in clinic for, at least, the next decades. Their side effects are in highly variable from drug to drug with mechanisms remaining to be fully established. The withdrawal of tacrine (Cognex) in the market makes it as an interesting case study. Here, we found tacrine could disrupt the proper trafficking of proline-rich membrane anchor-linked tetrameric acetylcholinesterase (AChE) in the endoplasmic reticulum (ER). The exposure of tacrine in cells expressing AChE, e.g., neurons, caused an accumulation of the misfolded AChE in the ER. This misfolded enzyme was not able to transport to the Golgi/plasma membrane, which subsequently induced ER stress and its downstream signaling cascade of unfolded protein response. Once the stress was overwhelming, the cooperation of ER with mitochondria increased the loss of mitochondrial membrane potential. Eventually, the tacrine-exposed cells lost homeostasis and underwent apoptosis. The ER stress and apoptosis, induced by tacrine, were proportional to the amount of AChE. Other AChEIs (rivastigmine, bis(3)-cognitin, daurisoline, and dauricine) could cause the same problem as tacrine by inducing ER stress in neuronal cells. The results provide guidance for the drug design and discovery of AChEIs for AD treatment. SIGNIFICANCE STATEMENT: Acetylcholinesterase inhibitors (AChEIs) are the most developed treatment strategies for Alzheimer's disease (AD) and will be used in clinic for at least the next decades. This study reports that tacrine and other AChEIs disrupt the proper trafficking of acetylcholinesterase in the endoplasmic reticulum. Eventually, the apoptosis of neurons and other cells are induced. The results provide guidance for drug design and discovery of AChEIs for AD treatment.

The multiple biological roles of the cholinesterases

It is tacitly assumed that the biological role of acetylcholinesterase is termination of synaptic transmission at cholinergic synapses. However, together with its structural homolog, butyrylcholinesterase, it is widely distributed both within and outside the nervous system, and, in many cases, the role of both enzymes remains obscure. The transient appearance of the cholinesterases in embryonic tissues is especially enigmatic. The two enzymes' extra-synaptic roles, which are known as 'non-classical' roles, are the topic of this review. Strong evidence has been presented that AChE and BChE play morphogenetic roles in a variety of eukaryotic systems, and they do so either by acting as adhesion proteins, or as trophic factors. As trophic factors, one mode of action is to directly regulate morphogenesis, such as neurite outgrowth, by poorly understood mechanisms. The other mode is by regulating levels of acetylcholine, which acts as the direct trophic factor. Alternate substrates have been sought for the cholinesterases. Quite recently, it was shown that levels of the aggression hormone, ghrelin, which also controls appetite, are regulated by butyrylcholinesterase. The rapid hydrolysis of acetylcholine by acetylcholinesterase generates high local proton concentrations. The possible biophysical and biological consequences of this effect are discussed. The biological significance of the acetylcholinesterases secreted by parasitic nematodes is reviewed, and, finally, the involvement of acetylcholinesterase in apoptosis is considered.

Solar light induces expression of acetylcholinesterase in skin keratinocytes: Signalling mediated by activator protein 1 transcription factor

Acetylcholinesterase (AChE) hydrolyses acetylcholine to choline and acetate, playing an important role in terminating the neurotransmission in brain and muscle. Recently, the non-neuronal functions of AChE have been proposed in different tissues, in which there are various factors to regulate the expression of AChE. In mammalian skin, AChE was identified in melanocytes and keratinocytes. Our previous study has indicated that AChE in keratinocyte affects the process of solar light-induced skin pigmentation; however, the expression of AChE in keratinocytes in responding to sunlight remains unknown. Here, we provided several lines of evidence to support a notion that AChE could be upregulated at transcriptional and translational levels in keratinocytes when exposed to solar light. The light-mediated AChE expression was triggered by Ca²⁺, supported by an induction of Ca²⁺ ionophore A23187 and a blockage by Ca²⁺ chelator BAPTA-AM. In addition, this increase on AChE transcriptional expression was eliminated by mutagenesis on the activating protein 1 (AP1) site in ACHE gene. Hence, the solar light-induced AChE expression is mediated by Ca²⁺ signalling through AP1 site. This finding supports the role of solar light in affecting the cholinergic system in skin cells, and which may further influence the dermatological function.

Interacting with α 7 nAChR is a new mechanism for AChE to enhance the inflammatory response in macrophages

Acetylcholine (ACh) regulates inflammation via α7 nicotinic acetylcholine receptor (α7 nAChR). Acetylcholinesterase (AChE), an enzyme hydrolyzing ACh, is expressed in immune cells suggesting non-classical function in inflammatory responses. Here, the expression of PRiMA-linked G4 AChE was identified on the surface of macrophages. In lipopolysaccharide-induced inflammatory processes, AChE was upregulated by the binding of NF-κB onto the ACHE promotor. Conversely, the overexpression of G4 AChE inhibited ACh-suppressed cytokine release and cell migration, which was in contrast to that of applied AChE inhibitors. AChEmt, a DNA construct without enzymatic activity, was adopted to identify the protein role of AChE in immune system. Overexpression of G4 AChEmt induced cell migration and inhibited ACh-suppressed cell migration. The co-localization of α7 nAChR and AChE was found in macrophages, suggesting the potential interaction of α7 nAChR and AChE. Besides, immunoprecipitation showed a close association of α7 nAChR and AChE protein in cell membrane. Hence, the novel function of AChE in macrophage by interacting with α7 nAChR was determined. Together with hydrolysis of ACh, AChE plays a direct role in the regulation of inflammatory response. As such, AChE could serve as a novel target to treat age-related diseases by anti-inflammatory responses.

Diagnoses of Pathological States Based on Acetylcholinesterase and Butyrylcholinesterase

Two cholinesterases exist: Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). While AChE plays a crucial role in neurotransmissions, BChE has no specific function apart from the detoxification of some drugs and secondary metabolites from plants. Thus, both AChE and BChE can serve as biochemical markers of various pathologies. Poisoning by nerve agents like sarin, soman, tabun, VX, novichok and overdosing by drugs used in some neurodegenerative disorders like Alzheimer´s disease and myasthenia gravis, as well as poisoning by organophosphorus pesticides are relevant to this issue. But it appears that changes in these enzymes take place in other processes including oxidative stress, inflammation, some types of cancer and genetically conditioned diseases. In this review, the cholinesterases are introduced, the mechanism of inhibitors action is explained and the relations between the cholinesterases and pathologies are explained.

Solar light induces the release of acetylcholine from skin keratinocytes affecting melanogenesis

Cholinergic system conducts signal transmission in brain and muscle. Besides nervous system, the nonneuronal functions of cholinergic system have been proposed in various tissues. The expression of cholinergic proteins and release of acetylcholine in human skin have been reported, but its mechanism and influence on dermatological functions is not elucidated. Here, the expression profile of cholinergic markers was further investigated in skin and keratinocyte. The expression levels of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), vesicular acetylcholine transporter (VAChT), and synaptophysin, were upregulated during differentiation of keratinocytes. In cultured keratinocytes, a transient exposure of solar light induced the release of acetylcholine, which was mediated by intracellular Ca²⁺ mobilization. The light-induced acetylcholine release was mediated by the present of opsin. The light-induced melanogenesis was inhibited by acetylcholine or AChE inhibitor in melanocyte in vitro and mouse skin ex vivo. These results indicated that the potential role of cholinergic system could be a negative regulator in skin pigmentation.

Microphthalmia-associated transcription factor up-regulates acetylcholinesterase expression during melanogenesis of murine melanoma cells

Acetylcholinesterase (AChE) hydrolyzes the neurotransmitter acetylcholine in neurons. However, AChE has been proposed to also have nonneuronal functions in different cell types. Here, we report that AChE is expressed in melanocytes and melanoma cells, and that the tetrameric (G4) form is the major AChE isoform in these cells. During melanogenesis of B16F10 murine melanoma cells, AChE levels decreased markedly. The differentiation of melanoma cells led to (i) an increase in melanin and tyrosinase, (ii) a change in intracellular cAMP levels, and (iii) a decrease in microphthalmia-associated transcription factor (MITF). We hypothesized that the regulation of AChE during melanogenesis is mediated by two transcription factors: cAMP-response element-binding protein (CREB) and MITF. In melanoma cells, exogenous cAMP suppressed AChE expression and the promoter activity of the ACHE gene. This suppression was mediated by a cAMP-response element (CRE) located on the ACHE promoter, as mutation of CRE relieved the suppression. In melanoma, MITF overexpression induced ACHE transcription, and mutation of an E-box site in human ACHE promoter blocked this induction. An AChE inhibitor greatly enhanced acetylcholine-mediated responses of melanogenic gene expression levels in vitro; however, this enhancement was not observed in the presence of agonists of the muscarinic acetylcholine receptor. These results indicate that ACHE transcription is regulated by cAMP-dependent signaling during melanogenesis of B16F10 cells, and the effect of this enzyme on melanin production suggests that it has a potential role in skin pigmentation.