Over-expression of acetylcholinesterase stimulates the expression of agrin in NG108-15 cells

Alleviating Sepsis-Induced Neuromuscular Dysfunction Linked With Acetylcholine Receptors by Agrin

BACKGROUND

Abnormal expression and distribution of nicotinic acetylcholine receptors (nAChRs) in skeletal muscle caused by sepsis can lead to neuromuscular dysfunction. Here, we asked whether neural agrin regulates nAChRs to ameliorate muscle function, which could be associated with the agrin/muscle-specific kinase pathway.

METHODS

Rats were subjected to cecal ligation and puncture (CLP) group, sham group, or control group to observe the alteration caused by sepsis. To verify the effect of improving function, rats were injected with agrin or normal saline intramuscularly after CLP. Electromyogram was used to measure neuromuscular function. Cytokines levels of serum and the expression of related proteins and mRNA were tested after treatment.

RESULTS

Compared with the rats in control or sham group, CLP-treated rats showed an acute inflammatory status and a reduction of neuromuscular dysfunction in tibialis anterior muscle, which was associated with abnormal expression in agrin/muscle-specific kinase pathway and increased expression of γ- and α7-nAChR. Exogenous agrin alleviated neuromuscular dysfunction and decreased the expression of γ- and α7-nAChR through agrin-related signaling pathway.

CONCLUSIONS

The decreased expression of agrin may lead to skeletal muscle dysfunction. Early enhancement of intramuscular agrin levels after sepsis may be a potential strategy for the treatment of sepsis-induced muscle dysfunction.

Bioinspired Three-Dimensional Human Neuromuscular Junction Development in Suspended Hydrogel Arrays

The physical connection between motoneurons and skeletal muscle targets is responsible for the creation of neuromuscular junctions (NMJs), which allow electrical signals to be translated to mechanical work. NMJ pathology contributes to the spectrum of neuromuscular, motoneuron, and dystrophic disease. Improving in vitro tools that allow for recapitulation of the physiology of the neuromuscular connection will enable researchers to better understand the development and maturation of NMJs, and will help to decipher mechanisms leading to NMJ degeneration. In this work, we first describe robust differentiation of bungarotoxin-positive human myotubes, as well as a reproducible method for encapsulating and aligning human myoblasts in three-dimensional (3D) suspended culture using bioprinted silk fibroin cantilevers as cell culture supports. Further analysis with coculture of motoneuron-like cells demonstrates feasibility of fully human coculture using two-dimensional and 2.5-dimensional culture methods, with appropriate differentiation of both cell types. Using these coculture differentiation conditions with motoneuron-like cells added to monocultures of 3D suspended human myotubes, we then demonstrate synaptic colocalization in coculture as well as acetylcholine and glutamic acid stimulation of human myocytes. This method represents a unique platform to coculture suspended human myoblast-seeded 3D hydrogels with integrated motoneuron-like cells derived from human induced neural stem cells. The platform described is fully customizable using 3D freeform printing into standard laboratory tissue culture materials, and allows for human myoblast alignment in 3D with precise motoneuron integration into preformed myotubes. The coculture method will ideally be useful in observation and analysis of neurite outgrowth and myogenic differentiation in 3D with quantification of several parameters of muscle innervation and function.

Possibility of Acetylcholinesterase Overexpression in Alzheimer Disease Patients after Therapy with Acetylcholinesterase Inhibitors

Acetylcholinesterase is an enzyme responsible for termination of excitatory transmission at cholinergic synapses by the hydrolyzing of a neurotransmitter acetylcholine. Nowadays, other functions of acetylcholinesterase in the organism are considered, for example its role in regulation of apoptosis. Cholinergic nervous system as well as acetylcholinesterase activity is closely related to pathogenesis of Alzheimer disease. The mostly used therapy of Alzheimer disease is based on enhancing cholinergic function using inhibitors of acetylcholinesterase like rivastigmine, donepezil or galantamine. These drugs can influence not only the acetylcholinesterase activity but also other processes in treated organism. The paper is aimed mainly on possibility of increased expression and protein level of acetylcholinesterase caused by the therapy with acetylcholinesterase inhibitors.

Non-synaptic roles of acetylcholinesterase and agrin

Proteins in living organisms have names that are usually derived from their function in the biochemical system their discoverer was investigating. Typical examples are acetylcholinesterase and agrin; however, for both of these, various other functions that are not related to the cholinergic system have been revealed. Our investigations have been focused on the alternative roles of acetylcholinesterase and agrin in the processes of muscle development and regeneration. Previously, we described a role for agrin in the development of excitability in muscle contraction. In this study, we report the effects of agrin on secretion of interleukin 6 in developing human muscle. At the myoblast stage, agrin increases interleukin 6 secretion. This effect seems to be general as it was observed in all of the cell models analysed (human, mouse, cell lines). After fusion of myoblasts into myotubes, the effects of agrin are no longer evident, although agrin has further effects at the innervation stage, at least in in vitro innervated human muscle. These effects of agrin are another demonstration of its non-synaptic roles that are apparently developmental-stage specific. Our data support the view that acetylcholinesterase and agrin participate in various processes during development of skeletal muscle.

The use of cholinesterases in ecotoxicology

Cholinesterase (ChE) is one of the most employed biomakers in environmental analysis. Among ChEs, potentially the most significant in environmental terms is acetylcholinesterase (AChE), an enzymatic form that terminates the nerve impulse . Because of its physiological role, Ache has long been considered a highly specific biomarker for organisms exposed to anticholinesterasic agents, primarily agro-chemicals (organophosphate and carbamate pesticides). The effects of these pesticides depends upon their selective inhibition of AChE. Because large amounts of such pesticides are employed, it is plausible that they exert neurotoxic effects on some non-target species. Therefore, AChE is among the most valuable of diagnostic tools that can be used to verify exposure to such chemical agents. It is well known that assays are available for use quantifying AChE in multiple tissues of several test organisms. Enzymes other than AChE (e.g., butyrylcholinesterase and carboxylesterases) have also been used as putative markers for detecting the environmental presence of contaminating compounds. Researchers must use a step-by-step approach to identify the most prominent cholinesterasic form present in a given species, so that this form can be distinguished from others that may interfere with its use. Such fundamental work must be completed prior to using ChEs for any monitoring to assess for anticholinesterasic effects. Despite massive employment in environmental analysis, using ChE inhibition as an endpoint or effect criterion has been unsettled by the discovery the ChEs may interact in the environmental in previously unknown ways. Several chemicals, in addition to anticholinesterasic pesticides, are now known to inhibit ChE activity. Such chemical include detergents, metals, and certain organic compounds such as hydrocarbons. The situation is made worse, because the literature is contradictory as to the ability of such chemicals and elements to interact with ChEs. Some results indicate that ChE inhibition by metals, detergents , and complex mixtures do not or are unlikely to occur. These problems and contradictions are addressed in this review. It is purpose in this review to address the following practical issues related to the ChEs: 1. The situation and organisms in which ChEs have been employed as biomarkers in laboratory trials, and the need to fully characterize these enzymatic forms before they are used for environmental assessment purposes. 2. The ways in which ChEs have been used in field monitoring, and the potential for use of others complimentary markers to diagnose organophosphate exposure, and how drawbacks (such as the absence of reference values) can be overcome. 3. What requirements must be satisfied prior implementing the use of ChEs as biomarkers in species not yet studied. 4. How direct linkages have been established between ChE inhibition and effects from inhibition observed at higher levels of integration (e.g., behavioral changes and population effects, or others indices of ecological relevance). 5. The potential for ChE inhibition to be applied as an effective parameter of toxicity to detect for the environmental presence of compounds other than the organo-phosphate and carbamate pesticides, and the limitations associated therewith.

Functional characterization of heterotrimeric G-proteins in rat diaphragm muscle

Seven-transmembrane receptors mediate diverse skeletal muscle responses for a wide variety of stimuli, via activation of heterotrimeric G-proteins. Herein we evaluate the expression and activation of rat diaphragm or cultured skeletal muscle G-proteins using [(35)S]GTPγS. Total membrane Gα subunit content was 4-7 times higher in rat primary cultured myotubes and L6 cell line than in diaphragm (32.6±1.2fmol/mg protein) and 7-27% of them were in the active conformational state. Immunoprecipitation assay showed equal expression of diaphragm Gαs, Gαq and Gαi/o. Addition of GDP allowed the measurement of G-protein activation by different GPCR, including adrenoceptor, adenosine, melatonin and muscarinic receptors. Diaphragm denervation resulted in a marked increase in both total and active state G-protein levels. Together, the results show that [(35)S]GTPγS binding assay is a sensitive and valuable method to evaluate GPCR activity in skeletal muscle cells, which is of particular interest for pharmacological analysis of drugs with potential use in the management of respiratory muscle failure.

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

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

Sarin (nerve agent GB)-induced differential expression of mRNA coding for the acetylcholinesterase gene in the rat central nervous system

We carried out a time-course study on the effects of a single intramuscular (i.m.) dose (0.5x LD(50)) of sarin (O-isopropyl methylphosphonofluoridate), also known as nerve agent GB, on the mRNA expression of acetylcholinesterase (AChE) in the brain of male Sprague-Dawley rats. Sarin inactivates the enzyme AChE which is responsible for the breakdown of the neurotransmitter acetylcholine (ACh), leading to its accumulation at ACh receptors and overstimulation of the cholinergic system. Rats were treated with 50 microg/kg of sarin (0.5x LD(50)) in 1 mL saline/kg and terminated at the following time points: 1 and 2 hr and 1, 3, and 7 days post-treatment. Control rats were treated with normal saline. Total RNA was extracted, and northern blots were hybridized with cDNA probes for AChE and 28S RNA (control). Poly-A RNA from both treated and control cortex was used for reverse transcription-polymerase chain reaction (RT-PCR)-based verification of the data from the northern blots. The results obtained indicate that a single (i.m.) dose of sarin (0.5x LD(50)) produced differential induction and persistence of AChE mRNA levels in different regions of the brain. Immediate induction of AChE transcripts was noted in the brainstem (126+/-6%), cortex (149+/-4%), midbrain (153+/-5%), and cerebellum (234+/-2%) at 1 hr. The AChE expression level, however, increased over time and remained elevated after a decline at 1 day in the previously shown more susceptible brainstem. The transcript levels remained elevated at a later time point (3 days) in the midbrain, after a dramatic decline at day 1 (110+/-2%). In the cortex, transcript levels came down to control values by day 1. The cerebellum also showed a decline of the elevated levels observed at 2 hr (275+/-2%) to control values by day 1. RT-PCR analysis of the AChE transcript at 30 min in the cortex showed an induction to 213+/-3% of the control level, confirming the expression pattern obtained by the northern blot data. The immediate induction followed by the complex pattern of the AChE mRNA time-course in the CNS may indicate that the activation of both cholinergic-related and unrelated functions of the gene plays an important role in the pathological manifestations of sarin-induced neurotoxicity.