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

Acetylcholinesterase is regulated by exposure of ultraviolet B in skin keratinocytes: A potential inducer of cholinergic urticaria

Cholinergic urticaria is a dermatological disease characterized by the presence of large patches of red skin and transient hives triggered by factors, such as exercise, sweating, and psychological tension. This skin problem is hypothesized to be attributed to a reduced expression of acetylcholinesterase (AChE), an enzyme responsible for hydrolyzing acetylcholine (ACh). Consequently, ACh is thought to the leak from sympathetic nerves to skin epidermis. The redundant ACh stimulates the mast cells to release histamine, triggering immune responses in skin. Here, the exposure of ultraviolet B in skin suppressed the expression of AChE in keratinocytes, both in in vivo and in vitro models. The decrease of the enzyme was resulted from a declined transcription of ACHE gene mediated by micro-RNAs, that is, miR-132 and miR-212. The levels of miR-132 and miR-212 were markedly induced by exposure to ultraviolet B, which subsequently suppressed the transcriptional rate of ACHE. In the presence of low level of AChE, the overflow ACh caused the pro-inflammatory responses in skin epidermis, including increased secretion of cytokines and COX-2. These findings suggest that ultraviolet B exposure is one of the factors contributing to cholinergic urticaria in skin.

Design of Recombinant Spider Silk Proteins for Cell Type Specific Binding

Cytophilic (cell-adhesive) materials are very important for tissue engineering and regenerative medicine. However, for engineering hierarchically organized tissue structures comprising different cell types, cell-specific attachment and guidance are decisive. In this context, materials made of recombinant spider silk proteins are promising scaffolds, since they exhibit high biocompatibility, biodegradability, and the underlying proteins can be genetically functionalized. Here, previously established spider silk variants based on the engineered Araneus diadematus fibroin 4 (eADF4(C16)) are genetically modified with cell adhesive peptide sequences from extracellular matrix proteins, including IKVAV, YIGSR, QHREDGS, and KGD. Interestingly, eADF4(C16)-KGD as one of 18 tested variants is cell-selective for C2C12 mouse myoblasts, one out of 11 tested cell lines. Co-culturing with B50 rat neuronal cells confirms the cell-specificity of eADF4(C16)-KGD material surfaces for C2C12 mouse myoblast adhesion.

ALK5 i II Accelerates Induction of Adipose-Derived Stem Cells toward Schwann Cells through a Non-Smad Signaling Pathway

Schwann cells (SCs) are likely to be a vital component of cell-based therapies for nerve regeneration. There are various methods for inducing SC-like cells (SCLCs) from adipose-derived stem cells (ADSCs), but their phenotypic and functional characteristics remain unsatisfactory. Here, we report a novel efficient procedure to induce SCLCs by culturing ADSCs with ALK5 inhibitor (ALK5 i) II, a specific inhibitor of activin-like kinase 5 (ALK5) (transforming growth factor-β receptor 1 (TGFβR1)) that is also known as Repsox. The resultant cells that we named "modified SCLCs (mSCLCs)" expressed SC-specific genes more strongly than conventional SCLCs (cSCLCs) and displayed a neurosupportive capacity in vitro, similarly to genuine SCs. Regarding the mechanism of the mSCLC induction by ALK5 i II, knockdown of Smad2 and Smad3, key proteins in the TGFβ/Smad signaling pathway, did not induce SC markers. Meanwhile, expression of multipotent stem cell markers such as Sex-determining region Y- (SRY-) box 2 (Sox2) was upregulated during induction. These findings imply that ALK5 i II exerts its effect via the non-Smad pathway and following upregulation of undifferentiated cell-related genes such as Sox2. The procedure described here results in highly efficient induction of ADSCs into transgene-free and highly functional SCLCs. This approach might be applicable to regeneration therapy for peripheral nerve injury.

Toxic effects of subacute exposure to acrylamide on motor endplates of the gastrocnemius in rats

Acrylamide (ACR) is a recognized toxin that is known to induce neurotoxicity in humans and experimental animals. This study aimed to investigate the toxic effects of subacute exposure of the motor endplate (MEP) of the gastrocnemius in rats to ACR. All rats were randomly divided into control, 9, 18, and 36 mg/kg ACR groups, and ACR was administered by gastric gavage for 21 days. The behavioral tests were performed weekly. On the 22nd day, the wet weight of the gastrocnemius was measured. The changes in muscle fiber structure, nerve endings, and MEP in the gastrocnemius were examined by hematoxylin-eosin (HE) and gold chloride staining. Acetylcholinesterase (AChE) content in the gastrocnemius was detected by AChE staining. The expression of AChE and calcitonin gene-related peptide was detected by immunohistochemistry and western blot. Rats exposed to ACR showed a significant increase in gait scores and hind limb splay distance compared with the control group, and the wet weight of the gastrocnemius was reduced, HE staining showed that the muscle fiber structure of the gastrocnemius became thin and the arrangement was dense with nuclear aggregation, gold chloride staining showed that nerve branches decreased and became thin, nerve fibers became short and light, the number of MEPs was decreased, the staining became light, and the structure was not clear. AChE staining showed that the number of MEPs was significantly reduced after exposure to ACR, the shape became small, and the AChE content decreased in a dose-dependent manner. Immunohistochemistry and western blot analysis results of the expression levels of AChE and CGRP showed a decreasing trend as compared to the control group with increasing ACR exposure dose. The reduction in protein levels may be the mechanism by which ACR has a toxic effect on the MEP in the gastrocnemius of rats.

New perspective on the regulation of acetylcholinesterase via the aryl hydrocarbon receptor

Acetylcholinesterase (AChE, EC 3.1.1.7) plays important roles in cholinergic neurotransmission and has been widely recognized as a biomarker for monitoring pollution by organophosphate (OP) and carbamate pesticides. Dioxin is an emerging environmental AChE disruptor and is a typical persistent organic pollutant with multiple toxic effects on the nervous system. Growing evidence has shown that there is a significant link between dioxin exposure and neurodegenerative diseases and neurodevelopmental disorders, most of which involve AChE and cholinergic dysfunctions. Therefore, an in-depth understanding of the effects of dioxin on AChE and the related mechanisms of action might help to shed light on the molecular bases of dioxin impacts on the nervous system. In the past decade, the effects of dioxins on AChE have been revealed in cultured cells of different origins and in rodent animal models. Unlike OP and carbamate pesticides, dioxin-induced AChE disturbance is not due to direct inhibition of enzymatic activity; instead, dioxin causes alterations of AChE expression in certain models. As a widely accepted mechanism for most dioxin effects, the aryl hydrocarbon receptor (AhR)-dependent pathway has become a research focus in studies on the mechanism of action of dioxin-induced AChE dysregulation. In this mini-review, the effects of dioxin on AChE and the diverse roles of the AhR pathway in AChE regulation are summarized. Additionally, the involvement of AhR in AChE regulation during different neurodevelopmental processes is discussed. These AhR-related findings might also provide new insight into AChE regulation triggered by diverse xenobiotics capable of interacting with AhR.

Highly Efficient Conversion of Motor Neuron-Like NSC-34 Cells into Functional Motor Neurons by Prostaglandin E2

Motor neuron diseases are a group of progressive neurological disorders that degenerate motor neurons. The neuroblastoma × spinal cord hybrid cell line NSC-34 is widely used as an experimental model in studies of motor neuron diseases. However, the differentiation efficiency of NSC-34 cells to neurons is not always sufficient. We have found that prostaglandin E₂ (PGE₂) induces morphological differentiation in NSC-34 cells. The present study investigated the functional properties of PGE₂-differentiated NSC-34 cells. Retinoic acid (RA), a widely-used agent inducing cell differentiation, facilitated neuritogenesis, which peaked on day 7, whereas PGE₂-induced neuritogenesis took only 2 days to reach the same level. Whole-cell patch-clamp recordings showed that the current threshold of PGE₂-treated cell action potentials was lower than that of RA-treated cells. PGE₂ and RA increased the protein expression levels of neuronal differentiation markers, microtubule-associated protein 2c and synaptophysin, and to the same extent, motor neuron-specific markers HB9 and Islet-1. On the other hand, protein levels of choline acetyltransferase and basal release of acetylcholine in PGE₂-treated cells were higher than in RA-treated cells. These results suggest that PGE₂ is a rapid and efficient differentiation-inducing factor for the preparation of functionally mature motor neurons from NSC-34 cells.

Directed differentiation of granular cells from crayfish hematopoietic tissue cells

Hemocytes are the major immune cells of crustaceans. New hemocyte production is required throughout the life cycle of these animals to maintain a functional immune system. The mechanism of crustacean hematopoiesis has just begun to be understood and new methods are needed for the investigation of this process. Here we report the directed differentiation of granular cells (GCs) from the hematopoietic tissue (HPT) cells of Cherax quadricarinatus in vitro. We started by providing the cultured HPT cells with different additives to induce possible differentiation. We found that crayfish muscle extract greatly promoted the physical status of the cells and induced the formation of refractile cytoplasmic granules. The transcription of marker genes and the production of functional prophenoloxidase further confirmed the formation of mature GCs. In our experiments, young GCs usually started to develop in ∼2 weeks post induction and over 60% of the cells became mature within 3-4 weeks. This is the first time that the fully differentiation of crustacean hemocytes is accomplished in vitro. It provides a powerful tool for in-depth study of crustacean hematopoiesis.

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

Acetylcholinesterase (AChE; EC 3.1.1.7) is known to hydrolyze acetylcholine at cholinergic synapses. In mammalian erythrocyte, AChE exists as a dimer (G₂ ) and is proposed to play role in erythropoiesis. To reveal the regulation of AChE during differentiation of erythroblast, erythroblast-like cells (TF-1) were induced to differentiate by application of erythropoietin (EPO). The expression of AChE was increased in parallel to the stages of differentiation. Application of EPO in cultured TF-1 cells induced transcriptional activity of ACHE gene, as well as its protein product. This EPO-induced event was in parallel with erythrocytic proteins, for example, α- and β-globins. The EPO-induced AChE expression was mediated by phosphorylations of Akt and GATA-1; because the application of Akt kinase inhibitor blocked the gene activation. Erythroid transcription factor also known as GATA-1, a downstream transcription factor of EPO signaling, was proposed here to account for regulation of AChE in TF-1 cell. A binding sequence of GATA-1 was identified in ACHE gene promoter, which was further confirmed by chromatin immunoprecipitation (ChIP) assay. Over-expression of GATA-1 in TF-1 cultures induced AChE expression, as well as activity of ACHE promoter tagged with luciferase gene (pAChE-Luc). The deletion of GATA-1 sequence on the ACHE promoter, pAChE_ΔGATA-1 -Luc, reduced the promoter activity during erythroblastic differentiation. On the contrary, the knock-down of AChE in TF-1 cultures could lead to a reduction in EPO-induced expression of erythrocytic proteins. These findings indicated specific regulation of AChE during maturation of erythroblast, which provided an insight into elucidating possible mechanisms in regulating erythropoiesis.

Fine Localization of Acetylcholinesterase in the Synaptic Cleft of the Vertebrate Neuromuscular Junction

Acetylcholinesterase (AChE) is concentrated at cholinergic synapses, where it is a major factor in controlling the duration of transmitter action. The concentration and localization of AChE within the synaptic cleft are in keeping with the functional requirements of the particular type of synapse. The densities of synaptic AChE at various neuromuscular junctions (NMJs) had been evaluated by quantitative EM-autoradiography using radiolabeled probes. Yet, fundamental issues concerning the precise distribution and location of the enzyme in the cleft remained open: whether and to what extent synaptic AChE is associated with pre- or postsynaptic membranes, or with synaptic basal lamina (BL), and whether it occurs only in the primary cleft (PC) or also in postjunctional folds (PJFs). Nanogold-conjugates of fasciculin, an anticholinesterase polypeptide toxin, were prepared and used to label AChE at NMJs of mouse and frog muscles. Selective intense labeling was obtained at the NMJs, with gold-labeled AChE sites distributed over the BL in the PC and the PJFs. Quantitative analysis demonstrated that AChE sites are almost exclusively located on the BL rather than on pre- or postsynaptic membranes and are distributed in the PC and down the PJFs, with a defined pattern. This localization pattern of AChE is suggested to ensure full hydrolysis of acetylcholine (ACh) bouncing off receptors, thus eliminating its unnecessary detrimental reattachment.

Three-dimensional co-culture of C2C12/PC12 cells improves skeletal muscle tissue formation and function

Engineered muscle tissues demonstrate properties far from native muscle tissue. Therefore, fabrication of muscle tissues with enhanced functionalities is required to enable their use in various applications. To improve the formation of mature muscle tissues with higher functionalities, we co-cultured C2C12 myoblasts and PC12 neural cells. While alignment of the myoblasts was obtained by culturing the cells in micropatterned methacrylated gelatin (GelMA) hydrogels, we studied the effects of the neural cells (PC12) on the formation and maturation of muscle tissues. Myoblasts cultured in the presence of neural cells showed improved differentiation, with enhanced myotube formation. Myotube alignment, length and coverage area were increased. In addition, the mRNA expression of muscle differentiation markers (Myf-5, myogenin, Mefc2, MLP), muscle maturation markers (MHC-IId/x, MHC-IIa, MHC-IIb, MHC-pn, α-actinin, sarcomeric actinin) and the neuromuscular markers (AChE, AChR-ε) were also upregulated. All these observations were amplified after further muscle tissue maturation under electrical stimulation. Our data suggest a synergistic effect on the C2C12 differentiation induced by PC12 cells, which could be useful for creating improved muscle tissue. Copyright © 2014 John Wiley & Sons, Ltd.

Quantification of the transcripts encoding different forms of AChE in various cell types: real-time PCR coupled with standards in revealing the copy number

Acetylcholinesterase (AChE) is encoded by a single gene, and the alternative splicing at the 3' end produces different isoforms, including tailed (AChET), read-through (AChER), and hydrophobic (AChEH). Different forms of this enzyme exist in different cell types. Each AChE form has been proposed to have unique function, and all of them could be found in same cell type. Thus, the splicing process of different AChE forms remains unclear. Here, we aimed to establish a quantification method in measuring the absolute amount of each AChE splicing variants within a cell type. By using real-time PCR coupled with standard curves of defined copy of AChE variants, the copies of AChET transcript per 100 ng of total RNA were 5.7 × 10(4) in PC12 (rat neuronal cell), 1.3 × 10(4) in Caco-2 (human intestinal cell), 0.67 × 10(4) in TF-1 (human erythropoietic precursor), 133.3 in SH-SY5Y (human neuronal cell), and 56.7 in human umbilical vein endothelial cells (human endothelial cells). The copies of AChEH in these cell types were 0.3 × 10(4), 3.3 × 10(4), 2.7 × 10(4), 133.3, and 46.7, respectively, and AChER were 0.07 × 10(4), 0.13 × 10(4), 890, 3.3, and 2.7, respectively. Furthermore, PC12 and TF-1 cells were chosen for the analysis of AChE splicing pattern during differentiation. The results demonstrated a selective increase in AChET mRNA but not AChER or AChEH mRNAs in PC12 upon nerve growth factor-induced neuronal differentiation. PC12 cells could therefore act as a good cell model for the study on alternative splicing mechanism and regulation of AChET.

AhR-mediated effects of dioxin on neuronal acetylcholinesterase expression in vitro

BACKGROUND

Deficits in cognitive functioning have been reported in humans exposed to dioxins and dioxin-like compounds. Evidence suggests that dioxins induce cholinergic dysfunction mediated by hypothyroidism. However, little is known about direct effects of dioxins on the cholinergic system.

OBJECTIVES

We investigated the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetylcholinesterase (AChE), a key enzyme in cholinergic neurotransmission.

METHODS

We used SK-N-SH human-derived neuronal cells to evaluate the effect of dioxin exposure on AChE.

RESULTS

We consistently found a significant decrease in enzymatic activity of AChE in cultured neurons treated with TCDD. We also found that, unlike organophosphate pesticides that directly act on the catalytic center of AChE, the suppressive effect of dioxin was through transcriptional regulation. The addition of CH223191, an inhibitor of the aryl hydrocarbon receptor (AhR)-dependent pathway, counteracted the TCDD-induced suppression of AChE, suggesting involvement of the AhR-dependent pathway. The existence of putative dioxin-responsive element (DRE) consensus sequences in the human ACHE promoter region further supported this hypothesis. Consistent with the absence of DRE elements in mouse or rat ACHE promoter regions, suppression of AChE by TCDD did not occur in rat neuronal cells, indicating a potential species-specific effect.

CONCLUSIONS

In SK-N-SH cells, dioxin suppressed the activity of neuronal AChE via AhR-mediated transcriptional down-regulation. This is the first study to report direct interference by dioxin with the cholinergic neurotransmission system.

Glial differentiation of human adipose-derived stem cells: implications for cell-based transplantation therapy

Increasing evidence has shown that adipose-derived stem cells (ASCs) could transdifferentiate into Schwann cell (SC)-like cells to enhance nerve regeneration, suggesting potential new cell-based transplantation therapy for peripheral nerve injuries and neurodegenerative disorders. For the implementation of these results to the clinical setting, it is of great importance to establish the differentiation of human ASCs (hASCs) into a SC phenotype. In this study, we studied hASCs obtained from subcutaneous fat tissue of healthy donors. By a mixture of glial growth factors we differentiated them into Schwann cell-like cells (dhASCs). We then assessed their ability to act as Schwann cells in vitro and in vivo and also compared them with primary human Schwann cells (hSCs). Enzyme-linked immunosorbent assay showed that dhASCs secreted brain-derived neurotrophic factor (BDNF)/nerve growth factor (NGF) at a comparable level, and glial cell-derived neurotrophic factor (GDNF) at a level even higher than hSCs, whereas undifferentiated hASCs (uhASCs) secreted low levels of these neurotrophic factors. In co-culture with NG108-15 neuronal cells we found that both dhASCs and hSCs significantly increased the percentage of cells with neurites, the neurite length, and the number of neurites per neuron, whereas uhASCs increased only the percentage of cells with neurites. Finally, we transplanted green fluorescent protein (GFP)-labeled hASCs into the crushed tibial nerve of athymic nude rats. The transplanted hASCs showed a close association with PGP9.5-positive axons and myelin basic protein (MBP)-positive myelin at 8weeks after transplantation. Quantitative analysis revealed that dhASCs transplantation resulted in significantly improved survival and myelin formation rates (a 7-fold and a 10-fold increase, respectively) as compared with uhASCs transplantation. These findings suggest that hASCs took part in supporting and myelinating regenerating axons, and thus have achieved full glial differentiation in vivo. In conclusion, hASCs can differentiate into SC-like cells that possess a potent capacity to secrete neurotrophic factors as well as to form myelin in vivo. These findings make hASCs an interesting prospect for cell-based transplantation therapy for various peripheral nerve disorders.

Electrophysiological characterization of sodium-activated potassium channels in NG108-15 and NSC-34 motor neuron-like cells

AIMS

The electrical properties of Na(+) -activated K(+) current (I(K(Na)) ) and its contribution to spike firing has not been characterized in motor neurons.

METHODS

We evaluated how activation of voltage-gated K(+) current (I(K) ) at the cellular level could be coupled to Na(+) influx through voltage-gated Na(+) current (I(N) (a) ) in two motor neuron-like cells (NG108-15 and NSC-34 cells).

RESULTS

Increasing stimulation frequency altered the amplitudes of both I(Na) and I(K) simultaneously. With changes in stimulation frequency, the kinetics of both I(Na) inactivation and I(K) activation were well correlated at the same cell. Addition of tetrodotoxin or ranolazine reduced the amplitudes of both I(Na) and I(K) simultaneously. Tefluthrin (Tef) increased the amplitudes of both I(Na) and I(K) throughout the voltages ranging from -30 to + 10 mV. In cell-attached recordings, single-channel conductance from a linear current-voltage relation was 94 ± 3 pS (n = 7). Tef (10 μm) enhanced channel activity with no change in single-channel conductance. Tef increased spike firing accompanied by enhanced facilitation of spike-frequency adaptation. Riluzole (10 μm) reversed Tef-stimulated activity of K(Na) channels. In motor neuron-like NSC-34 cells, increasing stimulation frequency altered the kinetics of both I(Na) and I(K) . Modelling studies of motor neurons were simulated to demonstrate that the magnitude of I(K(Na)) modulates AP firing.

CONCLUSIONS

There is a direct association of Na(+) and K(Na) channels which can provide the rapid activation of K(Na) channels required to regulate AP firing occurring in motor neurons.

Model for studying Clostridium botulinum neurotoxin using differentiated motor neuron-like NG108-15 cells

Cancerous cell lines have traditionally shown low sensitivity to laboratory or pharmaceutical preparations of botulinum neurotoxin. The work presented here demonstrates that the mouse neuroblastoma/rat glioma hybrid cell line NG108-15 is capable of more sensitively detecting BoNT/A1 than any cell line previously described. This cell line has previously been described to have motor neuron like characteristics, therefore making it a good model to study BoNTs. Differentiation of NG108-15 cells in serum-free medium containing retinoic acid and purmorphamine dramatically increased sensitivity of the neurons to BoNT/A (EC(50) = ~16 LD(50) U). Additional pre-treatment with triasialoganglioside GT1B prior to toxin exposure reduced the EC(50) further to ~11 LD(50) U. Co-culture of the neurons with C2C12 myotubes also significantly increased BoNT/A sensitivity of NG108-15 cells (EC(50) = 26 U) in the absence of differentiation factors.

Trans-acting factors governing acetylcholinesterase mRNA metabolism in neurons

The most characterized function of acetylcholinesterase (AChE) is to terminate cholinergic signaling at neuron-neuron and neuro-muscular synapses. In addition, AChE is causally or casually implicated in neuronal development, stress-response, cognition, and neurodegenerative diseases. Given the importance of AChE, many studies have focused on identifying the molecular mechanisms that govern its expression. Despite these efforts, post-transcriptional control of AChE mRNA expression is still relatively unclear. Here, we review the trans-acting factors and cis-acting elements that are known to control AChE pre-mRNA splicing, mature mRNA stability and translation. Moreover, since the Hu/ELAV family of RNA-binding proteins (RBPs) have emerged in recent years as “master” post-transcriptional regulators, we discuss the possibility that predominantly neuronal ELAVs (nELAVs) play multiple roles in regulating splicing, stability, localization, and translation of AChE mRNA.

Counter-regulation of cholinesterases: differential activation of PKC and ERK signaling in retinal cells through BChE knockdown

The ubiquitous cholinesterase (ChE) enzymes, functioning in the termination of acetylcholine mediated neural transmission, are also reported to have additional functions. Through application of siRNAs against butyrylcholinesterase (BChE) in R28 cells, a retinal cell line with pluripotent properties, a counter-regulation between ChEs was revealed. BChE knock down resulted in an up-regulation of not only acetylcholinesterase (AChE), but also altered the signaling status of PKC and ERK. Knockdown of BChE modified ERK signaling most notably through ERK1/2 proteins, together with the transcription activator P90RSK1 and c-fos. Stimulation of the R28 cell line by forskolin revealed that ChEs are involved in an intricate cross talk between different signaling pathways. Forskolin-stimulated R28 cells displayed a robust cholinergic response, as detected by both electrophysiology and ChE expression, and changed the activation status of PKC/ERK signaling pathways. The findings in R28 cells show that ChE expressions are inversely co-regulated and act through the transcription factors c-fos and P90RSK1. Since R28 cells have the capacity to differentiate into different cell types through stimulation of signaling pathways, ChEs are likely to be associated with cell fate determination, rather than just terminating cholinergic responses.

Expression and Localization of PRiMA-linked globular form acetylcholinesterase in vertebrate neuromuscular junctions

Acetylcholinesterase (AChE) is well known to process different molecular forms via the distinct interacting partners. Proline-rich membrane anchor (PRiMA)-linked tetrameric globular AChE (G4 AChE) is mainly found in the vertebrate brain; however, recent studies from our laboratory have suggested its existence at neuromuscular junctions (nmjs). Both muscle and motor neuron express AChE at the nmjs. In muscle, the expression of PRiMA-linked AChE is down-regulated during myogenic differentiation and by motor neuron innervation. As compared with muscle, spinal cord possessed higher total AChE activity and contained PRiMA-linked AChE forms. The spinal cord expression of this form increased during development. More importantly, PRiMA-linked G4 AChE identified as aggregates localized at nmjs. These findings suggest that the restricted localization of PRiMA-linked G4 AChE at the nmjs could be contributed by the pre-synaptic motor neuron and/or the post-synaptic muscle fiber.

Restricted localization of proline-rich membrane anchor (PRiMA) of globular form acetylcholinesterase at the neuromuscular junctions--contribution and expression from motor neurons

The expression and localization of the proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form acetylcholinesterase (G(4) AChE), were studied at vertebrate neuromuscular junctions. Both muscle and motor neuron contributed to this synaptic expression pattern. During the development of rat muscles, the expression of PRiMA and AChE(T) and the enzymatic activity increased dramatically; however, the proportion of G(4) AChE decreased. G(4) AChE in muscle was recognized specifically by a PRiMA antibody, indicating the association of this enzyme with PRiMA. Using western blot and ELISA, both PRiMA protein and PRiMA-linked G(4) AChE were found to be present in large amounts in fast-twitch muscle (e.g. tibialis), but in relatively low abundance in slow-twitch muscle (e.g. soleus). These results indicate that the expression level of PRiMA-linked G(4) AChE depends on muscle fiber type. In parallel, the expression of PRiMA, AChE(T) and G(4) AChE also increased in the spinal cord during development. Such expression in motor neurons contributed to the synaptic localization of G(4) AChE. After denervation, the expression of PRiMA, AChE(T) and G(4) AChE decreased markedly in the spinal cord, and in fast- and slow-twitch muscles.

Transcriptional regulation of proline-rich membrane anchor (PRiMA) of globular form acetylcholinesterase in neuron: an inductive effect of neuron differentiation

The transcriptional regulation of proline-rich membrane anchor (PRiMA), an anchoring protein of tetrameric globular form of acetylcholinesterase (G(4) AChE), was revealed in cultured cortical neurons during differentiation. The level of AChE(T) protein, total enzymatic activity and the amount of G(4) AChE were dramatically increased during the neuron differentiation. RT-PCR analyses revealed that the transcript encoding PRiMA was significantly up-regulated in the differentiated neurons. To investigate the transcriptional mechanism on PRiMA regulation, a reporter construct of human PRiMA promoter-tagged luciferase was employed in this study. Upon the neuronal differentiation in cortical neurons, a mitogen-activated protein (MAP) kinase-dependent pathway was stimulated: this signaling cascade was shown to regulate the transcriptional activity of PRiMA. In addition, both PRiMA and AChE(T) transcripts were induced by the over expression of an active mutant of Raf in the cultured neurons. The treatment of a MAP kinase inhibitor (U0126) significantly blocked the expression of PRiMA transcript and promoter-driven luciferase activity as induced by the differentiation of cortical neurons. These results suggested that a MAP kinase signaling pathway served as one of the transcriptional regulators in controlling PRiMA gene expression during the neuronal differentiation process.

Effect of embryonic fibroblast cell co-culture on development of mouse embryos following exposure to visible light

PURPOSE

To determine the effects of visible light on development of mouse embryos and the potential of fibroblast cells to overcome deleterious effects of visible light on mouse preimplantation stage embryos.

METHODS

Two-cell mouse embryos were randomly allocated to un-exposed group (control) and exposed group receiving 1600 lx visible light for various time lengths. Both exposed and un-exposed embryos were co-cultured with either Mouse Embryonic Fibroblast (MEF) or Human Embryonic Fibroblast (HEF). Developmental rate of embryos at day 3 (morula), 4 (expanded blastocyst) and 5 (hatching or hatched blastocyst) was evaluated.

RESULTS

Exposure of embryos to visible light for 30 min decreased developmental rate significantly (P<0.01). Developmental rate of exposed embryos co-cultured with MEF (58%; p<0.05 both at day 4 and 5) and HEF (67%; P<0.01 both at day 4 and 5) was higher than control.

CONCLUSIONS

Visible light adversely affects embryo development in a time-dependent manner. Feeder cells may enhance embryo development particularly when suboptimal conditions are involved.

Regulation of PRiMA-linked G(4) AChE by a cAMP-dependent signaling pathway in cultured rat pheochromocyoma PC12 cells

The catalytic subunit of acetylcholinesterase (AChE(T)) interacts with proline-rich membrane anchor (PRiMA) to form PRiMA-linked G(4) AChE on membrane surface for its cholinergic function. Cultured PC12 cells expressed the transcripts encoding AChE(T) and PRiMA I, but the expression of PRiMA II transcript was below detection. Upon the treatment of dibutyryl-cAMP (Bt(2)-cAMP) and forskolin in cultured cells to stimulate the cAMP-dependent signaling pathway, the mRNA expressions of both AChE(T) and PRiMA I, as well as the enzymatic activity were up-regulated. More importantly, sucrose density gradient analysis revealed that both G(1) and G(4) AChE isoforms were increased in the Bt(2)-cAMP-treated cultures. These results suggest that the regulation of PRiMA-linked G(4) AChE in terms of gene transcription and molecular assembly in the cultured PC12 cells could be mediated by a cAMP-dependent signaling mechanism.

Calcitonin gene-related peptide induces the expression of acetylcholinesterase-associated collagen ColQ in muscle: a distinction in driving two different promoters between fast- and slow-twitch muscle fibers

The presence of a collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase at vertebrate neuromuscular junctions (nmjs). Two ColQ transcripts as ColQ-1 and ColQ-1a, driven by two promoters: pColQ-1 and pColQ-1a, were found in mammalian slow- and fast-twitch muscles, respectively, which have distinct expression pattern in different muscle fibers. In this study, we show the differential expression of CoQ in different muscles is triggered by calcitonin gene-related peptide (CGRP), a known motor neuron-derived factor. Application of CGRP, or dibutyryl-cAMP (Bt(2)-cAMP), in cultured myotubes induced the expression of ColQ-1a transcript and promoter activity; however, the expression of ColQ-1 transcript did not respond to CGRP or Bt(2)-cAMP. The CGRP-induced gene activation was blocked by an adenylyl cyclase inhibitor or a dominant negative mutant of cAMP-responsive element (CRE) binding protein (CREB). Two CRE sites were mapped within the ColQ-1a promoter, and mutations of the CRE sites abolished the response of CGRP or Bt(2)-cAMP. In parallel, CGRP receptor complex was dominantly expressed at the nmjs of fast muscle but not of slow muscle. These results suggested that the expression of ColQ-1a at the nmjs of fast-twitch muscle was governed by a CGRP-mediated cAMP signaling mechanism.

Adipose-derived stem cells differentiate into a Schwann cell phenotype and promote neurite outgrowth in vitro

Experimentally, peripheral nerve repair can be enhanced by Schwann cell transplantation but the clinical application is limited by donor site morbidity and the inability to generate a sufficient number of cells quickly. We have investigated whether adult stem cells, isolated from adipose tissue, can be differentiated into functional Schwann cells. Rat visceral fat was enzymatically digested to yield rapidly proliferating fibroblast-like cells, a proportion of which expressed the mesenchymal stem cell marker, stro-1, and nestin, a neural progenitor protein. Cells treated with a mixture of glial growth factors (GGF-2, bFGF, PDGF and forskolin) adopted a spindle-like morphology similar to Schwann cells. Immunocytochemical staining and western blotting indicated that the treated cells expressed the glial markers, GFAP, S100 and p75, indicative of differentiation. When co-cultured with NG108-15 motor neuron-like cells, the differentiated stem cells enhanced the number of NG108-15 cells expressing neurites, the number of neurites per cell and the mean length of the longest neurite extended. Schwann cells evoked a similar response whilst undifferentiated stem cells had no effect. These results indicate adipose tissue contains a pool of regenerative stem cells which can be differentiated to a Schwann cell phenotype and may be of benefit for treatment of peripheral nerve injuries.

Sustained CGRP1 receptor stimulation modulates development of EC coupling by cAMP/PKA signalling pathway in mouse skeletal myotubes

We investigated modulation of excitation-contraction (EC) coupling by calcitonin gene-related peptide (CGRP), which is released by motorneurons during neuromuscular transmission. Mouse skeletal myotubes were cultured either under control conditions or in the presence of 100 nm CGRP ( approximately 4-72 h). T- and L-type Ca(2+) currents, immobilization resistant charge movement, and intracellular Ca(2+) transients were characterized in whole-cell patch-clamp experiments. CGRP treatment increased the amplitude of voltage-gated Ca(2+) release ((DeltaF/F)(max)) approximately 75-350% and moderately increased both maximal L-current conductance (G(max)) and charge movement (Q(max)). In contrast, CGRP treatment did not affect their corresponding voltage dependence of activation (V(1/2) and k) or T-current density. CGRP treatment enhanced voltage-gated Ca(2+) release in approximately 4 h, whereas the effect on L-channel magnitude took longer to develop ( approximately 24 h), suggesting that short-term potentiation of EC coupling may lead to subsequent long-term up-regulation of DHPR expression. CGRP treatment also drastically increased caffeine-induced Ca(2+) release in approximately 4 h ( approximately 400%). Thus, short-term potentiation of EC coupling is due to an increase in sarcoplasmic reticulum Ca(2+) content. Both application of a phosphodiesterase inhibitor (papaverine) and a membrane-permeant cAMP analogue (Db-cAMP) produced a similar potentiation of EC coupling. Conversely, this potentiation was prevented by pretreatment with either CGRP1 receptor antagonist (CGRP(8-37)) or a PKA inhibitor (H-89). Thus, CGRP acts through CGRP1 receptors and the cAMP/PKA signalling pathway to enhance voltage-gated Ca(2+) release. Effects of CGRP on both EC coupling and L-channels were attenuated at later times during myotube differentiation. Therefore, we conclude that CGRP accelerates maturation of EC coupling.

Transcriptional control of different acetylcholinesterase subunits in formation and maintenance of vertebrate neuromuscular junctions

Acetylcholinesterase (AChE; EC 3.1.1.7) is a highly polymorphic enzyme (Massoulié, 2002). Asingle ACHE gene produces several types of catalytic subunits by alternative splicing, but a single splice variant, called type T (AChET), is expressed in adult mammalian muscle and brain. Catalytic subunits of AChET produce amphiphilic monomers and dimers, nonamphiphilic homotetramers, as well as heteromeric associations with anchoring proteins, ColQ (collagenous subunit) and PRiMA (proline-rich membrane anchor), which allow their functional localization in cholinergic synapses (Massoulié, 2002). ColQ characterizes the collagen-tailed forms (Aforms) of AChE and butyrylcholinesterase (BChE), which are localized in the basal lamina at neuromuscular junctions (NMJs) of vertebrates (Krejci et al., 1999); in these molecules (A4, A8, A12), one, two, or three tetramers of catalytic subunits are disulfide-linked to the strands of a triple helix of ColQ collagen. The cDNAs encoding ColQ, which have two transcripts, have been cloned: ColQ-1a predominantly in fast-twitch muscle, and ColQ-1 predominantly in slow-twitch muscle. The tetrameric globular (G4) form of AChE is characterized by linkage to PRiMA. PRiMAcDNA encodes a single-pass approximately 20-kDa type-I transmembrane protein and, similar to that of ColQ, contains a short PRAD (proline-rich attachment domain) that is able to organize AChE catalytic subunits into tetramers and anchor the enzyme at the surface of neuron and muscle (Massoulié, 2002).

The RNA-binding protein HuD binds acetylcholinesterase mRNA in neurons and regulates its expression after axotomy

After axotomy, expression of acetylcholinesterase (AChE) is greatly reduced in the superior cervical ganglion (SCG); however, the molecular events involved in this response remain unknown. Here, we first examined AChE mRNA levels in the brain of transgenic mice that overexpress human HuD. Both in situ hybridization and reverse transcription-PCR demonstrated that AChE transcript levels were increased by more than twofold in the hippocampus of HuD transgenic mice. Additionally, direct interaction between the HuD transgene product and AChE mRNA was observed. Next, we examined the role of HuD in regulating AChE expression in intact and axotomized rat SCG neurons. After axotomy of the adult rat SCG neurons, AChE transcript levels decreased by 50 and 85% by the first and fourth day, respectively. In vitro mRNA decay assays indicated that the decrease in AChE mRNA levels resulted from changes in the stability of presynthesized transcripts. A combination of approaches performed using the region that directly encompasses an adenylate and uridylate (AU)-rich element within the AChE 3'-untranslated region demonstrated a decrease in RNA-protein complexes in response to axotomy of the SCG and, specifically, a decrease in HuD binding. After axotomy, HuD transcript and protein levels also decreased. Using a herpes simplex virus construct containing the human HuD sequence to infect SCG neurons in vivo, we found that AChE and GAP-43 mRNA levels were maintained in the SCG after axotomy. Together, the results of this study demonstrate that AChE expression in neurons of the rat SCG is regulated via post-transcriptional mechanisms that involve the AU-rich element and HuD.

Forskolin, an inducer of cAMP, up-regulates acetylcholinesterase expression and protects against organophosphate exposure in neuro 2A cells

Bioscavenger prophylactic therapy using purified human acetylcholinesterase (AChE) or butylcholinesterase (BChE) is a promising treatment for future protection against chemical warfare nerve agent exposure. Potential immune response due to the complex structure of cholinesterases, mutations, post-translational modifications, and genetic variation is a limiting factor against purified enzyme therapy. We investigated an alternative bioscavenger approach using forskolin, an inducer of intracellular cyclic AMP (cAMP), which activates AChE promoter and up-regulates its expression. A mouse neuronal cell line, Neuro 2A, was treated with various doses of forskolin and analysis of the expressed enzyme indicates that the AChE activity was significantly increased in cells exposed to repeated administration of the drug every other day for 7-10 days. Cholinesterase enzyme assays showed that the enzyme activity was increased approximately 2-fold for the extracellular enzyme and 3-fold for the intracellular enzyme. The optimal dose found for extracellular enzyme production was 12-24 microM forskolin, while the optimal dose for intracellular was 12 microM. In parallel with the rise in the AChE level, the morphology of forskolin-treated cells showed neurite growth with increasing doses. Forskolin treatment protects Neuro 2A cells from diisopropylflurophophate (DFP), a surrogate of the organophosphate chemical warfare agents soman and sarin, induced toxicity in Neuro 2A cells. These results indicate that transcriptional inducers, such as forskolin, can sufficiently up-regulate cellular AChE production and protect cells against organophosphate toxicity.

PKCdelta-mediated regulation of FLIP expression in human colon cancer cells

FLICE-like inhibitory protein (FLIP), a naturally occurring caspase-inhibitory protein that lacks the critical cysteine domain necessary for catalytic activity, is a negative regulator of Fas-induced apoptosis. Decreased FLIP levels sensitize tumor cells to Fas- and TRAIL-mediated apoptosis; however, the cellular mechanisms regulating FLIP expression have not been defined. Here, we examined the roles of the PKC and NF-kappaB pathway in the regulation of FLIP in human colon cancers. FLIP mRNA levels were increased in Caco-2 cells by treatment with PMA; actinomycin D completely inhibited the induction of FLIP by PMA, indicating transcriptional regulation. PKC inhibitors Gö6983 and Ro-31-8220 blocked PMA-stimulated FLIP expression. Pretreatment with the PKCdelta-selective inhibitor rottlerin or transfection with PKCdelta siRNA inhibited PMA-induced FLIP expression, which identifies a role for PKCdelta in FLIP induction. Treatment with the proteasome inhibitor, MG132, or the NF-kappaB inhibitor (e.g., PDTC and gliotoxin), or overexpression of the superrepressor of IkappaB-alpha inhibited PMA-induced upregulation of FLIP. Moreover, PMA-induced NF-kappaB transactivation was blocked by GF109203x. In conclusion, our results demonstrate a critical role for PKCdelta/NF-kappaB in the regulation of FLIP in human colon cancer cells.

Transcriptional regulation of acetylcholinesterase-associated collagen ColQ in fast- and slow-twitch muscle fibers

The presence of a collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase (AChE) and butyrylcholinesterase at vertebrate neuromuscular junctions, which is tethered in the synaptic basal lamina. ColQ subunits, differing mostly by their signal sequences, are encoded by transcripts ColQ-1 and ColQ-1a, which are differentially expressed in slow- and fast-twitch muscles in mammals, respectively. Both ColQ transcripts are derived from a single COLQ gene. Transcripts encoding ColQ increased during myogenic differentiation of C2C12 cells; the increase was in parallel with AChE catalytic subunit. Quantitative PCR analysis indicated that the increase during the myotube formation was due to the up regulation of ColQ-1 transcript instead of ColQ-1a. In order to reveal the regulatory mechanism of ColQ transcripts, two distinct promoters, pColQ-1 and pColQ-1a, were isolated from human COLQ gene. The ColQ promoters showed a muscle fiber type-specific expression pattern, and which was in line with the expression of endogenous transcript. After in vivo DNA transfection, pColQ-1 showed strong activity in slow-twitch muscle (e.g. soleus), while pColQ-1a was preferably expressed in fast-twitch muscle (e.g. tibialis). Mutation analysis of the ColQ promoters suggested that the muscle fiber type-specific expression pattern of ColQ transcripts was regulated by a slow upsteam regulatory element (SURE) and a fast intronic regulatory element (FIRE). These results explain the specific expression patterns of collagen-tailed AChE in slow and fast muscle fibers.

Lead-induced attenuation in the aggregation of acetylcholine receptors during the neuromuscular junction formation

Lead (Pb2+) toxicity is more common in children and is associated with cognitive deficits, which may reflect lead-induced changes in central synaptic development and function. Aside from neurotoxicity, lead exposure may also impact mature neuromuscular junction (NMJ) and cause muscle weakness. NMJ is known as a peripheral cholinergic synapse and its signaling cascades responsible for development are similar to those for the central synapses. However, the effect of lead exposure on the formation of NMJ in mammals is unclear. In the present study, a NG108-15/C2C12 coculture model was used to measure the acetylcholine receptor (AChR) aggregates formed on the myotubes which was an early hallmark for the NMJ formation. AChR aggregates were identified by alpha-bungarotoxin under fluorescent microscope. Single dose of lead acetate with final concentrations at 10(-3), 10(-1), or 10 microM was applied to dishes at the beginning of coculturing. Following 3-day exposure, although NG108-15 cells could extend long neurites to nearby myotubes, obvious dose-dependent attenuation in AChR aggregation was shown. The averaged area of an AChR aggregate, the averaged number of AChR aggregates per myotube, and the total area of AChR aggregates per myotube were all significantly decreased. In addition, the distribution percentages of various sizes of AChR aggregates showed that almost half of the AChR aggregates were formed with a size of 2-5 microm2 regardless of lead exposure. After treating 10 microM of lead acetate, significantly more AChR aggregates ranged from 2 to 20 microm2 were formed and significantly less AChR aggregates larger than 20 microm2 were formed. These results indicated that lead exposure reduced the extent of AChR aggregation concerning both the size and number of AChR aggregates and large AChR aggregates could hardly be formed after acute high-level lead exposure. No significant change was found in the total amount of AChRs on the myotubes after lead exposure, which indicated that the attenuation of AChR aggregation was not caused by reducing the synthesis of AChRs but by remaining dispersed pattern of AChRs on the myotubes. These data suggest that lead exposure exerts detrimental effects on the formation of NMJ.

Expression and distribution of acetylcholinesterase among the cellular components of the neuromuscular junction formed in human myotube in vitro

The results of our recent investigations on the expression and distribution of acetylcholinesterase (EC. 3.1.1.7, AChE) in the experimental model of the in vitro innervated human muscle are summarized and discussed here. This is the only model allowing studies on AChE expression at all stages of the neuromuscular junction (NMJ) formation in the human muscle. Since it consists not only of the motor neurons and myotubes but also of glial cells, which are essential for the normal development of the motor neurons, NMJs become functional and differentiated in this system. We followed AChE expression at various stages of the NMJ formation and in the context of other events characteristic for this process. Neuronal and muscular part were analysed at both, mRNA and mature enzyme level. AChE is expressed in motor neurons and skeletal muscle at the earliest stages of their development, long before NMJ starts to form and AChE begins to act as a cholinergic component. Temporal pattern of AChE mRNA expression in motor neurons is similar to the pattern of mRNA encoding synaptogenetic variant of agrin. There are no AChE accummulations at the NMJ at the early stage of its formation, when immature clusters of nicotinic receptors are formed at the neuromuscular contacts and when occasional NMJ-mediated contractions are already observed. The transformation from immature, bouton-like neuromuscular contacts into differentiated NMJs with mature, compact receptor clusters, myonuclear accumulations and dense AChE patches begins at the time when basal lamina starts to form in the synaptic cleft. Our observations support the concept that basal lamina formation is the essential event in the transformation of immature neuromuscular contact into differentiated NMJ, with the accumulation of not only muscular but also neuronal AChE in the synaptic cleft.

Origin of acetylcholinesterase in the neuromuscular junction formed in the in vitro innervated human muscle

Synaptic basal lamina is interposed between the pre- and postsynaptic membrane of the neuromuscular junction (NMJ). This position permits deposition of basal lamina-bound NMJ components of both neuronal and muscle fibre origin. One such molecule is acetylcholinesterase (AChE). The origin of NMJ AChE has been investigated previously as the answer would elucidate the relative contributions of muscle fibers and motor neurons to NMJ formation. However, in the experimental models used in prior investigations either the neuronal or muscular components of the NMJs were removed, or the NMJs were poorly differentiated. Therefore, the question of AChE origin in the intact and functional NMJ remains open. Here, we have approached this question using an in vitro model in which motor neurons, growing from embryonic rat spinal cord explants, form well differentiated NMJs with cultured human myotubes. By immunocytochemical staining with species-specific anti-AChE antibodies, we are able to differentiate between human (muscular) and rat (neuronal) AChE at the NMJ. We observed strong signal at the NMJ after staining with human AChE antibodies, which suggests a significant muscular AChE contribution. However, a weaker, but still clearly recognizable signal is observed after staining with rat AChE antibodies, suggesting a smaller fraction of AChE was derived from motor neurons. This is the first report demonstrating that both motor neuron and myotube contribute synaptic AChE under conditions where they interact with each other in the formation of an intact and functional NMJ.

Transcriptional regulation of acetylcholinesterase-associated collagen ColQ: differential expression in fast and slow twitch muscle fibers is driven by distinct promoters

The presence of a collagenous protein (ColQ) characterizes the collagen-tailed forms of acetylcholinesterase and butyrylcholinesterase at vertebrate neuromuscular junctions which is tethered in the synaptic basal lamina. ColQ subunits, differing mostly by their signal sequences, are encoded by transcripts ColQ-1 and ColQ-1a, which are differentially expressed in slow and fast twitch muscles in mammals. Two distinct promoters, pColQ-1 and pColQ-1a, were isolated from the upstream sequences of human COLQ gene; they showed muscle-specific expression and were activated by myogenic transcriptional elements in cultured myotubes. After in vivo DNA transfection, pColQ-1 showed strong activity in slow twitch muscle (e.g. soleus), whereas pColQ-1a was preferably expressed in fast twitch muscle (e.g. tibialis). Mutation analysis of the ColQ promoters suggested that the muscle fiber type-specific expression pattern of ColQ transcripts were regulated by a slow upsteam regulatory element (SURE) and a fast intronic regulatory element (FIRE). These regulatory elements were responsive to a calcium ionophore and to calcineurin inhibition by cyclosporine A. The slow fiber type-specific expression of ColQ-1 was abolished by the mutation of an NFAT element in pColQ-1. Moreover, both the ColQ promoters contained N-box element that was responsible for the synapse-specific expression of ColQ transcripts. These results explain the specific expression patterns of collagen-tailed acetylcholinesterase in slow and fast muscle fibers.