Choline acetyltransferase activities in single spinal motor neurons from patients with amyotrophic lateral sclerosis

Neurotransmitter systems in the etiology of major neurological disorders: Emerging insights and therapeutic implications

Neurotransmitters serve as chemical messengers playing a crucial role in information processing throughout the nervous system, and are essential for healthy physiological and behavioural functions in the body. Neurotransmitter systems are classified as cholinergic, glutamatergic, GABAergic, dopaminergic, serotonergic, histaminergic, or aminergic systems, depending on the type of neurotransmitter secreted by the neuron, allowing effector organs to carry out specific functions by sending nerve impulses. Dysregulation of a neurotransmitter system is typically linked to a specific neurological disorder. However, more recent research points to a distinct pathogenic role for each neurotransmitter system in more than one neurological disorder of the central nervous system. In this context, the review provides recently updated information on each neurotransmitter system, including the pathways involved in their biochemical synthesis and regulation, their physiological functions, pathogenic roles in diseases, current diagnostics, new therapeutic targets, and the currently used drugs for associated neurological disorders. Finally, a brief overview of the recent developments in neurotransmitter-based therapeutics for selected neurological disorders is offered, followed by future perspectives in that area of research.

Neuromuscular Junction Dysfunction in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disorder characterized by progressive degeneration of motor neurons leading to skeletal muscle denervation. Earlier studies have shown that motor neuron degeneration begins in motor cortex and descends to the neuromuscular junction (NMJ) in a dying forward fashion. However, accumulating evidences support that ALS is a distal axonopathy where early pathological changes occur at the NMJ, prior to onset of clinical symptoms and propagates towards the motor neuron cell body supporting "dying back" hypothesis. Despite several evidences, series of events triggering NMJ disassembly in ALS are still obscure. Neuromuscular junction is a specialized tripartite chemical synapse which involves a well-coordinated communication among the presynaptic motor neuron, postsynaptic skeletal muscle, and terminal Schwann cells. This review provides comprehensive insight into the role of NMJ in ALS pathogenesis. We have emphasized the molecular alterations in cellular components of NMJ leading to loss of effective neuromuscular transmission in ALS. Further, we provide a preview into research involved in exploring NMJ as potential target for designing effective therapies for ALS.

Basal Forebrain Cholinergic Neurons: Linking Down Syndrome and Alzheimer's Disease

Down syndrome (DS, trisomy 21) is characterized by intellectual impairment at birth and Alzheimer's disease (AD) pathology in middle age. As individuals with DS age, their cognitive functions decline as they develop AD pathology. The susceptibility to degeneration of a subset of neurons, known as basal forebrain cholinergic neurons (BFCNs), in DS and AD is a critical link between cognitive impairment and neurodegeneration in both disorders. BFCNs are the primary source of cholinergic innervation to the cerebral cortex and hippocampus, as well as the amygdala. They play a critical role in the processing of information related to cognitive function and are directly engaged in regulating circuits of attention and memory throughout the lifespan. Given the importance of BFCNs in attention and memory, it is not surprising that these neurons contribute to dysfunctional neuronal circuitry in DS and are vulnerable in adults with DS and AD, where their degeneration leads to memory loss and disturbance in language. BFCNs are thus a relevant cell target for therapeutics for both DS and AD but, despite some success, efforts in this area have waned. There are gaps in our knowledge of BFCN vulnerability that preclude our ability to effectively design interventions. Here, we review the role of BFCN function and degeneration in AD and DS and identify under-studied aspects of BFCN biology. The current gaps in BFCN relevant imaging studies, therapeutics, and human models limit our insight into the mechanistic vulnerability of BFCNs in individuals with DS and AD.

Neuroprotective Effect of Vascular Endothelial Growth Factor on Motoneurons of the Oculomotor System

Vascular endothelial growth factor (VEGF) was initially characterized as a potent angiogenic factor based on its activity on the vascular system. However, it is now well established that VEGF also plays a crucial role as a neuroprotective factor in the nervous system. A deficit of VEGF has been related to motoneuronal degeneration, such as that occurring in amyotrophic lateral sclerosis (ALS). Strikingly, motoneurons of the oculomotor system show lesser vulnerability to neurodegeneration in ALS compared to other motoneurons. These motoneurons presented higher amounts of VEGF and its receptor Flk-1 than other brainstem pools. That higher VEGF level could be due to an enhanced retrograde input from their target muscles, but it can also be produced by the motoneurons themselves and act in an autocrine way. By contrast, VEGF’s paracrine supply from the vicinity cells, such as glial cells, seems to represent a minor source of VEGF for brainstem motoneurons. In addition, ocular motoneurons experiment an increase in VEGF and Flk-1 level in response to axotomy, not observed in facial or hypoglossal motoneurons. Therefore, in this review, we summarize the differences in VEGF availability that could contribute to the higher resistance of extraocular motoneurons to injury and neurodegenerative diseases.

Progress in progestin-based therapies for neurological disorders

Hormone therapy, primarily progesterone and progestins, for central nervous system (CNS) disorders represents an emerging field of regenerative medicine. Following a failed clinical trial of progesterone for traumatic brain injury treatment, attention has shifted to the progestin Nestorone for its ability to potently and selectively transactivate progesterone receptors at relatively low doses, resulting in robust neurogenetic, remyelinating, and anti-inflammatory effects. That CNS disorders, including multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), spinal cord injury (SCI), and stroke, develop via demyelinating, cell death, and/or inflammatory pathological pathways advances Nestorone as an auspicious candidate for these disorders. Here, we assess the scientific and clinical progress over decades of research into progesterone, progestins, and Nestorone as neuroprotective agents in MS, ALS, SCI, and stroke. We also offer recommendations for optimizing timing, dosage, and route of the drug regimen, and identifying candidate patient populations, in advancing Nestorone to the clinic.

Very Early Involvement of Innate Immunity in Peripheral Nerve Degeneration in SOD1-G93A Mice

Recent preclinical and clinical evidence suggest that immune system has a role in the progression and prognosis of Amyotrophic Lateral Sclerosis (ALS), but the identification of a clear mechanism and immune players remains to be elucidated. Here, we have investigated, in 30 and 60 days (presymptomatic) and 120 days (symptomatic) old SOD1-G93A mice, systemic, peripheral, and central innate and adaptive immune and inflammatory response, correlating it with the progression of the neurodegeneration in neuromuscular junction, sciatic nerves, and spinal cord. Surprisingly, we found a very initial (45-60 days) presence of IgG in sciatic nerves together with a gradual enhancement of A20/TNFAIP3 (protein controlling NF-κB signalling) and a concomitantly significant increase and activation of circulating mast cells (MCs) as well as MCs and macrophages in sciatic nerve and an enhancement of IL-6 and IL-10. This immunological frame coincided with a myelin aggregation. The 30-60 days old SOD1-G93A mice didn't show real elements of neuroinflammation and neurodegeneration in spinal cord. In 120 days old mice macrophages and monocytes are widely diffused in sciatic nerves, peripheral neurodegeneration reaches the tip, high circulating levels of TNFα and IL-2 were found and spinal cord exhibits clear signs of neural damage and infiltrating immune cells. Our results underpin a clear immunological disorder at the origin of ALS axonopathy, in which MCs are involved in the initiation and sustaining of inflammatory events. These data cannot be considered a mere epiphenomenon of motor neuron degeneration and reveal new potential selective immune targets in ALS therapy.

Postnatal Expression Patterns of Estrogen Receptor Subtypes and Choline Acetyltransferase in Different Regions of the Papez Circuit

The Papez circuit is crucial for several brain functions, including long-term memory and emotion. Estradiol modulates cognitive functions based on the expression pattern of its receptor subtypes including estrogen receptor (ER) α, β, and G protein-coupled receptor 30 (GPR30). Similarly, the activity in the cholinergic system correlates with several brain functions, such as learning and memory. In this study, we used immunofluorescence to examine the expression patterns of ERβ and Western blotting to analyze GPR30 and choline acetyltransferase (ChAT) expression, in different regions of the Papez circuit, including the prefrontal cortex, hippocampus, hypothalamus, anterior nucleus of the thalamus, and cingulum in female rats at postnatal days (PND) 1, 10, and 56. Our main finding was that the highest expression of ERβ and GPR30 was noted in each brain area of the Papez circuit in the PND1 rats, whereas the expression of ChAT was the highest in PND10 rats. These results provide vital information on the postnatal expression patterns of ER subtypes and ChAT in different regions of the Papez circuit.

Cholinergic Stimulation of the Adult Zebrafish Brain Induces Phosphorylation of Glycogen Synthase Kinase-3 β and Extracellular Signal-Regulated Kinase in the Telencephalon

The sequencing of the zebrafish genome, the emergence of powerful gene-editing tools, and the development of in vivo imaging techniques have propelled the economical zebrafish into prominence as a biomedical research model. Neurodegenerative disorders with a cholinergic component, such as Alzheimer's and Parkinson's diseases, are currently modeled using zebrafish. Still, the utility of zebrafish as a research model will not be fully realized until their neurophysiological properties are thoroughly characterized. In mammals, the coupling of cholinergic receptors to the phosphorylation of glycogen synthase kinase-3 β (GSK3β) and extracellular signal-regulated kinase 1/2 (ERK1/2) is of critical importance to cognitive processes and imparts protection against neuropathogenic events. Similarly, it is known that cholinergic receptors are required for learning and memory in zebrafish and that in vivo activation of cholinergic receptors induces transient changes in evoked synaptic transmission in the telencephalon. However, the intracellular events mediating cholinergic processes in zebrafish have yet to be elucidated. In the current study, an ex vivo drug treatment assay was used to demonstrate that carbachol (CCh)-mediated cholinergic stimulation of the intact adult zebrafish brain induces phosphorylation of GSK3β and ERK1/2 in the zebrafish telencephalon. These findings suggest GSK3β and ERK1/2 may underly cognitive processes in zebrafish.

Cholinergic Stimulation of the Adult Zebrafish Brain Induces Phosphorylation of Glycogen Synthase Kinase-3 β and Extracellular Signal-Regulated Kinase in the Telencephalon

The sequencing of the zebrafish genome, the emergence of powerful gene-editing tools, and the development of in vivo imaging techniques have propelled the economical zebrafish into prominence as a biomedical research model. Neurodegenerative disorders with a cholinergic component, such as Alzheimer's and Parkinson's diseases, are currently modeled using zebrafish. Still, the utility of zebrafish as a research model will not be fully realized until their neurophysiological properties are thoroughly characterized. In mammals, the coupling of cholinergic receptors to the phosphorylation of glycogen synthase kinase-3 β (GSK3β) and extracellular signal-regulated kinase 1/2 (ERK1/2) is of critical importance to cognitive processes and imparts protection against neuropathogenic events. Similarly, it is known that cholinergic receptors are required for learning and memory in zebrafish and that in vivo activation of cholinergic receptors induces transient changes in evoked synaptic transmission in the telencephalon. However, the intracellular events mediating cholinergic processes in zebrafish have yet to be elucidated. In the current study, an ex vivo drug treatment assay was used to demonstrate that carbachol (CCh)-mediated cholinergic stimulation of the intact adult zebrafish brain induces phosphorylation of GSK3β and ERK1/2 in the zebrafish telencephalon. These findings suggest GSK3β and ERK1/2 may underly cognitive processes in zebrafish.

Vascular Endothelial Growth Factor (VEGF) Prevents the Downregulation of the Cholinergic Phenotype in Axotomized Motoneurons of the Adult Rat

Vascular endothelial growth factor (VEGF) was initially characterized by its activity on the vascular system. However, there is growing evidence indicating that VEGF also acts as a neuroprotective factor, and that its administration to neurons suffering from trauma or disease is able to rescue them from cell death. We questioned whether VEGF could also maintain damaged neurons in a neurotransmissive mode by evaluating the synthesis of their neurotransmitter, and whether its action would be direct or through its well-known angiogenic activity. Adult rat extraocular motoneurons were chosen as the experimental model. Lesion was performed by monocular enucleation and immediately a gelatine sponge soaked in VEGF was implanted intraorbitally. After 7 days, abducens, trochlear, and oculomotor nuclei were examined by immunohistochemistry against choline acetyltransferase (ChAT), the biosynthetic enzyme of the motoneuronal neurotransmitter acetylcholine. Lesioned motoneurons exhibited a noticeable ChAT downregulation which was prevented by VEGF administration. To explore whether this action was mediated via an increase in blood vessels or in their permeability, we performed immunohistochemistry against laminin, glucose transporter-1 and the plasmatic protein albumin. The quantification of the immunolabeling intensity against these three proteins showed no significant differences between VEGF-treated, axotomized and control animals. Therefore, the present data indicate that VEGF is able to sustain the cholinergic phenotype in damaged motoneurons, which is a first step for adequate neuromuscular neurotransmission, and that this action seems to be mediated directly on neurons since no sign of angiogenic activity was evident. These data reinforces the therapeutical potential of VEGF in motoneuronal diseases.

TRK-fused Gene Protein Localization Is Prominent in Serotonergic and Noradrenergic Cell Groups, and Some Lower Motor Neurons in the Corticospinal Tract of the Rat Brainstem

The TRK-fused gene (TFG) is reported to be involved in the regulation of cell size, apoptosis, cell growth, ER-Golgi protein secretion, NF-κβ pathway signaling, the ubiquitin-proteasome system, and pancreatic β-cell mass and function. TFG mutations were reported in some neurodegenerative diseases affecting sensory and motor functions. However, the function of TFG in the nervous system and how TFG mutations lead to neurodegeneration remain unclear. In this study, we employed double immunohistochemistry to investigate the details of TFG localization patterns in monoaminergic and cholinergic neurons in the brainstem. Intense TFG immunoreactivity was observed in the dorsal raphe nucleus, the locus coeruleus, and the ventral horn of the spinal cord. TFG immunoreactivity was observed in some serotonergic neurons in all B1–B9 cell groups, and some noradrenergic neurons in all A1–A7 cell groups in the rat brainstem, while no immunoreactivity was observed in the dopaminergic neurons in A8–A10 cell groups. TFG immunoreactivity was observed in all ChAT-positive motor nuclei in the lower corticospinal tract of the rat brainstem.

Chaperone-Mediated Regulation of Choline Acetyltransferase Protein Stability and Activity by HSC/HSP70, HSP90, and p97/VCP

Choline acetyltransferase (ChAT) synthesizes the neurotransmitter acetylcholine in cholinergic neurons, and mutations of this enzyme are linked to the neuromuscular disorder congenital myasthenic syndrome (CMS). One CMS-related mutation, V18M, reduces ChAT enzyme activity and cellular protein levels, and is located within a highly-conserved N-terminal proline-rich motif at residues ₁₄PKLPVPP₂₀. We showed previously that disruption of this proline-rich motif by either proline-to-alanine mutation (P17A/P19A) or mutation of residue Val¹⁸ (V18M) enhances ubiquitination and degradation of these mutant ChAT proteins expressed in cholinergic SN56 cells by an unknown mechanism. In this study, using proximity-dependent biotin identification (BioID), co-immunoprecipitation and in situ proximity-ligation assay (PLA), we identified the heat shock proteins (HSPs) HSC/HSP70 and HSP90 as novel ChAT protein-interactors. These molecular chaperones are well-known for promoting the folding and stabilization of cellular proteins. Thus, we found that inhibition of HSPs by treatment of cells with either the HSC/HSP70 inhibitors 2-phenylethynesulfonamide (PES) or VER-155008, or the HSP90 inhibitor 17-AAG reduced cellular ChAT activity and solubility, and enhanced the ubiquitination and proteasome-dependent loss of ChAT protein. Importantly, the effects of HSP inhibition were greater for mutant ChAT proteins (P17A/P19A-ChAT and CMS-related V18M- and A513T-ChAT) compared to wild-type ChAT. HSPs can promote ubiquitination and degradation of terminally misfolded proteins through cooperative interaction with the E3 ubiquitin ligase CHIP/Stub1, and while we show that ChAT interacts with CHIP in situ, siRNA-mediated knock-down of CHIP had no effect on either wild-type or mutant ChAT protein levels. However, inhibition of the endoplasmic reticulum (ER)- and HSP-associated co-chaperone p97/VCP prevented degradation of ubiquitinated ChAT. Together, these results identify novel mechanisms for the functional regulation of wild-type and CMS-related mutant ChAT by pro-stabilizing HSPs and the pro-degradative co-chaperone p97/VCP that may have broader implications for ChAT function during cellular stress and disease.

Neuromuscular Junction Impairment in Amyotrophic Lateral Sclerosis: Reassessing the Role of Acetylcholinesterase

Amyotrophic Lateral Sclerosis (ALS) is a highly debilitating disease caused by progressive degeneration of motorneurons (MNs). Due to the wide variety of genes and mutations identified in ALS, a highly varied etiology could ultimately converge to produce similar clinical symptoms. A major hypothesis in ALS research is the “distal axonopathy” with pathological changes occurring at the neuromuscular junction (NMJ), at very early stages of the disease, prior to MNs degeneration and onset of clinical symptoms. The NMJ is a highly specialized cholinergic synapse, allowing signaling between muscle and nerve necessary for skeletal muscle function. This nerve-muscle contact is characterized by the clustering of the collagen-tailed form of acetylcholinesterase (ColQ-AChE), together with other components of the extracellular matrix (ECM) and specific key molecules in the NMJ formation. Interestingly, in addition to their cholinergic role AChE is thought to play several “non-classical” roles that do not require catalytic function, most prominent among these is the facilitation of neurite growth, NMJ formation and survival. In all this context, abnormalities of AChE content have been found in plasma of ALS patients, in which AChE changes may reflect the neuromuscular disruption. We review these findings and particularly the evidences of changes of AChE at neuromuscular synapse in the pre-symptomatic stages of ALS.

Adult ciliary neurotrophic factor receptors help maintain facial motor neuron choline acetyltransferase expression in vivo following nerve crush

Exogenous ciliary neurotrophic factor (CNTF) administration promotes the survival of motor neurons in a wide range of models. It also increases the expression of the critical neurotransmitter enzyme choline acetyltransferase (ChAT) by in vitro motor neurons, likely independent of its effects on their survival. We have used the adult mouse facial nerve crush model and adult-onset conditional disruption of the CNTF receptor α (CNTFRα) gene to directly examine the in vivo roles played by endogenous CNTF receptors in adult motor neuron survival and ChAT maintenance, independent of developmental functions. We have previously shown that adult activation of the CreER gene construct in floxed CNTFRα mice depletes this essential receptor subunit in a large subset of motor neurons (and all skeletal muscle, as shown in this study) but has no effect on the survival of intact or lesioned motor neurons, indicating that these adult CNTF receptors play no essential survival role in this model, in contrast to their essential role during embryonic development. Here we show that this same CNTFRα depletion does not affect ChAT labeling in nonlesioned motor neurons, but it significantly increases the loss of ChAT following nerve crush. The data suggest that, although neither motor neuron nor muscle CNTF receptors play a significant, nonredundant role in the maintenance of ChAT in intact adult motor neurons, the receptors become essential for ChAT maintenance when the motor neurons are challenged by nerve crush. Therefore, the data suggest that the receptors act as a critical component of an endogenous neuroprotective mechanism. J. Comp. Neurol. 525:1206-1215, 2017. © 2016 Wiley Periodicals, Inc.

Alzheimer's disease: Targeting the Cholinergic System

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients.

Enhanced ubiquitination and proteasomal degradation of catalytically deficient human choline acetyltransferase mutants

Choline acetyltransferase (ChAT) is essential for cholinergic neuron function as it mediates synthesis of the neurotransmitter acetylcholine. ChAT mutations have been linked to the neuromuscular disorder congenital myasthenic syndrome (CMS). One CMS-related ChAT mutation, V18M, reduces enzyme activity and cellular protein levels, and is positioned within a highly conserved proline-rich motif with the sequence 14 PKLPVPP20 . We demonstrate that N-terminal truncation that includes this proline-rich motif, as well as mutation of prolines-17/19 together to alanine (P17A/P19A), dramatically reduces ChAT steady-state protein levels and cellular activity when expressed in cholinergic SN56 neural cells. The in vitro activity of bacterially expressed recombinant P17A/P19A-ChAT is also reduced, although this is not caused by changes in protein secondary structure or thermal stability. Treatment of SN56 cells with the proteasome inhibitor MG132 increases cellular P17A/P19A-ChAT steady-state protein levels, and by immunoprecipitation we found that ChAT is ubiquitinated and that polyubiquitination of P17A/P19A-ChAT is increased compared to wild-type (WT) ChAT. Using a novel fluorescent-biorthogonal pulse-chase protocol in SN56 cells, we determined that the protein half-life of P17A/P19A-ChAT (2.2 h) is substantially reduced compared to WT-ChAT (19.7 h). Lastly, we show that two CMS-related ChAT mutants (V18M and A513T) have enhanced ubiquitination, and that treatment with MG132 can partially restore both the steady-state protein levels as well as cellular activity of some CMS-mutant ChAT. These results identify a novel mechanism for regulation of ChAT through the ubiquitin-proteasome system that is influenced by the conserved N-terminal proline-rich motif of ChAT and may be implicated in CMS pathology. Choline acetyltransferase (ChAT) synthesizes acetylcholine in cholinergic neurons. In this study we find that steady-state protein levels of human 69-kDa ChAT are regulated by the ubiquitin-proteasome system. Mutation of a highly conserved N-terminal proline-rich motif in human 69-kDa ChAT reduces both cellular ChAT protein levels, through enhanced ubiquitination and proteasomal degradation, and enzyme activity. Ubiquitination of catalytically deficient congenital myasthenic syndrome (CMS)-mutant ChAT is increased in cells, and importantly proteasome inhibition partially restores steady-state protein levels as well as cellular activity of some CMS-mutant ChAT proteins.

Experimental and clinical evidence for the protective role of progesterone in motoneuron degeneration and neuroinflammation

Far beyond its role in reproduction, progesterone exerts neuro-protective, promyelinating, and anti-inflammatory effects in the nervous system. These effects are amplified under pathological conditions, implying that changes of the local environment sensitize nervous tissues to steroid therapy. The present survey covers our results of progesterone neuroprotection in a motoneuron neurodegeneration model and a neuroinflammation model. In the degenerating spinal cord of the Wobbler mouse, progesterone reverses the impaired expression of neurotrophins, increases enzymes of neurotransmission and metabolism, prevents oxidative damage of motoneurons and their vacuolar degeneration (paraptosis), and attenuates the development of mitochondrial abnormalities. After long-term treatment, progesterone also increases muscle strength and the survival of Wobbler mice. Subsequently, this review describes the effects of progesterone in mice with induced experimental autoimmune encephalomyelitis (EAE), a commonly used model of multiple sclerosis. In EAE mice, progesterone attenuates the clinical severity, decreases demyelination and neuronal dysfunction, increases axonal counts, reduces the formation of amyloid precursor protein profiles, and decreases the aberrant expression of growth-associated proteins. These actions of progesterone may be due to multiple mechanisms, considering that classic nuclear receptors, extranuclear receptors, and membrane receptors are all expressed in the spinal cord. Although many aspects of progesterone action in humans remain unsolved, data provided by experimental models makes getting to this objective closer than previously expected.

Early presymptomatic cholinergic dysfunction in a murine model of amyotrophic lateral sclerosis

Sporadic and familiar amyotrophic lateral sclerosis (ALS) cases presented lower cholinergic activity than in healthy individuals in their still preserved spinal motoneurons (MNs) suggesting that cholinergic reduction might occur before MN death. To unravel how and when cholinergic function is compromised, we have analyzed the spatiotemporal expression of choline acetyltransferase (ChAT) from early presymptomatic stages of the SOD1(G93A) ALS mouse model by confocal immunohistochemistry. The analysis showed an early reduction in ChAT content in soma and presynaptic boutons apposed onto MNs (to 76%) as well as in cholinergic interneurons in the lumbar spinal cord of the 30-day-old SOD1(G93A) mice. Cholinergic synaptic stripping occurred simultaneously to the presence of abundant surrounding major histocompatibility complex II (MHC-II)-positive microglia and the accumulation of nuclear Tdp-43 and the appearance of mild oxidative stress within MNs. Besides, there was a loss of neuronal MHC-I expression, which is necessary for balanced synaptic stripping after axotomy. These events occurred before the selective raise of markers of denervation such as ATF3. By the same time, alterations in postsynaptic cholinergic-related structures were also revealed with a loss of the presence of sigma-1 receptor, a Ca2+ buffering chaperone in the postsynaptic cisternae. By 2 months of age, ChAT seemed to accumulate in the soma of MNs, and thus efferences toward Renshaw interneurons were drastically diminished. In conclusion, cholinergic dysfunction in the local circuitry of the spinal cord may be one of the earliest events in ALS etiopathogenesis.

Regulation of choline acetyltransferase expression by 17 β-oestradiol in NSC-34 cells and in the spinal cord

Motoneurones located in the ventral horn of the spinal cord conciliate cholinergic innervation of skeletal muscles. These neurones appear to be exceedingly affected in neurodegenerative diseases such as amyotrophic lateral sclerosis. The dysfunction of motoneurones is typically accompanied by alterations of cholinergic metabolism and signalling, as demonstrated by a decrease in choline acetyltransferase (ChAT) expression. 17 β-Oestradiol (E(2)) is generally accepted as neuroprotective factor in the brain under acute toxic and neurodegenerative conditions and also appears to exert a protective role for motoneurones. In the present study, we attempted to analyse the role of E(2) signalling on ChAT expression in the motoneurone-like cell line NSC-34 and in vivo. In a first step, we demonstrated the presence of oestrogen receptor α and β in NSC-34 cells, as well as in the cervical and lumbar parts, of the male mouse spinal cord. Subsequently, we investigated the effect of E(2) treatment on ChAT expression. The application of E(2) significantly increased the transcription of ChAT in NSC-34 cells and in the cervical but not lumbar part of the spinal cord. Our results indicate that E(2) can influence the cholinergic system by increasing ChAT expression in the mouse spinal cord. This mechanism might support motoneurones, in addition to survival-promoting mechanisms, in the temporal balance toxic or neurodegenerative challenges.

Microtubule associated protein 2 and choline acetyltransferase immunoreactivity in the lumbar spinal cord of young adult and aged dogs

German Shepherds are a good model for research about aging and neurological disorders such as lumbosacral spinal canal stenosis. We compared neurons, glia and cholinergic neurons in the ventral horn of the lumbar spinal cord (L(3)) between adult (1-2 years old) and aged (10-12 years old) groups. Any pathological findings were not found by hematoxylin and eosin staining and neurological examination, and the number of NeuN (a marker for neurons)-positive neurons were similar in both groups. Microtubule-associated protein 2 (MAP2) immunoreactive dendrites in the aged dog were decreased without any change in β-tubulin protein level. Glial fibrillary acidic protein (a marker for astrocytes) and ionized calcium-binding adapter molecule 1 (a marker for microglia) immunoreactivity were not significantly changed in both groups. The number of ChAT immunoreactive neurons was decreased; however, its protein level was not significantly changed in the aged group. These results suggest that numbers of ventral horn neurons are not changed, but cholinergic neurons may change in aged dogs compared to adult dogs.

Appearance of phagocytic microglia adjacent to motoneurons in spinal cord tissue from a presymptomatic transgenic rat model of amyotrophic lateral sclerosis

Microglial activation occurs early during the pathogenesis of amyotrophic lateral sclerosis (ALS). Recent evidence indicates that the expression of mutant Cu(2+)/Zn(2+) superoxide dismutase 1 (SOD1) in microglia contributes to the late disease progression of ALS. However, the mechanism by which microglia influence the neurodegenerative process and disease progression in ALS remains unclear. In this study, we revealed that activated microglia aggregated in the lumbar spinal cord of presymptomatic mutant SOD1(H46R) transgenic rats, an animal model of familial ALS. The aggregated microglia expressed a marker of proliferating cell, Ki67, and phagocytic marker proteins ED1 and major histocompatibility complex (MHC) class II. The motoneurons near the microglial aggregates showed weak choline acetyltransferase (ChAT) immunoreactivity and contained reduced granular endoplasmic reticulum and altered nucleus electron microscopically. Furthermore, immunopositive signals for tumor necrosis factor-alpha (TNFalpha) and monocyte chemoattractant protein-1 (MCP-1) were localized in the aggregated microglia. These results suggest that the activated and aggregated microglia represent phagocytic features in response to early changes in motoneurons and possibly play an important role in ALS disease progression during the presymptomatic stage.

Progesterone modulates brain-derived neurotrophic factor and choline acetyltransferase in degenerating Wobbler motoneurons

Progesterone (PROG) shows neuroprotective effects in nervous system diseases. The Wobbler mouse, a model of motoneuron degeneration, suffers a mutation of the Vsp154 gene on chromosome 11 leading to motoneuron vacuolation and astrocytosis of the spinal cord. Previous work has demonstrated beneficial effects of PROG in the Wobbler mouse. As an extension of this work, we now studied steroid effects on neuronal brain-derived neurotrophic factor (BDNF) mRNA and protein, on choline acetyltransferase (ChAT) immunoreactivity (IR) and activity in the spinal cord, and on recovery of muscle atrophy. Wobbler mice received implants of PROG pellets (20 mg) at 6 and 10 weeks of age and were killed at 14 weeks. In situ hybridization for BDNF mRNA demonstrated that grain density in large (>600 microm2) and medium size (<600 microm2) ventral horn neurons was decreased in untreated Wobblers, whereas PROG treatment increased BDNF mRNA in both neuronal types. PROG also induced a subcellular redistribution of BDNF protein, which in controls and steroid-naive Wobblers showed a predominant perinuclear and nucleolar location, whereas after PROG treatment, it was detected in cytoplasmic aggregates. ChAT activity was reduced by 55.3% in muscles of untreated Wobbler mice, whereas a significant increment was obtained after PROG treatment. Wobblers also showed reduced number of ChAT positive motoneurons, but this number was restored to normal by PROG. Finally, the pronounced biceps atrophy of steroid-naive Wobbler mice was slightly but significantly increased by PROG-treatment. Considering the important role played by neurotrophins on neuronal function, changes in BDNF might be part of the PROG activated-pathways to provide neuroprotection and re-establish neurotransmission and neuromuscular function in this degeneration model.

The "ins" and "outs" of the high-affinity choline transporter CHT1

Maintenance of acetylcholine (ACh) synthesis depends on the activity of the high-affinity choline transporter (CHT1), which is responsible for the reuptake of choline from the synaptic cleft into presynaptic neurons. In this review, we discuss the current understanding of mechanisms involved in the cellular trafficking of CHT1. CHT1 protein is mainly found in intracellular organelles, such as endosomal compartments and synaptic vesicles. The presence of CHT1 at the plasma membrane is limited by rapid endocytosis of the transporter in clathrin-coated pits in a mechanism dependent on a dileucine-like motif present in the carboxyl-terminal region of the transporter. The intracellular pool of CHT1 appears to constitute a reserve pool of transporters, important for maintenance of cholinergic neurotransmission. However, the physiological basis of the presence of CHT1 in intracellular organelles is not fully understood. Current knowledge about CHT1 indicates that stimulated and constitutive exocytosis, in addition to endocytosis, will have major consequences for regulating choline uptake. Future investigations of CHT1 trafficking should elucidate such regulatory mechanisms, which may aid in understanding the pathophysiology of diseases that affect cholinergic neurons, such as Alzheimer's disease.

Disease-related regressive alterations of forebrain cholinergic system in SOD1 mutant transgenic mice

Transgenic mice carrying the human mutated SOD1 gene with a glycine/alanine substitution at codon 93 (G93A) are a widely used model for the fatal human disease amyotrophic lateral sclerosis (ALS). In these transgenic mice, we carried out a neurochemical study not only restricted to the primarily affected regions, the cervical and lumbar segments of the spinal cord, but also to several other brain regions. At symptomatic (110 and 125 days of age), but not at pre-symptomatic (55 days of age) stages, we found significant decreases in catalytic activity of the cholinergic enzyme, choline acetyltransferase (ChAT) in the hippocampus, olfactory cortex and fronto-parietal cortex. In parallel, we observed a decreased number of basal forebrain cholinergic neurons projecting to these areas. No alterations of the cholinergic markers were noticed in the striatum and the cerebellum. A widespread marker for GABAergic neurons, glutamate decarboxylase (GAD), was unaffected in all the areas examined. Alteration of cholinergic markers in forebrain areas was paralleled by concomitant alterations in the spinal cord and brainstem, as a consequence of progressive apoptotic elimination of cholinergic motor neuron. Gestational supplementation of choline, while able to result in long-term enhancement of cholinergic activity, did not improve transgenic mice lifespan nor counteracted cholinergic impairment in brain regions and spinal cord.

Choline acetyltransferase detection in normal and denervated electrocyte from Electrophorus electricus (L.) using a confocal scanning optical microscopy analysis

Acetylcholine is the neurotransmitter responsible for the transmission of impulses from cholinergic neurons to cells of innervated tissues. Its biosynthesis is catalyzed by the enzyme Choline acetyltransferase that is considered to be a phenotypically specific marker for cholinergic system. It is well known that the regulation of Choline acetyltransferase activity under physiological and pathological conditions is important for development and neuronal activities of cholinergic functions. We observed the distribution of Choline acetyltransferase in sections from the normal and denervated main electric organ sections of Electrophorus electricus (L.) by immunofluorescence using a anti-Choline acetyltransferase antibody. The animals were submitted to a surgical procedure to remove about 20 nerves and after 30 and 60 days, they were sacrificed. After 30 days, the results from immunohistochemistry demonstrated an increase on the Choline acetyltransferase distribution at denervated tissue sections when compared with the sections from the normal contralateral organ. A very similar labeling was observed between normal and denervated tissue sections of the animals after 60 days. However, Choline acetyltransferase activity (nmolesACh/ min/ mg of protein) in extracts obtained from electrocyte microsomal preparation, estimated by Fonnun's method (Fonnun 1975), was 70% lower in the denervated extracts.

Choline acetyltransferase: the structure, distribution and pathologic changes in the central nervous system

Choline acetyltransferase (ChAT), the enzyme responsible for the biosynthesis of acetylcholine, is presently the most specific indicator for monitoring the functional state of cholinergic neurones in the central and peripheral nervous systems. ChAT is a single-strand globular protein. The enzyme is synthesized in the perikaryon of cholinergic neurones and transported to the nerve terminals probably by both slow and rapid axoplasmic flows. ChAT exists in at least two forms in cholinergic nerve terminals: (i) soluble; and (ii) non-ionically membrane-bound forms. Multiple mRNA species of ChAT (R-, N-and M-types) are transcribed from different promoter regions and produced by different splicing in the mouse, rat, and human. All transcripts encode the same ChAT protein in rodents, while in human M-type mRNA has the capability to generate both large and small forms of ChAT proteins and R-and N-types ChAT mRNA generate a small form, which corresponds to the rodent ChAT. The genomic structure of ChAT is unique compared with other enzymes for neurotransmitters. The first intron of the ChAT gene encompasses the open reading frame encoding another protein, vesicular acetylcholine transporter (VAChT), which is responsible for the transportation of acetylcholine from the cytoplasm into the synaptic vesicles. The expressions of ChAT and VAChT appear to be coordinately regulated by multiple regulatory elements in cholinergic neurones. Immunohistochemical and in situ hybridization studies have revealed the localization of cholinergic neurones in the central nervous system: the medial septal nucleus, the nucleus of the diagonal band of Broca, the basal nucleus of Meynert, the caudate nucleus, the putamen, the nucleus accumbens, the pedunculopontine tegmental nucleus, the laterodorsal tegmental nucleus, the medial habenular nucleus, the parabigeminal nucleus, some cranial nerve nuclei, and the anterior horn of the spinal cord. Focally distributed cholinergic neurones project fibers to many areas in the central nervous system and construct a complicated cholinergic network, playing an important role in neuropsychic activities, such as learning, memory, arousal, sleep and movement. Central cholinergic neurones are involved in several neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis, in which disturbance of the central cholinergic system does not appear to be closely related to the etiology, but rather to the development of clinical symptoms. In addition, abnormalities of ChAT in the brain have been recently demonstrated in schizophrenia and sudden infant death syndrome.

Immunohistochemical study on choline acetyltransferase in the spinal cord of patients with amyotrophic lateral sclerosis

The authors developed a polyclonal antibody against a fusion protein containing 598 amino acids from a human choline acetyltransferase (ChAT) cDNA and 12 amino acids derived from an expression vector, and examined immunohistochemical reactivity for ChAT in large motor neurons (30 microns and more in somal minimal diameter) of the lumbar spinal cords of four patients with amyotrophic lateral sclerosis (ALS) and of four control cases. In controls, the number of large neurons included in the tissue with a total thickness of 100 microns ranged from 74 to 105 (average 87). About 60-90% (average 80%) of the neurons were positively stained in their perikarya with an anti-human ChAT antibody. In the cases of ALS, the number of large motor neurons was greatly reduced (25-60, average 38). About 4-13% (average 8%) were positively stained. These results indicate that not only large neurons are reduced in number, but also their positivity for ChAT is decreased in the anterior horn of ALS spinal cord.

Positive and negative effects of nuclear receptors on transcription activation by AP-1 of the human choline acetyltransferase proximal promoter

We have examined the 5'-flanking region (944 bp) of the human choline acetyltransferase (hChAT) gene for sequences that modulate its transcriptional activity and identified a sequence 5'-TGACCCA-3' which confers c-Jun/c-Fos (AP-1) inducibility of homologous and heterologous promoters. Using transient transfections in neuroblastoma NE-1-115 and COS-1 cells, we show that ligand-activated estrogen receptor (HEGo) represses the transcriptional activation by c-Fos/c-Jun. Testing HEGo mutants in transfection assays reveals that the ligand-binding domain is crucial for this repression, whereas the N-terminal (A/B) region and the DNA-binding domain are not essential. Gel retardation assays show that the hChAT AP-1 recognition sequence binds in vitro baculovirus-produced c-Jun/c-Fos proteins. This binding is inhibited by addition of baculovirus-produced HEGo. In contrast to HEGo, ligand-activated glucocorticoid, androgen, and retinoic acid receptors (RARs) enhance the transcription activation induced by c-Jun/c-Fos. All three types of RARs--RAR alpha, beta, gamma--and RXR alpha are able to stimulate AP-1 activity on the proximal hChAT promoter. Several mechanism possibilities involving protein-protein interaction are discussed to explain the phenomena.

1,1,3 Tricyano-2-amino-1-propene (Triap) stimulates choline acetyltransferase activity in vitro and in vivo

1,1,3 Tricyano-2-amino-1-propene (Triap) is a small molecule that has neurotrophic properties similar to nerve growth factor (NGF). Studies have shown that NGF increases choline acetyltransferase (ChAT) activity, the enzyme responsible for the synthesis of acetylcholine, in several cell lines and in the CNS of adult animals. To investigate whether Triap can cause similar increases in ChAT enzyme activity, we used the PC12 cell line and primary cultures of rat fetal brain tissue to examine Triap's effects. Nanomolar concentrations of Triap produced a 4.2- and 2.1-fold increase in the ChAT activity of PC12 cells and cultured rat fetal brain cells, respectively. This stimulation reached a plateau within 4 days of treatment in the primary fetal brain cultures with the first increases evident within 24 h. In the PC12 cell line, Triap's stimulation of ChAT activity was significantly greater than increases produced by optimal concentrations of NGF. Triap also matched NGF's stimulation of ChAT activity in primary neuronal culture. Triap also potentiated NGF's actions on ChAT activity in the PC12 cell line and in primary fetal neuronal cultures. These increases in enzyme activity correlated with increases in cellular enzyme levels as assessed using immunochemical identification of the ChAT enzyme. We also conducted experiments to determine if Triap also induced these same increases in ChAT activity in adult animals. Ten-day chronic injections of Triap in mice resulted in significant increases in specific ChAT enzyme activity in the cortex and septal-hippocampal area. Similar increases in ChAT enzyme levels were also detected using western blotting techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic markers in ALS spinal cord

We analyzed binding sites for quinuclidinyl benzilate (QNB) and hemicholinium-3 (HC-3) by quantitative slice autoradiography and the activities of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in spinal cord of 5-7 patients with amyotrophic lateral sclerosis (ALS). In the ventral horn, QNB binding sites were markedly reduced (38% of controls; P less than 0.001), whereas HC-3 binding sites were only moderately affected (76%, P less than 0.01). Losses in cholinergic marker enzymes were inconsistent. The loss of muscarinic binding sites in the ventral horn was the most reliable cholinergic disease marker in ALS.

Isolation and sub-chromosomal localization of a DNA fragment of the human choline acetyltransferase gene

A DNA fragment of 219 bp was obtained by polymerase chain reaction (PCR) on human genomic DNA using two oligonucleotide mixtures derived from peptide sequences of human placenta choline acetyltransferase (ChAT) and from partially conserved amino acid sequences of rat, porcine and Drosophila ChAT. Sequence homology with porcine ChAT demonstrated that this fragment is part of the human ChAT gene. This gene was assigned to chromosome 10 by hybridization of the 219 bp DNA probe with DNA from human-hamster somatic cell hybrids, and to region 10q11.2-10qter by PCR experiments.

Motor neuron disease (amyotrophic lateral sclerosis)

Amyotrophic lateral sclerosis is an insidiously developing, adult-onset, progressive anterior horn cell degeneration with associated degeneration of descending motor pathways. It has been recognized as an important clinical syndrome since the middle of the 19th century. Despite increasing clinical and research interest in this condition, its cause remains obscure, even in the broadest terms. Epidemiologic characteristics of the disease have been interpreted as evidence of both genetic and environmental causes. A major change in the view of this disease is the widely developing perception that it is a disease of elderly persons more than of middle-aged adults as was previously taught. Etiologic hypotheses encompass a broad range of postulated pathophysiologic mechanisms, and we review these in detail. The clinical limits of the disease can now be better defined by using modern diagnostic techniques. Although interest in supportive symptomatic therapy is growing, no intervention has yet been shown to modify the biologically determined motor system degeneration.