Choline acetyltransferase-like activity bound to neuronal plasma membranes

The potential role of pumpkin seeds oil on methotrexate-induced lung toxicity

Many chemotherapeutic drugs cause adverse pulmonary reactions leading to severe pulmonary disease. Though methotrexate (MTX) is used for the treatment of cancer and other diseases, it is highly toxic with multiple adverse effects including pulmonary toxicity. Essential oils represent an open frontier for pharmaceutical sciences due to their wide range of pharmacological properties. Pumpkin seeds oil (PSO) was used to investigate its ability to alleviate methotrexate-induced lung toxicity in rats. Lung tissue from MTX-treated group revealed a decrease in malondialdehyde, glutathione, and nitric oxide accompanied by a marked inhibition in cholinesterase activity, and enhanced catalase activity, tumor necrosis factor-α, interleukin-6 and vascular endothelial growth factor levels. Analysis of PSO revealed that the oil was rich in hexadecanoic acid, decane methyl esters, squalene, polydecane, docosane, and other derivatives. Administration of PSO ameliorated the oxidant/antioxidant and proinflammatory changes induced by MTX in the lung tissue. Histological examinations confirmed the potency of PSO in reducing the histopathological alterations induced by MTX. Immunohistochemical analysis showed decreased nuclear factor-kappa B and caspase 3 expression after PSO. The present data indicated the protective efficiency of PSO against MTX-induced lung injury by decreasing oxidative damage, inflammation and apoptosis and could thus be recommended as an adjuvant therapy.

Restrained Phosphatidylcholine Synthesis in a Cellular Model of Down's Syndrome is Associated with the Overexpression of Dyrk1A

Aberrant formation of the cerebral cortex could be attributed to the lack of suitable substrates that direct the migration of neurons. Previous work carried out at our laboratory has shown that oleic acid is a neurotrophic factor. In order to characterize the effect of oleic acid in a cellular model of Down's syndrome (DS), here, we used immortalized cell lines derived from the cortex of trisomy Ts16 and euploid mice. We report that in the plasma membrane of euploid cells, an increase in phosphatidylcholine concentrations occurs in the presence of oleic acid. However, in trisomic cells, oleic acid failed to increase phosphatidylcholine incorporation into the plasma membrane. Gene expression analysis of trisomic cells revealed that the phosphatidylcholine biosynthetic pathway was deregulated. Taken together, these results suggest that the overdose of specific genes in trisomic lines delays differentiation in the presence of oleic acid. The dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A (DYRK1A) gene is located on human chromosome 21. DYRK1A contributes to intellectual disability and the early onset of Alzheimer's disease in DS patients. Here, we explored the potential role of Dyrk1A in the reduction of phosphatidylcholine concentrations in trisomic cells in the presence of oleic acid. The downregulation of Dyrk1A by small interfering RNA (siRNA) in trisomic cells returned phosphatidylcholine concentrations up to similar levels to those of euploid cells in the presence of oleic acid. Thus, our results highlight the role of Dyrk1A in brain development through the modulation of phosphatidylcholine location, levels and synthesis.

Overexpression of DYRK1A inhibits choline acetyltransferase induction by oleic acid in cellular models of Down syndrome

Histological brain studies of individuals with DS have revealed an aberrant formation of the cerebral cortex. Previous work from our laboratory has shown that oleic acid acts as a neurotrophic factor and induces neuronal differentiation. In order to characterize the effects of oleic acid in a cellular model of DS, immortalized cell lines derived from the cortex of trisomy Ts16 (CTb) and normal mice (CNh) were incubated in the absence or presence of oleic acid. Oleic acid increased choline acetyltransferase expression (ChAT), a marker of cholinergic differentiation in CNh cells. However, in trisomic cells (CTb line) oleic acid failed to increase ChAT expression. These results suggest that the overdose of specific genes in trisomic lines delays differentiation in the presence of oleic acid by inhibiting acetylcholine production mediated by ChAT. The dual-specificity tyrosine (Y) phosphorylation-regulated kinase 1A (DYRK1A) gene is located on human chromosome 21 and encodes a proline-directed protein kinase. It has been proposed that DYRK1A plays a prominent role in several biological functions, leading to mental retardation in DS patients. Here we explored the potential role of DYRK1A in the modulation of ChAT expression in trisomic cells and in the signaling pathways of oleic acid. Down-regulation of DYRK1A by siRNA in trisomic CTb cells rescued ChAT expression up to levels similar to those of normal cells in the presence of oleic acid. In agreement with these results, oleic acid was unable to increase ChAT expression in neuronal cultures of transgenic mice overexpressing DYRK1A. In summary, our results highlight the role played by DYRK1A in brain development through the control of ChAT expression. In addition, the overexpression of DYRK1A in DS models prevented the neurotrophic effect of oleic acid, a fact that may account for mental retardation in DS patients.

Increased levels of methylated intermediates of phosphatidylcholine lead to enhanced phospholipase D activity

Previous work from this laboratory and others has shown that neurotransmitters can activate phospholipase D. Unlike the phospholipase C that specifically hydrolyzes inositol-containing phospholipids, phospholipase D in neuronal tissue specifically hydrolyzes phosphatidylcholine. One route for the synthesis of phosphatidylcholine, is via methylation of phosphatidylethanolamine. Using an in vitro assay, we have previously shown that methylated intermediates are also good substrates for phospholipase D (1). In this manuscript we demonstrate that these intermediates are also substrates in the intact PC12 cells. Cells incubated with methyl and dimethylethanolamine incorporate more [3H]palmitic acid into the corresponding phospholipid, phosphatidyl-N-methylethanolamine and phosphatidyl-N,N-dimethylethanolamine. In these cells bradykinin causes a greater increase in [3H]phosphatidylethanol production. Elevated levels of [3H]phosphatidylcholine do not enhance bradykinin-stimulated [3H]phosphatidylethanol production, therefore, this effect is specific for the methylated intermediates. Finally, this effect is not due to some generalized enhancement of receptor coupling because incubation of the cells with methylethanolamine does not lead to an increase in bradykinin stimulated inositol phosphate production.

Choline acetyltransferase: celebrating its fiftieth year

It is well known that the regulation of choline acetyltransferase (ChAT) activity under physiological and pathological conditions is important for the development and neuronal activities of cholinergic systems involved in many fundamental brain functions. This review focuses on recent progress in understanding the regulation of ChAT at the levels of both the protein and the mRNA. A deficiency in ChAT activity has been reported for neurodegenerative conditions such as Alzheimer's disease, amyotrophic lateral sclerosis, and schizophrenia. Although a major feature of ChAT regulation is likely to involve the spatial and temporal control of transcription, regulation of expression can also be at the level of RNA processing, transport/translocation, turnover, or translation. In addition, there is increasing evidence that ChAT might be regulated at the posttranslational level by compartmentation and/or covalent modification, i.e., phosphorylation, as well as noncovalent modification (protein-protein interaction, etc.). Synaptic activity and the state of neuronal transmission may also involve the regulation of ChAT at different levels via both positive and negative feedback loops, as was demonstrated in the characterization of two ChAT mutant Drosophila strains. Clearly, identification of cholinergic-specific elements and the characterization of the trans-acting factors that bind to them represent an important area of future research. Equally important is research on the mechanisms governing ChAT as an enzymatic entity. The future should be an exciting time during which we look forward to the elucidation of the cholinergic signal and its regulation as well as the determination of the three-dimensional structure of the enzyme.

Bradykinin and phorbol dibutyrate activate phospholipase D in PC12 cells by different mechanisms

Bradykinin is known to activate phospholipase D in PC12 cells. Because bradykinin may also activate protein kinase C in these cells, the possible role of this kinase in mediating the action of bradykinin was investigated. Phospholipase D activity in PC12 cells was assayed by measuring the formation of [3H]phosphatidylethanol in cells prelabeled with [3H]palmitic acid and incubated in the presence of ethanol. The phorbol ester phorbol dibutyrate mimicked the effect of bradykinin on [3H]phosphatidylethanol formation. The protein kinase C inhibitor staurosporine (1 microM) significantly attenuated the effect of phorbol dibutyrate (35-70%) but did not block bradykinin-stimulated [3H]phosphatidylethanol formation. In addition, the effect of phorbol dibutyrate was additive with that of bradykinin. Prolonged treatment of PC12 cells with phorbol dibutyrate (24 h), which depletes cells of protein kinase C, greatly attenuated bradykinin-stimulated [3H]phosphatidylethanol accumulation in intact cells. This treatment caused a 55% decrease in both fluoride-stimulated [3H]phosphatidylethanol production in the intact cell and phospholipase D activity as assessed by an in vitro assay using an exogenous substrate. Therefore, the effect of prolonged phorbol dibutyrate pretreatment on bradykinin-stimulated [3H]phosphatidylethanol production could not be attributed exclusively to the depletion of protein kinase C. Thus, although the data with phorbol ester suggest that activation of protein kinase C leads to an increase in phospholipase D activity, this kinase probably does not play a role in mediating the effect of bradykinin. Finally, although pretreatment with phorbol dibutyrate completely blocked bradykinin-stimulated [3H]phosphatidylethanol production in the intact cell, it only partially (approximately 50%) inhibited bradykinin-stimulated [3H]diacylglycerol formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential sensitivity of cholinergic and GABAergic neurons in chick embryos treated intracerebrally with ethanol at 8 days of embryonic age

We have shown that in embryos treated with ethanol in ovo during days 1-3, a critical period of neuroembryogenesis, cholinergic neuronal phenotypic expression is decreased whereas GABAergic and catecholaminergic neuronal populations are increased as assessed by neuronal markers choline acetyltransferase (ChAT), glutamic acid decarboxylase (GAD) and tyrosine hydroxylase (TH) respectively. In this study, ethanol was administered intracerebrally to embryos at embryonic day 8, embryos were sacrificed at day 9 and ChAT and GAD activities assayed separately in cerebral hemispheres and remaining brain (diencephalon-midbrain and optic lobes). We found that ChAT activity was enhanced in the cerebral hemispheres only, whereas GAD activity was decreased in both cerebral hemispheres and remaining brain. We have concluded that the differential responses of neuronal phenotypes to ethanol may reflect compensatory mechanisms to ethanol insult. Moreover, these findings emphasize the vulnerability of the GABAergic neuronal phenotypes to ethanol neurotoxicity during early brain development in the chick.

Ethanol increases cholinergic and decreases GABAergic neuronal expression in cultures derived from 8-day-old chick embryo cerebral hemispheres: interaction of ethanol and growth factors

We have shown that ethanol exposure during embryogenesis affects a variety of parameters of neuronal growth both in ovo and in vitro. Moreover, we have found that growth factors significantly attenuate the in ovo neurotoxicity produced by ethanol. In this study, we further examined the direct effects of ethanol exposure on neuron-enriched cultures derived from 8-day-old chick embryo cerebral hemispheres consisting primarily of differentiated neurons. In addition, we examined the interaction of ethanol and nerve growth factor (NGF) or epidermal growth factor (EGF) when the growth factors were given concomitantly with ethanol. Choline acetyltransferase (ChAT) and glutamic acid decarboxylase (GAD) were used as markers for cholinergic and GABAergic neuronal phenotypic expression, respectively. We found that ethanol alone enhanced ChAT and reduced GAD activities in a dose-dependent manner. NGF and EGF given alone enhanced the expression of both neuronal phenotypes. When NGF was given concomitantly with ethanol at C4-8 the decline in GAD produced by ethanol was reversed. The effects of concomitant administration of ethanol and growth factors on ChAT activity revealed that ethanol interfered with the increases produced by the growth factors and especially with NGF when given alone. We conclude from these findings that ethanol may interfere with neuronal phenotypic expression by altering neuronal responsiveness to neurotrophic signals important for neuronal differentiation.

Isolation of monoaminergic synaptosomes from rat brain by immunomagnetophoresis

Monoaminergic synaptosomes have been isolated and purified from rat brain by immunomagnetophoresis. This novel technique uses magnetic beads to which Protein A is bound. Noradrenergic, dopaminergic, and serotonergic synaptosomes (previously cell-surface labelled with anti-dopamine-beta-hydroxylase, anti-tyrosine hydroxylase, and anti-tryptophan hydroxylase, respectively) may be isolated in a highly purified state. The synaptosomal subpopulations are recovered in a viable metabolic state and show glucose-stimulated respiration and Ca2(+)-dependent neurotransmitter release. A novel subtype of dopamine-beta-hydroxylase was found in dopaminergic terminals. No evidence for glutamate corelease from monoaminergic synaptosomes was obtained.

Critical periods to ethanol exposure during early neuroembryogenesis in the chick embryo: cholinergic neurons

The acute and chronic effects of ethanol on cholinergic neuronal expression were studied in the chick embryo during early neuroembryogenesis using choline acetyltransferase (ChAT) activity as a cholinergic marker. Ethanol administered to embryos in ovo on day 1 (E1) produced a 30% decrease in ChAT activity, while ethanol administration on day 3 elicited no significant change. Similar effects were produced by ethanol on ChAT activity in the spinal cord. The decrease in ChAT activity in both brain and spinal cord was not accompanied by a significant change in protein content. Of significance were our findings with chronic ethanol treatment: in embryos treated from E1 to E5 and sacrificed at E6, ChAT activity was decreased. In contrast, in embryos treated similarly but sacrificed at E8 ChAT activity was increased. These findings establish that the critical period of cholinergic neuronal sensitivity to ethanol is confined to E. Moreover, the increase in ChAT activity observed after chronic ethanol treatment indicates that the developing neurons have the capability to adapt to ethanol. This apparent adaptation results in overcompensation, as reflected by the increase in ChAT activity. Whether this overcompensation is at the expanse of another neuronal population remains to be investigated.