Nicotinic Acetylcholine Receptor Gene Expression Research Articles

Berberine Ameliorates Glucose Metabolism in Diabetic Rats through the alpha7 Nicotinic Acetylcholine Receptor-Related Cholinergic Anti-Inflammatory Pathway.

Berberine is an isoquinoline derivative alkaloid extracted from Chinese herbs. Recent studies have demonstrated the therapeutic effect of berberine on glucose metabolic disorders. However, its specific mechanism is still unclear. Our study aimed to research the glucose-lowering effect of berberine in diabetic rats and to reveal the possible role of the cholinergic anti-inflammatory pathway. Diabetic rats induced by administration of a high-calorie diet and streptozocin tail vein injection were assessed by the oral glucose tolerance test. Then, the diabetic rats were divided into two groups, those with or without the alpha7 nicotinic acetylcholine receptor gene downregulated, respectively, followed by treatment including berberine for 6 weeks. Results of this study show that the administration of berberine downregulated levels of fasting blood glucose and fasting insulin, and ameliorated insulin resistance in diabetic rats. Treatment with berberine inhibited acetylcholinesterase activity, and upregulated acetylcholine levels in the serum and alpha7 nicotinic acetylcholine receptor gene expression in the liver tissue. Meanwhile, berberine reversed elevated expression of cytokines interleukin-1β and TNF-α in the serum and downregulated nuclear factor κB expression. However, berberine administration showed no glucose-lowering or anti-inflammatory effect in diabetic rats in which alpha7 nicotinic acetylcholine receptor gene expression was downregulated, and acetylcholinesterase activity was also significantly inhibited. In conclusion, berberine may ameliorate glucose metabolism by activating the alpha7 nicotinic acetylcholine receptor-mediated cholinergic anti-inflammatory pathway.

The Effect of Swimming Endurance Exercise on Cell Death and Nicotinic Acetylcholine Receptor Gene Expression in Brain of Rat: An Experimental Study of Alzheimer's Disease Model

The Effect of Swimming Endurance Exercise on Cell Death and Nicotinic Acetylcholine Receptor Gene Expression in Brain of Rat: An Experimental Study of Alzheimer's Disease Model

Oral exposure to aluminum leads to reduced nicotinic acetylcholine receptor gene expression, severe neurodegeneration and impaired hippocampus dependent learning in mice

Aluminum (Al) is known for its neurotoxicity for over a century and is reported to have specifically high toxicity for cholinergic system. The effect of Al on muscarinic acetylcholine receptors is widely reported, but its effect on nicotinic acetylcholine receptors (nAChRs) is less well known. The aim of this study was to determine the effects of Al on hippocampus dependent learning and memory, function and expression of nAChRs in the hippocampus. Al concentration and neurodegeneration were also measured in the hippocampus following Al treatment. The mice were treated with 250 mg/kg AlCl3.6H2O in drinking water for a period of 42 days. Results show that Al treated animals have significantly reduced spatial reference memory as compared to control animals in Morris water maze test. Similarly, Al treated animals showed reduced contextual memory for Pavlovian fear compared to control animals. Al treated animals show higher anxiety in elevated plus maze as compared to control animals. The analysis of nAChR expression via RT-PCR showed reduced expression of α7, α4 and β2 nAChR gene expression in the hippocampus of Al treated animals. High Al accumulation was observed in Al-treated animals (688.14 ± 242.82 μg/g) compared to the control group (115.14 ± 18.18 μg/g) that resulted in severe neurodegeneration in the hippocampus. These results demonstrated that Al exposure caused neurotoxicity in mice hippocampus which is manifested by reduced memory and elevated anxiety. The results were further validated by high Al accumulation in the hippocampus, severe neurodegeneration and reduced expression of nAChRs.

Increased Active OMI/HTRA2 Serine Protease Displays a Positive Correlation with Cholinergic Alterations in the Alzheimer\u2019s Disease Brain

OMI/HTRA2 (high-temperature requirement serine protease A2) is a mitochondrial serine protease involved in several cellular processes, including autophagy, chaperone activity, and apoptosis. Few studies on the role of OMI/HTRA2 in Alzheimer’s disease (AD) are available, but none on its relationship with the cholinergic system and neurotrophic factors as well as other AD-related proteins. In this study, immunohistochemical analyses revealed that AD patients had a higher cytosolic distribution of OMI/HTRA2 protein compared to controls. Quantitative analyses on brain extracts indicated a significant increase in the active form of OMI/HTRA2 in the AD brain. Activated OMI/HTRA2 protein positively correlated with stress-associated read-through acetylcholinesterase activity. In addition, α7 nicotinic acetylcholine receptor gene expression, a receptor also known to be localized on the outer membrane of mitochondria, showed a strong correlation with OMI/HTRA2 gene expression in three different brain regions. Interestingly, the activated OMI/HTRA2 levels also correlated with the activity of the acetylcholine-biosynthesizing enzyme, choline acetyltransferase (ChAT); with levels of the neurotrophic factors, NGF and BDNF; with levels of the soluble fragments of amyloid precursor protein (APP); and with gene expression of the microtubule-associated protein tau in the examined brain regions. Overall, the results demonstrate increased levels of the mitochondrial serine protease OMI/HTRA2, and a coherent pattern of association between the activated form of OMI/HTRA2 and several key proteins involved in AD pathology. In this paper, we propose a new hypothetical model to highlight the importance and needs of further investigation on the role of OMI/HTRA2 in the mitochondrial function and AD.

Cortex- and Amygdala-Dependent Learning and Nicotinic Acetylcholine Receptor Gene Expression is Severely Impaired in Mice Orally Treated with AlCl3.

Recent industrialization has increased human exposure to bio-available aluminum (Al). If more Al enters the brain than leaves, Al concentration will rise in the brain leading to neurodegenerative disorders. The aim of the present study was to determine Al concentration, neurodegeneration, and nicotinic acetylcholine receptor (nAChR) gene expression in the cortex and amygdala after oral ingestion of Al salt. The effect of Al on cortex- and amygdala-dependent learning and memory functions was also assessed. Mice were given AlCl3 (250mg/kg) in drinking water for 42days. nAChR gene expression was determined in the cortex and amygdala. The mice were subjected to behavior tests (fear conditioning, fear extinction, and open field), to assess memory deficits. The acquisition of fear memory in the fear conditioning test remained unaffected due to the Al administration. However, fear extinction (which is a new learning) was severely impaired. The behavioral analysis in the open field test showed greater anxiety and less adaptability to the new environment in Al-treated animals. High Al concentration and severe neurodegeneration in the cortex were observed following Al treatment while a slight, non-significant elevation in Al concentration was observed in the amygdala of Al-treated animals. The analysis of nAChR gene expression via RT-PCR showed a significant reduction in expression of α7, α4, and β2 nAChR genes in the cortex of Al-treated animals, while in the amygdala, the level of the α4 nAChR gene remained unaltered. Oral Al ingestion causes neuropathological changes and suppresses expression of nAChR genes that lead to deficits in learning and higher anxiety in Al-treated animals.

Influence of inhibited α7 nicotinic acetylcholine receptor gene expression on the production of β-amyloid peptide in SH-SY5Y cells

To investigate the influence of inhibited α7 neuronal nicotinic acetylcholine receptor (nAChR) by small interference RNA (siRNA) in SH-SY5Y cells and to explore the connection of these changes with the β-amyloid precursor protein (APP) metabolism and the pathogenesis of Alzheimer's disease (AD). The siRNA of α7 nAChR was transfected into SH-SY5Y cells, and the expression of α7 nAChR and two subtypes of β-secretases (BACE1 and BACE2) at mRNA and protein levels was studied by real-time PCR and Western blot, respectively. The variation of Aβ(1-42) content was detected by ELISA. As compared with controls, the expression of α7 nAChR at mRNA and protein levels in the SH-SY5Y cells transfected with the α7 nAChR siRNA were decreased by 84% and 79% (P < 0.01), respectively. The expressions of BACE1 mRNA and protein levels was increased by 527% and 71% (P < 0.01), respectively, while the expression of BACE2 decreased by 58% and 75% (P < 0.01), respectively. The Aβ(1-42) content increased by 208% (P < 0.01). An inhibited α7 nAChR mRNA induced by siRNA may markedly stimulate the production of Aβ through the mechanism of increased expression of BACE1 and inhibited expression of BACE2, which may be related to the pathogenesis of AD.

A Histone Deacetylase 4/Myogenin Positive Feedback Loop Coordinates Denervation-dependent Gene Induction and Suppression

Muscle activity contributes to formation of the neuromuscular junction and affects muscle metabolism and contractile properties through regulated gene expression. However, the mechanisms coordinating these diverse activity-regulated processes remain poorly characterized. Recently, it was reported that histone deacetylase 4 (HDAC4) can mediate denervation-induced myogenin and nicotinic acetylcholine receptor gene expression. Here, we report that HDAC4 is not only necessary for denervation-dependent induction of genes involved in synaptogenesis (nicotinic acetylcholine receptor and muscle-specific receptor tyrosine kinase) but also for denervation-dependent suppression of genes involved in glycolysis (muscle-specific enolase and phosphofructokinase). In addition, HDAC4 differentially regulates genes involved in muscle fiber type specification by inducing myosin heavy chain IIA and suppressing myosin heavy chain IIB. Consistent with these regulated gene profiles, HDAC4 is enriched in fast oxidative fibers of innervated tibialis anterior muscle and HDAC4 knockdown enhances glycolysis in cultured myotubes. HDAC4 mediates gene induction indirectly by suppressing the expression of Dach2 and MITR that function as myogenin gene corepressors. In contrast, HDAC4 is directly recruited to myocyte enhancer factor 2 sites within target promoters to mediate gene suppression. Finally, we discovered an HDAC4/myogenin positive feedback loop that coordinates gene induction and repression underlying muscle phenotypic changes after muscle denervation.

The Signal Transduction Pathway Underlying Ion Channel Gene Regulation by Sp1-c-Jun Interactions

During neuronal differentiation, an exquisitely controlled program of signal transduction events takes place, leading to the temporally and spatially regulated expression of genes associated with the differentiated phenotype. A critical class of genes involved in this phenomenon is that made up of genes encoding neurotransmitter-gated ion channels that play a central role in signal generation and propagation within the nervous system. We used the well established PC12 cell line to investigate the molecular details underlying the expression of the neuronal nicotinic acetylcholine receptor class of ion channels. Neuronal differentiation of PC12 cells can be induced by nerve growth factor, leading to an increase in neuronal nicotinic acetylcholine receptor gene expression. Nerve growth factor initiates several signal transduction cascades. Here, we show that the Ras-dependent mitogen-activated protein kinase and phosphoinositide 3-kinase pathways are critical for the nerve growth factor-mediated increase in the transcriptional activity of a neuronal nicotinic acetylcholine receptor gene promoter. In addition, we show that a component of the Ras-dependent mitogen-activated protein kinase pathway, nerve growth factor-inducible c-Jun, exerts its effects on receptor gene promoter activity most likely through protein-protein interactions with Sp1. Finally, we demonstrate that the target for nerve growth factor signaling is an Sp1-binding site within the neuronal nicotinic acetylcholine receptor gene promoter.

Nicotinic acetylcholine receptor gene expression in developing chick autonomic ganglia

The developmental expression patterns of ten genes encoding nicotinic acetylcholine receptor subunits were analyzed using Northern blots and in situ hybridization in chick peripheral ganglia of neural crest, placodal and dual embryonic origin. The superior cervical and ciliary ganglia were investigated in detail because they accumulated relatively abundant transcripts of the α3, β4, α5 and α7 genes. In the superior cervical ganglion, these four mRNA species had similar developmental time-courses. They appeared at embryonic day 8 (E8), increased steadily until E16 and maintained a rather high plateau level until E18. In the ciliary ganglion, α7 transcripts were already abundant at E6, increased until E10, and considerably decreased thereafter. High-resolution in situ hybridization showed that α7 transcripts were present in all cell types of the E6 ciliary ganglion, whereas they were restricted to large neuronal somas at E16. Transfections with a reporter gene under the control of the α7 promoter demonstrated that a sharp developmental divide occurred at E11-12, after which stage the promoter was activatable in neurons exclusively.

Role for calcium from the sarcoplasmic reticulum in coupling muscle activity to nicotinic acetylcholine receptor gene expression in rat.

Neurally evoked muscle electrical activity suppresses nicotinic acetylcholine receptor (nAChR) gene expression in extrajunctional domains of adult muscle fibers. It has been proposed that this regulation is mediated by calcium influx through voltage-dependent L-type calcium channels but bypasses the sarcoplasmic reticulum in chick and mouse C2C12 cells. Here we report that in rat muscle calcium influx through L-type calcium channels preferentially reduced nAChR epsilon-subunit RNA via a post-transcriptional mechanism. In contrast, calcium release from the sarcoplasmic reticulum (SR) suppressed nAChR subunit RNA levels as a result of decreasing nAChR subunit promoter activity. Finally, we show that this decreased promoter activity is mediated through the same DNA sequences that control activity-dependent gene expression. Therefore, we propose that in rat muscle, calcium release from the SR participates in coupling muscle depolarization to nAChR gene expression.

Electrical Activity Suppresses Nicotinic Acetylcholine Receptor γ Subunit Promoter Activity

Nicotinic acetylcholine receptors are pentameric, transmembrane, ligand-gated ion channels critical for neuromuscular signal transmission. Prior to innervation, the genes encoding these receptors are expressed in nuclei throughout the muscle fiber. Muscle innervation leads to a dramatic decrease in expression of these genes in extrasynaptic nuclei. This reduction in gene expression can be reversed by muscle denervation. The effects of denervation on receptor gene expression can be blocked by electrical stimulation of muscle using extracellular electrodes. The molecular mechanisms by which muscle electrical activity leads to altered patterns of nicotinic acetylcholine receptor gene expression are not well understood. Using an in vitro electrical stimulation paradigm to induce muscle activity, we have been able to mimic the effect of innervation on extrasynaptic acetylcholine receptor gene expression. We have found that a 93-bp region of 5′-flanking DNA, spanning nucleotides -150 to -57 relative to the transcription start site of the γ subunit gene, is required for the suppression of gene expression in response to muscle activity. Sequences downstream of this region are transcriptionally active but are not responsive to muscle activity. However, these downstream sequences become responsive to muscle activity when placed under the control of the γ subunit muscle-specific enhancer.

Protein-tyrosine phosphatases specifically regulate muscle adult-type nicotinic acetylcholine receptor gene expression.

Innervation of skeletal muscles results in expression of adult-type nicotinic acetylcholine receptors (alpha 2 beta epsilon delta) beneath the neuromuscular junction. This local expression is largely a result of selective induction of adult-type nicotinic acetylcholine receptor (nAChR) genes in endplate-associated myonuclei. The molecular mechanism by which the nerve induces gene expression in these nuclei is not known. We have shown previously that ionophore-induced calcium influx across the plasma membrane preferentially decreases expression from the adult-type specific nAChR epsilon-subunit gene (Walke, W., Staple, J., Adams, L., Gnegy, M., Chahine, K., and Goldman, D. (1994) J. Biol. Chem. 269, 19447-19456). Here we provide evidence that the genes encoding adult-type nAChRs are specifically regulated by protein-tyrosine phosphatase activity. Orthovanadate, a specific protein-tyrosine phosphatase inhibitor, caused increased expression of the epsilon-subunit gene in rat primary myotubes and was able to completely block the suppressive effects of increased calcium influx on epsilon-subunit RNA expression. Overexpression of protein-tyrosine phosphatases selectively decreased expression from the adult-type nAChR genes with no effect on the embryonic-type specific gamma-subunit gene. These results demonstrate that protein-tyrosine phosphatases regulate mammalian adult-type nAChR gene expression and suggest a mechanism by which muscle innervation selectively regulates gene expression in endplate-associated myonuclei.

Induction of adult-type nicotinic acetylcholine receptor gene expression in noninnervated regenerating muscle

Expression of adult-type nicotinic acetylcholine receptors at the neuromuscular junction is thought to result from selective induction of their genes in endplate-associated nuclei due to local neurotrophic control. However, denervation studies indicate that endplate-specific expression can be maintained in the absence of the nerve. We investigated the role played by the basal lamina in this expression by assaying for the adult-type-specific ε RNA in noninnervated regenerating muscle. We found that this RNA is locally expressed beneath the old endplates after 10 days of regeneration. At earlier times ε RNA is also found in areas other than the endplate region. These results indicate that in adult muscle the basal lamina contains all the components necessary to direct nicotinic acetylcholine receptor gene expression to the endplate.