Nicotine modulates the expression of a diverse set of genes in the neuronal SH-SY5Y cell line

Label-Free Assessment of Neuronal Activity Using Raman Micro-Spectroscopy

Given the pivotal role of neuronal populations in various biological processes, assessing their collective output is crucial for understanding the nervous system's complex functions. Building on our prior development of a spiral scanning mechanism for the rapid acquisition of Raman spectra from single cells and incorporating machine learning for label-free evaluation of cell states, we investigated whether the Paint Raman Express Spectroscopy System (PRESS) can assess neuronal activities. We tested this hypothesis by examining the chemical responses of glutamatergic neurons as individual neurons and autonomic neuron ganglia as neuronal populations derived from human-induced pluripotent stem cells. The PRESS successfully acquired Raman spectra from both individual neurons and ganglia within a few seconds, achieving a signal-to-noise ratio sufficient for detailed analysis. To evaluate the ligand responsiveness of the induced neurons and ganglia, the Raman spectra were subjected to principal component and partial least squares discriminant analyses. The PRESS detected neuronal activity in response to glutamate and nicotine, which were absent in the absence of calcium. Additionally, the PRESS induced dose-dependent neuronal activity changes. These findings underscore the capability of the PRESS to assess individual neuronal activity and elucidate neuronal population dynamics and pharmacological responses, heralding new opportunities for drug discovery and regenerative medicine advancement.

Epigenetic mechanisms of nicotine dependence

Smoking continues to be a leading cause of preventable disease and death worldwide. Nicotine dependence generates a lifelong propensity towards cravings and relapse, presenting an ongoing challenge for the development of treatments. Accumulating evidence supports a role for epigenetics in the development and maintenance of addiction to many drugs of abuse, however, the involvement of epigenetics in nicotine dependence is less clear. Here we review evidence that nicotine interacts with epigenetic mechanisms to enable the maintenance of nicotine-seeking across time. Research across species suggests that nicotine increases permissive histone acetylation, decreases repressive histone methylation, and modulates levels of DNA methylation and noncoding RNA expression throughout the brain. These changes are linked to the promoter regions of genes critical for learning and memory, reward processing and addiction. Pharmacological manipulation of enzymes that catalyze core epigenetic modifications regulate nicotine reward and associative learning, demonstrating a functional role of epigenetic modifications in nicotine dependence. These findings are consistent with nicotine promoting an overall permissive chromatin state at genes important for learning, memory and reward. By exploring these links through next-generation sequencing technologies, epigenetics provides a promising avenue for future interventions to treat nicotine dependence.

Decreased mitochondrial DNA copy number in nerve cells and the hippocampus during nicotine exposure is mediated by autophagy

Cigarette smoke is a harmful air pollutant and nicotine dependence is the essential cause of the tobacco epidemic. Since mitochondrial abnormalities are associated with substance addiction, in this work we used mitochondrial DNA (mtDNA) copy number as an indicator of mitochondrial function to investigate whether nicotine addicts also exhibit mitochondrial abnormalities. We found significantly lower mtDNA copy number in the peripheral blood of healthy nicotine addicts than in non-smokers, indicating that long-term nicotine exposure through smoking has detrimental effects on mitochondria. We also examined the effects of nicotine on mtDNA levels in a rat conditioned place preference (CPP) model of addiction and in cultured neuron cells, which revealed that the mtDNA copy number was significantly reduced in the hippocampus of CPP rats, in human neuroblastoma SH-SY5Y cells, and in rat pheochromocytoma PC12 cells, suggesting that significantly reduced mtDNA copy number is a potential biomarker of nicotine addiction. In SH-SY5Y cells, nicotine treatment induced several mitochondrial defects, such as increased mtDNA damage, increased reactive oxygen species (ROS) levels, decreased mitochondrial membrane potential (△Ψm), and stimulation of autophagic flux via transcriptional up-regulation of several autophagy-related genes and elevated marker protein accumulation, although genes controlling mtDNA replication were unaffected. In addition, pretreatment with the autophagy inhibitor Bafilomycin A1 led to accumulation of microtubule-associated protein 1 light chain 3b-II (LC3B-II) and counteracted the nicotine-induced decrease in mtDNA copy number. These results were recapitulated in PC12 cells, which also showed significant down-regulation of the marker SQSTM1/P62, suggesting that the decrease in mtDNA copy number is mediated by autophagy. This study shows that prolonged nicotine exposure, such as that in nicotine addicts, leads to a decrease of mtDNA copy number in neurons due to enhanced induction of autophagy. CAPSULE: It was found that smoking or nicotine exposure decreased mtDNA copy number based on population, animal, and cell models, and these effects appear to be mediated by autophagy.

Anxiolytic, Promnesic, Anti-Acetylcholinesterase and Antioxidant Effects of Cotinine and 6-Hydroxy-L-Nicotine in Scopolamine-Induced Zebrafish (Danio rerio) Model of Alzheimer's Disease

Cotinine (COT) and 6-hydroxy-L-nicotine (6HLN) are two nicotinic derivatives that possess cognitive-improving abilities and antioxidant properties in different rodent models of Alzheimer's disease (AD), eluding the side-effects of nicotine (NIC), the parent molecule. In the current study, we evaluated the impact of COT and 6HLN on memory deterioration, anxiety, and oxidative stress in the scopolamine (SCOP)-induced zebrafish model of AD. For this, COT and 6HLN were acutely administered by immersion to zebrafish that were treated with SCOP before testing. The memory performances were assessed in Y-maze and object discrimination (NOR) tasks, while the anxiety-like behavior was evaluated in the novel tank diving test (NTT). The acetylcholinesterase (AChE) activity and oxidative stress were measured from brain samples. The RT-qPCR analysis was used to evaluate the npy, egr1, bdnf, and nrf2a gene expression. Our data indicated that both COT and 6HLN attenuated the SCOP-induced anxiety-like behavior and memory impairment and reduced the oxidative stress and AChE activity in the brain of zebrafish. Finally, RT-qPCR analysis indicated that COT and 6HLN increased the npy, egr1, bdnf, and nrf2a gene expression. Therefore, COT and 6HLN could be used as tools for improving AD conditions.

Nicotine exposure potentiates lung tumorigenesis by perturbing cellular surveillance

BACKGROUND

Nicotine is a major tobacco component and found at circulating concentrations in smokers' bloodstreams. Although considered a non-carcinogenic substance, nicotine rapidly defuses to tissues after being inhaled, inviting effects on cellular physiology, particularly in the lung. Widespread increased use of nicotine-based e-cigarettes, especially in younger adults, creates an urgent need for improved understanding of nicotine's potential to impact human health.

METHODS

Biological and biochemistry methods were used to interrogate the potential for nicotine to weaken the genetic integrity of murine and human-lung epithelial cells.

RESULTS

We demonstrate that nicotine potentiates the growth of the lung epithelial cells in a dose-response fashion. Nicotine elicits an acute increase in reactive oxygen species (ROS), which persists at moderately high levels throughout the duration of nicotine exposure. The aberrant increases in ROS appear to induce ER stress and UPR activation, as reflected by BIP upregulation and PERK phosphorylation. Furthermore, prolonged nicotine exposure interferes with p53 function triggered by sodium arsenite. Unless p53 is suppressed, persistent nicotine exposure does not induce colony formation by lung epithelial cells in soft agar.

CONCLUSION

The data suggest that nicotine treatment, by perturbing intracellular redox state and altering p53 function, can create a pro-tumorigenic environment in lung epithelium. The results suggest caution in using nicotine replacement therapies and e-cigarettes.

Attenuation in Nicotinic Acetylcholine Receptor α9 and α10 Subunit Double Knock-Out Mice of Experimental Autoimmune Encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is attenuated in nicotinic acetylcholine receptor (nAChR) α9 subunit knock-out (α9 KO) mice. However, protection is incomplete, raising questions about roles for related, nAChR α10 subunits in ionotropic or recently-revealed metabotropic contributions to effects. Here, we demonstrate reduced EAE severity and delayed onset of disease signs in nAChR α9/α10 subunit double knock-out (DKO) animals relative to effects in wild-type (WT) control mice. These effects are indistinguishable from contemporaneously-observed effects in nicotine-treated WT or in α9 KO mice. Immune cell infiltration into the spinal cord and brain, reactive oxygen species levels in vivo, and demyelination, mostly in the spinal cord, are reduced in DKO mice. Disease severity is not altered relative to WT controls in mice harboring a gain-of-function mutation in α9 subunits. These findings minimize the likelihood that additional deletion of nAChR α10 subunits impacts disease differently than α9 KO alone, whether through ionotropic, metabotropic, or alternative mechanisms. Moreover, our results provide further evidence of disease-exacerbating roles for nAChR containing α9 subunits (α9*-nAChR) in EAE inflammatory and autoimmune responses. This supports our hypothesis that α9*-nAChR or their downstream mediators are attractive targets for attenuation of inflammation and autoimmunity.

Snail-Modulated MicroRNA 493 Forms a Negative Feedback Loop with the Insulin-Like Growth Factor 1 Receptor Pathway and Blocks Tumorigenesis

In this study, we have identified one microRNA, microRNA 493 (miR-493), which could simultaneously and directly regulate multiple genes downstream of the insulin-like growth factor 1 receptor (IGF1R) pathway, including IGF1R, by binding with complementary sequences in the 3' untranslated region (UTR) of mRNAs of IGF1R, insulin receptor substrate 1 (IRS1), and mitogen-activated protein kinase 1 (MAPK1), thereby potentiating their inhibitory function at multiple levels in development and progression of cancers. This binding was further confirmed by pulldown of miR with AGO-2 antibody. Further, results from head and neck samples showed that miR-493 levels were significantly downregulated in tumors, with a concomitant increase in the expression of IGF1R and key downstream effectors. Functional studies from miR-493 overexpression cells and nude-mouse models revealed the tumor suppressor functions of miR-493. Regulation studies revealed that Snail binds to the miR-493 promoter and represses it. We found the existence of a dynamic negative feedback loop in the regulation of IGF1R and miR-493 mediated via Snail. Our study showed that nicotine treatment significantly decreases the levels of miR-493-with a concomitant increase in the levels of Snail-an indication of progression of cells toward tumorigenesis, reestablishing the role of tobacco as a major risk factor for head and neck cancers and elucidating the mechanism behind nicotine-mediated tumorigenesis.

Global gene expression profile of peripheral blood mononuclear cells challenged with Theileria annulata in crossbred and indigenous cattle

Bovine tropical theileriosis is an important haemoprotozoan disease associated with high rates of morbidity and mortality particularly in exotic and crossbred cattle. It is one of the major constraints of the livestock development programmes in India and Southeast Asia. Indigenous cattle (Bos indicus) are reported to be comparatively less affected than exotic and crossbred cattle. However, genetic basis of resistance to tropical theileriosis in indigenous cattle is not well documented. Recent studies incited an idea that differentially expressed genes in exotic and indigenous cattle play significant role in breed specific resistance to tropical theileriosis. The present study was designed to determine the global gene expression profile in peripheral blood mononuclear cells derived from indigenous (Tharparkar) and cross-bred cattle following in vitro infection of T. annulata (Parbhani strain). Two separate microarray experiments were carried out each for cross-bred and Tharparkar cattle. The cross-bred cattle showed 1082 differentially expressed genes (DEGs). Out of total DEGs, 597 genes were down-regulated and 485 were up-regulated. Their fold change varied from 2283.93 to -4816.02. Tharparkar cattle showed 875 differentially expressed genes including 451 down-regulated and 424 up-regulated. The fold change varied from 94.93 to -19.20. A subset of genes was validated by qRT-PCR and results were correlated well with microarray data indicating that microarray results provided an accurate report of transcript level. Functional annotation study of DEGs confirmed their involvement in various pathways including response to oxidative stress, immune system regulation, cell proliferation, cytoskeletal changes, kinases activity and apoptosis. Gene network analysis of these DEGs plays an important role to understand the interaction among genes. It is therefore, hypothesized that the different susceptibility to tropical theileriosis exhibited by indigenous and crossbred cattle is due to breed-specific differences in the dealing of infected cells with other immune cells, which ultimately influence the immune response responded against T. annulata infection.

Nucleosome Repositioning: A Novel Mechanism for Nicotine- and Cocaine-Induced Epigenetic Changes

Drugs of abuse modify behavior by altering gene expression in the brain. Gene expression can be regulated by changes in DNA methylation as well as by histone modifications, which alter chromatin structure, DNA compaction and DNA accessibility. In order to better understand the molecular mechanisms directing drug-induced changes in chromatin structure, we examined DNA-nucleosome interactions within promoter regions of 858 genes in human neuroblastoma cells (SH-SY5Y) exposed to nicotine or cocaine. Widespread, drug- and time-resolved repositioning of nucleosomes was identified at the transcription start site and promoter region of multiple genes. Nicotine and cocaine produced unique and shared changes in terms of the numbers and types of genes affected, as well as repositioning of nucleosomes at sites which could increase or decrease the probability of gene expression based on DNA accessibility. Half of the drug-induced nucleosome positions approximated a theoretical model of nucleosome occupancy based on physical and chemical characteristics of the DNA sequence, whereas the basal or drug naïve positions were generally DNA sequence independent. Thus we suggest that nucleosome repositioning represents an initial dynamic genome-wide alteration of the transcriptional landscape preceding more selective downstream transcriptional reprogramming, which ultimately characterizes the cell- and tissue-specific responses to drugs of abuse.

Connections of nicotine to cancer

This Opinion article discusses emerging evidence of direct contributions of nicotine to cancer onset and growth. The list of cancers reportedly connected to nicotine is expanding and presently includes small-cell and non-small-cell lung carcinomas, as well as head and neck, gastric, pancreatic, gallbladder, liver, colon, breast, cervical, urinary bladder and kidney cancers. The mutagenic and tumour-promoting activities of nicotine may result from its ability to damage the genome, disrupt cellular metabolic processes, and facilitate growth and spreading of transformed cells. The nicotinic acetylcholine receptors (nAChRs), which are activated by nicotine, can activate several signalling pathways that can have tumorigenic effects, and these receptors might be able to be targeted for cancer therapy or prevention. There is also growing evidence that the unique genetic makeup of an individual, such as polymorphisms in genes encoding nAChR subunits, might influence the susceptibility of that individual to the pathobiological effects of nicotine. The emerging knowledge about the carcinogenic mechanisms of nicotine action should be considered during the evaluation of regulations on nicotine product manufacturing, distribution and marketing.

Nicotine-induced expression of low-density lipoprotein receptor in oral epithelial cells

Background

Nicotine use is one of the most important risk factors for the development of cardiovascular and periodontal diseases. Numerous reports have suggested the possible contribution of disturbed lipid metabolism for the development of both disease groups. Despite these observations, little is known about the relationship between tobacco smoking and the development of these diseases. Our previous microarray data revealed that nicotine induced low-density lipoprotein receptor (LDLR) expression in oral epithelial cells (OECs). The aim of the present study was to confirm nicotine-mediated LDLR induction and to elucidate the signaling mechanisms leading to the augmented expression of LDLR in OECs.

Methods and Results

LDLR and nicotinic acetylcholine receptor (nAChR) subunit expression was detected by real-time PCR. The production of LDLR was demonstrated by immunofluorescence staining. nAChR-mediated LDLR induction was examined by pre-incubation of the cells with its specific inhibitor, α-bungarotoxin (α-BTX). The functional importance of transcription factor specific protein 1 (Sp1) was examined by luciferase assay, mithramycin pre-incubation or by small interfering RNA (siRNA) transfection. The specific binding of Sp1 to R3 region of LDLR 5’-untranslated region was demonstrated with electrophoretic mobility shift assay (EMSA) and streptavidin-agarose precipitation assay followed by western blotting. The results confirmed that nicotine induced LDLR expression at the transcriptional level. Nicotine was sensed by nAChR and the signal was transduced by Sp1 which bound to the R3 region of LDLR gene. Augmented production of LDLR in the gingival epithelial cells was further demonstrated by immunofluorescence staining using the gingival tissues obtained from the smoking patients.

Conclusions

Taken together, the results suggested that nicotine might contribute to the development of both cardiovascular and periodontal diseases by inducing the LDLR in OECs thereby disturbing lipid metabolism.

Development of novel approach to diagnostic imaging of lung cancer with 18F-Nifene PET/CT using A/J mice treated with NNK

Development of novel methods of early diagnosis of lung cancer is one of the major tasks of contemporary clinical and experimental oncology. In this study, we utilized the tobacco nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung cancer in A/J mice as an animal model for development of a new imaging technique for early diagnosis of lung cancer. Lung cancer cells in A/J mice overexpress nicotinic acetylcholine receptors. Longitudinal CT scans were carried out over a period of 8 months after NNK treatment, followed by PET/CT scans with 18F-Nifene that binds to α4-made nicotinic receptors with high affinity. PET/CT scans of lungs were also obtained ex vivo. CT revealed the presence of lung nodules in 8-month NNK-treated mice, while control mice had no tumors. Imaging of live animals prior to necropsy allowed correlation of results of tumor load via PET/CT and histopathological findings. Significant amount of 18F-Nifene was seen in the lungs of NNK-treated mice, whereas lungs of control mice showed only minor uptake of 18F-Nifene. Quantitative analysis of the extent and amount of 18F-Nifene binding in lung in vivo and ex vivo demonstrated a higher tumor/nontumor ratio due to selective labeling of tumor nodules expressing abundant α4 nicotinic receptor subunits. For comparison, we performed PET/CT studies with 18F-FDG, which is used for the imaging diagnosis of lung cancer. The tumor/nontumor ratios for 18F-FDG were lower than for 18F-Nifene. Thus, we have developed a novel diagnostic imaging approach to early diagnosis of lung cancer using 18F-Nifene PET/CT. This technique allows quantitative assessment of lung tumors in live mice, which is critical for establishing tumor size and location, and also has salient clinical implications.

Muscle sarcomas and alopecia in A/J mice chronically treated with nicotine

AIMS

To evaluate the pathobiologic effects of long-term treatment with nicotine of A/J mice susceptible to tobacco-induced lung carcinogenesis.

MAIN METHODS

Experimental group of mice received subcutaneous injections of the LD(50) dose of (-)nicotine hydrogen tartrate of 3 mg/kg/day, 5 days per week for 24 months, and control group received the vehicle phosphate-buffered saline.

KEY FINDINGS

Nicotine treated mice, 78.6%, but none of control of mice, developed neoplasms originating from the uterus or skeletal muscle. Examination of the uterine neoplasms revealed leiomyosarcomas, composed of whorled bundles of smooth-muscle like cells with large and hyperchromatic nuclei. Sections of the thigh neoplasms revealed densely cellular tumors composed of plump spindle cells, with occasional formation of 'strap' cells, containing distorted striations. Both neoplasms were positive for desmin staining. A solitary pulmonary adenoma with papillary architecture also occurred in one nicotine treated mouse. Experimental mice also developed transient balding starting as small patches of alopecia that progressed to distinct circumscribed areas of complete hair loss or large areas of diffuse hair loss.

SIGNIFICANCE

We demonstrate for the first time that chronic nicotine treatment can induce the development of muscle sarcomas as well as transient hair loss. These findings may help explain the association of childhood rhabdomyosarcoma with parental smoking and earlier onset of balding in smokers. It remains to be determined whether the pathobiologic effects of nicotine result from its receptor-mediated action and/or its tissue metabolites cotinine and N'-nitrosonornicotine, or toxic effects of reactive oxygen species activated due to possible intracellular accumulation of nicotine.

Modulation of innate immune-related pathways in nicotine-treated SH-SY5Y cells

Although nicotine has a broad impact on both the central and peripheral nervous systems, the molecular mechanisms remain largely unknown, especially at the signaling pathway level. To investigate that aspect, we employed both conventional molecular techniques, such as quantitative real-time PCR and Western blotting analysis, and high-throughput microarray approach to identify the genes and signaling pathways that are modulated by nicotine. We found 14 pathways significantly altered in SH-SY5Y neuroblastoma cells. Of these, the Toll-like receptor pathway (TLR; p = 2.57 × 10(-4)) is one of the most important innate immune pathways. The death receptor pathway (DR; p = 8.71 × 10(-4)), whose transducers coordinate TLR signals and help conduct the host immune response to infection, was also significantly changed by nicotine. Furthermore, we found that several downstream pathways of TLR and DR signaling, such as PI3K/AKT signaling (p = 9.55 × 10(-6)), p38 signaling (p = 2.40 × 10(-6)), and ERK signaling (p = 1.70 × 10(-4)), were also significantly modulated by nicotine. Interestingly, most of the differentially expressed genes in these pathways leading to nuclear factor κB (NF-κB) activation and those important inhibitors of pathways leading to apoptosis, including FLIP and Bcl-2, were up-regulated by nicotine. Taken together, our findings demonstrate that nicotine can regulate multiple innate immune-related pathways, and our data thus provide new clues to the molecular mechanisms underlying nicotine's regulatory effects on neurons.

RUNX transcription factors: association with pediatric asthma and modulated by maternal smoking

Intrauterine smoke exposure (IUS) is a strong risk factor for development of airways responsiveness and asthma in childhood. Runt-related transcription factors (RUNX1-3) have critical roles in immune system development and function. We hypothesized that genetic variations in RUNX1 would be associated with airway responsiveness in asthmatic children and that this association would be modified by IUS. Family-based association testing analysis in the Childhood Asthma Management Program genome-wide genotype data showed that 17 of 100 RUNX1 single-nucleotide polymorphisms (SNPs) were significantly (P < 0.03-0.04) associated with methacholine responsiveness. The association between methacholine responsiveness and one of the SNPs was significantly modified by a history of IUS exposure. Quantitative PCR analysis of immature human lung tissue with and without IUS suggested that IUS increased RUNX1 expression at the pseudoglandular stage of lung development. We examined these associations by subjecting murine neonatal lung tissue with and without IUS to quantitative PCR (N = 4-14 per group). Our murine model showed that IUS decreased RUNX expression at postnatal days (P)3 and P5 (P < 0.05). We conclude that 1) SNPs in RUNX1 are associated with airway responsiveness in asthmatic children and these associations are modified by IUS exposure, 2) IUS tended to increase the expression of RUNX1 in early human development, and 3) a murine IUS model showed that the effects of developmental cigarette smoke exposure persisted for at least 2 wk after birth. We speculate that IUS exposure-altered expression of RUNX transcription factors increases the risk of asthma in children with IUS exposure.

Nicotine-mediated suppression of the retinoic acid metabolizing enzyme CYP26A1 limits the oncogenic potential of breast cancer

Tobacco smoke influences cancer development in tissues that are not directly exposed, and epidemiological studies have indicated that smoking women might experience decreased risk of breast cancer as a result of antiestrogenic effects. However, it remains to be clarified whether nicotine, one of the major addictive and best-investigated constituents of tobacco smoke, has any effect on breast cancer. Our recent work demonstrated that the retinoic acid metabolizing enzyme CYP26A1 enhances oncogenic and cell survival properties of breast carcinoma cells, implying a role as an oncogene. Here, we present evidence that nicotine significantly suppresses constitutive expression of CYP26A1, and that cells treated with nicotine exhibit enhanced sensitivity to apoptosis. In addition, nicotine may inhibit anchorage independent growth, cellular invasiveness and motility. These data show that nicotine can limit CYP26A1-mediated oncogenic characteristics, and suggest mechanisms by which nicotine might inhibit breast cancer development.

Nicotinic modulation of gene expression in osteoblast cells, MG-63

Exposure to nicotine causes a broad range of biological and molecular effects on osteoblasts which are known to play a crucial role in bone metabolism and fracture healing. Most effects of nicotine on the osteoblasts are long-term adaptations at the genomic level. To identify the nicotine-regulated genes, the Agilent technologies whole human genome gene expression microarray was performed on RNA samples from osteoblast-like cells, MG-63, exposed to 100 μM nicotine. Repeat and cross-controlled microarray analyses revealed 842 genes whose expression was consistently altered at P<0.05 level following nicotine treatment. Gene ontology analysis suggested effects of nicotine on various biological and cellular processes which were associated with survival, proliferation, differentiation and apoptosis processes within the cell. Quantitative real-time reverse transcriptase PCR analysis confirmed altered expression in 7 out of 9 genes tested. The identified genes tested in the current study support our previous report that nicotine regulates the expression of genes that promote osteoblast proliferation and/or anti-apoptosis processes. Furthermore, using nicotinic acetylcholine receptor antagonists blocked the majority of the nicotine effects, indicating that these changes are dependent on nAChR activation. These results established a novel and consistent nicotinic activation of nAChR in osteoblast cells which has a broad role affecting cellular physiology through modulation of gene expression.

Genome-wide expression analysis reveals diverse effects of acute nicotine exposure on neuronal function-related genes and pathways

Previous human and animal studies demonstrate that acute nicotine exposure has complicated influences on the function of the nervous system, which may lead to long-lasting effects on the behavior and physiology of the subject. To determine the genes and pathways that might account for long-term changes after acute nicotine exposure, a pathway-focused oligoarray specifically designed for drug addiction research was used to assess acute nicotine effect on gene expression in the neuron-like SH-SY5Y cells. Our results showed that 295 genes involved in various biological functions were differentially regulated by 1 h of nicotine treatment. Among these genes, the expression changes of 221 were blocked by mecamylamine, indicating that the majority of nicotine-modulated genes were altered through the nicotinic acetylcholine receptors (nAChRs)-mediated signaling process. We further identified 14 biochemical pathways enriched among the nicotine-modulated genes, among which were those involved in neural development/synaptic plasticity, neuronal survival/death, immune response, or cellular metabolism. In the genes significantly regulated by nicotine but blocked by mecamylamine, 13 enriched pathways were detected. Nine of these pathways were shared with those enriched in the genes regulated by nicotine, including neuronal function-related pathways such as glucocorticoid receptor signaling, p38 MAPK signaling, PI3K/AKT signaling, and PTEN signaling, implying that nAChRs play important roles in the regulation of these biological processes. Together, our results not only provide insights into the mechanism underlying the acute response of neuronal cells to nicotine but also provide clues to how acute nicotine exposure exerts long-term effects on the nervous system.

Replication and extension of association of choline acetyltransferase with nicotine dependence in European and African American smokers

Choline acetyltransferase is critical in the synthesis of acetylcholine and regulation of cholinergic neuron functions. We recently reported association of the encoding gene ChAT with both smoking cessation and nicotine dependence (ND) in two independent European American (EA) samples; however, in the replication sample, only limited SNPs partially covering the gene were examined. In this study, we examined the association of 14 SNPs, which cover the entire gene, with ND, assessed by smoking quantity (SQ), heaviness of smoking index (HSI), and Fagerström Test for ND (FTND), in 2,037 subjects from 602 families of African American (AA) or EA origin. Individual SNP-based association analysis revealed that five SNPs showed nominal association with at least one ND measure in one of the samples (P = 0.022-0.042); none remained significant after correction for multiple testing. Haplotype-based association analysis revealed that haplotypes G-G-A-C, formed by rs1880676-rs3810950-rs10082479-rs8178990 (P = 0.005-0.0178), and G-G-T-C-G-C, formed by rs1880676-rs3810950-rs10082479-rs8178990-rs3793790-rs12266458 (P = 0.00247-0.00468), displayed significant association with all three ND measures in the AA sample, as did haplotype T-C-G-A-T, formed by rs12266458-rs11101191-rs8178991-rs4838544-rs4838547 (P = 0.00741-0.0103), in the EA sample. All these detected haplotype-based associations remained significant after correction for all major haplotypes for a given SNP combination. Together, our findings, in conjunction with the previous report of the association, warrant further investigation of ChAT in ND.

Genes associated with alcohol abuse and tobacco smoking in the human nucleus accumbens and ventral tegmental area

BACKGROUND

The incidence of alcohol and tobacco co-abuse is as high as 80%. The molecular mechanism underlying this comorbidity is virtually unknown, but interactions between these drugs have important implications for the development of and recovery from drug dependence.

METHODS

We investigated the effects of chronic tobacco and alcohol abuse and the interaction of the 2 behaviors on global gene expression in the human nucleus accumbens using cDNA microarrays and 20 alcoholic and control cases, with and without smoking comorbidity. Changes in gene expression were established by factorial ANOVA. Unsupervised hierarchical clustering was utilized to probe the strength of the data sets. Applying real-time PCR differential expression of candidate genes was confirmed in the nucleus accumbens and explored further in a second core region of the mesolimbic system, the ventral tegmental area.

RESULTS

Subjecting the data sets derived from microarray gene expression screening to unsupervised hierarchical clustering tied the cases into distinct groups. When considering all alcohol-responsive genes, alcoholics were separated from nonalcoholics with the exception of 1 control case. All smokers were distinguished from nonsmokers based on similarity in expression of smoking-sensitive genes. In the nucleus accumbens, alcohol-responsive genes were associated with transcription, lipid metabolism, and signaling. Smoking-sensitive genes were predominantly assigned to functional groups concerned with RNA processing and the endoplasmic reticulum. Both drugs influenced the expression of genes involved in matrix remodeling, proliferation, and cell morphogenesis. Additionally, a gene set encoding proteins involved in the canonical pathway "regulation of the actin cytoskeleton" was induced in response to alcohol and tobacco co-abuse and included. Alcohol abuse elevated the expression of candidate genes in this pathway in the nucleus accumbens and ventral tegmental area, while smoking comorbidity blunted this induction in the ventral tegmental area.

CONCLUSIONS

The region-specific modulation of alcohol-sensitive gene expression by smoking may have important consequences for alcohol-induced aberrations within the mesolimbic dopaminergic system.

Gene regulation of alpha4beta2 nicotinic receptors: microarray analysis of nicotine-induced receptor up-regulation and anti-inflammatory effects

alpha4beta2 Nicotinic acetylcholine receptors play an important role in the reward pathways for nicotine. We investigated whether receptor up-regulation of alpha4beta2 nicotinic acetylcholine receptors involves expression changes for non-receptor genes. In a microarray analysis, 10 muM nicotine altered expression of 41 genes at 0.25, 1, 8 and 24 h in halpha4beta2 SH-EP1 cells. The maximum number of gene changes occurred at 8 h, around the initial increase in (3)[H]-cytisine binding. Quantitative RT-PCR corroborated gene induction of endoplasmic reticulum proteins CRELD2, PDIA6, and HERPUD1, and suppression of the pro-inflammatory cytokines IL-1beta and IL-6. Nicotine suppresses IL-1beta and IL-6 expression at least in part by inhibiting NFkappaB activation. Antagonists dihydro-beta-erythroidine and mecamylamine blocked these nicotine-induced changes showing that receptor activation is required. Antagonists alone or in combination with nicotine suppressed CRELD2 message while increasing alpha4beta2 binding. Additionally, small interfering RNA knockdown of CRELD2 increased basal alpha4beta2 receptor expression, and antagonists decreased CRELD2 expression even in the absence of alpha4beta2 receptors. These data suggest that endoplasmic reticulum proteins such as CRELD2 can regulate alpha4beta2 expression, and may explain antagonist actions in nicotine-induced receptor up-regulation. Further, the unexpected finding that nicotine suppresses inflammatory cytokines suggests that nicotinic alpha4beta2 receptor activation promotes anti-inflammatory effects similar to alpha7 receptor activation.

Nicotinic acetylcholine receptor-mediated calcium signaling in the nervous system

Based on the composition of the five subunits forming functional neuronal nicotinic acetylcholine receptors (nAChRs), they are grouped into either heteromeric (comprising both alpha and beta subunits) or homomeric (comprising only alpha subunits) receptors. The nAChRs are known to be differentially permeable to calcium ions, with the alpha7 nAChR subtype having one of the highest permeabilities to calcium. Calcium influx through nAChRs, particularly through the alpha-bungarotoxin-sensitive alpha7-containing nAChRs, is a very efficient way to raise cytoplasmic calcium levels. The activation of nAChRs can mediate three types of cytoplasmic calcium signals: (1) direct calcium influx through the nAChRs, (2) indirect calcium influx through voltage-dependent calcium channels (VDCCs) which are activated by the nAChR-mediated depolarization, and (3) calcium-induced calcium release (CICR) (triggered by the first two sources) from the endoplasmic reticulum (ER) through the ryanodine receptors and inositol (1,4,5)-triphosphate receptors (IP(3)Rs). Downstream signaling events mediated by nAChR-mediated calcium responses can be grouped into instantaneous effects (such as neurotransmitter release, which can occur in milliseconds after nAChR activation), short-term effects (such as the recovery of nAChR desensitization through cellular signaling cascades), and long-term effects (such as neuroprotection via gene expression). In addition, nAChR activity can be regulated by cytoplasmic calcium levels, suggesting a complex reciprocal relationship. Further advances in imaging techniques, animal models, and more potent and subtype-selective ligands for neuronal nAChRs would help in understanding the neuronal nAChR-mediated calcium signaling, and lead to the development of improved therapeutic treatments.

Nicotine modulates expression of miR-140*, which targets the 3'-untranslated region of dynamin 1 gene (Dnm1)

Nicotine stimulation regulates expression of a diversity of genes, but the underlying mechanisms are largely unknown. MicroRNAs (miRNAs) are short endogenous RNAs known to post-transcriptionally regulate gene expression. To test our hypothesis that miRNAs could mediate nicotine's effect on gene expression regulation, we profiled miRNA expression to explore to what extent miRNAs are modulated by nicotine. Using a rodent miRNA microarray and rat PC12 cell model, we revealed that nicotine selectively modulates expression of multiple miRNAs, indicating that the miRNA pathway is one of cellular mechanisms involved in gene expression regulated by nicotine. Specifically, we demonstrated that nicotine increases expression of miR-140*, coordinated with the nicotine-augmented expression of its host gene WWP2. Further, we demonstrated that miR-140* targets the 3'-untranslated region of dynamin 1 gene (Dnm1), by direct base-pairing. This targeting represses gene translation in the luciferase reporter assay and induces messenger RNA degradation in Dnm1 expression analysis. Consequently, our data indicate that nicotine regulates Dnm1 expression via the miRNA pathway. Because dynamin 1 has an essential role in synaptic endocytosis in the central nervous system, nicotine-induced miRNA-mediated dynamin 1 expression regulation may illustrate its importance in neural plasticity, which underlies a molecular mechanism of nicotine addiction.

Molecular and cellular mechanisms of action of nicotine in the CNS

Nicotine achieves its psychopharmacological effects by interacting with nicotinic acetylcholine receptors (nAChRs) in the brain. There are numerous subtypes of nAChR that differ in their properties, including their sensitivity to nicotine, permeability to calcium and propensity to desensitise. The nAChRs are differentially localised to different brain regions and are found on presynaptic terminals as well as in somatodendritic regions of neurones. Through their permeability to cations, these ion channel proteins can influence both neuronal excitability and cell signalling mechanisms, and these various responses can contribute to the development or maintenance of dependence. However, many questions and uncertainties remain in our understanding of these events and their relevance to tobacco addiction. In this chapter, we briefly overview the fundamental characteristics of nAChRs that are germane to nicotine's effects and then consider the cellular responses to acute and chronic nicotine, with particular emphasis on dopamine systems because they have been the most widely studied in the context of nicotine dependence. Where appropriate, methodological aspects are critically reviewed.

Nicotine promotes mammary tumor migration via a signaling cascade involving protein kinase C and CDC42

Nicotine, one of the major components in tobacco, is at high concentrations in the bloodstream of cigarette smokers. However, the mechanisms of how nicotine affects tumor development and whether nicotine is a potential carcinogen for malignancies induced by secondhand smoking are not fully understood yet. Here, we investigate the signaling pathways by which nicotine potentiates tumorigenesis in human mammary epithelial-like MCF10A or cancerous MCF7 cells. We show that human MCF10A and MCF7 cells both express four subunits of nicotine acetylcholine receptor (nAChR). The treatment of these cells with nicotine enhances the activity of protein kinase C (PKC) alpha without altering the expression level of this kinase. Nicotine also stimulates [(3)H]thymidine incorporation into the genome of these cells as well as forces serum-starved cells to enter S phase of the cell cycle, resulting in growth promotion. Importantly, on nicotine treatment, the mobility of MCF10A and MCF7 cells is enhanced, which can be blocked by the addition of nAChR or PKC inhibitor. Experiments using small interfering RNA knockdown or ectopic expression of cdc42 showed that cdc42 functions as a downstream effector of PKC and is crucial in the regulation of nicotine-mediated migratory activity in the cells. Together, our findings suggest that nicotine, through interacting with its receptor, initiates a signaling cascade that involves PKC and cdc42 and consequently promotes migration in mammary epithelial or tumor cells.

Association of PTPRB gene polymorphism with drug addiction

Several lines of evidence support the involvement of protein tyrosine phosphatase receptor type beta (PTPRB) in addiction. Generally, PTPs interact with both neuronal receptors and cell adhesion molecules, and appear to play roles in neurite growth and neuronal differentiation. We previously identified a role of the cell adhesion molecule NrCAM in polysubstance abuse vulnerability in humans, as well as in the rewarding effects of abused drugs in animals. Furthermore, we have identified genomic regions containing several cell adhesion molecules as polysubstance abuse vulnerability loci by whole-genome association study. The present study of human chromosome 12 loci revealed that the Ser127Gly polymorphism in PTPRB is associated with substance abuse vulnerability in three independent case-control samples (European-American from COGA families, USA, n = 177, P = 0.047; European-American from Maryland, USA, n = 650, P = 0.018; and African-American from Maryland, USA, n = 331, P = 0.009). However, this polymorphism was not associated with alcoholism in Japanese subjects (n = 1,599, P = 0.37). To confirm the importance of PTPRB in responses to drugs of abuse the expression of Ptprb in mouse brain was examined after chronic morphine treatment and found to be up-regulated in some brain regions. Thus, PTPRB is an addiction-associated and drug-regulated gene whose variants may affect substance abuse vulnerability.

Nicotine-induced phosphorylation of phosphorylated cyclic AMP response element-binding protein (pCREB) in hippocampal neurons is potentiated by agrin

The scope of this study was to test whether increased levels of the extracellular matrix molecule (ECM) agrin might enhance nicotine effects on those molecular mechanisms that initiate neuroadaptative processes in the hippocampus, a key brain area for learning and memory. We studied the effects of repetitive applications of neuronal agrin to primary hippocampal cell culture on nicotine-induced phosphorylated cyclic AMP response element-binding protein (pCREB) expression, a marker of neuroadaptation, by using immunofluorescence-based assessment of pCREB-positive neurons. We also tested agrin effects on nicotine-induced expression of a marker of metabolic activation, the immediate early gene c-fos. Agrin was shown to significantly enhance nicotine-induced pCREB, but not c-fos, expression. By using Western blotting analysis, cumulative agrin has been shown to increase nicotine-induced pCREB phosphorylation. These analyses, however, showed that inhibition of the CaMKII pathway blocked general pCREB phosphorylation, whereas inhibition of the MAPK pathway potentiated the synergistic effect of cumulative agrin and nicotine. These findings suggest that increasing the concentration of an ECM molecule, i.e. agrin, may enhance nicotine effects on pCREB and that both MAPK and CaMKII signalling may play a regulatory role.

Nicotine and apoptosis

Cigarette smoking is associated with a plethora of different diseases. Nicotine is the addictive component of cigarette but also acts onto cells of the non-neuronal system, including immune effector cells. Although nicotine itself is usually not referred to as a carcinogen, there is ongoing debate whether nicotine functions as a 'tumor enhancer.' By binding to nicotinic acetylcholine receptors, nicotine deregulates essential biological processes like angiogenesis, apoptosis, and cell-mediated immunity. Apoptosis plays critical roles in a wide variety of physiologic processes during fetal development and in adult tissue and is also a fundamental aspect of the biology of malignant diseases. This review provides an overlook how nicotine influences apoptotic processes and is thus directly involved in the etiology of pathological conditions like cancer and obstructive diseases.

Analysis of gene expression profiles in rat hippocampus following treatment with nicotine and an alpha7 nAChR selective agonist

The nicotinic acetylcholine receptors (nAChRs) play critical roles in neuronal transmission and modulation. Among the diverse nAChRs, the alpha7 subtype has been considered as a potential therapeutic target for treating cognitive deficits associated with neuropsychiatric and neurodegenerative diseases. Although a number of mechanisms including neurotransmitter and biochemical effects linking alpha7 nAChR activation and cognitive function are beginning to be described, the underlying molecular processes especially following repeated administration remain unclear. To address this, we have performed gene expression analysis in rats treated with nicotine and a selective alpha7 nAChR agonist, PNU-282987. Our results showed significant overlap in gene expression changes induced by PNU-282987 and nicotine, suggesting convergent pathways triggered by these compounds. Treatment with nicotine also resulted in regulation of a number of genes that were not regulated by PNU-282987, consistent with the interaction of nicotine with other nAChRs beyond the alpha7 subtype. Interestingly, these gene expression changes were observed 24 h post-dose, suggesting that both nicotine and PNU-282987 cause protracted changes in gene expression. Overall, our results identify gene expression changes that may contribute to further defining the roles of nAChR activation in cognitive function.

Neuroproteomics and its applications in research on nicotine and other drugs of abuse

The rapidly growing field of neuroproteomics is able to track changes in protein expression and protein modifications underlying various physiological conditions, including the neural diseases related to drug addiction. Thus, it presents great promise in characterizing protein function, biochemical pathways, and networks to understand the mechanisms underlying drug dependence. In this article, we first provide an overview of proteomics technologies and bioinformatics tools available to analyze proteomics data. Then we summarize the recent applications of proteomics to profile the protein expression pattern in animal or human brain tissues after the administration of nicotine, alcohol, amphetamine, butorphanol, cocaine, and morphine. By comparing the protein expression profiles in response to chronic nicotine exposure with those appearing in response to treatment with other drugs of abuse, we identified three biological processes that appears to be regulated by multiple drugs of abuse: energy metabolism, oxidative stress response, and protein degradation and modification. Such similarity indicates that despite the obvious differences among their chemical properties and the receptors with which they interact, different substances of abuse may cause some similar changes in cellular activities and biological processes in neurons.

Muscle and neuronal nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) are integral membrane proteins and prototypic members of the ligand-gated ion-channel superfamily, which has precursors in the prokaryotic world. They are formed by the assembly of five transmembrane subunits, selected from a pool of 17 homologous polypeptides (alpha1-10, beta1-4, gamma, delta, and epsilon). There are many nAChR subtypes, each consisting of a specific combination of subunits, which mediate diverse physiological functions. They are widely expressed in the central nervous system, while, in the periphery, they mediate synaptic transmission at the neuromuscular junction and ganglia. nAChRs are also found in non-neuronal/nonmuscle cells (keratinocytes, epithelia, macrophages, etc.). Extensive research has determined the specific function of several nAChR subtypes. nAChRs are now important therapeutic targets for various diseases, including myasthenia gravis, Alzheimer's and Parkinson's diseases, and schizophrenia, as well as for the cessation of smoking. However, knowledge is still incomplete, largely because of a lack of high-resolution X-ray structures for these molecules. Nevertheless, electron microscopy studies on 2D crystals of nAChR from fish electric organs and the determination of the high-resolution X-ray structure of the acetylcholine binding protein (AChBP) from snails, a homolog of the extracellular domain of the nAChR, have been major steps forward and the data obtained have important implications for the design of subtype-specific drugs. Here, we review some of the latest advances in our understanding of nAChRs and their involvement in physiology and pathology.

Strain- and region-specific gene expression profiles in mouse brain in response to chronic nicotine treatment

A pathway-focused complementary DNA microarray and gene ontology analysis were used to investigate gene expression profiles in the amygdala, hippocampus, nucleus accumbens, prefrontal cortex (PFC) and ventral tegmental area of C3H/HeJ and C57BL/6J mice receiving nicotine in drinking water (100 mug/ml in 2% saccharin for 2 weeks). A balanced experimental design and rigorous statistical analysis have led to the identification of 3.5-22.1% and 4.1-14.3% of the 638 sequence-verified genes as significantly modulated in the aforementioned brain regions of the C3H/HeJ and C57BL/6J strains, respectively. Comparisons of differential expression among brain tissues showed that only a small number of genes were altered in multiple brain regions, suggesting presence of a brain region-specific transcriptional response to nicotine. Subsequent principal component analysis and Expression Analysis Systematic Explorer analysis showed significant enrichment of biological processes both in C3H/HeJ and C57BL/6J mice, i.e. cell cycle/proliferation, organogenesis and transmission of nerve impulse. Finally, we verified the observed changes in expression using real-time reverse transcriptase polymerase chain reaction for six representative genes in the PFC region, providing an independent replication of our microarray results. Together, this report represents the first comprehensive gene expression profiling investigation of the changes caused by nicotine in brain tissues of the two mouse strains known to exhibit differential behavioral and physiological responses to nicotine.

Regulation of platelet-derived growth factor signaling pathway by ethanol, nicotine, or both in mouse cortical neurons

BACKGROUND

The higher incidence of smoking among alcoholic subjects suggests the presence of common molecular mechanisms underlying nicotine and alcohol use and abuse. However, these mechanisms are largely unknown. By using cultured fetal mouse cortical neurons as a model system, we sought to identify genes and pathways that are modulated in the cells by ethanol, nicotine, or both.

METHODS

Primary cerebral cortical cultures were prepared from the brains of 14-day-old C57BL/6 mouse fetuses and exposed to ethanol (75 mM), nicotine (0.1 mM), or both for 5 consecutive days. A homeostatic pathway-focused microarray consisting of 638 sequence-verified genes was used to measure transcripts differentially regulated by ethanol, nicotine, or both in 5 drug-treated cortical neuron samples and 5 control samples. Quantitative real-time reverse transcriptase-polymerase chain reaction analysis was used to verify the mRNA expression levels of genes of interest detected from the microarray experiments.

RESULTS

Through a pathway-focused cDNA microarray and balanced experimental design, we identified 65, 111, and 81 significantly regulated genes in the ethanol, nicotine, and ethanol/nicotine-treated neurons, respectively. Of them, the genes of Akt2, Nsg1, Pdgfa, Pfn1, Rbbp7, and Tcfeb were comodulated. The genes differentially expressed in 1 or more treatment groups could be classified into 4 major clusters, with each cluster consisting of genes involved in different biological processes. The platelet-derived growth factor (PDGF) signaling pathway was significantly regulated by all 3 treatments, but by different mechanisms, which may lead to different cellular consequences.

CONCLUSIONS

Our results indicate that the PDGF pathway represents one of the major biochemical mechanisms in the cellular and molecular responses to each drug in cortical neurons. Finally, we demonstrated that the pathway-focused microarray system used in the present study is a valuable tool for dissecting the mechanisms of complex signaling pathways such as the PDGF pathway.

Ventral Tegmental Transcriptome Response to Intermittent Nicotine Treatment and Withdrawal in BALB/cJ, C57BL/6ByJ, and Quasi-Congenic RQI Mice

The aim of this study was to identify neurochemical pathways and candidate genes involved in adaptation to nicotine treatment and withdrawal. Locomotor sensitization was assessed in a nicotine challenge test after exposure to intermittent nicotine treatment and withdrawal. About 24 h after the challenge test the ventral tegmentum of the mesencephaion was dissected and processed using oligonucleotide microarrays with 22,690 probe sets (Affymetrix 430A 2.0). Quasi-congenic RQI, and donor BALB/cJ mice developed significant locomotor sensitization, while sensitization was not significant in the background partner, C57BL/6By. Comparing saline treated controls of C57BL/6ByJ and BALB/cJ by a rigorous statistical microarray analysis method we identified 238 differentially expressed transcripts. Quasi-congenic strains B6.Cb4i5-alpha4/Vad and B6.Ib5i7-beta25A/Vad significantly differed from the background strain in 11 and 11 transcripts, respectively. Identification of several cis- and trans-regulated genes indicates that further work with quasi-congenic strains can quickly lead to mapping of Quantitative Trait Loci for nicotine susceptibility because donor chromosome regions have been mapped in quasi-congenic strains. Nicotine treatment significantly altered the abundance of 41, 29, 54, and 14 ventral tegmental transcripts in strains C57BL/6ByJ, BALB/cJ, B6.Cb4i5-alpha4/Vad, and B6.Ib5i7-beta25A/Vad, respectively. Although transcript sets overlapped to some extent, each strain showed a distinct profile of nicotine sensitive genes, indicating genetic effects on nicotine-induced gene expression. Nicotine-responsive genes were related to processes including regulation of signal transduction, intracellular protein transport, proteasomal ubiquitin-dependent protein catabolism, and neuropeptide signaling pathway. Our results suggest that while there are common regulatory mechanisms across inbred strains, even relatively small differences in genetic constitution can significantly affect transcriptome response to nicotine.

Echinoderm microtubule-associated protein like protein 4, a member of the echinoderm microtubule-associated protein family, stabilizes microtubules

Echinoderm microtubule-associated protein (EMAP) is the major microtubule binding protein in dividing sea urchin (Strongylocentrotus purpuratus) eggs. Echinoderm microtubule-associated protein like protein 4 (Eml4, restrictedly overexpressed proliferation-associated protein 120 kDa (Ropp120)) is one of the five mammalian EMAP homologues, the cellular function of which remains to be elucidated. In our first set of experiments we determined the spatio-temporal expression pattern of Eml4 in mouse brain. Our results demonstrate that Eml4 is a highly developmentally regulated gene with high expression levels in the developing nervous system of E11 embryos declining to low levels in adult. Spatially, Eml4 expression becomes restricted to the olfactory bulb, hippocampus and cerebellum. Transient transfection of a fusion construct of full-length mouse Eml4 with green fluorescent protein (GFP-Eml4) into Cos7 and HeLa cells resulted in colocalization of GFP-Eml4 with microtubules. This colocalization was observed both with microtubules of non-dividing cells and with the mitotic spindle of dividing cells. In addition, transient overexpression of GFP-Eml4 in Cos7 cells resulted in microtubules that were resistant to nocodazole treatment suggesting that Eml4 stabilizes microtubules. A consequence of microtubule stabilization is a net reduction in the amount of free tubulin. Microtubule stabilizing proteins therefore are expected to indirectly decrease the microtubule growth rate. Indeed, transient transfection of GFP-Eml4 resulted in a marked decrease in the microtubule growth rate, which is in line with our hypothesis that Eml4 functions as a microtubule stabilizing protein. In summary, our results suggest that Eml4 is a developmentally regulated protein that colocalizes with and stabilizes microtubules.

Nicotine causes age-dependent changes in gene expression in the adolescent female rat brain

Humans often start smoking during adolescence. Recent results suggest that rodents may also be particularly vulnerable to nicotine dependence during adolescence. We examined the effect of chronic nicotine exposure on gene expression profiles during adolescence in female rats, who were dosed with nicotine (and control animals were dosed with saline) via subcutaneously implanted osmotic minipumps. Brain samples were collected at four ages: before puberty (postnatal day 25), at about the time of puberty in females (postnatal day 35), and after puberty (postnatal days 45 and 55). The expression of 7931 genes in three brain areas was measured using DNA microarrays. Quantitative RT-PCR was also employed to confirm the expression patterns of selected genes. We used a novel clustering technique (principal cluster analysis) to classify 162 nicotine-regulated genes into five clusters, of which only one (cluster A) showed similar patterns of gene expression across all three brain areas (ventral striatum, prefrontal cortex, and hippocampus). Three clusters of genes (A, B, and C) showed dramatic peaks in their nicotine responses at the same age (p35). The other two clusters (D1 and D2) showed smaller peaks and/or valleys in their nicotine responses at p35 and p45. Thus, the age of maximal gene expression response to nicotine in female rats corresponds approximately to the age of maximal behavioral response and the age of puberty.

The nicotinic receptor antagonists abolish pathobiologic effects of tobacco-derived nitrosamines on BEP2D cells

Identification of the mechanisms leading to malignant transformation of respiratory cells may prove useful in the prevention and treatment of tobacco-related lung cancer. Nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) can induce tumors both locally and systemically. In addition to the genotoxic effect, they have been shown to affect lung cells due to ligating the nicotinic acetylcholine receptors (nAChRs) expressed on the plasma membrane. In this study, we sought to establish the role for nAChRs in malignant transformation caused by NNK and NNN. We used the BEP2D cells that represent a suitable model for studying the various stages of human bronchial carcinogenesis. We found that these cells express alpha1, alpha3, alpha5, alpha7, alpha9, alpha10, beta1, beta2, and beta4 nAChR subunits that can form high-affinity binding sites for NNK and NNN. Exposure of BEP2D cells to either NNK or NNN in both cases increased their proliferative potential which could be abolished in the presence of nAChR antagonists alpha-bungarotoxin, which worked most effectively against NNK, or mecamylamine, which was most efficient against NNN. The BEP2D cells stimulated with the nitrosamines showed multifold increases of the transcription of the PCNA and Bcl-2 genes by both real-time polymerase chain reaction and in-cell western assays. To gain a mechanistic insight into NNK- and NNN-initiated signaling, we investigated the expression of genes encoding the signal transduction effectors GATA-3, nuclear factor-kappaB, and STAT-1. Experimental results indicated that stimulation of nAChRs with NNK led to activation of all three signal transduction effectors under consideration, whereas NNN predominantly activated GATA-3 and STAT-1. The GATA-3 protein-binding activity induced by NNK and NNN correlated with elevated gene expression. The obtained results support the novel concept of receptor-mediated action of NNK and NNN placing cellular nAChRs in the center of the pathophysiologic loop, and suggest that an nAChR antagonist may serve as a chemopreventive agent.

Receptor-mediated tobacco toxicity: cooperation of the Ras/Raf-1/MEK1/ERK and JAK-2/STAT-3 pathways downstream of alpha7 nicotinic receptor in oral keratinocytes

The use of tobacco products is associated with an increased incidence of periodontal disease, poor response to periodontal therapy, and a high risk for developing head and neck cancer. Nicotine and tobacco-derived nitrosamines have been shown to exhibit their pathobiologic effects due in part to activation of the nicotinic acetylcholine (ACh) receptors (nAChRs), mainly alpha7 nAChR, expressed by oral keratinocytes (KCs). This study was designed to gain mechanistic insight into alpha7-mediated morbidity of tobacco products in the oral cavity. We investigated the signaling pathways downstream of alpha7 nAChR in monolayers of oral KCs exposed for 24 h to aged and diluted sidestream cigarette smoke (ADSS) or an equivalent concentration of pure nicotine. By both real-time polymerase chain reaction (PCR) and In-cell Western, the KCs stimulated with ADSS or nicotine showed multifold increases of STAT-3. These effects could be completely blocked or significantly (P<0.05) diminished if the cells were pretreated with the alpha7 antagonist alpha-bungarotoxin (alphaBTX) or transfected with anti-alpha7 small interfering RNA (siRNA-alpha7). The use of pathway inhibitors revealed that signaling through the Ras/Raf-1/MEK1/ERK steps mediated alpha7-dependent up-regulation of STAT-3. Targeted mutation of the alpha7 gene prevented ERK1/2 activation by nicotine. Using the gel mobility shift assay, we demonstrated that an increased protein binding activity of STAT-3 caused by ADSS or pure nicotine was mediated by janus-activated kinase (JAK)-2. Activation of JAK-2/STAT-3 pathway could be prevented by alphaBTX or siRNA-alpha7. Thus, nuclear transactivation of STAT-3 in KCs exposed to tobacco products is mediated via intracellular signaling downstream from alpha7, which proceeds via two complementary pathways. The Ras/Raf-1/MEK1/ERK cascade culminates in up-regulated expression of the gene encoding STAT-3, whereas recruitment and activation of tyrosine kinase JAK-2 phosphorylates it. Elucidation of this novel mechanism of nicotine-dependent nuclear transactivation of STAT-3 identifies oral alpha7 nAChR as a promising molecular target to prevent, reverse, or retard tobacco-related periodontal disease and progression of head and neck cancer by receptor inhibitors.

Desensitization of neuronal nicotinic receptors of human neuroblastoma SH-SY5Y cells during short or long exposure to nicotine

Neuronal nicotinic ACh receptors (nAChRs) readily desensitize in the presence of an agonist. However, when the agonist is applied for minutes, hours or days, it is unclear how extensive desensitization is, how long it persists after agonist removal and whether nAChRs consequently change their pharmacological properties. These issues were explored with electrophysiological studies of native receptors of voltage-clamped human neuroblastoma SH-SY5Y cells. Puffer pulses of nicotine (1 mM)-evoked inward currents partly antagonized by methyllycaconitine (MLA; 10 nM) or alpha-conotoxin MII (MII; 10 nM), suggesting contribution by alpha7 and alpha3 subunit containing receptors, respectively. Nicotine-evoked currents desensitized with 150 ms time constant and fully recovered after a few s washout. Although the current induced by 10 min application of nicotine (10 microM) decayed to baseline indicating complete desensitization, puffer applications of maximally effective doses of nicotine still generated small responses (22% of control). Similar responses to puffer-applied nicotine were observed when nicotine was chronically incubated for 8 or 48 h. On nicotine washout, cells recovered their response amplitude within 5 min and then increased it (about 50% of untreated controls) after 30 min without altering response kinetics or sensitivity to MLA and MII. The present results suggest that native nAChRs of SH-SY5Y cells preserved a degree of responsiveness during chronic application of nicotine, and that they rapidly recovered on washout to generate larger responses without changes in kinetics or pharmacology. These data indicate strong compensatory mechanisms to retain nicotinic receptor function during long-term exposure to nicotine.

Nicotinic modulation of gene expression in SH-SY5Y neuroblastoma cells

Exposure to nicotine has a broad range of physiological and psychological effects that can be long lasting and contribute to nicotine dependence. On a time course longer than that needed to activate nicotinic acetylcholine receptor (nAChR) function, nicotine exposure induces functional inactivation of nAChR, upregulation of nAChR radioligand binding sites, and other alterations of cellular functions. To identify possible mechanisms underlying nicotine-induced changes in nAChR numbers and function, we defined changes in gene expression in neuron-like, SH-SY5Y human neuroblastoma cells following 24 h of continuous exposure to 1 mM nicotine. This treatment condition produces both functional inactivation and upregulation of nAChR. Repeat and cross-controlled microarray ( approximately 5000 genes queried) analyses revealed 163 genes whose expression was consistently altered at the p<0.01 level following nicotine treatment. Quantitative, real-time, reverse transcription-polymerase chain reaction analyses confirmed altered expression of thirteen out of fourteen of these genes chosen for further study, including contactin 1, myozenin 2, and ubiquitin-conjugating enzymes E2C and E2S. Inhibition or reversal of these effects by the general nAChR antagonist, d-tubocurarine, indicated that gene expression changes are dependent on nAChR activation. Studies using other nAChR subtype-selective antagonists identified gene expression changes that required activation of both alpha7- and alpha3*-nAChR, alpha7-nAChR alone, or either alpha7- or alpha3beta4*-nAChR, suggesting some convergent and some divergent pathways of gene activation coupled to these nAChR subtypes. These results suggest that longer-term physiological and psychological effects of nicotine exposure and changes in nAChR expression may be due in part to effects on gene expression initiated by interactions with nAChR.

Nicotinic receptor agonists as neuroprotective/neurotrophic drugs. Progress in molecular mechanisms

In the present work we reviewed recent advances concerning neuroprotective/neurotrophic effects of acute or chronic nicotine exposure, and the signalling pathways mediating these effects, including mechanisms implicated in nicotine addiction and nAChR desensitization. Experimental and clinical data largely indicate long-lasting effects of nicotine and nicotinic agonists that imply a neuroprotective/neurotrophic role of nAChR activation, involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR agonists. Compounds interacting with neuronal nAChRs have the potential to be neuroprotective and treatment with nAChR agonists elicits long-lasting neurotrophic effects, e.g. improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Nicotine addiction, which is mediated by interaction with nACh receptors, is believed to involve the modification of signalling cascades that modulate synaptic plasticity and gene expression. Desensitization, in addition to protecting cells from uncontrolled excitation, is recently considered as a form of signal plasticity. nAChR can generate these longe-lasting effects by elaboration of complex intracellular signals that mediate medium to long-term events crucial for neuronal maintenance, survival and regeneration. Although a comprehensive survey of the gene-based molecular mechanisms that underlie nicotine effects has yet not been performed a growing amount of data is beginning to improve our understanding of signalling mechanisms that lead to neurotrophic/neuroprotective responses. Evidence for an involvement of the fibroblast growth factor-2 gene in nAChR mechanisms mediating neuronal survival, trophism and plasticity has been obtained. However, more work is needed to establish the mechanisms involved in the effects of nicotinic receptor subtype activation from cognition-enhancing and neurotrophic effects to smoking behaviour and to determine more precisely the therapeutic objectives in potential nicotinic drug treatments of neurodegenerative diseases.

Proteins differentially expressed in response to nicotine in five rat brain regions: identification using a 2-DE/MS-based proteomics approach

To determine protein expression patterns within the central nervous system (CNS) in response to nicotine, 2-DE/MS was performed on samples from five brain regions of rats that had received nicotine bitartrate by osmotic minipump infusion at a dose of 3.15 mg/kg/day for 7 days. After spot matching and statistical analysis, 41 spots in the amygdala, 49 in the nucleus accumbens (NA), 46 in the prefrontal cortex (PFC), 36 in the striatum, and 28 in the ventral tegmental area (VTA) showed significant differences in the nicotine-treated compared with control samples. Using MALDI-TOF MS peptide fingerprinting, 14 proteins in the amygdala, 11 in the NA, 19 in the PFC, 13 in the striatum, and 19 in the VTA were identified. Several proteins (e.g. dynamin 1, laminin receptors, aldolase A, enolase 1 alpha, Hsc70-ps1, and N-ethylmaleimide-sensitive fusion protein) were differentially expressed in multiple brain regions. By gene ontology analysis, these differentially expressed proteins were grouped into biological process categories, such as energy metabolism, synaptic function, and oxidative stress metabolism. These data, in combination with microarray analysis of mRNA transcripts, have the potential to identify the CNS gene products that show coordinated changes in expression at both the RNA and protein levels in response to nicotine.

Mitogen-activated protein kinase pathway was significantly activated in human bronchial epithelial cells by nicotine

Nicotine is potentially associated with the onset of chronic obstructive pulmonary disease (COPD) and lung cancer. To gain insights into the molecular mechanism underlying such nicotine-induced conditions, microarray- bioinformatics analysis was carried out in the present study to explore the gene expression profiles in human bronchial epithelial cells (HBECs) treated with 5 microM nicotine for 4, 8, and 10 h. Of 1,800 assessed genes overall, 260 (14.4%) were upregulated and 17 (0.9%) down regulated significantly. Gene ontology analysis demonstrated that most of the differentially expressed genes belonged to the category of molecular function, especially to the subcategories of enzyme activity. The integration of obtained information with bioinformatics tools in DAVID and KEGG databases indicated that the greatest number of overexpressed genes was involved in mitogen-activated protein kinase (MAPK) pathway. Membrane array analysis subsequently suggested that both extracellular signal-regulated kinase (ERK) 1/2 and c-Jun-NH(2)-terminal kinase (JNK) signalings but not p38 MAPK signaling were activated in response to nicotine. Pretreatment of HBECs with specific inhibitors against ERK 1/2 and JNK but not p38 could significantly inhibit nicotine-induced interleukin- 8 production. These results suggest that MAPK pathway may mediate the effect of nicotine through ERK 1/2 and JNK but not p38 in HBECs treated with nicotine.

Nicotine modulates expression of amyloid precursor protein and amyloid precursor-like protein 2 in mouse brain and in SH-SY5Y neuroblastoma cells

Epidemiological studies indicate that tobacco smoking can be protective against neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). The objective of the present study was to examine the changes in gene expression induced by chronic oral nicotine administration (100 mug/ml in 2% saccharin for 14 days), with special emphasis on amyloid precursor protein (APP) and its homologue, amyloid precursor-like protein 2 (APLP2), in different brain regions of C57BL/6 mice using a pathway-focused microarray. Our results revealed that nicotine stimulated mRNA expression of APP in the amygdala (64%; P = 0.003) and hippocampus (32%; P = 0.034) and of APLP2 in the amygdala (39%; P = 0.002). These results were verified by quantitative real-time RT-PCR except that expression of APLP2 was also significantly upregulated by nicotine in the hippocampus. In addition, in vitro nicotine treatment of SH-SY5Y neuroblastoma cells resulted in a significant increase in expression of APP protein, soluble APP, and APLP2, whereas co-treatment with mecamylamine (an antagonist of nicotinic acetylcholine receptors) attenuated the stimulating effect of nicotine on APP and APLP2 expression. These findings suggest that nicotine treatment facilitates the increase in the expression of mRNA and protein of the APP and APLP2 genes in rat brain and SH-SY5Y neuroblastoma cells.

Gene expression is differentially regulated by neurotransmitters in embryonic neuronal cortical culture

Neurotransmitters and their receptors have been involved in both proper brain development and neurodevelopmental disorders. The role that nicotinic receptors play in immature cortical neurons was initially investigated by gene profiling using Affymetrix DNA arrays. Both short (15 min) and prolonged (18 h) treatments with nicotine did not induce modification in gene expression, whereas a significant down-regulation of c-fos protein levels was observed after 18 h treatment. Conversely, a brief treatment with the glutamatergic agonist NMDA triggered up-regulation of immediate early genes and transcription factors, which remained unaffected by pre-treatment for 18 h with nicotine. Calcium imaging studies revealed that NMDA activated a sustained increase in intracellular calcium concentration in the majority of neurons, whereas nicotine evoked only a transient calcium increase in a smaller percentage of neurons, suggesting that the calcium signalling response was correlated with activation of gene expression. Nicotine effects on immature cortical neurons perhaps do not require gene regulation but may be still acting on signalling pathways.

NrCAM in addiction vulnerability: positional cloning, drug-regulation, haplotype-specific expression, and altered drug reward in knockout mice

Several lines of evidence support roles for the cell adhesion molecule NrCAM in addictions. Fine mapping within a chromosome 7 region that contains previously linked and associated genomic markers identifies NrCAM haplotypes that are associated with substance abuse vulnerabilities in four samples of abusers and controls. Differential display identifies NrCAM as a drug regulated gene. NrCAM is expressed in neurons linked to reward and memory. NrCAM displays haplotype-specific gene expression in human post-mortem brain samples. Knockout mice display reduced opiate- and stimulant-conditioned place preferences. These observations support NrCAM as a positionally cloned and drug-regulated gene whose variants are likely to change expression and alter substance abuse vulnerabilities in human addictions and animal models of drug reward.

Nicotine-induced sensitization in mice: changes in locomotor activity and mesencephalic gene expression

It is believed that drug-induced behavioral sensitization is an important process in the development of substance dependence. In order to explore mechanisms of sensitization, a mouse model of nicotine-induced locomotor sensitization was established, and effects of the sensitization process on mesencepahlic gene expression were examined. A schedule, which included 3 weeks of intermittent nicotine exposure (0.5 mg/kg, s.c.) and 3 weeks of withdrawal, resulted in locomotor sensitization. Effects of sensitization on mesencephalic expression of approximately 14,000 genes were assessed using oligonucleotide microarrays. Signal intensity differences in samples obtained from repeated nicotine- and saline-exposed animals were analyzed with z-test after False Discovery Rate (FDR) multiple test correction. Genes related to GABA-A receptors and protein phosphatases were among 68 genes showing significantly different expression levels between the saline and the nicotine groups. We hypothesize that some of the gene expression changes in the mesencephalon are involved in pathways leading to nicotine-induced sensitization. Down-regulation of GABA-A receptors induced by repeated nicotine exposure may facilitate dopaminergic neuronal transmission and may contribute to increased locomotor activity.