Background: Drug-induced alterations in gene expression play an important role in the development of addictive behavior. Numerous transcription factors have been implicated in mediating the gene expression changes that occur in drug addiction. Nuclear factor kappa B is an inducible transcription factor complex that is rapidly activated by diverse stimuli. Methods: We performed next-generation high-throughput sequencing of the prefrontal cortex in a mouse model of repeated cocaine administration combined with pharmacological nuclear factor kappa B inhibition to identify nuclear factor kappa B target genes that participate in the cocaine addiction process. Results: We found that the nuclear factor kappa B antagonist sodium diethyldithiocarbamate trihydrate significantly reversed the cocaine-induced expression changes of the amphetamine addiction pathway. Genes that demonstrated differential expression in response to cocaine treatment that was also reversed by sodium diethyldithiocarbamate trihydrate were enriched for the axon guidance pathway. Furthermore, the nuclear factor kappa B homo-dimer motif could be mapped to 86 of these sodium diethyldithiocarbamate trihydrate-reversed genes, which were also enriched for axon guidance. Conclusions: We suggest that nuclear factor kappa B directly modifies the expression of axon guidance pathway members, leading to cocaine sensitization. Our findings reveal the role of prefrontal cortex nuclear factor kappa B activity in addiction and uncover the molecular mechanisms by which nuclear factor kappa B drives changes in the addicted brain. Keywords: addiction, cocaine, nuclear factor kappa B, prefrontal cortex, sodium diethyldithiocarbamate trihydrate Introduction Drug addiction is a global issue that generates extensive harm alter the structure and function of numerous and distinct brain to the health and socioeconomic status of affected individuals regions, at least one of the major constinuents of the mesolim- and inflicts further burdens on society. Chronic addictive behav- bic reward pathway—the ventral tegmental area, the nucleus ior develops as a consequence of progressive and multifaceted accumbens, and the prefrontal cortex (PFC)—is modified by alterations to neural circuits upon repeated administration of all addictive substances (Levy, 2013). In the context of cocaine drugs of abuse (Chao and Nestler, 2004). Though various drugs addiction, it has been demonstrated that the PFC is involved in Received: January 14, 2018; Revised: February 28, 2018; Accepted: March 19, 2018 © The Author(s) 2018. Published by Oxford University Press on behalf of CINP. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, 1 provided the original work is properly cited. For commercial re-use, please contact firstname.lastname@example.org Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 2 | International Journal of Neuropsychopharmacology, 2018 Significance Statement Despite a growing number of treatments, drug addiction continues to be a source of tremendous physical, psychological, social, and economic harm. Understanding the molecular mechanisms by which the brain is altered during the onset of addiction can lead to the development of more effective therapies. It is widely accepted that chronic drug exposure results in changes in gene expression. Here, we investigate the role of the transcription factor NF-κB in mediating these gene expression changes in the prefrontal cortex. Our findings demonstrate the role of NF-κB activity in the prefrontal cortrex in the establishment of cocaine addiction and uncover target genes and biological pathways through which this process occurs. both the primary reinforcing effects of cocaine and long-term through which NF-κB may mediate cocaine-induced cellular and sensitization to cocaine. Previous studies have further demon- behavioral plasticities. To do so, we examined the effects of an strated that PFC-dependent processes, such as executive func- NF-κB inhibitor on the behavioral response to repeated cocaine tion, explicit learning, and memory, are damaged in animal administration and combined our model with high-throughput models of cocaine addiction and in human cocaine abusers transcriptome sequencing to identify target genes activated by (Chao et al., 2014). However, the molecular mechanisms driv- NF-κB in the PFC upon cocaine treatment. We demonstrate the ing altered PFC biology in response to cocaine addiction remain efficacy of pharmacological NF-κB inhibition in counteracting poorly understood, and, as a result, there continues to be a lack the effects of cocaine and, by establishing the genes and path- of effective therapies for addicted patients. ways modulated by NF-κB in response to cocaine, we reveal Though drug-induced changes in the expression of numer - novel targets for further therapeutic intervention. ous neuronal genes contribute to behavioral abnormalities, the origin and causality of these genetic signatures are unclear Materials and Methods (Zhou et al., 2014). Consistent changes in characteristic path- ways suggest the action of specific transcription factors, which Animals respond to environmental changes by binding to regulatory regions of target genes to alter their expression (Baldwin, 1996). Male C57BL/6J mice (purchased from the Academy of Military Medical Science) weighing 25 to 30 g (8 weeks old) at the beginning In the past several decades, numerous transcription factors, such as Fos family protein, cyclic adenosine monophosphate of the experiments were used in this study. Five mice were housed per cage and all mice were given food and water ad libitum. The response element binding protein, nuclear factor kappa B (NF- κB), and myocyte enhancing factor-2, have been implicated in colony was maintained at 22 ± 2°C with a standard 12-h-light/- dark cycle (lights on at 7:00 am). The animals were handled daily the addiction process (Nestler, 2012). NF-κB represents a small family of inducible transcription for 1 week before injection. Testing was performed during the light cycle. All animal protocols were approved by the Review Board of factors that are rapidly activated by diverse external stimuli and therefore serve as critical mediators of many environmen- the Institute of Psychology, Chinese Academy of Sciences, and were performed strictly in accordance with the Guideline for Care and tal inputs (Nestler, 2012). The NF-κB complex is typically held in an inactive form in the cytosol by interaction with members of Use of Laboratory Animals of the Chinese Academy of Sciences. the inhibitor of NF-κB (IκB) family of inhibitory proteins. Upon stimulation by extracellular inducers, IκBs are phosphoryl- Drugs ated by an IκB kinase complex, which leads to ubiquitination and proteosome-mediated degradation of the IκBs. Then, active Cocaine hydrochloride (Qinghai Pharmaceutical Co., Ltd.) and NF-κB, through classical or noncanonical pathways, translo- sodium diethyldithiocarbamate trihydrate (DDTC; NF-κB antag- cates to the nucleus, where it binds consensus κB sequences in onist, Sigma-Aldrich) were dissolved in sterile 0.9% saline and the promoter and enhancer regions of responsive genes (Widera administered i.p. at 20 and 200 mg/kg, respectively. et al., 2006). NF-κB binding sites are found in numerous genes that are known to participate in memory formation and drug Locomotor Sensitization Test addiction: brain-derived growth factor, inducible nitric oxide synthase, and various opioid receptors (Simeonidis et al., 1999; Mice were placed in the center of the field (30 x 30 cm), and total Malek et al., 2001). However, these examples represent a small distance travelled by each animal was recorded for 60 minutes number of NF-κB targets, and there is no evidence whether and analyzed by a computer-based system (Anilab). After each these and other genes are regulated by NF-κB in the PFC during trial, the apparatus was cleaned with a 30% ethanol solution. cocaine addiction or whether they play a causal role in addiction The order of testing was balanced by group. onset and persistence. It had been previously demonstrated that the NF-κB signal- Treatment and Behavioral Testing Procedures ing pathway, including several candidate downstream genes, is Mice were randomly assigned to 4 treatment groups: (1) activated in the nucleus accumbens of mice exposed to chronic cocaine and inhibition of this pathway by a virally expressed saline + saline (SS, n = 10), (2) DDTC + saline (DS, n = 10), (3) DDTC + cocaine (DC, n = 10), and (4) cocaine + saline (CS, n = 10). dominant-negative form of IκB kinase attenuates the addictive effects of cocaine (Russo et al., 2009). However, in the context of The treatment period was 8 days, as shown in Figure 1. On days 1 to 3, baseline locomoter activity of every treatment group cocaine addiction, the importance of NF-κB signaling in the PFC has not been investigated, and the great genome-wide diversity was assessed for 1 hour immediately following an i.p. injection of saline. On days 4 to 8, groups (2) and (3) received an of NF-κB target genes has not been explored. The major goals of this study were to determine whether injection of saline or cocaine, respectively, 30 minutes after an injection of DDTC, while groups (1) and (4) also received an injec- NF-κB signaling in the PFC is important in the development of cocaine addiction and to identify the potential target genes tion of saline or cocaine, respectively, but 30 minutes following Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 Wang et al. | 3 (Tripathi et al., 2015) with a cutoff of P < .05 and a minimum over - lap of 3. These raw sequencing data sets were deposited in the Gene Expression Omnibus of the NCBI (https://www.ncbi.nlm. nih.gov/geo) under accession number GSE108836. Real-Time PCR Validation Validation of DEGs was performed by quantitative reverse-tran- scription PCR (RT-qPCR) using the Maxima SYBR Green qPCR Master Mix kit (Fermentas), according to the manufacturer’s instructions, in an ABI Prism 7500 Sequence Detection System machine (Applied Biosystems Inc). All real-time RT-qPCR data were normalized to SS expression level (see additional data file for primer information). Figure 1. Effect of behavior of sodium diethyldithiocarbamate trihydrate (DDTC; 200 mg/kg) in response to cocaine-addicted mice (20 mg/kg, i.p.). CS, saline+cocaine; DC, DDTC+cocaine; ds, DDTC+saline; SS, saline+saline. All Motif Search results represent means ± SD of 10 independent determinations (n = 10/group) in the behavioral test experiments. ****P < .0001, ***P < .001. To discover DEGs with NF-κB binding sites, we applied the UniProbe Database (http://thebrain.bwh.harvard.edu/nfkb/) to an injection of saline. All mice were put into the locomotor box promoters (-500 to +200 bp relative to the transcription start site) immediately following the second injection and monitored for of DEGs. The z-score cutoff was set to the default value of 4. 1 hour. Data Analysis RNA Sequencing and Bioinformatics Data are expressed as the mean± SEM. Statistical analyses were Two hours after the final (day 8) locomotor activity test, animals performed with GraphPad Prism 6.0 software. Comparisons were killed and their PFCs were surgically excised. The tissue was of means of behavioral sensitization were analyzed by 2-way stored in liquid nitrogen immediately and then transferred to a repeated-measures ANOVA followed by Tukey’s posthoc tests. -80°C freezer. Total RNA was extracted from the frozen tissues using the TIANamp DNA/RNA Isolation Kit (TIANGEN), including Results additional treatment with RNase-free DNase I (Ambion) for 30 minutes at 37°C to remove contaminating DNA. Effects of DDTC on Cocaine-Induced Behavior Then 1 µg of RNA from a pool of 5 animals (200 ng each) per experimental condition was used to generate an mRNA First, we analyzed the effects of the injection of (1) saline + saline sequencing library using the TruSeq RNA Sample Prep Kit (SS), (2) DDTC + saline (DS), (3) DDTC+ cocaine (DC), and (4) (Illumina) following the manufacturer’s protocol. Briefly, polyA cocaine + saline (CS), repeated daily for 5 days, on mouse loco- mRNA was purified and fragmented. Then, first and second motor activity after 3 days of baseline testing. As shown in strand cDNA synthesis was performed, ends were repaired and Figure 1, 2-way repeated-measures ANOVA of the locomotion adenylated, adapters were ligated, and fragments were enriched test results demonstrated that there were significant differences with PCR amplification. High library qualities were verified with in the total distance traveled between the 4 treatment groups an Agilent Technologies 2100 Bioanalyzer (Agilent Technologies). (F = 44.34, P < .001). Posthoc analysis revealed that there was (3,27) Libraries were sequenced using the Illumina HiSEQ2K platform no significant difference between the locomotor activities of (Illumina). each group at baseline (days 1–3). However, total distance trave- FastQC was used to assess RNA-seq quality. Because of the led increased significantly following cocaine treatment (SS vs low quality of the 3’ end of raw reads, the last 20 base-pairs were CS P < .001) and DDTC administration significantly inhibited trimmed from each read. Reads were also trimmed sequen- cocaine-induced activity (CS vs DC P < .001). Additionally, there tially for adapter content. The paired-end reads were aligned was no significant difference between the locomotor activi- to the mouse reference genome (mm9, Jul. 2007) with TopHat ties of DC and SS groups on Day 5 onwards, suggesting that 2.0.9 (Trapnell et al., 2012) using default parameters. Aligned DDTC can completely inhibit the hyperlocomotion induced by bam files were processed by Cufflinks v.2.2.1 (Trapnell et al., repeated cocaine administration. 2010) to generate a transcriptome assembly and to estimate the expression level (fragments per kilobase of transcript per mil- GO and KEGG Pathways Induced by Cocaine lion mapped reads [FPKM]) of all detected isoforms. FPKM was calculated as the number of paired-end reads (a single fragment To understand the molecular mechanisms underlying the effects per end-paired reads) mapped to a gene divided by the number of cocaine and to delineate the functional consequences of DDTC of all fragments mapped to the genome (in millions) and the treatment in the context of cocaine addiction, we performed length of the transcript (in kilobases). The tagwise dispersion mRNA-sequencing of extracted PFCs of mice from each of the 4 was estimated and then used for log fold change calculation. treatment groups, immediately following the 8th and final day Differentially expressed genes (DEGs) were identified by apply- of treatment and testing. A total of approximately 60 million 100 ing the threshold false discovery rate of 0.2 to adjusted P values base-pair paired-end reads were obtained per sample. following Fisher’s exact test (Chen et al., 2011). DEGs induced Of 266 DEGs, 175 genes were upregulated and 91 genes were by cocaine sensitization (logfold_change [CS/SS]) were plotted downregulated in the CS group compared with the SS group against baseline gene expression levels of the SS group (lo Fg - (Figure 2A). We then analyzed whether certain (KEGG) path- PKM) using ggplot2 in R. KEGG pathway, and Gene Ontology ways were enriched for in the list of PFC DEGs and discovered (GO) analyses of DEGs were performed with Metascape software 13 significantly enriched pathways upon repeated cocaine Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 4 | International Journal of Neuropsychopharmacology, 2018 Figure 2. Cocaine and sodium diethyldithiocarbamate trihydrate (DDTC) cause broad changes to the transcriptome. mRNA from prefrontal cortex (PFC) of SS (saline+saline), CS (saline+cocaine), and DS (DDTC+saline) was subjected to RNA sequencing and analysis as described in the methods. (A) MA-plot [M (log ratios); A (mean average)] of differentially expressed genes (DEGs) of cocaine+saline (CS), respectively < (q 0.2). DEGs are represented by green dots. Log2 fold change values for CS vs SS are plotted against average log expression values (fragments per kilobase of transcript per million mapped reads [FPKM]). (B) Chart of enriched pathways of significantly expressed genes in CS (P < .05). (C) MA-plot of DEGs of DDTC+saline (DS), respectively (q < 0.2). DEGs are represented by green dots. Log2 fold change values for DS vs SS are plotted against average log expression values (FPKM). (D) Chart of enriched pathways of significantly expressed genes in DS (P < .05). administration. Among these, 3 pathways were directly related GO and KEGG Analyses Reveal the Effects of to central nervous system function: most notably, the amphet- DDTC on Pathways Altered by Repeated Cocaine amine addiction pathway, as well as the circadian rhythm Administration pathway and amyotrophic lateral sclerosis (ALS) (Figure 2B). Next, we applied the same analyses to study the effects of com- Additional GO analysis revealed multiple terms relevant to bining cocaine with DDTC treatment. As a major goal of this neurological function (supplimentary Figure 1), including reg- study was to identify the target genes by which NF-κB mediates ulation of circadian rhythm (GO:0042752), synaptic vesicles the develoment of cocaine addiction, we sought to find genes (GO:0008021), and MAPK function (GO:0043408 and GO:0017017), whose expression was altered by repeated cocaine treatment which were reported to be involved in the control of synaptic with the condition that this differential expression is abolished plasticity (Thomas and Huganir, 2004). upon NF-κB inhibition by DDTC treatment. In the process of identifying these genes, the next step was to perform a differ - GO and KEGG Pathways Induced by DDTC ential expression analysis between DC and CS groups to obtain a list of DEGs whose expression is affected by DDTC treatment We simultaneously analyzed how DDTC treatment modi- in the context of cocaine treatment. A total 451 DEGs were fies the mouse transcriptome (Figure 2C). A total 143 DEGs upregulated and 410 DEGs were downregulated in DC-treated were upregulated while 58 DEGs were downregulated in DS mice compared with CS-treated mice (Figure 3A). The top 20 sig- compared with SS. KEGG pathway analysis of all DS DEGs nificantly enriched pathways showed that DDTC can regulate revealed a stastically significant enrichment for 11 pathways pathways known to be related to addiction, such as ampheta- (Figure 2D). Interestingly, the MAPK signaling pathway, the cir - mine, calcium signaling, ABC transporters, gap junctions, glu- cadian rhythm (entrainment) pathway, and the focal adhesion tathione metabolism, ALS, glycolysis, Alzheimer’s disease, and pathway, which were significantly enriched in cocaine treat- neuroactive ligand-receptor interaction (Li et al., 2008), as well ment (CS vs SS), were also affected by DDTC treatment, indi- as other pathways related to neuronal function such as circa- cating that cocaine and DDTC modulate several of the same dian entrainment, neuotrophin signaling, and axon guidance molecular pathways in the PFC. GO analysis again revealed (Figure 3B). GO analysis (supplementary Figure 3) showed that numerous enriched pathways related to neuronal function, the terms neuron projection development (GO:0031175), behav- including MAPKs (GO:0017017), synapse (GO:0045202), neuro- ior (GO:0007610), calcium channel activity (GO:0005262), synapse transmitter transport (GO:0006836), central nervous system (GO:0045202), and axon (GO:0030424) were enriched. development (GO:0007417), learning or memory (GO:0007611), We were then interested in isolating pathways from DEGs and neuron projection development (GO:0031175) (supplemen- that met 3 requirements: (1) are altered by cocaine alone tary Figure 2). Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 Wang et al. | 5 Figure 3. Transcriptome-wide response of sodium diethyldithiocarbamate trihydrate (DDTC) to cocaine addiction. (A) MA-plot of differentially expressed genes (DEGs) of DDTC+cocaine (DC), respectively (q < 0.2). DEGs are represented by green dots. Log2 fold change values for DC vs saline+cocaine (CS) are plotted against average log expression values (fragments per kilobase of transcript per million mapped reads [FPKM]). (B) Chart of enriched pathways of significantly expressed genes in DS (P < .05). (C) Venn diagram depicting the overlap of DEGs among DC, DDTC+saline (DS), and CS. (D) Heatmap of comparison of enriched pathways of CS, DS, and DC. (E) Scatter plot of all genes in amphetamine addiction pathway. (Figure 2A); (2) are modulated by DDTC in cocaine-treated (DC) Interestingly, scatter plots (Figure 3Esupplementar ; y mice (Figure 3A); and (3) result from DDTC treatment alone Figure 5) showed that DDTC (DC) significantly reversed the (DS) (Figure 2C). These DEGs and pathways would represent direction of cocaine-induced (CS) gene expression changes of changes in cocaine-sentization that are specifically caused by the amphetamine addiction pathway (P = .0498) but not of the DDTC in DC-treated mice rather than representing a combined ALS pathway (P = .078), indicating that the amphetamine addic- effect of DDTC and cocaine coadministration. The 3 requisite tion pathway is an important pathway by which DDTC modu- DEG data sets are plotted in a Venn diagram (Figure 3C http:// ; lates gene expression changes in response to repeated cocaine bioinfogp.cnb.csic.es/tools/venny/), which interestingly depicts administration. a significant overlap between all 3 data sets, between DC and DS DEGs as well as DC and CS DEGs, but not between CS and DS DDTC Reverses Cocaine-Induced Changes in DEGs, which are not present in the DC group (chi-squared test). Expression of Genes in the Axon Guidance Pathway Next, we performed a 3-way statistical comparison of enriched pathways and GO terms from DEGs induced in CS, DC, and DS While the previous analyses identified common pathways treatments (Figure 3D). The KEGG pathways common to all 3 by which DDTC can reverse changes seen upon repeated DEG groups were fluid shear stress and atherosclerosis, focal cocaine treatment, pathways consist of many genes whose adhesion, MAPK signaling, and circadian entrainment. products exert contradictory functions on pathway activity, However, common pathways significantly enriched in both obscuring conclusions as to whether DDTC clearly reversed cocaine treatment alone (CS) and DDTC+cocaine (DC) treatment cocaine-induced behavior of these pathways. Therefore, we DEGs included pathways in cancer, ALS, and amphetamine wished to determine if DDTC is able to antagonize cocaine- addiction, and several common GO iterms were related to neu- related expression changes of specific genes. We plotted the ral signal conduction (supplementary Figure 4,) such as calcium log fold change of DEGs from DC, CS, and DS conditions in channel activity (GO:0005262), neurotransmitter receptor activ- a heatmap, with which it was immediately visible that many ity (GO:0030594), and presynapse (GO:0098793). more genes exhibited fold changes in opposite directions in Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 6 | International Journal of Neuropsychopharmacology, 2018 the DC mice compared with CS and DS mice, an observation Candidate NF-κB Target Genes Involved in Response that was confirmed by hierarchial clustering (Figure 4A). In to Repeated Cocaine Administration fact, the log fold changes of DEGs in DC and CS displayed -15 2 NF-κB is a protein complex composed of homo- or heterodimers a significantly negative relationship ( =P 2.994e , R = 0.2647), of 5 different family members: c-Rel (Rel), RelA/p65 (Rela), RelB while those of DS and CS had a significantly positive rela- -16 2 (Relb), NF-κB /p50/p105 (Nfkb1), and NF-κB /p52/p100 (Nfkb2) tionship (P = 2.2e , R = 0.4723) (Figure 4B; supplementary 1 2 (Natoli, 2006). Studies of protein-DNA crystal structures and Figure 5). These results indicate that DDTC reverses specific DNA-binding studies have shown that NF-κB and NF-κB recog- gene expression changes that occur in response to cocaine 1 2 nize the 5 base-pair motif of 5’-GGGRN-3’, whereas c-Rel, RelA/ treatment. p65, and RelB recognize a 4 base-pair 5’-GGRR-3’ motif, and the We then performed an additional pathway analysis to entire κB family recognizes a concensus motif of 5’-GGGRN(Y) determine which pathways were enriched in the list of YYCC-3’ (Hoffmann et al., 2006; Bracchi-Ricard et al., 2007). genes whose cocaine-induced expression changes were spe- Using this information, we applied online tools (see Methods) cifically reversed by DDTC (i.e., fold change in the opposite to scan the promoter regions of DEGs for NF-κB family bind- direction). There were a total of 142 such genes, 58 of which ing sites. The NF-κB motif could be mapped to the promoter were upregulated and 84 of which were downregulated by regions 86 DEGs (supplementary Table 3). This gene list was also cocaine, while these changes were reversed by DDTC (supple- enriched in the axon guidance term (mmu04360, P = .089), sup- mentary Table 2). KEGG analysis revealed that the most sig- porting the hypotheses that NF-κB directly regulates the axon nificantly enriched pathway was axon guidance (mmu04360, guidance pathway in cocaine addiction and that DDTC inter - P = .0088). Interestingly, when we analyzed the lo gfold feres with this activity. changes of all DEGs in the axon guidance pathway posthoc, that is, in a less stringent manner, not only were the DEGs with significant cocaine-induced expression changes signifi- Validation of Genes Reversed by DDTC cantly reversed by DDTC but there was a significantly nega- -08 tive relationship between CS and DC groups ( = P 4.211e ), The top-ranked DEGs by fold-change expression were Epha8 (Ephrin Type-A Receptor 8), a member of the axon guidance thereby further demonstrating that DDTC can reverse the axon guidance behavior that is modified by cocaine treatment pathway, and Dpf3 (Double PHD Finger 3), which belongs to the neuron-specific chromatin remodeling complex involved in (Figure 4C). Figure 4. Sodium diethyldithiocarbamate trihydrate (DDTC) reverses genes regulated by cocaine addiction. (A) Heatmap of all significantly differentially expressed genes in each group (saline+cocaine [CS], DDTC+saline [DS], and DDTC+cocaine [DC]). Red, upregulated; blue, downregulated. (B) Scatter plot of all differentially expressed genes of log2 fold_change of CS (X axis) and log2 fold_change of DC (Y axis). (C) Scatter plot of all genes in axon guidance pathway. Downloaded from https://academic.oup.com/ijnp/advance-article-abstract/doi/10.1093/ijnp/pyy031/4948030 by Ed 'DeepDyve' Gillespie user on 08 June 2018 Wang et al. | 7 Figure 5. Expression of cocaine and sodium diethyldithiocarbamate trihydrate (DDTC) target genes as determined by qPCR. (A) Normalized mRNA expression quanti- fied by RT-qPCR for genes whose expression is altered by cocaine treatment and reversed by DDTC: Epha8 and Dpf3. Results represent mean ± SD of 3 determinations in each of the 2 types of experiments; ****P < .0001; ***P < .001; **P < .01; *P < .05. (B) Chart of fragments per kilobase of transcript per million mapped reads (FPKM) of Epha8 and Dpf3 from mRNA-seq. dendrite growth. An RT-qPCR assay confirmed that expression significantly reversed the cocaine-induced changes in the of these 2 tested genes was significantly altered by cocaine and amphetamine addiction pathway, indicating that this pathway, reversed by DDTC, which coincided with the results obtained but not MAPK and circadian pathways, is an important mecha- from RNA-sequencing (Figure 5). nism by which DDTC modifies the effects of cocaine. Axon guidance is modulated during the development of drug addiction (Bahi and Dreyer, 2005). For example, cocaine exposure Discussion alters the expression of axon guidance molecules that regulate The first major finding of this study was that the NF-κB inhibitor the formation of axon-target connections (Bahi et al., 2005), DDTC, when coadministered with cocaine, is capable of produc- which contribute to the structural adaptations that underlie the ing stastistically significant partial (>50%) rescue of cocaine- long-term effects of prolonged drug exposure (Pasterkamp et al., induced locomotor stimulation on the first day of treatment, 2009). We found that DDTC can significantly reverse changes in while completely desensitizing this response to cocaine when gene expression of the axon guidance pathway that are induced coadministered over several consecutive days. While virus- by repeated cocaine administration, suggesting that it may mediated gene therapy that results in NF-κB inhibition has be able to prevent structural changes associated with chronic shown success in animal models of cocaine sensitization, it is cocaine addiction. Though DDTC is known to have other func- faced with obvious barriers to clinical implementation. DDTC is tions, such as zinc chelation and and superoxide dismutase a pharmacological inhibitor that has been demonstrated to be inhibition, it is important to note that the NF-κB homo-dimer safe in clinical trials and is a small lipid-soluble molecule that motif can be mapped to 86 genes whose expression changes is capable of crossing the blood-brain barrier (Hersh et al., 1991; were reversed by DDTC and that these genes are also enriched Kodama et al., 2005) and as such could be considered for the in axon guidance. Thus, we suggest that NF-κB responds to treatment of cocaine-addicted patients pending more thorough cocaine exposure by directly modifying the expression levels analyses of its effects on the development and persistence of of members of the axon guidance pathway, leading to cocaine addictive behavior. The major goal of this study, however, was sensitization. The amphetamine addiction pathway may then not to evaluate the efficacy of DDTC as a treatment for cocaine be modified indirectly by downstream NF-κB pathway effectors. addiction but rather to use DDTC to reveal genes and pathways In summary, our results shed light on NF-κB target genes at regulated by NF-κB during repeated cocaine administration. a genome-wide level in an effort to understand the mechanisms We found that the MAPK signaling cascade is a key molecu- by which this critical transcription factor complex mediates the lar pathway in the PFC that is altered in response to cocaine and functional effects of repeated cocaine administration. Our work that inhibition of NF-κB by DDTC with or without cocaine treat- provides new insight into the molecular mechanisms underly- ment also results in gene expression changes of MAPK pathway ing the role of NF-κB in addiction. members. The MAPK signaling cascade involves the activation of extracellular signal-regulated kinases-1 and -2 (ERK1 and ERK2) Funding and is known to play an important role in the control of synaptic plasticity in the adult brain (Thomas and Huganir, 2004). In fact, This work was financially supported by the National Natural MAPK/ERK signaling contributes to various behavioral effects of Science Foundation of China (nos. 91132728, 30870821, and cocaine, such as psychomotor sensitization, conditioned place 61401459) and Key Laboratory of Mental HealthInstitute of , preference, and reconsolidation of memories for cocaine cues Psychology , Chinese Academy of Sciences. (Lu et al., 2004, 2005, 2006) (Radwanska et al., 2005). Our previ- ous study also demonstrated that cocaine treatment induced Acknowledgments long-lasting changes of the ERK signaling pathway in the PFC (Li et al., 2017). Consistent with this (Li et al., 2017) and other We appreciate the support we received from the National Natural Science Foundation of China and the Institute of Psychology, studies (Abarca et al., 2002L ; ynch et al., 2008; Imbesi et al., 2009), our results also show that the circadian pathway can play a role Chinese Academy of Sciences during our study. in cocaine sensitization. However, while both the MAPK and cir - cadian pathways were involved in cocaine response and DDTC Statement of Interest also generally affected both pathways, they were not enriched in the list of DEGs reversed by DDTC. On the other hand, DDTC None. 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International Journal of Neuropsychopharmacology – Oxford University Press
Published: Mar 21, 2018
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