Human dopamine transporter gene: differential regulation of 18-kb haplotypes

Association of SLC6A3 variants with treatment-resistant schizophrenia: a genetic association study of dopamine-related genes in schizophrenia

Background

Most genetic analyses that have attempted to identify a locus or loci that can distinguish patients with treatment-resistant schizophrenia (TRS) from those who respond to treatment (non-TRS) have failed. However, evidence from multiple studies suggests that patients with schizophrenia who respond well to antipsychotic medication have a higher dopamine (DA) state in brain synaptic clefts whereas patients with TRS do not show enhanced DA synthesis/release pathways.

Patients and methods

To examine the contribution (if any) of genetics to TRS, we conducted a genetic association analysis of DA-related genes in schizophrenia patients (TRS, n = 435; non-TRS, n = 539) and healthy controls (HC: n = 489).

Results

The distributions of the genotypes of rs3756450 and the 40-bp variable number tandem repeat on SLC6A3 differed between the TRS and non-TRS groups. Regarding rs3756450, the TRS group showed a significantly higher ratio of the A allele, whereas the non-TRS group predominantly had the G allele. The analysis of the combination of COMT and SLC6A3 yielded a significantly higher ratio of the putative low-DA type (i.e., high COMT activity + high SLC6A3 activity) in the TRS group compared to the two other groups. Patients with the low-DA type accounted for the minority of the non-TRS group and exhibited milder psychopathology.

Conclusion

The overall results suggest that (i) SLC6A3 could be involved in responsiveness to antipsychotic medication and (ii) genetic variants modulating brain DA levels may be related to the classification of TRS and non-TRS.

The dopamine transporter gene SLC6A3: multidisease risks

The human dopamine transporter gene SLC6A3 has been consistently implicated in several neuropsychiatric diseases but the disease mechanism remains elusive. In this risk synthesis, we have concluded that SLC6A3 represents an increasingly recognized risk with a growing number of familial mutants associated with neuropsychiatric and neurological disorders. At least five loci were related to common and severe diseases including alcohol use disorder (high activity variant), attention-deficit/hyperactivity disorder (low activity variant), autism (familial proteins with mutated networking) and movement disorders (both regulatory variants and familial mutations). Association signals depended on genetic markers used as well as ethnicity examined. Strong haplotype selection and gene-wide epistases support multimarker assessment of functional variations and phenotype associations. Inclusion of its promoter region's functional markers such as DNPi (rs67175440) and 5'VNTR (rs70957367) may help delineate condensate-based risk action, testing a locus-pathway-phenotype hypothesis for one gene-multidisease etiology.

Epistatic evidence for gender-dependant slow neurotransmission signalling in substance use disorders: PPP1R12B versus PPP1R1B

BACKGROUND

Slow neurotransmission including DARPP-32 signalling is implicated in substance use disorders (SUDs) by experimental systems but not yet in the human aetiology. PPP1R12B, encoding another protein in the DARPP-32 family, hasn't been studied in the brain.

METHODS

Brain-regional gene activity was assessed in three different animal models of SUDs for mRNA level alterations. Genetic associations were assessed by meta-analysis of pre-existing dbGaP GWAS datasets for main effects and epistasis with known genetic risks, followed by cell type-specific pathway delineation. Parkinson's disease (PD) was included as a dopamine-related disease control for SUDs.

FINDINGS

In animal models of SUDs, environmentally-altered PPP1R12B expression sex-dependently involves motivation-related brain regions. In humans with polysubstance abuse, meta-analysis of pre-existing datasets revealed that PPP1R12B and PPP1R1B, although expressed in dopamine vs. dopamine-recipient neurons, exerted similar interactions with known genetic risks such as ACTR1B and DRD2 in men but with ADH1B, HGFAC and DRD3 in women. These interactions reached genome-wide significances (P_meta<10^-20) for SUDs but not for PD (disease selectivity: P = 4.8 × 10^-142, OR = 6.7 for PPP1R12B; P = 8.0 × 10^-8, OR = 2.1 for PPP1R1B). CADM2 was the common risk in the molecular signalling regardless of gender and cell type.

INTERPRETATION

Gender-dependant slow neurotransmission may convey both genetic and environmental vulnerabilities selectively to SUDs.

FUNDING

Grants from National Institute on Drug Abuse (NIDA) and National Institute on Alcohol Abuse and Alcoholism (NIAAA) of U.S.A. and National Natural Science Foundation of China (NSFC).

Identification of HIVEP2 as a dopaminergic transcription factor related to substance use disorders in rats and humans

Playing an important role in the etiology of substance use disorder (SUD), dopamine (DA) neurons are subject to various regulations but transcriptional regulations are largely understudied. For the first time, we report here that the Human Immunodeficiency Virus Type I Enhancer Binding Protein 2 (HIVEP2) is a dopaminergic transcriptional regulator. HIVEP2 is expressed in both the cytoplasm and nuclei of DA neurons. Therein, HIVEP2 can target the intronic sequence GTGGCTTTCT of SLC6A3 and thereby activate the gene. In naive rats from the bi-directional selectively bred substance-preferring P vs -nonpreferring NP rat model of substance abuse vulnerability, increased gene activity in males was associated with the vulnerability, whereas decreased gene activity in the females was associated with the same vulnerability. In clinical subjects, extensive and significant HIVEP2-SLC6A3 interactions were observed for SUD. Collectively, HIVEP2-mediated transcriptional mechanisms are implicated in dopaminergic pathophysiology of SUD.

Multiple pathways for natural product treatment of Parkinson's disease: A mini review

BACKGROUND

It is established that natural medicines for Parkinson's disease (PD) provide an antioxidant activity in preventing dopaminergic neurons from degeneration. However, the underlying and related molecular details remain poorly understood.

METHODS AND AIM

We review published in vitro and rodent studies of natural products in PD models with the aim to identify common molecular pathways contributing to the treatment efficacy. Commonly regulated genes were identified through the systemic literature search and further analyzed from a network perspective.

FINDINGS

Approximately thirty different types of natural products have been investigated for their ability to regulate protein density and gene activity in various experimental systems. Most were found to attenuate neurotoxin-induced regulations. Three common PD pathways are involved. The most studied pathway was neuronal development/anti-apoptosis consisting of Bax/Bcl-2, caspases 3/9, and MAPK signaling. Another well studied was anti-inflammation comprising iNOS, nNOS, Nrf2/ARE, cytokines, TNFα, COX2 and MAPK signaling. The third pathway referred to dopamine transmission modulation with upregulated VMAT2, DAT, NURR1 and GDNF levels. To date, HIPK2, a conserved serine/threonine kinase and transcriptional target of Nrf2 in an anti-apoptosis signaling pathway, is the first protein identified as the direct binding target of a natural product (ZMHC).

IMPLICATIONS

Natural products may utilize multiple and intercellular pathways at various steps to prevent DA neurons from degeneration. Molecular delineation of the mechanisms of actions is revealing new, perhaps combinational therapeutic approaches to stop the progression of DA degeneration.

Presence of recombination hotspots throughout SLC6A3

The human dopamine transporter gene SLC6A3 is involved in substance use disorders (SUDs) among many other common neuropsychiatric illnesses but allelic association results including those with its classic genetic markers 3'VNTR or Int8VNTR remain mixed and unexplainable. To better understand the genetics for reproducible association signals, we report the presence of recombination hotspots based on sequencing of the entire 5' promoter regions in two small SUDs cohorts, 30 African Americans (AAs) and 30 European Americans (EAs). Recombination rate was the highest near the transcription start site (TSS) in both cohorts. In addition, each cohort carried 57 different promoter haplotypes out of 60 and no haplotypes were shared between the two ethnicities. A quarter of the haplotypes evolved in an ethnicity-specific manner. Finally, analysis of five hundred subjects of European ancestry, from the 1000 Genome Project, confirmed the promoter recombination hotspots and also revealed several additional ones in non-coding regions only. These findings provide an explanation for the mixed results as well as guidance for selection of effective markers to be used in next generation association validation (NGAV), facilitating the delineation of pathogenic variation in this critical neuropsychiatric gene.

RETRACTED: Human Suicide, Modern Diagnosis Assistance and Magic Bullet Discovery

The article entitled “Human Suicide, Modern Diagnosis Assistance and Magic Bullet Discovery”, by Da-Yong Lu, Peng- Peng Zhu, Hong-Ying Wu, Nagendra Sastry Yarla, Bin Xu, Jian Ding, Ajit Varki and Ting-Ren Lu, has been retracted on the request of the co-authors, Dr. Ajit Varki, Dr. Nagendra Sastry Yarla and Dr. Jian Ding available at: Cent Nerv Syst Agents Med Chem 2019; 19(1): 15-23. http://www.eurekaselect.com/169003/article. The Corresponding Author Dr. Da-Yong Lu has included the names of the co-authors, Dr. Ajit Varki, Dr. Nagendra Sastry Yarla and Dr. Jian Ding without their consent and the manuscript has been published in the journal, Central Nervous System Agents in Medicinal Chemistry (CNSAMC). Kindly see Bentham Science Policy on Article retraction at the link given below: (https://benthamscience.com/journals/central-nervous-system-agents-in-medicinal-chemistry/author-guidelines/) Submission of a manuscript to the respective journals implies that all authors have read and agreed to the content of the Copyright Letter or the Terms and Conditions. As such, this article represents a severe abuse of the scientific publishing system. Bentham Science Publishers takes a very strong view on this matter and apologizes to the readers of the journal for any inconvenience this may cause.

Intragenic Transcriptional cis-Antagonism Across SLC6A3

A promoter can be regulated by various cis-acting elements so that delineation of the regulatory modes among them may help understand developmental, environmental and genetic mechanisms in gene activity. Here we report that the human dopamine transporter gene SLC6A3 carries a 5' distal 5-kb super enhancer (5KSE) which upregulated the promoter by 5-fold. Interestingly, 5KSE is able to prevent 3' downstream variable number tandem repeats (3'VNTRs) from silencing the promoter. This new enhancer consists of a 5'VNTR and three repetitive sub-elements that are conserved in primates. Two of 5KSE's sub-elements, E-9.7 and E-8.7, upregulate the promoter, but only the later could continue doing so in the presence of 3'VNTRs. Finally, E-8.7 is activated by novel dopaminergic transcription factors including SRP54 and Nfe2l1. Together, these results reveal a multimodal regulatory mechanism in SLC6A3.

Activation of RHO-1 in cholinergic motor neurons competes with dopamine signalling to control locomotion

The small GTPase RhoA plays a crucial role in the regulation of neuronal signalling to generate behaviour. In the developing nervous system RhoA is known to regulate the actin cytoskeleton, however the effectors of RhoA-signalling in adult neurons remain largely unidentified. We have previously shown that activation of the RhoA ortholog (RHO-1) in C. elegans cholinergic motor neurons triggers hyperactivity of these neurons and loopy locomotion with exaggerated body bends. This is achieved in part through increased diacylglycerol (DAG) levels and the recruitment of the synaptic vesicle protein UNC-13 to synaptic release sites, however other pathways remain to be identified. Dopamine, which is negatively regulated by the dopamine re-uptake transporter (DAT), has a central role in modulating locomotion in both humans and C. elegans. In this study we identify a new pathway in which RHO-1 regulates locomotory behaviour by repressing dopamine signalling, via DAT-1, linking these two pathways together. We observed an upregulation of dat-1 expression when RHO-1 is activated and show that loss of DAT-1 inhibits the loopy locomotion phenotype caused by RHO-1 activation. Reducing dopamine signalling in dat-1 mutants through mutations in genes involved in dopamine synthesis or in the dopamine receptor DOP-1 restores the ability of RHO-1 to trigger loopy locomotion in dat-1 mutants. Taken together, we show that negative regulation of dopamine signalling via DAT-1 is necessary for the neuronal RHO-1 pathway to regulate locomotion.

The correlation between DNA methylation and transcriptional expression of human dopamine transporter in cell lines

This study aims to investigate the relationship between DNA methylation and expression of human dopamine transporter (hDAT). We examined methylation status of hDAT in cells with various hDAT expression levels, including two dopaminergic neural cell lines (SK-N-AS and SH-SY-5Y) and one non-dopaminergic cell line (HEK293) by bisulfite sequencing PCR(BSP). The effects of DNA methyltransferase inhibitor 5-aza-dC or/and histone deacetylase inhibitor (HDACi, sodium butyrate, NaB) on the DNA methylation status and mRNA expression levels of hDAT were examined. The results revealed marked hypomethylation of the two promoter regions (-1214 to -856bp and -48 to 439bp, the first base of exon 1 was taken as +1 bp)of hDAT in SK-N-AS (4.7%±2.0^mC and 3.5%±1.0^mC, respectively) compared with SH-SY-5Y (88.0%±4.4%^mC and 81.1%±8.8%^mC) and HEK293 (90.7%±2.4^mC and 84.4%±8.6% ^mC) cell lines, indicating a cell-specific methylation regulation of hDAT. 5-aza-dC and NaB decreased hypermethylation,while increase hDAT expression in SH-SY-5Y cells and recovered hDAT mRNA expression in HEK293 cells. DNA methylation enabled the cell-specific differential expression of the hDAT gene. hDAT silencing was reversed by the introduction of DNA hypomethylation via 5-aza-dC or/and NaB.

hVMAT2: A Target of Individualized Medication for Parkinson's Disease

Vesicular monoamine transporter 2 (VMAT2) is responsible for sequestering cytosolically toxic dopamine into intracellular secretory vesicles. Animal genetic studies have suggested that reduced VMAT2 activity contributes to the genetic etiology of Parkinson's disease (PD), but this role has not been established in humans. Based on human genetic association and meta-analysis, we first confirm the human VMAT2 (hVMAT2 or SLC18A2) promoter as a risk factor for PD in both family and unrelated US white people: marker rs363324 at -11.5 kb in the hVMAT2 promoter is reproducibly associated with PD in a cohort of nuclear families (p = 0.04506 in early-onset PD) and 3 unrelated US white people (meta-analysis p = 0.01879). In SH-SY5Y cells, low activity-associated hVMAT2 promoter confers high methylpiperidinopyrazole iodide cytotoxicity, which is likely attributed to functional polymorphisms bound by nuclear proteins. Interestingly, treatments with the dopamine neuron-protecting agent puerarin upregulates the promoter activity in a haplotype- and cell line-dependent manner. These pharmacogenetic findings suggest that hVMAT2 could be a risk factor and imply it as a target of genetic medications for PD.

Increased Nigral SLC6A3 Activity in Schizophrenia Patients: Findings From the Toronto-McLean Cohorts

SLC6A3, which encodes the primary regulator of extracellular dopamine (DA) concentration, the DA transporter, has been implicated in schizophrenia (SCZ). However, the details of its genetic effect on risk remain largely unknown. The purpose of this candidate gene study was to identify a specificSLC6A3activity associated with SCZ by using functional genetic approaches. We first examined gene activity in DA neurons isolated from case-control postmortem nigral tissue and found that the averageSLC6A3mRNA level in controls was only 0.37-fold of that in cases (P= .0034). To understand this expression difference, we examined the association of 10 genetic markers, mostly located in the promoter region, with SCZ in 1717 subjects collected from Toronto and McLean cohorts, including 881 controls and 836 cases and identified the 5' promoter SNP rs1478435 as having a significant association signal (uncorrectedPvalue: .00462; adjustedPvalue: .0319) in unrelated Caucasians. Allele T was over-represented in controls (OR = .75); T-carrier controls had decreased mRNA levels in nigral DA neurons, contributing to the reduced activity in the controls. In vitro functional analysis confirmed that T carriers displayed attenuated enhancement of promoter activity. These findings collectively suggest that increased nigralSLC6A3activity may be a risk factor for SCZ, and may help to explain high rates of comorbidity with substance abuse.

Epigenetic Regulation of Dopamine Transporter mRNA Expression in Human Neuroblastoma Cells

The dopamine transporter (DAT) is a key regulator of dopaminergic neurotransmission. As such, proper regulation of DAT expression is important to maintain homeostasis, and disruption of DAT expression can lead to neurobehavioral dysfunction. Based on genomic features within the promoter of the DAT gene, there is potential for DAT expression to be regulated through epigenetic mechanisms, including DNA methylation and histone acetylation. However, the relative contribution of these mechanisms to DAT expression has not been empirically determined. Using pharmacologic and genetic approaches, we demonstrate that inhibition of DNA methyltransferase (DNMT) activity increased DAT mRNA approximately 1.5-2 fold. This effect was confirmed by siRNA knockdown of DNMT1. Likewise, the histone deacetylase (HDAC) inhibitors valproate and butyrate also increased DAT mRNA expression, but the response was much more robust with expression increasing over tenfold. Genetic knockdown of HDAC1 by siRNA also increased DAT expression, but not to the extent seen with pharmacological inhibition, suggesting additional isoforms of HDAC or other targets may contribute to the observed effect. Together, these data identify the relative contribution of DNMTs and HDACs in regulating expression. These finding may aid in understanding the mechanistic basis for changes in DAT expression in normal and pathophysiological states.

DAT1 methylation changes in alcohol-dependent individuals vs. controls

INTRODUCTION

The dopaminergic system plays a crucial role in the development of alcohol dependence. Regulation of the extracellular dopamine concentration is driven by dopamine transporter. Both, the expression and function of dopamine transporter, are influenced by chronic alcohol intake. Dopamine transporter (DAT) gene is also supposed to be differentially methylated in alcohol-dependent patients than in controls.

MATERIAL AND METHODS

DNA was extracted from peripheral blood leukocytes. We analyzed the methylation status in 23 CpG islands of DAT gene promoter in alcohol dependent subjects (n = 171) and control (n = 160) group.

RESULTS

No statistical differences in the general frequency of DAT CpG islands was revealed between patients (altogether 175 methylated islands) and control subjects (170 methylated islands (p = 0.86). However it was revealed that one of analyzed positions is significantly more often methylated in control subjects than in alcohol dependent individuals (p = 0.0296).

CONCLUSION

Further subsequent studies are necessary to determine whether the methylation change of one (out of 23) CpG site results in DAT expression changes.