Genetic targeting of the amphetamine and methylphenidate-sensitive dopamine transporter: On the path to an animal model of attention-deficit hyperactivity disorder

Mergy, Marc; Gowrishankar, Raajaram; Davis, Gwynne L.; Jessen, Tammy; Wright, Jane; Stanwood, Gregg D.; Hahn, Maureen K.; Blakely, Randy D.

doi:10.1016/j.neuint.2013.11.009

Cited by 24 publications

(26 citation statements)

References 187 publications

(213 reference statements)

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“…Recently, we reported the generation and general growth characteristics of DAT Val559 knock-in mice (59). As noted in the prior publication, these mice reproduce normally and display no overt sensorimotor deficits.…”

Section: Resultsmentioning

confidence: 65%

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

Mergy¹,

Gowrishankar²,

Gresch

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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113

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Despite the critical role of the presynaptic dopamine (DA) transporter (DAT, SLC6A3) in DA clearance and psychostimulant responses, evidence that DAT dysfunction supports risk for mental illness is indirect. Recently, we identified a rare, nonsynonymous Slc6a3 variant that produces the DAT substitution Ala559Val in two male siblings who share a diagnosis of attention-deficit hyperactivity disorder (ADHD), with other studies identifying the variant in subjects with bipolar disorder (BPD) and autism spectrum disorder (ASD). Previously, using transfected cell studies, we observed that although DAT Val559 displays normal total and surface DAT protein levels, and normal DA recognition and uptake, the variant transporter exhibits anomalous DA efflux (ADE) and lacks capacity for amphetamine (AMPH)-stimulated DA release. To pursue the significance of these findings in vivo, we engineered DAT Val559 knock-in mice, and here we demonstrate in this model the presence of elevated extracellular DA levels, altered somatodendritic and presynaptic D2 DA receptor (D2R) function, a blunted ability of DA terminals to support depolarization and AMPHevoked DA release, and disruptions in basal and psychostimulant-evoked locomotor behavior. Together, our studies demonstrate an in vivo functional impact of the DAT Val559 variant, providing support for the ability of DAT dysfunction to impact risk for mental illness.T he neurotransmitter dopamine (DA) plays a key role in regulating brain circuits that control reward, attention, and locomotor activity (1-3), Accordingly, dopaminergic dysfunction is believed to contribute to several neuropsychiatric disorders including Parkinson's disease (4), bipolar disorder (BPD) (5), drug abuse and addiction (6), and attention-deficit hyperactivity disorder (ADHD) (7,8). The presynaptic DA transporter (DAT) is the primary mechanism for terminating DA signaling at the synapse (9) and is the primary target for several psychostimulant drugs including cocaine (COC), methylphenidate (MPH), and amphetamine (AMPH). COC and MPH are DAT antagonists, elevating extracellular DA levels by preventing DAT-mediated DA reuptake (10). AMPH actions are more complex (11). AMPH is structurally similar to DA and, as a result, is transported by DAT, competing with DA during the reuptake process. AMPH also induces DAT-mediated nonvesicular release, also termed "DA efflux," a process that involves the actions of intracellular signaling proteins such as CamKIIα (12-16) and , alterations in interactions with DAT-associated proteins and phospholipids (12,14,20), and changes in DAT phosphorylation (12,16,(21)(22)(23)) that biases the transporter toward an efflux-competent mechanism. Despite their mechanistic differences, MPH and AMPH both rapidly elevate DA in the CNS and are components of the most frequently prescribed medications for ADHD, Ritalin and Adderall, respectively. The DA modulatory actions of MPH and AMPH reinforce hypotheses derived from brain imaging studies (24) and the analysis of common genetic variation (25-30)...

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Section: Resultsmentioning

confidence: 65%

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

Mergy¹,

Gowrishankar²,

Gresch

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

113

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“…Thus, ADE is not a shared feature for all the disease-associated variants, but nevertheless a remarkable 'gain of function' phenotype that apparently can arise from very different mutations. Importantly, A559V knock in mice were recently found to display both behavioral and functional alteration, supporting a significant impact of ADE in vivo (66). It is therefore also highly interesting that the R615C variant, has been found to undergo dysregulated trafficking with enhanced constitutive internalization and altered microdomain distribution (28,67).…”

Section: Discussionmentioning

confidence: 94%

Neuropsychiatric disease–associated genetic variants of the dopamine transporter display heterogeneous molecular phenotypes

Herborg

Andreassen

Berlin

et al. 2018

Journal of Biological Chemistry

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Genetic factors are known to significantly contribute to the etiology of psychiatric diseases such as attention deficit hyperactivity disorder (ADHD) and autism spectrum and bipolar disorders, but the underlying molecular processes remain largely elusive. The dopamine transporter (DAT) has received continuous attention as a potential risk factor for psychiatric disease, as it is critical for dopamine homeostasis and serves as principal target for ADHD medications. Constrain metrics for the DAT-encoding gene solute carrier family 6 member 3 (SLC6A3) indicate that missense mutations are under strong negative selection, pointing to pathophysiological outcomes when DAT function is compromised. Here, we systematically characterized six rare genetic variants of DAT (I312F, T356M, D421N, A559V, E602G, and R615C) identified in patients with neuropsychiatric disorders. We evaluated dopamine uptake and ligand interactions, along with ion coordination and electrophysiological properties, to elucidate functional phenotypes, and applied Zn 2+ exposure and a substituted cysteineaccessibility approach to identify shared structural changes. Three variants (I312F, T356M, and D421N) exhibited impaired dopamine uptake associated with changes in ligand binding, ion coordination, and distinct conformational disturbances. Remarkably, we found that all three variants displayed gain-offunction electrophysiological phenotypes. I312F mediated an increased uncoupled anion conductance previously suggested to modulate neuronal excitability. T356M and D421N both mediated a cocaine-sensitive leakage of cations, which for T356M, was potentiated by Zn 2+ , concurrent with partial functional rescue. Collectively, our findings support that gain of disruptive functions due to missense mutations in SLC6A3 may be key to understanding how dopaminergic dyshomeostasis arises in heterozygous carriers.A substantial proportion of the disease etiology of common psychiatric disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorders (ASD), bipolar disorder, and schizophrenia is attributed genetic components (1). The underlying neurobiological mechanisms are not clear, but dopamine disturbances are believed to constitute a central component (2-7). The allelic spectrum of these dopamine-related disorders is rapidly expanding and comprises both common variants and rare structural or exonic mutations, including de novo variants (1,(8)(9)(10)(11)(12). Moreover, an interesting overlap in the genetic architecture of psychiatric disorders has been observed, and this pleiotrophy is seen for both common and rare variants (13)(14)(15)(16)(17)(18). Despite progress, much of the genetic component remains unaccounted for, and we also have the challenge ahead of translating most of the comprehensive genetic information into an understanding of underlying biological processes, and subsequently into clinically applicable knowledge. Rare variants may provide a unique handle for obtaining new disease insights as they are expected to h...

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“…Further studies revealed that these cells however have abnormal outward “leak” of cytoplasmic DA and AMPH application on transfected cells did not change efflux of DA and its effect was similar to cocaine action(Mazei-Robison et al, 2008). DAT-KI mouse line with Val559 mutation in DAT gene was created (Mergy et al, 2014b). These mice have normal levels of DA and its metabolites in the brain tissue.…”

Section: Other Dat Mutant Micementioning

confidence: 99%

Dopamine transporter mutant animals: a translational perspective

Efimova

Gainetdinov

Budygin

et al. 2016

Journal of Neurogenetics

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The dopamine transporter (DAT) plays an important homeostatic role in the control of both the extracellular and intraneuronal concentrations of dopamine, thereby providing effective control over activity of dopaminergic transmission. Since brain dopamine is known to be involved in numerous neuropsychiatric disorders, investigations using mice with genetically altered DAT function and thus intensity of dopamine-mediated signaling have provided numerous insights into the pathology of these disorders and highlight novel pathological mechanisms that could be targeted to provide new therapeutic approaches for these disorders. In this brief overview we discuss recent investigations involving animals with genetically altered DAT function, particularly focusing on translational studies providing new insights into pathology and pharmacology of dopamine-related disorders. Perspective applications of these and newly developed models of DAT dysfunction are also discussed.

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Genetic targeting of the amphetamine and methylphenidate-sensitive dopamine transporter: On the path to an animal model of attention-deficit hyperactivity disorder

Cited by 24 publications

References 187 publications

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

The rare DAT coding variant Val559 perturbs DA neuron function, changes behavior, and alters in vivo responses to psychostimulants

Neuropsychiatric disease–associated genetic variants of the dopamine transporter display heterogeneous molecular phenotypes

Dopamine transporter mutant animals: a translational perspective

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