1
|
Bernstein DL, Lewandowski SI, Besada C, Place D, España RA, Mortensen OV. Inactivation of ERK1/2 Signaling in Dopaminergic Neurons by Map Kinase Phosphatase MKP3 Regulates Dopamine Signaling and Motivation for Cocaine. J Neurosci 2024; 44:e0727232023. [PMID: 38296649 PMCID: PMC10860627 DOI: 10.1523/jneurosci.0727-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 10/27/2023] [Accepted: 11/28/2023] [Indexed: 02/02/2024] Open
Abstract
The mesolimbic dopamine system is a crucial component of reward and reinforcement processing, including the psychotropic effects of drugs of abuse such as cocaine. Drugs of abuse can activate intracellular signaling cascades that engender long-term molecular changes to brain reward circuitry, which can promote further drug use. However, gaps remain about how the activity of these signaling pathways, such as ERK1/2 signaling, can affect cocaine-induced neurochemical plasticity and cocaine-associated behaviors specifically within dopaminergic cells. To enable specific modulation of ERK1/2 signaling in dopaminergic neurons of the ventral tegmental area, we utilize a viral construct that Cre dependently expresses Map kinase phosphatase 3 (MKP3) to reduce the activity of ERK1/2, in combination with transgenic rats that express Cre in tyrosine hydroxylase (TH)-positive cells. Following viral transfection, we found an increase in the surface expression of the dopamine transporter (DAT), a protein associated with the regulation of dopamine signaling, dopamine transmission, and cocaine-associated behavior. We found that inactivation of ERK1/2 reduced post-translational phosphorylation of the DAT, attenuated the ability of cocaine to inhibit the DAT, and decreased motivation for cocaine without affecting associative learning as tested by conditioned place preference. Together, these results indicate that ERK1/2 signaling plays a critical role in shaping the dopamine response to cocaine and may provide additional insights into the function of dopaminergic neurons. Further, these findings lay important groundwork toward the assessment of how signaling pathways and their downstream effectors influence dopamine transmission and could ultimately provide therapeutic targets for treating cocaine use disorders.
Collapse
Affiliation(s)
- David L Bernstein
- Departments of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Stacia I Lewandowski
- Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Christina Besada
- Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Delaney Place
- Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Rodrigo A España
- Departments of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| | - Ole V Mortensen
- Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102
| |
Collapse
|
2
|
Besada C, Lewandowski SI, Mortensen OV. MKP3 Overexpression and ERK1/2 Phosphorylation in Dopaminergic Neurons Regulate DAT Trafficking and Function. FASEB J 2022. [DOI: 10.1096/fasebj.2022.36.s1.r5533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Christina Besada
- Pharmacology and PhysiologyDrexel University College of MedicinePhiladelphiaPA
| | | | - Ole V. Mortensen
- Pharmacology and PhysiologyDrexel University College of MedicinePhiladelphiaPA
| |
Collapse
|
3
|
Reeb KL, Mortensen OV, Fontana ACK. Modulation of glutamate transporters as a potential therapeutic intervention for neurological disorders. FASEB J 2022. [DOI: 10.1096/fasebj.2022.36.s1.r3702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Katelyn L. Reeb
- Pharmacology & PhysiologyDrexel University College of MedicinePhiladelphiaPA
| | - Ole V. Mortensen
- Pharmacology & PhysiologyDrexel University College of MedicinePhiladelphiaPA
| | | |
Collapse
|
4
|
Refai O, Aggarwal S, Cheng MH, Gichi Z, Salvino JM, Bahar I, Blakely RD, Mortensen OV. Allosteric Modulator KM822 Attenuates Behavioral Actions of Amphetamine in Caenorhabditis elegans through Interactions with the Dopamine Transporter DAT-1. Mol Pharmacol 2022; 101:123-131. [PMID: 34906999 PMCID: PMC8969146 DOI: 10.1124/molpharm.121.000400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 12/03/2021] [Indexed: 11/22/2022] Open
Abstract
Aberrant dopamine (DA) signaling is associated with several psychiatric disorders, such as autism, bipolar disorder, addiction, and Parkinson's disease, and several medications that target the DA transporter (DAT) can induce or treat these disorders. In addition, psychostimulants, such as cocaine and D-amphetamine (AMPH), rely on the competitive interactions with the transporter's substrate binding site to produce their rewarding effects. Agents that exhibit noncompetitive, allosteric modulation of DAT remain an important topic of investigation due to their potential therapeutic applications. We previously identified a novel allosteric modulator of human DAT, KM822, that can decrease the affinity of cocaine for DAT and attenuate cocaine-elicited behaviors; however, whether DAT is the sole mediator of KM822 actions in vivo is unproven given the large number of potential off-target sites. Here, we provide in silico and in vitro evidence that the allosteric site engaged by KM822 is conserved between human DAT and Caenorhabditis elegans DAT-1. KM822 binds to a similar pocket in DAT-1 as previously identified in human DAT. In functional dopamine uptake assays, KM822 affects the interaction between AMPH and DAT-1 by reducing the affinity of AMPH for DAT-1. Finally, through a combination of genetic and pharmacological in vivo approaches we provide evidence that KM822 diminishes the behavioral actions of AMPH on swimming-induced paralysis through a direct allosteric modulation of DAT-1. More broadly, our findings demonstrate allosteric modulation of DAT as a behavior modifying strategy and suggests that Caenorhabditis elegans can be operationalized to identify and investigate the interactions of DAT allosteric modulators. SIGNIFICANCE STATEMENT: We previously demonstrated that the dopamine transporter (DAT) allosteric modulator KM822 decreases cocaine affinity for human DAT. Here, using in silico and in vivo genetic approaches, we extend this finding to interactions with amphetamine, demonstrating evolutionary conservation of the DAT allosteric site. In Caenorhabditis elegans, we report that KM822 suppresses amphetamine behavioral effects via specific interactions with DAT-1. Our findings reveal Caenorhabditis elegans as a new tool to study allosteric modulation of DAT and its behavioral consequences.
Collapse
Affiliation(s)
- Osama Refai
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Shaili Aggarwal
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Mary Hongying Cheng
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Zayna Gichi
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Joseph M Salvino
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Ivet Bahar
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Randy D Blakely
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| | - Ole V Mortensen
- Department of Biomedical Science, Charles E. Schmidt College of Medicine, Florida Atlantic University, Jupiter, Florida (O.R., Z.G., R.D.B.); Stiles-Nicholson Brain Institute, Florida Atlantic University, Jupiter, Florida (O.R., R.D.B.); Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania (S.A., O.V.M.); Department of Computational and Systems Biology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania (M.H.C., I.B.); and The Wistar Institute, Philadelphia, Pennsylvania (J.M.S.)
| |
Collapse
|
5
|
Camicia F, Vaca HR, Guarnaschelli I, Koziol U, Mortensen OV, Fontana ACK. Molecular characterization of the serotonergic transporter from the cestode Echinococcus granulosus: pharmacology and potential role in the nervous system. Parasitol Res 2022; 121:1329-1343. [PMID: 35169884 PMCID: PMC9487190 DOI: 10.1007/s00436-022-07466-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 02/08/2022] [Indexed: 10/19/2022]
Abstract
Echinococcus granulosus, the etiological agent of human cystic echinococcosis (formerly known as hydatid disease), represents a serious worldwide public health problem with limited treatment options. The essential role played by the neuromuscular system in parasite survival and the relevance of serotonin (5-HT) in parasite movement and development make the serotonergic system an attractive source of drug targets. In this study, we cloned and sequenced a cDNA coding for the serotonin transporter from E. granulosus (EgSERT). Bioinformatic analyses suggest that EgSERT has twelve transmembrane domains with highly conserved ligand and ionic binding sites but a less conserved allosteric site compared with the human orthologue (HsSERT). Modeling studies also suggest a good degree of conservation of the overall structure compared with HsSERT. Functional and pharmacological studies performed on the cloned EgSERT confirm that this protein is indeed a serotonin transporter. EgSERT is specific for 5-HT and does not transport other neurotransmitters. Typical monoamine transport inhibitors also displayed inhibitory activities towards EgSERT, but with lower affinity than for the human SERT (HsSERT), suggesting a high divergence of the cestode transporter compared with HsSERT. In situ hybridization studies performed in the larval protoscolex stage suggest that EgSERT is located in discrete regions that are compatible with the major ganglia of the serotonergic nervous system. The pharmacological properties, the amino acidic substitutions at important functional regions compared with the HsSERT, and the putative role of EgSERT in the nervous system suggest that it could be an important target for pharmacological intervention.
Collapse
Affiliation(s)
- Federico Camicia
- Laboratorio de Toxinopatología, Centro de Patología Experimental y Aplicada, Facultad de Medicina, Universidad de Buenos Aires (UBA), Buenos Aires, Argentina
| | - Hugo R Vaca
- Departamento de Microbiología, Parasitología e Inmunología, Facultad de Medicina, Universidad de Buenos Aires (UBA), Ciudad Autónoma de Buenos Aires, Argentina.,Universidad de Buenos Aires (UBA), CONICET, Instituto de Investigaciones en Microbiología y Parasitología Médica (IMPaM), Ciudad Autónoma de Buenos Aires, Argentina
| | - Ines Guarnaschelli
- Sección Biología Celular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Uriel Koziol
- Sección Biología Celular, Facultad de Ciencias, Universidad de la República, Montevideo, Uruguay
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Andreia C K Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA.
| |
Collapse
|
6
|
Aggarwal S, Liu X, Rice C, Menell P, Clark PJ, Paparoidamis N, Xiao YC, Salvino JM, Fontana ACK, España RA, Kortagere S, Mortensen OV. Identification of a Novel Allosteric Modulator of the Human Dopamine Transporter. ACS Chem Neurosci 2019; 10:3718-3730. [PMID: 31184115 PMCID: PMC6703927 DOI: 10.1021/acschemneuro.9b00262] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The dopamine transporter (DAT) serves a pivotal role in controlling dopamine (DA)-mediated neurotransmission by clearing DA from synaptic and perisynaptic spaces and controlling its action at postsynaptic DA receptors. Major drugs of abuse such as amphetamine and cocaine interact with DAT to mediate their effects by enhancing extracellular DA concentrations. We previously identified a novel allosteric site in the related human serotonin transporter that lies outside the central substrate and inhibitor binding pocket. We used the hybrid structure based (HSB) method to screen for allosteric modulator molecules that target a similar site in DAT. We identified a compound, KM822, that was found to be a selective, noncompetitive inhibitor of DAT. We confirmed the structural determinants of KM822 allosteric binding within the allosteric site by structure/function and substituted cysteine scanning accessibility biotinylation experiments. In the in vitro cell-based assay and ex vivo in both rat striatal synaptosomal and slice preparations, KM822 was found to decrease the affinity of cocaine for DAT. The in vivo effects of KM822 on cocaine were tested on psychostimulant-associated behaviors in a planarian model where KM822 specifically inhibited the locomotion elicited by DAT-interacting stimulants amphetamine and cocaine. Overall, KM822 provides a unique opportunity as a molecular probe to examine allosteric modulation of DAT function.
Collapse
Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Xiaonan Liu
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Caitlyn Rice
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Paul Menell
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Philip J. Clark
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, United States
| | | | - You-cai Xiao
- The Wistar Institute, Philadelphia, Pennsylvania 19104, United States
| | - Joseph M. Salvino
- The Wistar Institute, Philadelphia, Pennsylvania 19104, United States
| | - Andréia C. K. Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Rodrigo A. España
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, United States
| | - Sandhya Kortagere
- Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, United States
| | - Ole V. Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| |
Collapse
|
7
|
Meleka MM, Edwards AJ, Xia J, Dahlen SA, Mohanty I, Medcalf M, Aggarwal S, Moeller KD, Mortensen OV, Osei-Owusu P. Anti-hypertensive mechanisms of cyclic depsipeptide inhibitor ligands for G q/11 class G proteins. Pharmacol Res 2019; 141:264-275. [PMID: 30634050 DOI: 10.1016/j.phrs.2019.01.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Revised: 01/04/2019] [Accepted: 01/04/2019] [Indexed: 01/14/2023]
Abstract
Augmented vasoconstriction is a hallmark of hypertension and is mediated partly by hyper-stimulation of G protein couple receptors (GPCRs) and downstream signaling components. Although GPCR blockade is a key component of current anti-hypertensive strategies, whether hypertension is better managed by directly targeting G proteins has not been thoroughly investigated. Here, we tested whether inhibiting Gq/11 proteins in vivo and ex vivo using natural cyclic depsipeptide, FR900359 (FR) from the ornamental plant, Ardisia crenata, and YM-254890 (YM) from Chromobacterium sp. QS3666, or it's synthetic analog, WU-07047 (WU), was sufficient to reverse hypertension in mice. All three inhibitors blocked G protein-dependent vasoconstriction, but to our surprise YM and WU and not FR inhibited K+-induced Ca2+ transients and vasoconstriction of intact vessels. However, each inhibitor blocked whole-cell L-type Ca2+ channel current in vascular smooth muscle cells. Subcutaneous injection of FR or YM (0.3 mg/kg, s.c.) in normotensive and hypertensive mice elicited bradycardia and marked blood pressure decrease, which was more severe and long lasting after the injection of FR relative to YM (FRt1/2 ≅ 12 h vs. YMt1/2 ≅ 4 h). In deoxycorticosterone acetate (DOCA)-salt hypertension mice, chronic injection of FR (0.3 mg/kg, s.c., daily for seven days) reversed hypertension (vehicle SBP: 149 ± 5 vs. FR SBP: 117 ± 7 mmHg), without any effect on heart rate. Our results together support the hypothesis that increased LTCC and Gq/11 activity is involved in the pathogenesis of hypertension, and that dual targeting of both proteins can reverse hypertension and associated cardiovascular disorders.
Collapse
Affiliation(s)
- Matthew M Meleka
- Departments of Pharmacology & Physiology, United States; Internal Medicine, Drexel University College of Medicine, Philadelphia, PA, 19102, United States
| | | | - Jingsheng Xia
- Departments of Pharmacology & Physiology, United States
| | | | | | - Matthew Medcalf
- Department of Chemistry, Washington University, St. Louis, MO, 63130, United States
| | | | - Kevin D Moeller
- Department of Chemistry, Washington University, St. Louis, MO, 63130, United States
| | | | | |
Collapse
|
8
|
Marshall CA, Brodnik ZD, Mortensen OV, Reith MEA, Shumsky JS, Waterhouse BD, España RA, Kortagere S. Selective activation of Dopamine D3 receptors and norepinephrine transporter blockade enhances sustained attention. Neuropharmacology 2019; 148:178-188. [PMID: 30633928 DOI: 10.1016/j.neuropharm.2019.01.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Revised: 12/28/2018] [Accepted: 01/06/2019] [Indexed: 11/17/2022]
Abstract
Catecholamine transmitters dopamine (DA) and norepinephrine (NE) regulate prefrontal cortical (PFC) circuit activity and PFC-mediated executive functions. Accordingly, pharmacological agents that influence catecholamine neurotransmission exert prominent effects on cognition. Many such agents are used clinically to treat attention disorders. For example, methylphenidate blocks DA and NE reuptake and is the leading choice for attention deficit hyperactivity disorder (ADHD) treatment. Recently, we have designed SK609 - a selective small molecule agonist of the DA D3 receptor (D3R). In this study, we further characterized SK609's ability to selectively inhibit the reuptake of NE by NE transporters (NET). Our results indicate SK609 selectively inhibits NET with a Ki value of ∼500 nM and behaves as a NET substrate. Systemic dosing of SK609 (4 mg/kg; i.p.) in naïve rats produced a 300% and 160% increase in NE and DA, respectively, in the PFC as measured by microdialysis. Based on these neurochemical results, SK609 was tested in a PFC-dependent, visually-guided sustained attention task in rats. SK609 improved performance in a dose-dependent manner with a classical inverted-U dose response function with a peak effect at 4 mg/kg. SK609's peak effect was blocked by a pre-treatment with either the D2/D3R antagonist raclopride (0.05 mg/kg; i.p) or the alpha-1 adrenergic receptor antagonist prazosin (0.25 mg/kg; i.p), confirming a role for both DA and NE in promoting sustained attention. Additionally, SK609 improved sustained attention more prominently among low-performing animals. Doses of SK609 (2, 4, and 8 mg/kg) associated with cognitive enhancement did not produce an increase in spontaneous locomotor activity, suggesting a lack of side effects mediated by DA transporter (DAT) activity. These results demonstrate that the novel catecholaminergic modulator SK609 has the potential to treat sustained attention deficits without affecting DAT activity, distinguishing it from amphetamines and methylphenidate.
Collapse
Affiliation(s)
- Courtney A Marshall
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Zachary D Brodnik
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Maarten E A Reith
- Department of Psychiatry and of Biochemistry and Molecular Pharmacology, New York University Langone Medical Center, New York City, NY, USA
| | - Jed S Shumsky
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Barry D Waterhouse
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA; Department of Cell Biology and Neurscience, Rowan University School of Osteopathic Medicine, Stratford, NJ, USA
| | - Rodrigo A España
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Sandhya Kortagere
- Department of Microbiology and Immunology, Institute for Molecular Medicine, Drexel University College of Medicine, Philadelphia, PA, USA; Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, USA.
| |
Collapse
|
9
|
Kortagere S, Mortensen OV, Xia J, Lester W, Fang Y, Srikanth Y, Salvino JM, Fontana ACK. Identification of Novel Allosteric Modulators of Glutamate Transporter EAAT2. ACS Chem Neurosci 2018; 9:522-534. [PMID: 29140675 DOI: 10.1021/acschemneuro.7b00308] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Dysfunction of excitatory amino acid transporters (EAATs) has been implicated in the pathogenesis of various neurological disorders, such as stroke, brain trauma, epilepsy, and neurodegenerative diseases, among others. EAAT2 is the main subtype responsible for glutamate clearance in the brain, having a key role in regulating transmission and preventing excitotoxicity. Therefore, compounds that increase the expression or activity of EAAT2 have therapeutic potential for neuroprotection. Previous studies identified molecular determinants for EAAT2 transport stimulation in a structural domain that lies at the interface of the rigid trimerization domain and the central substrate binding transport domain. In this work, a hybrid structure based approach was applied, based on this molecular domain, to create a high-resolution pharmacophore. Subsequently, virtual screening of a library of small molecules was performed, identifying 10 hit molecules that interact at the proposed domain. Among these, three compounds were determined to be activators, four were inhibitors, and three had no effect on EAAT2-mediated transport in vitro. Further characterization of the two best ranking EAAT2 activators for efficacy, potency, and selectivity for glutamate over monoamine transporters subtypes and NMDA receptors and for efficacy in cultured astrocytes is demonstrated. Mutagenesis studies suggest that the EAAT2 activators interact with residues forming the interface between the trimerization and transport domains. These compounds enhance the glutamate translocation rate, with no effect on substrate interaction, suggesting an allosteric mechanism. The identification of these novel positive allosteric modulators of EAAT2 offers an innovative approach for the development of therapies based on glutamate transport enhancement.
Collapse
Affiliation(s)
- Sandhya Kortagere
- Department of Microbiology and Immunology, Centers for Molecular Parasitology, Virology and Translational Neuroscience, Institute for Molecular Medicine, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, United States
| | - Ole V. Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Jingsheng Xia
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - William Lester
- Analytical Chemistry, Division of Pre-Clinical Innovation (DPI), NCATS, National Institutes of Health, Rockville, Maryland 20850, United States
| | - Yuhong Fang
- Analytical Chemistry, Division of Pre-Clinical Innovation (DPI), NCATS, National Institutes of Health, Rockville, Maryland 20850, United States
| | - Yellamelli Srikanth
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Joseph M. Salvino
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| | - Andréia C. K. Fontana
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, United States
| |
Collapse
|
10
|
Abstract
Detailed in this unit are protocols for studying the in vitro uptake of dopamine (DA) as a means for defining the functional characteristics of dopamine transporters. All assays are performed using commercially available cell lines that transiently express the transporter under investigation. The three main assays provided are: a kinetic assay to calculate the affinity (KM ) and maximal velocity (Vmax ) of radiolabeled DA uptake into cells; concentration-response assays to measure the potencies (IC50 /Ki values) of test compounds as transport inhibitors; and an efflux assay to assess the ability and potency (EC50 ) of a ligand to elicit reverse transport of DA accumulated in the cell. Although the methods are described using DAT and its ligands, the same procedure can be employed for studying serotonin and norepinephrine transporters as well. © 2017 by John Wiley & Sons, Inc.
Collapse
Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| |
Collapse
|
11
|
Abstract
The dopamine (DAT), serotonin (SERT), and norepinephrine (NET) transporters, which are collectively referred to as monoamine transporters (MATs), play significant roles in regulating the neuronal response to these neurotransmitters. MATs terminate the action of these neurotransmitters by translocating them from the synaptic space into the presynaptic neurons. These three transmitters are responsible for controlling a number of physiological, emotional, and behavioral functions, with their transporters being the site of action of drugs employed for the treatment of a variety of conditions, including depression, anxiety, ADHD, schizophrenia, and psychostimulant abuse. Provided in this unit is information on the localization and regulation of MATs and the structural components of these proteins most responsible for the translocation process. Also included is a brief description of the evolution of ligands that interact with these transporters, as well as current theories concerning the pharmacological effects of substances that interact with these sites, including the molecular mechanisms of action of uptake inhibitors and allosteric modulators. Data relating to the presence, structure, and functions of allosteric modulators are included as well. The aim of this review is to provide background information on MATs to those who are new to this field, with a focus on the therapeutic potential of compounds that interact with these substrate transport sites. © 2017 by John Wiley & Sons, Inc.
Collapse
Affiliation(s)
- Shaili Aggarwal
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Pennsylvania
| | - Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Pennsylvania
| |
Collapse
|
12
|
Mortensen OV, Larsen MB, Amara SG. MAP Kinase Phosphatase 3 (MKP3) Preserves Norepinephrine Transporter Activity by Modulating ERK1/2 Kinase-Mediated Gene Expression. Front Cell Neurosci 2017; 11:253. [PMID: 28878626 PMCID: PMC5572231 DOI: 10.3389/fncel.2017.00253] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 08/08/2017] [Indexed: 12/03/2022] Open
Abstract
The norepinephrine transporter (NET) mediates the clearance of norepinephrine (NE) from the extracellular space and is a target of therapeutic antidepressants and psychostimulants. Previously we identified a MAP kinase phosphatase 3 (MKP3), as an important modulator of protein kinase C (PKC) mediated internalization of the related dopamine transporter (DAT). Here we show that MKP3 decreases PKC-mediated down regulation of NET expressed in PC12 cells. We demonstrate that this process involves a PKC-stimulated decrease of NET surface expression that is dependent on dynamin. Surprisingly, MAP kinase inhibitors have no effect on the PKC-mediated regulation of NET activity, suggesting that, like PKC-mediated regulation of the DAT, the acute activation of MAP kinases is not likely to be involved. To elucidate potential mechanisms we used a substrate trap-based assay to identify extracellular-signal-regulated kinase (ERK)1/2 as the predominant substrate of MKP3. Furthermore we also established that brief chemical stabilization of a modified destabilized MKP3 does not alter PKC-mediated down regulation of NET. Finally, the expression of a dominant negative version of H-Ras, an upstream activator of ERK1/2, abolishes phorbol 12-myristate 13-acetate (PMA)-mediated down regulation of NET in a manner similar to MKP3. Taken together we propose that chronic MKP3 expression regulates surface NET through the sustained inhibition of ERK1/2 MAP kinase signaling that alters gene expression in PC12 cells. This is supported by gene expression data from naïve and MKP3-expressing PC12 cells that reveal robust decreases in gene expression of several genes in the MKP3-tranfected cells. Interestingly, caveolin-1, a protein with a critical role in membrane protein trafficking is down regulated by MKP3 expression. We further show that selective silencing of the caveolin-1 gene in naïve PC12 cells attenuates PKC-mediated downregulation of NET activity, consistent with a potential role for caveolins in regulating NET surface expression. In summary, these results suggest that chronic MKP3 expression alters the expression of genes in PC12 cells that are involved in the regulation of NET surface expression.
Collapse
Affiliation(s)
- Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of MedicinePhiladelphia, PA, United States
| | - Mads B Larsen
- Department of Cell Biology and Physiology, University of Pittsburgh School of MedicinePittsburgh, PA, United States
| | - Susan G Amara
- National Institute of Mental HealthBethesda, MD, United States
| |
Collapse
|
13
|
Mortensen OV, Kortagere S. Designing modulators of monoamine transporters using virtual screening techniques. Front Pharmacol 2015; 6:223. [PMID: 26483692 PMCID: PMC4586420 DOI: 10.3389/fphar.2015.00223] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 09/17/2015] [Indexed: 12/15/2022] Open
Abstract
The plasma-membrane monoamine transporters (MATs), including the serotonin (SERT), norepinephrine (NET) and dopamine (DAT) transporters, serve a pivotal role in limiting monoamine-mediated neurotransmission through the reuptake of their respective monoamine neurotransmitters. The transporters are the main target of clinically used psychostimulants and antidepressants. Despite the availability of several potent and selective MAT substrates and inhibitors the continuing need for therapeutic drugs to treat brain disorders involving aberrant monoamine signaling provides a compelling reason to identify novel ways of targeting and modulating the MATs. Designing novel modulators of MAT function have been limited by the lack of three dimensional structure information of the individual MATs. However, crystal structures of LeuT, a bacterial homolog of MATs, in a substrate-bound occluded, substrate-free outward-open, and an apo inward-open state and also with competitive and non-competitive inhibitors have been determined. In addition, several structures of the Drosophila DAT have also been resolved. Together with computational modeling and experimental data gathered over the past decade, these structures have dramatically advanced our understanding of several aspects of SERT, NET, and DAT transporter function, including some of the molecular determinants of ligand interaction at orthosteric substrate and inhibitor binding pockets. In addition progress has been made in the understanding of how allosteric modulation of MAT function can be achieved. Here we will review all the efforts up to date that has been made through computational approaches employing structural models of MATs to design small molecule modulators to the orthosteric and allosteric sites using virtual screening techniques.
Collapse
Affiliation(s)
- Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine , Philadelphia, PA, USA
| | - Sandhya Kortagere
- Department of Microbiology and Immunology, Drexel University College of Medicine , Philadelphia, PA, USA
| |
Collapse
|
14
|
Mortensen OV, Liberato JL, Coutinho-Netto J, dos Santos WF, Fontana ACK. Molecular determinants of transport stimulation of EAAT2 are located at interface between the trimerization and substrate transport domains. J Neurochem 2015; 133:199-210. [DOI: 10.1111/jnc.13047] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Revised: 01/18/2015] [Accepted: 01/21/2015] [Indexed: 01/04/2023]
Affiliation(s)
- Ole V. Mortensen
- Department of Pharmacology and Physiology; Drexel University College of Medicine; Philadelphia Pennsylvania USA
| | - José L. Liberato
- Neurobiology and Venoms Laboratory; Department of Biology; College of Philosophy; Sciences and Literature of Ribeirão Preto; University of São Paulo; Ribeirão Preto SP Brazil
| | - Joaquim Coutinho-Netto
- Department of Biochemistry and Immunology; Ribeirão Preto School of Medicine; University of São Paulo; SP Brazil
| | - Wagner F. dos Santos
- Neurobiology and Venoms Laboratory; Department of Biology; College of Philosophy; Sciences and Literature of Ribeirão Preto; University of São Paulo; Ribeirão Preto SP Brazil
| | - Andréia C. K. Fontana
- Department of Pharmacology and Physiology; Drexel University College of Medicine; Philadelphia Pennsylvania USA
| |
Collapse
|
15
|
Mortensen OV. MKP3 eliminates depolarization-dependent neurotransmitter release through downregulation of L-type calcium channel Cav1.2 expression. Cell Calcium 2013; 53:224-30. [PMID: 23337371 DOI: 10.1016/j.ceca.2012.12.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Revised: 12/06/2012] [Accepted: 12/24/2012] [Indexed: 01/17/2023]
Abstract
Release of neurotransmitters is a fundamental and regulated process that is essential for normal brain functioning. Regulation of this process is potentially important for any neuronal process, and disruption of the release process may contribute to the pathophysiology associated with psychiatric diseases. In this work it is shown that expression of the negative regulator of mitogen-activated protein kinase (MAPK) signaling the MAPK phosphatase MKP3/DUSP6 eliminates depolarization-dependent release of dopamine in rat PC12 cells. Pharmacologic interventions with latrotroxin (LTX) or A23187, which make the cells permeable to calcium, reestablish the dopamine release. Calcium imaging also reveals that calcium influx is impaired in MKP3-expressing cells. Because acute pharmacologic inhibition of MAPKs has no effect on dopamine release in naïve PC12 cells, the MKP3-mediated elimination of neurotransmitter release must be caused by a long-term process, such as changes in gene expression. In support of this the expression of the L-type calcium channel cav1.2 alpha subunit (Cacna1c) is decreased in MKP3-expressing PC12 cells. With the reintroduction of cav1.2 expression, neurotransmitter release is restored in the MKP3-expressing PC12 cells. Thus, MKP3 expression reduces neurotransmitter release by decreasing the expression of cav1.2. Because MKP3 is increased when neuronal activity is elevated, this process could play a role in regulating neurotransmitter homeostasis.
Collapse
Affiliation(s)
- Ole V Mortensen
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
| |
Collapse
|
16
|
Larsen MB, Fontana ACK, Magalhães LG, Rodrigues V, Mortensen OV. A catecholamine transporter from the human parasite Schistosoma mansoni with low affinity for psychostimulants. Mol Biochem Parasitol 2011; 177:35-41. [PMID: 21251927 DOI: 10.1016/j.molbiopara.2011.01.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 12/21/2010] [Accepted: 01/07/2011] [Indexed: 11/25/2022]
Abstract
The trematode Schistosoma mansoni is the primary cause of schistosomiasis, a devastating neglected tropical disease that affects 200 million individuals. Identifying novel therapeutic targets for the treatment of schistosomiasis is therefore of great public interest. The catecholamines norepinephrine (NE) and dopamine (DA) are essential for the survival of the parasite as they cause muscular relaxation and a lengthening in the parasite and thereby control movement. Here we characterize a novel dopamine/norepinephrine transporter (SmDAT) gene transcript, from S. mansoni. The SmDAT is expressed in the adult form and in the sporocyst form (infected snails) of the parasite, and also in the egg and miracidium stage. It is absent in the cercariae stage but curiously a transcript missing the exon encoding transmembrane domain 8 was identified in this stage. Heterologous expression of the cDNA in mammalian cells resulted in saturable, dopamine transport activity with an apparent affinity for dopamine comparable to that of the human dopamine transporter. Efflux experiments reveal notably higher substrate selectivity compared with its mammalian counterparts as amphetamine is a much less potent efflux elicitor against SmDAT compared to the human DAT. Pharmacological characterization of the SmDAT revealed that most human DAT inhibitors including psychostimulants such as cocaine were significantly less potent in inhibiting SmDAT. Like DATs from other simpler organisms the pharmacology for SmDAT was more similar to the human norepinephrine transporter. We were not able to identify other dopamine transporting carriers within the completed parasite genome and we hypothesize that the SmDAT is the only catecholamine transporter in the parasite and could be responsible for not only clearing DA but also NE.
Collapse
Affiliation(s)
- Mads B Larsen
- Department of Neurobiology, University of Pittsburgh School of Medicine, PA 15260, USA
| | | | | | | | | |
Collapse
|
17
|
Redman PT, Jefferson BS, Ziegler CB, Mortensen OV, Torres GE, Levitan ES, Aizenman E. A vital role for voltage-dependent potassium channels in dopamine transporter-mediated 6-hydroxydopamine neurotoxicity. Neuroscience 2006; 143:1-6. [PMID: 17027171 PMCID: PMC2673085 DOI: 10.1016/j.neuroscience.2006.08.039] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Revised: 08/09/2006] [Accepted: 08/18/2006] [Indexed: 11/16/2022]
Abstract
6-Hydroxydopamine (6-OHDA), a neurotoxic substrate of the dopamine transporter (DAT), is widely used in Parkinson's disease models. However, the molecular mechanisms underlying 6-OHDA's selectivity for dopamine neurons and the injurious sequelae that it triggers are not well understood. We tested whether ectopic expression of DAT induces sensitivity to 6-OHDA in non-dopaminergic rat cortical neurons and evaluated the contribution of voltage-dependent potassium channel (Kv)-dependent apoptosis to the toxicity of this compound in rat cortical and midbrain dopamine neurons. Cortical neurons expressing DAT accumulated dopamine and were highly vulnerable to 6-OHDA. Pharmacological inhibition of DAT completely blocked this toxicity. We also observed a p38-dependent Kv current surge in DAT-expressing cortical neurons exposed to 6-OHDA, and p38 antagonists and Kv channel blockers were neuroprotective in this model. Thus, DAT-mediated uptake of 6-OHDA recruited the oxidant-induced Kv channel dependent cell death pathway present in cortical neurons. Finally, we report that 6-OHDA also increased Kv currents in cultured midbrain dopamine neurons and this toxicity was blocked with Kv channel antagonists. We conclude that native DAT expression accounts for the dopamine neuron specific toxicity of 6-OHDA. Following uptake, 6-OHDA triggers the oxidant-associated Kv channel-dependent cell death pathway that is conserved in non-dopaminergic cortical neurons and midbrain dopamine neurons.
Collapse
Affiliation(s)
- Patrick T. Redman
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Bahiyyah S. Jefferson
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Chandra B. Ziegler
- Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Ole V. Mortensen
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Gonzalo E. Torres
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Edwin S. Levitan
- Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Elias Aizenman
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
- Corresponding author: Dr. Elias Aizenman, Department of Neurobiology, University of Pittsburgh School of Medicine, E1456 BST, Pittsburgh, PA 15261 U.S.A. Tel: (412) 648-9434; fax: (412) 648-1441;
| |
Collapse
|
18
|
Mortensen OV, Amara SG. Gain of function mutants reveal sites important for the interaction of the atypical inhibitors benztropine and bupropion with monoamine transporters. J Neurochem 2006; 98:1531-40. [PMID: 16923164 DOI: 10.1111/j.1471-4159.2006.04060.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two atypical inhibitors of the dopamine transporter, benztropine, used in the treatment of Parkinson's disease, and bupropion, used as an antidepressant, show very different psychostimulant effects when compared with another inhibitor, cocaine. Taking advantage of the differential sensitivity of the dopamine and the norepinephrine transporters (DAT and NET) to benztropine and bupropion, we have used site-directed mutagenesis to produce gain-of-function mutants in NET which demonstrate that Ala279 in the trans-membrane domain 5 (TM5) and Ser359 in the TM7 of DAT are responsible for the higher sensitivity of DAT to both bupropion and benztropine. Substitution of these two DAT residues into the NET background does not alter the potency of NET-selective inhibitors, such as desipramine. The results from experiments examining the ability of DAT-selective inhibitors to displace [3H]nisoxetine binding in NET gain-of-function mutants suggest that Ser359 contributes to the initial binding of the inhibitor, and that Ala279 may influence subsequent steps involved in the blockade of translocation. Thus, these studies begin to identify residues that are important for the unique molecular interactions of benztropine and bupropion with the DAT, and that ultimately may contribute to the distinct behavioral actions of these drugs.
Collapse
Affiliation(s)
- Ole V Mortensen
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
| | | |
Collapse
|
19
|
Abstract
In the mammalian central nervous system the dopamine transporter (DAT) is the primary mechanism for clearance of dopamine from the extracellular space. Presynaptic receptors for dopamine and other neurotransmitters (auto-receptors and hetero-receptors) present on dopaminergic neurons are poised to regulate the activity of the dopamine transporter acutely through their actions on intracellular signaling systems. The mechanisms proposed for acute presynaptic regulation of dopamine transport include direct effects of phosphorylation on enzymatic rate, indirect effects through the alteration of the electrical and chemical gradients that drive transport and/or the modulation of transporter number through the trafficking of carriers to and from the cell surface. This review focuses on recent evidence for several distinct mechanisms which dynamically regulate dopamine transporter activity and thus have an important role in shaping the duration and amplitude of dopamine signals in the brain.
Collapse
Affiliation(s)
- Ole V Mortensen
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
| | | |
Collapse
|
20
|
Mortensen OV, Kristensen AS, Wiborg O. Species-scanning mutagenesis of the serotonin transporter reveals residues essential in selective, high-affinity recognition of antidepressants. J Neurochem 2001; 79:237-47. [PMID: 11677251 DOI: 10.1046/j.1471-4159.2001.00587.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The serotonin transporter (SERT) is a high-affinity sodium/chloride-dependent neurotransmitter transporter responsible for reuptake of serotonin from the extracellular space. SERT is a selective target of several clinically important antidepressants. In a cross-species analysis comparing human and bovine SERTs, the kinetic parameters for serotonin uptake were found to be similar, however, the pharmacological profiles of the two transporters differ. Following transient expression in COS-1 cells, IC(50) values were determined for several antidepressants and psychostimulants. The potencies of the antidepressants citalopram, fluoxetine, paroxetine and imipramine were several-fold higher at hSERT compared with bSERT. No species selectivity was observed for the antidepressants fluvoxamine, and sertraline or for the psychostimulants cocaine, the cocaine analogue beta-carbomethoxy-3beta-(4-iodophenyl)tropane, or for 3,4-methylenedioxymethamphetamine (MDMA). Analysis of six hSERT/bSERT chimeras and subsequent species-scanning mutagenesis of each isoform revealed methionine-180, tyrosine-495, and phenylalanine-513 to be responsible for the increase in citalopram and paroxetine potencies at hSERT and methionine-180 and phenylalanine-513 to confer species selectivity at hSERT for fluoxetine and imipramine. Results were obtained by doing the forward, bovine to human, mutations and confirmed by doing the reverse mutations. Citalopram analogues were used to define the roles of methionine-180, tyrosine-495, and phenylalanine-513 and to reveal molecular interactions with individual functional groups of citalopram. We suggest that methionine-180 interacts with the heterocyclic nucleus of citalopram or stabilizes the binding pocket and phenylalanine-513 to be a steric blocker of antidepressant recognition.
Collapse
Affiliation(s)
- O V Mortensen
- Laboratory of Molecular Neurobiology, Department of Biological Psychiatry, Psychiatric University Hospital, Risskov, Denmark
| | | | | |
Collapse
|
21
|
Mortensen OV, Kristensen AS, Rudnick G, Wiborg O. Molecular cloning, expression and characterization of a bovine serotonin transporter. Brain Res Mol Brain Res 1999; 71:120-6. [PMID: 10407194 DOI: 10.1016/s0169-328x(99)00178-3] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The serotonin transporter (SERT) is a member of a highly homologous family of sodium/chloride dependent neurotransmitter transporters responsible for reuptake of biogenic amines from the extracellular fluid. SERT constitutes the pharmacological target of several clinically important antidepressants. Here we report the molecular cloning of SERT from the bovine species. Translation of the nucleotide sequence revealed 44 amino acid differences compared to human SERT. When transiently expressed in HeLa cells and compared with rat and human SERTs the K(m) value for uptake was increased 2-fold. V(max) and B(max) were both increased about 4-fold indicating the turnover number is conserved. The pharmacological profile revealed a decreased sensitivity towards imipramine, desipramine, citalopram, fluoxetine and paroxetine compared with human SERT, while the sensitivity towards 3, 4-methylenedioxymethamphetamine (MDMA) was mainly unchanged. RT-PCR amplification of RNA from different tissues demonstrated expression of SERT in placenta, brain stem, bone marrow, kidney, lung, heart, adrenal gland, liver, parathyroid gland, thyroid gland, small intestine and pancreas.
Collapse
Affiliation(s)
- O V Mortensen
- Department of Biological Psychiatry, Psychiatric University Hospital, Skovagervej 2, 8240 Risskov, Denmark
| | | | | | | |
Collapse
|
22
|
Mortensen OV, Thomassen M, Larsen MB, Whittemore SR, Wiborg O. Functional analysis of a novel human serotonin transporter gene promoter in immortalized raphe cells. Brain Res Mol Brain Res 1999; 68:141-8. [PMID: 10320791 DOI: 10.1016/s0169-328x(99)00083-2] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To investigate the structural basis for genetic regulation of the human serotonin transporter gene, a 1.8 kb fragment upstream to the cap site was cloned and sequenced. The promoter possesses a polymorphic repeat region with 16 and 14 repeats, respectively. Both were cloned and characterized. The promoter sequence revealed an internal 379 bp fragment not reported in previous publications. This novel fragment contains consensus sequences for several transcription factors including SpI and GATA. DNA from 48 unrelated individuals was PCR amplified, in this region, to test for allelic variations. All were found to possess the additional 379 bp fragment. The integrity of the promoter was furthermore confirmed by genomic Southern blotting. The promoter activity was analyzed by reporter gene assays in neuronal and non-neuronal serotonergic cell lines. In immortalized serotonergic raphe neurons, RN46A, three cis-acting, cell specific, activating elements and a silencer were located. One of the activators and the silencer are located in the repeat region and one activator is positioned in the novel fragment. A fourth activating element was found to be active in both RN46A cells and in a non-neuronal serotonergic cell line, JAR. A 3.5 kb fragment from intron 1 was cloned and found to possess cell specific activity in JAR cells indicating the presence of an alternative promoter in intron 1.
Collapse
Affiliation(s)
- O V Mortensen
- Department of Biological Psychiatry, Psychiatric University Hospital, Skovagervej 2, 8240 Risskov, Denmark
| | | | | | | | | |
Collapse
|