RESUMEN
Parkinson disease is typically treated with L-3,4-dihydroxyphenylalanine (or levodopa) co-prescribed with concentration stabilizers to prevent undesired motor fluctuations. However, the beneficial role of the chronic combined therapy on disease progression has not been thoroughly explored. We hypothesized that tolcapone, a catechol-O-methyl-transferase inhibitor, co-administered with levodopa may offer beneficial long-term disease-modifying effects through its dopamine stabilization actions. Here, we followed vesicular monoamine transporter 2-deficient and wild-type mice treated twice daily per os with vehicle, levodopa (20 mg/kg), tolcapone (15 mg/kg) or levodopa (12.5 mg/kg) + tolcapone (15 mg/kg) for 17 weeks. We assessed open field, bar test and rotarod performances at baseline and every 4th week thereafter, corresponding to OFF-medication weeks. Finally, we collected coronal sections from the frontal caudate-putamen and determined the reactivity level of dopamine transporter. Vesicular monoamine transporter 2-deficient mice responded positively to chronic levodopa + tolcapone intervention in the bar test during OFF-periods. Neither levodopa nor tolcapone interventions offered significant improvements on their own. Similarly, chronic levodopa + tolcapone intervention was associated with partially rescued dopamine transporter levels, whereas animals treated solely with levodopa or tolcapone did not present this effect. Interestingly, 4-month progression of bar test scores correlated significantly with dopamine-transporter-label density. Overall, we observed a moderate functional and histopathological improvement effect by chronic dopamine replacement when combined with tolcapone in vesicular monoamine transporter 2-deficient mice. Altogether, chronic stabilization of dopamine levels by catechol-O-methyl-transferase inhibition, besides its intended immediate actions, arises as a potential long-term beneficial approach during the progression of Parkinson disease.
Asunto(s)
Antiparkinsonianos/uso terapéutico , Inhibidores de Catecol O-Metiltransferasa/farmacología , Levodopa/uso terapéutico , Enfermedad de Parkinson/tratamiento farmacológico , Enfermedad de Parkinson/genética , Tolcapona/uso terapéutico , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Proteínas de Transporte Vesicular de Monoaminas/genética , Animales , Conducta Animal/efectos de los fármacos , Proteínas de Transporte de Dopamina a través de la Membrana Plasmática/metabolismo , Ingestión de Alimentos/efectos de los fármacos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Enfermedad de Parkinson/psicología , Desempeño Psicomotor/efectos de los fármacosRESUMEN
The type 2 vesicular monoamine transporter (VMAT2), by regulating the storage of monoamines transmitters into synaptic vesicles, has a protective role against their cytoplasmic toxicity. Increasing evidence suggests that impairment of VMAT2 neuroprotection contributes to the pathogenesis of Parkinson's disease (PD). Several transgenic VMAT2 mice models have been developed, however these models lack specificity regarding the monoaminergic system targeting. To circumvent this limitation, we created VMAT2-KO mice specific to the dopamine (DA) nigrostriatal pathway to analyze VMAT2's involvement in DA depletion-induced motor features associated to PD and examine the relevance of DA toxicity in the pathogenesis of neurodegeneration. Adult VMAT2 floxed mice were injected in the substancia nigra (SN) with an adeno-associated virus (AAV) expressing the Cre-recombinase allowing VMAT2 removal in DA neurons of the nigrostriatal pathway solely. VMAT2 deletion in the SN induced both DA depletion exclusively in the dorsal striatum and motor dysfunction. At 16 weeks post-injection, motor symptoms were accompanied with a decreased in food and water consumption and weight loss. However, despite an accelerating death, degeneration of nigrostriatal neurons was not observed in this model during this time frame. This study highlights a non-cytotoxic role of DA in our genetic model of VMAT2 deletion exclusively in nigrostriatal neurons.
Asunto(s)
Dopamina/deficiencia , Neuronas Dopaminérgicas/metabolismo , Enfermedad de Parkinson Secundaria/genética , Sustancia Negra/metabolismo , Vesículas Sinápticas/metabolismo , Proteínas de Transporte Vesicular de Monoaminas/genética , Animales , Cuerpo Estriado/metabolismo , Cuerpo Estriado/patología , Dependovirus/genética , Dependovirus/metabolismo , Neuronas Dopaminérgicas/patología , Ingestión de Líquidos , Ingestión de Alimentos , Eliminación de Gen , Expresión Génica , Inyecciones Intraventriculares , Integrasas/genética , Integrasas/metabolismo , Masculino , Ratones , Ratones Transgénicos , Enfermedad de Parkinson Secundaria/metabolismo , Enfermedad de Parkinson Secundaria/patología , Enfermedad de Parkinson Secundaria/fisiopatología , Sustancia Negra/patología , Vesículas Sinápticas/patología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Pérdida de PesoRESUMEN
Model-based optimization approaches are valuable in developing new drugs for human metabolic disorders. The core objective in most optimal drug designs is positive therapeutic effects. In this study, we considered the effects of therapeutic, adverse, and target variation simultaneously. A fuzzy optimization method was applied to formulate a multiobjective drug design problem for detecting enzyme targets in the presynaptic dopamine metabolic network to remedy two types of enzymopathies caused by deficiencies of vesicular monoamine transporter 2 (VMAT2) and tyrosine hydroxylase (TH). The fuzzy membership approach transforms a two-stage drug discovery problem into a unified decision-making problem. We developed a nested hybrid differential evolution algorithm to efficiently identify a set of potential drug targets. Furthermore, we also simulated the effects of current clinical drugs for Parkinson's disease (PD) in this model and tried to clarify the possible causes of neurotoxic and neuroprotective effects. The optimal drug design could yield 100% satisfaction grade when both therapeutic effect and the number of targets were considered in the objective. This scenario required regulating one to three and one or two enzyme targets for 50%-95% and 50%-100% VMAT2 and TH deficiencies, respectively. However, their corresponding adverse and target variation effect grades were less satisfactory. For the most severe deficiencies of VMAT2 and TH, a compromise design could be obtained when the effects of therapeutic, adverse, and target variation were simultaneously applied to the optimal drug discovery problem. Such a trade-off design followed the no free lunch theorem for optimization; that is, a more serious dopamine deficiency required more enzyme targets and lower satisfaction grade. In addition, the therapeutic effects of current clinical medications for PD could be enhanced in combination with new enzyme targets. The increase of toxic metabolites after treatment might be the cause of neurotoxic effects of some current PD medications.
Asunto(s)
Dopaminérgicos/farmacología , Trastornos Distónicos/congénito , Redes y Vías Metabólicas/efectos de los fármacos , Terminales Presinápticos/enzimología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Algoritmos , Diseño de Fármacos , Cálculo de Dosificación de Drogas , Trastornos Distónicos/enzimología , Lógica Difusa , Humanos , Modelos Teóricos , Enfermedad de Parkinson/tratamiento farmacológico , Enfermedad de Parkinson/enzimología , Terminales Presinápticos/efectos de los fármacosRESUMEN
Dopamine (DA) neurons in the ventral tegmental area (VTA) help mediate stress susceptibility and resilience. However, upstream mechanisms controlling these neurons remain unknown. Noradrenergic (NE) neurons in the locus coeruleus, implicated in the pathophysiology of depression, have direct connections within the VTA. Here we demonstrate that NE neurons regulate vulnerability to social defeat through inhibitory control of VTA DA neurons.
Asunto(s)
Neuronas Adrenérgicas/fisiología , Neuronas Dopaminérgicas/metabolismo , Inhibición Neural/fisiología , Resiliencia Psicológica , Estrés Psicológico/metabolismo , Animales , Enfermedad Crónica , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Norepinefrina/fisiología , Estrés Psicológico/genética , Estrés Psicológico/psicología , Área Tegmental Ventral/metabolismo , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Proteínas de Transporte Vesicular de Monoaminas/genéticaRESUMEN
In Parkinson's disease (PD), profound putamen dopamine (DA) depletion reflects denervation and a shift from vesicular sequestration to oxidative deamination of cytoplasmic DA in residual terminals. PD also involves cardiac sympathetic denervation. Whether PD entails myocardial norepinephrine (NE) depletion and a sequestration-deamination shift have been unknown. We measured apical myocardial tissue concentrations of NE, DA, and their neuronal metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC) from 23 PD patients and 23 controls and ascertained the extent of myocardial NE depletion in PD. We devised, validated in VMAT2-Lo mice, and applied 5 neurochemical indices of the sequestration-deamination shift-concentration ratios of DOPAC:DA, DA:NE, DHPG:NE, DOPAC:NE, and DHPG:DOPAC-and used a kinetic model to estimate the extent of the vesicular storage defect. The PD group had decreased myocardial NE content (p < 0.0001). The majority of patients (70%) had severe NE depletion (mean 2% of control), and in this subgroup all five indices of a sequestration-deamination shift were increased compared to controls (p < 0.001 for each). Vesicular storage in residual nerves was estimated to be decreased by 84-91% in this subgroup. We conclude that most PD patients have severe myocardial NE depletion, because of both sympathetic denervation and decreased vesicular storage in residual nerves. We found that the majority (70%) of Parkinson's disease (PD) patients have profound (98%) myocardial norepinephrine depletion, because of both cardiac sympathetic denervation and a shift from vesicular sequestration to oxidative deamination of cytoplasmic catecholamines in the residual nerves. This shift may be part of a final common pathogenetic pathway in the loss of catecholaminergic neurons that characterizes PD.
Asunto(s)
Miocardio/metabolismo , Estrés Oxidativo/fisiología , Enfermedad de Parkinson/metabolismo , Fibras Simpáticas Posganglionares/metabolismo , Vesículas Sinápticas/metabolismo , Anciano , Anciano de 80 o más Años , Animales , Desaminación/fisiología , Dopamina/metabolismo , Femenino , Humanos , Masculino , Ratones , Miocardio/patología , Norepinefrina/metabolismo , Enfermedad de Parkinson/patología , Fibras Simpáticas Posganglionares/patología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Proteínas de Transporte Vesicular de Monoaminas/metabolismoRESUMEN
Vesicular monoamine transporters (VMAT) are involved in presynaptic storage and release of neurotransmitters. While it was thought initially that only VMAT2 is brain expressed and VMAT1 is present only in the periphery, recent data have challenged the exclusive expression of VMAT2 in the brain. To further elucidate the role of VMAT1 brain expression and its potential role in neuropsychiatric disorders, we have investigated mice lacking VMAT1. Comparison of wildtype and knock-out (KO) mice using qPCR and immunohistochemistry documents the expression of VMAT1 in the brain. Deletion of VMAT1 leads to increased hippocampal apoptosis and reduced neurogenesis as assessed by caspase-3-labeling and 5-bromo-deoxy-uridine-labeling. Behavioral data show that mice lacking VMAT1 have neurocognitive deficits. VMAT2 expression is not altered in VMAT1 KO mice, suggesting a distinct role of VMAT1. Our data support VMAT1 brain expression and suggest that VMAT1 plays a key role in survival of hippocampal neurons and thus might contribute to neurocognitive deficits observed in neuropsychiatric disorders.
Asunto(s)
Encéfalo/fisiopatología , Trastornos del Conocimiento/fisiopatología , Discriminación en Psicología/fisiología , Neuronas/patología , Percepción Espacial/fisiología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Animales , Apoptosis/fisiología , Encéfalo/patología , Caspasa 3/metabolismo , Trastornos del Conocimiento/patología , Condicionamiento Psicológico/fisiología , Miedo/fisiología , Masculino , Ratones Noqueados , Neurogénesis/fisiología , Neuronas/fisiología , ARN Mensajero/metabolismo , Reconocimiento en Psicología/fisiología , Sinaptofisina/metabolismo , Proteínas de Transporte Vesicular de Monoaminas/genética , Proteínas de Transporte Vesicular de Monoaminas/metabolismoRESUMEN
The vesicular monoamine transporter type 2 gene (VMAT2) has a crucial role in the storage and synaptic release of all monoamines, including serotonin (5-HT). To evaluate the specific role of VMAT2 in 5-HT neurons, we produced a conditional ablation of VMAT2 under control of the serotonin transporter (slc6a4) promoter. VMAT2(sert-cre) mice showed a major (-95%) depletion of 5-HT levels in the brain with no major alterations in other monoamines. Raphe neurons contained no 5-HT immunoreactivity in VMAT2(sert-cre) mice but developed normal innervations, as assessed by both tryptophan hydroxylase 2 and 5-HT transporter labeling. Increased 5-HT(1A) autoreceptor coupling to G protein, as assessed with agonist-stimulated [(35)S]GTP-γ-S binding, was observed in the raphe area, indicating an adaptive change to reduced 5-HT transmission. Behavioral evaluation in adult VMAT2(sert-cre) mice showed an increase in escape-like reactions in response to tail suspension and anxiolytic-like response in the novelty-suppressed feeding test. In an aversive ultrasound-induced defense paradigm, VMAT2(sert-cre) mice displayed a major increase in escape-like behaviors. Wild-type-like defense phenotype could be rescued by replenishing intracellular 5-HT stores with chronic pargyline (a monoamine oxidase inhibitor) treatment. Pargyline also allowed some form of 5-HT release, although in reduced amounts, in synaptosomes from VMAT2(sert-cre) mouse brain. These findings are coherent with the notion that 5-HT has an important role in anxiety, and provide new insights into the role of endogenous 5-HT in defense behaviors.
Asunto(s)
Reacción de Fuga/fisiología , Neuronas Serotoninérgicas/metabolismo , Neuronas Serotoninérgicas/patología , Serotonina/deficiencia , Serotonina/genética , Índice de Severidad de la Enfermedad , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Proteínas de Transporte Vesicular de Monoaminas/genética , Animales , Eliminación de Gen , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones TransgénicosAsunto(s)
Monoaminas Biogénicas/metabolismo , Modelos Animales de Enfermedad , Enfermedad de Parkinson/fisiopatología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Animales , Ratones , Neurotoxinas/toxicidad , Enfermedad de Parkinson/etiología , Enfermedad de Parkinson/genética , Proteínas de Transporte Vesicular de Monoaminas/genéticaRESUMEN
Parkinson's disease (PD) is a progressive neurodegenerative disorder that is characterized by the loss of dopamine neurons in the substantia nigra pars compacta, culminating in severe motor symptoms, including resting tremor, rigidity, bradykinesia, and postural instability. In addition to motor deficits, there are a variety of nonmotor symptoms associated with PD. These symptoms generally precede the onset of motor symptoms, sometimes by years, and include anosmia, problems with gastrointestinal motility, sleep disturbances, sympathetic denervation, anxiety, and depression. Previously, we have shown that mice with a 95% genetic reduction in vesicular monoamine transporter expression (VMAT2-deficient, VMAT2 LO) display progressive loss of striatal dopamine, L-DOPA-responsive motor deficits, alpha-synuclein accumulation, and nigral dopaminergic cell loss. We hypothesized that since these animals exhibit deficits in other monoamine systems (norepinephrine and serotonin), which are known to regulate some of these behaviors, the VMAT2-deficient mice may display some of the nonmotor symptoms associated with PD. Here we report that the VMAT2-deficient mice demonstrate progressive deficits in olfactory discrimination, delayed gastric emptying, altered sleep latency, anxiety-like behavior, and age-dependent depressive behavior. These results suggest that the VMAT2-deficient mice may be a useful model of the nonmotor symptoms of PD. Furthermore, monoamine dysfunction may contribute to many of the nonmotor symptoms of PD, and interventions aimed at restoring monoamine function may be beneficial in treating the disease.
Asunto(s)
Conducta Animal , Encéfalo/metabolismo , Catecolaminas/metabolismo , Enfermedad de Parkinson/fisiopatología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Análisis de Varianza , Animales , Ansiedad/etiología , Ansiedad/metabolismo , Ansiedad/psicología , Cromatografía Líquida de Alta Presión , Depresión/etiología , Depresión/metabolismo , Depresión/psicología , Discriminación en Psicología , Modelos Animales de Enfermedad , Electrorretinografía , Femenino , Vaciamiento Gástrico , Masculino , Aprendizaje por Laberinto , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Enfermedad de Parkinson/complicaciones , Enfermedad de Parkinson/genética , Trastornos Intrínsecos del Sueño/etiología , Trastornos Intrínsecos del Sueño/metabolismo , Trastornos Intrínsecos del Sueño/psicología , Natación , Proteínas de Transporte Vesicular de Monoaminas/genética , Percepción VisualAsunto(s)
Proteínas de Transporte de Dopamina a través de la Membrana Plasmática/deficiencia , Receptores de Dopamina D2/metabolismo , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Animales , Unión Competitiva/efectos de los fármacos , Cuerpo Estriado/efectos de los fármacos , Domperidona/farmacocinética , Dopamina/farmacología , Antagonistas de Dopamina/farmacocinética , Relación Dosis-Respuesta a Droga , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones NoqueadosRESUMEN
Neurotransmitters have emerged as important players in the control of programmed cell death in the cerebral cortex. We report that genetic depletion of serotonin, dopamine, and norepinephrine in mice lacking the vesicular monoamine transporter (VMAT2 KO mice) causes an increase in cell death in the superficial layers of the cingulate and retrosplenial cortices during early postnatal life (postnatal days 0-4). Electron microscopy and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling indicated that this represents a form of apoptosis. Caspase-3 and -9 are over activated in the VMAT2 KO cortex and Bcl-X(L) is downregulated, whereas the apoptosis-inducing factor caspase-8 and FasL/FasR pathway are not involved. Partial inhibition of serotonin or/and catecholamine synthesis by pharmacological treatments or genetic reduction of serotonin neuron number in mice lacking the transcription factor Pet-1 (pheochromocytoma 12 E26 transformation-specific) did not modify the cell death ratios in the cerebral cortex. However, when monoamine oxidase type A was invalidated in the VMAT2 KO background (VMAT2-MAOA DKO mice), increases in 5-HT levels coincided with a reduction of cell death and a normalization of Bcl-X(L) expression. trkB signaling is not implicated in the anti-apoptotic effects of MAOA inhibition because BDNF mRNA levels were unchanged in VMAT2-MAOA DKO mice and because the massive cell death in the cerebral cortex of trkB KO mice is also reverted by genetic invalidation of the MAOA gene. Finally the broad 5-HT2 receptor agonist (-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride prevented the increase in cell death of VMAT2 KO mice. Altogether, these results suggest that high levels of serotonin, acting through 5-HT2 receptors, have neuroprotective action on cortical neurons by controlling Bcl-X(L) mRNA levels and that this action is independent of trkB signaling.
Asunto(s)
Apoptosis/fisiología , Corteza Cerebral/patología , Serotonina/fisiología , Proteínas de Transporte Vesicular de Monoaminas/deficiencia , Anfetaminas/farmacología , Animales , Caspasa 3/fisiología , Caspasa 9/fisiología , Corteza Cerebral/crecimiento & desarrollo , Dopamina/fisiología , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/fisiología , Giro del Cíngulo/crecimiento & desarrollo , Giro del Cíngulo/patología , Ratones , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Ratones Noqueados , Monoaminooxidasa/deficiencia , Monoaminooxidasa/genética , Factores de Crecimiento Nervioso/biosíntesis , Factores de Crecimiento Nervioso/genética , Neuronas/patología , Norepinefrina/fisiología , Receptor de Serotonina 5-HT2A/fisiología , Receptor de Serotonina 5-HT2C/fisiología , Agonistas del Receptor de Serotonina 5-HT2 , Agonistas de Receptores de Serotonina/farmacología , Transducción de Señal , Proteínas de Transporte Vesicular de Monoaminas/genética , Proteína X Asociada a bcl-2/fisiología , Proteína bcl-X/fisiologíaRESUMEN
Dopamine cytotoxicity is thought to contribute towards the selective loss of substantia nigra pars compacta dopamine neurons and disease progression in Parkinson's disease. However, the long-term toxicity of dopamine in vivo has not previously been established. The vesicular monoamine transporter 2 (VMAT2) sequesters monoamines into synaptic vesicles, a process that, in addition to being important in normal transmission, may also act to keep intracellular levels of monoamine neurotransmitters below potentially toxic thresholds. The homozygous VMAT2-hypomorphic mouse has an insertion in the VMAT2 gene (Slc18a2). Consequently, VMAT2-deficient mice (VD(-/-)) have an approximately 95% reduction in VMAT2 expression and an equivalent level of dopamine depletion in the striatum which results in moderate motor impairment. Here, we show that L-DOPA induces locomotor hyperactivity in VD(-/-) mice and reverses the deficit in motor coordination and balance as tested with the rotarod. We report that evidence for cytosolic accumulation of dopamine in substantia nigra neurons in these mice is two-fold: firstly, there is reduced phosphorylation of tyrosine hydroxylase at the residue associated with catechol feedback inhibition; and, secondly, there are increased rates of dopamine turnover at 6, 12 and 24 months of age. These animals exhibit a progressive decline in striatal monoamine levels and rotarod performance with increasing age. However, despite these data, there was no loss of nigral dopamine neurons as estimated by quantification of tyrosine hydroxylase-immunoreactive cells in the substantia nigra pars compacta of old VD(-/-) mice (24-month-old), implying that these age-dependent manifestations may be due to senescence alone.