RESUMO
Although dystonia represents the third most common movement disorder, its pathophysiology remains still poorly understood. In the past two decades, multiple models have been generated, improving our knowledge on the molecular and cellular bases of this heterogeneous group of movement disorders. In this short survey, we will focus on recently generated novel models of DYT1 dystonia, the most common form of genetic, "isolated" dystonia. These models clearly indicate the existence of multiple signaling pathways affected by the protein mutation causative of DYT1 dystonia, torsinA, paving the way for potentially multiple, novel targets for pharmacological intervention.
Assuntos
Distonia , Distúrbios Distônicos , Transtornos dos Movimentos , Distonia/genética , Distúrbios Distônicos/genética , Humanos , Mutação/genética , Transdução de SinaisRESUMO
Dystonia refers to a heterogeneous group of movement disorders characterized by involuntary, sustained muscle contractions leading to repetitive twisting movements and abnormal postures. A better understanding of the etiology, pathogenesis and molecular mechanisms underlying dystonia may be obtained from animal models. Indeed, while studies in vitro using cell and tissue models are helpful for investigating molecular pathways, animal models remain essential for studying the pathogenesis of these disorders and exploring new potential treatment strategies. To date, the mouse is the most common choice for mammalian models in most laboratories, particularly when manipulations of the genome are planned. Dystonia animal models can be classified into two categories, etiological and symptomatic, although neither is able to recapitulate all features of these disorders in humans. Nevertheless, etiological and symptomatic animal models have advantages and limitations that should be taken into consideration according to the specific proposed hypothesis and experimental goals. Etiological mouse models of inherited dystonia can reproduce the etiology of the disorder and help to reveal biochemical and cellular alterations, although a large majority of them lack motor symptoms. Conversely, symptomatic models can partially mimic the phenotype of human dystonia and test novel pharmacological agents, and also identify the anatomical and physiological processes involved, although the etiology remains unknown. Thus, our brief survey aims to review the state of the art as regards most of the commonly used animal models available for dystonia research.
Assuntos
Distonia/fisiopatologia , Distonia/terapia , Animais , Modelos Animais de Doenças , Distúrbios Distônicos , Humanos , Especificidade da EspécieRESUMO
Striatal dysfunction is implicated in many movement disorders. However, the precise nature of defects often remains uncharacterized, which hinders therapy development. Here we examined striatal function in a mouse model of the incurable movement disorder, myoclonus dystonia, caused by SGCE mutations. Using RNAseq we found surprisingly normal gene expression, including normal levels of neuronal subclass markers to strongly suggest that striatal microcircuitry is spared by the disease insult. We then functionally characterized Sgce mutant medium spiny projection neurons (MSNs) and cholinergic interneurons (ChIs). This revealed normal intrinsic electrophysiological properties and normal responses to basic excitatory and inhibitory neurotransmission. Nevertheless, high-frequency stimulation in Sgce mutants failed to induce normal long-term depression (LTD) at corticostriatal glutamatergic synapses. We also found that pharmacological manipulation of MSNs by inhibiting adenosine 2A receptors (A2AR) restores LTD, again pointing to structurally intact striatal circuitry. The fact that Sgce loss specifically inhibits LTD implicates this neurophysiological defect in myoclonus dystonia, and emphasizes that neurophysiological changes can occur in the absence of broad striatal dysfunction. Further, the positive effect of A2AR antagonists indicates that this drug class be tested in DYT11/SGCE dystonia.
Assuntos
Antagonistas do Receptor A2 de Adenosina/farmacologia , Corpo Estriado/efeitos dos fármacos , Distúrbios Distônicos/tratamento farmacológico , Plasticidade Neuronal/efeitos dos fármacos , Animais , Corpo Estriado/fisiopatologia , Modelos Animais de Doenças , Distúrbios Distônicos/fisiopatologia , Feminino , Ácido Glutâmico/metabolismo , Masculino , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Plasticidade Neuronal/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Técnicas de Patch-Clamp , RNA Mensageiro/metabolismo , Receptor A2A de Adenosina/metabolismo , Sarcoglicanas/genética , Sarcoglicanas/metabolismo , Técnicas de Cultura de TecidosRESUMO
Early onset torsion dystonia (DYT1) is an autosomal dominantly inherited disorder caused by deletion in TOR1A gene. Evidence suggests that TOR1A mutation produces dystonia through an aberrant neuronal signalling within the striatum, where D2 dopamine receptors (D2R) produce an abnormal excitatory response in cholinergic interneurons (ChIs) in different models of DYT1 dystonia. The excitability of ChIs may be modulated by group I metabotropic glutamate receptor subtypes (mGlu1 and 5). We performed electrophysiological and calcium imaging recordings from ChIs of both knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) and transgenic mice overexpressing human torsinA (hMT1). We demonstrate that the novel negative allosteric modulator (NAM) of metabotropic glutamate 5 (mGlu) receptor, dipraglurant (ADX48621) counteracts the abnormal membrane responses and calcium rise induced either by the D2R agonist quinpirole or by caged dopamine (NPEC-Dopamine) in both models. These inhibitory effects were mimicked by two other well-characterized mGlu5 receptor antagonists, SIB1757 and MPEP, but not by mGlu1 antagonism. D2R and mGlu5 post-receptor signalling may converge on PI3K/Akt pathway. Interestingly, we found that the abnormal D2R response was prevented by the selective PI3K inhibitor, LY294002, whereas PLC and PKC inhibitors were both ineffective. Currently, no satisfactory pharmacological treatment is available for DYT1 dystonia patients. Our data show that negative modulation of mGlu5 receptors may counteract abnormal D2R responses, normalizing cholinergic cell excitability, by modulating the PI3K/Akt post-receptor pathway, thereby representing a novel potential treatment of DYT1 dystonia.
Assuntos
Encéfalo/efeitos dos fármacos , Corpo Estriado/efeitos dos fármacos , Distúrbios Distônicos/tratamento farmacológico , Receptor de Glutamato Metabotrópico 5/antagonistas & inibidores , Receptor de Glutamato Metabotrópico 5/metabolismo , Receptores de Dopamina D2/metabolismo , Animais , Encéfalo/fisiopatologia , Cálcio/metabolismo , Neurônios Colinérgicos/efeitos dos fármacos , Neurônios Colinérgicos/fisiologia , Corpo Estriado/fisiologia , Modelos Animais de Doenças , Distúrbios Distônicos/fisiopatologia , Humanos , Interneurônios/efeitos dos fármacos , Interneurônios/fisiologia , Camundongos Transgênicos , Chaperonas Moleculares/genética , Chaperonas Moleculares/metabolismo , Mutação , Fosfatidilinositol 3-Quinases/metabolismo , Inibidores de Fosfoinositídeo-3 Quinase , Receptores de Glutamato Metabotrópico/antagonistas & inibidores , Receptores de Glutamato Metabotrópico/metabolismo , Técnicas de Cultura de TecidosRESUMO
DYT1 dystonia is a movement disorder caused by a deletion in the C-terminal of the protein torsinA. It is unclear how torsinA mutation might disrupt cellular processes encoding motor activity, and whether this impairment occurs in specific brain regions. Here, we report a selective impairment of corticostriatal synaptic plasticity in knock-in mice heterozygous for Δ-torsinA (Tor1a(+/Δgag) mice) as compared to controls (Tor1a(+/+) mice). In striatal spiny neurons from Tor1a(+/Δgag) mice, high-frequency stimulation failed to induce long-term depression (LTD), whereas long-term potentiation (LTP) exhibited increased amplitude. Of interest, blockade of D2 dopamine receptors (D2Rs) increased LTP in Tor1a(+/+) mice to a level comparable to that measured in Tor1a(+/Δgag) mice and normalized the levels of potentiation across mouse groups. A low-frequency stimulation (LFS) protocol was unable to depotentiate corticostriatal synapses in Tor1a(+/Δgag) mice. Muscarinic M1 acetylcholine receptor (mAChR) blockade rescued plasticity deficits. Additionally, we found an abnormal responsiveness of cholinergic interneurons to D2R activation, consisting in an excitatory response rather than the expected inhibition, further confirming an imbalance between dopaminergic and cholinergic signaling in the striatum. Conversely, synaptic activity and plasticity in the CA1 hippocampal region were unaltered in Tor1a(+/Δgag) mice. Importantly, the M1 mAChR-dependent enhancement of hippocampal LTP was unaffected in both genotypes. Similarly, both basic properties of dopaminergic nigral neurons and their responses to D2R activation were normal. These results provide evidence for a regional specificity of the electrophysiological abnormalities observed and demonstrate the reproducibility of such alterations in distinct models of DYT1 dystonia.
Assuntos
Encéfalo/patologia , Distonia/genética , Distonia/patologia , Chaperonas Moleculares/genética , Plasticidade Neuronal/genética , Sinapses/patologia , Animais , Modelos Animais de Doenças , Dopamina/farmacologia , Relação Dose-Resposta a Droga , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/genética , Antagonistas GABAérgicos/farmacologia , Regulação da Expressão Gênica/genética , Técnicas In Vitro , Camundongos , Camundongos Transgênicos , Antagonistas Muscarínicos/farmacologia , Mutação/genética , Neurônios/fisiologia , Picrotoxina/farmacologia , Pirenzepina/farmacologia , Sinapses/genéticaRESUMO
Cholinergic interneurons (ChIs) of dorsal striatum play a key role in motor control and in behavioural learning. Neuropeptides regulate cholinergic transmission and mu opioid receptor (MOR) activation modulates striatal acetylcholine release. However, the mechanisms underlying this effect are yet uncharacterized. Here, we examined the electrophysiological responses of ChIs to the selective MOR agonist, DAMGO {[D-Ala2-MePhe4-Gly(ol)5] enkephalin}. We observed a robust, dose-dependent inhibition of spontaneous firing activity (0.06-3 µM) which was reversible upon drug washout and blocked by the selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) (1 µM). Voltage-clamp analysis of the reversal potential of the DAMGO effect did not provide univocal results, indicating the involvement of multiple membrane conductances. The MOR-dependent effect persisted in the presence of GABAA and ionotropic glutamate receptor antagonists, ruling out an indirect effect. Additionally, it depended upon G-protein activation, as it was prevented by intrapipette GDP-ß-S. Because D2 dopamine receptors (D2R) and MOR share a common post-receptor signalling pathway, occlusion experiments were performed with maximal doses of both D2R and MOR agonists. The D2R agonist quinpirole decreased spike discharge, which was further reduced by adding DAMGO. Then, D2R or MOR antagonists were used to challenge the response to the respective agonists, DAMGO or quinpirole. No cross-effect was observed, suggesting that the two receptors act independently. Our findings demonstrate a postsynaptic inhibitory modulation by MOR on ChIs excitability. Such opioidergic regulation of cholinergic transmission might contribute to shape information processing in basal ganglia circuits, and represent a potential target for pharmacological intervention.
Assuntos
Potenciais de Ação/fisiologia , Neurônios Colinérgicos/fisiologia , Corpo Estriado/citologia , Inibição Neural/fisiologia , Receptores Opioides mu/metabolismo , Potenciais de Ação/efeitos dos fármacos , Analgésicos Opioides/farmacologia , Anestésicos Locais/farmacologia , Animais , Cloreto de Cádmio/farmacologia , Neurônios Colinérgicos/efeitos dos fármacos , Agonistas de Dopamina/farmacologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , Fármacos Atuantes sobre Aminoácidos Excitatórios/farmacologia , Técnicas In Vitro , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Inibição Neural/efeitos dos fármacos , Quimpirol/farmacologia , Receptores Opioides mu/antagonistas & inibidores , Somatostatina/análogos & derivados , Somatostatina/farmacologia , Tetrodotoxina/farmacologiaRESUMO
In the recent past, the pathogenesis of Parkinson's disease (PD) has evolved from a neurodegenerative disorder considered entirely sporadic to a disease with an unequivocal genetic component. Indeed, different inherited forms of PD have been discovered and characterized, although the functional roles of the gene products identified are still under intense investigation. To gain a better understanding of the cellular and molecular pathogenic mechanisms of hereditary forms of PD, different animal models have been generated. Although most of the rodent models display neither obvious behavioral impairment nor evidence for neurodegeneration, remarkable abnormalities of dopamine-mediated neurotransmission and corticostriatal synaptic plasticity have been described, indicative of a fundamental distortion of network function within the basal ganglia. The picture emerging from a critical review of recent data on monogenic parkinsonisms suggests that mutations in PD genes might cause developmental rearrangements in the corticobasal ganglia circuitry, compensating the dopaminergic dysfunction observed both in mice and humans, in order to maintain proper motor function.