RESUMO
Cannabinoid receptor 1 (CB(1) receptor) controls several neuronal functions, including neurotransmitter release, synaptic plasticity, gene expression and neuronal viability. Downregulation of CB(1) expression in the basal ganglia of patients with Huntington's disease (HD) and animal models represents one of the earliest molecular events induced by mutant huntingtin (mHtt). This early disruption of neuronal CB(1) signaling is thought to contribute to HD symptoms and neurodegeneration. Here we determined whether CB(1) downregulation measured in patients with HD and mouse models was ubiquitous or restricted to specific striatal neuronal subpopulations. Using unbiased semi-quantitative immunohistochemistry, we confirmed previous studies showing that CB(1) expression is downregulated in medium spiny neurons of the indirect pathway, and found that CB(1) is also downregulated in neuropeptide Y (NPY)/neuronal nitric oxide synthase (nNOS)-expressing interneurons while remaining unchanged in parvalbumin- and calretinin-expressing interneurons. CB(1) downregulation in striatal NPY/nNOS-expressing interneurons occurs in R6/2 mice, Hdh(Q150/Q150) mice and the caudate nucleus of patients with HD. In R6/2 mice, CB(1) downregulation in NPY/nNOS-expressing interneurons correlates with diffuse expression of mHtt in the soma. This downregulation also occludes the ability of cannabinoid agonists to activate the pro-survival signaling molecule cAMP response element-binding protein in NPY/nNOS-expressing interneurons. Loss of CB(1) signaling in NPY/nNOS-expressing interneurons could contribute to the impairment of basal ganglia functions linked to HD.
Assuntos
Gânglios da Base/metabolismo , Regulação para Baixo , Doença de Huntington/metabolismo , Interneurônios/metabolismo , Neuropeptídeo Y/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Adulto , Idoso , Animais , Gânglios da Base/citologia , Calbindina 2 , Agonistas de Receptores de Canabinoides/farmacologia , Estudos de Casos e Controles , AMP Cíclico/metabolismo , Modelos Animais de Doenças , Feminino , Expressão Gênica , Humanos , Proteína Huntingtina , Interneurônios/classificação , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Pessoa de Meia-Idade , Proteínas do Tecido Nervoso/genética , Neuropeptídeo Y/genética , Óxido Nítrico Sintase/genética , Óxido Nítrico Sintase/metabolismo , Proteínas Nucleares/genética , Parvalbuminas/genética , Parvalbuminas/metabolismo , Receptor CB1 de Canabinoide/agonistas , Receptor CB1 de Canabinoide/genética , Proteína G de Ligação ao Cálcio S100/genética , Proteína G de Ligação ao Cálcio S100/metabolismo , Proteínas da Membrana Plasmática de Transporte de Serotonina/genética , Proteínas da Membrana Plasmática de Transporte de Serotonina/metabolismoRESUMO
Agonists at cannabinoid receptors, such as the phytocannabinoid Δ(9)-tetrahydrocannabinol, exert a remarkable array of therapeutic effects but are also associated with undesirable psychoactive side effects. Conversely, targeting enzymes that hydrolyze endocannabinoids (eCBs) allows for more precise fine-tuning of cannabinoid receptor signaling, thus providing therapeutic relief with reduced side effects. Here, we report the development and characterization of an inhibitor of eCB hydrolysis, UCM710, which augments both N-arachidonoylethanolamine and 2-arachidonoylglycerol levels in neurons. This compound displays a unique pharmacological profile in that it inhibits fatty acid amide hydrolase and α/ß-hydrolase domain 6 but not monoacylglycerol lipase. Thus, UCM710 represents a novel tool to delineate the therapeutic potential of compounds that manipulate a subset of enzymes that control eCB signaling.
Assuntos
Amidoidrolases/antagonistas & inibidores , Ácidos Araquidônicos/metabolismo , Moduladores de Receptores de Canabinoides/metabolismo , Endocanabinoides , Inibidores Enzimáticos/farmacologia , Glicerídeos/metabolismo , Monoacilglicerol Lipases/antagonistas & inibidores , Proteínas do Tecido Nervoso/antagonistas & inibidores , Neurônios/metabolismo , Amidoidrolases/metabolismo , Animais , Células COS , Chlorocebus aethiops , Camundongos , Monoacilglicerol Lipases/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Alcamidas Poli-Insaturadas , Receptores de CanabinoidesRESUMO
In this issue of Chemistry & Biology, Blankman et al. identify new enzymes hydrolyzing the endocannabionoid 2-arachidonoyl glycerol (2-AG), increasing the complexity of endocannabinoid signaling in the brain, but also pinpointing additional therapeutic targets.
Assuntos
Ácidos Araquidônicos/metabolismo , Encéfalo/enzimologia , Glicerídeos/metabolismo , Monoacilglicerol Lipases/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Moduladores de Receptores de Canabinoides/metabolismo , Catálise/efeitos dos fármacos , Endocanabinoides , Inibidores Enzimáticos/farmacologia , Humanos , Proteínas de Membrana/metabolismo , Camundongos , Modelos Biológicos , Transdução de Sinais/efeitos dos fármacos , Frações Subcelulares/metabolismoRESUMO
N-methyl-D-aspartate (NMDA)/glutamate receptor antagonists, such as phencyclidine (PCP), induce behavioral abnormalities (locomotor hyperactivity, sensorimotor gating deficits, impairments of cognition) in animals that are thought to model aspects of schizophrenia. The administration of PCP increases noradrenaline transmission in the rat prefrontal cortex, a brain structure required for normal cognitive processes. Noradrenaline, in turn, works through a set of receptors that have themselves been implicated directly in NMDA antagonist-induced deficits; we recently reported that the alpha-2 agonist, clonidine, is effective at preventing PCP-induced deficits of working memory and visual attention in rats. Here, we further investigated the role for alpha-2 adrenoreceptors in the effects of PCP on spatial working memory performance. The alpha-2 agonist clonidine (0.001-0.01 mg/kg, subcutaneously (s.c.)) produced a significant amelioration of PCP-induced working memory deficits; the effects of PCP (1.0 mg/kg, s.c.), but not clonidine, were reduced in noradrenaline-depleted rats. In addition, the alpha-2A-preferring agonist guanfacine (0.05-1.0 mg/kg, s.c.) dose-dependently prevented the deficits of spatial working memory performance produced by PCP. Although the highly selective alpha-2 receptor antagonist, atipamezole (ATI), failed to affect spatial working memory on its own, at the doses studied (0.1-0.5 mg/kg, s.c.), it dramatically enhanced the working memory deficit produced by PCP. These data indicate that alpha-2 adrenoreceptors tonically inhibit PCP-induced deficits of spatial working memory, suggesting an important role for these receptors in cognitive deficits associated with NMDA receptor hypofunction.
Assuntos
Agonistas alfa-Adrenérgicos/uso terapêutico , Transtornos da Memória/prevenção & controle , Memória de Curto Prazo/efeitos dos fármacos , Fenciclidina , Receptores Adrenérgicos alfa 2/fisiologia , Comportamento Espacial/efeitos dos fármacos , Agonistas de Receptores Adrenérgicos alfa 2 , Agonistas alfa-Adrenérgicos/administração & dosagem , Antagonistas Adrenérgicos alfa/farmacologia , Análise de Variância , Animais , Comportamento Animal , Benzilaminas/farmacologia , Clonidina/administração & dosagem , Relação Dose-Resposta a Droga , Interações Medicamentosas , Feminino , Guanfacina/administração & dosagem , Imidazóis/farmacologia , Masculino , Transtornos da Memória/induzido quimicamente , Inibidores da Captação de Neurotransmissores/farmacologia , Ratos , Ratos Long-Evans , Fatores SexuaisRESUMO
The serine hydrolase α/ß-hydrolase domain 6 (ABHD6) hydrolyzes the most abundant endocannabinoid (eCB) in the brain, 2-arachidonoylglycerol (2-AG), and controls its availability at cannabinoid receptors. We show that ABHD6 inhibition decreases pentylenetetrazole (PTZ)-induced generalized tonic-clonic and myoclonic seizure incidence and severity. This effect is retained in Cnr1(-/-) or Cnr2(-/-) mice, but blocked by addition of a subconvulsive dose of picrotoxin, suggesting the involvement of GABAA receptors. ABHD6 inhibition also blocked spontaneous seizures in R6/2 mice, a genetic model of juvenile Huntington's disease known to exhibit dysregulated eCB signaling. ABHD6 blockade retained its antiepileptic activity over chronic dosing and was not associated with psychomotor or cognitive effects. While the etiology of seizures in R6/2 mice remains unsolved, involvement of the hippocampus is suggested by interictal epileptic discharges, increased expression of vGLUT1 but not vGAT, and reduced Neuropeptide Y (NPY) expression. We conclude that ABHD6 inhibition may represent a novel antiepileptic strategy.
Assuntos
Anticonvulsivantes/uso terapêutico , Encéfalo/efeitos dos fármacos , Carbamatos/uso terapêutico , Monoacilglicerol Lipases/antagonistas & inibidores , Convulsões/tratamento farmacológico , Animais , Anticonvulsivantes/farmacologia , Comportamento Animal/efeitos dos fármacos , Encéfalo/fisiopatologia , Carbamatos/farmacologia , Masculino , Camundongos , Camundongos Knockout , Pentilenotetrazol , Receptores de Canabinoides/genética , Convulsões/induzido quimicamente , Convulsões/fisiopatologiaRESUMO
BACKGROUND: Cannabinoids represent unique compounds for treating tumors, including astrocytomas. Whether CB(1) and CB(2) receptors mediate this therapeutic effect is unclear. PRINCIPAL FINDINGS: We generated astrocytoma subclones that express set levels of CB(1) and CB(2), and found that cannabinoids induce apoptosis only in cells expressing low levels of receptors that couple to ERK1/2. In contrast, cannabinoids do not induce apoptosis in cells expressing high levels of receptors because these now also couple to the prosurvival signal AKT. Remarkably, cannabinoids applied at high concentration induce apoptosis in all subclones independently of CB(1), CB(2) and AKT, but still through a mechanism involving ERK1/2. SIGNIFICANCE: The high expression level of CB(1) and CB(2) receptors commonly found in malignant astrocytomas precludes the use of cannabinoids as therapeutics, unless AKT is concomitantly inhibited, or cannabinoids are applied at concentrations that bypass CB(1) and CB(2) receptors, yet still activate ERK1/2.
Assuntos
Apoptose , Astrocitoma/metabolismo , Neoplasias Encefálicas/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Receptor CB2 de Canabinoide/metabolismo , Astrocitoma/enzimologia , Astrocitoma/patologia , Neoplasias Encefálicas/enzimologia , Neoplasias Encefálicas/patologia , Linhagem Celular Tumoral , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , Transdução de SinaisRESUMO
The endocannabinoid 2-arachidonoylglycerol (2-AG) regulates neurotransmission and neuroinflammation by activating CB1 cannabinoid receptors on neurons and CB2 cannabinoid receptors on microglia. Enzymes that hydrolyze 2-AG, such as monoacylglycerol lipase, regulate the accumulation and efficacy of 2-AG at cannabinoid receptors. We found that the recently described serine hydrolase alpha-beta-hydrolase domain 6 (ABHD6) also controls the accumulation and efficacy of 2-AG at cannabinoid receptors. In cells from the BV-2 microglia cell line, ABHD6 knockdown reduced hydrolysis of 2-AG and increased the efficacy with which 2-AG can stimulate CB2-mediated cell migration. ABHD6 was expressed by neurons in primary culture and its inhibition led to activity-dependent accumulation of 2-AG. In adult mouse cortex, ABHD6 was located postsynaptically and its selective inhibition allowed the induction of CB1-dependent long-term depression by otherwise subthreshold stimulation. Our results indicate that ABHD6 is a rate-limiting step of 2-AG signaling and is therefore a bona fide member of the endocannabinoid signaling system.
Assuntos
Ácidos Araquidônicos/metabolismo , Encéfalo/metabolismo , Glicerídeos/metabolismo , Monoacilglicerol Lipases/metabolismo , Receptor CB1 de Canabinoide/metabolismo , Receptor CB2 de Canabinoide/metabolismo , Transdução de Sinais/fisiologia , Animais , Células COS , Linhagem Celular , Movimento Celular , Chlorocebus aethiops , Endocanabinoides , Potenciais Pós-Sinápticos Excitadores/fisiologia , Técnicas de Silenciamento de Genes , Imuno-Histoquímica , Camundongos , Camundongos Endogâmicos C57BL , Microglia/metabolismo , Microscopia Eletrônica de Transmissão , Neurônios/metabolismo , Técnicas de Patch-Clamp , Reação em Cadeia da Polimerase , RNA Mensageiro/análise , TransfecçãoRESUMO
Endocannabinoids (eCBs) are lipid transmitters that are released from membrane precursors in response to specific stimuli, activate cannabinoid receptors--the molecular targets of compounds produced by Cannabis sativa--and are then rapidly inactivated by uptake and enzymatic hydrolysis. This signaling system is implicated in a wide range of biological processes, including pain sensation, immunomodulation, appetite regulation, development, and cognitive and emotional states. The balance between eCB release and inactivation determines the extent of eCB accumulation, with enzymatic hydrolysis functioning as an important limiting step. Pharmacological inhibition of eCB-hydrolyzing enzymes offers great therapeutic and experimental promise for enhancing this ubiquitous signaling system only where and when these transmitters are naturally produced. The following mini-review summarizes the latest developments concerning eCB-hydrolyzing enzymes, with an emphasis on the techniques used to measure their activities and how these have helped increase our understanding of the role that eCBs play in regulating fundamental biological functions.