RESUMO
The mechanisms leading to the neurocognitive deficits in humans with immunodeficiency virus type 1 (HIV-1) are not well resolved. A number of cell culture models have demonstrated that the HIV-envelope glycoprotein 120 (gp120) decreases the reuptake of glutamate, which is necessary for learning, memory, and synaptic plasticity. However, the impact of brain HIV-1 gp120 on glutamate uptake systems in vivo remains unknown. Notably, alterations in brain glutamate uptake systems are implicated in a number of neurodegenerative and neurocognitive disorders. We characterized the kinetic properties of system XAG (sodium-dependent) and systems xc- (sodium-independent) [3H]-L-glutamate uptake in the striatum and hippocampus of HIV-1 gp120 transgenic mice, an established model of HIV neuropathology. We determined the kinetic constant Vmax (maximal velocity) and Km (affinity) of both systems XAG and xc- using subcellular preparations derived from neurons and glial cells. We show significant (30-35 %) reductions in the Vmax of systems XAG and xc- in both neuronal and glial preparations derived from the striatum, but not from the hippocampus of gp120 mice relative to wild-type (WT) controls. Moreover, immunoblot analysis showed that the protein expression of glutamate transporter subtype-1 (GLT-1), the predominant brain glutamate transporter, was significantly reduced in the striatum but not in the hippocampus of gp120 mice. These extensive and region-specific deficits of glutamate uptake likely contribute to the development and/or severity of HIV-associated neurocognitive disorders. Understanding the role of striatal glutamate uptake systems in HIV-1 gp120 may advance the development of new therapeutic strategies to prevent neuronal damage and improve cognitive function in HIV patients.
Assuntos
Disfunção Cognitiva/metabolismo , Corpo Estriado/metabolismo , Transportador 2 de Aminoácido Excitatório/genética , Proteína gp120 do Envelope de HIV/genética , Infecções por HIV/metabolismo , HIV-1/patogenicidade , Neuroglia/metabolismo , Animais , Disfunção Cognitiva/complicações , Disfunção Cognitiva/genética , Disfunção Cognitiva/virologia , Corpo Estriado/virologia , Modelos Animais de Doenças , Transportador 2 de Aminoácido Excitatório/deficiência , Ácido Glutâmico/metabolismo , Proteína gp120 do Envelope de HIV/metabolismo , Infecções por HIV/complicações , Infecções por HIV/genética , Infecções por HIV/virologia , HIV-1/fisiologia , Hipocampo/metabolismo , Hipocampo/virologia , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Neuroglia/virologia , Neurônios/metabolismo , Neurônios/virologia , Especificidade de Órgãos , Sinapses/metabolismo , Sinapses/virologia , TransgenesRESUMO
RATIONALE: There is a high degree of comorbidity between alcohol use disorder and post-traumatic stress disorder (PTSD), but little is known about the interactions of ethanol with traumatic memories. OBJECTIVES: Using auditory fear conditioning in rats, we asked if repeated exposure to ethanol could modify the retrieval of fear memories acquired prior to ethanol exposure. METHODS: Following auditory fear conditioning, Sprague-Dawley rats were given daily injections of ethanol (1.5 g/kg) or saline over 5 days. Two days later, they were given 20 trials of extinction training and then tested for extinction memory the following day. In a separate experiment, conditioned rats were given repeated ethanol injections and processed for c-Fos immunohistochemistry following a fear retrieval session. RESULTS: Two days following the cessation of ethanol, the magnitude of conditioned fear responses (freezing and suppression of bar pressing) was significantly increased. This increase persisted the following day. Waiting 10 days following cessation of ethanol eliminated the effect on fear retrieval. In rats conditioned with low shock levels, repeated exposure to ethanol converted a sub-threshold fear memory into a supra-threshold fear memory. It also increased c-Fos expression in the prelimbic prefrontal cortex, paraventricular thalamus, and the central and basolateral nuclei of the amygdala, areas implicated in the retrieval of fear memories. CONCLUSIONS: These results suggest that repeated exposure to ethanol may exacerbate pre-existing traumatic memories.
Assuntos
Condicionamento Clássico/efeitos dos fármacos , Etanol/administração & dosagem , Medo/efeitos dos fármacos , Memória/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-fos/biossíntese , Tonsila do Cerebelo/efeitos dos fármacos , Tonsila do Cerebelo/metabolismo , Animais , Condicionamento Clássico/fisiologia , Esquema de Medicação , Medo/psicologia , Masculino , Memória/fisiologia , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
Approximately 30-50% of the >30 million HIV-infected subjects develop neurological complications ranging from mild symptoms to dementia. HIV does not infect neurons, and the molecular mechanisms behind HIV-associated neurocognitive decline are not understood. There are several hypotheses to explain the development of dementia in HIV(+) individuals, including neuroinflammation mediated by infected microglia and neuronal toxicity by HIV proteins. A key protein associated with the neurological complications of HIV, gp120, forms part of the viral envelope and can be found in the CSF of infected individuals. HIV-1-gp120 interacts with several receptors including CD4, CCR5, CXCR4, and nicotinic acetylcholine receptors (nAChRs). However, the role of nAChRs in HIV-associated neurocognitive disorder has not been investigated. We studied the effects of gp120(IIIB) on the expression and function of the nicotinic receptor α7 (α7-nAChR). Our results show that gp120, through activation of the CXCR4 chemokine receptor, induces a functional up-regulation of α7-nAChRs. Because α7-nAChRs have a high permeability to Ca(2+), we performed TUNEL staining to investigate the effects of receptor up-regulation on cell viability. Our data revealed an increase in cell death, which was blocked by the selective antagonist α-bungarotoxin. The in vitro data are supported by RT-PCR and Western blot analysis, confirming a remarkable up-regulation of the α7-nAChR in gp120-transgenic mice brains. Specifically, α7-nAChR up-regulation is observed in mouse striatum, a region severely affected in HIV(+) patients. In summary, CXCR4 activation induces up-regulation of α7-nAChR, causing cell death, suggesting that α7-nAChR is a previously unrecognized contributor to the neurotoxicity associated with HIV infection.