RESUMEN
Traumatic brain injury (TBI) is one of the most prevalent causes of worldwide mortality and morbidity. We previously had evidenced that TBI induced Na-K-2Cl co-transporter (NKCC1) upregulation in hippocampus. Here, we aim to investigate the role of NKCC1 in TBI-induced neurogenesis and the detailed mechanisms. The TBI-associated alternations in the expression of NKCC1, HIF-1α, VEGF, MAPK cascade, and CREB phosphorylation were analyzed by Western blot. TBI-induced neurogenesis was determined by immuno-fluorescence labeling. Chromatin immunoprecipitation was used to elucidate whether HIF-1α would activate VEGF gene after TBI. We found that the level of hippocampal NKCC1 and VEGF began to rise 8 h after TBI, and both of them reached maxima at day 7. Along with the upregulation of NKCC1 and VEGF, MAPK cascade was activated and hippocampal neurogenesis was promoted. Administration of CREB antisense oligonucleotide significantly attenuated the expression of HIF-1α, while HIF-1α antisense oligonucleotide exhibited little effect on the expression of CREB. However, HIF-1α antisense oligonucleotide administration did effectively suppress the expression of VEGF. Our results of the chromosome immunoprecipitation also indicated that HIF-1α could directly act on the VEGF promoter and presumably would elevate the VEGF expression after TBI. All these results have illustrated the correlation between NKCC1 upregulation and TBI-associated neurogenesis. The pathway involves the activation of Raf/MEK/ERK cascade, CREB phosphorylation, and HIF-1α upregulation, and finally leads to the stimulation of VEGF expression and the induction of neurogenesis.
Asunto(s)
Lesiones Encefálicas/metabolismo , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Hipocampo/metabolismo , Subunidad alfa del Factor 1 Inducible por Hipoxia/metabolismo , Neurogénesis , Neuronas/metabolismo , Miembro 2 de la Familia de Transportadores de Soluto 12/metabolismo , Animales , Sitios de Unión , Lesiones Encefálicas/genética , Lesiones Encefálicas/patología , Lesiones Encefálicas/fisiopatología , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/genética , Modelos Animales de Enfermedad , Regulación de la Expresión Génica , Hipocampo/patología , Hipocampo/fisiopatología , Subunidad alfa del Factor 1 Inducible por Hipoxia/genética , Sistema de Señalización de MAP Quinasas , Masculino , Neuronas/patología , Oligonucleótidos Antisentido/genética , Oligonucleótidos Antisentido/metabolismo , Fosforilación , Regiones Promotoras Genéticas , Ratas Wistar , Factores de Tiempo , Transcripción Genética , Factor A de Crecimiento Endotelial Vascular/metabolismoRESUMEN
Adult neurogenesis occurs in the subgranular zone of the hippocampal dentate gyrus, and can be modulated by physiological and pathological events. We examined the effect of vascular endothelial growth factor (VEGF), and the correlation between VEGF and the Raf/MEK/ERK cascade in neurogenesis after traumatic brain injury (TBI). The expression of VEGF and the phosphorylation level of Raf/MEK/ERK were analyzed by Western blot, and TBI-induced neurogenesis was determined by immunofluorescence labeling and confocal microscopic detection. Hippocampal VEGF began to increase after 12 h, and reached a peak at day 7. Along with the upregulation of VEGF, neurogenesis in the hippocampus also increased. Administration of the VEGF antisense oligodeoxynucleotide, or the VEGF receptor-2 antagonist SU1498 (10 µg, ICV), attenuated the phosphorylation of the MAPK cascade proteins and caused a decrease in neurogenesis in the hippocampus. Similarly, administration of the ERK inhibitor PD98059 (500 ng, ICV) also exhibited a suppressive effect on neurogenesis. Our results indicate that VEGF plays an important role in neurogenesis after TBI, and that the process involves VEGF receptor-2 and the Raf/MEK/ERK cascade.