RESUMO
Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.
Assuntos
Hipóxia Celular/genética , Fatores de Crescimento Endotelial/genética , Linfocinas/genética , Neurônios Motores/patologia , Degeneração Neural/genética , Elementos de Resposta/genética , Esclerose Lateral Amiotrófica/genética , Esclerose Lateral Amiotrófica/patologia , Animais , Axônios/fisiologia , Sítios de Ligação , Eletrofisiologia , Fatores de Crescimento Endotelial/metabolismo , Humanos , Linfocinas/metabolismo , Camundongos , Camundongos Knockout , Neurônios Motores/fisiologia , Contração Muscular , Fibras Musculares Esqueléticas/patologia , Atrofia Muscular/genética , Atrofia Muscular/patologia , Degeneração Neural/patologia , Degeneração Neural/fisiopatologia , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neuropilina-1 , Nervos Periféricos/patologia , Regiões Promotoras Genéticas , Receptores Proteína Tirosina Quinases/genética , Receptores Proteína Tirosina Quinases/metabolismo , Receptores de Fatores de Crescimento/genética , Receptores de Fatores de Crescimento/metabolismo , Receptores de Fatores de Crescimento do Endotélio Vascular , Deleção de Sequência , Medula Espinal/fisiologia , Fator A de Crescimento do Endotélio Vascular , Fatores de Crescimento do Endotélio VascularRESUMO
Although tumors can activate vascular endothelial growth factor (VEGF) promoter in host stromal cells, the relative contribution to VEGF production of host versus tumor cells and the resulting vascular response have not been quantitated to date. To this end, we implanted VEGF-/- and wild-type (WT) embryonic stem (ES) cells in transparent dorsal skin windows in severe combined immunodeficient mice. VEGF-/- ES cell-derived tumors produced approximately 50% of VEGF compared with the WT tumors, suggesting significant contribution of host stromal cells. To discern the hypoxia-induced hypoxia inducible factor (HIF)-1alpha --> hypoxia response element (HRE) --> VEGF signaling cascade, we also examined tumors derived from HIF-1alpha-/- and HRE-/- ES cells. As expected, the VEGF protein level in HIF-1alpha-/- ES tumors was intermediate between VEGF-/- and WT ES cell tumors. Surprisingly, HRE-/- ES tumors produced the same level of VEGF as the VEGF-/- ES tumors, suggesting a critical role of HRE in tumor cell VEGF production. Angiogenesis in these tumors was proportional to their VEGF levels (VEGF-/- approximate to HRE-/- < HIF-1alpha-/- < WT). In contrast, vascular permeability, leukocyte-endothelial adhesion, and tumor growth were reduced in VEGF-/- and HRE-/- tumors but were comparable in HIF-1a-/- and WT tumors. This discrepancy suggests that different intracellular signaling pathways may be involved in each of these functions of VEGF. More importantly, these data suggest that host cells are active players in tumor angiogenesis and growth and need to be taken into account in the design of any therapeutic strategy.
Assuntos
Proteínas de Ligação a DNA/fisiologia , Fatores de Crescimento Endotelial/fisiologia , Linfocinas/fisiologia , Neoplasias Experimentais/irrigação sanguínea , Neovascularização Patológica/metabolismo , Proteínas Nucleares/fisiologia , Elementos de Resposta/fisiologia , Transdução de Sinais/fisiologia , Fatores de Transcrição , Animais , Permeabilidade Capilar/fisiologia , Comunicação Celular/fisiologia , Divisão Celular/fisiologia , Proteínas de Ligação a DNA/genética , Modelos Animais de Doenças , Fatores de Crescimento Endotelial/biossíntese , Fatores de Crescimento Endotelial/genética , Endotélio Vascular/patologia , Genes Letais/fisiologia , Fator 1 Induzível por Hipóxia , Subunidade alfa do Fator 1 Induzível por Hipóxia , Leucócitos/patologia , Linfocinas/biossíntese , Linfocinas/genética , Camundongos , Camundongos Knockout , Camundongos SCID , Neoplasias Experimentais/metabolismo , Neoplasias Experimentais/patologia , Neovascularização Patológica/patologia , Proteínas Nucleares/genética , Transplante de Células-Tronco , Células-Tronco/metabolismo , Células-Tronco/patologia , Células Estromais/metabolismo , Fator A de Crescimento do Endotélio Vascular , Fatores de Crescimento do Endotélio VascularRESUMO
Vascular endothelial cadherin, VE-cadherin, mediates adhesion between endothelial cells and may affect vascular morphogenesis via intracellular signaling, but the nature of these signals remains unknown. Here, targeted inactivation (VEC-/-) or truncation of the beta-catenin-binding cytosolic domain (VECdeltaC/deltaC) of the VE-cadherin gene was found not to affect assembly of endothelial cells in vascular plexi, but to impair their subsequent remodeling and maturation, causing lethality at 9.5 days of gestation. Deficiency or truncation of VE-cadherin induced endothelial apoptosis and abolished transmission of the endothelial survival signal by VEGF-A to Akt kinase and Bcl2 via reduced complex formation with VEGF receptor-2, beta-catenin, and phosphoinositide 3 (PI3)-kinase. Thus, VE-cadherin/ beta-catenin signaling controls endothelial survival.