Publicação
Molecular mechanisms of microglia reactivity to bilirubin : evaluation of potential neurological effects
| Resumo: | Microglia are active sensors in the brain that rapidly engage adequate functional activity states in response to injury to restore homeostasis. During the neonatal period, the brain is more vulnerable to several injury conditions such as the one induced by hyperbilirubinemia, a common situation observed in the newborn, where excessive levels of unconjugated bilirubin (UCB) can reach and damage the brain. Although UCB-induced neuronal and astrocytic toxicity have already been approached, the role of microglia in this condition remains unclear. Thus, this thesis intended to investigate microglial reactivity to UCB and to characterize the intervention of other brain cells in the modulation of their response. Isolated microglial cells showed to acquire a phagocytic phenotype upon UCB exposure that preceded the release of pro-inflammatory cytokines. This release showed to involve activation of upstream signalling pathways such as mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). We next investigated whether and how the microenvironment influenced microglial response to UCB. Our findings revealed that soluble factors released by UCB-stimulated astrocytes refrained microglial activation while neuron-microglia interaction, evaluated using conditioned media and mixed culture models, signalled microglial clearance functions but also enhanced its inflammatory potential, ultimately leading to microglia demise. Finally, we evaluated microglial neuroprotective or neurotoxic effects in a cell-to-cell concerted action in response to UCB. Microglia revealed to participate in glutamate homeostasis, and to induce the release of this neurotransmitter and of nitric oxide (NO) in UCB-treated organotypiccultured hippocampal slices, molecules that showed to be key players in UCB-induced neurotoxicity. Moreover, our results point to interleukin (IL)-10 and glycoursodeoxycholic acid (GUDCA) as promising therapies in neonatal hyperbilirubinemia. In conclusion, microglia displays a dual activation profile in response to UCB stimulation which is tailored by the influence of neighbouring cells. Collectively, these data contribute for the understanding of microglia’s role in hyperbilirubinemia and reinforce their remarkable functional plasticity. |
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| Autores principais: | Silva, Sandra Isabel Leitão da, 1984- |
| Assunto: | Biologia celular Biologia molecular Astrócitos Hiperbilirrubinémia Inflamação Micróglia Neurónios Tese de doutoramento - 2010 |
| Ano: | 2010 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Microglia are active sensors in the brain that rapidly engage adequate functional activity states in response to injury to restore homeostasis. During the neonatal period, the brain is more vulnerable to several injury conditions such as the one induced by hyperbilirubinemia, a common situation observed in the newborn, where excessive levels of unconjugated bilirubin (UCB) can reach and damage the brain. Although UCB-induced neuronal and astrocytic toxicity have already been approached, the role of microglia in this condition remains unclear. Thus, this thesis intended to investigate microglial reactivity to UCB and to characterize the intervention of other brain cells in the modulation of their response. Isolated microglial cells showed to acquire a phagocytic phenotype upon UCB exposure that preceded the release of pro-inflammatory cytokines. This release showed to involve activation of upstream signalling pathways such as mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). We next investigated whether and how the microenvironment influenced microglial response to UCB. Our findings revealed that soluble factors released by UCB-stimulated astrocytes refrained microglial activation while neuron-microglia interaction, evaluated using conditioned media and mixed culture models, signalled microglial clearance functions but also enhanced its inflammatory potential, ultimately leading to microglia demise. Finally, we evaluated microglial neuroprotective or neurotoxic effects in a cell-to-cell concerted action in response to UCB. Microglia revealed to participate in glutamate homeostasis, and to induce the release of this neurotransmitter and of nitric oxide (NO) in UCB-treated organotypiccultured hippocampal slices, molecules that showed to be key players in UCB-induced neurotoxicity. Moreover, our results point to interleukin (IL)-10 and glycoursodeoxycholic acid (GUDCA) as promising therapies in neonatal hyperbilirubinemia. In conclusion, microglia displays a dual activation profile in response to UCB stimulation which is tailored by the influence of neighbouring cells. Collectively, these data contribute for the understanding of microglia’s role in hyperbilirubinemia and reinforce their remarkable functional plasticity. |
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