Autor(es):
Coutinho, Eduarda Cristina Duarte de Magalhães 
Data: 2009
Identificador Persistente: http://hdl.handle.net/10451/1804
Origem: Repositório da Universidade de Lisboa
Assunto(s): Neurobiologia; Hipocampo; Citosqueleto; Técnicas biológicas; Teses de mestrado
Descrição
Tese de mestrado, Biologia (Biologia Molecular Humana), 2009, Universidade de Lisboa, Faculdade de Ciências Hyperbilirubinemia is frequently observed in the neonatal period due to the transient accumulation of unconjugated bilirubin (UCB) in serum, which in certain circumstances it may trigger neurological deficits. We have recently shown that exposure of immature hippocampal neurons to UCB, in conditions mimicking moderate to severe neonatal jaundice, impairs neuronal development, with reduced neurogenesis, neurite arborization, and synaptogenesis. This project aimed to appraise the molecular mechanisms by which UCB may induce mild or severe alterations in the establishment of the normal neuronal architecture and inter-neurons communication that may ultimately elicit the appearance of neurological disabilities. As a first step to address this question we evaluated the effect of UCB at the neuronal cytoskeletal dynamics focusing on: (i) axonal elongation, (ii) microtubule polymerization and stabilization, and (iii) axonal transport. We first observed that UCB exposure lead to a higher percentage of neurons with decreased axonal length. Since microtubules polymerization and stability have crucial roles in axogenesis, we further investigated the polymerization rate of microtubules and found that it was also impaired after UCB exposure. In addition, hippocampal neurons treated with UCB revealed a more stable microtubules array, which may be related to a decreased axonal outgrowth. As our former results demonstrated that UCB increases microtubules stability, we decided to assess the UCB effects on microtubule associated proteins, MAP2 and Tau1. Curiously, we observed that UCB increases MAP2 axonal entry while it also enhances MAP2 and Tau1 expression along the axon, as well as their binding to microtubules. It is known that microtubule-bound Tau1 is able to interfere with the progress of motor proteins such as kinesin and dynein along the axon. Interestingly, in UCB-treated neurons we found a decreased expression of kinesin and a marked elevated expression of dynein, which may compromise the normal axonal transport. One of the cargoes transported via motor proteins are mitochondria. In this regard we demonstrated that UCB exposure induces mitochondria to aggregate and accumulate on the distal portion of the axon, suggesting a deficient axonal transport. These findings are new clues on the mechanisms of neurologic impairment induced by bilirubin in moderate to severe neonatal jaundice, showing cytoskeleton alterations similar to those often observed in neurological and neurodegenerative diseases. Resumo alargado em português disponível no documento
