Research Institute for Medicines and Pharmaceutical Sciences, Faculty of Pharmacy, University of Lisbon, Lisbon, Portugal.
Mol Cell Neurosci. 2011 Sep;48(1):82-93. doi: 10.1016/j.mcn.2011.06.008. Epub 2011 Jun 25.
Hippocampus is one of the brain regions most vulnerable to unconjugated bilirubin (UCB) encephalopathy, although cerebellum also shows selective yellow staining in kernicterus. We previously demonstrated that UCB induces oxidative stress in cortical neurons, disruption of neuronal network dynamics, either in developing cortical or hippocampal neurons, and that immature cortical neurons are more prone to UCB-induced injury. Here, we studied if immature rat neurons isolated from cortex, cerebellum and hippocampus present distinct features of oxidative stress and cell dysfunction upon UCB exposure. We also explored whether oxidative damage and its regulation contribute to neuronal dysfunction induced by hyperbilirubinemia, considering neurite extension and ramification, as well as cell death. Our results show that UCB induces nitric oxide synthase expression, as well as production of nitrites and cyclic guanosine monophosphate in immature neurons, mainly in those from hippocampus. After exposure to UCB, hippocampal neurons presented the highest content of reactive oxygen species, disruption of glutathione redox status and cell death, when compared to neurons from cortex or cerebellum. In particular, the results indicate that cells exposed to UCB undertake an adaptive response that involves DJ-1, a multifunctional neuroprotective protein implicated in the maintenance of cellular oxidation status. However, longer neuronal exposure to UCB caused down-regulation of DJ-1 expression, especially in hippocampal neurons. In addition, a greater impairment in neurite outgrowth and branching following UCB treatment was also noticed in immature neurons from hippocampus. Interestingly, pre-incubation with N-acetylcysteine, a precursor of glutathione synthesis, protected neurons from UCB-induced oxidative stress and necrotic cell death, preventing DJ-1 down-regulation and neuritic impairment. Taken together, these data point to oxidative injury and disruption of neuritic network as hallmarks in hippocampal susceptibility to UCB. Most importantly, they also suggest that local differences in glutathione content may account to the different susceptibility between brain regions exposed to UCB.
海马体是未结合胆红素（UCB）脑病最易受影响的脑区之一，尽管小脑在核黄疸中也显示出选择性的黄色染色。我们之前证明，UCB 会在皮质神经元中引起氧化应激，破坏神经元网络动态，无论是在发育中的皮质神经元还是海马体神经元中，并且未成熟的皮质神经元更容易受到 UCB 诱导的损伤。在这里，我们研究了从皮质、小脑和海马体分离的未成熟大鼠神经元在接触 UCB 时是否表现出不同的氧化应激和细胞功能障碍特征。我们还探讨了氧化损伤及其调节是否会导致高胆红素血症引起的神经元功能障碍，考虑到神经突延伸和分支以及细胞死亡。我们的结果表明，UCB 会诱导一氧化氮合酶的表达，以及未成熟神经元中硝酸盐和环鸟苷单磷酸的产生，主要是在海马体神经元中。与皮质或小脑神经元相比，暴露于 UCB 后，海马体神经元表现出最高的活性氧含量、谷胱甘肽氧化还原状态的破坏和细胞死亡。特别是，结果表明，暴露于 UCB 的细胞会产生适应性反应，涉及 DJ-1，一种涉及维持细胞氧化状态的多功能神经保护蛋白。然而，更长时间的 UCB 暴露会导致 DJ-1 表达下调，尤其是在海马体神经元中。此外，在未成熟的海马体神经元中，UCB 处理后神经突生长和分支的损伤也更大。有趣的是，用 N-乙酰半胱氨酸（谷胱甘肽合成的前体）预先孵育可以保护神经元免受 UCB 诱导的氧化应激和坏死性细胞死亡，防止 DJ-1 下调和神经突损伤。综上所述，这些数据表明氧化损伤和神经突网络的破坏是海马体对 UCB 易感性的特征。最重要的是，它们还表明，暴露于 UCB 的脑区之间谷胱甘肽含量的差异可能导致其易感性的不同。
