Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL), Faculty of Pharmacy, University of Lisbon, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal.
Neuromolecular Med. 2012 Dec;14(4):285-302. doi: 10.1007/s12017-012-8187-9. Epub 2012 Jun 17.
Research on the mechanisms of bilirubin-induced neurological dysfunction focuses mainly on neuronal death, astrocyte-mediated events and microglia activation. Although myelin damage by unconjugated bilirubin (UCB) has been documented in neonatal kernicterus cases, the events leading to myelination impairment were never explored. This condition may occur by reduced oligodendrocyte precursor cells (OPC) number, or failure of OPC to differentiate in myelinating oligodendrocytes. We have shown that UCB elicits an inflammatory response, glutamate release and reactive oxygen species (ROS) generation in neurons and glial cells, biomolecules with toxic properties on OPC. Hence, we propose to examine whether UCB determines OPC demise and, if so, which signaling pathways are involved. Our results show that OPC display increased apoptosis and necrosis-like cell death upon UCB exposure, mediated by early signals of endoplasmic reticulum (ER) stress [e.g. upregulation of glucose-regulated protein (GRP)78, inositol-requiring enzyme (IRE)-1α and activation transcription factor (ATF)-6, as well as activation of caspase-2 and c-Jun N-terminal kinase (JNK)], followed by mitochondrial dysfunction (e.g. loss of mitochondria membrane potential and caspase-9 activation). The later calpain activation points to intracellular Ca(2+) overload and intervention of both ER and mitochondria. Downstream production of ROS may derive from mitochondria damage and secondary injuries, possibly determining the second cycle of GRP78, IRE-1α, caspase-2 and JNK activation. Moreover, inhibition of caspases, calpains and oxidative stress, by using specific inhibitors, prevented UCB-induced OPC death. UCB did not induce the release of cytokines or glutamate by OPC. These results indicate that UCB by reducing OPC survival, through a cascade of programmed intracellular events triggered by ER stress and mitochondria dysfunction, can compromise myelinogenesis.
胆红素诱导的神经功能障碍的机制研究主要集中在神经元死亡、星形胶质细胞介导的事件和小胶质细胞激活上。虽然未结合胆红素 (UCB) 引起的髓鞘损伤在新生儿核黄疸病例中已有记载，但导致髓鞘损伤的事件从未被探索过。这种情况可能是由于少突胶质前体细胞 (OPC) 数量减少，或 OPC 未能分化为髓鞘形成的少突胶质细胞所致。我们已经表明，UCB 在神经元和神经胶质细胞中引发炎症反应、谷氨酸释放和活性氧 (ROS) 的产生，这些生物分子对 OPC 具有毒性。因此，我们假设检查 UCB 是否确定 OPC 的死亡，如果是，哪些信号通路参与其中。我们的结果表明，OPC 在暴露于 UCB 后显示出增加的细胞凋亡和坏死样细胞死亡，这是由内质网 (ER) 应激的早期信号介导的[例如葡萄糖调节蛋白 (GRP)78、肌醇需求酶 (IRE)-1α 和激活转录因子 (ATF)-6 的上调，以及半胱天冬酶-2 和 c-Jun N 末端激酶 (JNK) 的激活]，随后是线粒体功能障碍（例如线粒体膜电位丧失和半胱天冬酶-9 的激活）。晚期钙蛋白酶的激活表明细胞内 Ca(2+) 过载以及内质网和线粒体的干预。ROS 的后续产生可能源自线粒体损伤和二次损伤，可能决定了 GRP78、IRE-1α、半胱天冬酶-2 和 JNK 激活的第二个循环。此外，通过使用特定抑制剂抑制半胱天冬酶、钙蛋白酶和氧化应激，可防止 UCB 诱导的 OPC 死亡。UCB 不会诱导 OPC 释放细胞因子或谷氨酸。这些结果表明，UCB 通过 ER 应激和线粒体功能障碍引发的一系列程序性细胞内事件降低 OPC 的存活率，从而损害髓鞘生成。
