Developing Novel Therapeutic Approaches for White Matter Injury in the Neonatal Brain

 描述(申请人提供)：新生儿大脑对缺氧损伤(HI)特别敏感。早产儿HI表现为脑室周围白质软化症(PVL)，而足月儿HI表现为缺氧缺血性脑病(HIE)。在中-重度PVL或HIE的新生儿中，60%-75%的新生儿由于广泛的白质损伤(WMI)而发展为终生神经残疾，原因是髓鞘少突胶质细胞(OL)丢失。这种OL的丧失，加上它们不能再生，导致神经元功能受损，临床表现为脑性瘫痪(CP)。在这个方案中，我们将使用两种不同的方法来解决HI后重新髓鞘形成的关键问题：OLP的分化和轴突完整性的维持。我们的研究已经确定了四种化合物，它们作用于不同的途径，有助于抑制再髓鞘形成，我们将在新生儿大脑中测试HI期间和之后的情况。白质病变的OLP的一个特征是WNT信号水平的升高，该信号的功能是抑制WMI后的再生髓鞘形成。因此，抑制OLP中的Wnt信号是刺激HI后重新髓鞘形成的一种治疗策略。最近，我们发现在发育中的中枢神经系统中，Daam2是Wnt信号的关键近端调节器，它通过PIP5K-PIP2信号轴发挥作用。利用开发过程中的这一知识，我们发现了两种抑制PIP5K活性的化合物(例如Sp-8-PCPT-cAMP和UNC3230)，它们可以刺激急性缺氧后WMI后的重新髓鞘形成。在这里，我们将确定这些化合物在HI和缺血后是否在新生儿脑中发挥类似的功能，以及DAAM2-PIP5K轴是否在人类HIE/PVL病变的OLP中表达。轴突的完整性在髓鞘形成过程中也起着核心作用。最近，我们发现皮质神经元中轴突起始段(AIS)的破坏会由于轴突特性的丧失而阻止其最终的髓鞘形成。此外，我们还发现，成人脑缺血损伤后，AIS受到干扰。因此，我们认为，HI诱导的AIS的丢失抑制了髓鞘形成，而保存AIS可能促进了HI后的髓鞘形成。缺血损伤激活钙依赖的蛋白水解酶--钙蛋白酶，该酶能分解必需的AIS支架蛋白，导致轴突完整性的丧失。钙蛋白酶抑制剂(如MDL28170)在体外和体内都能保护缺血后的AIS。因此，我们将确定通过抑制Calain来维持AIS是否能刺激HI后的重新髓鞘形成和恢复，以及AIS的这些组成部分在人类HIE/PVL损伤中是否存在失调。

 DESCRIPTION (provided by applicant): The newborn brain is particularly sensitive to hypoxic injury (HI). Preterm HI manifests itself as periventricular leukomalacia (PVL), while in full-term infants HI presents as hypoxic ischemic encephalopathy (HIE). In newborns with moderate-severe forms of either PVL or HIE, 60-75% develop life-long neurological disabilities, resulting from extensive white matter injury (WMI), due to the loss of myelinating oligodendrocytes (OLs). This loss of OLs, coupled with their failure to regenerate, leads to impaired neuronal function, which clinically manifests as cerebral palsy (CP). In this proposal we will attack the critical problem of remyelination after HI using two distinct approaches: the differentiation of OLPs and the maintenance of axonal integrity. Our studies have identified four compounds that act on distinct pathways that contribute to the suppression of remyelination, which we will test in the neonatal brain during- and after- HI. One feature of OLPs populating white matter lesions is elevated levels of Wnt signaling, which functions to suppress regenerative myelination after WMI. Therefore, inhibition of Wnt signaling in OLPs represents a therapeutic strategy for stimulating remyelination after HI. Recently we identified Daam2 as a key proximal modulator of Wnt signaling in the developing CNS that functions through the PIP5K-PIP2 signaling axis. Leveraging this knowledge from development, we found two compounds that inhibit PIP5K activity (e.g. Sp-8-pCPT-cAMP and UNC3230) stimulate remyelination after WMI after acute hypoxia. Here we will determine whether these compounds function similarly in the neonatal brain after HI and ischemia, and whether the Daam2-PIP5K axis is expressed in OLPs in human HIE/PVL lesions. Axon integrity also plays a central role in myelination. Recently, we found that disruption of the axon initial segment (AIS) in cortical neurons blocks their eventual myelination due to loss of axonal identity. Moreover, we found that the AIS is disrupted after ischemic injury in the adult brain. Thus, we propose HI- induced loss of the AIS inhibits myelination, whereas preservation of the AIS may promote myelination after HI. Ischemic injury activates the calcium dependent protease, calpain, which proteolyzes essential AIS scaffolding proteins, resulting in the loss of axonal integrity. Calpain inhibitors (e.g. MDL28170) preserve the AIS after ischemia both in vitro and in vivo. Therefore, we will determine if maintenance of the AIS through inhibition of calpain stimulates remyelination and recovery after HI, and whether these components of the AIS are dysregulated in human HIE/PVL lesions.