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

 描述（由申请人提供）：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（PVL），而足月儿HI表现为缺氧缺血性脑病（HIE）。在患有中度至重度PVL或HIE的新生儿中，60-75%的新生儿发展为终身神经功能障碍，这是由于髓鞘形成少突胶质细胞（OL）的丧失导致的广泛的白色损伤（OLS）。这种OL的丧失，加上它们不能再生，导致神经元功能受损，临床上表现为脑瘫（CP）。在这个建议中，我们将使用两种不同的方法来解决HI后髓鞘再生的关键问题：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作用于不同途径的化合物，这些途径有助于抑制髓鞘再生，我们将在HI期间和之后在新生儿大脑中进行测试。 OLP占据白色病变的一个特征是Wnt信号传导水平升高，其功能是抑制再生髓鞘形成。因此，抑制OLP中的Wnt信号传导代表了刺激HI后髓鞘再生的治疗策略。最近，我们鉴定了Daam 2作为发育中CNS中Wnt信号传导的关键近端调节剂，其通过PIP 5 K-PIP 2信号传导轴发挥作用。利用来自开发的这一知识，我们发现了两种抑制PIP 5 K活性的化合物（例如Sp-8-pCPT-cAMP和UNC 3230）在急性缺氧后刺激髓鞘再生。在这里，我们将确定这些化合物是否在HI和缺血后的新生儿脑中具有相似的功能，以及Daam 2-PIP 5 K轴是否在人类HIE/PVL病变的OLP中表达。 轴突完整性在髓鞘形成中也起着重要作用。最近，我们发现，在皮层神经元的轴突起始段（AIS）的中断阻断其最终髓鞘形成由于轴突身份的损失。此外，我们发现，AIS在成人脑缺血性损伤后被破坏。因此，我们提出HI诱导的AIS损失抑制髓鞘形成，而保留AIS可促进HI后的髓鞘形成。缺血性损伤激活钙依赖性蛋白酶，钙蛋白酶，其蛋白水解必需的AIS支架蛋白，导致轴突完整性的丧失。钙蛋白酶抑制剂（例如，MDL 28170）在体外和体内均保护缺血后的AIS。因此，我们将确定通过抑制钙蛋白酶维持AIS是否刺激HI后的髓鞘再生和恢复，以及AIS的这些组分在人类HIE/PVL病变中是否失调。

 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.