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.
This project will test the effects of four compounds on remyelination in the neonatal brain after hypoxic injury (HI). Moreover, we will determine the expression of key targets of these compounds in human neonatal brain tissue. Knowledge gained from these studies will provided needed insight into treating neonatal white matter injuries, which are the leading causes of Cerebral Palsy (CP), for which there are currently no treatments.
