Glutamate Receptors in Hypoxic-ischemic Injury to Developing Oligodendrocytes

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DESCRIPTION (provided by applicant): Hypoxic-ischemic injury to the developing brain leads to devastating neurological consequences. Strikingly, the pattern of hypoxic-ischemic brain injury is highly age-dependent. In term infants, hypoxia-ischemia predominantly affects cerebral cortex with characteristic neuronal loss. However, in premature infants, hypoxia- ischemia selectively affects cerebral white matter with prominent injury to the developing oligodendrocyte (OL), a disorder termed periventricular leukomalacia (PVL). The developing OL (pre-myelinating OL, termed "preOL") is highly vulnerable to hypoxic-ischemic injury and is the major cellular substrate of PVL. We have shown that glutamate receptor (GluR) expression is developmentally regulated on OLs in vivo and in vitro, and that ionotropic GluRs (iGluRs) mediate hypoxic-ischemic injury to preOLs, but metabotropic GluRs (mGluRs) can modulate this injury. However, the role of specific iGluRs and mGluRs in hypoxic-ischemic preOL injury and the signaling mechanisms remain largely unknown. The central hypothesis of the proposal is that Ca2+-permeable iGluRs mediate hypoxic-ischemic preOL injury and that group 1 mGluRs can modulate this injury, entailing the molecular interplay between iGluRs and mGluRs and the integration of distinct post-receptor signaling events. We will focus on determining the mechanisms of the crosstalk between iGluRs and mGluRs in preOL injury. The goal of this project is to provide new insights into the age-specific mechanisms of hypoxic-ischemic preOL injury, and to determine potential age-specific therapeutic strategies for treating preOL injury that underlies cerebral white matter disorders. Aim 1 of this proposal is to determine the sequence of alterations of iGluR function and signaling in preOL excitotoxicity, with the aim to identify specific therapeutically accessible targets. Aim 2 will expand upon our preliminary results and further investigate the novel role of mGluRs in preOL injury in developing cerebral white matter injury in vivo. Aim 3 will determine the molecular mechanisms of the interplay between iGluRs and mGluRs. We will examine whether mGluR modulation leads to changes in iGluR subunit expression, phosphorylation state, and internalization, and also investigate intracellular Ca2+ and oxidative stress, and the specific roles of signaling molecules such as Akt (protein kinase B), CaMKII (Ca2+/calmodulin kinase II), CaN (calcineurin), and PKC (protein kinase C) in the modulation of iGluR-mediated preOL injury by mGluRs. Completion of this project will help to elucidate novel mechanisms of hypoxic-ischemic preOL injury and to identify new targets for the development of therapeutic strategies to control preOL injury that underlies cerebral white matter disorders, such as PVL, for which no specific therapy currently exists. PUBLIC HEALTH RELEVANCE: Periventricular leukomalacia (PVL) is the predominant form of brain injury in the premature infant, and the most common cause of cerebral palsy. PVL affects up to 50% of the 56,000 premature infants born in the U. S. every year, yet currently no therapy exists for this serious human disorder. This project seeks to determine the mechanisms of the molecular interplay between ionotropic and metabotropic glutamate receptors in hypoxic- ischemic injury to the developing oligodendrocyte - the cellular substrate of PVL. The scientific knowledge to be acquired through this project is of likely benefit to the development of preventive strategies for PVL and the care of children with cerebral palsy.