Glial Dysgenesis in the Injured Developing Brain

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DESCRIPTION (provided by applicant): There are a number of neurological disorders that result from perinatal brain damage. While there is no single cause of these disorders, there is a strong correlation between hypoxia-ischemia (H/I) and damage to the cerebral gray and white matter. Despite progress in understanding the pathogenesis of hypoxic-ischemic injury, we have an incomplete appreciation for the mechanisms leading to permanent brain injury and more importantly there is no clear explanation for the failure of regeneration. Increasingly, investigators are beginning to appreciate the impact of this injury on the subventricular zone (SVZ), which is that region of the immature brain that harbors the multipotential neural stem cells/progenitors (NSPs) that are endowed with the ability to generate neurons, astrocytes and oligodendrocytes. The specific goal of this proposal is to identify signals that induce the differentiation of glial precursors towards astrocytes and to evaluate recovery from H/I when specific astrocyte inducers are antagonized. Our preliminary data indicate that there is an increase in the production of astrocytes from SVZ cells at the expense of myelinating oligodendrocytes following recovery from perinatal H/I. Thus, our hypothesis is that as a result of injury-induced cytokines, that there is aberrant production of astrocytes from glial progenitors in the SVZ and that this glial dysgnesis contributes to the permanent deficit in white matter oligodendrocytes that occurs subsequent to H/I. Seminal studies on brain development have shown that neural precursors are responsive to extrinsic signals that govern their differentiation choices. We hypothesize that as a result of an H/I insult that specific signals are now present that would otherwise be absent. The specific aims of this proposal are to: 1) Test the hypothesis that perinatal H/I increases the production of astrocytes from glial progenitors in the SVZ; 2) Test the hypothesis that the damaged neonatal brain produces factors that promote astrocyte generatation from postnatal SVZ cells; 3) Establish which transcription factors are active in postnatal SVZ cells by relevant astroglial inducers; and 4) Establish whether a pharmacological antagonist of the TGF-¿ receptor, ALK5, will prevent the aberrant production of astrocytes in vitro and in vivo after H/I. We anticipate that the knowledge obtained from these studies will lead to pharmacological interventions for infants surviving H/I or other disturbances of brain development to enable the infant brain to develop more normally. The insights we gain from our studies also will be applicable to a broad range of injuries and diseases of the CNS, as well as to studies where exogenous neural precursors will be transplanted into the brain, where excessive astroglial differentiation or astrogliosis are deemed undesirable. PUBLIC HEALTH RELEVANCE: Despite progress in understanding the pathogenesis of hypoxic-ischemic injury, we have an incomplete appreciation for the mechanisms leading to permanent brain injury and more importantly there is no clear explanation for the failure of regeneration. The specific goal of this proposal is to identify signals that induce the differentiation of neural precursors towards astrocytes and to evaluate recovery from H/I when specific astrocyte inducers are antagonized. The insights we gain from our studies also will be applicable to a broad range of injuries and diseases of the CNS, as well as to studies where exogenous neural precursors will be transplanted into the brain, where excessive astroglial differentiation or astrogliosis are deemed undesirable.