Injury and Recovery in Developing Brain

Yale University, New Haven CT

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Abstract

As many as 50% of low-birth-weight infants suffer cognitive deficits due to chronic hypoxia and circulatory complications. Longitudinal studies suggest recovery in both brain volume and cognitive functions by early adulthood in some children, however this recovery is variable and the neurobiological basis of this improvement are not understood. Our mouse model of chronic sublethal hypoxic injury reproduces the initial cortical volume deficit and ventriculomegaly, as well as the subsequent recovery, although some neuron loss and cognitive abnormalities persist long-term in these mice. Identifying the cellular and molecular events that underlie neuronal recovery and finding ways to enhance this process are the common goals of this program project. We hypothesize that recovery from hypoxic brain injury is due to a coupled neurogenic/angiogenic response. This includes (1) proliferation of neural stem cells and progenitors, which requires specific growth factors in neural stem cells and vascular endothelium;(2) survival of newly-born neuronal and glial populations, which requires improved energetic metabolism in the newly-generated cells and trophic influences from neural and vascular compartments. Specific projects in this program will test these hypotheses by generating tissue-specific and time-dependent loss- or gain-of function genetic models to test the function of several proliferative, survival and differentiation factors in neural stem cells, oligodendrocyte progenitors, and vascular endothelium. The factors under investigation include Fibroblast growth factor 2 (FGF2), the Epidermal growth factor receptor (EGFR), TrkB and its ligand Brain derived neurotropic growth factor (BDNF), the mitochondrial uncoupling protein 2 (UCP2) and the gut hormone ghrelin. Elucidating the role of these genes in specific cell types will reveal the reciprocal and dynamic interactions between vascular, neural and metabolic components as the animals recover from injury in standard or enriched environment. A multidisciplinary approach, which includes morphometric and immunocytochemical analyses, electron microscopy and electrophysiology, is used to assess whether the signaling systems under study contribute adaptive changes triggered by the enriched environment in hypoxic animals. Furthermore, the beneficial effect of enhancing specific components of these signaling systems will be tested at the cellular and behavioral level. The long-term goal of these studies is to identify new means of therapeutic intervention to decrease the developmental disability and neurobehavioral sequelae of preterm birth.