Germinal matrix hemorrhage (GMH)-intraventricular hemorrhage (IVH) occurs in thousands of premature infants and predisposes them to white matter injury and to the attendant neurologic dysfunctions-- cerebral palsy plus cognitive deficits. The most common white matter injury in these infants is "hypomyelination and gliosis". Treatment and prevention of both the IVH and the resultant white matter damage is non-existent. Therefore, it is necessary to elucidate the mechanism of white matter injury associated with IVH and then to develop a therapeutic strategy either to prevent or minimize it. We have developed a model of IVH in which premature pups with IVH exhibit apoptosis and proliferation of pre-oligodendrocyte (pre-OL) with subsequent maturation-arrest in pre-OL stage, resulting in hypomyelination and gliosis. Oligodendrocyte (OL) development is regulated by transcription factors, including Olig-1, Olig-2, Mash 1, Id2, Id4, Nkx2.2 and Sox 10;and these factors are controlled by sonic hedgehog (Shh), Notch and Bone Morphogenetic Protein (BMP) signaling pathways. Notch and BMP overexpression promotes astrocytosis and inhibits OL development. Of note, suppression of BMP levels in animal models increases OL density;and Notch modulation improves the neurological recovery. Thyroid hormone is a key promoter of oligodendrogenesis and myelination. Accordingly, our experiments have revealed higher BMP-4 and Notch levels in the germinal matrix of premature subjects with IVH compared to non-IVH controls. More importantly, thyroxine treatment or BMP inhibition restored the density of myelinating (O1+) OL and myelination in IVH pups (Preliminary data). On this basis our overall hypotheses are that 1) IVH disturbs the OL development and affects the expression of transcription factors involved in OL specification and differentiation via BMP, Shh and Notch signaling, and that 2) the disturbed OL development, hypomyelination, gliosis and motor impairment in IVH can be restored by modulating BMP and Notch signaling or thyroxine treatment. Our approach is to use our rabbit pup model and autopsy materials from premature infants. The following specific aims will be addressed:
Aim # 1: Compare proliferation, maturation and apoptosis of cells of OL lineage in premature rabbit pups (E29) and human infants (23-35 weeks gestation) with IVH vs. without IVH.
Aim # 2: Determine temporal expression of transcription factors (Olig1, Olig2, Mash 1, Id2, Id4, Nkx2.2 and Sox 10) and the key signaling pathways (BMP, Shh and Notch) involved in OL specification and differentiation in the forebrain of the premature rabbit pups (E29) and human infants (23-35 weeks gestation) with IVH compared to non-IVH controls.
Aim # 3: Promote OL development and myelination to facilitate neurological recovery in premature pups with IVH by a) thyroxine treatment and by b) modulating BMP and Notch signaling pathways. Hence, the proposed study will elucidate the mechanism of white matter injury in IVH and may lead to novel strategies in prevention of cerebral palsy in premature infants.
In the United States, about 12,240 premature infants develop bleeding in and around the ventricle (cavity) of the brain each year, which enhances the risk of white matter injuries and consequent cerebral palsy (weakness in extremities), and cognitive problems (writing and reading difficulties). In this proposal, we seek to determine the mechanism of brain injuries in these infants with hemorrhage that leads to impairment in walking, reading and writing. In addition, we will test therapeutic strategies that can minimize brain injuries in them. To address these issues, we will use prematurely delivered rabbit pups as an experimental animal and will also use autopsy materials from premature infants with and without brain hemorrhage.
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