Chondroitin Sulfate Proteoglycan and Myelination in Intraventricular Hemorrhage

DESCRIPTION (provided by applicant): Intraventricular hemorrhage (IVH) in premature infants predisposes to white matter injury and subsequent cerebral palsy. The most common white matter injury in premature infants is 'gliosis and hypomyelination with intact axons'. In our model of IVH in premature rabbits, there is an arrest of oligodendrocyte (OL) maturation at a pre-myelinating stage. However, the mechanism underlying the maturational arrest of pre-OL and subsequent hypomyelination is unclear. Myelination is a dynamic process that needs an appropriate microenvironment containing growth factors, extracellular matrix molecules and myelinating OL. Chrondroitin sulfate proteoglycans (CSPG)-- neuracan, phosphacan, brevican, decorin, NG2 &versican--are important components of the extracellular matrix (ECM) and are increased in adult and neonatal brain injuries. They are primarily produced by reactive astrocytes and are regulated by transforming growth factor-2 (TGF-2) and epidermal growth factor (EGF). CSPGs have key regulatory functions during migration, proliferation and differentiation of pre-OL. Specifically, degradation of CSPGs by either chondroitinase or protease facilitates migration of OL, loosens the physical barriers in ECM, enhances formation of OL process outgrowths to unsheathe axons and improves interaction of growth factors with OL. Despite this evidence, direct effect(s) of CSPGs on myelination have not been studied. We hypothesize that CSPGs are elevated in premature newborns with IVH and that suppression of CSPG formation will restore myelination of axons and maturation of pre- OL into myelinating OL. Our preliminary data show that expression of CSPGs and growth factors (TGF2 and EGF) are elevated in premature infants and rabbit pups with IVH;and treatment with decorin, a CSPG and natural antagonist of TGF-2, reduces their levels. Our approach is to use a rabbit model that induces IVH with intraperitoneal glycerol. This model results in pups with hemorrhage to exhibit inflammation, cell death and subsequently, lesser myelination and more enhanced gliosis (day 14) compared to controls without IVH. The following specific aims will be addressed: Aim #1. Determine whether the expression of CSPGs (neuracan, phosphacan, brevican, decorin, NG2 &versican) and their regulating growth factors (TGF-2 and EGF) are higher in both premature rabbit pups and infants with IVH compared to controls without IVH. Aim # 2. Determine whether suppression of CSPGs either by chondroitinase or decorin (via TGF-2 inhibition) facilitates maturation of pre-OL, myelination and neurological recovery in premature rabbit pups with IVH. Our study that links CSPGs with failure to myelinate coupled with our novel approaches to regulate CSPG expression may provide effective strategies for prevention of cerebral palsy in infants with IVH. PUBLIC HEALTH RELEVANCE: 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 deficits--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 or prevent cerebral palsy 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.