Intraventricular Hemorrhage Disrupts the Blood Brain Barrier in Premature Infants

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Abstract Intraventricular hemorrhage (IVH) remains a major neurological complication of prematurity that results in cerebral palsy, hydrocephalus, and cognitive deficits. No effective therapy exists to prevent these disorders in infants with IVH. IVH triggers inflammation in the periventricular germinal matrix and adjacent white matter, resulting in maturational arrest of oligodendrocyte progenitor cells (OPCs) and myelination failure. Moreover, there is increased CSF production and concurrent obstruction in CSF flow, which leads to hydrocephalus. IVH- induced injury may disrupt the integrity and function of the blood brain barrier (BBB) and blood-CSF barrier (BCB), allowing myeloid cells to infiltrate the brain, and fluids to exude from it, thus worsening the consequences of IVH. Sphingosine 1 phosphate (S1P) is a lipid mediator and a key regulator of BBB and BCB function. S1P binds and stimulates G-protein coupled receptors (S1PR1 through S1PR5). S1PR1 contributes to vessel maturation, regulates adherens and tight junction assembly and function, and limits trafficking of immune cells across the BBB. In contrast, S1PR2 promotes immune responses, increases BBB permeability, and facilitates leukocyte entry into the brain. Thus, constitutively-expressed S1PR1 antagonizes S1PR2, which is often induced under pathological conditions in the BBB. Both S1PR1 activation and S1PR2 inhibition offer neuroprotection in brain injury models. However, the role of S1PR1 and S1PR2 in BBB and BCB damage, hydrocephalus, and white matter injury is unclear in neonates with IVH. Our central hypotheses are: i) IVH will induce inflammation, disrupt the BBB and BCB, and alter S1PR1 and S1PR2 expressions in the BBB and BCB in both humans and rabbits and ii) modulation of S1PR1 and S1PR2 signaling by receptor subtype- specific agents will restore BBB and BCB integrity, minimize cerebral inflammation, and reverse white matter injury and hydrocephalus in preterm rabbits with IVH. We will test these hypotheses in a rabbit model of glycerol-induced IVH and autopsy samples from human premature infants. In Aim 1, we will determine the effect of IVH on a) BBB and BCB permeability and immune cell infiltration across the BBB and BCB, b) endothelial tight and adherens junction, endothelial transcytosis, and key transporters, and c) transcriptional changes in the capillary endothelium of the periventricular brain region and choroid plexus. The observations made in rabbit will be validated in autopsy samples from preterm infants with and without IVH. In Aim 2 and 3, we will evaluate the effect of S1PR1 and S1PR2 modulation on a) BBB and BCB permeability, endothelial tight and adherens junction assembly, endothelial transcytosis and transcriptome, b) immune cell infiltration, ventriculomegaly, and c) myelination and neurobehavior. We will also determine whether S1PR1 and S1PR2 signaling affect adherens and tight junction as well as myelination via sonic hedgehog and Rho-ROCK pathways, respectively. These studies will enhance our understanding of S1P biology in the maturing brain and hasten development of new therapies to minimize white matter injury and hydrocephalus in survivors of IVH.