Targeting the Choroid Plexus-Cerebrospinal Fluid System to Treat Post-Hemorrhagic Hydrocephalus

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PROJECT SUMMARY Post-hemorrhagic hydrocephalus (PHH) is a leading cause of morbidity in premature infants. PHH is triggered by germinal matrix intraventricular hemorrhage (IVH) that results in accumulation of cerebrospinal fluid (CSF) in the brain compression of surrounding brain tissue, and permanent neurological deficits. While PHH is clearly caused by an altered balance of CSF production and removal, the mechanisms are poorly understood, limiting our ability to guide rational therapies. Here, we propose to examine two processes that could be manipulated therapeutically to alleviate PHH: (1) ion and fluid transport by the choroid plexus (ChP), and (2) ventricular blood clearance by macrophages. In adults under normal physiological conditions, sheets of specialized ChP epithelial cells secrete CSF via an incompletely understood set of membrane proteins including NKCC1, a phosphorylation activated bi-directional Na-K-Cl cotransporter. Strikingly, we recently discovered that NKCC1 participates in CSF removal rather than CSF secretion during early stages of brain development. CSF-K+ levels are significantly higher in embryos than adults, likely explaining this opposite direction of NKCC1 water transport8. Experimental introduction of blood into the ventricles during development appears to further elevate CSF-K levels, and to drive intracellular calcium activity in ChP epithelial cells, expression of the immediate early gene c-fos, and increased expression/phosphorylation of NKCC1. Our findings suggest a novel counter-regulatory response to IVH in premature infants: ChP absorption of CSF via NKCC1, driven by K+. We will test this hypothesis by determining if NKCC1 activation either worsens or mitigates hydrocephalus in our mouse IVH model (Aim 1; preliminary data suggests the latter). We also found that following IVH, blood products linger in the developing ventricles and may account for the persistence of PHH. The brain's ventricles and the apical surface of the ChP are home to specific macrophages known as Kolmer cells. While Kolmer cells have been implicated as responders to brain hemorrhage, their scavenging and other functions have remained elusive. Our data suggest that during early stages of brain development, ventricular macrophages/Kolmer cells are activated and recruited to the site of blood leakage within the ventricle (Aim 2A) and that these macrophages are necessary and sufficient to clear blood and/or inflammatory signals from the ventricles (Aim 2B, C). Collectively, our data suggest that the ultimate severity of PHH depends on a developmental stage-specific interplay between blood products, ion concentrations (e.g. [K]), immune and inflammatory reactions, and NKCC1 expression levels. An estimated 20% of infants that experience intraventricular bleeds develop PHH. We suspect this is due to insufficient endogenous compensatory responses. The ultimate goal of this proposal is to improve outcomes by laying the groundwork for development of clinical treatments that boost endogenous removal of CSF and blood that drive the pathogenic processes that lead to PHH. This proposal should also guide therapies for adult IVH and other conditions with disrupted extracellular ionic homeostasis.