Investigating the Impact of Hydrocephalus on Epiplexus Cells of the Choroid Plexus

Hydrocephalus is characterized by accumulation of cerebrospinal fluid (CSF) in the brain, resulting from over-production, under-absorption, or blockage of the flow of CSF. Current treatments are limited to surgically placed shunts that often require follow-up procedures. The goal of this research group is to understand the mechanisms of hydrocephalus with the aim of finding effective pharmacological treatments. The animal model used exhibits a mutation in the transmembrane 67 (Tmem67) gene. Homozygous recessive animals present with ventriculomegaly at birth and severe hydrocephalus by postnatal day 15 (P15). Experiments in this study compare tissue obtained from wildtype animals and homozygous mutant animals. The choroid plexus (CP) is the main producer of CSF, making it a target structure in hydrocephalus research. It is a branched tissue that includes a stroma with fenestrated capillaries, wrapped by a tightly regulated barrier epithelium. Choroid plexus epithelial cells (CPe) are multiciliated cells that strictly regulate the osmotic balance of CSF. Epiplexus cells are poorly understood immune cells localized on the apical (CSF-facing) side of the CPe. These cells are believed to share functional characteristics with microglia and macrophages. Microglia are the innate immune cells of the central nervous system; a specialized type of glial cell that interact with neurons, and aid in the structure and immunosurveillance of the brain. Macrophages originate from monocytes and reside in most tissues of the body, responding to cellular signals of injury and infection. Macrophages can be found free-roaming in tissues or associated to epithelial cells, known as border-associated macrophages (BAMs). Due to their association with the CPe, epiplexus cells are considered BAMs. Beyond their apparent similarities to other immune cells, little else is known about the properties and functions of epiplexus cells or their interaction with the CPe or CSF, nor if they play a role in the development of hydrocephalus. This study furthers the understanding of epiplexus cells, specifically how they impact, or are impacted by hydrocephalus. Rat pups (P15) were terminally anesthetized, perfused with 1x PBS, and fixed with 4% PFA. In the lateral ventricle CP, we have visualized CPe-associated cells with morphology consistent with epiplexus cells. These cells are labeled with microglial/macrophage/epiplexus cell markers: allograft inflammatory factor1/ionized calcium-binding adaptor molecule 1 (Iba1), macrosialin (CD68), and mannose receptor type C-1 lectin (CD206). Iba1 is thought to play a role in restructuring the actin cytoskeleton in cells of monocyte lineage (macrophages and microglia), resulting in morphological differences across levels of activation. CD68 is a transmembrane protein commonly expressed in macrophages and monocytes, supposedly related to the oxidized low-density lipoprotein (OxLDL) pathway, which is involved in exacerbating oxidative stress. CD206 is a transmembrane protein that may aid in the roles of detecting pathogens, removing proteins, and sending waste through lymphatic system. Confocal analysis combining cell morphology and immunohistochemical labeling will be used to quantify CPe-associated epiplexus cells in wildtype and hydrocephalic animals. The results will be substantiated using quantitative real-time PCR. Funding: United States Department of Defense Congressionally Directed Medical Research Program Award; Hydrocephalus Association. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.