# Endothelial PROX1 induces blood-brain barrier disruption in the central nervous system

## TL;DR

This study shows that PROX1, a protein involved in lymphatic development, disrupts the blood-brain barrier when expressed in brain endothelial cells.

## Contribution

The paper reveals that PROX1 induces BBB disruption by downregulating key genes and Wnt/β-catenin signaling in endothelial cells.

## Key findings

- Ectopic PROX1 expression in endothelial cells causes hybrid blood-lymphatic phenotypes and vascular malformations.
- PROX1 downregulates β-catenin and claudin-5, essential for BBB integrity.
- BBB disruption occurs during both embryonic and postnatal stages of PROX1 overexpression.

## Abstract

The central nervous system (CNS) parenchyma has conventionally been believed to lack lymphatic vasculature, likely owing to a non-permissive microenvironment that hinders the formation and growth of lymphatic endothelial cells (LECs). Recent findings of ectopic expression of LEC markers including prospero homeobox 1 (PROX1), a master regulator of lymphatic differentiation, and the vascular permeability marker plasmalemma vesicle–associated protein (PLVAP) in certain glioblastomas (GBM) and brain arteriovenous malformations have prompted investigation into their roles in cerebrovascular malformations, tumor environments, and blood-brain barrier (BBB) abnormalities. To explore the relationship between ectopic LEC properties and BBB disruption, we used endothelial cell–specific Prox1 overexpression mutants. When induced during embryonic stages of BBB formation, endothelial Prox1 expression induces hybrid blood-lymphatic phenotypes in the developing CNS vasculature. This effect is not observed when Prox1 is overexpressed during postnatal BBB maturation. Ectopic Prox1 expression leads to significant vascular malformations and enhanced vascular leakage, resulting in BBB disruption when induced during both embryonic and postnatal stages. Mechanistically, PROX1 downregulates critical BBB-associated genes, including β-catenin and claudin-5, which are essential for BBB development and maintenance. These findings suggest that PROX1 compromises BBB integrity by negatively regulating BBB-associated gene expression and Wnt/β-catenin signaling.

Ectopic PROX1 expression in brain endothelial cells disrupts the blood-brain barrier (BBB), leading to vascular leakage by inhibiting key BBB-associated gene expression and Wnt/ß-catenin signaling.