Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 116, Issue 10, Pages 4518-4527Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1814766116
Keywords
blood-brain barrier; podocalyxin; endothelial; barrier function; CD34 family
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Podocalyxin (Podxl) is broadly expressed on the luminal face of most blood vessels in adult vertebrates, yet its function on these cells is poorly defined. In the present study, we identified specific functions for Podxl in maintaining endothelial barrier function. Using electrical cell substrate impedance sensing and live imaging, we found that, in the absence of Podxl, human umbilical vein endothelial cells fail to form an efficient barrier when plated on several extracellular matrix substrates. In addition, these monolayers lack adherens junctions and focal adhesions and display a disorganized cortical actin cytoskeleton. Thus, Podxl has a key role in promoting the appropriate endothelial morphogenesis required to form functional barriers. This conclusion is further supported by analyses of mutant mice in which we conditionally deleted a floxed allele of Podxl in vascular endothelial cells (vECs) using Tie2Cre mice (Podxl(Delta Tie2Cre)). Although we did not detect substantially altered permeability in naive mice, systemic priming with lipopolysaccharide (LPS) selectively disrupted the blood-brain barrier (BBB) in Podxl(Delta Tie2Cre) mice. To study the potential consequence of this BBB breach, we used a selective agonist (TFLLR-NH2) of the protease-activated receptor-1 (PAR-1), a thrombin receptor expressed by vECs, neuronal cells, and glial cells. In response to systemic administration of TFLLR-NH2, LPS-primed Podxl(Delta Tie2Cre) mice become completely immobilized for a 5-min period, coinciding with severely dampened neuro-electric activity. We conclude that Podxl expression by CNS tissue vECs is essential for BBB maintenance under inflammatory conditions.
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