VEGF increases BMEC monolayer permeability by affecting occludin expression and tight junction assembly

Area of Science:

• Neuroscience
• Cell Biology
• Physiology

Background:

• The blood-brain barrier (BBB), formed by tight junctions between brain microvessel endothelial cells (BMECs), is crucial for central nervous system homeostasis.
• BBB breakdown is implicated in neurological diseases and brain tumors, often associated with increased vascular permeability.
• Vascular endothelial growth factor (VEGF) secreted by tumor cells is known to increase microvasculature permeability and contribute to brain edema.

Purpose of the Study:

• To investigate the specific effects of VEGF on the permeability of BMECs.
• To elucidate the mechanisms by which VEGF influences tight junction integrity and formation.
• To determine the role of occludin and ZO-1 in VEGF-mediated BBB permeability changes.

Main Methods:

• Utilized BMEC monolayer cultures to assess permeability using [(14)C]sucrose flux.
• Measured transendothelial electrical resistance (TER) to evaluate barrier integrity.
• Analyzed the expression and localization of tight junction proteins occludin and ZO-1 via immunofluorescence and Western blotting.

Main Results:

• VEGF treatment significantly increased sucrose permeability across BMEC monolayers.
• VEGF decreased transendothelial electrical resistance (TER), indicating reduced barrier function.
• VEGF caused the dissociation of occludin and ZO-1 from endothelial cell junctions and reduced occludin protein levels.

Conclusions:

• VEGF enhances BMEC permeability by disrupting tight junctions, specifically by downregulating occludin expression and altering the organization of occludin and ZO-1.
• These findings identify occludin and ZO-1 as key downstream targets in the VEGF signaling pathway that mediates BBB breakdown.
• Understanding this mechanism is vital for developing therapeutic strategies targeting brain edema in tumors and other CNS diseases.