Roundabout 4 regulates blood-tumor barrier permeability through the modulation of ZO-1, Occludin, and Claudin-5 expression

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• The blood-tumor barrier (BTB) impedes chemotherapy drug delivery to brain tumors.
• Endothelial cells (ECs) form the BTB, and their properties regulate barrier function.
• Understanding BTB regulation is crucial for improving cancer treatment.

Purpose of the Study:

• To investigate the role of endothelial cell receptor Roundabout 4 (Robo4) in regulating BTB permeability.
• To elucidate the molecular mechanisms by which Robo4 influences BTB integrity.
• To assess the therapeutic potential of targeting Robo4 for enhanced drug delivery.

Main Methods:

• Utilized a BTB model involving co-cultured glioma endothelial cells.
• Employed short hairpin RNA (shRNA) to knockdown Robo4 expression.
• Measured transendothelial electrical resistance (TEER) and expression of tight junction proteins (ZO-1, occludin, claudin-5).
• Assessed matrix metalloproteinase-9 (MMP-9) activity and phosphorylation of Src and Erk1/2 signaling pathways.
• Used specific inhibitors (GM6001, PP2, PD98059) to block signaling pathways.

Main Results:

• Robo4 knockdown significantly increased BTB permeability and decreased TEER.
• shRobo4 downregulated tight junction proteins ZO-1, occludin, and claudin-5.
• Robo4 knockdown enhanced MMP-9 activity and expression.
• shRobo4 upregulated Src and Erk1/2 phosphorylation.
• Inhibitor treatments partially reversed the effects of shRobo4 on TEER and tight junction protein expression.

Conclusions:

• Robo4 knockdown increases BTB permeability by disrupting endothelial cell tight junctions.
• The Src-Erk1/2-MMP-9 signaling cascade is involved in Robo4-mediated BTB regulation.
• Robo4 represents a potential therapeutic target for increasing BTB permeability and improving chemotherapy delivery.