Shear stress regulates occludin content and phosphorylation.

Area of Science:

• Endothelial cell biology
• Mechanotransduction
• Vascular physiology

Background:

• Previous studies show shear stress increases endothelial hydraulic conductivity (L(P)).
• The underlying molecular mechanisms remain unclear.
• Tight junction proteins regulate endothelial barrier function.

Purpose of the Study:

• To investigate if shear stress alters occludin expression and phosphorylation.
• To determine the role of occludin in shear-induced changes in L(P).
• To test the hypothesis that shear stress regulates paracellular transport via occludin.

Main Methods:

• Bovine aortic endothelial cell (BAEC) monolayers were exposed to shear stress (10-20 dyn/cm²).
• Occludin expression and phosphorylation were analyzed using Western blot.
• Hydraulic conductivity (L(P)) was measured.
• Tyrosine kinase activity was inhibited with erbstatin A.
• Effects of dibutyryl (DB) cAMP on shear-induced changes were assessed.

Main Results:

• Shear stress significantly decreased occludin content in a time-dependent manner.
• High shear stress (20 dyn/cm²) increased L(P) by 4.7-fold.
• Tyrosine kinase inhibition attenuated shear-induced decreases in occludin and increases in L(P).
• Shear stress rapidly increased occludin phosphorylation within 5 minutes.
• DB-cAMP reduced shear-induced occludin phosphorylation.

Conclusions:

• Shear stress increases occludin phosphorylation rapidly (< or = 5 min).
• Shear stress significantly decreases occludin expression over 1-4 hours.
• Altered occludin phosphorylation and expression are key mechanisms for shear-induced increases in L(P).