Cadherin selectivity filter regulates endothelial sieving properties.

Area of Science:

• Vascular Biology
• Cellular Physiology
• Biophysics

Background:

• Endothelial protein sieving is a vital vascular barrier function controlling plasma protein and fluid exchange.
• The precise molecular mechanisms governing endothelial sieving at adherens junctions remain largely unknown.
• Understanding this process is crucial for regulating tissue fluid balance and preventing edema.

Purpose of the Study:

• To elucidate the molecular basis of endothelial protein sieving at adherens junctions.
• To investigate the role of cadherin interactions and actin cytoskeleton in regulating vascular permeability.
• To identify key structural components of adherens junctions that determine macromolecular transport.

Main Methods:

• Development of a novel assay to measure macromolecular penetrance at endothelial adherens junction microdomains.
• Utilized cadherin-GFP expression to visualize adherens junction density and distribution.
• Employed site-directed mutagenesis of cadherin and α-actinin-1 to probe their roles in junctional function and permeability.

Main Results:

• Adherens junctions exhibit heterogeneous density (high- and low-density segments) at the endothelial cell perimeter.
• Low-density segments, but not high-density ones, allowed passage of 70-kDa fluorescent dextran (albumin-sized molecule).
• Mutations disrupting cadherin adhesive binding or F-actin bundling increased junctional mobility and dextran penetrance at high-density segments.

Conclusions:

• Adhesive interactions within the cadherin EC1 ectodomain are critical determinants of endothelial protein sieving.
• Adherens junction structure, influenced by cadherin binding and actin cytoskeleton, directly regulates vascular permeability.
• These findings provide new insights into the molecular regulation of the endothelial barrier function.