Microvascular permselectivity in the chick chorioallantoic membrane during endothelial cell senescence

Area of Science:

• Vascular Biology
• Developmental Biology
• Physiology

Background:

• The chick embryo chorioallantoic membrane (CAM) is a model for studying microvascular function.
• CAM endothelium undergoes distinct phases: proliferation, differentiation, and senescence.
• Senescence involves non-proliferation and aging of endothelial cells.

Purpose of the Study:

• To characterize microvascular barrier functions of the CAM endothelium during its senescent phase.
• To assess macromolecular selectivity of the aging CAM capillary endothelium.
• To correlate ultrastructural features with barrier function in senescent CAM microvasculature.

Main Methods:

• Utilized a graded series of fluorescein isothiocyanate (FITC) dextrans to probe macromolecular permeability.
• Quantified extravasation of FITC dextrans (40 and 150 kDa) and accumulation of FITC dextran (10 kDa).
• Examined endothelial vesicle densities and junctional cleft lengths and widths via electron microscopy.

Main Results:

• FITC dextran 40 and 150 showed restricted extravasation, indicating barrier integrity.
• FITC dextran 10 accumulated in the interstitium, suggesting size-selective permeability.
• Ultrastructural analysis revealed uniform junctional cleft widths (20 nm) but heterogeneous vesicle densities and cleft lengths.

Conclusions:

• The senescent CAM endothelium retains a selective barrier function.
• Uniform junctional cleft widths, not vesicle density or cleft length, likely determine permselectivity.
• This selective barrier is critical for maintaining colloid oncotic balance and supporting gas exchange in the CAM.