Identification of a subpopulation of highly adherent endothelial cells for seeding synthetic vascular grafts.

Objective: There is an unmet clinical need for alternatives to autologous vessel grafts. Small-diameter (<6 mm) synthetic vascular grafts are not suitable because of unacceptable patency rates. This mainly occurs due to the lack of an endothelial cell (EC) monolayer to prevent platelet activation, thrombosis, and intimal hyperplasia. There are no reliable methods to endothelialize small-diameter grafts because most seeded ECs are lost due to exposure to fluid shear stress after implantation. The goal of this work is to determine if EC loss is a random process or if it is possible to predict which cells are more likely to remain adherent.

Methods: In initial studies, we sorted ECs using fluid shear stress and identified a subpopulation of ECs that are more likely to resist detachment. We use RNA sequencing to examine gene expression of adherent ECs compared with the whole population. Using fluorescence activated cell sorting, we sorted ECs based on the expression level of a candidate marker and studied their retention in small-diameter vascular grafts in vitro.

Results: Transcriptomic analysis revealed that fibronectin leucine rich transmembrane protein 2 (FLRT2), encoding protein FLRT2, is downregulated in the ECs that are more likely to resist detachment. When seeded onto vascular grafts and exposed to shear stress, ECs expressing low levels of FLRT2 exhibit 59.2% ± 7.4% retention compared with 24.5% ± 6.1% retention for the remainder of the EC population.

Conclusions: For the first time, we show EC detachment is not an entirely random process. This provides validation for the concept that we can seed small-diameter vascular grafts only with highly adherent ECs to maintain a stable endothelium and improve graft patency rates.