Conditional Plasminogen Activator Inhibitor Type 1 Deletion in the Endothelial Compartment Has No Beneficial Effect on Radiation-Induced Whole-Lung Damage in Mice.

Purpose: To investigate whether the endothelial pool of plasminogen activator inhibitor type 1 (PAI-1) plays a role in the development of radiation-induced lung damage, as previously demonstrated in the intestine.

Methods And Materials: Human lung microvascular endothelial cells were exposed to 10 Gy irradiation so as to study their ability to acquire an "activated" phenotype. Mice in which the Cre-Lox strategy was used to produce PAI-1 deletion specifically in the endothelial compartment were exposed to 17 Gy whole-thorax irradiation and followed up for 2, 13, and 23 weeks after irradiation.

Results: Human lung microvascular endothelial cells had an activated phenotype after radiation exposure, overexpressed PAI-1, and underwent endothelial-to-mesenchymal transition. In mice, knockout of PAI-1 in the endothelium had no beneficial effect on radiation-induced lung damage and showed a tendency to worsen acute lesions.

Conclusions: As opposed to the intestine, the endothelial pool of PAI-1 does not play a determinant role in the development of radiation-induced lung damage. The therapeutic value of PAI-1 inhibition in lung radiation injury may be associated with other types of cells.