Ionizing Radiation Enhances Paracellular Permeability Through Alteration of Intercellular Junctions in Cultured Human Lymphatic Endothelial Cells

Background: A problematic complication after radiation therapy is lymphedema. Development of lymphedema is associated with an increase in lymphatic paracellular permeability. The current study investigated the effects of radiation on intercellular junctions and paracellular permeability in cultured human dermal lymphatic endothelial cells (HDLECs). Methods and Results: Double immunofluorescence staining with vascular endothelial (VE)-cadherin and actin immediately after X-ray irradiation (5 or 20Gy) was performed. Morphological changes induced by irradiation were assessed. Cell viability and paracellular permeability after irradiation were also evaluated. Broad junctions in which VE-cadherin was accumulated at cell-cell contacts and almost colocalized with actin were significantly decreased in a dose-dependent manner in confluent and sparse irradiated HDLECs. Irradiation shortened the width of VE-cadherin-positive areas at the cell-cell contacts. Actin filaments did not colocalize with VE-cadherin after 20Gy irradiation. Although cell viability was not affected by irradiation, paracellular permeability significantly increased in a dose-dependent manner. Conclusions: A dose of 5 or 20Gy irradiation in HDLECs does not affect cell viability, but changes VE-cadherin mediated intercellular junctions and actin structure, resulting in an increase of paracellular permeability. Further investigations on the regulatory proteins involved in radiation-induced changes, which were observed in the current study, may contribute to development of lymphedema therapy.