BRCA1 protects cardiac microvascular endothelial cells against irradiation by regulating p21-mediated cell cycle arrest

Microvascular endothelial cell dysfunction is a leading cause of radiation-induced heart disease (RIHD). BRCA1 plays an important role in DNA damage repair. The study aims to explore the effect of BRCA1 in endothelial cells involved in RIHD. BRCA1 and p21 expression were detected in human umbilical vein endothelial cells (HUVECs) and in mouse heart tissue after irradiation exposure. The effects of BRCA1 on cell proliferation, cell cycle and radiosensitivity were determined in HUVECs with overexpression and knockdown of BRCA1. A mouse model of RIHD was established. Heart damage was detected in C57BL/6J mice and endothelial cell specific knockout BRCA1 mice (EC-BRCA1−/−). BRCA1 and p21 expression was significantly increased both in vitro and vivo response to irradiation. BRCA1 overexpression in endothelial cells enhanced cell growth and G1/S phase arrest, and the opposite results were observed in BRCA1 knockdown endothelial cells. BRCA1 downregulated endothelial cell cycle-related genes cyclin A, cyclin D1, cyclin E and p-Rb through increasing p21 expression, and HUVECs with BRCA1 gene knockdown were more sensitive to radiation. In vivo, a decrease in cardiac microvascular density, as well as cardiomyocyte hypoxia and apoptosis were observed in a time-dependent manner. EC-BRCA1−/− mice were more prone to severe RIHD than EC-BRCA1+/− mice after 16Gy radiation exposure due to endothelial dysfunction caused by loss of BRCA1, and p21 was declined in EC-BRCA1−/− mice heart. These findings indicate that BRCA1 plays a protective role in RIHD by regulating endothelial cell cycle arrest mediated by p21 signal.