Abstract: OBJECTIVE： To investigate whether premature aging occurs after irradiation of human microvascular endothelial cells (HMEC-1) with ionizing radiation and the mechanism of its generation. METHODS： HMEC-1 cells were irradiated with X-rays at a dose rate of 11.79 mGy/s for 0，2 and 4 Gy，for 0，2.83 and 5.65 min，respectively，and cultured for 24，48 and 72 h after irradiation. The CCK-8 kit was used to detect the changes in cell viability after exposure to ionizing radiation；the β-galactosidase staining kit was used to detect the onset of cellular senescence after irradiation；Giemsa staining was used to observe the changes in the morphology of irradiated cells；and the expression levels of the senescence marker proteins，P53 and P21，were detected using the Western blot method. RESULTS： Compared with the unirradiated group，cell viability decreased significantly at 0 h after irradiation in the 4 Gy dose group (P<0.05)；cell viability decreased significantly at 24，48 and 72 h after irradiation in the 2 and 4 Gy X-ray irradiation groups (P<0.01)；and β-galactosidase staining of the cells at 72 h after irradiation in the 2 and 4 Gy X-rays irradiation groups increased significantly compared with the unirradiated group (P<0.05). And compared with the non-senescent cells，the morphology of the cells that underwent premature senescence became larger，and with the increase of irradiation dose，the more obvious the changes in cell morphology；compared with the non-irradiated group，the expression level of cellular senescence-related proteins P53 and P21 in the irradiated group was significantly elevated (P<0.05). CONCLUSION： Ionizing radiation can cause premature senescence of HMEC-1 cells by activating the P53-P21 pathway.

Key words: ionising radiation, X-ray, vascular endothelial cells, premature aging