X-irradiation induces ER stress, apoptosis, and senescence in pulmonary artery endothelial cells.
OBJECTIVE
The use of clinical radiation for cancer treatment is limited by damage to underlying normal tissue including to the vascular endothelium. We investigated the mechanisms of X-ray-induced cell damage to endothelial cells.


METHODS
We evaluated necrosis, apoptosis, cellular senescence, and the contribution of endoplasmic reticulum (ER) stress in pulmonary artery endothelial cells (PAEC) irradiated with X-rays (2-50 Gray [Gy]).


RESULTS
Clonogenic assays showed that 10 Gy induced ∼99.9% loss of cell viability. No necrosis was detected using lactate dehydrogenase assays, but a low population underwent extrinsic and intrinsic apoptosis, as indicated by the activation of caspases 3, 8, and 9 as well as by neutral comet assay. A majority of PAEC underwent accelerated senescence, as indicated by morphological changes, increased 21 kD cyclin-dependent kinase inhibitor (p21/waf1), decreased sirtuin 1 (SIRT1), and elevated senescence-associated β-galactosidase (SA-β-gal). ER stress was detected by assays for glucose-regulated protein 78 (GRP78), CCAAT/enhancer-binding protein homologous protein (CHOP), and growth arrest and DNA damage-inducible protein 34 (GADD34) mRNA, and transient phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α). The ER stress inhibitor salubrinal blocked ∼50% of apoptosis with no effect on senescence.


CONCLUSIONS
X-rays primarily induced cellular senescence with limited levels of apoptosis in endothelial cells. ER stress contributed to apoptosis but not to senescence.
Department of Pharmacology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799, USA.
Ronald Allan M
RA
Panganiban
Ognoon
O
Mungunsukh
Regina M
RM
Day
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D002417:Cattle; D002470:Cell Survival / Q000528:radiation effects; D016922:Cellular Senescence / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D059865:Endoplasmic Reticulum Stress / Q000528:radiation effects*; D042783:Endothelial Cells / Q000166:cytology* / Q000528:radiation effects*; D011651:Pulmonary Artery / Q000166:cytology*; D013997:Time Factors; D014965:X-Rays / Q000009:adverse effects