Abstract
ObjectivesVasculature damage is an important contributor to the side-effects of radiotherapy. The aim of this study is to provide insights into the radiobiology of the autophagic response of endothelial cells.Methods and MaterialsHuman umbilical vascular endothelial cells (HUVEC) were exposed to 2 Gy of ionizing radiation (IR) and studied using confocal microscopy and western blot analysis, at 4 and 8 days post-irradiation. The role of autophagy flux in HUVEC radio-sensitivity was also examined.ResultsIR-induced accumulation of LC3A+, LC3B+ and p62 cytoplasmic vacuoles, while in double immunostaining with lysosomal markers (LAMP2a and CathepsinD) repression of the autophagolysosomal flux was evident. Autophagy-related proteins (ATF4, HIF1α., HIF2α, Beclin1) were, however, induced excluding an eventual repressive effect of radiation on autophagy initiating protein expression. Exposure of HUVEC to SMER28, an mTOR-independent inducer of autophagy, enhanced proLC3 and LC3A, B-I protein expression and accelerated the autophagic flux. Pre-treatment of HUVEC with SMER28 protected against the blockage of autophagic flux induced by IR and conferred radio-resistance. Suppression of LC3A/LC3B proteins with siRNAs resulted in radio-sensitization.ConclusionsThe current data provide a rationale for the development of novel radioprotection policies targeting the autophagic pathway.
Highlights
Endothelial cell damage is a major effect of radiotherapy
ionizing radiation (IR)-induced accumulation of LC3A+, LC3B+ and p62 cytoplasmic vacuoles, while in double immunostaining with lysosomal markers (LAMP2a and CathepsinD) repression of the autophagolysosomal flux was evident
Pre-treatment of Human umbilical vascular endothelial cells (HUVEC) with SMER28 protected against the blockage of autophagic flux induced by IR and conferred radio-resistance
Summary
Endothelial cell damage is a major effect of radiotherapy. Increased permeability leads to oedema and inflammation of organs which contributes to acute side effects. Vascular and lymphatic damage is a main component of the unpredictable and sometimes life-threatening late side effects, appearing even years after radiotherapy [1,2,3]. Cytoprotection policies alleviating the radiation-induced vascular damage may improve the therapeutic index of radiotherapy [4]. Macro-autophagy (autophagy), is an important biological process responsible for the turnover and recycling of long-lived proteins and dysfunctional organelles. This could have an important role in the elimination of damage by intracellular structures exposed to radiation [5,6]. Abnormal function of autophagy may interfere with the protein and organelle quality control in irradiated cells, which may lead to cell death or degeneration followed by cellular and tissue dysfunction [7]
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