Worldwide, people are being exposed to natural and man-made sources of radiation. Epidemiological studies have shown an increased risk of vascular diseases in populations that have been exposed to ionizing radiation. Vascular endothelium is implicated as one of the targets for radiation leading to the development of cardiovascular diseases. However, the molecular mechanisms behind the development of radiation-induced cardiovascular disease in acute or chronic exposed people are not fully elucidated. The hypothesis that chronic low dose rate ionizing radiation accelerates the onset of senescence of primary human umbilical vein endothelial cells has been tested in papers I and II presented in this thesis. In vitro studies show that, when exposed to continuous low dose rate gamma radiation these cells enter premature senescence much earlier than non-irradiated control cells. Quantitative proteomic analysis using isotope coded protein labeling coupled to LC-ESI-mass spectrometry and followed by protein network analysis identified changes in senescence-related biological pathways including cytoskeletal organisation, cell-cell communication and adhesion, and inflammation influenced by radiation. Moreover, the role of PI3K/Akt/mTOR pathway was implicated during the senescence process. Thus, chronic low dose rated endothelial senescence may contribute to increased risk of radiation-induced cardiovascular disease.

Paper III analyse the long-term effects of local high doses of radiation to the heart using a mouse model. The results from proteomic and bioinformatics analysis indicated that an impaired activity of the peroxisome proliferator-activated receptor-alpha (PPARA) is involved in mediating the radiation response. Ionizing radiation markedly changed the phosphorylation and ubiquitination status of PPARA. This was reflected by the decreased expression of PPARA target genes involved in energy metabolism and mitochondrial respiratory chain. This in vivo study suggests that alteration of cardiac metabolism contributes to the impairment of heart structure and function after radiation.

Taken together, these in vitro and in vivo studies provide novel information on the pathways in heart and endothelial cells that are affected over longer periods of time by ionizing radiation.