Cellular Adaptive Response and Regulation of HIF after Low Dose Gamma-radiation Exposure

PurposeCellular damage due to low dose of {gamma}-radiation ([≤]0.1 Gy) is generally extrapolated from observing the effects at higher doses. These estimations are not accurate. This has led to uncertainties while assessing the radiation risk factors at low doses. Although there are reports on the radiation induced adaptive response, the mechanism of action is not fully elucidated, leading to the uncertainties. One of the outcomes of low dose radiation exposure is believed to be adaptive response. The mechanism of adaptive response is not fully understood. Therefore, the study was undertaken to understand the role of hypoxia inducible factor (HIF) on radiation induced adaptive response.\n\nMaterials and methodsMCF-7 cells pre-exposed to low dose {gamma}-radiation (0.1 Gy; Priming dose) were exposed to 2 Gy (challenging dose) 8 hrs after the priming dose and studied for the adaptive response. Cell death was measured by MTT assay, and apoptosis was measured by FACS analysis. DNA damage was measures by alkaline comet assay. HIF transcription activity was assayed using transiently transfected plasmid having HIF consensus sequence and luciferase as the reporter gene.\n\nResultsCells when exposed to 0.1 Gy priming dose 8 hrs prior to the higher dose (2 Gy; Challenging dose) results in lower amount of radiation induced damages compared to the cells exposed to 2 Gy alone. Cobalt chloride treatment in place of priming dose also results in the protection to cells when exposed to challenging dose. There was up-regulation of HIF activity when cells were exposed to priming dose, indicating the role of HIF in radiation induced response.\n\nConclusionResults indicate the {gamma}-radiation induced adaptive response. One of the mechanism proposed is up-regulation of HIF after low dose exposure, which protects the cells from damages when they are exposed to challenging dose of 2 Gy radiation dose.