Dose response and adaptive response of Non-Homologous End Joining (NHEJ) repair genes and proteins in resting human peripheral blood mononuclear cells exposed to gamma radiation

Ionizing radiation (IR) induces single strand breaks, double strand breaks (DSB), base damages in human cell. Double strand breaks are the most deleterious and if not repaired may lead to genomic instability and cell death. DSB can be repaired through Non-Homologous End Joining (NHEJ) pathway in resting lymphocytes. In the present study, radiation induced NHEJ genes and proteins were studied in resting Peripheral Blood Mononuclear Cells (PBMC) exposed to various doses of gamma radiation. Dose response, time point kinetics and adaptive response studies were conducted in irradiated PBMC and various end points such as DNA damage quantitation, transcription and protein expression profile were studied. Venous blood samples were collected from 20 random, normal, and healthy donors with written informed consent. PBMC was separated and irradiated with various doses between 0.1 Gy to 2.0 Gy (⁶⁰Co-γ source) for dose response study. Repair kinetics of DNA damage and time point changes in expression of genes and proteins were studied in post-irradiated PBMC at 2.0 Gy at various time points up to 240 min. Adaptive response study was conducted with a priming dose of 0.1 Gy followed by a challenging dose of 2.0 Gy after 4 h incubation. Our results revealed that significant increase in DNA double strand breaks at higher doses. Both slow and fast repair kinetics were observed among the donors. DNA double strand break recognizing Ku proteins (Ku70 and Ku80), XLF and Ligase IV were significantly up regulated at transcript as well as protein expression level, indicating the active role of NHEJ pathway in repairing and rejoining DNA DSBs. Radio-adaptive study also showed significant up regulation of Ku70, Ku80, DNA-PKcs, XRCC4 and Ligase IV suggesting the involvement of NHEJ proteins in radio-adaptive response in human PBMC at G₀/G₁, which has important implications to human health. (author)