Effect of ionizing radiation exposure on proliferation and cell cycle distribution in cells derived from shwachman-diamond syndrome affected patients

Background: Shwachman-Diamond syndrome (SDS) is an autosomic recessive disorder characterized by pancreas insufficiency, skeletal abnormalities, neutropenia and predisposition to leukaemia [1]. SBDS protein is involved in many cellular functions, like stress response, ribosomal biogenesis and DNA metabolism. Due to the high number of radiological investigations necessary for SDS patients, and to the probability they have to go through bone marrow transplantation, a deeper knowledge about mechanisms involved in their response to ionizing radiation (IR) is mandatory. Purpose: Evaluation of the radiosensitivity of SDS lymphoblastoid cell lines, i.e. evaluation of proliferation and cell cycle distribution in cell lines from patients, patients' parents and control. Experimental Setup and Methods: After isolation and immortalization of lymphocytes, lymphoblastoid cells were irradiated with different doses (2÷5Gy) of 6MV X-rays from a medical linear accelerator. Both proliferation, assessed with MTT assay, and temporal dynamic study on DNA content analysis was performed collecting cells over 48 hours after irradiation, to assess SDS cells radiosensitivity. Results: Our data indicate that proliferation changes over a wide spectrum in SDS cells. Two patients are similar to the control, while the third patient shows a strongly reduced proliferation rate. DNA content analysis shows an increase in the G2/M population, which is recovered in 48 hours. After 5Gy, patients' cells show a huge increase in the G2/M fraction, which is recovered only in one patient. Conclusion: In patients, IR exposure affects cell proliferation in different ways. Cell cycle distributions are compatible with an increased activation of cell cycle checkpoints in SDS cells, which are less capable to recover after IR compared to control. These data suggest a role of SBDS in pathways involved in the response to IR-induced damage; affected cells are more radiosensitive than control ones, and this might give new guidelines for patients management.