Genistein induces radioprotection by hematopoietic stem cell quiescence

Purpose: In this study we addressed whether genistein-induced radioprotection in mice is associated with alterations of the cell cycle of hematopoietic stem and progenitor cells. Materials and methods: C57BL/6J female mice received a single subcutaneous injection of genistein (200 mg/kg) 24 h prior to a lethal dose (7.75 Gy, 60Co) of total body irradiation. Proliferation-associated Ki-67 protein/7-aminoactinomycin-D (Ki67/7AAD) cell cycle staining was used to differentiate between G0, G1, and S/G2/M in bone marrow cell populations negative for expression of mature hematopoietic lineage marker cells but positive for expression of stem cell antigen-1 and tyrosine kinase receptor for stem cell factor (Lin-Sca-1+cKit+, LSK+). Quantitative real-time polymerase chain reaction (qRT-PCR) microarrays were utilized to examine cell cycle specific genes. Results: At 24 h following radiation exposure, a greater percentage of LSK+ in genistein-treated mice accumulated in the G0 phase of the cell cycle, whereas a large percentage of LSK+ bone marrow cells from untreated and vehicle (PEG-400)-treated mice progressed into the G1 and S/G2/M phases. Moreover, the absolute number of marrow total LSK+, long-term LSK+, and short-term LSK+ increased 2.8, 12.1, and 4.2-fold, respectively, at 7 days post-irradiation in genistein-treated vs. untreated irradiated mice. Lin- cells from genistein-treated mice expressed fewer DNA damage responsive and cell cycle checkpoint genes than LSK+ from untreated or vehicle-treated mice. Conclusion: Pretreatment with genistein provides in vivo protection from acute myelotoxicity through extended quiescence followed by reduced senescence of marrow repopulating LSK+.