FancD2 plays a central role in the human Fanconi anemia DNA damage response (DDR) pathway. Fancd2–/– mice exhibit many features of human Fanconi anemia including cellular DNA repair defects. Whether the DNA repair defect in Fancd2–/– mice results in radiologic changes in all cell lineages is unknown. We measured stress of hematopoiesis in long-term marrow cultures and radiosensitivity in clonogenic survival curves, as well as comet tail intensity, total antioxidant stores and radiation-induced gene expression in hematopoietic progenitor compared to bone marrow stromal cell lines. We further evaluated radioprotection by a mitochondrial-targeted antioxidant GS-nitroxide, JP4-039. Hematopoiesis longevity in Fancd2–/– mouse long-term marrow cultures was diminished and bone marrow stromal cell lines were radiosensitive compared to Fancd2 / stromal cells (Fancd2–/– D0 = 1.4 ± 0.1 Gy, ñ = 5.0 ± 0.6 vs. Fancd2 / D0 = 1.6 ± 0.1 Gy, ñ = 6.7 ± 1.6), P = 0.0124 for D0 and P = 0.0023 for ñ, respectively). In contrast, Fancd2–/– IL-3-dependent hematopoietic progenitor cells were radioresistant (D0 = 1.71 ± 0.04 Gy and ñ = 5.07 ± 0.52) compared to Fancd2 / (D0 = 1.39 ± 0.09 Gy and ñ = 2.31 ± 0.85, P = 0.001 for D0). CFU-GM from freshly explanted Fancd2–/– marrow was also radioresistant. Consistent with radiosensitivity, irradiated Fancd2–/– stromal cells had higher DNA damage by comet tail intensity assay compared to Fancd2 / cells (P < 0.0001), slower DNA damage recovery, lower baseline total antioxidant capacity, enhanced radiation-induced depletion of antioxidants, and increased CDKN1A-p21 gene transcripts and protein. Consistent with radioresistance, Fancd2–/– IL-3-dependent hematopoietic cells had higher baseline and post irradiation total antioxidant capacity. While, there was no detectable alteration of radiation-induced cell cycle arrest with Fancd2–/– stromal cells, hematopoietic progenitor cells showed reduced G2/M cell cycle arrest. The absence of the mouse Fancd2 gene product confers radiosensitivity to bone marrow stromal but not hematopoietic progenitor cells.
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Vol. 181 • No. 1