In Fanconi anemia, impaired accumulation of bone marrow neutrophils during emergency granulopoiesis induces hematopoietic stem cell stress.

Fanconi anemia (FA) is an inherited disorder of DNA repair due to mutation in one of 20+ interrelated genes that repair intrastrand DNA crosslinks and rescue collapsed or stalled replication forks. The most common hematologic abnormality in FA is anemia, but progression to bone marrow failure (BMF), clonal hematopoiesis, or acute myeloid leukemia may also occur. In prior studies, we found that Fanconi DNA repair is required for successful emergency granulopoiesis; the process for rapid neutrophil production during the innate immune response. Specifically, Fancc mice did not develop neutrophilia in response to emergency granulopoiesis stimuli, but instead exhibited apoptosis of bone marrow hematopoietic stem cells and differentiating neutrophils. Repeated emergency granulopoiesis challenges induced BMF in most Fancc mice, with acute myeloid leukemia in survivors. In contrast, we found equivalent neutrophilia during emergency granulopoiesis in FanccTp53 mice and WT mice, without BMF. Since termination of emergency granulopoiesis is triggered by accumulation of bone marrow neutrophils, we hypothesize neutrophilia protects FanccTp53 bone marrow from the stress of a sustained inflammation that is experienced by Fancc mice. In the current work, we found that blocking neutrophil accumulation during emergency granulopoiesis led to BMF in FanccTp53 mice, consistent with this hypothesis. Blocking neutrophilia during emergency granulopoiesis in FanccTp53 mice (but not WT) impaired cell cycle checkpoint activity, also found in Fancc mice. Mechanisms for loss of cell cycle checkpoints during infectious disease challenges may define molecular markers of FA progression, or suggest therapeutic targets for bone marrow protection in this disorder.