Nuclear Factor I-X May Regulate a Myeloid-Biased Hematopoietic Stem Cell Population during Stress Hematopoiesis

Hematopoietic stem and progenitor cells (HSPC) are routinely exploited in the clinic to treat patients with cancers or other hematologic diseases. The transcription factor nuclear factor I-X (NFIX) has a proven role regulating migration, adhesion, differentiation and quiescence in neural stem cells. Importantly, Nfix was recently shown to be upregulated in FLT3-ITD+ acute myeloid leukemia (AML) patient samples and the NFI binding motif was protected during DNase hypersensitivity screening. We recently identified Nfix as a novel regulator of HSPC repopulating potential. Using our mouse models, Nfix^flox/floxRosa26-CreER^T2 and Nfix^+/+Rosa26-CreER^T2, we induced the deletion of Nfix and performed competitive transplants; here we observe a 50% increase in chimerism 20 weeks post-transplant accompanied by a 10% increase in reconstitution of peripheral blood (PB) B cells. Primary recipient whole bone marrow (WBM) was then transplanted into secondary recipients. Beginning four weeks post-transplant, a 2.5-fold loss of PB myeloid reconstitution was observed in secondary recipients of Nfix-deficient WBM. This effect persisted beyond 20 weeks post-secondary transplant, suggesting that a self-renewing myeloid-biased HSPC is functionally perturbed by the loss of Nfix. To identify genes transcriptionally regulated by NFIX, we recently validated an anti-NFIX monoclonal antibody that is currently being used for chromatin immunoprecipitation (ChIP) followed by paired-end sequencing. Future efforts will focus on investigating Nfix-deficient myeloid-biased HSC subsets. This study will illuminate the transcriptional control of specific HSC subsets.