Cooperating, congenital neutropenia associated Csf3r and Runx1 mutations activate pro-inflammatory signaling and inhibit myeloid differentiation of mouse HSPCs

Patients with the pre-leukemia bone marrow failure syndrome called severe congenital neutropenia (CN) have an approximately 15% risk of developing acute myeloid leukemia (AML; called here CN/AML). Most CN/AML patients co-acquireCSF3RandRUNX1mutations, which play cooperative roles in the development of AML. To establish an in vitro model of leukemogenesis, we utilized bone marrow lin(-)cells from transgenic C57BL/6-d715Csf3rmice expressing a CN patient-mimicking truncatedCSF3Rmutation. We transduced these cells with vectors encodingRUNX1wild type (WT) orRUNX1mutant proteins carrying the R139G or R174L mutations. Cells transduced with theseRUNX1mutants showed diminished in vitro myeloid differentiation and elevated replating capacity, compared with those expressing WTRUNX1. mRNA expression analysis showed that cells transduced with theRUNX1mutants exhibited hyperactivation of inflammatory signaling and innate immunity pathways, including IL-6, TLR, NF-kappaB, IFN, and TREM1 signaling. These data suggest that the expression of mutatedRUNX1in aCSF3R-mutated background may activate the pro-inflammatory cell state and inhibit myeloid differentiation.