Inhibitor of MyoD Family A (I-mfa) regulates HSPC and myeloid differentiation

Abstract

Abstract Hematopoietic stem and progenitor cell (HSPC) populations are capable of expanding in response to immunological insult or homeostatic turnover. Regulation of the fate decision between self-renewal and differentiation allows for both maintenance of blood cell populations and sustained hematopoiesis across the entire life-span. I-mfa, a small cytosolic protein, has been shown to inhibit lineage-specific transcription factors as well as regulate β-catenin/Wnt signaling. We have previously shown that I-mfa-null mice have increased myeloid cells resulting in increased osteoclasts and hypothesized that I-mfa regulates myeloid lineage differentiation and may affect HSPC populations. In order to test this, bone marrow (BM) from I-mfa−/− mice was analyzed by flow cytometry, showing increases in both long-term and short-term hematopoietic stem cells compared to WT controls, an effect which increased with age. Additionally, both common myeloid precursors (CMP) and granulocyte-macrophage precursors (GMP) were increased in I-mfa−/− mice. Conditional knockout of I-mfa in all hematopoietic lineages using Vav1-Cre lead to similar findings, while conditional knockout in myeloid cells with LysM-Cre showed only increases in myeloid progenitors. These data indicate that I-mfa has separate roles in regulating HSPC expansion and myeloid cell differentiation. Mechanistically, M-CSF-stimulated I-mfa−/− BM had significantly increased transcription of β-catenin signaling target genes Ccnd1, Axin2, and Myc, as well as myelopoietic transcription factors Spi1, Irf8, and Klf4, compared to WT. Further studies are being conducted to determine the effect of I-mfa on quiescence, Wnt ligand sensitivity, and BM reconstitution capacity.