Dual Deficiency of mDia1 and Mir-146a in an Age-Related Inflammatory Bone Marrow Microenvironment Induces Ineffective Erythropoiesis in Del(5q) MDS

Myelodysplastic syndromes (MDS) are a group of age-related clonal hematologic diseases characterized by anemia, neutropenia, and thromobocytopenia. The mechanisms of anemia in MDS are unclear, which is partially due to the heterogeneity of MDS involving many cytogenetic and molecular abnormalities. Using a mouse genetic approach, here we show that dual deficiency of mDia1 and miR-146a, two genes located at chromosome 5q that is commonly deleted in MDS, causes an aged-related anemia and ineffective erythropoiesis that closely mimics human MDS. Bone marrow erythropoiesis at various stages was dramatically affected in mDia1/miR-146a double knockout mice, which induced a massive splenomegaly with potent extramedullary erythropoiesis. Old (> 1 year of age), but not young (2-4 months of age), wild type recipient mice that were transplanted with bone marrow cells from mDia1/miR-146a double knockout mice, exhibited severe anemia and rapid lethality, which indicates that the aged microenvironment is important for the development of ineffective erythropoiesis. Consistent with the roles of mDia1 and miR-146a in the innate immune response, the serum levels of TNFα and IL-6 were significantly elevated in mDia1/miR-146a double knockout mice. Pathogen-associated molecular pattern proteins (PAMPs), or damage-associated molecular pattern proteins (DAMPs), whose levels increase in aged microenvironment, both induced TNFα and IL-6 upregulation in mDia1/miR-146a double knockout granulocytes and T cells. Mechanistically, we demonstrated that the anemia and ineffective erythropoiesis was independent of hepcidin expression in mDia1/miR-146a double knockout mice. Instead, pathologic levels of TNFα and IL-6 inhibit erythroid colony formation and differentially affect terminal erythropoiesis through reactive oxygen species-induced caspase-3 activation and cell apoptosis. Our study highlights the dual roles of age-related microenvironment and cytogenetic abnormalities in the pathogenesis of ineffective erythropoiesis in MDS.