Aberrant Overexpression Of CD14 In Granulocytes Sensitizes Innate Immune Response In mDia1 Heterozygous Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) are a group of pre-leukemic diseases characterized by increased risk of acute myeloid leukemia (AML). Heterozygous loss of chromosome 5q (5q-) is the most common cytogenetic abnormality in MDS. DIAPH1 is localized to 5q31 and encodes one of the formin family proteins, mDia1, involved in the regulation of linear actin polymerization. Mice with mDia1 deficiency develop hematologic features mimicking human myeloproliferative neoplasm, but its role in the pathogenesis of MDS is unclear. Here we report that mDia1 is largely dispensable for normal hematopoiesis. However, the committed or mature granulocytes in mDia1 heterozygous and knockout mice were activated and showed increased actin polarization. Strikingly, CD14 was aberrantly overexpressed in the bone marrow and peripheral granulocytes of mDia1 heterozygous and knockout mice in a cell-autonomous manner, leading to a hypersensitivity of the innate immune response to lipopolysaccharide (LPS) stimuli through CD14-Toll like receptor 4 (TLR4) signaling. Chronic stimulation with LPS accelerated the occurrence of MDS in mDia1 heterozygous and knockout mice. Similar findings of CD14 overexpression were observed in the bone marrow granulocytes of 5q- MDS patients, but not normal patients or MDS patients without 5q deletion. These patients exhibited relatively frequent infections with long duration of disease. Mechanistically, mDia1 was required for the endocytosis of CD14 upon LPS stimulation. Heterozygosity and loss of mDia1 led to diminished interferon expression that is dependent on CD14 endocytosis. Thus, our study revealed an essential role of the innate immune signaling in the pathogenesis of 5q- MDS. Specifically, heterozygosity or loss of mDia1 leads to a cell autonomous hypersensitivity of innate immune system in the granulocytes that causes myeloid dysplasia. Together with previous reported evidence of dyserythropoiesis due to loss of RPS14, and dysmegakaryopoiesis due to loss of mir-145/146a, these data fully recapitulate the pathogenesis of tri-lineage dysplasia in 5q- MDS. In addition, our study highlighted the significance of the activated CD14/TLR signaling pathway in the pathogenesis of MDS, which could serve as a novel target for therapeutic management.