3043 - Elevation of IL4 Signaling Contributes to Thrombocytopenia in AML

Abstract

Thrombocytopenia is a major and fatal complication in the patients with acute leukemia. However, the mechanisms underlying defective thrombopoiesis in leukemia remains unclear. In this study, we employed the non-irradiated MLL-AF9 induced acute myeloid leukemia (AML) murine model (Cheng et al, 2015) to define how megakaryopoiesis is suppressed during AML development. We measured the frequency of hematopoietic stem and progenitor (HSPC) subsets in the residual hematopoietic cells along the path of megakaryopoiesis and found that the frequency of megakaryocytic/erythroid progenitors (preMegEs) declined dramatically (14 ± 4% of healthy state), whereas the frequency of Lin-Sca-1 + c-kit+CD150+ hematopoietic stem cells (HSCs) gradually increased (3.1 ± 0.4 folds of healthy control), suggesting a blockade of megakaryopoiesis from CD150+ HSCs. Consistently, we observed reduced megakaryocyte (MK) colony forming ability (72.3 ± 3.4 vs 89.0 ± 1.0%, p = 0.097) in vitro and defective platelet reconstitution potential after transplantation of CD150+ LKS cells (4.3 ± 0.8 vs 13.8 ± 2.3%, p = 0.002) from AML mice. To search for a novel soluble factor involved in the suppressive megakaryopoiesis, we detected elevated Interleukin 4 (IL4) protein level in bone marrow plasma and upregulated IL4 mRNA expression in bone marrow endothelial cells in AML mice. Notably, platelet counts325 ± 58 vs 991 ± 87 X1012/L, p < 0.001), the frequency of MKs0.008 ± 0.001 vs 0.02 ± 0.002%, p < 0.001and preMegEs0.089 ± 0.003 vs 0.19 ± 0.026%, p = 0.0043in the mice receiving IL4 dropped dramatically, which indicated that IL4 had negative effects on megakaryocytic differentiation of HSPCs and MK maturation, and IL4 treatment could phenocopy thrombocytopenia in AML to some extent. Moreover, administration of IL4 neutralizing antibody partially recovered the yield of MK colonies in the presence of leukemia bone marrow plasma32.5 ± 1.555 vs 46.5 ± 2.598, p = 0.0036.In summary, our current study demonstrates that defective megakaryopoiesis in AML was at least partially contributed by the suppression of HSC differentiation toward megakaryocytic lineage and also reveals a previously unrecognized link between IL4 signaling and megakaryopoiesis.