Effects of Macrophage Colony-Stimulating Factor Isoforms on Leukemia Progression in Mouse Acute Myeloid Leukemia Model

Oncogenic events occur by a variety of mechanisms, including point mutations, in-frame deletions or insertions, epigenetic modifications or even surrounding changes. As an important growth factor, M-CSF plays different roles in complicated pathological context and there are complex heterogeneities between M-CSF different splicing isoforms (sM-CSF and mM-CSF). The role of M-CSF and the difference between the two isoforms in hematological malignancies, which are significantly different from solid tumors, is poorly understood. In this study, we studied the different effects of mM-CSF and sM-CSF on both intrinsic factor-leukemia cells and surrounding linker-macrophage in acute myeloid leukemia mice model.

The high level expression of M-CSF was found in myeloid leukemia patients from bloodspot database. We established MLL-AF9 induced AML mouse model with high level expression of sM-CSF or mM-CSF. We found mM-CSF could delay the progression of leukemia. Subsequently, we investigated the effect of the two isoforms on both leukemia cells and macrophages. More proliferative cells were detected in leukemia cells with high level M-CSF isoforms. In vitro colony assay experiments showed sM-CSF could promote the self-renew of leukemia cells. Morphological and flow cytometry analysis indicated M-CSF isoforms had different potential in promoting leukemia cell differentiation. Moreover, myeloid differentiation associated transcription factor-Cebpe and Runx1 might account for differentiation promoting effect by mM-CSF. As for macrophages, M-CSF isoforms could increase monocytes and macrophages in leukemic microenvironment by both growth-promoting and recruitment effects. Additionally, mM-CSF promoted the expression of both M1 and M2-associated genes. Meanwhile mM-CSF promoted the specific phagocytosis potential of macrophages to leukemia cells. Furthermore, the gene expression profiles of LAMs (leukemia associated macrophages) revealed mM-CSF did make macrophages a special phenotype with enhanced oxidative phosphorylation, metabolism and phagocytosis pathway. Moreover, phagocytosis of LAMs educated by mM-CSF may be mediated by oxidative phosphorylation.

Our results suggested that the diverse effects of M-CSF two isoforms in leukemic microenvironment and mM-CSF delayed the leukemia course by affecting both leukemia cell differentiation and macrophage frequencies along with specific phagocytosis to leukemia cells. The work reveals that both the intrinsic and surrounding factors participate in tumor progression and the complex of carcinogenesis and the interaction between tumor cell itself and microenvironment linkers should be further studied.

This work was supported by Grants 81370634 and 81570153 from the National Natural Science Foundation of China (NSFC); program 2016-I2M-2-006 from CAMS Initiative for Innovative Medicine; grant 17JCZDJC35000 from the Tianjin Science and Technology Committee.