Pre-Leukemic Transformation of the Bone Marrow Microenvironment Induced By AML1-ETO Fusion Protein

Objective: The bone marrow (BM) microenvironment, especially stromal cells (SCs) and cytokines, plays a critical role in supporting normal hematopoiesis. However, in cases of hematological malignancies such as acute myeloid leukemia (AML), leukemia cells can reshape the BM microenvironment to promote their survival. Despite this, there is still limited understanding of the changes in AML1-ETO fusion protein induced pre-leukemia microenvironment niche. In this study, the alterations of the BM microenvironment in the Aml1 Eto/+; Mx1-Cre (AE KI) mouse model are thoroughly explored and analyzed. This investigation will encompass the study of SCs, cytokines, their sources, and their potential impacts on the occurrence and progression of AML induced by AML1-ETO. Methods: After 4 weeks of PIPC induction, proportion changes of endothelial cells (ECs), osteoblasts, mesenchymal stem cells (MSCs) in the BM of Aml1 Eto/+; Mx1-Cre mice (experimental group) and Aml1 Eto/+; w/o Mx1-Cre mice (control group) were analyzed by flow cytometry. Bulk RNA sequencing (RNAseq) and single cell RNA sequencing (scRNAseq) techniques were applied for analysis of abnormal hematopoietic Lin -Sca-1 +c-Kit + (LSK) stem cells. Cytokine levels were detected using ELISA and Luminex bead assay. Additionally, CRISPR-Cas9 technology was used to knock out the target genes and their functions were validated. Results: Following 4 weeks of PIPC induction, the experimental group exhibited a considerable reduction in the proportion and absolute number of ECs, osteoblasts and MSCs, with ECs being the most significantly reduced. The Luminex assay revealed a substantial increase in cytokine release in the BM of the experimental group, including IL4, IL10, TNFa, Cxcl10, Cxcl11, Ccl1, Ccl2, Ccl4, Ccl7, etc. Bulk RNAseq studies of LSK cells showed that the inflammatory pathway in the experimental group was significantly upregulated. To further explore the release sources of cytokines in the BM and heterogeneity in LSK cell cytokine secretion, scRNAseq analysis of LSK cells was conducted in the AE KI group, which were classified into 9 subgroups. Subgroups 1 and 5 exhibited a significant upregulation of Ccl2, Ccl4, Cxcl2, and IL15. Subgroups 4 and 8 showed upregulation of Ccl2 and IL4. Subgroups 0 and 2 exhibited upregulation of Ccl4, while subgroups 6, 7, and 9 showed upregulation of Cxcl2. Notably, subgroups 1 and 5 also displayed increased expression of Ccr5, which is the receptor for Ccl2. To further val