[Bone Marrow Osteoblasts Promotes the Proliferation Leukemia Stem Cell by Up-regulating Interleukin-1].

Objective: To explore the extrinsic regulation mechanism of bone marrow microenvironment in leukemia cells, and investigate the promoting effect of osteoblast niche on the proliferation and self-renewal of leukemia stem cell by up-regulating the expression of interleukin-1 (IL-1) in leukemia cell.

Methods: The gene expression profiles on leukemia cells derived from AE9a mouse bone marrow endosteum and central bone marrow were determined by RNA sequencing and gene set enrichment analysis (GSEA). Quantitative real-time PCR (qRT-PCR) was used to detect the expression of IL-1 in AE9a mouse leukemia cells co-cultured with or without osteoblasts in vitro. In addition, qRT-PCR was also used to determine the expression of IL-1 in bone marrow mononuclear cell (BMMNC) from 43 patients with acute myeloid leukemia (AML). For leukemia cells co-cultured with osteoblasts or treated with IL-1β, colony forming ability of AE9a leukemia cells was determined by colony formation assay.

Results: In AE9a leukemia mouse, RNA-seq data and GSEA showed that the enrichment of the upregulated genes in leukemia cells located in endosteum fell into inflammatory response gene set, among them, IL-1α and IL-1β were significantly higher expressed in AE9a leukemia cells that located osteoblast niche (IL-1α: P<0.001, IL-1β:P<0.001). After AE9a leukemia cells were co-cultured with osteoblasts in vitro, the expression of IL-1α and IL-1β in leukemia cells were increased by 2.5 and 3.5 times respectively. In colony formation assay, the number of colonies was increased significantly after leukemia cells were co-cultured with osteoblasts (P<0.001). In addition, when AE9a leukemia cells were treated with IL-1β, the number of colonies was also increased significantly (P<0.01). In AML patients, BMMNC with high percentage of CD34 positive cells exhibited higher level of IL-1 expression.

Conclusion: Osteoblast niche can promote leukemia cell proliferation and self-renewal through up-regulating the expression of IL-1 in leukemia cells. In AML patients, the expression level of IL-1 was correlated to the percentage of CD34 positive cells in BMMNC.