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Introduction
The bone marrow microenvironment consists of a specialized population of cells that play essential roles in regulation, self-renewal and differentiation of adult stem cells (1–4). The microenvironment supports maturation of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) and their release into the vascular system (5–7). Human bone marrow-derived stromal cell lines HS5 and HS27A, co-cultured with myeloid cells, are frequently used in studies of crosstalk between cells in the bone marrow microenvironment and hematopoietic cells (8–13). For example, HS5 and HS27A have been used to establish a xenotransplantation murine model of myelodysplastic syndromes (MDS), a group of clonal hematopoietic disorders characterized by dysregulation of programmed cell death (apoptosis) and ineffective hematopoiesis in both normal and clonal (transformed) hematopoietic cells (12,14). Kerbauy et al (14) observed engraftment of distinct clonal MDS-derived hematopoietic precursors when stromal cells (HS5 and HS27A combined) were co-injected via an intramedullary route. Our previous study found that intravenous co-administration of HS27A cells (but not HS5 cells) with HPCs from MDS patients facilitated engraftment of clonal CD34+ cells of any karyotype (12), indicating that HS27A cells were more effective than HS5 in supporting primitive clonal MDS precursors (12).
Glycans, a major category of biomolecules, are commonly attached to proteins and lipids to form glycoproteins, glycolipids, glycosaminoglycans and other types of glycoconjugates (15–17). Glycans play key roles in a variety of biological processes, including cell adhesion, molecular trafficking, receptor activation and signal transduction (17,18). They are also involved in malignant hematopoiesis. CoCl2 (hypoxia mimic) induced expression of cell surface glycans recognized by both β-galactoside- and GlcNAc-binding lectins in HL-60 cells (19). Galectin-3 is developmentally expressed in human myeloid cells, and is strongly upregulated on the surface of late mature myeloid cells (20). Conversely, it also promotes proliferation and angiogenesis of endothelial cells differentiated from bone marrow mesenchymal stem cells (21). An important characteristic of the HSC microenvironment is that low oxygen (O2) tension and hypoxia (defined as O2 tension <2%) is essential for HSC function (22–25). In vitro BM cells are always cultured under hypoxic conditions in order to maintain their primitive phenotype and self-renewal ability (26). In addition, the key regulator of cellular adaptation to hypoxic stress, hypoxia-inducible factor 1 α (HIF-1α) can be...