Over-Expression of Stromal Cell-Derived Factor-1 in Non-Specialized Endothelium Enhances the Endothelium-Supported Transmigration, Maintenance, and Proliferation of Hematopoietic Progenitor Cells.

Stromal cell-derived factor-1 (SDF-1) plays a central role in the homing of hematopoietic stem cells and progenitor cells (HPCs) to bone marrow (BM). Tissue damage, most notably ischemia, induces the recruitment of bone marrow (BM)-derived stem/progenitor cells, which can lead to tissue repair. Moreover, damaged tissues and endothelium express and produce SDF-1. However, the effects of aberrant expression and production of SDF-1 in human endothelium on the biology of BM-derived stem/progenitor cells are not fully understood. To clarify this, we over-expressed the SDF-1 gene in human umbilical vein endothelial cells using an adenoviral vector (HUVEC/AdeSDF-1) and examined the transmigration, maintenance, and proliferation of HPCs supported by the endothelium. HUVEC/AdeSDF-1 monolayers induced the migration of MO7e cells and mobilized peripheral blood (mPB) CD34⁺ cells underneath the endothelium within a few hours, while HUVEC monolayers transfected with adenoviral vectors expressing LacZ (HUVEC/AdeLacZ) did not. A transmigration assay revealed that HUVEC/AdeSDF-1 monolayers supported the spontaneous transmigration of CD34⁺ cells to a greater degree than did HUVEC/LacZ monolayers (15 ± 4% vs. 5 ± 3%) and that transmigration was blocked with pretreatment of the input cells with pertussis toxin (PTX). The co-culturing of mPB CD34⁺ cells with HUVEC/AdeSDF-1 for up to 2 weeks led to a greater expansion of CD45⁺ cells and colony-forming cells, and reduced cell apoptosis. Furthermore, the co-culturing of mPB CD34⁺ cells with HUVEC/AdeSDF-1 led to the formation of numerous cobblestone areas, while mPB CD34⁺ cells plus HUVEC/AdeLacZ supported the formation of only a few cobblestone areas (253 ± 28 vs. 10 ± 3 per 2 x 10⁴ mPB CD34⁺ cells at week-2), which were further enhanced by adding a combination of early-acting hematopoietic growth factors at low concentrations. To further elucidate whether SDF-1 is directly involved in the formation of cobblestone areas, mPB CD34+ cells were co-cultured with murine BM MS-5 stromal cells. Weekly PTX treatment, beginning 24 hours after start of co-culturing, markedly decreased the numbers of cobblestone areas by weeks 2 and 5, which indicates that SDF-1 is involved not only in the localization of primitive HPCs underneath the endothelium or BM stroma but also in the maintenance and proliferation of the cells. These results indicate that aberrant SDF-1 over-expression in any non-specialized endothelium induces BM-derived progenitor cell trafficking into extravasculr sites and promotes the maintenance and proliferation of the migrated cells.