MT1-MMP and RECK are involved in human CD34⁺ progenitor cell retention, egress, and mobilization

The mechanisms governing hematopoietic progenitor cell mobilization are not fully understood. We report higher membrane type 1-MMP (MT1-MMP) and lower expression of the MT1-MMP inhibitor, reversioninducing cysteine-rich protein with Kazal motifs (RECK), on isolated circulating human CD34⁺ progenitor cells compared with immature BM cells. The expression of MT1-MMP correlated with clinical mobilization of CD34⁺ cells in healthy donors and patients with lymphoid malignancies. Treatment with G-CSF further increased MT1-MMP and decreased RECK expression in human and murine hematopoietic cells in a PI3K/ Akt-dependent manner, resulting in elevated MT1-MMP activity. Blocking MT1-MMP function by Abs or siRNAs impaired chemotaxis and homing of G-CSF-mobilized human CD34⁺ progenitors. The mobilization of immature and maturing human progenitors in chimeric NOD/SCID mice by G-CSF was inhibited by anti-MT1-MMP treatment, while RECK neutralization promoted motility and egress of BM CD34⁺ cells. BM c-kit⁺ cells from MT1-MMP-deficient mice also exhibited inferior chemotaxis, reduced homing and engraftment capacities, and impaired G-CSF-induced mobilization in murine chimeras. Membranal CD44 cleavage by MT1-MMP was enhanced following G-CSF treatment, reducing CD34⁺ cell adhesion. Accordingly, CD44-deficient mice had a higher frequency of circulating progenitors. Our results reveal that the motility, adhesion, homing, and mobilization of human hematopoietic progenitor cells are regulated in a cell-autonomous manner by dynamic and opposite changes in MT1-MMP and RECK expression.