Use of Matrix Metalloproteinase (MMP)‐9 Knockout Mice Demonstrates that MMP‐9 Activity Is not Absolutely Required for G‐CSF or Flt‐3 Ligand‐Induced Hematopoietic Progenitor Cell Mobilization or Engraftment

Abstract

Recombinant growth factors (GFs) are used to mobilize hematopoietic stem cells (HSCs) for autologous and allogeneic transplantation; however, little is known about the mechanism(s) critical to this process. Increased levels of serum matrix metalloproteinase (MMP)-9 are detected during mobilization by G-CSF in humans or interleukin (IL)-8 in primates and mice, suggesting a role for this molecule in mobilization. Further, antibodies to MMP-9 block IL-8-induced mobilization. To investigate the role of MMP-9, we compared G-CSF and Flt-3 ligand (Flt-3L)-induced mobilization in wildtype (WT) and MMP-9 knockout (KO) mice. The absence of MMP-9 in the KO mice was confirmed by zymography, which also revealed that serum MMP-9 levels were elevated in WT mice following G-CSF administration. We report that MMP-9 KO mice did not have impaired G-CSF-or Flt-3L-induced hematopoietic progenitor mobilization, suggesting that MMP-9 is not an absolute requirement for this process. In addition, MMPs produced by HSCs have been demonstrated to be important for their transmigration; however, we demonstrate that the engraftment of MMP-9-deficient bone marrow HSCs was not impaired in sublethally irradiated WT recipients. We conclude that while MMP-9 may play an important role in GF-induced hematopoietic progenitor mobilization and engraftment in WT animals, compensatory upregulation of enzymes with a similar activity profile to MMP-9 may obscure the impact of MMP-9 deficiency in the KO model. Stem

Mechanisms of G-CSF-mediated hematopoietic stem and progenitor mobilization

“…25,26 In addition, mice deficient in the protease matrix metalloproteinase 9 (MMP-9), which is thought to mediate kitL cleavage, mobilize normally in most strains of mice. [27][28][29][30] VCAM-1/VLA-4 axis Together with its major ligand very late antigen 4 (VLA-4, also known as a4b1 integrin), vascular cell adhesion molecule 1 (VCAM-1) has a major role in anchoring HSPCs to bone marrow stromal cells 31 and regulating HSPC trafficking between the marrow and peripheral sites. 32 VLA-4 on HSPCs tethers them to VCAM-1-expressing cells, such as sinusoid endothelium and stromal reticular cells 33 and also fibronectin 34 in the extracellular matrix.…”

“…12,59 However, the role that proteases have in mobilization was thrown into question when it was shown that MMP-9-deficient mice mobilize normally in response to IL-8, 27 and other groups were unable to reproduce the mobilization defect previously seen in these mice using G-CSF. [27][28][29][30] Moreover, mice lacking combinations of neutrophil elastase, cathepsin G, or MMP-9 mobilize normally even in the presence of a broad-spectrum metalloproteinase inhibitor. 27 Collectively, these data suggest that while not absolutely required, neutrophil proteases may augment G-CSF-induced HSPC mobilization in the appropriate genetic background.…”

Mobilizing Endothelial Progenitor Cells

“…44,46,47 This controversy might be explained by the fact that MMP-9 plays a pivotal role in growth factor-induced hematopoietic progenitor mobilization in wild-type animals, whereas compensatory upregulation of enzymes with a similar activity profile to MMP-9 might mask the impact of MMP-9 deficiency in the knockout model.…”

The Collagen Binding Domain of Gelatinase A Modulates Degradation of Collagen IV by Gelatinase B

“…[7][8][9][10] Gene knockout studies have suggested that the gelatinases may cooperate in vivo. [11][12][13] In this respect, an example may be represented by the process of inflammation, wherein the degranulation of extravasated neutrophils allows MMP2 and MMP9 to share the same extracellular space, thus enhancing the probability to interact with the same substrates. 14 Neutrophil degranulation is associated with the ability of neutrophils to cross basement membranes, composed mainly of a type IV collagen network; 15,16 therefore, the enzymatic activities of MMP2 and MMP9 on type IV collagen are likely relevant for this process.…”