Metalloproteases: On the Watch in the Hematopoietic Niche
Authors: Sanjay Saw, Ashley Weiss, Rama Khokha, Paul D. Waterhouse
Journal: Trends in Immunology (2019)

Metalloproteases and their inhibitors can impact the bioavailability of important local signals that instruct mammalian hematopoietic stem cell (HSC) fate and function in the hematopoietic niche.The metalloprotease network regulates the biomechanical and biochemical characteristics of the niche through the processing of the extracellular matrix, integrins, growth factors, and cell surface receptors.TIMPs can exert a multilayered regulation on HSCs via both protease-dependent and protease-independent actions on stromal and other cells.Despite growing evidence, metalloprotease/tissue inhibitors of metalloproteases (TIMP) proteins are currently underappreciated as important modulators of hematopoiesis. Hematopoietic stem cells (HSCs) self-renew or differentiate into blood cell lineages following extrinsic cues propagated in specialized niches. Support cells and soluble factors in the niche respond to stress and enable progenitor activity. Metalloproteases (MMPs, ADAMs, ADAMTSs) and their inhibitors (TIMPs) control certain physical and biochemical features of the niche by altering protease-dependent bioavailability of local niche factors (e.g., CXCL12, SCF, TGFβ, VEGF), matrix turnover, and cellular interactions. With over 40 examples of diverse metalloprotease substrates known to trigger fate-changing decisions, the spatially confined activity of this multi-member protease family is ideally positioned to constitute a higher order control over hematopoiesis. Comprehension of regulated proteolysis in the bone marrow may fuel innovative strategies to harness HSC fate and function. Hematopoietic stem cells (HSCs) self-renew or differentiate into blood cell lineages following extrinsic cues propagated in specialized niches. Support cells and soluble factors in the niche respond to stress and enable progenitor activity. Metalloproteases (MMPs, ADAMs, ADAMTSs) and their inhibitors (TIMPs) control certain physical and biochemical features of the niche by altering protease-dependent bioavailability of local niche factors (e.g., CXCL12, SCF, TGFβ, VEGF), matrix turnover, and cellular interactions. With over 40 examples of diverse metalloprotease substrates known to trigger fate-changing decisions, the spatially confined activity of this multi-member protease family is ideally positioned to constitute a higher order control over hematopoiesis. Comprehension of regulated proteolysis in the bone marrow may fuel innovative strategies to harness HSC fate and function. HSCs are the only cells able to reconstitute all blood cell lineages. HSCs reside in a niche that provides instructions for self-renewal or the signals to develop into specific progenitors. The niche serves as a physical address (perivascular bone marrow for most adult HSC) and comprises various entities, including support cells (macrophages, megakaryocytes, osteoblasts, endothelial, perivascular, and specialized reticular cells), the extracellular matrix (ECM; comprising structural collagens, fibronectin, and laminin), local growth factors and cytokines, shear forces of circulation, oxygen tension, and sympathetic innervation [1Crane G.M. et al.Adult haematopoietic stem cell niches.Nat. Rev. Immunol. 2017; 17: 573-590Crossref PubMed Scopus (173) Google Scholar, 2Wei Q. Frenette P.S. Niches for hematopoietic stem cells and their progeny.Immunity. 2018; 48: 632-648Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 3Lee H.J. et al.Biomechanical force in blood development: extrinsic physical cues drive pro-hematopoietic signaling.Differentiation. 2013; 86: 92-103Crossref PubMed Scopus (19) Google Scholar]. These features create a discrete environment for the quiescence and maintenance of the HSC pool or proliferation and differentiation into progenitors, which give rise to all effector blood cells during homeostasis and following stress (e.g., pregnancy, anemia, infection, and irradiation). In both mice and humans, the initial location of hematopoietic cells is the early embryonic yolk sac and aorta–gonad–mesonephros; they subsequently reside in the embryonic liver before taking up residence in the bone marrow (BM) [4Sykes S.M. Scadden D.T. Modeling human hematopoietic stem cell biology in the mouse.Semin. Hematol. 2013; 50: 92-100Crossref PubMed Google Scholar]. The spleen and liver provide additional poststress sites of hematopoiesis for mobilized HSCs in the adult. Most HSCs are perivascular in the BM, with other cellular players providing support through cell–cell contact or delivery of soluble factors (detailed elsewhere) [1Crane G.M. et al.Adult haematopoietic stem cell niches.Nat. Rev. Immunol. 2017; 17: 573-590Crossref PubMed Scopus (173) Google Scholar, 2Wei Q. Frenette P.S. Niches for hematopoietic stem cells and their progeny.Immunity. 2018; 48: 632-648Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar]. Along with structural and physical properties of the ECM shaping the niche, the ECM is a growth factor-rich scaffold that mediates many of the extracellular interactions. Multiple aspects of the niche entities are subject to regulation by metalloproteases and their natural inhibitors. Metalloproteases are the largest of the five groups of proteases in the human genome (Box 1), where metzincins have a zinc at the active site and include enzymes such as matrix metalloproteases (MMPs), a disintegrin and metalloproteases (ADAMs), and ADAM with thrombospondin motifs (ADAMTSs); these are inhibited by tissue inhibitors of metalloproteases (TIMPs). First discovered as regulators of ECM turnover [5Jackson H.W. et al.TIMPs: versatile extracellular regulators in cancer.Nat. Rev. Cancer. 2017; 17: 38-53Crossref PubMed Scopus (115) Google Scholar], metalloprotease functions also include the processing of growth factors, cytokines, their receptors, and many cell surface molecules [6Khokha R. et al.Metalloproteinases and their natural inhibitors in inflammation and immunity.Nat. Rev. Immunol. 2013; 13: 649-665Crossref PubMed Scopus (279) Google Scholar, 7Murphy G. et al.Clipping, shedding and RIPping keep immunity on cue.Trends Immunol. 2008; 29: 75-82Abstract Full Text Full Text PDF PubMed Scopus (79) Google Scholar]. Proteolysis adds post-translational control through modulation of proteins that comprise the biophysical and biochemical nature of the stem cell niches, as modeled in Figure 1.Box 1Metalloproteases and Their Inhibitors in the BMThe human genome encodes more than 560 proteases, which are categorized into five classes based on their catalytic activity. Metalloproteases are the largest class, with five superfamilies, including the metzincins, and 27 subfamilies with a range of substrates. As the name suggests, they require a divalent metal ion for their activity. Metzincins comprise 23 matrix metalloproteases (MMPs; which can be secreted, or membrane anchored), 13 disintegrins [a disintegrin and metalloprotease (ADAMs), which are membrane anchored], and 19 ADAM with thrombospondin motifs (ADAMTSs; which are secreted) [125Lopez-Otin C. Matrisian L.M. Emerging roles of proteases in tumour suppression.Nat. Rev. Cancer. 2007; 7: 800-808Crossref PubMed Scopus (0) Google Scholar], all of which participate in a range of cellular processes and activities [5Jackson H.W. et al.TIMPs: versatile extracellular regulators in cancer.Nat. Rev. Cancer. 2017; 17: 38-53Crossref PubMed Scopus (115) Google Scholar].Metalloproteases can be secreted by several cells in BM and can affect hematopoietic processes in pathological conditions and in homeostasis. HSPCs themselves can secrete MMP 2, 9, and 14, whereas Schwann cells are reported as a source of MMP 2, 3, and 9 and ADAM10 [34Janowska-Wieczorek A. et al.Differential MMP and TIMP production by human marrow and peripheral blood CD34(+) cells in response to chemokines.Exp. Hematol. 2000; 28: 1274-1285Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar, 48Oliveira A.L. et al.Schwann cells producing matrix metalloproteinases under Mycobacterium leprae stimulation may play a role in the outcome of leprous neuropathy.J. Neuropathol. Exp. Neurol. 2010; 69: 27-39Crossref PubMed Scopus (0) Google Scholar]. Endothelial cells, macrophages, and fibroblasts produce a range of metalloproteases. Endothelial cells produce MMP1, 2, 3, 9, 13, and 14, and ADAM10, 15, and 17; macrophages secrete MMP1, 2, 7, 9, 12, and 14, and ADAM10, 15, and 17; fibroblasts can produce MMP1, 2, 3, 9, 11, 13, and 14, and ADAMTS5; osteoblasts and osteocytes express MMP2 and 9 and ADAM10; granulocyte and their precursors exhibit high expression of MMP8 and 9; and mesenchymal stem cells (MSCs) can produce MMP2, 9, and 14. Lymphocytes can produce MMP2 and 9, and ADAM17 and 28; osteoclasts can produce MMP2 and 9 [126Nyman J.S. et al.Differential effects between the loss of MMP-2 and MMP-9 on structural and tissue-level properties of bone.J. Bone. Miner. Res. 2011; 26: 1252-1260Crossref PubMed Scopus (0) Google Scholar]. MMP2 and 9 proteins were also reported in megakaryocytes and platelets depending on their preparation, as well as their developmental stage [127Mannello F. Medda V. Differential expression of MMP-2 and MMP-9 activity in megakaryocytes and platelets.Blood. 2011; 118: 6470-6471Crossref PubMed Scopus (8) Google Scholar]. BM cells express TIMPs, which regulate metalloprotease activity. TIMP1, 2, and 3 are expressed by fibroblasts, macrophages, and endothelial cells, whereas neutrophils and lymphocytes can produce TIMP1. HSPCs produce TIMP1 and 2. The human genome encodes more than 560 proteases, which are categorized into five classes based on their catalytic activity. Metalloproteases are the largest class, with five superfamilies, including the metzincins, and 27 subfamilies with a range of substrates. As the name suggests, they require a divalent metal ion for their activity. Metzincins comprise 23 matrix metalloproteases (MMPs; which can be secreted, or membrane anchored), 13 disintegrins [a disintegrin and metalloprotease (ADAMs), which are membrane anchored], and 19 ADAM with thrombospondin motifs (ADAMTSs; which are secreted) [125Lopez-Otin C. Matrisian L.M. Emerging roles of proteases in tumour suppression.Nat. Rev. Cancer. 2007; 7: 800-808Crossref PubMed Scopus (0) Google Scholar], all of which participate in a range of cellular processes and activities [5Jackson H.W. et al.TIMPs: versatile extracellular regulators in cancer.Nat. Rev. Cancer. 2017; 17: 38-53Crossref PubMed Scopus (115) Google Scholar]. Metalloproteases can be secreted by several cells in BM and can affect hematopoietic processes in pathological conditions and in homeostasis. HSPCs themselves can secrete MMP 2, 9, and 14, whereas Schwann cells are reported as a source of MMP 2, 3, and 9 and ADAM10 [34Janowska-Wieczorek A. et al.Differential MMP and TIMP production by human marrow and peripheral blood CD34(+) cells in response to chemokines.Exp. Hematol. 2000; 28: 1274-1285Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar, 48Oliveira A.L. et al.Schwann cells producing matrix metalloproteinases under Mycobacterium leprae stimulation may play a role in the outcome of leprous neuropathy.J. Neuropathol. Exp. Neurol. 2010; 69: 27-39Crossref PubMed Scopus (0) Google Scholar]. Endothelial cells, macrophages, and fibroblasts produce a range of metalloproteases. Endothelial cells produce MMP1, 2, 3, 9, 13, and 14, and ADAM10, 15, and 17; macrophages secrete MMP1, 2, 7, 9, 12, and 14, and ADAM10, 15, and 17; fibroblasts can produce MMP1, 2, 3, 9, 11, 13, and 14, and ADAMTS5; osteoblasts and osteocytes express MMP2 and 9 and ADAM10; granulocyte and their precursors exhibit high expression of MMP8 and 9; and mesenchymal stem cells (MSCs) can produce MMP2, 9, and 14. Lymphocytes can produce MMP2 and 9, and ADAM17 and 28; osteoclasts can produce MMP2 and 9 [126Nyman J.S. et al.Differential effects between the loss of MMP-2 and MMP-9 on structural and tissue-level properties of bone.J. Bone. Miner. Res. 2011; 26: 1252-1260Crossref PubMed Scopus (0) Google Scholar]. MMP2 and 9 proteins were also reported in megakaryocytes and platelets depending on their preparation, as well as their developmental stage [127Mannello F. Medda V. Differential expression of MMP-2 and MMP-9 activity in megakaryocytes and platelets.Blood. 2011; 118: 6470-6471Crossref PubMed Scopus (8) Google Scholar]. BM cells express TIMPs, which regulate metalloprotease activity. TIMP1, 2, and 3 are expressed by fibroblasts, macrophages, and endothelial cells, whereas neutrophils and lymphocytes can produce TIMP1. HSPCs produce TIMP1 and 2. The hematopoietic niche is an area of intensive study because it holds the secrets of stem cell regulation and differentiation. In this review, we present the concept that metalloproteases are active players in the HSC niche. Some of the examples offered are correlative, albeit there are well-defined demonstrations of growth factor bioavailability being dependent on a specific metalloprotease, proven by the appearance of a specific proteolytic fragment, processed growth factor, an altered signaling pathway, and/or biological outcome. We highlight various functions of the metalloprotease system in the BM niche, where structural integrity, cellular crosstalk, local instructive signals, and precise cell signaling are all essential elements of proper immune cell development. Most pathways are subject to metalloprotease actions, which are rapid, irreversible, and may trigger a cascade of fate-changing events. HSCs and hematopoietic stem progenitor cells (HSPCs) have been defined by heterogenous markers across studies or have been functionally evaluated by colony-forming units. Markers for the purest form of HSC are debatable, but here we use CD34−(FLT3−)-LSK; LSK-SPlow; CD150+(CD48−)CD41−-LSK as long-term HSC (LT-HSC), and CD34+(FLT3+)-LSK; CD150+(CD48+)CD41+ cells as short-term HSC (ST-HSC) for both human and mouse. The term 'HSPC' has also been used to refer to combined HSC and progenitor cell populations. Reactive oxygen species (ROS)low HSCs are considered more primitive and localize adjacent to arterioles in the endosteal region of BM, which contains important niche cells, including endothelial cells and Nestin–GFPbright perivascular cells [8Itkin T. et al.Distinct bone marrow blood vessels differentially regulate haematopoiesis.Nature. 2016; 532: 323-328Crossref PubMed Google Scholar, 9Lo Celso C. et al.Live-animal tracking of individual haematopoietic stem/progenitor cells in their niche.Nature. 2009; 457: 92-96Crossref PubMed Scopus (582) Google Scholar]. By contrast, ROShigh HSCs generally associate with sinusoidal endothelium supported by Nestin–GFPdim and leptin receptor-positive (LepR+) niche cells [8Itkin T. et al.Distinct bone marrow blood vessels differentially regulate haematopoiesis.Nature. 2016; 532: 323-328Crossref PubMed Google Scholar, 9Lo Celso C. et al.Live-animal tracking of individual haematopoietic stem/progenitor cells in their niche.Nature. 2009; 457: 92-96Crossref PubMed Scopus (582) Google Scholar]. Supporting cells in a niche secrete an array of critical growth factors, including CXCL12, SCF, TGFβ, VEGF, and others. CXCL12 signaling via its cognate receptor, CXCR4, is critical for HSC quiescence as well as HSC retention in BM. Disruption of this signaling pathway using Mx-Cre-induced (HSPC/myeloid specific)-Cxcr4 deletion reduced LT-HSC numbers and increased sensitivity to myelotoxic injury compared with control mice [10Sugiyama T. et al.Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches.Immunity. 2006; 25: 977-988Abstract Full Text Full Text PDF PubMed Scopus (1349) Google Scholar] [all knockout results referred herein are relative to Cre− or wild-type (WT) controls]. Whole-body deletion of Cxcl12 in adult mice by tamoxifen-inducible Cre-ER reduced LT-HSC quiescence and expanded the progenitor pool [11Tzeng Y.-S. et al.Loss of Cxcl12/Sdf-1 in adult mice decreases the quiescent state of hematopoietic stem/progenitor cells and alters the pattern of hematopoietic regeneration after myelosuppression.Blood. 2011; 117: 429-439Crossref PubMed Scopus (166) Google Scholar]. Cxcl12 is expressed by perivascular stromal cells, endothelial cells, and osteoblasts [10Sugiyama T. et al.Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches.Immunity. 2006; 25: 977-988Abstract Full Text Full Text PDF PubMed Scopus (1349) Google Scholar, 12Ponomaryov T. et al.Induction of the chemokine stromal-derived factor-1 following DNA damage improves human stem cell function.J. Clin. Invest. 2000; 106: 1331-1339Crossref PubMed Google Scholar]. Cell-specific deletion of Cxcl12 from osteoblasts or osteoblastic progenitors, using Col2.3-Cre, osteocalcin-Cre, or osterix-Cre, did not reduce LT-HSC numbers, indicating that osteolineage-derived Cxcl12 was dispensable for HSC maintenance [13Greenbaum A. et al.CXCL12 in early mesenchymal progenitors is required for haematopoietic stem-cell maintenance.Nature. 2013; 495: 227-230Crossref PubMed Scopus (655) Google Scholar, 14Ding L. Morrison S.J. Haematopoietic stem cells and early lymphoid progenitors occupy distinct bone marrow niches.Nature. 2013; 495: 231-235Crossref PubMed Scopus (599) Google Scholar, 15Ding L. et al.Endothelial and perivascular cells maintain haematopoietic stem cells.Nature. 2012; 481: 457-462Crossref PubMed Scopus (942) Google Scholar], whereas Prx1-Cre (mesenchymal progenitor) and Tie2 (see Glossary)-Cre (endothelial cell-specific)-mediated deletion of Cxcl12 each reduced the repopulating activity and HSC quiescence [13Greenbaum A. et al.CXCL12 in early mesenchymal progenitors is required for haematopoietic stem-cell maintenance.Nature. 2013; 495: 227-230Crossref PubMed Scopus (655) Google Scholar]. Therefore, both perivascular and endothelial-derived CXCL12 have been deemed important for HSC maintenance, at least in mice. Hematopoietic cell retention in the BM is mostly accomplished via the interaction of CXCL12 with heparan sulfate proteoglycans, which immobilize cells onto the matrix. Mice expressing mutant Cxcl12, precluding interactions with heparan sulfate but preserving normal signaling, showed increased CXCL12 concentrations as well as HSPC numbers in peripheral blood compared with WT [16Rueda P. et al.Homeostatic and tissue reparation defaults in mice carrying selective genetic invalidation of CXCL12/proteoglycan interactions.Circulation. 2012; 126: 1882-1895Crossref PubMed Scopus (0) Google Scholar]; this suggested an important role for heparan sulfate in HSPC retention in the hematopoietic niche. Metalloprotease degradation of proteoglycan reduced the ability of matrix to retain CXCL12, impacting HSPCs [16Rueda P. et al.Homeostatic and tissue reparation defaults in mice carrying selective genetic invalidation of CXCL12/proteoglycan interactions.Circulation. 2012; 126: 1882-1895Crossref PubMed Scopus (0) Google Scholar]. MMP2 has been shown to release CXCL12 from the ECM in vitro; the addition of an MMP2 small-molecule inhibitor (cis-9-octadeconyl-N-hydroxylamide, OA-Hy) reduced the concentration of CXCL12 in BM stromal cell culture supernatants [17Clutter S.D. et al.MMP-2 is required for bone marrow stromal cell support of pro-B-cell chemotaxis.Exp. Hematol. 2005; 33: 1192-1200Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar]. Moreover, BM stromal cell cultures from Mmp2–/– mice failed to support pro-B cell chemotaxis, which was restored by the addition of either MMP2 or CXCL12. This study provided both genetic and pharmacological evidence that MMP2 activity decreased in MSCs after chemotherapeutic drug treatment, lowering CXCL12 release from the ECM [17Clutter S.D. et al.MMP-2 is required for bone marrow stromal cell support of pro-B-cell chemotaxis.Exp. Hematol. 2005; 33: 1192-1200Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar]. CXCL12-CXCR4 signaling is crucial for HSPC retention. In fact, the CXCR4 inhibitor AMD3100 is used in the clinic along with G-CSF to mobilize HSPCs from the BM to peripheral blood for collection in transplants [18Pusic I. DiPersio J.F. Update on clinical experience with AMD3100, an SDF-1/CXCL12-CXCR4 inhibitor, in mobilization of hematopoietic stem and progenitor cells.Curr. Opin. Hematol. 2010; 17: 319-326Crossref PubMed Scopus (101) Google Scholar]. Multiple MMPs, such as MMP1, 2, 3, 9, and 13, can disable CXCL12 signaling by direct truncation of the N-terminal at position 4–5, which results in loss of binding to CXCR4 [19McQuibban G.A. et al.Matrix metalloproteinase activity inactivates the CXC chemokine stromal cell-derived factor-1.J. Biol. Chem. 2001; 276: 43503-44358Crossref PubMed Scopus (500) Google Scholar] (Table 1). Induction of HSPC mobilization can trigger the secretion of several proteases, including MMP2 and 9 in the BM microenvironment in mice [20Levesque J.P. et al.Mobilization by either cyclophosphamide or granulocyte colony-stimulating factor transforms the bone marrow into a highly proteolytic environment.Exp. Hematol. 2002; 30: 440-449Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar]. In vitro evidence has since confirmed the proteolytic degradation of CXCL12 by MMP9 from human BM-derived samples [21Jin F. et al.Degradation of BM SDF-1 by MMP-9: the role in G-CSF-induced hematopoietic stem/progenitor cell mobilization.Bone Marrow Transplant. 2008; 42: 581-588Crossref PubMed Scopus (54) Google Scholar]. HSPC mobilization post myelosuppression by 5-fluorouracil (5-FU) also shows a strong association with MMP9 activity in BM as well as with CXCL12 concentrations in mouse plasma [21Jin F. et al.Degradation of BM SDF-1 by MMP-9: the role in G-CSF-induced hematopoietic stem/progenitor cell mobilization.Bone Marrow Transplant. 2008; 42: 581-588Crossref PubMed Scopus (54) Google Scholar], and high concentrations of inactivated cleaved CXCL12(5–67) have been reported in the plasma and BM of patients with myeloproliferative neoplasm, a disease characterized by constitutive HSPC mobilization to peripheral blood [21Jin F. et al.Degradation of BM SDF-1 by MMP-9: the role in G-CSF-induced hematopoietic stem/progenitor cell mobilization.Bone Marrow Transplant. 2008; 42: 581-588Crossref PubMed Scopus (54) Google Scholar]. Impaired HSPC mobilization in Mmp9–/– mice was demonstrated both as reduced recovery of peripheral myeloid and megakaryocytic lineages following 5-FU and as impaired G-CSF mobilization of progenitors to the periphery in transplant studies; these corresponded to a greatly reduced white blood cell count in peripheral blood of metalloprotease inhibitor-treated MMP9-competent mice relative to controls [22Heissig B. et al.Recruitment of stem and progenitor cells from the bone marrow niche requires MMP-9 mediated release of kit-ligand.Cell. 2002; 109: 625-637Abstract Full Text Full Text PDF PubMed Scopus (1410) Google Scholar] (Table 2). However, another study challenged these observations, reporting no difference in G-CSF-induced HSPC egress in Mmp9–/– mice (or neutrophil elastase, cathepsin G, or dipeptidyl peptidase I-null mice) [23Levesque J.P. et al.Characterization of hematopoietic progenitor mobilization in protease-deficient mice.Blood. 2004; 104: 65-72Crossref PubMed Scopus (195) Google Scholar]. Recently, an MMP9 genetic polymorphism that lowers MMP9 affinity to its inhibitor TIMP1 was reported in mice with a DBA/2 background; this lowered affinity significantly enhanced hematopoietic cell mobilization in response to mobilizing agents relative to controls [24Hoggatt J. et al.Rapid mobilization reveals a highly engraftable hematopoietic stem cell.Cell. 2018; 172: 191-204Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar]. Moreover, in nonhuman primates, direct inhibition of MMP9 activity by an inhibitory antihuman MMP9 monoclonal antibody (crossreacting with monkey MMP9) impaired HSPC mobilization following IL-8 induction compared with control antibody-treated animals (murine antihuman anti-CD5) [25Pruijt J.F. et al.Prevention of interleukin-8-induced mobilization of hematopoietic progenitor cells in rhesus monkeys by inhibitory antibodies against the metalloproteinase gelatinase B (MMP-9).Proc. Natl. Acad. Sci. U S A. 1999; 96: 10863-10868Crossref PubMed Scopus (0) Google Scholar]. Collectively, these studies demonstrate that MMP9 can upregulate post HSPC mobilization, and that inhibition or absence of this protease can reduce hematopoietic cell numbers in peripheral blood.Table 1Known and Hypothesized Metalloprotease Substrates in HematopoiesisLigandEnzymeReceptor/ Binding PartnerEnzymeFunctionSolubleAngiopoietin-1UnknownTie2MMP14HSC quiescenceCXCL12MMP1, 2, 3, 9, 13, 14CXCR4Elastase, Cathepsin GHSC and B cell maintenance, mobilizationCXCL4MMP9CXCR2UnknownHSC pool maintenance, self-renewalFGF1ThrombinFGFR1MMP2HSC expansion, repopulating potentialFGF2Thrombin, MMP2FGFR1/2MMP2, ADAM9, 15HSPC expansion, CXCL12 reductionFGFR3γ-secretaseUnknownFLT3LADAM17FLT3UnknownIncreases common lymphoid progenitor, lymphoid commitmentG-CSFG-CSFRNeutrophil elastaseHSPC mobilizationHB-EGFADAM9, 10, 17HER-1UnknownMSC expansion, prevention of differentiationIL-2UnknownIL-2RαMMP9HSC repopulating abilityIL-1MMP2, 3, 9IL-1R1UnknownHSC to myeloid differentiation, erodes self-renewal capacityIL-1R2ADAM17UnknownIL-6UnknownIL-6RADAM17HSC expansionIL-8MMP9CXCR1/2UnknownRemodeling of endothelial nicheIL-11UnknownIL-11RADAM10HSC expansionIL-15UnknownIL-15RαADAM17Lymphoid and natural killer cell developmentM-CSFADAM17CSF1RADAM17Myelopoiesis from HSCMCP1MMP1, 3CCR2UnknownLimits proliferation of myeloid progenitorsMCP3MMP1, 2, 3, 13, 14CCRUnknownHSPC mobilization to inflammationOsteopontinMMP2, 3, 7, 9, 12IntegrinsN/AHSC engraftment, repopulationPlasminogenMMP12N/AN/AHematopoietic regenerationPDGFβUnknownPDGFRβADAM10Blood vessel formation, early hematopoiesisSCFADAM17, 19, MMP9c-KitADAM17Hematopoietic regeneration, survival, growthSLIT3UnknownROBOKuzbanianHSPC migration, homingTGFβMMP2, 9, 13, 14TGFβR1ADAM17Cytostatic effects on HSCsTNFADAM17TNFRADAM17Suppressor of HSC activityThrombopoietinThrombinMpl/c-MplUnknownIncreases HSC quiescenceVEGFMMP3, 7, 9, 19VEGFR2ADAM10Survival and repopulation of HSCVEGFR1MMP14, MMP7UnknownCell surfaceAmphiregulinADAM17EGFR/ErbBInhibits osteoblastic differentiationCD44MMP14, ADAM10Selectin/hyaluronanADAM17HSPC proliferation, maturation, adhesion, migrationE-cadherinMMP7, ADAM10E-cadherinMMP7, ADAM10Maturation of erythroid lineageEPCRADAM17Protein CUnknownHSC homing to BMICAM1MMP9, ADAM17IntegrinsUnknownHSC quiescence, repopulationIntegrinsMMP7, 9UnknownN/AAdhesion, proliferationKlothoADAM10, 17UnknownN/AMaintains hematopoiesis and erythropoiesisLAG3ADAM10, 17UnknownN/ABlocks T cell expansionN-cadherinADAM10N-cadherinADAM10HSPC to MSC interactionSyndecan1MMP14N/AN/APromotes hematopoietic tumor potentialVCAM1ADAM17IntegrinsUnknownVascular cell adhesionVE cadherinADAM10VE cadherinADAM10Migration through blood vesselECMCollagen IMMP2, 8, 9, 14IntegrinsUnknownEnhances colony-forming unit cell frequency of HSCsCol IVMMP2, 8, 9, 12, 14IntegrinsUnknownSupports hematopoietic differentiation of embryonic stem cell-derived Flk1 progenitorsCollagen XMMP1, 2, 3IntegrinsUnknownAlters lymphopoiesisFibronectinMMP2, 3, 13, 14VLA4/5UnknownClonogenic growth of HSPCsHeparan sulfateMMP9N/AN/AMigration engraftment of HSPCLamininsMMP2, 3, 13, 14IntegrinsUnknownProliferation, differentiationTenascin CMMP2, 3IntegrinsUnknownSustains colony-forming capacity of HSCs Open table in a new tab Table 2Bone and Bone Marrow Phenotypes in Mice Lacking MMP, ADAM, or TIMPGenotypeEmbryonic Stem cell strain: blastocyst strainNo. of crosses into C57BL/6PhenotypeMmp2–/–E14: C57Bl/6J>5• Increased osteopontin expression by osteoblasts• Increased osteoblast and osteoclast numbers at birth• Reduction in pro-B cell chemotactic support, rescue by recombinant CXCL12Mmp9–/–129/SvJ: C57Bl/6J>5• Reduced skeletal fracture repair, persistent cartilage at injury site, rescue by recombinant (r)VEGF• Delayed hematopoietic recovery, fewer HSCs enter cell cycle post 5-FU, reduced reconstitution of myeloid lineage, reduced SCF in plasmaMmp13–/–129/SvJ: C57Bl/6>6• Delayed vascularization of primary ossification centersMmp14–/– (Mt1-mmp–/–)129P2/OlaHsd>9• Postnatal runting, multiple skeletal abnormality• Lack of periosteocytic collagen cleavage• Reduced BM cellularity in all lineages; B, T, and myeloid developmental defects, reduced plasma levels of CXCL12, SCF, and IL-7• Reduced homing to BM upon transplant• Defective B lymphopoiesis, increased Notch signalingDermo1-Cre+ Mmp14fl/fl129P2/OlaHsd>9• Delayed membranous ossification, decreased osteogenesis, increased BM adiposity, defective osteogenic and enhanced chondrogenic/adipogenic potential from MSCsMmp16–/– (Mt3-mmp–/–)W4129S6Unknown• Growth inhibition and decreased viability of MSCsMx1-Cre+ Adam10fl/fl129/SvEv: C57Bl/6Unknown• Increased myeloid cell numbers in spleen and increased HSC numbers in BMAdam10Tg (overexpress)pHSE3' vector: C57Bl/6>5• Abrogated B cell development, disrupted Notch cleavageTie2-Cre+ Adam10fl/fl Adam17fl/fl129/Ola: C57Bl/6; 129/SvJ: C57Bl/6Unknown• Shortened long bones, disrupted metaphyseal vessel organizationAdam15–/–129/SvJ: C57Bl/6>6• Increased bone mass, volume, osteoblast numberAdam17–/–129/SvJ: C57Bl/6Unknown• Embryonic lethal, vascular defectsCol2a1-Cre+ Adam17fl/fl129/SvJ: C57Bl/6Unknown• UnknownKrt14-Cre+ Adam17fl/fl129/SvJ: C57Bl/6>9• Fewer B cells, more myeloid cells in BMVav1-iCre+ Adam17fl/fl129/SvJ: C57Bl/6Unknown• Low expression of CSF1R in HSCPs, decreased myeloid potentialSox9-Cre+ Adam17fl/fl129/SvJ: C57Bl/6Unknown• Shortened long bones, bone loss, increased osteoclast activity in BM, extramedullary hematopoiesis in spleen, inc