Hematopoietic Stem Cell Mobilization and Homing after Transplantation: The Role of MMP-2, MMP-9, and MT1-MMP

Hematopoietic stem/progenitor cells (HSPCs) are used in clinical transplantation to restore hematopoietic function. Here we review the role of the soluble matrix metalloproteinases MMP-2 and MMP-9, and membrane type (MT)1-MMP in modulating processes critical to successful transplantation of HSPC, such as mobilization and homing. Growth factors and cytokines which are employed as mobilizing agents upregulate MMP-2 and MMP-9. Recently we demonstrated that MT1-MMP enhances HSPC migration across reconstituted basement membrane, activates proMMP-2, and contributes to a highly proteolytic bone marrow microenvironment that facilitates egress of HSPC. On the other hand, we reported that molecules secreted during HSPC mobilization and collection, such as hyaluronic acid and thrombin, increase MT1-MMP expression in cord blood HSPC and enhance (prime) their homing-related responses. We suggest that modulation of MMP-2, MMP-9, and MT1-MMP expression has potential for development of new therapies for more efficient mobilization, homing, and engraftment of HSPC, which could lead to improved transplantation outcomes

The Expanding Family of Bone Marrow Homing Factors for Hematopoietic Stem Cells: Stromal Derived Factor 1 Is Not the Only Player in the Game

The α-chemokine stromal derived factor 1 (SDF-1), which binds to the CXCR4 and CXCR7 receptors, directs migration and homing of CXCR4+ hematopoietic stem/progenitor cells (HSPCs) to bone marrow (BM) and plays a crucial role in retention of these cells in stem cell niches. However, this unique role of SDF-1 has been recently challenged by several observations supporting SDF-1-CXCR4-independent BM homing. Specifically, it has been demonstrated that HSPCs respond robustly to some bioactive lipids, such as sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), and migrate in response to gradients of certain extracellular nucleotides, including uridine triphosphate (UTP) and adenosine triphosphate (ATP). Moreover, the responsiveness of HSPCs to an SDF-1 gradient is enhanced by some elements of innate immunity (e.g., C3 complement cascade cleavage fragments and antimicrobial cationic peptides, such as cathelicidin/LL-37 or β2-defensin) as well as prostaglandin E2 (PGE2). Since all these factors are upregulated in BM after myeloblative conditioning for transplantation, a more complex picture of homing emerges that involves several factors supporting, and in some situations even replacing, the SDF-1-CXCR4 axis

Enhancing the Migration Ability of Mesenchymal Stromal Cells by Targeting the SDF-1/CXCR4 Axis

Mesenchymal stromal cells (MSCs) are currently being investigated in numerous clinical trials of tissue repair and various immunological disorders based on their ability to secrete trophic factors and to modulate inflammatory responses. MSCs have been shown to migrate to sites of injury and inflammation in response to soluble mediators including the chemokine stromal cell-derived factor-(SDF-)1, but during in vitro culture expansion MSCs lose surface expression of key homing receptors particularly of the SDF-1 receptor, CXCR4. Here we review studies on enhancement of SDF-1-directed migration of MSCs with the premise that their improved recruitment could translate to therapeutic benefits. We describe our studies on approaches to increase the CXCR4 expression in in vitro-expanded cord blood-derived MSCs, namely, transfection, using the commercial liposomal reagent IBAfect, chemical treatment with the histone deacetylase inhibitor valproic acid, and exposure to recombinant complement component C1q. These methodologies will be presented in the context of other cell targeting and delivery strategies that exploit pathways involved in MSC migration. Taken together, these findings indicate that MSCs can be manipulated in vitro to enhance their in vivo recruitment and efficacy for tissue repair

Hyaluronic Acid and Thrombin Upregulate MT1-MMP Through PI3K and Rac-1 Signaling and Prime the Homing-Related Responses of Cord Blood Hematopoietic Stem/Progenitor Cells

One of the hurdles of cord blood (CB) transplantation is delayed hematopoietic engraftment. Previously, we demonstrated that supernatants isolated from leukapheresis products of granulocyte-colony stimulating factor (G-CSF)-mobilized patients primed the homing of hematopoietic stem/progenitor cells (HSPC) by enhancing their chemotactic responses to stromal cell-derived factor (SDF)-1 and stimulating matrix metalloproteinases (MMPs) MMP-2 and MMP-9. Since membrane type 1 (MT1)-MMP activates proMMP-2 and localizes proteolytic activity at the leading edge of migrating cells, in this study we investigated whether MT1-MMP contributes to the priming of the homing-related responses of CB HSPC. We found that components of supernatants of leukapheresis products such as hyaluronic acid and thrombin (i) increase the secretion of proMMP-9 and transcription and protein synthesis of MT1-MMP in CB CD34+ cells; (ii) increase the levels of active MMP-2 in co-cultures of CD34+ cells with endothelial cells; (iii) increase the chemoinvasion across reconstituted basement membrane Matrigel of CD34+ cells toward a low SDF-1 gradient (20 ng/mL); and (iv) activate mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and Rac-1 signaling pathways. Inhibition of phosphatidylinositol 3-kinase and Rac-1 by their respective inhibitors LY290042 and NSC23766 attenuated MT1-MMP expression in CB CD34+ cells, leading to reduced proMMP-2 activation and HSPC trans-Matrigel chemoinvasion toward SDF-1. Thus, our data suggest that MT1-MMP plays an important role in the homing-related responses of HSPC, and we propose that pretreatment of CB HSPC with hyaluronic acid or thrombin before transplantation could improve their homing and engraftment

Migration, Proliferation, and Differentiation of Cord Blood Mesenchymal Stromal Cells Treated with Histone Deacetylase Inhibitor Valproic Acid

Mesenchymal stromal cells (MSC) have great potential for cellular therapies as they can be directed to differentiate into certain lineages or to exert paracrine effects at sites of injury. The interactions between stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 play pivotal roles in the migration of MSC to injured tissues. We evaluated whether a histone deacetylase inhibitor valproic acid (VPA) modulates the migration of cord blood (CB-) derived MSC towards SDF-1 and their proliferation and differentiation. We found that in MSC, VPA increased (i) the gene and total protein expression of CXCR4 and CXCR7 and primed migration towards a low gradient of SDF-1, (ii) the gene expression of MMP-2 and secretion and activation of proMMP-2, (iii) the proliferation and gene expression of pluripotency markers SOX2 and Oct-4, and exposure to lower concentrations of VPA (≤5 mM) had no effect on their differentiation to osteocytes and chondrocytes. Thus, our study indicates that VPA enhances the migration of CB MSC towards SDF-1 by increasing the expression of CXCR4, CXCR7, and MMP-2. VPA at low concentrations may be used for ex vivo treatment of MSC to increase their recruitment to sites of injury without compromising their ability to proliferate or differentiate

Membrane Type-1 Matrix Metalloproteinase Expression in Acute Myeloid Leukemia and Its Upregulation by Tumor Necrosis Factor-α

Membrane type-1 matrix metalloproteinase (MT1-MMP) has been implicated in tumor invasion, as well as trafficking of normal hematopoietic cells, and acts as a physiologic activator of proMMP-2. In this study we examined MT1-MMP expression in primary acute myeloid leukemia (AML) cells. Because tumor necrosis factor (TNF)-α is known to be elevated in AML, we also investigated the effect of TNF-α on MT1-MMP expression. We found (i) MT1-MMP mRNA expression in 41 out of 43 primary AML samples tested; (ii) activation of proMMP-2 in co-cultures of AML cells with normal bone marrow stromal cells; and (iii) inhibition of proMMP-2 activation and trans-Matrigel migration of AML cells by gene silencing using MT1-MMP siRNA. Moreover, recombinant human TNF-α upregulated MT1-MMP expression in AML cells resulting in enhanced proMMP-2 activation and trans-Matrigel migration. Thus, AML cells express MT1-MMP and TNF-α enhances it leading to increased MMP-2 activation and most likely contributing to the invasive phenotype. We suggest that MT1-MMP, together with TNF-α, should be investigated as potential therapeutic targets in AML