Prevention of interleukin-8-induced mobilization of hematopoietic progenitor cells in rhesus monkeys by inhibitory antibodies against the metalloproteinase gelatinase B (MMP-9)

New strategies for targeting matrix metalloproteinases

The development of matrix metalloproteinase (MMP) inhibitors has often been frustrated by a lack of specificity and subsequent off-target effects. More recently, inhibitor design has considered secondary binding sites (exosites) to improve specificity. Small molecules and peptides have been developed that bind exosites in the catalytic (CAT) domain of MMP-13, the CAT or hemopexin-like (HPX) domain of MT1-MMP, and the collagen binding domain (CBD) of MMP-2 and MMP-9. Antibody-based approaches have resulted in selective inhibitors for MMP-9 and MT1-MMP that target CAT domain exosites. Triple-helical “mini-proteins” have taken advantage of collagen binding exosites, producing a family of novel probes. A variety of non-traditional approaches that incorporate exosite binding into the design process has yielded inhibitors with desirable selectivities within the MMP family.

A novel molecule Me6TREN promotes angiogenesis via enhancing endothelial progenitor cell mobilization and recruitment

Critical limb ischaemia is the most severe clinical manifestation of peripheral arterial disease. The circulating endothelial progenitor cells (EPCs) play important roles in angiogenesis and ischemic tissue repair. The increase of circulating EPC numbers by using mobilization agents is critical for obtaining a better therapeutic outcome in patients with ischemic disease. Here, we firstly report a novel small molecule, Me6TREN (Me6), can efficiently mobilize EPCs into the blood circulation. Single injection of Me6 induced a long-lasting increase in circulating Flk-1⁺ Sca-1⁺ EPC numbers. In a mouse hind limb ischemia (HLI) model, local intramuscular transplantation of these Me6-mobilized cells accelerated the blood flow restoration in the ischemic muscles. More importantly, systemic administration of Me6 notably increased the capillary density, arteriole density and regenerative muscle weight in the ischemic tissue of HLI. Mechanistically, we found Me6 reduced stromal cell-derived factor-1α level in bone marrow by up-regulation of matrix metallopeptidase-9 expression, which allowed the dissemination of EPCs into peripheral blood. These data indicate that Me6 may represent a potentially useful therapy for ischemic disease via enhancing autologous EPC recruitment and promote angiogenesis.

Peripheral blood hematopoietic stem and progenitor cell frequency is unchanged in patients with alpha-1-antitrypsin deficiency

Granulocyte-colony-stimulating factor (G-CSF)-induced hematopoietic stem and progenitor cell (HSPC) mobilization is associated with the release of neutrophil-derived proteases. Previously, we have shown that alpha-1-antitrypsin (AAT) inhibits these proteases in mice, resulting in inhibition of HSPC mobilization. Here, we studied the relationship between AAT and HSPC in steady state and cytokine-induced mobilization in humans. Patients with alpha-1-antitrypsin deficiency (AATD) have an 85-90 % decrease of AAT in the peripheral blood (PB). We hypothesized that this leads to increased proteolytic activity in the bone marrow and increased steady-state PB HSPC numbers. Using flow cytometry and semi-solid cell culture, we found no significant difference in PB HSPC in AATD patients (n = 18) as compared to controls (n = 22). Healthy stem cell donors (n = 43) were mobilized with G-CSF for 5 days and the number of CD45(+)/CD34(+) HSPC were determined in PB. We found that, during mobilization, PB AAT levels increased significantly, positively correlating with PB CD45(+)/CD34(+) cells (r = 0.31, p = 0.005). In conclusion, although serum AAT levels and HSPC mobilization in healthy stem cell donors are positively correlated, AAT is not an indispensable protease-inhibitor in the constitutive circulation of HSPC. These findings suggest a model in which both protease-dependent and -independent pathways contribute to HSPC mobilization.

Small molecule Me6TREN mobilizes hematopoietic stem/progenitor cells by activating MMP-9 expression and disrupting SDF-1/CXCR4 axis

The small molecule Me6TREN is a new potent and efficacious mobilizing agent of HSPCs and works more effectively than G-CSF or AMD3100. Me6 mobilizes murine HSPCs and functions by upregulating MMP-9 expression and disrupting the SDF-1α/CXCR4 axis.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Generation of AQP2-Cre transgenic mini-pigs specifically expressing Cre recombinase in kidney collecting duct cells

The important differences in physiological parameters and anatomical characteristics of the kidney between humans and mice make it difficult to replicate the precise progression of human renal cystic diseases in gene modification mouse models. In contrast to mice, pigs are a better animal model of human diseases, as they are more similar in terms of organ size, structure, and physiological parameters. Here, we report the generation and initial examination of an AQP2-Cre transgenic (Tg) Chinese miniature (mini)-pig line that expresses Cre recombinase exclusively in kidney collecting duct cells. An 8-kb fragment of the mini-pig aquaporin 2 (AQP2) 5'-flanking region was utilized to direct Cre expression in Tg mini-pigs. Two Tg mini-pigs were generated by pig somatic cell nuclear transfer and both carried the entire coding sequence of Cre recombinase. RT-PCR and western blotting analysis revealed that Cre recombinase was uniquely expressed in the kidney, while immunohistochemical studies located its expression in kidney collecting duct cells. Furthermore, six integration sites and 12-14 copies of the Cre gene were detected in various tissues by high-efficiency thermal asymmetric interlaced PCR and absolute quantitative real-time PCR, respectively. Combined with previous studies of Cre recombinase activity, we believe that this AQP2-Cre Tg mini-pig line will be a useful tool to generate kidney collecting duct cell-specific gene knockout mini-pig models, thereby allowing the investigation of gene functions in kidney development and the mechanisms of human renal cystic disease.

Role of stress-inducible protein-1 in recruitment of bone marrow derived cells into the ischemic brains

Stress-inducible protein-1 (STI-1) is the proposed ligand for the cellular prion protein (PrP^C), which is thought to facilitate recovery following stroke. Whether STI-1 expression is affected by stroke and how its signalling facilitates recovery remain elusive. Brain slices from patients that died of ischemic stroke were collected for STI-1 immunohistochemistry. These findings were compared to results from cell cultures, mice with or without the PrP^C knockout, and rats. Based on these findings, molecular and pharmacological interventions were administered to investigate the underlying mechanisms and to test the possibility for therapy in experimental stroke models. STI-1 was upregulated in the ischemic brains from humans and rodents. The increase in STI-1 expression in vivo was not cell-type specific, as it was found in neurons, glia and endothelial cells. Likewise, this increase in STI-1 expression can be mimicked by sublethal hypoxia in primary cortical cultures (PCCs) in vitro, and appear to have resulted from the direct binding of the hypoxia inducible factor-1α (HIF-1α) to the STI-1 promoter. Importantly, this STI-1 signalling promoted bone marrow derived cells (BMDCs) proliferation and migration in vitro and recruitment to the ischemic brain in vivo, and augmenting its signalling facilitated neurological recovery in part by recruiting BMDCs to the ischemic brain. Our results thus identified a novel mechanism by which ischemic insults can trigger a self-protective mechanism to facilitate recovery.

This work identifies HIF-1α-mediated transcription of STI-1 and PrPc interaction as leading to BMDCs recruitment into ischemic brains following stroke in both patients and animal models of stroke, highlighting novel neuroprotective possibilities.

Release of matrix metalloproteinase-8 during physiological trafficking and induced mobilization of human hematopoietic stem cells

Previous studies indicate that the release of proteases, including the gelatinase matrix metalloproteinase (MMP)-9, from mature granulocytes plays a crucial role in cytokine-induced hematopoietic stem and progenitor cell (HSPC) mobilization. However, studies with MMP-9-deficient mice revealed that HSPC mobilization was normal in these animals, suggesting that additional proteases must be active at clinically relevant cytokine concentrations. In the present study, we provide evidence that the collagenase MMP-8 is involved in stem cell mobilization. A rapid release of MMP-8 from isolated neutrophil granulocytes can be observed during an in vitro culture. During granulocyte colony-stimulating factor-induced HSPC mobilization, highly elevated serum concentrations of MMP-8 were observed on days 4 to 6 of the mobilization regimen, concomitantly with elevated MMP-9 serum levels and higher numbers of circulating CD34(+) cells. Elevated serum concentrations of both proteases were also found in umbilical cord blood serum. In functional assays, adhesion of HSPC to osteoblasts as an essential component of the endosteal stem cell niche is negatively influenced by MMP-8. The chemokine CXCL12, which is critically involved in stem cell trafficking, can be proteolytically processed by MMP-8 treatment. This degradation has a strong inhibitory influence on HSPC migration. Taken together, our data strongly suggest that MMP-8 can be directly involved in hematopoietic stem cell mobilization and trafficking.

Chemokines and adult bone marrow stem cells

The adult bone contains a number of distinct populations of stem cells, including haematopoietic stem cells, mesenchymal stem cells, endothelial progenitor cells and fibrocytes. While haematopoietic stem cells are required to provide a lifelong supply of blood cells it is thought that the other populations of stem cells play a role in tissue regeneration and potentially disease. The chemokine CXCL12 is produced constitutively in the bone marrow and, acting via CXCR4, is critical in maintaining HSPCs in a quiescent state and retaining all subsets of stem and progenitor cells in the bone marrow environment. The cytokine G-CSF, used clinically to mobilize haematopoietic stem cells for bone marrow transplants, activates the sympathetic nervous system and bone marrow macrophages to reduce the expression of CXCL12 by bone marrow stromal cells, thereby promoting the exit of haematopoietic stem cells from the bone marrow. Understanding the molecular mechanisms underlying G-CSF stimulated mobilization has led to development of CXCR4 antagonists as fast acting mobilizing agents for haematopoietic stem cells. Evidence now suggests that CXCR4 antagonists can similarly mobilize distinct subsets of progenitor cells, namely the endothelial progenitor cells and mesenchymal stem cells, but this requires conditioning of the bone marrow with VEGF rather than G-CSF.

VEGF-A recruits a proangiogenic MMP-9-delivering neutrophil subset that induces angiogenesis in transplanted hypoxic tissue

Recruitment and retention of leukocytes at a site of blood vessel growth are crucial for proper angiogenesis and subsequent tissue perfusion. Although critical for many aspects of regenerative medicine, the mechanisms of leukocyte recruitment to and actions at sites of angiogenesis are not fully understood. In this study, we investigated the signals attracting leukocytes to avascular transplanted pancreatic islets and leukocyte actions at the engraftment site. Expression of the angiogenic stimulus VEGF-A by mouse pancreatic islets was elevated shortly after syngeneic transplantation to muscle. High levels of leukocytes, predominantly CD11b(+)/Gr-1(+)/CXCR4(hi) neutrophils, were observed at the site of engraftment, whereas VEGF-A-deficient islets recruited only half of the amount of leukocytes when transplanted. Acute VEGF-A exposure of muscle increased leukocyte extravasation but not the levels of SDF-1α. VEGF-A-recruited neutrophils expressed 10 times higher amounts of MMP-9 than neutrophils recruited to an inflammatory stimulus. Revascularization of islets transplanted to MMP-9-deficient mice was impaired because blood vessels initially failed to penetrate grafts, and after 2 weeks vascularity was still disturbed. This study demonstrates that VEGF-A recruits a proangiogenic circulating subset of CD11b(+)/Gr-1(+) neutrophils that are CXCR4(hi) and deliver large amounts of the effector protein MMP-9, required for islet revascularization and functional integration after transplantation.

An emerging link in stem cell mobilization between activation of the complement cascade and the chemotactic gradient of sphingosine-1-phosphate

Under steady-state conditions, hematopoietic stem/progenitor cells (HSPCs) egress from bone marrow (BM) and enter peripheral blood (PB) where they circulate at low levels. Their number in PB, however, increases significantly in several stress situations related to infection, organ/tissue damage, or strenuous exercise. Pharmacologically mediated enforced egress of HSPCs from the BM microenvironment into PB is called "mobilization", and this phenomenon has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present the accumulated evidence that innate immunity, including the complement cascade and the granulocyte/monocyte lineage, and the PB plasma level of the bioactive lipid sphingosine-1-phosphate (S1P) together orchestrate this evolutionarily conserved mechanism that directs trafficking of HSPCs.

Glucocorticosteroids differentially regulate MMP-9 and neutrophil elastase in COPD

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is currently the fifth leading cause of death worldwide. Neutrophilic inflammation is prominent, worsened during infective exacerbations and is refractory to glucocorticosteroids (GCs). Deregulated neutrophilic inflammation can cause excessive matrix degradation through proteinase release. Gelatinase and azurophilic granules within neutrophils are a major source of matrix metalloproteinase (MMP)-9 and neutrophil elastase (NE), respectively, which are elevated in COPD.

METHODS

Secreted MMP-9 and NE activity in BALF were stratified according to GOLD severity stages. The regulation of secreted NE and MMP-9 in isolated blood neutrophils was investigated using a pharmacological approach. In vivo release of MMP-9 and NE in mice exposed to cigarette smoke (CS) and/or the TLR agonist lipopolysaccharide (LPS) in the presence of dexamethasone (Dex) was investigated.

RESULTS

Neutrophil activation as assessed by NE release was increased in severe COPD (36-fold, GOLD II vs. IV). MMP-9 levels (8-fold) and activity (21-fold) were also elevated in severe COPD, and this activity was strongly associated with BALF neutrophils (r = 0.92, p<0.001), but not macrophages (r = 0.48, p = 0.13). In vitro, release of NE and MMP-9 from fMLP stimulated blood neutrophils was insensitive to Dex and attenuated by the PI3K inhibitor, wortmannin. In vivo, GC resistant neutrophil activation (NE release) was only seen in mice exposed to CS and LPS. In addition, GC refractory MMP-9 expression was only associated with neutrophil activation.

CONCLUSIONS

As neutrophils become activated with increasing COPD severity, they become an important source of NE and MMP-9 activity, which secrete proteinases independently of TIMPs. Furthermore, as NE and MMP-9 release was resistant to GC, targeting of the PI3K pathway may offer an alternative pathway to combating this proteinase imbalance in severe COPD.

New functions of the fibrinolytic system in bone marrow cell-derived angiogenesis

Angiogenesis is a process by which new blood vessels form from preexisting vasculature. This process includes differentiation of angioblasts into endothelial cells with the help of secreted angiogenic factors released from cells such as bone marrow (BM)-derived cells. The fibrinolytic factor plasmin, which is a serine protease, has been shown to promote endothelial cell migration either directly, by degrading matrix proteins such as fibrin, or indirectly, by converting matrix-bound angiogenic growth factors into a soluble form. Plasmin can also activate other pericellular proteases such as matrix metalloproteinases (MMPs). Recent studies indicate that plasmin can additionally alter cellular adhesion and migration. We showed that factors of the fibrinolytic pathway can recruit BM-derived hematopoietic cells into ischemic/hypoxic tissues by altering the activation status of MMPs. These BM-derived cells can function as accessory cells that promote angiogenesis by releasing angiogenic signals. This review will discuss recent data regarding the role of the fibrinolytic system in controlling myeloid cell-driven angiogenesis. We propose that plasmin/plasminogen may be a potential target not only for development of effective angiogenic therapeutic strategies for the treatment of cancer, but also for development of strategies to promote ischemic tissue regeneration.

Classically activated macrophages use stable microtubules for matrix metalloproteinase-9 (MMP-9) secretion

As major effector cells of the innate immune response, macrophages must adeptly migrate from blood to infected tissues. Endothelial transmigration is accomplished by matrix metalloproteinase (MMP)-induced degradation of basement membrane and extracellular matrix components. The classical activation of macrophages with LPS and IFN-γ causes enhanced microtubule (MT) stabilization and secretion of MMPs. Macrophages up-regulate MMP-9 expression and secretion upon immunological challenge and require its activity for migration during the inflammatory response. However, the dynamics of MMP-9 production and intracellular distribution as well as the mechanisms responsible for its trafficking are unknown. Using immunofluorescent imaging, we localized intracellular MMP-9 to small Golgi-derived cytoplasmic vesicles that contained calreticulin and protein-disulfide isomerase in activated RAW 264.7 macrophages. We demonstrated vesicular organelles of MMP-9 aligned along stable subsets of MTs and showed that selective modulation of MT dynamics contributes to the enhanced trafficking of MMP-9 extracellularly. We found a Rab3D-dependent association of MMP-9 vesicles with the molecular motor kinesin, whose association with the MT network was greatly enhanced after macrophage activation. Finally, we implicated kinesin 5B and 3B isoforms in the effective trafficking of MMP-9 extracellularly.

Mobilization of hematopoietic stem and progenitor cells using inhibitors of CXCR4 and VLA-4

Successful hematopoietic stem cell transplant requires the infusion of a sufficient number of hematopoietic stem/progenitor cells (HSPCs) that are capable of homing to the bone marrow cavity and regenerating durable trilineage hematopoiesis in a timely manner. Stem cells harvested from peripheral blood are the most commonly used graft source in HSCT. Although granulocyte colony-stimulating factor (G-CSF) is the most frequently used agent for stem cell mobilization, the use of G-CSF alone results in suboptimal stem cell yields in a significant proportion of patients. Both the chemokine receptor CXCR4 and the integrin α(4)β(1) (very late antigen 4 (VLA-4)) have important roles in the homing and retention of HSPCs within the bone marrow microenvironment. Preclinical and/or clinical studies have shown that targeted disruption of the interaction of CXCR4 or VLA-4 with their ligands results in the rapid and reversible mobilization of hematopoietic stem cells into the peripheral circulation and is synergistic when combined with G-CSF. In this review, we discuss the development of small-molecule CXCR4 and VLA-4 inhibitors and how they may improve the utility and convenience of peripheral blood stem cell transplantation.

Accelerated hematopoietic toxicity by high energy (56)Fe radiation

PURPOSE

There is little information on the relative toxicity of highly charged (Z) high-energy (HZE) radiation in animal models compared to γ or X-rays, and the general assumption based on in vitro studies has been that acute toxicity is substantially greater.

METHODS

C57BL/6J mice were irradiated with (56)Fe ions (1 GeV/nucleon), and acute (within 30 d) toxicity compared to that of γ rays or protons (1 GeV). To assess relative hematopoietic and gastrointestinal toxicity, the effects of (56)Fe ions were compared to γ rays using complete blood count (CBC), bone marrow granulocyte-macrophage colony forming unit (GM-CFU), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay for apoptosis in bone marrow, and intestinal crypt survival.

RESULTS

Although onset was more rapid, (56)Fe ions were only slightly more toxic than γ rays or protons with lethal dose (LD)(50/30) (a radiation dose at which 50% lethality occurs at 30-day) values of 5.8, 7.25, and 6.8 Gy, respectively, with relative biologic effectiveness for (56)Fe ions of 1.25 and 1.06 for protons.

CONCLUSIONS

(56)Fe radiation caused accelerated and more severe hematopoietic toxicity. Early mortality correlated with more profound leukopenia and subsequent sepsis. Results indicate that there is selective enhanced toxicity to bone marrow progenitor cells, which are typically resistant to γ rays, and bone marrow stem cells, because intestinal crypt cells did not show increased HZE toxicity.

Mobilization of hematopoietic stem and leukemia cells

HSC mobilization is an essential homeostatic process during inflammation and for the maintenance of hematopoietic progenitors. It has been exploited for the therapeutic application of HSC transplantation. Recent evidence suggests that leukemic cells share surface molecules in common with stem cells and may be mobilized under similar conditions. This effect could be used for therapeutic interventions. In this review, we will provide evidence showing that leukemia cells and stem cells traffic similarly and may share a common niche. Studies are discussed comparing and contrasting the mechanism of normal stem cells and leukemic cell mobilization through the CXCR4/CXCL12 axis and other key intermediaries.

MT1-MMP and RECK: opposite and essential roles in hematopoietic stem and progenitor cell retention and migration

Migratory capacity is a fundamental property of hematopoietic stem and progenitor cells (HSPCs). This feature is employed in clinical mobilization of HSPCs to the circulation and constitutes the basis for modern bone marrow (BM) transplantation procedures which are routinely used to treat hematological malignancies. Therefore, characterization of new players in the complex process of HSPC motility in steady-state conditions as well as during stress situations is a major challenge. We report that while the metalloproteinase membrane type 1-metalloprotease (MT1-MMP) has an essential role in human HSPC trafficking during granulocyte colony-stimulating factor (G-CSF)-induced mobilization, its inhibitor reversion-inducing cysteine-rich protein with Kazal motifs (RECK) and the adhesion molecule CD44 are required for HSPC retention to the BM in steady-state conditions. The nervous system via Wnt signaling along with HGF/c-Met signaling and the complement cascade play a major role in regulating MT1-MMP increased activity, CD44 cleavage, and RECK-reduced expression during G-CSF-induced mobilization. This review will elaborate on the opposite roles of MT1-MMP and RECK in HSPC migration and retention and suggest targeting them in order to facilitate HSPC mobilization and engraftment upon BM transplantation in patients.

Functional genomics reveals the induction of inflammatory response and metalloproteinase gene expression during lethal Ebola virus infection

Ebola virus is the etiologic agent of a lethal hemorrhagic fever in humans and nonhuman primates with mortality rates of up to 90%. Previous studies with Zaire Ebola virus (ZEBOV), mouse-adapted virus (MA-ZEBOV), and mutant viruses (ZEBOV-NP(ma), ZEBOV-VP24(ma), and ZEBOV-NP/VP24(ma)) allowed us to identify the mutations in viral protein 24 (VP24) and nucleoprotein (NP) responsible for acquisition of high virulence in mice. To elucidate specific molecular signatures associated with lethality, we compared global gene expression profiles in spleen samples from mice infected with these viruses and performed an extensive functional analysis. Our analysis showed that the lethal viruses (MA-ZEBOV and ZEBOV-NP/VP24(ma)) elicited a strong expression of genes 72 h after infection. In addition, we found that although the host transcriptional response to ZEBOV-VP24(ma) was nearly the same as that to ZEBOV-NP/VP24(ma), the contribution of a mutation in the NP gene was required for a lethal phenotype. Further analysis indicated that one of the most relevant biological functions differentially regulated by the lethal viruses was the inflammatory response, as was the induction of specific metalloproteinases, which were present in our newly identify functional network that was associated with Ebola virus lethality. Our results suggest that this dysregulated proinflammatory response increased the severity of disease. Consequently, the newly discovered molecular signature could be used as the starting point for the development of new drugs and therapeutics. To our knowledge, this is the first study that clearly defines unique molecular signatures associated with Ebola virus lethality.

Plasminogen regulates stromal cell-derived factor-1/CXCR4-mediated hematopoietic stem cell mobilization by activation of matrix metalloproteinase-9

OBJECTIVE

Granulocyte colony-stimulating factor (G-CSF) is a widespread therapeutic agent for stimulation of hematopoietic progenitor and stem cell (HPSC) mobilization from bone marrow (BM). Plasminogen (Plg) has been shown to be critical for HPSC mobilization. Here, we investigated the role of Plg in G-CSF-induced HPSC mobilization and the underlying mechanism.

METHODS AND RESULTS

By using gene-targeted mice, our data show that Plg is required for G-CSF-induced HPSC egress to sinusoidal capillaries in BM and subsequent mobilization to peripheral circulation. G-CSF induced Plg-dependent activation of matrix metalloproteinase-9 (MMP-9) in BM, and MMP-9 neutralization or deficiency suppressed HPSC migration and mobilization. Reconstitution of MMP-9 activity by BM transplantation after lentiviral overexpression rescued HPSC mobilization in Plg-deficient mice, indicating that MMP-9 activation is required for Plg-mediated HPSC mobilization. Interestingly, after G-CSF simulation, Plg downregulated stromal cell-derived factor-1 in BM and spatiotemporally regulated the expression of C-X-C chemokine receptor type 4 (CXCR4) on mobilized HPSCs, and reconstitution of MMP-9 activity in Plg-deficient mice reversed CXCR4 expression on HPSCs in plasma and BM, suggesting that CXCR4 serves as a new downstream signal of Plg/MMP-9 in HPSC mobilization.

CONCLUSIONS

Our data elucidated a novel mechanism that Plg regulates MMP-9-dependent CXCR4 expression to facilitate HPSC mobilization in response to G-CSF.

Mobilization of hematopoietic stem cells into the peripheral blood

Hematopoietic stem cells can be mobilized out of the bone marrow into the blood for the reconstitution of hematopoiesis following high-dose therapy. Methods to improve mobilization efficiency and yields are rapidly emerging. Traditional methods include chemotherapy with or without myeloid growth factors. Plerixafor, a novel agent that disrupts the CXCR4-CXCL12 bond, the primary hematopoietic stem cell anchor in the bone marrow, has recently been US FDA-approved for mobilizing hematopoietic stem cells in patients with non-Hodgkin lymphoma and multiple myeloma. Plerixafor and myeloid growth factors as single agents appear safe to use in family or volunteer hematopoietic stem cells donors. Plerixafor mobilizes leukemic stem cells and is not approved for use in patients with acute leukemia. Patients failing to mobilize adequate hematopoietic stem cells with myeloid growth factors can often be successfully mobilized with chemotherapy plus myeloid growth factors or with plerixafor and granulocyte colony-stimulating factor.

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

Under normal conditions, the great majority of hematopoietic stem/progenitors cells (HSPCs) reside in the bone marrow. The number of HSPCs in the circulation can be markedly increased in response to a number of stimuli, including hematopoietic growth factors, myeloablative agents and environmental stresses such as infection. The ability to 'mobilize' HSPCs from the bone marrow to the blood has been exploited clinically to obtain HSPCs for stem cell transplantation and, more recently, to stimulate therapeutic angiogenesis at sites of tissue ischemia. Moreover, there is recent interest in the use of mobilizing agents to sensitize leukemia and other hematopoietic malignancies to cytotoxic agents. Key to optimizing clinical mobilizing regimens is an understanding of the fundamental mechanisms of HSPC mobilization. In this review, we discuss recent advances in our understanding of the mechanisms by which granulocyte colony-stimulating factor (G-CSF), the prototypical mobilizing agent, induces HSPC mobilization.

Innate immunity as orchestrator of stem cell mobilization

Hematopoietic stem and progenitor cells (HSPCs), as well as other types of stem cells, circulate under steady-state conditions at detectable levels in peripheral blood (PB), with their numbers increasing in response to stress, inflammation and tissue/organ injury. This mobilization process may be envisioned as a danger-sensing response mechanism triggered by hypoxia or mechanical or infection-induced tissue damage that recruits into PB different types of stem cells that have a role in immune surveillance and organ/tissue regeneration. Mobilization is also significantly enhanced by the administration of pharmacological agents, which has been exploited in hematological transplantology as a means to obtain HSPCs for hematopoietic reconstitution. In this review we will present mounting evidence that innate immunity orchestrates this evolutionarily conserved mechanism of HSPC mobilization.

Tissue inhibitor of metalloproteinase-3 (TIMP-3) regulates hematopoiesis and bone formation in vivo

Background

Tissue inhibitor of metalloproteinases-3 (TIMP-3) inhibits matrix metalloproteinases and membrane-bound sheddases. TIMP-3 is associated with the extracellular matrix and is expressed in highly remodeling tissues. TIMP-3 function in the hematopoietic system is unknown.

Methodology/Principal Findings

We now report that TIMP-3 is highly expressed in the endosteal region of the bone marrow (BM), particularly by osteoblasts, endothelial and multipotent mesenchymal stromal cells which are all important cellular components of hematopoietic stem cell (HSC) niches, whereas its expression is very low in mature leukocytes and hematopoietic stem and progenitor cells. A possible role of TIMP-3 as an important niche component was further suggested by its down-regulation during granulocyte colony-stimulating factor-induced mobilization. To further investigate TIMP-3 function, mouse HSC were retrovirally transduced with human TIMP-3 and transplanted into lethally irradiated recipients. TIMP-3 overexpression resulted in decreased frequency of B and T lymphocytes and increased frequency of myeloid cells in blood and BM, increased Lineage-negative Sca-1⁺KIT⁺ cell proliferation in vivo and in vitro and increased colony-forming cell trafficking to blood and spleen. Finally, over-expression of human TIMP-3 caused a late onset fatal osteosclerosis.

Conclusions/Significance

Our results suggest that TIMP-3 regulates HSC proliferation, differentiation and trafficking in vivo, as well as bone and bone turn-over, and that TIMP-3 is expressed by stromal cells forming HSC niches within the BM. Thus, TIMP-3 may be an important HSC niche component regulating both hematopoiesis and bone remodeling.

Vitamin A upregulates matrix metalloproteinase-9 activity by murine myeloid dendritic cells through a nonclassical transcriptional mechanism

Myeloid dendritic cells (DC) are specialized antigen-presenting immune cells. Upon activation in peripheral tissues, DC migrate to lymph nodes to activate T lymphocytes. Matrix metalloproteinase (MMP)-9 is a gelatinase essential for DC migration. We have previously shown that all-trans retinoic acid (atRA), a bioactive metabolite of vitamin A, significantly augmented DC MMP-9 mRNA and protein production. We investigated the mechanisms by which atRA increased MMP-9 activity in vitro. Mouse myeloid DC cultured with atRA demonstrated increased gelatinase activity compared with cells cultured with retinoic acid receptor (RAR)-alpha antagonist. Adding MMP-9 inhibitor significantly blocked DC gelatinase activity and increased adherence of DC in a dose-dependent manner. AtRA-induced Mmp-9 gene expression in DC was blocked by transcriptional inhibition. Because the Mmp-9 promoter contains no canonical retinoic acid response element (RARE), we performed additional studies to determine how atRA regulated DC Mmp-9 transcription. Electrophoretic mobility shift assays for the consensus Sp1, activating protein-1, and nuclear factor-kappaB binding sites located in the Mmp-9 promoter did not indicate greater nuclear protein binding in response to atRA. Chromatin immunoprecipitation assays indicated RARalpha and histone acetyltransferase p300 recruitment to, and acetylation of, histone H3 at the Mmp-9 promoter was greater after atRA treatment. These data suggest that atRA regulated DC adhesion in vitro partly through MMP-9 gelatinase activity. Mmp-9 expression was enhanced through a transcriptional mechanism involving greater RARalpha promoter binding, recruitment of p300, and subsequent histone H3 acetylation, despite the absence of a consensus RARE.

Mobilization of CD133(+)CD34(-) cells in healthy individuals following whole-body acupuncture for spinal cord injuries

Acupuncture can alleviate symptoms of spinal cord injuries (SCI). The underlying mechanism, however, is unknown. We hypothesized that stem cells could be mobilized by acupuncture. Therefore, we enrolled 14 healthy study participants using acupuncture points for the treatment of SCI. The frequency of CD133 and CD34 cells in peripheral blood and the serum concentrations of matrix metalloproteinase (MMP)-9, brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and interleukin-6 were determined before and after acupuncture (<1 hr, 24 hr, and 48 hr). CD133(+)34(-) cells were doubled 48 hr after acupuncture, with concomitant decreases in BDNF and MMP-9 levels. Interleukin-6 remained below detectable levels, eliminating a stress-induced cell release. Individuals acupunctured on control counterpoints showed no changes in CD133(+) cells. Our results indicate that acupuncture for SCI can mobilize human CD133(+)34(-) cells. (c) 2009 Wiley-Liss, Inc.

Novel insight into stem cell mobilization-plasma sphingosine-1-phosphate is a major chemoattractant that directs the egress of hematopoietic stem progenitor cells from the bone marrow and its level in peripheral blood increases during mobilization due to activation of complement cascade/membrane attack complex

Complement cascade (CC) becomes activated and its cleavage fragments play a crucial role in the mobilization of hematopoietic stem/progenitor cells (HSPCs). Here, we sought to determine which major chemottractant present in peripheral blood (PB) is responsible for the egress of HSPCs from the BM. We noticed that normal and mobilized plasma strongly chemoattracts HSPCs in a stromal derived factor-1 (SDF-1)-independent manner because i) plasma SDF-1 level does not correlate with mobilization efficiency, ii) the chemotactic plasma gradient is not affected in the presence of AMD3100, and iii) it is resistant to denaturation by heat. Surprisingly, the observed loss of plasma chemotactic activity after charcoal stripping suggested involvement of bioactive lipids and we focused on sphingosine-1 phosphate (S1P), a known chemoattracant of HSPCs. We found that S1P i) creates in plasma a continuously present gradient for BM-residing HSPCs, ii) is at physiologically relevant concentrations a chemoattractant several magnitudes stronger than SDF-1, and iii) its plasma level increases during mobilization due to CC activation and the interaction of membrane attack complex (MAC) with erythrocytes that are a major reservoir of S1P. We conclude and propose a new paradigm that S1P is a crucial chemoattractant for BM-residing HSPCs and that CC via MAC induces release of S1P from erythrocytes for optimal egress/mobilization of HSPCs.

Novel insight into stem cell mobilization-plasma sphingosine-1-phosphate is a major chemoattractant that directs the egress of hematopoietic stem progenitor cells from the bone marrow and its level in peripheral blood increases during mobilization due to activation of complement cascade/membrane attack complex

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during mobilization of hematopoietic stem/progenitor cells (HSPCs) induced by granulocyte-colony stimulating factor (G-CSF) and C5 cleavage plays an important role in optimal egress of HSPCs. In the current work, we explored whether CC is involved in mobilization of HSPCs induced by the CXCR4 antagonist, AMD3100. To address this question, we performed mobilization studies in mice that display a defect in the activation of the proximal steps of CC (Rag^−/−, SCID, C2.Cfb^−/−) as well as in mice that do not activate the distal steps of CC (C5^−/−). We noticed that proximal CC activation-deficient mice (above C5 level), in contrast to distal step CC activation-deficient C5^−/− ones mobilize normally in response to AMD3100 administration. We hypothesized that this discrepancy in mobilization could be explained by AMD3100 activating C5 in Rag^−/−, SCID, C2.Cfb^−/− animals in a non-canonical mechanism involving activated granulocytes. To support this granulocytes i) as first egress from BM and ii) secrete several proteases that cleave/activate C5 in response to AMD3100. We conclude that AMD3100-directed mobilization of HSPCs, similarly to G-CSF-induced mobilization, depends on activation of CC; however, in contrast to G-CSF, AMD3100 activates the distal steps of CC directly at the C5 level. Overall, these data support that C5 cleavage fragments and distal steps of CC activation are required for optimal mobilization of HSPCs.

Impaired mobilization of hematopoietic stem/progenitor cells in C5-deficient mice supports the pivotal involvement of innate immunity in this process and reveals novel promobilization effects of granulocytes

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during granulocyte colony-stimulating factor (G-CSF) mobilization of hematopoietic stem/progenitor cells (HSPCs) and showed that, although third CC component (C3)-deficient mice are easy mobilizers, fifth CC component (C5)-deficient mice mobilize very poorly. To explain this, we postulated that activation/cleavage of CC releases C3a and C5a anaphylatoxins that differently regulate mobilization. Accordingly, C3a, by enhancing responsiveness of HSPCs to decreasing concentrations of stromal-derived growth factor-1 (SDF-1) in BM, prevents mobilization and promotes their BM retention. Therefore, in this study, we focused on the mobilization-enhancing role of C5a. We found that C5a receptor (C5aR) is not expressed on the surface of HSPCs, and that C5a-mediated promobilization effects are mediated by stimulation of granulocytes. Overall, our data support the following model. First C5aR(+) granulocytes are chemoattracted by plasma C5 cleavage fragments, being the first wave of cells leaving BM. This facilitates a subsequent egress of HSPCs. In the next step, after leaving BM, granulocytes undergo degranulation in response to plasma C5a and secrete some cationic peptides (cathelicidin, beta-defensin) that, as shown here for the first time, highly enhance the responsiveness of HSPCs to plasma SDF-1 gradient. In conclusion, our data reveal the underappreciated central role of innate immunity in mobilization, in which C5 cleavage fragments through granulocytes orchestrate this process.

Innate immunity: a key player in the mobilization of hematopoietic stem/progenitor cells

The mobilization of hematopoietic stem/progenitor cells (HSPCs) from bone marrow into peripheral blood (PB) is still not fully understood. Different chemokines, cytokines, growth factors, and neurotransmitters have been described that facilitate this process. However, mounting evidence suggests that mobilization of HSPCs is a part of the immune response and is mediated by innate immunity. We discuss evidence showing that complement system cleavage fragments play a crucial role in both the retention and mobilization of HSPCs by modulating their responsiveness to stromal-derived growth factor-1 (SDF-1) gradient (by C3-derived anaphylatoxins) and by modulating the release of granulocytes into PB that subsequently facilitate the egress of HSPCs (by C5-derived anaphylatoxins).

Serpina1 (alpha1-AT) is synthesized in the osteoblastic stem cell niche

OBJECTIVE

Previously, we identified Serpina1 as a potent inhibitor of hematopoietic stem and progenitor cell (HSC/HPC) mobilization. Serpina1 protein is found in the bone marrow (BM) extracellular fluid and concentrations are decreased during granulocyte colony-stimulating factor-induced HSC/HPC mobilization in mice. In addition, administration of exogenous Serpina1 protein inhibits HSC/HPC mobilization. BM cells responsible for production and secretion of Serpina1 remain unknown. Here, we examined the expression of Serpina1 in order to identify cell populations of the BM that synthesize Serpina1.

MATERIALS AND METHODS

Osteoblast (OB) and hematopoietic BM cell fractions were isolated from femurs, tibias, and humeri obtained from untreated mice. Subsequently, each BM fraction was examined for the production of Serpina1 messenger RNA and protein by quantitative real-time polymerase chain reaction, Western blotting, and immunohistochemistry.

RESULTS

Quantitative real-time polymerase chain reaction analysis showed that Serpina1 messenger RNA is produced at high levels by OB compared to hematopoietic BM cells. Furthermore, Western blot analysis indicated that Serpina1 protein was secreted by OB. In contrast, no Serpina1 protein could be detected in the supernatant obtained from overnight cultured hematopoietic BM cells. Finally, in BM sections obtained from the femurs of untreated mice, Serpina1 protein was detected in OB cells lining the bone.

CONCLUSION

Serpina1 protein in the BM extracellular fluid is predominantly produced by OB. This indicates that Serpina1 may play a regulatory role in the maintenance of HSC in the OB stem cell niche.

Suppression of CXCL12 production by bone marrow osteoblasts is a common and critical pathway for cytokine-induced mobilization

Current evidence suggests that hematopoietic stem/progenitor cell (HSPC) mobilization by granulocyte colony-stimulating factor (G-CSF) is mediated by induction of bone marrow proteases, attenuation of adhesion molecule function, and disruption of CXCL12/CXCR4 signaling in the bone marrow. The relative importance and extent to which these pathways overlap or function independently are uncertain. Despite evidence of protease activation in the bone marrow, HSPC mobilization by G-CSF or the chemokine Grobeta was abrogated in CXCR4(-/-) bone marrow chimeras. In contrast, HSPC mobilization by a VLA-4 antagonist was intact. To determine whether other mobilizing cytokines disrupt CXCR4 signaling, we characterized CXCR4 and CXCL12 expression after HSPC mobilization with Flt3 ligand (Flt3L) and stem cell factor (SCF). Indeed, treatment with Flt3L or SCF resulted in a marked decrease in CXCL12 expression in the bone marrow and a loss of surface expression of CXCR4 on HSPCs. RNA in situ and sorting experiments suggested that the decreased CXCL12 expression is secondary to a loss of osteoblast lineage cells. Collectively, these data suggest that disruption of CXCR4 signaling and attenuation of VLA-4 function are independent mechanisms of mobilization by G-CSF. Loss of CXCL12 expression by osteoblast appears to be a common and key step in cytokine-induced mobilization.

Matrix metalloproteinase-9 derived from polymorphonuclear neutrophils increases gut barrier dysfunction and bacterial translocation in rat severe acute pancreatitis

BACKGROUND

The role of polymorphonuclear neutrophil granulocytes (PMNs) and the PMN-derived protease, which is called matrix metalloproteinase-9 (MMP-9), for the gut barrier dysfunction in severe acute pancreatitis (SAP) has not yet been clarified. The aim of this study was to evaluate the effects of PMNs and MMP-9 on gut barrier dysfunction in rat SAP.

METHODS

SAP was induced by the injection of 5% sodium taurocholate, and anti-rat PMN serum or BB-94 were administered 48 h and 24 h, respectively, before the induction of acute pancreatitis. Twenty-four hours after the induction of acute pancreatitis, the gut barrier dysfunction and the incidence of bacterial translocation (BT) and PMN transmigration were investigated by bacterial, histologic, and biochemical (MPO) analysis. Inhibition of MMP-9 was achieved by depletion of PMNs or inhibition of MMP-activity by a broad-spectrum MMP inhibitor and confirmed by zymography. In addition, reactive oxygen species were evaluated by spin trap assay.

RESULTS

The mucosal injury and the infiltration of PMNs into the gut tissue of rats with SAP were significantly increased in comparison with rats treated with anti-rat PMN serum or BB-94. The levels of MMP-9 and reactive oxygen species in the gut of rats with SAP were significantly higher than those of the rats treated with anti-rat PMN serum or BB-94. Pretreatment with anti-rat PMN serum or BB-94 reduced the incidence of BT in SAP.

CONCLUSION

The incidence of BT in SAP was prevented by the depletion of PMNs or less pronounced by the injection of the MMP inhibitor BB-94. PMNs play an important pathophysiologic role in the occurrence of BT, and MMP-9 is involved in both BT and PMN transmigration in rat SAP.

CXCR2 antagonists for the treatment of pulmonary disease

Chemokines have long been implicated in the initiation and amplification of inflammatory responses by virtue of their role in leukocyte chemotaxis. The expression of one of the receptors for these chemokines, CXCR2, on a variety of cell types and tissues suggests that these receptors may have a broad functional role under both constitutive conditions and in the pathophysiology of a number of acute and chronic diseases. With the development of several pharmacological, immunological and genetic tools to study CXCR2 function, an important role for this CXC chemokine receptor subtype has been identified in chronic obstructive pulmonary disease (COPD), asthma and fibrotic pulmonary disorders. Interference with CXCR2 receptor function has demonstrated different effects in the lungs including inhibition of pulmonary damage induced by neutrophils (PMNs), antigen or irritant-induced goblet cell hyperplasia and angiogenesis/collagen deposition caused by lung injury. Many of these features are common to inflammatory and fibrotic disorders of the lung. Clinical trials evaluating small molecule CXCR2 antagonists in COPD, asthma and cystic fibrosis are currently underway. These studies hold considerable promise for identifying novel and efficacious treatments of pulmonary disorders.

Degradation of BM SDF-1 by MMP-9: the role in G-CSF-induced hematopoietic stem/progenitor cell mobilization

The major involvement of chemokines and proteolytic enzymes has recently been discovered in the mobilization process. Here, we report that the degradation of BM stromal cell-derived factor (SDF-1) by matrix metalloproteinase (MMP)-9 is important in G-CSF-mediated hematopoietic stem/progenitor cells (HSPCs) mobilization. In this study, the SDF-1 concentration in healthy donors BM plasma decreased significantly after 5 days of G-CSF administration, with no obvious change of SDF-1 in the peripheral blood. We also observed a similar result by immunohistochemical staining on the BM biopsy slides. In vitro, mobilized BM plasma exhibited decreased chemotactic effect on CD34(+) cells, compared with steady-state BM plasma. MMP-9 protein and mRNA increased dramatically in the BM plasma in accordance with SDF-1 decrease. MMP-9 enriched supernatant from HT1080 cell-conditioned medium upregulated CXCR4 expression and the migration of BM CD34(+) cells toward SDF-1. SDF-1 was a substrate for MMP-9, furthermore, SDF-1 also stimulated MMP-9 proteolytic enzyme activity of BM CD34(+) cells, which facilitate HSPCs migration. In BALB/c mice, HSPCs mobilization was significantly inhibited by anti-SDF-1 antibodies or MMP inhibitor, o-phenanthroline. In conclusion, the degradation of BM SDF-1 by MMP-9 is a vital step in mobilization.

Retinoic acid decreases adherence of murine myeloid dendritic cells and increases production of matrix metalloproteinase-9

Myeloid dendritic cells (DC) are professional antigen presenting cells (APC) that migrate to secondary lymphoid tissues upon antigen stimulation, where they activate naïve T cells. Vitamin A is essential for normal immune function. We investigated the ability of all-trans retinoic acid (atRA), a bioactive metabolite of vitamin A, to modulate DC adhesion in culture. Male BALB/cJ mouse bone marrow cells cultured with granulocyte-macrophage colony-stimulating factor in the presence of retinoic acid receptor (RAR) alpha-specific antagonist showed an increase in the percentage of developing DC that remained adherent compared with cells rescued with atRA treatment from d 8 to 10 of culture (P < 0.05). Replacement of the RARalpha antagonist with atRA on d 8 of the culture period decreased DC surface expression of the adhesion molecule CD11a (P < 0.0001) but not the gene expression. Rescue with atRA also dramatically increased gene and protein expression of pro-matrix metalloproteinase (MMP)-9 (P < 0.05). However, gene expression and protein production of tissue inhibitor of metalloproteinase (TIMP)-1 was unaffected by atRA rescue, altering the molar ratio of secreted pro-MMP-9:TIMP-1, resulting in a fold excess of pro-MMP-9 to its primary inhibitor (P < 0.05). These data suggest that atRA is essential to augment MMP-9 expression in myeloid DC and can alter their surface expression of adhesion molecules.

The stem cell movement

Stem or progenitor cell-based strategies to combat ischemic heart disease and myocardial infarction, whether autologous transplantation or stimulation of resident populations, not only require detailed insight into transdifferentiation potential and functional coupling, but the efficacy of this approach is underpinned by the need to induce appropriate migration and homing to the site of injury. This review focuses on existing insights into the trafficking of stem cells in the context of cardiac regenerative therapy, with particular focus on the wide variety of potential sources of cells, critical factors that may regulate their migration, and how extrapolating from embryonic stem/progenitor cell behavior during cardiogenesis may reveal pathways implicit in the adult heart postinjury.

Migration across the sinusoidal endothelium regulates neutrophil mobilization in response to ELR + CXC chemokines

An increase in circulating neutrophils is a characteristic feature of many inflammatory reactions and is a result of the rapid mobilization of neutrophils from the bone marrow, driven by inflammatory mediators, including the ELR + CXC chemokines. In this paper, using a combination of light and electron microscopy and an in situ perfusion system of the rat femoral bone marrow, we examined this mobilization process in detail. We show that mobilization of neutrophils stimulated by the CXC chemokine, rat MIP-2, involves neutrophil migration from the haematopoietic compartment of the bone marrow across the bone marrow sinusoidal endothelium via a transcellular route. The critical role of the bone marrow sinusoidal endothelium in regulating neutrophil mobilization was demonstrated by artificially disrupting the bone marrow endothelial barrier by treatment with cytochalasin D, which results in the non-selective release of leucocytes from the bone marrow. In contrast, inhibiting the activity of p38 mitogen-activated protein kinase, inhibited both MIP-2 stimulated chemotaxis of bone marrow neutrophils in vitro and neutrophil mobilization in situ while, a broad spectrum matrix metalloproteinase inhibitor, BB94, had no effect on neutrophil mobilization. These results support the hypothesis that neutrophil migration drives their mobilization and highlights the function of the sinusoidal endothelium in regulating this process.

Mobilization of hematopoietic progenitor cells by yeast-derived beta-glucan requires activation of matrix metalloproteinase-9

Poly-(1,6)-beta-d-glucopyranosyl-(1,3)-beta-d-glucopyranose (PGG) beta-glucan is a soluble yeast-derived polysaccharide that has previously been shown to induce hematopoietic progenitor cell (HPC) mobilization. However, the mobilizing mechanism of action remains unknown. Here, we confirmed that PGG beta-glucan alone or in combination with granulocyte colony-stimulating factor (G-CSF) mobilizes HPC into the periphery. Optimal mobilizing effects were seen 24-48 hours after PGG beta-glucan doses of 4.8-9.6 mg/kg. Animals treated with G-CSF and PGG beta-glucan showed a collaborative effect in HPC mobilization compared with G-CSF treatment alone. Additional studies demonstrated that neither complement 3 nor complement receptor 3 played a role in this effect and that PGG beta-glucan treatment did not induce proinflammatory cytokine secretion. However, bone marrow cells from PGG beta-glucan-treated mice secreted abundant matrix metalloproteinase-9 (MMP-9), and PGG beta-glucan-induced HPC mobilization was abrogated in MMP-9 knockout mice. Moreover, we demonstrated that both hematopoietic and nonhematopoietic cells contributed to MMP-9 secretion upon PGG beta-glucan treatment. In addition, HPCs mobilized by PGG beta-glucan had similar levels of engraftment in host and lineage differentiation capability compared with those mobilized by G-CSF. Thus, PGG beta-glucan is an agent that enhances HPC mobilization and may improve the outcome of clinical stem cell transplantation.

Elevated serum levels of human matrix metalloproteinase-9 (MMP-9) during the induction of peripheral blood stem cell mobilization by granulocyte colony-stimulating factor (G-CSF)

To investigate the role of matrix metalloproteinases (MMPs) in the mobilization of peripheral blood stem cells stimulated by granulocyte colony-stimulating factor (G-CSF), we analyzed MMP serum levels in 11 healthy donors and 9 patients who had hematological malignancies or germ cell tumors. A dose of 5-10 microg/kg per day of G-CSF (lenograstim) was administered for 4-8 days to each subject. The serum levels of MMP-2, and MMP-9; interleukin-3, -6, -8, and -10; stem cell factor; interferon-gamma; and tumor necrosis factor-alpha were measured both before and during G-CSF administration. MMP-9 was found to be increased in both the cancer patients and the healthy donor group. In contrast, the levels of each of the other factors tested were unchanged. No significant positive correlation was observed between the MMP-9 levels and the number of CD34+ cells. Hence, we found no significant role for MMPs during the mobilization of peripheral blood stem cells stimulated by G-CSF.

A novel role of complement in mobilization: immunodeficient mice are poor granulocyte-colony stimulating factor mobilizers because they lack complement-activating immunoglobulins

Complement (C) and innate immunity emerge as important and underappreciated modulators of mobilization of hematopoietic stem/progenitor cells (HSPC). We reported that (a) C becomes activated in bone marrow (BM) during granulocyte-colony-stimulating factor (G-CSF)-induced mobilization by the classic immunoglobulin (Ig)-dependent pathway and that (b) C3 cleavage fragments increase the responsiveness of HSPC to a stromal derived factor-1 gradient. Since patients suffering from severe combined immunodeficiency (SCID) mobilize poorly, we hypothesized that this could be directly linked to the lack of C activating Ig in these patients. In the current study to better elucidate the role of C activation in HSPC mobilization, we mobilized mice that lack Ig (RAG2, SCID, and Jh) by G-CSF or zymosan, compounds that activate C by the classic Ig-dependent and the alternative Ig-independent pathways, respectively. In addition, we evaluated mobilization in C5-deficient animals. Mobilization was evaluated by measuring the number of colony-forming unit-granulocyte macrophage and leukocytes circulating in peripheral blood. We found that (a) G-CSF- but not zymosan-induced mobilization was severely reduced in RAG2, SCID, and Jh mice; (b) impaired G-CSF-induced mobilization was restored after infusion of purified wild-type Ig; and (c) mobilization was severely reduced in C5-deficient mice. These data provide strong evidence that the C system plays a pivotal role in mobilization of HSPC and that egress of HSPC from BM occurs as part of an immune response. Disclosure of potential conflicts of interest is found at the end of this article.

Src family kinase-mediated negative regulation of hematopoietic stem cell mobilization involves both intrinsic and microenvironmental factors

OBJECTIVE

The intracellular signals that contribute to granulocyte colony-stimulating factor (G-CSF) receptor induced stem cell mobilization are poorly characterized.

METHODS

We show enhanced G-CSF induced mobilization of stem cells in mice deficient in expression of Src family kinases (SFK-/-), which is associated with hypersensitivity of SFK-/- bone marrow cells to G-CSF as well as sustained activation of signal transducer and activator of transcription-3.

RESULTS

A proteome map of the bone marrow fluid derived from wild-type and SFK-/- mice revealed a significant global reduction in the number of proteins in SFK-/- mice compared to controls, which was associated with elevated matrix metalloproteinase-9 levels, reduced stromal-derived factor-1 expression, and enhanced breakdown of vascular cell adhesion molecule-1. Transplantation of wild-type or SFK-/- stem cells into wild-type mice and treatment with G-CSF recapitulated the G-CSF-induced increase in stem cell mobilization noted in SFK-/- nontransplanted mice; however, the increase was significantly less. G-CSF treatment of SFK-/- mice engrafted with wild-type stem cells also demonstrated a modest increase in stem cell mobilization compared to controls, however, the observed increase was greatest in mice completely devoid of SFKs.

CONCLUSIONS

These data suggest an involvement of both hematopoietic intrinsic and microenvironmental factors in Src kinase-mediated mobilization of stem cells and identify Src kinases as potential targets for modulating stem cell mobilization.