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

Evolutionarily conserved mechanisms regulating stress-induced neutrophil redistribution in fish

Introduction

Stress may pose a serious challenge to immune homeostasis. Stress however also may prepare the immune system for challenges such as wounding or infection, which are likely to happen during a fight or flight stress response.

Methods

In common carp (Cyprinus carpio L.) we studied the stress-induced redistribution of neutrophils into circulation, and the expression of genes encoding CXC chemokines known to be involved in the regulation of neutrophil retention (CXCL12) and redistribution (CXCL8), and their receptors (CXCR4 and CXCR1-2, respectively) in blood leukocytes and in the fish hematopoietic organ - the head kidney. The potential involvement of CXC receptors and stress hormone receptors in stress-induced neutrophil redistribution was determined by an in vivo study with selective CXCR inhibitors and antagonists of the receptors involved in stress regulation: glucocorticoid/mineralocorticoid receptors (GRs/MRs), adrenergic receptors (ADRs) and the melanocortin 2 receptor (MC2R).

Results

The stress-induced increase of blood neutrophils was accompanied by a neutrophil decrease in the hematopoietic organs. This increase was cortisol-induced and GR-dependent. Moreover, stress upregulated the expression of genes encoding CXCL12 and CXCL8 chemokines, their receptors, and the receptor for granulocytes colony-stimulation factor (GCSFR) and matrix metalloproteinase 9 (MMP9). Blocking of the CXCR4 and CXCR1 and 2 receptors with selective inhibitors inhibited the stress-induced neutrophil redistribution and affected the expression of genes encoding CXC chemokines and CXCRs as well as GCSFR and MMP9.

Discussion

Our data demonstrate that acute stress leads to the mobilization of the immune system, characterized by neutrophilia. CXC chemokines and CXC receptors are involved in this stress-induced redistribution of neutrophils from the hematopoietic tissue into the peripheral blood. This phenomenon is directly regulated by interactions between cortisol and the GR/MR. Considering the pivotal importance of neutrophilic granulocytes in the first line of defense, this knowledge is important for aquaculture, but will also contribute to the mechanisms involved in the stress-induced perturbation in neutrophil redistribution as often observed in clinical practice.

High ploidy large cytoplasmic megakaryocytes are hematopoietic stem cells regulators and essential for platelet production

Megakaryocytes (MK) generate platelets. Recently, we and others, have reported MK also regulate hematopoietic stem cells (HSC). Here we show high ploidy large cytoplasmic megakaryocytes (LCM) are critical negative regulators of HSC and critical for platelet formation. Using a mouse knockout model (Pf4-Srsf3^Δ/Δ) with normal MK numbers, but essentially devoid of LCM, we demonstrate a pronounced increase in BM HSC concurrent with endogenous mobilization and extramedullary hematopoiesis. Severe thrombocytopenia is observed in animals with diminished LCM, although there is no change in MK ploidy distribution, uncoupling endoreduplication and platelet production. When HSC isolated from a microenvironment essentially devoid of LCM reconstitute hematopoiesis in lethally irradiated mice, the absence of LCM increases HSC in BM, blood and spleen, and the recapitulation of thrombocytopenia. In contrast, following a competitive transplant using minimal numbers of WT HSC together with HSC from a microenvironment with diminished LCM, sufficient WT HSC-generated LCM regulates a normal HSC pool and prevents thrombocytopenia. Importantly, LCM are conserved in humans.

The extracellular microenvironment in immune dysregulation and inflammation in retinal disorders

Inherited retinal dystrophies (IRDs) as well as genetically complex retinal phenotypes represent a heterogenous group of ocular diseases, both on account of their phenotypic and genotypic characteristics. Therefore, overlaps in clinical features often complicate or even impede their correct clinical diagnosis. Deciphering the molecular basis of retinal diseases has not only aided in their disease classification but also helped in our understanding of how different molecular pathologies may share common pathomechanisms. In particular, these relate to dysregulation of two key processes that contribute to cellular integrity, namely extracellular matrix (ECM) homeostasis and inflammation. Pathological changes in the ECM of Bruch's membrane have been described in both monogenic IRDs, such as Sorsby fundus dystrophy (SFD) and Doyne honeycomb retinal dystrophy (DHRD), as well as in the genetically complex age-related macular degeneration (AMD) or diabetic retinopathy (DR). Additionally, complement system dysfunction and distorted immune regulation may also represent a common connection between some IRDs and complex retinal degenerations. Through highlighting such overlaps in molecular pathology, this review aims to illuminate how inflammatory processes and ECM homeostasis are linked in the healthy retina and how their interplay may be disturbed in aging as well as in disease.

Autoantigen characterization in the lower esophageal sphincter muscle of patients with achalasia

BACKGROUND

Serum anti-myenteric autoantibodies define autoimmune achalasia and tissue MMP-9 activity may locally process autoantigenic proteins in the muscle of the lower esophageal sphincter (LES) of achalasia patients.

METHODS

Biopsies of the LES muscle from 36 achalasia patients, 6 esophagogastric junction outflow obstruction (EGJOO) patients, and 16 transplant donors (TD) were compared in a blind cross-sectional study. Histological characteristics such as inflammation, fibrosis, presence of ganglion cells, cells of Cajal, GAD65, PNMA2, S-100, P substance, and MMP-9 proteoforms in tissue were assessed by H&E and Picrosirius Red staining and immunohistochemistry analysis. Anti-neuronal antibodies, onconeural antigens, recoverin, SOX-1, titin, zic4, GAD65, and Tr were evaluated by immunoblot/line assay.

KEY RESULTS

Tissue of achalasia patients had heterogeneous inflammatory infiltrates with fibrosis and contrasting higher levels of activated MMP-9, as compared with EGJOO and TD. Moreover, lower ganglion cell percentages and cell of Cajal percentages were determined in esophageal tissues of achalasia patients versus TD. The tissues of achalasia versus EGJOO patients had higher GAD65 and PNMA2 protein expression. Unexpectedly, these proteins were absent in TD tissue. S-100 and P substance had similar expression levels in tissues of achalasia patients versus TD and EGJOO. Most of the achalasia sera had anti-GAD65 (83%) and anti-PNMA2 (90%) autoantibodies versus EGJOO (17% and 33%, respectively) and healthy volunteers (10% and 0%, respectively).

CONCLUSIONS AND INFERENCES

Tissue-specific ectopic expression of GAD65 and PNMA/Ta2 and active MMP-9, associated with the presence of specific autoantibodies directed against these proteins, might participate in the pathophysiology of achalasia triggering and/or perpetuating autoimmune disease.

Mechanical Stretch Induced Skin Regeneration: Molecular and Cellular Mechanism in Skin Soft Tissue Expansion

Skin soft tissue expansion is one of the most basic and commonly used techniques in plastic surgery to obtain excess skin for a variety of medical uses. However, skin soft tissue expansion is faced with many problems, such as long treatment process, poor skin quality, high retraction rate, and complications. Therefore, a deeper understanding of the mechanisms of skin soft tissue expansion is needed. The key to skin soft tissue expansion lies in the mechanical stretch applied to the skin by an inflatable expander. Mechanical stimulation activates multiple signaling pathways through cellular adhesion molecules and regulates gene expression profiles in cells. Meanwhile, various types of cells contribute to skin expansion, including keratinocytes, dermal fibroblasts, and mesenchymal stem cells, which are also regulated by mechanical stretch. This article reviews the molecular and cellular mechanisms of skin regeneration induced by mechanical stretch during skin soft tissue expansion.

Neutrophil Homeostasis and Emergency Granulopoiesis: The Example of Systemic Juvenile Idiopathic Arthritis

Neutrophils are key pathogen exterminators of the innate immune system endowed with oxidative and non-oxidative defense mechanisms. More recently, a more complex role for neutrophils as decision shaping cells that instruct other leukocytes to fine-tune innate and adaptive immune responses has come into view. Under homeostatic conditions, neutrophils are short-lived cells that are continuously released from the bone marrow. Their development starts with undifferentiated hematopoietic stem cells that pass through different immature subtypes to eventually become fully equipped, mature neutrophils capable of launching fast and robust immune responses. During severe (systemic) inflammation, there is an increased need for neutrophils. The hematopoietic system rapidly adapts to this increased demand by switching from steady-state blood cell production to emergency granulopoiesis. During emergency granulopoiesis, the de novo production of neutrophils by the bone marrow and at extramedullary sites is augmented, while additional mature neutrophils are rapidly released from the marginated pools. Although neutrophils are indispensable for host protection against microorganisms, excessive activation causes tissue damage in neutrophil-rich diseases. Therefore, tight regulation of neutrophil homeostasis is imperative. In this review, we discuss the kinetics of neutrophil ontogenesis in homeostatic conditions and during emergency myelopoiesis and provide an overview of the different molecular players involved in this regulation. We substantiate this review with the example of an autoinflammatory disease, i.e. systemic juvenile idiopathic arthritis.

Structure-based molecular insights into matrix metalloproteinase inhibitors in cancer treatments

Protease inhibitors are of considerable interest as anticancer agents. Matrix metalloproteinases (MMPs) were the earliest type of proteases considered as anticancer targets. The developments of MMP inhibitors (MMPIs) by pharmaceutical companies can be dated from the early 1980s. Thus far, none of the over 50 MMPIs entering clinical trials have been approved. This work summarizes the reported studies on the structure of MMPs and complexes with ligands and inhibitors, based on which, the authors analyzed the clinical failures of MMPIs in a structural biological manner. Furthermore, MMPs were systematically compared with urokinase, a protease-generating plasmin, which plays similar pathological roles in cancer development; the reasons for the clinical successes of urokinase inhibitors and the clinical failures of MMPIs are discussed.

Signaling through TLR5 mitigates lethal radiation damage by neutrophil-dependent release of MMP-9

Acute radiation syndrome (ARS) is a major cause of lethality following radiation disasters. A TLR5 agonist, entolimod, is among the most powerful experimental radiation countermeasures and shows efficacy in rodents and non-human primates as a prophylactic (radioprotection) and treatment (radiomitigation) modality. While the prophylactic activity of entolimod has been connected to the suppression of radiation-induced apoptosis, the mechanism by which entolimod functions as a radiomitigator remains poorly understood. Uncovering this mechanism has significant and broad-reaching implications for the clinical development and improvement of TLR5 agonists for use as an effective radiation countermeasure in scenarios of mass casualty resulting from accidental exposure to ionizing radiation. Here, we demonstrate that in contrast to radioprotection, neutrophils are essential for the radiomitigative activity of entolimod in a mouse model of lethal ARS. Neutrophils express functional TLR5 and rapidly exit the bone marrow (BM), accumulate in solid tissues, and release MMP-9 following TLR5 stimulation which is accompanied by an increase in the number of active hematopoietic pluripotent precursors (HPPs) in the BM. Importantly, recombinant MMP-9 by itself has radiomitigative activity and, in the absence of neutrophils, accelerates the recovery of the hematopoietic system. Unveiling this novel TLR5-neutrophil-MMP-9 axis of radiomitigation opens new opportunities for the development of efficacious radiation countermeasures to treat ARS following accidental radiation disasters.

Role of macrophages and phagocytes in orchestrating normal and pathologic hematopoietic niches

The bone marrow (BM) contains a mosaic of niches specialized in supporting different maturity stages of hematopoietic stem and progenitor cells such as hematopoietic stem cells and myeloid, lymphoid, and erythroid progenitors. Recent advances in BM imaging and conditional gene knockout mice have revealed that niches are a complex network of cells of mesenchymal, endothelial, neuronal, and hematopoietic origins, together with local physicochemical parameters. Within these complex structures, phagocytes, such as neutrophils, macrophages, and dendritic cells, all of which are of hematopoietic origin, have been found to be important in regulating several niches in the BM, including hematopoietic stem cell niches, erythropoietic niches, and niches involved in endosteal bone formation. There is also increasing evidence that these macrophages have an important role in adapting hematopoiesis, erythropoiesis, and bone formation in response to inflammatory stressors and play a key part in maintaining the integrity and function of these. Likewise, there is also accumulating evidence that subsets of monocytes, macrophages, and other phagocytes contribute to the progression and response to treatment of several lymphoid malignancies such as multiple myeloma, Hodgkin lymphoma, and non-Hodgkin lymphoma, as well as lymphoblastic leukemia, and may also play a role in myelodysplastic syndrome and myeloproliferative neoplasms associated with Noonan syndrome and aplastic anemia. In this review, the potential functions of macrophages and other phagocytes in normal and pathologic niches are discussed, as are the challenges in studying BM and other tissue-resident macrophages at the molecular level.

A Review of Advances in Hematopoietic Stem Cell Mobilization and the Potential Role of Notch2 Blockade

Hematopoietic stem cell (HSC) transplantation can be a potential cure for hematological malignancies and some nonhematologic diseases. Hematopoietic stem and progenitor cells (HSPCs) collected from peripheral blood after mobilization are the primary source to provide HSC transplantation. In most of the cases, mobilization by the cytokine granulocyte colony-stimulating factor with chemotherapy, and in some settings, with the CXC chemokine receptor type 4 antagonist plerixafor, can achieve high yield of hematopoietic progenitor cells (HPCs). However, adequate mobilization is not always successful in a significant portion of donors. Research is going on to find new agents or strategies to increase HSC mobilization. Here, we briefly review the history of HSC transplantation, current mobilization regimens, some of the novel agents that are under investigation for clinical practice, and our recent findings from animal studies regarding Notch and ligand interaction as potential targets for HSPC mobilization.

Predicting the Key Genes Involved in Aortic Valve Calcification Through Integrated Bioinformatics Analysis

Background: Valvular heart disease is obtaining growing attention in the cardiovascular field and it is believed that calcific aortic valve disease (CAVD) is the most common valvular heart disease (VHD) in the world. CAVD does not have a fully effective treatment to delay its progression and the specific molecular mechanism of aortic valve calcification remains unclear.

Materials and Methods: We obtained the gene expression datasets GSE12644 and GSE51472 from the public comprehensive free database GEO. Then, a series of bioinformatics methods, such as GO and KEGG analysis, STING online tool, Cytoscape software, were used to identify differentially expressed genes in CAVD and healthy controls, construct a PPI network, and then identify key genes. In addition, immune infiltration analysis was used via CIBERSORT to observe the expression of various immune cells in CAVD.

Results: A total of 144 differential expression genes were identified in the CAVD samples in comparison with the control samples, including 49 up-regulated genes and 95 down-regulated genes. GO analysis of DEGs were most observably enriched in the immune response, signal transduction, inflammatory response, proteolysis, innate immune response, and apoptotic process. The KEGG analysis revealed that the enrichment of DEGs in CAVD were remarkably observed in the chemokine signaling pathway, cytokine-cytokine receptor interaction, and PI3K-Akt signaling pathway. Chemokines CXCL13, CCL19, CCL8, CXCL8, CXCL16, MMP9, CCL18, CXCL5, VCAM1, and PPBP were identified as the hub genes of CAVD. It was macrophages that accounted for the maximal proportion among these immune cells. The expression of macrophages M0, B cells memory, and Plasma cells were higher in the CAVD valves than in healthy valves, however, the expression of B cells naïve, NK cells activated, and macrophages M2 were lower.

Conclusion: We detected that chemokines CXCL13, CXCL8, CXCL16, and CXCL5, and CCL19, CCL8, and CCL18 are the most important markers of aortic valve disease. The regulatory macrophages M0, plasma cells, B cells memory, B cells naïve, NK cells activated, and macrophages M2 are probably related to the occurrence and the advancement of aortic valve stenosis. These identified chemokines and these immune cells may interact with a subtle adjustment relationship in the development of calcification in CAVD.

Lubricin Contributes to Homeostasis of Articular Cartilage by Modulating Differentiation of Superficial Zone Cells

Lubricin encoded by the proteoglycan 4 (Prg4) gene is produced from superficial zone (SFZ) cells of articular cartilage and synoviocytes, which is indispensable for lubrication of joint surfaces. Loss-of-function of human and mouse Prg4 results in early-onset arthropathy accompanied by lost SFZ cells and hyperplastic synovium. Here, we focused on increases in the thickness of articular cartilage in Prg4-knockout joints and analyzed the underlying mechanisms. In the late stage of articular cartilage development, the articular cartilage was thickened at 2 to 4 weeks and the SFZ disappeared at 8 weeks in Prg4-knockout mice. Similar changes were observed in cultured Prg4-knockout femoral heads. Cell tracking showed that Prg4-knockout SFZ cells at 1 week of age expanded to deep layers after 1 week. In in vitro experiments, overexpression of Prg4 lacking a mucin-like domain suppressed differentiation of ATDC5 cells markedly, whereas pellets of Prg4-knockout SFZ cells showed enhanced differentiation. RNA sequencing identified matrix metalloproteinase 9 (Mmp9) as the top upregulated gene by Prg4 knockout. Mmp9 expressed in the SFZ was further induced in Prg4-knockout mice. The increased expression of Mmp9 by Prg4 knockout was canceled by IκB kinase (IKK) inhibitor treatment. Phosphorylation of Smad2 was also enhanced in Prg4-knockout cell pellets, which was canceled by the IKK inhibitor. Expression of Mmp9 and phosphorylated Smad2 during articular cartilage development was enhanced in Prg4-knockout joints. Lubricin contributes to homeostasis of articular cartilage by suppressing differentiation of SFZ cells, and the nuclear factor-kappa B-Mmp9-TGF-β pathway is probably responsible for the downstream action of lubricin. © 2020 American Society for Bone and Mineral Research (ASBMR).

Proteases and Their Modulators in Cancer Therapy: Challenges and Opportunities

Proteostasis is the process of regulating intracellular proteins to maintain the balance of the cell proteome, which is crucial for cancer cell survival. Several proteases located in the cytoplasm, mitochondria, lysosome, and extracellular environment have been identified as potential antitumor targets because of their involvement in proteostasis. Although the discovery of small-molecule inhibitors targeting proteases faces particular challenges, rapid advances in chemical biology and structural biology, and the new technology of drug discovery have facilitated the development of promising protease modulators. In this review, the protein structure and function of important tumor-related proteases and their inhibitors are presented. We also provide a prospective on advances and the outlook of new drug strategies that target these proteases.

Concerted actions by MMPs, ADAMTS and serine proteases during remodeling of the cartilage callus into bone during osseointegration of hip implants

INTRODUCTION

Although the number of patients undergoing total hip arthroplasty is constantly on the rise, we only have limited knowledge of the molecular mechanisms necessary for successful osseointegration of implants or the reasons why some fail. Understanding the spatiotemporal characteristics of signaling pathways involved in bone healing of implants is therefore of particular importance for our ability to identify factors causing implants to fail. The current study investigated the role of three families of proteases, i.e. MMPs (matrix metalloproteinases), ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) and serine proteases, as well as their endogenous inhibitors during osseointegration of hip implants that have endured two decades of use without clinical or radiological signs of loosening.

MATERIALS AND METHODS

Twenty-four patients that had undergone primary THA due to one-sided osteoarthritis (OA) were monitored during 18 years (Y) with repeated measurements of plasma biomarkers, clinical variables and radiographs. All implants were clinically and radiographically well-fixed throughout the follow-up. Eighty-one healthy donors divided in three gender and age-matched groups and twenty OA patients awaiting THA, served as controls. Plasma was analyzed for MMP-1, -2, -3, -8, -9, -10, -13, -14, tissue inhibitor of metalloproteinase (TIMP)-1, -2, -3, ADAMTS4, ADAMTS5, the serine proteases neutrophil elastase (NE), proteinase 3 (PR3) and their endogenous inhibitors, secretory leucocyte proteinase inhibitor (SLPI), trappin-2/elafin and serpina1 (α-1 antitrypsin). Cartilage turnover was monitored using two markers of cartilage synthesis, type II procollagen and PIICP (procollagen II C-terminal propeptide), and two markers of cartilage degradation, CTX-II (C-terminal telopeptide fragments of type II collagen) and split products of aggrecan (G1-IGD-G2).

RESULTS

MMP-1, MMP-9, ADAMTS4, NE and PR3 were above healthy in presurgery OA patients but returned to the level of healthy within 6 weeks (W) after surgery. MMPs and serine proteases were counter-regulated during this phase by TIMP-1, SLPI and trappin-2/elafin. Type II procollagen, PIICP and CTX-II increased to a peak 6 W after surgery with a gradual return to the level of controls within weeks. Significant increases by MMP-8, MMP-9, ADAMTS4, ADAMTS5, NE, PR3 and the protease inhibitors, TIMP-3 and serpina1, were seen 5 Y after hip arthroplasty paralleled by a sharp increase in the levels of the cartilage degradation markers, CTX-II and G1-IGD-G2. All the above mediators were normalized before 18 Y, except MMP-1 and MMP-9 that remained above healthy at 18 Y. MMP-14 increased immediately after surgery and remained elevated until 5 Y postsurgery before returning to the level of controls at 7 Y.

CONCLUSION

Notwithstanding temporal differences, the molecular processes of bone repair in arthroplasty patients show great spatial similarities with the classical phases of fracture repair as previously shown in animal models. Cartilagenous callus, produced and remodeled early after hip arthroplasty, is replaced with bone 5 Y to7 Y after surgery by the concerted actions of MMP-8, MMP-9, ADAMTS4, ADAMTS5, NE and PR3, thus suggesting that a complex regulatory cross-talk may exist between different families of proteases during this transitional phase of cartilage degradation. Regulation and fine-tuning of cartilage remodeling by MMPs and ADAMTS is controlled by TIMP-3 whereas serine proteases are regulated by serpina1. Increased MMP-1 and MMP-9 beyond 10Y post-THA support a role during coupled bone remodeling.

Citrullination as a novel posttranslational modification of matrix metalloproteinases

Matrix metalloproteinases (MMPs) are enzymes with critical roles in biology and pathology. Glycosylation, nitrosylation and proteolysis are known posttranslational modifications (PTMs) regulating intrinsically the activities of MMPs. We discovered MMP citrullination by peptidyl arginine deiminases (PADs) as a new PTM. Upon hypercitrullination, MMP-9 acquired a higher affinity for gelatin than control MMP-9. Furthermore, hypercitrullinated proMMP-9 was more efficiently activated by MMP-3 compared to control MMP-9. JNJ0966, a specific therapeutic inhibitor of MMP-9 activation, inhibited the activation of hypercitrullinated proMMP-9 by MMP-3 significantly less in comparison with control proMMP-9. The presence of citrullinated/homocitrullinated MMP-9 was detected in vivo in neutrophil-rich sputum samples of cystic fibrosis patients. In addition to citrullination of MMP-9, we report efficient citrullination of MMP-1 and lower citrullination levels of MMP-3 and MMP-13 by PAD2 in vitro. In conclusion, citrullination of MMPs is a new PTM worthy of additional biochemical and biological studies.

Challenges with matrix metalloproteinase inhibition and future drug discovery avenues

INTRODUCTION

Matrix metalloproteinases have been in the scope of pharmaceutical drug discovery for decades as promising targets for drug development. Until present, no modulator of the enzyme class survived clinical trials, all failing for various reasons. Nevertheless, the target family did not lose its attractiveness and there is ever more evidence that MMP modulators are likely to overcome the hurdles and result in successful clinical therapies.

AREAS COVERED

This review provides an overview of past efforts that were taken in the development of MMP inhibitors and insight into promising strategies that might enable drug discovery in the field in the future. Small molecule inhibitors as well as biomolecules are reviewed.

EXPERT OPINION

Despite the lack of successful clinical trials in the past, there is ongoing research in the field of MMP modulation, proving the target class has not lost its appeal to pharmaceutical research. With ever-growing insights from different scientific fields that shed light on previously unknown correlations, it is now time to use synergies deriving from biological knowledge, chemical structure generation, and clinical application to reach the ultimate goal of bringing MMP derived drugs on a broad front for the benefit of patients into therapeutic use.

Bivalent Inhibitor with Selectivity for Trimeric MMP-9 Amplifies Neutrophil Chemotaxis and Enables Functional Studies on MMP-9 Proteoforms

A fundamental part of the immune response to infection or injury is leukocyte migration. Matrix metalloproteinases (MMPs) are a class of secreted or cell-bound endopeptidases, implicated in every step of the process of inflammatory cell migration. Hence, specific inhibition of MMPs is an interesting approach to control inflammation. We evaluated the potential of a bivalent carboxylate inhibitor to selectively inhibit the trimeric proteoform of MMP-9 and compared this with a corresponding monovalent inhibitor. The bivalent inhibitor efficiently inhibited trimeric MMP-9 (IC₅₀ = 0.1 nM), with at least 500-fold selectivity for MMP-9 trimers over monomers. Surprisingly, in a mouse model for chemotaxis, the bivalent inhibitor amplified leukocyte influxes towards lipopolysaccharide-induced inflammation. We verified by microscopic and flow cytometry analysis increased amounts of neutrophils. In a mouse model for endotoxin shock, mice treated with the bivalent inhibitor had significantly increased levels of MMP-9 in plasma and lungs, indicative for increased inflammation. In conclusion, we propose a new role for MMP-9 trimers in tempering excessive neutrophil migration. In addition, we have identified a small molecule inhibitor with a high selectivity for the trimeric proteoform of MMP-9, which will allow further research on the functions of MMP-9 proteoforms.

Etoposide-mediated interleukin-8 secretion from bone marrow stromal cells induces hematopoietic stem cell mobilization

Background

We assessed the mechanism of hematopoietic stem cell (HSC) mobilization using etoposide with granulocyte-colony stimulating factor (G-CSF), and determined how this mechanism differs from that induced by cyclophosphamide with G-CSF or G-CSF alone.

Methods

We compared the clinical features of 173 non-Hodgkin’s lymphoma patients who underwent autologous peripheral blood stem cell transplantation (auto-PBSCT). Additionally, we performed in vitro experiments to assess the changes in human bone marrow stromal cells (hBMSCs), which support the HSCs in the bone marrow (BM) niche, following cyclophosphamide or etoposide exposure. We also performed animal studies under standardized conditions to ensure the following: exclude confounding factors, mimic the conditions in clinical practice, and identify the changes in the BM niche caused by etoposide-induced chemo-mobilization or other mobilization methods.

Results

Retrospective analysis of the clinical data revealed that the etoposide with G-CSF mobilization group showed the highest yield of CD34+ cells and the lowest change in white blood cell counts during mobilization. In in vitro experiments, etoposide triggered interleukin (IL)-8 secretion from the BMSCs and caused long-term BMSC toxicity. To investigate the manner in which the hBMSC-released IL-8 affects hHSCs in the BM niche, we cultured hHSCs with or without IL-8, and found that the number of total, CD34+, and CD34+/CD45- cells in IL-8-treated cells was significantly higher than the respective number in hHSCs cultured without IL-8 (p = 0.014, 0.020, and 0.039, respectively). Additionally, the relative expression of CXCR2 (an IL-8 receptor), and mTOR and c-MYC (components of IL-8-related signaling pathways) increased 1 h after IL-8 treatment. In animal studies, the etoposide with G-CSF mobilization group presented higher IL-8-related cytokine and MMP9 expression and lower SDF-1 expression in the BM, compared to the groups not treated with etoposide.

Conclusion

Collectively, the unique mechanism of etoposide with G-CSF-induced mobilization is associated with IL-8 secretion from the BMSCs, which is responsible for the enhanced proliferation and mobilization of HSCs in the bone marrow; this was not observed with mobilization using cyclophosphamide with G-CSF or G-CSF alone. However, the long-term toxicity of etoposide toward BMSCs emphasizes the need for the development of more efficient and safe chemo-mobilization strategies.

Matrix metalloproteinase-9 (MMP-9) and its inhibitors in cancer: A minireview

Matrix metalloproteinases (MMPs) are zinc dependent proteolytic metalloenzyme. MMP-9 is one of the most complex forms of matrix metalloproteinases. MMP-9 has the ability to degrade the extracellular matrix (ECM) components and has important role in the pathophysiological functions. Overexpression and dysregulation of MMP-9 is associated with various diseases. Thus, regulation and inhibition of MMP-9 is an important therapeutic approach for combating various diseases including cancer. Inhibitors of MMP-9 can be used as anticancer agents. Till date no selective MMP-9 inhibitors passed the clinical trials. In this review the structure, activation, function and inhibitors of MMP-9 are mainly focused. Some highly active and/or selective MMP-9 inhibitors have been discussed which may be helpful to explore the structural significance of MMP-9 inhibitors. This study may be useful to design new potent and selective MMP-9 inhibitors against cancer in future.

Thrombopoietin enhances hematopoietic stem and progenitor cell homing by impeding matrix metalloproteinase 9 expression

We reported a novel function of recombinant human thrombopoietin (TPO) in increasing hematopoietic stem and progenitor cell (HSPC) homing to the bone marrow (BM). Single doses of TPO treatment to the recipients immediately after BM transplantation showed significantly improved homing of HSPCs to the BM, which subsequently resulted in enhanced short‐ and long‐term engraftment of HSPCs in mice. We found that TPO could downregulate the expression and secretion of matrix metalloproteinase 9 in BM cells. As a result, SDF‐1α level was increased in the BM niche. Blocking the interaction of SDF‐1α and CXCR4 on HSPCs by using AMD3100 could significantly reverse the TPO‐enhanced HSPC homing effect. More importantly, a single dose of TPO remarkably promoted human HSPC homing and subsequent engraftment to the BM of nonobese diabetic/severe combined immunodeficiency mice. We then performed a clinical trial to evaluate the effect of TPO treatment in patients receiving haploidentical BM and mobilized peripheral blood transplantation. Surprisingly, single doses of TPO treatment to patients followed by hematopoietic stem cell transplantation significantly improved platelet engraftment in the cohort of patients with severe aplastic anemia (SAA). The mean volume of platelet and red blood cell transfusion was remarkably reduced in the cohort of patients with SAA or hematological malignancies receiving TPO treatment. Thus, our data provide a simple, feasible, and efficient approach to improve clinical outcomes in patients with allogenic hematopoietic stem cell transplantation. The clinical trial was registered in the Chinese Clinical Trial Registry website (http://www.chictr.org.cn) as ChiCTR‐OIN‐1701083.

Mobilized peripheral blood: an updated perspective

Enforced egress of hematopoietic stem cells (HSCs) out of the bone marrow (BM) into the peripheral circulation, termed mobilization, has come a long way since its discovery over four decades ago. Mobilization research continues to be driven by the need to optimize the regimen currently available in the clinic with regard to pharmacokinetic and pharmacodynamic profile, costs, and donor convenience. In this review, we describe the most recent findings in the field and how we anticipate them to affect the development of mobilization strategies in the future. Furthermore, the significance of mobilization beyond HSC collection, i.e. for chemosensitization, conditioning, and gene therapy as well as a means to study the interactions between HSCs and their BM microenvironment, is reviewed. Open questions, controversies, and the potential impact of recent technical progress on mobilization research are also highlighted.

MMP9 inhibition increases erythropoiesis in RPS14-deficient del(5q) MDS models through suppression of TGF-β pathways

The del(5q) myelodysplastic syndrome (MDS) is a distinct subtype of MDS, associated with deletion of the ribosomal protein S14 (RPS14) gene that results in macrocytic anemia. This study sought to identify novel targets for the treatment of patients with del(5q) MDS by performing an in vivo drug screen using an rps14-deficient zebrafish model. From this, we identified the secreted gelatinase matrix metalloproteinase 9 (MMP9). MMP9 inhibitors significantly improved the erythroid defect in rps14-deficient zebrafish. Similarly, treatment with MMP9 inhibitors increased the number of colony forming unit-erythroid colonies and the CD71+ erythroid population from RPS14 knockdown human BMCD34+ cells. Importantly, we found that MMP9 expression is upregulated in RPS14-deficient cells by monocyte chemoattractant protein 1. Double knockdown of MMP9 and RPS14 increased the CD71+ population compared with RPS14 single knockdown, suggesting that increased expression of MMP9 contributes to the erythroid defect observed in RPS14-deficient cells. In addition, transforming growth factor β (TGF-β) signaling is activated in RPS14 knockdown cells, and treatment with SB431542, a TGF-β inhibitor, improved the defective erythroid development of RPS14-deficient models. We found that recombinant MMP9 treatment decreases the CD71+ population through increased SMAD2/3 phosphorylation, suggesting that MMP9 directly activates TGF-β signaling in RPS14-deficient cells. Finally, we confirmed that MMP9 inhibitors reduce SMAD2/3 phosphorylation in RPS14-deficient cells to rescue the erythroid defect. In summary, these study results support a novel role for MMP9 in the pathogenesis of del(5q) MDS and the potential for the clinical use of MMP9 inhibitors in the treatment of patients with del(5q) MDS.

The Rebirth of Matrix Metalloproteinase Inhibitors: Moving Beyond the Dogma

The pursuit of matrix metalloproteinase (MMP) inhibitors began in earnest over three decades ago. Initial clinical trials were disappointing, resulting in a negative view of MMPs as therapeutic targets. As a better understanding of MMP biology and inhibitor pharmacokinetic properties emerged, it became clear that initial MMP inhibitor clinical trials were held prematurely. Further complicating matters were problematic conclusions drawn from animal model studies. The most recent generation of MMP inhibitors have desirable selectivities and improved pharmacokinetics, resulting in improved toxicity profiles. Application of selective MMP inhibitors led to the conclusion that MMP-2, MMP-9, MMP-13, and MT1-MMP are not involved in musculoskeletal syndrome, a common side effect observed with broad spectrum MMP inhibitors. Specific activities within a single MMP can now be inhibited. Better definition of the roles of MMPs in immunological responses and inflammation will help inform clinic trials, and multiple studies indicate that modulating MMP activity can improve immunotherapy. There is a U.S. Food and Drug Administration (FDA)-approved MMP inhibitor for periodontal disease, and several MMP inhibitors are in clinic trials, targeting a variety of maladies including gastric cancer, diabetic foot ulcers, and multiple sclerosis. It is clearly time to move on from the dogma of viewing MMP inhibition as intractable.

Gelatinase B/matrix metalloproteinase-9 and other neutrophil proteases switch off interleukin-2 activity

Interleukin 2 (IL-2) is critical for T cell development and homeostasis, being a key regulator of adaptive immune responses in autoimmunity, hypersensitivity reactions and cancer. Therefore, its abundance in serum and peripheral tissues needs tight control. Here, we described a new mechanism contributing to the immunobiology of IL-2. We demonstrated, both in biochemical and cell-based assays, that IL-2 is subject to proteolytic processing by neutrophil matrix metalloproteinase-9 (MMP-9). IL-2 fragments produced after cleavage by MMP-9 remained linked by a disulfide bond and displayed a reduced affinity for all IL-2 receptor subunits and a distinct pattern and timing of signal transduction. Stimulation of IL-2-dependent cells, including murine CTLL-2 and primary human regulatory T cells, with cleaved IL-2 resulted in significantly decreased proliferation. The concerted action of neutrophil proteases destroyed IL-2. Our data suggest that in neutrophil-rich inflammatory conditions in vivo, neutrophil MMP-9 may reduce the abundance of signaling-competent IL-2 and generate a fragment that competes with IL-2 for receptor binding, whereas the combined activity of granulocyte proteases has the potential to degrade and thus eliminate bioavailable IL-2.

Inhibitory Antibodies Designed for Matrix Metalloproteinase Modulation

The family of matrix metalloproteinases (MMPs) consists of a set of biological targets that are involved in a multitude of severe pathogenic events such as different forms of cancers or arthritis. Modulation of the target class with small molecule drugs has not led to the anticipated success until present, as all clinical trials failed due to unacceptable side effects or a lack of therapeutic outcome. Monoclonal antibodies offer a tremendous therapeutic potential given their high target selectivity and good pharmacokinetic profiles. For the treatment of a variety of diseases there are already antibody therapies available and the number is increasing. Recently, several antibodies were developed for the selective inhibition of single MMPs that showed high potency and were therefore investigated in in vivo studies with promising results. In this review, we highlight the progress that has been achieved toward the design of inhibitory antibodies that successfully modulate MMP-9 and MMP-14.

Mechanisms of Action of Novel Drugs Targeting Angiogenesis-Promoting Matrix Metalloproteinases

Angiogenesis is facilitated by the proteolytic activities of members of the matrix metalloproteinase (MMP) family. More specifically, MMP-9 and MT1-MMP directly regulate angiogenesis, while several studies indicate a role for MMP-2 as well. The correlation of MMP activity to tumor angiogenesis has instigated numerous drug development programs. However, broad-based and Zn²⁺-chelating MMP inhibitors have fared poorly in the clinic. Selective MMP inhibition by antibodies, biologicals, and small molecules has utilized unique modes of action, such as (a) binding to protease secondary binding sites (exosites), (b) allosterically blocking the protease active site, or (c) preventing proMMP activation. Clinical trials have been undertaken with several of these inhibitors, while others are in advanced pre-clinical stages. The mechanistically non-traditional MMP inhibitors offer treatment strategies for tumor angiogenesis that avoid the off-target toxicities and lack of specificity that plagued Zn²⁺-chelating inhibitors.

Targeting VLA4 integrin and CXCR2 mobilizes serially repopulating hematopoietic stem cells

Mobilized peripheral blood has become the primary source of hematopoietic stem and progenitor cells (HSPCs) for stem cell transplantation, with a five-day course of granulocyte colony stimulating factor (G-CSF) as the most common regimen used for HSPC mobilization. The CXCR4 inhibitor, plerixafor, is a more rapid mobilizer, yet not potent enough when used as a single agent, thus emphasizing the need for faster acting agents with more predictable mobilization responses and fewer side effects. We sought to improve hematopoietic stem cell transplantation by developing a new mobilization strategy in mice through combined targeting of the chemokine receptor CXCR2 and the very late antigen 4 (VLA4) integrin. Rapid and synergistic mobilization of HSPCs along with an enhanced recruitment of true HSCs was achieved when a CXCR2 agonist was co-administered in conjunction with a VLA4 inhibitor. Mechanistic studies revealed involvement of CXCR2 expressed on BM stroma in addition to stimulation of the receptor on granulocytes in the regulation of HSPC localization and egress. Given the rapid kinetics and potency of HSPC mobilization provided by the VLA4 inhibitor and CXCR2 agonist combination in mice compared to currently approved HSPC mobilization methods, it represents an exciting potential strategy for clinical development in the future.

Cytokine-induced hematopoietic stem and progenitor cell mobilization: unraveling interactions between stem cells and their niche

Peripheral blood hematopoietic stem and progenitor cells (HSPCs), mobilized by granulocyte colony‐stimulating factor, are widely used as a source for both autologous and allogeneic stem cell transplantation. The use of mobilized HSPCs has several advantages over traditional bone marrow–derived HSPCs, including a less invasive harvesting process for the donor, higher HSPC yields, and faster hematopoietic reconstitution in the recipient. For years, the mechanisms by which cytokines and other agents mobilize HSPCs from the bone marrow were not fully understood. The field of stem cell mobilization research has advanced significantly over the past decade, with major breakthroughs in the elucidation of the complex mechanisms that underlie stem cell mobilization. In this review, we provide an overview of the events that underlie HSPC mobilization and address the relevant cellular and molecular components of the bone marrow niche. Furthermore, current and future mobilizing agents will be discussed.

Peripheral blood stem cell mobilization; a look ahead

THE PURPOSE OF REVIEW

Mobilized peripheral blood is the predominant source of stem and progenitor cells for hematologic transplantation. Successful transplant requires sufficient stem cells of high enough quality to recapitulate lifelong hematopoiesis, but in some patients and normal donors, reaching critical threshold stem cell numbers are difficult to achieve. Novel strategies, particularly those offering rapid mobilization and reduced costs, remains an area of interest.This review summarizes critical scientific underpinnings in understanding the process of stem cell mobilization, with a focus on new or improved strategies for their efficient collection and engraftment.

RECENT FINDINGS

Studies are described that provide new insights into the complexity of stem cell mobilization. Agents that target new pathways such HSC egress, identify strategies to collect more potent competing HSC and new methods to optimize stem cell collection and engraftment are being evaluated.

SUMMARY

Agents and more effective strategies that directly address the current shortcomings of hematopoietic stem cell mobilization and transplantation and offer the potential to facilitate collection and expand use of mobilized stem cells have been identified.

The ectoenzyme-side of matrix metalloproteinases (MMPs) makes inflammation by serum amyloid A (SAA) and chemokines go round

During an inflammatory response, a large number of distinct mediators appears in the affected tissues or in the blood circulation. These include acute phase proteins such as serum amyloid A (SAA), cytokines and chemokines and proteolytic enzymes. Although these molecules are generated within a cascade sequence in specific body compartments allowing for independent action, their co-appearance in space and time during acute or chronic inflammation points toward important mutual interactions. Pathogen-associated molecular patterns lead to fast induction of the pro-inflammatory endogenous pyrogens, which are evoking the acute phase response. Interleukin-1, tumor necrosis factor-α and interferons simultaneously trigger different cell types, including leukocytes, endothelial cells and fibroblasts for tissue-specific or systemic production of chemokines and matrix metalloproteinases (MMPs). In addition, SAA induces chemokines and both stimulate secretion of MMPs from multiple cell types. As a consequence, these mediators may cooperate to enhance the inflammatory response. Indeed, SAA synergizes with chemokines to increase chemoattraction of monocytes and granulocytes. On the other hand, MMPs post-translationally modify chemokines and SAA to reduce their activity. Indeed, MMPs internally cleave SAA with loss of its cytokine-inducing and direct chemotactic potential whilst retaining its capacity to synergize with chemokines in leukocyte migration. Finally, MMPs truncate chemokines at their NH₂- or COOH-terminal end, resulting in reduced or enhanced chemotactic activity. Therefore, the complex interactions between chemokines, SAA and MMPs either maintain or dampen the inflammatory response.

Monoclonal antibodies against metzincin targets

The metzincin clan of metalloproteinases includes the MMP, disintegrin and metalloproteinase (ADAM) and ADAM with thrombospondin motifs families, which cleave extracellular targets in a wide range of (patho)physiological processes. Antibodies constitute a powerful tool to modulate the activity of these enzymes for both therapeutic and research purposes. In this review, we give an overview of monoclonal antibodies (mAbs) that have been tested in preclinical disease models, human trials and important studies of metzincin structure and function. Initial attempts to develop therapeutic small molecule inhibitors against MMPs were hampered by structural similarities between metzincin active sites and, consequently, off-target effects. Therefore, more recently, mAbs have been developed that do not bind to the active site but bind to surface-exposed loops that are poorly conserved in closely related family members. Inhibition of protease activity by these mAbs occurs through a variety of mechanisms, including (i) barring access to the active site, (ii) disruption of exosite binding, and (iii) prevention of protease activation. These different modes of inhibition are discussed in the context of the antibodies' potency, selectivity and, importantly, the effects in models of disease and clinical trials. In addition, various innovative strategies that were used to generate anti-metzincin mAbs are discussed. LINKED ARTICLES: This article is part of a themed section on Translating the Matrix. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.1/issuetoc.

The impact of hypoxic-ischemic brain injury on stem cell mobilization, migration, adhesion, and proliferation

Neonatal hypoxic-ischemic encephalopathy continues to be a significant cause of death or neurodevelopmental delays despite standard use of therapeutic hypothermia. The use of stem cell transplantation has recently emerged as a promising supplemental therapy to further improve the outcomes of infants with hypoxic-ischemic encephalopathy. After the injury, the brain releases several chemical mediators, many of which communicate directly with stem cells to encourage mobilization, migration, cell adhesion and differentiation. This manuscript reviews the biomarkers that are released from the injured brain and their interactions with stem cells, providing insight regarding how their upregulation could improve stem cell therapy by maximizing cell delivery to the injured tissue.

Role of Mitochondrial Reactive Oxygen Species in the Activation of Cellular Signals, Molecules, and Function

Mitochondria are a major source of intracellular energy and reactive oxygen species in cells, but are also increasingly being recognized as a controller of cell death. Here, we review evidence of signal transduction control by mitochondrial superoxide generation via the nuclear factor-κB (NF-κB) and GATA signaling pathways. We have also reviewed the effects of ROS on the activation of MMP and HIF. There is significant evidence to support the hypothesis that mitochondrial superoxide can initiate signaling pathways following transport into the cytosol. In this study, we provide evidence of TATA signal transductions by mitochondrial superoxide. Oxidative phosphorylation via the electron transfer chain, glycolysis, and generation of superoxide from mitochondria could be important factors in regulating signal transduction, cellular homeostasis, and cell death.

Tumor p38MAPK signaling enhances breast carcinoma vascularization and growth by promoting expression and deposition of pro-tumorigenic factors

The breast carcinoma microenvironment strikingly influences cancer progression and response to therapy. Various cell types in the carcinoma microenvironment show significant activity of p38 mitogen-activated protein kinase (MAPK), although the role of p38MAPK in breast cancer progression is still poorly understood. The present study examined the contribution of tumor p38MAPK to breast carcinoma microenvironment and metastatic capacity. Inactivation of p38MAPK signaling in metastatic breast carcinoma cells was achieved by forced expression of the kinase-inactive mutant of p38/MAPK14 (a dominant-negative p38, dn-p38). Disruption of tumor p38MAPK signaling reduced growth and metastases of breast carcinoma xenografts. Importantly, dn-p38 markedly decreased tumor blood-vessel density and lumen sizes. Mechanistic studies revealed that p38 controls expression of pro-angiogenic extracellular factors such as matrix protein Fibronectin and cytokines VEGFA, IL8, and HBEGF. Tumor-associated fibroblasts enhanced tumor growth and vasculature as well as increased expression of the pro-angiogenic factors. These effects were blunted by dn-p38. Metadata analysis showed elevated expression of p38 target genes in breast cancers and this was an unfavorable marker of disease recurrence and poor-outcome. Thus, our study demonstrates that tumor p38MAPK signaling promotes breast carcinoma growth, invasive and metastatic capacities. Importantly, p38 enhances carcinoma vascularization by facilitating expression and deposition of pro-angiogenic factors. These results argue that p38MAPK is a valuable target for anticancer therapy affecting tumor vasculature. Anti-p38 drugs may provide new therapeutic strategies against breast cancer, including metastatic disease.

Network pharmacology-based approach of novel traditional Chinese medicine formula for treatment of acute skin inflammation in silico

Matrix metalloproteinase-9 (MMP-9) appears to play an important role in acute skin inflammation. Subantimicrobial dose of tetracycline has been demonstrated to inhibit the activity of MMP-9 protein. However, long-term use tetracycline will induce side effect. The catalytic site of MMP-9 is located at zinc-binding amino acids, His401, His405 and His411. We attempted to search novel medicine formula as MMP-9 inhibitors from traditional Chinese medicine (TCM) database by using in silico studies. We utilized high-throughput virtual screening to find which natural compounds could bind to the zinc-binding site. The quantitative structure-activity relationship (QSAR) models, which constructed by scaffold of MMP-9 inhibitors and its activities, were employed to predict the bio-activity of the natural compounds for MMP-9. The results showed that Celacinnine, Lobelanidine and Celallocinnine were qualified to interact with zinc-binding site and displayed well predictive activity. We found that celallocinnine was the best TCM compound for zinc binging sites of MMP-9 because the stable interactions were observed under dynamic condition. In addition, Celacinnine and Lobelanidine could interact with MMP-9 related protein that identified by drug-target interaction network analysis. Thus, we suggested the herbs Hypericum patulum, Sedum acre, and Tripterygium wilfordii that containing Celallocinnine, Celacinnine and Lobelanidine might be a novel medicine formula to avoid the side effect of tetracycline and increase the efficacy of treatment.

Shedding of Syndecan-1/CXCL1 Complexes by Matrix Metalloproteinase 7 Functions as an Epithelial Checkpoint of Neutrophil Activation

Although neutrophils play critical roles in innate immunity, in excess these cells cause severe tissue damage. Thus, neutrophil activation must be tightly regulated to prevent indiscriminant damage. Previously, we reported that mice lacking matrix metalloproteinase (MMP) 7 are protected from lung injury owing to markedly impaired neutrophil movement from the interstitium into mucosal lumenal spaces. This phenotype resulted from a lack of MMP7 shedding of syndecan-1, a heparan sulfate proteoglycan that carries the neutrophil chemokine CXCL1 as cargo. Here, we assessed if shedding syndecan-1/CXCL1 complexes affects neutrophil activation. Whereas injured monolayers of wild-type alveolar type II cells potently stimulated neutrophil activation, as gauged by release of myeloperoxidase, cells from Mmp7(-/-) or syndecan-1-null (Sdc1(-/-)) mice or human cells with MMP7 knockdown did not. In vivo, we observed reduced myeloperoxidase release relative to neutrophil numbers in bleomycin-injured Mmp7(-/-) and Sdc1(-/-) mice. Furthermore, we determined that soluble syndecan-1 directly stimulated neutrophil activation in the absence of cellular damage. These data indicate that MMP7 shedding of syndecan-1/CXCL1 complexes functions as a checkpoint that restricts neutrophil activation at sites of epithelial injury.

Next generation matrix metalloproteinase inhibitors - Novel strategies bring new prospects

Enzymatic proteolysis of cell surface proteins and extracellular matrix (ECM) is critical for tissue homeostasis and cell signaling. These proteolytic activities are mediated predominantly by a family of proteases termed matrix metalloproteinases (MMPs). The growing evidence in recent years that ECM and non-ECM bioactive molecules (e.g., growth factors, cytokines, chemokines, on top of matrikines and matricryptins) have versatile functions redefines our view on the roles matrix remodeling enzymes play in many physiological and pathological processes, and underscores the notion that ECM proteolytic reaction mechanisms represent master switches in the regulation of critical biological processes and govern cell behavior. Accordingly, MMPs are not only responsible for direct degradation of ECM molecules but are also key modulators of cardinal bioactive factors. Many attempts were made to manipulate ECM degradation by targeting MMPs using small peptidic and organic inhibitors. However, due to the high structural homology shared by these enzymes, the majority of the developed compounds are broad-spectrum inhibitors affecting the proteolytic activity of various MMPs and other zinc-related proteases. These inhibitors, in many cases, failed as therapeutic agents, mainly due to the bilateral role of MMPs in pathological conditions such as cancer, in which MMPs have both pro- and anti-tumorigenic effects. Despite the important role of MMPs in many human diseases, none of the broad-range synthetic MMP inhibitors that were designed have successfully passed clinical trials. It appears that, designing highly selective MMP inhibitors that are also effective in vivo, is not trivial. The challenges related to designing selective and effective metalloprotease inhibitors, are associated in part with the aforesaid high structural homology and the dynamic nature of their protein scaffolds. Great progress was achieved in the last decade in understanding the biochemistry and biology of MMPs activity. This knowledge, combined with lessons from the past has drawn new "boundaries" for the development of the next-generation MMP inhibitors. These novel agents are currently designed to be highly specific, capable to discriminate between the homologous MMPs and ideally administered as a short-term topical treatment. In this review we discuss the latest progress in the fields of MMP inhibitors in terms of structure, function and their specific activity. The development of novel highly specific inhibitors targeting MMPs paves the path to study complex biological processes associated with ECM proteolysis in health and disease. This article is part of a Special Issue entitled: Matrix Metalloproteinases edited by Rafael Fridman.

Second Generation Triple-Helical Peptide Inhibitors of Matrix Metalloproteinases

The design of selective matrix metalloproteinase (MMP) inhibitors that also possess favorable solubility properties has proved to be especially challenging. A prior approach using collagen-model templates combined with transition state analogs produced a first generation of triple-helical peptide inhibitors (THPIs) that were effective in vitro against discrete members of the MMP family. These THPI constructs were also highly water-soluble. The present study sought improvements in the first generation THPIs by enhancing thermal stability and selectivity. A THPI selective for MMP-2 and MMP-9 was redesigned to incorporate non-native amino acids (Flp and mep), resulting in an increase of 18 °C in thermal stability. This THPI was effective in vivo in a mouse model of multiple sclerosis, reducing clinical severity and weight loss. Two other THPIs were developed to be more selective within the collagenolytic members of the MMP family. One of these THPIs was serendipitously more effective against MMP-8 than MT1-MMP and was utilized successfully in a mouse model of sepsis. The THPI targeting MMP-8 minimized lung damage, increased production of the anti-inflammatory cytokine IL-10, and vastly improved mouse survival.

Extracellular molecules in hematopoietic stem cell mobilisation

Hematopoietic stem cells are a remarkable resource currently used for the life saving treatment, hematopoietic stem cell transplantation. Today, hematopoietic stem cells are primarily obtained from mobilized peripheral blood following treatment of the donor with the cytokine G-CSF, and in some settings, chemotherapy and/or the CXCR4 antagonist plerixafor. The collection of hematopoietic stem cells is contingent on adequate and timely mobilization of these cells into the peripheral blood. The use of healthy donors, particularly when unrelated to the patient, requires mobilization strategies be safe for the donor. While current mobilization strategies are largely successful, adequate mobilization fails to occur in a significant portion of donors. Understanding the mechanisms involved in the egress of stem cells from the bone marrow provides opportunities to further improve the process of collecting hematopoietic stem cells. Here, the role extracellular components of the blood and bone marrow in the mobilization process are discussed.

The functional interplay between systemic cancer and the hematopoietic stem cell niche

Hematopoietic cells are increasingly recognized as playing key roles in tumor growth and metastatic progression. Although many studies have focused on the functional interaction of hematopoietic cells with tumor cells, few have examined the regulation of hematopoiesis by the hematopoietic stem cell (HSC) niche in the setting of cancer. Hematopoiesis occurs primarily in the bone marrow, and processes including expansion, mobilization, and differentiation of hematopoietic progenitors are tightly regulated by the specialized stem cell niche. Loss of niche components or the ability of stem cells to localize to the stem cell niche relieves HSCs of the restrictions imposed under normal homeostasis. In this review, we discuss how tumor-derived factors and therapeutic interventions disrupt structural and regulatory properties of the stem cell niche, resulting in niche invasion by hematopoietic malignancies, extramedullary hematopoiesis, myeloid skewing by peripheral tissue microenvironments, and lymphopenia. The key regulatory roles played by the bone marrow niche in hematopoiesis has implications for therapy-related toxicity and the successful development of immune-based therapies for cancer.

Multidimensional Contribution of Matrix Metalloproteinases to Atherosclerotic Plaque Vulnerability: Multiple Mechanisms of Inhibition to Promote Stability

The prevalence of atherosclerotic disease continues to increase, and despite significant reductions in major cardiovascular events with current medical interventions, an additional therapeutic window exists. Atherosclerotic plaque growth is a complex integration of cholesterol penetration, inflammatory cell infiltration, vascular smooth muscle cell (VSMC) migration, and neovascular invasion. A family of matrix-degrading proteases, the matrix metalloproteinases (MMPs), contributes to all phases of vascular remodeling. The contribution of specific MMPs to endothelial cell integrity and VSMC migration in atherosclerotic lesion initiation and progression has been confirmed by the increased expression of these proteases in plasma and plaque specimens. Endogenous blockade of MMPs by the tissue inhibitors of metalloproteinases (TIMPs) may attenuate proteolysis in some regions, but the progression of matrix degeneration suggests that MMPs predominate in atherosclerotic plaque, precipitating vulnerability. Plaque neovascularization also contributes to instability and, coupling the known role of MMPs in angiogenesis to that of atherosclerotic plaque growth, interest in targeting MMPs to facilitate plaque stabilization continues to accumulate. This article aims to review the contributions of MMPs and TIMPs to atherosclerotic plaque expansion, neovascularization, and rupture vulnerability with an interest in promoting targeted therapies to improve plaque stabilization and decrease the risk of major cardiovascular events.

The leukemogenic fusion gene MLL-AF9 alters microRNA expression pattern and inhibits monoblastic differentiation via miR-511 repression

Background

In this study we explored the role of microRNAs (miRNAs) as mediators of leukemogenic effects of the fusion gene MLL-AF9, which results from a frequent chromosomal translocation in infant and monoblastic acute myeloid leukemia (AML).

Methods

We performed a specific and efficient knockdown of endogenous MLL-AF9 in the human monoblastic AML cell line THP1.

Results

The knockdown associated miRNA expression profile revealed 21 MLL-AF9 dependently expressed miRNAs. Gene ontology analyses of target genes suggested an impact of these miRNAs on downstream gene regulation via targeting of transcriptional modulators as well as involvement in many functions important for leukemia maintenance as e.g. myeloid differentiation, cell cycle and stem cell maintenance. Furthermore, we identified one of the most intensely repressed miRNAs, miR-511, to raise CCL2 expression (a chemokine ligand important for immunosurveillance), directly target cyclin D1, inhibit cell cycle progression, increase cellular migration and promote monoblastic differentiation. With these effects, miR-511 may have a therapeutic potential as a pro-differentiation agent as well as in leukemia vaccination approaches.

Conclusions

Our study provides new insights into the understanding of miRNAs as functional mediators of the leukemogenic fusion gene MLL-AF9 and opens new opportunities to further investigate specific therapeutic options for AML via the miRNA level.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0283-5) contains supplementary material, which is available to authorized users.

Bioactive poly(ethylene glycol) hydrogels to recapitulate the HSC niche and facilitate HSC expansion in culture

Hematopoietic stem cells (HSCs) have been used therapeutically for decades, yet their widespread clinical use is hampered by the inability to expand HSCs successfully in vitro. In culture, HSCs rapidly differentiate and lose their ability to self-renew. We hypothesize that by mimicking aspects of the bone marrow microenvironment in vitro we can better control the expansion and differentiation of these cells. In this work, derivatives of poly(ethylene glycol) diacrylate hydrogels were used as a culture substrate for hematopoietic stem and progenitor cell (HSPC) populations. Key HSC cytokines, stem cell factor (SCF) and interferon-γ (IFNγ), as well as the cell adhesion ligands RGDS and connecting segment 1 were covalently immobilized onto the surface of the hydrogels. With the use of SCF and IFNγ, we observed significant expansion of HSPCs, ∼97 and ∼104 fold respectively, while maintaining c-kit(+) lin(-) and c-kit(+) Sca1(+) lin(-) (KSL) populations and the ability to form multilineage colonies after 14 days. HSPCs were also encapsulated within degradable poly(ethylene glycol) hydrogels for three-dimensional culture. After expansion in hydrogels, ∼60% of cells were c-kit(+), demonstrating no loss in the proportion of these cells over the 14 day culture period, and ∼50% of colonies formed were multilineage, indicating that the cells retained their differentiation potential. The ability to tailor and use this system to support HSC growth could have implications on the future use of HSCs and other blood cell types in a clinical setting.

Fish Oil-Rich Diet Promotes Hematopoiesis and Alters Hematopoietic Niche

The self-renewal and differentiation of hematopoietic stem cells (HSCs) in bone marrow are essential to replenish all blood cell types, but how this process is influenced by diet remains largely unclear. Here we show that a diet rich in fish oils promotes self-renewal of HSCs and extramedullary hematopoiesis. Chronic intake of a fish oil-rich diet increases the abundance of HSCs, alters the hematopoietic microenvironment, and, intriguingly, induces the expression of matrix metalloproteinase 12 (MMP12) in the bone marrow. Pointing to a direct effect of fish oil on MMP12 expression, omega-3 polyunsaturated fatty acids induce the expression of MMP12 in a dose-dependent manner in bone marrow cells. Importantly, down-regulation of MMP12 activity using an MMP12-specific inhibitor attenuates diet-induced myelopoiesis in both bone marrow and spleen. Thus, a fish oil-rich diet promotes hematopoiesis in the bone marrow and spleen, in part via the activity of MMP12. Taken together, these data provide new insights into diet-mediated regulation of hematopoiesis.

Therapy with plasma purified alpha1-antitrypsin (Prolastin®) induces time-dependent changes in plasma levels of MMP-9 and MPO

The common Z mutation (Glu342Lys) of α1-antitrypsin (A1AT) results in the polymerization and intracellular retention of A1AT protein. The concomitant deficiency of functional A1AT predisposes PiZZ subjects to early onset emphysema. Clinical studies have implied that, among the biomarkers associated with emphysema, matrix metalloproteinase 9 (MMP-9) is of particular importance. Increased plasma MMP-9 levels are proposed to predict the decline of lung function as well as greater COPD exacerbations in A1AT deficiency-associated emphysema. The aim of the present study was to investigate the effect of A1AT therapy (Prolastin) on plasma MMP-9 and myeloperoxidase (MPO) levels. In total 34 PiZZ emphysema patients were recruited: 12 patients without and 22 with weekly intravenous (60 mg/kg body weight) A1AT therapy. The quantitative analysis of A1AT, MMP-9 and MPO was performed in serum and in supernatants of blood neutrophils isolated from patients before and after therapy. Patients with Prolastin therapy showed significantly lower serum MMP-9 and MPO levels than those without therapy. However, parallel analysis revealed that a rapid infusion of Prolastin is accompanied by a transient elevation of plasma MMP-9 and MPO levels. Experiments with freshly isolated blood neutrophils confirmed that therapy with Prolastin causes transient MMP-9 and MPO release. Prolastin induced the rapid release of MMP-9 and MPO when added directly to neutrophil cultures and this reaction was associated with the presence of IgA in A1AT preparation. Our data support the conclusion that changes in plasma levels of MMP-9 and MPO mirror the effect of Prolastin on blood neutrophils.

Matrix metalloproteinases in stem cell mobilization

Hematopoietic stem cells (HSCs) have the capability to migrate back and forth between their preferred microenvironment in bone marrow niches and the peripheral blood, but under steady-state conditions only a marginal number of stem cells can be found in the circulation. Different mobilizing agents, however, which create a highly proteolytic milieu in the bone marrow, can drastically increase the number of circulating HSCs. Among other proteases secreted and membrane-bound matrix metalloproteinases (MMPs) are known to be involved in the induced mobilization process and can digest niche-specific extracellular matrix components and cytokines responsible for stem cell retention to the niches. Iatrogenic stem cell mobilization and stem cell homing to their niches are clinically employed on a routine basis, although the exact mechanisms of both processes are still not fully understood. In this review we provide an overview on the various roles of MMPs in the induced release of HSCs from the bone marrow.

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.