MMP-9 sheds the beta2 integrin subunit (CD18) from macrophages

Identification of circulating T-cell immunoglobulin and mucin domain 4 as a potential biomarker for coronary heart disease

Efferocytosis, the process of engulfing and removing apoptotic cells, is attenuated in vulnerable plaques of advanced atherosclerosis. T-cell immunoglobulin and mucin domain 4 (TIMD4) is a recognition receptor protein for efferocytosis that has been implicated in atherosclerosis mouse models. However, the role of serum-soluble TIMD4 (sTIMD4) in coronary heart disease (CHD) remains unknown. In this study, we analyzed serum samples collected from two groups: Group 1 (36 healthy controls and 70 CHD patients) and Group 2 (44 chronic coronary syndrome [CCS]) and 81 acute coronary syndrome [ACS] patients). We found that sTIMD4 levels in patients with CHD were significantly higher than those in healthy controls and were also higher in ACS than in CCS patients. The area under the receiver operating characteristic curve was 0.787. Furthermore, our in vitro results showed that low-density lipoprotein/lipopolysaccharide activated p38 mitogen-activated protein kinase, which in turn enhanced a disintegrin and metalloproteinase 17, resulting in increased secretion of sTIMD4. This impairment of macrophage efferocytosis promoted inflammation. Thus, this study is not only the first identification of a potential novel biomarker of CHD, sTIMD4, but also demonstrated its pathogenesis mechanism, providing a new direction for the diagnosis and treatment of CHD.

Novel Matrix Metalloproteinase-9 (MMP-9) Inhibitors in Cancer Treatment

Matrix metalloproteinases (MMPs) belong to a family of zinc-dependent proteolytic metalloenzymes. MMP-9, a member of the gelatinase B family, is characterized as one of the most intricate MMPs. The crucial involvement of MMP-9 in extracellular matrix (ECM) remodeling underscores its significant correlation with each stage of cancer pathogenesis and progression. The design and synthesis of MMP-9 inhibitors is a potentially attractive research area. Unfortunately, to date, there is no effective MMP-9 inhibitor that passes the clinical trials and is approved by the FDA. This review primarily focuses on exploring the diverse strategies employed in the design and advancement of MMP-9 inhibitors, along with their anticancer effects and selectivity. To illuminate the essential structural characteristics necessary for the future design of novel MMP-9 inhibitors, the current narrative review highlights several recently discovered MMP-9 inhibitors exhibiting notable selectivity and potency.

MMP-9 reinforces radiation-induced delayed invasion and metastasis of neuroblastoma cells through second-signaling positive feedback with NFκB via both ERK and IKK activation

Neuroblastoma (NB) progression is branded with hematogenous metastasis and frequent relapses. Despite intensive multimodal clinical therapy, outcomes for patients with progressive disease remain poor, with negligible long-term survival. Therefore, understanding the acquired molecular rearrangements in NB cells with therapy pressure and developing improved therapeutic strategies is a critical need to improve the outcomes for high-risk NB patients. We investigated the rearrangement of MMP9 in NB with therapy pressure, and unveiled the signaling that facilitates NB evolution. Radiation-treatment (RT) significantly increased MMP9 expression/activity, and the induced enzyme activity was persistently maintained across NB cell lines. Furthermore, RT-triggered NFκB transcriptional activity and this RT-induced NFκB were required/adequate for MMP9 maintenance. RT-triggered NFκB-dependent MMP9 actuated a second-signaling feedback to NFκB, facilitating a NFκB-MMP9-NFκB positive feedback cycle (PFC). Critically, MMP9-NFκB feedback is mediated by MMP9-dependent activation of IKKβ and ERK phosphotransferase activity. Beyond its tumor invasion/metastasis function, PFC-dependent MMP9 lessens RT-induced apoptosis and favors survival pathway through the activation of NFκB signaling. In addition, PFC-dependent MMP9 regulates 19 critical molecular determinants that play a pivotal role in tumor evolution. Interestingly, seven of 19 genes possess NFκB-binding sites, demonstrating that MMP9 regulates these molecules by activating NFκB. Collectively, these data suggest that RT-triggered NFκB-dependent MMP9 actuates feedback to NFκB though IKKβ- and ERK1/2-dependent IκBα phosphorylation. This RT-triggered PFC prompts MMP9-dependent survival advantage, tumor growth, and dissemination. Targeting therapy-pressure-driven PFC and/or selective inhibition of MMP9 maintenance could serve as promising therapeutic strategies for treatment of progressive NB.

Macrophage-Mediated Inflammation in Skin Wound Healing

Macrophages are key immune cells that respond to infections, and modulate pathophysiological conditions such as wound healing. By possessing phagocytic activities and through the secretion of cytokines and growth factors, macrophages are pivotal orchestrators of inflammation, fibrosis, and wound repair. Macrophages orchestrate the process of wound healing through the transitioning from predominantly pro-inflammatory (M1-like phenotypes), which present early post-injury, to anti-inflammatory (M2-like phenotypes), which appear later to modulate skin repair and wound closure. In this review, different cellular and molecular aspects of macrophage-mediated skin wound healing are discussed, alongside important aspects such as macrophage subtypes, metabolism, plasticity, and epigenetics. We also highlight previous studies demonstrating interactions between macrophages and these factors for optimal wound healing. Understanding and harnessing the activity and capability of macrophages may help to advance new approaches for improving healing of the skin.

MMP9: A Tough Target for Targeted Therapy for Cancer

Having the capability to proteolyze diverse structural and signaling proteins, matrix metalloproteinase 9 (MMP9), one of the best-studied secretory endopeptidases, has been identified as a crucial mediator of processes closely associated with tumorigenesis, such as the extracellular matrix reorganization, epithelial to mesenchymal transition, cell migration, new blood vessel formation, and immune response. In this review, we present the current state of knowledge on MMP9 and its role in cancer growth in the context of cell adhesion/migration, cancer-related inflammation, and tumor microenvironment formation. We also summarize recent achievements in the development of selective MMP9 inhibitors and the limitations of using them as anticancer drugs.

Global Proteomic Analyses Reveals Abnormal Immune Regulation in Patients With New Onset Ankylosing Spondylitis

Background

Ankylosing spondylitis (AS) is a chronic inflammatory disease with serious consequences and a high rate of morbidity and mortality, In our previous work, we reveal the key features of proteins in new-onset ankylosing spondylitis patients.

Material and Methods

Ankylosing spondylitis (AS) is a chronic inflammatory condition that affects the spine, and inflammation plays an essential role in AS pathogenesis. The inflammatory process in AS, however, is still poorly understood due to its intricacy. Systematic proteomic and phosphorylation analyses of peripheral blood mononuclear cells (PBMCs) were used to investigate potential pathways involved in AS pathogenesis.

Results

Liquid chromatography-tandem mass spectrometry (LC–MS/MS) analysis was performed and discovered 782 differentially expressed proteins (DEPs) and 122 differentially phosphorylated proteins (DPPs) between 9 new-onset AS patients and 9 healthy controls. The DEPs were further verified using parallel reaction monitoring (PRM) analysis. PRM analysis verified that 3 proteins (HSP90AB1, HSP90AA1 and HSPA8) in the antigen processing and presentation pathway, 6 proteins (including ITPR1, MYLK and STIM1) in the platelet activation pathway and 10 proteins (including MYL12A, MYL9 and ROCK2) in the leukocyte transendothelial migration pathway were highly expressed in the PBMCs of AS patients.

Conclusion

The key proteins involved in antigen processing and presentation, platelet activation and leukocyte transendothelial migration revealed abnormal immune regulation in patients with new-onset AS. These proteins might be used as candidate markers for AS diagnosis and new therapeutic targets, as well as elucidating the pathophysiology of AS.

Modulation of Microenvironment Signals by Proteolytic Shedding of Cell Surface Extracellular Matrix Receptors

Multicellular organisms are composed of cells and extracellular matrix (ECM). ECM is a network of multidomain macromolecules that fills gaps between cells. It acts as a glue to connect cells, provides scaffolding for migrating cells, and pools cytokines and growth factors. ECM also directly sends signals to the cells through ECM receptors, providing survival signals and migration cues. Altogether, ECM provides a correct microenvironment for the cells to function in the tissue. Although ECM acts as a signaling molecule, they are insoluble solid molecules, unlike soluble receptor ligands such as cytokines and growth factors. Upon cell binding to the ECM through ECM receptors and signals transmitted, cells then need to have a mechanism to release from ECM to prevent prolonged signals, which may be tumorigenic, and migrate on ECM. One effective means to release the cells from ECM is to cleave the ECM receptors by proteinases. In this mini-review, current knowledge of ECM receptor shedding will be discussed.

Intravascular Crawling of Patrolling Monocytes: A Lèvy-Like Motility for Unique Search Functions?

Patrolling monocytes (PMo) are the organism’s preeminent intravascular guardians by their continuous search of damaged endothelial cells and harmful microparticles for their removal and to restore homeostasis. This surveillance is accomplished by PMo crawling on the apical side of the endothelium through regulated interactions of integrins and chemokine receptors with their endothelial ligands. We propose that the search mode governs the intravascular motility of PMo in vivo in a similar way to T cells looking for antigen in tissues. Signs of damage to the luminal side of the endothelium (local death, oxidized LDL, amyloid deposits, tumor cells, pathogens, abnormal red cells, etc.) will change the diffusive random towards a Lèvy-like crawling enhancing their recognition and clearance by PMo damage receptors as the integrin αMβ2 and CD36. This new perspective can help identify new actors to promote unique PMo intravascular actions aimed at maintaining endothelial fitness and combating harmful microparticles involved in diseases as lung metastasis, Alzheimer’s angiopathy, vaso-occlusive disorders, and sepsis.

Computational study of effective matrix metalloproteinase 9 (MMP9) targeting natural inhibitors

Object: The present study screened ideal lead natural compounds that could target and inhibit matrix metalloproteinase 9 (MMP9) protein from the ZINC database to develop drugs for clear cell renal cell carcinoma (CCRCC)-targeted treatment.

Methods: Discovery Studio 4.5 was used to compare and screen the ligands with the reference drug, solasodine, to identify ideal candidate compounds that could inhibit MMP9. The LibDock module was used to analyze compounds that could strongly bind to MMP9, and the top 20 compounds determined by the LibDock score were selected for further research. ADME and TOPKAT modules were used to choose the safe compounds from these 20 compounds. The selected compounds were analyzed using the CDOCKER module for molecular docking and feature mapping for pharmacophore prediction. The stability of these compound–MMP9 complexes was analyzed by molecular dynamic simulation. Cell counting kit-8, colony-forming, and scratch assays were used to analyze the anti-CCRCC effects of these ligands.

Results: Strong binding to MMP9 was exhibited by 6,762 ligands. Among the top 20 compounds, sappanol and sventenin exhibited nearly undefined blood–brain barrier level and lower aqueous solubility, carcinogenicity, and hepatotoxicity than the positive control drug, solasodine. Additionally, these compounds exhibited lower potential energies with MMP9, and the ligand–MMP9 complexes were stable in the natural environment. Furthermore, sappanol inhibited CCRCC cell migration and proliferation.

Conclusion: Sappanol and sventenin are safe and reliable compounds to target and inhibit MMP9. Sappanol can CCRCC cell migration and proliferation. These two compounds may give new thought to the targeted therapy for patients with CCRCC.

Platelet α-granule cargo packaging and release are affected by the luminal proteoglycan, serglycin

BACKGROUND

Serglycin (SRGN) is an intragranular, sulfated proteoglycan in hematopoietic cells that affects granule composition and function.

OBJECTIVE

To understand how SRGN affects platelet granule packaging, cargo release, and extra-platelet microenvironments.

METHODS

Platelets and megakaryocytes from SRGN-/- mice were assayed for secretion kinetics, cargo levels, granule morphology upon activation, and receptor shedding.

RESULTS

Metabolic, 35 SO4 labeling identified SRGN as a major sulfated macromolecule in megakaryocytes. SRGN colocalized with α-granule markers (platelet factor 4 [PF4], von Willebrand factor [VWF], and P-selectin), but its deletion did not affect α-granule morphology or number. Platelet α-granule composition was altered, with a reduction in basic proteins (pI ≥8; e.g., PF4, SDF-1, angiogenin) and constitutive release of PF4 from SRGN-/- megakaryocytes. P-Selectin, VWF, and fibrinogen were unaffected. Serotonin (5-HT) uptake and β-hexosaminidase (HEXB) were slightly elevated. Thrombin-induced exocytosis of PF4 from platelets was defective; however, release of RANTES/CCL5 was normal and osteopontin secretion was more rapid. Release of 5-HT and HEXB (from dense granules and lysosomes, respectively) were unaffected. Ultrastructural studies showed distinct morphologies in activated platelets. The α-granule lumen of SRGN-/- platelet had a grainy staining pattern, whereas that of wild-type granules had only fibrous material remaining. α-Granule swelling and decondensation were reduced in SRGN-/- platelets. Upon stimulation of platelets, a SRGN/PF4 complex was released in a time- and agonist-dependent manner. Shedding of GPVI from SRGN-/- platelets was modestly enhanced. Shedding of GP1b was unaffected.

CONCLUSION

The polyanionic proteoglycan SRGN influences α-granule packaging, cargo release, and shedding of platelet membrane proteins.

Innate Immunity Effector Cells as Inflammatory Drivers of Cardiac Fibrosis

Despite relevant advances made in therapies for cardiovascular diseases (CVDs), they still represent the first cause of death worldwide. Cardiac fibrosis and excessive extracellular matrix (ECM) remodeling are common end-organ features in diseased hearts, leading to tissue stiffness, impaired myocardial functional, and progression to heart failure. Although fibrosis has been largely recognized to accompany and complicate various CVDs, events and mechanisms driving and governing fibrosis are still not entirely elucidated, and clinical interventions targeting cardiac fibrosis are not yet available. Immune cell types, both from innate and adaptive immunity, are involved not just in the classical response to pathogens, but they take an active part in “sterile” inflammation, in response to ischemia and other forms of injury. In this context, different cell types infiltrate the injured heart and release distinct pro-inflammatory cytokines that initiate the fibrotic response by triggering myofibroblast activation. The complex interplay between immune cells, fibroblasts, and other non-immune/host-derived cells is now considered as the major driving force of cardiac fibrosis. Here, we review and discuss the contribution of inflammatory cells of innate immunity, including neutrophils, macrophages, natural killer cells, eosinophils and mast cells, in modulating the myocardial microenvironment, by orchestrating the fibrogenic process in response to tissue injury. A better understanding of the time frame, sequences of events during immune cells infiltration, and their action in the injured inflammatory heart environment, may provide a rationale to design new and more efficacious therapeutic interventions to reduce cardiac fibrosis.

The Impact of Matrix Metalloproteinase-9 on the Sequential Steps of the Metastatic Process

In industrialized countries, cancer is the second leading cause of death after cardiovascular disease. Most cancer patients die because of metastases, which consist of the self-transplantation of malignant cells in anatomical sites other than the one from where the tumor arose. Disseminated cancer cells retain the phenotypic features of the primary tumor, and display very poor differentiation indices and functional regulation. Upon arrival at the target organ, they replace preexisting, normal cells, thereby permanently compromising the patient's health; the metastasis can, in turn, metastasize. The spread of cancer cells implies the degradation of the extracellular matrix by a variety of enzymes, among which the matrix metalloproteinase (MMP)-9 is particularly effective. This article reviews the available published literature concerning the important role that MMP-9 has in the metastatic process. Additionally, information is provided on therapeutic approaches aimed at counteracting, or even preventing, the development of metastasis via the use of MMP-9 antagonists.

Phyto-derived Products as Matrix Metalloproteinases Inhibitors in Cardiovascular Diseases

Matrix metalloproteinases (MMPs) are enzymes that present a metallic element in their structure. These enzymes are ubiquitously distributed and function as extracellular matrix (ECM) remodelers. MMPs play a broad role in cardiovascular biology regulating processes such as cell adhesion and function, cellular communication and differentiation, integration of mechanical force and force transmission, tissue remodeling, modulation of damaged-tissue structural integrity, cellular survival or apoptosis and regulation of inflammation-related cytokines and growth factors. MMPs inhibition and downregulation are correlated with minimization of cardiac damage, i.e., Chinese herbal medicine has shown to stabilize abdominal aorta aneurysm due to its antiinflammatory, antioxidant and MMP-2 and 9 inhibitory properties. Thus phyto-derived products rise as promising sources for novel therapies focusing on MMPs inhibition and downregulation to treat or prevent cardiovascular disorders.

Matrix Metalloproteases as Influencers of the Cells' Social Media

Matrix metalloproteinases (MMPs) have been studied in the context of cancer due to their ability to increase cell invasion, and were initially thought to facilitate metastasis solely through the degradation of the extracellular matrix (ECM). MMPs have also been investigated in the context of their ECM remodeling activity in several acute and chronic inflammatory diseases. However, after several MMP inhibitors failed in phase III clinical trials, a global reassessment of their biological functions was undertaken, which has revealed multiple unanticipated functions including the processing of chemokines, cytokines, and cell surface receptors. Despite what their name suggests, the matrix aspect of MMPs could contribute to a lesser part of their physiological functions in inflammatory diseases, as originally anticipated. Here, we present examples of MMP substrates implicated in cell signaling, independent of their ECM functions, and discuss the impact for the use of MMP inhibitors.

Matrix metalloproteinases in the CNS: interferons get nervous

Matrix metalloproteinases (MMPs) have been investigated in context of chronic inflammatory diseases and demonstrated to degrade multiple components of the extracellular matrix (ECM). However, following several disappointing MMP clinical trials, recent studies have demonstrated unexpected novel functions of MMPs in viral infections and autoimmune inflammatory diseases in unanticipated locations. Thus, MMPs play additional functions in inflammation than just ECM degradation. They can regulate the activity of chemokines and cytokines of the immune response by precise proteolytic processing resulting in activation or inactivation of signaling pathways. MMPs have been demonstrated to cleave multiple substrates of the central nervous systems (CNS) and contribute to promoting and dampening diseases of the CNS. Initially, believed to be solely promoting pathologies, more than 10 MMPs to date have been shown to have protective functions. Here, we present some of the beneficial and destructive roles of MMPs in CNS pathologies and discuss strategies for the use of MMP inhibitors.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Structural Immunology of Complement Receptors 3 and 4

Complement receptors (CR) 3 and 4 belong to the family of beta-2 (CD18) integrins. CR3 and CR4 are often co-expressed in the myeloid subsets of leukocytes, but they are also found in NK cells and activated T and B lymphocytes. The heterodimeric ectodomain undergoes considerable conformational change in order to switch the receptor from a structurally bent, ligand-binding in-active state into an extended, ligand-binding active state. CR3 binds the C3d fragment of C3 in a way permitting CR2 also to bind concomitantly. This enables a hand-over of complement-opsonized antigens from the cell surface of CR3-expressing macrophages to the CR2-expressing B lymphocytes, in consequence acting as an antigen presentation mechanism. As a more enigmatic part of their functions, both CR3 and CR4 bind several structurally unrelated proteins, engineered peptides, and glycosaminoglycans. No consensus motif in the proteinaceous ligands has been established. Yet, the experimental evidence clearly suggest that the ligands are primarily, if not entirely, recognized by a single site within the receptors, namely the metal-ion dependent adhesion site (MIDAS). Comparison of some recent identified ligands points to CR3 as inclined to bind positively charged species, while CR4, by contrast, binds strongly negative-charged species, in both cases with the critical involvement of deprotonated, acidic groups as ligands for the Mg²⁺ ion in the MIDAS. These properties place CR3 and CR4 firmly within the realm of modern molecular medicine in several ways. The expression of CR3 and CR4 in NK cells was recently demonstrated to enable complement-dependent cell cytotoxicity toward antibody-coated cancer cells as part of biological therapy, constituting a significant part of the efficacy of such treatment. With the flexible principles of ligand recognition, it is also possible to propose a response of CR3 and CR4 to existing medicines thereby opening a possibility of drug repurposing to influence the function of these receptors. Here, from advances in the structural and cellular immunology of CR3 and CR4, we review insights on their biochemistry and functions in the immune system.

Matrix Metalloproteinase-9 (MMP-9) as a Cancer Biomarker and MMP-9 Biosensors: Recent Advances

As one of the most widely investigated matrix metalloproteinases (MMPs), MMP-9 is a significant protease which plays vital roles in many biological processes. MMP-9 can cleave many extracellular matrix (ECM) proteins to regulate ECM remodeling. It can also cleave many plasma surface proteins to release them from the cell surface. MMP-9 has been widely found to relate to the pathology of cancers, including but not limited to invasion, metastasis and angiogenesis. Some recent research evaluated the value of MMP-9 as biomarkers to various specific cancers. Besides, recent research of MMP-9 biosensors discovered various novel MMP-9 biosensors to detect this enzyme. In this review, some recent advances in exploring MMP-9 as a biomarker in different cancers are summarized, and recent discoveries of novel MMP-9 biosensors are also presented.

Matrix metalloproteinases in emphysema

Several studies have implicated a causative role for specific matrix metalloproteinases (MMPs) in the development and progression of cigarette smoke-induced chronic obstructive pulmonary disease (COPD) and its severe sequela, emphysema. However, the precise function of any given MMP in emphysema remains an unanswered question. Emphysema results from the degradation of alveolar elastin - among other possible mechanisms - a process that is often thought to be caused by elastolytic proteinases made by macrophages. In this article, we discuss the data suggesting, supporting, or refuting causative roles of macrophage-derived MMPs, with a focus on MMPs-7, -9, -10, -12, and 28, in both the human disease and mouse models of emphysema. Findings from experimental models suggest that some MMPs, such as MMP-12, may directly breakdown elastin, whereas others, particularly MMP-10 and MMP-28, promote the development of emphysema by influencing the proteolytic and inflammatory activities of macrophages.

Macrophages, Wound Healing, and Fibrosis: Recent Insights

PURPOSE OF REVIEW

Macrophages are central players in the immune response following tissue injury. These cells perform many functions, and the changing tissue microenvironment during injury shapes macrophage phenotype down a variety of polarized pathways. This review summarizes the current knowledge on the roles of macrophages during different stages of tissue injury, repair, and-if repair is not achieved-fibrosis.

RECENT FINDINGS

Macrophages present early in inflammation are functionally distinct from those at later stages. The predominant macrophage phenotype must transition from pro-inflammatory to pro-reparative to facilitate wound healing and scar resolution. If macrophages fail to acquire a tissue-healing phenotype, dysregulated signals can be drivers of disease processes, such as sustained, exuberant inflammation-as occurs in arthropathies-and fibrosis. Comprehensive understanding of the roles of specific macrophage populations at different stages of the repair process will support the development of immune-targeted therapies for diseases such as fibrosis.

MT4-MMP deficiency increases patrolling monocyte recruitment to early lesions and accelerates atherosclerosis

Matrix metalloproteinases are involved in vascular remodeling. Little is known about their immune regulatory role in atherosclerosis. Here we show that mice deficient for MT4-MMP have increased adherence of macrophages to inflamed peritonea, and larger lipid deposits and macrophage burden in atherosclerotic plaques. We also demonstrate that MT4-MMP deficiency results in higher numbers of patrolling monocytes crawling and adhered to inflamed endothelia, and the accumulation of Mafb+ apoptosis inhibitor of macrophage (AIM)+ macrophages at incipient atherosclerotic lesions in mice. Functionally, MT4-MMP-null Mafb+AIM+ peritoneal macrophages express higher AIM and scavenger receptor CD36, are more resistant to apoptosis, and bind acLDL avidly, all of which contribute to atherosclerosis. CCR5 inhibition alleviates these effects by hindering the enhanced recruitment of MT4-MMP-null patrolling monocytes to early atherosclerotic lesions, thus blocking Mafb+AIM+ macrophage accumulation and atherosclerosis acceleration. Our results suggest that MT4-MMP targeting may constitute a novel strategy to boost patrolling monocyte activity in early inflammation.

Matrix Metalloproteinases and Leukocyte Activation

As their name implies, matrix metalloproteinases (MMPs) are thought to degrade extracellular matrix proteins, a function that is indeed performed by some members. However, regardless of their cell source, matrix degradation is not the only function of these enzymes. Rather, individual MMPs have been shown to regulate specific immune processes, such as leukocyte influx and migration, antimicrobial activity, macrophage activation, and restoration of barrier function, typically by processing a range of nonmatrix protein substrates. Indeed, MMP expression is low under steady-state conditions but is markedly induced during inflammatory processes including infection, wound healing, and cancer. Increasing research is showing that MMPs are not just a downstream consequence of a generalized inflammatory process, but rather are critical factors in the overall regulation of the pattern, type, and duration of immune responses. This chapter outlines the role of leukocytes in tissue remodeling and describes recent progress in our understanding of how MMPs alter leukocyte activity.

Dentin Sialoprotein is a Novel Substrate of Matrix Metalloproteinase 9 in vitro and in vivo

Dentin sialoprotein (DSP) is essential for dentinogenesis and processed into fragments in the odontoblast-like cells and the tooth compartments. Matrix metalloproteinase 9 (MMP9) is expressed in teeth from early embryonic to adult stage. Although MMP9 has been reported to be involved in some physiological and pathological conditions through processing substrates, its role in tooth development and whether DSP is a substrate of MMP9 remain unknown. In this study, the function of MMP9 in the tooth development was examined by observation of Mmp9 knockout (Mmp9−/−) mouse phenotype, and whether DSP is a substrate of MMP9 was explored by in vitro and in vivo experiments. The results showed that Mmp9−/− teeth displayed a phenotype similar to dentinogenesis imperfecta, including decreased dentin mineral density, abnormal dentin architecture, widened predentin and irregular predentin-dentin boundary. The distribution of MMP9 and DSP overlapped in the odontoblasts, the predentin, and the mineralized dentin, and MMP9 was able to specifically bind to DSP. MMP9 highly efficiently cleaved DSP into distinct fragments in vitro, and the deletion of Mmp9 caused improper processing of DSP in natural teeth. Therefore, our findings demonstrate that MMP9 is important for tooth development and DSP is a novel target of MMP9 during dentinogenesis.

Matrix Metalloproteinase 9 in Epilepsy: The Role of Neuroinflammation in Seizure Development

Matrix metalloproteinase 9 is a proteolytic enzyme which is recently one of the more often studied biomarkers. Its possible use as a biomarker of neuronal damage in stroke, heart diseases, tumors, multiple sclerosis, and epilepsy is being widely indicated. In epilepsy, MMP-9 is suggested to play a role in epileptic focus formation and in the stimulation of seizures. The increase of MMP-9 activity in the epileptic focus was observed both in animal models and in clinical studies. MMP-9 contributes to formation of epileptic focus, for example, by remodeling of synapses. Its proteolytic action on the elements of blood-brain barrier and activation of chemotactic processes facilitates accumulation of inflammatory cells and induces seizures. Also modification of glutamatergic transmission by MMP-9 is associated with seizures. In this review we will try to recapitulate the results of previous studies about MMP-9 in terms of its association with epilepsy. We will discuss the mechanisms of its actions and present the results revealed in animal models and clinical studies. We will also provide a comparison of the results of various studies on MMP-9 levels in the context of its possible use as a biomarker of the activity of epilepsy.

A novel role for β2-microglobulin: a precursor of antibacterial chemokine in respiratory epithelial cells

We analyzed a panel of cationic molecules secreted in the culture medium of human respiratory epithelial cells (REC) upon activation by IL-1β and different pathogen-associated molecular patterns. A 9 kDa fragment derived from β2-microglobulin (B2M) was identified and named shed 9 kDa B2M (sB2M-9). The primary structure of sB2M-9 was revealed to increase its pI value that potentially could play an important role in innate defense. sB2M-9 exhibits antibacterial activity against Gram positive Staphylococcus aureus (SA) but not against Gram negative Klebsiella pneumonia (KP). Upon its binding to SA, sB2M-9 induces clumps, a phenomenon not observed with B2M. Migration of THP-1 monocytes exposed to SA clumps was significantly greater than that to SA without clumps. sB2M-9 binds to SA, more likely as a chemokine, to facilitate THP-1 migration. As a whole, we demonstrated that REC release a novel chemokine with antibacterial activity that is shed from B2M to facilitate THP-1 migration.

Thioredoxin fusion construct enables high-yield production of soluble, active matrix metalloproteinase-8 (MMP-8) in Escherichia coli

Matrix metalloproteinases (MMPs) are crucial proteases in maintaining the health and integrity of many tissues, however their dysregulation often facilitates disease progression. In disease states these remodeling and repair functions support, for example, metastasis of cancer by both loosening the matrix around tumors to enable cellular invasion and by affecting proliferation and apoptosis, and they promote degradation of biological restorations by weakening the substrate to which the restoration is attached. As such, MMPs are important therapeutic targets. MMP-8 participates in cancer, arthritis, asthma and failure of dental fillings. MMP-8 differs from other MMPs in that it has an insertion that enlarges its active site. To elucidate the unique features of MMP-8 and develop selective inhibitors to this therapeutic target, a stable and active form of the enzyme is needed. MMP-8 has been difficult to express at high yield in a soluble, active form. Typically recombinant MMPs accumulate in inclusion bodies and complex methods are applied to refold and purify protein in acceptable yield. Presented here is a streamlined approach to produce in Escherichia coli a soluble, active, stable MMP-8 fusion protein in high yield. This fusion shows much greater retention of activity when stored refrigerated without glycerol. A variant of this construct that contains the metal binding claMP Tag was also examined to demonstrate the ability to use this tag with a metalloprotein. SDS-PAGE, densitometry, mass spectrometry, circular dichroism spectroscopy and an activity assay were used to analyze the chemical integrity and function of the enzyme.

Changes in Soluble CD18 in Murine Autoimmune Arthritis and Rheumatoid Arthritis Reflect Disease Establishment and Treatment Response

INTRODUCTION

In rheumatoid arthritis (RA) immune activation and presence of autoantibodies may precede clinical onset of disease, and joint destruction can progress despite remission. However, the underlying temporal changes of such immune system abnormalities in the inflammatory response during treat-to-target strategies remain poorly understood. We have previously reported low levels of the soluble form of CD18 (sCD18) in plasma from patients with chronic RA and spondyloarthritis. Here, we study the changes of sCD18 before and during treatment of early RA and following arthritis induction in murine models of rheumatoid arthritis.

METHODS

The level of sCD18 was analyzed with a time-resolved immunoflourometric assay in 1) plasma from early treatment naïve RA patients during a treat-to-target strategy (the OPERA cohort), 2) plasma from chronic RA patients, 3) serum from SKG and CIA mice following arthritis induction, and 4) supernatants from synovial fluid mononuclear cells (SFMCs) and peripheral blood mononuclear cells (PBMCs) from 6 RA patients cultured with TNFα or adalimumab.

RESULTS

Plasma levels of sCD18 were decreased in chronic RA patients compared with early RA patients and in early RA patients compared with healthy controls. After 12 months of treatment the levels in early RA patients were similar to healthy controls. This normalization of plasma sCD18 levels was more pronounced in patients with very early disease who achieved an early ACR response. Plasma sCD18 levels were associated with radiographic progression. Correspondingly, the serum level of sCD18 was decreased in SKG mice 6 weeks after arthritis induction compared with healthy littermates. The sCD18 levels in both SKG and CIA mice exhibited a biphasic course after arthritis induction with an initial increase above baseline followed by a decline. Shedding of CD18 from RA SFMC and RA PBMC cultures was increased by TNFα and decreased by adalimumab.

CONCLUSIONS

The plasma sCD18 levels were altered in patients with RA, in mice with autoimmune arthritis and in cell cultures treated with TNFα and adalimumab. Decreased levels of plasma sCD18 could reflect autoimmunity in transition from early to chronic disease and normalization in response to treatment could reflect autoimmunity in remission.

Interleukin 20 regulates dendritic cell migration and expression of co-stimulatory molecules

Background

Psoriasis is an inflammatory disease characterized by leukocyte skin infiltration. Interestingly, recent works suggest that the migration of dendritic cells (DCs) is abnormal in psoriatic skin. DCs have significant role in regulating the function of T lymphocytes, at least in part influenced by the local environment of cytokines. In psoriatic skin lesions the expression of IL-20 is highly up-regulated. It is unclear if this cytokine has any influence on DCs.

Methods

Here, we investigated the influence of IL-20 in monocyte-derived dendritic cell (MDDCs) in vitro. This work addressed IL-20 effects on DC maturation, receptor expression and signaling. By use of extra cellular matrix components mimicking the skin environment, we also studied the functional effects of IL-20 on the chemotactic migration of DCs. Based on the recent finding that CD18 integrin are shed during migration of myeloid leukocytes, the concentration of these adhesion molecules was measured in MDDCs culture supernatants post migration.

Results

Following stimulation with IL-20, immature human MDDCs enhanced the expression of the co-stimulatory molecule CD86, further enabling activation of the p38 MAPK, but not the STAT3, pathway. IL-20 increased the migration of MDDCs in a biphasic response narrowly controlled by the interleukin concentration. A concomitant change in the shedding of CD18 integrins suggested that these adhesion molecules play a role in the migration of the MDDCs through the extracellular matrix layer.

Conclusion

Taken together, our findings points to a possible, yet subtle, role of IL-20 in DCs migration. The biphasic response suggests that the aberrant IL-20 expression in psoriasis impedes DC migration, which could be a part of the processes that precipitates the dysregulated inflammatory response associated with this disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s40591-016-0046-x) contains supplementary material, which is available to authorized users.

Interleukin 20 regulates dendritic cell migration and expression of co-stimulatory molecules

BACKGROUND

Psoriasis is an inflammatory disease characterized by leukocyte skin infiltration. Interestingly, recent works suggest that the migration of dendritic cells (DCs) is abnormal in psoriatic skin. DCs have significant role in regulating the function of T lymphocytes, at least in part influenced by the local environment of cytokines. In psoriatic skin lesions the expression of IL-20 is highly up-regulated. It is unclear if this cytokine has any influence on DCs.

METHODS

Here, we investigated the influence of IL-20 in monocyte-derived dendritic cell (MDDCs) in vitro. This work addressed IL-20 effects on DC maturation, receptor expression and signaling. By use of extra cellular matrix components mimicking the skin environment, we also studied the functional effects of IL-20 on the chemotactic migration of DCs. Based on the recent finding that CD18 integrin are shed during migration of myeloid leukocytes, the concentration of these adhesion molecules was measured in MDDCs culture supernatants post migration.

RESULTS

Following stimulation with IL-20, immature human MDDCs enhanced the expression of the co-stimulatory molecule CD86, further enabling activation of the p38 MAPK, but not the STAT3, pathway. IL-20 increased the migration of MDDCs in a biphasic response narrowly controlled by the interleukin concentration. A concomitant change in the shedding of CD18 integrins suggested that these adhesion molecules play a role in the migration of the MDDCs through the extracellular matrix layer.

CONCLUSION

Taken together, our findings points to a possible, yet subtle, role of IL-20 in DCs migration. The biphasic response suggests that the aberrant IL-20 expression in psoriasis impedes DC migration, which could be a part of the processes that precipitates the dysregulated inflammatory response associated with this disease.

Integrins and integrin-related proteins in cardiac fibrosis

Cardiac fibrosis is one of the major components of the healing mechanism following any injury of the heart and as such may contribute to both systolic and diastolic dysfunction in a range of pathophysiologic conditions. Canonically, it can occur as part of the remodeling process that occurs following myocardial infarction or that follows as a response to pressure overload. Integrins are cell surface receptors which act in both cellular adhesion and signaling. Most importantly, in the context of the continuously contracting myocardium, they are recognized as mechanotransducers. They have been implicated in the development of fibrosis in several organs, including the heart. This review will focus on the involvement of integrins and integrin-related proteins, in cardiac fibrosis, outlining the roles of these proteins in the fibrotic responses in specific cardiac pathologies, discuss some of the common end effectors (angiotensin II, transforming growth factor beta 1 and mechanical stress) through which integrins function and finally discuss how manipulation of this set of proteins may lead to new treatments which could prove useful to alter the deleterious effects of cardiac fibrosis.

The circular relationship between matrix metalloproteinase-9 and inflammation following myocardial infarction

Matrix metalloproteinase-9 (MMP-9) regulates remodeling of the left ventricle after myocardial infarction (MI) and is tightly linked to the inflammatory response. The inflammatory response serves to recruit leukocytes as part of the wound healing reaction to the MI injury, and infiltrated leukocytes produce cytokines and chemokines that stimulate MMP-9 production and release. In turn, MMP-9 proteolyzes cytokines and chemokines. Although in most cases, MMP-9 cleavage of the cytokine or chemokine substrate serves to increase activity, there are cases where cleavage results in reduced activity. Global MMP-9 deletion in mouse MI models has proven beneficial, suggesting inhibition of some aspects of MMP-9 activity may be valuable for clinical use. At the same time, overexpression of MMP-9 in macrophages has also proven beneficial, indicating that we still do not fully understand the complexity of MMP-9 mechanisms of action. In this review, we summarize the cycle of MMP-9 effects on cytokine production and cleavage to regulate leukocyte functions. Although we use MI as the example process, similar events occur in other inflammatory and wound healing conditions.

Matrix remodeling by MMPs during wound repair

Repair following injury involves a range of processes - such as re-epithelialization, scar formation, angiogenesis, inflammation, and more - that function, often together, to restore tissue architecture. MMPs carry out diverse roles in all of these activities. In this article, we discuss how specific MMPs act on ECM during two critical repair processes: re-epithelialization and resolution of scar tissue. For wound closure, we discuss how two MMPs - MMP1 in human epidermis and MMP7 in mucosal epithelia - facilitate re-epithelialization by cleaving different ECM or ECM-associated proteins to affect similar integrin:matrix adhesion. In scars and fibrotic tissues, we discuss that a variety of MMPs carry out a diverse range of activities that can either promote or limit ECM deposition. However, few of these MMP-driven activities have been demonstrated to be due a direct action on ECM.

Proteomic approaches to uncover MMP function

Proteomics has revolutionized protease research and particularly contributed to the identification of novel substrates and their sites of cleavage as key determinants of protease function. New technologies and rapid advancements in development of powerful mass spectrometers allowed unprecedented insights into activities of matrix metalloproteinases (MMPs) within their complex extracellular environments. Mass spectrometry-based proteomics extended our knowledge on MMP cleavage specificities and will help to develop more specific inhibitors as new therapeutics. Quantitative proteomics and N-terminal enrichment strategies have revealed numerous novel MMP substrates and shed light on their modes of action in vitro and in vivo. In this review, we provide an overview of current proteomic technologies in protease research and their application to the functional characterization of MMPs.

Neutrophil migration under normal and sepsis conditions

Neutrophil migration is critical for pathogen clearance and host survival during severe sepsis. Interaction of neutrophil adhesion receptors with ligands on endothelial cells results in firm adhesion of the circulating neutrophils, followed by neutrophil activation and directed migration to sites of infection through the basement membrane and interstitial extracellular matrix. Proteolytic enzymes and reactive oxygen species are produced and released by neutrophils in response to a variety of inflammatory stimuli. Although these mediators are important for host defense, they also promote tissue damage. Excessive neutrophil migration during the early stages of sepsis may lead to an exaggerated inflammatory response with associated tissue damage and subsequent organ dysfunction. On the other hand, dysregulation of migration and insufficient migratory response that occurs during the latter stages of severe sepsis contributes to neutrophils' inability to contain and control infection and impaired wound healing. This review discusses the major steps and associated molecules involved in the balance of neutrophil trafficking, the precise regulation of which during sepsis spells life or death for the host.

Role of MMP2 and MMP9 in TRPV4-induced lung injury

Ca(2+) entry through transient receptor potential vanilloid 4 (TRPV4) results in swelling, blebbing, and detachment of the epithelium and capillary endothelium in the intact lung. Subsequently, increased permeability of the septal barrier and alveolar flooding ensue. In this study, we tested the hypothesis that TRPV4 activation provides a Ca(2+) source necessary for proteolytic disruption of cell-cell or cell-matrix adhesion by matrix metalloproteinases (MMPs) 2 and 9, thus increasing septal barrier permeability. In our study, C57BL/6 or TRPV4(-/-) mouse lungs were perfused with varying doses of the TRPV4 agonist GSK-1016790A (Sigma) and then prepared for Western blot. Lung injury, assessed by increases in lung wet-to-dry weight ratios and total protein levels in the bronchoalveolar lavage fluid, was increased in a dose-dependent fashion in TRPV4(+/+) but not TRPV4(-/-) lungs. In concert with lung injury, we detected increased active MMP2 and MMP9 isoforms, suggesting that TRPV4 can provide the Ca(2+) source necessary for increased MMP2/9 activation. Furthermore, tissue inhibitor of metalloproteinases (TIMP) 2 levels in the TRPV4-injured lungs were decreased, suggesting that TRPV4 activation increases the availability of these active MMPs. We then determined whether MMP2 and MMP9 mediate TRPV4-induced lung injury. Pharmacological blockade (SB-3CT, 1 μM; Sigma) of MMP2 and MMP9 resulted in protection against TRPV4-induced lung injury. We conclude that TRPV4 activation and the subsequent Ca(2+) transient initiates a rapid cascade of events leading to release and activation of the gelatinase MMPs, which then contribute to lung injury.

Matrix metalloproteinase-9 involvement in the structural plasticity of dendritic spines

Dendritic spines are the locus for excitatory synaptic transmission in the brain and thus play a major role in neuronal plasticity. The ability to alter synaptic connections includes volumetric changes in dendritic spines that are driven by scaffolds created by the extracellular matrix (ECM). Here, we review the effects of the proteolytic activity of ECM proteases in physiological and pathological structural plasticity. We use matrix metalloproteinase-9 (MMP-9) as an example of an ECM modifier that has recently emerged as a key molecule in regulating the morphology and dysmorphology of dendritic spines that underlie synaptic plasticity and neurological disorders, respectively. We summarize the influence of MMP-9 on the dynamic remodeling of the ECM via the cleavage of extracellular substrates. We discuss its role in the formation, modification, and maintenance of dendritic spines in learning and memory. Finally, we review research that implicates MMP-9 in aberrant synaptic plasticity and spine dysmorphology in neurological disorders, with a focus on morphological abnormalities of dendritic protrusions that are associated with epilepsy.

Discovery of Emphysema Relevant Molecular Networks from an A/J Mouse Inhalation Study Using Reverse Engineering and Forward Simulation (REFS™)

Chronic obstructive pulmonary disease (COPD) is a respiratory disorder caused by extended exposure of the airways to noxious stimuli, principally cigarette smoke (CS). The mechanisms through which COPD develops are not fully understood, though it is believed that the disease process includes a genetic component, as not all smokers develop COPD. To investigate the mechanisms that lead to the development of COPD/emphysema, we measured whole genome gene expression and several COPD-relevant biological endpoints in mouse lung tissue after exposure to two CS doses for various lengths of time. A novel and powerful method, Reverse Engineering and Forward Simulation (REFS™), was employed to identify key molecular drivers by integrating the gene expression data and four measured COPD-relevant endpoints (matrix metalloproteinase (MMP) activity, MMP-9 levels, tissue inhibitor of metalloproteinase-1 levels and lung weight). An ensemble of molecular networks was generated using REFS™, and simulations showed that it could successfully recover the measured experimental data for gene expression and COPD-relevant endpoints. The ensemble of networks was then employed to simulate thousands of in silico gene knockdown experiments. Thirty-three molecular key drivers for the above four COPD-relevant endpoints were therefore identified, with the majority shown to be enriched in inflammation and COPD.

Decreased plasma levels of soluble CD18 link leukocyte infiltration with disease activity in spondyloarthritis

INTRODUCTION

Spondyloarthritis (SpA) comprises a group of diseases often associated with HLA-B27 and characterized by inflammation of the entheses and joints of the axial skeleton. The inflammatory process in SpA is presumably driven by innate immune cells but is still poorly understood. Thus, new tools for monitoring and treating inflammation are needed. The family of CD18 integrins is pivotal in guiding leukocytes to sites of inflammation, and CD18 hypomorphic mice develop a disease resembling SpA. Previously, we demonstrated that altered soluble CD18 (sCD18) complexes in the blood and synovial fluid of patients with arthritis have anti-inflammatory functions. Here, we study the mechanisms for these alterations and their association with SpA disease activity.

METHODS

Plasma levels of sCD18 in a study population with 84 patients with SpA and matched healthy controls were analyzed with a time-resolved immunoflourometric assay (TRIFMA). Binding of sCD18 to endothelial cells and fibroblast-like synoviocytes (FLSs) was studied with confocal microscopy. Shedding of CD18 from peripheral blood mononuclear cells (PBMCs) was studied with flow cytometry and TRIFMA.

RESULTS

Plasma levels of sCD18 were decreased in patients with SpA compared with healthy volunteers (P <0.001), and the lowest levels were in the HLA-B27-positive subgroup (P <0.05). In a multiple regression model, the sCD18 levels exhibited an inverse correlation with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) (P <0.05), the level of morning stiffness (P <0.05), the Bath Ankylosing Spondilitis Metrology Index (P <0.05), the physician global assessment score (P <0.01), and the sacroiliac magnetic resonance imaging activity score (P <0.05). The mechanisms for these changes could be simulated in vitro. First, sCD18 in plasma adhered to inflammation-induced intercellular adhesion molecule 1 (ICAM-1) on endothelial cells and FLS, indicating increased consumption. Second, CD18 shedding from SpA PBMCs correlated inversely with the BASDAI (P <0.05), suggesting insufficient generation. CD18 was shed primarily from intermediate CD14⁺⁺ CD16⁺ monocytes, supporting the view that alterations in innate immunity can regulate the inflammatory processes in SpA.

CONCLUSIONS

Taken together, the failure of patients with SpA to maintain adequate sCD18 levels may reflect insufficient CD18 shedding from monocytes to counterbalance the capture of sCD18 complexes to inflammation-induced ICAM-1. This could increase the availability of ICAM-1 molecules on the endothelium and in the synovium, facilitating leukocyte migration to the entheses and joints and aggregating disease activity.

Gelatinase B/MMP-9 in Tumour Pathogenesis and Progression

Since its original identification as a leukocyte gelatinase/type V collagenase and tumour type IV collagenase, gelatinase B/matrix metalloproteinase (MMP)-9 is now recognised as playing a central role in many aspects of tumour progression. In this review, we relate current concepts concerning the many ways in which gelatinase B/MMP-9 influences tumour biology. Following a brief outline of the gelatinase B/MMP-9 gene and protein, we analyse the role(s) of gelatinase B/MMP-9 in different phases of the tumorigenic process, and compare the importance of gelatinase B/MMP-9 source in the carcinogenic process. What becomes apparent is the importance of inflammatory cell-derived gelatinase B/MMP-9 in tumour promotion, early progression and triggering of the "angiogenic switch", the integral relationship between inflammatory, stromal and tumour components with respect to gelatinase B/MMP-9 production and activation, and the fundamental role for gelatinase B/MMP-9 in the formation and maintenance of tumour stem cell and metastatic niches. It is also apparent that gelatinase B/MMP-9 plays important tumour suppressing functions, producing endogenous angiogenesis inhibitors, promoting inflammatory anti-tumour activity, and inducing apoptosis. The fundamental roles of gelatinase B/MMP-9 in cancer biology underpins the need for specific therapeutic inhibitors of gelatinase B/MMP-9 function, the use of which must take into account and substitute for tumour-suppressing gelatinase B/MMP-9 activity and also limit inhibition of physiological gelatinase B/MMP-9 function.

A proteomic approach for the elucidation of the specificity of ectodomain shedding

Ectodomain shedding (shedding) is a posttranslational modification mechanism, which liberates extracellular domains of membrane proteins through juxtamembrane processing. Because shedding alters cell characteristics in a rapid and irreversible manner, it must be strictly regulated. However, the regulatory mechanisms of shedding in response to environmental changes remain obscure. To evaluate the regulatory mechanisms of endogenous shedding, we previously developed a proteomic screening system to identify shedding targets. This system revealed a comprehensive picture of membrane proteins shed under defined conditions. In this study, we have improved the screening system to compare the shedding patterns in a mouse macrophage cell line treated with two different shedding inducers, lipopolysaccharide (LPS) and 12-O-tetradecanoylphorbol 13-acetate (TPA). We show here that LPS simultaneously activates the shedding of multiple membrane proteins. We further show that TPA specifically activates the shedding of αM/β2 integrin (Mac-1), which was not shed upon LPS-stimulation of macrophages. These results clearly demonstrate that the regulation of endogenous membrane protein shedding is both stimulus- and substrate-specific.

BIOLOGICAL SIGNIFICANCE

The shedding targets reported to date play pivotal roles in a variety of biological phenomena, including the immunological response, cell growth, cell adhesion and cell movement. In addition, several disease-related membrane proteins are shedding targets. Thus, understanding the regulation of shedding is important for the elucidation of pathogenesis and the development of therapeutic strategies. We submit that a comprehensive characterization of endogenous shedding is indispensable for understanding the regulatory mechanisms of shedding, and thus have developed a proteomic screening system to identify shedding targets. In this study, using our screening system, we demonstrate that different extracellular stimuli activate different types of shedding, even in a single cell. Our results prove that this proteomic approach is quite effective for the elucidation of the regulatory mechanisms of shedding.

Detection of soluble CR3 (CD11b/CD18) by time-resolved immunofluorometry

In the cell membrane complement receptor 3 (CR3) consists of one alpha chain (CD11b) and one beta chain (CD18). CR3 participates in many immunological processes, especially those involving cell migration, adhesion, and phagocytosis of complement-opsonized microbes. Recent findings of soluble CR3 in body fluids and in culture supernatant from experiments in vitro point to the involvement of ecto domain shedding as a part of the CR3 biology. To monitor such shedding on a quantitative basis, we have developed time-resolved immunofluorometric assays (TRIFMA) to detect soluble CD11b and CD18 in plasma or serum of either human or murine origin. Compared with most enzyme-linked immunosorbent assays methodologies, TRIFMA possesses prominent advantages, including better dynamic range and reproducibility. These assays may contribute to the understanding of the role of shedding of CR3 and other cell adhesion molecules in human disease and animal models involving inflammation.

Characterization of the shear stress regulation of CD18 surface expression by HL60-derived neutrophil-like cells

Shear stress-induced cleavage of cell surface CD18 integrins is reported to be part of an anti-inflammatory control mechanism that minimizes neutrophil activity in the blood under physiologic conditions. The cysteine protease, cathepsin B (catB), has been implicated in this mechanoregulatory mechanism, but its molecular dynamics remain to be elucidated. Moreover, attempts to do so using molecular approaches are hindered by the limited ex vivo life span of primary neutrophils. As an alternative, we explored the potential use of HL60-derived neutrophilic cells as a transfectable culture model that exhibits a shear-induced CD18 cleavage response comparable to primary neutrophils. HL60 cells were differentiated into neutrophil-like cells (dHL60-NCs) and exposed to laminar shear stress ([Formula: see text] for 10 min). Based on cytometric analyses, sheared cells cleaved CD18 and CD11a, but not CD11b, integrins. Treatment of cells with E64 or doxycycline prior to and during shear exposure inhibited CD18, but only attenuated CD11a, cleavage. Neither aprotinin nor pepstatin affected shear-induced CD18 or CD11a cleavage. Notably, dHL60-NCs expressed minimal catB. Thus, multiple cysteine proteases in addition to catB may cleave CD18 on sheared leukocytes. In fact, our findings indicate that multiple non-cysteine proteases also participate in the shear-related cleavage of CD11/CD18 heterodimers. Finally, shear-induced cleavage of CD18 and CD11a by dHL60-NCs was inhibited by fMLP concentrations of at least [Formula: see text]. Collectively, our findings indicate that shear-induced CD11/CD18 cleavage is phenotypic of neutrophilic cells, including those derived from HL60 cells. Moreover, our results verify shear stress as a key anti-inflammatory stimulus for neutrophils under physiologic conditions.

Monocyte ADAM17 promotes diapedesis during transendothelial migration: identification of steps and substrates targeted by metalloproteinases

Despite expanded definition of the leukocyte adhesion cascade and mechanisms underlying individual steps, very little is known about regulatory mechanisms controlling sequential shifts between steps. We tested the hypothesis that metalloproteinases provide a mechanism to rapidly transition monocytes between different steps. Our study identifies diapedesis as a step targeted by metalloproteinase activity. Time-lapse video microscopy shows that the presence of a metalloproteinase inhibitor results in a doubling of the time required for human monocytes to complete diapedesis on unactivated or inflamed human endothelium, under both static and physiological-flow conditions. Thus, diapedesis is promoted by metalloproteinase activity. In contrast, neither adhesion of monocytes nor their locomotion over the endothelium is altered by metalloproteinase inhibition. We further demonstrate that metalloproteinase inhibition significantly elevates monocyte cell surface levels of integrins CD11b/CD18 (Mac-1), specifically during transendothelial migration. Interestingly, such alterations are not detected for other endothelial- and monocyte-adhesion molecules that are presumed metalloproteinase substrates. Two major transmembrane metalloproteinases, a disintegrin and metalloproteinase (ADAM)17 and ADAM10, are identified as enzymes that control constitutive cleavage of Mac-1. We further establish that knockdown of monocyte ADAM17, but not endothelial ADAM10 or ADAM17 or monocyte ADAM10, reproduces the diapedesis delay observed with metalloproteinase inhibition. Therefore, we conclude that monocyte ADAM17 facilitates the completion of transendothelial migration by accelerating the rate of diapedesis. We propose that the progression of diapedesis may be regulated by spatial and temporal cleavage of Mac-1, which is triggered upon interaction with endothelium.

Proteomic Identification of Matrix Metalloproteinase Substrates in the Human Vasculature

Background—

Matrix metalloproteinases (MMPs) play a key role in cardiovascular disease, in particular aneurysm formation and plaque rupture. Surprisingly, little is known about MMP substrates in the vasculature.

Methods and Results—

We used a proteomics approach to identify vascular substrates for 3 MMPs, 1 of each of the 3 major classes of MMPs: Human arteries were incubated with MMP-3 (a member of stromelysins), MMP-9 (considered a gelatinase), and MMP-14 (considered a member of the collagenases and of the membrane-bound MMPs). Candidate substrates were identified by mass spectrometry based on increased release from the arterial tissue on digestion, spectral evidence for proteolytic degradation after gel separation, and identification of nontryptic cleavage sites. Using this approach, novel candidates were identified, including extracellular matrix proteins associated with the basement membrane, elastic fibers (emilin-1), and other extracellular proteins (periostin, tenascin-X). Seventy-four nontryptic cleavage sites were detected, many of which were shared among different MMPs. The proteomics findings were validated by immunoblotting and by digesting recombinant/purified proteins with exogenous MMPs. As proof-of-principle, results were related to in vivo pathology by searching for corresponding degradation products in human aortic tissue with different levels of endogenous MMP-9.

Conclusions—

The application of proteomics to identify MMP targets is a new frontier in cardiovascular research. Our current classification of MMPs based on few substrates is an oversimplification of a complex area of biology. This study provides a more comprehensive assessment of potential MMP substrates in the vasculature and represents a valuable resource for future investigations.

On the roles of polyvalent binding in immune recognition: perspectives in the nanoscience of immunology and the immune response to nanomedicines

Immunology often conveys the image of large molecules, either in the soluble state or in the membrane of leukocytes, forming multiple contacts with a target for actions of the immune system. Avidity names the ability of a polyvalent molecule to form multiple connections of the same kind with ligands tethered to the same surface. Polyvalent interactions are vastly stronger than their monovalent equivalent. In the present review, the functional consequences of polyvalent interactions are explored in a perspective of recent theoretical advances in understanding the thermodynamics of such binding. From insights on the structural biology of soluble pattern recognition molecules as well as adhesion molecules in the cell membranes or in their proteolytically shed form, this review documents the prominent role of polyvalent interactions in making the immune system a formidable barrier to microbial infection as well as constituting a significant challenge to the application of nanomedicines.

The relationship between the MMP system, adrenoceptors and phosphoprotein phosphatases

The MMPs and their inhibitors [tissue inhibitor of MMPs (TIMPs)] form the mainstay of extracellular matrix homeostasis. They are expressed in response to numerous stimuli including cytokines and GPCR activation. This review highlights the importance of adrenoceptors and phosphoprotein phosphatases (PPP) in regulating MMPs in the cardiovascular system, which may help explain some of the beneficial effects of targeting the adrenoceptor system in tissue remodelling and will establish emerging crosstalk between these three systems. Although α- and β-adrenoceptor activation increases MMP but decreases TIMP expression, MMPs are implicated in the growth stimulatory effects of adrenoceptor activation through transactivation of epidermal growth factor receptor. Furthermore, they have recently been found to catalyse the proteolysis of β-adrenoceptors and modulate vascular tone. While the mechanisms underpinning these effects are not well defined, reversible protein phosphorylation by kinases and phosphatases may be key. In particular, PPP (Ser/Thr phosphatases) are not only critical in resensitization and internalization of adrenoceptors but also modulate MMP expression. The interrelationship is complex as isoprenaline (ISO) inhibits okadaic acid [phosphoprotein phosphatase type 1/phosphoprotein phosphatase type 2A (PP2A) inhibitor]-mediated MMP expression. While this may be simply due to its ability to transiently increase PP2A activity, there is evidence for MMP-9 that ISO prevents okadaic acid-mediated expression of MMP-9 through a β-arrestin, NF-κB-dependent pathway, which is abolished by knock-down of PP2A. It is essential that crosstalk between MMPs, adrenoceptors and PPP are investigated further as it will provide important insight into how adrenoceptors modulate cardiovascular remodelling, and may identify new targets for pharmacological manipulation of the MMP system.