Membrane-type matrix metalloproteinases: key mediators of leukocyte function

Autoimmunity: A New Focus on Nasal Polyps

Chronic rhinosinusitis with nasal polyps (CRSwNP) has long been considered a benign, chronic inflammatory, and hyperplastic disease. Recent studies have shown that autoimmune-related mechanisms are involved in the pathology of nasal polyps. Activated plasma cells, eosinophils, basophils, innate type 2 lymphocytes, mast cells, and proinflammatory cytokine in polyp tissue indicate the mobilization of innate and adaptive immune pathways during polyp formation. The discovery of a series of autoantibodies further supports the autoimmune nature of nasal polyps. Local homeostasis dysregulation, infection, and chronic inflammation may trigger autoimmunity through several mechanisms, including autoantigens overproduction, microbial translocation, molecular mimicry, superantigens, activation or inhibition of receptors, bystander activation, dysregulation of Toll-Like Receptors (TLRs), epitope spreading, autoantigens complementarity. In this paper, we elaborated on the microbiome-mediated mechanism, abnormal host immunity, and genetic changes to update the role of autoimmunity in the pathogenesis of chronic rhinosinusitis with nasal polyps.

Changes in the expression of membrane type-matrix metalloproteinases genes (MMP14, MMP15, MMP16, MMP24) during treatment and their potential impact on the survival of patients with non-small cell lung cancer (NSCLC)

The analysis concerned the comparison of the expression of membrane type matrix metalloproteinases genes in the blood and tissue of NSCLC patients during the course of the disease and comparison to the control group. Blood and neoplastic tissue taken from 45 patients diagnosed with non-small cell lung cancer was a research material. The expression level of MMP14, MMP15, MMP16 and MMP24 was evaluated by qPCR and the results were compared with controls. The expression of MMP14 and MMP24 before tumor removal surgery and 100 days after was lower than in the control group. Interestingly, one year after surgery the levels of expression of these genes were identical to those in the control group. This suggests that the expression of metalloproteinase genes changes in the course of cancer and that effective treatment results in the normalization of gene expression. Lower expression of MMP15 in the blood of patients with more advanced cancer disease was observed, confirming the suppressive nature of changes in the blood. It has also been demonstrated that higher expression of MMP14 and MMP15 in the tissue is associated with more advanced stage of disease development or more invasive nature of the lesion. There is a noticeable increase of expression level in the environment surrounding the tumor, while a lower can be observed in the blood. This may indicate that changes in the expression of metalloproteinases in cancer are much more complex than merely the tumor tissue, which may also account for the inadequacies of metalloproteinase inhibitors.

Dysregulation of Leukocyte Trafficking in Type 2 Diabetes: Mechanisms and Potential Therapeutic Avenues

Type 2 Diabetes Mellitus (T2DM) is a chronic inflammatory disorder that is characterized by chronic hyperglycemia and impaired insulin signaling which in addition to be caused by common metabolic dysregulations, have also been associated to changes in various immune cell number, function and activation phenotype. Obesity plays a central role in the development of T2DM. The inflammation originating from obese adipose tissue develops systemically and contributes to insulin resistance, beta cell dysfunction and hyperglycemia. Hyperglycemia can also contribute to chronic, low-grade inflammation resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under inflammatory condition is dysregulated in T2DM. We particularly highlight the obesity-related accumulation of leukocytes in the adipose tissue leading to insulin resistance and beta-cell dysfunction and resulting in hyperglycemia and consequent changes of adhesion and migratory behavior of leukocytes in different vascular beds. Thus, here we discuss how potential therapeutic targeting of leukocyte trafficking could be an efficient way to control inflammation as well as diabetes and its vascular complications.

MT1-MMP activatable fluorogenic probes with enhanced specificity via high-affinity peptide conjugation for tumor imaging

Overlapping substrate specificities within the family of matrix metalloproteinases (MMPs), usually caused by their highly conserved structural topology, increase the potential for a substrate to be cleaved by multiple enzymes within this family, which leads to the decrease in the selectivity of MMP substrate-based probes. To resolve this issue, MT1-MMP activatable fluorogenic probes for tumor detection with enhanced specificity were developed by combining a fluorescence resonance energy transfer (FRET) peptide substrate and its specific binding peptide with different lengths of linkers. The specificity of the probes increased profiting from the high affinity of the MT1-MMP specific binding peptide while keeping the ability to amplify the output imaging signals in response to MMP activity with the FRET substrate. Enzyme kinetics analysis clearly demonstrated that the conjugation of P-1 and MT1-AF7p enhanced both the specificity and selectivity of the fluorogenic probes for MT1-MMP, and introducing a linker composed of 12 PEG subunits into these two fragments led to optimized specificity and selectivity of the fluorogenic probe for MT1-MMP. Both in vitro and in vivo results revealed that the imaging probe with the linker composed of 12 PEG subunits based on our designed strategy could be effectively applied for MT1-MMP positive tumor imaging. Since this strategy for enhancing the specificity of protease sensing probes can be applied to other proteases and is not just limited to MT1-MMP, it is an appealing platform to achieve selective tumor imaging.

MMP targeting in the battle for vision: Recent developments and future prospects in the treatment of diabetic retinopathy

Matrix metalloproteinases (MMPs) are enzymes capable of degrading nearly all types of extracellular matrix. They perform a wide range of roles in physiological processes, which is the reason for their strict regulation by numerous mechanisms including natural tissue inhibitors of metalloproteinases (TIMP). Research only started to shed light on more troublesome aspects of MMPs function, like cancer progression, Alzheimer's disease, atherosclerosis, ageing. Moreover, their profound role in diabetes is being carefully investigated including one of its most debilitating complications - diabetic retinopathy (DR), the leading cause of acquired blindness worldwide. Traditional treatment of this condition seems to be only mildly satisfactory, which elicited substantial interest in the field of new therapeutic methods including MMP targeting. So far, significant roles of MMP-2 and MMP-9 in the development of retinopathy have been established, with special attention given to the process of blood-retinal barrier impairment. Further exploration revealed MMP-10 and MMP-14 involvement as well as changes in MMP/TIMP ratio. In this review, we provide insight into MMPs role in diabetic retinopathy with a clarification of various mechanisms regulating MMP activity in the light of the recent studies. We conclude with an overview of novel DR therapies targeting MMPs and point to the need of further examination of their usefulness in clinical setting, with an eye towards future research.

Biological activities of interleukin (IL)-21 in human monocytes and macrophages

The biological roles of interleukin (IL)-21 in human monocytes and macrophages have been neglected. We previously demonstrated that IL-21 induce phagocytosis and established that Syk is a new molecular target of IL-21. Herein, we found that IL-21 is not chemoattractant for immature THP-1 and primary monocytes but can increase the capacity of THP-1 cells (not primary monocytes) to adhere onto a cell substratum by a Syk-dependent mechanism without altering the expression of a panel of cell surface molecules. Unlike THP- 1 and monocytes, IL-21 can increase metalloproteinase (MMP)-9 secretion and activity in monocyte-derived macrophages (HMDM), as assessed by western blot and zymography experiments, respectively. We reported that IL-21 did not increase the production of IL-6 and the chemokines MIP-1α and GRO-α in HMDM. Therefore, IL-21 can increase functions other that phagocytosis, but this cytokine does not have a large spectrum of biological activities in monocytes and macrophages.

MicroRNA and mRNA expression associated with ectopic germinal centers in thymus of myasthenia gravis

BACKGROUND

A characteristic pathology of early onset myasthenia gravis is thymic hyperplasia with ectopic germinal centers (GC). However, the mechanisms that trigger and maintain thymic hyperplasia are poorly characterized. Dysregulation of small, non-coding microRNAs (miRNAs) and their target genes has been identified in the pathology of several autoimmune diseases. We assessed the miRNA and mRNA profiles of the MG thymus and have investigated their role in GC formation and maintenance.

METHODS

MG thymus samples were assessed by histology and grouped based upon the appearance of GC; GC positive and GC negative. A systems biology approach was used to study the differences between the groups. Our study included miRNA and mRNA profiling, quantitative real-time PCR validation, miRNA target identification, pathway analysis, miRNA-mRNA reciprocal expression pairing and interaction.

RESULTS

Thirty-eight mature miRNAs and forty-six annotated mRNA transcripts were differentially expressed between the two groups (>1.5 fold change, ANOVA p<0.05). The miRNAs were found to be involved in immune response pathways and identified in other autoimmune diseases. The cellular and molecular functions of the mRNAs showed involvement in cell death and cell survival, cellular proliferation, cytokine signaling and extra-cellular matrix reorganization. Eleven miRNA and mRNA pairs were reciprocally regulated. The Regulator of G protein Signalling 13 (RGS13), known to be involved in GC regulation, was identified in specimens with GC and was paired with downregulation of miR-452-5p and miR-139-5p. MiRNA target sites were validated by dual luciferase assay. Transfection of miRNA mimics led to down regulation of RGS13 expression in Raji cells.

CONCLUSION

Our study indicates a distinct miRNA and mRNA expression pattern in ectopic GC in MG thymus. These miRNAs and mRNAs are involved in regulatory pathways common to inflammation and immune response, cell cycle regulation and anti-apoptotic pathways suggesting their involvement in support of GC formation in the thymus. We demonstrate for the first time that miR-139-5p and miR-452-5p negatively regulate RGS13 expression.

Optimization of a MT1-MMP-targeting Peptide and Its Application in Near-infrared Fluorescence Tumor Imaging

Membrane type 1 metalloproteinase (MT1-MMP) is an important regulator of cancer invasion, growth and angiogenesis, thus making it an attractive target for cancer imaging and therapy. A non-substrate peptide (MT1-AF7p) that bonded to the "MT-Loop" region of MT1-MMP was identified by using a phage-displayed peptide library and was used to image the MT1-MMP expression in vivo through optical imaging. However, the substrate in the screening did not have a 3D structure, thus resulting in a loose bonding of MT1-AF7p. To simulate the real conformation of the "MT-Loop" and improve the performance of MT1-AF7p, molecular simulations were performed, because this strategy provides multiple methods for predicting the conformation and interaction of proteinase in 3D. In view of the binding site of the receptor-ligand interactions, histidine 4 was selected for mutation to achieve an increased affinity effect. The optimized peptides were further identified and conformed by atomic force microscopy, isothermal titration calorimetry, cell fluorescence imaging in vitro, and near-infrared fluorescence tumor optical imaging in vivo. The results revealed that the optimized peptide with a mutation of histidine 4 to arginine has the highest affinity and specificity, and exhibited an increased fluorescence intensity in the tumor site in optical imaging.

Peripheral Ulcerative Keratitis Associated with Autoimmune Disease: Pathogenesis and Treatment

Peripheral ulcerative keratitis (PUK) is type of crescent-shaped inflammatory damage that occurs in the limbal region of the cornea. PUK is always combined with an epithelial defect and the destruction of the peripheral corneal stroma. PUK may have a connection to systemic conditions, such as long-standing rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Wegener granulomatosis (WG), relapsing polychondritis, classic polyarteritis nodosa and its variants, microscopic polyangiitis, and Churg-Strauss syndrome. However, the most common connection is with RA, which is also the focus of this review. The pathogenesis of PUK is still unclear. It is thought that circulating immune complexes and cytokines exert an important influence on the progression of this syndrome. Treatment is applied to inhibit certain aspects of PUK pathogenesis.

Metalloproteinases: a Functional Pathway for Myeloid Cells

Myeloid cells have diverse roles in regulating immunity, inflammation, and extracellular matrix turnover. To accomplish these tasks, myeloid cells carry an arsenal of metalloproteinases, which include the matrix metalloproteinases and the adamalysins. These enzymes have diverse substrate repertoires, and are thus involved in mediating proteolytic cascades, cell migration, and cell signaling. Dysregulation of metalloproteinases contributes to pathogenic processes, including inflammation, fibrosis, and cancer. Metalloproteinases also have important nonproteolytic functions in controlling cytoskeletal dynamics during macrophage fusion and enhancing transcription to promote antiviral immunity. This review highlights the diverse contributions of metalloproteinases to myeloid cell functions.

Evidence for the Involvement of Matrix-Degrading Metalloproteinases (MMPs) in Atherosclerosis

Atherosclerosis leads to blockage of arteries, culminating in myocardial infarction, and stroke. The involvement of matrix-degrading metalloproteinases (MMPs) in atherosclerosis is established and many studies have highlighted the importance of various MMPs in this process. MMPs were first implicated in atherosclerosis due to their ability to degrade extracellular matrix components, which can lead to increased plaque instability. However, more recent work has highlighted a multitude of roles for MMPs in addition to breakdown of extracellular matrix proteins. MMPs are now known to be involved in various stages of plaque progression: from initial macrophage infiltration to plaque rupture. This chapter summarizes the development and progression of atherosclerotic plaques and the contribution of MMPs. We provide data from human studies showing the effect of MMP polymorphisms and the expression of MMPs in both the atherosclerotic plaque and within plasma. We also discuss work in animal models of atherosclerosis that show the effect of gain or loss of function of MMPs. Together, the data provided from these studies illustrate that MMPs are ideal targets as both biomarkers and potential drug therapies for atherosclerosis.

Chronic Pelvic Pain Development and Prostate Inflammation in Strains of Mice With Different Susceptibility to Experimental Autoimmune Prostatitis

BACKGROUND

Experimental autoimmune prostatitis (EAP) is an autoimmune inflammatory disease of the prostate characterized by peripheral prostate-specific autoimmune responses associated with prostate inflammation. EAP is induced in rodents upon immunization with prostate antigens (PAg) plus adjuvants and shares important clinical and immunological features with the human disease chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS).

METHODS

EAP was induced in young NOD, C57BL/6, and BALB/c male mice by immunization with PAg plus complete Freund́s adjuvant. Tactile allodynia was assessed using Von Frey fibers as a measure of pelvic pain at baseline and at different time points after immunization. Using conventional histology, immunohistochemistry, FACS analysis, and protein arrays, an interstrain comparative study of prostate cell infiltration and inflammation was performed.

RESULTS

Chronic pelvic pain development was similar between immunized NOD and C57BL/6 mice, although the severity of leukocyte infiltration was greater in the first case. Coversely, minimal prostate cell infiltration was observed in immunized BALB/c mice, who showed no pelvic pain development. Increased numbers of mast cells, mostly degranulated, were detected in prostate samples from NOD and C57BL/6 mice, while lower total counts and resting were observed in BALB/c mice. Prostate tissue from NOD mice revealed markedly increased expression levels of inflammatory cytokines, chemokines, adhesion molecules, vascular endothelial growth factor, and metalloproteinases. Similar results, but to a lesser extent, were observed when analyzing prostate tissue from C57BL/6 mice. On the contrary, the expression of the above mediators was very low in prostate tissue from immunized BALB/c mice, showing significantly slight increments only for CXCL1 and IL4.

CONCLUSIONS

Our results provide new evidence indicating that NOD, C57BL/6, and BALB/c mice develop different degrees of chronic pelvic pain, type, and amount of prostate cell infiltration and secretion of inflammatory mediators. Our results corroborate and support the notion that mice with different genetic background have different susceptibility to EAP induction. Prostate 77:94-104, 2017. © 2016 Wiley Periodicals, Inc.

On Chip Bioelectric Impedance Spectroscopy Reveals the Effect of P-Glycoprotein Efflux Pumps on the Paracellular Impedance of Tight Junctions at the Blood-Brain Barrier

Bioelectric impedance spectroscopy was used to elucidate the influence of P-gp efflux pumps on the kinetics of tight junction down-regulation in confluent monolayers of Madine Darby Canine Kidney Epithelial Cells (MDCK) following administration of phenylarsine oxide (PAO), a molecule that inhibits protein tyrosine phosphatases (PTP) and induces matrix metalloproteinase activity. Matrix metalloproteinases (MMPs) and phosphatase inhibitors induce modification of occludin tight junction proteins critical for the proper function of the blood-brain barrier. The addition of PAO to MDCKII cell lines resulted in a dramatic decrease in monolayer resistance. In contrast, MDCKII-MDR1 cells transfected with the MDR1 gene treated with PAO showed an initial decrease in monolayer resistance followed by a partial recovery and subsequent decrease. This resistance decay reversal was suppressed with the addition of the P-glycoprotein (P-gp) pump inhibitor elacridar, and is attributed to PAO efflux. These results illustrate impedance spectroscopy can be used to characterize the competing kinetics of efflux and down-regulation of tight junctions. In addition, the resistance decay reversal effect can be used to evaluate P-gp pump inhibitor efficacy.

Sustained Immune Complex-Mediated Reduction in CD16 Expression after Vaccination Regulates NK Cell Function

Cross-linking of FcγRIII (CD16) by immune complexes induces antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells, contributing to control of intracellular pathogens; this pathway can also be targeted for immunotherapy of cancerous or otherwise diseased cells. However, downregulation of CD16 expression on activated NK cells may limit or regulate this response. Here, we report sustained downregulation of CD16 expression on NK cells in vivo after intramuscular (but not intranasal) influenza vaccination. CD16 downregulation persisted for at least 12 weeks after vaccination and was associated with robust enhancement of influenza-specific plasma antibodies after intramuscular (but not intranasal) vaccination. This effect could be emulated in vitro by co-culture of NK cells with influenza antigen and immune serum and, consistent with the sustained effects after vaccination, only very limited recovery of CD16 expression was observed during long-term in vitro culture of immune complex-treated cells. CD16 downregulation was most marked among normally CD16^high CD57⁺ NK cells, irrespective of NKG2C expression, and was strongly positively associated with degranulation (surface CD107a expression). CD16 downregulation was partially reversed by inhibition of ADAM17 matrix metalloprotease, leading to a sustained increase in both CD107a and CD25 (IL-2Rα) expression. Both the degranulation and CD25 responses of CD57+ NK cells were uniquely dependent on trivalent influenza vaccine-specific IgG. These data support a role for CD16 in early activation of NK cells after vaccination and for CD16 downregulation as a means to modulate NK cell responses and maintain immune homeostasis of both antibody and T cell-dependent pathways.

Localization, Shedding, Regulation and Function of Aminopeptidase N/CD13 on Fibroblast like Synoviocytes

Aminopeptidase N/CD13 is highly expressed by fibroblast like synoviocytes (FLS) and may play a role in rheumatoid arthritis (RA). CD13 was previously detected in human synovial fluid where it was significantly increased in RA compared to osteoarthritis. In this study we found that CD13 in biological fluids (plasma, synovial fluid, FLS culture supernatant) is present as both a soluble molecule and on extracellular vesicles, including exosomes, as assessed by differential ultracentrifugation and density gradient separation. Having determined CD13 could be released as a soluble molecule from FLS, we examined potential mechanisms by which CD13 might be shed from the FLS membrane. The use of protease inhibitors revealed that CD13 is cleaved from the FLS surface by metalloproteinases. siRNA treatment of FLS revealed one of those proteases to be MMP14. We determined that pro-inflammatory cytokines (TNFα, IFNγ, IL-17) upregulated CD13 mRNA in FLS, which may contribute to the increased CD13 in RA synovium and synovial fluid. Inhibition of CD13 function by either inhibitors of enzymatic activity or anti-CD13 antibodies resulted in decreased growth and diminished migration of FLS. This suggests that CD13 may be involved in the pathogenic hyperplasia of RA FLS. This data expands potential roles for CD13 in the pathogenesis of RA.

Pyoderma gangrenosum and its syndromic forms: evidence for a link with autoinflammation

Pyoderma gangrenosum is a rare inflammatory neutrophilic dermatosis manifesting as painful ulcers with violaceous, undermined borders on the lower extremities. It may occur in the context of classic syndromes like PAPA (pyogenic arthritis, pyoderma gangrenosum and acne) and SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis), as well as in a recently described entity named PASH (pyoderma gangrenosum, acne and suppurative hidradenitis). Pyoderma gangrenosum has recently been included within the spectrum of autoinflammatory diseases, which are characterized by recurrent episodes of sterile inflammation, without circulating autoantibodies and autoreactive T cells. In PAPA syndrome, different mutations involving the PSTPIP1 gene, via an increased binding affinity to pyrin, induce the assembly of inflammasomes. These are molecular platforms involved in the activation of caspase 1, a protease that cleaves inactive prointerleukin (pro-IL)-1β to its active isoform IL-1β. The overproduction of IL-1β triggers the release of a number of proinflammatory cytokines and chemokines, which are responsible for the recruitment and activation of neutrophils, leading to neutrophil-mediated inflammation. In SAPHO syndrome, the activation of the PSTPIP2 inflammasome has been suggested to play a role in inducing the dysfunction of the innate immune system. Patients with PASH have recently been reported to present alterations of genes involved in well-known autoinflammatory diseases, such as PSTPIP1, MEFV, NOD2 and NLRP3. Pyoderma gangrenosum and its syndromic forms can be regarded as a single clinicopathological spectrum in the context of autoinflammation.

MMP-25 Metalloprotease Regulates Innate Immune Response through NF-κB Signaling

Matrix metalloproteases (MMPs) regulate innate immunity acting over proinflammatory cytokines, chemokines, and other immune-related proteins. MMP-25 (membrane-type 6-MMP) is a membrane-bound enzyme predominantly expressed in leukocytes whose biological function has remained largely unknown. We have generated Mmp25-deficient mice to elucidate the in vivo function of this protease. These mutant mice are viable and fertile and do not show any spontaneous phenotype. However, Mmp25-null mice exhibit a defective innate immune response characterized by low sensitivity to bacterial LPS, hypergammaglobulinemia, and reduced secretion of proinflammatory molecules. Moreover, these immune defects can be tracked to a defective NF-κB activation observed in Mmp25-deficient leukocytes. Globally, our findings provide new mechanistic insights into innate immunity through the activity of MMP-25, suggesting that this proteinase could be a potential therapeutic target for immune-related diseases.

Metalloproteinase production from macrophages - a perfect storm leading to atherosclerotic plaque rupture and myocardial infarction

What is the topic of this review? The review discusses how in atherosclerotic plaques, a combination of inflammatory mediators together with loss of anti inflammatory factors is most likely to be responsible for the excess of MMP over TIMP expression that causes plaque rupture and myocardial infarction. What advances does it highlight? Regulation of matrix metalloproteinases (MMPs) and tissue inhibitors of MMP (TIMPs) is divergent between human and mouse macrophages. There is prostaglandin E₂ -dependent and -independent regulation. Inflammatory cytokines act through distinct (albeit overlapping) signalling pathways to elicit different patterns of MMP and TIMP expression. Transcriptional and epigenetic regulation occurs. Matrix metalloproteinases (MMPs) produced from macrophages contribute to plaque rupture, atherothrombosis and myocardial infarction. New treatments could emerge from defining the mediators and underlying mechanisms. In human monocytes, prostaglandin E₂ (PGE₂ ) stimulates MMP production, and inflammatory mediators such as tumour necrosis factor α, interleukin-1 and Toll-like receptor ligands can act either through or independently of PGE₂ . Differentiation of human monocytes to non-foamy macrophages increases constitutive expression of MMP-7, -8, -9, -14 and -19 and tissue inhibitor of MMP (TIMP)-1 to -3 through unknown, PGE₂ -independent mechanisms. Human macrophages express more MMP-1, -7 and -9 and TIMP-3 and less MMP-12 and -13 than mouse macrophages. Inflammatory mediators working through activator protein-1 and nuclear factor-κB transcription factor pathways upregulate MMP-1, -3, -10, -12 and -14 in human macrophages (MMP-9, -12 and -13 in mice), and studies with plaque tissue sections and isolated foam cells confirm this conclusion in vivo. Classical activation with granulocyte-macrophage colony-stimulating factor upregulates MMP-12, whereas interferon-γ upregulates MMP-12, -14 and -25 and downregulates TIMP-3 in human but not mouse macrophages. Alternative activation with interleukin-4 markedly stimulates the expression of only MMP-12 in humans and MMP-19 in mice. The anti-inflammatory cytokines interleukin-10 and transforming growth factor-β decrease production of several MMPs. Epigenetic upregulation of MMP-14 during foam cell formation or by granulocyte-macrophage colony-stimulating factor occurs by decreasing miRNA-24. A 'perfect storm' caused by a combination of these mechanisms is most likely to promote MMP-mediated macrophage invasion, tissue destruction and atherosclerotic plaque rupture.

Placental membrane-type metalloproteinases (MT-MMPs): Key players in pregnancy

Membrane-type matrix metalloproteinases (MT-MMPs) are a sub-family of zinc-dependent endopeptidases involved in the degradation of the extracellular matrix. Although MT-MMPs have been mainly characterized in tumor biology, they also play a relevant role during pregnancy. Placental MT-MMPs are required for cytotrophoblast migration and invasion of the uterine wall and in the remodeling of the spiral arteries. They are involved in the fusion of cytotrophoblasts to form the syncytiotrophoblast as well as in angiogenesis. All these processes are crucial for establishing and maintaining a successful pregnancy and, thus, MT-MMP activity has to be tightly regulated in time and space. Indeed, a de-regulation of MT-MMP expression has been linked with pregnancy complications such as preeclampsia (PE), fetal growth restriction (FGR), gestational diabetes mellitus (GDM) and was also found in maternal obesity. Here we review what is currently known about MT-MMPs in the placenta, with a focus on their general features, their localization and their involvement in pregnancy disorders.

Mechanism of Diapedesis: Importance of the Transcellular Route

The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. Neutrophil recruitment to inflamed tissues occurs in a well-defined stepwise manner, which includes elements of neutrophil rolling, firm adhesion, and crawling onto the endothelial cell surface before transmigrating across the endothelial barrier. This latter step known as diapedesis can occur at the endothelial cell junction (paracellular) or directly through the endothelial cell body (transcellular). The extravasation cascade is controlled by series of engagement of various adhesive modules, which result in activation of bidirectional signals to neutrophils and endothelial cells for adequate cellular response. This review will focus on recent advances in our understanding of mechanism of leukocyte crawling and diapedesis, with an emphasis on leukocyte-endothelial interactions and the signaling pathways they transduce to determine the mode of diapedesis, junctional or nonjunctional. I will also discuss emerging evidence highlighting key differences in the two modes of diapedesis and why it is clinically important to understand specificity in the regulation of diapedesis.

Leukocyte transcellular diapedesis: Rap1b is in control

The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. It is well known that neutrophils cross the endothelial barrier by transmigrating at the endothelial cell junction ('paracellular'). However, in vivo and in vitro evidence have clearly demonstrated occurrence of an alternate mode of migration directly through the endothelial cell body ('transcellular'). Despite our knowledge on mechanisms of transendothelial migration, it remains unclear which factors determine distinct modes of migration. We recently found that the Ras-like Rap1b GTPase limits neutrophil transcellular migration. Rap1b restrains transcellular migration by suppressing Akt-driven invasive protrusions while leaving the paracellular route unaffected. Furthermore, Rap1b limits neutrophil tissue infiltration in mice and prevents hyper susceptibility to endotoxin shock. These findings uncover a novel role for Rap1b in neutrophil migration and inflammation. Importantly, they offer emerging evidences that paracellular and transcellular migration of neutrophils are regulated by separate mechanisms. Here, we discuss the mechanisms of neutrophil transmigration and their clinical importance for vascular integrity and innate inflammation.

Adult vascular wall resident multipotent vascular stem cells, matrix metalloproteinases, and arterial aneurysms

Evidences have shown the presence of multipotent stem cells (SCs) at sites of arterial aneurysms: they can differentiate into smooth muscle cells (SMCs) and are activated after residing in a quiescent state in the vascular wall. Recent studies have implicated the role of matrix metalloproteinases in the pathogenesis of arterial aneurysms: in fact the increased synthesis of MMPs by arterial SMCs is thought to be a pivotal mechanism in aneurysm formation. The factors and signaling pathways involved in regulating wall resident SC recruitment, survival, proliferation, growth factor production, and differentiation may be also related to selective expression of different MMPs. This review explores the relationship between adult vascular wall resident multipotent vascular SCs, MMPs, and arterial aneurysms.

Addressing the Inflammatory Response to Clinically Relevant Polymers by Manipulating the Host Response Using ITIM Domain-Containing Receptors

Tissue contacting surfaces of medical devices initiate a host inflammatory response, characterized by adsorption of blood proteins and inflammatory cells triggering the release of cytokines, reactive oxygen species (ROS) and reactive nitrogen species (RNS), in an attempt to clear or isolate the foreign object from the body. This normal host response contributes to device-associated pathophysiology and addressing device biocompatibility remains an unmet need. Although widespread attempts have been made to render the device surfaces unreactive, the establishment of a completely bioinert coating has been untenable and demonstrates the need to develop strategies based upon the molecular mechanisms that define the interaction between host cells and synthetic surfaces. In this review, we discuss a family of transmembrane receptors, known as immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors, which show promise as potential targets to address aberrant biocompatibility. These receptors repress the immune response and ensure that the intensity of an immune response is appropriate for the stimuli. Particular emphasis will be placed on the known ITIM-containing receptor, Signal Regulatory Protein Alpha (SIRPhα), and its cognate ligand CD47. In addition, this review will discuss the potential of other ITIM-containing proteins as targets for addressing the aberrant biocompatibility of polymeric biomaterials.

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.

Mmp25β facilitates elongation of sensory neurons during zebrafish development

Matrix metalloproteinases (MMPs) are a large and complex family of zinc-dependent endoproteinases widely recognized for their roles in remodeling the extracellular matrix (ECM) during embryonic development, wound healing, and tissue homeostasis. Their misregulation is central to many pathologies, and they have therefore been the focus of biomedical research for decades. These proteases have also recently emerged as mediators of neural development and synaptic plasticity in vertebrates, however, understanding of the mechanistic basis of these roles and the molecular identities of the MMPs involved remains far from complete. We have identified a zebrafish orthologue of mmp25 (a.k.a. leukolysin; MT6-MMP), a membrane-type, furin-activated MMP associated with leukocytes and invasive carcinomas, but which we find is expressed by a subset of the sensory neurons during normal embryonic development. We detect high levels of Mmp25β expression in the trigeminal, craniofacial, and posterior lateral line ganglia in the hindbrain, and in Rohon-Beard cells in the dorsal neural tube during the first 48 h of embryonic development. Knockdown of Mmp25β expression with morpholino oligonucleotides results in larvae that are uncoordinated and insensitive to touch, and which exhibit defects in the development of sensory neural structures. Using in vivo zymography, we observe that Mmp25β morphant embryos show reduced Type IV collagen degradation in regions of the head traversed by elongating axons emanating from the trigeminal ganglion, suggesting that Mmp25β may play a pivotal role in mediating ECM remodeling in the vicinity of these elongating axons.

Lysosomal acid lipase is critical for myeloid-derived suppressive cell differentiation, development, and homeostasis

Lysosomal acid lipase (LAL) cleaves cholesteryl esters (CE) and triglycerides (TG) to generate cholesterol and free fatty acid in lysosomes of cells. The downstream metabolic products of fatty acids are ligands for activation of peroxisome proliferator-activated receptor gamma (PPARγ). Accumulation of CEs and TGs is resulted from lack of functional LAL in lysosomes of cells, especially in myeloid cells. One characteristic phenotype in LAL knock-out (lal-/-) mice is systemic elevation of myeloid-derived suppressive cells (MDSCs). MDSCs infiltrate into multiple distal organs, alter T cell development, and suppress T cell proliferation and lymphokine production in lal-/- mice, which lead to severe pathogeneses in multiple organs. The gene transcriptional profile analysis in MDSCs from the bone marrow has identified multiple defects responsible for MDSCs malformation and malfunction in lal-/- mice, including G protein signaling, cell cycles, glycolysis metabolism, mitochondrial bioenergetics, mTOR pathway etc. In a separate gene transcriptional profile analysis in the lung of lal-/- mice, matrix metalloproteinase 12 (MMP12) and apoptosis inhibitor 6 (Api6) are highly overexpressed due to lack of ligand synthesis for PPARγ. PPARγ negatively regulates MMP12 and Api6. Blocking the PPAR signaling by overexpression of a dominant negative PPARγ (dnPPARγ) form, or overexpressing MMP12 or Api6 in myeloid or lung epithelial cells in inducible transgenic mouse models results in elevated MDSCs and inflammation-induced tumorigenesis. These studies demonstrate that LAL and its downstream effectors are critical for MDSCs development, differentiation and malfunction.

Host matrix metalloproteinases in cerebral malaria: new kids on the block against blood-brain barrier integrity?

Cerebral malaria (CM) is a life-threatening complication of falciparum malaria, associated with high mortality rates, as well as neurological impairment in surviving patients. Despite disease severity, the etiology of CM remains elusive. Interestingly, although the Plasmodium parasite is sequestered in cerebral microvessels, it does not enter the brain parenchyma: so how does Plasmodium induce neuronal dysfunction? Several independent research groups have suggested a mechanism in which increased blood–brain barrier (BBB) permeability might allow toxic molecules from the parasite or the host to enter the brain. However, the reported severity of BBB damage in CM is variable depending on the model system, ranging from mild impairment to full BBB breakdown. Moreover, the factors responsible for increased BBB permeability are still unknown. Here we review the prevailing theories on CM pathophysiology and discuss new evidence from animal and human CM models implicating BBB damage. Finally, we will review the newly-described role of matrix metalloproteinases (MMPs) and BBB integrity. MMPs comprise a family of proteolytic enzymes involved in modulating inflammatory response, disrupting tight junctions, and degrading sub-endothelial basal lamina. As such, MMPs represent potential innovative drug targets for CM.