MT1-MMP-mediated cleavage of decorin in corneal angiogenesis

Up-to-date molecular medicine strategies for management of ocular surface neovascularization

Ocular surface neovascularization and its resulting pathological changes significantly alter corneal refraction and obstruct the light path to the retina, and hence is a major cause of vision loss. Various factors such as infection, irritation, trauma, dry eye, and ocular surface surgery trigger neovascularization via angiogenesis and lymphangiogenesis dependent on VEGF-related and alternative mechanisms. Recent advances in antiangiogenic drugs, nanotechnology, gene therapy, surgical equipment and techniques, animal models, and drug delivery strategies have provided a range of novel therapeutic options for the treatment of ocular surface neovascularization. In this review article, we comprehensively discuss the etiology and mechanisms of corneal neovascularization and other types of ocular surface neovascularization, as well as emerging animal models and drug delivery strategies that facilitate its management.

Differential MMP-14 targeting by biglycan, decorin, fibromodulin, and lumican unraveled by in silico approach

Small leucine-rich proteoglycans (SLRPs) are major regulators of extracellular matrix assembly and cell signaling. Lumican, a member of the SLRPs family, and its derived peptides were shown to possess antitumor activity by interacting directly with the catalytic domain of MMP-14 leading to the inhibition of its activity. The aim of the present report was to characterize by in silico three-dimensional (3D) modeling the structure and the dynamics of four SLRPs including their core protein and their specific polysaccharide chains to assess their capacity to bind to MMP-14 and to regulate its activity. Molecular docking experiments were performed to identify the specific amino acids of MMP-14 interacting with each of the four SLRPs. The inhibition of each SLRP (100 nM) on MMP-14 activity was measured and the constants of inhibition (K_i) were evaluated. The impact of the number of glycan chains, structures, and dynamics of lumican on the interaction with MMP-14 was assessed by molecular dynamics simulations. Molecular docking analysis showed that all SLRPs bind to MMP-14 through their concave face, but in different regions of the catalytic domain of MMP-14. Each SLRPs inhibited significantly the MMP-14 activity. Finally, molecular dynamics showed the role of glycan chains in interaction with MMP-14 and shielding effect of SLRPs. Altogether, the results demonstrated that each SLRP exhibited inhibition of MMP-14 activity. However, the differential targeting of MMP-14 by the SLRPs was shown to be related not only to the core protein conformation but also to the glycan chain structures and dynamics.

Selective Inhibitors of Medium-Size S1' Pocket Matrix Metalloproteinases: A Stepping Stone of Future Drug Discovery

Among various matrix metalloproteinases (MMPs), MMPs having medium-size S1' pockets are established as promising biomolecular targets for executing crucial roles in cancer, cardiovascular diseases, and neurodegenerative diseases. However, no such MMP inhibitors (MMPIs) are available to date as drug candidates despite a lot of continuous research work for more than three decades. Due to a high degree of structural resemblance among these MMPs, designing selective MMPIs is quite challenging. However, the variability and uniqueness of the S1' pockets of these MMPs make them promising targets for designing selective MMPIs. In this perspective, the overall structural aspects of medium-size S1' pocket MMPs including the unique binding patterns of enzyme-inhibitor interactions have been discussed in detail to acquire knowledge regarding selective inhibitor designing. This overall knowledge will surely be a curtain raiser for the designing of selective MMPIs as drug candidates in the future.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

Differential MMP-14 Targeting by Lumican-Derived Peptides Unraveled by In Silico Approach

Lumican, a small leucine-rich proteoglycan (SLRP) of the extracellular matrix (ECM), displays anti-tumor properties through its direct interaction with MMP-14. Lumican-derived peptides, such as lumcorin (17 amino acids) or L9M (10 amino acids), are able to inhibit the proteolytic activity of MMP-14 and melanoma progression. This work aimed to visualize the interactions of lumican-derived peptides and MMP-14. Molecular modeling was used to characterize the interactions between lumican-derived peptides, such as lumcorin, L9M, and cyclic L9M (L9Mc, 12 amino acids), and MMP-14. The interaction of L9Mc with MMP-14 was preferential with the MT-Loop domain while lumcorin interacted more with the catalytic site. Key residues in the MMP-14 amino acid sequence were highlighted for the interaction between the inhibitory SLRP-derived peptides and MMP-14. In order to validate the in silico data, MMP-14 activity and migration assays were performed using murine B16F1 and human HT-144 melanoma cells. In contrast to the HT-144 melanoma cell line, L9Mc significantly inhibited the migration of B16F1 cells and the activity of MMP-14 but with less efficacy than lumican and lumcorin. L9Mc significantly inhibited the proliferation of B16F1 but not of HT-144 cells in vitro and primary melanoma tumor growth in vivo. Thus, the site of interaction between the domains of MMP-14 and lumcorin or L9Mc were different, which might explain the differences in the inhibitory effect of MMP-14 activity. Altogether, the biological assays validated the prediction of the in silico study. Possible and feasible improvements include molecular dynamics results.

Topical bevacizumab for the treatment of corneal vascularization in dogs: A case series

Objective

To evaluate the effect and safety of topical anti‐human vascular endothelial growth factor bevacizumab in dogs with persistent corneal vascularization.

Animals studied

Prospective case series of 15 adult dogs (20 eyes).

Procedures

Dogs received 0.25% bevacizumab eye drops BID for 28 days. Follow‐ups were scheduled 28 days and 6–7 months after treatment start. Macroscopic findings were scored for conjunctival hyperemia, chemosis, ocular discharge, corneal edema, vascularization, and pigmentation. Vascularized area was assessed by analyzing photographs using an imaging software.

Results

The treatment response was variable. Some cases showed a marked reduction in vascularized area and edema, while other eyes had subtle signs of improvement. Vascularization score decreased from 1.5 to 1.1 and vascularized area was reduced by 48.8% after 28 days. A thinning of vessels, consolidation of areal bleedings into fine vascular networks, decrease in distal vessel branching, and a change from blurry vascularized beds into demarcated thin vessels were observed. One dog developed a SCCED 6 months after the last bevacizumab administration. Two dogs died 4 and 4.5 months after the last bevacizumab administration, aged 16 and 12 years, respectively. In all events, a causal relationship is unlikely but cannot be ruled out with certainty.

Conclusions

Our findings suggest that topical 0.25% bevacizumab may be an effective treatment option for corneal vascularization in dogs. Further long‐term placebo‐controlled studies with larger patient cohorts are recommended to provide scientific evidence of efficacy and to investigate dosage, safety, possible use as a single treatment, and routes of administration.

Relationship between increased serum & synovial fluid decorin levels & knee osteoarthritis

Background & objectives

Decorin is a proteoglycan that plays a role in the binding of collagen and has an important role in the pathogenesis of osteoarthritis (OA). This study was aimed to determine serum and synovial fluid decorin levels in patients with knee OA and to investigate whether these levels were associated with OA and the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) score.

Methods

In this prospective study 88 participants were included (44 knee OA and 44 with other knee joint diseases) in the study and control groups. Knee function was assessed using the WOMAC score. The serum and synovial fluid decorin levels were analyzed using a human decorin ELISA. Binary logistic regression with a single and multi-categorical predictor was used to determine the possible risk factors for OA.

Results

The serum decorin levels were significantly higher in the OA group than the control group (P<0.002).s The synovial fluid decorin levels were not significantly different between OA and control groups. WOMAC score [odds ratio (OR)=1.073, 95% confidence interval (CI): 1.032-1.116, P<0.001] and high serum decorin levels (OR=1.114, 95%CI: 1.030-1.205, P=0.007) were found to be significant in the determination of OA. Serum decorin levels were positively correlated with the WOMAC score in OA.

Interpretation & conclusions

An increased serum decorin levels may be indicative of changes in extracellular matrix structure. The positive correlation between serum decorin level and WOMAC score supports this result. Increased serum decorin levels and WOMAC score were found to be risk factors associated with OA. However, the decorin level in the joint fluid was not associated with OA.

The functional role of decorin in corneal neovascularization in vivo

Our earlier decorin (Dcn) gene overexpression studies found that the targeted Dcn gene transfer into the cornea inhibited corneal angiogenesis in vivo using a rabbit model. In this study, we tested the hypothesis that anti-angiogenic effects of decorin in the cornea are mediated by alterations in a normal physiologic balance of pro- and anti-angiogenic factors using decorin deficient (Dcn^-/-) and wild type (Dcn^+/+) mice. Corneal neovascularization (CNV) in Dcn^-/- and Dcn^+/+ mice was produced with a standard chemical injury technique. The clinical progression of CNV in mice was monitored with stereo- and slit-lamp microscopes, and histopathological hematoxylin and eosin (H&E) staining. Protein and mRNA expression of pro- and anti-angiogenic factors in the cornea were evaluated using immunofluorescence and quantitative real-time PCR, respectively. Slit-lamp clinical eye examinations revealed significantly more CNV in Dcn^-/- mice than the Dcn^+/+ mice post-injury (p < 0.05) and AAV5-Dcn gene therapy significantly reduced CNV in Dcn^-/- mice compered to no AAV5-Dcn gene therapy controls (p < 0.001). H&E-stained corneal sections exhibited morphology with several neovessels in injured corneas of the Dcn^-/- mice than the Dcn^+/+ mice. Immunofluorescence of corneal sections displayed significantly higher expression of α-smooth muscle actin (α-SMA) and endoglin proteins in Dcn^-/- mice than Dcn^+/+ mice (p < 0.05). Quantitative real-time PCR found significantly increased mRNA levels of pro-angiogenic factors endoglin (2.53-fold; p < 0.05), Vegf (2.47-fold; p < 0.05), and Pecam (2.14-fold; p < 0.05) and anti-angiogenic factor Vegfr2 (1.56-fold; p < 0.05) in the normal cornea of the Dcn^-/- mice than the Dcn^+/+ mice. Furthermore, neovascularized Dcn^-/- mice corneas showed greater increase in mRNA expression of pro-angiogenic factors endoglin (4.58-fold; p < 0.0001), Vegf (4.16-fold; p < 0.0001), and Pdgf (2.15-fold; p < 0.0001) and reduced expression of anti-angiogenic factors Ang2 (0.12-fold; p < 0.05), Timp1 (0.22-fold; p < 0.05), and Vegfr2 (0.67-fold; p > 0.05) compared to neovascularized Dcn^+/+ mice corneas. These gene deficience studies carried with transgenic Dcn^-/- mice revealed decorin's role in influencing a physiologic balance between pro-and anti-angiogenic factors in the normal and injured cornea. We infer that the functional deletion of Dcn promotes irregular corneal repair and aggravates CNV.

Glycosaminoglycan Modification of Decorin Depends on MMP14 Activity and Regulates Collagen Assembly

Proper processing of collagens COL1 and COL6 is required for normal function of adipose tissue and skeletal muscle. Proteoglycan decorin (DCN) regulates collagen fiber formation. The amino-terminus of DCN is modified with an O-linked glycosaminoglycan (GAG), the function of which has remained unclear. Previously, non-glycanated DCN (ngDCN) was identified as a marker of adipose stromal cells. Here, we identify MMP14 as the metalloprotease that cleaves DCN to generate ngDCN. We demonstrate that mice ubiquitously lacking DCN GAG (ngDCN mice) have reduced matrix rigidity, enlarged adipocytes, fragile skin, as well as skeletal muscle hypotrophy, fibrosis, and dysfunction. Our results indicate that DCN deglycanation results in reduced intracellular DCN—collagen binding and increased production of truncated COL6 chains, leading to aberrant procollagen processing and extracellular localization. This study reveals that the GAG of DCN functions to regulate collagen assembly in adipose tissue and skeletal muscle and uncovers a new mechanism of matrix dysfunction in obesity and aging.

Neointimal Hyperplasia after Carotid Transection and Anastomosis Surgery is Associated with Degradation of Decorin and Platelet Derived Growth Factor Signaling

Objective

Intimal hyperplasia (IH) is the expansion of the vascular intimal region after intervention, which can lead to stenosis and eventual failure of vascular grafts or interventional procedures such as angioplasty or stent placement. Our goals were to investigate the development of IH in a rabbit open surgical model and to evaluate the associated pathophysiologic processes involving decorin and the platelet-derived growth factor-BB/platelet-derived growth factor receptor-β/mitogen-activated protein kinase (PDGF-BB/PDGFR-β/MAPK) pathway.

Methods

We conducted carotid transection and primary anastomosis on five New Zealand white rabbits to induce IH and examined the associated pathophysiologic changes. Tissue was obtained for histological and protein analysis on postoperative day 21 using the contralateral vessel as a control. Intimal medial thickness (IMT) was calculated to measure IH and compared with the unoperated side. Western blot analysis was performed on tissue lysates to determine the expression of decorin core protein, PDGF-BB, PDGFR-β, and phosphorylated-MAPK (ph-MAPK). Immunofluorescence microscopy was used to assess tissue distribution of matrix metalloproteinase-2 (MMP-2) and ph-PDGFR-β.

Results

Bilateral carotid arteries were harvested on postoperative day 21. We compared the IMT in operated with unoperated specimens. IMT was significantly elevated in operated arteries vs unoperated arteries in all five animals (148.6 μm ± 9.09 vs 103.40 μm ± 7.08; 135.2 μm ± 8.30 vs 92.40 μm ± 2.35; 203.1 μm ± 30.23 vs 104.00 μm ± 4.52; 236.2 μm ± 27.22 vs 141.50 μm ± 9.95; 226.9 μm ± 11.12 vs 98.8 μm ± 3.78). Western blot analysis revealed degradation of decorin protein in the operated tissue, including loss of a 50 kDa band and the appearance of a cleaved fragment at 10 kDa. Decorin and MMP-2 were observed, via immunofluorescence microscopy, in the neointima of the operated vessels. Western blot analysis also revealed increased PDGF-BB, PDGFR-β, and ph-MAPK levels in operated tissue. Immunofluorescent staining for ph-PDGFR-β primarily localized to the neointima, indicating increased signaling through PDGF in this region.

Conclusions

Carotid transection and primary reanastomosis in rabbits induced IH that was associated with MMP-2 activation, degradation of decorin, and activation of the PDGF/PDGFR-β/MAPK pathway. The findings in this study should lead to further mechanistic evaluation of these pathways to better understand the potential to modify the intimal hyperplastic response to surgery. (JVS–Vascular Science 2020;2:2-12.)

Clinical Relevance

Intimal hyperplasia remains a significant challenge to the vascular surgeon in open and interventional procedures. Basic science studies have made headway into understanding the process, but this has not translated into many therapeutic options particularly for primary prevention after a procedure. Decorin is gaining popularity as an important mediator of various pathophysiologic processes involving the extracellular matrix. We sought to determine the possible role of decorin in the development of neointimal hyperplasia in an open surgical model. This study provides a replicable model for the development of intimal hyperplasia and potential therapeutic targets going forward.

Stromal metalloproteinases: Crucial contributors to the tumor microenvironment

Proteolytic balance is crucial for the maintenance of tissue homeostasis. In cancer, dysregulated proteolysis is involved in unregulated tissue remodeling and inflammation, leading to the promotion of tumor growth, local invasion, and metastasis. Metalloproteinases, which were first identified as collagen cleaving enzymes, have been shown to extensively degrade extracellular matrix proteins or selectively release cell surface-bound cytokines, growth factors, or their receptors, thereby impacting extracellular matrix integrity, immune cell recruitment and tissue turnover. Although tumor cells produce various metalloproteinases, the major source is thought to be stromal cells infiltrating the tumor. Different types of stromal cells express specific sets of metalloproteinases and their inhibitors, which specifically alter the milieu within the tumor. In this review, recent findings and knowledge regarding metalloproteinases derived from stromal cells during the creation of the tumor microenvironment are described and their contribution to the tumor progression and metastasis discussed.

Decorin in the Tumor Microenvironment

The tumor microenvironment plays a determining role in cancer development through a plethora of interactions between the extracellular matrix and tumor cells. Decorin is a prototype member of the SLRP family found in a variety of tissues and is expressed in the stroma of various forms of cancer. Decorin has gained recognition for its essential roles in inflammation, fibrotic disorders, and cancer, and due to its antitumor properties, it has been proposed to act as a "guardian from the matrix." Initially identified as a natural inhibitor of transforming growth factor-β, soluble decorin is emerging as a pan-RTK inhibitor targeting a multitude of RTKs, including EGFR, Met, IGF-IR, VEGFR2, and PDGFR. Besides initiating signaling, decorin/RTK interaction can induce caveosomal internalization and receptor degradation. Decorin also triggers cell cycle arrest and apoptosis and evokes antimetastatic and antiangiogenic processes. In addition, as a novel regulatory mechanism, decorin was shown to induce conserved catabolic processes, such as endothelial cell autophagy and tumor cell mitophagy. Therefore, decorin is a promising candidate for combatting cancer, especially the cancer types heavily dependent on RTK signaling.

Extracellular Matrix Composition and Remodeling: Current Perspectives on Secondary Palate Formation, Cleft Lip/Palate, and Palatal Reconstruction

Craniofacial development comprises a complex process in humans in which failures or disturbances frequently lead to congenital anomalies. Cleft lip with/without palate (CL/P) is a common congenital anomaly that occurs due to variations in craniofacial development genes, and may occur as part of a syndrome, or more commonly in isolated forms (non-syndromic). The etiology of CL/P is multifactorial with genes, environmental factors, and their potential interactions contributing to the condition. Rehabilitation of CL/P patients requires a multidisciplinary team to perform the multiple surgical, dental, and psychological interventions required throughout the patient's life. Despite progress, lip/palatal reconstruction is still a major treatment challenge. Genetic mutations and polymorphisms in several genes, including extracellular matrix (ECM) genes, soluble factors, and enzymes responsible for ECM remodeling (e.g., metalloproteinases), have been suggested to play a role in the etiology of CL/P; hence, these may be considered likely targets for the development of new preventive and/or therapeutic strategies. In this context, investigations are being conducted on new therapeutic approaches based on tissue bioengineering, associating stem cells with biomaterials, signaling molecules, and innovative technologies. In this review, we discuss the role of genes involved in ECM composition and remodeling during secondary palate formation and pathogenesis and genetic etiology of CL/P. We also discuss potential therapeutic approaches using bioactive molecules and principles of tissue bioengineering for state-of-the-art CL/P repair and palatal reconstruction.

Lumican as a multivalent effector in wound healing

Wound healing, a complex physiological process, is responsible for tissue repair after exposure to destructive stimuli, without resulting in complete functional regeneration. Injuries can be stromal or epithelial, and most cases of wound repair have been studied in the skin and cornea. Lumican, a small leucine-rich proteoglycan, is expressed in the extracellular matrices of several tissues, such as the cornea, cartilage, and skin. This molecule has been shown to regulate collagen fibrillogenesis, keratinocyte phenotypes, and corneal transparency modulation. Lumican is also involved in the extravasation of inflammatory cells and angiogenesis, which are both critical in stromal wound healing. Lumican is the only member of the small leucine-rich proteoglycan family expressed by the epithelia during wound healing. This review summarizes the importance of lumican in wound healing and potential methods of lumican drug delivery to target wound repair are discussed. The involvement of lumican in corneal wound healing is described based on in vitro and in vivo models, with critical emphasis on its underlying mechanisms of action. Similarly, the expression and role of lumican in the healing of other tissues are presented, with emphasis on skin wound healing. Overall, lumican promotes normal wound repair and broadens new therapeutic perspectives for impaired wound healing.

Decorin is a pivotal effector in the extracellular matrix and tumour microenvironment

Decorin (DCN), an extracellular matrix (ECM) protein, belongs to the small leucine-rich proteoglycan family. As a pluripotent molecule, DCN regulates the bioactivities of cell growth factors and participates in ECM assembly. Accumulating evidence has shown that DCN acts as a ligand of various cytokines and growth factors by directly or indirectly interacting with the corresponding signalling molecules involved in cell growth, differentiation, proliferation, adhesion and metastasis and that DCN especially plays vital roles in cancer cell proliferation, spread, pro-inflammatory processes and anti-fibrillogenesis. The multifunctional nature of DCN thus enables it to be a potential therapeutic agent for a variety of diseases and shows good prospects for clinical and research applications.

DCN, an extracellular matrix (ECM) protein that belongs to the small leucine-rich proteoglycan family, is widely distributed and plays multifunctional roles in the stroma and epithelial cells. Originally, DCN was known as an effective collagen-binding partner for fibrillogenesis [1] and to modulate key biomechanical parameters of tissue integrity in the tendon, skin and cornea [2]; thus, it was named decorin (DCN). Since being initially cloned in 1986, DCN was discovered to be a structural constituent of the ECM [3]. However, the paradigm has been shifted; it has become increasingly evident that in addition to being a matrix structural protein, DCN affects a wide range of biological processes, including cell growth, differentiation, proliferation, adhesion, spread and migration, and regulates inflammation and fibrillogenesis [4–7]. Two main themes for DCN functions have emerged: maintenance of cellular structure and regulation of signal transduction pathways, culminating in anti-tumourigenic effects. Here, we review the interaction network of DCN and emphasize the biological correlations between these interactions, some of which are expected to be therapeutic intervention targets.

Matrix Metalloproteinases, Vascular Remodeling, and Vascular Disease

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that degrade various proteins in the extracellular matrix (ECM). Typically, MMPs have a propeptide sequence, a catalytic metalloproteinase domain with catalytic zinc, a hinge region or linker peptide, and a hemopexin domain. MMPs are commonly classified on the basis of their substrates and the organization of their structural domains into collagenases, gelatinases, stromelysins, matrilysins, membrane-type (MT)-MMPs, and other MMPs. MMPs are secreted by many cells including fibroblasts, vascular smooth muscle (VSM), and leukocytes. MMPs are regulated at the level of mRNA expression and by activation through removal of the propeptide domain from their latent zymogen form. MMPs are often secreted in an inactive proMMP form, which is cleaved to the active form by various proteinases including other MMPs. MMPs degrade various protein substrates in ECM including collagen and elastin. MMPs could also influence endothelial cell function as well as VSM cell migration, proliferation, Ca²⁺ signaling, and contraction. MMPs play a role in vascular tissue remodeling during various biological processes such as angiogenesis, embryogenesis, morphogenesis, and wound repair. Alterations in specific MMPs could influence arterial remodeling and lead to various pathological disorders such as hypertension, preeclampsia, atherosclerosis, aneurysm formation, as well as excessive venous dilation and lower extremity venous disease. MMPs are often regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP ratio often determines the extent of ECM protein degradation and tissue remodeling. MMPs may serve as biomarkers and potential therapeutic targets for certain vascular disorders.

Roles of exosomes in the normal and diseased eye

Exosomes are nanometer-sized vesicles that are released by cells in a controlled fashion and mediate a plethora of extra- and intercellular activities. Some key functions of exosomes include cell-cell communication, immune modulation, extracellular matrix turnover, stem cell division/differentiation, neovascularization and cellular waste removal. While much is known about their role in cancer, exosome function in the many specialized tissues of the eye is just beginning to undergo rigorous study. Here we review current knowledge of exosome function in the visual system in the context of larger bodies of data from other fields, in both health and disease. Additionally, we discuss recent advances in the exosome field including use of exosomes as a therapeutic vehicle, exosomes as a source of biomarkers for disease, plus current standards for isolation and validation of exosome populations. Finally, we use this foundational information about exosomes in the eye as a platform to identify areas of opportunity for future research studies.

Proangiogenic Interactions of Vascular Endothelial MMP14 With VEGF Receptor 1 in VEGFA-Mediated Corneal Angiogenesis

Purpose

Matrix metalloproteinase 14 (MMP14) has been shown to be required for corneal angiogenesis. We hypothesized that the proangiogenic activity of MMP14 may be based on its selective binding to, and cleaving of, vascular endothelial growth factor receptor 1 (VEGFR1), but not VEGFR2 or VEGFR3.

Methods

Recombinant human (rh)VEGFR1, R2, and R3 were incubated with human MMP14, and the reaction mixtures were analyzed by SDS-PAGE and Coomassie blue staining. Surface plasmon resonance was used to determine the equilibrium constants (K_D) for binding between MMP14 and VEGFA versus rhVEGFR1, R2, and R3. Extracellular signal-regulated kinase (ERK) phosphorylation was assayed in vascular endothelial cells after incubation with VEGF and various concentrations of MMP14. Ex vivo aortic ring tube formation assays and VEGFA micropocket corneal neovascularization assays were performed using Flk1Cre/Flk1mCherry/MMP14lox and Flk1mCherry/MMP14lox control mice.

Results

Maxtrix metalloproteinase 14 increased VEGFA-induced ERK phosphorylation in a time- and concentration-dependent manner in vascular endothelial cells. Aortic ring assays showed diminished vessel sprouting in vitro in response to VEGFA, but not to basic fibroblast growth factor, in mice with conditional deletion of vascular MMP14 (Flk1creMMP14lox) compared with that in MMP14lox control mice. In addition, diminished VEGFA-induced corneal angiogenesis was seen in flk1creMMP14lox mice compared with MMP14lox mice in vivo.

Conclusions

Our findings indicate that VEGFR1 interaction with MMP14 and the enzymatic activity of MMP14 are necessary for VEGFA-induced angiogenesis. Additionally, selective cleavage of VEGFR1 by MMP14 may play an important role in VEGFA-induced corneal angiogenesis.

Matrix Metalloproteinase Inhibitors as Investigational and Therapeutic Tools in Unrestrained Tissue Remodeling and Pathological Disorders

Matrix metalloproteinases (MMPs) are zinc-dependent proteolytic enzymes that degrade various proteins in the extracellular matrix (ECM). MMPs may also regulate the activity of membrane receptors and postreceptor signaling mechanisms and thereby affect cell function. The MMP family includes collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and other MMPs. Inactive proMMPs are cleaved by other MMPs or proteases into active MMPs, which interact with various protein substrates in ECM and cell surface. MMPs regulate important biological processes such as vascular remodeling and angiogenesis and may be involved in the pathogenesis of cardiovascular disorders such as hypertension, atherosclerosis, and aneurysm. The role of MMPs is often assessed by measuring their mRNA expression, protein levels, and proteolytic activity using gel zymography. MMP inhibitors are also used to assess the role of MMPs in different biological processes and pathological conditions. MMP activity is regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP balance could determine the net MMP activity, ECM turnover, and tissue remodeling. Also, several synthetic MMP inhibitors have been developed. Synthetic MMP inhibitors include a large number of zinc-binding globulins (ZBGs), in addition to non-ZBGs and mechanism-based inhibitors. MMP inhibitors have been proposed as potential tools in the management of osteoarthritis, cancer, and cardiovascular disorders. However, most MMP inhibitors have broad-spectrum actions on multiple MMPs and could cause undesirable musculoskeletal side effects. Currently, doxycycline is the only MMP inhibitor approved by the Food and Drug Administration. New generation biological and synthetic MMP inhibitors may show greater MMP specificity and fewer side effects and could be useful in targeting specific MMPs, reducing unrestrained tissue remodeling, and the management of MMP-related pathological disorders.

Proteoglycan neofunctions: regulation of inflammation and autophagy in cancer biology

Inflammation and autophagy have emerged as prominent issues in the context of proteoglycan signaling. In particular, two small, leucine-rich proteoglycans, biglycan and decorin, play pivotal roles in the regulation of these vital cellular pathways and, as such, are intrinsically involved in cancer initiation and progression. In this minireview, we will address novel functions of biglycan and decorin in inflammation and autophagy, and analyze new emerging signaling events triggered by these proteoglycans, which directly or indirectly modulate these processes. We will critically discuss the dual role of proteoglycan-driven inflammation and autophagy in tumor biology, and delineate the potential mechanisms through which soluble extracellular matrix constituents affect the microenvironment associated with inflammatory and neoplastic diseases.

Decorin interacting network: A comprehensive analysis of decorin-binding partners and their versatile functions

Decorin, a prototype small leucine-rich proteoglycan, regulates a vast array of cellular processes including collagen fibrillogenesis, wound repair, angiostasis, tumor growth, and autophagy. This functional versatility arises from a wide array of decorin/protein interactions also including interactions with its single glycosaminoglycan side chain. The decorin-binding partners encompass numerous categories ranging from extracellular matrix molecules to cell surface receptors to growth factors and enzymes. Despite the diversity of the decorin interacting network, two main roles emerge as prominent themes in decorin function: maintenance of cellular structure and outside-in signaling, culminating in anti-tumorigenic effects. Here we present contemporary knowledge regarding the decorin interacting network and discuss in detail the biological relevance of these pleiotropic interactions, some of which could be targeted by therapeutic interventions.

Degradomic and yeast 2-hybrid inactive catalytic domain substrate trapping identifies new membrane-type 1 matrix metalloproteinase (MMP14) substrates: CCN3 (Nov) and CCN5 (WISP2)

Members of the CCN family of matricellular proteins are cytokines linking cells to the extracellular matrix. We report that CCN3 (Nov) and CCN5 (WISP2) are novel substrates of MMP14 (membrane-type 1-matrix metalloproteinase, MT1-MMP) that we identified using MMP14 "inactive catalytic domain capture" (ICDC) as a yeast two-hybrid protease substrate trapping platform in parallel with degradomics mass spectrometry screens for MMP14 substrates. CCN3 and CCN5, previously unknown substrates of MMPs, were biochemically validated as substrates of MMP14 and other MMPs in vitro-CCN5 was processed in the variable region by MMP14 and MMP2, as well as by MMP1, 3, 7, 8, 9 and 15. CCN1, 2 and 3 are proangiogenic factors yet we found novel opposing activity of CCN5 that was potently antiangiogenic in an aortic ring vessel outgrowth model. MMP14, a known regulator of angiogenesis, cleaved CCN5 and abrogated the angiostatic activity. CCN3 was also processed in the variable region by MMP14 and MMP2, and by MMP1, 8 and 9. In addition to the previously reported cleavages of CCN1 and CCN2 by several MMPs we found that MMPs 8, 9, and 1 process CCN1, and MMP8 and MMP9 also process CCN2. Thus, our study reveals additional and pervasive family-wide processing of CCN matricellular proteins/cytokines by MMPs. Furthermore, CCN5 cleavage by proangiogenic MMPs results in removal of an angiogenic brake held by CCN5. This highlights the importance of thorough dissection of MMP substrates that is needed to reveal higher-level control mechanisms beyond type IV collagen and other extracellular matrix protein remodelling in angiogenesis.

SUMMARY

We find CCN family member cleavage by MMPs is more pervasive than previously reported and includes CCN3 (Nov) and CCN5 (WISP2). CCN5 is a novel antiangiogenic factor, whose function is abrogated by proangiogenic MMP cleavage. By processing CCN proteins, MMPs regulate cell responses angiogenesis in connective tissues.

Molecular underpinnings of corneal angiogenesis: advances over the past decade

The cornea is maintained in an avascular state by maintaining an environment whereby anti-angiogenic factors take the upper hand over factors promoting angiogenesis. Many of the common pathologies affecting the cornea involve the disruption of such equilibrium and the shift towards new vessel formation, leading to corneal opacity and eventually-vision loss. Therefore it is of paramount importance that the molecular underpinnings of corneal neovascularization (CNV) be clearly understood, in order to develop better targeted treatments. This article is a review of the literature on the recent discoveries regarding pro-angiogenic factors of the cornea (such as vascular endothelial growth factors, fibroblast growth factor and matrix metalloproteinases) and anti-angiogenic factors of the cornea (such as endostatins and neostatins). Further, we review the molecular underpinnings of lymphangiogenesis, a process now known to be almost separate from (yet related to) hemangiogenesis.

Matrix metalloproteinase 14 modulates signal transduction and angiogenesis in the cornea

The cornea is transparent and avascular, and retention of these characteristics is critical to maintaining vision clarity. Under normal conditions, wound healing in response to corneal injury occurs without the formation of new blood vessels; however, neovascularization may be induced during corneal wound healing when the balance between proangiogenic and antiangiogenic mediators is disrupted to favor angiogenesis. Matrix metalloproteinases (MMPs), which are key factors in extracellular matrix remodeling and angiogenesis, contribute to the maintenance of this balance, and in pathologic instances, can contribute to its disruption. Here, we elaborate on the facilitative role of MMPs, specifically MMP-14, in corneal neovascularization. MMP-14 is a transmembrane MMP that is critically involved in extracellular matrix proteolysis, exosome transport, and cellular migration and invasion, processes that are critical for angiogenesis. To aid in developing efficacious therapies that promote healing without neovascularization, it is important to understand and further investigate the complex pathways related to MMP-14 signaling, which can also involve vascular endothelial growth factor, basic fibroblast growth factor, Wnt/β-catenin, transforming growth factor, platelet-derived growth factor, hepatocyte growth factor or chemokines, epidermal growth factor, prostaglandin E2, thrombin, integrins, Notch, Toll-like receptors, PI3k/Akt, Src, RhoA/RhoA kinase, and extracellular signal-related kinase. The involvement and potential contribution of these signaling molecules or proteins in neovascularization are the focus of the present review.

Decorin: A Growth Factor Antagonist for Tumor Growth Inhibition

Decorin (DCN) is the best characterized member of the extracellular small leucine-rich proteoglycan family present in connective tissues, typically in association with or “decorating” collagen fibrils. It has substantial interest to clinical medicine owing to its antifibrotic, anti-inflammatory, and anticancer effects. Studies on DCN knockout mice have established that a lack of DCN is permissive for tumor development and it is regarded as a tumor suppressor gene. A reduced expression or a total disappearance of DCN has been reported to take place in various forms of human cancers during tumor progression. Furthermore, when used as a therapeutic molecule, DCN has been shown to inhibit tumor progression and metastases in experimental cancer models. DCN affects the biology of various types of cancer by targeting a number of crucial signaling molecules involved in cell growth, survival, metastasis, and angiogenesis. The active sites for the neutralization of different growth factors all reside in different parts of the DCN molecule. An emerging concept that multiple proteases, especially those produced by inflammatory cells, are capable of cleaving DCN suggests that native DCN could be inactivated in a number of pathological inflammatory conditions. In this paper, we review the role of DCN in cancer.

MMP14 Cleavage of VEGFR1 in the Cornea Leads to a VEGF-Trap Antiangiogenic Effect

PURPOSE

To determine the possible antiangiogenic effect of metalloproteinase (MMP) 14 cleavage of vascular endothelial growth factor receptor 1 (VEGFR1) in the cornea.

METHODS

Recombinant mouse (rm) VEGFR1 was incubated with various concentrations of recombinant MMP14 to examine proteolysis in vitro. The reaction mixture was analyzed by SDS-PAGE and stained with Coomassie blue. The fragments resulting from rmVEGFR1 cleavage by MMP14 were subjected to Edman degradation, and the amino acid sequences were aligned with rmVEGFR1 sequences. Surface plasmon resonance was used to determine the equilibrium dissociation constant (KD) between MMP14 and rmVEGFR1. The KD value of rmVEGFR1 and the 59.8-kDa cleavage product binding to VEGF-A₁₆₅ was also determined. Cell proliferation assays were performed in the presence of VEGF-A₁₆₅ plus the 59.8-kDa VEGFR1 fragment or VEGF-A₁₆₅ alone.

RESULTS

Matrix metalloproteinase 14 binds and cleaves rmVEGFR1 to produce 59.8-kDa (N-terminal fragment, Ig domains 1-5), 35-kDa (C-terminal fragment containing IgG and His-tag), and 21-kDa (Ig domains 6-7) fragments. The 59.8-kDa fragment showed binding to VEGF-A₁₆₅ and inhibited VEGF-induced endothelial cell mitogenesis.

CONCLUSIONS

Our findings suggest that VEGFR1 cleavage by MMP14 in the cornea leads to a VEGF-trap effect, reducing the proangiogenic effect of VEGF-A₁₆₅, thereby reducing corneal angiogenesis.

Proteoglycans in Normal and Healing Skin

Significance: Proteoglycans have a distinct spatial localization in normal skin and are essential for the correct structural development, organization, hydration, and functional properties of this tissue. The extracellular matrix (ECM) is no longer considered to be just an inert supportive material but is a source of directive, spatial and temporal, contextual information to the cells via components such as the proteoglycans. There is a pressing need to improve our understanding of how these important molecules functionally interact with other matrix structures, cells and cellular mediators in normal skin and during wound healing. Recent Advances: New antibodies to glycosaminoglycan side chain components of skin proteoglycans have facilitated the elucidation of detailed localization patterns within skin. Other studies have revealed important proliferative activities of proteinase-generated fragments of proteoglycans and other ECM components (matricryptins). Knockout mice have further established the functional importance of skin proteoglycans in the assembly and homeostasis of the normal skin ECM. Critical Issues: Our comprehension of the molecular and structural complexity of skin as a complex, dynamic, constantly renewing, layered connective tissue is incomplete. The impact of changes in proteoglycans on skin pathology and the wound healing process is recognized as an important area of pathobiology and is an area of intense investigation. Future Directions: Advanced technology is allowing the development of new artificial skins. Recent knowledge on skin proteoglycans can be used to incorporate these molecules into useful adjunct therapies for wound healing and for maintenance of optimal tissue homeostasis in aging skin.

Fibromodulin promoted in vitro and in vivo angiogenesis

Fibromodulin (FMOD) is an extracellular matrix (ECM) small leucine-rich proteoglycan (SLRP) that plays an important role in cell fate determination. Previous studies revealed that not only is FMOD critical in fetal-type scarless wound healing, but it also promotes adult wound closure and reduces scar formation. In addition, FMOD-deficient mice exhibit significantly reduced blood vessel regeneration in granulation tissues during wound healing. In this study, we investigated the effects of FMOD on angiogenesis, which is an important event in wound healing as well as embryonic development and tumorigenesis. We found that FMOD accelerated human umbilical vein endothelial HUVEC-CS cell adhesion, spreading, actin stress fiber formation, and eventually tube-like structure (TLS) network establishment in vitro. On a molecular level, by increasing expression of collagen I and III, angiopoietin (Ang)-2, and vascular endothelial growth factor (VEGF), as well as reducing the ratio of Ang-1/Ang-2, FMOD provided a favorable network to mobilize quiescent endothelial cells to an angiogenic phenotype. Moreover, we also confirmed that FMOD enhanced angiogenesis in vivo by using an in ovo chick embryo chorioallantoic membrane (CAM) assay. Therefore, our data demonstrate that FMOD is a pro-angiogenic and suggest a potential therapeutic role of FMOD in the treatment of conditions related to impaired angiogenesis.

MT1-MMP modulates bFGF-induced VEGF-A expression in corneal fibroblasts

The cornea is physiologically avascular. Following a corneal injury, wound healing often proceeds without neovascularization (NV); however, corneal NV may be induced during wound healing in certain inflammatory, infectious, degenerative, and traumatic states. Such states disrupt the physiologic balance between pro-angiogenic and antiangiogenic mediators, favoring angiogenesis. Contributors to such states are matrix metalloproteinases (MMPs), which are key factors in both extracellular matrix remodeling and angiogenesis. Similarly, vascular endothelial growth factor A (VEGF-A) and basic fibroblast growth factor (bFGF) exert pro-angiogenic effects. Here, we elaborate on the facilitative role of MMPs-specifically Membrane Type 1 MMP (MT1-MMP, MMP14)-in corneal NV. Additionally, we provide new insight into the signaling relating to MT1-MMP, Ras, and ERK in the bFGF-induced VEGF-A expression pathways within the corneal fibroblasts.

Wound healing after keratorefractive surgery: review of biological and optical considerations

The introduction of the excimer laser for keratorefractive surgery in the 1990 s permanently reshaped the treatment landscape for correcting refractive errors, such as myopia, hyperopia, and astigmatism. Until that point, these treatments had relied on less predictable techniques, such as radial keratotomy and automated lamellar keratectomy. In recent years, other new technologies, along with increased understanding of the basic science of refractive errors, higher-order aberrations, biomechanics, and the biology of corneal wound healing, have allowed for a reduction in the surgical complications of keratorefractive surgery. Novel technologies, such as eye tracking, anterior segment imaging, the femtosecond laser, and asphericity-optimized and wavefront-guided custom laser in situ keratomileusis, have assisted refractive surgeons in achieving greater predictability of their laser vision correction procedures. Understanding the cascade of events involved in the corneal wound healing process and examination of how corneal wound healing influences corneal biomechanics and optics are crucial to improve the efficacy and safety of laser vision correction.

New and paradoxical roles of matrix metalloproteinases in the tumor microenvironment

Processes such as cell proliferation, angiogenesis, apoptosis, or invasion are strongly influenced by the surrounding microenvironment of the tumor. Therefore, the ability to change these surroundings represents an important property through which tumor cells are able to acquire specific functions necessary for tumor growth and dissemination. Matrix metalloproteinases (MMPs) constitute key players in this process, allowing tumor cells to modify the extracellular matrix (ECM) and release cytokines, growth factors, and other cell-surface molecules, ultimately facilitating protease-dependent tumor progression. Remodeling of the ECM by collagenolytic enzymes such as MMP1, MMP8, MMP13, or the membrane-bound MT1-MMP as well as by other membrane-anchored proteases is required for invasion and recruitment of novel blood vessels. However, the multiple roles of the MMPs do not all fit into a simple pattern. Despite the pro-tumorigenic function of certain metalloproteinases, recent studies have shown that other members of these families, such as MMP8 or MMP11, have a protective role against tumor growth and metastasis in animal models. These studies have been further expanded by large-scale genomic analysis, revealing that the genes encoding metalloproteinases, such as MMP8, MMP27, ADAM7, and ADAM29, are recurrently mutated in specific tumors, while several ADAMTSs are epigenetically silenced in different cancers. The importance of these proteases in modifying the tumor microenvironment highlights the need for a deeper understanding of how stroma cells and the ECM can modulate tumor progression.

Corneal neovascularization and the utility of topical VEGF inhibition: ranibizumab (Lucentis) vs bevacizumab (Avastin)

Corneal avascularity is necessary for the preservation of optimal vision. The cornea maintains a dynamic balance between pro- and antiangiogenic factors that allows it to remain avascular under normal homeostatic conditions; however, corneal avascularity can be compromised by pathologic conditions that negate the cornea's "angiogenic privilege." The clinical relevance of corneal neovascularization has long been recognized, but management of this condition has been hindered by a lack of safe and effective therapeutic modalities. Herein, the etiology, epidemiology, pathogenesis, and treatment of corneal neovascularization are reviewed. Additionally, the authors' recent findings regarding the clinical utility of topical ranibizumab (Lucentis®) and bevacizumab (Avastin®) in the treatment of corneal neovascularization are summarized. These findings clearly indicate that ranibizumab and bevacizumab are safe and effective treatments for corneal neovascularization when appropriate precautions are observed. Although direct comparisons are not conclusive, the results suggest that ranibizumab may be modestly superior to bevacizumab in terms of both onset of action and degree of efficacy. In order to justify the increased cost of ranibizumab, it will be necessary to demonstrate meaningful treatment superiority in a prospective, randomized, head-to-head comparison study.

Matrix metalloproteinase inhibitors as investigative tools in the pathogenesis and management of vascular disease

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade various components of the extracellular matrix (ECM). MMPs could also regulate the activity of several non-ECM bioactive substrates and consequently affect different cellular functions. Members of the MMPs family include collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and others. Pro-MMPs are cleaved into active MMPs, which in turn act on various substrates in the ECM and on the cell surface. MMPs play an important role in the regulation of numerous physiological processes including vascular remodeling and angiogenesis. MMPs may also be involved in vascular diseases such as hypertension, atherosclerosis, aortic aneurysm, and varicose veins. MMPs also play a role in the hemodynamic and vascular changes associated with pregnancy and preeclampsia. The role of MMPs is commonly assessed by measuring their gene expression, protein amount, and proteolytic activity using gel zymography. Because there are no specific activators of MMPs, MMP inhibitors are often used to investigate the role of MMPs in different physiologic processes and in the pathogenesis of specific diseases. MMP inhibitors include endogenous tissue inhibitors (TIMPs) and pharmacological inhibitors such as zinc chelators, doxycycline, and marimastat. MMP inhibitors have been evaluated as diagnostic and therapeutic tools in cancer, autoimmune disease, and cardiovascular disease. Although several MMP inhibitors have been synthesized and tested both experimentally and clinically, only one MMP inhibitor, i.e., doxycycline, is currently approved by the Food and Drug Administration. This is mainly due to the undesirable side effects of MMP inhibitors especially on the musculoskeletal system. While most experimental and clinical trials of MMP inhibitors have not demonstrated significant benefits, some trials still showed promising results. With the advent of new genetic and pharmacological tools, disease-specific MMP inhibitors with fewer undesirable effects are being developed and could be useful in the management of vascular disease.

Human matrix metalloproteinases: an ubiquitarian class of enzymes involved in several pathological processes

Human matrix metalloproteinases (MMPs) belong to the M10 family of the MA clan of endopeptidases. They are ubiquitarian enzymes, structurally characterized by an active site where a Zn(2+) atom, coordinated by three histidines, plays the catalytic role, assisted by a glutamic acid as a general base. Various MMPs display different domain composition, which is very important for macromolecular substrates recognition. Substrate specificity is very different among MMPs, being often associated to their cellular compartmentalization and/or cellular type where they are expressed. An extensive review of the different MMPs structural and functional features is integrated with their pathological role in several types of diseases, spanning from cancer to cardiovascular diseases and to neurodegeneration. It emerges a very complex and crucial role played by these enzymes in many physiological and pathological processes.

Targeted decorin gene therapy delivered with adeno-associated virus effectively retards corneal neovascularization in vivo

Decorin, small leucine-rich proteoglycan, has been shown to modulate angiogenesis in nonocular tissues. This study tested a hypothesis that tissue-selective targeted decorin gene therapy delivered to the rabbit stroma with adeno-associated virus serotype 5 (AAV5) impedes corneal neovascularization (CNV) in vivo without significant side effects. An established rabbit CNV model was used. Targeted decorin gene therapy in the rabbit stroma was delivered with a single topical AAV5 titer (100 µl; 5×10¹² vg/ml) application onto the stroma for two minutes after removing corneal epithelium. The levels of CNV were examined with stereomicroscopy, H&E staining, lectin, collagen type IV, CD31 immunocytochemistry and CD31 immunoblotting. Real-time PCR quantified mRNA expression of pro- and anti-angiogenic genes. Corneal health in live animals was monitored with clinical, slit-lamp and optical coherence tomography biomicroscopic examinations. Selective decorin delivery into stroma showed significant 52% (p<0.05), 66% (p<0.001), and 63% (p<0.01) reduction at early (day 5), mid (day 10), and late (day 14) stages of CNV in decorin-delivered rabbit corneas compared to control (no decorin delivered) corneas in morphometric analysis. The H&E staining, lectin, collagen type IV, CD31 immunostaining (57–65, p<0.5), and CD31 immunoblotting (62–67%, p<0.05) supported morphometric findings. Quantitative PCR studies demonstrated decorin gene therapy down-regulated expression of VEGF, MCP1 and angiopoietin (pro-angiogenic) and up-regulated PEDF (anti-angiogenic) genes. The clinical, biomicroscopy and transmission electron microscopy studies revealed that AAV5–mediated decorin gene therapy is safe for the cornea. Tissue-targeted AAV5-mediated decorin gene therapy decreases CNV with no major side effects, and could potentially be used for treating patients.

MT-MMPS as Regulators of Vessel Stability Associated with Angiogenesis

The development of vascular system depends on the coordinated activity of a number of distinct families of molecules including growth factors and their receptors, cell adhesion molecules, extracellular matrix (ECM) molecules, and proteolytic enzymes. Matrix metalloproteases (MMPs) are a family of ECM degrading enzymes required for both physiological and pathological angiogenesis. Increasing evidence, point to a direct role of membrane type-MMPs (MT-MMPs) in vascular system stabilization, maturation, and leakage. Our understanding of the nature of MT-MMP interaction with extracellular and cell surface molecules and their multiple roles in vessel walls and perivascular stroma may provide new insights into mechanisms underlying vascular cell–ECM interactions and cell fate decisions in pathological conditions. Regulation of vascular leakage by MT-MMP interactions with the ECM could also lead to novel targeting opportunities for drug delivery in tumor. This review will shed lights on the emerging roles of MT1-MMP and MT4-MMP in vascular system alterations associated with cancer progression.

Matrix metalloproteinase 14 overexpression reduces corneal scarring

Once a corneal scar develops, surgical management remains the only option for visual rehabilitation. Corneal transplantation is the definitive treatment for a corneal scar. In addition to the challenges posed by graft rejections and other postoperative complications, the lack of high-quality donor corneas can limit the benefits possible with keratoplasty. The purpose of our study was to evaluate a new therapeutic strategy for treating corneal scarring by targeting collagen deposition. We overexpressed a fibril collagenase (matrix metalloproteinase 14 (MMP14)) to prevent collagen deposition in the scar tissue. We demonstrated that a single and simple direct injection of recombinant adeno-associated virus-based vector expressing murine MMP14 can modulate gene expression of murine stromal keratocytes. This tool opens new possibilities with regard to treatment. In a mouse model of corneal full-thickness incision, we observed that MMP14 overexpression reduced corneal opacity and expression of the major genes involved in corneal scarring, especially type III collagen and α-smooth muscle actin. These results represent proof of concept that gene transfer of MMP14 can reduce scar formation, which could have therapeutic applications after corneal trauma.

MT1-MMP-mediated basement membrane remodeling modulates renal development

Extracellular matrix (ECM) remodeling regulates multiple cellular functions required for normal development and tissue repair. Matrix metalloproteinases (MMPs) are key mediators of this process and membrane targeted MMPs (MT-MMPs) in particular have been shown to be important in normal development of specific organs. In this study we investigated the role of MT1-MMP in kidney development. We demonstrate that loss of MT1-MMP leads to a renal phenotype characterized by a moderate decrease in ureteric bud branching morphogenesis and a severe proliferation defect. The kidneys of MT1-MMP-null mice have increased deposition of collagen IV, laminins, perlecan, and nidogen and the phenotype is independent of the MT-1MMP target, MMP-2. Utilizing in vitro systems we demonstrated that MTI-MMP proteolytic activity is required for renal tubule cells to proliferate in three dimensional matrices and to migrate on collagen IV and laminins. Together these data suggest an important role for MT1-MMP in kidney development, which is mediated by its ability to regulate cell proliferation and migration by proteolytically cleaving kidney basement membrane components.

Corneal epithelial MT1-MMP inhibits vascular endothelial cell proliferation and migration

PURPOSE

To determine the effects of corneal epithelial membrane-type 1 matrix metalloproteinase (MT1-MMP) on vascular endothelial migration and proliferation.

METHODS

We generated immortalized wild-type, MT1-MMP knockout and MT1-MMP knock-in corneal epithelial cells. Calf pulmonary arterial endothelial (CPAE) cell proliferation and Boyden chamber migration were assayed.

RESULTS

Conditioned media from MT1-MMP epithelial knockout cells significantly increased CPAE proliferation 5-bromo-2'-deoxy-uridine (BrdU) incorporation, and CPAE migration as compared with wild-type epithelial cells. Conditioned media from knock-in cells reversed the increase in CPAE proliferation, BrdU incorporation and CPAE migration. Knock-in cells transfected with mutant MT1-MMP (E240A) did not abrogate the reversal effect.

CONCLUSIONS

Corneal epithelial MT1-MMP is antiangiogenic. This antiangiogenic activity does not require the catalytic domain.

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.