Degradation of connective tissue matrices by macrophages. I. Proteolysis of elastin, glycoproteins, and collagen by proteinases isolated from macrophages

The potential inhibitory effect of ginsenoside Rh2 on mitophagy in UV-irradiated human dermal fibroblasts

Background

In addition to its use as a health food, ginseng is used in cosmetics and shampoo because of its extensive health benefits. The ginsenoside, Rh2, is a component of ginseng that inhibits tumor cell proliferation and differentiation, promotes insulin secretion, improves insulin sensitivity, and shows antioxidant effects.

Methods

The effects of Rh2 on cell survival, extracellular matrix (ECM) protein expression, and cell differentiation were examined. The antioxidant effects of Rh2 in UV-irradiated normal human dermal fibroblast (NHDF) cells were also examined. The effects of Rh2 on mitochondrial function, morphology, and mitophagy were investigated in UV-irradiated NHDF cells.

Results

Rh2 treatment promoted the proliferation of NHDF cells. Additionally, Rh2 increased the expression levels of ECM proteins and growth-associated immediate-early genes in ultraviolet (UV)-irradiated NHDF cells. Rh2 also affected antioxidant protein expression and increased total antioxidant capacity. Furthermore, treatment with Rh2 ameliorated the changes in mitochondrial morphology, induced the recovery of mitochondrial function, and inhibited the initiation of mitophagy in UV-irradiated NHDF cells.

Conclusion

Rh2 inhibits mitophagy and reinstates mitochondrial ATP production and membrane potential in NHDF cells damaged by UV exposure, leading to the recovery of ECM, cell proliferation, and antioxidant capacity.

Directionality of Macrophages Movement in Tumour Invasion: A Multiscale Moving-Boundary Approach

Invasion of the surrounding tissue is one of the recognised hallmarks of cancer (Hanahan and Weinberg in Cell 100: 57–70, 2000. 10.1016/S0092-8674(00)81683-9), which is accomplished through a complex heterotypic multiscale dynamics involving tissue-scale random and directed movement of the population of both cancer cells and other accompanying cells (including here, the family of tumour-associated macrophages) as well as the emerging cell-scale activity of both the matrix-degrading enzymes and the rearrangement of the cell-scale constituents of the extracellular matrix (ECM) fibres. The involved processes include not only the presence of cell proliferation and cell adhesion (to other cells and to the extracellular matrix), but also the secretion of matrix-degrading enzymes. This is as a result of cancer cells as well as macrophages, which are one of the most abundant types of immune cells in the tumour micro-environment. In large tumours, these tumour-associated macrophages (TAMs) have a tumour-promoting phenotype, contributing to tumour proliferation and spread. In this paper, we extend a previous multiscale moving-boundary mathematical model for cancer invasion, by considering also the multiscale effects of TAMs, with special focus on the influence that their directional movement exerts on the overall tumour progression. Numerical investigation of this new model shows the importance of the interactions between pro-tumour TAMs and the fibrous ECM, highlighting the impact of the fibres on the spatial structure of solid tumour.

Autologously transplanted dermal fibroblasts improved diabetic wound in rat model

Healing of diabetic wounds are delayed due to late initiation and prolongation of the inflammatory phase, and inadequate growth factor synthesis, which may lead to chronic ulcers that may cause limb amputation, besides making the patients vulnerable to infections. In recent years, it has been extensively discussed whether different cell types transplanted to diabetic wound models accelerate wound healing. In this study, the effect of dermis-derived cells on Streptozotocin (STZ) induced experimental diabetic Sprague-Dawley rats were investigated. Animals were divided into 3 groups. First group was control, second group included diabetic animals with wounds. In the third group, firstly, skin specimens were obtained from animal's back, and then primary explant culture was performed. STZ induced experimental diabetes was applied to these animals and then wound was opened. The cells grown in primary culture were transplanted autologously. In all three groups, the samples taken from the wound areas on the 5th and 15th days of the wound were examined at the level of histochemical and immunohistochemical and electron microscopy. In the study, it was observed that the decreasing α-SMA and KGF (FGF-7) expression in the early period especially in the case of experimental diabetes increased as a result of cell transplantation, and in the sections belonging to the experimental diabetic group, a large number of inflammatory cells in the wound area were removed from the environment. In the cell transplanted group, the collagen fiber bundles as if in the control group. As a result, healthy cells of dermis can act as mesenchymal stem cells under certain conditions and have a positive effect on diabetic wound healing.

MMP12 preferentially attenuates axial stiffening of aging arteries

Arterial stiffening is a hallmark of aging, but how aging affects the arterial response to pressure is still not completely understood, especially with regard to specific matrix metalloproteinases (MMPs). Here, we used pressure myography of carotid arteries from C57BL/6 mice to study the effects of age and MMP12, a major arterial elastase, on arterial biomechanics. Aging from 2 to 24 months leads to both circumferential and axial stiffening with stretch, and these changes are associated with an increased wall thickness, decreased inner radius, and a decreased in vivo axial stretch ratio (IVSR). Analysis of IVSR and stress-stretch curves with arteries from age- and sex-matched wild-type and MMP12-null arteries demonstrate that MMP12 deletion attenuates age-dependent arterial stiffening, mostly in the axial direction. MMP12 deletion also prevents the aging-associated decrease in the in vivo stretch ratio and, in general, leads to an axial mechanics phenotype characteristic of much younger mice. Circumferential arterial mechanics were much less affected by deletion of MMP12. We conclude that the induction of MMP12 during aging preferentially controls axial arterial mechanics.

Alpha-1 Antitrypsin-Deficient Macrophages Have Increased Matriptase-Mediated Proteolytic Activity

Alpha-1 antitrypsin (AAT) deficiency-associated emphysema is largely attributed to insufficient inhibition of neutrophil elastase released from neutrophils. Correcting AAT levels using augmentation therapy only slows disease progression, and that suggests a more complex process of lung destruction. Because alveolar macrophages (Mɸ) express AAT, we propose that the expression and intracellular accumulation of mutated Z-AAT (the most common mutation) compromises Mɸ function and contributes to emphysema development. Extracellular matrix (ECM) degradation is a hallmark of emphysema pathology. In this study, Mɸ from individuals with Z-AAT (Z-Mɸ) have greater proteolytic activity on ECM than do normal Mɸ. This abnormal Z-Mɸ activity is not abrogated by supplementation with exogenous AAT and is likely the result of cellular dysfunction induced by intracellular accumulation of Z-AAT. Using pharmacologic inhibitors, we show that several classes of proteases are involved in matrix degradation by Z-Mɸ. Importantly, compared with normal Mɸ, the membrane-bound serine protease, matriptase, is present in Z-Mɸ at higher levels and contributes to their proteolytic activity on ECM. In addition, we identified matrix metalloproteinase (MMP)-14, a membrane-anchored metalloproteinase, as a novel substrate for matriptase, and showed that matriptase regulates the levels of MMP-14 on the cell surface. Thus, high levels of matriptase may contribute to increased ECM degradation by Z-Mɸ, both directly and through MMP-14 activation. In summary, the expression of Z-AAT in Mɸ confers increased proteolytic activity on ECM. This proteolytic activity is not rescued by exogenous AAT supplementation and could thus contribute to augmentation resistance in AAT deficiency-associated emphysema.

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.

Effects of acute inflammation induced in the rat paw on the deep digital flexor tendon

The tendon is commonly affected by inflammation, and in such situations, the tissue undergoes a process of reorganization of the extracellular matrix to improve and regenerate the affected region. Little is known about the mechanisms that trigger inflammation in the tissues surrounding the affected area. The objective of this study was to biochemically and morphologically analyze the deep digital flexor tendon at the peak of acute inflammation in the rat paw. Wistar rats were divided into the following three groups: those that received injection of 1% carrageenan, those that received 0.9% NaCl, and those that received nothing. The deep digital flexor tendon was divided into the distal, proximal, and intermediate regions. For biochemical analysis, the tendons were treated with guanidine hydrochloride and analyzed by sodium dodecyl sulfate-polyacrilamide gel electrophoresis. Proteins, glycosaminoglycans (GAGs), and hydroxyproline were quantified, and metalloproteinases were analyzed. The GAGs were analyzed by agarose gel electrophoresis. Tissue sections were stained with hematoxylin-eosin, toluidine blue, and Ponceau SS. The content of proteins and GAGs was smaller in the group receiving the application of carrageenan. The concentration of hydroxyproline in the two tendon regions that respond to tension forces was higher in the inflammation group. The metalloproteinase-9 was detected in the distal region, and a thicker epitenon with cellular infiltrate was observed in the groups with inflamed paws. Meanwhile, a better organization of collagen bundles was observed in the two tension regions of that same group. Our results show that although the tendon was not directly inflamed, changes in the surrounding structural and biochemical parameters were observed.

The ecology of brain tumors: lessons learned from neurofibromatosis-1

Traditionally, cancer studies have primarily focused on mutations that activate growth or survival pathways in susceptible pre-neoplastic/neoplastic cells. However, recent research has revealed a critical role for non-neoplastic cells within the tumor microenvironment in the process of cancer formation and progression. In addition, the existence of regional and developmental variations in susceptible cell types and supportive microenvironments support a model of tumorigenesis in which the dynamic symbiotic relationship between neoplastic and non-neoplastic cell types dictate where and when cancers form and grow. In this review, we highlight advances in neurofibromatosis type 1 (NF1) genetically engineered mouse brain tumor (glioma) modeling to reveal how cellular and molecular heterogeneity in both the pre-neoplastic/neoplastic and non-neoplastic cellular compartments contribute to gliomagenesis and glioma growth.

Transcriptional profiling of equine endometrium during the time of maternal recognition of pregnancy

Establishment and maintenance of pregnancy are critically dependent on embryo-maternal communication during the preimplantation period. To gain new insights into this complex process in the horse, transcriptional profiling of Day 13.5 pregnant and cyclic endometrial tissue samples was carried out using custom-designed microarrays. Selected array data were validated using quantitative RT-PCR, and proteins of interest were localized using immunohistochemistry. One hundred and six transcripts were up-regulated, whereas 47 transcripts showed lower expression levels in pregnant mares, that is, were down-regulated in pregnant mares. Half of the genes with known or inferred function are classically regulated by estrogens. Elevated transcript levels were found for genes involved in cell-cell signaling, heat shock response, and secretory proteins, among others. Solute carrier family 36 (proton/amino acid symporter), member 2, SLC36A2, was one of the most highly up-regulated genes, potentially reflecting the nutritional needs of the rapidly developing embryo. Among the genes showing lower expression in pregnant mares, estrogen receptor 1 was of particular interest because of its potential involvement in the initiation of luteolysis in cyclic mares. We hypothesize that either conceptus' estrogens or luteinizing hormone of uterine origin is involved in the observed down-regulation of estrogen receptor 1. Several of the genes identified in the current study are known to play a role in early pregnancy in species other than the horse. Thus, products of these commonly expressed genes likely contain universal activities for controlling endometrial receptivity to the conceptus, whereas other factors play unique roles within specific species in ensuring ongoing corpus luteum function. This is the first systematic study of endometrial transcriptome changes in response to the presence of an embryo during maternal recognition of pregnancy and an important step toward deciphering the embryo-maternal dialogue in equids.

Soluble elastin decreases in the progress of atheroma formation in human aorta

BACKGROUND

The serum levels of soluble elastin increase in patients with aortic dissection, but its distribution and characteristics are unclear.

METHODS AND RESULTS

The 173 aortic specimens were categorized into 4 groups under microscopy (non-atherosclerotic aorta, n=13; fiber-rich plaque, n=77; lipid-rich plaque, n=66; ruptured plaque, n=17). Soluble elastin was abundant within the intima of both the non-atherosclerotic aorta and fiber-rich plaque, rather than in the media, and was decreased within the intima of lipid-rich and ruptured plaques. Soluble elastin levels decreased with progress of atherosclerosis (6.0 +/-0.3 microg/mg protein in non-atherosclerotic aorta; 5.8 +/-0.2 microg/mg protein in fiber-rich plaque; 4.9 +/-0.2 microg/mg protein in lipid-rich plaque; 2.8 +/-0.4 microg/mg protein in ruptured plaque, P<0.05). As well, both matrix metalloprotease-9 activity and elastin mRNA expression showed inverse distribution against soluble elastin (r=0.437, P<0.0001; r=0.186, P<0.05, respectively). Multivariable analysis revealed a decrease in the level of soluble elastin in ruptured plaque (2.8 +/-0.4 microg/mg protein in ruptured plaque, n=18; 5.5 +/-0.2 microg/mg protein in non-ruptured plaque, n=155, P<0.01). Furthermore, western blot showed soluble elastin consists of heterogeneous molecular pattern proteins.

CONCLUSIONS

Both the synthesis and degradation of elastin may be enhanced in active atherosclerotic lesions.

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Vascular remodeling and extracellular matrix breakdown in the uterine spiral arteries during pregnancy

During pregnancy, trophoblasts invade and transform the maternal spiral arteries that supply blood to the placenta. Recent work has revealed that this process occurs in several stages, and details of the molecular and cellular mechanisms are beginning to emerge, including changes that precede or accompany trophoblastic colonization of the vascular media. Disruption and eventual loss of smooth muscle cells and their associated extracellular matrix are central to physiological transformation. Advances in understanding will lead to the identification of the causative factors involved in failure of remodeling in pathological pregnancies and suggest novel diagnostic and therapeutic avenues.

Elevated tissue plasminogen activator in patients with screening-detected abdominal aortic aneurysm

OBJECTIVE

A population-based case-control study with historical and current data was conducted in a population with a high prevalence of disease to explore the hypothesis that the fibrinolytic system may be involved in the early pathogenesis of abdominal aortic aneurysm (AAA).

METHODS

Forty-two patients found to have AAA at population-based screening were compared with 100 controls matched for age and sex. Mass concentration of tissue plasminogen activator (tPA mass) and tissue plasminogen activator/plasminogen activator inhibitor-1 complex (tPA/PAI-1 complex mass) were analyzed in blood samples obtained at the screening (current), and in blood samples obtained from a study conducted 12 years previously on the same population (historical).

RESULTS

Current tPA mass levels were significantly higher in AAA patients compared with controls (13.6 vs 11.4 microg/L, P=.016). A similar trend was observed in historical tPA mass levels (9.8 vs 8.2 microg/L, P=.062). Current and historical mass concentrations of tPA/PAI complex in AAA patients were similar to those in controls. Current tPA mass levels retained the associations with AAA in a logistic regression model after adjustment for history of atherosclerosis (odds ratio [OR], 1.1 per microg/L, P=.039) and current smoking (OR 1.1 per microg/L, P=.039). When family history of AAA was added in a logistic regression model, the OR for current tPA mass was 1.1 per microg/L (P=.056) and 1.1 per microg/L (P=.070) when treated hypertension was added.

CONCLUSION

The finding of elevated tPA mass, in contrast to tPA/PAI-1 complex, in plasma among patients with screening-detected AAA supports the hypothesis that the fibrinolytic system may be important in the early pathogenesis of AAA.

Interaction between human cathepsins K, L, and S and elastins: mechanism of elastinolysis and inhibition by macromolecular inhibitors

Proteolytic degradation of elastic fibers is associated with a broad spectrum of pathological conditions such as atherosclerosis and pulmonary emphysema. We have studied the interaction between elastins and human cysteine cathepsins K, L, and S, which are known to participate in elastinolytic activity in vivo. The enzymes showed distinctive preferences in degrading elastins from bovine neck ligament, aorta, and lung. Different susceptibility of these elastins to proteolysis was attributed to morphological differences observed by scanning electron microscopy. Kinetics of cathepsin binding to the insoluble substrate showed that the process occurs in two steps. The enzyme is initially adsorbed on the elastin surface in a nonproductive manner and then rearranges to form a catalytically competent complex. In contrast, soluble elastin is bound directly in a catalytically productive manner. Studies of enzyme partitioning between the phases showed that cathepsin K favors adsorption on elastin; cathepsin L prefers the aqueous environment, and cathepsin S is equally distributed among both phases. Our results suggest that elastinolysis by cysteine cathepsins proceeds in cycles of enzyme adsorption, binding of a susceptible peptide moiety, hydrolysis, and desorption. Alternatively, the enzyme may also form a new catalytic complex without prior desorption and re-adsorption. In both cases the active center of the enzymes remains at least partly accessible to inhibitors. Elastinolytic activity was readily abolished by cystatins, indicating that, unlike enzymes such as leukocyte elastase, pathological elastinolytic cysteine cathepsins might represent less problematic drug targets. In contrast, thyropins were relatively inefficient in preventing elastinolysis by cysteine cathepsins.

Promotion of Human Dermal Fibroblast Migration, Matrix Remodelling and Modification of Fibroblast Morphology within a Novel 3D Model by Lucilia sericata Larval Secretions

Lucilia sericata larvae, or green bottle fly maggots are applied to chronic wounds to aid healing. Previously, our laboratory has characterized the enzymatic activities present within maggot excretions/secretions (ES). Since then, we have related these to the degradation of extracellular matrix components, alteration of human, dermal fibroblast adhesion to surfaces and the stimulation of fibroblast migration within a two-dimensional in vitro assay. In this study, we developed a novel three-dimensional in vitro assay in which to observe fibroblast migration and morphology in response to maggot ES. Here, primary human foreskin fibroblasts were embedded within collagen gels containing fibronectin. Phase contrast and confocal microscopy were used in conjunction with image analysis software to examine and quantify aspects of fibroblast behavior. Our results showed that maggot ES stimulated fibroblast migration through the matrix and induced altered cell morphologies. Remodelling of the extracellular matrix located between individual fibroblasts was also induced, providing a mechanism by which cells may detect each other's presence over considerable distances. Thus, mechanisms by which maggots enhance tissue formation within wounds may be via the promotion of fibroblast motility, acceleration of extracellular matrix remodelling and coordination of cellular responses.

Chronic Inflammation, Immune Response, and Infection in Abdominal Aortic Aneurysms

Abdominal aortic aneurysms (AAA) are associated with atherosclerosis, transmural degenerative processes, neovascularization, decrease in content of vascular smooth muscle cells, and a chronic infiltration, mainly located in the outer aortic wall. The chronic infiltration consists mainly of macrophages, lymphocytes, and plasma cells. The dominant cells are Th2 restricted CD3+ lymphocytes expressing interleukine 4, 5, 8, and 10, and tumor necrosis factor-alpha for regulation of the local immune response. They also produce interferon-gamma and CD40 ligand to stimulate surrounding cells to produce matrix metalloproteases and cysteine proteases for aortic matrix remodeling. The lymphocyte activation may be mediated by microorganisms as well as autoantigens generated from vascular structural proteins, perhaps through molecular mimicry. As in autoimmune diseases, the risk of AAA is increased by certain genotypes concerning human leucocyte antigen class II. These types are also associated with increased aneurysmal inflammation indicating a genetic susceptibility to aortic inflammation. Chlamydia pneumoniae is often detected in AAA but the validity of the methods can be questioned, and two small antibiotic trials have been disappointing. However, serum antibodies against C. pneumoniae have been associated with AAA growth and cross-react with AAA wall proteins. Thus, immune responses mediated by microorganisms and autoantigens may play a pivotal role in AAA pathogenesis.

Maggots and wound healing: an investigation of the effects of secretions from Lucilia sericata larvae upon the migration of human dermal fibroblasts over a fibronectin-coated surface

Lucilia sericata larvae, or greenbottle fly maggots, placed within chronic wounds have been observed to remove necrotic tissue and infection. They are also believed to actively promote granulation tissue formation. Interactions between fibroblasts and the surrounding extracellular matrix play a crucial role in tissue formation, influencing fibroblast proliferation, migration, and tissue remodeling. For example, the strength of cell adhesion to surfaces coated with extracellular matrix influences cell motility. L. sericata larval excretory/secretory products having previously been shown to modify fibroblast adhesion to collagen and particularly fibronectin, it was hypothesized that these products would alter fibroblast migration. This was investigated using a two-dimensional in vitro wound assay, time-lapse digital photography, enzyme class-specific substrates and inhibitors, and gel electrophoresis. Results showed that L. sericata excretory/secretory products promoted fibroblast migration upon a fibronectin-coated surface. This was related to the degradation of fibronectin by serine proteinases within maggot excretion/secretions. The presence of a metalloproteinase activity may also have played a role. Thus, a possible mechanism by which maggots enhance tissue formation within wounds may be via the promotion of fibroblast motility, providing for a wider distribution of viable fibroblasts.

Acute wounds

The most important factors in the management of acute wounds are the history and physical examination. The goals of wound care are fivefold: avoid further tissue damage, achieve wound closure as rapidly as possible, restore function to the injured tissue, facilitate the patient's expedient return to normal daily activities, and restore the patient's quality of life. The treating physician must have a good understanding of the wound healing mechanism. One must rule out all associated occult injuries that may be life threatening. Proper wound assessment and management with minimal discomfort to the patient are crucial. The primary goal is to facilitate the healing process to achieve a cosmetically pleasing and functional result.

Mechanics of wound healing and importance of Vacuum Assisted Closure in urology

PURPOSE

We discuss the mechanisms of wound healing and our experience with the Vacuum Assisted Closure device (Kinetic Concepts, Inc., San Antonio, Texas) for complex urogenital wounds.

MATERIALS AND METHODS

The literature obtained from a Medline search on wound healing, wound failure and vacuum assisted closure was reviewed. In addition, we reviewed our experience with negative pressure wound therapy.

RESULTS

Wound healing is a complex interaction between the reticuloendothelial and immune systems, in addition to correctable internal and external factors. Understanding the healing process improves outcomes and decreases patient morbidity. Negative pressure wound therapy has hastened wound healing and it adds significant improvement in the arsenal of choices available.

CONCLUSIONS

Vacuum Assisted Closure is a therapeutic alternative that complements surgical and medical intervention in patients with complex wounds.

Epithelial expression of profibrotic mediators in a model of allergen-induced airway remodeling

Airway remodeling, including subepithelial fibrosis, is a characteristic feature of asthma and likely contributes to the pathogenesis of airway hyperresponsiveness. We examined expression of genes related to airway wall fibrosis in a model of chronic allergen-induced airway dysfunction using laser capture microdissection and quantitative real-time PCR. BALB/c mice were sensitized and subjected to chronic ovalbumin exposure over a 12-wk period, after which they were rested and then harvested 2 and 8 wk after the last exposure. Chronic allergen-exposed mice had significantly increased indices of airway remodeling and airway hyperreactivity at all time points, although no difference in expression of fibrosis-related genes was found when mRNA extracted from whole lung was examined. In contrast, fibrosis-related gene expression was significantly upregulated in mRNA obtained from microdissected bronchial wall at 2 wk after chronic allergen exposure. In addition, when bronchial wall epithelium and smooth muscle were separately microdissected, gene expression of transforming growth factor-beta1 and plasminogen activating inhibitor-1 were significantly upregulated only in the airway epithelium. These data suggest that transforming growth factor-beta1 and other profibrotic mediators produced by airway wall, and specifically, airway epithelium, play an important role in the pathophysiology of airway remodeling.

Cathepsin V, a novel and potent elastolytic activity expressed in activated macrophages

Atherosclerosis is characterized by a thickening and loss of elasticity of the arterial wall. Loss of elasticity has been attributed to the degradation of the arterial elastin matrix. Cathepsins K and S are papain-like cysteine proteases with known elastolytic activities, and both enzymes have been identified in macrophages present in plaque areas of diseased blood vessels. Here we demonstrate that macrophages express a third elastolytic cysteine protease, cathepsin V, which exhibits the most potent elastase activity yet described among human proteases and that cathepsin V is present in atherosclerotic plaque specimens. Approximately 60% of the total elastolytic activity of macrophages can be attributed to cysteine proteases with cathepsins V, K, and S contributing equally. From this 60%, two-thirds occur extracellularly and one-third intracellularly with the latter credited to cathepsin V. Ubiquitously expressed glycosaminoglycans (GAGs) such as chondroitin sulfate specifically inhibit the elastolytic activities of cathepsins V and K via the formation of specific cathepsin-GAG complexes. In contrast, cathepsin S, which does not form complexes with chondroitin sulfate is not inhibited; thus suggesting a specific regulation of elastolytic activities of cathepsins by GAGs. Because the GAG content is reduced in atherosclerotic plaques, an increase of cathepsins V and K activities may accelerate the destruction of the elastin matrix in diseased arteries.

Annexin II regulates fibrin homeostasis and neoangiogenesis in vivo

A central tenet of fibrinolysis is that tissue plasminogen activator-dependent (t-PA- dependent) conversion of plasminogen to active plasmin requires the presence of the cofactor/substrate fibrin. However, previous in vitro studies have suggested that the endothelial cell surface protein annexin II can stimulate t-PA-mediated plasminogen activation in the complete absence of fibrin. Here, homozygous annexin II-null mice displayed deposition of fibrin in the microvasculature and incomplete clearance of injury-induced arterial thrombi. While these animals demonstrated normal lysis of a fibrin-containing plasma clot, t-PA-dependent plasmin generation at the endothelial cell surface was markedly deficient. Directed migration of annexin II-null endothelial cells through fibrin and collagen lattices in vitro was also reduced, and an annexin II peptide mimicking sequences necessary for t-PA binding blocked endothelial cell invasion of Matrigel implants in wild-type mice. In addition, annexin II-deficient mice displayed markedly diminished neovascularization of fibroblast growth factor-stimulated cornea and of oxygen-primed neonatal retina. Capillary sprouting from annexin II-deficient aortic ring explants was markedly reduced in association with severe impairment of activation of metalloproteinase-9 and -13. These data establish annexin II as a regulator of cell surface plasmin generation and reveal that impaired endothelial cell fibrinolytic activity constitutes a barrier to effective neoangiogenesis.

Annexin II regulates fibrin homeostasis and neoangiogenesis in vivo

A central tenet of fibrinolysis is that tissue plasminogen activator-dependent (t-PA- dependent) conversion of plasminogen to active plasmin requires the presence of the cofactor/substrate fibrin. However, previous in vitro studies have suggested that the endothelial cell surface protein annexin II can stimulate t-PA-mediated plasminogen activation in the complete absence of fibrin. Here, homozygous annexin II-null mice displayed deposition of fibrin in the microvasculature and incomplete clearance of injury-induced arterial thrombi. While these animals demonstrated normal lysis of a fibrin-containing plasma clot, t-PA-dependent plasmin generation at the endothelial cell surface was markedly deficient. Directed migration of annexin II-null endothelial cells through fibrin and collagen lattices in vitro was also reduced, and an annexin II peptide mimicking sequences necessary for t-PA binding blocked endothelial cell invasion of Matrigel implants in wild-type mice. In addition, annexin II-deficient mice displayed markedly diminished neovascularization of fibroblast growth factor-stimulated cornea and of oxygen-primed neonatal retina. Capillary sprouting from annexin II-deficient aortic ring explants was markedly reduced in association with severe impairment of activation of metalloproteinase-9 and -13. These data establish annexin II as a regulator of cell surface plasmin generation and reveal that impaired endothelial cell fibrinolytic activity constitutes a barrier to effective neoangiogenesis.

Elastolytic activity in women with stress urinary incontinence and pelvic organ prolapse

AIMS

Weakening of pelvic supportive tissues is thought to be a contributing etiology in female pelvic floor disorders such as stress urinary incontinence and/or pelvic organ prolapse (SUI/POP). Since elastin modulates the mechanical properties of supportive tissues, we examined elastase activity in vaginal tissue from women with pelvic floor dysfunction compared to asymptomatic controls, by comparing overall elastase activity, human neutrophil elastase, cathepsin K, and alpha-1 antitrypsin (a serine protease inhibitor) mRNA and protein levels.

METHODS

Full-thickness peri-urethral vaginal wall tissues were collected from age and menstrual-phase matched SUI/POP and control women at the time of pelvic surgery. Elastolytic activity in the homogenized tissue was determined by the generation of amino groups from succinylated elastin. To quantify mRNA levels of each protein, quantitative competitive-PCR and confirmatory Western blot analyses were performed on the samples for human neutrophil elastase, cathepsin K, and alpha-1 antitrypsin.

RESULTS

The mean elastolytic activity in vaginal tissues from the SUI/POP group was similar to that in the control group. With respect to the proteolytic enzymes, neither human neutrophil elastase nor cathepsin K differed between the two groups. However, alpha-1 antitrypsin mRNA and protein levels were significantly decreased in tissues from affected women.

CONCLUSIONS

A significant decrease in alpha-1 antitrypsin expression was seen in tissues from women with SUI/POP compared to controls. This data suggest that altered elastin metabolism may contribute to the connective tissue alterations observed in pelvic floor dysfunction. Future investigations are warranted to help define the role of elastin turnover in pelvic floor dysfunction.

Inflammatory mediators in wound healing

This article provides much evidence that the inflammatory process has direct effects on normal and abnormal wound healing. As better understanding develops for the mechanism for these outcomes, targeted proinflammatory and anti-inflammatory interventions are likely to be successful. When inflammation is maintained as a regulated and orchestrated response, effective and normal wound healing is likely to result.

Maggots and wound healing: an investigation of the effects of secretions from Lucilia sericata larvae upon interactions between human dermal fibroblasts and extracellular matrix components

BACKGROUND

Through clinical observation, Lucilia sericata (greenbottle fly) larvae are credited with exerting the following beneficial effects upon a chronic nonhealing wound: removal of necrotic tissue ('debridement'), disinfection of the wound and active promotion of granulation tissue formation. As a major cellular component of granulation tissue, fibroblasts play an extensive role in healing. The composition of extracellular matrix (ECM) located in the wound is another important factor, partaking in a dynamic feedback loop with the fibroblasts that produce it. Fibroblast-ECM interactions therefore exert considerable influence upon new tissue formation.

OBJECTIVES

To investigate the effects of L. sericata larval excretory/secretory products (ES) upon the behaviour of fibroblasts, seeded upon ECM component surfaces.

METHODS

ES were collected by washing freshly hatched larvae in phosphate-buffered saline. Human dermal neonatal fibroblast cells were seeded upon fibronectin- or collagen-coated surfaces, together with untreated (or 'native') ES, heat-treated ES, or no ES (ES blank). Following incubation, fibroblast adhesion was determined using an adenosine triphosphate assay and, for confirmation, a total nucleic acid content assay. Cell spreading was observed using microscopy. The effect of ES upon fibronectin structure was observed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Peptide sequencing of suspected fibronectin fragments was performed using an 'electrospray' type time of flight mass spectrometer and 'Peptident' database search.

RESULTS

ES significantly reduced fibroblast adhesion to both fibronectin and, to a lesser extent, collagen. Cell spreading was also reduced, yet cells remained viable. For both spreading and adhesion, heat-treated ES exerted significantly less activity than native, untreated ES. However, they still exhibited significant activity when compared with the ES blank. ES appeared to modify fibroblast adhesion indirectly via proteolytic fragmentation of the fibronectin protein surface.

CONCLUSIONS

L. sericata larval secretions modify fibroblast adhesion and spreading across ECM protein surfaces, while keeping cells viable. Proteolytic activity of the ES played a significant role. If transferred to the wound situation, such alteration of fibroblast-ECM interactions may enhance new tissue formation.

Acute wound healing an overview

The ability to heal an injury is a biologic necessity for all organisms, with mammals lagging in proficiency when compared with lower life forms that have the ability to regenerate differentiated structures. Technology and increased scientific knowledge have established a coordinated interplay that has improved the ability to manage wounds in a logical manner, and, on occasion, to accelerate the healing process. Insight into the complex chain of events leading to the formation of scar is a necessity for every individual who attempts wound management.

Applications of the neodymium:YAG laser in plastic surgery of the face and lacrimal surgery. Wound repair. A review

The physical and clinical features of a number of laser energy sources presently being used in plastic and endonasal surgery, such as the Nd:YAG, KTP, Ho:YAG, Er:YAG and CO(2) lasers, are emphasized. Particular attention is paid to the Nd:YAG laser and to an Nd:YAG laser-powered quartz laser scalpel.

Alveolar macrophage-mediated elastolysis: roles of matrix metalloproteinases, cysteine, and serine proteases

Chronic obstructive pulmonary disease (COPD) is a common lung disease with cigarette smoking as the major etiological factor, but only 15% of smokers develop COPD. Destruction of lung elastin observed in COPD is mediated by many enzymes, including cysteine, serine, and matrix metalloproteinases (MMP). The contribution of these enzymes to the lung elastolytic load, released from alveolar macrophages collected from nonsmokers, healthy smokers, and COPD patients, was examined by radiolabeled elastin as substrate in the presence of specific enzyme inhibitors. The activity of MMP was further examined by zymography and Western blotting. COPD macrophages degraded more elastin than either of the other groups. Elastolysis was greatest in the initial 24 h. Through the 72-h culture period, the contribution to elastolysis of serine elastases decreased, MMP increased, and cysteine elastases remained constant. The increased release of elastolytic enzymes in COPD subjects may explain why some smokers develop COPD. This difference may be due to unknown susceptibility factors. Serine proteases play a significant role; however, other enzymes, particularly the MMP, deserve further investigation.

Urokinase is required for the formation of mactinin, an alpha-actinin fragment that promotes monocyte/macrophage maturation

We have previously shown that lysates from HL-60 myeloid leukemia cells or from peripheral blood monocytes are able to degrade alpha-actinin to form a 31-kDa amino-terminal fragment with monocyte/macrophage maturation promoting activity. In contrast, intact alpha-actinin, which is a 100-kDa actin-binding protein, has no differentiating activity. The aim of this study was to investigate the enzyme responsible for the degradation of alpha-actinin to form this fragment, named mactinin. The ability of cell lysates to degrade [125I]alpha-actinin in the presence of various enzyme inhibitors, including inhibitors of metalloproteinases, cysteine proteinases, and serine proteases, was measured. Phenylmethylsulfonyl fluoride (PMSF) was the only inhibitor able to prevent formation of mactinin by cell lysate degradation of alpha-actinin, suggesting that a serine protease is responsible for the digestion. Of the various serine proteases tested (thrombin, plasmin, and urokinase), only urokinase was able to produce a 31-kDa band. The urokinase-generated 31-kDa band promoted maturation in HL-60 cells. Amiloride, a specific inhibitor of urokinase, inhibited production of the 31-kDa alpha-actinin fragment by HL-60 cell lysates. For in vivo tests, inflammatory fluid (from bronchoalvelolar lavage) was collected from uPA (urokinase) knockout mice and their wild-type counterparts after intratracheal challenge with Pneumocystis carinii. Although most (6 of 8) wild-type mice had mactinin in their inflammatory fluid samples, none (0 of 8) of the uPA knockout mice had mactinin present (P<0.01). These results demonstrate that urokinase is necessary and sufficient for the formation of the monocyte/macrophage maturation promoting fragment, mactinin, in vitro and in vivo. These findings support the role of urokinase in the regulation of monocyte/macrophage functions, such as that occurring in inflammatory reactions.

Matrix metalloproteinase expression in the coronary circulation induced by coronary angioplasty

Recent studies have revealed that matrix metalloproteinases (MMPs) play an important role in cardiovascular remodeling by degrading the extracellular matrix. We investigated changes in the expression of MMPs due to percutaneous transluminal coronary angioplasty (PTCA). We studied 47 patients with ischemic heart disease who underwent elective PTCA on isolated stenotic lesion of left coronary arteries. Twelve patients received conventional balloon angioplasty, 14 percutaneous transluminal rotational atherectomy and 21 stent implantation. Blood samples were drawn from the coronary sinus immediately before and after, as well as 4 and 24 h, after PTCA. Plasma levels of MMP-1, MMP-2, tissue inhibitor of MMP (TIMP)-1 and TIMP-2 were measured by enzyme-linked immunosorbent assay. Plasma MMP-2 activity was determined with the digestion of a specific chromogenic peptide substrate. We could observe serial changes in plasma MMP-1 levels in the coronary circulation only in one patient, because MMP-1 levels were lower than the limit of detection in other patients. On the other hand, plasma MMP-2 levels in the coronary sinus were detectable in all subjects and increased significantly 4 and 24 h after PTCA. Plasma TIMP-1 levels also showed significant increases 4 and 24 h after PTCA, whereas TIMP-2 did not show significant changes. Plasma MMP-2/TIMP-2 ratio and MMP-2 activity in the coronary sinus showed significant increases 4 and 24 h after PTCA. A positive correlation was observed between MMP-2 levels in the coronary sinus 4 h after PTCA and late loss index 6 months after PTCA. MMP-2 levels in the coronary sinus blood were significantly higher in patients with late restenosis than in those without restenosis. PTCA induces increases in plasma MMP-2 levels and activity in the coronary circulation, which may contribute to vascular remodeling and late restenosis after PTCA.

Effect of malondialdehyde-acetaldehyde-protein adducts on the protein kinase C-dependent secretion of urokinase-type plasminogen activator in hepatic stellate cells

Previous studies from our laboratory have shown that malondialdehyde-acetaldehyde-protein adducts (MAA adducts) are formed in hepatocytes of ethanol-fed rats and directly influence the hepatic stellate cells (HSCs) to induce their secretion of chemokines and to up-regulate their expression of adhesion molecules. Since protein kinase C (PKC) is known to play a major role in many diverse intracellular signal transduction processes, we investigated whether MAA adducts influence the function of HSCs via a PKC-dependent pathway. HSCs in culture were exposed to MAA adducts, and PKC activity was determined. We observed a time- and concentration-dependent activation of PKC when cultures were exposed to BSA-MAA as compared with unmodified BSA. Using PKC isoform-specific inhibitors, we also showed that BSA-MAA induces the activation of a specific isoform of PKC, PKC-alpha, in HSCs. No activation of PKC was observed when HSCs were exposed to other aldehyde adducts such as BSA-acetaldehyde or BSA-malondialdehyde, indicating that the effects of MAA adducts on HSCs were somewhat specific. We further examined whether the observed increase in PKC activation induced by MAA adducts in HSCs, in turn, causes a functional effect. We observed that BSA-MAA induces the increased secretion of urokinase-type plasminogen activator, a key component of the plasmin-generating system, and that PKC activation is necessary for this enhanced urokinase-type plasminogen activator secretion. These results indicate that MAA adducts via a PKC-mediated pathway may regulate plasmin-mediated matrix degradation in the liver, thereby contributing to the progression of hepatic fibrosis.

Plasma levels of plasmin-antiplasmin-complexes are predictive for small abdominal aortic aneurysms expanding to operation-recommendable sizes

OBJECTIVE

Three proteolytic systems seem involved in the aneurysmal degradation of the aortic wall. Plasmin is a common activator of the systems and could thus be predictive for the progression of abdominal aortic aneurysms (AAAs).

METHODS AND MATERIALS

In 1994, 112 of 141 male patients with AAA diagnosed through population screening (defined as 3 cm or more) were interviewed and examined and had blood samples taken. One hundred twelve cases were scanned annually for 1 to 5 years (mean, 2.5 years) and referred for surgery if the AAA exceeded 5 cm in diameter. A random sample of 70 of the 112 cases had P-plasmin-antiplasmin-complexes (PAPs), P-plasminogen, and S-elastin-peptides (SEPs).

RESULTS

PAP was positively correlated with annual expansion rate (r = 0.39, 0.16-0.56), persisting after adjustment for initial AAA size, SEP, age, and smoking. However, PAP levels did not correlate with the initial AAA size or SEP. Furthermore, PAP levels were significantly predictive for cases expanding to operation-recommendable AAA sizes. Combined with the initial AAA size, both optimal sensitivity and specificity were 82%, increasing to 95% and 96%, respectively, excluding those lost to follow-up and accepting 2 mm of interobserver variation.

CONCLUSION

The progression of AAA is correlated with the PAP level, which seems to have a predictive value similar to the best serologic predictor known, serum-elastin-peptides.

Expression of matrix metalloproteinases in patients with acute myocardial infarction

This study investigated the clinical significance of matrix metalloproteinases (MMPs) in acute myocardial infarction (AMI) and the involvement of peripheral blood mononuclear cells (PBMCs), which are a possible source of MMPs in AMI. Forty patients with AMI were recruited. Plasma and PBMCs were isolated from peripheral blood on days 1, 7, 14 and 21 after the onset of AMI. Levels of MMP-1 and MMP-2 were measured by enzyme-linked immunosorbent assay. The MMP-1 level in the culture medium of PBMCs after incubation for 24h was designated as 'PBMC-MMP-1 level.' Plasma MMP-1 did not significantly change during the course of AMI, but the plasma MMP-2 levels increased gradually after the onset of AMI with maximum elevation on day 21 after onset. Plasma MMP-2 activity also became significantly elevated during the course of AMI. PBMC-MMP-1 levels in the patients were significantly higher than those in control subjects over the course of AMI. Significant positive correlations were observed between maximum PBMC-MMP-1 levels and maximum plasma C-reactive protein levels (r=+0.55, p<0.01) and left ventricular end-diastolic volume index (r=+0.63, p<0.001). In conclusion, plasma MMP-2 levels and activity and MMP-1 production by PBMCs are increased in patients with AMI. Inflammation after AMI may enhance production of MMP-1 by PBMCs. These changes may play an important role in the ventricular remodeling that occurs after AMI by promoting the degradation of the extracellular matrix.

Liver cirrhosis is reverted by urokinase-type plasminogen activator gene therapy

Liver cirrhosis represents a worldwide health problem and is a major cause of mortality. Cirrhosis is the result of extensive hepatocyte death and fibrosis induced by chronic alcohol abuse and hepatitis B and C viruses. Successful gene therapy approaches to this disease may require both reversal of fibrosis and stimulation of hepatocyte growth. Urokinase-type plasminogen activator (uPA) may serve this function, as it is an initiator of the matrix proteolysis cascade and induces hepatocyte growth factor expression. In a rat cirrhosis model, a single iv administration of a replication-deficient adenoviral vector encoding a nonsecreted form of human uPA resulted in high production of functional uPA protein in the liver. This led to induction of collagenase expression and reversal of fibrosis with concomitant hepatocyte and improved liver function. Thus, uPA gene therapy may be an effective strategy for treating cirrhosis in humans.

Rac1-induced endocytosis is associated with intracellular proteolysis during migration through a three-dimensional matrix

Transfection of Rat1 fibroblasts with an activated form of rac1 (V12rac1) stimulated cell migration in vitro compared to transfection of Rat1 fibroblasts with vector only or with dominant negative rac1 (N17rac1). To investigate the involvement of proteases in this migration, we used a novel confocal assay to evaluate the ability of the Rat1 transfectants to degrade a quenched fluorescent protein substrate (DQ-green bovine serum albumin) embedded in a three-dimensional gelatin matrix. Cleavage of the substrate results in fluorescence, thus enabling one to image extracellular and intracellular proteolysis by living cells. The Rat1 transfectants accumulated degraded substrate intracellularly. V12rac1 increased accumulation of the fluorescent product in vesicles that also labeled with the lysosomal marker LysoTracker. Treatment of the V12rac1-transfected cells with membrane-permeable inhibitors of lysosomal cysteine proteases and a membrane-permeable selective inhibitor of the cysteine protease cathepsin B significantly reduced intracellular accumulation of degraded substrate, indicating that degradation occurred intracellularly. V12rac1 stimulated uptake of dextran 70 (a marker of macropinocytosis) and polystyrene beads (markers of phagocytosis) into vesicles that also labeled for cathepsin B. Thus, stimulation of the endocytic pathways of macropinocytosis and phagocytosis by activated Rac1 may be responsible for the increased internalization and subsequent degradation of extracellular proteins.

Growth factors in glioma angiogenesis: FGFs, PDGF, EGF, and TGFs

It has become well accepted that solid tumors must create a vascular system for nutrient delivery and waste removal in order to grow appreciably. This process, angiogenesis, is critical to the progression of gliomas, with vascular changes accompanying the advancement of these tumors. The cascade of events in this process of blood vessel formation involves a complex interplay between tumor cells, endothelial cells, and their surrounding basement membranes in which enzymatic degradation of surrounding ground substance and subsequent endothelial cell migration, proliferation, and tube formation occurs. It is likely that a host of growth factors is responsible for mediating these key events. To date, a role for Vascular Endothelial Growth Factor (VEGF) in glioma angiogenesis has been convincingly demonstrated. This review explores the contribution of other growth factors--Fibroblast Growth Factors (FGFs), Platelet-Derived Growth Factor (PDGF), Epidermal Growth Factor (EGF), and Transforming Growth Factors (TGFs)--to glioma angiogenesis. These growth factors may influence glioma angiogenesis by directly stimulating endothelial cell proliferation, by mediating the expression of key proteases on endothelial cells necessary for angiogenesis, or by regulating the expression of VEGF and of each other.

Production of plasminogen activator inhibitor-1 by human mast cells and its possible role in asthma

The plasminogen activator inhibitor type 1 (PAI-1) has an essential role in tissue remodeling. The PAI-1 gene was induced by a combination of phorbol ester and calcium ionophore at the highest level among the inducible human mast cell genes that we have analyzed on a DNA microarray. PAI-1 was secreted by both a human mast cell line (HMC)-1 and primary cultured human mast cells upon stimulation, whereas PAI-1 was undetectable in either group of unstimulated cells. The secretion of PAI-1 was due to de novo synthesis of PAI-1 rather than secretion of preformed PAI-1. The functional significance of PAI-1 secretion was demonstrated by complete inhibition of tissue-type plasminogen activator activity with supernatants of stimulated HMC-1 cells. Furthermore, we were able to regulate PAI-1 gene expression in HMC-1 cells by known therapeutic agents. High-dose (1 microM) dexamethasone induced PAI-1 mRNA expression. Cyclosporin down-regulated the expression of the PAI-1 gene. Cycloheximide abrogated PAI-1 mRNA expression, suggesting that transcription of the PAI-1 gene requires de novo synthesis of early gene products, including transcription factors. Finally, we demonstrated PAI-1 in lung mast cells from a patient with asthmatic attack by double-immunofluorescence study. This is the first report demonstrating that activated human mast cells release a striking amount of functionally active PAI-1. These results suggest that PAI-1 could play an important role in airway remodeling of asthma, and inhibition of PAI-1 activity could represent a novel therapeutic approach in the management of airway remodeling.

Matrix metalloproteinase-1 expression by interaction between monocytes and vascular endothelial cells

There is accumulating evidence of complicated interactions among vascular cells, i.e. endothelial cells, smooth muscle cells and monocytes/macrophages, in the regulation of vascular function and remodeling. We have investigated the mechanisms responsible for matrix metalloproteinase (MMP)-1 expression by interactions between monocytes and vascular endothelial cells. THP-1 cells (human monocytic cell line) and human umbilical vein endothelial cells (HUVECs) were cocultured. MMP-1 levels in the culture medium were measured by enzyme-linked immunosorbent assays. Collagenolytic activity in the culture medium was measured by fluorescence labeled-collagen digestion. Immunohistochemistry using an anti-MMP antibody was carried out to determine which types of cell produce MMP-1. The addition of THP-1 cells to HUVECs for 48 h induced increases in MMP-1 levels and collagenolytic activity, which were 5- and 2-fold relative to those of HUVECs alone, respectively. A separate coculture experiment revealed that direct contact of THP-1 cells and HUVECs contributed to enhanced MMP-1 production in the cocolture. Immunohistochemical analysis revealed that both types of cell produce MMP-1 in the coculture. Neutralizing anti-interleukin-1 beta and tumor necrosis factor- alpha antibodies inhibited MMP-1 production by the coculture. The Src kinase and MEK inhibitors significantly inhibited MMP-1 production by the coculture. Coculture of THP-1 cells and HUVECs induced significant increases in Src and mitogen activated protein (MAP) kinase activities. Enhanced MMP-1 expression induced by monocyte-endothelial cell interactions may play an important role in the pathogenesis of atherosclerosis and plaque rupture.

Angiogenesis in head and neck squamous cell carcinoma

Tumour angiogenesis has recently attracted a great deal of attention as a critical part of oncogenesis and a necessary prerequisite for a malignant phenotype. Research into this process not only offers new insights into tumour biology but is also leading to the development of realistic novel and minimally toxic anti-tumour therapies. Various pro-angiogenic and anti-angiogenic cytokines and pathways have been characterized and their interrelationships are becoming increasingly complex as new findings are made. This article reviews the current understanding of tumour angiogenesis, the basic mechanisms involved and the more important and investigated pathways and proteins involved.

The generation of enzymatically active plasmin on the surface of spirochetes

The spirochete Borrelia burgdorferi, the etiologic agent of Lyme disease, is transmitted to the host by a feeding Ixodid tick. The spirochete subsequently disseminates through the skin, enters the bloodstream, and becomes systemic. A potential mechanism for this invasiveness was identified with the discovery that B. burgdorferi can bind components of the plasminogen activation system (PAS). The methodology for analyzing the generation of enzymatically active plasmin on the surface of this organism is given, and applied to measure spirochete viability, strain differences, and breakdown of extracellular matrix (ECM) macromolecules. Plasmin acquisition by B. burgdorferi was measured photometrically by a specific chromogenic substrate. The growth of B. burgdorferi in culture was not affected by the presence of active plasmin on the spirochete surface. Plasmin-coated B. burgdorferi degraded the purified (ECM) components fibronectin, laminin, and vitronectin, but not collagen. The addition of B. burgdorferi with surface plasmin to a radiolabeled, native ECM resulted in degradation of noncollagenous protein, as measured by release of solubilized radioactivity. Breakdown of purified ECM components or native ECM did not occur after exposure to untreated spirochetes or spirochetes treated with uPA or PLG alone. These results provide in vitro evidence that enzymatically active plasmin on the surface of B. burgdorferi may be partially responsible for its invasiveness.

Biomechanical regulation of human monocyte/macrophage molecular function

When the monocyte infiltrates a tissue, adhesion to the extracellular matrix provides structural anchors, and the cell may be deformed through these attachments. To test the hypothesis that human monocytes/macrophages are mechanically responsive, we studied the effects of small cyclic mechanical deformations on cultured human monocytes/macrophages. When monocytes/macrophages were subjected to 4% strain at 1 Hz for 24 hours, neither matrix metalloproteinase (MMP)-1 nor MMP-3 was induced; however, in the presence of phorbol myristate acetate, strain augmented MMP-1 expression by 5.1 +/- 0.7-fold (P < 0.05) and MMP-3 expression by 1. 6 +/- 0.1-fold (P < 0.05). In contrast, MMP-9 expression was not changed by mechanical strain in the presence or absence of phorbol myristate acetate. Deformation rapidly induced the immediate early response genes c-fos and c-jun. In addition, mechanical deformation induced the transcription factor PU.1, an ets family member that is essential in monocyte differentiation, as well as mRNA for the M-CSF receptor. These studies demonstrate that human monocytes/macrophages respond to mechanical deformation with selective augmentation of MMPs, induction of immediate early genes, and induction of the M-CSF receptor. In addition to enhancing the proteolytic activity of macrophages within repairing tissues, cellular deformation within tissues may play a role in monocyte differentiation.

Plasmin triggers rapid contraction and degradation of fibroblast-populated collagen lattices

We examined the role of the serine proteinase plasmin in regulating fibroblast-mediated tissue remodeling during wound healing. As an in vitro model system, collagen lattices were seeded with human dermal fibroblasts, and various concentrations of plasmin were added to the medium of the contracting lattices. Within 16 h, fibroblast-populated collagen lattices treated with plasmin rapidly contracted from approximately 20 mm to less than 2 mm in diameter. Measurements of collagen lattices with radiolabeled collagen indicated that, when these lattices included either fibroblasts or conditioned medium derived from fibroblast-populated collagen lattices, exogenous plasmin induced collagen degradation and rapid lattice contraction. Western blot analyses of conditioned medium demonstrated that fibroblasts in collagen lattices secreted the latent matrix metalloproteinase, MMP-1, which was subsequently cleaved by plasmin. Additionally, rapidlattice contraction and collagen degradation were blocked when collagen lattices were treated simultaneously with plasmin and aprotinin or a tissue inhibitor of metalloproteinases, TIMP-1. These results provide strong evidence that plasmin regulates rapid contraction of collagen lattices by activating fibroblast-secreted MMP-1 that triggers collagen degradation. The findings from this study suggest that fibroblast-populated collagen lattices can be used as an in vitro model system to investigate the mechanisms by which plasmin and cell-secreted plasminogen activators control MMP-1 mediated extracellular lattice degradation and remodeling during wound healing.