Matrix metalloproteinase-9 and tissue inhibitor of metalloproteinase-3 are key regulators of extracellular matrix degradation by mouse embryos

Embryo implantation in humans and rodents is a highly invasive yet tightly controlled process involving extracellular matrix (ECM) degradation. Matrix metalloproteinase 9 (MMP-9) has been implicated as the major facilitator of this ECM degradation. MMP-9 is expressed by the embryo's trophoblast cells, whereas tissue inhibitor of metalloproteinases 3 (TIMP-3) is expressed by the maternal uterine cells immediately adjacent to the trophoblast. We examined the functional roles of MMP-9 and TIMP-3 during in vitro ECM degradation by mouse embryos. Blastocysts were treated with either MMP-9 antisense or sense oligonucleotides and incubated on an ECM gel. The extent of ECM degradation exhibited by the blastocysts due to proteinase secretion was quantified. Embryos exposed to MMP-9 antisense oligonucleotides exhibited reduced ECM-degrading activity as compared with controls, and this reduced activity was correlated with the level of MMP-9 secreted by the embryos. The functional role of TIMP-3 was then examined by incubating blastocysts on an ECM gel that had been impregnated with various amounts of TIMP-3. In a dose-dependent manner, increases in TIMP-3 resulted in a reduction in ECM degradation and were correlated with diminished MMP-9 activity. These results provide important functional evidence that in vitro ECM degradation is regulated by embryo-derived MMP-9 and ECM-derived TIMP-3.     

Temporal changes in matrix metalloproteinase expression and inflammatory response associated with cardiac rupture after myocardial infarction in mice

We previously found that male mice with myocardial infarction (MI) had a high rate of cardiac rupture, which generally occurred at 3 to 5 days after MI. Since matrix metalloproteinases (MMPs) play an important role in infarct healing, tissue repair and extracellular matrix (ECM) remodeling post-MI, we studied the temporal relationship of MMP expression and inflammatory response to cardiac rupture after acute MI. Male C57BL/6J mice were subjected to MI (induced by ligating the left anterior descending coronary artery) and killed 1, 2, 4, 7 or 14 days after MI. MMP-2 and MMP-9 activity in the heart were measured by zymography. Collagen content was measured by hydroxyproline assay. We found that after MI, MMP-9 activity increased as early as 1 day and reached a maximum by 2-4 days, associated with a similar increase in neutrophil and macrophage infiltration in the infarct area. MMP-2 started to increase rapidly within 4 days, reaching a maximum by 7 days and remaining high even at 14 days. Intense macrophage infiltration appeared by 4 days after MI and then gradually decreased within 7 to 14 days. Collagen content was unchanged until 4 days after MI, at which point it increased and remained high thereafter. Our data suggest that in mice, overexpression of MMP-2 and MMP-9 (possibly expressed mainly by neutrophils and macrophages) may lead to excessive ECM degradation in the early phase of MI, impairing infarct healing and aggravating early remodeling which in turn causes cardiac rupture.     

Wild-type amyloid beta 1-40 peptide induces vascular smooth muscle cell death independently from matrix metalloprotease activity

Cerebral amyloid angiopathy (CAA) is an important cause of intracerebral hemorrhages in the elderly, characterized by amyloid-β (Aβ) peptide accumulating in central nervous system blood vessels. Within the vessel walls, Aβ-peptide deposits [composed mainly of wild-type (WT) Aβ(1-40) peptide in sporadic forms] induce impaired adhesion of vascular smooth muscle cells (VSMCs) to the extracellular matrix (ECM) associated with their degeneration. This process often results in a loss of blood vessel wall integrity and ultimately translates into cerebral ischemia and microhemorrhages, both clinical features of CAA. In this study, we decipher the molecular mechanism of matrix metalloprotease (MMP)-2 activation in WT-Aβ(1-40) -treated VSMC and provide evidence that MMP activity, although playing a critical role in cell detachment disrupting ECM components, is not involved in the WT-Aβ(1-40) -induced degeneration of VSMCs. Indeed, whereas this peptide clearly induced VSMC apoptosis, neither preventing MMP-2 activity nor hampering the expression of membrane type1-MMP, or preventing tissue inhibitors of MMPs-2 (TIMP-2) recruitment (two proteins evidenced here as involved in MMP-2 activation), reduced the number of dead cells. Even the use of broad-range MMP inhibitors (GM6001 and Batimastat) did not affect WT-Aβ(1-40) -induced cell apoptosis. Our results, in contrast to those obtained using the Aβ(1-40) Dutch variant suggesting a link between MMP-2 activity, VSMC mortality and degradation of specific matrix components, indicate that the ontogenesis of the Dutch familial and sporadic forms of CAAs is different. ECM degradation and VSMC degeneration would be tightly connected in the Dutch familial form while being two independent processes in sporadic forms of CAA.     

Synthesis and characterization of injectable poly(N-isopropylacrylamide-co-acrylic acid) hydrogels with proteolytically degradable cross-links

Hydrogels composed of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were prepared by redox polymerization with peptide cross-linkers to create an artificial extracellular matrix (ECM) amenable for testing hypotheses regarding cell proliferation and migration in three dimensions. Peptide degradable cross-linkers were synthesized by the acrylation of the amine groups of glutamine and lysine residues within peptide sequences potentially cleavable by matrix metalloproteinases synthesized by mammalian cells (e.g., osteoblasts). With the peptide cross-linker, loosely cross-linked poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content, and enzymatic degradation properties were investigated. The peptide-cross-linked P(NIPAAm-co-AAc) hydrogels were pliable and fluidlike at room temperature and could be injected through a small-diameter aperture. The LCST of peptide-cross-linked hydrogel was influenced by the monomer ratio of NIPAAm/AAc but not by cross-linking density within the polymer network. A peptide-cross-linked hydrogel with a 97/3 molar ratio of NIPAAm/AAc exhibited a LCST of approximately 34.5 degrees C. Swelling was influenced by NIPAAm/AAc monomer ratio, cross-linking density, and swelling media; however, all hydrogels maintained more than 90% water even at 37 degrees C. In enzymatic degradation studies, breakdown of the peptide-cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on both the concentration of collagenase and the cross-linking density. These results suggest that peptide-cross-linked P(NIPAAm-co-AAc) hydrogels can be tailored to create environmentally-responsive artificial extracellular matrixes that are degraded by proteases.     

Matrix metalloproteinase expression in cardiac myocytes following myocardial infarction in the rabbit

Myocardial infarction (MI), leads to cardiac remodeling, thinning of the ventricle wall, ventricular dilation, and heart failure, and is a leading cause of death. Interactions between the contractile elements of the cardiac myocytes and the extracellular matrix (ECM) help maintain myocyte alignment required for the structural and functional integrity of the heart. Following MI, reorganization of the ECM and the myocytes occurs, contributing to loss of heart function. In certain pathological circumstances, the ECM is modulated such that the structure of the tissue becomes damaged. The matrix metalloproteinases (MMPs) are a family of enzymes that degrade molecules of the ECM. The present experiments were performed to define the time-course, isozyme subtypes, and cellular source of increased MMP expression that occurs following MI in an experimental rabbit model. Heart tissue samples from infarcted and sham animals were analyzed over a time-course of 1-14 days. By zymography, it was demonstrated that, unlike the sham controls, MMP-9 expression was induced within 24 hours following MI. MMP-3 expression, also absent in sham controls, was induced 2 days after MI. MMP-2 expression was detected in both the sham and infarcted samples and was modestly up-regulated following MI. Tissue inhibitor of metalloproteinase-1 (TIMP-1) expression was evaluated and shown to be down-regulated following MI, inverse of MMP-9 and MMP-3 expression. Further, MMP-9 and MMP-3 expression was detected by immunohistochemistry in myocytes within the infarct. Additional studies were conducted in which cultured rat cardiac myocytes were exposed to a hypoxic environment (2% O2) for 24 hours and the media analyzed for MMP expression. MMP-9 and MMP-3 were induced following exposure to hypoxia. It is speculated that the net increase in proteolytic activity by myocytes is a contributing factor leading to myocyte misalignment and slippage. Additional studies with a MMP inhibitor would elucidate this hypothesis.     

Neutrophil elastase cleaves laminin-332 (laminin-5) generating peptides that are chemotactic for neutrophils

Proteolytic processing of laminin-332 by matrix metalloproteinase (MMP)-2 and MMP-14 has been shown to yield fragments that are promigratory for epithelial cells. During acute and chronic inflammation, proteases are elaborated by neutrophils and macrophages that can degrade basement membranes. We investigated the susceptibility of laminin-332 to degradation by the following neutrophil and macrophage proteases: neutrophil elastase (NE), cathepsin G, proteinase-3, and MMPs-2, -8, -9, and -12. Protease-specific differences were seen in the capacity to cleave the individual chains of laminin-332. NE and MMP-12 showed the greatest activity toward the gamma2 chain, generating a fragment similar in size to the gamma2x fragment generated by MMP-2. The digestion pattern of laminin-332 by degranulated neutrophils was nearly identical to that generated with NE alone. Digestion by supernatants of degranulated neutrophils was blocked by an inhibitor of NE, and NE-deficient neutrophils were essentially unable to digest laminin-332, suggesting that NE is the major neutrophil-derived protease that degrades laminin-332. In vivo, laminin gamma2 fragments were found in the bronchoalveolar lavage fluid of wild-type mice treated with lipopolysaccharide, whereas that obtained from NE-deficient mice showed a different cleavage pattern. In addition, NE cleaved a synthetic peptide derived from the region of human laminin gamma2 containing the MMP-2 cleavage site, suggesting that NE may generate laminin-332 fragments that are also promigratory. Both laminin-332 fragments generated by NE digestion and NE-digested laminin gamma2 peptide were found to be chemotactic for neutrophils. Collectively, these data suggest that degradation of laminin-332 by NE generates fragments with important biological activities.     

The Use of 3-D Culture in Peptide Hydrogel for Analysis of Discoidin Domain Receptor 1-Collagen Interaction

The aim of this study is to examine a novel drop culture model using a biologically inspired self-assembling peptide: hydrogel (RAD16-I, also called PuraMatrix), which produces a nanoscale environment similar to native extracellular matrix (ECM) for a cell line weakly adherent to a plastic surface during cell culture. Our work investigates quantitatively analyzing discoidin domain receptor (DDR) 1-mediated protein interactions between collagen type I and matrix metalloproteinase (MMP)-2 or -9, as well as cell invasion, using, as a scaffold, PuraMatrix, a novel peptide hydrogel. Results demonstrate that the dynamic cell culture technique produced a highly stable reharvesting of cells throughout the constructs with HP-75, human pituitary adenoma cell line when compared to the traditional seeding methods. Secretion of MMP via collagen type I was observed quantitatively in the supernatant (EC50; MMP-2, 50.4 ng/ml: MMP-9, 57.6 ng/ml). In PuraMatrix gel impregnated with 50 ng/ml of collagen type I, transfection of the vector encoding full-length DDR1 or siRNA targeting DDR1 up- or downregulated respectively secretion of MMP-2 and -9, and cell invasion. Our results show that incorporation of this peptide with each ECM component provides a more permissive environment to elucidate ECM to cell signal interaction.Key Words: biological scaffolds, cell invasion, ionic self-complementary peptides, nano-fiber hydrogels, pituitary adenoma     

In Vivo Assessment of Bone Regeneration in Alginate/Bone ECM Hydrogels with Incorporated Skeletal Stem Cells and Single Growth Factors

The current study has investigated the use of decellularised, demineralised bone extracellular matrix (ECM) hydrogel constructs for in vivo tissue mineralisation and bone formation. Stro-1-enriched human bone marrow stromal cells were incorporated together with select growth factors including VEGF, TGF-β3, BMP-2, PTHrP and VitD3, to augment bone formation, and mixed with alginate for structural support. Growth factors were delivered through fast (non-osteogenic factors) and slow (osteogenic factors) release PLGA microparticles. Constructs of 5 mm length were implanted in vivo for 28 days within mice. Dense tissue assessed by micro-CT correlated with histologically assessed mineralised bone formation in all constructs. Exogenous growth factor addition did not enhance bone formation further compared to alginate/bone ECM (ALG/ECM) hydrogels alone. UV irradiation reduced bone formation through degradation of intrinsic growth factors within the bone ECM component and possibly also ECM cross-linking. BMP-2 and VitD3 rescued osteogenic induction. ALG/ECM hydrogels appeared highly osteoinductive and delivery of angiogenic or chondrogenic growth factors led to altered bone formation. All constructs demonstrated extensive host tissue invasion and vascularisation aiding integration and implant longevity. The proposed hydrogel system functioned without the need for growth factor incorporation or an exogenous inducible cell source. Optimal growth factor concentrations and spatiotemporal release profiles require further assessment, as the bone ECM component may suffer batch variability between donor materials. In summary, ALG/ECM hydrogels provide a versatile biomaterial scaffold for utilisation within regenerative medicine which may be tailored, ultimately, to form the tissue of choice through incorporation of select growth factors.     

Degradation of extracellular matrix proteins by hemorrhagic metalloproteinases

The proteolytic activity of four hemorrhagic metalloproteinases (Ht-a, c, d, and e) isolated from the venom of the Western diamondback rattlesnake (Crotalus atrox) was investigated using isolated extracellular matrix (ECM) proteins. We determined that all of the proteinases are capable of cleaving fibronectin, laminin, type IV collagen, nidogen (entactin), and gelatins. However, none of the proteinases were proteolytic against the interstitial collagen types I and III or type V collagen. With all of the substrates listed above Ht-c and Ht-d produced identical digestion patterns, as would be expected for these isoenzymes. With fibronectin, Ht-a produces a different ratio of products from Ht-c and Ht-d, while Ht-e produces a unique pattern of digestion. Ht-e and Ht-a produced nonidentical patterns with the laminin/nidogen preparation although some similarity was shared between them as well as with the Ht-c/d digestion pattern. Similar results were also observed for these proteinases with nidogen 150 as the substrate. The type IV collagen digestion patterns by Ht-e and Ht-a were similar to the pattern observed with Ht-c/d but differed by two bands. The digestion patterns of the three gelatins produced by the proteinases show differences between Ht-c and Ht-d when compared to Ht-e and Ht-a. This investigation clearly shows that several of the ECM proteins are efficiently digested by these toxins. The proteinases have some digestion sites in common but show differing specificities. In addition, the range of ECM proteins digested by these hemorrhagic proteinases is nearly identical to that demonstrated by the ECM proteinase stromelysin (MMP-3). From these data, and the knowledge of the roles these ECM proteins have in maintaining basement membrane structural/functional integrity, one can envision that the degradation of these ECM proteins could readily lead to loss of capillary integrity resulting in hemorrhage occurring at those sites.     

Increase in extracellular cross-linking by tissue transglutaminase and reduction in expression of MMP-9 contribute differentially to focal segmental glomerulosclerosis in rats

Tissue transglutaminase (tTG) is a Ca²⁺-dependent enzyme which stabilizes the extracellular matrix (ECM) through post-translational modification, and may play an important role in the pathogenesis of focal and segmental glomerulosclerosis (FSGS). Here, we have investigated whether tTG contributes to the glomerular ECM expansion in the puromycin aminonucleoside (PAN)-injection-induced experimental rat model of FSGS. The localization and expression of tTG, MMP-9 gelatinase, and the ECM component fibronectin (FN) in kidneys was determined by immunohistochemistry and measured by semi-quantitative analysis. Protein levels of tTG and MMP-9 were also analyzed by Western blotting.In situtransglutaminase activity was assayed by measurement of incorporated substrate and the immunofluorescence staining for the cross-linking product, ε-(γ-glutamyl) lysine. Prominent proteinuria, a typical pathological feature of FSGS, was observed in PAN injection group rats. tTG immunoreactivity was located markedly in glomeruli and the levels of this protein in whole-kidney homogenates of PAN injection group rats were significantly increased (361± 106% control, P< 0.05). Similarly, transglutaminase activity and ε-(γ-glutamyl) lysine were also predominately located within glomeruli and were much more intense in the PAN-injected group than that in control animals. MMP-9 was also located primarily within glomeruli. In PAN-injected kidneys, protein levels of active MMP-9 were significantly reduced (59± 27% control, P< 0.01), while pro-MMP-9 levels increased (148± 42% control, P< 0.05). Remarkable expression of glomerular fibronectin (FN) was found in PAN injection group rats. Semi-quantitative analysis demonstrated this increased intensity of FN staining in the PAN-injected rats was 149± 23% of the control values (P< 0.05). Enhanced cross-linking of ECM by tissue transglutaminase and decreased degradation due to reduced active MMP-9 expression may be at least partially responsible for the deposition of FN within injured glomeruli in experimental FSGS.     

Hypochlorous acid generated by myeloperoxidase modifies adjacent tryptophan and glycine residues in the catalytic domain of matrix metalloproteinase-7 (matrilysin): an oxidative mechanism for restraining proteolytic activity during inflammation

Dysregulation of matrix metalloproteinase (MMP) activity is implicated in tissue destruction under inflammatory conditions. An important mechanism controlling enzymatic activity might involve reactive oxygen species generated by phagocytes. Myeloperoxidase, a heme protein secreted by neutrophils, monocytes, and macrophages, uses hydrogen peroxide to generate hypochlorous acid (HOCl). We demonstrate that HOCl inhibits the activity of human matrilysin (MMP-7) in vitro, suggesting that it might limit proteolytic activity during inflammation. When MMP-7 was exposed to HOCl generated by myeloperoxidase, the proteinase lost activity. High performance liquid chromatographic analysis of the tryptic digest of the HOCl-treated proteinase demonstrated the absence of two peptides that were present in the untreated enzyme. Tandem mass spectrometric analysis revealed that both of the lost peptides contained methionine and tryptophan-glycine residues. The methionine residue of one of the peptides had been oxidized to methionine sulfoxide. In contrast, the major product from the other peptide was 4 atomic mass units smaller than its precursor (WG-4). This novel oxidation product was derived though modification of adjacent tryptophan and glycine residues in the catalytic domain of the enzyme. Loss of proteolytic activity was associated with conversion of the precursor peptide to WG-4 but not with methionine oxidation. In contrast, hydrogen peroxide failed to oxidize MMP-7 or to inactivate the enzyme. Thus, HOCl inactivates MMP-7, perhaps by site-specific conversion of tryptophan-glycine to WG-4. This inactivation mechanism is distinct from the well studied mechanisms involving tissue inhibitors of metalloproteinases. Our findings suggest that local pericellular production of HOCl by phagocytes is a physiological mechanism for governing MMP activity during inflammation.     

Blueberry flavonoids inhibit matrix metalloproteinase activity in DU145 human prostate cancer cells.

Regulation of the matrix metalloproteinases (MMPs), the major mediators of extracellular matrix (ECM) degradation, is crucial to regulate ECM proteolysis, which is important in metastasis. This study examined the effects of 3 flavonoid-enriched fractions (a crude fraction, an anthocyanin-enriched fraction, and a proanthocyanidin-enriched fraction), which were prepared from lowbush blueberries (Vaccinium angustifolium), on MMP activity in DU145 human prostate cancer cells in vitro. Using gelatin gel electrophoresis, MMP activity was evaluated from cells after 24-hr exposure to blueberry fractions. All fractions elicited an ability to decrease the activity of MMP-2 and MMP-9. Of the fractions tested, the proanthocyanidin-enriched fraction was found to be the most effective at inhibiting MMP activity in these cells. No induction of either necrotic or apoptotic cell death was noted in these cells in response to treatment with the blueberry fractions. These findings indicate that flavonoids from blueberry possess the ability to effectively decrease MMP activity, which may decrease overall ECM degradation. This ability may be important in controlling tumor metastasis formation.     

Matrix metalloproteinase expression and activity following prostaglandin F(2 alpha)-induced luteolysis

Luteal tissue contains matrix metalloproteinases (MMPs) that cleave specific components of the extracellular matrix (ECM) and are inhibited by tissue inhibitors of metalloproteinases (TIMPs). We previously reported a decrease in luteal TIMP-1 within 15 min of prostaglandin F(2 alpha) (PGF(2 alpha))-induced luteolysis. An increase in the MMP:TIMP ratio may promote ECM degradation and apoptosis, as observed in other tissues that undergo involution. The objectives of these experiments were to determine whether 1) PGF(2 alpha) affects expression of mRNA encoding fibrillar collagenases (MMP-1 and -13), gelatinases A and B (MMP-2 and -9), membrane type (mt)-1 MMP (MMP-14), stromelysin (MMP-3), and matrilysin (MMP-7), and 2) PGF(2 alpha) increases MMP activity during PGF(2 alpha)-induced luteolysis in sheep. Corpora lutea (n = 3-10/time point) were collected at 0, 15, and 30 min and 1, 2, 4, 6, 12, 24, and 48 h after PGF(2 alpha) administration. Northern blot analysis confirmed the presence of all MMPs except MMP-9. Expression of mRNA for the above MMPs (except MMP-2) increased significantly (P < 0.05) by 30 min, and all MMPs increased significantly (P < 0.05) by 6 h after PGF(2 alpha) administration. Expression of MMP-14 mRNA increased significantly (P < 0.05) by 15 min post-PGF(2 alpha) and remained elevated through 48 h. MMP activity in luteal homogenates (following proenzyme activation and inactivation of inhibitors) was increased significantly (P < 0.05) by 15 min and remained elevated through 48 h post-PGF(2 alpha). MMP activity was localized (in situ zymography) to the pericellular area of various cell types in the 0-h group and was markedly increased by 30 min post-PGF(2 alpha). MMP mRNA expression and activity were significantly increased following PGF(2 alpha) treatment. Increased MMP activity may promote ECM degradation during luteolysis.     

Effect of fibroblast activation protein and alpha2-antiplasmin cleaving enzyme on collagen types I, III, and IV

The circulating enzyme, α₂-antiplasmin cleaving enzyme (APCE), has very similar sequence homology and proteolytic specificity as fibroblast activation protein (FAP), a membrane-bound proteinase. FAP is expressed on activated fibroblasts associated with rapid tissue growth as in embryogenesis, wound healing, and epithelial-derived malignancies, but not in normal tissues. Its presence on stroma suggests that FAP functions to remodel extracellular matrix (ECM) during neoplastic growth. Precise biologic substrates have not been defined for FAP, although like APCE, it cleaves α₂-antiplasmin to a derivative more easily cross-linked to fibrin. While FAP has been shown to cleave gelatin, evidence for cleavage of native collagen, the major ECM component, remains indistinct. We examined the potential proteolytic effects of FAP or APCE alone and in concert with selected matrix metalloproteinases (MMPs) on collagens I, III, and IV. SDS-PAGE analyses demonstrated that neither FAP nor APCE cleaves collagen I. Following collagen I cleavage by MMP-1, however, FAP or APCE digested collagen I into smaller peptides. These peptides were analogous to, yet different from, those produced by MMP-9 following MMP-1 cleavage. Amino-terminal sequencing and mass spectrometry analyses of digestion mixtures identified several peptide fragments within the sequences of the two collagen chains. The proteolytic synergy of APCE in the cleavage of collagen I and III was not observed with collagen IV. We conclude that FAP works in synchrony with other proteinases to cleave partially degraded or denatured collagen I and III as ECM is excavated, and that derivative peptides might function to regulate malignant cell growth and motility.     

Entrapment and in vitro release of delta-sleep inducing peptide from polymer hydrogels based on modified polyvinyl alcohol

The aim of this study was to entrap delta-sleep inducing peptide (DSIP) in cross-linked poly(vinyl alcohol)-based hydrogels of different structures and to determine kinetics of the peptide release from these hydrogels using an in vitro model. Isotropic and macroporous hydrogels based on poly(vinyl alcohol) acrylic derivative (Acr-PVA) and also macroporous epoxy groups containing hydrogels synthesized by copolymerization of this macromer and glycidyl methacrylate, have been used in this study. Isotropic hydrogels were prepared at positive temperatures while macroporous ones were obtained by formation in cryo-conditions. The peptide was entrapped into macroporous PVA hydrogels by adding the peptide solution onto preformed matrices, while peptide immobilization on PVA-GMA hydrogels, containing free epoxy groups, was carried out by sorption of peptide from its aqueous solution. In the case of DSIP entrapment into isotropic PVA gel the peptide solution was added into the polymer mixture at hydrogel formation. The kinetics of peptide release from hydrogels was studied by incubating matrices in PBS solution (pH 7.4), in physiological solution (0.9% NaCl) and in water. DSIP concentration in supernatants was determined by reverse-phase HPLC. Incubation of macroporous PVA gels in PBS, 0.9% NaCl, and water for 30 min caused release of 74, 70, and 64% DSIP, respectively, and this processes completed within 3 h. From hydrogel containing epoxy groups the release of neither peptide nor its degradation products was observed even after incubation for 48 h. For freshly prepared isotropic hydrogel the release kinetics was as follows: 27 and 78% DSIP were released within first 30 min and 33 h, relatively. For the lyophilized hydrogel samples the peptide release was 63% after incubation for 30 min, while drying of samples at room temperature for 3 days caused significant peptide loss because of its structure damage.     

Cigarette smoke-induced lung emphysema in mice is associated with prolyl endopeptidase, an enzyme involved in collagen breakdown

There is increasing evidence that the neutrophil chemoattractant proline-glycine-proline (PGP), derived from the breakdown of the extracellular matrix, plays an important role in neutrophil recruitment to the lung. PGP formation is a multistep process involving neutrophils, metalloproteinases (MMPs), and prolyl endopeptidase (PE). This cascade of events is now investigated in the development of lung emphysema. A/J mice were whole body exposed to cigarette smoke for 20 wk. After 20 wk or 8 wk after smoking cessation, animals were killed, and bronchoalveolar lavage fluid and lung tissue were collected to analyze the neutrophilic airway inflammation, the MMP-8 and MMP-9 levels, the PE activity, and the PGP levels. Lung tissue degradation was assessed by measuring the mean linear intercept. Additionally, we investigated the effect of the peptide L-arginine-threonine-arginine (RTR), which binds to PGP sequences, on the smoke-induced neutrophil influx in the lung after 5 days of smoke exposure. Neutrophilic airway inflammation was induced by cigarette smoke exposure. MMP-8 and MMP-9 levels, PE activity, and PGP levels were elevated in the lungs of cigarette smoke-exposed mice. PE was highly expressed in epithelial and inflammatory cells (macrophages and neutrophils) in lung tissue of cigarette smoke-exposed mice. After smoking cessation, the neutrophil influx, the MMP-8 and MMP-9 levels, the PE activity, and the PGP levels were decreased or reduced to normal levels. Moreover, RTR inhibited the smoke-induced neutrophil influx in the lung after 5 days' smoke exposure. In the present murine model of cigarette smoke-induced lung emphysema, it is demonstrated for the first time that all relevant components (neutrophils, MMP-8, MMP-9, PE) involved in PGP formation from collagen are upregulated in the airways. Together with MMPs, PE may play an important role in the formation of PGP and thus in the pathophysiology of lung emphysema.     

Extracellular matrix composition and remodeling in human abdominal aortic aneurysms: a proteomics approach

Abdominal aortic aneurysms (AAA) are characterized by pathological remodeling of the aortic extracellular matrix (ECM). However, besides the well-characterized elastolysis and collagenolysis little is known about changes in other ECM proteins. Previous proteomics studies on AAA focused on cellular changes without emphasis on the ECM. In the present study, ECM proteins and their degradation products were selectively extracted from aneurysmal and control aortas using a solubility-based subfractionation methodology and analyzed by gel-liquid chromatography-tandem MS and label-free quantitation. The proteomics analysis revealed novel changes in the ECM of AAA, including increased expression as well as degradation of collagen XII, thrombospondin 2, aortic carboxypeptidase-like protein, periostin, fibronectin and tenascin. Proteomics also confirmed the accumulation of macrophage metalloelastase (MMP-12). Incubation of control aortic tissue with recombinant MMP-12 resulted in the extensive fragmentation of these glycoproteins, most of which are novel substrates of MMP-12. In conclusion, our proteomics methodology allowed the first detailed analysis of the ECM in AAA and identified markers of pathological ECM remodeling related to MMP-12 activity.     

Cross-linking and degradation of step-growth hydrogels formed by thiol-ene photoclick chemistry

Thiol-ene photoclick hydrogels have been used for a variety of tissue engineering and controlled release applications. In this step-growth photopolymerization scheme, four-arm poly(ethylene glycol) norbornene (PEG4NB) was cross-linked with dithiol containing cross-linkers to form chemically cross-linked hydrogels. While the mechanism of thiol-ene gelation was well described in the literature, its network ideality and degradation behaviors are not well-characterized. Here, we compared the network cross-linking of thiol-ene hydrogels to Michael-type addition hydrogels and found thiol-ene hydrogels formed with faster gel points and higher degree of cross-linking. However, thiol-ene hydrogels still contained significant network nonideality, demonstrated by a high dependency of hydrogel swelling on macromer contents. In addition, the presence of ester bonds within the PEG-norbornene macromer rendered thiol-ene hydrogels hydrolytically degradable. Through validating model predictions with experimental results, we found that the hydrolytic degradation of thiol-ene hydrogels was not only governed by ester bond hydrolysis, but also affected by the degree of network cross-linking. In an attempt to manipulate network cross-linking and degradation of thiol-ene hydrogels, we incorporated peptide cross-linkers with different sequences and characterized the hydrolytic degradation of these PEG-peptide hydrogels. In addition, we incorporated a chymotrypsin-sensitive peptide as part of the cross-linkers to tune the mode of gel degradation from bulk degradation to surface erosion.