Structure and function of matrix metalloproteinases and TIMPs

Vascular adaptation and mechanical homeostasis at tissue, cellular, and sub-cellular levels

Blood vessels exhibit a remarkable ability to adapt throughout life that depends upon genetic programming and well-orchestrated biochemical processes. Findings over the past four decades demonstrate, however, that the mechanical environment experienced by these vessels similarly plays a critical role in governing their adaptive responses. This article briefly reviews, as illustrative examples, six cases of tissue level growth and remodeling, and then reviews general observations at cell-matrix, cellular, and sub-cellular levels, which collectively point to the existence of a "mechanical homeostasis" across multiple length and time scales that is mediated primarily by endothelial cells, vascular smooth muscle cells, and fibroblasts. In particular, responses to altered blood flow, blood pressure, and axial extension, disease processes such as cerebral aneurysms and vasospasm, and diverse experimental manipulations and clinical treatments suggest that arteries seek to maintain constant a preferred (homeostatic) mechanical state. Experiments on isolated microvessels, cell-seeded collagen gels, and adherent cells isolated in culture suggest that vascular cells and sub-cellular structures such as stress fibers and focal adhesions likewise seek to maintain constant a preferred mechanical state. Although much is known about mechanical homeostasis in the vasculature, there remains a pressing need for more quantitative data that will enable the formulation of an integrative mathematical theory that describes and eventually predicts vascular adaptations in response to diverse stimuli. Such a theory promises to deepen our understanding of vascular biology as well as to enable the design of improved clinical interventions and implantable medical devices.

Clinical trials and basic research: defining mechanisms and improving treatment in connective tissue disease

Despite advances in elucidating the pathogenic factors responsible for its development, systemic sclerosis remains complex and poorly understood, and treatment options are limited. Multidisciplinary collaborative efforts are needed to better characterize clinical and prognostic parameters and to design and implement large-scale clinical trials in well defined populations with therapies that target potential disease modulators.

How does endothelial cell injury start? The role of endothelin in systemic sclerosis

A considerable amount of research time has been invested in studies aimed at elucidating pathogenic processes in systemic sclerosis (SSc). Despite this, major challenges for biomedical science remain, such as identification of the key factors that determine susceptibility to SSc, and elucidation of the precise nature of the initiating event that causes endothelial cell injury and ultimately brings about the biological cascade(s) that lead to the pathologic vascular changes. Involved factors are likely to include genetic perturbations, environmental cues, tissue injury, infection and hypoxia/oxidative stress. As important as determining the initiating events are the identification and characterization of key factors that are functionally important in driving vascular disease progression, because these factors are potential targets for therapeutic intervention. This article reviews the role of endothelin as an example of a pleiotropic mediator with effects on various aspects of SSc pathogenesis, such as inflammation, vasculopathy and tissue remodelling.

Comparison of MMP-2 and MMP-9 secretion from T helper 0, 1 and 2 lymphocytes alone and in coculture with macrophages

Metalloproteinases (MMPs) participate in extracellular matrix remodelling and regulatory signalling during chronic inflammatory states such as atherosclerosis formation. However, the sources and mediators of MMP upregulation need clarification. We investigated whether proinflammatory mouse T helper type 1 (Th1) lymphocytes are more active in MMP secretion than naïve Th0 or anti-inflammatory Th2 phenotypes, in the absence of specific antigenic stimulation, under baseline conditions and after contact with irradiated macrophages. We also compared the effect of Th0, Th1 or Th2 lymphocyte-conditioned medium and irradiated lymphocytes on MMP production from macrophages. Finally, we investigated whether CD40-CD40 ligand (CD40L) interactions were involved in T-cell-stimulated MMP secretion from macrophages. Under baseline conditions, MMP-2 messenger RNA (mRNA) and protein levels were greater in Th1 than Th0 or Th2 lymphocytes; MMP-9 mRNA, but not protein, was also upregulated. In the presence of irradiated macrophages MMP-2 and MMP-9 production from Th1 and Th2 was greater than from Th0 lymphocytes. Conditioned media from Th1 but not Th0 or Th2 cells increased MMP-9 secretion from macrophages. Irradiated Th1 lymphocytes stimulated both MMP-2 and MMP-9 secretion from macrophages more than irradiated Th2 or Th0 cells; this activation was independent of CD40-CD40L interaction. These findings demonstrate for the first time greater MMP secretion by Th1 than Th2 or Th0 lymphocytes and their greater ability to upregulate macrophage MMP secretion in the absence of specific antigenic stimulation. These mechanisms could promote matrix turnover in inflammatory states and, for example, promote atherosclerotic plaque rupture.

Matrix metalloproteinases: useful and deleterious

MMPs (matrix metalloproteinases) are zinc-dependent endopeptidases that degrade both matrix and non-matrix proteins. They play an important role in morphogenesis, and in a wide range of processes including tissue repair and remodelling. Their abnormal expression contributes to pathological processes including arthritis, cancer, and cardiac and central nervous system diseases, which explains the large interest in finding specific MMP inhibitors for therapeutic use. In this review we describe the structural features of MMPs, with special emphasis on their interaction with specific inhibitors. The effect of new, hydroxamatebased inhibitors on MMP isolated from bovine brain is evaluated.

Membrane type-1 matrix metalloproteinases and tissue inhibitor of metalloproteinases-2 RNA levels mimic each other during Xenopus laevis metamorphosis

Matrix metalloproteinases (MMPs) and their endogenous inhibitors TIMPs (tissue inhibitors of MMPs), are two protein families that work together to remodel the extracellular matrix (ECM). TIMPs serve not only to inhibit MMP activity, but also aid in the activation of MMPs that are secreted as inactive zymogens. Xenopus laevis metamorphosis is an ideal model for studying MMP and TIMP expression levels because all tissues are remodeled under the control of one molecule, thyroid hormone. Here, using RT-PCR analysis, we examine the metamorphic RNA levels of two membrane-type MMPs (MT1-MMP, MT3-MMP), two TIMPs (TIMP-2, TIMP-3) and a potent gelatinase (Gel-A) that can be activated by the combinatory activity of a MT-MMP and a TIMP. In the metamorphic tail and intestine the RNA levels of TIMP-2 and MT1-MMP mirror each other, and closely resemble that of Gel-A as all three are elevated during periods of cell death and proliferation. Conversely, MT3-MMP and TIMP-3 do not have similar RNA level patterns nor do they mimic the RNA levels of the other genes examined. Intriguingly, TIMP-3, which has been shown to have anti-apoptotic activity, is found at low levels in tissues during periods of apoptosis.

Acute exacerbations of idiopathic pulmonary fibrosis

The natural history of idiopathic pulmonary fibrosis (IPF) has been characterized as a steady, predictable decline in lung function over time. Recent evidence suggests that some patients may experience a more precipitous course, with periods of relative stability followed by acute deteriorations in respiratory status. Many of these acute deteriorations are of unknown etiology and have been termed acute exacerbations of IPF. This perspective is the result of an international effort to summarize the current state of knowledge regarding acute exacerbations of IPF. Acute exacerbations of IPF are defined as acute, clinically significant deteriorations of unidentifiable cause in patients with underlying IPF. Proposed diagnostic criteria include subjective worsening over 30 days or less, new bilateral radiographic opacities, and the absence of infection or another identifiable etiology. The potential pathobiological roles of infection, disordered cell biology, coagulation, and genetics are discussed, and future research directions are proposed.

Targeting MMPs in acute and chronic neurological conditions

The matrix metalloproteinases (MMPs) are important enzymes that regulate developmental processes, maintain normal physiology in adulthood and have reparative roles at specific stages after an insult to the nervous system. Conversely, the concordant presence and significant upregulation of several MMP members in virtually all neurological conditions result in pathology. Thus, the MMPs have diverse functions, capable of mediating repair and recovery on the one hand and being involved in producing injury on the other. Therefore, targeting MMPs in neurological conditions has become a complicated challenge. This article highlights the beneficial roles of MMPs in normal and reparative processes within the nervous system and discusses the detriments of MMPs encountered in pathology. We review the availability of MMP inhibitors for clinical use and propose that an important consideration for these inhibitors is timing and duration of their use. With acute injuries where a massive upregulation of several MMPs are observed in the early periods after the insult, early and short-term use of broad spectrum MMP inhibitors would seem logical. In chronic conditions where recurrent insults to the CNS are accompanied by prolonged upregulation of MMPs, thereby necessitating the chronic use of medications, the beneficial effects of MMPs in repair may be compromised by the long-term application of MMP inhibitors. In this review we have used spinal cord injury and multiple sclerosis as examples of acute and chronic neurological conditions, respectively, and we consider the use of MMP inhibitors in these states.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

Endocannabinoid regulation of matrix metalloproteinases: implications in ischemic stroke

Stroke is a major cause of morbidity and mortality and follows heart disease and cancer as the third leading cause of death in Western societies [1]. Despite many advances in stroke research and pharmacotherapy, clinical treatment of this debilitating disorder is still inadequate. Recent findings from several laboratories have identified the endocannabinoid signaling pathway, comprised of the endocannabinoid agonist anandamide and its pharmacological targets, CB1 and CB2 cannabinoid receptors and associated anandamide receptors, as a physiological system with capacity to mitigate cardiovascular and cerebrovascular disorders through neuronal and endothelial actions. Variability in experimental stroke models and modes of outcome evaluation, however, have provoked controversy regarding the precise roles of endocannabinoid signals in mediating neural and/or vascular protection versus neurovascular damage. Clinical trials of the CB1 antagonist rimonabant demonstrate that modulation of endocannabinoid signaling during metabolic regulation of vascular disorders can significantly impact clinical outcomes, thus providing strong argument for therapeutic utility of endocannabinoids and/or cannabinoid receptors as targets for therapeutic intervention in cases of stroke and associated vascular disorders. The purpose of this review is to provide updated information from basic science and clinical perspectives on endocannabinoid ligands and their effects in the pathophysiologic genesis of stroke. Particular emphasis will be placed on the endocannabinoids anandamide and 2-arachidonylglycerol and CB1 receptor-mediated mechanisms in the neurovascular unit during stroke pathogenesis. Deficiencies in our knowledge of endocannabinoids in the etiology and pathogenesis of stroke, caveats and limitations of existing studies, and future directions for investigation will be addressed.

Expression of matrix metalloproteinases MMP-1, MMP-11 and MMP-19 is correlated with the WHO-grading of human malignant gliomas

Glioblastomas (GBM) are the most prevalent type of malignant primary brain tumor in adults. They may manifest de novo or develop from low-grade astrocytomas (LGA) or anaplastic astrocytomas. They are characterized by an aggressive local growth pattern and a marked degree of invasiveness, resulting in poor prognosis. Tumor progression is facilitated by an increased activity of proteolytic enzymes such as matrix metalloproteinases (MMPs). Elevated levels of several MMPs were found in glioblastomas compared to LGA and normal brain (NB). However, data for some MMPs, like MMP-1, are controversially discussed and other MMPs like MMP-11 and MMP-19 have as yet not been analysed in detail. We examined the expression of MMP-1, MMP-9, MMP-11 and MMP-19 in NB, LGA and GBM by semiquantitative RT-PCR, Western blotting and immunohistochemistry and found an enhanced expression of these MMPs in GBM compared to LGA or NB in signal strength and in the percentage of tumors displaying MMP expression. The transition from LGA to GBM was characterized by a shift of pro-MMP-11 to expression of the active enzyme. Therefore, MMP-1, MMP-11 and MMP-19 might be of importance for the development of high-grade astrocytic tumors and may be promising targets for therapy.

All-transRetinoic Acid Enhances Murine Dendritic Cell Migration to Draining Lymph Nodes via the Balance of Matrix Metalloproteinases and Their Inhibitors

Cancers escape immune surveillance through the manipulation of the host's immune system. Sequestration of dendritic cells (DCs) within tumor tissues and the subsequent inhibition of their migration is one of the several mechanisms by which tumors induce immunosuppression. In view of recent findings depicting the improvement of tumor immune responses in cancer patients following all-trans retinoic acid (ATRA) treatment, we sought to identify the effects of ATRA on DC mobility in the context of tumor immunotherapy. Our results demonstrate that ATRA, added to differentiating murine bone marrow progenitor cells, enhances the invasive capacity of the resulting DCs. Immature DCs injected intratumorally in mice show increased accumulation in draining lymph nodes, but not in nondraining lymph nodes and spleens, when differentiated in the presence of ATRA. The in vitro migration of mature DCs through the basement membrane matrix toward the lymphoid chemokines CCL19 and CCL21 is enhanced in these cells, albeit not in the presence of a matrix metalloproteinase (MMP) inhibitor. An increase in MMP production with a simultaneous decrease in the production of their inhibitors (tissue inhibitors of matrix metalloproteinase or TIMPs) is provoked by ATRA. This affects the MMP/TIMP balance in DCs, in particular that of MMP-9 and TIMP-1, favoring protease activity and thus allowing for enhanced DC mobilization. In conclusion, this study demonstrates that ATRA is capable of improving DC trafficking in a tumor milieu and, in view of the encouraging results obtained in the clinic, further supports the notion that ATRA might be a valuable chemical adjuvant to current immunotherapeutic strategies for cancer.

Myeloperoxidase inactivates TIMP-1 by oxidizing its N-terminal cysteine residue: an oxidative mechanism for regulating proteolysis during inflammation

An imbalance between the proteolytic activity of matrix metalloproteinases (MMPs) and the activity of tissue inhibitors of metalloproteinases (TIMPs) is implicated in tissue injury during inflammation. The N-terminal cysteine of TIMP-1 plays a key role in the inhibitory activity of the protein because it coordinates the essential catalytic Zn2+ of the MMP, preventing the metal ion from functioning. An important mechanism for controlling the interaction of TIMPs with MMPs might involve hypochlorous acid (HOCl), a potent oxidant produced by the myeloperoxidase (MPO) system of phagocytes. Here, we show that HOCl generated by the MPO-H2O2-chloride system inactivates TIMP-1 by oxidizing its N-terminal cysteine. The product is a novel 2-oxo acid. Liquid chromatography-mass spectrometry and tandem mass spectrometry analyses demonstrated that methionine and N-terminal cysteine residues were rapidly oxidized by MPO-derived HOCl but only oxidation of the N-terminal cysteine of TIMP-1 correlated well with loss of inhibitory activity. Importantly, we detected the signature 2-oxo-acid N-terminal peptide in tryptic digests of bronchoalveolar lavage fluid from patients with acute respiratory distress syndrome, demonstrating that TIMP-1 oxidation occurs in vivo. Loss of the N-terminal amino group and disulfide structure are crucial for preventing TIMP-1 from inhibiting MMPs. Our findings suggest that pericellular production of HOCl by phagocytes is a pathogenic mechanism for impairing TIMP-1 activity during inflammation.

Genomic and proteomic profiling II: comparative assessment of gene expression profiles in leiomyomas, keloids, and surgically-induced scars

BACKGROUND

Leiomyoma have often been compared to keloids because of their fibrotic characteristic and higher rate of occurrence among African Americans as compared to other ethnic groups. To evaluate such a correlation at molecular level this study comparatively analyzed leiomyomas with keloids, surgical scars and peritoneal adhesions to identify genes that are either commonly and/or individually distinguish these fibrotic disorders despite differences in the nature of their development and growth.

METHODS

Microarray gene expression profiling and realtime PCR.

RESULTS

The analysis identified 3 to 12% of the genes on the arrays as differentially expressed among these tissues based on P ranking at greater than or equal to 0.005 followed by 2-fold cutoff change selection. Of these genes about 400 genes were identified as differentially expressed in leiomyomas as compared to keloids/incisional scars, and 85 genes as compared to peritoneal adhesions (greater than or equal to 0.01). Functional analysis indicated that the majority of these genes serve as regulators of cell growth (cell cycle/apoptosis), tissue turnover, transcription factors and signal transduction. Of these genes the expression of E2F1, RUNX3, EGR3, TBPIP, ECM-2, ESM1, THBS1, GAS1, ADAM17, CST6, FBLN5, and COL18A was confirmed in these tissues using quantitative realtime PCR based on low-density arrays.

CONCLUSION

the results indicated that the molecular feature of leiomyomas is comparable but may be under different tissue-specific regulatory control to those of keloids and differ at the levels rather than tissue-specific expression of selected number of genes functionally regulating cell growth and apoptosis, inflammation, angiogenesis and tissue turnover.

Effects of autologous stem cells on immunohistochemical patterns and gene expression of metalloproteinases and their tissue inhibitors in doxorubicin cardiomyopathy in a rabbit model

This study aims to investigate the expression of metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) in chronic doxorubicin cardiomyopathy in a rabbit model and to evaluate the effects of bone marrow-derived mesenchymal stem cell (MSC) transplantation in this disease. Thirty-nine 3-month-old New Zealand rabbits were divided into 4 groups: group 1 (n = 9) was the untreated control. Groups 2-4 were treated with 6 weeks of doxorubicin (3 mg/kg). Group 2 (n = 6) received no further treatment. In group 3 (n = 9), animals were treated with culture medium (CM) alone. In group 4 (n = 15), autologous MSCs (1.5-2.0 x 10(6)/ml) were injected in the left ventricular (LV) wall. Hearts were stained with HE and picrosirius red. MMP-1, -2, -3 and -9 and TIMP-2 and -3 were detected immunohistochemically. The mRNA levels were determined by real-time polymerase chain reaction. The results confirmed that doxorubicin treatment resulted in minimal myocardial fibrosis and showed that expression of MMPs increased and TIMP-3 decreased. The injection procedure resulted in increased myocardial fibrosis in groups 3 and 4. After MSC injection, MMP-1, MMP-2, and TIMP-3 expression was higher than that in group 2. CM injection led to more fibrosis, elevated TIMP-3, but diminished MMP-1 and MMP-2 expression compared with MSC injection. The mRNA levels of MMPs and TIMPs were not significantly different among all groups. In conclusion, chronic doxorubicin cardiomyopathy was characterized by increased MMP and decreased TIMP-3 expression. MSCs injection into the LV resulted in marked differences of collagen content and MMP/TIMP expression in the whole heart, although significant numbers of living MSCs were not detected after 4 weeks.

Matrix metalloproteinase–inhibitor interaction: the solution structure of the catalytic domain of human matrix metalloproteinase-3 with different inhibitors

We structurally characterized the adducts of the catalytic domain of matrix metalloproteinase-3 (MMP3) with three different nonpeptidic inhibitors by solving the solution structure of one adduct [MMP3-N-isobutyl-N-(4-methoxyphenylsulfonyl)glycyl hydroxamic acid] and then by calculating structural models of the other two adducts using a reduced set of experimental NMR data, following a recently proposed procedure (Bertini et al. in J. Med. Chem. 48:7544-7559, 2005). The inhibitors were selected with the criteria of maintaining in all of them the same zinc-coordinating moiety and of selectively changing the substituents and/or the functional groups. The backbone dynamics on various time scales have been characterized as well. The comparison among these structures and with others previously reported allowed us to elucidate fine details of inhibitor-receptor interactions and to develop some criteria, which could guide in optimizing the design of selective inhibitors.

The biochemical, biological, and pathological kaleidoscope of cell surface substrates processed by matrix metalloproteinases

Matrix metalloproteinases (MMPs) constitute a family of more than 20 endopeptidases. Identification of specific matrix and non-matrix components as MMP substrates showed that, aside from their initial role as extracellular matrix modifiers, MMPs play significant roles in highly complex processes such as the regulation of cell behavior, cell-cell communication, and tumor progression. Thanks to the comprehensive examination of the expanded MMP action radius, the initial view of proteases acting in the soluble phase has evolved into a kaleidoscope of proteolytic reactions connected to the cell surface. Important classes of cell surface molecules include adhesion molecules, mediators of apoptosis, receptors, chemokines, cytokines, growth factors, proteases, intercellular junction proteins, and structural molecules. Proteolysis of cell surface proteins by MMPs may have extremely diverse biological implications, ranging from maturation and activation, to inactivation or degradation of substrates. In this way, modification of membrane-associated proteins by MMPs is crucial for communication between cells and the extracellular milieu, and determines cell fate and the integrity of tissues. Hence, insights into the processing of cell surface proteins by MMPs and the concomitant effects on physiological processes as well as on disease onset and evolution, leads the way to innovative therapeutic approaches for cancer, as well as degenerative and inflammatory diseases.

Crystal structures of human ADAMTS-1 reveal a conserved catalytic domain and a disintegrin-like domain with a fold homologous to cysteine-rich domains

The ADAMTS (a disintegrin-like and metalloproteinase domain with thrombospondin type I motifs) family of proteases plays a role in pathological conditions including arthritis, cancer, thrombotic thrombocytopenic purpura and the Ehlers-Danlos type VIIC and Weill-Marchesani genetic syndromes. Here, we report the first crystal structures for a member of the ADAMTS family, ADAMTS-1. Originally cloned as an inflammation-associated gene, ADAMTS-1 has been shown to be involved in tissue remodelling, wound healing and angiogenesis. The crystal structures contain catalytic and disintegrin-like domains, both in the inhibitor-free form and in complex with the inhibitor marimastat. The overall fold of the catalytic domain is similar to related zinc metalloproteinases such as matrix metalloproteinases and ADAMs (a disintegrin and metalloproteinases). The active site contains the expected organisation of residues to coordinate zinc but has a much larger S1' selectivity pocket than ADAM33. The structure also unexpectedly reveals a double calcium-binding site. Also surprisingly, the previously named disintegrin-like domain showed no structural homology to the disintegrin domains of other metalloproteinases such as ADAM10 but is instead very similar in structure to the cysteine-rich domains of other metalloproteinases. Thus, this study suggests that the D (for disintegrin-like) in the nomenclature of ADAMTS enzymes is likely to be a misnomer. The ADAMTS-1 cysteine-rich domain stacks against the active site, suggesting a possible regulatory role.

Crystal Structures of MMP-9 Complexes with Five Inhibitors: Contribution of the Flexible Arg424 Side-chain to Selectivity

Human matrix metalloproteinase 9 (MMP-9), also called gelatinase B, is particularly involved in inflammatory processes, bone remodelling and wound healing, but is also implicated in pathological processes such as rheumatoid arthritis, atherosclerosis, tumour growth, and metastasis. We have prepared the inactive E402Q mutant of the truncated catalytic domain of human MMP-9 and co-crystallized it with active site-directed synthetic inhibitors of different binding types. Here, we present the X-ray structures of five MMP-9 complexes with gelatinase-specific, tight binding inhibitors: a phosphinic acid (AM-409), a pyrimidine-2,4,6-trione (RO-206-0222), two carboxylate (An-1 and MJ-24), and a trifluoromethyl hydroxamic acid inhibitor (MS-560). These compounds bind by making a compromise between optimal coordination of the catalytic zinc, favourable hydrogen bond formation in the active-site cleft, and accommodation of their large hydrophobic P1' groups in the slightly flexible S1' cavity, which exhibits distinct rotational conformations of the Pro421 carbonyl group in each complex. In all these structures, the side-chain of Arg424 located at the bottom of the S1' cavity is not defined in the electron density beyond C(gamma), indicating its mobility. However, we suggest that the mobile Arg424 side-chain partially blocks the S1' cavity, which might explain the weaker binding of most inhibitors with a long P1' side-chain for MMP-9 compared with the closely related MMP-2 (gelatinase A), which exhibits a short threonine side-chain at the equivalent position. These novel structural details should facilitate the design of more selective MMP-9 inhibitors.

Nitric oxide and vascular remodeling: Spotlight on the kidney

Extracellular matrix (ECM) remodeling with successive tissue fibrosis is a key feature of chronic cardiovascular diseases, including atherosclerosis and restenosis. The atherogenic changes underlying these pathologies result from chronification of an acute repair response towards injurious and inflammatory stimuli. Thereby functional tissue is replaced by excessive ECM deposition. In the kidney, impaired remodeling is a major cause of perivascular, interstitial, and glomerular fibrosis but also a common complication of chronic hypertension. Experimental evidence points to the matrix metalloproteases (MMPs) and their intrinsic inhibitors, the tissue inhibitors of MMPs as key mediators of atherogenic and fibrotic pathologies. Mechanistically, a deregulation in ECM turnover tightly correlates with an increased production and release of proinflammatory and profibrotic factors including interleukin-1beta, transforming growth factor beta, angiotensin II, and reactive oxygen species. Unlike these factors the pleiotropic messenger molecule nitric oxide (NO) by acting as the major physiological vasodilator has emerged as one of the most atheroprotective factors. However, under inflammatory conditions NO does acquire proatherogenic and profibrotic properties thereby exacerbating tissue fibrosis. In this review, the mechanisms underlying both opposing properties of NO on perivascular ECM remodeling will exemplarily be discussed for renal fibrosis with a particular focus on the MMPs and intrinsic protease inhibitors.

Matrix metalloproteinase activity is necessary for thymosin beta 4 promotion of epithelial cell migration

Studies from our laboratory provide substantial evidence that thymosin beta 4, (Tbeta(4)), an actin-sequestering protein, promotes corneal wound healing through its ability to stimulate epithelial cell migration. Matrix metalloproteinases (MMPs), which are expressed in a wide variety of tissues including the cornea, also play a key role in epithelial cell migration and wound healing. In this study we investigated the role of MMPs in Tbeta(4)-stimulated corneal epithelial cell migration. In Boyden chamber assays, XG076, an inhibitor of the conversion of pro- to active MMPs, had no effect on epithelial cell migration stimulated by exogenous activated MMP-1. However, in in vitro migration assays where the activation of pro-MMPs was blocked, XG076 significantly inhibited cell migration and wound healing in the presence or absence of Tbeta(4). GM6001, a broad-spectrum inhibitor of active MMPs and selective MMP inhibitors, also suppressed Tbeta(4)-stimulated cell migration. Tbeta(4) upregulated MMP-1 gene and protein expression in primary human corneal epithelial cells and in transformed human corneal epithelial cells following scrape wounding. From these results we conclude that MMP catalytic activity is necessary for Tbeta(4) promotion of epithelial cell migration. These novel findings are the first to demonstrate a functional link between the two.

MMP25 (MT6-MMP) is highly expressed in human colon cancer, promotes tumor growth, and exhibits unique biochemical properties

MMP25 (MT6-MMP) is one of the two glycosylphosphatidylinositol-anchored matrix metalloproteinases (MMPs) that have been suggested to play a role in pericellular proteolysis. However, its role in cancer is unknown, and its biochemical properties are not well established. Here we found a marked increase in MT6-MMP expression within in situ dysplasia and invasive cancer in 61 samples of human colon cancer. Expression of MT6-MMP in HCT-116 human colon cancer cells promoted tumori-genesis in nude mice. Histologically, the MT6-MMP-expressing tumors demonstrated an infiltrative leading edge in contrast to a rounded leading edge in vector control tumors. Biochemical and biosynthesis analyses revealed that MT6-MMP displayed on the cell surface exists as a major form of 120 kDa that likely represents enzyme homodimers linked by disulfide bonds. Upon reduction, a single 57-kDa active MT6-MMP was detected. Interestingly, neither membrane-anchored nor phosphatidylinositol-specific phospholipase C-released MT6-MMPs were found to be associated with tissue inhibitor of metalloproteinases (TIMPs) and did not activate pro-gelatinases (pro-MMP-2 and pro-MMP-9) even in the presence of exogenous TIMP-2 or TIMP-1. A catalytic domain of MT6-MMP was inhibited preferentially by TIMP-1 (K(i) = 0.2 nm) over TIMP-2 (K(i) = 2.0 nm), because of a slower association rate. These results show that MT6-MMP may play a role in colon cancer and exhibit unique biochemical and structural properties that may regulate proteolytic function at the cell surface.

Role of matrix metalloproteinases and their tissue inhibitor of metalloproteinases in myxomatous change of cardiac floppy valves

To clarify the underlying cause of myxomatous changes in cardiac floppy valves, the expression of the matrix metalloproteinases (MMP) and the tissue inhibitors of metalloproteinases (TIMP) was investigated in cardiac valves. Valves were obtained from nine patients with floppy valves, from 13 patients with other valvular disease types, and from four patients with normal valves. Immunohistochemical analyses for MMP-2, MMP-9, TIMP-1, and TIMP-2, and gelatin zymography for MMP-2 and MMP-9 were performed. Compared with the spongiosa of normal valves, the myxomatous area of floppy valves had stronger immunohistochemical reaction to MMP-2 and MMP-9, and weaker reaction to TIMP-2. Activated MMP-2 and MMP-9 were detected in eight out of nine cases of floppy valves. Activated MMP-2 was detected at low levels in two cases of normal valves showing mild expansion of the spongiosa without macroscopic floppiness. The ratio of active/total MMP-2 and MMP-9 increased in floppy valves compared with normal valves. These results suggest that the imbalance between MMP and TIMP and the increased activity of MMP-2 and MMP-9 may correlate with myxomatous changes observed in floppy valves. Valves with a slight myxomatous change and activated MMP-2 may develop into floppy valves with increases in the activity of MMP.

Reduced secretion and expression of gelatinase profile in Toxoplasma gondii-infected human monocytic cells

The apicomplexan Toxoplasma gondii, an obligate intracellular parasite, can infect humans and a wide range of vertebrates. Following oral infection, the parasite invades tissues by crossing non-permissive biological barriers such as the placenta or the blood-brain barrier. But the molecular mechanisms underlying migration of T. gondii remain poorly characterized. The crossing of various basal membranes and infiltration into the extracellular matrix by T. gondii could involve matrix metalloproteinases (MMPs). We demonstrated a decrease in proMMP-2 and proMMP-9 secretion by THP-1 cells at 24 and 48h post invasion with regulation at the mRNA level throughout infection. This down regulation was associated with a decrease in TIMP-2 secretion and an inhibition of its expression. Moreover, results showed an activation of MT1-MMP; its expression was regulated after 6, 24, and 48h.

Chronic obstructive pulmonary disease: role of matrix metalloproteases and future challenges of drug therapy

COPD is a chronic disease of the lung that is characterised by decreased air flow and associated abnormal inflammatory responses of the lungs. A total of 80% of COPD incidences are observed in patients with history of smoking tobacco. The chronic condition of COPD is characterised by airway remodelling, which leads to emphysema and chronic bronchitis. Inflammatory cells of the immune system play a major role in pathophysiology of COPD. High levels of neutrophils, macrophages and CD8(+) T cells have been found in bronchoalveolar lavage samples of COPD patients. Matrix metalloproteases (MMPs), which are secreted by these inflammatory cells, have the enzymatic capacity to cause morphological changes in the lungs and contribute significantly to the COPD state. Increased concentrations of MMP-1, -2, -9, -12 and so on have been found in bronchoalveolar lavage samples of COPD patients compared with non-COPD individuals. COPD is rated as among the top five diseases with high mortality rates and it is estimated that in the next 20 years, the healthcare cost alone for COPD will be US $800 million worldwide. The present drug therapies are neither very efficacious nor cost effective; hence, there is unmet medical need to discover small-molecule drugs for COPD. In this regard, synthetic MMP inhibitors show a great promise for COPD treatment.

The matrix metalloproteinases and CNS plasticity: an overview

The matrix metalloproteinases (MMPs) are expressed in response to pro-inflammatory stimuli and other triggers. The MMPs cleave numerous substrates including extracellular matrix components, cytokines and growth factors. In the CNS, while most studied in the context of disease, the many physiological functions of the MMPs are now becoming appreciated. This review provides an overview of the growing body of evidence for physiological roles of MMPs both in CNS development and in CNS plasticity in normal brain functioning, including learning and memory, as well as in CNS repair and reorganization as part of the neuroimmune response to injury.

Zinc in wound healing: theoretical, experimental, and clinical aspects

Zinc is an essential trace element in the human body and its importance in health and disease is appreciated. It serves as a cofactor in numerous transcription factors and enzyme systems including zinc-dependent matrix metalloproteinases that augment autodebridement and keratinocyte migration during wound repair. Zinc confers resistance to epithelial apoptosis through cytoprotection against reactive oxygen species and bacterial toxins possibly through antioxidant activity of the cysteine-rich metallothioneins. Zinc deficiency of hereditary or dietary cause can lead to pathological changes and delayed wound healing. Oral zinc supplementation may be beneficial in treating zinc-deficient leg ulcer patients, but its therapeutic place in surgical patients needs further clarification. Topical administration of zinc appears to be superior to oral therapy due to its action in reducing superinfections and necrotic material via enhanced local defense systems and collagenolytic activity, and the sustained release of zinc ions that stimulates epithelialization of wounds in normozincemic individuals. Zinc oxide in paste bandages (Unna boot) protects and soothes inflamed peri-ulcer skin. Zinc is transported through the skin from these formulations, although the systemic effects seem insignificant. We present here the first comprehensive account of zinc in wound management in relation to current concepts of wound bed preparation and the wound-healing cascade. This review article suggests that topical zinc therapy is underappreciated even though clinical evidence emphasizes its importance in autodebridement, anti-infective action, and promotion of epithelialization.

Inhibition of interleukin 1-induced matrix metalloproteinase 13 expression in human chondrocytes by interferon gamma

BACKGROUND

Despite well-documented immunomodulation by interferon gamma (IFNgamma), its role and mechanism of regulation of matrix metalloproteinase 13 (MMP13) gene expression in human chondrocytes is unknown.

OBJECTIVE

To investigate the ability and mechanism of IFNgamma to suppress interleukin 1 (IL1)-induced MMP13 expression in articular chondrocytes.

METHODS

Human chondrocytes were treated with IFNgamma or IL1beta alone or in combination. MMP13 mRNA was analysed by semiquantitative reverse transcriptase-PCR. MMP13 protein, phospho-signal transducer and activator of transcription 1 (STAT1) and p44/42 mitogen-activated protein kinase levels were measured by western blotting. MMP13 promoter luciferase, cytomegalovirus cyclic AMP response element-binding protein (CBP)/p300 plasmids and STAT1 small interfering RNA (siRNA) were transfected by the calcium phosphate method. IFNgamma receptor was also neutralised. Activator protein (AP) 1 activity was monitored by the TransAM transcription factor kit. STAT1-CBP/p300 interaction was studied by immunoprecipitation.

RESULTS

IFNgamma potently suppressed IL1-induced expression of MMP13 and promoter activity. Blockade with neutralising IFNgamma R1 antibody revealed that MMP13 inhibition by IFNgamma is mediated by the IFN receptor. IFNgamma-stimulated activation of STAT1 was directly correlated with MMP13 suppression. Knockdown of the STAT1 gene by specific siRNA or its inhibition with fludarabine partially restored the IL1beta induction of MMP13 expression and promoter activity. IFNgamma did not alter AP1 binding ability but promoted physical interaction of STAT1 and CBP/p300 coactivator. p300 overexpression reversed IFNgamma inhibition of endogenous MMP13 mRNA expression and exogenous MMP13 promoter activity.

CONCLUSION

IFNgamma, through its receptor, activates STAT1, which binds with CBP/p300 coactivator, sequesters it from the cell system, and thus inhibits transcriptional induction of the MMP13 gene in chondrocytes. IFNgamma and its signalling pathways could be targeted therapeutically for diminishing IL1-induced cartilage degradation by MMP13 in patients with arthritis.

Calcium regulates tertiary structure and enzymatic activity of human endometase/matrilysin-2 and its role in promoting human breast cancer cell invasion

Human MMP-26 (matrix metalloproteinase-26) (also known as endometase or matrilysin-2) is a putative biomarker for human carcinomas of breast, prostate and other cancers of epithelial origin. Calcium modulates protein structure and function and may act as a molecular signal or switch in cells. The relationship between MMPs and calcium has barely been studied and is absent for MMP-26. We have investigated the calcium-binding sites and the role of calcium in MMP-26. MMP-26 has one high-affinity and one low-affinity calcium binding site. High-affinity calcium binding was restored at physiologically low calcium conditions with a calcium-dissociation constant of 63 nM without inducing secondary and tertiary structural changes. High-affinity calcium binding protects MMP-26 against thermal denaturation. Mutants of this site (D165A or E191A) lose enzymatic activity. Low-affinity calcium binding was restored at relatively high calcium concentrations and showed a K(d2) (low-affinity calcium-dissociation constant) value of 120 microM, which was accompanied with the recovery of enzymatic activity reversibly and tertiary structural changes, but without secondary structural rearrangements. Mutations at the low-affinity calcium-binding site (C3 site), K189E or D114A, induced enhanced affinity for the Ca2+ ion or an irreversible loss of enzymatic activity triggered by low-affinity calcium binding respectively. Mutation at non-calcium-binding site (V184D at C2 site) showed that C2 is not a true calcium-binding site. Observations from homology-modelled mutant structures correlated with these experimental results. A human breast cancer cell line, MDA-MB-231, transfected with wild-type MMP-26 cDNA showed a calcium-dependent invasive potential when compared with controls that were transfected with an inactive form of MMP-26 (E209A). Calcium-independent high invasiveness was observed in the K189E mutant MDA-MB-231 cell line.

ECM remodeling in hypertensive heart disease

Hypertensive heart disease (HHD) occurs in patients that clinically have both diastolic and systolic heart failure and will soon become the most common cause of heart failure. Two key aspects of heart failure secondary to HHD are the relatively highly prevalent LV hypertrophy and cardiac fibrosis, caused by changes in the local and systemic neurohormonal environment. The fibrotic state is marked by changes in the balance between MMPs and their inhibitors, which alter the composition of the ECM. Importantly, the fibrotic ECM impairs cardiomyocyte function. Recent research suggests that therapies targeting the expression, synthesis, or activation of the enzymes responsible for ECM homeostasis might represent novel opportunities to modify the natural progression of HHD.

Morphological and biochemical characterization of remodeling in aorta and vena cava of DOCA-salt hypertensive rats

Arterial remodeling occurs in response to mechanical and neurohumoral stimuli. We hypothesized that veins, which are not exposed to higher pressures in hypertension, would demonstrate less active remodeling than arteries. We assessed remodeling with two standard measures of arterial remodeling: vessel morphometry and the expression/function of matrix metalloproteinases (MMPs). Thoracic aorta and vena cava from sham normotensive and DOCA-salt hypertensive rats (110 ± 4 and 188 ± 8 mmHg systolic blood pressure, respectively) were used. Wall thickness was increased in DOCA-salt vs. sham aorta (301 ± 23 vs. 218 ± 14 μm, P < 0.05), as was medial area, but neither measure was altered in the vena cava. The aorta and vena cava expressed the gelatinases MMP-2, MMP-9, transmembrane proteinase MT1-MMP, and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemically, MMP-2 localized to smooth muscle in the aorta and densely in endothelium/smooth muscle of the vena cava. Western and zymographic analyses verified that MMP-2 was active in all vessels and less active in the vena cava than aorta. In hypertension, MMP-2 expression and activity in the aorta were increased (59.1 ± 3.7 and 74.5 ± 6.1 units in sham and DOCA, respectively, P < 0.05); similar elevations were not observed in the vena cava. MMP-9 was weakly expressed in all vessels. MT1-MMP was expressed by the aorta and vena cava and elevated in the vena cava from DOCA-salt rats. TIMP-2 expression was significantly increased in the aorta of DOCA rats compared with sham but was barely detectable in the vena cava of sham or DOCA-salt hypertensive rats. These findings suggest that large veins may not undergo vascular remodeling in DOCA-salt hypertension.

Transgenic MMP-2 expression induces latent cardiac mitochondrial dysfunction

Matrix metalloproteinases (MMPs) are central to the development and progression of dysfunctional ventricular remodeling after tissue injury. We studied 6 month old heterozygous mice with cardiac-specific transgenic expression of active MMP-2 (MMP-2 Tg). MMP-2 Tg hearts showed no substantial gross alteration of cardiac phenotype compared to age-matched wild-type littermates. However, buffer perfused MMP-2 Tg hearts subjected to 30 min of global ischemia followed by 30 min of reperfusion had a larger infarct size and greater depression in contractile performance compared to wild-type hearts. Importantly, cardioprotection mediated by ischemic preconditioning (IPC) was completely abolished in MMP-2 Tg hearts, as shown by abnormalities in mitochondrial ultrastructure and impaired respiration, increased lipid peroxidation, cell necrosis and persistently reduced recovery of contractile performance during post-ischemic reperfusion. We conclude that MMP-2 functions not only as a proteolytic enzyme but also as a previously unrecognized active negative regulator of mitochondrial function during superimposed oxidative stress.

The evolution of the vertebrate metzincins; insights from Ciona intestinalis and Danio rerio

BACKGROUND

The metzincins are a large gene superfamily of proteases characterized by the presence of a zinc protease domain, and include the ADAM, ADAMTS, BMP1/TLL, meprin and MMP genes. Metzincins are involved in the proteolysis of a wide variety of proteins, including those of the extracellular matrix. The metzincin gene superfamily comprises eighty proteins in the human genome and ninety-three in the mouse. When and how the level of complexity apparent in the vertebrate metzincin gene superfamily arose has not been determined in detail. Here we present a comprehensive analysis of vertebrate metzincins using genes from both Ciona intestinalis and Danio rerio to provide new insights into the complex evolution of this gene superfamily.

RESULTS

We have identified 19 metzincin genes in the ciona genome and 83 in the zebrafish genome. Phylogenetic analyses reveal that the expansion of the metzincin gene superfamily in vertebrates has occurred predominantly by the simple duplication of pre-existing genes rather than by the appearance and subsequent expansion of new metzincin subtypes (the only example of which is the meprin gene family). Despite the number of zebrafish metzincin genes being relatively similar to that of tetrapods (e.g. man and mouse), the pattern of gene retention and loss within these lineages is markedly different. In addition, we have studied the evolution of the related TIMP gene family and identify a single ciona and four zebrafish TIMP genes.

CONCLUSION

The complexity seen in the vertebrate metzincin gene families was mainly acquired during vertebrate evolution. The metzincin gene repertoire in protostomes and invertebrate deuterostomes has remained relatively stable. The expanded metzincin gene repertoire of extant tetrapods, such as man, has resulted largely from duplication events associated with early vertebrate evolution, prior to the sarcopterygian-actinopterygian split. The teleost repertoire of metzincin genes in part parallels that of tetrapods but has been significantly modified, perhaps as a consequence of a teleost-specific duplication event.

Increase in matrix metalloproteinases from endothelial cells exposed to umbilical cord plasma from high birth weight newborns

Large for gestational age infants have increased risk of developing the metabolic syndrome and cardiovascular disease in child- and adulthood. The vascular endothelium is a target site in the pathogenesis of many cardiovascular disorders. The matrix metalloproteinases (MMP) are important modulators of the extracellular matrix and serve as markers of these disorders. Here, we asked whether umbilical cord plasma of high birth weight (HBW; >4 kg) infants could modulate functional properties of human umbilical vein endothelial cells (HUVEC) compared with plasma from normal birth weight (NBW; 3.1–3.6 kg) infants. To test this, HUVECs were exposed for 48 h to 20% venous cord plasma from HBW or NBW infants. The MMP activity in supernatants of HUVECs exposed to HBW plasma was nearly three times higher ( P < 0.05) than that obtained with NBW plasma. MMP-9, but not MMP-2, protein concentration and mRNA expression were enhanced in HBW ( P < 0.05). With specific blockers, MMP activity and mRNA-MMP-9 were inhibited by ∼60–70%. Cord lipid and insulin concentrations were similar ( P > 0.05) among the two groups. We could not detect any significant differences between the two groups in the concentrations of proinflammatory cytokines or specific tissue inhibitors of MMP in plasma or HUVEC supernatants. In conclusion, cord plasma from HBW infants induced more MMP-9 in HUVECs compared with cord plasma from NBW infants. Although not identified, cord plasma of HBW infants may contain factors that increase endothelial cell MMP. These findings may indicate an association between fetal nutritional conditions and endothelial cell functions.

Caveolin-1 inhibits matrix metalloproteinase-2 activity in the heart

Apart from its ability to degrade extracellular matrix proteins, matrix metalloproteinase-2 (MMP-2) was recently revealed to have targets and actions within the cardiac myocyte. The localization of MMP-2 in caveolae of endothelial cells suggests that caveolin-1 (Cav-1) may play a role in regulating MMP-2. The caveolin scaffolding domain (CSD) of Cav-1 regulates several proteins including those involved with signaling cascades. Whether Cav-1 is responsible for regulating MMP-2 in the heart is unknown. Hearts from Cav-1(-/-) or Cav-1(+/+) mice were isolated and heart extracts or lipid raft enriched membrane fractions were prepared. MMP-2 activity in Cav-1(-/-) hearts was markedly enhanced when compared with Cav-1(+/+) hearts with no changes in MMP-2 protein levels between groups. In contrast, MMP-2 activity and protein level were greatly reduced in lipid raft enriched fractions of Cav-1(-/-) hearts. Purified CSD inhibited MMP-2 activity in a concentration-dependent manner as assessed using an in vitro degradation assay with a fluorogenic MMP-2 substrate (OmniMMP). These data suggest that Cav-1 plays a role in regulating MMP-2 activity. Cav-1 may thus be a novel mechanism to regulate MMP-2 activity in the heart.

Matrix metalloproteinases: influence on smooth muscle cells and atherosclerotic plaque stability

Atherosclerotic plaque rupture, with subsequent occlusive thrombosis, is the underlying cause of most cases of sudden cardiac death. Matrix metalloproteinases (MMPs) are thought to mediate the progression of stable atherosclerotic lesions to an unstable phenotype that is prone to rupture through the destruction of strength-giving extracellular matrix (ECM) proteins. Smooth muscle cells secrete and deposit ECM proteins and are, therefore, considered protective against atherosclerotic plaque destabilization. However, similar to inflammatory cells (e.g., macrophages), smooth muscle cells release numerous MMPs that are capable of digesting ECM proteins. Thus, the interaction of smooth muscle cells and MMPs in atherosclerotic plaques is complex and not fully understood. Recently, research into the roles of MMPs and their endogenous inhibitors (tissue inhibitors of metalloproteinases), and their effects on smooth muscle behavior during plaque destabilization has been aided by the development of reproducible animal models of plaque instability. A plethora of studies has demonstrated that MMPs directly modulate smooth muscle behavior with both beneficial and deleterious effects on atherosclerotic plaque stability, in addition to their canonical effects on ECM remodeling. Consequently, broad-spectrum MMP inhibition may inhibit plaque-stabilizing mechanisms, such as smooth muscle cell growth, while conversely retarding ECM destruction and subsequent rupture. Hence the development of selective MMP inhibitors, that spare inhibitory effects on smooth muscle cell function, may be useful therapies to prevent plaque rupture and in this regard MMP-12 appears to be a particularly attractive target.

Expression of matrix metalloproteinases and endogenous inhibitors within ascending aortic aneurysms of patients with bicuspid or tricuspid aortic valves

OBJECTIVE

The mechanisms contributing to ascending thoracic aortic aneurysms associated with bicuspid aortic valves may differ from ascending thoracic aortic aneurysms with tricuspid aortic valves. Matrix metalloproteinases and their endogenous inhibitors have been causally linked to ascending thoracic aortic aneurysm formation. This study tested the hypothesis that specific and different matrix metalloproteinase and tissue inhibitors of metalloproteinase profiles would be observed in ascending thoracic aortic aneurysm samples from patients with bicuspid aortic valves versus tricuspid aortic valves.

METHODS

Ascending thoracic aortic aneurysm samples taken from patients with bicuspid aortic valve (n = 53) and patients with tricuspid aortic valve (n = 46) were assessed for representative subtypes of all matrix metalloproteinase classes and all 4 known tissue inhibitors of metalloproteinases. Levels were compared [optical density units, median (interquartile range)] both to reference control ascending aortic samples (n = 26) and within each valve group by aneurysm diameter (< or =3.9 cm, 4.0-5.9 cm and > or =6.0 cm).

RESULTS

Different and specific matrix metalloproteinase and tissue inhibitors of metalloproteinase profiles were observed in the ascending thoracic aortic aneurysm groups. In bicuspid aortic valves, matrix metalloproteinase-2 increased by 34% when compared with either tricuspid aortic valves or control (P < .05), and matrix metalloproteinase-14 decreased by 59% compared with tricuspid aortic valves (P < .05). In tricuspid aortic valve samples, tissue inhibitors of metalloproteinase-2 decreased by 35% when compared with either tricuspid aortic valves or control (P < .05), and matrix metalloproteinase-13 increased by 140% in the 4.0- to 5.9-cm diameter range (P < .05).

CONCLUSIONS

A unique matrix metalloproteinase and tissue inhibitor of metalloproteinase portfolio was observed in ascending thoracic aortic aneurysms from patients with bicuspid aortic valve compared with patients with tricuspid aortic valve. These differences, suggesting disparate mechanisms of extracellular matrix remodeling, may provide unique biochemical targets for ascending thoracic aortic aneurysm prognostication and treatment in these 2 groups of patients.

Characterization of p43(ARF), a derivative of the p43 component of multiaminoacyl-tRNA synthetase complex released during apoptosis

In human, nine aminoacyl tRNA synthetases are associated with the three auxiliary proteins, p18, p38, and p43, to form a stable multiprotein complex. The p43 component, which has a potent tRNA binding capacity, is associated to the complex via its N-terminal moiety. This protein is also the precursor of the endothelial monocyte-activating polypeptide II (p43(EMAPII), corresponding to the C-terminal moiety of p43), a cytokine generated during apoptosis. Here we examined the cellular pathway that, starting from the p43 subunit of the complex, leads to this extracellular cytokine. We identified a new intermediate in this pathway, named p43(ARF) for Apoptosis-released Factor. This intermediate is produced in cellulo by proteolytic cleavage of endogenous p43 and is rapidly recovered in the culture medium. This p43 derivative was purified from the medium of human U937 cells subjected to serum starvation. It contains 40 additional N-terminal amino acid residues as compared with the cytokine p43(EMAPII) and may be generated by a member of the matrix metalloproteinase family. Recombinant p43(ARF) is a monomer in solution and binds tRNA with a Kd of approximately 6 nM, 30-fold lower than that of p43. Highly purified p43(ARF) or p43(EMAPII) do not stimulate the expression of E-selectin by human umbilical vein endothelial cells. Our results suggest that the cleavage of p43 and its cellular delocalization, and thus the release of this tRNA binding subunit from the complex, is one of the molecular mechanisms leading to the shut down of protein synthesis in apoptosis.

The role of matrix metalloproteinases in the oral environment

This review focuses specifically on matrix metalloproteinases (MMPs) and their role in physiological and pathological extracellular matrix (ECM) remodeling and degradation processes in the oral environment. A group of enzymes capable of degrading almost all ECM proteins, MMPs contribute to both normal and pathological tissue remodeling. The expression of different MMPs may be upregulated in pathological conditions such as inflammation and tumor invasion. The balance between activated MMPs and tissue inhibitors of metalloproteinases (TIMPs) controls the extent of ECM remodeling. Prior to mineralization, MMPs may participate in the organization of enamel and dentin organic matrix, or they may regulate mineralization by controlling the proteoglycan turnover. There is evidence indicating that MMPs could be involved in the etiology of enamel fluorosis and amelogenesis imperfecta. They seem to play a part in dentinal caries progression, since they have a crucial role in dentin collagen breakdown in caries lesions. MMPs have been identified in pulpal and periapical inflammation and are strongly correlated with periodontal diseases, since they are the major players in collagen breakdown during periodontal tissue destruction. The use of MMP inhibitors could help the prevention and treatment of many MMP-related oral diseases.

Activation of matrix metalloproteinase-3 is altered at the frog neuromuscular junction following changes in synaptic activity

The extracellular matrix surrounding the neuromuscular junction is a highly specialized and dynamic structure. Matrix Metalloproteinases are enzymes that sculpt the extracellular matrix. Since synaptic activity is critical to the structure and function of this synapse, we investigated whether changes in synaptic activity levels could alter the activity of Matrix Metalloproteinases at the neuromuscular junction. In particular, we focused on Matrix Metalloproteinase 3 (MMP3), since antibodies to MMP3 recognize molecules at the frog neuromuscular junction, and MMP3 cleaves a number of synaptic basal lamina molecules, including agrin. Here we show that the fluorogenic compound (M2300) can be used to perform in vivo proteolytic imaging of the frog neuromuscular junction to directly measure the activity state of MMP3. Application of this compound reveals that active MMP3 is concentrated at the normal frog neuromuscular junction, and is tightly associated with the terminal Schwann cell. Blocking presynaptic activity via denervation, or TTX nerve blockade, results in a decreased level of active MMP3 at the neuromuscular junction. The loss of active MMP3 at the neuromuscular junction in denervated muscles can result from decreased activation of pro-MMP3, or it could result from increased inhibition of MMP3. These results support the hypothesis that changes in synaptic activity can alter the level of active MMP3 at the neuromuscular junction.

Matrix metalloproteinases in inflammatory bowel disease: boon or a bane?

Matrix metalloproteinases (MMPs) are a family of Zn(2+)-dependent extracellular matrix (ECM) degrading endopeptidases that share common functional domains, activation mechanisms, and collectively have the capacity to degrade all types of ECM proteins. In addition to playing a central role in ECM turnover, MMPs proteolytically activate or degrade a variety of nonmatrix substrates including chemokines, cytokines, growth factors, and junctional proteins. Thus, they are increasingly recognized as critical players in inflammatory response. Indeed, accumulating data from several studies indicate that they are the predominant proteases involved in the pathogenesis of inflammatory bowel disease (IBD) via their influence on the function and migration of inflammatory cells, mucosal ulceration, as well as matrix deposition and degradation. Some MMPs are constitutively expressed and play a protective role in IBD through their effect on cellular homeostasis, while others are induced during inflammation-mediated tissue damage. This article focuses on the role of the various MMPs in IBD, discussing their physiologic and pathogenetic role in the context of intestinal defense, mucosal inflammatory response, and immune cell-epithelial interaction.

Visions for novel biophysical elucidations of extracellular matrix networks

The extracellular matrix consists of multifunctional molecules, which are composed of a large numbers of different domains. Clearly these domains and even the entire molecules do not function independently as isolated species, but interact with each other in large networks. In many cases specific regions of the networks may be considered as molecular machines in which the different molecules are arranged in highly defined spatial structures and act in a dynamic, concerted fashion. At present most structural information is limited to single molecules, and dynamics have been measured mainly for pairs of interacting partners in solution. Work needs to be extended to large integrated systems and the functions of molecular machines need to be explored. Electron tomography, fluorescence resonance energy transfer, and other biophysical techniques are very promising.

Elastin-elastases and inflamm-aging

Degradation of elastin, the main amorphous component of elastic fibers, by elastases belonging to the serine, metallo, or cysteine families leads to the generation of elastin fragments, designated as elastokines in keeping with their cytokine-like properties. Generation of elastokines from one of the longest lived protein in human might represent a strong tissue repair signal. Indeed, they (1) exhibit potent chemotactic activity for leukocytes, (2) stimulate fibroblast and smooth muscle cell proliferation, and (3) display proangiogenic activity as potent as VEGF. However, continuous exposure of cells to these matrikines, through increased elastase(s) expression with age, can contribute to the formation of a chronic inflammatory state, that is, inflamm-aging. Importantly, binding of elastokines to S-Gal, their cognate receptor, proved to stimulate matrix metalloproteinase expression in normal and cancer cells. Besides, these elastin fragments can polarize lymphocytes toward a Th-1 response or induce an osteogenic response in smooth muscle cells, and arterial wall calcification. In this chapter, emphasis will be made on the contribution of elastokines on the genesis of age-related arterial wall diseases, particularly abdominal aortic aneurysms (AAAs). An elastokine theory of AAAs progression will be proposed. Age is one main risk factor of cancer incidence and development. The myriad of biological effects exerted by elastokines on stromal and inflammatory cells led us to hypothesize that they might be main actors in elaborating a favorable cancerization field in melanoma; for instance these peptides could catalyze the vertical growth phase transition in melanoma through increased expression of gelatinase A and membrane-type 1 matrix metalloproteinase.