Unaltered secretion of beta-amyloid precursor protein in gelatinase A (matrix metalloproteinase 2)-deficient mice

Mmp2 Deficiency Leads to Defective Parturition and High Dystocia Rates in Mice

Parturition is the final and essential step for mammalian reproduction. While the uterus is quiescent during pregnancy, fundamental changes arise in the myometrial contractility, inducing fetal expulsion. Extracellular matrix (ECM) remodeling is fundamental for these events. The gelatinases subgroup of matrix metalloproteinases (MMPs), MMP2 and MMP9, participate in uterine ECM remodeling throughout pregnancy and parturition. However, their loss-of-function effect is unknown. Here, we determined the result of eliminating Mmp2 and/or Mmp9 on parturition in vivo, using single- and double-knockout (dKO) mice. The dystocia rates were measured in each genotype, and uterine tissue was collected from nulliparous synchronized females at the ages of 2, 4, 9 and 12 months. Very high percentages of dystocia (40-55%) were found in the Mmp2-/- and dKO females, contrary to the Mmp9-/- and wild-type females. The histological analysis of the uterus and cervix revealed that Mmp2-/- tissues undergo marked structural alterations, including highly enlarged myometrial, endometrial and luminal cavity. Increased collagen deposition was also demonstrated, suggesting a mechanism of extensive fibrosis in the Mmp2-/- myometrium, which may result in dystocia. Overall, this study describes a new role for MMP2 in myometrium remodeling during mammalian parturition process, highlighting a novel cause for dystocia due to a loss in MMP2 activity in the uterine tissue.

Secretomics reveals gelatinase substrates at the blood-brain barrier that are implicated in astroglial barrier function

The gelatinases, matrix metalloproteinase 2 (MMP-2) and MMP-9, are key for leukocyte penetration of the brain parenchymal border in neuroinflammation and the functional integrity of this barrier; however, it is unclear which MMP substrates are involved. Using a tailored, sensitive, label-free mass spectrometry-based secretome approach, not previously applied to nonimmune cells, we identified 119 MMP-9 and 21 MMP-2 potential substrates at the cell surface of primary astrocytes, including known substrates (β-dystroglycan) and a broad spectrum of previously unknown MMP-dependent events involved in cell-cell and cell-matrix interactions. Using neuroinflammation as a model of assessing compromised astroglial barrier function, a selection of the potential MMP substrates were confirmed in vivo and verified in human samples, including vascular cell adhesion molecule-1 and neuronal cell adhesion molecule. We provide a unique resource of potential MMP-2/MMP-9 substrates specific for the astroglia barrier. Our data support a role for the gelatinases in the formation and maintenance of this barrier but also in astrocyte-neuron interactions.

Roles of Matrix Metalloproteinases and Their Natural Inhibitors in Metabolism: Insights into Health and Disease

Matrix metalloproteinases (MMPs) are a family of zinc-activated peptidases that can be classified into six major classes, including gelatinases, collagenases, stromelysins, matrilysins, membrane type metalloproteinases, and other unclassified MMPs. The activity of MMPs is regulated by natural inhibitors called tissue inhibitors of metalloproteinases (TIMPs). MMPs are involved in a wide range of biological processes, both in normal physiological conditions and pathological states. While some of these functions occur during development, others occur in postnatal life. Although the roles of several MMPs have been extensively studied in cancer and inflammation, their function in metabolism and metabolic diseases have only recently begun to be uncovered, particularly over the last two decades. This review aims to summarize the current knowledge regarding the metabolic roles of metalloproteinases in physiology, with a strong emphasis on adipose tissue homeostasis, and to highlight the consequences of impaired or exacerbated MMP actions in the development of metabolic disorders such as obesity, fatty liver disease, and type 2 diabetes.

Fibroblast growth factor 8 (FGF8) up-regulates gelatinase expression in chondrocytes through nuclear factor-κB p65

INTRODUCTION

Gelatinases, namely MMP2 and MMP9, are involved in the natural turnover of articular cartilage, as well as the loss of the cartilage matrix in osteoarthritis (OA). Studies have reported that fibroblast growth factor 8 (FGF8) promoted the degradation of cartilage in OA. In the present study, we predicted that FGF8 promoted chondrocyte expression and secretion of gelatinases by activating NF-κB p65 signaling.

MATERIALS AND METHODS

Primary chondrocytes from C57 mice were cultured with recombinant FGF8. RNA sequencing was employed to explore the gene expression changes of gelatinases. Gelatin zymography was used to determine the activation of gelatinases. Western blot was used to investigate the expression of the gelatinases and NF-κB p65 signaling pathways, and immunofluorescence staining and NF-κB inhibitor assays were performed to confirm the activation of NF-κB p65 signaling.

RESULTS

FGF8 could increase the expression and activity of gelatinases in primary chondrocytes. And FGF8-induced expression of gelatinases was regulated through activation of NF-κB signaling with acetylated p65 accumulating in the cell nucleus. We further found that the NF-κB inhibitor, BAY 11-7082, could suppress up-regulation of gelatinase induced by FGF8.

CONCLUSION

FGF8 enhanced the expression and activity of MMP2 and MMP9 in chondrocytes via NF-κB p65 signaling.

Craniofacial tendon development—Characterization of extracellular matrix morphology and spatiotemporal protein distribution

Craniofacial (CF) tendons are often affected by traumatic injuries and painful disorders that can severely compromise critical jaw functions, such as mastication and talking. Unfortunately, tendons lack the ability to regenerate, and there are no solutions to restore their native properties or function. An understanding of jaw tendon development could inform tendon regeneration strategies to restore jaw function, however CF tendon development has been relatively unexplored. Using the chick embryo, we identified the jaw-closing Tendon of the musculus Adductor Mandibulae Externus (TmAM) and the jaw-opening Tendon of the musculus Depressor Mandibulae (TmDM) that have similar functions to the masticatory tendons in humans. Using histological and immunohistochemical (IHC) analyses, we characterized the TmAM and TmDM on the basis of cell and extracellular matrix (ECM) morphology and spatiotemporal protein distribution from early to late embryonic development. The TmAM and TmDM were detectable as early as embryonic day (d) 9 based on histological staining and tenascin-C (TNC) protein distribution. Collagen content increased and became more organized, cell density decreased, and cell nuclei elongated over time during development in both the TmAM and TmDM. The TmAM and TmDM exhibited similar spatiotemporal patterns for collagen type III (COL3), but differential spatiotemporal patterns for TNC, lysyl oxidase (LOX), and matrix metalloproteinases (MMPs). Our results demonstrate markers that play a role in limb tendon formation are also present in jaw tendons during embryonic development, implicate COL3, TNC, LOX, MMP2, and MMP9 in jaw tendon development, and suggest TmAM and TmDM possess different developmental programs. Taken together, our study suggests the chick embryo may be used as a model with which to study CF tendon extracellular matrix development, the results of which could ultimately inform therapeutic approaches for CF tendon injuries and disorders.

Role of matrix metalloprotease-2 and MMP-9 in experimental lung fibrosis in mice

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a diffuse parenchymal lung disease characterized by exuberant deposition of extracellular matrix (ECM) proteins in the lung interstitium, which contributes to substantial morbidity and mortality in IPF patients. Matrix metalloproteinases (MMPs) are a large family of zinc-dependent endopeptidases, many of which have been implicated in the regulation of ECM degradation in lung fibrosis. However, the roles of MMP-2 and -9 (also termed gelatinases A and B) have not yet been explored in lung fibrosis in detail.

METHODS

AdTGF-β1 was applied via orotracheal routes to the lungs of WT, MMP-2 KO, MMP-9 KO and MMP-2/-9 dKO mice on day 0 to induce lung fibrosis. Using hydroxyproline assay, FlexiVent based lung function measurement, histopathology, western blot and ELISA techniques, we analyzed MMP-2 and MMP-9 levels in BAL fluid and lung, collagen contents in lung and lung function in mice on day 14 and 21 post-treatment.

RESULT

IPF lung homogenates exhibited significantly increased levels of MMP-2 and MMP-9, relative to disease controls. Enzymatically active MMP-2 and MMP-9 was increased in lungs of mice exposed to adenoviral TGF-β1, suggesting a role for these metalloproteinases in lung fibrogenesis. However, we found that neither MMP-2 or MMP-9 nor combined MMP-2/-9 deletion had any effect on experimental lung fibrosis in mice.

CONCLUSION

Together, our data strongly suggest that both gelatinases MMP-2 and MMP-9 play only a subordinate role in experimental lung fibrosis in mice.

Matrix Metalloproteinases: From Molecular Mechanisms to Physiology, Pathophysiology, and Pharmacology

The first matrix metalloproteinase (MMP) was discovered in 1962 from the tail of a tadpole by its ability to degrade collagen. As their name suggests, matrix metalloproteinases are proteases capable of remodeling the extracellular matrix. More recently, MMPs have been demonstrated to play numerous additional biologic roles in cell signaling, immune regulation, and transcriptional control, all of which are unrelated to the degradation of the extracellular matrix. In this review, we will present milestones and major discoveries of MMP research, including various clinical trials for the use of MMP inhibitors. We will discuss the reasons behind the failures of most MMP inhibitors for the treatment of cancer and inflammatory diseases. There are still misconceptions about the pathophysiological roles of MMPs and the best strategies to inhibit their detrimental functions. This review aims to discuss MMPs in preclinical models and human pathologies. We will discuss new biochemical tools to track their proteolytic activity in vivo and ex vivo, in addition to future pharmacological alternatives to inhibit their detrimental functions in diseases. SIGNIFICANCE STATEMENT: Matrix metalloproteinases (MMPs) have been implicated in most inflammatory, autoimmune, cancers, and pathogen-mediated diseases. Initially overlooked, MMP contributions can be both beneficial and detrimental in disease progression and resolution. Thousands of MMP substrates have been suggested, and a few hundred have been validated. After more than 60 years of MMP research, there remain intriguing enigmas to solve regarding their biological functions in diseases.

Antioxidant, anti-inflammatory, and wound healing effects of topical silver-doped zinc oxide and silver oxide nanocomposites

Silver nanoparticles (Ag-NPs), silver oxide nanoparticles (AgO-NPs), and zinc oxide nanoparticles (ZnO-NPs) have healing, antibacterial, and antioxidant properties. Furthermore, Ag-NPs and ZnO-NPs also have anti-inflammatory properties. In this study, we synthesized a nanocomposite using Ag-ZnO and AgO-NPs (Ag-ZnO/AgO NPs). The structural and morphological properties of nanocrystals and nanocomposite were investigated by X-ray diffraction and scanning electronics microscopic. The wurtzite crystalline structure of Ag-ZnO and two morphologies for the nanocomposite (nanorods and nanoplatelets) were determined. Topical treatment with 1% Ag-ZnO/AgO NPs was compared to untreated wounds (control group). Wounds were induced in the dorsal region of BALB/c mice and evaluated after 3, 7, 14, and 21 days of treatment. The nanocomposite demonstrated anti-inflammatory and antioxidant capacities. In addition, wounds treated with Ag-ZnO/AgO NPs showed accelerated closure, non-cytotoxicity, especially on keratinocytes and collagen deposition, and increased metalloproteinases 2 and 9 activity. The nanocomposite improved healing by reducing the inflammatory process, protecting tissues from damage caused by free radicals, and increasing collagen deposition in the extracellular matrix. These characteristics contributed to the accelerated wound closure process. Thus, Ag-ZnO/AgO NPs show potential for can be a strategy for topical use in formulations of new drugs to treat wounds.

Metalloproteases in gonad formation and ovulation

Changes in expression or activation of various metalloproteases including matrix metalloproteases (Mmp), a disintegrin and metalloprotease (Adam) and a disintegrin and metalloprotease with thrombospondin motif (Adamts), and their endogenous inhibitors (tissue inhibitors of metalloproteases, Timp), have been shown to be critical for ovulation in various species from studies in past decades. Some of these metalloproteases such as Adamts1, Adamts9, Mmp2, and Mmp9 have also been shown to be regulated by luteinizing hormone (LH) and/or progestin, which are essential triggers for ovulation in all vertebrate species. Most of these metalloproteases also express broadly in various tissues and cells including germ cells and somatic gonad cells. Thus, metalloproteases likely play roles in gonad formation processes comprising primordial germ cell (PGC) migration, development of germ and somatic cells, and sex determination. However, our knowledge on the functions and mechanisms of metalloproteases in these processes in vertebrates is still lacking. This review will summarize our current knowledge on the metalloproteases in ovulation and gonad formation with emphasis on PGC migration and germ cell development.

Initial immune response to a FRET-based MMP sensor-immobilized silk fibroin hydrogel in vivo

To investigate the initial immune response to biodegradable silk fibroin (SF) hydrogels in vivo, a Förster/fluorescence resonance energy transfer (FRET)-based sensor was developed to detect matrix metalloproteinase (MMP) activity (FRET-MMPS) and immobilized to SF hydrogel. FRET-MMPS immobilized to SF hydrogel in vitro displayed intra-molecular FRET more than inter-molecular FRET, and MMP activity was detected through a decrease in FRET signal intensity. Then, the SF hydrogel modified with FRET-MMPS was implanted into mice subcutaneously, and it was observed that the FRET signal intensity decreased significantly soon (< 3 h) after implantation. Although the intensity exhibited a sharp decrease toward 24 h post-implantation, histological evaluation proved that bulk-level hydrogel degradation, such as breakdown, was mainly caused by macrophages and foreign body giant cells on a timescale of weeks. These results indicated that, immediately upon implantation, active MMPs reached the SF hydrogel and began cleaving SF networks, which might result in the loosening of the networks and then enabled immune cells, such as macrophages, to start the bulk-level hydrogel degradation. The sensor clarified the initial immune response to SF hydrogels and will provide clues for designing the biodegradation behaviors of scaffolds for regenerative medicine. STATEMENT OF SIGNIFICANCE: Silk fibroin (SF) materials are degraded gradually by the immune response. Immune cells, such as macrophages, break down implanted SF materials on a timescale of weeks or months, but the initial (< 24 h) immune response to SF materials remains unclear. In this study, SF hydrogels modified with Förster/fluorescence resonance energy transfer (FRET)-based matrix metalloproteinase (MMP) sensors were implanted in mice and within 3 h post-implantation, the SF hydrogels were degraded by MMPs. Although this molecular-level biodegradation was not correlated with the hydrogel breakdown, the MMPs were likely to loosen the SF networks to enable immune cells to infiltrate and degrade the hydrogel. This is the first study to unveil the initial stage of immune response to biomaterials.

MMP2 Modulates Inflammatory Response during Axonal Regeneration in the Murine Visual System

Neuroinflammation has been put forward as a mechanism triggering axonal regrowth in the mammalian central nervous system (CNS), yet little is known about the underlying cellular and molecular players connecting these two processes. In this study, we provide evidence that MMP2 is an essential factor linking inflammation to axonal regeneration by using an in vivo mouse model of inflammation-induced axonal regeneration in the optic nerve. We show that infiltrating myeloid cells abundantly express MMP2 and that MMP2 deficiency results in reduced long-distance axonal regeneration. However, this phenotype can be rescued by restoring MMP2 expression in myeloid cells via a heterologous bone marrow transplantation. Furthermore, while MMP2 deficiency does not affect the number of infiltrating myeloid cells, it does determine the coordinated expression of pro- and anti-inflammatory molecules. Altogether, in addition to its role in axonal regeneration via resolution of the glial scar, here, we reveal a new mechanism via which MMP2 facilitates axonal regeneration, namely orchestrating the expression of pro- and anti-inflammatory molecules by infiltrating innate immune cells.

Post-translational activation of Mmp2 correlates with patterns of active collagen degradation during the development of the zebrafish tail

Matrix metalloproteinase-2 (a.k.a. Gelatinase A, or Mmp2 in zebrafish) is known to have roles in pathologies such as arthritis, in which its function is protective, as well as in cancer metastasis, in which it is activated as part of the migration and invasion of metastatic cells. It is also required during development and the regeneration of tissue architecture after wound healing, but its roles in tissue remodelling are not well understood. Gelatinase A is activated post-translationally by proteolytic cleavage, making information about its transcription and even patterns of protein accumulation difficult to relate to biologically relevant activity. Using a transgenic reporter of endogenous Mmp2 activation in zebrafish, we describe its accumulation and post-translational proteolytic activation during the embryonic development of the tail. Though Mmp2 is expressed relatively ubiquitously, it seems to be active only at specific locations and times. Mmp2 is activated robustly in the neural tube and in maturing myotome boundaries. It is also activated in the notochord during body axis straightening, in patches scattered throughout the epidermal epithelium, in the gut, and on cellular protrusions extending from mesenchymal cells in the fin folds. The activation of Mmp2 in the notochord, somite boundaries and fin folds associates with collagen remodelling in the notochord sheath, myotome boundary ECM and actinotrichia respectively. Mmp2 is likely an important effector of ECM remodelling during the morphogenesis of the notochord, a driving structure in vertebrate development. It also appears to function in remodelling the ECM associated with growing epithelia and the maturation of actinotrichia in the fin folds, mediated by mesenchymal cell podosomes.

Targeted Delivery of a Matrix Metalloproteinases-2 Specific Inhibitor Using Multifunctional Nanogels to Attenuate Ischemic Skeletal Muscle Degeneration and Promote Revascularization

Critical limb ischemia (CLI) is a severe form of peripheral artery disease (PAD). It is featured by degenerated skeletal muscle and poor vascularization. During the development of CLI, the upregulated matrix metalloproteinase-2 (MMP-2) degrades muscle extracellular matrix to initiate the degeneration. Meanwhile, MMP-2 is necessary for blood vessel formation. It is thus hypothesized that appropriate MMP-2 bioactivity in ischemic limbs will not only attenuate muscle degeneration but also promote blood vessel formation. Herein, we developed ischemia-targeting poly(N-isopropylacrylamide)-based nanogels to specifically deliver an MMP-2 inhibitor CTTHWGFTLC (CTT) into ischemic limbs to tailor MMP-2 bioactivity. Besides acting as an MMP-2 inhibitor, CTT promoted endothelial cell migration under conditions mimicking the ischemic limbs. The nanogels were sensitive to the pH of ischemic tissues, allowing them to largely aggregate in the injured area. To help reduce nanogel uptake by macrophages and increase circulation time, the nanogels were cloaked with a platelet membrane. An ischemia-targeting peptide CSTSMLKA (CST) was further conjugated on the platelet membrane for targeted delivery of nanogels into the ischemic area. CTT gradually released from the nanogels for 4 weeks. The nanogels mostly accumulated in the ischemic area for 28 days. The released CTT preserved collagen in the muscle and promoted its regeneration. In addition, CTT stimulated angiogenesis. Four weeks after CLI, the blood flow and vessel density of the ischemic limbs treated with the nanogels were remarkably higher than the control groups without CTT release. These results demonstrate that the developed nanogel-based CTT release system has the potential to stimulate ischemic limb regeneration.

Different roles of matrix metalloproteinase 2 in osteolysis of skeletal dysplasia and bone metastasis (Review)

Matrix metalloproteinase 2 (MMP2) is a well-characterized protein that is indispensable for extracellular matrix remodeling and other pathological processes, such as tumor progression and skeletal dysplasia. Excessive activation of MMP2 promotes osteolytic metastasis and bone destruction in late-stage cancers, while its loss-of-function mutations result in the decreased bone mineralization and generalized osteolysis occurring progressively in skeletal developmental disorders, particularly in multicentric osteolysis, nodulosis and arthropathy (MONA). Either upregulation or downregulation of MMP2 activity can result in the same osteolytic effects. Thus, different functions of MMP2 have been recently identified that could explain this observation. While MMP2 can degrade bone matrix, facilitate osteoclastogenesis and amplify various signaling pathways that enhance osteolysis in bone metastasis, its role in maintaining the number of bone cells, supporting osteocytic canalicular network formation and suppressing leptin-mediated inhibition of bone formation has been implicated in osteolytic disorders caused by MMP2 deficiency. Furthermore, the proangiogenic activity of MMP2 is one of the potential mechanisms that are associated with both pathological situations. In the present article, the latest research on MMP2 in bone homeostasis is reviewed and the mechanisms underlying the role of this protein in skeletal metastasis and developmental osteolysis are discussed.

SIX1 and SIX4 homeoproteins regulate PAX7+ progenitor cell properties during fetal epaxial myogenesis

Pax7 expression marks stem cells in developing skeletal muscles and adult satellite cells during homeostasis and muscle regeneration. The genetic determinants that control the entrance into the myogenic program and the appearance of PAX7+ cells during embryogenesis are poorly understood. SIX homeoproteins are encoded by the sine oculis-related homeobox Six1-Six6 genes in vertebrates. Six1, Six2, Six4 and Six5 are expressed in the muscle lineage. Here, we tested the hypothesis that Six1 and Six4 could participate in the genesis of myogenic stem cells. We show that fewer PAX7+ cells occupy a satellite cell position between the myofiber and its associated basal lamina in Six1 and Six4 knockout mice (s1s4KO) at E18. However, PAX7+ cells are detected in remaining muscle masses present in the epaxial region of the double mutant embryos and are able to divide and contribute to muscle growth. To further characterize the properties of s1s4KO PAX7+ cells, we analyzed their transcriptome and tested their properties after transplantation in adult regenerating tibialis anterior muscle. Mutant stem cells contribute to hypotrophic myofibers that are not innervated but retain the ability to self-renew.

Conserved role of matrix metalloproteases 2 and 9 in promoting the migration of neural crest cells in avian and mammalian embryos

Neural crest cells (NCCs) are a unique embryonic cell population that initially reside at the dorsal neural tube but later migrate in the embryo and differentiate into multiple types of derivatives. To acquire motility, NCCs undergo epithelial-to-mesenchymal transition and invade the surrounding extracellular matrix (ECM). Matrix metalloproteases (MMPs) are a large family of proteases which regulate migration of various embryonic and adult cells via ECM remodeling. The gelatinase's subgroup of MMPs is the most studied one due to its key role in metastasis. As it is composed of only two proteases, MMP2 and MMP9, it is important to understand whether each is indispensable or redundant in its biological function. Here we explored the role of the gelatinases in executing NCC migration, by determining whether MMP2 and/or MMP9 regulate migration across species in singular, combined, or redundant manners. Chick and mouse embryos were utilized to compare expression and activity of both MMPs using genetic and pharmacological approaches in multiple in vivo and ex vivo assays. Both MMPs were found to be expressed and active in mouse and chick NCCs. Inhibition of each MMP was sufficient to prevent NCC migration in both species. Yet, NCC migration was maintained in MMP2^-/- or MMP9^-/- mouse mutants due to compensation between the gelatinases, but reciprocal pharmacological inhibition in each mutant prevented NCC migration. This study reveals for the first time that both gelatinases are expressed in avian and mammalian NCCs, and demonstrates their fundamental and conserved role in promoting embryonic cell migration.

The Versatile Role of Matrix Metalloproteinase for the Diverse Results of Fibrosis Treatment

Fibrosis is a type of chronic organ failure, resulting in the excessive secretion of extracellular matrix (ECM). ECM protects wound tissue from infection and additional injury, and is gradually degraded during wound healing. For some unknown reasons, myofibroblasts (the cells that secrete ECM) do not undergo apoptosis; this is associated with the continuous secretion of ECM and reduced ECM degradation even during de novo tissue formation. Thus, matrix metalloproteinases (MMPs) are considered to be a potential target of fibrosis treatment because they are the main groups of ECM-degrading enzymes. However, MMPs participate not only in ECM degradation but also in the development of various biological processes that show the potential to treat diseases such as stroke, cardiovascular diseases, and arthritis. Therefore, treatment involving the targeting of MMPs might impede typical functions. Here, we evaluated the links between these MMP functions and possible detrimental effects of fibrosis treatment, and also considered possible approaches for further applications.

A tale of two tracts: history, current advances, and future directions of research on sexual differentiation of reproductive tracts†

Alfred Jost's work in the 1940s laid the foundation of the current paradigm of sexual differentiation of reproductive tracts, which contends that testicular hormones drive the male patterning of reproductive tract system whereas the female phenotype arises by default. Once established, the sex-specific reproductive tracts undergo morphogenesis, giving rise to anatomically and functionally distinct tubular organs along the rostral-caudal axis. Impairment of sexual differentiation of reproductive tracts by genetic alteration and environmental exposure are the main causes of disorders of sex development, and infertility at adulthood. This review covers past and present work on sexual differentiation and morphogenesis of reproductive tracts, associated human disorders, and emerging technologies that have made impacts or could radically expand our knowledge in this field.

Distribution and activation of matrix metalloproteinase-2 in skeletal muscle fibers

A substantial intracellular localization of matrix metalloproteinase 2 (MMP2) has been reported in cardiomyocytes, where it plays a role in the degradation of the contractile apparatus following ischemia-reperfusion injury. Whether MMP2 may have a similar function in skeletal muscle is unknown. This study determined that the absolute amount of MMP2 is similar in rat skeletal and cardiac muscle and human muscle (~10-18 nmol/kg muscle wet wt) but is ~50- to 100-fold less than the amount of calpain-1. We compared mechanically skinned muscle fibers, where the extracellular matrix (ECM) is completely removed, with intact fiber segments and found that ~30% of total MMP2 was associated with the ECM, whereas ~70% was inside the muscle fibers. Concordant with whole muscle fractionation, further separation of skinned fiber segments into cytosolic, membranous, and cytoskeletal and nuclear compartments indicated that ~57% of the intracellular MMP2 was freely diffusible, ~6% was associated with the membrane, and ~37% was bound within the fiber. Under native zymography conditions, only 10% of MMP2 became active upon prolonged (17 h) exposure to 20 μM Ca²⁺, a concentration that would fully activate calpain-1 in seconds to minutes; full activation of MMP2 would require ~1 mM Ca²⁺. Given the prevalence of intracellular MMP2 in skeletal muscle, it is necessary to investigate its function using physiological conditions, including isolation of any potential functional relevance of MMP2 from that of the abundant protease calpain-1.

Multicentric osteolytic syndromes represent a phenotypic spectrum defined by defective collagen remodeling

Frank-Ter Haar syndrome (FTHS), Winchester syndrome (WS), and multicentric osteolysis, nodulosis, and arthropathy (MONA) are ultra-rare multisystem disorders characterized by craniofacial malformations, reduced bone density, skeletal and cardiac anomalies, and dermal fibrosis. These autosomal recessive syndromes are caused by homozygous mutation or deletion of respectively SH3PXD2B (SH3 and PX Domains 2B), MMP14 (matrix metalloproteinase 14), or MMP2. Here, we give an overview of the clinical features of 63 previously reported patients with an SH3PXD2B, MMP14, or MMP2 mutation, demonstrating considerable clinical overlap between FTHS, WS, and MONA. Interestingly, the protein products of SH3PXD2B, MMP14, and MMP2 directly cooperate in collagen remodeling. We review animal models for these three disorders that accurately reflect the major clinical features and likewise show significant phenotypical similarity with each other. Furthermore, they demonstrate that defective collagen remodeling is central in the underlying pathology. As such, we propose a nosological revision, placing these SH3PXD2B, MMP14, and MMP2 related syndromes in a novel "defective collagen-remodelling spectrum (DECORS)". In our opinion, this revised nosology better reflects the central role for impaired collagen remodeling, a potential target for pharmaceutical intervention.

Fibrillin microfibrils and proteases, key integrators of fibrotic pathways

Supramolecular networks composed of multi-domain ECM proteins represent intricate cellular microenvironments which are required to balance tissue homeostasis and direct remodeling. Structural deficiency in ECM proteins results in imbalances in ECM-cell communication resulting often times in fibrotic reactions. To understand how individual components of the ECM integrate communication with the cell surface by presenting growth factors or providing fine-tuned biomechanical properties is mandatory for gaining a better understanding of disease mechanisms in the quest for new therapeutic approaches. Here we provide an overview about what we can learn from inherited connective tissue disorders caused primarily by mutations in fibrillin-1 and binding partners as well as by altered ECM processing leading to defined structural changes and similar functional knock-in mouse models. We will utilize this knowledge to propose new molecular hypotheses which should be tested in future studies.

Visualizing the Distribution of Matrix Metalloproteinases in Ischemic Brain Using In Vivo 19F-Magnetic Resonance Spectroscopic Imaging

Matrix metalloproteinases (MMPs) damage the neurovascular unit, promote the blood-brain barrier (BBB) disruption following ischemic stroke, and play essential roles in hemorrhagic transformation (HT), which is one of the most severe side effects of thrombolytic therapy. However, no biomarkers have presently been identified that can be used to track changes in the distribution of MMPs in the brain. Here, we developed a new ¹⁹F-molecular ligand, TGF-019, for visualizing the distribution of MMPs in vivo using ¹⁹F-magnetic resonance spectroscopic imaging (¹⁹F-MRSI). We demonstrated TGF-019 has sufficient sensitivity for the specific MMPs suspected in evoking HT during ischemic stroke, i.e., MMP2, MMP9, and MMP3. We then utilized it to assess those MMPs at 22 to 24 hours after experimental focal cerebral ischemia on MMP2-null mice, as well as wild-type mice with and without the systemic administration of the recombinant tissue plasminogen activator (rt-PA). The ¹⁹F-MRSI of TGN-019-administered mice showed high signal intensity within ischemic lesions that correlated with total MMP2 and MMP9 activity, which was confirmed by zymographic analysis of ischemic tissues. Based on the results of this study, ¹⁹F-MRSI following TGN-019 administration can be used to assess potential therapeutic strategies for ischemic stroke.

Pathologies of matrix metalloproteinase-2 underactivity: a perspective on a neglected condition 1

A member of the matrix metalloproteinase family, matrix metalloproteinase-2 (MMP-2, gelatinase A), has been extensively studied for its role in both normal physiology and pathological processes. Whereas most research efforts in recent years have investigated the pathologies associated with MMP-2 overactivity, the pathological mechanisms elicited by MMP-2 underactivity are less well understood. Here, we distinguish between 2 states and describe their causes: (i) MMP-2 deficiency (complete loss of MMP-2 activity) and (ii) MMP-2 insufficiency (defined as MMP-2 activity below baseline levels). Further, we review the biology of MMP-2, summarizing the current literature on MMP-2 underactivity in both mice and humans, and describe research being conducted by our lab towards improving our understanding of the pathological mechanisms elicited by MMP-2 deficiency/insufficiency. We think that this research could stimulate the discovery of new therapeutic approaches for managing pathologies associated with MMP-2 underactivity. Moreover, similar concepts could apply to other members of the matrix metalloproteinase family.

Impact of MMP-2 and MMP-9 enzyme activity on wound healing, tumor growth and RACPP cleavage

Matrix metalloproteinases-2 and -9 (MMP-2/-9) are key tissue remodeling enzymes that have multiple overlapping activities critical for wound healing and tumor progression in vivo. To overcome issues of redundancy in studying their functions in vivo, we created MMP-2/-9 double knockout (DKO) mice in the C57BL/6 background to examine wound healing. We then bred the DKO mice into the polyomavirus middle T (PyVmT) model of breast cancer to analyze the role of these enzymes in tumorigenesis. Breeding analyses indicated that significantly fewer DKO mice were born than predicted by Mendelian genetics and weaned DKO mice were growth compromised compared with wild type (WT) cohorts. Epithelial wound healing was dramatically delayed in adult DKO mice and when the DKO was combined with the PyVmT oncogene, we found that the biologically related process of mammary tumorigenesis was inhibited in a site-specific manner. To further examine the role of MMP-2/-9 in tumor progression, tumor cells derived from WT or DKO PyVmT transgenic tumors were grown in WT or DKO mice. Ratiometric activatable cell penetrating peptides (RACPPs) previously used to image cancer based on MMP-2/-9 activity were used to understand differences in MMP activity in WT or knockout syngeneic tumors in WT and KO animals. Analysis of an MMP-2 selective RACPP in WT or DKO mice bearing WT and DKO PyVmT tumor cells indicated that the genotype of the tumor cells was more important than the host stromal genotype in promoting MMP-2/-9 activity in the tumors in this model system. Additional complexities were revealed as the recruitment of host macrophages by the tumor cells was found to be the source of the tumor MMP-2/-9 activity and it is evident that MMP-2/-9 from both host and tumor is required for maximum signal using RACPP imaging for detection. We conclude that in the PyVmT model, the majority of MMP-2/-9 activity in mammary tumors is associated with host macrophages recruited into the tumor rather than that produced by the tumor cells themselves. Thus therapies that target tumor-associated macrophage functions have the potential to slow tumor progression.

Mapping novel genetic loci associated with female liver weight variations using Collaborative Cross mice

BACKGROUND

Liver weight is a complex trait, controlled by polygenic factors and differs within populations. Dissecting the genetic architecture underlying these variations will facilitate the search for key role candidate genes involved directly in the hepatomegaly process and indirectly involved in related diseases etiology.

METHODS

Liver weight of 506 mice generated from 39 different Collaborative Cross (CC) lines with both sexes at age 20 weeks old was determined using an electronic balance. Genomic DNA of the CC lines was genotyped with high-density single nucleotide polymorphic markers.

RESULTS

Statistical analysis revealed a significant (P < 0.05) variation of liver weight between the CC lines, with broad sense heritability (H 2) of 0.32 and genetic coefficient of variation (CVG) of 0.28. Subsequently, quantitative trait locus (QTL) mapping was performed, and results showed a significant QTL only for females on chromosome 8 at genomic interval 88.61-93.38 Mb (4.77 Mb). Three suggestive QTL were mapped at chromosomes 4, 12 and 13. The four QTL were designated as LWL1-LWL4 referring to liver weight loci 1-4 on chromosomes 8, 4, 12 and 13, respectively.

CONCLUSION

To our knowledge, this report presents, for the first time, the utilization of the CC for mapping QTL associated with baseline liver weight in mice. Our findings demonstrate that liver weight is a complex trait controlled by multiple genetic factors that differ significantly between sexes.

Cleavage of the leptin receptor by matrix metalloproteinase-2 promotes leptin resistance and obesity in mice

Obesity and related morbidities pose a major health threat. Obesity is associated with increased blood concentrations of the anorexigenic hormone leptin; however, obese individuals are resistant to its anorexigenic effects. We examined the phenomenon of reduced leptin signaling in a high-fat diet-induced obesity model in mice. Obesity promoted matrix metalloproteinase-2 (Mmp-2) activation in the hypothalamus, which cleaved the leptin receptor's extracellular domain and impaired leptin-mediated signaling. Deletion of Mmp-2 restored leptin receptor expression and reduced circulating leptin concentrations in obese mice. Lentiviral delivery of short hairpin RNA to silence Mmp-2 in the hypothalamus of wild-type mice prevented leptin receptor cleavage and reduced fat accumulation. In contrast, lentiviral delivery of Mmp-2 in the hypothalamus of Mmp-2-/- mice promoted leptin receptor cleavage and higher body weight. In a genetic mouse model of obesity, transduction of cleavage-resistant leptin receptor in the hypothalamus reduced the rate of weight gain compared to uninfected mice or mice infected with the wild-type receptor. Immunofluorescence analysis showed that astrocytes and agouti-related peptide neurons were responsible for Mmp-2 secretion in mice fed a high-fat diet. These results suggest a mechanism for leptin resistance through activation of Mmp-2 and subsequent cleavage of the extracellular domain of the leptin receptor.

Comparison of triadimefon and its metabolite on acute toxicity and chronic effects during the early development of Rana nigromaculata tadpoles

Pesticides are one of major causes for amphibian population declines and the behavior of pesticide metabolite products to amphibians has become a rising concern. In this study, the acute toxicity and the chronic effects of triadimefon and triadimenol (the metabolite of triadimefon) on Rana. nigromaculata were investigated. In the acute assay, significant differences were observed in antioxidant enzyme activities and malondialdehyde levels between the triadimefon and triadimenol. The 96 h-acute toxicity of triadimefon (25.97 mg/L) and triadimenol (34.55 mg/L) to tadpoles was low. In 28d-chronic exposure, we studied the relative expression of tadpoles genes related to thyroid hormone-dependent metamorphic development, histological examination of liver and some biological index, including wet weight, snout-to-vent length (SVL) and development stages. The results revealed that the effects of triadimefon and triadimenol on tadpole development are driven by a disruption of the hormonal pathways involved in metamorphosis. Interestingly, triadimefon was more harmful on R. nigromaculata than triadimenol at high dose, whereas the reverse result was observed at low doses. According to the relative expression of thyroid hormone-dependent genes, we also found that the two compounds may have different mechanisms of toxic action on R. nigromaculata. Our study developed a pragmatic approach for use in the risk assessment of pesticide and its metabolite，and increased the information and understanding of the impacts of fungicides and other potential endocrine disrupting environmental contaminants on amphibians.

Tracking the Cartoon mouse phenotype: Hemopexin domain-dependent regulation of MT1-MMP pericellular collagenolytic activity

Following ENU mutagenesis, a phenodeviant line was generated, termed the "Cartoon mouse," that exhibits profound defects in growth and development. Cartoon mice harbor a single S466P point mutation in the MT1-MMP hemopexin domain, a 200-amino acid segment that is thought to play a critical role in regulating MT1-MMP collagenolytic activity. Herein, we demonstrate that the MT1-MMP_S466P mutation replicates the phenotypic status of Mt1-mmp-null animals as well as the functional characteristics of MT1-MMP^-/- cells. However, rather than a loss-of-function mutation acquired as a consequence of defects in MT1-MMP proteolytic activity, the S466P substitution generates a misfolded, temperature-sensitive mutant that is abnormally retained in the endoplasmic reticulum (ER). By contrast, the WT hemopexin domain does not play a required role in regulating MT1-MMP trafficking, as a hemopexin domain-deletion mutant is successfully mobilized to the cell surface and displays nearly normal collagenolytic activity. Alternatively, when MT1-MMP_S466P-expressing cells are cultured at a permissive temperature of 25 °C that depresses misfolding, the mutant successfully traffics from the ER to the trans-Golgi network (ER → trans-Golgi network), where it undergoes processing to its mature form, mobilizes to the cell surface, and expresses type I collagenolytic activity. Together, these analyses define the Cartoon mouse as an unexpected gain-of-abnormal function mutation, wherein the temperature-sensitive mutant phenocopies MT1-MMP^-/- mice as a consequence of eliciting a specific ER → trans-Golgi network trafficking defect.

Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Inflammation and Fibrosis of Skeletal Muscles

In skeletal muscles, levels and activity of Matrix MetalloProteinases (MMPs) and Tissue Inhibitors of MetalloProteinases (TIMPs) have been involved in myoblast migration, fusion and various physiological and pathological remodeling situations including neuromuscular diseases. This has opened perspectives for the use of MMPs' overexpression to improve the efficiency of cell therapy in muscular dystrophies and resolve fibrosis. Alternatively, inhibition of individual MMPs in animal models of muscular dystrophies has provided evidence of beneficial, dual or adverse effects on muscle morphology or function. We review here the role played by MMPs/TIMPs in skeletal muscle inflammation and fibrosis, two major hurdles that limit the success of cell and gene therapy. We report and analyze the consequences of genetic or pharmacological modulation of MMP levels on the inflammation of skeletal muscles and their repair in light of experimental findings. We further discuss how the interplay between MMPs/TIMPs levels, cytokines/chemokines, growth factors and permanent low-grade inflammation favor cellular and molecular modifications resulting in fibrosis.

Cleavage of β-dystroglycan occurs in sarcoglycan-deficient skeletal muscle without MMP-2 and MMP-9

BACKGROUND

The dystroglycan complex consists of two subunits: extracellular α-dystroglycan and membrane-spanning β-dystroglycan, which provide a tight link between the extracellular matrix and the intracellular cytoskeleton. Previous studies showed that 43 kDa β-dystroglycan is proteolytically cleaved into the 30 kDa fragment by matrix metalloproteinases (MMPs) in various non-muscle tissues, whereas it is protected from cleavage in muscles by the sarcoglycan complex which resides close to the dystroglycan complex. It is noteworthy that cleaved β-dystroglycan is detected in muscles from patients with sarcoglycanopathy, sarcoglycan-deficient muscular dystrophy. In vitro assays using protease inhibitors suggest that both MMP-2 and MMP-9 contribute to the cleavage of β-dystroglycan. However, this has remained uninvestigated in vivo.

METHODS

We generated triple-knockout (TKO) mice targeting MMP-2, MMP-9 and γ-sarcoglycan to examine the status of β-dystroglycan cleavage in the absence of the candidate matrix metalloproteinases in sarcoglycan-deficient muscles.

RESULTS

Unexpectedly, β-dystroglycan was cleaved in muscles from TKO mice. Muscle pathology was not ameliorated but worsened in TKO mice compared with γ-sarcoglycan single-knockout mice. The gene expression of MMP-14 was up-regulated in TKO mice as well as in γ-sarcoglycan knockout mice. In vitro assay showed MMP-14 is capable to cleave β-dystroglycan.

CONCLUSIONS

Double-targeting of MMP-2 and MMP-9 cannot prevent cleavage of β-dystroglycan in sarcoglycanopathy. Thus, matrix metalloproteinases contributing to β-dystroglycan cleavage are redundant, and MMP-14 could participate in the pathogenesis of sarcoglycanopathy.

Regulation of RhoA by STAT3 coordinates glial scar formation

The transcription factor STAT3 is known to control glial scar formation, but the underlying mechanism is unknown. Renault-Mihara et al. show that inhibition of the small GTPase RhoA by STAT3 coordinates reactive astrocyte dynamics during glial scar formation.

Understanding how the transcription factor signal transducer and activator of transcription–3 (STAT3) controls glial scar formation may have important clinical implications. We show that astrocytic STAT3 is associated with greater amounts of secreted MMP2, a crucial protease in scar formation. Moreover, we report that STAT3 inhibits the small GTPase RhoA and thereby controls actomyosin tonus, adhesion turnover, and migration of reactive astrocytes, as well as corralling of leukocytes in vitro. The inhibition of RhoA by STAT3 involves ezrin, the phosphorylation of which is reduced in STAT3-CKO astrocytes. Reduction of phosphatase and tensin homologue (PTEN) levels in STAT3-CKO rescues reactive astrocytes dynamics in vitro. By specific targeting of lesion-proximal, reactive astrocytes in Nestin-Cre mice, we show that reduction of PTEN rescues glial scar formation in Nestin-Stat3^+/− mice. These findings reveal novel intracellular signaling mechanisms underlying the contribution of reactive astrocyte dynamics to glial scar formation.

Genetic specification of left-right asymmetry in the diaphragm muscles and their motor innervation

The diaphragm muscle is essential for breathing in mammals. Its asymmetric elevation during contraction correlates with morphological features suggestive of inherent left–right (L/R) asymmetry. Whether this asymmetry is due to L versus R differences in the muscle or in the phrenic nerve activity is unknown. Here, we have combined the analysis of genetically modified mouse models with transcriptomic analysis to show that both the diaphragm muscle and phrenic nerves have asymmetries, which can be established independently of each other during early embryogenesis in pathway instructed by Nodal, a morphogen that also conveys asymmetry in other organs. We further found that phrenic motoneurons receive an early L/R genetic imprint, with L versus R differences both in Slit/Robo signaling and MMP2 activity and in the contribution of both pathways to establish phrenic nerve asymmetry. Our study therefore demonstrates L–R imprinting of spinal motoneurons and describes how L/R modulation of axon guidance signaling helps to match neural circuit formation to organ asymmetry.

DOI:http://dx.doi.org/10.7554/eLife.18481.001

The diaphragm is a dome-shaped muscle that forms the floor of the rib cage, separating the lungs from the abdomen. As we breathe in, the diaphragm contracts. This causes the chest cavity to expand, drawing air into the lungs. A pair of nerves called the phrenic nerves carry signals from the spinal cord to the diaphragm to tell it when to contract. These nerves project from the left and right sides of the spinal cord to the left and right sides of the diaphragm respectively.

The left and right sides of the diaphragm are not entirely level, but it was not known why. To investigate, Charoy et al. studied how the diaphragm develops in mouse embryos. This revealed that the left and right phrenic nerves are not symmetrical. Neither are the muscles on each side of the diaphragm. Further investigation revealed that a genetic program that establishes other differences between the left and right sides of the embryo also gives rise to the differences between the left and right sides of the diaphragm. This program switches on different genes in the left and right phrenic nerves, which activate different molecular pathways in the left and right sides of the diaphragm muscle.

The differences between the nerves and muscles on the left and right sides of the diaphragm could explain why some muscle disorders affect only one side of the diaphragm. Similarly, they could explain why congenital hernias caused by abdominal organs pushing through the diaphragm into the chest cavity mostly affect the left side of the diaphragm. Further studies are now needed to investigate these possibilities. The techniques used by Charoy et al. to map the molecular diversity of spinal cord neurons could also lead to new strategies for repairing damage to the spinal cord following injury or disease.

DOI:http://dx.doi.org/10.7554/eLife.18481.002

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

Non-apoptotic cell death in animal development

Programmed cell death (PCD) is an important process in the development of multicellular organisms. Apoptosis, a form of PCD characterized morphologically by chromatin condensation, membrane blebbing, and cytoplasm compaction, and molecularly by the activation of caspase proteases, has been extensively investigated. Studies in Caenorhabditis elegans, Drosophila, mice, and the developing chick have revealed, however, that developmental PCD also occurs through other mechanisms, morphologically and molecularly distinct from apoptosis. Some non-apoptotic PCD pathways, including those regulating germ cell death in Drosophila, still appear to employ caspases. However, another prominent cell death program, linker cell-type death (LCD), is morphologically conserved, and independent of the key genes that drive apoptosis, functioning, at least in part, through the ubiquitin proteasome system. These non-apoptotic processes may serve as backup programs when caspases are inactivated or unavailable, or, more likely, as freestanding cell culling programs. Non-apoptotic PCD has been documented extensively in the developing nervous system, and during the formation of germline and somatic gonadal structures, suggesting that preservation of these mechanisms is likely under strong selective pressure. Here, we discuss our current understanding of non-apoptotic PCD in animal development, and explore possible roles for LCD and other non-apoptotic developmental pathways in vertebrates. We raise the possibility that during vertebrate development, apoptosis may not be the major PCD mechanism.

Fibrillin-2 Degradation by Matrix Metalloproteinase-2 in Periodontium

Elastic system fibers, comprised of microfibrils and tropoelastin, are extracellular components of periodontal tissue. During development, the microfibrils act as a template on which tropoelastin is deposited. However, the process of elastic system fiber remodeling is not fully understood. Therefore, we examined whether matrix metalloproteinases (MMPs) are involved in the remodeling of fibrillins (major components of microfibrils) by human gingival fibroblasts and periodontal ligament (PDL) fibroblasts. Gingival and PDL fibroblasts were cultured for 6 weeks. In some cultures, MMP inhibitor or tissue inhibitor of matrix metalloproteinsase-2 (TIMP-2) was added to the medium for an additional 2 weeks. Active MMP-2 (62 kDa) appeared as cell-membrane-associated or in extracellular matrix only in PDL fibroblast cell layers. The addition of MMP inhibitor or TIMP-2 significantly increased fibrillin-2 accumulation in PDL fibroblast cell layers, and decreased the amount of fibrillin-2 fragments, suggesting that active MMP-2 may degrade fibrillin-2, and that MMPs may play a role in the remodeling of elastic system fibers in PDL.

Functional roles of MMP14 and MMP15 in early postnatal mammary gland development

During late embryogenesis, mammary epithelial cells initiate migration programs that drive ductal invasion into the surrounding adipose-rich mesenchyme. Currently, branching morphogenesis is thought to depend on the mobilization of the membrane-anchored matrix metalloproteinases MMP14 (MT1-MMP) and MMP15 (MT2-MMP), which drive epithelial cell invasion by remodeling the extracellular matrix and triggering associated signaling cascades. However, the roles that these proteinases play during mammary gland development in vivo remain undefined. Here, we characterize the impact of global Mmp14 and Mmp15 targeting on early postnatal mammary gland development in mice. Unexpectedly, both Mmp14^-/- and Mmp15^-/- mammary glands retain the ability to generate intact ductal networks. Although neither proteinase is required for branching morphogenesis, transcriptome profiling reveals a key role for MMP14 and MMP15 in regulating mammary gland adipocyte differentiation. Whereas MMP14 promotes the generation of white fat depots crucial for energy storage, MMP15 differentially controls the formation of thermogenic brown fat. Taken together, these data not only indicate that current paradigms relevant to proteinase-dependent morphogenesis need be revisited, but also identify new roles for the enzymes in regulating adipocyte fate determination in the developing mammary gland.

Deficiency in matrix metalloproteinase-2 results in long-term vascular instability and regression in the injured mouse spinal cord

Angiogenesis plays a critical role in wound healing after spinal cord injury. Therefore, understanding the events that regulate angiogenesis has considerable relevance from a therapeutic standpoint. We evaluated the contribution of matrix metalloproteinase (MMP)-2 to angiogenesis and vascular stability in spinal cord injured MMP-2 knockout and wildtype (WT) littermates. While MMP-2 deficiency resulted in reduced endothelial cell division within the lesioned epicenter, there were no genotypic differences in vascularity (vascular density, vascular area, and endothelial cell number) over the first two weeks post-injury. However, by 21days post-injury MMP-2 deficiency resulted in a sharp decline in vascularity, indicative of vascular regression. Complementary in vitro studies of brain capillary endothelial cells confirmed MMP-2 dependent proliferation and tube formation. As deficiency in MMP-2 led to prolonged MMP-9 expression in the injured spinal cord, we examined both short-term and long-term exposure to MMP-9 in vitro. While MMP-9 supported endothelial tube formation and proliferation, prolonged exposure resulted in loss of tubes, findings consistent with vascular regression. Vascular instability is frequently associated with pericyte dissociation and precedes vascular regression. Quantification of PDGFrβ+ pericyte coverage of mature vessels within the glial scar (the reactive gliosis zone), a known source of MMP-9, revealed reduced coverage in MMP-2 deficient animals. These findings suggest that acting in the absence of MMP-2, MMP-9 transiently supports angiogenesis during the early phase of wound healing while its prolonged expression leads to vascular instability and regression. These findings should be considered while developing therapeutic interventions that block MMPs.

The High Mobility Group A1 (HMGA1) gene is highly overexpressed in human uterine serous carcinomas and carcinosarcomas and drives Matrix Metalloproteinase-2 (MMP-2) in a subset of tumors

OBJECTIVES

Although uterine cancer is the fourth most common cause for cancer death in women worldwide, the molecular underpinnings of tumor progression remain poorly understood. The High Mobility Group A1 (HMGA1) gene is overexpressed in aggressive cancers and high levels portend adverse outcomes in diverse tumors. We previously reported that Hmga1a transgenic mice develop uterine tumors with complete penetrance. Because HMGA1 drives tumor progression by inducing MatrixMetalloproteinase (MMP) and other genes involved in invasion, we explored the HMGA1-MMP-2 pathway in uterine cancer.

METHODS

To investigate MMP-2 in uterine tumors driven by HMGA1, we used a genetic approach with mouse models. Next, we assessed HMGA1 and MMP-2 expression in primary human uterine tumors, including low-grade carcinomas (endometrial endometrioid) and more aggressive tumors (endometrial serous carcinomas, uterine carcinosarcomas/malignant mesodermal mixed tumors).

RESULTS

Here, we report for the first time that uterine tumor growth is impaired in Hmga1a transgenic mice crossed on to an Mmp-2 deficient background. In human tumors, we discovered that HMGA1 is highest in aggressive carcinosarcomas and serous carcinomas, with lower levels in the more indolent endometrioid carcinomas. Moreover, HMGA1 and MMP-2 were positively correlated, but only in a subset of carcinosarcomas. HMGA1 also occupies the MMP-2 promoter in human carcinosarcoma cells.

CONCLUSIONS

Together, our studies define a novel HMGA1-MMP-2 pathway involved in a subset of human carcinosarcomas and tumor progression in murine models. Our work also suggests that targeting HMGA1 could be effective adjuvant therapy for more aggressive uterine cancers and provides compelling data for further preclinical studies.

Matrix metalloproteinases as therapeutic targets for idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a restrictive lung disease that is associated with high morbidity and mortality. Current medical therapies are not fully effective at limiting mortality in patients with IPF, and new therapies are urgently needed. Matrix metalloproteinases (MMPs) are proteinases that, together, can degrade all components of the extracellular matrix and numerous nonmatrix proteins. MMPs and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the pathogenesis of IPF based upon the results of clinical studies reporting elevated levels of MMPs (including MMP-1, MMP-7, MMP-8, and MMP-9) in IPF blood and/or lung samples. Surprisingly, studies of gene-targeted mice in murine models of pulmonary fibrosis (PF) have demonstrated that most MMPs promote (rather than inhibit) the development of PF and have identified diverse mechanisms involved. These mechanisms include MMPs: (1) promoting epithelial-to-mesenchymal transition (MMP-3 and MMP-7); (2) increasing lung levels or activity of profibrotic mediators or reducing lung levels of antifibrotic mediators (MMP-3, MMP-7, and MMP-8); (3) promoting abnormal epithelial cell migration and other aberrant repair processes (MMP-3 and MMP-9); (4) inducing the switching of lung macrophage phenotypes from M1 to M2 types (MMP-10 and MMP-28); and (5) promoting fibrocyte migration (MMP-8). Two MMPs, MMP-13 and MMP-19, have antifibrotic activities in murine models of PF, and two MMPs, MMP-1 and MMP-10, have the potential to limit fibrotic responses to injury. Herein, we review what is known about the contributions of MMPs and TIMPs to the pathogenesis of IPF and discuss their potential as therapeutic targets for IPF.

Matrix Metalloproteinase-2 Knockout and Heterozygote Mice Are Protected from Hydronephrosis and Kidney Fibrosis after Unilateral Ureteral Obstruction

Matrix Metalloproteinase-2 (Mmp2) is a collagenase known to be important in the development of renal fibrosis. In unilateral ureteral obstruction (UUO) the obstructed kidney (OK) develops fibrosis, while the contralateral (CL) does not. In this study we investigated the effect of UUO on gene expression, fibrosis and pelvic remodeling in the kidneys of Mmp2 deficient mice (Mmp2-/-), heterozygous animals (Mmp2+/-) and wild-type mice (Mmp2+/+). Sham operated animals served as controls (Cntrl). UUO was prepared under isoflurane anaesthesia, and the animals were sacrificed after one week. UUO caused hydronephrosis, dilation of renal tubules, loss of parenchymal thickness, and fibrosis. Damage was most severe in Mmp2+/+ mice, while both Mmp2-/- and Mmp2+/- groups showed considerably milder hydronephrosis, no tubular necrosis, and less tubular dilation. Picrosirius red quantification of fibrous collagen showed 1.63±0.25% positivity in OK and 0.29±0.11% in CL (p<0.05) of Mmp2+/+, Mmp2-/- OK and Mmp2-/- CL exhibited only 0.49±0.09% and 0.23±0.04% (p<0.05) positivity, respectively. Mmp2+/- OK and Mmp2+/- CL showed 0.43±0.09% and 0.22±0.06% (p<0.05) positivity, respectively. Transcriptomic analysis showed that 26 genes (out of 48 examined) were differentially expressed by ANOVA (p<0.05). 25 genes were upregulated in Mmp2+/+ OK compared to Mmp2+/+ CL: Adamts1, -2, Col1a1, -2, -3a1, -4a1, -5a1, -5a2, Dcn, Fbln1, -5, Fmod, Fn1, Itga2, Loxl1, Mgp, Mmp2, -3, Nid1, Pdgfb, Spp1, Tgfb1, Timp2, Trf, Vim. In Mmp2-/- and Mmp2+/- 18 and 12 genes were expressed differentially between OK and CL, respectively. Only Mmp2 was differentially regulated when comparing Mmp2-/- OK and Mmp2+/- OK. Under stress, it appears that Mmp2+/- OK responds with less Mmp2 upregulation than Mmp2+/+ OK, suggesting that there is a threshold level of Mmp2 necessary for damage and fibrosis to occur. In conclusion, reduced Mmp2 expression during UUO protects mice against hydronephrosis and renal fibrosis.

Matrix metalloproteinase 14 is required for fibrous tissue expansion

Type I collagen-containing fibrils are major structural components of the extracellular matrix of vertebrate tissues, especially tendon, but how they are formed is not fully understood. MMP14 is a potent pericellular collagenase that can cleave type I collagen in vitro. In this study, we show that tendon development is arrested in Scleraxis-Cre::Mmp14 lox/lox mice that are unable to release collagen fibrils from plasma membrane fibripositors. In contrast to its role in collagen turnover in adult tissue, MMP14 promotes embryonic tissue formation by releasing collagen fibrils from the cell surface. Notably, the tendons grow to normal size and collagen fibril release from fibripositors occurs in Col-r/r mice that have a mutated collagen-I that is uncleavable by MMPs. Furthermore, fibronectin (not collagen-I) accumulates in the tendons of Mmp14-null mice. We propose a model for cell-regulated collagen fibril assembly during tendon development in which MMP14 cleaves a molecular bridge tethering collagen fibrils to the plasma membrane of fibripositors.

DOI:http://dx.doi.org/10.7554/eLife.09345.001

A scaffold of proteins called the extracellular matrix surrounds each of the cells that make up our organs and tissues. This matrix, which contains fibres made of proteins called collagens, provides the physical support needed to hold organs and tissues together. This support is especially important in the tendons—a tough tissue that connects the muscle to bone—and other ‘connective’ tissues.

An enzyme called MMP14 is able to cut through chains of collagen proteins. It belongs to a family of proteins that are involved in breaking down the extracellular matrix to enable cells to divide and for other important processes in cells. Some cancer cells exploit MMP14 to enable them to leave their tissue of origin and spread around the body. Therefore, when researchers bred mutant mice that lacked MMP14, they expected to see excessive growth of collagen fibres in the connective tissues of the mice. However, these mice actually have extremely thin, fragile connective tissue and die soon after birth.

Earlier in 2015, a group of researchers demonstrated that the first stage of tendon development in mice involves the formation of collagen fibres, which are attached to structures that project from tendon cells called fibripositors. Then, soon after the mice are born, the fibripositors disappear and the collagen fibres are released into the extracellular matrix where they grow longer and become thicker. Now, Taylor, Yeung, Kalson et al.—including some of the researchers from the earlier work—have used electron microscopy to investigate how a lack of MMP14 leads to fragile tendons in young mice.

The experiments show that MMP14 plays a crucial role in the first stage of tendon development by detaching the collagen fibres from the fibripositors. MMP14 also promotes the formation of new collagen fibres; the tendons of mutant mice that lack MMP14 have fewer collagen fibres than normal mice. Further experiments revealed that the release of collagen fibres from fibripositors does not require MMP14 to cleave the chains of collagen proteins themselves. Instead, it appears that MMP14 cleaves another protein that is associated with the fibres, called fibronectin.

Taylor, Yeung, Kalson et al.'s findings show that MMP14 plays an important role in the development of tendons by releasing collagen fibres from fibripositors and promoting the formation of new fibres. The next challenge is to find out how MMP14 regulates the number of collagen fibres in mature tendons and other tissues, and how defects in this enzyme can lead to cancer and other diseases.

DOI:http://dx.doi.org/10.7554/eLife.09345.002

Decreased TNF Levels and Improved Retinal Ganglion Cell Survival in MMP-2 Null Mice Suggest a Role for MMP-2 as TNF Sheddase

Matrix metalloproteinases (MMPs) have been designated as both friend and foe in the central nervous system (CNS): while being involved in many neurodegenerative and neuroinflammatory diseases, their actions appear to be indispensable to a healthy CNS. Pathological conditions in the CNS are therefore often related to imbalanced MMP activities and disturbances of the complex MMP-dependent protease network. Likewise, in the retina, various studies in animal models and human patients suggested MMPs to be involved in glaucoma. In this study, we sought to determine the spatiotemporal expression profile of MMP-2 in the excitotoxic retina and to unravel its role during glaucoma pathogenesis. We reveal that intravitreal NMDA injection induces MMP-2 expression to be upregulated in the Müller glia. Moreover, MMP-2 null mice display attenuated retinal ganglion cell death upon excitotoxic insult to the retina, which is accompanied by normal glial reactivity, yet reduced TNF levels. Hence, we propose a novel in vivo function for MMP-2, as an activating sheddase of tumor necrosis factor (TNF). Given the pivotal role of TNF as a proinflammatory cytokine and neurodegeneration-exacerbating mediator, these findings generate important novel insights into the pathological processes contributing to glaucomatous neurodegeneration and into the interplay of neuroinflammation and neurodegeneration in the CNS.

Matrix Metalloproteinase-2 (MMP-2) Gene Deletion Enhances MMP-9 Activity, Impairs PARP-1 Degradation, and Exacerbates Hepatic Ischemia and Reperfusion Injury in Mice

Hepatic ischemia and reperfusion injury (IRI) is an inflammatory condition and a significant cause of morbidity and mortality after surgery. Matrix metalloproteinases (MMPs) have been widely implicated in the pathogenesis of inflammatory diseases. Among the different MMPs, gelatinases (MMP-2 and MMP-9) are within the most prominent MMPs detected during liver IRI. While the role of MMP-9 in liver damage has been fairly documented, direct evidence of the role for MMP-2 activity in hepatic IRI remains to be established. Due to the lack of suitable inhibitors to target individual MMPs in vivo, gene manipulation is as an essential tool to assess MMP direct contribution to liver injury. Hence, we used MMP-2^-/- deficient mice and MMP-2^+/+ wild-type littermates to examine the function of MMP-2 activity in hepatic IRI. MMP-2 expression was detected along the sinusoids of wild-type livers before and after surgery and in a small population of leukocytes post-IRI. Compared to MMP-2^+/+ mice, MMP-2 null (MMP-2^-/-) mice showed exacerbated liver damage at 6, 24, and 48 hours post-reperfusion, which was fatal in some cases. MMP-2 deficiency resulted in upregulation of MMP-9 activity, spontaneous leukocyte infiltration in naïve livers, and amplified MMP-9-dependent transmigration of leukocytes in vitro and after hepatic IRI. Moreover, complete loss of MMP-2 activity impaired the degradation of poly (ADP-ribose) polymerase (PARP-1) in extensively damaged livers post-reperfusion. However, the administration of a PARP-1 inhibitor to MMP-2 null mice restored liver preservation to almost comparable levels of MMP-2^+/+ mice post-IRI. Deficient PARP-1 degradation in MMP-2-null sinusoidal endothelial cells correlated with their increased cytotoxicity, evaluated by the measurement of LDH efflux in the medium. In conclusion, our results show for the first time that MMP-2 gene deletion exacerbates liver IRI. Moreover, they offer new insights into the MMP-2 modulation of inflammatory responses, which could be relevant for the design of new pharmacological MMP-targeted agents to treat hepatic IRI.