The first stage of transforming growth factor beta1 activation is release of the large latent complex from the extracellular matrix of growth plate chondrocytes by matrix vesicle stromelysin-1 (MMP-3)

TGF-β as a therapeutic target in the infarcted and failing heart: cellular mechanisms, challenges, and opportunities

INTRODUCTION

Myocardial fibrosis accompanies most cardiac conditions and can be reparative or maladaptive. Transforming Growth Factor (TGF)-β is a potent fibrogenic mediator, involved in repair, remodeling, and fibrosis of the injured heart.

AREAS COVERED

This review manuscript discusses the role of TGF-β in heart failure focusing on cellular mechanisms and therapeutic implications. TGF-β is activated in infarcted, remodeling and failing hearts. In addition to its fibrogenic actions, TGF-β has a broad range of effects on cardiomyocytes, immune, and vascular cells that may have both protective and detrimental consequences. TGF-β-mediated effects on macrophages promote anti-inflammatory transition, whereas actions on fibroblasts mediate reparative scar formation and effects on pericytes are involved in maturation of infarct neovessels. On the other hand, TGF-β actions on cardiomyocytes promote adverse remodeling, and prolonged activation of TGF-β signaling in fibroblasts stimulates progression of fibrosis and heart failure.

EXPERT OPINION

Understanding of the cell-specific actions of TGF-β is necessary to design therapeutic strategies in patients with myocardial disease. Moreover, to implement therapeutic interventions in the heterogeneous population of heart failure patients, mechanism-driven classification of both HFrEF and HFpEF patients is needed. Heart failure patients with prolonged or overactive fibrogenic TGF-β responses may benefit from cautious TGF-β inhibition.

Plasma matrix metalloproteinase-3 predicts mortality in acute respiratory distress syndrome: a biomarker analysis of a randomized controlled trial

BACKGROUND

Matrix metalloproteinase-3 (MMP-3) is a proteolytic enzyme involved in acute respiratory distress syndrome (ARDS) pathophysiology that may serve as a lung-specific biomarker in ARDS.

METHODS

This study was a secondary biomarker analysis of a subset of Albuterol for the Treatment of Acute Lung Injury (ALTA) trial patients to determine the prognostic value of MMP-3. Plasma sample MMP-3 was measured by enzyme-linked immunosorbent assay. The primary outcome was the area under the receiver operating characteristic (AUROC) of MMP-3 at day 3 for the prediction of 90-day mortality.

RESULTS

A total of 100 unique patient samples were evaluated and the AUROC analysis of day three MMP-3 showed an AUROC of 0.77 for the prediction of 90-day mortality (95% confidence interval: 0.67-0.87), corresponding to a sensitivity of 92% and specificity of 63% and an optimal cutoff value of 18.4 ng/mL. Patients in the high MMP-3 group (≥ 18.4 ng/mL) showed higher mortality compared to the non-elevated MMP-3 group (< 18.4 ng/mL) (47% vs. 4%, p < 0.001). A positive difference in day zero and day three MMP-3 concentration was predictive of mortality with an AUROC of 0.74 correlating to 73% sensitivity, 81% specificity, and an optimal cutoff value of + 9.5 ng/mL.

CONCLUSIONS

Day three MMP-3 concentration and difference in day zero and three MMP-3 concentrations demonstrated acceptable AUROCs for predicting 90-day mortality with a cut-point of 18.4 ng/mL and + 9.5 ng/mL, respectively. These results suggest a prognostic role of MMP-3 in ARDS.

Fibroblasts-Warriors at the Intersection of Wound Healing and Disrepair

Wound healing is triggered by inflammation elicited after tissue injury. Mesenchymal cells, specifically fibroblasts, accumulate in the injured tissues, where they engage in tissue repair through the expression and assembly of extracellular matrices that provide a scaffold for cell adhesion, the re-epithelialization of tissues, the production of soluble bioactive mediators that promote cellular recruitment and differentiation, and the regulation of immune responses. If appropriately deployed, these processes promote adaptive repair, resulting in the preservation of the tissue structure and function. Conversely, the dysregulation of these processes leads to maladaptive repair or disrepair, which causes tissue destruction and a loss of organ function. Thus, fibroblasts not only serve as structural cells that maintain tissue integrity, but are key effector cells in the process of wound healing. The review will discuss the general concepts about the origins and heterogeneity of this cell population and highlight the specific fibroblast functions disrupted in human disease. Finally, the review will explore the role of fibroblasts in tissue disrepair, with special attention to the lung, the role of aging, and how alterations in the fibroblast phenotype underpin disorders characterized by pulmonary fibrosis.

Extracellular Targets to Reduce Excessive Scarring in Response to Tissue Injury

Excessive scar formation is a hallmark of localized and systemic fibrotic disorders. Despite extensive studies to define valid anti-fibrotic targets and develop effective therapeutics, progressive fibrosis remains a significant medical problem. Regardless of the injury type or location of wounded tissue, excessive production and accumulation of collagen-rich extracellular matrix is the common denominator of all fibrotic disorders. A long-standing dogma was that anti-fibrotic approaches should focus on overall intracellular processes that drive fibrotic scarring. Because of the poor outcomes of these approaches, scientific efforts now focus on regulating the extracellular components of fibrotic tissues. Crucial extracellular players include cellular receptors of matrix components, macromolecules that form the matrix architecture, auxiliary proteins that facilitate the formation of stiff scar tissue, matricellular proteins, and extracellular vesicles that modulate matrix homeostasis. This review summarizes studies targeting the extracellular aspects of fibrotic tissue synthesis, presents the rationale for these studies, and discusses the progress and limitations of current extracellular approaches to limit fibrotic healing.

Role of MMP3 and fibroblast-MMP14 in skin homeostasis and repair

Early lethality of mice with complete deletion of the matrix metalloproteinase MMP14 emphasized the proteases' pleiotropic functions. MMP14 deletion in adult dermal fibroblasts (MMP14^Sf-/-) caused collagen type I accumulation and upregulation of MMP3 expression. To identify the compensatory role of MMP3, mice were generated with MMP3 deletion in addition to MMP14 loss in fibroblasts. These double deficient mice displayed a fibrotic phenotype in skin and tendons as detected in MMP14^Sf-/- mice, but no additional obvious defects were detected. However, challenging the mice with full thickness excision wounds resulted in delayed closure of early wounds in the double deficient mice compared to wildtype and MMP14 single knockout controls. Over time wounds closed and epidermal integrity was restored. Interestingly, on day seven, post-wounding myofibroblast density was lower in the wounds of all knockout than in controls, they were higher on day 14. The delayed resolution of myofibroblasts from the granulation tissue is paralleled by reduced apoptosis of these cells, although proliferation of myofibroblasts is induced in the double deficient mice. Further analysis showed comparable TGFβ1 and TGFβR1 expression among all genotypes. In addition, in vitro, fibroblasts lacking MMP3 and MMP14 retained their ability to differentiate into myofibroblasts in response to TGFβ1 treatment and mechanical stress. However, in vivo, p-Smad2 was reduced in myofibroblasts at day 5 post-wounding, in double, but most significant in single knockout, indicating their involvement in TGFβ1 activation. Thus, although MMP3 does not compensate for the lack of fibroblast-MMP14 in tissue homeostasis, simultaneous deletion of both proteases in fibroblasts delays wound closure during skin repair. Notably, single and double deficiency of these proteases modulates myofibroblast formation and resolution in wounds.

Matrix Metalloproteinases and Their Inhibitors in Pulmonary Fibrosis: EMMPRIN/CD147 Comes into Play

Pulmonary fibrosis (PF) is characterized by aberrant extracellular matrix (ECM) deposition, activation of fibroblasts to myofibroblasts and parenchymal disorganization, which have an impact on the biomechanical traits of the lung. In this context, the balance between matrix metalloproteinases (MMPs) and their tissue inhibitors of metalloproteinases (TIMPs) is lost. Interestingly, several MMPs are overexpressed during PF and exhibit a clear profibrotic role (MMP-2, -3, -8, -11, -12 and -28), but a few are antifibrotic (MMP-19), have both profibrotic and antifibrotic capacity (MMP7), or execute an unclear (MMP-1, -9, -10, -13, -14) or unknown function. TIMPs are also overexpressed in PF; hence, the modulation and function of MMPs and TIMP are more complex than expected. EMMPRIN/CD147 (also known as basigin) is a transmembrane glycoprotein from the immunoglobulin superfamily (IgSF) that was first described to induce MMP activity in fibroblasts. It also interacts with other molecules to execute non-related MMP aactions well-described in cancer progression, migration, and invasion. Emerging evidence strongly suggests that CD147 plays a key role in PF not only by MMP induction but also by stimulating fibroblast myofibroblast transition. In this review, we study the structure and function of MMPs, TIMPs and CD147 in PF and their complex crosstalk between them.

Research progress on drugs targeting the TGF-β signaling pathway in fibrotic diseases

Tissue fibrosis is a key factor leading to disability and death worldwide; however, thus far, there are no approved treatments for fibrosis. Transforming growth factor (TGF)-β is a major pro-fibrotic cytokine, which is expected to become a target in the treatment of fibrosis; however, since TGF-β has a wide range of biological functions involving a variety of biological processes in the body, a slight change in TGF-β may have a systematic effect. Indiscriminate inhibition of TGF-β can lead to adverse reactions, which can affect the efficacy of treatment. Therefore, it has become very important to explore how both the TGF-β signaling pathway is inhibited and the safe and efficient TGF-β small molecule inhibitors or neutralizing antibodies are designed in the treatment of fibrotic diseases. In this review, we mainly discuss the key role of the TGF-β signaling pathway in fibrotic diseases, as well as the development of fibrotic drugs in recent years, and explore potential targets in the treatment of fibrotic diseases in order to guide subsequent drug development.

Decellularized Colorectal Cancer Matrices as Bioactive Scaffolds for Studying Tumor-Stroma Interactions

More than a physical structure providing support to tissues, the extracellular matrix (ECM) is a complex and dynamic network of macromolecules that modulates the behavior of both cancer cells and associated stromal cells of the tumor microenvironment (TME). Over the last few years, several efforts have been made to develop new models that accurately mimic the interconnections within the TME and specifically the biomechanical and biomolecular complexity of the tumor ECM. Particularly in colorectal cancer, the ECM is highly remodeled and disorganized and constitutes a key component that affects cancer hallmarks, such as cell differentiation, proliferation, angiogenesis, invasion and metastasis. Therefore, several scaffolds produced from natural and/or synthetic polymers and ceramics have been used in 3D biomimetic strategies for colorectal cancer research. Nevertheless, decellularized ECM from colorectal tumors is a unique model that offers the maintenance of native ECM architecture and molecular composition. This review will focus on innovative and advanced 3D-based models of decellularized ECM as high-throughput strategies in colorectal cancer research that potentially fill some of the gaps between in vitro 2D and in vivo models. Our aim is to highlight the need for strategies that accurately mimic the TME for precision medicine and for studying the pathophysiology of the disease.

Transforming growth factor-β in myocardial disease

Transforming growth factor-β (TGFβ) isoforms are upregulated and activated in myocardial diseases and have an important role in cardiac repair and remodelling, regulating the phenotype and function of cardiomyocytes, fibroblasts, immune cells and vascular cells. Cardiac injury triggers the generation of bioactive TGFβ from latent stores, through mechanisms involving proteases, integrins and specialized extracellular matrix (ECM) proteins. Activated TGFβ signals through the SMAD intracellular effectors or through non-SMAD cascades. In the infarcted heart, the anti-inflammatory and fibroblast-activating actions of TGFβ have an important role in repair; however, excessive or prolonged TGFβ signalling accentuates adverse remodelling, contributing to cardiac dysfunction. Cardiac pressure overload also activates TGFβ cascades, which initially can have a protective role, promoting an ECM-preserving phenotype in fibroblasts and preventing the generation of injurious, pro-inflammatory ECM fragments. However, prolonged and overactive TGFβ signalling in pressure-overloaded cardiomyocytes and fibroblasts can promote cardiac fibrosis and dysfunction. In the atria, TGFβ-mediated fibrosis can contribute to the pathogenic substrate for atrial fibrillation. Overactive or dysregulated TGFβ responses have also been implicated in cardiac ageing and in the pathogenesis of diabetic, genetic and inflammatory cardiomyopathies. This Review summarizes the current evidence on the role of TGFβ signalling in myocardial diseases, focusing on cellular targets and molecular mechanisms, and discussing challenges and opportunities for therapeutic translation.

Matrix metalloproteinases inhibitors in idiopathic pulmonary fibrosis: Medicinal chemistry perspectives

Idiopathic pulmonary fibrosis (IPF) is a lethal disease with limited therapeutic options and a particularly poor prognosis. Matrix metalloproteinases (MMPs), promising targets for the treatment of IPF, have been identified as playing a pivotal role in IPF. Although the pathological processes of MMPs and IPF have been verified, there are no MMP inhibitors for the treatment of IPF in the clinic. In this review, we will present the latest developments in MMP inhibitors, including pharmacophores, binding modes, selectivity and optimization strategies. In addition, we will also discuss the future development direction of MMP inhibitors based on emerging tools and techniques.

Extracellular matrix and its therapeutic potential for cancer treatment

The extracellular matrix (ECM) is one of the major components of tumors that plays multiple crucial roles, including mechanical support, modulation of the microenvironment, and a source of signaling molecules. The quantity and cross-linking status of ECM components are major factors determining tissue stiffness. During tumorigenesis, the interplay between cancer cells and the tumor microenvironment (TME) often results in the stiffness of the ECM, leading to aberrant mechanotransduction and further malignant transformation. Therefore, a comprehensive understanding of ECM dysregulation in the TME would contribute to the discovery of promising therapeutic targets for cancer treatment. Herein, we summarized the knowledge concerning the following: (1) major ECM constituents and their functions in both normal and malignant conditions; (2) the interplay between cancer cells and the ECM in the TME; (3) key receptors for mechanotransduction and their alteration during carcinogenesis; and (4) the current therapeutic strategies targeting aberrant ECM for cancer treatment.

Diverse origins and activation of fibroblasts in cardiac fibrosis

Cardiac fibroblasts (cFBs) have emerged as a heterogenous cell population. Fibroblasts are considered the main cell source for synthesis of the extracellular matrix (ECM) and as such a dysregulation in cFB function, activity, or viability can lead to disrupted ECM structure or fibrosis. Fibrosis can be initiated in response to different injuries and stimuli, and can be reparative (beneficial) or reactive (damaging). FBs need to be activated to myofibroblasts (MyoFBs) which have augmented capacity in synthesizing ECM proteins, causing fibrosis. In addition to the resident FBs in the myocardium, a number of other cells (pericytes, fibrocytes, mesenchymal, and hematopoietic cells) can transform into MyoFBs, further driving the fibrotic response. Multiple molecules including hormones, cytokines, and growth factors stimulate this process leading to generation of activated MyoFBs. Contribution of different cell types to cFBs and MyoFBs can result in an exponential increase in the number of MyoFBs and an accelerated pro-fibrotic response. Given the diversity of the cell sources, and the array of interconnected signalling pathways that lead to formation of MyoFBs and subsequently fibrosis, identifying a single target to limit the fibrotic response in the myocardium has been challenging. This review article will delineate the importance and relevance of fibroblast heterogeneity in mediating fibrosis in different models of heart failure and will highlight important signalling pathways implicated in myofibroblast activation.

Neurturin regulates the lung-resident macrophage inflammatory response to viral infection

The neurotrophic factor RET is induced in lung macrophages by viral triggers and activation via its ligand neurturin regulates matrix proteins and cytokines that shape the inflammatory response.

Lung-resident macrophages are crucial to the maintenance of health and in the defence against lower respiratory tract infections. Macrophages adapt to local environmental cues that drive their appropriate function; however, this is often dysregulated in many inflammatory lung pathologies. In mucosal tissues, neuro-immune interactions enable quick and efficient inflammatory responses to pathogenic threats. Although a number of factors that influence the antimicrobial response of lung macrophages are known, the role of neuronal factors is less well understood. Here, we show an intricate circuit involving the neurotrophic factor, neurturin (NRTN) on human lung macrophages that dampens pro-inflammatory cytokine release and modulates the type of matrix metalloproteinases produced in response to viral stimuli. This circuit involves type 1 interferon–induced up-regulation of RET that when combined with the glial cell line-derived neurotrophic factor (GDNF) receptor α2 (GFRα2) allows binding to epithelial-derived NRTN. Our research highlights a non-neuronal immunomodulatory role for NRTN and a novel process leading to a specific antimicrobial immune response by human lung-resident macrophages.

Prostate cancer-derived MMP-3 controls intrinsic cell growth and extrinsic angiogenesis

Bone metastatic prostate cancer significantly impacts patient quality of life and overall survival, and despite available therapies, it is presently incurable with an unmet need for improved treatment options. As mediators of tumor progression, matrix metalloproteinases (MMPs) can degrade extracellular matrix components and regulate growth factor and cytokine bioactivity. Depending on tissue context, MMPs can either promote or inhibit tumorigenesis. Therefore, it is essential to study individual MMPs in specific cancer contexts and microenvironments to support the design and application of selective MMP inhibitors. Here we report that tumor-derived MMP-3 contributes to bone metastatic prostate cancer progression via intrinsic and extrinsic routes. MMP-3 ablation in prostate cancer cell lines significantly reduced in vitro growth combined with lowered AKT and ERK phosphorylation and total VEGFR1 and FGFR3 protein levels. In vivo, MMP-3 ablated tumors grew at a slower rate and were significantly less vascularized. Quantitative PCR analyses of wild type and MMP-3 silenced prostate cancer cells also demonstrate downregulation of a wide array of angiogenic factors. The extrinsic role for MMP-3 in angiogenesis was supported by in vitro endothelial tube formation assays where the lack of MMP-3 in prostate cancer conditioned media resulted in slower rates of tube formation. Taken together, our results suggest that tumor-derived MMP-3 contributes to prostate cancer growth in bone. These data indicate that selective inhibition of MMP-3 and/or targeting MMP generated products could be efficacious for the treatment of prostate to bone metastases.

Cysteinyl cathepsins in cardiovascular diseases

Cysteinyl cathepsins are lysosomal/endosomal proteases that mediate bulk protein degradation in these intracellular acidic compartments. Yet, studies indicate that these proteases also appear in the nucleus, nuclear membrane, cytosol, plasma membrane, and extracellular space. Patients with cardiovascular diseases (CVD) show increased levels of cathepsins in the heart, aorta, and plasma. Plasma cathepsins often serve as biomarkers or risk factors of CVD. In aortic diseases, such as atherosclerosis and abdominal aneurysms, cathepsins play pathogenic roles, but many of the same cathepsins are cardioprotective in hypertensive, hypertrophic, and infarcted hearts. During the development of CVD, cathepsins are regulated by inflammatory cytokines, growth factors, hypertensive stimuli, oxidative stress, and many others. Cathepsin activities in inflammatory molecule activation, immunity, cell migration, cholesterol metabolism, neovascularization, cell death, cell signaling, and tissue fibrosis all contribute to CVD and are reviewed in this article in memory of Dr. Nobuhiko Katunuma for his contribution to the field.

Multiscale Coupling of an Agent-Based Model of Tissue Fibrosis and a Logic-Based Model of Intracellular Signaling

Wound healing and fibrosis following myocardial infarction (MI) is a dynamic process involving many cell types, extracellular matrix (ECM), and inflammatory cues. As both incidence and survival rates for MI increase, management of post-MI recovery and associated complications are an increasingly important focus. Complexity of the wound healing process and the need for improved therapeutics necessitate a better understanding of the biochemical cues that drive fibrosis. To study the progression of cardiac fibrosis across spatial and temporal scales, we developed a novel hybrid multiscale model that couples a logic-based differential equation (LDE) model of the fibroblast intracellular signaling network with an agent-based model (ABM) of multi-cellular tissue remodeling. The ABM computes information about cytokine and growth factor levels in the environment including TGFβ, TNFα, IL-1β, and IL-6, which are passed as inputs to the LDE model. The LDE model then computes the network signaling state of individual cardiac fibroblasts within the ABM. Based on the current network state, fibroblasts make decisions regarding cytokine secretion and deposition and degradation of collagen. Simulated fibroblasts respond dynamically to rapidly changing extracellular environments and contribute to spatial heterogeneity in model predicted fibrosis, which is governed by many parameters including cell density, cell migration speeds, and cytokine levels. Verification tests confirmed that predictions of the coupled model and network model alone were consistent in response to constant cytokine inputs and furthermore, a subset of coupled model predictions were validated with in vitro experiments with human cardiac fibroblasts. This multiscale framework for cardiac fibrosis will allow for systematic screening of the effects of molecular perturbations in fibroblast signaling on tissue-scale extracellular matrix composition and organization.

Interferon-γ enhances the antifibrotic effects of pirfenidone by attenuating IPF lung fibroblast activation and differentiation

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) pathogenesis involves multiple pathways, and combined antifibrotic therapy is needed for future IPF therapy. Inhaled interferon-γ (IFN-γ) was recently shown to be safe and without systemic effects in patients with IPF.

AIM

To examine the in vitro effects of individual and combined treatment with IFN-γ and pirfenidone (PFD) on normal and IPF fibroblast activation and extracellular matrix remodeling after TGF-β1 and PDGF-BB stimulation.

METHODS

IPF and normal human lung fibroblasts (NHLF) were treated with IFN-γ, PFD or a combination of both drugs in the presence of either TGF-β1 or PDGF-BB. The effects of TGF-β1 and PDGF-BB treatment on cell viability, proliferation, differentiation and migration were examined. The expression of collagen 1, matrix metalloproteinases (MMPs) and tissue inhibitors of MMP (TIMPs) was analyzed using qPCR, Western blotting and gelatin zymography. Total collagen content in conditioned media was also measured using a Sircol assay.

RESULTS

Compared to that of PFD, the effect of IFN-γ in downregulating normal and IPF lung fibroblast differentiation to myofibroblasts in response to TGF-β1 was more potent. Importantly, the combination of IFN-γ and PFD had a possibly synergistic/additive effect in inhibiting the TGF-β1- and PDGF-BB-induced proliferation, migration and differentiation of normal and IPF lung fibroblasts. Furthermore, both drugs reversed TGF-β1-induced effects on MMP-1, - 2, - 3, - 7, and - 9, while only PFD promoted TIMP-1 and-2 expression and release.

CONCLUSIONS

Our findings demonstrate that the antifibrotic effects of IFN-γ and PFD on normal and IPF lung fibroblasts are different and complementary. Combination therapy with inhaled IFN-γ and PFD in IPF is promising and should be further explored in IPF clinical trials.

Matrix Metalloproteases as Influencers of the Cells' Social Media

Matrix metalloproteinases (MMPs) have been studied in the context of cancer due to their ability to increase cell invasion, and were initially thought to facilitate metastasis solely through the degradation of the extracellular matrix (ECM). MMPs have also been investigated in the context of their ECM remodeling activity in several acute and chronic inflammatory diseases. However, after several MMP inhibitors failed in phase III clinical trials, a global reassessment of their biological functions was undertaken, which has revealed multiple unanticipated functions including the processing of chemokines, cytokines, and cell surface receptors. Despite what their name suggests, the matrix aspect of MMPs could contribute to a lesser part of their physiological functions in inflammatory diseases, as originally anticipated. Here, we present examples of MMP substrates implicated in cell signaling, independent of their ECM functions, and discuss the impact for the use of MMP inhibitors.

MMPs and ADAMs in neurological infectious diseases and multiple sclerosis

Metalloproteinases-such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs)-are involved in various diseases of the nervous system but also contribute to nervous system development, synaptic plasticity and neuroregeneration upon injury. MMPs and ADAMs proteolytically cleave many substrates including extracellular matrix components but also signaling molecules and receptors. During neuroinfectious disease with associated neuroinflammation, MMPs and ADAMs regulate blood-brain barrier breakdown, bacterial invasion, neutrophil infiltration and cytokine signaling. Specific and broad-spectrum inhibitors for MMPs and ADAMs have experimentally been shown to decrease neuroinflammation and brain damage in diseases with excessive neuroinflammation as a common denominator, such as pneumococcal meningitis and multiple sclerosis, thereby improving the disease outcome. Timing of metalloproteinase inhibition appears to be critical to effectively target the cascade of pathophysiological processes leading to brain damage without inhibiting the neuroregenerative effects of metalloproteinases. As the critical role of metalloproteinases in neuronal repair mechanisms and regeneration was only lately recognized, the original idea of chronic MMP inhibition needs to be conceptually revised. Recently accumulated research urges for a second chance of metalloproteinase inhibitors, which-when correctly applied and dosed-harbor the potential to improve the outcome of different neuroinflammatory diseases.

Mechanochemical Signaling of the Extracellular Matrix in Epithelial-Mesenchymal Transition

Epithelial-Mesenchymal Transition (EMT) is a critical process in embryonic development in which epithelial cells undergo a transdifferentiation into mesenchymal cells. This process is essential for tissue patterning and organization, and it has also been implicated in a wide array of pathologies. While the intracellular signaling pathways that regulate EMT are well-understood, there is increasing evidence that the mechanical properties and composition of the extracellular matrix (ECM) also play a key role in regulating EMT. In turn, EMT drives changes in the mechanics and composition of the ECM, creating a feedback loop that is tightly regulated in healthy tissues, but is often dysregulated in disease. Here we present a review that summarizes our understanding of how ECM mechanics and composition regulate EMT, and how in turn EMT alters ECM mechanics and composition.

Current Understanding of the Molecular Basis of Venezuelan Equine Encephalitis Virus Pathogenesis and Vaccine Development

Dedication

This review is dedicated in the memory of Dr Radha K. Maheshwari, a great mentor and colleague, whose passion for research and student training has left a lasting effect on this manuscript and many other works.

Abstract

Venezuelan equine encephalitis virus (VEEV) is an alphavirus in the family Togaviridae. VEEV is highly infectious in aerosol form and a known bio-warfare agent that can cause severe encephalitis in humans. Periodic outbreaks of VEEV occur predominantly in Central and South America. Increased interest in VEEV has resulted in a more thorough understanding of the pathogenesis of this disease. Inflammation plays a paradoxical role of antiviral response as well as development of lethal encephalitis through an interplay between the host and viral factors that dictate virus replication. VEEV has efficient replication machinery that adapts to overcome deleterious mutations in the viral genome or improve interactions with host factors. In the last few decades there has been ongoing development of various VEEV vaccine candidates addressing the shortcomings of the current investigational new drugs or approved vaccines. We review the current understanding of the molecular basis of VEEV pathogenesis and discuss various types of vaccine candidates.

Extracellular Vesicles and Matrix Remodeling Enzymes: The Emerging Roles in Extracellular Matrix Remodeling, Progression of Diseases and Tissue Repair

Extracellular vesicles (EVs) are membrane enclosed micro- and nano-sized vesicles that are secreted from almost every species, ranging from prokaryotes to eukaryotes, and from almost every cell type studied so far. EVs contain repertoire of bioactive molecules such as proteins (including enzymes and transcriptional factors), lipids, carbohydrates and nucleic acids including DNA, coding and non-coding RNAs. The secreted EVs are taken up by neighboring cells where they release their content in recipient cells, or can sail through body fluids to reach distant organs. Since EVs transport bioactive cargo between cells, they have emerged as novel mediators of extra- and intercellular activities in local microenvironment and inter-organ communications distantly. Herein, we review the activities of EV-associated matrix-remodeling enzymes such as matrix metalloproteinases, heparanases, hyaluronidases, aggrecanases, and their regulators such as extracellular matrix metalloproteinase inducers and tissue inhibitors of metalloproteinases as novel means of matrix remodeling in physiological and pathological conditions. We discuss how such EVs act as novel mediators of extracellular matrix degradation to prepare a permissive environment for various pathological conditions such as cancer, cardiovascular diseases, arthritis and metabolic diseases. Additionally, the roles of EV-mediated matrix remodeling in tissue repair and their potential applications as organ therapies have been reviewed. Collectively, this knowledge could benefit the development of new approaches for tissue engineering.

Long-chain polyphosphate in osteoblast matrix vesicles: Enrichment and inhibition of mineralization

BACKGROUND

Inorganic polyphosphate (polyP) is a fundamental and ubiquitous molecule in prokaryotes and eukaryotes. PolyP has been found in mammalian tissues with particularly high levels of long-chain polyP in bone and cartilage where critical questions remain as to its localization and function. Here, we investigated polyP presence and function in osteoblast-like SaOS-2 cells and cell-derived matrix vesicles (MVs), the initial sites of bone mineral formation.

METHODS

PolyP was quantified by 4',6-diamidino-2-phenylindole (DAPI) fluorescence and characterized by enzymatic methods coupled to urea polyacrylamide gel electrophoresis. Transmission electron microscopy and confocal microscopy were used to investigate polyP localization. A chicken embryo cartilage model was used to investigate the effect of polyP on mineralization.

RESULTS

PolyP increased in concentration as SaOS-2 cells matured and mineralized. Particularly high levels of polyP were observed in MVs. The average length of MV polyP was determined to be longer than 196 P_i residues by gel chromatography. Electron micrographs of MVs, stained by two polyP-specific staining approaches, revealed polyP localization in the vicinity of the MV membrane. Additional extracellular polyP binds to MVs and inhibits MV-induced hydroxyapatite formation.

CONCLUSION

PolyP is highly enriched in matrix vesicles and can inhibit apatite formation. PolyP may be hydrolysed to phosphate for further mineralization in the extracellular matrix.

GENERAL SIGNIFICANCE

PolyP is a unique yet underappreciated macromolecule which plays a critical role in extracellular mineralization in matrix vesicles.

The impaired proteases and anti-proteases balance in Idiopathic Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis (IPF) is a devastating chronic, progressive and irreversible disease that remains refractory to current therapies. Matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the development of pulmonary fibrosis since decades. Coagulation signalling deregulation, which influences several key inflammatory and fibro-proliferative responses, is also essential in IPF pathogenesis, and a growing body of evidence indicates that Protease-Activated Receptors (PARs) inhibition in IPF may be promising for future evaluation. Therefore, proteases and anti-proteases aroused great biomedical interest over the past years, owing to the identification of their potential roles in lung fibrosis. During these last decades, numerous other proteases and anti-proteases have been studied in lung fibrosis, such as matriptase, Human airway trypsin-like protease (HAT), Hepatocyte growth factor activator (HGFA)/HGFA activator inhibitor (HAI) system, Plasminogen activator inhibitor (PAI)-1, Protease nexine (PN)-1, cathepsins, calpains, and cystatin C. Herein, we provide a general overview of the proteases and anti-proteases unbalance during lung fibrogenesis and explore potential therapeutics for IPF.

Polyphosphate as a donor of high-energy phosphate for the synthesis of ADP and ATP

Here, we studied the potential role of inorganic polyphosphate (polyP) as an energy source for ADP and ATP formation in the extracellular space. In SaOS-2 cells, we show that matrix vesicles are released into the extracellular space after incubation with polyP. These vesicles contain both alkaline phosphatase (ALP) and adenylate kinase (AK) activities (mediated by ALPL and AK1 enzymes). Both enzymes translocate to the cell membrane in response to polyP. To distinguish the process(es) of AMP and ADP formation during ALP hydrolysis from the ATP generated via the AK reaction, inhibition studies with the AK inhibitor A(5')P5(5')A were performed. We found that ADP formation in the extracellular space occurs after enzymatic ATP synthesis. After exposure to polyP, a significant increase of the ADP level was observed, which is likely to be been catalyzed by ALP. This increase is not due to an intensified ATP release via exocytosis. The ATP level in the extracellular space of SaOS-2 cells is strongly increased in response to polyP, very likely mediated by the AK. We propose that the ALP and AK enzymes are involved in the extracellular ADP and ATP synthesis.

The Role of Matrix Metalloproteinases in Development, Repair, and Destruction of the Lungs

Normal gas exchange after birth requires functional lung alveolar units that are lined with epithelial cells, parts of which are intricately fused with microvascular capillaries. A significant phase of alveolar lung development occurs in the perinatal period, continues throughout early stages in life, and requires activation of matrix-remodeling enzymes. Failure to achieve an optimum number of alveoli during lung maturation can cause several untoward medical consequences including disabling obstructive and/or restrictive lung diseases that limit physiological endurance and increase mortality. Several members of the matrix metalloproteinase (MMP) family are critical in lung remodeling before and after birth; however, their resurgence in response to environmental factors, infection, and injury can also compromise lung function. Therefore, temporal expression, regulation, and function of MMPs play key roles in developing and maintaining adequate oxygenation under steady state, as well as in diseased conditions. Broadly, with the exception of MMP2 and MMP14, most deletional mutations of MMPs fail to perturb lung development; however, their individual absence can alter the pathophysiology of respiratory diseases. Specifically, under stressed conditions such as acute respiratory infection and allergic inflammation, MMP2 and MMP9 can play a protective role through bacterial clearance and production of chemotactic gradient, while loss of MMP12 can protect mice from smoke-induced lung disease. Therefore, better understanding of the expression and function of MMPs under normal lung development and their resurgence in response respiratory diseases could provide new therapeutic options in the future.

Extracellular matrix remodeling in idiopathic pulmonary fibrosis. It is the 'bed' that counts and not 'the sleepers'

INTRODUCTION

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disease characterized by irreversible fibrosis. Current disease pathogenesis assumes an aberrant wound healing process in response to repetitive injurious stimuli leading to apoptosis of epithelial cells, activation of fibroblasts and accumulation of extracellular matrix (ECM). Particularly, lung ECM is a highly dynamic structure that lies at the core of several physiological and developmental pathways. The scope of this review article is to summarize current knowledge on the role of ECM in the pathogenesis of IPF, unravel novel mechanistic data and identify future more effective therapeutic targets. Areas covered: The exact mechanisms through which lung microenvironment activates fibroblasts and inflammatory cells, regulates profibrotic signaling cascades through growth factors, integrins and degradation enzymes ultimately leading to excessive matrix deposition are discussed. Furthermore, the potential therapeutic usefulness of specific inhibitors of matrix deposition or activators of matrix degradation pathways are also presented. Expert commentary: With a gradually increasing worldwide incidence IPF still present a major challenge in clinical research due to its unknown etiopathogenesis and current ineffective treatment approaches. Today, there is an amenable need for more effective therapeutic targets and ECM components may represent one.

Matrix metalloproteinases: an emerging role in regulation of actin microfilament system

Matrix metalloproteinases (MMPs) are implicated in many physiological and pathological processes, including contraction, migration, differentiation, and proliferation. These processes all involve cell phenotype changes, known to be accompanied by reorganization of actin cytoskeleton. Growing evidence indicates a correlation between MMP activity and the dynamics of actin system, suggesting their mutual regulation. Here, data on the influence of MMPs on the actin microfilament system, on the one hand, and the dependence of MMP expression and activation on the organization of actin structures, on the other hand, are reviewed. The different mechanisms of putative actin-MMP regulation are discussed.

Stromal Modulators of TGF-β in Cancer

Transforming growth factor-β (TGF-β) is an intriguing cytokine exhibiting dual activities in malignant disease. It is an important mediator of cancer invasion, metastasis and angiogenesis, on the one hand, while it exhibits anti-tumor functions on the other hand. Elucidating the precise role of TGF-β in malignant development and progression requires a better understanding of the molecular mechanisms involved in its tumor suppressor to tumor promoter switch. One important aspect of TGF-β function is its interaction with proteins within the tumor microenvironment. Several stromal proteins have the natural ability to interact and modulate TGF-β function. Understanding the complex interplay between the TGF-β signaling network and these stromal proteins may provide greater insight into the development of novel therapeutic strategies that target the TGF-β axis. The present review highlights our present understanding of how stroma modulates TGF-β activity in human cancers.

TGFβ-2 signaling is essential for osteoblast migration and differentiation during fracture healing in medaka fish

TGFβ is known as a canonical coupling factor based on its effects on bone formation and bone resorption. There are 3 different isoforms of it related to bone metabolism in mammals. TGFβ function in vivo is complicated, and each isoform shows a different function. Since TGFβs are secreted during inflammation accompanied by the release of latent TGFβ from inside of the bones where they are stored in the extracellular matrix, TGFβ function is potentially related to fracture healing. Although a few reports examined the TGFβ expression during fracture healing, the function of TGFβ in this process is poorly understood. To investigate TGFβ function during fracture healing in vivo, we used the fracture healing model of the medaka fish, which enabled us to observe the behavior and function of living cells in response to a bone-specific injury. RNA in-situ hybridization analysis showed that only tgfβ-2 of the 4 TGFβ isoforms in medaka was expressed in the bone-forming region. To examine the TGFβ-2 function for bone formation by osteoblasts, we used a medaka transgenic line, Tg (type X collagen: GFP); and the results revealed that type X collagen-positive immature osteoblasts migrated to the fracture site and differentiated to osterix-positive osteoblasts. However, only a few type X collagen-positive osteoblasts exhibited BrdU incorporation after the fracture. Then we inhibited TGFβ signaling by using a chemical TGFβ receptor kinase inhibitor (SB431542), and demonstrated that inhibition of TGFβ strongly impaired osteoblast migration and differentiation. In addition, this TGFβ inhibitor reduced the RANKL expression and caused a delay of osteoclast differentiation. Our findings thus demonstrated that TGFβ-2 functioned specifically during fracture healing to stimulate the migration of osteoblasts as well as the differentiation of osteoblasts and osteoclasts.

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.

The cartilage extracellular matrix as a transient developmental scaffold for growth plate maturation

The cartilage growth plate is a specialized developmental tissue containing characteristic zonal arrangements of chondrocytes. The proliferative and differentiative states of chondrocytes are tightly regulated at all stages including the initial limb bud and rudiment cartilage stages of development, the establishment of the primary and secondary ossification centers, development of the growth plates and laying down of bone. A multitude of spatio-temporal signals, including transcription factors, growth factors, morphogens and hormones, control chondrocyte maturation and terminal chondrocyte differentiation/hypertrophy, cell death/differentiation, calcification and vascular invasion of the growth plate and bone formation during morphogenetic transition of the growth plate. This involves hierarchical, integrated signaling from growth and factors, transcription factors, mechanosensory cues and proteases in the extracellular matrix to regulate these developmental processes to facilitate progressive changes in the growth plate culminating in bone formation and endochondral ossification. This review provides an overview of selected components which have particularly important roles in growth plate biology including collagens, proteoglycans, glycosaminoglycans, growth factors, proteases and enzymes.

Matrix vesicles: Are they anchored exosomes?

Numerous studies have documented that matrix vesicles are unique extracellular membrane-bound microparticles that serve as initial sites for mineral formation in the growth plate and most other vertebrate mineralizing tissues. Microparticle generation is not confined to hard tissues, as cells in soft tissues generate similar structures; numerous studies have shown that a common type of extracellular particle, termed an exosome, a product of the endosomal pathway, shares many characteristics of matrix vesicles. Indeed, analyses of size, morphology and lipid and protein content indicate that matrix vesicles and exosomes are homologous structures. Such a possibility impacts our understanding of the biogenesis, processing and function of matrix vesicles (exosomes) in vertebrate hard tissues and explains in part how cells control the earliest stages of mineral deposition. Moreover, since exosomes influence a spectrum of functions, including cell-cell communication, it is suggested that this type of microparticle may provide a mechanism for the transfer of signaling molecules between cells within the growth plate and thereby regulate endochondral bone development and formation.

Matrix metalloproteinases and protein tyrosine kinases: potential novel targets in acute lung injury and ARDS

Acute lung injury (ALI) and ARDS fall within a spectrum of pulmonary disease that is characterized by hypoxemia, noncardiogenic pulmonary edema, and dysregulated and excessive inflammation. While mortality rates have improved with the advent of specialized ICUs and lung protective mechanical ventilation strategies, few other therapies have proven effective in the management of ARDS, which remains a significant clinical problem. Further development of biomarkers of disease severity, response to therapy, and prognosis is urgently needed. Several novel pathways have been identified and studied with respect to the pathogenesis of ALI and ARDS that show promise in bridging some of these gaps. This review will focus on the roles of matrix metalloproteinases and protein tyrosine kinases in the pathobiology of ALI in humans, and in animal models and in vitro studies. These molecules can act independently, as well as coordinately, in a feed-forward manner via activation of tyrosine kinase-regulated pathways that are pivotal in the development of ARDS. Specific signaling events involving proteolytic processing by matrix metalloproteinases that contribute to ALI, including cytokine and chemokine activation and release, neutrophil recruitment, transmigration and activation, and disruption of the intact alveolar-capillary barrier, will be explored in the context of these novel molecular pathways.

Addressing the Inflammatory Response to Clinically Relevant Polymers by Manipulating the Host Response Using ITIM Domain-Containing Receptors

Tissue contacting surfaces of medical devices initiate a host inflammatory response, characterized by adsorption of blood proteins and inflammatory cells triggering the release of cytokines, reactive oxygen species (ROS) and reactive nitrogen species (RNS), in an attempt to clear or isolate the foreign object from the body. This normal host response contributes to device-associated pathophysiology and addressing device biocompatibility remains an unmet need. Although widespread attempts have been made to render the device surfaces unreactive, the establishment of a completely bioinert coating has been untenable and demonstrates the need to develop strategies based upon the molecular mechanisms that define the interaction between host cells and synthetic surfaces. In this review, we discuss a family of transmembrane receptors, known as immunoreceptor tyrosine-based inhibitory motif (ITIM)-containing receptors, which show promise as potential targets to address aberrant biocompatibility. These receptors repress the immune response and ensure that the intensity of an immune response is appropriate for the stimuli. Particular emphasis will be placed on the known ITIM-containing receptor, Signal Regulatory Protein Alpha (SIRPhα), and its cognate ligand CD47. In addition, this review will discuss the potential of other ITIM-containing proteins as targets for addressing the aberrant biocompatibility of polymeric biomaterials.

Targeting TGFβ signaling in subchondral bone and articular cartilage homeostasis

Osteoarthritis (OA) is the most common degenerative joint disease and no disease-modifying therapy for OA is currently available. Targeting articular cartilage alone may not be sufficient to halt this disease progression. Articular cartilage and subchondral bone act as a functional unit. Increasing evidence indicates that transforming growth factor β (TGFβ) plays a crucial role in maintaining homeostasis of both articular cartilage and subchondral bone. Activation of extracellular matrix (ECM) latent TGFβ at the appropriate time and location is a prerequisite for its function. Aberrant activation of TGFβ in the subchondral bone in response to an abnormal mechanical loading environment induces formation of osteroid islets at the onset of OA. As a result, alteration of subchondral bone structure changes the stress distribution on the articular cartilage and leads to its degeneration. Thus, inhibition of TGFβ activity in the subchondral bone may provide a new avenue of treatment for OA. In this review we will discuss the role of TGFβ in the homeostasis of articular cartilage and subchondral bone as a novel target for OA therapy.

Accumulation of exogenous activated TGF-β in the superficial zone of articular cartilage

It was recently demonstrated that mechanical shearing of synovial fluid (SF), induced during joint motion, rapidly activates latent transforming growth factor β (TGF-β). This discovery raised the possibility of a physiological process consisting of latent TGF-β supply to SF, activation via shearing, and transport of TGF-β into the cartilage matrix. Therefore, the two primary objectives of this investigation were to characterize the secretion rate of latent TGF-β into SF, and the transport of active TGF-β across the articular surface and into the cartilage layer. Experiments on tissue explants demonstrate that high levels of latent TGF-β1 are secreted from both the synovium and all three articular cartilage zones (superficial, middle, and deep), suggesting that these tissues are capable of continuously replenishing latent TGF-β to SF. Furthermore, upon exposure of cartilage to active TGF-β1, the peptide accumulates in the superficial zone (SZ) due to the presence of an overwhelming concentration of nonspecific TGF-β binding sites in the extracellular matrix. Although this response leads to high levels of active TGF-β in the SZ, the active peptide is unable to penetrate deeper into the middle and deep zones of cartilage. These results provide strong evidence for a sequential physiologic mechanism through which SZ chondrocytes gain access to active TGF-β: the synovium and articular cartilage secrete latent TGF-β into the SF and, upon activation, TGF-β transports back into the cartilage layer, binding exclusively to the SZ.

TGF-beta1 on osteoimmunology and the bone component cells

TGF-β1 is an immunoregulatory cytokine that regulates immune cell proliferation, survival, differentiation, and migration. Compelling evidence has demonstrated a strong association between the immune and skeletal systems (so called Osteoimmunology), such as the critical role of TGF-β1 in the development and maintenance of the skeletal tissue. This review provides an overview of the mechanisms in which TGF-β1 interacts with bone component cells, such as osteoblasts, osteoclasts, chondrocytes, mesenchymal stem cells, and hematopoietic stem cells, in concert with other cytokines and hormones.

MMP-3 provokes CTGF/CCN2 production independently of protease activity and dependently on dynamin-related endocytosis, which contributes to human dental pulp cell migration

Matrix metalloproteinase-3 (MMP-3) expression is promoted after pulpotomy, and application of MMP-3 to dental pulp after pulpotomy accelerates angiogenesis and hard tissue formation. However, the mechanism by which MMP-3 promotes dental pulp wound healing is still unclear. Connective tissue growth factor/CCN family 2 (CTGF/CCN2), a protein belonging to the CCN family, is considered to participate in wound healing, angiogenesis, and cell migration. In this study, we examined the involvement of CTGF/CCN2 in MMP-3-induced cell migration in human dental pulp (fibroblast-like) cells. In human dental pulp cells, MMP-3 promoted cell migration, but this effect was clearly blocked in the presence of anti-CTGF/CCN2 antibody. MMP-3 provoked mRNA and protein expression and secretion of CTGF/CCN2 in a concentration- and time-dependent manner. The MMP-3 inhibitor NNGH failed to suppress MMP-3-induced CTGF/CCN2 protein expression. The potent dynamin inhibitor dynasore clearly inhibited MMP-3-induced CTGF/CCN2 expression. These results strongly suggest that MMP-3 induces CTGF/CCN2 production independently of the protease activity of MMP-3 and dependently on dynamin-related endocytosis, which is involved in cell migration in human dental pulp cells.

A mechanobiological model of orthodontic tooth movement

Orthodontic tooth movement is achieved by the process of repeated alveolar bone resorption on the pressure side and new bone formation on the tension side. In order to optimize orthodontic treatment, it is important to identify and study the biological processes involved. This article presents a mechanobiological model using partial differential equations to describe cell densities, growth factor concentrations, and matrix densities occurring during orthodontic tooth movement. We hypothesize that such a model can predict tooth movement based on the mechanobiological activity of cells in the PDL. The developed model consists of nine coupled non-linear partial differential equations, and two distinct signaling pathways were modeled: the RANKL-RANK-OPG pathway regulating the communication between osteoblasts and osteoclasts and the TGF-β pathway mediating the differentiation of mesenchymal stem cells into osteoblasts. The predicted concentrations and densities were qualitatively validated by comparing the results to experiments reported in the literature. In the current form, the model supports our hypothesis, as it is capable of conceptually simulating important features of the biological interactions in the alveolar bone-PDL complex during orthodontic tooth movement.

An osteoblast-derived proteinase controls tumor cell survival via TGF-beta activation in the bone microenvironment

BACKGROUND

Breast to bone metastases frequently induce a "vicious cycle" in which osteoclast mediated bone resorption and proteolysis results in the release of bone matrix sequestered factors that drive tumor growth. While osteoclasts express numerous proteinases, analysis of human breast to bone metastases unexpectedly revealed that bone forming osteoblasts were consistently positive for the proteinase, MMP-2. Given the role of MMP-2 in extracellular matrix degradation and growth factor/cytokine processing, we tested whether osteoblast derived MMP-2 contributed to the vicious cycle of tumor progression in the bone microenvironment.

METHODOLOGY/PRINCIPAL FINDINGS

To test our hypothesis, we utilized murine models of the osteolytic tumor-bone microenvironment in immunocompetent wild type and MMP-2 null mice. In longitudinal studies, we found that host MMP-2 significantly contributed to tumor progression in bone by protecting against apoptosis and promoting cancer cell survival (caspase-3; immunohistochemistry). Our data also indicate that host MMP-2 contributes to tumor induced osteolysis (μCT, histomorphometry). Further ex vivo/in vitro experiments with wild type and MMP-2 null osteoclast and osteoblast cultures identified that 1) the absence of MMP-2 did not have a deleterious effect on osteoclast function (cd11B isolation, osteoclast differentiation, transwell migration and dentin resorption assay); and 2) that osteoblast derived MMP-2 promoted tumor survival by regulating the bioavailability of TGFβ, a factor critical for cell-cell communication in the bone (ELISA, immunoblot assay, clonal and soft agar assays).

CONCLUSION/SIGNIFICANCE

Collectively, these studies identify a novel "mini-vicious cycle" between the osteoblast and metastatic cancer cells that is key for initial tumor survival in the bone microenvironment. In conclusion, the findings of our study suggest that the targeted inhibition of MMP-2 and/or TGFβ would be beneficial for the treatment of bone metastases.

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

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

Matrix metalloproteinase 3 is a mediator of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) may be triggered by epithelial injury that results in aberrant production of growth factors, cytokines, and proteinases, leading to proliferation of myofibroblasts, excess deposition of collagen, and destruction of the lung architecture. The precise mechanisms and key signaling mediators responsible for this aberrant repair process remain unclear. We assessed the importance of matrix metalloproteinase-3 (MMP-3) in the pathogenesis of IPF through i) determination of MMP-3 expression in patients with IPF, ii) in vivo experiments examining the relevance of MMP-3 in experimental models of fibrosis, and iii) in vitro experiments to elucidate possible mechanisms of action. Gene expression analysis, quantitative RT-PCR, and Western blot analysis of explanted human lungs revealed enhanced expression of MMP-3 in IPF, compared with control. Transient adenoviral vector-mediated expression of recombinant MMP-3 in rat lung resulted in accumulation of myofibroblasts and pulmonary fibrosis. Conversely, MMP-3-null mice were protected against bleomycin-induced pulmonary fibrosis. In vitro treatment of cultured lung epithelial cells with purified MMP-3 resulted in activation of the β-catenin signaling pathway, via cleavage of E-cadherin, and induction of epithelial-mesenchymal transition. These processes were inhibited in bleomycin-treated MMP-3-null mice, as assessed by cytosolic translocation of β-catenin and cyclin D1 expression. These observations support a novel role for MMP-3 in the pathogenesis of IPF, through activation of β-catenin signaling and induction of epithelial-mesenchymal transition.

Exploring anti-TGF-β therapies in cancer and fibrosis

Transforming growth factor-β (TGF-β) is a multifunctional cytokine, with important roles in maintaining tissue homeostasis. TGF-β signals via transmembrane serine/threonine kinase receptors and intracellular Smad transcriptional regulators. Perturbed TGF-β signaling has been implicated in a large variety of pathological conditions. Increased TGF-β levels have been found in patients with cancer, fibrosis, and systemic sclerosis, and were correlated with disease severity. In cancer, TGF-β mediates tumor invasion and metastasis by affecting both tumor cells and the tumor microenvironment including fibroblast activation and immune suppression. Furthermore, TGF-β is a strong stimulator of extracellular matrix deposition. On the basis of these observations, small molecule inhibitors of the TGF-β receptor kinases, neutralizing antibodies that interfere with ligand?receptor interactions, antisense oligonucleotides reducing TGF-β expression, and soluble receptor ectodomains that sequester TGF-β have been developed to intervene with excessive TGF-β signaling activity in the aforementioned disorders. Here, we review the current state of anti-TGF-β therapy in clinical trials.

Differential effects between the loss of MMP-2 and MMP-9 on structural and tissue-level properties of bone

Matrix metalloproteinases (MMPs) are capable of processing certain components of bone tissue, including type 1 collagen, a determinant of the biomechanical properties of bone tissue, and they are expressed by osteoclasts and osteoblasts. Therefore, we posit that MMP activity can affect the ability of bone to resist fracture. To explore this possibility, we determined the architectural, compositional, and biomechanical properties of bones from wild-type (WT), Mmp2(-/-) , and Mmp9(-/-) female mice at 16 weeks of age. MMP-2 and MMP-9 have similar substrates but are expressed primarily by osteoblasts and osteoclasts, respectively. Analysis of the trabecular compartment of the tibia metaphysis by micro-computed tomography (µCT) revealed that these MMPs influence trabecular architecture, not volume. Interestingly, the loss of MMP-9 improved the connectivity density of the trabeculae, whereas the loss of MMP-2 reduced this parameter. Similar differential effects in architecture were observed in the L(5) vertebra, but bone volume fraction was lower for both Mmp2(-/-) and Mmp9(-/-) mice than for WT mice. The mineralization density and mineral-to-collagen ratio, as determined by µCT and Raman microspectroscopy, were lower in the Mmp2(-/-) bones than in WT control bones. Whole-bone strength, as determined by three-point bending or compression testing, and tissue-level modulus and hardness, as determined by nanoindentation, were less for Mmp2(-/-) than for WT bones. In contrast, the Mmp9(-/-) femurs were less tough with lower postyield deflection (more brittle) than the WT femurs. Taken together, this information reveals that MMPs play a complex role in maintaining bone integrity, with the cell type that expresses the MMP likely being a contributing factor to how the enzyme affects bone quality.