Deficiency of matrix metalloproteinase-13 increases inflammation after acute lung injury

Pulmonary Fibrosis and Diabetes Mellitus: Two coins with the same face

Idiopathic pulmonary fibrosis (IPF) constitutes a long-term disease with a complex pathophysiology composed of multiple molecular actors that lead to the deposition of extracellular matrix, the loss of pulmonary function and ultimately the patient's death. Despite the approval of pirfenidone and nintedanib for the treatment of the disease, lung transplant is the only long-term solution to fully recover the respiratory capacity and gain quality of life. One of the risk factors for the development of IPF is the pre-existing condition of diabetes mellitus. Both, IPF and diabetes mellitus, share similar pathological damage mechanisms, including inflammation, endoplasmic reticulum stress, mitochondrial failure, oxidative stress, senescence and signaling from glycated proteins through receptors. In this critical review article, we provide information about this interrelationship, examining molecular mediators that play an essential role in both diseases and identify targets of interest for the development of potential drugs. We review the findings of clinical trials examining the progression of IPF and how novel molecules may be used to stop this process. The results highlight the importance of early detection and addressing multiple therapeutic targets simultaneously to achieve better therapeutic efficacy and potentially reverse lung fibrosis.

Amelioration of Pulmonary Fibrosis by Matrix Metalloproteinase-2 Overexpression

Idiopathic pulmonary fibrosis is a progressive and fatal disease with a poor prognosis. Matrix metalloproteinase-2 is involved in the pathogenesis of organ fibrosis. The role of matrix metalloproteinase-2 in lung fibrosis is unclear. This study evaluated whether overexpression of matrix metalloproteinase-2 affects the development of pulmonary fibrosis. Lung fibrosis was induced by bleomycin in wild-type mice and transgenic mice overexpressing human matrix metalloproteinase-2. Mice expressing human matrix metalloproteinase-2 showed significantly decreased infiltration of inflammatory cells and inflammatory and fibrotic cytokines in the lungs compared to wild-type mice after induction of lung injury and fibrosis with bleomycin. The computed tomography score, Ashcroft score of fibrosis, and lung collagen deposition were significantly reduced in human matrix metalloproteinase transgenic mice compared to wild-type mice. The expression of anti-apoptotic genes was significantly increased, while caspase-3 activity was significantly reduced in the lungs of matrix metalloproteinase-2 transgenic mice compared to wild-type mice. Active matrix metalloproteinase-2 significantly decreased bleomycin-induced apoptosis in alveolar epithelial cells. Matrix metalloproteinase-2 appears to protect against pulmonary fibrosis by inhibiting apoptosis of lung epithelial cells.

Interleukin 36 receptor-inducible matrix metalloproteinase 13 mediates intestinal fibrosis

Background

Fibrostenotic disease is a common complication in Crohn's disease (CD) patients hallmarked by transmural extracellular matrix (ECM) accumulation in the intestinal wall. The prevention and medical therapy of fibrostenotic CD is an unmet high clinical need. Although targeting IL36R signaling is a promising therapy option, downstream mediators of IL36 during inflammation and fibrosis have been incompletely understood. Candidate molecules include matrix metalloproteinases which mediate ECM turnover and are thereby potential targets for anti-fibrotic treatment. Here, we have focused on understanding the role of MMP13 during intestinal fibrosis.

Methods

We performed bulk RNA sequencing of paired colon biopsies taken from non-stenotic and stenotic areas of patients with CD. Corresponding tissue samples from healthy controls and CD patients with stenosis were used for immunofluorescent (IF) staining. MMP13 gene expression was analyzed in cDNA of intestinal biopsies from healthy controls and in subpopulations of patients with CD in the IBDome cohort. In addition, gene regulation on RNA and protein level was studied in colon tissue and primary intestinal fibroblasts from mice upon IL36R activation or blockade. Finally, in vivo studies were performed with MMP13 deficient mice and littermate controls in an experimental model of intestinal fibrosis. Ex vivo tissue analysis included Masson's Trichrome and Sirius Red staining as well as evaluation of immune cells, fibroblasts and collagen VI by IF analysis.

Results

Bulk RNA sequencing revealed high upregulation of MMP13 in colon biopsies from stenotic areas, as compared to non-stenotic regions of patients with CD. IF analysis confirmed higher levels of MMP13 in stenotic tissue sections of CD patients and demonstrated αSMA+ and Pdpn+ fibroblasts as a major source. Mechanistic experiments demonstrated that MMP13 expression was regulated by IL36R signaling. Finally, MMP13 deficient mice, as compared to littermate controls, developed less fibrosis in the chronic DSS model and showed reduced numbers of αSMA+ fibroblasts. These findings are consistent with a model suggesting a molecular axis involving IL36R activation in gut resident fibroblasts and MMP13 expression during the pathogenesis of intestinal fibrosis.

Conclusion

Targeting IL36R-inducible MMP13 could evolve as a promising approach to interfere with the development and progression of intestinal fibrosis.

Stabil idiyopatik pulmoner fibrozde hastalik şiddeti ve prognostik belirteçler ile matriks metallaproteinaz düzeyleri arasindaki ilişki

Purpose: Blood-derived biomarkers have been extensively considered as possible prognostic indicators in idiopathic pulmonary fibrosis (IPF) recently. In order to assess the value of circulating biomarkers in common IPF clinical practice, the study intends to draw conclusions regarding the link between disease severity, prognostic indicators, and serum matrix metalloproteinase in patients with stable idiopathic pulmonary fibrosis. Materials and Methods: The study comprised 22 people with an IPF diagnosis that had been verified by a multidisciplinary approach. The sociodemographic details, clinical and radiologic symptoms, pulmonary function tests and the Gender-Age-Physiology (GAP) score were noted. ELISA has been used to research serum MMP concentrations. Results: There is no statistically significant correlation between the Matrix Metalloproteinase (MMP) 2, MMP 7, MMP 9, and MMP13 and the GAP index and, pulmonary function tests, or disease severity. GAP score was found to be higher in stage 3 in patients with severe disease, in stage 2 in patients with moderate disease, and in stage 1 in patients with mild disease. Conclusion: There are consistent findings in the literature, despite the fact that the association between MMP and IPF prognostic markers, pulmonary function tests, and disease severity could not be seen in this investigation. However, because they could open the door to a cutting-edge treatment strategy, these indicators should be investigated prospectively in larger series.

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.

The Critical Role of MMP13 in Regulating Tooth Development and Reactionary Dentinogenesis Repair Through the Wnt Signaling Pathway

Matrix-metalloproteinase-13 (MMP13) is important for bone formation and remodeling; however, its role in tooth development remains unknown. To investigate this, MMP13-knockout (Mmp13^−/−) mice were used to analyze phenotypic changes in the dentin–pulp complex, mineralization-associated marker-expression, and mechanistic interactions. Immunohistochemistry demonstrated high MMP13-expression in pulp-tissue, ameloblasts, odontoblasts, and dentin in developing WT-molars, which reduced in adults, with human-DPC cultures demonstrating a >2000-fold increase in Mmp13-expression during mineralization. Morphologically, Mmp13^−/− molars displayed critical alterations in the dentin-phenotype, affecting dentin-tubule regularity, the odontoblast-palisade and predentin-definition with significantly reduced dentin volume (∼30% incisor; 13% molar), and enamel and dentin mineral-density. Reactionary-tertiary-dentin in response to injury was reduced at Mmp13^−/− molar cusp-tips but with significantly more dystrophic pulpal mineralization in MMP13-null samples. Odontoblast differentiation-markers, nestin and DSP, reduced in expression after MMP13-loss in vivo, with reduced calcium deposition in MMP13-null DPC cultures. RNA-sequencing analysis of WT and Mmp13^−/− pulp highlighted 5,020 transcripts to have significantly >2.0-fold change, with pathway-analysis indicating downregulation of the Wnt-signaling pathway, supported by reduced in vivo expression of the Wnt-responsive gene Axin2. Mmp13 interaction with Axin2 could be partly responsible for the loss of odontoblastic activity and alteration to the tooth phenotype and volume which is evident in this study. Overall, our novel findings indicate MMP13 as critical for tooth development and mineralization processes, highlighting mechanistic interaction with the Wnt-signaling pathway.

Engineering of tissue inhibitor of metalloproteinases TIMP-1 for fine discrimination between closely-related stromelysins MMP-3 and MMP-10

Matrix metalloproteinases (MMPs) have long been known as key drivers in the development and progression of diseases, including cancer and neurodegenerative, cardiovascular, and many other inflammatory and degenerative diseases, making them attractive potential drug targets. Engineering selective inhibitors based upon tissue inhibitors of metalloproteinases (TIMPs), endogenous human proteins that tightly yet nonspecifically bind to the family of MMPs, represents a promising new avenue for therapeutic development. Here, we used a counter-selective screening strategy for directed evolution of yeast-displayed human TIMP-1 to obtain TIMP-1 variants highly selective for the inhibition of MMP-3 in preference over MMP-10. As MMP-3 and MMP-10 are the most similar MMPs in sequence, structure, and function, our results thus clearly demonstrate the capability for engineering full-length TIMP proteins to be highly selective MMP inhibitors. We show using protein crystal structures and models of MMP-3-selective TIMP-1 variants bound to MMP-3 and counter-target MMP-10 how structural alterations within the N-terminal and C-terminal TIMP-1 domains create new favorable and selective interactions with MMP-3 and disrupt unique interactions with MMP-10. While our MMP-3-selective inhibitors may be of interest for future investigation in diseases where this enzyme drives pathology, our platform and screening strategy can be employed for developing selective inhibitors of additional MMPs implicated as therapeutic targets in disease.

Distinct Metalloproteinase Expression and Functions in Systemic Sclerosis and Fibrosis: What We Know and the Potential for Intervention

Systemic sclerosis (SSc) is a chronic debilitating idiopathic disorder, characterized by deposition of excessive extracellular matrix (ECM) proteins such as collagen which leads to fibrosis of the skin and other internal organs. During normal tissue repair and remodeling, the accumulation and turnover of ECM proteins are tightly regulated by the interaction of matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of metalloproteinases (TIMPs). SSc is associated with dysregulation of the activity of these proteolytic and inhibitory proteins within the tissue microenvironment, tipping the balance toward fibrosis. The resultant ECM accumulation further perpetuates tissue stiffness and decreased function, contributing to poor clinical outcomes. Understanding the expression and function of these endogenous enzymes and inhibitors within specific tissues is therefore critical to the development of therapies for SSc. This brief review describes recent advances in our understanding of the functions and mechanisms of ECM remodeling by metalloproteinases and their inhibitors in the skin and lungs affected in SSc. It highlights recent progress on potential candidates for intervention and therapeutic approaches for treating SSc fibrosis.

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.

Trypanosoma cruzi Induces the PARP1/AP-1 Pathway for Upregulation of Metalloproteinases and Transforming Growth Factor β in Macrophages: Role in Cardiac Fibroblast Differentiation and Fibrosis in Chagas Disease

Cardiomyopathy is the most important clinical manifestation of T. cruzi-driven CD. Recent studies have suggested the detrimental role of the matrix metalloproteinases MMP2 and MMP9 in extracellular matrix (ECM) degradation during cardiac remodeling in T. cruzi infection. Peripheral TGF-β levels are increased in clinically symptomatic CD patients over those in clinically asymptomatic seropositive individuals. We provide the first evidence that during T. cruzi infection, Mϕ release of MMP2 and MMP9 plays an active role in activation of TGF-β signaling of ECM remodeling and cardiac fibroblast-to-myofibroblast differentiation. We also determined that PARP1 signals c-Fos- and JunB-mediated AP-1 transcriptional activation of profibrotic gene expression and demonstrated the significance of PARP1 inhibition in controlling chronic fibrosis in Chagas disease. Our study provides a promising therapeutic approach for controlling T. cruzi-driven fibroblast differentiation in CD by PARP1 inhibitors through modulation of the Mϕ signaling of the AP-1–MMP9–TGF-β pathway.

Chagas disease (CD), caused by Trypanosoma cruzi, is a degenerative heart condition. In the present study, we investigated the role of poly [ADP-ribose] polymerase 1/activator protein 1 (PARP1/AP-1) in upregulation of profibrotic macrophages (Mϕ) and subsequent development of cardiac fibrosis in CD. We used in vitro and in vivo models of T. cruzi infection and chemical and genetic inhibition of Parp1 to examine the molecular mechanisms by which Mϕ might augment profibrotic events in CD. Cultured (RAW 264.7 and THP-1) Mϕ infected with T. cruzi and primary cardiac and splenic Mϕ of chronically infected mice exhibited a significant increase in the expression, activity, and release of metalloproteinases (MMP2, MMP9, and MMP12) and the cytokine transforming growth factor β (TGF-β). Mϕ release of MMPs and TGF-β signaled the cardiac fibroblast to myofibroblast differentiation, as evidenced by a shift from S100A4 to alpha smooth muscle actin (α-SMA) expression. Incubation of infected Mϕ with MMP2 and MMP9 inhibitors resulted in 60 to 74% decline in TGF-β release, and MMP9 and PARP1 inhibitors resulted in 57 to 70% decline in Mϕ TGF-β-driven cardiac fibroblast differentiation. Likewise, histological studies showed a 12- to 16-fold increase in myocardial expression of CD68 (Mϕ marker) and its colocalization with MMP9/TGF-β, galectin-3, and vimentin in wild-type mice with CD. In comparison, chronically infected Parp1^−/− mice exhibited a >50% decline in myocardial levels of Mϕ and associated fibrosis markers. Further study showed that PARP1 synergized with c-Fos and JunB AP-1 family members for transcriptional activation of profibrotic response after T. cruzi infection. We conclude that PARP1 inhibition offers a potential therapy for controlling the T. cruzi-driven fibroblast differentiation in CD through modulation of the Mϕ signaling of the AP-1–MMP9–TGF-β pathway.

Circulating matrix metalloproteinases and tissue metalloproteinase inhibitors in patients with idiopathic pulmonary fibrosis in the multicenter IPF-PRO Registry cohort

Background

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) play important roles in the turnover of extracellular matrix and in the pathogenesis of idiopathic pulmonary fibrosis (IPF). This study aimed to determine the utility of circulating MMPs and TIMPs in distinguishing patients with IPF from controls and to explore associations between MMPs/TIMPs and measures of disease severity in patients with IPF.

Methods

The IPF cohort (n = 300) came from the IPF-PRO Registry, an observational multicenter registry of patients with IPF that was diagnosed or confirmed at the enrolling center in the past 6 months. Controls (n = 100) without known lung disease came from a population-based registry. Generalized linear models were used to compare circulating concentrations of MMPs 1, 2, 3, 7, 8, 9, 12, and 13 and TIMPs 1, 2, and 4 between patients with IPF and controls, and to investigate associations between circulating levels of these proteins and measures of IPF severity. Multivariable models were fit to identify the MMP/TIMPs that best distinguished patients with IPF from controls.

Results

All the MMP/TIMPs analyzed were present at significantly higher levels in patients with IPF compared with controls except for TIMP2. Multivariable analyses selected MMP8, MMP9 and TIMP1 as top candidates for distinguishing patients with IPF from controls. Higher concentrations of MMP7, MMP12, MMP13 and TIMP4 were significantly associated with lower diffusion capacity of the lung for carbon monoxide (DL_CO) % predicted and higher composite physiologic index (worse disease). MMP9 was associated with the composite physiologic index. No MMP/TIMPs were associated with forced vital capacity % predicted.

Conclusions

Circulating MMPs and TIMPs were broadly elevated among patients with IPF. Select MMP/TIMPs strongly associated with measures of disease severity. Our results identify potential MMP/TIMP targets for further development as disease-related biomarkers.

Twist1 in Infiltrating Macrophages Attenuates Kidney Fibrosis via Matrix Metallopeptidase 13-Mediated Matrix Degradation

BACKGROUND

Following an acute insult, macrophages regulate renal fibrogenesis through the release of various factors that either encourage the synthesis of extracellular matrix synthesis or the degradation of matrix via endocytosis, proteolysis, or both. However, the roles of infiltrating versus resident myeloid cells in these opposing processes require elucidation. The transcription factor Twist1 controls diverse essential cellular functions through induction of several downstream targets, including matrix metalloproteinases (MMPs). In macrophages, Twist1 can influence patterns of cytokine generation, but the role of macrophage Twist1 in renal fibrogenesis remains undefined.

METHODS

To study Twist1 functions in different macrophage subsets during kidney scar formation, we used two conditional mutant mouse models in which Twist1 was selectively ablated either in infiltrating, inflammatory macrophages or in resident tissue macrophages. We assessed fibrosis-related parameters, matrix metallopeptidase 13 (MMP13, or collagen 3, which catalyzes collagen degradation), inflammatory cytokines, and other factors in these Twist1-deficient mice compared with wild-type controls after subjecting the animals to unilateral ureteral obstruction. We also treated wild-type and Twist1-deficient mice with an MMP13 inhibitor after unilateral ureteral obstruction.

RESULTS

Twist1 in infiltrating inflammatory macrophages but not in resident macrophages limited kidney fibrosis after ureteral obstruction by driving extracellular matrix degradation. Moreover, deletion of Twist1 in infiltrating macrophages attenuated the expression of MMP13 in CD11b+Ly6Clo myeloid cells. Inhibition of MMP13 abrogated the protection from renal fibrosis afforded by macrophage Twist1.

CONCLUSIONS

Twist1 in infiltrating myeloid cells mitigates interstitial matrix accumulation in the injured kidney by promoting MMP13 production, which drives extracellular matrix degradation. These data highlight the complex cell-specific actions of Twist1 in the pathogenesis of kidney fibrosis.

Delayed resolution of bleomycin-induced pulmonary fibrosis in absence of MMP13 (collagenase 3)

Matrix metalloprotease 13 (MMP13) deficiency in pulmonary fibrosis has described contradictory phenotypes on inflammatory and fibrotic responses after lung injury, and its role during lung fibrosis resolution is still undefined. MMP13 has been considered the main collagenase in rodents, and the remodeling of fibrillar collagen is widely attributed to the action of this enzyme. In this study we aimed to explore the role of MMP13 during lung fibrosis progression and resolution. Lung fibrosis was induced by intratracheal instillation, and inflammatory, fibrotic, and resolution stages were evaluated in Mmp13-null and wild-type (WT) mice. Bronchoalveolar lavage fluid was taken for cytokine array analysis and activity of gelatinases. Our results showed that MMP13 is upregulated mainly during two stages after lung injury, inflammation and resolution of fibrosis, and it is mainly expressed by alveolar and interstitial macrophages. Mmp13-null mice exhibited more extensive inflammation at 7 days after bleomycin treatment, and it was characterized by increased macrophage infiltration and significant alterations in proinflammatory cytokines. We also documented that Mmp13-deficient mice experienced more severe and prolonged lung fibrosis compared with WT mice. Delayed resolution in Mmp13-deficient lungs was characterized by a decreased overall collagenolytic activity and persistent fibrotic foci associated with emphysema-like areas. Together, our findings indicate that MMP13 plays an antifibrotic role and its activity is crucial in lung repair and restoration of tissue integrity during fibrosis resolution.

Resolution of organ fibrosis

Fibrosis is the excessive accumulation of extracellular matrix that often occurs as a wound healing response to repeated or chronic tissue injury, and may lead to the disruption of organ architecture and loss of function. Although fibrosis was previously thought to be irreversible, recent evidence indicates that certain circumstances permit the resolution of fibrosis when the underlying causes of injury are eradicated. The mechanism of fibrosis resolution encompasses degradation of the fibrotic extracellular matrix as well as elimination of fibrogenic myofibroblasts through their adaptation of various cell fates, including apoptosis, senescence, dedifferentiation, and reprogramming. In this Review, we discuss the present knowledge and gaps in our understanding of how matrix degradation is regulated and how myofibroblast cell fates can be manipulated, areas that may identify potential therapeutic approaches for fibrosis.

Induction of the Matrix Metalloproteinase 13 Gene in Bronchial Epithelial Cells by Interferon and Identification of its Novel Functional Polymorphism

Matrix metalloproteinases (MMPs) are a class of extra-cellular and membrane-bound proteases involved in a wide array of physiological and pathological processes including tissue remodeling, inflammation, and cytokine secretion and activation. MMP-13 has been shown to be involved in lung diseases such as acute lung injury, viral infections, and chronic obstructive pulmonary disease; however, the molecular pathogenesis of MMP-13 in these conditions is not well understood. In this study, we investigated the mechanisms and roles of MMP-13 secretion in human small airway epithelial cells (SAECs) and functional polymorphisms of the MMP13 gene. Polyinosinic-polycytidylic acid (poly(I:C)) and interferon β (IFN-β) stimulated the secretion of MMP-13 from SAECs by more than several hundred-fold. Stimulation of the secretion by poly(I:C) was abolished by SB304680 (p38 inhibitor), LY294002 (PI3K inhibitor), Janus kinase (JAK) inhibitor I, RNA-activated protein kinase (PKR) inhibitor, and Bay 11-7082 (NF-κB inhibitor), while stimulation by IFN-β was inhibited by all except Bay 11-7082. These data suggested that the secretion of MMP-13 was mediated through IFN receptor pathways independently of nuclear factor kappa B (NF-κB) and that poly(I:C) stimulated IFN secretion in an NF-κB-dependent manner from SAECs, leading to IFN-stimulated MMP-13 secretion. Chemical MMP-13 inhibitors and MMP-13 small interfering RNA (siRNA) inhibited IFN-stimulated secretion of interferon gamma-inducible protein 10 (IP-10) and regulated on activation, normal T-cell expressed and secreted (RANTES), suggesting that MMP-13 is involved in the secretion of these virus-induced proinflammatory chemokines. We identified a novel functional polymorphism in the promoter region of the MMP13 gene. The MMP13 gene may play important roles in defense mechanisms of airway epithelial cells.

Role of matrix metalloproteinases in the pathogenesis of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and devastating lung disorder of unknown origin, with very poor prognosis and no effective treatment. The disease is characterized by abnormal activation of alveolar epithelial cells, which secrete numerous mediators involved in the expansion of the fibroblast population, its differentiation to myofibroblasts, and in the exaggerated accumulation of extracellular matrix provoking the loss of lung architecture. Among the excessively produced mediators are several matrix metalloproteases (MMPs) which may contribute to modify the lung microenvironment by various mechanisms. Thus, these enzymes can not only degrade all the components of the extracellular matrix, but they are also able to release, cleave and activate a wide range of growth factors, cytokines, chemokines and cell surface receptors affecting numerous cell functions including adhesion, proliferation, differentiation, recruiting and transmigration, and apoptosis. Therefore, dysregulated expression of MMPs may have profound impact on the biopathological mechanisms implicated in the development of IPF. This review focuses on the current and emerging evidence regarding the role of MMPs on the fibrotic processes in IPF as well as in mouse models of lung fibrosis.

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.

Diverse functions of matrix metalloproteinases during fibrosis

Fibrosis--a debilitating condition that can occur in most organs - is characterized by excess deposition of a collagen-rich extracellular matrix (ECM). At first sight, the activities of proteinases that can degrade matrix, such as matrix metalloproteinases (MMPs), might be expected to be under-expressed in fibrosis or, if present, could function to resolve the excess matrix. However, as we review here, some MMPs are indeed anti-fibrotic, whereas others can have pro-fibrotic functions. MMPs modulate a range of biological processes, especially processes related to immunity and tissue repair and/or remodeling. Although we do not yet know precisely how MMPs function during fibrosis--that is, the protein substrate or substrates that an individual MMP acts on to effect a specific process--experiments in mouse models demonstrate that MMP-dependent functions during fibrosis are not limited to effects on ECM turnover. Rather, data from diverse models indicate that these proteinases influence cellular activities as varied as proliferation and survival, gene expression, and multiple aspects of inflammation that, in turn, impact outcomes related to fibrosis.

Metalloproteinases and their natural inhibitors in inflammation and immunity

Over the past 50 years, steady growth in the field of metalloproteinase biology has shown that the degradation of extracellular matrix components represents only a fraction of the functions performed by these enzymes and has highlighted their fundamental roles in immunity. Metalloproteinases regulate aspects of immune cell development, effector function, migration and ligand-receptor interactions. They carry out ectodomain shedding of cytokines and their cognate receptors. Together with their endogenous inhibitors TIMPs (tissue inhibitor of metalloproteinases), these enzymes regulate signalling downstream of the tumour necrosis factor receptor and the interleukin-6 receptor, as well as that downstream of the epidermal growth factor receptor and Notch, which are all pertinent for inflammatory responses. This Review discusses the metalloproteinase family as a crucial component in immune cell development and function.

Always cleave up your mess: targeting collagen degradation to treat tissue fibrosis

Pulmonary fibrosis is a vexing clinical problem with no proven therapeutic options. In the normal lung there is continuous collagen synthesis and collagen degradation, and these two processes are precisely balanced to maintain normal tissue architecture. With lung injury there is an increase in the rate of both collagen production and collagen degradation. The increase in collagen degradation is critical in preventing the formation of permanent scar tissue each time the lung is exposed to injury. In pulmonary fibrosis, collagen degradation does not keep pace with collagen production, resulting in extracellular accumulation of fibrillar collagen. Collagen degradation occurs through both extracellular and intracellular pathways. The extracellular pathway involves cleavage of collagen fibrils by proteolytic enzyme including the metalloproteinases. The less-well-described intracellular pathway involves binding and uptake of collagen fragments by fibroblasts and macrophages for lysosomal degradation. The relationship between these two pathways and their relevance to the development of fibrosis is complex. Fibrosis in the lung, liver, and skin has been associated with an impaired degradative environment. Much of the current scientific effort in fibrosis is focused on understanding the pathways that regulate increased collagen production. However, recent reports suggest an important role for collagen turnover and degradation in regulating the severity of tissue fibrosis. The objective of this review is to evaluate the roles of the extracellular and intracellular collagen degradation pathways in the development of fibrosis and to examine whether pulmonary fibrosis can be viewed as a disease of impaired matrix degradation rather than a disease of increased matrix production.

ADAMTS-12 metalloprotease is necessary for normal inflammatory response

ADAMTSs (a disintegrin and metalloprotease with thrombospondin domains) are a family of enzymes with both proteolytic and protein interaction functions, which have been implicated in distinct pathologies. In this work, we have investigated the putative role of ADAMTS-12 in inflammation by using a mouse model deficient in this metalloprotease. Control and mutant mice were subjected to different experimental conditions to induce colitis, endotoxic sepsis, and pancreatitis. We have observed that Adamts12-deficient mice exhibit more severe inflammation and a delayed recovery from these challenges compared with their wild-type littermates. These changes are accompanied by an increase in inflammatory markers including several cytokines, as assessed by microarray expression analysis and proteomic-based approaches. Interestingly, the clinical symptoms observed in Adamts12-deficient mice are also concomitant with an elevation in the number of neutrophils in affected tissues. Finally, isolation and in vitro culture of human neutrophils demonstrate that the presence of ADAMTS-12 induces neutrophil apoptosis. On the basis of these results, we propose that ADAMTS-12 is implicated in the inflammatory response by modulating normal neutrophil apoptosis.