Regulation of versican expression in macrophages is mediated by canonical type I interferon signaling via ISGF3.

Growing evidence supports a role for versican as an important component of the inflammatory response, with both pro- and anti-inflammatory roles depending on the specific context of the system or disease under investigation. Our goal is to understand the regulation of macrophage-derived versican and the role it plays in innate immunity. In previous work, we showed that LPS triggers a signaling cascade involving Toll-like receptor (TLR)4, the Trif adaptor, type I interferons, and the type I interferon receptor, leading to increased versican expression by macrophages. In the present study, we used a combination of chromatin immunoprecipitation, siRNA, chemical inhibitors, and mouse model approaches to investigate the regulatory events downstream of the type I interferon receptor to better define the mechanism controlling versican expression. Results indicate that transcriptional regulation by canonical type I interferon signaling via interferon-stimulated gene factor 3 (ISGF3), the heterotrimeric transcription factor complex of Irf9, Stat1, and Stat2, controls versican expression in macrophages exposed to LPS. This pathway is not dependent on MAPK signaling, which has been shown to regulate versican expression in other cell types. The stability of versican mRNA may also contribute to prolonged versican expression in macrophages. These findings strongly support a role for macrophage-derived versican as a type I interferon-stimulated gene and further our understanding of versican's role in regulating inflammation.NEW & NOTEWORTHY We report the novel finding that versican expression is regulated by the interferon-stimulated gene factor 3 (ISGF3) arm of canonical type I Ifn signaling in LPS-stimulated macrophages. This pathway is distinct from mechanisms that control versican expression in other cell types. This suggests that macrophage-derived versican may play a role in limiting a potentially excessive inflammatory response. The detailed understanding of how versican expression is regulated in different cells could lead to unique approaches for enhancing its anti-inflammatory properties.

MAP2K1 DAMPENS CIGARETTE SMOKE-INDUCED LUNG INFLAMMATION VIA SUPPRESSION OF TYPE I INTERFERON PATHWAY ACTIVATION.

Chronic Obstructive Pulmonary Disease (COPD), comprised of chronic bronchitis and emphysema, is a leading cause of morbidity and mortality worldwide. MAP2K (mitogen-activated protein 2 kinase) pathway activation is present in COPD lung tissue and a genetic polymorphism in Map2k1 associates with FEV1 decline in COPD, suggesting it may contribute to disease pathogenesis. To test the functional contribution of Map2k1 in cigarette smoke (CS)-induced lung inflammation, we used a short-term CS exposure model in mice deficient in myeloid Map2k1 (LysmCre+Mek1fl) and wild-type mice (Mek1fl). Mice deficient in myeloid Map2k1 had enhanced CS-induced lung inflammation characterized by increased neutrophil recruitment, augmented expression of elastolytic matrix metalloproteinases, and increased type I interferon-stimulated gene expression. The augmented neutrophilic inflammatory response could be abrogated by IFNAR1 blockade. These findings indicate that myeloid Map2k1 regulates the immune response to CS via inhibition of the type I interferon pathway. Overall, these results suggest that Map2k1 is a critical determinant in modulating the severity of CS-induced lung inflammation and its expression is protective.

MAP2K2 Delays Recovery in Murine Models of Acute Lung Injury and Associates with Acute Respiratory Distress Syndrome Outcome.

Acute respiratory distress syndrome (ARDS) remains a significant problem in need of new pharmaceutical approaches to improve its resolution. Studies comparing gene expression signatures in rodents and humans with lung injury reveal conserved pathways, including MAPK (mitogen-activated protein kinase)/ERK (extracellular signal-related protein kinase) activation. In preclinical acute lung injury (ALI) models, inhibition of MAP2K1 (MAPK kinase 1)/MAP2K2 (MAPK kinase 2) improves measures of ALI. Myeloid cell deletion of MAP2K1 results in sustained MAP2K2 activation and nonresolving ALI, suggesting that MAP2K2 deactivation may be a key driver of ALI resolution. We used human genomic data from the iSPAAR (Identification of SNPs Predisposing to Altered Acute Lung Injury Risk) Consortium to assess genetic variants in MAP2K1 and MAP2K2 for association with mortality from ARDS. To determine the role of MAP2K2 in ALI recovery, we studied mice deficient in Map2k2 (Mek2-/-) and wild-type control mice in ALI models. We identified a MAP2K2 variant that was associated with death in ARDS and MAP2K2 expression. In Pseudomonas aeruginosa ALI, Mek2-/- mice had similar early alveolar neutrophilic recruitment but faster resolution of alveolar neutrophilia and vascular leak. Gene expression analysis revealed a role for MAP2K2 in promoting and sustaining select proinflammatory pathway activation in ALI. Bone marrow chimera studies indicate that leukocyte MAP2K2 is the key regulator of ALI duration. These studies implicate a role for MAP2K2 in ALI duration via transcriptional regulation of inflammatory programming with potential relevance to ARDS. Targeting leukocyte MAP2K2 may be an effective strategy to promote ALI resolution.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report.

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Excitation Emission Matrix Fluorescence Spectroscopy for Combustion Generated Particulate Matter Source Identification.

The inhalation of particulate matter (PM) is a significant health risk associated with reduced life expectancy due to increased cardio-pulmonary disease and exacerbation of respiratory diseases such as asthma and pneumonia. PM originates from natural and anthropogenic sources including combustion engines, cigarettes, agricultural burning, and forest fires. Identifying the source of PM can inform effective mitigation strategies and policies, but this is difficult to do using current techniques. Here we present a method for identifying PM source using excitation emission matrix (EEM) fluorescence spectroscopy and a machine learning algorithm. We collected combustion generated PM2.5 from wood burning, diesel exhaust, and cigarettes using filters. Filters were weighted to determine mass concentration followed by extraction into cyclohexane and analysis by EEM fluorescence spectroscopy. Spectra obtained from each source served as training data for a convolutional neural network (CNN) used for source identification in mixed samples. This method can predict the presence or absence of the three laboratory sources with an overall accuracy of 89% when the threshold for classifying a source as present is 1.1 µg/m3 in air over a 24-hour sampling time. The limit of detection for cigarette, diesel and wood are 0.7, 2.6, 0.9 µg/m3, respectively, in air assuming a 24-hour sampling time at an air sampling rate of 1.8 liters per minute. We applied the CNN algorithm developed using the laboratory training data to a small set of field samples and found the algorithm was effective in some cases but would require a training data set containing more samples to be more broadly applicable.

Alveolar Macrophage Transcriptional Programs Are Associated with Outcomes in Acute Respiratory Distress Syndrome.

Rationale: Serial measurements of alveolar macrophage (AM) transcriptional changes in patients with acute respiratory distress syndrome (ARDS) could identify cell-specific biological programs that are associated with clinical outcomes.Objectives: To determine whether AM transcriptional programs are associated with prolonged mechanical ventilation and 28-day mortality in individuals with ARDS.Methods: We performed genome-wide transcriptional profiling of AMs purified from BAL fluid collected from 35 subjects with ARDS. Cells were obtained at baseline (Day 1), Day 4, and Day 8 after ARDS onset (N = 68 total samples). We identified biological pathways that were enriched at each time point in subjects alive and extubated within 28 days after ARDS onset (alive/extubatedDay28) versus those dead or persistently supported on mechanical ventilation at Day 28 (dead/intubatedDay28).Measurements and Main Results: "M1-like" (classically activated) and proinflammatory gene sets such as IL-6/JAK/STAT5 (Janus kinase/signal transducer and activator of transcription 5) signaling were significantly enriched in AMs isolated on Day 1 in alive/extubatedDay28 versus dead/intubatedDay28 subjects. In contrast, by Day 8, many of these same proinflammatory gene sets were enriched in AMs collected from dead/intubatedDay28 compared with alive/extubatedDay28 subjects. Serially sampled alive/extubatedDay28 subjects were characterized by an AM temporal expression pattern of Day 1 enrichment of innate immune programs followed by prompt downregulation on Days 4 and 8. Dead/intubatedDay28 subjects exhibited an opposite pattern, characterized by progressive upregulation of proinflammatory programs over the course of ARDS. The relationship between AM expression profiles and 28-day clinical status was distinct in subjects with direct (pulmonary) versus indirect (extrapulmonary) ARDS.Conclusions: Clinical outcomes in ARDS are associated with highly distinct AM transcriptional programs.

Transcriptional and functional diversity of human macrophage repolarization.

BACKGROUND: Macrophage plasticity allows cells to adopt different phenotypes, a property with important implications in disorders such as cystic fibrosis (CF) and asthma. OBJECTIVE: We sought to examine the transcriptional and functional significance of macrophage repolarization from an M1 to an M2 phenotype and assess the role of a common human genetic disorder (CF) and a prototypical allergic disease (asthma) in this transformation. METHODS: Monocyte-derived macrophages were collected from healthy subjects and patients with CF and polarized to an M2 state by using IL-4, IL-10, glucocorticoids, apoptotic PMNs, or azithromycin. We performed transcriptional profiling and pathway analysis for each stimulus. We assessed the ability of M2-repolarized macrophages to respond to LPS rechallenge and clear apoptotic neutrophils and used murine models to determine conserved functional responses to IL-4 and IL-10. We investigated whether M2 signatures were associated with alveolar macrophage phenotypes in asthmatic patients. RESULTS: We found that macrophages exhibit highly diverse responses to distinct M2-polarizing stimuli. Specifically, IL-10 activated proinflammatory pathways and abrogated LPS tolerance, allowing rapid restoration of LPS responsiveness. In contrast, IL-4 enhanced LPS tolerance, dampening proinflammatory responses after repeat LPS challenge. A common theme observed across all M2 stimuli was suppression of interferon-associated pathways. We found that CF macrophages had intact reparative and transcriptional responses, suggesting that macrophage contributions to CF-related lung disease are primarily shaped by their environment. Finally, we leveraged in vitro-derived signatures to show that allergen provocation induces distinct M2 state transcriptional patterns in alveolar macrophages. CONCLUSION: Our findings highlight the diversity of macrophage polarization, attribute functional consequences to different M2 stimuli, and provide a framework to phenotype macrophages in disease states.

A Flow Cytometric Method for Isolating Cystic Fibrosis Airway Macrophages from Expectorated Sputum.

Research to understand the contribution of macrophages to nonresolving airway inflammation in cystic fibrosis (CF) and other chronic suppurative airways diseases has been hindered by a lack of methods for isolating and studying these cells. With the development of technologies that can characterize small numbers of cells or individual cells, there is an even greater need for methodologies to isolate rare cells in heterogeneous specimens. Here, we describe a method that overcomes the technical obstacles imposed by sputum debris and apoptotic cells, and allows isolation of pure populations of macrophages from CF sputum. In addition to enhancing our ability to study human CF airway macrophages, this protocol can be adapted to study cells in sputum from other chronic suppurative lung diseases (e.g., chronic obstructive pulmonary disease) and used for isolation of individual cells for single cell analyses.

Stat5 Is Required for CD103+ Dendritic Cell and Alveolar Macrophage Development and Protection from Lung Injury.

We tested the role of Stat5 in dendritic cell and alveolar macrophage (AM) homeostasis in the lung using CD11c-cre mediated deletion (Cre+5f/f). We show that Stat5 is required for CD103+ dendritic cell and AM development. We found that fetal monocyte maturation into AMs was impaired in Cre+5f/f mice, and we also confirmed impaired AM development of progenitor cells using mixed chimera experiments. In the absence of Stat5 signaling in AMs, mice developed alveolar proteinosis with altered lipid homeostasis. In addition, loss of Stat5 in CD11c+ cells was associated with exaggerated LPS-induced inflammatory responses and vascular leak. In Cre+5f/f mice, there was loss of immune-dampening effects on epithelial cells, a key source of CCL2 that serves to recruit monocytes and macrophages. These findings demonstrate the critical importance of Stat5 signaling in maintaining lung homeostasis, and underscore the importance of resident macrophages in moderating tissue damage and excess inflammation.

MEK1/2 Inhibition Promotes Macrophage Reparative Properties.

Macrophages have important functional roles in regulating the timely promotion and resolution of inflammation. Although many of the intracellular signaling pathways involved in the proinflammatory responses of macrophages are well characterized, the components that regulate macrophage reparative properties are less well understood. We identified the MEK1/2 pathway as a key regulator of macrophage reparative properties. Pharmacological inhibition of the MEK1/2 pathway by a MEK1/2 inhibitor (MEKi) significantly increased expression of IL-4/IL-13 (M2)-responsive genes in murine bone marrow-derived and alveolar macrophages. Deletion of the MEK1 gene using LysMCre+/+Mek1fl/fl macrophages as an alternate approach yielded similar results. MEKi enhanced STAT6 phosphorylation, and MEKi-induced changes in M2 polarization were dependent on STAT6. In addition, MEKi treatment significantly increased murine and human macrophage efferocytosis of apoptotic cells, independent of macrophage polarization and STAT6. These phenotypes were associated with increased gene and protein expression of Mertk, Tyro3, and Abca1, three proteins that promote macrophage efferocytosis. We also studied the effects of MEKi on in vivo macrophage efferocytosis and polarization. MEKi-treated mice had increased efferocytosis of apoptotic polymorphonuclear leukocytes instilled into the peritoneum. Furthermore, administration of MEKi after LPS-induced lung injury led to improved recovery of weight, fewer neutrophils in the alveolar compartment, and greater macrophage M2 polarization. Collectively, these results show that MEK1/2 inhibition is capable of promoting the reparative properties of murine and human macrophages. These studies suggest that the MEK1/2 pathway may be a therapeutic target to promote the resolution of inflammation via modulation of macrophage functions.

Deletion of LysM in LysMCre Recombinase Homozygous Mice is Non-contributory in LPS-Induced Acute Lung Injury.

Lysozyme is an important component of the innate immune system and has roles in peptidoglycan cleavage of gram-positive organisms. Myeloid cells highly express the isoform, lysozyme M, and its promoter has been used to direct Cre recombinase expression to target deletion of floxed genes in myeloid cells. However, generation of the LysMCre mouse effectively disrupts the LysM gene, and mice homozygous for the Cre allele lack the LysM gene product. To test the contribution of LysM in sterile acute lung injury, we generated LysMCre mice homozygous for the Cre allele (+/+) or wild-type allele (-/-). These mice were challenged with LPS delivered via oropharygneal aspiration. Mice were monitored and weighed daily, and BAL cell counts, differential, protein, and cytokine levels were assessed at days 2 and 4. LysMCre+/+ and LysMCre-/- had similar weight loss and recovery, and similar inflammatory responses to LPS at days 2 and 4. These findings indicate that loss of LysM and expression of Cre recombinase are non-contributory in sterile acute lung injury.

Upregulation and Nuclear Location of MMP28 in Alveolar Epithelium of Idiopathic Pulmonary Fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive aging-associated disease of unknown etiology. A growing body of evidence indicates that aberrant activated alveolar epithelial cells induce the expansion and activation of the fibroblast population, leading to the destruction of the lung architecture. Some matrix metalloproteinases (MMPs) are upregulated in IPF, indicating that they may be important in the pathogenesis and/or progression of IPF. In the present study, we examined the expression of MMP28 in this disease and evaluated its functional effects in two alveolar epithelial cell lines and in human primary bronchial epithelial cells. We found that the enzyme is expressed in bronchial (apical and cytoplasmic localization) and alveolar (cytoplasmic and nuclear localization) epithelial cells in two different groups of patients with IPF. In vitro MMP28 epithelial silencing decreased the proliferation rate and delayed wound closing, whereas overexpression showed opposite effects, protecting from apoptosis and enhanced epithelial-mesenchymal transition. Our findings demonstrate that MMP28 is upregulated in epithelial cells from IPF lungs, where it may play a role in increasing the proliferative and migratory phenotype in a catalysis-dependent manner.

Matrix Metalloproteinase-28 Is a Key Contributor to Emphysema Pathogenesis.

Chronic obstructive pulmonary disease (COPD) comprises chronic bronchitis and emphysema, and is a leading cause of morbidity and mortality. Because tissue destruction is the prominent characteristic of emphysema, extracellular proteinases, particularly those with elastolytic ability, are often considered to be key drivers in this disease. Several human and mouse studies have implicated roles for matrix metalloproteinases (MMPs), particularly macrophage-derived proteinases, in COPD pathogenesis. MMP-28 is expressed by the pulmonary epithelium and macrophage, and we have found that it regulates macrophage recruitment and polarization. We hypothesized that MMP-28 has contributory roles in emphysema via alteration of macrophage numbers and activation. Because of the established association of emphysema pathogenesis to macrophage influx, we evaluated the inflammatory changes and lung histology of Mmp28-/- mice exposed to 3 and 6 months of cigarette smoke. At earlier time points, we found altered macrophage polarization in the smoke-exposed Mmp28-/- lung consistent with other published findings that MMP-28 regulates macrophage activation. At both 3 and 6 months, Mmp28-/- mice had blunted inflammatory responses more closely resembling nonsmoked mice, with a reduction in neutrophil recruitment and CXCL1 chemokine expression. By 6 months, Mmp28-/- mice were protected from emphysema. These results highlight a previously unrecognized role for MMP-28 in promoting chronic lung inflammation and tissue remodeling induced by cigarette smoke and highlight another potential target to modulate COPD.

Stromelysin-2 (MMP10) Moderates Inflammation by Controlling Macrophage Activation.

Several members of the matrix metalloproteinase (MMP) family control a range of immune processes, such as leukocyte influx and chemokine activity. Stromelysin-2 (MMP10) is expressed by macrophages in numerous tissues after injury; however, little is known of its function. In this study, we report that MMP10 is expressed by macrophages in human lungs from patients with cystic fibrosis and induced in mouse macrophages in response to Pseudomonas aeruginosa infection both in vivo and by isolated resident alveolar and bone marrow-derived macrophages (BMDM). Our data indicates that macrophage MMP10 serves a beneficial function in response to acute infection. Whereas wild-type mice survived infection with minimal morbidity, 50% of Mmp10(-/-) mice died and all showed sustained weight loss (morbidity). Although bacterial clearance and neutrophil influx did not differ between genotypes, macrophage numbers were ∼3-fold greater in infected Mmp10(-/-) lungs than in wild-types. Adoptive transfer of wild-type BMDM normalized infection-induced morbidity in Mmp10(-/-) recipients to wild-type levels, demonstrating that the protective effect of MMP10 was due to its production by macrophages. Both in vivo and in cultured alveolar macrophages and BMDM, expression of several M1 macrophage markers was elevated, whereas M2 markers were reduced in Mmp10(-/-) tissue and cells. Global gene expression analysis revealed that infection-mediated transcriptional changes persisted in Mmp10(-/-) BMDM long after they were downregulated in wild-type cells. These results indicate that MMP10 serves a beneficial role in response to acute infection by moderating the proinflammatory response of resident and infiltrating macrophages.

Versican is produced by Trif- and type I interferon-dependent signaling in macrophages and contributes to fine control of innate immunity in lungs.

Growing evidence suggests that versican is important in the innate immune response to lung infection. Our goal was to understand the regulation of macrophage-derived versican and the role it plays in innate immunity. We first defined the signaling events that regulate versican expression, using bone marrow-derived macrophages (BMDMs) from mice lacking specific Toll-like receptors (TLRs), TLR adaptor molecules, or the type I interferon receptor (IFNAR1). We show that LPS and polyinosinic-polycytidylic acid [poly(I:C)] trigger a signaling cascade involving TLR3 or TLR4, the Trif adaptor, type I interferons, and IFNAR1, leading to increased expression of versican by macrophages and implicating versican as an interferon-stimulated gene. The signaling events regulating versican are distinct from those for hyaluronan synthase 1 (HAS1) and syndecan-4 in macrophages. HAS1 expression requires TLR2 and MyD88. Syndecan-4 requires TLR2, TLR3, or TLR4 and both MyD88 and Trif. Neither HAS1 nor syndecan-4 is dependent on type I interferons. The importance of macrophage-derived versican in lungs was determined with LysM/Vcan-/- mice. These studies show increased recovery of inflammatory cells in the bronchoalveolar lavage fluid of poly(I:C)-treated LysM/Vcan-/- mice compared with control mice. IFN-ß and IL-10, two important anti-inflammatory molecules, are significantly decreased in both poly(I:C)-treated BMDMs from LysM/Vcan-/- mice and bronchoalveolar lavage fluid from poly(I:C)-treated LysM/Vcan-/- mice compared with control mice. In short, type I interferon signaling regulates versican expression, and versican is necessary for type I interferon production. These findings suggest that macrophage-derived versican is an immunomodulatory molecule with anti-inflammatory properties in acute pulmonary inflammation.

CD11b(+) Mononuclear Cells Mitigate Hyperoxia-Induced Lung Injury in Neonatal Mice.

Bronchopulmonary dysplasia (BPD) is a common consequence of life-saving interventions for infants born with immature lungs. Resident tissue myeloid cells regulate lung pathology, but their role in BPD is poorly understood. To determine the role of lung interstitial myeloid cells in neonatal responses to lung injury, we exposed newborn mice to hyperoxia, a neonatal mouse lung injury model with features of human BPD. In newborn mice raised in normoxia, we identified a CD45(+) F4/80(+) CD11b(+), Ly6G(lo-int) CD71(+) population of cells in lungs of neonatal mice present in significantly greater percentages than in adult mice. In response to hyperoxia, surface marker and gene expression in whole lung macrophages/monocytes was biased to an alternatively activated phenotype. Partial depletion of these CD11b(+) mononuclear cells using CD11b-diphtheria toxin (DT) receptor transgenic mice resulted in 60% mortality by 40 hours of hyperoxia exposure with more severe lung injury, perivascular edema, and alveolar hemorrhage compared with DT-treated CD11b-DT receptor-negative controls, which displayed no mortality. These results identify an antiinflammatory population of CD11b(+) mononuclear cells that are protective in hyperoxia-induced neonatal lung injury in mice, and suggest that enhancing their beneficial functions may be a treatment strategy in infants at risk for BPD.

Diet-induced obesity alters myeloid cell populations in naïve and injured lung.

BACKGROUND: There are pulmonary consequences to obesity, including increased prevalence of asthma, greater susceptibility to influenza, and possibly reduced susceptibility to lung injury. Although it is well established that obesity is associated with alterations to the immune system, little is known about obesity-associated changes to pulmonary immune cells. OBJECTIVES: We hypothesized that obesity would alter the inflammatory milieu in the unchallenged lung and circulation; thereby contributing to altered susceptibility to lung injury. METHODS: We used a murine model of diet-induced obesity and evaluated bone marrow and blood leukocytes at 3 months, and pulmonary leukocytes at 3 and 6 months for changes in their adhesion and chemokine receptors, markers of activation states, and cell numbers. We also evaluated the inflammatory response to LPS in obese mice. RESULTS: In the lung, diet-induced obesity was associated with increased leukocyte numbers over-time. Adhesion receptors were increased in a cell- and site-specific fashion, and there was an evolution of macrophage and neutrophil polarization toward M1 and N1, respectively. After LPS-challenge, obesity was associated with increased neutrophil recruitment to the lung with impaired migration into the alveolar space. Associated with these changes, obesity increased LFA-1 and ICAM-1 neutrophil expression and altered CXCL1 gradients. CONCLUSION: Our results highlight the effects of diet-induced obesity on the murine blood and lung leukocyte populations, including increases in adhesion receptor expression that may contribute to altered recruitment or retention within the lung. Translation of these findings to people with obesity will be critical for determining the basic inflammatory underpinnings of pulmonary disease susceptibility.

Matrix metalloproteinase-28 deletion exacerbates cardiac dysfunction and rupture after myocardial infarction in mice by inhibiting M2 macrophage activation.

RATIONALE: Matrix metalloproteinase (MMP)-28 regulates the inflammatory and extracellular matrix responses in cardiac aging, but the roles of MMP-28 after myocardial infarction (MI) have not been explored. OBJECTIVE: To determine the impact of MMP-28 deletion on post-MI remodeling of the left ventricle (LV). METHODS AND RESULTS: Adult C57BL/6J wild-type (n=76) and MMP null (MMP-28((-/-)), n=86) mice of both sexes were subjected to permanent coronary artery ligation to create MI. MMP-28 expression decreased post-MI, and its cell source shifted from myocytes to macrophages. MMP-28 deletion increased day 7 mortality because of increased cardiac rupture post-MI. MMP-28(-/-) mice exhibited larger LV volumes, worse LV dysfunction, a worse LV remodeling index, and increased lung edema. Plasma MMP-9 levels were unchanged in the MMP-28((-/-)) mice but increased in wild-type mice at day 7 post-MI. The mRNA levels of inflammatory and extracellular matrix proteins were attenuated in the infarct regions of MMP-28(-/-) mice, indicating reduced inflammatory and extracellular matrix responses. M2 macrophage activation was impaired when MMP-28 was absent. MMP-28 deletion also led to decreased collagen deposition and fewer myofibroblasts. Collagen cross-linking was impaired as a result of decreased expression and activation of lysyl oxidase in the infarcts of MMP-28(-/-) mice. The LV tensile strength at day 3 post-MI, however, was similar between the 2 genotypes. CONCLUSIONS: MMP-28 deletion aggravated MI-induced LV dysfunction and rupture as a result of defective inflammatory response and scar formation by suppressing M2 macrophage activation.