A compensatory RNase E variation increases Iron Piracy and Virulence in multidrug-resistant Pseudomonas aeruginosa during Macrophage infection.

During chronic cystic fibrosis (CF) infections, evolved Pseudomonas aeruginosa antibiotic resistance is linked to increased pulmonary exacerbations, decreased lung function, and hospitalizations. However, the virulence mechanisms underlying worse outcomes caused by antibiotic resistant infections are poorly understood. Here, we investigated evolved aztreonam resistant P. aeruginosa virulence mechanisms. Using a macrophage infection model combined with genomic and transcriptomic analyses, we show that a compensatory mutation in the rne gene, encoding RNase E, increased pyoverdine and pyochelin siderophore gene expression, causing macrophage ferroptosis and lysis. We show that iron-bound pyochelin was sufficient to cause macrophage ferroptosis and lysis, however, apo-pyochelin, iron-bound pyoverdine, or apo-pyoverdine were insufficient to kill macrophages. Macrophage killing could be eliminated by treatment with the iron mimetic gallium. RNase E variants were abundant in clinical isolates, and CF sputum gene expression data show that clinical isolates phenocopied RNase E variant functions during macrophage infection. Together these data show how P. aeruginosa RNase E variants can cause host damage via increased siderophore production and host cell ferroptosis but may also be targets for gallium precision therapy.

Senescence of alveolar epithelial progenitor cells: a critical driver of lung fibrosis.

Pulmonary fibrosis comprises a range of chronic interstitial lung diseases (ILDs) that impose a significant burden on patients and public health. Among these, idiopathic pulmonary fibrosis (IPF), a disease of aging, is the most common and most severe form of ILD and is treated largely by lung transplantation. The lack of effective treatments to stop or reverse lung fibrosis-in fact, fibrosis in most organs-has sparked the need to understand causative mechanisms with the goal of identifying critical points for potential therapeutic intervention. Findings from many groups have indicated that repeated injury to the alveolar epithelium-where gas exchange occurs-leads to stem cell exhaustion and impaired alveolar repair that, in turn, triggers the onset and progression of fibrosis. Cellular senescence of alveolar epithelial progenitors is a critical cause of stemness failure. Hence, senescence impairs repair and thus contributes significantly to fibrosis. In this review, we discuss recent evidence indicating that senescence of epithelial progenitor cells impairs alveolar homeostasis and repair creating a profibrotic environment. Moreover, we discuss the impact of senescent alveolar epithelial progenitors, alveolar type 2 (AT2) cells, and AT2-derived transitional epithelial cells in fibrosis. Emerging evidence indicates that transitional epithelial cells are prone to senescence and, hence, are a new player involved in senescence-associated lung fibrosis. Understanding the complex interplay of cell types and cellular regulatory factors contributing to alveolar epithelial progenitor senescence will be crucial to developing targeted therapies to mitigate their downstream profibrotic sequelae and to promote normal alveolar repair.NEW & NOTEWORTHY With an aging population, lung fibrotic diseases are becoming a global health burden. Dysfunctional repair of the alveolar epithelium is a key causative process that initiates lung fibrosis. Normal alveolar regeneration relies on functional progenitor cells; however, the senescence of these cells, which increases with age, hinders their ability to contribute to repair. Here, we discuss studies on the control and consequence of progenitor cell senescence in fibrosis and opportunities for research.

Differential Responses to Targeting Matrix Metalloproteinase 9 in Idiopathic Pulmonary Fibrosis.

Rationale: Aberrant lung remodeling in idiopathic pulmonary fibrosis (IPF) is characterized by elevated MMP9 (matrix metalloproteinase 9) expression, but the precise role of this matrix metalloproteinase in this disease has yet to be fully elucidated.Objectives: To evaluate antifibrotic effects of MMP9 inhibition on IPF.Methods: Quantitative genomic, proteomic, and functional analyses both in vitro and in vivo were used to determine MMP9 expression in IPF cells and the effects of MMP9 inhibition on profibrotic mechanisms.Measurements and Main Results: In the present study, we demonstrate that MMP9 expression was increased in airway basal cell (ABC)-like cells from IPF lungs compared with ABC cells from normal lungs. The inhibition of MMP9 activity with an anti-MMP9 antibody, andecaliximab, blocked TGF-ß1 (transforming growth factor ß1)-induced Smad2 phosphorylation. However, in a subset of cells from patients with IPF, TGF-ß1 activation in their ABC-like cells was unaffected or enhanced by MMP9 blockade (i.e., nonresponders). Further analysis of nonresponder ABC-like cells treated with andecaliximab revealed an association with type 1 IFN expression, and the addition of IFNα to these cells modulated both MMP9 expression and TGF-ß1 activation. Finally, the inhibition of MMP9 ameliorated pulmonary fibrosis induced by responder lung cells but not a nonresponder in a humanized immunodeficient mouse model of IPF.Conclusions: Together, these data demonstrate that MMP9 regulates the activation of ABC-like cells in IPF and that targeting this MMP might be beneficial to a subset of patients with IPF who show sufficient expression of type 1 IFNs.

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.

Syndecan-1 Controls Lung Tumorigenesis by Regulating miRNAs Packaged in Exosomes.

Syndecan-1 is a transmembrane proteoglycan expressed prominently by lung epithelium and has pleiotropic functions such as regulating cell migration, proliferation, and survival. Loss of syndecan-1 expression by lung cancer cells is associated with higher-grade cancers and worse clinical prognosis. We evaluated the effects of syndecan-1 in various cell-based and animal models of lung cancer and found that lung tumorigenesis was moderated by syndecan-1. We also demonstrate that syndecan-1 (or lack thereof) alters the miRNA cargo carried within exosomes exported from lung cancer cells. Analysis of the changes in miRNA expression identified a distinct shift toward augmented procancer signaling consistent with the changes found in lung adenocarcinoma. Collectively, our work identifies syndecan-1 as an important factor in lung cancer cells that shapes the tumor microenvironment through alterations in miRNA packaging within exosomes.

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.

Defensins Potentiate a Neutralizing Antibody Response to Enteric Viral Infection.

α-defensins are abundant antimicrobial peptides with broad, potent antibacterial, antifungal, and antiviral activities in vitro. Although their contribution to host defense against bacteria in vivo has been demonstrated, comparable studies of their antiviral activity in vivo are lacking. Using a mouse model deficient in activated α-defensins in the small intestine, we show that Paneth cell α-defensins protect mice from oral infection by a pathogenic virus, mouse adenovirus 1 (MAdV-1). Survival differences between mouse genotypes are lost upon parenteral MAdV-1 infection, strongly implicating a role for intestinal defenses in attenuating pathogenesis. Although differences in α-defensin expression impact the composition of the ileal commensal bacterial population, depletion studies using broad-spectrum antibiotics revealed no effect of the microbiota on α-defensin-dependent viral pathogenesis. Moreover, despite the sensitivity of MAdV-1 infection to α-defensin neutralization in cell culture, we observed no barrier effect due to Paneth cell α-defensin activation on the kinetics and magnitude of MAdV-1 dissemination to the brain. Rather, a protective neutralizing antibody response was delayed in the absence of α-defensins. This effect was specific to oral viral infection, because antibody responses to parenteral or mucosal ovalbumin exposure were not affected by α-defensin deficiency. Thus, α-defensins play an important role as adjuvants in antiviral immunity in vivo that is distinct from their direct antiviral activity observed in cell culture.

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.

Macrophages, Wound Healing, and Fibrosis: Recent Insights.

PURPOSE OF REVIEW: Macrophages are central players in the immune response following tissue injury. These cells perform many functions, and the changing tissue microenvironment during injury shapes macrophage phenotype down a variety of polarized pathways. This review summarizes the current knowledge on the roles of macrophages during different stages of tissue injury, repair, and-if repair is not achieved-fibrosis. RECENT FINDINGS: Macrophages present early in inflammation are functionally distinct from those at later stages. The predominant macrophage phenotype must transition from pro-inflammatory to pro-reparative to facilitate wound healing and scar resolution. If macrophages fail to acquire a tissue-healing phenotype, dysregulated signals can be drivers of disease processes, such as sustained, exuberant inflammation-as occurs in arthropathies-and fibrosis. Comprehensive understanding of the roles of specific macrophage populations at different stages of the repair process will support the development of immune-targeted therapies for diseases such as fibrosis.

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.

Filamentous Bacteriophage Produced by Pseudomonas aeruginosa Alters the Inflammatory Response and Promotes Noninvasive Infection In Vivo.

Pseudomonas aeruginosa is an important opportunistic human pathogen that lives in biofilm-like cell aggregates at sites of chronic infection, such as those that occur in the lungs of patients with cystic fibrosis and nonhealing ulcers. During growth in a biofilm, P. aeruginosa dramatically increases the production of filamentous Pf bacteriophage (Pf phage). Previous work indicated that when in vivo Pf phage production was inhibited, P. aeruginosa was less virulent. However, it is not clear how the production of abundant quantities of Pf phage similar to those produced by biofilms under in vitro conditions affects pathogenesis. Here, using a murine pneumonia model, we show that the production of biofilm-relevant amounts of Pf phage prevents the dissemination of P. aeruginosa from the lung. Furthermore, filamentous phage promoted bacterial adhesion to mucin and inhibited bacterial invasion of airway epithelial cultures, suggesting that Pf phage traps P. aeruginosa within the lung. The in vivo production of Pf phage was also associated with reduced lung injury, reduced neutrophil recruitment, and lower cytokine levels. Additionally, when producing Pf phage, P. aeruginosa was less prone to phagocytosis by macrophages than bacteria not producing Pf phage. Collectively, these data suggest that filamentous Pf phage alters the progression of the inflammatory response and promotes phenotypes typically associated with chronic infection.

Lung pericyte-like cells are functional interstitial immune sentinel cells.

Pericytes are perivascular PDGF receptor-ß+ (PDGFRß+) stromal cells required for vasculogenesis and maintenance of microvascular homeostasis in many organs. Because of their unique juxtaposition to microvascular endothelium, lung PDGFRß+ cells are well situated to detect proinflammatory molecules released following epithelial injury and promote acute inflammatory responses. Thus we hypothesized that these cells represent an unrecognized immune surveillance or injury-sentinel interstitial cell. To evaluate this hypothesis, we isolated PDGFRß+ cells from murine lung and demonstrated that they have characteristics consistent with a pericyte population (referred to as pericyte-like cells for simplicity hereafter). We showed that pericyte-like cells expressed functional Toll-like receptors and upregulated chemokine expression following exposure to bronchoalveolar lavage fluid (BALF) collected from mice with sterile lung injury. Interestingly, BALF from mice without lung injury also induced chemokine expression in pericyte-like cells, suggesting that pericyte-like cells are primed to sense epithelial injury (permeability changes). Following LPS-induced lung inflammation, increased numbers of pericyte-like cells expressed IL-6, chemokine (C-X-C motif) ligand-1, chemokine (C-C motif) ligand 2/ monocyte chemotactic protein-1, and ICAM-1 in vivo. Sterile lung injury in pericyte-ablated mice was associated with decreased inflammation compared with normal mice. In summary, we found that pericyte-like cells are immune responsive and express diverse chemokines in response to lung injury in vitro and in vivo. Furthermore, pericyte-like cell ablation attenuated inflammation in sterile lung injury, suggesting that these cells play an important functional role in mediating lung inflammatory responses. We propose a model in which pericyte-like cells function as interstitial immune sentinels, detecting proinflammatory molecules released following epithelial barrier damage and participating in recruitment of circulating leukocytes.

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.

Integrative pathway genomics of lung function and airflow obstruction.

Chronic respiratory disorders are important contributors to the global burden of disease. Genome-wide association studies (GWASs) of lung function measures have identified several trait-associated loci, but explain only a modest portion of the phenotypic variability. We postulated that integrating pathway-based methods with GWASs of pulmonary function and airflow obstruction would identify a broader repertoire of genes and processes influencing these traits. We performed two independent GWASs of lung function and applied gene set enrichment analysis to one of the studies and validated the results using the second GWAS. We identified 131 significantly enriched gene sets associated with lung function and clustered them into larger biological modules involved in diverse processes including development, immunity, cell signaling, proliferation and arachidonic acid. We found that enrichment of gene sets was not driven by GWAS-significant variants or loci, but instead by those with less stringent association P-values. Next, we applied pathway enrichment analysis to a meta-analyzed GWAS of airflow obstruction. We identified several biologic modules that functionally overlapped with those associated with pulmonary function. However, differences were also noted, including enrichment of extracellular matrix (ECM) processes specifically in the airflow obstruction study. Network analysis of the ECM module implicated a candidate gene, matrix metalloproteinase 10 (MMP10), as a putative disease target. We used a knockout mouse model to functionally validate MMP10's role in influencing lung's susceptibility to cigarette smoke-induced emphysema. By integrating pathway analysis with population-based genomics, we unraveled biologic processes underlying pulmonary function traits and identified a candidate gene for obstructive lung disease.

Interplay of extracellular matrix and leukocytes in lung inflammation.

During inflammation, leukocytes influx into lung compartments and interact with extracellular matrix (ECM). Two ECM components, versican and hyaluronan, increase in a range of lung diseases. The interaction of leukocytes with these ECM components controls leukocyte retention and accumulation, proliferation, migration, differentiation, and activation as part of the inflammatory phase of lung disease. In addition, bronchial epithelial cells from asthmatic children co-cultured with human lung fibroblasts generate an ECM that is adherent for monocytes/macrophages. Macrophages are present in both early and late lung inflammation. Matrix metalloproteinase 10 (MMP10) is induced in alveolar macrophages with injury and infection and modulates macrophage phenotype and their ability to degrade collagenous ECM components. Collectively, studies outlined in this review highlight the importance of specific ECM components in the regulation of inflammatory events in lung disease. The widespread involvement of these ECM components in the pathogenesis of lung inflammation make them attractive candidates for therapeutic intervention.

Syndecan-1 Attenuates Lung Injury during Influenza Infection by Potentiating c-Met Signaling to Suppress Epithelial Apoptosis.

RATIONALE: Syndecan-1 is a cell surface heparan sulfate proteoglycan primarily expressed in the lung epithelium. Because the influenza virus is tropic to the airway epithelium, we investigated the role of syndecan-1 in influenza infection. OBJECTIVES: To determine the mechanism by which syndecan-1 regulates the lung mucosal response to influenza infection. METHODS: Wild-type (WT) and Sdc1(-/-) mice were infected with a H1N1 virus (PR8) as an experimental model of influenza infection. Human and murine airway epithelial cell cultures were also infected with PR8 to study the mechanism by which syndecan-1 regulates the inflammatory response. MEASUREMENT AND MAIN RESULTS: We found worsened outcomes and lung injury in Sdc1(-/-) mice compared with WT mice after influenza infection. Our data demonstrated that syndecan-1 suppresses bronchial epithelial apoptosis during influenza infection to limit widespread lung inflammation. Furthermore, we determined that syndecan-1 attenuated apoptosis by crosstalking with c-Met to potentiate its cytoprotective signals in airway epithelial cells during influenza infection. CONCLUSIONS: Our work shows that cell-associated syndecan-1 has an important role in regulating lung injury. Our findings demonstrate a novel mechanism in which cell membrane-associated syndecan-1 regulates the innate immune response to influenza infection by facilitating cytoprotective signals through c-Met signaling to limit bronchial epithelial apoptosis, thereby attenuating lung injury and inflammation.

Shedding of Syndecan-1/CXCL1 Complexes by Matrix Metalloproteinase 7 Functions as an Epithelial Checkpoint of Neutrophil Activation.

Although neutrophils play critical roles in innate immunity, in excess these cells cause severe tissue damage. Thus, neutrophil activation must be tightly regulated to prevent indiscriminant damage. Previously, we reported that mice lacking matrix metalloproteinase (MMP) 7 are protected from lung injury owing to markedly impaired neutrophil movement from the interstitium into mucosal lumenal spaces. This phenotype resulted from a lack of MMP7 shedding of syndecan-1, a heparan sulfate proteoglycan that carries the neutrophil chemokine CXCL1 as cargo. Here, we assessed if shedding syndecan-1/CXCL1 complexes affects neutrophil activation. Whereas injured monolayers of wild-type alveolar type II cells potently stimulated neutrophil activation, as gauged by release of myeloperoxidase, cells from Mmp7(-/-) or syndecan-1-null (Sdc1(-/-)) mice or human cells with MMP7 knockdown did not. In vivo, we observed reduced myeloperoxidase release relative to neutrophil numbers in bleomycin-injured Mmp7(-/-) and Sdc1(-/-) mice. Furthermore, we determined that soluble syndecan-1 directly stimulated neutrophil activation in the absence of cellular damage. These data indicate that MMP7 shedding of syndecan-1/CXCL1 complexes functions as a checkpoint that restricts neutrophil activation at sites of epithelial injury.

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.

Nonhematopoietic Peroxisome Proliferator-Activated Receptor-α Protects Against Cardiac Injury and Enhances Survival in Experimental Polymicrobial Sepsis.

OBJECTIVES: Peroxisome proliferator-activated receptor-α is significantly down-regulated in circulating leukocytes from children with sepsis. Peroxisome proliferator-activated receptor-α null (Ppara) mice have greater mortality than wild-type mice when subjected to sepsis by cecal ligation and puncture. We sought to characterize the role of peroxisome proliferator-activated receptor-α in sepsis and to identify the mechanism whereby peroxisome proliferator-activated receptor-α confers a survival advantage. DESIGN: Prospective randomized preclinical study. SETTING: Laboratory investigation. SUBJECTS: Male C57Bl/6J and Ppara mice (B6.129S4-Ppara/J), aged 12-16 weeks. INTERVENTIONS: Bone marrow chimeric mice were generated and subjected to cecal ligation and puncture. Survival was measured for 7 days. Separate groups of nontransplanted mice underwent cecal ligation and puncture and were euthanized 24 hours later for plasma and tissue analyses. MEASUREMENTS AND MAIN RESULTS: Ppara mice had dramatically reduced survival compared with wild-type mice irrespective of the peroxisome proliferator-activated receptor-α status of the bone marrow they received (3% vs 63%; p < 0.0001). No difference in survival was observed between Ppara mice that received wild-type versus Ppara marrow or in wild-type mice receiving wild-type versus Ppara marrow. In septic, nontransplanted mice at 24 hours, Ppara mice had elevated cardiac troponin levels compared with wild-type mice. Cardiac histologic injury scores were greater in Ppara versus wild-type mice. Expression of transcription factors and enzymes related to fatty acid oxidation in the heart were profoundly down-regulated in both wild-type and Ppara mice, but more so in the Ppara mice. CONCLUSIONS: Peroxisome proliferator-activated receptor-α expression in nonhematopoietic tissues plays a critical role in determining clinical outcome in experimental polymicrobial sepsis and is more important to survival in sepsis than hematopoietic peroxisome proliferator-activated receptor-α expression. Cardiac injury due to inadequate energy production from fatty acid substrate is a probable mechanism of decreased survival in Ppara mice. These results suggest that altered peroxisome proliferator-activated receptor-α-mediated cellular metabolism may play an important role in sepsis-related end-organ injury and dysfunction, especially in the heart.

Syndecan-1 controls cell migration by activating Rap1 to regulate focal adhesion disassembly.

After injury, residual epithelial cells coordinate contextual clues from cell-cell and cell-matrix interactions to polarize and migrate over the wound bed. Protrusion formation, cell body translocation and rear retraction is a repetitive process that allows the cell to move across the substratum. Fundamental to this process is the assembly and disassembly of focal adhesions that facilitate cell adhesion and protrusion formation. Here, we identified syndecan-1 as a regulator of focal adhesion disassembly in migrating lung epithelial cells. Syndecan-1 altered the dynamic exchange of adhesion complex proteins, which in turn regulates migration speed. Moreover, we provide evidence that syndecan-1 controls this entire process through Rap1. Thus, syndecan-1 restrains migration in lung epithelium by activating Rap1 to slow focal adhesion disassembly.