Induction of STAT3-Dependent CXCL5 Expression and Neutrophil Recruitment by Oncostatin-M during Pneumonia

Acute bacterial pneumonia is a significant public health concern worldwide. Understanding the signals coordinating lung innate immunity may foster the development of therapeutics that limit tissue damage and promote host defense. We have previously shown that lung messenger RNA expression of the IL-6 family cytokine oncostatin-M (OSM) is significantly elevated in response to bacterial stimuli. However, its physiological significance during pneumonia is unknown. Here we demonstrate that OSM is rapidly increased in the airspaces of mice after pulmonary infection with Escherichia coli. Neutralization of OSM caused a substantial decrease in airspace neutrophils and macrophages. OSM blockade also caused a marked reduction in lung chemokine (C-X-C motif) ligand (CXCL) 5 expression, whereas other closely related neutrophil chemokines, CXCL1 and CXCL2, were unaffected. Intratracheal administration of recombinant OSM was sufficient to recapitulate the effect on CXCL5 induction, associated with robust activation of the signal transducer and activator of transcription 3 (STAT3) transcription factor. Cell sorting revealed that OSM effects were specific to lung epithelial cells, including a positive feedback loop in which OSM may facilitate expression of its own receptor. Finally, in vitro studies demonstrated that STAT3 was required for maximal OSM-induced CXCL5 expression. These studies demonstrate a novel role for OSM during pneumonia as an important signal to epithelial cells for chemokine induction mediating neutrophil recruitment.

The Lung-Liver Axis: A Requirement for Maximal Innate Immunity and Hepatoprotection during Pneumonia

The hepatic acute-phase response (APR), stimulated by injury or inflammation, is characterized by significant changes in circulating acute-phase protein (APP) concentrations. Although individual functions of liver-derived APPs are known, the net consequence of APP changes is unclear. Pneumonia, which induces the APR, causes an inflammatory response within the airspaces that is coordinated largely by alveolar macrophages and is typified by cytokine production, leukocyte recruitment, and plasma extravasation, the latter of which may enable delivery of hepatocyte-derived APPs to the infection site. To determine the functional significance of the hepatic APR during pneumonia, we challenged APR-null mice lacking hepatocyte signal transducer and activator of transcription 3 (STAT3) and v-rel avian reticuloendotheliosis viral oncogene homolog A (RelA) with Escherichia coli in the airspaces. APR-null mice displayed ablated APP induction, significantly increased mortality, liver injury and apoptosis, and a trend toward increased bacterial burdens. TNF-α neutralization reversed hepatotoxicity, but not mortality, suggesting that APR-dependent survival is not solely due to hepatoprotection. After a milder (nonlethal) E. coli infection, hepatocyte-specific mutations decreased APP concentrations and pulmonary inflammation in bronchoalveolar lavage fluid. Cytokine expression in airspace macrophages, but not other airspace or circulating cells, was significantly dependent on APP extravasation into the alveoli. These data identify a novel signaling axis whereby the liver response enhances macrophage activation and pulmonary inflammation during pneumonia. Although hepatic acute-phase changes directly curb injury induced by TNF-α in the liver itself, APPs downstream of these same signals promote survival in association with innate immunity in the lungs, thus demonstrating a critical role for the lung-liver axis during pneumonia.

Myeloid ZFP36L1 does not regulate inflammation or host defense in mouse models of acute bacterial infection

Zinc finger protein 36, C3H type-like 1 (ZFP36L1) is one of several Zinc Finger Protein 36 (Zfp36) family members, which bind AU rich elements within 3' untranslated regions (UTRs) to negatively regulate the post-transcriptional expression of targeted mRNAs. The prototypical member of the family, Tristetraprolin (TTP or ZFP36), has been well-studied in the context of inflammation and plays an important role in repressing pro-inflammatory transcripts such as TNF-α. Much less is known about the other family members, and none have been studied in the context of infection. Using macrophage cell lines and primary alveolar macrophages we demonstrated that, like ZFP36, ZFP36L1 is prominently induced by infection. To test our hypothesis that macrophage production of ZFP36L1 is necessary for regulation of the inflammatory response of the lung during pneumonia, we generated mice with a myeloid-specific deficiency of ZFP36L1. Surprisingly, we found that myeloid deficiency of ZFP36L1 did not result in alteration of lung cytokine production after infection, altered clearance of bacteria, or increased inflammatory lung injury. Although alveolar macrophages are critical components of the innate defense against respiratory pathogens, we concluded that myeloid ZFP36L1 is not essential for appropriate responses to bacteria in the lungs. Based on studies conducted with myeloid-deficient ZFP36 mice, our data indicate that, of the Zfp36 family, ZFP36 is the predominant negative regulator of cytokine expression in macrophages. In conclusion, these results imply that myeloid ZFP36 may fully compensate for loss of ZFP36L1 or that Zfp36l1-dependent mRNA expression does not play an integral role in the host defense against bacterial pneumonia.

Dynamics of lung defense in pneumonia: resistance, resilience, and remodeling

Pneumonia is initiated by microbes in the lung, but physiological processes integrating responses across diverse cell types and organ systems dictate the outcome of respiratory infection. Resistance, or actions of the host to eradicate living microbes, in the lungs involves a combination of innate and adaptive immune responses triggered by air-space infection. Resilience, or the ability of the host tissues to withstand the physiologically damaging effects of microbial and immune activities, is equally complex, precisely regulated, and determinative. Both immune resistance and tissue resilience are dynamic and change throughout the lifetime, but we are only beginning to understand such remodeling and how it contributes to the incidence of severe pneumonias, which diminishes as childhood progresses and then increases again among the elderly. Here, we review the concepts of resistance, resilience, and remodeling as they apply to pneumonia, highlighting recent advances and current significant knowledge gaps.

Roles of lung epithelium in neutrophil recruitment during pneumococcal pneumonia

Epithelial cells line the respiratory tract and interface with the external world. Epithelial cells contribute to pulmonary inflammation, but specific epithelial roles have proven difficult to define. To discover unique epithelial activities that influence immunity during infection, we generated mice with nuclear factor-κB RelA mutated throughout all epithelial cells of the lung and coupled this approach with epithelial cell isolation from infected and uninfected lungs for cell-specific analyses of gene induction. The RelA mutant mice appeared normal basally, but in response to pneumococcus in the lungs they were unable to rapidly recruit neutrophils to the air spaces. Epithelial cells expressed multiple neutrophil-stimulating cytokines during pneumonia, all of which depended on RelA. Cytokine expression by nonepithelial cells was unaltered by the epithelial mutation of RelA. Epithelial cells were the predominant sources of CXCL5 and granulocyte-macrophage colony-stimulating factor (GM-CSF), whereas nonepithelial cells were major sources for other neutrophil-activating cytokines. Epithelial RelA mutation decreased whole lung levels of CXCL5 and GM-CSF during pneumococcal pneumonia, whereas lung levels of other neutrophil-recruiting factors were unaffected. Defective neutrophil recruitment in epithelial mutant mice could be rescued by administration of CXCL5 or GM-CSF. These results reveal a specialized immune function for the pulmonary epithelium, the induction of CXCL5 and GM-CSF, to accelerate neutrophil recruitment in the infected lung.

IL-6 trans-signaling promotes pancreatitis-associated lung injury and lethality

Acute lung injury (ALI) is an inflammatory disease with a high mortality rate. Although typically seen in individuals with sepsis, ALI is also a major complication in severe acute pancreatitis (SAP). The pathophysiology of SAP-associated ALI is poorly understood, but elevated serum levels of IL-6 is a reliable marker for disease severity. Here, we used a mouse model of acute pancreatitis-associated (AP-associated) ALI to determine the role of IL-6 in ALI lethality. Il6-deficient mice had a lower death rate compared with wild-type mice with AP, while mice injected with IL-6 were more likely to develop lethal ALI. We found that inflammation-associated NF-κB induced myeloid cell secretion of IL-6, and the effects of secreted IL-6 were mediated by complexation with soluble IL-6 receptor, a process known as trans-signaling. IL-6 trans-signaling stimulated phosphorylation of STAT3 and production of the neutrophil attractant CXCL1 in pancreatic acinar cells. Examination of human samples revealed expression of IL-6 in combination with soluble IL-6 receptor was a reliable predictor of ALI in SAP. These results demonstrate that IL-6 trans-signaling is an essential mediator of ALI in SAP across species and suggest that therapeutic inhibition of IL-6 may prevent SAP-associated ALI.

Lentiviral delivery of RNAi for in vivo lineage-specific modulation of gene expression in mouse lung macrophages

Although RNA interference (RNAi) has become a ubiquitous laboratory tool since its discovery 12 years ago, in vivo delivery to selected cell types remains a major technical challenge. Here, we report the use of lentiviral vectors for long-term in vivo delivery of RNAi selectively to resident alveolar macrophages (AMs), key immune effector cells in the lung. We demonstrate the therapeutic potential of this approach by RNAi-based downregulation of p65 (RelA), a component of the pro-inflammatory transcriptional regulator, nuclear factor κB (NF-κB) and a key participant in lung disease pathogenesis. In vivo RNAi delivery results in decreased induction of NF-κB and downstream neutrophilic chemokines in transduced AMs as well as attenuated lung neutrophilia following stimulation with lipopolysaccharide (LPS). Through concurrent delivery of a novel lentiviral reporter vector (lenti-NF-κB-luc-GFP) we track in vivo expression of NF-κB target genes in real time, a critical step towards extending RNAi-based therapy to longstanding lung diseases. Application of this system reveals that resident AMs persist in the airspaces of mice following the resolution of LPS-induced inflammation, thus allowing these localized cells to be used as effective vehicles for prolonged RNAi delivery in disease settings.

Direct control of hepatic glucose production by interleukin-13 in mice

Hyperglycemia is a result of impaired insulin action on glucose production and disposal, and a major target of antidiabetic therapies. The study of insulin-independent regulatory mechanisms of glucose metabolism may identify new strategies to lower blood sugar levels. Here we demonstrate an unexpected metabolic function for IL-13 in the control of hepatic glucose production. IL-13 is a Th2 cytokine known to mediate macrophage alternative activation. Genetic ablation of Il-13 in mice (Il-13-/-) resulted in hyperglycemia, which progressed to hepatic insulin resistance and systemic metabolic dysfunction. In Il-13-/- mice, upregulation of enzymes involved in hepatic gluconeogenesis was a primary event leading to dysregulated glucose metabolism. IL-13 inhibited transcription of gluconeogenic genes by acting directly on hepatocytes through Stat3, a noncanonical downstream effector. Consequently, the ability of IL-13 to suppress glucose production was abolished in liver cells lacking Stat3 or IL-13 receptor α1 (Il-13rα1), which suggests that the IL-13Rα1/Stat3 axis directs IL-13 signaling toward metabolic responses. These findings extend the implication of a Th1/Th2 paradigm in metabolic homeostasis beyond inflammation to direct control of glucose metabolism and suggest that the IL-13/Stat3 pathway may serve as a therapeutic target for glycemic control in insulin resistance and type 2 diabetes.

Zcchc11 uridylates mature miRNAs to enhance neonatal IGF-1 expression, growth, and survival

The Zcchc11 enzyme is implicated in microRNA (miRNA) regulation. It can uridylate let-7 precursors to decrease quantities of the mature miRNA in embryonic stem cell lines, suggested to mediate stem cell maintenance. It can uridylate mature miR-26 to relieve silencing activity without impacting miRNA content in cancer cell lines, suggested to mediate cytokine and growth factor expression. Broader roles of Zcchc11 in shaping or remodeling the miRNome or in directing biological or physiological processes remain entirely speculative. We generated Zcchc11-deficient mice to address these knowledge gaps. Zcchc11 deficiency had no impact on embryogenesis or fetal development, but it significantly decreased survival and growth immediately following birth, indicating a role for this enzyme in early postnatal fitness. Deep sequencing of small RNAs from neonatal livers revealed roles of this enzyme in miRNA sequence diversity. Zcchc11 deficiency diminished the lengths and terminal uridine frequencies for diverse mature miRNAs, but it had no influence on the quantities of any miRNAs. The expression of IGF-1, a liver-derived protein essential to early growth and survival, was enhanced by Zcchc11 expression in vitro, and miRNA silencing of IGF-1 was alleviated by uridylation events observed to be Zcchc11-dependent in the neonatal liver. In neonatal mice, Zcchc11 deficiency significantly decreased IGF-1 mRNA in the liver and IGF-1 protein in the blood. We conclude that the Zcchc11-mediated terminal uridylation of mature miRNAs is pervasive and physiologically significant, especially important in the neonatal period for fostering IGF-1 expression and enhancing postnatal growth and survival. We propose that the miRNA 3′ terminus is a regulatory node upon which multiple enzymes converge to direct silencing activity and tune gene expression.

MicroRNAs (miRNAs) are molecules that regulate gene expression, usually serving silencing functions. Mechanisms regulating miRNAs are poorly understood. In test tube experiments, the enzyme Zcchc11 adds uridines to the ends of miRNAs and their precursors, with uridyation of miRNA precursors decreasing the quantities of mature miRNAs and uridylation of mature miRNAs decreasing their silencing activity. Whether, when, and to what effect Zcchc11 alters miRNA in living animals has never previously been reported. To understand functions of Zcchc11 in integrative biology, we generated mice deficient in Zcchc11. Mutant mice were born normally, but some died soon after birth and survivors grew poorly. No miRNA quantities were changed in tissues sampled from these mice, but mature miRNAs were less likely to have additional uridines on their ends. Some miRNAs that were uridylated by Zcchc11 targeted a critical growth factor known as insulin-like growth factor 1 (IGF-1), but they did so less effectively when uridylated. Zcchc11-deficient mice had decreased amounts of IGF-1 in the liver and blood. These data reveal that Zcchc11 is an important enzyme in living animals for uridylating mature miRNAs, enhancing IGF-1 expression, and promoting neonatal growth and survival, suggesting a novel mode of gene regulation that is biologically significant.

Defining critical roles for NF-κB p65 and type I interferon in innate immunity to rhinovirus

The importance of NF-κB activation and deficient anti-viral interferon induction in the pathogenesis of rhinovirus-induced asthma exacerbations is poorly understood. We provide the first in vivo evidence in man and mouse that rhinovirus infection enhanced bronchial epithelial cell NF-κB p65 nuclear expression, NF-κB p65 DNA binding in lung tissue and NF-κB-regulated airway inflammation. In vitro inhibition of NF-κB reduced rhinovirus-induced pro-inflammatory cytokines but did not affect type I/III interferon induction. Rhinovirus-infected p65-deficient mice exhibited reduced neutrophilic inflammation, yet interferon induction, antiviral responses and virus loads were unaffected, indicating that NF-κB p65 is required for pro-inflammatory responses, but redundant in interferon induction by rhinoviruses in vivo. Conversely, IFNAR1^−/− mice exhibited enhanced neutrophilic inflammation with impaired antiviral immunity and increased rhinovirus replication, demonstrating that interferon signalling was critical to antiviral immunity. We thus provide new mechanistic insights into rhinovirus infection and demonstrate the therapeutic potential of targeting NF-κB p65 (to suppress inflammation but preserve anti-viral immunity) and type I IFN signalling (to enhance deficient anti-viral immunity) to treat rhinovirus-induced exacerbations of airway diseases.

Type I alveolar epithelial cells mount innate immune responses during pneumococcal pneumonia

Pneumonia results from bacteria in the alveoli. The alveolar epithelium consists of type II cells, which secrete surfactant and associated proteins, and type I cells, which constitute 95% of the surface area and meet anatomic and structural needs. Other than constitutively expressed surfactant proteins, it is unknown whether alveolar epithelial cells have distinct roles in innate immunity. Because innate immunity gene induction depends on NF-κB RelA (also known as p65) during pneumonia, we generated a murine model of RelA mutated throughout the alveolar epithelium. In response to LPS, only 2 of 84 cytokine transcripts (CCL20 and CXCL5) were blunted in lungs of mutants, suggesting that a very limited subset of immune mediators is selectively elaborated by the alveolar epithelium. Lung CCL20 induction required epithelial RelA regardless of stimulus, whereas lung CXCL5 expression depended on RelA after instillation of LPS but not pneumococcus. RelA knockdown in vitro suggested that CXCL5 induction required RelA in type II cells but not type I cells. Sorted cell populations from mouse lungs revealed that CXCL5 was induced during pneumonia in type I cells, which did not require RelA. TLR2 and STING were also induced in type I cells, with RelA essential for TLR2 but not STING. To our knowledge, these data are the first direct demonstration that type I cells, which constitute the majority of the alveolar surface, mount innate immune responses during bacterial infection. These are also, to our knowledge, the first evidence for entirely RelA-independent pathways of innate immunity gene induction in any cell during pneumonia.

Respiratory infection and the impact of pulmonary immunity on lung health and disease

Acute lower respiratory tract infection is responsible for an inordinate disease burden. Pulmonary immunity determines the outcomes of these infections. The innate and adaptive immune responses to microbes in the lung are critical to maintaining a healthy respiratory system and preventing pulmonary disease. In addition to balancing antimicrobial defense against the risk of lung injury during the immediate infection, the shaping of pulmonary immunity by respiratory infection contributes to the pathophysiology of many and even perhaps most chronic pulmonary diseases. This Pulmonary Perspective aims to communicate two interconnected points. First, tremendous morbidity and mortality result from inadequate, misguided, or excessive pulmonary immunity. Second, our understanding of pulmonary immunity is at an exciting stage of rapid developments and discoveries, but many questions remain. Further advances in pulmonary immunity and elucidation of the cellular and molecular responses to microbes in the lung are needed to develop novel approaches to predicting, preventing, and curing respiratory disease.

Leukemia inhibitory factor signaling is required for lung protection during pneumonia

Lung infections represent a tremendous disease burden and a leading cause of acute lung injury. STAT3 signaling is essential for controlling lung injury during pneumonia. We previously identified LIF as a prominent STAT3-activating cytokine expressed in the airspaces of pneumonic lungs, but its physiological significance in this setting has never been explored. To do so, Escherichia coli was intratracheally instilled into C57BL/6 mice in the presence of neutralizing anti-LIF IgG or control IgG. Anti-LIF completely eliminated lung LIF detection and markedly exacerbated lung injury compared with control mice as evidenced by airspace albumin content, lung liquid accumulation, and histological analysis. Although lung bacteriology was equivalent between groups, bacteremia was more prevalent with anti-LIF treatment, suggestive of compromised barrier function rather than impaired antibacterial defense as the cause of dissemination. Inflammatory cytokine expression was also exaggerated in anti-LIF-treated lungs, albeit after injury had ensued. Interestingly, alveolar neutrophil recruitment was modestly but significantly reduced compared with control mice despite elevated cytokine levels, indicating that inflammatory injury was not a consequence of excessive neutrophilic alveolitis. Lastly, the lung transcriptome was dramatically remodeled during pneumonia, but far more so following LIF neutralization, with gene changes implicating cell death and epithelial homeostasis among other processes relevant to tissue injury. From these findings, we conclude that endogenous LIF facilitates tissue protection during pneumonia. The LIF-STAT3 axis is identified in this study as a critical determinant of lung injury with clinical implications for pneumonia patients.

Hepatocyte-specific mutation of both NF-κB RelA and STAT3 abrogates the acute phase response in mice

The acute phase response is an evolutionarily conserved reaction in which physiological stress triggers the liver to remodel the blood proteome. Although thought to be involved in immune defense, the net biological effect of the acute phase response remains unknown. As the acute phase response is stimulated by diverse cytokines that activate either NF-κB or STAT3, we hypothesized that it could be eliminated by hepatocyte-specific interruption of both transcription factors. Here, we report that the elimination in mice of both NF-κB p65 (RelA) and STAT3, but neither alone, abrogated all acute phase responses measured. The failure to respond was consistent across multiple different infectious, inflammatory, and noxious stimuli, including pneumococcal pneumonia. When the effects of infection were analyzed in detail, pneumococcal pneumonia was found to alter the expression of over a thousand transcripts in the liver. This outcome was inhibited by the combined loss of RelA and STAT3. Moreover, this interruption of the acute phase response increased mortality and exacerbated bacterial dissemination during pneumonia, possibly as a result of acute humoral enhancement of macrophage opsonophagocytosis, which was impaired in the mutant mice. Thus, we conclude that RelA and STAT3 are essential for stress-induced transcriptional remodeling in the liver and the subsequent activation of the acute phase response, whose functional role includes compartmentalization of local infection.

Terminal uridyltransferase enzyme Zcchc11 promotes cell proliferation independent of its uridyltransferase activity

Zcchc11 is a uridyltransferase protein with enzymatic activity directed against diverse RNA species. On the basis of its known uridylation targets, we hypothesized that Zcchc11 might regulate cell proliferation. Confirming this, loss-of-function and complementary gain-of-function experiments consistently revealed that Zcchc11 promotes the transition from G(1) to S phase of the cell cycle. This activity takes place through both Rb-dependent and Rb-independent mechanisms by promoting the expression of multiple G(1)-associated proteins, including cyclins D(1) and A and CDK4. Surprisingly, a Zcchc11 construct with point mutations inactivating the uridyltransferase domain enhanced cell proliferation as effectively as wild-type Zcchc11. Furthermore, truncated mutant constructs revealed that the cell cycle effects of Zcchc11 were driven by the N-terminal region of the protein that lacks the RNA-binding domains and uridyltransferase activity of the full protein. Therefore, the N-terminal portion of Zcchc11, which lacks nucleotidyltransferase capabilities, is biologically active and mediates a previously unrecognized role for Zcchc11 in facilitating cell proliferation.

Earliest innate immune responses require macrophage RelA during pneumococcal pneumonia

NF-κB regulates cytokine expression to initiate and control the innate immune response to lung infections. The NF-κB protein RelA is critical for pulmonary host defense during Streptococcus pneumoniae pneumonia, but the cell-specific roles of this transcription factor remain to be determined. We hypothesized that RelA in alveolar macrophages contributes to cytokine expression and host defense during pneumococcal pneumonia. To test this hypothesis, we compared mice lacking RelA exclusively in myeloid cells (RelA(Δ/Δ)) with littermate controls (RelA(F/F)). Alveolar macrophages from RelA(Δ/Δ) mice expressed no full-length RelA, demonstrating effective targeting. Alveolar macrophages from RelA(Δ/Δ) mice exhibited reduced, albeit detectable, proinflammatory cytokine responses to S. pneumoniae, compared with alveolar macrophages from RelA(F/F) mice. Concentrations of these cytokines in lung homogenates were diminished early after infection, indicating a significant contribution of macrophage RelA to the initial expression of cytokines in the lungs. However, the cytokine content in infected lungs was equivalent by 15 hours. Neutrophil recruitment during S. pneumoniae pneumonia reflected a delayed onset in RelA(Δ/Δ) mice, followed by similar rates of accumulation. Bacterial clearance was eventually effective in both genotypes, but began later in RelA(Δ/Δ) mice. Thus, during pneumococcal pneumonia, only the earliest induction of the cytokines measured depended on transcription by RelA in myeloid cells, and this transcriptional activity contributed to effective immunity.

NF-κB and STAT3 signaling hubs for lung innate immunity

Innate immune responses to lung pathogens involve the coordinated expression of myriad affector and effector molecules of innate immunity, which must be induced and appropriately regulated in response to diverse stimuli generated by microbes or the infected host. Many intercellular and intracellular signaling pathways are involved, but we propose NF-κB and STAT3 transcription factors to be especially important signaling hubs for integrating these pathways to orchestrate effective host defense without excessive inflammatory injury.

Mice lacking both TNF and IL-1 receptors exhibit reduced lung inflammation and delay in onset of death following infection with a highly virulent H5N1 virus

BACKGROUND

Highly pathogenic avian influenza viruses of the H5N1 subtype continue to cross the species barrier to infect humans and cause severe disease. It has been suggested that an exaggerated immune response contributes to the pathogenesis of H5N1 virus infection in mammals. In particular, H5N1 virus infections are associated with a high expression of the proinflammatory cytokines, including interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-α).

METHODS

We investigated the compounding affects of both cytokines on the outcome of H5N1 virus disease by using triple mutant mice deficient in 3 signaling receptors, TNF-R1, TNF-R2, and IL-1-RI.

RESULTS

Triple mutant mice exhibited reduced morbidity and a significant delay in mortality following lethal challenge with a lethal H5N1 virus, whereas no such differences were observed with the less virulent A/PR/8/34 (H1N1) virus. H5N1-infected triple mutant mice displayed diminished cytokine production in lung tissue and a quantifiable decrease of macrophages and neutrophils in the lungs postinfection. Moreover, morphometric analysis of airway sections revealed less extensive inflammation in H5N1-infected triple mutant mice, compared with infected wild-type mice.

CONCLUSIONS

The combined signaling from the TNF or IL-1 receptors promotes maximal lung inflammation that may contribute to the severity of disease caused by H5N1 virus infection.

Induction of cytoplasmic accumulation of p53: a mechanism for low levels of arsenic exposure to predispose cells for malignant transformation

Although epidemiologic studies have linked arsenic exposure to the development of human cancer, the mechanisms underlying the tumorigenic role of arsenic remain largely undefined. We report here that treatment of cells with sodium arsenite at the concentrations close to environmental exposure is associated with the up-regulation of Hdm2 and the accumulation of p53 in the cytoplasm. Through the mitogen-activated protein kinase pathway, arsenite stimulates the P2 promoter-mediated expression of Hdm2, which then promotes p53 nuclear export. As a consequence, the p53 response to genotoxic stress is compromised, as evidenced by the impaired p53 activation and apoptosis in response to UV irradiation or 5FU treatment. The ability of arsenite to impede p53 activation is further demonstrated by a significantly blunted p53-dependent tissue response to 5FU treatment when mice were fed with arsenite-containing water. Together, our data suggests that arsenic compounds predispose cells to malignant transformation by up-regulation of Hdm2 and subsequent p53 inactivation.

Effect of obesity on pulmonary inflammation induced by acute ozone exposure: role of interleukin-6

To determine the role of interleukin (IL)-6 in the increased ozone (O3)-induced inflammation and injury observed in obese vs. lean mice, lean wild-type and leptin-deficient obese (ob/ob) mice were injected with anti-IL-6 antibody (Ab) or isotype control Ab 24 h before exposure to either O3 (2 ppm for 3 h) or room air. Four or 24 h after O3 exposure, bronchoalveolar lavage (BAL) was performed, and the lungs were harvested for Western blotting. Anti-IL-6 Ab caused substantial reductions in O3-induced increases in BAL IL-6 in mice of both genotypes. Four hours following O3, ob/ob mice had increased BAL neutrophils compared with controls, and anti-IL-6-Ab virtually abolished this difference. At 24 h, O3-induced increases in BAL protein and BAL serum albumin were augmented in ob/ob vs. wild-type mice, and anti-IL-6 Ab ablated these obesity-related differences in epithelial barrier injury. O3 increased tyrosine phosphorylation of STAT-3 and STAT-1. There was no effect of obesity on STAT-3 phosphorylation, whereas obesity decreased STAT-1 expression, resulting in reduced STAT-1 phosphorylation. IL-6 neutralization did not alter STAT-3 or STAT-1 phosphorylation in ob/ob or wild-type mice. O3 increased BAL leukemia inhibitory factor (LIF) to a greater extent in obese than in lean mice, and LIF may account for effects on STAT phosphorylation. Our results suggest that IL-6 plays a complex role in pulmonary responses to O3, a role that differs between wild-type and ob/ob mice. Moreover, obesity-related differences in activation of STAT proteins may contribute to some of the differences in the response of obese vs. lean mice.

Alveolar epithelial STAT3, IL-6 family cytokines, and host defense during Escherichia coli pneumonia

While signal transducer and activator of transcription (STAT) 3 signaling has been linked to multiple pathways influencing immune function and cell survival, the direct influence of this transcription factor on innate immunity and tissue homeostasis during pneumonia is unknown. Human patients with dominant-negative mutations in the Stat3 gene develop recurrent pneumonias, suggesting a role for STAT3 in pulmonary host defense. We hypothesized that alveolar epithelial STAT3 is activated by IL-6 family cytokines and is required for effective responses during gram-negative bacterial pneumonia. STAT3 phosphorylation was increased in pneumonic mouse lungs and in murine lung epithelial (MLE)-15 cells stimulated with pneumonic bronchoalveolar lavage fluid (BALF) through 48 hours of Escherichia coli pneumonia. Mice lacking active STAT3 in alveolar epithelial cells (Stat3(Delta/Delta)) had fewer alveolar neutrophils and more viable bacteria than control mice early after intratracheal E. coli. By 48 hours after E. coli infection, however, lung injury was increased in Stat3(Delta/Delta) mice. Bacteria were cleared from lungs of both genotypes, albeit more slowly in Stat3(Delta/Delta) mice. Of the IL-6 family cytokines measured in lungs from infected C57BL/6 mice, IL-6, oncostatin M, leukemia inhibitory factor (LIF), and IL-11 were significantly elevated. Neutralization studies demonstrated that LIF and IL-6 mediated BALF-induced STAT3 activation in MLE-15 cells. Together, these results indicate that during E. coli pneumonia, select IL-6 family members activate alveolar epithelial STAT3, which functions to promote neutrophil recruitment and to limit both infection and lung injury.

Animal models of human pneumonia

Pneumonia is a medical and public health priority, and advances against this disease will require improved knowledge of biological mechanisms. Human pneumonia is modeled with experimental infections of animals, most frequently mice. Mouse models are leading to important discoveries relevant to pneumonia, but their limitations must be carefully considered. Several approaches to establishing pneumonia in mice have been developed, and each has specific strengths and weaknesses. Similarly, procedures for characterizing microbial and host responses to infection have unique advantages and disadvantages. Mice are not small humans, and the applicability of results from murine models to human disease depends on understanding the similarities and differences between species. Additional considerations such as mouse strain, microbe strain, and prior mouse-microbe interactions also influence the design and interpretation of experiments. Results from studies of pneumonia in animals, combined with complementary basic and translational studies, are elucidating mechanisms responsible for susceptibility to and pathophysiology of lung infection.

Type I interleukin-1 receptor is required for pulmonary responses to subacute ozone exposure in mice

Interleukin (IL)-1, a proinflammatory cytokine, is expressed in the lung after ozone (O(3)) exposure. IL-1 mediates its effects through the type I IL-1 receptor (IL-1RI), the only signaling receptor for both IL-1alpha and IL-1beta. The purpose of this study was to determine the role of IL-1RI in pulmonary responses to O(3.) To that end, wild-type, C57BL/6 (IL-1RI(+/+)) mice and IL-1RI-deficient (IL-1RI(-/-)) mice were exposed to O(3) either subacutely (0.3 ppm for 72 h) or acutely (2 ppm for 3 h). Subacute O(3) exposure increased bronchoalveolar lavage fluid (BALF) protein, interferon-gamma-inducible protein (IP)-10, soluble tumor necrosis factor receptor 1 (sTNFR1), and neutrophils in IL-1RI(+/+) and IL-1RI(-/-) mice. With the exception of IP-10, all outcome indicators were reduced in IL-1RI(-/-) mice. Furthermore, subacute O(3) exposure increased IL-6 mRNA expression in IL-1RI(+/+), but not IL-1RI(-/-) mice. Acute (2 ppm) O(3) exposure increased BALF protein, IL-6, eotaxin, KC, macrophage inflammatory protein (MIP)-2, IP-10, monocyte chemotactic protein-1, sTNFR1, neutrophils, and epithelial cells in IL-1RI(+/+) and IL-1RI(-/-) mice. For IL-6, eotaxin, MIP-2, and sTNFR1, there were small but significant reductions of these outcome indicators in IL-1RI(-/-) versus IL-1RI(+/+) mice at 6 hours after exposure, but not at other time points, whereas other outcome indicators were unaffected by IL-1RI deficiency. These results suggest that IL-1RI is required for O(3)-induced pulmonary inflammation during subacute O(3) exposure, but plays a more minor role during acute O(3) exposure. In addition, these results suggest that the induction of IL-6 via IL-1RI may be important in mediating the effects of O(3) during subacute exposure.