S-nitrosylation of surfactant protein-D controls inflammatory function

New insights into the role of ficolins in the lectin pathway of innate immunity

In the innate immune system, a variety of recognition molecules provide the first-line host defense to prevent infection and maintain endogenous homeostasis. Ficolin is a soluble recognition molecule, which senses pathogen-associated molecular patterns on microbes and aberrant sugar structures on self-cells. It consists of a collagen-like stalk and a globular fibrinogen-like domain, the latter binding to carbohydrates such as N-acetylglucosamine. Ficolins have been widely identified in animals from higher invertebrates to mammals. In mammals, ficolins form complexes with mannose-binding lectin-associated serine proteases (MASPs), and ficolin-MASP complexes trigger complement activation via the lectin pathway. Once activated, complement mediates many immune responses including opsonization, phagocytosis, and cytokine production. Although the precise function of each ficolin is still under investigation, accumulating information suggests that ficolins have a crucial role in host defense by recognizing a variety of microorganisms and interacting with effector proteins.

Eosinophil-associated lung diseases. A cry for surfactant proteins A and D help?

Surfactant proteins (SP)-A and SP-D (SP-A/-D) play important roles in numerous eosinophil-dominated diseases, including asthma, allergic bronchopulmonary aspergillosis, and allergic rhinitis. In these settings, SP-A/-D have been shown to modulate eosinophil chemotaxis, inhibit eosinophil mediator release, and mediate macrophage clearance of apoptotic eosinophils. Dysregulation of SP-A/-D function in eosinophil-dominated diseases is also not uncommon. Alterations in serum SP-A/-D levels are associated with disease severity in allergic rhinitis and chronic obstructive pulmonary disease. Furthermore, oligimerization of SP-A/-D, necessary for their proper function, can be perturbed by reactive nitrogen species, which are increased in eosinophilic disease. In this review, we highlight the associations of eosinophilic lung diseases with SP-A and SP-D levels and functions.

Radiation-induced lung injury and inflammation in mice: role of inducible nitric oxide synthase and surfactant protein D

Reactive nitrogen species (RNS) generated after exposure to radiation have been implicated in lung injury. Surfactant protein D (SP-D) is a pulmonary collectin that suppresses inducible nitric oxide synthase (iNOS)-mediated RNS production. Herein, we analyzed the role of iNOS and SP-D in radiation-induced lung injury. Exposure of wild-type (WT) mice to γ-radiation (8 Gy) caused acute lung injury and inflammation, as measured by increases in bronchoalveolar lavage (BAL) protein and cell content at 24 h. Radiation also caused alterations in SP-D structure at 24 h and 4 weeks post exposure. These responses were blunted in iNOS(-/-) mice. Conversely, loss of iNOS had no effect on radiation-induced expression of phospho-H2A.X or tumor necrosis factor (TNF)-α. Additionally, at 24 h post radiation, cyclooxygenase expression and BAL lipocalin-2 levels were increased in iNOS(-/-) mice, and heme oxygenase (HO)-1(+) and Ym1(+) macrophages were evident. Loss of SP-D resulted in increased numbers of enlarged HO-1(+) macrophages in the lung following radiation, along with upregulation of TNF-α, CCL2, and CXCL2, whereas expression of phospho-H2A.X was diminished. To determine if RNS play a role in the altered sensitivity of SP-D(-/-) mice to radiation, iNOS(-/-)/SP-D(-/-) mice were used. Radiation-induced injury, oxidative stress, and tissue repair were generally similar in iNOS(-/-)/SP-D(-/-) and SP-D(-/-) mice. In contrast, TNF-α, CCL2, and CXCL2 expression was attenuated. These data indicate that although iNOS is involved in radiation-induced injury and altered SP-D structure, in the absence of SP-D, it functions to promote proinflammatory signaling. Thus, multiple inflammatory pathways contribute to the pathogenic response to radiation.

Impact of a Met(11)Thr single nucleotide polymorphism of surfactant protein D on allergic airway inflammation in a murine asthma model

The surfactant-associated proteins SP-A and D are pattern recognition molecules with collectin structure. A single nucleotide polymorphism (SNP) exchanging a methionine (Met) for a threonine (Thr) in the amino-terminal SP-D domain influences the oligomeric structure and function of the protein. In this study, we investigated the susceptibility of mice transgenic for the human SP-D Met(11)Thr SNP to allergic airway inflammation and consequences for microRNA (miRNA, miR) expression. Mice expressing either human Met or Thr SP-D were sensitized and challenged with ovalbumin (OVA) in an acute model of allergic asthma. The influence of the SP-D polymorphism on the allergic airway inflammation was evaluated by lung function measurement, pulmonary inflammation parameters, morphological analysis and miRNA expression. Airway hyperresponsiveness, allergic inflammation, and mucus metaplasia were not significantly different between mice expressing one or the other allelic variant of SP-D. OVA sensitization and challenge led to significant airway hyperresponsiveness in wildtype mice and significantly lower eosinophil numbers and interleukin 5 levels in Thr SP-D mice. OVA challenge induced an upregulation of miR-21 and 155 in Thr SP-D mice and a downregulation of miR-21 in Met SP-D mice. Our results show that murine expression of human polymorphic SP-D variants does not significantly influence the severity of allergic airway inflammation. MiR-21 and 155 are differentially regulated in transgenic mice in response to allergic inflammation. Further studies are required to elucidate the impact of this SNP on inflammatory conditions of the lung.

Computational prediction of candidate proteins for S-nitrosylation in Arabidopsis thaliana

Nitric oxide (NO) is an important signaling molecule that regulates many physiological processes in plants. One of the most important regulatory mechanisms of NO is S-nitrosylation-the covalent attachment of NO to cysteine residues. Although the involvement of cysteine S-nitrosylation in the regulation of protein functions is well established, its substrate specificity remains unknown. Identification of candidates for S-nitrosylation and their target cysteine residues is fundamental for studying the molecular mechanisms and regulatory roles of S-nitrosylation in plants. Several experimental methods that are based on the biotin switch have been developed to identify target proteins for S-nitrosylation. However, these methods have their limits. Thus, computational methods are attracting considerable attention for the identification of modification sites in proteins. Using GPS-SNO version 1.0, a recently developed S-nitrosylation site-prediction program, a set of 16,610 candidate proteins for S-nitrosylation containing 31,900 S-nitrosylation sites was isolated from the entire Arabidopsis proteome using the medium threshold. In the compartments "chloroplast," "CUL4-RING ubiquitin ligase complex," and "membrane" more than 70% of the proteins were identified as candidates for S-nitrosylation. The high number of identified candidates in the proteome reflects the importance of redox signaling in these compartments. An analysis of the functional distribution of the predicted candidates showed that proteins involved in signaling processes exhibited the highest prediction rate. In a set of 46 proteins, where 53 putative S-nitrosylation sites were already experimentally determined, the GPS-SNO program predicted 60 S-nitrosylation sites, but only 11 overlap with the results of the experimental approach. In general, a computer-assisted method for the prediction of targets for S-nitrosylation is a very good tool; however, further development, such as including the three dimensional structure of proteins in such analyses, would improve the identification of S-nitrosylation sites.

Differential expression of collectins in human placenta and role in inflammation during spontaneous labor

Collectins, collagen-containing Ca²⁺ dependent C-type lectins and a class of secretory proteins including SP-A, SP-D and MBL, are integral to immunomodulation and innate immune defense. In the present study, we aimed to investigate their placental transcript synthesis, labor associated differential expression and localization at feto-maternal interface, and their functional implication in spontaneous labor. The study involved using feto-maternal interface (placental/decidual tissues) from two groups of healthy pregnant women at term (≥37 weeks of gestation), undergoing either elective C-section with no labor (‘NLc’ group, n = 5), or normal vaginal delivery with spontaneous labor (‘SLv’ group, n = 5). The immune function of SP-D, on term placental explants, was analyzed for cytokine profile using multiplexed cytokine array. SP-A, SP-D and MBL transcripts were observed in the term placenta. The ‘SLv’ group showed significant up-regulation of SP-D (p = 0.001), and down-regulation of SP-A (p = 0.005), transcripts and protein compared to the ‘NLc’ group. Significant increase in 43 kDa and 50 kDa SP-D forms in placental and decidual tissues was associated with the spontaneous labor (p<0.05). In addition, the MMP-9-cleaved form of SP-D (25 kDa) was significantly higher in the placentae of ‘SLv’ group compared to the ‘NLc’ group (p = 0.002). Labor associated cytokines IL-1α, IL-1β, IL-6, IL-8, IL-10, TNF-α and MCP-1 showed significant increase (p<0.05) in a dose dependent manner in the placental explants treated with nSP-D and rhSP-D. In conclusion, the study emphasizes that SP-A and SP-D proteins associate with the spontaneous labor and SP-D plausibly contributes to the pro-inflammatory immune milieu of feto-maternal tissues.

Nitric oxide donors rescue diabetic nephropathy through oxidative-stress-and nitrosative-stress-mediated Wnt signaling pathways

AIMS/INTRODUCTION

The role of the renal nitric oxide (NO) system in the pathophysiology of diabetic nephropathy constitutes a very challenging and fertile field for future investigation. The purpose of the present study was to investigate whether NO donors can attenuate diabetic renal fibrosis and apoptosis through modulating oxidative-and nitrosative-stress, and Wnt signaling using in vivo diabetic models.

MATERIALS AND METHODS

Diabetic rat was induced by a single intraperitoneal injection of streptozotocin. Rats in each group were intraperitoneally given 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (1 U/kg/day) and vehicle for 28 and 56 consecutive days. Expression of the oxidative-and nitrosative-stress, and Wnt signaling components were examined in kidneys from diabetic animals by quantitative reverse transcription polymerase chain reaction, western blot analysis and immunohistochemical staining.

RESULTS

NO donor treatment significantly reduced the ratio of kidney weight to bodyweight and proteinuria. This treatment also significantly restored the suppressive effect of diabetes on urinary NO2 + NO3 levels. Immunohistochemistry showed that NO donor treatment significantly reduced transforming growth factor (TGF)-β1, fibronectin, cleaved caspase-3 and triphosphate-biotin nick end-labeling expression in the glomeruli of diabetic rats. We found that diabetes promoted 8-hydroxy-2'-deoxyguanosine, and peroxynitrite expression coincided with reduced endothelial NO synthase expression in glomeruli. Interestingly, NO donor treatment completely removed oxidative stress and nitrosative stress, and restored endothelial NO synthase expression in diabetic renal glomeruli. Immunohistomorphometry results showed that NO donor treatment significantly restored suppressed Wnt5a expression and β-catenin immunoreactivities in glomeruli. Based on laser-captured microdissection for quantitative reverse transcription polymerase chain reaction, diabetes significantly increased TGF-β1, and fibronectin expression coincided with depressed Wnt5a expression. NO donor treatment reduced TGF-β1, fibronectin activation, and the suppressing effect of diabetes on Wnt5a and β-catenin expression in renal glomeruli.

CONCLUSIONS

NO donor treatment alleviates extracellular matrix accumulation and apoptosis in diabetic nephropathy in vivo by not only preventing the diabetes-mediated oxidative and nitrostative stress, but also restoring downregulation of endothelial NO synthase expression and Wnt/β-catenin signaling. These findings suggest that modulation of NO is a viable alternative strategy for rescuing diabetic renal injury.

Leukocyte-associated Ig-like receptor-1 is a novel inhibitory receptor for surfactant protein D

The collagenous C-type lectin, SP-D, is a multitrimeric glycoprotein present at mucosal surfaces and is involved in host defense against infections in mammals. SP-D has immunomodulatory properties, but the underlying mechanisms are incompletely understood. SP-D contains collagen domains. LAIR-1 is an inhibitory immune receptor at the cell surface of various immune-competent cells that binds collagen. We hypothesized that the immunomodulatory functions of SP-D can be mediated via interactions between its collagen domain and LAIR-1. Binding assays show that SP-D interacts via its collagenous domain with LAIR-1 and the related LAIR-2. This does not affect the mannan-binding capacities of SP-D, which induces cross-linking of LAIR-1 in a cellular reporter assay. Functional assays show that SP-D inhibits the production of FcαR-mediated reactive oxygen via LAIR-1. Our studies indicate that SP-D is a functional ligand of the immune inhibitory receptor LAIR-1. Thus, we have identified a novel pathway for the immunomodulatory functions of SP-D mediated via binding of its collagenous domains to LAIR-1. This may provide a mechanism for the unexplained immunomodulatory function of the collagenous domains of SP-D.

NOS2 is critical to the development of emphysema in Sftpd deficient mice but does not affect surfactant homeostasis

Rationale

Surfactant protein D (SP-D) has important immuno-modulatory properties. The absence of SP-D results in an inducible NO synthase (iNOS, coded by NOS2 gene) related chronic inflammation, development of emphysema-like pathophysiology and alterations of surfactant homeostasis.

Objective

In order to test the hypothesis that SP-D deficiency related abnormalities in pulmonary structure and function are a consequence of iNOS induced inflammation, we generated SP-D and iNOS double knockout mice (DiNOS).

Methods

Structural data obtained by design-based stereology to quantify the emphysema-like phenotype and disturbances of the intracellular surfactant were correlated to invasive pulmonary function tests and inflammatory markers including activation markers of alveolar macrophages and compared to SP-D (Sftpd^−/−) and iNOS single knockout mice (NOS2^−/−) as well as wild type (WT) littermates.

Measurements and Results

DiNOS mice had reduced inflammatory cells in BAL and BAL-derived alveolar macrophages showed an increased expression of markers of an alternative activation as well as reduced inflammation. As evidenced by increased alveolar numbers and surface area, emphysematous changes were attenuated in DiNOS while disturbances of the surfactant system remained virtually unchanged. Sftpd^−/− demonstrated alterations of intrinsic mechanical properties of lung parenchyma as shown by reduced stiffness and resistance at its static limits, which could be corrected by additional ablation of NOS2 gene in DiNOS.

Conclusion

iNOS related inflammation in the absence of SP-D is involved in the emphysematous remodeling leading to a loss of alveoli and associated alterations of elastic properties of lung parenchyma while disturbances of surfactant homeostasis are mediated by different mechanisms.

Reactive species and pulmonary edema

Pulmonary edema occurs when fluid flux into the lung interstitium exceeds its removal, resulting in hypoxemia and even death. Noncardiogenic pulmonary edema (NPE) generally results when microvascular and alveolar permeability to plasma proteins increase, one possible etiology being oxidant injury. Reactive oxygen and nitrogen species (RONS) can modify or damage ion channels, such as epithelial sodium channels, which alters fluid balance. Experimental systems in which either RONS are increased or protective antioxidant mechanisms are decreased result in alterations of epithelial sodium channel activity and support the hypothesis that RONS are important in NPE. Both basic and clinical studies are needed to critically define the RONS-NPE connection and the capacity of antioxidant therapy (either alone or as a supplement to β-agonists) to improve patient outcome.

Antibiotics modulate intestinal immunity and prevent necrotizing enterocolitis in preterm neonatal piglets

Preterm birth, bacterial colonization, and formula feeding predispose to necrotizing enterocolitis (NEC). Antibiotics are commonly administered to prevent sepsis in preterm infants, but it is not known whether this affects intestinal immunity and NEC resistance. We hypothesized that broad-spectrum antibiotic treatment improves NEC resistance and intestinal structure, function, and immunity in neonates. Caesarean-delivered preterm pigs were fed 3 days of parenteral nutrition followed by 2 days of enteral formula. Immediately after birth, they were assigned to receive either antibiotics (oral and parenteral doses of gentamycin, ampicillin, and metronidazole, ANTI, n = 11) or saline in the control group (CON, n = 13), given twice daily. NEC lesions and intestinal structure, function, microbiology, and immunity markers were recorded. None of the ANTI but 85% of the CON pigs developed NEC lesions by day 5 (0/11 vs. 11/13, P < 0.05). ANTI pigs had higher intestinal villi (+60%), digestive enzyme activities (+53-73%), and goblet cell densities (+110%) and lower myeloperoxidase (-51%) and colonic microbial density (10(5) vs. 10(10) colony-forming units, all P < 0.05). Microarray transcriptomics showed strong downregulation of genes related to inflammation and innate immune response to microbiota and marked upregulation of genes related to amino acid metabolism, in particular threonine, glucose transport systems, and cell cycle in 5-day-old ANTI pigs. In a follow-up experiment, 5 days of antibiotics prevented NEC at least until day 10. Neonatal prophylactic antibiotics effectively reduced gut bacterial load, prevented NEC, intestinal atrophy, dysfunction, and inflammation and enhanced expression of genes related to gut metabolism and immunity in preterm pigs.

Increased susceptibility to Klebsiella pneumonia and mortality in GSNOR-deficient mice

S-nitrosoglutathione reductase (GSNOR) is a key denitrosylase and critically important for protecting immune and other cells from nitrosative stress. Pharmacological inhibition of GSNOR is being actively pursued as a therapeutic approach to increase S-nitrosoglutathione levels for the treatment of asthma and cystic fibrosis. In the present study, we employed GSNOR-deficient (GSNOR(-/-)) mice to investigate whether inactivation of GSNOR may increase susceptibility to pulmonary infection by Klebsiella pneumoniae, a common cause of nosocomial pneumonia. We found that compared to wild-type mice, bacterial colony forming units 48 h after intranasal infection with K. pneumoniae were increased over 4-folds in lung and spleen and strikingly, over a 1000-folds in blood of GSNOR(-/-) mice. Lung injury was comparable between infected wild-type and GSNOR(-/-) mice, but inflammation and injury was significantly elevated in spleen of GSNOR(-/-) mice. Whereas all wild-type mice survived 48 h after infection, 10 of 23 GSNOR(-/-) mice died. Thus, GSNOR appears to play a crucial role in controlling pulmonary and systemic infection by K. pneumoniae. Our results suggest that patients treated in clinical trials with inhibitors of GSNOR should be carefully monitored for signs of infection.

The amazing innate immune response to influenza A virus infection

Influenza A viruses (IAVs) remain a major health threat and a prime example of the significance of innate immunity. Our understanding of innate immunity to IAV has grown dramatically, yielding new concepts that change the way we view innate immunity as a whole. Examples include the role of p53, autophagy, microRNA, innate lymphocytes, endothelial cells and gut commensal bacteria in pulmonary innate immunity. Although the innate response is largely beneficial, it also contributes to major complications of IAV, including lung injury, bacterial super-infection and exacerbation of reactive airways disease. Research is beginning to dissect out which components of the innate response are helpful or harmful. IAV uses its limited genetic complement to maximum effect. Several viral proteins are dedicated to combating innate responses, while other viral structural or replication proteins multitask as host immune modulators. Many host innate immune proteins also multitask, having roles in cell cycle, signaling or normal lung biology. We summarize the plethora of new findings and attempt to integrate them into the larger picture of how humans have adapted to the threat posed by this remarkable virus. We explore how our expanded knowledge suggests ways to modulate helpful and harmful inflammatory responses, and develop novel treatments.

Age-related increases in ozone-induced injury and altered pulmonary mechanics in mice with progressive lung inflammation

In these studies we determined whether progressive pulmonary inflammation associated with aging in surfactant protein D (Sftpd)-/- mice leads to an exacerbated response to ozone. In Sftpd-/- mice, but not wild-type (WT) mice, age-related increases in numbers of enlarged vacuolated macrophages were observed in the lung, along with alveolar wall rupture, type 2 cell hyperplasia, and increased bronchoalveolar lavage protein and cell content. Numbers of heme oxygenase+ macrophages also increased with age in Sftpd-/- mice, together with classically (iNOS+) and alternatively (mannose receptor+, YM-1+, or galectin-3+) activated macrophages. In both WT and Sftpd-/- mice, increasing age from 8 to 27 wk was associated with reduced lung stiffness, as reflected by decreases in resistance and elastance spectra; however, this response was reversed in 80-wk-old Sftpd-/- mice. Ozone exposure (0.8 ppm, 3 h) caused increases in lung pathology, alveolar epithelial barrier dysfunction, and numbers of iNOS+ macrophages in 8- and 27-wk-old Sftpd-/-, but not WT mice at 72 h postexposure. Conversely, increases in alternatively activated macrophages were observed in 8-wk-old WT mice following ozone exposure, but not in Sftpd-/- mice. Ozone also caused alterations in both airway and tissue mechanics in Sftpd-/- mice at 8 and 27 wk, but not at 80 wk. These data demonstrate that mild to moderate pulmonary inflammation results in increased sensitivity to ozone; however, in senescent mice, these responses are overwhelmed by the larger effects of age-related increases in baseline inflammation and lung injury.

Immunofluorescent detection of S-nitrosoproteins in cell culture

The role of S-nitrosylation in cellular signaling has been clearly demonstrated. There a number of mechanisms whereby this post-translational modification can occur and the number of protein targets continue to expand. The need to be able to monitor when this important signaling process occurs within cells is increasingly important. Previously we have identified immunohistochemistry approaches effective for monitoring S-nitrosylation within fixed tissue. Within this paper we show how these techniques can be adapted to use in a cell culture system using immunofluorescence. We have used this protocol to detect S-nitrosoprotein formation within LPS stimulated microglial cells using both transformed and primary cultured cells.

Lung surfactant levels are regulated by Ig-Hepta/GPR116 by monitoring surfactant protein D

Lung surfactant is a complex mixture of lipids and proteins, which is secreted from the alveolar type II epithelial cell and coats the surface of alveoli as a thin layer. It plays a crucial role in the prevention of alveolar collapse through its ability to reduce surface tension. Under normal conditions, surfactant homeostasis is maintained by balancing its release and the uptake by the type II cell for recycling and the internalization by alveolar macrophages for degradation. Little is known about how the surfactant pool is monitored and regulated. Here we show, by an analysis of gene-targeted mice exhibiting massive accumulation of surfactant, that Ig-Hepta/GPR116, an orphan receptor, is expressed on the type II cell and sensing the amount of surfactant by monitoring one of its protein components, surfactant protein D, and its deletion results in a pulmonary alveolar proteinosis and emphysema-like pathology. By a coexpression experiment with Sp-D and the extracellular region of Ig-Hepta/GPR116 followed by immunoprecipitation, we identified Sp-D as the ligand of Ig-Hepta/GPR116. Analyses of surfactant metabolism in Ig-Hepta^+/+ and Ig-Hepta^−/− mice by using radioactive tracers indicated that the Ig-Hepta/GPR116 signaling system exerts attenuating effects on (i) balanced synthesis of surfactant lipids and proteins and (ii) surfactant secretion, and (iii) a stimulating effect on recycling (uptake) in response to elevated levels of Sp-D in alveolar space.

Methods for detection and characterization of protein S-nitrosylation

Reversible protein S-nitrosylation, defined as the covalent addition of a nitroso moiety to the reactive thiol group on a cysteine residue, has received increasing recognition as a critical post-translational modification that exerts ubiquitous influence in a wide range of cellular pathways and physiological processes. Due to the lability of the S-NO bond, which is a dynamic modification, and the low abundance of endogenously S-nitrosylated proteins in vivo, unambiguous identification of S-nitrosylated proteins and S-nitrosylation sites remains methodologically challenging. In this review, we summarize recent advancements and the use of state-of-art approaches for the enrichment, systematic identification and quantitation of S-nitrosylation protein targets and their modification sites at the S-nitrosoproteome scale. These advancements have facilitated the global identification of >3000 S-nitrosylated proteins that are associated with wide range of human diseases. These strategies hold promise to site-specifically unravel potential molecular targets and to change S-nitrosylation-based pathophysiology, which may further the understanding of the potential role of S-nitrosylation in diseases.

Aquaporin 11 insufficiency modulates kidney susceptibility to oxidative stress

Aquaporin 11 (AQP11) is a newly described member of the protein family of transport channels. AQP11 associates with the endoplasmic reticulum (ER) and is highly expressed in proximal tubular epithelial cells in the kidney. Previously, we identified and characterized a recessive mutation of the highly conserved Cys227 to Ser227 in mouse AQP11 that caused proximal tubule (PT) injury and kidney failure in mutant mice. The current study revealed induction of ER stress, unfolded protein response, and apoptosis as molecular mechanisms of this PT injury. Cys227Ser mutation interfered with maintenance of AQP11 oligomeric structure. AQP11 is abundantly expressed in the S1 PT segment, a site of major renal glucose flux, and Aqp11 mutant mice developed PT-specific mitochondrial injury. Glucose increased AQP11 protein expression in wild-type kidney and upregulation of AQP11 expression by glucose in vitro was prevented by phlorizin, an inhibitor of sodium-dependent glucose transport across PT. Total AQP11 levels in heterozygotes were higher than in wild-type mice but were not further increased in response to glucose. In Aqp11 insufficient PT cells, glucose potentiated increases in reactive oxygen species (ROS) production. ROS production was also elevated in Aqp11 mutation carriers. Phenotypically normal mice heterozygous for the Aqp11 mutation repeatedly treated with glucose showed increased blood urea nitrogen levels that were prevented by the antioxidant sulforaphane or by phlorizin. Our results indicate an important role for AQP11 to prevent glucose-induced oxidative stress in proximal tubules.

Lung surfactant protein D (SP-D) response and regulation during acute and chronic lung injury

BACKGROUND

Surfactant protein D (SP-D) is a collection that plays important roles in modulating host defense functions and maintaining phospholipid homeostasis in the lung. The aim of current study was to characterize comparatively the SP-D response in bronchoalveolar lavage (BAL) and serum in three murine models of lung injury, using a validated ELISA technology for estimation of SP-D levels.

METHODS

Mice were exposed to lipopolysaccharide, bleomycin, or Pneumocystis carinii (Pc) and sacrificed at different time points.

RESULTS

In lipopolysaccharide-challenged mice, the level of SP-D in BAL increased within 6 h, peaked at 51 h (4,518 ng/ml), and returned to base level at 99 h (612 ng/ml). Serum levels of SP-D increased immediately (8.6 ng/ml), peaked at 51 h (16 ng/ml), and returned to base levels at 99 h (3.8 ng/ml). In a subacute bleomycin inflammation model, SP-D levels were 4,625 and 367 ng/ml in BAL and serum, respectively, 8 days after exposure. In a chronic Pc inflammation model, the highest level of SP-D was observed 6 weeks after inoculation, with BAL and serum levels of 1,868 and 335 ng/ml, respectively.

CONCLUSIONS

We conclude that serum levels of SP-D increase during lung injury, with a sustained increment during chronic inflammation compared with acute inflammation. A quick upregulation of SP-D in serum in response to acute airway inflammation supports the notion that SP-D translocates from the airways into the vascular system, in favor of being synthesized systemically. The study also confirms the concept of using increased SP-D serum levels as a biomarker of especially chronic airway inflammation.

Nitrosothiols in the immune system: signaling and protection

SIGNIFICANCE

In the immune system, nitric oxide (NO) has been mainly associated with antibacterial defenses exerted through oxidative, nitrosative, and nitrative stress and signal transduction through cyclic GMP-dependent mechanisms. However, S-nitrosylation is emerging as a post-translational modification (PTM) involved in NO-mediated cell signaling.

RECENT ADVANCES

Precise roles for S-nitrosylation in signaling pathways have been described both for innate and adaptive immunity. Denitrosylation may protect macrophages from their own S-nitrosylation, while maintaining nitrosative stress compartmentalized in the phagosomes. Nitrosothiols have also been shown to be beneficial in experimental models of autoimmune diseases, mainly through their role in modulating T-cell differentiation and function.

CRITICAL ISSUES

Relationship between S-nitrosylation, other thiol redox PTMs, and other NO-signaling pathways has not been always taken into account, particularly in the context of immune responses. Methods for assaying S-nitrosylation in individual proteins and proteomic approaches to study the S-nitrosoproteome are constantly being improved, which helps to move this field forward.

FUTURE DIRECTIONS

Integrated studies of signaling pathways in the immune system should consider whether S-nitrosylation/denitrosylation processes are among the PTMs influencing the activity of key signaling and adaptor proteins. Studies in pathophysiological scenarios will also be of interest to put these mechanisms into broader contexts. Interventions modulating nitrosothiol levels in autoimmune disease could be investigated with a view to developing new therapies.

Nitrosothiols in bacterial pathogens and pathogenesis

SIGNIFICANCE

The formation and degradation of S-nitrosothiols (SNOs) are important mechanisms of post-translational protein modification and appear to be ubiquitous in biology. These processes play well-characterized roles in eukaryotic cells, including a variety of pathologies and in relation to chronic conditions. We know little of the roles of these processes in pathogenic and other bacteria.

RECENT ADVANCES

It is clear, mostly from growth and transcriptional studies, that bacteria sense and respond to exogenous SNOs. These responses are phenotypically and mechanistically distinct from the responses of bacteria to nitric oxide (NO) and NO-releasing agents, as well as peroxynitrite. Small SNOs, such as S-nitrosoglutathione (GSNO), are accumulated by bacteria with the result that intracellular S-nitrosoproteins (the 'S-nitrosoproteome') are detectable. Recently, conditions for endogenous SNO formation in enterobacteria have been described.

CRITICAL ISSUES

The propensity of intracellular proteins to form SNOs is presumably constrained by the same rules of selectivity that have been discovered in eukaryotic systems, but is also influenced by uniquely bacterial NO detoxification systems, exemplified by the flavohemoglobin Hmp in enterobacteria and NO reductase of meningococci. Furthermore, the bacterial expression of such proteins impacts upon the formation of SNOs in mammalian hosts.

FUTURE DIRECTIONS

The impairment during bacterial infections of specific SNO events in the mammalian host is of considerable interest in the context of proteins involved in innate immunity and intracellular signalling. In bacteria, numerous mechanisms of S-nitrosothiol degradation have been reported (e.g., GSNO reductase); others are thought to operate, based on consideration of their mammalian counterparts. The nitrosothiols of bacteria and particularly of pathogens warrant more intensive investigation.

Increased surfactant protein D fails to improve bacterial clearance and inflammation in serpinB1-/- mice

Previously, we described the protective role of the neutrophil serine protease inhibitor serpinB1 in preventing early mortality of Pseudomonas aeruginosa lung infection by fostering bacterial clearance and limiting inflammatory cytokines and proteolytic damage. Surfactant protein D (SP-D), which maintains the antiinflammatory pulmonary environment and mediates bacterial removal, was degraded in infected serpinB1-deficient mice. Based on the hypothesis that increased SP-D would rescue or mitigate the pathological effects of serpinB1 deletion, we generated two serpinB1(-/-) lines overexpressing lung-specific rat SP-D and inoculated the mice with P. aeruginosa. Contrary to predictions, bacterial counts in the lungs of SP-D(low)serpinB1(-/-) and SP-D(high) serpinB1(-/-) mice were 4 logs higher than wild-type and not different from serpinB1(-/-) mice. SP-D overexpression also failed to mitigate inflammation (TNF-α), lung injury (free protein, albumin), or excess neutrophil death (free myeloperoxidase, elastase). These pathological markers were higher for infected SP-D(high)serpinB1(-/-) mice than for serpinB1(-/-) mice, although the differences were not significant after controlling for multiple comparisons. The failure of transgenic SP-D to rescue antibacterial defense of serpinB1-deficient mice occurred despite 5-fold or 20-fold increased expression levels, largely normal structure, and dose-dependent bacteria-aggregating activity. SP-D of infected wild-type mice was intact in 43-kD monomers by reducing SDS-PAGE. By contrast, proteolytic fragments of 35, 17, and 8 kD were found in infected SP-D(low)serpinB1(-/-), SP-D(high) serpinB1(-/-) mice, and serpinB1(-/-) mice. Thus, although therapies to increase lung concentration of SP-D may have beneficial applications, the findings suggest that therapy with SP-D may not be beneficial for lung inflammation or infection if the underlying clinical condition includes excess proteolysis.

Experimental therapeutics of Nrf2 as a target for prevention of bacterial exacerbations in COPD

A growing body of evidence indicates that oxidative stress plays a central role in the progression of chronic obstructive pulmonary disease (COPD). Chronic oxidative stress caused by cigarette smoke generates damage-associated molecular patterns (DAMPs), such as oxidatively or nitrosatively modified proteins and extracellular matrix fragments, which induce abnormal airway inflammation by activating innate and adaptive immune responses. Furthermore, oxidative stress-induced histone deacetylase 2 (HDAC2) inactivity is implicated in amplifying inflammatory responses and corticosteroid resistance in COPD. Oxidative stress also mediates disruption of innate immune defenses, which is associated with acute exacerbation of COPD. Host defense transcription factor Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates a multifaceted cytoprotective response to counteract oxidative stress-induced pathological injuries. A decrease in Nrf2 signaling is associated with the progression of diseases. Recent evidence indicates that targeting Nrf2 can be a novel therapy to mitigate inflammation, improve innate antibacterial defenses, and restore corticosteroid responses in patients with COPD.

Can nitric oxide-based therapy prevent bronchopulmonary dysplasia?

A growing understanding of endogenous nitric oxide (NO) biology is helping to explain how and when exogenous NO may confer benefit or harm; this knowledge is also helping to identify new better-targeted NO-based therapies. In this review, results of the bronchopulmonary dysplasia clinical trials that used inhaled NO in the preterm population are placed in context, the biologic basis for novel NO therapeutics is considered, and possible future directions for NO-focused clinical and basic research in developmental lung disease are identified.

Prolonged injury and altered lung function after ozone inhalation in mice with chronic lung inflammation

Surfactant protein-D (Sftpd) is a pulmonary collectin important in down-regulating macrophage inflammatory responses. In these experiments, we analyzed the effects of chronic macrophage inflammation attributable to loss of Sftpd on the persistence of ozone-induced injury, macrophage activation, and altered functioning in the lung. Wild-type (Sftpd(+/+)) and Sftpd(-/-) mice (aged 8 wk) were exposed to air or ozone (0.8 parts per million, 3 h). Bronchoalveolar lavage (BAL) fluid and tissue were collected 72 hours later. In Sftpd(-/-) mice, but not Sftpd(+/+) mice, increased BAL protein and nitrogen oxides were observed after ozone inhalation, indicating prolonged lung injury and oxidative stress. Increased numbers of macrophages were also present in BAL fluid and in histologic sections from Sftpd(-/-) mice. These cells were enlarged and foamy, suggesting that they were activated. This conclusion was supported by findings of increased BAL chemotactic activity, and increased expression of inducible nitric oxide synthase in lung macrophages. In both Sftpd(+/+) and Sftpd(-/-) mice, inhalation of ozone was associated with functional alterations in the lung. Although these alterations were limited to central airway mechanics in Sftpd(+/+) mice, both central airway and parenchymal mechanics were modified by ozone exposure in Sftpd(-/-) mice. The most notable changes were evident in resistance and elastance spectra and baseline lung function, and in lung responsiveness to changes in positive end-expiratory pressure. These data demonstrate that a loss of Sftpd is associated with prolonged lung injury, oxidative stress, and macrophage accumulation and activation in response to ozone, and with more extensive functional changes consistent with the loss of parenchymal integrity.

Unifying thoracic biomarkers: surfactant protein-D and beyond

Chronic obstructive pulmonary disease (COPD) is a progressive disorder that affects 300 million people worldwide and is responsible for 3 million deaths annually. Currently, there are no accepted biomarkers of COPD, which has impaired drug development and management of patients with COPD. Pneumoproteins, which are proteins synthesized predominantly in the lungs, are promising blood biomarkers because they have high specificity for lung disease. The most promising is surfactant protein-D, which is synthesized largely in Type 2 pneumocytes, and its blood concentrations have been associated with COPD and with certain clinical end points such as mortality. In this paper, we discuss surfactant protein-D and other pneumoproteins as promising biomarkers of COPD.

An Insight into the Diverse Roles of Surfactant Proteins, SP-A and SP-D in Innate and Adaptive Immunity

Surfactant proteins SP-A and SP-D are hydrophilic, collagen-containing calcium-dependent lectins, which appear to have a range of innate immune functions at pulmonary as well as extrapulmonary sites. These proteins bind to target ligands on pathogens, allergens, and apoptotic cells, via C-terminal homotrimeric carbohydrate recognition domains, while the collagen region brings about the effector functions via its interaction with cell surface receptors. SP-A and SP-D deal with various pathogens, using a range of innate immune mechanisms such as agglutination/aggregation, enhancement of phagocytosis, and killing mechanisms by phagocytic cells and direct growth inhibition. SP-A and SP-D have also been shown to be involved in the control of pulmonary inflammation including allergy and asthma. Emerging evidence suggest that SP-A and SP-D are capable of linking innate immunity with adaptive immunity that includes modulation of dendritic cell function and helper T cell polarization. This review enumerates immunological properties of SP-A and SP-D inside and outside lungs and discusses their importance in human health and disease.

Diverse functions of pulmonary collectins in host defense of the lung

Pulmonary surfactant is a mixture of lipids and proteins that covers alveolar surfaces and keeps alveoli from collapsing. Four specific proteins have been identified in surfactant. Among them, two C-type lectins, surfactant proteins A and D (SP-A and SP-D), are known to be implicated in host defense and regulation of inflammatory responses of the lung. These host defense lectins are structurally characterized by N-terminal collagen-like domains and lectin domains and are called pulmonary collectins. They prevent dissemination of infectious microbes by their biological activities including agglutination and growth inhibition. They also promote clearance of microbes by enhancing phagocytosis in macrophages. In addition, they interact with the other pattern-recognition molecules, including Toll-like receptors (TLRs) and TLR-associated molecules, CD14 and MD-2, and regulate inflammatory responses. Furthermore, recent studies have demonstrated that these collectins modulate functions of neutrophil-derived innate immune molecules by interacting with them. These findings indicate that pulmonary collectins play critical roles in host defense of the lung.

Surfactant protein d deficiency in mice is associated with hyperphagia, altered fat deposition, insulin resistance, and increased basal endotoxemia

Pulmonary surfactant protein D (SP-D) is a host defence lectin of the innate immune system that enhances clearance of pathogens and modulates inflammatory responses. Recently it has been found that systemic SP-D is associated with metabolic disturbances and that SP-D deficient mice are mildly obese. However, the mechanism behind SP-D's role in energy metabolism is not known.

Here we report that SP-D deficient mice had significantly higher ad libitum energy intake compared to wild-type mice and unchanged energy expenditure. This resulted in accumulation but also redistribution of fat tissue. Blood pressure was unchanged. The change in energy intake was unrelated to the basal levels of hypothalamic Pro-opiomelanocortin (POMC) and Agouti-related peptide (AgRP) gene expression. Neither short time systemic, nor intracereberoventricular SP-D treatment altered the hypothalamic signalling or body weight accumulation.

In ad libitum fed animals, serum leptin, insulin, and glucose were significantly increased in mice deficient in SP-D, and indicative of insulin resistance. However, restricted diets eliminated all metabolic differences except the distribution of body fat. SP-D deficiency was further associated with elevated levels of systemic bacterial lipopolysaccharide.

In conclusion, our findings suggest that lack of SP-D mediates modulation of food intake not directly involving hypothalamic regulatory pathways. The resulting accumulation of adipose tissue was associated with insulin resistance. The data suggest SP-D as a regulator of energy intake and body composition and an inhibitor of metabolic endotoxemia. SP-D may play a causal role at the crossroads of inflammation, obesity, and insulin resistance.

Enzymatic mechanisms regulating protein S-nitrosylation: implications in health and disease

Nitric oxide participates in cellular signal transduction largely through S-nitrosylation of allosteric and active-site cysteine thiols within proteins, forming S-nitroso-proteins (SNO-proteins). S-nitrosylation of proteins has been demonstrated to affect a broad range of functional parameters including enzymatic activity, subcellular localization, protein-protein interactions, and protein stability. Analogous to other ubiquitous posttranslational modifications that are regulated enzymatically, including phosphorylation and ubiquitinylation, accumulating evidence suggests the existence of enzymatic mechanisms for regulating protein S-nitrosylation. In particular, studies have led to the identification of multiple enzymes (nitrosylases and denitrosylases) that participate in targeted S-nitrosylation or denitrosylation of proteins in physiological settings. Nitrosylases are best characterized in the context of transnitrosylation in which a SNO-protein transfers an NO group to an acceptor protein (Cys-to-Cys transfer), but examples of transnitrosylation catalyzed by metalloproteins (Metal-to-Cys transfer) also exist. By contrast, denitrosylases remove the NO group from SNO-proteins, ultimately using reducing equivalents derived from NADH or NADPH. Here, we focus on the recent discoveries of nitrosylases and denitrosylases and the notion that their aberrant activities may play roles in health and disease.

Surfactant Protein D modulates allergen particle uptake and inflammatory response in a human epithelial airway model

Background

Allergen-containing subpollen particles (SPP) are released from whole plant pollen upon contact with water or even high humidity. Because of their size SPP can preferentially reach the lower airways where they come into contact with surfactant protein (SP)-D. The aim of the present study was to investigate the influence of SP-D in a complex three-dimensional human epithelial airway model, which simulates the most important barrier functions of the epithelial airway. The uptake of SPP as well as the secretion of pro-inflammatory cytokines was investigated.

Methods

SPP were isolated from timothy grass and subsequently fluorescently labeled. A human epithelial airway model was built by using human Type II-pneumocyte like cells (A549 cells), human monocyte derived macrophages as well as human monocyte derived dendritic cells. The epithelial cell model was incubated with SPP in the presence and absence of surfactant protein D. Particle uptake was evaluated by confocal microscopy and advanced computer-controlled analysis. Finally, human primary CD4⁺ T-Cells were added to the epithelial airway model and soluble mediators were measured by enzyme linked immunosorbent assay or bead array.

Results

SPP were taken up by epithelial cells, macrophages, and dendritic cells. This uptake coincided with secretion of pro-inflammatory cytokines and chemokines. SP-D modulated the uptake of SPP in a cell type specific way (e.g. increased number of macrophages and epithelial cells, which participated in allergen particle uptake) and led to a decreased secretion of pro-inflammatory cytokines.

Conclusion

These results display a possible mechanism of how SP-D can modulate the inflammatory response to inhaled allergen.

Ozone-induced lung injury and sterile inflammation. Role of toll-like receptor 4

Inhalation of toxic doses of ozone is associated with a sterile inflammatory response characterized by an accumulation of macrophages in the lower lung which are activated to release cytotoxic/proinflammatory mediators that contribute to tissue injury. Toll-like receptor 4 (TLR4) is a pattern recognition receptor present on macrophages that has been implicated in sterile inflammatory responses. In the present studies we used TLR4 mutant C3H/HeJ mice to analyze the role of TLR4 in ozone-induced lung injury, oxidative stress and inflammation. Acute exposure of control C3H/HeOuJ mice to ozone (0.8ppm for 3h) resulted in increases in bronchoalveolar lavage (BAL) lipocalin 24p3 and 4-hydroxynonenal modified protein, markers of oxidative stress and lipid peroxidation. This was correlated with increases in BAL protein, as well as numbers of alveolar macrophages. Levels of surfactant protein-D, a pulmonary collectin known to regulate macrophage inflammatory responses, also increased in BAL following ozone inhalation. Ozone inhalation was associated with classical macrophage activation, as measured by increased NF-κB binding activity and expression of TNFα mRNA. The observation that these responses to ozone were not evident in TLR4 mutant C3H/HeJ mice demonstrates that functional TLR4 contributes to ozone-induced sterile inflammation and macrophage activation.

Pulmonary Collectins in Diagnosis and Prevention of Lung Diseases

Pulmonary surfactant is a complex mixture of lipids and proteins, and is synthesized and secreted by alveolar type II epithelial cells and bronchiolar Clara cells. It acts to keep alveoli from collapsing during the expiratory phase of the respiratory cycle. After its secretion, lung surfactant forms a lattice structure on the alveolar surface, known as tubular myelin. Surfactant proteins (SP)-A, B, C and D make up to 10% of the total surfactant. SP-B and SPC are relatively small hydrophobic proteins, and are involved in the reduction of surface-tension at the air-liquid interface. SP-A and SP-D, on the other hand, are large oligomeric, hydrophilic proteins that belong to the collagenous Ca²⁺-dependent C-type lectin family (known as “Collectins”), and play an important role in host defense and in the recycling and transport of lung surfactant (Awasthi 2010) (Fig. 43.1). In particular, there is increasing evidence that surfactant-associated proteins A and -D (SP-A and SP-D, respectively) contribute to the host defense against inhaled microorganisms (see 10.1007/978-3-7091-1065_24 and 10.1007/978-3-7091-1065_25). Based on their ability to recognize pathogens and to regulate the host defense, SP-A and SP-D have been recently categorized as “Secretory Pathogen Recognition Receptors”. While SP-A and SP-D were first identified in the lung; the expression of these proteins has also been observed at other mucosal surfaces, such as lacrimal glands, gastrointestinal mucosa, genitourinary epithelium and periodontal surfaces. SP-A is the most prominent among four proteins in the pulmonary surfactant-system. The expression of SP-A is complexly regulated on the transcriptional and the chromosomal level. SP-A is a major player in the pulmonary cytokine-network and moreover has been described to act in the pulmonary host defense. This chapter gives an overview on the understanding of role of SP-A and SP-D in for human pulmonary disorders and points out the importance for pathology-orientated research to further elucidate the role of these molecules in adult lung diseases. As an outlook, it will become an issue of pulmonary pathology which might provide promising perspectives for applications in research, diagnosis and therapy (Awasthi 2010).

Genetic variant associations of human SP-A and SP-D with acute and chronic lung injury

Pulmonary surfactant, a lipoprotein complex, maintains alveolar integrity and plays an important role in lung host defense, and control of inflammation. Altered inflammatory processes and surfactant dysfunction are well described events that occur in patients with acute or chronic lung disease that can develop secondary to a variety of insults. Genetic variants of surfactant proteins, including single nucleotide polymorphisms, haplotypes, and other genetic variations have been associated with acute and chronic lung disease throughout life in several populations and study groups. The hydrophilic surfactant proteins SP-A and SP-D, also known as collectins, in addition to their surfactant-related functions, are important innate immunity molecules as these, among others, exhibit the ability to bind and enhance clearance of a wide range of pathogens and allergens. This review focuses on published association studies of human surfactant proteins A and D genetic polymorphisms with respiratory, and non-respiratory diseases in adults, children, and newborns. The potential role of genetic variations in pulmonary disease or pathogenesis is discussed following an evaluation, and comparison of the available literature.

Biomarkers of therapeutic response in patients with chronic obstructive pulmonary disease: a critical review of the literature

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbidity and mortality across the world. Unfortunately, none of the current therapies, except for smoking cessation and supplemental domiciliary oxygen for hypoxaemic patients, can modify its natural course or alter survival. The pipeline for new compounds is not very promising owing to repeated failures, and many large pharmaceutical companies have abandoned COPD drug discovery altogether. One major barrier to new drug discovery is the lack of modifiable biomarkers that can be used as surrogates of clinical outcomes such as exacerbation and mortality. The only accepted marker in COPD is forced expiratory volume in 1 second (FEV(1)). However, by definition, COPD is a non-reversible or poorly reversible condition with respect to FEV(1). Thus, very few drugs except for bronchodilators have been able to address this endpoint. Of many candidate molecules, sputum neutrophil counts, exhaled corrected alveolar nitric oxide and proline-glycine-proline (PGP) and N-α-PGP, which are breakdown products of collagen, are promising lung-based biomarkers. However, their clinical utility has not been validated in large clinical trials. Promising blood biomarkers include surfactant protein D, and pulmonary- and activation-regulated chemokine (PARC/CCL-18). However, the clinical data have been inconsistent. Non-specific inflammatory biomarkers such as C-reactive protein and interleukin-6 lack specificity for COPD and thus are of limited clinical usefulness.

S-nitrosylation of surfactant protein D as a modulator of pulmonary inflammation

BACKGROUND

Surfactant protein D (SP-D) is a member of the family of proteins termed collagen-like lectins or "collectins" that play a role in non-antibody-mediated innate immune responses [1]. The primary function of SP-D is the modulation of host defense and inflammation [2].

SCOPE OF REVIEW

This review will discuss recent findings on the physiological importance of SP-D S-nitrosylation in biological systems and potential mechanisms that govern SP-D mediated signaling.

MAJOR CONCLUSIONS

SP-D appears to have both pro- and anti-inflammatory signaling functions. SP-D multimerization is a critical feature of its function and plays an important role in efficient innate host defense. Under baseline conditions, SP-D forms a multimer in which the N-termini are hidden in the center and the C-termini are on the surface. This multimeric form of SP-D is limited in its ability to activate inflammation. However, NO can modify key cysteine residues in the hydrophobic tail domain of SP-D resulting in a dissociation of SP-D multimers into trimers, exposing the S-nitrosylated N-termini. The exposed S-nitrosylated tail domain binds to the calreticulin/CD91 receptor complex and initiates a pro-inflammatory response through phosphorylation of p38 and NF-κB activation [3,4]. In addition, the disassembled SP-D loses its ability to block TLR4, which also results in activation of NF-κB.

GENERAL SIGNIFICANCE

Recent studies have highlighted the capability of NO to modify SP-D through S-nitrosylation, causing the activation of a pro-inflammatory role for SP-D [3]. This represents a novel mechanism both for the regulation of SP-D function and NO's role in innate immunity, but also demonstrates that the S-nitrosylation can control protein function by regulating quaternary structure. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Early alveolar epithelial dysfunction promotes lung inflammation in a mouse model of Hermansky-Pudlak syndrome

RATIONALE

The pulmonary phenotype of Hermansky-Pudlak syndrome (HPS) in adults includes foamy alveolar type 2 cells, inflammation, and lung remodeling, but there is no information about ontogeny or early disease mediators.

OBJECTIVES

To establish the ontogeny of HPS lung disease in an animal model, examine disease mediators, and relate them to patients with HPS1.

METHODS

Mice with mutations in both HPS1/pale ear and HPS2/AP3B1/pearl (EPPE mice) were studied longitudinally. Total lung homogenate, lung tissue sections, and bronchoalveolar lavage (BAL) were examined for phospholipid, collagen, histology, cell counts, chemokines, surfactant protein D (SP-D), and S-nitrosylated SP-D. Isolated alveolar epithelial cells were examined for expression of inflammatory mediators, and chemotaxis assays were used to assess their importance. Pulmonary function test results and BAL from patients with HPS1 and normal volunteers were examined for clinical correlation.

MEASUREMENTS AND MAIN RESULTS

EPPE mice develop increased total lung phospholipid, followed by a macrophage-predominant pulmonary inflammation, and lung remodeling including fibrosis. BAL fluid from EPPE animals exhibited early accumulation of both SP-D and S-nitrosylated SP-D. BAL fluid from patients with HPS1 exhibited similar changes in SP-D that correlated inversely with pulmonary function. Alveolar epithelial cells demonstrated expression of both monocyte chemotactic protein (MCP)-1 and inducible nitric oxide synthase in juvenile EPPE mice. Last, BAL from EPPE mice and patients with HPS1 enhanced migration of RAW267.4 cells, which was attenuated by immunodepletion of SP-D and MCP-1.

CONCLUSIONS

Inflammation is initiated from the abnormal alveolar epithelial cells in HPS, and S-nitrosylated SP-D plays a significant role in amplifying pulmonary inflammation.

Anti-nucleocapsid protein immune responses counteract pathogenic effects of Rift Valley fever virus infection in mice

The known virulence factor of Rift Valley fever virus (RVFV), the NSs protein, counteracts the antiviral effects of the type I interferon response. In this study we evaluated the expression of several genes in the liver and spleen involved in innate and adaptive immunity of mice immunized with a RVFV recombinant nucleocapsid protein (recNP) combined with Alhydrogel adjuvant and control animals after challenge with wild type RVFV. Mice immunized with recNP elicited an earlier IFNβ response after challenge compared to non-immunized controls. In the acute phase of liver infection in non-immunized mice there was a massive upregulation of type I and II interferon, accompanied by high viral titers, and the up- and downregulation of several genes involved in the activation of B- and T-cells, indicating that both humoral and cellular immunity is modulated during RVFV infection. Various genes involved in pro-inflammatory responses and with pro-apoptotic effects were strongly upregulated and anti-apoptotic genes were downregulated in liver of non-immunized mice. Expression of many genes involved in B- and T-cell immunity were downregulated in spleen of non-immunized mice but normal in immunized mice. A strong bias towards apoptosis and inflammation in non-immunized mice at an acute stage of liver infection associated with suppression of several genes involved in activation of humoral and cellular immunity in spleen, suggests that RVFV evades the host immune response in more ways than only by inhibition of type I interferon, and that immunopathology of the liver plays a crucial role in RVF disease progression.

Surfactant and its role in the pathobiology of pulmonary infection

Pulmonary surfactant is a complex surface-active substance comprised of key phospholipids and proteins that has many essential functions. Surfactant's unique composition is integrally related to its surface-active properties, its critical role in host defense, and emerging immunomodulatory activities ascribed to surfactant lipids. Together these effector functions provide for lung stability and protection from a barrage of potentially virulent infectious pathogens.

Circulating surfactant protein-D and the risk of cardiovascular morbidity and mortality

AIMS

Surfactant protein-D (SP-D) is a lung-specific protein that is detectable in human plasma. We determined the relationship of circulating SP-D to cardiovascular disease (CVD) and total mortality in subjects with and without CVD.

METHODS AND RESULTS

Plasma SP-D levels were measured in 806 patients who underwent coronary angiography to assess its predictive value for cardiovascular mortality. Serum SP-D levels were also measured in a replication cohort to assess its relationship with CVD events in 4468 ex- and current smokers without a known history of coronary artery disease (CAD). Patients who died during follow-up had significantly higher plasma SP-D levels than those who survived (median 85.4 vs. 64.8 ng/mL; P < 0.0001). Those in the highest quintile of SP-D had 4.4-fold higher risk of CVD mortality than those in the lowest quintile (P < 0.0001) independent of age, sex, and plasma lipid levels. In a group of current and ex-smokers without a known history of CAD, serum SP-D levels were elevated in those who died or were hospitalized for CVD compared with those who did not (median 99.8 vs. 90.6 ng/mL; P = 0.0001).

CONCLUSION

Circulating SP-D is a good predictor of cardiovascular morbidity and mortality and adds prognostic information to well-established risk factors such as age, sex, and plasma lipids and is a promising biomarker to link lung inflammation/injury to CVD.

Strategies and tools to explore protein S-nitrosylation

BACKGROUND

A biochemical pathway by which nitric oxide accomplishes functional diversity is the specific modification of protein cysteine residues to form S-nitrosocysteine. This post-translational modification, S-nitrosylation, impacts protein function, interactions and location. However, comprehensive studies exploring protein signaling pathways or interrelated protein clusters that are regulated by S-nitrosylation have not been performed on a global scale.

SCOPE OF REVIEW

To provide insights to these important biological questions, sensitive, validated and quantitative proteomic approaches are required. This review summarizes current approaches for the global identification of S-nitrosylated proteins.

MAJOR CONCLUSIONS

The application of novel methods for identifying S-nitrosylated proteins, especially when combined with mass-spectrometry based proteomics to provide site-specific identification of the modified cysteine residues, promises to deliver critical clues for the regulatory role of this dynamic posttranslational modification in cellular processes.

GENERAL SIGNIFICANCE

Though several studies have established S-nitrosylation as a regulator of protein function in individual proteins, the biological chemistry and the structural elements that govern the specificity of this modification in vivo are vastly unknown. Additionally, a gap in knowledge exists concerning the potential global regulatory role(s) this modification may play in cellular physiology. By further studying S-nitrosylation at a global scale, a greater appreciation of nitric oxide and protein S-nitrosylation in cellular function can be achieved. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Mitochondrial Cu,Zn-superoxide dismutase mediates pulmonary fibrosis by augmenting H2O2 generation

The release of H(2)O(2) from alveolar macrophages has been linked to the development of pulmonary fibrosis, but little is known about its source or mechanism of production. We found that alveolar macrophages from asbestosis patients spontaneously produce high levels of H(2)O(2) and have high expression of Cu,Zn-superoxide dismutase (SOD). Because Cu,Zn-SOD is found in the mitochondrial intermembrane space (IMS), we hypothesized that mitochondrial Cu,Zn-SOD-mediated H(2)O(2) generation contributed to pulmonary fibrosis. Asbestos-induced translocation of Cu,Zn-SOD to the IMS was unique to macrophages and dependent on functional mitochondrial respiration and the presence of at least one of the conserved cysteines required for disulfide bond formation. These conserved cysteine residues were also necessary for enzyme activation and H(2)O(2) generation. Cu,Zn-SOD-mediated H(2)O(2) generation was inhibited by knockdown of the iron-sulfur protein, Rieske, in complex III. The role of Cu,Zn-SOD was biologically relevant in that Cu,Zn-SOD(-/-) mice generated significantly less H(2)O(2) and had less oxidant stress in bronchoalveolar lavage fluid and lung parenchyma. Furthermore, Cu,Zn-SOD(-/-) mice did not develop pulmonary fibrosis, and knockdown of Cu,Zn-SOD in monocytes attenuated collagen I deposition by lung fibroblasts. Our findings demonstrate a novel mechanism for the pathogenesis of pulmonary fibrosis where the antioxidant enzyme Cu,Zn-SOD translocates to the mitochondrial IMS to increase H(2)O(2) generation in alveolar macrophages.

Segmental allergen challenge alters multimeric structure and function of surfactant protein D in humans

RATIONALE

Surfactant protein D (SP-D), a 43-kD collectin, is synthesized and secreted by airway epithelia as a dodecamer formed by assembly of four trimeric subunits. We have previously shown that the quaternary structure of SP-D can be altered during inflammatory lung injury through its modification by S-nitrosylation, which in turn alters its functional behavior producing a proinflammatory response in effector cells.

OBJECTIVES

We hypothesized that alterations in structure and function of SP-D may occur in humans with acute allergic inflammation.

METHODS

Bronchoalveolar lavage (BAL) fluid was collected from 15 nonsmoking patients with mild intermittent allergic asthma before and 24 hours after segmental provocation with saline, allergen, LPS, and mixtures of allergen and LPS. Structural modifications of SP-D were analyzed by native and sodium dodecyl sulfate gel electrophoresis.

MEASUREMENTS AND MAIN RESULTS

The multimeric structure of native SP-D was found to be disrupted after provocation with allergen or a mixture of allergen and LPS. Interestingly, under reducing conditions, sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated that 7 of 15 patients with asthma developed an abnormal cross-linked SP-D band after segmental challenge with either allergen or a mixture of allergen with LPS but not LPS alone. Importantly, patients with asthma with cross-linked SP-D demonstrated significantly higher levels of BAL eosinophils, nitrogen oxides, IL-4, IL-5, IL-13, and S-nitrosothiol-SP-D compared with patients without cross-linked SP-D.

CONCLUSIONS

We conclude that segmental allergen challenge results in changes of SP-D multimeric structure and that these modifications are associated with an altered local inflammatory response in the distal airways.

Comprehensive characterisation of pulmonary and serum surfactant protein D in COPD

Background

Pulmonary surfactant protein D (SP-D) is considered as a candidate biomarker for the functional integrity of the lung and for disease progression, which can be detected in serum. The origin of SP-D in serum and how serum concentrations are related to pulmonary concentrations under inflammatory conditions is still unclear.

Methods

In a cross-sectional study comprising non-smokers (n = 10), young - (n = 10), elderly smokers (n = 20), and smokers with COPD (n = 20) we simultaneously analysed pulmonary and serum SP-D levels with regard to pulmonary function, exercise, repeatability and its quaternary structure by native gel electrophoresis. Statistical comparisons were conducted by ANOVA and post-hoc testing for multiple comparisons; repeatability was assessed by Bland-Altman analysis.

Results

In COPD, median (IQR) pulmonary SP-D levels were lower (129(68) ng/ml) compared to smokers (young: 299(190), elderly: 296(158) ng/ml; p < 0.01) and non-smokers (967(708) ng/ml; p < 0.001). The opposite was observed in serum, with higher concentrations in COPD (140(89) ng/ml) as compared to non-smokers (76(47) ng/ml; p < 0.01). SP-D levels were reproducible and correlated with the degree of airway obstruction in all smokers. In addition, smoking lead to disruption of the quaternary structure.

Conclusions

Pulmonary and serum SP-D levels are stable markers influenced by smoking and related to airflow obstruction and disease state. Smaller subunits of pulmonary SP-D and the rapid increase of serum SP-D levels in COPD due to exercise support the translocation hypothesis and its use as a COPD biomarker.

Trial registration

no interventional trial