Genomic organization of the mouse gene for lung surfactant protein D

Surfactant protein D facilitates Cryptococcus neoformans infection

Concurrent with the global escalation of the AIDS pandemic, cryptococcal infections are increasing and are of significant medical importance. Furthermore, Cryptococcus neoformans has become a primary human pathogen, causing infection in seemingly healthy individuals. Although numerous studies have elucidated the virulence properties of C. neoformans, less is understood regarding lung host immune factors during early stages of fungal infection. Based on our previous studies documenting that pulmonary surfactant protein D (SP-D) protects C. neoformans cells against macrophage-mediated defense mechanisms in vitro (S. Geunes-Boyer et al., Infect. Immun. 77:2783-2794, 2009), we postulated that SP-D would facilitate fungal infection in vivo. To test this hypothesis, we examined the role of SP-D in response to C. neoformans using SP-D⁻/⁻ mice. Here, we demonstrate that mice lacking SP-D were partially protected during C. neoformans infection; they displayed a longer mean time to death and decreased fungal burden at several time points postinfection than wild-type mice. This effect was reversed by the administration of exogenous SP-D. Furthermore, we show that SP-D bound to the surface of the yeast cells and protected the pathogenic microbes against macrophage-mediated defense mechanisms and hydrogen peroxide (H₂O₂)-induced oxidative stress in vitro and in vivo. These findings indicate that C. neoformans is capable of coopting host SP-D to increase host susceptibility to the yeast. This study establishes a new paradigm for the role played by SP-D during host responses to C. neoformans and consequently imparts insight into potential future preventive and/or treatment strategies for cryptococcosis.

Genetic ecotoxicology of asbestos pollution in the house mouse Mus musculus domesticus

PURPOSE

We tested the genetic diversity in wild mice (Mus musculus domesticus) inhabiting the asbestos-polluted area as a model for the long-term mutagenic effect of asbestos. Hazardous effects of deposited asbestos persist in the environment because of low rate of fiber disintegration. The upper layers of the soil in the vicinity of a former asbestos factory are nearly "saturated" with asbestos fibers and dust. Natural populations of mice dwell in this area and are constantly exposed to asbestos fibers.

METHODS

We measured the microsatellites genetic diversity of wild mice (Mus musculus domesticus) inhabiting the asbestos-polluted area as a model for the long-term mutagenic effect of this environmental toxin.

RESULTS

The six tested microsatellites were highly polymorphic, revealing 111 different alleles for the two sampled populations. Effective number of alleles was slightly higher in the polluted population relative to the control population, while observed heterozygosity was lower. The chromatographic profile of the polluted population exhibited a significantly higher number of bands, probably resulting from somatic mutations, in addition to the ordinary microsatellite band profiles.

CONCLUSIONS

Long-term exposure to asbestos fibers significantly elevates the level of somatic mutations. It also leads to a relatively high level of observed homozygosity, a phenomenon that may be associated with loss of heterozygosity. Based on the mice population, our data suggest elevated health risks for humans living in an asbestos-polluted area.

SP-D and regulation of the pulmonary innate immune system in allergic airway changes

The airway mucosal surfaces are constantly exposed to inhaled particles that can be potentially toxic, infectious or allergenic and should elicit inflammatory changes. The proximal and distal air spaces, however, are normally infection and inflammation free due to a specialized interplay between cellular and molecular components of the pulmonary innate immune system. Surfactant protein D (SP-D) is an epithelial-cell-derived immune modulator that belongs to the small family of structurally related Ca(2+)-dependent C-type collagen-like lectins. While collectins can be detected in mucosal surfaces of various organs, SP-A and SP-D (the 'lung collectins') are constitutively expressed in the lung at high concentrations. Both proteins are considered important players of the pulmonary immune responses. Under normal conditions however, SP-A-/- mice display no pathological features in the lung. SP-D-/- mice, on the other hand, show chronic inflammatory alterations indicating a special importance of this molecule in regulating immune homeostasis and the function of the innate immune cells. Recent studies in our laboratory and others implied significant associations between changes in SP-D levels and the presence of airway inflammation both in animal models and patients raising a potential usefulness of this molecule as a disease biomarker. Research on wild-type and mutant recombinant molecules in vivo and in vitro showed that SP-D binds carbohydrates, lipids and nucleic acids with a broad spectrum specificity and initiates phagocytosis of inhaled pathogens as well as apoptotic cells. Investigations on gene-deficient and conditional over expressor mice in addition, provided evidence that SP-D directly modulates macrophage and dendritic cell function as well as T cell-dependent inflammatory events. Thus, SP-D has a unique, dual functional capacity to induce pathogen elimination on the one hand and control of pro-inflammatory mechanisms on the other, suggesting a potential suitability for therapeutic prevention and treatment of chronic airway inflammation without compromising the host defence function of the airways. This paper will review recent findings on the mechanisms of immune-protective function of SP-D in the lung.

Surfactant protein D binding to Aspergillus fumigatus hyphae is calcineurin-sensitive

Surfactant protein D (SP-D) plays a central role in pulmonary innate immune responses to microbes and allergens, often enhancing clearance of inhaled material. Although SP-D functions during bacterial and viral infections are well established, much less is known about its possible roles during invasive fungal infections. Aspergillus fumigatus is a prominent fungal pathogen in immunocompromised individuals, and can cause allergic or invasive aspergillosis. SP-D has been shown to be protective against both of these disease modalities. The moieties present on the fungal surface responsible for SP-D binding remain largely unclear, although cell wall 1,3-beta-D-glucan is bound by SP-D in other fungal species. There is little information regarding the interaction of SP-D with A. fumigatus hyphae which are responsible for the invasive form of disease. Here, we show that SP-D binding to A. fumigatus hyphae is sensitive to the activity of the calcium-activated protein phosphatase calcineurin. Deletion of the catalytic subunit calcineurin A (DeltacnaA) or pharmacologic inhibition of calcineurin through FK506 abrogated SP-D binding. In contrast, SP-D binding to Cruptococcus neoformans was calcineurin-independent. Pharmacologic inhibition of A. fumigatus cell wall components by caspofungin (inhibits 1,3-beta-D-glucan synthesis) and nikkomycin Z (inhibits chitin synthesis) increased SP-D binding to the wild-type strain. In contrast, SP-D binding increased in the DeltacnaA strain only after nikkomycin Z treatment. We conclude that SP-D binding to A. fumigatus hyphae is calcineurin-sensitive, presumably as a consequence of calcineurin's role in regulating production of key cell wall binding partners, such as 1,3-beta-D-glucan. Elucidation of the interaction between lung innate immune factors and A. fumigatus could lead to the development of novel therapeutic interventions.

Global transcriptional characterization of a mouse pulmonary epithelial cell line for use in genetic toxicology

Prior to its application for in vitro toxicological assays, thorough characterization of a cell line is essential. The present study uses global transcriptional profiling to characterize a lung epithelial cell line (FE1) derived from MutaMouse [White, P.A., Douglas, G.R., Gingerich, J., Parfett, C., Shwed, P., Seligy, V., Soper, L., Berndt, L., Bayley, J., Wagner, S., Pound, K., Blakey, D., 2003. Development and characterization of a stable epithelial cell line from Muta Mouse lung. Environmental and Molecular Mutagenesis 42, 166-184]. Results presented here demonstrate the origin of the FE1 lung cell line as epithelial, presenting both type I and type II alveolar phenotype. An assessment of toxicologically-relevant genes, including those involved in the response to stress and stimuli, DNA repair, cellular metabolism, and programmed cell death, revealed changes in expression of 22-27% of genes in one or more culture type (proliferating and static FE1 cultures, primary epithelial cultures) compared with whole lung isolates. Gene expression analysis at 4 and 24h following benzo(a)pyrene exposure revealed the induction of cyp1a1, cyp1a2, and cyp1b1 in FE1 cells and lung isolates. The use of DNA microarrays for gene expression profiling allows an improved understanding of global, coordinated cellular events arising in cells under different physiological conditions. Taken together, these data indicate that the FE1 cell line is derived from a cell type relevant to toxic responses in vivo, and shows some similarity in response to chemical insult as the original tissue.

Protective role of the lung collectins surfactant protein A and surfactant protein D in airway inflammation

The acute inflammatory airway response is characterized by a time-dependent onset followed by active resolution. Emerging evidence suggests that epithelial cells of the proximal and distal air spaces release host defense mediators that can facilitate both the initiation and the resolution part of inflammatory airway changes. These molecules, also known as the hydrophilic surfactant proteins (surfactant protein [SP]-A and SP-D) belong to the class of collagenous lectins (collectins). The collectins are a small family of soluble pattern recognition receptors containing collagenous regions and C-type lectin domains. SP-A and SP-D are most abundant in the lung. Because of their structural uniqueness, specific localization, and functional versatility, lung collectins are important players of the pulmonary immune responses. Recent studies in our laboratory and others indicated significant associations of lung collectin levels with acute and chronic airway inflammation in both animal models and patients, suggesting the usefulness of these molecules as disease biomarkers. Research on wild-type and mutant recombinant molecules in vivo and in vitro showed that SP-A and SP-D bind carbohydrates, lipids, and nucleic acids with a broad-spectrum specificity and initiate phagocytosis of inhaled pathogens as well as apoptotic cells. Investigations on gene-deficient and conditional overexpresser mice indicated that lung collectins also directly modulate innate immune cell function and T-cell-dependent inflammatory events. Thus, these molecules have a unique, dual-function capacity to induce pathogen elimination and control proinflammatory mechanisms, suggesting a potential suitability for therapeutic prevention and treatment of chronic airway inflammation. This article reviews evidence supporting that the lung collectins play an immune-protective role and are essential for maintenance of the immunologic homeostasis in the lung.

Surfactant protein D protects against acute hyperoxic lung injury

RATIONALE

Surfactant protein D (SP-D) is a member of the collectin family of soluble, innate, host defense molecules with demonstrated immunomodulatory properties in vitro. Constitutive absence of SP-D in mice is associated with lung inflammation, alteration in surfactant lipid homeostasis, and increased oxidative-nitrative stress.

OBJECTIVES

To test the hypothesis that SP-D would protect against acute lung injury from hyperoxia in vivo.

METHODS

Transgenic mice overexpressing rat SP-D constitutively (SP-D OE) or conditionally via regulation with doxycycline (SP-D Dox-on) were subjected to continuous hyperoxic challenge for up to 14 days.

MEASUREMENTS AND MAIN RESULTS

Compared with littermate control mice (wild-type [WT]), SP-D OE mice exposed to 80% O(2) demonstrated substantially increased survival accompanied by significant reductions in wet to dry lung ratios and bronchoalveolar lavage (BAL) protein. Although SP-D OE and WT mice exhibited a twofold increase in total BAL cells and neutrophilia in response to hyperoxia, the SP-D OE group had lower levels of BAL proinflammatory cytokines and chemokines, including IL-6, tumor necrosis factor-alpha, and monocyte chemotactic protein-1; increased mRNA levels of the transcription factor NF-E2 related factor-2 (NRF-2) and phase 2 antioxidants hemoxygenase-1 (HO-1), glutathione peroxidase-2 (GPx-2) and NAD(P)H quinone oxidoreductase-1 (Nqo-1); and decreases in lung tissue thiobarbituric acid-reactive substances. As proof of principle, the protective role of SP-D on hyperoxic injury was confirmed as SP-D Dox-on mice exposed to 85% O(2) demonstrated increased mortality upon withdrawal of doxycycline.

CONCLUSIONS

Local expression of SP-D protects against hyperoxic lung injury through modulation of proinflammatory cytokines and antioxidant enzymatic scavenger systems.

The dynamic of the t-haplotype in wild populations of the house mouse Mus musculus domesticus in Israel

The t-haplotype, a variant of the proximal part of the mouse chromosome 17, is composed of at least four inversions and is inherited as a single genetic unit. The haplotype causes embryonic mortality or male sterility when homozygous. Genes within the complex are responsible for distortion of Mendelian transmission ratio in males. Thus, the t-haplotype in heterozygous males is transferred to over 95% of the progeny. We examined the dynamic and behavior of the t-haplotype in wild populations of the house mouse in Israel. The Israeli populations show high frequency (15%-20%) of both partial and complete t-carrying mice, supporting the suggestion that the t-complex evolved in the M. domesticus line in the Israeli region. In one population that had the highest frequency of t-carrying individuals, we compared the level of gene diversity between t-carrying and normal mice in the marker's loci: H-2 locus of the major histocompatibility complex (MHC) on the t-haplotype of chromosome 17, three microsatellites on other chromosomes, and the mitochondrial D-loop. Genetic variability was high in all tested loci in both t and (+) mice. All t mice carried the same chromosome and showed the same H-2 haplotype. While t-carrying mice showed significant H-2 heterozygotes access, (+) mice expressed significant H-2 heterozygote deficiency. There were no differences in the level of gene diversity between t and (+) mice in the other loci. Heterozygosity level at the MHC may be an additional factor in the selective forces balancing the t-haplotype polymorphism.

Evolution of collagens

The extracellular matrix is often defined as the substance that gives multicellular organisms (from plants to vertebrates) their structural integrity, and is intimately involved in their development. Although the general functions of extracellular matrices are comparable, their compositions are quite distinct. One of the specific components of metazoan extracellular matrices is collagen, which is present in organisms ranging from sponges to humans. By comparing data obtained in diploblastic, protostomic, and deuterostomic animals, we have attempted to trace the evolution of collagens and collagen-like proteins. Moreover, the collagen story is closely involved with the emergence and evolution of metazoa. The collagen triple helix is one of numerous modules that arose during the metazoan radiation which permit the formation of large multimodular proteins. One of the advantages of this module is its involvement in oligomerization, in which it acts as a structural organizer that is not only relatively resistant to proteases but also permits the creation of multivalent supramolecular networks.

Surfactant protein D gene regulation. Interactions among the conserved CCAAT/enhancer-binding protein elements

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following acute lung injury. Given the importance of CCAAT/enhancer-binding protein (C/EBP)-binding elements in the systemic acute-phase response and lung development and the expression of C/EBP isoforms by lung epithelial cells, we hypothesized that conserved C/EBP motifs in the near-distal and proximal promoters contribute to the regulation of SP-D expression by C/EBPs. Five SP-D motifs (-432, -340, -319, -140, and -90) homologous to the C/EBP consensus sequence specifically bound to C/EBPs in gel shift assays, and four of the five sites (-432, -340, -319, and -90) efficiently competed for the binding of C/EBPalpha, C/EBPbeta, or C/EBPdelta to consensus oligomers. Cotransfection of C/EBPalpha, C/EBPbeta, or C/EBPdelta cDNA in H441 lung adenocarcinoma cells significantly increased the luciferase activity of a wild-type SP-D promoter construct containing 698 bp of upstream sequence (SS698). Transfection of C/EBP also increased the level of endogenous SP-D mRNA in H441 cells. Transactivation of the reporter construct was abrogated by deletion of sequences upstream of -205. Independent site-directed mutagenesis of the sites at -432, -340, and -319 reduced C/EBP-mediated activation by approximately 50%, and mutagenesis of the site at -432 in combination with either of the tandem sites at -340 and -319 blocked activation. The conserved AP-1 element at -109 was required for maximal promoter activity, but not for the transactivation of SS698 by C/EBPs. Thus, interactions among C/EBP elements in the near-distal promoter can modulate the promoter activity of SP-D.

The pulmonary collectins and surfactant metabolism

Lung surfactant covers and stabilizes a large, delicate surface at the interface between the host and the environment. The surfactant system is placed at risk by a number of environmental challenges such as inflammation, infection, or oxidant stress, and perhaps not surprisingly, it demonstrates adaptive changes in metabolism in response to alterations in the alveolar microenvironment. Recent experiments have shown that certain components of the surfactant system are active participants in the regulation of the alveolar response to a wide variety of environmental challenges. These components are capable not only of maintaining a low interfacial surface tension but also of amplifying or dampening inflammatory responses. These observations suggest that regulatory molecules are capable of both sensing the environment of the alveolus and providing feedback to the cells regulating surfactant synthesis, secretion, alveolar conversion, and clearance. In this review we examine the evidence from in vitro systems and gene-targeted mice that two surfactant-associated collectins (SP-A and SP-D) may serve in these roles and help modify surfactant homeostasis as part of a coordinated host response to environmental challenges.

Proximal promoter of the surfactant protein D gene: regulatory roles of AP-1, forkhead box, and GT box binding proteins

Surfactant protein D (SP-D) plays roles in pulmonary host defense and surfactant homeostasis and is increased following lung injury. Because AP-1 proteins regulate cellular responses to diverse environmental stimuli, we hypothesized that the conserved AP-1 motif (at -109) and flanking sequences in the human SP-D promoter contribute to the regulation of SP-D expression. The AP-1 sequence specifically bound to fra-1, junD, and junB in H441 lung adenocarcinoma nuclear extracts. Mutagenesis of the AP-1 motif in a chloramphenicol acetyltransferase reporter construct containing 285 base pairs of upstream sequence nearly abolished promoter activity, and co-transfection of junD significantly increased wild type but not mutant promoter activity. The sequence immediately downstream of the AP-1 element contained a binding site for HNF-3 (FOXA), and simultaneous mutation of this site (fox-d) and an upstream FoxA binding site (-277, fox-u) caused a 4-fold reduction in chloramphenicol acetyltransferase activity. Immediately upstream of the AP-1-binding site, we identified a GT box-containing positive regulatory element. Despite finding regions of limited homology to the thyroid transcription factor 1-binding site, SP-D promoter activity did not require thyroid transcription factor 1. Thus, transcriptional regulation of SP-D gene expression involves complex interactions with ubiquitous and lineage-dependent factors consistent with more generalized roles in innate immunity.

Collectins and innate immunity in the lung

Evidence from both in vitro and in vivo studies suggests that the collectins are important elements in host innate immune defences against infectious agents. Study of the collectins in specific disease settings now raises the prospects of developing therapies exploiting these mechanisms of innate immunity.

Porcine lung surfactant protein D: complementary DNA cloning, chromosomal localization, and tissue distribution

Porcine organs and lung surfactant have medically important applications in both xenotransplantation and therapy. We have started to characterize porcine lung surfactant by cloning the cDNA of porcine surfactant protein D (SP-D). SP-D and SP-A are important mediators in innate immune defense for the lung and possibly other mucosal surfaces. Porcine SP-D will also be an important reagent for use in existing porcine animal models for human lung infections. The complete cDNA sequence of porcine SP-D, including the 5' and 3' untranslated regions, was determined from two overlapping bacteriophage clones and by PCR cloning. Three unique features were revealed from the porcine sequence in comparison to SP-D from other previously characterized species, making porcine SP-D an intriguing species addition to the SP-D/collectin family. The collagen region contains an extra cysteine residue, which may have important structural consequences. The other two differences, a potential glycosylation site and an insertion of three amino acids, lie in the loop regions of the carbohydrate recognition domain, close to the carbohydrate binding region and thus may have functional implications. These variations were ruled out as polymorphisms or mutations by confirming the sequence at the genomic level in four different pig breeds. Porcine SP-D was shown to localize primarily to the lung and with less abundance to the duodenum, jejunum, and ileum. The genes for SP-D and SP-A were also shown to colocalize to a region of porcine chromosome 14 that is syntenic with the human and murine collectin loci.