Production Of Surfactant Protein A Research Articles

MON-005 Inhibition of Glucocorticoid Signaling in SRC-1/-2 Double-Deficient Mice Results in Impaired Lung Maturation and Delayed Parturition

The mechanisms that lead to the initiation of parturition are incompletely defined. Parturition timing is mediated by signals from both mother and fetus. Our previous findings using mice that were double-deficient in steroid receptor coactivators (Src)1 and 2 (Src-1/-2d/d) suggest that the fetus signals its mother when it is ready to be born through fetal lung production of surfactant components, surfactant protein A (SP-A) and platelet-activating factor (PAF). Notably, mice that are double knockout for Src-1/-2 die at birth of respiratory distress, due to decreased surfactant lipoprotein production. Intriguingly, we observed that wild-type (WT) mothers carrying Src-1/-2d/d fetuses manifested a ~38 h delay in parturition compared to WT mothers carrying WT fetuses. This was associated with decreased production of SP-A and PAF by the Src-1/-2d/d fetal lungs. Our findings suggested that these effects of Src-1/-2d/d were caused by impaired glucocorticoid receptor (GR) transcriptional activity in fetal lung cells. To identify other genes in fetal lung that were affected by Src-1/-2d/d, we conducted RNA-seq analysis of lungs from 18.5 days post-coitum Src-1/-2d/dvs. WT fetuses. We observed that one of the genes most highly downregulated in Src-1/-2d/d fetal lungs was 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). 11β-HSD1 catalyzes the conversion of inactive cortisone or 11-dehydrocorticosterone into active cortisol or corticosterone, respectively, which are ligands for the glucocorticoid receptor (GR). We validated the RNA-seq results by RT-qPCR and immunoblotting and observed a striking reduction of 11β-HSD1 mRNA and protein in lungs of Src-1/2d/d fetuses, compared to WT. Others observed that glucocorticoids potently increased 11β-HSD1 expression in various cell types via activation of transcription factors C/EBPα and C/EBPβ, providing a potential positive feed-forward loop. Notably, we observed that C/EBPα and C/EBPβ mRNA and protein were markedly reduced in Src-1/-2d/d fetal lungs, compared to WT. Deletion of the Cebpa gene in respiratory epithelium of fetal mice caused respiratory failure at birth due to surfactant lipid and protein deficiency. This was associated with increased expression of TGF-β2, which inhibits fetal lung maturation. Notably, we observed that expression of TGF-β2 and TGF-β3 were increased in Src-1/-2d/d fetal lungs. Thus, impaired lung development, surfactant synthesis and delayed parturition in Src-1/-2d/d fetuses are likely caused by decreased 11β-HSD1 and GR signaling, resulting in decreased C/EBPα/β expression and increased TGF-β signaling.

Steroid receptor coactivators 1 and 2 mediate fetal-to-maternal signaling that initiates parturition.

The precise mechanisms that lead to parturition are incompletely defined. Surfactant protein-A (SP-A), which is secreted by fetal lungs into amniotic fluid (AF) near term, likely provides a signal for parturition; however, SP-A-deficient mice have only a relatively modest delay (~12 hours) in parturition, suggesting additional factors. Here, we evaluated the contribution of steroid receptor coactivators 1 and 2 (SRC-1 and SRC-2), which upregulate SP-A transcription, to the parturition process. As mice lacking both SRC-1 and SRC-2 die at birth due to respiratory distress, we crossed double-heterozygous males and females. Parturition was severely delayed (~38 hours) in heterozygous dams harboring SRC-1/-2-deficient embryos. These mothers exhibited decreased myometrial NF-κB activation, PGF2α, and expression of contraction-associated genes; impaired luteolysis; and elevated circulating progesterone. These manifestations also occurred in WT females bearing SRC-1/-2 double-deficient embryos, indicating that a fetal-specific defect delayed labor. SP-A, as well as the enzyme lysophosphatidylcholine acyltransferase-1 (LPCAT1), required for synthesis of surfactant dipalmitoylphosphatidylcholine, and the proinflammatory glycerophospholipid platelet-activating factor (PAF) were markedly reduced in SRC-1/-2-deficient fetal lungs near term. Injection of PAF or SP-A into AF at 17.5 days post coitum enhanced uterine NF-κB activation and contractile gene expression, promoted luteolysis, and rescued delayed parturition in SRC-1/-2-deficient embryo-bearing dams. These findings reveal that fetal lungs produce signals to initiate labor when mature and that SRC-1/-2-dependent production of SP-A and PAF is crucial for this process.

The effects of porcine pulmonary surfactant on smoke inhalation injury

BackgroundOur previous study, consistent with others, demonstrated that administering an exogenous surfactant was a potential therapy for acute lung injury and acute respiratory distress syndrome. However, the underlying mechanisms remain largely unknown. In the present study, we investigated the effect of instilled porcine pulmonary surfactant (PPS) on rat inhalation injury model induced by smoke and the possible mechanism. Materials and methodsFifteen Sprague–Dawley rats were equally randomized to three groups as follows (n = 5 in each group): sham control group (C group), inhalation injury group (II group), and inhalation injury + PPS treatment group (PPS group). Lung tissues were assayed for wet/dry ratio, histologic, terminal dUTP nick-end labeling staining, and Western blotting examinations. The myeloperoxidase activity was tested in lung tissues as well. Bronchoalveolar lavage fluid was collected to determine the total protein concentrations, inflammatory cytokines, surfactant protein A (SP-A), and SP-D. ResultsOur present work exhibited that PPS had therapeutic effects on smoke inhalation injury reflected by significant increase of PaO2 values, improved edema status, decreased vascular permeability, amelioration of lung histopathology, and reduction of inflammatory response. In addition, PPS treatment could increase endogenous SP-A levels both in lung tissue and bronchoalveolar lavage fluid. Further correlation analysis showed that SP-A was negatively correlated with both myeloperoxidase activity and interleukin 8 levels. ConclusionsThese results indicate that PPS can attenuate smoke-induced inhalation injury at least partly through stimulating production of endogenous SP-A and inhibiting the release of proinflammatory cytokines such as interleukin 8. The increasing production of endogenous SP-A may be due to the antioxidant effect of PPS, which contains no SP-A.

Investigation of IL-6 Effects on SP-A Expression in A549 Lung Cell Line

ABSTRACTInterleukin-6 (IL-6) is a multifunctional cytokine that is important in inflammatory processes, cell differentiation and growth.Pulmonary surfactant is a protein-lipid complex, which reduce surface tension at the alveolar air-liquid interface, thereby preventing lung collapse. Surfactant protein A (SP-A) is the most abundant of four surfactant proteins (SP-A, SP-B, SP-C and SP-D). It binds to alveolar macrophages, stimulates their chemotaxis and serves as an opsonin in the phagocytosis.Low SP-A levels are associated with increased inflammation in the lung. In the absence of infection SP-A inhibited IL-6 production. In infected macrophages, SP-A augmented IL-6 production. In humans, SP-A levels are altered by a number of disease states. In some of them there is increased levels of SP-A in the bronchoalveolar lavage fluid.Here we investigate presence/absence of correlation between increased levels of IL-6 and production of SP-A from A549 lung cell line. Our results suggest that incubation of A549 cells with IL-6 for different time changes significantly the expression levels of SP-A.

Bordetella bronchisepticaAdherence to Cilia Is Mediated by Multiple Adhesin Factors and Blocked by Surfactant Protein A

In the virulent state (Bvg+), Bordetella bronchiseptica expresses adhesins and toxins that mediate adherence to the upper airway epithelium, an essential early step in pathogenesis. In this study, we used a rabbit tracheal epithelial cell binding assay to test how specific host or pathogen factors contribute to ciliary binding. The host antimicrobial agent surfactant protein A (SP-A) effectively reduced ciliary binding by Bvg+ B. bronchiseptica. To evaluate the relative contributions of bacterial adhesins and toxins to ciliary binding, we used mutant strains of B. bronchiseptica in the binding assay. When compared to Bvg+ or Bvg- phase-locked B. bronchiseptica strains, single-knockout strains lacking one of the known adhesins (filamentous hemagglutinin, pertactin, or fimbriae) displayed an intermediate ciliary binding capacity throughout the coincubation. A B. bronchiseptica strain deficient in adenylate cyclase-hemolysin toxin also displayed an intermediate level of adherence between Bvg+ and Bvg- strains and had the lowest ciliary affinity of any of the Bvg+ phase strains tested. A B. bronchiseptica strain that was missing dermonecrotic toxin also displayed intermediate binding; however, this strain displayed ciliary binding significantly higher than most of the adhesin knockouts tested. Taken together, these findings suggest that virulent-state B. bronchiseptica expresses multiple adhesins with overlapping contributions to ciliary adhesion and that host production of SP-A can provide innate immunity by blocking bacterial adherence to the ciliated epithelium.

Differences in the translation efficiency and mRNA stability mediated by 5′-UTR splice variants of human SP-A1 and SP-A2 genes

Surfactant protein A (SP-A) plays an important role in host defense, modulation of inflammatory processes, and surfactant-related functions of the lung. The human SP-A (hSP-A) locus consists of two functional genes, SP-A1 and SP-A2. Several hSP-A 5'-untranslated region (UTR) splice variants for each gene have been characterized and shown to be translated in vitro and in vivo. In this report, we investigated the role of hSP-A 5'-UTR splice variants on SP-A production and molecular mechanisms involved. We used in vitro transient expression of hSP-A 5'-UTR constructs containing luciferase as the reporter gene and quantitative real-time PCR to study hSP-A 5'-UTR-mediated gene expression. We found that 1) the four (A'D', ABD, AB'D', and A'CD') 5'-UTR splice variants under study enhanced gene expression, by increasing luciferase activity from 2.5- to 19.5-fold and luciferase mRNA from 4.3- to 8.8-fold compared with the control vector that lacked hSP-A 5'-UTR; 2) all four 5'-UTR splice variants studied regulated mRNA stability. The ABD variant exhibited the lowest rate of mRNA decay compared with the other three constructs (A'D', AB'D', and A'CD'). These three constructs also exhibited significantly lower rate of mRNA decay compared with the control vector; 3) based on the indexes of translational efficiency (luciferase activity/mRNA), ABD and AB'D' exhibited higher translational efficiency compared with the control vector, whereas the translational efficiency of each A'D' and A'CD' was lower than that of the control vector. These findings indicate that the hSP-A 5'-UTR splice variants play an important role in both SP-A translation and mRNA stability.

Surfactant protein secreted by the maturing mouse fetal lung acts as a hormone that signals the initiation of parturition.

Parturition is timed to begin only after the developing embryo is sufficiently mature to survive outside the womb. It has been postulated that the signal for the initiation of parturition arises from the fetus although the nature and source of this signal remain obscure. Herein, we provide evidence that this signal originates from the maturing fetal lung. In the mouse, secretion of the major lung surfactant protein, surfactant protein A (SP-A), was first detected in amniotic fluid (AF) at 17 days postcoitum, rising progressively to term (19 days postcoitum). Expression of IL-1beta in AF macrophages and activation of NF-kappaB in the maternal uterus increased with the gestational increase in SP-A. SP-A stimulated IL-1beta and NF-kappaB expression in cultured AF macrophages. Studies using Rosa 26 Lac-Z (B6;129S-Gt(rosa)26Sor) (Lac-Z) mice revealed that fetal AF macrophages migrate to the uterus with the gestational increase in AF SP-A. Intraamniotic (i.a.) injection of SP-A caused preterm delivery of fetuses within 6-24 h. By contrast, injection of an SP-A antibody or NF-kappaB inhibitor into AF delayed labor by >24 h. We propose that augmented production of SP-A by the fetal lung near term causes activation and migration of fetal AF macrophages to the maternal uterus, where increased production of IL-1beta activates NF-kappaB, leading to labor. We have revealed a response pathway that ties augmented surfactant production by the maturing fetal lung to the initiation of labor. We suggest that SP-A secreted by the fetal lung serves as a hormone of parturition.

Cyclophosphamide prevents systemic keratinocyte growth factor-induced up-regulation of surfactant protein A after allogeneic transplant in mice.

We reported that systemic keratinocyte growth factor (KGF) given before bone marrow transplantation (BMT) prevents allogeneic T cell-dependent lung inflammation assessed on Day 7 post-BMT, but the antiinflammatory effects of KGF were impaired in mice injected with both T cells and conditioning regimen of cyclophosphamide (Cy). Intratracheal KGF is known to stimulate the expression of surfactant protein A (SP-A), an oxidant-sensitive T cell immunomodulator produced by alveolar type II cells. We hypothesized that systemic KGF up-regulates SP-A after allogeneic BMT, and the addition of Cy may interfere with the ability of KGF to enhance SP-A production. The subcutaneous administration of recombinant human KGF (5 mg/kg on Days -6, -5, and -4 pre-BMT) increased SP-A protein and mRNA in allogeneic T cell-recipient irradiated mice measured on Day 7 post-BMT. In contrast, the same KGF treatment in irradiated mice given T cells and Cy failed to up-regulate SP-A mRNA and protein expression. In mixed lymphocyte reaction experiments designed to simulate the in vivo model, the addition of human SP-A (5-50 microg) to alloactivated T cells suppressed the production of interleukin-2 in a dose-dependent fashion. We conclude that the systemic pre-BMT injection of KGF in recipients of allogeneic T cells up-regulates SP-A, which may contribute to the early antiinflammatory effects of KGF. The protective KGF-mediated SP-A production is abolished in mice given alloreactive T cells plus Cy.

Neuregulin-1 and human epidermal growth factor receptors 2 and 3 play a role in human lung development in vitro.

The human epidermal growth factor receptor (HER) family consists of four distinct receptors: HER1 (epidermal growth factor receptor), HER2, HER3, and HER4. Their specific activating ligands are collectively known as neuregulins (NRG). We hypothesized that one member of the NRG family, NRG-1, and the HER family would play a role in fetal lung development. To test this hypothesis, we defined NRG-1 and HER gene expression in mid-trimester human fetal lung tissue. HER2 and HER3 messenger RNA and protein were detected in the fetal lung, but HER4 expression was not detected. Immunohistochemical staining of fetal lung tissue localized HER2 and HER3 protein to the developing lung epithelium. NRG-1 expression was not found in freshly isolated human fetal lung, but it was observed in fetal lung explants after 2 d of explant culture. Immunohistochemistry of cultured human fetal lung explants revealed that NRG-1 protein was also expressed in pulmonary epithelial cells. Exposing human fetal lung to recombinant NRG-1 activated the HER receptor complex as measured by approximately 4-fold increases in receptor phosphotyrosine content. In addition, NRG-1 increased explant epithelial cell volume density approximately 2-fold (P < 0. 03); increased epithelial cell proliferation approximately 2-fold, as determined by bromodeoxyuridine labeling (P = 0.002); and reduced surfactant protein-A (SP-A) levels by 53% (P < 0.05). These data are consistent with an autocrine regulatory process mediated by NRG-1 activation of HER2/HER3 heterodimers expressed on developing human fetal lung epithelial cells. Receptor activation results in increased lung epithelial cell proliferation and volume density, and decreased SP-A production, a marker of type II pneumocyte differentiation.

Inhibition of Surfactant Protein A Release by Oleic Acid Induced Lung Injury. 1806

Oleic acid (OA) causes reversible lung injury which resolves in 5-7 days. This injury is characterized by inflammatory cell infiltration, changes in surfactant phospholipids and derangements in pulmonary function which peaks at 4-24 h after injury and begins to resolve by 72 h without permanent damage to alveolar epithelium. Surfactant protein A (SP-A) has been shown to be involved in pulmonary defense during lung inflammation, and SP-A may also be a proinflammatory mediator. Our hypothesis is that OA causes a reversible change in SP-A production and/or release and that SP-A may be involved in the reversible injury that occurs after OA administration. Adult rats were treated with either saline or OA i.v. after which lung lavage was collected at 1, 4, 24, 72h and 120h. Lungs were also removed. Lavage samples were centrifuged, to remove debris and cells, and then concentrated 15-fold. Lungs were homogenized and protein content was measured. Equivalent amounts of lung lavage and lung homogenates were separated by SDS-PAGE. Immunoblots were processed using polyclonal anti-rat SP-A antibody, and SP-A bands were analyzed by densitometry. There was a decrease in SP-A protein levels in lavage at 1, 4, and 24 hours after OA injury. Levels returned to normal by 72 h after injury. In contrast there was an increase in SP-A protein levels in lung homogenates at 1, 4, 24 and 72 hours after OA injury. The peak response was a 2-fold increase over controls at 4-24 h. We conclude that OA injury inhibits release of SP-A during the acute injury phase which resolves as the injury heals. It is possible that OA directly inhibits secretion of SP-A by type II cells and Clara cells. Alternatively, OA may cause release of both proinflammatory and antiinflammatory cytokines which in turn affect SP-A release. We speculate that the decreased release of SP-A (with known inflammatory actions) into the alveolus may be involved in the reversibilty of the OA injury. Funded in part by NIH grant HL-49099 (MJK).

Surfactant Protein A in Fetal Rats With Congenital Diaphragmatic Hernia

Concentrations of disaturated phosphatidylcholine and surfactant protein A(SP-A) in amniotic fluid (AF) of pregnancies with fetuses that have congenital diaphragmatic hernia (CDH) are decreased (Am J OB Gyn 173, 1995). However, it is not well established if these abnormalities reflect alterations of fetal lung development or variations in the amount of AF. To distinguish between these possibilities we determined SP-A in fetal lungs from rats between 19-21 days of gestation (term=22 days), with or without CDH produced by maternal ingestion of the herbicide Nitrofen, and in the lungs of a control group of fetuses not exposed to Nitrofen. Using immunohistochemistry with an anti-human SP-A polyclonal antibody, SP-A was not detected in any fetal lung on day 19 of gestation. At 21 days of gestation there was abundant SP-A which appeared to be decreased in the air spaces of fetuses with CDH compared with fetuses without CDH or those not exposed to Nitrofen. To confirm these findings we used the same antibody for Western Blotting. A small amount of SP-A could be detected in the fetal lungs of the three groups without differences between them. At 21 days of gestation a marked decreased of SP-A was found in lungs from fetuses with CDH compared with the other groups (p<0.05 by ANOVA). Nonetheless, no differences were found between groups in the levels of mRNA for SP-A using a cDNA for human SP-A. These findings suggest that in rat fetuses with CDH there is decreased production of SP-A at post-translational levels. This abnormality probably explains the lower AF concentrations of SP-A found in human fetuses with CDH.

Localization of Pulmonary Surfactant Proteins Using Immunohistochemistry and Tissue in Situ Hybridization

Surfactant, a complex mixture of lipids and proteins, is produced by the type II alveolar epithelial cells. Numerous studies have localized surfactant protein A (SP-A) to type II cells of the lung, and recent studies have shown that the type II cells in the human lung are also the site of synthesis of SP-B, one of the hydrophobic surfactant proteins. There have been conflicting reports about additional sites of SP-A production. We have studied the localization of the mRNAs for SP-A, SP-B, and SP-C in the rat and for SP-C in the human lung by tissue in situ hybridization using cRNA probes. The mRNAs for all three rat surfactant proteins and for human SP-C were found in type II alveolar epithelial cells. In addition, the mRNAs for rat SP-A and SP-B were found in nonciliated bronchiolar cells. SP-C mRNA was not detectable in the bronchiolar cells of both rat and human lung tissue. Immunohistochemical studies in the rat lung with antisera to SP-A and SP-B confirmed the presence of the protein in cell types where the mRNA was found, as well as in some alveolar macrophages. Alveolar macrophages in both rat and human lung tissue were negative for all mRNAs. Further studies are required to ascertain whether there are differences in the processing, function, and regulation of these proteins in the different cell types that produce them.

Expression and characterization of rat surfactant protein A synthesized in Chinese hamster ovary cells

Rat surfactant protein A (SP-A) was expressed in a Chinese hamster ovary (CHO-K1) cell line and characterized for biologic activity using assays for receptor binding and modulation of phospholipid secretion from isolated type II cells. The CHO-K1 cell line was cotransfected with separate plasmids encoding for the rat SP-A, dihydrofolate reductase and neomycin phosphotransferase, respectively. Antibiotic (Geneticin-G418)-resistant transformants were screened by ELISA for the secretion of recombinant SP-A into the media. Northern analysis of the transfected cell lines demonstrated the expression of both 1.6 kb and 0.9 kb mRNA species for SP-A, consistent with the proposed differential polyadenylation of the primary transcript. Amplification with methotrexate resulted in a dose-dependent increase in mRNA for SP-A and a 20-fold increase in the production of recombinant SP-A relative to untreated cells. Maximum production of SP-A was 370 μg of SP-A / 1 of media in a 4-day incubation. Recombinant SP-A was purified from the serum-free media of large scale cultures of transfected, amplified CHO cells by affinity chromatography on mannose-Sepharose. The recombinant SP-A migrated similarly to native SP-A by NaDodSO 4-PAGE analysis under reducing and nonreducing conditions and under reducing conditions after digestion with N-glycanase. Recombinant SP-A effectively competed with 125I-native SP-A for binding to the high affinity receptor for SP-A on isolated plasma membranes from rat alveolar type II cells. The recombinant SP-A was as effective as native SP-A in the inhibition of secretion of phospholipid from isolated type II cells. We conclude that recombinant rat SP-A produced in Chinese hamster ovary cells is physically and functionally similar to native rat SP-A.