Surfactant Proteins SP-B Research Articles

The expression of the surfactant proteins SP-A and SP-B during postnatal alveolarization of the rat lung.

Surfactant-specific proteins (SP) are responsible for the functional and structural integrity as well as for the stabilization of the intra-alveolar surfactant. Morphological lung maturation starts in rat lungs after birth. The aim of this study was to investigate whether the expression of the hydrophilic SP-A and the hydrophobic SP-B is associated with characteristic postnatal changes characterizing morphological lung maturation. Stereological methods were performed on the light microscope. Using immunohistochemical and molecular biological methods (Western Blot, RT-qPCR), the SP-A and SP-B of adult rat lungs and of those with different postnatal developmental stages (3, 7, 14 and 21 days after birth) were characterized. As signs of alveolarization the total septal surface and volume increased and the septal thickness decreased. The significantly highest relative surface fraction of SP-A labeled alveolar epithelial cells type II (AEII) was found together with the highest relative SP-A gene expression before the alveolarization (3th postnatal day). With the downregulation of SP-A gene expression during and after alveolarization (between postnatal days 7 and 14), the surface fraction of the SP-A labeled AEII also decreased, so they are lowest in adult animals. The surface fraction of SP-B labeled AEII and the SP-B gene expression showed the significantly highest levels in adults, the protein expression increased also significantly at the end of morphological lung maturation. There were no alterations in the SP-B expression before and during alveolarization until postnatal day 14. The protein expression as well as the gene expression of SP-A and SP-B correlated very well with the total surface of alveolar septa independent of the postnatal age. The expression of SP-A and SP-B is differentially associated with morphological lung maturation and correlates with increased septation of alveoli as indirect clue for alveolarization.

Cumulative evidence of the genetic association between SP-B C1580T polymorphisms and risk of neonatal respiratory distress syndrome

Objective: Surfactant protein SP-B, an important protein in pulmonary surfactant, is required for the stabilization of surfactant films in the lung and maintenance of postnatal lung function. Although the association between SP-B polymorphisms and the risk of neonatal respiratory distress syndrome (RDS) has been evaluated, the results have been inconsistent. We investigated the association between SP-B polymorphisms and the risk of neonatal RDS. Methods: Relevant studies were systematically searched in PubMed, EMBASE, Web of Science, and Chinese National Knowledge Infrastructure (CNKI) electronic databases until June 2022. Data were collected independently by two reviewers and converted to odds ratios (ORs) with 95% confidence intervals (CIs). Meta-analysis, subgroup analysis, sensitivity analysis, and publication bias assessment were performed using Stata 12.1 software and Review Manager 5.3. Results: Fourteen studies were included. SP-B C1580T polymorphism was significantly associated with neonatal RDS in five genetic models (T vs. C: OR = 0.70, 95% CI 0.57–0.86, I2 = 78%; TT vs. CC: OR = 0.63, 95% CI 0.53–0.86, I2 = 39%; CT vs. CC: OR = 0.65, 95% CI 0.50–0.84, I2 = 54%; TT + CT vs. CC: OR = 0.62, 95% CI 0.49–0.78, I2 = 59%; TT vs. CC + CT: OR = 0.78, 95% CI 0.67–0.91, I2 = 43%). The CT and TT genotypes may decrease the risk of RDS in neonates. Subgroup analyses revealed that the association of SP-B C1580T polymorphism with neonatal RDS was stable, independent of preterm birth and Hardy–Weinberg equilibrium. In addition, the Han Chinese were more likely to be affected by SP-B C1580T polymorphisms than Caucasians and Finnish. Conclusions: Our findings suggest that SP-B C1580T polymorphism may be a protective factor against neonatal RDS.

Surfactant Proteins SP-B and SP-C in Pulmonary Surfactant Monolayers: Physical Properties Controlled by Specific Protein-Lipid Interactions.

The lining of the alveoli is covered by pulmonary surfactant, a complex mixture of surface-active lipids and proteins that enables efficient gas exchange between inhaled air and the circulation. Despite decades of advancements in the study of the pulmonary surfactant, the molecular scale behavior of the surfactant and the inherent role of the number of different lipids and proteins in surfactant behavior are not fully understood. The most important proteins in this complex system are the surfactant proteins SP-B and SP-C. Given this, in this work we performed nonequilibrium all-atom molecular dynamics simulations to study the interplay of SP-B and SP-C with multicomponent lipid monolayers mimicking the pulmonary surfactant in composition. The simulations were complemented by z-scan fluorescence correlation spectroscopy and atomic force microscopy measurements. Our state-of-the-art simulation model reproduces experimental pressure-area isotherms and lateral diffusion coefficients. In agreement with previous research, the inclusion of either SP-B and SP-C increases surface pressure, and our simulations provide a molecular scale explanation for this effect: The proteins display preferential lipid interactions with phosphatidylglycerol, they reside predominantly in the lipid acyl chain region, and they partition into the liquid expanded phase or even induce it in an otherwise packed monolayer. The latter effect is also visible in our atomic force microscopy images. The research done contributes to a better understanding of the roles of specific lipids and proteins in surfactant function, thus helping to develop better synthetic products for surfactant replacement therapy used in the treatment of many fatal lung-related injuries and diseases.

Contribution of surface-associated membranes to pulmonary surfactant-mediated drug delivery.

Pulmonary surfactant (PS) exhibits unique composition and biophysical properties to transport different type of therapeutic molecules. This has motivated its study as an efficient delivery vehicle for various drugs, especially molecules with hydrophobic character. PS is synthesized and secreted to the alveolar space by type II pneumocytes, where it spontaneously adsorbs into the air-liquid interface to reduce the surface tension. The adsorbed surfactant film is constituted by an interfacial monolayer with multi-layered membranes associated to it. Surfactant proteins SP-B and SP-C are responsible for maintaining the contact between these reservoirs and the interfacial layer. In order to study whether the multi-layered and multi-vesicular structures spread along the interface together with the interfacial monolayer, potentially serving as a vehicle for drugs, we have designed a novel vehiculization surface balance that connects a donor with a recipient compartment through a long interfacial pathway. Typically, the vehiculization of drugs mediated by PS has been evaluated in vitro by setups that combine different compartments through interfacial paper bridges. By incorporating a lipid fluorescent probe and the model hydrophobic drug Budesonide (BUD) into a porcine derived PS or into proteo-lipid vesicles, we determined that the amount of material transferred from a donor to a recipient compartment was substantially reduced due to the barrier imposed by the paper bridge. The bridge reduced the spreading to a simpler interfacial layer, while our novel setup reveals that a larger three-dimensional layer of liquid may facilitate the spreading of associated membranes and surfactant/drug complexes. We have determined that the three-dimensional structures associated to the interfacial layer spread along the air-liquid interface and entail an important contribution to the transport of lipids and drugs in surfactant-mediated delivery.

Acinetobacter baumannii pneumonia increases surfactant proteins SP-A, SP-B, and SP-D levels, while decreasing SP-C level in bronchoalveolar lavage in rats

Acinetobacter baumannii is an opportunistic pathogen which causes nosocomial infections and high mortality. It is one of the most isolated microorganisms from patients with nosocomial pneumonia. Lung surfactant proteins (SP) are crucial for lung functions, and levels of SP-A, SP-B, SP-C, and SP-D change in the presence of infection. How they are affected in A. baumannii pneumonia, however, has not been conclusively researched. Therefore, the aim of the present study is to investigate the effect of A. baumannii pneumonia on surfactant proteins. 54 six-to-seven-month-old Sprague–Dawley rats were divided into two groups: sham and A. baumannii. The rats were administered 100 μl 0.5 McFarland A. baumannii or sterile saline intratracheally according to their group. Following the inoculation, lung and bronchoalveolar lavage fluids (BALF) were collected on the 3rd, 24th, and 48th hours of instillation. The lungs were examined histopathologically and the SP-A, SP-B, SP-C, and SP-D levels in BALF were measured with ELISA. The rats challenged with A. baumannii had significantly higher SP-A, SP-B, and SP-D levels while having a significantly lower SP-C level compared to their sham equivalents. Furthermore, a strong positive correlation between SP-A and SP-D, and a moderate negative correlation between SP-B and SP-C were observed.

Paraquat Induces Lung Injury via miR-199-Mediated SET in a Mouse Model.

Objective: To explore the molecular mechanism of lung injury caused by paraquat (PQ) poisoning by investigating miR-199-mediated SET. Methods: A paraquat poisoning model was established in C57BL/6 male mice via intraperitoneal injection of paraquat. The mice were transfected with miR-199 siRNA and or mimic. After 14 days of treatment, pathophysiological changes of the lung were observed and lung tissue was analyzed via Hematoxylin-Eosin staining. The levels of miR-199, SETs, surfactant protein SP-A and SP-B, and inflammatory and oxidative factors were analyzed by qPCR, Western Blot, and ELISA kits. Results: A acute lung-injury (ALI) model was established using PQ treatment and confirmed with edema of pulmonary endothelium with low electronic density of endothelial cytoplasm, presence of protein-rich fluid, and numerous erythrocytes in alveolar space, concentric figures of damaged tubular myelin, alveolar destruction, and increase in inflammatory cell numbers. Compared with the control group, miR-199 and SET levels were reduced in the PQ-treated group. miR-199 siRNA increased the SET level, inflammatory and oxidative levels, and reduced the levels of SP-A and SP-B, and miR-199 mimic reduced the SET level, inflammatory and oxidative levels, and increased the levels of SP-A and SP-B. PQ treatment reduced miR-199 level. Conclusion: Paraquat induces ALI by affecting miR-199-mediated SET.

A dominant negative variant of RAB5B disrupts maturation of surfactant protein B and surfactant protein C

Pathogenic variants in surfactant proteins SP-B and SP-C cause surfactant deficiency and interstitial lung disease. Surfactant proteins are synthesized as precursors (proSP-B, proSP-C), trafficked, and processed via a vesicular-regulated secretion pathway; however, control of vesicular trafficking events is not fully understood. Through the Undiagnosed Diseases Network, we evaluated a child with interstitial lung disease suggestive of surfactant deficiency. Variants in known surfactant dysfunction disorder genes were not found in trio exome sequencing. Instead, a de novo heterozygous variant in RAB5B was identified in the Ras/Rab GTPases family nucleotide binding domain, p.Asp136His. Functional studies were performed in Caenorhabditis elegans by knocking the proband variant into the conserved position (Asp135) of the ortholog, rab-5 Genetic analysis demonstrated that rab-5[Asp135His] is damaging, producing a strong dominant negative gene product. rab-5[Asp135His] heterozygotes were also defective in endocytosis and early endosome (EE) fusion. Immunostaining studies of the proband's lung biopsy revealed that RAB5B and EE marker EEA1 were significantly reduced in alveolar type II cells and that mature SP-B and SP-C were significantly reduced, while proSP-B and proSP-C were normal. Furthermore, staining normal lung showed colocalization of RAB5B and EEA1 with proSP-B and proSP-C. These findings indicate that dominant negative-acting RAB5B Asp136His and EE dysfunction cause a defect in processing/trafficking to produce mature SP-B and SP-C, resulting in interstitial lung disease, and that RAB5B and EEs normally function in the surfactant secretion pathway. Together, the data suggest a noncanonical function for RAB5B and identify RAB5B p.Asp136His as a genetic mechanism for a surfactant dysfunction disorder.

Pulmonary surfactant inactivation by β-D-glucan and protective role of surfactant protein A

Pulmonary fungal infections lead to damage of the endogenous lung surfactant system. However, the molecular mechanism underlying surfactant inhibition is unknown. β-D-glucan is the major component of pathogenic fungal cell walls and is also present in organic dust, which increases the risk of respiratory diseases. The objective of this study was to characterize the interaction of this D-glucopyranose polymer with pulmonary surfactant. Our results show that β-D-glucan induced a concentration-dependent inhibition of the surface adsorption, respreading, and surface tension-lowering activity of surfactant preparations containing surfactant proteins SP-B and SP-C. Our data support a new mechanism of surfactant inhibition that consists in the extraction of phospholipid molecules from surfactant membranes by β-D-glucan. As a result, surfactant membranes became more fluid, as demonstrated by fluorescence anisotropy, and showed decreased Tm and transition enthalpy. Surfactant preparations containing surfactant protein A (SP-A) were more resistant to β-D-glucan inhibition. SP-A bound to different β-D-glucans with high affinity (Kd = 1.5 ± 0.1 nM), preventing and reverting β-D-glucan inhibitory effects on surfactant interfacial adsorption and partially abrogating β-D-glucan inhibitory effects on surfactant’s reduction of surface tension. We conclude that β-D-glucan inhibits the biophysical function of surfactant preparations lacking SP-A by subtraction of phospholipids from surfactant bilayers and monolayers. The increased resistance of SP-A-containing surfactant preparations to β-D-glucan reinforces its use in surfactant replacement therapy.

Polyhexamethylene guanidine aerosol triggers pulmonary fibrosis concomitant with elevated surface tension via inhibiting pulmonary surfactant

Environmental chemicals inhalation exposure could induce pulmonary fibrosis, which is characterized by the excessive proliferation of fibroblasts and accumulation of extracellular matrix components, in which surface tension usually plays vital roles. Polyhexamethylene guanidine (PHMG) was first recognized as a potential hazard ingredient in humidifier disinfectants, which caused an outbreak of pulmonary fibrosis in South Korea. However, the underlying mechanisms involved in PHMG-induced pulmonary fibrosis have not yet been fully elucidated. Therefore, this study mainly focuses on the effect of PHMG on surface tension to unveil the influence and involved mechanisms in PHMG-induced pulmonary fibrosis. C57BL/6J mice were exposed to sub-acute PHMG aerosol for 8 weeks. The results indicated that PHMG induced pulmonary fibrosis combined with elevated surface tension. Results from in vitro study further confirmed PHMG elevated surface tension by inhibited pulmonary surfactant. Mechanistically, PHMG suppressed the key surfactant protein SP-B and SP-C by inhibiting protein expression and block their active sites. The present study, for the first time, revealed the molecular mechanism of PHMG-induced pulmonary fibrosis based on pulmonary surfactant inhibition mediated surface tension elevated. And pulmonary surfactant may be a potential target for further intervention to prevent PHMG-induced fibrosis or alleviate the symptom of relevant patients.

Suppression of Lα/Lβ Phase Coexistence in the Lipids of Pulmonary Surfactant

To determine how different constituents of pulmonary surfactant affect its phase behavior, we measured wide-angle x-ray scattering (WAXS) from oriented bilayers. Samples contained the nonpolar and phospholipids (N&PL) obtained from calf lung surfactant extract (CLSE), which also contains the hydrophobic surfactant proteins SP-B and SP-C. Mixtures with different ratios of N&PL and CLSE provided the same set of lipids with different amounts of the proteins. At 37°C, N&PL by itself forms coexisting Lα and Lβ phases. In the Lβ structure, the acyl chains of the phospholipids occupy an ordered array that has melted by 40°C. This behavior suggests that the Lβ composition is dominated by dipalmitoyl phosphatidylcholine (DPPC), which is the most prevalent component of CLSE. The Lβ chains, however, lack the tilt of the Lβ′ phase formed by pure DPPC. At 40°C, WAXS also detects an additional diffracted intensity, the location of which suggests a correlation among the phospholipid headgroups. The mixed samples of N&PL with CLSE show that increasing amounts of the proteins disrupt both the Lβ phase and the headgroup correlation. With physiological levels of the proteins in CLSE, both types of order are absent. These results with bilayers at physiological temperatures indicate that the hydrophobic surfactant proteins disrupt the ordered structures that have long been considered essential for the ability of pulmonary surfactant to sustain low surface tensions. They agree with prior fluorescence micrographic results from monomolecular films of CLSE, suggesting that at physiological temperatures, any ordered phase is likely to be absent or occupy a minimal interfacial area.

Towards the Molecular Mechanism of Pulmonary Surfactant Protein SP-B: At the Crossroad of Membrane Permeability and Interfacial Lipid Transfer

Pulmonary surfactant is a lipid-protein complex that coats the alveolar air-liquid interface, enabling the proper functioning of lung mechanics. The hydrophobic surfactant protein SP-B, in particular, plays an indispensable role in promoting the rapid adsorption of phospholipids into the interface. For this, formation of SP-B ring-shaped assemblies seems to be important, as oligomerization could be required for the ability of the protein to generate membrane contacts and to mediate lipid transfer among surfactant structures. SP-B, together with the other hydrophobic surfactant protein SP-C, also promotes permeability of surfactant membranes to polar molecules although the molecular mechanisms underlying this property, as well as its relevance for the surface activity of the protein, remain undefined. In this work, the contribution of SP-B and SP-C to surfactant membrane permeability has been further investigated, by evaluation of the ability of differently-sized fluorescent polar probes to permeate through giant vesicles with different lipid/protein composition. Our results are consistent with the generation by SP-B of pores with defined size in surfactant membranes. Furthermore, incubation of surfactant with an anti-SP-B antibody not only blocked membrane permeability but also affected lipid transfer into the air-water interface, as observed in a captive bubble surfactometer device. Our findings include the identification of SP-C and anionic phospholipids as modulators required for maintaining native-like permeability features in pulmonary surfactant membranes. Proper permeability through membrane assemblies could be crucial to complement the overall role of surfactant in maintaining alveolar equilibrium, beyond its biophysical function in stabilizing the respiratory air-liquid interface.

DETECTION OF SPECIFIC SURFACTANT PROTEINS IN GASTRIC ASPIRATES FROM PREMATURELY BORN CHILDREN AFTER CORTICOSTEROID THERAPY

Purpose: Alveolar surfactant (AS) components, including the specific surfactant proteins (SPs) SP-A, SP-B, SP-C, and SP-D, provides stability during the dynamic process of inhalation/exhalation. In prematurely born children different respiratory pathologies due to surfactant components deficiency, like Neonatal Respiratory Distress Syndrome, can be observed. Administration of corticosteroids to pregnant women at risk of preterm birth is an established intervention in clinical practice. In this study, we analyzed gastric aspirates (GAs), as alternative samples of tracheal aspirates and amniotic fluids for AS maturity determination. Samples were taken from prematurely born babies after antenatal corticosteroid therapy (CST) of pregnant women and were analyzed for the presence of specific surfactant proteins. Materials and Methods: Clinical samples of gastric aspirates were collected in the first minutes after delivery by using of a nasogastric tube and were analyzed by Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot assays for detection of SP-A, SP-B, and SP-C. Results: Our results showed the expression of different isoforms of each specific surfactant protein (SP) in all GA samples, depending on the stage of maturation. Conclusions: Our results showed that CST plays a role in AS components production and maturation. Moreover, GA can be considered as an adequate sample for assessment of surfactant maturity at birth.

Pulmonary glycogen deficiency as a new potential cause of respiratory distress syndrome.

The glycogenin knockout mouse is a model of Glycogen Storage Disease type XV. These animals show high perinatal mortality (90%) due to respiratory failure. The lungs of glycogenin-deficient embryos and P0 mice have a lower glycogen content than that of wild-type counterparts. Embryonic lungs were found to have decreased levels of mature surfactant proteins SP-B and SP-C, together with incomplete processing of precursors. Furthermore, non-surviving pups showed collapsed sacculi, which may be linked to a significantly reduced amount of surfactant proteins. A similar pattern was observed in glycogen synthase1-deficient mice, which are devoid of glycogen in the lungs and are also affected by high perinatal mortality due to atelectasis. These results indicate that glycogen availability is a key factor for the burst of surfactant production required to ensure correct lung expansion at the establishment of air breathing. Our findings confirm that glycogen deficiency in lungs can cause respiratory distress syndrome and suggest that mutations in glycogenin and glycogen synthase 1 genes may underlie cases of idiopathic neonatal death.

Pulmonary surfactant protein SP-B nanorings induce the multilamellar organization of surfactant complexes

Surfactant protein SP-B is absolutely required for the generation of functional pulmonary surfactant, a unique network of multilayered membranes, which stabilizes the respiratory air-liquid interface. It has been proposed that SP-B assembles into hydrophobic rings and tubes that facilitate the rapid transfer of phospholipids from membrane stores into the interface and the formation of multilayered films, ensuring the stability of the alveoli against physical forces leading to their collapse. To elucidate the molecular organization of SP-B-promoted multilamellar membrane structures, time-resolved Förster Resonance Energy Transfer (FRET) experiments between BODIPY-PC or BODIPY-derivatized SP-B (BODIPY/SP-B), as donor probes, and octadecylrhodamine B, as acceptor probe, were performed in liposomes containing SP-B or BODIPY/SP-B. Our results show that both SP-B and fluorescently labeled SP-B oligomers mediate the connection of adjacent bilayers. Furthermore, by applying rational models to the FRET data, we have been able to provide quantitative details of the structure of SP-B-induced multilayered membrane arrays at the nanometer scale, defining interactions between SP-B rings as key elements for connecting surfactant membranes. The data sustain the structural model and the mechanism of action of SP-B assemblies to sustain the crucial surfactant function.

Mild Hypothermia Enhances Lung Surfactant Activity: Delving into the Molecular Mechanisms

Pulmonary surfactant (PS) is a lipid-protein complex that reduces the surface tension at the respiratory air-liquid interface of alveoli, minimizing the work of breathing. The composition and structure of PS are directly responsible for its mechanical properties in a healthy lung or under pathological conditions. We previously demonstrated that PS activity improves after 72h of Whole Body Hypothermia (WBH, 33 °C) in neonates with and without lung injury. PS performance is significantly better when samples are tested under cooling condition. Moreover, decreasing neonatal lung temperature, SP-C and poli-unsaturated phospholipids are significantly reduced in surfactant large aggregates, promoting the simultaneous increase in DPPC percentage. To understand the molecular mechanisms under this temperature-dependent improvement, we designed a surfactant in vitro model. We combined surfactant lipids at different percentages (DPPC, POPG, POPC and DOPC) with purified porcine surfactant proteins SP-B and SP-C. We tested the biophysical activity of the resulting synthetic models upon breathing-like dynamics in a Captive Bubble Surfactometer, at both 37 °C and 33 °C. We also analyzed the thermotropic profiles of these protein-lipid mixtures by Differential Scanning Calorimetry. Finally, to further confirm our results, we studied both the lateral structure and the lipid composition of porcine PS once subjected to compression at the air-liquid interface. To do so, we coupled Langmuir-Blodgett Balance experiments with Epifluorescence Microscopy and Lipidomic Analysis. Our in vitro data suggests that the improvement in PS activity at 33 °C depends on a better and preferential exclusion from the air-liquid interface of less active phospholipids. This process occurs during compression (at expiration) and SP-C may play a crucial role.

Structure and Function of a Soluble Precursor of Human Pulmonary Surfactant Protein SP-B

Structure and Function of a Soluble Precursor of Human Pulmonary Surfactant Protein SP-B

In Vitro Functional and Structural Characterization of A Synthetic Clinical Pulmonary Surfactant with Enhanced Resistance to Inhibition

CHF5633 is a novel synthetic clinical pulmonary surfactant preparation composed by two phospholipid species, dipalmitoyl phosphatidylcholine (DPPC) and palmitoyloleoyl phosphatidylglycerol (POPG), and synthetic analogues of the hydrophobic surfactant proteins SP-B and SP-C. In this study, the interfacial properties of CHF5633 in the absence and in the presence of inhibitory serum proteins have been assessed in comparison with a native surfactant purified from porcine lungs and with poractant alpha, a widely used clinical surfactant preparation. The study of the spreading properties of CHF5633 in a Wilhelmy balance, its ability to adsorb and accumulate at air-liquid interfaces as revealed by a multiwell fluorescence assay, and its dynamic behavior under breathing-like compression-expansion cycling in a Captive Bubble Surfactometer (CBS), all revealed that CHF5633 exhibits a good behavior to reduce and sustain surface tensions to values below 5 mN/m. CHF5633 shows somehow slower initial interfacial adsorption than native surfactant or poractant alpha, but a better resistance to inhibition by serum proteins than the animal-derived clinical surfactant, comparable to that of the full native surfactant complex. Interfacial CHF5633 films formed in a Langmuir-Blodgett balance coupled with epifluorescence microscopy revealed similar propensity to segregate condensed lipid domains under compression than films made by native porcine surfactant or poractant alpha. This ability of CHF5633 to segregate condensed lipid phases can be related with a marked thermotropic transition from ordered to disordered membrane phases as exhibited by differential scanning calorimetry (DSC) of CHF5633 suspensions, occurring at similar temperatures but with higher associated enthalpy than that shown by poractant alpha. The good interfacial behavior of CHF5633 tested under physiologically meaningful conditions in vitro and its higher resistance to inactivation by serum proteins, together with its standardized and well-defined composition, makes it a particularly useful therapeutic preparation to be applied in situations associated with lung inflammation and edema, alone or in combined strategies to exploit surfactant-facilitated drug delivery.

Native supramolecular protein complexes in pulmonary surfactant: Evidences for SP-A/SP-B interactions

Pulmonary surfactant is a lipid-protein complex which coats lung alveoli. It displays the essential function of reducing surface tension at the air-liquid interface, avoiding alveolar collapse during expiration. The optimized biophysical properties of surfactant rely on its defined composition, constituted mainly by phospholipids and tiny amounts of lipid-associated specific proteins. Due to the highly hydrophobic nature of surfactant, organic solvents have been traditionally employed to obtain and characterize surfactant lipids and proteins, very likely leading to disruption of native interactions among its components. In the present work we have addressed the search of native protein complexes in pulmonary surfactant, which could have an essential role in the optimal function of the system. By solubilizing native lipid-protein membranes of surfactant with non-denaturing detergents, and with the use of a two-dimensional electrophoresis strategy, we have been able to detect the presence of supramolecular complexes composed of surfactant proteins SP-A, SP-B and SP-C. Furthermore, by co-immunoprecipitation assays, we have confirmed for the first time the existence of a direct interaction between SP-A and SP-B, an important feature which could explain the known functional cooperation of both proteins in several aspects of surfactant biology. SignificanceThis paper deepens for the first time in the existence of complex interaction networks of surfactant proteins in native surfactant membranes. By the use of non-denaturing detergents, two-dimensional electrophoresis and immunoprecipitation, we have been able to make progress in the elucidation of native protein complexes in this essential system, that had been previously hindered by the classical purification protocols employing organic solvents. In this work, we have described the presence of interactions between SP-B and SP-A, two important proteins whose functional cooperation has been broadly reported in the literature. Pioneer determination of such native complexes could have potential implications for understanding the wide variety of roles of pulmonary surfactant system.

Expression of Lung Surfactant Proteins SP-B and SP-C and Their Regulatory Factors in Fetal Lung of GDM Rats.

This study investigated the expression of lung surfactant proteins (SP-B and SP-C), and regulatory factors [forkhead box A2 (FOXA2) and nitrolyogenic FOXA2 (N-FOXA2)] in the fetal lung of rats with gestational diabetes mellitus (GDM) in order to study the mechanism of pulmonary dysplasia. The rat GDM model was established by using streptozotocin intraperitoneally in the first stage of pregnancy. There were 10 rats in the GDM group, and 10 healthy rats in normal control group without any treatment. Fetal lungs of two groups were taken at day 21 of pregnancy. Blood glucose levels of maternal rats and fetal rats were measured by Roche blood glucose meter. The histological changes in the fetal lung were observed under the light microscope in both groups. The SP-B, SP-C and FOXA2 were determined in the fetal lung of two groups immunohistochemically. The expression levels of SP-B, SP-C, total FOXA2, FOXA2 in nucleus (n-FOXA2), N-FOXA2 proteins were detected by Western blotting, and the relative expression levels of SP-B, SP-C, FOXA2 mRNA in the fetal lung of two groups were detected by RTPCR. The results showed that blood glucose levels of maternal rats and fetal rats in GDM group were higher than those in control group. The light microscope revealed fetal lung development retardation in GDM group. The expression of SP-B and SP-C in GDM group was significantly reduced as compared with control group (P<0.05). As compared with control group, the n-FOXA2 expression was significantly decreased in the fetal lung tissue, and N-FOXA2 was significantly increased in control group (P<0.05), but there was no significant changes in the total FOXA2 (P>0.05). It was concluded that GDM can cause fetal lung development and maturation disorders, and FOXA2 in fetal lung tissue decreases while nitrocellulose FOXA2 increases.

Progress towards recombinant synthesis of pulmonary surfactant proteins SP-B and SP-C

Progress towards recombinant synthesis of pulmonary surfactant proteins SP-B and SP-C