Analysis of pulmonary surfactant apoproteins by electrophoresis

Structural and Ontogenetic Relationships of Rat Lung Surfactant Apoproteins

Glycoproteins of molecular weights (MW) of 38,000, 32,000, and 26,000 are found in surfactant isolated from rat lungs. These proteins were further examined for their specificity to pulmonary surfactant, structural and metabolic interrelationships, and relation to the ontogenesis of pulmonary surfactant. With ultracentrifugations in salt and sucrose density gradients, a preparation of pulmonary surfactant was isolated from rat lung lavage fluid, which was rich in surfactant lipids (phosphatidylcholine and phosphatidylglycerol), and contained exclusively the 38,000-, 32,000-, 26,000-, and 10,000- to 12,000-dalton proteins. The 38,000-, 32,000-, and 26,000-dalton proteins are not serum proteins. Using an antiserum specific for the combined 38,000-, 32,000-, and 26,000-dalton proteins and the immunoperoxidase technique, the source of one or more of these three proteins was found to be alveolar epithelial type II cells, the cells involved in the synthesis and secretion of pulmonary surfactant. These proteins, when dissociated from lipids, show considerable self-association and form homopolymers. On isoelectric focusing, these proteins show considerable charge heterogeneity, which, in large part, is due to terminally linked sialic acid residues. Partial proteolysis of these proteins and subsequent analyses of the released polypeptides suggest the existence of large segments of homology between the 38,000-, and 32,000-dalton proteins. The relationship of the 38,000-, and 32,000-dalton proteins with the 26,000-, and 10,000- to 12,000-dalton proteins is not clear as yet. The results of protein analyses of purified tubular myelin and of lamellar bodies suggest that the 26,000-dalton protein may be derived extracellularly, possibly from other surfactant proteins by the action of enzymes present in the alveolar lining layer. We observed no reactivity of the antibody raised against the 38,000-, 32,000-, and 26,000-dalton proteins with the 10,000- to 12,000-dalton protein. The 38,000-, 32,000-, and 26,000-dalton proteins appear during fetal lung maturation at the same gestational time as the surfactant is known to appear, and their combined content increases thereafter in fetal lungs and in amniotic fluid. It appears that the less glycosylated (32,000-dalton protein) of the 38,000- and 32,000-dalton proteins appears first during fetal lung development.

Surfactant proteins in bronchoalveolar lavage fluid of horses: assay technique and changes following road transport

An enzyme-linked immunosorbent assay (ELISA) was developed for equine surfactant proteins SP-A and SP-D in bronchoalveolar lavage fluid (BALF). Anti-equine SP-A or SP-D monoclonal antibodies (mAb) were produced by hybridoma technology, purified by the antibody purification reagent, and analysed by Western blotting analysis. The immunoreaction (two-site sandwich ELISA) with a mAb, peroxidase-labelled mAb and BALF sample was carried out simultaneously and analytical recovery and precision were assayed. Six mAb for SP-A and four mAb for SP-D were successfully cloned in limiting dilution to monoclonality. These mAb were reacted with equine SP-A or SP-D on Western blotting analysis. For SP-A, a combination of solid-phase TA08 and horseradish peroxidase (HRP)-conjugated WA28 was found to be more sensitive than other combinations, gave a good dose response and was capable of measuring 0.78 to 100 ng of protein/ml. For SP-D, a combination of solid-phase TD13 and HRP-conjugated WD19 was found to be more sensitive than other combinations, had a good dose response and was capable of measuring 0.78 to 200 ng of protein/ml. The assay was used to determine the effect of 41 hours of road transport on the concentrations of SP-A and SP-D in the BALF of 30 horses. The concentrations of SP-A and SP-D decreased by 55 per cent and 36 per cent, respectively, decreases similar to the decrease in phosphatidylglycerol concentration previously reported by the authors.

Purification of surfactant protein A from dog lung by reconstitution with surfactant lipids

We have developed a simple method for purification of surfactant major apoprotein (SP-A, MW 34-38 kD) from dog lungs with high yield and purity. Lipids and proteins of partially purified surfactant were dissociated by sodium deoxycholate (DOC, 100 mM, 37 degrees C, 30 min), diluted 1:10 with borate buffer containing 3 mM CaCl2, and dialysate in the same buffer to reconstitute the lipids and proteins (4 degrees C, 48 h). The reconstituent and the partially purified surfactant were purified by ultracentrifugation on a discontinuous sucrose density gradient. Protein was isolated from the reconstituent and from the purified surfactant by delipidation, and the yields and purities were assessed by one-dimensional SDS-PAGE and 2-dimensional electrophoresis (isoelectric focusing, SDS-PAGE). We found that the surface pressure-time adsorption isotherm, minimum surface tension, and the yield and composition of lipids of the reconstituent were identical with those from the purified surfactant. Only about 0.25% of the DOC used for dissociation remained with the reconstituent and it did not affect surface properties of the reconstituent. The yield of SP-A in the reconstituent was almost the same as that in the purified surfactant, but the former contained no plasma protein whereas the latter contained significant amounts. The amino acid composition and the partial N-terminal amino acid sequence of SP-A were the same as those from the purified surfactant. Reconstituent prepared from surfactant lipids and SP-A adsorbed more rapidly and reached a higher final surface pressure than did the surfactant lipids alone. These results demonstrate that large quantities of SP-A can be purified by reconstitution with surfactant lipids, and that the purified protein is biophysically active.

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 micrograms of SP-A/l 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 NaDodSO4-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.

Effects of surfactant protein-A on surfactant function in preterm ventilated rabbits

Surfactant protein-A (SP-A) isolated from cow surfactant was added to organic solvent extracts of natural bovine surfactant or of Survanta (Abbott Laboratories), and dynamic compliances and pressure-volume curves were measured in rabbits with a gestational age of 27 days. Organic solvent extracts of natural surfactant and Survanta significantly improved dynamic compliances and lung volumes compared with those in control rabbits, but the effects were less than for natural surfactant. Adding 1 to 10% by weight SP-A to organic solvent extracts of natural surfactant increased dynamic compliances and maximal lung volumes on pressure-volume curves to values comparable with natural surfactant. Lung volumes at 10 cm H2O on deflation curves increased in a dose-dependent fashion at concentrations of SP-A between 0.5 and 5% by weight with no further improvement at 10% SP-A, although the volumes were significantly lower than for natural surfactant. Five percent by weight SP-A did not improve any measurements for Survanta. These results indicated that SP-A favorably improved organic solvent extracted natural surfactant function in vivo. However, the responses could not be generalized to another surfactant.

Immunohistochemical localization of pulmonary surfactant apoproteins in various lung tumors. Special reference to nonmucus producing lung adenocarcinomas

Eighty-nine primary lung carcinomas and 23 metastatic lung tumors were immunohistochemically studied for the expression of pulmonary surfactant apoproteins, by using monoclonal (PE-10) and polyclonal antibodies. Surfactant apoprotein was demonstrated in the cytoplasm and/or nuclear inclusion bodies of only primary lung adenocarcinomas (36 of 75 cases), not in any other histologic type of primary lung carcinoma or in metastatic lung tumors. In primary lung adenocarcinoma, although typical type II pneumocyte type adenocarcinoma was not included in the current series, the majority of surfactant apoprotein-positive single cell type tumors were of the Clara cell type, with a single bronchial surface epithelial cell type, according to the light microscopic subclassification of adenocarcinoma cells. The Clara cell type adenocarcinomas could at times be distinguished only with difficulty from adenocarcinoma of type II pneumocyte type. Normal and hyperplastic type II pneumocytes were of course positive for surfactant apoprotein in the cytoplasm. However, none of the positive cells could definitely be identified as Clara cells in non-neoplastic lungs. The findings obtained in this study indicate that surfactant apoprotein is a good marker to distinguish adenocarcinoma of the lung from other histologic types of lung cancer and from neoplasms metastatic to the lung, and that type II pneumocytes and Clara cells, non-neoplastic and neoplastic, are morphologically and functionally closely related and might belong to the same cell lineage.

Pulmonary damage induced in mice by a monoclonal antibody to proteins associated with pig pulmonary surfactant

Severe pulmonary damage was induced in mice inoculated with hybridomas (8B5E) secreting a monoclonal antibody to the 15,000-dalton protein associated with pig pulmonary surfactant. These mice exhibited severe respiratory distress starting 8-9 days after inoculation and died. Microscopically, lungs were airless and congested with hyaline membrane formation in patent terminal airways. Purified antibody from this hybridoma also induced similar damage in mouse lungs. However, neither hybridomas (1B6A) nor purified antibody, which is specific to pig 35,000-dalton protein but not to the mouse counterpart, induced these changes. Electron microscopically, many unexpanded lamellar bodies were seen floating in the edema fluid in these damaged lungs, and fragmentary lipid membranes were found in the electron dense material around these lamellar bodies, suggesting disintegration of these structures. Alveolar epithelial cells were desquamated, leaving the basement membranes bare, and mouse C3 was demonstrated in the damaged lungs. This low-molecular-weight protein of mouse surfactant cross-reacted with this antibody in the immunoblotting method, and the antigen was located in the inclusions of alveolar wall cells. These observations indicate that this low-molecular-weight protein of mouse surfactant has an antigenic structure similar to pig surfactant protein and that antigen-antibody complex formation may have triggered the damage of the lungs through inactivation of surfactant and induction of immunological tissue damage.

Hydrophobic surfactant-associated proteins: electrophoretic and immunologic analyses and cellular localization in human lung

Pulmonary surfactant isolated from a number of animal species contains a protein of molecular weight 38,000 and several very hydrophobic proteins soluble in solvents often used to extract lipids. Although found to be intimately associated with surfactant lipids, localization of the very hydrophobic proteins to alveolar epithelial type II cells, the cells involved in the synthesis and secretion of pulmonary surfactant, has not been demonstrated. Hydrophobic proteins were extracted along with lipids from human surfactant, and, after extraction with deoxycholate, were used to raise an antiserum. The antiserum was characterized by the immunoblotting ("Western") technique, using blots of pulmonary surfactant, and of hydrophobic proteins prepared by deoxycholate extraction and by Sephadex LH-20 chromatography. The antiserum shows reactivity to a 6.5- to 18-kDa surfactant-associated hydrophobic protein, which appears to be the major component of deoxycholate extracted proteins, and has Phe as the N-terminal amino acid. In addition, 28-kDa, 40-kDa, 50-kDa, and 70-kDa bands (chemically unreduced) are seen in human pulmonary surfactant. Whether these bands represent precursors of the major surfactant-associated hydrophobic proteins, different proteolytic cleavage products of the precursor protein, distinct proteins, or associated forms of the same protein is not yet clear. When used in the immunoperoxidase staining of human lung sections, the antiserum yielded a staining pattern identical to that obtained by the use of an antiserum to the 35-kDa surfactant protein. The number, size, and location of the stained cells are consistent with their being the alveolar epithelial type II cells.

Functional abnormalities of lung surfactant in experimental acute alveolar injury in the dog

Acute alveolar injury (AAI) was induced in dogs by injection of N-nitroso-N-methylurethane. Two to 20 days after injection, alveolar lavage phospholipids were quantified. Lavage surfactant was partially purified by centrifugation (27,000 g for 2 h), and further purified by centrifugation in NaBr density gradient (100,000 g for 4 h). Phospholipids, neutral lipids, surfactant-associated proteins, and surface properties of partially purified and purified surfactants were analyzed. Lavage disaturated phosphatidylcholine (DSPC) decreased to 37% of control at peak injury (Days 6 to 8) and increased to near normal during recovery (Days 10 to 20). Lavage phosphatidylglycerol (PG) decreased to 22% of control at peak injury and remained in that range through recovery. In both partially purified and purified surfactants, percentages of phosphatidylcholine (PC), DSPC, phosphatidylethanolamine, and cholesterol in all phases of injury and recovery were not different from those in control animals. However, percentage of PG decreased markedly during injury and remained low through recovery, whereas those of phosphatidylinositol and lysoPC increased with injury and remained elevated through recovery. The PC-to-sphingomyelin ratio (L/S ratio) and percentage of triglyceride decreased during injury and returned to control values during recovery. Surfactant apoprotein of molecular weight 38,000 from partially purified and purified surfactant decreased markedly at peak injury and recovered to normal during recovery. During early and peak injury, both preparations failed to reduce surface tension below 19 dyne/cm and their isopycnic densities were altered. These studies indicate that, in addition to decreased quantity, qualitative changes in lipids and apoproteins and reduced surface activity of the surfactant occur during nitrosourethane-induced AAI.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and turnover of lung surfactant

Despite the grave difficulties that beset researchers who are trying to isolate and characterize the various intracellular and extracellular forms of lung surfactant; despite the serious ambiguities of interpretation of experimental data caused by the multicomponent nature of the surfactant; despite the inaccessibility for diagnostic purposes of this material, which functions deep in the lungs; despite the fact that incisive methods of protein chemistry and molecular biology have only recently been brought to bear on lung surfactant; despite all these problems, our knowledge and understanding of lung surfactant are rapidly increasing. We know now that it is a dynamic system with many parts, and that the reserves of these are normally not large and are recycled. We believe that tight metabolic control must exist to maintain these reserves, and we already have experimental techniques to raise or lower the reserves. Heroic methods of surfactant substitution are now being tested in patients whose deficiency or risk thereof is sufficiently desperate, and the results of these clinical trials, if they are carefully documented with lung function data, will add a new dimension to our knowledge of surfactant dynamics. We may expect in the future that more subtle alterations in surfactant function will become detectable and more sophisticated methods to manipulate the system will be invented. Essential to these will be a deeper understanding of surfactant forms, pathways, kinetics, and controls. Fortunately, research on surfactant structure, metabolism, and turnover intrigues many investigators. They, we may hope, will soon provide the necessary information.

The 35 kd pulmonary surfactant-associated protein is encoded on chromosome 10

The genomic components identified by each of two closely related cDNA clones for the major 35 kilodalton non-serum surfactant-associated proteins (PSP-A) were shown to derive from human chromosome 10 by Southern blot analysis of DNAs from human-rodent somatic cell hybrids. By in situ hybridization to human metaphase chromosomes, the cDNA probes were localized to the region 10q21-q24.

Development of the pulmonary acinus in fetal rat lung: a study based on an antiserum recognizing surfactant-associated proteins

In this study on the development of the pulmonary acinus in fetal rat lung use was made of an antiserum, rabbit anti-mouse, that recognizes the type II alveolar epithelial cell or its precursor (a cuboidal cell lacking multilamellar bodies) by the presence of a cell-specific antigen. This serum had already been used in studies on mouse-lung development in our laboratory. Immunoblotting experiments showed that this serum reacts with surfactant-associated proteins in the pellet fraction of rat-lung lavage fluid having molecular weights of about 26,000, 32,000, and 38,000 daltons. In adult and fetal rat-lung homogenates the antiserum reacts with proteins with apparent molecular weights of about 40,000 and 42,000 daltons, probably also surfactant-associated proteins. No reaction with serum proteins was seen. Use of this antiserum in immuno-incubations of frozen sections of lungs of 15- to 21-day-old rat embryos showed that the type II epithelial cell or its precursor first appears on day 16 in embryos weighing 349-398 mg. Our results indicate that in the rat - as in the mouse - the bronchial and respiratory portions develop from morphologically and immunologically different parts of the tubular system in the fetal lung. The basic structure in the genesis of the pulmonary acinus is a tubule, called the acinar tubule, which is lined by the type II epithelial cell or its precursor.

Regulation of pulmonary surfactant apoprotein SP 28-36 gene in fetal human lung

Pulmonary surfactant stabilizes lung alveoli, preventing respiratory failure and hyaline membrane disease in premature infants. In addition to lipids, surfactant contains apoproteins that are thought to be critical for normal surfactant function. We have examined the ontogeny and regulation of the major surfactant-associated protein of molecular mass 28-36 kDa (SP 28-36) in human fetal lung. SP 28-36 was not detected in tissue from second trimester abortuses by either immunoblot analysis or enzyme-linked immunosorbent assay (less than 0.02 microgram per mg of DNA). Levels of mRNA for SP 28-36, assayed by cDNA hybridization, were low or undetectable in all preculture specimens. The concentration of saturated phosphatidylcholine in lung tissue was 30% of the adult value with no apparent increase between 15 and 24 weeks gestation. SP 28-36 content increased during explant culture in the absence of serum and hormones, exceeding adult levels (3.2 +/- 1.0 micrograms per mg of DNA) after 5 days. In cultures treated with triiodothyronine (2 nM) and dexamethasone (10 nM), hormones that regulate phosphatidylcholine synthesis, the increase in SP 28-36 was accelerated (treated/control ratio was 7.1 and 3.4 at 3 and 5 days, respectively). Levels of mRNA for SP 28-36 also increased during culture and were stimulated by hormones (treated/control = 8.6 and 1.9 at 3 and 5 days, respectively). SP 28-36 and its mRNA increased similarly in the presence of dexamethasone alone, whereas triiodothyronine alone had no apparent effect. The molecular weight and charge pattern was similar for SP 28-36 of adult and cultured fetal tissue. These findings indicate that expression of the SP 28-36 gene is low during the second trimester, increases during explant culture, and is accelerated by glucocorticoid treatment.

Histochemical characterization of an antigen specific for the great alveolar cell in the mouse lung

Previous papers reported on a specific antigenic marker for the great alveolar (type-II) cell of the mouse lung and described its recognition by a specific rabbit anti-adult mouse lung serum. In the present study light- and electron-microscopical immunohistochemistry on fixed mouse lung sections showed the presence of the marker on the alveolar surface. The antigenic determinants recognized by the antibody were further characterized by immunoblotting and immunoprecipitation studies after in vitro translation of mouse lung messenger RNA. Immunoblots of a surfactant-enriched pellet of a bronchoalveolar lavage fraction of mouse lung showed that the antibody reacted with surfactant-associated proteins having apparent molecular weights of about 27,000, 32,000, and 38,000 daltons in SDS gels. Immunoblots of mouse-lung homogenate revealed the presence of 27,000, 30,000, 39,000, and 41,000 daltons proteins, presumably also surfactant-associated proteins. Immunoprecipitation after in vitro translation of mouse-lung mRNA showed specific reactivity only with a 12,000 dalton polypeptide, a component of the cell marker we were unable to relate to surfactant. Our findings indicate that the 12,000 dalton component of the antigenic marker for the great alveolar cell is a polypeptide whose synthesis is a lung-specific process and that the immunoreaction of the larger and surfactant-associated components is due to post-translational modifications.

Alterations in rat alveolar surfactant phospholipids and proteins induced by administration of chlorphentermine

Chlorphentermine is a cationic amphiphilic drug which produces a phospholipid storage disorder in rat lungs. Experiments were carried out to characterize changes in the composition of acellular alveolar lavage materials and to study possible mechanisms by which pulmonary surfactant phospholipidosis is produced by administration of the drug. Following ten daily injections of chlorphentermine (25 mg/kg body weight), there are 12.2- and 13.6-fold increases of pulmonary lavage total phospholipids and disaturated phosphatidylcholines (disaturated PC), respectively. In addition, there is a 2.8-fold increase in total protein and a 12.7-fold increase in the surfactant apoprotein group with molecular weights from 28,000 to 32,000. We measured incorporation of labeled palmitate, choline and glycerol into disaturated PC in type II cells and alveolar macrophages isolated from control and chlorphentermine-treated animals. The drug does not affect the incorporation of labeled substrates into disaturated PC in either cell type. However, in alveolar macrophages there is a decrease in the rate of intracellular degradation of recently synthesized disaturated PC in chlorphentermine-treated animals. The drug also inhibits the phospholipase-induced catabolism of rat surfactant disaturated PC which occurs during incubation of alveolar lavage fluid in vitro at 37 degrees C. When the lavage fluid is divided into subfractions by differential centrifugation, a larger percentage of the phospholipid is distributed in the less sedimentable subfractions in chlorphentermine-treated animals relative to controls, suggesting the accumulation of older surfactant materials. These results suggest that chlorphentermine-induced phospholipidosis of pulmonary surfactant materials is due to decreased rates of phospholipid degradation.

Structure of canine pulmonary surfactant apoprotein: cDNA and complete amino acid sequence

The apoproteins of pulmonary surfactant (PSAP) are thought to be critical for normal surfactant function. They bind to surfactant phospholipids and enhance their ability to form surface films in vitro. These acidic glycoproteins have monomeric molecular weights of 36,000, 32,000, and 28,000 (PSAP-36, -32, and -28). Each member of this family of proteins has a similar amino acid composition and their differences in electrophoretic mobility are due in part to glycosylation. We have derived the full amino acid sequence of PSAP-32 from the nucleotide sequence of PSAP cDNA. A cDNA library was prepared from canine lung poly(A)+ RNA and screened with oligonucleotide probes that were based on the NH2-terminal amino acids of PSAP-32 determined by Edman degradation. This protein has the striking feature of collagen-like and non-collagen-like sequences in the same polypeptide chain. There are 24 Gly-Xaa-Yaa triplets, where Yaa is often hydroxyproline. These repeats comprise one-third of PSAP near the NH2 terminus. The remaining two-thirds of PSAP is resistant to bacterial collagenase digestion and contains a possible N-glycosylation site near the carboxyl terminus. The NH2-terminal one-third of PSAP-32 probably contains the cysteine involved in interchain disulfide bonds.

Isolation and characterization of the human pulmonary surfactant apoprotein gene

Pulmonary surfactant is a phospholipid-protein complex which serves to lower the surface tension at the air-liquid interface in the alveoli of the mammalian lung and is essential for normal respiration. Inadequate levels of surfactant at birth, a frequent situation in premature infants, results in respiratory failure. In all species examined, surfactant is composed primarily of dipalmitoylphosphatidylcholine and two major protein species of relative molecular mass (Mr) 32,000 (32K) and 10K (refs 2-5). Reconstitution in vitro of purified 32K pulmonary surfactant apoprotein (PSAP) with synthetic lipids forms a lipoprotein complex that lowers surface tension by spreading to create a thin interfacial film. Here we describe the cloning of the human PSAP gene and complementary DNA, and discuss features of the unusual encoded protein.

Bronchoalveolar lavage proteins

Since the discovery of the extra-cellular lining material of the lung and the possibility harvesting this source by endobronchial lavage this material has been the object of many studies directed to analyze its components, function and possible change in the diseased lung. The best known component of the extra-cellular lining material is the phospholipid and its fatty acid composition. But also on the cellular material much emphasis has been taken with the aim using its cytology as diagnostic parameter. However, very few informations were obtained about the protein material also washed out during the endobronchial lavage. As it was demonstrated by immunological methods the proteins of the extra-cellular lining material consist of serum identical proteins and those being obviously specific for the lung tissue. As found, most serum identical proteins occur in the same amounts as found in the blood serum, and the molecular weight in general range up to 160,000 daltons indicating that there must be a restriction in passage of high molecular weight proteins through the lumen walls of the endothelium. Some proteins, IgG, IgA, do occur in a higher level in the extra-cellular lining material leading to the suggestion that these proteins were synthesized and secreted by the lung tissue itself. The molecular weight of the lung specific proteins range from 16,000-340,000 daltons. Under reducing conditions however, for all species listed, two classes of subunits -36,000 and 12,000 daltons --result, indicating that these proteins might have comparable functions in the different species.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologically related multimeric forms of 30-40 kDa peptides associated with lung surfactant in various mammalian species

A comparative study of lung surfactant associated proteins was undertaken to determine which mammalian species would best serve as models for investigating alterations of the human lung surfactant system. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified surfactants in the presence of dithiothreitol revealed that surfactant invariably contains at least one peptide with molecular weight of 30 000-40 000. In the absence of disulfide reducing agents, the above peptides were in the form of high-molecular-weight proteins (greater than 400 kDa) in primates and cat, whereas in dog, rat and rabbit, the protein was a 72 kDa dimer. The 30-40 kDa peptide subunits were isolated from human, rat and dog surfactants and found to contain four or five residues of hydroxyproline. Antisera to either the human 34 kDa peptide or high-molecular-weight proteins reacted with the high-molecular-weight bands, the 34 kDa subunit and at least six intermediate disulfide-linked forms separated from purified human surfactant by electrophoresis under nonreducing conditions. Following electrophoresis in the presence of dithiothreitol, both antisera detected the 34 kDa peptide as well as other peptides ranging in molecular weight from 23 000 to 160 000. The isolated 34 kDa peptide readily reaggregated into disulfide-linked forms including 68 and 100 kDa complexes which were not reduced by 40 mM dithiothreitol. We conclude that the 34 kDa surfactant-associated peptide forms a complex system of monomeric and multimeric proteins, which varies among the species and could conceivably vary in distribution during lung development or disease.

In vitro translation of rat lung surfactant apoprotein mRNA

Rat pulmonary surfactant contains apoproteins of molecular weights 38,000, 32,000, 26,000 and 10,000-12,000. The structural and metabolic interrelationships of these proteins are not clear as yet. In order to investigate if they arise from a single or multiple precursor protein (s), we isolated total poly(A)RNA from rat lungs, performed its translation in vitro in the presence of [35s]-methionine and reticulocyte lysate, immunoprecipitated the translation products with anti-rat surfactant antibody, and analyzed them by SDS-polyacrylamide gel electrophoresis and autoradiography. A single translation product of molecular weight 35,000 was detected. Since the antibody used in the immunoprecipitation recognizes the 38,000, 32,000 and 26,000 dalton proteins, it is concluded that at least these three proteins arise from the 35,000 dalton precursor by post-translational modifications.

A comparison of the major surfactant-associated proteins in different species

We examined the major surfactant-associated proteins in a number of species by using two-dimensional gel electrophoresis, protein blotting and immunostaining. All species have a 30,000 to 35,000 mol. wt protein group consisting of multiple isoforms with isoelectric points ranging from pH 4.4 to 5.6. The techniques used in this study have resolved three component subgroups within the 35 K group. A group of proteins at 60,000-65,000 mol. wt has also been consistently identified. We conclude that remarkable similarity exists among the major surfactant-associated proteins from various mammals with regard to isoelectric points, molecular weights and antigenic sites.

Effects of a surfactant-associated protein and calcium ions on the structure and surface activity of lung surfactant lipids

Previous studies have demonstrated that lung-specific proteins are associated with surfactant lipids, particularly the highly surface active subfraction known as tubular myelin. We have isolated a surfactant-associated protein complex with molecular weight components of 36 000, 32 000, and 28 000 and reassembled it with protein-free lung surfactant lipids prepared as small unilamellar liposomes. The effects of divalent cations on the structure and surface activity of this protein-lipid mixture were investigated by following (1) the state of lipid dispersion by changes in turbidity and by electron microscopy and (2) the ability of the surfactant lipids to form a surface film from an aqueous subphase at 37 degrees C. The protein complex markedly increased the rate of Ca2+-induced surfactant-lipid aggregation. Electron microscopy demonstrated transformation of the small unilamellar liposomes (median diameter 440 A) into large aggregates. The threshold Ca2+ concentration required for rapid lipid aggregation was reduced from 13 to 0.5 mM by the protein complex. This protein-facilitated lipid aggregation did not occur if Mg2+ was the only divalent cation present. Similarly, 5 mM Ca2+ but not 5 mM Mg2+ improved the ability of the protein-lipid mixture to form a surface film at 37 degrees C. Extensive aggregation of the surfactant lipids without protein by 20 mM Ca2+ or 20 mM Mg2+ did not promote rapid surface film formation. These results add to the growing evidence that specific Ca2+-protein-lipid interactions are important in determining both the structure and function of extracellular lung surfactant fractions.

An electrophoretic and immunochemical characterization of human surfactant-associated proteins

We have prepared an antiserum against a serum-free extract of alveolar proteinosis lavage that recognizes the same proteins as an antiserum to human surfactant. Using one and two-dimensional gel electrophoresis, protein blotting and immunostaining we have found proteins with Mr of approx. 35 and 60 kDa to be present in every source of human surfactant we have examined. These proteins are immunologically related to those found in the lavage from alveolar proteinosis patients, have the same electrophoretic characteristics and are not found in serum. The 35 kDa protein is a group of at least eight isoforms ranging in relative molecular mass Mr from 32 to 36 kDa with isoelectric points between 4.8 and 5.5. Neuraminidase digestion studies have shown that at least part of this charge heterogeneity may be due to sialic acid residues. The less abundant form, with a Mr of about 60 kDa is also a sialoglycoprotein with similar isoelectric points.

Analysis of pulmonary surfactant apoproteins by isoelectric focusing

Apoproteins of Mr 38 000, 32 000 and 26 000 are found in surfactant isolated from rat lungs. The surfactant isolated from monkey lungs, on the other hand, contains the 38 kDa apoprotein and not the 32 and 26 kDa apoproteins. These preparations of pulmonary surfactant contain, in addition, several serum proteins. We have used a combination of salt- and sucrose-density gradient centrifugations to isolate and further purify surfactant from the washings of rat lungs. Thus, a preparation of pulmonary surfactant was obtained which contained exclusively the 38, 32, 26 and 10-12 kDa apoproteins, and which was rich in phosphatidylcholine and phosphatidylglycerol. Using an immunoassay and an immunoblotting technique, it was established that the 38, 32 and 26 kDa apoproteins are not serum proteins. The surfactant apoproteins of rat and monkey were further subjected to the high-resolution of isoelectric focusing. Thus, rat surfactant apoproteins resolved into 11 bands in the pH range 4.64-5.53. A second-dimensional electrophoresis in a sodium dodecyl sulfate system led to the migration of the 11 bands, separated by first-dimensional isoelectric focusing, into three distinct groups with apparent molecular weights of 38 000, 32 000 and 26 000, respectively. Upon isoelectric focusing, the apoproteins from monkey lung surfactant also separated into several bands in the pH range 5.18-5.82. After electrophoresis in the second dimension as above, these bands migrated as a single group with an apparent molecular weight of 38 000. Neuraminidase treatment of rat surfactant apoproteins, and subsequent IEF, led to the disappearance of several low-pI variants with a concomitant increase in the amounts of higher-pI variants. Thus, the sialic acid content of surfactant apoproteins accounts for, in large part, the observed charge heterogeneity.

Deficient lung surfactant apoproteins in amniotic fluid with mature phospholipid profile from diabetic pregnancies

An enzyme-linked immunoassay to quantitate lung surfactant apoproteins (15 to 250 ng/ml) in human amniotic fluid is described. The immunoassay was used to quantify lung surfactant in 72 samples of amniotic fluid, for which lecithin/sphingomyelin (L/S) ratios, lecithin and phosphatidylglycerol concentrations, and foam stability indices were also available. The results obtained with the immunoassay were in general agreement with those of the other methods. Measurement of the apoproteins, however, may be a better predictor of fetal lung immaturity and of respiratory distress syndrome than the L/S ratio and the concentration of lecithin. This conclusion is based on the data obtained in the analyses of samples of amniotic fluid from four diabetic and five nondiabetic pregnancies, the infants of which developed respiratory distress. In all cases, the apoprotein concentration was less than 2.1 micrograms/ml, which indicated fetal lung immaturity. In six of these cases (one diabetic and five nondiabetic pregnancies), lung immaturity was also predicted on the basis of other tests. However, in three other cases of diabetic pregnancy, the L/S ratio and lecithin concentration falsely indicated lung maturity. In addition to its being an effective predictor of fetal lung maturity in diabetic, as well as nondiabetic, pregnancies, the immunoassay is better suited for clinical use because of its high specificity, sensitivity, and ease of performance.

Extramembraneous particles and structural variations of tubular myelin figures in rat lung surfactant

Tubular myelin figures of pulmonary surfactant were examined by electron microscopy after fixation in glutaraldehyde and postfixation in an osmium tetroxide-ferrocyanide mixture. Bilayered membranes were seen as parallel arrays or as lattices with spacings varying from about 36 to 50 nm. This method also produced good visualization of drumstick-like particles, 5 nm in diameter and about 15 nm in length. The particles were regularly spaced at intervals of 16 nm in rows along the rectangular angles of myelin membranes. Depending on the size of the tubules the particles contacted each other in the center of the tubules at low diameters (tubular diameter less than 40 nm) and formed a continuous filamentous central core, or they were separated from one another (tubular diameter greater than 40 nm). In the latter case the central core had a hollow appearance. Based on further findings employing tannic acid, lipid extraction with 2,2-dimethoxypropane, and a ruthenium red-osmium tetroxide technique for the demonstration of polyanionic proteins it is suggested that these particles are protein in nature and that they are involved in the formation and maintenance of the structure of tubular myelin. A new concept of the ultrastructure of tubular myelin figures is proposed.

Phospholipid and protein analysis of pulmonary surfactant

Quantitative analysis of the phospholipid composition of pulmonary surfactant preparations has been achieved by a modification of the phosphorus-31 nuclear magnetic resonance method of E London and G Feigenson (J. Lipid Res. 20, 408-412, 1979). Resolution of the protein components by a 2-dimensional isoelectric-focussing-SDS/polyacrylamide-gel-electrophoresis technique is reported for the first time.

Pulmonary alveolar proteinosis. Staining for surfactant apoprotein in alveolar proteinosis and in conditions simulating it

Formalin fixed paraffin-embedded lung tissues (n = 13) or lavage material (n = 4) from 17 patients in whom alveolar proteinosis was the primary disease and ten patients with other primary diagnoses but lung morphology similar to alveolar proteinosis were examined. The tissues were stained by the periodic acid-Schiff method and by the immunoperoxidase method for surfactant specific apoprotein. The intra-alveolar material in patients with primary alveolar proteinosis stained uniformly for surfactant specific apoprotein, whereas the staining was focal in patients with other primary diseases associated with intra-alveolar accumulation of proteinacious material. In both situations, the number of inflammatory cells, especially macrophages, was small. These observations extend an earlier impression about the presence of surfactant specific apoprotein in alveolar spaces in patients with primary alveolar proteinosis and provide a distinction between primary alveolar proteinosis and morphologically similar appearance due to other causes, ie, secondary alveolar proteinosis. The lack of macrophages in the affected tissue appears to be the major pathogenetic factor in alveolar proteinosis.

Carcinoma of type II pneumocytes. PAS staining as a screening test for nuclear inclusions of surfactant specific apoprotein

Bronchioloalveolar carcinomas (n = 15) and other primary lung carcinomas (n = 9) were studied by PAS staining. The bronchioloalveolar carcinoma group contained three cases of carcinomas of type II pneumocytes. Cytoplasmic staining with PAS was most intense in mucus secreting carcinomas. Carcinomas of type II pneumocytes could not be differentiated from other tumors on the basis of cytoplasmic PAS staining. However, PAS positive nuclear "inclusion" were seen only in the three carcinomas of type II pneumocytes. The study indicates that PAS staining, though nonspecific, may serve as a screening test for carcinomas of type II pneumocytes by highlighting the nuclear inclusions of surfactant specific apoprotein.