The microfibrillar components of porcine lung elastic fiber

Elastin metabolism during recovery from impaired crosslink formation

Accelerated proteolysis of tropoelastin and elastin occurs in the arteries of chicks rendered nutritionally copper-deficient. The process results in part from decreased elastin crosslinking. Repletion of copper-deficient chicks with copper causes a deposition of elastin that is proteinase resistant. Resistance to proteolysis is conferred within 48 h of dietary copper repletion. Deposition of aorta elastin to near normal values occurs after 3-4 days in copper-repleted chicks. Moreover, elastolysis was enhanced when the content of dehydrolysinonorleucine in elastin was abnormally low. The chemical modification of lysyl residue in elastin by citroconylation, however, did not influence the rate of elastolysis. We have shown previously that tropoelastin messenger RNA activity and synthesis are not influenced by dietary copper deprivation (1986, Biochem. J. 236, 17-23). Rather, as demonstrated herein, the decrease in elastin content in arteries of copper-deficient birds appears to be more the result of enhanced degradation. Restoration of normal crosslinking restores deposition and imparts resistance to elastolysis. Moreover, serum appears to be a good source of elastolytic proteinases when the elastin substrate is partially or abnormally crosslinked.

Elastin and elastin-associated-protein of porcine aorta and lung

Elastic fibers comprise elastin and other proteins termed as elastin-associated proteins. The nature of association between the elastin and elastin-associated-protein is not known. We have isolated elastic fibers from 5-month-old porcine aorta and lung parenchyma using urea, dithiothreitol and 1% sodium dodecyl sulfate at 55 degrees C. Lysyl-derived crosslinks were stabilized by sodium borohydride reduction. The methionine residues and associated peptides were decreased by CNBr treatment. Limited proteolysis of elastic fibers obtained by this procedure by trypsin (TPCK) and chymotrypsin (TLCK), removed 3% and 11% of the elastic fibers from aorta and lung, respectively. Limited elastase digestion solubilized a further 12 to 14% of the elastic fiber from aorta and lung samples, respectively. The insoluble residue remaining after elastase digestion had amino acid composition similar to alkali extracted elastin and to tropoelastin. The material solubilized by chymotrypsin and trypsin contained lysinonorleucine, whereas desmosine crosslinks were present only in the elastase digests. Aorta and lung elastic fibers differ in their structures as indicated by quantitative differences in limited proteolysis. These results strongly indicate that elastin and elastin-associated proteins interact strongly through lysyl-derived crosslinks.

Evidence against lung galaptin being important to the synthesis or organization of the elastic fibril

Previously it has been suggested that galaptin, an endogenous beta-galactoside-binding lectin, may function in the organization of lung elastic fibres. Galaptin was not present in preparations of rat or porcine lung elastic fibrils, neither did it bind to any of the fibril-associated proteins when these were separated by SDS/polyacrylamide-gel electrophoresis. Elastin and galaptin synthesis and secretion were investigated in lung fibroblast cultures and in anatomically preserved slices from developing rat lung. In both systems the synthesis and secretion of elastin was unmodified by the presence of beta-galactosides or antigalaptin in the culture medium. The synthesis of galaptin was unmodified by the presence of anti-elastin or beta-aminoproprionitrile in the culture medium. Cultured fibroblasts secreted elastin but only trivial amounts of galaptin. When cultures were treated with iodoacetamide (10(-5)M) galaptin synthesis was maintained but elastin synthesis ceased. These results argue against galaptin having an important role in the synthesis, secretion or organization of the elastic fibril.

A quantitative assay for the adhesion of alveolar type II cells: application to the study of epithelial-fibroblast interactions

A quantitative assay for the adhesion of rat lung epithelial cells has been developed. Cells are adhered to 96 well tissue culture plates and quantitated by their reaction with monoclonal antibodies to cytokeratin in an enzyme linked assay. Using this technique we have shown that rat lung alveolar Type II cells preferentially adhere to a fibroblast monolayer. There was no preferential adhesion of epithelial cells to fibroblast secreted matrix or to the separate components of alveolar matrix.

Incorporation of methylsulfonylmethane sulfur into guinea pig serum proteins

Methionine, an essential amino acid, and cysteine are the major sulfur-containing amino acids in the body and both are thought to be synthesized predominantly in plants and micro-organisms. Methylsulfonylmethane (MSM) is a natural constituent of the environment in which it is found in plants, in milk and urine of both bovines and humans, is a normal oxidation product of dimethyl sulfoxide (DMSO) also in the natural environment and may be part of the natural global sulfur cycle. To determine whether sulfur from methylsulfonylmethane (MSM) is incorporated into sulfur amino acids, I fed 35S-MSM to guinea pigs. 35S was incorporated into peptidyl methionine and cysteine of guinea pig serum proteins. The specific activity of 35S-methionine was 30% greater than for 35S-cysteine, suggesting a precursor-product relationship. Total specific activity of serum proteins was increased by only 30% with a 100% increase of administered 35S-MSM, suggesting a limiting step in synthesis. Approximately 1% of the radioactivity was recovered in serum proteins, none in the feces and most was excreted in the urine. Microorganisms of intestinal lumen may be responsible for the incorporation of the 35S of MSM into sulfur amino acids. MSM may provide a source of sulfur for essential animal methionine by mechanisms not yet elucidated in either animals or micro-organisms.

Treatment of dialysis membranes for simultaneous dialysis and concentration

Dialysis membranes used for simultaneous dialysis-concentration required pretreatment to remove uv-absorbing compounds leached from the membranes and to reduce the absorption of protein to the membranes. This was accomplished with sodium carbonate and ethanol or with "sulfur-removal solutions." Protein determinations were made with a micro-Bradford protein reaction and with uv absorbance at 280 nm. Soluble membrane components contributed to aberrant uv spectra and altered the ratio of 280/260-nm absorbance. Simultaneous dialysis and concentration in the micro protein dialyzer-concentrator apparatus, combining aspects of thin-layer dialysis and ultrafiltration, resulted in rapid removal of salts from the protein solutions. Prior treatment of membranes reduced uncertainties in retentate recoveries, eliminated uv-absorbing components of membranes, and improved recoveries of protein.

Ultrastructural cytochemistry of oxytalan fibers in the periodontal ligament and microfibrils in the aorta with the periodic acid-thiocarbohydrazide-silver proteinate method

Fullmer's oxytalan fibers are special connective tissue fibers in periodontal ligaments and some non-dental sites of certain animal species, and, ultrastructurally appear to resemble microfibrils related to elastogenesis. The present study has ultrastructurally examined the applicability of Thiéry's periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) method for vicinal glycol-containing complex carbohydrates to the study of oxytalan fibers in rat periodontal ligaments and microfibrils of the tunica adventitia in the rat aorta, where microfibrils are often associated with amorphous elastin and are thought to be oxytalan fibers. In the periodontal ligaments, the PA-TCH-SP method weakly to moderately stained collagen fibrils, moderately stained thin fibrils composing the oxytalan fibers, and intensely stained cytoplasmic granules of fibroblasts. In the aortic adventitia, the PA-TCH-SP method moderately stained collagen fibrils. Heavier staining was observed in microfibrils, whereas the amorphous elastin lacked staining. The most intense staining was seen in cytoplasmic granules and glycogen of mural cells. These studies demonstrate that oxytalan fibers in the periodontal ligament of rats and microfibrils in the aorta of rats contain vicinal glycol-containing glycoproteins and the PA-TCH-SP method is a useful tool in ultrastructural studies of oxytalan fibers and microfibrils of rats.

The infrastructure of aortic elastic fibers

Elastic fibers are composed of a central core of elastin that is amorphous and electron-lucent in conventional transmission electron micrographs and peripheral microfibrils. A complex infrastructure within the amorphous elastin of mature rat aorta is made visible by fixation and staining with a glutaraldehyde-ruthenium red mixture in phosphate buffer or osmium-ruthenium red in cacodylate buffer. The infrastructure is composed of at least two interlacing but distinct elastic structural components; a framework of circumferentially orientated microfibrils and a three-dimensional meshwork of filaments that permeate the fiber. The latter resembles a reticulum that has previously been observed in freeze-fractured and negatively stained elastin and attributed to the supramolecular organization of elastin. Microfibrils also extend from the core of the elastic fiber into the surrounding matrix where they appear to function as anchoring fibers. These observations indicate that the elastic properties of the arterial wall are an integrated function of both elastin and microfibrils.

Isolation and characterization of lung connective-tissue glycoproteins

1. Glycoproteins of hamster, rat and baboon lung parenchyma were investigated by using [14C]glucosamine incorporation in vitro followed by sequential extraction of the macromolecular components and characterization of the glycoproteins in the extracts. 2. Slices of lung parenchyma maintained in vitro incorporated [U-14C]glucosamine linearly with time into non-diffusible macromolecules for up to 5h. All the macromolecule-associated 14C label was present as [14C]glucosamine. 3. These 14C-labelled macromolecules were extracted from previously delipidated and salt-extracted lung by 5M-guanidinium chloride in the presence of dithiothreitol and proteinase inhibitors before (extract A1) and after (extract A2) hydrolysis of the collagen by collagenase. The [14C]glucosamine-labelled glycoproteins in extracts A1 and A2 contained 55 and 5% respectively of the total [14C]glucosamine incorporated in the lung of all three species studied. 4. The [14C]glucosamine-labelled glycoproteins were analysed by gel-filtration chromatography, sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectric focusing. The major [14C]glucosamine-labelled glycoproteins of baboon lung parenchyma had apparent mol.wts. of about 400 000, 140 000 and 65 000 with isoelectric points respectively of 4.8, 5.4 and 5.4. The hamster lung glycoproteins with isoelectric points of 4.1 and 5.8 were devoid of hydroxyproline and contained galactose, mannose and N-acetylglucosamine. These experiments indicate that several distinct glycoproteins are synthesized in situ by the cells of pulmonary parenchyma and may well play a role in its structure and function.