Antibiotic Stewardship and Treatment of Uncomplicated Urinary Tract Infection (UTI) in Children and Adolescents in the Emergency Department of a Community Hospital

A retrospective, cross-sectional study of children with suspected urinary tract infections (UTIs) 3 months to 18 years of age who had a urinalysis and urine culture (UC) during an emergency department (ED) visit between 2019 and 2020 was performed. Chi-square, Fisher exact, and independent samples T tests were used as appropriate. Median age was 6.6 years (interquartile range = 3.3-12.4). Urinalysis positivity was 92.8%, of which 81.9% of children were prescribed a first-line antibiotic. First-line antibiotic use was 82.7%. Positive UC rate was 84.7%, with 84% receiving a first-line antibiotic (P = .025). The correlation between a positive urinalysis and a positive UC was 80.8% (P < .001). Change of antibiotics based on the uropathogen of positive UCs was 6.3% (P < .001). The urinalysis and UC guided the diagnosis and treatment of UTIs. First-line antibiotics can be safely administered in the ED and prescribed for positive urinalyses. Studies are needed to evaluate the discontinuation of antibiotics with negative UCs as part of antibiotic stewardship initiatives.

The compact conformation of fibronectin is determined by intramolecular ionic interactions

Fibronectin exists in a compact or extended conformation, depending upon environmental pH and salt concentration. Using recombinant fragments expressed in bacteria and baculovirus, we determined the domains responsible for producing fibronectin's compact conformation. Our velocity and equilibrium sedimentation data show that FN2-14 (a protein containing FN-III domains 2 through 14) forms dimers in low salt. Experiments with smaller fragments indicates that the compact conformation is produced by binding of FN12-14 of one subunit to FN2-3 of the other subunit in the dimer. The binding is weakened at higher salt concentrations, implying an electrostatic interaction. Furthermore, segment FN7-14+A, which contains the alternatively spliced A domain between FN11 and 12, forms dimers, whereas FN7-14 without A does not. Segment FN12-14+A also forms dimers, but the isolated A domain does not. These data imply an association of domain A with FN12-14, and the presence of A may favor an open conformation by competing with FN2-3 for binding to FN12-14.

The copper- and zinc-containing superoxide dismutase from Escherichia coli: molecular weight and stability

The periplasmic Cu,Zn superoxide dismutase (Cu,ZnSOD) from Escherichia coli has been shown by sedimentation equilibrium to be a monomer with a molecular weight of approximately 17,000. The enzyme suffered a reversible inactivation when heated to 70 degrees C. This was minimized by added Cu(II) or Zn(II). Heat lability was greater in phosphate than in Tris buffer. The enzyme exhibited a time-dependent inactivation by Hg(II) and this too was greater in phosphate than in Tris. This behavior can be explained by a modest affinity of the enzyme for Cu(II) and Zn(II) which results in a dissociation/association equilibrium. Elevation of the temperature shifts this equilibrium toward dissociation and phosphate sequesters the released metals making them less available for reinsertion at the active site. Hg(II) competes for occupancy of the active site and there were more unoccupied sites in phosphate than in Tris. A parallel was drawn between the E. coli Cu,ZnSOD and FALS varients of human Cu,ZnSOD, which are also relatively unstable and exhibit low affinity for Cu(II).

Synthesis of type VIII collagen by epithelial cells of human gingiva

The composition of the extracellular matrix produced by epithelial cells in contact with metabolically inert substrata was studied with antibodies specific for type VIII collagen. Type VIII collagen was present in the cell layer of cultured gingival epithelial cells, and at the epithelium-substratum interface of an explant culture model for junctional epithelium. Samples of the epithelial attachment apparatus (EAA) in vivo were collected by removing the junctional cells directly attached to the tooth (DAT cells) and the associated EAA matrix. The amount of material collected was sufficient for biochemical analysis of both intra- and extracellular components of the junctional cell-EAA complex. Immunological examination of the samples revealed that type VIII collagen was associated with epithelial cells forming the EAA in vivo. We suggest that this collagen type functions in the extracellular space as an attachment-promoting factor for gingival epithelial cells at the tooth surface.

Thrombospondin exerts an antiangiogenic effect on cord formation by endothelial cells in vitro

The response of endothelial cells to angiogenic stimuli has been shown to be influenced by the extracellular microenvironment. We tested whether thrombospondin, an extracellular matrix protein, modulated the spontaneous formation of cords by endothelial cells in vitro. Despite continued proliferation, a decrease in secreted thrombospondin was detected in cord-containing, as compared with subconfluent, cultures of both aortic and microvascular endothelial cells. Consistent with this trend, mRNA levels of thrombospondin decreased by factors of 16 in aortic and 60 in microvascular cultures that contained endothelial cords. Since thrombospondin was immunolocalized to fibrillar arrays that appeared to be associated with endothelial cords, we added anti-thrombospondin IgG to cord-forming cultures to limit the availability of the protein during this process. In the presence of anti-thrombospondin antibodies, there was a 33-50% increase in cord formation. These results suggest that thrombospondin is an inhibitor of angiogenesis in vitro and are consistent with its proposed roles as a destabilizer of endothelial cell focal contacts and as an inhibitor of endothelial cell proliferation.

Differential expression of extracellular proteins is correlated with angiogenesis in vitro

Strains of bovine aortic endothelial cells, grown on plastic under conventional culture conditions and in the absence of growth factor supplementation, exhibited a sprouting phenotype and a predisposition toward the formation of cords and tubular structures. We examined endothelial cells at different stages of tube formation. Analysis of metabolically labeled proteins showed that the synthesis of type I collagen was initiated in sprouting cells and during the formation of tubular structures. SPARC (secreted protein, acidic and rich in cysteine) a Ca2(+)-binding protein associated with cellular shape change and morphogenetic processes (Sage H, Vernon RB, Funk SE, Everitt EA, Angello J: J Cell Biol 109:341, 1989), was upregulated during spontaneous tube formation. Levels of messenger RNA for type I collagen and SPARC corroborated the stage-specific increases observed for these proteins. Differential levels of transcription were apparent in multilayered cells directly involved in tube formation, in comparison with cells comprising either the tubes or the confluent monolayers at a distance from the tubes. Analysis of DNA synthesis indicated that multilayered sprouting cells in the proximity of the endothelial tubes were actively proliferating, whereas cells that had been incorporated into tubes showed low levels of DNA synthesis. Immunolabeling studies revealed a dense accumulation of SPARC and type I collagen in the cytoplasm of cells that were situated near the growing tubes. Two other secreted proteins, type III collagen and thrombospondin, were expressed constitutively by subconfluent cultures and were increased in those cells contributing to tube formation. We propose that type I collagen and SPARC are specifically related to the angiogenesis-like phenomenon displayed by bovine aortic endothelial cells in vitro. Type I collagen might facilitate the active migration of endothelial cells, or the stabilization of the resulting tubes, with SPARC directing the re-organization and dynamic assembly of the tubular network.

Adhesion, shape, proliferation, and gene expression of mouse Leydig cells are influenced by extracellular matrix in vitro

Interactions between Leydig cells and the extracellular matrix (ECM) within the interstitial compartment of the mammalian testis have not been characterized. We have examined the influence of ECM on adult mouse Leydig cells by culturing the cells on different ECM substrates. Leydig cells adhere weakly to hydrated gels of type I collagen (including those supplemented with collagen types IV, V, or VIII), or to air-dried films of collagen types I, V, or VIII. In contrast, the cells attach firmly to substrates of purified type IV collagen, fibronectin, or laminin. Leydig cells also attach rapidly and adhere strongly to gelled basement membrane matrix derived from the murine Englebreth-Holm-Swarm sarcoma (Matrigel). Leydig cells assume spherical shapes and form aggregates on thick (1.5-mm) layers of Matrigel; however, on thin (0.1-mm) layers, networks of cell clusters linked by cords of elongated cells are formed within 48 h. Similar networks are formed on thick layers of Matrigel that are supplemented with type I collagen. On substrates with high ratios of collagen I to Matrigel or on untreated tissue culture plastic, Leydig cells flatten and do not aggregate. On substrates that induce rounded shapes, proliferation is inhibited and the cells maintain the steroidogenic enzyme 3 beta-hydroxysteroid dehydrogenase for as long as 2 wk. Under conditions where Leydig cells are flattened, they divide and cease expressing the enzyme. Proliferating Leydig cells also exhibit elevated levels of mRNA for SPARC (Secreted Protein, Acidic and Rich in Cysteine), a Ca2(+)-binding glycoprotein associated with changes in cell shape that accompany morphogenesis and tissue remodeling. Our results indicate that the shape, association, proliferation, and expression of gene products by Leydig cells can be significantly affected in vitro by altering the composition of the extracellular substratum.

Collagen type III induced ex vivo thrombogenesis in humans. Role of platelets and leukocytes in deposition of fibrin

Exposure of type III collagen coats on plastic cover slips in parallel-plate perfusion chambers to flowing nonanticoagulated human blood resulted in deposition of platelets and fibrin. Blood was drawn directly from an antecubital vein by an occlusive roller pump over the collagen coats in chambers having flow slits of different dimensions, so that wall shear rates of 100, 650, and 2600 s-1 were obtained at 10 ml/min. Coagulation was minimally activated during the passage of blood from the vein to the chamber as shown by fibrinopeptide A levels of 3.7 ng/ml after 5-minute perfusions. The surface coverage with platelets increased from 18% at 100 s-1 to 59% at 2600 s-1, and the corresponding thrombus volumes increased from 2 to 22 microns 3/microns 2, respectively. This contrasted with the coverage with fibrin on collagen, which decreased from 28% at 100 s-1 to 9% at 2600 s-1. Fibrin deposits on the thrombi covered 6% of the surface irrespective of the shear rate, indicating that some of the deposited platelets accelerated the deposition of fibrin. The type III collagen preparation did not activate factor XII and did not possess tissue factor activity, indicating that the surface itself was not procoagulant. However, a correlation between deposited leukocytes and surface coverage with fibrin was observed (r = 0.78, p less than 0.01), suggesting a role for these cells in the deposition of fibrin. The data demonstrate that thrombogenesis is triggered by pure type III collagen, although the deposition of fibrin is not initiated by the collagen itself but presumably by deposited leukocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Type VIII collagen in murine development. Association with capillary formation in vitro

Bovine endothelial and human astrocytoma cells, and a limited number of other normal and malignant cells, synthesize three chains that have been identified as type VIII collagen (180 kDa, 125 kDa, and 100 kDa). Digestion with pepsin converts these forms to major fragments of 65 kD (based on globular protein standards). In this study we have examined the structure and distribution of type VIII collagen in developing mice by immunohistological and immunoblotting techniques. Temporal and tissue-specific expression was observed in embryonic heart, cranial mesenchyme, and placental capillaries. Western blotting of embryonic and neonatal tissues showed major species of 125 and 65 kDa in the brain, placenta, heart, lung, and thymus. The predominant band in pepsin-treated tissues was 60-70 kDa, with additional forms of 250 and 150 kDa in neonatal heart and lung. Type VIII collagen was also synthesized by endothelial cells, forming capillary tubes in vitro. We suggest that type VIII collagen functions in cellular organization and differentiation, and that its various forms reflect not only tissue-specific processing but the presence of several related chains.

SPARC, a secreted protein associated with cellular proliferation, inhibits cell spreading in vitro and exhibits Ca+2-dependent binding to the extracellular matrix

SPARC (Secreted Protein Acidic and Rich in Cysteine) is a Ca+2-binding glycoprotein that is differentially associated with morphogenesis, remodeling, cellular migration, and proliferation. We show here that exogenous SPARC, added to cells in culture, was associated with profound changes in cell shape, caused rapid, partial detachment of a confluent monolayer, and inhibited spreading of newly plated cells. Bovine aortic endothelial cells, exposed to 2-40 micrograms SPARC/ml per 2 x 10(6) cells, exhibited a rounded morphology in a dose-dependent manner but remained attached to plastic or collagen-coated surfaces. These round cells synthesized protein, uniformly excluded trypan blue, and grew in aggregates after replating in media without SPARC. SPARC caused rounding of bovine endothelial cells, fibroblasts, and smooth muscle cells; however, the cell lines F9, PYS-2, and 3T3 were not affected. The activity of native SPARC was inhibited by heat denaturation and prior incubation with anti-SPARC IgG. The effect of SPARC on endothelial cells appeared to be independent of the rounding phenomenon produced by the peptide GRGDSP. Immunofluorescence localization of SPARC on endothelial cells showed preferential distribution at the leading edges of membranous extensions. SPARC bound Ca+2 in both amino- and carboxyl-terminal (EF-hand) domains and required this cation for maintenance of native structure. Solid-phase binding assays indicated a preferential affinity of native SPARC for several proteins comprising the extracellular matrix, including types III and V collagen, and thrombospondin. This binding was saturable, Ca+2 dependent, and inhibited by anti-SPARC IgG. Endothelial cells also failed to spread on a substrate of native type III collagen complexed with SPARC. We propose that SPARC is an extracellular modulator of Ca+2 and cation-sensitive proteins or proteinases, which facilitates changes in cellular shape and disengagement of cells from the extracellular matrix.

The calcium-binding protein SPARC is secreted by Leydig and Sertoli cells of the adult mouse testis

In mammals, polypeptides secreted by cells of the testis are believed to influence spermatogenesis and to affect the behavior of the resident somatic cell populations. The 43,000-MW, secreted, calcium-binding glycoprotein SPARC (Secreted Protein, Acidic and Rich in Cysteine) is synthesized by a number of embryonic, fetal, and adult somatic cells and is associated with areas of cellular differentiation, proliferation, and morphological reorganization. Here, we report on the expression of SPARC in the testes of adult mice. By immunohistochemistry, SPARC was observed in the cytoplasm of Leydig cells and of Sertoli cells bearing late-stage, elongate spermatids. Testicular mRNA, translated in vitro, yielded a polypeptide of approximately 42,000 MW that bound anti-SPARC antibodies. Northern blot analysis revealed 2.3 kilobase (kb) SPARC mRNA in the testis, a size comparable to that of SPARC mRNA in nongonadal cells. Western blot assays of proteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed an immunoreactive polypeptide of 43,000 MW in purified mouse Sertoli cells and their culture supernatants. Similar assays of testis interstitial fluid revealed 43,000 MW and 30,000 MW immunoreactive polypeptides. By indirect immunofluorescence, purified mouse Leydig cells cultured 24-48 h expressed SPARC in cytoplasmic granules. Cultured Leydig cells incorporated [35S]methionine into a secreted polypeptide of 43,000 MW that was recognized by anti-SPARC antibodies. In metal binding assays, purified SPARC bound Ca2+, Fe2+ and Cu2+. The function of SPARC in testes may be to sequester or transport certain metallic cations. Our recent discovery that SPARC induces changes in shape of certain nongonadal cell types also suggests that this glycoprotein may influence the functions of both Leydig and Sertoli cells by affecting their morphology.

Distribution of the calcium-binding protein SPARC in tissues of embryonic and adult mice

SPARC (Secreted Protein that is Acidic and Rich in Cysteine), a Ca++-binding glycoprotein also known as osteonectin, is produced in significant amounts by injured or proliferating cells in vitro. To elucidate the possible function of SPARC in growth and remodeling, we examined its distribution in embryonic and adult murine tissues. Immunohistochemistry on adult mouse tissues revealed a preferential association of SPARC protein with epithelia exhibiting high rates of turnover (gut, skin, and glandular tissue). Fetal tissues containing high levels of SPARC included heart, thymus, lung, and gut. In the 14-18-day developing fetus, SPARC expression was particularly enhanced in areas undergoing chondrogenesis, osteogenesis, and somitogenesis, whereas 10-day embryos exhibited selective staining for this protein in Reichert's membrane, maternal sinuses, and trophoblastic giant cells. SPARC displayed a Ca++-dependent affinity for hydrophobic surfaces and was not incorporated into the extracellular matrix produced by cells in vitro. We propose that in some tissues SPARC associates with cell surfaces to facilitate proliferation during embryonic morphogenesis and normal cell turnover in the adult.

SPARC: a Ca2+-binding extracellular protein associated with endothelial cell injury and proliferation

SPARC (Secreted Protein that is Acidic and Rich in Cysteine) is a Ca2+-binding, stress-related protein released in vitro by both malignant and normal cells derived from all primordial germ layers. It is specifically elevated in endothelial cells as a result of "culture shock" (characterized by high levels of proliferation and migration) and exhibits density-dependent secretion. Exposure of bovine aortic endothelial cells to endotoxin results in a 70-100% increase in secreted protein, with a three-fold increase in SPARC. Immunofluorescence histochemistry on mouse tissues revealed (a) a preferential association of SPARC with highly proliferative cells (e.g., gut epithelia, mammary gland, and epidermis), (b) a cell surface or stromal location in thymus, lung, and salivary gland, (c) staining of epididymidal epithelium and testicular cells, and (d) an association with somites of 14 d mouse embryos. We envision SPARC as an extracellular modulator of Ca2+ and other cation-sensitive proteins/proteinases, that facilitates cellular proliferation in response to injury and to developmental signals.

Calcium binding domains and calcium-induced conformational transition of SPARC/BM-40/osteonectin, an extracellular glycoprotein expressed in mineralized and nonmineralized tissues

SPARC, BM-40, and osteonectin are identical or very closely related extracellular proteins of apparent Mr 43,000 (Mr 33,000 predicted from sequence). They were originally isolated from parietal endoderm cells, basement membrane producing tumors, and bone, respectively, but are rather widely distributed in various tissues. In view of the calcium binding activity reported for osteonectin, we analyzed the SPARC sequence and found two putative calcium binding domains. One is an N-terminal acidic region with clusters of glutamic acid residues. This region, although neither gamma-carboxylated nor homologous, resembles the gamma-carboxyglutamic acid (Gla) domain of vitamin K dependent proteins of the blood clotting system in charge density, size of negatively charged clusters, and linkage to the rest of the molecule by a cysteine-rich domain. The other region is an EF-hand calcium binding domain located near the C-terminus. A disulfide bond between the E and F helix is predicted from modeling the EF-hand structure with the known coordinates of intestinal calcium binding protein. The disulfide bridge apparently serves to stabilize the isolated calcium loop in the extracellular protein. As observed for cytoplasmic EF-hand-containing proteins and for Gla domain containing proteins, a major conformational transition is induced in BM-40 upon binding of several Ca2+ ions. This is accompanied by a 35% increase in alpha-helicity. A pronounced sigmoidicity of the dependence of the circular dichroism signal at 220 nm on calcium concentration indicates that the process is cooperative. In view of its properties, abundance, and wide distribution, it is proposed that SPARC/BM-40/osteonectin has a rather general regulatory function in calcium-dependent processes of the extracellular matrix.

Distinct patterns of glycosylation of colligin, a collagen-binding glycoprotein, and SPARC (osteonectin), a secreted Ca2+-binding glycoprotein. Evidence for the localisation of colligin in the endoplasmic reticulum

Mouse parietal endoderm PYS cells were labelled with [2-3H]mannose for 16-24 h. Colligin, an Mr-47000 collagen-binding protein, and SPARC, a Mr-43000 protein, highly homologous to the Ca2+-binding protein osteonectin, were isolated from labelled cell extracts and culture medium respectively. Glycopeptides obtained by exhaustive digestion with pronase were analysed by lectin-affinity, ion-exchange, and gel-filtration chromatography and by paper chromatography of high-mannose oligosaccharides after endo H release. The results show that the N-linked carbohydrate chains of colligin are exclusively the high-mannose type, of which (Man)8(GlcNAc)2 and (Man)9(GlcNAc)2 make up 77%. This carbohydrate structure provides strong evidence that colligin is a component of the endoplasmic reticulum, and argues against a role in cell-surface interactions. By contrast to colligin, SPARC secreted by PYS cells contains predominantly a diantennary complex type of chain containing a variable number of sialic acid and core-substituted fucose residues. Similar glycosylation patterns to those discussed above were seen in colligin isolated from primary mouse embryonic parietal endoderm cells and the murine 3T3 cell line, and in SPARC secreted by bovine corneal endothelial cells. Unlike the type-IV-collagen-binding glycoprotein studied by Dennis, J., Waller, C. and Schirrmacher, V. [J. Cell Biol. 99, 1416-1423 (1984)], removal of N-linked oligosaccharides from colligin had no effect on its binding to native type IV collagen.

Extracellular matrix-induced synthesis of a low molecular weight collagen by fetal calf ligament fibroblasts

Fetal calf ligamentum nuchae fibroblasts, cultured from animals of different gestational age, synthesize a unique, low molecular weight collagen termed FCL-1 (Sage, H., Mecham, R., Johnson, C., and Bornstein, P., 1983, J. Cell Biol. 97:1933-1938). Previous studies on the elastogenic differentiation of these cells in vitro demonstrated that the extracellular matrix (ECM) protein elastin was specifically induced in undifferentiated fibroblasts when they were grown on ligament ECM isolated from animals at later stages of development (Mecham, R.P., Madaras, J.G., and Senior, R.M., 1984. J. Cell Biol. 98:1804-1812). To investigate the expression of FCL-1 as a function of developmental age, we grew fetal calf ligament fibroblasts from an 85 d (first trimester) animal (FCL 85d) on three different substrata: ligament from a 120 d (second trimester) animal, ligament from a 270 d (term) animal, and unmodified plastic tissue culture dishes. FCL 270d fibroblasts were grown on plastic substrata and served as a differentiated cellular control. Analysis of metabolically radiolabeled proteins from both the culture media and the cell layers showed that the synthesis of FCL-1 was selectively increased in those cells cultured on ligament ECM. For FCL 85d fibroblasts grown on 120 d and 270 d ligaments, FCL-1 comprised 17% and 22%, respectively, of the culture medium proteins that precipitated at concentrations of ammonium sulfate from 20-50%. FCL 85d and 270d fibroblasts grown on plastic substrata yielded values of 2.5% and 1.0%, respectively. This effect appeared to be specific for this collagen and did not reflect a general increase in the synthesis of connective tissue proteins of the ECM (e.g., types I and III procollagen). As percent of total newly-synthesized cellular protein, the output of FCL-1 was 10-fold higher by FCL 85d cells grown on 270d ligament ECM (5.8%) as compared to that of the same cellular population grown on a plastic surface (0.56%). The presence of the ligament ECM also altered the levels and distribution of secreted proteins between the culture medium and the cell layer. These studies provide evidence for differential expression of the novel collagen FCL-1 by FCL fibroblasts during development and suggest that such expression is affected, at least in part, by interaction of the cell with a ligament ECM.

Structural characteristics and intermolecular organization of human pulmonary-surfactant-associated proteins

The structural relationships and intermolecular organization among the proteins associated with pulmonary surfactant are largely unknown. We studied the pulmonary-surfactant-associated proteins in the bronchoalveolar lavage fluid obtained from a patient with the clinical syndrome of alveolar proteinosis. The major proteins with Mr values of 32,000-36,000 and 62,000 formed thiol-dependent complexes (Mr greater than 400,000) with intermolecular disulphide bonds present in the collgenase-sensitive domains of these proteins. In contrast, other proteins, which were collagenase-insensitive, formed thiol-dependent oligomers that were not covalently linked to the major proteins. The associations of these proteins in the surfactant of a normal individual were similar. By amino acid analysis, two-dimensional peptide mapping and bacterial-collagenase digestion the 32,000-36,000-Mr and 62,000-Mr proteins were nearly identical. Differences in CNBr cleavage products suggested that the larger of the proteins was formed by non-disulphide, covalent, cross-links in the collagenase-sensitive domains of the 32,000-36,000-Mr proteins. Thus the evidence suggested that the lipid-associated proteins of Mr 32,000-36, 000 contained both disulphide and non-disulphide cross-links in the collagen-like N-terminal region of the proteins and form higher-Mr complexes. This organization may support the three-dimensional conformation of surfactant in the alveolar space.

Interaction of platelets and purified collagens in a laminar flow model

Damage to the endothelial surface of the vessel wall can result in exposure of circulating blood components to collagen and other subendothelial structures. Collagen types I, III, IV, and V have been demonstrated in the vessel wall by chemical and immunohistological methods; type V is thrombin-sensitive, and is present on the endothelial cell surface. In an earlier study using a rocking model, both unstimulated and ADP-induced platelet adherence was reduced on wells coated with type V collagen in comparison to uncoated wells; and increased on plastic surfaces coated with types III and IV collagen in comparison to those coated with type V collagen. The present study was designed to determine the effect of erythrocytes and shear rate on platelet adherence to these purified collagen types in a laminar flow system. With platelet-rich plasma, adherence of labeled platelets was much lower in the laminar flow system compared with the rocking model. Erythrocytes significantly enhanced platelet adherence to surfaces that were untreated or absorbed with collagen types I, III, and IV. However, this enhancement was not seen in the presence of type V collagen. These studies provide additional evidence for the selectively nonthrombogenic nature of type V collagen.

Evidence from molecular cloning that SPARC, a major product of mouse embryo parietal endoderm, is related to an endothelial cell ‘culture shock’ glycoprotein of Mr 43,000

We describe the molecular cloning and characterization of a secreted, acidic, cysteine-rich glycoprotein (SPARC) of apparent Mr 43,000 which is a major product of mouse embryo parietal endoderm. These cells are specialized for the synthesis of a rapidly expanding basement membrane, but SPARC is not itself an integral matrix component. We show that SPARC is related structurally and antigenically to an Mr 43,000 glycoprotein secreted in large amounts by bovine aortic endothelial cells as part of a 'culture shock' response to in vitro conditions promoting their proliferation and migration.

Endothelial cell injury in vitro is associated with increased secretion of an Mr 43,000 glycoprotein ligand

A novel, serum albumin-binding glycoprotein of molecular weight (mw) 43,000 (43K protein) was initially purified from the culture medium of bovine aortic endothelial (BAE) cells (Sage, H., Johnson, C., and Bornstein, P., J. Biol. Chem. 259:3993-4007, 1984). Its secretion by normal mesenchymal cells and by transformed cells of both ectodermal and endodermal origin suggested a general role in cellular function. To examine the effect of sublethal injury in vitro on the biosynthesis of 43K protein, BAE cells were exposed to endotoxin. At concentrations which produced minimal cell detachment and lysis, the cells secreted 70-100% more protein compared to control cultures, and the relative increase in 43K protein over total protein was approximately three-fold. A second type of cellular injury, manifested by rapid cellular proliferation and migration in response to sparse plating density (a condition that we have termed 'culture shock'), was also accompanied by a significant increase in the secretion of 43K protein. Pulse-chase studies revealed that the initial product secreted within 1.5 h was of Mr 38,000, and that between 6 and 21 h this molecule was converted to the final form of Mr 43,000. The 43K protein was not associated with RNA or glycosaminoglycan, but appeared to be linked to complex oligosaccharides containing peripheral sialosyl residues. Treatment with tunicamycin produced lower mw forms that displayed reduced affinity for albumin. By immunologic criteria, peptide mapping, and amino acid analysis, the 43K protein was shown to be structurally distinct from several proteins of Mr 40,000-50,000 associated with endothelium or with serum, including tissue factor, a plasminogen anti-activator, and several apolipoproteins. In addition, the 43K protein was not present in the extracellular matrices of endothelial, fibroblastic, or smooth muscle cells, nor was it found in plasma, serum, platelet releasate, or alveolar lavage fluids. These studies identify a unique Mr 43,000 glycoprotein that is associated with cellular stress or injury in vitro. As a secreted but nonmatrix macromolecule, this protein may be part of a 'survival kit' used by the endothelium to cope with cellular injury.

Culture shock. Selective uptake and rapid release of a novel serum protein by endothelial cells in vitro

A novel protein has been purified from fetal calf serum and from serum-free bovine aortic endothelial cell conditioned culture medium. This protein consists of a single polypeptide chain of reduced Mr 70,000 (70K protein) and was separated from bovine serum albumin and other proteins by ion-exchange chromatography and immunoabsorption on Sepharose-coupled anti-70K protein antiserum. The 70K protein was shown to be structurally and immunologically distinct from bovine serum albumin, alpha-fetoprotein, and vitronectin by one- and two-dimensional peptide mapping, amino acid analysis, and enzyme-linked immunosorbent assay and/or immunoblotting. The 70K protein was located in endothelial cell cytoplasmic granules of irregular size and distribution. Metabolic radiolabeling studies showed that the 70K protein was not a biosynthetic product of these cells; its cytoplasmic location was due to a selective uptake from the fetal calf serum in which the cells were initially grown. After subconfluent cultures of endothelial cells were shifted to serum-free medium, nearly 80% of the total 70K protein that was measurable in the medium was released between 0 and 20 min. Moreover, sparse, rapidly proliferating cells released approximately 18-fold more 70K protein within 2 min as compared to dense, nonproliferating cultures. The concentration of 70K protein in fetal calf serum was estimated to be 400-600 micrograms/ml. Proliferating bovine aortic endothelial cells, 24 h after plating at an intermediate density, released approximately 250 pg of 70K protein/cell within the first 20 min after exposure to serum-free conditions. The data provide evidence for a novel protein in serum which is selectively internalized by endothelial cells in vitro and which in turn is released rapidly under conditions such as osmotic imbalance due to serum removal, or during periods of cellular proliferation, conditions which we term "culture shock."

Low molecular weight fibroblast collagen: structure, secretion, and differential expression as a function of fetal and cellular age

A unique low molecular weight collagen that was highly resistant to proteolytic degradation was originally isolated from fetal calf ligamentum nuchae fibroblasts and hence termed FCL-1 [Sage, H., Mecham, R., Johnson, C., & Bornstein, P. (1983) J. Cell Biol. 97, 1933-1938]. The differential expression of this protein was studied as a function both of fetal (donor) age and of subcultivation in vitro. Concomitant isolation, subculture, and metabolic radiolabeling experiments performed on cell strains from fetal calf ligament (FCL) and fetal bovine skin (FBS) representing different gestational ages (85-270 days in utero) showed that (a) FCL-1 was synthesized preferentially by fibroblasts from younger animals and (b) expression of FCL-1 diminished as a function of increased passage in culture. Levels of FCL-1, measured as percent of total radiolabeled culture medium protein that precipitated in a concentration range of 20-50% ammonium sulfate, ranged from 22% in FCL 85 cells to 7.7% in FCL 270 (term) cells. FBS fibroblasts at passages 6-10 secreted from 13% to 6% FCL-1, respectively. When cells from an 85-day fetal ligament were allowed to accumulate copious extracellular matrix in vitro, the production of FCL-1 was increased to 32%. FCL-1 was not immunoreactive with polyclonal antibodies directed toward most of the sequences of the interstitial type I and type III procollagens. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the apparent molecular weight of FCL-1 was 13 000 (on the basis of collagen peptide standards) and approximately 30 000 (on the basis of globular protein standards). Incubation with bacterial collagenase produced a stable cleavage product of Mr 8000 (by collagen standards) or 17 000 (by globular standards). In contrast, pepsin removed a small peptide of approximately 1000-2000 in molecular weight from FCL-1, and a gradual but progressive proteolysis of the collagen was observed over a period of 1-6 h. Pulse-chase studies revealed a secretion time of approximately 60 min for FCL-1, without the appearance of any processed, intermediate forms. These studies confirm that FCL-1 represents a novel member of the collagen gene family that manifests differential expression as a function of development.

Proteinases from invasive larvae of the trematode parasite Schistosoma mansoni degrade connective-tissue and basement-membrane macromolecules

Larvae of the human parasite Schistosoma mansoni, which invade the vascular system through the skin, secrete proteinases that degrade radioactively labeled extracellular matrices produced by smooth-muscle cells, dermal fibroblasts and endothelial cells. The proteinase purified from one larval form, the cercaria, degrades fibronectin and laminin and is a type-specific collagenase with activity against basement-membrane collagens IV and VIII, but not interstitial collagens I, III and V. The substrate specificity of this enzyme resembles that of the proteolytic enzymes which facilitate tissue invasion by inflammatory cells and tumour cells.

Characterization of a type VI collagen-related Mr-140 000 protein from cutis-laxa fibroblasts in culture

The precise biochemical defects in connective-tissue metabolism that are responsible for the laxity of skin seen in the syndrome of cutis laxa are largely unknown. We have studied fibroblasts cultured from skin explants of a 2-year-old male with the syndrome. Electron-microscopic examination of this skin revealed decreased amounts of amorphous elastin and an increase in elastin-associated microfibrils. Although the cultured fibroblasts were similar to control skin fibroblasts in morphology, growth rate and total protein synthesis, there was a 4-6-fold increase in accumulation of a collagenous protein of Mr 140 000 in both the culture medium and in the cell layer. This protein was structurally distinct from collagen types I, III, IV, V and VIII. It was found to be related to a cell-surface-associated glycoprotein, GP140, by both antigenic cross-reactivity and peptide mapping. Our data support observations that GP140 is a precursor of at least one form of pepsin-extracted type VI collagen.

Localization of collagen types IV and V, laminin, and heparan sulfate proteoglycan to the basal lamina of kidney epithelial cells in transfilter metanephric culture

Mouse metanephric mesenchyme and embryonic spinal cord were cultured on opposite sides of a filter membrane. This resulted in formation of prenephronic vesicles after 36 hours in culture, S-shaped bodies after 2-3 days, and glomeruli and tubules after 4-7 days. The glomeruli consisted of an arborizing tuft of podocytes lying on a basement membrane without vascularization or a mesangial ingrowth. We have used antibodies to study the molecular composition of the nephron basement membrane at each stage of development. By immunofluorescence light microscopy, collagen Types IV and V, laminin, and heparin sulfate proteoglycan were expressed within the pericellular/intercellular matrix at the onset of morphologic differentiation. The molecules were organized into a linear basement membrane associated with epithelial cells during the prenephronic vesicle, S-shaped body, and glomerulus and tubule stages of development.

Characterization of a novel serum albumin-binding glycoprotein secreted by endothelial cells in culture

A unique and heretofore undescribed glycoprotein with unusual properties has been purified and characterized from the culture medium of endothelial cells. This protein is synthesized constitutively by bovine, porcine, and human endothelial cells, by vascular smooth muscle cells, and by fibroblasts from dermis and ligament. It is also a biosynthetic product of some murine malignant and/or transformed cell lines but was not uniformly observed in cells derived from human neoplasms. The glycoprotein exhibited an apparent molecular weight by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of approximately 39,000 before reduction, and of approximately 43,000 (43K protein) in the presence of dithiothreitol. Amino acid analysis revealed high levels of potentially acidic residues (Asx + Glx = 303 residues/1000) and of cysteine (35 residues/1000). Limited proteolysis indicated that both disulfide bonds and mannosylated sites were distributed throughout the protein chain. Neither phosphate nor sulfate was incorporated into the 43K protein during biosynthetic labeling of endothelial cells. In addition, the 43K protein did not bind to heparin, thrombin, gelatin, or fibronectin and displayed no affinity for [3H]diisopropyl fluorophosphate. In contrast, the 43K protein demonstrated a high affinity binding to bovine serum albumin which was dissociable only by sodium dodecyl sulfate. A complete lack of identity with several prominent serum and platelet proteins and with other mesenchymal cell products was shown by one- and two-dimensional peptide mapping, affinity chromatography, and immunological studies. Immunofluorescence staining of endothelial cells showed a granular distribution for the 43K protein that was typical of a secreted protein. The function of this apparently novel glycoprotein is presently not known. Its synthesis by normal mesenchymal cells and by malignant or transformed cells of both ectodermal and endodermal origin suggests a general role in cell function that is independent of transformation.

Effects of deglycosylation on the architecture of ovine submaxillary mucin glycoprotein

The structural features of native and deglycosylated ovine submaxillary mucin (OSM) were determined by electron microscopy of platinum unidirectionally shadowed preparations and by ultracentrifugation. Thin filamentous molecules, of which 90% were 100-230 nm in length with estimated diameters of 1.0-1.4 nm, were observed with dilute samples of OSM in high ionic strength solvents (5-30 micrograms/ml in 0.8 M NaCl or NH4Ac). Ultracentrifugation studies indicated that these filamentous structures were monomers and/or dimers. At higher mucin concentrations or in lower ionic strength solvents, OSM molecules were oligomers that appeared as long rope-like strands. Removal of sialic acid residues by incubation with Clostridium perfringens neuraminidase yielded filamentous structures similar to those observed with OSM and some smaller less extended structures. Subsequent removal of the GalNAc residues of asialo-OSM with C. perfringens alpha-N-acetylgalactosaminidase resulted in a dramatic change in appearance, from an extended filament to a globular form. The frictional ratios of OSM and deglycosylated OSM were consistent with the marked structural differences of these molecules. Native OSM had a frictional ratio of 3.09, comparable to that of highly asymmetric tropomyosin (3.22); deglycosylated OSM had a frictional ratio of 1.11, comparable to that of globular ovalbumin (1.08).

Type VIII collagen. Synthesis by normal and malignant cells in culture

A novel protein belonging to the collagen family was originally purified from the culture medium of bovine aortic endothelial cells. This endothelial collagen, termed EC, was also found to comprise the major collagen type synthesized by a malignant astrocytoma-derived cell line. Examination of several cell strains derived from normal tissues revealed that EC was not synthesized by all endothelial cells; it was absent from human endothelial cells cultured from both large and small vessels but was present in bovine cells, including those from capillaries. Human foreskin fibroblasts also secreted this protein in small amounts relative to interstitial procollagens, but it was not detected in two human epithelial cell strains. EC was consistently observed in human cell lines derived from several carcinomas and comprised the major collagenous protein secreted by cells cultured from a Ewing's sarcoma. In contrast, malignant or transformed murine cells did not produce EC in vitro. In addition, the protein was not apparent after metabolic labeling of human cells from an epidermoid carcinoma, a fibrosarcoma, and two Wilms' tumors. EC-like proteins were isolated from cell culture medium by ion-exchange chromatography and were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after cleavage with vertebrate collagenase, mast cell protease, and CNBr. In addition to the homologies displayed by comparative peptide mapping, these collagens exhibited other unusual properties that collectively were characteristic of EC from endothelial and astrocytoma-derived cells. These studies support the existence of a novel class of collagenous proteins that are secreted by a wide variety of cells derived from both normal and neoplastic tissues. This class of proteins, which manifests several unusual structural characteristics, has been designated type VIII collagen.

Properties of cultured endothelium from adult human vessels

Endothelium was isolated from samples of aorta and vena cava obtained from cadaver donors at the time kidneys were harvested for transplantation. Digestion with collagenase and gentle swabbing were used to free the cells from the intimal surface. Low density seeding permitted isolation of individual colonies with typical endothelial morphology. Modified Medium 199 supplemented with 10%-20% human plasma-derived serum and an extract from the bovine hypothalamus (500 micrograms/ml) enabled subcultured colonies to grow to confluency when culture surfaces were coated with fibronectin (1 micrograms/cm2). The presence of Factor VIII antigen was demonstrated using an indirect immunofluorescence technique. A monoclonal antibody to cultured umbilical vein endothelium, specific for endothelium, reacted with the subcultured cells from the aorta and vena cava. Type IV procollagen, fibronectin, and thrombospondin were identified as labeled proteins secreted by cultures of adult endothelium that had been incubated with 3H-proline and 3H-glycine. When the cultured endothelium was used in a sodium-m-periodate stimulated T lymphocyte mitogenic culture system, the endothelium exhibited accessory cell function. Prostacyclin production stimulated by incubation with arachidonic acid and PGH2 was variable from vessel to vessel. However, average values were lower than normally seen with cultured primary umbilical vein endothelium.

Fetal calf ligament fibroblasts in culture secrete a low molecular weight collagen with a unique resistance to proteolytic degradation

A highly unusual collagen was secreted by fibroblasts cultured from 150- and 270-d-old fetal calf nuchal ligaments. Purification revealed that this protein (which may be synthesized in a higher molecular weight form) was precipitated at unusually high concentrations of ammonium sulfate and was also eluted from DEAE-cellulose at greater salt concentrations than were types I and III procollagens. On SDS PAGE, the collagenous protein exhibited an Mr of approximately 12,750 that was not altered in the presence of reducing agent. The low molecular weight collagen (FCL-1) was sensitive to bacterial collagenase and had a [3H]glycine content comparable to that found in type I procollagen, although the [3H]Hyp to [3H]Pro ratio was 0.43. FCL-1 was not cleaved by human skin collagenase, mast cell protease, trypsin, Staphylococcal V8 protease, or proteinase K at 37 degrees C. The collagen was susceptible to trypsin, but not to V8 protease, only after heating at 80 degrees C for 30 min. Preliminary structural studies indicate that FCL-1 was resistant to cleavage by CNBr but exhibited limited proteolysis with pepsin. Both 150- and 270-d-old fibroblasts produced comparable levels of interstitial (types I and III) procollagens, which comprised approximately 70% of the total protein secreted into the culture medium. However, 270-d-old (term) fibroblasts secreted approximately 50% more FCL-1, as percent of total culture medium protein, in comparison to the cells from the earlier gestational stage. This collagen may therefore play a role in the development of the nuchal ligament.

Biosynthetic and structural properties of endothelial cell type VIII collagen

A highly unusual endothelial cell collagen (Sage, H., Pritzl, P., and Bornstein, P., (1980) Biochemistry 19, 5747-5755) has been characterized in greater detail. Pulse-chase experiments with bovine aortic endothelial cells revealed two nondisulfide-bonded collagens, of apparent chain Mr = 177,000 and 125,000, with an estimated synthesis and secretion time of 75 min. Stepwise, quantitative processing to stable lower molecular weight forms as described for type I procollagen was not observed. Endothelial collagen was secreted over a temperature range of 24-37 degrees C and, prior to heat denaturation, did not display affinity for a gelatin-binding fragment of fibronectin coupled to Sepharose. The presence of a pepsin-resistant domain (Mr = 50,000) in both the soluble and cell layer-associated forms of this protein was shown by ion exchange chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Endothelial collagen was cleaved by vertebrate collagenase into several discrete fragments that differed in molecular weight from the characteristic alpha A and alpha B fragments generated from the interstitial collagens. Nontriple helical domains corresponding to the NH2- and COOH-terminal propeptides of other procollagen types were not found after incubation of endothelial collagen with bacterial collagenase. Additional evidence for the lack of extended noncollagenous sequences was provided by studies with mast cell proteases, which convert native procollagen to collagen but are unreactive toward native interstitial collagens. Endothelial collagen was not cleaved by these enzymes at 37 degrees C, but, as observed for interstitial collagen alpha chains, required prior heating at elevated temperatures for cleavage to occur. In view of this unique set of structural characteristics, and a distribution that is not restricted to the endothelium, we have designated this protein as type VIII collagen.

Diminished platelet adherence to type V collagen

Different types of collagen vary in their influence on platelet reactivity. Collagen Types III, IV, and V were obtained from human placental tissue, and Type I collagen was prepared from rat skin. Each collagen type was coated onto a plastic surface. Each collagen-coated surface or appropriate plastic surface control was studied using citrated human 51Cr-labeled platelet-rich plasma in both the presence and absence of 10 microM adenosine 5'-diphosphate (ADP). Both unstimulated and ADP-induced platelet adherence were: 1) reduced by Type V collagen coating in comparison to uncoated wells; and 2) increased by Types III and IV collagen coating in comparison to Type V coated or plastic surfaces. Addition of the fast-acting thrombin inhibitor dansylarginine (DAPA) had no significant effect on unstimulated and ADP-induced platelet adherence to Type III, IV or V collagen-coated surfaces. Type I collagen-coated surfaces, studied only in the presence of DAPA, caused greater platelet adherence than those coated with Types III, IV, or V collagen. We conclude that Type V collagen may be less thrombogenic than Types, I, III, or IV.

Granular pneumocytes in primary culture secrete several major components of the extracellular matrix

Primary cultures of rat alveolar type II epithelial cells (granular pneumocytes) produced several components of the pulmonary extracellular matrix. Fractionation by ion-exchange chromatography of radiolabeled protein secreted into the culture medium resulted in the partial purification of two of these components: fibronectin and type IV procollagen. Identification of these proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was confirmed by radioimmune-precipitation studies with affinity-purified antibodies. Thrombospondin, a platelet alpha-granule protein that was recently shown to be secreted by endothelial and other mesenchymally derived cells and may be involved in platelet aggregation, was, in addition, purified by elution from diethylaminoethylcellulose with 0.5 M NaCl. The levels of these secreted proteins were measured by radioimmune precipitation. Of the total radiolabeled culture medium protein secreted during a 24-h period by the granular pneumocytes, fibronectin, type IV procollagen, and thrombospondin represented 3-15%, 2%, and 3%, respectively. The biosynthesis, by alveolar epithelial cells, of proteins that constitute or are closely associated with the alveolar basement membrane implies that this structure is at least partially derived from the cells themselves. Furthermore, it suggests that the type II epithelial cell is involved in pulmonary cytodifferentiation, in lung morphogenesis and repair, and in certain interstitial lung disorders in which derangement of the extracellular matrix occurs.

Endothelial cells secrete a novel collagen type in vitro independently of prolyl hydroxylation

Endothelial cells from bovine aorta, vena cava, and cornea secrete a novel collagen in vitro (Sage et al., 1980). Endothelial collagen (EC), which is sensitive to pepsin and to several neutral proteases, exhibited an additional unusual property in its mode of secretion. In the absence of added sodium ascorbate, EC was secreted by both aortic and corneal endothelial cells at levels which were very similar to those observed in cultures supplemented with this vitamin. In contrast, the secretion of type III procollagen, which normally constitutes 75-80% of collagenous protein in the culture medium, was significantly decreased in ascorbate-deficient cultures. Incubation of aortic endothelial cells with alpha, alpha'-dipyridyl, an inhibitor of prolyl and lysyl hydroxylases, reduced the extent of prolyl hydroxylation in total culture medium protein by 98% but also did not affect the secretion of EC. The secretion of EC by endothelial cells appears to be independent of a requirement for prolyl hydroxylation. This property differs markedly from the secretory characteristics of the interstitial procollagens and more closely resembles that described for type IV (basement membrane) procollagen.

Biosynthesis of type V procollagen by A204, a human rhabdomyosarcoma cell line

The A204 cell line, derived from a human rhabdomyosarcoma, was studied in culture for its capacity to synthesize collagen types and other extracellular matrix proteins. The cells synthesized and secreted into the culture medium collagenous proteins with apparent molecular weights of 220,000 and 150,000. These were identified as the pro alpha 1 and pro alpha 2 chains of type V collagen by immunoprecipitation and by peptide mapping. The pro alpha 1(V) chain was made in excess of a 2:1 ratio for pro alpha 1(V) to pro alpha 2(V), and a fraction of the pro alpha 1(V) chains together with all of the pro alpha 2(V) chains participated in intermolecular disulfide bonding. The chains were extensively glycosylated at hydroxylysyl residues in ascorbate-supplemented cultures. A fraction of the secreted pro alpha 1(V) chains was processed to the p alpha 1(V) form, but further processing in the culture medium was very slow and the type V collagen molecules deposits in the extracellular matrix apparently retained large non-triple helical domains. Since the A204 cell line does not produce other collagen types, it may prove useful in further studies of the biosynthesis of type V procollagen.

Collagens of basement membranes

Recent biochemical and immunohistochemical studies have described several components of basement membranes including heparan sulfate proteoglycan, 2 high molecular weight glycoproteins (fibronectin and laminin), and 2 collagen types (IV and V). These collagens have several properties which distinguish them from other types that are located in the interstitium: (a) type IV forms an amorphous, felt-like matrix, and neither IV nor V is found in large, cross-banded fibrils, (b) both have an increased content of hydrophobic amino acids, (c) the precursor (pro) forms are larger than those of interstitial collagens, (d) type IV contains interruptions within the triple helix, and e) both IV and V are resistant to human skin collagenase but are substrates for selected neutral proteases derived from mast cells, macrophages, and granulocytes. By immunofluorescence staining, type IV collagen has been localized to basement membranes at the dermal-epidermal junction, in capillaries, and beneath endothelial cells in larger vessels. Ultrastructurally it has been shown to be a specific component of the lamina densa. Type V collagen has been localized to the pericellular matrices of several cells types and may be specific for extramembranous structures which are closely associated with basal laminae. Other collagenous proteins have been described which may be associated with the extracellular matrix. One of these is secreted by endothelial cells in culture and by peptide mapping represents a novel collagen type. It is secreted under ascorbate-free conditions and is highly sensitive to proteolytic degradation. It has been proposed that a dynamic reciprocity exists between cells and their extracellular matrix which partially determines cell shape, biosynthesis, migration, and attachment. Examples of phenotypic modulation in several of these phenomena have been shown with endothelial cells grown on different substrates and isolated from different vascular environments.

Structure-function relationship in the evolution of elastin

The evolution of the structure of the rubber-like protein elastin, found in connective tissues which are subjected to periodic physiological stress, was studied with respect to its phylogenetic distribution, fiber morphology and arrangement, response to deformation, and amino acid composition. Aortae and other tissues from several vertebrates and invertebrates were examined for the presence of elastin, which was defined on the basis of a characteristic amino acid composition, the presence of the unique crosslinks desmosine and isodesmosine, and by histologic criteria. The protein was present in all vertebrates except the primitive jawless fishes and was absent from all invertebrates which were examined. In addition, the morphology of aortic elastin fibers differed markedly among the vertebrate families. Biochemical analysis revealed increases in both the degree of crosslinking and hydrophobicity in elastins from higher vertebrates (mammals, birds) as compared to those from bony fish. Mammalian elastin displayed an increased tendency toward coacervation (polymerization into aggregated structures) at 37 degrees C and behaved differently from a conventional elastomer when stretched in a microcalorimeter. Selection for an increasingly hydrophobic elastin appears to have paralleled the development of a highly-pressurized, closed circulatory system in homeothermic animals. The data do not support a common genetic origin for elastin and other connective tissue proteins. Significant variations in amino acid composition among aortic elastins from different species, however, indicate that genetically distinct elastin types could have arisen by divergence from a common ancestral gene.

Endothelial cells from umbilical vein and a hemangioendothelioma secrete basement membrane largely to the exclusion of interstitial procollagens

The biosynthesis of extracellular matrix proteins by primary cultures of endothelial cells from human umbilical vein, and by clones from a murine hemangioendothelioma, was studied and compared to that reported for endothelium cultured from other sources. Umbilical vein endothelial cells secreted two glycoproteins-fibronectin and thrombospondin-which comprise the major proportion of the protein in the culture media of bovine aortic, venous, and corneal endothelial cells. These biosynthetic products were absent from hemangioendothelioma cultures. However, in contrast to bovine endothelium from large vessels and cornea, which secrete primarily Type III procollagen into the culture medium, both the umbilical vein and hemangioendothelioma cultures secrete Type IV (basement membrane) procollagen. In addition, EC, a novel endothelial collagen type that has been characterized in bovine endothelial cell supernates, was not present in the umbilical vein or tumor-derived endothelium. The production of basement membrane procollagen as the major collagen type in the medium of these cultures probably reflects the nature of the vascular bed from which the endothelial cells originated, rather than differences in species of in cellular isolation and subculture. We suggest that endothelial cells from different vascular environments could display variations in growth, migration, morphology, and response to exogenous blood-borne factors as a result of their relationship to an extracellular matrix/subendothelium composed of diverse structural glycoproteins.

Interactions of vascular wall cells with collagen gels

Culture properties of bovine aortic endothelial cells and bovine aortic smooth muscle cells have been examined in relation to collagen gels. Endothelial cells grown on collagen maintain typical monolayer morphology not only in relationship to the overlying medium but also with respect to the collagen substrate. Endothelial cells placed within a collagen matrix assume a mycelial pattern resembling that of the microvasculature. Overlayment of confluent endothelial cells with collagen induces separation of the cells, changes in morphology, and reinitiation of growth. These shape changes do not require protein synthesis, appear to be independent of fibronectin, are not inhibited by cytochalasin D, but are inhibited by colchicine. Endothelial cell growth can be reinitiated by collagen. This phenomenon appears to be related to a change in cell shape and perhaps to separation of cells at the intercellular junction. In contrast, smooth muscle cells plated on collagen infiltrate the gels and assume a spindle-like, elongated morphologic appearance. Overlayment with collagen does not alter smooth muscle cell shape. Migration into the collagen gels is significantly enhanced when cells are cultured in medium containing platelet-released products, independent of growth stimulation itself. Migration is accompanied by collagen gel degradation. Release of labeled collagen into the medium by smooth muscle cells and appearance of TCA fragments in collagenase assay suggest secretion of collagenase. In summary, endothelial cells, but not smooth muscle cells, are restricted to the surface of collagen gels. The ability of the smooth muscle cells to invade is stimulated by platelet products and may be related to the synthesis of a smooth muscle collagenase.

Isolation and characterization of a glycoprotein secreted by aortic endothelial cells in culture. Apparent identity with platelet thrombospondin

A high molecular weight glycoprotein, reported to be secreted by endothelial cells (Sage, H., Crouch, E., and Bornstein, P. (1979) Biochemistry 18, 5433-5442), has been purified to apparent homogeneity from culture medium of adult bovine aortic endothelial cells. Purification was achieved by ammonium sulfate fractionation and successive chromatography on gelatin-Sepharose, Sephacryl S-300, and hydroxylapatite. The glycoprotein was found to be a disulfide-linked oligomer with a subunit molecular weight of 190,000, as judged by its mobility on sodium dodecyl sulfate (NaDodSO4)-polyacrylamide gels. The endothelial cell-derived protein is distinct from high molecular weight serum glycoproteins such as fibronectin and alpha 2-macroglobulin. However, immunological and structural studies indicate that the Mr = 190,000 glycoprotein is either identical with or closely related to thrombospondin, a glycoprotein contained in platelet granules and released in response to thrombin-induced aggregation.