Synthesis of interstitial collagens by pig aortic endothelial cells in culture

Biochemical properties of vascular endothelial cells

Present knowledge in the field of vascular endothelial cells is reviewed. The role of endothelial cells in the synthesis of matrix proteins and glycosaminoglycans is described. Endothelial cells play a considerable role in the processes of coagulation and fibrinolysis. They also interact with neurotransmitters and vasomotoric substances, and participate in inflammation and immunological responses. They produce several different growth factors. Their role in lipoprotein metabolism is of special importance to research into atherosclerosis.

Increased collagen around deformed finger nailfold capillaries in type I diabetes mellitus

Quantitative finger nailfold capillary microscopy was performed in 25 patients with type I diabetes and in 27 healthy control subjects. In the last consecutive 6 patients and 7 controls of these populations, finger nailfold biopsies were taken. Measurements of loop width as an in vivo parameter for deformities of the capillary loops showed significantly higher values in diabetic patients than in controls. Histopathological examination showed markedly and significantly increased deposition of collagen in nailfold dermal papillae of the diabetic patients. The deposition of collagen was positively correlated with the number of capillary endothelial cells in the nailfold dermal papillae and with the size of the papillae in diabetic patients. It is concluded that, in addition to deformity of nailfold capillaries, collagen deposition may also be a sign of metabolic disturbance and perhaps of proliferation of capillary endothelial cells in diabetic microangiopathy.

Evidence that the primary binding site of von Willebrand factor that mediates platelet adhesion on subendothelium is not collagen

We have studied the binding of von Willebrand factor to extracellular matrices of endothelial cells and to the vessel wall of human umbilical arteries in relation to its function in supporting platelet adhesion. CLB-RAg 201, an MAb against von Willebrand factor, completely inhibits the binding of von Willebrand factor to collagen type I and type III. CLB-RAg 201 does not inhibit the binding of 125I-von Willebrand factor to extracellular matrices of endothelial cells, to smooth muscle cells, or to the subendothelium. CLB-RAg 201 partly inhibits platelet adhesion to these surfaces, but this directly affects the interaction between von Willebrand factor and platelets and is not due to inhibition of binding of von Willebrand factor to these surfaces. Another MAb, CLB-RAg 38, does not inhibit the binding of von Willebrand factor to collagen. CLB-RAg 38 completely inhibits the binding of von Willebrand factor to extracellular matrices. CLB-RAg 38 inhibits platelet adhesion to cellular matrices completely insofar as it is dependent on plasma von Willebrand factor. CLB-RAg 38 does not inhibit the total binding of von Willebrand factor to subendothelium, as there are too many different binding sites, but it completely inhibits the functional binding sites for von Willebrand factor that support platelet adhesion. The epitopes for CLB-RAg 38 and 201 on the von Willebrand factor molecule are located on different fragments of the molecule. These results indicate that von Willebrand factor binds to subendothelium and matrices of cultured cells by a mechanism that is different from that by which it binds to collagen.

The biosynthesis of extracellular-matrix components by bovine retinal endothelial cells displaying distinctive morphological phenotypes

Previous studies have indicated that the morphology and behaviour of bovine retinal microvessel endothelial cells are influenced by culture conditions in vitro. Data are presented here concerning the biosynthesis of matrix macromolecules by bovine retinal endothelial cells cultured under conditions in which the cells display either the 'cobblestone' or the 'sprouting' phenotype. Newly synthesized matrix proteins were identified by their characteristic electrophoretic mobilities, immunoprecipitation with specific antibodies, susceptibilities to enzymic digestions and chromatographic behaviour. Type IV procollagen was the major collagenous species synthesized by early-passage cells forming a 'cobblestone' monolayer. In contrast, cells displaying the 'sprouting' morphology switched to the predominant synthesis of interstitial fibrillar collagens (types I and III). Fibronectin was synthesized by retinal endothelial cells under all the experimental conditions studied. A non-collagenous glycoprotein of Mr approx. 47,000 was also a major biosynthetic product of these cells. The synthesis of thrombospondin was very much dependent on the nature of the substratum on which the cells were cultured. This glycoprotein was synthesized in large amounts by 'cobblestone' endothelial cells cultured on gelatin-coated dishes, whereas its synthesis was markedly decreased by culturing the cells on collagen gels, and the protein appeared to be absent when the cells were plated within collagen gels ('sprouting' cells). Late-passage retinal cells synthesized predominantly type I procollagen, variable amounts of type III procollagen and only traces of type IV procollagen, irrespective of whether the cells displayed a 'cobblestone' or 'sprouting' morphology.

Collagens of the retinal microvascular basement membrane and of retinal microvascular cells in vitro

We have analysed the collagens present in vascular basement membranes isolated from bovine retinal and cerebral microvessels and bovine renal glomeruli, and from the non-vascular basement membrane of bovine lens capsule. These are compared with the collagens produced by cultured bovine retinal microvascular pericytes and lens epithelial cells, and by canine retinal microvascular endothelial cells, in vitro. Biochemical and immunocytochemical analyses indicate that all of the vascular basement membrane preparations have an identical collagenous composition, consisting of the same polypeptides present in lens capsule (primarily type IV collagen), together with other polypeptides that are identified as type I, and a small amount of type III collagen. Identification of the latter is based on two-dimensional gel electrophoresis in the presence and absence of a reducing agent. Immunocytochemical studies, however, demonstrate type I, type IV and some type V collagen in the basement membranes of the isolated microvessels. The cultured microvascular cells produce predominantly type I collagen molecules, but they also produce other collagen peptides that appear to be type IV, and, at least in some experiments, small amounts of type III collagen. The biochemical identification of collagens type I and IV is confirmed by immunocytochemistry. However, results with anti-type I collagen and procollagen antibodies in cultured pericytes vary with antibodies from different sources. The quantities of the type IV peptides produced by the cultured cells also vary in different experiments.

Characterization of rabbit stromal fibroblasts derived from red and yellow bone marrow

Rabbit stromal fibroblasts subcultured from red and yellow bone marrow and implanted beneath the renal capsule form ossicles the hemic cellularity of which mirrors the cellularity of the marrow used for culture. Although the cultured red and yellow marrow cells are similar in fine-structural appearance, they differ strikingly in enzymatic content of alpha-naphthylbutyrate esterase, which is abundant only in the cells derived from yellow marrow. Other observers (20, 21) have proposed that stromal fibroblasts are preadipocytes, and this data suggests that those derived from yellow marrow have the phenotype of more differentiated adipocytes. On the other hand, fibroblasts derived from red and yellow bone marrow show no differences in their profiles of procollagen synthesis. Both types of fibroblasts secrete type III procollagen as the major species, with a I/III ratio of 1:3; in contrast, rabbit dermal fibroblasts have a prominent peak of type I procollagen. The similarity of stromal cells derived from red and yellow bone marrow in procollagen synthesis suggests that the collagen part of the extracellular matrix is not the only basis for their intrinsic difference in capacity for hematopoiesis.

Phenotypic changes in morphology and collagen polymorphism of cultured bovine and porcine aortic endothelium

Endothelial cells derived from the pig aorta grow in culture with typical cobblestone morphology; after about 7 days they elongate to a more fibroblastic appearance followed by the appearance of sprouts. The sprouts can be removed by 24 h treatment with either 8-bromo-cyclic AMP or cholera toxin, when the cells revert to their original cobblestone morphology. Examination of phenotypic markers as exemplified by the collagen types synthesised in the cell layer and those released into the medium, indicated the presence of types I, III and V in the cobblestone phase; the result of sprouting and desprouting was to alter the various proportions of I, III and V in both cells and medium with the exception that type V disappeared from the medium of sprouting porcine cells. When bovine endothelial aortic cells were similarly examined, I, III and V type collagens were found in the cell layer and medium, but in vastly different proportions from those found in the pig. Sprouting and desprouting bovine endothelium produced profound changes--in the cell layer, only type V could be demonstrated, whereas I, III and V were demonstrable in the medium, albeit in differing proportions. The conclusions are firstly, that phenotypic morphological changes may or may not be accompanied by phenotypic changes in the synthesis of the various collagen markers; secondly, that the secreted collagens do not always reflect those collagens retained by the cell layer which shows sequestration of one of the collagen types; finally there is a very distinct species difference and it is not possible to extrapolate from one species to another. The ultrastructural observation that the sprouts in cultured bovine endothelium resemble everted capillaries adds value to the culture as a model system.

Collagen synthesis by cloned pulmonary artery endothelial cells

Pulmonary artery endothelial cells were isolated from bovine fetal blood vessels and used for biosynthetic studies. At confluence, cultures were incubated in minimal essential medium (MEM) without serum containing [U-14C]proline. After 24 hours, medium was removed and labeled proteins were precipitated by the addition of ammonium sulfate and fractionated by diethylaminoethyl (DEAE)-cellulose chromatography. The elution profile showed four major peaks and one minor peak. Fractions within each peak were pooled, subjected to digestion by chymotrypsin and/or collagenase, and analyzed by polyacrylamide gel electrophoresis. Peak l contained a collagen which contained approximately 6% of the 3-hydroxyproline isomer while total hydroxyproline content was approximately 45%. This material was digested by purified bacterial collagenase and had a mobility slightly slower than that of alpha 1(III) which did not change under conditions that reduce disulfide bonds. Upon digestion with chymotrypsin under conditions where native procollagens are converted to alpha-chains, this material was digested. These properties suggest that this material is type VIII or EC (endothelial cell) collagen. Peak 2 contained substantial fibronectin while peak 3 contained primarily type III procollagen. The last major peak contained a mixture of collagenous and noncollagenous material. Upon digestion with chymotrypsin, several peptides were generated which were sensitive to bacterial collagenases. The two major chymotrypsin-resistant components had mobilities slower than that of alpha(III) and were not disulfide-bonded.

Comparison of the collagenous products synthesized in culture by pig aortic endothelial and smooth-muscle cells. Variability in endothelial-cell cultures

In contrast with smooth-muscle cells from the same tissue, endothelial cells from pig aorta were found to exhibit in culture considerable variability in the pattern of collagen synthesis between one isolation of cells and the next. Synthesis varied from largely collagen type I to virtually all type III in the absence of type I but with small amounts still of collagens types IV and V, to, in one instance, synthesis basically of only type V. Synthesis usually by these cells of collagen predominantly of the interstitial type (I and III) rather than, as might be expected, that from basement membrane (type IV) was not attributable to the influence of subculture. All four collagen types were deposited in the cell layer to an increased extent in primary compared with secondary cultures of either smooth muscle or endothelial origin. Endothelial cells appeared sometimes to synthesize a large-Mr collagenous entity that might conceivably be related to 'short-chain' collagen. In addition, small-Mr hydroxyproline-containing peptides were detected that might reflect rapid collagen(s) turnover in endothelial cultures.

Collagen production by human mesothelial cells in vitro

Serous effusions from a variety of malignant and non-malignant conditions were found to contain cells which had the morphological, histochemical and ultrastructural characteristics of mesothelial cells. In culture they were the predominant cell type and synthesised large quantities of the interstitial collagens type I and III, with the proportion of type III frequently approaching or exceeding 50 per cent. There was no evidence that they synthesised basement membrane collagen chains of type IV or type V. Since mesothelial cells are assumed to secrete the mesothelial basement membrane, the synthesis of interstitial collagens by desquamated mesothelial cells appears to reflect a change in the phenotype of collagen synthesis. We suggest that this change may be an important factor in the fibrosis of the serosal wall which frequently accompanies diseases with chronic serious effusion.

A biochemical and immunohistological study of collagen synthesis in Ewing's tumour

The synthesis and localization of collagen have been studied on material from a total of 16 primary Ewing's tumours. The predominant collagen extracted from the tissues and synthesized in short-term cultures was type I. The proportion of type III collagen was relatively small and variable (0-8%) in the direct tumour extracts, but a higher proportion (29-38% of the total collagens) was synthesized in culture. Immunofluorescence studies showed that positive staining for all types of collagen tested (types I, III, IV and V) was restricted to stroma; there was no evidence of collagen either within the tumour cells or in their pericellular matrix, a finding endorsed by negative staining for reticulin in the same areas. The absence of any evidence for type IV or V collagen synthesis by Ewing's cells argues against an endothelial origin for the tumour, and indicates that collagen analysis is unlikely to be of value in the diagnosis of this particular sarcoma.

The effect of hypoxia on the synthesis of collagen and glycosaminoglycans by cultured pig aortic endothelium

Porcine aortic endothelium cultured at 20% oxygen concentration synthesizes collagen and three of its marker enzymes - proline and lysine hydroxylases and lysine oxidase, the cross-link enzyme. It also synthesizes and secretes hyaluronic acid, dermatan sulphate, possibly heparan sulphate, large amounts of chondroitin 4-sulphate and smaller amounts of chondroitin 6-sulphate. Growth of these cells for 24 h in 0%, or 2% oxygen results in little change in cell numbers or cell protein but a fall in collagen synthesis and in proline and lysine hydroxylases, but a rise in lysine oxidase. There is a considerable increase in synthesis and secretion of all the glycosaminoglycans found. The cell lipids appear qualitatively unchanged. Apart from increased lysosomes seen at 0% oxygen, no ultrastructural changes appear to occur. These findings illustrate the lability of the endothelial response to oxygen lack.

Characterization of marrow-derived adherent cells. Evidence against an endothelial subpopulation

Cultured, marrow-derived, adherent cells (MDAC) provide a microenvironment which supports the proliferation of haemopoietic stem cells (HSC) for extended periods in vitro. Morphological characterization suggested that MDAC populations consisted of a variety of cell types, including mononuclear phagocytes, fibroblastoid cells, fat cells and vascular endothelial cells. Recently performed functional characterization studies suggest that they consist largely of collagen-producing, fibroblastic cells. MDAC were not, however, examined systematically for endothelial cell characteristics. Unrecharged cultures of MDAC, shown in parallel studies to support in vitro haemopoiesis, were examined for endothelial cell markers. These included the presence of Weibel-Palade bodies and synthesis of factor VII related antigen. They were also examined biochemically for synthesis of basement membrane (type IV) collagen. The results of these investigations were negative in all cultures examined. It is thus concluded that vascular endothelial cells are not present as a significant component of the unrecharged MDAC population and do not, therefore, contribute to the functional haemopoietic microenvironment in vitro or in vitro.

Collagen polymorphism in the normal and diseased blood vessel wall. Investigation of collagens types I, III and V

Estimation of collagens types I and III in pepsin digests and by analysis of specific cyanogen-bromide derived peptides by SDS-polyacrylamide gel electrophoresis, has indicated that both the undiseased human aortic media and the atherosclerotic plaque of the diseased intima contain more type I collagen than type III. There was only a relatively small shift in composition in favour of type I collagen in the diseased compared to the undiseased tissue. Diffusely thickened intima was similar in composition to the atherosclerotic plaque. These results suggest that both atherogenesis and diffuse intimal thickening may involve primarily smooth muscle cell hyperplasia with increased overall collagen production but little alteration in cell phenotype as regards the relative proportions of the individual collagens produced. They do not support the contention that atherosclerosis involves a 'transformation' of smooth muscle cells to fibroblast in type, whereby a major switch in synthesis occurs from largely type III collagen to mainly type I in disease. Type V collagen(s) containing both alpha A- and alpha B-chains has been detected throughout the vessel wall in diffusely thickened intima, media and adventitia, as well as in the plaque where, in the latter case, a marked enrichment relative to interstitial collagens was noted. This is presumed to reflect the relatively cellular nature of the atherosclerotic lesion. The alpha C-chain of type V collagen was detected in porcine but not human aorta.

Fibroblast growth factor modulates synthesis of collagen in cultured vascular endothelial cells

Vascular endothelial cells derived from adult bovine aortic arch can be grown in two ways, either in the presence or absence of fibroblast growth factor. The types of collagen produced by cultures under these two conditions have been compared. In the presence of fibroblast growth factor, cells grow in an orderly fashion, express their normal phenotype and synthesize primarily type III collagen plus collagens types IV and V at a ratio of 10:1:3. Cultures grown in the absence of the factor lose their orderly pattern of growth, lose polarity and normal phenotypic expression. They devote twice the proportion of total protein-synthesizing capacity to collagen, and now synthesize type I in addition to the other collagen types. The ratio of collagen types I:III:IV:V is approximately 30:70:1:13. The kinds of type V collagen chains expressed are also altered. Fibroblast growth factor appears to modulate collagen synthesis, the major component of the extracellular matrix, and indirectly modulates the phenotypic expression of cultured vascular endothelial cells. In atherosclerosis, type I collagen is found in association with the intimal layer. The disorderly growth and the abnormal production of type I collagen by these vascular endothelial cells cultured in the absence of fibroblast growth factor is a model for a number of pathological situations including atherosclerotic plaque formation.

Nonparenchymal cells cultivated from explants of fibrotic liver resemble endothelial and smooth muscle cells from blood vessel walls

Tissue specimens from human fibrotic liver obtained by needle biopsy were cultured. Two cell types emerged from the tissue explants. From their morphology and biosynthetic products they resembled smooth muscle cells and endothelial cells from blood vessel walls. In the "endothelial" cells, factor VIII-associated protein was demonstrated by indirect immunofluorescence. Synthesis of collagen types I and III, basement membrane collagen types IV and V, and fibronectin by both cell types was observed by immunofluorescence microscopy. Homogeneous cultures of "smooth muscle cells" were observed in subcultures. After incubation with [14C]glycine, collagen was isolated and characterized by CM cellulose chromatography, and consisted mainly of types I and III. These data suggest involvement of mesenchymal cells in hepatic fibrosis; they presumably originate from blood vessel or sinusoidal walls.

Secretory phenotypes of endothelial cells in culture: comparison of aortic, venous, capillary, and corneal endothelium

Endothelial cells from different tissues display variations in morphology, intercellular junctions, cell surface and growth properties, and in production of basal lamina components, both in vivo and in vitro. We have investigated the spectra of extracellular proteins secreted by bovine endothelial cells cultured from large vessels, cornea, and capillaries. Aortic, venous, and corneal endothelial cells displayed highly similar patterns of protein synthesis as judged by analysis of the culture medium; the major products were fibronectin, a glycoprotein similar or identical to platelet thrombospondin, and Type III procollagen. Ion-exchange chromatography, followed by peptide mapping, confirmed the presence of EC, a novel endothelial collagen previously described in bovine aortic endothelial cell cultures. Minor variations were found in the collagens of the cell layers: Type III, the predominant interstitial collagen, was associated with the basement membrane Types IV and V and, in the case of corneal endothelium, with Type I. In contrast, capillary endothelial cells secreted significantly more collagen than did the aortic, venous, and corneal cells. Approximately 50% of the protein in the culture medium was collagenous and consisted of Types I and III collagen in a ratio of 2:3. These interstitial collagens were the only types detected in capillary cell layers as well. The pattern and overall rate of collagen synthesis by capillary endothelial cells in vitro contrasted significantly with that of the other endothelial cell types and closely resembled that described for cultures of sprouting endothelium. These alterations in secretory phenotype may reflect: 1) a true difference in cell type between capillary and other types of endothelium, 2) differences resulting from cell isolation and initial culture conditions, or 3) a correlation between growth regulation and protein synthesis.

Analysis of the collagen types synthesized by bovine corneal endothelial cells in culture

Bovine corneal endothelial cells synthesize in culture predominantly type III collagen, with lesser amounts of types I and V and apparently little if any type IV. This pattern of synthesis is observed in both dividing and post-confluent cultures and irrespective of whether cells are attached to plastic or collagen-coated surface.

Characterization of cell matrix associated collagens synthesized by aortic endothelial cells in culture

Several collagen types have been isolated and characterized from bovine aortic endothelial cells and their associated extracellular matrix. Two collagens, which comigrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the alpha 1(III), alpha 1(V), and alpha 2(V) collagen chains, were isolated by salt precipitation from pepsin digests of cell layer proteins. Two of these chains were further purified by molecular-sieve and ion-exchange chromatography and were identified as alpha 1(III) and alpha 1(V) by one-dimensional peptide maps generated with mast cell protease and cyanogen bromide. In contrast to type III collagen, which was found in both the culture medium and cell layer, type V collagen appeared to be restricted to the cell layer. In addition to their occurrence as cell layer constituents, both types III and V collagens were localized to an extracellular matrix after the cells had been removed from the culture dishes by detergent. Preliminary studies based on peptide maps comparing type III collagen from the cell layer and culture medium provide evidence for structural heterogeneity within this collagen type.

The distribution of collagen types I, III and V (AB) in normal and atherosclerotic human aorta

Collagen of types I, III and V has been identified and localised in adult human aorta, coronary arteries and atherosclerotic plaques using an indirect immunofluorescent method with specific antibodies to human collagen antigens. The distribution of the three types of collagen was distinct. Type I collagen was found around smooth muscle cells in the aortic media and in large amounts in the atherosclerotic plaque. Type III collagen was found in dense deposits alongside the elastic laminae in the aortic media and in diffuse intimal thickening. In the aortic media, there appeared to be more type III collagen than type I. The reverse was true in advanced atherosclerotic plaques. Type V collagen was distributed throughout the extracellular matrix in the aortic media and in the subendothelial region of plaques. These findings confirm earlier biochemical studies and suggest that a major shift in the nature of collagen synthesis occurs within advanced atherosclerotic plaques.