Interaction of epithelial cells and fibroblasts in culture: effect on glycosaminoglycan levels

Atheroprotective effect of exogenous heparin-derivative treatment on the aortic disturbances and lipoprotein oxidation in hypercholesterolemic diet fed rats

BACKGROUND

The present work explores the myriad of biochemical and cellular changes that are featured in the early stages of atherosclerosis; if unchecked these changes lead to the complicated atherosclerotic plaque formation. The influence of a low-molecular-weight heparin derivative on the aortic aberrations and lipoprotein oxidation has been assessed in an experimental model of hypercholesterolemic atherogenesis.

METHODS

Two groups of male Wistar rats (140+/-10 g) were fed a hypercholesterolemic atherogenic diet (rat chow supplemented with 4% cholesterol, 1% cholic acid and 0.5% thiouracil; CCT diet) for 2 weeks; one of these groups received LMWH (Certoparin) treatment of 300 microg/day/rat, s.c. for 7 days. An untreated control and a LMWH drug control group were also included.

RESULTS

Abnormal increase in the aortic lipids -glycosaminoglycans levels (p<0.001) in CCT-diet fed group was circumvented by the exogenous glycosaminoglycan (LMWH) treatment (p<0.001). The escalation of oxidative stress (markers-lipid peroxidation and thiol levels, superoxide dismutase and catalase activities) in the atherogenic aorta was minimised by LMWH treatment. Further, an increased susceptibility of the apo B-containing lipoproteins (LDL+VLDL) to oxidation in vitro, induced by copper ions and Fenton's reagent, was observed in the untreated CCT diet fed group. This paper reports the favorable modulation of these oxidative changes by LMWH administration. Vascular protection by LMWH is further substantiated by the normal aortic histologic findings as against the appearance of foam cells in the untreated atherogenic group.

CONCLUSION

The exogenous heparin-derivative (LMWH) treatment attempted in this experimental model of hypercholesterolemic atherogenesis affords substantial protection against abnormal levels of aortic lipids and glycosaminoglycans, aortic oxidative stress and also stunts the lipoprotein peroxidative process, thereby proving its multi-faceted anti-atherogenic effects.

Functional characteristics of gingival and periodontal ligament fibroblasts

In periodontal surgery, healing after guided tissue regeneration (GTR) may be explained by differences in functional activities of gingival and periodontal ligament fibroblasts (GF and PDLF). Several studies in vitro have supported this hypothesis, but much remains to be defined. In the present work, gingival and periodontal ligament fibroblasts derived from five healthy subjects were isolated and compared in vitro. The morphology of the cells was observed under scanning electron microscopy (SEM). Several extracellular matrix components (ECM) were studied to compare the effects on fibroblast attachment, proliferation, and protein synthesis. Several biochemical markers were examined in both cellular extract (CE) and conditioned medium (CM). We also examined the muscle differentiation markers alpha-smooth muscle actin, desmin, and smooth-muscle myosin. Finally, we studied the effects of epithelial cells on the proliferation and protein synthesis of the two types of fibroblasts. GF and PDLF appeared identical under the SEM. All ECM components enhanced attachment; however, while collagen types I and IV promoted the attachment of GF, gelatin, laminin, and vitronectin promoted that of PDLF. Most ECM components increased the proliferation rate of GF and the biosynthetic activity of PDLF. The biochemical markers were similarly distributed between the two cell types, except for alkaline phosphatase, which was detected only in the CE of PDLF. Both GF and PDLF strongly expressed alpha-smooth-muscle actin and were negative for desmin; only PDLF were positive for smooth-muscle myosin. Epithelial cells increased the proliferation of both GF and PDLF but had no effect on their biosynthetic activity. These in vitro results may better explain the in vivo functional differences between GF and PDLF.

Development of the murine periodontium. II. Role of the epithelial root sheath in formation of the periodontal attachment

Experimental manipulation of the developing murine tooth germ has provided evidence that basement membrane components on the forming root surface are involved in early periodontal attachment formation. The purpose of this investigation was to determine the role of epithelial root sheath (ERS) cells in murine cementogenesis and periodontal ligament formation using tissue separation and recombination techniques. Root dentin specimens, with and without root-associated basement membrane components (D + RBM or D - RBM), were recombined with dental sac in the presence or absence of ERS. Recombinations were cultured for 2 weeks, harvested, and examined by light, electron, and immunofluorescence microscopy. Mineralized tissue formed in all tissue recombinations. However, when ERS was included in recombinations between D + RBM and dental sac, 25% of recombinations formed a periodontal ligament with fibrous attachment of the root specimen to adjacent bone. These results support the hypothesis that root and periodontal ligament formation is influenced by epithelio-mesenchymal interactions and further support a key role for ERS in these processes.

Epithelial cell-fibroblast interactions: modulation of extracellular matrix proteins in cultured oral cells

A model system involving co-cultures of human gingival or periodontal ligament fibroblasts with mouse epithelial root sheath cells or human gingival epithelial cells was used to study epithelial cell-fibroblast interactions. Double-labeled immunofluorescence and microfluorometry were used to investigate the expression of extracellular matrix molecules of collagen type I (collagen I), type III (collagen III) and fibronectin in fibroblasts. When fibroblasts from either source were cultured alone, the fluorescence for collagen I and fibronectin ranged from strongly positive to almost negative. Collagen III staining was relatively weak compared with that of collagen I. After 2-3 days of co-culture, gingival fibroblasts and ligament fibroblasts adjacent to the mouse sheath cells exhibited enhanced intracellular fluorescence for collagen I and fibronectin. Very little change was observed for collagen III. Gingival fibroblasts cultured with gingival epithelial cells showed increased fluorescence for collagen I but decreased fluorescence for fibronectin. In contrast, the fluorescence intensity for both collagen I and fibronectin in ligament fibroblasts were reduced after 3 days of co-culture with gingival epithelial cells. Ultrastructural changes in fibroblasts co-cultured with mouse root sheath cells included increased Golgi cisternae and vesicles and an increased abundance of rough endoplasmic reticulum, polyribosomes, secretory vesicles and pinocytotic vesicles. Thus, the expression of extracellular matrix proteins and the metabolic activity of fibroblasts can be modulated by oral epithelial cells.

Feeder cells impart a growth stimulus to recipient epithelial cells by direct contact

Mouse mammary epithelial cells have been shown to proliferate when cultured in the same vessel with lethally irradiated cells of the LA7 rat mammary tumor line. Presented here are experiments that indicate that the LA7 feeder cells stimulate growth of the normal mouse mammary cells by a mechanism that involves direct contact between the two cell types. It is possible that the LA7 feeder cells stimulate proliferation by secretion of a labile growth factor, by secretion of a soluble growth factor in such low concentrations that dilution by travel over a distance makes it less effective, that the stimulus is transduced directly through membrane receptors on the recipient epithelial cells, or that a growth message is sent through gap junctions between cells. This feeder cell system is proposed as an in vitro model for epithelial wound healing.

Neoplastic modulation of extracellular matrix: stimulation of chondroitin sulfate proteoglycan and hyaluronic acid synthesis in co-cultures of human colon carcinoma and smooth muscle cells

Previous studies have shown that human colon carcinomas contain elevated amounts of chondroitin sulfate proteoglycan (CS-PG) and hyaluronic acid, and that the major site of synthesis of these products is the host mesenchyme surrounding the tumor. These findings have led to the proposal that the abnormal formation of the tumor stroma is modulated by the neoplastic cells. The experiments of this paper were designed to explore further this complex phenomenon in an in vitro system using co-cultures of phenotypically stable human colon smooth muscle (SMC) and carcinoma cells (WiDr). The results showed a 3-5-fold stimulation of CS-PG and hyaluronic acid biosynthesis in the co-cultures as compared to the values predicted from the individual cell type cultured separately. The increase in CS-PG was not due to changes in specific activity of the precursor pool, but was rather due to a net increase in synthesis, inasmuch as it was associated with neither a stimulation of cell proliferation nor with an inhibition of intracellular breakdown. These biochemical changes were corroborated by ultrastructural studies which showed a marked deposition of proteoglycan granules in the co-cultures. Several lines of evidence indicated that the SMC were responsible for the overproduction of CS-PG: i) SMC synthesized primarily CS-PG when cultured alone, in contrast to the WiDr, which synthesized exclusively heparan sulfate proteoglycan; ii) only the SMC in co-culture stained with an antibody raised against the amino terminal peptide of a CS-PG (PG-40), structurally and immunologically related to that synthesized by the SMC; iii) the stimulation of CS-PG in SMC could be reproduced, though to a lesser extent, using medium conditioned by WiDr, whereas medium conditioned by SMC had no effects on WiDr. In conclusion this study has reproduced in vitro a tumor-associated matrix with a proteoglycan composition similar to that observed in vivo and provides further support to the concept that production of a proteoglycan-rich extracellular environment is regulated by specific tumor-host cell interactions.

The ectodermal control of mesodermal patterns of differentiation in the developing chick wing

The influence of limb ectoderm on the dorso-ventral muscle and skeletal patterns in the chick wing was studied by recombining stage 14-21 limb mesoderm with the same stage ectoderm in dorso-ventrally reversed orientation. Recombinants grafted to the flank of host embryos were allowed to develop for 10 days. Fully developed wings obtained from stage 15-21 donor embryos have at their distal half d-v polarity conforming to the reversed ectoderm and proximally polarity conforming with the mesoderm. The ectodermal effect is generally observed as a bidorsal feather pattern at the autopod and an almost complete d-v reversal of muscle and skeletal patterns. In experimental wings from donor embryos younger than stage 15, the dorso-ventral pattern conforms with the polarity of the limb mesoderm. The results suggest that control of dorso-ventral polarity resides in the mesoderm until the onset of limb development at stage 15. At this stage, the ectoderm acquires dorso-ventral information which it can impose on the mesoderm.

Stimulation of smooth muscle cell glycosaminoglycan synthesis by cultured endothelial cells is dependent on endothelial cell density

Smooth muscle cells (SMC) cultured in the presence of endothelial cells (EC), or in EC-conditioned medium, show increased synthesis of glycosaminoglycans (GAG). We have found that both the amount and type of GAG produced by the SMC are dependent on the density of the EC. EC (porcine) at a low density (0.1-0.5 X 10(6) cells/25 cm2), or their conditioned media, where the most active per cell in stimulating GAG. All GAG were stimulated but the increase was due mostly to hyaluronic acid (HA). At intermediate densities (1.0 X 10(6)/25 cm2) stimulation was markedly reduced, but still present, and both HA and sulphated GAG were similarly increased. At high densities (1.5-3 X 10(6)/25 cm2) where EC were confluent there was very little stimulation of HA but continued stimulation of sulphated GAG synthesis. The shift in stimulation from HA to sulphated GAG with increasing density was most clearly demonstrated by the decrease in the HA to the chondroitin sulphate ratio. These findings provide support for the general concept that SMC metabolism may be affected by changes in the state of the endothelium.

Somite chondrogenesis in vitro: 2. Changes in the hyaluronic acid synthesis

The role of hyaluronic acid in limb morphogenesis (chondrogenesis) has been well defined. In the present study, we found that hyaluronic acid synthesis in somite explants steadily increased until day 6, then decreased, and inclusion of notochord did not accelerate the rate of synthesis. Analysis of hyaluronidase activity in the somite explants indicated an increase in the enzyme level in day-6 cultures. Again, inclusion of notochord did not alter this pattern. The decrease in hyaluronic acid after day 6 and the increase in sulfated proteoglycan synthesis from day 6 resemble the pattern described during limb development. Subsequent studies showed that, with time, the size of the hyaluronic acid synthesized by somites increased and, again, inclusion of notochord did not influence this pattern. The results indicate that unstimulated somites are capable of synthesizing cartilage-specific proteoglycans in a relatively restricted manner, and the inclusion of notochord resulted in accelerated synthesis of stable proteoglycan aggregates typical of differentiated chondrocytes. Metabolic events in somites related to hyaluronic acid are not influenced by the notochord.

Altered glycosaminoglycan metabolism in injured arterial wall

Glycosaminoglycans (GAG) are believed to be important in the pathogenesis of atherosclerosis. We have previously demonstrated that areas of injured aorta that have been re-endothelialized accumulate increased amounts of lipid and GAG when compared to areas remaining de-endothelialized. We have now examined the net incorporation of labeled precursors into the individual GAG present in both re-endothelialized and de-endothelialized areas of rabbit aorta. Aortic tissue was examined at 2-3 and 10-14 weeks after a denuding injury by incubating tissue minces with [3H]glucosamine and sodium [35S]sulfate for 24 hr. Following incubation, the aortic GAG were isolated and assayed for uronic acid concentration and radioactivity. Results indicate that the total GAG concentration was significantly greater (P less than 0.001) in the re-endothelialized (9.46 +/- 0.29 micrograms/mg lipid-free dry residues (LFDR), mean +/- SE) as compared to de-endothelialized (7.89 +/- 0.43 micrograms/mg LFDR) areas. The concentration in uninjured aorta was 9.01 +/- 0.69. The difference between the injured tissues was attributable to increased concentrations of sulfated GAG. Hyaluronic acid and chondroitin sulfate were the most metabolically active of the GAG in either uninjured or injured aorta, together accounting for over 75% of the 3H label. The 3H specific radioactivities of the four GAG in the short-term, re-endothelialized subgroup were all increased nearly twice that found in uninjured and de-endothelialized tissues. With the exception of heparan sulfate, no significant differences were noted in the 3H specific radioactivities between the re-endothelialized and de-endothelialized areas in the long-term subgroup. These results indicate that, relative to adjacent areas of de-endothelialization, GAG preferentially accumulate in re-endothelialized areas even as early as 2-3 weeks following a denuding injury. Overall, metabolic data suggest that increased synthesis is responsible for this effect, although the net contribution of degradative processes cannot be overlooked since GAG turnover was not specifically examined. Thus, it is possible that regenerated endothelium may modify the GAG metabolism of the arterial wall following arterial injury.

Interactions between human tumor cells and fibroblasts stimulate hyaluronate synthesis

Several types of tumors contain high concentrations of hyaluronate, yet isolated tumor cells in culture often produce little glycosaminoglycan. To explore the possibility that interactions between tumor cells and host fibroblasts stimulate hyaluronate synthesis, human tumor cells were grown separately from and in coculture with normal human fibroblasts. Stimulation was observed with each of the three types of tumor cells used: LX-1 lung carcinoma, DAN pancreatic carcinoma, and TRIG melanoma. The interaction between LX-1 cells and fibroblasts was studied in detail. Under serum-free conditions, cocultures of LX-1 and fibroblasts synthesized 3-fold more hyaluronate than the sum of that produced by LX-1 and fibroblast cultures grown separately. This stimulation was linear over 72 hr and hyaluronate represented 80% of the glycosaminoglycan synthesized. Maximum stimulation occurred at a ratio of fibroblasts to LX-1 cells of 1-2:1. Quantitation of unlabeled glycosaminoglycans by HPLC analysis of disaccharides generated by digestion with chondroitin ABC and AC lyases (EC 4.2.2.4 and 4.2.2.5) demonstrated that net accumulation of hyaluronate increased 2-fold and that hyaluronate represented 80% of total chondroitinase-sensitive glycosaminoglycan produced by the cocultures. The disaccharide patterns obtained showed that accumulations of chondroitin-4- and chondroitin-6-sulfates were stimulated proportionately to that of hyaluronate in these cocultures. Similar levels of stimulation due to coculture were obtained in serum-containing and serum-free media. Stimulation was not effected by addition of LX-1-conditioned medium to fibroblast cultures or by culturing LX-1 and fibroblasts under conditions where they shared the same medium but were physically separated. Cell contact between LX-1 and fibroblasts thus appears to be necessary for the stimulation of hyaluronate synthesis.

Quantitation of cell proliferation, colony formation, and carcinogen induced cytotoxicity of rat tracheal epithelial cells grown in culture on 3T3 feeder layers

A cell culture system is described for the growth of rat tracheal epithelial (RTE) cells at clonal density. The system uses normal, early passage RTE cells grown on feeder layers of lethally irradiated 3T3 cells. The RTE cells have a high colony forming efficiency (5 to 10%) in culture, can be passaged up to 5 times, and are capable of more than 20 cumulative doublings per colony forming cell. The epithelial nature of the cells was confirmed by cell and colony morphology, immunoperoxidase staining of intracellular keratin, and cellular ultrastructural studies. The cytotoxic response of RTE cells to a variety of carcinogens, including a direct acting chemical carcinogen, a physical carcinogen, and a series of polycyclic aromatic hydrocarbons, was quantitated. A linear decrease in the logarithm of survival was observed with increasing doses of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), gamma-irradiation, 7,12-dimethylbenz(a)anthracene, and a diol-ep-oxide of benzo(a)pyrene. No toxicity was observed after treatment with benzo(a)pyrene or 3-methylcholanthrene over the concentration range examined. In contrast, phorbol ester tumor promoters stimulated cell growth markedly. Based on these and other studies, the RTE cell culture system represents a model system that will be useful for quantitative studies of epithelial cell growth, differentiation, and carcinogenesis.

Influence of collagen substrata on glycosaminoglycan production by B16 melanoma cells

A cloned metastatic murine melanoma cell line exhibited similar growth characteristics when propagated on either type I collagen, type IV collagen, or plastic. However, cells grown on both types of collagen exhibited an altered cellular morphology and on type IV collagen only, an increased substrate adhesiveness, relative to those maintained on a plastic substratum. Incorporation of [3H]glucosamine and [35S]sulfate into glycosaminoglycans (GAGs) of cells grown on collagen substrates was 20% and 40% less, respectively, than cells grown on plastic, whereas degradation of cell-associated [35S]sulfate-labeled GAGs was similar in cells grown on collagen or plastic. Although the composition of GAGs was similar in all cultures, consisting of approximately 60% chondroitin and 40% heparin or heparan sulfate, the degree of sulfation of the heparin or heparan sulfate molecules was markedly decreased in cultures grown on collagen. The results indicate that the composition of the extracellular matrix influences the biological behavior of B16 melanoma cells, in part by altering the amount and nature of the GAG molecules produced.

Effects of cells of epithelial rests of Malassez and endothelial cells on synthesis of glycosaminoglycans by periodontal ligament fibroblasts in vitro

Cultures of fibroblast-like cells (PLF) and epithelial rest cells (PLE) prepared from explants of porcine periodontal ligament synthesized and secreted four glycosaminoglycans (GAG) in differing proportions. The PLF produced predominantly chondroitin sulfate (greater than 60%) with smaller amounts of hyaluronic acid (HA) (17%), dermatan sulfate (13%), and heparan sulfate (7%), whereas PLE produced predominantly HA (greater than 80%). In coculture and under conditions of reciprocal transfer of conditioned media neither cell type affected the other's GAG synthesis. Endothelial cells (EC), however, or their conditioned growth media, were able to stimulate increased GAG synthesis, especially HA, in PLF. A similar result was obtained with smooth muscles cells (SMC) cultured in EC growth media but here again PLE were unable to stimulate GAG synthesis by SMC. These findings suggest that the spectrum of GAG found in whole ligament results both from independent production by, and from interaction between, the different cell types within the ligament. The results also provide support for a general hypothesis that loose connective tissues, which are rich in HA, are formed and maintained under the influence of epithelial, including endothelial, cells.

Hyaluronate and hyaluronidase in the developing chick embryo kidney

Changes in hyaluronate concentration and hyaluronidase activity were measured at progressive stages of chick embryo kidney development. Hyaluronate accumulates in the immature metanephros containing undifferentiated mesenchyme and early stages of tubular epithelium formation. Differentiation of the epithelium to mature tubules and renal corpuscles occurs over a period when hyaluronate concentrations are decreasing. The initial decrease in hyaluronate is accompanied by an increase in hyaluronidase activity in the metanephros. A similar peak of hyaluronidase activity was found to occur during mesonephros development. Chondroitin sulfate levels remain almost constant throughout the course of metanephric differentiation.

Morphological studies of synapses and varicosities in dissociated cell cultures of sympathetic neurons

Neurons dissociated from the superior cervical ganglia of newborn rats can be grown under conditions which support either adrenergic or cholinergic differentiation. In both cases, the neurons form numerous morphologically specialized synaptic terminals or synapses as well as relatively unspecialized varicosities. The ultrastructure of both types of terminal was compared in mature neuronal cultures and the effects of growth conditions on terminal morphology examined. After aldehyde-osmium fixation, synapses in cultures grown under adrenergic or cholinergic conditions were characterized by asymmetrical membrane specializations comparable to type I or asymmetric synapses; bismuth iodide and ethanolic phosphotungstic acid impregnation of neuronal cultures revealed the presence of characteristic synaptic membrane specializations: a presynaptic grid of dense projections and a wide postsynaptic dense band of uniform thickness. No membrane specializations were apparent in varicosities after aldehyde-osmium fixations or with these stains. Intramembranous particle distributions were examined in freeze-fracture replicas of neurons. Aggregates of large, 10-12 nm particles were found on P-face membrane leaflets of cell bodies and large diameter processes; this distribution is the same as that of synapses in thin-sectioned preparations. These particle aggregates may represent postsynaptic membrane specializations or acetylcholine receptors. The cytoplasmic leaflet of boutons contained large, 12-14 nm particles, which appeared to be concentrated at the region of synaptic contact at putative synapses, but were diffusely distributed in varicosity membranes. Similar large particles were also seen at a much lower density in the membrane E-face. None of these ultrastructural characteristics appeared to vary with transmitter identity or growth conditions. Synaptic vesicle shape, however, did vary in glutaraldehyde-fixed cultures. At all ages examined, neurons grown on monolayers of heart cells contained predominantly round vesicles, whereas neurons grown in the virtual absence of non-neuronal cells possessed pleiomorphic synaptic vesicles. This difference in vesicle shape appeared to be correlated more closely with growth in the presence of non-neuronal cells than with the transmitter present at the time of fixation.

A role for glycosaminoglycans in the development of collagen fibrils

Extensive data on the glycosaminoglycan (GAG) composition and the collagen fibril diameter distribution have been collected for a diverse range of connective tissues. It is shown that tissues with the smallest diameter collagen fibrils (mass-average diameter less than 60 nm) have high concentrations of hyaluronic acid and that tissues with the largest diameter collagen fibrils (mass-average diameter approximately 200 nm) have high concentrations of dermatan sulphate. It is suggested that the lateral growth of fibrils beyond a diameter of about 60 nm is inhibited by the presence of an excess of hyaluronic acid but that this inhibitory effect may be removed by an increasing concentration of chondroitin sulphate and/or dermatan sulphate. It is also postulated that high concentrations of chondroitin sulphate will inhibit fibril growth beyond a mass-average diameter of approximately 150 nm. Such an inhibition may in turn be removed by an increasing concentration of dermatan sulphate such that it becomes the dominant GAG present in the tissue.

Alterations in alveolar basement membranes during postnatal lung growth

We studied the ultrastructural characteristics of alveolar basement membranes (ABM) and capillary basement membranes (CBM) in rat lungs at birth, at 8-10 d of age, during alveolar formation, and at 6-10 wk of age, after most alveoli have formed. We also measured in vitro lung proteoglycan and heparan sulfate synthesis at each age. We noted three major age-related changes in pulmonary basement membranes. (a) Discontinuities in the ABM through which basilar cytoplasmic foot processes extend are present beneath alveolar type-2 cells but not alveolar type-1 cells. These discontinuities are most prevalent at birth but also exist in the adult. (b) Discontinuities are also present in CBM at the two earliest time points but are maximal at 8 d of age rather than at birth. Fusions between ABM and CBM are often absent at 8 d of age, but CBM and CBM/ABM fusions were complete in the adult. (c) Heparan sulfate proteoglycans identified with ruthenium red and selective enzyme degradation are distributed equally on epithelial and interstitial sides of the ABM lamina densa at birth, but decrease on the interstitial side with age. In vitro proteoglycan and heparan sulfate accumulation at birth was two times that at 8 d and five times that in the adult. Discontinuities in ABM allow epithelial-mesenchymal interactions that may influence type-2 cells cytodifferentiation. Discontinuities in CBM suggest that capillary proliferation and neovascularization are associated with alveolar formation at 8 d. When CBM becomes complete and forms junctions with ABM, lung neovascularization likely ends as does the ability to form new alveoli.

Interaction of aortic endothelial and smooth muscle cells in culture. Effect on glycosaminoglycan levels

Co-cultivation of various intra- and interspecific combinations of pig and rat aortic endothelial cells (AEC) and smooth muscle cells (SMC) resulted in a marked increase in hyaluronic acid (HA) levels, a smaller but significant increase in sulphated glycosaminoglycans (GAG), and an increase in the HA/sulphated GAG ratio, compared with the separate culture of the two cell types. Culture of SMC in AEC-conditioned medium produced similar changes in GAG levels whereas SMC-conditioned medium had no effect on AEC GAG levels. These results add further support for the concept that epithelial cells in general can modulate the GAG composition of adjacent connective tissue and thereby influence its morphological and physiological properties. It is suggested that the normal amounts, types and distribution of GAG in the arterial wall, and especially in the intima, may be partly dependent on interaction between the endothelium and SMC. It is further suggested that injury to endothelium, with a consequent failure in this interaction, could lead directly to changes in intimal GAG composition that contribute to lesion development.

Sulfated glycoproteins and extracellular matrix of cultured human pulmonary endothelial cells

Endothelial cells derived from human pulmonary arteries incorporate (3H)-glucosamine and 35SO4 into glycosaminoglycans and into the carbohydrate side chains of glycoproteins. These 3H/35S-carbohydrate chains were isolated from cells and culture medium after Pronase digestion. The 3H/35S-glycosaminoglycans were separated from the 3H/35S glycopeptides by chromatography on Sephadex G-50. The distribution of cellular glycosaminoglycans and glycopeptides indicated that 30-60% of the cellular 35S-glycopeptides may be associated with the matrix components that are synthesized by the cell and attached to a plastic substratum. Human pulmonary arterial endothelial cells were grown on collagen or on a matrix derived from vascular smooth muscle cells in order to investigate how smooth muscle cell extracellular matrix components may regulate the synthesis of endothelial cell glycoconjugates. Endothelial cells grown on plastic release various proportions of the glycoconjugates they synthesize into the culture medium. However, these same cells, when grown on substratum composed of extracellular matrix materials, synthesized altered proportions of cell-associated glycosaminoglycans and reduced the levels of total glycosaminoglycans they released into the culture medium. Thus the growth of endothelial cells on a matrix of smooth muscle cell components indicates that the glycosaminoglycan materials released into the culture medium by cells grown on a plastic substratum may not be an accurate reflection of the levels or composition of extracellular matrix materials made by endothelial cells in vivo.