Effect of thrombin on glycosaminoglycans in fibroblast cultures

Redox status of cultured fibroblasts. Possible relations with specific catabolic rates of proteoglycans

In cultured embyonic rat fibroblast the cytoplasmic NAD/NADH ratio was determined from the lactate/pyruvate ratio under acidic, hypoxic and lactic acid-rich conditions.

RESULTS AND CONCLUSIONS

The NAD/NADH ratio is reduced when the lactate concentration increases at pH 7.4 with and without hypoxia. At pH 6.6 this ratio is not reduced by lactate in normoxia: Conditions of aerobic glycolysis did not increase NADH. The NAD/NADH ratio was strongly lowered at pH 6.6 by lactate plus hypoxia. At low cell density this condition of hypoxic glycolysis is correlated with the increase of the specific activities of CS- and DS-proteoglycans (DS much greater than CS). But only the CS concentration was increased. Conditions of aerobic glycolysis at low cell density caused a moderate increase of both the specific activity and concentration of DS. The different regulation of the turnover of CS- and DS-proteoglycans is suggested to be based on their different synthetic capacities (CS greater than DS) on the one side and on the effect of specifically acting proteoglycanases on the other side. Maximal degradation of proteoglycans seems to be stimulated by NADH-activated proteases, supposedly thiol proteases. Lower degradation seems to be effectuated under non-reductive acidic conditions. Both these types of degradation seem stronger to affect DS-proteoglycan. Some neutral proteases seem stronger to affect CS-proteoglycan. Improved oxygen supply might reduce the CS concentration in proliferating tissue, such as in chronic inflammation, and thus reduce this process.

Type, location and role of glycosaminoglycans in cloned differentiated chick retinal pigmented epithelium

In clonal culture, colonies of 3-4 week old chick retinal pigmented epithelial cells exhibit Alcian Blue positive extracellular matrix (ECM) material on the surface of the cells. Alcian blue positive ECM is located between undifferentiated cells at the edges of the disc-shaped colonies and beneath the differentiated cells in the colony center. The latter material is associated with the basement membrane. The staining properties suggest that glycosaminoglycans (GAG) are present in these regions. Extraction of GAG from homogenates of colonies, followed by electrophoresis on cellulose acetate strips, results in three bands with mobilities similar to those of hyaluronic acid, heparan sulfate, and chondroitin sulfate, respectively. All three bands label with [3H]glucosamine, and the last two also label with [35S]sulfate. The composition appeared to differ when colonies were grown in different media. Digestion of the GAG preparations with various enzymes suggests that bands II and III represent heparan sulfate and chondroitin sulfate, respectively, in colonies grown in Ham's F10g medium. The composition of band I is as yet undetermined. In minimal Eagle's medium (MEM), bands I and III consisted of hyaluronic acid and chondroitin sulfate, respectively, while band II had properties suggestive of a copolymer of heparan sulfate and an unidentified GAG. Cells release only one [3H]glucosamine-labelled GAG into the medium. This material has a mobility similar to hyaluronic acid and is digested by Streptomyces hyaluronidase, suggesting that it is hyaluronic acid. Staining with Alcian Blue at different pH suggests that it may represent the material associated with the upper surface of the cells. Some of the ECM located between the undifferentiated cells and associated with the basement membrane in the differentiated regions of the colonies stains with Alcian Blue at pH 1.0 and 0.2 suggesting that it may contain GAGs found in bands I and II. Colonies treated with medium containing 6-diazo-5-oxo-L-norleucine (DON), an inhibitor of GAG synthesis, for 48 hr showed a reduced Alcian Blue staining of the ECM in the undifferentiated regions. After 72 hr of treatment with DON, the undifferentiated cells had detached from the plate, whereas the differentiated cells remained intact. The results suggest that the GAG may be involved in cellular adhesion, particularly of the undifferentiated cells.