Metabolism of sulfated glycosaminoglycans in cultivated bovine arterial cells. I. Characterization of different pools of sulfated glycosaminoglycans

"Fibroblast-like" cells from the intimal layer of bovine aorta were grown in culture. The formation, composition, molecular weight and turnover rate of different pools of glycosaminoglycans were investigated in cultures incubated in the presence [35S]sulfate or [14C]glucosamine. The newly synthesized glycosaminoglycans are distributed into an extracellular pool (37 - 58%), a cell-membrane associated or pericellular pool (23 - 33%), and an intracellular pool (19 - 30%), each pool exhibiting a characteristic distribution pattern of chondroitin sulfate, dermatan sulfate, heparan sulfate and hyaluronate. The distribution pattern of the extracellular glycosaminoglycans resembles closely that found in bovine aorta. A small subfraction of the pericellular pool - tentatively named "undercellular" pool--has been characterized by its high heparan sulfate content. The intracellular and pericellular [35S]glycosaminoglycan pools reach a constant radioactivity after 8-12 h and 24 h, respectively, whereas the extracellular [35S]glycosaminoglycans are secreted into the medium at a linear rate over a period of at least 6 days. The intracellular glycosaminoglycans are mainly in the process of degradation, as indicated by their low molecular weight and by their half-life of 7 h, but intracellular dermatan sulfate is degraded more rapidly (half-life 4-5 h) than intracellular chondroitin sulfate and heparan sulfate (half-life 7-8 h). Glycosaminoglycans leave the pericellular pool with a half-life of 12-14 h by 2 different routes: about 60% disappear as macromolecules into the culture medium, and the remainder is pinocytosed and degraded to a large extent. Extracellular and at least a part of the pericellular glycosaminoglycans are proteoglycans. Even under dissociative conditions (4M guanidinium chloride) their hydrodynamic volume is sufficient for partial exclusion from Sepharose 4B gel. The existence of topographically distinct glycosaminoglycan pools with varying metabolic characteristics and differing accessibility for degradation requiresa reconsideration and a more reserved interpretation of results concerning the turnover rates of glycosaminoglycans as determined in arterial tissue.

Evidence for different glycohydrolase and glycosyltransferase activities of beta-N-acetylglucosaminidases A and B

1) Two forms of beta-N-acetylglucosaminidase--known as form A and form B - were purified from bovine spleen homogenates and efficaciously separated by preparative disc electrophoresis on polyacrylamide gel. Studies on the enzymatic specificity revealed that the two forms have different glycoside hydrolase and glycosyl transferase activities towards substrates of natural origin. 2) With the trisaccharide GlcNAc-GlcUA-GlcNAc from hyaluronate as substrate, form A released free N-acetylglucosamine at a rate 35-40 times higher than form B. The B form, however, transferred N-acetyl-[6-3H]glucosamine from phenyl-beta-N-acetyl-D[6-3H]glucosaminide to the tetrasaccharides GlcUA-GalNAc-4-sulfate-GlcUA--GalNAc-4-sulfate or GlcUA-GlcNAc-GlcUA-GlcNAc isolated from chondroitin 4-sulfate or hyaluronate at rates 5-10 times higher than beta-N-acetyl-glucosaminidase A, the corresponding 3H-pentasaccharides being isolated as reaction products. 3) The pH optimum of the glycoside hydrolase activity is 4.5, while optimum glycosyl transfer proceeds at pH 6.5. Under condition optimum for glycoside transferase, hydrolytic activity is still observed with each form, but the B form exhibits about equal glycoside hydrolase and glycoside transferase activity, whereas the A form has a predominant glycoside hydrolase action.

¹⁴C and ³⁵S-SO₄ Metabolism of Acid Glycosaminoglycans in Bovine Heart Valves

Bovine heart valves metabolize up to 96% of exogenous ¹⁴C-glucose to lactate when incubated <i>in vitro </i>under appropriate conditions. Small proportions of the ¹⁴C-radioactivity are incorporated into glycogen, glycosaminoglycans and lipids and are oxydized to ¹⁴CO₂. Difference between the valves of the left ventricle (aortic and mitral valve) and of the right ventricle (pulmonary and tricuspid valve) were found in the rate of glycolysis as well as in the collagen, glycogen and glycosaminoglycan content. The <i>in vitro</i> incorporation of [U-¹⁴C] glucose radioactivity into the total glycosaminoglycans resulted in a specific labelling of hyaluronic acid, dermatan sulfate and chondroitin sulfate, but the specific radioactivities of the individual glycosaminoglycans and their relative rates of biosynthesis differed markedly. The relative rates of biosynthesis were 2.9–7.6 for hyaluronate, 1.0 for dermatan sulfate and 0.26–0.59 for chondroitin sulfate. After labelling the sulfated glycosaminoglycans with ³⁵S-sulfate, the metabolic heterogeneity of dermatan sulfate and chondroitin sulfate was confirmed, but, in addition, heparan sulfate – not previously detected in heart valves – was identified as a third sulfated glycosaminoglycan. Chemical analyses of heparan sulfate revealed a sulfate/uronic ratio of 0.5; its relative amount was found to be 2–4% of the total glycosaminoglycans. Analogous chemical and metabolic data were obtained with chordae tendineae, except that a higher relative percentage of dermatan sulfate was found than in the corresponding heart valves.

Comparative studies on the chemistry and the metabolism of arterial and venous tissue

Comparative studies of the chemistry and metabolism of human and bovine arterial and venous tissue had the following results (values for bovine tissue in parenthesis): 1. In arterial tissue the contents of collagen were 21% (37%) and of elastin 20% (31%) referred to the dry weight. In veins collagen amounted to 47% (30%) and elastin to 7% (18%). The mucopolysaccharide concentration was higher in arterial (1.2 and 1.5 resp.) than in venous tissue (0.4 and 0.2% resp.). Hyaluronate, chondroitin 6-sulphate (chondroitin 4-sulphate), dermatan sulphate and heparan sulphate were identified. In arterial tissue chondroitin sulphate was predominant with 59 % and 49 % resp. In human venous tissue the main component was dermatan sulphate (65%), in bovine veins it was hyaluronate (75%). No dermatan sulphate was found in bovine venous tissue. The number of cells was higher in arteries (4.5 × 10⁷ nuclei/g w. wt.) than in veins (2.8 × 10⁷). 2. On in vitro incubation bovine arterial tissue metabolized 73 %, venous tissue 32% of the added [U-^I4C] glucose within 12 h. In this period 2.8 and 2.4 mg lactate resp./g wet tissue were formed by arteries and veins. The specific radioactivity of lactate synthesized in arterial tissue reached that of the added [U-^I4C] glucose whereas lactate formed by veins had only 36 % of the specific activity of the [U-^I4C] glucose. The specific radioactivity of the acid mucopolysaccharides was 5–6 times higher in venous tissue than in arterial tissue. After labelling with ³⁵S-sulphate a 3-fold higher specific radioactivity of venous sulphated mucopolysaccharides was observed. 3. After incubation of bovine venous tissue in the presence of ^I4C-acetate the specific radioactivity of phospholipids was 45 % higher than that of arterial tissue in contrast to a 50 % lower labelling of cholesterol in venous tissue.