Studies on proteoglycans obtained from bovine knee joint and ear cartilages: sequential extraction, fractionation, characterization and their effects on fibril formation

Extracellular matrix composition of different regions of the knee joint cartilage in cattle

Articular cartilage covering the bone ends at the joint shows different chemical composition in different regions, depending on the mechanical and biological properties of that region. Several studies have shown a relationship between the chemical composition of the cartilage and biomechanical forces. In the present study we analysed five different knee joints divided into the following regions: F1-medial and lateral border of the patellar surface, F2-patellar surface of the femur, F3-medial and lateral condyles, P-articular surface of the patella and T-medial and lateral condyle of the tibia. The main glycosaminoglycan (GAG) present in these regions was chondroitin sulfate. Analysis of total GAG after digestion of the tissue with papain showed that in F2 and F3 there was a larger quantity of GAG/mg tissue, probably due to the dynamic character of the biomechanical forces in these regions. No significant differences were found for the extract and D1 fractions of the different regions. Analysis of the D4 fraction showed that the protein content was higher in the F3 and P regions than in their opposite T and F2 regions. The differences among the five regions may be a result of the non-uniform presence of biomechanical forces supported by these regions. It is important to consider that the intensity and direction of stress in different parts of a tissue may influence the composition of the extracellular matrix.

Normally sulphated and highly sulphated glycosaminoglycans (GAG) affecting fibrillogenesis of type I and type II collagen in vitro

Proteoglycans (PG) and glycosaminoglycans (GAG) influence the aggregation of collagen molecules during fibrillogenesis and the ultimate fibril width. The current in vitro experiments suggest that collagen type II may interact more strongly with highly sulphated GAG than type I collagen. Electron microscopic investigations indicate that, after addition of highly sulphated GAG, the fibrils of type II collagen become significantly (p less than 0.001) thicker than fibrils of a control experiment.

The formation and thermal stability of in vitro assembled fibrils from acid-soluble and pepsin-treated collagens

The role of the non-helical regions of the collagen molecule in fibrillogenesis has been investigated by comparing the kinetics of fibril formation of pepsin-treated acid-soluble collagen, acid-soluble collagen and mixtures of the two and by comparison of the thermal stabilities of the fibrils formed. The acid-soluble collagen was found to aggregate more rapidly than the pepsin-treated collagen under physiological conditions of pH and ionic strength. Variations in ionic strength, at physiological pH, were found to have differing effects on the aggregation of these two forms of soluble collagen. Fibrils formed from the pepsinized-collagen had a lower thermal stability tha n those formed from the intact collagen. The behavior observed with mixtures of acid-soluble and pepsin-treated collagens was found to be quantitatively consistent with the pepsinized collagen being able to utilize the nuclei formed by the acid-soluble collagen for subsequent growth. However, the use of the acid-soluble nuclei by the pepsinized collagen for growth did not enhance its rate of precipitation during the growth phase, nor did it enhance the thermal stability of the fibrils formed from the pepsinized collagen.

Changes with age in the glycosaminoglycans of human articular cartilage

Human articular cartilage was obtained post mortem from the lateral femoral condyles of 30 subjects aged from under 1 to 70 years. Cryostat sections taken 0--100 micrometers and 900--100 micrometers deep to the cartilage surface were exhaustively extracted to recover the glycosaminoglycans (GAG). After fractionation by cellulose acetate electrophoresis and enzyme depolymerisation individual GAG were determined by alcian blue -0.05 M MgCl2 and disaccharide microassay procedures. Changes with age were observed in GAG concentration and in the proportion of individual GAG. Large alterations occurred during the period of skeletal growth (0--16y). At birth GAG formed about 50% of the dry weight of cartilage, a value that decreased to about 15% in adult cartilage. Chondroitin sulphates (ChS) formed the principal GAG of articular cartilage and accounted for almost all of the GAG of the infant material. The ChS decreased with age and were partially replaced by keratan sulphate (KS), so the KS eventually comprised 12% of the GAG. Hyaluronic acid (HA) was identified and was found to increase linearly with age to form 6% by weight of the cartilage GAG by 60y.