Age-related changes in glycosaminoglycan distribution in different anatomical sites on the surface of knee-joint articular cartilage in young rabbits

Articular cartilage in the knee joint of the African elephant, Loxodonta africana, Blumenbach 1797

Knee joints of one adult and three juvenile African elephants were dissected. The specific features of the articular cartilage with particular reference to matrix components were studied by light and electron microscopy and immunohistochemistry. The elephant knee joint cartilage contains an unusually low concentration of proteoglycans resulting in rather eosinophilic staining properties of the matrix. The very thick collagen fibers of the cartilage possibly represent collagen I. Except for the different thickness of cartilage at the weight-bearing surfaces of femur (approximately 6.7 mm) and tibia (approximately 11.2 mm) in juvenile elephants, light and electron microscopy did not reveal distinct topographical differences in cartilage structure, perhaps because of the high congruency of the articulating surfaces and resulting uniform load distribution in the knee. The number of cell profiles per section area of both femoral (approximately 950 cell profiles/mm(2)) and tibial cartilage (approximately 898 cell profiles/mm(2)) was low, indicating excessive matrix production by the chondrocytes during cartilage development. These unique properties could be a result of the enormous compressive load resting on the elephant knee. Maintenance of the equilibrium between biological function and resistance to compression seems to be crucial in the elephant knee joint cartilage. Any disturbance that interferes with this equilibrium appears to lead to arthrotic alterations, as particularly seen in captive elephants.

Distribution of small proteoglycans and glycosaminoglycans in humerus-related articular cartilage of chickens

The expression of components present in the cartilaginous extracellular matrix is related to development, gender, and genotype, as well as to the biomechanical properties of each type of cartilage. In the present study, we analyzed small proteoglycans and glycosaminoglycans present in different cartilages of the chicken wing after extraction with guanidine hydrochloride or papain. Quantitative analysis of glycosaminoglycans showed a larger amount in humeral cartilage (around 200 mg/g tissue) than in articular cartilage of the radius and ulna, with 138 and 80 mg/g tissue, respectively. Non-collagenous proteins isolated were predominantly from cartilage in the proximal regions of the humerus and radius. D4 fractions obtained by ultracentrifugation were separated by DEAE-Sephacel and Octyl-Sepharose chromatography and analyzed by SDS-PAGE. Two bands of 57 and 70-90 kDa were observed for all samples treated with beta-mercaptoethanol. Immunoblotting of these proteins was positive for the small proteoglycans fibromodulin and decorin, respectively. Apparently, the 57-kDa protein is present in macromolecular complexes of 160 and 200 kDa. Chondroitin sulfate was detected in all regions. HPLC analysis of the products formed by chondroitinase AC and ABC digestion mainly revealed beta-D-glucuronic acid and N-acetyl beta-D-galactosamine residues. The 4-sulfation/6-sulfation ratio was close to 3, except for the proximal cartilage of the radius (2.5). These results suggest functional differences between the scapula-humerus, humerus-ulna, and humerus-radius joints of the chicken wing. This study contributes to the understanding of the physiology of cartilage and joints of birds under different types of mechanical stress.

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.