Running Exercise as a Modulator of Proteoglycan Matrix in the Articular Cartilage of Young Rabbits

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Abstract
Proteoglycans (PGs) and collagen were quantified in the knee articular cartilages of femoral and tibial medial condyles following 1-8 weeks of moderate running exercise of 4- to 6-month-old rabbits. The total content of PGs extractable with 4 mol/l guanidinium chloride was elevated in the weight-bearing cartilage of the tibial medial condyle, while their concentration, expressed as uronic acid per wet weight, and collagen remained unchanged. The content of glucosamine (GIcN) and its ratio to galactosamine (GaIN) was elevated in femoral cartilage PGs purified by centrifugation in dissociative CsCI gradients, indicating an increase in keratan sulfate. After 8 weeks of running, the chondroitin sulfate chains of PGs from tibial medial condyle contained less unsulfated disaccharide units. The content of chondroitin sulfate was elevated in the nonextractable residue of the tibial medial condyle as indicated by uronic acid and GaN assays. The content of nonextractable GIcN was increased even more, both in tibial medial and femoral cartilages. Moderate running thus increased (1) keratan sulfate-rich PGs, (2) the degree of sulfation of the chondroitin sulfate chains, and (3) nonextractable PGs; these modulatory alterations probably enhance the stability and elastic stiffness of the PG matrix.