The effect of bacterial lipopolysaccharides on the biosynthesis and release of proteoglycans from calf articular cartilage cultures

Abstract

Organ cultures of bovine articular cartilage from metacarpophalangeal joints of calf maintain steady state metabolism of cartilage proteoglycans over the course of several weeks. Bacterial lipopolysaccharides (LPS) depress biosynthesis of proteoglycans in such cultures to approximately 60% of control values after 1-2 days of treatment. A glycolipid from the Salmonella minnesota Re 595 mutant, which lacks the polysaccharide chains of LPS, also depresses proteoglycan synthesis. If LPS is removed from the medium as late as after 12 days of exposure, proteoglycan synthesis returns to control values. Proteoglycans synthesized during the first week of LPS treatment are indistinguishable from those synthesized by control cultures in terms of their hydrodynamic size and the relative amounts of disaccharides released by chondroitin lyase ABC digestion of their glycosaminoglycan chains. However, after 15-18 days of treatment, significant proportions of a smaller proteoglycan are synthesized. For cultures prelabeled with [35S]sulfate, the rate of release of 35S-labeled proteoglycans from the matrix is accelerated approximately 2-fold over control during the first week of LPS treatment. This effect is completely reversed upon removal of LPS from the medium. For cultures prelabeled with [35S]sulfate, approximately 40 and 90% of the 35S-labeled proteoglycans are lost from the matrix after 18 days in control and LPS-treated cultures, respectively. The labeled proteoglycans remaining in the matrix of the control after 18 days were indistinguishable from newly synthesized proteoglycans in terms of hydrodynamic size as were those in 7-day LPS-treated cultures when approximately 40% of the labeled proteoglycans had been lost. Even after 18 days of LPS treatment, more than 60% of the remaining labeled molecules were unchanged. LPS stimulates prostaglandin E2 synthesis in these cultures while indomethacin in the presence of LPS blocks synthesis. However, indomethacin did not alter the metabolism of proteoglycans in either control or LPS-treated cultures, indicating that prostaglandins are not directly involved in regulating proteoglycan metabolism in this system.