The effects of acid glycosaminoglycans on neonatal calvarian cultures--a role of keratan sulfate in Morquio syndrome?

Morquio syndrome (mucopolysaccharidosis IV) presents with multiple bone dysplasia and is characterized by the inability to degrade keratan sulfate due to deficient N-acetylgalactosamine-6-sulfate sulfatase in Morquio A syndrome and deficient beta-D-galactosidase in Morquio B syndrome. The aim of our study was to investigate into the pathogenetic mechanism as it is not clear whether the accumulation of keratan sulfate is toxic for osteoblasts or inhibits osteoblast activity as e.g. bone resorption. The glycosaminoglycans keratan sulfate, heparan sulfate, dermatan sulfate, chondroitin-4,6-sulfate and hyaluronic acid were tested in rat neonatal calvarian cultures for their effects on bone resorption, osteoblast activity and toxicity. Bone resorption was evaluated by calcium release into the medium, osteoblast activity by the determination of alkaline phosphatase and toxicity by measuring lactate dehydrogenase in the culture media. Keratan sulfate had no effect on bone resorption but inhibited osteoblast activity at the low, nontoxic concentration of 10 ng per ml organ culture supernatant significantly (p<0.05). At a concentration of 100 ng per ml keratan sulfate revealed toxic effects as reflected by significantly (p<0.05) elevated lactate dehydrogenase activity. None of the other glycosaminoglycans inhibited osteoblast activities. Heparan sulfate showed at toxic levels (10 microg per ml supernatant) significantly increased bone resorption (p<0.05) accompanied by increased alkaline phosphatase activity. The specific keratan sulfate effects of inhibiting osteoblast activity and toxicity towards bone, which were never tested before, suggest a role for this glycosaminoglycan in the pathogenesis of bone dysplasia in Morquio syndrome.