Proteoglycans and glycosaminoglycans in cartilage from the brachymorphic (bm/bm) mouse

The brachymorphic (bm/bm) mouse is a disproportionate dwarf with a disturbance of the endochondral growth of the skeleton. Rib cartilage from 25-day-old affected animals and their normal siblings was analyzed for its contents and composition of proteoglycans. In addition to the previously reported undersulfation of chondroitin sulfate, it was demonstrated that one of the two types of aggregating proteoglycan and possibly the small ones are decreased in bm/bm costal cartilage, both in the growth region and in the remaining part. The molecular defect of the bm/bm condition is known to affect the synthesis of 3-phosphoadenosine 5-phosphosulfate (Sugahara and Schwartz, Proc. Natl. Acad. Sci. USA 76: 6615-6618, 1979). The above finding therefore suggests the existence of feedback mechanisms for the regulation of proteoglycan synthesis, whereby the undersulfation of glycosaminoglycans would result in decreased synthesis or increased turnover of certain proteoglycan subpopulations. Analysis of the glycosaminoglycan side chains indicated that mouse rib cartilage contains small amounts of keratan sulfate of extremely small size. The affected and control tissues, however, seemed to contain equal amounts of both glucosamine and galactosamine.