Abnormalities in the Biosynthesis of Cartilage and Bone Proteoglycans in Experimental Diabetes

Proteoglycans synthesized in developing cartilage and bone were investigated in control and streptozotocininduced (65 mg/kg, i.v.) diabetic rats. Ten days after streptozotocin injection, animals were implanted subcutaneously with demineralized bone matrix particles. This system induces formation of cartilage and bone on days 7 and 14, respectively. Two hours before they were killed, animals were injected with ³⁵SO₄ and the labeled proteoglycans were extracted from the explants and metaphyses by either a direct associative extraction (0.5 M GuCl₂) or a direct dissociative extraction (4.0 M GuCl₂). These procedures extract 80–90% of the total counts incorporated. To characterize the proteoglycans, extracts were subjected to cesium chloride density gradient centrifugation and molecular sieve chromatography. These data showed that (1) there is less proteoglycan made in diabetic bone; (2) the proteoglycan aggregate is of a smaller molecular weight in bone than in cartilage; (3) 10% of the proteoglycan synthesized in diabetic bone was in the form of aggregates compared with 48% of the control bone; (4) aggregates did form in the diabetic cartilage, and their molecular weight was smaller than in normal cartilage. This investigation shows that proteoglycans, structurally important macromolecules of cartilage and bone, are altered in experimental diabetes. This metabolic abnormality may be an important factor contributing to decreased bone formation observed in diabetes.