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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 undersulf ation of glycosaminoglycans would result in decreased synthesis or increased turnover of certain proteoglycan subpopulations. Analysis of the glycosamino glycan 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.

An analytical protocol for the analysis of proteoglycans and proteins extracted from small sections of cartilage has been applied to the upper and lower parts of the epiphyseal growth plate of normal rats and rats with strontium-induced rickets. Only one polydisperse proteoglycan population was found in each of the four tissue portions. In strontium-induced rachitic animals the aggregability of proteoglycan monomers with hyaluronate was considerably increased in the lower part of the growth plate. The proteoglycans in the upper portion of the epiphysis contained somewhat less of chondroitin sulfate and keratan sulfate both in normal and strontium-induced rachitic rats. The chondroitin sulfate chains were somewhat larger in samples from strontiuminduced rachitic rats compared with controls while in all groups about 90 per cent of the galactosamine in chondroitin sulfate was sulfated at position four. The findings of an altered composition of proteoglycans in strontium-induced rickets demonstrate that strontium not only prevents the mineral growth but may also induce the chondrocytes to produce a matrix with a different macromolecular composition.

The composition of the weight bearing portion of the femoral head articular cartilage from both sides of greyhounds 11–32 months of age was studied with regard to variability of proteoglycans. Extractability of proteoglycans was very similar for all samples. Other parameters, i.e. contents of proteoglycans in the cartilage, hyaluronic acid content of the proteoglycan fraction, as well as contents of keratan sulfate and chondroitin sulfate, size of proteoglycans and ability of proteoglycans to aggregate with hyaluronic acid, were similar in samples from the right and left side of each dog. The variability from one dog to another was large and not related to age. The data show that in experimental studies of joint disease the contralateral joint can be used as a control to a treated joint, while the large interindividual variability makes comparison difficult between individuals.

The composition of proteoglycans and glycosaminoglycans in two portions of the rat epiphyseal growth cartilage in florid and healing low phosphate, vitamin D deficiency rickets was studied. The concentration of both chondroitin sulfate and keratan sulfate was reduced with about 25 per cent in the lower (mineralizing) part of the growth plate in healing rickets compared to the lower (hypertrophic) part in florid rickets. In all samples about 85 per cent of the chondroitin sulfate chains had a sulfate ester group in the fourth position. Both in florid and healing rickets only one main population of polydisperse proteoglycans was found. In florid rickets the capacity to form aggregates with hyaluronic acid was the same in the upper and lower parts of the growth plate. With the onset of mineralization in healing rickets, however, a substantial decrease in this aggregability was demonstrated. These results give further support to the hypothesis that proteoglycans and, especially, proteoglycan aggregates, play a role in the mineralization process.

Chondroprogenitor cells of newborn murine mandibular condyles were cultured on top of collagen sponges for up to 18 days. After 24 h in culture, new chondroblasts developed which subsequently matured showing signs of hypertrophy, while the extracellular matrix revealed positive reactivity for type II collagen, cartilage proteoglycans and mineralization. Light and electron microscopy examinations showed signs of new osteoid formation, a feature that was preceeded by positive immunohistochemical reaction for type I collagen, fibronectin and bone specific sialoprotein. A close temporal and spatial association was noted between the development of mature, mineralized cartilage and new osteoid. The differentiation of new cartilage and bone cells was linked to an increased activity of DNA synthesis and cellular proliferation. The de novo bone formation was accompanied by increasing rates of alkaline phosphatase activity and uptake of [ 45 Ca] features that were found to be tightly correlated to each other. The collagen substrata appeared also to facilitate the migration of cells, their replication and their subsequent differentiation to their respective cellular lineage. Hence, collagen sponges in vitro appear to serve as a promising substrata for culture systems involved with the growth and differentiation of mineralizing tissues such as cartilage and bone.

The influence of synovial fluid and serum from patients with inflammatory joint disease on proteoglycan metabolism was studied in organ culture of bovine nasal cartilage. Proteoglycan biosynthesis, i.e. incorporation of [35S]-sulphate, was reduced after addition of synovial fluid from rheumatoid arthritis and reactive arthritis patients. Also some rheumatoid arthritis sera but no reactive arthritis serum reduced the biosynthesis compared to control sera. Proteoglycan degradation, i.e. release of proteoglycans prelabelled with [35S]-sulphate, as well as release of proteoglycans determined by chemical methods, was highest under the influence of rheumatoid arthritis synovial fluid. This effect appears to represent an activity truly stimulating degradation, since added control serum did not prevent the effect. The lowest proteoglycan degradation was observed in culture medium only. Addition of synovial fluid compared to addition of control serum did not increase proteoglycan degradation in freeze-killed cartilage indicating that the effect requires living cells. The findings are consistent with the presence in synovial fluid of mediators stimulating the chondrocytes both to activate proteoglycan degradation and to reduce proteoglycan biosynthesis (Less)