GROWTH PLATE STUDIES IN THE CHONDRODYSTROPHIES

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The chondrodystrophies (CDX) are a heterogeneous group of disorders of endochondral bone growth that are characterized clinically by shortening and deformities of the limbs and trunk. The delineation of the pathogenetic mechanisms responsible for the disorders would be highly desirable because not only would it lead to definitive therapy for the CDX, but it would provide valuable insights into the causes of skeletal deformities in general as well as normal bone growth. Unfortunately, the understanding of the abnormalities in the CDX has been hampered by a variety of problems primarily related to obtaining and investigating the affected tissue, the skeletal growth plate. Addressing these problems, the proposed investigator has developed an approach tailored to studying these disorders. It involves the use of highly specific histochemistry to localize matrix constituents in plastic embedded tissues combined with biochemical analysis of extremely small samples of cartilage. Preliminary studies have demonstrated its potential value as a means to probe the growth plate as a dynamic structure. It is now proposed to expand this approach to systematically and comprehensively examine endochondral ossification in growth plate tissue from normal control and CDX patients. The tissue will be studied by light and electron microscopic immune and lectin histochemistry, autoradiography, and in situ hybridization. Monoclonal antibodies to matrix components: types I-VI, IX (G), X (M), and 1Alpha, 2Alpha, 3Alpha collagens; chondroitin-4- and -6- sulfate, keratan sulfate and hyaluronic acid binding region substructures of cartilage proteoglycan; link protein; fibronectin; and cDNA probes to specific skeletal procollagen mRNAs will be employed. To biochemically confirm the microscopic observations, microsamples of the cartilages corresponding to different stages of chondrocyte proliferation and differentiation will be studied in organ culture by HPLC and SDS-PAGE methods to determine the presence of and relative proportions of isotopically labeled major and minor collagens and glycosaminoglycans in newly synthesized matrix. These studies should permit an accurate representation of the events of normal endochondral ossification to be constructed and defects therein to be identified.