Type X collagen, a product of hypertrophic chondrocytes

C. M. Kielty, A. P L Kwan, D. F. Holmes, S. L. Schor, M. E. Grant

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    The synthesis of collagen types IX and X by explants of chick-embryo cartilages was investigated. When sternal cartilage labelled for 24 h with [3H]proline was extracted with 4M-guanidinium chloride, up to 20% of the 3H-labelled collagen laid down in the tissue could be accounted for by the low-M(r) collagenous polypeptides (H and J chains) of type IX collagen; but no type X collagen could be detected. Explants of tibiotarsal and femoral cartilages were found to synthesize type IX collagen mainly in zones 1 and 2 of chondrocyte proliferation and elongation, whereas type X collagen was shown to be a product of the hypertrophic chondrocytes in zone 3. Pulse-chase experiments with tibiotarsal (zone-3) explants demonstrated a time-dependent conversion of type X procollagen into a smaller species whose polypeptides were of M(r) 49,000. The processed chains [α1(X) chains] were shown by peptide mapping techniques to share a common identity with the proα1(X) chains of M(r) 59,000. No evidence for processing of type IX collagen was obtained in analogous pulse-chase experiments with sternal tissue. When chondrocytes from tibiotarsal cartilage (zone 3) were cultured on plastic under standard conditions for 4-10 weeks they released large amounts of type X procollagen into the medium. However, 2M-MgCl2 extracts of the cell layer were found to contain mainly the processed collagen comprising α1(X) chains. The native type X procollagen purified from culture medium was shown by rotary shadowing to occur as a short rod-like molecule 148 nm in length with a terminal globular extension, whereas the processed species comprising α1(X) chains of M(r) 49,000 was detected by electron microscopy as the linear 148 nm segment.
    Original languageEnglish
    Pages (from-to)545-554
    Number of pages9
    JournalBiochemical Journal
    Issue number2
    Publication statusPublished - 1985


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