BASEMENT-MEMBRANE COMPOSITION OF CARTILAGE CANALS DURING DEVELOPMENT AND OSSIFICATION OF THE EPIPHYSIS

Background: Cartilage canals are perichondral invaginations of blood v essels and connective tissue that are found within the epiphyses of mo st mammalian long bones. Functionally, they provide a means of transpo rt of nutrients to the hyaline cartilage, a mechanism for removal of m etabolic wastes, and a conduit for stem cells that are capable of init iating and sustaining ossification of the chondroepiphysis. Morphologi cal and biomolecular changes of the chondroepiphyses appear to potenti ate vascular invasion and enable regional formation of secondary cente rs of ossification within the chondroepiphyses of developing bones. Me thods: As both cell migration and vascular invasion are anchorage depe ndent processes, antibodies to laminin and Type IV collagen were used to assess compositional changes in the basement membrane of cartilage canals accompanying epiphyseal ossification. Results: Differences in c hronological appearance, as well as, in distribution between the two c omponents were noted in the chondroepiphysis. Laminin was distributed throughout the connective tissue of cartilage canal at all stages of d evelopment, and not limited to an association with the vascular lumen. Type IV collagen was not present during the initial perichondral inva gination. Although staining for Type IV collagen was later acquired, i ts distribution was restricted to a discontinuous rimming of the perip hery of the canal, and a diffuse presence within the intra-canalicular mesenchyme. Conclusions: Concurrent with chondrocyte hypertrophy and mineralization of the hyaline matrix, rapid changes in both the morpho logy of the vessel and distribution of the antibodies were detected. I n addition to the presence of laminin at the interface of the endothel ium and the hyaline matrix, a wide distribution within the connective tissue components of the newly ossifying matrix of epiphyseal bone cou ld be detected. Type IV collagen remained closely associated with the lumens of the intra-canalicular vessels throughout the transition. Fol lowing ossification of the secondary center, staining for Type IV coll agen could then be detected in the bone-forming regions of transformin g matrix as well, clearly delineating the individual vessels within th e newly formed marrow spaces. This suggests that bone formation is int imately related to vessel staining for collagen type IV, and that acqu ired vessel competence is a facet of endochondral bone formation that results from provisional matrix changes. Furthermore, the data suggest s that during bone formation under tension, basement membrane depositi on can be demonstrated without an intermediary hyaline matrix hypertro phic chondrocyte phase. This data was interpreted to suggest that chon drocyte hypertrophy at the growth plate may be a reaction to vascular invasion, that in turn, stimulates adjacent chondrocyte proliferation. (C) 1995 Wiley-Liss, Inc.