Localization of the expression of type I, II and III collagen genes in human normal and hypochondrogenesis cartilage canals.

The expression of type I, II and III collagens genes was examined in human normal and hypochondrogenesis cartilage canals employing electrophoretic analysis, immunohistochemistry and in situ hybridization techniques. In normal cartilage, collagens type I and III were present in perichondrium, in the connective tissue surrounding the vessels of cartilage canals and in the dense fibrous tissue. However, types I and III procollagen mRNAs were detected only in fibroblasts of the perichondrium and of the canals, but not in the polymorphic cells. Type II collagen was present in the cartilage matrix and in the dense fibrous tissue, in good accordance with the localization of type II procollagen mRNAs detected in the chondrocytes and in the polymorphic cells. These data suggest that there are no transitional cells expressing type I, II and III collagen genes and that polymorphic cells are of chondrocytic origin. In the case of hypochondrogenesis, type II collagen was less abundant than in normal cartilage, whereas the corresponding mRNA level was equivalent. That suggests that a postranscriptional regulation of this protein is involved in the decrease of type II collagen production. Type I collagen, unexpectedly detected in the cartilage matrix, was synthesized by chondrocytes and polymorphic cells, suggesting a replacement of type II by type I collagen. The canal hypertrophy observed in this pathological case could thus be due to a modification in the regulation of the growth of cartilage canals caused by a defective cartilage matrix.