Type X collagen is not localized in hypertrophic or calcified cartilage in the developing rat trachea

Our previous studies have shown that rat tracheal chondrocytes become larger and hypertrophic, and that the cartilage matrix calcifies during development. Type X collagen is a short collagen molecule identified in hypertrophic and calcified cartilage in the growth plate of long bones during endochondral ossification. The present study was designed to investigate the distribution of type X collagen in rat tracheal cartilage during development before and after hypertrophization and calcification. Tracheas from postnatal Wistar rats, newborn, and at 4, 8 and 10 weeks were fixed along with hind limbs from newborn rats. Serial sections were made and adjacent sections were processed for von Kossa staining or immunohistochemistry for type X collagen. In addition, the immunoreactivity to type II collagen was examined as a control. The anti-type X collagen antibody stained hypertrophic and/or calcified cartilage in the newborn rat tibia. The immunoreaction for type X collagen was localized in the uncalcified peripheral region of tracheal cartilage in 4, 8 and 10-week-old rats. In contrast, the anti-type X collagen antibody did not show immunoreactivity to hypertrophic or calcified cartilage in the central region of the 10-week-old rat tracheal cartilage. The present study has suggested that type X collagen is not involved in hypertrophization of chondrocytes or calcification of the matrix in developing rat tracheal cartilage.