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 durin g development. Type X collagen is a short collagen molecule identified in hypertrophic and calcified cartilage in the growth plate of long b ones during endochondral ossification. The present study was designed to investigate the distribution of type X collagen in rat tracheal car tilage during development before and after hypertrophization and calci fication. Tracheas from postnatal Wistar rats, newborn, and at 4, 8 an d 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 a nti-type X collagen antibody stained hypertrophic and/or calcified car tilage in the newborn rat tibia. The immunoreaction for type X collage n was localized in the uncalcified peripheral region of tracheal carti lage in 4, 8 and 10-week-old rats. In contrast, the anti-type X collag en antibody did not show immunoreactivity to hypertrophic or calcified cartilage in the central region of the 10-week-old rat tracheal carti lage. The present study has suggested that type X collagen is not invo lved in hypertrophization of chondrocytes or calcification of the matr ix in developing rat tracheal cartilage.