VARIATION WITH AGE IN THE PATTERN OF TYPE-X COLLAGEN EXPRESSION IN NORMAL AND SCOLIOTIC HUMAN INTERVERTEBRAL DISCS

The distribution and expression of type X collagen, a calcium-binding collagen, which is a marker of hypertrophic chondrocytes and thought t o be involved in cartilage calcification, was examined in situ in nond egenerate (grade I or II) human discs taken at autopsy over a wide age range (fetal->80 years) and also in scoliotic discs removed at surger y. In the fetal vertebral column, type X collagen was strongly express ed in the hypertrophic chondrocytes of the endplate, but was not seen in other areas. In the cartilaginous endplate of adults, it was found over the whole age range examined, with intensity increasing with age. In the disc matrix itself, type X collagen was demonstrated around in dividual cells from all individuals older than 50 years, but not in an y fetal or autopsy disc from individuals younger than 40 years. In sco liotic discs, however, focal type X collagen expression was seen in 3/ 8 patients younger than 40 years including one 12-year-old. No type X collagen was found in the outer annulus in any autopsy or scoliotic di sc, supporting the idea that cells of the outer annulus are phenotypic ally distinct from cells of the inner annulus and the nucleus. Our res ults demonstrate for the first time that type X collagen is a possible gene product of the intervertebral disc cells and a potential biochem ical component of the disc matrix. They indicate that with age or in s coliosis, some cells from the inner annulus or nucleus of the disc dif ferentiate to the hypertrophic chondrocyte phenotype. This might be th e initiating event for the abnormal calcification described in aged an d scoliotic discs in other studies.