The role of proteoglycans in ossification of spinal ligaments

Proteoglycans (PGs) are considered to have important functions that influence the properties of the extracellular matrix. In this study, PGs were purified from human yellow ligaments by ion-exchange and gel-filtration chromatography. Age-related changes in PG and glycosaminoglycan (GAG) chains were studied using specimens obtained from patients divided into four age groups. Small PGs were present in similar amounts in all groups. Conversely, large PGs increased with aging. GAG in large PGs mainly consisted of chondroitin 6-sulfate (Ch6S), whereas in small PGs, it mainly consisted of dermatan sulfate (DS), although the ratio of Ch6S increased with aging. The major components of GAG chains in normal and ossified yellow ligaments were DS and ChS, respectively. Also, the affinity of high-performance liquid chromatography (HPLC) on hydroxyapatite columns showed that DS chains bound to the hydroxyapatite more strongly than ChS chains. These results indicate that the change from DS to ChS is important in age-related changes and ossification of the ligaments, because ChS chains, which have a lower affinity for hydroxyapatite, might contribute to facilitation of the crystallization of hydroxyapatite.