Age-dependent changes on the state of aggregation of cartilage matrix

The state of aggregation of cartilage matrix and its variations with age have been studied by biochemical, cytochemical, and ultrastructural methods. Determination of proteoglycans and collagen in costal cartilage from newborn, 4-week-, and 4-year-old rabbits showed that marked changes occurred during the first 4 weeks, i.e., a 30 percent decrease in proteoglycan content and a 3-fold increase in collagen. No significant changes were observed thereafter. The extractability of the proteoglycans after treatment with 4 M guanidinium chloride varied drastically, depending upon the age of the animal. Whereas 73 per cent of the proteoglycans was extracted from the neonatal tissue, the yield from old tissue was only 10 per cent. It is suggested that the decrease in extractability with age is related to the increase in collagen content. Cytochemical observations demonstrated that, in the neonatal tissue, metachromatic staining of the matrix was lost after guanidinium chloride treatment, with the exception of chromotropic granules still present in the lacunae. In the 1-month-old animals, a general decrease in the staining reaction ensued, except in the perilacunar areas. In the extracted tissues, instead, the picture changed drastically in that metachromasia was decreased in the interterritory but was not modified, as in the neonatal tissue, in the areas adjacent to the cell nests. In the old tissue, the patchy and irregular staining, typical of the cartilage of this age, was not modified by extraction with the guanidium salt. At the ultrastructural level, the proteoglycans in the neonatal tissue appeared as granules of different size, the largest having dimensions of about 900 A, In the 1-month-old animals, degenerative changes were already observed in the chondrocytes, including loss of the perilacunar space, reduction of the endoplasmic reticulum, and an increase of intracellular glycogen and lipids. The proteoglycan droplets, so prominent at the neonatal stage, were no longer evident. In the older animals, apart from the many foci of mineralization, the chondrocytes were almost all degenerated and showed signs of extensive vacuolation and lipid infiltration.