Light- and electron- microscopic observations of aged human articular chondrocytes in cell culture

As part of the development of an in-vitro model of aged human articular chondrocytes a descriptive light- and electron-microscopic study of articular chondrocytes in cell culture from elderly individuals was performed. Monolayer cultures of human articular chondrocytes were established from fifteen cartilage samples from patients with the average age of 85 years (range from 75 to 99). For the surface and transmission electron-microscopic study the isolated cells were seeded on polyethylene-terephtalat membrane inserts. During the cultivation time of six weeks the differentiated phenotype of human articular chondrocytes characterized by collagen type II synthesis and spherical morphology was lost and replaced by dedifferentiated cells producing predominately collagen type I and showing flattened "fibroblast-like" morphology. In light microscopy the dedifferentiated cells show no further staining with alcian blue and safranin-O. Surface electron-microscopy demonstrates the morphological change from spherical to various fibroblastic-like, spindle-shaped cells. In transmission electron-microscopy freshly isolated cells contained an abundance of single membrane-bound electron dense bodies. These cellular organelles represent secondary lysosomes and are interpreted as residual bodies due to the high biologic age of the cultured cells. During the observed cultivation period the density of the secondary lysosomes is reduced as a sign of cell proliferation.