F. Binette et al., EXPRESSION OF A STABLE ARTICULAR-CARTILAGE PHENOTYPE WITHOUT EVIDENCEOF HYPERTROPHY BY ADULT HUMAN ARTICULAR CHONDROCYTES IN-VITRO, Journal of orthopaedic research, 16(2), 1998, pp. 207-216
Chondrocytes that were isolated from adult human articular cartilage c
hanged phenotype during monolayer tissue culture, as characterized by
a fibroblastic morphology and cellular proliferation. Increased prolif
eration was accompanied by downregulation of the cartilage-specific ex
tracellular matrix proteoglycan, aggrecan, by cessation of type-II col
lagen expression, and by upregulation of type-I collagen and versican.
This phenomenon observed in monolayer was reversible after the transf
er of cells to a suspension culture system. The transfer of chondrocyt
es to suspension culture in alginate beads resulted in the rapid upreg
ulation of aggrecan and type-II collagen and the downregulation of exp
ression of versican and type-I collagen. Type-X collagen and osteopont
in, markers of chondrocyte hypertrophy and commitment to endochondral
ossification, were not expressed by adult articular chondrocytes cultu
red in alginate, even after 5 months. In contrast, type-X collagen was
expressed within 2 weeks in a population of cells derived from a feta
l growth plate. The inability of adult articular chondrocytes to expre
ss markers of chondrocyte hypertrophy has underscored the fundamental
distinction between the differentiation pathways that lead to articula
r cartilage or to bone. Adult articular chondrocytes expressed only hy
aline articular cartilage markers without evidence of hypertrophy.