Chondrocyte cloning in aging and osteoarthritis of the hip cartilage: morphometric analysis in transgenic mice expressing bovine growth hormone.

An arthritic disorder resembling human osteoarthritis occurs in transgenic mice expressing the fusion gene coding for bovine growth hormone (bGH). In these animals, we performed a morphometric evaluation of cellular density, clonal density and the relationship between both parameters in articular cartilage. These parameters were determined in the femoral head of bGH (+) mice at 1, 6 and 12 months of age and compared to values in the control mice. The transgenic mouse showed a reduction in cellular density of the superficial and middle zones of the articular cartilage with age. In the uncalcified cartilage at 6 and 12 months of age, cellular density was significantly lower in age-matched transgenic mice than in the control group. In the former, the changes in cellular density were accompanied by a gradual reduction in the clonal density in the superficial and middle zones. The clonal density/cellular density ratio was similar in transgenic mice and the control group at 12 months of age. These findings indicate that these transgenic mice develop an osteoarthritic process characterized by loss of cellularity and a gradual decline in chondrocyte cloning in the superficial and middle zones.