Influence of 17β-estradiol and insulin on type II collagen and protein synthesis of articular chondrocytes

Clinical observations have suggested a relationship between osteoarthritis and a changed estrogen metabolism in menopausal women. Type II collagen is one main structural protein of articular cartilage matrix and its synthesis is increased by insulin in growth plate cartilage. Therefore, it was investigated if [3H]-proline incorporation and type II collagen synthesis (immunocytochemistry, ELISA) in female bovine articular chondrocytes are affected by 17β-estradiol and/or insulin. Articular chondrocytes were cultured in monolayers at 5% O2 in medium containing serum for 5–9 days, followed by application of 10−13 to 10−9 M estradiol or 5 μg/ml insulin during a serum-free culture phase of 2–3 days. Immunostaining for type II collagen was strong in the serum-free culture phase whereas it was negative for type I collagen, indicating that cells did not dedifferentiate to fibroblast-like cells during culture in serum-free medium. Whereas insulin raised the proline incorporation and the type II collagen synthesis significantly, physiological doses of estradiol did not show significant effects. The stimulating effect of insulin on the [3H]-proline incorporation or the type II collagen synthesis was significantly suppressed after preincubation of cells with 10−11 to 10−9 M estradiol resembling an unfavorable effect for articular cartilage. The suppression was reversed if cells were incubated with 10−11 to 10−7 M tamoxifen or ICI 182,780 combined with 10−11 or 10−9 M estradiol followed by incubation with 5 μg/ml insulin, indicating an estrogen receptor-mediated process. Because the articular cartilage of diabetic patients is biomechanically less stable, further experiments are needed to clarify the role of estradiol and insulin in the metabolism of articular chondrocytes.