In vitro synthesis and degradation of collagen by chick chondrocytes and fibroblasts

Effect of retinoids on collagen production by chondrocytes in culture

The effect of vitamin A and of some of its derivatives on chondrocytes in culture has been studied. In the presence of retinoids the proliferation of the cells decreased and they lost their characteristic polygonal shape and assumed a fibroblast-like morphology. All retinoids also caused dedifferentiation of chondrocytes as indicated by the induction of types I and III collagen. 13-cis retinoic acid (= isotretinoin) was the most active derivative in this aspect. Since appropriate control of the synthesis of extracellular matrix proteins is a prerequisite for their normal physiological function, alterations such as those observed here may be involved in the pathogenesis of side effects which are observed during the treatment of dermatological disorders with retinoic acid derivatives.

Effect of elevated temperature on the intracellular degradation of different collagen types

The intracellular degradation of newly synthesized collagen of types I, II and IV was studied under cell culture conditions at normal and elevated body temperatures. The degradation of type I procollagen was studied in both human skin and chicken tendon fibroblasts, type II procollagen in chicken sternal chondrocytes and type IV procollagen in a human tumor cell line (HT-1080). To avoid the effect of the different temperatures on isotope penetration and protein synthesis, the cells were pulsed at 37 degrees C. The degradation of the newly synthesized procollagen was then followed during the chase period at 37 degrees C and at different temperatures slightly above the melting temperature of type I procollagen. Degradation was clearly increased in the human skin fibroblasts when the temperature was raised to 41 degrees C, whereas the result in the chicken tendon fibroblasts at 43 degrees C was not as dramatic. The extent of degradation in chicken chondrocytes was resistant to changes in temperature, whereas that in the HT-1080 cells was clearly increased when the incubation temperature was raised to 43 degrees C.

Rapid intracellular degradation of newly synthesized collagen by bone cells. Effect of dichloromethylenebisphosphonate

Experiments were carried out to determine whether bone cells isolated from rat calvaria degrade newly synthesized collagen intracellularly prior to secretion and to assess the effect of dichloromethylenebisphosphonate, a compound shown to stimulate collagen synthesis during this event. The findings indicate that isolated bone cells grown in culture degraded a proportion (average 16%) of newly synthesized collagen prior to secretion. This process was markedly reduced by exposure to dichloromethylenebisphosphonate in a dose-related manner. Concomitantly with the observed decrease of degradation, an increase of collagen synthesis was detected as determined by the incorporation of [3H]proline into collagenase-digestible proteins or by the conversion of [3H]proline into [3H]hydroxyproline. No similar enhancement on total non-collagenous protein synthesis was evident. Dichloromethylenebisphosphonate did not influence the extracellular degradation of collagen. Although the reduction in intracellular degradation accounted only for part of the bisphosphonate mediated increase in net collagen synthesis, it is conceivable that the rate of collagen synthesis is regulated, at least in part, by mechanisms that modulate the level of intracellular degradation.