Selective decrease of type I collagen synthesis in Fraser mice skin

Collagen breakdown products and lung collagen metabolism: an in vitro study on fibroblast cultures

BACKGROUND

In fibrotic diseases such as pulmonary fibrosis there is evidence suggesting enhanced synthesis and degradation of lung connective tissue components, including collagen. It has therefore been hypothesised that products of collagen degradation may have a role in the promotion of collagen deposition. In support of this hypothesis, it has recently been shown that intravenous injection of lung collagen degradation products in experimental animals stimulated collagen synthesis leading to increased collagen deposition and diffuse interstitial lung disease.

METHODS

Rabbit and human fibroblast cultures from lung and skin were used as an in vitro model to study the responses of these cells to rabbit collagen degradation products. The effects of an acute exposure to collagen degradation products on synthesis of collagen and noncollagenous protein have been studied in confluent cultures by [3H]-proline incorporation. The effects of collagen degradation products on fibroblast proliferation and production of genetic types of collagen have also been investigated.

RESULTS

The acute exposure of rabbit lung fibroblast cultures to collagen degradation products significantly increased collagen synthesis without affecting non-collagenous protein synthesis. This effect was dose related, specific for lung fibroblasts, and species specific. Collagen degradation products altered the rate of synthesis of genetic types of collagen with a consequent decrease of type III/I+III collagen ratio (0.26 (0.04) treated with collagen degradation products; 0.45 (0.02) controls). These effects occurred without the intervention of serum factors. In addition, collagen degradation products neither affected fibroblast proliferation nor selected specific clones emphasising one type of collagen.

CONCLUSIONS

These results suggest that collagen degradation products can influence lung collagen metabolism by stimulating collagen synthesis. The regulation of collagen mass by collagen degradation products may be of importance in lung collagen homeostasis in vivo.

Relative rates of biosynthesis of collagen type I, type V and type VI in calf cornea

The biosynthesis of type I, type V and type VI collagens was studied by incubation of calf corneas in vitro with [3H]proline as a marker. Pepsin-solubilized collagen types were isolated by salt fractionation and quantified by SDS/PAGE. Expressed as proportions of the total hydroxyproline solubilized, corneal stroma comprised 75% type I, 8% type V and 17% type VI collagen. The rates of [3H]proline incorporation, linear up to 24 h for each collagen type, were highest for type VI collagen and lowest for type I collagen. From pulse-chase experiments, the calculated apparent half-lives for types I, V and VI collagens were 36 h, 10 h and 6 h respectively.

Heparin fragments regulate collagen phenotype and fibronectin synthesis in the skin of genetically diabetic mice

The biosyntheses of interstitial collagens of type I and III and of fibronectin were studied in genetically diabetic KK mice, as compared to control C57 Black mice, as well as the effect of low-Mr heparin fragments (CY 222) on these biosyntheses. An increased production of type III collagen, as compared to type I collagen, could be demonstrated in explant cultures of KK mice skins. Fibronectin biosynthesis was also increased. In vivo treatment of KK mice with 1 mg/kg of CY 222 decreased the biosyntheses of type III collagen and of fibronectin to normal levels. These experiments suggest that low-Mr heparin fragments can modulate the expression of extracellular matrix macromolecules.