Susan Shull

Bleomycin selectively elevates mRNA levels for procollagen and fibronectin following acute lung injury.

We employed the technique of dot blot hydridization of radiolabeled cDNA probes to examine the role of specific mRNA content in the control of extracellular matrix turnover in the remodeling rat lung. Following bleomycin instillation, total RNA content gradually doubled during the first 5 days following the initial lung injury, then rose much more rapidly during the ensuing 9 days. Individual mRNAs for procollagens I and III and for fibronectin were selectively enriched 2- to 4-fold above total RNA during the first week after bleomycin instillation. No comparable increases were observed in specific RNAs from liver, indicating that the response observed in the lung was not generalized to other organs. Moreover, the increases in mRNA species for procollagen types I or III in the lung could not be related to the influx of inflammatory cells which migrate into the lungs during acute injury, as cells obtained by alveolar lavage contained no mRNAs for procollagens.

Glucocorticoid-induced down regulation of transforming growth factor-β1 in adult rat lung fibroblasts

Transforming growth factor-β1 mRNA and transforming growth factor β activity are decreased with exposure of normal adult rat lung fibroblasts to dexamethasone. Dexamethasone caused a decrease in transforming growth factor-β1 mRNA within 2 hours, which was sustained at least over a 24-hour period. The decrease in transforming growth factor-β1 mRNA was dose related. Dexamethasone treatment of rat lung fibroblasts also resulted in a decrease of transforming growth factor β activity as determined by the mink lung cell growth inhibition assay. These data indicate that glucocorticoids may regulate collagen synthesis at least in part through the mediation of transforming growth factor-β1 in rat lung fibroblasts.

Glucocorticoids Change the Ratio of Type III to Type I Procollagen Extracellularly

Rat skin fibroblasts were treated with dexamethasone and labeled with radioactive proline for 2 hours. Intracellular and extracellular procollagens were immunoprecipitated with monospecific polyclonal antibodies. Both intracellular and extracellular types I and III procollagen were decreased coordinately by glucocorticoid treatment. The ratio of type III to type I procollagen was the same for control and dexamethasone-treated cell cultures. However, when rat skin fibroblasts were prelabeled with radioactive proline and chased in the presence of unlabeled proline the ratio of type III to type I extracellular procollagens remained constant in the glucocorticoid-treated cells and increased in control fibroblasts.

Skin lysyl oxidase activity is not rate limiting for collagen crosslinking in the glucocorticoid-Treated rat

Lysyl oxidase activity in the skin of rats receiving triamcinolone diacetate (12 mg/kg) for three consecutive days was decreased by sixty-four percent as compared to control values. A decrease of lysyl oxidase activity was observed twelve hours after the initial glucocorticoid injection. The decreased lysyl oxidase activity was accompanied by a forty-nine percent decrease of acetic acid extractable collagen. There was also a forty-two percent decrease in the alpha/beta ratio of the acetic acid soluble skin collagen of glucocorticoid-treated animals. These data indicate that although skin lysyl oxidase activity is decreased by glucocorticoid treatment, the crosslinking of acid extracted collagen as measured by the alpha/beta ratio and collagen solubility is increased. Accordingly lysyl oxidase activity is not rate limiting for collagen crosslink formation in the skins of rats treated with glucocorticoids.