Hypoxia increases transforming growth factor-β1 concomitantly with types I and III collagen without further enhancement by reoxygenation in cultured rat cardiac fibroblasts

The effects of oxygen concentration and reoxygenation following hypoxic culture on transforming growth factor-β1 (TGF-β1) expression and types I and III collagen [α2(I) and α1(III)] mRNA expression were examined in neonatal rat cardiac fibroblasts cultured with medium containing 10% or 1% fetal calf serum at confluency. The oxygen tension was varied using a N₂- CO₂-O₂ controllable incubator. Cells were exposed to continuous hypoxia (2% O₂) or were reoxygenated (21% O₂) after hypoxic culture. The TGF-β1 protein expression level was determined by an enzyme-linked immunosorbent assay, and the expression levels of TGF-β1, α2(I) and α1(III) mRNA were measured by a Northern blot analysis. Both the TGF-β1 mRNA and protein levels were higher in the continuous hypoxic cultures than in the continuous normoxic cultures. Their levels in reoxygenation cultures were not substantially different from those in the continuous normoxic cultures. Similarly, the expressions of both α2(I) and α1(III) mRNA were enhanced in continuous hypoxic culture, and no differences were obtained between normoxic and reoxygenation cultures. The present results indicate that hypoxia induces high expression levels of TGF-β1 and types I and III collagen in rat cardiac fibroblasts and that reoxygenation does not further enhance this hypoxia- induced upregulation.