Stimulation of Collagen Production by Transforming Growth Factor-β 1 During Differentiation of Cardiac Fibroblasts to Myofibroblasts

The aim of the present study was to elucidate how transforming growth factor-β1 (TGF-β1 ) can stimulate collagen deposition in cardiac tissue by interstitial cells via stimulation of fibroblasts, via myofibroblasts, or via differentiation of fibroblasts to myofibroblasts. The dose- and time-dependent stimulation of collagen production and of expression of α-smooth muscle actin (α-SMA), a marker of myofibroblasts, was studied in cultures of second-passage adult rat cardiac fibroblasts. The TGF-β1 -stimulated collagen production is positively correlated (r =0.68,P <0.001) with the appearance of α-SMA. Only at high concentrations (40 to 600 pmol/L) and after a long time (24 to 48 hours) of incubation, TGF-β1 increases the collagen production and stimulates the differentiation of fibroblasts to myofibroblasts. The maximal stimulation of the collagen production (2-fold,P <0.001) observed after incubation of cultures of fibroblasts with 600 pmol/L TGF-β1 for 48 hours is accompanied by a maximal stimulation of α-SMA expression (3.5-fold,P <0.001), when cultures consist mainly of myofibroblasts. The stimulation of collagen production cannot be reversed either after additional incubation of TGF-β1 -stimulated second-passage cultures for 2 days or in their offspring in the next third passage after incubation for 7 days without TGF-β1 . The increased collagen production in these third-passage cultures cannot be further stimulated by TGF-β1 . Our data suggest that TGF-β1 -stimulated collagen production in cultures of adult rat cardiac ventricular fibroblasts cannot be explained by a direct stimulation of the collagen production either in fibroblasts or in myofibroblasts. Instead, TGF-β1 induces the differentiation of fibroblasts to myofibroblasts, which have a higher activity for collagen production than fibroblasts.