Animal Model of Sclerotic Skin. V: Increased Expression of α-Smooth Muscle Actin in Fibroblastic Cells in Bleomycin-Induced Scleroderma

Scleroderma is a connective tissue disorder with unknown etiology. Myofibroblasts appear during fibrotic processes such as scleroderma, hypertrophic scaring, and wound healing. We previously established a mouse model for scleroderma by local injections of bleomycin. To determine the phenotype of the fibroblasts in sclerotic skin after bleomycin treatment, we examined the expression of α-smooth muscle actin (α-SMA), a marker for myofibroblasts, in lesional skin as well as in fibrous lung in this model. Dermal sclerosis was induced by daily local injections of bleomycin (100 μg/ml) for 3 weeks in C3H mice. Immunohistochemical examination showed that α-SMA-reactive cells were detectable on fibroblastic cells in bleomycin-injected skin at 1 week. There was a significant increase in the immunoreactive fibroblastic cells for α-SMA in lesional skin in parallel with the induction of dermal sclerosis. After 3 weeksʹ treatment with bleomycin, the number of α-SMA-reactive fibroblasts showed an 11-fold increase compared with that in control PBS-treated mice. α-SMA-positive cells were also detected in lung parenchyma after bleomycin treatment. Following concomitant treatment with anti-transforming growth factor-β (TGF-β) antibody with bleomycin, the number of α-SMA-positive fibroblastic cells was significantly reduced up to 50%, along with the reduction of dermal sclerosis. To confirm the protein level of α-SMA, immunoblotting was carried out. Results showed an increase of α-SMA expression in lesional skin at 3 weeks of bleomycin treatment, which was reduced following anti-TGF-β antibody treatment. These data suggest that fibroblastic cells are phenotypically altered into myofibroblasts during the fibrotic process in the experimental model of bleomycin-induced scleroderma, which was considered mediated, for the most part, by TGF-β. Blockade of TGF-β may be a therapeutic intervention for scleroderma.