TGF-β1 and integrin synergistically facilitate the differentiation of rat podocytes by increasing α-smooth muscle actin expression

Phenotypic changes can be found in certain glomerular diseases, and the cell origin is not defined. This study was designed to identify whether podocytes can differentiate by the expression of α-smooth muscle actin (α-SMA), under the effects of TGF-β1 (transforming growth factor-β1) and integrin. Western and Northern blot analyses were performed to identify the protein and mRNA (messenger ribonucleic acid) expression of α-SMA. The number of podocytes, which express α-SMA, was measured by immunocytochemical staining. The results showed that TGF-β1 dose-dependently increased α-SMA protein and mRNA expression at 4 and 2 days, respectively. TGF-β1 also dose-dependently increased the α-SMA staining of podocytes. The α-SMA-positive podocytes showed front-end and back-end polarity. The integrinα3β1 antagonists, anti-integrinβ1 monoclonal antibody and Gly-Arg-Gly-Asp (GRGD), decreased the expression of α-SMA protein and the percentage of α-SMA positive cells stimulated by TGF-β1 (both P < 0.01). The addition of calphostin [inhibitor of protein kinase C (PKC)] and genistein [inhibitor of focal adhesion kinase (FAK)] also decreased the expression of α-SMA protein and the percentage of α-SMA positive cells stimulated by TGF-β1 (both P < 0.01). In conclusion, this study indicated that TGF-β1 may act synergistically with integrins, through activation of PKC and FAK, to induce the phenotypic changes of rat podocytes with increasing α-SMA expression.