Akt1 mediates α-smooth muscle actin expression and myofibroblast differentiation via myocardin and serum response factor.

ABSTRACT

Myofibroblast (MF) differentiation, marked by the de novo expression of smooth muscle α-actin (αSMA) stress fibers, plays a central role in wound healing and its persistence is a hallmark of fibrotic diseases. We have previously shown that Akt1 is necessary for wound healing through matrix regulation. However, the role of Akt1 in regulating MF differentiation with implications in fibrosis remains poorly defined. Here, we show that sustained activation of Akt1 was associated with a 6-fold increase in αSMA expression and assembly; an effect that is blunted in cells expressing inactive Akt1 despite TGFß stimulation. Mechanistically, Akt1 mediated TGFß-induced αSMA synthesis through the contractile gene transcription factors myocardin and serum response factor (SRF), independent of mammalian target of rapamycin in mouse embryonic fibroblasts and fibroblasts overexpressing active Akt1. Akt1 deficiency was associated with decreased myocardin, SRF, and αSMA expressions in vivo. Furthermore, sustained Akt1-induced αSMA synthesis markedly decreased upon RNA silencing of SRF and myocardin. In addition to its integral role in αSMA synthesis, we also show that Akt1 mediates fibronectin splice variant expression, which is required for MF differentiation, as well as total fibronectin, which generates the contractile force that promotes MF differentiation. In summary, our results constitute evidence that sustained Akt1 activation is crucial for TGFß-induced MF formation and persistent differentiation. These findings highlight Akt1 as a novel potential therapeutic target for fibrotic diseases.