Abstract 221: Integral Role of Akt-Serum Response Factor-Myocardin Signaling in Myofibroblast Differentiation with Implications in Pulmonary Arterial Hypertension
Objectives Myofibroblast (MF) differentiation is marked by the de novo expression of smooth muscle alpha-actin (αSMA) stress fibers, a function critical for tissue repair both physiologically and pathophysiologically. However, the role of Akt in regulating MFs with implications in pulmonary arterial hypertension (PAH) and fibrosis, and the effect of pharmacological inhibition of Akt pathway on PAH and fibrosis remains poorly defined.
Methods We used NIH 3T3 fibroblasts and primary human lung fibroblasts (HLFs) in the current study. Cells were treated with TGFβ, the profibrotic cytokine and the role of Akt, SRF and myocardin in αSMA expression, MF differentiation and collagen gel contraction was studied with the use of various constructs encoding expression of specific genes.
Results Here, we show that Akt mediates MF differentiation as evident by a 5-fold increase in αSMA expression and assembly in mouse embryonic fibroblasts (NIH 3T3) over-expressing active Akt1 (myr-Akt). As for the molecular mechanisms governing MFs, we found that αSMA expression was mediated by Akt, independent of mTOR; noteworthy, fibronectin expression, an ECM protein, is Akt-mTOR dependent. Inhibiting Akt activation utilizing triciribine blunted αSMA and its transcriptional activators, myocardin and SRF, inhibiting MF differentiation in NIH 3T3, myr-Akt-NIH 3T3, and human lung fibroblasts. Furthermore, blocking Akt reversed MF differentiation as evident by a blunted gel contraction primed with TGFβ.
Conclusions In conclusion, our study clearly demonstrates the crucial role of Akt in mediating TGFβ-induced MF differentiation. We show a previously uncharacterized link between Akt and TGFβ-induced αSMA synthesis through myocardin and SRF, independent of mTOR, in MFs. These data constitute evidence of novel signaling cascade and targeting Akt pathway might be beneficial for the treatment of PAH and fibrosis.
- © 2013 by American Heart Association, Inc.