Abstract 329: Simvastatin Inhibits TGF-β1-induced Proliferation and Activation of Cardiac Fibroblasts Through Inhibition of SMAD Pathway

Abstract

Background: HMG-CoA reductase inhibitors (statins) have been shown to reduce the incidence of atrial fibrillation (AF) and its progression but the underlying mechanisms are not fully elucidated. Since atrial fibrosis plays a major role in the development of the substrate for AF progression, we hypothesized that statins antagonize the effect of profibrotic cytokines, reducing their stimulatory effect on fibroblast proliferation, differentiation and activation. Methods: The effect of TGF-β1, a major profibrotic cytokine, on fibroblast proliferation and activation of myofibroblasts was assessed by expression of alpha smooth muscle actin (α-SMA) message (qPCR) and proteins (western and immunofluorocytochemistry) in the presence and absence of simvastatin (1-10μM). The inhibitory effect of simvastatin on SMAD 2/3 phosphorylation (western) and its nuclear translocation by TGF-β1 (5ng) was determined by immunofluorescence antibodies using fluorescent microscopy. Results: TGF-β1 treatment increased fibroblast proliferation (cell count) by 63% compared to control (p<0.001) at 96 hours, which was inhibited by simvastatin by 61% (p<0.001) (Fig a). Simvastatin also reduced TGF-β1-mediated myofibroblast differentiation (α-SMA positive) by 75% (p=0.02); (Fig b and c). TGF-β1 increased SMAD2/3 phosphorylation with increase in nuclear localization was inhibited by simvastatin. Conclusion: Simvastatin inhibits TGFβ-1-mediated cardiac fibroblast proliferation and myofibroblast differentiation by antagonizing SMAD phosphorylation and its translocation into the nucleus.