3-Hydroxy-3-Methylglutaryl CoA Reductase Inhibitors up-Regulate Transforming Growth factor-β Signaling in Cultured Heart Cells via Inhibition of Geranylgeranylation of RhoA GTPase

Transforming growth factor-β (TGFβ) signaling has been shown to play a role in cardiac development as well as in the pathogenesis of cardiovascular disease. Prior studies have suggested a relationship between cholesterol metabolism and TGFβ signaling. Here we demonstrate that induction of the cholesterol metabolic pathway by growth of embryonic chicken atrial cells in medium supplemented with lipoprotein-depleted serum coordinately decreased the expression of the TGFβ type II receptor (TGFβ RII), TGFβ1, and TGFβ signaling as measured by plasminogen activator inhibitor-1 (PAI-1) promoter activity. Inhibition of the cholesterol metabolic pathway by the hydrophobic 3-hydroxy-3-methylglutaryl CoA (HMGCoA) reductase inhibitors, simvastatin and atorvastatin, reversed the effect of lipoprotein-depleted serum and up-regulated TGFβ RII expression, whereas the hydrophilic HMGCoA reductase inhibitor, pravastatin, had no effect. Simvastatin stimulated the expression of TGFβ RII, TGFβ1, and PAI-1 at the level of transcription. Experiments using specific inhibitors of different branches of the cholesterol metabolic pathway demonstrated that simvastatin exerted its effect on TGFβ signaling by inhibition of the geranylgeranylation pathway. C3 exotoxin, which specifically inactivates geranylgeranylated Rho GTPases, mimicked the effect of simvastatin on PAI-1 promoter activity. Cotransfection of cells with a PAI-1 promoter-reporter and a dominant-negative RhoA mutant increased PAI-1 promoter activity, whereas cotransfection with a dominant-active RhoA mutant decreased PAI-1 promoter activity. These data support the conclusion that TGFβ signaling is regulated by RhoA GTPase and demonstrate a relationship between cholesterol metabolism and TGFβ signaling. Our data suggest that in patients treated with HMGCoA reductase inhibitors, these agents may exert effects independent of cholesterol lowering on TGFβ signaling in the heart.