P336	The forkhead transcription factor FoxO1a regulates cellular Caveolin-1 expression: impact on apoptosis of vascular smooth muscle cells.
1D.Sedding, 1S.Vogel, 1H.Tillmanns, 2R.Braun-Dullaeus
1Cardiology - Giessen University Clinic, Gießen, DE; 2Cardiology - Dresden University of Technology, Dresden, DE.

Background: The forkhead transcription factor FoxO1a represents an important physiological target of phosphatidylinositol-3 kinase (PI3-K)/protein kinase B (Akt) signaling and we previously demonstrated that FoxO1a is a key regulator for the cell cycle entry of vascular smooth muscle cells (VSMC). In the present study we sought to determine the effect of adenovirus-mediated expression of a transgene encoding a constitutively-active form of FoxO1a (Ad-FoxO1a;AAA) on VSMC apoptosis. Methods and Results: Following transduction with Ad-FoxO1a;AAA, the number of apoptotic VSMC was increased compared to controls (14.8 ± 2.3 vs. 3.6 ± 0.8%, P< 0.01) as determined by TUNEL assay. Caveolin-1 expression was increased at both, the mRNA and protein level in a dose-dependent manner. Over expression of caveolin-1 itself reduced serum-induced Akt phosphorylation and significantly increased the number of apoptotic VSMC. Accordingly, knock down of caveolin-1 using antisense oligonucleotides significantly reduced the number of apoptotic cells induced by 72 h serum starvation. Knock down of caveolin-1 also significantly reduced the FoxO1a;AAA-induced apoptosis of VSMC. Similarly, VSMC isolated from caveolin-1-/- mice were resistant to FoxO1a;AAA-induced apoptosis. For in vivo studies, the femoral artery of C57BL/6J mice was dilated and adenoviral vectors were delivered intraluminally to the denuded segment. Four days after dilation, caveolin-1 expression as well as the apoptotic rate of medial VSMC in FoxO1a-transduced arteries was significantly increased as determined by TUNEL assay (9.7 ± 2.5 vs. 2.3 ± 0.9; P<0.05). Morphological analysis of femoral arteries 28 days after dilation revealed a significantly reduced neointima/media ratio (0.7 ± 0.2 vs. 1.8 ± 0.4;P<0.005). Conclusion: By transactivating and increasing cellular caveolin-1 expression levels, FoxO1a interferes with cellular PI3-K/Akt-dependent survival signaling, thereby restoring the sensitivity of (neointimal) VSMC to apoptotic stimuli. This pro-apoptotic effect adds to the anti-proliferative properties of FoxO1a resulting in impaired neointima formation in vivo. Thus, modulating FoxO1a-function may represent a novel approach to prevent vascular proliferative disease.

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