Abstract 18488: Sirt1 Mediated Deacetylation of Foxo1 Is Involved in Starvation Induced Autophagy in the Heart
Autophagy, a bulk degradation process through lysosomes, is activated by glucose deprivation (GD) in order to preserve ATP in cardiac myocytes. The FoxO family transcription factors regulate a wide variety of cellular functions, including autophagy, as a fundamental mechanism for adaptation. We investigated the role of FoxOs in mediating autophagy during GD. FoxO1 and Sirt1, an NAD+ -dependent histone deacetylase, are upregulated (1.8 and 1.6 fold, p<0.05) upon GD in cardiac myocytes. Upregulation of Sirt1 during GD was accompanied by an increase in total FoxO1 (1.6 fold, p<0.05), a decrease in acetylated FoxO1 (−60%, p<0.05), and nuclear accumulation of FoxO1, all of which were attenuated in the presence of adenovirus harboring shRNA Sirt1 (Ad-shSirt1). Knockdown of FoxO1 (Ad-shFoxO1) and Sirt1 significantly inhibited autophagic flux both at baseline and during GD, as indicated by increased expression of p62 (2.5 and 2.8 fold, p<0.01), as well as by accumulation of autophagosomes (5.7 and 6.5 fold, p<0.01) without a parallel increase in autolysosomes (0.2 and 0.3 fold, p<0.01), evaluated by tandem fluorescent LC3 puncta. Transduction with adenoviruses harboring either a FoxO1 mutant (Ad-3A/LXXAA) which cannot be deacetylated by Sirt1 or p300 (Ad-p300), a histone acetylase, induced accumulation of p62 (1.6 and 2.2 fold, p<0.01) and autophagosomes (4 fold) without increases in autolysosomes (0.2 fold) at baseline and in response to GD indicating that deacetylation of FoxO1 by Sirt1 is required for autophagy. In transgenic mice with cardiac specific expression of FoxO1 3A/LXXAA (DN-Tg) and cardiac specific FoxO1 homozygous knockout mice (CKO), autophagy was inhibited both at baseline (B) and after 48 hours of starvation (S), as indicated by accumulation of p62 (S 0.7, DN-Tg-B 2.1, DN-Tg-S 2.2, CKO-B 2.8, CKO-S 2.6 fold vs control, p<0.01). Left ventricular (LV) ejection fraction after starvation was significantly reduced in DN-Tg and CKO mice (59.3 and 52.5%, p<0.01), and also in beclin1 +/− mice (46.8%), in which autophagy is suppressed, but not in control mice (74.8%). These results suggest that FoxO1 and its deacetylation by Sirt1 are required for inducing autophagy and preserving cardiac function in response to starvation in the heart.
- © 2010 by American Heart Association, Inc.