Abstract 1372: Sirt3 Promotes Survival of Cardiac Myocytes under oxidative stress and Upregulates Mitochondrial Genes Through Nuclear Respiratory Factor

Silent information regulator 1 (Sirt1), the prototype member of the sirtuin family, has been implicated in longevity and stress resistance. Sirt3, another member of the sirtuin family, is localized primarily in mitochondria and involved in metabolism in both white and brown adipose tissues. However, the cardiac role of Sirt3 is not well understood. Here, we examined the cellular function of Sirt3 in cardiac myocytes. Western blot analysis revealed that Sirt3 is highly expressed in cardiac myocytes, at the level comparable to Sirt3 in white and brown adipose tissues. Although Sirt1 in the heart was upregulated in response to glucose deprivation, high-fat diet, or pressure overload, expression of Sirt3 was unchanged in these conditions. Expression of Sirt3 was increased two-fold, however, after H 2 O 2 (100 μ M) treatment in primary cardiac myocytes and two-fold by aging (18 vs 3 months) in the heart. Sirt3 is localized primarily in the mitochondria in myocytes under normal conditions, but it translocates into the nucleus when cells are treated with H 2 O 2 . Adenovirus-mediated overexpression of Sirt3 significantly reduced myocyte cell death in serum free media or in the presence of H 2 O 2 as determined by cytoplasmic accumulation of mono- and oligonucleosomes (p<0.05), suggesting that Sirt3 protects myocytes from apoptosis under oxidative stress. Furthermore, Sirt3 increased expression of NRF1, a transcriptional modulator of metabolic genes and mitochondrial DNA transcription, by 2.5-fold. There was a 3.4-fold increase in Glut4 expression as well as a 4-fold increase in COX IV. On the other hand, Sirt1 failed to upregulate NRF1. Sirt3 neither interacted with PGC-1 α nor stimulated PGC-1 α -mediated transcription. Thus, although both Sirt1 and Sirt3 exert their function by regulating metabolic genes, their mechanism of action is different. In summary, cardiac myocytes abundantly express Sirt3 in mitochondria. Sirt3 is upregulated by oxidative stress and translocates into the nucleus, where Sirt3 regulates expression of mitochondrial genes, such as Glut4 and COX IV, through upregulation of NRF1 and plays a protective role against oxidative stress in cardiac myocytes.