Sirtuins [sirtuin (SIRT)1-SIRT7] mediate the longevity-promoting effects of calorie restriction in yeast, worms, flies, and mice. Additionally, SIRT3 is the only SIRT analog whose increased expression has been shown to be associated with longevity in humans. The polyphenol resveratrol (RSV) is the first compound discovered able to mimic calorie restriction by stimulating SIRTs. In the present study, we report that RSV activated SIRT3 in cardiac fibroblasts both in vivo and in vitro. Moreover, in wild-type mice, RSV prevented cardiac hypertrophy in response to hypertrophic stimuli. However, this protective effect was not observed in SIRT3 knockout mice. Additionally, the activation of SIRT3 by RSV ameliorated collagen deposition and improved cardiac function. In isolated cardiac fibroblasts, pretreatment with RSV suppressed fibroblast-to-myoblast transformation by inhibiting the transforming growth factor-β/Smad3 pathway. Therefore, these data indicate that the activation of SIRT3 by RSV could ameliorate cardiac fibrosis and improve cardiac function via the transforming growth factor-β/Smad3 pathway.

Cardiac hypertrophy is an adaptive response to pressure, volume stress, and loss of contractile mass from prior infarction. Metabolic changes in cardiac hypertrophy include suppression of fatty acid oxidation and enhancement of glucose utilization, which could result in lipid accumulation in the heart. SIRT3, a mitochondrial NAD+-dependent deacetylase, has been demonstrated to play a crucial role in controlling the acetylation status of many enzymes participating in energy metabolism. However, the role of SIRT3 in the pathogenesis of hypertrophy-related lipid accumulation remains unclear. In this study, hypertrophy-related lipid accumulation was investigated using a mouse cardiac hypertrophy model induced by transverse aortic constriction (TAC). We showed that mice developed heart failure six weeks after TAC. Furthermore, abnormal lipid accumulation and decreased palmitate oxidation rates were observed in the hypertrophic hearts, and these changes were particularly significant in SIRT3-KO mice. We also demonstrated that the short form of SIRT3 was downregulated in wild-type (WT) hypertrophic hearts and that this change was accompanied by a higher acetylation level of long-chain acyl CoA dehydrogenase (LCAD), which is a key enzyme participating in fatty acid oxidation. In addition, SIRT3 may play an essential role in attenuating lipid accumulation in the heart through the deacetylation of LCAD.

Sirt3, a mitochondrial NAD+-dependent histone deacetylase, is the only member proven to promote longevity in mammalian Sirtuin family. The processed short form of Sirt3 has been demonstrated to target many mediators of energy metabolism and mitochondrial stress adaptive program. Autophagy serves as a dynamic recycling mechanism and provides energy or metabolic substrates. Among the mechanisms triggered by cardiac stress, opinions vary as to whether autophagy is a protective or detrimental response. Here, by inducing the Sirt3-knockout mice to myocardial hypertrophy with chronic angiotensin II infusion for four weeks, we determined the role of Sirt3 in myocardial hypertrophy and autophagy. In this study, the Sirt3-knockout mice developed deteriorated cardiac function and impaired autophagy compared to wild-type mice. What's more, the overexpression of Sirt3 by lentivirus transfection attenuated cardiomyocytes hypertrophy by promoting autophagy. We further demonstrated that Sirt3 could bind to FoxO1 and activate its deacetylation. Sequentially, deacetylated FoxO1 translocates to the nucleus where it facilitates downstream E3 ubiquitin ligases such as Muscle RING Finger 1 (MuRF1) and muscle atrophy F-box (MAFbx, Atrogin1). Altogether, these results revealed that Sirt3 activation is essential to improve autophagy flux by reducing the acetylation modification on FoxO1, which in turn alleviates myocardial hypertrophy.

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