The Role Of SIRT3 In The Metabolism Of Ang Ⅱ-induced Cardiac Hypertrophy And The Underlying Mechanism

Heart Failure is an important health issue worldwide. Although the prevalence of this devastating disease, particularly in low-middle income countries, is steadily increasing, its mortality rate remains at a relatively high level in the past two decades. Therefore, heart failure would remain as a major global public health problem in the foreseeable future. One of the main features of the pathophysiological events during the process of heart failure is the substantial alterations in cardiac energy metabolism. Under pathological conditions, such as myocardial lesions and pressure overload, the heart undergoes an energy shift in the source of ATP substrates, indicative of a decrease in fatty acid oxidation and an increase in glycolysis. SIRT3 is a member of the sirtuin family of class Ⅲ deacetylases. Its expression levels in tissues largely depends on metabolic stimulus such as calorie restriction, high-fat diet, fasting and exercise. Previous studies showed a protective role of SIRT3 against cardiac hypertrophy; SIRT3 exerts its beneficial effects through Foxo3a-dependent regulation of oxidative stress. Nevertheless, whether SIRT3 also impact on the modulation of fatty acid oxidation and glucose metabolism in hypertrophic heart, as well as the underlying molecular mechanisms remain unclear. The objective of this study is to investigate the biological role of SIRT3 in the regulation of fatty acid oxidation and glucose metabolism in hypertrophic heart. In addition, we also explored the potential molecular mechanism of SIRT3-mediated metabolic effects. Thus, we employed Ang Ⅱ-induced mouse cardiac hypertrophy model. We demonstrates that, in the setting of cardiac hypertrophy, the expression levels of SIRT3 in the heart was decreased. Next, we studied the impact of SIRT3 ablation on cardiac fatty acid and glucose metabolism using genetic manipulations of SIRT3. In SIRT3 knockout (KO) mice, we observed significantly repressed expression levels of a myriad of key enzymes for fatty acid oxidation. Conversely, the expression levels of glycolysis-and glycogenesis-associated enzymes were significantly increased in the hearts of SIRT3-KO mice, whereas that of pentose phosphate pathway was downregulated upon SIRT3 deletion. Mechanistically, we showed that SIRT3-ablation was associated with a significant inactivation of PPAR-α/PGC-1α signaling pathway, a central regulator of both fatty acid and glucose metabolism in cardiac hypertrophy. The mRNA expression levels of PPAR-a and PGC-la were decreased in the heart of SIRT3-KO mice compared to WT controls. To further confirm the regulatory role of SIRT3 in PPAR-α/PGC-1α signaling pathway, we overexpressed SIRT3 in H9C2 cell lines. We observed moderate but significant upregulation of PPAR-a and PGC-1α mRNA levels, as well as that of their target genes. In addition, we generated Adenovirus harboring wild-type SIRT3 construct (AdSIRT3). Compared to AdGFP controls, AdSIRD infection significantly upregulated expression levels of PPAR-a and PGC-la, as well as that of fatty acid oxidation enzyme carnitine palmitoyltransferase 1 (CPT1) and long chain acyl-CoA dehydrogenase (LCAD) in H9C2 cell lines. However, the expression level of pyruvate kinase (PK), an enzyme essential for glycolysis, was downregulated upon SIRT3 overexpression. Collectively, these data demonstrate that SIRT3 expression level is crucial to protect against the adverse energy shift during cardiac hypertrophy and Ang II-induced hypertrophic effects. Therefore, SIRT3 may be a potential therapeutic target for metabolic dysfunction in the setting of cardiac hypertrophy.