Sirt3-dependent deacetylation of COX-1 counteracts oxidative stress-induced cell apoptosis.

The mitochondrial complexes are prone to sirtuin (Sirt)3-mediated deacetylation modification, which may determine cellular response to stimuli, such as oxidative stress. In this study, we show that the cytochrome c oxidase (COX)-1, a core catalytic subunit of mitochondrial complex IV, was acetylated and deactivated both in 2,2'-azobis(2-amidinopropane) dihydrochloride-treated NIH/3T3 cells and hydrogen peroxide-treated primary neuronal cells, correlating with apoptotic cell death induction by oxidative stress. Inhibition of Sirt3 by small interfering RNA or the inhibitor nicotinamide induced accumulation of acetylation of COX-1, reduced mitochondrial membrane potential, and increased cell apoptosis. In contrast, overexpression of Sirt3 enhanced deacetylation of COX-1 and inhibited oxidative stress-induced apoptotic cell death. Significantly, rats treated with ischemia/reperfusion injury, a typical oxidative stress-related disease, presented an inhibition of Sirt3-induced hyperacetylation of COX-1 in the brain tissues. Furthermore, K13, K264, K319, and K481 were identified as the acetylation sits of COX-1 in response to oxidative stress. In conclusion, COX-1 was discovered as a new deacetylation target of Sirt3, indicating that the Sirt3/COX-1 axis is a promising therapy target of stress-related diseases.-Tu, L.-F., Cao, L.-F., Zhang, Y.-H., Guo, Y.-L., Zhou, Y.-F., Lu, W.-Q., Zhang, T.-Z., Zhang, T., Zhang, G.-X., Kurihara, H., Li, Y.-F., He, R.-R. Sirt3-dependent deacetylation of COX-1 counteracts oxidative stress-induced cell apoptosis.

Phloridzin improves lipoprotein lipase activity in stress-loaded mice via AMPK phosphorylation.

Long-term stress exposure can lead to disturbed homeostasis and cause many life-style diseases. Phloridzin possesses various bioactivities, but the understanding of the effects of phloridzin on stress-related lipid metabolism disorder is limited. Our results demonstrate that phloridzin improved plasma lipoprotein lipase (LPL) activity and triglyceride metabolism in restrained mice. A decrease of angiopoietin-like protein 4 (ANGPTL4) mRNA expression and an increase of AMP-activated protein kinase (AMPK) phosphorylation were observed after phloridzin treatment. After inhibiting AMPK phosphorylation, the effects of phloridzin on the amelioration of plasma LPL activity and suppression of ANGPTL4 expression were blocked. In addition, cardiac AMPK phosphorylation, plasma LPL activity and ANGPTL4 expression were also affected by phloridzin, even if the glucocorticoid receptor was blocked. Taken together, the down-regulation of ANGPTL4 expression by phloridzin was probably via a direct activation of AMPK pathway. This discovery can provide a biochemical and nutritional basis for the use of phloridzin-containing food and beverage in daily life.

Comparing antioxidant capacity of purine alkaloids: a new, efficient trio for screening and discovering potential antioxidants in vitro and in vivo.

The most commonly applied strategies for the evaluation of antioxidant capacity are the chemical- or cell-based approaches. However, the results obtained from these methods might not reflect the antioxidant ability of test samples within organisms. In this study, we propose a combination of experiments, including oxygen radical absorbance capacity (ORAC), cellular antioxidant activity assay (CAA), and the chick embryo model, as an efficient trio to evaluate antioxidant capacity of food components. Taking purine alkaloids as example, results demonstrate that chemical and cellular method might misinterpret their true ability on antioxidation. In chick embryo model, caffeine and theacrine can significantly improve vessel density on chorioallantoic membrane and myocardial apoptosis. The mechanism can be involving multiple targets within the organism. We believe that the trio proposed can be widely utilized in screening massive number of antioxidant in a cost-effective way. It will also help discovering new antioxidants that are easily being omitted due to their relatively poor in vitro activities.

Caffeine ameliorates high energy diet-induced hepatic steatosis: sirtuin 3 acts as a bridge in the lipid metabolism pathway.

The beneficial effect of caffeine-containing food on non-alcoholic fatty liver disease (NAFLD) has been widely reported. The aim of this study was to explore the effect of caffeine on hepatic steatosis. C57BL/6 mice were randomly assigned to a normal diet or a high energy diet (HED). Caffeine was given to HED mice by oral gavage. Body weights, lipids in the liver and liver damage were measured. Meanwhile, cAMP, SIRT3 or AMPK inhibitors were treated respectively before incubation with caffeine in oleate-treated HepG2 cells. SIRT3 was further silenced by siRNA to confirm the results. Caffeine significantly decreased the mass of fat tissues, lipids, ALT and AST levels in the liver of HED-treated mice. Caffeine increased the transformation of ADP to ATP and activated the cAMP/CREB/SIRT3/AMPK/ACC pathway in the liver. Nile red staining demonstrated that suppression of cAMP, SIRT3 or AMPK in oleate-treated HepG2 cells counteracted the effect of caffeine. Moreover, knocking down SIRT3 could down-regulate AMPK and ACC phosphorylation by caffeine. These results demonstrate that caffeine could improve HED-induced hepatic steatosis by promoting lipid metabolism via the cAMP/CREB/SIRT3/AMPK/ACC pathway. SIRT3 functioned as a molecular bridge connecting caffeine and lipid metabolism.