Sirtuin 1 (SIRT1) is known to deacetylate histones and non-histone proteins including transcription factors thereby regulating metabolism, stress resistance, cellular survival, cellular senescence/aging, inflammation-immune function, and endothelial functions, and circadian rhythms. Naturally occurring dietary polyphenols, such as resveratrol, curcumin, quercetin, and catechins, have antioxidant and anti-inflammatory properties via modulating different pathways, such as NF-κB-and mitogen activated protein kinase-dependent signaling pathways. In addition, these polyphenols have also been shown to activate SIRT1 directly or indirectly in a variety of models. Therefore, activation of SIRT1 by polyphenols is beneficial for regulation of calorie restriction, oxidative stress, inflammation, cellular senescence, autophagy/apoptosis, autoimmunity, metabolism, adipogenesis, circadian rhythm, skeletal muscle function, mitochondria biogenesis and endothelial dysfunction. In this review, we describe the regulation of SIRT1 by dietary polyphenols in various cellular functions in response to environmental and pro-inflammatory stimuli.

Background and PurposeEndothelial dysfunction can be detected at an early stage in the development of diabetes-related microvascular disease and is associated with accelerated endothelial senescence and ageing. Hyperglycaemia-induced oxidative stress is a major contributing factor to the development of endothelial dysfunction. Clinical data indicate that the hypoglycaemic agent, metformin, has an endothelial protective action; however, its molecular and cellular mechanisms remain elusive. In the present study, we have investigated the protective effect of metformin during hyperglycaemia-induced senescence in mouse microvascular endothelial cells (MMECs).Experimental ApproachMMECs were cultured in normal glucose (11 mM) and high glucose (HG; 40 mM) in the presence and absence of metformin (50 μM) for 72 h. The expression of sirtuin-1 (SIRT1) and senescence/apoptosis-associated markers was determined by immunoblotting and immunocyto techniques. SIRT1 expression was inhibited with appropriate siRNA.Key ResultsExposure of MMECs to HG significantly reduced SIRT1 protein expression, increased forkhead box O1 (FoxO-1) and p53 acetylation, increased p21 and decreased Bcl2 expression. In addition, senescence-associated β-galactosidase activity in MMECs was increased in HG. Treatment with metformin attenuated the HG-induced reduction of SIRT1 expression, modulated the SIRT1 downstream targets FoxO-1 and p53/p21, and protected endothelial cells from HG-induced premature senescence. However, following gene knockdown of SIRT1 the effects of metformin were lost.Conclusions and ImplicationsHG-induced down-regulation of SIRT1 played a crucial role in diabetes-induced endothelial senescence. Furthermore, the protective effect of metformin against HG-induced endothelial dysfunction was partly due to its effects on SIRT1 expression and/or activity.

Extracellular superoxide dismutase (ECSOD or SOD3) is highly expressed in lungs and functions as a scavenger of O 2 • ─ . ECM fragmentation, which can be triggered by oxidative stress, participates in the pathogenesis of chronic obstructive pulmonary disease (COPD) through attracting inflammatory cells into the lungs. The level of SOD3 is significantly decreased in lungs of patients with COPD. However, the role of endogenous SOD3 in the development/progression of emphysema is unknown. We hypothesized that SOD3 protects against emphysema by attenuating oxidative fragmentation of ECM in mice. To test this hypothesis, SOD3-deficient, SOD3-transgenic, and WT C57BL/6J mice were exposed to cigarette smoke (CS) for 3 d (300 mg total particulate matter/m 3 ) to 6 mo (100 mg/m 3 total particulate matter) or by intratracheal elastase injection. Airspace enlargement, lung inflammation, lung mechanical properties, and exercise tolerance were determined at different time points during CS exposure or after elastase administration. CS exposure and elastase administration caused airspace enlargement as well as impaired lung function and exercise capacity in SOD3-null mice, which were improved in mice overexpressing SOD3 and by pharmacological SOD mimetic. These phenomena were associated with SOD3-mediated protection against oxidative fragmentation of ECM, such as heparin sulfate and elastin, thereby attenuating lung inflammatory response. In conclusion, SOD3 attenuates emphysema and reduces oxidative fragmentation of ECM in mouse lung. Thus, pharmacological augmentation of SOD3 in the lung may have a therapeutic potential in the intervention of COPD/emphysema.antioxidants | cigarette smoke | chronic obstructive pulmonary disease | oxidants | glutathione E xtracellular superoxide dismutase (ECSOD or SOD3) is one of the three SOD antioxidant enzyme isoforms, and is highly expressed in lungs and vessels (1, 2). It is located in the ECM, the junctions of airway epithelial cells, the surface of airway smooth muscle, and the lining of vessels of the lung. SOD3 functions as a superoxide anion scavenger, thereby attenuating oxidative stress, which may play an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). Acute loss of SOD3 in adult mice causes death, whereas low mortality rates are seen in SOD3-overexpressing animals exposed to hyperoxia, suggesting an essential role of SOD3 for survival (3,4). Accumulating evidence shows that SOD3 polymorphism is associated with a decline in lung function in rodents and humans, and susceptibility to COPD, which may be a result of alteration of its encoding protein structure, function, and level (5-14). However, it is unclear whether endogenous SOD3 participates in the development/ progression of the inflammatory response, leading to COPD/ emphysema.Cigarette smoke (CS) is the major etiological factor in the pathogenesis of COPD, which is characterized by chronic lung inflammation, parenchymal destruction (i.e., emphysema), and accelerated decline in lung function....

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Endothelial nitric oxide synthase (eNOS) plays a crucial role in endothelial cell functions. SIRT1, a NAD+-dependent deacetylase, is shown to regulate endothelial function and hence any alteration in endothelial SIRT1 will affect normal vascular physiology. Cigarette smoke (CS)-mediated oxidative stress is implicated in endothelial dysfunction. However, the role of SIRT1 in regulation of eNOS by CS and oxidants are not known. We hypothesized that CS-mediated oxidative stress downregulates SIRT1 leading to acetylation of eNOS which results in reduced nitric oxide (NO)-mediated signaling and endothelial dysfunction. Human umbilical vascular endothelial cells (HUVECs) exposed to cigarette smoke extract (CSE) and H2O2 showed decreased SIRT1 levels, activity, but increased phosphorylation concomitant with increased eNOS acetylation. Pre-treatment of endothelial cells with resveratrol significantly attenuated the CSE- and oxidant-mediated SIRT1 levels and eNOS acetylation. These findings suggest that oxidant-mediated reduction of SIRT1 is associated with acetylation of eNOS which have implications in endothelial dysfunction.

Autophagy is a fundamental cellular process that eliminates long-lived proteins and damaged organelles through lysosomal degradation pathway. Cigarette smoke (CS)-mediated oxidative stress induces cytotoxic responses in lung cells. However, the role of autophagy and its mechanism in CS-mediated cytotoxic responses is not known. We hypothesized that NAD+-dependent deacetylase, sirtuin 1 (SIRT1) plays an important role in regulating autophagy in response to CS. CS exposure resulted in induction of autophagy in lung epithelial cells, fibroblasts and macrophages. Pretreatment of cells with SIRT1 activator resveratrol attenuated CS-induced autophagy whereas the SIRT1 inhibitor, sirtinol, augmented CS-induced autophagy. Elevated levels of autophagy were induced by CS in the lungs of SIRT1 deficient mice. Inhibition of poly(ADP-ribose)-polymerase-1 (PARP-1) attenuated CS-induced autophagy via SIRT1 activation. These data suggest that the SIRT1-PARP-1 axis plays a critical role in the regulation of CS-induced autophagy and have important implications in understanding the mechanisms of CS-induced cell death and senescence.

Impaired angiogenesis is a prominent risk factor that contributes to the development of diabetes-associated cardiovascular disease. MicroRNAs (miRNAs), small noncoding RNAs, are implicated as important regulators of vascular function, including endothelial cell differentiation, proliferation, and angiogenesis. In silico analysis and in vitro studies indicate that silent information regulator 1 (SIRT1) is a potential target for endothelial cell-specific miRNAs. In this study, we investigated the molecular crosstalk between miR-34a, the protein product of SIRT1 (sirtuin1), and the antidiabetic drug, metformin, in hyperglycemia-mediated impaired angiogenesis in mouse microvascular endothelial cells (MMECs). MMECs were cultured, transfected with either a miR-34a inhibitor or mimic in normal glucose (11 mM) or high glucose (HG, 40 mM) in the presence or absence of metformin. The expression of miR-34a, sirtuin1, and their signaling targets was evaluated. miR-34a expression is upregulated in a hyperglycemic milieu and parallels changes in the expression of sirtuin1, post-translational modification of endothelial nitric oxide synthase (phospho/acetylation), as well as an impairment in angiogenesis. The presence of metformin, or the inhibition of miR-34a using an anti-miR-34a inhibitor, increases the expression of sirtuin1 and attenuates the impairment in angiogenesis in HG-exposed MMECs. In contrast, overexpression of a miR-34a mimic prevents metformin-mediated protection. These data indicate that miR-34a, via the regulation of sirtuin1 expression, has an anti-angiogenic action in MMECs, which can be modulated by metformin. In summary, miR-34a represents both a target whereby metformin mediates its vasculoprotective actions and also a potential therapeutic target for the prevention/treatment of diabetic vascular disease.

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