Sirtuin 1 is upregulated in young obese Zucker rat cerebral arteries

Caloric restriction induces H2O2 formation as a trigger of AMPK-eNOS-NO pathway in obese rats: Role for CAMKII

Caloric restriction (CR) improves endothelial function through the upregulation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric oxide synthase (eNOS). Moreover, hydrogen peroxide (H₂O₂) is upregulated in yeast subjected to CR. Our aim was to assess if mild short-term CR increases vascular H₂O₂ formation as a link with AMPK and eNOS activation. Twelve-week old Zucker obese (fa/fa) and control Zucker lean male rats were fed a standard chow either ad libitum (AL, n=10) or with a 20% CR (CR, n=10) for two weeks. CR significantly improved relaxation to ACh in fa/fa rats because of an enhanced endogenous production of H₂O₂ in aortic rings (H₂O₂ levels _fa/faAL=0.5 ± 0.05 nmol/mg vs. H₂O₂ levels _fa/faCR=0.76 ± 0.07 nmol/mg protein; p<0.05). Expression of mitochondrial superoxide dismutase (Mn-SOD) and total SOD activity were increased in aorta from fa/fa animals after CR. In cultured aortic endothelial cells, serum deprivation or 2-deoxy-d-glucose induced a significant increase in: i) superoxide anion and H₂O₂ levels, ii) p-AMPK/AMPK and p-eNOS/eNOS expression and iii) nitric oxide levels. This effect was reduced by catalase and strongly inhibited by Ca²⁺/calmodulin-dependent kinase II (CamkII) silencing. In conclusion, we propose that mild short-term CR might be a trigger of mechanisms aimed at protecting the vascular wall by the increase of H₂O₂, which then activates AMPK and nitric oxide release, thus improving endothelium-dependent relaxation. In addition, we demonstrate that CAMKII plays a key role in mediating CR-induced AMPK activation through H₂O₂ increase.

Overexpressed eNOS upregulates SIRT1 expression and protects mouse pancreatic β cells from apoptosis

Loss of sirtuin 1 (SIRT1) activity may be associated with metabolic diseases, including diabetes. The aim of the present study was to investigate the potential effects of overexpressed endothelial nitric oxide synthase (eNOS) on cell proliferation and apoptosis with SIRT1 activation in the Min6 mouse pancreatic β cell line. A pcDNA3.0-eNOS plasmid was constructed and transfected into Min6 cells for 24 h prior to harvesting. eNOS expression was validated and SIRT1 expression was detected following plasmid transfection using reverse transcription-quantitative polymerase chain reaction and western blot analysis, which demonstrated that the expression levels of eNOS and SIRT1 were significantly upregulated. Furthermore, the cell proliferation and cell apoptosis of the Min6 cells were evaluated, using a cell counting kit-8 assay and flow cytometry, respectively. The results suggested that overexpressed eNOS promoted cell proliferation and inhibited cell apoptosis in Min6 cells. The interaction between eNOS and SIRT1 was explored through co-immunoprecipitation, and it found that there was a strong interaction between eNOS and SIRT1. In conclusion, overexpressed eNOS may induce SIRT1 activation, which is implied to play a protective role in Min6 cells, and eNOS may be a new therapeutic target for diseases such as type 2 diabetes.

Cross-Talk Between Sirtuin 1 and High-Mobility Box 1 in Steatotic Liver Graft Preservation

BACKGROUND

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide +-dependent histone deacetylase that regulates various pathways involved in ischemia-reperfusion injury (IRI). Moreover, high-mobility group box 1 protein (HMGB1) has also been involved in inflammatory processes during IRI. However, the roles of both SIRT1 and HMGB1 in liver preservation is poorly understood. In this communication, we evaluated the potential relationship between SIRT1 and HMGB1 in steatotic and non-steatotic liver grafts preserved in Institute Georges Lopez solution (IGL-1) preservation solution enriched or not enriched with trimetazidine (TMZ).

METHODS

Steatotic and non-steatotic livers were preserved in IGL-1 preservation solution (24 hours, 4°C), enriched or not enriched with TMZ (10 μmol/L), and then submitted to ex vivo reperfusion (2 hours; 37°C). Liver injury (AST/ALT) and function (bile output, vascular resistance) were evaluated. SIRT1, HMGB1, autophagy parameters (beclin-1, LC3B), PPAR-γ, and heat-shock protein (HO-1, HSP70) expression were determined by means of Western blot. Also, we assessed oxidative stress, mitochondrial damage (glutamate dehydrogenase), and TNF-α levels.

RESULTS

Elevated SIRT1 and enhanced autophagy were found after reperfusion in steatotic livers preserved in IGL-1+TMZ when compared with IGL-1. However, these changes were not seen in the case of non-steatotic livers. Also, HO-1 increases in the IGL-1 + TMZ group were evident only in the case of steatotic livers, whereas HSP70 and PPAR-γ protein expression were enhanced only in non-steatotic livers. All reported changes were consistent with decreased liver injury diminution, ameliorated hepatic function, and decreased TNF-α and HMGB levels. In addition, the oxidative stress and mitochondrial damage were efficiently prevented by the IGL-1 + TMZ use.

CONCLUSIONS

SIRT1 is associated with HMGB1 decreases and increased autophagy in steatotic livers, contributing to increased tolerance to cold IRI.

Compromised endothelium-dependent hyperpolarization-mediated dilations can be rescued by NS309 in obese Zucker rats

OBJECTIVE

NO and a non-NO/prostacyclin EDH mechanism are major contributors of vascular tone and cerebral blood flow. However, the effect of metabolic syndrome on EDH-mediated responses in cerebral vessels remains unknown and may offer another avenue for therapeutic targeting. The purpose of this study was to investigate EDH-dependent responses in cerebral arteries during metabolic syndrome.

METHODS

EDH-dependent dilations were assessed in MCAs isolated from nondiabetic obese and lean Zucker rats in the presence and absence of NS309, an activator of SKCa and IKCa channels. IKCa channel expression and activity were assessed by western blotting and pressure myography, respectively.

RESULTS

EDH-mediated dilations were significantly attenuated in the obese compared to the lean Zucker rat MCA. Luminal delivery of 1 μM NS309 enhanced EDH-mediated responses in lean and obese Zucker cerebral vessels. Both dose-dependent dilations to luminal NS309 and IKCa protein expression in pooled cerebral arteries were comparable between the two groups.

CONCLUSIONS

Our results suggest that pharmacological targeting of IKCa channels can rescue EDH-mediated dilations in obese Zucker rat MCAs. Compromised EDH-mediated dilations in obesity are not due to impaired IKCa channel expression or activity.

Sirtuin 1 in rat orthotopic liver transplantation: an IGL-1 preservation solution approach

AIM

To investigate the possible involvement of Sirtuin 1 (SIRT1) in rat orthotopic liver transplantation (OLT), when Institute Georges Lopez 1 (IGL-1) preservation solution is enriched with trimetazidine (TMZ).

METHODS

Male Sprague-Dawley rats were used as donors and recipients. Livers were stored in IGL-1 preservation solution for 8h at 4 °C, and then underwent OLT according to Kamada's cuff technique without arterialization. In another group, livers were stored in IGL-1 preservation solution supplemented with TMZ, at 10(-6) mol/L, for 8 h at 4 °C and then underwent OLT. Rats were sacrificed 24 h after reperfusion, and liver and plasma samples were collected. Liver injury (transaminase levels), mitochondrial damage (glutamate dehydrogenase activity) oxidative stress (malondialdehyde levels), and nicotinamide adenine dinucleotide (NAD(+)), the co-factor necessary for SIRT1 activity, were determined by biochemical methods. SIRT1 and its substrates (ac-FoxO1, ac-p53), the precursor of NAD(+), nicotinamide phosphoribosyltransferase (NAMPT), as well as the phosphorylation of adenosine monophosphate activated protein kinase (AMPK), p-mTOR, p-p70S6K (direct substrate of mTOR), autophagy parameters (beclin-1, LC3B) and MAP kinases (p-p38 and p-ERK) were determined by Western blot.

RESULTS

Liver grafts preserved in IGL-1 solution enriched with TMZ presented reduced liver injury and mitochondrial damage compared with those preserved in IGL-1 solution alone. In addition, livers preserved in IGL-1 + TMZ presented reduced levels of oxidative stress. This was consistent with enhanced SIRT1 protein expression and elevated SIRT1 activity, as indicated by decreased acetylation of p53 and FoxO1. The elevated SIRT1 activity in presence of TMZ can be attributed to the enhanced NAMPT protein and NAD(+)/NADH levels. Up-regulation of SIRT1 was consistent with activation of AMPK and inhibition of phosphorylation of mTOR and its direct substrate (p-p70S6K). As a consequence, autophagy mediators (beclin-1 and LC3B) were over-expressed. Furthermore, MAP kinases were regulated in livers preserved with IGL-1 + TMZ, as they were characterized by enhanced p-ERK and decreased p-p38 protein expression.

CONCLUSION

Our study shows that IGL-1 preservation solution enriched with TMZ protects liver grafts from the IRI associated with OLT, through SIRT1 up-regulation.

Differential Telomere Shortening in Blood versus Arteries in an Animal Model of Type 2 Diabetes

Vascular dysfunction is an early feature of diabetic vascular disease, due to increased oxidative stress and reduced nitric oxide (NO) bioavailability. This can lead to endothelial cell senescence and clinical complications such as stroke. Cells can become senescent by shortened telomeres and oxidative stress is known to accelerate telomere attrition. Sirtuin 1 (SIRT1) has been linked to vascular health by upregulating endothelial nitric oxide synthase (eNOS), suppressing oxidative stress, and attenuating telomere shortening. Accelerated leukocyte telomere attrition appears to be a feature of clinical type 2 diabetes (T2D) and therefore the telomere system may be a potential therapeutic target in preventing vascular complications of T2D. However the effect of T2D on vascular telomere length is currently unknown. We hypothesized that T2D gives rise to shortened leukocyte and vascular telomeres alongside reduced vascular SIRT1 expression and increased oxidative stress. Accelerated telomere attrition was observed in circulating leukocytes, but not arteries, in T2D compared to control rats. T2D rats had blunted arterial SIRT1 and eNOS protein expression levels which were associated with reduced antioxidant defense capacity. Our findings suggest that hyperglycemia and a deficit in vascular SIRT1 per se are not sufficient to prematurely shorten vascular telomeres.

Endothelial NADPH oxidases: which NOX to target in vascular disease?

NADPH oxidases (NOXs) are reactive oxygen species (ROS)-generating enzymes implicated in the pathophysiology of vascular diseases such as hypertension and stroke. Endothelial cells express four NOX isoforms including the superoxide-generating enzymes NOX1, NOX2, and NOX5 and the hydrogen peroxide-generating enzyme NOX4. Studies on arteries from patients with coronary artery disease, and in animals with experimentally induced hypertension, diabetes, or atherosclerosis, suggest that NOX1, NOX2, and NOX5 promote endothelial dysfunction, inflammation, and apoptosis in the vessel wall, whereas NOX4 is by contrast vasoprotective in increasing nitric oxide bioavailability and suppressing cell death pathways. Based on these findings and promising preclinical studies with the NOX1/NOX2 antagonist, apocynin, we suggest that the field is poised for clinical evaluation of NOX inhibitors as therapeutics for cardiovascular disease.

Local sympathetic denervation of femoral artery in a rabbit model by using 6-hydroxydopamine in situ

Both artery bundle and sympathetic nerve were involved with the metabolism of bone tissues. Whether the enhancing effects of artery bundle result from its accompanying sympathetic nerve or blood supply is still unknown. There is no ideal sympathetic nerve-inhibited method for the in situ denervation of artery bundle. Therefore, we dipped the femoral artery in the 6-hydroxydopamine (6-OHDA) locally and observed its effect. Compared with control group, the in situ treatment of 6-OHDA did not damage the normal structure of vascular bundle indicated by hematoxylin-eosin (HE) staining. However, the functions of sympathetic nerve was completely inhibited for more than 2 weeks, and only a few function of sympathetic nerve resumed 4 weeks later, evidenced by glyoxylic acid staining and the expression of tyrosine hydroxylase (TH) and nerve peptide Y (NPY). Thus, 6-OHDA is promising as an ideal reagent for the local denervation of sympathetic nerve from artery system.