Change in mRNA expression of sirtuin 1 and sirtuin 3 in cats fed on high fat diet

Species differences of fatty liver diseases: comparisons between human and feline

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most widespread chronic liver disease that poses significant threats to public health due to changes in dietary habits and lifestyle patterns. The transition from simple steatosis to nonalcoholic steatohepatitis (NASH) markedly increases the risk of developing cirrhosis, hepatocellular carcinoma, and liver failure in patients. However, there is only one Food and Drug Administration-approved therapeutic drug in the world, and the clinical demand is huge. There is significant clinical heterogeneity among patients with NAFLD, and it is challenging to fully understand human NAFLD using only a single animal model. Interestingly, felines, like humans, are particularly prone to spontaneous fatty liver disease. This review summarized and compared the etiology, clinical features, pathological characteristics, and molecular pathogenesis between human fatty liver and feline hepatic lipidosis (FHL). We analyzed the key similarities and differences between those two species, aiming to provide theoretical foundations for developing effective strategies for the treatment of NAFLD in clinics.

Melatonin Lowers HIF-1α Content in Human Proximal Tubular Cells (HK-2) Due to Preventing Its Deacetylation by Sirtuin 1

Although melatonin is widely known for its nephroprotective properties, there are no reports clearly pointing at its impact on the activity of hypoxia-inducible factor-1 (HIF-1), the main mediator of metabolic responses to hypoxia, in kidneys. The aim of the present study was to elucidate how melatonin affects the expression of the regulatory subunit HIF-1α in renal proximal tubules. HK-2 cells, immortalized human proximal tubular cells, were cultured under hypoxic conditions (1% O₂). Melatonin was applied at 100 μM concentration. Protein and mRNA contents were determined by Western blot and RT-qPCR, respectively. HIF-1α acetylation level was established by means of immunoprecipitation followed by Western blot. Melatonin receptors MT1 and MT2 localization in HK-2 cells was visualized using immunofluorescence confocal analysis. It was found that melatonin in HK-2 cells (1) lowered HIF-1α protein, but not mRNA, content; (2) attenuated expression of HIF-1 target genes; (3) increased HIF-1α acetylation level; and (4) diminished sirtuin 1 expression (both protein and mRNA). Sirtuin 1 involvement in the regulation of HIF-1α level was confirmed applying cells with silenced Sirt1 gene. Moreover, the presence of membrane MT1 and MT2 receptors was identified in HK-2 cells and their ligand, ramelteon, turned out to mimic melatonin action on both HIF-1α and sirtuin 1 levels. Thus, it is concluded that the mechanism of melatonin-evoked decline in HIF-1α content in renal proximal tubular cells involves increased acetylation of this subunit which results from the attenuated expression of sirtuin 1, an enzyme reported to deacetylate HIF-1α. This observation provides a new insight to the understanding of melatonin action in kidneys.

The association between left ventricular mass index and serum sirtuin 3 level in patients with hypertension

Objectives

Sirtuin 3 (SIRT3) can protect cardiomyocytes from oxidative stress-mediated cell damage and prevent cardiac hypertrophy development. The aim of this study was to evaluate whether a relationship existed between left ventricular mass index (LVMI) and serum SIRT3 levels in patients with hypertension.

Patients and methods

This study was conducted as a cross-sectional study of 83 patients between April 2018 and October 2018. The LVMI of all patients was calculated using the formula of the American Echocardiography Association and patients were divided into two groups according to results (increased LVMI and normal LVMI).

Results

Increased LVMI was determined in 37.3% of patients, whereas 62.7% had normal LVMI. There was no significant difference between serum SIRT3 levels between those with increased LVMI and normal LVMI (5.8 versus 5.4 ng/ml; P = 0.914). Serum pro-brain natriuretic peptide levels (69 versus 41 ng/ml; P = 0.019) were found to be higher in patients with increased LVMI than in those with normal LVMI. A positive correlation between SIRT3 levels and Sm (myocardial systolic) velocity was also determined (r = 0.338; P = 0.002).

Conclusion

The serum levels of SIRT3, a molecule which has been proposed to have protective properties against myocardial hypertrophy, were not found to be correlated with LVMI values; however, SIRT3 levels were found to be correlated with Sm velocity, which is accepted to be an indicator of myocardial early diastolic dysfunction.

Nicotinamide and NAFLD: Is There Nothing New Under the Sun?

Nicotinamide adenine dinucleotide (NAD) has a critical role in cellular metabolism and energy homeostasis. Its importance has been established early with the discovery of NAD's therapeutic role for pellagra. This review addresses some of the recent findings on NAD physiopathology and their effects on nonalcoholic fatty liver disease (NAFLD) pathogenesis, which need to be considered in the search for a better therapeutic approach. Reduced NAD concentrations contribute to the dysmetabolic imbalance and consequently to the pathogenesis of NAFLD. In this perspective, the dietary supplementation or the pharmacological modulation of NAD levels appear to be an attractive strategy. These reviewed studies open the doors to growing interest in NAD metabolism for NAFLD diagnosis, prevention, and treatment. Future rigorous clinical studies in humans will be necessary to validate these preliminary but promising results.

The Association between SIRT1 Genetic Variation and Type 2 Diabetes Mellitus Is Influenced by Dietary Intake in Elderly Chinese

BACKGROUND

To examine whether polymorphisms of SIRT1 and dietary product intake can be implicated in type 2 diabetes mellitus (T2DM).

METHODS

In this community-based, case-control study, 568 subjects (284 patients and 284 controls) were enrolled in a community located in northern Guangzhou, China. The four polymorphisms of SIRT1 (rs4746720, rs10509291, rs2236319, rs10823116) were examined using TaqMan nuclease technology. The dietary data were collected by an inquiring officer through face-to-face method.

RESULTS

The rs4746720 CC+TT genotype had higher risk compared with CT genotype to develop T2DM [odds ratio (OR) =1.42, 95% confidence interval (CI) = 1.02-1.97]. The subjects with rs4746720 CC+TT genotype and eat sugar food over 30g per day increased the risk of T2DM to 2.22(1.21-4.06) times. The subjects with rs4746720 CC+TT genotype and smoking increased the risk of T2DM to 1.65 (1.10-2.47) times. The unhealthy eating habits such as red meat, salty food, use animal fat yielded higher risks of T2DM, the OR of risk of T2DM was 2.89 (1.38-6.01), 2.73 (1.61-4.64) and 27.91(9.24-84.32) respectively. However, the milk, soy, white meat, vegetables and low-salt diet decreased the risk of T2DM, the OR of risk of T2DM was 0.51 (0.29-0.88), 0.43 (0.26-0.74), 0.51(0.32-0.83), 0.21(0.10-0.44), 0.28(0.12-0.65), 0.35(0.21-0.51) respectively.

CONCLUSION

Variants in SIRT1 with rs4746720 CC+TT genotype increased the risk of T2DM, especially with the unhealthy eating habits.

Detection of Sirtuin-1 protein expression in peripheral blood leukocytes in dogs

Sirtuin-1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD⁺)-dependent histone deacetylase with a large number of protein substrates. It has attracted a lot of attention in association with extending lifespan. The objective of this study was to enable the evaluation of SIRT1 expression in peripheral blood mononuclear cells (PBMCs) from dogs by flow cytometry. Three transcript variants were amplified from PBMCs by reverse transcription PCR and the nucleotide sequences were analyzed. On the basis of deduced amino acid sequence, a monoclonal antibody against human SIRT1, 1F3, was selected to detect canine SIRT1. Canine SIRT1 in peripheral blood mononuclear cells was successfully detected by western blotting using this antibody. Intracellular canine SIRT1 was also detected in permeabilized 293T cells transfected with a canine SIRT1 expression plasmid by flow cytometry using this antibody. SIRT1 was detected in all leukocyte subsets including lymphocytes, granulocytes and monocytes. The expression level was markedly different among individual dogs. These results indicated that the method applied in this study is useful for evaluating canine SIRT1 levels in PBMCs from dogs.

High-fat diet aggravates postoperative cognitive dysfunction in aged mice

Background

Silent Information Regulator 1 (Sirt1) and apoptosis play key roles in postoperative cognitive dysfunction (POCD). Consuming a high-fat diet (HFD), a prevalent type of diet in modern society, has been increasingly recognized as contributing to neurodegenerative diseases. Although Sirt1 and apoptosis are significant responders to HFD in the brain, little is known regarding the functional correlations between HFD and POCD.

Methods

Thirty-two aged C57BL/6 male mice were randomly divided into 2 groups: an ad libitum (AL) group (fed a regular diet) and high-fat diet (HF) group (fed a high-fat diet). After 8 weeks, the animals were divided into four sub-groups: an ad libitum control (ALC) group, ad libitum surgery (ALS) group, high-fat diet control (HFC) group, and high-fat diet surgery (HFS) group. The ALS and HFS groups were exposed to 3% sevoflurane in 33% oxygen for 3 h and were subsequently subjected to exploratory surgery to establish the POCD model. The ALC and HFC groups were treated with 33% oxygen for 3 h without surgery. After 48 h, the learning and memory abilities of mice in each group were tested using the Morris water maze (MWM). The expression levels of Sirt1, Bcl-2, Bax and caspase-3 cleaved were detected by western blot.

Results

The MWM and western blotting results showed that the learning and memory abilities were decreased in the HFC group compared with the ALC group. The learning and memory abilities and the expression of Sirt1 in the hippocampus in the HFS group were significantly decreased compared with the other groups. A significant decrease in Sirt1 expression was also observed in the HFC group compared with the ALS group. The level of Bcl-2 was lower in the HFS group than in the HFC and ALC groups. The expression levels of caspase-3 cleaved and Bax increased in the HFS group compared with the HFC group. Moreover, the expression of caspase-3 cleaved was higher in the HFC group than in the ALS group.

Conclusion

HFD can aggravate POCD in aged C57BL/6 mice, an effect that may be related to the inhibition expression of Sirt1 and the promotion of neuronal apoptosis.

Tissue-specific regulation of sirtuin and nicotinamide adenine dinucleotide biosynthetic pathways identified in C57Bl/6 mice in response to high-fat feeding

The sirtuin (SIRT)/nicotinamide adenine dinucleotide (NAD) system is implicated in development of type 2 diabetes (T2D) and diet-induced obesity, a major risk factor for T2D. Mechanistic links have not yet been defined. SIRT/NAD system gene expression and NAD/NADH levels were measured in liver, white adipose tissue (WAT) and skeletal muscle from mice fed either a low-fat diet or high-fat diet (HFD) for 3 days up to 16 weeks. An in-house custom-designed multiplex gene expression assay assessed all 7 mouse SIRTs (SIRT1-7) and 16 enzymes involved in conversion of tryptophan, niacin, nicotinamide riboside and metabolic precursors to NAD. Significantly altered transcription was correlated with body weight, fat mass, plasma lipids and hormones. Regulation of the SIRT/NAD system was associated with early (SIRT4, SIRT7, NAPRT1 and NMNAT2) and late phases (NMNAT3, NMRK2, ABCA1 and CD38) of glucose intolerance. TDO2 and NNMT were identified as markers of HFD consumption. Altered regulation of the SIRT/NAD system in response to HFD was prominent in liver compared with WAT or muscle. Multiple components of the SIRTs and NAD biosynthetic enzymes network respond to consumption of dietary fat. Novel molecular targets identified above could direct strategies for dietary/therapeutic interventions to limit metabolic dysfunction and development of T2D.

Sirtuins, aging, and cardiovascular risks

The sirtuins comprise a highly conserved family proteins present in virtually all species from bacteria to mammals. Sirtuins are members of the highly conserved class III histone deacetylases, and seven sirtuin genes (sirtuins 1-7) have been identified and characterized in mammals. Sirtuin activity is linked to metabolic control, apoptosis, cell survival, development, inflammation, and healthy aging. In this review, we summarize and discuss the potential mutual relations between each sirtuin and cardiovascular health and the impact of sirtuins on oxidative stress and so age-related cardiovascular disorders, underlining the possibility that sirtuins will be novel targets to contrast cardiovascular risks induced by aging.

Sirtuin 1 suppresses nuclear factor κB induced transactivation and pro-inflammatory cytokine expression in cat fibroblast cells

Nuclear factor κB (NF-κB) is a key factor in the development of chronic inflammation and is deeply involved in age-related and metabolic diseases development. These diseases have become a serious problem in cats. Sirtuin 1 (SIRT1) is associated with aging and metabolism through maintaining inflammation via NF-κB. In addition, fibroblasts are considered an important factor in the development of chronic inflammation. Therefore, we aimed to examine the effect of cat SIRT1 (cSIRT1) on NF-κB in cat fibroblast cells. The up-regulation of NF-κB transcriptional activity and pro-inflammatory cytokine mRNA expression by p65 subunit of NF-κB and lipopolysaccharide was suppressed by cSIRT1 in cat fibroblast cells. Our findings show that cSIRT1 is involved in the suppression of inflammation in cat fibroblast cells.

A redox-resistant sirtuin-1 mutant protects against hepatic metabolic and oxidant stress

Sirtuin-1 (SirT1), a member of the NAD(+)-dependent class III histone deacetylase family, is inactivated in vitro by oxidation of critical cysteine thiols. In a model of metabolic syndrome, SirT1 activation attenuated apoptosis of hepatocytes and improved liver function including lipid metabolism. We show in SirT1-overexpressing HepG2 cells that oxidants (nitrosocysteine and hydrogen peroxide) or metabolic stress (high palmitate and high glucose) inactivated SirT1 by reversible oxidative post-translational modifications (OPTMs) on three cysteines. Mutating these oxidation-sensitive cysteines to serine preserved SirT1 activity and abolished reversible OPTMs. Overexpressed mutant SirT1 maintained deacetylase activity and attenuated proapoptotic signaling, whereas overexpressed wild type SirT1 was less protective in metabolically or oxidant-stressed cells. To prove that OPTMs of SirT1 are glutathione (GSH) adducts, glutaredoxin-1 was overexpressed to remove this modification. Glutaredoxin-1 overexpression maintained endogenous SirT1 activity and prevented proapoptotic signaling in metabolically stressed HepG2 cells. The in vivo significance of oxidative inactivation of SirT1 was investigated in livers of high fat diet-fed C57/B6J mice. SirT1 deacetylase activity was decreased in the absence of changes in SirT1 expression and associated with a marked increase in OPTMs. These results indicate that glutathione adducts on specific SirT1 thiols may be responsible for dysfunctional SirT1 associated with liver disease in metabolic syndrome.