Activating transcription factor 3 is a target molecule linking hepatic steatosis to impaired glucose homeostasis.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD) contributes to impaired glucose tolerance, leading to type 2 diabetes (T2D); however, the precise mechanisms and target molecules that are involved remain unclear. Activating transcription factor 3 (ATF3) is associated with ß-cell dysfunction that is induced by severe stress signals in T2D. We aimed to explore the exact functional role of ATF3 as a mechanistic link between hepatic steatosis and T2D development. METHODS: Zucker diabetic fatty (ZDF) rats were utilized for animal experiments. An in vivo-jetPEI siRNA delivery system against ATF3 was used for loss-of-function experiments. We analyzed the baseline cross-sectional data derived from the biopsy-proven NAFLD registry (n=322). Human sera and liver tissues were obtained from 43 patients with biopsy-proven NAFLD and from seven healthy participants. RESULTS: ATF3 was highly expressed in the livers of ZDF rats and in human participants with NAFLD and/or T2D. Insulin resistance and hepatic steatosis were associated with increased ATF3 expression and decreased fatty acid oxidation via mitochondrial dysfunction and were attenuated by in vivo ATF3 silencing. Knockdown of ATF3 also ameliorated glucose intolerance, impaired insulin action, and inflammatory responses in ZDF rats. In patients with NAFLD and/or T2D, a significant positive correlation was observed between hepatic ATF3 expression and surrogate markers of T2D, mitochondrial dysfunction, and macrophage infiltration. CONCLUSIONS: Increased hepatic ATF3 expression is closely associated with hepatic steatosis and incident T2D; therefore, ATF3 may serve as a potential therapeutic target for NAFLD and hepatic steatosis-induced T2D. LAY SUMMARY: Hepatic activating transcription factor 3 (ATF3) may play an important role in oxidative stress-mediated hepatic steatosis and the development of type 2 diabetes (T2D) in a Zucker diabetic fatty (ZDF) rat model and in human patients with non-alcoholic fatty liver disease (NAFLD). Therefore, ATF3 may be a useful biomarker for predicting the progression of NAFLD and the development of T2D. Furthermore, given the significant association between hepatic ATF3 expression and both hepatic steatosis and impaired glucose homeostasis, in vivo ATF3 silencing may be a potential central strategy for preventing and managing NAFLD and T2D.

A mitochondrial division inhibitor, Mdivi-1, inhibits mitochondrial fragmentation and attenuates kainic acid-induced hippocampal cell death.

BACKGROUND: Kainic acid (KA)-induced excitotoxicity promotes cytoplasmic calcium accumulation, oxidative stress, and apoptotic signaling, leading to hippocampal neuronal death. Mitochondria play a critical role in neuroinflammation and the oxidative stress response. Mitochondrial morphology is disrupted during KA-induced seizures; however, it is not clear whether mitochondrial fission or fusion factors are involved in KA-induced neuronal death. RESULTS: We investigated the effect of Mdivi-1, a chemical inhibitor of the mitochondrial fission protein Drp1, on mitochondrial morphology and function in KA-injected mice. Mdivi-1 pretreatment significantly reduced seizure activity and increased survival rates of KA-treated mice. Mdivi-1 was protective against mitochondrial morphological disruption, and it reduced levels of phosphorylated Drp1 (Ser616) and Parkin recruitment to mitochondria. By contrast, levels of mitochondrial fusion factors did not change. Mdivi-1 also reduced KA-induced neuroinflammation and glial activation. CONCLUSIONS: We conclude that inhibition of mitochondrial fission attenuates Parkin-mediated mitochondrial degradation and protects from KA-induced hippocampal neuronal cell death.

Chronic ethanol consumption inhibits glucokinase transcriptional activity by Atf3 and triggers metabolic syndrome in vivo.

Chronic ethanol consumption induces pancreatic ß-cell dysfunction through glucokinase (Gck) nitration and down-regulation, leading to impaired glucose tolerance and insulin resistance, but the underlying mechanism remains largely unknown. Here, we demonstrate that Gck gene expression and promoter activity in pancreatic ß-cells were suppressed by chronic ethanol exposure in vivo and in vitro, whereas expression of activating transcription factor 3 (Atf3) and its binding to the putative Atf/Creb site (from -287 to -158 bp) on the Gck promoter were up-regulated. Furthermore, in vitro ethanol-induced Atf3 inhibited the positive effect of Pdx-1 on Gck transcriptional regulation, enhanced recruitment of Hdac1/2 and histone H3 deacetylation, and subsequently augmented the interaction of Hdac1/Pdx-1 on the Gck promoter, which were diminished by Atf3 siRNA. In vivo Atf3-silencing reversed ethanol-mediated Gck down-regulation and ß-cell dysfunction, followed by the amelioration of impaired glucose tolerance and insulin resistance. Together, we identified that ethanol-induced Atf3 fosters ß-cell dysfunction via Gck down-regulation and that its loss ameliorates metabolic syndrome and could be a potential therapeutic target in treating type 2 diabetes. The Atf3 gene is associated with the induction of type 2 diabetes and alcohol consumption-induced metabolic impairment and thus may be the major negative regulator for glucose homeostasis.

Visfatin exerts angiogenic effects on human umbilical vein endothelial cells through the mTOR signaling pathway.

The biologically active factors known as adipocytokines are secreted primarily by adipose tissues and can act as modulators of angiogenesis. Visfatin, an adipocytokine that has recently been reported to have angiogenic properties, is upregulated in diabetes, cancer, and inflammatory diseases. Because maintenance of an angiogenic balance is critically important in the management of these diseases, understanding the molecular mechanism by which visfatin promotes angiogenesis is very important. In this report, we describe our findings demonstrating that visfatin stimulates the mammalian target of the rapamycin (mTOR) pathway, which plays important roles in angiogenesis. Visfatin induced the expression of hypoxia-inducible factor 1α (HIF1α) and vascular endothelial growth factor (VEGF) in human endothelial cells. Inhibition of the mTOR pathway by rapamycin eliminated the angiogenic and proliferative effects of visfatin. The visfatin-induced increase in VEGF expression was also eliminated by RNA interference-mediated knockdown of the 70-kDa ribosomal protein S6 kinase (p70S6K), a downstream target of mTOR. Visfatin inactivated glycogen synthase kinase 3ß (GSK3ß) by phosphorylating it at Ser-9, leading to the nuclear translocation of ß-catenin. Both rapamycin co-treatment and p70S6K knockdown inhibited visfatin-induced GSK3ß phosphorylation at Ser-9 and nuclear translocation of ß-catenin. Taken together, these results indicate that mTOR signaling is involved in visfatin-induced angiogenesis, and that this signaling leads to visfatin-induced VEGF expression and nuclear translocation of ß-catenin. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Associations between local acidosis induced by renal LDHA and renal fibrosis and mitochondrial abnormalities in patients with diabetic kidney disease.

During the progression of diabetic kidney disease (DKD), renal lactate metabolism is rewired. The relationship between alterations in renal lactate metabolism and renal fibrosis in patients with diabetes has only been partially established due to a lack of biopsy tissues from patients with DKD and the intricate mechanism of lactate homeostasis. The role of lactate dehydrogenase A (LDHA)-mediated lactate generation in renal fibrosis and dysfunction in human and animal models of DKD was explored in this study. Measures of lactate metabolism (urinary lactate levels and LDHA expression) and measures of DKD progression (estimated glomerular filtration rate and Wilms' tumor-1 expression) were strongly negatively correlated in patients with DKD. Experiments with streptozotocin-induced DKD rat models and the rat renal mesangial cell model confirmed our findings. We found that the pathogenesis of DKD is linked to hypoxia-mediated lactic acidosis, which leads to fibrosis and mitochondrial abnormalities. The pathogenic characteristics of DKD were significantly reduced when aerobic glycolysis or LDHA expression was inhibited. Further studies will aim to investigate whether local acidosis caused by renal LDHA might be exploited as a therapeutic target in patients with DKD.

Alcohol consumption before pregnancy causes detrimental fetal development and maternal metabolic disorders.

Alcohol consumption before or during pregnancy poses serious health risks to the fetus; however, the underlying mechanisms involved remain obscure. Here, we investigated whether ethanol consumption before pregnancy affects maternal or fetal health and whether pharmacological inhibition of CYP2E1, a major ethanol oxidation enzyme, by 4-methylpyrazole (4-MP) has therapeutic effects. We found that ethanol consumption (5%) 2 weeks before pregnancy resulted in a decrease in the number of viable fetuses and abnormal fetal development, and these effects were accompanied by impaired maternal glucose homeostasis and hepatic steatosis during pregnancy. Neonates of ethanol-fed mice had postnatal macrosomia and significantly decreased growth rates during the lactation period. However, treatment with 4-MP, a CYP2E1 inhibitor, markedly ameliorated the reduction in insulin action and glucose disposal responsiveness in the livers of ethanol-fed mice. Blockage of CYP2E1 significantly reduced the alteration in hepatic lipid deposition, fatty acid oxidation, mitochondrial energy status, and macrophage infiltration observed in ethanol-fed mice. Finally, there was a positive correlation between postnatal macrosomia or growth retardation and increased inflammatory responses. Collectively, our study suggests that even moderate ethanol intake may be detrimental to fetal development and may cause growth retardation through maternal metabolic disorders.

Association between alcohol intake and incident hypertension in the Korean population.

BACKGROUND AND AIMS: Alcohol consumption is generally associated with increased risk of hypertension. However, the effect of alcohol intake on the incidence of hypertension remains controversial due to inconsistent results across studies. We investigated the association between alcohol intake and hypertension in a Korean population. METHODS AND RESULTS: The two studies that we evaluated herein, the CAVAS study (N = 6259) and the Ansan-Ansung study (N = 2461), were part of the Korean Genome and Epidemiology study on participants aged between 40 and 69 years who underwent community-based health checkups (2 years for the CAVAS study follow-up and 12 years for the Ansan-Ansung study follow-up). We categorized the participants into four groups based on baseline and follow-up period measurements. We found that baseline alcohol consumption increased the risk of incident hypertension in the CAVAS study [HR (95% CI), low: 1.094 (0.848-1.411); intermediate: 1.661 (1.227-2.141); high: 1.723 (1.274-2.330)]. Intermediate and high alcohol consumption were associated with increased risk of incident hypertension in men [2.086 (1.438-3.027) for intermediate, and 1.952 (1.294-2.944) for high], but only women had increased risk of incident hypertension with high consumption [1.950 (1.100-3.455)]. In addition, we found a positive association between the alcohol consumption pattern (over 10 years) and the risk of incident hypertension in the Ansan-Ansung study [HR (95% CI), light: 1.316 (1.126-1.539); moderate: 1.445 (1.193-1.750); heavy: 1.897 (1.488-2.419)]. Moderate and heavy consumption patterns carried higher risks of incident hypertension compared with never-drinking in men [moderate: 1.292 (1.033-1.617); heavy: 1.703 (1.293-2.242)], but women with light consumption patterns were at increased risk of incident hypertension [1.572 (1.302-1.899)]. CONCLUSIONS: This large prospective cohort study revealed a linear association between baseline alcohol consumption, subsequent alcohol consumption patterns (over more than 10 years), and hypertension risk in the Korean population.

2-Aminoadipic acid (2-AAA) as a potential biomarker for insulin resistance in childhood obesity.

Insulin resistance is an important clinical feature of metabolic syndrome, which includes obesity and type 2 diabetes. Increased adipose energy storage in obesity promote insulin resistance and other metabolic adverse effects. To identify a new link between adipocyte and insulin resistance, we performed targeted metabolite profiling of differentiated adipocytes and studied the association between adipogenic metabolites and insulin resistance. We found a correlation between 2-aminoadipic acid (2-AAA) and adipogenic differentiation. Also, circulatory 2-AAA was positively associated with obesity-related factors (fat mass, fat percent, waist circumference, BMI, BMI z-score, triglycerides, insulin, and HOMA-IR) at baseline and after 2 years in the children cohort study. Of these factors, increased BMI z-score and HOMA-IR were the primary independent factors associated with higher 2-AAA levels, and the baseline 2-AAA level was an indicator of the BMI z-score after 2 years. To validate the relationship between 2-AAA and obesity-related factors, we analyzed changes in 2-AAA levels following obesity intervention programs in two independent studies. In both studies, changes in 2-AAA levels during the intervention period were positively correlated with changes in the BMI z-score and HOMA-IR after adjusting for confounders. Moreover, the 2-AAA levels were increased in cell and mouse models of obesity-related insulin resistance. Excess 2-AAA levels led to impaired insulin signaling in insulin-sensitive cells (liver, skeletal muscle and adipose cells) and caused abnormal gluconeogenesis. Our results demonstrate that 2-AAA is associated with adipogenesis and insulin resistance. In this regard, 2-AAA could be a potential biomarker of obesity and obesity-related metabolic disorders.

The association between alcohol metabolism and genetic variants of ADH1A, SRPRB, and PGM1 in Korea.

BACKGROUND: Excessive alcohol consumption is a major public health problem in East Asian countries. Alcohol use leads to a cascade of problems including increased chances of risky behavior and a wide range of negative health consequences, from alcoholic liver disease to upper gastric and liver cancer. These alcohol effects are known to be influenced by ethnic variability and genetics. METHODS: In this study, subjects were administered a single dose of alcohol (0.6 g/kg for men or 0.4 g/kg for women), and blood alcohol and acetaldehyde concentrations were measured eight times over 5 hours. To investigate genetically susceptible factors to alcohol metabolism, we selected single-nucleotide polymorphisms (SNP) of genes identified by prior genetic association studies for alcohol metabolism, alcohol consumption, alcohol dependence, and related traits, and performed genotyping on all subjects (n = 104). RESULTS: We identified variations in the ADH1A, SRPRB, and PGM1 genes, which are directly associated with blood alcohol or acetaldehyde concentrations. Namely, the T allele of SRPRB rs17376019 and the C allele of PGM1 rs4643 were associated with lower blood alcohol levels, while the ADH1 rs1229976 C allele group exhibited markedly higher blood acetaldehyde levels than those of the ADH1 rs1229976 T allele group. CONCLUSION: This study demonstrates that genetic variations in ADH1A, SRPRB, and PGM1 are associated with variations in blood alcohol and acetaldehyde concentration after alcohol intake.

Chronic alcohol consumption potentiates the development of diabetes through pancreatic ß-cell dysfunction.

Chronic ethanol consumption is well established as a major risk factor for type-2 diabetes (T2D), which is evidenced by impaired glucose metabolism and insulin resistance. However, the relationships between alcohol consumption and the development of T2D remain controversial. In particular, the direct effects of ethanol consumption on proliferation of pancreatic ß-cell and the exact mechanisms associated with ethanol-mediated ß-cell dysfunction and apoptosis remain elusive. Although alcoholism and alcohol consumption are prevalent and represent crucial public health problems worldwide, many people believe that low-to-moderate ethanol consumption may protect against T2D and cardiovascular diseases. However, the J- or U-shaped curves obtained from cross-sectional and large prospective studies have not fully explained the relationship between alcohol consumption and T2D. This review provides evidence for the harmful effects of chronic ethanol consumption on the progressive development of T2D, particularly with respect to pancreatic ß-cell mass and function in association with insulin synthesis and secretion. This review also discusses a conceptual framework for how ethanol-produced peroxynitrite contributes to pancreatic ß-cell dysfunction and metabolic syndrome.

Protective effects of peroxiredoxin on hydrogen peroxide induced oxidative stress and apoptosis in cardiomyocytes.

BACKGROUND AND OBJECTIVES: The redox system is an important anti-oxidative system composed of thioredoxin, thioredoxin reductase, and peroxiredoxin (PRx). The fine details of PRx expression and its protective effects in various cells in cardiovascular tissue under oxidative stress created by hydrogen peroxide have not been fully elucidated. SUBJECTS AND METHODS: Oxidative stress was induced by adding hydrogen peroxide at 0.25 mM for 2 hours to rat neonatal cardiomyocytes (rCMCs), rat vascular smooth muscle cells (rVSMCs), and human umbilical vein endothelial cells (HUVECs). Apoptosis was quantified by flow cytometry and the expression patterns of the six PRx isoforms were evaluated by western blotting in the three cell lines after hydrogen peroxide stimulation. Apoptosis and the cell survival signal pathway were evaluated by PRx1 gene delivery using lentiviral vector in hydrogen peroxide stimulated rCMCs versus green fluorescence protein gene delivery. RESULTS: Hydrogen peroxide induced 25% apoptosis in rCMCs. Furthermore, the PRx1 and 5 isoforms were found to be overexpressed in hydrogen peroxide treated rCMCs, and PRx1 overexpression by gene delivery was found to reduce hydrogen peroxide induced rCMCs apoptosis significantly. In addition, this effect was found to originate from cell survival pathway modification. CONCLUSION: Hydrogen peroxide induced significant oxidative stress in rCMCs, rVSMCs, and HUVECs, and PRx1 overexpression using a lentiviral vector system significantly reduced hydrogen peroxide induced rCMCs apoptosis by upregulation of cell survival signals and downregulation of apoptotic signals. These findings suggest that PRx1 could be used as a treatment strategy for myocardial salvage in conditions of oxidative stress.

Expression pattern of the thioredoxin system in human endothelial progenitor cells and endothelial cells under hypoxic injury.

BACKGROUND AND OBJECTIVES: The thioredoxin (TRx) system is a ubiquitous thiol oxidoreductase pathway that regulates cellular reduction/oxidation status. Although endothelial cell (EC) hypoxic damage is one of the important pathophysiologic mechanisms of ischemic heart disease, its relationship to the temporal expression pattern of the TRx system has not yet been elucidated well. The work presented here was performed to define the expression pattern of the TRx system and its correlation with cellular apoptosis in EC lines in hypoxic stress. These results should provide basic clues for applying aspects of the TRx system as a therapeutic molecule in cardiovascular diseases. SUBJECTS AND METHODS: Hypoxia was induced with 1% O(2), generated in a BBL GasPak Pouch (Becton Dickinson, Franklin Lakes, NJ, USA) in human endothelial progenitor cells (hEPC) and human umbilical vein endothelial cells (HUVEC). Apoptosis of these cells was confirmed by Annexin-V: Phycoerythrin flow cytometry. Expression patterns of TRx; TRx reductase; TRx interacting protein; and survival signals, such as Bcl-2 and Bax, in ECs under hypoxia were checked. RESULTS: Apoptosis was evident after hypoxia in the two cell types. Higher TRx expression was observed at 12 hours after hypoxia in hEPCs and 12, 36, 72 hours of hypoxia in HUVECs. The expression patterns of the TRx system components showed correlation with EC apoptosis and cell survival markers. CONCLUSION: Hypoxia induced significant apoptosis and its related active changes of the TRx system were evident in human EC lines. If the cellular impact of TRx expression pattern in various cardiovascular tissues under hypoxia or oxidative stress was studied meticulously, the TRx system could be applied as a new therapeutic target in cardiovascular diseases, such as ischemic heart disease or atherosclerosis.