Kyu Yeon Hur

Autophagy deficiency in beta cells leads to compromised unfolded protein response and progression from obesity to diabetes in mice

Aims/hypothesisThe unfolded protein response (UPR) in endoplasmic reticulum (ER) and autophagy are known to be related. We investigated the role of autophagy in UPR of pancreatic beta cells and the susceptibility of autophagy-deficient beta cells to the ER stress that is implicated in the development of diabetes.MethodsRat insulin promoter (RIP)-Cre+;autophagy-related 7 (Atg7)F/W mice were bred with ob/w mice to derive RIP-Cre+;Atg7F/F-ob/ob mice and to induce ER stress in vivo. GFP-LC3+-ob/ob mice were generated to examine in vivo autophagic activity. Real-time RT-PCR was performed to study the expression of the genes of the UPR machinery. Proteolysis was assessed by determining release of incorporated radioactive leucine.ResultsProduction of UPR machinery was reduced in autophagy-deficient beta cells, which was associated with diminished production of p85α and p85β regulatory subunits of phosphoinositide 3-kinase. Because of compromised UPR machinery, autophagy-deficient beta cells were susceptible to ER stressors in vitro. When mice with beta cell-specific autophagy deficiency, which have mild hyperglycaemia, were bred with ob/ob mice to induce ER stress in vivo, severe diabetes developed, which was accompanied by an increase in beta cell death and accumulation of reactive oxygen species. The increased demand for UPR present in obesity was unmet in autophagy-deficient beta cells. Autophagy level and autophagic activity were enhanced by lipid, while proteolysis was reduced.Conclusions/interpretationThese results suggest that autophagy is important for intact UPR machinery and appropriate UPR in response to lipid injury that increases demand for UPR. Autophagy deficiency in pancreatic beta cells may contribute to the progression from obesity to diabetes.

Systemic autophagy insufficiency compromises adaptation to metabolic stress and facilitates progression from obesity to diabetes.

Despite growing interest in the relationship between autophagy and systemic metabolism, how global changes in autophagy affect metabolism remains unclear. Here we show that mice with global haploinsufficiency of an essential autophagy gene (Atg7(+/-) mice) do not show metabolic abnormalities but develop diabetes when crossed with ob/ob mice. Atg7(+/-)-ob/ob mice show aggravated insulin resistance with increased lipid content and inflammatory changes, suggesting that autophagy haploinsufficiency impairs the adaptive response to metabolic stress. We further demonstrate that intracellular lipid content and insulin resistance after lipid loading are increased as a result of autophagy insufficiency, and provide evidence for increased inflammasome activation in Atg7(+/-)-ob/ob mice. Imatinib or trehalose improves metabolic parameters of Atg7(+/-)-ob/ob mice and enhances autophagic flux. These results suggest that systemic autophagy insufficiency could be a factor in the progression from obesity to diabetes, and autophagy modulators have therapeutic potential against diabetes associated with obesity and inflammation.

A Polymorphism in the Zinc Transporter Gene, SLC30A8, Confers Resistance Against Posttransplantation Diabetes Mellitus in Renal Allograft Recipients

OBJECTIVE—Posttransplantation diabetes mellitus (PTDM) is a major metabolic complication in renal transplant recipients, and insulin secretory defects play an important role in the pathogenesis of PTDM. The R325W (rs13266634) nonsynonymous polymorphism in the islet-specific zinc transporter protein gene, SLC30A8, has been reported to be associated with type 2 diabetes and possibly with a defect in insulin secretion. This study investigated the association between genetic variations in the SLC30A8 gene and PTDM in renal allograft recipients. RESEARCH DESIGN AND METHODS—A total of 624 unrelated renal allograft recipients without previously diagnosed diabetes were enrolled. Rs13266634 was genotyped in the cohort, which consisted of 174 posttransplantation diabetic patients and 450 non-posttransplantation diabetic subjects. The genotyping of the SLC30A8 polymorphism was performed using real-time PCR. RESULTS—The prevalence of PTDM was 33.8% in patients carrying the R/R genotype, 26.8% in patients with the R/W genotype, and 19.8% in patients with the W/W genotype. There was a strong association between the number of W-alleles and PTDM risk reduction (P for trend = 0.007). Patients with at least one T-allele showed a decreased risk of PTDM compared with those with the R/R genotype (R/W, risk ratio [RR] 0.78, P = 0.126; W/W, RR 0.52, P = 0.007). The effect of the SLC30A8 genotype remained significant after adjustments for age, sex, body weight gain, and type of immunosuppressant (R/W, hazard ratio [HR] 0.77, P = 0.114; W/W, HR 0.58, P = 0.026). CONCLUSIONS—These data provide evidence that the SLC30A8 rs13266634 gene variation is associated with protection from the development of PTDM in renal allograft recipients.

Gut Microbiota and Metabolic Disorders

Gut microbiota plays critical physiological roles in the energy extraction and in the control of local or systemic immunity. Gut microbiota and its disturbance also appear to be involved in the pathogenesis of diverse diseases including metabolic disorders, gastrointestinal diseases, cancer, etc. In the metabolic point of view, gut microbiota can modulate lipid accumulation, lipopolysaccharide content and the production of short-chain fatty acids that affect food intake, inflammatory tone, or insulin signaling. Several strategies have been developed to change gut microbiota such as prebiotics, probiotics, certain antidiabetic drugs or fecal microbiota transplantation, which have diverse effects on body metabolism and on the development of metabolic disorders.

Regular Exercise Is Associated with a Reduction in the Risk of NAFLD and Decreased Liver Enzymes in Individuals with NAFLD Independent of Obesity in Korean Adults

Background We evaluated the association of regular physical exercise with the presence of non-alcoholic fatty liver disease (NAFLD) and liver enzymes in relation to obesity and insulin resistance. Methodology/Principal Findings A cross-sectional analysis was conducted in 72,359 healthy Korean adults without diabetes who participated in a comprehensive health check-up. Subjects who have been exercising regularly (more than 3 times per week, at least for 30 minutes each time and for consecutive 3 month) were categorized into exercise group. All subjects were categorized into deciles based on their body mass index (BMI) and we estimated the odds ratios (ORs) for having NAFLD according to exercise regularity in each decile. The diagnosis of NAFLD was based on ultrasonography findings. Individuals with NAFLD (n = 19,921) were analyzed separately to evaluate ORs for having elevated liver enzymes based on regularity of exercise. The risk for NAFLD was significantly reduced in exercise group with age- and sex-adjusted ORs of 0.53–0.72 for all BMI deciles except at BMI categories of <19.6 and 20.7–21.6 kg/m2. While no difference was seen in BMI between subjects in exercise and non-exercise group across the BMI deciles, the values of body fat percentage and metabolic risk factors differed. Among NAFLD patients, subjects in exercise group had a lower risk for having elevated liver enzymes with multivariable adjusted OR of 0.85 (95% CI 0.74–0.99, for AST) and 0.74 (95% CI 0.67–0.81, for ALT) than did subjects in non-exercise group. Conclusions/Significance Regular exercise was associated with a reduced risk for having NAFLD and decreased liver enzymes in patients with NAFLD, and this relationship was also independent of obesity.

New mechanisms of metformin action: Focusing on mitochondria and the gut.

The most well‐known mechanism of metformin action, one of the most commonly prescribed antidiabetic drugs, is adenosine monophosphate‐activated protein kinase activation; however, recent investigations have shown that adenosine monophosphate‐activated protein kinase‐independent pathways can explain some of metformins beneficial metabolic effects as well as undesirable side‐effects. Such novel pathways include induction of mitochondrial stress, inhibition of mitochondrial shuttles, alteration of intestinal microbiota, suppression of glucagon signaling, activation of autophagy, attenuation of inflammasome activation, induction of incretin receptors and reduction of terminal endoplasmic reticulum stress. Together, these studies have broadened our understanding of the mechanisms of antidiabetic agents as well as the pathogenic mechanism of diabetes itself. The results of such investigations might help to identify new target molecules and pathways for treatment of diabetes and metabolic syndrome, and could also have broad implications in diseases other than diabetes. Accordingly, new antidiabetic drugs with better efficacy and fewer adverse effects will likely result from these studies.

Protective effects of magnesium lithospermate B against diabetic atherosclerosis via Nrf2-ARE-NQO1 transcriptional pathway

Hyperglycemia-induced oxidative stress is known to play an important role in the development of several diabetic complications, including atherosclerosis. Although a number of antioxidants are available, none have been found to be suitable for regulating the oxidative stress response and enhancing antioxidative defense mechanisms. In this study, we evaluated the effects of magnesium lithospermate B (LAB) against oxidative stress. We also endeavored to identify the target molecule of LAB in vascular smooth muscle cells (VSMCs) and the underlying biochemical pathways related to diabetic atherosclerosis. Modified MTT and transwell assays showed that the increased proliferation and migration of rat aortic VSMCs in culture with high glucose was significantly inhibited by LAB. LAB also attenuated neointimal hyperplasia after balloon catheter injury in diabetic rat carotid arteries. To determine molecular targets of LAB, we studied the effects of LAB on aldose reductase (AR) activity, O-GlcNAcylation, and protein kinase C (PKC) activity in VSMCs under normoglycemic or hyperglycemic conditions and showed the improvement of major biochemical pathways by LAB. Potential involvement of the nuclear factor erythroid 2-related factor-2 (Nrf2)--antioxidant responsive element (ARE)-NAD(P)H: quinone oxidoreductase-1 (NQO1) pathway was assessed using siRNA methods. We found that LAB activates the NQO1 via the Nrf2-ARE pathway, which plays an important role in inhibition of the major molecular mechanisms that lead to vascular damage and the proliferation and migration of VSMCs. Together, these findings demonstrate that the induction of the Nrf2-ARE-NQO1 pathway by LAB could be a new therapeutic strategy to prevent diabetic atherosclerosis.

Therapeutic effect of magnesium lithospermate B on neointimal formation after balloon-induced vascular injury

Vascular smooth muscle cell (VSMC) proliferation and migration in response to platelet-derived growth factor (PDGF) play an important role in the development of atherosclerosis and restenosis. Recent evidence indicates that PDGF increases intracellular levels of reactive oxygen species in VSMCs and that both PDGF-induced VSMC proliferation and migration are reactive oxygen species-dependent. Danshen is a representative oriental medicine used for the treatment of vascular disease. Previously, we reported that magnesium lithospermate B, an active component of Danshen, is a potent antioxidant. Thus we investigated the therapeutic potential of magnesium lithospermate B in neointimal formation after carotid artery injury in rats along with its effects on the PDGF signaling pathway for stimulating VSMC proliferation and migration in vitro. PDGF is dimeric glycoprotein composed of two A or two B chains. In this study, we used PDGF-BB, which is one of the isoforms of PDGF (i.e., PDGF-AA, PDGF-BB, and PDGF-AB). Our results demonstrated that magnesium lithospermate B directly scavenged reactive oxygen species in a xanthine/xanthine oxidase system and reduced PDGF-BB-induced intracellular reactive oxygen species generation in VSMCs. In a rat carotid artery balloon injury model, magnesium lithospermate B treatment (10 mg/kg/day, i.p) showed a significant effect on the prevention of neointimal formation compared with vehicle treatment. In cultured VSMCs, magnesium lithospermate B significantly attenuated PDGF-BB-induced cell proliferation and migration as measured by 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2-tetrazolium bromide (MTT) assay and transwell migration assays, respectively. Further, magnesium lithospermate B inhibited PDGF-BB-induced phosphorylation of phospatidylinositol 3-kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathways by scavenging reactive oxygen species. Together, these data indicated that magnesium lithospermate B, a potent reactive oxygen species scavenger, prevented both injury-induced neointimal formation in vivo and PDGF-BB-induced VSMC proliferation and migration in vitro, suggesting that magnesium lithospermate B may be a promising agent to prevent atherosclerosis and restenosis following angioplasty.

Association of common type 2 diabetes risk gene variants and posttransplantation diabetes mellitus in renal allograft recipients in Korea.

Background. Posttransplantation diabetes mellitus (PTDM) is a major metabolic complication in renal transplant recipients. Recent genome-wide association studies have identified several genes associated with type 2 diabetes. Here, we examined the association between PTDM and 17 single nucleotide polymorphisms (SNPs) located within 15 genes in a cohort of renal allograft recipients in Korea. Materials and Methods. A total of 589 patients who received kidney transplants between 1989 and 2007, without a history of diabetes and had a pretransplant fasting glucose less than 5.5 mmol/L were included in this study. We analyzed the association between the PTDM development and the following SNPs: TCF7L2 rs7903146, SLC30A8 rs13266634, HHEX (rs1111875, rs7923837, and rs5015480), CDKAL1 rs10946398, CDKN2A/B rs10811661, IGF2BP2 rs4402960, FTO rs8050136, WFS1 rs734312, JAZF1 rs864745, CDC123/CAMK1D rs12779790, TSPAN8 rs7961581, THADA rs7578597, ADAMTS9 rs4607103, NOTCH2 rs1092391, and KCNQ1 rs2237892. Results. Eight SNPs in six genes were significantly associated with the PTDM development: TCF7L2 rs7903146 (odds ratio [OR]=2.20, P =0.016), SLC30A8 rs13266634 (OR=1.52, P =0.003), HHEX rs1111875 (OR=1.47, P =0.007), HHEX rs7923837 (OR=2.32, P =0.014), HHEX rs5015480 (OR=1.59, P =0.003), CDKAL1 rs10946398 (OR=1.43, P =0.008), CDKN2A/B rs10811661 (OR=1.33, P =0.039), and KCNQ1 rs2237892 (OR=1.46, P =0.009). Conclusions. These data suggest that genetic variations in TCF7L2, SLC30A8, HHEX, CDKAL1, CDKN2A/B, and KCNQ1 are associated with PTDM in Korea.

Statins and the risk of gastric cancer in diabetes patients

BackgroundSeveral studies have suggested a cancer risk reduction in statin users although the evidence remains weak for stomach cancer. The purpose of this study was to use an exact-matching case–control design to examine the risk of gastric cancer associated with the use of statins in a cohort of patients with diabetes.MethodsCases were defined as patients with incident gastric cancer identified by International Classification of Diseases 16.0 ~ 16.9 recorded at Samsung Medical Center database during the period of 1999 to 2008, at least 6 months after the entry date of diabetes code. Each gastric cancer case patient was matched with one control patient from the diabetes patient registry in a 1:1 fashion, blinded to patient outcomes.ResultsA total of 983 cases with gastric cancer and 983 controls without gastric cancer, matched by age and sex, were included in the analysis. The presence of prescription for any statin was inversely associated with gastric cancer risk in the unadjusted conditional logistic regression model (OR: 0.18; 95% CI: 0.14 – 0.24; P < .0001). Multivariate analysis using conditional logistic regression with Bonferroni’s correction against aspirin indicated a significant reduction in the risk of gastric cancer in diabetes patients with statin prescriptions (OR: 0.21; 95% CI: 0.16 – 0.28; P < .0001). After adjustment for aspirin use, a longer duration of statin use was associated with reduced risk of gastric cancer, with statistical significance (P<.0001).ConclusionsA strong inverse association was found between the risk of gastric adenocarcinoma and statin use in diabetic patients.