Kwan-Woo Lee

Protective Role of Autophagy in Palmitate-Induced INS-1 β-Cell Death

Autophagy, a vacuolar degradative pathway, constitutes a stress adaptation that avoids cell death or elicits the alternative cell-death pathway. This study was undertaken to determine whether autophagy is activated in palmitate (PA)-treated beta-cells and, if activated, what the role of autophagy is in the PA-induced beta-cell death. The enhanced formation of autophagosomes and autolysosomes was observed by exposure of INS-1 beta-cells to 400 microm PA in the presence of 25 mm glucose for 12 h. The formation of green fluorescent protein-LC3-labeled structures (green fluorescent protein-LC3 dots), with the conversion from LC3-I to LC3-II, was also distinct in the PA-treated cells. The phospho-mammalian target of rapamycin level, a typical signal pathway that inhibits activation of autophagy, was gradually decreased by PA treatment. Blockage of the mammalian target of rapamycin signaling pathway by treatment with rapamycin augmented the formation of autophagosomes but reduced PA-induced INS-1 cell death. In contrast, reduction of autophagosome formation by knocking down the ATG5, inhibition of fusion between autophagosome and lysosome by treatment with bafilomycin A1, or inhibition of proteolytic degradation by treatment with E64d/pepstatin A, significantly augmented PA-induced INS-1 cell death. These findings showed that the autophagy system could be activated in PA-treated INS-1 beta-cells, and suggested that the induction of autophagy might play an adaptive and protective role in PA-induced cell death.

Conditional loss of TGF-beta signalling leads to increased susceptibility to gastrointestinal carcinogenesis in mice.

Downregulation of TGF‐β receptors is implicated in colon cancer development. Inactivation of either of the two transmembrane serine/threonine kinases, TGF‐β1 types I/II receptors, is now implicated in carcinogenesis, especially gastrointestinal carcinogenesis.

Fermented kimchi reduces body weight and improves metabolic parameters in overweight and obese patients

Kimchi is a traditional fermented Korean food that has garnered international interest due to its various beneficial effects. Focusing on the effect of fermentation, this study hypothesized that consumption of fermented kimchi would have more beneficial effects compared with that of fresh kimchi on metabolic parameters that are related to cardiovascular disease and metabolic syndrome risks in overweight and obese subjects. Twenty-two overweight and obese patients with body mass indexes greater than 25 kg/m(2) were randomly assigned to two 4-week diet phases separated by a 2-week washout period (crossover design). During each diet phase, the subjects consumed either fresh or fermented kimchi. Anthropometric data showed significant decreases in body weight, body mass index, and body fat in both groups, and the fermented kimchi group showed a significant decrease in the waist-hip ratio and fasting blood glucose. Net differences in the systolic blood pressure, diastolic blood pressure, percent body fat, fasting glucose, and total cholesterol in the fermented kimchi group were significantly greater than those in the fresh kimchi group. There was also a tendency for a decrease in fasting insulin after consumption of fermented kimchi. Therefore, the ingestion of fermented kimchi had positive effects on various factors associated with metabolic syndrome, including systolic and diastolic blood pressures, percent body fat, fasting glucose, and total cholesterol, compared with the fresh kimchi. These results suggest that the maturity of kimchi (fresh vs fermented) may affect obesity, lipid metabolism, and inflammatory processes.

A chemical chaperone 4-PBA ameliorates palmitate-induced inhibition of glucose-stimulated insulin secretion (GSIS).

Free fatty acids (FFAs) are believed to be a stimulus to elicit beta cell dysfunction. The present study was undertaken to determine whether endoplasmic reticulum (ER) stress was involved in palmitate-induced inhibition of glucose-stimulated insulin secretion (GSIS) and whether reduction of ER stress using a chemical chaperone restored the GSIS-inhibition. Treatment of INS-1 cells with 300 microM palmitate for 24h elicited ER stress, showing increased levels of phospho-eIF2alpha, Bip and spliced XBP, and also induced GSIS-inhibition without reduction of cell viability. Replenishment with 4-phenyl butyric acid (4-PBA) as a chemical chaperone reduced the palmitate-induced-ER stress and significantly reversed the palmitate-induced GSIS-inhibition. Furthermore, 4-PBA ameliorated palmitate-induced GSIS-inhibition in primary rat islet cells. These data suggested that ER stress was involved in FFA-induced GSIS-inhibition and that the FFA-induced beta cell dysfunction could be ameliorated by treatment with a chemical chaperone.

Fibroblast growth factor-21 protects human skeletal muscle myotubes from palmitate-induced insulin resistance by inhibiting stress kinase and NF-κB

We investigated the effects of fibroblast growth factor-21 (FGF-21) on palmitate-induced insulin resistance in skeletal muscle myotubes. First, to determine the effect of FGF-21 on palmitate-induced insulin resistance, we measured 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-d-glucose uptake and levels of proteins involved in insulin signaling pathways (IRS-1 and Akt) in human skeletal muscle myotubes (HSMMs) exposed to palmitate for 24h, and compared HSMMs exposed to palmitate and different doses of recombinant FGF-21. Second, to determine the mechanisms underlying the contribution of FGF-21 to palmitate-induced insulin resistance, we compared levels of proteins linked to palmitate-induced insulin resistance (PKC-θ, IKKα/β, JNK, p38, IκBα, and NF-κB) in HSMMs exposed to palmitate and different doses of recombinant FGF-21 for 24h. Palmitate-reduced glucose uptake was restored by FGF-21. Palmitate inhibited phosphorylation of Akt and thereby impaired insulin signaling in HSMMs. FGF-21 prevented palmitate from inhibiting the phosphorylation of Akt. These results indicate that FGF-21 prevented palmitate-induced insulin resistance in HSMMs. Palmitate activated NF-κB in HSMMs, thereby impairing the action of insulin and initiating chronic inflammation. FGF-21 inhibited palmitate-induced NF-κB activation in HSMMs. The results of the present study suggest that FGF-21 prevents palmitate-induced insulin resistance in HSMMs by inhibiting the activation of stress kinase and NF-κB.

Serum fibroblast growth factor 21 was elevated in subjects with type 2 diabetes mellitus and was associated with the presence of carotid artery plaques

AIMS Fibroblast growth factor 21 (FGF21) is an important regulator of glucose/lipid metabolism. Although there are studies examining the relationship between serum FGF21 levels and glucose homeostasis, the role of FGF21 remains unclear. The objective of this study was to examine whether serum FGF21 levels are associated with metabolic parameters in subjects with varying degrees of obesity and glucose tolerance and with complications in subjects with type2 diabetes mellitus (T2DM). METHODS The study consisted of 213 subjects who were lean and had normal glucose tolerance (lean NGT), were overweight with NGT, had impaired glucose tolerance (IGT) or had T2DM. Serum FGF21 levels and their associations with the parameters of adiposity, glucose tolerance and the presence of diabetic complications were examined. RESULTS The serum FGF21 levels in T2DM were higher than in lean NGT. Serum FGF21 levels showed a positive correlation with the urine albumin-to-creatinine ratio (ACR) in all subjects except for the T2DM subjects, who showed a correlation after adjustment of age, gender and body mass index. Moreover, the subjects with carotid artery plaque showed higher serum FGF21 levels than those without complications. CONCLUSION Serum FGF21 levels were associated with the urine ACR and diabetic complications including carotid artery plaque.

Involvement of Ca2+-mediated apoptotic signals in palmitate-induced MIN6N8a beta cell death.

The extracellular Ca(2+) chelator EGTA and L-type Ca(2+) channel blockers, such as, nifedipine and nimodipine were found to have a protective effect on palmitate-induced MIN6N8a beta cell apoptosis, whereas the Ca(2+) channel opener, Bay K8644, enhanced the apoptotic process. Moreover, the phospho-form of Bad, in conjunction with phospho-Akt, was reduced in response to palmitate and the palmitate-induced dephosphorylations of Akt and Bad were dependent on Ca(2+) influx. The transient expression of catalytically active Akt prevented MIN6N8a cells from palmitate-induced apoptosis. Deltamethrin, an inhibitor of Ca(2+)-activated phosphatase, delayed Akt and Bad dephosphorylations, and then protected MIN6N8a cells from palmitate-induced apoptosis. On the other hand, palmitate was found to induce CHOP, an apoptotic transcription factor in response to ER stress, and this induction was enhanced by Ca(2+) influx. Our studies suggested that Ca(2+) influx and subsequent Ca(2+)-mediated apoptotic signals are involved in palmitate-induced beta cell death.

Stimulation of Lipogenesis as Well as Fatty Acid Oxidation Protects against Palmitate-Induced INS-1 β-Cell Death

Saturated fatty acids are generally cytotoxic to β-cells. Accumulation of lipid intermediates and subsequent activation of lipid-mediated signals has been suggested to play a role in fatty acid-induced toxicity. To determine the effects of lipid metabolism in fatty acid-induced toxicity, lipid metabolism was modulated by up- and down-regulation of a lipogenic or fatty acid oxidation pathway, and the effects of various modulators on palmitate (PA)-induced INS-1 β-cell death were then evaluated. Treatment with the liver X receptor agonist T0901317 reduced PA-induced INS-1 cell death, regardless of its enhanced lipogenic activity. Furthermore, transient expression of a lipogenic transcription factor sterol regulatory element binding protein-1c (SREBP-1c) was also protective against PA-induced cytotoxicity. In contrast, knockdown of SREBP-1c or glycerol-3-phosphate acyltransferase 1 significantly augmented PA-induced cell death and reduced T0901317-induced protective effects. Conversely, T0901317 increased carnitine PA transferease-1 (CPT-1) expression and augmented PA oxidation. CPT-1 inhibitor etomoxir or CPT-1 knockdown augmented PA-induced cell death and reduced T0901317-induced protective effects, whereas the peroxisome proliferator-activated receptor (PPAR)-α agonist bezafibrate reduced PA-induced toxicity. In particular, T0901317 reduced the levels of PA-induced endoplasmic reticulum (ER) stress markers, including phospho-eukaryotic initiation factor-2α, phospho-C-Jun N terminal kinase, and CCAAT/enhancer-binding protein homologous protein. In contrast, knockdown of SREBP-1c or glycerol-3-phosphate acyltransferase 1 augmented PA-induced ER stress responses. Results of these experiments suggested that stimulation of lipid metabolism, including lipogenesis and fatty acid oxidation, protected β-cells from PA-induced lipotoxicity and that protection through enhanced lipogenesis was likely due to reduced ER stress.

Association of Vascular Endothelial Growth Factor Polymorphisms with Nonproliferative and Proliferative Diabetic Retinopathy

CONTEXT Vascular endothelial growth factor (VEGF) is a potent angiogenic and vascular permeability factor, and its polymorphisms are associated with proliferative diabetic retinopathy (PDR) and macular edema. OBJECTIVE We investigated the contributions of VEGF gene polymorphisms to nonproliferative diabetic retinopathy (NPDR) as well as PDR. DESIGN, SETTING, AND SUBJECTS In this study we compared VEGF gene variants in a sample of Korean type 2 diabetes patients with and without diabetic retinopathy (DR) and in healthy controls. Of the diabetes patients, 145 had PDR, 108 had NPDR, and 134 had no retinopathy (noDR). They were all duration matched. Samples were genotyped for rs699947, rs1570360, and rs2010963 polymorphisms. RESULTS We found a significant association between the A allele at rs699947 with DR (odds ratio = 1.84 (95% confidence interval = 1.28-2.66); P = 0.001 vs. noDR). Patients with NPDR, as well as PDR, had increased incidence of the A allele. The AGG haplotype was more frequently found in patients with DR than in patients with noDR (odds ratio = 4.79 (95% confidence interval = 1.42-16.16); P = 0.006). PDR and NPDR patients exhibited an increased incidence of the AGG haplotype. CONCLUSIONS VEGF polymorphisms might be a useful predictive marker for the development and progression of DR at an earlier stage of diabetes.

Capsaicin attenuates palmitate-induced expression of macrophage inflammatory protein 1 and interleukin 8 by increasing palmitate oxidation and reducing c-Jun activation in THP-1 (human acute monocytic leukemia cell) cells

Capsaicin, a spicy component of hot peppers, has been shown to improve inflammatory disease and obesity. In this study, we tested the hypothesis that the anti-inflammatory activity of capsaicin can be used to improve free fatty acid (FFA)-induced inflammation by reducing gene expression of macrophage inflammatory protein 1 (MIP-1) and interleukin 8 (IL-8) in THP-1 (human acute monocytic leukemia cell) macrophages. To investigate whether capsaicin ameliorates palmitate-induced MIP-1 and IL-8 gene expressions, we treated THP-1 cells with palmitate in the presence or absence of capsaicin and measured MIP-1 and IL-8 by real-time polymerase chain reaction. To elucidate the mechanism by which capsaicin effects on palmitate-induced MIP-1 and IL-8 gene expressions, we performed immunoblotting with stress kinase-related antibodies and measured palmitate oxidation and palmitate oxidation-related gene expression. Palmitate and stearate but not the unsaturated FFA oleate significantly increased MIP-1 and IL-8 expressions in THP-1 macrophages. Treatment with capsaicin or FFA oxidation stimulators inhibited palmitate-induced MIP-1 and IL-8 expressions in THP-1 macrophages. Capsaicin increased the gene expression of carnitine palmitoyltransferase 1 and the β-oxidation of palmitate. Furthermore, capsaicin significantly reduced palmitate-stimulated activation of c-Jun N-terminal kinase, c-Jun, and p38. Our data suggest that the attenuation of palmitate-induced MIP-1 and IL-8 gene expressions by capsaicin is associated with reduced activation of c-Jun N-terminal kinase, c-Jun, and p38 and preserved β-oxidation activity.