Glycerol-3-phosphate acyltransferase-4-deficient mice are protected from diet-induced insulin resistance by the enhanced association of mTOR and rictor

Glycerol-3-phosphate acyltransferase (GPAT) activity is highly induced in obese individuals with insulin resistance, suggesting a correlation between GPAT function, triacylglycerol accumulation, and insulin resistance. We asked whether microsomal GPAT4, an isoform regulated by insulin, might contribute to the development of hepatic insulin resistance. Compared with control mice fed a high fat diet, Gpat4 −/− mice were more glucose tolerant and were protected from insulin resistance. Overexpression of GPAT4 in mouse hepatocytes impaired insulin-suppressed gluconeogenesis and insulin-stimulated glycogen synthesis. Impaired glucose homeostasis was coupled to inhibited insulin-stimulated phosphorylation of Akt(Ser473) and Akt(Thr308). GPAT4 overexpression inhibited rictor's association with the mammalian target of rapamycin (mTOR), and mTOR complex 2 (mTORC2) activity. Compared with overexpressed GPAT3 in mouse hepatocytes, GPAT4 overexpression increased phosphatidic acid (PA), especially di16:0-PA. Conversely, in Gpat4 −/− hepatocytes, both mTOR/rictor association and mTORC2 activity increased, and the content of PA in Gpat4 −/− hepatocytes was lower than in controls, with the greatest decrease in 16:0-PA species. Compared with controls, liver and skeletal muscle from Gpat4 −/−-deficient mice fed a high-fat diet were more insulin sensitive and had a lower hepatic content of di16:0-PA. Taken together, these data demonstrate that a GPAT4-derived lipid signal, likely di16:0-PA, impairs insulin signaling in mouse liver and contributes to hepatic insulin resistance.

Download Full-text

12/15-Lipoxygenase signaling in the endoplasmic reticulum stress response

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00373.2011 ◽

2012 ◽

Vol 302 (6) ◽

pp. E654-E665 ◽

Cited By ~ 35

Author(s):

Banumathi K. Cole ◽

Norine S. Kuhn ◽

Shamina M. Green-Mitchell ◽

Kendall A. Leone ◽

Rebekah M. Raab ◽

...

Keyword(s):

Insulin Resistance ◽

Endoplasmic Reticulum ◽

Stress Response ◽

Er Stress ◽

Pancreatic Islets ◽

High Fat Diet ◽

Wild Type ◽

High Fat ◽

Stress Markers ◽

Deficient Mice

Central obesity is associated with chronic inflammation, insulin resistance, β-cell dysfunction, and endoplasmic reticulum (ER) stress. The 12/15-lipoxygenase enzyme (12/15-LO) promotes inflammation and insulin resistance in adipose and peripheral tissues. Given that obesity is associated with ER stress and 12/15-LO is expressed in adipose tissue, we determined whether 12/15-LO could mediate ER stress signals. Addition of 12/15-LO lipid products 12(S)-HETE and 12(S)-HPETE to differentiated 3T3-L1 adipocytes induced expression and activation of ER stress markers, including BiP, XBP-1, p-PERK, and p-IRE1α. The ER stress inducer, tunicamycin, upregulated ER stress markers in adipocytes with concomitant 12/15-LO activation. Addition of a 12/15-LO inhibitor, CDC, to tunicamycin-treated adipocytes attenuated the ER stress response. Furthermore, 12/15-LO-deficient adipocytes exhibited significantly decreased tunicamycin-induced ER stress. 12/15-LO action involves upregulation of interleukin-12 (IL-12) expression. Tunicamycin significantly upregulated IL-12p40 expression in adipocytes, and IL-12 addition increased ER stress gene expression; conversely, LSF, an IL-12 signaling inhibitor, and an IL-12p40-neutralizing antibody attenuated tunicamycin-induced ER stress. Isolated adipocytes and liver from 12/15-LO-deficient mice fed a high-fat diet revealed a decrease in spliced XBP-1 expression compared with wild-type C57BL/6 mice on a high-fat diet. Furthermore, pancreatic islets from 12/15-LO-deficient mice showed reduced high-fat diet-induced ER stress genes compared with wild-type mice. These data suggest that 12/15-LO activity participates in ER stress in adipocytes, pancreatic islets, and liver. Therefore, reduction of 12/15-LO activity or expression could provide a new therapeutic target to reduce ER stress and downstream inflammation linked to obesity.

Download Full-text

Estrogens Protect against High-Fat Diet-Induced Insulin Resistance and Glucose Intolerance in Mice

Endocrinology ◽

10.1210/en.2008-0971 ◽

2009 ◽

Vol 150 (5) ◽

pp. 2109-2117 ◽

Cited By ~ 244

Author(s):

Elodie Riant ◽

Aurélie Waget ◽

Haude Cogo ◽

Jean-François Arnal ◽

Rémy Burcelin ◽

...

Keyword(s):

Insulin Resistance ◽

Adipose Tissue ◽

Glucose Intolerance ◽

High Fat Diet ◽

Chow Diet ◽

High Fat ◽

Normal Chow ◽

Visceral Adipose ◽

Deficient Mice ◽

Normal Chow Diet

Although corroborating data indicate that estrogens influence glucose metabolism through the activation of the estrogen receptor α (ERα), it has not been established whether this pathway could represent an effective therapeutic target to fight against metabolic disturbances induced by a high-fat diet (HFD). To this end, we first evaluated the influence of chronic 17β-estradiol (E2) administration in wild-type ovariectomized mice submitted to either a normal chow diet or a HFD. Whereas only a modest effect was observed in normal chow diet-fed mice, E2 administration exerted a protective effect against HFD-induced glucose intolerance, and this beneficial action was abolished in ERα-deficient mice. Furthermore, E2 treatment reduced HFD-induced insulin resistance by 50% during hyperinsulinemic euglycemic clamp studies and improved insulin signaling (Akt phosphorylation) in insulin-stimulated skeletal muscles. Unexpectedly, we found that E2 treatment enhanced cytokine (IL-6, TNF-α) and plasminogen activator inhibitor-1 mRNA expression induced by HFD in the liver and visceral adipose tissue. Interestingly, although the proinflammatory effect of E2 was abolished in visceral adipose tissue from chimeric mice grafted with bone marrow cells from ERα-deficient mice, the beneficial effect of the hormone on glucose tolerance was not altered, suggesting that the metabolic and inflammatory effects of estrogens can be dissociated. Eventually comparison of sham-operated with ovariectomized HFD-fed mice demonstrated that endogenous estrogens levels are sufficient to exert a full protective effect against insulin resistance and glucose intolerance. In conclusion, the regulation of the ERα pathway could represent an effective strategy to reduce the impact of high-fat diet-induced type 2 diabetes.

Download Full-text

An impaired gut immune response to a high‐fat diet is associated with visceral adipose inflammation and peripheral insulin resistance in leptin‐deficient mice

The FASEB Journal ◽

10.1096/fasebj.22.1_supplement.450.1 ◽

2008 ◽

Vol 22 (S1) ◽

Author(s):

Sin Hoa Gieng ◽

Aria Eshraghi ◽

Elizabeth Hawley ◽

Patrick Sanger ◽

Julia Menshenina ◽

...

Keyword(s):

Insulin Resistance ◽

Immune Response ◽

High Fat Diet ◽

High Fat ◽

Peripheral Insulin Resistance ◽

Adipose Inflammation ◽

Visceral Adipose ◽

Deficient Mice

Download Full-text

CaMKIV limits metabolic damage through induction of hepatic autophagy by CREB in obese mice

Journal of Endocrinology ◽

10.1530/joe-19-0251 ◽

2020 ◽

Vol 244 (2) ◽

pp. 353-367 ◽

Cited By ~ 2

Author(s):

Jiali Liu ◽

Yue Li ◽

Xiaoyan Zhou ◽

Xi Zhang ◽

Hao Meng ◽

...

Keyword(s):

Insulin Resistance ◽

Insulin Sensitivity ◽

Inflammatory Response ◽

Mitochondrial Dysfunction ◽

High Fat Diet ◽

Insulin Action ◽

Hepatic Insulin Resistance ◽

Obese Mice ◽

High Fat ◽

Impaired Insulin

High-fat diet (HFD) not only induces insulin resistance in liver, but also causes autophagic imbalance and metabolic disorders, increases chronic inflammatory response and induces mitochondrial dysfunction. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) has recently emerged as an important regulator of glucose metabolism and skeletal muscle insulin action. Its activation has been involved in the improvement of hepatic and adipose insulin action. But the underlying mechanism is not fully understood. In the present study, we aimed to address the direct effects of CaMKIV in vivo and to evaluate the potential interaction of impaired insulin sensitivity and autophagic disorders in hepatic insulin resistance. Our results indicated obese mice receiving CaMKIV showed decreased blood glucose and serum insulin and improved insulin sensitivity as well as increased glucose tolerance compared with vehicle injection. Meanwhile, defective hepatic autophagy activity, impaired insulin signaling, increased inflammatory response and mitochondrial dysfunction in liver tissues which are induced by high-fat diet were also effectively alleviated by injection of CaMKIV. Consistent with these results, the addition of CaMKIV to the culture medium of BNL cl.2 hepatocytes markedly restored palmitate-induced hepatic insulin resistance and autophagic imbalance. These effects were nullified by blockade of cyclic AMP response element-binding protein (CREB), indicating the causative role of CREB in action of CaMKIV. Our findings suggested that CaMKIV restores hepatic autophagic imbalance and improves impaired insulin sensitivity via phosphorylated CREB signaling pathway, which may offer novel opportunities for treatment of obesity and diabetes.

Download Full-text

Ethno-pharmacological insulin signaling induction of aqueous extract of Syzygium paniculatum fruits in a high-fat diet induced hepatic insulin resistance

Journal of Ethnopharmacology ◽

10.1016/j.jep.2020.113576 ◽

2020 ◽

pp. 113576

Author(s):

Prabhakar Yellanur Konda ◽

Vidyasagar Chennupati ◽

Sreenivasulu Dasari ◽

Nishesh Sharma ◽

Muthukumaran Muthulingam ◽

...

Keyword(s):

Insulin Resistance ◽

Aqueous Extract ◽

Insulin Signaling ◽

High Fat Diet ◽

Hepatic Insulin Resistance ◽

High Fat

Download Full-text

CXCL12-CXCR4 pathway activates brown adipocytes and induces insulin resistance in CXCR4-deficient mice under high-fat diet

Scientific Reports ◽

10.1038/s41598-019-42127-8 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Kenichi Kurita ◽

Ko Ishikawa ◽

Kenji Takeda ◽

Masanori Fujimoto ◽

Hiraku Ono ◽

...

Keyword(s):

Insulin Resistance ◽

High Fat Diet ◽

High Fat ◽

Brown Adipocytes ◽

Deficient Mice

Download Full-text

PKCε contributes to lipid-induced insulin resistance through cross talk with p70S6K and through previously unknown regulators of insulin signaling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1804379115 ◽

2018 ◽

Vol 115 (38) ◽

pp. E8996-E9005 ◽

Cited By ~ 20

Author(s):

Brandon M. Gassaway ◽

Max C. Petersen ◽

Yulia V. Surovtseva ◽

Karl W. Barber ◽

Joshua B. Sheetz ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Phosphorylation ◽

Cross Talk ◽

Insulin Signaling ◽

High Fat Diet ◽

Large Scale ◽

Kinase Assay ◽

Hepatic Insulin Resistance ◽

High Fat ◽

The Impact

Insulin resistance drives the development of type 2 diabetes (T2D). In liver, diacylglycerol (DAG) is a key mediator of lipid-induced insulin resistance. DAG activates protein kinase C ε (PKCε), which phosphorylates and inhibits the insulin receptor. In rats, a 3-day high-fat diet produces hepatic insulin resistance through this mechanism, and knockdown of hepatic PKCε protects against high-fat diet-induced hepatic insulin resistance. Here, we employed a systems-level approach to uncover additional signaling pathways involved in high-fat diet-induced hepatic insulin resistance. We used quantitative phosphoproteomics to map global in vivo changes in hepatic protein phosphorylation in chow-fed, high-fat–fed, and high-fat–fed with PKCε knockdown rats to distinguish the impact of lipid- and PKCε-induced protein phosphorylation. This was followed by a functional siRNA-based screen to determine which dynamically regulated phosphoproteins may be involved in canonical insulin signaling. Direct PKCε substrates were identified by motif analysis of phosphoproteomics data and validated using a large-scale in vitro kinase assay. These substrates included the p70S6K substrates RPS6 and IRS1, which suggested cross talk between PKCε and p70S6K in high-fat diet-induced hepatic insulin resistance. These results identify an expanded set of proteins through which PKCε may drive high-fat diet-induced hepatic insulin resistance that may direct new therapeutic approaches for T2D.

Download Full-text

Kupffer cell activation is a causal factor for hepatic insulin resistance

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00391.2009 ◽

2010 ◽

Vol 298 (1) ◽

pp. G107-G116 ◽

Cited By ~ 138

Author(s):

Nicolas Lanthier ◽

Olivier Molendi-Coste ◽

Yves Horsmans ◽

Nico van Rooijen ◽

Patrice D. Cani ◽

...

Keyword(s):

Insulin Resistance ◽

Kupffer Cell ◽

High Fat Diet ◽

Cell Activation ◽

Hepatic Insulin Resistance ◽

High Fat ◽

Short Term ◽

Adipose Tissue Macrophages ◽

Diet Model

Recruited adipose tissue macrophages contribute to chronic and low-grade inflammation causing insulin resistance in obesity. Similarly, we hypothesized here that Kupffer cells, the hepatic resident macrophages, play a pathogenic role in hepatic insulin resistance induced by a high-fat diet. Mice were fed a normal diet or high-fat diet for 3 days. Kupffer cell activation was evaluated by immunohistochemistry and quantitative RT-PCR. Insulin sensitivity was assessed in vivo by hyperinsulinemic-euglycemic clamp and insulin-activated signaling was investigated by Western blot. Liposome-encapsulated clodronate was injected intravenously to deplete macrophages prior to a short-term exposure to high-fat diet. Here, we characterized a short-term high-fat diet model in mice and demonstrated early hepatic insulin resistance and steatosis concurrent with Kupffer cell activation. We demonstrated that selective Kupffer cell depletion obtained by intravenous clodronate, without affecting adipose tissue macrophages, was sufficient to enhance insulin-dependent insulin signaling and significantly improve hepatic insulin sensitivity in vivo in this short-term high-fat diet model. Our study clearly shows that hepatic macrophage response participates to the onset of high-fat diet-induced hepatic insulin resistance and may therefore represent an attractive target for prevention and treatment of diet- and obesity-induced insulin resistance.

Download Full-text

Resveratrol Ameliorates High-Fat-Diet-Induced Abnormalities in Hepatic Glucose Metabolism in Mice via the AMP-Activated Protein Kinase Pathway

Evidence-based Complementary and Alternative Medicine ◽

10.1155/2021/6616906 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Caiping Lu ◽

Hanying Xing ◽

Linquan Yang ◽

Kaiting Chen ◽

Linyi Shu ◽

...

Keyword(s):

Insulin Resistance ◽

Protein Kinase ◽

Glucose Metabolism ◽

Glucose Uptake ◽

High Fat Diet ◽

Blood Glucose Concentration ◽

Glycogen Synthesis ◽

Liver Fat ◽

High Fat ◽

Amp Activated Protein Kinase

Diabetes mellitus is highly prevalent worldwide. High-fat-diet (HFD) consumption can lead to liver fat accumulation, impair hepatic glycometabolism, and cause insulin resistance and the development of diabetes. Resveratrol has been shown to improve the blood glucose concentration of diabetic mice, but its effect on the abnormal hepatic glycometabolism induced by HFD-feeding and the mechanism involved are unknown. In this study, we determined the effects of resveratrol on the insulin resistance of high-fat-diet-fed mice and a hepatocyte model by measuring serum biochemical indexes, key indicators of glycometabolism, glucose uptake, and glycogen synthesis in hepatocytes. We found that resveratrol treatment significantly ameliorated the HFD-induced abnormalities in glucose metabolism in mice, increased glucose absorption and glycogen synthesis, downregulated protein phosphatase 2A (PP2A) and activated Ca2+/CaM-dependent protein kinase kinase β (CaMKKβ), and increased the phosphorylation of AMP-activated protein kinase (AMPK). In insulin-resistant HepG2 cells, the administration of a PP2A activator or CaMKKβ inhibitor attenuated the effects of resveratrol, but the administration of an AMPK inhibitor abolished the effects of resveratrol. Resveratrol significantly ameliorates abnormalities in glycometabolism induced by HFD-feeding and increases glucose uptake and glycogen synthesis in hepatocytes. These effects are mediated through the activation of AMPK by PP2A and CaMKKβ.

Download Full-text