Project description: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 epsilon (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 employ 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.
Project description:Gene transcription profiling in Epidydimal fat pad (EPD) following High fat versus normal diet in C57/Bl6 mice. Characterisation of molecular mechanisms of in vivo insulin action in mouse models of experimentally induced Insulin resistance. Switched the diet when mice were 5 weeks old, then sampled at 8 days.
Project description:We previously demonstrated that antisense oligonucleotide (ASO)-mediated knockdown of Mboat7, the gene encoding Membrane Bound O-Acyltransferase 7, in the liver and adipose tissue of mice promoted high fat diet-induced hepatic steatosis, hyperinsulinemia, and systemic insulin resistance. Thereafter, other groups showed that hepatocyte-specific genetic deletion of Mboat7 promoted striking fatty liver and NAFLD progression in mice but does not alter insulin sensitivity, suggesting the potential for cell autonomous roles. Here, we show that MBOAT7 function in adipocytes contributes to diet-induced metabolic disturbances including hyperinsulinemia and systemic insulin resistance. We generated floxed Mboat7 mice and created hepatocyte- and adipocyte-specific knockout mice using Cre-recombinase mice under the control of the albumin and adiponectin promoter, respectively. After chow and high fat diet feeding (60% kCal fat), mice were subjected to metabolic phenotyping and tissues to molecular workup and analysis. Here, we show that MBOAT7 function in adipocytes contributes to diet-induced metabolic disturbances including hyperinsulinemia and systemic insulin resistance. The expression of Mboat7 in white adipose tissue closely correlates with diet-induced obesity across a panel of ~100 inbred strains of mice fed a high fat/high sucrose diet. Moreover, we found that adipocyte-specific genetic deletion of Mboat7 is sufficient to promote hyperinsulinemia, systemic insulin resistance, and mild fatty liver. Unlike in the liver, where Mboat7 plays a relatively minor role in maintaining arachidonic acid (AA)-containing PI pools, Mboat7 is the major source of AA-containing PI pools in adipose tissue. Our data demonstrate that MBOAT7 is a critical regulator of adipose tissue PI homeostasis, and adipocyte MBOAT7-driven PI biosynthesis is closely linked to hyperinsulinemia and insulin resistance in mice.
Project description:Lipid overload and adipocyte dysfunction are key to the development of insulin resistance and can be induced by a high-fat diet. CD1d-restricted invariant natural killer T (iNKT) cells have been proposed as mediators between lipid overload and insulin resistance, but recent studies found decreased iNKT cell numbers and marginal effects of iNKT cell depletion on insulin resistance under high-fat diet conditions. Here, we focused on the role of iNKT cells under normal conditions. We showed that iNKT cell–deficient mice on a low-fat diet, considered a normal diet for mice, displayed a distinctive insulin resistance phenotype without overt adipose tissue inflammation. Insulin resistance was characterized by adipocyte dysfunction, including adipocyte hypertrophy, increased leptin, and decreased adiponectin levels. The lack of liver abnormalities in CD1d-null mice together with the enrichment of CD1d-restricted iNKT cells in both mouse and human adipose tissue indicated a specific role for adipose tissue–resident iNKT cells in the development of insulin resistance. Strikingly, iNKT cell function was directly modulated by adipocytes, which acted as lipid antigen-presenting cells in a CD1d-mediated fashion. Based on these findings, we propose that, especially under low-fat diet conditions, adipose tissue–resident iNKT cells maintain healthy adipose tissue through direct interplay with adipocytes and prevent insulin resistance. four samples
Project description:Obesity-induced inflammation metabolic dysfunction, but the mechanisms remain elusive. Here we showed that the innate immune factor IRF3 is a direct transcriptional regulator of glucose homeostasis through induction of endogenous FAHFA hydrolase Aig1 in adipocytes. Adipocyte-specific knockout IRF3 protects mice against high-fat diet-induced insulin resistance, whereas overexpression of IRF3 in adipocytes promotes insulin resistance on a high-fat diet. Furthermore, pharmacological inhibition of AIG1 reversed obesity-induced insulin resistance and restored glucose homeostasis in the setting of adipocyte IRF3 overexpression. We therefore, identify the adipocyte IRF3/AIG1 axis as a crucial link between obesity-induced inflammation and insulin resistance and suggest an approach for limiting the metabolic dysfunction accompanying obesity.