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Integrated Control of Hepatic Lipogenesis vs. Glucose Production Requires FoxO Transcription Factors

ABSTRACT: Insulin integrates hepatic glucose and lipid metabolism, directing nutrients to storage as glycogen and triglyceride. In type 2 diabetes, levels of the former are low and the latter are exaggerated, posing a pathophysiologic and therapeutic conundrum. A branching model1 of insulin signaling, with FoxO1 presiding over glucose production2-5 and Srebp–1c regulating lipogenesis,6-8 provides a potential explanation. Here we illustrate an alternative mechanism that integrates glucose production and lipogenesis under the unifying control of FoxO. Liver–specific ablation of three FoxOs (L–FoxO1,3,4) prevents the induction of glucose–6–phosphatase and the repression of glucokinase during fasting, thus increasing lipogenesis at the expense of glucose production. We document a similar pattern in the early phases of diet-induced insulin resistance, and propose that FoxOs are required to enable the liver to direct nutritionally derived carbons to glucose vs. lipid metabolism. Our data underscore the heterogeneity of hepatic insulin resistance during progression from the metabolic syndrome to overt diabetes, and the conceptual challenge of designing therapies that curtail glucose production without promoting hepatic lipid accumulation. We used microarrays to detail the change of gene expression in liver after knocking out FoxO1,3 and 4.

ORGANISM(S): Mus musculus

PROVIDER: GSE60527 | GEO | 2014/08/20

SECONDARY ACCESSION(S): PRJNA258469

REPOSITORIES: GEO

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Project description:In an effort to reduce hepatic glucose production and lower plasma glucose levels that are characteristics of diabetes, we have devised a treatment whereby we enhance glycolysis in the liver of a type 2 diabetic mouse model (KK/H1J). We achieve this by raising the levels of a potent regulator of glucose metabolism, fructose-2,6-bisphosphate (F26BP). Treating the mice in this way, we have demonstrated amelioration of the diabetic phenotype in terms of lowering plasma glucose and insulin levels. These treated mice also display reduced weight gain, reduced adiposity, and normalized plasma and hepatic lipid levels. These latter metabolic changes brought about by raising F26BP levels are counterintuitive. A concurrent increase in glycolysis and lipogenesis is expected, however, we observe an increase in glycolysis with a concurrent decrease in lipogenesis. Preliminary analysis of gene expression in these mice has revealed alterations in gene expression of several genes that support the therapeutic effect of raising F26BP levels. To further profile F26BP effects on hepatic gene expression, we have applied a comprehensive approach to identify sets of genes and thereby biological pathways that are differentially regulated when hepatic glycolysis is accelerated in diabetic mice. Comparing diabetic and treated animals, we hope to further clarify the molecular and genetic signature of type 2 diabetes and obesity and elucidate how this signature is affected by raising F26BP levels. Our study examining gene array as well as the hepatic proteome has identified multiple gene and protein expression changes. Of particular relevance, we note that fatty acid metabolism and cholesterol metabolism pathways are significantly down-regulated in diabetic mice treated with a PFK-2 mutant engineered to raise F26BP levels, which underlie the changes we see in the metabolic parameters. 6 KK/H1J mice, a polygenic model of type 2 diabetes and obesity, weighing approximately 35g were used in this study. 3 mice were injected with GFP control adenovirus and 3 mice were injected with bisphosphatase deficient PFK-2 adenovirus (BPD). Mice were followed for 7 days before livers were extracted. Total cellular RNA was extracted from each mouse and analyzed by microarray separately.

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Integrated Control of Hepatic Lipogenesis vs. Glucose Production Requires FoxO Transcription Factors

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