Peripheral Insulin Regulates a Broad Network of Gene Expression in Hypothalamus, Hippocampus, and Nucleus Accumbens.

The brain is now recognized as an insulin-sensitive tissue; however, the role of changing insulin concentrations in the peripheral circulation in gene expression in the brain is largely unknown. Here, we performed a hyperinsulinemic-euglycemic clamp on 3-month-old male C57BL/6 mice for 3 h. We show that, in comparison with results in saline-infused controls, increases in peripheral insulin within the physiological range regulate expression of a broad network of genes in the brain. Insulin regulates distinct pathways in the hypothalamus (HTM), hippocampus, and nucleus accumbens. Insulin shows its most robust effect in the HTM and regulates multiple genes involved in neurotransmission, including upregulating expression of multiple subunits of GABA-A receptors, Na+ and K+ channels, and SNARE proteins; differentially modulating glutamate receptors; and suppressing multiple neuropeptides. Insulin also strongly modulates metabolic genes in the HTM, suppressing genes in the glycolysis and pentose phosphate pathways, while increasing expression of genes regulating pyruvate dehydrogenase and long-chain fatty acyl-CoA and cholesterol biosynthesis, thereby rerouting of carbon substrates from glucose metabolism to lipid metabolism required for the biogenesis of membranes for neuronal and glial function and synaptic remodeling. Furthermore, based on the transcriptional signatures, these changes in gene expression involve neurons, astrocytes, oligodendrocytes, microglia, and endothelial cells. Thus, peripheral insulin acutely and potently regulates expression of a broad network of genes involved in neurotransmission and brain metabolism. Dysregulation of these pathways could have dramatic effects in normal physiology and diabetes.

Hyperinsulinemia drives hepatic insulin resistance in male mice with liver-specific Ceacam1 deletion independently of lipolysis.

BACKGROUND: CEACAM1 regulates insulin sensitivity by promoting insulin clearance. Accordingly, global C57BL/6J.Cc1-/- null mice display hyperinsulinemia due to impaired insulin clearance at 2 months of age, followed by insulin resistance, steatohepatitis, visceral obesity and leptin resistance at 6 months. The study aimed at investigating the primary role of hepatic CEACAM1 in insulin and lipid homeostasis independently of its metabolic effect in extra-hepatic tissues. METHODS: Liver-specific C57BL/6J.AlbCre+Cc1fl/fl mice were generated and their metabolic phenotype was characterized by comparison to that of their littermate controls at 2-9 months of age, using hyperinsulinemic-euglycemic clamp analysis and indirect calorimetry. The effect of hyperphagia on insulin resistance was assessed by pair-feeding experiments. RESULTS: Liver-specific AlbCre+Cc1fl/fl mutants exhibited impaired insulin clearance and hyperinsulinemia at 2 months, followed by hepatic insulin resistance (assessed by hyperinsulinemic-euglycemic clamp analysis) and steatohepatitis at ~ 7 months of age, at which point visceral obesity and hyperphagia developed, in parallel to hyperleptinemia and blunted hypothalamic STAT3 phosphorylation in response to an intraperitoneal injection of leptin. Hyperinsulinemia caused hypothalamic insulin resistance, followed by increased fatty acid synthase activity, which together with defective hypothalamic leptin signaling contributed to hyperphagia and reduced physical activity. Pair-feeding experiment showed that hyperphagia caused systemic insulin resistance, including blunted insulin signaling in white adipose tissue and lipolysis, at 8-9 months of age. CONCLUSION: AlbCre+Cc1fl/fl mutants provide an in vivo demonstration of the key role of impaired hepatic insulin clearance and hyperinsulinemia in the pathogenesis of secondary hepatic insulin resistance independently of lipolysis. They also reveal an important role for the liver-hypothalamic axis in the regulation of energy balance and subsequently, systemic insulin sensitivity.

Dietary Betaine Supplementation Increases Fgf21 Levels to Improve Glucose Homeostasis and Reduce Hepatic Lipid Accumulation in Mice.

Identifying markers of human insulin resistance may permit development of new approaches for treatment and prevention of type 2 diabetes. To this end, we analyzed the fasting plasma metabolome in metabolically characterized human volunteers across a spectrum of insulin resistance. We demonstrate that plasma betaine levels are reduced in insulin-resistant humans and correlate closely with insulin sensitivity. Moreover, betaine administration to mice with diet-induced obesity prevents the development of impaired glucose homeostasis, reduces hepatic lipid accumulation, increases white adipose oxidative capacity, and enhances whole-body energy expenditure. In parallel with these beneficial metabolic effects, betaine supplementation robustly increased hepatic and circulating fibroblast growth factor (Fgf)21 levels. Betaine administration failed to improve glucose homeostasis and liver fat content in Fgf21(-/-) mice, demonstrating that Fgf21 is necessary for betaine's beneficial effects. Together, these data indicate that dietary betaine increases Fgf21 levels to improve metabolic health in mice and suggest that betaine supplementation merits further investigation as a supplement for treatment or prevention of type 2 diabetes in humans.

Carcinoembryonic antigen-related cell adhesion molecule 2 controls energy balance and peripheral insulin action in mice.

BACKGROUND & AIMS: The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein with pleotropic functions, including clearance of hepatic insulin. We investigated the functions of the related protein CEACAM2, which has tissue-specific distribution (kidney, uterus, and crypt epithelia of intestinal tissues), in genetically modified mice. METHODS: Ceacam2-null mice (Cc2-/-) were generated from a 129/SvxC57BL/6J background. Female mice were assessed by hyperinsulinemic-euglycemic clamp analysis and indirect calorimetry and body fat composition was measured. Cc2-/- mice and controls were fed as pairs, given insulin tolerance tests, and phenotypically characterized. RESULTS: Female, but not male Cc2-/- mice exhibited obesity that resulted from hyperphagia and reduced energy expenditure. Pair feeding experiments showed that hyperphagia led to peripheral insulin resistance. Insulin action was normal in liver but compromised in skeletal muscle of female Cc2-/- mice; the mice had incomplete fatty acid oxidation and impaired glucose uptake and disposal. The mechanism of hyperphagia in Cc2-/- mice is not clear, but appears to result partly from increased hyperinsulinemia-induced hypothalamic fatty acid synthase levels and activity. Hyperinsulinemia was caused by increased insulin secretion. CONCLUSIONS: In mice, CEACAM2 is expressed by the hypothalamus. Cc2-/- mice develop obesity from hyperphagia and reduced energy expenditure, indicating its role in regulating energy balance and insulin sensitivity.

The melanocortin-3 receptor is required for entrainment to meal intake.

Entrainment of anticipatory activity and wakefulness to nutrient availability is a poorly understood component of energy homeostasis. Restricted feeding (RF) paradigms with a periodicity of 24 h rapidly induce entrainment of rhythms anticipating food presentation that are independent of master clocks in the suprachiasmatic nucleus (SCN) but do require other hypothalamic structures. Here, we report that the melanocortin system, which resides in hypothalamic structures required for food entrainment, is required for expression of food entrainable rhythms. Food anticipatory activity was assessed in wild-type (WT) and melanocortin-3 receptor-deficient (Mc3r-/-) C57BL/J mice by wheel running, spontaneous locomotory movement, and measurement of wakefulness. WT mice housed in wheel cages subject to RF exhibited increased wheel activity during the 2 h preceding meal presentation, which corresponded with an increase in wakefulness around meal time and reduced wakefulness during the dark. WT mice also exhibited increased x- and z-movements centered around food initiation. The activity-based responses to RF were significantly impaired in mice lacking Mc3r. RF also failed to increase wakefulness in the 2 h before food presentation in Mc3r-/- mice. Food entrainment requires expression of Neuronal PAS domain 2 (Npas2) and Period2 (Per2) genes, components of the transcriptional machinery maintaining a clock rhythm. Analysis of cortical gene expression revealed severe abnormalities in rhythmic expression of clock genes (Bmal1, Npas2, Per2) under ad libitum and RF conditions. In summary, Mc3r are required for expression of anticipatory patterns of activity and wakefulness during periods of limited nutrient availability and for normal regulation of cortical clock function.