Hypothalamic SIRT1 prevents age-associated weight gain by improving leptin sensitivity in mice.

AIMS/HYPOTHESIS: Obesity is associated with ageing and increased energy intake, while restriction of energy intake improves health and longevity in multiple organisms; the NAD(+)-dependent deacetylase sirtuin 1 (SIRT1) is implicated in this process. Pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP) neurons in the arcuate nucleus (ARC) of the hypothalamus are critical for energy balance regulation, and the level of SIRT1 protein decreases with age in the ARC. In the current study we tested whether conditional Sirt1 overexpression in mouse POMC or AgRP neurons prevents age-associated weight gain and diet-induced obesity. METHODS: We targeted Sirt1 cDNA sequence into the Rosa26 locus and generated conditional Sirt1 knock-in mice. These mice were crossed with mice harbouring either Pomc-Cre or Agrp-Cre and the metabolic variables, food intake, energy expenditure and sympathetic activity in adipose tissue of the resultant mice were analysed. We also used a hypothalamic cell line to investigate the molecular mechanism by which Sirt1 overexpression modulates leptin signalling. RESULTS: Conditional Sirt1 overexpression in mouse POMC or AgRP neurons prevented age-associated weight gain; overexpression in POMC neurons stimulated energy expenditure via increased sympathetic activity in adipose tissue, whereas overexpression in AgRP neurons suppressed food intake. SIRT1 improved leptin sensitivity in hypothalamic neurons in vitro and in vivo by downregulating protein-tyrosine phosphatase 1B, T cell protein-tyrosine phosphatase and suppressor of cytokine signalling 3. However, these phenotypes were absent in mice consuming a high-fat, high-sucrose diet due to decreases in ARC SIRT1 protein and hypothalamic NAD(+) levels. CONCLUSIONS/INTERPRETATION: ARC SIRT1 is a negative regulator of energy balance, and decline in ARC SIRT1 function contributes to disruption of energy homeostasis by ageing and diet-induced obesity.

Miglitol prevents diet-induced obesity by stimulating brown adipose tissue and energy expenditure independent of preventing the digestion of carbohydrates.

Miglitol is an alpha-glucosidase inhibitor that improves post-prandial hyperglycemia, and it is the only drug in its class that enters the bloodstream. Anecdotally, miglitol lowers patient body weight more effectively than other alpha-glucosidase inhibitors, but the precise mechanism has not been addressed. Therefore, we analyzed the anti-obesity effects of miglitol in mice and in the HB2 brown adipocyte cell line. Miglitol prevented diet-induced obesity by stimulating energy expenditure without affecting food intake in mice. Long-term miglitol treatment dose-dependently prevented diet-induced obesity and induced mitochondrial gene expression in brown adipose tissue. The anti-obesity effect was independent of preventing carbohydrate digestion in the gastrointestinal tract. Miglitol effectively stimulated energy expenditure in mice fed a high-fat high-monocarbohydrate diet, and intraperitoneal injection of miglitol was sufficient to stimulate energy expenditure in mice. Acarbose, which is a non-absorbable alpha glucosidase inhibitor, also prevented diet-induced obesity, but through a different mechanism: it did not stimulate energy expenditure, but caused indigestion, leading to less energy absorption. Miglitol promoted adrenergic signaling in brown adipocytes in vitro. These data indicate that circulating miglitol stimulates brown adipose tissue and increases energy expenditure, thereby preventing diet-induced obesity. Further optimizing miglitol's effect on brown adipose tissue could lead to a novel anti-obesity drug.

FoxO1 as a double-edged sword in the pancreas: analysis of pancreas- and ß-cell-specific FoxO1 knockout mice.

Diabetes is characterized by an absolute or relative deficiency of pancreatic ß-cells. New strategies to accelerate ß-cell neogenesis or maintain existing ß-cells are desired for future therapies against diabetes. We previously reported that forkhead box O1 (FoxO1) inhibits ß-cell growth through a Pdx1-mediated mechanism. However, we also reported that FoxO1 protects against ß-cell failure via the induction of NeuroD and MafA. Here, we investigate the physiological roles of FoxO1 in the pancreas by generating the mice with deletion of FoxO1 in the domains of the Pdx1 promoter (P-FoxO1-KO) or the insulin 2 promoter (ß-FoxO1-KO) and analyzing the metabolic parameters and pancreatic morphology under two different conditions of increased metabolic demand: high-fat high-sucrose diet (HFHSD) and db/db background. P-FoxO1-KO, but not ß-FoxO1-KO, showed improved glucose tolerance with HFHSD. Immunohistochemical analysis revealed that P-FoxO1-KO had increased ß-cell mass due to increased islet number rather than islet size, indicating accelerated ß-cell neogenesis. Furthermore, insulin-positive pancreatic duct cells were increased in P-FoxO1-KO but not ß-FoxO1-KO. In contrast, db/db mice crossed with P-FoxO1-KO or ß-FoxO1-KO showed more severe glucose intolerance than control db/db mice due to decreased glucose-responsive insulin secretion. Electron microscope analysis revealed fewer insulin granules in FoxO1 knockout db/db mice. We conclude that FoxO1 functions as a double-edged sword in the pancreas; FoxO1 essentially inhibits ß-cell neogenesis from pancreatic duct cells but is required for the maintenance of insulin secretion under metabolic stress.

Overexpression of FoxO1 in the hypothalamus and pancreas causes obesity and glucose intolerance.

Recent studies have revealed that insulin signaling in pancreatic ß-cells and the hypothalamus is critical for maintaining nutrient and energy homeostasis, the failure of which are hallmarks of metabolic syndrome. We previously reported that forkhead transcription factor forkhead box-containing protein of the O subfamily (FoxO)1, a downstream effector of insulin signaling, plays important roles in ß-cells and the hypothalamus when we investigated the roles of FoxO1 independently in the pancreas and hypothalamus. However, because metabolic syndrome is caused by the combined disorders in hypothalamus and pancreas, to elucidate the combined implications of FoxO1 in these organs, we generated constitutively active FoxO1 knockin (KI) mice with specific activation in both the hypothalamus and pancreas. The KI mice developed obesity, insulin resistance, glucose intolerance, and hypertriglyceridemia due to increased food intake, decreased energy expenditure, and impaired insulin secretion, which characterize metabolic syndrome. The KI mice also had increased hypothalamic Agouti-related protein and neuropeptide Y levels and decreased uncoupling protein 1 and peroxisome proliferator-activated receptor γ coactivator 1α levels in adipose tissue and skeletal muscle. Impaired insulin secretion was associated with decreased expression of pancreatic and duodenum homeobox 1 (Pdx1), muscyloaponeurotic fibrosarcoma oncogene homolog A (MafA), and neurogenic differentiation 1 (NeuroD) in islets, although ß-cell mass was paradoxically increased in KI mice. Based on these results, we propose that uncontrolled FoxO1 activation in the hypothalamus and pancreas accounts for the development of obesity and glucose intolerance, hallmarks of metabolic syndrome.

FoxO1 gain of function in the pancreas causes glucose intolerance, polycystic pancreas, and islet hypervascularization.

Genetic studies revealed that the ablation of insulin/IGF-1 signaling in the pancreas causes diabetes. FoxO1 is a downstream transcription factor of insulin/IGF-1 signaling. We previously reported that FoxO1 haploinsufficiency restored ß cell mass and rescued diabetes in IRS2 knockout mice. However, it is still unclear whether FoxO1 dysregulation in the pancreas could be the cause of diabetes. To test this hypothesis, we generated transgenic mice overexpressing constitutively active FoxO1 specifically in the pancreas (TG). TG mice had impaired glucose tolerance and some of them indeed developed diabetes due to the reduction of ß cell mass, which is associated with decreased Pdx1 and MafA in ß cells. We also observed increased proliferation of pancreatic duct epithelial cells in TG mice and some mice developed a polycystic pancreas as they aged. Furthermore, TG mice exhibited islet hypervascularities due to increased VEGF-A expression in ß cells. We found FoxO1 binds to the VEGF-A promoter and regulates VEGF-A transcription in ß cells. We propose that dysregulation of FoxO1 activity in the pancreas could account for the development of diabetes and pancreatic cysts.

Genetic defect in phospholipase Cδ1 protects mice from obesity by regulating thermogenesis and adipogenesis.

OBJECTIVE: Regulation of obesity development is an important issue to prevent metabolic syndromes. Gene-disrupted mice of phospholipase Cδ1 (PLCδ1), a key enzyme of phosphoinositide turnover, seemed to show leanness. Here we examined whether and how PLCδ1 is involved in obesity. RESEARCH DESIGN AND METHODS: Weight gain, insulin sensitivity, and metabolic rate in PLCδ1(-/-) mice were compared with PLCδ1(+/-) littermate mice on a high-fat diet. Thermogenic and adipogenetic potentials of PLCδ1(-/-) immortalized brown adipocytes and adipogenesis of PLCδ1-knockdown (KD) 3T3L1 cells, or PLCδ1(-/-) white adipose tissue (WAT) stromal-vascular fraction (SVF) cells, were also investigated. RESULTS: PLCδ1(-/-) mice showed marked decreases in weight gain and mass of epididymal WAT and preserved insulin sensitivity compared with PLCδ1(+/-) mice on a high-fat diet. In addition, PLCδ1(-/-) mice have a higher metabolic rate such as higher oxygen consumption and heat production. When control immortalized brown adipocytes were treated with thermogenic inducers, expression of PLCδ1 was decreased and thermogenic gene uncoupling protein 1 (UCP1) was upregulated to a greater extent in PLCδ1(-/-) immortalized brown adipocytes. In contrast, ectopic expression of PLCδ1 in PLCδ1(-/-) brown adipocytes induced a decrease in UCP expression, indicating that PLCδ1 negatively regulates thermogenesis. Importantly, accumulation of lipid droplets was severely decreased when PLCδ1-KD 3T3L1 cells, or PLCδ1(-/-) WAT SVF cells, were differentiated, whereas differentiation of PLCδ1(-/-) brown preadipocytes was promoted. CONCLUSIONS: PLCδ1 has essential roles in thermogenesis and adipogenesis and thereby contributes to the development of obesity.