Deficient ganglioside synthesis restores responsiveness to leptin and melanocortin signaling in obese KKAy mice.

GM3, a precursor for synthesis of a- and b-series gangliosides, is elevated in adipocytes of obese model animals and in sera of obese human patients with type 2 diabetes and/or dyslipidemia. GM3 synthase (GM3S)-KO C57BL/6 mice display enhanced insulin sensitivity and reduced development of high-fat diet-induced insulin resistance. However, the pathophysiological roles of GM3 and related gangliosides in the central control of feeding and metabolism remain unclear. We found that a mouse model (KKAy GM3S KO) generated by KO of the GM3S gene in the yellow obese strain, KKAy, displayed significant amelioration of obese phenotype. Whereas KKAy mice were hyperphagic and developed severe obesity, KKAy GM3S KO mice had significantly lower body weight and food intake, and greater glucose and insulin tolerance. The hypothalamic response to intraperitoneal administration of leptin was greatly reduced in KKAy mice, but was retained in KKAy GM3S KO mice. In studies of a cultured mouse hypothalamic neuronal cell line, enhanced leptin-dependent phosphorylation of ERK was observed in GM3S-deficient cells. Furthermore, KKAy GM3S KO mice did show altered coat color, suggesting that GM3S is also involved in melanocortin signaling. Our findings, taken together, indicate that GM3-related gangliosides play key roles in leptin and melanocortin signaling.

Selective insulin resistance with differential expressions of IRS-1 and IRS-2 in human NAFLD livers.

BACKGROUND/OBJECTIVE: Insulin signals, via the regulation of key enzyme expression, both suppress gluconeogenesis and enhance lipid synthesis in the liver. Animal studies have revealed insulin signaling favoring gluconeogenesis suppression to be selectively impaired in steatotic livers. However, whether, and if so how, such selective insulin resistance occurs in human steatotic livers remains unknown. Our aim was to investigate selective insulin resistance in human livers with non-alcoholic fatty liver disease (NAFLD). SUBJECTS/METHODS: We examined mRNA expressions of key molecules for insulin signaling, gluconeogenesis and lipogenesis in human liver biopsy samples obtained from 51 non-diabetic subjects: 9 healthy controls and 42 NAFLD patients, and analyzed associations of these molecules with each other and with detailed pathological and clinical biochemistry data. RESULTS: In NAFLD patients, insulin receptor substrate (IRS)-2 expression was decreased, while those of key enzymes for gluconeogenesis were increased. These alterations of IRS-2 and gluconeogenesis enzymes were induced both in simple steatosis (SS) and non-alcoholic steatohepatitis (NASH), while these expression levels did not differ between SS and NASH. Furthermore, alterations in the expressions of IRS-2 and gluconeogenesis enzymes showed strong negative correlations and were concurrently induced in the early histological stage of NAFLD. In contrast, fatty acid synthase (FAS) expression was not decreased in NAFLD, despite IRS-2 downregulation, but correlated strongly with IRS-1 expression. Furthermore, no histological scores were associated with these molecules. Thus, IRS-1 signaling, which is not impaired in NAFLD, appears to modulate FAS expression. CONCLUSION: These analyses revealed that selective insulin resistance is present in human NAFLD livers and occurs in its early phases. The effect of insulin, during the IRS step, on gene expressions for lipogenesis and gluconeogenesis are apparently distinct and preferential downregulation of IRS-2 may contribute to selective resistance to the suppressive effects of insulin on gluconeogenesis.

Olfactory receptors are expressed in pancreatic ß-cells and promote glucose-stimulated insulin secretion.

Olfactory receptors (ORs) mediate olfactory chemo-sensation in OR neurons. Herein, we have demonstrated that the OR chemo-sensing machinery functions in pancreatic ß-cells and modulates insulin secretion. First, we found several OR isoforms, including OLFR15 and OLFR821, to be expressed in pancreatic islets and a ß-cell line, MIN6. Immunostaining revealed OLFR15 and OLFR821 to be uniformly expressed in pancreatic ß-cells. In addition, mRNAs of Olfr15 and Olfr821 were detected in single MIN6 cells. These results indicate that multiple ORs are simultaneously expressed in individual ß-cells. Octanoic acid, which is a medium-chain fatty acid contained in food and reportedly interacts with OLFR15, potentiated glucose-stimulated insulin secretion (GSIS), thereby improving glucose tolerance in vivo. GSIS potentiation by octanoic acid was confirmed in isolated pancreatic islets and MIN6 cells and was blocked by OLFR15 knockdown. While Gα olf expression was not detectable in ß-cells, experiments using inhibitors and siRNA revealed that the pathway dependent on phospholipase C-inositol triphosphate, rather than cAMP-protein kinase A, mediates GSIS potentiation via OLFR15. These findings suggest that the OR system in pancreatic ß-cells has a chemo-sensor function allowing recognition of environmental substances obtained from food, and potentiates insulin secretion in a cell-autonomous manner, thereby modulating systemic glucose metabolism.

Metformin directly binds the alarmin HMGB1 and inhibits its proinflammatory activity.

Metformin is the first-line drug in the treatment of type 2 diabetes. In addition to its hypoglycemic effect, metformin has an anti-inflammatory function, but the precise mechanism promoting this activity remains unclear. High mobility group box 1 (HMGB1) is an alarmin that is released from necrotic cells and induces inflammatory responses by its cytokine-like activity and is, therefore, a target of anti-inflammatory therapies. Here we identified HMGB1 as a novel metformin-binding protein by affinity purification using a biotinylated metformin analogue. Metformin directly bound to the C-terminal acidic tail of HMGB1. Both in vitro and in vivo, metformin inhibited inflammatory responses induced by full-length HMGB1 but not by HMGB1 lacking the acidic tail. In an acetaminophen-induced acute liver injury model in which HMGB1 released from injured cells exacerbates the initial injury, metformin effectively reduced liver injury and had no additional inhibitory effects when the extracellular HMGB1 was blocked by anti-HMGB1-neutralizing antibody. In summary, we report for the first time that metformin suppresses inflammation by inhibiting the extracellular activity of HMGB1. Because HMGB1 plays a major role in inflammation, our results suggest possible new ways to manage HMGB1-induced inflammation.

ER Stress Protein CHOP Mediates Insulin Resistance by Modulating Adipose Tissue Macrophage Polarity.

Obesity represents chronic inflammatory states promoted by pro-inflammatory M1-macrophage infiltration into white adipose tissue (WAT), thereby inducing insulin resistance. Herein, we demonstrate the importance of an ER stress protein, CHOP, in determining adipose tissue macrophage (ATM) polarity and systemic insulin sensitivity. A high-fat diet (HFD) enhances ER stress with CHOP upregulation in adipocytes. CHOP deficiency prevents HFD-induced insulin resistance and glucose intolerance with ATM M2 predomination and Th2 cytokine upregulation in WAT. Whereas ER stress suppresses Th2 cytokine expression in cultured adipocytes, CHOP knockdown inhibits this downregulation. In contrast, macrophage responsiveness to Th1/Th2 cytokines is unchanged regardless of whether CHOP is expressed. Furthermore, bone marrow transplantation experiments showed recipient CHOP to be the major determinant of ATM polarity. Thus, CHOP in adipocytes plays important roles in ATM M1 polarization by altering WAT micro-environmental conditions, including Th2 cytokine downregulation. This molecular mechanism may link adipose ER stress with systemic insulin resistance.

Activation of the Hypoxia Inducible Factor 1α Subunit Pathway in Steatotic Liver Contributes to Formation of Cholesterol Gallstones.

BACKGROUND & AIMS: Hypoxia-inducible factor 1α subunit (HIF1A) is a transcription factor that controls the cellular response to hypoxia and is activated in hepatocytes of patients with nonalcoholic fatty liver disease (NAFLD). NAFLD increases the risk for cholesterol gallstone disease by unclear mechanisms. We studied the relationship between HIF1A and gallstone formation associated with liver steatosis. METHODS: We performed studies with mice with inducible disruption of Hif1a in hepatocytes via a Cre adenoviral vector (inducible hepatocyte-selective HIF1A knockout [iH-HIFKO] mice), and mice without disruption of Hif1a (control mice). Mice were fed a diet rich in cholesterol and cholate for 1 or 2 weeks; gallbladders were collected and the number of gallstones was determined. Livers and biliary tissues were analyzed by histology, quantitative reverse-transcription polymerase chain reaction, immunohistochemistry, and immunoblots. We measured concentrations of bile acid, cholesterol, and phospholipid in bile and rates of bile flow. Primary hepatocytes and cholangiocytes were isolated and analyzed. HIF1A was knocked down in Hepa1-6 cells with small interfering RNAs. Liver biopsy samples from patients with NAFLD, with or without gallstones, were analyzed by quantitative reverse-transcription polymerase chain reaction. RESULTS: Control mice fed a diet rich in cholesterol and cholate developed liver steatosis with hypoxia; levels of HIF1A protein were increased in hepatocytes around central veins and 90% of mice developed cholesterol gallstones. Only 20% of the iH-HIFKO mice developed cholesterol gallstones. In iH-HIFKO mice, the biliary lipid concentration was reduced by 36%, compared with control mice, and bile flow was increased by 35%. We observed increased water secretion from hepatocytes into bile canaliculi to mediate these effects, resulting in suppression of cholelithogenesis. Hepatic expression of aquaporin 8 (AQP8) protein was 1.5-fold higher in iH-HIFKO mice than in control mice. Under hypoxic conditions, cultured hepatocytes increased expression of Hif1a, Hmox1, and Vegfa messenger RNAs (mRNAs), and down-regulated expression of AQP8 mRNA and protein; AQP8 down-regulation was not observed in cells with knockdown of HIF1A. iH-HIFKO mice had reduced inflammation and mucin deposition in the gallbladder compared with control mice. Liver tissues from patients with NAFLD with gallstones had increased levels of HIF1A, HMOX1, and VEGFA mRNAs, compared with livers from patients with NAFLD without gallstones. CONCLUSIONS: In steatotic livers of mice, hypoxia up-regulates expression of HIF1A, which reduces expression of AQP8 and concentrates biliary lipids via suppression of water secretion from hepatocytes. This promotes cholesterol gallstone formation. Livers from patients with NAFLD and gallstones express higher levels of HIF1A than livers from patients with NAFLD without gallstones.

MicroRNAs 106b and 222 Improve Hyperglycemia in a Mouse Model of Insulin-Deficient Diabetes via Pancreatic ß-Cell Proliferation.

Major symptoms of diabetes mellitus manifest, once pancreatic ß-cell numbers have become inadequate. Although natural regeneration of ß-cells after injury is very limited, bone marrow (BM) transplantation (BMT) promotes their regeneration through undetermined mechanism(s) involving inter-cellular (BM cell-to-ß-cell) crosstalk. We found that two microRNAs (miRNAs) contribute to BMT-induced ß-cell regeneration. Screening murine miRNAs in serum exosomes after BMT revealed 42 miRNAs to be increased. Two of these miRNAs (miR-106b-5p and miR-222-3p) were shown to be secreted by BM cells and increased in pancreatic islet cells after BMT. Treatment with the corresponding anti-miRNAs inhibited BMT-induced ß-cell regeneration. Furthermore, intravenous administration of the corresponding miRNA mimics promoted post-injury ß-cell proliferation through Cip/Kip family down-regulation, thereby ameliorating hyperglycemia in mice with insulin-deficient diabetes. Thus, these identified miRNAs may lead to the development of therapeutic strategies for diabetes.

Lipoprotein Lipase Deficiency (R243H) in a Type 2 Diabetes Patient with Multiple Arterial Aneurysms.

Lipoprotein lipase (LPL) deficiency is a rare monogenic disorder that manifests as severe hypertriglyceridemia. Whether or not LPL deficiency accelerates the development of atherosclerosis remains controversial. We herein report a 66-year-old woman who was homozygous for the R243H LPL mutation. She had developed multiple arterial aneurysms and systemic atherosclerosis despite good control of other atherogenic risk factors, including diabetes. Furthermore, although intensive pharmaceutical therapies had been minimally effective, medium chain triglyceride (MCT) therapy reduced the serum triglyceride levels. Thus, this case suggests important role that mutated LPL protein plays in the progression of atherosclerosis and that MCT therapy is potentially effective, even for severe hypertriglyceridemia due to LPL deficiency.

Dapagliflozin, a Sodium-Glucose Co-Transporter 2 Inhibitor, Acutely Reduces Energy Expenditure in BAT via Neural Signals in Mice.

Selective sodium glucose cotransporter-2 inhibitor (SGLT2i) treatment promotes urinary glucose excretion, thereby reducing blood glucose as well as body weight. However, only limited body weight reductions are achieved with SGLT2i treatment. Hyperphagia is reportedly one of the causes of this limited weight loss. However, the effects of SGLT2i treatment on systemic energy expenditure have not been fully elucidated. Herein, we investigated the acute effects of dapagliflozin, a SGLT2i, on systemic energy expenditure in mice. Eighteen hours after dapagliflozin treatment oxygen consumption and brown adipose tissue (BAT) expression of ucp1, a thermogenesis-related gene, were significantly decreased as compared to those after vehicle treatment. In addition, dapagliflozin significantly suppressed norepinephrine (NE) turnover in BAT and c-fos expression in the rostral raphe pallidus nucleus (rRPa) which contains the sympathetic premotor neurons responsible for thermogenesis. These findings indicate that the dapagliflozin-mediated acute decrease in energy expenditure involves a reduction in BAT thermogenesis via decreased sympathetic nerve activity from the rRPa. Furthermore, common hepatic branch vagotomy abolished the reductions in ucp1 expression and NE contents in BAT and c-fos expression in the rRPa. In addition, alterations in hepatic carbohydrate metabolism, such as decreases in glycogen contents and upregulation of phosphoenolpyruvate carboxykinase, manifested prior to the suppression of BAT thermogenesis, e.g. 6 hours after dapagliflozin treatment. Collectively, these results suggest that SGLT2i treatment acutely suppresses energy expenditure in BAT via regulation of an inter-organ neural network consisting of the common hepatic vagal branch and sympathetic nerves.

Rho-kinase inhibition ameliorates metabolic disorders through activation of AMPK pathway in mice.

BACKGROUND: Metabolic disorders, caused by excessive calorie intake and low physical activity, are important cardiovascular risk factors. Rho-kinase, an effector protein of the small GTP-binding protein RhoA, is an important cardiovascular therapeutic target and its activity is increased in patients with metabolic syndrome. We aimed to examine whether Rho-kinase inhibition improves high-fat diet (HFD)-induced metabolic disorders, and if so, to elucidate the involvement of AMP-activated kinase (AMPK), a key molecule of metabolic conditions. METHODS AND RESULTS: Mice were fed a high-fat diet, which induced metabolic phenotypes, such as obesity, hypercholesterolemia and glucose intolerance. These phenotypes are suppressed by treatment with selective Rho-kinase inhibitor, associated with increased whole body O2 consumption and AMPK activation in the skeletal muscle and liver. Moreover, Rho-kinase inhibition increased mRNA expression of the molecules linked to fatty acid oxidation, mitochondrial energy production and glucose metabolism, all of which are known as targets of AMPK in those tissues. In systemic overexpression of dominant-negative Rho-kinase mice, body weight, serum lipid levels and glucose metabolism were improved compared with littermate control mice. Furthermore, in AMPKα2-deficient mice, the beneficial effects of fasudil, a Rho-kinase inhibitor, on body weight, hypercholesterolemia, mRNA expression of the AMPK targets and increase of whole body O2 consumption were absent, whereas glucose metabolism was restored by fasudil to the level in wild-type mice. In cultured mouse myocytes, pharmacological and genetic inhibition of Rho-kinase increased AMPK activity through liver kinase b1 (LKB1), with up-regulation of its targets, which effects were abolished by an AMPK inhibitor, compound C. CONCLUSIONS: These results indicate that Rho-kinase inhibition ameliorates metabolic disorders through activation of the LKB1/AMPK pathway, suggesting that Rho-kinase is also a novel therapeutic target of metabolic disorders.

Simultaneous copy number losses within multiple subtelomeric regions in early-onset type 2 diabetes mellitus.

Genetic factors play very important roles in the onset and progression of type 2 diabetes mellitus (T2DM). However, the genetic factors correlating with T2DM onset have not as yet been fully clarified. We previously found that copy number losses in the subtelomeric region on chromosome 4p16.3 were detected in early-onset Japanese T2DM patients (onset age <35 years) at a high frequency. Herein, we additionally found two novel copy number losses within the subtelomeric regions on chromosomes 16q24.2-3 and 22q13.31-33, which have significant associations with early-onset Japanese T2DM. The associations were statistically significant by Fisher's exact tests with P values of 5.19 × 10(-3) and 1.81 × 10(-3) and odds ratios of 5.7 and 4.4 for 16q24.2-3 and 22q13.31-33, respectively. Furthermore, copy number variation (CNV) analysis of the whole genome using the CNV BeadChip system verified simultaneous copy number losses in all three subtelomeric regions in 11 of our 100 T2DM subjects, while none of 100 non-diabetic controls showed the copy number losses in all three regions. Our results suggest that the mechanism underlying induction of CNVs is involved in the pathogenesis of early-onset T2DM. Thus, copy number losses within multiple subtelomeric regions are strongly associated with early-onset T2DM and examination of simultaneous CNVs in these three regions may lead to the development of an accurate and selective procedure for detecting genetic susceptibility to T2DM.

Identification of a novel interorgan mechanism favoring energy storage in overnutrition.

While body weight is essentially determined by the balance of energy intake and energy consumption, it is not necessarily the case that changes in daily food intakes and exercise directly reflect changes in body weight. In recent years, it has been revealed that numerous metabolic interactions between organs, which are organized by the brain, function as a feedback mechanism, and are involved in maintaining body weight homeostasis against excess energy intake. On the other hand, since obesity has seen an explosive increase in this age of plenty, there must be other interactions between organs working as feedforward mechanisms favoring weight gain. However, no such interaction has yet been demonstrated. Recently, we discovered a new interorgan neural network, from the liver, which may represent the feedforward mechanism.(1) Under conditions of excessive energy intake, changes in glucose metabolism occur in the liver with increased expression of hepatic glucokinase (GK) and the induction of neuronal signal transmission via the afferent vagus nerve. These signals are received by the medulla and result in inactivation of sympathetic nerve to brown adipose tissue (BAT), thereby suppressing thermogenesis in BAT and promoting adiposity. Furthermore, the efficacy of the liver-to-BAT interaction differs among mouse strains and these differences may contribute to determining the obesity predispositions of various strains. In conclusion, this novel interorgan neuronal relay system functions to suppress energy expenditure when energy intake is increased, and thus, is considered to be a thrifty mechanism operating on the whole body level. During periods when sufficient food was not always available, this system worked in favor of survival. However, in the current age of plenty, it is assumed to work as a mechanism flipping a metabolic switch toward obesity.

Chronic mild stress alters circadian expressions of molecular clock genes in the liver.

Chronic stress is well known to affect metabolic regulation. However, molecular mechanisms interconnecting stress response systems and metabolic regulations have yet to be elucidated. Various physiological processes, including glucose/lipid metabolism, are regulated by the circadian clock, and core clock gene dysregulation reportedly leads to metabolic disorders. Glucocorticoids, acting as end-effectors of the hypothalamus-pituitary-adrenal (HPA) axis, entrain the circadian rhythms of peripheral organs, including the liver, by phase-shifting core clock gene expressions. Therefore, we examined whether chronic stress affects circadian expressions of core clock genes and metabolism-related genes in the liver using the chronic mild stress (CMS) procedure. In BALB/c mice, CMS elevated and phase-shifted serum corticosterone levels, indicating overactivation of the HPA axis. The rhythmic expressions of core clock genes, e.g., Clock, Npas2, Bmal1, Per1, and Cry1, were altered in the liver while being completely preserved in the hypothalamic suprachiasmatic nuculeus (SCN), suggesting that the SCN is not involved in alterations in hepatic core clock gene expressions. In addition, circadian patterns of glucose and lipid metabolism-related genes, e.g., peroxisome proliferator activated receptor (Ppar) α, Pparγ-1, Pparγ-coactivator-1α, and phosphoenolepyruvate carboxykinase, were also disturbed by CMS. In contrast, in C57BL/6 mice, the same CMS procedure altered neither serum corticosterone levels nor rhythmic expressions of hepatic core clock genes and metabolism-related genes. Thus, chronic stress can interfere with the circadian expressions of both core clock genes and metabolism-related genes in the liver possibly involving HPA axis overactivation. This mechanism might contribute to metabolic disorders in stressful modern societies.

A case of slowly progressive type 1 diabetes with insulin independence maintained for 10 years with α-glucosidase inhibitor monotherapy.

Slowly Progressive Type 1 Diabetes (SPT1D) is characterized by the absence of insulin dependence at the onset of diabetes and persistent detection of islet cell autoantibodies. These patients with high titers of glutamic acid decarboxylase autoantibodies (GADA) are known to progress to insulin dependence within several years. Low-dose insulin injections have been reported to prevent or delay the decline of insulin secretion in SPT1D patients. We experienced the case of an SPT1D patient with preserved endogenous insulin secretion and good glycemic control achieved with α-glucosidase inhibitor (α-GI) treatment alone for 10 years despite having continuously elevated GADA titers. The details of this case suggest that α-GI treatment might have preventive effects on SPT1D progression.

Hepatic glucokinase modulates obesity predisposition by regulating BAT thermogenesis via neural signals.

Considering the explosive increase in obesity worldwide, there must be an unknown mechanism(s) promoting energy accumulation under conditions of overnutrition. We identified a feed-forward mechanism favoring energy storage, originating in hepatic glucokinase (GK) upregulation. High-fat feeding induced hepatic GK upregulation, and hepatic GK overexpression dose-dependently decreased adaptive thermogenesis by downregulating thermogenesis-related genes in brown adipose tissue (BAT). This intertissue (liver-to-BAT) system consists of the afferent vagus from the liver and sympathetic efferents from the medulla and antagonizes anti-obesity effects of leptin on thermogenesis. Furthermore, upregulation of endogenous GK in the liver by high-fat feeding was more marked in obesity-prone than in obesity-resistant strains and was inversely associated with BAT thermogenesis. Hepatic GK overexpression in obesity-resistant mice promoted weight gain, while hepatic GK knockdown in obesity-prone mice attenuated weight gain with increased adaptive thermogenesis. Thus, this intertissue energy-saving system may contribute to determining obesity predisposition.

Obesity alters circadian expressions of molecular clock genes in the brainstem.

Major components of energy homeostasis, including feeding behavior and glucose and lipid metabolism, are subject to circadian rhythms. Recent studies have suggested that dysfunctions of molecular clock genes are involved in the development of obesity and diabetes. To examine whether metabolic states per se alter the circadian clock in the central nervous system (CNS), we analyzed the daily mRNA expression profiles of core clock genes in the caudal brainstem nucleus of the solitary tract (NTS). In lean C57BL/6 mice, transcript levels of the core clock genes (Npas2, Bmal1, Per1, Per2 and Rev-erbalpha) clearly showed 24-h rhythmicity. On the other hand, the expression profiles of Bmal1 and Rev-erbalpha were attenuated in mice with high fat diet-induced obesity as well as genetically obese KK-A(y) and ob/ob mice. Clock expression levels were increased in mice with high fat diet-induced obesity and Cry1 expression levels were decreased in KK-A(y) and ob/ob mice. In addition, peroxisome proliferator-activated receptor alpha (PPARalpha), which reportedly increases the BMAL1 transcriptional level, was up-regulated in the NTS of these murine models of obesity and insulin resistance, suggesting involvement of PPARalpha in the attenuation of circadian rhythms in the NTS in obese states. Furthermore, a circadian expression profile of a downstream target of clock genes, the large conductance Ca(2+)-activated K(+)channel, was disturbed in the NTS of these murine obesity models. These perturbations might contribute to neuronal dysfunction in obese states. This is the first report showing that obesity perturbs the circadian expressions of core clock genes in the CNS.