👤 Michiru Harada

Fructose ingestion increases circulating glucagon-like peptide-1 (GLP-1) and insulin, yet the specific contributions of these hormonal responses to glycaemic control remain incompletely defined. We hypothesised that fructose metabolism in intestinal L-cells triggers GLP-1 secretion, which then potentiates insulin secretion and counteracts fructose-induced hyperglycaemia. To test this hypothesis, we systematically characterised metabolic responses across multiple mouse strains after 24 h ad libitum fructose ingestion. In both lean (NSY.B6-a/a) and obese diabetic (NSY.B6-A Show less

The next generation of obesity medicines harness the activity of the glucose-dependent insulinotropic polypeptide and glucagon-like peptide 1 receptors (GIPR and GLP-1R), but their mechanism of action remains unclear. Here, we report that the GIPR is enriched in oligodendrocytes and GIPR signaling bidirectionally regulates oligodendrogenesis. In mice with adult-onset deletion of GIPR in oligodendrocytes, GIPR agonism fails to enhance the weight-loss effects of GLP-1R agonism. Mechanistically, GIPR agonism increases brain access of GLP-1R agonists, and GIPR signaling in oligodendrocytes is required for this effect. In addition, we show that vasopressin neurons of the paraventricular hypothalamus are necessary for the weight-loss response to GLP-1R activation, targeted by peripherally administered GLP-1R agonists via their axonal compartment, and this access is increased by activation of the GIPR in oligodendrocytes. Collectively, our findings identify a novel mechanism by which incretin therapies may function to promote synergistic weight loss in the management of excess adiposity. Show less

Glucose-dependent insulinotropic polypeptide (GIP) is secreted by enteroendocrine K cells, primarily located in the upper small intestine, in response to food intake and plays a significant role in the postprandial regulation of nutrient metabolism. Although the importance of GIP in metabolic regulation has long been recognized, progress in developing GIP as a therapeutic target has been limited. However, the GIP/GIP receptor (GIPR) axis has garnered increasing attention in recent years. Emerging evidence suggests that dual GIP/GLP-1 receptor agonists and triple GIP/GLP-1/glucagon receptor agonists provide beneficial metabolic effects in individuals with type 2 diabetes and obesity. In this review, we outline the physiological roles of GIP, detailing the mechanisms of GIP secretion from K cells in response to macronutrients, its actions on key target organs involved in metabolic regulation, and ongoing developments in its therapeutic applications. Show less

Estrogen is synthesized throughout various tissues in the body, and its production is regulated by the rate-limiting enzyme aromatase (encoded by the Cyp19a1 gene). Notably, aromatase is also expressed in central nervous system cells, allowing for localized estrogen synthesis in regions such as the hypothalamus. Estrogens produced within these neurons are referred to as neuroestrogens. In this study, we investigated the role of neuroestrogens in the regulation of appetite through modulation of hypothalamic pathways in OVX, ArKO, and aromatase-restored mice. Estrogen suppresses appetite by influencing the expression of appetite-regulating peptides, including POMC and NPY, via MC4R. We explored the direct effects of neuroestrogens, independent from ovarian estrogen, on appetite suppression and the underlying molecular mechanisms. We monitored body weight and food intake and evaluated the expression of Cyp19a1, Mc4r, and other appetite-related genes. Our findings indicate that OVX and ArKO mice exhibited increased body weight and food consumption, which correlated with altered expression of Mc4r and Cyp19a1. Conversely, restoration of Cyp19a1 expression in a neuron specific manner significantly decreased food intake and increased Mc4r expression in the hypothalamus. Furthermore, neuroestrogens enhanced leptin responsiveness. Our results imply that neuroestrogens likely contribute to appetite regulation and may be relevant for body weight reduction. Show less

Long noncoding RNAs (lncRNAs) are involved in various biological events. Previously we reported that lncRNA CCDC26 controls myeloid leukemia cell proliferation and mortality by regulating the proto-oncogene KIT. However, the mechanism of lncRNA CCDC26 effects on carcinogenesis and cell differentiation remains unclarified. To investigate the mechanism of lncRNA CCDC26 activity, we analyzed its protein partners using the S1 aptamer/cross-linking-immunoprecipitation (S1-CLIP) experiment. We identified a cytoskeleton protein (vimentin), chromatin proteins (chromobox 1/5 transcription factors [CBX1 and CBX5]) and a nuclear splicing-related protein heterogeneous nuclear ribonucleoprotein C (HNRNPC) as its interaction partners. As lncRNA CCDC26 is ubiquitously present in the cell (in cytoplasm, nucleoplasm, and chromatin cellular fractions); these results evidence that lncRNA CCDC26 is a unique multifunctional lncRNA that functions by interacting with several proteins in multiple intracellular compartments. We further identified the sequence through which it interacts with proteins by using a series of truncated-lncRNA CCDC26 fragments and RNA immunoprecipitation (RIP) experiments. Furthermore, using RIP, we identified the vimentin domain required for the lncRNA CCDC26 binding. Notably, CCDC26 knockdown reduced CBX1/CBX5 binding at certain gene promoters, correlating with increased gene expression. These findings suggest that CCDC26 may regulate transcription by interacting with CBX1 and CBX5. Show less

Pancreas-specific lipase and lipase activity measured by immunological assays (Spec cPL and Spec fPL) and colorimetric assays (1,2-o-dilauryl-rac-glycelo-3-glutaric acid-(6'-methylresorufin) ester [DGGR] and triolein), respectively, are used to diagnose pancreatitis in both dogs and cats. However, DGGR and triolein assays may be influenced by extrapancreatic lipases, including hepatic triglyceride lipase (HTGL) and lipoprotein lipase (LPL). To investigate the effect of extrapancreatic lipases on immunological and colorimetric assays by measuring changes in HTGL and LPL activity following heparin administration. Six healthy Beagles and six adult purpose-bred cats were enrolled. HTGL and LPL activities were induced by intravenous heparin administration. Serum samples were collected at baseline and at 5-, 10-, 15-, and 60-min following heparin injection. Spec cPL, Spec fPL, and lipase activities were measured using DGGR and triolein assays, whereas HTGL and LPL activities were measured using their respective assays. Spec cPL and Spec fPL levels showed no significant changes following heparin administration. Conversely, DGGR-based and triolein-based lipase activities, as well as HTGL and LPL activities, were significantly increased after heparin administration in both dogs and cats. HTGL and LPL activities showed significant positive correlations with DGGR-based (P < .001, r = .90 for both) and triolein-based (P < .001, r = .63 and P < .001, r = .68, respectively) lipase activities, but not with Spec cPL and Spec fPL. DGGR- and triolein-based lipase activities are influenced by HTGL and LPL activities, as their substrates are hydrolyzed by pancreatic lipase, HTGL, and LPL. Show less

Cyclic adenosine monophosphate-response element-binding protein-1-regulated transcription coactivator-1 (CRTC1), a cytoplasmic coactivator that translocates to the nucleus in response to cAMP, is associated with obesity. We previously reported that Show less

Central glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) signaling is critical in GIP-based therapeutics' ability to lower body weight, but pathways leveraged by GIPR pharmacology in the brain remain incompletely understood. We explored the role of Gipr neurons in the hypothalamus and dorsal vagal complex (DVC) - brain regions critical to the control of energy balance. Hypothalamic Gipr expression was not necessary for the synergistic effect of GIPR/GLP-1R coagonism on body weight. While chemogenetic stimulation of both hypothalamic and DVC Gipr neurons suppressed food intake, activation of DVC Gipr neurons reduced ambulatory activity and induced conditioned taste avoidance, while there was no effect of a short-acting GIPR agonist (GIPRA). Within the DVC, Gipr neurons of the nucleus tractus solitarius (NTS), but not the area postrema (AP), projected to distal brain regions and were transcriptomically distinct. Peripherally dosed fluorescent GIPRAs revealed that access was restricted to circumventricular organs in the CNS. These data demonstrate that Gipr neurons in the hypothalamus, AP, and NTS differ in their connectivity, transcriptomic profile, peripheral accessibility, and appetite-controlling mechanisms. These results highlight the heterogeneity of the central GIPR signaling axis and suggest that studies into the effects of GIP pharmacology on feeding behavior should consider the interplay of multiple regulatory pathways. Show less

Histiocytic sarcoma (HS) is an incurable aggressive tumor, and no consensus has been made on the treatment due to its rare occurrence. Since dogs spontaneously develop the disease and several cell lines are available, they have been advocated as translational animal models. In the present study, therefore, we explored gene mutations and aberrant molecular pathways in canine HS by next generation sequencing to identify molecular targets for treatment. Whole exome sequencing and RNA-sequencing revealed gene mutations related to receptor tyrosine kinase pathways and activation of ERK1/2, PI3K-AKT, and STAT3 pathways. Analysis by quantitative PCR and immunohistochemistry revealed that fibroblast growth factor receptor 1 (FGFR1) is over-expressed. Moreover, activation of ERK and Akt signaling were confirmed in all HS cell lines, and FGFR1 inhibitors showed dose-dependent growth inhibitory effects in two of the twelve canine HS cell lines. The findings obtained in the present study indicated that ERK and Akt signaling were activated in canine HS and drugs targeting FGFR1 might be effective in part of the cases. The present study provides translational evidence that leads to establishment of novel therapeutic strategies targeting ERK and Akt signaling in HS patients. Show less

Lipid management, especially with respect to triglyceride (TG) metabolism, in patients with diabetes is not sufficient with current therapeutic agents, and new approaches for improvement are needed. Members of the angiopoietin-like protein (ANGPTL) family, specifically ANGPTL3, 4, and 8, have been reported as factors that inhibit lipoprotein lipase (LPL) activity and affect TGs. The present study investigated the association between lipid and glucose metabolism markers and the mechanism by which these proteins affect lipid metabolism. A total of 84 patients hospitalized for diabetes treatment were evaluated. Lipid and glucose metabolism markers in blood samples collected before breakfast, on the day after hospitalization, were analyzed. ANGPTL8 showed a significant positive correlation with TG values. HDL-C values displayed a significant positive correlation with ANGPTL3 but a negative correlation with ANGPTL4 and ANGPTL8. The results did not indicate a significant correlation among ANGPTL3, 4, and 8 levels. Thus, it is possible that the distribution of these proteins differs among patients. When patients were divided into groups according to the levels of ANGPTL3 and ANGPTL8, those with high levels of both ANGPTL3 and ANGPTL8 also had high levels of TG and small dense LDL-C/LDL-C (%). Multiple regression analysis indicated that low LPL, high ApoC2, high ApoC3, high ApoE, and high ANGPTL8 levels were the determinants of fasting hypertriglyceridemia. By contrast, no clear association was observed between any of the ANGPTLs and glucose metabolism markers, but ANGPTL8 levels were positively correlated with the levels of HOMA2-IR and BMI. Patients with high levels of both ANGPTL3 and ANGPTL8 had the worst lipid profiles. Among ANGPTL3, 4, and 8, ANGPTL8 is more important as a factor determining plasma TG levels. We anticipate that the results of this research will facilitate potential treatments targeting ANGPTL8 in patients with diabetes. Show less

Heparan sulfate (HS), a linear polysaccharide, is involved in diverse biological functions of various tissues. HS is expressed in pancreatic β-cells and may be involved in β-cell functions. However, the importance of HS for β-cell function remains unknown. Here, we generated mice with β-cell-specific deletion of Ext1 (βExt1CKO), which encodes an enzyme essential for HS synthesis, to investigate the detailed roles of HS in β-cell function. βExt1CKO mice decreased body weights compared with control mice, despite increased food intake. Additionally, βExt1CKO mice showed impaired glucose tolerance associated with decreased insulin secretion upon glucose challenge. Glucose-induced insulin secretion (GIIS) from isolated βExt1CKO islets was also significantly reduced, highlighting the contribution of HS to insulin secretion and glucose homeostasis. The gene expression essential for GIIS was decreased in βExt1CKO islets. Pdx1 and MafA were downregulated in βExt1CKO islets, indicating that HS promoted β-cell development and maturation. BrdU- or Ki67-positive β-cells were reduced in βExt1CKO pancreatic sections, suggesting the involvement of HS in the proliferation of β-cells. Moreover, insufficient vascularization in βExt1CKO islets may contribute to central distribution of α-cells. These data demonstrate HS plays diverse roles in β-cells, and that loss of HS leads to insufficient insulin secretion and dysregulation of glucose homeostasis. Show less

Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are genetically and phenotypically heterogeneous. Cardiac function is improved after treatment in some cardiomyopathy patients, but little is known about genetic predictors of long-term outcomes and myocardial recovery following medical treatment. To elucidate the genetic basis of cardiomyopathy in Japan and the genotypes involved in prognosis and left ventricular reverse remodeling (LVRR), we performed targeted sequencing on 120 DCM (70 sporadic and 50 familial) and 52 HCM (15 sporadic and 37 familial) patients and integrated their genotypes with clinical phenotypes. Among the 120 DCM patients, 20 (16.7%) had TTN truncating variants and 13 (10.8%) had LMNA variants. TTN truncating variants were the major cause of sporadic DCM (21.4% of sporadic cases) as with Caucasians, whereas LMNA variants, which include a novel recurrent LMNA E115M variant, were the most frequent in familial DCM (24.0% of familial cases) unlike Caucasians. Of the 52 HCM patients, MYH7 and MYBPC3 variants were the most common (12 (23.1%) had MYH7 variants and 11 (21.2%) had MYBPC3 variants) as with Caucasians. DCM patients harboring TTN truncating variants had better prognosis than those with LMNA variants. Most patients with TTN truncating variants achieved LVRR, unlike most patients with LMNA variants. Show less

Glucose-dependent insulinotropic polypeptide (GIP) is released during meals and promotes nutrient uptake and storage. GIP receptor knockout mice are protected from diet induced weight gain and thus GIP antagonists have been proposed as a treatment for obesity. In this study, we assessed the role of GIP in hyperphagia induced obesity and metabolic abnormalities in leptin deficient (Lep We crossbred GIP-GFP knock-in homozygous mice (GIP Postprandial GIP levels were markedly elevated in Lep Our results indicate that GIP knockout does not prevent excess weight gain and metabolic derangement in hyperphagic leptin deficient mice. Show less

Gastric inhibitory polypeptide receptor (GIPR) directly induces energy accumulation in adipose tissue in vitro. However, the importance of the direct effect of GIPR signaling on adipose tissue in vivo remains unclear. In the current study, we generated adipose tissue-specific GIPR knockout (GIPR Show less

Excess carbohydrate intake causes obesity in humans. On the other hand, acute administration of fructose, glucose or sucrose in experimental animals has been shown to increase the plasma concentration of anti-obesity hormones such as glucagon-like peptide 1 (GLP-1) and Fibroblast growth factor 21 (FGF21), which contribute to reducing body weight. However, the secretion and action of GLP-1 and FGF21 in mice chronically fed a high-sucrose diet has not been investigated. To address the role of anti-obesity hormones in response to increased sucrose intake, we analyzed mice fed a high-sucrose diet, a high-starch diet or a normal diet for 15 weeks. Mice fed a high-sucrose diet showed resistance to body weight gain, in comparison with mice fed a high-starch diet or control diet, due to increased energy expenditure. Plasma FGF21 levels were highest among the three groups in mice fed a high-sucrose diet, whereas no significant difference in GLP-1 levels was observed. Expression levels of uncoupling protein 1 (UCP-1), FGF receptor 1c (FGFR1c) and β-klotho (KLB) mRNA in brown adipose tissue were significantly increased in high sucrose-fed mice, suggesting increases in FGF21 sensitivity and energy expenditure. Expression of carbohydrate responsive element binding protein (ChREBP) mRNA in liver and brown adipose tissue was also increased in high sucrose-fed mice. These results indicate that FGF21 production in liver and brown adipose tissue is increased in high-sucrose diet and participates in resistance to weight gain. Show less

Angiosarcoma is a malignant vascular tumor originating from endothelial cells of blood vessels or lymphatic vessels. The specific driver mutations in angiosarcoma remain unknown. In this study, we investigated this issue by transcriptome sequencing of patient-derived angiosarcoma cells (ISO-HAS), identifying a novel fusion gene NUP160-SLC43A3 found to be expressed in 9 of 25 human angiosarcoma specimens that were examined. In tumors harboring the fusion gene, the duration between the onset of symptoms and the first hospital visit was significantly shorter, suggesting more rapid tumor progression. Stable expression of the fusion gene in nontransformed human dermal microvascular endothelial cells elicited a gene-expression pattern mimicking ISO-HAS cells and increased cell proliferation, an effect traced in part to NUP160 truncation. Conversely, RNAi-mediated attenuation of NUP160 in ISO-HAS cells decreased cell number. Confirming the oncogenic effects of the fusion protein, subcutaneous implantation of NUP160-SLC43A3-expressing fibroblasts induced tumors resembling human angiosarcoma. Collectively, our findings advance knowledge concerning the genetic causes of angiosarcoma, with potential implications for new diagnostic and therapeutic approaches. Show less

Gastric inhibitory polypeptide (GIP) is an incretin secreted from the gastrointestinal tract after an ingestion of nutrients, and stimulates an insulin secretion from the pancreatic islets. Additionally, GIP has important roles in extrapancreatic tissues: fat accumulation in adipose tissue, neuroprotective effects in the central nervous system and an inhibition of bone resorption. In the current study, we investigated the effects of GIP signaling on the peripheral nervous system (PNS). First, the presence of the GIP receptor (GIPR) in mouse dorsal root ganglion (DRG) was evaluated utilizing immunohistochemical analysis, western blotting and reverse transcription polymerase chain reaction. DRG neurons of male wild-type mice (WT) were cultured with or without GIP, and their neurite lengths were quantified. Functions of the PNS were evaluated in GIPR-deficient mice (gipr-/-) and WT by using current perception thresholds (CPTs), Thermal Plantar Test (TPT), and motor (MNCV) and sensory nerve conduction velocity (SNCV, respectively). Sciatic nerve blood flow (SNBF) and plantar skin blood flow (PSBF) were also evaluated. We confirmed the expression of GIPR in DRG neurons. The neurite outgrowths of DRG neurons were promoted by the GIP administrations. The gipr-/- showed impaired perception functions in the examination of CPTs and TPT. Both MNCV and SNCV were delayed in gipr-/- compared with these in WT. There was no difference in SNBF and PSBF between WT and gipr-/-. Our findings show that the GIP signal could exert direct physiological roles in the PNS, which might be directly exerted on the PNS. Show less

We have previously reported the discovery of a new class of potent inhibitors of 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) derived from benzylidene oxazolidinedione and thiazolidinedione scaffolds. In this study, these analogs were designed, synthesized, and evaluated in a human cell-based assay. The detailed structure-activity relationship (SAR) surrounding this pharmacophore were developed, and consequently a number of compounds from this series demonstrated single-digit nanomolar 17β-HDS3 inhibitory activity in vitro. Subsequent optimization work in pursuit of the improvement of oral bioavailability demonstrated in vivo proof-of-concept by prodrug strategy based on phosphate esters for these 17β-HSD3 inhibitors. When a phosphate ester 16 was administered orally at a high dose of 100mg/kg, 16 showed approximately two times more potent testosterone (T)-lowering effect against a positive control in the luteinizing hormone-releasing hormone (LH-RH)-induced T production assay. The T-lowering effect continued at ca 10% level of control over 4h after administration. The nonsteroidal molecules based on this series have the potential to provide unique and effective clinical opportunities for treatment of prostate cancer. Show less

Novel and potent inhibitors of 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) were identified based on oxazolidinedione and thiazolidinedione derivatives, starting from a high-throughput screening hit, 5-(3-bromo-4-hydroxybenzyl)-3-(4-methoxyphenyl)-1,3-thiazol-2-one. 5-(3-Bromo-4-hydroxybenzylidene)-3-(4-methoxyphenyl)-2-thioxo-1,3-thiazolidin-4-one exhibited a promising activity profile and demonstrated significant selectivity over the related 17β-HSD isoenzymes and nuclear receptors. Show less

The synthesis and SAR studies of 3- and 4-substituted 7-hydroxycoumarins as novel 17beta-HSD3 inhibitors are discussed. The most potent compounds from this series exhibited low nanomolar inhibitory activity with acceptable selectivity versus other 17beta-HSD isoenzymes and nuclear receptors. Show less

Mice lacking apolipoprotein A-V (apoA-V) displayed an increase in serum triglyceride (TG) levels; however, the correlation of apoA-V levels with TG levels in humans is controversial, and the exact mechanism by which apoA-V affects TG levels is unclear. The aim of the present study was to clarify the impact of apoA-V on the lipoprotein subclass profile in preadolescent children, which has not been studied. The study subjects were 178 (89 male, 89 female) 4th grade elementary school children (mean+/-SD: 9.5+/-0.5 years old). ApoA-V levels were determined by an enzyme-linked immunosorbent assay, and the lipid component of each lipoprotein fraction and their particle sizes were measured by HPLC. Levels of apoA-V showed no gender difference in preadolescent children, and were not affected by anthropometric variables. ApoA-V had a negative association with serum TG levels and TG levels in each lipoprotein fraction, and a positive association with HDL-C. In particular, apoA-V appears to contribute to the increase in cholesterol levels in the larger HDL fraction. It was suggested that apoA-V is a potent modulator of HDL and VLDL components in preadolescent children. Show less

We previously studied fatty acid metabolism in the liver of nonalcoholic fatty liver disease (NAFLD) and reported the activation of the LXRalpha-SREBP-1c pathway in hepatocytes. LXRalpha regulates cholesterol metabolism as well as fatty acid metabolism, and its agonistic ligands are oxysterols. Moreover, there is some evidence that excess cholesterol intake is involved in the onset of NAFLD. Therefore, in this study, we examined the expression of cholesterol metabolism-associated genes in the NAFLD liver by real-time PCR. Expression of LXRalpha and ACAT1 was up-regulated in NAFLD and this was more noticeable in non-obese rather than in obese patients. Although the expression of the LDL receptor, which acts on cholesterol uptake, and of SREBP-2, a positive key regulator of cholesterol, was suppressed, the expression of enzymes that promote cholesterol synthesis was uniformly increased in NAFLD. Gene expression of apoB100 and microsomal triglyceride transfer protein, which are associated with VLDL secretion, and ABCG5, which is involved in cholesterol excretion, was significantly elevated in NAFLD. Because cholesterol accumulates in hepatocytes in NAFLD liver, cholesterol uptake and synthesis should be physiologically down-regulated. However, cholesterol synthesis was activated in NAFLD liver, meaning that cholesterol metabolism is dysregulated in NAFLD. Overproduction of cholesterol may lead to an increased level of oxysterols, activation of LXRalpha and SREBP-1c, and enhanced fatty acid synthesis. Show less

Riccardin C, a nuclear receptor LXRalpha selective agonist, is an 18-membered macrocyclic bisbibenzyl isolated from several liverworts. Synthesis of riccardin C and its seven O-methylated derivatives was accomplished. The synthetic sequence highlights an intramolecular Suzuki-Miyaura coupling in the formation of the 18-membered biaryl linkage present in riccardin C. The structure-activity relationship of these compounds suggests that all of the phenolic hydroxy groups present in riccardin C are essential for the activation of LXRalpha. Show less

Gastric inhibitory polypeptide (GIP) is an incretin and directly promotes fat accumulation in adipocytes. Inhibition of GIP signaling prevents onset of obesity and increases fat oxidation in peripheral tissues under high-fat diet (HFD), but the mechanism is unknown. In the present study, we investigated the effects of inhibition of GIP signaling on adiponectin levels after 3 weeks of HFD by comparing wild-type (WT) mice and GIP receptor-deficient (Gipr(-/-)) mice. In HFD-fed Gipr(-/-) mice, fat oxidation was significantly increased and adiponectin mRNA levels in white adipose tissue and plasma adiponectin levels were significantly increased compared to those in HFD-fed WT mice. In addition, the PPARalpha mRNA level was increased and the ACC mRNA level was decreased in skeletal muscle of HFD-fed Gipr(-/-) mice compared with those in HFD-fed WT mice. These results indicate that inhibition of GIP signaling increases adiponectin levels, resulting in increased fat oxidation in peripheral tissues under HFD. Show less

Gastric inhibitory polypeptide (GIP) is an incretin that potentiates insulin secretion from pancreatic beta-cells by binding to GIP receptor (GIPR) and subsequently increasing the level of intracellular adenosine 3',5'-cyclic monophosphate (cAMP). We have identified a novel GIPR splice variant in mouse beta-cells that retains intron 8, resulting in a COOH-terminal truncated form (truncated GIPR). This isoform was coexpressed with full-length GIPR (wild-type GIPR) in normal GIPR-expressing tissues. In an experiment using cells transfected with both GIPRs, truncated GIPR did not lead to cAMP production induced by GIP but inhibited GIP-induced cAMP production through wild-type GIPR (n = 3-4, P < 0.05). Wild-type GIPR was normally located on the cell surface, but its expression was decreased in the presence of truncated GIPR, suggesting a dominant negative effect of truncated GIPR against wild-type GIPR. The functional relevance of truncated GIPR in vivo was investigated. In high-fat diet-fed obese mice (HFD mice), blood glucose levels were maintained by compensatory increased insulin secretion (n = 8, P < 0.05), and cAMP production (n = 6, P < 0.01) and insulin secretion (n = 10, P < 0.05) induced by GIP were significantly increased in isolated islets, suggesting hypersensitivity of the GIPR. Total GIPR mRNA expression was not increased in the islets of HFD mice, but the expression ratio of truncated GIPR to total GIPR was reduced by 32% compared with that of control mice (n = 6, P < 0.05). These results indicate that a relative reduction of truncated GIPR expression may be involved in hypersensitivity of GIPR and hyperinsulinemia in diet-induced obese mice. Show less

Canonical Wnt/beta-catenin signaling has central roles in development and diseases, and is initiated by the action of the frizzled (Fz) receptor, its coreceptor LDL receptor-related protein 6 (Lrp6), and the cytoplasmic dishevelled (Dvl) protein. The functional relationships among Fz, Lrp6 and Dvl have long been enigmatic. We demonstrated previously that Wnt-induced Lrp6 phosphorylation via glycogen synthase kinase 3 (Gsk3) initiates Wnt/beta-catenin signaling. Here we show that both Fz and Dvl functions are critical for Wnt-induced Lrp6 phosphorylation through Fz-Lrp6 interaction. We also show that axin, a key scaffolding protein in the Wnt pathway, is required for Lrp6 phosphorylation via its ability to recruit Gsk3, and inhibition of Gsk3 at the plasma membrane blocks Wnt/beta-catenin signaling. Our results suggest a model that upon Wnt-induced Fz-Lrp6 complex formation, Fz recruitment of Dvl in turn recruits the axin-Gsk3 complex, thereby promoting Lrp6 phosphorylation to initiate beta-catenin signaling. We discuss the dual roles of the axin-Gsk3 complex and signal amplification by Lrp6-axin interaction during Wnt/beta-catenin signaling. Show less

Aging is associated with increased fat mass and decreased lean mass, which is strongly associated with the development of insulin resistance. Gastric inhibitory polypeptide (GIP) is known to promote efficient storage of ingested nutrients into adipose tissue; we examined aging-associated changes in body composition using 10-week-old and 50-week-old wild-type (WT) and GIP receptor knockout (Gipr-/-) mice on a normal diet, which show no difference in body weight. We found that Gipr-/- mice showed significantly reduced fat mass without reduction of lean mass or food intake, while WT mice showed increased fat mass and decreased lean mass associated with aging. Moreover, aged Gipr-/- mice showed improved insulin sensitivity, which is associated with amelioration in glucose tolerance, higher plasma adiponectin levels, and increased spontaneous physical activity. We therefore conclude that genetic inactivation of GIP signaling can prevent the development of aging-associated insulin resistance through body composition changes. Show less