Gastric inhibitory polypeptide modulates adiposity and fat oxidation under diminished insulin action

Gut hormone gastric inhibitory polypeptide (GIP) stimulates insulin secretion from pancreatic β-cells upon ingestion of nutrients. Inhibition of GIP signaling prevents the onset of obesity and consequent insulin resistance induced by high-fat diet. In this study, we investigated the role of GIP in accumulation of triglycerides into adipocytes and in fat oxidation peripherally using insulin receptor substrate (IRS)-1-deficient mice and revealed that IRS-1^−/−GIPR^−/− mice exhibited both reduced adiposity and ameliorated insulin resistance. Furthermore, increased gene expression of CD36 and UCP2 in liver, and increased expression and enzyme activity of 3-hydroxyacyl-CoA dehydrogenase in skeletal muscle of IRS-1^−/−GIPR^−/− mice might contribute to the lower respiratory quotient and the higher fat oxidation in light phase. These results suggest that GIP plays a crucial role in switching from fat oxidation to fat accumulation under the diminished insulin action as a potential target for secondary prevention of insulin resistance.     

Suppression of the caspase cleavage of beta-amyloid precursor protein by its cytoplasmic phosphorylation

beta-Amyloid precursor protein (APP) is a type I transmembrane protein. Its cleavages by beta- and gamma-secretases yield beta-amyloid, which is the main constituent of senile plaques in Alzheimer's disease (AD). In apoptotic cells and AD brains, APP is alternatively cleaved by caspases in the cytoplasmic region after the Asp664 residue (with respect to the numbering conversion for the APP695 isoform). Caspase-cleaved fragments of APP are cytotoxic and have been implicated in AD pathogenesis; however, the mechanisms regulating the cleavage have not been studied. APP is constitutively phosphorylated at Thr668 in brain. In the present study, we demonstrate that APP phosphorylated at Thr668 is less vulnerable to cytoplasmic cleavage by caspase-3 and caspase-8. This suggests that APP phosphorylation suppresses the generation of caspase-cleaved fragments of APP in the brain and that perturbation of this phosphorylation may be involved in APP-mediated neurotoxicity.     

Treatment with leucine stimulates the production of hepatocyte growth factor in vivo

Hepatocyte growth factor (HGF) has pleiotropic effects. Up-regulation of HGF activity in vivo may be beneficial. Branched-chain amino acids (BCAAs) are known to modulate various cellular functions. When starved rats received intraperitoneal injections of valine, leucine or isoleucine, only leucine treatment increased both hepatic and circulating levels of HGF in a dose-dependent manner, up to 1.5 and 2.3 times higher, respectively, than in controls. When young growing rats with free access to food were injected with leucine once a day for a week, HGF levels and liver weights were significantly higher than those of control rats. Furthermore, 1 week of leucine treatment of adult rats resulted in elevated serum albumin levels with an increase in HGF levels. Taken together with our previous report showing that leucine stimulates HGF production by hepatic stellate cells in culture, leucine, among BCAAs, may induce an increase in HGF production by the liver in vivo.     

Localization of the 31-amino-acid endothelin-1 in hamster tissue

Endothelin (ET)-1(1-31) is a novel vasoconstrictor peptide produced by human mast cell chymase, which selectively cleaves big ET-1 at the Try(31)-Gly(32) bond. We investigated the localization of ET-1(1-31) in various hamster tissues by immunohistochemistry and compared it to the distribution of ET-1(1-21). We found that the localization and amount of ET-1(1-31) were different from those of ET-1(1-21) in each tissue. ET-1(1-31)-like immunoreactivities (IR) in the heart, lung, and adrenal gland were observed in the same areas as ET-1(1-21) but were significantly weaker, suggesting that ET-1(1-31) might play a role only in mast cell/chymase-related pathological conditions in these tissues. In the liver, ET-1(1-31)-like IR was strongly detected in Kupffer cells where ET-1(1-21)-like IR was seen more weakly. In the kidney, ET-1(1-31)-like IR was slightly higher than ET-1(1-21). These results suggest that ET-1(1-31) might have physiological roles distinct from those of ET-1(1-21) in some hamster tissues.     

Numerical quantification of the significance of aquatic vegetation affecting spatial distribution of Japanese medaka (Oryzias latipes) in an agricultural canal

Aquatic vegetation plays a very important role in providing food, shelter, and nursery habitat and is also regarded as hydraulic resistance in the stream environment. To achieve better ecological restoration, this trade-off should be solved both hydraulically and ecologically. This study quantifies the effect of aquatic vegetation on the spatial distribution of Japanese medaka (Oryzias latipes) to evaluate its importance to fish habitat preference. The preference for aquatic vegetation index is calculated using a fuzzy preference intensity model (FPIM) with interactions among water depth, current velocity and cover ratio in an agricultural canal. In this model, simplified fuzzy reasoning is introduced to explicitly take the essential vagueness of fish behavior into consideration, and a simple genetic algorithm is used to search for an optimum model representation. Uncertainties in measurement errors and dispersions of the physical environment are positively taken into the model using symmetric triangular fuzzy numbers. To overcome the difficulty in model construction with insufficient data observed in an agricultural canal, this model was conjugated with a model developed in a laboratory experiment. The model obtained was then assessed using the AIC (Akaikes Information Criterion) to evaluate the significance of vegetation index with a statistical approach. The results suggest the significance of vegetation index to habitat selection by Japanese medaka and that utilization of the AIC enables us to grasp the validity of an additional factor contributing to habitat prediction with a view to a definite scale     

Analysis of total N-glycans in cell membrane fractions of cancer cells using a combination of serotonin affinity chromatography and normal phase chromatography

Cell surface glycans and recognition molecules of these glycans play important roles in cellular recognition and trafficking, such as in the inflammation response by sialyl LewisX oligosaccharides. Malignant cells also utilize a similar mechanism during colonization and establishment of tumor tissues in the host. These considerations prompt us to develop a screening method for comprehensive analysis of N-glycans derived from membrane fractions of cancer cells. The method involves two step separations. Initially, N-glycans released from cell membrane fractions with N-glycoamidase F were labeled with 2-aminobenzoic acid and separated based on the number of sialic acid residues attached to the oligosaccharides using affinity chromatography on a serotonin-immobilized stationary phase. Each of the nonretarded fractions containing asialo- and high-mannose type oligosaccharides and mono-, di-, tri-, and tetra-sialooligosaccharide fractions which were desialylated with neuraminidase was analyzed by a combination of HPLC using an Amide-80 column as the stationary phase and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). We analyzed total N-glycan pools of membrane fractions obtained from some cancer cells, and found that U937 cells (Histocytic lymphoma cells) expressed a large amount of oligosaccharides having polylactosamine residues and MKN45 cells (Gastric adenocarcinoma cells) contained hyper-fucosylated oligosaccharides which contained multiple fucose residues. The method described here will be a powerful technique for glycomics studies in cell surface glycoproteins, and will enable one to search marker oligosaccharides characteristically observed in various diseases such as cancer, inflammation, and congenital disorder.     

High density lipoprotein inhibits the activation of sterol regulatory element-binding protein-1 in cultured cells

A link between cellular uptake of high density lipoprotein (HDL) and regulation of sterol regulatory element-binding protein-1 (SREBP-1) was investigated in vitro. HDL decreased nuclear SREBP-1 levels as well as SREBP-1 target gene expression in HepG2 and HEK293 cells. However, HDL did not repress an exogenously expressed, constitutively active form of SREBP-1. HDL increased cellular cholesterol levels, and cellular cholesterol depletion by methyl-β-cyclodextrin abolished the effects of HDL. These results suggest that HDL inhibits the activation of SREBP-1 through a cholesterol-dependent mechanism, which may play an important role in regulating lipid synthetic pathways mediated by SREBP-1.     

Induction of Manganese Superoxide Dismutase by Nuclear Translocation and Activation of SIRT1 Promotes Cell Survival in Chronic Heart Failure

Oxidative stress plays a pivotal role in chronic heart failure. SIRT1, an NAD⁺-dependent histone/protein deacetylase, promotes cell survival under oxidative stress when it is expressed in the nucleus. However, adult cardiomyocytes predominantly express SIRT1 in the cytoplasm, and its function has not been elucidated. The purpose of this study was to investigate the functional role of SIRT1 in the heart and the potential use of SIRT1 in therapy for heart failure. We investigated the subcellular localization of SIRT1 in cardiomyocytes and its impact on cell survival. SIRT1 accumulated in the nucleus of cardiomyocytes in the failing hearts of TO-2 hamsters, postmyocardial infarction rats, and a dilated cardiomyopathy patient but not in control healthy hearts. Nuclear but not cytoplasmic SIRT1-induced manganese superoxide dismutase (Mn-SOD), which was further enhanced by resveratrol, and increased the resistance of C2C12 myoblasts to oxidative stress. Resveratrol''s enhancement of Mn-SOD levels depended on the level of nuclear SIRT1, and it suppressed the cell death induced by antimycin A or angiotensin II. The cell-protective effects of nuclear SIRT1 or resveratrol were canceled by the Mn-SOD small interfering RNA or SIRT1 small interfering RNA. The oral administration of resveratrol to TO-2 hamsters increased Mn-SOD levels in cardiomyocytes, suppressed fibrosis, preserved cardiac function, and significantly improved survival. Thus, Mn-SOD induced by resveratrol via nuclear SIRT1 reduced oxidative stress and participated in cardiomyocyte protection. SIRT1 activators such as resveratrol could be novel therapeutic tools for the treatment of chronic heart failure.     

Effects of chlorogenic acid and its metabolites on spontaneous locomotor activity in mice

Chlorogenic acid possessed a weak caffeine-like psychostimulant property when assessed for its effect on spontaneous locomotor activity in mice. In the evaluation of the effects for the major metabolites of chlorogenic acid which were detected upon incubation with rat feces and/or excreted in urine after oral administration to rats, caffeic and m-coumaric acids were found to be the principal active metabolites, while the others contributed little to this caffeine-like psychostimulant activity.     

Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.