Insulin Receptor mRNA Levels Research Articles

Developmental regulation of insulin receptor gene in sciatic nerves and role of insulin on glycoprotein P0 in the Schwann cells

In view of the observations that Schwann cells contain insulin receptors, in the present study, we have investigated the developmental regulation of insulin receptor gene in the sciatic nerves of different postnatal age group rats. We have also investigated the role of insulin in the expression of the major PNS myelin glycoprotein P zero (P0) in normal as well as high glucose conditions in primary rat Schwann cells. The expression of insulin receptor gene in sciatic nerves appeared to be differentially regulated. The steady-state levels of insulin receptor mRNA increased remarkably during development and after postnatal day 10, when the peak of myelin structural gene (P0) expression occur and slowly increased further until at least postnatal day 90 in parallel with the growth of the myelin sheath. By employing immunofluorescence and RT-PCR, we observed significant increase in the P0 protein and mRNA levels in Schwann cells in response to the insulin than in insulin deprived counterparts. The presence of insulin in the high glucose medium ameliorated the altered protein and mRNA of P0 in Schwann cells compared to the insulin deprived counterparts. These studies demonstrate the importance of insulin and its receptor as possible regulatory factors in the PNS and also emphasizes their novel therapeutic applications in demyelinating diseases, especially in diabetic poly-neuropathy.

Impaired insulin and leptin sensitivity in the offspring of moderate caloric-restricted dams during gestation is early programmed

We aimed to assess the mechanisms responsible for hyperphagia and metabolic alterations caused by maternal moderate caloric restriction during gestation. Male and female offspring of control and 20% caloric-restricted rats (CR) were studied. They were fed a normal-fat diet until 4 months of age and then moved to a high-fat diet until 6 months of age. Blood parameters and expression of selected genes in hypothalamus, retroperitoneal white adipose tissue (rWAT) and liver were analyzed at 25 days and 6 months of age. Plasma leptin was measured during suckling. Levels of proteins involved in insulin and leptin signaling were determined at 6 months of age. CR ate more calories than controls, but only males gained more weight. A peak in plasma leptin was found in 9-day-old controls, but was absent in CR. Twenty-five-day-old CR showed lower insulin receptor mRNA levels in hypothalamus, rWAT and liver, and long-form leptin receptor (ObRb) in hypothalamus. At the age of 6 months, homeostatic model assessment for insulin resistance index was higher in CR than controls, and CR males also displayed hyperleptinemia. Adult CR also showed lower ObRb mRNA levels in the hypothalamus (only females, but both showed altered neuropeptide Y/proopiomelanocortin mRNA ratio), rWAT and liver (males), and a decrease of protein kinase C zeta levels in rWAT (females) and liver (males) and of phosphorylated signal transducer and activator of transcription 3 in liver (females). These results suggest that CR animals are programmed for insulin and central leptin resistance, which may explain the dysregulation of appetite and other metabolic alterations, favoring obesity development, although only manifested in males. These early programming effects could be associated with the absence of leptin surge during lactation.

Fucoxanthin promotes translocation and induction of glucose transporter 4 in skeletal muscles of diabetic/obese KK-Ay mice

Fucoxanthin (Fx) isolated from Undaria pinnatifida suppresses the development of hyperglycemia and hyperinsulinemia of diabetic/obese KK-Ay mice after 2 weeks of feeding 0.2% Fx-containing diet. In the soleus muscle of KK-Ay mice that were fed Fx, glucose transporter 4 (GLUT4) translocation to plasma membranes from cytosol was promoted. On the other hand, Fx increased GLUT4 expression levels in the extensor digitorum longus (EDL) muscle, although GLUT4 translocation tended to increase. The expression levels of insulin receptor (IR) mRNA and phosphorylation of Akt, which are in upstream of the insulin signaling pathway regulating GLUT4 translocation, were also enhanced in the soleus and EDL muscles of the mice fed Fx. Furthermore, Fx induced peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α), which has been reported to increase GLUT4 expression, in both soleus and EDL muscles. These results suggest that in diabetic/obese KK-Ay mice, Fx improves hyperglycemia by activating the insulin signaling pathway, including GLUT4 translocation, and inducing GLUT4 expression in the soleus and EDL muscles, respectively, of diabetic/obese KK-Ay mice.

Vascular Smooth Muscle Cell Alterations Triggered by Mice Adipocytes: Role of High-Fat Diet

Inherent mechanisms leading to vascular smooth muscle cells (VSMC) alterations in obesitylinked type 2 diabetes (T2D) situation remain to be clarified. This study evaluates the impact of supernatant of adipocytes extracted from mice fed high-fat-diets (HFD) on the proliferation and apoptosis of VSMC. Adipocytes were extracted from visceral white fat pads of male and female C57Bl6 mice showing different stages of metabolic alterations after 20 weeks of vegetal or animal HFD feeding. These cells were stimulated or not with insulin or glucose to condition VSMC media. After 24h of stimulation with adipocyte supernatants (AdS), VSMC proliferation and sustainability were assessed in the absence and presence of AdS. CD36 and insulin receptor mRNA levels were also evaluated. Proliferation and viability of VSMC were significantly modulated by the nature of the AdS used and the gender of mice from which adipocytes have been extracted. The most extensive effects on VSMC were triggered by adipocytes from males fed animal HFD and females fed vegetal HFD. These effects were concurrent with increased leptin concentration and decreased adiponectin levels in AdS. In addition, adipocytes of HFD-fed mice increased caspase-3 activity and apoptosis in VSMC. Significant up-regulation of CD36 mRNA was also found in these cells. Adipocytes of HFD-fed mice induce VSMC alterations. These changes involved mouse gender, most probably correlated to the diet-induced adipocyte secretion profile. Greater sensitivity to AdS effects in VSMC raises concerns about the more frequent cardiovascular events associated with obesity in the presence of T2D, which impairs adipocyte activity.

Regulation of organic nucleic acids and serum biochemistry parameters by dietary chromium picolinate supplementation in swine model

The relationships between chromium and metabolism are sophisticated. Organic nucleic acids and serum biochemistry parameters are affected by dietary chromium levels. The objective of this work was to study the effect of chromium picolinate (CrPic) supplementation on total DNA and RNA contents, the ratio of RNA/DNA in muscle and in pancreatic tissue, the level of insulin receptor (IR) mRNA and some serum biochemistry parameters in a porcine model. Young animals (48) were assigned randomly into three groups of 16 piglets, fed with three different dietary levels of Cr (common basal feedstuff alone or supplemented with CrPic at a dose of 1.61 μg/g or 3.22 μg/g, which corresponds to 0.2 μg/g and 0.4 μg/g Cr). After 80 days, the animals were sacrificed and skeletal muscle and pancreatic tissues were analyzed to detect differences caused by different levels of dietary Cr. The total content of RNA in muscle was increased significantly ( P < 0.05) in the CrPic supplemented groups. There was no significant difference between groups in the concentrations of total RNA in the pancreas or DNA in the muscle and pancreatic tissues. The RNA/DNA ratio in pancreas showed no significant change but the ratio was increased significantly ( P < 0.05) in muscle. There was a slight increase of the mRNA level of IR but there was no significant difference between groups. The content of serum cholesterol and insulin were reduced significantly ( P < 0.05) in the CrPic-supplemented groups and the content of high-density lipoprotein cholesterol (HDLC) was increased significantly ( P < 0.05) as the CrPic dose increased. There was a slight (non-significant) reduction of the concentrations of serum triglyceride and low-density lipoprotein cholesterol (LDLC) in the CrPic supplementation groups. Supplementary CrPic caused no significant change of muscular mRNA level of IR in healthy animals. An increased content of RNA in muscle, improved cholesterol metabolism and improved insulin sensitivity were found in these CrPic-treated groups in the porcine model.

Comparisons of insulin related parameters in commercial-type chicks: Evidence for insulin resistance in broiler chicks

The aim of this study is to elucidate whether insulin acts differentially within the central nervous system (CNS) of two types of commercial chicks to control ingestive behavior. Male layer and broiler chicks (4-day-old) were intracerebroventricularly (ICV) injected with saline or insulin under satiated and starved conditions. Feed intake was measured at 30, 60 and 120 min after treatment. Secondly, blood and hypothalamus were collected from both chick types under ad libitum feeding and fasting for 24 h. Plasma insulin concentration was measured by time-resolved fluoro-immunoassay. Hypothalamic insulin receptor mRNA expression levels were measured by quantitative RT-PCR. The ICV injection of insulin significantly inhibited feed consumption in layer chicks when compared with saline (P<0.05), but not broiler chicks (P>0.1). Plasma insulin concentration of both chick types significantly decreased following 24 h of fasting, while insulin concentrations in the broiler chicks were significantly higher compared to the layers fed under ad libitum conditions. Hypothalamic insulin receptor mRNA expression levels were significantly lower (P<0.05) in broiler chicks than in layer ones under ad libitum feeding. Feed deprivation significantly decreased insulin receptor mRNA levels in layer chicks (P<0.01), but not in broiler chicks (P>0.1). Moreover, plasma insulin concentrations correlated negatively with hypothalamic insulin receptor protein expression in the two types of chicks fed ad libitum (P<0.05). These results suggest that insulin resistance exists in the CNS of broiler chicks, possibly due to persistent hyperinsulinemia, which results in a down-regulation of CNS insulin receptor expression compared to that in layer chicks.

Sex steroids influence glucose oxidation through modulation of insulin receptor expression and IRS-1 serine phosphorylation in target tissues of adult male rat

Skeletal muscle, liver, and adipose tissue are major insulin responsive target organs that also express androgen receptor. Testosterone (T) plays a role in maintaining normal insulin sensitivity in men but its effects on insulin target tissues are not fully understood. Our previous study showed that orchidectomy impairs glucose oxidation through decreased insulin receptor (IR) mRNA expression in skeletal muscles, liver, and adipose tissue of male rat. Furthermore, T replacement restored IR mRNA expression in skeletal muscles and liver, but did not have any effect in adipose tissue. In the present study, orchidectomy decreased IR mRNA and protein levels in muscle, liver, and adipose tissue. Treatment with a combination of T plus estradiol (E) was necessary to restore the IR mRNA and protein to control levels in adipose tissue. T or E treatment alone had no effect on IR mRNA levels in adipose tissue. T alone also had no effect on the IR protein, whereas E alone had a stimulatory effect. In comparison, in muscle and liver, T or T plus E restored the IR mRNA and protein to control levels. In muscle and liver, E alone had no effect on IR mRNA expression but restored the IR protein. In addition, orchidectomy was seen to have a stimulatory effect on IRS-1 Serine(636/639) phosphorylation in the three tissues studied. Following T, E or combined supplementation to castrated rats, the pattern of IRS-1 serine phosphorylation was restored to normal control levels. Furthermore, orchidectomy decreased serum insulin and glucose oxidation in all three tissues, and this was restored by T and its combination with E replacement, whereas E alone had no effect. It is concluded from the present study that sex steroid deficiency induces impaired glucose oxidation in insulin responsive tissues, which is mediated through reduced IR expression, and increased IRS-1 serine phosphorylation.

Insulin receptor is downregulated in the nitrofen-induced hypoplastic lung

Purpose The pathogenesis of pulmonary hypoplasia in congenital diaphragmatic hernia (CDH) is still poorly understood. During fetal lung development, the insulin receptor (IR) plays an important role by mediating the cellular uptake of glucose, which is a major substrate for the biosynthesis of surfactant phospholipids. In fetal rat lung, IR gene expression has been revealed on type II pneumocytes. Recent studies have demonstrated that downregulation of pulmonary IR in late gestation causes pulmonary hypoplasia by inhibition of surfactant synthesis. We hypothesized that pulmonary gene expression of IR is downregulated during the late stages of lung development in the nitrofen-induced CDH model. Methods Timed pregnant Sprague-Dawley rats were exposed to either olive oil or nitrofen on day 9 of gestation (D9). Cesarean deliveries were performed on D15, D18, and D21. Fetal lungs were divided into 3 groups: control, nitrofen without CDH (CDH[−]), and nitrofen with CDH (CDH[+]) (n = 8 at each time-point, respectively). Relative messenger RNA (mRNA) levels of IR were determined by using real time reverse transcription polymerase chain reaction. Immunohistochemistry was performed to evaluate protein expression of IR. Results Relative expression levels of IR mRNA on D21 were significantly decreased in CDH(−) and CDH(+) group (3.99 ± 1.50 and 5.14 ± 0.99, respectively) compared to control (7.45 ± 3.95; P < .05). Immunohistochemistry showed decreased IR expression in the proximal alveolar epithelium on D21 in hypoplastic lungs compared to control lungs. Conclusion Downregulation of IR gene and protein expression in hypoplastic lung during late stages of lung development may interfere with normal surfactant synthesis, causing pulmonary hypoplasia in the nitrofen-induced CDH model.

Insulin Sensitivity and Glucose Tolerance Are Altered by Maintenance on a Ketogenic Diet

Low-carbohydrate, ketogenic diets (KD) are frequently implemented in efforts to reduce or maintain body weight, although the metabolic effects of long-term exposure to this type of diet remain controversial. This study assessed the responsivity to peripheral and central insulin, glucose tolerance, and meal-induced effects of consuming a KD in the rat. After 8 wk of consuming chow or KD, caloric intake after peripheral or central insulin and insulin and glucose levels after a glucose challenge were assessed. In a separate group of rats, glucose and insulin responses to either a low- or high-carbohydrate test meal were measured. Finally, rats maintained on KD were switched back to a chow diet, and insulin sensitivity and glucose tolerance were evaluated to determine whether the effects of KD were reversible. Maintenance on KD resulted in decreased sensitivity to peripheral insulin and impaired glucose tolerance. Furthermore, consumption of a high-carbohydrate meal in rats that habitually consumed KD induced significantly greater insulin and glucose levels for an extended period of time, as compared with chow-fed controls. Responsivity to central insulin was heightened in KD rats and associated with increased expression levels of insulin receptor mRNA. Finally, returning to a chow diet rapidly reversed the effects of KD on insulin sensitivity and glucose tolerance. These data suggest that maintenance on KD negatively affects glucose homeostasis, an effect that is rapidly reversed upon cessation of the diet.

Abstract 4133: Comparative gene expression and proteomic analysis of IGF-I and insulin signaling in a large panel of breast cancer cell lines

Abstract IGF-I signaling is involved in tumor progression and drug resistance and many anti-IGF-IR therapeutic agents are currently in clinical trials. Moreover, growing evidence also suggests that insulin signaling may play an important role in cancer development and progression. However, little is known regarding similarities and difference in IGF-I and insulin signaling in cancer, and there are currently no biomarkers to predict patient response to IGF targeted therapy. To gain a better understanding of these signaling pathways in human breast cancer, we measured the levels of insulin receptor (IR) and IGF-IR, and the activity of insulin and IGF-I, in a large panel of human breast cancer cell lines. Comparative gene expression analysis was performed using publicly available gene expression data and IR and IGF-IR mRNA levels in 17 breast cancer cell lines were measured by Q-RT-PCR. IGF-IR and IR levels were found to be highly variable in breast cancer cell lines. MCF7 and MDA-MB-134 have high levels of IGF-IR expression and MDA-MB-468 and ZR-75-1 have high levels of IR expression, relative to other breast cancer cell lines. Reverse phase protein array (RPPA) analysis using 134 different antibodies was performed on MCF7 cells stimulated with increasing doses of insulin or IGF-I. One Way ANOVA was performed to identify proteins affected by insulin and/or IGF stimulation. Maximal response to insulin and IGF-I stimulation was observed at a 10nM concentration of both ligands. Therefore, we further performed RPPA on 21 breast cancer cell lines treated with 10nM of insulin and IGF-I for 6 time points (5min, 10min, 30 min, 6hrs, 24hrs, and 48hrs). Spearman rank correlation was performed on IR and IGF-IR protein levels to mRNA levels from Q-RT-PCR. There was a significant correlation between IGF-IR protein and mRNA levels (r=0.559, p=0.024), but not between IR protein and mRNA levels. Principle component analysis showed that MCF7, MDA-MB-134, T47D and ZR-75-1 are insulin and IGF-I responsive. Results from ANOVA with contrast in MCF7 cells showed that insulin and IGF-I affected similar set of proteins at 10 minute and 24 hours time points, however, there were several proteins affected only by IGF-I or insulin stimulation. For example, phospho-estrogen receptor (p-ER) was found to be increased by 10 minutes IGF-I stimulation, but not by insulin stimulation. Beta-catenin and c-Myc were significantly suppressed by IGF stimulation while PARP was significantly suppressed by insulin stimulation at the 24 hour time point. Moreover, IGF affected twice the number of proteins compared to insulin at the 48 hour time point. For instance, Bcl2 and SMAD3 were suppressed and Raf and FOXO3a were increased by IGF stimulation after 48 hours of stimulation. Further statistical and system biology analysis of the temporal activation of signaling by IGF-I and insulin in the 21 cell lines is ongoing and will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4133.

Age-related changes in insulin receptor mRNA and protein expression in genetically obese Zucker rats

Aim The mechanisms underlying the age-related decrease in insulin-receptor (IR) binding in genetically obese Zucker rats are not well understood. For this reason, the present study analyzed the expression of IR mRNA and protein in selected tissues from 1- to 4-month-old obese (fa/fa) Zucker rats and lean (Fa/–) age-matched controls. Methods The following parameters were evaluated: (1) IR mRNA level, and proportion of isotypes A (exon 11–) and B (exon 11+) of IR mRNA in liver, brain and kidney; (2) level, molecular size and tyrosine phosphorylation of IR-β subunit in liver subcellular fractions; and (3) stability of liver IR based on sensitivity in vivo of insulin-binding activity and IR-β levels in response to tunicamycin, a glycosylation inhibitor. Results At one month, IR mRNA level was increased in liver and brain, but decreased in kidneys and, at four months, both mRNA level and isotype B proportion were decreased in liver. From age two months, the following changes in liver IR protein expression were observed: (1) decreased IR-β level in whole homogenates, but increased IR-β levels in endosomal fractions; (2) increased IR-β tyrosine phosphorylation; and (3) at four months, increased levels of both intact IR-β (95 kDa) and IR-β fragments (72 and 52 kDa) in lysosomal fractions, along with decreased stability in vivo of the IR. Conclusion These data show that obese Zucker rats display age-related alterations of IR gene expression at both pre- and post-translational stages and, in particular, increased endocytosis and degradation of IR protein.

Green tea improves carbohydrate and lipid metabolism and regulates cardiac mRNA expression related to insulin, lipid and inflammatory signaling pathways

Green tea has multiple benefits to human health. Epidemiologic studies demonstrate that the consumption of green tea polyphenols (GTP) reduces the risk of coronary artery disease and cardiac events. To explore the underlying mechanisms of action at a molecular level, we examined the effects of GTP on the expression of the cardiac genes involved in insulin, lipid and inflammatory signaling pathways, using quantitative real‐time PCR. Rats, fed a high fructose diet for four weeks to induce insulin resistance, were divided into two groups: the control group and GTP group (200 mg/kg body weight daily dissolved in distilled water for 6 weeks). There were no significant differences in average food intake and bodyweight gain between groups. GTP reduced serum blood glucose, cholesterol, triglycerides, free fatty acids and LDL‐C levels, compared with the controls. Supplementation with GTP also increased insulin receptor, IRS1, IRS2, PI3K, Akt1, GLUT1 and GLUT4 mRNA levels in the myocardium; increased cardiac CD36, PTEN, PPARg mRNA levels; but decreased the inflammatory factors: TNFa and IL1ß mRNA levels. In summary, our data demonstrate that green tea polyphenols improve glucose and lipid metabolism and regulate the cardiac gene expression related to insulin, lipid and inflammatory pathways in fructose‐fed insulin resistant rats. (Funded by USDA/ARS and Integrity Nutraceuticals).

Chromium Improves Glucose Uptake and Metabolism Through Upregulating the mRNA Levels of IR, GLUT4, GS, and UCP3 in Skeletal Muscle Cells

The aim of this study was to evaluate the impact of three different chromium forms as chromic chloride (CrCl), chromium picolinate (CrPic), and a newly synthesized complex of chromium chelated with small peptides (CrSP) on glucose uptake and metabolism in vitro. In cultured skeletal muscle cells, chromium augmented insulin-stimulated glucose uptake and metabolism as assessed by a reduced glucose concentration of culture medium. At the molecular level, insulin significantly increased the mRNA levels of insulin receptor (IR), glucose transporter 4 (GLUT4), glycogen synthase (GS), and uncoupling protein-3 (UCP3), and these impacts can be enhanced by the addition of chromium, especially in the form of CrSP. Collectively, results of this study demonstrate that chromium improves glucose uptake and metabolism through upregulating the mRNA levels of IR, GLUT4, GS, and UCP3 in skeletal muscle cells, and CrSP has higher efficacy on glucose uptake and metabolism compared to the forms of CrCl and CrPic.

Expression of the insulin-like growth factor and insulin systems in the luteinizing macaque ovarian follicle

To determine intrafollicular hormone levels and characterize the mRNA expression of the insulin-like growth factor (IGF) receptors, IGF binding proteins (IGFBP), and pregnancy-associated plasma protein-A (PAPP-A) in granulosa cells before and after an ovulatory hCG stimulus. Experimental animal study. Academic medical center. Adult rhesus macaques. Animals received exogenous FSH to promote the development of multiple preovulatory follicles. Follicles were aspirated before (0 hours) or 3, 6, 12, or 24 hours after an ovulatory hCG bolus. IGF1, IGF2, and insulin levels in follicular fluid were determined by radioimmunoassay. Messenger RNA (mRNA) levels in granulosa cells were determined by real-time reverse transcriptase-polymerase chain reaction. IGFBPs and PAPP-A in follicular fluid were determined by Western blot analysis and enzyme-linked immunosorbent assay. IGF1, IGF2, and insulin in follicular fluid did not change during luteinization. IGF1R, IGFBP1, and IGFBP2 mRNAs were unchanged by hCG. IGF2R, IGFBP3, -5, and -6 and PAPP-A mRNA levels increased after hCG administration, while insulin receptor and IGFBP4 mRNA levels decreased after hCG administration. IGFBP3 and -6 and PAPP-A protein increased after hCG administration. Dynamic changes in the expression of the IGFBPs and PAPP-A suggest tight regulation of IGF action during ovulation and corpus luteum formation.

Evidence that inhibition of insulin receptor signaling activity by PC-1/ENPP1 is dependent on its enzyme activity

Plasma cell membrane glycoprotein-1 or ectonucleotide pyrophosphatase/phosphodiesterase (PC-1/ENPP1) has been shown to inhibit insulin signaling, and its genetic polymorphism or increased expression is associated with type 2 diabetes in humans. Therefore, PC-1 inhibition represents a potential strategy in treating diabetes. Since patients with phosphodiesterase/pyrophosphatase deficient PC-1 manifest abnormal calcification, enhancing insulin signaling by inhibiting PC-1 for the treatment of diabetes will be feasible only if PC-1 phosphodiesterase/pyrophosphatase activity needs not be significantly diminished. However, whether inhibition of insulin receptor signaling by PC-1 is dependent upon its phosphodiesterase/pyrophosphatase activity remains controversial. In this study, the extracellular domain of the human PC-1 in its native form or with a T256A or T256S mutation was overexpressed and purified. Enzymatic assays showed that both mutants have less than 10% of the activity of the wild-type protein. In HEK293 cells stably expressing recombinant insulin receptor or insulin-like growth factor 1 (IGF1) receptor, transient expression of wild-type full length PC-1 (PC-1.FL.WT) but not the T256A or T256S mutants inhibits insulin signaling without affecting IGF1 signaling. Western blot and FACS analysis showed that the wild-type and mutant full length PC-1 proteins are expressed at similar levels in the cells, and were localized to the similar levels on the cell surface. Overexpression of PC-1.FL.WT did not affect insulin receptor mRNA level, total protein and cell surface levels. Together, these results suggest that the inhibition of insulin signaling by PC-1 is somewhat specific and is dependent upon the enzymatic activity of the phosphodiesterase/pyrophosphatase.

Astrocytes express glucose transporter 3 in response to ischemic and/or reperfusion stress

Children and adolescent populations chronically exposed to high doses of inorganic arsenic (iAs) in drinking water in some regions around the world have shown behavioral and memory deficits. Recent studies have also associated iAs exposure with dysregulation of glucose metabolism. The hippocampus is a cerebral region well known for its role in learning and memory. Studies in vitro and in vivo have shown that the hippocampus is vulnerable to iAs exposure, and to changes in glucose metabolism. The glucose transporters (GLUTs) and insulin receptor (IR) regulate glucose metabolism in brain; they are expressed by hippocampal cells, and alterations in these proteins have been associated with memory deficits. The aims of this study were to evaluate the effects of iAs exposure via drinking water (DW) on GLUT1, GLUT3 and insulin receptor (INSR) mRNA expression in the hippocampus, on performance in a spatial memory task, and on peripheral glucose regulation. C57Bl/6 male mice were exposed to 50 mg iAs/L via DW for one, two, or three months. The qRT-PCR analyses indicated that, compared to a control group, GLUT1 and GLUT3 mRNA levels were decreased, while INSR mRNA levels were increased in the hippocampus of iAs exposed animals. The levels of iAs and its methylated species in the hippocampus of the iAs-exposed group were significantly higher than in controls. Mice exposed to iAs learned the spatial task but showed increased latency to find the submerged platform 48 h after the last training session; these animals also showed dysregulation of peripheral glucose. These results suggest that the effects of iAs exposure on a spatial memory task performance could be mediated by disruptions of glucose regulation in the CNS.

Maternal prenatal undernutrition alters the response of POMC neurons to energy status variation in adult male rat offspring

Epidemiological studies suggest that maternal undernutrition predisposes the offspring to development of energy balance metabolic pathologies in adulthood. Using a model of a prenatal maternal 70% food-restricted diet (FR30) in rats, we evaluated peripheral parameters involved in nutritional regulation, as well as the hypothalamic appetite-regulatory system, in nonfasted and 48-h-fasted adult offspring. Despite comparable glycemia in both groups, mild glucose intolerance, with a defect in glucose-induced insulin secretion, was observed in FR30 animals. They also exhibited hyperleptinemia, despite similar visible fat deposits. Using semiquantitative RT-PCR, we observed no basal difference of hypothalamic proopiomelanocortin (POMC) and neuropeptide Y (NPY) gene expression, but a decrease of the OB-Rb and an increase of insulin receptor mRNA levels, in FR30 animals. These animals also exhibited basal hypercorticosteronemia and a blunted increase of corticosterone in fasted compared with control animals. After fasting, FR30 animals showed no marked reduction of POMC mRNA levels or intensity of beta-endorphin-immunoreactive fiber projections. By contrast, NPY gene expression and immunoreactive fiber intensity increased. FR30 rats also displayed subtle alterations of food intake: body weight-related food intake was higher and light-dark phase rhythm and refeeding time course were modified after fasting. At rest, in the morning, hyperinsulinemia and a striking increase in the number of c-Fos-containing cells in the arcuate nucleus were observed. About 30% of the c-Fos-expressing cells were POMC neurons. Our data suggest that maternal undernutrition differently programs the long-term appetite-regulatory system of offspring, especially the response of POMC neurons to energy status and food intake rhythm.

Cinnamon extract inhibits the postprandial overproduction of apolipoprotein B48-containing lipoproteins in fructose-fed animals

We have reported previously that a cinnamon extract (CE), high in type A polyphenols, prevents fructose feeding-induced decreases in insulin sensitivity and suggested that improvements of insulin sensitivity by CE were attributable, in part, to enhanced insulin signaling. In this study, we examined the effects of CE on postprandial apolipoprotein (apo) B-48 increase in fructose-fed rats, and the secretion of apoB48 in freshly isolated intestinal enterocytes of fructose-fed hamsters. In an olive oil loading study, a water-soluble CE (Cinnulin PF, 50 mg/kg body weight, orally) decreased serum triglyceride (TG) levels and the over production of total- and TG-rich lipoprotein-apoB48. In ex vivo 35S labeling study, significant decreases were also observed in apoB48 secretion into the media in enterocytes isolated from fructose-fed hamsters. We also investigated the molecular mechanisms of the effects of CE on the expression of genes of the insulin signaling pathway [insulin receptor (IR), IR substrate (IRS)1, IRS2 and Akt1], and lipoprotein metabolism [microsomal TG transfer protein (MTP), sterol regulatory element-binding protein (SREBP1c) in isolated primary enterocytes of fructose-fed hamsters, using quantitative real-time polymerase chain reaction. The CE reversed the expression of the impaired IR, IRS1, IRS2 and Akt1 mRNA levels and inhibited the overexpression of MTP and SREBP1c mRNA levels of enterocytes. Taken together, our data suggest that the postprandial hypertriglycerides and the overproduction of apoB48 can be acutely inhibited by a CE by a mechanism involving improvements of insulin sensitivity of intestinal enterocytes and regulation of MTP and SREBP1c levels. We present both in vivo and ex vivo evidence that a CE improves the postprandial overproduction of intestinal apoB48-containing lipoproteins by ameliorating intestinal insulin resistance and may be beneficial in the control of lipid metabolism.

Effects of eicosapentaenoic acid ethyl ester on visfatin and apelin in lean and overweight (cafeteria diet-fed) rats

Previous studies have demonstrated that the n-3 fatty acid EPA improves insulin resistance induced by high-fat diets. The aim of the present study was to investigate the potential role of visfatin and apelin in the insulin-sensitising effects of EPA ethyl ester. The effects of EPA on muscle and adipose GLUT mRNA, as well as on liver glucokinase (GK) and glucose-6-phosphatase (G6Pase) activity, were investigated. Male Wistar rats fed on a standard diet or a high-fat cafeteria diet were daily treated by oral administration with EPA ethyl ester (1 g/kg) for 5 weeks. A significant decrease (P < 0.01) in white adipose tissue (WAT) visfatin mRNA levels was found in the cafeteria-fed rats, which was reversed by EPA administration (P < 0.05). Moreover, a negative relationship was observed between homeostatic model assessment (HOMA) and the visfatin:total WAT ratio. In contrast, cafeteria-diet feeding caused a significant increase (P < 0.01) in apelin mRNA in visceral WAT. EPA increased (P < 0.01) apelin gene expression, and a negative relationship between HOMA index with visceral apelin mRNA and serum apelin:total WAT ratio was also observed. EPA treatment did not induce changes in skeletal muscle GLUT1, GLUT4 or insulin receptor mRNA levels. Neither liver GK and G6Pase activity nor the GK:G6Pase ratio was modified by EPA. These data suggest that somehow the insulin-sensitising effects of EPA could be related to its stimulatory action on both visfatin and apelin gene expression in visceral fat, while changes in skeletal muscle GLUT, as well as in hepatic glucose production, are not likely to be the main contributing factors in the improvement in insulin resistance induced by EPA.

Effects of Dietary Supplementation with Cysteamine on Growth Hormone Receptor and Insulin-Like Growth Factor System in Finishing Pigs

The present study was conducted to test the hypothesis that chronic cysteamine (CS) supplementation may affect serum insulin-like growth factor (IGF)-I concentrations and growth hormone (GH) receptor (GHR), IGF-I, IGF-I receptor (IGF-IR), IGF binding protein (IGFBP)-3, and insulin receptor (IR) mRNA levels in different tissues of finishing pigs. A total of 24 finishing pigs (60.05 +/- 1.24 kg; 12 gilts and 12 barrows) were assigned randomly to one of the three dietary groups, with four pens/group (per pen: one gilt, one barrow). The pigs were fed a basal diet containing 0 (control), 70, or 140 mg/kg cysteamine feed additive (containing 28% cysteamine hydrochloride) for 47 days. The results indicated that CS supplementation (70 mg/kg) increased the average daily gain (ADG) and serum IGF-I level, upregulated mRNA levels of GHR and IGF-I (liver, stomach, muscle), IGF-IR (stomach, duodenum, muscle), and IGFBP-3 (liver) but downregulated IGFBP-3 (stomach, duodenum, muscle). CS supplementation (70 mg/kg) did not affect mRNA levels of GHR and IGF-I (duodenum), IGF-IR (liver), and IR (liver, stomach, duodenum, muscle). CS supplementation (140 mg/kg) downregulated GHR (duodenum), IGF-I, and IGF-IR mRNA (liver, stomach, duodenum, muscle) but upregulated IGFBP-3 and IR mRNA (liver, stomach, duodenum, muscle) and did not affect ADG and serum IGF-I concentration. Collectively, the results suggest that dietary CS supplementation modulates the growth rate, serum IGF-I concentrations, and the gene expression of GHR, IGF-I, IGF-IR, IGFBP-3, and IR in a dose-dependent manner. CS supplementation has tissue-specific regulation of GHR, IGF-I, IGF-IR, and IGFBP-3 mRNA levels. Moreover, the results also imply the possible physiologic role of the GH-IGF axis in mediating the dietary CS supplementation-supported growth of finishing pigs.