Organisation of the musculature of the rat stomach.

The strengths, directions and coupling of the movements of the stomach depend on the organisation of its musculature. Although the rat has been used as a model species to study gastric function, there is no detailed, quantitative study of the arrangement of the gastric muscles in rat. Here we provide a descriptive and quantitative account, and compare it with human gastric anatomy. The rat stomach has three components of the muscularis externa, a longitudinal coat, a circular coat and an internal oblique (sling) muscle in the region of the gastro-oesophageal junction. These layers are similar to human. Unlike human, the rat stomach is also equipped with paired muscular oesophago-pyloric ligaments that lie external to the longitudinal muscle. There is a prominent muscularis mucosae throughout the stomach and strands of smooth muscle occur in the mucosa, between the glands of the corpus and antrum. The striated muscle of the oesophageal wall reaches to the stomach, unlike the human, in which the wall of the distal oesophagus is smooth muscle. Thus, the continuity of gastric and oesophageal smooth muscle bundles, that occurs in human, does not occur in rat. Circular muscle bundles extend around the circumference of the stomach, in the fundus forming a cap of parallel muscle bundles. This arrangement favours co-ordinated circumferential contractions. Small bands of muscle make connections between the circular muscle bundles. This is consistent with a slower conduction of excitation orthogonal to the circular muscle bundles, across the corpus towards the distal antrum. The oblique muscle merged and became continuous with the circular muscle close to the gastro-oesophageal junction at the base of the fundus, and in the corpus, lateral to the lesser curvature. Quantitation of muscle thickness revealed gradients of thickness of both the longitudinal and circular muscle. This anatomical study provides essential data for interpreting gastric movements.

Endoplasmic reticulum stress up-regulates Nedd4-2 to induce autophagy.

The accumulation of unfolded proteins within the endoplasmic reticulum (ER) causes ER stress and activation of unfolded protein response (UPR). This response can trigger ER-associated degradation and autophagy, which clear unfolded proteins and restore protein homeostasis. Recently, it has become clear that ubiquitination plays an important role in the regulation of autophagy. In the present study, we investigated how the E3 ubiquitin ligase neural precursor cell-expressed, developmentally down-regulated protein 4-2 (Nedd4-2) interacts with ER stress and autophagy. In mice, we found that an increase in the expression of Nedd4-2, which was concomitant with the activation of the UPR and autophagy, was caused by a prolonged high-fructose and high-fat diet that induces ER stress in the liver. Pharmacologic induction of ER stress also led to an increase in Nedd4-2 expression in cultured cells, which was coincident with UPR and autophagy activation. The inhibition of inositol-requiring enzyme 1 significantly suppressed Nedd4-2 expression. Moreover, increased Nedd4-2 expression in vivo was closely associated with the activation of inositol-requiring enzyme 1 and increased expression of the spliced form of X-box binding protein 1. Furthermore, knockdown of Nedd4-2 in cultured cells suppressed both basal autophagy and ER stress-induced autophagy, whereas overexpression of Nedd4-2-induced autophagy. Taken together, our findings provide evidence that Nedd4-2 is up-regulated in response to ER stress by the spliced form of X-box binding protein 1 and that this is important in the induction of an appropriate autophagic response.-Wang, H. Sun, R.-Q., Camera, D., Zeng, X.-Y., Jo, E., Chan, S. M. H., Herbert, T. P., Molero, J. C., Ye, J.-M. Endoplasmic reticulum stress up-regulates Nedd4-2 to induce autophagy.

IRE1 impairs insulin signaling transduction of fructose-fed mice via JNK independent of excess lipid.

The unfolded protein response (UPR) pathways have been implicated in the development of hepatic insulin resistance during high fructose (HFru) feeding. The present study investigated their roles in initiating impaired insulin signaling transduction in the liver induced by HFru feeding in mice. HFru feeding resulted in hepatic steatosis, increased de novo lipogenesis and activation of two arms of the UPR pathways (IRE1/XBP1 and PERK/eIF2α) in similar patterns from 3days to 8weeks. In order to identify the earliest trigger of impaired insulin signaling in the liver, we fed mice a HFru diet for one day and revealed that only the IRE1 branch was activated (by 2-fold) and insulin-mediated Akt phosphorylation was blunted (~25%) in the liver. There were significant increases in phosphorylation of JNK (~50%) and IRS at serine site (~50%), protein content of ACC and FAS (up to 2.5-fold) and triglyceride level (2-fold) in liver (but not in muscle or fat). Blocking IRE1 activity abolished increases in JNK activity, IRS serine phosphorylation and protected insulin-stimulated Akt phosphorylation without altering hepatic steatosis or PKCε activity, a key link between lipids and insulin resistance. Our findings together suggest that activation of IRE1-JNK pathway is a key linker of impaired hepatic insulin signaling transduction induced by HFru feeding.

Orally administered [¹4C]DPA and [¹4C]DHA are metabolised differently to [¹4C]EPA in rats.

Previous studies have revealed that C20 PUFA are significantly less oxidised to CO2 in whole-body studies compared with SFA, MUFA and C18 PUFA. The present study determined the extent to which three long-chain PUFA, namely 20:5n-3 EPA, 22:5n-3 docosapentaenoic acid (DPA) and 22:6n-3 DHA, were catabolised to CO2 or, conversely, incorporated into tissue lipids. Rats were administered a single oral dose of 2·5 µCi [1-¹4C]DPA, [1-¹4C]EPA, [1-¹4C]DHA or [1-¹4C]oleic acid (18:1n-9; OA), and were placed in a metabolism chamber for 6 h where exhaled ¹4CO2 was trapped and counted for radioactivity. Rats were euthanised after 24 h and tissues were removed for analysis of radioactivity in tissue lipids. The results showed that DPA and DHA were catabolised to CO2 significantly less compared with EPA and OA (P<0·05). The phospholipid (PL) fraction was the most labelled for all three n-3 PUFA compared with OA in all tissues, and there was no difference between C20 and C22 n-3 PUFA in the proportion of label in the PL fraction. The DHA and DPA groups showed significantly more label than the EPA group in both skeletal muscle and heart. In the brain and heart tissue, there was significantly less label in the cholesterol fraction from the C22 n-3 PUFA group compared with the C20 n-3 PUFA group. The higher incorporation of DHA and DPA into the heart and skeletal muscle, compared with EPA, suggests that these C22 n-3 PUFA might play an important role in these tissues.

Development of the aganglionic colon following surgical rescue in a cell therapy model of Hirschsprung disease in rat.

Patients with Hirschsprung disease lack enteric ganglia in the distal colon and propulsion of colorectal content is substantially impaired. Proposed stem cell therapies to replace neurons require surgical bypass of the aganglionic bowel during re-colonization, but there is inadequate knowledge of the consequences of bypass. We performed bypass surgery in Ednrb-/- Hirschsprung rat pups. Surgically rescued rats failed to thrive, an outcome reversed by supplying electrolyte- and glucose-enriched drinking water. Histologically, the bypassed colon had normal structure, but grew substantially less in diameter than the functional region proximal to the bypass. Extrinsic sympathetic and spinal afferent neurons projected to their normal targets, including arteries and the circular muscle, in aganglionic regions. However, although axons of intrinsic excitatory and inhibitory neurons grew into the aganglionic region, their normally dense innervation of circular muscle was not restored. Large nerve trunks that contained tyrosine hydroxylase (TH)-, calcitonin gene-related peptide (CGRP, encoded by Calca or Calcb)-, neuronal nitric oxide synthase (nNOS or NOS1)-, vasoactive intestinal peptide (VIP)- and tachykinin (encoded by Tac1)-immunoreactive axons occurred in the distal aganglionic region. We conclude that the rescued Ednrb-/- rat provides a good model for the development of cell therapies for the treatment of Hirschsprung disease.

Effects and sites of action of a M1 receptor positive allosteric modulator on colonic motility in rats and dogs compared with 5-HT4 agonism and cholinesterase inhibition.

BACKGROUND: Muscarinic receptor 1 positive allosteric modulators (M1PAMs) enhance colonic propulsive contractions and defecation through the facilitation of M1 receptor (M1R)-mediated signaling. We examined M1R expression in the colons of 5 species and compared colonic propulsion and defecation caused by the M1PAM, T440, the 5-HT4 agonist, prucalopride, and the cholinesterase inhibitor, neostigmine, in rats and dogs. METHODS: M1R expression was profiled by immunostaining and in situ hybridization. In vivo studies utilized male SD rats and beagle dogs. Colonic propulsive contractions were recorded by manometry in anesthetized rats. Gut contractions in dogs were assessed using implanted force transducers in the ileum, proximal, mid, and distal colons. KEY RESULTS: M1R was localized to neurons of myenteric and submucosal plexuses and the epithelium of the human colon. A similar receptor localization was observed in rat, dog, mouse, and pig. T440 enhanced normal defecation in rats in a dose-dependent manner. Prucalopride also enhanced defecation in rats, but the maximum effect was half that of T440. Neostigmine and T440 were similarly effective in enhancing defecation, but the effective dose of neostigmine was close to its lethal dose. In rats, all 3 compounds induced colonic contractions, but the associated propulsion was strongest with T440. In dogs, intestinal contractions elicited by T440 propagated from ileum to distal colon. Prucalopride and neostigmine also induced intestinal contractions, but these were less well coordinated. No loss of effectiveness of T440 on defecation occurred after 5 days of repeated dosing. CONCLUSION AND INFERENCES: These results suggest that M1PAMs produce highly coordinated propagating contraction by actions on the enteric nervous system of the colon. The localization of M1R to enteric neurons in both animals and humans suggests that the M1PAM effects would be translatable to human. M1PAMs provide a potential novel therapeutic option for constipation disorders.

Genetic ablation of the c-Cbl ubiquitin ligase domain results in increased energy expenditure and improved insulin action.

Casitas b-lineage lymphoma (c-Cbl) is a multiadaptor protein with E3-ubiquitin ligase activity residing within its RING finger domain. We have previously reported that c-Cbl-deficient mice exhibit elevated energy expenditure, reduced adiposity, and improved insulin action. In this study, we examined mice expressing c-Cbl protein with a loss-of-function mutation within the RING finger domain (c-Cbl(A/-) mice). Compared with control animals, c-Cbl(A/-) mice display a phenotype that includes reduced adiposity, despite greater food intake; reduced circulating insulin, leptin, and triglyceride levels; and improved glucose tolerance. c-Cbl(A/-) mice also display elevated oxygen consumption (13%) and are protected against high-fat diet-induced obesity and insulin resistance. Unlike c-Cbl(A/-) mice, mice expressing a mutant c-Cbl with the phosphatidylinositol (PI) 3-kinase binding domain ablated (c-Cbl(F/F) mice) exhibited an insulin sensitivity, body composition, and energy expenditure similar to that of wild-type animals. These results indicate that c-Cbl ubiquitin ligase activity, but not c-Cbl-dependent activation of PI 3-kinase, plays a key role in the regulation of whole-body energy metabolism.

Casitas b-lineage lymphoma-deficient mice are protected against high-fat diet-induced obesity and insulin resistance.

Casitas b-lineage lymphoma (c-Cbl) is a multiadaptor protein with E3-ubiquitin ligase activity involved in regulating the degradation of receptor tyrosine kinases. We have recently reported that c-Cbl(-/-) mice exhibit a lean phenotype and enhanced peripheral insulin action likely due to elevated energy expenditure. In the study reported here, we examined the effect of a high-fat diet on energy homeostasis and glucose metabolism in these animals. When c-Cbl(-/-) mice were fed a high-fat diet for 4 weeks, they maintained hyperphagia, higher whole-body oxygen consumption (27%), and greater activity (threefold) compared with wild-type animals fed the same diet. In addition, the activity of several enzymes involved in mitochondrial fat oxidation and the phosphorylation of acetyl CoA carboxylase was significantly increased in muscle of high-fat-fed c-Cbl-deficient mice, indicating a greater capacity for fat oxidation in these animals. As a result of these differences, fat-fed c-Cbl(-/-) mice were 30% leaner than wild-type animals and were protected against high-fat diet-induced insulin resistance. These studies are consistent with a role for c-Cbl in regulating nutrient partitioning in skeletal muscle and emphasize the potential of c-Cbl as a therapeutic target in the treatment of obesity and type 2 diabetes.

c-Cbl-deficient mice have reduced adiposity, higher energy expenditure, and improved peripheral insulin action.

Casitas b-lineage lymphoma (c-Cbl) is an E3 ubiquitin ligase that has an important role in regulating the degradation of cell surface receptors. In the present study we have examined the role of c-Cbl in whole-body energy homeostasis. c-Cbl-/- mice exhibited a profound increase in whole-body energy expenditure as determined by increased core temperature and whole-body oxygen consumption. As a consequence, these mice displayed a decrease in adiposity, primarily due to a reduction in cell size despite an increase in food intake. These changes were accompanied by a significant increase in activity (2- to 3-fold). In addition, c-Cbl-/- mice displayed a marked improvement in whole-body insulin action, primarily due to changes in muscle metabolism. We observed increased protein levels of the insulin receptor (4-fold) and uncoupling protein-3 (2-fold) in skeletal muscle and a significant increase in the phosphorylation of AMP-activated protein kinase and acetyl-CoA carboxylase. These findings suggest that c-Cbl plays an integral role in whole-body fuel homeostasis by regulating whole-body energy expenditure and insulin action.

Overfeeding during a critical postnatal period exacerbates hypothalamic-pituitary-adrenal axis responses to immune challenge: a role for adrenal melanocortin 2 receptors.

Early life diet can critically program hypothalamic-pituitary-adrenal (HPA) axis function. We have previously shown rats that are overfed as neonates have exacerbated pro-inflammatory responses to immune challenge with lipopolysaccharide (LPS), in part by altering HPA axis responses, but how this occurs is unknown. Here we examined neonatal overfeeding-induced changes in gene expression in each step of the HPA axis. We saw no differences in glucocorticoid or mineralocorticoid receptor expression in key regions responsible for glucocorticoid negative feedback to the brain and no differences in expression of key HPA axis regulatory genes in the paraventricular nucleus of the hypothalamus or pituitary. On the other hand, expression of the adrenal melanocortin 2 receptor (MC2R) is elevated after LPS in control rats, but significantly less so in the neonatally overfed. The in vitro adrenal response to ACTH is also dampened in these rats, while the in vivo response to ACTH does not resolve as efficiently as it does in controls. These data suggest neonatal diet affects the efficiency of the adrenally-mediated response to LPS, potentially influencing how neonatally overfed rats combat bacterial infection.

Restoration of autophagy alleviates hepatic ER stress and impaired insulin signalling transduction in high fructose-fed male mice.

High-carbohydrate (mainly fructose) consumption is a major dietary factor for hepatic insulin resistance, involving endoplasmic reticulum (ER) stress and lipid accumulation. Because autophagy has been implicated in ER stress, the present study investigated the role of autophagy in high-fructose (HFru) diet-induced hepatic ER stress and insulin resistance in male C57BL/6J mice. The results show that chronic HFru feeding induced glucose intolerance and impaired insulin signaling transduction in the liver, associated with ER stress and the accumulation of lipids. Intriguingly, hepatic autophagy was suppressed as a result of activation of mammalian target of rapamycin. The suppressed autophagy was detected within 6 hours after HFru feeding along with activation of both inositol-requiring enzyme 1 and protein kinase RNA-like endoplasmic reticulum kinase pathways. These events occurred prior to lipid accumulation or lipogenesis and were sufficient to blunt insulin signaling transduction with activation of c-Jun N-terminal kinase/inhibitory-κB kinase and serine phosphorylation of insulin receptor substrate 1. The stimulation of autophagy attenuated ER stress- and c-Jun N-terminal kinase/inhibitory-κB kinase-associated impairment in insulin signaling transduction in a mammalian target of rapamycin -independent manner. Taken together, our data suggest that restoration of autophagy functions disrupted by fructose is able to alleviate ER stress and improve insulin signaling transduction.

Hepatic FoxO1 acetylation is involved in oleanolic acid-induced memory of glycemic control: novel findings from Study 2.

Our recent study (referred as Study 1) showed that the triterpenoid oleanolic acid (OA) was able to produce a sustained correction of hyperglycemia beyond treatment period in type 2 diabetes (T2D) mice with liver as a responsible site. To follow up the previous observations, the present study (referred as Study 2) investigated the possible role of acetylation of FoxO1 and associated events in this therapeutic memory by characterizing the pathways regulating the acetylation status during and post-OA treatments. OA treatment (100 mg/kg/day for 4 weeks, during OA treatment) reduced hyperglycemia in T2D mice by ∼87% and this effect was largely (∼70%) maintained even 4 weeks after the cessation of OA administration (post-OA treatment). During OA treatment, the acetylation and phosphorylation of FoxO1 were markedly increased (1.5 to 2.5-fold) while G6Pase expression was suppressed by ∼80%. Consistent with this, OA treatment reversed pyruvate intolerance in high-fat fed mice. Histone acetyltransferase 1 (HAT1) content was increased (>50%) and histone deacetylases (HDACs) 4 and 5 (not HDAC1) were reduced by 30-50%. The OA-induced changes in FoxO1, G6Pase, HAT1 and HDACs persisted during the post-OA treatment period when the increased phosphorylation of AMPK, SIRT1 content and reduced liver triglyceride had subsided. These results confirmed the ability of OA to control hyperglycemia far beyond treatment period in T2D mice. Most importantly, in the present study we demonstrated acetylation of FoxO1 in the liver is involved in OA-induced memory for the control of hyperglycemia. Our novel findings suggest that acetylation of the key regulatory proteins of hepatic gluconeogenesis is a plausible mechanism by the triterpenoid to achieve a sustained glycemic control for T2D.

Screening for the efficacy on lipid accumulation in 3T3-L1 cells is an effective tool for the identification of new anti-diabetic compounds.

Reducing lipid accumulation in insulin target tissues is critical for the treatment of type 2 diabetes. This study aimed to develop a biochemical assay in cells for high throughput (HTP) screening of anti-diabetic drugs by reducing lipid accumulation via different mechanisms. We designed a new method to extract triglyceride (TG) with KOH to allow biochemical quantification of TGs for HTP screening in 3T3-L1 cells. This new method was validated for its biochemical properties with identical results of TG obtained with or without KOH (r(2) = 0.9978, p < 0.001) and a fourfold improvement in TG extraction recovery rate (88-95%, p < 0.001) as compared to the conventional chloroform/methanol extraction (12-18%). The ability of this phenotype screening to capture potential anti-diabetic drugs was verified by pharmacological agents well known to alter lipid accumulation by different mechanisms including AMPK activators, fatty acid synthesis inhibitors, PPARγ activator and several lipogenic substrates. To further demonstrate the application of this screening tool for discovery of new anti-diabetic drugs, we screened >200 new candidates selected from Chinese medicine and identified 49 compounds from different classes which reduced TG content by >50% at 1 µM or >75% at 10 µM. Finally, we tested two selected leads (albiflorin and oxymatrine) in vivo and confirmed their efficacy in reducing visceral adiposity, glucose intolerance and hepatic steatosis in high fat-fed or high fructose-fed mice. Our results indicate that screening for the efficacy on lipid accumulation in cells by biochemical quantification of TGs with KOH extraction is an effective tool for the identification of new anti-diabetic compounds.

Methazolamide is a new hepatic insulin sensitizer that lowers blood glucose in vivo.

We previously used Gene Expression Signature technology to identify methazolamide (MTZ) and related compounds with insulin sensitizing activity in vitro. The effects of these compounds were investigated in diabetic db/db mice, insulin-resistant diet-induced obese (DIO) mice, and rats with streptozotocin (STZ)-induced diabetes. MTZ reduced fasting blood glucose and HbA(1c) levels in db/db mice, improved glucose tolerance in DIO mice, and enhanced the glucose-lowering effects of exogenous insulin administration in rats with STZ-induced diabetes. Hyperinsulinemic-euglycemic clamps in DIO mice revealed that MTZ increased glucose infusion rate and suppressed endogenous glucose production. Whole-body or cellular oxygen consumption rate was not altered, suggesting MTZ may inhibit glucose production by different mechanism(s) to metformin. In support of this, MTZ enhanced the glucose-lowering effects of metformin in db/db mice. MTZ is known to be a carbonic anhydrase inhibitor (CAI); however, CAIs acetazolamide, ethoxyzolamide, dichlorphenamide, chlorthalidone, and furosemide were not effective in vivo. Our results demonstrate that MTZ acts as an insulin sensitizer that suppresses hepatic glucose production in vivo. The antidiabetic effect of MTZ does not appear to be a function of its known activity as a CAI. The additive glucose-lowering effect of MTZ together with metformin highlights the potential utility for the management of type 2 diabetes.