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1.
Mol Metab ; 70: 101700, 2023 04.
Article in English | MEDLINE | ID: mdl-36870604

ABSTRACT

OBJECTIVE: Deregulation of hepatic glucose production is a key driver in the pathogenesis of diabetes, but its short-term regulation is incompletely deciphered. According to textbooks, glucose is produced in the endoplasmic reticulum by glucose-6-phosphatase (G6Pase) and then exported in the blood by the glucose transporter GLUT2. However, in the absence of GLUT2, glucose can be produced by a cholesterol-dependent vesicular pathway, which remains to be deciphered. Interestingly, a similar mechanism relying on vesicle trafficking controls short-term G6Pase activity. We thus investigated whether Caveolin-1 (Cav1), a master regulator of cholesterol trafficking, might be the mechanistic link between glucose production by G6Pase in the ER and glucose export through a vesicular pathway. METHODS: Glucose production from fasted mice lacking Cav1, GLUT2 or both proteins was measured in vitro in primary culture of hepatocytes and in vivo by pyruvate tolerance tests. The cellular localization of Cav1 and the catalytic unit of glucose-6-phosphatase (G6PC1) were studied by western blotting from purified membranes, immunofluorescence on primary hepatocytes and fixed liver sections and by in vivo imaging of chimeric constructs overexpressed in cell lines. G6PC1 trafficking to the plasma membrane was inhibited by a broad inhibitor of vesicular pathways or by an anchoring system retaining G6PC1 specifically to the ER membrane. RESULTS: Hepatocyte glucose production is reduced at the step catalyzed by G6Pase in the absence of Cav1. In the absence of both GLUT2 and Cav1, gluconeogenesis is nearly abolished, indicating that these pathways can be considered as the two major pathways of de novo glucose production. Mechanistically, Cav1 colocalizes but does not interact with G6PC1 and controls its localization in the Golgi complex and at the plasma membrane. The localization of G6PC1 at the plasma membrane is correlated to glucose production. Accordingly, retaining G6PC1 in the ER reduces glucose production by hepatic cells. CONCLUSIONS: Our data evidence a pathway of glucose production that relies on Cav1-dependent trafficking of G6PC1 to the plasma membrane. This reveals a new cellular regulation of G6Pase activity that contributes to hepatic glucose production and glucose homeostasis.


Subject(s)
Glucose-6-Phosphatase , Glucose , Animals , Mice , Caveolin 1/metabolism , Cholesterol/metabolism , Glucose/metabolism , Glucose-6-Phosphatase/metabolism , Liver/metabolism
2.
Hum Mol Genet ; 31(6): 914-928, 2022 03 21.
Article in English | MEDLINE | ID: mdl-34617103

ABSTRACT

Glycogen Storage Disease Type I (GSDI) is an inherited disease caused by glucose-6 phosphatase (G6Pase) deficiency, leading to a loss of endogenous glucose production and severe hypoglycemia. Moreover, most GSDI patients develop a chronic kidney disease (CKD) due to lipid accumulation in the kidney. Similar to diabetic CKD, activation of renin-angiotensin system (RAS) promotes renal fibrosis in GSDI. Here, we investigated the physiological and molecular effects of RAS blockers in GSDI patients and mice. A retrospective analysis of renal function was performed in 21 GSDI patients treated with RAS blockers. Cellular and metabolic impacts of RAS blockade were analyzed in K.G6pc-/- mice characterized by G6pc1 deletion in kidneys. GSDI patients started RAS blocker treatment at a median age of 21 years and long-term treatment reduced the progression of CKD in about 50% of patients. However, CKD progressed to kidney failure in 20% of treated patients, requiring renal transplantation. In K.G6pc-/- mice, CKD was associated with an impairment of autophagy and ER stress. RAS blockade resulted in a rescue of autophagy and decreased ER stress, concomitantly with decreased fibrosis and improved renal function, but without impact on glycogen and lipid contents. In conclusion, these data confirm the partial beneficial effect of RAS blockers in the prevention of CKD in GSDI. Mechanistically, we show that these effects are linked to a reduction of cell stress, without affecting metabolism.


Subject(s)
Glycogen Storage Disease Type I , Renal Insufficiency, Chronic , Animals , Female , Glucose/metabolism , Glycogen Storage Disease Type I/complications , Glycogen Storage Disease Type I/drug therapy , Glycogen Storage Disease Type I/genetics , Humans , Lipids , Male , Mice , Renal Insufficiency, Chronic/drug therapy , Renal Insufficiency, Chronic/genetics , Renin-Angiotensin System/genetics , Retrospective Studies
3.
Mol Metab ; 31: 14-23, 2020 01.
Article in English | MEDLINE | ID: mdl-31918916

ABSTRACT

OBJECTIVE: Roux-en-Y gastric surgery (RYGB) promotes a rapid and sustained weight loss and amelioration of glucose control in obese patients. A high number of molecular hypotheses were previously tested using duodenal-jejunal bypass (DJB) performed in various genetic models of mice with knockouts for various hormones or receptors. The data were globally negative or inconsistent. Therefore, the mechanisms remained elusive. Intestinal gluconeogenesis is a gut function that has been suggested to contribute to the metabolic benefits of RYGB in obese patients. METHODS: We studied the effects of DJB on body weight and glucose control in obese mice fed a high fat-high sucrose diet. Wild type mice and mice with a genetic suppression of intestinal gluconeogenesis were studied in parallel using glucose- and insulin-tolerance tests. Fecal losses, including excretion of lipids, were studied from the feces recovered in metabolic cages. RESULTS: DJB induced a dramatic decrease in body weight and improvement in glucose control (glucose- and insulin-tolerance) in obese wild type mice fed a high calorie diet, for 25 days after the surgery. The DJB-induced decrease in food intake was transient and resumed to normal in 7-8 days, suggesting that decreased food intake could not account for the benefits. Total fecal losses were about 5 times and lipid losses 7 times higher in DJB-mice than in control (sham-operated and pair-fed) mice, and could account for the weight loss of mice. The results were comparable in mice with suppression of intestinal gluconeogenesis. There was no effect of DJB on food intake, body weight or fecal loss in lean mice fed a normal chow diet. CONCLUSIONS: DJB in obese mice fed a high calorie diet promotes dramatic fecal loss, which could account for the dramatic weight loss and metabolic benefits observed. This could dominate the effects of the mouse genotype/phenotype. Thus, fecal energy loss should be considered as an essential process contributing to the metabolic benefits of DJB in obese mice.


Subject(s)
Gastric Bypass , Obesity/metabolism , Obesity/surgery , Animals , Body Weight , Male , Mice , Mice, Inbred C57BL , Weight Loss
4.
Mol Metab ; 16: 100-115, 2018 10.
Article in English | MEDLINE | ID: mdl-30100243

ABSTRACT

OBJECTIVE: Ectopic lipid accumulation in the liver and kidneys is a hallmark of metabolic diseases leading to non-alcoholic fatty liver disease (NAFLD) and chronic kidney disease (CKD). Moreover, recent data have highlighted a strong correlation between NAFLD and CKD incidences. In this study, we use two mouse models of hepatic steatosis or CKD, each initiated independently of the other upon the suppression of glucose production specifically in the liver or kidneys, to elucidate the mechanisms underlying the development of CKD in the context of NAFLD-like pathology. METHODS: Mice with a deletion of G6pc, encoding glucose-6 phosphatase catalytic subunit, specifically in the liver (L.G6pc-/- mice) or the kidneys (K.G6pc-/- mice), were fed with either a standard diet or a high fat/high sucrose (HF/HS) diet during 9 months. These mice represent two original models of a rare metabolic disease named Glycogen Storage Disease Type Ia (GSDIa) that is characterized by both NAFLD-like pathology and CKD. Two other groups of L.G6pc-/- and K.G6pc-/- mice were fed a standard diet for 6 months and then treated with fenofibrate for 3 months. Lipid and glucose metabolisms were characterized, and NAFLD-like and CKD damages were evaluated. RESULTS: Lipid depot exacerbation upon high-calorie diet strongly accelerated hepatic and renal pathologies induced by the G6pc-deficiency. In L.G6pc-/- mice, HF/HS diet increased liver injuries, characterized by higher levels of plasmatic transaminases and increased hepatic tumor incidence. In K.G6pc-/- mice, HF/HS diet increased urinary albumin and lipocalin 2 excretion and aggravated renal fibrosis. In both cases, the worsening of NAFLD-like injuries and CKD was independent of glycogen content. Furthermore, fenofibrate, via the activation of lipid oxidation significantly decreased the hepatic or renal lipid accumulations and prevented liver or kidney damages in L.G6pc-/- and K.G6pc-/- mice, respectively. Finally, we show that L.G6pc-/- mice and K.G6pc-/- mice developed NAFLD-like pathology and CKD independently. CONCLUSIONS: This study highlights the crucial role that lipids play in the independent development of both NAFLD and CKD and demonstrates the importance of lipid-lowering treatments in various metabolic diseases featured by lipid load, from the "rare" GSDIa to the "epidemic" morbid obesity or type 2 diabetes.


Subject(s)
Glucose-6-Phosphatase/metabolism , Glycogen Storage Disease Type I/metabolism , Lipid Metabolism/physiology , Animals , Diabetes Mellitus, Type 2/metabolism , Diet, High-Fat , Disease Models, Animal , Fatty Liver/metabolism , Fatty Liver/physiopathology , Glucose/metabolism , Glucose-6-Phosphatase/genetics , Glycogen Storage Disease Type I/physiopathology , Intracellular Space , Kidney/metabolism , Lipid Accumulation Product/physiology , Lipid Metabolism/genetics , Lipids/physiology , Liver/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Non-alcoholic Fatty Liver Disease/metabolism , Non-alcoholic Fatty Liver Disease/physiopathology , Renal Insufficiency, Chronic/metabolism , Renal Insufficiency, Chronic/physiopathology
5.
Mol Metab ; 16: 203-212, 2018 10.
Article in English | MEDLINE | ID: mdl-29960865

ABSTRACT

OBJECTIVE: The respective contributions to endogenous glucose production (EGP) of the liver, kidney and intestine vary during fasting. We previously reported that the deficiency in either hepatic or intestinal gluconeogenesis modulates the repartition of EGP via glucagon secretion (humoral factor) and gut-brain-liver axis (neural factor), respectively. Considering renal gluconeogenesis reportedly accounted for approximately 50% of EGP during fasting, we examined whether a reduction in renal gluconeogenesis could promote alterations in the repartition of EGP in this situation. METHODS: We studied mice whose glucose-6-phosphatase (G6Pase) catalytic subunit (G6PC) is specifically knocked down in the kidneys (K-G6pc-/- mice) during fasting. We also examined the additional effects of intestinal G6pc deletion, renal denervation and vitamin D administration on the altered glucose metabolism in K-G6pc-/- mice. RESULTS: Compared with WT mice, K-G6pc-/- mice exhibited (1) lower glycemia, (2) enhanced intestinal but not hepatic G6Pase activity, (3) enhanced hepatic glucokinase (GK encoded by Gck) activity, (4) increased hepatic glucose-6-phosphate and (5) hepatic glycogen spared from exhaustion during fasting. Increased hepatic Gck expression in the post-absorptive state could be dependent on the enhancement of insulin signal (AKT phosphorylation) in K-G6pc-/- mice. In contrast, the increase in hepatic GK activity was not observed in mice with both kidney- and intestine-knockout (KI-G6pc-/- mice). Hepatic Gck gene expression and hepatic AKT phosphorylation were reduced in KI-G6pc-/- mice. Renal denervation by capsaicin did not induce any effect on glucose metabolism in K-G6pc-/- mice. Plasma level of 1,25 (OH)2 D3, an active form of vitamin D, was decreased in K-G6pc-/- mice. Interestingly, the administration of 1,25 (OH)2 D3 prevented the enhancement of intestinal gluconeogenesis and hepatic GK activity and blocked the accumulation of hepatic glycogen otherwise observed in K-G6pc-/- mice during fasting. CONCLUSIONS: A diminution in renal gluconeogenesis that is accompanied by a decrease in blood vitamin D promotes a novel repartition of EGP among glucose producing organs during fasting, featured by increased intestinal gluconeogenesis that leads to sparing glycogen stores in the liver. Our data suggest a possible involvement of a crosstalk between the kidneys and intestine (via the vitamin D system) and the intestine and liver (via a neural gut-brain axis), which might take place in the situations of deficient renal glucose production, such as chronic kidney disease.


Subject(s)
Gluconeogenesis/physiology , Glucose/biosynthesis , Kidney/physiology , Animals , Blood Glucose/metabolism , Fasting/physiology , Glucose/metabolism , Glucose-6-Phosphatase/metabolism , Glycogen/metabolism , Glycogen Storage Disease Type I , Hypoglycemia/metabolism , Insulin/metabolism , Kidney/metabolism , Liver/metabolism , Liver Glycogen/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Vitamin D/metabolism
6.
Sci Rep ; 7: 44856, 2017 03 23.
Article in English | MEDLINE | ID: mdl-28332577

ABSTRACT

Roux-en-Y gastric bypass (RYGB) induces remission or substantial improvement of type 2 diabetes mellitus (T2D) but underlying mechanisms are still unclear. The beneficial effects of dietary proteins on energy and glucose homeostasis are mediated by the antagonist effects of peptides toward mu-opioid receptors (MORs), which are highly expressed in the distal gut. We hypothesized that the beneficial effects of RYGB could depend at least in part on the interaction of peptides from food with intestinal MORs. Duodenal-jejunal bypass (DJB) was performed in obese and lean wild-type (WT) or MOR deficient (MOR-/-) mice. Food intake and body weight was monitored daily during 3 weeks. Glucose homeostasis was assessed from glucose and insulin tolerance tests. In obese WT and MOR-/- mice, DJB induced a rapid and sustained weight loss partly independent of food intake, and a rapid improvement in glycaemic parameters. Weight loss was a major determinant of the improvements observed. In lean WT and MOR-/- mice, DJB had no effect on weight loss but significantly enhanced glucose tolerance. We found that MORs are not essential in the metabolic beneficial effects of DJB, suggesting that protein sensing in the distal gut is not a link in the metabolic benefits of gastric surgery.


Subject(s)
Dietary Proteins/metabolism , Duodenum/physiology , Gastric Bypass , Jejunum/physiology , Animals , Energy Metabolism , Gastric Bypass/methods , Male , Mice , Mice, Knockout , Obesity/metabolism , Receptors, Opioid, mu/genetics , Receptors, Opioid, mu/metabolism , Weight Loss
7.
Cell Metab ; 24(1): 151-7, 2016 07 12.
Article in English | MEDLINE | ID: mdl-27411015

ABSTRACT

Beneficial effects of dietary fiber on glucose and energy homeostasis have long been described, focusing mostly on the production of short-chain fatty acids by the gut commensal bacteria. However, bacterial fermentation of dietary fiber also produces large amounts of succinate and, to date, no study has focused on the role of succinate on host metabolism. Here, we fed mice a fiber-rich diet and found that succinate was the most abundant carboxylic acid in the cecum. Dietary succinate was identified as a substrate for intestinal gluconeogenesis (IGN), a process that improves glucose homeostasis. Accordingly, dietary succinate improved glucose and insulin tolerance in wild-type mice, but those effects were absent in mice deficient in IGN. Conventional mice colonized with the succinate producer Prevotella copri exhibited metabolic benefits, which could be related to succinate-activated IGN. Thus, microbiota-produced succinate is a previously unsuspected bacterial metabolite improving glycemic control through activation of IGN.


Subject(s)
Gluconeogenesis/drug effects , Glucose/metabolism , Homeostasis/drug effects , Intestinal Mucosa/metabolism , Microbiota , Succinic Acid/pharmacology , Animals , Cecum/drug effects , Cecum/metabolism , Feeding Behavior/drug effects , Genotype , Liver/drug effects , Liver/metabolism , Male , Mice, Inbred C57BL , Microbiota/drug effects , Oligosaccharides/pharmacology , Prevotella/drug effects , Prevotella/metabolism
8.
Hum Mol Genet ; 25(17): 3784-3797, 2016 09 01.
Article in English | MEDLINE | ID: mdl-27436577

ABSTRACT

Glycogen storage disease type I (GSDI) is a rare metabolic disease due to glucose-6 phosphatase deficiency, characterized by fasting hypoglycemia. Patients also develop chronic kidney disease whose mechanisms are poorly understood. To decipher the process, we generated mice with a kidney-specific knockout of glucose-6 phosphatase (K.G6pc-/- mice) that exhibited the first signs of GSDI nephropathy after 6 months of G6pc deletion. We studied the natural course of renal deterioration in K.G6pc-/- mice for 18 months and observed the progressive deterioration of renal functions characterized by early tubular dysfunction and a later destruction of the glomerular filtration barrier. After 15 months, K.G6pc-/- mice developed tubular-glomerular fibrosis and podocyte injury, leading to the development of cysts and renal failure. On the basis of these findings, we were able to detect the development of cysts in 7 out of 32 GSDI patients, who developed advanced renal impairment. Of these 7 patients, 3 developed renal failure. In addition, no renal cysts were detected in six patients who showed early renal impairment. In conclusion, renal pathology in GSDI is characterized by progressive tubular dysfunction and the development of polycystic kidneys that probably leads to the development of irreversible renal failure in the late stages. Systematic observations of cyst development by kidney imaging should improve the evaluation of the disease's progression, independently of biochemical markers.


Subject(s)
Glomerular Filtration Barrier/pathology , Glucose-6-Phosphatase/genetics , Glycogen Storage Disease Type I/complications , Kidney Diseases, Cystic/etiology , Renal Insufficiency/etiology , Adolescent , Adult , Animals , Child , Child, Preschool , Disease Models, Animal , Disease Progression , Female , Gene Knockout Techniques , Glomerular Filtration Barrier/physiopathology , Glycogen Storage Disease Type I/genetics , Glycogen Storage Disease Type I/physiopathology , Humans , Infant , Kidney Diseases, Cystic/pathology , Male , Mice , Middle Aged , Renal Insufficiency/pathology , Young Adult
9.
Ann Surg ; 262(6): 1006-15, 2015 Dec.
Article in English | MEDLINE | ID: mdl-25575265

ABSTRACT

OBJECTIVE: To evaluate the role of bile routing modification on the beneficial effects of gastric bypass surgery on glucose and energy metabolism. BACKGROUND: Gastric bypass surgery (GBP) promotes early improvements in glucose and energy homeostasis in obese diabetic patients. A suggested mechanism associates a decrease in hepatic glucose production to an enhanced intestinal gluconeogenesis. Moreover, plasma bile acids are elevated after GBP and bile acids are inhibitors of gluconeogenesis. METHODS: In male Sprague-Dawley rats, we performed bile diversions from the bile duct to the midjejunum or the mid-ileum to match the modified bile delivery in the gut occurring in GBP. Body weight, food intake, glucose tolerance, insulin sensitivity, and food preference were analyzed. The expression of gluconeogenesis genes was evaluated in both the liver and the intestine. RESULTS: Bile diversions mimicking GBP promote an increase in plasma bile acids and a marked improvement in glucose control. Bile bioavailability modification is causal because a bile acid sequestrant suppresses the beneficial effects of bile diversions on glucose control. In agreement with the inhibitory role of bile acids on gluconeogenesis, bile diversions promote a blunting in hepatic glucose production, whereas intestinal gluconeogenesis is increased in the gut segments devoid of bile. In rats fed a high-fat-high-sucrose diet, bile diversions improve glucose control and dramatically decrease food intake because of an acquired disinterest in fatty food. CONCLUSIONS: This study shows that bile routing modification is a key mechanistic feature in the beneficial outcomes of GBP.


Subject(s)
Bile Acids and Salts/metabolism , Bile/physiology , Blood Glucose/metabolism , Energy Metabolism , Gastric Bypass , Animals , Biomarkers/metabolism , Food Preferences/physiology , Gene Expression Regulation , Gluconeogenesis/genetics , Homeostasis , Ileum/surgery , Insulin Resistance , Intestinal Mucosa/metabolism , Jejunum/surgery , Liver/metabolism , Male , Obesity/metabolism , Obesity/surgery , Rats , Rats, Sprague-Dawley
10.
Cell ; 156(1-2): 84-96, 2014 Jan 16.
Article in English | MEDLINE | ID: mdl-24412651

ABSTRACT

Soluble dietary fibers promote metabolic benefits on body weight and glucose control, but underlying mechanisms are poorly understood. Recent evidence indicates that intestinal gluconeogenesis (IGN) has beneficial effects on glucose and energy homeostasis. Here, we show that the short-chain fatty acids (SCFAs) propionate and butyrate, which are generated by fermentation of soluble fiber by the gut microbiota, activate IGN via complementary mechanisms. Butyrate activates IGN gene expression through a cAMP-dependent mechanism, while propionate, itself a substrate of IGN, activates IGN gene expression via a gut-brain neural circuit involving the fatty acid receptor FFAR3. The metabolic benefits on body weight and glucose control induced by SCFAs or dietary fiber in normal mice are absent in mice deficient for IGN, despite similar modifications in gut microbiota composition. Thus, the regulation of IGN is necessary for the metabolic benefits associated with SCFAs and soluble fiber.


Subject(s)
Gluconeogenesis , Intestinal Mucosa/metabolism , Intestines/innervation , Animals , Brain/metabolism , Dietary Fats/metabolism , Dietary Fiber/metabolism , Fatty Acids, Volatile/metabolism , Glucose/metabolism , Glucose-6-Phosphatase/genetics , Glucose-6-Phosphatase/metabolism , Homeostasis , Insulin Resistance , Mice , Microbiota , Obesity/metabolism , Oligosaccharides/metabolism , Rats
11.
Obesity (Silver Spring) ; 22(3): 713-20, 2014 Mar.
Article in English | MEDLINE | ID: mdl-23894080

ABSTRACT

OBJECTIVE: High-protein diets favor weight loss and its maintenance. Whether these effects might be recapitulated by certain amino acids is unknown. Therefore, the impact of leucine supplementation on energy balance and associated metabolic changes in diet-induced obese (DIO) mice during and after weight loss was investigated. METHODS: DIO C57BL/6J mice were fed a normocaloric diet to induce weight loss while receiving or not the amino acid leucine in drinking water. Body weight, food intake, body composition, energy expenditure, glucose tolerance, insulin, and leptin sensitivity were evaluated. Q-PCR analysis was performed on muscle, brown and white adipose tissues. RESULTS: DIO mice decreased body weight and fat mass in response to chow, but supplementation with leucine did not affect these parameters. During weight maintenance, mice supplemented with leucine had improved glucose tolerance, increased leptin sensitivity, and lower respiratory quotient. The latter was associated with changes in the expression of several genes modulating fatty acid metabolism and mitochondrial activity in the epididymal white and the brown adipose tissues, but not muscle. CONCLUSIONS: Leucine supplementation might represent an adjuvant beneficial nutritional therapy during weight loss and maintenance, because it improves lipid and glucose metabolism and restores leptin sensitivity in previously obese animals.


Subject(s)
Blood Glucose/metabolism , Dietary Supplements , Leucine/administration & dosage , Adipose Tissue, Brown/drug effects , Adipose Tissue, Brown/metabolism , Adipose Tissue, White/drug effects , Adipose Tissue, White/metabolism , Animals , Body Composition , Calorimetry, Indirect , Diet, High-Fat/adverse effects , Energy Metabolism/drug effects , Gluconeogenesis/drug effects , Glucose Tolerance Test , Insulin/blood , Intestinal Mucosa/metabolism , Intestines/drug effects , Leptin/blood , Lipid Metabolism/drug effects , Male , Mice , Mice, Inbred C57BL , Mice, Obese , Obesity/drug therapy , Weight Loss
12.
PLoS One ; 8(9): e74705, 2013.
Article in English | MEDLINE | ID: mdl-24086364

ABSTRACT

BACKGROUND: Leucine supplementation might have therapeutic potential in preventing diet-induced obesity and improving insulin sensitivity. However, the underlying mechanisms are at present unclear. Additionally, it is unclear whether leucine supplementation might be equally efficacious once obesity has developed. METHODOLOGY/PRINCIPAL FINDINGS: Male C57BL/6J mice were fed chow or a high-fat diet (HFD), supplemented or not with leucine for 17 weeks. Another group of HFD-fed mice (HFD-pairfat group) was food restricted in order to reach an adiposity level comparable to that of HFD-Leu mice. Finally, a third group of mice was exposed to HFD for 12 weeks before being chronically supplemented with leucine. Leucine supplementation in HFD-fed mice decreased body weight and fat mass by increasing energy expenditure, fatty acid oxidation and locomotor activity in vivo. The decreased adiposity in HFD-Leu mice was associated with increased expression of uncoupling protein 3 (UCP-3) in the brown adipose tissue, better insulin sensitivity, increased intestinal gluconeogenesis and preservation of islets of Langerhans histomorphology and function. HFD-pairfat mice had a comparable improvement in insulin sensitivity, without changes in islets physiology or intestinal gluconeogenesis. Remarkably, both HFD-Leu and HFD-pairfat mice had decreased hepatic lipid content, which likely helped improve insulin sensitivity. In contrast, when leucine was supplemented to already obese animals, no changes in body weight, body composition or glucose metabolism were observed. CONCLUSIONS/SIGNIFICANCE: These findings suggest that leucine improves insulin sensitivity in HFD-fed mice by primarily decreasing adiposity, rather than directly acting on peripheral target organs. However, beneficial effects of leucine on intestinal gluconeogenesis and islets of Langerhans's physiology might help prevent type 2 diabetes development. Differently, metabolic benefit of leucine supplementation is lacking in already obese animals, a phenomenon possibly related to the extent of the obesity before starting the supplementation.


Subject(s)
Adiposity/drug effects , Dietary Supplements , Insulin Resistance , Leucine/pharmacology , Animals , Diet, High-Fat , Energy Metabolism/drug effects , Fatty Acids/metabolism , Glucose/metabolism , Homeostasis/drug effects , Insulin/pharmacology , Leucine/blood , Lipids/blood , Male , Mice , Mice, Inbred C57BL , Mice, Obese , Oxidation-Reduction/drug effects , Phenotype , Weight Gain/drug effects
13.
Eur J Neurosci ; 38(10): 3476-86, 2013 Nov.
Article in English | MEDLINE | ID: mdl-24011250

ABSTRACT

The detection of glucose in the hepatoportal area is a simple but crucial peripheral cue initiating a nervous signal that ultimately leads to a wide array of metabolic and behavioural responses, such as decreased food intake, tighter control of glucose homeostasis, or appearance of food preference. This signal has been suggested to mediate the effects of high-protein diets, as opposed to high-fat/high-sucrose diets. Nevertheless, the central targets of the signal originating from the hepatoportal area remain largely undocumented. Using immunohistochemistry on the brain of male rats, we show here that portal glucose increases c-Fos expression in the brainstem, in the hypothalamus (in particular in neurons expressing pro-opiomelanocortin) and also in olfactory and other limbic and cortical areas, including those functionally implicated in reward (Experiment 1). In similar postabsorptive conditions, a high-protein diet induced similar effects in the hypothalamus and the granular cells of the main olfactory bulb, whereas the high-fat/high-sucrose diet actually reduced the basal expression of c-Fos in cortical layers. Both diets also decreased the number of neurons expressing c-Fos in the amygdala and gustatory areas (Experiment 2). Altogether, these findings suggest that the peripheral signal primed by portal glucose sensing may influence behavioural adaptation such as food preference via a network including the olfactory pathway, central amygdala, nucleus accumbens and orbitofrontal cortex, in addition to satiety and metabolic effects primarily implicating the hypothalamic response.


Subject(s)
Cerebral Cortex/metabolism , Glucose/physiology , Hypothalamus/metabolism , Olfactory Bulb/metabolism , Portal System/physiology , Reward , Animals , Brain Stem/metabolism , Brain Stem/physiology , Cerebral Cortex/physiology , Eating/physiology , Hypothalamus/physiology , Male , Olfactory Bulb/physiology , Rats , Rats, Sprague-Dawley
14.
Cell ; 150(2): 377-88, 2012 Jul 20.
Article in English | MEDLINE | ID: mdl-22771138

ABSTRACT

Intestinal gluconeogenesis is involved in the control of food intake. We show that mu-opioid receptors (MORs) present in nerves in the portal vein walls respond to peptides to regulate a gut-brain neural circuit that controls intestinal gluconeogenesis and satiety. In vitro, peptides and protein digests behave as MOR antagonists in competition experiments. In vivo, they stimulate MOR-dependent induction of intestinal gluconeogenesis via activation of brain areas receiving inputs from gastrointestinal ascending nerves. MOR-knockout mice do not carry out intestinal gluconeogenesis in response to peptides and are insensitive to the satiety effect induced by protein-enriched diets. Portal infusions of MOR modulators have no effect on food intake in mice deficient for intestinal gluconeogenesis. Thus, the regulation of portal MORs by peptides triggering signals to and from the brain to induce intestinal gluconeogenesis are links in the satiety phenomenon associated with alimentary protein assimilation.


Subject(s)
Dietary Proteins/metabolism , Eating , Gluconeogenesis , Receptors, Opioid, mu/metabolism , Satiety Response , Animals , Brain/metabolism , Humans , Intestinal Mucosa/metabolism , Male , Mice , Mice, Knockout , Rats , Rats, Sprague-Dawley , Receptors, Opioid, mu/antagonists & inhibitors
15.
PLoS One ; 7(1): e30686, 2012.
Article in English | MEDLINE | ID: mdl-22295104

ABSTRACT

CD36 is a ubiquitous membrane glycoprotein that binds long-chain fatty acids. The presence of a functional CD36 is required for the induction of satiety by a lipid load and its role as a lipid receptor driving cellular signal has recently been demonstrated. Our project aimed to further explore the role of intestinal CD36 in the regulation of food intake. Duodenal infusions of vehicle or sulfo-N-succinimidyl-oleate (SSO) was performed prior to acute infusions of saline or Intralipid (IL) in mice. Infusion of minute quantities of IL induced a decrease in food intake (FI) compared to saline. Infusion of SSO had the same effect but no additive inhibitory effect was observed in presence of IL. No IL- or SSO-mediated satiety occurred in CD36-null mice. To determine whether the CD36-mediated hypophagic effect of lipids was maintained in animals fed a satietogen diet, mice were subjected to a High-Protein diet (HPD). Concomitantly with the satiety effect, a rise in intestinal CD36 gene expression was observed. No satiety effect occurred in CD36-null mice. HPD-fed WT mice showed a diminished FI compared to control mice, after saline duodenal infusion. But there was no further decrease after lipid infusion. The lipid-induced decrease in FI observed on control mice was accompanied by a rise in jejunal oleylethanolamide (OEA). Its level was higher in HPD-fed mice than in controls after saline infusion and was not changed by lipids. Overall, we demonstrate that lipid binding to intestinal CD36 is sufficient to produce a satiety effect. Moreover, it could participate in the satiety effect induced by HPD. Intestine can modulate FI by several mechanisms including an increase in OEA production and CD36 gene expression. Furthermore, intestine of mice adapted to HPD have a diminished capacity to modulate their food intake in response to dietary lipids.


Subject(s)
CD36 Antigens/metabolism , Diet , Intestinal Mucosa/metabolism , Satiety Response , Animals , CD36 Antigens/genetics , Eating/drug effects , Gene Expression Regulation/drug effects , Intestines/drug effects , Ligands , Male , Mice , Mice, Inbred C57BL , Oleic Acids/biosynthesis , Oleic Acids/metabolism , Oleic Acids/pharmacology , Protein Binding , Satiety Response/drug effects , Succinimides/metabolism , Succinimides/pharmacology , Time Factors
16.
Mol Metab ; 2(1): 47-53, 2012.
Article in English | MEDLINE | ID: mdl-24024129

ABSTRACT

Portal vein glucose sensors detect variations in glycemia to induce a nervous signal that influences food intake and glucose homeostasis. Previous experiments using high infusions of glucose suggested a metabolic sensing involving glucose transporter 2 (GLUT2). Here we evaluated the afferent route for the signal and candidate molecules for detecting low glucose fluxes. Common hepatic branch vagotomy did not abolish the anorectic effect of portal glucose, indicating dorsal transmission. GLUT2-null mice reduced their food intake in response to portal glucose signal initiated by protein-enriched diet. A similar response of Trpm5-null mice and portal infusions of sweeteners also excluded sugar taste receptors. Conversely, infusions of alpha-methylglucose, but not 3-O-methylglucose, decreased food intake, while phlorizin prevented the effect of glucose. This suggested sensing through SGLT3, which was expressed in the portal area. From these results we propose a finely tuned dual mechanism for portal glucose sensing that responds to different physiological conditions.

17.
Cell Metab ; 8(3): 201-11, 2008 Sep.
Article in English | MEDLINE | ID: mdl-18762021

ABSTRACT

Unlike the adjustable gastric banding procedure (AGB), Roux-en-Y gastric bypass surgery (RYGBP) in humans has an intriguing effect: a rapid and substantial control of type 2 diabetes mellitus (T2DM). We performed gastric lap-band (GLB) and entero-gastro anastomosis (EGA) procedures in C57Bl6 mice that were fed a high-fat diet. The EGA procedure specifically reduced food intake and increased insulin sensitivity as measured by endogenous glucose production. Intestinal gluconeogenesis increased after the EGA procedure, but not after gastric banding. All EGA effects were abolished in GLUT-2 knockout mice and in mice with portal vein denervation. We thus provide mechanistic evidence that the beneficial effects of the EGA procedure on food intake and glucose homeostasis involve intestinal gluconeogenesis and its detection via a GLUT-2 and hepatoportal sensor pathway.


Subject(s)
Gastric Bypass , Gastroplasty , Gluconeogenesis , Glucose/metabolism , Intestine, Small/metabolism , Obesity, Morbid/metabolism , Animals , Dietary Fats/administration & dosage , Eating , Glucose Transporter Type 1/deficiency , Glucose Transporter Type 2/deficiency , Insulin/blood , Insulin Resistance , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Models, Biological , Obesity, Morbid/surgery , Portal Vein/metabolism , Reproducibility of Results , Time Factors
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