The Glucagon-Like Peptide 1 Receptor Agonist Liraglutide Stimulates Mechanistic Target of Rapamycin (mTOR) Signaling via PKA And Akt

Abstract Glucagon-like peptide 1 receptor (GLP-1R) agonists enhance glucose-stimulated insulin secretion and act on several regions of the brain to reduce food intake and body weight, making the GLP-1R a major therapeutic target for the treatment of type 2 diabetes and obesity. Surprisingly, little is known about the signaling mechanisms mediating the food intake-lowering effects of GLP-1R agonists. We have previously shown that inhibiting the mechanistic Target of Rapamycin (mTOR) in the ventromedial hypothalamus blocks anorexia induced by GLP-1R activation in this brain nucleus (1). Therefore, the goal of the present studies is to elucidate the mechanisms by which GLP-1R activation stimulates mTOR signaling. To accomplish this, we treated Chinese Hamster Ovary cells stably expressing the human GLP-1R with the GLP-1R agonist liraglutide (Lira) in combination with inhibitors of various signaling molecules. Since PKA is a canonical target of GLP-1R signaling, and PKA phosphorylates mTOR and its regulating protein Raptor following β-adrenergic stimulation (2), we used the PKA inhibitors H89 and KT 5720 to examine whether PKA is required for the stimulation of mTOR activity by Lira. We expressed myc-tagged mTOR or Raptor in GLP-1R stably expressing CHO cells, treated them with Lira, immunoprecipitated myc-mTOR or myc-Raptor, and immunoblotted for the PKA substrate RRXS/T motif. We found that Lira significantly increased PKA-substrate motif phosphorylation of myc-Raptor but not myc-mTOR, and this was blocked by pre-treatment with H89. Lira also failed to stimulate phosphorylation of a Ser791Ala Raptor mutant that cannot be phosphorylated by PKA (2). To test whether Akt, a well-known regulator of mTOR activity, contributes to the activation of mTOR signaling by Lira, we pre-treated GLP-1R stably expressing CHO cells with either of the Akt inhibitors Akt-i 1/2 and MK-2206 followed by treatment with Lira or forskolin (Fsk), a cAMP inducer and PKA activator. Pre-treatment with either Akt-i 1/2 or MK-2206 blocked mTOR activation by both Lira and Fsk. This suggests that the contribution of Akt to Lira-induced mTOR activation is likely downstream of cAMP production. Taken together, our results suggest a novel two-pronged, PKA-dependent mechanism for the stimulation of mTOR signaling following GLP-1R activation – directly via phosphorylation of Raptor and indirectly via stimulation of Akt. Future studies will assess the respective contributions and temporal dynamics of each of these pathways. Reference: (1) Burmeister et al., Am J Physiol Endocrinol Metab. 2017 Aug;313: E651–E662. (2) Liu et al., J Clin Invest. 2016;126(5):1704-1716.

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Gastric Mammalian Target of Rapamycin Signaling Regulates Ghrelin Production and Food Intake

Endocrinology ◽

10.1210/en.2009-0372 ◽

2009 ◽

Vol 150 (8) ◽

pp. 3637-3644 ◽

Cited By ~ 54

Author(s):

Geyang Xu ◽

Yin Li ◽

Wenjiao An ◽

Shenduo Li ◽

Youfei Guan ◽

...

Keyword(s):

Food Intake ◽

Energy Homeostasis ◽

Mammalian Target Of Rapamycin ◽

Reciprocal Relationship ◽

Mtor Signaling ◽

Target Of Rapamycin ◽

Energy Status ◽

Ghrelin Receptor ◽

Ghrelin Receptor Antagonist ◽

Mtor Activity

Ghrelin, a gastric hormone, provides a hunger signal to the central nervous system to stimulate food intake. Mammalian target of rapamycin (mTOR) is an intracellular fuel sensor critical for cellular energy homeostasis. Here we showed the reciprocal relationship of gastric mTOR signaling and ghrelin during changes in energy status. mTOR activity was down-regulated, whereas gastric preproghrelin and circulating ghrelin were increased by fasting. In db/db mice, gastric mTOR signaling was enhanced, whereas gastric preproghrelin and circulating ghrelin were decreased. Inhibition of the gastric mTOR signaling by rapamycin stimulated the expression of gastric preproghrelin and ghrelin mRNA and increased plasma ghrelin in both wild-type and db/db mice. Activation of the gastric mTOR signaling by l-leucine decreased the expression of gastric preproghrelin and the level of plasma ghrelin. Overexpression of mTOR attenuated ghrelin promoter activity, whereas inhibition of mTOR activity by overexpression of TSC1 or TSC2 increased its activity. Ghrelin receptor antagonist d-Lys-3-GH-releasing peptide-6 abolished the rapamycin-induced increment in food intake despite that plasma ghrelin remained elevated. mTOR is therefore a gastric fuel sensor whose activity is linked to the regulation of energy intake through ghrelin.

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Takeda G Protein-Coupled Receptor 5-Mechanistic Target of Rapamycin Complex 1 Signaling Contributes to the Increment of Glucagon-Like Peptide-1 Production after Roux-en-Y Gastric Bypass

EBioMedicine ◽

10.1016/j.ebiom.2018.05.026 ◽

2018 ◽

Vol 32 ◽

pp. 201-214 ◽

Cited By ~ 15

Author(s):

Hening Zhai ◽

Zhi Li ◽

Miao Peng ◽

Zhaoqi Huang ◽

Tingfeng Qin ◽

...

Keyword(s):

Gastric Bypass ◽

G Protein ◽

Target Of Rapamycin ◽

G Protein Coupled Receptor ◽

Mechanistic Target Of Rapamycin ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1 ◽

G Protein Coupled

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The Molecular Mechanism of Glucagon-Like Peptide-1 Therapy in Alzheimer’s Disease, Based on a Mechanistic Target of Rapamycin Pathway

CNS Drugs ◽

10.1007/s40263-017-0431-2 ◽

2017 ◽

Vol 31 (7) ◽

pp. 535-549 ◽

Cited By ~ 6

Author(s):

Lin Li

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Molecular Mechanism ◽

Target Of Rapamycin ◽

Mechanistic Target Of Rapamycin ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1

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Modulation of Food Intake by Differential TAS2R Stimulation in Rat

Nutrients ◽

10.3390/nu12123784 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3784

Author(s):

Carme Grau-Bové ◽

Alba Miguéns-Gómez ◽

Carlos González-Quilen ◽

José-Antonio Fernández-López ◽

Xavier Remesar ◽

...

Keyword(s):

Food Intake ◽

Peptide Yy ◽

Reduce Food Intake ◽

Intestinal Segments ◽

Regulate Food Intake ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1 ◽

Specific Stimulation ◽

Ghrelin Secretion ◽

Stimulation Of

Metabolic surgery modulates the enterohormone profile, which leads, among other effects, to changes in food intake. Bitter taste receptors (TAS2Rs) have been identified in the gastrointestinal tract and specific stimulation of these has been linked to the control of ghrelin secretion. We hypothesize that optimal stimulation of TAS2Rs could help to modulate enteroendocrine secretions and thus regulate food intake. To determine this, we have assayed the response to specific agonists for hTAS2R5, hTAS2R14 and hTAS2R39 on enteroendocrine secretions from intestinal segments and food intake in rats. We found that hTAS2R5 agonists stimulate glucagon-like peptide 1 (GLP-1) and cholecystokinin (CCK), and reduce food intake. hTAS2R14 agonists induce GLP1, while hTASR39 agonists tend to increase peptide YY (PYY) but fail to reduce food intake. The effect of simultaneously activating several receptors is heterogeneous depending on the relative affinity of the agonists for each receptor. Although detailed mechanisms are not clear, bitter compounds can stimulate differentially enteroendocrine secretions that modulate food intake in rats.

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Effects of fat digestion on appetite, APD motility, and gut hormones in response to duodenal fat infusion in humans

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00512.2002 ◽

2003 ◽

Vol 284 (5) ◽

pp. G798-G807 ◽

Cited By ~ 126

Author(s):

Christine Feinle ◽

Deirdre O'Donovan ◽

Selena Doran ◽

Jane M. Andrews ◽

Judith Wishart ◽

...

Keyword(s):

Food Intake ◽

Gut Hormones ◽

Crossover Fashion ◽

Double Blind ◽

Triglyceride Hydrolysis ◽

Fat Infusion ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1 ◽

Lipase Inhibition ◽

Stimulation Of

The presence of nutrients in the small intestine slows gastric emptying and suppresses appetite and food intake; these effects are partly mediated by the release of gut hormones, including CCK. We investigated the hypothesis that the modulation of antropyloroduodenal motility, suppression of appetite, and stimulation of CCK and glucagon-like peptide-1 secretion by intraduodenal fat are dependent on triglyceride hydrolysis by lipase. Sixteen healthy, young, lean men were studied twice in double-blind, randomized, crossover fashion. Ratings for appetite-related sensations, antropyloroduodenal motility, and plasma CCK and glucagon-like peptide-1 concentrations were measured during a 120-min duodenal infusion of a triglyceride emulsion (2.8 kcal/min) on one day with, on the other day without, 120 mg tetrahydrolipstatin, a potent lipase inhibitor. Immediately after the duodenal fat infusion, food intake at a buffet lunch was quantified. Lipase inhibition with tetrahydrolipstatin was associated with reductions in tonic and phasic pyloric pressures, increased numbers of isolated antral and duodenal pressure waves, and stimulation of antropyloroduodenal pressure-wave sequences (all P < 0.05). Scores for prospective consumption and food intake at lunch were greater, and nausea scores were slightly less, and the rises in plasma CCK and glucagon-like peptide-1 were abolished (all P < 0.05). In conclusion, lipase inhibition attenuates the effects of duodenal fat on antropyloroduodenal motility, appetite, and CCK and glucagon-like peptide-1 secretion.

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Central glucagon-like peptide 1 receptor-induced anorexia requires glucose metabolism-mediated suppression of AMPK and is impaired by central fructose

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00446.2012 ◽

2013 ◽

Vol 304 (7) ◽

pp. E677-E685 ◽

Cited By ~ 34

Author(s):

Melissa A. Burmeister ◽

Jennifer Ayala ◽

Daniel J. Drucker ◽

Julio E. Ayala

Keyword(s):

Food Intake ◽

Glucose Metabolism ◽

Dependent Manner ◽

Anorectic Effect ◽

Dependent Inhibition ◽

Glycolytic Inhibitor ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1 ◽

Amp Activated Protein Kinase ◽

Mediated Reduction

Glucagon-like peptide-1 (GLP-1) suppresses food intake via activation of a central (i.e., brain) GLP-1 receptor (GLP-1R). Central AMP-activated protein kinase (AMPK) is a nutrient-sensitive regulator of food intake that is inhibited by anorectic signals. The anorectic effect elicited by hindbrain GLP-1R activation is attenuated by the AMPK stimulator AICAR. This suggests that central GLP-1R activation suppresses food intake via inhibition of central AMPK. The present studies examined the mechanism(s) by which central GLP-1R activation inhibits AMPK. Supporting previous findings, AICAR attenuated the anorectic effect elicited by intracerebroventricular (icv) administration of the GLP-1R agonist exendin-4 (Ex-4). We demonstrate that Ex-4 stimulates glycolysis and suppresses AMPK phosphorylation in a glucose-dependent manner in hypothalamic GT1-7 cells. This suggests that inhibition of AMPK and food intake by Ex-4 requires central glucose metabolism. Supporting this, the glycolytic inhibitor 2-deoxyglucose (2-DG) attenuated the anorectic effect of Ex-4. However, icv glucose did not enhance the suppression of food intake by Ex-4. AICAR had no effect on Ex-4-mediated reduction in locomotor activity. We also tested whether other carbohydrates affect the anorectic response to Ex-4. Intracerebroventricular pretreatment with the sucrose metabolite fructose, an AMPK activator, attenuated the anorectic effect of Ex-4. This potentially explains the increased food intake observed in sucrose-fed mice. In summary, we propose a model whereby activation of the central GLP-1R reduces food intake via glucose metabolism-dependent inhibition of central AMPK. We also suggest that fructose stimulates food intake by impairing central GLP-1R action. This has significant implications given the correlation between sugar consumption and obesity.

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Hindbrain glucagon-like peptide-1 neurons track intake volume and contribute to injection stress-induced hypophagia in meal-entrained rats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00243.2015 ◽

2016 ◽

Vol 310 (10) ◽

pp. R906-R916 ◽

Cited By ~ 9

Author(s):

Alison D. Kreisler ◽

Linda Rinaman

Keyword(s):

Food Intake ◽

Potential Role ◽

Liquid Diet ◽

Neural Activation ◽

Intracerebroventricular Injection ◽

Glucagon Like Peptide ◽

Glucagon Like Peptide 1 ◽

Diet Intake ◽

Published Research ◽

Diet Type

Published research supports a role for central glucagon-like peptide 1 (GLP-1) signaling in suppressing food intake in rodent species. However, it is unclear whether GLP-1 neurons track food intake and contribute to satiety, and/or whether GLP-1 signaling contributes to stress-induced hypophagia. To examine whether GLP-1 neurons track intake volume, rats were trained to consume liquid diet (LD) for 1 h daily until baseline intake stabilized. On test day, schedule-fed rats consumed unrestricted or limited volumes of LD or unrestricted volumes of diluted (calorically matched to LD) or undiluted Ensure. Rats were perfused after the test meal, and brains processed for immunolocalization of cFos and GLP-1. The large majority of GLP-1 neurons expressed cFos in rats that consumed satiating volumes, regardless of diet type, with GLP-1 activation proportional to intake volume. Since GLP-1 signaling may limit intake only when such large proportions of GLP-1 neurons are activated, a second experiment examined the effect of central GLP-1 receptor (R) antagonism on 2 h intake in schedule-fed rats. Compared with baseline, intracerebroventricular vehicle (saline) suppressed Ensure intake by ∼11%. Conversely, intracerebroventricular injection of vehicle containing GLP-1R antagonist increased intake by ∼14% compared with baseline, partly due to larger second meals. We conclude that GLP-1 neural activation effectively tracks liquid diet intake, that intracerebroventricular injection suppresses intake, and that central GLP-1 signaling contributes to this hypophagic effect. GLP-1 signaling also may contribute to satiety after large volumes have been consumed, but this potential role is difficult to separate from a role in the hypophagic response to intracerebroventricular injection.

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