Glucagon-like Peptide-1 Receptor Activation Research Articles

Dipeptidyl peptidase-4 disturbs adipocyte differentiation via the negative regulation of the glucagon-like peptide-1/adiponectin-cathepsin K axis in mice under chronic stress conditions.

Exposure to chronic psychosocial stress is a risk factor for metabolic disorders. Because dipeptidyl peptidase-4 (DPP4) and cysteinyl cathepsin K (CTSK) play important roles in human pathobiology, we investigated the role(s) of DPP4 in stress-related adipocyte differentiation, with a focus on the glucagon-like peptide-1 (GLP-1)/adiponectin-CTSK axis invivo and invitro. Plasma and inguinal adipose tissue from non-stress wild-type (DPP4+/+), DPP4-knockout (DPP4-/-) and CTSK-knockout (CTSK-/-) mice, and stressed DPP4+/+, DPP4-/-, CTSK-/-, and DPP4+/+ mice underwent stress exposure plus GLP-1 receptor agonist exenatide loading for 2 weeks and then were analyzed for stress-related biological and/or morphological alterations. On day 14 under chronic stress, stress decreased the weights of adipose tissue and resulted in harmful changes in the plasma levels of DPP4, GLP-1, CTSK, adiponectin, and tumor necrosis factor-α proteins and the adipose tissue levels of CTSK, preadipocyte factor-1, fatty acid binding protein-4, CCAAT/enhancer binding protein-α, GLP-1 receptor, peroxisome proliferator-activated receptor-γ, perilipin2, secreted frizzled-related protein-4, Wnt5α, Wnt11 and β-catenin proteins and/or mRNAs as well as macrophage infiltration in adipose tissue; these changes were rectified by DPP4 deletion. GLP-1 receptor activation and CTSK deletion mimic the adipose benefits of DPP4 deficiency. Invitro, CTSK silencing and overexpression respectively prevented and facilitated stress serum and oxidative stress-induced adipocyte differentiation accompanied with changes in the levels of pref-1, C/EBP-α, and PPAR-γ in 3T3-L1 cells. Thus, these findings indicated that increased DPP4 plays an essential role in stress-related adipocyte differentiation, possibly through a negative regulation of GLP-1/adiponectin-CTSK axis activation in mice under chronic stress conditions.

Will Tirzepatide become a game-changer in the pharmacological treatment of obesity? - literature review

Introduction and objective: Obesity has become an important public health issue in Poland. Furthermore, it is one of the most common preventable causes of diseases and mortality. Pharmacological methods of treating obesity have been developing significantly in recent years.Tirzepatide is a new dual incretin receptor agonist that activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. The aim of this review is to assess the effectiveness of this medication in reducing body weight. Current state of knowledge: According to data from the Central Statistical Office (GUS) in Poland, 65% of men and 49% of women are struggling with the issue of excessive body weight [1]. Obesity in Polish society is steadily increasing in every age group. However, it affects most significantly children aged 7-13 years and adolescents. In 2022, the novel dual GLP and GIP-1 agonist has been registered for the treatment of type 2 diabetes which is not satisfactorily controlled. It can be also used together with diet and physical activity in patients diagnosed with obesity (BMI of 30 kg/m2 or more) or who are overweight (BMI 27-30 kg/m2) and have weight-related health problems such as hypertension, metabolic syndrome, dislipidaemia and diabetes mellitus [2]. Summary: The increasing prevalence of obesity leads to a dynamic search for the most effective pharmacological methods of treating obesity. The combined activation of GLP-1 and GIP receptors by Tirzepatide has been shown to have additional benefits beyond satisfying glucose control. The biological mechanism of action of this medication additionally causes decreased food intake, slowed gastric emptying and enhanced insulin secretion, all of which can contribute to weight reduction.

The Role of GLP-1 Affects Fate of Astrocytes Following Ischemic Stroke in Mice

Stroke is one of the leading causes of physical and intellectual disability and mortality in adults of most of the developed countries. The most of studies in ischemic stroke focus on neuronal pathological mechanisms and neuronal death trying to rescue neurons via stopping the detrimental pathological processes or enhancing neuronal viability. Although astrocytes are the most abundant cells and in mammal central nervous system (CNS), they were ignored for period of time but are return to spotlight in recent years. Astrocyte play multiple roles in maintain normal function of central nervous system and respond to all kinds of CNS injury and disease. Responses of astrocytes to CNS damage lead to both detrimental and beneficial consequences. Previous studies have reported that astrocyte inflammatory responses to ischemic stroke may devastate the ischemic lesion, but other astrocytic responses lead to anti-excitotoxicity, secreting neurotrophic factors, neurogenesis, synaptogenesis, axonal remodeling, and angiogenesis promoting neuroprotective effects. Glucagon-like peptide-1 (GLP-1) have been intensively studied on beneficial effects of neurons, but not many studies work on effects of GLP-1 to astrocytes. Our early study has found that activation of GLP-1 receptors prevented ischemia-induced brain cell death and observed newly neuronal progenitor cells were from astrocyte-lineage in penumbral area of 3-day post-ischemic mouse brains by immunohistochemistry (IHC). RT-PCR, immunoblotting, and immunofluorescent results also clearly indicated the astrocytes expressed GLP-1 receptors. Furthermore, Western blotting results showed administration of GLP-1 analogue, exendin-4 (EX-4), suppressed expression of pro-inflammatory proteins in oxygen-glucose deprivation (OGD) treated mouse primary astrocytes. Interestingly, we also observed that infarct site obtained sever DNA damage and less GFAP positive astrocytes, on contrary, the penumbral area had more GFAP positive astrocytes and less DNA damage in IHC images of stroke brains. The results implied that A1 and A2 astrocytes play certain roles in ischemic brains and recovery. The goal of this study is to determine the mechanisms of GLP-1 involving in astrocytic fate decision and approach on minimizing detrimental effects and amplifying the beneficial effects, which possibly develop innovative therapies for ischemic stroke. The study is supported by 108-2320-B-182A-005-MY3 and 112-2320-B-182A-003- from Taiwan National Science and Technology Council. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Glucagon-based therapy for people with diabetes and obesity: What is the sweet spot?

People with obesity and type 2 diabetes have a high prevalence of metabolic-associated steatotic liver disease, hyperlipidemia and cardiovascular disease. Glucagon increases hepatic glucose production; it also decreases hepatic fat accumulation, improves lipidemia and increases energy expenditure. Pharmaceutical strategies to antagonize the glucagon receptor improve glycemic outcomes in people with diabetes and obesity, but they increase hepatic steatosis and worsen dyslipidemia. Co-agonism of the glucagon and glucagon-like peptide-1 (GLP-1) receptors has emerged as a promising strategy to improve glycemia in people with diabetes and obesity. Addition of glucagon receptor agonism enhances weight loss, reduces liver fat and ameliorates dyslipidemia. Prior to clinical use, however, further studies are needed to investigate the safety and efficacy of glucagon and GLP-1 receptor co-agonists in people with diabetes and obesity and related conditions, with specific concerns regarding a higher prevalence of gastrointestinal side effects, loss of muscle mass and increases in heart rate. Furthermore, co-agonists with differing ratios of glucagon:GLP-1 receptor activity vary in their clinical effect; the optimum balance is yet to be identified.

DPP-4 inhibitors sitagliptin and PF-00734,200 mitigate dopaminergic neurodegeneration, neuroinflammation and behavioral impairment in the rat 6-OHDA model of Parkinson's disease.

Epidemiological studies report an elevated risk of Parkinson's disease (PD) in patients with type 2 diabetes mellitus (T2DM) that is mitigated in those prescribed dipeptidyl peptidase 4 (DPP-4) inhibitors. With an objective to characterize clinically translatable doses of DPP-4 inhibitors (gliptins) in a well-characterized PD rodent model, sitagliptin, PF-00734,200 or vehicle were orally administered to rats initiated either 7-days before or 7-days after unilateral medial forebrain bundle 6-hydroxydopamine (6-OHDA) lesioning. Measures of dopaminergic cell viability, dopamine content, neuroinflammation and neurogenesis were evaluated thereafter in ipsi- and contralateral brain. Plasma and brain incretin and DPP-4 activity levels were quantified. Furthermore, brain incretin receptor levels were age-dependently evaluated in rodents, in 6-OHDA challenged animals and human subjects with/without PD. Cellular studies evaluated neurotrophic/neuroprotective actions of combined incretin administration. Pre-treatment with oral sitagliptin or PF-00734,200 reduced methamphetamine (meth)-induced rotation post-lesioning and dopaminergic degeneration in lesioned substantia nigra pars compacta (SNc) and striatum. Direct intracerebroventricular gliptin administration lacked neuroprotective actions, indicating that systemic incretin-mediated mechanisms underpin gliptin-induced favorable brain effects. Post-treatment with a threefold higher oral gliptin dose, likewise, mitigated meth-induced rotation, dopaminergic neurodegeneration and neuroinflammation, and augmented neurogenesis. These gliptin-induced actions associated with 70-80% plasma and 20-30% brain DPP-4 inhibition, and elevated plasma and brain incretin levels. Brain incretin receptor protein levels were age-dependently maintained in rodents, preserved in rats challenged with 6-OHDA, and in humans with PD. Combined GLP-1 and GIP receptor activation in neuronal cultures resulted in neurotrophic/neuroprotective actions superior to single agonists alone. In conclusion, these studies support further evaluation of the repurposing of clinically approved gliptins as a treatment strategy for PD.

Synthetic exendin-4 disrupts responding to reward predictive incentive cues in male rats.

Synthetic exendin-4 (EX4, exenatide), is a GLP-1 receptor agonist used clinically to treat glycemia in Type-2 diabetes mellitus. EX4 also promotes weight loss and alters food reward-seeking behaviors in part due to activation of GLP-1 receptors in the mesolimbic dopamine system. Evidence suggests that GLP-1 receptor activity can directly attenuate cue-induced reward seeking. Here, we tested the effects of EX4 (0.6, 1.2, and 2.4 μg/kg, i.p.) on incentive cue (IC) responding, using a task where rats emit a nosepoke response during an intermittent reward-predictive IC to obtain a sucrose reward. EX4 dose-dependently attenuated responding to ICs and increased the latencies to respond to the IC and enter the sucrose reward cup. Moreover, EX4 dose-dependently decreased the total number of active port nosepokes for every cue presented. There was no effect of EX4 on the number of reward cup entries per reward earned, a related reward-seeking metric with similar locomotor demand. There was a dose-dependent interaction between the EX4 dose and session time on the responding to ICs and nosepoke response latency. The interaction indicated that effects of EX4 at the beginning and end of the session differed by the dose of EX4, suggesting dose-dependent pharmacokinetic effects. EX4 had no effect on free sucrose consumption behavior (i.e., total volume consumed, bout size, number of bouts) within the range of total sucrose volumes obtainable during the IC task (~3.5 ml). However, when rats were given unrestricted access for 1 h, where rats obtained much larger total volumes of sucrose (~30 ml), we observed some dose-dependent EX4 effects on drinking behavior, including decreases in total volume consumed. Together, these findings suggest that activation of the GLP-1 receptor modulates the incentive properties of cues attributed with motivational significance.

Baicalein: a potential GLP-1R agonist improves cognitive disorder of diabetes through mitophagy enhancement

There is increasing evidence that the activation of glucagon-like peptide-1 receptor (GLP-1R) can be used as a therapeutic intervention for cognitive disorders. Here, we have screened GLP-1R targeted compounds from Scutellaria baicalensis, which revealed baicalein is a potential GLP-1R small-molecule agonist. Mitophagy, a selective autophagy pathway for mitochondrial quality control, plays a neuroprotective role in multiple cognitive impairment diseases. We noticed that Glp1r knock-out (KO) mice present cognitive impairment symptoms and appear worse in spatial learning memory and learning capacity in Morris water maze (MWM) test than their wide-type (WT) counterparts. Our mechanistic studies revealed that mitophagy is impaired in hippocampus tissue of diabetic mice and Glp1r KO mice. Finally, we verified that the cognitive improvement effects of baicalein on diabetic cognitive dysfunction occur through the enhancement of mitophagy in a GLP-1R-dependent manner. Our findings shed light on the importance of GLP-1R for cognitive function maintenance, and revealed the vital significance of GLP-1R for maintaining mitochondrial homeostasis. Furthermore, we identified the therapeutic potential of baicalein in the treatment of cognitive disorder associated with diabetes.

Maternal GLP-1 receptor activation inhibits fetal growth.

Glucagon-like peptide 1 (GLP-1) regulates food intake, insulin production, and metabolism. Our recent study demonstrated that pancreatic α-cells-secreted (intraislet) GLP-1 effectively promotes maternal insulin secretion and metabolic adaptation during pregnancy. However, the role of circulating GLP-1 in maternal energy metabolism remains largely unknown. Our study aims to investigate systemic GLP-1 response to pregnancy and its regulatory effect on fetal growth. Using C57BL/6 mice, we observed a gradual decline in maternal blood GLP-1 concentrations. Subsequent administration of the GLP-1 receptor agonist semaglutide (Sem) to dams in late pregnancy revealed a modest decrease in maternal food intake during initial treatment. At the same time, no significant alterations were observed in maternal body weight or fat mass. Notably, Sem-treated dams exhibited a significant decrease in fetal body weight, which persisted even following the restoration of maternal blood glucose levels. Despite no observable change in placental weight, a marked reduction in the placenta labyrinth area from Sem-treated dams was evident. Our investigation further demonstrated a substantial decrease in the expression levels of various pivotal nutrient transporters within the placenta, including glucose transporter one and sodium-neutral amino acid transporter one, after Sem treatment. In addition, Sem injection led to a notable reduction in the capillary area, number, and surface densities within the labyrinth. These findings underscore the crucial role of modulating circulating GLP-1 levels in maternal adaptation, emphasizing the inhibitory effects of excessive GLP-1 receptor activation on both placental development and fetal growth.NEW & NOTEWORTHY Our study reveals a progressive decline in maternal blood glucagon-like peptide 1 (GLP-1) concentration. GLP-1 receptor agonist injection in late pregnancy significantly reduced fetal body weight, even after restoration of maternal blood glucose concentration. GLP-1 receptor activation significantly reduced the placental labyrinth area, expression of some nutrient transporters, and capillary development. Our study indicates that reducing maternal blood GLP-1 levels is a physiological adaptation process that benefits placental development and fetal growth.

GLP-1 Receptor Signaling Has Different Effects on the Perikarya and Axons of the Hypophysiotropic Thyrotropin-Releasing Hormone Synthesizing Neurons in Male Mice.

Background: Glucagon-like peptide 1 (GLP-1) is involved in the regulation of energy and glucose homeostasis. As GLP-1 has similar effects on the energy homeostasis as the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons that regulate the hypothalamic-pituitary-thyroid (HPT) axis, we raised the possibility that the TRH neurons are involved in the mediation of the effects of GLP-1. Therefore, the relationship and interaction of the GLP-1 system and the TRH neurons of the hypothalamic paraventricular nucleus (PVN) were studied. Methods: To examine the anatomical and functional relationship of TRH neurons and the GLP-1 system in the PVN, immunocytochemistry, in situ hybridization, in vitro patch-clamp electrophysiology, metabolic phenotyping, and explant experiments were performed. Results: Our data demonstrate that the TRH neurons of the PVN are innervated by GLP-1 producing neurons and express the GLP-1 receptor (GLP-1R). However, not only do the GLP-1-innervated TRH neurons express GLP-1R but the receptor is also present in the axons of the hypophysiotropic TRH neurons in the blood-brain barrier free median eminence (ME) suggesting that peripherally derived GLP-1 may also influence the TRH neurons. In vitro, GLP-1 increased the firing rate of TRH neurons and depolarized them. In addition, GLP-1 directly stimulated the GABAergic input of a population of TRH neurons. Furthermore, GLP-1 inhibited the release of TRH from the hypophysiotropic axons in the ME. In vivo, peripheral GLP-1R agonist administration markedly inhibited the food intake and the energy expenditure, but had no effect on the TRH expression in the PVN and resulted in lower circulating free T4 levels. Conclusions: Our results indicate that GLP-1R activation has a direct stimulatory effect on TRH neurons in the PVN, but the activation of GLP-1R may also inhibit TRH neurons by facilitating their inhibitory inputs or by inhibiting the axon terminals of these cells in the ME. The innervation of TRH neurons by GLP-1 neurons suggests that TRH neurons might be influenced by both circulating GLP-1 and by GLP-1 neurons of the nucleus tractus solitarii. The lack of GLP-1R agonist-induced regulation of TRH neurons in vivo suggests that the HPT axis does not mediate the GLP-1R agonist-induced weight loss.

Glucagon-like peptide-1 receptor blockade impairs islet secretion and glucose metabolism in humans.

BACKGROUNDProglucagon can be processed to glucagon-like peptide1 (GLP-1) within the islet, but its contribution to islet function in humans remains unknown. We sought to understand whether pancreatic GLP-1 alters islet function in humans and whether this is affected by type 2 diabetes.METHODSWe therefore studied individuals with and without type 2 diabetes on two occasions in random order. On one occasion, exendin 9-39, a competitive antagonist of the GLP-1 Receptor (GLP1R), was infused, while on the other, saline was infused. The tracer dilution technique ([3-3H] glucose) was used to measure glucose turnover during fasting and during a hyperglycemic clamp.RESULTSExendin 9-39 increased fasting glucose concentrations; fasting islet hormone concentrations were unchanged, but inappropriate for the higher fasting glucose observed. In people with type 2 diabetes, fasting glucagon concentrations were markedly elevated and persisted despite hyperglycemia. This impaired suppression of endogenous glucose production by hyperglycemia.CONCLUSIONThese data show that GLP1R blockade impairs islet function, implying that intra-islet GLP1R activation alters islet responses to glucose and does so to a greater degree in people with type 2 diabetes.TRIAL REGISTRATIONThis study was registered at ClinicalTrials.gov NCT04466618.FUNDINGThe study was primarily funded by NIH NIDDK DK126206. AV is supported by DK78646, DK116231 and DK126206. CDM was supported by MIUR (Italian Minister for Education) under the initiative "Departments of Excellence" (Law 232/2016).

Glucagon-like peptide-1 receptor activation stimulates PKA-mediated phosphorylation of Raptor and this contributes to the weight loss effect of liraglutide.

The canonical target of the glucagon-like peptide-1 receptor (GLP-1R), Protein Kinase A (PKA), has been shown to stimulate mechanistic Target of Rapamycin Complex 1 (mTORC1) by phosphorylating the mTOR-regulating protein Raptor at Ser791 following β-adrenergic stimulation. The objective of these studies is to test whether GLP-1R agonists similarly stimulate mTORC1 via PKA phosphorylation of Raptor at Ser791 and whether this contributes to the weight loss effect of the therapeutic GLP-1R agonist liraglutide. We measured phosphorylation of the mTORC1 signaling target ribosomal protein S6 in Chinese Hamster Ovary cells expressing GLP-1R (CHO-Glp1r) treated with liraglutide in combination with PKA inhibitors. We also assessed liraglutide-mediated phosphorylation of the PKA substrate RRXS*/T* motif in CHO-Glp1r cells expressing Myc-tagged wild-type (WT) Raptor or a PKA-resistant (Ser791Ala) Raptor mutant. Finally, we measured the body weight response to liraglutide in WT mice and mice with a targeted knock-in of PKA-resistant Ser791Ala Raptor. Liraglutide increased phosphorylation of S6 and the PKA motif in WT Raptor in a PKA-dependent manner but failed to stimulate phosphorylation of the PKA motif in Ser791Ala Raptor in CHO-Glp1r cells. Lean Ser791Ala Raptor knock-in mice were resistant to liraglutide-induced weight loss but not setmelanotide-induced (melanocortin-4 receptor-dependent) weight loss. Diet-induced obese Ser791Ala Raptor knock-in mice were not resistant to liraglutide-induced weight loss; however, there was weight-dependent variation such that there was a tendency for obese Ser791Ala Raptor knock-in mice of lower relative body weight to be resistant to liraglutide-induced weight loss compared to weight-matched controls. Together, these findings suggest that PKA-mediated phosphorylation of Raptor at Ser791 contributes to liraglutide-induced weight loss.

GLP-1 receptor agonism and GIP receptor antagonism induce substantial alterations in enteroendocrine and islet cell populations in obese high fat fed mice

Effects of sustained activation of glucagon-like peptide-1 (GLP-1) receptors (GLP-1R) as well as antagonism of receptors for glucose-dependent insulinotropic peptide (GIP) on intestinal morphology and related gut hormone populations have not been fully investigated. The present study assesses the impact of 21-days twice daily treatment with the GLP-1R agonist exendin-4 (Ex-4), or the GIP receptor (GIPR) antagonist mGIP(3−30), on these features in obese mice fed a high fat diet (HFD). HFD mice presented with reduced crypt depth when compared to normal diet (ND) controls, which was reversed by Ex-4 treatment. Both regimens lead to an enlargement of villi length in HFD mice. HFD mice had increased numbers of GIP and PYY positive ileal cells, with both treatment interventions reversing the effect on PYY positive cells, but only Ex-4 restoring GIP ileal cell populations to ND levels. Ex-4 and mGIP (3−30) marginally decreased GLP-1 villi immunoreactivity and countered the reduction of ileal GLP-1 content caused by HFD. As expected, HFD mice presented with elevated pancreatic islet area. Interestingly, mGIP(3−30), but not Ex-4, enhanced islet and beta-cell areas in HFD mice despite lack of effect of beta-cell turnover, whilst Ex-4 increased delta-cell area. Co-localisation of islet PYY or GLP-1 with glucagon was increased by Ex-4, whilst islet PYY co-immunoreactivity with somatostatin was enhanced by mGIP(3−30) treatment. These observations highlight potential new mechanisms linked to the metabolic benefits of GLP-1R agonism and GIPR antagonism in obesity.

Exendin-4 promotes retinal ganglion cell survival and function by inhibiting calcium channels in experimental diabetes

Progressive damage of retinal ganglion cells (RGCs) is observed in early diabetic retinopathy. Intracellular Ca2+ overload mediated by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) is involved in neurodegeneration, whereas glucagon-like peptide-1 (GLP-1) provides neuroprotection. However, whether GLP-1 plays a neuroprotective role in diabetic retinas by modulating VGCCs remains unknown. We found that eye drops of exendin-4, a long-acting GLP-1 receptor (GLP-1R) agonist, prevented the increase of L-type Ca2+ current (ILCa) densities of RGCs induced by 4-week hyperglycemia and promoted RGC survival by suppressing L-type VGCC (L-VGCC) activity in streptozotocin-induced diabetic rats. Moreover, exendin-4-induced suppression of ILCa in RGCs may be mediated by a GLP-1R/Gs/cAMP-PKA/ryanodine/Ca2+/calmodulin/calcineurin/PP1 signaling pathway. Furthermore, exendin-4 functionally improved the light-evoked spiking ability of diabetic RGCs. These results suggest that GLP-1R activation enhances cAMP to PP1 signaling and that PP1 inactivates L-VGCCs by dephosphorylating them, thereby reducing Ca2+ influx, which could protect RGCs against excitotoxic Ca2+ overload.

The importance of glucose-dependent insulinotropic polypeptide receptor activation for the effects of tirzepatide.

Tirzepatide is a unimolecular co-agonist of the glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors recently approved for the treatment of type 2 diabetes by the US Food and Drug Administration and the European Medicine Agency. Tirzepatide treatment results in an unprecedented improvement of glycaemic control and lowering of body weight, but the contribution of the GIP receptor-activating component of tirzepatide to these effects is uncertain. In this review, we present the current knowledge about the physiological roles of the incretin hormones GLP-1 and GIP, their receptors, and previous results of co-targeting the two incretin hormone receptors in humans. We also analyse the molecular pharmacological, preclinical and clinical effects of tirzepatide to discuss the role of GIP receptor activation for the clinical effects of tirzepatide. Based on the available literature on the combination of GLP-1 and GIP receptor activation, tirzepatide does not seem to have a classical co-activating mode of action in humans. Rather, in vitro studies of the human GLP-1 and GIP receptors reveal a biased GLP-1 receptor activation profile and GIP receptor downregulation. Therefore, we propose three hypotheses for the mode of action of tirzepatide, which can be addressed in future, elaborate clinical trials.

Liraglutide restores impaired associative learning in individuals with obesity

Survival under selective pressure is driven by the ability of our brain to use sensory information to our advantage to control physiological needs. To that end, neural circuits receive and integrate external environmental cues and internal metabolic signals to form learned sensory associations, consequently motivating and adapting our behaviour. The dopaminergic midbrain plays a crucial role in learning adaptive behaviour and is particularly sensitive to peripheral metabolic signals, including intestinal peptides, such as glucagon-like peptide 1 (GLP-1). In a single-blinded, randomized, controlled, crossover basic human functional magnetic resonance imaging study relying on a computational model of the adaptive learning process underlying behavioural responses, we show that adaptive learning is reduced when metabolic sensing is impaired in obesity, as indexed by reduced insulin sensitivity (participants: N = 30 with normal insulin sensitivity; N = 24 with impaired insulin sensitivity). Treatment with the GLP-1 receptor agonist liraglutide normalizes impaired learning of sensory associations in men and women with obesity. Collectively, our findings reveal that GLP-1 receptor activation modulates associative learning in people with obesity via its central effects within the mesoaccumbens pathway. These findings provide evidence for how metabolic signals can act as neuromodulators to adapt our behaviour to our body’s internal state and how GLP-1 receptor agonists work in clinics.

Liraglutide pretreatment attenuates sepsis-induced acute lung injury.

There are no effective targeted therapies to treat acute respiratory distress syndrome (ARDS). Recently, the commonly used diabetes and obesity medications, glucagon-like peptide-1 (GLP-1) receptor agonists, have been found to have anti-inflammatory properties. We, therefore, hypothesized that liraglutide pretreatment would attenuate murine sepsis-induced acute lung injury (ALI). We used a two-hit model of ALI (sepsis+hyperoxia). Sepsis was induced by intraperitoneal injection of cecal slurry (CS; 2.4 mg/g) or 5% dextrose (control) followed by hyperoxia [HO; fraction of inspired oxygen ([Formula: see text]) = 0.95] or room air (control; [Formula: see text] = 0.21). Mice were pretreated twice daily with subcutaneous injections of liraglutide (0.1 mg/kg) or saline for 3 days before initiation of CS+HO. At 24-h post CS+HO, physiological dysfunction was measured by weight loss, severity of illness score, and survival. Animals were euthanized, and bronchoalveolar lavage (BAL) fluid, lung, and spleen tissues were collected. Bacterial burden was assessed in the lung and spleen. Lung inflammation was assessed by BAL inflammatory cell numbers, cytokine concentrations, lung tissue myeloperoxidase activity, and cytokine expression. Disruption of the alveolar-capillary barrier was measured by lung wet-to-dry weight ratios, BAL protein, and epithelial injury markers (receptor for advanced glycation end products and sulfated glycosaminoglycans). Histological evidence of lung injury was quantified using a five-point score with four parameters: inflammation, edema, septal thickening, and red blood cells (RBCs) in the alveolar space. Compared with saline treatment, liraglutide improved sepsis-induced physiological dysfunction and reduced lung inflammation, alveolar-capillary barrier disruption, and lung injury. GLP-1 receptor activation may hold promise as a novel treatment strategy for sepsis-induced ARDS. Additional studies are needed to better elucidate its mechanism of action.NEW & NOTEWORTHY In this study, pretreatment with liraglutide, a commonly used diabetes medication and glucagon-like peptide-1 (GLP-1) receptor agonist, attenuated sepsis-induced acute lung injury in a two-hit mouse model (sepsis + hyperoxia). Septic mice who received the drug were less sick, lived longer, and displayed reduced lung inflammation, edema, and injury. These therapeutic effects were not dependent on weight loss. GLP-1 receptor activation may hold promise as a new treatment strategy for sepsis-induced acute respiratory distress syndrome.

Cerebral glucagon-like peptide-1 receptor activation alleviates traumatic brain injury by glymphatic system regulation in mice.

We aimed to assess the effects of cerebral glucagon-like peptide-1 receptor (GLP-1R) activation on the glymphatic system and whether this effect was therapeutic for traumatic brain injury (TBI). Immunofluorescence was employed to evaluate glymphatic system function. The blood-brain barrier (BBB) permeability, microvascular basement membrane, and tight junction expression were assessed using Evans blue extravasation, immunofluorescence, and western blot. Immunohistochemistry was performed to assess axonal damage. Neuronal apoptosis was evaluated using Nissl staining, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining, and western blot. Cognitive function was assessed using behavioral tests. Cerebral GLP-1R activation restored glymphatic transport following TBI, alleviating BBB disruption and neuronal apoptosis, thereby improving cognitive function following TBI. Glymphatic function suppression by treatment using aquaporin 4 inhibitor TGN-020 abolished the protective effect of the GLP-1R agonist against cognitive impairment. Cerebral GLP-1R activation can effectively ameliorate neuropathological changes and cognitive impairment following TBI; the underlying mechanism could involve the repair of the glymphatic system damaged by TBI.

1547-P: The Differential Effect of Glucagon-Like Peptide-1 Receptor Blockade on Glucose Metabolism in People With and Without Type 2 Diabetes

Glucagon-Like Peptide-1 (GLP-1) is present within the islet but the effects of GLP-1 Receptor (GLP1R) blockade on islet function in humans remains unknown. To address this, we studied 12 nondiabetic individuals (54 ± 2 years, 33 ± 1 kg/m2) and 11 people with type 2 diabetes (DM2 - 58 ± 2 years, 34 ± 2 kg/m2) on 2 occasions in random order. On each occasion, after an overnight fast, [3-3H] glucose was used to measure glucose turnover during fasting and a hyperglycemic clamp (~9 mmol/l) using the tracer dilution technique. On one occasion exendin-9,39 (300pmol/kg/min) was infused to block GLP1R, while on the other saline was infused. Exendin-9,39 increased fasting glucose concentrations in those without (4.6 ± 0.4 vs. 5.5 ± 0.1 mmol/l, saline vs. exendin-9,39 respectively, p = 0.04) and in those with DM2 (7.3 ± 0.5 vs. 8.3 ± 0.6 mmol/l, p = 0.03). Fasting islet hormone concentrations were unchanged, but inappropriate for the higher fasting glucose observed during exendin-9,39 infusion. The same pattern was seen in people with DM2 except that fasting glucagon concentrations increased (8.3 ± 0.5 vs. 10.2 ± 0.6 pmol/l, p < 0.01) and remained elevated throughout hyperglycemia (4.7 ± 0.4 vs. 7.7 ± 0.6 pmol/l, p < 0.02). Insulin secretion rate calculated by deconvolution of C-peptide concentrations was also decreased in DM2 (0.54 ± 0.08 vs. 0.51 ± 0.08 nmol/min, p = 0.02). Consequently, suppression of endogenous glucose production by hyperglycemia was impaired in people with DM2 (2.9 ± 0.4 vs. 5.7 ± 0.3 μmol/kg/min, p < 0.01). Intriguingly, 1st phase response to hyperglycemia was decreased in those without DM2 (3.5 ± 0.6 vs. 2.5 ± 0.5 nmol per 10 min, p = 0.04). These data show that in humans, GLP1R blockade impairs fasting α- and β-cell function resulting in fasting hyperglycemia. Subtle effects are also present in response to hyperglycemia. This implies that intra-islet GLP1R activation sustains islet responses to glucose and it does so to a greater degree in people with DM2. Disclosure A.A. Welch: None. R.A. Farahani: None. M. Zeini: None. A.M. Egan: None. M.C. Laurenti: None. C. Cobelli: None. C. Dalla Man: Research Support; Sanofi-Aventis Deutschland GmbH, Becton, Dickinson and Company. A. Vella: Other Relationship; Novo Nordisk. Advisory Panel; Rezolute, Inc. Consultant; Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Zealand Pharma A/S. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK126206)

767-P: TERN-601, a Novel Oral GLP-1R Agonist, Suppresses Food Intake and Improves Glucose Tolerance in Transgenic Mice Expressing Human GLP-1 Receptor

Synthetic peptide agonists of the GLP-1 receptor (GLP-1R) are approved for the treatment of diabetes and obesity based on their ability to lower blood glucose and induce weight loss. TERN-601 is a novel, oral small molecule GLP-1R agonist in preclinical development. In vitro, TERN-601 potently stimulated (EC50 = 2.9 ± 0.8 nM) intracellular cAMP generation, a downstream consequence of GLP-1R activation, in CHO-K1 cells stably expressing human GLP-1R. In vivo, single oral doses of TERN-601 (10, 30, or 60 mg/kg) led to significant dose-dependent suppression of food intake (2- to 24-hours post dose) in transgenic C57BL/6J mice (n = 10 per group) expressing human GLP-1R (hGLP-1R). In an intraperitoneal glucose tolerance test (IPGTT) on overnight fasted hGLP-1R mice (n = 7 per group), single oral doses of TERN-601 (0.3, 1, and 3 mg/kg) administered 30 minutes prior to IP glucose injection significantly lowered blood glucose area under the curve (AUC0-120min) with comparable efficacy to liraglutide (0.3 mg/kg). TERN-601 is a potent, orally bioavailable small molecule agonist of human GLP-1R in preclinical development for the treatment of chronic obesity. In transgenic mice expressing human GLP-1R, single oral doses of TERN-601 significantly suppressed food intake and improved glucose tolerance. Together these data support the continued development of TERN-601. Disclosure C.Jones: Employee; Terns Pharmaceuticals. K.P.Quinn: None. C.H.Nelson: Employee; Terns Pharmaceuticals, Gilead Sciences, Inc., Stock/Shareholder; Terns Pharmaceuticals, Gilead Sciences, Inc. O.Osborn: Employee; Terns, Stock/Shareholder; ClicBio. G.Luehr: None. J.R.Jasper: Advisory Panel; Rubedo Life Sciences, Employee; Terns Pharmaceuticals, Rubedo Life Sciences.

Optical tools for visualizing and controlling human GLP-1 receptor activation with high spatiotemporal resolution

The glucagon-like peptide-1 receptor (GLP1R) is a broadly expressed target of peptide hormones with essential roles in energy and glucose homeostasis, as well as of the blockbuster weight-loss drugs semaglutide and liraglutide. Despite its large clinical relevance, tools to investigate the precise activation dynamics of this receptor with high spatiotemporal resolution are limited. Here, we introduce a novel genetically encoded sensor based on the engineering of a circularly permuted green fluorescent protein into the human GLP1R, named GLPLight1. We demonstrate that fluorescence signal from GLPLight1 accurately reports the expected receptor conformational activation in response to pharmacological ligands with high sensitivity (max ΔF/F0=528%) and temporal resolution (τON = 4.7 s). We further demonstrated that GLPLight1 shows comparable responses to glucagon-like peptide-1 (GLP-1) derivatives as observed for the native receptor. Using GLPLight1, we established an all-optical assay to characterize a novel photocaged GLP-1 derivative (photo-GLP1) and to demonstrate optical control of GLP1R activation. Thus, the new all-optical toolkit introduced here enhances our ability to study GLP1R activation with high spatiotemporal resolution.