Exendin-4 Treatment Research Articles

Exendin-4 Caused Growth Arrest by Regulating Sugar Metabolism in Hyphantria cunea (Lepidoptera: Erebidae) Larvae.

Insects' growth and development are highly dependent on energy supply, with sugar metabolism playing a pivotal role in maintaining homeostasis and regulating physiological processes. The present study investigated the effects of exendin-4, a glucagon-like peptide-1 receptor (GLP-1R) agonist, on the growth, development, glycolysis, and energy metabolism of fourth-instar larvae of the fall webworm, Hyphantria cunea. We determined the impact of exendin-4 on larval growth and nutritional indices, analyzed the responses of glycolytic and metabolic pathways, and revealed the underlying regulatory mechanisms. Exendin-4 treatment significantly decreased growth and nutritional indices, influenced the activity of digestive enzymes, and induced changes in metabolite profiles, particularly affecting energy substance metabolism. We observed an increase in the glycogen content and a decrease in glucose and trehalose levels in the hemolymph, suggesting a regulatory effect on blood sugar homeostasis. Furthermore, exendin-4 promoted glycolysis by enhancing the activities and expressions of key glycolytic enzymes, leading to an increase in pyruvate production. This was accompanied by a reduction in ATP levels and the activation of AMP-activated protein kinase (AMPK), which may underlie the growth arrest in larvae. Our findings provide novel insights into the effects of exendin-4 on insect responses from an energy metabolism perspective and may contribute to the development of GLP-1R agonists for pest management.

GLP-1 receptor agonist attenuates tubular cell ferroptosis in diabetes via enhancing AMPK-fatty acid metabolism pathway through macropinocytosis

Kidney tubules are mostly responsible for pathogenesis of diabetic kidney disease. Actively reabsorption of iron, high rate of lipid metabolism and exposure to concentrated redox-active compounds constructed the three main pillars of ferroptosis in tubular cells. However, limited evidence has indicated that ferroptosis is indispensable for diabetic tubular injury. Glucagon-like peptide-1 receptor agonist (GLP-1RA) processed strong benefits on kidney outcomes in people with diabetes. Moreover, GLP-1RA may have additive effects by improving dysmetabolism besides glucose control and weight loss. Therefore, the present study aimed at exploring the benefits of exendin-4, a high affinity GLP-1RA on kidney tubular dysregulation in diabetes and the possible mechanisms involved, with focus on ferroptosis and adenosine 5′-monophosphate-activated protein kinase (AMPK)-mitochondrial lipid metabolism pathway. Our data revealed that exendin-4 treatment markedly improved kidney structure and function by reducing iron overload, oxidative stress, and ACSL4-driven lipid peroxidation taken place in diabetic kidney tubules, along with reduced GPX4 expression and GSH content. AMPK signaling was identified as the downstream target of exendin-4, and enhancement of AMPK triggered the transmit of its downstream signal to activate fatty acid oxidation in mitochondria and suppress lipid synthesis and glycolysis, and ultimately alleviated toxic lipid accumulation and ferroptosis. Further study suggested that exendin-4 was taken up by tubular cells via macropinocytosis. The protective effect of exendin-4 on tubular ferroptosis was abolished by macropinocytosis blockade. Taken together, present work demonstrated the beneficial effects of GLP-1RA treatment on kidney tubular protection in diabetes by suppressing ferroptosis through enhancing AMPK-fatty acid metabolic signaling via macropinocytosis.

Glucagon-like peptide 1 receptor agonist, exendin-4, reduces alcohol-associated fatty liver disease

Fatty liver is the earliest response to excessive ethanol consumption, which increases the susceptibility of the liver to develop advanced stage of liver disease. Our previous studies have revealed that chronic alcohol administration alters metabolic hormone levels and their functions. Of current interest to our laboratory is glucagon-like peptide 1 (GLP-1), a widely studied hormone known to reduce insulin resistance and hepatic fat accumulation in patients with metabolic-associated fatty liver disease. In this study, we examined the beneficial effects of exendin-4 (a GLP-1 receptor agonist) in an experimental rat model of ALD. Male Wistar rats were pair-fed the Lieber-DeCarli control or ethanol diet. After 4 weeks of this feeding regimen, a subset of rats in each group were intraperitoneally injected every other day with either saline or exendin-4 at a dose of 3 nmol/kg/day (total 13 doses) while still being fed their respective diet. At the end of the treatment, rats were fasted for 6 h and glucose tolerance test was conducted. The following day, the rats were euthanized, and the blood and tissue samples collected for subsequent analysis. We found that exendin-4 treatment had no significant effect on body weight gain among the experimental groups. Exendin-4-treated ethanol rats exhibited improved alcohol-induced alterations in liver/body weight and adipose/body weight ratio, serum ALT, NEFA, insulin, adiponectin and hepatic triglyceride levels. Reduction in indices of hepatic steatosis in exendin-4 treated ethanol-fed rats was attributed to improved insulin signaling and fat metabolism. These results strongly suggest that exendin-4 mitigates alcohol-associated hepatic steatosis by regulating fat metabolism.

Acute Cholesterol-Lowering Effect of Exendin-4 in Ldlr-/- and C57BL/6J Mice.

We previously reported that glucagon-like peptide-1 receptor agonists (GLP-1RAs) reduced serum low-density lipoprotein cholesterol (LDL-C) levels in patients with type 2 diabetes mellitus receiving statins, which increased LDL receptor (LDLR) expression. Nevertheless, it remains unclear how much LDLR expression contributes to the LDL-C-lowering effect of GLP-1RAs. We examined the effect of a GLP-1RA, namely, exendin-4, on serum LDL-C levels and its mechanism in Ldlr-/- and C57BL/6J mice. Ten-week-old Ldlr-/- and C57BL/6J mice received exendin-4 or saline for 5 days, and serum lipid profiles and hepatic lipid levels were examined. Cholesterol metabolism-related gene expression and protein levels in the liver and ileum and the fecal bile acid (BA) composition were also examined. Exendin-4 treatment significantly decreased serum very-low-density lipoprotein cholesterol (VLDL-C) and LDL-C levels and mature hepatic SREBP2 levels and increased hepatic Insig1/2 mRNA expression in both mouse strains. In Ldlr-/- mice, exendin-4 treatment also significantly decreased hepatic cholesterol levels and fecal BA excretion, decreased hepatic Cyp7a1 mRNA expression, and increased small intestinal Fgf15 mRNA expression. In C57BL/6J mice, exendin-4 treatment significantly decreased small intestinal NPC1L1 levels. Our findings demonstrate that exendin-4 treatment decreased serum VLDL-C and LDL-C levels in a manner that was independent of LDLR. Exendin-4 treatment might decrease serum cholesterol levels by lowering hepatic SREBP2 levels and cholesterol absorption in Ldlr-/- and C57BL/6J mice. Exendin-4 treatment might decrease cholesterol absorption by different mechanisms in Ldlr-/- and C57BL/6J mice.

Considering the protective effect of exendin-4 against oxidative stress in spiral ganglion neurons.

The protection of spiral ganglion neurons (SGNs) is crucial for hearing loss. Exendin-4 has been shown to have neuroprotective effects in several neurological disorders. Therefore, this study aimed to investigate the effect of the glucagon-like protein-1 receptor (GLP-1R) agonist exendin-4 on kanamycin-induced injury in mouse SGNs in vitro. In this study, GLP-1R expression in SGNs was verified by immunofluorescence and immunohistochemical staining. In vitro-cultured SGNs and the organ of Corti were exposed to kanamycin with or without exendin-4 treatment. The cell survival rate was measured using the cell counting kit-8 assay, and the damage to auditory nerve fibers (ANF) projecting radially from the SGNs was evaluated using immunofluorescence staining. Reactive oxygen species (ROS) content was determined by flow cytometry, and glutathione peroxidase (GSH-Px) content, superoxide dismutase (SOD) activity, and malondialdehyde (MDA) content were determined by spectrophotometry. Protein expression of nuclear factor erythroid-2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) was detected using western blotting. GLP-1R was expressed in SGNs. Treatment with 1 mM kanamycin for 24 hr induced SGN damage. Exendin-4 (100 nM) had a protective effect against kanamycin-induced SGN cell injury, improved cell survival rate, reduced nerve fiber injury, increased SOD activity and GSH-Px level, and reduced MDA and ROS contents. The Nrf2/HO-1 pathway was activated. Exendin-4 alleviates oxidative damage and exerts neuroprotective effects in kanamycin-induced SGN injury through the Nrf2/HO-1 signaling pathway. Exendin-4 has the potential to prevent or treat hearing loss due to SGN damage.

Exendin-4 Exacerbates Burn-Induced Mortality in Mice by Switching to Th2 Response

IntroductionTo determine if Exendin-4 could be a therapeutic agent for burn-induced hyperglycemia. Materials and methodsMale Balb/c mice received a bolus of Exendin-4 intraperitoneally immediately after 15% total body surface area scald injury. Tail glucose levels were recorded and T-cell functions were analyzed at 4 h and 24 h postburn (pb). Pancreatic pathology was observed consecutively. The secretions of cytokines were detected in serum, spleen, and lung. Apoptosis of splenic CD3+ T-cells was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and flow cytometry. ResultsAlthough Exendin-4 could attenuate burn-induced hyperglycemia in mice at 4 h pb, it accelerated their survival dose dependently with progressive depletion of splenocyte number. T-cell function underwent two-phasic changes following Exendin-4 treatment. Compared to placebo mice, T-cell from Exendin-4–treated mice was manifested with increased proliferation, while decreased IL-2 secretion and lower ratio of IL-4/IFN-γ at 4 h pb. However, at 24 h pb, it showed decreased proliferation, while increased IL-2 secretion and higher ratio of IL-4/IFN-γ. Exendin-4 could elicit higher circulating IL-6 and IL-10 levels at 4 h pb, which were pronounced in the lung at 24 h pb. In the meanwhile, severe inflammation could be found in the pancreas. At 24 h pb, the numbers of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling or caspase-3 positive cells and the apoptosis of CD3+ T-cells were significantly increased in the spleens of Exendin-4 mice relative to placebo mice. ConclusionsThese data support a pathogenic role of Exendin-4 signaling during thermal injury, warning against its clinical application in acute insults.

Exendin-4 alleviates β-Amyloid peptide toxicity via DAF-16 in a Caenorhabditis elegans model of Alzheimer's disease.

Epidemiological analyses indicate that type 2 diabetes mellitus (T2DM) is a risk factor for Alzheimer's disease (AD). They share common pathophysiological mechanisms. Thus, it has been increasingly suggested that several anti-T2DM drugs may have therapeutic potential in AD. Exendin-4, as a glucagon-like peptide-1 (GLP-1) receptor agonist, is an approved drug used to treat T2DM. In this research, the neuroprotective effect of Exendin-4 was investigated for the first time using transgenic Caenorhabditis elegans. Our results demonstrated that Exendin-4 attenuated the amyloid-β (1-42) (Aβ1-42) toxicity via multiple mechanisms, such as depressing its expression on protein and mRNA and reducing Aβ (1-42) accumulation. Exendin-4 at 0.5 mg/ml had been shown to extend life by 34.39% in CL4176 and delay the onset of paralysis in CL4176 and CL2006 which were increased by 8.18 and 8.02%, respectively. With the treatment of Exendin-4, the nuclear translocation of DAF-16 in the transgenic nematode TJ356 was enhanced. Superoxide dismutase-3 (SOD-3), as a downstream target gene regulated by DAF-16, was upregulated on mRNA level and activity. The reactive oxygen species (ROS) level was decreased. In contrast, we observed that the ability of Exendin-4 to regulate SOD was decreased in CL4176 worms with the DAF-16 gene silenced. The activity of SOD and the mRNA level of sod-3 were downregulated by 30.45 and 43.13%, respectively. Taken together, Exendin-4 attenuated Aβ (1-42) toxicity in the C. elegans model of AD via decreasing the expression and the accumulation of Aβ (1-42). Exendin-4 exhibited the ability of antioxidant stress through DAF-16. With continuous research, Exendin-4 would become a potential therapeutic strategy for treating AD.

GLP-1 regulates exercise endurance and skeletal muscle remodeling via GLP-1R/AMPK pathway

Exercise-induced physical endurance enhancement and skeletal muscle remodeling can prevent and delay the development of multiple diseases, especially metabolic syndrome. Herein, the study explored the association between glucagon-like peptide-1 (GLP-1) secretion and exercise, and its effect on skeletal muscle remodeling to enhance endurance capacity. We found both acute exercise and short-term endurance training significantly increased the secretion of GLP-1 in mice. Recombinant adeno-associated virus (AAV) encoding Gcg (proglucagon) was used to induce the overexpression of GLP-1 in skeletal muscle of mice. Overexpression of GLP-1 in skeletal muscle enhanced endurance capacity. Meanwhile, glycogen synthesis, glucose uptake, type I fibers proportion, and mitochondrial biogenesis were augmented in GLP-1-AAV skeletal muscle. Furthermore, the in vitro experiment showed that exendin-4 (a GLP-1 receptor agonist) treatment remarkably promoted glucose uptake, type I fibers formation, and mitochondrial respiration. Mechanistically, the knockdown of AMPK could reverse the effects imposed by GLP-1R activation in vitro. Taken together, these results verify that GLP-1 regulates skeletal muscle remodeling to enhance exercise endurance possibly via GLP-1R signaling-mediated phosphorylation of AMPK.

Preventing Oxidative Stress in the Liver: An Opportunity for GLP-1 and/or PASK.

The liver’s high metabolic activity and detoxification functions generate reactive oxygen species, mainly through oxidative phosphorylation in the mitochondria of hepatocytes. In contrast, it also has a potent antioxidant mechanism for counterbalancing the oxidant’s effect and relieving oxidative stress. PAS kinase (PASK) is a serine/threonine kinase containing an N-terminal Per-Arnt-Sim (PAS) domain, able to detect redox state. During fasting/feeding changes, PASK regulates the expression and activation of critical liver proteins involved in carbohydrate and lipid metabolism and mitochondrial biogenesis. Interestingly, the functional inactivation of PASK prevents the development of a high-fat diet (HFD)-induced obesity and diabetes. In addition, PASK deficiency alters the activity of other nutrient sensors, such as the AMP-activated protein kinase (AMPK) and the mammalian target of rapamycin (mTOR). In addition to the expression and subcellular localization of nicotinamide-dependent histone deacetylases (SIRTs). This review focuses on the relationship between oxidative stress, PASK, and other nutrient sensors, updating the limited knowledge on the role of PASK in the antioxidant response. We also comment on glucagon-like peptide 1 (GLP-1) and its collaboration with PASK in preventing the damage associated with hepatic oxidative stress. The current knowledge would suggest that PASK inhibition and/or exendin-4 treatment, especially under fasting conditions, could ameliorate disorders associated with excess oxidative stress.

Exendin-4 may improve type 2 diabetes by modulating the epigenetic modifications of pancreatic histone H3 in STZ-induced diabetic C57BL/6J mice.

Type 2 diabetes (T2D) is a complicated systemic disease that might be improved by exendin-4, although the epigenetic role remains unclear. In the current study, C57BL/6J mice were used to generate a T2D model, followed by treatment with exendin-4 (10μg/kg). Histone H3K9 and H3K23 acetylation, H3K4 mono-methylation, and H3K9 di-methylation were explored by western blot analysis of pancreatic histone extracts. Real-time polymerase chain reaction (PCR) was used to examine the expression levels of pancreatic beta cell development-related genes, and chromatin immunoprecipitation (ChIP) was applied to analyze H3 and H3K9 acetylation, H3K4 mono-methylation, and H3K9 di-methylation in the promoter region of the pancreatic and duodenal homeobox 1 (Pdx1) gene. The results showed that total H3K9 di-methylation and H3K9 and H3K23 acetylation increased in pancreatic tissues of diabetic mice, whereas H3K4 mono-methylation was reduced. All of these changes could be abrogated by treatment with exendin-4. Our data indicated that T2D progression might be improved by exendin-4 treatment through the reversal of global pancreatic histone H3K9 and H3K23 acetylation, H3K4 mono-methylation, and H3K9 di-methylation. A better understanding of these epigenetic alterations may, therefore, lead to novel therapeutic strategies for T2D.

Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent.

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

A quinoxaline-based compound ameliorates bone loss in ovariectomized mice.

DMB (6,7-dichloro-2-methylsulfonyl-3-Ntert-butylaminoquinoxaline) is a quinoxaline-based compound that has been investigated as a glucagon-like peptide-1 receptor (GLP-1R) agonist. To clarify anti-osteoporosis effect of DMB, an osteoporotic mice model was established by ovariectomy (OVX) operation. The OVX mice were given intraperitoneally DMB, exendin-4 (EX-4), or 17β-estradiol (E2) for two months. Then bone mass and structure, and bone morphometric parameters were examined by micro-CT. Weight gain and food consumption, bone turnover markers, and biomechanical strength of the femur were tested, and bone histomorphometry was analyzed. The food intake and weight gain was obviously reduced by E2 or EX-4, but not DMB. However, DMB or EX-4 treatment obviously inhibited skeletal deterioration and enhanced bone strength. The improvement involved in the increased osteoblast number and level of bone formation markers, and reduced osteoclasts number and level of bone resorption markers. In addition, DMB was found to stimulate osteoblastogenesis-related marker gene expression. These results demonstrated that DMB ameliorated bone loss mainly via induction of bone formation, which suggests that the small molecule compound might be applied to the management of postmenopausal osteoporosis.

388-P: GLP-1 Receptor Agonists Attenuates Secretion of Extracellular Matrix via Inhibiting HMGB1 Signaling in Rat Mesangial Cells

Background: GLP-1R agonists can exhibit a direct renoprotective effect in patients with diabetic nephropathy (DN) beyond the hypoglycemic effect, but the underlying mechanisms remain unknown. Recent studies have suggested that high mobility group box 1 (HMGB1) contributes to the development and progression of DN. In this study, we assessed whether GLP-1R agonists acts through HMGB1 and explored its downstream signaling pathways in DN. Methods: Rat glomerular mesangial cells (GMCs) were divided into four groups: normal control (NG), normal control with 10 nmol/L exendin-4 treatment (GLP-1 analog) (NGE), high glucose (HG), and high glucose with 10 nmol/L exendin-4 treatment (HGE) groups. GMCs were transfected with GLP-1R-siRNA using Lipofectamine TM2000 and divided as HG, HGE, HGE + GLP-1R-siRNA, or HGE + scrambled siRNA. FN and type IV collagen (COL-IV) were evaluated by enzyme-linked immunosorbent assay (ELISA). GLP-1R, HMGB1, TGF-β1, phosphorylated and total extracellular signal-regulated kinases (ERK), c-Jun NH2-terminal kinases (JNK), p38 mitogen-activated protein kinases (p38MAPK), and NF-κB p65 were measured by western blot analysis. Results: FN and COL-IV were higher in the HG group than NG group (P<0.05). Compared with NG group, the level of GLP-1R was decreased, HMGB1 and TGF-β1 were increased in the HG group (P<0.05). Additionally, NF-κB p65, the phosphorylation levels of ERK, JNK, and p38MAPK were all significantly elevated in the HG group (P<0.05). However, all these effects were reversed by Exendin-4 treatment (P<0.05), except phosphorylated p38MAPK (P>0.05). Moreover, the protective effects of Exendin-4 were abolished by GLP-1R knockdown (P<0.05). Conclusion: These results suggest that GLP-1 receptor agonists attenuates the ECM secretion of GMCs induced by high glucose. The potential mechanism involves it binding to and activating GLP-1R, which prevents ECM production by inhibiting HMGB1 and its signaling pathways. Disclosure W. Gu: None. M. Shi: None. H. Zhang: None. Funding National Natural Science Foundation of China (81200595, 81400807, 81700723)

228-LB: ß-arrestin-2 Deletion Influences GLP-1 Receptor Signaling in Pancreatic ß Cells In Vivo

β-arrestin-2 (Barr2) is typically associated with G protein-coupled receptor desensitization and endocytosis, and reduced Barr2 recruitment is thought to enable prolongation of pharmacodynamic effects of biased glucagon-like peptide-1 receptor (GLP-1R) agonists. However, the precise role of Barr2 in GLP-1R function in β-cells is poorly understood. To study this role, a tamoxifen-inducible β-cell specific Barr2 knockout mouse model was generated (Pdx1CreERT/Barr2 fl/fl, referred to as β-Barr2 KO). β-Barr2 KO animals on high-fat high-sucrose diet were less glucose tolerant and tended to respond worse to acute exendin-4 (Ex4) treatment vs. controls (Barr2 fl/fl). However, Ex4 effects on blood glucose were more pronounced in KO mice 6h post-agonist injection [IPGTT AUC (6h) for Ex4/ vehicle: 0.84 ± 0.04 vs. 1.08 ± 0.05, p<0.001; ΔAUC (6h-0h): -49.8 ± 65.8 vs. 158.2 ± 43.6, p<0.05; KO vs. control]. This effect was not apparent with Ex-phe1, an Ex4 derivative biased away from Barr2 recruitment. Ex4-induced potentiation of insulin secretion in β-Barr2 KO islets was reduced acutely, but tended to increase overnight, resulting in significantly reduced desensitization vs. control islets. On chow diet, acute Ex4-stimulated calcium increases were unaffected, but acute cAMP responses were attenuated in KO islets [Emax (vs. baseline): 1.51 ± 0.17 vs. 1.72 ± 0.07, p<0.05; KO vs. control]. The latter was corroborated in INS1 832/3 Barr2 KO CRISPR cells, as NanoBiT™ functional assays showed reduced Ex4-induced Gs protein activation vs. control. GLP-1R trafficking profiles observed in vivo by imaging of Ex4-TMR uptake into islets implanted in the anterior chamber of the eye, as well as in vitro with GLP-1R-NLuc - KRAS/Rab5 NanoBRET assays were unaltered by Barr2 deletion. Thus, we provide evidence for opposing effects of Barr2 in acute vs. prolonged GLP-1R signaling, supporting a direct role for Barr2 in mediating the anti-hyperglycemic effects of biased GLP-1R agonists, but dispensability for GLP-1R trafficking. Disclosure S. Bitsi: None. K. Suba: None. N. Mohamed: None. I. Leclerc: Consultant; Spouse/Partner; Sun Pharmaceutical Industries Ltd. G. A. Rutter: Advisory Panel; Self; Sun Pharmaceutical Industries Ltd. V. Salem: None. B. Jones: Research Support; Self; Sun Pharmaceutical Industries Ltd. A. Tomas: Other Relationship; Self; Sun Pharmaceutical Industries Ltd. Funding Medical Research Council (MR/R010676/1)

Exendin-4 improves long-term potentiation and neuronal dendritic growth in vivo and in vitro obesity condition

Metabolic syndrome, which increases the risk of obesity and type 2 diabetes has emerged as a significant issue worldwide. Recent studies have highlighted the relationship between metabolic imbalance and neurological pathologies such as memory loss. Glucagon-like peptide 1 (GLP-1) secreted from gut L-cells and specific brain nuclei plays multiple roles including regulation of insulin sensitivity, inflammation and synaptic plasticity. Although GLP-1 and GLP-1 receptor agonists appear to have neuroprotective function, the specific mechanism of their action in brain remains unclear. We investigated whether exendin-4, as a GLP-1RA, improves cognitive function and brain insulin resistance in metabolic-imbalanced mice fed a high-fat diet. Considering the result of electrophysiological experiments, exendin-4 inhibits the reduction of long term potentiation (LTP) in high fat diet mouse brain. Further, we identified the neuroprotective effect of exendin-4 in primary cultured hippocampal and cortical neurons in in vitro metabolic imbalanced condition. Our results showed the improvement of IRS-1 phosphorylation, neuronal complexity, and the mature of dendritic spine shape by exendin-4 treatment in metabolic imbalanced in vitro condition. Here, we provides significant evidences on the effect of exendin-4 on synaptic plasticity, long-term potentiation, and neural structure. We suggest that GLP-1 is important to treat neuropathology caused by metabolic syndrome.

Neuroprotection of Exendin-4 by Enhanced Autophagy in a Parkinsonian Rat Model of α-Synucleinopathy.

Glucagon-like peptide-1 (GLP-1) receptor stimulation ameliorates parkinsonian motor and non-motor deficits in both experimental animals and patients; however, the disease-modifying mechanisms of GLP-1 receptor activation have remained unknown. The present study investigated whether exendin-4 (a GLP-1 analogue) can rescue motor deficits and exert disease-modifying effects in a parkinsonian rat model of α-synucleinopathy. This model was established by unilaterally injecting AAV-9-A53T-α-synuclein into the right substantia nigra pars compacta, followed by 4 or 8 weeks of twice-daily intraperitoneal injections of exendin-4 (5μg/kg/day) starting at 2 weeks after AAV-9-A53T-α-synuclein injections. Positron emission tomography/computed tomography (PET/CT) scanning and immunostaining established that treatment with exendin-4 attenuated tyrosine-hydroxylase-positive neuronal loss and terminal denervation and mitigated the decrease in expression of vesicular monoamine transporter 2 within the nigrostriatal dopaminergic systems of rats injected with AAV-9-A53T-α-synuclein. It also mitigated the parkinsonian motor deficits assessed in behavioral tests. Furthermore, through both in vivo and in vitro models of Parkinson's disease, we showed that exendin-4 promoted autophagy and mediated degradation of pathological α-synuclein, the effects of which were counteracted by 3-methyladenine or chloroquine, the autophagic inhibitors. Additionally, exendin-4 attenuated dysregulation of the PI3K/Akt/mTOR pathway in rats injected with AAV-9-A53T-α-synuclein. Taken together, our results demonstrate that exendin-4 treatment relieved behavioral deficits, dopaminergic degeneration, and pathological α-synuclein aggregation in a parkinsonian rat model of α-synucleinopathy and that these effects were mediated by enhanced autophagy via inhibiting the PI3K/Akt/mTOR pathway. In light of the safety and tolerance of exendin-4 administration, our results suggest that exendin-4 may represent a promising disease-modifying treatment for Parkinson's disease.

Dipeptidyl peptidase 4 promotes peritoneal fibrosis and its inhibitions prevent failure of peritoneal dialysis

Peritoneal dialysis (PD) possesses multiple advantages for end stage renal disease. However, long-term PD triggers peritoneal fibrosis (PF). From the nationwide analysis of diabetic PD patients (n = 19,828), we identified the incidence of PD failure was significantly lower in diabetic patients treated with dipeptidyl peptidase 4 (DPP4) inhibitors. Experimental study further showed high concentration of glucose remarkably enhanced DPP4 to promote epithelial-mesenchymal transition (EMT) in the mesothelial cells. In chlorhexidine gluconate (CG)-induced PF model of rats, DPP4 expression was enriched at thickening peritoneum. Moreover, as to CG-induced PF model, DPP4 deficiency (F344/DuCrlCrlj strain), sitagliptin and exendin-4 treatments significantly inhibited DPP4 to reverse the EMT process, angiogenesis, oxidative stress, and inflammation, resulting in the protection from PF, preservation of peritoneum and the corresponding functional integrity. Furthermore, DPP4 activity was significantly correlated with peritoneal dysfunction. Taken together, DPP4 caused peritoneal dysfunction/PF, whereas inhibition of DPP4 protected the PD patients against PD failure.

Exendin-4 promotes bone formation in diabetic states via HDAC1-Wnt/β-catenin axis

Exendin-4 has been found to have hypoglycemic effect and prevent bone loss in diabetic patients, but its mechanism of preventing bone loss is still unclear. In this study, high-fat diet combined with streptozotocin was used to establish type 2 diabetes mellitus (T2DM) mice, and bone marrow mesenchyme stem cells (BMSCs) were isolated for osteogenic induction in vitro. Alizarin red staining and ALP activity detection were used to observe the effect of exendin-4 on osteogenic differentiation of BMSCs. Western blot was used to detect the proteins expression in BMSCs. In vivo, the effects of exendin-4 treatment on body weight, blood glucose, bone density and bone quality of T2DM mice were observed by treatment with exendin-4. The results showed that exendin-4 promoted osteogenic differentiation of T2DM derived BMSCs, down-regulated histone deacetylase 1 (HDAC1) and p-β-Catenin proteins expression, and up-regulated Wnt3, β-Catenin and runt-related transcription factor 2 (Runx 2) proteins expression. In vivo, exendin-4 effectively suppressed the blood glucose and increased body weight of T2DM mice, and significantly improved bone density and bone quality of the right tibia. Interestingly, by over-expression of HDAC1 in BMSCs, the effect of exendin-4 on promoting osteogenic differentiation of BMSCs was attenuated, and the regulation of Wnt3a, β-Catenin, p-β-Catenin or Runx2 proteins were reversed. By injecting adenovirus containing HDAC1 into the right tibia of mice, the effect of exendin-4 on bone density and bone quality of T2DM mice was significantly attenuated. All above results suggest that the HDAC1-Wnt/β-Catenin signal axis is involved in the anti-diabetic bone loss effect of exendin-4, and HDAC1 may be the target of exendin-4.

A GLP-1 analog lowers ER stress and enhances protein folding to ameliorate homocysteine-induced endothelial dysfunction.

Hyperhomocysteinemia (HHcy) is an independent risk factor for cardiovascular diseases and increases mortality in type 2 diabetic patients. HHcy induces endoplasmic reticulum (ER) stress and oxidative stress to impair endothelial function. The glucagon-like peptide 1 (GLP-1) analog exendin-4 attenuates endothelial ER stress, but the detailed vasoprotective mechanism remains elusive. The present study investigated the beneficial effects of exendin-4 against HHcy-induced endothelial dysfunction. Exendin-4 pretreatment reversed homocysteine-induced impairment of endothelium-dependent relaxations in C57BL/6 mouse aortae ex vivo. Four weeks subcutaneous injection of exendin-4 restored the impaired endothelial function in both aortae and mesenteric arteries isolated from mice with diet-induced HHcy. Exendin-4 treatment lowered superoxide anion accumulation in the mouse aortae both ex vivo and in vivo. Exendin-4 decreased the expression of ER stress markers (e.g., ATF4, spliced XBP1, and phosphorylated eIF2α) in human umbilical vein endothelial cells (HUVECs), and this change was reversed by cotreatment with compound C (CC) (AMPK inhibitor). Exendin-4 induced phosphorylation of AMPK and endothelial nitric oxide synthase in HUVECs and arteries. Exendin-4 increased the expression of endoplasmic reticulum oxidoreductase (ERO1α), an important ER chaperone in endothelial cells, and this effect was mediated by AMPK activation. Experiments using siRNA-mediated knockdown or adenoviral overexpression revealed that ERO1α mediated the inhibitory effects of exendin-4 on ER stress and superoxide anion production, thus ameliorating HHcy-induced endothelial dysfunction. The present results demonstrate that exendin-4 reduces HHcy-induced ER stress and improves endothelial function through AMPK-dependent ERO1α upregulation in endothelial cells and arteries. AMPK activation promotes the protein folding machinery in endothelial cells to suppress ER stress.

Protective effect of exendin-4 treatment on oxidative status of liver in rats exposed to chronic methylglyoxal

Protective effect of exendin-4 treatment on oxidative status of liver in rats exposed to chronic methylglyoxal