Glucagon-like peptide-2-induced memory improvement and anxiolytic effects in mice

GLP-2 regulation of intestinal lipid handling

Lipid handling in the intestine is important for maintaining energy homeostasis and overall health. Mishandling of lipids in the intestine contributes to dyslipidemia and atherosclerotic cardiovascular diseases. Despite advances in this field over the past few decades, significant gaps remain. The gut hormone glucagon-like peptide-2 (GLP-2) has been shown to play pleotropic roles in the regulation of lipid handling in the intestine. Of note, GLP-2 exhibits unique actions on post-prandial lipid absorption and post-absorptive release of intestinally stored lipids. This review aims to summarize current knowledge in how GLP-2 regulates lipid processing in the intestine. Elucidating the mechanisms of GLP-2 regulation of intestinal lipid handling not only improves our understanding of GLP-2 biology, but also provides insights into how lipids are processed in the intestine, which offers opportunities for developing novel strategies towards prevention and treatment of dyslipidemia and atherosclerotic cardiovascular diseases.

The effect of gastric bypass surgery on cognitive function of Alzheimer's disease and the role of GLP1-SGLT1 pathway

OBJECTIVE

Gastric bypass surgery has been shown to improve metabolic profiles via GLP1, which may also have cognitive benefits for Alzheimer's disease (AD) patients. However, the exact mechanism requires further investigation.

METHODS

Roux-en-Y gastric bypass or sham surgery was performed on APP/PS1/Tau triple transgenic mice (an AD mice model) or wild type C57BL/6 mice. Morris Water Maze (MWM) test was used to evaluate the cognitive function of mice and animal tissue samples were obtained for measurements two months after the surgery. Additionally, STC-1 intestine cells were treated with siTAS1R2 and siSGLT1, and HT22 nerve cells were treated with Aβ, siGLP1R, GLP1 and siSGLT1 in vitro to explore the role of GLP1-SGLT1 related signaling pathway in cognitive function.

RESULTS

The MWM test showed that bypass surgery significantly improved cognitive function in AD mice as measured by navigation and spatial probe tests. Moreover, bypass surgery reversed neurodegeneration, down-regulated hyperphosphorylation of Tau protein and Aβ deposition, improved glucose metabolism, and up-regulated the expression of GLP1, SGLT1, and TAS1R2/3 in the hippocampus. Furthermore, GLP1R silencing down-regulated SGLT1 expression, whereas SGLT1 silencing increased Tau protein deposition and exacerbated dysregulated of glucose metabolism in HT22 cells. However, RYGB did not alter the level of GLP1 secretion in the brainstem (where central GLP1 is mainly produced). Additionally, GLP1 expression was upregulated by RYGB via TAS1R2/3-SGLT1 activation sequentially in the small intestine.

CONCLUSION

RYGB surgery could improve cognition function in AD mice through facilitating glucose metabolism and reducing Tau phosphorylation and Aβ deposition in the hippocampus, mediated by peripheral serum GLP1 activation of SGLT1 in the brain. Furthermore, RYGB increased GLP1 expression through sequential activation of TAS1R2/TAS1R3 and SGLT1 in the small intestine.

Glucose and Several Mitogenic Agents Modulate the Glucagon-Like Peptide-2 Receptor Expression in Cultured Rat Astrocytes

Background

Glucagon-like peptide-2 (GLP-2) is an intestinal trophic factor that induces astrocyte proliferation through its own receptor (GLP-2R), but the control of its expression is not well known.

Objective

To study the effects of glucose and of different mitogenic agents on the control of GLP-2R expression in cultured rat astrocytes.

Methods

GLP-2R mRNA content was measured by quantitative RT-PCR.

Results

GLP-2R expression was higher in proliferating than in resting cells. The expression was dependent of glucose concentration both in the absence and in the presence of GLP-2. In the presence of a high glucose concentration, GLP-2, PDGF, and PDGF plus GLP-2 presented opposite effects depending on the incubation time. However, insulin, IGF-1, and EGF alone, and plus GLP-2 had no effect. IGF-2, but not IGF-2 plus GLP-2, increased the expression. On the contrary, NGF decreased the GLP-2R expression, but NGF plus GLP-2 increased it even until values similar to those obtained with GLP-2 alone. Interestingly, in the presence of a low glucose concentration, leptin and NPY produced a significant reduction of GLP-2R expression.

Conclusion

Astrocytes are distributed throughout the brain, where GLP-2 appears to have important functions. Since these cells express the GLP-2R, the results of this study could be considered of interest to advance the knowledge of the role of GLP-2 signaling in the CNS, which should lead a better understanding of the events that occur under normal and pathophysiological conditions.

GLP-2 restores impairments in spatial working memory and hippocampal LTD via the MEK/ERK pathway in juvenile-onset diabetes rats

Type 1 diabetic animal models, generated by injecting streptozotocin (STZ), have been widely used in research. We previously reported that juvenile-onset diabetes mellitus (JDM) rats, which were prepared by administering STZ to 17-day-old rats, developed cognitive impairments and hippocampal synaptic plasticity deficiencies, which were restored by glucagon-like peptide-1 (GLP-1). GLP-1 and GLP-2 are simultaneously derived from proglucagon and act through their own specific receptors. The present study was performed to investigate the potential of GLP-2 in JDM rats. The results obtained demonstrated that GLP-2 restored impairments in spatial working memory and hippocampal long-term depression (LTD) in JDM rats, and that the MEK1/2 inhibitor, U0126, inhibited this recovery. Therefore, GLP-2 has potential in the treatment of cognitive deficits in childhood-onset diabetes.

Neuroprotective Effects of a GLP-2 Analogue in the MPTP Parkinson's Disease Mouse Model

BACKGROUND

Glucagon-like peptide 2 (GLP-2) is a peptide hormone derived from the proglucagon gene expressed in the intestines, pancreas and brain. Some previous studies showed that GLP-2 improved aging and Alzheimer's disease related memory impairments. Parkinson's disease (PD) is a progressive neurodegenerative disorder, and to date, there is no particular medicine reversed PD symptoms effectively.

OBJECTIVE

The aim of this study was to evaluate neuroprotective effects of a GLP-2 analogue in the 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) PD mouse model.

METHODS

In the present study, the protease resistant Gly(2)-GLP-2 (50 nmol/kg ip.) analogue has been tested for 14 days by behavioral assessment, transmission electron microscope, immunofluorescence histochemistry, enzyme-linked immunosorbent assay and western blot in an acute PD mouse model induced by MPTP. For comparison, the incretin receptor dual agonist DA5-CH was tested in a separate group.

RESULTS

The GLP-2 analogue treatment improved the locomotor and exploratory activity of mice, and improved bradykinesia and movement imbalance of mice. Gly(2)-GLP-2 treatment also protected dopaminergic neurons and restored tyrosine hydroxylase expression levels in the substantia nigra. Gly(2)-GLP-2 furthermore reduced the inflammation response as seen in lower microglia activation, and decreased NLRP3 and interleukin-1β pro-inflammatory cytokine expression levels. In addition, the GLP-2 analogue improved MPTP-induced mitochondrial dysfunction in the substantia nigra. The protective effects were comparable to those of the dual agonist DA5-CH.

CONCLUSION

The present results demonstrate that Gly(2)-GLP-2 can attenuate NLRP3 inflammasome-mediated inflammation and mitochondrial damage in the substantia nigra induced by MPTP, and Gly(2)-GLP-2 shows neuroprotective effects in this PD animal model.

A GLP-2 Analogue Protects SH-SY5Y and Neuro-2a Cells Against Mitochondrial Damage, Autophagy Impairments and Apoptosis in a Parkinson Model

Glucagon-like peptide-2 (GLP-2) is a peptide hormone that belongs to the glucagon-derived peptide family. We have previously shown that analogues of the sister hormone Glucagon-like peptide-1 (GLP-1) showed neuroprotective effects. Here we investigated the effect of a GLP-2 agonist in a cell model of Parkinson's disease (PD) created by treating SH-SY5Y or Neuro-2a cells with 1-Methyl-4-phenyl-pyridine ion (MPP+). Cell viability and cell cytotoxicity was detected by MTT and LDH assays, respectively. The protein expression levels of mitochondrial, autophagy and apoptotic biomarkers including PGC-1α, Mfn2, IRE1, ATG7, LC3B, Beclin1 and Bcl-2 were detected by western blot. Mitochondrial superoxide was detected by MitoSOX Red. In addition, mitochondrial morphology, autophagosome and apoptotic corpuscles were observed by transmission electron microscope (TEM). We found that the GLP-1 and the GLP-2 agonists both protect cells against mitochondrial damage, autophagy impairments and apoptosis induced by MPP+both in SH-SY5Y and Neuro-2a cells. Cell signaling for mitogenesis was enhanced, and oxidative stress levels much reduced by the drugs. This demonstrates for the first time the neuroprotective effects of a GLP-2 analogue in PD cellular models, in which oxidative stress, autophagy and apoptosis play crucial roles. The protective effects were comparable to those seen with the GLP-1 analogue liraglutide. The results suggest that not only GLP-1, but also GLP-2 has neuroprotective properties and may be useful as a novel treatment of PD.

Glucagon-like peptide-2 interferes with the neurally-induced relaxant responses in the mouse gastric strips through VIP release

Glucagon-like peptide-2 (GLP-2) has been reported to indirectly relax gastric smooth muscle. In the present study we investigated, through a combined mechanical and immunohistochemical approach, whether GLP-2 interferes with the electrical field stimulation (EFS)-induced vipergic relaxant responses and the mechanism through which it occurs. For functional experiments, strips from the mouse gastric fundus were mounted in organ baths for isometric recording of the mechanical activity. Vasoactive intestinal peptide (VIP) immunoreactivity in GLP-2 exposed specimens was also evaluated by immunohistochemistry. In carbachol pre-contracted strips, GLP-2 (20 nM) evoked a tetrodotoxin (TTX)-sensitive relaxation, similar in shape to the TTX-insensitive of 100 nM VIP. In the presence of GLP-2, VIP had no longer effects and no more response to GLP-2 was observed following VIP receptor saturation. EFS (4-16 Hz) induced a fast relaxant response followed, at the higher stimulation frequencies (≥ 8 Hz), by a slow one. This latter was abolished either by GLP-2 or VIP receptor saturation as well as by the VIP receptor antagonist, VIP 6-28 (10 μM). A decrease of VIP-immunoreactive nerve structures in the GLP-2 exposed specimens was observed. These results suggest that, in the mouse gastric fundus, GLP-2 influences the EFS-induced slow relaxant response by promoting neuronal VIP release.

Mirogabalin prevents repeated restraint stress-induced dysfunction in mice

Gabapentinoids, which are the common analgesics, are also thought to be an effective treatment for anxiety disorder, which is one of several psychiatric disorders triggered and exacerbated by stress. The aim of the present study was to investigate whether mirogabalin, a recently launched gabapentinoid, protects multiple brain functions against repeated restraint stress. Adult male ddY mice were restrained for 7 days (repeated restraint stress: 2 h/day) or for 30 min (single restraint stress). Mirogabalin (intraperitoneal, intracerebroventricular or intrahippocampal injection) was administered prior to the restraint stress. Y-maze, elevated-plus maze and c-Fos immunohistochemistry were performed to evaluate learning function, anxiety levels and hippocampal neuronal activities, respectively, after the 7th day of the repeated restraint stress. Intestinal function was evaluated in terms of defecation, which was scored after the 5th day of repeated restraint stress and by the number of fecal pellets excreted after a single session of restraint stress. Repeated restraint stress induced memory dysfunction, anxiety-like behavior, an abnormal defecation score and increased hippocampal c-Fos expression. These changes were prevented by systemic administration of mirogabalin. Abnormal defecation was also induced by single restraint stress, and was inhibited by both systemic and central administration of mirogabalin, suggesting that the effect on the intestinal function was also mediated via the central nervous system. Enhancement of c-Fos expression by repeated stress was decreased by intrahippocampal injection of mirogabalin. Together, these observations suggest that mirogabalin protects multiple brain functions from repeated stress, which may be mediated by inhibition of hippocampal neuron hyperactivation.

Glucagon-Like Peptide-2 Receptor is Involved in Spatial Cognitive Dysfunction in Rats After Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) affects the aging population and especially patients with neurodegenerative diseases, such as Alzheimer's disease or Parkinson's disease. CCH is closely related to the cognitive dysfunction in these diseases. Glucagon-like peptide-2 receptor (GLP2R) mRNA and protein are highly expressed in the gut and in hippocampal neurons. This receptor is involved in the regulation of food intake and the control of energy balance and glucose homeostasis. The present study employed behavioral techniques, electrophysiology, western blotting, immunohistochemistry, quantitative real time polymerase chain reaction (qRT-PCR), and Golgi staining to investigate whether the expression of GLP2R changes after CCH and whether GLP2R is involved in cognitive impairment caused by CCH. Our findings show that CCH significantly decreased hippocampal GLP2R mRNA and protein levels. GLP2R upregulation could prevent CCH-induced cognitive impairment. It also improved the CCH-induced impairment of long-term potentiation and long-term depression. Additionally, GLP2R modulated after CCH the AKT-mTOR-p70S6K pathway in the hippocampus. Moreover, an upregulation of the GLP2R increased the neurogenesis in the dentate gyrus, neuronal activity, and density of dendritic spines and mushroom spines in hippocampal neurons. Our findings reveal the involvement of GLP2R via a modulation of the AKT-mTOR-p70S6K pathway in the mechanisms underlying CCH-induced impairments of spatial learning and memory. We suggest that the GLP2R and the AKT-mTOR-p70S6K pathway in the hippocampus are promising targets to treat cognition deficits in CCH.

Glucagon-like peptide-2 rescues memory impairments and neuropathological changes in a mouse model of dementia induced by the intracerebroventricular administration of streptozotocin

Glucagon-like peptide 2 (GLP-2) is derived from the proglucagon gene expressed in the intestines, pancreas and brain. Our previous study showed that GLP-2 improved lipopolysaccharide-induced memory impairments. The current study was designed to further investigated the potential of GLP-2 in memory impairment induced by intracerebroventricular administration of streptozotocin (ICV-STZ) in mice, which have been used as an animal model of sporadic Alzheimer’s disease (AD). STZ was administered on alternate days (Day-1 and Day-3) in order to induce dementia in male ddY mice. ICV-STZ-treated mice were administered GLP-2 (0.6 μg/mouse, ICV) for 5 days from 14 days after the first ICV administration of STZ. In these mice, we examined spatial working memory, the biochemical parameters of oxidative stress, or neurogenesis. The GLP-2 treatment restored spatial working memory in ICV-STZ-treated mice. ICV-STZ-treated mice showed markedly increased thiobarbituric acid reactive species (TBARS) and decreased glutathione (GSH) levels, and GLP-2 significantly restored these ICV-STZ-induced changes. GLP-2 also significantly restored neurogenesis in the subgranular zone of the dentate gyrus in ICV-STZ-treated mice. We herein demonstrated that GLP-2 significantly restored ICV-STZ-induced memory impairments as well as biochemical and histopathological alterations, and accordingly, propose that the memory restorative ability of GLP-2 is due to its potential to reduce oxidative stress.

[Improving Effects of Peptides on Brain Malfunction and Intranasal Delivery of Those Derivatives to the Brain]

This review focuses on the anti-dementia and antidepressant-like effects of peptides including glucagon-like peptide (GLP)-1, GLP-2, neuromedin U (NmU), and oxytocin, and the intranasal delivery of these peptides to the brain. Intracerebroventricularly administered GLP-1, NmU, and oxytocin improved impairment of learning and memory in mice treated with lipopolysaccharide or β-amyloid protein. GLP-1 also improved impairment of learning and memory in juvenile diabetes model rats. On the other hand, GLP-2 exhibited antidepressant-like effects in mice during the forced-swim test, which were associated with 5-HT_1A, α₂, β₁, and D₂ receptors. GLP-2 also exerted antidepressant-like effects in adrenocorticotropic hormone (ACTH)-treated mice through restoration of the hypothalamic-pituitary-adrenal-axis and neurogenesis in the subgranular zone of the dentate gyrus. Because intracerebroventricular administration is invasive and the peptides are unable to penetrate the blood-brain barrier, we introduced our new method of intranasal administration to deliver the peptides to the brain. We prepared a GLP-2 derivative containing cell-penetrating peptides (CPPs) and a penetration accelerating sequence (PAS). Intranasally administered PAS-CPPs-GLP-2 was distributed throughout the brain, and exhibited antidepressant-like effects in both naive and ACTH-treated mice. The derivatives of GLP-1, NmU, and oxytocin with the PAS and CPPs were also distributed throughout the brain after intranasal administration, and improved impairment of learning and memory. We confirmed that our peptide derivatives were effectively delivered into the brain by intranasal administration. As such, these derivatives may be useful for the clinical treatment of psychiatric and neurological diseases.

Glucagon-like peptide-2 reduces the obesity-associated inflammation in the brain

Growing evidence suggests a link between obesity and neurodegeneration. The purpose of the present study was to explore the neuroprotective potential of glucagon-like peptide-2 (GLP-2) in the brain of high fat diet (HFD)-fed mice. Markers of inflammation and oxidative stress were analysed in the brains of obese mice chronically treated with [Gly²]-GLP-2 (teduglutide), the stable analogue of the GLP-2, and they were compared to age-matched untreated obese and lean animals. Neurodegeneration was examined by TUNEL assay. HFD feeding increased the expression of pro-inflammatory mediators (NF-kB, IL-8, TNF-α, IL-1β and IL-6), glial fibrillary acidic protein (GFAP), index of gliosis and neurodegeneration, stress marker proteins (p-ERK, Hsp60 and i-NOS), amyloid-β precursor protein (APP). [Gly²]-GLP-2 treatment significantly attenuated the HFD-induced increased expression of the various markers, as well as the higher levels of reactive oxygen species found in brains of untreated-HFD mice. Immunofluorescence confirmed that the increase of GFAP or APP in the brain cortex of HFD mice were less prominent in the [Gly²]-GLP-2 treated group. TUNEL-positive cell number in brain sections of [Gly²]-GLP-2-treated HFD-fed mice was significantly lesser in comparison with untreated-HFD animals and similar to STD fed mice. In conclusion, the results of the present study suggest that GLP-2 stable analogue improves the obesity-associated neuroinflammation and the central stress conditions, it reduces the neuronal apoptotic death, providing evidence for a neuroprotective role of the peptide.

Role of Incretin Axis in Inflammatory Bowel Disease

The inflammatory bowel diseases (IBDs), including Crohn's disease (CD) and ulcerative colitis (UC), are chronic inflammatory conditions of the gastrointestinal tract and involve a complicated reciprocity of environmental, genetic, and immunologic factors. Despite substantial advances in the foundational understanding of the immunological pathogenesis of IBD, the detailed mechanism of the pathological progression in IBD remains unknown. In addition to Th1/Th2 cells, whose role in IBD has been previously well defined, recent evidence indicates that Th17 cells and Tregs also play a crucial role in the development of IBD. Diets which contain excess sugars, salt, and fat may also be important actors in the pathogenesis of IBD, which may be the cause of high IBD incidence in western developed and industrialized countries. Up until now, the reason for the variance in prevalence of IBD between developed and developing countries has been unknown. This is partly due to the increasing popularity of western diets in developing countries, which makes the data harder to interpret. The enterocrinins glucagon-like peptides (GLPs), including GLP-1 and GLP-2, exhibit notable benefits on lipid metabolism, atherosclerosis formation, plasma glucose levels, and maintenance of gastric mucosa integrity. In addition to the regulation of nutrient metabolism, the emerging role of GLPs and their degrading enzyme dipeptidyl peptidase-4 (DPP-4) in gastrointestinal diseases has gained increasing attention. Therefore, here we review the function of the DPP-4/GLP axis in IBD.

Antidepressant-like effects exerted by the intranasal administration of a glucagon-like peptide-2 derivative containing cell-penetrating peptides and a penetration-accelerating sequence in mice

The intracerebroventicular (i.c.v.) administration of glucagon-like peptide-2 (GLP-2) to rodents was shown to have antidepressant-like effects in imipramine-resistant depression-model mice. In order to utilize GLP-2 as a clinical treatment tool for depression, we herein focused on the intranasal delivery that is non-invasive approach, because the i.c.v. administration is invasive and impractical. In the present study, we prepared a GLP-2 derivative containing cell penetrating peptides (CPPs) and a penetration accelerating sequence (PAS) (PAS-CPPs-GLP-2) for the intranasal (i.n.) administration. PAS-CPPs-GLP-2 (i.n.) exhibited antidepressant-like effects in the forced-swim test (FST) and tail suspension test (TST) in naïve mice as well as adrenocorticotropic hormone (ACTH) treated-mice. However, PAS-CPPs-GLP-2 (i.v.) and the GLP-2 derivative containing CPPs without a PAS (CPPs-GLP-2) (i.n.) did not affect the immobility time in the mouse FST. Moreover, fluorescein isothiocyanate (FITC)-labeled PAS-CPPs-GLP-2 (i.n.), but not FITC-labeled CPPs-GLP-2 (i.n.) was distributed through the mouse brain after the FST session. These results suggest that PAS-CPPs-GLP-2 is effective for i.n. delivery to the brain, and may be useful in the clinical treatment of major depression.

Neoechinulin A induced memory improvements and antidepressant-like effects in mice

Neoechinulin A is an isoprenyl indole alkaloid that exhibits scavenging, neurotrophic factor-like, and anti-apoptotic activities. However, the effectiveness of neoechinulin A in animal models of disease has not yet been explored. In the present study, we investigated the effects of neoechinulin A on memory impairment in lipopolysaccharide (LPS)-treated mice and its antidepressant-like effects in mice. In the Y-maze test, the intracerebroventicular (i.c.v.) administration of LPS (10μg/mouse) significantly decreased spontaneous alternation behavior, which was prevented by the prior administration of neoechinulin A (300ng/mouse, i.c.v.). None of the treatments altered the locomotor activity of mice. Moreover, the administration of neoechinulin A decreased the immobility time in the forced-swim test or tail suspension test, which was prevented by the prior administration of WAY100635 (an antagonist of 5-HT1A receptors) and parachlorophenylalanine (an inhibitor of tryptophan hydroxylase). These results suggest that neoechinulin A improves memory functions in LPS-treated mice, and also exerts antidepressant-like effects through changes in the 5-HT system.

Glucagon-like peptide 2 and its beneficial effects on gut function and health in production animals

Numerous endocrine cell subtypes exist within the intestinal mucosa and produce peptides contributing to the regulation of critical physiological processes including appetite, energy metabolism, gut function, and gut health. The mechanisms of action and the extent of the physiological effects of these enteric peptides are only beginning to be uncovered. One peptide in particular, glucagon-like peptide 2 (GLP-2) produced by enteroendocrine L cells, has been fairly well characterized in rodent and swine models in terms of its ability to improve nutrient absorption and healing of the gut after injury. In fact, a long-acting form of GLP-2 recently has been approved for the management and treatment of human conditions like inflammatory bowel disease and short bowel syndrome. However, novel functions of GLP-2 within the gut continue to be demonstrated, including its beneficial effects on intestinal barrier function and reducing intestinal inflammation. As knowledge continues to grow about GLP-2's effects on the gut and its mechanisms of release, the potential to use GLP-2 to improve gut function and health of food animals becomes increasingly more apparent. Thus, the purpose of this review is to summarize: (1) the current understanding of GLP-2's functions and mechanisms of action within the gut; (2) novel applications of GLP-2 (or stimulators of its release) to improve general health and production performance of food animals; and (3) recent findings, using dairy calves as a model, that suggest the therapeutic potential of GLP-2 to reduce the pathogenesis of intestinal protozoan infections.