Intestinal Gpr17 deficiency improves glucose metabolism by promoting GLP-1 secretion

Microbiome affects mice metabolic homeostasis via differential regulation of gene expression in the brain and gut

The gut microbiome (GMB) regulates digestion, metabolism, immunity, and energy homeostasis. This study investigates how gut microbiota integrate the regulation in the neuroendocrine and enteroendocrine systems, with a focus on G protein-coupled receptors (GPCRs) in the brain-gut axis and sex differences. Germ-free (GF) mice exhibited increased hypothalamic expression of the anorexigenic neuropeptide and decreased expression of the negative regulator of leptin signaling. GF males had significantly lower serum leptin levels compared to conventional (CON) males, highlighting a potential link between the microbiome and leptin resistance. In the gut, GF mice demonstrated heightened expression of anorexigenic gut hormones, including peptide YY (Pyy) and cholecystokinin (Cck), in addition to increased levels of G protein-coupled receptors (GPCRs) involved in gut hormone secretion and nutrient metabolism, particularly in females. While carbohydrate metabolism genes were upregulated in CON mice, lipid metabolism genes were predominantly higher in GF mice. These findings suggest that the gut microbiota downregulates genes involved in appetite suppression, modulates GPCRs linked to gut hormone secretion, and contributes to leptin resistance, particularly in males. This research underscores the importance of the gut microbiome in host metabolism and reveals potential molecular targets for novel treatments of metabolic diseases.

The role of gut-islet axis in pancreatic islet function and glucose homeostasis

The gastrointestinal tract plays a vital role in the occurrence and treatment of metabolic diseases. Recent studies have convincingly demonstrated a bidirectional axis of communication between the gut and islets, enabling the gut to influence glucose metabolism and energy homeostasis in animals strongly. The 'gut-islet axis' is an essential endocrine signal axis that regulates islet function through the dialogue between intestinal microecology and endocrine metabolism. The discovery of glucagon-like peptide-1 (GLP-1), gastric inhibitory peptide (GIP) and other gut hormones has initially set up a bridge between gut and islet cells. However, the influence of other factors remains largely unknown, such as the homeostasis of the gut microbiota and the integrity of the gut barrier. Although gut microbiota primarily resides and affect intestinal function, they also affect extra-intestinal organs by absorbing and transferring metabolites derived from microorganisms. As a result of this transfer, islets may be continuously exposed to gut-derived metabolites and components. Changes in the composition of gut microbiota can damage the intestinal barrier function to varying degrees, resulting in increased intestinal permeability to bacteria and their derivatives. All these changes contribute to the severe disturbance of critical metabolic pathways in peripheral tissues and organs. In this review, we have outlined the different gut-islet axis signalling mechanisms associated with metabolism and summarized the latest progress in the complex signalling molecules of the gut and gut microbiota. In addition, we will discuss the impact of the gut renin-angiotensin system (RAS) on the various components of the gut-islet axis that regulate energy and glucose homeostasis. This work also indicates that therapeutic approaches aiming to restore gut microbial homeostasis, such as probiotics and faecal microbiota transplantation (FMT), have shown great potential in improving treatment outcomes, enhancing patient prognosis and slowing down disease progression. Future research should further uncover the molecular links between the gut-islet axis and the gut microbiota and explore individualized microbial treatment strategies, which will provide an innovative perspective and approach for the diagnosis and treatment of metabolic diseases.

Effect of Verapamil on Blood Glucose in Type 1 and Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis

PURPOSE

Verapamil, an L-type calcium channel blocker treating hypertension, arrhythmia, and other cardiovascular diseases, has emerged as a potential drug for lowering blood glucose by regulating cellular calcium homeostasis and affecting expression of apoptosis-related proteins in pancreatic β-cells. However, this promising effect must be weighed against potential risks, including cardiovascular adverse effects of this drug.

METHODS

We conducted a systematic review and meta-analysis and included randomized controlled trials (RCTs) assessing verapamil in individuals with type 1 or type 2 diabetes. The primary outcomes were glycated hemoglobin (HbA1c) and serum glucose concentration. The secondary outcomes were area under the curve (AUC) values for C-peptide level, body weight, changes in HbA1c and blood glucose concentration pre- and post-intervention, and adverse drug reactions.

RESULTS

A total of eight RCTs involving 1100 patients were included in the analysis. Meta-analysis showed that verapamil effectively lowered blood glucose levels (weighted mean difference [WMD] -6.38, 95% CI -12.52, -0.25 mg/dL, P = 0.04; 6 trials), decreased HbA1c (WMD -0.45, 95% CI -0.66, -0.23%, P < 0.001; 7 trials), and increased C-peptide AUC (WMD 0.27, 95% CI 0.21, 0.32 pmol/mL, P < 0.0001; 2 trials) in patients with both type 1 and type 2 diabetes, without significant trial-related adverse events (OR 1.33, 95% CI 0.85, 2.09, P = 0.21).

CONCLUSION

The adjunctive use of verapamil to standard hypoglycemic therapy is a safe and effective means of improving glycemic control in diabetic patients. However, the limited scale of RCTs and heterogeneity of basic glucose-lowering regimens across studies might constrain generalizability of these findings. Future high-quality research is warranted to further elucidate the role of verapamil in diabetes management.

G Protein-Coupled Receptor 17 Inhibits Glucagon-like Peptide-1 Secretion via a Gi/o-Dependent Mechanism in Enteroendocrine Cells

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered. Here, we expressed the human GPR17 long isoform (hGPR17L) in GLUTag cells, a murine EEC line, and we used the GPR17 synthetic agonist MDL29,951 together with pharmacological probes and genetic approaches to quantitatively assess the contribution of GPR17 signaling to GLP-1 secretion. Constitutive hGPR17L activity inhibited GLP-1 secretion, and MDL29,951 treatment further inhibited this secretion, which was attenuated by treatment with the GPR17 antagonist HAMI3379. MDL29,951 promoted both Gi/o and Gq protein coupling to mediate cyclic AMP (cAMP) and calcium signaling. hGPR17L regulation of GLP-1 secretion appeared to be Gq-independent and dependent upon Gi/o signaling, but was not correlated with MDL29,951-induced whole-cell cAMP signaling. Our studies revealed key signaling mechanisms underlying the role of GPR17 in regulating GLP-1 secretion and suggest future opportunities for pharmacologically targeting GPR17 with inverse agonists to maximize GLP-1 secretion.

G protein-coupled receptor 17 inhibits glucagon-like peptide-1 secretion via a Gi/o-dependent mechanism in enteroendocrine cells

Gut peptides, including glucagon-like peptide-1 (GLP-1), regulate metabolic homeostasis and have emerged as the basis for multiple state-of-the-art diabetes and obesity therapies. We previously showed that G protein-coupled receptor 17 (GPR17) is expressed in intestinal enteroendocrine cells (EECs) and modulates nutrient-induced GLP-1 secretion. However, the GPR17-mediated molecular signaling pathways in EECs have yet to be fully deciphered. Here, we expressed the human GPR17 long isoform (hGPR17L) in GLUTag cells, a murine EEC line, and we used the GPR17 synthetic agonist MDL29,951 together with pharmacological probes and genetic approaches to quantitatively assess the contribution of GPR17 signaling to GLP-1 secretion. Constitutive hGPR17L activity inhibited GLP-1 secretion, and MDL29,951 treatment further inhibited this secretion, which was attenuated by treatment with the GPR17 antagonist HAMI3379. MDL29,951 promoted both Gi/o and Gq protein coupling to mediate cyclic AMP (cAMP) and calcium signaling. hGPR17L regulation of GLP-1 secretion was Gq-independent and dependent upon Gi/o signaling, but was not correlated with MDL29,951-induced whole-cell cAMP signaling. Our studies revealed key signaling mechanisms underlying the role of GPR17 in regulating GLP-1 secretion and suggest future opportunities for pharmacologically targeting GPR17 with inverse agonists to maximize GLP-1 secretion.

Sympathetic nerve-enteroendocrine L cell communication modulates GLP-1 release, brain glucose utilization, and cognitive function

Glucose homeostasis is controlled by brain-gut communications. Yet our understanding of the neuron-gut interface in the glucoregulatory system remains incomplete. Here, we find that sympathetic nerves elevate postprandial blood glucose but restrict brain glucose utilization by repressing the release of glucagon-like peptide-1 (GLP-1) from enteroendocrine L cells. Sympathetic nerves are in close apposition with the L cells. Importantly, sympathetic denervation or intestinal deletion of the adrenergic receptor α2 (Adra2a) augments postprandial GLP-1 secretion, leading to reduced blood glucose levels and increased brain glucose uptake. Conversely, sympathetic activation shows the opposite effects. At the cellular level, adrenergic signaling suppresses calcium flux to limit GLP-1 secretion upon sugar ingestion. Consequently, abrogation of adrenergic signal results in a significant improvement in learning and memory ability. Together, our results reveal a sympathetic nerve-enteroendocrine unit in constraining GLP-1 secretion, thus providing a therapeutic nexus of mobilizing endogenous GLP-1 for glucose management and cognitive improvement.

Illuminating the druggable genome: Pathways to progress

There are ∼4500 genes within the 'druggable genome', the subset of the human genome that expresses proteins able to bind drug-like molecules, yet existing drugs only target a few hundred. A substantial subset of druggable proteins are largely uncharacterized or understudied, with many falling within G protein-coupled receptor (GPCR), ion channel, and kinase protein families. To improve scientific understanding of these three understudied protein families, the US National Institutes of Health launched the Illuminating the Druggable Genome Program. Now, as the program draws to a close, this review will lay out resources developed by the program that are intended to equip the scientific community with the tools necessary to explore previously understudied biology with the potential to rapidly impact human health.

Organoids in gastrointestinal diseases: from experimental models to clinical translation

We are entering an era of medicine where increasingly sophisticated data will be obtained from patients to determine proper diagnosis, predict outcomes and direct therapies. We predict that the most valuable data will be produced by systems that are highly dynamic in both time and space. Three-dimensional (3D) organoids are poised to be such a highly valuable system for a variety of gastrointestinal (GI) diseases. In the lab, organoids have emerged as powerful systems to model molecular and cellular processes orchestrating natural and pathophysiological human tissue formation in remarkable detail. Preclinical studies have impressively demonstrated that these organs-in-a-dish can be used to model immunological, neoplastic, metabolic or infectious GI disorders by taking advantage of patient-derived material. Technological breakthroughs now allow to study cellular communication and molecular mechanisms of interorgan cross-talk in health and disease including communication along for example, the gut-brain axis or gut-liver axis. Despite considerable success in culturing classical 3D organoids from various parts of the GI tract, some challenges remain to develop these systems to best help patients. Novel platforms such as organ-on-a-chip, engineered biomimetic systems including engineered organoids, micromanufacturing, bioprinting and enhanced rigour and reproducibility will open improved avenues for tissue engineering, as well as regenerative and personalised medicine. This review will highlight some of the established methods and also some exciting novel perspectives on organoids in the fields of gastroenterology. At present, this field is poised to move forward and impact many currently intractable GI diseases in the form of novel diagnostics and therapeutics.

NMDA Receptor Antagonists Increase the Release of GLP-1 From Gut Endocrine Cells

Type 2 diabetes mellitus (T2DM) remains one of the most pressing health issues facing modern society. Several antidiabetic drugs are currently in clinical use to treat hyperglycaemia, but there is a need for new treatments that effectively restore pancreatic islet function in patients. Recent studies reported that both murine and human pancreatic islets exhibit enhanced insulin release and β-cell viability in response to N-methyl-D-aspartate (NMDA) receptor antagonists. Furthermore, oral administration of dextromethorphan, an over-the-counter NMDA receptor antagonist, to diabetic patients in a small clinical trial showed improved glucose tolerance and increased insulin release. However, the effects of NMDA receptor antagonists on the secretion of the incretin hormone GLP-1 was not tested, and nothing is known regarding how NMDA receptor antagonists may alter the secretion of gut hormones. This study demonstrates for the first time that, similar to β-cells, the NMDA receptor antagonist MK-801 increases the release of GLP-1 from a murine L-cell enteroendocrine model cell line, GLUTag cells. Furthermore, we report the 3′ mRNA expression profiling of GLUTag cells, with a specific focus on glutamate-activated receptors. We conclude that if NMDA receptor antagonists are to be pursued as an alternative, orally administered treatment for T2DM, it is essential that the effects of these drugs on the release of gut hormones, and specifically the incretin hormones, are fully investigated.