Global deletion of G protein-coupled receptor 55 impairs glucose homeostasis during obesity by reducing insulin secretion and β-cell turnover.

Aim: To investigate the effect of G protein-coupled receptor 55 (GPR55) deletion on glucose homeostasis and islet function following diet-induced obesity.

Methods: GPR55 and wild-type (WT) mice were fed ad libitum either standard chow (SC) or a high-fat diet (HFD) for 20 weeks. Glucose and insulin tolerance tests were performed at 9/10 and 19/20 weeks of dietary intervention.

The selective serotonin reuptake inhibitors, sertraline and paroxetine, improve islet beta-cell mass and function in vitro.

Aims: To investigate the effects of the selective serotonin reuptake inhibitors (SSRIs) sertraline and paroxetine at therapeutically relevant concentrations on beta-cell mass and function.

Methods: Viability was quantified in mouse insulinoma (MIN6) beta cells and mouse islets after 48-h exposure to sertraline (1-10 μM) or paroxetine (0.01-1 μM) using the Trypan blue exclusion test.

Identification of Potential Plant-Derived Pancreatic Beta-Cell-Directed Agents Using New Custom-Designed Screening Method: as an Example.

Background: Folk medicines are attractive therapeutic agents for treating type 2 diabetes mellitus (T2DM). Most plant extracts that have been suggested to restore β-cells function were tested in vivo. Some only have been tested in vitro to determine whether they have a direct effect on β-cells islets of Langerhans.

Mouse islet-derived stellate cells are similar to, but distinct from, mesenchymal stromal cells and influence the beta cell function.

Aims: Evidence is accumulating of the therapeutic benefits of mesenchymal stromal cells (MSCs) in diabetes-related conditions. We have identified a novel population of stromal cells within islets of Langerhans - islet stellate cells (ISCs) - which have a similar morphology to MSCs. In this study we characterize mouse ISCs and compare their morphology and function to MSCs to determine whether ISCs may also have therapeutic potential in diabetes.

Effects of miR-33 Deficiency on Metabolic and Cardiovascular Diseases: Implications for Therapeutic Intervention.

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally inhibit gene expression. These small molecules are involved in several biological conditions such as inflammation, cell growth and proliferation, and regulation of energy metabolism. In the context of metabolic and cardiovascular diseases, miR-33 is of particular interest as it has been implicated in the regulation of lipid and glucose metabolism.

Single-cell transcriptomic and spatial landscapes of the developing human pancreas.

Current differentiation protocols have not been successful in reproducibly generating fully functional human beta cells in vitro, partly due to incomplete understanding of human pancreas development. Here, we present detailed transcriptomic analysis of the various cell types of the developing human pancreas, including their spatial gene patterns. We integrated single-cell RNA sequencing with spatial transcriptomics at multiple developmental time points and revealed distinct temporal-spatial gene cascades.

Commiphora myrrha stimulates insulin secretion from β-cells through activation of atypical protein kinase C and mitogen-activated protein kinase.

Ethnopharmacological Relevance: Ayurvedic medicine has been used in the treatment of diabetes mellitus for centuries. In Arabia and some areas of Africa, Commiphora myrrha (CM) has been extensively used as a plant-based remedy. We have previously shown that an aqueous CM resin solution directly stimulates insulin secretion from MIN6 cells, a mouse β-cell line, and isolated mouse and human islets.

Using single-cell multi-omics screening of human fetal pancreas to identify novel players in human beta cell development.

Islet transplantation from organ donors can considerably improve glucose homeostasis and well-being in individuals with type 1 diabetes, where the beta cells are destroyed by the autoimmune attack, but there are insufficient donor islets to make this a widespread therapy. Strategies are therefore being developed to generate unlimited amounts of insulin-producing beta cells from pluripotent stem cells, with the aim that they will be transplanted to treat diabetes. Whilst much progress has been made in recent years in the directed differentiation of pluripotent stem cells to beta-like cells, essential gaps still exist in generating stem cell-derived beta cells that are fully functional in vitro.

Quantification of changes in human islet G protein-coupled receptor mRNA expression in obesity.

Background: G protein-coupled receptors (GPCRs) play crucial roles in regulating islet function, with Gαs- and Gαq-coupled receptors being linked to the stimulation of insulin secretion. We have quantified the mRNA expression of 384 non-olfactory GPCRs in islets isolated from lean and obese organ donors to determine alterations in islet GPCR mRNA expression in obesity.

Methods: RT-qPCR was used to quantify GPCR mRNAs relative to five reference genes (ACTB, GAPDH, PPIA, TBP, and TFRC) in human islets isolated from lean (BMI = 22.

Alterations in mouse visceral adipose tissue mRNA expression of islet G-protein-coupled receptor ligands in obesity.

Background: Adipose tissue mass expansion in obesity leads to alterations in expression and secretion of adipokines, some of which may alter islet function by binding to G-protein-coupled receptors (GPCRs) expressed by islets. We have therefore quantified expression of mRNAs encoding islet GPCR ligands in visceral adipose tissue retrieved from lean and diet-induced obese mice to determine alterations in islet GPCR ligand mRNAs in obesity.

Methods: Epididymal adipose tissue was retrieved from C57BL/6 mice that had been maintained on a control-fat diet (10% fat) or high-fat diet (60% fat) for 16 weeks and RT-qPCR was used to quantify mRNAs encoding ligands for islet GPCRs.

The selective serotonin reuptake inhibitor fluoxetine has direct effects on beta cells, promoting insulin secretion and increasing beta-cell mass.

Aim: This study investigated whether therapeutically relevant concentrations of fluoxetine, which have been shown to reduce plasma glucose and glycated haemoglobin independent of changes in food intake and body weight, regulate beta-cell function and improve glucose homeostasis.

Methods: Cell viability, insulin secretion, beta-cell proliferation and apoptosis were assessed after exposure of MIN6 beta cells or isolated mouse and human islets to 0.1, 1 or 10 μmol/L fluoxetine.

Neuropeptide Neuromedin B does not alter body weight and glucose homeostasis nor does it act as an insulin-releasing peptide.

Neuromedin B (NMB) is a member of the neuromedin family of neuropeptides with a high level of region-specific expression in the brain. Several GWAS studies on non-obese and obese patients suggested that polymorphisms in NMB predispose to obesity by affecting appetite control and feeding preference. Furthermore, several studies proposed that NMB can act as an insulin releasing peptide.

In vitro profiling and functional assessments of the anti-diabetic capacity of phenolic-rich extracts of Bulbine natalensis and Bulbine frutescens.

Aims: Bulbine natalensis (BN) and Bulbine frutescens (BF) are recommended in South African traditional medicine to treat diabetes, but their modes of action are unknown. This study assessed the phenolic acid profiles, mineral composition and in vitro functional effects of BN and BF to better understand their glucose-lowering capabilities.

Methods: Phenolic acid and mineral composition of BN and BF methanolic extracts were determined by HPLC and inductively coupled plasma optical emission spectroscopy respectively.

SNAP-tag-enabled super-resolution imaging reveals constitutive and agonist-dependent trafficking of GPR56 in pancreatic β-cells.

Objective: Members of the adhesion G protein-coupled receptor (aGPCR) subfamily are important actors in metabolic processes, with GPR56 (ADGRG1) emerging as a possible target for type 2 diabetes therapy. GPR56 can be activated by collagen III, its endogenous ligand, and by a synthetic seven amino-acid peptide (TYFAVLM; P7) contained within the GPR56 Stachel sequence. However, the mechanisms regulating GPR56 trafficking dynamics and agonist activities are not yet clear.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation.

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese.

Drug reformulation for a neglected disease. The NANOHAT project to develop a safer more effective sleeping sickness drug.

Background: Human African trypanosomiasis (HAT or sleeping sickness) is caused by the parasite Trypanosoma brucei sspp. The disease has two stages, a haemolymphatic stage after the bite of an infected tsetse fly, followed by a central nervous system stage where the parasite penetrates the brain, causing death if untreated. Treatment is stage-specific, due to the blood-brain barrier, with less toxic drugs such as pentamidine used to treat stage 1.

Direct Stimulatory Effects of the CB Ligand JTE 907 in Human and Mouse Islets.

Aims: The endocannabinoid system is a complex cell-signaling network through which endogenous cannabinoid ligands regulate cell function by interaction with CB and CB cannabinoid receptors, and with the novel cannabinoid receptor GPR55. CB, CB, and GPR55 are expressed by islet β-cells where they modulate insulin secretion. We have previously shown that administration of the putative CB antagonist/inverse agonist JTE 907 to human islets did not affect the insulinotropic actions of CB agonists and it unexpectedly stimulated insulin secretion on its own.

The role of the CCL25-CCR9 axis in beta-cell function: potential for therapeutic intervention in type 2 diabetes.

Background And Purpose: Chemokines are known to play essential roles mediating immunity and inflammation in many physiological and pathophysiological processes, with reports linking their action to the development of obesity, insulin resistance and type 2 diabetes (T2D). Given our findings of highly upregulated mRNA expression of the chemokine receptor CCR9 in islets from obese human donors, we have determined the effects of CCR9 activation by CCL25 on islet function and viability.

Basic Procedures: RT-qPCR was used to measure expression of 384 GPCR mRNAs in human islets from organ donors with normal and elevated BMI.

Assessing Mouse Islet Function.

Islets of Langerhans are clusters of endocrine cells embedded within the exocrine pancreas. Islets constitute only approximately 1-2% of the total pancreas mass in all species, so methods have been developed to digest the pancreas and purify islets from the surrounding acinar cells. This chapter provides detailed protocols for isolation of mouse islets and their in vitro functional characterization in terms of assessments of islet viability, hormone content and secretion, second messenger generation and β-cell proliferation.

The cannabinoid ligands SR141716A and AM251 enhance human and mouse islet function via GPR55-independent signalling.

Aims: Endocannabinoids are lipid mediators involved in the regulation of glucose homeostasis. They interact with the canonical cannabinoid receptors CB and CB, and it is now apparent that some cannabinoid receptor ligands are also agonists at GPR55. Thus, CB antagonists such as SR141716A, also known as rimonabant, and AM251 act as GPR55 agonists in some cell types.

The Association Between Selective Serotonin Reuptake Inhibitors and Glycemia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Objective: Individual studies have reported conflicting effects of selective serotonin reuptake inhibitors (SSRIs) on glycemia. We systematically reviewed the effects of SSRIs on glycemia and whether metabolic and psychological factors moderated these effects.

Methods: We systematically searched for placebo-controlled randomized controlled trials investigating the effect of SSRIs on glycemia (fasting blood glucose or HbA1c) as a primary or secondary outcome.

CXCL14 Inhibits Insulin Secretion Independently of CXCR4 or CXCR7 Receptor Activation or cAMP Inhibition.

Background/aims: CXCL14, a secreted chemokine peptide that promotes obesity-induced insulin resistance, is expressed by islets, but its effects on islet function are unknown. The aim of this study was to determine the role of CXCL14 in β-cells and investigate how it transduces these effects.

Methods: Cxcl14 and Cxc-receptor mRNA expression was quantified by qPCR and CXCL14 expression in the pancreas was determined by immunohistochemistry.

Adhesion G-protein coupled receptors: Implications for metabolic function.

Adhesion G-protein coupled receptors (aGPCRs) are emerging as important actors in energy homeostasis. Recent biochemical and functional studies using transgenic mice indicate that aGPCRs play important roles in endocrine and metabolic functions including β-cell differentiation, insulin secretion, adipogenesis and whole body fuel homeostasis. Most aGPCRs are orphans, for which endogenous ligands have not yet been identified, and many of the endogenous ligands of the already de-orphanised aGPCRs are components of the extracellular matrix (ECM).