G-protein-coupled receptors and islet function-implications for treatment of type 2 diabetes

The role of glucagon-like peptide-1/GLP-1R and autophagy in diabetic cardiovascular disease

Diabetes leads to a significantly accelerated incidence of various related macrovascular complications, including peripheral vascular disease and cardiovascular disease (the most common cause of mortality in diabetes), as well as microvascular complications such as kidney disease and retinopathy. Endothelial dysfunction is the main pathogenic event of diabetes-related vascular disease at the earliest stage of vascular injury. Understanding the molecular processes involved in the development of diabetes and its debilitating vascular complications might bring up more effective and specific clinical therapies. Long-acting glucagon-like peptide (GLP)-1 analogs are currently available in treating diabetes with widely established safety and extensively evaluated efficacy. In recent years, autophagy, as a critical lysosome-dependent self-degradative process to maintain homeostasis, has been shown to be involved in the vascular endothelium damage in diabetes. In this review, the GLP-1/GLP-1R system implicated in diabetic endothelial dysfunction and related autophagy mechanism underlying the pathogenesis of diabetic vascular complications are briefly presented. This review also highlights a possible crosstalk between autophagy and the GLP-1/GLP-1R axis in the treatment of diabetic angiopathy.

Xelaglifam, a novel GPR40/FFAR1 agonist, exhibits enhanced β-arrestin recruitment and sustained glycemic control for type 2 diabetes

Xelaglifam, developed as a GPR40/FFAR1 agonist, induces glucose-dependent insulin secretion and reduces circulating glucose levels for Type 2 diabetes treatment. This study investigated the effects of Xelaglifam in comparison with Fasiglifam on the in vitro/in vivo anti-diabetic efficacy and selectivity, and the mechanistic basis. In vitro studies on downstream targets of Xelaglifam were performed in GPR40-expressing cells. Xelaglifam treatment exhibited dose-dependent effects, increasing inositol phosphate-1, Ca2+ mobilization, and β-arrestin recruitment (EC50: 0.76 nM, 20 nM, 68 nM), supporting its role in Gq protein-dependent and G-protein-independent mechanisms. Despite a lack of change in the cAMP pathway, the Xelaglifam-treated group demonstrated increased insulin secretion compared to Fasiglifam in HIT-T15 β cells under high glucose conditions. High doses of Xelaglifam (<30 mg/kg) did not induce hypoglycemia in Sprague-Dawley rats. In addition, Xelaglifam lowered glucose and increased insulin levels in diabetic rat models (GK, ZDF, OLETF). In GK rats, 1 mg/kg of Xelaglifam improved glucose tolerance (33.4 % and 15.6 % for the 1 and 5 h) after consecutive glucose challenges. Moreover, repeated dosing in ZDF and OLETF rats resulted in superior glucose tolerance (34 % and 35.1 % in ZDF and OLETF), reducing fasting hyperglycemia (18.3 % and 30 % in ZDF and OLETF) at lower doses; Xelaglifam demonstrated a longer-lasting effect with a greater effect on β-cells including 3.8-fold enhanced insulin secretion. Co-treatment of Xelaglifam with SGLT-2 inhibitors showed additive or synergistic effects. Collectively, these results demonstrate the therapeutic efficacy and selectivity of Xelaglifam on GPR40, supportive of its potential for the treatment of Type 2 diabetes.

Identification of compounds present in lipophilic extracts from Brachystola magna (Girard): substances with potential healing properties

Insects from the Orthoptera order possess important biological activities such as wound healing and represent a therapeutic resource in traditional medicine worldwide. Hence, this study addressed the characterisation of lipophilic extracts from Brachystola magna (Girard), identifying compounds with potential healing properties. For that, four extracts were obtained from sample 1 (head-legs) and sample 2 (abdomen): extract A (hexane/sample 1), extract B (hexane/sample 2), extract C (ethyl acetate/sample 1) and extract D (ethyl acetate/sample 2). All extracts were analysed by Gas Chromatography-Mass Spectrometry (GC-MS), Gas Chromatography-Flame Ionization Detection (GC-FID) and Fourier-Transform Infrared Spectroscopy (FTIR). Compounds identified were squalene, cholesterol and fatty acids, having a higher concentration of linolenic acid in extracts A and B, while extracts C and D had a higher content of palmitic acid. Additionally, FTIR detected characteristic peaks of lipids and triglycerides. Components of the lipophilic extracts suggested that this product could be used for skin illnesses treatment.

What the BTBR/J mouse has taught us about diabetes and diabetic complications

Human and mouse genetics have delivered numerous diabetogenic loci, but it is mainly through the use of animal models that the pathophysiological basis for their contribution to diabetes has been investigated. More than 20 years ago, we serendipidously identified a mouse strain that could serve as a model of obesity-prone type 2 diabetes, the BTBR (Black and Tan Brachyury) mouse (BTBR T+ Itpr3tf/J, 2018) carrying the Lepob mutation. We went on to discover that the BTBR-Lepob mouse is an excellent model of diabetic nephropathy and is now widely used by nephrologists in academia and the pharmaceutical industry. In this review, we describe the motivation for developing this animal model, the many genes identified and the insights about diabetes and diabetes complications derived from >100 studies conducted in this remarkable animal model.

VPAC2 receptor mediates VIP-potentiated insulin secretion via ion channels in rat pancreatic β cells

Vasoactive intestinal peptide (VIP), a small neuropeptide composing of 28 amino acids, functions as a neuromodulator with insulinotropic effect on pancreatic β cells, in which it is of vital importance in regulating the levels of blood glucose. VIP potently agonizes VPAC2 receptor (VPAC2-R). Agonists of VPAC2-R stimulate glucose-dependent insulin secretion. The purpose of this study was to further investigate the possible ion channel mechanisms in VPAC2-R-mediated VIP-potentiated insulin secretion. The results of insulin secretion experiments showed that VIP augmented insulin secretion in a glucose-dependent manner. The insulinotropic effect was mediated by VPAC2-R rather than VPAC1 receptor (VPAC1-R), through the adenylyl cyclase (AC)/protein kinase A (PKA) signalling pathway. The calcium imaging analysis demonstrated that VIP increased intracellular Ca²⁺ concentration ([Ca²⁺]_i). In addition, in the whole-cell voltage-clamp mode, we found that VIP blocked the voltage-dependent potassium (Kv) channel currents, while this effect was reversed by inhibiting the VPAC2-R, AC or PKA respectively. Taken together, these findings suggest that VIP stimulates insulin secretion by inhibiting the Kv channels, activating the Ca²⁺ channels, and increasing [Ca²⁺]_i through the VPAC2-R and AC/PKA signalling pathway. These findings provide theoretical basis for the research of VPAC2-R as a novel therapeutic target.

Hyperaminoacidemia induces pancreatic α cell proliferation via synergism between the mTORC1 and CaSR-Gq signaling pathways

Glucagon has emerged as a key regulator of extracellular amino acid (AA) homeostasis. Insufficient glucagon signaling results in hyperaminoacidemia, which drives adaptive proliferation of glucagon-producing α cells. Aside from mammalian target of rapamycin complex 1 (mTORC1), the role of other AA sensors in α cell proliferation has not been described. Here, using both genders of mouse islets and glucagon receptor (gcgr)-deficient zebrafish (Danio rerio), we show α cell proliferation requires activation of the extracellular signal-regulated protein kinase (ERK1/2) by the AA-sensitive calcium sensing receptor (CaSR). Inactivation of CaSR dampened α cell proliferation, which was rescued by re-expression of CaSR or activation of Gq, but not Gi, signaling in α cells. CaSR was also unexpectedly necessary for mTORC1 activation in α cells. Furthermore, coactivation of Gq and mTORC1 induced α cell proliferation independent of hyperaminoacidemia. These results reveal another AA-sensitive mediator and identify pathways necessary and sufficient for hyperaminoacidemia-induced α cell proliferation.

Islet cilia and glucose homeostasis

Diabetes is a growing pandemic affecting over ten percent of the U.S. population. Individuals with all types of diabetes exhibit glucose dysregulation due to altered function and coordination of pancreatic islets. Within the critical intercellular space in pancreatic islets, the primary cilium emerges as an important physical structure mediating cell-cell crosstalk and signal transduction. Many events leading to hormone secretion, including GPCR and second-messenger signaling, are spatiotemporally regulated at the level of the cilium. In this review, we summarize current knowledge of cilia action in islet hormone regulation and glucose homeostasis, focusing on newly implicated ciliary pathways that regulate insulin exocytosis and intercellular communication. We present evidence of key signaling proteins on islet cilia and discuss ways in which cilia might functionally connect islet endocrine cells with the non-endocrine compartments. These discussions aim to stimulate conversations regarding the extent of cilia-controlled glucose homeostasis in health and in metabolic diseases.

Insights into the regulation of podocyte and glomerular function by lactate and its metabolic sensor G-protein-coupled receptor 81

Podocytes and their foot processes are an important cellular layer of the renal filtration barrier that is involved in regulating glomerular permeability. Disturbances of podocyte function play a central role in the development of proteinuria in diabetic nephropathy. The retraction and effacement of podocyte foot processes that form slit diaphragms are a common feature of proteinuria. Correlations between the retraction of foot processes and the development of proteinuria are not well understood. Unraveling peculiarities of podocyte energy metabolism notably under diabetic conditions will provide insights into the pathogenesis of diabetic nephropathy. Intracellular metabolism in the cortical area of podocytes is regulated by glycolysis, whereas energy balance in the central area is controlled by oxidative phosphorylation and glycolysis. High glucose concentrations were recently reported to force podocytes to switch from mitochondrial oxidative phosphorylation to glycolysis, resulting in lactic acidosis. In this review, we hypothesize that the lactate receptor G-protein-coupled receptor 81 (also known as hydroxycarboxylic acid receptor 81) may contribute to the control of podocyte function in both health and disease.

Role of Reactive Oxygen Species in Glucose Metabolism Disorder in Diabetic Pancreatic β-Cells

The dysfunction of pancreatic β-cells plays a central role in the onset and progression of type 2 diabetes mellitus (T2DM). Insulin secretory defects in β-cells are characterized by a selective impairment of glucose stimulation, and a reduction in glucose-induced ATP production, which is essential for insulin secretion. High glucose metabolism for insulin secretion generates reactive oxygen species (ROS) in mitochondria. In addition, the expression of antioxidant enzymes is very low in β-cells. Therefore, β-cells are easily exposed to oxidative stress. In islet studies using a nonobese T2DM animal model that exhibits selective impairment of glucose-induced insulin secretion (GSIS), quenching ROS generated by glucose stimulation and accumulated under glucose toxicity can improve impaired GSIS. Acute ROS generation and toxicity cause glucose metabolism disorders through different molecular mechanisms. Nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor, is a master regulator of antioxidant defense and a potential therapeutic target in oxidative stress-related diseases, suggesting the possible involvement of Nrf2 in β-cell dysfunction caused by ROS. In this review, we describe the mechanisms of insulin secretory defects induced by oxidative stress in diabetic β-cells.

Emerging molecular technologies for light-mediated modulation of pancreatic beta-cell function

Background

Optogenetic modalities as well as optochemical and photopharmacological strategies, collectively termed optical methods, have revolutionized the control of cellular functions via light with great spatiotemporal precision. In comparison to the major advances in the photomodulation of signaling activities noted in neuroscience, similar applications to endocrine cells of the pancreas, particularly insulin-producing β-cells, have been limited. The availability of tools allowing light-mediated changes in the trafficking of ions such as K⁺ and Ca²⁺ and signaling intermediates such as cyclic adenosine monophosphate (cAMP), renders β-cells and their glucose-stimulated insulin secretion (GSIS) amenable to optoengineering for drug-free control of blood sugar.

Scope of review

The molecular circuit of the GSIS in β-cells is described with emphasis on intermediates which are targetable for optical intervention. Various pharmacological agents modifying the release of insulin are reviewed along with their documented side effects. These are contrasted with optical approaches, which have already been employed for engineering β-cell function or are considered for future such applications. Principal obstacles are also discussed as the implementation of optogenetics is pondered for tissue engineering and biology applications of the pancreas.

Major Conclusions

Notable advances in optogenetic, optochemical and photopharmacological tools are rendering feasible the smart engineering of pancreatic cells and tissues with light-regulated function paving the way for novel solutions for addressing pancreatic pathologies including diabetes.

Unravelling innervation of pancreatic islets

The central and peripheral nervous systems play critical roles in regulating pancreatic islet function and glucose metabolism. Over the last century, in vitro and in vivo studies along with examination of human pancreas samples have revealed the structure of islet innervation, investigated the contribution of sympathetic, parasympathetic and sensory neural pathways to glucose control, and begun to determine how the structure and function of pancreatic nerves are disrupted in metabolic disease. Now, state-of-the art techniques such as 3D imaging of pancreatic innervation and targeted in vivo neuromodulation provide further insights into the anatomy and physiological roles of islet innervation. Here, we provide a summary of the published work on the anatomy of pancreatic islet innervation, its roles, and evidence for disordered islet innervation in metabolic disease. Finally, we discuss the possibilities offered by new technologies to increase our knowledge of islet innervation and its contributions to metabolic regulation.

Metabolic Adaptions/Reprogramming in Islet Beta-Cells in Response to Physiological Stimulators—What Are the Consequences

Irreversible pancreatic β-cell damage may be a result of chronic exposure to supraphysiological glucose or lipid concentrations or chronic exposure to therapeutic anti-diabetic drugs. The β-cells are able to respond to blood glucose in a narrow concentration range and release insulin in response, following activation of metabolic pathways such as glycolysis and the TCA cycle. The β-cell cannot protect itself from glucose toxicity by blocking glucose uptake, but indeed relies on alternative metabolic protection mechanisms to avoid dysfunction and death. Alteration of normal metabolic pathway function occurs as a counter regulatory response to high nutrient, inflammatory factor, hormone or therapeutic drug concentrations. Metabolic reprogramming is a term widely used to describe a change in regulation of various metabolic enzymes and transporters, usually associated with cell growth and proliferation and may involve reshaping epigenetic responses, in particular the acetylation and methylation of histone proteins and DNA. Other metabolic modifications such as Malonylation, Succinylation, Hydroxybutyrylation, ADP-ribosylation, and Lactylation, may impact regulatory processes, many of which need to be investigated in detail to contribute to current advances in metabolism. By describing multiple mechanisms of metabolic adaption that are available to the β-cell across its lifespan, we hope to identify sites for metabolic reprogramming mechanisms, most of which are incompletely described or understood. Many of these mechanisms are related to prominent antioxidant responses. Here, we have attempted to describe the key β-cell metabolic adaptions and changes which are required for survival and function in various physiological, pathological and pharmacological conditions.

Therapeutic potential of vasoactive intestinal peptide and its receptor VPAC2 in type 2 diabetes

Owing to the increasing prevalence of type 2 diabetes, the development of novel hypoglycemic drugs has become a research hotspot, with the ultimate goal of developing therapeutic drugs that stimulate glucose-induced insulin secretion without inducing hypoglycemia. Vasoactive intestinal peptide (VIP), a 28-amino-acid peptide, can stimulate glucose-dependent insulin secretion, particularly by binding to VPAC2 receptors. VIP also promotes islet β-cell proliferation through the forkhead box M1 pathway, but the specific molecular mechanism remains to be studied. The clinical application of VIP is limited because of its short half-life and wide distribution in the human body. Based on the binding properties of VIP and VPAC2 receptors, VPAC2-selective agonists have been developed to serve as novel hypoglycemic drugs. This review summarizes the physiological significance of VIP in glucose homeostasis and the potential therapeutic value of VPAC2-selective agonists in type 2 diabetes.

Carbon monoxide enhances calcium transients and glucose-stimulated insulin secretion from pancreatic β-cells by activating Phospholipase C signal pathway in diabetic mice

In early stage of diabetes, insulin secretion from pancreatic β-cells is increased to deal with the elevated blood glucose. Previous studies have reported that islet-produced carbon monoxide (CO) is associated with increased glucose-stimulated insulin secretion from β-cells. However, this compensatory mechanism by which CO may act to enhance β-cell function remain unclear. In this study, we revealed that CO promoted intracellular calcium ([Ca²⁺]_i) elevation and glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells in leptin receptor deficient db/db mice but not in C57 mice. The stimulatory effects of CO on β-cell function in db/db mice was blocked by inhibition of Phospholipase C (PLC) signaling pathway. We further demonstrated that CO triggered [Ca²⁺]_i transients and enhanced GSIS in C57 islets when β-cells overexpressed with PLCγ1 and PLCδ1, but not PLCβ1. On the other hand, reducing PLCγ1 and PLCδ1 expressions in db/db islets dramatically attenuated the stimulatory effects of CO on β-cell function, whereas interfering PLCβ1 expression had no effects on CO-induced β-cell function enhancement. Our findings showing that CO elevated [Ca²⁺]_i and enhanced GSIS by activating PLC signaling through PLCγ1 and PLCδ1 isoforms in db/db pancreatic β-cells may suggest an important mechanism by which CO promotes β-cell function to prevent hyperglycemia. Our study may also provide new insights into the therapy for type II diabetes and offer a potential target for therapeutic applications of CO.

The relevance of adhesion G protein-coupled receptors in metabolic functions

G protein-coupled receptors (GPCRs) modulate a variety of physiological functions and have been proven to be outstanding drug targets. However, approximately one-third of all non-olfactory GPCRs are still orphans in respect to their signal transduction and physiological functions. Receptors of the class of Adhesion GPCRs (aGPCRs) are among these orphan receptors. They are characterized by unique features in their structure and tissue-specific expression, which yields them interesting candidates for deorphanization and testing as potential therapeutic targets. Capable of G-protein coupling and non-G protein-mediated function, aGPCRs may extend our repertoire of influencing physiological function. Besides their described significance in the immune and central nervous systems, growing evidence indicates a high importance of these receptors in metabolic tissue. RNAseq analyses revealed high expression of several aGPCRs in pancreatic islets, adipose tissue, liver, and intestine but also in neurons governing food intake. In this review, we focus on aGPCRs and their function in regulating metabolic pathways. Based on current knowledge, this receptor class represents high potential for future pharmacological approaches addressing obesity and other metabolic diseases.

PDX1- /NKX6.1+ progenitors derived from human pluripotent stem cells as a novel source of insulin-secreting cells

AIM

Beta cell replacement strategies are a promising alternative for diabetes treatment. Human pluripotent stem cells (hPSCs) serve as a scalable source for producing insulin-secreting cells for transplantation therapy. We recently generated novel hPSC-derived pancreatic progenitors, expressing high levels of the transcription factor NKX6.1, in the absence of PDX1 (PDX1^- /NKX6.1⁺ ). Herein, our aim was to characterize this novel population and assess its ability to differentiate into insulin-secreting beta cells in vitro.

MATERIALS AND METHODS

Three different hPSC lines were differentiated into PDX1^- /NKX6.1⁺ progenitors, which were further differentiated into insulin-secreting cells using two different protocols. The progenitors and beta cells were extensively characterized. Transcriptome analysis was performed at different stages and compared with the profiles of various pancreatic counterparts.

RESULTS

PDX1^- /NKX6.1⁺ progenitors expressed high levels of nestin, a key marker of pancreatic islet-derived progenitors, in the absence of E-cadherin, similar to pancreatic mesenchymal stem cells. At progenitor stage, comparison of the two populations showed downregulation of pancreatic epithelial genes and upregulation of neuronal development genes in PDX1^- /NKX6.1⁺ cells in comparison to the PDX1⁺ /NKX6.1⁺ cells. Interestingly, on further differentiation, PDX1^- /NKX6.1⁺ cells generated mono-hormonal insulin⁺ cells and activated pancreatic key genes, such as PDX1. The transcriptome profile of PDX1^- /NKX6.1⁺ -derived beta (3D-beta) was closely similar to those of human pancreatic islets and purified hPSC-derived beta cells. Also, the 3D-beta cells secreted C-peptide in response to increased glucose concentrations indicating their functionality.

CONCLUSION

These findings provide a novel source of insulin-secreting cells that can be used for beta cell therapy for diabetes.

Thiazolidinediones (TZDs) enhance insulin secretory response via GPR40 and adenylate cyclase (AC)

Thiazolidinediones are synthetic PPARγ ligands that enhance insulin sensitivity, and that could increase insulin secretion from β‐cells. However, the functional role and mechanism(s) of action in pancreatic β‐cells have not been investigated in detail.

Novel advances in understanding fatty acid-binding G protein-coupled receptors and their roles in controlling energy balance

Diabetes, obesity, and other metabolic diseases have been recognized as the main factors that endanger human health worldwide. Most of these metabolic syndromes develop when the energy balance in the body is disrupted. Energy balance depends upon the systemic regulation of food intake, glucose homeostasis, and lipid metabolism. Fatty acid-binding G protein-coupled receptors (GPCRs) are widely expressed in various types of tissues and cells involved in energy homeostasis regulation. In this review, the distribution and biological functions of fatty acid-binding GPCRs are summarized, particularly with respect to the gut, pancreas, and adipose tissue. A systematic understanding of the physiological functions of the fatty acid-binding GPCRs involved in energy homeostasis regulation will help in identifying novel pharmacological targets for metabolic diseases.

GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo

BACKGROUND

Insulin secretion from the pancreatic β-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed.

RESULTS

Using GRK2 hemizygous mice, isolated pancreatic islets, and model β-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/- mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/- mice. Using nanoBRET in β-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent β-arrestin recruitment.

CONCLUSIONS

Overall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor β-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.

Metabolic Functions of G Protein-Coupled Receptors and β-Arrestin-Mediated Signaling Pathways in the Pathophysiology of Type 2 Diabetes and Obesity

Seven transmembrane receptors (7TMRs), often termed G protein-coupled receptors (GPCRs), are the most common target of therapeutic drugs used today. Many studies suggest that distinct members of the GPCR superfamily represent potential targets for the treatment of various metabolic disorders including obesity and type 2 diabetes (T2D). GPCRs typically activate different classes of heterotrimeric G proteins, which can be subgrouped into four major functional types: G_αs, G_αi, G_αq/11, and G_12/13, in response to agonist binding. Accumulating evidence suggests that GPCRs can also initiate β-arrestin-dependent, G protein-independent signaling. Thus, the physiological outcome of activating a certain GPCR in a particular tissue may also be modulated by β-arrestin-dependent, but G protein-independent signaling pathways. In this review, we will focus on the role of G protein- and β-arrestin-dependent signaling pathways in the development of obesity and T2D-related metabolic disorders.

Regulation of the JAK2-STAT5 Pathway by Signaling Molecules in the Mammary Gland

Janus kinase 2 (JAK2) and signal transducers and activators of transcription 5 (STAT5) are involved in the proliferation, differentiation, and survival of mammary gland epithelial cells. Dysregulation of JAK2-STAT5 activity invariably leads to mammary gland developmental defects and/or diseases, including breast cancer. Proper functioning of the JAK2-STAT5 signaling pathway relies on crosstalk with other signaling pathways (synergistically or antagonistically), which leads to normal biological performance. This review highlights recent progress regarding the critical components of the JAK2-STAT5 pathway and its crosstalk with G-protein coupled receptor (GPCR) signaling, PI3K-Akt signaling, growth factors, inflammatory cytokines, hormone receptors, and cell adhesion.

A preliminary study: proteomic analysis of exosomes derived from thyroid-stimulating hormone-stimulated HepG2 cells

BACKGROUND

Thyroid-stimulating hormone (TSH) plays an important role in the regulation of lipid metabolism. However, little is known about the role that exosomes play in the process of TSH-induced lipotoxicity in non-alcoholic fatty liver disease (NAFLD). As a preliminary step, the present study set out to investigate alterations in protein expression in exosomes derived from TSH-stimulated HepG2 cells.

METHODS

HepG2 cells were treated with TSH, exosomes were collected, and proteins were identified by mass spectrometry (MS). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genome (KEGG) pathway analysis were performed to analyze the identified proteins.

RESULTS

TSH treatment significantly increased exosomal production and changed the exosomal proteomic profile in HepG2 cells. Among the 1728 proteins, 140 identified proteins were upregulated and seven proteins were downregulated. GO analysis and KEGG analysis revealed that these proteins were involved in multiple processes including metabolism, apoptosis, and inflammation.

CONCLUSION

Our preliminary study demonstrated that exosomes derived from TSH-stimulated hepatocytes were increased and showed a specific altered spectrum of proteins, many of which were involved in metabolism, signal transduction, apoptosis, and inflammation. This study offers new insights into the pathogenesis of TSH-induced lipotoxicity in NAFLD.

Involvement of the Adhesion GPCRs Latrophilins in the Regulation of Insulin Release

Insulin secretion from pancreatic β cells is a highly complex and tightly regulated process. Its dysregulation is one characteristic of type 2 diabetes, and thus, an in-depth understanding of the mechanisms controlling insulin secretion is essential for rational therapeutic intervention. G-protein-coupled receptors (GPCRs) have been established as major regulators of insulin exocytosis. Recent studies also suggest the involvement of adhesion GPCRs, a non-prototypical class of GPCRs. Here, we identify latrophilins, which belong to the class of adhesion GPCRs, to be highly expressed in different cell types of pancreatic islets. In vitro and ex vivo analyses show that distinct splice variants of the latrophilin LPHN3/ADGRL3 decrease insulin secretion from pancreatic β cells by reducing intracellular cyclic AMP levels via the G_i-mediated pathway. Our data highlight the key role of LPHN3 in modulating insulin secretion and its potential as therapeutic target for type 2 diabetes.

The expanding functional roles and signaling mechanisms of adhesion G protein-coupled receptors

The adhesion class of G protein-coupled receptors (GPCRs) is the second largest family of GPCRs (33 members in humans). Adhesion GPCRs (aGPCRs) are defined by a large extracellular N-terminal region that is linked to a C-terminal seven transmembrane (7TM) domain via a GPCR-autoproteolysis inducing (GAIN) domain containing a GPCR proteolytic site (GPS). Most aGPCRs undergo autoproteolysis at the GPS motif, but the cleaved fragments stay closely associated, with the N-terminal fragment (NTF) bound to the 7TM of the C-terminal fragment (CTF). The NTFs of most aGPCRs contain domains known to be involved in cell-cell adhesion, while the CTFs are involved in classical G protein signaling, as well as other intracellular signaling. In this workshop report, we review the most recent findings on the biology, signaling mechanisms, and physiological functions of aGPCRs.

Free Fatty Acid Receptors in Health and Disease

Fatty acids are metabolized and synthesized as energy substrates during biological responses. Long- and medium-chain fatty acids derived mainly from dietary triglycerides, and short-chain fatty acids (SCFAs) produced by gut microbial fermentation of the otherwise indigestible dietary fiber, constitute the major sources of free fatty acids (FFAs) in the metabolic network. Recently, increasing evidence indicates that FFAs serve not only as energy sources but also as natural ligands for a group of orphan G protein-coupled receptors (GPCRs) termed free fatty acid receptors (FFARs), essentially intertwining metabolism and immunity in multiple ways, such as via inflammation regulation and secretion of peptide hormones. To date, several FFARs that are activated by the FFAs of various chain lengths have been identified and characterized. In particular, FFAR1 (GPR40) and FFAR4 (GPR120) are activated by long-chain saturated and unsaturated fatty acids, while FFAR3 (GPR41) and FFAR2 (GPR43) are activated by SCFAs, mainly acetate, butyrate, and propionate. In this review, we discuss the recent reports on the key physiological functions of the FFAR-mediated signaling transduction pathways in the regulation of metabolism and immune responses. We also attempt to reveal future research opportunities for developing therapeutics for metabolic and immune disorders.

Gut microbiota confers host resistance to obesity by metabolizing dietary polyunsaturated fatty acids

Gut microbiota mediates the effects of diet, thereby modifying host metabolism and the incidence of metabolic disorders. Increased consumption of omega-6 polyunsaturated fatty acid (PUFA) that is abundant in Western diet contributes to obesity and related diseases. Although gut-microbiota-related metabolic pathways of dietary PUFAs were recently elucidated, the effects on host physiological function remain unclear. Here, we demonstrate that gut microbiota confers host resistance to high-fat diet (HFD)-induced obesity by modulating dietary PUFAs metabolism. Supplementation of 10-hydroxy-cis-12-octadecenoic acid (HYA), an initial linoleic acid-related gut-microbial metabolite, attenuates HFD-induced obesity in mice without eliciting arachidonic acid-mediated adipose inflammation and by improving metabolic condition via free fatty acid receptors. Moreover, Lactobacillus-colonized mice show similar effects with elevated HYA levels. Our findings illustrate the interplay between gut microbiota and host energy metabolism via the metabolites of dietary omega-6-FAs thereby shedding light on the prevention and treatment of metabolic disorders by targeting gut microbial metabolites.

The gut microbiome is an important regulator of metabolic health. Here the authors show that intestinal bacteria metabolize dietary linoleic acid to 10-hydroxy-cis-12-octadecenoic acid (HYA) which confers host resistance to high fat diet-induced obesity in mice.

Activating Effects of Phenolics from Apache Red Zea mays L. on Free Fatty Acid Receptor 1 and Glucokinase Evaluated with a Dual Culture System with Epithelial, Pancreatic, and Liver Cells

The aim was to characterize a phenolic-rich water extract from the pericarp of an improved genotype of Apache red maize (RPE) and evaluate its ability to activate the type 2 diabetes markers free fatty acid receptor 1 (GPR40) and glucokinase (GK) in vitro. The extract contained mainly phenolic acids, anthocyanins, and other flavonoids. RPE inhibited α-amylase (IC₅₀ = 88.3 μg/mL), α-glucosidase (IC₅₀ = 169.3 μg/mL), and reduced glucose transport in a Caco-2 cell monolayer (up to 25%). Furthermore, RPE activated GPR40 (EC₅₀ = 77.7 μg/mL) in pancreatic INS-1E cells and GK (EC₅₀ = 43.4 μg/mL) in liver HepG2 cells, potentially through allosteric modulation. RPE activated GPR40-related insulin secretory pathway and activated the glucose metabolism regulator AMPK (up to 78%). Our results support the hypothesis that foods with a high concentration of anthocyanins and phenolic acids, such as in the selected variety of maize used, could ameliorate obesity and type 2 diabetes comorbidities.

Translational assessment of a genetic engineering methodology to improve islet function for transplantation

Background

The functional quality of insulin-secreting islet beta cells is a major factor determining the outcome of clinical transplantations for diabetes. It is therefore of importance to develop methodological strategies aiming at optimizing islet cell function prior to transplantation. In this study we propose a synthetic biology approach to genetically engineer cellular signalling pathways in islet cells.

Methods

We established a novel procedure to modify islet beta cell function by combining adenovirus-mediated transduction with reaggregation of islet cells into pseudoislets. As a proof-of-concept for the genetic engineering of islets prior to transplantation, this methodology was applied to increase the expression of the V1b receptor specifically in insulin-secreting beta cells. The functional outcomes were assessed in vitro and in vivo following transplantation into the anterior chamber of the eye.

Findings

Pseudoislets produced from mouse dissociated islet cells displayed basic functions similar to intact native islets in terms of glucose induced intracellular signalling and insulin release, and after transplantation were properly vascularized and contributed to blood glucose homeostasis. The synthetic amplification of the V1b receptor signalling in beta cells successfully modulated pseudoislet function in vitro. Finally, in vivo responses of these pseudoislet grafts to vasopressin allowed evaluation of the potential benefits of this approach in regenerative medicine.

Interpretation

These results are promising first steps towards the generation of high-quality islets and suggest synthetic biology as an important tool in future clinical islet transplantations. Moreover, the presented methodology might serve as a useful research strategy to dissect cellular signalling mechanisms of relevance for optimal islet function.

Functional characterization of β2-adrenergic and insulin receptor heteromers

This study aimed to functionally characterize β₂-adrenergic (β₂AR) and insulin receptor (IR) heteromers in regard to β-arrestin 2 (βarr2) recruitment and cAMP signaling and to examine the involvement of the cytoplasmic portion of the IR β chain in heteromerization with β₂AR. Evidence for β₂AR:IR:βarr2 complex formation and the specificity of the IR:βarr2 interaction was first provided by bioinfomatics analysis. Receptor-heteromer investigation technology (HIT) then provided functional evidence of β₂AR:IR heterodimerization by showing isoproterenol-induced but not insulin-induced GFP²-βarr2 recruitment to the β₂AR:IR complex; the IR:βarr2 interaction was found to only be constitutive. The constitutive IR:βarr2 BRET signal (BRET_const) was significantly smaller in cells coexpressing IR-RLuc8 and a GFP²-βarr2 1-185 mutant lacking the proposed IR binding domain. β₂AR:IR heteromerization also influenced the pharmacological phenotype of β₂AR, i.e., its efficacy in recruiting βarr2 and activating cAMP signaling. Evidence suggesting involvement of the cytoplasmic portion of the IR β chain in the interaction with β₂AR was provided by BRET² saturation and HIT assays using an IR 1-1271 stop mutant lacking the IR C-terminal tail region. For the complex consisting of IR 1-1271-RLuc8:β₂AR-GFP², saturation was not reached, most likely reflecting random collisions between IR 1-1271 and β₂AR. Furthermore, in the HIT assay, no substantial agonist-induced increase in the BRET² signal was detected that would be indicative of βarr2 recruitment to the IR 1-1271:β₂AR heteromer. Complementary 3D visualization of β₂AR:IR provided supporting evidence for stability of the heterotetramer complex and identified amino acid residues involved in β₂AR:IR heteromerization. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.

The regulation of insulin secretion via phosphoinositide-specific phospholipase Cβ signaling

Phospholipase Cβ (PLCβ) is a membrane-associated enzyme activated by membrane receptors, especially G-protein coupled receptors (GPCRs). It propagates intracellular signaling by mediating phospholipid metabolism and generating key second messengers, such as inositol triphosphate and diacylglycerol, leading to intracellular Ca²⁺ mobilization and activation of kinases, such as protein kinases C. In pancreatic β-cells, PLCβ-mediated signaling activated by various factors, such as free fatty acids and neuronal and hormonal ligands, has been confirmed as being involved in the regulation of insulin secretion, and PLCβs have been regarded as essential mediators for augmenting insulin secretion. In this review, we describe the physiological function of PLCβs in the regulation of glucose-stimulated insulin secretion and discuss emerging data on GPCR/PLCβ signaling that is being developed as a target for the treatment of diabetes mellitus.

IGF-1 and somatocrinin trigger islet differentiation in human amniotic membrane derived mesenchymal stem cells

AIM

To induce differentiation of human amniotic membrane derived mesenchymal stem cells (hAMMSCs) into insulin producing cells (IPCs) by treating with somatocrinin or growth hormone releasing hormone (GHRH) and Insulin-like growth factor-1 (IGF-1).

MAIN METHOD

In this investigation, we cultivated and characterized hAMMSCs and then treated with IGF-1 and somatocrinin to find out whether this combination gives better yield of insulin producing cells. We showed that hAMMSCs can give rise to IPCs on exposure to serum-free defined media containing specific growth factors and differentiating agents in presence of IGF-1 and somatocrinin.

KEY FINDING

A combination of IGF-1 and somatocrinin lead to differentiation of large number of IPCs from hAMMSCs. These IPCs were found to be positive for dithizone indicating their insulin secretory mechanism. Moreover these cells were also found to be positive for C-peptide. IPCs released insulin in response to glucose challenge. Gene expression analysis exhibited significant up-regulation of pancreatic transcription factor GLUT2 and Insulin.

SIGNIFICANCE

Our data thus demonstrates for the first time that somatocrinin and IGF-1 synergistically enhance the differentiation of hAMMSCs into IPCs.

β-Cell Receptor Tyrosine Kinases in Controlling Insulin Secretion and Exocytotic Machinery: c-Kit and Insulin Receptor

Insulin secretion from pancreatic β-cells is initiated through channel-mediated depolarization, cytoskeletal remodeling, and vesicle tethering at the cell membrane, all of which can be regulated through cell surface receptors. Receptor tyrosine kinases (RTKs) promote β-cell development and postnatal signaling to improve β-cell mass and function, yet their activation has also been shown to initiate exocytotic events in β-cells. This review examines the role of RTK signaling in insulin secretion, with a focus on RTKs c-Kit and insulin receptor (IR). Pathways that control insulin release and the potential interplay between c-Kit and IR signaling are discussed, along with clinical implications of RTK therapy on insulin secretion.

Sympathetic innervation is essential for metabolic homeostasis and pancreatic beta cell function in adult rats

Obesity is associated with an imbalance in the activity of the autonomic nervous system (ANS), specifically in the organs involved in energy metabolism. The pancreatic islets are richly innervated by the ANS, which tunes the insulin release due to changes in energy demand. Therefore, changes in the sympathetic input that reach the pancreas can lead to metabolic dysfunctions. To evaluate the role of the sympathetic ends that innervate the pancreas, 60-day-old male Wistar rats were subjected to sympathectomy (SYM) or were sham-operated (SO). At 120 day-old SYM rats exhibited an increase in body weight, fat pads and metabolic dysfunctions. Decreases in the HOMA-IR and reductions in insulin release were observed both in vivo and in vitro. Furthermore, the SYM rats exhibited altered pancreatic islet function in both muscarinic and adrenergic assays and exhibited high protein expression of the alpha-2 adrenergic receptor (α2AR). Because α2AR has been linked to type 2 diabetes, these findings demonstrate the clinical implications of this study.

Structure Based Virtual Screening Studies to Identify Novel Potential Compounds for GPR142 and Their Relative Dynamic Analysis for Study of Type 2 Diabetes

GPR142 (G protein receptor 142) is a novel orphan GPCR (G protein coupled receptor) belonging to "Class A" of GPCR family and expressed in β cells of pancreas. In this study, we reported the structure based virtual screening to identify the hit compounds which can be developed as leads for potential agonists. The results were validated through induced fit docking, pharmacophore modeling, and system biology approaches. Since, there is no solved crystal structure of GPR142, we attempted to predict the 3D structure followed by validation and then identification of active site using threading and ab initio methods. Also, structure based virtual screening was performed against a total of 1171519 compounds from different libraries and only top 20 best hit compounds were screened and analyzed. Moreover, the biochemical pathway of GPR142 complex with screened compound2 was also designed and compared with experimental data. Interestingly, compound2 showed an increase in insulin production via Gq mediated signaling pathway suggesting the possible role of novel GPR142 agonists in therapy against type 2 diabetes.

Insights into unbound-bound states of GPR142 receptor in a membrane-aqueous system using molecular dynamics simulations

G protein coupled receptors (GPCRs) are source machinery in signal transduction pathways and being one of the major therapeutic targets play a significant in drug discovery. GPR142, an orphan GPCR, has been implicated in the regulation of insulin, thereby having a crucial role in Type II diabetes management. Deciphering of the structures of orphan, GPCRs (O-GPCRs) offer better prospects for advancements in research in ion translocation and transduction of extracellular signals. As the crystallographic structure of GPR142 is not available in PDB, therefore, threading and ab initio-based approaches were used for 3D modeling of GPR142. Molecular dynamic simulations (900 ns) were performed on the 3D model of GPR142 and complexes of GPR142 with top five hits, obtained through virtual screening, embedded in lipid bilayer with aqueous system using OPLS force field. Compound 1, 3, and 4 may act as scaffolds for designing potential lead agonists for GPR142. The finding of GPR142 MD simulation study provides more comprehensive representation of the functional properties. The concern for Type II diabetes is increasing worldwide and successful treatment of this disease demands novel drugs with better efficacy.

Combined immunotherapy with "anti-insulin resistance" therapy as a novel therapeutic strategy against neurodegenerative diseases

Protein aggregation is a pathological hallmark of and may play a central role in the neurotoxicity in age-associated neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Accordingly, inhibiting aggregation of amyloidogenic proteins, including amyloid β and α-synuclein, has been a main therapeutic target for these disorders. Among various strategies, amyloid β immunotherapy has been extensively investigated in Alzheimer's disease, followed by similar studies of α-synuclein in Parkinson's disease. Notably, a recent study of solanezumab, an amyloid β monoclonal antibody, raises hope for the further therapeutic potential of immunotherapy, not only in Alzheimer's disease, but also for other neurodegenerative disorders, including Parkinson's disease. Thus, it is expected that further refinement of immunotherapy against neurodegenerative diseases may lead to increasing efficacy. Meanwhile, type II diabetes mellitus has been associated with an increased risk of neurodegenerative disease, such as Alzheimer's disease and Parkinson's disease, and studies have shown that metabolic dysfunction and abnormalities surrounding insulin signaling may underlie disease progression. Naturally, "anti-insulin resistance" therapy has emerged as a novel paradigm in the therapy of neurodegenerative diseases. Indeed, incretin agonists, which stimulate pancreatic insulin secretion, reduce dopaminergic neuronal loss and suppress Parkinson's disease disease progression in clinical trials. Similar studies are ongoing also in Alzheimer's disease. This paper focuses on critical issues in "immunotherapy" and "anti-insulin resistance" therapy in relation to therapeutic strategies against neurodegenerative disease, and more importantly, how they might merge mechanistically at the point of suppression of protein aggregation, raising the possibility that combined immunotherapy and "anti-insulin resistance" therapy may be superior to either monotherapy.

SCFA Receptors in Pancreatic β Cells: Novel Diabetes Targets?

Nutrient sensing receptors are key metabolic mediators of responses to dietary and endogenously derived nutrients. These receptors are largely G-protein-coupled receptors (GPCRs) and many are gaining significant interest as drug targets with a potential therapeutic role in metabolic diseases. A distinct subclass of nutrient sensing GPCRs, two short chain fatty acid (SCFA) receptors (FFA2 and FFA3) are uniquely responsive to gut microbiota derived nutrients (such as acetate, propionate, and butyrate). Pharmacological, molecular, and genetic studies have investigated their role in organismal glucose metabolism and recently in pancreatic β cell biology. Here, we summarize the present knowledge on the role of these receptors as metabolic sensors in β cell function and physiology, revealing new therapeutic opportunities for type 2 diabetes.

Loss of Free Fatty Acid Receptor 2 leads to impaired islet mass and beta cell survival

The regulation of pancreatic β cell mass is a critical factor to help maintain normoglycemia during insulin resistance. Nutrient-sensing G protein-coupled receptors (GPCR) contribute to aspects of β cell function, including regulation of β cell mass. Nutrients such as free fatty acids (FFAs) contribute to precise regulation of β cell mass by signaling through cognate GPCRs, and considerable evidence suggests that circulating FFAs promote β cell expansion by direct and indirect mechanisms. Free Fatty Acid Receptor 2 (FFA2) is a β cell-expressed GPCR that is activated by short chain fatty acids, particularly acetate. Recent studies of FFA2 suggest that it may act as a regulator of β cell function. Here, we set out to explore what role FFA2 may play in regulation of β cell mass. Interestingly, Ffar2(-/-) mice exhibit diminished β cell mass at birth and throughout adulthood, and increased β cell death at adolescent time points, suggesting a role for FFA2 in establishment and maintenance of β cell mass. Additionally, activation of FFA2 with Gαq/11-biased agonists substantially increased β cell proliferation in in vitro and ex vivo proliferation assays. Collectively, these data suggest that FFA2 may be a novel therapeutic target to stimulate β cell growth and proliferation.

Pancreatic Beta Cell G-Protein Coupled Receptors and Second Messenger Interactions: A Systems Biology Computational Analysis

Insulin secretory in pancreatic beta-cells responses to nutrient stimuli and hormonal modulators include multiple messengers and signaling pathways with complex interdependencies. Here we present a computational model that incorporates recent data on glucose metabolism, plasma membrane potential, G-protein-coupled-receptors (GPCR), cytoplasmic and endoplasmic reticulum calcium dynamics, cAMP and phospholipase C pathways that regulate interactions between second messengers in pancreatic beta-cells. The values of key model parameters were inferred from published experimental data. The model gives a reasonable fit to important aspects of experimentally measured metabolic and second messenger concentrations and provides a framework for analyzing the role of metabolic, hormones and neurotransmitters changes on insulin secretion. Our analysis of the dynamic data provides support for the hypothesis that activation of Ca²⁺-dependent adenylyl cyclases play a critical role in modulating the effects of glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP) and catecholamines. The regulatory properties of adenylyl cyclase isoforms determine fluctuations in cytoplasmic cAMP concentration and reveal a synergistic action of glucose, GLP-1 and GIP on insulin secretion. On the other hand, the regulatory properties of phospholipase C isoforms determine the interaction of glucose, acetylcholine and free fatty acids (FFA) (that act through the FFA receptors) on insulin secretion. We found that a combination of GPCR agonists activating different messenger pathways can stimulate insulin secretion more effectively than a combination of GPCR agonists for a single pathway. This analysis also suggests that the activators of GLP-1, GIP and FFA receptors may have a relatively low risk of hypoglycemia in fasting conditions whereas an activator of muscarinic receptors can increase this risk. This computational analysis demonstrates that study of second messenger pathway interactions will improve understanding of critical regulatory sites, how different GPCRs interact and pharmacological targets for modulating insulin secretion in type 2 diabetes.

GPR40 agonist ameliorates liver X receptor-induced lipid accumulation in liver by activating AMPK pathway

Hepatic steatosis is strongly linked to insulin resistance and type 2 diabetes. GPR40 is a G protein-coupled receptor mediating free fatty acid-induced insulin secretion and thus plays a beneficial role in the improvement of diabetes. However, the impact of GPR40 agonist on hepatic steatosis still remains to be elucidated. In the present study, we found that activation of GPR40 by its agonist GW9508 attenuated Liver X receptor (LXR)-induced hepatic lipid accumulation. Activation of LXR in the livers of C57BL/6 mice fed a high-cholesterol diet and in HepG2 cells stimulated by chemical agonist caused increased expression of its target lipogenic genes and subsequent lipid accumulation. All these effects of LXR were dramatically downregulated after GW9508 supplementation. Moreover, GPR40 activation was accompanied by upregulation of AMPK pathway, whereas the inhibitive effect of GPR40 on the lipogenic gene expression was largely abrogated by AMPK knockdown. Taken together, our results demonstrated that GW9508 exerts a beneficial effect to ameliorate LXR-induced hepatic steatosis through regulation of AMPK signaling pathway.

Trimeprazine increases IRS2 in human islets and promotes pancreatic β cell growth and function in mice

The capacity of pancreatic β cells to maintain glucose homeostasis during chronic physiologic and immunologic stress is important for cellular and metabolic homeostasis. Insulin receptor substrate 2 (IRS2) is a regulated adapter protein that links the insulin and IGF1 receptors to downstream signaling cascades. Since strategies to maintain or increase IRS2 expression can promote β cell growth, function, and survival, we conducted a screen to find small molecules that can increase IRS2 mRNA in isolated human pancreatic islets. We identified 77 compounds, including 15 that contained a tricyclic core. To establish the efficacy of our approach, one of the tricyclic compounds, trimeprazine tartrate, was investigated in isolated human islets and in mouse models. Trimeprazine is a first-generation antihistamine that acts as a partial agonist against the histamine H1 receptor (H1R) and other GPCRs, some of which are expressed on human islets. Trimeprazine promoted CREB phosphorylation and increased the concentration of IRS2 in islets. IRS2 was required for trimeprazine to increase nuclear Pdx1, islet mass, β cell replication and function, and glucose tolerance in mice. Moreover, trimeprazine synergized with anti-CD3 Abs to reduce the progression of diabetes in NOD mice. Finally, it increased the function of human islet transplants in streptozotocin-induced (STZ-induced) diabetic mice. Thus, trimeprazine, its analogs, or possibly other compounds that increase IRS2 in islets and β cells without adverse systemic effects might provide mechanism-based strategies to prevent the progression of diabetes.

Differential expression network analysis for diabetes mellitus type 2 based on expressed level of islet cells

OBJECTIVE

Diabetes mellitus type 2 (T2DM) is a metabolic disease that has become a pressing issue, with potential adverse impact on mental health. We aimed to explore the potential molecular mechanism of T2DM.

MATERIAL AND METHODS

GSE38642 microarray data downloaded from gene expression omnibus was used to identify the differentially expressed genes (DEGs). Profiling of complex functionality (ProfCom) was used to analyze the complex function and mine T2DM signature genes. Finally, the differential expression network (DEN) was constructed.

RESULTS

We identified 147 DEGs including 59 up- and 88 down-regulated genes. With increasing of degree, the specificity of functional description of DEGs was higher. GO term of "integral to membrane and immune response (not receptor activity) not regulation of immune response" in degree 4 was enriched by 6 DEGs, while the GO term of "immune response" in degree 1 was enriched by 12 DEGs. Two complex functions of integral to membrane an immune response and response to glucose stimulus were enriched by 11 T2DM signature genes including ARG2, GLP1R, PFKFB2, PTPRN, ACSL5, CCR7, IL2RA, IL7R, IL1R2, IL1RL1 and CHST4. Finally, DEN including 11 signature genes and 491 edges was obtained.

CONCLUSION

The identified DEGs especially 11 signature genes such as PTPRN, GLP1R, CCR7 and IL2RA may play important roles in the pathogenesis of T2DM.

Growth Hormone-Releasing Hormone in Diabetes

Growth hormone-releasing hormone (GHRH) is produced by the hypothalamus and stimulates growth hormone synthesis and release in the anterior pituitary gland. In addition, GHRH is an important regulator of cellular functions in many cells and organs. Expression of GHRH G-Protein Coupled Receptor (GHRHR) has been demonstrated in different peripheral tissues and cell types, including pancreatic islets. Among the peripheral activities, recent studies demonstrate a novel ability of GHRH analogs to increase and preserve insulin secretion by beta-cells in isolated pancreatic islets, which makes them potentially useful for diabetes treatment. This review considers the role of GHRHR in the beta-cell and addresses the unique engineered GHRH agonists and antagonists for treatment of type 2 diabetes mellitus. We discuss the similarity of signaling pathways activated by GHRHR in pituitary somatotrophs and in pancreatic beta-cells and possible ways as to how the GHRHR pathway can interact with glucose and other secretagogues to stimulate insulin secretion. We also consider the hypothesis that novel GHRHR agonists can improve glucose metabolism in Type 2 diabetes by preserving the function and survival of pancreatic beta-cells. Wound healing and cardioprotective action with new GHRH agonists suggest that they may prove useful in ameliorating certain diabetic complications. These findings highlight the future potential therapeutic effectiveness of modulators of GHRHR activity for the development of new therapeutic approaches in diabetes and its complications.