Ghrelin Inhibition Restores Glucose Homeostasis in Hepatocyte Nuclear Factor-1α (MODY3)-Deficient Mice

Ghrelin as a Biomarker of "Immunometabolic Depression" and Its Connection with Dysbiosis

Ghrelin, a gastrointestinal peptide, is an endogenous ligand of growth hormone secretagogue receptor 1a (GHSR1a), which is mainly produced by X/A-like cells in the intestinal mucosa. Beyond its initial description as a growth hormone (GH) secretagogue stimulator of appetite, ghrelin has been revealed to have a wide range of physiological effects, for example, the modulation of inflammation; the improvement of cardiac performance; the modulation of stress, anxiety, taste sensation, and reward-seeking behavior; and the regulation of glucose metabolism and thermogenesis. Ghrelin secretion is altered in depressive disorders and metabolic syndrome, which frequently co-occur, but it is still unknown how these modifications relate to the physiopathology of these disorders. This review highlights the increasing amount of research establishing the close relationship between ghrelin, nutrition, microbiota, and disorders such as depression and metabolic syndrome, and it evaluates the ghrelinergic system as a potential target for the development of effective pharmacotherapies.

Ghrelin does not impact the blunted counterregulatory response to recurrent hypoglycemia in mice

Introduction

Recurrent episodes of insulin-induced hypoglycemia in patients with diabetes mellitus can result in hypoglycemia-associated autonomic failure (HAAF), which is characterized by a compromised response to hypoglycemia by counterregulatory hormones (counterregulatory response; CRR) and hypoglycemia unawareness. HAAF is a leading cause of morbidity in diabetes and often hinders optimal regulation of blood glucose levels. Yet, the molecular pathways underlying HAAF remain incompletely described. We previously reported that in mice, ghrelin is permissive for the usual CRR to insulin-induced hypoglycemia. Here, we tested the hypothesis that attenuated release of ghrelin both results from HAAF and contributes to HAAF.

Methods

C57BL/6N mice, ghrelin-knockout (KO) + control mice, and GhIRKO (ghrelin cell-selective insulin receptor knockout) + control mice were randomized to one of three treatment groups: a "Euglycemia" group was injected with saline and remained euglycemic; a 1X hypoglycemia ("1X Hypo") group underwent a single episode of insulin-induced hypoglycemia; a recurrent hypoglycemia ("Recurrent Hypo") group underwent repeated episodes of insulin-induced hypoglycemia over five successive days.

Results

Recurrent hypoglycemia exaggerated the reduction in blood glucose (by ~30%) and attenuated the elevations in plasma levels of the CRR hormones glucagon (by 64.5%) and epinephrine (by 52.9%) in C57BL/6N mice compared to a single hypoglycemic episode. Yet, plasma ghrelin was equivalently reduced in "1X Hypo" and "Recurrent Hypo" C57BL/6N mice. Ghrelin-KO mice exhibited neither exaggerated hypoglycemia in response to recurrent hypoglycemia, nor any additional attenuation in CRR hormone levels compared to wild-type littermates. Also, in response to recurrent hypoglycemia, GhIRKO mice exhibited nearly identical blood glucose and plasma CRR hormone levels as littermates with intact insulin receptor expression (floxed-IR mice), despite higher plasma ghrelin in GhIRKO mice.

Conclusions

These data suggest that the usual reduction of plasma ghrelin due to insulin-induced hypoglycemia is unaltered by recurrent hypoglycemia and that ghrelin does not impact blood glucose or the blunted CRR hormone responses during recurrent hypoglycemia.

HNF1A Mutations and Beta Cell Dysfunction in Diabetes

Understanding the genetic factors of diabetes is essential for addressing the global increase in type 2 diabetes. HNF1A mutations cause a monogenic form of diabetes called maturity-onset diabetes of the young (MODY), and HNF1A single-nucleotide polymorphisms are associated with the development of type 2 diabetes. Numerous studies have been conducted, mainly using genetically modified mice, to explore the molecular basis for the development of diabetes caused by HNF1A mutations, and to reveal the roles of HNF1A in multiple organs, including insulin secretion from pancreatic beta cells, lipid metabolism and protein synthesis in the liver, and urinary glucose reabsorption in the kidneys. Recent studies using human stem cells that mimic MODY have provided new insights into beta cell dysfunction. In this article, we discuss the involvement of HNF1A in beta cell dysfunction by reviewing previous studies using genetically modified mice and recent findings in human stem cell-derived beta cells.

Ghrelin cell-expressed insulin receptors mediate meal- and obesity-induced declines in plasma ghrelin

Mechanisms underlying postprandial and obesity-associated plasma ghrelin reductions are incompletely understood. Here, using ghrelin cell-selective insulin receptor-KO (GhIRKO) mice, we tested the impact of insulin, acting via ghrelin cell-expressed insulin receptors (IRs), to suppress ghrelin secretion. Insulin reduced ghrelin secretion from cultured gastric mucosal cells of control mice but not from those of GhIRKO mice. Acute insulin challenge and insulin infusion during both hyperinsulinemic-hypoglycemic clamps and hyperinsulinemic-euglycemic clamps lowered plasma ghrelin in control mice but not GhIRKO mice. Thus, ghrelin cell-expressed IRs are required for insulin-mediated reductions in plasma ghrelin. Furthermore, interventions that naturally raise insulin (glucose gavage, refeeding following fasting, and chronic high-fat diet) also lowered plasma ghrelin only in control mice - not GhIRKO mice. Thus, meal- and obesity-associated increases in insulin, acting via ghrelin cell-expressed IRs, represent a major, direct negative modulator of ghrelin secretion in vivo, as opposed to ingested or metabolized macronutrients. Refed GhIRKO mice exhibited reduced plasma insulin, highlighting ghrelin's actions to inhibit insulin release via a feedback loop. Moreover, GhIRKO mice required reduced glucose infusion rates during hyperinsulinemic-hypoglycemic clamps, suggesting that suppressed ghrelin release resulting from direct insulin action on ghrelin cells usually limits ghrelin's full potential to protect against insulin-induced hypoglycemia.

Ghrelin Response to Acute and Chronic Exercise: Insights and Implications from a Systematic Review of the Literature

BACKGROUND

Ghrelin is a peptide hormone predominantly produced by the stomach. It exerts a wide range of functions including stimulating growth hormone release and regulating appetite, food intake, and glucose and lipid metabolism. Since physical exercise affects all these aspects, a particular interest is accorded to the relationship between ghrelin and exercise. This systematic review aimed to summarize the current available data on the topic for a better understanding of the relationship.

METHODS

An extensive computerized search was performed in the PubMed and SPORTDiscus databases for retrieving relevant articles. The search contained the following keywords: ghrelin, appetite-related peptides, gastrointestinal peptides, gastrointestinal hormones, exercise, acute exercise, chronic exercise, training, and physical activity. Studies investigating the effects of acute/chronic exercise on circulating forms of ghrelin were included.

RESULTS

The initial search identified 840 articles. After screening, 80 articles were included. Despite a heterogeneity of studies and a variability of the findings, the review suggests that acute exercise suppresses acyl ghrelin production regardless of the participants and the exercise characteristics. Long- and very long-term exercise training programs mostly resulted in increased total and des-acyl ghrelin production. The increase is more noticeable in overweight/obese individuals, and is most likely due to weight loss resulting from the training program.

CONCLUSION

The review suggests that exercise may impact ghrelin production. While the precise mechanisms are unclear, the effects are likely due to blood flow redistribution and weight loss for acute and chronic exercise, respectively. These changes are expected to be metabolically beneficial. Further research is needed for a better understanding of the relationship between ghrelin and exercise.

"A LEAP 2 conclusions? Targeting the ghrelin system to treat obesity and diabetes"

BACKGROUND

The hormone ghrelin stimulates food intake, promotes adiposity, increases body weight, and elevates blood glucose. Consequently, alterations in plasma ghrelin levels and the functioning of other components of the broader ghrelin system have been proposed as potential contributors to obesity and diabetes. Furthermore, targeting the ghrelin system has been proposed as a novel therapeutic strategy for obesity and diabetes.

SCOPE OF REVIEW

The current review focuses on the potential for targeting ghrelin and other proteins comprising the ghrelin system as a treatment for obesity and diabetes. The main components of the ghrelin system are introduced. Data supporting a role for the endogenous ghrelin system in the development of obesity and diabetes along with data that seemingly refute such a role are outlined. An argument for further research into the development of ghrelin system-targeted therapeutic agents is delineated. Also, an evidence-based discussion of potential factors and contexts that might influence the efficacy of this class of therapeutics is provided.

MAJOR CONCLUSIONS

It would not be a "leap to" conclusions to suggest that agents which target the ghrelin system - including those that lower acyl-ghrelin levels, raise LEAP2 levels, block GHSR activity, and/or raise desacyl-ghrelin signaling - could represent efficacious novel treatments for obesity and diabetes.

Ghrelin system is involved in improvements in glucose metabolism mediated by hyperbaric oxygen treatment in a streptozotocin‑induced type 1 diabetes mouse model

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder for which the only effective therapy is insulin replacement. Hyperbaric oxygen (HBO) therapy has demonstrated potential in improving hyperglycemia and as a treatment option for T1DM. Ghrelin and HBO have been previously reported to exert proliferative, anti-apoptotic and anti-inflammatory effects in pancreatic cells. The present study investigated the mechanism underlying HBO- and ghrelin system-mediated regulation of glucose metabolism. Male C57BL/6 mice were intraperitoneally injected with streptozotocin (STZ; 150 mg/kg) to induce T1DM before the diabetic mice were randomly assigned into the T1DM and T1DM + HBO groups. Mice in the T1DM + HBO group received HBO (1 h; 100% oxygen; 2 atmospheres absolute) daily for 2 weeks. Significantly lower blood glucose levels and food intake were observed in mice in the T1DM + HBO group. Following HBO treatment, islet β-cell area were increased whereas those of α-cell were decreased in the pancreas. In addition, greater hepatic glycogen storage in liver was observed, which coincided with higher pancreatic glucose transporter 2 (GLUT2) expression levels and reduced hepatic GLUT2 membrane trafficking. There were also substantially higher total plasma ghrelin concentrations and gastric ghrelin-O-acyl transferase (GOAT) expression levels in mice in the T1DM + HBO group. HBO treatment also abolished reductions in pancreatic GOAT expression levels in T1DM mice. Additionally, hepatic growth hormone secretagogue receptor-1a levels were found to be lower in mice in the T1DM + HBO group compared with those in the T1DM group. These results suggest that HBO administration improved glucose metabolism in a STZ-induced T1DM mouse model. The underlying mechanism involves improved insulin-release, glucose-sensing and regulation of hepatic glycogen storage, an observation that was also likely dependent on the ghrelin signalling system.

LEAP2 changes with body mass and food intake in humans and mice

Acyl-ghrelin administration increases food intake, body weight, and blood glucose. In contrast, mice lacking ghrelin or ghrelin receptors (GHSRs) exhibit life-threatening hypoglycemia during starvation-like conditions, but do not consistently exhibit overt metabolic phenotypes when given ad libitum food access. These results, and findings of ghrelin resistance in obese states, imply nutritional state dependence of ghrelin's metabolic actions. Here, we hypothesized that liver-enriched antimicrobial peptide-2 (LEAP2), a recently characterized endogenous GHSR antagonist, blunts ghrelin action during obese states and postprandially. To test this hypothesis, we determined changes in plasma LEAP2 and acyl-ghrelin due to fasting, eating, obesity, Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG), oral glucose administration, and type 1 diabetes mellitus (T1DM) using humans and/or mice. Our results suggest that plasma LEAP2 is regulated by metabolic status: its levels increased with body mass and blood glucose and decreased with fasting, RYGB, and in postprandial states following VSG. These changes were mostly opposite of those of acyl-ghrelin. Furthermore, using electrophysiology, we showed that LEAP2 both hyperpolarizes and prevents acyl-ghrelin from activating arcuate NPY neurons. We predict that the plasma LEAP2/acyl-ghrelin molar ratio may be a key determinant modulating acyl-ghrelin activity in response to body mass, feeding status, and blood glucose.

Acyl-ghrelin Is Permissive for the Normal Counterregulatory Response to Insulin-Induced Hypoglycemia

Insulin-induced hypoglycemia leads to far-ranging negative consequences in patients with diabetes. Components of the counterregulatory response (CRR) system that help minimize and reverse hypoglycemia and coordination between those components are well studied but not yet fully characterized. Here, we tested the hypothesis that acyl-ghrelin, a hormone that defends against hypoglycemia in a preclinical starvation model, is permissive for the normal CRR to insulin-induced hypoglycemia. Ghrelin knockout (KO) mice and wild-type (WT) littermates underwent an insulin bolus-induced hypoglycemia test and a low-dose hyperinsulinemic-hypoglycemic clamp procedure. Clamps also were performed in ghrelin-KO mice and C57BL/6N mice administered the growth hormone secretagogue receptor agonist HM01 or vehicle. Results show that hypoglycemia, as induced by an insulin bolus, was more pronounced and prolonged in ghrelin-KO mice, supporting previous studies suggesting increased insulin sensitivity upon ghrelin deletion. Furthermore, during hyperinsulinemic-hypoglycemic clamps, ghrelin-KO mice required a 10-fold higher glucose infusion rate (GIR) and exhibited less robust corticosterone and growth hormone responses. Conversely, HM01 administration, which reduced the GIR required by ghrelin-KO mice during the clamps, increased plasma corticosterone and growth hormone. Thus, our data suggest that endogenously produced acyl-ghrelin not only influences insulin sensitivity but also is permissive for the normal CRR to insulin-induced hypoglycemia.

Ghrelin Protects Against Insulin-Induced Hypoglycemia in a Mouse Model of Type 1 Diabetes Mellitus

Insulin-induced hypoglycemia is a major limiting factor in maintaining optimal blood glucose in patients with type 1 diabetes and advanced type 2 diabetes. Luckily, a counterregulatory response (1) system exists to help minimize and reverse hypoglycemia, although more studies are needed to better characterize its components. Recently, we showed that the hormone ghrelin is permissive for the normal CRR to insulin-induced hypoglycemia when assessed in mice without diabetes. Here, we tested the hypothesis that ghrelin also is protective against insulin-induced hypoglycemia in the streptozotocin (2) mouse model of type 1 diabetes. STZ-treated ghrelin-knockout (KO) (3) mice as well as STZ-treated wild-type (WT) littermates were subjected to a low-dose hyperinsulinemic-hypoglycemic clamp procedure. The STZ-treated ghrelin-KO mice required a much higher glucose infusion rate than the STZ-treated WT mice. Also, the STZ-treated ghrelin-KO mice exhibited attenuated plasma epinephrine and norepinephrine responses to the insulin-induced hypoglycemia. Taken together, our data suggest that without ghrelin, STZ-treated mice modeling type 1 diabetes are unable to mount the usual CRR to insulin-induced hypoglycemia.

Modeling Monogenic Diabetes using Human ESCs Reveals Developmental and Metabolic Deficiencies Caused by Mutations in HNF1A

Human monogenic diabetes, caused by mutations in genes involved in beta cell development and function, has been a challenge to study because multiple mouse models have not fully recapitulated the human disease. Here, we use genome edited human embryonic stem cells to understand the most common form of monogenic diabetes, MODY3, caused by mutations in the transcription factor HNF1A. We found that HNF1A is necessary to repress an alpha cell gene expression signature, maintain endocrine cell function, and regulate cellular metabolism. In addition, we identified the human-specific long non-coding RNA, LINKA, as an HNF1A target necessary for normal mitochondrial respiration. These findings provide a possible explanation for the species difference in disease phenotypes observed with HNF1A mutations and offer mechanistic insights into how the HNF1A gene may also influence type 2 diabetes.

Ghrelin's Relationship to Blood Glucose

Much effort has been directed at studying the orexigenic actions of administered ghrelin and the potential effects of the endogenous ghrelin system on food intake, food reward, body weight, adiposity, and energy expenditure. Although endogenous ghrelin's actions on some of these processes remain ambiguous, its glucoregulatory actions have emerged as well-recognized features during extreme metabolic conditions. The blood glucose-raising actions of ghrelin are beneficial during starvation-like conditions, defending against life-threatening falls in blood glucose, but they are seemingly detrimental in obese states and in certain monogenic forms of diabetes, contributing to hyperglycemia. Also of interest, blood glucose negatively regulates ghrelin secretion. This article reviews the literature suggesting the existence of a blood glucose-ghrelin axis and highlights the factors that mediate the glucoregulatory actions of ghrelin, especially during metabolic extremes such as starvation and diabetes.

HNF4α is a novel regulator of intestinal glucose-dependent insulinotropic polypeptide

Mutations in the HNF4A gene cause MODY1 and are associated with an increased risk of Type 2 diabetes mellitus. On the other hand, incretins are hormones that potentiate reductions in blood glucose levels. Given the established role of incretin-based therapy to treat diabetes and metabolic disorders, we investigated a possible regulatory link between intestinal epithelial HNF4α and glucose-dependent insulinotropic polypeptide (GIP), an incretin that is specifically produced by gut enteroendocrine cells. Conditional deletion of HNF4α in the whole intestinal epithelium was achieved by crossing Villin-Cre and Hnf4α^loxP/loxP C57BL/6 mouse models. GIP expression was measured by qPCR, immunofluorescence and ELISA. Gene transcription was assessed by luciferase and electrophoretic mobility shift assays. Metabolic parameters were analyzed by indirect calorimetry and dual-energy X-ray absorptiometry. HNF4α specific deletion in the intestine led to a reduction in GIP. HNF4α was able to positively control Gip transcriptional activity in collaboration with GATA-4 transcription factor. Glucose homeostasis and glucose-stimulated insulin secretion remained unchanged in HNF4α deficient mice. Changes in GIP production in these mice did not impact nutrition or energy metabolism under normal physiology but led to a reduction of bone area and mineral content, a well described physiological consequence of GIP deficiency. Our findings point to a novel regulatory role between intestinal HNF4α and GIP with possible functional impact on bone density.

The Homeostatic Force of Ghrelin

Ghrelin, a gastric-derived acylated peptide, regulates energy homeostasis by transmitting information about peripheral nutritional status to the brain, and is essential for protecting organisms against famine. Ghrelin operates brain circuits to regulate homeostatic and hedonic feeding. Recent research advances have shed new light on ghrelin's multifaceted roles in cellular homeostasis, which could maintain the internal environment and overcome metaflammation in metabolic organs. Here, we highlight our current understanding of the regulatory mechanisms of the ghrelin system in energy metabolism and cellular homeostasis and its clinical trials. Future studies of ghrelin will further elucidate how the stomach regulates systemic homeostasis.

Ghrelin regulation of glucose metabolism

The a 28-amino acid peptide ghrelin was discovered in 1999 as a growth hormone (GH) releasing peptide. Soon after its discovery, ghrelin was found to increase body weight and adiposity by acting on the hypothalamic melanocortinergic system. Subsequently, ghrelin was found to exert a series of metabolic effects, overall testifying ghrelin a pleiotropic nature of broad pharmacological interest. Ghrelin acts through the growth hormone secretagogue-receptor (GHS-R), a seven transmembrane G protein-coupled receptor with high expression in the anterior pituitary, pancreatic islets, thyroid gland, heart and various regions of the brain. Among ghrelins numerous metabolic effects are the most prominent the stimulation of appetite via activation of orexigenic hypothalamic neurocircuits and the food-intake independent stimulation of lipogenesis, which both together lead to an increase in body weight and adiposity. Ghrelin effects beyond the regulation of appetite and GH secretion include the regulation of gut motility, sleep-wake rhythm, taste sensation, reward seeking behaviour, and the regulation of glucose metabolism. The latter received recently increasing recognition because pharmacological inhibition of ghrelin signaling might be of therapeutic value to improve insuin resistance and type 2 diabetes. In this review we highlight the multifaceted nature of ghrelin and summarize its glucoregulatory action and discuss the pharmacological value of ghrelin pathway inhibition for the treatment of glucose intolerance and type 2 diabetes.

Ghrelin as a Survival Hormone

Ghrelin administration induces food intake and body weight gain. Based on these actions, the ghrelin system was initially proposed as an antiobesity target. Subsequent studies using genetic mouse models have raised doubts about the role of the endogenous ghrelin system in mediating body weight homeostasis or obesity. However, this is not to say that the endogenous ghrelin system is not important metabolically or otherwise. Here we review an emerging concept in which the endogenous ghrelin system serves an essential function during extreme nutritional and psychological challenges to defend blood glucose, protect body weight, avoid exaggerated depression, and ultimately allow survival.

Hypoglycemic Effect of Combined Ghrelin and Glucagon Receptor Blockade

Glucagon receptor (GcgR) blockade has been proposed as an alternative to insulin monotherapy for treating type 1 diabetes since deletion or inhibition of GcgRs corrects hyperglycemia in models of diabetes. The factors regulating glycemia in a setting devoid of insulin and glucagon function remain unclear but may include the hormone ghrelin. Not only is ghrelin release controlled by glucose but also ghrelin has many actions that can raise or reduce falls in blood glucose level. Here, we tested the hypothesis that ghrelin rises to prevent hypoglycemia in the absence of glucagon function. Both GcgR knockout (Gcgr^-/-) mice and db/db mice that were administered GcgR monoclonal antibody displayed lower blood glucose levels accompanied by elevated plasma ghrelin levels. Although treatment with the pancreatic β-cell toxin streptozotocin induced hyperglycemia and raised plasma ghrelin levels in wild-type mice, hyperglycemia was averted in similarly treated Gcgr^-/- mice and the plasma ghrelin level was further increased. Notably, administration of a ghrelin receptor antagonist further reduced blood glucose levels into the markedly hypoglycemic range in overnight-fasted, streptozotocin-treated Gcgr^-/- mice. A lowered blood glucose level also was observed in overnight-fasted, streptozotocin-treated ghrelin receptor-null mice that were administered GcgR monoclonal antibody. These data suggest that when glucagon activity is blocked in the setting of type 1 diabetes, the plasma ghrelin level rises, preventing hypoglycemia.

HNF1α defect influences post-prandial lipid regulation

Purpose

Hepatocyte nuclear factor 1 alpha (HNF1α) defects cause Mature Onset Diabetes of the Young type 3 (MODY3), characterized by defects in beta-cell insulin secretion. However, HNF1α is involved in many other metabolic pathways with relevance for monogenic or polygenic type 2 diabetes. We aimed to investigate gut hormones, lipids, and insulin regulation in response to a meal test in HNF1α defect carriers (MODY3) compared to non-diabetic subjects (controls) and type 2 diabetes (T2D).

Methods

We administered a standardized liquid meal to each participant. Over 6 hours, we measured post-meal responses of insulin regulation (blood glucose, c-peptide, insulin), gut hormones (ghrelin, glucose-dependent insulinotropic polypeptide, glucagon-like peptide-1) and lipids (non-esterified fatty acids [NEFA] and triglycerides).

Results

We found that MODY3 participants had lower insulin secretion indices than controls and T2D participants, showing the expected β-cell defect. MODY3 had similar glycated hemoglobin levels (HbA1c median [IQR]: 6.5 [5.6–7.6]%) compared to T2D (median: 6.6 [6.2–6.9]%; P<0.05). MODY3 had greater insulin sensitivity (Matsuda index: 71.9 [29.6; 125.5]) than T2D (3.2 [4.0; 6.0]; P<0.05). MODY3 experienced a larger decrease in the ratio of NEFA to insulin (NEFA 30–0 / insulin 30–0: -39 [-78; -30] x10⁴) in the early post-prandial period (0–30 minutes) compared to controls and to T2D (-2.0 [-0.6; -6.4] x10⁴; P<0.05). MODY3 had lower fasting (0.66 [0.46; 1.2] mM) and post-meal triglycerides levels compared to T2D (fasting: 2.3 [1.7; 2.7] mM; P<0.05). We did not detect significant post-meal differences in ghrelin and incretins between MODY3 and other groups.

Conclusion

In response to a standard meal test, MODY3 showed greater early post-prandial NEFA diminution in response to relatively low early insulin secretion, and they maintained very low post-prandial triglycerides levels.

Therapeutic Potential of Targeting the Ghrelin Pathway

Ghrelin was discovered in 1999 as the endogenous ligand of the growth-hormone secretagogue receptor 1a (GHSR1a). Since then, ghrelin has been found to exert a plethora of physiological effects that go far beyond its initial characterization as a growth hormone (GH) secretagogue. Among the numerous well-established effects of ghrelin are the stimulation of appetite and lipid accumulation, the modulation of immunity and inflammation, the stimulation of gastric motility, the improvement of cardiac performance, the modulation of stress, anxiety, taste sensation and reward-seeking behavior, as well as the regulation of glucose metabolism and thermogenesis. Due to a variety of beneficial effects on systems’ metabolism, pharmacological targeting of the endogenous ghrelin system is widely considered a valuable approach to treat metabolic complications, such as chronic inflammation, gastroparesis or cancer-associated anorexia and cachexia. The aim of this review is to discuss and highlight the broad pharmacological potential of ghrelin pathway modulation for the treatment of anorexia, cachexia, sarcopenia, cardiopathy, neurodegenerative disorders, renal and pulmonary disease, gastrointestinal (GI) disorders, inflammatory disorders and metabolic syndrome.

A suppressor locus for MODY3-diabetes

Maturity Onset Diabetes of the Young type 3 (MODY3), linked to mutations in the transcription factor HNF1A, is the most prevalent form of monogenic diabetes mellitus. HNF1alpha-deficiency leads to defective insulin secretion via a molecular mechanism that is still not completely understood. Moreover, in MODY3 patients the severity of insulin secretion can be extremely variable even in the same kindred, indicating that modifier genes may control the onset of the disease. With the use of a mouse model for HNF1alpha-deficiency, we show here that specific genetic backgrounds (C3H and CBA) carry a powerful genetic suppressor of diabetes. A genome scan analysis led to the identification of a major suppressor locus on chromosome 3 (Moda1). Moda1 locus contains 11 genes with non-synonymous SNPs that significantly interacts with other loci on chromosomes 4, 11 and 18. Mechanistically, the absence of HNF1alpha in diabetic-prone (sensitive) strains leads to postnatal defective islets growth that is remarkably restored in resistant strains. Our findings are relevant to human genetics since Moda1 is syntenic with a human locus identified by genome wide association studies of fasting glycemia in patients. Most importantly, our results show that a single genetic locus can completely suppress diabetes in Hnf1a-deficiency.

Monogenic Diabetes: What It Teaches Us on the Common Forms of Type 1 and Type 2 Diabetes

To date, more than 30 genes have been linked to monogenic diabetes. Candidate gene and genome-wide association studies have identified > 50 susceptibility loci for common type 1 diabetes (T1D) and approximately 100 susceptibility loci for type 2 diabetes (T2D). About 1-5% of all cases of diabetes result from single-gene mutations and are called monogenic diabetes. Here, we review the pathophysiological basis of the role of monogenic diabetes genes that have also been found to be associated with common T1D and/or T2D. Variants of approximately one-third of monogenic diabetes genes are associated with T2D, but not T1D. Two of the T2D-associated monogenic diabetes genes-potassium inward-rectifying channel, subfamily J, member 11 (KCNJ11), which controls glucose-stimulated insulin secretion in the β-cell; and peroxisome proliferator-activated receptor γ (PPARG), which impacts multiple tissue targets in relation to inflammation and insulin sensitivity-have been developed as major antidiabetic drug targets. Another monogenic diabetes gene, the preproinsulin gene (INS), is unique in that INS mutations can cause hyperinsulinemia, hyperproinsulinemia, neonatal diabetes mellitus, one type of maturity-onset diabetes of the young (MODY10), and autoantibody-negative T1D. Dominant heterozygous INS mutations are the second most common cause of permanent neonatal diabetes. Moreover, INS gene variants are strongly associated with common T1D (type 1a), but inconsistently with T2D. Variants of the monogenic diabetes gene Gli-similar 3 (GLIS3) are associated with both T1D and T2D. GLIS3 is a key transcription factor in insulin production and β-cell differentiation during embryonic development, which perturbation forms the basis of monogenic diabetes as well as its association with T1D. GLIS3 is also required for compensatory β-cell proliferation in adults; impairment of this function predisposes to T2D. Thus, monogenic forms of diabetes are invaluable "human models" that have contributed to our understanding of the pathophysiological basis of common T1D and T2D.