Loss of Glp2r signaling activates hepatic stellate cells and exacerbates diet-induced steatohepatitis in mice

Targeting the GLP-2 receptor in the management of obesity

Recent advancements in understanding glucagon-like peptide 2 (GLP-2) biology and pharmacology have sparked interest in targeting the GLP-2 receptor (GLP-2R) in the treatment of obesity. GLP-2 is a proglucagon-derived 33-amino acid peptide co-secreted from enteroendocrine L cells along with glucagon-like peptide 1 (GLP-1) and has a range of actions via the GLP-2R, which is particularly expressed in the gastrointestinal tract, the liver, adipose tissue, and the central nervous system (CNS). In humans, GLP-2 evidently induces intestinotrophic effects (i.e., induction of intestinal mucosal proliferation and improved gut barrier function) and promotes mesenteric blood flow. However, GLP-2 does not seem to have appetite or food intake-reducing effects in humans, but its gut barrier-promoting effect may be of interest in the context of obesity. Obesity is associated with reduced gut barrier function, increasing the translocation of proinflammatory gut content to the circulation. This phenomenon constitutes a strong driver of obesity-associated systemic low-grade inflammation, which in turn plays a major role in the development of most obesity-associated complications. Thus, the intestinotrophic and gut barrier-improving effect of GLP-2, which in obese rodent models shows strong anti-inflammatory potential, may, in combination with food intake-reducing strategies, e.g., GLP-1 receptor (GLP-1) agonism, be able to rectify core pathophysiological mechanism of obesity. Here, we provide an overview of GLP-2 physiology in the context of obesity pathophysiology and review the pharmacological potential of GLP-2R activation in the management of obesity and related comorbidities.

GLP-2 regulation of intestinal lipid handling

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

Found in translation-Fibrosis in metabolic dysfunction-associated steatohepatitis (MASH)

Metabolic dysfunction-associated steatohepatitis (MASH) is a severe form of liver disease that poses a global health threat because of its potential to progress to advanced fibrosis, leading to cirrhosis and liver cancer. Recent advances in single-cell methodologies, refined disease models, and genetic and epigenetic insights have provided a nuanced understanding of MASH fibrogenesis, with substantial cellular heterogeneity in MASH livers providing potentially targetable cell-cell interactions and behavior. Unlike fibrogenesis, mechanisms underlying fibrosis regression in MASH are still inadequately understood, although antifibrotic targets have been recently identified. A refined antifibrotic treatment framework could lead to noninvasive assessment and targeted therapies that preserve hepatocellular function and restore the liver's architectural integrity.

GLP-2 Improves Hepatic Inflammation and Fibrosis in Mdr2-/- Mice Via Activation of NR4a1/Nur77 in Hepatic Stellate Cells and Intestinal FXR Signaling

BACKGROUND & AIMS

Glucagon-like peptide (GLP)-2 may exert antifibrotic effects on hepatic stellate cells (HSCs). Thus, we aimed to test whether application of the GLP-2 analogue teduglutide has hepatoprotective and antifibrotic effects in the Mdr2/Abcb4-/- mouse model of sclerosing cholangitis displaying hepatic inflammation and fibrosis.

METHODS

Mdr2-/- mice were injected daily for 4 weeks with teduglutide followed by gene expression profiling (bulk liver; isolated HSCs) and immunohistochemistry. Activated HSCs (LX2 cells) and immortalized human hepatocytes and human intestinal organoids were treated with GLP-2. mRNA profiling by reverse transcription polymerase chain reaction and electrophoretic mobility shift assay using cytosolic and nuclear protein extracts was performed.

RESULTS

Hepatic inflammation, fibrosis, and reactive cholangiocyte phenotype were improved in GLP-2-treated Mdr2-/- mice. Primary HSCs isolated from Mdr2-/- mice and LX2 cells exposed to GLP-2 in vitro displayed significantly increased mRNA expression levels of NR4a1/Nur77 (P < .05). Electrophoretic mobility shift assay revealed an increased nuclear NR4a1 binding after GLP-2 treatment in LX2 cells. Moreover, GLP-2 alleviated the Tgfβ-mediated reduction of NR4a1 nuclear binding activity. In vivo, GLP-2 treatment of Mdr2-/- mice resulted in increased intrahepatic levels of muricholic acids (accordingly Cyp2c70 mRNA expression was significantly increased), and in reduced mRNA levels of Cyp7a1 and FXR. Serum Fgf15 levels were increased in Mdr2-/- mice treated with GLP-2. Accordingly, GLP-2 treatment of human intestinal organoids activated their FXR-FGF19 signaling axis.

CONCLUSIONS

GLP-2 treatment increased NR4a1/Nur77 activation in HSCs, subsequently attenuating their activation. GLP-2 promoted intestinal Fxr-Fgf15/19 signaling resulting in reduced Cyp7a1 and increased Cyp2c70 expression in the liver, contributing to hepatoprotective and antifibrotic effects of GLP-2 in the Mdr2-/- mouse model.

Emerging Therapeutic Targets for Portal Hypertension

Purpose of Review

Portal hypertension is responsible of the main complications of cirrhosis, which carries a high mortality. Recent treatments have improved prognosis, but this is still far from ideal. This paper reviews new potential therapeutic targets unveiled by advances of key pathophysiologic processes.

Recent Findings

Recent research highlighted the importance of suppressing etiologic factors and a safe lifestyle and outlined new mechanisms modulating portal pressure. These include intrahepatic abnormalities linked to inflammation, fibrogenesis, vascular occlusion, parenchymal extinction, and angiogenesis; impaired regeneration; increased hepatic vascular tone due to sinusoidal endothelial dysfunction with insufficient NO availability; and paracrine liver cell crosstalk. Moreover, pathways such as the gut-liver axis modulate splanchnic vasodilatation and systemic inflammation, exacerbate liver fibrosis, and are being targeted by therapy. We have summarized studies of new agents addressing these targets.

Summary

New agents, alone or in combination, allow acting in complementary mechanisms offering a more profound effect on portal hypertension while simultaneously limiting disease progression and favoring regression of fibrosis and of cirrhosis. Major changes in treatment paradigms are anticipated.

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

Background

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

Objective

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

Methods

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

Results

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

Conclusion

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

Differential importance of endothelial and hematopoietic cell GLP-1Rs for cardiometabolic versus hepatic actions of semaglutide

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are used to treat diabetes and obesity and reduce rates of major cardiovascular events, such as stroke and myocardial infarction. Nevertheless, the identity of GLP-1R–expressing cell types mediating the cardiovascular benefits of GLP-1RA remains incompletely characterized. Herein, we investigated the importance of murine Glp1r expression within endothelial and hematopoietic cells. Mice with targeted inactivation of Glp1r in Tie2⁺ cells exhibited reduced levels of Glp1r mRNA transcripts in aorta, liver, spleen, blood, and gut. Glp1r expression in bone marrow cells was very low and not further reduced in Glp1r^Tie2–/– mice. The GLP-1RA semaglutide reduced the development of atherosclerosis induced by viral PCSK9 expression in both Glp1r^Tie2+/+ and Glp1r^Tie2–/– mice. Hepatic Glp1r mRNA transcripts were reduced in Glp1r^Tie2–/– mice, and liver Glp1r expression was localized to γδ T cells. Moreover, semaglutide reduced hepatic Tnf, Abcg1, Tgfb1, Cd3g, Ccl2, and Il2 expression; triglyceride content; and collagen accumulation in high-fat, high-cholesterol diet–fed Glp1r^Tie2+/+ mice but not Glp1r^Tie2–/– mice. Collectively, these findings demonstrate that Tie2⁺ endothelial or hematopoietic cell GLP-1Rs are dispensable for the antiatherogenic actions of GLP-1RA, whereas Tie2-targeted GLP-1R⁺ cells are required for a subset of the antiinflammatory actions of semaglutide in the liver.

Multi-organ Coordination of Lipoprotein Secretion by Hormones, Nutrients and Neural Networks

Plasma triglyceride-rich lipoproteins (TRL), particularly atherogenic remnant lipoproteins, contribute to atherosclerotic cardiovascular disease. Hypertriglyceridemia may arise in part from hypersecretion of TRLs by the liver and intestine. Here we focus on the complex network of hormonal, nutritional, and neuronal interorgan communication that regulates secretion of TRLs and provide our perspective on the relative importance of these factors. Hormones and peptides originating from the pancreas (insulin, glucagon), gut [glucagon-like peptide 1 (GLP-1) and 2 (GLP-2), ghrelin, cholecystokinin (CCK), peptide YY], adipose tissue (leptin, adiponectin) and brain (GLP-1) modulate TRL secretion by receptor-mediated responses and indirectly via neural networks. In addition, the gut microbiome and bile acids influence lipoprotein secretion in humans and animal models. Several nutritional factors modulate hepatic lipoprotein secretion through effects on the central nervous system. Vagal afferent signaling from the gut to the brain and efferent signals from the brain to the liver and gut are modulated by hormonal and nutritional factors to influence TRL secretion. Some of these factors have been extensively studied and shown to have robust regulatory effects whereas others are "emerging" regulators, whose significance remains to be determined. The quantitative importance of these factors relative to one another and relative to the key regulatory role of lipid availability remains largely unknown. Our understanding of the complex interorgan regulation of TRL secretion is rapidly evolving to appreciate the extensive hormonal, nutritional, and neural signals emanating not only from gut and liver but also from the brain, pancreas, and adipose tissue.

Distinct Identity of GLP-1R, GLP-2R, and GIPR Expressing Cells and Signaling Circuits Within the Gastrointestinal Tract

Enteroendocrine cells directly integrate signals of nutrient content within the gut lumen with distant hormonal responses and nutrient disposal via the production and secretion of peptides, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1) and glucagon-like peptide 2 (GLP-2). Given their direct and indirect control of post-prandial nutrient uptake and demonstrated translational relevance for the treatment of type 2 diabetes, malabsorption and cardiometabolic disease, there is significant interest in the locally engaged circuits mediating these metabolic effects. Although several specific populations of cells in the intestine have been identified to express endocrine receptors, including intraepithelial lymphocytes (IELs) and αβ and γδ T-cells (Glp1r+) and smooth muscle cells (Glp2r+), the definitive cellular localization and co-expression, particularly in regards to the Gipr remain elusive. Here we review the current state of the literature and evaluate the identity of Glp1r, Glp2r, and Gipr expressing cells within preclinical and clinical models. Further elaboration of our understanding of the initiating G-protein coupled receptor (GPCR) circuits engaged locally within the intestine and how they become altered with high-fat diet feeding can offer insight into the dysregulation observed in obesity and diabetes.

TCF7 is not essential for glucose homeostasis in mice

Objective

Glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1) are incretin hormones that exert overlapping yet distinct actions on islet β-cells. We recently observed that GIP, but not GLP-1, upregulated islet expression of Transcription Factor 7 (TCF7), a gene expressed in immune cells and associated with the risk of developing type 1 diabetes. TCF7 has also been associated with glucose homeostasis control in the liver. Herein we studied the relative metabolic importance of TCF7 expression in hepatocytes vs. islet β-cells in mice.

Methods

Tcf7 expression was selectively inactivated in adult mouse hepatocytes using adenoviral Cre expression and targeted in β-cells using two different lines of insulin promoter-Cre mice. Glucose homeostasis, plasma insulin and triglyceride responses, islet histology, hepatic and islet gene expression, and body weight gain were evaluated in mice fed regular chow or high fat diets. Tcf7 expression within pancreatic islets and immune cells was evaluated using published single cell RNA-seq (scRNA-seq) data, and in islet RNA from immunodeficient Rag2^−/−Il2rg^−/− mice.

Results

Reduction of hepatocyte Tcf7 expression did not impair glucose homeostasis, lipid tolerance or hepatic gene expression profiles linked to control of metabolic or immune pathways. Similarly, oral and intraperitoneal glucose tolerance, plasma insulin responses, islet histology, body weight gain, and insulin tolerance were not different in mice with targeted recombination of Tcf7 in insulin-positive β-cells. Surprisingly, islet Tcf7 mRNA transcripts were not reduced in total islet RNA containing endocrine and associated non-endocrine cell types from Tcf7^{βcell−/−} mice, despite Cre-mediated recombination of islet genomic DNA. Furthermore, glucose tolerance was normal in whole body Tcf7^−/− mice. Analysis of scRNA-seq datasets localized pancreatic Tcf7 expression to islet progenitors during development, and immune cells, but not within differentiated islet β-cells or endocrine lineages within mature islets. Moreover, the expression of Tcf7 was extremely low in islet RNA from Rag2^−/−Il2rg^−/− mice and, consistent with expression within immune cells, Tcf7 was highly correlated with levels of Cd3g mRNA transcripts in RNA from wild type mouse islets.

Conclusions

These findings demonstrate that Tcf7 expression is not a critical determinant of glucose homeostasis in mice. Moreover, the detection of Tcf7 expression within islet mRNA is attributable to the expression of Tcf7 RNA in islet-associated murine immune cells, and not in islet β-cells.

•Reduction of hepatocyte Tcf7 does not impair glucose homeostasis.

•Targeting beta cell Tcf7 using insulin-promoter-Cre does not reduce islet Tcf7 expression.

•RNA-seq localizes pancreatic Tcf7 to islet progenitors and lymphocytes.

•Tcf7 expression is markedly reduced in islet RNA from Rag2^−/−Il2rg^−/− mice.

The GLP-1R agonist liraglutide limits hepatic lipotoxicity and inflammatory response in mice fed a methionine-choline deficient diet

Nonalcoholic fatty liver disease (NAFLD) is the most common hepatic disorder related to type 2 diabetes (T2D). The disease can evolve toward nonalcoholic steatohepatitis (NASH), a state of hepatic inflammation and fibrosis. There is presently no drug that effectively improves and/or prevents NAFLD/NASH/fibrosis. GLP-1 receptor agonists (GLP-1Ra) are effective in treating T2D. As with the endogenous gut incretins, GLP-1Ra potentiate glucose-induced insulin secretion. In addition, GLP-1Ra limit food intake and weight gain, additional beneficial properties in the context of obesity/insulin-resistance. Nevertheless, these pleiotropic effects of GLP-1Ra complicate the elucidation of their direct action on the liver. In the present study, we used the classical methionine-choline deficient (MCD) dietary model to investigate the potential direct hepatic actions of the GLP-1Ra liraglutide. A 4-week infusion of liraglutide (570 µg/kg/day) did not impact body weight, fat accretion or glycemic control in MCD-diet fed mice, confirming the suitability of this model for avoiding confounding factors. Liraglutide treatment did not prevent lipid deposition in the liver of MCD-fed mice but limited the accumulation of C16 and C24-ceramide/sphingomyelin species. In addition, liraglutide treatment alleviated hepatic inflammation (in particular accumulation of M1 pro-inflammatory macrophages) and initiation of fibrosis. Liraglutide also influenced the composition of gut microbiota induced by the MCD-diet. This included recovery of a normal Bacteroides proportion and, among the Erysipelotrichaceae family, a shift between Allobaculum and Turicibacter genera. In conclusion, liraglutide prevents accumulation of C16 and C24-ceramides/sphingomyelins species, inflammation and initiation of fibrosis in MCD-diet-fed mice liver, suggesting beneficial hepatic actions independent of weight loss and global hepatic steatosis.

GLP-2 Is Locally Produced From Human Islets and Balances Inflammation Through an Inter-Islet-Immune Cell Crosstalk

Glucagon-like peptide-1 (GLP-1) shows robust protective effects on β-cell survival and function and GLP-1 based therapies are successfully applied for type-2 diabetes (T2D) and obesity. Another cleavage product of pro-glucagon, Glucagon-like peptide-2 (GLP-2; both GLP-1 and GLP-2 are inactivated by DPP-4) has received little attention in its action inside pancreatic islets. In this study, we investigated GLP-2 production, GLP-2 receptor (GLP-2R) expression and the effect of GLP-2R activation in human islets. Isolated human islets from non-diabetic donors were exposed to diabetogenic conditions: high glucose, palmitate, cytokine mix (IL-1β/IFN-γ) or Lipopolysaccharide (LPS) in the presence or absence of the DPP4-inhibitor linagliptin, the TLR4 inhibitor TAK-242, the GLP-2R agonist teduglutide and/or its antagonist GLP-2(3-33). Human islets under control conditions secreted active GLP-2 (full-length, non-cleaved by DPP4) into the culture media, which was increased by combined high glucose/palmitate, the cytokine mix and LPS and highly potentiated by linagliptin. Low but reproducible GLP-2R mRNA expression was found in all analyzed human islet isolations from 10 donors, which was reduced by pro-inflammatory stimuli: the cytokine mix and LPS. GLP-2R activation by teduglutide neither affected acute or glucose stimulated insulin secretion nor insulin content. Also, teduglutide had no effect on high glucose/palmitate- or LPS-induced dysfunction in cultured human islets but dampened LPS-induced macrophage-dependent IL1B and IL10 expression, while its antagonist GLP-2(3-33) abolished such reduction. In contrast, the expression of islet macrophage-independent cytokines IL6, IL8 and TNF was not affected by teduglutide. Medium conditioned by teduglutide-exposed human islets attenuated M1-like polarization of human monocyte-derived macrophages, evidenced by a lower mRNA expression of pro-inflammatory cytokines, compared to vehicle treated islets, and a reduced production of itaconate and succinate, marker metabolites of pro-inflammatory macrophages. Our results reveal intra-islet production of GLP-2 and GLP-2R expression in human islets. Despite no impact on β-cell function, local GLP-2R activation reduced islet inflammation which might be mediated by a crosstalk between endocrine cells and macrophages.