GIP receptor deletion in mice confers resistance to high-fat diet-induced obesity via alterations in energy expenditure and adipose tissue lipid metabolism

Reduced incretin receptor trafficking upon activation enhances glycemic control and reverses obesity in diet-induced obese mice

Activation of incretin receptors by their cognate agonist augments sustained cAMP generation both from the plasma membrane as well as from the endosome. To address the functional outcome of this spatiotemporal signaling, we developed a nonacylated glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor dual agonist I-M-150847 that reduced receptor internalization following activation of the incretin receptors. The incretin receptor dual agonist I-M-150847 was developed by replacing the tryptophan cage of exendin-4 tyrosine substituted at the amino terminus with the C-terminal undecapeptide sequence of oxyntomodulin that placed lysine 30 of I-M-150847 in frame with the corresponding lysine residue of GIP. The peptide I-M-150847 is a partial agonist of GLP-1R and GIPR; however, the receptors, upon activation by I-M-150847, undergo reduced internalization that promotes agonist-mediated iterative cAMP signaling and augments glucose-stimulated insulin exocytosis in pancreatic β cells. Chronic administration of I-M-150847 improved glycemic control, enhanced insulin sensitivity, and provided profound weight loss in diet-induced obese (DIO) mice. Our results demonstrated that despite being a partial agonist, I-M-150847, by reducing the receptor internalization upon activation, enhanced the incretin effect and reversed obesity.NEW & NOTEWORTHY Replacement of the tryptophan cage (Trp-cage) with the C-terminal oxyntomodulin undecapeptide along with the tyrosine substitution at the amino terminus converts the selective glucagon-like peptide-1 receptor (GLP-1R) agonist exendin-4 to a novel GLP-1R and GIPR dual agonist I-M-150847. Reduced internalization of incretin receptors upon activation by the GLP-1R and GIPR dual agonist I-M-150847 promotes iterative receptor signaling that enhances the incretin effect and reverses obesity.

GIP-derived GIP receptor antagonists - a review of their role in GIP receptor pharmacology

Surprisingly, agonists, as well as antagonists of the glucose-dependent insulinotropic polypeptide receptor (GIPR), are currently being used or investigated as treatment options for type 2 diabetes and obesity - and both, when combined with glucagon-like peptide 1 receptor (GLP-1R) agonism, enhance GLP-1-induced glycemia and weight loss further. This paradox raises several questions regarding not only the mechanisms of actions of GIP but also the processes engaged during the activation of both the GIP and GLP-1 receptors. Here, we provide an overview of studies of the properties and actions of peptide-derived GIPR antagonists, focusing on GIP(3-30)NH2, a naturally occurring N- and C-terminal truncation of GIP(1-42). GIP(3-30)NH2 was the first GIPR antagonist administered to humans. GIP(3-30)NH2 and a few additional antagonists, like Pro3-GIP, have been used in both in vitro and in vivo studies to elucidate the molecular and cellular consequences of GIPR inhibition, desensitization, and internalization and, at a larger scale, the role of the GIP system in health and disease. We provide an overview of these studies combined with recent knowledge regarding the effects of naturally occurring variants of the GIPR system and species differences within the GIP system to enhance our understanding of the GIPR as a drug target.

Regulation of energy metabolism through central GIPR signaling

In recent years, significant progress has been made to pharmacologically combat the obesity pandemic, particularly with regard to biochemically tailored drugs that simultaneously target the receptors for glucagon-like peptide-1 (GLP-1) and the glucose-dependent insulinotropic polypeptide (GIP). But while the pharmacological benefits of GLP-1 receptor (GLP-1R) agonism are widely acknowledged, the role of the GIP system in regulating systems metabolism remains controversial. When given in adjunct to GLP-1R agonism, both agonism and antagonism of the GIP receptor (GIPR) improves metabolic outcome in preclinical and clinical studies, and despite persistent concerns about its potential obesogenic nature, there is accumulating evidence indicating that GIP has beneficial metabolic effects via central GIPR agonism. Nonetheless, despite growing recognition of the GIP system as a valuable pharmacological target, there remains great uncertainty as to where and how GIP acts in the brain to regulate metabolism, and how GIPR agonism may differ from GIPR antagonism in control of energy metabolism. In this review we highlight current knowledge on the central action of GIP, and discuss open questions related to its multifaceted biology in the brain and the periphery.

Circulating total and H-specific GDF15 levels are elevated in subjects with MASLD but not in hyperlipidemic but otherwise metabolically healthy subjects with obesity

BACKGROUND

Growth differentiation factor 15 (GDF15) is a mitokine, the role of which, total or H-specific, in modulating energy metabolism and homeostasis in obesity-related diseases, such as metabolic dysfunction associated steatotic liver disease (MASLD), has not been fully elucidated in adult humans. We aimed to investigate the fasting and stimulated levels of GDF15, total and H-specific, glucose-dependent insulinotropic polypeptide (GIP) and C-peptide, in two physiology interventional studies: one focusing on obesity, and the other on MASLD.

METHODS

Study 1 investigated individuals with normal weight or with obesity, undergoing a 3-h mixed meal test (MMT); and study 2, examined adults with MASLD and controls undergoing a 120-min oral glucose tolerance test (OGTT). Exploratory correlations of total and H-specific GDF15 with clinical, hormonal and metabolomic/lipidomic parameters were also performed.

RESULTS

In study 1, 15 individuals were included per weight group. Fasting and postprandial total and H-specific GDF15 were similar between groups, whereas GIP was markedly higher in leaner individuals and was upregulated following a MMT. Baseline and postprandial C-peptide were markedly elevated in people with obesity compared with lean subjects. GIP was higher in leaner individuals and was upregulated after a MMT, while C-peptide and its overall AUC after a MMT was markedly elevated in people with obesity compared with lean subjects. In study 2, 27 individuals were evaluated. Fasting total GDF15 was similar, but postprandial total GDF15 levels were significantly higher in MASLD patients compared to controls. GIP and C-peptide remained unaffected. The postprandial course of GDF15 was clustered among those of triglycerides and molecules of the alanine cycle, was robustly elevated under MASLD, and constituted the most notable differentiating molecule between healthy and MASLD status. We also present robust positive correlations of the incremental area under the curve of total and H-specific GDF15 with a plethora of lipid subspecies, which remained significant after adjusting for confounders.

CONCLUSION

Serum GDF15 levels do not differ in relation to weight status in hyperlipidemic but otherwise metabolically healthy individuals. In contrast, GDF15 levels are significantly increased in MASLD patients at baseline and they remain significantly higher compared to healthy participants during OGTT, pointing to a role for GDF15 as a mitokine with important roles in the pathophysiology and possibly therapeutics of MASLD. Trial registration ClinicalTrials.gov NCT03986684, NCT04430946.

Pharmacological Advances in Incretin-Based Polyagonism: What We Know and What We Don't

The prevalence of obesity continues to rise in both adolescents and adults, in parallel obesity is strongly associated with the increased incidence of type 2 diabetes, heart failure, certain types of cancer, and all-cause mortality. In relation to obesity, many pharmacological approaches of the past have tried and failed to combat the rising obesity epidemic, particularly due to insufficient efficacy or unacceptable side effects. However, while the history of antiobesity medication is plagued by failures and disappointments, we have witnessed over the last 10 years substantial progress, particularly in regard to biochemically optimized agonists at the receptor for glucagon-like peptide-1 (GLP-1R) and unimolecular coagonists at the receptors for GLP-1 and the glucose-dependent insulinotropic polypeptide (GIP). Although the GIP receptor:GLP-1R coagonists are being heralded as premier pharmacological tools for the treatment of obesity and diabetes, uncertainty remains as to why these drugs testify superiority over best-in-class GLP-1R monoagonists. Particularly with regard to GIP, there remains great uncertainty if and how GIP acts on systems metabolism and if the GIP system should be activated or inhibited to improve metabolic outcome in adjunct to GLP-1R agonism. In this review, we summarize recent advances in GLP-1- and GIP-based pharmacology and discuss recent findings and open questions related to how the GIP system affects systemic energy and glucose metabolism.

Characterization of metabolic phenotypes and distinctive genes in mice with low-weight gain

Being overweight exacerbates various metabolic diseases, necessitating the identification of target molecules for obesity control. In the current study, we investigated common physiological features related to metabolism in mice with low weight gain: (1) G protein-coupled receptor, family C, group 5, member B-knockout; (2) gastric inhibitory polypeptide receptor-knockout; and (3) Iroquois-related homeobox 3-knockout. Moreover, we explored genes involved in metabolism by analyzing differentially expressed genes (DEGs) between low-weight gain mice and the respective wild-type control mice. The common characteristics of the low-weight gain mice were low inguinal white adipose tissue (iWAT) and liver weight despite similar food intake along with lower blood leptin levels and high energy expenditure. The DEGs of iWAT, epididymal (gonadal) WAT, brown adipose tissue, muscle, liver, hypothalamus, and hippocampus common to these low-weight gain mice were designated as candidate genes associated with metabolism. One such gene tetraspanin 7 (Tspan7) from the iWAT was validated using knockout and overexpressing mouse models. Mice with low Tspan7 expression gained more weight, while those with high Tspan7 expression gained less weight, confirming the involvement of the Tspan7 gene in weight regulation. Collectively, these findings suggest that the candidate gene list generated in this study contains potential target molecules for obesity regulation. Further validation and additional data from low-weight gain mice will aid in understanding the molecular mechanisms associated with obesity.

Surfactant-like photosensitizer for endoscopic duodenal ablation: Modulating meal-stimulated incretin hormones in obese and type 2 diabetes

Duodenal ablation improves glycaemic control and weight loss, so it has been applied using hydrothermal catheters in obese and type 2 diabetes patients, indicating similar mechanisms and therapeutic effects as bariatric surgeries. Endoscopic photodynamic therapy is an innovative procedure that easily accessible to endocrine or gastrointestinal organs, so it is critical for the sprayed photosensitizer (PS) to long-term interact with target tissues for enhancing its effects. Surfactant-like PS was more stable in a wide range of pH and 2.8-fold more retained in the duodenum at 1 h than hydrophilic PS due to its amphiphilic property. Endoscopic duodenal ablation using surfactant-like PS was performed in high fat diet induced rat models, demonstrating body weight loss, enhanced insulin sensitivity, and modulation of incretin hormones. Locoregional ablation of duodenum could affect the profiles of overall intestinal cells secreting meal-stimulated hormones and further the systemic glucose and lipid metabolism, regarding gut-brain axis. Our strategy suggests a potential for a treatment of minimally invasive bariatric and metabolic therapy if accompanied by detailed clinical trials.

GLP-1 receptor agonism and GIP receptor antagonism induce substantial alterations in enteroendocrine and islet cell populations in obese high fat fed mice

Effects of sustained activation of glucagon-like peptide-1 (GLP-1) receptors (GLP-1R) as well as antagonism of receptors for glucose-dependent insulinotropic peptide (GIP) on intestinal morphology and related gut hormone populations have not been fully investigated. The present study assesses the impact of 21-days twice daily treatment with the GLP-1R agonist exendin-4 (Ex-4), or the GIP receptor (GIPR) antagonist mGIP(3-30), on these features in obese mice fed a high fat diet (HFD). HFD mice presented with reduced crypt depth when compared to normal diet (ND) controls, which was reversed by Ex-4 treatment. Both regimens lead to an enlargement of villi length in HFD mice. HFD mice had increased numbers of GIP and PYY positive ileal cells, with both treatment interventions reversing the effect on PYY positive cells, but only Ex-4 restoring GIP ileal cell populations to ND levels. Ex-4 and mGIP (3-30) marginally decreased GLP-1 villi immunoreactivity and countered the reduction of ileal GLP-1 content caused by HFD. As expected, HFD mice presented with elevated pancreatic islet area. Interestingly, mGIP(3-30), but not Ex-4, enhanced islet and beta-cell areas in HFD mice despite lack of effect of beta-cell turnover, whilst Ex-4 increased delta-cell area. Co-localisation of islet PYY or GLP-1 with glucagon was increased by Ex-4, whilst islet PYY co-immunoreactivity with somatostatin was enhanced by mGIP(3-30) treatment. These observations highlight potential new mechanisms linked to the metabolic benefits of GLP-1R agonism and GIPR antagonism in obesity.

Dietary Vitamin A Affects the Function of Incretin-Producing Enteroendocrine Cells in Male Mice Fed a High-Fat Diet

BACKGROUND

Retinol-binding protein 2 (RBP2) is an intracellular carrier for vitamin A in the absorptive enterocytes. Mice lacking RBP2 (Rbp2-/-) display an unexpected phenotype of obesity, glucose intolerance, and elevated glucose-dependent insulinotropic polypeptide (GIP) levels. GIP and glucagon-like peptide 1 (GLP-1) are incretin hormones secreted by enteroendocrine cells (EECs). We recently demonstrated the presence of RBP2 and other retinoid-related proteins in EECs.

OBJECTIVES

Given RBP2's role in intracellular retinoid trafficking, we aimed to evaluate whether dietary vitamin A affects incretin-secreting cell function and gene expression.

METHODS

Male Rbp2-/- mice and sex- and age-matched controls (n = 6-9) were fed a high-fat diet (HFD) for 18 wk containing normal (VAN, 4000 IU/kg of diet) or low (VAL, 25% of normal) vitamin A concentrations. Body weight was recorded biweekly. Plasma GIP and GLP-1 levels were obtained fasting and 30 min after an oral fat gavage at week 16. Glucose tolerance tests were also performed. Mice were killed at week 18, and blood and tissue samples were obtained.

RESULTS

Rbp2-/- mice displayed greater weight gain on the VAN compared with the VAL diet from week 7 of the intervention (P ≤ 0.01). Stimulated GIP levels were elevated in Rbp2-/- mice compared with their controls fed the VAN diet (P = 0.02), whereas their GIP response was lower when fed the VAL diet (P = 0.03). Although no differences in GLP-1 levels were observed in the VAN diet group, a lower GLP-1 response was seen in Rbp2-/- mice fed the VAL diet (P = 0.02). Changes in incretin gene expression and that of other genes associated with EEC lineage and function were consistent with these observations. Circulating and hepatic retinoid levels revealed no systemic vitamin A deficiency across dietary groups.

CONCLUSIONS

Our data support a role for RBP2 and dietary vitamin A in incretin secretion and gene expression in mice fed a HFD.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

Gut Microbiota Remodeling and Intestinal Adaptation to Lipid Malabsorption After Enteroendocrine Cell Loss in Adult Mice

BACKGROUND & AIMS

Enteroendocrine cells (EECs) and their hormones are essential regulators of whole-body energy homeostasis. EECs sense luminal nutrients and microbial metabolites and subsequently secrete various hormones acting locally or at a distance. Impaired development of EECs during embryogenesis is life-threatening in newborn mice and humans due to compromised nutrient absorption. However, the physiological importance of the EEC system in adult mice has yet to be directedly studied. Herein, we aimed to determine the long-term consequences of a total loss of EECs in healthy adults on energy metabolism, intestinal transcriptome, and microbiota.

METHODS

We depleted intestinal EECs by tamoxifen treatment of adult Neurog3^fl/fl; Villin-CreER^T2 male mice. We studied intestinal cell differentiation, food efficiency, lipid absorption, microbiota composition, fecal metabolites, and transcriptomic responses in the proximal and distal small intestines of mice lacking EECs. We also determined the high-fat diet-induced transcriptomic changes in sorted Neurog3^eYFP/+ EECs.

RESULTS

Induction of EEC deficiency in adults is not life-threatening unless fed with a high-fat diet. Under a standard chow diet, mice lose 10% of weight due to impaired food efficiency. Blood concentrations of cholesterol, triglycerides, and free fatty acids are reduced, and lipid absorption is impaired and delayed in the distal small intestine. Genes controlling lipogenesis, carbohydrate metabolism, and neoglucogenesis are upregulated. Microbiota composition is rapidly altered after EECs depletion and is characterized by decreased a-diversity. Bacteroides and Lactobacillus were progressively enriched, whereas Lachnospiraceae declined without impacting fecal short-chain fatty acid concentrations.

CONCLUSIONS

EECs are dispensable for survival in adult male mice under a standard chow diet. The absence of EECs impairs intestinal lipid absorption, leading to transcriptomic and metabolic adaptations and remodeling of the gut microbiota.

Obesity pharmacotherapy: incretin action in the central nervous system

The prevalence of obesity is rising, creating an urgent need for efficacious therapies. Recent clinical trials show that tirzepatide, a dual agonist of receptors for the incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), yields more weight loss than selective GLP-1 receptor (GLP-1R) agonists. Incretin receptors in the central nervous system (CNS) may contribute to these effects. Yet exactly how each receptor regulates body weight from within the CNS is not clearly understood. It remains especially unclear how GIP receptor (GIPR) signalling contributes to the effects of tirzepatide because both stimulation and inhibition of CNS GIPRs yield weight loss in preclinical models. We summarise current knowledge on CNS incretin receptor pharmacology to provide insight into the potential mechanisms of action of dual GIPR/GLP-1R agonists, with tirzepatide as the exemplar. In addition, we discuss recent developments in incretin-based dual- and tri-agonism for inducing weight loss in obese individuals.

Novel Therapies for Cardiometabolic Disease: Recent Findings in Studies with Hormone Peptide-Derived G Protein Coupled Receptor Agonists

The increasing prevalence of obesity and type 2 diabetes (T2DM) is provoking an important socioeconomic burden mainly in the form of cardiovascular disease (CVD). One successful strategy is the so-called metabolic surgery whose beneficial effects are beyond dietary restrictions and weight loss. One key underlying mechanism behind this surgery is the cooperative improved action of the preproglucagon-derived hormones, glucagon, glucagon-like peptide-1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) which exert their functions through G protein-coupled receptors (GPCR). Great success has been reached with therapies based on the GLP-1 receptor monoagonism; therefore, a logical and rational approach is the use of the dual and triagonism of GCPC to achieve complete metabolic homeostasis. The present review describes novel findings regarding the complex biology of the preproglucagon-derived hormones, their signaling, and the drug development of their analogues, especially those acting as dual and triagonists. Moreover, the main investigations into animal models and ongoing clinical trials using these unimolecular dual and triagonists are included which have demonstrated their safety, efficacy, and beneficial effects on the CV system. These therapeutic strategies could greatly impact the treatment of CVD with unprecedented benefits which will be revealed in the next years.

Hindbrain circuits in the control of eating behaviour and energy balance

Body weight and adiposity represent biologically controlled parameters that are influenced by a combination of genetic, developmental and environmental variables. Although the hypothalamus plays a crucial role in matching caloric intake with energy expenditure to achieve a stable body weight, it is now recognized that neuronal circuits in the hindbrain not only serve to produce nausea and to terminate feeding in response to food consumption or during pathological states, but also contribute to the long-term control of body weight. Additionally, recent work has identified hindbrain neurons that are capable of suppressing food intake without producing aversive responses like those associated with nausea. Here we review recent advances in our understanding of the hindbrain neurons that control feeding, particularly those located in the area postrema and the nucleus tractus solitarius. We frame this information in the context of new atlases of hindbrain neuronal populations and develop a model of the hindbrain circuits that control food intake and energy balance, suggesting important areas for additional research.

GIP receptor antagonist treatment causes a reduction in weight gain in ovariectomised high fat diet-fed mice

Background and purpose

The incretin hormone, gastric inhibitory peptide/glucose‐dependent insulinotropic polypeptide (GIP), secreted by the enteroendocrine K‐cells in the proximal intestine, may regulate lipid metabolism and adiposity, but its exact role in these processes is unclear.

Experimental approach

We characterized in vitro and in vivo antagonistic properties of a novel GIP analogue, mGIPAnt‐1. We further assessed the in vivo pharmacokinetic profile of this antagonist, as well as its ability to affect high‐fat diet (HFD)‐induced body weight gain in ovariectomised mice during an 8‐week treatment period.

Key results

mGIPAnt‐1 showed competitive antagonistic properties to the GIP receptor in vitro as it inhibited GIP‐induced cAMP accumulation in COS‐7 cells. Furthermore, mGIPAnt‐1 was capable of inhibiting GIP‐induced glucoregulatory and insulinotropic effects in vivo and has a favourable pharmacokinetic profile with a half‐life of 7.2 h in C57Bl6 female mice. Finally, sub‐chronic treatment with mGIPAnt‐1 in ovariectomised HFD mice resulted in a reduction of body weight and fat mass.

Conclusion and Implications

mGIPAnt‐1 successfully inhibited acute GIP‐induced effects in vitro and in vivo and sub‐chronically induces resistance to HFD‐induced weight gain in ovariectomised mice. Our results support the development of GIP antagonists for the therapy of obesity.

Glucose-Dependent Insulinotropic Polypeptide-A Postprandial Hormone with Unharnessed Metabolic Potential

Glucose-dependent insulinotropic polypeptide (GIP) is released from the upper small intestine in response to food intake and contributes to the postprandial control of nutrient disposition, including of sugars and fats. Long neglected as a potential therapeutic target, the GIPR axis has received increasing interest recently, with the emerging data demonstrating the metabolically favorable outcomes of adding GIPR agonism to GLP-1 receptor agonists in people with type 2 diabetes and obesity. This review examines the physiology of the GIP axis, from the mechanisms underlying GIP secretion from the intestine to its action on target tissues and therapeutic development. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The Enteroendocrine System in Obesity

The enteroendocrine system coordinates the physiological response to food intake by regulating rates of digestion, nutrient absorption, insulin secretion, satiation and satiety. Gut hormones with important anorexigenic and/or insulinotropic roles include glucagon-like peptide 1 (GLP-1), peptide YY (PYY_3-36), cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP). High BMI or obesogenic diets do not markedly disrupt this enteroendocrine system, which represents a critical target for inducing weight loss and treating co-morbidities in individuals with obesity.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

Loss of Function Glucose-Dependent Insulinotropic Polypeptide Receptor Variants Are Associated With Alterations in BMI, Bone Strength and Cardiovascular Outcomes

Glucose-dependent insulinotropic polypeptide (GIP) and its receptor (GIPR) are involved in multiple physiological systems related to glucose metabolism, bone homeostasis and fat deposition. Recent research has surprisingly indicated that both agonists and antagonists of GIPR may be useful in the treatment of obesity and type 2 diabetes, as both result in weight loss when combined with GLP-1 receptor activation. To understand the receptor signaling related with weight loss, we examined the pharmacological properties of two rare missense GIPR variants, R190Q (rs139215588) and E288G (rs143430880) linked to lower body mass index (BMI) in carriers. At the molecular and cellular level, both variants displayed reduced G protein coupling, impaired arrestin recruitment and internalization, despite maintained high GIP affinity. The physiological phenotyping revealed an overall impaired bone strength, increased systolic blood pressure, altered lipid profile, altered fat distribution combined with increased body impedance in human carriers, thereby substantiating the role of GIP in these physiological processes.