Molecular Integration of Incretin and Glucocorticoid Action Reverses Immunometabolic Dysfunction and Obesity
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ABSTRACT: Chronic inflammation has been proposed to contribute to the pathogenesis of diet-induced obesity. However, scarce therapeutic options are available to treat obesity and the associated immunometabolic complications. Glucocorticoids are routinely employed for the management of inflammatory diseases, but their pleiotropic nature leads to detrimental metabolic side effects. We developed a glucagon-like peptide-1 (GLP-1)-Dexamethasone co-agonist in which GLP-1 selectively delivers Dexamethasone to GLP-1 receptor-expressing cells. GLP-1-Dexamethasone lowers body weight up to 25% in obese mice by targeting the hypothalamic control of feeding and by increasing energy expenditure. This strategy reverses hypothalamic and systemic inflammation while improving glucose tolerance and insulin sensitivity. The selective preference for GLP-1 receptors bypasses deleterious effects of Dexamethasone on glucose handling, bone integrity, and hypothalamus-pituitary-adrenal axis activity. Thus, GLP-1-directed glucocorticoid pharmacology represents an efficacious therapy option for diet-induced immunometabolic derangements and the resulting obesity.
Project description:The central nervous system (CNS) hypothalamus controls systemic metabolism. Inflammatory CNS processes evolving upon exposure to calorie-rich diet are thought to promote impaired metabolic CNS control, thereby triggering obesity and Type-2 diabetes (T2D). However, immune cells relevant for maintaining hypothalamic integrity remain incompletely understood. Here, we identify hypothalamic CD4+Foxp3+regulatory T(Treg) cells which control local tissue-inflammation. Specifically, upon exposure to a calorie-rich diet, a significant decline in hypothalamus-residing Foxp3+Tregs occurred and was accompanied by increased immune activation of CD4+T cells, infiltrating macrophages and microglia. Microglial proteomes of mice exposed to the hypercaloric challenge confirmed characteristics of immune activation; specifically, mRNA expression profiling of hypothalamic CD4+T cells indicated a Th1-mediated inflammatory state evidenced by high levels of Tbx21, Cxcr3, Cd226 and reduced expression of Ccr7 and S1P1 receptors relevant for recruitment to and retention at inflammatory sites. Using Treg depletion and transfer experiments in vivo, we found that Foxp3+Tregs critically limit hypothalamic immune activation induced by hyper-caloric challenge. Our findings open new avenues in the design of tailored concepts to improve immunometabolic health in obesity and T2D.
Project description:A greater understanding of the glucose homeostasis mediated by glucagon-like peptide-1 (GLP-1) will facilitate the development of novel glucose-lowering treatments. Here we show that improved glucose metabolism in hypothyroid mice after treatment of T3, the active form of thyroid hormone (TH), is accompanied with increased GLP-1 production and insulin secretion. Treatment of a GLP-1 receptor antagonist is able to attenuate the observed T3 effect on insulin and glucose levels, suggesting that GLP-1 is critically involved in the regulation of glucose homeostasis by T3. By using a mouse model lacking hepatic TH receptor β (TRβ) and a liver-specific TRβ-selective agonist, we demonstrate that TRβ-mediated hepatic TH signalling is not only required for the regulation of GLP-1 production by T3 but also the insulinotropic and glucose-lowering effects of T3. Accordingly, administration of the liver-targeted TRβ-selective agonist is capable of increasing GLP-1 and insulin levels and alleviating hyperglycemia in diet-induced obesity. Mechanistically, through suppressing CYP8B1 expression, T3 shapes the bile acid (BA) composition and increases the levels of Farnesoid X receptor (FXR)-antagonistic BAs, thereby potentiating the GLP-1 production and insulin secretion by repressing intestinal FXR signalling. Consistently, correlations between the T3 levels and either GLP-1 or FXR-antagonistic BA levels can be observed in euthyroid human subjects. Thus, our study reveals a previously undescribed role of hepatic TH signalling in glucose homeostasis through the regulation of GLP-1 production via BA-mediated FXR antagonism, which will underpin the development of novel therapeutics.
Project description:A greater understanding of the glucose homeostasis mediated by glucagon-like peptide-1 (GLP-1) will facilitate the development of novel glucose-lowering treatments. Here we show that improved glucose metabolism in hypothyroid mice after treatment of T3, the active form of thyroid hormone (TH), is accompanied with increased GLP-1 production and insulin secretion. Treatment of a GLP-1 receptor antagonist is able to attenuate the observed T3 effect on insulin and glucose levels, suggesting that GLP-1 is critically involved in the regulation of glucose homeostasis by T3. By using a mouse model lacking hepatic TH receptor β (TRβ) and a liver-specific TRβ-selective agonist, we demonstrate that TRβ-mediated hepatic TH signalling is not only required for the regulation of GLP-1 production by T3 but also the insulinotropic and glucose-lowering effects of T3. Accordingly, administration of the liver-targeted TRβ-selective agonist is capable of increasing GLP-1 and insulin levels and alleviating hyperglycemia in diet-induced obesity. Mechanistically, through suppressing CYP8B1 expression, T3 shapes the bile acid (BA) composition and increases the levels of Farnesoid X receptor (FXR)-antagonistic BAs, thereby potentiating the GLP-1 production and insulin secretion by repressing intestinal FXR signalling. Consistently, correlations between the T3 levels and either GLP-1 or FXR-antagonistic BA levels can be observed in euthyroid human subjects. Thus, our study reveals a previously undescribed role of hepatic TH signalling in glucose homeostasis through the regulation of GLP-1 production via BA-mediated FXR antagonism, which will underpin the development of novel therapeutics.
Project description:Glucagon-like peptide 1 receptor agonists (GLP-1RAs) have been shown to impact glucose homeostasis and, more recently, the somatotropic axis. While the effects of GLP-1RAs have been extensively studied in the context of diet-induced obesity, their impact on physiology in other nutritional contexts have been less explored. We investigated the potential beneficial effects of the GLP-1RA semaglutide during juvenile protein malnutrition, a dietary challenge known to cause stunted growth and to disrupt metabolic homeostasis. We used a murine model to assess the effects of twice-weekly subcutaneous injections of semaglutide during juvenile protein malnutrition. Glucose metabolism was evaluated through in vivo oral glucose tolerance test, ex vivo glucose-stimulated insulin secretion in isolated pancreatic islets and histology of the pancreas. We combined linear growth monitoring, analysis of the growth hormone/insulin-like growth factor 1 signaling pathway and liver bulk RNA sequencing to characterize the effects of semaglutide on the somatotropic axis during juvenile protein malnutrition. Semaglutide improved glucose tolerance in control and malnourished mice, but differentially impacted pancreatic islet physiology depending on the dietary protein intake. While semaglutide did not alter growth in control conditions, it further inhibited growth of malnourished mice associated with reduction in fat but not lean mass. Surprisingly, semaglutide had no discernible effect on the functionality of the somatotropic axis in malnourished mice. Liver transcriptomics revealed that semaglutide could interfere with the growth of malnourished juvenile mice by altering circadian rhythm and thermogenesis. Our data reveal that semaglutide interacts differentially with the physiology of juvenile mice depending on their dietary protein intake. We found that semaglutide influences glucose metabolism and linear growth in a diet-dependent manner, underscoring the importance of examining the effects of GLP-1RAs across various nutritional contexts and developmental stages.
Project description:We demonstrate that high fat diet (HFD)-induced obesity alters the transcriptional state of lateral hypothalamic glutamate neurons in mice.
Project description:G-protein-coupled receptors (GPCRs) represent targets for improved low-side-effect therapies to tackle the evolving Western obesity epidemic. The orphan (o) GPCR GPR101 emerged as an attractive candidate in this regard. Expressed on cells in brain areas regulating energy homeostasis, including the hunger-suppressing proopiomelanocortin (POMC) + neurons, it is minimally expressed outside the brain. To understand the function of this receptor in vivo, we herein generated and comprehensively characterized a Gpr101 knockout mouse line, either under standard feeding conditions or with chronic high-fat diet (HFD) access (16 weeks). GPR101 loss accelerated the risk for diet-induced obesity (DIO), hyperinsulinemia and disrupted glucose homeostasis. Hypothalamic transcriptomic analysis revealed also decreased Pomc activation with HFD suggesting impaired hunger suppression. Moreover, on a standard diet, there was a molecular signature of downregulated tristetrapolin (TTP) pathway gene activation suggesting impaired inflammation resolution and one of aberrant microglial phagocytosis and lipid metabolism on HFD. Morphometry revealed altered hypothalamic arcuate nucleus microglial morphology consistent with the transcriptomic profile. We discuss how the GPR101 specialized pro-resolving mediator (SPM) receptor capacity likely underlies the aberrant microglial function and contributes to DIO risk. Thus, this evidence shows that GPR101 is a potential therapeutic target for DIO through, among other factors, effects on hypothalamic inflammation resolution.
Project description:Recent genome-wide association studies (GWAS) identified Dusp8, a dual-specificity phosphatase targeting MAP kinases, as type 2 diabetes risk gene. Here, we unravel Dusp8 as gatekeeper in the hypothalamic control of glucose homeostasis in mice and humans. Male but not female Dusp8 loss-of-function mice, either with global or CRH neuron-specific deletion, had impaired systemic glucose tolerance and insulin sensitivity when exposed to high-fat diet (HFD). Mechanistically, we found impaired hypothalamic–pituitary–adrenal (HPA) axis feedback, blunted sympathetic responsiveness, and chronically elevated corticosterone levels driven by hypothalamic hyperactivation of Jnk signaling. Accordingly, global Jnk1 ablation, AAV-mediated Dusp8 overexpression in the mediobasal hypothalamus, or metyrapone-induced chemical adrenalectomy rescued the impaired glucose homeostasis of male Dusp8 KO mice, respectively. This sex-specific and rheostatic role of murine Dusp8 in governing hypothalamic Jnk signaling, insulin sensitivity and systemic glucose tolerance was consistent with fMRI data in human volunteers that revealed an association of the DUSP8 rs2334499 risk variant with hypothalamic insulin resistance in men. In summary, our findings suggest GWAS-identified gene Dusp8 as novel hypothalamic factor that plays a functional role in the etiology of type 2 diabetes.
Project description:Alterations in endoplasmic reticulum (ER) homeostasis have been implicated in the pathophysiology of obesity and type-2 diabetes (T2D). Acute ER stress induction in the hypothalamus produces glucose metabolism perturbations. However, the neurobiological basis linking hypothalamic ER stress with abnormal glucose metabolism remains unknown. Here we report that genetic and induced models of hypothalamic ER stress are associated with alterations in systemic glucose homeostasis due to increased gluconeogenesis (GNG) independent of body weight changes. Defective alpha melanocyte-stimulating hormone (a-MSH) production underlies this metabolic phenotype, as pharmacological strategies aimed at rescuing hypothalamic a-MSH content reversed this phenotype at metabolic and molecular level. Collectively, our results posit defective a-MSH processing as a fundamental mediator of enhanced GNG in the context of hypothalamic ER stress, and establish a-MSH deficiency in proopiomelanocortin (POMC) neurons as a potential contributor to the pathophysiology of T2D. Total RNA was extracted from whole-liver of 6-week old control (3 biological replicates) and POMCMfn2KO mice (5 biological replicates)
Project description:The crucial role of nutrition for cerebral health and the impact of dietary habits on brain structure and function have been long far recognized. To date a major health concern is associated with the increased consumption of fructose as added sugar in many types of drinks and processed foods, especially among young people. High-fructose intake has been pointed out as the possible culprit for the raised incidence of chronic diseases, such as obesity, cardiovascular disease, nonalcoholic fatty liver disease, and type 2 diabete. Further, it has been reported that high-fructose intake is associated with the over-activation of its cerebral metabolism, which was proposed to negatively impact on whole brain physiology and cognitive function. Notably, we previously reported that short-term fructose-rich diet induces mitochondrial dysfunction, oxidative stress, and neuroinflammation in hippocampus of young rats, as well as the imbalance of redox homeostasis, autophagic mechanisms and representation of synaptic markers in frontal cortex of both adult and young rats. Animal studies have also revealed the damaging effect of high-fructose diets on hippocampal functions during periods of neurocognitive development, such as childhood and adolescence. Hypothalamus plays a crucial role in maintaining whole body homeostasis. Long-term fructose overfeeding was reported to alter hypothalamic-pituitary-adrenal axis, leading to elevations in glucocorticoids in peri-adolescent rats [22]. Further, fructose overconsumption was associated with impairment of hypothalamic insulin signalling, oxidative stress and inflammation , and it was proposed that fructose-driven perturbations of hypothalamic function may compromise the potential for satiety, thereby increasing the prospect of developing obesity. Data currently available on hypothalamic dysfunctions related to a high-fructose diet essentially refer to the effects of long-term sugar feeding, while information on corresponding alterations associated with a short-term dietary treatment, particularly in the critical period of adolescence, is still lacking. Due to complexity and multiplicity of hypothalamic functions, there is also the need for a holistic characterization aimed at unveiling the general picture of hypothalamic dysfunctions associated with a high-fructose diet. To fill this gap, we investigated adolescent rats fed a fructose-rich or control diet, for 3 weeks. To verify whether the fructose-driven changes are rescued after the switch to a control diet, half of the rats from both animal groups were then fed a control diet for additional 3 weeks until young adulthood phase. Quantitative proteomics on hypothalamic extracts of all animal groups was used to identify molecular alterations triggered by fructose-rich diet and to obtain insights into the relationship between sugar feeding and possible dysfunctions of hypothalamus.