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:An 8-week high fat palm oil diet causes obesity and insulin resistance in C57BL/6J mice, but induces only small changes in the muscle transcriptome. Introduction: The metabolic syndrome (MS) is a cluster of metabolic abnormalities linked to an increased risk of type 2 diabetes and cardiovascular diseases. Two major characteristics of the MS are obesity and insulin resistance. In the present study we investigated the effect of obesity and insulin resistance on the mouse muscle transcriptome. Methods: C57BL/6J mice were fed a palm oil-based low fat diet (LFD) or high fat diet (HFD) for eight weeks. Microarray analysis was performed by using two complementary strategies: (1) 8-week HFD transcriptome versus 8-week LFD transcriptome and (2) transcriptome of mice sacrificed at the start of the intervention versus 8-week LFD transcriptome and 8-week HFD transcriptome, respectively. Results: HFD mice develop obesity and whole-body insulin resistance. Despite these metabolic disturbances we found that HFD induces relatively small changes in gene expression (< 1.3 fold). Only the up-regulation of FA oxidation and the down-regulation of the MAPK cascade were specific for the HFD intervention. Eight-weeks of aging induced more changed gene expression levels than the HFD, including genes involved in cell-cell interaction and development. Conclusion: Eight weeks of aging induce more pronounced changes in the muscle transcriptome than an HFD. Since only one strategy revealed the transcriptional down-regulation of the MAPK cascade, whereas both strategies showed the up-regulation of FA oxidation we suggest the use of complementary analysis strategies by the genome-wide search of gene expression changes induced by mild interventions, such as an HFD. Keywords: diet intervention and time course In this study, C57BL/6J mice were fed a high fat (HF) diet for 8 weeks to induce obesity and insulin resistance. Plasma levels of the adipokines leptin and adiponectin were measured. To investigate how these metabolic disturbances will influence the skeletal muscle transcriptome we performed whole-genome microarray analysis. Functional implications were assessed by analyses of predefined gene sets based on Gene Ontology, biochemical, metabolic and signaling pathways.
Project description:Insulin resistance is the hallmark of obese and type 2 diabetes patients. Defective insulin sensitivity in the liver results in increased glucsoe production, which is the major cause of hyperglycemia in diabetic patients. Increased lipopolysaccharide (LPS) leakage from the gut of diet-induced obesity causes insulin resisitance; moreover, activation of deacetylase Sirtuin1 restore insulin sensitivity in obesity. However, the mechanism resulting in insulin resistance by LPS remains poorly understood. Here, we show that Ep300 (P300) harboring an intrinsic acetyltransferase activity was rapidly induced in the liver of animals fed a high-fat diet, and the induction of Ep300 is through LPS-stimulated activation of ER stress. Induced Ep300 impairs insulin signaling by acetylating mediators in insulin signaling. Inhibition of P300 acetyltransferase activity improves insulin signaling. Thus, Ep300 acetyltransferase activity is a therapeutic target.
Project description:An 8-week high fat palm oil diet causes obesity and insulin resistance in C57BL/6J mice, but induces only small changes in the muscle transcriptome. Introduction: The metabolic syndrome (MS) is a cluster of metabolic abnormalities linked to an increased risk of type 2 diabetes and cardiovascular diseases. Two major characteristics of the MS are obesity and insulin resistance. In the present study we investigated the effect of obesity and insulin resistance on the mouse muscle transcriptome. Methods: C57BL/6J mice were fed a palm oil-based low fat diet (LFD) or high fat diet (HFD) for eight weeks. Microarray analysis was performed by using two complementary strategies: (1) 8-week HFD transcriptome versus 8-week LFD transcriptome and (2) transcriptome of mice sacrificed at the start of the intervention versus 8-week LFD transcriptome and 8-week HFD transcriptome, respectively. Results: HFD mice develop obesity and whole-body insulin resistance. Despite these metabolic disturbances we found that HFD induces relatively small changes in gene expression (< 1.3 fold). Only the up-regulation of FA oxidation and the down-regulation of the MAPK cascade were specific for the HFD intervention. Eight-weeks of aging induced more changed gene expression levels than the HFD, including genes involved in cell-cell interaction and development. Conclusion: Eight weeks of aging induce more pronounced changes in the muscle transcriptome than an HFD. Since only one strategy revealed the transcriptional down-regulation of the MAPK cascade, whereas both strategies showed the up-regulation of FA oxidation we suggest the use of complementary analysis strategies by the genome-wide search of gene expression changes induced by mild interventions, such as an HFD. Keywords: diet intervention and time course
Project description:Cyclic AMP-responsive element-binding protein H (CREBH, encoded by Creb3l3) is a transcription factor that regulates the expression of genes that control lipid and glucose metabolism, as well as inflammation. CREBH is upregulated in the liver under conditions of overnutrition, and mice globally lacking the gene (CREBH-/-) are highly susceptible to diet-induced obesity, insulin resistance (IR) and hepatic steatosis. The net protective effects of CREBH have been attributed in large part to the activities of Fibroblast growth factor (Fgf)-21 (Fgf21), a target gene that promotes weight loss, improves glucose homeostasis and reduces hepatic lipid accumulation. To explore the possibility that activation of the CREBH-Fgf21 axis could ameliorate established effects of high fat feeding, we generated an inducible transgenic hepatocyte-specific CREBH overexpression mouse model (Tg-rtTA). Acute overexpression of CREBH in livers of Tg-rtTA mice effectively reversed diet-induced obesity, IR and hepatic steatosis. These changes were associated with increased activities of thermogenic brown and beige adipose tissues in Tg-rtTA mice, leading to reductions in fat mass, along with enhanced insulin sensitivity and glucose tolerance. Genetically silencing of Fgf21 in Tg-rtTA mice abrogated the CREBH-mediated reductions in body weight loss, but only partially reversed the observed improvements in glucose metabolism. These findings reveal that the protective effects of CREBH activation may be leveraged to mitigate diet-induced obesity and associated metabolic abnormalities in both Fgf21-dependent and -independent pathways.
Project description:Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here, we report that IL-37, a newly-described antiinflammatory member of the IL-1 family, affects obesity-induced inflammation and insulin resistance. IL-37 transgenic mice (IL-37tg) did not develop an obese phenotype in response to a high-fat diet (HFD). Unlike WT mice, IL-37tg mice exhibited reduced numbers of adipose tissue macrophages and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. A short-term HFD intervention revealed that the IL-37-mediated improvement in glucose tolerance is independent of bodyweight. IL-37tg mice manifested a beneficial metabolic profile with higher circulating levels of the anti-inflammatory adipokine adiponectin. In vitro treatment of differentiating adipocytes with recombinant IL-37 reduced adipogenesis. The beneficial effects of recombinant IL-37 involved activation of AMPK signaling. In humans, steady-state IL-37 adipose tissue mRNA levels were positively correlated with insulin sensitivity, lower adipose tissue levels of leptin and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes. Gene arrays were performed on epidydimal white adipose tissue samples from wild type and human IL37-overexpressing transgenic mice fed a high fat diet for 16 weeks.
Project description:Insulin resistance not compensated by secretion reduces energy storage, but little is known about its effect upon energy expenditure (EE). Insulin receptor substrates Irs1 and Irs2 mediate signaling in all tissues, resulting in the inhibition of FoxO transcription factors. We found that hepatic disruption of Irs1 and Irs2 (LDKO mice) attenuated high-fat diet (HFD)-induced obesity and increased whole-body EE in a FoxO1-dependent manner. Hepatic disruption of Fst (follistatin), a FoxO1-regulated hepatokine, normalized EE in LDKO mice and restored adipose mass during HFD consumption. Moreover, hepatic Fst disruption alone increased fat mass accumulation, whereas hepatic overexpression of Fst attenuated high HFD-induced obesity. Excess circulating Fst in overexpressing mice neutralized Mstn (myostatin), activating mTORC1-promoted pathways of nutrient uptake and EE in skeletal muscle. Similar to Fst overexpression, direct activation of muscle mTORC1 also reduced adipose mass. We conclude that Fst-promoted EE in muscle attenuates obesity during hepatic insulin resistance.
Project description:Obesity-induced inflammation is a major driving force in the development of insulin resistance, type 2 diabetes (T2D) and related metabolic disorders. During obesity, macrophages accumulate in the visceral adipose tissue, creating a low grade inflammatory environment through the production of inflammatory cytokines. NF-κB signaling is a central coordinator of these inflammatory responses and is tightly regulated by the anti-inflammatory protein A20. To understand the role of inflammatory macrophages in insulin resistance and T2D development, we fed myeloid-specific A20 deficient mice (A20myel-KO mice) with a high fat diet, and demonstrate that these mice are completely protected from diet-induced obesity and insulin resistance, despite an inflammatory environment in their metabolic tissues. Macrophages lacking A20 show impaired mitochondrial respiratory function and metabolize more palmitate both in vitro and in vivo. Given the increased macrophage numbers in A20myel-KO mice, we hypothesize that A20 deficient macrophages rely more on palmitate oxidation and metabolize the fat present in the diet, resulting in a lean phenotype and protection from metabolic disease. These findings reveal an unexpected role for A20 in regulating macrophage immunometabolism.
Project description:Obesity impairs tissue insulin sensitivity and signaling, promoting type-2 diabetes. Although improving insulin signaling is key to reversing diabetes, the multi-organ mechanisms regulating this process are poorly defined. We screened the secretome and receptome in Drosophila to identify the hormonal crosstalk affecting diet-induced insulin resistance and obesity. We discovered a complex interplay between muscle, neuronal, and adipose tissues, mediated by Bone Morphogenetic Protein (BMP) signaling and the hormone Bursicon, that enhances insulin signaling and sugar tolerance. Muscle-derived BMP signaling, induced by sugar, governs neuronal Bursicon signaling. Bursicon, through its receptor Rickets, a Leucine-rich-repeat-containing G-protein coupled receptor (LGR), improves insulin secretion and insulin sensitivity in adipose tissue, mitigating hyperglycemia. In mouse adipocytes, loss of the Rickets ortholog LGR4 blunts insulin responses, showing an essential role of LGR4 in adipocyte insulin sensitivity. Our findings reveal a muscle-neuronal-fat-tissue axis driving metabolic adaptation to high-sugar conditions, identifying LGR4 as a critical mediator in this regulatory network.
Project description:Obesity is associated with insulin resistance, an important risk factor of type 2 diabetes, atherogenic dyslipidemia, nonalcoholic fatty liver disease (NAFLD), and cardiovascular disease. It has been postulated that accumulation of visceral adipose tissue (VAT) causes obesity-induced insulin resistance. The major purpose of this study was to test hypothesis that prophylactic VAT removal prevents the development of obesity-induced multi-organ (liver, skeletal muscle, adipose tissue) insulin resistance, dyslipidemia, and NAFLD. Accordingly, we surgically removed epididymal VAT from adult C57BL/6J mice and then evaluated in vivo and cellular metabolic pathways involved in glucose and lipid metabolism following feeding of chronic high-fat diet (HFD). We found that VAT removal prevented HFD-induced insulin resistance and markedly increased AKT-mediated insulin signaling in subcutaneous adipose tissue (SAT), liver, and skeletal muscle. VAT removal improved plasma lipid profiling and prevented obesity-induced NAFLD. In addition, VAT removal significantly increased circulating level of adiponectin, a key insulin-sensitizing adipokine, whereas it decreased interleukin-6, a pro-inflammatory adipokine. Data obtained from RNA-sequencing suggest that VAT removal prevents obesity-induced oxidative stress and inflammation in liver and SAT respectively. These findings demonstrate the causative role of VAT in the development of obesity and related systemic metabolic complications, such as insulin resistance, dyslipidemia, and NAFLD.