👤 Myriam Beaudry

The contribution of glucose-dependent insulinotropic polypeptide receptor (GIPR) signalling in brown adipose tissue (BAT) remains underexplored. We studied the acute effects of exogenous acyl-GIP (1 nmol/kg) administration on whole-body lipid handling and fatty acid oxidation, using lipid tolerance tests (LTT) and indirect calorimetry, respectively. We demonstrate that in obese male mice, acute acyl-GIP administration improves lipid tolerance; however, pharmacological inhibition of GIPR, or genetic removal of GIPR globally or with the Myf5-Cre driver, completely abolishes GIP-mediated improvements in lipid tolerance, implicating GIPR in BAT. GIP-mediated improvements in lipid tolerance are associated with an increase in BAT lipid uptake, linked to increases in BAT lipoprotein lipase activity. Our data also reveal that BAT GIPR signalling is necessary for GIP-mediated increases in whole-body fatty acid oxidation, as Myf5-Cre: Gipr mice do not shift substrate oxidation upon GIP administration. Our findings suggest that BAT should be more closely considered in studies examining GIP's effects on whole-body metabolism in rodent models. Show less

An acute increase of lipids in the upper small intestine (USI) of rodents and humans triggers lipid-sensing pathways to reduce food intake. However, USI lipid sensing does not reduce feeding in high-fat (HF) fed conditions, and the underlying mechanism remains elusive. Here, we report that HF feeding in male rats impaired USI lipid infusion to stimulate glucose-dependent insulinotropic polypeptide (GIP) secretion and decrease refeeding, and the defects of USI lipid sensing were restored by metformin. Next, we found that infusion of GIP receptor (GIPR) agonist in the nucleus of the solitary tract (NTS), but not mediobasal hypothalamus or area postrema, resulted in decreased refeeding in chow-fed rats. The anorectic effect of NTS GIPR agonist remained intact in HF rats and was inhibited by a genetic knockdown of GIPR. Finally, an inhibition of NTS GIPR also negated the ability of USI lipid sensing with metformin to decrease refeeding despite an increase in plasma GIP levels in HF rats. Thus, USI lipid sensing in HF rats is enhanced by metformin to trigger an endocrine GIP to NTS GIPR axis to reduce food intake, thereby unveiling small intestinal lipid-sensing pathways as potential targets to enhance GIP action and reduce weight in obesity. High-fat (HF) feeding in rats impairs upper small intestine (USI) lipid sensing to increase plasma glucose-dependent insulinotropic polypeptide (GIP) levels and reduce feeding. Metformin enhances USI lipids to increase GIP and reduce feeding in HF-fed rats. GIP activates the GIP receptor (GIPR) in the nucleus of the solitary tract (NTS), which reduces food intake in HF-fed rats. GIPR in the NTS is required for small intestinal lipids with metformin to reduce feeding. Show less

Adipose tissue was once known as a reservoir for energy storage but is now considered a crucial organ for hormone and energy flux with important effects on health and disease. Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted from the small intestinal K cells, responsible for augmenting insulin release, and has gained attention for its independent and amicable effects with glucagon-like peptide 1 (GLP-1), another incretin hormone secreted from the small intestinal L cells. The GIP receptor (GIPR) is found in whole adipose tissue, whereas the GLP-1 receptor (GLP-1R) is not, and some studies suggest that GIPR action lowers body weight and plays a role in lipolysis, glucose/lipid uptake/disposal, adipose tissue blood flow, lipid oxidation, and free-fatty acid (FFA) re-esterification, which may or may not be influenced by other hormones such as insulin. This review summarizes the research on the effects of GIP in adipose tissue (distinct depots of white and brown) using cellular, rodent, and human models. In doing so, we explore the mechanisms of GIPR-based medications for treating metabolic disorders, such as type 2 diabetes and obesity, and how GIPR agonism and antagonism contribute to improvements in metabolic health outcomes, potentially through actions in adipose tissues. Show less

Elevated numbers of atherogenic lipoproteins (apoB) predict the incidence of type 2 diabetes (T2D). We reported that this may be mediated via the activation of the NLRP3 inflammasome, as low-density lipoproteins (LDL) induce interleukin-1 beta (IL-1β) secretion from human white adipose tissue (WAT) and macrophages. However, mitigating nutritional approaches remained unknown. We tested whether omega-3 eicosapentaenoic and docosahexaenoic acids (EPA and DHA) treat LDL-induced upregulation of WAT IL-1β-secretion and its relation to T2D risk factors. Twelve-week intervention with EPA and DHA (2.7 g/day, Webber Naturals) abolished baseline group-differences in WAT IL-1β-secretion between subjects with high-apoB (N = 17) and low-apoB (N = 16) separated around median plasma apoB. Post-intervention LDL failed to trigger IL-1β-secretion and inhibited it in lipopolysaccharide-stimulated WAT. Omega-3 supplementation also improved β-cell function and postprandial fat metabolism in association with higher blood EPA and mostly DHA. It also blunted the association of WAT NLRP3 and IL1B expression and IL-1β-secretion with multiple cardiometabolic risk factors including adiposity. Ex vivo, EPA and DHA inhibited WAT IL-1β-secretion in a dose-dependent manner. In conclusion, EPA and DHA treat LDL-induced upregulation of WAT NLRP3 inflammasome/IL-1β pathway and related T2D risk factors. This may aid in the prevention of T2D and related morbidities in subjects with high-apoB.Clinical Trail Registration ClinicalTrials.gov (NCT04496154): Omega-3 to Reduce Diabetes Risk in Subjects with High Number of Particles That Carry "Bad Cholesterol" in the Blood - Full Text View - ClinicalTrials.gov. Show less

The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) augments glucose-dependent insulin secretion through its receptor expressed on islet β-cells. GIP also acts on adipose tissue; yet paradoxically, both enhanced and reduced GIP receptor (GIPR) signaling reduce adipose tissue mass and attenuate weight gain in response to nutrient excess. Moreover, the precise cellular localization of GIPR expression within white adipose tissue (WAT) remains uncertain. We used mouse genetics to target Gipr expression within adipocytes. Surprisingly, targeting Cre expression to adipocytes using the adiponectin (Adipoq) promoter did not produce meaningful reduction of WAT Gipr expression in Adipoq-Cre:Giprflx/flx mice. In contrast, adenoviral expression of Cre under the control of the cytomegalovirus promoter, or transgenic expression of Cre using nonadipocyte-selective promoters (Ap2/Fabp4 and Ubc) markedly attenuated WAT Gipr expression. Analysis of single-nucleus RNA-sequencing, adipose tissue data sets localized Gipr/GIPR expression predominantly to pericytes and mesothelial cells rather than to adipocytes. Together, these observations reveal that adipocytes are not the major GIPR+ cell type within WAT-findings with mechanistic implications for understanding how GIP and GIP-based co-agonists control adipose tissue biology. Show less

Glucose-dependent insulinotropic polypeptide (GIP) is secreted from the gut in response to nutrient ingestion and promotes meal-dependent insulin secretion and lipid metabolism. Loss or attenuation of GIP receptor (GIPR) action leads to resistance to diet-induced obesity through incompletely understood mechanisms. The GIPR is expressed in white adipose tissue; however, its putative role in brown adipose tissue (BAT) has not been explored. We investigated the role of the GIPR in BAT cells in vitro and in BAT-specific (Gipr The mouse Gipr gene is expressed in BAT, and GIP directly increased Il6 mRNA and IL-6 secretion in BAT cells. Additionally, levels of thermogenic, lipid and inflammation mRNA transcripts were altered in BAT cells transfected with Gipr siRNA. Body weight gain, energy expenditure, and glucose and insulin tolerance were normal in HFD-fed Gipr The BAT GIPR is linked to the control of metabolic gene expression, fuel utilization, and oxygen consumption. However, the selective loss of the GIPR within BAT is insufficient to recapitulate the findings of decreased weight gain and resistance to obesity arising in experimental models with systemic disruption of GIP action. Show less

The Ras/mitogen-activated protein kinase (MAPK) pathway controls fundamental cellular processes such as proliferation, differentiation, and apoptosis. The dual-specificity phosphatase 6 (DUSP6) regulates cytoplasmic MAPK signaling by dephosphorylating and inactivating extracellular signal-regulated kinase (ERK1/2) MAPK. To determine the role of DUSP6 in the maintenance of intestinal homeostasis, we characterized the intestinal epithelial phenotype of Dusp6 knockout (KO) mice under normal, oncogenic, and proinflammatory conditions. Our results show that loss of Dusp6 increased crypt depth and epithelial cell proliferation without altering colonic architecture. Crypt regeneration capacity was also enhanced, as revealed by ex vivo Dusp6 KO organoid cultures. Additionally, loss of Dusp6 induced goblet cell expansion without affecting enteroendocrine and absorptive cell differentiation. Our data also demonstrate that Dusp6 KO mice were protected from acute dextran sulfate sodium-induced colitis, as opposed to wild-type mice. In addition, Dusp6 gene deletion markedly enhanced tumor load in Apc Show less