FTO Obesity Variant Circuitry and Adipocyte Browning in Humans

Background Genomewide association studies can be used to identify disease-relevant genomic regions, but interpretation of the data is challenging. The FTO region harbors the strongest genetic association with obesity, yet the mechanistic basis of this association remains elusive. Methods We examined epigenomic data, allelic activity, motif conservation, regulator expression, and gene coexpression patterns, with the aim of dissecting the regulatory circuitry and mechanistic basis of the association between the FTO region and obesity. We validated our predictions with the use of directed perturbations in samples from patients and from mice and with endogenous CRISPR–Cas9 genome editing in samples from patients. Results Our data indicate that the FTO allele associated with obesity represses mitochondrial thermogenesis in adipocyte precursor cells in a tissue-autonomous manner. The rs1421085 T-to-C single-nucleotide variant disrupts a conserved motif for the ARID5B repressor, which leads to derepression of a potent preadipocyte enhancer and a doubling of IRX3 and IRX5 expression during early adipocyte differentiation. This results in a cell-autonomous developmental shift from energy-dissipating beige (brite) adipocytes to energy-storing white adipocytes, with a reduction in mitochondrial thermogenesis by a factor of 5, as well as an increase in lipid storage. Inhibition of Irx3 in adipose tissue in mice reduced body weight and increased energy dissipation without a change in physical activity or appetite. Knockdown of IRX3 or IRX5 in primary adipocytes from participants with the risk allele restored thermogenesis, increasing it by a factor of 7, and overexpression of these genes had the opposite effect in adipocytes from nonrisk-allele carriers. Repair of the ARID5B motif by CRISPR–Cas9 editing of rs1421085 in primary adipocytes from a patient with the risk allele restored IRX3 and IRX5 repression, activated browning expression programs, and restored thermogenesis, increasing it by a factor of 7. Conclusions Our results point to a pathway for adipocyte thermogenesis regulation involving ARID5B, rs1421085, IRX3, and IRX5, which, when manipulated, had pronounced pro-obesity and anti-obesity effects. (Funded by the German Research Center for Environmental Health and others.)National Institutes of Health (U.S.) (R01HG004037)National Institutes of Health (U.S.) (R01GM113708)National Institutes of Health (U.S.) (R01HG008155)National Institutes of Health (U.S.) (RC1HG005334

Road avoidance and its energetic consequences for reptiles

CITATION: Paterson, J. E., et al. 2019. Road avoidance and its energetic consequences for reptiles. Ecology and Evolution, 9(17):9794-9803, doi:10.1002/ece3.5515.The original publication is available at https://onlinelibrary.wiley.comRoads are one of the most widespread human-caused habitat modifications that can increase wildlife mortality rates and alter behavior. Roads can act as barriers with variable permeability to movement and can increase distances wildlife travel to access habitats. Movement is energetically costly, and avoidance of roads could therefore impact an animal's energy budget. We tested whether reptiles avoid roads or road crossings and explored whether the energetic consequences of road avoidance decreased individual fitness. Using telemetry data from Blanding's turtles (Emydoidea blandingii; 11,658 locations of 286 turtles from 15 sites) and eastern massasaugas (Sistrurus catenatus; 1,868 locations of 49 snakes from 3 sites), we compared frequency of observed road crossings and use of road-adjacent habitat by reptiles to expected frequencies based on simulated correlated random walks. Turtles and snakes did not avoid habitats near roads, but both species avoided road crossings. Compared with simulations, turtles made fewer crossings of paved roads with low speed limits and more crossings of paved roads with high speed limits. Snakes made fewer crossings of all road types than expected based on simulated paths. Turtles traveled longer daily distances when their home range contained roads, but the predicted energetic cost was negligible: substantially less than the cost of producing one egg. Snakes with roads in their home range did not travel further per day than snakes without roads in their home range. We found that turtles and snakes avoided crossing roads, but road avoidance is unlikely to impact fitness through energetic expenditures. Therefore, mortality from vehicle strikes remains the most significant impact of roads on reptile populations.https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.5515Publisher's versio

An examination of the development of rapid onset diabetes induced by elevated exogenous glucocorticoids and a high-fat diet in young Sprague-Dawley rats

Acute increases in glucocorticoids (GCs) during a perceived stressful event are functionally important for many biological processes that include energy homeostasis. Perpetual hypothalamic-pituitary-adrenal (HP.A) axis activity continually elevates GC secretion and may induce many metabolic complications, such as peripheral insulin resistance, ectopic fat accumulation, hyperglycemia, and dyslipidemia that can increase risks of developing type 2 diabetes mellitus (T2DM). The progression into T2DM remains complex and many controversies hav1e yet to be resolved. In particular, the effect of GCs on pancreatic islet function remains relatively understudied. Therefore, we set out to develop a novel rodent model ofT2DM in young male Sprague-Dawley rats. First, we demonstrated that 2 weeks of elevated GCs and HFD induced rapid-onset diabetes (ROD), which included the following symptoms: body weight loss, hepatic steatosis, increased glucose intolerance, insulin resistance, and ectopic fat accumulation. Next, we further examined the effects of ROD on pancreatic islet function and found that ROD animals had increased β-and α-cell mass, but impaired β-cell glucose responsiveness, resulting in hyperglycemia. Regular exercise restores alterations in HPA activity and helps to protect against GC-induced hyperglycemia. This led us to investigate if regular exercise in our ROD model would help to protect against T2DM development. We found that volitional exercise was sufficient to attenuate symptoms of ROD, however not all symptoms were successfully restored, i.e. normalized glucose control and peripheral insulin resistance. We next investigated if pharmacologic agents would be able to fully reverse ROD. We demonstrated that non-selective GC receptor (GRII) antagonist fully normalized our ROD phenotype, whereas selective GRII antagonists only partially attenuated some of the ROD symptoms. Collectively, these studies take an integrative approach to T2DM development induced by GCs and HFD. We developed a model that mimics symptoms ofT2DM and concluded that GCs and HFD synergistically, not independently act to induce severe insulin resistance that burdens islet adaptive capacity. Regular exercise and pharmacological interventions were sufficient to attenuate ROD development and these therapies may be useful techniques to individuals suffering from HPA axis hyperactivity and dyslipidemia

Genomic and Non-Genomic Actions of Glucocorticoids on Adipose Tissue Lipid Metabolism

Glucocorticoids (GCs) are hormones that aid the body under stress by regulating glucose and free fatty acids. GCs maintain energy homeostasis in multiple tissues, including those in the liver and skeletal muscle, white adipose tissue (WAT), and brown adipose tissue (BAT). WAT stores energy as triglycerides, while BAT uses fatty acids for heat generation. The multiple genomic and non-genomic pathways in GC signaling vary with exposure duration, location (adipose tissue depot), and species. Genomic effects occur directly through the cytosolic GC receptor (GR), regulating the expression of proteins related to lipid metabolism, such as ATGL and HSL. Non-genomic effects act through mechanisms often independent of the cytosolic GR and happen shortly after GC exposure. Studying the effects of GCs on adipose tissue breakdown and generation (lipolysis and adipogenesis) leads to insights for treatment of adipose-related diseases, such as obesity, coronary disease, and cancer, but has led to controversy among researchers, largely due to the complexity of the process. This paper reviews the recent literature on the genomic and non-genomic effects of GCs on WAT and BAT lipolysis and proposes research to address the many gaps in knowledge related to GC activity and its effects on disease

A rodent model of rapid-onset diabetes induced by glucocorticoids and high-fat feeding

SUMMARY Glucocorticoids (GCs) are potent pharmacological agents used to treat a number of immune conditions. GCs are also naturally occurring steroid hormones (e.g. cortisol, corticosterone) produced in response to stressful conditions that are thought to increase the preference for calorie dense ‘comfort’ foods. If chronically elevated, GCs can contribute to the development of type 2 diabetes mellitus (T2DM), although the mechanisms for the diabetogenic effects are not entirely clear. The present study proposes a new rodent model to investigate the combined metabolic effects of elevated GCs and high-fat feeding on ectopic fat deposition and diabetes development. Male Sprague-Dawley rats (aged 7–8 weeks) received exogenous corticosterone or wax (placebo) pellets, implanted subcutaneously, and were fed either a standard chow diet (SD) or a 60% high-fat diet (HFD) for 16 days. Animals given corticosterone and a HFD (cort-HFD) had lower body weight and smaller relative glycolytic muscle mass, but increased relative epididymal mass, compared with controls (placebo-SD). Cort-HFD rats exhibited severe hepatic steatosis and increased muscle lipid deposition compared with placebo-SD animals. Moreover, cort-HFD animals were found to exhibit severe fasting hyperglycemia (60% increase), hyperinsulinemia (80% increase), insulin resistance (60% increase) and impaired β-cell response to oral glucose load (20% decrease) compared with placebo-SD animals. Thus, a metabolic syndrome or T2DM phenotype can be rapidly induced in young Sprague-Dawley rats by using exogenous GCs if a HFD is consumed. This finding might be valuable in examining the physiological and molecular mechanisms of GC-induced metabolic disease

Hematopoietic cell– versus enterocyte-derived dipeptidyl peptidase-4 differentially regulates triglyceride excursion in mice

Postprandial triglycerides (TGs) are elevated in people with type 2 diabetes (T2D). Glucose-lowering agents, such as glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, also reduce postprandial TG excursion. Although the glucose-lowering mechanisms of DPP-4 have been extensively studied, how the reduction of DPP-4 activity improves lipid tolerance remains unclear. Here, we demonstrate that gut-selective and systemic inhibition of DPP-4 activity reduces postprandial TG excursion in young mice. Genetic inactivation of Dpp4 simultaneously within endothelial cells and hematopoietic cells using Tie2-Cre reduced intestinal lipoprotein secretion under regular chow diet conditions. Bone marrow transplantation revealed a key role for hematopoietic cells in modulation of lipid responses arising from genetic reduction of DPP-4 activity. Unexpectedly, deletion of Dpp4 in enterocytes increased TG excursion in high-fat diet–fed (HFD-fed) mice. Moreover, chemical reduction of DPP-4 activity and increased levels of GLP-1 were uncoupled from TG excursion in older or HFD-fed mice, yet lipid tolerance remained improved in older Dpp4–/– and Dpp4EC–/– mice. Taken together, this study defines roles for specific DPP-4 compartments, age, and diet as modifiers of DPP-4 activity linked to control of gut lipid metabolism

Inhibition of proliferation, migration and proteolysis contribute to corticosterone-mediated inhibition of angiogenesis.

The angiostatic nature of pharmacological doses of glucocorticoid steroids is well known. However, the consequences of pathophysiological elevation of endogenous glucocorticoids are not well established. In the current study, we hypothesized that the angiostatic effect of corticosterone, an endogenous glucocorticoid in rodents, occurs through multi-faceted alterations in skeletal muscle microvascular endothelial cell proliferation, migration, and proteolysis. Chronic corticosterone treatment significantly reduced the capillary to fiber ratio in the tibialis anterior muscle compared to that of placebo-treated rats. Corticosterone inhibited endothelial cell sprouting from capillary segments ex vivo. Similarly, 3-dimensional endothelial cell spheroids treated with corticosterone for 48 hours showed evidence of sprout regression and reduced sprout length. Endothelial cell proliferation was reduced in corticosterone treated cells, coinciding with elevated FoxO1 and reduced VEGF production. Corticosterone treated endothelial cells exhibited reduced migration, which correlated with a reduction in RhoA activity. Furthermore, corticosterone treated endothelial cells in both 3-dimensional and monolayer cultures had decreased MMP-2 production and activation resulting in decreased proteolysis by endothelial cells, limiting their angiogenic potential. Promoter assays revealed that corticosterone treatment transcriptionally repressed MMP-2, which may map to a predicted GRE between -1510 and -1386 bp of the MMP-2 promoter. Additionally, Sp1, a known transcriptional activator of MMP-2 was decreased following corticosterone treatment. This study provides new insights into the mechanisms by which pathophysiological levels of endogenous glucocorticoids may exert angiostatic effects

The brown adipose tissue glucagon receptor is functional but not essential for control of energy homeostasis in mice

Objective: Administration of glucagon (GCG) or GCG-containing co-agonists reduces body weight and increases energy expenditure. These actions appear to be transduced by multiple direct and indirect GCG receptor (GCGR)-dependent mechanisms. Although the canonical GCGR is expressed in brown adipose tissue (BAT) the importance of BAT GCGR activity for the physiological control of body weight, or the response to GCG agonism, has not been defined. Methods: We studied the mechanisms linking GCG action to acute increases in oxygen consumption using wildtype (WT), Ucp1−/− and Fgf21−/− mice. The importance of basal GCGR expression within the Myf5+ domain for control of body weight, adiposity, glucose and lipid metabolism, food intake, and energy expenditure was examined in GcgrBAT−/− mice housed at room temperature or 4 °C, fed a regular chow diet (RCD) or after a prolonged exposure to high fat diet (HFD). Results: Acute GCG administration induced lipolysis and increased the expression of thermogenic genes in BAT cells, whereas knockdown of Gcgr reduced expression of genes related to thermogenesis. GCG increased energy expenditure (measured by oxygen consumption) both in vivo in WT mice and ex vivo in BAT and liver explants. GCG also increased acute energy expenditure in Ucp1−/− mice, but these actions were partially blunted in Ffg21−/− mice. However, acute GCG administration also robustly increased oxygen consumption in GcgrBAT−/− mice. Moreover, body weight, glycemia, lipid metabolism, body temperature, food intake, activity, energy expenditure and adipose tissue gene expression profiles were normal in GcgrBAT−/− mice, either on RCD or HFD, whether studied at room temperature, or chronically housed at 4 °C. Conclusions: Exogenous GCG increases oxygen consumption in mice, also evident both in liver and BAT explants ex vivo, through UCP1-independent, FGF21-dependent pathways. Nevertheless, GCGR signaling within BAT is not physiologically essential for control of body weight, whole body energy expenditure, glucose homeostasis, or the adaptive metabolic response to cold or prolonged exposure to an energy dense diet. Keywords: Glucagon, brown adipose tissue, Energy expenditure, Adiposity, Lipolysis, Thermogenesi

GIPR Is Predominantly Localized to Nonadipocyte Cell Types Within White Adipose Tissue.

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