GDF15 promotes weight loss by enhancing energy expenditure in muscle.

Caloric restriction that promotes weight loss is an effective strategy for treating non-alcoholic fatty liver disease and improving insulin sensitivity in people with type 2 diabetes1. Despite its effectiveness, in most individuals, weight loss is usually not maintained partly due to physiological adaptations that suppress energy expenditure, a process known as adaptive thermogenesis, the mechanistic underpinnings of which are unclear2,3. Treatment of rodents fed a high-fat diet with recombinant growth differentiating factor 15 (GDF15) reduces obesity and improves glycaemic control through glial-cell-derived neurotrophic factor family receptor α-like (GFRAL)-dependent suppression of food intake4-7. Here we find that, in addition to suppressing appetite, GDF15 counteracts compensatory reductions in energy expenditure, eliciting greater weight loss and reductions in non-alcoholic fatty liver disease (NAFLD) compared to caloric restriction alone. This effect of GDF15 to maintain energy expenditure during calorie restriction requires a GFRAL-ß-adrenergic-dependent signalling axis that increases fatty acid oxidation and calcium futile cycling in the skeletal muscle of mice. These data indicate that therapeutic targeting of the GDF15-GFRAL pathway may be useful for maintaining energy expenditure in skeletal muscle during caloric restriction.

The phosphorylation of AMPKß1 is critical for increasing autophagy and maintaining mitochondrial homeostasis in response to fatty acids.

Fatty acids are vital for the survival of eukaryotes, but when present in excess can have deleterious consequences. The AMP-activated protein kinase (AMPK) is an important regulator of multiple branches of metabolism. Studies in purified enzyme preparations and cultured cells have shown that AMPK is allosterically activated by small molecules as well as fatty acyl-CoAs through a mechanism involving Ser108 within the regulatory AMPK ß1 isoform. However, the in vivo physiological significance of this residue has not been evaluated. In the current study, we generated mice with a targeted germline knock-in (KI) mutation of AMPKß1 Ser108 to Ala (S108A-KI), which renders the site phospho-deficient. S108A-KI mice had reduced AMPK activity (50 to 75%) in the liver but not in the skeletal muscle. On a chow diet, S108A-KI mice had impairments in exogenous lipid-induced fatty acid oxidation. Studies in mice fed a high-fat diet found that S108A-KI mice had a tendency for greater glucose intolerance and elevated liver triglycerides. Consistent with increased liver triglycerides, livers of S108A-KI mice had reductions in mitochondrial content and respiration that were accompanied by enlarged mitochondria, suggestive of impairments in mitophagy. Subsequent studies in primary hepatocytes found that S108A-KI mice had reductions in palmitate- stimulated Cpt1a and Ppargc1a mRNA, ULK1 phosphorylation and autophagic/mitophagic flux. These data demonstrate an important physiological role of AMPKß1 Ser108 phosphorylation in promoting fatty acid oxidation, mitochondrial biogenesis and autophagy under conditions of high lipid availability. As both ketogenic diets and intermittent fasting increase circulating free fatty acid levels, AMPK activity, mitochondrial biogenesis, and mitophagy, these data suggest a potential unifying mechanism which may be important in mediating these effects.

Differential changes in appetite hormones post-prandially based on menstrual cycle phase and oral contraceptive use: A preliminary study.

This was a preliminary study that examined whether appetite regulation is altered during the menstrual cycle or with oral contraceptives. Ten naturally cycling females (NON-USERS) and nine tri-phasic oral contraceptive using females (USERS) completed experimental sessions during each menstrual phase (follicular phase: FP; ovulatory phase: OP; luteal phase: LP). Appetite perceptions and blood samples were obtained fasted, 30, 60, and 90 min post-prandial to measure acylated ghrelin, active glucagon-like peptide-1 (GLP-1), and total peptide tyrosine tyrosine (PYY). Changes were considered important if p < 0.100 and the effect size was ≥medium. There appeared to be a three-way (group x phase x time) interaction for acylated ghrelin where concentrations appeared to be greater in USERS versus NON-USERS during the OP 90-min post-prandial and during the LP fasted, and 90-min post-prandial. In USERS, ghrelin appeared to be greater 90-min post-prandial in the OP versus the FP with no other apparent differences between phases. There were no apparent differences between phases in NON-USERS. There appeared to be a three-way interaction for PYY where concentrations appeared to be greater in USERS during the FP 60-min post-prandial and during the OP 30-min post-prandial. In USERS PYY appeared to be greater 60-min post-prandial during the OP versus the LP with no other apparent differences. There were no apparent differences between phases in NON-USERS. There appeared to be no effect of group or phase on GLP-1, or appetite perceptions. These data demonstrate small effects of menstrual cycle phase and oral contraceptive use on the acylated ghrelin and total PYY response to a standardized meal, with no effects on active GLP-1 or perceived appetite, though more work with a large sample size is necessary.

Ketogenic diet-induced weight loss occurs independent of housing temperature and is followed by hyperphagia and weight regain after cessation in mice.

Ketogenic diets (KDs) are a popular tool used for weight management. Studies in mice have demonstrated that KDs reduce food intake, increase energy expenditure and cause weight loss. These studies were completed at room temperature, a condition below the animal's thermal neutral zone which induces thermal stress. As energy intake and expenditure are sensitive to environmental temperature it is not clear if a KD would exert the same beneficial effects under thermal neutral conditions. Adherence to restrictive diets is poor and consequently it is important to examine the effects, and underlying mechanisms, of cycling from a ketogenic to an obesogenic diet. The purpose of the current study was to determine if housing temperature impacted the effects of a KD in obese mice and to determine if the mechanisms driving KD-induced weight loss reverse when mice are switched to an obesogenic high fat diet. We demonstrate that KD-induced reductions in food intake, increases in energy expenditure, weight loss and improvements in glucose homeostasis are not dependent upon housing temperature. KD-induced weight loss seems to be largely explained by reductions in caloric intake while cycling mice back to an obesogenic diet following a period of KD feeding leads to hyperphagia-induced weight gain. Collectively, our results suggest that prior findings with mice fed a KD at room temperature are likely not an artifact of how mice were housed and that initial changes in weight when transitioning from an obesogenic to a ketogenic diet or back are largely dependent on food intake. KEY POINTS: Ketogenic diets reduce food intake, increase energy expenditure and cause weight loss in rodents Prior preclinical studies have been completed at room temperature, a condition which induces thermal stress and limits clinical translatability Here it is demonstrated that ketogenic diet-induced reductions in food intake, increases in energy expenditure, weight loss and improvements in glucose homeostasis are similar in mice housed at room temperature or thermal neutrality Ketogenic diet-induced reductions in food intake appear to explain a large degree of weight loss. Similarly, switching mice from a ketogenic to an obesogenic diet leads to hyperphagia-mediated weight gain.

AMPK mediates energetic stress-induced liver GDF15.

Growth differentiating factor-15 (GDF15) is an emerging target for the treatment of obesity and metabolic disease partly due to its ability to suppress food intake. GDF15 expression and secretion are thought to be regulated by a cellular integrated stress response, which involves endoplasmic reticulum (ER) stress. AMPK is another cellular stress sensor, but the relationship between AMPK, ER stress, and GDF15 has not been assessed in vivo. Wildtype (WT), AMPK ß1 deficient (AMPKß1-/- ), and CHOP-/- mice were treated with three distinct AMPK activators; AICAR, which is converted to ZMP mimicking the effects of AMP on the AMPKγ isoform, R419, which indirectly activates AMPK through inhibition of mitochondrial respiration, or A769662, a direct AMPK activator which binds the AMPKß1 isoform ADaM site causing allosteric activation. Following treatments, liver Gdf15, markers of ER-stress, AMPK activity, adenine nucleotides, circulating GDF15, and food intake were assessed. AICAR and R419 caused ER and energetic stress, increased GDF15 expression and secretion, and suppressed food intake. Direct activation of AMPK ß1 containing complexes by A769662 increased hepatic Gdf15 expression, circulating GDF15, and suppressed food intake, independent of ER stress. The effects of AICAR, R419, and A769662 on GDF15 were attenuated in AMPKß1-/- mice. AICAR and A769662 increased GDF15 to a similar extent in WT and CHOP-/- mice. Herein, we provide evidence that AMPK plays a role in mediating the induction of GDF15 under conditions of energetic stress in mouse liver in vivo.

Individual patterns of response to traditional and modified sprint interval training.

We compared the incidence of response between a traditional sprint interval training (SIT) protocol (30:240: 4-6 x 30-s, 240-s recovery) and 2 modified SIT protocols (15:120: 8-12 x 15-s, 120-s recovery; 5:40: 24-36 x 5-s, 40-s recovery) over 4 weeks of training in 84 recreationally active individuals (n = 23 per SIT group/15 control participants). Pre- and post-testing measures included V. O2max, 5-km time trial, and anaerobic capacity. Responders were classified using 2x typical error and seven other approaches to explore the impact of classification method on response rates. There was no difference in the proportion (2x typical error) of V.O2max responders across groups (30:240: 64%; 15:120: 39%; 5:40: 41%; CTRL: 33%; P= 0.190). The 30:240 group had more responders (P< 0.05) for time trial performance (70%) and peak speed during the 30 s running test (48%) compared to CTRL (21% and 0%, respectively). There were no other between-group differences (P> 0.112). Approaches with the largest response thresholds resulted in the fewest responders highlighting response rates are influenced by the method used. Additionally, we observed intra-individual differences in responsiveness across outcomes. This is the first study to empirically test the difference in the incidence of response and demonstrate individual patterns of response across different SIT protocols.

Reactive oxygen species-dependent regulation of pyruvate dehydrogenase kinase-4 in white adipose tissue.

Reactive oxygen species (ROS) are important signaling molecules mediating the exercise-induced adaptations in skeletal muscle. Acute exercise also drives the expression of genes involved in reesterification and glyceroneogenesis in white adipose tissue (WAT), but whether ROS play any role in this effect has not been explored. We speculated that exercise-induced ROS would regulate acute exercise-induced responses in WAT. To address this question, we utilized various models to alter redox signaling in WAT. We examined basal and exercise-induced gene expression in a genetically modified mouse model of reduced mitochondrial ROS emission [mitochondrial catalase overexpression (MCAT)]. Additionally, H2O2, various antioxidants, and the ß3-adrenergic receptor agonist CL316243 were used to assess gene expression in white adipose tissue culture. MCAT mice have reduced ROS emission from WAT, enlarged WAT depots and adipocytes, and greater pyruvate dehydrogenase kinase-4 (Pdk4) gene expression. In WAT culture, H2O2 reduced glyceroneogenic gene expression. In wild-type mice, acute exercise induced dramatic but transient increases in Pdk4 and phosphoenolpyruvate carboxykinase (Pck1) mRNA in both subcutaneous inguinal WAT and epididymal WAT depots, which was almost completely absent in MCAT mice. Furthermore, the induction of Pdk4 and Pck1 in WAT culture by CL316243 was markedly reduced in the presence of antioxidants N-acetyl-cysteine or vitamin E. Genetic and nutritional approaches that attenuate redox signaling prevent exercise- and ß-agonist-induced gene expression within WAT. Combined, these data suggest that ROS represent important mediators of gene expression within WAT.

Deficiency of the autophagy gene ATG16L1 induces insulin resistance through KLHL9/KLHL13/CUL3-mediated IRS1 degradation.

Connections between deficient autophagy and insulin resistance have emerged, however, the mechanism through which reduced autophagy impairs insulin-signaling remains unknown. We examined mouse embryonic fibroblasts lacking Atg16l1 (ATG16L1 KO mouse embryonic fibroblasts (MEFs)), an essential autophagy gene, and observed deficient insulin and insulin-like growth factor-1 signaling. ATG16L1 KO MEFs displayed reduced protein content of insulin receptor substrate-1 (IRS1), pivotal to insulin signaling, whereas IRS1myc overexpression recovered downstream insulin signaling. Endogenous IRS1 protein content and insulin signaling were restored in ATG16L1 KO mouse embryonic fibroblasts (MEF) upon proteasome inhibition. Through proximity-dependent biotin identification (BioID) and co-immunoprecipitation, we found that Kelch-like proteins KLHL9 and KLHL13, which together form an E3 ubiquitin (Ub) ligase complex with cullin 3 (CUL3), are novel IRS1 interactors. Expression of Klhl9 and Klhl13 was elevated in ATG16L1 KO MEFs and siRNA-mediated knockdown of Klhl9, Klhl13, or Cul3 recovered IRS1 expression. Moreover, Klhl13 and Cul3 knockdown increased insulin signaling. Notably, adipose tissue of high-fat fed mice displayed lower Atg16l1 mRNA expression and IRS1 protein content, and adipose tissue KLHL13 and CUL3 expression positively correlated to body mass index in humans. We propose that ATG16L1 deficiency evokes insulin resistance through induction of Klhl9 and Klhl13, which, in complex with Cul3, promote proteasomal IRS1 degradation.

Mitochondria-associated ER membranes in glucose homeostasis and insulin resistance.

Obesity and insulin resistance (IR) are associated with endoplasmic reticulum (ER) stress and mitochondrial dysfunction in several tissues. Although for many years mitochondrial and ER function were studied separately, these organelles also connect to produce interdependent functions. Communication occurs at mitochondria-associated ER membranes (MAMs) and regulates lipid and calcium homeostasis, apoptosis, and the exchange of adenine nucleotides, among other things. Recent evidence suggests that MAMs contribute to organelle, cellular, and systemic metabolism. In obesity and IR models, metabolic tissues such as the liver, skeletal muscle, pancreas, and adipose tissue present alterations in MAM structure or function. The purpose of this mini review is to highlight the MAM disruptions that occur in each tissue during obesity and IR and its relationship with glucose homeostasis and IR. We also discuss the current controversy that surrounds MAMs' role in the development of IR.

Loss of glucagon signaling alters white adipose tissue browning.

Various endocrine factors contribute to cold-induced white adipose tissue (WAT) browning, but glucagon has largely been ignored. The purpose of the current investigation was to determine if glucagon was required for the effects of cold on WAT browning. Utilizing whole-body glucagon receptor knockout (Gcgr-/-) mice and their wild-type (WT) littermate controls, we examined the response of inguinal WAT (iWAT) and interscapular brown adipose tissue (BAT) to an acute (48 h) cold stress or challenge with the ß3-adrenergic agonist CL316,243. The effects of glucagon alone on the induction of thermogenic genes in adipose tissue from C57BL6/J mice were also examined. Gcgr-/- mice displayed modest increases in indices of browning at room temperature while displaying a blunted induction of Ucp1, Cidea, and Ffg21 mRNA expression in iWAT following cold exposure. Similarly, cold induced increases in mitochondrial DNA copy number, and the protein content of mitochondrial respiratory chain complexes, UCP1, and PGC1α were attenuated in iWAT from Gcgr-/- mice. In BAT, the induction of thermogenic markers following cold exposure was reduced, but the effect was less pronounced than in iWAT. Glucagon treatment increased the expression of thermogenic genes in both iWAT and BAT of C57BL6/J mice. In response to CL316,243, circulating fatty acids, glycerol, and the phosphorylation of hormone-sensitive lipase were attenuated in iWAT of Gcgr-/- mice. We provide evidence that glucagon is sufficient for the induction of thermogenic genes in iWAT, and the absence of intact glucagon signaling blunts the cold-induced browning of WAT, possibly due, in part, to impaired adrenergic signaling.-Townsend, L. K., Medak, K. D., Knuth, C. M., Peppler, W. T., Charron, M. J., Wright, D. C. Loss of glucagon signaling alters white adipose tissue browning.

AMPK ß1 activation suppresses antipsychotic-induced hyperglycemia in mice.

Olanzapine (OLZ) is a second-generation antipsychotic that is used to treat schizophrenia but also causes acute hyperglycemia. This study aimed to determine if the ablation of AMPK ß1-containing complexes potentiates acute OLZ-induced metabolic dysfunction and if the activation of AMPK ß1 suppresses these effects. Female AMPK ß1-/- or wild-type (WT) control mice were treated with OLZ, and changes in blood glucose, serum and liver metabolites, whole-body fuel oxidation, and pyruvate-induced increases in blood glucose were measured. Additionally, WT mice were cotreated with OLZ and A769662, a specific AMPK ß1 activator, and we determined if cotreatment protected against acute, OLZ-induced metabolic dysfunction. OLZ-induced increases in blood glucose were exacerbated in AMPK ß1-/- mice compared with WT mice, and this was paralleled by greater OLZ-induced increases in markers of liver glucose production, such as pyruvate tolerance, serum glucagon, and glucagon responsiveness. Cotreatment with A769662 attenuated OLZ-induced increases in blood glucose, serum nonesterified fatty acid, and glycerol. Furthermore, this effect was absent in AMPK ß1-/- mice, consistent with A769662's specificity for the AMPK ß1 subunit. Reductions in AMPK activity potentiate the effects of acute OLZ treatment on blood glucose, whereas specifically targeting AMPK ß1-containing complexes is sufficient to protect against OLZ-induced hyperglycemia.-Shamshoum, H., Medak, K. D., Townsend, L. K., Ashworth, K. E., Bush, N. D., Hahn, M. K., Kemp, B. E., Wright, D. C. AMPK ß1 activation suppresses antipsychotic-induced hyperglycemia in mice.

High-saturated-fat diet-induced obesity causes hepatic interleukin-6 resistance via endoplasmic reticulum stress.

The relationship between liver interleukin-6 (IL-6) resistance following high-fat diet (HFD)-induced obesity and glucose intolerance is unclear. The purpose of this study was to assess the temporal development of hepatic IL-6 resistance and the role of endoplasmic reticulum (ER) stress in this process. We hypothesized that HFD would rapidly induce hepatic IL-6 resistance through a mechanism involving ER stress. Male C57BL/6N mice consumed chow or a HFD (60%) derived from lard (saturated) or olive oil (monounsaturated) for 4 days or 7 weeks before being injected intraperitoneally with IL-6 (6 ng·kg-1). Glucose, insulin, and pyruvate tolerance tests were used as proxies for systemic glucose metabolism and hepatic glucose production, respectively. Primary mouse hepatocytes were incubated with palmitate (saturated) and oleate (unsaturated) overnight, then treated with 20 ng/ml IL-6. ER stress was induced via tunicamycin or prevented by sodium phenylbutyrate (PBA). Seven weeks of a saturated, but not monounsaturated, HFD reduced hepatic IL-6 signaling in conjunction with hepatic ER stress. Palmitate directly impaired IL-6 signaling in hepatocytes along with inducing ER stress. Pharmacologically induced ER stress caused hepatic IL-6 resistance, whereas PBA reversed HFD-induced IL-6 resistance. Chronic HFD-induced obesity is associated with hepatic IL-6 resistance due to saturated FA-induced ER stress.

Housing temperature affects the acute and chronic metabolic adaptations to exercise in mice.

KEY POINTS: Mice are commonly housed at room temperatures below their thermoneutral zone meaning they are exposed to chronic thermal stress. Endurance exercise induces browning and mitochondrial biogenesis in white adipose tissue of rodents, but there are conflicting reports of this phenomenon in humans. We hypothesized that the ambient room temperature at which mice are housed could partially explain these discrepant reports between humans and rodents. We housed mice at room temperature or thermoneutrality and studied their physiological responses to acute and chronic exercise. We found that thermoneutral housing altered running behaviour and glucose homeostasis, and further, that exercise-induced markers of mitochondrial biogenesis and the browning of white adipose tissue were reduced in mice housed at thermoneutrality. ABSTRACT: Mice are often housed at temperatures below their thermoneutral zone resulting in compensatory increases in thermogenesis. Despite this, many studies report housing mice at room temperature (RT), likely for the convenience of the researchers studying them. As such, the conflicting reports between humans and rodents regarding the ability of exercise to increase mitochondrial and thermogenic markers in white adipose tissue may be explained by the often-overlooked variable, housing temperature. To test this hypothesis, we housed male C57BL/6 mice at RT (22°C) or thermoneutrality (TN) (29°C) with or without access to a voluntary running wheel for 6 weeks or subjected them to an acute exhaustive bout of treadmill running. We examined the gene expression and protein content of select mitochondrial and thermogenic markers in skeletal muscle, epididymal white adipose tissue (eWAT), inguinal white adipose tissue (iWAT) and brown adipose tissue (BAT). We also assessed adipocyte morphology and indices of glucose homeostasis. Housing temperature influenced glucose tolerance and insulin action in vivo, yet the beneficial effects of exercise, both acute and chronic, remained intact in eWAT, BAT and skeletal muscle irrespective of housing temperature. Housing mice at TN led to an attenuation of some of the effects of exercise on iWAT. Collectively, we present data characterizing the acute and chronic metabolic adaptations to exercise at different housing temperatures and demonstrate, for the first time, that temperature influences the ability of exercise to increase markers of mitochondrial biogenesis and the browning of white adipose tissue.

Looking on the "brite" side exercise-induced browning of white adipose tissue.

The need for effective and convenient ways of combatting obesity has created great interest in brown adipose tissue (BAT). However, because adult humans have relatively little amounts of BAT, the possibility of browning white adipose tissue (WAT), i.e., switching the metabolism of WAT from an energy storing to energy burning organ, has gained considerable attention. Exercise has countless health benefits, and has consistently been shown to cause browning in rodent white adipose tissue. The purpose of this review is to provide an overview of recent studies examining the effects of exercise and other interventions on the browning of white adipose tissue. The role of various endocrine factors, including catecholamines, interleukin-6, irisin, and meteorin-like in addition to local re-esterification-mediated mechanisms in inducing the browning of WAT will be discussed. The physiological importance of browning will be discussed, as will discrepancies in the literature between human and rodent studies.

Acute administration of IL-6 improves indices of hepatic glucose and insulin homeostasis in lean and obese mice.

Obesity can lead to impairments in hepatic glucose and insulin homeostasis, and although exercise is an effective treatment, the molecular targets remain incompletely understood. As IL-6 is an exercise-inducible cytokine, we aimed to identify whether IL-6 itself influences hepatic glucose and insulin homeostasis and whether this response differs during obesity. In vivo, male mice were fed a low-fat diet (LFD; 10% kcal) or a high-fat diet (HFD; 60% kcal) for 7 wk, which induced obesity and hepatic lipid accumulation. LFD- and HFD-fed mice were injected with IL-6 (400 ng, 75 min) or PBS and then with insulin (1 U/kg; ~15 min) or saline, at which point livers were collected. In both LFD- and HFD-fed mice, IL-6 decreased blood glucose and mRNA expression of gluconeogenic genes alongside increased phosphorylation of AKT in comparison to PBS controls, and this occurred without changes in circulating insulin. To determine whether this effect of IL-6 was directly on the liver, we completed in vitro isolated primary hepatocyte experiments from chow-fed mice and cultured with or without exposure to free fatty acid (250 µm palmitate and 250 µm oleate, 24 h) to induce lipid accumulation. In both control and free fatty acid-treated hepatocytes, IL-6 (20 ng/ml, 75 min) slightly attenuated insulin-stimulated (10 nM; ~15 min) AKT phosphorylation. Together, these data suggest that IL-6 may lead to improvements in indices of hepatic glucose and insulin homeostasis in vivo; however, this is likely due to an indirect effect on the hepatocyte. NEW & NOTEWORTHY In this study, we used lean and obese mice and found that a single injection of IL-6 improved glucose tolerance, decreased hepatic gluconeogenic gene expression, and increased hepatic phosphorylation of AKT. In primary hepatocytes cultured under control and lipid-laden conditions, IL-6 had a mild, but deleterious, effect on phosphorylation of AKT. Our results show that the beneficial effects of IL-6 on glucose and insulin homeostasis, in vivo, are maintained in obesity.

Prior exercise training improves cold tolerance independent of indices associated with non-shivering thermogenesis.

KEY POINTS: Mammals defend against cold-induced reductions in body temperature through both shivering and non-shivering thermogenesis. The activation of non-shivering thermogenesis is primarily driven by uncoupling protein-1 in brown adipose tissue and to a lesser degree by the browning of white adipose tissue. Endurance exercise has also been shown to increase markers of white adipose tissue browning. This study aimed to determine whether prior exercise training would alter the response to a cold challenge and if this would be associated with differences in indices of non-shivering thermogenesis. It is shown that exercise training protects against cold-induced weight loss by increasing food intake. Exercise-trained mice were better able to maintain their core temperature, independent of differences in markers of non-shivering thermogenesis. ABSTRACT: Shivering is one of the first defences against cold, and as skeletal muscle fatigues there is an increased reliance on non-shivering thermogenesis. Brown and beige adipose tissues are the primary thermogenic tissues regulating this process. Exercise has also been shown to increase the thermogenic capacity of subcutaneous white adipose tissue. Whether exercise has an effect on the adaptations to cold stress within adipose tissue and skeletal muscle remains to be shown. Male C57BL/6 mice were either subjected to voluntary wheel running or remained sedentary for 12 days. Exercise led to decreased body weight and increased glucose tolerance. Mice were then divided into groups kept at 25°C room temperature or a cold challenge of 4°C for 48 h. Exercised mice were protected against cold-induced reductions in weight and in parallel with increased food intake. Providing exercised mice with the same amount of food as sedentary mice eliminated the protection against cold-induced weight loss. Cold exposure led to greater reductions in rectal temperature in sedentary compared to exercised mice. This protective effect was not explained by differences in the browning of white adipose tissue or brown adipose tissue mass. Similarly, the ability of the ß3 -adrenergic agonist CL 316,243 to increase energy expenditure was attenuated in previously exercised mice, suggesting that the activation of uncoupling protein-1 in brown and/or beige adipocytes is not the source of protective effects. We speculate that the protection against cold-induced reductions in rectal temperature could potentially be linked to exercise-induced alterations in skeletal muscle.

Subcutaneous inguinal white adipose tissue is responsive to, but dispensable for, the metabolic health benefits of exercise.

Exercise training has robust effects on subcutaneous inguinal white adipose tissue (iWAT), characterized by a shift to a brown adipose tissue (BAT)-like phenotype. Consistent with this, transplantation of exercise-trained iWAT into sedentary rodents activates thermogenesis and improves glucose homeostasis, suggesting that iWAT metabolism may contribute to the beneficial effects of exercise. However, it is yet to be determined if adaptations in iWAT are necessary for the beneficial systemic effects of exercise. To test this, male C57BL/6 mice were provided access to voluntary wheel running (VWR) or remained as a cage control (SED) for 11 nights after iWAT removal via lipectomy (LIPX) or SHAM surgery. We found that SHAM and LIPX mice with access to VWR ran similar distances and had comparable reductions in body mass, increased food intake, and increased respiratory exchange ratio (RER). Further, VWR improved indexes of glucose homeostasis and insulin tolerance in both SHAM and LIPX mice. The lack of effect of LIPX in the response to VWR was not explained by compensatory increases in markers of mitochondrial biogenesis and thermogenesis in skeletal muscle, epididymal white adipose tissue, or interscapular brown adipose tissue. Together, these data demonstrate that mice with and without iWAT have comparable adaptations to VWR, suggesting that iWAT may be dispensable for the metabolic health benefits of exercise.

AICAR Prevents Acute Olanzapine-Induced Disturbances in Glucose Homeostasis.

Olanzapine (OLZ) is an antipsychotic drug used in the treatment of schizophrenia. Although effective in reducing psychoses, OLZ causes acute increases in blood glucose. The acute effects of OLZ on hyperglycemia are likely caused by reductions in insulin secretion, insulin resistance, and increased hepatic glucose production. 5AMP-activated protein kinase (AMPK) is an energy sensor activated during exercise that can increase insulin sensitivity and insulin-independent glucose uptake in muscle. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) is a pharmacologic agent that, among other effects, can activate AMPK in vivo. Conversely, hypothalamic activation of AMPK has been suggested to mediate the hyperglycemic effects of OLZ. The purpose of this investigation was to determine whether cotreatment with AICAR could prevent acute OLZ-induced hyperglycemia in lean and obese C57BL6/J mice. OLZ (5 mg/kg, i.p.) caused rapid increases in blood glucose, a blunted insulin response, and pyruvate intolerance, all of which were prevented with AICAR cotreatment in both lean and obese mice. AICAR did not affect OLZ-induced changes in whole-body substrate oxidation or energy expenditure. Peripheral injection of AICAR, but not OLZ, activated AMPK signaling in the hypothalamus. The results of the current study provide evidence that AICAR prevents OLZ-induced hyperglycemia, despite increasing hypothalamic AMPK signaling. These protective effects were associated with the preservation of whole-body insulin action and reductions in markers of liver glucose production.