A Synthetic ERR Agonist Alleviates Metabolic Syndrome.

Physical exercise induces physiologic adaptations and is effective at reducing the risk of premature death from all causes. Pharmacological exercise mimetics may be effective in the treatment of a range of diseases including obesity and metabolic syndrome. Previously, we described the development of SLU-PP-332, an agonist for the estrogen-related receptor (ERR)α, ß, and γ nuclear receptors that activates an acute aerobic exercise program. Here we examine the effects of this exercise mimetic in mouse models of obesity and metabolic syndrome. Diet-induced obese or ob/ob mice were administered SLU-PP-332, and the effects on a range of metabolic parameters were assessed. SLU-PP-332 administration mimics exercise-induced benefits on whole-body metabolism in mice including increased energy expenditure and fatty acid oxidation. These effects were accompanied by decreased fat mass accumulation. Additionally, the ERR agonist effectively reduced obesity and improved insulin sensitivity in models of metabolic syndrome. Pharmacological activation of ERR may be an effective method to treat metabolic syndrome and obesity. SIGNIFICANCE STATEMENT: An estrogen receptor-related orphan receptor agonist, SLU-PP-332, with exercise mimetic activity, holds promise as a therapeutic to treat metabolic diseases by decreasing fat mass in mouse models of obesity.

Therapeutic Benefits of Adropin in Aged Mice After Transient Ischemic Stroke via Reduction of Blood-Brain Barrier Damage.

BACKGROUND: Adropin is a peptide encoded by the energy homeostasis-associated gene (Enho) that is highly expressed in the brain. Aging and stroke are associated with reduced adropin levels in the brain and plasma. We showed that treatment with synthetic adropin provides long-lasting neuroprotection in permanent ischemic stroke. However, it is unknown whether the protective effects of adropin are observed in aged animals following cerebral ischemia/reperfusion. We hypothesized that adropin provides neuroprotection in aged mice subjected to transient middle cerebral artery occlusion. METHODS: Aged (18-24 months old) male mice were subjected to 30 minutes of middle cerebral artery occlusion followed by 48 hours or 14 days of reperfusion. Sensorimotor (weight grip test and open field) and cognitive tests (Y-maze and novel object recognition) were performed at defined time points. Infarct volume was quantified by 2,3,5-triphenyltetrazolium chloride staining at 48 hours or Cresyl violet staining at 14 days post-middle cerebral artery occlusion. Blood-brain barrier damage, tight junction proteins, and MMP-9 (matrix metalloproteinase-9) were assessed 48 hours after middle cerebral artery occlusion by ELISA and Western blots. RESULTS: Genetic deletion of Enho significantly increased infarct volume and worsened neurological function, whereas overexpression of adropin dramatically reduced stroke volume compared to wild-type controls. Postischemic treatment with synthetic adropin peptide given at the onset of reperfusion markedly reduced infarct volume, brain edema, and significantly improved locomotor function and muscular strength at 48 hours. Delayed adropin treatment (4 hours after the stroke onset) reduced body weight loss, infarct volume, and muscular strength dysfunction, and improved long-term cognitive function. Postischemic adropin treatment significantly reduced blood-brain barrier damage. This effect was associated with reduced MMP-9 and preservation of tight junction proteins by adropin treatment. CONCLUSIONS: These data unveil a promising neuroprotective role of adropin in the aged brain after transient ischemic stroke via reducing neurovascular damage. These findings suggest that poststroke adropin therapy is a potential strategy to minimize brain injury and improve functional recovery in ischemic stroke patients.

Role of adropin in arterial stiffening associated with obesity and type 2 diabetes.

Adropin is a peptide largely secreted by the liver and known to regulate energy homeostasis; however, it also exerts cardiovascular effects. Herein, we tested the hypothesis that low circulating levels of adropin in obesity and type 2 diabetes (T2D) contribute to arterial stiffening. In support of this hypothesis, we report that obesity and T2D are associated with reduced levels of adropin (in liver and plasma) and increased arterial stiffness in mice and humans. Establishing causation, we show that mesenteric arteries from adropin knockout mice are also stiffer, relative to arteries from wild-type counterparts, thus recapitulating the stiffening phenotype observed in T2D db/db mice. Given the above, we performed a set of follow-up experiments, in which we found that 1) exposure of endothelial cells or isolated mesenteric arteries from db/db mice to adropin reduces filamentous actin (F-actin) stress fibers and stiffness, 2) adropin-induced reduction of F-actin and stiffness in endothelial cells and db/db mesenteric arteries is abrogated by inhibition of nitric oxide (NO) synthase, and 3) stimulation of smooth muscle cells or db/db mesenteric arteries with a NO mimetic reduces stiffness. Lastly, we demonstrated that in vivo treatment of db/db mice with adropin for 4 wk reduces stiffness in mesenteric arteries. Collectively, these findings indicate that adropin can regulate arterial stiffness, likely via endothelium-derived NO, and thus support the notion that "hypoadropinemia" should be considered as a putative target for the prevention and treatment of arterial stiffening in obesity and T2D.NEW & NOTEWORTHY Arterial stiffening, a characteristic feature of obesity and type 2 diabetes (T2D), contributes to the development and progression of cardiovascular diseases. Herein we establish that adropin is decreased in obese and T2D models and furthermore provide evidence that reduced adropin may directly contribute to arterial stiffening. Collectively, findings from this work support the notion that "hypoadropinemia" should be considered as a putative target for the prevention and treatment of arterial stiffening in obesity and T2D.

Adropin transgenesis improves recognition memory in diet-induced obese LDLR-deficient C57BL/6J mice.

Obesity-related metabolic dysregulation causes mild cognitive impairment and increased risk for dementia. We used an LDLR-deficient C57BL/6J mouse model (LDLRKO) to investigate whether adropin, a neuropeptide linked to neurodegenerative diseases, improves cognitive function in situations of metabolic dysregulation. Adropin transgenic mice (AdrTG) were crossed with LDLRKO; male and female progeny were fed a high fat diet for 3-months. Male chow-fed wild type (WT) mice were used as controls. Diet-induced obesity and LDLR-deficiency caused severe dyslipidemia, irrespective of sex. The AdrTG prevented reduced adropin protein levels in LDLRKO cortex. In males, metabolic dysregulation and AdrTG genotype significantly and bi-directionally affected performance in the novel object recognition (NOR) test, a declarative hippocampal memory task (discrimination index mean ± SE for WT, 0.02 ± 0.088; LDLRKO, -0.115 ± 0.077; AdrTG;LDLRKO, 0.265 ± 0.078; genotype effect, p = 0.009; LDLRKO vs. AdrTG;LDLRKO, P < 0.05). A 2-way ANOVA (fixed variables: sex, AdrTG genotype) indicated a highly significant effect of AdrTG (P = 0.003). The impact of the diet-genotype interaction on the male mouse brain was investigated using RNA-seq. Gene-ontology analysis of transcripts showing fold-changes of>1.3 or <-1.3 (P < 0.05) indicated metabolic dysregulation affected gene networks involved in intercellular/neuronal signaling, immune processes, angiogenesis, and extracellular matrix organization. The AdrTG selectively attenuated the impact of metabolic dysregulation on intercellular/neuronal signaling pathways. Intercellular/neuronal signaling pathways were also the predominant processes overrepresented when directly comparing AdrTG;LDLRKO with LDRKO. In summary, adropin overexpression improves cognitive function in severe metabolic dysregulation through pathways related to cell-cell communication and neuronal processes, and independently of preventing inflammatory responses.

The Importance of Keeping Time in the Liver.

The liver is a "front line" in the homeostatic defenses against variation in nutrient intake. It orchestrates metabolic responses to feeding by secreting factors essential for maintaining metabolic homeostasis, converting carbohydrates to triglycerides for storage, and releasing lipids packaged as lipoproteins for distribution to other tissues. Between meals, it provides fuel to the body by releasing glucose produced from glucogenic precursors and ketones from fatty acids and ketogenic amino acids. Modern diets enriched in sugars and saturated fats increase lipid accumulation in hepatocytes (nonalcoholic fatty liver disease). If untreated, this can progress to liver inflammation (nonalcoholic steatohepatitis), fibrosis, cirrhosis, and hepatocellular carcinoma. Dysregulation of liver metabolism is also relatively common in modern societies. Increased hepatic glucose production underlies fasting hyperglycemia that defines type 2 diabetes, while increased production of atherogenic, large, triglyceride-rich, very low-density lipoproteins raises the risk of cardiovascular disease. Evidence has accrued of a strong connection between meal timing, the liver clock, and metabolic homeostasis. Metabolic programming of the liver transcriptome and posttranslation modifications of proteins is strongly influenced by the daily rhythms in nutrient intake governed by the circadian clock. Importantly, whereas cell-autonomous clocks have been identified in the liver, the complete circadian programing of the liver transcriptome and posttranslational modifications of essential metabolic proteins is strongly dependent on nutrient flux and circadian signals from outside the liver. The purpose of this review is to provide a basic understanding of liver circadian physiology, drawing attention to recent research on the relationships between circadian biology and liver function.

Hepatocyte expression of the micropeptide adropin regulates the liver fasting response and is enhanced by caloric restriction.

The micropeptide adropin encoded by the clock-controlled energy homeostasis-associated gene is implicated in the regulation of glucose metabolism. However, its links to rhythms of nutrient intake, energy balance, and metabolic control remain poorly defined. Using surveys of Gene Expression Omnibus data sets, we confirm that fasting suppresses liver adropin expression in lean C57BL/6J (B6) mice. However, circadian rhythm data are inconsistent. In lean mice, caloric restriction (CR) induces bouts of compulsive binge feeding separated by prolonged fasting intervals, increasing NAD-dependent deacetylase sirtuin-1 signaling important for glucose and lipid metabolism regulation. CR up-regulates adropin expression and induces rhythms correlating with cellular stress-response pathways. Furthermore, adropin expression correlates positively with phosphoenolpyruvate carboxokinase-1 (Pck1) expression, suggesting a link with gluconeogenesis. Our previous data suggest that adropin suppresses gluconeogenesis in hepatocytes. Liver-specific adropin knockout (LAdrKO) mice exhibit increased glucose excursions following pyruvate injections, indicating increased gluconeogenesis. Gluconeogenesis is also increased in primary cultured hepatocytes derived from LAdrKO mice. Analysis of circulating insulin levels and liver expression of fasting-responsive cAMP-dependent protein kinase A (PKA) signaling pathways also suggests enhanced responses in LAdrKO mice during a glucagon tolerance test (250 µg/kg intraperitoneally). Fasting-associated changes in PKA signaling are attenuated in transgenic mice constitutively expressing adropin and in fasting mice treated acutely with adropin peptide. In summary, hepatic adropin expression is regulated by nutrient- and clock-dependent extrahepatic signals. CR induces pronounced postprandial peaks in hepatic adropin expression. Rhythms of hepatic adropin expression appear to link energy balance and cellular stress to the intracellular signal transduction pathways that drive the liver fasting response.

Role of angiopoietin-like protein 3 in sugar-induced dyslipidemia in rhesus macaques: suppression by fish oil or RNAi.

Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ∼30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques.

Fructose-induced hypertriglyceridemia in rhesus macaques is attenuated with fish oil or ApoC3 RNA interference.

Dyslipidemia and insulin resistance are significant adverse outcomes of consuming high-sugar diets. Conversely, dietary fish oil (FO) reduces plasma lipids. Diet-induced dyslipidemia in a rhesus model better approximates the pathophysiology of human metabolic syndrome (MetS) than rodent models. Here, we investigated relationships between metabolic parameters and hypertriglyceridemia in rhesus macaques consuming a high-fructose diet (n = 59) and determined the effects of FO supplementation or RNA interference (RNAi) on plasma ApoC3 and triglyceride (TG) concentrations. Fructose supplementation increased body weight, fasting insulin, leptin, TGs, and large VLDL particles and reduced adiponectin concentrations (all P < 0.001). In multiple regression analyses, increased plasma ApoC3 was the most consistent and significant variable related to diet-induced hypertriglyceridemia. FO supplementation, which attenuated increases of plasma TG and ApoC3 concentrations, reversed fructose-induced shifts of lipoprotein particle size toward IDL and VLDL, a likely mechanism contributing to beneficial metabolic effects, and reduced hepatic expression of genes regulated by the SREBP pathway, particularly acetyl-CoA carboxylase. Furthermore, RNAi-mediated ApoC3 inhibition lowered plasma TG concentrations in animals with diet-induced hypertriglyceridemia. In summary, ApoC3 is an important independent correlate of TG-rich lipoprotein concentrations in rhesus macaques consuming a high-fructose diet. ApoC3 is a promising therapeutic target for hypertriglyceridemia in patients with MetS and diabetes.

Doubled lifespan and patient-like pathologies in progeria mice fed high-fat diet.

Hutchinson-Gilford Progeria Syndrome (HGPS) is a devastating premature aging disease. Mouse models have been instrumental for understanding HGPS mechanisms and for testing therapies, which to date have had only marginal benefits in mice and patients. Barriers to developing effective therapies include the unknown etiology of progeria mice early death, seemingly unrelated to the reported atherosclerosis contributing to HGPS patient mortality, and mice not recapitulating the severity of human disease. Here, we show that progeria mice die from starvation and cachexia. Switching progeria mice approaching death from regular diet to high-fat diet (HFD) rescues early lethality and ameliorates morbidity. Critically, feeding the mice only HFD delays aging and nearly doubles lifespan, which is the greatest lifespan extension recorded in progeria mice. The extended lifespan allows for progeria mice to develop degenerative aging pathologies of a severity that emulates the human disease. We propose that starvation and cachexia greatly influence progeria phenotypes and that nutritional/nutraceutical strategies might help modulate disease progression. Importantly, progeria mice on HFD provide a more clinically relevant animal model to study mechanisms of HGPS pathology and to test therapies.

Adropin: An endocrine link between the biological clock and cholesterol homeostasis.

OBJECTIVE: Identify determinants of plasma adropin concentrations, a secreted peptide translated from the Energy Homeostasis Associated (ENHO) gene linked to metabolic control and vascular function. METHODS: Associations between plasma adropin concentrations, demographics (sex, age, BMI) and circulating biomarkers of lipid and glucose metabolism were assessed in plasma obtained after an overnight fast in humans. The regulation of adropin expression was then assessed in silico, in cultured human cells, and in animal models. RESULTS: In humans, plasma adropin concentrations are inversely related to atherogenic LDL-cholesterol (LDL-C) levels in men (n = 349), but not in women (n = 401). Analysis of hepatic Enho expression in male mice suggests control by the biological clock. Expression is rhythmic, peaking during maximal food consumption in the dark correlating with transcriptional activation by RORα/γ. The nadir in the light phase coincides with the rest phase and repression by Rev-erb. Plasma adropin concentrations in nonhuman primates (rhesus monkeys) also exhibit peaks coinciding with feeding times (07:00 h, 15:00 h). The ROR inverse agonists SR1001 and the 7-oxygenated sterols 7-ß-hydroxysterol and 7-ketocholesterol, or the Rev-erb agonist SR9009, suppress ENHO expression in cultured human HepG2 cells. Consumption of high-cholesterol diets suppress expression of the adropin transcript in mouse liver. However, adropin over expression does not prevent hypercholesterolemia resulting from a high cholesterol diet and/or LDL receptor mutations. CONCLUSIONS: In humans, associations between plasma adropin concentrations and LDL-C suggest a link with hepatic lipid metabolism. Mouse studies suggest that the relationship between adropin and cholesterol metabolism is unidirectional, and predominantly involves suppression of adropin expression by cholesterol and 7-oxygenated sterols. Sensing of fatty acids, cholesterol and oxysterols by the RORα/γ ligand-binding domain suggests a plausible functional link between adropin expression and cellular lipid metabolism. Furthermore, the nuclear receptors RORα/γ and Rev-erb may couple adropin synthesis with circadian rhythms in carbohydrate and lipid metabolism.

Inverse association between carbohydrate consumption and plasma adropin concentrations in humans.

OBJECTIVE: The role of metabolic condition and diet in regulating circulating levels of adropin, a peptide hormone linked to cardiometabolic control, is not well understood. In this study, weight loss and diet effects on plasma adropin concentrations were examined. METHODS: This report includes data from (1) a weight loss trial, (2) an evaluation of acute exercise effects on mixed-meal (60% kcal from carbohydrates) tolerance test responses, and (3) a meta-analysis to determine normal fasting adropin concentrations. RESULTS: Distribution of plasma adropin concentrations exhibited positive skew and kurtosis. The effect of weight loss on plasma adropin concentrations was dependent on baseline plasma adropin concentrations, with an inverse association between baseline and a decline in concentrations after weight loss (Spearman's ρ = -0.575; P < 0.001). When ranked by baseline plasma adropin concentrations, only values in the upper quartile declined with weight loss. Plasma adropin concentrations under the main area of the bell curve correlated negatively with habitual carbohydrate intake and plasma lipids. There was a negative correlation between baseline values and a transient decline in plasma adropin during the mixed-meal tolerance test. CONCLUSIONS: Plasma adropin concentrations in humans are sensitive to dietary macronutrients, perhaps due to habitual consumption of carbohydrate-rich diets suppressing circulating levels. Very high adropin levels may indicate cardiometabolic conditions sensitive to weight loss.

Differential Responses of Plasma Adropin Concentrations To Dietary Glucose or Fructose Consumption In Humans.

Adropin is a peptide hormone encoded by the Energy Homeostasis Associated (ENHO) gene whose physiological role in humans remains incompletely defined. Here we investigated the impact of dietary interventions that affect systemic glucose and lipid metabolism on plasma adropin concentrations in humans. Consumption of glucose or fructose as 25% of daily energy requirements (E) differentially affected plasma adropin concentrations (P < 0.005) irrespective of duration, sex or age. Glucose consumption reduced plasma adropin from 3.55 ± 0.26 to 3.28 ± 0.23 ng/ml (N = 42). Fructose consumption increased plasma adropin from 3.63 ± 0.29 to 3.93 ± 0.34 ng/ml (N = 45). Consumption of high fructose corn syrup (HFCS) as 25% E had no effect (3.43 ± 0.32 versus 3.39 ± 0.24 ng/ml, N = 26). Overall, the effect of glucose, HFCS and fructose on circulating adropin concentrations were similar to those observed on postprandial plasma triglyceride concentrations. Furthermore, increases in plasma adropin levels with fructose intake were most robust in individuals exhibiting hypertriglyceridemia. Individuals with low plasma adropin concentrations also exhibited rapid increases in plasma levels following consumption of breakfasts supplemented with lipids. These are the first results linking plasma adropin levels with dietary sugar intake in humans, with the impact of fructose consumption linked to systemic triglyceride metabolism. In addition, dietary fat intake may also increase circulating adropin concentrations.

Assessing interactions between Ghsr and Mc3r reveals a role for AgRP in the expression of food anticipatory activity in male mice.

The stomach hormone ghrelin and hypothalamic melanocortin neurons belong to a gut-brain circuit controlling appetite and metabolic homeostasis. Mice lacking melanocortin-3 receptor (Mc3rKO) or growth hormone secretagogue receptor (GhsrKO) genes exhibit attenuated food anticipatory activity (FAA), a rise in locomotor activity anticipating mealtime, suggesting common circuitry regulating anticipatory responses to nutrient loading. To investigate the interaction between Ghsrs and Mc3rs, we compared food anticipatory responses in GhsrKO, Mc3rKO, and double Ghsr;Mc3r knockout (DKO) mice subjected to a hypocaloric restricted feeding (RF) protocol in constant dark or 12-hour light, 12-hour dark settings. DKO are viable, exhibiting no overt behavioral or metabolic phenotypes in ad libitum or fasting conditions. FAA was initially attenuated in all mutant strains in constant darkness. However, GhsrKO eventually exhibited a robust food anticipatory response, suggesting compensation. Mc3rKO and DKO did not compensate, indicating a continued requirement for Mc3rs in maintaining the expression of FAA in situations of RF. Abnormal regulation of hypothalamic agouti-related peptide/neuropeptide Y (AgRP/Npy) neurons previously observed during fasting may contribute to attenuated FAA in Mc3rKO. AgRP and Npy expression measured 1 hour before food presentation correlated positively with FAA. Absence of Mc3rs (but not Ghsrs) was associated with lower AgRP/Npy expression, suggesting attenuated responses to signals of negative energy balance. These observations support the importance of Mc3rs as modulators of anticipatory responses to feeding, with mice able to compensate for loss of Ghsrs. The behavioral deficits of Mc3rKO displayed during RF may be partially explained by reduced hunger sensations owing to abnormal regulation of orexigenic AgRP/Npy neurons.

Fasting plasma adropin concentrations correlate with fat consumption in human females.

OBJECTIVE: This study investigated whether plasma adropin concentrations are influenced by sleep restriction and correlate with dietary preferences. METHODS: Plasma adropin concentrations were measured by ELISA using samples from a study that investigated feeding behavior in sleep deprived lean (body mass index 22-26 kg/m(2) ) men and women aged 30-45 y. Sleep (habitual or restricted to 4h/night) and diet were controlled during a 4-day inpatient period. On day 5, food was self-selected (FS). Adropin was measured on day 4 in samples collected throughout the day, and then after an overnight fast at 0730 on days 5 (Pre-FS) and 6 (Post-FS). RESULTS: Plasma adropin concentrations were not affected by sleep restriction. However, circulating adropin concentrations correlated with food selection preferences in women, irrespective of sleep status. Pre-FS adropin correlated positively with fat intake (total fat, r = 0.867, P < 0.05; saturated fat, r = 0.959, P < 0.01) and negatively with carbohydrate intake (r = -0.894, P < 0.05) as a percent total energy. Post-FS adropin correlated with total (r = 0.797, P < 0.05) and saturated fat intake (r = 0.945, P < 0.01), and negative with total carbohydrate intake (r = -0.929, P < 0.01). Pre-FS adropin also correlated with fat intake in kcal adjusted for body size (total fat, r = 0.852, P < 0.05; saturated fat, r = 0.927, P < 0.01). CONCLUSIONS: Plasma adropin concentrations correlate with fat consumption in women.

Blocking lactate export by inhibiting the Myc target MCT1 Disables glycolysis and glutathione synthesis.

Myc oncoproteins induce genes driving aerobic glycolysis, including lactate dehydrogenase-A that generates lactate. Here, we report that Myc controls transcription of the lactate transporter SLC16A1/MCT1 and that elevated MCT1 levels are manifest in premalignant and neoplastic Eµ-Myc transgenic B cells and in human malignancies with MYC or MYCN involvement. Notably, disrupting MCT1 function leads to an accumulation of intracellular lactate that rapidly disables tumor cell growth and glycolysis, provoking marked alterations in glycolytic intermediates, reductions in glucose transport, and in levels of ATP, NADPH, and ultimately, glutathione (GSH). Reductions in GSH then lead to increases in hydrogen peroxide, mitochondrial damage, and ultimately, cell death. Finally, forcing glycolysis by metformin treatment augments this response and the efficacy of MCT1 inhibitors, suggesting an attractive combination therapy for MYC/MCT1-expressing malignancies.

Low circulating adropin concentrations with obesity and aging correlate with risk factors for metabolic disease and increase after gastric bypass surgery in humans.

CONTEXT: Mouse studies suggest that adropin, a peptide hormone, is required for metabolic homeostasis and prevention of obesity-associated insulin resistance. Whether obesity and insulin resistance are associated with low plasma adropin levels in humans is not known. OBJECTIVES: Our objective was to investigate the hypothesis that obesity and indicators of insulin resistance are associated with low adropin levels and determine whether weight loss regulates adropin levels. DESIGN AND PARTICIPANTS: Plasma was obtained from 85 female [age 21-67 yr, body mass index (BMI) 19.4-71.5 kg/m2] and 45 male (age 18-70 yr, BMI 19.1-62.6 kg/m2) volunteers for other clinical studies. The impact of Roux-en-Y gastric bypass was investigated in 19 obese females (BMI 37-65 kg/m2) using samples collected at baseline and 1-12 months after surgery. RESULTS: Adropin levels correlate negatively with BMI (r=-0.335, P<0.001) and age (r=-0.263, P=0.003). Age-adjusted adropin levels are higher in males [4.1 ng/ml; 95% confidence interval (CI)=3.6-4.6 ng/ml] than females (3.0 ng/ml; 95% CI=2.6-3.4 ng/ml) (P=0.001). In all subjects, lower age-adjusted adropin levels were observed in overweight (3.3 ng/ml; 95% CI=2.8-3.8 ng/ml, P=0.033) and obese (2.7 ng/ml; 95% CI=2.1-3.3 ng/ml, P=0.001) compared with healthy-weight subjects (4.1 ng/ml; 95% CI=3.6-4.5 ng/ml). This effect was gender specific (weight category×gender, P<0.001) and was observed in males only. Aging and diagnosis with two or more metabolic syndrome risk factors was associated with low adropin levels, irrespective of sex. Adropin concentrations increased after Roux-en-Y gastric bypass, peaking 3 months after surgery (P<0.01). CONCLUSIONS: Although males exhibit higher adropin levels that are reduced by obesity, aging and markers of insulin resistance are associated with low plasma adropin irrespective of sex.

Central nervous system melanocortin-3 receptors are required for synchronizing metabolism during entrainment to restricted feeding during the light cycle.

Melanocortin-3 receptors (Mc3rs) in the central nervous system are involved in expression of anticipatory rhythms and synchronizing clocks maintaining circadian rhythms during restricted feeding (RF) [mice housed under a 12-h light-dark cycle with lights on between zeitgeber time (ZT) 0 to ZT12 fed 60% of normal calories between ZT7 and ZT11]. Because the systems governing circadian rhythms are important for adaptation to RF, we investigated whether Mc3rs are required for metabolic adaption to RF. Mc3r(-/-) mice subjected to RF exhibited normal weight loss; however, they developed hyperinsulinemia, glucose intolerance, increased expression of lipogenic genes, and increased ketogenesis relative to controls. Rhythmic expression of transcription factors regulating liver clock activity and energy metabolism (Bmal1, Rev-erbalpha, Pgc1, Foxo1, Hnf4alpha, and Pck1) was severely compromised in Mc3r(-/-) mice during RF. Inhibition of neural melanocortin receptors by agouti-related peptide also attenuated rhythmicity in the hepatic expression of these genes during RF. Collectively, these data suggest that neural Mc3rs are important for adapting metabolism and maintaining rhythms of liver metabolism during periods when feeding is restricted to the light cycle.-Sutton, G. M., Begriche, K., Kumar, K. G., Gimble, J. M., Perez-Tilve, D., Nogueiras, R., McMillan, R. P., Hulver, M. W., Tschöp, M. H., Butler, A. A. Central nervous system melanocortin-3 receptors are required for synchronizing metabolism during entrainment to restricted feeding during the light cycle.

Obesity accelerates thymic aging.

As the expanding obese population grows older, their successful immunologic aging will be critical to enhancing the health span. Obesity increases risk of infections and cancer, suggesting adverse effects on immune surveillance. Here, we report that obesity compromises the mechanisms regulating T-cell generation by inducing premature thymic involution. Diet-induced obesity reduced thymocyte counts and significantly increased apoptosis of developing T-cell populations. Obesity accelerated the age-related reduction of T-cell receptor (TCR) excision circle bearing peripheral lymphocytes, an index of recently generated T cells from thymus. Consistent with reduced thymopoiesis, dietary obesity led to reduction in peripheral naive T cells with increased frequency of effector-memory cells. Defects in thymopoiesis in obese mice were related with decrease in the lymphoid-primed multipotent progenitor (Lin-Sca1+Kit+ Flt3+) as well as common lymphoid progenitor (Lin-Sca1+CD117(lo)CD127+) pools. The TCR spectratyping analysis showed that obesity compromised V-beta TCR repertoire diversity. Furthermore, the obesity induced by melanocortin 4 receptor deficiency also constricted the T-cell repertoire diversity, recapitulating the thymic defects observed with diet-induced obesity. In middle-aged humans, progressive adiposity with or without type 2 diabetes also compromised thymic output. Collectively, these findings establish that obesity constricts T-cell diversity by accelerating age-related thymic involution.

Identification of adropin as a secreted factor linking dietary macronutrient intake with energy homeostasis and lipid metabolism.

Obesity and nutrient homeostasis are linked by mechanisms that are not fully elucidated. Here we describe a secreted protein, adropin, encoded by a gene, Energy Homeostasis Associated (Enho), expressed in liver and brain. Liver Enho expression is regulated by nutrition: lean C57BL/6J mice fed high-fat diet (HFD) exhibited a rapid increase, while fasting reduced expression compared to controls. However, liver Enho expression declines with diet-induced obesity (DIO) associated with 3 months of HFD or with genetically induced obesity, suggesting an association with metabolic disorders in the obese state. In DIO mice, transgenic overexpression or systemic adropin treatment attenuated hepatosteatosis and insulin resistance independently of effects on adiposity or food intake. Adropin regulated expression of hepatic lipogenic genes and adipose tissue peroxisome proliferator-activated receptor gamma, a major regulator of lipogenesis. Adropin may therefore be a factor governing glucose and lipid homeostasis, which protects against hepatosteatosis and hyperinsulinemia associated with obesity.