DHCR24 inhibitor SH42 increases desmosterol without preventing atherosclerosis development in mice

The liver X receptor (LXR) is considered a therapeutic target for atherosclerosis treatment, but synthetic LXR agonists generally also cause hepatic steatosis and hypertriglyceridemia. Desmosterol, a final intermediate in cholesterol biosynthesis, has been identified as a selective LXR ligand that suppresses inflammation without inducing lipogenesis. Δ24-Dehydrocholesterol reductase (DHCR24) converts desmosterol into cholesterol, and we previously showed that the DHCR24 inhibitor SH42 increases desmosterol to activate LXR and attenuate experimental peritonitis and metabolic dysfunction-associated steatotic liver disease. Here, we aimed to evaluate the effect of SH42 on atherosclerosis development in APOE∗3-Leiden.CETP mice and low-density lipoproteins (LDL) receptor knockout mice, models for lipid- and inflammation-driven atherosclerosis, respectively. In both models, SH42 increased desmosterol without affecting plasma lipids. While reducing liver lipids in APOE∗3-Leiden.CETP mice, and regulating populations of circulating monocytes in LDL receptor knockout mice, SH42 did not attenuate atherosclerosis in either model.

Time-restricted feeding attenuates hypercholesterolaemia and atherosclerosis development during circadian disturbance in APOE∗3-Leiden.CETP mice

BACKGROUND

Circadian disturbance (CD) is the consequence of a mismatch between endogenous circadian rhythms, behaviour, and/or environmental cycles, and frequently occurs during shift work. Shift work has been associated with elevated risk for atherosclerotic cardiovascular disease (asCVD) in humans, but evidence for the effectiveness of prevention strategies is lacking.

METHODS

Here, we applied time-restricted feeding (TRF) as a strategy to counteract atherosclerosis development during CD in female APOE∗3-Leiden.CETP mice, a well-established model for humanized lipoprotein metabolism. Control groups were subjected to a fixed 12:12 h light-dark cycle, while CD groups were subjected to 6-h phase advancement every 3 days. Groups had either ad libitum (AL) access to food or were subjected to TRF with restricted food access to the dark phase.

FINDINGS

TRF did not prevent the increase in the relative abundance of circulating inflammatory monocytes and elevation of (postprandial) plasma triglycerides during CD. Nonetheless, TRF reduced atherosclerotic lesion size and prevented an elevation in macrophage content of atherosclerotic lesions during CD, while it increased the relative abundance of anti-inflammatory monocytes, prevented activation of T cells, and lowered plasma total cholesterol levels and markers of hepatic cholesterol synthesis. These effects were independent of total food intake.

INTERPRETATION

We propose that time restricted eating could be a promising strategy for the primary prevention of asCVD risk in shift workers, which warrants future study in humans.

FUNDING

This work was funded by the Novo Nordisk Foundation, the Netherlands Ministry of Social Affairs and Employment, Amsterdam Cardiovascular Sciences, and the Dutch Heart Foundation.

Dietary choline increases brown adipose tissue activation markers and improves cholesterol metabolism in female APOE*3-Leiden.CETP mice

OBJECTIVES

Studies in mice have recently linked increased dietary choline consumption to increased incidence of obesity-related metabolic diseases, while several clinical trials have reported an anti-obesity effect of high dietary choline intake. Since the underlying mechanisms by which choline affects obesity are incompletely understood, the aim of the present study was to investigate the role of dietary choline supplementation in adiposity.

METHODS

Female APOE*3-Leiden.CETP mice, a well-established model for human-like lipoprotein metabolism and cardiometabolic diseases, were fed a Western-type diet supplemented with or without choline (1.2%, w/w) for up to 16 weeks.

RESULTS

Dietary choline reduced body fat mass gain, prevented adipocyte enlargement, and attenuated adipose tissue inflammation. Besides, choline ameliorated liver steatosis and damage, associated with an upregulation of hepatic genes involved in fatty acid oxidation. Moreover, choline reduced plasma cholesterol, as explained by a reduction of plasma non-HDL cholesterol. Mechanistically, choline reduced hepatic VLDL-cholesterol secretion and enhanced the selective uptake of fatty acids from triglyceride-rich lipoprotein (TRL)-like particles by brown adipose tissue (BAT), consequently accelerating the clearance of the cholesterol-enriched TRL remnants by the liver.

CONCLUSIONS

In APOE*3-Leiden.CETP mice, dietary choline reduces body fat by enhancing TRL-derived fatty acids by BAT, resulting in accelerated TRL turnover to improve hypercholesterolemia. These data provide a mechanistic basis for the observation in human intervention trials that high choline intake is linked with reduced body weight.

Circadian disruption impairs glucose homeostasis in male but not in female mice and is dependent on gonadal sex hormones

Circadian disruption (CD) is the consequence of a mismatch between endogenous circadian rhythms and behavior, and frequently occurs in shift workers. CD has often been linked to impairment of glucose and lipid homeostasis. It is, however, unknown if these effects are sex dependent. Here, we subjected male and female C57BL/6J mice to 6-h light phase advancements every 3 days to induce CD and assessed glucose and lipid homeostasis. Within this model, we studied the involvement of gonadal sex hormones by injecting mice with gonadotropin-releasing hormone-antagonist degarelix. We demonstrate that CD has sex-specific effects on glucose homeostasis, as CD elevated fasting insulin levels in male mice while increasing fasting glucose levels in female mice, which appeared to be independent of behavior, food intake, and energy expenditure. Absence of gonadal sex hormones lowered plasma insulin levels in male mice subjected to CD while it delayed glucose clearance in female mice subjected to CD. CD elevated plasma triglyceride (TG) levels and delayed plasma clearance of TG-rich lipoproteins in both sexes, coinciding with reduced TG-derived FA uptake by adipose tissues. Absence of gonadal sex hormones did not notably alter the effects of CD on lipid metabolism. We conclude that CD causes sex-dependent effects on glucose metabolism, as aggravated by male gonadal sex hormones and partly rescued by female gonadal sex hormones. Future studies on CD should consider the inclusion of both sexes, which may eventually contribute to personalized advice for shift workers.

FGF21 protects against hepatic lipotoxicity and macrophage activation to attenuate fibrogenesis in nonalcoholic steatohepatitis

Analogues of the hepatokine fibroblast growth factor 21 (FGF21) are in clinical development for type 2 diabetes and nonalcoholic steatohepatitis (NASH) treatment. Although their glucose-lowering and insulin-sensitizing effects have been largely unraveled, the mechanisms by which they alleviate liver injury have only been scarcely addressed. Here, we aimed to unveil the mechanisms underlying the protective effects of FGF21 on NASH using APOE*3-Leiden.CETP mice, a well-established model for human-like metabolic diseases. Liver-specific FGF21 overexpression was achieved in mice, followed by administration of a high-fat high-cholesterol diet for 23 weeks. FGF21 prevented hepatic lipotoxicity, accompanied by activation of thermogenic tissues and attenuation of adipose tissue inflammation, improvement of hyperglycemia and hypertriglyceridemia, and upregulation of hepatic programs involved in fatty acid oxidation and cholesterol removal. Furthermore, FGF21 inhibited hepatic inflammation, as evidenced by reduced Kupffer cell (KC) activation, diminished monocyte infiltration, and lowered accumulation of monocyte-derived macrophages. Moreover, FGF21 decreased lipid- and scar-associated macrophages, which correlated with less hepatic fibrosis as demonstrated by reduced collagen accumulation. Collectively, hepatic FGF21 overexpression limits hepatic lipotoxicity, inflammation, and fibrogenesis. Mechanistically, FGF21 blocks hepatic lipid influx and accumulation through combined endocrine and autocrine signaling, respectively, which prevents KC activation and lowers the presence of lipid- and scar-associated macrophages to inhibit fibrogenesis.

Time to run: Late rather than early exercise training in mice remodels the gut microbiome and reduces atherosclerosis development

The metabolic and inflammatory processes that are implicated in the development of cardiovascular diseases are under control of the biological clock. While skeletal muscle function exhibits circadian rhythms, it is unclear to what extent the beneficial health effects of exercise are restricted to unique time windows. We aimed to study whether the timing of exercise training differentially modulates the development of atherosclerosis and elucidate underlying mechanisms. We endurance-trained atherosclerosis-prone female APOE*3-Leiden.CETP mice fed a Western-type diet, a well-established human-like model for cardiometabolic diseases, for 1 h five times a week for 4 weeks either in their early or in their late active phase on a treadmill. We monitored metabolic parameters, the development of atherosclerotic lesions in the aortic root and assessed the composition of the gut microbiota. Late, but not early, exercise training reduced fat mass by 19% and the size of early-stage atherosclerotic lesions by as much as 29% compared to sedentary animals. No correlation between cholesterol exposure and lesion size was evident, as no differences in plasma lipid levels were observed, but circulating levels of the pro-inflammatory markers ICAM-1 and VCAM-1 were reduced with late exercise. Strikingly, we observed a time-of-day-dependent effect of exercise training on the composition of the gut microbiota as only late training increased the abundance of gut bacteria producing short-chain fatty acids with proposed anti-inflammatory properties. Together, these findings indicate that timing is a critical factor to the beneficial anti-atherosclerotic effects of exercise with a great potential to further optimize training recommendations for patients.

Acute and long-term exercise differently modulate plasma levels of oxylipins, endocannabinoids, and their analogues in young sedentary adults: A sub-study and secondary analyses from the ACTIBATE randomized controlled-trial

BACKGROUND

Fatty acid-derived lipid mediators including oxylipins, endocannabinoids (eCBs), and their analogues, have emerged as key metabolites in the inflammatory and immune response to physiological stressors.

METHODS

This report was based on a sub-study and secondary analyses the ACTIBATE single-center unblinded randomized controlled trial (ClinicalTrials.gov ID: NCT02365129). The study was performed in the Sport and Health University Research Institute and the Virgen de las Nieves University Hospital of the University of Granada. Eligible participants were young, sedentary adults with no chronic diseases. Here, we performed both an acute endurance and resistance exercise sub-studies (n.ß=.ß14 and 17 respectively), and a 24-week supervised exercise intervention, combining endurance and resistance exercise training at moderate-intensity (MOD-EX) or vigorous-intensity (VIG-EX) exercise groups, in young sedentary adults. Randomization was performed by unrestricted randomization. Plasma levels of oxylipins, eCBs, and their analogues were measured using liquid chromatography-tandem mass spectrometry.

FINDINGS

Both endurance and resistance exercise increased by.ß+50% the plasma levels of dihomo-..-linolenic acid and arachidonic acid (AA) omega-6 derived oxylipins, as well as eicosapentaenoic acid and docosahexaenoic acid omega-3 derived after 3 and 120.ßmin of the bout of exercise (all ..².ß....ß0.219 and P.ß..±.ß0.039). These exercise modalities also increased the levels of anandamide and eCBs analogues (+25%). 145 young sedentary adults were assigned to a control (CON, n.ß=.ß54), a MOD-EX (n.ß=.ß48) or a VIG-EX (n.ß=.ß43). 102 participants were included in the final long-term analyses (CON, n.ß=.ß36; MOD-EX, n.ß=.ß33; and VIG-EX, n.ß=.ß33) of the trial. After 24-week of supervised exercise, MOD-EX decreased plasma levels of omega-6 oxylipins, concretely linoleic acid (LA) and adrenic acid derived oxylipins, and the eCBs analogues OEA and LEA in comparison to the CON (all P.ß..±.ß0.021). VIG-EX decreased LA-derived oxylipins and LEA compared to CON. No relevant adverse events were recorded.

INTERPRETATION

Endurance and resistance exercises acutely increased plasma levels of oxylipins, eCBs, and their analogues, whereas 24 weeks of exercise training decreased fasting plasma levels of omega-6 oxylipins, and eCBs analogues in young, sedentary adults.

FUNDING

See Acknowledgments section.

No evidence of brown adipose tissue activation after 24 weeks of supervised exercise training in young sedentary adults in the ACTIBATE randomized controlled trial

Exercise modulates both brown adipose tissue (BAT) metabolism and white adipose tissue (WAT) browning in murine models. Whether this is true in humans, however, has remained unknown. An unblinded randomized controlled trial (ClinicalTrials.gov ID: NCT02365129) was therefore conducted to study the effects of a 24-week supervised exercise intervention, combining endurance and resistance training, on BAT volume and activity (primary outcome). The study was carried out in the Sport and Health University Research Institute and the Virgen de las Nieves University Hospital of the University of Granada (Spain). One hundred and forty-five young sedentary adults were assigned to either (i) a control group (no exercise, n = 54), (ii) a moderate intensity exercise group (MOD-EX, n = 48), or (iii) a vigorous intensity exercise group (VIG-EX n = 43) by unrestricted randomization. No relevant adverse events were recorded. 97 participants (34 men, 63 women) were included in the final analysis (Control; n = 35, MOD-EX; n = 31, and VIG-EX; n = 31). We observed no changes in BAT volume (Δ Control: −22.2 ± 52.6 ml; Δ MOD-EX: −15.5 ± 62.1 ml, Δ VIG-EX: −6.8 ± 66.4 ml; P = 0.771) or ¹⁸F-fluorodeoxyglucose uptake (SUVpeak Δ Control: −2.6 ± 3.1 ml; Δ MOD-EX: −1.2 ± 4.8, Δ VIG-EX: −2.2 ± 5.1; p = 0.476) in either the control or the exercise groups. Thus, we did not find any evidence of an exercise-induced change on BAT volume or activity in young sedentary adults.

Exercise modulates brown adipose tissue (BAT) metabolism in murine models. Here the authors report that there is no evidence that 24 weeks of supervised exercise training modulates BAT volume or function in young sedentary adults in the ACTIBATE randomized controlled trial.

Angiopoietin-like 4 governs diurnal lipoprotein lipase activity in brown adipose tissue

Objective

Brown adipose tissue (BAT) burns fatty acids (FAs) to produce heat, and shows diurnal oscillation in glucose and triglyceride (TG)-derived FA-uptake, peaking around wakening. Here we aimed to gain insight in the diurnal regulation of metabolic BAT activity.

Methods

RNA-sequencing, chromatin immunoprecipitation (ChIP)-sequencing, and lipidomics analyses were performed on BAT samples of wild type C57BL/6J mice collected at 3-hour intervals throughout the day. Knockout and overexpression models were used to study causal relationships in diurnal lipid handling by BAT.

Results

We identified pronounced enrichment of oscillating genes involved in extracellular lipolysis in BAT, accompanied by oscillations of FA and monoacylglycerol content. This coincided with peak lipoprotein lipase (Lpl) expression, and was predicted to be driven by peroxisome proliferator-activated receptor gamma (PPARγ) activity. ChIP-sequencing for PPARγ confirmed oscillation in binding of PPARγ to Lpl. Of the known LPL-modulators, angiopoietin-like 4 (Angptl4) showed the largest diurnal amplitude opposite to Lpl, and both Angptl4 knockout and overexpression attenuated oscillations of LPL activity and TG-derived FA-uptake by BAT.

Conclusions

Our findings highlight involvement of PPARγ and a crucial role of ANGPTL4 in mediating the diurnal oscillation of TG-derived FA-uptake by BAT, and imply that time of day is essential when targeting LPL activity in BAT to improve metabolic health.

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The transcriptome and lipidome of brown fat show clusters with distinct circadian phases.

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The peak in metabolic brown fat activity is defined by activation of lipolytic processes.

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PPARγ shows oscillating binding to lipolytic genes and may drive diurnal brown fat activity.

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Genetic modulation of the lipoprotein lipase inhibitor Angptl4 flattens rhythmic activity in brown fat.

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Time of day should be considered when studying the metabolic benefits of targeting brown fat.

Rev1 deficiency induces replication stress to cause metabolic dysfunction differently in males and females

DNA damage responses compete for cellular resources with metabolic pathways, but little is known about the metabolic consequences of impaired DNA replication, a process called replication stress. Here we characterized the metabolic consequences of DNA replication stress at endogenous DNA lesions by using mice with a disruption of Rev1, a translesion DNA polymerase specialized in the mutagenic replication of damaged DNA. Male and female Rev1 knockout (KO) mice were compared with wild-type (WT) mice and followed over time to study the natural course of body weight gain and glucose tolerance. Follow-up measurements were performed in female mice for in-depth metabolic characterization. Body weight and fat mass were only increased in female KO mice versus WT mice, whereas glucose intolerance and a reduction in lean mass were observed in both sexes. Female KO mice showed reduced locomotor activity while male KO mice showed increased activity as compared with their WT littermates. Further characterization of female mice revealed that lipid handling was unaffected by Rev1 deletion. An increased respiratory exchange ratio, combined with elevated plasma lactate levels and increased hepatic gluconeogenesis indicated problems with aerobic oxidation and increased reliance on anaerobic glycolysis. Supplementation with the NAD⁺ precursor nicotinamide riboside to stimulate aerobic respiration failed to restore the metabolic phenotype. In conclusion, replication stress at endogenous DNA lesions induces a complex metabolic phenotype, most likely initiated by muscular metabolic dysfunction and increased dependence on anaerobic glycolysis. Nicotinamide riboside supplementation after the onset of the metabolic impairment did not rescue this phenotype.NEW & NOTEWORTHY An increasing number of DNA lesions interferes with cellular replication leading to metabolic inflexibility. We utilized Rev1 knockout mice as a model for replication stress, and show a sex-dependent metabolic phenotype, with a pronounced reduction of lean mass and glucose tolerance. These data indicate that in obesity, we may end up in an infinite loop where metabolic disturbance promotes the formation of DNA lesions, which in turn interferes with cellular replication causing further metabolic disturbances.

Atlas of exercise metabolism reveals time-dependent signatures of metabolic homeostasis

Tissue sensitivity and response to exercise vary according to the time of day and alignment of circadian clocks, but the optimal exercise time to elicit a desired metabolic outcome is not fully defined. To understand how tissues independently and collectively respond to timed exercise, we applied a systems biology approach. We mapped and compared global metabolite responses of seven different mouse tissues and serum after an acute exercise bout performed at different times of the day. Comparative analyses of intra- and inter-tissue metabolite dynamics, including temporal profiling and blood sampling across liver and hindlimb muscles, uncovered an unbiased view of local and systemic metabolic responses to exercise unique to time of day. This comprehensive atlas of exercise metabolism provides clarity and physiological context regarding the production and distribution of canonical and novel time-dependent exerkine metabolites, such as 2-hydroxybutyrate (2-HB), and reveals insight into the health-promoting benefits of exercise on metabolism.

Sexual Dimorphism in Transcriptional and Functional Glucocorticoid Effects on Mouse Skeletal Muscle

Muscle atrophy is common in patients with increased glucocorticoid exposure. Glucocorticoid effects are often sex-specific, and while different glucocorticoid responses between male and female subjects are reported, it is unclear why this is. In this study, we evaluated the effects of corticosterone and synthetic glucocorticoid treatment on muscle atrophy in male and female mice. We found that corticosterone treatment reduced grip strength in female mice only, whereas muscle mass was reduced in both sexes. Skeletal muscle transcriptional responses to corticosterone treatment were more pronounced and widespread in male mice. Synthetic glucocorticoid treatment reduced grip strength in both sexes, while female mice were more sensitive to muscle atrophy than male mice. To evaluate the role of androgens, chemically-castrated male mice were treated with synthetic glucocorticoids. We observed additively reduced muscle mass, but did not observe any interaction effects. Although sex differences in glucocorticoid responses in skeletal muscle are partly influenced by androgen signaling, further studies are warranted to fully delineate the underlying mechanisms.

Pharmacological treatment with FGF21 strongly improves plasma cholesterol metabolism to reduce atherosclerosis

Aims 

Fibroblast growth factor (FGF) 21, a key regulator of energy metabolism, is currently evaluated in humans for treatment of type 2 diabetes and non-alcoholic steatohepatitis. However, the effects of FGF21 on cardiovascular benefit, particularly on lipoprotein metabolism in relation to atherogenesis, remain elusive.

Methods and results  

Here, the role of FGF21 in lipoprotein metabolism in relation to atherosclerosis development was investigated by pharmacological administration of a half-life extended recombinant FGF21 protein to hypercholesterolaemic APOE*3-Leiden.CETP mice, a well-established model mimicking atherosclerosis initiation and development in humans. FGF21 reduced plasma total cholesterol, explained by a reduction in non-HDL-cholesterol. Mechanistically, FGF21 promoted brown adipose tissue (BAT) activation and white adipose tissue (WAT) browning, thereby enhancing the selective uptake of fatty acids from triglyceride-rich lipoproteins into BAT and into browned WAT, consequently accelerating the clearance of the cholesterol-enriched remnants by the liver. In addition, FGF21 reduced body fat, ameliorated glucose tolerance and markedly reduced hepatic steatosis, related to up-regulated hepatic expression of genes involved in fatty acid oxidation and increased hepatic VLDL-triglyceride secretion. Ultimately, FGF21 largely decreased atherosclerotic lesion area, which was mainly explained by the reduction in non-HDL-cholesterol as shown by linear regression analysis, decreased lesion severity, and increased atherosclerotic plaque stability index.

Conclusion 

FGF21 improves hypercholesterolaemia by accelerating triglyceride-rich lipoprotein turnover as a result of activating BAT and browning of WAT, thereby reducing atherosclerotic lesion severity and increasing atherosclerotic lesion stability index. We have thus provided additional support for the clinical use of FGF21 in the treatment of atherosclerotic cardiovascular disease.

Mild Exercise Does Not Prevent Atherosclerosis in APOE*3-Leiden.CETP Mice or Improve Lipoprotein Profile of Men with Obesity

OBJECTIVE

Exercise has been shown to improve cardiometabolic health, yet neither the molecular connection nor the effects of exercise timing have been elucidated. The aim of this study was to investigate whether ad libitum or time-restricted mild exercise reduces atherosclerosis development in atherosclerosis-prone dyslipidemic APOE*3-Leiden.CETP mice and whether mild exercise training in men with obesity affects lipoprotein levels.

METHODS

Mice were group-housed and subjected to ad libitum or time-restricted (first or last 6 hours of the active phase) voluntary wheel running for 16 weeks while on a cholesterol-rich diet, after which atherosclerosis development was assessed in the aortic root. Furthermore, nine men with obesity followed a 12-week mild exercise training program. Lipoprotein levels were measured by nuclear magnetic resonance spectroscopy in plasma collected pre and post exercise training.

RESULTS

Wheel running did not affect plasma lipid levels, uptake of triglyceride-derived fatty acids by tissues, and aortic atherosclerotic lesion size or severity. Markers of training status were unaltered. Exercise training in men with obesity did not alter lipoprotein levels.

CONCLUSIONS

Mild exercise training does not reduce dyslipidemia or atherosclerosis development in APOE*3-Leiden.CETP mice or affect lipoprotein levels in humans. Future research on the effects of (time-restricted) exercise on atherosclerosis or lipid metabolism should consider more vigorous exercise protocols.

Role of the endocannabinoid system in the regulation of the skeletal muscle response to exercise

Exercise is a valuable tool in the prevention and treatment of cardiometabolic diseases like obesity and type 2 diabetes. Interestingly, endocannabinoids (eCBs), involved in a large range of physiological processes, are elevated with both obesity and acute exercise. In this review we outline this paradox overlap in the context of metabolic health and delineate the transcriptomic response of skeletal muscle to acute and chronic aerobic and resistance exercise in relation to the endocannabinoid system by utilizing a meta-analyses tool. We show that exercise modulates the expression of receptors and enzymes involved in the synthesis and breakdown of eCBs and discuss that eCBs possibly interfere with the anti-inflammatory effect of exercise. The endocannabinoid system (ECS), consisting of certain endogenous lipids (i.e. endocannabinoids), their receptors and associated metabolic enzymes, is involved in the modulation of a plethora of cognitive and physiological processes. Besides its role in the control of, for example, mood formation and immune responses, the ECS takes part in the regulation of appetite and energy metabolism [1,2]. In this current opinion review we will focus on the increased activity of the ECS that is associated with cardiometabolic diseases like obesity and type 2 diabetes (T2D), which paradoxically overlaps with the acute physiological response to exercise. After 1) outlining the role of the ECS in metabolic health, we will 2) discuss the link between endocannabinoid (eCB) action in skeletal muscle and cardiometabolic disease, 3) investigate how exercise modulates the gene expression of ECS components in skeletal muscle and 4) delineate the impact of the ECS on the immune response by skeletal muscle.

Time of Exercise Specifies the Impact on Muscle Metabolic Pathways and Systemic Energy Homeostasis

While the timing of food intake is important, it is unclear whether the effects of exercise on energy metabolism are restricted to unique time windows. As circadian regulation is key to controlling metabolism, understanding the impact of exercise performed at different times of the day is relevant for physiology and homeostasis. Using high-throughput transcriptomic and metabolomic approaches, we identify distinct responses of metabolic oscillations that characterize exercise in either the early rest phase or the early active phase in mice. Notably, glycolytic activation is specific to exercise at the active phase. At the molecular level, HIF1α, a central regulator of glycolysis during hypoxia, is selectively activated in a time-dependent manner upon exercise, resulting in carbohydrate exhaustion, usage of alternative energy sources, and adaptation of systemic energy expenditure. Our findings demonstrate that the time of day is a critical factor to amplify the beneficial impact of exercise on both metabolic pathways within skeletal muscle and systemic energy homeostasis.

Modified UCN2 Peptide Acts as an Insulin Sensitizer in Skeletal Muscle of Obese Mice

The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin-releasing hormone receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance and glucose metabolism. We investigated a modified UCN2 peptide as a potential therapeutic agent for the treatment of obesity and insulin resistance, with a specific focus on skeletal muscle. High-fat-fed mice (C57BL/6J) were injected daily with a PEGylated UCN2 peptide (compound A) at 0.3 mg/kg subcutaneously for 14 days. Compound A reduced body weight, food intake, whole-body fat mass, and intramuscular triglycerides compared with vehicle-treated controls. Furthermore, whole-body glucose tolerance was improved by compound A treatment, with increased insulin-stimulated Akt phosphorylation at Ser⁴⁷³ and Thr³⁰⁸ in skeletal muscle, concomitant with increased glucose transport into extensor digitorum longus and gastrocnemius muscle. Mechanistically, this is linked to a direct effect on skeletal muscle because ex vivo exposure of soleus muscle from chow-fed lean mice to compound A increased glucose transport and insulin signaling. Moreover, exposure of GLUT4-Myc-labeled L6 myoblasts to compound A increased GLUT4 trafficking. Our results demonstrate that modified UCN2 peptides may be efficacious in the treatment of type 2 diabetes by acting as an insulin sensitizer in skeletal muscle.

Acute sleep loss results in tissue-specific alterations in genome-wide DNA methylation state and metabolic fuel utilization in humans

Curtailed sleep promotes weight gain and loss of lean mass in humans, although the underlying molecular mechanisms are poorly understood. We investigated the genomic and physiological impact of acute sleep loss in peripheral tissues by obtaining adipose tissue and skeletal muscle after one night of sleep loss and after one full night of sleep. We find that acute sleep loss alters genome-wide DNA methylation in adipose tissue, and unbiased transcriptome-, protein-, and metabolite-level analyses also reveal highly tissue-specific changes that are partially reflected by altered metabolite levels in blood. We observe transcriptomic signatures of inflammation in both tissues following acute sleep loss, but changes involving the circadian clock are evident only in skeletal muscle, and we uncover molecular signatures suggestive of muscle breakdown that contrast with an anabolic adipose tissue signature. Our findings provide insight into how disruption of sleep and circadian rhythms may promote weight gain and sarcopenia.

Effects of high-fat diet and AMP-activated protein kinase modulation on the regulation of whole-body lipid metabolism

Metabolic flexibility, the capacity to adapt to fuel availability for energy production, is crucial for maintaining whole-body energy homeostasis. An inability to adequately promote FA utilization is associated with lipid accumulation in peripheral tissues and contributes to the development of insulin resistance. In vivo assays to quantify whole-body lipid oxidation in mouse models of insulin resistance are lacking. We describe a method for assessing whole-body FA oxidation in vivo, as well as tissue-specific lipid uptake in conscious mice. The method relies on intravenous administration of [9,10-³H(N)]palmitic acid combined with a non-β-oxidizable palmitate analog, [1-¹⁴C]2-bromopalmitic acid. Pretreatment with etomoxir, a CPT1 inhibitor that prevents the shuttling of FAs into mitochondria, markedly reduced the appearance of the β-oxidation product ³H₂O in circulation and reduced lipid uptake by oxidative tissues including heart and soleus muscle. Whole-body fatty oxidation was unaltered between chow- or high-fat-fed WT and transgenic mice expressing a mutant form of the AMPK γ3 subunit (AMPKγ3^R225Q) in skeletal muscle. High-fat feeding increased lipid oxidation in WT and AMPKγ3^R225Q transgenic mice. In conclusion, this technique allows for the assessment of the effect of pharmaceutical agents, as well as gene mutations, on whole-body FA oxidation in mice.

Proteomics Analysis of Skeletal Muscle from Leptin-Deficient ob/ob Mice Reveals Adaptive Remodeling of Metabolic Characteristics and Fiber Type Composition

Skeletal muscle insulin resistance, an early metabolic defect in the pathogenesis of type 2 diabetes (T2D), may be a cause or consequence of altered protein expression profiles. Proteomics technology offers enormous promise to investigate molecular mechanisms underlying pathologies, however, the analysis of skeletal muscle is challenging. Using state-of-the-art multienzyme digestion and filter-aided sample preparation (MED-FASP) and a mass spectrometry (MS)-based workflow, we performed a global proteomics analysis of skeletal muscle from leptin-deficient, obese, insulin resistant (ob/ob) and lean mice in mere two fractions in a short time (8 h per sample). We identified more than 6000 proteins with 118 proteins differentially regulated in obesity. This included protein kinases, phosphatases, and secreted and fiber type associated proteins. Enzymes involved in lipid metabolism in skeletal muscle from ob/ob mice were increased, providing evidence against reduced fatty acid oxidation in lipid-induced insulin resistance. Mitochondrial and peroxisomal proteins, as well as components of pyruvate and lactate metabolism, were increased. Finally, the skeletal muscle proteome from ob/ob mice displayed a shift toward the "slow fiber type." This detailed characterization of an obese rodent model of T2D demonstrates an efficient workflow for skeletal muscle proteomics, which may easily be adapted to other complex tissues.

Human Carboxylesterase 2 Reverses Obesity-Induced Diacylglycerol Accumulation and Glucose Intolerance

Serine hydrolases are a large family of multifunctional enzymes known to influence obesity. Here, we performed activity-based protein profiling to assess the functional level of serine hydrolases in liver biopsies from lean and obese humans in order to gain mechanistic insight into the pathophysiology of metabolic disease. We identified reduced hepatic activity of carboxylesterase 2 (CES2) and arylacetamide deacetylase (AADAC) in human obesity. In primary human hepatocytes, CES2 knockdown impaired glucose storage and lipid oxidation. In mice, obesity reduced CES2, whereas adenoviral delivery of human CES2 reversed hepatic steatosis, improved glucose tolerance, and decreased inflammation. Lipidomic analysis identified a network of CES2-regulated lipids altered in human and mouse obesity. CES2 possesses triglyceride and diacylglycerol lipase activities and displayed an inverse correlation with HOMA-IR and hepatic diacylglycerol concentrations in humans. Thus, decreased CES2 is a conserved feature of obesity and plays a causative role in the pathogenesis of obesity-related metabolic disturbances.

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Obesity decreases hepatic activity of AADAC and CES2 in humans

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CES2 depletion impairs lipid and glucose metabolism in primary human hepatocytes

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Human CES2 expression reverses hepatic steatosis and glucose intolerance in mice

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CES2 controls a hepatic lipid network dysregulated in human and mouse obesity

Diacylglycerol kinase ε deficiency preserves glucose tolerance and modulates lipid metabolism in obese mice

Diacylglycerol kinases (DGKs) catalyze the phosphorylation and conversion of diacylglycerol (DAG) into phosphatidic acid. DGK isozymes have unique primary structures, expression patterns, subcellular localizations, regulatory mechanisms, and DAG preferences. DGKε has a hydrophobic segment that promotes its attachment to membranes and shows substrate specificity for DAG with an arachidonoyl acyl chain in the sn-2 position of the substrate. We determined the role of DGKε in the regulation of energy and glucose homeostasis in relation to diet-induced insulin resistance and obesity using DGKε-KO and wild-type mice. Lipidomic analysis revealed elevated unsaturated and saturated DAG species in skeletal muscle of DGKε KO mice, which was paradoxically associated with increased glucose tolerance. Although skeletal muscle insulin sensitivity was unaltered, whole-body respiratory exchange ratio was reduced, and abundance of mitochondrial markers was increased, indicating a greater reliance on fat oxidation and intracellular lipid metabolism in DGKε KO mice. Thus, the increased intracellular lipids in skeletal muscle from DGKε KO mice may undergo rapid turnover because of increased mitochondrial function and lipid oxidation, rather than storage, which in turn may preserve insulin sensitivity. In conclusion, DGKε plays a role in glucose and energy homeostasis by modulating lipid metabolism in skeletal muscle.

Altered DNA methylation of glycolytic and lipogenic genes in liver from obese and type 2 diabetic patients

OBJECTIVE

Epigenetic modifications contribute to the etiology of type 2 diabetes.

METHOD

We performed genome-wide methylome and transcriptome analysis in liver from severely obese men with or without type 2 diabetes and non-obese men to discover aberrant pathways underlying the development of insulin resistance. Results were validated by pyrosequencing.

RESULT

We identified hypomethylation of genes involved in hepatic glycolysis and insulin resistance, concomitant with increased mRNA expression and protein levels. Pyrosequencing revealed the CpG-site within ATF-motifs was hypomethylated in four of these genes in liver of severely obese non-diabetic and type 2 diabetic patients, suggesting epigenetic regulation of transcription by altered ATF-DNA binding.

CONCLUSION

Severely obese non-diabetic and type 2 diabetic patients have distinct alterations in the hepatic methylome and transcriptome, with hypomethylation of several genes controlling glucose metabolism within the ATF-motif regulatory site. Obesity appears to shift the epigenetic program of the liver towards increased glycolysis and lipogenesis, which may exacerbate the development of insulin resistance.

Skeletal muscle AMP-activated protein kinase γ1(H151R) overexpression enhances whole body energy homeostasis and insulin sensitivity

AMP-activated protein kinase (AMPK) is a major sensor of energy homeostasis and stimulates ATP-generating processes such as lipid oxidation and glycolysis in peripheral tissues. The heterotrimeric enzyme consists of a catalytic α-subunit, a β-subunit that is important for enzyme activity, and a noncatalytic γ-subunit that binds AMP and activates the AMPK complex. We generated a skeletal muscle Cre-inducible transgenic mouse model expressing a mutant γ1-subunit (AMPKγ1(H151R)), resulting in chronic AMPK activation. The expression of the predominant AMPKγ3 isoform in skeletal muscle was reduced in extensor digitorum longus (EDL) muscle (81-83%) of AMPKγ1(H151R) transgenic mice, whereas the abundance and phosphorylation of the AMPK target acetyl-CoA carboxylase was increased in tibialis anterior muscle. Glycogen content was increased 10-fold in gastrocnemius muscle. Whole body carbohydrate oxidation was increased by 11%, and whereas glucose tolerance was unaffected, insulin sensitivity was increased in AMPKγ1(H151R) transgenic mice. Furthermore, perigonadal white adipose tissue mass and serum leptin were reduced in female AMPKγ1(H151R) transgenic mice by 38 and 51% respectively. Conversely, in male AMPKγ1(H151R) transgenic mice, food intake was increased (14%), but body weight and body composition were unaltered, presumably because of increased energy expenditure. In conclusion, transgenic activation of skeletal muscle AMPKγ1 in this model plays an important sex-specific role in skeletal muscle metabolism and whole body energy homeostasis.

The role of GluN2A and GluN2B NMDA receptor subunits in AgRP and POMC neurons on body weight and glucose homeostasis

OBJECTIVE

Hypothalamic agouti-related peptide (AgRP) and pro-opiomelanocortin (POMC) expressing neurons play critical roles in control of energy balance. Glutamatergic input via n-methyl-d-aspartate receptors (NMDARs) is pivotal for regulation of neuronal activity and is required in AgRP neurons for normal body weight homeostasis. NMDARs typically consist of the obligatory GluN1 subunit and different GluN2 subunits, the latter exerting crucial differential effects on channel activity and neuronal function. Currently, the role of specific GluN2 subunits in AgRP and POMC neurons on whole body energy and glucose balance is unknown.

METHODS

We used the cre-lox system to genetically delete GluN2A or GluN2B only from AgRP or POMC neurons in mice. Mice were then subjected to metabolic analyses and assessment of AgRP and POMC neuronal function through morphological studies.

RESULTS

We show that loss of GluN2B from AgRP neurons reduces body weight, fat mass, and food intake, whereas GluN2B in POMC neurons is not required for normal energy balance control. GluN2A subunits in either AgRP or POMC neurons are not required for regulation of body weight. Deletion of GluN2B reduces the number of AgRP neurons and decreases their dendritic length. In addition, loss of GluN2B in AgRP neurons of the morbidly obese and severely diabetic leptin-deficient Lep (ob/ob) mice does not affect body weight and food intake but, remarkably, leads to full correction of hyperglycemia. Lep (ob/ob) mice lacking GluN2B in AgRP neurons are also more sensitive to leptin's anti-obesity actions.

CONCLUSIONS

GluN2B-containing NMDA receptors in AgRP neurons play a critical role in central control of body weight homeostasis and blood glucose balance via mechanisms that likely involve regulation of AgRP neuronal survival and structure, and modulation of hypothalamic leptin action.