PGC-1α is required for exercise- and exercise training-induced UCP1 up-regulation in mouse white adipose tissue

Adaptive gene expression of alternative splicing variants of PGC-1α regulates whole-body energy metabolism

The transcriptional coactivator PGC-1α has been implicated in the regulation of multiple metabolic processes. However, the previously reported metabolic phenotypes of mice deficient in PGC-1α have been inconsistent. PGC-1α exists as multiple isoforms, including variants transcribed from an alternative first exon. We show here that alternative PGC-1α variants are the main entity that increases PGC-1α during exercise. These variants, unlike the canonical isoform of PGC-1α, are robustly upregulated in human skeletal muscle after exercise. Furthermore, the extent of this upregulation correlates with oxygen consumption. Mice lacking these variants manifest impaired energy expenditure during exercise, leading to the development of obesity and hyperinsulinemia. The alternative variants are also upregulated in brown adipose tissue in response to cold exposure, and mice lacking these variants are intolerant of a cold environment. Our findings thus indicate that an increase in PGC-1α expression, attributable mostly to upregulation of alternative variants, is pivotal for adaptive enhancement of energy expenditure and heat production and thereby essential for the regulation of whole-body energy metabolism.

Changes in the Expression of Inflammatory Genes Induced by Chronic Exercise in the Adipose Tissue: Differences by Sex

The impact of obesity on adipose tissue function is well acknowledged, but the role of physical exercise in regulating inflammatory markers and gene expression in obese individuals remains uncertain. This study aims to investigate the effects of chronic exercise on inflammatory gene expression in adipose tissue and to explore sex differences in response to exercise. The study involved 29 obese participants (13 men, 16 women) aged 38 to 54 years with a mean BMI of 36.05 ± 4.99 kg/m2. Participants underwent an 8-week concurrent training program comprising three weekly sessions of ~60 min each. The sessions included joint mobility exercises, cardiovascular activation, and cardiorespiratory resistance exercises at medium to low intensity. A fine-needle aspiration biopsy of abdominal subcutaneous adipose tissue was performed for gene expression analysis using quantitative polymerase chain reaction (qPCR). The study demonstrated that chronic exercise modulates the expression of pro-inflammatory genes in subcutaneous adipose tissue, particularly ADIPOR2 (p = 0.028), leptin (p = 0.041), and IFNg (p = 0.040) (downregulated). Interestingly, regardless of sex, the exercise programs had an independent effect on pro-inflammatory genes. Overall, this study provides insight into the role of chronic exercise in modulating adipose tissue gene expression in obese individuals. Further research involving both sexes is recommended to tailor exercise interventions for better outcomes.

Exercise attenuates high-fat diet-induced PVAT dysfunction through improved inflammatory response and BMP4-regulated adipose tissue browning

Background

Perivascular adipose tissue (PVAT) dysfunction impairs vascular homeostasis. Impaired inflammation and bone morphogenetic protein-4 (BMP4) signaling are involved in thoracic PVAT dysfunction by regulating adipokine secretion and adipocyte phenotype transformation. We investigated whether aerobic exercise training could ameliorate high-fat diet (HFD)-induced PVAT dysfunction via improved inflammatory response and BMP4-mediated signaling pathways.

Methods

Sprague-Dawley rats (n = 24) were divided into three groups, namely control, high-fat diet (HFD), and HFD plus exercise (HEx). After a 6-week intervention, PVAT functional efficiency and changes in inflammatory biomarkers (circulating concentrations in blood and mRNA expressions in thoracic PVAT) were assessed.

Results

Chronic HFD feeding caused obesity and dyslipidemia in rats. HFD decreased the relaxation response of PVAT-containing vascular rings and impaired PVAT-regulated vasodilatation. However, exercise training effectively reversed these diet-induced pathological changes to PVAT. This was accompanied by significantly (p < 0.05) restoring the morphological structure and the decreased lipid droplet size in PVAT. Furthermore, HFD-induced impaired inflammatory response (both in circulation and PVAT) was notably ameliorated by exercise training (p < 0.05). Specifically, exercise training substantially reversed HFD-induced WAT-like characteristics to BAT-like characteristics as evidenced by increased UCP1 and decreased FABP4 protein levels in PVAT against HFD. Exercise training promoted transcriptional activation of BMP4 and associated signaling molecules (p38/MAPK, ATF2, PGC1α, and Smad5) that are involved in browning of adipose tissue. In conjunction with gene expressions, exercise training increased BMP4 protein content and activated downstream cascades, represented by upregulated p38/MAPK and PGC1α proteins in PVAT.

Conclusion

Regular exercise training can reverse HFD-induced obesity, dyslipidemia, and thoracic PVAT dysfunction in rats. The browning of adipose tissue through exercise appears to be modulated through improved inflammatory response and/or BMP4-mediated signaling cascades in obese rats.

Effect of YC-1102 on the Improvement of Obesity in High-Fat Diet-Induced Obese Mice

Obesity is one of the major risk factors for metabolic diseases worldwide. This study examined the effects of YC-1102, an extract derived from the roots of Rosa multiflora, on 3T3-L1 preadipocytes and high-fat diet (HFD)-induced obese mice. In vivo experiments involved the oral administration of YC-1102 (100, 150, and 200 mg/kg body weight) daily to mice for eight weeks. YC-1102 was found to downregulate the expressions of PPARγ and C/EBPα during adipogenesis, inhibiting adipocyte differentiation and upregulating the expression of PGC-1α for energy metabolism to enhance mitochondrial biogenesis and fatty acid oxidation. It has been shown that daily administration of YC-1102 to mice receiving a HFD prevented an increase in body weight and the accumulation of body fat. YC-1102 administration also reduced TG, TC, and LDL cholesterol levels, as well as glucose and leptin levels, and increased adiponectin levels, thus effectively inhibiting the metabolism of lipids. YC-1102-treated mice showed significant reductions in the mRNA expression of PPARγ and C/EBPα. The levels of PGC-1α involved in energy metabolism increased significantly in the YC-1102-treated mice when compared to the HFD-treated mice. According to the findings of this study, YC-1102 has a dual mechanism that reduces transcription factors that promote the differentiation of adipocytes and increases transcription factors that promote energy consumption.

Adipose tissue browning and thermogenesis under physiologically energetic challenges: a remodelled thermogenic system

Metabolic diseases such as obesity and diabetes are often thought to be caused by reduced energy expenditure, which poses a serious threat to human health. Cold exposure, exercise and caloric restriction have been shown to promote adipose tissue browning and thermogenesis. These physiological interventions increase energy expenditure and thus have emerged as promising strategies for mitigating metabolic disorders. However, that increased adipose tissue browning and thermogenesis elevate thermogenic consumption is not a reasonable explanation when humans and animals confront energetic challenges imposed by these interventions. In this review, we collected numerous results on adipose tissue browning and whitening and evaluated this bi-directional conversion of adipocytes from the perspective of energy homeostasis. Here, we propose a new interpretation of the role of adipose tissue browning under energetic challenges: increased adipose tissue browning and thermogenesis under energy challenge is not to enhance energy expenditure, but to reestablish a more economical thermogenic pattern to maintain the core body temperature. This can be achieved by enhancing the contribution of non-shivering thermogenesis (adipose tissue browning and thermogenesis) and lowering shivering thermogenesis and high intensity shivering. Consequently, the proportion of heat production in fat increases and that in skeletal muscle decreases, enabling skeletal muscle to devote more energy reserves to overcoming environmental stress.

Impact of physical fitness and exercise training on subcutaneous adipose tissue beiging markers in humans with and without diabetes and a high-fat diet-fed mouse model

AIMS

Exercise training induces white adipose tissue (WAT) beiging and improves glucose homeostasis and mitochondrial function in rodents. This could be relevant for type 2 diabetes in humans, but the effect of physical fitness on beiging of subcutaneous WAT (scWAT) remains unclear. This translational study investigates if beiging of scWAT associates with physical fitness in healthy humans and recent-onset type 2 diabetes and if a voluntary running wheel intervention is sufficient to induce beiging in mice.

MATERIALS AND METHODS

Gene expression levels of established beiging markers were measured in scWAT biopsies of humans with (n = 28) or without type 2 diabetes (n = 28), stratified by spiroergometry into low (L-FIT; n = 14 each) and high physical fitness (H-FIT; n = 14 each). High-fat diet-fed FVB/N mice underwent voluntary wheel running, treadmill training or no training (n = 8 each group). Following the training intervention, mitochondrial respiration and content of scWAT were assessed by high-resolution respirometry and citrate synthase activity, respectively.

RESULTS

Secreted CD137 antigen (Tnfrsf9/Cd137) expression was three-fold higher in glucose-tolerant H-FIT than in L-FIT, but not different between H-FIT and L-FIT with type 2 diabetes. In mice, both training modalities increased Cd137 expression and enhanced mitochondrial content without changing respiration in scWAT. Treadmill but not voluntary wheel running led to improved whole-body insulin sensitivity.

CONCLUSIONS

Higher physical fitness and different exercise interventions associated with higher gene expression levels of the beiging marker CD137 in healthy humans and mice on a high-fat diet. Humans with recent-onset type 2 diabetes show an impaired adipose tissue-specific response to physical activity.

Depot-specific adaption of adipose tissue for different exercise approaches in high-fat diet/streptozocin-induced diabetic mice

Background: Adipose tissue pathology plays a crucial role in the pathogenesis of type 2 diabetes mellitus. Understanding the impact of exercise training on adipose tissue adaptation is of paramount importance in enhancing metabolic health. In this study, we aimed to investigate the effects of various exercise modalities on three distinct adipose tissue depots, namely, interscapular brown adipose tissue (iBAT), subcutaneous white adipose tissue (sWAT), and epididymal white adipose tissue (eWAT), in a murine model of diabetes. Methods: Male C57BL/6J mice received a 12-week high-fat diet and a single injection of streptozotocin, followed by an 8-week exercise intervention. The exercise intervention included swimming, resistance training, aerobic exercise, and high-intensity interval training (HIIT). Results: We found that exercise training reduced body weight and body fat percentage, diminished adipocyte size and increased the expression of mitochondria-related genes (PGC1, COX4, and COX8B) in three adipose tissue depots. The effects of exercise on inflammatory status include a reduction in crown-like structures and the expression of inflammatory factors, mainly in eWAT. Besides, exercise only induces the browning of sWAT, which may be related to the expression of the sympathetic marker tyrosine hydroxylase. Among the four forms of exercise, HIIT was the most effective in reducing body fat percentage, increasing muscle mass and reducing eWAT adipocyte size. The expression of oxidative phosphorylation and thermogenesis-related genes in sWAT and eWAT was highest in the HIIT group. Conclusion: When targeting adipose tissue to improve diabetes, HIIT may offer superior benefits and thus represents a more advantageous choice.

Chronic voluntary wheel running exercise ameliorates metabolic dysfunction via PGC-1α expression independently of FNDC5/irisin pathway in high fat diet-induced obese mice

Exercise is an effective intervention to ameliorate metabolic diseases including obesity and insulin resistance, but the mechanisms involved in the metabolic amelioration have not yet been fully elucidated. This study aimed to determine whether AMPK-SIRT1-PGC-1α-FNDC5/Irisin-UCP1 expression is activated and whether metabolic dysfunction is ameliorated by chronic voluntary wheel running (VWR) in high-fat diet (HFD) induced obese mice. C57BL6J mice were randomly assigned into three groups at the age of 7 weeks for 10 weeks: normal chow diet (CON) group, HFD group, and HFD + VWR group. Chronic VWR ameliorates metabolic parameters and leads to increases in the expression of PGC-1α in the gastrocnemius muscle in HFD-induced obese mice. In contrast, the expression of AMPKα, SIRT1, and FNDC5, or circulating irisin levels did not lead to alteration. Improvement of metabolic health was partly mediated via PGC-1α expression by chronic VWR, but not FNDC5/Irisin pathway in HFD-induced obese mice.

Cancer cell-derived exosomal miR-425-3p induces white adipocyte atrophy

White adipose tissue wasting plays a critical role in the development and progression of cancer cachexia. However, the mechanism behind the loss of adipose tissue remains ill-defined. In this study, we found that cancer cell-derived exosomes highly expressed miR-425-3p. Administration of cancer cell-derived exosomes significantly inhibited proliferation and differentiation of human preadipocytes-viscereal (HPA-v) cells. In mature adipocytes, cancer cell-derived exosomes activated cAMP/PKA signalling and lipophagy, leading to adipocyte lipolysis and browning of white adipocytes. These exosomes-induced alterations were almost abolished by endocytosis inhibitor cytochalasin D (CytoD) and antagomiR-425-3p, or reproduced by miR-425-3p mimics. In addition, bioinformatics analysis and luciferase reporter assay revealed that miR-425-3p directly targeted proliferation-related genes such as GATA2, IGFBP4, MMP15, differentiation-related gene CEBPA, and phosphodiesterase 4B gene (PDE4B). Depletion of PDE4B enhanced cAMP/PKA signalling and lipophagy, but had no effects on HPA-v proliferation and differentiation. Taken together, these results suggested that cancer cell-derived exosomal miR-425-3p inhibited preadipocyte proliferation and differentiation, increased adipocyte lipolysis, and promoted browning of white adipocytes, all of which might contribute to adipocyte atrophy and ultimately the loss of adipose tissue in cancer cachexia.

Abbreviations: ADPN: adiponectin; aP2: adipocyte protein 2 or fatty acid binding protein 4 (FABP4); BCA: bicinchoninic acid assay; BFA: bafilomycin A1; BMI: body mass index; C/EBP: CCAAT/enhancer binding protein; CEBPA: CCAAT/enhancer-binding protein-alpha; C-Exo: cancer cell-derived exosomes; CNTL: control; CREB: cAMP-response element binding protein; CytoD: cytochalasin D; ECL: chemiluminescence; GATA2: GATA Binding Protein 2; HFD: high fat diet; HSL: hormone-sensitive lipase; IGFBP4: insulin like growth factor binding protein 4; IRS-1: insulin receptor substrate-1; ISO: isoproterenol hydrochloride; KD: knockdown; KO: knock out; LC3: microtubule-associated protein 1A/1B-light chain 3; LMF: lipid mobilizing factor; LPL: lipoprotein lipase; MMP15: matrix metallopeptidase 15; Mir-Inh-C-Exo: cancer cell-derived exosomes with miR-425-3p inhibition; mTOR: mammalian target of rapamycin; Mut: mutant; N-Exo: normal cell-derived exosomes; NSCLC: non-small cell lung cancer; PBS, phosphate buffered saline; PGC-1: peroxisome proliferator-activated receptor-gamma coactivator-1; PDEs: phosphodiesterases; PKI: PKA inhibitor; PKA: cAMP-dependent protein kinase; PLIN1: Perilipin 1; PTHRP: parathyroid hormone-related protein; PVDF: polyvinylidene difluoride; shRNA: short hairpin RNA; UCP1: uncoupling protein 1; WT: wild type.

Exercise-Induced Adipose Tissue Thermogenesis and Browning: How to Explain the Conflicting Findings?

Brown adipose tissue (BAT) has been widely studied in targeting against metabolic diseases such as obesity, type 2 diabetes and insulin resistance due to its role in nutrient metabolism and energy regulation. Whether exercise promotes adipose tissue thermogenesis and browning remains controversial. The results from human and rodent studies contradict each other. In our opinion, fat thermogenesis or browning promoted by exercise should not be a biomarker of health benefits, but an adaptation under the stress between body temperature regulation and energy supply and expenditure of multiple organs. In this review, we discuss some factors that may contribute to conflicting experimental results, such as different thermoneutral zones, gender, training experience and the heterogeneity of fat depots. In addition, we explain that a redox state in cells potentially causes thermogenesis heterogeneity and different oxidation states of UCP1, which has led to the discrepancies noted in previous studies. We describe a network by which exercise orchestrates the browning and thermogenesis of adipose tissue with total energy expenditure through multiple organs (muscle, brain, liver and adipose tissue) and multiple pathways (nerve, endocrine and metabolic products), providing a possible interpretation for the conflicting findings.

An exercise-inducible metabolite that suppresses feeding and obesity

Exercise confers protection against obesity, type 2 diabetes and other cardiometabolic diseases1-5. However, the molecular and cellular mechanisms that mediate the metabolic benefits of physical activity remain unclear6. Here we show that exercise stimulates the production of N-lactoyl-phenylalanine (Lac-Phe), a blood-borne signalling metabolite that suppresses feeding and obesity. The biosynthesis of Lac-Phe from lactate and phenylalanine occurs in CNDP2+ cells, including macrophages, monocytes and other immune and epithelial cells localized to diverse organs. In diet-induced obese mice, pharmacological-mediated increases in Lac-Phe reduces food intake without affecting movement or energy expenditure. Chronic administration of Lac-Phe decreases adiposity and body weight and improves glucose homeostasis. Conversely, genetic ablation of Lac-Phe biosynthesis in mice increases food intake and obesity following exercise training. Last, large activity-inducible increases in circulating Lac-Phe are also observed in humans and racehorses, establishing this metabolite as a molecular effector associated with physical activity across multiple activity modalities and mammalian species. These data define a conserved exercise-inducible metabolite that controls food intake and influences systemic energy balance.

Many Ways to Rome: Exercise, Cold Exposure and Diet-Do They All Affect BAT Activation and WAT Browning in the Same Manner?

The discovery of functional brown adipose tissue (BAT) in adult humans and the possibility to recruit beige cells with high thermogenic potential within white adipose tissue (WAT) depots opened the field for new strategies to combat obesity and its associated comorbidities. Exercise training as well as cold exposure and dietary components are associated with the enhanced accumulation of metabolically-active beige adipocytes and BAT activation. Both activated beige and brown adipocytes increase their metabolic rate by utilizing lipids to generate heat via non-shivering thermogenesis, which is dependent on uncoupling protein 1 (UCP1) in the inner mitochondrial membrane. Non-shivering thermogenesis elevates energy expenditure and promotes a negative energy balance, which may ameliorate metabolic complications of obesity and Type 2 Diabetes Mellitus (T2DM) such as insulin resistance (IR) in skeletal muscle and adipose tissue. Despite the recent advances in pharmacological approaches to reduce obesity and IR by inducing non-shivering thermogenesis in BAT and WAT, the administered pharmacological compounds are often associated with unwanted side effects. Therefore, lifestyle interventions such as exercise, cold exposure, and/or specified dietary regimens present promising anchor points for future disease prevention and treatment of obesity and T2DM. The exact mechanisms where exercise, cold exposure, dietary interventions, and pharmacological treatments converge or rather diverge in their specific impact on BAT activation or WAT browning are difficult to determine. In the past, many reviews have demonstrated the mechanistic principles of exercise- and/or cold-induced BAT activation and WAT browning. In this review, we aim to summarize not only the current state of knowledge on the various mechanistic principles of diverse external stimuli on BAT activation and WAT browning, but also present their translational potential in future clinical applications.

AMP-activated protein kinase activation in skeletal muscle modulates exercise-induced uncoupled protein 1 expression in brown adipocyte in mouse model

Abstract

Aerobic exercise is an effective intervention in preventing obesity and is also an important factor associated with thermogenesis. There is an increasing interest in the factors and mechanisms induced by aerobic exercise that can influence the metabolism and thermogenic activity in an individual. Recent studies suggest that exercise induced circulating factors (known as ‘exerkines’), which are able to modulate activation of brown adipose tissue (BAT) and browning of white adipose tissue. However, the underlying molecular mechanisms associated with the effect of exercise‐induced peripheral factors on BAT activation remain poorly understood. Furthermore, the role of exercise training in BAT activation is still debatable. Hence, the purpose of our study is to assess whether exercise training affects the expression of uncoupled protein 1 (UCP1) in brown adipocytes via release of different blood factors. Four weeks of exercise training significantly decreased the body weight gain and fat mass gain. Furthermore, trained mice exhibit higher levels of energy expenditure and UCP1 expression than untrained mice. Surprisingly, treatment with serum from exercise‐trained mice increased the expression of UCP1 in differentiated brown adipocytes. To gain a better understanding of these mechanisms, we analysed the conditioned media obtained after treating the C2C12 myotubes with an AMP‐activated protein kinase (AMPK) activator (AICAR; 5‐aminoimidazole‐4‐carboxamide ribonucleotide), which leads to an increased expression of UCP1 when added to brown adipocytes. Our observations suggest the possibility of aerobic exercise‐induced BAT activation via activation of AMPK in skeletal muscles.

Key points

Exercise promotes thermogenesis by activating uncoupling protein 1 (UCP1), which leads to a decrease in the body weight gain and body fat content. However, little is known about the role of exerkines in modulating UCP1 expression and subsequent brown adipose tissue (BAT) activation.

Four weeks of voluntary wheel‐running exercise reduces body weight and fat content.

Exercise induces the increase in AMP‐activated protein kinase (AMPK) and slow‐type muscle fibre marker genes in skeletal muscles and promotes UCP1 expression in white and brown adipose tissues.

Incubation of brown adipocytes with serum isolated from exercise‐trained mice significantly increased their UCP1 gene and protein levels; moreover, conditioned media of AMPK‐activator‐treated C2C12 myotubes induces increased UCP1 expression in brown adipocytes.

These results show that aerobic exercise‐induced skeletal muscle AMPK has a significant effect on UCP1 expression in BAT.

Exercise induces favorable metabolic changes in white adipose tissue preventing high-fat diet obesity

Diet and/or exercise are cost effective interventions to treat obesity. However, it is unclear if the type of exercise undertaken can prevent the onset of obesity and if it can act through different effects on fat depots. In this study we did not allow obesity to develop so we commenced the high-fat diet (HFD) and exercise programs concurrently and investigated the effect of endurance exercise (END) and high-intensity interval training (HIIT) on changes in cellular adipogenesis, thermogenesis, fibrosis, and inflammatory markers in three different fat depots, on a HFD and a chow diet. This was to assess the effectiveness of exercise to prevent the onset of obesity-induced changes. Mice fed with chow or HFD (45% kcal fat) were trained and performed either END or HIIT for 10 weeks (3 x 40 min sessions/week). In HFD mice, both exercise programs significantly prevented the increase in body weight (END: 17%, HIIT: 20%), total body fat mass (END: 46%, HIIT: 50%), increased lean mass as a proportion of body weight (Lean mass/BW) by 14%, and improved insulin sensitivity by 22%. Further evidence of the preventative effect of exercise was seen significantly decreased markers for adipogenesis, inflammation, and extracellular matrix accumulation in both subcutaneous adipose tissue (SAT) and epididymal adipose tissue (EPI). In chow, no such marked effects were seen with both the exercise programs on all the three fat depots. This study establishes the beneficial effect of both HIIT and END exercise in preventing metabolic deterioration, collagen deposition, and inflammatory responses in fat depots, resulting in an improved whole body insulin resistance in HFD mice.

Eight Weeks of High-Intensity Interval Static Strength Training Improves Skeletal Muscle Atrophy and Motor Function in Aged Rats via the PGC-1α/FNDC5/UCP1 Pathway

Background

Sarcopenia is a syndrome characterized by the loss of skeletal muscle mass and strength. Most studies have focused on dynamic resistance exercises for preventing muscular decline and maintaining the muscle strength of older individuals. However, this training mode is impractical for older people with osteoarthritis and a limited range of motion. The static strength training mode is more suitable for older people. Therefore, a determination of the effect and mechanism of static strength training on sarcopenia is critical.

Methods

In this study, we developed a training device designed to collect training data and evaluate the effects of static training on the upper limbs of rats. The expression of PGC-1α was locally blocked by injecting a siRNA at the midpoint of the biceps to determine whether PGC-1α signal transduction participates in the effects of high-intensity interval static training on muscle strength. Then, the rat’s motor capacity was measured after static strength training. Immunohistochemistry and Western blotting were applied to determine PGC-1α/FNDC5/UCP1 expression levels in the muscle and adipose tissue. The serum irisin level was also detected using an enzyme-linked immunosorbent assay (ELISA).

Results

Increased levels of serum irisin and local expression of FNDC5, PGC-1α, and UCP1 were observed in the biceps brachii and surrounding fatty tissue after static strength training. Static strength training showed an advantage in reducing body weight and white fat accumulation while increasing the muscle fiber volume, which resulted in a longer training time and shorter rest time.

Conclusion

Overall, these results indicated that high-intensity interval static training prevents skeletal muscle atrophy and improves the motor function of aged rats through the PGC-1α/FNDC5/UCP1 signaling pathway.

Biochemical adaptations in white adipose tissue following aerobic exercise: from mitochondrial biogenesis to browning

Our understanding of white adipose tissue (WAT) biochemistry has evolved over the last few decades and it is now clear that WAT is not simply a site of energy storage, but rather a pliable endocrine organ demonstrating dynamic responsiveness to the effects of aerobic exercise. Similar to its established effects in skeletal muscle, aerobic exercise induces many biochemical adaptations in WAT including mitochondrial biogenesis and browning. While past research has focused on the regulation of these biochemical processes, there has been renewed interest as of late given the potential of harnessing WAT mitochondrial biogenesis and browning to treat obesity and type II diabetes. Unfortunately, despite increasing evidence that innumerable factors, both exercise induced and pharmacological, can elicit these biochemical adaptations in WAT, the underlying mechanisms remain poorly defined. Here, we begin with a historical account of our understanding of WAT exercise biochemistry before presenting detailed evidence in favour of an up-to-date model by which aerobic exercise induces mitochondrial biogenesis and browning in WAT. Specifically, we discuss how aerobic exercise induces increases in WAT lipolysis and re-esterification and how this could be a trigger that activates the cellular energy sensor 5' AMP-activated protein kinase to mediate the induction of mitochondrial biogenesis and browning via the transcriptional co-activator peroxisome proliferator-activated receptor gamma co-activator-1 alpha. While this review primarily focuses on mechanistic results from rodent studies special attention is given to the translation of these results, or lack thereof, to human physiology.

Human white-fat thermogenesis: Experimental and meta-analytic findings

White adipose tissue (WAT) thermogenic activity may play a role in whole-body energy balance and two of its main regulators are thought to be environmental temperature (T_env) and exercise. Low T_env may increase uncoupling protein one (UCP1; the main biomarker of thermogenic activity) in WAT to regulate body temperature. On the other hand, exercise may stimulate UCP1 in WAT, which is thought to alter body weight regulation. However, our understanding of the roles (if any) of T_env and exercise in WAT thermogenic activity remains incomplete. Our aim was to examine the impacts of low T_env and exercise on WAT thermogenic activity, which may alter energy homeostasis and body weight regulation. We conducted a series of four experimental studies, supported by two systematic reviews and meta-analyses. We found increased UCP1 mRNA (p = 0.03; but not protein level) in human WAT biopsy samples collected during the cold part of the year, a finding supported by a systematic review and meta-analysis (PROSPERO review protocol: CRD42019120116). Additional clinical trials (NCT04037371; NCT04037410) using Positron Emission Tomography/Computed Tomography (PET/CT) revealed no impact of low T_env on human WAT thermogenic activity (p > 0.05). Furthermore, we found no effects of exercise on UCP1 mRNA or protein levels (p > 0.05) in WAT biopsy samples from a human randomized controlled trial (Clinical trial: NCT04039685), a finding supported by systematic review and meta-analytic data (PROSPERO review protocol: CRD42019120213). Taken together, the present experimental and meta-analytic findings of UCP1 and SUV_max, demonstrate that cold and exercise may play insignificant roles in human WAT thermogenic activity. Abbreviations: WAT:White adipose tissue; T_env: Environmental temperature; UCP1: Uncoupling protein one; BAT: Brown adipose tissue; BMI:Body mass index; mRNA: Messenger ribonucleic acid; RCT: Randomized controlled trial; WHR: Waist-to-hip ratio; PRISMA: Preferred Reporting Items for Systematic Reviews and Meta-analyses; PET/CT: Positron Emission Tomography and Computed Tomography; REE: Resting energy expenditure; ¹⁸F-FDG: F¹⁸ fludeoxyglucose; VO₂peak:Peak oxygen consumption; 1RM: One repetition maximum; SUV_max: Maximum standardized uptake value; Std: Standardized mean difference.

The Impact of Moderate-Intensity Continuous or High-Intensity Interval Training on Adipogenesis and Browning of Subcutaneous Adipose Tissue in Obese Male Rats

This study compares the effect of two types of exercise training, i.e., moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) on the browning of subcutaneous white adipose tissue (scWAT) in obese male rats. Effects on fat composition, metabolites, and molecular markers of differentiation and energy expenditure were examined. Forty male Wistar rats were assigned to lean (n = 8) or obese (n = 32) groups and fed either a standard chow or high-fat obesogenic diet for 10 weeks. Eight lean and obese rats were then blood and tissue sampled, and the remaining obese animals were randomly allocated into sedentary, MICT, or HIIT (running on a treadmill 5 days/week) groups that were maintained for 12 weeks. Obesity increased plasma glucose and insulin and decreased irisin and FGF-21. In scWAT, this was accompanied with raised protein abundance of markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and PPAR-γ, whereas brown fat-related genes, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, were reduced as was UCP1 and markers of fatty acid transport, i.e., CD36 and CPT1. Exercise training increased protein expression of brown fat-related markers, i.e., PRDM-16, AMPK/SIRT1/PGC-1α, and UCP1, together with gene expression of fatty acid transport, i.e., CD36 and CPT1, but decreased markers of adipocyte differentiation, i.e., C/EBP-α, C/EBP-β, and plasma glucose. The majority of these adaptations were greater with HIIT compared to MICT. Our findings indicate that prolonged exercise training promotes the browning of white adipocytes, possibly through suppression of adipogenesis together with white to beige trans-differentiation and is dependent on the intensity of exercise.

Indirubin, a small molecular deriving from connectivity map (CMAP) screening, ameliorates obesity-induced metabolic dysfunction by enhancing brown adipose thermogenesis and white adipose browning

Background

Obesity occurs when the body’s energy intake is constantly greater than its energy consumption and the pharmacological enhancing the activity of brown adipose tissue (BAT) and (or) browning of white adipose tissue (WAT) has been considered promising strategies to treat obesity.

Methods

In this study, we took a multi-pronged approach to screen UCP1 activators, including in silico predictions, in vitro assays, as well as in vivo experiments.

Results

Base on Connectivity MAP (CMAP) screening, we obtained multiple drugs that possess a remarkably correlating gene expression pattern to that of enhancing activity in BAT and (or) sWAT signature. Particularly, we focused on a previously unreported drug-indirubin, a compound obtained from the Indigo plant, which is now mainly used for the treatment of chronic myelogenous leukemia (CML). In the current study, our results shown that indirubin could enhance the BAT activity, as evidenced by up-regulated Ucp1 expression and enhanced mitochondrial respiratory function in vitro cellular model. Furthermore, indirubin treatment restrained high-fat diet (HFD)-induced body weight gain, improved glucose homeostasis and ameliorated hepatic steatosis which were associated with the increase of energy expenditure in the mice model. Moreover, we revealed that indirubin treatment increased BAT activity by promoting thermogenesis and mitochondrial biogenesis in BAT and induced browning of subcutaneous inguinal white adipose tissue (sWAT) of mice under HFD. Besides, our results indicated that indirubin induced UCP1 expression in brown adipocytes, at least in part, via activation of PKA and p38MAPK signaling pathways.

Conclusions

Our results clearly show that as an effective BAT (as well as beige cells) activator, indirubin may have a protective effect on the prevention and treatment of obesity and its complications.

Jiang Gui Fang activated interscapular brown adipose tissue and induced epididymal white adipose tissue browning through the PPARγ/SIRT1-PGC1α pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Gui Zhi Tang, a well-known Chinese herbal formula recorded in the Eastern Han Dynasty, has been widely used to treat exogenous cold for thousands of years. Recent studies have shown that Gui Zhi Tang has the effect of regulating the body temperature. Because of its effect on heat production, protecting vital organs of the body and avoiding damage from the cold environment, Jiang Gui Fang (JG) was obtained from the Department of Traditional Chinese Medicine at the General Hospital of Northern Theatre Command where it has been used clinically for many years and has exhibited favourable efficacy. Based on research on Gui Zhi Tang, the principles of traditional Chinese medicine and survey of a large number of studies, this empirical formula was developed. The composition of JG included Dried ginger, Cassia twig, and Liquorice in Gui Zhi Tang, which play a major role in the treatment of exogenous cold, and combined these components with other Chinese medicines, such as Pueraria, Spatholobus, Acanthopanacis cortex, Evodiae fructus, and Codonopsis pilosula.

AIM OF THE STUDY

To promote the core body temperature and prevent invasion of the major organs from the cold environment, we studied the effect of JG on the core body temperature of mice and then explored its regulation of interscapular brown adipose tissue (iBAT) and epididymal white adipose tissue (eWAT) and the possible mechanism. Finally, we determined the phytochemical composition of JG that plays a role in heat production.

MATERIALS AND METHODS

In vivo study, we performed a 4-week treatment of JG in acute cold environment at -20 °C and chronic cold exposure at 4 °C. The core temperature, adipose tissue weight, serum parameters, and morphological observation of adipocytes, liver and kidney were measured. Then we investigated the expression levels of adipogenic factors, thermogenic factors and lipoprotein. In vitro, we determined the lipid droplet content, ATP content, and the maximum oxygen consumption of mitochondria.

RESULTS

JG treatment promoted core temperature, inhibited eWAT weight, protected liver, and reduced glucose and lipids in Kunming (KM) mice. JG also increased the expression of BAT-associated thermogenic factors, including uncoupling protein 1 (UCP1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC1α). The levels of the lipogenic factor peroxisome proliferate-activator receptor gamma (PPARγ) and the lipolytic protein hormone-sensitive triglyceride lipase (HSL) in eWAT were elevated. The results of H&E and immunohistochemistry showed that JG significantly reduced the size of iBAT and eWAT and increased the content of UCP1. In vitro, JG reduced the content of lipid droplets and ATP in brown fat cells. The maximum oxygen consumption capacity of mitochondria and the expression levels of UCP1, PGC1α and silent mating type information regulation 2 homologue 1 (SIRT1) were enhanced after JG treatment.

CONCLUSIONS

In vivo and in vitro studies, the results demonstrated that JG obviously increased the core temperature of mice by activating iBAT and inducing eWAT browning, which proved the mechanism is closely related to the PPARγ/SIRT1- PGC1α pathway. In this paper, we will provide a reference for further study of iBAT activation and eWAT browning.

An anti-inflammatory phenotype in visceral adipose tissue of old lean mice, augmented by exercise

Visceral adipose tissue is an immunogenic tissue, which turns detrimental during obesity by activation of proinflammatory macrophages. During aging, chronic inflammation increases proportional to visceral adipose tissue (VAT) mass and associates with escalating morbidity and mortality. Here, we utilize a mouse model to investigate the inflammatory status of visceral adipose tissue in lean aging mice and assess the effects of exercise training interventions. We randomized adult (11 months; n = 21) and old (23 months; n = 27) mice to resistance training (RT) or endurance training (ET), or to a sedentary control group (S). Strikingly, we observed an anti-inflammatory phenotype in the old mice, consisting of higher accumulation of M2 macrophages and IL-10 expression, compared to the adult mice. In concordance, old mice also had less VAT mass and smaller adipocytes compared to adult mice. In both age groups, exercise training enhanced the anti-inflammatory phenotype and increased PGC1-α mRNA expression. Intriguingly, the brown adipose tissue marker UCP1 was modestly higher in old mice, while remained unchanged by the intervention. In conclusion, in the absence of obesity, visceral adipose tissue possesses a pronounced anti-inflammatory phenotype during aging which is further enhanced by exercise.

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.

Ccr7 null mice are protected against diet-induced obesity via Ucp1 upregulation and enhanced energy expenditure

Background

The chemokine receptor CCR7, expressed on various immune cells, is associated with cell migration and lympho-node homing. Mice lacking Ccr7 are protected from diet-induced obesity and subsequent insulin resistance. We evaluated the mechanism underlying these protective effects from the standpoint of energy expenditure.

Methods

Wild-type and Ccr7 null mice were fed a high-fat diet, and the regulation of energy metabolism and energy metabolism-related molecules, e.g., Ucp1, Cidea, and Pgc1α, were evaluated.

Results

Food intake did not differ between groups. O₂ consumption and CO₂ production were higher in Ccr7 null mice than in wild-type mice, despite a similar respiratory quotient and glucose and lipid utilization, suggesting that energy expenditure increased in Ccr7 null mice via enhanced metabolism. In white adipose tissues of Ccr7 null mice, Prdm16, Cd137, Tmem26, Th, and Tbx1 expression increased. Similarly, in brown adipose tissues of Ccr7 null mice, Dio2, Pgc1α, Cidea, Sirt1, and Adiponectin expression increased. In both white and brown adipose tissues, Ucp1 gene and protein expression levels were higher in null mice than in wild-type mice.

Conclusions

In Ccr7 null mice, browning of white adipocytes as well as the activation of brown adipocytes cause enhanced energy metabolism, resulting in protection against diet-induced obesity.

Electronic supplementary material

The online version of this article (10.1186/s12986-019-0372-5) contains supplementary material, which is available to authorized users.

Constant-Moderate and High-Intensity Interval Training Have Differential Benefits on Insulin Sensitive Tissues in High-Fat Fed Mice

In a mouse model of diet-induced obesity, this study determined if two exercise prescriptions with equivalent time and distance covered, [constant-moderate endurance (END) and high intensity interval training (HIIT)], exert differential metabolic benefits on insulin sensitive tissues. Male 10 week old C57BL/6 mice were fed a high fat diet (HFD; 45% kcal fat) ad libitum for 10 weeks and for a further 10 weeks they underwent END or HIIT training (3 × 40 min sessions/wk). Untrained HFD and chow-fed mice acted as controls. At 30 weeks of age, mice were sacrificed and quadriceps muscle, subcutaneous adipose tissue (SAT) and liver were excised. Neither END nor HIIT altered body weight or composition in HFD mice. In quadriceps, HFD decreased high-molecular weight adiponectin protein, which was normalized by END and HIIT. In contrast, HIIT but not END reversed the HFD-driven decrease in the adiponectin receptor 1 (AdipoR1). In SAT, both programs tended to decrease collagen VI protein (p = 0.07–0.08) in HFD, whereas only HIIT induced an increase in the mRNA (3-fold vs. HFD untrained) and protein (2-fold vs. HFD untrained) of UCP1. In liver, only END reversed collagen I accumulation seen in HFD untrained mice. Our results suggest that HIIT may promote better systemic metabolic changes, compared to END, which may be the result of the normalization of muscle AdipoR1 and increased UCP1 seen in SAT. However, END was more effective in normalizing liver changes, suggesting differential metabolic effects of END and HIIT in different tissues during obesity.

Voluntary wheel running in the late dark phase ameliorates diet-induced obesity in mice without altering insulin action

Metabolic dysfunction and Type 2 diabetes are associated with perturbed circadian rhythms. However, exercise appears to ameliorate circadian disturbances, as it can phase-shift or reset the internal clock system. Evidence is emerging that exercise at a distinct time of day can correct misalignments of the circadian clock and influence energy metabolism. This suggests that timing of exercise training can be important for the prevention and management of metabolic dysfunction. In this study, obese, high-fat diet-fed mice were subjected to voluntary wheel running (VWR) at two different periods of the day to determine the effects of time-of-day-restricted VWR on basal and insulin-stimulated glucose disposal. VWR in the late dark phase reduced body weight gain compared with VWR in the beginning of the dark phase. Conversely, time-of-day-restricted VWR did not influence insulin action and glucose disposal, since skeletal muscle and adipose tissue glucose uptake and insulin signaling remained unaffected. Protein abundance of the core clock proteins, brain-muscle arnt-like 1 (BMAL1), and circadian locomotor output control kaput (CLOCK), were increased in skeletal muscle after VWR, independent of whether mice had access to running wheels in the early or late dark phase. Collectively, we provide evidence that VWR in the late dark phase ameliorates diet-induced obesity without altering insulin action or glucose homeostasis.

NEW & NOTEWORTHY Exercise appears to ameliorate circadian disturbances as it can entrain the internal clock system. We provide evidence that voluntary wheel running increases core clock protein abundance and influences diet-induced obesity in mice in a time-of-day-dependent manner. However, the effect of time-of-day-restricted voluntary wheel running on body weight gain is not associated with enhanced basal- and insulin-stimulated glucose disposal, suggesting that time-of-day-restricted voluntary wheel running affects energy homeostasis rather than glucose homeostasis.

Comparative studies on the effects of high-fat diet, endurance training and obesity on Ucp1 expression in male C57BL/6 mice

BACKGROUND

Obesity triggers a variety of severe conditions, therefore deteriorates metabolism rate of adipose tissues and muscles. Uncoupling proteins which are highly stimulated by fatty acids are potential targets for anti-obesity agents through breaking the electron gradient in the mitochondrial matrix and creating imbalances in the electron transport chain, thereby increasing the amount of substrate used to produce energy. Therefore, the aim of present study is assessment of exercise and high fat diet on expression level of Ucp1 subcutaneous white and brown adipose tissues (scWAT & BAT) respectively.

METHODS

To perform experiments, 48 male C57BL/6 mice were divided to two major groups and fed with high fat diet (HFD) or low fat diet (LFD) during a period of 12 weeks. After the first intervention, each groups was divided into four groups randomly as (HF-EX), (HF-SED), (LF-EX), (LF-SED) [EX: exercise; SED: sedentary] in form of treadmill running for 45 min/day, 5 days/week during 8 weeks. One day after the last practice session, mice were sacrificed and Ucp1 expression was assessed on scWAT & BAT.

RESULTS

Data indicated a down-regulation in scWAT Ucp1 in obese mice similar to what observed for the expression of Pgc1α. Both, BAT Ucp1 and Pgc1α mRNA decreased significantly in response to obesity and physical activity. Moreover, exercise caused significant decrease in scWAT mitochondrial proteins contradictory to BAT.

CONCLUSION

Taken together, exercise exerted controversial effects compared with HFD and obesity on expression of Ucp1 and Pgc1α in scWAT dissimilar to BAT tissues, concluding that obesity may cause a resistance to exercise in terms of metabolic demands for scWAT tissue.

PGC-1α as a Biomarker of Physical Activity-Protective Effect on Colorectal Cancer

Colorectal cancer is a significant public health concern. As a multistage and multifactorial disease, environmental and genetic factors interact at each stage of the process, and an individual's lifestyle also plays a relevant role. We set out to review the scientific evidence to study the need to investigate the role of the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) gene as a biomarker of the physical activity's (PA) effect on colorectal cancer. PA is a protective factor against colorectal cancer and usually increases the expression of PGC-1α This gene has pleiotropic roles and is the main regulator of mitochondrial functions. The development of colorectal cancer has been associated with mitochondrial dysfunction; in addition, alterations in this organelle are associated with colorectal cancer risk factors, such as obesity, decreased muscle mass, and the aging process. These are affected by PA acting, among other aspects, on insulin sensitivity and oxygen reactive species/redox balance. Therefore, this gene demands special attention in the understanding of its operation in the consensual protective effect of PA in colorectal cancer. A significant amount of indirect evidence points to PGC-1α as a potential biomarker in the PA-protective effect on colorectal cancer. The article focuses on the possible involvement of PGC-1α in the protective role that physical activity has on colorectal cancer. This is an important topic both in relation to advances in prevention of the development of this widespread disease and in its therapeutic treatment. We hope to generate an initial hypothesis for future studies associated with physical activity-related mechanisms that may be involved in the development or prevention of colorectal cancer. PGC-1α is highlighted because it is the main regulator of mitochondrial functions. This organelle, on one hand, is positively stimulated by physical activity; on the other hand, its dysfunction or reduction increases the probability of developing colorectal cancer. Therefore, we consider the compilation of existing information about the possible ways to understand the mechanisms of this gene to be highly relevant. This study is based on evidence of PGC-1α and physical activity, on PGC-1α and colorectal cancer, on colorectal cancer and physical activity/inactivity, and the absence of studies that have sought to relate all of these variables. Cancer Prev Res; 11(9); 523-34. ©2018 AACR.

Uncoupling protein 1 expression in adipocytes derived from skeletal muscle fibro/adipogenic progenitors is under genetic and hormonal control

BACKGROUND

Intramuscular fatty infiltration is generally associated with the accumulation of white adipocytes in skeletal muscle and unfavourable metabolic outcomes. It is, however, still unclear whether intramuscular adipocytes could also acquire a brown-like phenotype. Here, we detected intramuscular expression of brown adipocyte markers during fatty infiltration in an obesity-resistant mouse strain and extensively compared the potential of two different stem cell populations residing in skeletal muscle to differentiate into brown-like adipocytes.

METHODS

Fatty infiltration was induced using intramuscular glycerol or cardiotoxin injection in the tibialis anterior muscles of young or aged 129S6/SvEvTac (Sv/129) mice or interleukin-6 (IL-6) knockout mice, and the expression of general and brown adipocyte markers was assessed after 4 weeks. Fibro/adipogenic progenitors (FAPs) and myogenic progenitors were prospectively isolated using fluorescence-activated cell sorting from skeletal muscle of male and female C57Bl6/6J and Sv/129 mice, and monoclonal and polyclonal cultures were treated with brown adipogenic medium. Additionally, FAPs were differentiated with medium supplemented or not with triiodothyronine.

RESULTS

Although skeletal muscle expression of uncoupling protein 1 (Ucp1) was barely detectable in uninjected tibialis anterior muscle, it was drastically induced following intramuscular adipogenesis in Sv/129 mice and further increased in response to beta 3-adrenergic stimulation. Intramuscular Ucp1 expression did not depend on IL-6 and was preserved in aged skeletal muscle. Myogenic progenitors did not form adipocytes neither in polyclonal nor monoclonal cultures. Fibro/adipogenic progenitors, on the other hand, readily differentiated into brown-like, UCP1+ adipocytes. Uncoupling protein 1 expression in differentiated FAPs was regulated by genetic background, sex, and triiodothyronine treatment independently of adipogenic differentiation levels.

CONCLUSIONS

Intramuscular adipogenesis is associated with increased Ucp1 expression in skeletal muscle from obesity-resistant mice. Fibro/adipogenic progenitors provide a likely source for intramuscular adipocytes expressing UCP1 under control of both genetic and hormonal factors. Therefore, FAPs constitute a possible target for therapies aiming at the browning of intramuscular adipose tissue and the metabolic improvement of skeletal muscle affected by fatty infiltration.

Pycnogenol® Induces Browning of White Adipose Tissue through the PKA Signaling Pathway in Apolipoprotein E-Deficient Mice

Beige adipocytes in white adipose tissue (WAT) have received considerable recognition because of their potential protective effect against obesity. Pycnogenol (PYC), extracted from French maritime pine bark, has anti-inflammatory and antioxidant properties and can improve lipid profiles. However, the effect of PYC on obesity has never been explored. In this study, we investigated the effects of PYC on obesity and WAT browning in apolipoprotein E- (ApoE-) deficient mice. The results showed that PYC treatment clearly reversed body weight and the mass of eWAT gain resulting from a high-cholesterol and high-fat diet (HCD), but no difference in food intake. The morphology results showed that the size of the adipocytes in the PYC-treated mice was obviously smaller than that in the HCD-fed mice. Next, we found that PYC upregulated the expression of genes related to lipolysis (ATGL and HSL), while it decreased the mRNA level of PLIN1. PYC significantly increased the expression of UCP1 and other genes related to beige adipogenesis. Additionally, PYC increased the expression of proteins related to the protein kinase A (PKA) signaling pathway. The findings suggested that PYC decreased obesity by promoting lipolysis and WAT browning. Thus, PYC may be a novel therapeutic target for obesity.

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.

Impact of training state on fasting-induced regulation of adipose tissue metabolism in humans

Recruitment of fatty acids from adipose tissue is increased during fasting. However, the molecular mechanisms behind fasting-induced metabolic regulation in human adipose tissue and the potential impact of training state in this are unknown. Therefore the aim of the present study was to investigate 1) fasting-induced regulation of lipolysis and glyceroneogenesis in human adipose tissue as well as 2) the impact of training state on basal oxidative capacity and fasting-induced metabolic regulation in human adipose tissue. Untrained [maximal oxygen uptake (V̇o_2max) < 45 ml·min^-1·kg^-1] and trained subjects (V̇o_2max > 55 ml·min^-1·kg^-1) fasted for 36 h, and abdominal subcutaneous adipose tissue biopsies were obtained 2, 12, 24, and 36 h after a standardized meal. Adipose tissue oxidative phosphorylation complexes, phosphoenolpyruvate carboxykinase, and pyruvate dehydrogenase (PDH)-E1α protein as well as PDH kinase (PDK) 2, PDK4, and PDH phosphatase 2 mRNA content were higher in trained subjects than in untrained subjects. In addition, trained subjects had higher adipose tissue hormone-sensitive lipase Ser660 phosphorylation and adipose triglyceride lipase protein content as well as higher plasma free fatty acid concentration than untrained subjects during fasting. Moreover, adipose tissue PDH phosphorylation increased with fasting only in trained subjects. Taken together, trained subjects seem to possess higher basal adipose tissue oxidative capacity as well as higher capacity for regulation of lipolysis and for providing substrate for glyceroneogenesis in adipose tissue during fasting than untrained subjects. NEW & NOTEWORTHY This study shows for the first time higher protein content of lipolytic enzymes and higher oxidative phosphorylation protein in adipose tissue from trained subjects than from untrained subjects during fasting. Furthermore, trained subjects had higher capacity for adipose tissue glyceroneogenesis than untrained subjects.

No evidence of white adipocyte browning after endurance exercise training in obese men

BACKGROUND/OBJECTIVES

The phenomenon of adipocyte 'beiging' involves the conversion of non-classic brown adipocytes to brown-like adipose tissue with thermogenic, fat-burning properties, and this phenomenon has been shown in rodents to slow the progression of obesity-associated metabolic diseases. Rodent studies consistently report adipocyte beiging after endurance exercise training, indicating that increased thermogenic capacity in these adipocytes may underpin the improved health benefits of exercise training. The aim of this study was to determine whether prolonged endurance exercise training induces beige adipogenesis in subcutaneous adipose tissues of obese men.

SUBJECTS/METHODS

Molecular markers of beiging were examined in adipocytes obtained from abdominal subcutaneous (AbSC) and gluteofemoral (GF) subcutaneous adipose tissues before and after 6 weeks of endurance exercise training in obese men (n=6, 37.3±2.3 years, 30.1±2.3 kg m^-2).

RESULTS

The mRNAs encoding the brown or beige adipocyte-selective proteins were very lowly expressed in AbSC and GF adipose tissues and exercise training did not alter the mRNA expression of UCP1, CD137, CITED, TBX1, LHX8 and TCF21. Using immunohistochemistry, neither multilocular adipocytes, nor UCP1 or CD137-positive adipocytes were detected in any sample. MicroRNAs known to regulate brown and/or beige adipose development were highly expressed in white adipocytes but endurance exercise training did not impact their expression.

CONCLUSIONS

The present study reaffirms emerging data in humans demonstrating no evidence of white adipose tissue beiging in response to exercise training, and supports a growing body of work demonstrating divergence of brown/beige adipose location, molecular characterization and physiological function between rodents and humans.

PGC-1α and exercise intensity dependent adaptations in mouse skeletal muscle

The aim of the present study was to examine the role of PGC-1α in intensity dependent exercise and exercise training-induced metabolic adaptations in mouse skeletal muscle. Whole body PGC-1α knockout (KO) and littermate wildtype (WT) mice performed a single treadmill running bout at either low intensity (LI) for 40 min or moderate intensity (MI) for 20 min. Blood and quadriceps muscles were removed either immediately after exercise or at 3h or 6h into recovery from exercise and from resting controls. In addition PGC-1α KO and littermate WT mice were exercise trained at either low intensity (LIT) for 40 min or at moderate intensity (MIT) for 20 min 2 times pr. day for 5 weeks. In the first and the last week of the intervention period, mice performed a graded running endurance test. Quadriceps muscles were removed before and after the training period for analyses. The acute exercise bout elicited intensity dependent increases in LC3I and LC3II protein and intensity independent decrease in p62 protein in skeletal muscle late in recovery and increased LC3II with exercise training independent of exercise intensity and volume in WT mice. Furthermore, acute exercise and exercise training did not increase LC3I and LC3II protein in PGC-1α KO. In addition, exercise-induced mRNA responses of PGC-1α isoforms were intensity dependent. In conclusion, these findings indicate that exercise intensity affected autophagy markers differently in skeletal muscle and suggest that PGC-1α regulates both acute and exercise training-induced autophagy in skeletal muscle potentially in a PGC-1α isoform specific manner.

Habitual physical activity protects against lipopolysaccharide-induced inflammation in mouse adipose tissue

Sepsis is a systemic inflammatory response to infection, with no preventative strategies. In this study, we identify a role for habitual physical activity in the prevention of adipose tissue inflammation induced by a model of sepsis, lipopolysaccharide (LPS). Male C57BL/6J mice (8 weeks old) were housed with access to voluntary wheel running (VWR) or sedentary (SED) for 10 weeks. Mice were then injected with LPS (2 mg/kg) or saline (SAL), and tissues were removed 6 hours post-injection. VWR attenuated body, epididymal adipose tissue (eWAT), and subcutaneous inguinal adipose tissue (iWAT) mass gain, improved glucose tolerance, increased markers of mitochondrial biogenesis in iWAT and eWAT, and increased UCP-1 protein content in iWAT. In iWAT, VWR attenuated the LPS induced increase in mRNA expression of TNF-α, MCP-1, and follistatin, along with phosphorylation of STAT3. In addition, VWR had a main effect for reducing iWAT mRNA expression of IL-1β, IL-6, and SOCS3. In eWAT, VWR had a main effect for reducing mRNA expression of IL-1β, MCP-1, IL-6, and follistatin. Further, VWR increased SOCS3 mRNA expression and phosphorylation of STAT3 in SAL mice, thus the relative change in response to LPS for these markers was attenuated. The protective effect of prior physical activity occurred in conjunction with increases in the protein content of a component of the LPS binding complex, MyD88. Overall, the results from this study demonstrate that habitual physical activity can attenuate the LPS induced inflammatory response in adipose tissue and this occurs to a greater extent in iWAT compare with eWAT.

Prdm16 is crucial for progression of the multipolar phase during neural differentiation of the developing neocortex

The precise control of neuronal migration and morphological changes during differentiation is essential for neocortical development. We hypothesized that the transition of progenitors through progressive stages of differentiation involves dynamic changes in levels of mitochondrial reactive oxygen species (mtROS), depending on cell requirements. We found that progenitors had higher levels of mtROS, but that these levels were significantly decreased with differentiation. The Prdm16 gene was identified as a candidate modulator of mtROS using microarray analysis, and was specifically expressed by progenitors in the ventricular zone. However, Prdm16 expression declined during the transition into NeuroD1-positive multipolar cells. Subsequently, repression of Prdm16 expression by NeuroD1 on the periphery of ventricular zone was crucial for appropriate progression of the multipolar phase and was required for normal cellular development. Furthermore, time-lapse imaging experiments revealed abnormal migration and morphological changes in Prdm16-overexpressing and -knockdown cells. Reporter assays and mtROS determinations demonstrated that PGC1α is a major downstream effector of Prdm16 and NeuroD1, and is required for regulation of the multipolar phase and characteristic modes of migration. Taken together, these data suggest that Prdm16 plays an important role in dynamic cellular redox changes in developing neocortex during neural differentiation.

Acute exercise regulates adipogenic gene expression in white adipose tissue

White adipose tissue expansion is associated with both hypertrophy and hyperplasia of adipocytes. Exercise training results in adipocyte hypotrophy by activating lipolysis, but it is poorly understood whether exercise regulates adipogenesis by altering adipogenic gene expression. The purpose of this study was to evaluate the effect of a single bout of swimming exercise on adipogenic gene expression in white adipose tissue (WAT). Male C57BL/6J mice were divided into two groups: a sedentary control group and a 120-minute swimming exercise group. Immediately after acute exercise, adipogenic gene expression in WAT was analysed by RT-PCR, and tdTomato positive cells in WAT from UCP1-cre-tdTomato mice were observed under a confocal microscope. In epididymal white adipose tissue (eWAT), PPARγ2 and C/EBPα expression at the mRNA level was significantly decreased with high induction of Wnt10b and KLFs (KLF2, KLF3, KLF7, KLF6, KLF9 and KLF15), whereas PPARγ2, not C/EBPα, was decreased with high induction of Wnt6 and KLFs (KLF2, KLF3, KLF7, KLF6 and KLF9) in inguinal white adipose tissue (iWAT) after acute exercise. The expression of C/EBPβ and C/EBPδ was upregulated in both WATs with a high level of PGC-1α expression. Expression level of UCP1 was increased only in adipocytes of eWAT, while beige cell specific gene expression was comparable between groups and tdTomato positive cells were not found in WAT of UCP1-cre-tdTomato reporter mouse immediately after acute exercise. These results suggest that acute exercise suppresses adipogenic gene expression and may regulate thermogenesis by activating C/EBPβ, PGC-1α and UCP1 in WAT.

Browning of subcutaneous fat and higher surface temperature in response to phenotype selection for advanced endurance exercise performance in male DUhTP mice

For the assessment of genetic or conditional factors of fat cell browning, novel and polygenic animal models are required. Therefore, the long-term selected polygenic mouse line DUhTP originally established in Dummerstorf for high treadmill performance is used. DUhTP mice are characterized by increased fat accumulation in the sedentary condition and elevated fat mobilization during mild voluntary physical activity. In the present study, the phenotype of fat cell browning of subcutaneous fat and a potential effect on oral glucose tolerance, an indicator of metabolic health, were addressed in DUhTP mice. Analysis of peripheral fat pads revealed increased brite (brown-in-white) subcutaneous adipose tissues and in subcutaneous fat from DUhTP mice higher levels of irisin and different markers of fat cell browning like T-box transcription factor (Tbx1), PPARα, and uncoupling protein (UCP1) (P < 0.05) when compared to unselected controls. UCP1 was further increased in subcutaneous fat from DUhTP mice in response to mild exercise (fourfold, P < 0.05). In addition, surface temperature of DUhTP mice was increased when compared to controls indicating a physiological effect of increased UCP1 expression. The present study suggests that DUhTP mice exhibit different markers of mitochondrial biogenesis and fat browning without external stimuli. At an age of 43 days, sedentary DUhTP mice have improved metabolic health as judged from lower levels of blood glucose after an oral glucose tolerance test. Consequently, the non-inbred mouse model DUhTP represents a novel model for the identification of fat cell browning mechanisms in white adipose tissues.

Control of seizures by ketogenic diet-induced modulation of metabolic pathways

Epilepsy is too complex to be considered as a disease; it is more of a syndrome, characterized by seizures, which can be caused by a diverse array of afflictions. As such, drug interventions that target a single biological pathway will only help the specific individuals where that drug's mechanism of action is relevant to their disorder. Most likely, this will not alleviate all forms of epilepsy nor the potential biological pathways causing the seizures, such as glucose/amino acid transport, mitochondrial dysfunction, or neuronal myelination. Considering our current inability to test every individual effectively for the true causes of their epilepsy and the alarming number of misdiagnoses observed, we propose the use of the ketogenic diet (KD) as an effective and efficient preliminary/long-term treatment. The KD mimics fasting by altering substrate metabolism from carbohydrates to fatty acids and ketone bodies (KBs). Here, we underscore the need to understand the underlying cellular mechanisms governing the KD's modulation of various forms of epilepsy and how a diverse array of metabolites including soluble fibers, specific fatty acids, and functional amino acids (e.g., leucine, D-serine, glycine, arginine metabolites, and N-acetyl-cysteine) may potentially enhance the KD's ability to treat and reverse, not mask, these neurological disorders that lead to epilepsy.

Exercise-Mediated Effects on White and Brown Adipose Tissue Plasticity and Metabolism

Exercise training increases the thermogenic capacity of white adipose tissue (WAT), an effect known as "browning" of the WAT. Here, we discuss how this affects whole-body energy homeostasis. We put forth the hypothesis that browning of the subcutaneous WAT allows the organism to adjust its metabolic rate according to energy availability while coping with increased heat production through exercise.

Mitochondria in White, Brown, and Beige Adipocytes

Mitochondria play a key role in energy metabolism in many tissues, including cardiac and skeletal muscle, brain, liver, and adipose tissue. Three types of adipose depots can be identified in mammals, commonly classified according to their colour appearance: the white (WAT), the brown (BAT), and the beige/brite/brown-like (bAT) adipose tissues. WAT is mainly involved in the storage and mobilization of energy and BAT is predominantly responsible for nonshivering thermogenesis. Recent data suggest that adipocyte mitochondria might play an important role in the development of obesity through defects in mitochondrial lipogenesis and lipolysis, regulation of adipocyte differentiation, apoptosis, production of oxygen radicals, efficiency of oxidative phosphorylation, and regulation of conversion of white adipocytes into brown-like adipocytes. This review summarizes the main characteristics of each adipose tissue subtype and describes morphological and functional modifications focusing on mitochondria and their activity in healthy and unhealthy adipocytes.

Increased Energy Expenditure, Ucp1 Expression, and Resistance to Diet-induced Obesity in Mice Lacking Nuclear Factor-Erythroid-2-related Transcription Factor-2 (Nrf2)

The NRF2 (also known as NFE2L2) transcription factor is a critical regulator of genes involved in defense against oxidative stress. Previous studies suggest thatNrf2plays a role in adipogenesisin vitro, and deletion of theNrf2gene protects against diet-induced obesity in mice. Here, we demonstrate that resistance to diet-induced obesity inNrf2(-/-)mice is associated with a 20-30% increase in energy expenditure. Analysis of bioenergetics revealed thatNrf2(-/-)white adipose tissues exhibit greater oxygen consumption. White adipose tissue showed a >2-fold increase inUcp1gene expression. Oxygen consumption is also increased nearly 2.5-fold inNrf2-deficient fibroblasts. Oxidative stress induced by glucose oxidase resulted in increasedUcp1expression. Conversely, antioxidant chemicals (such asN-acetylcysteine and Mn(III)tetrakis(4-benzoic acid)porphyrin chloride) and SB203580 (a known suppressor ofUcp1expression) decreasedUcp1and oxygen consumption inNrf2-deficient fibroblasts. These findings suggest that increasing oxidative stress by limitingNrf2function in white adipocytes may be a novel means to modulate energy balance as a treatment of obesity and related clinical disorders.

Determination of UCP1 expression in subcutaneous and perirenal adipose tissues of patients with hypertension

The objective of this study is to determine the property of human perirenal adipose tissue (PAT) and assess the adipose property of PAT in hypertension. Ninety-four patients, including 64 normotensive patients (T-NP) and 30 hypertensive patients (HP), who underwent renal surgery were included. Expression analysis was performed using quantitative real-time polymerase chain reaction, Western blot, and immunohistochemistry in PAT and back subcutaneous adipose tissue (bSAT) depots. Compared with bSAT, PAT adipocytes were smaller, and the expressions of uncoupling protein-1 (UCP1) mRNA and protein were markedly higher, while the mRNA expressions of markers for classic beige and white adipocytes were lower in PAT. Immunohistochemistry analysis showed more multilocular UCP1-positive adipocytes in PAT than in bSAT. UCP1 expressions were lower in PAT in HP than in the T-NP or age- and body mass index-matched NP groups. Bigger unilocular adipocytes with less UCP1 staining in PAT were detected in HP than in NP group, although no such difference was observed in bSAT. PAT acts as a brown-like fat. UCP1 expression of PAT was lower in HP than in normotensive patients. UCP1 expression of PAT may serve as a protective indicator for hypertension.

Organ-specific physiological responses to acute physical exercise and long-term training in humans

Virtually all tissues in the human body rely on aerobic metabolism for energy production and are therefore critically dependent on continuous supply of oxygen. Oxygen is provided by blood flow, and, in essence, changes in organ perfusion are also closely associated with alterations in tissue metabolism. In response to acute exercise, blood flow is markedly increased in contracting skeletal muscles and myocardium, but perfusion in other organs (brain and bone) is only slightly enhanced or is even reduced (visceral organs). Despite largely unchanged metabolism and perfusion, repeated exposures to altered hemodynamics and hormonal milieu produced by acute exercise, long-term exercise training appears to be capable of inducing effects also in tissues other than muscles that may yield health benefits. However, the physiological adaptations and driving-force mechanisms in organs such as brain, liver, pancreas, gut, bone, and adipose tissue, remain largely obscure in humans. Along these lines, this review integrates current information on physiological responses to acute exercise and to long-term physical training in major metabolically active human organs. Knowledge is mostly provided based on the state-of-the-art, noninvasive human imaging studies, and directions for future novel research are proposed throughout the review.

Stochastic effects in adaptive reconstruction of body damage: implied the creativity of natural selection

After an injury occurs, mechanical/biochemical loads on muscles influence the composition and structure of recovering muscles; this effect likely occurs in other tissues, cells and biological molecules as well owing to the similarity, interassociation and interaction among biochemical reactions and molecules. The 'damage and reconstruction' model provides an explanation for how an ideal cytoarchitecture is created by reducing components not suitable for bearing loads; in this model, adaptive changes are induced by promoting the stochasticity of biochemical reactions. Biochemical and mechanical loads can direct the stochasticity of biochemical reactions, which can in turn induce cellular changes. Thus, mechanical and biochemical loads, under natural selection pressure, modify the direction of cell- and tissue-level changes and guide the formation of new structures and traits, thereby influencing microevolution. In summary, the 'damage and reconstruction' model accounts for the role of natural selection in the formation of new organisms, helps explain punctuated equilibrium, and illustrates how macroevolution arises from microevolution.