ABSTRACT
Thermogenesis in brown adipose tissue (BAT) is fundamental to energy balance and is also relevant for humans. Bone morphogenetic proteins (BMPs) regulate adipogenesis, and, here, we describe a role for BMP8B in the direct regulation of thermogenesis. BMP8B is induced by nutritional and thermogenic factors in mature BAT, increasing the response to noradrenaline through enhanced p38MAPK/CREB signaling and increased lipase activity. Bmp8b(-/-) mice exhibit impaired thermogenesis and reduced metabolic rate, causing weight gain despite hypophagia. BMP8B is also expressed in the hypothalamus, and Bmp8b(-/-) mice display altered neuropeptide levels and reduced phosphorylation of AMP-activated protein kinase (AMPK), indicating an anorexigenic state. Central BMP8B treatment increased sympathetic activation of BAT, dependent on the status of AMPK in key hypothalamic nuclei. Our results indicate that BMP8B is a thermogenic protein that regulates energy balance in partnership with hypothalamic AMPK. BMP8B may offer a mechanism to specifically increase energy dissipation by BAT.
Subject(s)
Adipose Tissue, Brown/metabolism , Bone Morphogenetic Proteins/metabolism , Diet , Obesity/metabolism , Thermogenesis , AMP-Activated Protein Kinases/metabolism , Adipogenesis , Animals , Bone Morphogenetic Proteins/genetics , Energy Metabolism , Female , Hypothalamus/metabolism , Mice , Mice, Inbred C57BL , Norepinephrine/metabolism , Rats , Rats, Sprague-DawleyABSTRACT
An increase in mitochondrial DNA (mtDNA) mutations and an ensuing increase in mitochondrial reactive oxygen species (ROS) production have been suggested to be a cause of the aging process ("the mitochondrial hypothesis of aging"). In agreement with this, mtDNA-mutator mice accumulate a large amount of mtDNA mutations, giving rise to defective mitochondria and an accelerated aging phenotype. However, incongruously, the rates of ROS production in mtDNA mutator mitochondria have generally earlier been reported to be lower - not higher - than in wildtype, thus apparently invalidating the "mitochondrial hypothesis of aging". We have here re-examined ROS production rates in mtDNA-mutator mice mitochondria. Using traditional conditions for measuring ROS (succinate in the absence of rotenone), we indeed found lower ROS in the mtDNA-mutator mitochondria compared to wildtype. This ROS mainly results from reverse electron flow driven by the membrane potential, but the membrane potential reached in the isolated mtDNA-mutator mitochondria was 33 mV lower than that in wildtype mitochondria, due to the feedback inhibition of succinate oxidation by oxaloacetate, and to a lower oxidative capacity in the mtDNA-mutator mice, explaining the lower ROS production. In contrast, in normal forward electron flow systems (pyruvate (or glutamate) + malate or palmitoyl-CoA + carnitine), mitochondrial ROS production was higher in the mtDNA-mutator mitochondria. Particularly, even during active oxidative phosphorylation (as would be ongoing physiologically), higher ROS rates were seen in the mtDNA-mutator mitochondria than in wildtype. Thus, when examined under physiological conditions, mitochondrial ROS production rates are indeed increased in mtDNA-mutator mitochondria. While this does not prove the validity of the mitochondrial hypothesis of aging, it may no longer be said to be negated in this respect. This paper is dedicated to the memory of Professor Vladimir P. Skulachev.
Subject(s)
DNA, Mitochondrial , Mitochondria , Mice , Animals , DNA, Mitochondrial/genetics , Reactive Oxygen Species , Mitochondria/genetics , Aging/genetics , Mutation , SuccinatesABSTRACT
Perfluorooctanoic acid (PFOA) is a synthetic organofluoride surfactant associated with several toxic effects in humans and animals. Particularly, it has been observed that PFOA treatment of mice results in weight loss associated with recruited brown adipose tissue (BAT), including an increased amount of uncoupling protein 1 (UCP1). The molecular mechanism behind this BAT recruitment is presently unknown. To investigate the existence of possible cell-autonomous effects of PFOA, we treated primary cultures of brown and white (inguinal) adipocytes with PFOA, or with the non-fluorinated equivalent octanoate, or with vehicle, for 48 h (from day 5 to day 7 of differentiation). PFOA in itself increased the gene expression (mRNA levels) of UCP1 and carnitine palmitoyltransferase 1A (CPT1α) (thermogenesis-related genes) in both brown and white adipocytes. In addition, PFOA increased the expression of fatty acid binding protein 4 (FABP4) and peroxisome proliferator-activated receptor α (PPARα) (adipogenesis-related genes). Also the protein levels of UCP1 were increased in brown adipocytes exposed to PFOA. This increase was more due to an increase in the fraction of cells that expressed UCP1 than to an increase in UCP1 levels per cell. The PFOA-induced changes were even more pronounced under simultaneous adrenergic stimulation. Octanoate induced less pronounced effects on adipocytes than did PFOA. Thus, PFOA in itself increased the levels of thermogenic markers in brown and white adipocytes. This could enhance the energy metabolism of animals (and humans) exposed to the compound, resulting in a negative energy balance, leading to diminished fitness.
Subject(s)
Adipogenesis , Caprylates , Fluorocarbons , Humans , Mice , Animals , Caprylates/toxicity , Adipocytes, White , Thermogenesis/geneticsABSTRACT
Cold- and diet-induced recruitment of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT) are dynamic processes, and the recruited state attained is a state of dynamic equilibrium, demanding continuous stimulation to be maintained. An involvement of macrophages, classical proinflammatory (M1) or alternatively activated anti-inflammatory (M2), is presently discussed as being an integral part of these processes. If these macrophages play a mediatory role in the recruitment process, such an involvement would have to be maintained in the recruited state. We have, therefore, investigated whether the recruited state of these tissues is associated with macrophage accretion or attrition. We found no correlation (positive or negative) between total UCP1 mRNA levels (as a measure of recruitment) and proinflammatory macrophages in any adipose depot. We found that in young chow-fed mice, cold-induced recruitment correlated with accretion of anti-inflammatory macrophages; however, such a correlation was not seen when cold-induced recruitment was studied in diet-induced obese mice. Furthermore, the anti-inflammatory macrophage accretion was mediated via ß1/ß2-adrenergic receptors; yet, in their absence, and thus in the absence of macrophage accretion, recruitment proceeded normally. We thus conclude that the classical recruited state in BAT and inguinal (brite/beige) WAT is not paralleled by macrophage accretion or attrition. Our results make mediatory roles for macrophages in the recruitment process less likely.NEW & NOTEWORTHY A regulatory or mediatory role-positive or negative-for macrophages in the recruitment of brown adipose tissue is presently discussed. As the recruited state in the tissue is a dynamic process, maintenance of the recruited state would need persistent alterations in macrophage complement. Contrary to this expectation, we demonstrate here an absence of alterations in macrophage complement in thermogenically recruited brown-or brite/beige-adipose tissues. Macrophage regulation of thermogenic capacity is thus less likely.
Subject(s)
Adipose Tissue, Beige/physiology , Adipose Tissue, Brown/physiology , Macrophages/physiology , Receptors, Adrenergic, beta-1/physiology , Receptors, Adrenergic, beta-2/physiology , Thermogenesis , Adipose Tissue, Beige/cytology , Adipose Tissue, Brown/cytology , Animals , Diet/adverse effects , Gene Expression Regulation , Macrophages/cytology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Obesity/etiology , Obesity/metabolism , Obesity/pathology , Uncoupling Protein 1/genetics , Uncoupling Protein 1/metabolismABSTRACT
The possibility to use leptin therapeutically for lowering glucose levels in patients with type 1 diabetes has attracted interest. However, earlier animal models of type 1 diabetes are severely catabolic with very low endogenous leptin levels, unlike most patients with diabetes. Here, we aim to test glucose-lowering effects of leptin in novel, more human-like murine models. We examined the glucose-lowering potential of leptin in diabetic models of two types: streptozotocin-treated mice and mice treated with the insulin receptor antagonist S961. To prevent hypoleptinemia, we used combinations of thermoneutral temperature and high-fat feeding. Leptin fully normalized hyperglycemia in standard chow-fed streptozotocin-treated diabetic mice. However, more humanized physiological conditions (high-fat diets or thermoneutral temperatures) that increased adiposity - and thus also leptin levels - in the diabetic mice abrogated the effects of leptin, i.e., the mice developed leptin resistance also in this respect. The glucose-lowering effect of leptin was not dependent on the presence of the uncoupling protein-1 and was not associated with alterations in plasma insulin, insulin-like growth factor 1, food intake or corticosterone but fully correlated with decreased plasma glucagon levels and gluconeogenesis. An important implication of these observations is that the therapeutic potential of leptin as an additional treatment in patients with type 1 diabetes is probably limited. This is because such patients are treated with insulin and do not display low leptin levels. Thus, the potential for a glucose-lowering effect of leptin would already have been attained with standard insulin therapy, and further effects on blood glucose level through additional leptin cannot be anticipated.
Subject(s)
Blood Glucose/drug effects , Diabetes Mellitus, Experimental/metabolism , Diabetes Mellitus, Type 1/metabolism , Leptin/metabolism , Adipose Tissue, Brown/metabolism , Adipose Tissue, White/metabolism , Animals , Blood Glucose/metabolism , Corticosterone/metabolism , Disease Models, Animal , Eating , Glucagon/metabolism , Gluconeogenesis , Humans , Insulin/metabolism , Insulin-Like Growth Factor I/metabolism , Leptin/pharmacology , Mice , Mice, Knockout , Oxygen Consumption , Peptides/pharmacology , Pyruvic Acid/metabolism , Receptor, Insulin/antagonists & inhibitors , Transcriptome , Uncoupling Protein 1/genetics , Uncoupling Protein 1/metabolismABSTRACT
OBJECTIVES: High-esterified pectin (HEP) is a prebiotic able to modulate gut microbiota, associated with health-promoting metabolic effects in glucose and lipid metabolism and adipostatic hormone sensitivity. Possible effects regulating adaptive thermogenesis and energy waste are poorly known. Therefore, we aimed to study how physiological supplementation with HEP is able to affect microbiota, energy metabolism and adaptive thermogenic capacity, and to contribute to the healthier phenotype promoted by HEP supplementation, as previously shown. We also attempted to decipher some of the mechanisms involved in the HEP effects, including in vitro experiments. SUBJECTS AND EXPERIMENTAL DESIGN: We used a model of metabolic malprogramming consisting of the progeny of rats with mild calorie restriction during pregnancy, both under control diet and an obesogenic (high-sucrose) diet, supplemented with HEP, combined with in vitro experiments in primary cultured brown and white adipocytes treated with the postbiotic acetate. RESULTS: Our main findings suggest that chronic HEP supplementation induces markers of brown and white adipose tissue thermogenic capacity, accompanied by a decrease in energy efficiency, and prevention of weight gain under an obesogenic diet. We also show that HEP promotes an increase in beneficial bacteria in the gut and peripheral levels of acetate. Moreover, in vitro acetate can improve adipokine production, and increase thermogenic capacity and browning in brown and white adipocytes, respectively, which could be part of the protection mechanism against excess weight gain observed in vivo. CONCLUSION: HEP and acetate stand out as prebiotic/postbiotic active compounds able to modulate both brown-adipocyte metabolism and browning and protect against obesity.
Subject(s)
Adipocytes, Brown/drug effects , Adipocytes, White/drug effects , Pectins/pharmacology , Prebiotics , Thermogenesis/drug effects , Acetates/metabolism , Acetates/pharmacology , Adipocytes, Brown/cytology , Adipocytes, Brown/metabolism , Adipocytes, White/cytology , Adipocytes, White/metabolism , Animals , Caloric Restriction , Dietary Supplements , Female , Gastrointestinal Microbiome/drug effects , Male , Pectins/administration & dosage , Pectins/metabolism , Pregnancy , Rats , Rats, WistarABSTRACT
NEW FINDINGS: What is the topic of this review? It has been suggested that human brown adipose tissue (BAT) is more similar to the brite/beige adipose tissue of mice than to classical BAT of mice. The basis of this is discussed in relationship to the physiological conditions of standard experimental mice. What advances does it highlight? We highlight that, provided mouse adipose tissues are examined under physiological conditions closer to those prevalent for most humans, the gene expression profile of mouse classical BAT is more similar to that of human BAT than is the profile of mouse brite/beige adipose tissue. Human BAT is therefore not different in nature from classical mouse BAT. ABSTRACT: Since the presence of brown adipose tissue (BAT) was established in adult humans some 13 years ago, its physiological significance and molecular characteristics have been discussed. In particular, it has been proposed that the mouse adipose tissue depot most closely resembling and molecularly parallel to human BAT is not classical mouse BAT. Instead, so-called brite or beige adipose tissue, which is characteristically observed in the inguinal 'white' adipose tissue depot of mice, has been proposed to be the closest mouse equivalent of human BAT. We summarize here the published evidence examining this question. We emphasize the differences in tissue appearance and tissue transcriptomes from 'standard' mice [young, chow fed and, in effect semi-cold exposed (20°C)] versus 'physiologically humanized' mice [middle-aged, high-fat diet-fed mice living at thermoneutrality (30°C)]. We find that in the physiologically humanized mice, classical BAT displays molecular and cellular characteristics that are more akin to human BAT than are those of brite/beige adipose tissues from either standard or physiologically humanized mice. We suggest, therefore, that mouse BAT is the more relevant tissue for translational studies. This is an invited summary of a presentation given at Physiology 2019 (Aberdeen).
Subject(s)
Adipose Tissue, Beige/physiology , Adipose Tissue, Brown/physiology , Animals , Humans , Mice , Models, Animal , TranscriptomeABSTRACT
The possibility that recruitment and activation of brown adipose tissue (BAT) thermogenesis could be beneficial for curtailing obesity development in humans prompts a need for a better understanding of the control of these processes [that are often referred to collectively as diet-induced thermogenesis (DIT)]. Dietary conditions are associated with large changes in blood-borne factors that could be responsible for BAT recruitment, but BAT is also innervated by the sympathetic nervous system. To examine the significance of the innervation for DIT recruitment, we surgically denervated the largest BAT depot, i.e., the interscapular BAT depot in mice and exposed the mice at thermoneutrality to a high-fat diet versus a chow diet. Denervation led to an alteration in feeding pattern but did not lead to enhanced obesity, but obesity was achieved with a lower food intake, as denervation increased metabolic efficiency. Conclusively, denervation totally abolished the diet-induced increase in total UCP1 protein levels observed in the intact mice, whereas basal UCP1 expression was not dependent on innervation. The denervation of interscapular BAT did not discernably hyper-recruit other BAT depots, and no UCP1 protein could be detected in the principally browning-competent inguinal white adipose tissue depot under any of the examined conditions. We conclude that intact innervation is essential for diet-induced thermogenesis and that circulating factors cannot by themselves initiate recruitment of brown adipose tissue under obesogenic conditions. Therefore, the processes that link food intake and energy storage to activation of the nervous system are those of significance for the further understanding of diet-induced thermogenesis.
Subject(s)
Adipose Tissue, Brown/innervation , Obesity/metabolism , Sympathectomy , Thermogenesis/physiology , Uncoupling Protein 1/metabolism , Adipose Tissue, Brown/metabolism , Adipose Tissue, White/metabolism , Animals , Calorimetry, Indirect , Diet , Diet, High-Fat , Energy Intake , Male , MiceABSTRACT
The attractive tenet that recruitment and activation of brown adipose tissue (BAT) and uncoupling protein 1 (UCP1) could counteract the development of obesity and its comorbidities in humans has been experimentally corroborated mainly by experiments demonstrating that UCP1-ablated mice on a C57Bl/6 background (exempt from thermal stress) become more obese when fed a high-fat diet. However, concerns may be raised that this outcome of UCP1 ablation is restricted to this very special inbred and particularly obesity-prone mouse strain. Therefore, we have examined to which degree UCP1 ablation has similar metabolic effects in a mouse strain known to be obesity resistant: the 129S strain. For this, male 129S2/sv or 129SV/Pas mice and corresponding UCP1-knockout mice were fed chow or a high-fat or a cafeteria diet for 4 wk. The absence of UCP1 augmented obesity (weight gain, body fat mass, %body fat, fat depot size) in high-fat diet- and cafeteria-fed mice, with a similar or lower food intake, indicating that, when present, UCP1 indeed decreases metabolic efficiency. The increased obesity was due to a decrease in energy expenditure. The consumption of a high-fat or cafeteria diet increased total BAT UCP1 protein levels in wild-type mice, and correspondingly, high-fat diet and cafeteria diet-fed mice demonstrated increased norepinephrine-induced oxygen consumption. There was a positive correlation between body fat and total BAT UCP1 protein content. No evidence for diet-induced adrenergic thermogenesis was found in UCP1-ablated mice. Thus, the obesity-reducing effect of UCP1 is not restricted to a particular, and perhaps not representative, mouse strain.
Subject(s)
Diet, High-Fat , Obesity/genetics , Thermogenesis/genetics , Uncoupling Protein 1/genetics , Adipose Tissue , Adipose Tissue, Brown/metabolism , Adrenergic alpha-Agonists/pharmacology , Animals , Eating , Energy Metabolism/genetics , Male , Mice , Mice, 129 Strain , Mice, Knockout , Norepinephrine/pharmacology , Obesity/metabolism , Oxygen Consumption/drug effects , Thermogenesis/drug effects , Uncoupling Protein 1/metabolism , Weight GainABSTRACT
Adrenergic stimulation of brown adipocytes (BA) induces mitochondrial uncoupling, thereby increasing energy expenditure by shifting nutrient oxidation towards thermogenesis. Here we describe that mitochondrial dynamics is a physiological regulator of adrenergically-induced changes in energy expenditure. The sympathetic neurotransmitter Norepinephrine (NE) induced complete and rapid mitochondrial fragmentation in BA, characterized by Drp1 phosphorylation and Opa1 cleavage. Mechanistically, NE-mediated Drp1 phosphorylation was dependent on Protein Kinase-A (PKA) activity, whereas Opa1 cleavage required mitochondrial depolarization mediated by FFAs released as a result of lipolysis. This change in mitochondrial architecture was observed both in primary cultures and brown adipose tissue from cold-exposed mice. Mitochondrial uncoupling induced by NE in brown adipocytes was reduced by inhibition of mitochondrial fission through transient Drp1 DN overexpression. Furthermore, forced mitochondrial fragmentation in BA through Mfn2 knock down increased the capacity of exogenous FFAs to increase energy expenditure. These results suggest that, in addition to its ability to stimulate lipolysis, NE induces energy expenditure in BA by promoting mitochondrial fragmentation. Together these data reveal that adrenergically-induced changes to mitochondrial dynamics are required for BA thermogenic activation and for the control of energy expenditure.
Subject(s)
Adipocytes, Brown/physiology , Energy Metabolism , Mitochondrial Dynamics/drug effects , Norepinephrine/metabolism , Adipocytes, Brown/metabolism , Animals , Dynamins/metabolism , GTP Phosphohydrolases/metabolism , Mice , Phosphorylation , Protein Processing, Post-Translational , ProteolysisABSTRACT
The significance of diet-induced thermogenesis (DIT) for metabolic control is still debated. Although obesogenic diets recruit UCP1 and adrenergically inducible thermogenesis, and although the absence of UCP1 may promote the development of obesity, no actual UCP1-related thermogenesis identifiable as diet-induced thermogenesis has to date been unambiguously demonstrated. Examining mice living at thermoneutrality, we have identified a process of facultative (directly elicited by acute eating), adaptive (magnitude develops over weeks on an obesogenic diet), and fully UCP1-dependent thermogenesis. We found no evidence for UCP1-independent diet-induced thermogenesis. The thermogenesis was proportional to the total amount of UCP1 protein in brown adipose tissue and was not dependent on any contribution of UCP1 in brite/beige adipose tissue, since no UCP1 protein was found there under these conditions. Total UCP1 protein amount developed proportionally to total body fat content. The physiological messenger linking obesity level and acute eating to increased thermogenesis is not known. Thus UCP1-dependent diet-induced thermogenesis limits obesity development during exposure to obesogenic diets but does not prevent obesity as such.
Subject(s)
Adaptation, Physiological/genetics , Adaptation, Physiological/physiology , Diet , Thermogenesis/genetics , Thermogenesis/physiology , Uncoupling Protein 1/genetics , Uncoupling Protein 1/physiology , Adipose Tissue, Brown/metabolism , Adipose Tissue, Brown/physiology , Animals , Body Composition , Calorimetry, Indirect , Energy Metabolism/physiology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Obesity/genetics , Obesity/metabolism , Oxygen Consumption/genetics , Oxygen Consumption/physiologyABSTRACT
Cidea is a gene highly expressed in thermogenesis-competent (UCP1-containing) adipose cells, both brown and brite/beige. Here, we initially demonstrate a remarkable adipose-depot specific regulation of Cidea expression. In classical brown fat, Cidea mRNA is expressed continuously and invariably, irrespective of tissue recruitment. However, Cidea protein levels are regulated posttranscriptionally, being conspicuously induced in the thermogenically recruited state. In contrast, in brite fat, Cidea protein levels are regulated at the transcriptional level, and Cidea mRNA and protein levels are proportional to tissue "briteness." Although routinely followed as a thermogenic molecular marker, Cidea function is not clarified. Here, we employed a gain-of-function approach to examine a possible role of Cidea in the regulation of thermogenesis. We utilized transgenic aP2-hCidea mice that overexpress human Cidea in all adipose tissues. We demonstrate that UCP1 activity is markedly suppressed in brown-fat mitochondria isolated from aP2-hCidea mice. However, mitochondrial UCP1 protein levels were identical in wild-type and transgenic mice. This implies a regulatory effect of Cidea on UCP1 activity, but as we demonstrate that Cidea itself is not localized to mitochondria, we propose an indirect inhibitory effect. The Cidea-induced inhibition of UCP1 activity (observed in isolated mitochondria) is physiologically relevant since the mice, through an appropriate homeostatic compensatory mechanism, increased the total amount of UCP1 in the tissue to exactly match the diminished thermogenic capacity of the UCP1 protein and retain unaltered nonshivering thermogenic capacity. Thus, we verified Cidea as being a marker of thermogenesis-competent adipose tissues, but we conclude that Cidea, unexpectedly, functions molecularly as an indirect inhibitor of thermogenesis.
Subject(s)
Adipose Tissue, Brown/metabolism , Apoptosis Regulatory Proteins/genetics , Mitochondria/metabolism , RNA, Messenger/metabolism , Thermogenesis/genetics , Uncoupling Protein 1/genetics , Adipose Tissue, Brown/pathology , Adipose Tissue, White/pathology , Animals , Apoptosis Regulatory Proteins/metabolism , Blotting, Western , Calorimetry, Indirect , Cold Temperature , Humans , Mice , Mice, Transgenic , Oxygen Consumption , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Uncoupling Protein 1/metabolismABSTRACT
Brown and brite/beige adipocytes are attractive therapeutic targets to treat metabolic diseases. To maximally utilize their functional potential, further understanding is required about their identities and their functional differences. Recent studies with ß3-adrenergic receptor knockout mice reported that brite/beige adipocytes, but not classical brown adipocytes, require the ß3-adrenergic receptor for cold-induced transcriptional activation of thermogenic genes. We aimed to further characterize this requirement of the ß3-adrenergic receptor as a functional distinction between classical brown and brite/beige adipocytes. However, when comparing wild-type and ß3-adrenergic receptor knockout mice, we observed no differences in cold-induced thermogenic gene expression (Ucp1, Pgc1a, Dio2, and Cidea) in brown or white (brite/beige) adipose tissues. Irrespective of the duration of the cold exposure or the sex of the mice, we observed no effect of the absence of the ß3-adrenergic receptor. Experiments with the ß3-adrenergic receptor agonist CL-316,243 verified the functional absence of ß3-adrenergic signaling in these knockout mice. The ß3-adrenergic receptor knockout model in the present study was maintained on a FVB/N background, whereas earlier reports used C57BL/6 and 129Sv mice. Thus our data imply background-dependent differences in adrenergic signaling mechanisms in response to cold exposure. Nonetheless, the present data indicate that the ß3-adrenergic receptor is dispensable for cold-induced transcriptional activation in both classical brown and, as opposed to earlier studies, brite/beige cells.
Subject(s)
Adipogenesis , Adipose Tissue, Beige/metabolism , Adipose Tissue, Brown/metabolism , Cold-Shock Response , Gene Expression Regulation , Intra-Abdominal Fat/metabolism , Receptors, Adrenergic, beta-3/metabolism , Adipogenesis/drug effects , Adipose Tissue, Beige/cytology , Adipose Tissue, Beige/drug effects , Adipose Tissue, Brown/cytology , Adipose Tissue, Brown/drug effects , Adrenergic beta-3 Receptor Agonists/pharmacology , Animals , Cold-Shock Response/drug effects , Dioxoles/pharmacology , Female , Gene Expression Regulation/drug effects , Intra-Abdominal Fat/cytology , Intra-Abdominal Fat/drug effects , Male , Mice , Mice, Knockout , RNA, Messenger/metabolism , Receptors, Adrenergic, beta-1/genetics , Receptors, Adrenergic, beta-1/metabolism , Receptors, Adrenergic, beta-3/chemistry , Receptors, Adrenergic, beta-3/genetics , Reproducibility of Results , Signal Transduction/drug effects , Species Specificity , Time FactorsABSTRACT
The development of obesity may be aggravated if obesity itself insulates against heat loss and thus diminishes the amount of food burnt for body temperature control. This would be particularly important under normal laboratory conditions where mice experience a chronic cold stress (at ≈20°C). We used Scholander plots (energy expenditure plotted against ambient temperature) to examine the insulation (thermal conductance) of mice, defined as the inverse of the slope of the Scholander curve at subthermoneutral temperatures. We verified the method by demonstrating that shaved mice possessed only half the insulation of nonshaved mice. We examined a series of obesity models [mice fed high-fat diets and kept at different temperatures, classical diet-induced obese mice, ob/ob mice, and obesity-prone (C57BL/6) vs. obesity-resistant (129S) mice]. We found that neither acclimation temperature nor any kind or degree of obesity affected the thermal insulation of the mice when analyzed at the whole mouse level or as energy expenditure per lean weight. Calculation per body weight erroneously implied increased insulation in obese mice. We conclude that, in contrast to what would be expected, obesity of any kind does not increase thermal insulation in mice, and therefore, it does not in itself aggravate the development of obesity. It may be discussed as to what degree of effect excess adipose tissue has on insulation in humans and especially whether significant metabolic effects are associated with insulation in humans.
Subject(s)
Acclimatization/physiology , Body Temperature Regulation , Cold Temperature , Energy Metabolism/physiology , Obesity , Thermal Conductivity , Animals , Body Composition , Calorimetry, Indirect , Diet, High-Fat , Magnetic Resonance Imaging , Male , Mice , Mice, 129 Strain , Mice, Inbred C57BL , Mice, ObeseABSTRACT
The metabolically inert perfluorinated fatty acids perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) can display fatty acid-like activity in biological systems. The uncoupling protein 1 (UCP1) in brown adipose tissue is physiologically (re)activated by fatty acids, including octanoate. This leads to bioenergetically uncoupled energy dissipation (heat production, thermogenesis). We have examined here the possibility that PFOA/PFOS can directly (re)activate UCP1 in isolated mouse brown-fat mitochondria. In wild-type brown-fat mitochondria, PFOS and PFOA overcame GDP-inhibited thermogenesis, leading to increased oxygen consumption and dissipated membrane potential. The absence of this effect in brown-fat mitochondria from UCP1-ablated mice indicated that it occurred through activation of UCP1. A competitive type of inhibition by increased GDP concentrations indicated interaction with the same mechanistic site as that utilized by fatty acids. No effect was observed in heart mitochondria, i.e., in mitochondria without UCP1. The stimulatory effect of PFOA/PFOS was not secondary to non-specific mitochondrial membrane permeabilization or to ROS production. Thus, metabolic effects of perfluorinated fatty acids could include direct brown adipose tissue (UCP1) activation. The possibility that this may lead to unwarranted extra heat production and thus extra utilization of food resources, leading to decreased fitness in mammalian wildlife, is discussed, as well as possible negative effects in humans. However, a possibility to utilize PFOA-/PFOS-like substances for activating UCP1 therapeutically in obesity-prone humans may also be envisaged.
Subject(s)
Adipocytes, Brown/drug effects , Adipose Tissue, Brown/drug effects , Alkanesulfonic Acids/toxicity , Caprylates/toxicity , Energy Metabolism/drug effects , Fluorocarbons/toxicity , Mitochondria/drug effects , Uncoupling Protein 1/metabolism , Adipocytes, Brown/metabolism , Adipose Tissue, Brown/metabolism , Animals , Dose-Response Relationship, Drug , Guanosine Diphosphate/metabolism , Hydrogen Peroxide/metabolism , Membrane Potential, Mitochondrial/drug effects , Mice, Inbred C57BL , Mice, Knockout , Mitochondria/metabolism , Mitochondria, Heart/drug effects , Mitochondria, Heart/metabolism , Mitochondrial Swelling/drug effects , Oxygen Consumption/drug effects , Thermogenesis/drug effects , Time Factors , Uncoupling Protein 1/geneticsABSTRACT
Based on results from a signal sequence trap, we investigated chemerin gene expression in brown adipose tissue. Male NMRI mice were exposed to 30, 22 or 4 °C for 3 weeks, or were fed control (chow) diet, cafeteria diet or high-fat diet at thermoneutrality for the same time. In brown adipose tissue, cold acclimation strongly diminished chemerin gene expression, whereas obesogenic diets augmented expression. Qualitatively, changes in expression were paralleled in brite/beige adipose tissues (e.g. inguinal), whereas white adipose tissue (epididymal) and muscle did not react to these cues. Changes in tissue expression were not directly paralleled by alterations in plasma levels. Both these intact animal studies and brown adipocyte cell culture studies indicated that the gene expression regulation was not congruent with a sympathetic/adrenergic control. The data are discussed in relation to suggested endocrine, paracrine and autocrine effects of chemerin.
Subject(s)
Acclimatization/genetics , Adipose Tissue, Brown/metabolism , Adipose Tissue, White/metabolism , Cold Temperature , Gene Expression Regulation , Obesity/genetics , Acclimatization/drug effects , Adipocytes, Brown/drug effects , Adipocytes, Brown/metabolism , Adipose Tissue, Brown/drug effects , Adipose Tissue, White/drug effects , Animals , Cells, Cultured , Chemokines , Chemotactic Factors/blood , Chemotactic Factors/genetics , Diet, High-Fat , Gene Expression Profiling , Gene Expression Regulation/drug effects , Intercellular Signaling Peptides and Proteins/blood , Intercellular Signaling Peptides and Proteins/genetics , Ion Channels/metabolism , Male , Mice , Mitochondrial Proteins/metabolism , Norepinephrine/pharmacology , RNA, Messenger/genetics , RNA, Messenger/metabolism , Uncoupling Protein 1 , Weight Gain/drug effects , Weight Gain/geneticsABSTRACT
Whether active UCP1 can reduce ROS production in brown-fat mitochondria is presently not settled. The issue is of principal significance, as it can be seen as a proof- or disproof-of-principle concerning the ability of any protein to diminish ROS production through membrane depolarization. We therefore undertook a comprehensive investigation of the significance of UCP1 for ROS production, by comparing the ROS production in brown-fat mitochondria isolated from wildtype mice (that display membrane depolarization) or from UCP1(-/-) mice (with a high membrane potential). We tested the significance of UCP1 for glycerol-3-phosphate-supported ROS production by three methods (fluorescent dihydroethidium and the ESR probe PHH for superoxide, and fluorescent Amplex Red for hydrogen peroxide), and followed ROS production also with succinate, acyl-CoA or pyruvate as substrate. We studied the effects of the reverse electron flow inhibitor rotenone, the UCP1 activity inhibitor GDP, and the uncoupler FCCP. We also examined the effect of a physiologically induced increase in UCP1 amount. We noted GDP effects that were not UCP1-related. We conclude that only ROS production supported by exogenously added succinate was affected by the presence of active UCP1; ROS production supported by any other tested substrate (including endogenously generated succinate) was unaffected. This conclusion indicates that UCP1 is not involved in control of ROS production in brown-fat mitochondria. Extrapolation of these data to other tissues would imply that membrane depolarization may not necessarily decrease physiologically relevant ROS production. This article is a part of a Special Issue entitled: 18th European Bioenergetics Conference (Biochim. Biophys. Acta, Volume 1837, Issue 7, July 2014).
Subject(s)
Adipose Tissue, Brown/metabolism , Ion Channels/metabolism , Mitochondria/metabolism , Mitochondrial Proteins/metabolism , Reactive Oxygen Species/metabolism , Animals , Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone/pharmacology , Cold Temperature , Electron Spin Resonance Spectroscopy , Glycerophosphates/pharmacology , Guanosine Diphosphate/pharmacology , Hydrogen Peroxide/metabolism , Immunoblotting , Ion Channels/genetics , Male , Membrane Potential, Mitochondrial/drug effects , Mice, Inbred C57BL , Mice, Knockout , Mitochondria/drug effects , Mitochondria/physiology , Mitochondrial Proteins/genetics , Oxygen Consumption/drug effects , Proton Ionophores/pharmacology , Pyruvic Acid/pharmacology , Succinic Acid/pharmacology , Superoxides/metabolism , Uncoupling Protein 1ABSTRACT
Brown adipose tissue (BAT) thermogenesis relies on blood flow to be supplied with nutrients and oxygen and for the distribution of the generated heat to the rest of the body. Therefore, it is fundamental to understand the mechanisms by which blood flow is regulated and its relation to thermogenesis. Here, we present high-resolution laser-Doppler imaging (HR-LDR) as a novel method for noninvasive in vivo measurement of BAT blood flow in mice. Using HR-LDR, we found that norepinephrine stimulation increases BAT blood flow in a dose-dependent manner and that this response is profoundly modulated by environmental temperature acclimation. Surprisingly, we found that mice lacking uncoupling protein 1 (UCP1) have fully preserved BAT blood flow response to norepinephrine despite failing to perform thermogenesis. BAT blood flow was not directly correlated to systemic glycemia, but glucose injections could transiently increase tissue perfusion. Inguinal white adipose tissue, also known as a brite/beige adipose tissue, was also sensitive to cold acclimation and similarly increased blood flow in response to norepinephrine. In conclusion, using a novel noninvasive method to detect BAT perfusion, we demonstrate that adrenergically stimulated BAT blood flow is qualitatively and quantitatively fully independent of thermogenesis, and therefore, it is not a reliable parameter for the estimation of BAT activation and heat generation.
Subject(s)
Adipose Tissue, Brown/drug effects , Norepinephrine/pharmacology , Regional Blood Flow/drug effects , Thermogenesis/physiology , Acclimatization/drug effects , Adipose Tissue, Brown/blood supply , Adipose Tissue, Brown/metabolism , Adrenergic Agents/pharmacology , Animals , Body Composition/drug effects , Body Composition/physiology , Female , Hemodynamics/drug effects , Laser-Doppler Flowmetry , Male , Mice , Mice, Inbred C57BL , Mice, KnockoutABSTRACT
The nature of brown adipose tissue in humans is presently debated: whether it is classical brown or of brite/beige nature. The dissimilar developmental origins and proposed distinct functions of the brown and brite/beige tissues make it essential to ascertain the identity of human depots with the perspective of recruiting and activating them for the treatment of obesity and type 2 diabetes. For identification of the tissues, a number of marker genes have been proposed, but the validity of the markers has not been well documented. We used established brown (interscapular), brite (inguinal), and white (epididymal) mouse adipose tissues and corresponding primary cell cultures as validators and examined the informative value of a series of suggested markers earlier used in the discussion considering the nature of human brown adipose tissue. Most of these markers unexpectedly turned out to be noninformative concerning tissue classification (Car4, Cited1, Ebf3, Eva1, Fbxo31, Fgf21, Lhx8, Hoxc8, and Hoxc9). Only Zic1 (brown), Cd137, Epsti1, Tbx1, Tmem26 (brite), and Tcf21 (white) proved to be informative in these three tissues. However, the expression of the brite markers was not maintained in cell culture. In a more extensive set of adipose depots, these validated markers provide new information about depot identity. Principal component analysis supported our single-gene conclusions. Furthermore, Zic1, Hoxc8, Hoxc9, and Tcf21 displayed anteroposterior expression patterns, indicating a relationship between anatomic localization and adipose tissue identity (and possibly function). Together, the observed expression patterns of these validated marker genes necessitates reconsideration of adipose depot identity in mice and humans.
Subject(s)
Adipose Tissue, Brown/metabolism , Adipogenesis/genetics , Adipose Tissue, White/metabolism , Animals , Animals, Outbred Strains , Biomarkers/analysis , Biomarkers/metabolism , Cell Differentiation/genetics , Cells, Cultured , Male , Mice , Organ Specificity/genetics , TranscriptomeABSTRACT
Because of the possible role of brown adipose tissue and UCP1 in metabolic regulation, even in adult humans, there is presently considerable interest in quantifying, from in-vitro data, the thermogenic capacities of brown and brite/beige adipose tissues. An important issue is therefore to establish which parameters are the most adequate for this. A particularly important issue is the relevance of UCP1 mRNA levels as estimates of the degree of recruitment and of the thermogenic capacity resulting from differences in physiological conditions and from experimental manipulations. By solely following UCP1 mRNA levels in brown adipose tissue, the conclusion would be made that the tissue's highest activation occurs after only 6h in the cold and then successively decreases to being only some 50% elevated after 1month in the cold. However, measurement of total UCP1 protein levels per depot ("mouse") reveals that the maximal thermogenic capacity estimated in this way is reached first after 1month but represents an approx. 10-fold increase in thermogenic capacity. Since this in-vitro measure correlates quantitatively and temporally with the acquisition of nonshivering thermogenesis, this must be considered the most physiologically relevant parameter. Similarly, observations that cold acclimation barely increases UCP1 mRNA levels in classical brown adipose tissue but leads to a 200-fold increase in UCP1 mRNA levels in brite/beige adipose tissue depots may overemphasise the physiological significance of these depots, as the high fold-increases are due to very low initial levels, and the UCP1 mRNA levels reached are at least an order of magnitude lower than in brown adipose tissue; furthermore, based on total UCP1 protein amounts, the brite/beige depots attain only about 10% of the thermogenic capacity of the classical brown adipose tissue depots. Consequently, inadequate conclusions may be reached if UCP1 mRNA levels are used as a proxy for the metabolic significance of recruited versus non-recruited brown adipose tissue and for estimating the metabolic significance of brown versus brite/beige adipose tissues. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.