UCP1-mediated Thermogenesis Research Articles

7624 m6A mRNA Methylation in Brown Adipose Tissue Regulates Systemic Insulin Sensitivity via an Inter-Organ Prostaglandin Signaling Axis

Abstract Disclosure: L. Xiao: None. D. F De Jesus: None. C. Ju: None. J. Wei: None. J. Hu: None. A. DiStefano-Forti: None. T. Tsuji: None. C. Cero: None. V. Männistö: None. S.M. Manninen: None. S. Wei: None. O. Ijaduola: None. M. Blüher: Consulting Fee; Self; Amgen Inc, AstraZeneca, Bayer, Inc., Boehringer Ingelheim, Lilly USA, LLC, Novo Nordisk, Pfizer, Inc., Sanofi. A.M. Cypess: None. J. Pihlajamäki: None. Y. Tseng: None. C. He: Advisory Board Member; Self; Accent Therapeutics. R.N. Kulkarni: Advisory Board Member; Self; Novo Nordisk, Biomea, Inversago, REDD. Brown adipose tissue (BAT) has the capacity to regulate systemic metabolism through the secretion of “Batokines” including signaling lipids. N6-methyladenosine (m6A) is the most prevalent and abundant post-transcriptional mRNA modification and has been reported to regulate BAT adipogenesis and energy expenditure. Here, we demonstrate that the absence of the m6A writer, methyltransferase-like 14 (METTL14), modifies the BAT secretome to initiate inter-organ communication to improve systemic insulin sensitivity. Importantly, these phenotypes are independent of UCP1-mediated energy expenditure and thermogenesis. Using lipidomics, we identified prostaglandin E2 (PGE2) and prostaglandin F2a (PGF2a) as M14KO-BAT-secreted insulin sensitizers. Notably, circulatory PGE2 and PGF2a levels are inversely correlated with insulin sensitivity in humans. Furthermore, in vivo administration of PGE2 and PGF2a in high-fat diet-induced insulin-resistant obese mice recapitulates the phenotypes of Mettl14-deficient animals. PGE2 or PGF2a improves insulin signaling by suppressing the expression of specific AKT phosphatases. Mechanistically, METTL14-mediated m6A installation promotes decay of transcripts encoding prostaglandin synthases and their regulators in human and mouse brown adipocytes in a YTHDF2/3-dependent manner. Collectively, these findings reveal a novel biological mechanism in the m6A-dependent regulation of the BAT secretome in modulating systemic insulin sensitivity in both mice and humans. Presentation: 6/1/2024

Sphingomyelin is involved in regulating UCP1-mediated nonshivering thermogenesis

Adipogenesis is one of the major mechanisms for adipose tissue expansion, during which spindle-shaped mesenchymal stem cells commit to the fate of adipocyte precursors and differentiate into round-shaped fat-laden adipocytes. Here, we investigated the lipidomic profile dynamics of ex vivo-differentiated brown and white adipocytes derived from the stromal vascular fractions of interscapular brown (iBAT) and inguinal white adipose tissues. We showed that sphingomyelin was specifically enriched in terminally differentiated brown adipocytes, but not white adipocytes. In line with this, freshly isolated adipocytes of iBAT showed higher sphingomyelin content than those of inguinal white adipose tissue. Upon cold exposure, sphingomyelin abundance in iBAT gradually decreased in parallel with reduced sphingomyelin synthase 1 protein levels. Cold-exposed animals treated with an inhibitor of sphingomyelin hydrolases failed to maintain core body temperature and showed reduced oxygen consumption and iBAT UCP1 levels. Conversely, blockade of sphingomyelin synthetic enzymes resulted in enhanced nonshivering thermogenesis, reflected by elevated body temperature and UCP1 levels. Taken together, our results uncovered a relation between sphingomyelin abundance and fine-tuning of UCP1-mediated nonshivering thermogenesis.

UCP1 and CKB are parallel players in BAT

It is generally believed that the contributions of the UCP1-independent thermogenic pathways are secondary to UCP1-mediated thermogenesis in BAT. Now, Rahbani etal. demonstrate invivo that adaptive thermogenesis in brown adipose tissue is regulated by UCP1 and CKB in parallel.

Chloroquine attenuates diet-induced obesity and glucose intolerance through a mechanism that might involve FGF-21, but not UCP-1-mediated thermogenesis and inhibition of adipocyte autophagy

Chloroquine diphosphate (CQ), a weak base used to inhibit autophagic flux and treat malaria and rheumatoid diseases, has been shown, through unknown mechanisms, to improve glucose and lipid homeostasis in patients and rodents. We investigate herein the molecular mechanisms underlying these CQ beneficial metabolic actions in diet-induced obese mice. For this, C57BL6/J mice fed with either a chow or a high-fat diet (HFD) and uncoupling protein 1 (UCP-1) KO and adipocyte Atg7-deficient mice fed with a HFD were treated or not with CQ (60 mg/kg of body weight/day) during 8 weeks and evaluated for body weight, adiposity, glucose homeostasis and brown and white adipose tissues (BAT and WAT) UCP-1 content. CQ reduced body weight gain and adipose tissue and liver masses in mice fed with a HFD, without altering food intake, oxygen consumption, respiratory exchange ratio, spontaneous motor activity and feces caloric content. CQ attenuated the insulin intolerance, hyperglycemia, hyperinsulinemia, hypertriglyceridemia and hypercholesterolemia induced by HFD intake, such effects that were associated with increases in serum and liver fibroblast growth factor 21 (FGF-21) and BAT and WAT UCP-1 content. Interestingly, CQ beneficial metabolic actions of reducing body weight and adiposity and improving glucose homeostasis were preserved in HFD-fed UCP-1 KO and adipocyte Atg7 deficient mice. CQ reduces body weight gain and adiposity and improves glucose homeostasis in diet-induced obese mice through mechanisms that might involve FGF-21, but not UCP1-mediated nonshivering thermogenesis or inhibition of adipocyte autophagy.

ISRIB alleviates aging-associated brown fat UCP1 translational repression and thermogenic deficiency

Upon cold exposure, aged people with lower metabolic rate cannot rapidly increase the higher levels of heat production, and are seriously threatened by the hypothermia, extensive cold stress responses and risk of mortality. Here, we show that brown fat thermogenic activity is obviously deficient in aged mice, associating with reduction of UCP1 expression and inhibition of its mRNA translation. As we considered, aging aggravates brown fat oxidative stress and activates the integrated stress response (ISR), inducing the phosphorylation of eIF2α to block the global mRNA translation. Therefore, small-molecule ISR inhibitor (ISRIB) treatment attenuates the higher level of eIF2α phosphorylation, restores the repression of Ucp1 mRNA translation and improves UCP1-mediated thermogenic function to defend cold stress in aged mice. Furthermore, ISRIB treatment increases the relative lower metabolic rates, and alleviates glucose intolerance and insulin resistance in aged mice. Thus, we have uncovered a promising drug that reverses the aged-related the deficiency of UCP1-mediated thermogenesis to combat cold stress and associated metabolic diseases.

CDK4/6 are necessary for UCP1-mediated thermogenesis of white adipose tissue

AimsIn white adipose tissue (WAT) the cell cycle regulators CDK4 and CDK6 (CDK4/6) promote adipogenesis and maintain the adipocyte mature state. Here we aimed to investigate their role in the Ucp1-mediated thermogenesis of WAT depots and in the biogenesis of beige adipocytes. Main methodsWe treated mice with the CDK4/6 inhibitor palbociclib at room temperature (RT) or cold and analyzed thermogenic markers in the epididymal (abdominal) and inguinal (subcutaneous) WAT depots. We also assessed the effect of in vivo palbociclib-treatment on the percentage of beige precursors in the stroma vascular fraction (SVF), and on its beige adipogenic potential. Finally, we treated SVFs and mature adipocytes from WAT depots with palbociclib in vitro to study the role of CDK4/6 in beige adipocytes biogenesis. Key findingsIn vivo CDK4/6 inhibition downregulated thermogenesis at RT and impaired cold-induced browning of both WAT depots. It also reduced the percentage of beige precursors and beige adipogenic potential of the SVF upon differentiation. A similar result was observed with direct CDK4/6 inhibition in the SVF of control mice in vitro. Importantly, CDK4/6 inhibition also downregulated the thermogenic program of beige differentiated- and depots-derived adipocytes. SignificanceCDK4/6 modulate Ucp1-mediated thermogenesis of WAT depots in basal and cold-stressing conditions controlling beige adipocytes biogenesis by adipogenesis and transdifferentiation. This shows a pivotal role of CDK4/6 in WAT browning that could be applied to fight obesity or browning-associated hypermetabolic conditions such as cancer cachexia.

Transdermal Delivery of Succinate Accelerates Energy Dissipation of Brown Adipocytes to Reduce Remote Fat Accumulation.

Weight loss by increasing energy consumption of thermogenic adipocytes to overcome obesity remains a challenge. Herein, we established a transdermal device that was based on the local and temporarily controlled delivery of succinate (SC), a tricarboxylic acid cycle metabolic intermediate to stimulate the thermogenesis pathway of uncoupling protein 1 (UCP1) and accelerate energy dissipation of brown adipose tissue (BAT) under the dorsal interscapular skin, further initiating the consumption of fatty acids by systemic metabolism. SC microneedle patches significantly suppressed weight gain and fat accumulation of remote organs, including liver and peripheral white adipose tissue (WAT) in high-fat diet-induced obese mice. mRNA expression levels of Ucp1 in BAT and other browning markers in WAT were significantly elevated in the mice that were treated with SC microneedle. Thus, the energy dissipation of BAT using UCP1-mediated thermogenesis accelerated by the transdermal delivery of SC may become a potential and effective strategy for preventing obesity.

FOXP4 differentially controls cold-induced beige adipocyte differentiation and thermogenesis.

Beige adipocytes have a discrete developmental origin and possess notable plasticity in their thermogenic capacity in response to various environmental cues, but the transcriptional machinery controlling beige adipocyte development and thermogenesis remains largely unknown. By analyzing beige adipocyte-specific knockout mice, we identified a transcription factor, forkhead box P4 (FOXP4), that differentially governs beige adipocyte differentiation and activation. Depletion of Foxp4 in progenitor cells impaired beige cell early differentiation. However, we observed that ablation of Foxp4 in differentiated adipocytes profoundly potentiated their thermogenesis capacity upon cold exposure. Of note, the outcome of Foxp4 deficiency on UCP1-mediated thermogenesis was confined to beige adipocytes, rather than to brown adipocytes. Taken together, we suggest that FOXP4 primes beige adipocyte early differentiation, but attenuates their activation by potent transcriptional repression of the thermogenic program.

The nonshivering thermogenesis of brown adipose tissue and fat mobilization of striped hamsters exposed to cycles of cold and warm temperatures

The adaptive adjustments in the capacity for metabolic thermogenesis are critical for the survival in many small mammals that are acclimated to cold winter conditions. In this study the striped hamsters (Cricetulus barabensis) were subjected to repeated cycles of cold (5°C) and warm (23°C) temperatures. Resting metabolic rate (RMR), nonshivering thermogenesis (NST) and energy intake, as well as the expression of uncoupling protein 1 (UCP1) of brown adipose tissue (BAT) and serum thyroid hormone levels were measured. Both RMR and NST were significantly increased in striped hamsters subjected to repeated cycles of short-term cold (5°C, 72 h) – warm (23°C, 4 days) temperatures compared to that of the hamsters consistently kept at 23°C. In these cycled hamsters, BAT UCP1 expression was significantly upregulated, whereas serum T3 and T4 concentration did not change significantly. Moreover, gross energy intake was considerably increased during both cold exposure and warm phases, whereas fat deposition was significantly decreased in these cycled hamsters compared to those consistently kept at 23°C. This indicates that small mammals may both increase energy intake and mobilize fat depots to cope with frequent cold exposure. Thyroid hormone may be not involved in the BAT UCP1-mediated thermogenesis and fat mobilization.

Delta-Tocopherol Suppresses the Dysfunction of Thermogenesis due to Inflammatory Stimulation in Brown Adipocytes.

Brown adipose tissue (BAT) functions as a radiator for thermogenesis and helps maintain body temperature and regulate metabolism. Inflammatory signals have been reported to inhibit PGC-1α activation and UCP1-mediated thermogenesis in brown adipocytes. Inflammation is mainly caused by cell hypertrophy and macrophage invasion due to obesity, and invading macrophages secrete inflammatory cytokines, including TNF-α, IL1β, and IL6, which suppress the thermogenesis in BAT. Tocopherol is a lipid-soluble vitamin with anti-inflammatory effects is expected to contribute to the suppression of inflammation in adipose tissue. In this study, we investigated the protective effect of tocopherols, α-tocopherol (α-toc) and δ-tocopherol (δ-toc), against brown adipocyte inflammation and thermogenesis dysfunction.Inflammatory stimulation by TNF-α, a major inflammatory cytokine, significantly decreased the protein expression levels of UCP1 and PGC-1α in rat primary brown adipocytes. The pre-incubation of α-toc or δ-toc significantly suppressed the decrease in UCP1 and PGC-1α expression and lipid accumulation. Additionally, α-toc and δ-toc suppress the induction of ERK1/2 gene expression, implying that an antiinflammatory effect is involved in this protective effect. We fed mice a high-fat diet for 16 weeks and investigated the effects of α-toc and δ-toc in the diet. Intake of α-toc and δ-toc significantly suppressed weight gain and hypertrophy of brown adipocytes. Our results suggest that α-toc and δ-toc suppress the dysfunction of thermogenesis in brown adipocytes due to inflammation and contribute to the treatment of obesity and obesity-related metabolic diseases.

Abstract 10267: Thermogenic Modulation of Perivascular Adipose Tissue Ameliorates Cardioautonomic Deterioration in Prediabetes

Introduction: Cardiac autonomic neuropathy, a risk factor of cardiovascular mortality, is a common manifestation of prediabetes. Evidence points to perivascular adipose tissue inflammation as a quintessential instigator of cardiovascular dysfunction in metabolic impairment. Interventions tailored to ameliorate such subtle cardiovascular involvement have not been forthcoming. Data emerging from our laboratory implicate alteration of adipocyte mitochondrial bioenergetics, particularly an upregulation of uncoupling protein 1 (UCP1) expression and subsequent augmentation of adipose tissue hypoxia, as a potential culprit driving localized adipose inflammation. Hypothesis: Inhibition of UCP1-mediated thermogenesis or activation of the alternative thermogenic pathway, futile creatine cycling, through supplementation with phosphate or creatine monohydrate, respectively, may ameliorate the inflammatory phenotype observed in non-obese prediabetic rats. Methods: A non-obese prediabetic rat model, developed in our laboratory was used. This phenotype is evoked by 12 weeks of hypercaloric feeding causing localized perivascular inflammation in absence of systemic markers of inflammation. Cardioautonomic function was assessed by invasive hemodynamics. Localized adipose tissue inflammation and macrophage polarization were examined. Results: UCP1 inhibition by phosphate supplementation reversed the blunted parasympathetic baroreflex sensitivity observed in prediabetic rats. This was associated with the alleviation of perivascular adipose tissue hypoxia, inflammation, and altered macrophage polarization. These changes were accompanied by normalization of metabolic efficiency that increased in prediabetic rats due to UCP1 upregulation. Similar functional effects were observed after creatine supplementation without changes in metabolic efficiency. Conclusions: Bypassing UCP1-mediated thermogenesis upregulated by increased caloric intake alleviates cardioautonomic deterioration triggered by perivascular inflammation. This is achieved by UCP1 inhibition with a potential risk of increased metabolic efficiency and weight gain, or by activation of the alternative thermogenic pathway of creatine cycling.

Isothermal microcalorimetry measures UCP1-mediated thermogenesis in mature brite adipocytes

The activation of thermogenesis in adipose tissue has emerged as an important target for the development of novel anti-obesity therapies. Using multi-well isothermal microcalorimetry, we have demonstrated that mature murine brown and brite adipocytes produce quantifiable heat upon β3-AR stimulation, independently of any anaerobic mechanisms. Additionally, in brite adipocytes lacking UCP1 protein, β3-AR stimulation still induces heat production, albeit to a much lower extent than in their wildtype counterparts, suggesting that UCP1 is an essential component of adrenergic induced thermogenesis in murine brite adipocytes exvivo. Similarly, we could observe an increase in heat production in human-derived adipocytes (hMADS) upon β-AR stimulation. Collectively, these results establish the use of isothermal microcalorimetry as a sensitive and accurate technique for measuring thermogenic responses in intact mature brite adipocytes from murine and human origin.

Overexpression of translationally controlled tumor protein ameliorates metabolic imbalance and increases energy expenditure in mice

Background/ObjectivesTranslationally controlled tumor protein (TCTP) exhibits numerous biological functions. It has been shown to be involved in the regulation of glucose. However, its specific role in metabolism has not yet been clearly elucidated. Here, we aimed to assess the effect of TCTP overexpression on metabolic tissues and systemic energy metabolism.Subjects/MethodsWe investigated whether TCTP can ameliorate the metabolic imbalance that causes obesity using TCTP-overexpressing transgenic (TCTP TG) mice. The mice were subjected to biochemical, morphological, physiological and protein expression studies to define the role of TCTP in metabolic regulation in response to normal chow diet (NCD) compared to high-fat diet (HFD) conditions, and cold environment.ResultsWe found that TCTP TG mice show improved metabolic homeostasis under both of NCD and HFD conditions with simultaneous enhancements in glucose tolerance and insulin sensitivity. In particular, we found coincident increases in energy expenditure with significant upregulation of uncoupling protein 1 (UCP1) in the brown adipose tissue (BAT). Moreover, TCTP overexpressing mice exhibit significantly enhanced adaptive thermogenesis of BAT in response to cold exposure.ConclusionsOverexpression of TCTP ameliorated systemic metabolic homeostasis by stimulating UCP1-mediated thermogenesis in the BAT. This suggests that TCTP may function as a modulator of energy expenditure. This study suggests TCTP may serve as a therapeutic target for obesity and obesity-associated metabolic disorders including type 2 diabetes.

AIDA directly connects sympathetic innervation to adaptive thermogenesis by UCP1.

The sympathetic nervous system-catecholamine-uncoupling protein 1 (UCP1) axis plays an essential role in non-shivering adaptive thermogenesis. However, whether there exists a direct effector that physically connects catecholamine signalling to UCP1 in response to acute cold is unknown. Here we report that outer mitochondrial membrane-located AIDA is phosphorylated at S161 by the catecholamine-activated protein kinase A (PKA). Phosphorylated AIDA translocates to the intermembrane space, where it binds to and activates the uncoupling activity of UCP1 by promoting cysteine oxidation of UCP1. Adipocyte-specific depletion of AIDA abrogates UCP1-dependent thermogenesis, resulting in hypothermia during acute cold exposure. Re-expression of S161A-AIDA, unlike wild-type AIDA, fails to restore the acute cold response in Aida-knockout mice. The PKA-AIDA-UCP1 axis is highly conserved in mammals, including hibernators. Denervation of the sympathetic postganglionic fibres abolishes cold-induced AIDA-dependent thermogenesis. These findings uncover a direct mechanistic link between sympathetic input and UCP1-mediated adaptive thermogenesis.

Alternative Polyadenylation and Differential Regulation of Ucp1: Implications for Brown Adipose Tissue Thermogenesis Across Species.

Brown adipose tissue (BAT) is a thermogenic organ owing to its unique expression of uncoupling protein 1 (UCP1), which is a proton channel in the inner mitochondrial membrane used to dissipate the proton gradient and uncouple the electron transport chain to generate heat instead of adenosine triphosphate. The discovery of metabolically active BAT in human adults, especially in lean people after cold exposure, has provoked the “thermogenic anti-obesity” idea to battle weight gain. Because BAT can expend energy through UCP1-mediated thermogenesis, the molecular mechanisms regulating UCP1 expression have been extensively investigated at both transcriptional and posttranscriptional levels. Of note, the 3′-untranslated region (3′-UTR) of Ucp1 mRNA is differentially processed between mice and humans that quantitatively affects UCP1 synthesis and thermogenesis. Here, we summarize the regulatory mechanisms underlying UCP1 expression, report the number of poly(A) signals identified or predicted in Ucp1 genes across species, and discuss the potential and caution in targeting UCP1 for enhancing thermogenesis and metabolic fitness.

Prolonged β2-adrenergic agonist treatment improves glucose homeostasis in diet-induced obese UCP1-/- mice.

Prolonged supplementation with the β2-agonist clenbuterol improves glucose homeostasis in diabetic rodents, likely via β2-adrenoceptor (β2-AR)-mediated effects in the skeletal muscle and liver. However, since rodents have, in contrast to-especially diabetic-humans, substantial quantities of brown adipose tissue (BAT) and clenbuterol has affinity to β1- and β3-ARs, the contribution of BAT to these improvements is unclear. Therefore, we investigated clenbuterol-mediated improvements in glucose homeostasis in uncoupling protein 1-deficient (UCP1-/-) mice, lacking thermogenic BAT, versus wild-type (WT) mice. Anesthetized WT and UCP1-/- C57Bl/6 mice were injected with saline or clenbuterol and whole body oxygen consumption was measured. Furthermore, male WT and UCP1-/- C57Bl/6 mice were subjected to 17-wk of chow feeding, high-fat feeding, or high-fat feeding with clenbuterol treatment between weeks 13 and 17. Body composition was measured weekly with MRI. Oral glucose tolerance and insulin tolerance tests were performed in week 15 and 17, respectively. Clenbuterol increased oxygen consumption approximately twofold in WT mice. This increase was blunted in UCP1-/- mice, indicating clenbuterol-mediated activation of BAT thermogenesis. High-fat feeding induced diabetogenic phenotypes in both genotypes. However, low-dose clenbuterol treatment for 2 wk significantly reduced fasting blood glucose by 12.9% in WT and 14.8% in UCP1-/- mice. Clenbuterol treatment improved glucose and insulin tolerance in both genotypes compared with HFD controls and normalized to chow-fed control mice independent of body mass and composition alterations. Clenbuterol improved whole body glucose homeostasis independent of UCP1. Given the low human abundancy of BAT, β2-AR agonist treatment provides a potential novel route for glucose disposal in diabetic humans.NEW & NOTEWORTHY Improvements in whole body glucose homeostasis of rodents upon prolonged β2-adrenergic agonist supplementation could potentially be attributed to UCP1-mediated BAT thermogenesis. Indeed, we show that acute injection with the β2-AR agonist clenbuterol induces BAT activation in mice. However, we also demonstrate that prolonged clenbuterol supplementation robustly improves whole body glucose and insulin tolerance in a similar way in both DIO WT and UCP1-/- mice, indicating that β2-AR agonist supplementation improves whole body glucose homeostasis independent of UCP1-mediated BAT thermogenesis.

Lipid Droplets in Brown Adipose Tissue Are Dispensable for Cold-Induced Thermogenesis

SUMMARYBrown adipocytes store metabolic energy as triglycerides (TGs) in lipid droplets (LDs). Fatty acids released from brown adipocyte LDs by lipolysis are thought to activate and fuel UCP1-mediated thermogenesis. Here, we test this hypothesis by preventing fatty acid storage in murine brown adipocytes through brown adipose tissue (BAT)-specific deletions of the TG synthesis enzymes DGAT1 and DGAT2 (BA-DGAT KO). Despite the absence of TGs in brown adipocytes, BAT is functional, and BA-DGAT-KO mice maintain euthermia during acute or chronic cold exposure. As apparent adaptations to the lack of TG, brown adipocytes of BA-DGAT-KO mice appear to use circulating glucose and fatty acids, and stored glycogen, to fuel thermogenesis. Moreover, BA-DGAT-KO mice are resistant to diet-induced glucose intolerance, likely because of increased glucose disposal by BAT. We conclude that TGs in BAT are dispensable for its contribution to cold-induced thermogenesis, at least when other fuel sources are available.

Brown adipose tissue lipoprotein and glucose disposal is not determined by thermogenesis in uncoupling protein 1-deficient mice

Adaptive thermogenesis is highly dependent on uncoupling protein 1 (UCP1), a protein expressed by thermogenic adipocytes present in brown adipose tissue (BAT) and white adipose tissue (WAT). Thermogenic capacity of human and mouse BAT can be measured by positron emission tomography-computed tomography quantifying the uptake of 18F-fluodeoxyglucose or lipid tracers. BAT activation is typically studied in response to cold exposure or treatment with β-3-adrenergic receptor agonists such as CL316,243 (CL). Currently, it is unknown whether cold-stimulated uptake of glucose or lipid tracers is a good surrogate marker of UCP1-mediated thermogenesis. In metabolic studies using radiolabeled tracers, we found that glucose uptake is increased in mildly cold-activated BAT of Ucp1-/- versus WT mice kept at subthermoneutral temperature. Conversely, lower glucose disposal was detected after full thermogenic activation achieved by sustained cold exposure or CL treatment. In contrast, uptake of lipoprotein-derived fatty acids into chronically activated thermogenic adipose tissues was substantially increased in UCP1-deficient mice. This effect is linked to higher sympathetic tone in adipose tissues of Ucp1-/- mice, as indicated by elevated levels of thermogenic genes in BAT and WAT. Thus, glucose and lipoprotein handling does not necessarily reflect UCP1-dependent thermogenic activity, but especially lipid uptake rather mirrors sympathetic activation of adipose tissues.

UCP1-dependent and UCP1-independent metabolic changes induced by acute cold exposure in brown adipose tissue of mice

BackgroundBrown adipose tissue (BAT) is a site of metabolic thermogenesis mediated by mitochondrial uncoupling protein 1 (UCP1) and represents a target for a therapeutic intervention in obesity. Cold exposure activates UCP1-mediated thermogenesis in BAT and causes drastic changes in glucose, lipid, and amino acid metabolism; however, the relationship between these metabolic changes and UCP1-mediated thermogenesis is not fully understood. MethodsWe conducted metabolomic and GeneChip array analyses of BAT after 4-h exposure to cold temperature (10 °C) in wild-type (WT) and UCP1-KO mice. ResultsCold exposure largely increased metabolites of the glycolysis pathway and lactic acid levels in WT, but not in UCP1-KO, mice, indicating that aerobic glycolysis is enhanced as a consequence of UCP1-mediated thermogenesis. GeneChip array analysis of BAT revealed that there were 2865 genes upregulated by cold exposure in WT mice, and 838 of these were upregulated and 74 were downregulated in UCP1-KO mice. Pathway analysis revealed the enrichment of genes involved in fatty acid (FA) β oxidation and triglyceride (TG) synthesis in both WT and UCP1-KO mice, suggesting that these metabolic pathways were enhanced by cold exposure independently of UCP1-mediated thermogenesis. FA and cholesterol biosynthesis pathways were enhanced only in UCP1-KO mice. Cold exposure also significantly increased the BAT content of proline, tryptophan, and phenylalanine amino acids in both WT and UCP1-KO mice. In WT mice, cold exposure significantly increased glutamine content and enhanced the expression of genes related to glutamine metabolism. Surprisingly, aspartate was almost completely depleted after cold exposure in UCP1-KO mice. Gene expression analysis suggested that aspartate was actively utilized after cold exposure both in WT and UCP1-KO mice, but it was replenished from intracellular N-acetyl-aspartate in WT mice. ConclusionsThese results revealed that cold exposure induces UCP1-mediated thermogenesis-dependent glucose utilization and UCP1-independent active lipid metabolism in BAT. In addition, cold exposure largely affects amino acid metabolism in BAT, especially UCP1-dependently enhances glutamine utilization. These results contribute a comprehensive understanding of UCP1-mediated thermogenesis-dependent and thermogenesis-independent metabolism in BAT.

Disruption of hypoxia-inducible fatty acid binding protein 7 induces beige fat-like differentiation and thermogenesis in breast cancer cells

BackgroundHumans produce heat through non-shivering thermogenesis, a metabolic process that occurs in inducible beige adipocytes expressing uncoupling protein 1 (UCP1). UCP1 dissipates the proton gradient of the mitochondrial inner membrane and converts that energy into heat. It is unclear whether cancer cells can exhibit autonomous thermogenesis. Previously, we found that the knockdown of hypoxia-inducible fatty acid binding protein 7 (FABP7) increased reactive oxygen species (ROS) in breast cancer cells. ROS are known to induce beige adipocyte differentiation.MethodsWe investigated the association of tumor hypoxia, FABP7, and UCP1 across breast cancer patients using METABRIC and TCGA data sets. Furthermore, using a breast cancer cell line, HCC1806, we tested the effect of FABP7 knockdown on cellular physiology including thermogenesis.ResultsWe found a strong mutual exclusivity of FABP7 and UCP1 expression both in METABRIC and in TCGA, indicating major metabolic phenotypic differences. FABP7 was preferentially distributed in poorly differentiated-, estrogen receptor (ER) negative tumors. In contrast, UCP1 was highly expressed in normal ducts and well-differentiated-, ER positive-, less hypoxic tumors. In the cell line-based experiments, UCP1 and its transcriptional regulators were upregulated upon FABP7 knockdown. UCP1 was induced in about 20% of cancer cells, and the effect was increased further in hypoxia. UCP1 depolarized mitochondrial membranes at the site of expression. UCP1 induction was associated with the increase in proton leak, glycolysis, and maximal respiration, mimicking the typical energy profile of beige adipocytes. Most importantly, UCP1 induction elevated cancer cell temperature associated with increased vulnerability to hypoxia and γ-irradiation.ConclusionsWe demonstrated that breast cancer cells can undergo thermogenesis through UCP1 induction. Disrupting FABP7-mediated fatty acid metabolism can unlock UCP1-mediated thermogenesis, potentially making it possible to develop therapies to target thermogenesis. Further study would be warranted to investigate the effect of rise in temperature of cancer cells on patients’ outcomes and the relationship to other metabolic pathways.