Stimulating Energy Expenditure Research Articles

Functionally Separate Populations of Ventromedial Hypothalamic Neurons in Obesity and Diabetes.

The Ventromedial hypothalamic nucleus (VMN) maintains healthy metabolic function through several important roles. Collectively, homeostasis is maintained via intermingled cells within the VMN that raise blood glucose, lower blood glucose, and stimulate energy expenditure when needed. This perspective discusses the defining factors for the VMN cell types that govern distinct functions induced by the VMN, particularly in relation to energy balance and blood glucose levels. Special attention is given to distinct features of VMN cells responsible for these processes. Finally, these topics are reviewed in the context of research funded by the Pathway to Stop Diabetes initiative, highlighting key findings and current unresolved questions for future investigations.

Doublecortin-like knockdown in mice attenuates obesity by stimulating energy expenditure in adipose tissue

Crosstalk between peripheral metabolic organs and the central nervous system is essential for body weight control. At the base of the hypothalamus, β-tanycytes surround the portal capillaries and function as gatekeepers to facilitate transfer of substances from the circulation into the cerebrospinal fluid and vice versa. Here, we investigated the role of the neuroplasticity gene doublecortin-like (DCL), highly expressed by β-tanycytes, in body weight control and whole-body energy metabolism. We demonstrated that DCL-knockdown through a doxycycline-inducible shRNA expression system prevents body weight gain by reducing adiposity in mice. DCL-knockdown slightly increased whole-body energy expenditure possibly as a result of elevated circulating thyroid hormones. In white adipose tissue (WAT) triglyceride uptake was increased while the average adipocyte cell size was reduced. At histological level we observed clear signs of browning, and thus increased thermogenesis in WAT. We found no indications for stimulated thermogenesis in brown adipose tissue (BAT). Altogether, we demonstrate an important, though subtle, role of tanycytic DCL in body weight control through regulation of energy expenditure, and specifically WAT browning. Elucidating mechanisms underlying the role of DCL in regulating brain-peripheral crosstalk further might identify new treatment targets for obesity.

Intracerebroventricular prokineticin 2 infusion may play a role on the hypothalamus-pituitary-thyroid axis and energy metabolism

AimThe hypothesis of this study is to determine the effects of intracerebroventricular (icv) prokineticin 2 infusion on food consumption and body weight and to elucidate whether it has effects on energy expenditure via the hypothalamus-pituitary-thyroid (HPT) axis in adipose tissue. Material and MethodsA total of 40 rats were used in the study and 4 groups were established: Control, Sham, Prokineticin 1.5 and Prokineticin 4.5 (n=10). Except for the Control group, rats were treated intracerebroventricularly via osmotic minipumps, the Sham group was infused with aCSF (vehicle), and the Prokineticin 1.5 and Prokineticin 4.5 groups were infused with 1.5 nMol and 4.5 nMol prokineticin 2, respectively. Food and water consumption and body weight were monitored during 7-day infusion in all groups. At the end of the infusion, the rats were decapitated and serum TSH, fT4 and fT3 levels were determined by ELISA. In addition, PGC-1α and UCP1 gene expression levels in white adipose tissue (WAT) and brown adipose tissue (BAT), TRH from rat hypothalamic tissue were determined by real-time PCR. ResultsIcv prokineticin 2 (4.5 nMol) infusion had no effect on water consumption but reduced daily food consumption and body weight (p<0.05). Icv prokineticin 2 (4.5 nMol) infusion significantly increased serum TSH, fT4 and fT3 levels when compared to Control and Sham groups (p<0.05). Also, icv prokineticin 2 (4.5 nMol) infusion increased the expression of TRH in the hypothalamus tissue and expression of PGC-1α UCP1 in the WAT and BAT (p<0.05). ConclusionIcv prokineticin 2 (4.5 nMol) infusion may suppress food consumption via its receptors in the hypothalamus and reduce body weight by stimulating energy expenditure and thermogenesis in adipose tissue through the HPT axis.

Ventromedial hypothalamic nucleus subset stimulates tissue thermogenesis via preoptic area outputs

ObjectiveHypothalamic signals potently stimulate energy expenditure by engaging peripheral mechanisms to restore energy homeostasis. Previous studies have identified several critical hypothalamic sites (e.g. preoptic area (POA) and ventromedial hypothalamic nucleus (VMN)) that could be part of an interconnected neurocircuit that controls tissue thermogenesis and essential for body weight control. However, the key neurocircuit that can stimulate energy expenditure has not yet been established. MethodsHere, we investigated the downstream mechanisms by which VMN neurons stimulate adipose tissue thermogenesis. We manipulated subsets of VMN neurons acutely as well as chronically and studied its effect on tissue thermogenesis and body weight control, using Sf1Cre and Adcyap1Cre mice and measured physiological parameters under both high-fat diet and standard chow diet conditions. To determine the node efferent to these VMN neurons, that is involved in modulating energy expenditure, we employed electrophysiology and optogenetics experiments combined with measurements using tissue-implantable temperature microchips. ResultsActivation of the VMN neurons that express the steroidogenic factor 1 (Sf1; VMNSf1 neurons) reduced body weight, adiposity and increased energy expenditure in diet-induced obese mice. This function is likely mediated, at least in part, by the release of the pituitary adenylate cyclase-activating polypeptide (PACAP; encoded by the Adcyap1 gene) by the VMN neurons, since we previously demonstrated that PACAP, at the VMN, plays a key role in energy expenditure control. Thus, we then shifted focus to the subpopulation of VMNSf1 neurons that contain the neuropeptide PACAP (VMNPACAP neurons). Since the VMN neurons do not directly project to the peripheral tissues, we traced the location of the VMNPACAP neurons' efferents. We identified that VMNPACAP neurons project to and activate neurons in the caudal regions of the POA whereby these projections stimulate tissue thermogenesis in brown and beige adipose tissue. We demonstrated that selective activation of caudal POA projections from VMNPACAP neurons induces tissue thermogenesis, most potently in negative energy balance and activating these projections lead to some similar, but mostly unique, patterns of gene expression in brown and beige tissue. Finally, we demonstrated that the activation of the VMNPACAP neurons' efferents that lie at the caudal POA are necessary for inducing tissue thermogenesis in brown and beige adipose tissue. ConclusionsThese data indicate that VMNPACAP connections with the caudal POA neurons impact adipose tissue function and are important for induction of tissue thermogenesis. Our data suggests that the VMNPACAP → caudal POA neurocircuit and its components are critical for controlling energy balance by activating energy expenditure and body weight control.

Au@16-pH-16/miR-21 mimic nanosystem: An efficient treatment for obesity through browning and thermogenesis induction

Despite the abundance of registered clinical trials worldwide, the availability of effective drugs for obesity treatment is limited due to their associated side effects. Thus, there is growing interest in therapies that stimulate energy expenditure in white adipose tissue. Recently, we demonstrated that the delivery of a miR-21 mimic using JetPEI effectively inhibits weight gain in an obese mouse model by promoting metabolism, browning, and thermogenesis, suggesting the potential of miR-21 mimic as a treatment for obesity. Despite these promising results, the implementation of more advanced delivery system techniques for miR-21 mimic would greatly enhance the advancement of safe and efficient treatment approaches for individuals with obesity in the future. Our objective is to explore whether a new delivery system based on gold nanoparticles and Gemini surfactants (Au@16-ph-16) can replicate the favorable effects of the miR-21 mimic on weight gain, browning, and thermogenesis. We found that dosages as low as 0.2 μg miR-21 mimic /animal significantly inhibited weight gain and induced browning and thermogenic parameters. This was evidenced by the upregulation of specific genes and proteins associated with these processes, as well as the biogenesis of beige adipocytes and mitochondria. Significant increases in miR-21 levels were observed in adipose tissue but not in other tissue types. Our data indicates that Au@16-ph-16 could serve as an effective delivery system for miRNA mimics, suggesting its potential suitability for the development of future clinical treatments against obesity.

Trans 10, cis 12-conjugated linoleic acid reduced reproductive ability by disrupting the estrus cycle in female mice

Trans 10, cis 12-conjugated linoleic acid reduced reproductive ability by disrupting the estrus cycle in female mice

1525-P: Ventromedial Hypothalamic Nucleus Subset Stimulates Tissue Thermogenesis via Preoptic Outputs

Changes in energy status ignite neural circuits that maintain body weight by engaging peripheral mechanisms that control energy expenditure; obesity results for when these responses are no longer sufficient. The key neural circuits that stimulate energy expenditure have not yet been established, but previous research has identified several critical sites (e.g. preoptic area (POA) and ventromedial hypothalamus (VMN)) that could be part of an interconnected system that controls tissue thermogenesis, which is essential for body weight control. Activating SF1-cre VMN cells in male diet-induced obese mice reduces body fat by 25% in 72 hours. This function is likely mediated at least in part by release of the peptide pituitary adenylate cyclase-activating polypeptide (PACAP), since knockout of PACAP in the VMN induces obesity at thermoneutrality (30C) and suppresses temperature above both the brown and beige adipose tissue in response to feeding. Because some VMN cells densely project to the POA, we hypothesized that VMN PACAP cells activate tissue thermogenesis via preoptic outputs. We placed temperature-sensing microchips above a traditional brown (interscapular brown adipose tissue (iBAT) and beige (inguinal white adipose tissue (iWAT) adipose tissue in Adcyap1(gene for PACAP)cre mice with DIO-ChR2 in the VMN and fiber optic implants in two major VMN outputs: the POA and the bed nucleus of the stria terminalis (BST). Activating VMN fibers in the POA that contain PACAP in both male and female mice, but not the BST, increased iBAT and iWAT temperature, and the effect was most robust when the mice were fasted. In summary, these data indicate that VMN PACAP connections with the POA is important for the induction of tissue thermogenesis, particularly when feeding conditions change. VMN PACAP, as well as associated signaling targets, are critical components to energy balance by activating adipose tissue mechanisms that stimulate energy expenditure. Disclosure A.J.Elmendorf: Other Relationship; Eli Lilly and Company. C.A.Mahler: Stock/Shareholder; AbbVie Inc., Pfizer Inc., AstraZeneca. B.Lorentz: Research Support; Eli Lilly and Company. J.Flak: Research Support; Eli Lilly and Company. Funding American Diabetes Association (Pathway 17-INI-15 to J.F.); Ralph W. and Grace M. Showalter Research Trust; Indiana University; Indiana Biosciences Research Institute

1612-P: Energetic Contributions of GLP1 and GCGR Activity in GLP1/GIP/GCGR Triagonism

Glucagon has been implicated as a key diabetogenic factor. However, agonists that couple the lipolytic and thermogenic properties of Glucagon Receptor (GCGR) activity with the antidiabetic actions of incretins (GLP1, GIP), lack hyperglycemic side effects associated with GCGR activity. GCGR agonism stimulates energy expenditure (EE) that contributes to weight loss. Interestingly, we also identified that the anti-obesity effects of GCGR agonism persisted for 50d after treatment cessation. Thus, we hypothesized that GCGR activity paired with incretin action (GGG) will result in increased EE during treatment and prolonged weight loss after cessation. Diet-induced obese mice were treated for 14d with vehicle, GGG, or single receptor agonism via IUB288 (GCGR), Semagutide (Sema;GLP1R), or GIP-FA 085 (GIPR). Indirect calorimetry was conducted for d 2-4 of treatment and d 16-18 after cessation. Congruent with our prior studies, IUB288 increased EE compared to vehicle controls. Conversely, Sema-treated mice displayed decreased EE (d 2 and 3) while EE following GIP treatment was similar to vehicle controls. Intriguingly, GGG reduced EE on d 2, had similar EE to vehicle controls on d 3, with a trend towards increased EE on d 4, suggesting GGG treatment stimulates characteristics of both GLP1 and GCGR activity. Nutrient utilization, measured via Respiratory Quotient (RQ), was reduced during the light period with IUB288 treatment. GIP, Sema, and GGG reduced RQ, regardless of time of day. Interestingly, GGG regulation of RQ appeared most like Sema. After treatment cessation, Sema mice gained significantly more weight than IUB288 or GGG mice, despite similar food intake during rebound. Surprisingly, EE was not elevated in mice that formerly received IUB288 or GGG, suggesting another mechanism may be driving this effect. RQ was similar in all groups, except IUB288 mice, which exhibited increased RQ across the day. These data suggest that GGG exhibits effects of both GLP1R and GCGR agonism with respect to EE and RQ. Disclosure S.Nason: None. J.Antipenko: None. K.M.Habegger: Consultant; Glyscend Inc., Research Support; Eli Lilly and Company, Novo Nordisk, Glyscend Inc., Stock/Shareholder; Glyscend Inc. Funding Eli Lilly and Company

Neuronal loss of TRPM8 leads to obesity and glucose intolerance in male mice

ObjectiveMice with global deletion of the transient receptor potential channel melastatin family member 8 (TRPM8) are obese, and treatment of diet-induced obese (DIO) mice with TRPM8 agonists decrease body weight. Whether TRPM8 signaling regulates energy metabolism via central or peripheral effects is unknow. Here we assessed the metabolic phenotype of mice with either Nestin Cre-mediated neuronal loss of TRPM8, or with deletion of TRPM8 in Advillin Cre positive sensory neurons of the peripheral nervous system (PNS). MethodsNestin Cre- and Advillin Cre-Trpm8 knock-out (KO) mice were metabolically phenotyped under chronic exposure to either chow or high-fat diet (HFD), followed by assessment of energy and glucose metabolism. ResultsAt room temperature, chow-fed neuronal Trpm8 KO are obese and show decreased energy expenditure when acutely treated with the TRPM8 selective agonist icilin. But body weight of neuronal Trpm8 KO mice is indistinguishable from wildtype controls at thermoneutrality, or when mice are chronically exposed to HFD-feeding. In contrast to previous studies, we show that the TRPM8 agonist icilin has no direct effect on brown adipocytes, but that icilin stimulates energy expenditure, at least in part, via neuronal TRPM8 signaling. We further show that lack of TRPM8 in sensory neurons of the PNS does not lead to a metabolically relevant phenotype. ConclusionsOur data indicate that obesity in TRPM8-deficient mice is centrally mediated and likely originates from alterations in energy expenditure and/or thermal conductance, but does not depend on TRPM8 signaling in brown adipocytes or sensory neurons of the PVN.

Neuronal Blockade of Thyroid Hormone Signaling Increases Sensitivity to Diet-Induced Obesity in Adult Male Mice.

Thyroid hormone increases energy expenditure. Its action is mediated by TR, nuclear receptors present in peripheral tissues and in the central nervous system, particularly in hypothalamic neurons. Here, we address the importance of thyroid hormone signaling in neurons, in general for the regulation of energy expenditure. We generated mice devoid of functional TR in neurons using the Cre/LoxP system. In hypothalamus, which is the center for metabolic regulation, mutations were present in 20% to 42% of the neurons. Phenotyping was performed under physiological conditions that trigger adaptive thermogenesis: cold and high-fat diet (HFD) feeding. Mutant mice displayed impaired thermogenic potential in brown and inguinal white adipose tissues and were more prone to diet-induced obesity. They showed a decreased energy expenditure on chow diet and gained more weight on HFD. This higher sensitivity to obesity disappeared at thermoneutrality. Concomitantly, the AMPK pathway was activated in the ventromedial hypothalamus of the mutants as compared with the controls. In agreement, sympathetic nervous system (SNS) output, visualized by tyrosine hydroxylase expression, was lower in the brown adipose tissue of the mutants. In contrast, absence of TR signaling in the mutants did not affect their ability to respond to cold exposure. This study provides the first genetic evidence that thyroid hormone signaling exerts a significant influence in neurons to stimulate energy expenditure in some physiological context of adaptive thermogenesis. TR function in neurons to limit weight gain in response to HFD and this effect is associated with a potentiation of SNS output.

Purinergic receptor: a crucial regulator of adipose tissue functions.

Obesity is a public-health challenge resulting from an imbalance between energy expenditure and calorie intake. This health problem exacerbates a variety of metabolic complications worldwide. Adipose tissue is an essential regulator of energy homeostasis, and the functions within it are regulated by purinergic receptors. A1R, P2X7R, and P2YR mainly mediate energy homeostasis primarily through regulating energy storage and adipokines secretion in white adipose tissue (WAT). P2X5R is a novel-specific cell surface marker in brown/beige adipocytes. A2R is a promising therapeutic target for stimulating energy expenditure in brown adipose tissue (BAT) and also mediating WAT browning. Based on these features, purinergic receptors may be an appropriate target in treating obesity. In this review, the role of purinergic receptors in different types of adipose tissue is summarized. An improved understanding of purinergic receptor functions in adipose tissue may lead to more effective treatment interventions for obesity and its related metabolic disorders.

Osteoblast/osteocyte-derived interleukin-11 regulates osteogenesis and systemic adipogenesis

Exercise results in mechanical loading of the bone and stimulates energy expenditure in the adipose tissue. It is therefore likely that the bone secretes factors to communicate with adipose tissue in response to mechanical loading. Interleukin (IL)−11 is known to be expressed in the bone, it is upregulated by mechanical loading, enhances osteogenesis and suppresses adipogenesis. Here, we show that systemic IL-11 deletion (IL-11−/−) results in reduced bone mass, suppressed bone formation response to mechanical loading, enhanced expression of Wnt inhibitors, and suppressed Wnt signaling. At the same time, the enhancement of bone resorption by mechanical unloading was unaffected. Unexpectedly, IL-11−/− mice have increased systemic adiposity and glucose intolerance. Osteoblast/osteocyte-specific IL-11 deletion in osteocalcin-Cre;IL-11fl/fl mice have reduced serum IL-11 levels, blunted bone formation under mechanical loading, and increased systemic adiposity similar to IL-11−/− mice. Adipocyte-specific IL-11 deletion in adiponectin-Cre;IL-11fl/fl did not exhibit any abnormalities. We demonstrate that osteoblast/osteocyte-derived IL-11 controls both osteogenesis and systemic adiposity in response to mechanical loading, an important insight for our understanding of osteoporosis and metabolic syndromes.

Effect of caffeine on mitochondrial biogenesis in the skeletal muscle - A narrative review.

Caffeine is one of the most widely used substances as recreational drug for performance-enhancement in sport, underpinned by a strong evidence base. Although the effects of caffeine are widely investigated within the scope of performance physiology, the molecular effects of caffeine within skeletal muscle remain unclear. Evidence from invitro and invivo models suggest that caffeine regulates the glucose metabolism in the skeletal muscle. Moreover, caffeine seems to stimulate CaMKII, PPARδ/β, AMPK and PGC1α, classical markers of exercise-adaptations, including mitochondrial biogenesis and mitochondrial content. This review summarizes evidence to suggest caffeine-effects within skeletal muscle fibers, focusing on the putative role of caffeine on mitochondrial biogenesis to explore whether caffeine supplementation might be a strategy to enhance mitochondrial biogenesis.

Ckmt1 is Dispensable for Mitochondrial Bioenergetics Within White/Beige Adipose Tissue.

Within brown adipose tissue (BAT), the brain isoform of creatine kinase (CKB) has been proposed to regulate the regeneration of ADP and phosphocreatine in a futile creatine cycle (FCC) that stimulates energy expenditure. However, the presence of FCC, and the specific creatine kinase isoforms regulating this theoretical model within white adipose tissue (WAT), remains to be fully elucidated. In the present study, creatine did not stimulate respiration in cultured adipocytes, isolated mitochondria or mouse permeabilized WAT. Additionally, while creatine kinase ubiquitous-type, mitochondrial (CKMT1) mRNA and protein were detected in human WAT, shRNA-mediated reductions in Ckmt1 did not decrease submaximal respiration in cultured adipocytes, and ablation of CKMT1 in mice did not alter energy expenditure, mitochondrial responses to pharmacological β3-adrenergic activation (CL 316, 243) or exacerbate the detrimental metabolic effects of consuming a high-fat diet. Taken together, these findings solidify CKMT1 as dispensable in the regulation of energy expenditure, and unlike in BAT, they do not support the presence of FCC within WAT.

Apoptotic brown adipocytes enhance energy expenditure via extracellular inosine

Brown adipose tissue (BAT) dissipates energy1,2 and promotes cardiometabolic health3. Loss of BAT during obesity and ageing is a principal hurdle for BAT-centred obesity therapies, but not much is known about BAT apoptosis. Here, untargeted metabolomics demonstrated that apoptotic brown adipocytes release a specific pattern of metabolites with purine metabolites being highly enriched. This apoptotic secretome enhances expression of the thermogenic programme in healthy adipocytes. This effect is mediated by the purine inosine that stimulates energy expenditure in brown adipocytes by the cyclic adenosine monophosphate–protein kinase A signalling pathway. Treatment of mice with inosine increased BAT-dependent energy expenditure and induced ‘browning’ of white adipose tissue. Mechanistically, the equilibrative nucleoside transporter 1 (ENT1, SLC29A1) regulates inosine levels in BAT: ENT1-deficiency increases extracellular inosine levels and consequently enhances thermogenic adipocyte differentiation. In mice, pharmacological inhibition of ENT1 as well as global and adipose-specific ablation enhanced BAT activity and counteracted diet-induced obesity, respectively. In human brown adipocytes, knockdown or blockade of ENT1 increased extracellular inosine, which enhanced thermogenic capacity. Conversely, high ENT1 levels correlated with lower expression of the thermogenic marker UCP1 in human adipose tissues. Finally, the Ile216Thr loss of function mutation in human ENT1 was associated with significantly lower body mass index and 59% lower odds of obesity for individuals carrying the Thr variant. Our data identify inosine as a metabolite released during apoptosis with a ‘replace me’ signalling function that regulates thermogenic fat and counteracts obesity.

Stimulation of uncoupling protein 1 expression by β-alanine in brown adipocytes

Carnosine, which is abundant in meat, is a dipeptide composed of β-alanine and histidine, known to afford various health benefits. It has been suggested that carnosine can elicit an anti-obesity effect via induction and activation of brown/beige adipocytes responsible for non-shivering thermogenesis. However, the relationship between carnosine and brown/beige adipocytes has not been comprehensively elucidated. We hypothesized that β-alanine directly modulates brown/beige adipogenesis and performed an in vitro assessment to test this hypothesis. HB2 brown preadipocytes were differentiated using insulin from day 0. Cells were treated with various concentrations of β-alanine (12.5–100 μM) during adipogenesis (days 0–8) and differentiation (days 8–10). Then, cells were further stimulated with or without forskolin, an activator of the cAMP-dependent protein kinase pathway, on day 8 or day 10 for 4 h before harvesting. We observed that HB2 cells expressed molecules related to the transport and signal transduction of β-alanine. Treatment with β-alanine during brown adipogenesis dose-dependently enhanced forskolin-induced Ucp1 expression; this was not observed in differentiated brown adipocytes. Consistent with these findings, treatment with β-alanine during days 0–8 increased phosphorylation levels of CREB in forskolin-treated HB2 cells. In addition, β-alanine treatment during brown adipogenesis increased the expression of Pparα, known to induce brown/beige adipogenesis, in a dose-dependent manner. These findings revealed that β-alanine could target HB2 adipogenic cells and enhance forskolin-induced Ucp1 expression during brown adipogenesis, possibly by accelerating phosphorylation and activation of CREB. Thus, β-alanine, a carnosine-constituting amino acid, might directly act on brown adipogenic cells to stimulate energy expenditure.

A Role of Stress Sensor Nrf2 in Stimulating Thermogenesis and Energy Expenditure.

During chronic cold stress, thermogenic adipocytes generate heat through uncoupling of mitochondrial respiration from ATP synthesis. Recent discovery of various dietary phytochemicals, endogenous metabolites, synthetic compounds, and their molecular targets for stimulating thermogenesis has provided promising strategies to treat or prevent obesity and its associated metabolic diseases. Nuclear factor E2 p45-related factor 2 (Nrf2) is a stress response protein that plays an important role in obesity and metabolisms. However, both Nrf2 activation and Nrf2 inhibition can suppress obesity and metabolic diseases. Here, we summarized and discussed conflicting findings of Nrf2 activities accounting for part of the variance in thermogenesis and energy metabolism. We also discussed the utility of Nrf2-activating mechanisms for their potential applications in stimulating energy expenditure to prevent obesity and improve metabolic deficits.

Myoglobin, expressed in brown adipose tissue of mice, regulates the content and activity of mitochondria and lipid droplets

The identification of novel physiological regulators that stimulate energy expenditure through brown adipose tissue (BAT) activity in substrate catalysis is of utmost importance to understand and treat metabolic diseases. Myoglobin (MB), known to store or transport oxygen in heart and skeletal muscles, has recently been found to bind fatty acids with physiological constants in its oxygenated form (i.e., MBO2). Here, we investigated the in vivo effect of MB expression on BAT activity. In particular, we studied mitochondrial function and lipid metabolism as essential determinants of energy expenditure in this tissue. We show in a MB-null (MBko) mouse model that MB expression in BAT impacts on the activity of brown adipocytes in a twofold manner: i) by elevating mitochondrial density plus maximal respiration capacity, and through that, by stimulating BAT oxidative metabolism along with the organelles` uncoupled respiration; and ii) by influencing the free fatty acids pool towards a palmitate-enriched composition and shifting the lipid droplet (LD) equilibrium towards higher counts of smaller droplets. These metabolic changes were accompanied by the up-regulated expression of thermogenesis markers UCP1, CIDEA, CIDEC, PGC1-α and PPAR-α in the BAT of MB wildtype (MBwt) mice. Along with the emergence of the “browning” BAT morphology, MBwt mice exhibited a leaner phenotype when compared to MBko littermates at 20 weeks of age. Our data shed novel insights into MB's role in linking oxygen and lipid-based thermogenic metabolism. The findings suggest potential new strategies of targeting the MB pathway to treat metabolic disorders related to diminishing energy expenditure.

Mig-6 is essential for glucose homeostasis and thermogenesis in brown adipose tissue

Brown adipose tissue (BAT) is an anti-obese and anti-diabetic tissue that stimulates energy expenditure in the form of adaptive thermogenesis through uncoupling protein 1 (UCP1). Mitogen-inducible gene-6 (Mig-6) is a negative regulator of epidermal growth factor receptor (EGFR) that interacts with many cellular partners and has multiple cellular functions. We have recently reported that Mig-6 is associated with diabetes and metabolic syndrome. However, its function in BAT is unknown. We generated a brown adipocyte-specific Mig-6 knock-in mouse (BKI) to examine the role of Mig-6 in BAT. Mig-6 BKI mice had improved glucose tolerance on a normal chow diet. Mig-6 BKI mice also revealed activated thermogenesis and the size of the BAT lipid droplets was reduced. Additionally, Mig-6 regulated cAMP-PKA signaling-induced UCP1 expression in brown adipocytes. Taken together, these results demonstrate that Mig-6 affects glucose tolerance and thermogenesis in BAT.

Helichrysum italicum ssp. italicum Infusion Promotes Fat Oxidation in Hepatocytes and Stimulates Energy Expenditure and Fat Oxidation after Acute Ingestion in Humans: A Pilot Study.

Helichrysum italicum is an aromatic plant with promising pharmacological activities. Bioactive compounds found in plants represent an important alternative treatment for weight loss and an infusion of H. italicum contains compounds which could have such effect. Our aim was, therefore, to investigate its acute effects on resting energy expenditure (REE) and possible differences in substrate oxidation in a pilot study. A dried, ground plant material of H. italicum ssp. italicum was infused with hot water and chemically characterized with HPLC-MS analysis. Sensory evaluation of herbal tea was performed. A randomized, crossover, controlled pilot study was then conducted on eleven healthy male subjects. The REE and substrate oxidation were measured by indirect calorimetry at baseline and 30 and 120 min after ingestion of infusion or hot water. The expression of genes involved in lipid metabolism was examined in H. italicum infusion-treated hepatocytes. Several phenolic classes were identified in the infusion, caffeoylquinic acids were the most abundant, followed by pyrones and flavonols. A single ingestion of H. italicum infusion significantly increased REE by 4% and fat oxidation by 12% compared to hot water ingestion. A significant 2-fold up-regulation of β-oxidation-related genes in HepG2 cells, exposed to H. italicum infusion, was detected. This pilot study suggests that H. italicum infusion possesses bioactive substances with potential application in obesity prevention, which could, with additional studies, become an economically interesting novel application of the plant. Clinical trial registration number: NCT04818905