Intrascapular Brown Adipose Tissue Research Articles

Dysfunction of the Brown Adipose Organ in HFD-Obese Rats and Effect of Tart Cherry Supplementation.

Obesity has a great impact on adipose tissue biology, based on its function as a master regulator of energy balance. Brown adipose tissue (BAT) undergoes remodeling, and its activity declines in obese subjects due to a whitening process. The anti-obesity properties of fruit extracts have been reported. The effects of tart cherry against oxidative stress, inflammation, and the whitening process in the BAT of obese rats were investigated. Intrascapular BAT (iBAT) alterations and effects of Prunus cerasus L. were debated in rats fed for 17 weeks with a high-fat diet (DIO), in DIO supplemented with seed powder (DS), and with seed powder plus the juice (DJS) of tart cherry compared to CHOW rats fed with a normo-caloric diet. iBAT histologic observations revealed a whitening process in DIO rats that was reduced in the DS and DJS groups. A modulation of uncoupling protein-1 (UCP-1) protein and gene expression specifically were detected in the obese phenotype. An upregulation of UCP-1 and related thermogenic genes after tart cherry intake was detected compared to the DIO group. Metabolic adjustment, endoplasmic reticulum stress, protein carbonylation, and the inflammatory microenvironment in the iBAT were reported in DIO rats. The analysis demonstrated an iBAT modulation that tart cherry promoted. In addition to our previous results, these data confirm the protective impact of tart cherry consumption on obesity.

Taurine supplementation alters gene expression profiles in white adipose tissue of obese C57BL/6J mice: Inflammation and lipid synthesis perspectives

This work aimed to identify the mechanisms by which taurine exerts its anti-obesity effects in the C57BL/6J ob/ob mice model and determine if taurine supplementation increases the amelioration of inflammation and lipogenesis linked genes in the adipose and liver tissues. Three groups of C57BL/6J mice were fed a standard chow diet for a period of 10 weeks the C57BL/6J normal group, the C57BL/6J ob/ob negative control group with no taurine intake and C57BL/6J ob/ob taurine group with taurine intake. Real time PCR was used to examine the gene expression profile in the experimental groups intrascapular brown adipose tissue (BAT), inguinal white adipose tissue (WAT) and liver. TNF-alpha, Ccl2, Adgre and illb genes that are associated with inflammation were found to have varying level of expression in the three tissues. In comparison to BAT and liver these genes were expressed at a much lower level in WAT, with enhanced serum adiponectin levels.

SAT667 Follicle-Stimulating Hormone Does Not Directly Regulate Adipogenesis Via The FSH Receptor In Mice

Abstract Disclosure: M. Loka: None. L. Ongaro Gambino: None. T. Uliasz: None. L.A. Jaffe: None. L. Kazak: None. D.J. Bernard: None. Rising rates of obesity are a serious public health challenge. Post-menopausal women are at higher risk of developing obesity and associated comorbidities than premenopausal women, with hormonal changes, such as reduced estrogens, likely to be contributing factors. Menopause is also characterized by increases in pituitary-derived follicle-stimulating hormone (FSH). Recent data suggest that FSH may directly stimulate adipogenesis and block thermogenesis in adipocytes. FSH reportedly decreased expression of thermogenic genes (Cox8b and Ucp1) in murine 3T3-L1 cells differentiated into adipocytes. FSH’s inhibitory effects were no longer apparent in the presence of an FSH-neutralizing antibody. The same FSH antibody reduced fat mass and increased lean mass in ovariectomized (OVX) female mice, a rodent model of menopause. In these studies, it was not established whether FSH acted directly through its canonical receptor (FSHR) in adipocytes to mediate its effects. To address this gap, we differentiated 3T3-L1 cells to adipocytes and treated with FSH. In contrast to the earlier report, FSH did not alter the expression of markers of lipogenesis (Cebpa and Pparg2) or thermogenesis (Cox8b and Ucp1) nor did it impact mitochondrial respiration or lipid accumulation. We also did not detect Fshr mRNA in these cells. We next differentiated the stromal vascular fraction from inguinal adipose tissue of adult male mice into white adipocytes. After 10 days of differentiation, FSH treatment did not alter expression of several markers of adipogenesis and did not affect lipid accumulation. To assess FSH actions in vivo, we generated adipocyte-specific Fshr knockout mice (Fshrfx/fx;Adipoq-Cre, hereafter cKO). Ten-week-old cKO and control female mice were OVX and maintained on standard chow. Eight to 10 weeks later, we performed glucose tolerance and insulin tolerance tests, and determined body composition by EchoMRI. Cre-mediated recombination of the floxed Fshr locus in adipocytes was successful, but did not alter body weight, fat or lean mass, or glucose metabolism in cKO relative to control OVX mice. Furthermore, using a newly developed FSHR-3xHA knockin mouse model, we detected FSHR protein expression in ovary, but not in inguinal and perigonadal white adipose depots or in intrascapular brown adipose tissue. We similarly failed to detect Fshr mRNA in various fat depots in control mice. Collectively, our results fail to show FSH effects on adipogenesis in vitro and challenge the hypothesis that FSH acts through the classical FSHR in adipocytes in vivo. Presentation: Saturday, June 17, 2023

Energy Expenditure Homeostasis Requires ErbB4, an Obesity Risk Gene, in the Paraventricular Nucleus.

Obesity affects more than a third adult population in the United States; the prevalence is even higher in patients with major depression disorders. GWAS studies identify the receptor tyrosine kinase ErbB4 as a risk gene for obesity and for major depression disorders. We found that ErbB4 was enriched in the paraventricular nucleus of the hypothalamus (PVH). To investigate its role in metabolism, we deleted ErbB4 by injecting a Cre-expressing virus into the PVH of ErbB4-floxed male mice and found that PVH ErbB4 deletion increased weight gain without altering food intake. ErbB4 PVH deletion also reduced nighttime activity and decreased intrascapular brown adipose tissue (iBAT) thermogenesis. Analysis of covariance (ANCOVA) revealed that ErbB4 PVH deletion reduced O2 consumption, CO2 production and heat generation in a manner independent of body weight. Immunostaining experiments show that ErbB4+ neurons in the PVH were positive for oxytocin (OXT); ErbB4 PVH deletion reduces serum levels of OXT. We characterized mice where ErbB4 was specifically mutated in OXT+ neurons and found reduction in energy expenditure, phenotypes similar to PVH ErbB4 deletion. Taken together, our data indicate that ErbB4 in the PVH regulates metabolism likely through regulation of OXT expressing neurons, reveal a novel function of ErbB4 and provide insight into pathophysiological mechanisms of depression-associated obesity.

Brown adipose tissue but not tibia exhibits a dramatic response to acute reduction in environmental temperature in growing male mice

Mice are typically housed at room temperature (∼22 °C), which is well below their thermoneutral zone and results in cold stress. Chronic cold stress leads to increased adaptive thermogenesis and reductions in cancellous bone volume and bone marrow adipose tissue mass in long bones of growing mice. There is strong evidence that increased neuronal activity initiates the metabolic response of intrascapular brown adipose tissue (BAT) to cold stress, but it is less clear whether bone is regulated through a similar mechanism. Therefore, we compared the short-term response of BAT and whole tibia to a reduction in environmental temperature. To accomplish this, we transferred a group of 6-week-old male mice from 32 °C to 22 °C housing and sacrificed the mice 24 h later. Age-matched controls were maintained at 32 °C. We then evaluated expression levels of a panel of genes related to adipocyte differentiation and fat metabolism in BAT and tibia, and a panel of genes related to bone metabolism in tibia. The decrease in housing temperature resulted in changes in expression levels for 47/86 genes related to adipocyte differentiation and fat metabolism in BAT, including 9-fold and 17-fold increases in Ucp1 and Dio2, respectively. In contrast, only 1/86 genes related to adipocyte differentiation and fat metabolism and 4/84 genes related to bone metabolism were differentially expressed in tibia. These findings suggest that bone, although innervated with sensory and sympathetic neurons, does not respond as rapidly as BAT to changes in environmental temperature.

PMON182 PACAP Receptor Expression in Sympathetic Ganglia of the Autonomic Nervous System

Abstract In obesity, energy intake exceeds energy expenditure and concomitantly increases risk of chronic diseases, including metabolic diseases such as diabetes. Therapeutics to correct dysregulations in energy balance are needed and one notable neuropeptide being studied is pituitary adenylate cyclase-activating polypeptide (PACAP), an overarching regulator of the stress response1,2. In the context of metabolism, PACAP has been shown to regulate adaptive thermogenesis, an energy burning process regulated by the sympathetic nervous system (SNS) in response to cold stress and overfeeding. While research suggests PACAP acts centrally at the level of the hypothalamus to regulate energy balance3-5, PACAP is also known to be expressed in the SNS. In preganglionic neurons innervating the adrenal medulla6, PACAP is co-localized with acetylcholine and regulates catecholamine synthesis and release. Recent neuronal tracing studies have shown that postganglionic fibres of the stellate ganglia innervate intrascapular brown adipose tissue (BAT), the main thermogenic tissue in mammals7. However, PACAP's role within the sympathetic nerves innervating and regulating energy metabolism in adipose tissues is not known. As such, our group is interested in characterizing PACAP and PACAP receptor expression in sympathetic nerves innervating and regulating energy metabolism in BAT (via the stellate ganglia) in response to metabolic stressors, such as cold stress. We hypothesize that PACAP is released from preganglionic nerves which binds PACAP receptors (PAC1, VPAC1, VPAC2) expressed in postganglionic nerves of the stellate ganglia. Here we report, for the first time, PAC1 and VPAC1 expression in the stellate ganglia with sex-specific differential gene expression based on housing temperature. Analysis of PAC1 splice variant expression identified at least two variants in tissues of the SNS (adrenal gland, superior cervical ganglia and the stellate ganglia). These results will support future functional studies characterizing PACAP regulation of catecholamine production in peripheral ganglia which will contribute to assessing G-protein coupled receptors (GPCRs) as potential therapeutic targets for obesity and metabolic disease.

Uncoupling Protein-1 Modulates Anxiety-Like Behavior in a Temperature-Dependent Manner.

A strong bidirectional link between metabolic and psychiatric disorders exists; yet, the molecular basis underlying this interaction remains unresolved. Here we explored the role of the brown adipose tissue (BAT) as modulatory interface, focusing on the involvement of uncoupling protein 1 (UCP-1), a key metabolic regulator highly expressed in BAT, in the control of emotional behavior. Male and female constitutive UCP-1 knock-out (KO) mice were used to investigate the consequences of UCP-1 deficiency on anxiety-related and depression-related behaviors under mild thermogenic (23°C) and thermoneutral (29°C) conditions. UCP-1 KO mice displayed a selective enhancement of anxiety-related behavior exclusively under thermogenic conditions, but not at thermoneutrality. Neural and endocrine stress mediators were not affected in UCP-1 KO mice, which showed an activation of the integrated stress response alongside enhanced fibroblast-growth factor-21 (FGF-21) levels. However, viral-mediated overexpression of FGF-21 did not phenocopy the behavioral alterations of UCP-1 KO mice and blocking FGF-21 activity did not rescue the anxiogenic phenotype of UCP-1 KO mice. No effects of surgical removal of the intrascapular BAT on anxiety-like behavior or FGF-21 levels were observed in either UCP-1 KO or WT mice. We provide evidence for a novel role of UCP-1 in the regulation of emotions that manifests as inhibitory constraint on anxiety-related behavior, exclusively under thermogenic conditions. We propose this function of UCP-1 to be independent of its activity in the BAT and likely mediated through a central role of UCP-1 in brain regions with converging involvement in energy and emotional control.SIGNIFICANCE STATEMENT In this first description of a temperature-dependent phenotype of emotional behavior, we propose uncoupling protein-1 (UCP-1), the key component of the thermogenic function of the brown adipose tissue, as molecular break controlling anxiety-related behavior in mice. We suggest the involvement of UCP-1 in fear regulation to be mediated through its expression in brain regions with converging roles in energy and emotional control. These data are important and relevant in light of the largely unexplored bidirectional link between metabolic and psychiatric disorders, which has the potential for providing insight into novel therapeutic strategies for the management of both conditions.

Distinct morphology of cardiac- and brown adipose tissue-projecting neurons in the stellate ganglia of mice.

Sympathetic neurons that innervate the heart are located primarily in the stellate ganglia (SG), which also contains neurons that project to brown adipose tissue (BAT). These studies were designed to examine the morphology of these two populations (cardiac‐ and BAT‐projecting) and their target connectivity. We examined SG neurons in C57BL/6J mice following injections of the retrograde tracer cholera toxin B (CTb) conjugated to Alexa Fluor 488 and Alexa Fluor 555, into cardiac tissue and intrascapular BAT. BAT‐projecting SG neurons were widely dispersed in SG, while cardiac‐projecting SG neurons were localized primarily near the inferior cardiac nerve base. SG neurons were not dual‐labeled, suggesting that sympathetic innervation is specific to the heart and BAT, supporting the idea of “labeled lines” of efferents. Morphologically, cardiac‐projecting SG somata had more volume and were less abundant than BAT‐projecting neurons using our tracer‐labeling paradigm. We found a positive correlation between the number of primary dendrites per neuron and soma volume in cardiac‐projecting SG neurons, though not in BAT‐projecting neurons. In both SG subpopulations, the number of cholinergic inputs marked with vesicular acetylcholine transporter (VAChT) puncta contacting the soma was positively correlated to soma volume, suggesting scaling of inputs across a range of neuronal sizes. In separate studies using dual tracing from left and right BAT, we found that BAT‐projecting SG neurons were located predominately ipsilateral to the injection, but a small subset of SG neurons project bilaterally to BAT. This tracing approach will allow the assessment of cell‐specific mechanisms of plasticity within subpopulations of SG neurons.

Diverse Morphology of Sympathetic Neuron Subpopulations in the Stellate Ganglia

Sympathetic nerves innervate the heart and changes in sympathetic efferent activity can modulate cardiac function. The post‐ganglionic sympathetic neurons that innervate the heart are located primarily in the stellate ganglia (SG), which also contains neurons that project to brown adipose tissue (BAT), among other target tissues. We aim to examine morphological changes in SG neurons after myocardial infarction, and characterize the specificity of neural plasticity within the ganglion. To interpret morphological changes induced by cardiac injury, we must first fully understand the normal morphology of distinct groups of SG neurons. To that end, we examined SG neurons following injections of retrograde tracers into cardiac tissue and/or intrascapular brown adipose tissue (BAT) in adult male and female C57BL/6J mice (8 males, 2 females, 28‐32 weeks, 24‐39 g; The Jackson Laboratory). Using cholera toxin B (CTb) tracers conjugated to two different fluorophores (1 mg/mL in 0.01 M PBS; Alexa Fluor 488 or Alexa Fluor 555), we assessed the number, dispersion, pre‐synaptic cholinergic inputs and morphology of BAT‐ and cardiac‐projecting SG neurons. We also examined the quality of the CTb tracer detection at varying times after BAT injection (7, 14 and 28 days; n=2 mice per time point). BAT‐projecting SG neuron visualization was optimal 7 days post‐injection compared to 14 and 28 days, and could be visualized directly or with antibodies against CTb. BAT‐projecting SG neurons were located in both left and right SG, predominately ipsilateral to the injection site and were widely dispersed. In contrast, cardiac‐projecting SG neurons were more localized near the base of the inferior cardiac nerve. In BAT‐ and cardiac‐injected mice (n=4), we found that SG neurons were not dual‐labeled, supporting the notion that sympathetic innervation to target tissues is specific. We found cardiac‐projecting SG neuron somas have more volume (mm3) and cardiac‐projecting cells are less abundant within the SG than BAT‐projecting neurons with our tracer‐labeling paradigm. We also discovered a positive correlation between number of primary dendrites per neuron and soma volume in cardiac‐projecting SG neurons, though not in BAT‐projecting SG neurons. Additionally, in both SG subpopulations, the number of cholinergic inputs marked with vesicular acetylcholine transporter (VAChT) on the cell body is positively correlated to soma volume. Tract tracing distinct subpopulations of neurons will allow us to characterize morphological changes after cardiac injury in specific cell groups. This approach will allow insights into whether mechanisms of plasticity are cell specific or occur globally within the SG.

Orexin receptor type 2 agonism inhibits thermogenesis in brown adipose tissue by attenuating afferent innervation.

Orexin signaling has been associated with energy expenditure and brown adipose tissue (BAT) function. However, conflicting data exist in the field about how orexin signaling regulates BAT thermogenesis. In this study, we show that a specific orexin receptor type 2 (OX2R) agonist [Ala11, D-Leu15]-OxB (OB-Ala) inhibited intrascapular brown adipose tissue (iBAT) thermogenesis by reducing sympathetic output to iBAT. This effect is mediated by OX2Rs located on afferent nerve endings innervating iBAT instead of brown adipocyte itself. Microinjection of OB-Ala into iBAT inhibited iBAT thermogenesis in mice upon cold exposure and neuronal activity in the paraventricular nucleus. Findings suggest that OB-Ala could inhibit iBAT thermogenesis by attenuating sensory input thereby inhibiting the sympathetic-sensory iBAT feedback loop. Our study uncovers a novel primary action site of orexin in the regulation of energy balance.

LETMD1 is required for mitochondrial structure and thermogenic function of brown adipocytes.

Obesity and metabolic disorders caused by energy surplus pose an increasing concern within the global population. Brown adipose tissue (BAT) dissipates energy through mitochondrial non-shivering thermogenesis, thus representing a powerful agent against obesity. Here we explore the novel role of a mitochondrial outer membrane protein, LETM1-domain containing 1 (LETMD1), in BAT. We generated a knockout (Letmd1KO ) mouse model and analyzed BAT morphology, function and gene expression under various physiological conditions. While the Letmd1KO mice are born normally and have normal morphology and body weight, they lose multilocular brown adipocytes completely and have diminished mitochondrial abundance, DNA copy number, cristae structure, and thermogenic gene expression in the intrascapular BAT, associated with elevated reactive oxidative stress. In consequence, the Letmd1KO mice fail to maintain body temperature in response to acute cold exposure without food and become hypothermic within 4h. Although the cold-exposed Letmd1KO mice can maintain body temperature in the presence of food, they cannot upregulate expression of uncoupling protein 1 (UCP1) and convert white to beige adipocytes, nor can they respond to adrenergic stimulation. These results demonstrate that LETMD1 is essential for mitochondrial structure and function, and thermogenesis of brown adipocytes.

Baicalin attenuates diet-induced obesity partially through promoting thermogenesis in adipose tissue

BackgroundAdipose tissues have essential roles on energy homeostasis and the development of metabolic syndrome and obesity, they have become critical targets for treating obesity and metabolic disorders. Baicalin is a flavonoid that derived from the root of Scutellaria baicalensis, and it has been reported to take part in the regulation of adipocyte function. All these highlighted the potential of baicalin in the regulation of fat accumulation and obesity. Yet the impact of baicalin on thermogenic function of adipocytes remains to be deciphered. ObjectiveThis study aims to explore the anti-obesity effects of baicalin. Materials & MethodsThe level of mRNA was detected by qRT-PCR and the protein expression level was examined by western blot. H&E staining was used for the observation of the structure of adipose tissue. Serum triglyceride and insulin levels were detected by commercial test kits. ResultsOur data demonstrated that baicalin up-regulates the expression of UCP1 and PGC1a in a dose-dependent manner in vitro. Baicalin also increases ERK phosphorylation, and the increased expression of UCP1 and PGC1a in adipocytes could be inhibited by an ERK inhibitor, U0126. Moreover, dietary baicalin ameliorates high fat diet (HFD)-induced obesity without affecting food intake. In addition, dietary baicalin inhibits adipocyte hypertrophy and enhances thermogenic gene program in sWAT and intrascapular brown adipose tissue (iBAT) in vivo. Discussion & ConclusionBaicalin prevents HFD-induced obesity partially through promoting adipocyte thermogenesis. Baicalin may be a promising compound against human obesity and related metabolic diseases.

Phosphorylation of STAT3 in hypothalamic nuclei is stimulated by lower doses of leptin than are needed to inhibit food intake.

This experiment investigated which hypothalamic nuclei were activated by a dose of leptin that inhibited food intake. Foodnot intake, energy expenditure, respiratory exchange ratio (RER), and intrascapular brown adipose tissue (IBAT) temperature were measured in male and female Sprague Dawley rats for 36 h following an intraperitoneal injection of 0, 50, 200, 500, or 1,000 µg leptin/kg with each rat tested with each dose of leptin in random order. In both males and females, RER and 12-h food intake were inhibited only by 1,000 µg leptin/kg, but there was no effect on energy expenditure or IBAT temperature. At the end of the experiment, phosphorylated signal transducer and activator of transcription 3 (pSTAT3) immunoreactivity was measured 1 h after injection of 0, 50, 500, or 1,000 µg leptin/kg. In male rats, the lowest dose of leptin produced a maximal activation of STAT3 in the Arc and nucleus of the solitary tract (NTS). There was no response in the dorsomedial hypothalamus, but there was a progressive increase in ventromedial nucleus of the hypothalamus (VMH) pSTAT3 with increasing doses of leptin. In female rats, there was no significant change in Arc and pSTAT3 NTS activation was maximal with 500 mg leptin/kg, but only the highest dose of leptin increased VMH pSTAT3. These results suggest that the VMH plays an important role in the energetic response to elevations of circulating leptin but do not exclude the possibility that multiple nuclei provide the appropriate integrated response to hyperleptinemia.NEW & NOTEWORTHY The results of this experiment show that doses of leptin too small to inhibit food intake produce a maximal response to leptin in the arcuate nucleus. By contrast the VMH shows a robust response that correlates with inhibition of food intake. This suggests that the VMH plays an important role in the energetic response to hyperleptinemia.

638-P: A Novel, Long-Acting Dual Agonist for GIPR/GLP-1R, HISHS-2001, Demonstrates Effects on HbA1c and Weight Loss in the db/db Mouse Model of Type 2 Diabetes

HISHS-2001 is a novel long-acting, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) dual receptor (R) agonist. In in vitro cAMP assays in human GIP/GLP-1 receptor-expressing cells, HISHS-2001 exerted half-maximal effects at concentrations of 2.3 nM and 4.1 nM on the receptors for GIP (GIPR) and GLP-1 (GLP-1R) respectively. After SC dosing every third day for four weeks, HISHS-2001 at 3, 10 and 21 nmol/kg demonstrated robust effects on HbA1c in db/db mice which were superior to semaglutide and tirzepatide (Table). The effect on body weight was more pronounced with HISHS-2001 than semaglutide and similar to tirzepatide which was associated with a reduction in food intake. Interestingly, HISHS-2001 led to a significant increase in uncoupling protein-1 (UCP-1) levels in intrascapular brown adipose tissue, in inguinal white adipose tissue and serum and liver fibroblast growth factor-21 (FGF-21) levels. A decrease in serum interleukin-6 (IL-6) level was also observed.In conclusion, HISHS-2001 is a potent, long acting GIP/GLP-1R dual agonist, which provides improved control of glucose homeostasis in diabetic mice compared to an existing GLP-1 agonist and a GIP/GLP-1R dual agonist.View largeDownload slideView largeDownload slide DisclosureV. S. Burade: None. A. Garcia-ocana: Consultant; Self; Sun Pharmaceutical Industries Ltd. R. E. Pratley: Other Relationship; Self; Hanmi Pharmaceutical, Merck Sharp & Dohme Corp., Metavention, Monster Energy Company, Inc., Novo Nordisk, Pfizer Inc., Poxel SA, Sanofi, Scohia Pharma Inc., Sun Pharmaceutical Industries Ltd. G. A. Rutter: Advisory Panel; Self; Sun Pharmaceutical Industries Ltd. T. Vilsbøll: Consultant; Self; Amgen Inc., AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Bristol-Myers Squibb Company, Gilead Sciences, Inc., Lilly Diabetes, Merck Sharp & Dohme Corp., Mundipharma International, Novo Nordisk, Sanofi, Sun Pharmaceutical Industries Ltd. B. Thorens: Advisory Panel; Self; Sun Pharmaceutical Industries Ltd. R. Thennati: None.

Central Apolipoprotein A-IV Stimulates Thermogenesis in Brown Adipose Tissue.

Stimulation of thermogenesis in brown adipose tissue (BAT) could have far-reaching health benefits in combatting obesity and obesity-related complications. Apolipoprotein A-IV (ApoA-IV), produced by the gut and the brain in the presence of dietary lipids, is a well-known short-term satiating protein. While our previous studies have demonstrated reduced diet-induced thermogenesis in ApoA-IV-deficient mice, it is unclear whether this reduction is due to a loss of peripheral or central effects of ApoA-IV. We hypothesized that central administration of ApoA-IV stimulates BAT thermogenesis and that sympathetic and sensory innervation is necessary for this action. To test this hypothesis, mice with unilateral denervation of interscapular BAT received central injections of recombinant ApoA-IV protein or artificial cerebrospinal fluid (CSF). The effects of central ApoA-IV on BAT temperature and thermogenesis in mice with unilateral denervation of the intrascapular BAT were monitored using transponder probe implantation, qPCR, and immunoblots. Relative to CSF, central administration of ApoA-IV significantly increased temperature and UCP expression in BAT. However, all of these effects were significantly attenuated or prevented in mice with unilateral denervation. Together, these results clearly demonstrate that ApoA-IV regulates BAT thermogenesis centrally, and this effect is mediated through sympathetic and sensory nerves.

Sensory neurons expressing calcitonin gene-related peptide α regulate adaptive thermogenesis and diet-induced obesity

ObjectivesHeat-sensory neurons from the dorsal root ganglia (DRG) play a pivotal role in detecting the cutaneous temperature and transmission of external signals to the brain, ensuring the maintenance of thermoregulation. However, whether these thermoreceptor neurons contribute to adaptive thermogenesis remains elusive. It is also unknown whether these neurons play a role in obesity and energy metabolism. MethodsWe used genetic ablation of heat-sensing neurons expressing calcitonin gene-related peptide α (CGRPα) to assess whole-body energy expenditure, weight gain, glucose tolerance, and insulin sensitivity in normal chow and high-fat diet-fed mice. Exvivo lipolysis and transcriptional characterization were combined with adipose tissue-clearing methods to visualize and probe the role of sensory nerves in adipose tissue. Adaptive thermogenesis was explored using infrared imaging of intrascapular brown adipose tissue (iBAT), tail, and core temperature upon various stimuli including diet, external temperature, and the cooling agent icilin. ResultsIn this report, we show that genetic ablation of heat-sensing CGRPα neurons promotes resistance to weight gain upon high-fat diet (HFD) feeding and increases energy expenditure in mice. Mechanistically, we found that loss of CGRPα-expressing sensory neurons was associated with reduced lipid deposition in adipose tissue, enhanced expression of fatty acid oxidation genes, higher exvivo lipolysis in primary white adipocytes, and increased mitochondrial respiration from iBAT. Remarkably, mice lacking CGRPα sensory neurons manifested increased tail cutaneous vasoconstriction at room temperature. This exacerbated cold perception was not associated with reduced core temperature, suggesting that heat production and heat conservation mechanisms were engaged. Specific denervation of CGRPα neurons in intrascapular BAT did not contribute to the increased metabolic rate observed upon global sensory denervation. ConclusionsTaken together, these findings highlight an important role of cutaneous thermoreceptors in regulating energy metabolism by triggering counter-regulatory responses involving energy dissipation processes including lipid fuel utilization and cutaneous vasodilation.

MiR17-92 cluster drives white adipose tissue browning.

White adipose tissue (WAT) browning may have beneficial effects for treating metabolic syndrome. miRNA are important regulators of the differentiation, development, and function of brown and beige adipocytes. Here, we found that the cold-inducible miRNA17-92 cluster is enriched in brown adipose tissue (BAT) compared with WAT. Overexpression of the miR17-92 cluster in C3H10T1/2 cells, a mouse mesenchymal stem cell line, enhanced the thermogenic capacity of adipocytes. Furthermore, we observed a significant reduction in adiposity in adipose tissue-specific miR17-92 cluster transgenic (TG) mice. This finding is partly explained by dramatic increases in white fat browning and energy expenditure. Interestingly, the miR17-92 cluster stimulated WAT browning without altering BAT activity in mice. In addition, when we removed the intrascapular BAT (iBAT), the TG mice could maintain their body temperature well under cold exposure. At the molecular level, we found that the miR17-92 cluster targets Rb1, a beige cell repressor in WAT. The present study reveals a critical role for the miR17-92 cluster in regulating WAT browning. These results may be helpful for better understanding the function of beige fat, which could compensate for the lack of BAT in humans, and may open new avenues for combatting metabolic syndrome.

Effects of corticosterone within the hypothalamic arcuate nucleus on food intake and body weight in male rats

ObjectiveObesity is a major cause of morbidity and mortality. Few weight-reducing medications are available, and these have limited efficacy. Cushing's Syndrome (caused by elevated glucocorticoid levels) and obesity have similar metabolic features. Though circulating glucocorticoid levels are not elevated in obesity, tissue-specific glucocorticoid levels have been implicated in the development of the metabolic phenotype of obesity. Tissue glucocorticoid levels are regulated by 11β-hydroxysteroid dehydrogenase type1 (11βHSD1), which increases the local concentration of active glucocorticoids by the production of corticosterone from 11-dehydrocorticosterone. 11βHSD1 is expressed in the hypothalamic arcuate nucleus (ARC), a major weight and appetite-regulating centre, and therefore represents a target for novel anti-obesity therapeutic agents. Thus, we sought to investigate the effect of chronic alterations of ARC corticosterone levels (mediated by 11βHSD1) on food intake and body weight in adult male rats. MethodsRecombinant adeno-associated virus particles bearing sense 11βHSD1 (rAAV-S11βHSD1) and small interfering 11βHSD1 (rAAV-si11βHSD1), respectively, were stereotactically injected into the ARC (bilaterally) of adult male Wistar rats. rAAV-GFP was injected into control groups of male Wistar rats. Food intake and body weight were measured three times a week for 70 days. Terminal brain, plasma and intrascapular brown adipose tissue (iBAT) samples were taken for measurement of mRNA expression and hormone levels. ResultsCompared to controls, rAAV-S11βHSD1 injection resulted in higher ARC corticosterone levels, hyperphagia and increased weight gain. Conversely, rAAV-si11βHSD1 injection (compared to controls) resulted in lower ARC corticosterone levels, higher iBAT uncoupling protein-1 mRNA expression and less weight gain despite similar food intake. ConclusionsTherefore ARC corticosterone, regulated by 11βHSD1, may play a role in food intake and body weight regulation. These data have important implications for the development of centrally-acting 11βHSD1 inhibitors, which are currently being developed for the treatment of obesity, metabolic disorders, and other conditions.

The lipidome of primary murine white, brite, and brown adipocytes-Impact of beta-adrenergic stimulation.

Lipid species patterns are conserved within cells to maintain physicochemical properties of membranes and cellular functions. We present the lipidome, including sterols, glycerolipids (GLs), glycerophospholipids (GPLs), and sphingolipids (SLs), of primary ex vivo differentiated (I) white, (II) brite, and (III) brown adipocytes derived from primary preadipocytes isolated from (I) epididymal white, (II) inguinal white, and (III) intrascapular brown adipose tissue. Quantitative lipidomics revealed significantly decreased fractions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), with longer (C > 36) and more polyunsaturated species, as well as lower levels of cardiolipin (CL) in white than in brite and brown adipocytes. Together, the brite and brown lipidome was comparable and indicates differences in membrane lipid packing density compared with white adipocytes. Changes in ceramide species profile could be related to the degree of browning. Beta-adrenergic stimulation of brown adipocytes led to generation of saturated lyso-PC (LPC) increasing uncoupling protein (UCP) 1-mediated leak respiration. Application of stable isotope labeling showed that LPC formation was balanced by an increased de novo synthesis of PC.

Adipose tissues of MPC1±mice display altered lipid metabolism-related enzyme expression levels.

Mitochondrial pyruvate carrier 1 (MPC1) is a component of the MPC1/MPC2 heterodimer that facilitates the transport of pyruvate into mitochondria. Pyruvate plays a central role in carbohydrate, fatty, and amino acid catabolism. The present study examined epididymal white adipose tissue (eWAT) and intrascapular brown adipose tissue (iBAT) from MPC1± mice following 24 weeks of feeding, which indicated low energy accumulation as evidenced by low body and eWAT weight and adipocyte volume. To characterize molecular changes in energy metabolism, we analyzed the transcriptomes of the adipose tissues using RNA-Sequencing (RNA-Seq). The results showed that the fatty acid oxidation pathway was activated and several genes involved in this pathway were upregulated. Furthermore, qPCR and western blotting indicated that numerous genes and proteins that participate in lipolysis were also upregulated. Based on these findings, we propose that the energy deficiency caused by reduced MPC1 activity can be alleviated by activating the lipolytic pathway.