Brown Adipose Tissue Activity In Mice Research Articles

Myoglobin-mediated lipid shuttling increases adrenergic activation of brown and white adipocyte metabolism and is as a marker of thermogenic adipocytes in humans.

Recruitment and activation of brown adipose tissue (BAT) results in increased energy expenditure (EE) via thermogenesis and represents an intriguing therapeutic approach to combat obesity and treat associated diseases. Thermogenesis requires an increased and efficient supply of energy substrates and oxygen to the BAT. The hemoprotein myoglobin (MB) is primarily expressed in heart and skeletal muscle fibres, where it facilitates oxygen storage and flux to the mitochondria during exercise. In the last years, further contributions of MB have been assigned to the scavenging of reactive oxygen species (ROS), the regulation of cellular nitric oxide (NO) levels and also lipid binding. There is a substantial expression of MB in BAT, which is induced during brown adipocyte differentiation and BAT activation. This suggests MB as a previously unrecognized player in BAT contributing to thermogenesis. This study analyzed the consequences of MB expression in BAT on mitochondrial function and thermogenesis in vitro and in vivo. Using MB overexpressing, knockdown or knockout adipocytes, we show that expression levels of MB control brown adipocyte mitochondrial respiratory capacity and acute response to adrenergic stimulation, signalling and lipolysis. Overexpression in white adipocytes also increases their metabolic activity. Mutation of lipid interacting residues in MB abolished these beneficial effects of MB. In vivo, whole-body MB knockout resulted in impaired thermoregulation and cold- as well as drug-induced BAT activation in mice. In humans, MB is differentially expressed in subcutaneous (SC) and visceral (VIS) adipose tissue (AT) depots, differentially regulated by the state of obesity and higher expressed in AT samples that exhibit higher thermogenic potential. These data demonstrate for the first time a functional relevance of MBs lipid binding properties and establish MB as an important regulatory element of thermogenic capacity in brown and likely beige adipocytes.

PACT establishes a posttranscriptional brake on mitochondrial biogenesis by promoting the maturation of miR-181c

The double-stranded RNA-dependent protein kinase activating protein (PACT), an RNA-binding protein that is part of the RNA-induced silencing complex, plays a key role in miR-mediated translational repression. Previous studies showed that PACT regulates the expression of various miRs, selects the miR strand to be loaded onto RNA-induced silencing complex, and determines proper miR length. Apart from PACT’s role in mediating the antiviral response in immune cells, what PACT does in other cell types is unknown. Strikingly, it has also been shown that cold exposure leads to marked downregulation of PACT protein in mouse brown adipose tissue (BAT), where mitochondrial biogenesis and metabolism play a central role. Here, we show that PACT establishes a posttranscriptional brake on mitochondrial biogenesis (mitobiogenesis) by promoting the maturation of miR-181c, a key suppressor of mitobiogenesis that has been shown to target mitochondrial complex IV subunit I (Mtco1) and sirtuin 1 (Sirt1). Consistently, we found that a partial reduction in PACT expression is sufficient to enhance mitobiogenesis in brown adipocytes in culture as well as during BAT activation in mice. In conclusion, we demonstrate an unexpected role for PACT in the regulation of mitochondrial biogenesis and energetics in cells and BAT.

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.

Predicted secreted protein analysis reveals synaptogenic function of Clstn3 during WAT browning and BAT activation in mice.

Promoting white adipose tissue (WAT) browning and enhancing brown adipose tissue (BAT) activity are attractive therapeutic strategies for obesity and its metabolic complications. Targeting sympathetic innervation in WAT and BAT represents a promising therapeutic concept. However, there are few reports on extracellular microenvironment remodeling, especially changes in nerve terminal connections. Identifying the key molecules mediating the neuro-adipose synaptic junctions is a key point. In this study, we used bioinformatics methods to identify the differentially expressed predicted secreted genes (DEPSGs) during WAT browning and BAT activation. These DEPSGs largely reflect changes of cytokines, extracellular matrix remodeling, vascularization, and adipocyte-neuronal cross-talk. We then performed functional enrichment and cellular distribution specificity analyses. The upregulated and downregulated DEPDGs during WAT browning displayed a distinctive biological pattern and cellular distribution. We listed a cluster of adipocyte-enriched DEPSGs, which might participate in the cross-talk between mature adipocytes and other cells; then identified a synaptogenic adhesion molecule, Clstn3, as the top gene expressed enriched in both mature white and brown adipocytes. Using Q-PCR and immunohistochemistry, we found significantly increased Clstn3 expression level during WAT browning and BAT activation in mice subjected to cold exposure (4 °C). We further demonstrated that treatment with isoproterenol significantly increased Clstn3 and UCP1 expression in differentiated white and beige adipocytes in vitro. In conclusion, our study demonstrates that the secretion pattern was somewhat different between WAT browning and BAT activation. We reveal that Clstn3 may be a key gene mediating the neuro-adipose junction formation or remodeling in WAT browning and BAT activation process.

Abstract 202: Inhibition of Central Melanocortin 4 Receptor Signaling Severely Impairs Brown Adipose Tissue Activity and VLDL Metabolism

Objectives: SNPs near the melanocortin 4 receptor (MC4R) gene are associated with cardiovascular diseases (CVD) and deficiency of MC4R is the most common monogenic cause of obesity, a major risk factor for the development of CVD. MC4R-deficient individuals not only show increased food intake but also lower basal energy expenditure. Furthermore, pharmacological inhibition of the central MC4R signaling by SHU9119 in mice increases weight gain independent of food intake. Since brown adipose tissue (BAT) importantly contributes to energy expenditure by combusting high amounts of triglycerides (TG) into heat, the aim of the study was to evaluate the effect of inhibiting MCR4 on VLDL-metabolism and BAT activity in mice. Methods and results: Female APOE*3-Leiden.CETP transgenic mice were fed a cholesterol-enriched Western-type diet for 4 weeks, matched on body weight and plasma lipids, and infused with either SHU9119 or vehicle for 2 weeks via an osmotic mini-pump into the lateral ventricle while being fed the same diet. SHU9119 increased body fat (+50%) and decreased fat oxidation (-42%). Shu9119 increased plasma VLDL-TG levels (+30%). Whereas hepatic VLDL-TG production rate was not affected, Shu9119 severely impaired clearance of VLDL-TG, explained by reduced uptake of [ 3 H]TG by BAT (-25%). In BAT, SHU9119 decreased UCP-1 protein (-60%) and induced large intracellular lipid droplets, indicative of severely disturbed BAT activity. Since SHU9119 increased food intake (+30%), SHU9119 was also administered in mice that were pair-fed with the vehicle-treated group. Under these conditions, SHU9119 still exhibited these effects, indicating MC4R inhibition impairs BAT activity independent of food intake. Conclusion: Inhibition of central MC4R signaling by SHU9119 increases VLDL-TG levels and decreases energy expenditure specifically by impairing BAT function. We anticipate that MC4R regulates adiposity and VLDL metabolism not only by regulating food intake, but also by modulating BAT activity, and that activation of MC4R is a promising strategy to combat obesity and CVD by increasing BAT activity.

A standardized infrared imaging technique that specifically detects UCP1-mediated thermogenesis invivo.

The activation and expansion of brown adipose tissue (BAT) has emerged as a promising strategy to counter obesity and the metabolic syndrome by increasing energy expenditure. The subsequent testing and validation of novel agents that augment BAT necessitates accurate pre-clinical measurements in rodents regarding the capacity for BAT-derived thermogenesis. We present a novel method to measure BAT thermogenesis using infrared imaging following β3-adrenoreceptor stimulation in mice. We show that the increased body surface temperature observed using this method is due solely to uncoupling protein-1 (UCP1)-mediated thermogenesis and that this technique is able to discern differences in BAT activity in mice acclimated to 23 °C or thermoneutrality (30 °C). These findings represent the first standardized method utilizing infrared imaging to specifically detect UCP1 activity in vivo.

Effects of burn injury, cold stress and cutaneous wound injury on the morphology and energy metabolism of murine brown adipose tissue (BAT) in vivo

AimsCold stress has been shown to produce dramatic increases in 2-fluoro-2-deoxy-D-Glucose (18FDG) accumulation by brown adipose tissue (BAT) in rodents. However, neither the effects of other types of stress on 18FDG accumulation nor the effects of stressors on the accumulation of tracers of other aspects of energy metabolism have been evaluated. In this report we studied the effects of cold stress, burn injury and cutaneous wounds on murine BAT at the macroscopic, microscopic and metabolic level. Main methodsGlucose metabolism was studied with 18FDG, fatty acid accumulation was evaluated with trans-9(RS)-18F-fluoro-3,4(RS,RS)-methyleneheptadecanoic acid (FCPHA) and tricarboxcylic acid cycle (TCA) activity was evaluated with 3H acetate. Key findingsAll three stressors produced dramatic changes in BAT at the macroscopic and microscopic level. Macroscopically, BAT from the stressed animals appeared to be a much darker brown in color. Microscopically BAT of stressed animals demonstrated significantly fewer lipid droplets and an overall decrease in lipid content. Accumulation of 18FDG by BAT was significantly (p<0.01) increased by all 3 treatments (Cold: ~16 fold, burn ~7 Fold and cutaneous wound ~14 fold) whereas uptake of FDG by white fat was unchanged. This effect was also demonstrated non invasively by μPET imaging. Although less prominent than with 18FDG, BAT uptake of FCPHA and acetate were also significantly increased by all three treatments. These findings suggest that in addition to cold stress, burn injury and cutaneous wounds produce BAT activation in mice. SignificanceThis study demonstrates brown fat activated by several stressors leads to increased uptake of various substrates.