Carnitine and brown adipose tissue metabolism in the rat during development.
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ABSTRACT:
SUBMITTER: Hahn P
PROVIDER: S-EPMC1178564 | biostudies-other | 1972 Mar
REPOSITORIES: biostudies-other
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Project description:The activities of two mitochondrial enzymes concerned in the utilization of acetoacetate, namely 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase, were high throughout the suckling and weanling period in brown adipose tissue of the rat. In contrast, 3-hydroxybutyrate dehydrogenase activity was comparatively low during this period. The activity of cytosolic acetoacetyl-CoA synthetase (involved in lipogenesis) declined after birth and remained low until the pups were weaned. Experiments with brown-adipose-tissue slices from weanling rats indicated that 70% of the [3-14C]acetoacetate utilized was oxidized to 14CO2, and this value was not altered appreciably by the addition of glucose and insulin.
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Project description:Brown adipose tissue (BAT) is vital for proper thermogenesis during cold exposure in rodents, but until recently its presence in adult humans and its contribution to human metabolism were thought to be minimal or insignificant. Recent studies using PET with 18F-fluorodeoxyglucose (18FDG) have shown the presence of BAT in adult humans. However, whether BAT contributes to cold-induced nonshivering thermogenesis in humans has not been proven. Using PET with 11C-acetate, 18FDG, and 18F-fluoro-thiaheptadecanoic acid (18FTHA), a fatty acid tracer, we have quantified BAT oxidative metabolism and glucose and nonesterified fatty acid (NEFA) turnover in 6 healthy men under controlled cold exposure conditions. All subjects displayed substantial NEFA and glucose uptake upon cold exposure. Furthermore, we demonstrated cold-induced activation of oxidative metabolism in BAT, but not in adjoining skeletal muscles and subcutaneous adipose tissue. This activation was associated with an increase in total energy expenditure. We found an inverse relationship between BAT activity and shivering. We also observed an increase in BAT radio density upon cold exposure, indicating reduced BAT triglyceride content. In sum, our study provides evidence that BAT acts as a nonshivering thermogenesis effector in humans.
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Project description:Brown adipose tissue (BAT) is a central organ that acts to increase energy expenditure; its regulatory factors could be clinically useful in the treatment of obesity. Tetrahydrobiopterin (BH4) is an essential cofactor of tyrosine hydroxylase and nitric oxide synthase (NOS). Although BH4 regulates the known regulatory factors of BAT, such as noradrenaline (NA) and NO, participation of BH4 in BAT function remains unclear. In the present study, we investigate the role of BH4 in the regulation of BAT. Hph-1 mice, a mouse model of BH4 deficiency, exhibit obesity, adiposity, glucose intolerance, insulin resistance, and impaired BAT function. Impaired BAT function was ameliorated together with systemic metabolic disturbances by BAT transplantation from BH4-sufficient mice (control mice) into BH4-deficient mice, strongly suggesting that BH4-induced BAT has a critical role in the regulation of systemic energy metabolism. Both NA derived from the sympathetic nerve and NO derived from endothelial NOS in the blood vessels participate in the regulation of BH4. In addition, a direct effect of BH4 in the stimulation of brown adipocytes via NO is implicated. Taken together, BH4 activates BAT and regulates systemic energy metabolism; this suggests an approach for metabolic disorders, such as obesity and diabetes.
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Project description:ObjectiveAging is accompanied by loss of brown adipocytes and a decline in their thermogenic potential, which may exacerbate the development of adiposity and other metabolic disorders. Presently, only limited evidence exists describing the molecular alterations leading to impaired brown adipogenesis with aging and the contribution of these processes to changes of systemic energy metabolism.MethodsSamples of young and aged murine brown and white adipose tissue were used to compare age-related changes of brown adipogenic gene expression and thermogenesis-related lipid mobilization. To identify potential markers of brown adipose tissue aging, non-targeted proteomic and metabolomic as well as targeted lipid analyses were conducted on young and aged tissue samples. Subsequently, the effects of several candidate lipid classes on brown adipocyte function were examined.ResultsCorroborating previous reports of reduced expression of uncoupling protein-1, we observe impaired signaling required for lipid mobilization in aged brown fat after adrenergic stimulation. Omics analyses additionally confirm the age-related impairment of lipid homeostasis and reveal the accumulation of specific lipid classes, including certain sphingolipids, ceramides, and dolichols in aged brown fat. While ceramides as well as enzymes of dolichol metabolism inhibit brown adipogenesis, inhibition of sphingosine 1-phosphate receptor 2 induces brown adipocyte differentiation.ConclusionsOur functional analyses show that changes in specific lipid species, as observed during aging, may contribute to reduced thermogenic potential. They thus uncover potential biomarkers of aging as well as molecular mechanisms that could contribute to the degradation of brown adipocytes, thereby providing potential treatment strategies of age-related metabolic conditions.
| S-EPMC6531832 | biostudies-literature
Project description:Overt carnitine palmitoyltransferase in mitochondria isolated from interscapular brown adipose tissue of cold-adapted rats or rats maintained at normal temperature is extremely sensitive to inhibition by malonyl-CoA.
| S-EPMC1158357 | biostudies-other
Project description:In mammals, white adipose tissue (WAT) stores and releases lipids, whereas brown adipose tissue (BAT) oxidizes lipids to fuel thermogenesis. In obese individuals, WAT undergoes profound changes; it expands, becomes dysfunctional, and develops a low-grade inflammatory state. Importantly, BAT content and activity decline in obese subjects, mainly as a result of the conversion of brown adipocytes to white-like unilocular cells. Here, we show that BAT "whitening" is induced by multiple factors, including high ambient temperature, leptin receptor deficiency, β-adrenergic signaling impairment, and lipase deficiency, each of which is capable of inducing macrophage infiltration, brown adipocyte death, and crown-like structure (CLS) formation. Brown-to-white conversion and increased CLS formation were most marked in BAT from adipose triglyceride lipase (Atgl)-deficient mice, where, according to transmission electron microscopy, whitened brown adipocytes contained enlarged endoplasmic reticulum, cholesterol crystals, and some degenerating mitochondria, and were surrounded by an increased number of collagen fibrils. Gene expression analysis showed that BAT whitening in Atgl-deficient mice was associated to a strong inflammatory response and NLRP3 inflammasome activation. Altogether, the present findings suggest that converted enlarged brown adipocytes are highly prone to death, which, by promoting inflammation in whitened BAT, may contribute to the typical inflammatory state seen in obesity.
| S-EPMC5928436 | biostudies-literature
Project description:ObjectiveBrown adipose tissue (BAT) thermogenesis is critical in maintaining body temperature. The dorsomedial hypothalamus (DMH) integrates cutaneous thermosensory signals and regulates adaptive thermogenesis. Here, we study the function and synaptic connectivity of input from DMH cholinergic neurons to sympathetic premotor neurons in the raphe pallidus (Rpa).MethodsIn order to selectively manipulate DMH cholinergic neuron activity, we generated transgenic mice expressing channelrhodopsin fused to yellow fluorescent protein (YFP) in cholinergic neurons (choline acetyltransferase (ChAT)-Cre::ChR2-YFP) with the Cre-LoxP technique. In addition, we used an adeno-associated virus carrying the Cre recombinase gene to delete the floxed Chat gene in the DMH. Physiological studies in response to optogenetic stimulation of DMH cholinergic neurons were combined with gene expression and immunocytochemical analyses.ResultsA subset of DMH neurons are ChAT-immunopositive neurons. The activity of these neurons is elevated by warm ambient temperature. A phenotype-specific neuronal tracing shows that DMH cholinergic neurons directly project to serotonergic neurons in the Rpa. Optical stimulation of DMH cholinergic neurons decreases BAT activity, which is associated with reduced body core temperature. Furthermore, elevated DMH cholinergic neuron activity decreases the expression of BAT uncoupling protein 1 (Ucp1) and peroxisome proliferator-activated receptor γ coactivator 1 α (Pgc1α) mRNAs, markers of BAT activity. Injection of M2-selective muscarinic receptor antagonists into the 4th ventricle abolishes the effect of optical stimulation. Single cell qRT-PCR analysis of retrogradely identified BAT-projecting neurons in the Rpa shows that all M2 receptor-expressing neurons contain tryptophan hydroxylase 2. In animals lacking the Chat gene in the DMH, exposure to warm temperature reduces neither BAT Ucp1 nor Pgc1α mRNA expression.ConclusionDMH cholinergic neurons directly send efferent signals to sympathetic premotor neurons in the Rpa. Elevated cholinergic input to this area reduces BAT activity through activation of M2 mAChRs on serotonergic neurons. Therefore, the direct DMH(ACh)-Rpa(5-HT) pathway may mediate physiological heat-defense responses to elevated environmental temperature.
| S-EPMC4443291 | biostudies-literature
Project description:In rodents, brown adipose tissue (BAT) plays an important role in producing heat to defend against the cold and can metabolize large amounts of dietary fatty acids (DFA). The role of BAT in DFA metabolism in humans is unknown. Here we show that mild cold stimulation (18 °C) results in a significantly greater fractional DFA extraction by BAT relative to skeletal muscle and white adipose tissue in non-cold-acclimated men given a standard liquid meal containing the long-chain fatty acid PET tracer, 14(R,S)-[18F]-fluoro-6-thia-heptadecanoic acid (18FTHA). However, the net contribution of BAT to systemic DFA clearance is comparatively small. Despite a 4-week cold acclimation increasing BAT oxidative metabolism 2.6-fold, BAT DFA uptake does not increase further. These findings show that cold-stimulated BAT can contribute to the clearance of DFA from circulation but its contribution is not as significant as the heart, liver, skeletal muscles or white adipose tissues.
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Project description:Polycystic ovary syndrome (PCOS) is a common endocrine disease accompanied by energetic metabolic imbalance. Because the etiology of PCOS is complex and remains unclear, there is no effective and specific treatment for PCOS. It is often accompanied by various metabolic disorders such as obesity, insulin resistances, and others. Activated brown adipose tissue (BAT) consumes excess energy via thermogenesis, which has positive effects on energy metabolism. Our previous research and that of others indicates that BAT activity is decreased in PCOS patients, and exogenous BAT transplantation can improve PCOS rodents. Notably however, it is difficult to apply this therapeutic strategy in clinical practice. Therapeutic strategies of enhancing endogenous BAT activity and restoring whole-body endocrine homeostasis may be more meaningful for PCOS treatment. In the current study, the dehydroepiandrosterone-induced PCOS rat was exposed to low temperature for 20 days. The results show that cold treatment could reverse acyclicity of the estrous cycle and reduce circulating testosterone and luteinizing hormone in PCOS rats by activating endogenous BAT. It also significantly reduced the expression of steroidogenic enzymes as well as inflammatory factors in the ovaries of PCOS rats. Histological investigations revealed that cold treatment could significantly reduce ovary cystic follicles and increase corpus luteum, indicating that ovulation was recovered to a normal level. Concordant with these results, cold treatment also improved fertility in PCOS rats. Collectively, these findings suggest that cold treatment could be a novel therapeutic strategy for PCOS.
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Project description:Although recent studies have shown that brown adipose tissue (BAT) arises from progenitor cells that also give rise to skeletal muscle, the developmental signals that control the formation of BAT remain largely unknown. Here, we show that brown preadipocytes possess primary cilia and can respond to Hedgehog (Hh) signaling. Furthermore, cell-autonomous activation of Hh signaling blocks early brown-preadipocyte differentiation, inhibits BAT formation in vivo, and results in replacement of neck BAT with poorly differentiated skeletal muscle. Finally, we show that Hh signaling inhibits BAT formation partially through up-regulation of chicken ovalbumin upstream promoter transcription factor II (COUP-TFII). Taken together, our studies uncover a previously unidentified role for Hh as an inhibitor of BAT development.
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