| 1. |
- Bartelt, Alexander, et al.
(author)
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Thermogenic adipocytes promote HDL turnover and reverse cholesterol transport
- 2017
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In: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 8
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Journal article (peer-reviewed)abstract
- Brown and beige adipocytes combust nutrients for thermogenesis and through their metabolic activity decrease pro-atherogenic remnant lipoproteins in hyperlipidemic mice. However, whether the activation of thermogenic adipocytes affects the metabolism and anti-atherogenic properties of high-density lipoproteins (HDL) is unknown. Here, we report a reduction in atherosclerosis in response to pharmacological stimulation of thermogenesis linked to increased HDL levels in APOE(star)3-Leiden. CETP mice. Both cold-induced and pharmacological thermogenic activation enhances HDL remodelling, which is associated with specific lipidomic changes in mouse and human HDL. Furthermore, thermogenic stimulation promotes HDL-cholesterol clearance and increases macrophage-to-faeces reverse cholesterol transport in mice. Mechanistically, we show that intravascular lipolysis by adipocyte lipoprotein lipase and hepatic uptake of HDL by scavenger receptor B-I are the driving forces of HDL-cholesterol disposal in liver. Our findings corroborate the notion that high metabolic activity of thermogenic adipocytes confers atheroprotective properties via increased systemic cholesterol flux through the HDL compartment.
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| 2. |
- Fischer, Alexander W., et al.
(author)
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Intact innervation is essential for diet-induced recruitment of brown adipose tissue
- 2019
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In: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 316:3, s. E487-E503
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Journal article (peer-reviewed)abstract
- The possibility that recruitment and activation of brown adipose tissue (BAT) thermogenesis could be beneficial for curtailing obesity development in humans prompts a need for a better understanding of the control of these processes [that are often referred to collectively as diet-induced thermogenesis (DIT)]. Dietary conditions are associated with large changes in blood-borne factors that could be responsible for BAT recruitment, but BAT is also innervated by the sympathetic nervous system. To examine the significance of the innervation for DIT recruitment, we surgically denervated the largest BAT depot, i.e., the interscapular BAT depot in mice and exposed the mice at thermoneutrality to a high-fat diet versus a chow diet. Denervation led to an alteration in feeding pattern but did not lead to enhanced obesity, but obesity was achieved with a lower food intake, as denervation increased metabolic efficiency. Conclusively. denervation totally abolished the diet-induced increase in total UCP1 protein levels observed in the intact mice, whereas basal UCP1 expression was not dependent on innervation. The denervation of interscapular BAT did not discernably hyper-recruit other BAT depots, and no UCP1 protein could be detected in the principally browning-competent inguinal white adipose tissue depot under any of the examined conditions. We conclude that intact innervation is essential for diet-induced thermogenesis and that circulating factors cannot by themselves initiate recruitment of brown adipose tissue under obesogenic conditions. Therefore, the processes that link food intake and energy storage to activation of the nervous system are those of significance for the further understanding of diet-induced thermogenesis.
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| 3. |
- Fischer, Alexander W., et al.
(author)
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Lysosomal lipoprotein processing in endothelial cells stimulates adipose tissue thermogenic adaptation
- 2021
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In: Cell Metabolism. - : Elsevier. - 1550-4131 .- 1932-7420. ; 33:3, s. 547-564.e7
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Journal article (peer-reviewed)abstract
- In response to cold exposure, thermogenic adipocytes internalize large amounts of fatty acids after lipoprotein lipase-mediated hydrolysis of triglyceride-rich lipoproteins (TRL) in the capillary lumen of brown adipose tissue (BAT) and white adipose tissue (WAT). Here, we show that in cold-exposed mice, vascular endothelial cells in adipose tissues endocytose substantial amounts of entire TRL particles. These lipoproteins subsequently follow the endosomal-lysosomal pathway, where they undergo lysosomal acid lipase (LAL)-mediated processing. Endothelial cell-specific LAL deficiency results in impaired thermogenic capacity as a consequence of reduced recruitment of brown and brite/beige adipocytes. Mechanistically, TRL processing by LAL induces proliferation of endothelial cells and adipocyte precursors via beta-oxidation-dependent production of reactive oxygen species, which in turn stimulates hypoxia-inducible factor-1α-dependent proliferative responses. In conclusion, this study demonstrates a physiological role for TRL particle uptake into BAT and WAT and establishes endothelial lipoprotein processing as an important determinant of adipose tissue remodeling during thermogenic adaptation.
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| 4. |
- Fischer, Alexander W., et al.
(author)
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Thermoneutrality-Induced Macrophage Accumulation in Brown Adipose Tissue Does Not Impair the Tissue's Competence for Cold-Induced Thermogenic Recruitment
- 2020
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In: Frontiers in Endocrinology. - : Frontiers Media SA. - 1664-2392. ; 11
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Journal article (peer-reviewed)abstract
- Brown adipose tissue from mice living under conditions approaching human thermal and nutritional conditions (prolonged exposure to thermoneutral temperature and to an energy-rich (high-fat, high-sugar) diet) - referred to as physiologically humanized mice, displays morphological and molecular characteristics significantly different from those observed in young, chow-fed mice maintained at room temperature - referred to as standard mice. Here, we further examined brown fat from physiologically humanized and standard mice, as well as from mice exposed to thermoneutrality for a long time but not to an energy-rich diet - referred to here as long-term thermoneutral mice. Global transcriptome analysis of brown fat revealed that genes that were the most upregulated in brown fat of thermoneutral mice (both physiologically humanized and long-term thermoneutral) were those related to inflammatory processes, including genes expressed selectively in macrophages. Cellular and molecular analyses confirmed that brown fat from thermoneutral mice was heavily infiltrated by macrophages, predominantly organized into crown-like structures. However, despite this, the brown fat of thermoneutral mice retained full competence to attain the greatest possible recruitment state and became macrophage-depleted during the process of cold acclimation. Thus, profound macrophage accumulation does not influence the thermogenic recruitment competence of brown fat.
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