RESUMEN
Lipid composition is conserved within sub-cellular compartments to maintain cell function. Lipidomic analyses of liver, muscle, white and brown adipose tissue (BAT) mitochondria revealed substantial differences in their glycerophospholipid (GPL) and free cholesterol (FC) contents. The GPL to FC ratio was 50-fold higher in brown than white adipose tissue mitochondria. Their purity was verified by comparison of proteomes with ER and mitochondria-associated membranes. A lipid signature containing PC and FC, calculated from the lipidomic profiles, allowed differentiation of mitochondria from BAT of mice housed at different temperatures. Elevating FC in BAT mitochondria prevented uncoupling protein (UCP) 1 function, whereas increasing GPL boosted it. Similarly, STARD3 overexpression facilitating mitochondrial FC import inhibited UCP1 function in primary brown adipocytes, whereas a knockdown promoted it. We conclude that the mitochondrial GPL/FC ratio is key for BAT function and propose that targeting it might be a promising strategy to promote UCP1 activity.
Asunto(s)
Tejido Adiposo Pardo , Colesterol , Lipidómica , Mitocondrias , Proteína Desacopladora 1 , Animales , Proteína Desacopladora 1/metabolismo , Proteína Desacopladora 1/genética , Ratones , Tejido Adiposo Pardo/metabolismo , Colesterol/metabolismo , Mitocondrias/metabolismo , Lipidómica/métodos , Especificidad de Órganos , Ratones Endogámicos C57BL , Tejido Adiposo Blanco/metabolismo , Glicerofosfolípidos/metabolismo , Masculino , Metabolismo de los LípidosRESUMEN
OBJECTIVE: Classical ATP-independent non-shivering thermogenesis enabled by uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) is activated, but not essential for survival, in the cold. It has long been suspected that futile ATP-consuming substrate cycles also contribute to thermogenesis and can partially compensate for the genetic ablation of UCP1 in mouse models. Futile ATP-dependent thermogenesis could thereby enable survival in the cold even when brown fat is less abundant or missing. METHODS: In this study, we explore different potential sources of UCP1-independent thermogenesis and identify a futile ATP-consuming triglyceride/fatty acid cycle as the main contributor to cellular heat production in brown adipocytes lacking UCP1. We uncover the mechanism on a molecular level and pinpoint the key enzymes involved using pharmacological and genetic interference. RESULTS: ATGL is the most important lipase in terms of releasing fatty acids from lipid droplets, while DGAT1 accounts for the majority of fatty acid re-esterification in UCP1-ablated brown adipocytes. Furthermore, we demonstrate that chronic cold exposure causes a pronounced remodeling of adipose tissues and leads to the recruitment of lipid cycling capacity specifically in BAT of UCP1-knockout mice, possibly fueled by fatty acids from white fat. Quantification of triglyceride/fatty acid cycling clearly shows that UCP1-ablated animals significantly increase turnover rates at room temperature and below. CONCLUSION: Our results suggest an important role for futile lipid cycling in adaptive thermogenesis and total energy expenditure.
Asunto(s)
Tejido Adiposo Pardo , Termogénesis , Adenosina Trifosfato/metabolismo , Tejido Adiposo Pardo/metabolismo , Animales , Ácidos Grasos/metabolismo , Ratones , Ratones Noqueados , Triglicéridos/metabolismo , Proteína Desacopladora 1/genética , Proteína Desacopladora 1/metabolismoRESUMEN
Recent studies indicate that adipose tissue in obesity promotes breast cancer progression by secreting protumorigenic chemokines, growth factors, and fatty acids. However, the detailed mechanisms by which hypertrophic adipose tissue influences breast cancer cells are still not well understood. Here we show that co-culture with adipose tissue from high-fat diet induced obese C57BL/6 mice alters transcriptome profiles in triple-negative breast cancer (TNBC) cells, leading to upregulation of genes involved in inflammation and lipid metabolism, such as IL1B, PLIN2, and ANGPTL4. Similar results were obtained by treating TNBC cells with adipose tissue conditioned media (ACM) generated from fat tissue of obese female patients. Many of the upregulated genes were activated by PPAR nuclear receptors, as shown by pathway analyses and gene expression experiments using PPAR agonists and antagonists. Metabolic analysis revealed that TNBC cells cultivated with ACM had significantly higher levels of ß-oxidation. Furthermore, ACM-treated TNBC cells displayed a pronounced aggressive cell phenotype, with enhanced wound healing, proliferation, and invasion capabilities. ACM-induced invasion was dependent on the PPAR-target ANGPTL4 and activated FAK signaling, as shown by ANGPTL4 depletion and FAK inhibition. Together, our data suggest that factors released by adipose tissue change PPAR-regulated gene expression and lipid metabolism and induce a more aggressive TNBC cell phenotype. These effects are, at least in parts, mediated by fatty acids provided by the adipose tissue. IMPLICATIONS: Adipose tissue provides factors for increased progression of TNBC cells, identifying PPAR- and FAK-signaling as potential novel targets for treatment of TNBC, especially in obese women.