Barquissau V, Beuzelin D, Pisani D F, Beranger G E, Mairal A, Montagner A, Roussel B, Tavernier G, Marques M-A, Moro C, Guillou H, Amri E-Z, Langin D
INSERM, UMR 1048, Institute of Metabolic and Cardiovascular Diseases, Toulouse, France; University of Toulouse, Paul Sabatier University, France.
University of Nice Sophia Antipolis, Nice, France; CNRS, iBV, UMR 7277, Nice, France; INSERM, iBV, U 1091, Nice, France.
Mol Metab. 2016 Mar 18;5(5):352-365. doi: 10.1016/j.molmet.2016.03.002. eCollection 2016 May.
Fat depots with thermogenic activity have been identified in humans. In mice, the appearance of thermogenic adipocytes within white adipose depots (so-called brown-in-white i.e., brite or beige adipocytes) protects from obesity and insulin resistance. Brite adipocytes may originate from direct conversion of white adipocytes. The purpose of this work was to characterize the metabolism of human brite adipocytes.
Human multipotent adipose-derived stem cells were differentiated into white adipocytes and then treated with peroxisome proliferator-activated receptor (PPAR)γ or PPARα agonists between day 14 and day 18. Gene expression profiling was determined using DNA microarrays and RT-qPCR. Variations of mRNA levels were confirmed in differentiated human preadipocytes from primary cultures. Fatty acid and glucose metabolism was investigated using radiolabelled tracers, Western blot analyses and assessment of oxygen consumption. Pyruvate dehydrogenase kinase 4 (PDK4) knockdown was achieved using siRNA. In vivo, wild type and PPARα-null mice were treated with a β3-adrenergic receptor agonist (CL316,243) to induce appearance of brite adipocytes in white fat depot. Determination of mRNA and protein levels was performed on inguinal white adipose tissue.
PPAR agonists promote a conversion of white adipocytes into cells displaying a brite molecular pattern. This conversion is associated with transcriptional changes leading to major metabolic adaptations. Fatty acid anabolism i.e., fatty acid esterification into triglycerides, and catabolism i.e., lipolysis and fatty acid oxidation, are increased. Glucose utilization is redirected from oxidation towards glycerol-3-phophate production for triglyceride synthesis. This metabolic shift is dependent on the activation of PDK4 through inactivation of the pyruvate dehydrogenase complex. In vivo, PDK4 expression is markedly induced in wild-type mice in response to CL316,243, while this increase is blunted in PPARα-null mice displaying an impaired britening response.
Conversion of human white fat cells into brite adipocytes results in a major metabolic reprogramming inducing fatty acid anabolic and catabolic pathways. PDK4 redirects glucose from oxidation towards triglyceride synthesis and favors the use of fatty acids as energy source for uncoupling mitochondria.
已在人类中鉴定出具有产热活性的脂肪库。在小鼠中，白色脂肪库内产热脂肪细胞（即所谓的白色脂肪中的褐色脂肪细胞，即米色脂肪细胞）的出现可预防肥胖和胰岛素抵抗。米色脂肪细胞可能起源于白色脂肪细胞的直接转化。本研究的目的是表征人类米色脂肪细胞的代谢。
将人多能脂肪来源干细胞分化为白色脂肪细胞，然后在第14天至第18天之间用过氧化物酶体增殖物激活受体（PPAR）γ或PPARα激动剂处理。使用DNA微阵列和RT-qPCR确定基因表达谱。在原代培养的分化人前脂肪细胞中证实了mRNA水平的变化。使用放射性标记示踪剂、蛋白质印迹分析和氧气消耗评估来研究脂肪酸和葡萄糖代谢。使用小干扰RNA实现丙酮酸脱氢酶激酶4（PDK4）的敲低。在体内，用β3-肾上腺素能受体激动剂（CL316,243）处理野生型和PPARα基因敲除小鼠，以诱导白色脂肪库中出现米色脂肪细胞。对腹股沟白色脂肪组织进行mRNA和蛋白质水平的测定。
PPAR激动剂促进白色脂肪细胞转化为呈现米色分子模式的细胞。这种转化与导致主要代谢适应性变化的转录变化相关。脂肪酸合成代谢，即脂肪酸酯化为甘油三酯，以及分解代谢，即脂解和脂肪酸氧化，均增加。葡萄糖利用从氧化转向用于甘油三酯合成的3-磷酸甘油的产生。这种代谢转变依赖于通过丙酮酸脱氢酶复合物的失活激活PDK4。在体内，野生型小鼠对CL316,243的反应中PDK4表达明显诱导，而在呈现米色化反应受损的PPARα基因敲除小鼠中这种增加减弱。
人类白色脂肪细胞向米色脂肪细胞的转化导致主要的代谢重编程，诱导脂肪酸合成代谢和分解代谢途径。PDK4将葡萄糖从氧化转向甘油三酯合成，并有利于使用脂肪酸作为线粒体解偶联的能量来源。
