Phospholipase C-related catalytically inactive protein-knockout mice exhibit uncoupling protein 1 upregulation in adipose tissues following chronic cold exposure

Objectives

We have previously demonstrated that phospholipase C-related catalytically inactive protein (PRIP) is involved in fat metabolism and energy consumption. However, whether PRIP participates in body energy metabolism in vivo remains to be determined. Therefore, we examined whether PRIP deficiency affects whole-body energy homeostasis, which is modulated by non-shivering thermogenesis in brown adipose tissue, using a cold exposure animal model.

GLP-1受体激动剂对肥胖小鼠脂肪组织的脂解作用及机制探讨

目的:探讨胰高血糖素样肽1(GLP-1)受体激动剂艾塞那肽(exendin-4)对肥胖小鼠脂肪组织的作用及机制。方法:8周龄C57BL/6J小鼠高脂喂养12周后随机分为艾塞那肽组和生理盐水对照组,另设正常饮食组。取附睾旁脂肪检测sirtuin 1(SIRT1)、脂肪甘油三酯脂酶(ATGL)、肿瘤坏死因子α(TNF-α)及脂联素mRNA的表达。Exendin-4或联合SIRT1激动剂/抑制剂处理3T3-L1脂肪细胞24 h;小鼠胚胎成纤维细胞(MEF)诱导成脂肪细胞后exendin-4干预24 h;检测SIRT1、ATGL和激素敏感性脂酶(HSL)的蛋白表达水平。结果:与生理盐水对照组相比,艾塞那肽组小鼠附睾旁脂肪量、空腹血糖及血甘油三酯水平降低(均P0.05),体重减轻,血TNF-α水平降低。艾塞那肽干预后,肥胖小鼠脂肪组织SIRT1、ATGL和脂联素mRNA表达明显上调,TNF-αmRNA表达明显下调(P0.05)。Exendin-4剂量依赖性促进3T3-L1脂肪细胞SIRT1、ATGL和HSL脂解相关蛋白的表达。联合SIRT1激动剂后,脂滴数量减少,上述脂解相关蛋白的表达上调。联合SIRT1抑制剂后上述作用减弱。敲除SIRT1后MEF脂肪细胞内脂滴增大,数量增多,exendin-4促进脂解的作用消失。结论:艾塞那肽通过激活SIRT1促进肥胖小鼠脂肪组织脂解作用。     

Activation of PI 3-kinase by the hexosamine biosynthesis pathway

It has been shown that hyperglycaemia-induced defects in glucose transport and insulin action are mediated by increased flux of excess glucose through the hexosamine biosynthesis pathway (HBP). We have previously demonstrated that in rat adipocytes, increased flux through the HBP activates protein kinase C (PKC). The aim of the present study was to explore the mechanism for HBP-mediated activation of PKC. We show that activation of the HBP by either high glucose or glucosamine causes the translocation of PKC-zeta/lambda and PKC-epsilon but not other PKC isoforms tested (alpha, beta, delta). This translocation was inhibited by wortmannin, a PI 3-kinase inhibitor. Both high glucose and glucosamine caused widespread cellular activation of PI 3-kinase. We demonstrate that HBP-mediated activation of PI 3-kinase has an insulin-like effect to translocate GLUT4. We conclude that an acute increase of glucose flux through the HBP activates PI 3-kinase.     

An analysis of the lipolysis in vitro of obese-hyperglycaemic and diabetic mice

Summary Mice homozygous for either the obese gene in linkage group XI or the diabetes gene in linkage VIII exhibit syndromes similar to those of diabetes mellitus in man, including obesity and hyperglycaemia. A study of the lipolysis in vitro of the epididymal adipose tissue of 5 genotypes of mice, namely, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db, and db ⁺/db ⁺, demonstrates that the mutant homozygotes respond differently from wild type homozygotes to various lipolytic agents. The agents tested were epinephrine, norepinephrine, isoproterenol, corticotropin 1–24, theophylline and N⁶, O²-dibutyryl-cyclic-adenosine3,5-monophosphate. The response of ob/ob ⁺ tissue was the same as that of ob ⁺/ob ⁺ tissue. The data indicate that there is a defect with respect to lipolysis in ob/ob and db/db mice. This is discussed in light of the involvement of cyclic AMP.

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Untersuchungen der Lipolyse in vitro bei der fettsüchtig-hyperglykämischen und der diabetischen Maus

Zusammenfassung Mäuse, die entweder für Fettsucht (ob) in der Verbindungskette XI oder für Diabetes (db) in der Verbindungskette VIII homozygot sind, weisen Syndrome auf, die denen des menschlichen Diabetes mellitus ähnlich sind. Das bezieht sich auch auf Fettsucht und Hyperglykämie. Eine Untersuchung der in vitro Lipolyse der epididymalen adipösen Gewebe von 5 Mausgenotypen, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db und db ⁺/db ⁺, zeigte, daß mutante Homozygoten anders auf lipolytische Mittel reagieren als homozygote Typen der Wildform. Die geprüften Wirkstoffe waren Adrenalin, Noradrenalin, Isoproterenol, Corticotropin 1–24, Theophyllin und N⁶, O²-Dibutyrylzyklo-adenosin 3,5-monophosphat. Die Reaktionen des ob/ob ⁺ Gewebes und des ob ⁺/ob ⁺ Gewebes sind gleichartig. Die Ergebnisse deuten auf einen Defekt der Lipolyse bei ob/ob und db/db Mäusen hin. Die Bedeutung des cyclischen AMP in dieser Hinsicht wird diskutiert.

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Une analyse de la lipolyse in vitro de souris obèses hyperglycémiques et diabétiques

Résumé Les souris homozygotes (que ce soit le gène obèse du groupe XI ou le gène diabétique du groupe VIII) présentent des syndromes semblables à ceux du diabète sucré chez l'homme, y compris obésité et hyperglycémie. Une étude de la lipolyse in vitro du tissu adipeux épididymaire de 5 génotypes de souris, soit, ob/ob, ob/ob ⁺, ob ⁺/ob ⁺, db/db, et db ⁺/db ⁺, démontre que la réaction des homozygotes mutants à divers agents lipolytiques diffère de celle des homozygotes normaux. Les substances étudiées ont été l'adrénaline, la noradrénaline, l'isoprotérénol, la corticotropine 1–24, la théophylline et le N⁶, O²-dibutyryl-cyclique-adénosine-3,5-monophosphate. La réponse des tissus ob/ob ⁺ est la même que celle des tissus ob ⁺/ob ⁺. Les données indiquent qu'il existe un trouble de la lipolyse chez les souris ob/ob et db/db. Ceci est examiné à la lumière du rôle joué par l' AMP cyclique.

     

Prospective and controlled studies of the actions of insulin and catecholamine in fat cells of obese women following weight reduction

Aims/hypothesis Enlarged fat cells from obese subjects are characterised by insulin resistance and abnormal adrenergic regulation of lipolysis. The aim of the present study was to examine whether these aberrations return to normal following weight reduction.Materials and methods Obese women (n=25) were investigated before and 3±1 years (mean±SD) after steady-state weight reduction and compared with control women who were matched to the cases at re-examination in terms of age and BMI. Adipocyte volume, lipogenesis and lipolysis were determined in isolated subcutaneous fat cells following stimulation or inhibition at different steps of the lipolytic cascade.Results Weight reduction decreased fat cell volume and basal and adrenergic-regulated lipolysis rates to values that were 20–40% lower than those in control women (p=0.0002–0.03), despite the fact that percentage body fat was almost identical in the two groups of women. Fat cell volume was directly proportional to lipolysis in obese subjects, both before and after weight reduction, and in control subjects. Insulin-induced antilipolysis and lipogenesis were completely normalised after weight reduction.Conclusions/interpretation Body-weight-reduced obese women had low basal and catecholamine-stimulated adipocyte lipolysis, presumably due to adipose tissue hyperplasia. This could make an important contribution to body weight gain following weight loss. Adipocyte insulin resistance is secondary to obesity.     

Adipose tissue and adipocyte dysregulation

Obesity-associated insulin resistance is a complex disorder involving a number of candidate molecules, pathways and transduction systems possessing potential causal actions. Inflammation in adipose tissue (AT) is one mechanism proposed to explain the development of insulin resistance, while identification of factors that lead to or cause AT dysfunction when it reaches its limit of expansion represents an important challenge. Pathological expansion of AT is characterized by changes in its blood flow, and the presence of enlarged and dysfunctional adipocytes that begin an inflammatory campaign of altered adipokine and cytokine secretions. Adipocyte senescence, necrosis and death are associated with increased immune cell and macrophage infiltration of AT in obesity. This can boost inflammation and reinforce fat cell dysfunction and death. In addition, pathological fat mass expansion is also related to limited recruitment of fat cell progenitors able to proliferate and differentiate into healthy small fat cells to compensate for cell death and preserve adipocyte numbers. Limiting vascular development and enhancing fibrotic processes worsen inflammation towards chronic irreversibility. The AT expandability hypothesis states that failure of AT expansion is one of the key factors linking positive energy balance and cardiometabolic risks, not obesity per se. Besides the usual treatment of obesity based on behavioral approaches (specific dietary/nutritional approaches together with increased physical activity), a number of questions remain concerning the possible recovery of metabolic health after inflammation-preventing interventions.     

非侵入性聚焦超声在融脂领域的研究状况

近年来,高强度聚焦超声及低强度聚焦超声在脂肪组织的无创消融领域受到广泛关注。该技术旨在实现脂肪消融,且其安全性和有效性已得到国内外的临床验证。脂肪消融实验表明,聚焦超声在被应用于脂肪消融时,产生的不良反应是瞬间的,并不会引起血脂等人体重要生理指标的变化。本文介绍了聚焦超声用于脂肪消融的基本原理,同时调研了聚焦超声用于脂肪消融的国内外研究现状及临床安全性验证等内容。     

Interleukin-6 stimulates lipolysis in porcine adipocytes

Interleukin (IL)-6 stimulates lipolysis in human and rodents adipocytes. However, the mechanism regulating this process is little known. In this study, we demonstrated that IL-6 increased lipolysis in differentiated porcine adipocytes by activation of extracellular signal-related kinase (ERK), which was inhibited by specific ERK inhibitor PD98059. IL-6 treatment did not elevate intracellular cAMP and specific PKA inhibitor H89 did not affect IL-6-induced lipolysis, which suggested that protein kinase A (PKA) pathway was not involved in IL-6-induced lipolysis. Also, the expressions of perilipin A and PPARγ2 were significantly reduced in response to IL-6 treatment, but the expressions of peroxisome proliferators-activated receptor gamma coactivator-1 alpha (PGC-1α), carnitinepalmitoyl-transferase-1 (CPT-1), and uncoupling protein 2 (UCP2) were significantly elevated. In conclusion, these results suggested that chronic high dose of IL-6 directly stimulated lipolysis in porcine adipocytes through activation of ERK, subsequently repressing perilipin A and promoting PGC-1α expression.     

Adenosine release from isolated fat cells and its significance for the effects of hormones on cyclic 3′,5′-AMP levels and lipolysis

Summary The effect of lipolytic stimulants on cyclic AMP levels and glycerol production is strongly dependent on the concentration of fat cells in the incubation medium. After addition of noradrenaline cyclic AMP levels in diluted fat cell suspensions (20 000 cells/ml) reached 10 fold higher levels and declined much more slowly than in concentrated cell suspensions (100 000 cells/ml). An inhibitory substance appeared in the incubation medium which, after addition to a suspension of fresh fat cells caused a dose-dependent inhibition of hormone effects. The inhibitor was produced during preincubation periods of the fat cells and was removed by washing the cells with fresh medium.Purification of the medium by acid extraction, gel filtration, thin layer chromatography and the identification by gas chromatography showed that the inhibitor released represents adenosine. After incubation with adenosine deaminase the inhibitory activity of the medium disappeared. No inhibitory activity was obtained from the incubation medium by solvent extraction, a procedure which fully recovered added PGE₂. Adenosine appeared in the medium after 5 min of incubation of fat cells and reached maximal levels (0.2 nmol/ml/10⁵ cells) after 20 min. Noradrenaline (10 M) did not stimulate the release of adenosine from fat cells. Addition of 0.01 to 0.1 M of adenosine to fat cells effectively inhibited cyclic AMP accumulation and lipolysis induced by noradrenaline. Hence, a delayed rise and the secondary decline of cyclic AMP levels after hormonal stimulation can be accounted for by adenosine released from fat cells.     

自聚焦超声在动物离体皮下脂肪组织中的融脂效应研究

目的：探索高频聚焦超声和低频聚焦超声在不同辐照时间和功率的条件下,对离体动物猪的皮下脂肪不同层产生生物学融脂效应的规律。方法：将离体动物猪脂肪生物实验分为两组,分别使用工作频率为6．5MHz和3MHz的换能器。两组使用的超声功率为2～5w,辐射时间为5S、10S、20S、4s、60s和80S;辐照后进行MTT检测脂肪细胞活性并计算融脂效应的面积。描述离体动物猪的皮下脂肪层生物学融脂效应,讨论不同条件下生物学融脂效应之间的区别。结果：随着超声功率和辐照时间的增加,脂肪组织形成融脂效应的程度呈规律性变化。辐照时间为5s时脂肪组织破坏不明显,辐照时间〉10s时脂肪组织则明显被破坏。相同超声功率和辐射时间条件下聚焦超声在深脂肪层的破坏程度比浅表脂肪层高。3MHz聚焦超声在辐射时间≥40s可穿过约5mm的表皮并凝固性破坏皮下不同层次的脂肪组织。结论：高频和低频聚焦超声均可有效破坏脂肪组织。