Objective: To investigate the mechanism of electroacupuncture （EA） in promoting the browning of white adipose tissue in middle-aged and aged obese rats induced by high fat by regulating AMP-activated protein kinase （AMPK） /silence-information regulatory factor 1 （Sirt1） pathway and neuregulin 4 （Nrg4）.
Methods: Twenty-four male SD rats were randomized into blank control, model and EA groups （n=8 per group）. The obesity model was established by feeding the rats with high-fat diet for 6 weeks. For the EA group, EA （2 Hz/15 Hz, 1.5 mA） was applied to "Guanyuan" （CV4） and bilateral "Shenshu" （BL23）, "Fenglong" （ST40） and "Tianshu" （ST25） for 20 min, once a day, 5 days a week for 6 weeks. Rats of the blank control and model groups were also restrained for 20 min. The body mass and food intake were measured every week, and the Lee's index, epididymal fat, perirenal fat and brown adipose tissue were weighed. The contents of serum total cholesterol （TC）, triglyceride （TG）, high density lipoprotein cholesterol （HDL-C）, low density lipoprotein cholesterol （LDL-C） and norepinephrine （NE） were determined by ELISA. H.E. staining was used to observe the morphological changes of white and brown adipose tissue. The mRNA expression levels of mitochondrial uncoupling protein 1 （UCP1）, peroxisome proliferator activated receptor γ co-activator 1α （PGC-1α）, PR-domain protein 16 （PRDM16）, peroxisome proliferator activated receptor γ （PPARγ） and Nrg4 in the adipose tissue were detected by quantitative real time PCR, and the protein expression levels of Nrg4, AMPKα, Sirt1 and interleukin-6 （IL-6） in the white and brown adipose tissue were detected by Western blot.
Results: Compared with the blank control group, the body mass, food intake, the Lee's index, epididymal fat and perirenal fat mass, and serum TG, TC and LDL-C contents and the expression level of IL-6 protein were significantly increased （P<0.01, P<0.05, P<0.001）, and the brown adipose mass, serum HDL-C and NE contents, the expression levels of UCP1, PGC-1α, PRDM16, PPARγ and Nrg4 mRNAs, and the protein expression levels of AMPKα, Sirt1 and Nrg4 proteins in both white and brown adipose tissues were significantly decreased in the model group （P<0.01, P<0.05）. After EA intervention, the increased levels of body mass, food intake, Lee's index, epididymal fat and perirenal fat mass, serum TG, TC and LDL-C contents, and the expression of IL-6 protein, and the decreased levels of brown adipose mass, serum HDL-C and NE contents, expression levels of UCP1, PGC-1α, PRDM16, PPARγ and Nrg4 mRNAs, and those of AMPKα, Sirt1 and Nrg4 proteins in both white and brown adipose tissues were apparently reversed（P<0.05, P<0.01, P<0.001）. H.E. staining showed an increase of the volume and content of intracellular vacuoles of both white and brown adipose tissues, disordered arrangement of cells with vague boundary in the model group, which was relatively milder including a decrease of volume and content of vacuoles of both white and brown adipose, neat arrangement of cells with clear boundary.
Conclusion: EA intervention can improve lipid metabolism and promote white adipose tissue browning in middle-aged and aged obese rats, which is possibly associated with its functions in activating AMPK/Sirt1 signaling pathway and up-regulating the level of Nrg4.
目的：探讨电针通过调控腺苷酸活化蛋白激酶（AMPK）/沉默信息调节因子1（Sirt1）通路及神经调节蛋白4（Nrg4）的含量促进高脂诱导的中老年肥胖大鼠白色脂肪棕色化的机制。方法：24只10月龄SD雄性大鼠，随机分为空白组、模型组和电针组，每组8只，以高脂饲料喂养6周建立肥胖模型。电针组电针“关元”和双侧“肾俞”“天枢”和“丰隆”（2 Hz/15 Hz，1.5 mA），留针20 min，每日1次，治疗5 d休息2 d，共治疗6周。每周测量大鼠体质量和摄食量。针刺6周末，计算大鼠Lee’s指数，称量附睾脂肪、肾周脂肪和棕色脂肪质量；ELISA法检测各组大鼠血清总胆固醇（TC）、甘油三酯（TG）、高密度脂蛋白胆固醇（HDL-C）、低密度脂蛋白胆固醇（LDL-C）、去甲肾上腺素（NE）含量；HE染色观察各组大鼠白色和棕色脂肪组织形态变化；荧光定量PCR法检测大鼠脂肪组织线粒体解偶联蛋白1（UCP1）、过氧化物酶体增殖物活化受体γ辅助激活因子-1α（PGC-1α）、PR结构域蛋白16（PRDM16）、过氧化物酶体增殖物激活受体γ（PPARγ）、Nrg4 mRNA的表达；Western blot法检测大鼠脂肪组织 Nrg4、AMPKα、Sirt1、白介素-6（IL-6）蛋白表达水平。结果：与空白组比较，模型组大鼠体质量与摄食量，Lee’s指数，附睾脂肪和肾周脂肪质量均明显增加（P<0.01，P<0.05，P<0.001），血清TG、TC、LDL-C含量，白色脂肪与棕色脂肪中IL-6蛋白表达明显升高（P<0.01，P<0.05）；棕色脂肪质量，血清HDL-C、NE含量，白色脂肪与棕色脂肪UCP1、PGC-1α、PRDM16、PPARγ、Nrg4 mRNA表达，AMPKα、Sirt1、Nrg4蛋白表达均明显降低（P<0.01， P<0.05）；HE染色下白色脂肪和棕色脂肪体积增大，细胞内空泡含量增多，细胞排列紊乱，边界不清晰。与模型组比较，电针组大鼠以上指标均有所逆转（P<0.05，P<0.01，P<0.001），HE染色下白色脂肪和棕色脂肪体积减小，细胞内空泡含量减少，且细胞排列整齐，边界清晰。结论：电针可以改善中老年肥胖大鼠脂质代谢，促进白色脂肪棕色化，其机制可能与激活AMPK/Sirt1通路和上调Nrg4含量相关。.
Keywords: AMPK/Sirt1 signaling pathway; Electroacupuncture; Lipid metabolism; Nrg4; Obesity; White adipose tissue browning.