猪胆通过调控Sirt6-内质网应激-瘦素信号通路减肥的机制研究

Leptin plays a key role in the regulation of feeding and energy homeostasis. Leptin resistance is a main cause of obesity. Recent studies have demonstrated that endoplasmic reticulum (ER) stress is involved in the development of leptin resistance. Thereby, the improvement of ER stress and increase of leptin sensitivity is a potential therapy for obesity. Our preliminary data have shown that hog bile extract and its major component, hyodeoxycholic acid (HDAC), could reduce body weight and fat mass significantly in high-fat induced obesity (DIO) mice. These drugs also increased Sirt6 activity, suppressed ER stress and increase leptin sensitivity in the hypothalamus of the DIO mice. Therefore, we suppose that the anti-obesity effect of HDAC may through improvement of ER stress induced by Sirt6 activation. To address our hypothesis, body weight as well as food intake, fat mass content, energy expenditure and leptin resistance will be assayed in DIO mice, ob/ob and db/db mice. Meanwhile, we will assay the link between the Sirt6 signaling, ER stress and leptin sensitivity in the hypothalamus. Furthermore, Sirt6 and CHOP gene deletion mice will be involved to confirm that the direct targeting Sirt6 to relieve ER stress by HDCA . The study would reveal the mechanisms for the anti-obesity effects of hog bile extracts and HDCA, and identify that HDCA is a major component for obesity in hog bile acid. Our data will provide the strong support for the R&D of HDCA-based anti-obesity drug with proprietary intellectual property rights.

瘦素是控制摄食与能量代谢的关键分子，目前认为瘦素抵抗是引起肥胖的主要机制。新近研究证明，下丘脑内质网应激是引起瘦素抵抗的重要机制。改善下丘脑内质网应激从而增加瘦素敏感性为潜在的减肥手段。我们发现，猪胆及主要成分猪去氧胆酸可通过改善肥胖小鼠瘦素抵抗降低摄食量、减轻体重。我们还发现其能增加Sirt6去乙酰化酶活性，抑制下丘脑内质网应激反应来激活下丘脑不同神经核团瘦素信号通路。因此我们提出猪胆及猪去氧胆酸通过激活Sirt6改善下丘脑内质网应激而减肥的假说。为验证这一假说，本项目拟观察猪胆及猪去氧胆酸对多种肥胖小鼠体重、能量代谢及瘦素抵抗等的影响，明确其减肥作用，考察下丘脑Sirt6信号与内质网应激和瘦素信号的联系。同时结合Sirt6和CHOP敲除小鼠证明其通过直接激活下丘脑Sirt6活性缓解内质网应激反应，揭示猪胆减肥作用的分子机制和主要活性物质基础，为开发具有自主知识产权的减肥药提供依据。

瘦素是控制摄食与能量代谢的关键分子，目前认为瘦素抵抗是引起肥胖的主要机制，而下丘脑内质网应激是引起瘦素抵抗的重要机制。改善下丘脑内质网应激从而增加瘦素敏感性为潜在的减肥手段。本项目通过使用高脂饲料诱导的肥胖小鼠（DIO）、ob/ob和 db/db肥胖小鼠研究发现，猪胆主要成分猪去氧胆酸可以显著降低DIO小鼠的摄食量及体重，减少肥胖小鼠腹部脂肪，肝脏、肾周脂肪和附睾脂肪，和脂肪细胞面积。降低小鼠空腹血糖，改善糖耐量，降低胰岛素抵抗，降低高瘦素血症和高胰岛素血症，并显著减轻小鼠肝脏脂肪堆积、血清谷丙转氨酶和谷草转氨酶水平。增加DIO小鼠O2、CO2和呼吸商，提高肥胖小鼠能量代谢。机制研究显示，猪去氧胆酸显著降低炎症因子IL-6基因在DIO小鼠肝脏的表达，增加甘油三酯脂肪酶基因mRNA水平，抑制脂蛋白脂酶基因mRNA水平。减轻衣霉素诱导的肝HepG2细胞内质网应激蛋白ATF4、CHOP和GRP78水平，同时减轻DIO小鼠肝脏CHOP和GRP78水平。使用DIO肥胖小鼠进行侧脑室注射猪去氧胆酸干预发现，侧脑室猪去氧胆酸注射后摄食量显著减少。但猪去氧胆酸对正常小鼠、和瘦素及瘦素受体缺失的ob/ob、 db/db小鼠体重、血糖、肝脏脂肪堆积等则无明显作用。研究结果提示，猪胆和猪去氧胆酸可能通过改善下丘脑摄食中枢的瘦素信号，以及抑制内质网应激而改善肝脏脂肪堆积而改善瘦素抵抗，从而发挥减肥、改善胰岛素抵抗和脂肪肝的作用。本研究结果揭示了中药猪胆在减肥中的作用的分子机制，发现了猪胆减肥发主要活性成分为猪去氧胆酸，为开发具有自主知识产权的减肥药提供依据。