饲源性鼠李糖乳杆菌GG胞外多糖（LGG EPS）降低鱼类肝脂积累的分子机制

High-fat diet-induced fatty liver in farmed fish is one of the major problems for the sustainable development of the current aquaculture. In the previous studies, we show that isolated exopolysaccharides (EPS) from the probiotic strain Lactobacillus rhamnosus GG (LGG) impart anti-hepatic steatosis effects on high-fat diet-fed zebrafish by reducing lipogenesis and enhancing lipid catabolism for energy expenditure. However, the underlying mechanism of anti-hepatic steatosis effect of LGG EPS are not clear. This involves the relative roles played by LGG EPS (direct effect) and the gut microbiota induced by LGG EPS (indirect effect), the influence of each effect on the pathways of lipid metabolism (lipogenesis, catabolism, or both), and the receptors that mediate the anti-hepatic-steatosis effect. The project will clarify the relative contribution of the direct effects of LGG EPS on hepatic lipogenesis and lipid catabolism and the indirect effects mediated by the gut microbiota by using the the hepatocyte fatty degeneration model and the germ-free zebrafish fatty liver model, combined with RT-qPCR, small RNA interference (siRNA), Morpholino gene knock down and 16s rRNA sequencing technologies. The results of this study will drive the application of LGG EPS in control of fish fatty liver and promote the healthy and sustainable development of aquaculture.

高脂饲料诱发的养殖鱼类脂肪肝是当前我国水产养殖可持续发展的障碍之一。申请人前期研究发现饲喂鼠李糖乳杆菌胞外多糖（LGG EPS）可通过抑制脂合成及促进脂分解双向降低高脂饲料诱导的斑马鱼肝脂积累，但具体机制不清：LGG EPS是依靠自身直接发挥降脂效应，还是介导肠道菌群间接起作用，还是二者协调推进？这两方面各自是介导单向通路还是双向同步实施调控？拟结合斑马鱼肝细胞（ZFL）脂肪变性模型和无菌斑马鱼脂肪肝模型，结合RT-qPCR、小RNA干扰（siRNA）、Morpholino基因敲降和16S rRNA测序等技术，从LGG EPS直接作用和介导肠道菌群间接作用2个方面及脂合成与脂分解2个方向着手，解析饲源性LGG EPS改善鱼类脂肪肝的代谢调控通路及介导靶点。研究结果将为养殖实践中应用LGG EPS改善鱼类脂肪肝提供理论支撑，有望推进我国水产养殖健康可持续发展。

在发现饲喂鼠李糖乳杆菌胞外多糖（LGG EPS）可通过抑制脂合成及促进脂分解双向降低高脂饲料诱导的斑马鱼肝脂积累的基础上，进一步从LGG EPS直接作用和介导肠道菌群间接作用2个方面探究了其效应机制。通过LGG EPS与斑马鱼肝细胞和无菌斑马鱼分别互作发现，LGG EPS只具有抑制肝脏脂合成的作用，不影响脂分解，而且脂合成效应是由TLR4ba受体介导的。同时发现饲料中LGG EPS可以显著鱼体肠道菌群结构，并进一步发现LGG EPS诱导的肠道菌群通过抑制脂合成和促进脂分解发挥降肝脂效应，并进一步证明禁食诱导因子Fiaf介导肠道菌群效应。从而在机制上阐明了饲源性LGG EPS改善高脂饲料诱导鱼类脂肪肝的分子机制，为养殖实践中应用LGG EPS改善鱼类脂肪肝提供理论支撑。