成纤维细胞生长因子21介导鼠李糖乳杆菌GG对果糖诱导的非酒精性脂肪肝的治疗作用

Nonalcoholic fatty liver disease (NAFLD) has become a significant public health concern worldwide, which is closely associated with two major metabolic disorders, obesity and diabetes. The current epidemics of NAFLD have been linked to the increased intake of fructose in food and drinks additives in the last decades. Fructose is distinct from glucose in its ability to induce features of metabolic syndrome including insulin resistance, fatty liver, dyslipidemia and intraabdominal fat accumulation both in human and laboratory animals. The understanding towards the mechanisms underlying the development and progression of fructose-induced NAFLD is still not clear, although intensive studies in last decades. Fibroblast growth factor 21 (FGF21) is a member of the fibroblast growth factor family with multiple metabolic functions. FGF21 regulates lipid metabolism and reduces hepatic lipid accumulation in an insulin-independent manner. Pharmacological administration of FGF21 reverses hepatic steatosis, counteracts obesity and alleviates insulin resistance in rodents and nonhuman primates. However, the application of FGF21 therapy is hindered due to the short life time. Agents inducing endogenous FGF21 under pathological conditions are needed. Probiotics is known to modulate intestinal microbiota, preventing the increase of pathogenic bacteria and protecting the intestinal barrier. Our preliminary study using LGG to treat fructose-induced NAFLD showed a significant improvement in NAFLD along with markedly increased FGF21 expression. We hypothesize that the effects of LGG in fructose-induced NAFLD is mediated by FGF21 induction in the liver which is regulated by gut microbiota change and consequent induction of hepatic PPARα induction. In this proposal, we will use two genetic mouse models including global FGF21 knockout and liver-specific PPARα knockout mouse models to test our hypothesis. Completion of this project will provide rich information on the therapeutic strategy using probiotic LGG on fructose-induced NAFLD and insights into the regulatory mechanisms.

非酒精性脂肪性肝病（NAFLD）是全球性的公共健康问题。近年来NAFLD的一个主要原因是从食品中摄入多过果糖，但果糖诱导NAFLD的作用机制尙不明确。成纤维细胞生长因子21（FGF21）是FGF家族中发挥多种代谢调节功能的重要成员。FGF21可不依赖胰岛素直接调节肝脏脂质堆积，药理性给药FGF21 可以逆转肝脏脂肪变性。然而，由于FGF21在体内的半衰期短限制了其治疗作用。因此在病理条件下就需要诱导内源性的FGF21表达。我们前期研究结果表明LGG 处理可以逆转果糖引起的肝脏脂肪堆积，同时LGG 可以促进外周血及肝脏中FGF21显著升高。我们假设LGG对果糖引起的NAFLD的治疗作用是由FGF21介导的，而LGG通过影响肠道菌群变化进而作用于肝脏PPARα调节FGF21的表达。因此本研究将利用FGF21基因敲除鼠和PPARα肝脏特异性基因敲除鼠，阐明LGG对NAFLD治疗作用的理论基础。

非酒精性脂肪性肝病（NAFLD）是一种常见的、与肥胖相关的慢性肝脏疾病。NAFLD的发生与不良的饮食习惯，尤其是糖类（特别是果糖）的大量摄取有关，并且随着果糖消耗量的大幅增长，果糖摄入过量所引起的NAFLD也在快速增多，严重危害着人们的健康。有研究表明益生菌在治疗NAFLD中是有益的，但其机制尚不清楚。成纤维细胞生长因子（FGF）21是一种重要的代谢调节因子，已有多项研究表明FGF21可以改善NAFLD。本研究中，我们利用FGF21基因敲除（KO）和C57BL/6野生型（WT）小鼠，给予30％果糖饮水处理12周诱导NAFLD模型，在果糖饲喂的最后4周每天灌胃给予LGG处理小鼠。我们研究发现：1.在WT小鼠中，果糖饮水5周后FGF21表达显著升高，而果糖饮水12周后FGF21表达显着降低。2.LGG处理可以逆转FGF21的表达降低，使FGF21的表达仍然维持极高水平，同时LGG处理可以显著改善果糖引起的肝脏脂肪堆积和炎症损伤，值得注意的是，在KO小鼠中LGG却丧失了这一保护作用。3.LGG可以逆转果糖诱导的NAFLD，是由于LGG通过诱导肝脏FGF21表达的增加，FGF21分泌到外周血中引起脂肪组织脂联素表达分泌的增多，脂联素经血液循环回到肝脏组织通过调节鞘氨醇代谢以及磷酸酶2A（PP2A）C甲基化，进而调节肝脏碳水化合物反应原件结合蛋白及其下游信号通路来逆转果糖诱导的非酒精性脂肪肝。因此，我们的研究结果表明FGF21介导LGG对果糖诱导NAFLD的保护性作用。在国家自然科学基金的支持下，我们已完成了本项目，并在国际知名期刊发表了2篇研究论文，同时培养了1中青年骨干教师和1名硕士研究生，使其掌握了NAFLD、FGF21以及益生菌研究方面所必需的基本分子生物学知识和实验技能。