中国科学院昆明动物研究所机构知识库

非酒精性脂肪肝病（non-alcoholic fatty liver disease，NAFLD）是由酒精之外的其他因素导致的肝脏中以脂肪积累为主要特征的临床病理综合征，高能量食物（尤其是高脂高胆固醇食物）的过多摄入和多坐少动等都是它的诱发因素。目前其正在逐渐成为一个严重的公共健康问题，在西方发达国家，大约有20-30%的人患有非酒精性脂肪肝，而在中国，也有12-24%的人承受同样的疾病折磨。一般而言，患有非酒精性脂肪肝的患者同时也伴有肥胖、高血糖、高血脂、胰岛素抵抗甚至2型糖尿病等代谢综合征（metabolic syndrome）的症状，对于这一类非酒精性脂肪肝已经建立了诸多的动物模型来供人们研究，尽管目前对其发病机理了解的不是很透彻，但还是取得了一些进展；但是，另一方面，在亚太地区，一些非酒精性脂肪肝患者（15-21%）却并没有表现出肥胖和糖尿病症状，因此被称为是非肥胖型非酒精性脂肪肝（non-obese NAFLD），遗憾的是，目前并没有十分理想的动物模型可用来对其开展研究，这也导致我们对这种非肥胖型非酒精性脂肪肝的发病机理知之甚少。树鼩（tree shrew）是一种小型哺乳动物，它在生物分类学上的位置介于啮齿类和灵长类之间，其进化地位比啮齿类更为高级。正因为如此，树鼩不断被应用于生物学研究领域，包括神经生物学、病毒学（乙型和丙型肝炎病毒）、行为学（应激和抑郁等）、癌症和代谢性疾病等方面的研究。然而树鼩能否被用来研究脂肪肝还不得而知。为了回答上述问题，在本研究中，首先，我们用不同高热量食物的组合（如高糖、高脂、高糖高脂以及高脂高胆固醇等）来对树鼩（Tupaia belangeri chinensis）进行食物诱导。结果发现，诱导之后，各组树鼩表现出不同程度的肝功能受损，同时伴随有高脂血症，但血糖并未呈现明显变化。进一步通过组织切片检查其肝脏组织发现，所有树鼩都出现肝脏脂肪积累，这意味着我们成功诱导了树鼩脂肪肝。但令人惊奇的是，和对照组树鼩相比，这些脂肪肝树鼩的体重并没有增加，而且在皮下和腹腔等处也没有脂肪组织的出现，说明它们没有形成肥胖。因此，我们认为树鼩可以作为一种较好的研究非肥胖型非酒精性脂肪肝的动物模型。接着，我们用高脂高胆固醇食物进一步研究发现，树鼩不仅能够形成非酒精性脂肪肝的早期阶段（单纯性脂肪肝），还能够出现脂肪性肝炎和纤维化，也就是说树鼩能够完整模拟非酒精性脂肪肝的发病过程，并且模拟这一过程需要的时间只有小鼠模型的三分之一。同时，在发病机理方面，经过对脂代谢基因的筛选，我们发现肝脏脂蛋白脂酶（lipoprotein lipase，LPL）在高脂高胆固醇诱导下高表达，而将LPL抑制之后，动物水平上，高脂高胆固醇导致的脂肪肝症状得到了明显的恢复；细胞水平上，氧化型 LDL引起的树鼩肝脏原代细胞内的脂肪积累现象也得到了显著改善。因此我们的研究结果说明，LPL在高脂高胆固醇诱导的树鼩非肥胖型非酒精性脂肪肝发病过程中起着关键作用。此外，在上述基础上，为了探究肝脏LPL的高表达到底是高脂和高胆固醇的共同作用诱导的、还是单独的胆固醇诱导的以及这其中蕴藏着怎样的调控机制等问题，我们在小鼠上设计了单独不同浓度的胆固醇诱导以及不同浓度的胆固醇与高脂组合诱导的实验并做了肝脏转录组检测，结果显示，单独的一定浓度胆固醇就可以诱导肝脏LPL的高表达。然而，由于转录组数据分析还在进行之中，因此关于这其中的调控机理还需要等待转录组数据的分析结果和实验验证来回答。

Non-alcoholic fatty liver disease (NAFLD) refers to the presence of aberrant lipids accumulation in the liver in the absence of a history of significant alcohol consumption, to which an over intake of high energy diets, especially the high fat and high cholesterol diet, as well as the lack of exercise are the risk factors. NAFLD is becoming a severe public health problem that is affecting a large proportion of the world population, for instance, it is estimated that NAFLD prevalence varys from 20 to 30% in Western countries and from 12 to 24% in China.Generally, NAFLD in patients is usually accompanied by obesity, hyperglycemia, hyperlipidemia, insulin resistance (IR) and type 2 diabetes (T2D), for which numerous animal models have been generated in order to explore the pathogenesis and therapies of NAFLD. On the contrary, quite a number of NAFLD subjects (15-21%), especially in Asian regions, are non-obese and non-diabetic; however, few animal models are available for the research of non-obese NAFLD.Tree shrew is a small mammal, which has a closer evolutionary relationship to primates than rodents. Due to this, it has been used as animal model in biology research field, including neurobiology, hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, stress and depression, cancer and metabolic disease. However, it is unclear whether tree shrew can be an alternative choice of animal model to study human NAFLD.To solve those questions mentioned above, here, variable compositions of high energy diets were used to treat tree shrews (Tupaia belangeri chinensis). Analysis of plasma biochemical parameters and hepatic histology revealed that all high energy diets led to hepatic lipids accumulation, liver injury and hypercholesterolemia, but had no effect on body weight and adipose tissue generation, or glycemia. In conclusion, the tree shrew displays hepatic steatosis and dyslipidemia, but remains non-obese and non-diabetic under high energy diets, which suggests that the tree shrew may be useful as a novel animal model for the research of human non-obese NAFLD.Next，by using high fat and high cholesterol (HFHC) diet, we found that not only hepatic steatosis but also the nonalcoholic steatohepatitis and fibrosis can be induced in tree shrew, which means that the tree shrew can mimic the entire spectrum of NAFLD. Moreover, the time required for this process is just one third of that needed in mice models. To explore the pathogenesis, the common genes of lipids metabolism were detected at mRNA expression level, the results showed that lipoprotein lipse (LPL) was up-regulated under the treatment of HFHC. Furthermore, inhibition of LPL significantly rescued the lipids accumulation in the liver induced by HFHC and in the primary tree shrew hepatocytes induced by ox-LDL. In conclusion, these results indicate that LPL plays an key role in the genesis and development of NAFLD in tree shrew model induced by HFHC.Inaddition, in order to investigate the mechanism underlying the regulation of LPL that whether LPL is controled by single effect of cholesterol or by synergistic effect of cholesterol and high fat, we set different diets containing various concentrations of cholesterol and the combination of that and high fat diet to treat mice and then assessed their liver transcription profile by RNA-Seq. Although the liver transcriptome analysis has not been completely finished yet, the preliminary transcriptome data and gene expression showed that diets just composed of certain concentration of cholesterol could induce the increased expression of liver LPL.