Pivotal role of the Keap1-Nrf2 pathway in the pathogenesis and prevention of non-alcoholic steatohepatitis induced cirrhosis

非酒精性脂肪性肝炎（NASH）是一种常见的疾病，涉及肝细胞中的脂肪积累和肝脏炎症。它的发病率正在迅速增加，因为它在糖尿病患者和肥胖者中普遍存在;据估计，英国约2.0%的成年人口可能患有NASH。这一趋势令人担忧，并对国家卫生服务产生巨大的成本影响，因为NASH可引起肝纤维化，肝硬化和癌症，其中没有一种是可治疗的。据认为，NASH在某些个体中出现，因为他们的肝脏不能科普饮食，糖尿病或环境产生的代谢变化。在这些情况中的每一种情况下，设想氧化应激代表产生肝脏疾病的生理和环境损伤的共同后果。被称为Nrf 2的蛋白质的活性正在成为NASH易感性的最重要决定因素，原因有三：（i）它使肝脏中的脂肪产生和储存保持在低水平;（ii）它有助于维持高水平的抗炎蛋白质，以及（iii）它是维持肝脏中高水平天然抗氧化剂的重要组分。我们假设Nrf 2通常起着最小化NASH发生的可能性的作用，并且通过使用药物增加其活性将保护发展NASH和疾病进一步进展的“风险”个体。迄今为止，涉及Nrf 2确定NASH易感性或预防疾病的实验使用了专门的非标准饮食（缺乏某些关键分子），这与人类疾病无关。不幸的是，不存在概括肝脏病理学的整个谱的标准动物模型（即，从脂肪变性到NASH，到纤维化，到肝硬化和肝癌），我们可以用它来测试Nrf 2在这种疾病中的作用。在一项初步研究中，我们发现给小鼠喂食“西方”高脂肪（HF）饮食24周会产生轻度NASH，而给完全缺乏Nrf 2的小鼠喂食相同的饮食相同的时间会产生完全的NASH，伴有纤维化和肝硬化。我们现在希望通过研究大量食用HF饲料的动物，并通过使用生物标志物检查疾病的时间进程来证实这些初步发现为了证明Nrf 2在NASH的发展及其向纤维化和肝硬化的进展中是否重要，我们首先需要至少一种反映人类疾病的可靠动物模型。为此，我们将产生两种模型，我们预计这两种模型将以不同的速度发展肝病：首先，我们将给正常小鼠喂食“西方”高脂肪（HF）饮食;其次，我们将给正常小鼠喂食“西方”高脂肪+果糖（即高糖; HFF）饮食。将使用与疾病发展相关的病理变化的临床化学、组织学和生物化学测量来建立喂食这两种饮食的小鼠中脂肪肝、NASH、纤维化和肝硬化发展的详细时间过程。一旦疾病的进展速度已经在置于“西方”HF和HFF饮食的正常小鼠中确定，我们将通过测试当这些小鼠被喂食相同的饮食时，去除这种蛋白质是否会导致NASH、纤维化和肝硬化的加速出现来检查Nrf 2对保护免受NASH的贡献。最后，我们将检查当动物喂食相同的“西方”HF和HFF饮食时，通过遗传手段或通过某种类型的药物治疗激活Nrf 2是否抑制NASH、纤维化或肝硬化的出现。

Non-alcoholic steatohepatitis (NASH) is a common disease that involves fat accumulation in liver cells and inflammation of the liver. Its incidence is increasing rapidly because it is prevalent in individuals with diabetes and those who are obese; it has been estimated that approximately 2.0% of the adult population in the UK may have NASH. This trend is alarming, and has huge cost implications for the National Health Service, because NASH can give rise to liver fibrosis, cirrhosis and cancer, none of which are treatable. It is thought that NASH arises in certain individuals because their livers do not cope with metabolic changes produced by diet, diabetes or the environment. In each of these cases, it is envisaged that oxidative stress represents a common consequence of the physiological and environmental insults that produce liver disease. The activity of a protein known as Nrf2 is emerging as the most important determinant of susceptibility to NASH for three reasons: (i) it keeps fat production and storage in the liver low; (ii) it helps maintain high levels of anti-inflammatory proteins and (iii) it is a vital component in maintaining high levels of natural anti-oxidant agents in the liver. We hypothesize that Nrf2 normally functions to minimise the likelihood of NASH arising, and that by increasing its activity using drugs will protect 'at risk' individuals of developing NASH and the disease progressing further. To date, experiments that have implicated Nrf2 in determining susceptibility to NASH or prevention of the disease have used a specialized, non-standard diet (deficient in certain key molecules), which is not relevant to the human disease. Unfortunately, no standard animal model exists that recapitulates the entire spectrum of liver pathology (i.e., from steatosis, to NASH, to fibrosis, to cirrhosis and to hepatoma), which we can use to test the role of Nrf2 in this disease. In a pilot study, we have found that feeding a 'Western' high fat (HF) diet to mice for 24 weeks produced mild NASH, whereas feeding the same diet to mice totally deficient of Nrf2 for the same period produced full-blown NASH with fibrosis and cirrhosis. We now wish to confirm these preliminary findings by studying a larger number of animals on the HF diet, and by examining the time-course of the disease using biomarkers (i.e. monitoring levels of certain disease-associated molecules in the blood).In order to prove whether Nrf2 is important in the development of NASH and its progression to fibrosis and cirrhosis, we first require at least one reliable animal model that reflects the human disease. To this end, we will generate two models, which we anticipate will develop liver disease at different rates: firstly, we will feed normal mice a 'Western' high fat (HF) diet; secondly, we will feed normal mice a 'Western' high fat + fructose (i.e. high levels of sugar; HFF) diet. A detailed time course of the development of fatty liver, NASH, fibrosis and cirrhosis in mice fed these two diets will be established using clinical chemistry, histology and biochemical measurements of pathological changes associated with development of the disease. Once the rate of progression of the disease has been established in the normal mice placed on the 'Western' HF and HFF diets, we will examine the contribution that Nrf2 makes to protection against NASH by testing whether removal of this protein results in an accelerated appearance of NASH, fibrosis and cirrhosis when these mice are fed the same diets. Lastly, we will examine whether activation of Nrf2, either by genetic means or by treatment with a certain type of drug, inhibits the appearance of NASH, fibrosis, or cirrhosis when the animals are fed the same 'Western' HF and HFF diets.