Molecular mechanisms of fatty liver disease: role of the protein DBC1

描述(申请人提供)：最近，美国肝病研究协会表示：“……总的来说，非酒精性脂肪性肝病(NAFLD)患者的长期存活率降低了，其中肝脏疾病约占总死亡率的10%……显然，NAFLD在未来几年将成为一个更普遍的问题……”这预示着NAFLD在不久的将来将成为一个重大的公共卫生问题。然而，到目前为止，这种疾病的治疗选择有限。在这方面，有必要进一步了解调节肝脏脂肪变性发展的分子机制。我们观察到乳腺癌1缺失蛋白(DBC1)在实验性肝脂肪变性的发生发展中起着关键作用。特别是，我们发现DBC1基因敲除的小鼠对高脂饮食诱导的肝脏脂肪变性具有抵抗力，而全身代谢综合征并未得到改善。这表明DBC1控制着参与肝脏脂肪变性发展的内在肝脏机制。到目前为止，人们对DBC1的生理生化作用知之甚少，但最近的研究表明，DBC1可以结合并抑制酶SIRT1。SIRT1是一种依赖NAD的脱乙酰酶，控制新陈代谢、衰老和长寿。事实上，已经有人提出SIRT1是一个代谢主开关。SIRT1的药理激活至少部分地通过刺激AMP激酶(AMPK)来预防肝脏脂肪变性，AMPK随后减少脂肪生成并增加脂肪酸氧化。虽然SIRT1的代谢作用是深入研究的主题，但对SIRT1的调控知之甚少。事实上，调节SIRT1表达和活性的机制仍然难以捉摸。在这方面，DBC1作为SIRT1的内源性抑制物的特征，以及调节DBC1-SIRT1相互作用的机制的确定是极其重要的。在不同的代谢条件下，包括饮食诱导的脂肪变性，DBC1-SIRT1相互作用的调节可能在SIRT1功能的调节中起关键作用。DBC1和SIRT1之间相互作用的增加也可能为饮食诱导的肝脏脂肪变性动物模型中SIRT1活性降低提供分子基础。因此，我们的中心假设是，DBC1通过直接结合和抑制SIRT1，进而通过AMPK调节SIRT1对肝脏脂肪生成和2-氧化的下游作用，在肝脏脂肪变性的发生发展中发挥关键作用。为了验证这一假说，将解决以下具体目标：目的1.研究SIRT1在DBC1介导的肝脏脂肪变性调节中的作用。目的2.研究DBC1在不同热量负荷下对SIRT1活性的调节作用，并确定DBC1-SIRT1相互作用的分子机制。目的3.确定DBC1在SIRT1下游调控肝脏脂肪变性发生的生化机制：AMPK的作用。总而言之，这些研究将导致对DBC1作为SIRT1、肝脏脂肪代谢和肝脏脂肪变性的调节因子的生理作用的深入和非常新颖的理解。公共卫生相关性：非酒精性脂肪性肝病(NAFLD)是一个世界性的主要健康问题。正如最近美国肝病研究协会未来趋势会议的成员所说：“……总的来说，非酒精性脂肪肝患者的长期存活率有所下降，其中肝病约占总死亡率的10%，仅次于恶性肿瘤和心血管死亡。显然，非酒精性脂肪肝在未来几年将成为一个更普遍的问题……”)。这些令人震惊的数据和预测清楚地表明，进一步了解调节肝脏脂肪变性发展的分子机制是势在必行的。

DESCRIPTION (provided by applicant): Recently the American Association for the Study of Liver Disease stated that "...Overall, patients with non-alcoholic fatty liver disease (NAFLD) have reduced long-term survival, with liver disease accounting for about 10% of overall mortality.... Clearly it appears that NAFLD will become a more prevalent problem in coming years..." This indicates that NAFLD will become a major public health issue in the near future. However, to date, therapeutic options for this disease are limited. In this regard, it is imperative to further understand the molecular mechanisms that modulate the development of liver steatosis. We observed that the protein Deleted in Breast Cancer 1 (DBC1) plays a crucial role in the development of experimental liver steatosis. In particular we found that mice knocked out for DBC1 are resistant to high fat diet-induced liver steatosis, while the systemic metabolic syndrome was not ameliorated. This suggests that DBC1 controls intrinsic hepatic mechanisms involved in the development of liver steatosis. To date very little is known about the physiological and biochemical roles of DBC1, however recent studies indicate that DBC1 binds and inhibits the enzyme SIRT1. SIRT1 is a NAD-dependent deacetylase that controls metabolism, ageing and longevity. In fact, it has been proposed that SIRT1 is a metabolic master switch. Pharmacological activation of SIRT1 protects against liver steatosis, at least in part, via stimulation of the AMP kinase (AMPK) that subsequently decreases lipogenesis and increases fatty acid oxidation. Although the metabolic actions of SIRT1 are the subject of intense investigation; much less is known about regulation of SIRT1. In fact, the mechanisms that modulate SIRT1 expression and activity remain elusive. In this regard, the characterization of DBC1 as an endogenous inhibitor of SIRT1, and the determination of the mechanisms that regulate the DBC1-SIRT1 interaction are of extreme importance. It is possible that modulation of DBC1-SIRT1 interaction plays a key role in the regulation of SIRT1 function during different metabolic conditions, including diet-induced steatosis. An increase in interaction between DBC1 and SIRT1 may also provide the molecular basis for the decrease in SIRT1 activity reported in animal models of diet-induced liver steatosis. Thus, our Central Hypothesis is that DBC1 plays a crucial role in the development of liver steatosis by direct binding and inhibiting SIRT1, with the subsequent modulation of downstream effects of SIRT1 on hepatic lipogenesis and 2-oxidation via AMPK. To test this hypothesis, the following specific aims will be addressed: Aim 1. Study the role of SIRT1 in DBC1-mediated regulation of liver steatosis. Aim 2. Characterize the role of DBC1 in the regulation of SIRT1 activity during different caloric loads and determine the molecular mechanisms that regulate the DBC1-SIRT1 interaction. Aim 3. Determine the biochemical mechanisms, downstream from SIRT1, by which DBC1 regulates the development of liver steatosis: role of AMPK. Collectively, these studies will lead to an in depth and extremely novel understanding of the physiological roles of DBC1 as a regulator of SIRT1, liver fat metabolism and hepatic steatosis. PUBLIC HEALTH RELEVANCE: Non alcoholic fatty liver disease (NAFLD) is a major health problem worldwide. As recently stated by members of the future trend meeting of the American Association for the Study of Liver Disease, "...Overall, patients with NAFLD have reduced long-term survival, with liver disease accounting for about 10% of overall mortality, surpassed only by malignancy and cardiovascular deaths. Clearly it appears that NAFLD will become a more prevalent problem in coming years..." ). These alarming data and predictions clearly show that it is imperative to further understand the molecular mechanisms that modulate the development of liver steatosis.