The Role of Gm4951 in Nonalcoholic Fatty Liver Disease

项目总结 非酒精性脂肪性肝病(NAFLD)正成为全球人类健康问题。我们的长期目标是 了解NAFLD的分子机制，并将这些知识转化为新的治疗策略。 由于人类和老鼠在生理上的相似之处，以及老鼠患疾病的倾向 小鼠与喂食高脂饮食(HFD)时的NAFLD非常相似，它为我们提供了对 NAFLD的发病机制。在人类和小鼠中，基因变异影响肝骨病的发生率和严重程度 在给定的环境条件下。为了确定影响这一过程的基因，我们使用了无偏倚 正向基因筛查和高度自动化的减数分裂图谱以识别导致小鼠NAFLD的突变 用HFD致敏。预测基因4951(Gm4951)的两个半显性错义等位基因，命名为Oy和 石炭纪，在这个屏幕上被检测到。与大多数NAFLD突变体不同的是， 肥胖，我们的初步数据显示，Gm4951缺陷小鼠的肝脏脂质显著增加 在HFD上积累而不伴随体重增加。Gm4951在细胞中高度表达 肝细胞。Gm4951基因敲除可增加脂质含量，过表达Gm4951可降低血脂 体外培养的原代肝细胞的含量，提示肝细胞对脂质含量的内在调节。Gm4951 基因敲除的肝脏显示脂质氧化基因的表达减少。质谱学分析 内源性GM4951相互作用蛋白与脂滴蛋白羟基类固醇17β- 脱氢酶13(HSD17B13)和脂质氧化酶。此外，Gm4951基因的转录在 肝细胞被干扰素-γ激活，这有效地降低了脂肪含量，与 GM4951基因过表达。这些结果导致了我们的中心假设，即GM4951对于促进 脂肪氧化，并限制肝脏脂肪堆积。为了验证这一假设，我们提出了三个具体的 目标。目的1进一步研究GM4951基因缺陷小鼠非酒精性脂肪肝的发生。目标2将决定 GM4951在调节脂代谢中的确切机制作用。目标3将研究转录 Gm4951的调控，包括肝脏特异性表达模式和干扰素-γ的诱导表达。 了解如何激活GM4951以及GM4951的人类同源基因将提供以下方法 预防或治疗非酒精性脂肪肝。这些也将在目标3中进行研究。GM4951引起的非酒精性脂肪肝表型 缺乏症从根本上不同于经典的肥胖相关的NAFLD小鼠模型。GM4951是 在肝脏中特异表达，并在那里发挥作用，限制脂肪堆积。因此，找到激活的方法 GM4951为降低肝脂含量提供了一种新的途径。拟议工作完成后， 建议新的治疗靶点来对抗非酒精性脂肪肝。

PROJECT SUMMARY Nonalcoholic fatty liver disease (NAFLD) is becoming a global human health problem. Our long-term goal is to understand molecular mechanisms of NAFLD, and to translate this knowledge into novel therapeutic strategies. Due to the physiologic similarities between humans and mice, and the propensity of mice to develop a disease closely mimicking NAFLD when fed a high fat diet (HFD), mice have provided us with fundamental insights into NAFLD pathogenesis. In humans and mice, genetic variation influences the rate and severity of hepatosteatosis under a given set of environmental conditions. To identify genes that influence the process, we utilized unbiased forward genetic screening and highly automated meiotic mapping to identify mutations that cause NAFLD in mice sensitized by a HFD. Two semi-dominant missense alleles of predicted gene 4951 (Gm4951), named Oily and Carboniferous, were detected in this screen. As distinct from most NAFLD mutants that are associated with obesity, our preliminary data showed that Gm4951 deficient mice had dramatically increased hepatic lipid accumulation without a concomitant increase of body weight on a HFD. Gm4951 was highly expressed in hepatocytes. Knockout of Gm4951 increased lipid content and overexpression of Gm4951 decreased lipid content of primary hepatocytes in vitro, suggesting hepatocyte-intrinsic regulation of lipid content. Gm4951 knockout livers showed decreased expression of lipid oxidation genes. Mass spectrometry analysis of endogenous GM4951 interacting proteins revealed interaction with lipid droplet protein Hydroxysteroid 17β- dehydrogenase 13 (HSD17B13) and lipid oxidation enzymes. Moreover, the transcription of Gm4951 in hepatocytes was activated by interferon gamma (IFN-γ), which effectively decreased lipid content, much as when GM4951 was overexpressed. These results led to our central hypothesis that GM4951 is critical for promoting lipid oxidation, and limits hepatic lipid accumulation. To test this hypothesis, we propose to pursue three Specific Aims. Aim 1 will further investigate the development of NAFLD in GM4951 deficient mice. Aim 2 will determine the precise mechanistic role of GM4951 in regulating lipid metabolism. Aim 3 will study the transcriptional regulation of Gm4951, including the liver-specific expression pattern and the inducible expression by IFN-γ. Understanding how to activate GM4951 and what’s the human homolog of GM4951 would offer approaches to preventing or treating NAFLD. These will be studied in Aim 3 as well. The NAFLD phenotype caused by GM4951 deficiency is fundamentally distinct from the classic obesity-associated NAFLD mouse models. GM4951 is specifically expressed in the liver and operates there to limit lipid accumulation. Thus, finding ways to activate GM4951 will provide a new means of reducing hepatic lipid content. Completion of the proposed work will suggest new therapeutic targets to combat NAFLD.