BTG1调控肝脏和脂肪组织脂质代谢的新功能与机制研究

In recent years, there has been an increase in the reported global prevalence of NAFLD (Non Alcoholic Fatty Liver Disease) and obesity. The dysregulation of lipid metabolism in the liver and white adipocytes tissue (WAT) leads to changes in systemic metabolic processes and ultimately to the pathophysiological manifestations that cause NAFLD and obesity.. Our previous study demonstrated that leucine deprivation represses fatty acid synthesis in the liver and decreases fat mass by stimulation of lipolysis in WAT (Cell Metabolism. 2007,5:103-114; Diabetes. 2010, 59:17-25). We propose that the genes changed under leucine deprivation may be involved in regulating lipid metabolism. Then a high-throughput screening technique, gene chip, was used to screen the differentially expressed genes in the liver of mice under leucine deprivation. The B-Cell Translocation Gene 1, BTG1, which was up-regulated in the liver of leucine-deprived mice, was identified by gene chip analysis. Our preliminary results demonstrated that the BTG1 transgenic mice are fat and protected from high-carbohydrate diet (HCD)-induced liver steatosis, suggesting a possible role for BTG1 in regulating lipid metabolism.. The objectives of this research are to 1) investigate the involvement of BTG1 in regulating lipid metabolism and elucidate the underlying mechanisms. 2) investigate the effects of nutrition condition such as high fat, high fructose or high cholesterol on BTG1 expression and the cellular and molecular mechanisms. We will explore these in various cell models, ob/ob mice, db/db mice and BTG1 transgenic mice.. This work will reveal the novel function of BTG1 in regulating lipid metabolism, and lead to new strategies for prevention and treatment of NAFLD and obesity.

脂质代谢紊乱是引发非酒精性脂肪肝和肥胖等慢性疾病的重要原因之一。申请人前期研究发现,亮氨酸缺乏能抑制小鼠肝脏脂质合成并促进白色脂肪组织的脂解；由此推测,亮氨酸缺乏时发生变化的基因可能具有调控脂质代谢的功能。利用基因芯片对亮氨酸缺乏时肝脏基因表达谱进行分析研究,申请人发现B细胞易位基因（B-Cell Translocation Gene ,BTG）1表达显著增加。之后申请人构建了BTG1全身转基因小鼠,发现该小鼠能够抵抗高糖饮食喂养造成的脂肪肝,而体重（尤其白色脂肪组织重量）显著高于野生型小鼠；提示BTG1参与调控脂质代谢。本项目将利用多种细胞和动物模型,从多个层次研究BTG1对肝脏与脂肪组织脂质代谢的调控作用及机制,并探讨各种营养条件对BTG1表达的影响。该研究将增加人们对BTG1生理功能的认识,有助于理解非酒精性脂肪肝和肥胖发生发展的分子机制, 为治疗这些代谢性疾病提供可能的药物靶点。

本项目探讨了BTG1在肝脏和脂肪组织中的作用与机制，包括以下两方面内容：1）我们研究发现，db/db小鼠（常用的遗传性肥胖模型）肝脏中BTG1表达显著下降。在db/db小鼠中注射BTG1过表达腺病毒可以缓解脂肪肝，在野生型小鼠中注射BTG1敲减腺病毒可以诱导脂肪肝，体外BTG1可以减少甘油三酯聚集。进一步检测发现，BTG1通过抑制ATF4的活性从而减少SCD1的表达。在野生型小鼠中，通过SCD1敲减腺病毒可以阻止BTG1敲减腺病毒诱导的脂肪肝。在db/db小鼠中，ATF4过表达腺病毒阻止了BTG1对脂肪肝的缓解。同时，BTG1全身转基因小鼠可以抵抗高蔗糖饮食引起的脂肪肝。高蔗糖饮食通过mTOR-S6K1和 CREB通路，抑制BTG1的表达。该工作阐明了BTG1调节肝脏脂质代谢的作用，为脂肪肝的发病机制及治疗提供了理论基础和新的思路。2）向小鼠注射地塞米松（一种糖皮质激素类药物）1周能够显著增加其全身脂肪和白色脂肪含量。我们发现地塞米松处理小鼠的棕色脂肪发生白色化：棕色脂肪组织中脂滴变大，脂质含量增加，UCP1表达下降，氧耗减少。进一步研究表明，地塞米松能够增加棕色脂肪细胞中自噬相关基因ATG7的表达从而激活自噬作用。自噬是维持内环境稳态的重要方式。向小鼠体内注射氯喹或利用病毒降低棕色脂肪ATG7表达能够抑制自噬作用，阻止地塞米松诱导的棕色脂肪白色化以及全身脂肪含量的增加。进一步检测发现，地塞米松对于ATG7表达的调控依赖BTG1/ CREB1信号通路。脂肪组织特异性过表达BTG1小鼠棕色脂肪发生白色化，全身脂肪含量增加。利用病毒降低棕色脂肪BTG1表达能够阻止地塞米松诱导的棕色脂肪白色化以及全身脂肪含量的增加。该工作证明了抑制自噬作用可有效缓解糖皮质激素诱导的肥胖，加深了人们对于糖皮质激素作用机制以及棕色脂肪白色化过程的理解和认识。