Vgll4在糖脂代谢调控中的功能和分子机制研究

The ketogenic diet is a low-carbohydrate, high-fat, adequate-protein diet that in medicine is used primarily to treat refractory epilepsy in children. When on ketogenic diet, our liver converts fat into ketone bodies. The ketone bodies pass into the brain and replace glucose as an energy source. In order to adapt to the diet change, the liver has to re-model its metabolic network to efficiently produce ketone bodies and harmonize glucose and lipid metabolism at the same place. The results of investigating the process of this re-modeling will shed light on our understanding of glucose and lipid metabolism system and may provide us new therapies or drug targets for metabolic syndromes. Vgll4 is a transcriptional co-factor, known for regulating Hippo and Wnt pathway, and plays important roles during the developments of organs and tumor formation. However, it remains unknown if Vgll4 plays roles in the regulation of lipid and glucose metabolism in liver or adipose tissues. Our preliminary data showed that, comparing to standard chow diet fed mice, the ketogenic diet fed mice had significantly higher expression lever of Vgll4 in the liver, but lower expression level in the adipose tissues. Data from Vgll4 whole body knockout mice showed that Vgll4 deficiency impaired adipogenesis in the adipose tissue but increased lipogenesis in the liver and caused severe metabolic phenotypes in both liver and adipose tissues.; Overexpression of Vgll4 in iWAT increased the weight of iWAT and the cell size of adipocytes in iWAT; Consistently, overexpression of Vgll4 increased adipogenesis in MEF cells and rescued the defect of Vgll4 knockout. Surprisingly, overexpression of Vgll4 in HepG2 cells caused opposite effects: decreasing the expression of genes related to lipogenesis but increasing the expression of genes related to fatty acid oxidation and ketogenesis. All the data suggest that Vgll4 may regulate glucose/lipid metabolism, and more importantly, may mediate the effect of the ketogenic diet during the re-modeling of the metabolic network. In this proposal, we propose a thorough investigation on the function of Vgll4 in liver and adipose tissues. The results from our proposed research will help us for a better understanding of the metabolic regulation network in both liver and adipose tissues.

生酮饮食时，生物体被迫使用脂类作为主要能量来源，以应对营养环境的变化。为此，生物体内主要代谢器官需要对其糖脂代谢网络进行重塑。研究这种糖脂能量来源切换造成的代谢网络重塑对于理解糖脂代谢时空调控有重要意义。Vgll4作为转录辅助因子能调控Hippo和Wnt通路，在器官发育和肿瘤形成中起重要功能，但其在代谢组织中调控代谢稳态的功能尚未有报道。前期研究发现在生酮饮食时，Vgll4在小鼠肝脏中显著上调，但在脂肪组织中显著下调；Vgll4全身性敲除小鼠出生即死亡并表现出明显的糖脂代谢紊乱；在小鼠脂肪组织中过表达Vgll4能够增加脂肪形成；在细胞中过表达Vgll4影响细胞糖脂代谢功能及其相关基因的表达。这些发现提示Vgll4在糖脂代谢调控中有重要作用。本项目将通过建立Vgll4在肝脏和脂肪组织特异性敲除小鼠研究Vgll4在糖脂代谢中的功能和分子机制，并探索其在生酮饮食重塑肝脏糖脂代谢网络的过程的作用。

一般情况下，生物机体各主要器官和细胞使用葡萄糖作为直接能量来源。但是，在生酮饮食时，生物机体的主要器官和细胞被迫使用脂类代谢产生的脂肪酸或酮体作为主要能量来源，并引起一系列代谢表型。研究生酮饮食引起的糖脂能量来源切换及其造成的糖脂代谢网络重塑及其分子机制对于我们理解糖脂代谢调控系统、加速治疗代谢综合征的新药研发有重要意义。在前期工作中，我们发现：生酮饮食显著影响小鼠肝脏和脂肪组织中Vgll4的表达量；Vgll4全身性敲除小鼠在出生不久后即死亡，且表现出明显的肝脏和脂肪组织糖脂代谢的紊乱。这些结果提示Vgll4在小鼠糖脂代谢调控过程中可能有重要功能。.在本项目中，我们建立了肝脏和脂肪组织特异性敲除Vgll4小鼠模型并研究Vgll4在调控肝脏以及脂肪组织糖脂代谢和介导生酮饮食体重减轻以及脂肪肝等代谢表型的作用及分子机制。通过研究发现：在高脂饮食诱导的肥胖小鼠中，肝脏Vgll4特异性缺失能够导致脂质代谢异常和更严重的胰岛素抵抗。而在非酒精性脂肪肝炎的疾病模型中肝脏Vgll4特异性缺失导致炎症恶化和肝纤维化加剧。提示Vgll4可能在治疗肝脏代谢性疾病中的潜在前景。分子机制方面，通过研究发现了Vgll4通过与AR-ETV1形成复合物并调控肝脏糖脂代谢的全新分子机制。另一方面，我们发现在小鼠脂肪细胞内的敲除Vgll4能够显著抑制高脂饮食小鼠的体重增长，但不改善小鼠的葡萄糖代谢紊乱和胰岛素抵抗。分子机制方面， PPARγ在Vgll4敲除后会被显著下调，同时基于RNA-seq的结果，通过KEGG富集分析也发现Vgll4敲除小鼠中PPARγ信号通路被显著下调，这提示脂肪Vgll4通过PPARγ通路调控脂肪组织代谢。.综上研究结果，我们证实了不同代谢组织中Vgll4调控体重和糖脂代谢的功能，并发现了Vgll4在肝脏中通过与AR-ETV1结合发挥调控作用的新机制。我们的研究对于理解糖脂代谢调控系统、加速治疗代谢综合征的新药研发提供了理论基础，拓宽了 Vgll4的功能和分子机制。同时，Vgll4在不同组织中的功能特异，提示在今后的研究中使用组织特异性敲除小鼠研究Vgll4功能的必要性。

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