Metformin与T0901317联用防治动脉粥样硬化的机理研究

The liver X receptors consist of two isoforms, LXRα and LXRβ. The ligand activated-LXRβ can substantially inhibit the development of atherosclerosis, while the simultaneous ligand activated-LXRα activates lipogenesis which results in fatty liver and hypertriglyceridemia. Our preliminary study indicated that metformin can selectively inhibit ligand-induced LXRα activity while having no effect on LXRβ functions by activating AMPKα. Meanwhile, we determine that deficiency of NgBR expression in hepatocytes inactivates AMPKα and activates LXRα, thereby inducing fatty liver, which implies that the combined metformin and T0901317 (an LXR ligand) can reduce atherosclerosis without lipogenic adverse effects. In this proposal, we anticipate to complete the following studies to determine: 1. If the co-treatment of pro-atherogenic animals with T0901317 and metformin can substantially reduce atherosclerotic lesions while eliminating T0901317-induced lipogenic side effects; 2. The mechanisms by which the co-treatment of metformin and T0901317 reduces atherosclerosis, such as enhancement of macrophage cholesterol efflux and reverse cholesterol transport, inhibition of macrophage/foam cell formation, amelioration of endothelial cell and smooth muscle cell functions; 3. The anti-lipogenic mechanisms in which metformin can selectively inhibit LXRα activity. Therefore, the combined metformin and T0901317 can reduce lipogenesis while enhancing lipid/energy metabolism thereby antagonizing T0901317-induced adverse side effects. 4. The important role of NgBR in AMPKα-mediated LXR expression/functions. By completing the above studies, we will be able to unveil the interaction between AMPKα and LXR signaling pathways, and demonstrate that the combined metformin and T0901317 is a novel strategy in anti-atherosclerosis.

肝X受体(LXR)包括α和β两个亚型，配体(T0901317，T317)激活的LXRβ有效防治动脉粥样硬化，但同时被激活的LXRα诱发脂肪肝等副作用。我们发现metformin通过激活AMPKα选择性抑制LXRα但不影响LXRβ功能；NgBR表达缺失抑制AMPKα、激活LXRα而导致脂肪肝，但NgBR表达缺失对LXRβ无作用。由此我们推断metformin与T317联用可防治动脉粥样硬化并通过对LXR两个亚型的差别性调控而阻断T317诱导的脂肪肝。基于此，本申请拟研究：1、metformin与T317联用能有效防治动脉硬化且消除脂肪肝等副作用；2、药物联用抗动脉硬化、保护血管的作用机理；3、metformin选择性抑制LXRα活性与拮抗脂肪肝作用机制；4、NgBR在AMPKα调控LXR中的作用。我们的工作将阐明AMPKα与LXR相互作用的机制，确定药物联用是抗动脉粥样硬化的新策略。

动脉粥样硬化是冠心病的主要病理，也是导致中老年人死亡的重要原因之一。动脉粥样硬化的发生与慢性炎症、胆固醇代谢紊乱、巨噬细胞泡沫化等密切相关。肝X受体(liver X receptor，LXR)激动剂(如T0901317，T317)可抑制动脉粥样硬化，但因激活脂质过度合成、从而引起严重的脂肪肝和高甘油三酯血症，限制了LXR激动剂在治疗动脉粥样硬化中的应用。二甲双胍(metformin)能够增强能量代谢从而可抑制肝脏脂肪变性，预示着metformin与LXR激动剂联用可拮抗LXR诱导的脂肪肝发生。基于此，本项目研究了T317和metformin两种药物的组合是否能够抑制动脉粥样硬化，同时不引起肝脏中脂质过度合成。. 我们通过喂食apoE基因敲除小鼠高脂食物(HFD)建立动脉粥样硬化模型，并分别给予T317、metformin或两种药物联用进行治疗，实验周期为16周。我们发现metformin能够增强T317对全主动脉和主动脉根部斑块的抑制作用。机制上，两种药物处理能够选择性激活LXR不同亚型，在巨噬细胞中刺激ATP结合盒转运体A1或G1(ABCA1/G1)的表达，进而抑制泡沫细胞的形成和积累，起到抑制动脉粥样硬化的作用。同时，两种药物联用能够通过调控血管细胞黏附分子-1 (vascular cell adhesion molecule，VCAM-1)和细胞间黏附分子-1 (intercellular adhesion molecule，ICAM-1)的表达调节内皮功能。进一步，我们还发现metformin能够选择性抑制T317诱导的LXRα核转移以及脂质合成相关基因的表达，从而抑制T317诱导的脂肪肝和高甘油三酯血症。此外，通过在肝脏中特异性过表达Nogo-B受体(Nogo-B receptor，NgBR)的实验发现，NgBR能够减少脂质积累相关基因的表达，表明NgBR对于维持脂质稳态具有重要作用。. 综上，通过本项目的完成，我们明确了metformin能够增强T317对动脉粥样硬化的抑制作用，而且还可以避免T317诱导的脂肪肝和高甘油三酯血症。这预示着metformin和T317的联用可以作为治疗动脉粥样硬化的新策略。因此，我们的研究不仅可以为LXR的未来研发方向提供重要参考，也可以为metformin的药物联用提供科学依据。