表观遗传调控对VEGF-B信号通路介导的追赶生长大鼠骨骼肌和血管内皮脂质转运的影响

Catch-up growth induced by rapid improvement in nutrition level has been generally recognized as an important reason for the high prevalence of diabetes mellitus in developing countries. Ectopic lipid deposition in skeletal muscle is considered as the key factor in triggering the process of insulin resistance in catch-up growth. However, the related mechanism still remains unclear. The latest research found that VEGF-B signaling pathway could mediate trans-endothelial transport of circulating fatty acids into skeletal muscle and play a decisive role in the direction of circulating lipid flow. Our research group has long been dedicated to the mechanism of insulin resistance in catch-up growth. Preliminary studies revealed that the expression of VEGF-B continued to rise from caloric restriction period to refeeding period in the skeletal muscle of catch-up growth rats. Thus, we postulate that catch-up growth might reinforce the lipid transport and deposition in skeletal muscle through epigenetic modification in the expression of VEGF-B. To prove this hypothesis, the present study intends to observe the VEGF-B signaling pathway and the change in epigenetic modification of skeletal muscle of catch-up growth rats in vivo and vitro. The process of lipid transport and insulin sensitivity are also to be examined. On this basis, we then plan to directionally regulate the epigenetic modification of VEGF-B and observe its influence on the process of lipid transport, and insulin resistance on catch-up growth model. Through these studies, we seek to illustrate that epigenetic modification of VEGF-B signaling pathway plays an crucial role in the formation of lipid deposition and insulin resistance of skeletal muscle in catch-up growth rats. We hope our findings would provide an important contribution to developing a new intervention target for the prevention and treatment of diabetes mellitus related to nutrition problem.

营养快速提升造成的追赶生长是发展中国家糖尿病急速蔓延的重要原因。骨骼肌脂质沉积是追赶生长胰岛素抵抗形成的关键，但其机制未明。新近研究发现VEGF-B信号通路介导的脂质由血管内皮向骨骼肌的转运对循环脂质流向起着决定性作用。本研究组长期致力于追赶生长胰岛素抵抗发生机制的研究，前期研究揭示，追赶生长大鼠骨骼肌VEGF-B从限食期至追赶期呈持续高表达。我们假设：追赶生长可能通过表观遗传修饰改变VEGF-B的表达，增强脂质转运，终致骨骼肌脂质沉积。为证明假设，本项目拟通过体内及体外实验，观察追赶生长骨骼肌脂质沉积形成过程中VEGF-B信号通路及其表观遗传修饰的变化；继而双向调控VEGF-B表观遗传修饰，观察对内皮-骨骼肌脂质转运及胰岛素敏感性的影响。藉此明确表观遗传修饰所介导的VEGF-B表达改变在追赶生长骨骼肌脂质沉积及胰岛素抵抗形成中的关键作用，为营养提升所致糖尿病的防治开辟新的干预靶点和途径。

营养快速提升造成的追赶生长是发展中国家糖尿病急速蔓延的重要原因。骨骼肌脂质沉积是追赶生长胰岛素抵抗形成的关键，但其机制未明。新近研究发现VEGF-B信号通路介导的脂质由血管内皮向骨骼肌的转运对循环脂质流向起着决定性作用。本研究通过体内及体外实验，观察追赶生长骨骼肌脂质沉积形成过程中VEGF-B信号通路及其表观遗传修饰的变化。研究结果如下：（1）在限食末，追赶生长动物骨骼肌VEGF-B信号通路激活和脂肪酸摄取增加；在恢复饮食后，骨骼肌VEGF-B信号通路激活和脂肪酸摄取增加仍然存在，并伴随着骨骼肌脂质沉积和胰岛素抵抗；（2）体外抑制VEGF-B信号通路可减少骨骼肌微血管内皮细胞对脂肪酸的摄取和转运；（3）敲低骨骼肌中VEGF-B，恢复饮食后的追赶生长小鼠可通过减少脂肪酸转运从而减轻脂质沉积，改善胰岛素敏感性；（4）限食导致VEGF-B启动子区H3K9me1、H3K14ac、H3K14ac水平升高，甲基化转移酶PHF2表达减少及其在VEGF-B启动子区富集减少，乙酰化酶P300表达增加及其在VEGF-B启动子区富集增加；在恢复饮食后仍然持续；（5）PHF2基因敲低后，L6细胞中VEGF-B表达量也明显增加，VEGF-B启动子区H3K9me1修饰水平明显下降；而过表达PHF2则反之。（6）P300基因敲低后，L6细胞中VEGF-B表达量也明显下降，VEGF-B启动子区H3K14ac、H3K14ac修饰水平明显下降。从上述研究结果得出如下结论：（1）骨骼肌VEGF-B信号通路异常激活而导致的脂质跨内皮转运增加和脂质沉积增多是追赶生长胰岛素抵抗形成中的关键机制（2）H3K9me1、H3K14ac、H3K14ac协同调节了追赶生长导致的VEGF-B表达改变；（3）甲基转移酶PHF2介导了骨骼肌中VEGF-B启动子区H3K9me1的募集，而乙酰化酶P300介导了骨骼肌中VEGF-B启动子区H3K14ac和H3K14ac的募集，可作为表观遗传修饰的靶点，为胰岛素抵抗及2型糖尿病的治疗提供了新的靶点及干预策略。