Ampelopsin Improves Insulin Resistance by Activating PPARγ and Subsequently Up-Regulating FGF21-AMPK Signaling Pathway

Ampelopsin (APL), a major bioactive constituent of Ampelopsis grossedentata, exerts a number of biological effects. Here, we explored the anti-diabetic activity of APL and elucidate the underlying mechanism of this action. In palmitate-induced insulin resistance of L6 myotubes, APL treatment markedly up- regulated phosphorylated insulin receptor substrate-1 and protein kinase B, along with a corresponding increase of glucose uptake capacity. APL treatment also increased expressions of fibroblast growth factor (FGF21) and phosphorylated adenosine 5’-monophosphate -activated protein kinase (p-AMPK), however inhibiting AMPK by Compound C or AMPK siRNA, or blockage of FGF21 by FGF21 siRNA, obviously weakened APL -induced increases of FGF21 and p-AMPK as well as glucose uptake capacity in palmitate -pretreated L6 myotubes. Furthermore, APL could activate PPAR γ resulting in increases of glucose uptake capacity and expressions of FGF21 and p-AMPK in palmitate -pretreated L6 myotubes, whereas all those effects were obviously abolished by addition of GW9662, a specific inhibitor of peroxisome proliferator- activated receptor –γ (PPARγ), and PPARγsiRNA. Using molecular modeling and the luciferase reporter assays, we observed that APL could dock with the catalytic domain of PPARγ and dose-dependently up-regulate PPARγ activity. In summary, APL maybe a potential agonist of PPARγ and promotes insulin sensitization by activating PPARγ and subsequently regulating FGF21- AMPK signaling pathway. These results provide new insights into the protective health effects of APL, especially for the treatment of Type 2 diabetes mellitus.

蛇葡萄素（Ampelopsin, APL）是显齿蛇葡萄（Ampelopsis grossedentata）的主要活性成分，具备多种生物学功效。本研究旨在探讨APL的抗糖尿病活性，并阐明其发挥该作用的潜在分子机制。在棕榈酸诱导的L6肌管胰岛素抵抗模型中，APL处理可显著上调磷酸化胰岛素受体底物-1（phosphorylated insulin receptor substrate-1, p-IRS-1）与蛋白激酶B（protein kinase B, PKB）的磷酸化水平，同时伴随葡萄糖摄取能力的显著提升。APL处理还可上调成纤维细胞生长因子21（fibroblast growth factor 21, FGF21）以及磷酸化腺苷5’-单磷酸活化蛋白激酶（phosphorylated adenosine 5’-monophosphate-activated protein kinase, p-AMPK）的表达水平。然而，使用化合物C（Compound C）抑制AMPK活性、或通过AMPK小干扰RNA（siRNA）沉默AMPK基因表达，亦或是利用FGF21小干扰RNA阻断FGF21功能，均可明显削弱经棕榈酸预处理的L6肌管中，APL诱导的FGF21与p-AMPK表达上调及葡萄糖摄取能力提升。进一步研究发现，APL可激活过氧化物酶体增殖物激活受体γ（peroxisome proliferator-activated receptor γ, PPARγ），进而提升棕榈酸预处理的L6肌管的葡萄糖摄取能力，并上调FGF21与p-AMPK的表达；而上述所有效应均可被PPARγ的特异性抑制剂GW9662，以及PPARγ小干扰RNA所显著阻断。通过分子建模与荧光素酶报告基因实验，本研究观察到APL可与PPARγ的催化结构域相结合，并呈剂量依赖性上调PPARγ的转录活性。综上，APL可能是一种潜在的PPARγ激动剂，可通过激活PPARγ，后续调控FGF21-AMPK信号通路，从而促进胰岛素增敏。本研究结果为APL的健康保护效应提供了新的科学见解，尤其为2型糖尿病（Type 2 diabetes mellitus）的临床治疗提供了潜在的新思路。