(+)-Rutamarin as a Dual Inducer of Both GLUT4 Translocation and Expression Efficiently Ameliorates Glucose Homeostasis in Insulin-Resistant Mice

Glucose transporter 4 (GLUT4) is a principal glucose transporter in response to insulin, and impaired translocation or decreased expression of GLUT4 is believed to be one of the major pathological features of type 2 diabetes mellitus (T2DM). Therefore, induction of GLUT4 translocation or/and expression is a promising strategy for anti-T2DM drug discovery. Here we report that the natural product (+)-Rutamarin (Rut) functions as an efficient dual inducer on both insulin-induced GLUT4 translocation and expression. Rut-treated 3T3-L1 adipocytes exhibit efficiently enhanced insulin-induced glucose uptake, while diet-induced obese (DIO) mice based assays further confirm the Rut-induced improvement of glucose homeostasis and insulin sensitivity in vivo. Subsequent investigation of Rut acting targets indicates that as a specific protein tyrosine phosphatase 1B (PTP1B) inhibitor Rut induces basal GLUT4 translocation to some extent and largely enhances insulin-induced GLUT4 translocation through PI3 kinase-AKT/PKB pathway, while as an agonist of retinoid X receptor α (RXRα), Rut potently increases GLUT4 expression. Furthermore, by using molecular modeling and crystallographic approaches, the possible binding modes of Rut to these two targets have been also determined at atomic levels. All our results have thus highlighted the potential of Rut as both a valuable lead compound for anti-T2DM drug discovery and a promising chemical probe for GLUT4 associated pathways exploration.

葡萄糖转运蛋白4（Glucose transporter 4, GLUT4）是响应胰岛素的核心葡萄糖转运蛋白，而GLUT4转位受损或表达水平降低被认为是2型糖尿病（type 2 diabetes mellitus, T2DM）的主要病理特征之一。因此，诱导GLUT4转位与/或表达是抗2型糖尿病药物研发的极具前景的策略。本文报道天然产物(+)-芸香内酯（(+)-Rutamarin，下文简称Rut）可作为同时调控胰岛素诱导的GLUT4转位与表达的高效双重诱导剂。经Rut处理的3T3-L1脂肪细胞可显著增强胰岛素介导的葡萄糖摄取，而基于饮食诱导肥胖（diet-induced obese, DIO）小鼠的体内实验进一步证实，Rut可改善机体葡萄糖稳态与胰岛素敏感性。后续对Rut作用靶点的机制探究表明：作为特异性蛋白酪氨酸磷酸酶1B（protein tyrosine phosphatase 1B, PTP1B）抑制剂，Rut可在一定程度上诱导基础状态下的GLUT4转位，并通过磷脂酰肌醇3激酶（PI3 kinase）-AKT/PKB信号通路大幅增强胰岛素诱导的GLUT4转位；同时，作为维甲酸X受体α（retinoid X receptor α, RXRα）的激动剂，Rut可有效提升GLUT4的表达水平。此外，本研究通过分子建模与晶体学方法，在原子层面阐明了Rut与这两个靶点的潜在结合模式。综上，本研究结果凸显了Rut作为抗2型糖尿病药物研发的潜在先导化合物，以及用于GLUT4相关通路探索的极具价值的化学探针的应用潜力。