Li Chunmei, Ma Bixia, Chen Junhong, Jeong Yoonhwa, Xu Xiulong
College of Veterinary Medicine, Yangzhou University, Yangzhou 225009, China.
College of Food Science and Engineering, Yangzhou University, Yangzhou 225009, China.
Mar Drugs. 2020 Sep 28;18(10):495. doi: 10.3390/md18100495.
Astaxanthin (AST) is a carotenoid with therapeutic values on hyperglycemia and diabetic complications. The mechanisms of action of AST remain incompletely understood. p70 S6 kinase 1 (S6K1) is a serine/threonine kinase that phosphorylates insulin receptor substrate 1 (IRS-1) and desensitizes the insulin receptor (IR). Our present study aims to determine if AST improves glucose metabolisms by targeting S6K1. Western blot analysis revealed that AST inhibited the phosphorylation of two S6K1 substrates, S6 and IRS-1, but enhanced the phosphorylation of AKT, AKT, and S6K1 by feedback activation of the phosphatidylinositol-3 (PI-3) kinase in 3T3-L1 adipocytes and L6 myotubes. In vitro kinase assays revealed that AST inhibited S6K1 activity with an IC value of approximately 13.8 μM. AST increased insulin-induced IR tyrosine phosphorylation and IRS-1 binding to the p85 subunit of PI-3 kinase. Confocal microscopy revealed that AST increased the translocation of the glucose transporter 4 (GLUT4) to the plasma membrane in L6 cells. Glucose uptake assays using a fluorescent dye, 2-NBDG (2--(Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose), revealed that AST increased glucose uptake in 3T3-L1 adipocytes and L6 myotubes under insulin resistance conditions. Our study identifies S6K1 as a previously unrecognized molecular target of AST and provides novel insights into the mechanisms of action of AST on IR sensitization.
虾青素（AST）是一种对高血糖和糖尿病并发症具有治疗价值的类胡萝卜素。AST的作用机制仍未完全明确。p70 S6激酶1（S6K1）是一种丝氨酸/苏氨酸激酶，可使胰岛素受体底物1（IRS-1）磷酸化并使胰岛素受体（IR）脱敏。我们目前的研究旨在确定AST是否通过靶向S6K1来改善葡萄糖代谢。蛋白质免疫印迹分析显示，在3T3-L1脂肪细胞和L6肌管中，AST抑制了两种S6K1底物S6和IRS-1的磷酸化，但通过磷脂酰肌醇-3（PI-3）激酶的反馈激活增强了AKT、AKT和S6K1的磷酸化。体外激酶分析显示，AST抑制S6K1活性，IC值约为13.8μM。AST增加了胰岛素诱导的IR酪氨酸磷酸化以及IRS-1与PI-3激酶p85亚基的结合。共聚焦显微镜显示，AST增加了L6细胞中葡萄糖转运蛋白4（GLUT4）向质膜的转位。使用荧光染料2-NBDG（2-（N-硝基苯-2-恶唑-1,3-二氮杂环丁烷-4-基）氨基）-2-脱氧葡萄糖）进行的葡萄糖摄取分析显示，在胰岛素抵抗条件下，AST增加了3T3-L1脂肪细胞和L6肌管中的葡萄糖摄取。我们的研究确定S6K1是AST以前未被认识的分子靶点，并为AST对IR致敏的作用机制提供了新的见解。
