Department of Pharmacy, Taishan Vocational College of Nursing, Taian, 271000, China.
Department of Endocrinology, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, 105 Jiefang Road, Jinan, 250013, Shandong Province, China.
J Endocrinol Invest. 2021 Aug;44(8):1753-1765. doi: 10.1007/s40618-020-01494-0. Epub 2021 Jan 9.
Evidence is accumulating that lipocalin2 (LCN2) is implicated in insulin resistance and glucose homeostasis, but the underlying possible mechanisms remain unclear. This study is to investigate the possible linkage between LCN2 and AMP-activated protein kinase (AMPK) or forkhead transcription factor O1 (FoxO1), which influences insulin sensitivity and gluconeogenesis in liver.
LCN2 knockout (LCN2KO) mice and wild-type littermates were used to evaluate the effect of LCN2 on insulin sensitivity and hepatic gluconeogenesis through pyruvate tolerance test (PTT), glucose tolerance test (ipGTT), insulin tolerance test (ITT), and hyperinsulinemic-euglycemic clamps, respectively. LCN2KO mice and WT mice in vivo, and in vitro HepG2 cells were co-transfected with adenoviral FoxO1-siRNA (Ad-FoxO1-siRNA) or adenovirus expressing constitutively active form of AMPK (Ad-CA-AMPK), or dominant negative adenovirus AMPK (Ad-DN-AMPK), the relative mRNA and protein levels of two key gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6P) were measured.
Improved insulin sensitivity and inhibited gluconeogenesis in the LCN2KO mice were confirmed by pyruvate tolerance tests and hyperinsulinemic-euglycemic clamps. Nuclear FoxO1 and its downstream genes PEECK and G6P were decreased in the livers of the LCN2KO mice, and AMPK activity was stimulated and directly phosphorylated FoxO1. In vitro, AMPK activity was inhibited in HepG2 cells overexpressing LCN2 leading to a decrease in phosphorylated FoxO1 and an increase in nuclear FoxO1.
The present study demonstrates that LCN2 regulates insulin sensitivity and glucose metabolism through inhibiting AMPK activity, and regulating FoxO1 and its downstream genes PEPCK/G6P, which regulate hepatic gluconeogenesis.
有证据表明脂联素 2（LCN2）与胰岛素抵抗和葡萄糖稳态有关，但潜在的机制尚不清楚。本研究旨在探讨 LCN2 与 AMP 激活的蛋白激酶（AMPK）或叉头转录因子 O1（FoxO1）之间的可能联系，这两个因子影响肝脏中的胰岛素敏感性和糖异生。
利用 LCN2 基因敲除（LCN2KO）小鼠及其野生型同窝仔鼠，分别通过丙酮酸耐量试验（PTT）、葡萄糖耐量试验（ipGTT）、胰岛素耐量试验（ITT）和高胰岛素-正常血糖钳夹试验评估 LCN2 对胰岛素敏感性和肝糖异生的影响。体内实验采用 LCN2KO 小鼠和 WT 小鼠以及体外 HepG2 细胞，共转染 FoxO1-siRNA 的腺病毒（Ad-FoxO1-siRNA）或表达组成型激活形式的 AMPK 的腺病毒（Ad-CA-AMPK），或显性失活的 AMPK 腺病毒（Ad-DN-AMPK），测定两种关键糖异生酶磷酸烯醇式丙酮酸羧激酶（PEPCK）和葡萄糖-6-磷酸酶（G6P）的相对 mRNA 和蛋白水平。
通过丙酮酸耐量试验和高胰岛素-正常血糖钳夹试验证实，LCN2KO 小鼠的胰岛素敏感性提高，糖异生受到抑制。LCN2KO 小鼠肝脏中核 FoxO1 及其下游基因 PEPCK 和 G6P 减少，AMPK 活性被激活并直接磷酸化 FoxO1。体外实验中，LCN2 过表达的 HepG2 细胞中 AMPK 活性受到抑制，导致磷酸化 FoxO1 减少和核 FoxO1 增加。
本研究表明，LCN2 通过抑制 AMPK 活性以及调节 FoxO1 及其下游基因 PEPCK/G6P 来调节肝糖异生，从而调节胰岛素敏感性和葡萄糖代谢。
