Nutrient overload is associated with the development of obesity, insulin 
resistance, and type 2 diabetes. However, the underlying mechanisms for 
developing insulin resistance in the presence of excess nutrients are 
incompletely understood. We investigated whether activation of AMP-activated 
protein kinase (AMPK) prevents the hepatic insulin resistance that is induced by 
the consumption of a high-protein diet (HPD) and the presence of excess amino 
acids. Exposure of HepG2 cells to excess amino acids reduced AMPK 
phosphorylation, upregulated Notch1 expression, and impaired the 
insulin-stimulated phosphorylation of Akt Ser(473) and insulin receptor 
substrate-1 (IRS-1) Tyr(612). Inhibition of Notch1 prevented amino acid-induced 
insulin resistance, which was accompanied by reduced expression of Rbp-Jk, hairy 
and enhancer of split-1, and forkhead box O1. Mechanistically, mTORC1 signaling 
was activated by excess amino acids, which then positively regulated Notch1 
expression through the activation of the signal transducer and activator of 
transcription 3 (STAT3). Activation of AMPK by metformin inhibited mTORC1-STAT3 
signaling, thereby preventing excess amino acid-impaired insulin signaling. 
Finally, HPD feeding suppressed AMPK activity, activated mTORC1/STAT3/Notch1 
signaling, and induced insulin resistance. Chronic administration of either 
metformin or rapamycin inhibited the HPD-activated mTORC1/STAT3/Notch1 signaling 
pathway and prevented hepatic insulin resistance. We conclude that the 
upregulation of Notch1 expression by hyperactive mTORC1 signaling is an 
essential event in the development of hepatic insulin resistance in the presence 
of excess amino acids. Activation of AMPK prevents amino acid-induced insulin 
resistance through the suppression of the mTORC1/STAT3/Notch1 signaling pathway.