Amyloid β oligomer-induced ERK1/2-dependent serine 636/639 phosphorylation of insulin receptor substrate-1 impairs insulin signaling and glycogen storage in human astrocytes

• Aβ1–42 oligomers inhibit serine phosphorylation of Akt at 473 and GSK3β at serine 9.
• Aβ1–42 oligomers increase GSK3β phosphorylation at tyrosine 216.
• Phosphorylation of IRS-1 at serine 636/639 is induced by Aβ1–42 oligomers.
• ERK1/2 phosphorylation is increased after Aβ1–42 oligomer treatment.
• Effects of Aβ1–42 oligomers on insulin signaling are partially reversed by PD98059.

AimsThis study is to investigate the effect of amyloid β1–42 oligomers on insulin signaling in astrocytes.MethodsSynthetic Aβ1–42 oligomers were prepared and the oligomeric form of Aβ1–42 was verified by an electron microscope. Normal human astrocytes were cultured in Dulbecco's Modified Eagle Medium. Western blotting was employed to measure the amount of lysate proteins. Immunofluorescence was performed to detect the distribution of phosphorylated insulin receptor substrate-1 and expression of P-GSK3β in astrocytes under confocal microscopy and fluorescent microscopy, respectively. Periodic Acid-Schiff staining was used to detect glycogen, the content of which was measured using glycogen assay.ResultsOur data showed that Aβ1–42 oligomers inhibited insulin-induced serine phosphorylation of Akt at 473 and GSK3β at serine 9, as well as glycogen storage. However, the levels of phosphorylated GSK3β at tyrosine 216 were significantly increased in the presence of Aβ1–42 oligomers. In addition, the levels of phosphorylated ERK1/2 and insulin receptor substrate-1 at serine 636/639 were significantly increased in response to treatment with Aβ1–42 oligomers. Of note, the responses and inhibitory effects of Aβ1–42 oligomers on insulin signaling were partially reversed by ERK1/2 upstream inhibitor PD98059.ConclusionsOur results demonstrated that Aβ1–42 oligomers impaired insulin signaling and suppressed insulin-induced glycogen storage in human astrocytes, probably due to ERK1/2-dependent serine phosphorylation of insulin receptor substrate-1 at 636/639 induced by Aβ1–42 oligomers.