IRS1 and Alzheimer disease: In line with these findings, the results of the present study showed that the protein expression levels of p-IRS1/IRS1 were increased, while the levels of p-AKT/AKT and p-ERK/ERK were decreased in the hippocampus and PFC of mice induced by the combination of HFD and STZ/I.P., which provides additional evidence linking insulin resistance and AD.