It was observed that diabetes remarkably increased the expressions of p-PERK, phosphorylated eukaryotic initiation factor 2α (p-eIF2α), glucose regulated protein 78 (GRP78) and protein disulfide isomerase (PDI) in the hippocampus of mice when comparing with those in db/m mice (Fig.6a-d). Here, P4HB is linked to diabetes mellitus.