ObjectiveTo explore the protective effect of glucocorticoid-induced transcription factor 1 （GLCCI1） on cognitive dysfunction in diabetic mice and its mechanism. MethodsTwenty-four C57BL/6J mice were randomly divided into 4 groups， namely Control， DM， DM+AAV-Glcci1， and DM+AAV-NC. The Control group was intraperitoneally injected with saline， while the other groups were all injected with streptozotocin （STZ）. Two weeks after successful modeling， the DM+AAV-Glcci1 group was brain stereotactic injected with Glcci1 overexpressing adeno-associated virus， and the DM+AAV-NC group was stereoscopically injected with the control virus. After 12 weeks， the Morris water maze test was used to evaluate the learning and memory abilities of mice in each group. Subsequently， the localized expression of GLCCI1 in the hippocampus were determined by immunofluorescence and immunohistochemistry experiments. The myelin morphology in the hippocampus was observed by LFB staining， the neuronal morphology was observed by Nissl staining， and the myelin-related proteins MBP and CNPase were stained by immunohistochemistry. Molecular docking was used to predict the interaction between GLCCI1 and HSPA5. The expression of endoplasmic reticulum stress-related proteins was detected by Western blot. ResultsThe results of the behavioral experiment showed that compared with the mice in the Control group， DM mice exhibited obvious cognitive dysfunction behaviors （P＜0.000 1）， and the learning and memory abilities of mice improved after overexpression of Glcci1 （P=0.000 7）. The results of immunofluorescence and immunohistochemistry showed that GLCCI1 was expressed in hippocampal neuron cells. Compared with Control mice， the expression level of GLCCI1 in DM mice was significantly downregulated （P＜0.000 1）. The molecular docking results revealed that GLCCI1 interacts with HSPA5. The Western blot results indicated that， compared with the Control group， the expression levels of endoplasmic reticulum stress-related proteins HSPA5 （P＜0.000 1）， ATF4 （P＜0.000 1）， ATF6 （P=0.001 1）， and p-ELF2α/elF2α （P=0.000 1） in the DM group were significantly increased； Compared with the DM group， the expression of the corresponding protein HSPA5 （P＜0.000 1）， ATF4 （P＜0.000 1）， ATF6 （P=0.000 2）， and p-ELF2α/elF2α （P=0.000 1） was significantly down-regulated after overexpression of Glcci1. LFB staining showed that compared with the Control group， the myelin integrity of DM mice decreased significantly （P=0.010 3）， the expressions of myelin-related proteins MBP and CNPase decreased significantly （P=0.000 4， P=0.000 2）， and Nissl staining observed disordered neuronal arrangement. Compared with the mice in the DM group， the myelin integrity in the hippocampal region significantly increased after overexpression of Glcci1 （P=0.000 3）， the expressions of myelin-related proteins MBP and CNPase significantly increased （P=0.001 4， P=0.000 1）， and the ordered arrangement of neurons was observed by Nissl staining. ConclusionThe down-regulation of GLCCI1 expression in hippocampal neurons promotes demyelination of hippocampal neurons and thereby induces diabetic cognitive dysfunction. The specific mechanism may be related to endoplasmic reticulum stress.