Several pathways were significantly dysregulated in EC and HIP, such as PI3K-Akt signaling pathway, MAPK signaling pathway, insulin signaling pathway, oxidative phosphorylation, synaptic vesicle cycle, cell-cell adhesion, proteasome, arginine, and proline metabolism, pentose phosphate pathway, calcium ion regulated exocytosis, and glutamate receptor signaling pathway. CTSD and VCAM1 were dysregulated significantly in blood, EC, and HIP, which were potential biomarkers for AD. Here, CTSD is linked to Alzheimer disease.