Figure 2. Molecular mechanism in the development of Alzheimer’s disease. (A) Differentially expressed genes between Alzheimer’s disease (AD) and mild cognitive impairment, and between mild cognitive impairment and the control. (B) The union of the two groups of the differentially expressed genes constitutes the PPI network. Each color represents a different module. (C) The expression heatmap of module genes in GSE63060 and GSE63061. The biological functions (D), cellular components (E) and molecular functions (F) of the modular genes. (G) The KEGG pathway of module genes. From control to mild cognitive impairment and then to AD, the signal pathway was continuously up-regulated (H) or down-regulated (I).