The MDD-related modules were further compared with the gene expression data from postmortem brain tissue of MDD patients in another group, and one of the gene modules which was enriched in the biological pathway related to mitochondrial oxidative phosphorylation and ubiquitination, was screened.Gene regulatory network analysis showed that the hub genes were PARK2, CUL1, SKP1, CYC1, and ATP5A1.The mitochondrial oxidative phosphorylation and ubiquitination related biological pathways are involved in the process of MDD. The gene discussed is CYC1; the disease is major depressive disorder.