INS and major depressive disorder: The result of the KEGG pathway analysis pointed out that some of the pathways the genes concentrated in were closely linked to MDD, such as the “MAPK signaling pathway,” “Ras signaling pathway,” “Wnt signaling pathway,” and “insulin resistance.” A study pointed out that the MAPK signaling pathway was activated in chronic unpredictable mildly stressed mice due to the elevated p-JNK and p-p38 protein expression in the hippocampus (Su et al., 2017).