Shared Biologic Pathways Between Alzheimer Disease and Major Depression: A Systematic Review of MicroRNA Expression Studies.

OBJECTIVE:The clinical-epidemiological relationship between major depressive disorder (MDD) and Alzheimer disease (AD) suggests that they may share common neurobiologic abnormalities. METHODS:The authors conducted a systematic review and identified microRNAs abnormally expressed in both AD and MDD. The pattern of microRNA regulation in each disorder and the genes regulated by each microRNA and the biologic processes and pathways regulated by these genes were identified. RESULTS:Seventy-four microRNAs were abnormally expressed in AD and 30 in MDD; 7 were common for both disorders (hsa-let-7f-5p, hsa-miR-664a-3p, hsa-miR-361-5p, hsa-let-7g-5p, hsa-let-7d-5p, hsa-miR-191-5p, hsa-miR-26b-5p). These microRNAs interact with 45 validated genes, and the main biologic pathways and processes regulated by them were proteostasis control, maintenance of genomic integrity, regulation of transcriptional activity, immune-inflammatory control, and neurotrophic support. CONCLUSION:The current results suggest that the maintenance of genomic integrity, proteostasis control, immune-inflammatory regulation, and neurotrophic support are key neurobiologic links between these conditions. A comprehensive hypothetical model for the interaction between MDD, aging, and the development of AD is provided.