UC San Diego

Major Depressive Disorder (MDD) is a neuropsychiatric disorder characterized by persistent episodes of depressed mood and loss of interest or pleasure in normal activities. MDD patients have disturbed patterns of mood, sleep, metabolism, all factors of which are linked to circadian rhythms. The connection between MDD and abnormalities in the circadian clock has been investigated through studies on human behavior, post-mortem human brains, and animal models. We hypothesize that the abnormalities in the circadian clock persist at the molecular level, and that we can model circadian rhythms in neurons associated with MDD using induced pluripotent stem cells (iPSCs).The MDD cell line donors in this study were categorized into two groups by antidepressant response: remitters (responders) and non-remitters (non-responders) (Mrazek et al., 2014). Primary patient fibroblasts were reprogrammed into iPSCs (Vadodaria et al., 2019), which were differentiated into glutamatergic neurons, a cell type previously implicated in MDD. To measure circadian oscillatory activity, neurons were transfected with a lentivirus to deliver Per2 promoter-activated lentiviral luciferase, and bioluminescence was recorded over 5+ days. We found that MDD non-remitters neurons had lower amplitude circadian rhythms. To better understand the potential mechanisms underlying this finding, we performed qRT-PCR gene expression analysis of nine core clock genes. We found that neurons from MDD SSRI non-remitters exhibited decreased gene expression of four core circadian clock genes, PER2, PER1, CRY2, and CLOCK. These findings suggest that MDD non-remitters have a weaker circadian clock at the transcriptional level. To understand the circadian clock in MDD at the protein level, we performed immunocytochemistry of PER2 and BMAL1. MDD remitter neurons had an elevated signal of PER2 and BMAL1. Together, we demonstrate abnormalities in the molecular clock that are specific to either MDD non-remitters or remitters.