¹Aarhus University, Department of Clinical Medicine, Aarhus, Denmark, ²Kerman University of Medical Sciences, Research Center for Hydatid Disease in Iran, Kerman, Iran, Islamic Republic of, ³Aarhus University, Department of Biomedicine, Aarhus, Denmark, ⁴Aarhus University, Department of Forensic Medicine, Aarhus, Denmark

Background: Major depressive disorder (MDD) exhibits pronounced sex differences in prevalence, symptom severity, and treatment response, implicating a possible role for sex steroid signaling in mood regulation. Mood disturbances linked to reproductive life stages, such as premenstrual syndrome (PMS), premenstrual dysphoric disorder (PMDD), postpartum depression, perimenopausal, and postmenopausal depression, highlight the sensitivity of affective states to fluctuations in ovarian hormones, particularly estrogen. Estrogen receptor alpha (ERα) mediates both classical genomic effects and rapid extranuclear signaling through kinase pathways. Although antidepressants are proven to act via monoaminergic systems, clinical observations, including the efficacy of selective serotonin reuptake inhibitors when administered intermittently in PMDD and PMS, suggest a possible engagement between antidepressant mechanisms and estrogen signaling. Whether antidepressants directly engage ERα and its components that further contribute to cellular responses remains largely unexplored.

Aims & Objectives: This study aimed to determine whether antidepressants interact with ERα and modulate its signaling pathways.

Method: A combined experimental and computational approach was employed. In vitro assays were performed in ERα-expressing MCF-7 cells, ERα-transfected HEK cells, and primary mouse cortical neurons to assess ERα activation, phosphorylation (Ser167), subcellular localization, downstream kinase signaling, and gene expression following acute exposure to antidepressants. Pharmacological blockade of ERα (fulvestrant) and inhibition of membrane localization (tunicamycin) were used to dissect signaling pathways. The possibility of direct antidepressant–ERα interactions was evaluated using proximity ligation assays. Molecular docking, induced-fit docking, and molecular dynamics simulations were conducted to characterize ligand–receptor interactions in silico.

Results: Tricyclic and rapid-acting antidepressants, including imipramine and ketamine, rapidly induced ERα phosphorylation at Ser167 within minutes, comparable to estradiol. This effect was abolished by ERα antagonism and significantly attenuated by inhibition of ERα palmitoylation, indicating preferential involvement of membrane-associated ERα. Antidepressants selectively activated MAPK signaling and rapidly regulated genes associated with extranuclear and nuclear ERα activity. Proximity ligation assays demonstrated a high likelihood of direct or receptor-mediated interactions between antidepressants and ERα, predominantly in extranuclear compartments. Computational analyses revealed favorable antidepressant binding within the ERα ligand-binding pocket, with binding energies comparable to estradiol and a membrane-selective ERα agonist.

Discussion & Conclusions: Our findings identify ERα, particularly its extranuclear signaling pool, as a previously unrecognized target of antidepressants. This mechanism may contribute to rapid antidepressant responses and offers a novel framework linking hormone signaling to antidepressant efficacy, with implications for hormonally sensitive mood disorders.