Disrupting the physical interaction between serotonin transporter and soluble guanylate cyclase produces a fast–acting antidepressant activity

Background Major depressive disorder (MDD) is a refractory neurological disorder often linked to dysregulated 5–hydroxytryptamine (5–HT) neurotransmission. Conventional selective serotonin reuptake inhibitors (SSRIs) face criticism due to their delayed therapeutic onsets and severe adverse effects. The present study aims to illustrate the molecular mechanism by which serotonin transporter (SERT) is regulated by its physical interaction with soluble guanylate cyclase (sGC) for exploring a new therapeutic target with a novel mechanism of action. Methods RBL-2H3 cells and synaptosomes isolated from the dorsal raphe nucleus (DRN) were employed to investigate the SERT–sGC association under physiological conditions or in response to various treatments by using the molecular and cellular approaches. The functional consequences of the SERT–sGC interaction were assessed by biotinylation of membrane proteins and 5–HT uptake assay. GST-tagged intracellular fragments were produced to map the structural motif of SERT responsible for the interaction with sGC and the forth internal loop (IL4)–mediated SERT–sGC association was further confirmed by mutagenesis. Finally, a peptide to dissociate SERT from sGC was synthesized and its antidepressant activity was evaluated with chronic unpredictable mild stress (CUMS) mouse models. Results A stable SERT–sGC complex was identified. Augmentation of the SERT–sGC interaction decreased SERT cell surface expression by interfering with its trafficking, thereby reducing 5–HT uptake. The specific SERT–sGC association was mediated by the IL4 motif with a unique structural folding in SERT and exerted a unilateral modulation of SERT without affecting sGC. Notably, the SERT–sGC interaction was altered in response to treatment of a variety of susceptibility factors in both cells and animal models. Two hours after administration, SERT–IL4 peptide reversed CUMS–induced enhancement of the SERT–sGC interaction and normalized 5–HT neurotransmission from the DRN to hippocampus, exerting a fast-onset antidepressant activity. Conclusion This study revealed the mechanism by which SERT is under the regulatory control by the SERT–sGC association and provided insights into a novel target toward the SERT–sGC interaction in developing rapid–onset agents in the treatment of MDD.