Attenuation of Oxytocin and Serotonin 2A Receptor Signaling through Novel Heteroreceptor Formation

Abstract

The oxytocin receptor (OTR) and the 5-hydroxytryptamine 2A receptor (5-HTR2A) are expressed in similar brain regions modulating central pathways critical for social and cognition-related behaviors. Signaling crosstalk between their endogenous ligands, oxytocin (OT) and serotonin (5-hydroxytryptamine, 5-HT), highlights the complex interplay between these two neurotransmitter systems and may be indicative of the formation of heteroreceptor complexes with subsequent downstream signaling changes. In this study, we assess the possible formation of OTR-5HTR2A heteromers in living cells and the functional downstream consequences of this receptor–receptor interaction. First, we demonstrated the existence of a physical interaction between the OTR and 5-HTR2A in vitro, using a flow cytometry-based FRET approach and confocal microscopy. Furthermore, we investigated the formation of this specific heteroreceptor complex ex vivo in the brain sections using the Proximity Ligation Assay (PLA). The OTR-5HTR2A heteroreceptor complexes were identified in limbic regions (including hippocampus, cingulate cortex, and nucleus accumbens), key regions associated with cognition and social-related behaviors. Next, functional cellular-based assays to assess the OTR-5HTR2A downstream signaling crosstalk showed a reduction in potency and efficacy of OT and OTR synthetic agonists, carbetocin and WAY267464, on OTR-mediated Gαq signaling. Similarly, the activation of 5-HTR2A by the endogenous agonist, 5-HT, also revealed attenuation in Gαq-mediated signaling. Finally, altered receptor trafficking within the cell was demonstrated, indicative of cotrafficking of the OTR/5-HTR2A pair. Overall, these results constitute a novel mechanism of specific interaction between the OT and 5-HT neurotransmitters via OTR-5HTR2A heteroreceptor formation and provide potential new therapeutic strategies in the treatment of social and cognition-related diseases.

The Role of Central Serotonin Neurons and 5-HT Heteroreceptor Complexes in the Pathophysiology of Depression: A Historical Perspective and Future Prospects

“…The hypothesis goes beyond the serotonin hypothesis of depression and moves into molecular integration performed in diverse 5-HT1A and other 5-HTR heterocomplexes where, e.g., fibroblast growth factor receptor 1 (FGFR1) [19] and oxytocin receptor [30] protomers participate. Thus, if one or more of these receptor protomers exist among the highly vulnerable complexes, they can become novel targets for antidepressant drugs.…”

“…OXTRs play a significant and impressive role in modulating social and cognitiverelated behaviors, like bonding and attachment, reward and motivation, as well as fear, anxiety and stress-related responses [57,58]. These modulations of the neuronal networks involve the formation of heteroreceptor complexes with other GPCRs, like 5-HT2AR, 5-HT2CR [30,31] and D2R [59,60]. The dynamic formation of OXTR-5-HT2AR, OXTR-5-HT2CR and OXTR-D2R heteroreceptor complexes, especially in the limbic cortex and nucleus accumbens, makes possible a fundamental integrative process in the plasma membrane for the modulation of social and cognitive behaviors.…”

“…Modulation by serotonin VT of, e.g., glutamate and GABA synapses in the hippocampus involves 5-HT homoreceptor complexes and many different subtypes of 5-HT heteroreceptor complexes located on neurons and/or astroglia, like serotonin 1A receptor (5-HT1A)-fibroblast growth factor receptor 1 (FGFR1) [16][17][18][19], serotonin 1a receptor (5-HT1A)-serotonin 2A receptor (5-HT2A) [20], serotonin 1A receptor (5-HT1A)-galanin receptor 1 (GalR1) [21][22][23][24], serotonin 1A receptor (5-HT1A)-galanin receptor 1 (GalR1)galanin receptor 2 (GalR2) [25], serotonin 1A receptor (5-HT1A)-G-protein coupled receptor 39 (GPR39) [26], serotonin 2C receptor (5-HT2C)-growth hormone secretagogue receptor 1A (GHS-R1a) [27][28][29], serotonin 2A receptor (5-HT2A)-oxytocin receptor (OXTR) [30] and serotonin 2C receptor (5-HT2C)-oxytocin receptor (OXTR) [31] heteroreceptor complexes. One emerging concept in depression is that disturbances in allosteric receptor-receptor interactions in highly vulnerable 5-HT1A heteroreceptor complexes can contribute to causing depression and become novel targets for the treatment of depression and anxiety [19,32,33].…”

Links Between the Neurobiology of Oxytocin and Human Musicality

“…Likely increasing its diversity of action, oxytocin also interacts with several other receptors and neuromodulatory systems. For example, the peptide: (i) potentiates excitatory dopamine-mediated synaptic transmission (Li et al, 2020 ); (ii) interacts with a class of serotonin receptor (Chruścicka et al, 2019 ) and affects serotonin release (Yoshida et al, 2009 ); (iii) modulates signaling mediated by opioid receptors (dal Monte et al, 2017 ; Meguro et al, 2018 ; Salighedar et al, 2019 ); and (iv) activates TRPV2 channels (Van den Burg et al, 2015 ). There are also dynamic interactions with steroids (Jirikowski et al, 2018 ) and oxytocin levels are negatively correlated with cortisol, significantly modifying responses to stress (Lee et al, 2015 ; Schladt et al, 2017 ; Latt et al, 2018 ; Masis-Calvo et al, 2018 ; Neumann and Landgraf, 2019 ).…”

Can Allosteric Receptor-Protein Interactions in Receptor Complexes Be a Molecular Mechanism Involved in Cancer Immune Therapy?

“…Many of the homo and heteroreceptor complexes studied so far are mainly found in the extrasynaptic and synaptic regions of the plasma membrane of the neuronal networks using in situ Proximity Ligation Assay (PLA) and a neuronal marker antibody (14, 50). However, they can also exist in e.g., the astroglia based on PLA and astroglial markers like antibodies against glial fibrillary acidic protein.…”