Signaling transduction regulated by 5-hydroxytryptamine 1A receptor and orexin receptor 2 heterodimers

Abstract

As G-protein-coupled receptors (GPCRs), 5-hydroxytryptamine 1A receptor (5-HT1AR) and orexin receptor 2 (OX2R) regulate the levels of the cellular downstream molecules. The heterodimers of different GPCRs play important roles in various of neurological diseases. Moreover, 5-HT1AR and OX2R are involved in the pathogenesis of neurological diseases such as depression with deficiency of hippocampus plasticity. However, the direct interaction of the two receptors remains elusive. In the present study, we firstly demonstrated the heterodimer formation of 5-HT1AR and OX2R. Exchange protein directly activated by cAMP (Epac) cAMP bioluminescence resonance energy transfer (BRET) biosensor analysis revealed that the expression levels of cellular cAMP significantly increased in HEK293T cells transfected with the two receptors compared with the 5-HT1AR group. Additionally, the cellular level of calcium was upregulated robustly in HEK293T cells co-transfected with 5-HT1AR and OX2R group after agonist treatment. Furthermore, western blotting data showed that 5-HT1AR and OX2R heterodimer decreased the levels of phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP-response element-binding protein (CREB). These results not only unraveled the formation of 5-HT1AR and OX2R heterodimer but also suggested that the heterodimer affected the downstream signaling pathway, which will provide new insights into the function of the two receptors in the brain.

Targeting orexin receptors: Recent advances in the development of subtype selective or dual ligands for the treatment of neuropsychiatric disorders

“…Cross‐pharmacology between the serotonin and orexin systems is very relevant and interesting due to the direct involvement of both receptor families in depression and neural pathological changes in the hippocampus. In 2019 Wang et al 215 described the heterodimer formation between 5‐HT1A‐R/OX2‐R, as observed in the hippocampus of adult rats, and in vitro experiments assessed the functional downstream signaling changes between the heterodimer in comparison to the single monomers. After stimulation with 8‐OH‐DPAT or orexin‐B (5‐HT1A‐R and OX2‐R agonists, respectively), the heterodimer showed significant increase in cAMP and Ca 2+ level, and downregulation of second messengers such as p‐CREB and p‐ERK.…”

“…A thorough understanding of the in vivo physiological relevance and the potential of this macro-complex as a target for small molecule treatment of neurological disorders needs to be further explored. 215 In 2022, Zhang et al 14 verified the formation of another heterodimer between 5-HT1A-R and OX1-R, and demonstrated that the functional complex retains similar β-arrestin recruitment, but prefers to couple with G s proteins instead of the canonical G i for 5-HT1A-R or G q for OX1-R. From a structural perspective, the authors observed that the heterodimer interface shifts from TM4/TM5 domains to TM6, when activated. Based on this, they also attempted to identify the physiological relevance of this complex, and they concluded that the endogenous formation of the heterodimers is directly associated with the pathological genesis of depression.…”

“…After stimulation with 8‐OH‐DPAT or orexin‐B (5‐HT1A‐R and OX2‐R agonists, respectively), the heterodimer showed significant increase in cAMP and Ca 2+ level, and downregulation of second messengers such as p‐CREB and p‐ERK. A thorough understanding of the in vivo physiological relevance and the potential of this macro‐complex as a target for small molecule treatment of neurological disorders needs to be further explored 215 …”