Heterocomplex formation of 5-HT2A-mGlu2 and its relevance for cellular signaling cascades

• Published in: Neuropharmacology 2012-06, Vol.62 (7), p.2183-2190
• Main Authors: Delille, Hannah K., Becker, Judith M., Burkhardt, Sabrina, Bleher, Barbara, Terstappen, Georg C., Schmidt, Martin, Meyer, Axel H., Unger, Liliane, Marek, Gerard J., Mezler, Mario
• Format: Article
• Language: English
• Subjects: 5-HT2A; Animals; Antagonists; Brain; Cells, Cultured; Cerebral Cortex - cytology; Cerebral Cortex - physiology; Competition; Cortex (prefrontal); Cyclic AMP; Dopamine; G protein-coupled receptors; Glutamic acid receptors; Glutamic acid receptors (metabotropic); GPCR crosstalk; HEK293 Cells; Heterocomplex; Humans; Intracellular signalling; Mental disorders; mGlu2; Neural networks; Oligomerization; Protein Multimerization - drug effects; Protein Multimerization - physiology; Rats; Rats, Wistar; Receptor Cross-Talk - physiology; Receptor mechanisms; Receptor, Serotonin, 5-HT2A - metabolism; Receptor, Serotonin, 5-HT2A - physiology; Receptors, Metabotropic Glutamate - agonists; Receptors, Metabotropic Glutamate - antagonists & inhibitors; Receptors, Metabotropic Glutamate - metabolism; Receptors, Metabotropic Glutamate - physiology; Schizophrenia; Second messengers; Serotonin receptors; Serotonin S2 receptors; Signal transduction; Signal Transduction - drug effects; Signal Transduction - physiology
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/j.neuropharm.2012.01.010

Dopamine, serotonin and glutamate play a role in the pathophysiology of schizophrenia. In the brain a functional crosstalk between the serotonin receptor 5-HT2A and the metabotropic glutamate receptor mGlu2 has been demonstrated. Such a crosstalk may be mediated indirectly through neuronal networks or directly by receptor oligomerization. A direct link of the 5-HT2A-mGlu2 heterocomplex formation to receptor function, i.e. to intracellular signaling, has not been fully demonstrated yet. Here we confirm the formation of 5-HT2A-mGlu2 heterocomplexes using quantitative Snap/Clip-tag based HTRF methods. Additionally, mGlu2 formed complexes with 5-HT2B and mGlu5 but not 5-HT2C indicating that complex formation is not specific to the 5-HT2A-mGlu2 pair. We studied the functional consequences of the 5-HT2A-mGlu2 heterocomplex addressing cellular signaling pathways. Co-expression of receptors in HEK-293 cells had no relevant effects on signaling mediated by the individual receptors when mGlu2 agonists, antagonists and PAMs, or 5-HT2A hallucinogenic and non-hallucinogenic agonists and antagonists were used. Hallucinogenic 5-HT2A agonists induced signaling through Gq/11, but not Gi and thus did not lead to modulation of intracellular cAMP levels. In membranes of the medial prefrontal cortex [3H]-LY341495 binding competition of mGlu2/3 agonist LY354740 was not influenced by 2,5-dimethoxy-4-iodoamphetamine (DOI). Taken together, the formation of GPCR heterocomplexes does not necessarily translate into second messenger effects. These results do not put into question the well-documented functional cross-talk of the two receptors in the brain, but do challenge the biological relevance of the 5-HT2A-mGlu2 heterocomplex. ► mGlu2 forms a heterocomplex with 5-HT2A, 5-HT2B, and mGlu5 but not 5-HT2C. ► 5-HT2A-mGlu2 heterocomplex formation does not alter intracellular signaling. ► 5-HT2A activation by DOI does not affect mGlu2 ligand binding in rat mPFC.