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

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.