Funtional characterization of 5 HT2A-mGluR2 complex at rat brain. Identification of the complexes in human peripheral blood cells

Abstract

It has been recently identified a functional complex between the 5 HT2A and mGluR2 G protein coupled receptors in brain cortex. In post mortem human brain from untreated schizophrenic subjects, the 5 HT2A receptor is up regulated and the mGluR2 receptor is down regulated, a pattern that could predispose to psychosis. Therefore, the 5 HT2A-mGluR2 complex may be involved in the altered brain processes of schizophrenia (Gonzalez Maeso et al, Nature, 2008). The 5 HT2A receptor is mainly coupled to Gαq,. However, it has been also suggested that 5 HT2A receptors can regulate cAMP accumulation through activation of Gi/o proteins. In the present study, we have further characterized in rat striatal membranes the G protein subtype coupled to the 5 HT2A receptor stimulation induced by the selective 5 HT2A agonist TCB 2 (4 Bromo 3,6 dimethoxybenzocyclobuten 1 methylamine), by immunoprecipitation of [35S]GTPγS labelled G protein subunits, as well as its modulation in the presence of the mGluR2 antagonist, LY341495. We have also aimed, by using fluorescence analyzer cell sorter together with QPCR (TaqMan® Gene Expression assay), to identify whether blood peripheral cells are co expressing both 5 HT2A and mGluR2 receptors at the same cell type. The agonist TCB 2 induced a concentration dependent increase in [35S]GTPS binding in rat striatal membranes (up to 51%) and this effect was partially attenuated by the 5 HT2A antagonist MDL11939 (from 51% to36%) while the mGluR2 antagonist LY341495 significantly increased [35S]GTPS binding induced by TCB 2 (up to 86%; p<0.05). 5 HT2A receptor activation by TCB 2 [35S]GTPS induced labelling of Gαq (29%), Gαo (39%), Gαi2 (57%) and Gαi3 (47%), but not of Gαi1, Gαz or Gαs protein subunits. The 5HT2A antagonist MDL11939 (10 M), blocked TCB 2 induced labelling of Gαq and Gαo proteins, without affecting Gαi2 and Gαi3 labelling. Notwithstanding , the mGluR2 antagonist, LY341495, blocked TCB 2 induced labelling of both Gαi2 and Gαi3, and it increased those of Gαq (from 29% to 49%). Altogether, these data demonstrate the functional signalling of the 5 HT2A mGluR2 complex at rat brain. Results of QPCR assays from sorted peripheral blood cells showed the co expression of both receptors (5 HT2A and mCluR2) on the granulocytes cells. However, [35S]GTPγS binding assay on blood cells failed to show TCB 2 induced [35S]GTPγS] binding, probability due to a low expression of receptors. In conclusion: 5 HT2A and mGluR2 receptors act as a functional dimmer with signalling relevance. Interestingly, the determination of this complex in human peripheral blood cells by fluorescence analyzer cell sorter and QPCR assays could be envisaged as a biomarker in schizophrenia.