Serotonin 5-HT2A receptor expression and functionality in postmortem frontal cortex of subjects with schizophrenia: Selective biased agonism via Gαi1-proteins

Abstract

Serotonin 5-HT2A receptors (5-HT(2A)Rs) have been implicated in schizophrenia. However, postmortem studies on 5-HT(2A)Rs expression and functionality in schizophrenia are scarce. The 5-HT2AR mRNA and immunoreactive protein expression were evaluated in postmortem tissue from dorsolateral prefrontal cortex (DLPFC) of antipsychotic-free (n = 18) and antipsychotic-treated (n = 9) subjects with schizophrenia, and matched controls (n = 27). Functional coupling of 5-HT2AR to G-proteins was tested by measuring the activation induced by the agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride ((+/-)DOI) in antibody-capture [S-35]GTP gamma S scintillation proximity assays (SPA). In antipsychotic-free schizophrenia subjects, 5-HT2AR mRNA expression and protein immunoreactivity in total homogenates was similar to controls. In contrast, in antipsychotic-treated schizophrenia subjects, lower mRNA expression (60 +/- 9% vs controls) and a trend to reduced protein immunoreactivity (86 +/- 5% vs antipsychotic-free subjects) just in membrane-enriched fractions was observed. [S-35]GTP gamma S SPA revealed a significant (similar to)6% higher stimulation of G(alpha i1)-protein by (+/-)DOI in schizophrenia, whereas activation of the canonical G(alpha q/11)-protein pathway by (+/-)DOI remained unchanged. Expression of G(alpha i1) - and G(alpha q/11)-proteins did not differ between groups. Accordingly, in rats chronically treated with clozapine, but not with haloperidol, a 30-40% reduction was observed in 5-HT2AR mRNA expression, 5-HT2AR protein immunoreactivity and [H-3]ketanserin binding in brain cortical membranes. Overall, the data suggest a supersensitive 5-HT2AR signaling through inhibitory G(alpha i1)-proteins in schizophrenia. Together with previous results, a dysfunctional pro-hallucinogenic agonist-sensitive 5-HT2AR conformation in postmortem DLPFC of subjects with schizophrenia is proposed. Atypical antipsychotic treatment would contribute to counterbalance this 5-HT2AR supersensitivity by reducing receptor expression. (C) 2019 The Author(s). Published by Elsevier B.V.