Neuropharmacology and Pain Group, Neuroscience Program, Institut d’Investigació Biomèdica de Bellvitge, IDIBELL, 08907 L’Hospitalet de Llobregat, Spain.

The striatal dopamine D2 receptor (D2R) is generally accepted to be involved in positive symptoms of schizophrenia and is a main target for clinically used antipsychotic drugs (APDs). In fact, D2R is highly expressed in the striatum, where they form heteromers with the adenosine A2A receptor
(A2AR). Changes in the density of A2AR-D2R heteromers have been reported in postmortem tissuefrom patients with schizophrenia,1 but the degree to which A2AR are involved in schizophrenia and the effect on antipsychotic drugs is unknown. Therefore, we first assessed the impact of A2AR expression on psychotic-like behaviour and dopaminergic transmission in mice. Interestingly, mice lacking A2AR showed behavioural alterations related to cognitive impairment, anxiety, and anhedonia. In addition, these animals have altered sensorimotor gating. These behavioural alterations are compatible with a psychotic-like phenotype. Importantly, while total adenosine levels in the striatum of the A2AR -/- mouse are increased, total dopamine was unaltered. However, alterations in dopamine release were observed in the open field arena in the A2AR -/- mouse. Next, we examine the effect of exposure of different prototypical APDs on A2AR-D2R heteromerization in mammalian cells using a NanoBiT assay. Interestingly, clozapine, but not haloperidol or aripiprazole, was associated with a significant decrease in A2AR-D2R heteromerization after 2 h of treatment. Computational binding models of these compounds revealed distinctive molecular signatures that explain their different influence on heteromerization. The bulky tricyclic moiety of clozapine displaces TM 5 of D2R, inducing a clash with A2AR, while the extended binding mode of haloperidol and aripiprazole stabilizes a specific conformation of the second extracellular loop of D2R that improves the interaction with A2AR.2 Finally, we evaluated the heteromerization capacity of the genetic variants of the D2R gene associated with schizophrenia.3 While the ICL2-based D2R schizophrenia associated genetic variants did not affect receptor’s heteromerization with A2AR, the R150H located at the TM4 stabilizes the D2R-A2AR heteromer. Interestingly, aripiprazole showed reduced efficacy in stabilizing D2R-A2AR heteromers containing the genetic variant D2R-R150H, compared to haloperidol, suggesting a differential impact of D2R schizophrenia associated genetic variants in antipsychotic treatments. Overall, there exists a clinical need for the development of mechanistically novel and more efficacious APDs, thus understanding the impact of D2R-A2AR heteromer formation on D2R downstream signalling will certainly contribute to the development of such novel APDs.

References
1. Valle-León, M. et al. Decreased striatal adenosine A2A-dopamine D2 receptor heteromerization in schizophrenia. Neuropsychopharmacology 46, 665–672 (2021).
2. Valle-León, M. et al. Unique effect of clozapine on adenosine A2A-dopamine D2 receptor heteromerization. Biomed Pharmacother 160, (2023).
3. Valle-León, M. et al. Insights of schizophrenia-associated dopamine D2 receptor variants: eƯects on antipsychotic-mediated modulation of receptor heteromerization. Transl Psychiatry In preparation,(2024).