The ADORA1 mutation linked to early-onset Parkinson's disease alters adenosine A1-A2A receptor heteromer formation and function

Adenosine modulates neurotransmission through inhibitory adenosine A1 receptors (A1Rs) and stimulatory A2A receptors (A2ARs). These G protein-coupled receptors are involved in motor function and related to neurodegenerative diseases such as Parkinson's disease (PD). An autosomal-recessive mutation (G2797.44S) within the transmembrane helix (TM) 7 of A1R (A1RG279S) has been associated with the development of early onset PD (EOPD). Here, we aimed at investigating the impact of this mutation on the structure and function of the A1R and the A1R-A2AR heteromer. Our results revealed that the G2797.44S mutation does not alter A1R expression, ligand binding, constitutive activity or coupling to transducer proteins (Gαi, Gαq, Gα12/13, Gαs, β-arrestin2 and GRK2) in transfected HEK-293 T cells. However, A1RG279S weakened the ability of A1R to heteromerize with A2AR, as shown in a NanoBiT assay, which led to the disappearance of the heteromerization-dependent negative allosteric modulation that A1R imposes on the constitutive activity and agonist-induced activation of the A2AR. Molecular dynamic simulations allowed to propose an indirect mechanism by which the G2797.44S mutation in TM 7 of A1R weakens the TM 5/6 interface of the A1R-A2AR heteromer. Therefore, it is demonstrated that a PD linked ADORA1 mutation is associated with dysfunction of adenosine receptor heteromerization. We postulate that a hyperglutamatergic state secondary to increased constitutive activity and sensitivity to adenosine of A2AR not forming heteromers with A1R could represent a main pathogenetic mechanism of the EOPD associated with the G2797.44S ADORA1 mutation.