The ADORA1 mutation linked to early-onset Parkinson's disease alters adenosine A(1)-A(2A) receptor heteromer formation and function.

Adenosine modulates neurotransmission through inhibitory adenosine A(1) receptors (A(1)Rs) and stimulatory A(2A) receptors (A(2A)Rs). 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 (G279(7.44)S) within the transmembrane helix (TM) 7 of A(1)R (A(1)R(G279S)) 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 A(1)R and the A(1)R-A(2A)R heteromer. Our results revealed that the G279(7.44)S mutation does not alter A(1)R expression, ligand binding, constitutive activity or coupling to transducer proteins (G(αi), G(αq), G(α12/13), G(αs), β-arrestin2 and GRK2) in transfected HEK-293 T cells. However, A(1)R(G279S) weakened the ability of A(1)R to heteromerize with A(2A)R, as shown in a NanoBiT assay, which led to the disappearance of the heteromerization-dependent negative allosteric modulation that A(1)R imposes on the constitutive activity and agonist-induced activation of the A(2A)R. Molecular dynamic simulations allowed to propose an indirect mechanism by which the G279(7.44)S mutation in TM 7 of A(1)R weakens the TM 5/6 interface of the A(1)R-A(2A)R 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 A(2A)R not forming heteromers with A(1)R could represent a main pathogenetic mechanism of the EOPD associated with the G279(7.44)S ADORA1 mutation.