Early and transient alteration of adenosine A2A receptor signaling in a mouse model of Huntington disease

Huntington Disease (HD) is characterized by choreic involuntary movements and striatal vulnerability. A(2A) receptors expressed on GABAergic striatal neurons have been suggested to play a pathogenetic role. Previous data demonstrated the presence of an aberrant alteration of A(2A) receptor-dependent adenylyl cyclase in an in vitro model of the disease (striatal cells expressing mutant huntingtin) and in peripheral circulating cells of HD patients. Here, we investigated whether this dysfunction is present in the R6/2 HD transgenic mouse model, by analyzing striatal A(2A) receptor-binding and adenylyl cyclase activity at different developmental stages in comparison with age-matched wild type animals. A transient increase in A(2A) receptor density (B-max) and A(2A) receptor-dependent cAMP production at early presymptomatic ages (7-14 postnatal days) was found. Both alterations normalized to control values starting from postnatal day 21. In contrast, A(2A) receptor mRNA, as detected by real time PCR, dramatically decreased starting from PND21 until late symptomatic stages (12 weeks of age). The discrepancy between A(2A) receptor expression and density suggests compensatory mechanisms. These data, reproducing ex vivo the previous observations in vitro, support the hypothesis that an alteration of A(2A) receptor signaling is present in HD and might represent an interesting target for neuroprotective therapies. (c) 2006 Elsevier Inc. All rights reserved.