The effect of oxidative stress on the adenosine A_2A receptor activity and signalling

The adenosine A_2A receptor (A_2AR) is a G-protein coupled receptor that has important anti-inflammatory effects in response to some agonists and consequently is considered a therapeutic target. Its activity is affected by local membrane lipid environment and presence of certain phospholipid classes, so studies should be conducted using extraction methods such as styrene maleic acid co-polymers (SMA) that retain the local lipids. Currently, little is known about the effect of oxidative stress, which may arise from inflammation, on the A_2AR. Therefore, it was over-expressed in Pichia pastoris, SMA was used to extract the A_2AR from cell membranes and its response to ligands was tested in the presence or absence of the radical initiator AAPH or reactive aldehyde acrolein. SMA-extracted A_2AR was able to undergo conformational changes, measured by tryptophan fluorescence, in response to its ligands but oxidative treatments had no effect on the structural changes. Similarly, the treatments did not affect temperature-dependent protein unfolding. In contrast, in HEK293 cells expressing the A_2AR, oxidative treatments increased cAMP levels in response to the agonist NECA but had no effect on direct activation of adenylate cyclase. Thus, oxidative stress may be a homeostatic mechanism that abrogates inflammation via the A_2AR signalling pathway.