The role of cholesterol in the regulation of adenosine A2A receptor: A basic and clinical approach

Abstract

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity worldwide and hypercholesterolemia is one of the main CVD risk factors. During inflammation, adenosine blood concentration increases and activates A2A adenosine receptors (expressed by endothelial cells and lymphocytes), thus producing a protective effect via its vasodilatory and immunosuppressive functions. Conversely, alterations of A2A receptor expression and properties have been found in CVD patients. Cholesterol seems to directly regulate the functional characteristics of this receptor and studies suggest that A2A receptor alterations are also associated with dyslipidemia. In order to study the role of cholesterol in A2A receptor regulation, two approaches are used: 1) basic, via the analysis in cellular models of the effect of cholesterol modulation on A2AR localization and signaling, and 2) clinical, by characterizing A2AR expression and functions in patients with familial hypercholesterolemia (FH) and by studying a possible correlation between A2AR, blood cholesterol levels and patient's clinical status. T cells (CEM) and endothelial cells (HMEC-1) are depleted (Methyl-β-Cyclodextrin) or supplemented with cholesterol (Water Soluble Cholesterol) and stimulated with a selective A2A receptor agonist, Adonis. Ligand interaction and A2A receptor activation are analyzed by western blot, flow cytometry and ELISA, A2AR localization by immunofluorescence and microscopy. 2) FH patients and healthy subjects are selected by age, gender and clinical status. After isolation of peripheral blood mononuclear cells (PBMCs), A2AR expression is analyzed by western blot. 1) Cholesterol depletion in CEM does not affect receptor affinity (KD) for its agonist, but increases its binding capacity (Bmax). 2) Our pilot study on a small cohort of patients shows a decrease in A2A receptor expression compared with healthy subjects and an inverse correlation between A2AR expression and total and LDL cholesterol blood levels. Our results demonstrate that cholesterol modulates A2A receptor and that alterations of A2A properties are associated with hypercholesterolemia, which might help to better understand the high cardiovascular risk in hypercholesterolemia patients.