Cholesterol 27-Hydroxylase but Not Apolipoprotein apoE Contributes to A_2A Adenosine Receptor Stimulated Reverse Cholesterol Transport

Movement of free cholesterol between the cellular compartment and acceptor is governed by cholesterol gradients that are determined by several enzymes and reverse cholesterol transport proteins. We have previously demonstrated that adenosine A_2A receptors inhibit foam cell formation and stimulate production of cholesterol 27-hydroxylase (CYP27A1), an enzyme involved in the conversion of cholesterol to oxysterols. We therefore asked whether the effect of adenosine A_2A receptors on foam cell formation in vitro is mediated by CYP27A1 or apoE, a carrier for cholesterol in the serum. We found that specific lentiviral siRNA infection markedly reduced apoE or 27-hydroxylase mRNA in THP-1 cells. Despite diminished apoE expression (p < 0.0002, interferon-gamma (IFNγ) CGS vs. IFNγ alone, n = 4), CGS-21680, an adenosine A_2A receptor agonist, inhibits foam cell formation. In contrast, CGS-21680 had no effect on reducing foam cell formation in CYP27A1 KD cells (4 ± 2%; p < 0.5113, inhibition vs. IFNγ alone, n = 4). Previously, we reported the A_2A agonist CGS-21680 increases apoAI-mediated cholesterol efflux nearly twofold in wild-type macrophages. Adenosine receptor activation had no effect on cholesterol efflux in CYP27A1 KD cells but reduced efflux in apoE KD cells. These results demonstrate that adenosine A_2A receptor occupancy diminishes foam cell formation by increasing expression and function of CYP27A1.