Polarization of Human THP-1 Macrophages: Link between Adenosine Receptors, Inflammation and Lipid Accumulation

Abstract

Abstract Rationale: Macrophages are key players in inflammation and atherosclerosis. They express surface receptors of different subtypes for the endogenous autocoid adenosine. Macrophages within atherosclerotic lesions attain two clear-cut functional phenotypes M1 (pro-inflammatory) and M2 (immunosuppressive). This study examines the relative expression of adenosine receptors and proteins involved in cholesterol transport in THP-1 human macrophages upon differentiation into M1 and M2 subtypes. Methods: THP-1 human monocytes were cultured in the presence of 100nM PMA. When a differentiated non-polarized phenotype (M0) was achieved, cells were incubated in the presence of 20ng/ ml interferon-γ+100ng/ml LPS to obtain M1 macrophages or 20ng/ml IL-4 to obtain M2 subset. Phenotypes were confirmed via QRT-PCR and by flow cytometry. Expression of cholesterol efflux proteins (ABCA1, ABCG1, SR-B1 and 27 hydroxylase) and scavenger receptors (CD36, SR-A1, LOX1 and CXCL16) was analyzed by QRT-PCR and confirmed by Western blot. Results: The M1 subset of macrophages display reduced expression of cholesterol efflux proteins: ABCA1, SR-B1 and 27 hydroxylase, as compared to M0 and M2. However, expressions of SR-B1 and 27-hydroxylase (27OH) are lower in both M1 and M2 when compared to not polarized M0 subset. Moreover, M2 polarized macrophages display an increased expression of the major scavenger receptors: CD36, SR-A1 and LOX1. This provides an explanation for significantly higher internalization of oxLDL and foam cell formation in M2 versus M1. Our results demonstrate that the M1 phenotype is associated with upregulation of the A2AR and A2BR while the M2 phenotype displays enhanced A1 and A3R expression. Keywords