The effect of cuox-LDL and MPO modified LDL on THP-1 macrophage polarization in vitro

Abstract

Background: Atherosclerosis is a chronic inflammatory disease that is characterized by a buildup of fat in the walls of arteries. Macrophages play a crucial role in the development of the disease by ingesting oxidized LDL particles and forming foam cells which are a hallmark of atherosclerosis. Oxidized low density lipoprotein (ox-LDL) is a major player in atherogenesis and many studies suggest that myeloperoxidase oxidized LDL (Mox-LDL) is an important patho-physiological model for LDL modification in vivo. While copper oxidized LDL (Cuox-LDL) is intensively studied in the context of atherosclerosis, little is known about the effects of Mox-LDL on monocyte and macrophage biology including their differentiation and polarization. Aim: Our study aimed at investigating Mox-LDL effects on macrophage polarization in vitro by comparing Mox-LDL to its Cuox-LDL counterpart and making use of the THP-1 cell line model. Methods: THP-1 monocytes were cultured and differentiated into M0 macrophages (MØs) by treatment with PMA in vitro. Then, resting macrophages were treated with both Mox-LDL and Cuox-LDL and then compared to M1 and M2 polarized macrophages. ELISA assays were performed to assess the levels of IL-6 and IL-10 cytokines in the culture supernatants under different conditions, while immunophenotyping was conducted by assessing the surface expression of CD80 and CD209 markers Results: CD80 expression was highly significant in M1-MØs when compared to all other subsets: M0-MØs, M2-MØs, and Mox-LDL treated M0-MØs. Similarly, CD209 was significantly expressed in M2-MØs when compared to the other subtypes. Although IL-6 release was minimal in all macrophages types except in the M1-MØs where it was upregulated as expected, the same M1-MØs subtype also showed a surprising and significant increase in IL-10 release. In our model, physiological concentrations of both Mox-LDL and Cuox-LDL had no significant effects on CD80/CD209 expression or IL-6/IL-10 release. Conclusion: In our model, we showed that Mox-LDL and Cuox-LDL treated M0-MØs did not exhibit any significant phenotypic changes in terms of CD surface expression or interleukins secretion. Our results suggest that both types of oxidized LDL are not able to stimulate M0-MØs towards an inflammatory nor an alternative phenotype. They also provide preliminary data that could help interpret better the role of Mox-LDL in macrophage differentiation in atherosclerosis.