PUMAs

Background : Fatty acids (FAs) appear to be essential for macrophage plasticity as they are ideally positioned at the crossroads between anabolic and catabolic pathways. Macrophages possess the ability to modulate dynamically and autonomously their intracellular FA metabolism including FA oxidation and FA synthesis. As observed for cholesterol, beyond the purely quantitative accumulation of fatty acid in the cells, it is likely that qualitative alterations of fatty acid profile and distribution may affect some biological functions of the macrophages either through the production of bioactive lipid mediators or to changes of cell membranes properties. Some recent studies support that view and have demonstrated that genetic modulation of FA pathways even though restricted to myeloid cells directly affects macrophage functions and subsequently influences atherosclerosis development. By using targeted lipidomic and transcriptomic approaches, we have characterized a tightly regulated set of genes that control membrane polyunsaturated fatty acid (PUFA) composition in macrophages. These genes are involved in the elongation of PUFAs (ELOVL5) and in their incorporation into phospholipids (LPCAT3). ELOVL5 and LPCAT3 display a strong specificity toward n-3 and n-6 PUFA with 20 carbons including arachidonic acid (AA) and eicosapentaenoic acid( EPA). Macrophages deficient for Elovl5 and/or Lpcat3 display dramatic alteration of AA and EPA metabolism. Unexpectedly, the TLR-sensitive transcription factor IRF5 (interferon regulatory factor -5) has been identified as a potential transcriptional regulator of both LPCAT3 and ELOVL5. Aims : The overall concept of this project is to demonstrate that the LCPAT3/ELOVL5 axis modulates atherosclerosis development by controlling key macrophages functions. Our research program will combine in vitro and in vivo approaches using genetically engineered mouse models and translational studies in human populations First, by using Lpcat3KOMAC and Elovl5-/- mice we will explore the role of the LPCAT3/ELOVL5 axis in macrophages in the context of atherosclerosis and we will decipher the molecular mechanisms involved. We will also test the ability of Elovl5/lpcat3 to modulate the antiatherogenic action of eicosapentaenoic acid (EPA) in a mouse model of atherosclerosis. In a second WP, we will investigate the involvement of IRF5 in the reprogramming of FA metabolism through ELOVL5 and LPCAT3 during inflammation. We will explore the interplay between IRF5, LPCAT3/ELOVL5 pathways, PUFA composition and synthesis of pro-resolving mediators following LPS activation. Additionally, we expect to characterize the atherogenic function of IRF5 in macrophages, which is to date unclear. In WP3, we will perform translational studies to validate our hypothesis and to determine whether biomarkers of LPCAT3/ELOVL5 activity are associated with CV risk in selected human populations, including Type 2 Diabetic subjects with low versus high cardiovascular risk. Finally, we will analyze whether these markers have significantly different levels in stable Vs vulnerable regions of human carotid atherosclerotic plaques. Perspectives : Our project fits into a context in which new therapies targeting macrophages and inflammation appear as potentially effective strategies for atherosclerosis treatment and prevention. On the one hand, this program may unravel new and original mechanisms associating fatty acids and macrophage activation thus paving the way for the development of therapeutic strategies. On the other hand, this project should lead to the identification of new biomarkers of CV risk, thus allowing earlier detection and improving the stratification of high-risk patients. Finally, our program should also provide new insights into the mechanisms that account for the potential atheroprotective effects of EPA at a time when the impact of omega 3 fatty acids on the cardiovascular risk is being reevaluated.