Abstract 105: Timely Removal of Lipid Oxidation Products is Mediated by Macrophages.

Abstract

Reciprocity of inflammation and oxidative stress is now significantly considered as an important mechanism underlying numerous diseases and cancers. As a mechanistic link connecting them, we have shown that one of the end products of lipid oxidation, 2-(ω-carboxyethyl)pyrrole (CEP) is generated during inflammation and wound healing and recognized by Toll-like receptor 2 (TLR2) on endothelial cells. It leads to angiogenesis, which is independent of vascular endothelial growth factor. Importantly, the levels of CEP are reduced back to normal when the wound is healed, but remain constitutively high in pathological conditions, including aging and cancers. Thus, for most tissue repair processes, it appears critical not only to generate CEP, but also to provide its timely removal. Accordingly, our hypothesis is that in order to avoid tissue damage by inflammation-induced oxidative products, CEP needs to be cleared from injured tissues when its role is complete. We have sought to determine a cellular and molecular mechanism of CEP clearance from injured tissues. At first, through CEP binding and internalization assay, comparing with other cell types, we verified that macrophage is the responsible cell type of CEP clearance. Specifically, resident, F4/80 hi , and M2 macrophages are much more efficient for CEP clearance rather than thioglycolate-elicited, F4/80 lo , and M1 macrophages, respectively. Secondly, by using several knockout mouse lines, we identified that both TLR2 and CD36 are largely involved in CEP clearance. To examine the in vivo relevance of CEP clearance besides skin injury model, we used ApoE deficient mice as an atherosclerotic model because atherosclerosis is known to be intimately associated with inflammation and oxidative stress. Using a CEP-specific antibody, we have been screening the CEP appearance and disappearance in early-to-late stages of atherosclerosis. Recently, we examined that CEP is strongly stained only in and adjacent to the atherosclerotic lesion of ApoE deficient mice fed with western diet for 20 weeks, but barely stained in 30 weeks. Moreover, in the plaque, macrophage-enriched region exhibits weak signals of CEP staining. Therefore, we suggest that timely removal of CEP is mediated by macrophages ex vivo and in vivo .