Abstract 397: Aldehyde-Modified Hdl Has CD36-dependent Pro-Atherogenic Effects in Macrophages

Abstract

The role of high density lipoproteins (HDL) in protecting against cardiovascular disease is compromised when HDL undergoes modification during conditions of oxidative stress; however, the mechanisms underlying these changes in HDL function are not well defined. Reactive aldehydes such as acrolein (a major component in cigarette smoke) or major products of lipid peroxidation such as 4-hydroxynonenal (HNE) or malondialdehyde (MDA) are known to oxidize HDL in cardiovascular disease. To test the hypothesis that modification of HDL with aldehydes impairs HDL’s athero-protective functions in macrophages, we first measured the ability of modified HDL to protect against foam cell formation. Cholesterol-loaded peritoneal macrophages isolated from wild-type C57Bl/J mice were incubated with native HDL, acrolein-modified HDL (acro-HDL), HNE-modified HDL (HNE-HDL) or MDA-modified HDL (MDA-HDL) for 24 h. Contrary to native HDL, oxidized forms of HDL were unable to prevent foam cell formation as shown by increased Oil red-O staining. Next, using a Boyden chamber assay, we demonstrated that acro- and MDA-HDL had impaired abilities to promote macrophage migration (64% and 67% of native HDL cell migration, respectively). Finally, using a secreted alkaline phosphatase reporter THP-1 cell-based assay, we determined that acro-HDL promotes activation of the pro-inflammatory NFkappaB pathway. Interestingly, immunoblot and quantitative RT-PCR analyses revealed that incubation of macrophages with acro- and MDA-HDL leads to increased expression of the pro-atherogenic receptor, cluster of differentiation 36 (CD36). Therefore, we repeated the foam cell formation and migration experiments using similar ligands, but this time, in CD36-null peritoneal macrophages. We found that both of these functions were dependent on CD36; however, the extent of the functional changes varied based on the type of oxidative modification present on HDL. In conclusion, modification of HDL with reactive aldehydes generates a particle that has pro-atherogenic effects in macrophages, many of which are dependent on CD36.