Oxidized LDL and 4-hydroxynonenal modulate tyrosine kinase receptor activity

Among the diverse risk factors involved in atherosclerosis, LDL are thought to become atherogenic after undergoing oxidative modifications, characterized by oxidized lipid formation and structural alterations of apoB. Oxidized LDL alter various signaling pathways and exhibit a broad range of biological responses including inflammation, gene expression, cell proliferation or apoptosis. The biological effects of oxidized LDL are related to the presence of peroxidation products such as hydroperoxides, lysophosphatidylcholines, oxysterols and aldehydes.4-Hydroxynonenal (HNE) is one of the most abundant aldehydes formed during the oxidation of polyunsaturated fatty acids in LDL and in membranes. It is able to react with thiols and free amino group residues of proteins. HNE is involved in apoB modifications that alter LDL metabolism and cell protein-adduct formation which may mediate in part the biological effects of oxidized LDL. We report here that HNE delivered to cells by oxidized LDL reacts with cellular proteins, for instance with tyrosine kinase receptors (RTK) such as EGFR and PDGFR. HNE induces in vitro derivatization and tyrosine phosphorylation of RTK (the fine molecular mechanism and conformational changes remain to be elucidated). In intact living cells, oxidized LDL (and pure HNE) trigger HNE-adduct formation and activation of PDGFR and EGFR, through an antioxidant-insensitive and reactive oxygen species independent mechanism. The presence of HNE-PDGFR adducts in atherosclerotic areas lead one to hypothesize that oxidized lipids may also react in vivo with membrane RTK, thereby disturbing their cellular functions.