Protein modification by oxidized phospholipids and hydrolytically released lipid electrophiles: Investigating cellular responses

Abstract

Oxygen is essential for the growth and function of mammalian cells. However, imbalances in oxygen or abnormalities in the ability of a cell to respond to oxygen levels can result in oxidative stress. Oxidative stress plays an important role in a number of diseases including atherosclerosis, rheumatoid arthritis, cancer, neurodegenerative diseases and asthma. When membrane lipids are exposed to high levels of oxygen or derived oxidants, they undergo lipid peroxidation to generate oxidized phospholipids (oxPL). Continual exposure to oxidants and decomposition of oxPL results in the formation of reactive electrophiles, such as 4-hydroxy-2-nonenal (HNE). Reactive lipid electrophiles have been shown to covalently modify DNA and proteins. Furthermore, exposure of cells to lipid electrophiles results in the activation of cytoprotective signaling pathways in order to promote cell survival and recovery from oxidant stress. However, if not properly managed by cellular detoxification mechanisms, the continual exposure of cells to electrophiles results in cytotoxicity. The following perspective will discuss the biological importance of lipid electrophile protein adducts including current strategies employed to identify and isolate protein adducts of lipid electrophiles as well as approaches to define cellular signaling mechanisms altered upon exposure to electrophiles. This article is part of a Special Issue entitled: Oxidized phospholipids-their properties and interactions with proteins.

Figure 1

Generation of lipid electrophiles from membrane polyunsaturated fatty acid (PUFA) side chains and their downstream effects.

Figure 2

Generation of oxidized phospholipids from parent glycerophosphotidylcholine molecules.

Figure 3

Method for adduct capture and analysis utilizing click chemistry compatible alkynyl-HNE analogues and a biotinylated linker.

Figure 4

Method for adduct capture and analysis utilizing click chemistry compatible HNE analogues and photocleavable biotin linker.

Figure 5

Structures of biotinylated glycerophospholipids used to capture adducted proteins for identification and analysis.

Figure 6

HNE-responsive signaling network [63]. Specific targets include cell cycle proteins, RNA splicing proteins, proteins involved in both cell cycle and RNA splicing, and proteins not involved in either process (colored in pink, cyan, green, and purple, respectively).

Figure 7

Highlighted cellular signaling pathways that are altered in response to HNE, including heat shock, antioxidant response, and inflammation.