Redox phospholipidomics of enzymatically generated oxygenated phospholipids as specific signals of programmed cell death

High fidelity and effective adaptive changes of the cell and tissue metabolism to changing environments require strict coordination of numerous biological processes. Multicellular organisms developed sophisticated signaling systems of monitoring and responding to these different contexts. Among these systems, oxygenated lipids play a significant role realized via a variety of re-programming mechanisms. Some of them are enacted as a part of pro-survival pathways that eliminate harmful or unnecessary molecules or organelles by a variety of degradation/hydrolytic reactions or specialized autophageal processes. When these "partial" intracellular measures are insufficient, the programs of cells death are triggered with the aim to remove irreparably damaged members of the multicellular community. These regulated cell death mechanisms are believed to heavily rely on signaling by a highly diversified group of molecules, oxygenated phospholipids (PLox). Out of thousands of detectable individual PLox species, redox phospholipidomics deciphered several specific molecules that seem to be diagnostic of specialized death programs. Oxygenated cardiolipins (CLs) and phosphatidylethanolamines (PEs) have been identified as predictive biomarkers of apoptosis and ferroptosis, respectively. This has led to decoding of the enzymatic mechanisms of their formation involving mitochondrial oxidation of CLs by cytochrome c and endoplasmic reticulum-associated oxidation of PE by lipoxygenases. Understanding of the specific biochemical radical-mediated mechanisms of these oxidative reactions opens new avenues for the design and search of highly specific regulators of cell death programs. This review emphasizes the usefulness of such selective lipid peroxidation mechanisms in contrast to the concept of random poorly controlled free radical reactions as instruments of non-specific damage of cells and their membranes. Detailed analysis of two specific examples of phospholipid oxidative signaling in apoptosis and ferroptosis along with their molecular mechanisms and roles in reprogramming has been presented.

A phosphatidylcholine-specific phospholipase C regulates activation of p42/44 mitogen-activated protein kinases in lipopolysaccharide-stimulated human alveolar macrophages

This study uses human alveolar macrophages to determine whether activation of a phosphatidylcholine (PC)-specific phospholipase C (PC-PLC) is linked to activation of the p42/44 (ERK) kinases by LPS. LPS-induced ERK kinase activation was inhibited by tricyclodecan-9-yl xanthogenate (D609), a relatively specific inhibitor of PC-PLC. LPS also increased amounts of diacylglycerol (DAG), and this increase in DAG was inhibited by D609. LPS induction of DAG was, at least in part, derived from PC hydrolysis. Ceramide was also increased in LPS-treated alveolar macrophages, and this increase in ceramide was inhibited by D609. Addition of exogenous C2 ceramide or bacterial-derived sphingomyelinase to alveolar macrophages increased ERK kinase activity. LPS also activated PKC zeta, and this activation was inhibited by D609. LPS-activated PKC zeta phosphorylated MAP kinase kinase, the kinase directly upstream of the ERK kinases. LPS-induced cytokine production (RNA and protein) was also inhibited by D609. As an aggregate, these studies support the hypothesis that one way by which LPS activates the ERK kinases is via activation of PC-PLC and that activation of a PC-PLC is an important component of macrophage activation by LPS.