Lipid aldehydes including isolevuglandins (IsoLG) and 4-hydroxynonenal (4-HNE) modify phosphatidylethanolamine (PE) to form proinflammatory and cytotoxic adducts. Therefore, cells may have evolved mechanisms to degrade and prevent accumulation of these potentially harmful compounds. To test if cells could degrade IsoLG-PE, we generated IsoLG-PE in HEK293 and HUVEC cells and measured its stability over time. We found that IsoLG-PE levels decreased more than 75% after 6h, suggesting that IsoLG-PE was indeed degraded. Because NAPE-hydrolyzing phospholipase D (NAPE-PLD) has been described as a key enzyme in the hydrolysis of NAPE (N-acyl phosphatidylethanoamine) and both NAPE and IsoLG-PE have large aliphatic headgroups, we considered the possibility that this enzyme might also hydrolyze IsoLG-PE. We found that knockdown of NAPE-PLD expression using siRNA significantly increased the persistence of IsoLG-PE in HEK293 cells. IsoLG-PE competed with NAPE for hydrolysis by recombinant mouse NAPE-PLD, with the catalytic efficiency (Vmax/Km) for hydrolysis of IsoLG-PE being 30% that for hydrolysis of NAPE. LC-MS/MS analysis confirmed that recombinant NAPE-PLD hydrolyzed IsoLG-PE to IsoLG-ethanolamine (IsoLG-Etn). These results demonstrate that NAPE-PLD contributes to the degradation of IsoLG-PE and suggest that a major physiological role of NAPE-PLD may be to degrade aldehyde-modified PE, thereby preventing the accumulation of these harmful compounds.

PMID:

 

24018423

 

[PubMed – as supplied by publisher]