Synergy between 15-lipoxygenase and secreted PLA 2 promotes inflammation by formation of TLR4 agonists from extracellular vesicles

Proc Natl Acad Sci U S A. 2020 Oct 13;117(41):25679-25689. doi: 10.1073/pnas.2005111117. Epub 2020 Sep 24.


Damage-associated endogenous molecules induce innate immune response, thus making sterile inflammation medically relevant. Stress-derived extracellular vesicles (stressEVs) released during oxidative stress conditions were previously found to activate Toll-like receptor 4 (TLR4), resulting in expression of a different pattern of immune response proteins in comparison to lipopolysaccharide (LPS), underlying the differences between pathogen-induced and sterile inflammation. Here we report that synergistic activities of 15-lipoxygenase (15-LO) and secreted phospholipase A2 (sPLA2) are needed for the formation of TLR4 agonists, which were identified as lysophospholipids (lysoPLs) with oxidized unsaturated acyl chain. Hydroxy, hydroperoxy, and keto products of 2-arachidonoyl-lysoPI oxidation by 15-LO were identified by mass spectrometry (MS), and they activated the same gene pattern as stressEVs. Extracellular PLA2 activity was detected in the synovial fluid from rheumatoid arthritis and gout patients. Furthermore, injection of sPLA2 promoted K/BxN serum-induced arthritis in mice, whereby ankle swelling was partially TLR4 dependent. Results confirm the role of oxidized lysoPL of stressEVs in sterile inflammation that promotes chronic diseases. Both 15-LO and sPLA2 enzymes are induced during inflammation, which opens the opportunity for therapy without compromising innate immunity against pathogens.

Keywords: 15-lipoxygenase; Toll-like receptor 4; extracellular vesicles; oxidative stress; phospholipase A2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arachidonate 15-Lipoxygenase / metabolism*
  • Arthritis, Rheumatoid / metabolism
  • Extracellular Vesicles / metabolism*
  • Female
  • Gout / metabolism
  • HEK293 Cells
  • Humans
  • Inflammation / metabolism*
  • Lysophospholipids / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Oxidation-Reduction
  • Oxidative Stress
  • Phospholipases A2 / metabolism*
  • Synovial Fluid / chemistry
  • Toll-Like Receptor 4 / agonists*


  • Lysophospholipids
  • Toll-Like Receptor 4
  • Arachidonate 15-Lipoxygenase
  • Phospholipases A2

Associated data

  • figshare/10.6084/m9.figshare.10008044