Citrullination alters immunomodulatory function of LL-37 essential for prevention of endotoxin-induced sepsis

J Immunol. 2014 Jun 1;192(11):5363-72. doi: 10.4049/jimmunol.1303062. Epub 2014 Apr 25.

Abstract

Cathelicidin LL-37 plays an essential role in innate immunity by killing invading microorganisms and regulating the inflammatory response. These activities depend on the cationic character of the peptide, which is conferred by arginine and lysine residues. At inflammatory foci in vivo, LL-37 is exposed to peptidyl arginine deiminase (PAD), an enzyme released by inflammatory cells. Therefore, we hypothesized that PAD-mediated citrullination of the arginine residues within LL-37 will abrogate its immunomodulatory functions. We found that, when citrullinated, LL-37 was at least 40 times less efficient at neutralizing the proinflammatory activity of LPS due to a marked decrease in its affinity for endotoxin. Also, the ability of citrullinated LL-37 to quench macrophage responses to lipoteichoic acid and poly(I:C) signaling via TLR2 and TLR3, respectively, was significantly reduced. Furthermore, in stark contrast to native LL-37, the modified peptide completely lost the ability to prevent morbidity and mortality in a mouse model of d-galactosamine-sensitized endotoxin shock. In fact, administration of citrullinated LL-37 plus endotoxin actually exacerbated sepsis due to the inability of LL-37 to neutralize LPS and the subsequent enhancement of systemic inflammation due to increased serum levels of IL-6. Importantly, serum from septic mice showed increased PAD activity, which strongly correlated with the level of citrullination, indicating that PAD-driven protein modification occurs in vivo. Because LL-37 is a potential treatment for sepsis, its administration should be preceded by a careful analysis to ensure that the citrullinated peptide is not generated in treated patients.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antimicrobial Cationic Peptides / genetics
  • Antimicrobial Cationic Peptides / immunology*
  • Antimicrobial Cationic Peptides / pharmacology
  • Cell Line
  • Citrulline / genetics
  • Citrulline / immunology*
  • Female
  • Humans
  • Hydrolases / genetics
  • Hydrolases / immunology
  • Immunity, Innate*
  • Interferon Inducers / pharmacology
  • Interleukin-6 / genetics
  • Interleukin-6 / immunology
  • Lipopolysaccharides / immunology
  • Macrophages / immunology*
  • Macrophages / pathology
  • Male
  • Mice
  • Poly I-C / pharmacology
  • Sepsis / genetics
  • Sepsis / immunology*
  • Sepsis / pathology
  • Sepsis / prevention & control*
  • Teichoic Acids / immunology
  • Toll-Like Receptor 2 / genetics
  • Toll-Like Receptor 2 / immunology
  • Toll-Like Receptor 4 / genetics
  • Toll-Like Receptor 4 / immunology

Substances

  • Antimicrobial Cationic Peptides
  • IL6 protein, human
  • Interferon Inducers
  • Interleukin-6
  • Lipopolysaccharides
  • TLR2 protein, human
  • TLR4 protein, human
  • Teichoic Acids
  • Tlr2 protein, mouse
  • Tlr4 protein, mouse
  • Toll-Like Receptor 2
  • Toll-Like Receptor 4
  • lipopolysaccharide, E. coli O26-B6
  • Citrulline
  • ropocamptide
  • lipoteichoic acid
  • Hydrolases
  • Poly I-C