Peptidylarginine Deiminases Present in the Airways During Tobacco Smoking and Inflammation can Citrullinate the Host Defense Peptide LL-37 Resulting in Altered Activities.

Bacterial colonization of the lower respiratory tract is frequently seen in COPD and may cause exacerbations leading to deterioration of the disease. An important part of the innate lung immunity is antimicrobial peptides, not least the cathelicidin hCAP-18/LL-37. Peptidylarginine deiminases (PADI) posttranslationally modifies proteins by converting cationic peptidylarginine residues to neutral peptidylcitrulline. Increased presence of PADI2 and citrullinated proteins has been demonstrated in the lungs of smokers. In this study, preformed PADI4, stored in granulocytes and extracellular in the lumen of bronchi, was found in lung tissue of individuals suffering from COPD. In vitro, recombinant human PADI2 and PADI4 both caused a time- and dose-dependent citrullination of LL-37. The citrullination resulted in impaired antibacterial activity against Staphylococcus aureus, Streptococcus pneumoniae, and non-typeable Haemophilus influenzae but less so against Pseudomonas aeruginosa. Using artificial lipid bilayers, discrete differences were observed comparing the disrupting activity of native and citrullinated LL-37, suggesting that differences in cell wall composition are important during interaction with whole bacteria. Furthermore, citrullinated LL-37 showed a higher chemotactic activity against mononuclear leukocytes than native LL-37, but was less efficient in neutralizing lipolysaccharide and also in converting apoptotic neutrophils into a state of secondary necrosis. In addition, citrullinated LL-37 was more prone to degradation by proteases, where the V8 endopetidase of Staphylococcus aureus cleaved the modified peptide at additional sites, compared with native LL-37. Together, these findings demonstrate novel mechanisms whereby the inflammation-dependent deiminases PADI2 and PADI4 can alter the activites of antibacterial polypeptides, affecting the course of inflammatory disorders such as COPD.