Peptidylarginine Deiminases Present in the Airways during Tobacco Smoking and Inflammation Can Citrullinate the Host Defense Peptide LL-37, Resulting in Altered Activities

Abstract

Bacterial colonization of the lower respiratory tract is frequently seen in chronic obstructive pulmonary disease (COPD), and may cause exacerbations leading to disease progression. Antimicrobial peptides comprise an important part of innate lung immunity, and not least the cathelicidin human cationic antimicrobial protein-18/LL-37. Peptidylarginine deiminases (PADIs) post-translationally modify proteins by converting cationic peptidylarginine residues to neutral peptidylcitrulline. An increased presence of PADI2 and citrullinated proteins was demonstrated in the lungs of smokers. In this study, preformed PADI4, stored in granulocytes and extracellularly in the lumina 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 nontypable Haemophilus influenzae, but less so against Pseudomonas aeruginosa. Using artificial lipid bilayers, we observed discrete differences when comparing the disrupting activity of native and citrullinated LL-37, suggesting that differences in cell wall composition are important during interactions with whole bacteria. Furthermore, citrullinated LL-37 showed higher chemotactic activity against mononuclear leukocytes than did native LL-37, but was less efficient at 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, whereas the V8 endopetidase of S. 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.

Pancreatic β-Cells Limit Autoimmune Diabetes via an Immunoregulatory Antimicrobial Peptide Expressed under the Influence of the Gut Microbiota

“…It has been estimated that one hundred thousand activated neutrophils secrete around 10 ng ml À1 of cathelicidin in 15 min culture (Jann et al, 2009), whereas we observed in the present study that similar number of islet cells secrete around 80 pg ml À1 of cathelicidin in overnight culture. Second, we suggest that, as many proteins of the NETs (Wang et al, 2009), cathelicidins produced by activated neutrophils might be citrullinated, while cathelicidins expressed by endocrine cells were not and it has been shown that this post-translation modification suppresses the immunoregulatory properties of cathelicidins (Kilsgå rd et al, 2012;Koziel et al, 2014). Collectively, these data support that the diverse cellular source and associated post-translational modifications of cathelicidins might explain their opposite roles in inflammation.…”

Comprehensive Proteomic and Metabolomic Signatures of Nontypeable Haemophilus influenzae-Induced Acute Otitis Media Reveal Bacterial Aerobic Respiration in an Immunosuppressed Environment

“…phosphatidylcholine derivatives, taurine and peptidyl arginine deiminase (PAD)). PAD deiminates cathelicidin and impairs the antimicrobial activity against NTHI (130). We observed increases in both the chinchilla ortholog of human antimicrobial peptide-cathelicidin (15 kDa protein A-like) and PAD during AOM (Table I).…”

Smoking and Air Pollution as Pro-Inflammatory Triggers for the Development of Rheumatoid Arthritis

“…In this context smoking, and possibly other inhaled pro-inflammatory agents, have been reported to promote protein citrullination in the lungs, a process mediated by peptidylarginine deiminase (PAD) enzymes [27][28][29][30]. PADs convert positively charged protein arginine residues to neutral, potentially immunogenic citrulline.…”