LL-37 and citrullinated LL-37: differential modulation of the oxylipin - chemokine axis

Inflammation plays a crucial role in the host immune system, and it involves a complex network of cellular and molecular events. In the lungs, human bronchial epithelial cells release cytokines/chemokines, and other mediators such as bioactive lipids and cationic host defence peptides (CHDPs) to facilitate and regulate airway inflammation. Oxylipins are bioactive lipids that are key mediators in the process of inflammation. The human host defence peptide LL-37 enhances specific oxylipins such as prostaglandin E2 (PGE2) in fibroblasts and endothelial cells. LL-37 plays a pivotal role in inflammation by orchestrating both pro-and anti-inflammatory responses; LL-37 enhances pro-inflammatory chemokines, but also selectively suppresses inflammatory cytokines and help maintain immune homeostasis. However, the mechanisms that govern these opposing roles of LL-37 remain unclear. Under inflammatory conditions, LL-37 can get citrullinated, a post-translational modification that impairs its antimicrobial and antiviral functions. In this thesis, I investigate the interplay of LL-37 and oxylipins, and how that is altered by citrullination, in the context of airway inflammation. In this study, a lipidomics analysis was performed to profile oxylipins enhanced in the presence of LL-37 and citrullinated LL-37 (citLL-37) in in human bronchial epithelial cells (HBEC). Subsequently, these peptide-mediated chemokine productions were examined by ELISA, transcriptional analysis by qRT-PCR, and impact of peptide on neutrophil migration was examined in a transwell assay using neutrophils isolated from human blood. LL-37 significantly enhanced oxylipins such as PGE2, 11- and 15-HETE, 15-HETrE, and cytochrome P450-derived 9,10- and 12,13-EpOME. Whereas citLL-37 only enhanced 15-HETrE, 9,10 EpOME and 12,13-EpOME, oxylipins that negatively regulates inflammation. I showed that LL-37, but not citLL-37, enhances COX-2, a central upstream mediator of PGE2 in HBEC. Inhibition of COX-2 suppressed LL-37-induced neutrophil chemoattractants IL-8, MIP-3 and GRO, thus establishing the link between peptide mediated oxylipin and chemokine production. I functionally confirmed that inhibition of COX-2 impairs LL-37-mediated neutrophil migration. Overall, my findings suggest that citrullination of LL-37 mitigates the peptide’s ability to induce pro-inflammatory oxylipins and chemokines, thus this post-translational modification may be a molecular switch to control LL-37-mediated pro- and anti-inflammatory responses in the lungs.

Author dc:creator

• Ramotar, Padmanie

Advisor dc:contributor.supervisor

• Mookherjee, Neeloffer

• Inflammation
• LL-37
• Citrullination
• Oxylipin

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1993/38455

OAI identifier oai:identifier

oai:mspace.lib.umanitoba.ca:1993/38455