CATHELICIDIN MODULATES SYNTHESIS OF TOLL-LIKE RECEPTORS (TLRs) 4 AND 9 IN THE COLONIC EPITHELIUM

MARIN M; HOLANI R; SHAH C; ODEÓN A; COBO E

Mar del Plata

Encuentro; XI Encuentro Biólogos en Red (BER) 2016; 2016

AJIF FCEyN, UNMDP

Cathelicidins are innate antimicrobial peptides with broad immunomodulatory functions however their role in regulating intestinal defenses remains elusive. This work investigates the role of cathelicidins modulating Toll-like receptors (TLRs) 4 and 9 expression in the colonic epithelium in response to bacterial patterns. Human colonic adenocarcinoma epithelial cells (HT29) were stimulated with an inducer of endogenous cathelicidins (sodium butyrate) or synthetic human cathelicidin (LL37) in association with agonists/antagonists of TLR4 and 9 or MAPK inhibitors. Gene expression of human TLR4 and TLR9 were quantified by real time RT-qPCR and protein synthesis by western blotting and corroborated by confocal immunofluorescence microscopy. Antimicrobial activity in HT29 cell lysates challenged with Escherichia coli and stimulated with LPS and LL37 was analyzed by bacterial counting. For statistical analysis between treatment groups the paired two tailed Student?s t test was used. We demonstrated that intestinal epithelial cells when primed by bacterial LPS responded to cathelicidins through a higher transcription and protein synthesis of TLR4. This cathelicidin-induced response required the interaction of TLR4 ligand-TLR4 and activation of MAPK signaling pathways. Cathelicidins blocked the TLR9 responses induced by TLR9 ligands in same colonic epithelial cells. These TLR modulations triggered by cathelicidins in intestinal epithelium occurred mainly at the apical compartment. Activation of TLR4 ligands in combination with cathelicidins promoted epithelial antimicrobial defenses against Escherichia coli. We conclude that cathelicidins selectively activate TLR synthesis in intestinal epithelium to respond only when cells are exposed to virulence factors, mostly from apical surfaces. Overexpression of intestinal epithelial TLR4, minimally expressed and hypo-responsive to LPS under physiologic conditions, is necessary during intestinal inflammation for epithelial restoration and integrity. It could be accompanied by suppression of agonist mediated TLR9 stimulation. Thus, cathelicidin is key in intestinal homeostasis to modulate the priming provided by TLR ligands and the synthesis of epithelial TLR4 and 9.