Chicken cathelicidin-2 promotes NLRP3 inflammasome activation in macrophages

Abstract

Chicken cathelicidin-2 (CATH-2) as a host defense peptide has been identified to have potent antimicrobial and immunomodulatory activities. Here, we reported the mechanism by which CATH-2 modulates NLRP3 inflammasome activation. Our results show that CATH-2 and ATP as a positive control induced secretion of IL-1β and IL-1α in LPS-primed macrophages but did not affect secretion of IL-6, IL-12 and TNF-α. Furthermore, CATH-2 induced caspase-1 activation and oligomerization of apoptosis-associated speck-like protein containing a carboxy- terminal caspase recruitment domain (ASC), which is essential for NLRP3 inflammasome activation. However, CATH-2 failed to induce IL-1β secretion in Nlrp3−/−, Asc−/− and Casp1−/− macrophages. Notably, IL-1β and NLRP3 mRNA expression were not affected by CATH-2. In addition, CATH-2-induced NLRP3 inflammasome activation was mediated by K+ efflux but independent of the P2X7 receptor that is required for ATP-mediated K+ efflux. Gene interference of NEK7 kinase which has been identified to directly interact with NLRP3, significantly reduced IL-1β secretion and caspase-1 activation induced by CATH-2. Furthermore, confocal microscopy shows that CATH-2 significantly induced lysosomal leakage with the diffusion of dextran fluorescent signal. Cathepsin B inhibitors completely abrogated IL-1β secretion and caspase-1 activation as well as attenuating the formation of ASC specks induced by CATH-2. These results all indicate that CATH-2-induced activation of NLRP3 inflammasome is mediated by K+ efflux, and involves the NEK7 protein and cathepsin B. In conclusion, our study shows that CATH-2 acts as a second signal to activate NLRP3 inflammasome. Our study provides new insight into CATH-2 modulating immune response.

The protective role of chicken cathelicidin-1 against Streptococcus suis serotype 2 in vitro and in vivo

“…However, overuse of antibiotics and the slow development of new antimicrobials are the major factors for the emergence of multidrug-resistant strains, and therefore alternative strategies are urgently needed. Cathelicidins belonging to antimicrobial peptides have attracted widespread attention for their strong broad spectrum of antimicrobial activity and their immunomodulatory activity [ 23 ]. Therefore, cathelicidins from different animals have been investigated in this study to find one of which has good protection from SS2 infection.…”

“…Similarly, activation of downstream signaling pathways of TLR such as NF-κB and ERK was also inhibited by CATH-1. Notably, CATH-1 dose-dependently upregulated the secretion of IL-1β when CATH-1 was incubated with cells at post-infection, which is similar to CATH-2 which promotes NLRP3 inflammasome activation, leading to IL-1β secretion [ 23 , 37 ], suggesting the possibility that CATH-1 serves as a second signal activating inflammasome. These results demonstrate that CATH-1 regulates pro-inflammatory cytokine expression by direct bactericidal effect and modulating TLR2/4-mediated activation of NF-κB and ERK1/2 pathways.…”