Requirement of CRAMP for mouse macrophages to eliminate phagocytosed E. coli through an autophagy pathway.

Keqiang Chen,Jiaqiang Huang,Cuimeng Tian,Wanghua Gong,Giorgio Trinchieri,Ji Ming Wang,Teizo Yoshimura

doi:10.1242/jcs.252148

Abstract

ABSTRACTHost-derived antimicrobial peptides play an important role in the defense against extracellular bacterial infections. However, the capacity of antimicrobial peptides derived from macrophages as potential antibacterial effectors against intracellular pathogens remains unknown. In this study, we report that normal (wild-type, WT) mouse macrophages increased their expression of cathelin-related antimicrobial peptide (CRAMP, encoded by Camp) after infection by viable E. coli or stimulation with inactivated E. coli and its product lipopolysaccharide (LPS), a process involving activation of NF-κB followed by protease-dependent conversion of CRAMP from an inactive precursor to an active form. The active CRAMP was required by WT macrophages for elimination of phagocytosed E. coli, with participation of autophagy-related proteins ATG5, LC3-II and LAMP-1, as well as for aggregation of the bacteria with p62 (also known as SQSTM1). This process was impaired in CRAMP−/− macrophages, resulting in retention of intracellular bacteria and fragmentation of macrophages. These results indicate that CRAMP is a critical component in autophagy-mediated clearance of intracellular E. coli by mouse macrophages.

Highlights

Macrophages comprise an essential part of the innate immune system in response to bacterial infections (Rosenberger and Finlay, 2003)
We report that normal mouse macrophages increased their expression of the cathelicidin-related antimicrobial peptide (CRAMP) after infection by viable E. coli or stimulation with inactivated E. coli and its product LPS, a process involving activation of NF-κB followed by protease-dependent conversion of CRAMP from an inactive precursor to an active form
The active CRAMP was required by WT macrophages to eliminate phagocytosed E. coli, with participation of autophagy-related proteins ATG5, LC3-II, and LAMP-1 as well as conjugation of the bacteria with p62

Summary

Introduction

Macrophages comprise an essential part of the innate immune system in response to bacterial infections (Rosenberger and Finlay, 2003). Because macrophages are highly phagocytic and are readily confronted by pathogenic bacteria, they must be equipped with effective mechanisms either for killing bacteria or controlling their replication to avoid becoming a reservoir of infection. Many host factors including inflammation and genetic predisposition markedly alter the colonic microbial composition and support the growth of either resident or introduced aerobic bacteria, those of the Enterobacteriaceae family (Lupp et al, 2007) such as E. coli, which are elevated in inflammatory bowel diseases (IBD) (Bambou et al, 2004; Martin et al, 2004; Rhodes, 2007; Zhang et al, 2017). Previous studies showed that increased mucosal adherent E. coli plays a central role in the pathogenesis of human IBD and colon cancer (Martin et al, 2004). Despite the observations that macrophages are capable of controlling E. coli expansion by direct killing or phagocytosis, there is scarce data concerning the mechanisms by which macrophages eliminate phagocytosed E. coli

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