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Published on: January 4, 2019
Requirement of CRAMP for mouse macrophages to eliminate phagocytosed E. coli through an autophagy pathway
Keqiang Chen1, Teizo Yoshimura2, Wanghua Gong3
1Laboratory of Cancer ImmunoMetabolism, Center for Cancer Research, National Cancer Institute at Frederick, Frederick, MD 21702, USA.
Abstract:
Host-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.
Insights
Cathelin-related antimicrobial peptide (CRAMP) is crucial for macrophages to clear intracellular bacteria like E. coli. CRAMP activation is essential for autophagy-mediated bacterial elimination and macrophage survival.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Host-derived antimicrobial peptides are vital for combating extracellular bacterial infections.
- The role of macrophage-derived antimicrobial peptides against intracellular pathogens is largely unknown.
Purpose of the Study:
- To investigate the role of cathelin-related antimicrobial peptide (CRAMP) in macrophage defense against intracellular bacteria.
- To elucidate the mechanism of CRAMP activation and its involvement in bacterial clearance.
Main Methods:
- Macrophage infection with viable and inactivated E. coli.
- Stimulation with lipopolysaccharide (LPS).
- Analysis of CRAMP expression, NF-κB activation, and protease activity.
- Assessment of autophagy-related proteins (ATG5, LC3-II, LAMP-1) and p62 aggregation.
- Comparison between wild-type (WT) and CRAMP knockout (CRAMP-/-) macrophages.
Main Results:
- WT macrophages upregulated CRAMP expression upon E. coli infection or LPS stimulation via NF-κB activation.
- Protease-dependent conversion of inactive CRAMP to its active form was observed.
- Active CRAMP, along with autophagy proteins, mediated the clearance of intracellular E. coli.
- CRAMP deficiency in CRAMP-/- macrophages led to impaired bacterial clearance, bacterial retention, and macrophage fragmentation.
Conclusions:
- CRAMP is a critical effector molecule for mouse macrophages in eliminating intracellular E. coli.
- CRAMP functions within an autophagy-dependent pathway involving ATG5, LC3-II, LAMP-1, and p62.
- This study highlights CRAMP's significance in host defense against intracellular bacterial infections.
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