Abstract
Peptide antibiotics possess potent antimicrobial activities against invading microorganisms and contribute to the innate host defense. We previously revealed that antibacterial cathelicidin CAP11 (cationic antibacterial polypeptide of 11 kDa) exhibits protective actions against endotoxin shock model. During Gram-negative bacterial sepsis, lipopolysaccharide (LPS) activates neutrophils and their apoptosis is suppressed. Prolonged presence of activated neutrophils causes uncontrolled release of toxic metabolites, leading to the systemic tissue injury. In this study, we investigate the action of CAP11 on LPS-induced suppression of neutrophil apoptosis using human neutrophils.
LPS suppressed neutrophil apoptosis, accompanied with the activation of NF-κB, phosphorylation of extracellular signal-related protein kinase, expression of Bcl-XL and inhibition of caspase 3 activation. Interestingly, CAP11 reversed the actions of LPS to trigger these changes, and induced neutrophil apoptosis. Furthermore, LPS activated monocytes to produce anti-apoptotic cytokines (IL-1β, TNF-α and IL-8) and suppressed neutrophil apoptosis. Importantly, CAP11 inhibited the cytokine production from LPS-stimulated monocytes, and induced neutrophil apoptosis. Finally, CAP11 strongly suppressed the LPS-binding to neutrophils and monocytes. These observations indicate that CAP11 can block the LPS-induced prolongation of neutrophil survival via the suppression of anti-apoptotic signaling in neutrophils and anti-apoptotic cytokine production from monocytes by inhibiting the binding of LPS to target cells.
