The study found that the human antimicrobial peptide LL-37 makes lung inflammation worse in sepsis by stopping the breakdown of damaged mitochondrial DNA, which blocks a protective cell-cleaning process called autophagy.

BACKGROUND Recent studies have proved that autophagy dysfunction in proinflammatory cells is involved in tissue damage and an excessive inflammatory response in sepsis. In the present study, we identified that the human antimicrobial peptide LL-37 facilitates resistance to DNase II-induced mitochondrial DNA (mtDNA) degradation and subsequent autophagy. MATERIAL AND METHODS We found higher serum levels of LL-37 in patients with severe sepsis compared to that in patients with mild sepsis. Neutrophils isolated from mice with sepsis after treatment with Cramp-mtDNA produced an excess of proinflammatory cytokines, including IL-1ß, IL-6, IL-8, MMP-8, and TNF-alpha. Cramp-mtDNA in the lung samples from model animals with sepsis was detected by immunohistochemical staining. RESULTS Exogenous delivery of Cramp-mtDNA complex significantly exacerbated lung inflammation but the antibody against Cramp-mtDNA attenuated the excessive inflammatory response in LPS-induced acute lung injury. The expression of proinflammatory cytokines in lungs was upregulated and downregulated after treatment with the complex and antibody, respectively. LC-3 expression in 16HBE cells increased after LPS induction, irrespective of stimulation with LL-37. CONCLUSIONS These data show that LL-37 treatment worsens local inflammation in sepsis-induced acute lung injury by preventing mtDNA degradation-induced autophagy.