Autophagy-associated Production of Antimicrobial Peptides hBD1 and LL37 Exhibits Anti-Bacillus Calmette-Guerin Effects in Lung Epithelial Cells.

Antimicrobial peptides (AMPs) constitute important groups of bactericidal polypeptides against various microorganisms that exhibit their anti-bacteria activity through cleavage of precursor peptides into the active form of 50-100 amino acids in length. Various AMP cleavage mechanisms have been reported in different cell types; however, those in Mycobacterium tuberculosis (MTB)-infected lung epithelial cells remain unknown. In the present study, we found that MTB-infected lung epithelial cells expressed high level of the AMPs hBD1 and LL37 to kill intracellular MTB as the first-line immune barrier against MTB infection. Notably, their production in the lung epithelial cells was closely related to the function of autophagosomes and lysosomes. Experimental induction of autophagy in lung epithelial cells could enhance the expression of active hBD1 and LL37 at the post-transcriptional level, whereas silencing of these two active AMPs could decrease the bactericidal effect of autophagy. These findings indicated that cleavage of peptide precursors to form active AMPs might constitute a previously unrecognized antibacterial mechanism of autophagy. Author summaryLM and RW conceived and designed the experiments; RW performed the experiments and analyzed the data; QW analyzed the data and contributed reagents/materials/analysis tools; HL performed the experiments; XZ, JY, YL and ZH analyzed the data. LM and RW drafted the manuscript.