Autophagy protects type II alveolar epithelial cells from Mycobacterium tuberculosis infection.

Abstract

This study was designed to investigate the protective effect of the autophagy signaling pathway against Mycobacterium tuberculosis infection in type II alveolar epithelial cells. An in vitro M. tuberculosis system was established using human A549 cells. Infection-induced changes in the expression of the autophagic marker LC3 were assessed by reverse transcription-PCR and Western blotting. Morphological changes in autophagosomes were detected by transmission electron microscopy (TEM). The function of the autophagy signaling pathway during infection was assessed by measuring the level of cell death and the amount of lactate dehydrogenase (LDH) released in the presence or absence of the inhibitor 3-methyladenine (3-MA). In addition, effects on LDH release were assessed after the siRNA-mediated knockdown of the essential autophagosomal structural membrane protein Atg5. LC3 mRNA expression was significantly reduced in M.tuberculosis-infected A549 cells (16888.76 ± 1576.34 vs. uninfected: 12744.29 ± 1089.37; P < 0.05). TEM revealed M.tuberculosis bacilli-containing compartments that were surrounded by double membranes characteristic of the autophagic process. M.tuberculosis-infected A549 cells released more LDH (1.45 ± 0.12 vs. uninfected: 0.45 ± 0.04; P < 0.05). The inhibition of autophagy signaling significantly enhanced M.tuberculosis-induced necrosis (3-MA: 75 ± 5% vs. untreated: 15 ± 1%; P < 0.05) and LDH release (3-MA: 2.50 ± 0.24 vs. untreated: 0.45 ± 0.04; Atg5 knockdown: 3.19 ± 0.29 vs. untreated: 1.28 ± 0.11; P < 0.05). Our results indicate that autophagy signaling pathway prevents apoptosis in type II alveolar epithelial cells infected with M.tuberculosis and may represent a molecular target for promoting cell survival during infection by respiratory pathogens.

• Authors: Xu-Guang Guo, Tian-Xing Ji, Yong Xia, Yue-Yun Ma
• Journal: Biochemical and biophysical research communications (Biochem Biophys Res Commun) Vol. 432 Issue 2 Pg. 308-13 (Mar 08 2013) ISSN: 1090-2104 [Electronic] United States
• PMID: 23396060 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2013 Elsevier Inc. All rights reserved.

Chemical References

• ATG5 protein, human
• Autophagy-Related Protein 5
• MAP1LC3A protein, human
• Microtubule-Associated Proteins
• RNA, Small Interfering
• L-Lactate Dehydrogenase

Topics

• Alveolar Epithelial Cells (immunology, microbiology, pathology)
• Autophagy (genetics, immunology)
• Autophagy-Related Protein 5
• Cell Line
• Gene Knockdown Techniques
• Humans
• L-Lactate Dehydrogenase (metabolism)
• Microtubule-Associated Proteins (biosynthesis, genetics, metabolism)
• Mycobacterium tuberculosis
• RNA, Small Interfering (genetics)
• Tuberculosis, Pulmonary (immunology, pathology)