Endoplasmic Reticulum Stress Pathway-Mediated Apoptosis in Macrophages Contributes to the Survival of Mycobacterium tuberculosis Yun-Ji Lim1, Ji-Ae Choi1, Hong-Hee Choi1,2, Soo-Na Cho 1 , Hwa-Jung Kim1,3, Eun-Kyeong Jo1,2,3, Jeong- Kyu Park1,3, Chang-Hwa Song1,3* 1 Department of Microbiology, College of Medicine, Chungnam National University, Daejeon, South Korea, 2 Infection Signaling Network Research Center, College of Medicine, Chungnam National University, Daejeon, South Korea, 3 Research Institute for Medical Sciences, College of Medicine, Chungnam National University, Daejeon, South Korea Abstract Background: Apoptosis is thought to play a role in host defenses against intracellular pathogens, including Mycobacterium tuberculosis (Mtb), by preventing the release of intracellular components and the spread of mycobacterial infection. This study aims to investigate the role of endoplasmic reticulum (ER) stress mediated apoptosis in mycobacteria infected macrophages. Methodology/Principal Findings: Here, we demonstrate that ER stress-induced apoptosis is associated with Mtb H37Rv- induced cell death of Raw264.7 murine macrophages. We have shown that Mtb H37Rv induced apoptosis are involved in activation of caspase-12, which resides on the cytoplasmic district of the ER. Mtb infection increase levels of other ER stress indicators in a time-dependent manner. Phosphorylation of eIF2a was decreased gradually after Mtb H37Rv infection signifying that Mtb H37Rv infection may affect eIF2a phosphorylation in an attempt to survive within macrophages. Interestingly, the survival of mycobacteria in macrophages was enhanced by silencing CHOP expression. In contrast, survival rate of mycobacteria was reduced by phosphorylation of the eIF2a. Futhermore, the levels of ROS, NO or CHOP expression were significantly increased by live Mtb H37Rv compared to heat-killed Mtb H37Rv indicating that live Mtb H37Rv could induce ER stress response. Conclusion/Significance: These findings indicate that eIF2a/CHOP pathway may influence intracellular survival of Mtb H37Rv in macrophages and only live Mtb H37Rv can induce ER stress response. The data support the ER stress pathway plays an important role in the pathogenesis and persistence of mycobacteria. Citation: Lim Y-J, Choi J-A, Choi H-H, Cho S-N, Kim H-J, et al. (2011) Endoplasmic Reticulum Stress Pathway-Mediated Apoptosis in Macrophages Contributes to the Survival of Mycobacterium tuberculosis. PLoS ONE 6(12): e28531. doi:10.1371/journal.pone.0028531 Editor: Beverley J. Shea, Central Institute of Educational Technology, Canada Received July 4, 2011; Accepted November 9, 2011; Published December 14, 2011 Copyright: 2011 Lim et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025985). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: songch@cnu.ac.kr Introduction Tuberculosis (TB) is a major problem despite current thera- peutic regimens. The spread of tuberculosis is exacerbated by the development of multidrug-resistant strains of Mycobacteria tubercu- losis (Mtb) infection [1]. Killing intracellular mycobacteria in MDR-TB patients and developing highly resistant therapeutic methods for treating TB patients are required to address this challenge. Mtb is one of the most successful human pathogens due to its ability to manipulate host cells via multiple pathways to achieve its survival. Macrophages in the lungs are the first cells that defend against pathogen invasion and play an important role in the initiation and maintenance of immune responses against Mtb. Mycobacterial infection leads to the activation of multiple microbicidal mechanisms, such as phagolysosome fusion and respiratory burst, and the production of proinflammatory cytokines [2]. Macro- phages infected with mycobacteria may undergo apoptosis to remove intracellular bacilli. Programmed cell death plays an important role in host responses against mycobacterial infection [3,4]. The inhibition of host cell apoptosis by Mtb has been considered a potential virulence factor [5,6]. However, the underlying mechanisms by which Mtb induces necrosis or inhibits apoptosis in macrophages are still largely unknown. Recently we reported that mycobacterial antigen ESAT-6 induced ER stress-mediated apoptosis [7]. Within the ER, the unfolded protein response (UPR) control many secretory and cellular proteins and plays an important role in folding these molecules during their transit through the organelle [8]. There are a number of insults lead to protein misfolding in the ER such as nutrient deprivation, alterations in the oxidation-reduction balance, changes in calcium concentration, failure of post-translational PLoS ONE | www.plosone.org 1 December 2011 | Volume 6 | Issue 12 | e28531