Autophagy Is a Defense Mechanism Inhibiting Invasion and Inflammation During High-Virulent Haemophilus parasuis Infection in PK-15 Cells.

Chaoxiong Yue,Yan Zeng,Dan Liu,Guirong Cheng,Kexin Hua,Jinquan Li,Lang Xu,Yueyi Wang,Wei Zhou,Hui Jin,Yushan Chen

doi:10.3389/fcimb.2019.00093

Abstract

Bacterial infections activate autophagy and autophagy restricts pathogens such as Haemophilus parasuis through specific mechanisms. Autophagy is associated with the pathogenesis of H. parasuis. However, the mechanisms have not been clarified. Here, we monitored autophagy processes using confocal microscopy, western blot, and transmission electron microscopy (TEM) and found that H. parasuis SH0165 (high-virulent strain) but not HN0001 (non-virulent strain) infection enhanced autophagy flux. The AMPK/mTOR autophagy pathway was required for autophagy initiation and ATG5, Beclin-1, ATG7, and ATG16L1 emerged as important components in the generation of the autophagosome during H. parasuis infection. Moreover, autophagy induced by H. parasuis SH0165 turned to fight against invaded bacteria and inhibit inflammation. Then we further demonstrated that autophagy blocked the production of the cytokines IL-8, CCL4, and CCL5 induced by SH0165 infection through the inhibition of NF-κB, p38, and JNK MAPK signaling pathway. Therefore, our findings suggest that autophagy may act as a cellular defense mechanism in response to H. parasuis and provide a new way that autophagy protects the host against H. parasuis infection.

Highlights

Autophagy is a double edge sword in microbial infection (Shintani and Klionsky, 2004)
To investigate whether SH0165 and HN0001 infection induce autophagy, PK-15 cells were infected with adenovirus GFPRFP-LC3, followed by infection with SH0165 and HN0001 in a time- and dose-dependent manner
Our results showed that SH0165 infection with 106, 107, and 108 CFU/mL led to a significant increase in LC3-I to LC3-II conversion, while HN0001 failed to induce LC3-II formation (Figures 1C,D). 107 and 108 CFU/mL SH0165 induced smaller amounts of LC3-II, which may be due to the increased cell death with higher infection doses

Summary

Introduction

Autophagy is a double edge sword in microbial infection (Shintani and Klionsky, 2004). Some viruses are eliminated by autophagy, while others use autophagy to benefit their replication, spread, and survival (Richards and Jackson, 2012; Ding et al, 2014). Autophagy targets bacteria while bacteria inhibit autophagy or promote survival (Fabri et al, 2011; Huang and Brumell, 2014). Autophagy can target intracellular bacteria Group A Streptococcus (GAS), Mycobacterium tuberculosis, and Salmonella enterica subsp. Some targeted bacteria are eliminated by autophagy, others have developed diverse strategies to escape the defense system period. Francisella tularensis, Yersinia enterocolitica, and Orientia tsutsugamushi (Deuretzbacher et al, 2009; Chong et al, 2012; Choi et al, 2013). Some bacteria exploit autophagy for their growth, for example, Autophagy Controls High-Virulent HPS

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Conclusion