Atg5-Deficient Mice Infected with Francisella tularensis LVS Demonstrate Increased Survival and Less Severe Pathology in Internal Organs

Ina Kelava,Valentina Marečić,Mateja Ožanič,Sanja Štifter,Mirna Mihelčić,Anders Sjöstedt,Marina Šantić,Marija Ćurlin,Maša Knežević

doi:10.3390/microorganisms8101531

Ina Kelava, Valentina Marečić + Show 7 more

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https://doi.org/10.3390/microorganisms8101531

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Abstract

Francisella tularensis is a highly virulent intracellular pathogen that proliferates within various cell types and can infect a multitude of animal species. Francisella escapes the phagosome rapidly after infection and reaches the host cell cytosol where bacteria undergo extensive replication. Once cytosolic, Francisella becomes a target of an autophagy-mediated process. The mechanisms by which autophagy plays a role in replication of this cytosolic pathogen have not been fully elucidated. In vitro, F. tularensis avoids degradation via autophagy and the autophagy process provides nutrients that support its intracellular replication, but the role of autophagy in vivo is unknown. Here, we investigated the role of autophagy in the pathogenesis of tularemia by using transgenic mice deficient in Atg5 in the myeloid lineage. The infection of Atg5-deficient mice with Francisella tularensis subsp. holarctica live vaccine strain (LVS) resulted in increased survival, significantly reduced bacterial burden in the mouse organs, and less severe histopathological changes in the spleen, liver and lung tissues. The data highlight the contribution of Atg5 in the pathogenesis of tularemia in vivo.

Highlights

Intracellular bacterial pathogens use various strategies to survive and replicate within the host cells [1,2]
In the control group of mice infected with 5 × 104 of the live vaccine strain (LVS) 50% of mice survived, and the mean time to death (MTTD) was 5 days (p = 0.0006) (Figure 1a, Table 1)
The survival of Atg5-deficient mice infected with a dose of 5 × 105 CFU/mouse was 70% (MTTD = 7.5 days), while in (Figure 1d, Table 1)

Summary

Introduction

Intracellular bacterial pathogens use various strategies to survive and replicate within the host cells [1,2]. When intracellular pathogens reach the cytosol, they become the targets of innate immune recognition via the autophagy pathway [3]. The protein Atg is essential for the formation of a double-membrane vacuole, the autophagosome in the canonical autophagy pathway [10]. A lot of cytosolic pathogens are targets for canonical autophagy after binding to polyubiquitin and p62/SQSTM1 [6,11,12]. For pathogens such as Streptococcus pyogens, Shigella flexneri, Salmonella, and Listeria, the autophagy mechanism is dependent on Atg5 [7,13,14,15]. Atg is not required for autophagy in the lifecycles of Mycobacterium marinum and Brucella abortus [17,18]

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