Quantitative Proteomic Reveals Defense Mechanism Of Listeria Infection In Immune Cells

Listeria monocytogenes is a Gram-positive bacterium that was first discovered in rabbits and guinea pigs during 1926.Listeria was identified as a pathogen of human disease in the 1970s,and it was later found to be spread through food.Although the number of Listeria infections each year is at a medium level(about 23150 people wordwide were estimated to have been infected in 2010),the mortality rate from infections is very high(20-30%).After ingestion of highly contaminated food(approximately 10~9 bacteria),most patients suffer mild to severe gastroenteritis.In contrast,for children,the elderly,individuals with low immune function and pregnant women,even low levels of food contamination(about 10~2-10~4 bacteria)may cause bacterial sepsis,and subsequent bacterial meningitis,the infection of fetuses,miscarriage or pregnancy complications.Listeria is also a rod-shaped facultative anaerobic bacterium that can grow at low temperatures(below 0?)and has strong resistance to the environmental stress such as low p H and high salt concentration.These characteristics make Listeria monocytogenes as a major concern for the food industry.Listeria is widely distributed in various environments,such as water,soil and decaying materials.Some regulators secreted by Listeria allow Listeria to travel back and forth in the environment and the infection of a mammalian host.Because of its broad adaptability,ability to overcome various host obstacles and unique intracellular lifestyle,Listeria monocytogenes has become the model organism for studying host-pathogen interactions,host or bacterial regulation and intestinal microbial interaction groups.Listeria can be internalized by host cells through both phagocytosis and non-phagocytosis.In contrast to the way that phagocytic cells(such as macrophages and dendritic cells)actively mediate bacteria enter host cells,the pattern of non-phagocytosis entry into host cells(such as epithelial cells)is initiated by bacteria that specifically hind host receptor triggers endocytosis.No matter how Listeria enters the host cells,it must interact with the host's membrane receptor.For example,Internalin A(Inl A)and Internalin B(Inl A)of Listeria can bind the eukaryotic cell membrane receptor E-Cadherin and the hepatocyte growth factor(HGF),respectively.Once Listeria is internalized by the host cell,it would secrete Listeriolysin O(LLO)and two phospholipases(Plc A and Plc B)which are used to lyse phagosomes and escape into the cytoplasm.This is a key step in the intracellular proliferation of Listeria.Listeria can also survive and divide in the cytoplasm of host cells and induce changes in the morphology of host organelles,which is conducive to its further infection.Earlier reports showed that LLO is key molecular for pore formation leading to phagosomal repture.However,some recent studies have emphasized that LLO may have other functions before entering the cell membrane and after internalization.For instance,LLO causes dramatic changes in mitochondrial morphology and function,and benefits pathogens through mechanisms that have not been known to date.In the process,mitochondria become smaller and round.If this procedure is abolished,bacteria would not be able to divide efficiently.In addition,LLO induces an atypical mitochondrial division process which is independent of Dynamin-related protein 1(DRP1).Finally,LLO also changed the morphology of lysosome.During Listeria infection,the membrane integrity of the lysosome is disrupted and the active cathepsins are released into the cytoplasm.Although the function of this process is still unknown,future research areas should clarify how it affects immune signals,bacterial load and lysosomal homeostasis.Summary,Listeria is a human pathogen which diverse and complex regulatory mechanisms and multiple responses to external pressures enable it to survive in extremely harsh environments and shift from saprophytic to toxic for humans.In the past few decades,a large number of applications of transcriptomics,genomics,5'and 3'RNA sequencing and forward genetics technologies have revealed a lot of new information about the mechanism of this bacterial-host interaction.However,there are still a large number of proteins with unknown functions in the host's membrane system,mitochondria and lysosomes that are regulated by bacterial infections.Explaining the molecular functions of these regulated proteins may reveal new virulence factors and pathogenic mechanisms which have important guiding significance for clinical drug treatment.Therefore,this study used proteomics techniques to investigate the dynamic changes of host membrane proteins,mitochondria and lysosomes and reveal the defense mechanism of host cells upon Listeria infection.The main conclusions are as follows:1.We depicted the dynamic expression landscape of dendritic cells(DC2.4 cells)membrane proteins upon Listeria infection,which lays a foundation for us to better understand the mechanism of host cells against Listeria infection.2.We first discover and explain the antibacterial mechanism of membrane associated protein Dynll1.In the resting state,Dynll1 and Cox4i1 in the mitochondria form a complex,which inhibits the release of reactive oxygen species,making the intracellular reactive oxygen species at normal levels.In the infected state,Dynll1dissociates from Cox4i1,causing Cox4i1 releasing active oxygen to kill intracellular pathogens.3.Dynll1 is involved in the cross presentation of antigens in dendritic cells.4.We dynamically depict the changes of lysosome and mitochondria of macrophages(Raw264.7 cells)upon bacterial infection which let us better understand the functions of mitochondria and lysosome during infection.5.We discover the lysosomal protein Ctsd is a broad-spectrum antibacterial protein and can be used as a target protein for antibacterial drug design.