The Regulatory Mechanisms Of Resistance To Enterococcus Faecalis Infection In Caenorhabditis Elegans By Mitochondrial Superoxide

Infectious diseases continue to be threats for human life.Recently it has been reported that mitochondrial reactive oxygen species(mROS)involve in host defenses against bacteria and viruses,mutation in mitochondrial electron transport chain(mETC)gene isp-1 causes mROS increase in Caenorhabditis elegans,which contributes to increase host immunity.This indicates mROS changes induced by mutations in mETC gene may be involved in defense response to regulate host immunity.Indeed,mitochondrial superoxide is in the center of mROS generation.It has been shown that mutations of the mETC gene induce significant changes of mitochondrial superoxide content in C.elegans,however,the roles and mechanisms of mitochondrial superoxide in bacterial infection remain unclear.Here C.elegans-E.faecalis is used as a host-pathogene infection model to investigate the antibacterial effects and possible mechanisms of mitochondrial superoxide.To identify the exact role of mitochondrial superoxide during E.faecalis infection,we thus knockdown the expression of mev-1 and isp-1 in C.elegans using RNAi to change the mitochondrial superoxide levels in the host.The knockdown of mev-1 and isp-1 cause increased susceptibility and increased resistance to E.faecalis infection,respectively.The mev-1RNAi can also down-regulate antimicrobial genes C17H12.8,mtl-1 and bli-3,whereas these antimicrobial genes are up-regulated in isp-1RNAi animals after bacterial infection.Further,significant increase of mitochondrial superoxide and mitochondrial sod expressions have been observed in isp-1RNAi animals.Conversely,the mev-1RNAi worms show a decrease of mitochondrial superoxide and mitochondrial sod expressions.Pretreatment of prooxidant paraquat(PQ)with mev-1RNAi animals,which induces mitochondrial superoxide generation,can increase survival rate of mev-1RNAi worms after E.faecalis infection.These results suggest that mitochondrial superoxide increase contributes to defense against bacterial infection in C.elegans.To further elucidate the mechanisms by which of mev-1RNAi defects E.faecalis resistance,we test the oxidative stress responses and the involvement of transcription factor DAF-16 in mev-1RNAi worms after E.faecalis infection.Here we show that mev-1RNAi causes increased lipofuscin accumulation and antioxidant enzyme(SOD-3 and GST-4)expressions after E.faecalis infection,suggesting a decrease in oxidative stress.mev-1RNAi animals do not display significant change in DAF-16 nuclear localization after E.faecalis infection,while pretreatment of PQ with mev-1RNAi animals to increase mitochondrial superoxide generation,can induce DAF-16 translocation after E.faecalis infection.Pretreatment of PQ could also trigger expression of antioxidant genes in mev-1RNAi C.elegans.The mev-1;daf-16 double RNAi results suggest that the expression decreases of SOD-3 and GST-4 mediated by mev-1 RNAi require DAF-16 activity.Killing assay in daf-16 mutants also shows that DAF-16 activity involves in mev-1RNAi-medicated susceptibility to E.faecalis infection.These results suggest that mitochondrial superoxide triggers expression decrease of oxidative stress genes through DAF-16 activity that lead less protection from oxidative stress response and cause more susceptibility to E.faecalis infection.All together,the enhancement of mitochondrial superoxide contributes to anti-bacterial immunity and a better knowledge of the mechanisms should open new avenues for preventive strategies against bacterial infection.