Study On Mechanism Of Immune Response Induced By Pneumolysin-mediated Mitochondrial Damage

Objective: To investigate the role of Ply in inducing mitochondrial damage in macrophages,and whether Ply-induced damaged mitochondria could release mt DNA into cytoplasm and how these ectopic mtDNA induce host immune response.Background: Streptococcus pneumoniae(S.pn)is a highly invasive Gram-positive bacteria that responsible for a variety of serious diseases such as community-acquired pneumonia,otitis media,meningitis and sepsis.S.pn infection causes high mortality and morbidity worldwide especially in aged persons and in children under 5?years old in developing countries.Pneumolysin(Ply)is a pore-forming protein and a major virulence factor of S.pn,which could breach the epithelial barriers of host and have numerous immunity effects on host cells.We previously confirmed that Ply was capable of inducing IFN-? expression.However,the underlying mechanism is unknown.It is generally recognized that IFN-? is a cytokine induced by nucleic acid derived from both pathogens and host in most of the time.Thus,we wondered whether is there some kinds of nucleic acid mediated the Ply-induced IFN-?.It has been reported that Ply has potential to damage mitochondria.Damaged mitochondria could release mtDAMPs including mtDNA into cytoplasm and stimulate IFN-? production via STING signaling pathway.Therefore,we speculated that IFN-? induced by purified Ply maybe mediated cytosolic mtDNA released from Ply-damaged mitochondria.Methods and Results:1.Ply-induced mitochondria damage lead to translocation of mtDNA into cytoplasm.Inhibition of mtROS by mitoTEMPO significantly suppressed the Ply-triggered release of mt DNA.2.Purified Ply could promote the production of IFN-? in macrophages of mice and human.Cytosolic mtDNA induced IFN-? production in Ply-treated macrophages3.STING signaling was related to I-IFN response in Ply-treated macrophagesConclusions: In conclusion,our current study explored a novel mechanism underlying Ply-induced mtDNA release and subsequent STING-mediated activation of I-IFN response.This study provided multiple evidences that Ply caused the secretion of IFN-? in macrophages and underlined the importance of mitochondrial homeostasis in initiating host immune system during S.pn infection.The mechanism revealed in this research might serve as a potential approach for S.pn to modulate host immune response.Further study on how mtDNA-induced I-IFN regulated the anti-S.pn response might provide a new prospective on improvement of therapeutic method and vaccine for S.pn infection.