Pneumolysin induced mitochondrial dysfunction leads to release of mitochondrial DNA

Abstract

Streptococcus pneumoniae (S.pn.) is the most common bacterial pathogen causing community acquired pneumonia. The pore-forming toxin pneumolysin (PLY) is the major virulence factor of S.pn. and supposed to affect alveolar epithelial cells thereby activating the immune system by liberation of danger-associated molecular patterns (DAMP). To test this hypothesis, we established a novel live-cell imaging based assay to analyse mitochondrial function and associated release of mitochondrial DNA (mtDNA) as DAMP in real-time. We first revealed that bacterially released PLY caused significant changes of the cellular ATP homeostasis and led to morphologic alterations of mitochondria in human alveolar epithelial cells in vitro and, by use of spectral live-tissue imaging, in human alveoli. This was accompanied by strong mitochondrial calcium influx and loss of mitochondrial membrane potential resulting in opening of the mitochondrial permeability transition pore and mtDNA release without activation of intrinsic apoptosis. Moreover, our data indicate cellular mtDNA liberation via microvesicles, which may contribute to S.pn. related pro-inflammatory immune activation in the human alveolar compartment.

Type I IFN expression is stimulated by cytosolic MtDNA released from pneumolysin‐damaged mitochondria via the STING signaling pathway in macrophages

“…During Pseudomonas aeruginosa infection, damaged mitochondria release mtDNA, which activates the nucleotide-binding domain, leucine-rich repeat containing family caspase recruitment domain containing 4 (NLRC4) inflammasome and leads to the production of IL-1b [32]. In the present study, we confirmed that Ply treatment can damage mitochondrial membrane to induce mtDNA release, and then promote the expression of type I IFN, which agreed with a recent report indicating that exposure to Ply leads to mitochondrial damage in epithelial cells, as well as the release of mtDNA, and contributes to IL-1b expression [33]. In addition to mtDNA, the c-di-AMP of Group B Streptococcus and Chlamydia trachomatis can also activate STING signaling pathway and then mediated the expression of IFN-b treated with Ply (400 ngÁmL À1 ) for 6 h, and then immunostained with anti-pIRF3 (red).…”

Mitochondrial DNA drives noncanonical inflammation activation via cGAS–STING signaling pathway in retinal microvascular endothelial cells

“…Nerlich reported that under pathological stimulation, the Ca 2+ in ux into the mitochondria changes (23), accompanied by morphological changes in the mitochondria (24). The mitochondrial Ca 2+ in ux and loss of mitochondrial membrane potential results in the opening of the MPTP, with the consequent release of cytochrome c and mtDNA into cytoplasm (23,25). In this study, we have shown that pathogenic stimulation causes MPTP opening and the escape of mtDNA, which was detected with immuno uorescence.…”

Mitochondrial DNA: A Key Regulator of Anti-Microbial Innate Immunity

“…Furthermore, pneumolysin, a pore-forming toxin is the key virulence factor of Gram-positive bacteria (Streptococcus pneumoniae) and is considered to influence alveolar epithelial cells to stimulate the immune system by the release of danger-associated molecular patterns [136,137]. Nerlich et al [138] demonstrated that bacterially released pore-forming toxin pneumolysin could remarkably alter the ATP homeostasis of cells and lead to morphologic changes of mitochondria in alveolar epithelial cells of human in vitro. Furthermore, this toxin is also responsible for the influx of mitochondrial calcium and loss of mitochondrial membrane potential causing the opening of the permeability transition pore of mitochondria and leak of mitochondrial DNA via microvesicles without activation of intrinsic apoptosis.…”