The mitochondrial apoptosis apparatus in the detection of microbial infection.

• Applicant: Professor Dr. Georg Häcker
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398228404

Apoptosis is a well-defined mechanism of cell death. However, recent literature data indicate that the apoptosis-pathway can also be activated to only a low level; the process is then ‘aborted’ and the cell stays alive. It has further been shown that mitochondrial apoptosis can induce cytokine secretion if apoptotic caspases are absent or experimentally inhibited. Combining these two observations, we provide evidence that low-level, ‘abortive’ apoptosis induces the secretion of interleukin (IL) 6 and IL-8 from epithelial cells. We further find that infection of epithelial cells with a number of viruses and bacteria induces ‘abortive apoptosis’, identified as damage to the genomic DNA in the absence of apoptosis but dependent on components of the apoptosis apparatus. Accordingly, cells with defects in mitochondrial apoptosis secreted less IL-6 and IL-8 upon infection with a number of infectious agents. We here propose to study the concept that abortive apoptosis serves as a mechanism of pathogen recognition by human cells. In the first part of the project we will test the hypothesis that pattern recognition receptors (PRR) can induce abortive apoptosis, and that this signaling is part of their activity during infection with a virus (we will use the vaccinia virus derivative MVA) and a bacterium (Chlamydia trachomatis). Pro-apoptotic activity of PRRs has been described before; we believe that abortive apoptosis may be a function of this signaling. We will either specifically trigger individual PRR and test for abortive apoptosis, or take away individual PRR or signaling components and test for the effect on abortive apoptosis induced by MVA or C. trachomatis. Chemical inhibition of Bcl-2 can trigger abortive apoptosis. We will here test the roles of the various pro- and anti-apoptotic Bcl-2-family members in the regulation of abortive apoptosis. In the second part of the project we will endeavor to understand signaling events in the reception of abortive apoptosis downstream of mitochondria. We find a role of the signaling molecule STING in abortive apoptosis, and literature data implicate mitochondrial DNA. We further show the release of the mitochondrial molecule Smac into the cytosol during abortive apoptosis. We will follow up on these observations, investigate Smac-release and its consequences and compare it to the release of cytochrome c. We will also test for the role of mitochondrial DNA and will analyse some of the core signaling events that are likely involved in cytokine induction. Abortive apoptosis is a novel concept, and the demonstration of its use in microbe recognition would be an important step to understand and to establish this concept.

• DFG Programme: Research Grants