Apoptosome-centered cell death restricts phagocyte entry into staphylococcal abscesses

Manipulation of macrophage responses by the human pathogen Staphylococcus aureus requires the activity of two synergistically acting enzymes, secreted nuclease (Nuc) and adenosine synthase A (AdsA). Specifically, Nuc-mediated disruption of neutrophil extracellular DNA traps and subsequent bioactivity of AdsA provokes the formation of staphylococcal death-effector deoxyribonucleosides that trigger a genotoxic buildup of deoxyribonucleoside triphosphates in phagocytes that attempt to infiltrate infectious foci. However, the cellular and pathophysiological consequences that S. aureus-driven modulation of immune cell nucleotide metabolism may trigger remain unknown. Powered by CRISPR/Cas9 mutagenesis and in-depth analysis of cell death modalities in phagocytes, we illustrate that death-effector deoxyribonucleoside-mediated intoxication of macrophages involves destruction of mitochondria, assembly of the apoptosome, and subsequent activation of the intrinsic pathway of apoptosis. Remarkably, mice lacking caspase-9, a dominant modulator of the intrinsic pathway of apoptosis, exhibit increased resistance toward S. aureus invasive disease as caspase-9-deficient macrophages are resistant to death-effector deoxyribonucleosides and readily invade abscess lesions filled with staphylococci to accelerate bacterial clearance in infected host tissues. Combined with the identification of a set of candidate resistance alleles in human CASP9 that protect macrophages from death-effector deoxyribonucleoside-mediated cytotoxicity, our data suggest that specific polymorphisms in genetic elements of the apoptotic signaling pathway may contribute to the wide array of susceptibility observed in human populations toward S. aureus diseases.