Host-pathogen interactions during Staphylococcus aureus spine infections - PROJECT SUMMARY Staphylococcus aureus (S. aureus), a leading global pathogen, is the primary microorganism implicated in spine infection. Because patients’ backpain symptoms are often misdiagnosed, paralysis may ensue in up to 75% of patients, and up to one-third of them may die from the disease. Despite recognition of the severe disease morbidity and mortality, the molecular mechanism of human spine infection remains undefined. S. aureus-human coevolution likely favor selection of isolates that are adept at virulence factor regulation adapt to the human host. One such adaptation is the ability to interfere with the C5a-hC5aR1 axis, a powerful component of the human innate immune system, through the production of three human-specific virulence factors, the Panton-Valentine Leukocidin (LukSF-PV/PL), γ-hemolysin CB (HlgCB), and the Chemotaxis Inhibitory Protein of S. aureus (CHIPS). These toxins target hC5aR1 to prevent C5a binding, thus disrupting neutrophil chemotaxis and function, enabling pathogen evasion of host killing. Up until now, species- specific receptor limitations have hindered accurate modeling of the effects of these toxins. However, the development of a novel humanized mouse model with knock-in hC5R1 (hC5aR1KI) set the stage for us to evaluate their contributions in invasive S. aureus infection. When we evaluated S. aureus bacteremia in wild-type and hC5aR1KI mice, we observed that hC5aR1KI mice developed highly penetrant mobility deficits involving the hindlimbs owing to infection of the spine, an important complication of S. aureus bacteremia in humans. We further dissected the contribution of each hC5aR1 targeting virulence factor, as well as examined the contribution of other S. aureus virulence factors, and implicated CHIPS and at least one of the 21 sortase A dependent cell wall-anchored surface proteins (SADCASP) as critical contributors to spine infection. To evaluate the roles of CHIPS and SADCASP in human spine infection, I will: 1) Clarify the role of surface proteins in spine infection, and prepare to test my hypothesis that immune interference and immune evasion properties of SADCASP and CHIPS contribute to their success in spine infection. 2) Determine the mechanism of injury in S. aureus spine infection with respect to CHIPS and SADCASP, and evaluate how CHIPS’ interference with C5a-hC5aR1 and SADCASP’s immune evasion properties contribute to primary and secondary spinal cord injury. With a better understanding of how CHIPS and SADCASP promote spine infection, I will 3) Explore vaccination approaches targeting CHIPS. Using a novel and clinically relevant mouse model of S. aureus infection, I hope to better understand the mechanisms behind how CHIPS and the SADCASP empower S. aureus to cause spine infection in humans, and use this information to identify potential vaccination strategies to prevent its debilitating impact.
