Collections > Electronic Theses and Dissertations > Cellular Mechanisms of Staphylococcus aureus α-hemolysinmediated Activation of the NLRP3 Inflammasome
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Background: Staphylococcus aureus toxin, α-hemolysin, is secreted as a soluble monomer that forms a heptameric pore in the membranes of a range of host cell types. Hemolysin binds and activates A Disintergin and Metalloprotease 10 (ADAM10) and is a well-chronicled virulence factor in staphylococcal disease. ADAM10 activity is important for toxin-mediated pathology in a number of cell types. In host monocytes, α-hemolysin activates the nucleotide-binding domain and leucine-rich repeat containing gene family, pyrin domain containing 3 (NLRP3) inflammasome leading to production of the pro-inflammatory cytokines (IL-1β, IL-18) and pyroptotic cell death. Human airway epithelial cells express the components of the NLRP3 inflammasome but the involvement of this signaling pathway in the cellular response to α-hemolysin is unknown. We hypothesized that both ADAM10 and NLRP3 are involved in host cellular responses to α-hemolysin in both monocytic and respiratory epithelial cells. Methods: To elucidate the role of ADAM10 and its protease activity in α-hemolysin-mediated activation of the inflammasome, we used the immortalized monocyte cells line, THP1 and U937. Cells were treated with siRNA against or chemical inhibitors of ADAM10, challenged with α-hemolysin, and NLRP3-inflammasome activation assessed by measuring secreted IL-1β, cell death, and activation of caspase-1. To test for evidence of α-hemolysin-mediated inflammasome activation in respiratory epithelial cells, we used primary human tracheobronchial epithelial (hTBE) cells and measured their secretion of IL-1β in response to hemolysin challenge. Results: Loss of ADAM10 cell surface expression led to diminished α-hemolysin-mediated activation of the NLRP3 inflammasome and cell death. ADAM10 protease activity, however, was not required for NLRP3 activation in human monocytes. hTBEs secrete mature IL-1β in response to α-hemolysin treatment, suggesting a role for the inflammasome in their response to α-hemolysin. Conclusions: This work demonstrates that ADAM10’s receptor and not its protease activity, is important for inflammasome activation by α-hemolysin in human monocytes. Preliminary evidence also suggests that the inflammasome may play a role in epithelial cell responses to α-hemolysin.