Molecular determinants of Streptococcus pyogenes adhesion to pyroptotic keratinocytes

PROJECT SUMMARY Streptococcus pyogenes (Group A Streptococcus, GAS) is a gram-positive obligate human pathogen and a significant public health burden. GAS causes diverse infections, ranging from relatively mild skin (impetigo) and throat (strep throat) infections to severe infections such as necrotizing fasciitis (“flesh-eating disease”) and streptococcal toxic shock syndrome. GAS strains are divided into more than 200 M types based on the variable surface protein M, as well as 9 fibronectin binding, collagen binding, T-antigen (FCT) genetic region types based on their surface pili. Some strains are specifically associated with either skin or throat infections, while others can infect either tissue. Tissue tropism is associated with emm genes and FCT genetic regions, but the precise molecular determinants for tissue tropism are unknown. This work will study host and bacterial determinants for GAS adhesion to skin cells. Additionally, keratinocytes trigger pyroptosis, a programmed cell death, in response to intracellular GAS. This work will also examine the effect of keratinocyte pyroptosis on GAS adhesion, and whether this contributes to infection mitigation. I hypothesize that keratinocytes vary in their exposure of targets for GAS adhesins throughout their differentiation and death, and that this consequently impacts GAS invasion of the skin. Aim 1 will examine GAS adhesion to keratinocytes and identify whether differentiation and death of these cells impact GAS adhesion. Aim 2 will reveal GAS adhesion factors using transposon screening to identify putative genes encoding adhesion determinants in GAS. These will be validated with genetic knockout and complementation experiments. The mentor for this F31 proposal, Christopher LaRock, has extensive experience studying pyroptosis resulting from GAS infection. This work will build on this discovery to identify factors influencing how mild infections can turn severe, determinants of infection resistance, and provide training for the PI Jacob Sherman in techniques of modern molecular Koch’s postulates for a research career in human health.