Identifying novel immune determinants that influence S. aureus biofilm infection using Collaborative Cross (CC) mouse lines - Staphylococcus aureus (S. aureus) is a leading cause of biofilm-associated prosthetic joint infection (PJI) typified by antibiotic tolerance and evasion of immune-mediated clearance. Our laboratory has extensively utilized a model of S. aureus PJI in inbred C57BL/6J mice to define immune attributes that promote biofilm persistence. This includes an abundance of anti-inflammatory granulocytic myeloid-derived suppressor cells (G-MDSCs) that inhibit monocyte/macrophage proinflammatory activity and neutrophil (PMN) killing of S. aureus through robust IL-10 production. Despite these advances, genetic diversity is not captured with inbred mouse strains, and it is well appreciated that genetic variability in humans contributes to heterogeneity in immunity and disease susceptibility. This is reflected in our studies of patients with PJI, where transcriptional profiles of leukocytes recovered from infected tissues displayed significant heterogeneity, even when infected with the same bacterial species. Furthermore, there are wide variations in the numbers of G-MDSCs associated with human PJI tissues. Therefore, despite their utility, inbred mice are not capable of capturing the diverse array of genetic factors that impact disease outcome during human PJI. To address this issue, this proposal leverages the Collaborative Cross (CC), a genetically diverse group of mouse strains representing > 30 million SNPs that were generated by crossing 5 classical inbred lines with 3 wild-derived inbred strains. The genomes of CC mice are fully sequenced, allowing genes of interest to be identified by quantitative trait locus (QTL) mapping to assign genotype-phenotype relationships. Only one report to date has utilized CC strains to examine host genes that influence S. aureus pathogenesis in a sepsis model, which is highly divergent from biofilm pathology. Therefore, due to the lack of comprehensive GWAS studies or the use of CC strains in PJI, little is known about host genes that regulate biofilm growth. We will leverage CC lines in a two-pronged approach to identify the effect of disease- associated QTLs on PJI outcome and the intrinsic genetic determinants that shape PMN acquisition of anti- inflammatory G-MDSC-like characteristics. This is expected to uncover novel host genetic factors that impact PJI pathogenesis, advancing the applicability of our findings to the clinical realm. This proposal will test the hypothesis that genetic diversity contributes to the regulation of biofilm growth and inflammation, which will be examined in the following Specific Aims: 1) Explore the genetic determinants that influence host immunity during PJI using CC mice; and 2) Identify host genetic loci that are critical for PMN acquisition of G-MDSC-like properties in response to S. aureus biofilm. These studies are expected to inform our long-term goal of targeting key host regulatory genes in combination with antibiotics to clear PJI without the need for additional surgeries, reducing the morbidity for patients suffering from these debilitating infections.
