Augmenting host innate immune responses against Staphylococcal osteomyelitis with antimicrobial nucleic acid structures - PROJECT SUMMARY Staphylococcus aureus is the principle causative agent of osteomyelitis (OM), a severe infection of the bone tissue that is characterized by damaging inflammation and progressive bone loss. Current therapy includes surgicaldebridement of necrotic bone tissue and prolonged treatment with antibiotics.However, S. aureus biofilm formation on bone tissue and invasion of resident bone cells limits antibiotic effectiveness and provides a protective niche for viable bacteria. Additionally, there is anincreased incidence of OM infectionsin part to the emergence of antibiotic resistant strains such as MRSA that account for one-third of S. aureus isolates. Collectively,these factors contribute torecurrent and persistent infections in 40% of patients. Therefore, development of novel treatment strategies is a high priority. It is now appreciated that resident bone cells including osteoblasts, osteocytes, and osteoclasts express a variety of pattern recognition receptors (PRRs) for identification of pathogens and initiation of immune responses. We have recently published the first demonstration of increased type I IFN production in infected femurs compared to the contralateral controls in an in vivo model of localized Staphylococcus osteomyelitis. Our pioneering studies demonstrated that murine osteoblasts produce significant increases in type I IFNs following S. aureus challenge and such production serves to limit intracellular S. aureus burden. Our other recent studies also indicate that the type I IFN, IFN-β functions as an antimicrobial peptide with bactericidal activity against S. aureus. Furthermore, resident bone cells release antimicrobial peptides, including β-defensins in response to S. aureus challenge that possess direct bactericidal activity, inhibit biofilm formation, and disrupt established biofilms. Collectively, this supports a protective role for resident bone cell production of antimicrobial peptides and type I IFNs during Staphylococcal OM and suggests augmentation of such responses is an attractive therapeutic target. In this high-risk high- reward R21 project, we will investigate the hypothesis that augmenting protective bone cell innate immune responses can restrict S. aureus burden by employing immunomodulatory and antimicrobial nucleic acid structures (IMANAS). We will design IMANAS to act as effective agonists for the cytosolic PRR, cyclic GMP- AMP synthase (cGAS) to augment protective antimicrobial peptides and type I IFN production that can restrict bacterial burden. Additionally, IMANAS will incorporate nanostructured silver that can kill bacteria via multiple mechanisms such as disruption of bacterial cell membrane, induction of DNA/RNA damage, generation of reactive oxygen species, and involvement in destabilizing proteins. This high-risk high-reward R21 is anticipated to demonstrate the efficacy of augmenting protective host innate immune responses as a strategy to restrict bacterial burden in isolated primary murine bone cells and in an established in vivo murine model of Staphylococcus OM. Furthermore, these studies represent an essential preclinical step in establishing the efficacy of these innovative IMANAS to combat bacterial infections including OM.
