Inflammasomes involvement in Staphylococcus aureus infection of human osteoblast-like cells MG-63

Inflammation is a coordinated immune response to infections or tissue damage. The inflammasome is a multi-protein signaling platform that assembles after recognition of danger signals and/or pathogens by a family of cytosolic receptors called NLRs (nucleotide-binding domain and leucine rich repeats containing receptors) or PYHIN protein family members. Once assembled, inflammasomes initiate signaling by activation of downstream proteases, most notably Caspase-1 and Caspase-11, which then proteolytically mature pro-IL-1β, pro-IL-18, and pro-IL-33, and promote their secretion from the cell. Furthermore, inflammasome activation triggers pyroptosis, an inflammatory form of cell death. Staphylococcus aureus is a highly adaptive and versatile gram-positive bacterium that has major importance to human and animal health. S. aureus can cause life-threatening infections such as bacteremia, pneumonia, meningitis, endocarditis and sepsis. S. aureus are also the predominant cause of bone infections worldwide. Comprehending the mechanisms by which staphylococci interact with and damage bone is critical to the development of new approaches to meet this challenge. While the role of inflammasomes formed in the different types of phagocytes during S. aureus infection was widely investigated, the involvement of inflammasomes in osteoblast cells have not been studied. Objective: To understand the mechanisms of Bone Joint Infection we investigated the involvement of inflammasomes in the model of persistent infection of human osteoblast-like cells.Materials and Methods: CRISPR/Cas9 technology was used to prepare Caspase-1 deficient line of MG-63 cells. Western blot analysis and ELISA were employed for the detection of activated cytokines.Results: An employment of wild type vs Caspase-1 deficient MG-63 osteoblast-like cells allow demonstrating the involvement of inflammasomes during S. aureus infection. Using deletion mutants and complemented S. aureus strains, we determined the role of its most important virulence factors for their capacity to activate Caspase-1 and produce IL-1β.Conclusions: Non-phagocytic osteoblast-like MG-63 cells form inflammasomes in the response to S. aureus infection, however the time of inflammasomes formation was different compared to the professional phagocytes. Many virulence factors induce the inflammasomes assemblage.