Nox2 Modification of LDL Is Essential for Optimal Apolipoprotein B-mediated Control of agr Type III Staphylococcus aureus Quorum-sensing

Abstract

Staphylococcus aureus contains an autoinducing quorum-sensing system encoded within the agr operon that coordinates expression of virulence genes required for invasive infection. Allelic variation within agr has generated four agr specific groups, agr I–IV, each of which secretes a distinct autoinducing peptide pheromone (AIP1-4) that drives agr signaling. Because agr signaling mediates a phenotypic change in this pathogen from an adherent colonizing phenotype to one associated with considerable tissue injury and invasiveness, we postulated that a significant contribution to host defense against tissue damaging and invasive infections could be provided by innate immune mechanisms that antagonize agr signaling. We determined whether two host defense factors that inhibit AIP1-induced agrI signaling, Nox2 and apolipoprotein B (apoB), also contribute to innate control of AIP3-induced agrIII signaling. We hypothesized that apoB and Nox2 would function differently against AIP3, which differs from AIP1 in amino acid sequence and length. Here we show that unlike AIP1, AIP3 is resistant to direct oxidant inactivation by Nox2 characteristic ROS. Rather, the contribution of Nox2 to defense against agrIII signaling is through oxidation of LDL. ApoB in the context of oxLDL, and not LDL, provides optimal host defense against S. aureus agrIII infection by binding the secreted signaling peptide, AIP3, and preventing expression of the agr-driven virulence factors which mediate invasive infection. ApoB within the context of oxLDL also binds AIP 1-4 and oxLDL antagonizes agr signaling by all four agr alleles. Our results suggest that Nox2-mediated oxidation of LDL facilitates a conformational change in apoB to one sufficient for binding and sequestration of all four AIPs, demonstrating the interdependence of apoB and Nox2 in host defense against agr signaling. These data reveal a novel role for oxLDL in host defense against S. aureus quorum-sensing signaling.

ω-Hydroxyemodin Limits Staphylococcus aureus Quorum Sensing-Mediated Pathogenesis and Inflammation

“…We chose to focus on the disruption of agr QS as an antivirulence approach to S. aureus SSTIs due to their predominance in S. aureus disease manifestations, as well as the established contribution of agr in facilitating these infections (11)(12)(13)(14)19). For example, agr deletion mutants (⌬agr) are less pathogenic and more readily cleared during SSTIs than are wild-type strains (14,19), and host innate effectors that disrupt agr signaling limit disease in skin infection models (20)(21)(22). Importantly, the sterile supernatant from agr ϩ but not from agr-null S. aureus strains is sufficient to cause skin lesions similar to those in an active infection, definitively demonstrating the role of agr-regulated secreted virulence factors in skin pathogenesis (58).…”

“…S. aureus isolates have one of four agr alleles (agr-I to agr-IV), each encoding factors that secrete a unique AIP (AIP1 to AIP4, respectively) that is detected by a cognate AgrC histidine kinase; isolates from each allele can cause human disease (17,18). Importantly, we and others have shown that the disruption of agr signaling by mutagenesis, monoclonal antibodies, or host factors limits S. aureus infection and reduces pathogenesis (14,(19)(20)(21)(22)(23)(24), demonstrating that agr QS is a robust target for combating invasive S. aureus infection.…”

Antiinfective therapy with a small molecule inhibitor of Staphylococcus aureus sortase

“…AIP-mediated activation of AgrC can be inhibited with peptide analogs and small molecules, which diminishes S. aureus colonization and invasion of skin and soft tissues (43,46). AIP is inactivated by neutrophil Nox2 NADPH oxidase modification and apolipoprotein B binding (47,48), which interferes with agr-mediated quorum sensing when S. aureus enters the bloodstream (49,50). In agreement with this model, AgrC inhibitors do not affect staphylococcal load, abscess formation, or disease outcome when mice are challenged by i.v.…”

Impact of Environmental Cues on Staphylococcal Quorum Sensing and Biofilm Development

“…The details of this mechanism have been unveiled through a series of studies (30,31,37). Initially, it was observed that pooled human serum, but not lipoproteindeficient serum, could inhibit quorum sensing by an agr type I reporter strain during in vitro growth (31).…”