Cyclic di-AMP Released from Staphylococcus aureus Biofilm Induces a Macrophage Type I Interferon Response

Abstract

Staphylococcus aureus is a leading cause of community-and nosocomial-acquired infections, with a propensity for biofilm formation. S. aureus biofilms actively skew the host immune response toward an anti-inflammatory state; however, the biofilm effector molecules and the mechanism(s) of action responsible for this phenomenon remain to be fully defined. The essential bacterial second messenger cyclic diadenylate monophosphate (c-di-AMP) is an emerging pathogen-associated molecular pattern during intracellular bacterial infections, as c-di-AMP secretion into the infected host cytosol induces a robust type I interferon (IFN) response. Type I IFNs have the potential to exacerbate infectious outcomes by promoting anti-inflammatory effects; however, the type I IFN response to S. aureus biofilms is unknown. Additionally, while several intracellular proteins function as c-di-AMP receptors in S. aureus, it has yet to be determined if any extracellular role for c-di-AMP exists and its release during biofilm formation has not yet been demonstrated. This study examined the possibility that c-di-AMP released during S. aureus biofilm growth polarizes macrophages toward an anti-inflammatory phenotype via type I interferon signaling. DacA, the enzyme responsible for c-di-AMP synthesis in S. aureus, was highly expressed during biofilm growth, and 30 to 50% of total c-di-AMP produced from S. aureus biofilm was released extracellularly due to autolytic activity. S. aureus biofilm c-di-AMP release induced macrophage type I IFN expression via a STING-dependent pathway and promoted S. aureus intracellular survival in macrophages. These findings identify c-di-AMP as another mechanism for how S. aureus biofilms promote macrophage anti-inflammatory activity, which likely contributes to biofilm persistence. Staphylococcus aureus is a leading cause of prosthetic joint infections (1, 2), whereupon adherence to the implant surface facilitates biofilm formation. These infections are particularly challenging to treat and typically require a two-stage surgical process for insertion of a new device (1). Moreover, biofilms actively skew the host immune response toward an anti-inflammatory state, thereby contributing to the chronic nature of biofilm-mediated infections (3-5). This is evident by macrophage polarization toward an alternatively activated phenotype and the recruitment of myeloid-derived suppressor cells (MDSCs) (3,(6)(7)(8). While this immune deviation appears to be driven by S. aureus biofilm products, the effectors and their mechanism(s) of action remain to be fully identified.To further understand mechanisms of immune modification by S. aureus biofilms, we investigated the role of the essential bacterial second messenger cyclic diadenylate monophosphate (c-di-AMP), since it has been identified as an emerging pathogen-associated molecular pattern (PAMP) that influences immune responsiveness (9, 10). While c-di-AMP has been found to regulate many important functions in bacteria, including cell wall stress and peptidoglycan homeostas...

Colonization of medical devices by staphylococci

“…Due to the absence of PSMs, which would otherwise disperse biofilm-like aggregates, this leads to pronounced clumping and increased resistance to antibiotic treatment. Finally, recent research suggests that S. aureus biofilms release specific factors, such as cyclic di-AMP, that limit inflammation (Gries et al, 2016). Thus, biofilm formation on indwelling medical devices can be seen as a strategy to evade elimination by the immune system by remaining in a relatively quiescent state that does not trigger pronounced inflammation, in addition to providing increased shelter from phagocyte attacks and antibiotics.…”

Cyclic Dinucleotides Inhibit Osteoclast Differentiation Through STING-Mediated Interferon-β Signaling

“…Increased expression of CDNs promotes extracellular matrix production and biofilm formation . CDNs released from bacterial biofilm can also activate host immune responses . Previous studies showed that CDNs could be used as novel vaccine adjuvants or immunostimulatory molecules for host defense .…”

“…(15)(16)(17) CDNs released from bacterial biofilm can also activate host immune responses. (18) Previous studies showed that CDNs could be used as novel vaccine adjuvants or immunostimulatory molecules for host defense. (19)(20)(21)(22) Intranasal administration with c-di-GMP enhances bacteria clearance and protects mice from Klebsiella pneumoniae infection through stimulation of dendritic cell-meditated responses.…”

The Role of Nucleic Acid Sensing in Controlling Microbial and Autoimmune Disorders

“…Finally, STING was shown to be a direct sensor of c-di-GMP (Burdette et al, 2011). Since then, studies have shown that STING mediates a type I IFN response specifically in response to CDNs such as those produced by Staphylococcus aureus and Chlamydia trachomatis (Barker et al, 2013; Gries et al, 2016; Zhang et al, 2014). Undoubtedly, the role of STING in detecting CDN-mediated type I IFN response was authenticated by the discovery that cGAS produces cGAMP in a DNA-dependent manner (Sun et al, 2013).…”