Staphylococcus aureus planktonic but not biofilm environment induces an IFN-β macrophage immune response via the STING/IRF3 pathway

ABSTRACT

Chronic implant-related bone infections are a severe complication in orthopaedic surgery. Biofilm formation on the implant impairs the immune response, leading to bacterial persistence. In a previous study, we found that Staphylococcus aureus (SA) induced interferon regulatory factor 3 (IRF3) activation and Ifnb expression only in its planktonic form but not in the biofilm. The aim of this study was to clarify the role of the stimulator of interferon genes (STING) in this process. We treated RAW 264.7 macrophages with conditioned media (CM) generated from planktonic or biofilm cultured SA in combination with agonists or inhibitors of the cyclic GMP-AMP synthase (cGAS)/STING pathway. We further evaluated bacterial gene expression of planktonic and biofilm SA to identify potential mediators. STING inhibition resulted in the loss of IRF3 activation and Ifnb induction in SA planktonic CM, whereas STING activation induced an IRF3 dependent IFN-β response in SA biofilm CM. The expression levels of virulence-associated genes decreased during biofilm formation, but genes associated with cyclic dinucleotide (CDN) synthesis did not correlate with Ifnb induction. We further observed that cGAS contributed to Ifnb induction by SA planktonic CM, although cGAS activation was not sufficient to induce Ifnb expression in SA biofilm CM. Our data indicate that the different degrees of virulence associated with SA planktonic and biofilm environments result in an altered induction of the IRF3 mediated IFN-β response via the STING pathway. This finding suggests that the STING/IRF3/IFN-β axis is a potential candidate as an immunotherapeutic target for implant-related bone infections.

KEYWORDS:

• Implant-related bone infections
• Staphylococcus aureus
• biofilm
• macrophages
• STING/IRF3 pathway
• IFN-β

Acknowledgements

We would like to thank Dafina Kadrijaj and Tabea Elschner for their assistance with the experiments. Furthermore, we thank Dr. Lan-Sun Chen for providing the human PBMCs.

Disclosure statement

The authors declare that they have no financial or non-financial interests to disclose.

Author contribution

ES was responsible for the study conception and design, acquisition, analysis, and interpretation of data, and wrote the manuscript. GS participated in the data acquisition and analysis. KFK contributed to the data interpretation and critically revised the manuscript. All authors have read and approved the final manuscript.

Data Availability statement

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21505594.2023.2254599

Additional information

Funding

This study was financially supported by a foundation fund (Dres. Majic/Majic-Schlez Stiftungsfonds) of the “Studienstiftungenverwaltung” of the Medical Faculty of Heidelberg University.