The ligand binding domain of the cell wall protein SraP modulates macrophage apoptosis and inflammatory responses in staphylococcus aureus infections

Authors: HE, SUN - Central South University; Li, Robert; Wang, Thomas; DING, LING - Shanghai Jiaotong University

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2025
Publication Date: 3/5/2025
Citation: He, S., Li, R.W., Wang, T.T., Ding, L. 2025. The ligand binding domain of the cell wall protein SraP modulates macrophage apoptosis and inflammatory responses in staphylococcus aureus infections. International Journal of Molecular Sciences. 30(5):1168. https://doi.org/10.3390/molecules30051168.
DOI: https://doi.org/10.3390/molecules30051168

Interpretive Summary: Alternative to antibiotic treatments is essential option toward combating antibiotics resistant bacterial infection. The current study examine molecular mechanisms of Staphylococcus aureus (S. aureus) infections to identify novel treatment target. The Staphylococcus aureus protein serine rich adhesin for platelets (SraP) belongs to a large surface glycoprotein family of adhesins involved in bacterial adhesion. Here we provided evidence that SraP L-lectin module (LLM) possessed properties to mediate macrophage functions. Our flow cytometry data demonstrated that macrophages infected by the LLM deletion mutant profoundly impacted apoptosis, reducing the apoptotic cells by approximately 50% while LLM overexpression significantly increased the percentage of early apoptotic cells (p < 0.001). LLM played an important role on maintaining macrophage functions. LLM deletion significantly enhanced phagocytosis by increasing the number of engulfed bacteria, resulting in a significant augmentation of bacterial killing and leading to a decrease in bacterial survival within macrophages (p < 0.001). Furthermore, LLM modulated the ability of S. aureus to elicit inflammatory responses. The LLM deletion strain dampened the expression of pro-inflammatory factors whereas increasing the expression of anti-inflammatory cytokines, such as IL10. Our evidence suggests that SraP likely plays a dual role in S. aureus pathogenesis, by acting as a virulence factor implicated in bacterial adhesion and invasion and by mediating macrophage functions. Developing LLM inhibitors, alone or in combination with traditional antibiotics, may represent a novel strategy for combating S. aureus infections. This study provide novel information on molecular regulation of the S. aureus infection. The information will benefit basic and translational scientist working on research related to prevention of S. aureus infection and identify alternative to antibiotics.

Technical Abstract: The Staphylococcus aureus cell wall protein serine rich adhesin for platelets (SraP) belongs to a large surface glycoprotein family of adhesins. Here, we provide experimental evidence that SraP mediates macrophage functions in a human monocyte-derived macrophage model via its N-terminal L-lectin module (LLM) in the ligand binding region. Our flow cytometry data demonstrated that macrophages infected by the LLM deletion strain profoundly impacted apoptosis, reducing the percentage of apoptotic cells by approximately 50%, whereas LLM overexpression significantly increased the percentage of early-stage apoptotic cells (p < 0.001). LLM deletion significantly enhanced phagocytosis by macrophages by increasing the number of engulfed bacteria, resulting in a significant increase in bacterial killing and leading to a notable decrease in bacterial survival within macrophages (p < 0.001). Furthermore, LLM modulated the ability of S. aureus to elicit inflammatory responses. The LLM deletion strain dampened the expression of proinflammatory factors but increased the expression of anti-inflammatory cytokines, such as IL10. Our evidence suggests that SraP likely plays a dual role in S. aureus pathogenesis, by acting as a virulence factor involved in bacterial adhesion and invasion and by mediating macrophage functions. Our future work will focus on the identification of small molecule inhibitors of LLM using molecular docking-based in silico screening and in vivo validation. Developing LLM inhibitors, alone or in combination with conventional antibiotics, may represent a novel strategy for combating S. aureus infections.