Differential signalling requirements for RIPK1-dependent pyroptosis in neutrophils and macrophages

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Toll-like receptor 4 (TLR4) and Tumor Necrosis Factor Receptor 1 (TNFR1) signaling pathways are crucial for potent pro-inflammatory responses and are frequently exploited by pathogens.
• Pathogenic microorganisms like Yersinia can hijack host cell signaling, including TAK1/IKK pathways, leading to complex cellular retaliations.
• Previous research indicated myeloid cells trigger RIPK1-dependent caspase-8 activation, resulting in pyroptosis mediated by GSDMD and GSDME in macrophages and neutrophils, respectively.

Purpose of the Study:

• To elucidate the upstream signaling events that trigger RIPK1 activation in myeloid cells during Yersinia infection.
• To differentiate the roles of TLR4 and TNFR1 signaling in RIPK1-driven pyroptosis and cytokine production in neutrophils versus macrophages.
• To investigate the necessity of IFN-γ priming for RIPK1-dependent pyroptosis in neutrophils.

Main Methods:

• Investigated RIPK1 activation and pyroptosis pathways in myeloid cells (macrophages and neutrophils) during Yersinia infection.
• Utilized genetic or pharmacological inhibition of TLR4, TNFR1, TRIF, and IFN-γ signaling pathways.
• Assessed pyroptosis (caspase-8, GSDMD/GSDME cleavage) and cytokine production (e.g., TNF) in response to Yersinia and specific signaling manipulations.

Main Results:

• Neutrophil pyroptosis and cytokine priming during Yersinia infection are driven by TNFR1 signaling, independent of TLR4-TRIF signaling.
• IFN-γ priming is essential for RIPK1-dependent pyroptosis in neutrophils by inducing surface TNFR1 expression and amplifying TNF secretion.
• Macrophages employ both TNFR1 and TLR4-TRIF signaling for cell death, but only require TRIF for cytokine production, not autocrine TNFR1 signaling.

Conclusions:

• Myeloid cell responses to Yersinia infection exhibit significant cell-type-specific regulation of cell death and immune signaling.
• TNFR1 signaling is a key driver of pyroptosis in IFN-γ-primed neutrophils, while macrophages utilize a dual TNFR1/TLR4-TRIF pathway.
• These findings underscore the complexity of innate immune signaling and highlight differential mechanisms governing cell death and inflammation in distinct myeloid cell populations.