The Circadian Clock Controls Immune Checkpoint Pathway in Sepsis

Area of Science:

• Immunology
• Circadian Biology
• Molecular Medicine

Background:

• Sepsis causes life-threatening organ dysfunction due to impaired host response to infection.
• Circadian clock disruption affects early inflammatory responses, but its role in post-septic immunosuppression is unclear.
• Bmal1, a core circadian clock gene, is investigated for its role in sepsis-induced immune dysregulation.

Purpose of the Study:

• To elucidate the role of the circadian clock gene Bmal1 in regulating host immune responses during experimental sepsis.
• To investigate the molecular mechanisms linking Bmal1 deficiency to immune suppression in sepsis.
• To explore potential therapeutic strategies targeting the identified pathways.

Main Methods:

• Utilized a mouse model of experimental sepsis.
• Assessed the impact of Bmal1 deficiency on macrophage function, including PKM2 expression and lactate production.
• Investigated the STAT1-dependent regulation of PD-L1 expression.
• Evaluated therapeutic interventions including Pkm2 ablation, anti-PD-L1 antibody, and IL-7 supplementation.

Main Results:

• Bmal1 deficiency in macrophages increased PKM2 expression and lactate production, promoting PD-L1 expression via STAT1.
• Targeted Pkm2 ablation, anti-PD-L1 treatment, or IL-7 supplementation improved microbial clearance.
• These interventions reduced T cell apoptosis, mitigated multiple organ dysfunction, and decreased mortality in Bmal1-deficient mice.

Conclusions:

• The circadian clock, specifically Bmal1, regulates the immune checkpoint pathway in macrophages during sepsis.
• Bmal1 deficiency exacerbates sepsis by promoting PD-L1-mediated immunosuppression.
• Targeting the circadian clock-controlled immune checkpoint pathway offers a potential therapeutic strategy for lethal infections like sepsis.