Caspase-8-mediated CYLD Cleavage boosts LPS-induced Endotoxic Shock

Caspase-8, a pivotal protease intricately involved in various cellular signaling pathways related to cell death and inflammation, has been identified as a contributor to cytokine production during septic shock. However, the mechanisms governing this regulatory role remain enigmatic. In this study, we uncovered that mice harboring a specific mutation in CYLD at its D215 position ( Cyld ^{D 215 A/D 215 A} mutant mice), rendering CYLD resistant to caspase8 cleavage, exhibited marked protection against lethal endotoxic shock. Moreover, the removal of Cyld in Caspase8 ^-/- Mlkl ^-/- mice restored their sensitivity to endotoxic shock, indicating Caspase8 promotes LPS-induced endotoxic shock by cleaving its substrate CYLD and maintaining CYLD stability confers resistance to endotoxic shock. Mechanistically, CYLD was found to catalyze the removal of LUBAC-mediated M1-linked ubiquitination of NF-kB p65 at K301/K303, thereby suppressing the nuclear translocation and activation of p65 for subsequent cytokines production. Notably, the cleaved N-terminal fragment of CYLD (named CP25) is secreted in a TRIF/Caspase8-dependent manner. Moreover, CP25 can be detected in the serum of septic mice, and its levels show a strong correlation with corresponding serum IL-1β, suggesting its potential utility as an inflammatory biomarker. Overall, these findings highlight the significance of CYLD cleavage as a promising therapeutic target and diagnostic marker for endotoxic shock.