CYLD links the TRAF6/sNASP axis to TLR4 signaling in sepsis-induced acute lung injury.

Abstract

Sepsis-induced acute lung injury (ALI) involves severe lung dysfunction and leads to high morbidity and mortality rates due to the lack of effective treatments. The somatic nuclear autoantigenic sperm protein (sNASP)/tumor necrosis factor receptor-associated factor 6 (TRAF6) axis plays a crucial role in regulating inflammatory responses during sepsis through Toll-like receptor 4 (TLR4) signaling. However, it is unclear whether deubiquitinating enzymes affect the TRAF6/sNASP axis. In this study, we showed that cylindromatosis (CYLD) directly binds to the sNASP and prevents TRAF6 activation. When TLR4 is activated, phosphorylation of sNASP releases CYLD from the TRAF6/sNASP complex, leading to TRAF6 autoubiquitination and the production of proinflammatory cytokines. To stop TRAF6 activation, a complex of sNASP, TRAF6, and CYLD is reformed once dephosphorylation of sNASP occurs by protein phosphatase 4 (PP4). Silencing sNASP negated the inhibitory effects of CYLD on interleukin (IL)-6 and TNF-α production after lipopolysaccharide (LPS) treatment. Similarly, the absence of CYLD also reduced PP4's negatively regulated production of proinflammatory cytokines, indicating that phosphorylation is crucial for the interaction between sNASP and CYLD as well as TRAF6 activation. Finally, mice infected with a recombinant adenovirus carrying the CYLD gene (Ad-CYLD WT), but not a mutation, showed significant reductions in cecal ligation and puncture (CLP)-mediated lung injury and proinflammatory cytokine production. In conclusion, CYLD alleviated sepsis-induced inflammation by interacting with the TRAF6/sNASP axis. These findings suggest that CYLD could be a potential therapeutic target for treating sepsis-induced ALI.