UBA6 confers neuroprotection against sepsis-associated encephalopathy through facilitating LCN2 ubiquitin-dependent degradation

Sepsis-associated encephalopathy (SAE) is a common secondary complication of sepsis, accompanied by neuroinflammation and neuronal apoptosis. As an E1 ubiquitin-activating enzyme, ubiquitin-like modifier-activating enzyme 6 (UBA6) deficiency aggravates inflammation. Herein, we first confirmed that UBA6 is decreased in brain tissues of cecal ligation and puncture (CLP)-induced SAE mice. Lentivirus was bilaterally injected into the hippocampus to establish in vivo UBA6 overexpression. Lentivirus-mediated overexpression of UBA6 effectively inhibited microglial activation, downregulated the levels of pro-inflammatory mediators, and reduced inflammatory cytokine release. Furthermore, UBA6 upregulation mitigated neuronal apoptosis and improved spatial learning and memory functions in SAE model mice. For in vitro validation, BV-2 microglial cells were stimulated with 100 ng/mL LPS for 24 h. Consistent with in vivo observations, exogenous UBA6 decreased the proportion of CD86-positive pro-inflammatory microglia. After culturing HT-22 neuronal cells with BV-2 cell conditioned medium, UBA6 overexpression elevated neuronal viability and restrained caspase-3-mediated neuronal apoptosis. Quantitative proteomics was applied to screen and identify lipocalin 2 (LCN2) as a downstream interacting partner of UBA6. Mechanistically, UBA6 binds LCN2 at residue 147 to accelerate K48 ubiquitination and degradation of LCN2, which attenuates neuronal apoptosis induced by LCN2 paracrine. Rescue assays revealed that ectopic LCN2 expression reversed the protective effects of UBA6 against neuroinflammation and neuronal apoptosis. In summary, UBA6 ameliorates SAE-induced cerebral damage, neuroinflammation and cognitive dysfunction via accelerating LCN2 ubiquitination and degradation. These findings advance the mechanistic understanding of SAE progression and establish UBA6/LCN2 as a prospective therapeutic target for SAE intervention.