Abstract / Summary
Abstract Background Proteostatic control of receptor-proximal endotoxin sensing remains poorly defined in sepsis. Although ubiquitin-specific protease 13 (USP13) has been implicated in inflammatory and antioxidant pathways, whether it regulates CD14/TLR4 availability through a defined substrate-dependent mechanism remains unknown. We investigated whether USP13 establishes a proteostatic checkpoint that constrains receptor-proximal innate immune signaling in sepsis. Methods Publicly available peripheral-blood transcriptomic data from GSE95233 (51 patients with sepsis and 22 healthy controls) were analyzed alongside prospectively collected peripheral blood mononuclear cells from 20 patients (10 with sepsis and 10 with septic shock) and 10 noninfected controls, including eight paired day-0/day-7 samples. USP13 function and substrate relationships were examined using lung parenchymal and human myeloid cell models, biochemical interaction and ubiquitination assays, and reciprocal genetic rescue experiments. Mechanistic relevance was further tested in LPS-induced endotoxemia and a human fecal slurry-induced peritoneal contamination and infection model of polymicrobial sepsis. Results USP13 expression was reduced in public sepsis transcriptomes and patient PBMCs and remained suppressed after adjustment for inferred neutrophil expansion, whereas paired longitudinal sampling showed partial recovery during the early clinical course. USP13 loss increased oxidative stress, apoptotic signaling, NLRP3 abundance, and inflammatory cytokine release. USP13 was directly associated with PHB1 and maintained PHB1 stability by limiting polyubiquitination, thereby preserving PHB1-dependent K48-linked CD14 ubiquitination and turnover and restricting CD14/TLR4 accumulation and NLRP3-associated inflammatory signaling. Usp13 or Phb1 depletion aggravated inflammation and mortality in endotoxemia and polymicrobial sepsis. Reciprocal epistasis placed PHB1 downstream of USP13: PHB1 restoration rescued phenotypes caused by Usp13 deficiency, whereas USP13 overexpression could not bypass Phb1 loss. Delayed recombinant PHB1 administration also reduced inflammation and mortality in Usp13-deficient endotoxemia. Conclusions These findings identify a USP13-PHB1-CD14 proteostatic axis that regulates CD14/TLR4 availability and the threshold of innate inflammatory signaling in sepsis. PHB1 rescue provides proof-of-concept evidence that the downstream component of this proteostatic checkpoint remains functionally restorable, without establishing PHB1 supplementation as a clinical therapy.