Daily Sepsis Research Analysis

BACKGROUND: Escherichia coli has an extensive accessory genome, though its role in affecting patient mortality is unknown. METHODS: We performed whole genome sequencing with E. coli bacteremia isolates. Pan-genome analysis was used to identify flexible genomic islands associated with in-hospital attributable mortality. Genomic islands of interest were investigated experimentally. RESULTS: We included 193 E. coli genomes. Two genomic islands were co-present within 41 (21%) genomes and associated with increased attributable mortality in an adjusted analysis (Odds ratio 3.0; 95% confidence interval 1.1-7.9; p=0.03). The two genomic islands together contain genes homologous to a type III secretion system (T3SS): 1) E. coli type III secretion system 2 (ETT2), encoding genes homologous to a T3SS basal body and needle complex, and 2) an ETT2 accessory region (ETT2-AR) encoding genes homologous to a T3SS needle tip, translocases, and adhesin. ETT2/ETT2-AR increased resistance to complement-mediated growth restriction by inhibiting classical complement pathway activation and impacted E. coli-host cell interactions by increasing adhesion to and death of mammalian cells. CONCLUSIONS: Genomic islands ETT2 and ETT2-AR are homologous to a T3SS, co-localize within specific E. coli lineages, associate with increased mortality, and increase bacterial virulence through resistance to complement and enhanced host cell adhesion and death.

OBJECTIVE: This study explored the molecular mechanism of adipose-derived stem cell-derived extracellular vesicles (ADSC-EVs) improving post-sepsis-associated acute kidney injury (S-AKI) tubular epithelial cell (TEC) apoptosis by modulating ADAM17/MerTK-mediated macrophage efferocytosis. METHODS: The S-AKI mouse model was established by caecal ligation and puncture and intravenously injected with ADSC-EVs. Mouse kidney macrophages were cultured with LPS, cultured with EVs while transfecting with oe-ADAM17 or si-MerTK, then incubated with Jurkat cells. Mouse serum urea and creatinine, and KIM-1, efferocytosis- and apoptosis-related protein, inflammatory factor, cytokine, and soluble MerTK (sMerTK) levels were determined using colorimetric assay, immunohistochemistry, Western blot, and ELISA. Renal tubular injury, TEC apoptosis, macrophage efferocytosis, and M1/M2 polarization levels were assessed via HE staining, TUNEL staining, immunofluorescence, and flow cytometry, respectively. In vivo validation experiments were conducted. RESULTS: S-AKI mice displayed elevated levels of serum urea, creatinine, KIM-1, pro-inflammatory factors, pro-apoptotic proteins and ADAM17 protein, decreased anti-apoptotic protein and MerTK protein levels, and diminished M2 polarization. ADSC-EVs down-regulated ADAM17 and sMerTK, and increased cell membrane MerTK, macrophage recognition of apoptotic cells and efferocytosis, and M2 polarization in renal tissues of S-AKI mice and LPS-induced mouse renal macrophages, indicating that ADSC-EVs regulated ADAM17/MerTK-mediated macrophage efferocytosis and promoted M2 polarization. MerTK silencing partially reversed ADSC-EVs-regulated LPS-induced mouse renal macrophage efferocytosis and M2 polarization. In vivo, ADAM17 upregulation partly averted ADSC-EVs-regulated post-S-AKI TEC apoptosis in mouse renal tissues. CONCLUSION: ADSC-EVs down-regulated sMerTK level and up-regulated macrophage membrane MerTK protein level by modulating ADAM17 to promote macrophage efferocytosis and ameliorate post-S-AKI TEC apoptosis and inflammation.

Our previous studies have demonstrated that neutrophils play a key role in septic organ injury partly through the excessive formation of neutrophil extracellular traps (NETs) and that exosomes participate in the regulation of NET formation during sepsis. Therefore, this study aimed to determine whether neutrophil-derived exosomes promote the formation of NETs and induce multiple organ dysfunction during sepsis. Initially, polymorphonuclear neutrophil (PMN)-derived exosomes following in vitro stimulation with PBS or LPS (1 μg/mL) for 6 h. In vivo, PMN-derived exosomes were intravenously administered to wild-type C57BL/6 mice. Then, histopathological injury and NET formation in multiple organs were evaluated. In vitro, PMN-derived exosomes were cocultured with PMNs freshly isolated from healthy volunteers, and subsequently, NET formation and activation of associated molecular pathways were detected. Administration of LPS-stimulated PMN-derived exosomes in mice significantly enhanced NET formation, resulting in multi-organ inflammation and tissue injury. In vitro coculture experiments also demonstrated that exosomes from LPS-stimulated PMNs promote ROS-dependent NET formation. Proteomic analysis revealed enrichment of matrix metalloproteinase 9 (MMP9) expression in exosomes from LPS-stimulated PMNs, and further mechanistic investigations showed that exosomal MMP9 induced NET formation through the p38 MAPK pathway. Clinical data analysis suggests a close association between sepsis severity/prognosis and plasma-derived exosomal MMP9 expression levels. PMN-derived exosomes facilitate the excessive formation of NETs in sepsis, leading to the subsequent development of multiple organ dysfunction. This discovery reveals a novel role for PMN-derived exosomes in the pathogenesis of sepsis-related multiple organ dysfunction and suggests their potential as prognostic indicators for this condition.