Plasma Proteome Signature of Sepsis: a Functionally Connected Protein Network

Abstract

Sepsis is an extreme host response to infection that leads to loss of organ function and cardiovascular integrity. Mortality from sepsis is on the rise. Despite more than three decades of research and clinical trials, specific diagnostic and therapeutic strategies for sepsis are still absent. The use of LFQ‐ and TMT‐based quantitative proteomics is reported here to study the plasma proteome in five mouse models of sepsis. A knowledge‐based interpretation of the data reveals a protein network with extensive connectivity through documented functional or physical interactions. The individual proteins in the network all have a documented role in sepsis and are known to be extracellular. The changes in protein abundance observed in the mouse models of sepsis have for the most part the same directionality (increased or decreased abundance) as reported in the literature for human sepsis. This network has been named the Plasma Proteome Signature of Sepsis (PPSS). The PPSS is a quantifiable molecular readout that can supplant the current symptom‐based approach used to diagnose sepsis. This type of molecular interpretation of sepsis, its progression, and its response to therapeutic intervention are an important step in advancing our understanding of sepsis, and for discovering and evaluating new therapeutic strategies.

Proteomic atlas of organ vasculopathies triggered by Staphylococcus aureus sepsis

“…Briefly, wildtype C57BL/6J mice were intravenously infected through the retroorbital route with 5 × 10 7 colony-forming units (cfu) of MRSA, a model that induces lethality within 48 h post-infection 27 , or with PBS as a control. Since changes in the vascular compartments are expected to precede organ damage and lethality, we focused on the early pre-mortality stages of the disease 24 h post-infection 28 .…”

“…However, we do not know if some of the proteome alterations reported in this study can also be detected in plasma. Plasma proteomics has been widely applied to identify fluid biomarkers of sepsis 28,45,46 . One major challenge with these analyses though is the broad dynamic range of plasma proteins, which exceeds 10 orders of magnitude 47 .…”

Time-dependent changes to sepsis-specific networks in the plasma proteome are mechanistic readouts of sepsis progression

“…Proteomics samples were prepared as described previously [15], with the exception of the depletion step, which we have optimized as described below. Albumin and Immunoglobulin depletion were performed by precipitating 10 μL of plasma with pre-chilled acetone (20 °C), air-dried and incubated for an hour at 4 °C with a mix of antibodies specific to Albumin (SigmaAldrich LSKMAGL10) and IgA/G (ThermoFisherScientific 88802), crosslinked to magnetic beads.…”

“…Each fraction was in turn separated at low pH in a high resolution C8 reverse phase and ionized for MS/MS fragmentation and MS determination. The separation and data collection methods were as described previously [15]. Data Protein identification assignments and TMT ratio calculations were performed using the latest version of MaxQuant (1.6.8) [16].…”

“…The motivation of this study rests on the hypothesis that measurable changes to sepsis-specific protein networks in the plasma proteome will help track sepsis progression and provide a mechanistic framework of the events that trigger the transition from early to late sepsis. To test this hypothesis, we have assessed abundance changes to the mouse plasma proteome at six time points, upon infection with Salmonella enterica serovar Typhimurium (ST), a murine model of sepsis optimized in our laboratory [14], and which we have recently used to integrate the Plasma Protein Signature of Sepsis (PPSS), a network of 84 secreted proteins that have a known role in human sepsis [15]. Our results show a two-step reconfiguration of the PPSS network.…”