Daily Sepsis Research Analysis
Three impactful studies advance sepsis science across mechanism and diagnostics: a JCI Insight study uncovers an ADAP–BTK–mTOR–STAT3 axis that induces PDPNhi macrophages to protect against sepsis; a Molecular Medicine study shows plasma extracellular vesicle miR-223-3p primes alveolar macrophages for autophagy/ferroptosis and predicts septic ARDS; and a Critical Care meta-analysis finds only moderate agreement between mNGS and traditional tests, with better concordance in sterile samples.
Summary
Three impactful studies advance sepsis science across mechanism and diagnostics: a JCI Insight study uncovers an ADAP–BTK–mTOR–STAT3 axis that induces PDPNhi macrophages to protect against sepsis; a Molecular Medicine study shows plasma extracellular vesicle miR-223-3p primes alveolar macrophages for autophagy/ferroptosis and predicts septic ARDS; and a Critical Care meta-analysis finds only moderate agreement between mNGS and traditional tests, with better concordance in sterile samples.
Research Themes
- Innate immune reprogramming and macrophage subsets in sepsis
- Extracellular vesicle biomarkers and ferroptosis in septic lung injury
- Clinical integration and limitations of metagenomic sequencing for pathogen detection
Selected Articles
1. Molecular control of PDPNhi macrophage subset induction by ADAP as a host defense in sepsis.
This mechanistic study shows that an ADAP–BTK–mTOR–STAT3 signaling axis drives TLR4-induced PDPN upregulation, generating an M2-like PDPNhi macrophage subset with enhanced phagocytosis that protects against sepsis. Pharmacologic STAT3 activation expanded PDPNhi macrophages and reduced sepsis severity in mice.
Impact: Reveals a novel, targetable pathway for reprogramming macrophage function in sepsis with in vivo efficacy via STAT3 agonism. It reframes PDPNhi macrophages as protective effectors rather than mere markers.
Clinical Implications: Suggests immunomodulatory strategies (e.g., STAT3 agonists or BTK/mTOR tuning) to enhance protective PDPNhi macrophages in sepsis. Human validation is needed before translation.
Key Findings
- ADAP-deficient macrophages failed to upregulate PDPN after TLR4 stimulation; reconstitution of ADAP rescued PDPN induction.
- A PDPNhi peritoneal macrophage subset with M2-like phenotype and enhanced phagocytosis formed in WT but not in ADAP-deficient septic mice; blocking this subset worsened sepsis.
- BTK-mediated phosphorylation of ADAP (Y571) with mTOR converged on STAT3 activation to transactivate the PDPN promoter.
- STAT3 agonism expanded PDPNhi macrophages and alleviated sepsis severity in vivo.
Methodological Strengths
- Integrated in vitro and in vivo mechanistic dissection with genetic deficiency and rescue experiments
- Pathway mapping from BTK–ADAP phosphorylation to mTOR–STAT3 transcriptional control with functional outcomes in sepsis models
Limitations
- Preclinical mouse-centric work without human validation of PDPNhi macrophages
- Potential off-target effects and safety of STAT3 agonists not addressed
Future Directions: Validate PDPNhi macrophages and ADAP–STAT3 signaling in human sepsis; test clinically tractable modulators (e.g., BTK inhibitors/agonists, STAT3 modulators) and delineate tissue-specific roles.
Induction of podoplanin (PDPN) expression is a critical response of macrophages to LPS stimulation or bacterial infection in sepsis, but how this key process of TLR4-stimulated PDPN upregulation is regulated and the effect of PDPN expression on macrophage function remain elusive. Here, we determined how this process is regulated in vitro and in vivo. PDPN failed to be upregulated in TLR4-stimulated macrophages deficient in adhesion and degranulation-promoting adapter protein (ADAP), which could be rescued by the reconstitution of ADAP. A distinct PDPNhi peritoneal macrophage (PM) subset, which exhibited an M2-like phenotype and enhanced phagocytic activity, was generated in WT but not in ADAP-deficient septic mice. The blockade of PDPNhi PMs mimicked the effect of ADAP deficiency, which exacerbated sepsis. Mechanistically, Bruton's tyrosine kinase-mediated (BTK-mediated) tyrosine phosphorylation of ADAP at Y571 worked together with mTOR to converge on STAT3 activation for the transactivation of the PDPN promoter. Moreover, agonist activation of STAT3 profoundly potentiated the PDPNhi PM subset generation and alleviated sepsis severity in mice. Together, our findings reveal a mechanism whereby ADAP resets macrophage function by controlling the TLR4-induced upregulation of PDPN as a host innate immune defense during sepsis.
2. Plasma-derived extracellular vesicles prime alveolar macrophages for autophagy and ferroptosis in sepsis-induced acute lung injury.
Plasma EV profiling identified a biomarker panel linked to sepsis severity and prognosis, with LCN2, miR-122-5p, and miR-223-3p independently predicting septic ARDS. Mechanistically, EV miR-223-3p activates Hippo signaling via MEF2C in alveolar macrophages, driving inflammation, autophagy, and ferroptosis; its inhibition attenuated lung injury in vivo.
Impact: Links circulating EV cargo to both risk stratification and mechanistic injury pathways in septic lung injury, offering actionable biomarkers and a therapeutic target (miR-223-3p).
Clinical Implications: EV miR-223-3p and LCN2 could support early identification of patients at risk for septic ARDS and guide monitoring. Therapeutic inhibition of miR-223-3p warrants translational evaluation.
Key Findings
- EV-based biomarker panel (miR-122-5p, miR-125b-5p, miR-223-3p, OLFM4, LCN2) correlated with sepsis severity/prognosis.
- LCN2, miR-122-5p, and miR-223-3p independently predicted septic ARDS.
- EV miR-223-3p promoted inflammation, autophagy, and ferroptosis in alveolar macrophages via MEF2C/Hippo signaling.
- Inhibition of miR-223-3p reduced lung inflammation, AM death, and histologic injury in vivo.
Methodological Strengths
- Combined EV multi-omic profiling with in vitro coculture and in vivo functional inhibition
- Identification of a mechanistic axis (miR-223-3p–MEF2C–Hippo) linked to clinically relevant ARDS outcomes
Limitations
- Clinical cohort size/details not fully specified; external validation cohorts not described
- LPS-based models may not recapitulate polymicrobial sepsis complexity
Future Directions: Prospectively validate EV biomarker thresholds for ARDS prediction and evaluate miR-223-3p-targeted therapeutics in clinically relevant sepsis models (e.g., CLP).
Sepsis-induced acute respiratory distress syndrome (ARDS) is a severe complication of sepsis and the leading cause of mortality. Although the role of alveolar macrophages (AMs) in stabilizing pulmonary homeostasis is well established, the effects of circulating extracellular vesicles (EVs) on AMs remain largely unknown. In this study, an investigation was conducted to map the miRNA and protein expression profiles of EVs derived from septic plasma. Notably, EV-based panels (miR-122-5p, miR-125b-5p, miR-223-3p, OLFM4, and LCN2) have been found to be associated with the severity or prognosis of sepsis, with promising AUC values. Moreover, the levels of LCN2, miR-122-5p, and miR-223-3p were identified as independent predictors of septic ARDS. The in vitro coculture results revealed that the effects of LPS-EVs from the plasma of sepsis-induced acute lung injury (ALI), which carry pro-inflammatory EVs, were partly mediated by miR-223-3p, as evidenced by the promotion of inflammation, autophagy and ferroptosis in AMs. Mechanistically, the upregulation of miR-223-3p in LPS-EVs triggers autophagy and ferroptosis in AMs by activating Hippo signaling via the targeting of MEF2C. In vivo, the inhibition of miR-223-3p effectively mitigated LPS-EV-induced inflammation and AM death in the lungs, as well as histological lesions. Overall, miR-223-3p in LPS-EVs contributes to sepsis-induced ALI by priming AMs for autophagy and ferroptosis through the MEF2C/Hippo signaling pathway. These findings suggest a novel mechanism of plasma-AM interaction in sepsis-induced ALI, offering a plausible strategy for assessing septic progression and treating lung injury.
3. Consistency between metagenomic next-generation sequencing versus traditional microbiological tests for infective disease: systemic review and meta-analysis.
Across 27 studies (n=4112), mNGS showed only moderate agreement with traditional tests (pooled kappa ~0.32), with better concordance in sterile samples (e.g., CSF) and lower in immunocompromised patients. mNGS had high positive percent agreement but modest negative agreement, supporting its complementary use rather than replacement.
Impact: Provides a quantitative synthesis defining when and how mNGS aligns with traditional diagnostics in sepsis workups, guiding specimen selection and interpretation.
Clinical Implications: Prioritize sterile-site sampling for mNGS, interpret results cautiously in immunocompromised hosts, and integrate mNGS with culture to improve pathogen detection and stewardship.
Key Findings
- Pooled kappa consistency between mNGS and traditional tests was 0.319 (moderate agreement).
- Cerebrospinal fluid had the highest agreement (kappa 0.500), while immunocompromised patients had lower agreement (kappa 0.294).
- mNGS showed high positive percent agreement (83.63%) but lower negative percent agreement (54.59%) versus traditional testing.
Methodological Strengths
- Systematic review and meta-analysis with QUADAS-2 quality assessment
- Subgroup analyses by specimen type and immune status
Limitations
- Heterogeneity in study designs, reference standards, and analytic pipelines
- Potential publication bias and limited data on clinical impact/cost-effectiveness
Future Directions: Conduct prospective studies to assess clinical outcomes, turnaround time, and cost-effectiveness of mNGS-integrated diagnostic pathways in sepsis.
BACKGROUND: Pathogen identification is essential in sepsis and septic shock. Metagenomic next-generation sequencing (mNGS) is a novel pathogen detection method with several advantages over traditional tests. However, the consistency between mNGS and traditional pathogen tests requires further investigation. OBJECTIVES: We aimed to assess the consistency between mNGS and traditional pathogen tests and to identify the factors influencing this consistency. METHODS: This systematic review and meta-analysis involved a comprehensive search of mNGS and traditional pathogen tests in PubMed, Embase, Scopus, Web of Science, and the Cochrane Library. Data from included studies were extracted, and kappa consistency between mNGS and traditional tests was calculated. Study quality was evaluated using the QUADAS-2 tool. RESULTS: The search identified 415 studies, of which 27 were included in the analysis, involving 4112 individuals. Meta-analysis showed a pooled consistency of 0.319 ± 0.013 (p < 0.001), indicating a moderate relationship. In terms of sample type, cerebrospinal fluid showed the highest pooled kappa consistency at 0.500 ± 0.029 (p < 0.001). Immunocompromised patients had a lower pooled kappa consistency of 0.294 ± 0.014 (p < 0.001) compared to 0.321 ± 0.028 (p < 0.001) in immunocompetent patients. Positive percent agreement of mNGS was 83.63% over traditional microbiological test, and negative percent agreement was 54.59%. CONCLUSION: This review demonstrates a moderate relationship between mNGS and traditional pathogen tests, indicating a complex relationship between these two methods. Sterile samples show higher consistency than non-sterile samples. Immune function deficiency may reduce the consistency between mNGS and traditional tests. Further research is needed on the use of mNGS in sepsis and septic shock.