Lactate-Driven HMGB1 Modification and Release in Sepsis

Study Background and Research Question

Sepsis is a life-threatening syndrome characterized by dysregulated inflammatory responses and organ dysfunction. Among its clinical hallmarks, elevated serum lactate and high mobility group box-1 (HMGB1) protein levels are closely associated with disease severity and mortality. While HMGB1 is a well-known damage-associated molecular pattern (DAMP) protein released during inflammation, the mechanistic link between lactate accumulation and HMGB1 release has remained unclear. The study by Yang et al. (Cell Death & Differentiation, 2022) addresses whether lactate actively promotes HMGB1 post-translational modifications (PTMs) and its export from macrophages during polymicrobial sepsis.

Key Innovation from the Reference Study

The principal innovation of the reference study lies in the identification of lactate as a direct modulator of HMGB1 function in macrophages through two distinct PTMs: lactylation and acetylation. This dual modification not only facilitates HMGB1 translocation from the nucleus to the cytoplasm but also drives its release via exosomes. The work elucidates previously uncharacterized signaling axes—including p300/CBP-dependent lactylation and Hippo/YAP-GPR81-mediated acetylation suppression—establishing a molecular connection between metabolic dysregulation and the propagation of inflammatory signals in sepsis.

Methods and Experimental Design Insights

The authors combined in vivo murine models of polymicrobial sepsis (using cecal ligation and puncture, CLP), genetic approaches, and a suite of cellular and molecular assays to dissect the role of lactate in HMGB1 regulation. Key elements of the design include:

• Use of wild-type and macrophage-specific YAP knockout mice, generated via the Cre/LoxP system, to probe the Hippo pathway's involvement in acetylation.
• Measurement of serum lactate and exosomal HMGB1 levels in septic mice, establishing their correlation.
• Pharmacological inhibition of lactate production and GPR81-mediated signaling, assessing effects on HMGB1 export and animal survival.
• In vitro treatment of bone marrow-derived macrophages (BMDMs) with exogenous lactate, followed by Western blotting and mass spectrometry to track HMGB1 PTMs.
• Application of inhibitors for p300/CBP (acetyltransferases) and SIRT1 (deacetylase) to dissect modification pathways.
• Endothelial permeability assays to evaluate the impact of macrophage-derived exosomal HMGB1.

Throughout, care was taken to preserve labile PTMs by using appropriate protein extraction protocols, often entailing the use of broad-spectrum protease and phosphatase inhibitor cocktails to prevent artifactual loss or dephosphorylation during lysis—a best practice highlighted in advanced workflows (see internal resource).

Core Findings and Why They Matter

The study's findings establish lactate not merely as a metabolic byproduct but as an active participant in sepsis pathology by modulating HMGB1:

• Lactate entry via MCTs enables HMGB1 lactylation in macrophages through a p300/CBP-dependent mechanism, promoting its nuclear export.
• Lactate also enhances HMGB1 acetylation by suppressing SIRT1 (a deacetylase) via the Hippo/YAP pathway and facilitating nuclear recruitment of p300/CBP through GPR81-β-arrestin2 signaling.
• Lactylated and acetylated HMGB1 is released from macrophages in exosomes, which in turn increase endothelial permeability—an event linked to vascular leakage and organ dysfunction in sepsis (reference study).
• Pharmacological inhibition of lactate production or GPR81 signaling reduces exosomal HMGB1 levels and improves survival in septic mice, highlighting these pathways as actionable therapeutic targets.

By clarifying how metabolic signals like lactate orchestrate inflammatory protein release, these discoveries advance our understanding of sepsis progression and open new avenues for intervention.

Comparison with Existing Internal Articles

This reference study extends themes found in leading internal resources that emphasize the importance of preserving PTMs and protein integrity during sample preparation. For instance, the resource "Preserving HMGB1 Signaling: Strategic Protease & Phosphatase Inhibition" highlights the vulnerability of inflammatory mediators like HMGB1 to degradation and dephosphorylation during extraction—issues that can compromise detection of labile modifications such as acetylation and lactylation. Similarly, "Unraveling Protein Homeostasis" discusses the role of EDTA-free broad-spectrum protease and phosphatase inhibitor cocktails in safeguarding PTMs across cell signaling and immunometabolic research. The current study underscores these points by demonstrating that accurate measurement of HMGB1 PTMs is central to elucidating disease mechanisms, and such fidelity relies on optimal sample handling.

Limitations and Transferability

While the study by Yang et al. provides compelling mechanistic insight, several limitations should be considered:

• Species specificity: Findings are primarily based on murine models and mouse macrophages; extrapolation to human pathophysiology requires further validation.
• Disease model scope: The polymicrobial sepsis model (CLP) recapitulates aspects of human sepsis but may not capture all clinical variability.
• PTM detection sensitivity: Even with advanced protocols, detection of transient modifications like lactylation can be technically challenging and may be influenced by sample handling (see workflow strategies in internal guide).
• Therapeutic translation: While targeting lactate-related signaling is promising, the safety and efficacy of such approaches in human sepsis remain to be established.

Despite these caveats, the core mechanistic pathways identified are likely to be relevant across diverse inflammatory and metabolic contexts, provided that technical precautions are observed to preserve protein and PTM integrity.

Protocol Parameters

• Exogenous lactate treatment in vitro: 10–20 mM sodium lactate for 12–24 hours to stimulate HMGB1 modification in macrophage cultures.
• Use of protease and phosphatase inhibitor cocktail: Add 1X working concentration (from 100X stock) to lysis buffer immediately prior to cell or tissue extraction to preserve HMGB1 PTMs.
• CLP model induction: Perform cecal ligation and puncture in anesthetized mice, followed by post-operative monitoring for 24–72 hours.
• Pharmacological inhibitors: Apply GPR81 antagonists or glycolytic inhibitors (e.g., 2-deoxyglucose) at published doses, with timing coordinated relative to sepsis induction based on experimental aims.
• Exosome isolation: Collect serum or culture supernatants, use ultracentrifugation or validated kits, and store samples at -80°C for subsequent HMGB1 measurement.

Research Support Resources

To ensure accurate assessment of HMGB1 and its PTMs in inflammatory or sepsis models, researchers are encouraged to employ robust sample preservation strategies. The Protease and Phosphatase Inhibitor Cocktail (EDTA Free, 100X in ddH2O) (SKU K4006) offers broad-spectrum protection against proteolytic and phosphatase activity, supporting the detection of labile modifications such as those described in this study. Its EDTA-free formulation is especially suitable where metal-dependent enzyme activity or downstream assays are a concern. This approach aligns with best practices outlined in recent internal and external resources, helping to ensure reproducible, high-fidelity results in cell signaling and immunometabolic research workflows.