Lactate-Driven HMGB1 Modification and Exosomal Release in Sepsis: Mechanistic Insights and Research Implications

Study Background and Research Question

Sepsis remains a critical clinical challenge, characterized by uncontrolled inflammatory responses and organ dysfunction. Elevated serum lactate is a well-established predictor of sepsis severity and mortality, but its functional role in disease progression is not fully elucidated. High mobility group box-1 (HMGB1), a nuclear protein released by activated macrophages, orchestrates potent inflammatory signaling and is similarly correlated with poor sepsis outcomes. The central question addressed by Yang et al. (reference study) is whether lactate actively drives HMGB1 post-translational modification and release from macrophages, thereby contributing to the propagation of inflammatory damage during polymicrobial sepsis.

Key Innovation from the Reference Study

The study by Yang et al. delivers a conceptual breakthrough by demonstrating that extracellular lactate is not merely a biomarker but a direct regulator of macrophage function in sepsis. Specifically, the authors identify two distinct lactate-induced post-translational modifications—lactylation and acetylation—on HMGB1, both of which promote its exosomal release. These mechanistic insights redefine the relationship between metabolic dysfunction and immune signaling in the context of acute systemic inflammation.

Methods and Experimental Design Insights

The investigation integrates in vivo and in vitro models to dissect the molecular interplay between lactate and HMGB1 in sepsis:

• Animal Models: Wild-type and genetically engineered mice (macrophage-specific YAP knockout via Cre/LoxP recombination) were subjected to polymicrobial sepsis, enabling assessment of specific signaling pathways.
• Macrophage Isolation and Stimulation: Primary macrophages were isolated and exposed to exogenous lactate to evaluate HMGB1 modification and release dynamics.
• Pharmacological Inhibition: Inhibitors targeting lactate production, monocarboxylate transporters (MCTs), G protein-coupled receptor 81 (GPR81), and acetyltransferases were used to probe pathway specificity.
• Molecular and Cellular Readouts: Post-translational modifications of HMGB1 (lactylation and acetylation) were determined via immunoprecipitation and immunoblotting. Exosomal HMGB1 levels were quantified, and endothelial permeability assays assessed functional impact.
• Correlative Analyses: Serum lactate and exosomal HMGB1 levels were correlated in septic mice to establish physiologic relevance.

This multi-layered approach enabled the authors to map out discrete signaling circuits linking extracellular lactate to HMGB1 modification and inflammatory sequelae.

Core Findings and Why They Matter

• Lactate Uptake and HMGB1 Modification: Macrophages internalize extracellular lactate via MCTs, which fuels HMGB1 lactylation in a p300/CBP-dependent manner. Independently, lactate also induces HMGB1 acetylation through two synergistic mechanisms: (1) Hippo/YAP-mediated suppression of the deacetylase SIRT1, and (2) β-arrestin2-mediated nuclear recruitment of p300/CBP acetyltransferases via GPR81 activation.
• Exosomal Release Mechanism: These modifications facilitate HMGB1 translocation to the cytoplasm and subsequent packaging into exosomes, which are then secreted by macrophages. Functionally, exosome-associated HMGB1 significantly increases endothelial cell permeability, linking this process to microvascular dysfunction in sepsis.
• Therapeutic Targeting Potential: In vivo, pharmacologic reduction of lactate production or inhibition of GPR81 signaling led to decreased circulating exosomal HMGB1 and improved survival in septic mice (reference), underscoring the translational relevance of these pathways.

Together, these results substantiate a direct causal axis between metabolic stress (lactate accumulation), post-translational modification of key inflammatory mediators, and vascular injury in sepsis. This mechanistic clarity opens new avenues for targeted intervention in inflammatory signaling pathway research.

Comparison with Existing Internal Articles

While the reference study centers on metabolic regulation of HMGB1 in sepsis, previous internal resources such as Bay 11-7821 (BAY 11-7082): Unveiling New Frontiers in NF-κB Inhibition and Unraveling NF-κB Pathway Inhibition focus on the molecular dissection of inflammatory signaling using small-molecule inhibitors. Notably, these articles highlight Bay 11-7821 as a selective IKK and NF-κB pathway inhibitor, a tool instrumental for probing apoptosis regulation and inflammatory signaling pathways in various disease models, including cancer and immunology. The current lactate-HMGB1 study complements this body of work by elucidating upstream metabolic triggers of inflammatory mediator release, which can be dissected further using pathway inhibitors like Bay 11-7821 in future research.

Other internal resources, such as Precision Interrogation of NF-κB-Driven Inflammation and Applied Workflows in Inflammatory Signaling Research, provide additional protocol guidance for integrating NF-κB pathway inhibitors into apoptosis regulation studies and inflammatory disease models. These workflows are directly relevant for researchers exploring the intersection of metabolic and signaling control in immune cell activation and tissue injury.

Limitations and Transferability

Despite its significant mechanistic advances, this study has limitations that warrant consideration. The primary findings are derived from murine models of polymicrobial sepsis and in vitro macrophage assays, which may not fully recapitulate the complexity of human sepsis pathophysiology. The specificity of lactylation and acetylation pathways for HMGB1, versus other nuclear proteins, remains to be clarified. Additionally, while pharmacological inhibition of lactate signaling showed benefit in mice, the translational potential and safety of such approaches in clinical settings require further validation.

Transferability to other inflammatory or cancer contexts is promising but should be approached cautiously. The mechanistic axis linking metabolic cues, post-translational HMGB1 modification, and exosomal release may operate differently across cell types or disease states, necessitating tailored experimental designs.

Protocol Parameters

• Lactate stimulation: In vitro, apply extracellular lactate to macrophages at physiologically relevant concentrations to assess HMGB1 modification and exosomal release.
• MCT inhibition: Use validated MCT inhibitors to block lactate uptake and examine downstream effects on HMGB1 lactylation.
• GPR81 pathway studies: Apply specific GPR81 antagonists to distinguish receptor-mediated acetylation mechanisms.
• p300/CBP modulation: Utilize pharmacological or genetic tools (e.g., siRNA) to inhibit p300/CBP and dissect their contribution to both lactylation and acetylation events.
• Endothelial permeability assays: Collect exosomes from stimulated macrophages and apply to endothelial cell monolayers to measure barrier integrity.
• In vivo intervention: For mice, co-administer lactate pathway inhibitors before and after sepsis induction to evaluate effects on survival and circulating exosomal HMGB1.

Research Support Resources

To enable the targeted interrogation of inflammatory signaling pathways—such as those linking metabolic stress to HMGB1 release—researchers can integrate pathway-selective inhibitors into their experimental workflows. Bay 11-7821 (BAY 11-7082) (SKU A4210, APExBIO) is a selective IKK inhibitor with established efficacy for blocking NF-κB activation and downstream inflammatory mediator expression. This compound is widely used in apoptosis regulation study, B-cell lymphoma research, and advanced inflammatory signaling pathway research, supporting both cell-based and in vivo models. For detailed workflows and mechanistic context, refer to internal articles on Bay 11-7821’s application in inflammatory and cancer research models.