Lactate promotes macrophage HMGB1 lactylation, acetylation, and exosomal release in polymicrobial sepsis

High circulating levels of lactate and high mobility group box-1 (HMGB1) are associated with the severity and mortality of sepsis. However, it is unclear whether lactate could promote HMGB1 release during sepsis. The present study demonstrated a novel role of lactate in HMGB1 lactylation and acetylation in macrophages during polymicrobial sepsis. We found that macrophages can uptake extracellular lactate via monocarboxylate transporters (MCTs) to promote HMGB1 lactylation via a p300/CBP-dependent mechanism. We also observed that lactate stimulates HMGB1 acetylation by Hippo/YAP-mediated suppression of deacetylase SIRT1 and β-arrestin2-mediated recruitment of acetylases p300/CBP to the nucleus via G protein-coupled receptor 81 (GPR81). The lactylated/acetylated HMGB1 is released from macrophages via exosome secretion which increases endothelium permeability. In vivo reduction of lactate production and/or inhibition of GPR81-mediated signaling decreases circulating exosomal HMGB1 levels and improves survival outcome in polymicrobial sepsis. Our results provide the basis for targeting lactate/lactate-associated signaling to combat sepsis.

ID: 120: REGULATION OF ENDOTHELIAL BARRIER PERMEABILITY BY PHOSPHOLIPASE D2

Pulmonary edema is a hallmark of several diseases including acute respiratory distress syndrome (ARDS) and is characterized by the disruption of the pulmonary endothelial barrier at its early stage. Maintaining the integrity of the adherens junctions (AJs) by stabilizing VE-Cadherin (VEC) at the cell membrane after injury could potentially be important to minimize endothelial barrier disruption. Since Phospholipase D (PLD) and its catalytic product, phosphatidic acid (PA), has been shown to be critical in membrane trafficking and in recycling of a number of cell surface receptors, we hypothesized that PLD/PA pathway accelerates the rate of VEC recycling to the lamellipodia to reassemble the AJs. We demonstrate, by measuring the trans endothelial resistance of human lung microvascular endothelial cells (HLMVECs), that inhibiting PLD2-dependent PA production increases the endothelium permeability in response to thrombin. Furthermore, immunostaining shows that the uniform redistribution of VEC to the AJs post thrombin insult is compromised when PLD-dependent PA production is inhibited, and resulted in the appearance of eminent intercellular gaps. Also, PLD2 inhibition prevented the HLMVECs from fully spreading after thrombin stimulation while the protrusive activity remained unaffected, suggesting that PLD2 is not required by HLMVECs to send protrusions, but is critical for the adherence of the protrusions. LPS-induced lung injury was more severe in PLD2 knockout mice compared to WT in an in vivo ARDS model. These observations suggest that PLD/PA signaling plays an important role in resealing of endothelial gaps post LPS-induced lung injury and could potentially be therapeutically utilized to enhance post-injury endothelium recovery.

Platelets mediate increased endothelium permeability in dengue through NLRP3-inflammasome activation

Key Points Dengue infection triggers functional inflammasome assembly in platelets. Platelets may contribute to increased vascular permeability in dengue virus infection by synthesis and release of IL-1β.

Injection of Staphylococcus aureus EDIN by the Bacillus anthracis Protective Antigen Machinery Induces Vascular Permeability

ABSTRACT Systemic injection of Bacillus anthracis lethal toxin (LT) produces vascular leakage and animal death. Recent studies suggest that LT triggers direct endothelial cell cytotoxicity that is responsible for the vascular leakage. LT is composed of heptamers of protective antigen (PA), which drives the endocytosis and translocation into host cells of the lethal factor (LF), a mitogen-activated protein kinase kinase protease. Here we investigated the consequences of injection of an endothelium-permeabilizing factor using LT as a “molecular syringe.” To this end, we generated the chimeric factor LE, corresponding to the PA-binding domain of LF (LF1-254) fused to EDIN exoenzyme. EDIN ADP ribosylates RhoA, leading to actin cable disruption and formation of transcellular tunnels in endothelial cells. We report that systemic injection of LET (LE plus PA) triggers a PA-dependent increase in the pulmonary endothelium permeability. We also report that native LT induces a progressive loss of endothelium barrier function. We established that there is a direct correlation between the extent of endothelium permeability induced by LT and the cytotoxic activity of LT. This suggests new ways to design therapeutic drugs against anthrax directed toward vascular permeability.