The MTOC is “speck”-tacular: Inflammasome complexes are formed in response to pathogen-associated molecules. They initiate both the maturation of inflammatory cytokines and pyroptosis, a type of programmed cell death. One notable feature for inflammasome activation is the formation of a single supramolecular punctum (or “speck”) in each affected cell. However, the location and mechanism of speck formation is poorly understood. Magupalli et al. report that for NLRP3- and pyrin-mediated inflammasomes, their assembly and downstream functions occur at the microtubule-organizing center (MTOC). This process requires the dynein adaptor HDAC6, which is also a central player in aggresome formation and autophagosomal degradation at the MTOC. This work links several important cellular processes and provides clues for how inflammasomes are efficiently regulated. Science , this issue p. eaas8995

Sepsis results in millions of deaths every year, with acute lung injury (ALI) being one of the leading causes of mortality in septic patients. As neutrophil extracellular traps (NETs) are abundant in sepsis, neutralizing components of NETs may be a useful strategy to improve outcomes of sepsis. Citrullinated histone H3 (CitH3) has been recently shown to be involved in the NET formation. In this study, we demonstrate that CitH3 damages human umbilical vein endothelial cells (HUVECs) and potentiates NET formation through a positive feedback mechanism. We developed a novel CitH3 monoclonal antibody to target peptidylarginine deiminase (PAD) 2 and PAD 4 generated CitH3. In a mouse model of lethal lipopolysaccharide (LPS) induced shock, neutralizing CitH3 with the newly developed anti-CitH3 monoclonal antibody attenuates inflammatory responses, ameliorates ALI, and improves survival. Our study suggests that effectively blocking circulating CitH3 might be a potential therapeutic method for the treatment of endotoxemia.

Current biomarkers for sepsis are limited by their non-specificity, short half-life, and insensitive response to therapy. Recently, we have demonstrated that citrullinated histone H3(CitH3) is released into the blood from neutrophil extracellular traps(NETs) in response to severe infection, and CitH3 may be a potential biomarker for sepsis. In the present study, we found that NET components were released in mouse models of both lipopolysaccharide(LPS)-induced shock (LPSS) and hemorrhagic shock (HS). To further quantify CitH3 in the NETs, we established a CitH3 specific enzyme-linked immunosorbent assay. Circulating CitH3 was found to be elevated only in LPSS but not in HS. Importantly, blood CitH3 was detected 30 minutes after LPS insult, and remained elevated for 24 hours (period of the highest mortality). Treatment of endotoxic mice with YW3-56, a peptidylarginine deiminase-2/4 inhibitor, significantly diminished levels of CitH3 in the blood. Interleukin-1β did not respond to LPS early, and interleukin-1β and interleukin-6 fluctuated although they responded to treatment. Procalcitonin reacted to LPS insult late. Compared to CitH3, these biomarkers were non-specifically induced in LPSS and HS. Collectively, our results demonstrate that YW3-56 protects animals from LPSS, and CitH3 is a reliable biomarker due to its early appearance, specificity, duration, and response to therapeutic intervention.

Purpose: Microbial infection stimulates neutrophil/macrophage/monocyte extracellular trap formation, which leads to the release of citrullinated histone H3 (CitH3) catalyzed by peptidylarginine deiminase (PAD) 2 and 4. Understanding these molecular mechanisms in the pathogenesis of septic shock will be an important next step for developing novel diagnostic and treatment modalities. We sought to determine the expression of CitH3 in patients with septic shock, and to correlate CitH3 levels with PAD2/PAD4 and clinically relevant outcomes. Methods: Levels of CitH3 were measured in serum samples of 160 critically ill patients with septic and non-septic shock, and healthy volunteers. Analyses of clinical and laboratory characteristics of patients were conducted. Results: Levels of circulating CitH3 at enrollment were significantly increased in septic shock patients (n = 102) compared to patients hospitalized with non-infectious shock (NIC) (n = 32, p < 0.0001). The area under the curve (95% CI) for distinguishing septic shock from NIC using CitH3 was 0.76 (0.65–0.86). CitH3 was positively correlated with PAD2 and PAD4 concentrations and Sequential Organ Failure Assessment Scores [total score (r = 0.36, p < 0.0001)]. The serum levels of CitH3 at 24 h (p < 0.01) and 48 h (p < 0.05) were significantly higher in the septic patients that did not survive. Conclusion: CitH3 is increased in patients with septic shock. Its serum concentrations correlate with disease severity and prognosis, which may yield vital insights into the pathophysiology of sepsis.