ALTERED LEVELS OF H3K9AC, H3K4ME3, AND H3K27ME3 IN PROMOTERS OF DIFFERENTIALLY EXPRESSED GENES RELATED TO INNATE IMMUNE RESPONSE IN SEPTIC PATIENTS WITH DIFFERENT CLINICAL OUTCOMES

Novel insights into the dynamic function of PRC2 in innate immunity

The polycomb repressive complex 2 (PRC2) is an established therapeutic target in cancer. PRC2 catalyzes methylation of histone H3 at lysine 27 (H3K27me3) and is known for maintaining eukaryote cell identity. Recent discoveries show that modulation of PRC2 not only impacts cell differentiation and tumor growth but also has immunomodulatory properties. Here, we integrate multiple immunological fields to understand PRC2 and its subunits in epigenetic canonical regulation and non-canonical mechanisms within innate immunity. We discuss how PRC2 regulates hematopoietic stem cell proliferation, myeloid cell differentiation, and shapes innate immune responses. The PRC2 catalytic domain EZH2 is upregulated in various human inflammatory diseases and its deletion or inhibition in experimental mouse models can reduce disease severity, emphasizing its importance in regulating inflammation.

GENETIC ABLATION OF THE C-TYPE LECTIN RECEPTOR CLEC2D INCREASES PERITONITIS MORTALITY, INFLAMMATION, AND PHYSIOLOGY WITHOUT DIMINISHING ORGAN INJURY

ABSTRACT

Background: Sepsis accounts for substantial morbidity and mortality motivating investigators to continue the search for pathways and molecules driving the pathogenesis of the disease. The current study examined if the novel C-type lectin receptor (CLR), Clec2d, plays a significant role in the pathogenesis of sepsis. Methods: Clec2d knockout (KO) mice were fully backcrossed onto the C57/BL6 background. Acute endotoxemia was induced with an intraperitoneal injection of lipopolysaccharide (LPS). Sepsis was induced in two different models, cecal ligation and puncture (CLP) and Pseudomonas aeruginosa pneumonia. Both models were treated with antibiotics and fluid resuscitation. In the sepsis models, physiologic and hematologic measurements were measured at 24 h by collecting a small sample of peripheral blood. Mortality was followed for 14 days. Results : A total of 197 mice were studied, 58 wild type (WT) and 54 knock-out (KO) in the LPS model; 27 wild type and 21 KO mice in the CLP model; and 22 WT and 15 KO mice in the pneumonia model. Clec2d KO mice had greater mortality in the LPS and CLP studies but not the pneumonia model. There were significant differences in multiple parameters determined 24 h post sepsis between mice who subsequently died and those lived. Consistent with previous reports in the CLP model, higher concentrations of IL-6, increased numbers of peripheral blood lymphocytes and greater renal injury were found in the dying mice. In contrast, in the pneumonia model, IL-6 was higher in the surviving mice; however, the IL-6 levels in the pneumonia model (0.6 ± 0.3 ng/mL mean ± SEM) were less than 2% of the IL-6 levels of mice that died in the CLP model (41 ± 9 ng/mL, mean ± SEM). There were no differences in the lymphocyte count or renal injury between living and dying mice in the pneumonia model. In both sepsis models, dying mice had lower heart rates, respiratory rates, and body temperatures. These values were also lower in the KO mice compared to the WT in CLP, but the breath rate and body temperature were increased in the KO pneumonia mice. Conclusion: The C-type lectin receptor Clec2d plays a complicated role in the pathogenesis of sepsis, which varies with source of infection as demonstrated in the models used to study the disease. These data highlight the heterogeneity of the responses to sepsis and provide further evidence that a single common pathway driving sepsis organ injury and death likely does not exist.

Surviving Sepsis Campaign Research Priorities 2023

OBJECTIVES

To identify research priorities in the management, epidemiology, outcome, and pathophysiology of sepsis and septic shock.

DESIGN

Shortly after publication of the most recent Surviving Sepsis Campaign Guidelines, the Surviving Sepsis Research Committee, a multiprofessional group of 16 international experts representing the European Society of Intensive Care Medicine and the Society of Critical Care Medicine, convened virtually and iteratively developed the article and recommendations, which represents an update from the 2018 Surviving Sepsis Campaign Research Priorities.

METHODS

Each task force member submitted five research questions on any sepsis-related subject. Committee members then independently ranked their top three priorities from the list generated. The highest rated clinical and basic science questions were developed into the current article.

RESULTS

A total of 81 questions were submitted. After merging similar questions, there were 34 clinical and ten basic science research questions submitted for voting. The five top clinical priorities were as follows: 1) what is the best strategy for screening and identification of patients with sepsis, and can predictive modeling assist in real-time recognition of sepsis? 2) what causes organ injury and dysfunction in sepsis, how should it be defined, and how can it be detected? 3) how should fluid resuscitation be individualized initially and beyond? 4) what is the best vasopressor approach for treating the different phases of septic shock? and 5) can a personalized/precision medicine approach identify optimal therapies to improve patient outcomes? The five top basic science priorities were as follows: 1) How can we improve animal models so that they more closely resemble sepsis in humans? 2) What outcome variables maximize correlations between human sepsis and animal models and are therefore most appropriate to use in both? 3) How does sepsis affect the brain, and how do sepsis-induced brain alterations contribute to organ dysfunction? How does sepsis affect interactions between neural, endocrine, and immune systems? 4) How does the microbiome affect sepsis pathobiology? 5) How do genetics and epigenetics influence the development of sepsis, the course of sepsis and the response to treatments for sepsis?

CONCLUSIONS

Knowledge advances in multiple clinical domains have been incorporated in progressive iterations of the Surviving Sepsis Campaign guidelines, allowing for evidence-based recommendations for short- and long-term management of sepsis. However, the strength of existing evidence is modest with significant knowledge gaps and mortality from sepsis remains high. The priorities identified represent a roadmap for research in sepsis and septic shock.