The role of nitric oxide in the epigenetic regulation of THP-1 induced by lipopolysaccharide

Defective Mitophagy Impairs Response to Inflammatory Activation of Macrophage-Like Cells

BACKGROUND AND AIMS

The role of mitophagy in atherosclerosis has been extensively studied during the last few years. It was shown that mitophagy is involved in the regulation of macrophages, which are important players as immune cells in atherosclerosis development. In this study, we investigated the relationship between mitophagy and response to inflammatory stimulation of macrophage-like cells. Six cybrid cell lines with normal mitophagy, that is, increasing in response to stimulation, and 7 lines with defective mitophagy not responding to stimulation were obtained. The objective of the study was to compare the nature of the inflammatory response in normal and defective mitophagy in order to elucidate the role of mitophagy defects in inflammation.

METHODS

We used cytoplasmic hybrids (cybrids) as cellular models, created using mitochondrial DNA from different atherosclerosis patients. Mitophagy was stimulated by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and assessed as the degree of colocalization of mitochondria with lysosomes using confocal microscopy. Western blotting methods were used for the determination of proteins involved in the exact mechanism of mitophagy. Experiments with stimulation of mitophagy show a high correlation between these two approaches (microscopy and blotting). The pro-inflammatory response of cybrids was stimulated with bacterial lipopolysaccharide (LPS). The extent of the inflammatory response was assessed by the secretion of cytokines CCL2, IL8, IL6, IL1β, and TNF measured by ELISA.

RESULTS

Basal level of secretion of cytokines CCL2, IL8 and TNF was 1.5-2 times higher in cultures of cybrids with defective mitophagy compared to cells with normal mitophagy. This suggests a persistently elevated inflammatory response in cells with defective mitophagy, even in the absence of an inflammatory stimulus. Such cells in the tissue will constantly recruit other immune cells, which is characteristic of macrophages derived from monocytes circulating in the blood of patients with atherosclerosis. We observed significant differences in the degree and type of response to inflammatory activation in cybrids with defective mitophagy. These differences were not so much quantitative as they were dramatically qualitative. Compared with cells with normal mitophagy, in cells with defective mitophagy, the relative (to basal) secretion of IL8, IL6 and IL1b increased after the second LPS activation. This indicates a possible lack of tolerance to inflammatory activation in cells with defective mitophagy, since typically, re-activation reveals a smaller pro-inflammatory cytokine response, allowing the inflammatory process to resolve. In cells with normal mitophagy, exactly this normal (tolerant) inflammatory reaction was observed.

CONCLUSION

Data on the involvement of mitophagy, including defective mitophagy, in disturbances of the inflammatory response in sepsis, viral infections, autoimmune diseases and other pathologies have previously been reported. In this work, we studied the role of defective mitophagy in non-infectious chronic inflammatory diseases using the example of atherosclerosis. We showed a dramatic disruption of the inflammatory response associated with defective mitophagy. Compared with cybrids with normal mitophagy, in cybrids with defective mitophagy, the secretion of all studied cytokines changed significantly both quantitatively and qualitatively. In particular, the secretion of 3 of 5 cytokines demonstrated an intolerant inflammatory response manifested by increased secretion after repeated inflammatory stimulation. Such an intolerant reaction likely indicates a significant disruption of the pro-inflammatory response of macrophages, which can contribute to the chronification of inflammation. Elucidating the mechanisms of chronification of inflammation is extremely important for the search for fundamentally new pharmacological targets and the development of drugs for the prevention and treatment of chronic inflammatory diseases, including atherosclerosis and diseases characteristic of inflammation. Such diseases account for up to 80% of morbidity and mortality.

Dexmedetomidine attenuates inflammation and organ injury partially by upregulating Nur77 in sepsis

PURPOSE

The aim of this study was to investigate the effect of dexmedetomidine (Dex) on inflammation and organ injury in sepsis, as well as the potential relationship between Dex and nuclear receptor 77 (Nur77).

METHODS

We investigated the effects of dexmedetomidine on lipopolysaccharide (LPS)-induced inflammation in RAW264.7 cells and organ injury in the cecal ligation and puncture (CLP) mouse model. Additionally, we examined the relationship between dexmedetomidine and Nur77. The expression levels of Nur77 in RAW264.7 cells were analyzed under various types of stimulation using quantitative reverse transcription polymerase chain reaction and western blot analysis. Inflammatory cytokine levels in the cells were evaluated using enzyme-linked immunoassay. Organ injuries were assessed by examining tissue histology and pathology of the lung, liver, and kidney.

RESULTS

Dexmedetomidine increased the expression of Nur77 and IL-10, and downregulated inflammatory cytokines (IL-1β and TNF-α) in LPS-treated RAW264.7 cells. The effect of dexmedetomidine on inhibiting inflammation in LPS-treated RAW264.7 cells was promoted by overexpressing Nur77, while it was reversed by downregulating Nur77. Additionally, dexmedetomidine promoted the expression of Nur77 in the lung and CLP-induced pathological changes in the lung, liver, and kidney. Activation of Nur77 with the agonist Cytosporone B (CsnB) significantly suppressed the production of IL-1β and TNF-α in LPS-treated RAW264.7 cells. In contrast, knockdown of Nur77 augmented IL-1β and TNF-α production in LPS-treated RAW264.7 cells.

CONCLUSION

Dexmedetomidine can attenuate inflammation and organ injury, at least partially, via upregulating Nur77 in sepsis.

Epigenetic mechanisms of Immune remodeling in sepsis: targeting histone modification

Sepsis is a life-threatening disorder disease defined as infection-induced dysregulated immune responses and multiple organ dysfunction. The imbalance between hyperinflammation and immunosuppression is a crucial feature of sepsis immunity. Epigenetic modifications, including histone modifications, DNA methylation, chromatin remodeling, and non-coding RNA, play essential roles in regulating sepsis immunity through epi-information independent of the DNA sequence. In recent years, the mechanisms of histone modification in sepsis have received increasing attention, with ongoing discoveries of novel types of histone modifications. Due to the capacity for prolonged effects on immune cells, histone modifications can induce immune cell reprogramming and participate in the long-term immunosuppressed state of sepsis. Herein, we systematically review current mechanisms of histone modifications involved in the regulation of sepsis, summarize their role in sepsis from an immune perspective and provide potential therapeutic opportunities targeting histone modifications in sepsis treatment.

Whey protein hydrolysate mitigates both inflammation and endotoxin tolerance in THP-1 human monocytic leukemia cells

INTRODUCTION

It is important to control both inflammation and immunosuppression after severe insults, such as sepsis, trauma, and surgery. Endotoxin tolerance is one of the immunosuppressive conditions and it has been known that endotoxin tolerance relates to poorer clinical outcomes in patients with severe insults. This study investigated whether whey protein hydrolysate (WPH) mitigates inflammation and endotoxin tolerance in THP-1 human monocytic leukemia cells.

METHODS

Endotoxin tolerance can be experimentally reproduced by two consecutive stimulations with lipopolysaccharide (LPS). THP-1 cells were incubated with LPS and WPH (first stimulation). After collecting the culture supernatant to evaluate the effect on inflammation, the cells were washed and restimulated by 100 ng/ml LPS (second stimulation). The culture supernatant was again collected to evaluate the effect on endotoxin tolerance. Concentrations of LPS and WPH in the first stimulation were adjusted to evaluate their dose dependency. Cytokine levels in the supernatant were determined by enzyme-linked immunosorbent assay. Statistical analysis was performed using the student's t-test or Dunnett's test.

RESULTS

Five mg/ml WPH significantly decreased interleukin (IL)-6 (p = .006) and IL-10 (p < .001) levels after the first LPS stimulation (1000 ng/ml). WPH significantly increased tumor necrosis factor-alpha (p < .001) and IL-10 (p = .014) levels after the second LPS stimulation. The suppressive effect of WPH on inflammation and endotoxin tolerance was dependent on the concentrations of LPS and WPH. The effective dose of WPH for endotoxin tolerance was lower than its effective dose for inflammation.

CONCLUSION

WPH mitigated both inflammation and endotoxin tolerance. Therefore, WPH might be a candidate for valuable food ingredients to control both inflammation and immunosuppression after severe insults.

ACT001 attenuates microglia-mediated neuroinflammation after traumatic brain injury via inhibiting AKT/NFκB/NLRP3 pathway

Background

Microglia-mediated neuroinflammatory response following traumatic brain injury (TBI) is considered as a vital secondary injury factor, which drives trauma-induced neurodegeneration and is lack of efficient treatment. ACT001, a sesquiterpene lactone derivative, is reportedly involved in alleviation of inflammatory response. However, little is known regarding its function in regulating innate immune response of central nervous system (CNS) after TBI. This study aimed to investigate the role and underlying mechanism of ACT001 in TBI.

Methods

Controlled cortical impact (CCI) models were used to establish model of TBI. Cresyl violet staining, evans blue extravasation, neurobehavioral function assessments, immunofluorescence and transmission electron microscopy were used to evaluate therapeutic effects of ACT001 in vivo. Microglial depletion was induced by administering mice with colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622. Cell-cell interaction models were established as co-culture system to simulate TBI conditions in vitro. Cytotoxic effect of ACT001 on cell viability was assessed by cell counting kit-8 and activation of microglia cells were induced by Lipopolysaccharides (LPS). Pro-inflammatory cytokines expression was determined by Real-time PCR and nitric oxide production. Apoptotic cells were detected by TUNEL and flow cytometry assays. Tube formation was performed to evaluate cellular angiogenic ability. ELISA and western blot experiments were used to determine proteins expression. Pull-down assay was used to analyze proteins that bound ACT001.

Results

ACT001 relieved the extent of blood-brain barrier integrity damage and alleviated motor function deficits after TBI via reducing trauma-induced activation of microglia cells. Delayed depletion of microglia with PLX5622 hindered therapeutic effect of ACT001. Furthermore, ACT001 alleviated LPS-induced activation in mouse and rat primary microglia cells. Besides, ACT001 was effective in suppressing LPS-induced pro-inflammatory cytokines production in BV2 cells, resulting in reduction of neuronal apoptosis in HT22 cells and improvement of tube formation in bEnd.3 cells. Mechanism by which ACT001 functioned was related to AKT/NFκB/NLRP3 pathway. ACT001 restrained NFκB nuclear translocation in microglia cells through inhibiting AKT phosphorylation, resulting in decrease of NLRP3 inflammasome activation, and finally down-regulated microglial neuroinflammatory response.

Conclusions

Our study indicated that ACT001 played critical role in microglia-mediated neuroinflammatory response and might be a novel potential chemotherapeutic drug for TBI.

Understanding the role of endotoxin tolerance in chronic inflammatory conditions and periodontal disease

OBJECTIVE

This review aims to present the current understanding of endotoxin tolerance (ET) in chronic inflammatory diseases and explores the potential connection with periodontitis.

SUMMARY

Subsequent exposure to lipopolysaccharides (LPS) triggers ET, a phenomenon regulated by different mechanisms and pathways, including toll-like receptors (TLRs), nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), apoptosis of immune cells, epigenetics, and microRNAs (miRNAs). These mechanisms interconnect ET with chronic inflammatory diseases that include periodontitis. While the direct correlation between ET and periodontal destruction has not been fully elucidated, emerging reports point towards the potential tolerization of human periodontal ligament cells (hPDLCs) and gingival tissues with a significant reduction of TLR levels.

CONCLUSIONS

There is a potential link between ET and periodontal diseases. Future studies should explore the crucial role of ET in the pathogenesis of periodontal diseases as evidence of a tolerized oral mucosa may represent an intrinsic mechanism capable of regulating the oral immune response. A clear understanding of this host immune regulatory mechanism might lead to effective and more predictable therapeutic strategies to treat chronic inflammatory diseases and periodontitis. This article is protected by copyright. All rights reserved.

Epigenetic Regulation in Sepsis, Role in Pathophysiology and Therapeutic Perspective

Sepsis is characterized by an initial hyperinflammatory response, with intense cell activation and cytokine storm. In parallel, a prolonged compensatory anti-inflammatory response, known as immunological tolerance, can lead to immunosuppression. Clinically, this condition is associated with multiple organ failure, resulting in the patient's death. The mechanisms underlying the pathophysiology of sepsis are not yet fully understood, but evidence is strong showing that epigenetic changes, including DNA methylation and post-translational modifications of histones, modulate the inflammatory response of sepsis. During the onset of infection, host cells undergo epigenetic changes that favor pathogen survival. Besides, epigenetic changes in essential genes also orchestrate the patient's inflammatory response. In this review, we gathered studies on sepsis and epigenetics to show the central role of epigenetic mechanisms in various aspects of the pathogenesis of sepsis and the potential of epigenetic interventions for its treatment.

Hepatitis B core antigen can regulate NLRP3 inflammasome pathway in HepG2 cells

Hepatitis B virus (HBV) has four open reading frames (ORFs) of which ORF C is consists of the pre Core and Core genes encodes the Hepatitis B core antigen (HBcAg) and Hepatitis B e antigen (HBeAg). Studies have shown that HBeAg significantly inhibits the NLRP3 inflammasome activation and interleukin-1β (IL-1β) production. However, the role of HBcAg and ORF C proteins (in this paper, ORF C proteins = HBcAg + HBeAg) were remain unclear. Our study aims to assess whether HBcAg and ORF C proteins can affect the NLRP3 inflammasome pathway. Vectors expressing ORF C proteins and HBcAg were designed and transfected into HepG2 cells. And then, cells were stimulated with lipopolysaccharide (LPS). Activation of the NLRP3 inflammasome and the levels of IL-1β and IL-18 were evaluated by Western blot analysis, quantitative reverse-transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and immunofluorescence. The expression of NLRP3 and IL-1β peaked when HepG2 cells were stimulated with 1000 ng/mL LPS for 18 to 24 hours. HBcAg, but not ORF C proteins, promoted LPS-induced NLRP3 inflammasome activation and IL-1β production. These findings provide a novel mechanism on how the HBV causes liver inflammation and may provide insights into the search for new therapeutic strategies.

Histone Deacetylation Inhibitors as Therapy Concept in Sepsis

Sepsis is characterized by dysregulated gene expression, provoking a hyper-inflammatory response occurring in parallel to a hypo-inflammatory reaction. This is often associated with multi-organ failure, leading to the patient’s death. Therefore, reprogramming of these pro- and anti-inflammatory, as well as immune-response genes which are involved in acute systemic inflammation, is a therapy approach to prevent organ failure and to improve sepsis outcomes. Considering epigenetic, i.e., reversible, modifications of chromatin, not altering the DNA sequence as one tool to adapt the expression profile, inhibition of factors mediating these changes is important. Acetylation of histones by histone acetyltransferases (HATs) and initiating an open-chromatin structure leading to its active transcription is counteracted by histone deacetylases (HDACs). Histone deacetylation triggers a compact nucleosome structure preventing active transcription. Hence, inhibiting the activity of HDACs by specific inhibitors can be used to restore the expression profile of the cells. It can be assumed that HDAC inhibitors will reduce the expression of pro-, as well as anti-inflammatory mediators, which blocks sepsis progression. However, decreased cytokine expression might also be unfavorable, because it can be associated with decreased bacterial clearance.

Epigenetics: The third pillar of nitric oxide signaling

Nitric oxide (NO), the endogenously produced free radical signaling molecule, is generally thought to function via its interactions with heme-containing proteins, such as soluble guanylyl cyclase (sGC), or by the formation of protein adducts containing nitrogen oxide functional groups (such as S-nitrosothiols, 3-nitrotyrosine, and dinitrosyliron complexes). These two types of interactions result in a multitude of down-stream effects that regulate numerous functions in physiology and disease. Of the numerous purported NO signaling mechanisms, epigenetic regulation has gained considerable interest in recent years. There is now abundant experimental evidence to establish NO as an endogenous epigenetic regulator of gene expression and cell phenotype. Nitric oxide has been shown to influence key aspects of epigenetic regulation that include histone posttranslational modifications, DNA methylation, and microRNA levels. Studies across disease states have observed NO-mediated regulation of epigenetic protein expression and enzymatic activity resulting in remodeling of the epigenetic landscape to ultimately influence gene expression. In addition to the well-established pathways of NO signaling, epigenetic mechanisms may provide much-needed explanations for poorly understood context-specific effects of NO. These findings provide more insight into the molecular mechanisms of NO signaling and increase our ability to dissect its functional role(s) in specific micro-environments in health and disease. This review will summarize the current state of NO signaling via epigenetic mechanisms (the "third pillar" of NO signaling).

Regulation of Cellular Immune Responses in Sepsis by Histone Modifications

Severe sepsis, septic shock, and related inflammatory syndromes are driven by the aberrant expression of proinflammatory mediators by immune cells. During the acute phase of sepsis, overexpression of chemokines and cytokines drives physiological stress leading to organ failure and mortality. Following recovery from sepsis, the immune system exhibits profound immunosuppression, evidenced by an inability to produce the same proinflammatory mediators that are required for normal responses to infectious microorganisms. Gene expression in inflammatory responses is influenced by the transcriptional accessibility of the chromatin, with histone posttranslational modifications determining whether inflammatory gene loci are set to transcriptionally active, repressed, or poised states. Experimental evidence indicates that histone modifications play a central role in governing the cytokine storm of severe sepsis, and that aberrant chromatin modifications induced during the acute phase of sepsis may mediate chronic immunosuppression in sepsis survivors. This review will focus on the role of histone modifications in governing immune responses in severe sepsis, with an emphasis on specific leukocyte subsets and the histone modifications observed in these cells during chronic stages of sepsis. Additionally, the expression and function of chromatin-modifying enzymes (CMEs) will be discussed in the context of severe sepsis, as potential mediators of epigenetic regulation of gene expression in sepsis responses. In summary, this review will argue for the use of chromatin modifications and CME expression in leukocytes as potential biomarkers of immunosuppression in patients with severe sepsis.