High mobility group box1 protein is involved in acute inflammation induced by Clostridium difficile toxin A

Plakoglobin and High-Mobility Group Box 1 Mediate Intestinal Epithelial Cell Apoptosis Induced by Clostridioides difficile TcdB

Clostridioides difficile infection (CDI) is the leading cause of antibiotic-associated intestinal disease, resulting in severe diarrhea and fatal pseudomembranous colitis. TcdB, one of the essential virulence factors secreted by this bacterium, induces host cell apoptosis through a poorly understood mechanism. Here, we performed an RNA interference (RNAi) screen customized to Caco-2 cells, a cell line model of the intestinal epithelium, to discover host factors involved in TcdB-induced apoptosis. We identified plakoglobin, also known as junction plakoglobin (JUP) or γ-catenin, a member of the catenin family, as a novel host factor and a previously known cell death-related chromatin factor, high-mobility group box 1 (HMGB1). Disruption of those host factors by RNAi and CRISPR resulted in resistance of cells to TcdB-mediated and mitochondrion-dependent apoptosis. JUP was redistributed from adherens junctions to the mitochondria and colocalized with the antiapoptotic factor Bcl-X_L. JUP proteins could permeabilize the mitochondrial membrane, resulting in the release of cytochrome c. Our results reveal a novel role of JUP in targeting the mitochondria to promote the mitochondrial apoptotic pathway. Treatment with glycyrrhizin, an HMGB1 inhibitor, resulted in significantly increased resistance to TcdB-induced epithelial damage in cultured cells and a mouse ligated colon loop model. These findings demonstrate the critical roles of JUP and HMGB1 in TcdB-induced epithelial cell apoptosis. IMPORTANCE Clostridioides difficile infection (CDI) is the leading cause of hospital-acquired diarrhea. Toxins, especially TcdB, cause epithelial cell apoptosis, but the underlying cell death mechanism is less clear. Through an apoptosis-focused RNAi screen using a bacterium-made small interfering (siRNA) library customized to a human colonic epithelial cell model, we found a novel host factor, plakoglobin (γ-catenin), as a key factor required for cell apoptosis induced by TcdB. Plakoglobin targets and permeabilizes mitochondria after stimulation by TcdB, demonstrating a hitherto underappreciated role of this catenin family member in the apoptosis of intestinal epithelial cells. We also found a previously known cell death-related chromatin factor, HMGB1, and explored the inhibition of HMGB1 for CDI therapy in vivo.

Advantages of Lateral Flow Assays Based on Fluorescent Submicrospheres and Quantum Dots for Clostridium difficile Toxin B Detection

Clostridium difficile colitis is caused by a cytotoxin produced by the anaerobic bacteria C. difficile in the epithelial cells of the large intestine, particularly C. difficile toxin B (TcdB). However, the sensitivity of currently utilized C. difficile endotoxin determination methods has been called into question, and, therefore, more accurate and convenient detection methods are needed. Our study is the first to systematically compare fluorescent submicrosphere-based and quantum-dot nanobead-based lateral fluidity measurement methods (FMs-LFA and QDNBs-LFA) with toxin B quantification in fecal samples via sandwich analysis. The limits of detection (LOD) of FMs-LFA and QDNBs-LFA in the fecal samples were 0.483 and 0.297 ng/mL, respectively. TcdB analyses of the fecal samples indicated that the results of QDNBs-LFA and FMs-LFA were consistent with those of a commercial enzyme-linked immunosorbent assay (ELISA) test kit. The sensitivity of QDNBs-LFA was highly correlated with clinical diagnoses. Therefore, quantum dot nanobeads (QDNBs) are deemed highly suitable for lateral fluidity analyses, which would facilitate the implementation of portable and rapid on-the-spot applications, such as food hygiene and safety tests and onsite medical testing.

Decreased Expression of the High Mobility Group Box 1 (HMGB1) Gene in Peripheral Blood in Patients with Mild or Moderate Clostridioides difficile Infection

Cytokines are mediators of inflammation induced in the course of Clostridioides difficile infection (CDI). High Mobility Group Box 1 (HMGB1) is a cytokine playing an important role in the pathogenesis of numerous inflammatory and autoimmune diseases. The aim of the study was to assess the HMGB1 gene expression in the course of CDI. We have performed a prospective case-control study- including 55 adult patients, among them 27 with CDI, who were hospitalized from October 2018 to February 2020 and 28 healthy volunteers. We assessed: a complete blood count with differential leukocyte count, blood creatinine, albumin, and C-reactive protein (CRP) levels. Then, the expression of the HMGB1 gene was evaluated using quantitative Real-Time PCR. Patients with CDI were found to have a significant increase in white blood cells (WBC), neutrophil count, and CRP levels, they also exhibited decreased levels of albumin compared with controls. The HMGB1 gene expression was significantly lower among patients with CDI compared with the control group and significantly, inversely correlated with CRP level in blood. In conclusion, we have observed a decreased expression of the HMGB1 gene in peripheral blood of patients with mild or moderate CDI, which hypothetically could reflect their diminished capability to fight the pathogen.

Atorvastatin protects cardiac progenitor cells from hypoxia-induced cell growth inhibition via MEG3/miR-22/HMGB1 pathway

Heart failure (HF) induced by ischemia myocardial infarction (MI) is one of the major causes of morbidity and mortality all around the world. Atorvastatin, a hydroxymethylglutaryl coenzyme A reductase inhibitor, has been demonstrated to benefit patients with ischemic or non-ischemic-induced HF, but the mechanism is still poorly understood. Increasing evidence indicates that lncRNAs play important role in variety of human disease. However, the role and underlying molecular mechanisms remain largely unclear. In our work, we applied 0.5% O2 to generate a hypoxia cardiac progenitor cell (CPC) model. Then, CCK8 and EdU assays were employed to investigate the role of atorvastatin in hypoxia CPC cell model. We found that hypoxia inhibits CPC viability and proliferation through modulating MEG3 expression, while atorvastatin application can protect CPCs from hypoxia-induced injury through inhibiting MEG3 expression. Then, we demonstrated that repression of MEG3 inhibited the hypoxia-induced injury of CPCs and overexpression of MEG3 inhibited the protective effect of atorvastatin in the hypoxia-induced injury of CPCs. Furthermore, our study illustrated that atorvastatin played its role in CPC viability and proliferation by modulating the expression of HMGB1 through the MEG3/miR-22 pathway. Our study, for the first time, uncovered the molecular mechanism of atorvastatin's protective role in cardiomyocytes under hypoxia condition, which may provide an exploitable target in developing effective therapy drugs for MI patients.

High-mobility group box 1 protein contributes to the immunogenicity of rTcdB-treated CT26 cells

Clostridium difficile TcdB is a key virulence factor that causes C. difficile-associated diseases. Our previous studies have shown that recombinant full-length TcdB (rTcdB) induces cell death in CT26 cells, and rTcdB-treated CT26 cells with high immunogenicity could stimulate dendritic cell (DC) activation and T cell activation in vitro. The rTcdB-treated CT26 cells also induce antitumor immunity in mice and protect mice from CT26 cells. High-mobility group box 1 protein (HMGB1) is a non-histone nuclear protein, which has various biological functions within the nucleus and also acts as an extracellular signal molecule involving in inflammatory diseases, cancers or autoimmune diseases. In this study, HMGB1 was found to be released from the rTcdB-treated CT26 cells. HMGB1 knockdown by using specific siRNA weakened the capacity of the BMDCs loaded with the rTcdB-treated CT26 cells to prime T cells in vitro and in vivo. The released HMGB1 from CT26 cells could interact with the receptor TLR4, which is closely related to DC activation and immune responses. The knockdown of HMGB1 also affected the phagocytosis of the rTcdB-treated CT26 cells by DCs in vitro. Furthermore, HMGB1 weakened the antitumor immunity of the rTcdB-treated CT26 cells, which protects mice from rechallenge of the live CT26 cells. Taken together, these results suggest that HMGB1 plays an important role on the immunogenicity of the rTcdB-treated dying CT26 cells.

Propofol inhibits the release of interleukin-6, 8 and tumor necrosis factor-α correlating with high-mobility group box 1 expression in lipopolysaccharides-stimulated RAW 264.7 cells

Background

Studies have found that propofol can inhibit endotoxin-induced monocyte-macrophages to produce various inflammatory factors. This study is to disclose whether the propofol affects the expression of high-mobility group box 1 (HMGB1) in lipopolysaccharides (LPS)-stimulated RAW 264.7 cells and the release of interleukin-6 (IL-6), 8 (IL-8) and tumor necrosis factor-α (TNF-α).

Methods

RAW 264.7 cells were divided into four groups for intervention. After culturing for 16 h, the cells and culture supernatants were collected. The expression of HMGB1 in RAW 264.7 cells was detected by Western blot. The levels of IL-6, IL-8 and TNF-α in supernatants of cells were determined by enzyme-linked immunosorbent assay (ELISA).

Results

Stimulation of LPS increased the expression of HMGB1 and promoted the release of IL-6, IL-8 and TNF-α in supernatants of RAW 264.7 cells (p < 0.05); however, propofol down-regulated the expression of LPS-stimulated HMGB1 and reduced the LPS-stimulated releases of IL-6, IL-8 and TNF-α in supernatants of RAW 264.7 cells (p < 0.05). Moreover, the releases of IL-6, IL-8 and TNF-α intimately correlated with the expression of HMGB1 in this process (p < 0.05).

Conclusion

Propofol inhibited the releases of IL-6, IL-8 and TNF-α in LPS-stimulated RAW 264.7 cells, and the levels of IL-6, IL-8 and TNF-α intimately correlated with the expression of HMGB1, which indicating that propofol may prevent inflammatory responses through reducing the releases of these cytokines and inflammatory mediators.

Toll Like Receptor 2, 4, and 9 Signaling Promotes Autoregulative Tumor Cell Growth and VEGF/PDGF Expression in Human Pancreatic Cancer

Toll like receptor (TLR) signaling has been suggested to play an important role in the inflammatory microenvironment of solid tumors and through this inflammation-mediated tumor growth. Here, we studied the role of tumor cells in their process of self-maintaining TLR expression independent of inflammatory cells and cytokine milieu for autoregulative tumor growth signaling in pancreatic cancer. We analyzed the expression of TLR2, -4, and -9 in primary human cancers and their impact on tumor growth via induced activation in several established pancreatic cancers. TLR-stimulated pancreatic cancer cells were specifically investigated for activated signaling pathways of VEGF/PDGF and anti-apoptotic Bcl-xL expression as well as tumor cell growth. The primary pancreatic cancers and cell lines expressed TLR2, -4, and -9. TLR-specific stimulation resulted in activated MAP-kinase signaling, most likely via autoregulative stimulation of demonstrated TLR-induced VEGF and PDGF expression. Moreover, TLR activation prompted the expression of Bcl-xL and has been demonstrated for the first time to induce tumor cell proliferation in pancreatic cancer. These findings strongly suggest that pancreatic cancer cells use specific Toll like receptor signaling to promote tumor cell proliferation and emphasize the particular role of TLR2, -4, and -9 in this autoregulative process of tumor cell activation and proliferation in pancreatic cancer.

High Mobility Group Box1 Protein Is Involved in Endoplasmic Reticulum Stress Induced by Clostridium difficile Toxin A

High Mobility Group Box1 (HMGB1), a damage-associated inflammatory factor, plays an important role in the pathogenesis of numerous chronic inflammatory and autoimmune diseases. In this study, the role of the HMGB1 in TcdA-induced ER stress was identified. Clostridium difficile toxin A is one of the major virulence factors of C. difficile infection (CDI) and has been proved to induce apoptotic cell death through ER stress. Our results showed that HMGB1 might play an important role in the TcdA-induced ER stress and unfolded protein response. HMGB1 activated molecular markers and induced the C/EBP homologous protein upregulation (CHOP). This study may provide the essential information for better understanding of the molecular mechanisms involved in CDI.