Alpha-ketoglutarate alleviates cadmium-induced inflammation by inhibiting the HIF1A-TNFAIP3 pathway in hepatocytes

The threat to public health posed by rapidly increasing levels of cadmium (Cd) in the environment is receiving worldwide attention. Although, Cd is known to be absorbed into the body and causes non-negligible damage to the liver, the detailed mechanisms underlying its hepatoxicity are incompletely understood. In the present study, investigated the effect of TNFAIP3 and α-ketoglutarate (AKG) on Cd-induced liver inflammation and hepatocyte death. Male C57BL/6 mice were exposed to cadmium chloride (1.0 mg/kg) while being fed a diet with 2 % AKG for two weeks. We found that Cd induced hepatocyte injury and inflammatory infiltration. In addition, TNFAIP3 expression was inhibited in the liver tissues and cells of CdCl₂-treated mice. Mouse hepatocyte-specific TNFAIP3 overexpression by tail vein injection of an adeno-associated virus (AAV) vector effectively alleviated Cd-induced hepatic necrosis and inflammation, which was mediated by the NF-κB signaling pathway. Notably, this inhibitory effect of TNFAIP3 on Cd-induced liver injury was dependent on AKG. Exogenous addition of AKG prevented Cd exposure-induced increases in serum ALT, AST and LDH levels, production of pro-inflammatory cytokines, activation of the NF-κB signaling pathway, and even significantly reduced Cd-induced oxidative stress and hepatocyte death. Mechanistically, AKG exerted its anti-inflammatory effect by promoting the hydroxylation and degradation of HIF1A to reduce its Cd-induced overexpression in vivo and in vitro, avoiding the inhibition of the TNFAIP3 promoter by HIF1A. Moreover, the protective effect of AKG was significantly weaker in Cd-treated primary hepatocytes transfected with HIF1A pcDNA. Overall, our results reveal a novel mechanism of Cd-induced hepatotoxicity.

Network analysis for the identification of hub genes and related molecules as potential biomarkers associated with the differentiation of bone marrow-derived stem cells into hepatocytes

The incidence of liver diseases has been increasing steadily. However, it has some shortcomings, such as high cost and organ donor scarcity. The application of stem cell research has brought new ideas for the treatment of liver diseases. Therefore, it is particularly important to clarify the molecular and regulatory mechanisms of differentiation of bone marrow-derived stem cells (BMSCs) into liver cells. Herein, we screened differentially expressed genes between hepatocytes and untreated BMSCs to identify the genes responsible for the differentiation of BMSCs into hepatocytes. GSE30419 gene microarray data of BMSCs and GSE72088 gene microarray data of primary hepatocytes were obtained from the Gene Expression Omnibus database. Transcriptome Analysis Console software showed that 1896 genes were upregulated and 2506 were downregulated in hepatocytes as compared with BMSCs. Hub genes were analyzed using the STRING and Cytoscape v 3.8.2, revealing that twenty-four hub genes, play a pivotal role in the differentiation of BMSCs into hepatocytes. The expression of the hub genes in the BMSCs and hepatocytes was verified by reverse transcription-quantitative PCR (RT-qPCR). Next, the target miRNAs of hub genes were predicted, and then the lncRNAs regulating miRNAs was discovered, thus forming the lncRNA-miRNA-mRNA interaction chain. The results indicate that the lncRNA-miRNA-mRNA interaction chain may play an important role in the differentiation of BMSCs into hepatocytes, which provides a new therapeutic target for liver disease treatment.

Knockout of the Cannabinoid Receptor 2 Gene Promotes Inflammation and Hepatic Stellate Cell Activation by Promoting A20/Nuclear Factor-κB (NF-κB) Expression in Mice with Carbon Tetrachloride-Induced Liver Fibrosis

Background

This study aimed to investigate the effect of deleting the cannabinoid receptor 2 (CB2) gene on the development of hepatic fibrosis induced by carbon tetrachloride (CCl₄) in mice via regulating inflammation.

Material/Methods

The DNA was extracted from the tails of mice to identify whether the cannabinoid receptor 2 gene was successfully knocked out. A liver fibrosis model was established by an intraperitoneal injection of CCl₄ into mice. Hepatic damage and hepatic fibrosis were evaluated by detecting serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), and staining paraffin sections of liver tissue with hematoxylin-eosin (HE). The secretion and distribution of collagen in liver tissue were observed by Masson staining. Western blot analysis was performed to detect the expression of α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), tumor necrosis factor alpha-induced protein 3 (A20), phosphorylated nuclear factor-κB p65 (p-NF-κB p65), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) in liver tissue. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expression of IL-6 and TNF-α mRNA in liver tissue.

Results

Compared with the control mice, the mice with CB2 knockout that were exposed to CCl₄ exhibited increased liver damage, liver fibrosis, and upregulated α-SMA, TGF-β1, A20, and p-NF-κB p65 protein levels. IL-6 and TNF-α protein levels and mRNA levels were upregulated.

Conclusions

The deletion of the CB2 gene promoted the activation of hepatic stellate cells in mice with liver fibrosis and aggravated liver fibrosis by up-regulating the protein expression of A20 and p-NF-κB p65 and inducing inflammatory response, potentially providing new insight into the treatment of liver fibrosis.

A20 Attenuates Lipopolysaccharide-Induced Inflammation Through MAPK/ERK/JNK Pathway in LX-2 Cells

Background: Hepatic stellate cells (HSCs) are liver-specific pericytes that transform into myofibroblasts, which are involved in pathological vascularization in liver fibrosis. We previously suggested that A20 overexpression suppresses lipopolysaccharide (LPS)-induced inflammation in HSC. We aimed to determine the mechanisms of the anti-inflammatory role of A20 in LX-2 cells. Methods: LX-2 cells were transfected with A20-siRNA or control-siRNA and control adenovirus or A20-carrying adenovirus. Quantitative reverse transcription PCR (RT-qPCR) analysis was employed to quantify mRNA levels of α-SMA, col-I, col-III, IL-6, TGF-β, and PDGF in A20-siRNA LX-2 cells stimulated with LPS. Multiple molecular indices of MAPK/ERK/JNK signal pathway were performed by using Western blotting. Results: Relative to control, the fibrosis-related mRNA levels of α-SMA, col-I, and col-III were increased in A20-siRNA LX-2 cells. Meanwhile, A20-siRNA cells significantly increased IL-6, TGF-β, and PDGF mRNA levels. Relative to controls, stimulating A20 overexpressing LX-2 cells with LPS for 5 and 30 minutes significantly reduced the levels of phosphorylated ERK and JNK, respectively. A20 knockdown in LX-2 cells promotes phosphorylated ERK and JNK levels with LPS for 30 minutes. Conclusions: Our data indicate that A20 could be functional in HSCs through the MAPK/ERK/JNK signaling pathway, highlighting a potential novel therapeutic strategy against liver fibrosis.

Potential role of the 3-mercaptopyruvate sulfurtransferase (3-MST)-hydrogen sulfide (H2S) pathway in cancer cells

Hydrogen sulfide (H₂S), produced by various endogenous enzyme systems, serves various biological regulatory roles in mammalian cells in health and disease. Over recent years, a new concept emerged in the field of H₂S biology, showing that various cancer cells upregulate their endogenous H₂S production, and utilize this mediator in autocrine and paracrine manner to stimulate proliferation, bioenergetics and tumor angiogenesis. Initial work identified cystathionine-beta-synthase (CBS) in many tumor cells as the key source of H₂S. In other cells, cystathionine-gamma-lyase (CSE) has been shown to play a pathogenetic role. However, until recently, less attention has been paid to the third enzymatic source of H₂S, 3-mercaptopyruvate sulfurtransferase (3-MST), even though several of its biological and biochemical features - e.g. its partial mitochondrial localization, its ability to produce polysulfides, which, in turn, can induce functionally relevant posttranslational protein modifications - makes it a potential candidate. Indeed, several lines of recent data indicate the potential role of the 3-MST system in cancer biology. In many cancers (e.g. colon adenocarcinoma, lung adenocarcinoma, urothelial cell carcinoma, various forms of oral carcinomas), 3-MST is upregulated compared to the surrounding normal tissue. According to in vitro studies, 3-MST upregulation is especially prominent in cancer cells that recover from oxidative damage and/or develop a multidrug-resistant phenotype. Emerging data with newly discovered pharmacological inhibitors of 3-MST, as well as data using 3-MST silencing approaches suggest that the 3-MST/H₂S system plays a role in maintaining cancer cell proliferation; it may also regulate bioenergetic and cell-signaling functions. Many questions remain open in the field of 3-MST/cancer biology; the last section of current article highlights these open questions and lays out potential experimental strategies to address them.

A20 Attenuates Liver Fibrosis in NAFLD and Inhibits Inflammation Responses

We previously reported A20 was able to inhibit lipid accumulation in nonalcoholic steatohepatitis. We want to investigate whether A20 influences liver fibrosis in this study. Liver tissues from patients with hepatic fibrosis (n = 9) and healthy individuals (n = 7) were studied for A20 protein level by immunohistochemistry. A20 messenger RNA (mRNA) and protein level were also analyzed in two murine hepatic fibrosis models: methionine- and choline-deficient (MCD) diet and extrahepatic bile duct ligation (BDL) operation by real-time PCR and western blot. In vitro, the LX-2 human hepatic stellate cell line was treated by LPS at 0, 0.001, 0.01, 0.1, and 1 μg/mL for 6 h or at the concentration of 0.1 μg/mL for 0, 6, 12, and 24 h, then A20 expression levels were detected by western blot and PCR. The mRNA level of α-SMA, collagen I, collagen III, TGF-β, IL-6, MCP-1, and TLR4 was also examined by PCR. We then overexpressed A20 in LX-2 cells using adenovirus technique. Levels of α-SMA, collagen I, collagen III, TGF-β, IL-6, MCP-1, and TLR4 were examined in A20-overexpression LX-2 cells. Patients with hepatic fibrosis showed significantly higher A20 protein level compared with healthy controls. A20 mRNA and protein levels were also increased in livers from MCD feeding or BDL operation mice in comparison to normal controls. In LX-2 cells, LPS induced A20 protein in a concentration-dependent manner. The mRNA levels of α-SMA, collagen I, collagen III, TGF-β, IL-6, MCP-1, and TLR4 were increased after LPS treatment. Overexpression of A20 in LX-2 cells inhibited α-SMA deposition and collagen I, collagen III secretion. TGF-β, IL-6, MCP-1, and TLR4 mRNA levels were also reduced in A20-overexpression LX-2 cells in response to LPS stimulation. A20 overexpression inhibits hepatic stellate cell activation, which could be the mechanism for high A20 expression protected livers from fibrosis. Enhancement of A20 expression seems to be rational therapeutic strategies for liver fibrosis.

A20 deficiency leads to angiogenesis of pulmonary artery endothelial cells through stronger NF-κB activation under hypoxia

A20 is a zinc finger protein associated with hypoxia. As chronic hypoxia is responsible for intimal hyperplasia and disordered angiogenesis of pulmonary artery, which are histological hallmarks of pulmonary artery hypertension, we intended to explore the role of A20 in angiogenesis of pulmonary artery endothelial cells (ECs). Here, we found a transient elevation of A20 expression in the lung tissues from hypoxic rats compared with normoxic controls. This rapid enhancement was mainly detected in the endothelium, and similar results were reproduced in vitro. During early hypoxia, genetic inhibition of A20 increased proliferation in pulmonary artery ECs, linking to advanced cell cycle progression as well as microtubule polymerization, and aggravated angiogenic effects including tube formation, cell migration and adhesion molecules expression. In addition, a negative feedback loop between nuclear factor-kappa B and A20 was confirmed. Our findings provide evidence for an adaptive role of A20 against pulmonary artery ECs angiogenesis via nuclear factor-kappa B activation.

Anti-inflammatory and anti-osteoclastogenic effects of zinc finger protein A20 overexpression in human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Although overexpression of the nuclear factor κB inhibitory and ubiquitin-editing enzyme A20 is thought to be involved in the pathogenesis of inflammatory diseases, its function in periodontal disease remains unknown. The aims of the present study were to evaluate A20 expression in patients with periodontitis and to study the effects of A20 overexpression, using a recombinant adenovirus encoding A20 (Ad-A20), on the inflammatory response and on osteoclastic differentiation in lipopolysaccharide (LPS)- and nicotine-stimulated human periodontal ligament cells (hPDLCs).

MATERIAL AND METHODS

The concentration of prostaglandin E2 was measured by radioimmunoassay. Reverse transcription-polymerase chain reactions and western blot analyses were used to measure mRNA and protein levels, respectively. Osteoclastic differentiation was assessed in mouse bone marrow-derived macrophages using conditioned medium from LPS- and nicotine-treated hPDLCs.

RESULTS

A20 was upregulated in the gingival tissues and neutrophils from patients with periodontitis and in LPS- and nicotine-exposed hPDLCs. Pretreatment with A20 overexpression by Ad-A20 markedly attenuated LPS- and nicotine-induced production of prostaglandin E2 , as well as expression of cyclooxygenase-2 and proinflammatory cytokines. Moreover, A20 overexpression inhibited the number and size of tartrate-resistant acid phosphatase-stained osteoclasts, and downregulated osteoclast-specific gene expression. LPS- and nicotine-induced p38 phosphorylation and nuclear factor κB activation were blocked by Ad-A20. Ad-A20 inhibited the effects of nicotine and LPS on the activation of pan-protein kinase C, Akt, GSK-3β and protein kinase Cα.

CONCLUSIONS

This study is the first to demonstrate that A20 overexpression has anti-inflammatory effects and blocks osteoclastic differentiation in a nicotine- and LPS-stimulated hPDLC model. Thus, A20 overexpression may be a potential therapeutic target in inflammatory bone loss diseases, such as periodontal disease.