Significant lethality following liver resection in A20 heterozygous knockout mice uncovers a key role for A20 in liver regeneration

Exploration of the role of oxidative stress-related genes in LPS-induced acute lung injury via bioinformatics and experimental studies

During the progression of acute lung injury (ALI), oxidative stress and inflammatory responses always promote each other. The datasets analyzed in this research were acquired from the Gene Expression Omnibus (GEO) database. The Weighted Gene Co-expression Network Analysis (WGCNA) and limma package were used to obtain the ALI-related genes (ALIRGs) and differentially expressed genes (DEGs), respectively. In total, two biological markers (Gch1 and Tnfaip3) related to oxidative stress were identified by machine learning algorithms, Receiver Operator Characteristic (ROC), and differential expression analyses. The area under the curve (AUC) value of biological markers was greater than 0.9, indicating an excellent power to distinguish between ALI and control groups. Moreover, 15 differential immune cells were selected between the ALI and control samples, and they were correlated to biological markers. The transcription factor (TF)-microRNA (miRNA)-Target network was constructed to explore the potential regulatory mechanisms. Finally, based on the quantitative reverse transcription polymerase chain reaction (qRT-PCR), the expression of Gch1 and Tnfaip3 was significantly higher in ALI lung tissue than in healthy controls. In conclusion, the differences in expression profiles between ALI and normal controls were found, and two biological markers were identified, providing a research basis for further understanding the pathogenesis of ALI.

BMAL1/FOXA2-induced rhythmic fluctuations in IL-6 contribute to nocturnal asthma attacks

The circadian clock is closely associated with inflammatory reactions. Increased inflammatory cytokine levels have been detected in the airways of nocturnal asthma. However, the mechanisms that contribute to the nocturnal increase in inflammatory responses and the relationship with circadian clock remain unknown.

Methods

Inflammatory cytokine levels were measured in asthma patients with and without nocturnal symptoms. Allergic airway disease was induced in mice by ovalbumin (OVA), and different periods of light/dark cycles were used to induce circadian rhythm disorders. Serum shock was used to stimulate the rhythmic expression in human bronchial epidermal cells (16HBE). The expression and oscillation of circadian clock genes and inflammatory cytokines in 16HBE cells subjected to brain and muscle ARNT-like protein-1 (BMAL1) and Forkhead Box A2 (FOXA2) knockdown and treatment with a FOXA2 overexpression plasmid were assessed.

Results

Serum IL-6 was found to be significantly higher in asthmatic patients with nocturnal symptoms than those without nocturnal symptoms. The OVA-induced asthma model with a circadian rhythm disorder and 16HBE cells treated with serum shock showed an increase in IL-6 levels and a negative correlation with BMAL1 and FOXA2. The knockdown of BMAL1 resulted in a lower correlation between IL-6 and other rhythm clock genes. Furthermore, knockdown of the BMAL1 and FOXA2 in 16HBE cells reduced the expression and rhythmic fluctuations of IL-6.

Conclusions

Our findings suggest that there are increased IL-6 levels in nocturnal asthma resulting from inhibition of the BMAL1/FOXA2 signalling pathway in airway epithelial cells.

Fibroblast A20 governs fibrosis susceptibility and its repression by DREAM promotes fibrosis in multiple organs

In addition to autoimmune and inflammatory diseases, variants of the TNFAIP3 gene encoding the ubiquitin-editing enzyme A20 are also associated with fibrosis in systemic sclerosis (SSc). However, it remains unclear how genetic factors contribute to SSc pathogenesis, and which cell types drive the disease due to SSc-specific genetic alterations. We therefore characterize the expression, function, and role of A20, and its negative transcriptional regulator DREAM, in patients with SSc and disease models. Levels of A20 are significantly reduced in SSc skin and lungs, while DREAM is elevated. In isolated fibroblasts, A20 mitigates ex vivo profibrotic responses. Mice haploinsufficient for A20, or harboring fibroblasts-specific A20 deletion, recapitulate major pathological features of SSc, whereas DREAM-null mice with elevated A20 expression are protected. In DREAM-null fibroblasts, TGF-β induces the expression of A20, compared to wild-type fibroblasts. An anti-fibrotic small molecule targeting cellular adiponectin receptors stimulates A20 expression in vitro in wild-type but not A20-deficient fibroblasts and in bleomycin-treated mice. Thus, A20 has a novel cell-intrinsic function in restraining fibroblast activation, and together with DREAM, constitutes a critical regulatory network governing the fibrotic process in SSc. A20 and DREAM represent novel druggable targets for fibrosis therapy.

NF-κB: At the Borders of Autoimmunity and Inflammation

The transcription factor NF-κB regulates multiple aspects of innate and adaptive immune functions and serves as a pivotal mediator of inflammatory response. In the first part of this review, we discuss the NF-κB inducers, signaling pathways, and regulators involved in immune homeostasis as well as detail the importance of post-translational regulation by ubiquitination in NF-κB function. We also indicate the stages of central and peripheral tolerance where NF-κB plays a fundamental role. With respect to central tolerance, we detail how NF-κB regulates medullary thymic epithelial cell (mTEC) development, homeostasis, and function. Moreover, we elaborate on its role in the migration of double-positive (DP) thymocytes from the thymic cortex to the medulla. With respect to peripheral tolerance, we outline how NF-κB contributes to the inactivation and destruction of autoreactive T and B lymphocytes as well as the differentiation of CD4⁺-T cell subsets that are implicated in immune tolerance. In the latter half of the review, we describe the contribution of NF-κB to the pathogenesis of autoimmunity and autoinflammation. The recent discovery of mutations involving components of the pathway has both deepened our understanding of autoimmune disease and informed new therapeutic approaches to treat these illnesses.

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.

Navigating immune cell immunometabolism after liver transplantation

Liver transplantation (LT) is the most effective treatment for end-stage liver diseases. The immunometabolism microenvironment undergoes massive changes at the interface of immune functionalities and metabolic regulations after LT. These changes considerably modify post-transplant complications, and immune cells play an influential role in the hepatic immunometabolism microenvironment after LT. Therefore, adequate studies on the complex pathobiology of immune cells are critical to prevent post-transplant complications, and the interplay between cellular metabolism and immune function is evident. Furthermore, immune cells perform their specified functions, such as activation or differentiation, accompanied by alterations in metabolic pathways, such as metabolic reprogramming. This transformation remarkably affects post-transplant complications like rejection. By targeting different metabolic pathways, regulations of metabolism are employed to shape immune responses. These differences of metabolic pathways allow for selective regulation of immune responses to further develop effective therapies that prevent graft loss after LT. This review examines immune cells in the hepatic immunometabolism microenvironment after LT, summarizes possible mechanisms and potential prevention on rejection to acquire immune tolerance, and offers some insight into references for scientific research along with clinical treatment.

A20/TNFAIP3 heterozygosity predisposes to behavioral symptoms in a mouse model for neuropsychiatric lupus

Background

Neuropsychiatric lupus (NPSLE) refers to the neurological and psychiatric manifestations that are commonly observed in patients with systemic lupus erythematosus (SLE). An important question regarding the pathogenesis of NPSLE is whether the symptoms are caused primarily by CNS-intrinsic mechanisms or develop as a consequence of systemic autoimmunity. Currently used spontaneous mouse models for SLE have already contributed significantly to unraveling how systemic immunity affects the CNS. However, they are less suited when interested in CNS primary mechanisms. In addition, none of these models are based on genes that are associated with SLE. In this study, we evaluate the influence of A20, a well-known susceptibility locus for SLE, on behavior and CNS-associated changes in inflammatory markers. Furthermore, given the importance of environmental triggers for disease onset and progression, the influence of an acute immunological challenge was evaluated.

Methods

Female and male A20 heterozygous mice (A20+/-) and wildtype littermates were tested in an extensive behavioral battery. This was done at the age of 10±2weeks and 24 ​± ​2 weeks to evaluate the impact of aging. To investigate the contribution of an acute immunological challenge, LPS was injected intracerebroventricularly at the age of 10±2weeks followed by behavioral analysis. Underlying molecular mechanisms were evaluated in gene expression assays on hippocampus and cortex. White blood cell count and blood-brain barrier permeability were analyzed to determine whether peripheral inflammation is a relevant factor.

Results

A20 heterozygosity predisposes to cognitive symptoms that were observed at the age of 10 ​± ​2 weeks and 24 ​± ​2 weeks. Young A20+/- males and females showed a subtle cognitive phenotype (10±2weeks) with distinct neuroinflammatory phenotypes. Aging was associated with clear neuroinflammation in female A20+/- mice only. The genetic predisposition in combination with an environmental stimulus exacerbates the behavioral impairments related to anxiety, cognitive dysfunction and sensorimotor gating. This was predominantly observed in females. Furthermore, signs of neuroinflammation were solely observed in female A20+/- mice. All above observations were made in the absence of peripheral inflammation and of changes in blood-brain barrier permeability, thus consistent with the CNS-primary hypothesis.

Conclusions

We show that A20 heterozygosity is a predisposing factor for NPSLE. Further mechanistic insight and possible therapeutic interventions can be studied in this mouse model that recapitulates several key hallmarks of the disease.

A20 rescues hepatocytes from apoptosis through the NF-κB signaling pathway in rats with acute liver failure

Background: Acute liver failure (ALF) is a disease of acute derangements in the hepatic synthetic function with defects involving innate immune responses, which was reported to be negatively regulated by tumor necrosis factor α-induced protein 3 (A20). Herein, the present study was conducted to investigate the effects the A20 protein on the proliferation and apoptosis of hepatocytes through the nuclear factor (NF)-κB signaling pathway in the rat models simulating ALF.Methods: Male Wistar rats were used to simulate ALF in the model rats. Next, the positive expression of A20 and Caspase-3 proteins was measured in liver tissues. Rat hepatocytes were separated and subjected to pyrrolidine dithiocarbamate (PDTC, inhibitor of NF-κB pathway) or A20 siRNA. Additionally, both mRNA and protein levels of A20, NF-κB, tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), and receptor-interacting protein 1 (RIP1) were determined. Finally, we detected the hepatocyte proliferation, cell cycle entry, and apoptosis.Results: ALF rats displayed a lower positive expression of A20 protein and a higher expression of Caspase-3 protein. Furthermore, A20 was down-regulated, while NF-κB, TRAF6, and RIP1 were all up-regulated in ALF rats. Notably, A20 inhibited activation of NF-κB signaling pathway. The blockade of NF-κB signaling pathway enhanced proliferation and cell cycle progression of hepatocytes, whereas inhibited apoptosis of hepatocytes. On the contrary, A20 siRNA reversed the above situation.Conclusion: A20 inhibits apoptosis of hepatocytes and promotes the proliferation through the NF-κB signaling pathway in ALF rats, potentially providing new insight into the treatment of ALF.

Role of IL-17RA in the proliferative priming of hepatocytes in liver regeneration

A tight link has been established between inflammation and cancer. Liver regeneration is a widely used model to study the correlation between inflammation and proliferation. IL-6 is essentially involved in liver regeneration and in cancer. Recently, IL-17A has been shown to regulate not only inflammation, but also cell proliferation. Here, we analyze the role played by IL-17A signaling in liver regeneration by comparing cell proliferation in Wild Type and IL-17RA-/- mice. Partial hepatectomy experiments performed in IL-17RA-/- mice showed a delay in expression of early-genes to prime the residual hepatocyte to proliferate, with subsequent delay in G1/S-phase transition. We demonstrated that IL-17RA regulates, by recruitment of non-parenchymal cell, the expression of IL-6, which in turn triggers the proliferation of residual hepatocytes. Our data indicate an important role played by IL-17RA in liver proliferation via IL-6.

The deubiquitinating enzyme TNFAIP3 mediates inactivation of hepatic ASK1 and ameliorates nonalcoholic steatohepatitis

Activation of apoptosis signal-regulating kinase 1 (ASK1) in hepatocytes is a key process in the progression of nonalcoholic steatohepatitis (NASH) and a promising target for treatment of the condition. However, the mechanism underlying ASK1 activation is still unclear, and thus the endogenous regulators of this kinase remain open to be exploited as potential therapeutic targets. In screening for proteins that interact with ASK1 in the context of NASH, we identified the deubiquitinase tumor necrosis factor alpha-induced protein 3 (TNFAIP3) as a key endogenous suppressor of ASK1 activation, and we found that TNFAIP3 directly interacts with and deubiquitinates ASK1 in hepatocytes. Hepatocyte-specific ablation of Tnfaip3 exacerbated nonalcoholic fatty liver disease- and NASH-related phenotypes in mice, including glucose metabolism disorders, lipid accumulation and enhanced inflammation, in an ASK1-dependent manner. In contrast, transgenic or adeno-associated virus-mediated TNFAIP3 gene delivery in the liver in both mouse and nonhuman primate models of NASH substantially blocked the onset and progression of the disease. These results implicate TNFAIP3 as a functionally important endogenous suppressor of ASK1 hyperactivation in the pathogenesis of NASH and identify it as a potential new molecular target for NASH therapy.

Association of the tandem polymorphisms (rs148314165, rs200820567) in TNFAIP3 with chronic hepatitis B virus infection in Chinese Han population

BACKGROUND

Chronic hepatitis B virus (HBV) infection remains an important public health issue. A20, a ubiquitin-editing protein encoded by tumor necrosis factor alpha-inducible protein 3 (TNFAIP3) gene, is complicated in HBV infection and liver injury. The tandem polymorphisms (rs148314165, rs200820567), deletion T followed by a T to A transversion and collectively referred to as TT > A in TNFAIP3, may attenuate A20 expression.

METHODS

The rs148314165 and rs200820567 polymorphisms were examined using PCR amplification followed by direct sequencing in 419 patients with chronic HBV infection, 77 HBV infection resolvers and 175 healthy controls of Chinese Han ethnicity.

RESULTS

The genotypes and alleles of rs148314165 and rs200820567 polymorphisms determined and the haplotypes constructed were consistently identical, confirming the reliable determination of the TT > A variant. The genotypes of rs148314165 and rs200820567 in HBV patients, HBV infection resolvers and healthy controls are in Hardy-Weinberg equilibrium (P > 0. 05). The patients with chronic HBV infection had higher frequency of TT > A variant than healthy controls (6.6% vs. 3.4%; OR, 1.979; 95% CI, 1.046-3.742; P = 0.033). The frequency of TT > A variant between patients with chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma had no significant differences.

CONCLUSIONS

The TT > A variant of TNFAIP3 may be associated with the susceptibility of chronic HBV infection but not the clinical diseases. Studies in large sample size of HBV patient and control populations are required to further clarify the role of this important variant in chronic HBV infection and the disease progression related to the infection.

Elevated serum A20 is associated with severity of chronic hepatitis B and A20 inhibits NF-κB-mediated inflammatory response

A20 is a powerful suppressor for inflammatory response. This study aims to determine A20 level in patients with chronic hepatitis B (CHB), and analyze its association with the disease severity. The role of A20 in inflammatory response was further investigated in vivo and in vitro. Our results showed significantly higher A20 in both serum and liver tissues in CHB patients than in health controls. Serum A20 level was positively correlated with ALT, AST and TNF-α. To induce hepatitis with inflammation and liver injury, mice were injected intraperitoneally with D-galactosamine (D-GalN), resulting in rapid increase of A20 in serum and liver tissues. Consistently, HepG2 and Huh-7 cells exposed to Lipopolysaccharide (LPS) or D-GalN were promoted to express A20. Moreover, overexpression or knockdown of A20 inhibited or increased TNF-α secretion separately. A20 significantly reduced pro-inflammatory cytokines expression and down-regulated phospho-IκBα and phospho-p65 in both cells. In conclusion, elevated A20 expression is involved in the severity of CHB, suggesting A20 to be a possible serological biomarker for the disease prognosis. Additionally, the inflammatory response is attenuated by A20 through inhibiting NF-κB activity, which partially contributes to the hepato-protective function of this molecule. Thus, up-regulating A20 might be a potential strategy for preventing the progress of CHB.

A20 Haploinsufficiency Aggravates Transplant Arteriosclerosis in Mouse Vascular Allografts: Implications for Clinical Transplantation

BACKGROUND

Inflammation is central to the pathogenesis of transplant arteriosclerosis (TA). We questioned whether physiologic levels of anti-inflammatory A20 influence TA severity.

METHODS

We performed major histocompatibility complex mismatched aorta to carotid artery interposition grafts, using wild type (WT) or A20 heterozygote (HET) C57BL/6 (H-2) donors and BALB/c (H-2) recipients, and conversely BALB/c donors and WT/HET recipients. We analyzed aortic allografts by histology, immunohistochemistry, immunofluorescence, and gene profiling (quantitative real-time reverse-transcriptase polymerase chain reaction). We validated select in vivo A20 targets in human and mouse smooth muscle cell (SMC) cultures.

RESULTS

We noted significantly greater intimal hyperplasia in HET versus WT allografts, indicating aggravated TA. Inadequate upregulation of A20 in HET allografts after transplantation was associated with excessive NF-кB activation, gauged by higher levels of IkBα, p65, VCAM-1, ICAM-1, CXCL10, CCL2, TNF, and IL-6 (mostly localized to SMC). Correspondingly, cytokine-induced upregulation of TNF and IL-6 in human and mouse SMC cultures inversely correlated with A20 expression. Aggravated TA in HET versus WT allografts correlated with increased intimal SMC proliferation, and a higher number of infiltrating IFNγ and Granzyme B CD4 T cells and natural killer cells, and lower number of FoxP3 regulatory T cells. A20 haploinsufficiency in allograft recipients did not influence TA.

CONCLUSIONS

A20 haploinsufficiency in vascular allografts aggravates lesions of TA by exacerbating inflammation, SMC proliferation, and infiltration of pathogenic T cells. A20 single nucleotide polymorphisms associating with lower A20 expression or function in donors of vascularized allografts may inform risk and severity of TA, highlighting the clinical implications of our findings.

A novel glucagon-like peptide 1/glucagon receptor dual agonist improves steatohepatitis and liver regeneration in mice

Because nonalcoholic steatohepatitis (NASH) is associated with impaired liver regeneration, we investigated the effects of G49, a dual glucagon-like peptide-1/glucagon receptor agonist, on NASH and hepatic regeneration. C57Bl/6 mice fed chow or a methionine and choline-deficient (MCD) diet for 1 week were divided into 4 groups: control (chow diet), MCD diet, chow diet plus G49, and M+G49 (MCD diet plus G49). Mice fed a high-fat diet (HFD) for 10 weeks were divided into groups: HFD and H+G49 (HFD plus G49). Following 2 (MCD groups) or 3 (HFD groups) weeks of treatment with G49, partial hepatectomy (PH) was performed, and all mice were maintained on the same treatment schedule for 2 additional weeks. Analysis of liver function, hepatic regeneration, and comprehensive genomic and metabolic profiling were conducted. NASH was ameliorated in the M+G49 group, manifested by reduced inflammation, steatosis, oxidative stress, and apoptosis and increased mitochondrial biogenesis. G49 treatment was also associated with replenishment of intrahepatic glucose due to enhanced gluconeogenesis and reduced glucose use through the pentose phosphate cycle and oxidative metabolism. Following PH, G49 treatment increased survival, restored the cytokine-mediated priming phase, and enhanced the proliferative capacity and hepatic regeneration ratio in mice on the MCD diet. NASH markers remained decreased in M+G49 mice after PH, and glucose use was shifted to the pentose phosphate cycle and oxidative metabolism. G49 administered immediately after PH was also effective at alleviating the pathological changes induced by the MCD diet. Benefits in terms of liver regeneration were also found in mice fed HFD and treated with G49.

CONCLUSION

Dual-acting glucagon-like peptide-1/glucagon receptor agonists such as G49 represent a novel therapeutic approach for patients with NASH and particularly those requiring PH. (Hepatology 2017;65:950-968).

A20 suppresses canonical Smad-dependent fibroblast activation: novel function for an endogenous inflammatory modulator

Background

The ubiquitin-editing cytosolic enzyme A20, the major negative regulator of toll-like receptor (TLR)-mediated cellular inflammatory responses, has tight genetic linkage with systemic sclerosis (SSc). Because recent studies implicate endogenous ligand-driven TLR signaling in SSc pathogenesis, we sought to investigate the regulation, role and mechanism of action of A20 in skin fibroblasts.

Method

A20 expression and the effects of forced A20 expression or siRNA-mediated A20 knockdown on fibrotic responses induced by transforming growth factor-ß (TGF-ß) were evaluated was evaluated in explanted human skin fibroblasts. Additionally, A20 regulation by TGF-ß, and by adiponectin, a pleiotropic adipokine with anti-fibrotic activity, was evaluated.

Results

In normal fibroblasts, TGF-ß induced sustained downregulation of A20, and abrogated its TLR4-dependent induction. Forced expression of A20 aborted the stimulation of collagen gene expression and myofibroblast transformation induced by TGF-ß, and disrupted canonical Smad signaling and Smad-dependent transcriptional responses. Conversely, siRNA-mediated knockdown of A20 enhanced the amplitude of fibrotic responses elicited by TGF-ß. Adiponectin, previously shown to block TLR-dependent fibrotic responses, elicited rapid and sustained increase in A20 accumulation in fibroblasts.

Conclusion

These results identify the ubiquitin-editing enzyme A20 as a novel endogenous mechanism for negative regulation of fibrotic response intensity. Systemic sclerosis-associated genetic variants of A20 that cause impaired A20 expression or function, combined with direct suppression of A20 by TGF-ß within the fibrotic milieu, might play a significant functional role in persistence of fibrotic responses, while pharmacological augmentation of A20 inhibitory pathway activity might represent a novel therapeutic strategy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1118-7) contains supplementary material, which is available to authorized users.

A20 prevents chronic liver inflammation and cancer by protecting hepatocytes from death

An important regulator of inflammatory signalling is the ubiquitin-editing protein A20 that acts as a break on nuclear factor-κB (NF-κB) activation, but also exerts important cytoprotective functions. A20 knockout mice are cachectic and die prematurely due to excessive multi-organ inflammation. To establish the importance of A20 in liver homeostasis and pathology, we developed a novel mouse line lacking A20 specifically in liver parenchymal cells. These mice spontaneously develop chronic liver inflammation but no fibrosis or hepatocellular carcinomas, illustrating an important role for A20 in normal liver tissue homeostasis. Hepatocyte-specific A20 knockout mice show sustained NF-κB-dependent gene expression in the liver upon tumor necrosis factor (TNF) or lipopolysaccharide injection, as well as hepatocyte apoptosis and lethality upon challenge with sublethal doses of TNF, demonstrating an essential role for A20 in the protection of mice against acute liver failure. Finally, chronic liver inflammation and enhanced hepatocyte apoptosis in hepatocyte-specific A20 knockout mice was associated with increased susceptibility to chemically or high fat-diet-induced hepatocellular carcinoma development. Together, these studies establish A20 as a crucial hepatoprotective factor.