The NF-κB subunit RelA/p65 is dispensable for successful liver regeneration after partial hepatectomy in mice

Rapid adaptive and acute stimulatory responses to low salinity stress in Pacific white shrimp (Litopenaeus vannamei): Insights from integrative transcriptomic and proteomic analysis

The Pacific white shrimp (Litopenaeus vannamei) is a euryhaline crustacean capable of tolerating a wide range of ambient salinity, but the strategies of hepatopancreas to rapid adaptive or acute stimulatory responses to extremely low salinity fluctuations remains unclear. In this study, we integrated transcriptomic and proteomic analyses on the hepatopancreas derived from rapid adaptative (RA) and acute stimulatory (AS) responses to extremely low salinity stress (0.3 ppt) to unveil specific regulatory mechanisms. The RA group displayed normal epithelial cells and tubule structures, while the AS group showed histological changes and lesions. A total of 754 and 649 differentially expressed genes (DEGs) were identified in RA and AS treatments, respectively. For proteome, a total of 206 and 66 differentially expressed proteins (DEPs) were obtained in the RA/CT and AS/CT comparison groups, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were conducted among the DEGs and DEPs, revealing that metabolic related pathways were significantly enriched pathways in both comparison groups. In addition, correlation analysis of transcriptomic and proteomic results showed that 20 and 3 pairs of DEGs/DEPs were identified in RA vs. CT and AS vs. CT comparison groups, respectively. This study is the first report on the rapid adaptive and acute stimulatory transcriptomic and proteomic responses of L. vannamei to extremely low salinity, shedding light on the mechanisms underlying osmoregulation in euryhaline crustaceans.

Targeting IKKβ Activity to Limit Sterile Inflammation in Acetaminophen-Induced Hepatotoxicity in Mice

The kinase activity of inhibitory κB kinase β (IKKβ) acts as a signal transducer in the activating pathway of nuclear factor-κB (NF-κB), a master regulator of inflammation and cell death in the development of numerous hepatocellular injuries. However, the importance of IKKβ activity on acetaminophen (APAP)-induced hepatotoxicity remains to be defined. Here, a derivative of caffeic acid benzylamide (CABA) inhibited the kinase activity of IKKβ, as did IMD-0354 and sulfasalazine which show therapeutic efficacy against inflammatory diseases through a common mechanism: inhibiting IKKβ activity. To understand the importance of IKKβ activity in sterile inflammation during hepatotoxicity, C57BL/6 mice were treated with CABA, IMD-0354, or sulfasalazine after APAP overdose. These small-molecule inhibitors of IKKβ activity protected the APAP-challenged mice from necrotic injury around the centrilobular zone in the liver, and rescued the mice from hepatic damage-associated lethality. From a molecular perspective, IKKβ inhibitors directly interrupted sterile inflammation in the Kupffer cells of APAP-challenged mice, such as damage-associated molecular pattern (DAMP)-induced activation of NF-κB activity via IKKβ, and NF-κB-regulated expression of cytokines and chemokines. However, CABA did not affect the upstream pathogenic events, including oxidative stress with glutathione depletion in hepatocytes after APAP overdose. N-acetyl cysteine (NAC), the only FDA-approved antidote against APAP overdose, replenishes cellular levels of glutathione, but its limited efficacy is concerning in late-presenting patients who have already undergone oxidative stress in the liver. Taken together, we propose a novel hypothesis that chemical inhibition of IKKβ activity in sterile inflammation could mitigate APAP-induced hepatotoxicity in mice, and have the potential to complement NAC treatment in APAP overdoses.

Trans-activation of eotaxin-1 by Brg1 contributes to liver regeneration

Infiltration of eosinophils is associated with and contributes to liver regeneration. Chemotaxis of eosinophils is orchestrated by the eotaxin family of chemoattractants. We report here that expression of eotaxin-1 (referred to as eotaxin hereafter), but not that of either eotaxin-2 or eotaxin-3, were elevated, as measured by quantitative PCR and ELISA, in the proliferating murine livers compared to the quiescent livers. Similarly, exposure of primary murine hepatocytes to hepatocyte growth factor (HGF) stimulated eotaxin expression. Liver specific deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated eosinophil infiltration and down-regulated eotaxin expression in mice. Brg1 deficiency also blocked HGF-induced eotaxin expression in cultured hepatocytes. Further analysis revealed that Brg1 could directly bind to the proximal eotaxin promoter to activate its transcription. Mechanistically, Brg1 interacted with nuclear factor kappa B (NF-κB)/RelA to activate eotaxin transcription. NF-κB knockdown or pharmaceutical inhibition disrupted Brg1 recruitment to the eotaxin promoter and blocked eotaxin induction in hepatocytes. Adenoviral mediated over-expression of eotaxin overcame Brg1 deficiency caused delay in liver regeneration in mice. On the contrary, eotaxin depletion with RNAi or neutralizing antibodies retarded liver regeneration in mice. More important, Brg1 expression was detected to be correlated with eotaxin expression and eosinophil infiltration in human liver specimens. In conclusion, our data unveil a novel role of Brg1 as a regulator of eosinophil trafficking by activating eotaxin transcription.

Analysis of miRNAs Profiles in Serum of Patients With Steatosis and Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is emerging as one of the most common chronic liver diseases worldwide, affecting 25% of the world population. In recent years, there has been increasing evidence for the involvement of microRNAs in the epigenetic regulation of genes taking part in the development of steatosis and steatohepatitis—two main stages of NAFLD pathogenesis. In the present study, miRNA profiles were studied in groups of patients with steatosis and steatohepatitis to compare the characteristics of RNA-dependent epigenetic regulation of the stages of NAFLD development. According to the results of miRNA screening, 23 miRNAs were differentially expressed serum in a group of patients with steatohepatitis and 2 in a group of patients with steatosis. MiR-195-5p and miR-16-5p are common differentially expressed miRNAs for both steatosis and steatohepatitis. We analyzed the obtained results: the search for target genes for the differentially expressed miRNAs in our study and the subsequent gene set enrichment analysis performed on KEGG and REACTOME databases revealed which metabolic pathways undergo changes in RNA-dependent epigenetic regulation in steatosis and steatohepatitis. New findings within the framework of this study are the dysregulation of neurohumoral pathways in the pathogenesis of NAFLD as an object of changes in RNA-dependent epigenetic regulation. The miRNAs differentially expressed in our study were found to target 7% of genes in the classic pathogenesis of NAFLD in the group of patients with steatosis and 50% in the group of patients with steatohepatitis. The effects of these microRNAs on genes for the pathogenesis of NAFLD were analyzed in detail. MiR-374a-5p, miR-1-3p and miR-23a-3p do not target genes directly involved in the pathogenesis of NAFLD. The differentially expressed miRNAs found in this study target genes largely responsible for mitochondrial function. The role of miR-423-5p, miR-143-5p and miR-200c-3 in regulating apoptotic processes in the liver and hepatocarcinogenesis is of interest for future experimental studies. These miR-374a, miR-143, miR-1, miR-23a, and miR-423 have potential for steatohepatitis diagnosis and are poorly studied in the context of NAFLD. Thus, this work opens up prospects for further studies of microRNAs as diagnostic and therapeutic biomarkers for NAFLD.

Nuclear factor-kappa B influences early phase of compensatory lung growth after pneumonectomy in mice

Background

Compensatory lung growth (CLG) is a well-established lung regeneration model. However, the sequential mechanisms, including unknown molecular triggers or regulators, remain unclear. Nuclear factor- kappa B (NF-κB) is known to be essential for inflammation and tissue regeneration; therefore, we investigated the role of NF-κB in CLG.

Methods

C57BL/6 J mice underwent either a left pneumonectomy or a thoracotomy (n = 77). Gene microarray analysis was performed to detect genes that were upregulated at 12 h after pneumonectomy. NF-κB protein expression was examined by immunohistochemistry and Western blot. To investigate the influence of NF-κB on CLG, either an NF-κB inhibitor SN50 or saline was administered following pneumonectomy and the degree of CLG was evaluated in each group by measuring the lung dry weight index (LDWI) and the mean linear intercept.

Results

Gene microarray analysis identified 11 genes that were significantly but transiently increased at 12 h after pneumonectomy. Among the 11 genes, NF-κB was selected based on its reported functions. Western blot analysis showed that NF-κB protein expression after pneumonectomy was significantly higher at 12 h compared to 48 h. Additionally, NF-κB protein expression at 12 h after pneumonectomy was significantly higher than at both 12 and 48 h after thoracotomy (p < 0.029 for all). NF-κB protein expression, evaluated through immunohistochemistry, was expressed mainly in type 2 alveolar epithelial cells and was significant increased 12 h after pneumonectomy compared to 48 h after pneumonectomy and both 12 and 48 h after thoracotomy (p < 0.001 for all). SN50 administration following pneumonectomy induced a significant decrease in NF-κB expression (p = 0.004) and LDWI compared to the vehicle administration (p = 0.009).

Conclusions

This is the first report demonstrating that NF-κB signaling may play a key role in CLG. Given its pathway is crucial in tissue regeneration of various organs, NF-κB may shed light on identification of molecular triggers or clinically usable key regulators of CLG.

mTOR activation protects liver from ischemia/reperfusion-induced injury through NF-κB pathway

Hepatic steatosis renders liver more vulnerable to ischemia/reperfusion injury (IRI), which commonly occurs in transplantation, trauma, and liver resection. The underlying mechanism is not fully characterized. We aimed to clarify the role of mechanistic target of rapamycin (mTOR) signaling in hepatic ischemia/reperfusion injury (HIRI) in normal and steatotic liver using Alb-TSC1^-/- (AT) and Alb-mTOR^-/- (Am) transgenic mice. Steatotic liver induced by high-fat diet was more vulnerable to IRI. Activation of hepatic mTOR in AT mice decreased lipid accumulation attenuated HIRI as measured by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, circulating levels of alanine aminotransferase and lactate dehydrogenase, and inflammatory mediators such as monocyte chemoattractant protein 1 (MCP-1), TNF-α, and IL-6 and hepatic cleaved caspase 3 in mice fed either a normal chow diet or a high-fat diet. The effects of mTOR activation on hepatic cleaved caspase 3 were reversed by rapamycin, an inhibitor of mTOR signaling. Inhibition of hepatic mTOR in Am mice increased hepatic lipid deposition and HIRI. The increment in hepatic susceptibility to IRI was significantly attenuated by pretreatment with IKKβ inhibitor. Further, suppression of mTOR facilitated nuclear translocation of NF-κB p65. In conclusion, our study suggests that mTOR activity in hepatocytes decreases hepatic vulnerability to injury through a mechanism dependent on NF-κB proinflammatory cytokine signaling pathway in both normal and steatotic liver.-Li, Z., Zhang, J., Mulholland, M., Zhang, W. mTOR activation protects liver from ischemia/reperfusion-induced injury through NF-κB pathway.

A RelA(p65) Thr505 phospho-site mutation reveals an important mechanism regulating NF-κB-dependent liver regeneration and cancer

Post-translational modifications of nuclear factor (NF)-κB subunits provide a mechanism to differentially regulate their activity in response to the many stimuli that induce this pathway. However, the physiological significance of these modifications is largely unknown, and it remains unclear if these have a critical role in the normal and pathological functions of NF-κB in vivo. Among these, phosphorylation of the RelA(p65) Thr505 residue has been described as an important regulator of NF-κB activity in cell lines, but its physiological significance was not known. Therefore, to learn more about the role of this pathway in vivo, we generated a knockin mouse with a RelA T505A mutation. Unlike RelA knockout mice, the RelA T505A mice develop normally but exhibit aberrant hepatocyte proliferation following liver partial hepatectomy or damage resulting from carbon tetrachloride (CCl4) treatment. Consistent with these effects, RelA T505A mice exhibit earlier onset of cancer in the N-nitrosodiethylamine model of hepatocellular carcinoma. These data reveal a critical pathway controlling NF-κB function in the liver that acts to suppress the tumour-promoting activities of RelA.

A novel comparative pattern count analysis reveals a chronic ethanol-induced dynamic shift in immediate early NF-κB genome-wide promoter binding during liver regeneration

Liver regeneration after partial hepatectomy is a clinically important process that is impaired by adaptation to chronic alcohol intake. We focused on the initial time points following partial hepatectomy (PHx) to analyze the genome-wide binding activity of NF-κB, a key immediate early regulator. We investigated the effect of chronic alcohol intake on immediate early NF-κB genome-wide localization, in the adapted state as well as in response to partial hepatectomy, using chromatin immunoprecipitation followed by promoter microarray analysis. We found many ethanol-specific NF-κB binding target promoters in the ethanol-adapted state, corresponding to the regulation of biosynthetic processes, oxidation-reduction and apoptosis. Partial hepatectomy induced a diet-independent shift in NF-κB binding loci relative to the transcription start sites. We employed a novel pattern count analysis to exhaustively enumerate and compare the number of promoters corresponding to the temporal binding patterns in ethanol and pair-fed control groups. The highest pattern count corresponded to promoters with NF-κB binding exclusively in the ethanol group at 1 h post PHx. This set was associated with the regulation of cell death, response to oxidative stress, histone modification, mitochondrial function, and metabolic processes. Integration with the global gene expression profiles to identify putative transcriptional consequences of NF-κB binding patterns revealed that several of ethanol-specific 1 h binding targets showed ethanol-specific differential expression through 6 h post PHx. Motif analysis yielded co-incident binding loci for STAT3, AP-1, CREB, C/EBP-β, PPAR-γ and C/EBP-α, likely participating in co-regulatory modules with NF-κB in shaping the immediate early response to PHx. We conclude that adaptation to chronic ethanol intake disrupts the NF-κB promoter binding landscape with consequences for the immediate early gene regulatory response to the acute challenge of PHx.

Liver regeneration after partial hepatectomy

Liver regeneration after partial hepatectomy is an extremely complicated pathophysiologic process, which involves the up-regulation of many proliferation associated proteins and genes. The molecular mechanisms responsible for initiating, maintaining, and terminating this process are still under active investigation and remain one of the research focuses in the field of regenerative medicine. Studies of the mechanism of liver regeneration can provide a theoretical foundation for regeneration promotion and hepatic failure prevention, which is extremely important in clinical practice. This review aims to elucidate the molecular mechanism responsible for the initiation, proliferation and termination of liver regeneration.

A novel, dynamic pattern-based analysis of NF-κB binding during the priming phase of liver regeneration reveals switch-like functional regulation of target genes

Following partial hepatectomy, a coordinated series of molecular events occurs to regulate hepatocyte entry into the cell cycle to recover lost mass. In rats during the first 6 h following resection, hepatocytes are primed by a tightly controlled cytokine response to prepare hepatocytes to begin replication. Although it appears to be a critical element driving regeneration, the cytokine response to resection has not yet been fully characterized. Specifically, the role of one of the key response elements to cytokine signaling (NF-κB) remains incompletely characterized. In this study, we present a novel, genome-wide, pattern-based analysis characterizing NF-κB binding during the priming phase of liver regeneration. We interrogated the dynamic regulation of priming by NF-κB through categorizing NF-κB binding in different temporal profiles: immediate sustained response, early transient response, and delayed response to partial hepatectomy. We then identified functional regulation of NF-κB binding by relating the temporal response profile to differential gene expression. We found that NF-κB bound genes govern negative regulation of cell growth and inflammatory response immediately following hepatectomy. NF-κB also transiently regulates genes responsible for lipid biosynthesis and transport as well as induction of apoptosis following hepatectomy. By the end of the priming phase, NF-κB regulation of genes involved in inflammatory response, negative regulation of cell death, and extracellular structure organization became prominent. These results suggest that NF-κB regulates target genes through binding and unbinding in immediate, transient, and delayed patterns. Such dynamic switch-like patterns of NF-κB binding may govern different functional transitions that drive the onset of regeneration.

Blockade of the apelin-APJ system promotes mouse liver regeneration by activating Kupffer cells after partial hepatectomy

BACKGROUND

Liver regeneration after massive hepatectomy or living donor liver transplantation is critical. The apelin-APJ system is involved in the regulation of cardiovascular function, inflammation, fluid homeostasis, the adipo-insular axis, and angiogenesis, but its function in liver regeneration remains unclear.

METHODS

We investigated the impact of pharmacologic blockade of the apelin-APJ system, using the specific APJ antagonist F13A on liver regeneration after hepatectomy in mice.

RESULTS

F13A-treated mice had significantly higher serum concentrations of tumor necrosis factor (TNF)-α and interleukin (IL)-6 than control mice, due to F13A-promoted activation of Kupffer cells. Compared with untreated mice, F13A enhanced the signal transducer and activator of transcription 3 and mitogen-activated protein kinase pathways, stimulated cell-cycle progression, and promoted hepatocyte proliferation and liver regeneration without inducing apoptosis or inflammation in regenerating livers. In vitro, Kupffer cells expressed APJ and were activated directly by F13A treatment, releasing TNF-α and IL-6. Moreover, F13A-treated mice had a higher survival rate than untreated mice in the extended hepatectomy model.

CONCLUSIONS

F13A treatment promotes early phase liver regeneration after hepatectomy by promoting the activation of Kupffer cells and increasing serum levels of TNF-α and IL-6. F13A treatment may become a therapeutic option to facilitate efficient liver regeneration after liver surgery.

Lineage fate of ductular reactions in liver injury and carcinogenesis

Ductular reactions (DRs) are observed in virtually all forms of human liver disease; however, the histogenesis and function of DRs in liver injury are not entirely understood. It is widely believed that DRs contain bipotential liver progenitor cells (LPCs) that serve as an emergency cell pool to regenerate both cholangiocytes and hepatocytes and may eventually give rise to hepatocellular carcinoma (HCC). Here, we used a murine model that allows highly efficient and specific lineage labeling of the biliary compartment to analyze the histogenesis of DRs and their potential contribution to liver regeneration and carcinogenesis. In multiple experimental and genetic liver injury models, biliary cells were the predominant precursors of DRs but lacked substantial capacity to produce new hepatocytes, even when liver injuries were prolonged up to 12 months. Genetic modulation of NOTCH and/or WNT/β-catenin signaling within lineage-tagged DRs impaired DR expansion but failed to redirect DRs from biliary differentiation toward the hepatocyte lineage. Further, lineage-labeled DRs did not produce tumors in genetic and chemical HCC mouse models. In summary, we found no evidence in our system to support mouse biliary-derived DRs as an LPC pool to replenish hepatocytes in a quantitatively relevant way in injury or evidence that DRs give rise to HCCs.

The direct and indirect roles of HBV in liver cancer: prospective markers for HCC screening and potential therapeutic targets

Chronic hepatitis B virus (HBV) infection remains the number one risk factor for hepatocellular carcinoma (HCC), accounting for more than 600 000 deaths/year. Despite highly effective antiviral treatment options, chronic hepatitis B (CHB), subsequent end-stage liver disease and HCC development remain a major challenge worldwide. In CHB, liver damage is mainly caused by the influx of immune cells and destruction of infected hepatocytes, causing necro-inflammation. Treatment with nucleoside/nucleotide analogues can effectively suppress HBV replication in patients with CHB and thus decrease the risk for HCC development. Nevertheless, the risk of HCC in treated patients showing sufficient suppression of HBV DNA replication is significantly higher than in patients with inactive CHB, regardless of the presence of baseline liver cirrhosis, suggesting direct, long-lasting, predisposing effects of HBV. Direct oncogenic effects of HBV include integration in the host genome, leading to deletions, cis/trans-activation, translocations, the production of fusion transcripts and generalized genomic instability, as well as pleiotropic effects of viral transcripts (HBsAg and HBx). Analysis of these viral factors in active surveillance may allow early identification of high-risk patients, and their integration into a molecular classification of HCC subtypes might help in the development of novel therapeutic approaches.

p38 MAPK: a dual role in hepatocyte proliferation through reactive oxygen species

p38 MAPKs are important mediators of signal transduction that respond to a wide range of extracellular stressors such as UV radiation, osmotic shock, hypoxia, pro-inflammatory cytokines, and oxidative stress. The most abundant family member is p38α, which helps to couple cell proliferation and growth in response to certain damaging stimuli. In fact, increased proliferation and impaired differentiation are hallmarks of p38α-deficient cells. It has been reported that reactive oxygen species (ROS) play a critical role in cytokine-induced p38α activation. Under physiological conditions, p38α can function as a mediator of ROS signaling and either activate or suppress cell cycle progression depending on the activation stimulus. The interplay between cell proliferation, p38 MAPK activation, and ROS production plays an important role in hepatocytes. In fact, low levels of ROS seem to be needed to activate several signaling pathways in response to hepatectomy and to orchestrate liver regeneration. p38 MAPK works as a sensor of oxidative stress and cells that have developed mechanisms to uncouple p38 MAPK activation from oxidative stress are more likely to become tumorigenic. So far, p38α influences the redox balance, determining cell survival, terminal differentiation, proliferation, and senescence. Further studies would be necessary in order to clarify the precise role of p38 MAPK signaling as a redox therapeutical target.

Direct effects of hepatitis B virus-encoded proteins and chronic infection in liver cancer development

Hepatocellular carcinoma (HCC) ranks as the third leading cause of cancer-related death worldwide with currently limited treatment options. Chronic hepatitis B virus (HBV) infection accounts for HCC development in more than 50% of cases. The lifetime risk of HBV carriers to develop cirrhosis, liver failure or HCC is estimated to be as high as 15-40%. Although several pathways and triggers contributing to HCC development have been described, many features of hepatocellular carcinogenesis and the attributed direct role of viral factors remain elusive. Host genetic factors, the geographic area and epidemiologic factors, as well as the direct risk related to chronic HBV and hepatitis C virus (HCV) infections, account for geographical and gender differences of HCC prevalence. There is growing evidence that hepatocarcinogenesis is a multistep process. Human HCC is typically preceded by chronic inflammation and apoptotic and nonapoptotic cell death with compensatory liver proliferation. However, we still lack a thorough understanding of the common underlying molecular mechanisms. High levels of HBV replication and chronicity of inflammation are known to independently increase the risk for HCC. A direct carcinogenic role of viral factors is very likely to contribute to liver cancer since HCC is known to also occur in noncirrhotic livers of individuals with an inactive chronic or even with occult HBV infection with no significant histological signs of inflammation or cytopathic effects. Furthermore, synergistic or independent viral risk factors for primary liver cancer development have been described, such as HBV genotype, integration of viral DNA into the host genome and direct effects of viral proteins. A broader understanding of these viral factors in hepatocarcinogenesis might give rise to new diagnostic and therapeutic means in the future. We review the current state of research in liver cancer development and focus on the role of direct viral factors in HBV infection.