Keap1 modulates the redox cycle and hepatocyte cell cycle in regenerating liver

Metabolic reprogramming in Nrf2-driven proliferation of normal rat hepatocytes

BACKGROUND AND AIMS

Cancer cells reprogram their metabolic pathways to support bioenergetic and biosynthetic needs and to maintain their redox balance. In several human tumors, the Keap1-Nrf2 system controls proliferation and metabolic reprogramming by regulating the pentose phosphate pathway (PPP). However, whether this metabolic reprogramming also occurs in normal proliferating cells is unclear.

APPROACH AND RESULTS

To define the metabolic phenotype in normal proliferating hepatocytes, we induced cell proliferation in the liver by 3 distinct stimuli: liver regeneration by partial hepatectomy and hepatic hyperplasia induced by 2 direct mitogens: lead nitrate (LN) or triiodothyronine. Following LN treatment, well-established features of cancer metabolic reprogramming, including enhanced glycolysis, oxidative PPP, nucleic acid synthesis, NAD + /NADH synthesis, and altered amino acid content, as well as downregulated oxidative phosphorylation, occurred in normal proliferating hepatocytes displaying Nrf2 activation. Genetic deletion of Nrf2 blunted LN-induced PPP activation and suppressed hepatocyte proliferation. Moreover, Nrf2 activation and following metabolic reprogramming did not occur when hepatocyte proliferation was induced by partial hepatectomy or triiodothyronine.

CONCLUSIONS

Many metabolic changes in cancer cells are shared by proliferating normal hepatocytes in response to a hostile environment. Nrf2 activation is essential for bridging metabolic changes with crucial components of cancer metabolic reprogramming, including the activation of oxidative PPP. Our study demonstrates that matured hepatocytes exposed to LN undergo cancer-like metabolic reprogramming and offers a rapid and useful in vivo model to study the molecular alterations underpinning the differences/similarities of metabolic changes in normal and neoplastic hepatocytes.

KEAP1 promotes anti-tumor immunity by inhibiting PD-L1 expression in NSCLC

Immunotherapy has become a prominent first-line cancer treatment strategy. In non-small cell lung cancer (NSCLC), the expression of PD-L1 induces an immuno-suppressive effect to protect cancer cells from immune elimination, which designates PD-L1 as an important target for immunotherapy. However, little is known about the regulation mechanism and the function of PD-L1 in lung cancer. In this study, we have discovered that KEAP1 serves as an E3 ligase to promote PD-L1 ubiquitination and degradation. We found that overexpression of KEAP1 suppressed tumor growth and promoted cytotoxic T-cell activation in vivo. These results indicate the important role of KEAP1 in anti-cancer immunity. Moreover, the combination of elevated KEAP1 expression with anti-PD-L1 immunotherapy resulted in a synergistic effect on both tumor growth and cytotoxic T-cell activation. Additionally, we found that the expressions of KEAP1 and PD-L1 were associated with NSCLC prognosis. In summary, our findings shed light on the mechanism of PD-L1 degradation and how NSCLC immune escape through KEAP1-PD-L1 signaling. Our results also suggest that KEAP1 agonist might be a potential clinical drug to boost anti-tumor immunity and improve immunotherapies in NSCLC.

Study of the effect of keap1 on oxidative stress in human umbilical cord mesenchymal stem cells

BACKGROUND

HucMSCs had shown promising efficacy in treating childhood diseases, but oxidative stress induced by the poor microenvironment at the site of damage resulted in low cell survival after transplantation, thus preventing the cells from maximizing therapeutic efficacy. Therefore, this study aimed to investigate the role and mechanism of keap1 in oxidative stress injury of human umbilical cord mesenchymal stem cells (hucMSCs), and to provide theoretical support for improving the efficacy of stem cell therapy.

METHODS

The hucMSCs were treated with hypoxic low-sugar-free serum (GSDH) to mimic the damaged site microenvironment after implantation. Adenoviral overexpression of keap1 gene of hucMSCs was performed in vitro, and cell proliferation ability was detected by CCK8 assay, crystal violet staining assay, and cell cycle assay. Cellular redox level was assessed by Amplex Red, MDA, and GSH/GSSG kit. Mitochondrial morphology was evaluated by mitotracker Red staining. ATP production was estimated by ATP detection kit. The mRNA and protein expression levels were tested by western blotting and RT-qPCR.

RESULTS

GSDH treatment substantially upregulated keap1 expression. Subsequently, we found that overexpression of keap1 notably inhibited cell proliferation and caused cells to stagnate in G1 phase. At the same time, overexpression of keap1 induced the production of large amounts of H2O2 and the accumulation of MDA, but suppressed the GSH/GSSG ratio and the expression of antioxidant proteins NQO1 and SOD1, which caused oxidative stress damage. Overexpression of keap1 induced cells to produce a large number of dysfunctional mitochondria resulting in reduced ATP production. Moreover, Overexpression of keap1 significantly decreased the IKKβ protein level, while upregulating IkB mRNA levels and downregulating P50 mRNA levels.

CONCLUSIONS

Overexpression of keap1 may induce oxidative stress injury in hucMSCs by down-regulating IKKβ expression and inhibiting NF-κB pathway activation. This implies the importance of keap1 in hucMSCs and it may be a potential gene for genetic modification of hucMSCs.

Advances in Understanding the Role of NRF2 in Liver Pathophysiology and Its Relationship with Hepatic-Specific Cyclooxygenase-2 Expression

Oxidative stress and inflammation play an important role in the pathophysiological changes of liver diseases. Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that positively regulates the basal and inducible expression of a large battery of cytoprotective genes, thus playing a key role in protecting against oxidative damage. Cyclooxygenase-2 (COX-2) is a key enzyme in prostaglandin biosynthesis. Its expression has always been associated with the induction of inflammation, but we have shown that, in addition to possessing other benefits, the constitutive expression of COX-2 in hepatocytes is beneficial in reducing inflammation and oxidative stress in multiple liver diseases. In this review, we summarized the role of NRF2 as a main agent in the resolution of oxidative stress, the crucial role of NRF2 signaling pathways during the development of chronic liver diseases, and, finally we related its action to that of COX-2, where it appears to operate as its partner in providing a hepatoprotective effect.

Targeting NRF2 to promote epithelial repair

The transcription factor NRF2 is well known as a master regulator of the cellular stress response. As such, activation of NRF2 has gained widespread attention for its potential to prevent tissue injury, but also as a possible therapeutic approach to promote repair processes. While NRF2 activation affects most or even all cell types, its effect on epithelial cells during repair processes has been particularly well studied. In response to tissue injury, these cells proliferate, migrate and/or spread to effectively repair the damage. In this review, we discuss how NRF2 governs repair of epithelial tissues, and we highlight the increasing number of NRF2 targets with diverse roles in regulating epithelial repair.

Transcription Factor NRF2 Participates in Cell Cycle Progression at the Level of G1/S and Mitotic Checkpoints

Transcription factor NRF2 is a master regulator of the multiple cytoprotective responses that confer growth advantages on a cell. However, its participation in the mechanisms that govern the cell division cycle has not been explored in detail. In this study, we used several standard methods of synchronization of proliferating cells together with flow cytometry and monitored the participation of NRF2 along the cell cycle by the knockdown of its gene expression. We found that the NRF2 levels were highest at S phase entry, and lowest at mitosis. NRF2 depletion promoted both G1 and M arrest. Targeted transcriptomics analysis of cell cycle regulators showed that NRF2 depletion leads to changes in key cell cycle regulators, such as CDK2, TFDP1, CDK6, CDKN1A (p21), CDKN1B (p27), CCNG1, and RAD51. This study gives a new dimension to NRF2 effects, showing their implication in cell cycle progression.

Pharmacological Activation of Nrf2 Enhances Functional Liver Regeneration

BACKGROUND AND AIMS

The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) regulates an array of cytoprotective genes, yet studies in transgenic mice have led to conflicting reports on its role in liver regeneration. We aimed to test the hypothesis that pharmacological activation of Nrf2 would enhance liver regeneration.

APPROACH AND RESULTS

Wild-type and Nrf2 null mice were administered bardoxolone methyl (CDDO-Me), a potent activator of Nrf2 that has entered clinical development, and then subjected to two-thirds partial hepatectomy. Using translational noninvasive imaging techniques, CDDO-Me was shown to enhance the rate of restoration of liver volume (MRI) and improve liver function (multispectral optoacoustic imaging of indocyanine green clearance) in wild-type, but not Nrf2 null, mice following partial hepatectomy. Using immunofluorescence imaging and whole transcriptome analysis, these effects were found to be associated with an increase in hepatocyte hypertrophy and proliferation, the suppression of immune and inflammatory signals, and metabolic adaptation in the remnant liver tissue. Similar processes were modulated following exposure of primary human hepatocytes to CDDO-Me, highlighting the potential relevance of our findings to patients.

CONCLUSIONS

Our results indicate that pharmacological activation of Nrf2 is a promising strategy for enhancing functional liver regeneration. Such an approach could therefore aid the recovery of patients undergoing liver surgery and support the treatment of acute and chronic liver disease.

Research Progress on Oxidative Stress and Its Nutritional Regulation Strategies in Pigs

Oxidative stress refers to the dramatic increase in the production of free radicals in human and animal bodies or the decrease in the ability to scavenging free radicals, thus breaking the antioxidation-oxidation balance. Various factors can induce oxidative stress in pig production. Oxidative stress has an important effect on pig performance and healthy growth, and has become one of the important factors restricting pig production. Based on the overview of the generation of oxidative stress, its effects on pigs, and signal transduction pathways, this paper discussed the nutritional measures to alleviate oxidative stress in pigs, in order to provide ideas for the nutritional research of anti-oxidative stress in pigs.

Nrf2 in Neoplastic and Non-Neoplastic Liver Diseases

Simple Summary

Although the Keap1-Nrf2 pathway represents a powerful cell defense mechanism against a variety of toxic insults, its role in acute or chronic liver damage and tumor development is not completely understood. This review addresses how Nrf2 is involved in liver pathophysiology and critically discusses the contrasting results emerging from the literature. The aim of the present report is to stimulate further investigation on the role of Nrf2 that could lead to define the best strategies to therapeutically target this pathway.

Abstract

Activation of the Keap1/Nrf2 pathway, the most important cell defense signal, triggered to neutralize the harmful effects of electrophilic and oxidative stress, plays a crucial role in cell survival. Therefore, its ability to attenuate acute and chronic liver damage, where oxidative stress represents the key player, is not surprising. On the other hand, while Nrf2 promotes proliferation in cancer cells, its role in non-neoplastic hepatocytes is a matter of debate. Another topic of uncertainty concerns the nature of the mechanisms of Nrf2 activation in hepatocarcinogenesis. Indeed, it remains unclear what is the main mechanism behind the sustained activation of the Keap1/Nrf2 pathway in hepatocarcinogenesis. This raises doubts about the best strategies to therapeutically target this pathway. In this review, we will analyze and discuss our present knowledge concerning the role of Nrf2 in hepatic physiology and pathology, including hepatocellular carcinoma. In particular, we will critically examine and discuss some findings originating from animal models that raise questions that still need to be adequately answered.

Beyond repression of Nrf2: An update on Keap1

Nrf2 (NFE2L2 - nuclear factor (erythroid-derived 2)-like 2) is a transcription factor, which is repressed by interaction with a redox-sensitive protein Keap1 (Kelch-like ECH-associated protein 1). Deregulation of Nrf2 transcriptional activity has been described in the pathogenesis of multiple diseases, and the Nrf2/Keap1 axis has emerged as a crucial modulator of cellular homeostasis. Whereas the significance of Nrf2 in the modulation of biological processes has been well established and broadly discussed in detail, the focus on Keap1 rarely goes beyond the regulation of Nrf2 activity and redox sensing. However, recent studies and scrutinized analysis of available data point to Keap1 as an intriguing and potent regulator of cellular function. This review aims to shed more light on Keap1 structure, interactome, regulation and non-canonical functions, thereby enhancing its significance in cell biology. We also intend to highlight the impact of balance between Keap1 and Nrf2 in the maintenance of cellular homeostasis.

Activation of Nrf2/AREs-mediated antioxidant signalling, and suppression of profibrotic TGF-β1/Smad3 pathway: a promising therapeutic strategy for hepatic fibrosis - A review

Hepatic fibrosis (HF) is a wound-healing response that occurs during chronic liver injury and features by an excessive accumulation of extracellular matrix (ECM) components. Activation of hepatic stellate cell (HSC), the leading effector in HF, is responsible for overproduction of ECM. It has been documented that transforming growth factor-β1 (TGF-β1) stimulates superfluous accumulation of ECM and triggers HSCs activation mainly via canonical Smad-dependent pathway. Also, the pro-fibrogenic TGF-β1 is correlated with generation of reactive oxygen species (ROS) and inhibition of antioxidant mechanisms. Moreover, involvement of oxidative stress (OS) can be clearly elucidated as a fundamental event in liver fibrogenesis. Nuclear factor erythroid 2-related factor 2-antioxidant response elements (Nrf2-AREs) pathway, a group of OS-mediated transcription factors with diverse downstream targets, is associated with the induction of diverse detoxifying enzymes and the most pivotal endogenous antioxidative system. More specifically, Nrf2-AREs pathway has recently assigned as a new therapeutic target for cure of HF. The overall goal of this review will focus on recent findings about activation of Nrf2-AREs-mediated antioxidant and suppression of profibrotic TGF-β1/Smad3 pathway in the liver, providing an overview of recent advances in transcriptional repressors that dislocated during HF formation, and highlighting possible novel therapeutic targets for liver fibrosis.

Pregnancy facilitates maternal liver regeneration after partial hepatectomy

Liver resection induces robust liver regrowth or regeneration to compensate for the lost tissue mass. In a clinical setting, pregnant women may need liver resection without terminating pregnancy in some cases. However, how pregnancy affects maternal liver regeneration remains elusive. We performed 70% partial hepatectomy (PH) in nonpregnant mice and gestation day 14 mice, and histologically and molecularly compared their liver regrowth during the next 4 days. We found that compared with the nonpregnant state, pregnancy altered the molecular programs driving hepatocyte replication, indicated by enhanced activities of epidermal growth factor receptor and STAT5A, reduced activities of cMet and p70S6K, decreased production of IL-6, TNFα, and hepatocyte growth factor, suppressed cyclin D1 expression, increased cyclin A1 expression, and early activated cyclin A2 expression. As a result, pregnancy allowed the remnant hepatocytes to enter the cell cycle at least 12 h earlier, increased hepatic fat accumulation, and enhanced hepatocyte mitosis. Consequently, pregnancy ameliorated maternal liver regeneration following PH. In addition, a report showed that maternal liver regrowth after PH is driven mainly by hepatocyte hypertrophy rather than hyperplasia during the second half of gestation in young adult mice. In contrast, we demonstrate that maternal liver relies mainly on hepatocyte hyperplasia instead of hypertrophy to restore the lost mass after PH. Overall, we demonstrate that pregnancy facilitates maternal liver regeneration likely via triggering an early onset of hepatocyte replication, accumulating excessive liver fat, and promoting hepatocyte mitosis. The results from our current studies enable us to gain more insights into how maternal liver regeneration progresses during gestation.NEW & NOTEWORTHY We demonstrate that pregnancy may generate positive effects on maternal liver regeneration following partial hepatectomy, which are manifested by early entry of the cell cycle of remnant hepatocytes, increased hepatic fat accumulation, enhanced hepatocyte mitosis, and overall accelerated liver regrowth.

In-Depth Proteome Analysis Highlights HepaRG Cells as a Versatile Cell System Surrogate for Primary Human Hepatocytes

Of the hepatic cell lines developed for in vitro studies of hepatic functions as alternatives to primary human hepatocytes, many have lost major liver-like functions, but not HepaRG cells. The increasing use of the latter worldwide raises the need for establishing the reference functional status of early biobanked HepaRG cells. Using deep proteome and secretome analyses, the levels of master regulators of the hepatic phenotype and of the structural elements ensuring biliary polarity were found to be close to those in primary hepatocytes. HepaRG cells proved to be highly differentiated, with functional mitochondria, hepatokine secretion abilities, and an adequate response to insulin. Among differences between primary human hepatocytes and HepaRG cells, the factors that possibly support HepaRG transdifferentiation properties are discussed. The HepaRG cell system thus appears as a robust surrogate for primary hepatocytes, which is versatile enough to study not only xenobiotic detoxification, but also the control of hepatic energy metabolism, secretory function and disease-related mechanisms.

Notch signaling pathway regulates cell cycle in proliferating hepatocytes involved in liver regeneration

BACKGROUND AND AIM

It has been well documented that Notch signaling is involved in liver regeneration. However, the exact molecular mechanism mediating this process is not fully elucidated. The current study aimed to investigate the role of Notch signaling regulating cell cycle in proliferating hepatocytes in liver regeneration after partial hepatectomy (PHx, 67% resection) and the related molecular mechanism.

METHODS

Partial hepatectomy was performed in Sprague Dawley rats, and remnant livers were harvested 0, 1, 3, 5, and 7 days after operation, and primary hepatocytes were isolated to investigate the molecular mechanism.

RESULTS

Notch signaling activation and hepatocyte proliferation were significantly increased after PHx, while treatment with FLI-06, the inhibitor of γ-secreting enzyme, blocked these trends. Besides, inhibition of Notch signaling led to dysregulation of cell cycle and cell-cycle components. Furthermore, Akti-1/2 (a selective Akt inhibitor) and PX-478 (a selective Hif-1α inhibitor) inhibited hepatocyte proliferation and liver regeneration after PHx, and the effect of downstream molecules activation by Jagged-1 (Notch-1 ligand) in hepatocytes was abolished by FLI-06, Akti-1/2, and PX-478.

CONCLUSION

The current study demonstrated for the first time that Notch signaling regulated cell cycle in proliferating hepatocytes involved in liver regeneration through NICD/Akt Akt/Hif-1α pathway.

Sustained blockade of ascorbic acid transport associated with marked SVCT1 loss in rat hepatocytes containing increased ascorbic acid levels after partial hepatectomy

The liver has an extraordinary regenerative capacity in response to partial hepatectomy (PHx), which develops with neither tissue inflammation response nor alterations in the whole organism. This process is highly coordinated and it has been associated with changes in glutathione (GSH) metabolism. However, there are no reports indicating ascorbic acid (AA) levels after partial hepatectomy. AA and GSH act integrally as an antioxidant system that protects cells and tissues from oxidative damage and imbalance observed in a variety of diseases that affect the liver. Although rat hepatocytes are able to synthesize AA and GSH, which are the providers of AA for the whole organism, they also acquire AA from extracellular sources through the sodium-coupled ascorbic acid transporter-1 (SVCT1). Here, we show that hepatocytes from rat livers subjected to PHx increase their GSH and AA levels from 1 to 7 days post hepatectomy, whose peaks precede the peak in cell proliferation observed at 3 days post-hepatectomy. The increase in both antioxidants was associated with higher expression of the enzymes involved in their synthesis, such as the modifier subunit of enzyme glutamine cysteine ligase (GCLM), glutathione synthetase (GS), gulonolactonase (GLN) and gulonolactone oxidase (GULO). Importantly, rat hepatocytes, that normally exhibit kinetic evidence indicating only SVCT1-mediated transport of AA, lost more than 90% of their capacity to transport it at day 1 after PHx without evidence of recovery at day 7. This observation was in agreement with loss of SVCT1 protein expression, which was undetectable in hepatocytes as early as 2h after PHx, with partial recovery at day 7, when the regenerated liver weight returns to normal. We conclude that after PHx, rat hepatocytes enhance their antioxidant capacity by increasing GSH and AA levels prior to the proliferative peak. GSH and AA are increased by de novo synthesis, however paradoxically hepatocytes from rat subjected to PHx also suppress their capacity to acquire AA from extracellular sources through SVCT1.

Transcriptome difference and potential crosstalk between liver and mammary tissue in mid-lactation primiparous dairy cows

Liver and mammary gland are among the most important organs during lactation in dairy cows. With the purpose of understanding both the different and the complementary roles and the crosstalk of those two organs during lactation, a transcriptome analysis was performed on liver and mammary tissues of 10 primiparous dairy cows in mid-lactation. The analysis was performed using a 4×44K Bovine Agilent microarray chip. The transcriptome difference between the two tissues was analyzed using SAS JMP Genomics using ANOVA with a false discovery rate correction (FDR). The analysis uncovered >9,000 genes differentially expressed (DEG) between the two tissues with a FDR<0.001. The functional analysis of the DEG uncovered a larger metabolic (especially related to lipid) and inflammatory response capacity in liver compared with mammary tissue while the mammary tissue had a larger protein synthesis and secretion, proliferation/differentiation, signaling, and innate immune system capacity compared with the liver. A plethora of endogenous compounds, cytokines, and transcription factors were estimated to control the DEG between the two tissues. Compared with mammary tissue, the liver transcriptome appeared to be under control of a large array of ligand-dependent nuclear receptors and, among endogenous chemical, fatty acids and bacteria-derived compounds. Compared with liver, the transcriptome of the mammary tissue was potentially under control of a large number of growth factors and miRNA. The in silico crosstalk analysis between the two tissues revealed an overall large communication with a reciprocal control of lipid metabolism, innate immune system adaptation, and proliferation/differentiation. In summary the transcriptome analysis confirmed prior known differences between liver and mammary tissue, especially considering the indication of a larger metabolic activity in liver compared with the mammary tissue and the larger protein synthesis, communication, and proliferative capacity in mammary tissue compared with the liver. Relatively novel is the indication by the data that the transcriptome of the liver is highly regulated by dietary and bacteria-related compounds while the mammary transcriptome is more under control of hormones, growth factors, and miRNA. A large crosstalk between the two tissues with a reciprocal control of metabolism and innate immune-adaptation was indicated by the network analysis that allowed uncovering previously unknown crosstalk between liver and mammary tissue for several signaling molecules.

Crosstalk between Nrf2 and Notch signaling

The transcription factor Nrf2 (nuclear factor, erythroid derived 2, like 2) belongs to the CNC-bZip protein family, forming a transcriptosome with its direct heterodimer partner, sMaf, and co-factors such as CBP/p300. Nrf2 binds to one or more AREs (antioxidant response elements) that are located in the gene regulatory regions of the hundreds of Nrf2 target genes. The AREs are key enhancers that are activated in response to endogenous or exogenous stresses to maintain cellular and tissue homeostasis. Data emanating from gene expression microarray analyses comparing Nrf2-disrupted and wild-type mouse embryonic fibroblasts (MEF) showed that expression of Notch1 and Notch-signaling-related genes were decreased in Nrf2-disrupted cells. This observation triggered our research on Nrf2-Notch crosstalk. A functional ARE has been identified upstream of the Notch1 major transcription start site. Furthermore, an Rbpjκ binding site is conserved on the promoters of Nrf2 among animal species. Notch1 is one of the transmembrane Notch family receptors that drive Notch signaling, together with the Rbpjκ transcription factor. After canonically accepting ligands such as Jags and Deltas, the receptor undergoes cleavage to yield the Notch intracellular domain, which translocates to the nucleus. Recent studies using conditional knockout mice indicate that Notch1 as well as Notch2 plays an important role postnatally in liver development and in maintenance of hepatic function. In this review, we summarize current understanding of the role of reciprocal transcriptional regulation between Nrf2 and Notch in adult liver from studies using Nrf2, Keap1, and Notch1 genetically engineered mice.

What is Known Regarding the Participation of Factor Nrf-2 in Liver Regeneration?

It has been known for years that, after chemical damage or surgical removal of its tissue, the liver initiates a series of changes that, taken together, are known as regeneration, which are focused on the recovery of lost or affected tissue in terms of the anatomical or functional aspect. The Nuclear factor-erythroid 2-related factor (Nrf-2) is a reduction-oxidation reaction (redox)-sensitive transcriptional factor, with the basic leucine Zipper domain (bZIP) motif, encoding the NFE2L2 gene. The Keap1-Nrf2-ARE pathway is transcendental in the regulation of various cellular processes, such as antioxidant defenses, redox equilibrium, the inflammatory process, the apoptotic processes, intermediate metabolism, detoxification, and cellular proliferation. Some reports have demonstrated the regulator role of Nrf-2 in the cellular cycle of the hepatocyte, as well as in the modulation of the antioxidant response and of apoptotic processes during liver regeneration. It has been reported that there is a delay in liver regeneration after Partial hepatectomy (PH) in the absence of Nrf-2, and similarly as a regulator of hepatic cytoprotection due to diverse chemical or biological agents, and in diseases such as hepatitis, fibrosis, cirrhosis, and liver cancer. This regulator/protector capacity is due to the modulation of the Antioxidant response elements (ARE). It is postulated that oxidative stress (OS) can participate in the initial stages of liver regeneration and that Nrf-2 can probably participate. Studies are lacking on the different initiation stages, maintenance, and the termination of liver regeneration alone or with ethanol.

WNT-3A regulates an Axin1/NRF2 complex that regulates antioxidant metabolism in hepatocytes

AIMS

Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a master regulator of oxidant and xenobiotic metabolism, but it is unknown how it is regulated to provide basal expression of this defense system. Here, we studied the putative connection between NRF2 and the canonical WNT pathway, which modulates hepatocyte metabolism.

RESULTS

WNT-3A increased the levels of NRF2 and its transcriptional signature in mouse hepatocytes and HEK293T cells. The use of short interfering RNAs in hepatocytes and mouse embryonic fibroblasts which are deficient in the redox sensor Kelch-like ECH-associated protein 1 (KEAP1) indicated that WNT-3A activates NRF2 in a β-Catenin- and KEAP1-independent manner. WNT-3A stabilized NRF2 by preventing its GSK-3-dependent phosphorylation and subsequent SCF/β-TrCP-dependent ubiquitination and proteasomal degradation. Axin1 and NRF2 were physically associated in a protein complex that was regulated by WNT-3A, involving the central region of Axin1 and the Neh4/Neh5 domains of NRF2. Axin1 knockdown increased NRF2 protein levels, while Axin1 stabilization with Tankyrase inhibitors blocked WNT/NRF2 signaling. The relevance of this novel pathway was assessed in mice with a conditional deletion of Axin1 in the liver, which showed upregulation of the NRF2 signature in hepatocytes and disruption of liver zonation of antioxidant metabolism.

INNOVATION

NRF2 takes part in a protein complex with Axin1 that is regulated by the canonical WNT pathway. This new WNT-NRF2 axis controls the antioxidant metabolism of hepatocytes.

CONCLUSION

These results uncover the participation of NRF2 in a WNT-regulated signalosome that participates in basal maintenance of hepatic antioxidant metabolism.

Drug resistance genomics of the antimalarial drug artemisinin

Across the globe, over 200 million annual malaria infections result in up to 660,000 deaths, 77% of which occur in children under the age of five years. Although prevention is important, malaria deaths are typically prevented by using antimalarial drugs that eliminate symptoms and clear parasites from the blood. Artemisinins are one of the few remaining compound classes that can be used to cure multidrug-resistant Plasmodium falciparum infections. Unfortunately, clinical trials from Southeast Asia are showing that artemisinin-based treatments are beginning to lose their effectiveness, adding renewed urgency to the search for the genetic determinants of parasite resistance to this important drug class. We review the genetic and genomic approaches that have led to an improved understanding of artemisinin resistance, including the identification of resistance-conferring mutations in the P. falciparum kelch13 gene.