Mkp-1 protects mice against toxin-induced liver damage by promoting the Nrf2 cytoprotective response

Inflammatory liver diseases and susceptibility to sepsis

Patients with inflammatory liver diseases, particularly alcohol-associated liver disease and metabolic dysfunction-associated fatty liver disease (MAFLD), have higher incidence of infections and mortality rate due to sepsis. The current focus in the development of drugs for MAFLD is the resolution of non-alcoholic steatohepatitis and prevention of progression to cirrhosis. In patients with cirrhosis or alcoholic hepatitis, sepsis is a major cause of death. As the metabolic center and a key immune tissue, liver is the guardian, modifier, and target of sepsis. Septic patients with liver dysfunction have the highest mortality rate compared with other organ dysfunctions. In addition to maintaining metabolic homeostasis, the liver produces and secretes hepatokines and acute phase proteins (APPs) essential in tissue protection, immunomodulation, and coagulation. Inflammatory liver diseases cause profound metabolic disorder and impairment of energy metabolism, liver regeneration, and production/secretion of APPs and hepatokines. Herein, the author reviews the roles of (1) disorders in the metabolism of glucose, fatty acids, ketone bodies, and amino acids as well as the clearance of ammonia and lactate in the pathogenesis of inflammatory liver diseases and sepsis; (2) cytokines/chemokines in inflammatory liver diseases and sepsis; (3) APPs and hepatokines in the protection against tissue injury and infections; and (4) major nuclear receptors/signaling pathways underlying the metabolic disorders and tissue injuries as well as the major drug targets for inflammatory liver diseases and sepsis. Approaches that focus on the liver dysfunction and regeneration will not only treat inflammatory liver diseases but also prevent the development of severe infections and sepsis.

Allyl-isothiocyanate against colorectal cancer via the mutual dependent regulation of p21 and Nrf2

Allyl-isothiocyanate (AITC) is a common Isothiocyanates (ITC) and its chemo-preventive and anti-tumor effects are believed to be related to the activation of NF-E2 p45-related Factor 2 (Nrf2). However, its anti-tumor effects on colorectal cancer (CRC) are not well elucidated. Here, we investigated the therapeutic in vitro and/or in vivo effects and mechanisms of action (MOA) for AITC on CRC cell line HCT116 (human) and MC38 (mouse). AITC treatment in a low concentration range (1 mg/kg in vivo) significantly inhibited the tumor cell growth and increased the expression of p21 and Nrf2. The AITC-mediated induction of p21 was dependent on Nrf2 but independent on p53 in vitro and in vivo at low dose. In contrast, the high dose of AITC (5 mg/kg in vivo) failed to increase substantial levels of p21/MdmX, and impaired the total antioxidant capacity of tumors and subsequent anti-tumor effect in vivo. These results suggest that an optimal dose of AITC is important and required for the proper Nrf2 activation and its anti-CRC effects and thus, providing insights into the potential applications of AITC for the prevention and treatment of CRC.

MKP1 promotes nonalcoholic steatohepatitis by suppressing AMPK activity through LKB1 nuclear retention

Nonalcoholic steatohepatitis (NASH) is triggered by hepatocyte death through activation of caspase 6, as a result of decreased adenosine monophosphate (AMP)-activated protein kinase-alpha (AMPKα) activity. Increased hepatocellular death promotes inflammation which drives hepatic fibrosis. We show that the nuclear-localized mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP1) is upregulated in NASH patients and in NASH diet fed male mice. The focus of this work is to investigate whether and how MKP1 is involved in the development of NASH. Under NASH conditions increased oxidative stress, induces MKP1 expression leading to nuclear p38 MAPK dephosphorylation and decreases liver kinase B1 (LKB1) phosphorylation at a site required to promote LKB1 nuclear exit. Hepatic deletion of MKP1 in NASH diet fed male mice releases nuclear LKB1 into the cytoplasm to activate AMPKα and prevents hepatocellular death, inflammation and NASH. Hence, nuclear-localized MKP1-p38 MAPK-LKB1 signaling is required to suppress AMPKα which triggers hepatocyte death and the development of NASH.

NRF2 has a splicing regulatory function involving the survival of motor neuron (SMN) in non-small cell lung cancer

The nuclear factor erythroid 2-like 2 (NFE2L2; NRF2) signaling pathway is frequently deregulated in human cancers. The critical functions of NRF2, other than its transcriptional activation, in cancers remain largely unknown. Here, we uncovered a previously unrecognized role of NRF2 in the regulation of RNA splicing. Global splicing analysis revealed that NRF2 knockdown in non-small cell lung cancer (NSCLC) A549 cells altered 839 alternative splicing (AS) events in 485 genes. Mechanistic studies demonstrated that NRF2 transcriptionally regulated SMN mRNA expression by binding to two antioxidant response elements in the SMN1 promoter. Post-transcriptionally, NRF2 was physically associated with the SMN protein. The Neh2 domain of NRF2, as well as the YG box and the region encoded by exon 7 of SMN, were required for their interaction. NRF2 formed a complex with SMN and Gemin2 in nuclear gems and Cajal bodies. Furthermore, the NRF2-SMN interaction regulated RNA splicing by expressing SMN in NRF2-knockout HeLa cells, reverting some of the altered RNA splicing. Moreover, SMN overexpression was significantly associated with alterations in the NRF2 pathway in patients with lung squamous cell carcinoma from The Cancer Genome Atlas. Taken together, our findings suggest a novel therapeutic strategy for cancers involving an aberrant NRF2 pathway.

MKP1 promotes nonalcoholic steatohepatitis by suppressing AMPK activity through LKB1 nuclear retention

Nonalcoholic steatohepatitis (NASH) is triggered by hepatocyte death through activation of caspase 6, as a result of decreased adenosine monophosphate (AMP)-activated protein kinase-alpha (AMPKα) activity. Increased hepatocellular death promotes inflammation which drives hepatic fibrosis. We show that the nuclear-localized mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP1) is upregulated in NASH patients and in NASH diet fed mice. The focus of this work was to investigate whether and how MKP1 is involved in the development of NASH. Under NASH conditions increased oxidative stress, induces MKP1 expression leading to nuclear p38 MAPK dephosphorylation and decreased liver kinase B1 (LKB1) phosphorylation at a site required to promote LKB1 nuclear exit. Hepatic deletion of MKP1 in NASH diet fed mice released nuclear LKB1 into the cytoplasm to activate AMPKα and prevent hepatocellular death, inflammation and NASH. Hence, nuclear-localized MKP1-p38 MAPK-LKB1 signaling is required to suppress AMPKα which triggers hepatocyte death and the development of NASH.

Nrf2-Dependent Protective Effect of Paeoniflorin on-[Formula: see text]Naphthalene Isothiocyanate-Induced Hepatic Injury

The pathological mechanism of cholestatic hepatic injury is associated with oxidative stress, hepatocyte inflammation, and dysregulation of hepatocyte transporters. Paeonia lactiflora Pall. and its compound can improve hepatic microcirculation, dilate bile duct, and promote bile flow, which is advantageous to ameliorate liver damage. Paeoniflorin (PEA), as the main efficacy component of Paeonia lactiflora Pall., has multiple pharmacological effects. PEA improves liver injury, but it remains obscure whether the protective action on [Formula: see text]-naphthalene isothiocyanate (ANIT)-induced cholestatic liver injury is dependent on the NF-E2 p45-related Factor 2 (Nrf2) signaling pathway. In this study, C57BL/6 mice were administrated with 80 mg⋅kg[Formula: see text]⋅d[Formula: see text] ANIT followed by PEA (75, 150, and 300 mg⋅kg[Formula: see text]⋅d[Formula: see text]) orally for 10 days, respectively. Tissue histology and liver function were detected, including serum enzymes, gallbladder (GB) weight, phenobarbital-induced sleeping time (PEN-induced ST), hepatic uridine di-phosphoglucuronosyltransferase (UDPG-T), malondialdehyde (MDA), and glutathione (GSH). The expressions of protein Nrf2, sodium taurocholate cotransporting polypeptide (Ntcp), and NADPH oxidase 4 (Nox4) were evaluated. Nrf2 plasmid or siRNA-Nrf2 transfection on LO2 cells and Nrf2^-/- mice were used to explore the liver protective mechanism of PEA. Compared to ANIT-treated mice, PEA decreased serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), total bilirubin (TBIL), direct bilirubin (DBIL), total bile acid (TBA), and phenobarbital-induced sleeping time. The bile secretion, hepatic UDPG-T, MDA, GSH, and liver histology were improved. The expressions of protein Nrf2 and Ntcp in liver tissues increased, but Nox4 decreased. After Nrf2 plasmid or small interfering RNA (siRNA)-Nrf2 transfection, the protective effects of PEA on LO2 cells were, respectively, strengthened or weakened. Moreover, PEA had no significant effects on ANIT-treated Nrf2^-/- mice. Our results suggest that Nrf2 is essential for PEA protective effects on ANIT-induced liver injury.

Nrf2 as a potential target for Parkinson's disease therapy

Parkinson's disease (PD) is a complex neurodegenerative disorder featuring both motor and nonmotor symptoms associated with a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Conventionally, PD treatment options have focused on dopamine replacement and provide only symptomatic relief. However, disease-modifying therapies are still unavailable. Mechanistically, genetic and environmental factors can produce oxidative stress which has been implicated as a core contributor to the initiation and progression of PD through the degeneration of dopaminergic neurons. Importantly, nuclear factor erythroid 2-related factor 2 (Nrf2) is essential for maintaining redox homeostasis by binding to the antioxidant response element which exists in the promoter regions of most genes coding for antioxidant enzymes. Furthermore, protein kinase C, mitogen-activated protein kinases, and phosphotidylinositol 3-kinase have been implicated in the regulation of Nrf2 activity during PD. Here, we review the evidence supporting the regulation of Nrf2 through Keap1-dependent and Keap1-independent mechanisms. We also address that targeting Nrf2 may provide a therapeutic option to mitigate oxidative stress-associated PD. Finally, we discuss currently known classes of small molecule activators of Nrf2, including Nrf2-activating compounds in PD.

NRF2 and the Ambiguous Consequences of Its Activation during Initiation and the Subsequent Stages of Tumourigenesis

NF-E2 p45-related factor 2 (NRF2, encoded in the human by NFE2L2) mediates short-term adaptation to thiol-reactive stressors. In normal cells, activation of NRF2 by a thiol-reactive stressor helps prevent, for a limited period of time, the initiation of cancer by chemical carcinogens through induction of genes encoding drug-metabolising enzymes. However, in many tumour types, NRF2 is permanently upregulated. In such cases, its overexpressed target genes support the promotion and progression of cancer by suppressing oxidative stress, because they constitutively increase the capacity to scavenge reactive oxygen species (ROS), and they support cell proliferation by increasing ribonucleotide synthesis, serine biosynthesis and autophagy. Herein, we describe cancer chemoprevention and the discovery of the essential role played by NRF2 in orchestrating protection against chemical carcinogenesis. We similarly describe the discoveries of somatic mutations in NFE2L2 and the gene encoding the principal NRF2 repressor, Kelch-like ECH-associated protein 1 (KEAP1) along with that encoding a component of the E3 ubiquitin-ligase complex Cullin 3 (CUL3), which result in permanent activation of NRF2, and the recognition that such mutations occur frequently in many types of cancer. Notably, mutations in NFE2L2, KEAP1 and CUL3 that cause persistent upregulation of NRF2 often co-exist with mutations that activate KRAS and the PI3K-PKB/Akt pathway, suggesting NRF2 supports growth of tumours in which KRAS or PKB/Akt are hyperactive. Besides somatic mutations, NRF2 activation in human tumours can occur by other means, such as alternative splicing that results in a NRF2 protein which lacks the KEAP1-binding domain or overexpression of other KEAP1-binding partners that compete with NRF2. Lastly, as NRF2 upregulation is associated with resistance to cancer chemotherapy and radiotherapy, we describe strategies that might be employed to suppress growth and overcome drug resistance in tumours with overactive NRF2.

Hepatoprotection of pine nut polysaccharide via NRF2/ARE/MKP1/JNK signaling pathways against carbon tetrachloride-induced liver injury in mice

Previously, we obtained a purified polysaccharide (PNP40c-1) from Pinus koraiensis pine nut and reported its protective effect on carbon tetrachloride (CCl₄)-induced liver injury in vitro. The object of this study is to investigate its hepatoprotective activity in vivo and elucidate the mechanism underlying the hepatoprotection. PNP40c-1 effectively prevented the accumulation of serum liver injury biomarkers including alanine aminotransferase, aspartate aminotransferase, alkaline phpsphatase and total bilirubin stimulated by CCl₄. The pathological changes in PNP40c-1-treated mice livers were also markedly ameliorated. Results showed that PNP40c-1 suppressed the production of reactive oxygen species (ROS) and lipid peroxidation, upregulated Nrf2/ARE pathway and enhanced the antioxidant capacity of hepatocytes. Furthermore, the reaction between Nrf2 and ARE promoted the generation of Mkp1, which inhibited the activation of JNK induced by CCl₄, and suppressed hepatocytes apoptosis by regulating the protein expression of Bax, cleaved-Caspase-3 and Bcl2, exerting hepatoprotective activity. Taken together, upregulation of Nrf2/ARE pathway and suppression of JNK activation via Nrf2/ARE/Mkp1/JNK signaling pathways are the main mechanisms underlying the hepatoprotective effect of PNP40c-1 against CCl₄-induced mice liver injury. These results indicated that PNP40c-1 has potential to serve as a hepatoprotective agent against chemical induced hepatotoxicity.

c-Jun NH2 -Terminal Protein Kinase Phosphorylates the Nrf2-ECH Homology 6 Domain of Nuclear Factor Erythroid 2-Related Factor 2 and Downregulates Cytoprotective Genes in Acetaminophen-Induced Liver Injury in Mice

BACKGROUND AND AIMS

Acetaminophen (APAP) overdose induces severe liver injury and hepatic failure. While the activation of c-Jun NH₂ -terminal kinase (JNK) has been implicated as a mechanism in APAP-induced liver injury, the hepatic defense system controlled by nuclear factor erythroid 2-related factor 2 (Nrf2) plays a central role in the mitigation of APAP toxicity. However, the link between the two signaling pathways in APAP-induced liver injury (AILI) remains unclear.

APPROACH AND RESULTS

In this study, we demonstrated that the activation of JNK in mouse liver following exposure to APAP was correlated with the phosphorylation of Nrf2 and down-regulation of the antioxidant response element (ARE)-driven genes, NAD(P)H:quinone dehydrogenase 1, glutathione S-transferase α3, glutathione S-transferase M1, glutathione S-transferase M5, and aldo-keto reductase 1C. The JNK inhibitor, SP600125, or knockdown of JNK by infection of adenovirus expressing JNK small interfering RNA, ameliorated the APAP induced liver toxicity, and inhibited the phosphorylation of Nrf2 and down-regulation of detoxifying enzymes by stabilizing the transcription factor. Mechanistically, JNK antagonized Nrf2- and ARE-driven gene expression in a Kelch-like ECH-associated protein 1-independent manner. Biochemical analysis revealed that phosphorylated JNK (P-JNK) directly interacted with the Nrf2-ECH homology (Neh) 1 domain of Nrf2 and phosphorylated the serine-aspartate-serine motif 1 (SDS1) region in the Neh6 domain of Nrf2.

CONCLUSIONS

Mass spectrometric analysis identified serine 335 in the SDS1 region of mNrf2 as the major phosphorylation site for modulation of Nrf2 ubiquitylation by P-JNK. This study demonstrates that Nrf2 is a target of P-JNK in AILI. Our finding may provide a strategy for the treatment of AILI.

Group II muscarinic acetylcholine receptors attenuate hepatic injury via Nrf2/ARE pathway

Parasympathetic nervous system dysfunction is common in patients with liver disease. We have previously shown that muscarinic acetylcholine receptors (mAchRs) play an important role in the regulation of hepatic fibrosis and that the receptor agonists and antagonists affect hepatocyte proliferation. However, little is known about the impact of the different mAchR subtypes and associated signaling pathways on liver injury. Here, we treated the human liver cell line HL7702 with 10 mmol/L carbon tetrachloride (CCL4) to induce hepatocyte damage. We found that CCL4 treatment increased the protein levels of group I mAchRs (M1, M3, M5) but reduced the expression of group II mAchRs (M2, M4) and activated the Nrf2/ARE and MAPK signaling pathways. Although overexpression of M1, M3, or M5 led to hepatocyte damage with an intact Nrf2/ARE pathway, overexpression of M2 or M4 increased, and siRNA-mediated knockdown of either M2 or M4 decreased the protein levels of Nrf2 and its downstream target genes. Moreover, CCL4 treatment increased serum ALT levels more significantly, but only induced slight changes in the expression of mAchRs, NQO1 and HO1, while reducing the expression of M2 and M4 in liver tissues of Nrf2-/- mice compared to wild type mice. Our findings suggest that group II mAchRs, M2 and M4, activate the Nrf2/ARE signaling pathway, which regulates the expression of M2 and M4, to protect the liver from CCL4-induced injury.

Transcriptomic profiling identifies a critical role of Nrf2 in regulating the inflammatory response to fly ash particles in mouse lung

Exposure to combustion-derived nanoparticles is recognized as a major health hazard, but the molecular responses are still insufficiently described. The transcription factor erythroid 2-related factor 2 (Nrf2, also known as NFE2L2) is a master regulator of the pulmonary defense system against insults by particulate matter. However, its downstream molecular processes are not fully characterized. In the current study, BALB/c wild-type (WT) and Nrf2^-/- mice were exposed by intranasal administration to fly ash particles (F3-S; 20 mg/kg BW), which were collected from a municipal waste incinerator in China, for three consecutive days. Using a comparative transcriptomics approach, the pulmonary global gene expression profiles to F3-S exposure were characterized for both genotypes. The preponderance of the differentially-expressed genes (DEGs) in WT mice induced by the fly ash particles, was related to inflammation. Functional enrichment and molecular pathway mapping of the DEGs specific to Nrf2^-/- mice exposed to the particles revealed that all of the top 10 perturbed molecular pathways were associated with the inflammatory response. Our study identified a transcriptional signature related to the initial pulmonary injury in mouse upon fly ash exposure, and suggests an anti-inflammatory role of Nrf2 in protecting the lung against such exposure.

Comparative transcriptome analysis reveals Dusp1 as a critical regulator of inflammatory response to fly ash particle exposure in mouse

Exposure to outdoor concentrations of fine particulate matter (PM2.5) is a leading global health concern. Waste incineration emission has been recognized as a potential major contributor of ambient PM2.5. Respiratory inflammation is a central feature induced by PM2.5 exposure by inhalation. However, the molecular mechanisms are not fully understood. Dual-specificity phosphatase 1 (Dusp1) plays an instrumental role in the regulation of airway inflammation. In this study, fly ash particles (20 mg/kg BW) collected from a municipal waste incinerator in China were given to BALB/c wild-type (WT) and Dusp1^-/- mice by intranasal administration daily for three consecutive days. While these particles induced mild inflammation in both genotypes, a significantly higher level of serum interleukin-6 (665 pg/ml) was measured in Dusp1^-/- mice challenged with fly ash particles than in their WT counterparts. Genome-wide transcriptome profiling of pulmonary coding genes in response to the exposure were performed in both genotypes by RNA sequencing. We identified 487 differentially-expressed genes (DEGs) in fly ash-challenged Dusp1^-/- mice versus their WT counterparts with a log₂fold-change >1.5 and p < 0.05. Functional enrichment and molecular pathway mapping of the DEGs specific to Dusp1^-/- mice exposed to the particles revealed that the top 10 perturbed molecular pathways were associated with the immune response. Our study demonstrates the anti-inflammatory role of Dusp1 in protecting the lung against insults by fly ash particles, suggesting that Dusp1 might be a therapeutic target for the treatment of PM2.5-induced respiratory diseases.

Interplay of MKP-1 and Nrf2 drives tumor growth and drug resistance in non-small cell lung cancer

Alterations in KEAP1/ NF-E2 p45-related factor 2 (NFE2L2/Nrf2) signaling pathway have been reported in 23% lung adenocarcinoma patients, suggesting that deregulation of the pathway is a major cancer driver. Here we report that mitogen-activated protein (MAP) kinase phosphatase 1 (MKP-1) drives tumor growth and drug resistance by up regulating transcription factor Nrf2. In non-small cell lung cancer (NSCLC) cells and xenografts, MKP-1 knockdown triggered the down-regulation of the metabolic enzymes and cytoprotective proteins, which are the target genes of Nrf2. Consequently, the cell growth was markedly inhibited with decrease of tumor metabolisms and GSH contents. Moreover, MKP-1 silencing sensitized NSCLC cells to cisplatin treatment. Mechanistically, MKP-1 inhibited the ubiquitylation of Nrf2 via a direct interaction with the transcription factor. Nrf2 was hence stabilized and its transcriptional program was activated. Notably, Nrf2 elevated MKP-1 expression at transcriptional level. In human lung adenoma tumor samples, high levels of expression of MKP-1, Nrf2, and its target gene heme oxygenase 1 were closely correlated. Thus, MKP-1 and Nrf2 form a forward feedback loop in lung cancer cells, which stabilizing and activating Nrf2 to promote anabolic metabolism and GSH biosynthesis. This study uncovers a novel role of MKP-1 in the malignant evolution of cancers.

"NRF2 addiction" in lung cancer cells and its impact on cancer therapy

Nuclear factor erythroid 2-like factor 2 (NRF2) is a master regulator of the antioxidant enzymes and the detoxification proteins that play major roles in redox homeostasis. Although it plays a protective role against tumorigenesis, emerging evidence has shown that the NRF2 pathway is frequently altered in different types of cancer, including lung cancer. NRF2 activation influences many of the hallmarks of cancer and their signaling pathways, mainly apoptosis, proliferation, angiogenesis, metastasis, and metabolic reprogramming to establish cellular metabolic processes leading to "NRF2 addiction" in lung cancer cells. Intriguingly, constitutive activation of NRF2 promotes cancer development as well as resistance to chemotherapy and radiotherapy, and these malignant phenotypes lead to a poor prognosis in lung cancer patients. Therefore, targeted inhibition of the NRF2 together with traditional chemotherapy, radiotherapy, and immunotherapy, may be a promising approach to improving the survival rates of the NRF2-addicted lung cancer cases. Here we summarize the recent advances in NRF2-addicted lung cancer.