Ghrelin alleviates intestinal ischemia-reperfusion injury by activating the GHSR-1α/Sirt1/FOXO1 pathway.

Ischemia-reperfusion (IR) injury is primarily characterized by the restoration of blood flow perfusion and oxygen supply to ischemic tissue and organs, but it paradoxically leads to tissue injury aggravation. IR injury is a challenging pathophysiological process that is difficult to avoid clinically and frequently occurs during organ transplantation, surgery, shock resuscitation, and other processes. The major causes of IR injury include increased levels of free radicals, calcium overload, oxidative stress, and excessive inflammatory response. Ghrelin is a newly discovered brain-intestinal peptide with anti-inflammatory and antiapoptotic effects that improve blood supply. The role and mechanism of ghrelin in intestinal ischemia-reperfusion (IIR) injury remain unclear. We hypothesized that ghrelin could attenuate IIR-induced oxidative stress and apoptosis. To investigate this, we established IIR by using a non-invasive arterial clip to clamp the root of the superior mesenteric artery (SMA) in mice. Ghrelin was injected intraperitoneally at a dose of 50 µg/kg 20 min before IIR surgery, and [D-Lys3]-GHRP-6 was injected intraperitoneally at a dose of 12 nmol/kg 20 min before ghrelin injection. We mimicked the IIR process with hypoxia-reoxygenation (HR) in Caco-2 cells, which are similar to intestinal epithelial cells in structure and biochemistry. Our results showed that ghrelin inhibited IIR/HR-induced oxidative stress and apoptosis by activating GHSR-1α. Moreover, it was found that ghrelin activated the GHSR-1α/Sirt1/FOXO1 signaling pathway. We further inhibited Sirt1 and found that Sirt1 was critical for ghrelin-mediated mitigation of IIR/HR injury. Overall, our data suggest that pretreatment with ghrelin reduces oxidative stress and apoptosis to attenuate IIR/HR injury by binding with GHSR-1α to further activate Sirt1.

Genetic loss of Nrf1 and Nrf2 leads to distinct metabolism reprogramming of HepG2 cells by opposing regulation of the PI3K-AKT-mTOR signalling pathway.

As a vital hallmarker of cancer, the metabolic reprogramming has been shown to play a pivotal role in tumour occurrence, metastasis and drug resistance. Amongst a vast variety of signalling molecules and metabolic enzymes involved in the regulation of cancer metabolism, two key transcription factors Nrf1 and Nrf2 are required for redox signal transduction and metabolic homeostasis. However, the regulatory effects of Nrf1 and Nrf2 (both encoded by Nfe2l1 and Nfe2l2, respectively) on the metabolic reprogramming of hepatocellular carcinoma cells have been not well understood to date. Here, we found that the genetic deletion of Nrf1 and Nrf2 from HepG2 cells resulted in distinct metabolic reprogramming. Loss of Nrf1α led to enhanced glycolysis, reduced mitochondrial oxygen consumption, enhanced gluconeogenesis and activation of the pentose phosphate pathway in the hepatocellular carcinoma cells. By striking contrast, loss of Nrf2 attenuated the glycolysis and gluconeogenesis pathways, but with not any significant effects on the pentose phosphate pathway. Moreover, knockout of Nrf1α also caused fat deposition and increased amino acid synthesis and transport, especially serine synthesis, whilst Nrf2 deficiency did not cause fat deposition, but attenuated amino acid synthesis and transport. Further experiments revealed that such distinctive metabolic programming of between Nrf1α-/- and Nrf2-/- resulted from substantial activation of the PI3K-AKT-mTOR signalling pathway upon the loss of Nrf1, leading to increased expression of critical genes for the glucose uptake, glycolysis, the pentose phosphate pathway, and the de novo lipid synthesis, whereas deficiency of Nrf2 resulted in the opposite phenomenon by inhibiting the PI3K-AKT-mTOR pathway. Altogether, these provide a novel insight into the cancer metabolic reprogramming and guide the exploration of a new strategy for targeted cancer therapy.

Melatonin Alleviates Acute Respiratory Distress Syndrome by Inhibiting Alveolar Macrophage NLRP3 Inflammasomes Through the ROS/HIF-1α/GLUT1 Pathway.

Sepsis-induced acute respiratory distress syndrome (ARDS) is a devastating clinically severe respiratory disorder, and no effective therapy is available. Melatonin (MEL), an endogenous neurohormone, has shown great promise in alleviating sepsis-induced ARDS, but the underlying molecular mechanism remains unclear. Using a lipopolysaccharide (LPS)-treated mouse alveolar macrophage cell line (MH-S) model, we found that MEL significantly inhibited NOD-like receptor protein 3 (NLRP3) inflammasome activation in LPS-treated macrophages, whereas this inhibitory effect of MEL was weakened in MH-S cells transfected with glucose transporter 1 (GLUT1) overexpressing lentivirus. Further experiments showed that MEL downregulated GLUT1 via inhibition of hypoxia-inducible factor 1 (HIF-1α). Notably, hydrogen peroxide (H2O2), a donor of reactive oxygen species (ROS), significantly increased the level of intracellular ROS and inhibited the regulatory effect of MEL on the HIF-1α/GLUT1 pathway. Interestingly, the protective effect of MEL was attenuated after the knockdown of melatonin receptor 1A (MT1) in MH-S cells. We also confirmed in vivo that MEL effectively downregulated the HIF-1α/GLUT1/NLRP3 pathway in the lung tissue of LPS-treated mice, as well as significantly ameliorated LPS-induced lung injury and improved survival in mice. Collectively, these findings revealed that MEL regulates the activation of the ROS/HIF-1α/GLUT1/NLRP3 pathway in alveolar macrophages via the MT1 receptor, further alleviating sepsis-induced ARDS.

Different Inhibition of Nrf2 by Two Keap1 Isoforms α and ß to Shape Malignant Behaviour of Human Hepatocellular Carcinoma.

Nrf2 (nuclear factor E2-related factor 2, encoded by Nfe2l2) acts as a master transcriptional regulator in mediating antioxidant, detoxification, and cytoprotective responses against oxidative, electrophilic, and metabolic stress, but also plays a crucial role in cancer metabolism and multiple oncogenic pathways, whereas the redox sensor Keap1 functions as a predominant inhibitor of Nrf2 and, hence, changes in its expression abundance directly affect the Nrf2 stability and transcriptional activity. However, nuanced functional isoforms of Keap1 α and ß have rarely been identified to date. Herein, we have established four distinct cell models stably expressing Keap1-/-, Keap1ß(Keap1Δ1-31), Keap1-Restored, and Keap1α-Restored aiming to gain a better understanding of similarities and differences of two Keap1 isoforms between their distinct regulatory profiles. Our experimental evidence revealed that although Keap1 and its isoforms are still localized in the cytoplasmic compartments, they elicited differential inhibitory effects on Nrf2 and its target HO-1. Furthermore, transcriptome sequencing unraveled that they possess similar but different functions. Such functions were further determined by multiple experiments in vivo (i.e., subcutaneous tumour formation in nude mice) and in vitro (e.g., cell cloning, infection, migration, wound healing, cell cycle, apoptosis, CAT enzymatic activity, and intracellular GSH levels). Of note, the results obtained from tumourigenesis experiments in xenograft model mice were verified based on the prominent changes in the PTEN signaling to the PI3K-AKT-mTOR pathways, in addition to substantially aberrant expression patterns of those typical genes involved in the EMT (epithelial-mesenchymal transition), cell cycle, and apoptosis.

Metformin leads to accumulation of reactive oxygen species by inhibiting the NFE2L1 expression in human hepatocellular carcinoma cells.

Metformin, as the first-line drug for the treatment of type 2 diabetes mellitus, has been shown to possess a capability to activate or inhibit the production of reactive oxygen species (ROS) in different ways. However, the detailed mechanisms of the opposite effect are poorly understood. Here we provide evidence that metformin induces accumulation of ROS by inhibiting the expression of a core antioxidant transcription factor nuclear factor erythroid 2 like 1 (NFE2L1/Nrf1) in human hepatocellular carcinoma HepG2 cells. In the present study, we originally found that the increased ROS induced by metformin was blunted in NFE2L1 knockdown cell line. Furtherly by examining the effects of metformin on endogenous and exogenous NFE2L1, we also found metformin could not only inhibit the transcription of NFE2L1 gene, but also promote the degradation of NFE2L1 protein at the post-transcriptional level, whereas this effect can be reversed by high glucose. The inhibitory effect of metformin on NFE2L1 was investigated to occur through the N-terminal domain (NTD) of NFE2L1 protein, and its downregulation by metformin was in an AMP-activated protein kinase (AMPK)-independent manner. But the activation of AMPK signaling pathway by metformin in NFE2L1 knockdown HepG2 cells is reversed, indicating that NFE2L1 may be an important regulator of AMPK signal. Altogether, this work provides a better understanding of the relationship between metformin and oxidative stress, and hence contributes to translational study of metformin through its hypoglycemic and tumor suppressive effects.

Adipocyte-specific deficiency of Nfe2l1 disrupts plasticity of white adipose tissues and metabolic homeostasis in mice.

The maintenance of healthy adipose tissues is essential for efficient regulation of energy homeostasis. Nuclear factor-erythroid 2-related factor 1 (NFE2L1, also known as Nrf1), a CNC-bZIP protein, is a master regulator of the cellular adaptive response to stresses. To investigate the role of NFE2L1 in adipocytes, we bred a line of mice with adipocyte-specific Nfe2l1 knockout (Nfe2l1(f)-KO), and found that Nfe2l1(f)-KO mice exhibited a dramatically reduced subcutaneous adipose tissue (SAT) mass, insulin resistance, adipocyte hypertrophy, and severe adipose inflammation. Mechanistic studies revealed that Nfe2l1 deficiency may disturb the expression of lipolytic genes in adipocytes, leading to adipocyte hypertrophy followed by inflammation, pyroptosis, and insulin resistance. Our findings reveal a novel role for NFE2L1 in regulating adipose tissue plasticity and energy homeostasis.

Nrf1 is paved as a new strategic avenue to prevent and treat cancer, neurodegenerative and other diseases.

Transcription factor Nrf1 acts as a unique vital player in maintaining cellular homeostasis and organ integrity during normal development and growth throughout the life process. Loss-of-function of Nrf1 results in severe oxidative stress, genomic instability, embryonic lethality, developmental disorders, and adult diseases such as non-alcoholic steatohepatitis, hepatocellular carcinoma, diabetes and neurogenerative diseases. Thereby, Nrf1 is critically implicated in a variety of important physio-pathological processes by governing robust target genes in order to reinforce antioxidant, detoxification and cytoprotective responses to cellular stress. Notably, there also exists a proteasomal 'bounce-back' response mediated by Nrf1, insofar as to enhance the drug resistance to proteasomal inhibitors in clinical treatment of neuroblastoma, multiple myeloma and triple-negative breast cancers. Recently, several drugs or chemicals are found or re-found in new ways to block the proteasomal compensatory process through inhibiting the multistep processing of Nrf1. Conversely, activation of Nrf1 induced by some drugs or chemicals leads to cytoprotection from cell apoptosis and promotes cell viability. This is the start of constructive and meaningful studies, approaching to explore the mechanism(s) by which Nrf1 is activated to protect neurons and other cells from malignant and degenerative diseases. Overall, Nrf1 has appealed attentions as a new attractive therapeutic strategy for human diseases including cancers.

Topovectorial mechanisms control the juxtamembrane proteolytic processing of Nrf1 to remove its N-terminal polypeptides during maturation of the CNC-bZIP factor.

The topobiological behaviour of Nrf1 dictates its post-translational modification and its ability to transactivate target genes. Here, we have elucidated that topovectorial mechanisms control the juxtamembrane processing of Nrf1 on the cyto/nucleoplasmic side of endoplasmic reticulum (ER), whereupon it is cleaved and degraded to remove various lengths of its N-terminal domain (NTD, also refolded into a UBL module) and acidic domain-1 (AD1) to yield multiple isoforms. Notably, an N-terminal ~12.5-kDa polypeptide of Nrf1 arises from selective cleavage at an NHB2-adjoining region within NTD, whilst other longer UBL-containing isoforms may arise from proteolytic processing of the protein within AD1 around PEST1 and Neh2L degrons. The susceptibility of Nrf1 to proteolysis is determined by dynamic repositioning of potential UBL-adjacent degrons and cleavage sites from the ER lumen through p97-driven retrotranslocation and -independent pathways into the cyto/nucleoplasm. These repositioned degrons and cleavage sites within NTD and AD1 of Nrf1 are coming into their bona fide functionality, thereby enabling it to be selectively processed by cytosolic DDI-1/2 proteases and also partiality degraded via 26S proteasomes. The resultant proteolytic processing of Nrf1 gives rise to a mature ~85-kDa CNC-bZIP transcription factor, which regulates transcriptional expression of cognate target genes. Furthermore, putative ubiquitination of Nrf1 is not a prerequisite necessary for involvement of p97 in the client processing. Overall, the regulated juxtamembrane proteolysis (RJP) of Nrf1, though occurring in close proximity to the ER, is distinctive from the mechanism that regulates the intramembrane proteolytic (RIP) processing of ATF6 and SREBP1.

Mechanisms controlling the multistage post-translational processing of endogenous Nrf1α/TCF11 proteins to yield distinct isoforms within the coupled positive and negative feedback circuits.

To gain a better understanding of the multistep processing of Nrf1 to yield various isoforms with confused molecular masses, we herein establish a generally acceptable criterion required for identification of its endogenous full-length proteins and derivative isoforms expressed differentially in distinct experimental cell lines. Further work has been focused on the molecular mechanisms that dictate the successive post-translational modifications (i.e. glycosylation by OST, deglycosylation by NGLY, and ubiquitination by Hrd1) of this CNC-bZIP protein and its proteolytic processing to give rise to multiple proteoforms. Several lines of experimental evidence have demonstrated that the nascent Nrf1α/TCF11 polypeptide (non-glycosylated) is transiently translocated into the endoplasmic reticulum (ER), in which it becomes an inactive glycoprotein-A, and is folded in a proper topology within and around membranes. Thereafter, dynamic repositioning of the ER-resident domains in Nrf1 glycoprotein is driven by p97-fueled retrotranslocation into extra-ER compartments. Therein, Nrf1 glycoprotein is allowed for deglycosylation digestion by glycosidases into a deglycoprotein-B and its progressive proteolytic processing by cytosolic DDI-1/2 and proteasomes so as to generate N-terminally-truncated protein-C/D. This processing is accompanied by removal of a major N-terminal ~12.5-kDa polypeptide from Nrf1α. Interestingly, our present study has further unraveled that there exist coupled positive and negative feedback circuits between Nrf1 and cognate target genes, including those encoding its regulators p97, Hrd1, DDI-1 and proteasomes. These key players are differentially or even oppositely involved in diverse cellular signaling responses to distinct extents of ER-derived proteotoxic and oxidative stresses induced by different concentrations of proteasomal inhibitors.

A Naturally-Occurring Dominant-Negative Inhibitor of Keap1 Competitively against Its Negative Regulation of Nrf2.

Transcription factor Nrf2 (nuclear factor-erythroid 2-related factor 2) is a master regulator of antioxidant and/or electrophile response elements (AREs/EpREs)-driven genes involved in homeostasis, detoxification, and adaptation to various stresses. The cytoprotective activity of Nrf2, though being oppositely involved in both cancer prevention and progression, is critically controlled by Keap1 (Kelch-like ECH-associated protein 1), which is an adaptor subunit of Cullin 3-based E3 ubiquitin ligase and also is a key sensor for oxidative and electrophilic stresses. Here, we first report a novel naturally-occurring mutant of Keap1, designated Keap1ΔC, which lacks most of its C-terminal Nrf2-interacting domain essential for inhibition of the cap'n'collar (CNC) basic-region leucine zipper (bZIP) factor. This mutant Keap1ΔC is yielded by translation from an alternatively mRNA-spliced variant lacking the fourth and fifth exons, but their coding sequences are retained in the wild-type Keap1 locus (with no genomic deletions). Although this variant was found primarily in the human highly-metastatic hepatoma (MHCC97H) cells, it was widely expressed at very lower levels in all other cell lines examined. Such Keap1ΔC retains no or less ability to inhibit Nrf2, so that it functions as a dominant-negative competitor of Keap1 against its inhibition of Nrf2 due to its antagonist effect on Keap1-mediated turnover of Nrf2 protein.

Nach Is a Novel Subgroup at an Early Evolutionary Stage of the CNC-bZIP Subfamily Transcription Factors from the Marine Bacteria to Humans.

Normal growth and development, as well as adaptive responses to various intracellular and environmental stresses, are tightly controlled by transcriptional networks. The evolutionarily conserved genomic sequences across species highlights the architecture of such certain regulatory elements. Among them, one of the most conserved transcription factors is the basic-region leucine zipper (bZIP) family. Herein, we have performed phylogenetic analysis of these bZIP proteins and found, to our surprise, that there exist a few homologous proteins of the family members Jun, Fos, ATF2, BATF, C/EBP and CNC (cap'n'collar) in either viruses or bacteria, albeit expansion and diversification of this bZIP superfamily have occurred in vertebrates from metazoan. Interestingly, a specific group of bZIP proteins is identified, designated Nach (Nrf and CNC homology), because of their strong conservation with all the known CNC and NF-E2 p45 subunit-related factors Nrf1 and Nrf2. Further experimental evidence has also been provided, revealing that Nach1 and Nach2 from the marine bacteria exert distinctive functions, when compared with human Nrf1 and Nrf2, in the transcriptional regulation of antioxidant response element (ARE)-battery genes. Collectively, further insights into these Nach/CNC-bZIP subfamily transcription factors provide a novel better understanding of distinct biological functions of these factors expressed in distinct species from the marine bacteria to humans.

Nrf1D Is the First Candidate Secretory Transcription Factor in the Blood Plasma, Its Precursor Existing as a Unique Redox-Sensitive Transmembrane CNC-bZIP Protein in Hemopoietic and Somatic Tissues.

Among multiple distinct isoforms, Nrf1D is synthesized from a de novo translation of an alternatively-spliced transcript of Nrf1 mRNA, as accompanied by a naturally-occurring deletion of its stop codon-flanking 1466 nucleotides. This molecular event leads to the generation of a reading frameshift mutation, which results in a constitutive substitution of the intact Nrf1's C-terminal 72 amino acids (aa, covering the second half of the leucine zipper motif to C-terminal Neh3L domain) by an additional extended 80-aa stretch to generate a unique variant Nrf1D. The C-terminal extra 80-aa region of Nrf1D was herein identified to be folded into a redox-sensitive transmembrane domain, enabling it to be tightly integrated within the endoplasmic reticulum (ER) membranes. Notably, the salient feature of Nrf1D enables it to be distinguishable from prototypic Nrf1, such that Nrf1D is endowed with a lesser ability than wild-type Nrf1 to mediate target gene expression. Further evidence has also been presented revealing that both mRNA and protein levels of Nrf1D, together with other isoforms similar to those of Nrf1, were detected to varying extents in hemopoietic and somatic tissues. Surprisingly, we found the existence of Nrf1D-derived isoforms in blood plasma, implying that it is a candidate secretory transcription factor, albeit its precursor acts as an integral transmembrane-bound CNC-bZIP protein that entails dynamic topologies across membranes, before being unleashed from the ER to enter the blood.

Molecular and cellular basis for the unique functioning of Nrf1, an indispensable transcription factor for maintaining cell homoeostasis and organ integrity.

The consensuscis-regulatory AP-1 (activator protein-1)-like AREs (antioxidant-response elements) and/or EpREs (electrophile-response elements) allow for differential recruitment of Nrf1 [NF-E2 (nuclear factor-erythroid 2)-related factor 1], Nrf2 and Nrf3, together with each of their heterodimeric partners (e.g. sMaf, c-Jun, JunD or c-Fos), to regulate different sets of cognate genes. Among them, NF-E2 p45 and Nrf3 are subject to tissue-specific expression in haemopoietic and placental cell lineages respectively. By contrast, Nrf1 and Nrf2 are two important transcription factors expressed ubiquitously in various vertebrate tissues and hence may elicit putative combinational or competitive functions. Nevertheless, they have de facto distinct biological activities because knockout of their genes in mice leads to distinguishable phenotypes. Of note, Nrf2 is dispensable during development and growth, albeit it is accepted as a master regulator of antioxidant, detoxification and cytoprotective genes against cellular stress. Relative to the water-soluble Nrf2, less attention has hitherto been drawn to the membrane-bound Nrf1, even though it has been shown to be indispensable for embryonic development and organ integrity. The biological discrepancy between Nrf1 and Nrf2 is determined by differences in both their primary structures and topovectorial subcellular locations, in which they are subjected to distinct post-translational processing so as to mediate differential expression of ARE-driven cytoprotective genes. In the present review, we focus on the molecular and cellular basis for Nrf1 and its isoforms, which together exert its essential functions for maintaining cellular homoeostasis, normal organ development and growth during life processes. Conversely, dysfunction of Nrf1 results in spontaneous development of non-alcoholic steatohepatitis, hepatoma, diabetes and neurodegenerative diseases in animal models.

Nrf2- and Bach1 May Play a Role in the Modulation of Ultraviolet A-Induced Oxidative Stress by Acetyl-11-Keto-ß-Boswellic Acid in Skin Keratinocytes.

BACKGROUND: Exposure of human skin to solar ultraviolet A (UVA) irradiation causes severe oxidative stress with damage to various cellular components and concomitant inflammation and carcinogenesis. OBJECTIVE: The aim of this study is to investigate the protective effect of acetyl-11-keto-ß-boswellic acid (AKBA) against UVA radiation on human skin keratinocytes. METHODS: HaCaT cells were pretreated with AKBA followed by UVA irradiation. Radiation effects on cell morphology, cell viability, intracellular reactive oxygen species (ROS) levels, and antioxidant enzymes were examined. RESULTS: AKBA reduces UVA irradiation-induced cell viability loss, accompanied by a decreased production of UVA-induced ROS, decreased malondialdehyde, and increased superoxide dismutase expression. In addition, AKBA increased basal and UVA-induced levels of Nrf2 (NF-E2-related factor 2), the redox-sensitive factor, and its target genes NQO1 and heme oxygenase-1 (HO-1), whereas expression of the transcriptional repressor Bach1 (BTB and CNC homology 1) was reduced. Furthermore, the cytoprotective effects of AKBA against UVA-derived oxidative damage were accompanied by modulating expression of inflammatory mediators (i.e., cyclooxygenase-2 and nuclear factor-κB) and NOX1. CONCLUSIONS: AKBA protects skin cells from UVA-induced damage by modulating inflammatory mediators and/or ROS production. Therefore, AKBA has potential in the development of skin care products.

NFE2L1/Nrf1 serves as a potential therapeutical target for neurodegenerative diseases.

The failure of the proper protein turnover in the nervous system is mainly linked to a variety of neurodegenerative disorders. Therefore, a better understanding of key protein degradation through the ubiquitin-proteasome system is critical for effective prevention and treatment of those disorders. The proteasome expression is tightly regulated by a CNC (cap'n'collar) family of transcription factors, amongst which the nuclear factor-erythroid 2-like bZIP factor 1 (NFE2L1, also known as Nrf1, with its long isoform TCF11 and short isoform LCR-F1) has been identified as an indispensable regulator of the transcriptional expression of the ubiquitin-proteasome system. However, much less is known about how the pivotal role of NFE2L1/Nrf1, as compared to its homologous NFE2L2 (also called Nrf2), is translated to its physiological and pathophysiological functions in the nervous system insomuch as to yield its proper cytoprotective effects against neurodegenerative diseases. The potential of NFE2L1 to fulfill its unique neuronal function to serve as a novel therapeutic target for neurodegenerative diseases is explored by evaluating the hitherto established preclinical and clinical studies of Alzheimer's and Parkinson's diseases. In this review, we have also showcased a group of currently available activators of NFE2L1, along with an additional putative requirement of this CNC-bZIP factor for healthy longevity based on the experimental evidence obtained from its orthologous SKN1-A in Caenorhabditis elegans.

Loss of Nrf1 rather than Nrf2 leads to inflammatory accumulation of lipids and reactive oxygen species in human hepatoma cells, which is alleviated by 2-bromopalmitate.

Since Nrf1 and Nrf2 are essential for regulating the lipid metabolism pathways, their dysregulation has thus been shown to be critically involved in the non-controllable inflammatory transformation into cancer. Herein, we have explored the molecular mechanisms underlying their distinct regulation of lipid metabolism, by comparatively analyzing the changes in those lipid metabolism-related genes in Nrf1α-/- and/or Nrf2-/- cell lines relative to wild-type controls. The results revealed that loss of Nrf1α leads to lipid metabolism disorders. That is, its lipid synthesis pathway was up-regulated by the JNK-Nrf2-AP1 signaling, while its lipid decomposition pathway was down-regulated by the nuclear receptor PPAR-PGC1 signaling, thereby resulting in severe accumulation of lipids as deposited in lipid droplets. By contrast, knockout of Nrf2 gave rise to decreases in lipid synthesis and uptake capacity. These demonstrate that Nrf1 and Nrf2 contribute to significant differences in the cellular lipid metabolism profiles and relevant pathological responses. Further experimental evidence unraveled that lipid deposition in Nrf1α-/- cells resulted from CD36 up-regulation by activating the PI3K-AKT-mTOR pathway, leading to abnormal activation of the inflammatory response. This was also accompanied by a series of adverse consequences, e.g., accumulation of reactive oxygen species (ROS) in Nrf1α-/- cells. Interestingly, treatment of Nrf1α-/- cells with 2-bromopalmitate (2BP) enabled the yield of lipid droplets to be strikingly alleviated, as accompanied by substantial abolishment of CD36 and critical inflammatory cytokines. Such Nrf1α-/- -led inflammatory accumulation of lipids, as well as ROS, was significantly ameliorated by 2BP. Overall, this study provides a potential strategy for cancer prevention and treatment by precision targeting of Nrf1, Nrf2 alone or both.

Distinct mechanisms by which Nrf1 and Nrf2 as drug targets contribute to the anticancer efficacy of cisplatin on hepatoma cells.

Cisplatin (cis-Dichlorodiamineplatinum[II], CDDP) is generally accepted as a platinum-based alkylating agent type of the DNA-damaging anticancer drug, which is widely administrated in clinical treatment of many solid tumors. The pharmacological effect of CDDP is mainly achieved by replacing the chloride ion (Cl-) in its structure with H2O to form active substances with the strong electrophilic properties and then react with any nucleophilic molecules, primarily leading to genomic DNA damage and subsequent cell death. In this process, those target genes driven by the consensus electrophilic and/or antioxidant response elements (EpREs/AREs) in their promoter regions are also activated or repressed by CDDP. Thereby, we here examined the expression profiling of such genes regulated by two principal antioxidant transcription factors Nrf1 and Nrf2 (both encoded by Nfe2l1 and Nfe2l2, respectively) in diverse cellular signaling responses to this intervention. The results demonstrated distinct cellular metabolisms, molecular pathways and signaling response mechanisms by which Nrf1 and Nrf2 as the drug targets differentially contribute to the anticancer efficacy of CDDP on hepatoma cells and xenograft tumor mice. Interestingly, the role of Nrf1, rather than Nrf2, is required for the anticancer effect of CDDP, to suppress malignant behavior of HepG2 cells by differentially monitoring multi-hierarchical signaling to gene regulatory networks. To our surprise, it was found there exists a closer relationship of Nrf1α than Nrf2 with DNA repair, but the hyperactive Nrf2 in Nrf1α-∕- cells manifests a strong correlation with its resistance to CDDP, albeit their mechanistic details remain elusive.

MCU inhibition protects against intestinal ischemia‒reperfusion by inhibiting Drp1-dependent mitochondrial fission.

Intestinal ischemia‒reperfusion (IIR) injury is a common complication of surgery, but clear molecular insights and valuable therapeutic targets are lacking. Mitochondrial calcium overload is an early sign of various diseases and is considered a vital factor in ischemia‒reperfusion injury. The mitochondrial calcium uniporter (MCU), which is located on the inner mitochondrial membrane, is the primary mediator of calcium ion entry into the mitochondria. However, the specific mechanism of MCU in IIR injury remains to be clarified. In this study, we generated an IIR model using C57BL/6 mice and Caco-2 cells and found increases in the calcium levels and MCU expression following IIR injury. The specific inhibition of MCU markedly attenuated IIR injury. Moreover, MCU knockdown alleviates mitochondrial dysfunction by reducing oxidative stress and apoptosis. Mechanistically, MCU knockdown substantially reduced the translocation of Drp1 and thus its binding to Fis1 receptors, resulting in decreased mitochondrial fission. Taken together, our findings demonstrated that MCU is a novel upstream regulator of Drp1 in ischemia‒reperfusion and represents a predictive and therapeutic target for IIR.

Sestrin2 reduces ferroptosis via the Keap1/Nrf2 signaling pathway after intestinal ischemia-reperfusion.

Sestrins are metabolic regulators that respond to stress by reducing the levels of reactive oxygen species (ROS) and inhibiting the activity of target of rapamycin complex 1 (mTORC1). Previous research has demonstrated that Sestrin2 mitigates ischemia-reperfusion (IR) injury in the heart, liver, and kidneys. However, its specific role in intestinal ischemia-reperfusion (IIR) injury remains unclear. To elucidate the role of Sestrin2 in IIR injury, we conducted an experimental study using a C57BL/6J mouse model of IIR. We noticed an increase in the levels of Sestrin2 expression and indicators associated with ferroptosis. Our study revealed that manipulating Sestrin2 expression in Caco-2 cells through overexpression or knockdown resulted in a corresponding decrease or increase, respectively, in ferroptosis levels. Furthermore, our investigation revealed that Sestrin2 alleviated ferroptosis caused by IIR injury through the activation of the Keap1/Nrf2 signal pathway. This finding highlights the potential of Sestrin2 as a therapeutic target for alleviating IIR injury. These findings indicated that the modulation of Sestrin2 could be a promising strategy for managing prolonged IIR injury.

A novel crosstalk between Nrf2 and Smad2/3 bridged by two nuanced Keap1 isoforms with their divergent effects on these distinct family transcription factors.

The Keap1-Nrf2 signalling to transcriptionally regulate antioxidant response element (ARE)-driven target genes has been accepted as key redox-sensitive pathway governing a vast variety of cellular stresses during healthy survival and disease development. Herein, we identified two nuanced isoforms α and ß of Keap1 in HepG2 cells, arising from its first and another in-frame translation starting codons, respectively. In identifying those differential expression genes monitored by Keap1α and/or Keap1ß, an unusual interaction of Keap1 with Smad2/3 was discovered by parsing transcriptome sequencing, Keap1-interacting protein profiling and relevant immunoprecipitation data. Further examination validated that Smad2/3 enable physical interaction with Keap1, as well as its isoforms α and ß, by both EDGETSD and DLG motifs in the linker regions between their MH1 and MH2 domains, such that the stability of Smad2/3 and transcriptional activity are enhanced with their prolonged half-lives and relevant signalling responses from the cytoplasmic to nuclear compartments. The activation of Smad2/3 by Keap1, Keap1α or Keap1ß was much likely contributable to a coordinative or another competitive effect of Nrf2, particularly in distinct Keap1-based cellular responses to its cognate growth factor (i.e. TGF-ß1) or redox stress (e.g. stimulated by tBHQ and DTT). Overall, this discovery presents a novel functional bridge crossing the Keap1-Nrf2 redox signalling and the TGF-ß1-Smad2/3 pathways so as to coordinately regulate the healthy growth and development.