Nrf2-ARE pathway regulates induction of Sestrin-2 expression

Inhibitory Effect of Sestrin 2 on Hepatic Stellate Cell Activation and Liver Fibrosis

Aims: Hepatic fibrosis results from chronic liver injury and inflammatory responses. Sestrin 2 (Sesn2), an evolutionarily conserved antioxidant enzyme, reduces the severities of acute hepatitis and metabolic liver diseases. However, the role of Sesn2 in the pathogenesis of liver fibrosis remains obscure. Here, we used cultured hepatic stellate cells (HSCs) and chronic carbon tetrachloride (CCl₄) and bile duct ligation (BDL) murine models to investigate the effects of Sesn2 on fibrogenesis. Results: Sesn2 protein and mRNA levels were upregulated in activated primary HSCs, and by increasing transcription, transforming growth factor-β (TGF-β) also increased Sesn2 expression in HSCs. Furthermore, Smad activation was primarily initiated by TGF-β signaling, and Smad3 activation increased Sesn2 luciferase activity. In silico analysis of the 5' upstream region of the Sesn2 gene revealed a putative Smad-binding element (SBE), and its deletion demonstrated that the SBE between -964 and -956 bp within human Sesn2 promoter was critically required for TGF-β-mediated response. Moreover, ectopic expression of Sesn2 reduced gene expressions associated with HSC activation, and this was accompanied by marked decreases in SBE luciferase activity and Smad phosphorylation. Infection of recombinant adenovirus Sesn2 reduced hepatic injury severity, as evidenced by reductions in CCl₄- or BDL-induced alanine aminotransferase and aspartate aminotransferase, and inhibited collagen accumulation. Furthermore, HSC-specific lentiviral delivery of Sesn2 prevented CCl₄-induced liver fibrosis. Finally, Sesn2 expression was downregulated in the livers of patients with liver cirrhosis and in mouse models of hepatic fibrosis. Innovation and Conclusion: Our findings suggest that Sesn2 has the potential to inhibit HSC activation and hepatic fibrosis.

Protective effect of sestrin2 against iron overload and ferroptosis-induced liver injury

Ferroptosis is the non-apoptotic form of cell death caused by small molecules or conditions that inhibit glutathione biosynthesis or resulting in iron-dependent accumulation of lipid peroxidation by lipid reactive oxygen species (ROS). Sestrin2 (Sesn2), a conserved antioxidant protein, is responsive to various stresses including genotoxic, metabolic, and oxidative stresses and acts to restore homeostatic balance. Sesn2 expression was reported to be regulated via stress-responsive transcription factors including p53, Nrf2, and HIF-1α. However, the role of Sesn2 in regulating ferroptosis is not known. In the current study, we investigated whether ferroptosis inducing compounds including erastin, sorafenib, and buthionine sulfoximine affect Sesn2 expression and the role of Sesn2 in cytoprotection against ferroptosis-mediated cell death. Our data demonstrate that ferroptosis inducers significantly increased Sesn2 in hepatocytes in a dose- and time-dependent manner. Treatment with erastin upregulated Sesn2 mRNA levels and luciferase reporter gene activity, and erastin-mediated Sesn2 induction was transcriptionally regulated by NF-E2-related factor 2 (Nrf2). Furthermore, deletion of the antioxidant response element (ARE) in the Sesn2 promoter or Nrf2 knockout or knockdown abolished erastin-induced Sesn2 expression. In cells expressing Sesn2, erastin-induced cell death, ROS formation, and glutathione depletion were almost completely inhibited compared to that in control cells. Treatment with phenylhydrazine in mice, well-reported iron overload liver injury model, increased ALT and AST levels and altered histological features, which were almost completely inhibited by adenoviral Sesn2 infection. Collectively, our results suggest that ferroptosis-mediated Sesn2 induction is dependent on Nrf2 and plays a protective role against iron overload and ferroptosis-induced liver injury.

Repositioning of niclosamide ethanolamine (NEN), an anthelmintic drug, for the treatment of lipotoxicity

Nonalcoholic steatohepatitis (NASH) is a common liver disease associated with metabolic disorders, including obesity and type 2 diabetes (T2D). Despite its worldwide prevalence, there are no effective drugs for the treatment of NASH. The progression of NASH is mainly accelerated by reactive oxygen species (ROS)-induced lipotoxicity. The transcription factor known as nuclear factor erythroid 2-related factor 2 (Nrf2) is pivotal for the elimination of ROS. Accordingly, activators of Nrf2 have been implicated as promising therapeutic targets for the treatment of NASH. Niclosamide (ethanolamine salt; NEN), a drug approved by the US Food and Drug Administration (USFDA), is currently used as an anthelmintic drug for the treatment of parasitic infections. Recently, NEN was shown to improve hepatic steatosis in high-fat diet (HFD)-fed mice. However, the underlying mechanism of its antioxidant function in NASH remains unknown. Here, we demonstrate that NEN induces AMPK-mediated phosphorylation of p62 at S351 that can lead to noncanonical Nrf2 activation. We also demonstrate that NEN protects cells and mouse liver from acute lipotoxic stress through activating p62-dependent Keap1-Nrf2 pathway. Taken together, NEN can be used for clinical applications and has the potential to provide a new therapeutic option for NASH.

Sestrin2 overexpression attenuates focal cerebral ischemic injury in rat by increasing Nrf2/HO-1 pathway-mediated angiogenesis

Sestrin2 (Sesn2) is a stress response protein which expresses neuroprotective characteristics in some neurodegenerative disorders. However, the impact of Sesn2 on the clinical outcome of stroke is unclear. The nuclear factor-erythroid 2 related factor 2/heme oxygenase-1 (Nrf2/HO-1) pathway is a key factor in angiogenesis, which aids in attenuating cerebral ischemia damage. In this study the investigators examine the effects of Sesn2 on cerebral ischemia damage by increasing angiogenesis through the Nrf2/HO-1 signaling pathway. Healthy adult Sprague-Dawley (SD) rats were exposed to photochemical cerebral ischemia while AAV injection was used to overexpress Sesn2. At 5 days after photochemical embolization, the investigators observed a reduction in neurological problems, decreased infarct volume, and diminished neuronal injury in the Sesn2 overexpression samples compared to the controls. To further explore these defensive mechanisms, the investigators also silenced Nrf2. While Sesn2, Nrf2, HO-1, and VEGF were significantly increased following cerebral ischemia, overexpression of Sesn2 further increased their expression. After silencing Nrf2, the opposite effect was observed. These results imply that Sestrin2 may activate the Nrf2 / HO-1 pathway, leading to enhanced angiogenesis following photothrombotic cerebral ischemia.

Regulation of Toll-Like Receptor (TLR) Signaling Pathway by Polyphenols in the Treatment of Age-Linked Neurodegenerative Diseases: Focus on TLR4 Signaling

Neuronal dysfunction initiates several intracellular signaling cascades to release different proinflammatory cytokines and chemokines, as well as various reactive oxygen species. In addition to neurons, microglia, and astrocytes are also affected by this signaling cascade. This release can either be helpful, neutral or detrimental for cell survival. Toll-like receptors (TLRs) activate and signal their downstream pathway to activate NF-κB and pro-IL-1β, both of which are responsible for neuroinflammation and linked to the pathogenesis of different age-related neurological conditions. However, herein, recent aspects of polyphenols in the treatment of neurodegenerative diseases are assessed, with a focus on TLR regulation by polyphenols. Different polyphenol classes, including flavonoids, phenolic acids, phenolic alcohols, stilbenes, and lignans can potentially target TLR signaling in a distinct pathway. Further, some polyphenols can suppress overexpression of inflammatory mediators through TLR4/NF-κB/STAT signaling intervention, while others can reduce neuronal apoptosis via modulating the TLR4/MyD88/NF-κB-pathway in microglia/macrophages. Indeed, neurodegeneration etiology is complex and yet to be completely understood, it may be that targeting TLRs could reveal a number of molecular and pharmacological aspects related to neurodegenerative diseases. Thus, activating TLR signaling modulation via natural resources could provide new therapeutic potentiality in the treatment of neurodegeneration.

Interactions between microRNA-200 family and Sestrin proteins in endometrial cancer cell lines and their significance to anoikis

In the present study, we intend to determine whether Sestrin proteins 1, 2, and 3 (SESN1-3) are targets of microRNA-200 family (miR-200) in endometrial cancer (EC) Ishikawa, AN3CA, KLE, and RL 95-2 cell lines and to investigate how these potential interactions influence anoikis resistance of EC cell lines. The luciferase reporter assay, qRT-PCR, and western blotting assays were used to verify whether SESN1-3 are direct targets of miR-200. Moreover, the anoikis assay and transient transfections of miR-200 mimics or inhibitors into EC cell lines were performed to evaluate the modulatory role of miR-200 and SESN proteins on anoikis resistance. We demonstrated that SESN2 protein is a direct target of mir-141 in KLE and RL-95-2 EC cell lines and the functional interaction of miR-141 and SESN2 protein has a downstream effect on anoikis resistance and SESN2 expression level in Ishikawa and AN3CA cell lines. Moreover, we have shown that SESN3 protein is a direct target of miR-200b, miR-200c, and miR-429 in Ishikawa, AN3CA, and KLE cell lines. Our results show that manipulation of miR-200b, miR-200c, and miR-429 expression patterns also has an influence on anoikis resistance in EC cell lines. In conclusion, we identified new interactions between miR-200 and the oxidative stress response SESN proteins that affect anoikis resistance in human EC cells.

Sestrins at the Interface of ROS Control and Autophagy Regulation in Health and Disease

Reactive oxygen species (ROS) and autophagy are two highly complex and interrelated components of cell physiopathology, but our understanding of their integration and their contribution to cell homeostasis and disease is still limited. Sestrins (SESNs) belong to a family of highly conserved stress-inducible proteins that orchestrate antioxidant and autophagy-regulating functions protecting cells from various noxious stimuli, including DNA damage, oxidative stress, hypoxia, and metabolic stress. They are also relevant modulators of metabolism as positive regulators of the key energy sensor AMP-dependent protein kinase (AMPK) and inhibitors of mammalian target of rapamycin complex 1 (mTORC1). Since perturbations in these pathways are central to multiple disorders, SESNs might constitute potential novel therapeutic targets of broad interest. In this review, we discuss the current understanding of regulatory and effector networks of SESNs, highlighting their significance as potential biomarkers and therapeutic targets for different diseases, such as aging-related diseases, metabolic disorders, neurodegenerative diseases, and cancer.

The interaction of Hemin and Sestrin2 modulates oxidative stress and colon tumor growth

Several large epidemiological and animal studies demonstrate a direct correlation between dietary heme iron intake and/or systemic iron levels and cancer risk in several cancers including colorectal cancer (CRC). However, the precise mechanisms for how heme iron contributes to CRC and how cancer cells respond to heme iron-induced stress are still unclear. Previously we have shown that one of the stress-inducible proteins, Sestrin2 (SESN2), is a novel tumor suppressor in colon by limiting endoplasmic reticulum stress and mammalian target of rapamycin complex 1 (mTORC1) signaling and tumor growth. But the relationship between heme iron and SESN2, especially in the context of colon carcinogenesis, was not investigated previously. Here, we found that hemin dose-dependently increased SESN2 expression in an oxidative stress and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, NRF2)-dependent manner. Since SESN2 overexpression reduced hemin-induced oxidative stress, SESN2 could be an important target of NRF2 exerting antioxidant function. Indeed, expression of several oxidative stress responsive proteins such as NRF2 and its target genes was reduced by SESN2. Although we formerly reported that SESN2 expression was reduced after p53 mutation in colon tumors, mouse colon tumors, which have intact p53 and NRF2, induced SESN2 expression in response to iron stimulus. Although SESN2 overexpression decreased murine colon tumor cell growth both in vitro and in vivo, it rendered colon cancer cells more resistant to hemin-induced apoptosis and therefore promoted tumor growth during hemin treatment. Taken together, although SESN2 generally suppresses tumorigenesis, it can produce tumor-promoting role in iron-rich environment by suppressing oxidative stress-associated cancer cell death.

Pentamethylquercetin protects against cardiac remodeling via activation of Sestrin2

Oxidative stress is widely involved in pathophysiological processes of cardiac remodeling. Molecules associated with antioxidant functions may be ideal targets for reversing cardiac remodeling. Sestrin2 is the important component of endogenous antioxidant defense, while there is little information on the pathophysiological roles of it in cardiac remodeling. The aim of this study was to investigate whether Sestrin2 is closely involved in cardiac remodeling, and whether the protective effect of pentamethylquercetin (PMQ) on cardiac remodeling is related to upregulation of the Sestrin2 endogenous antioxidant system. We generated a transverse aorta constriction (TAC)-induced pressure-overload cardiac-remodeling model in mice, and also established an isoproterenol (ISO)-induced neonatal rat cardiomyocyte (NRCM) hypertrophy model. The data showed Sestrin2 expression was downregulated significantly, and Nrf2 and HO-1 expression was also reduced in myocardial tissue or NRCM of model group, whereas keap1 expression was upregulated. PMQ significantly ameliorated cardiac remodeling and rectified the abnormal expression of Sestrin2/Nrf2/keap1. Sestrin2 small interfering RNA (SiRNA) reduced the protective effect of PMQ on NRCMs, as well as abolished its regulating effect on the Nrf2/keap1 pathway. In conclusion, Sestrin2 may be an important target in the anti-myocardial remodeling of PMQ.

Bamboo Stems (Phyllostachys nigra variety henosis) Containing Polyphenol Mixtures Activate Nrf2 and Attenuate Phenylhydrazine-Induced Oxidative Stress and Liver Injury

This study was designed to investigate the hepatoprotective effect of bamboo stems using in vitro and in vivo experimental liver damage models. Ethyl acetate fraction of 80% ethanol extract of Phyllostachys nigra stem (PN3) containing polyphenols had a higher NQO1-ARE reporter gene activity as monitored by the activity of the NF-E2-related factor (Nrf2) antioxidant pathway in cells in comparison to extracts from other species and under other conditions. The Nrf2 was translocated from the cytosol to the nucleus in response to PN3, followed by induction of the Nrf2 target gene expression, including HO-1, GCL, and NQO-1 in HepG2 cells. Phosphorylation of Nrf2 in HepG2 cells was enhanced in PN3, which was mediated by PKCδ, ERK, and p38 MAPK. Consequently, PN3 inhibited arachidonic acid (AA) + iron-induced reactive oxygen species generation and glutathione depletion, and, thus, highlighted their role in cytotoxicity. Treatment with major polyphenols of PN3, including catechin, chlorogenic acid, caffeic acid, and p-coumaric acid, also improved AA + iron-mediated oxidative stress and, thus, improved cell viability. Treatment with phenylhydrazine in mice, i.e., the iron overload liver injury model, increased plasma alanine aminotransferase and aspartate aminotransferase levels and changed histological features in mice—a response that was almost completely blocked by PN3 administration. Moreover, PN3 extract mitigated phenylhydrazine-induced oxidative stress and inflammatory responses. Conclusively, PN3 can exert a hepatoprotective effect against iron overload-induced acute liver damage due to its antioxidant properties.

Nrf2 inhibition reverses resistance to GPX4 inhibitor-induced ferroptosis in head and neck cancer

Glutathione peroxidase 4 (GPX4) is a regulator of ferroptosis (iron-dependent, non-apoptotic cell death); its inhibition can render therapy-resistant cancer cells susceptible to ferroptosis. However, some cancer cells develop mechanisms protective against ferroptosis; understanding these mechanisms could help overcome chemoresistance. In this study, we investigated the molecular mechanisms underlying resistance to ferroptosis induced by GPX4 inhibition in head and neck cancer (HNC). The effects of two GPX4 inhibitors, (1S, 3R)-RSL3 and ML-162, and of trigonelline were tested in HNC cell lines, including cisplatin-resistant (HN3R) and acquired RSL3-resistant (HN3-rslR) cells. The effects of the inhibitors and trigonelline, as well as of inhibition of the p62, Keap1, or Nrf2 genes, were assessed by cell viability, cell death, lipid ROS production, and protein expression, and in mouse tumor xenograft models. Treatment with RSL3 or ML-162 induced the ferroptosis of HNC cells to varying degrees. RSL3 or ML-162 treatment increased the expression of p62 and Nrf2 in chemoresistant HN3R and HN3-rslR cells, inactivated Keap1, and increased expression of the phospho-PERK-ATF4-SESN2 pathway. Transcriptional activation of Nrf2 was associated with resistance to ferroptosis. Overexpression of Nrf2 by inhibiting Keap1 or Nrf2 gene transfection rendered chemosensitive HN3 cells resistant to RSL3. However, Nrf2 inhibition or p62 silencing sensitized HN3R cells to RSL3. Trigonelline sensitized chemoresistant HNC cells to RSL3 treatment in a mouse model transplanted with HN3R. Thus, activation of the Nrf2-ARE pathway contributed to the resistance of HNC cells to GPX4 inhibition, and inhibition of this pathway reversed the resistance to ferroptosis in HNC.

Induction of REDD1 via AP-1 prevents oxidative stress-mediated injury in hepatocytes

Regulated in development and DNA damage responses 1 (REDD1) is an inducible gene in response to various stresses, which functions as a negative regulator of the mammalian target of rapamycin protein kinase in complex 1. In the present study, we identified the role of REDD1 under the oxidative stress-mediated hepatocyte injury and its regulatory mechanism. REDD1 protein was increased in H₂O₂ or tert-butylhydroperoxide (t-BHP)-treated hepatocytes_· H₂O₂ also elevated REDD1 mRNA levels. This event was inhibited by antioxidants such as diphenyleneiodonium chloride, N-acetyl-L-cysteine, or butylated hydroxy anisole. Interestingly, we found that H₂O₂-mediated REDD1 induction was transcriptionally regulated by activator protein-1 (AP-1), and that overexpression of c-Jun increased REDD1 protein levels and REDD1 promoter-driven luciferase activity. Deletion of the putative AP-1 binding site in proximal region of the human REDD1 promoter significantly abolished REDD1 transactivation by c-Jun. A NF-E2-related factor 2 activator, tert-butylhydroquinone treatment also elevated REDD1 levels, but it was independent on NF-E2-related factor 2 activation. Furthermore, we observed that REDD1 overexpression attenuated H₂O₂ or t-BHP-derived reactive oxygen species formation as well as cytotoxicity. Conversely, siRNA against REDD1 aggravated t-BHP-induced reactive oxygen species generation and cell death. In addition, we showed that REDD1 was induced by in vitro or in vivo ischemia/reperfusion model. Our results demonstrate that REDD1 induction by oxidative stress is mainly transcriptionally regulated by AP-1, and protects oxidative stress-mediated hepatocyte injury. These findings suggest REDD1 as a novel molecule that reduced susceptibility to oxidant-induced liver injury.

Carnosol, a dietary diterpene from rosemary (Rosmarinus officinalis) activates Nrf2 leading to sestrin 2 induction in colon cells

Background

Rosemary is abundant with phytochemicals and has recently been approved as an antioxidant food preservative in the European Union. The safety of rosemary is well established, however, the benefits on gastrointestinal health are less known. Our overall hypothesis is that the phytochemicals in rosemary including carnosol have the potential to promote gastrointestinal health by activation of the antioxidant sestrin-2 when consumed in our diet.

Methods

Colon cells HCT116 and SW480 were treated with carnosol and evaluated by MTT, immunofluorescence, ELISA, and Western blot analysis to understand the modulation of the PERK/Nrf2/Sestrin-2 pathway.

Results

Carnosol was found to modulate PERK and increase the concentration of nuclear Nrf2. Furthermore, a downstream marker of Nrf2 expression, Sestrin-2 was shown to be upregulated.

Conclusion

Based on these observations carnosol modulates the PERK and Nrf2 pathways along with increased expression of sestrin-2, a known stress inducible antioxidant.

mTORC1 pathway in DNA damage response

Living organisms have evolved various mechanisms to control their metabolism and response to various stresses, allowing them to survive and grow in different environments. In eukaryotes, the highly conserved mechanistic target of rapamycin (mTOR) signaling pathway integrates both intracellular and extracellular signals and serves as a central regulator of cellular metabolism, proliferation and survival. A growing body of evidence indicates that mTOR signaling is closely related to another cellular protection mechanism, the DNA damage response (DDR). Many factors important for the DDR are also involved in the mTOR pathway. In this review, we discuss how these two pathways communicate to ensure an efficient protection of the cell against metabolic and genotoxic stresses. We also describe how anticancer therapies benefit from simultaneous targeting of the DDR and mTOR pathways.

Skeletal muscle and liver gene expression profiles in finishing steers supplemented with Amaize

Our main objective was to evaluate the effects of feeding α-amylase (Amaize, Alltech Inc., Nicholasville, KY, USA) for 140 days on skeletal muscle and liver gene transcription in beef steers. Steers fed Amaize had lower average daily gain (p = .03) and gain:feed ratio (p = .05). No differences (p > .10) in serum metabolites or carcass traits were detected between the two groups but Amaize steers tended (p < .15) to have increased 12th rib fat depth. Microarray analysis of skeletal muscle revealed 21 differentially expressed genes (DEG), where 14 were up-regulated and seven were down-regulated in Amaize-fed steers. The bioinformatics analysis indicated that metabolic pathways involved in fat formation and deposition, stress response, and muscle function were activated, while myogenesis was inhibited in Amaize-fed steers. The quantitative PCR results for liver revealed a decrease (p < .01) in expression of fatty acid binding protein 1 (FABP1) and 3-hydroxybutyrate dehydrogenase 1 (BDH1) with Amaize. Because these genes are key for intracellular fatty acid transport, oxidation and ketone body production, data suggest a reduction in hepatic lipid catabolism. Future work to investigate potential positive effects of Amaize on cellular stress response, muscle function, and liver function in beef cattle appears warranted.

Epimedium koreanum Ameliorates Oxidative Stress-Mediated Liver Injury by Activating Nuclear Factor Erythroid 2-Related Factor 2

Oxidative stress induced by reactive oxygen species is the main cause of various liver diseases. This study investigated the hepatoprotective effect of Epimedium koreanum Nakai water extract (EKE) against arachidonic acid (AA)[Formula: see text][Formula: see text][Formula: see text]iron-mediated cytotoxicity in HepG2 cells and carbon tetrachloride (CCl₄-)-mediated acute liver injury in mice. Pretreatment with EKE (30 and 100[Formula: see text][Formula: see text]g/mL) significantly inhibited AA[Formula: see text][Formula: see text][Formula: see text]iron-mediated cytotoxicity in HepG2 cells by preventing changes in the expression of cleaved caspase-3 and poly(ADP-ribose) polymerase. EKE attenuated hydrogen peroxide production, glutathione depletion, and mitochondrial membrane dysfunction. EKE also increased the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2), transactivated anti-oxidant response element harboring luciferase activity, and induced the expression of anti-oxidant genes. Furthermore, the cytoprotective effect of EKE against AA[Formula: see text][Formula: see text][Formula: see text]iron was blocked in Nrf2 knockout cells. Ultra-performance liquid chromatography analysis showed that EKE contained icariin, icaritin, and quercetin; icaritin and quercetin were both found to protect HepG2 cells from AA[Formula: see text][Formula: see text][Formula: see text]iron via Nrf2 activation. In a CCl₄-induced mouse model of liver injury, pretreatment with EKE (300[Formula: see text]mg/kg) for four consecutive days ameliorated CCl₄-mediated increases in serum aspartate aminotransferase activity, histological activity index, hepatic parenchyma degeneration, and inflammatory cell infiltration. EKE also decreased the number of nitrotyrosine-, 4-hydroxynonenal-, cleaved caspase-3-, and cleaved poly(ADP-ribose) polymerase-positive cells in hepatic tissues. These results suggest EKE is a promising candidate for the prevention or treatment of oxidative stress-related liver diseases via Nrf2 activation.

Hemistepsin A ameliorates acute inflammation in macrophages via inhibition of nuclear factor-κB and activation of nuclear factor erythroid 2-related factor 2

Hemistepsin A (HsA) is a sesquiterpene lactone isolated from Hemistepta lyrata (Bunge) Bunge. We investigated the anti-inflammatory effects of HsA and sought to determine its mechanisms of action in macrophages. HsA pretreatment inhibited nitric oxide production, and reduced the expression of iNOS and COX-2 in Toll-like receptor ligand-stimulated RAW 264.7 cells. Additionally, HsA decreased the secretion of proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated Kupffer cells as well as in RAW 264.7 cells. HsA inhibited phosphorylation of IKKα/β and degradation of IκBα, resulting in decreased nuclear translocation of nuclear factor-κB (NF-κB) and its transcriptional activity. Moreover, HsA phosphorylated nuclear factor erythroid 2-related factor 2 (Nrf2), increased expression levels of antioxidant genes, and attenuated LPS-stimulated H₂O₂ production. Phosphorylation of p38 and c-Jun N-terminal kinase was required for HsA-mediated Nrf2 phosphorylation. In a D-galactosamine/LPS-induced liver injury model, HsA ameliorated D-galactosamine/LPS-induced hepatocyte degeneration and inflammatory cells infiltration. Moreover, immunohistochemical analyses using nitrotyrosine, 4-hydroxynonenal, and cleaved poly (ADP-ribose) polymerase antibodies revealed that HsA protected the liver from oxidative stress. Furthermore, HsA reduced the numbers of proinflammatory cytokine-positive cells in hepatic tissues. Thus, these results suggest HsA may be a promising natural product to manage inflammation-mediated tissue injuries through inhibition of NF-κB and activation of Nrf2.

Carbon monoxide protects against hepatic steatosis in mice by inducing sestrin-2 via the PERK-eIF2α-ATF4 pathway

Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has emerged as one of the most common causes of chronic liver disease in developed countries over the last decade. NAFLD comprises a spectrum of pathological hepatic changes, including steatosis, steatohepatitis, advanced fibrosis, and cirrhosis. Autophagy, a homeostatic process for protein and organelle turnover, is decreased in the liver during the development of NAFLD. Previously, we have shown that carbon monoxide (CO), a reaction product of heme oxygenase (HO) activity, can confer protection in NAFLD, though the molecular mechanisms remain unclear. We therefore investigated the mechanisms underlying the protective effect of CO on methionine/choline-deficient (MCD) diet-induced hepatic steatosis. We found that CO induced sestrin-2 (SESN2) expression through enhanced mitochondrial ROS production and protected against MCD-induced NAFLD progression through activation of autophagy. SESN2 expression was increased by CO or CO-releasing molecule (CORM2), in a manner dependent on signaling through the protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor-2 alpha (eIF2α)/ activating transcription factor-4 (ATF4)-dependent pathway. CO-induced SESN2 upregulation in hepatocytes contributed to autophagy induction through activation of 5'-AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) complex I (mTORC1). Furthermore, we demonstrate that CO significantly induced the expression of SESN2 and enhanced autophagy in the livers of MCD-fed mice or in MCD-media treated hepatocytes. Conversely, knockdown of SESN2 abrogated autophagy activation and mTOR inhibition in response to CO. We conclude that CO ameliorates hepatic steatosis through the autophagy pathway induced by SESN2 upregulation.

Potent Anti-Inflammatory and Antiadipogenic Properties of Bamboo (Sasa coreana Nakai) Leaves Extract and Its Major Constituent Flavonoids

The pro-inflammatory response and recruitment of macrophages into adipose tissue contribute to metabolic dysfunction. Here, we reported the anti-inflammatory and antiadipogenic effects of the methanol (MeOH) extract and ethyl acetate (EtOAc) fraction of bamboo leaf and its molecular mechanism in RAW264.7 cells and 3T3-L1 adipocytes, respectively. Functional macrophage migration assays also were performed. Surprisingly, the EtOAc fraction of MeOH extracts from native Korean plant species Sasa coreana Nakai (SCN) has shown potent anti-inflammatory properties; SCN pretreatment inhibited nitric oxide (NO) production (p < 0.01) and inducible nitric oxide synthase (iNOS) expression in lipopolysaccharide (LPS)-stimulated macrophages. Inflammatory genes induced by LPS, including TNFα, IL-1β, and IL-6, were significantly attenuated by SCN (p < 0.01). Pretreatment with SCN antagonized NF-κB nuclear translocation and the simultaneous degradation of inhibitory κB protein. Furthermore, SCN selectively inhibited the LPS-induced phosphorylation of JNK (p < 0.01) and p38 (p < 0.05) but not ERK (p > 0.05). Similar to leaf extracts of other bamboo species, we identified that SCN contained several flavonoids including orientin, isoorientin, and vitexin; these compounds inhibited LPS-induced NO production (p < 0.05) and iNOS expression. In addition, SCN inhibited adipocyte differentiation in a dose-dependent manner, as demonstrated by Oil Red O staining and the protein expression of mature adipogenic marker genes. Treatment with the major flavonoids of SCN also inhibited adipogenesis. Furthermore, conditioned medium obtained from adipocytes stimulated macrophage chemotaxis, whereas medium from adipocytes treated with SCN significantly inhibited macrophage migration. Therefore, SCN is a potential therapeutic agent for the prevention of inflammation and obesity.

Sestrin2 as a Novel Biomarker and Therapeutic Target for Various Diseases

Sestrin2 (SESN2), a highly conserved stress-inducible metabolic protein, is known to repress reactive oxygen species (ROS) and provide cytoprotection against various noxious stimuli including genotoxic and oxidative stress, endoplasmic reticulum (ER) stress, and hypoxia. Studies demonstrate that the upregulation of Sestrin2 under conditions of oxidative stress augments autophagy-directed degradation of Kelch-like ECH-associated protein 1 (Keap1), which targets and breaks down nuclear erythroid-related factor 2 (Nrf2), a key regulator of various antioxidant genes. Moreover, ER stress and hypoxia are shown to induce Sestrins, which ultimately reduce cellular ROS levels. Sestrin2 also plays a pivotal role in metabolic regulation through activation of the key energy sensor AMP-dependent protein kinase (AMPK) and inhibition of mammalian target of rapamycin complex 1 (mTORC1). Other downstream effects of Sestrins include autophagy activation, antiapoptotic effects in normal cells, and proapoptotic effects in cancer cells. As perturbations in the aforementioned pathways are well documented in multiple diseases, Sestrin2 might serve as a potential therapeutic target for various diseases. Thus, the aim of this review is to discuss the upstream regulators and the downstream effectors of Sestrins and to highlight the significance of Sestrin2 as a biomarker and a therapeutic target in diseases such as metabolic disorders, cardiovascular and neurodegenerative diseases, and cancer.

Sesn2 gene ablation enhances susceptibility to gentamicin-induced hair cell death via modulation of AMPK/mTOR signaling

The process of gentamicin-induced hair cell damage includes the activation of oxidative stress processes. Sestrins, as stress-responsive proteins, protect cells against oxidative stress. Sestrins, particularly Sestrin-2, suppress excessive reactive oxygen species (ROS) accumulation and inhibit mammalian target of rapamycin complex 1 (mTORC1). Thus, we addressed the role of Sestrin-2 in the regulation of sensory hair cell survival after gentamicin exposure. Here, we show that Sestrins were expressed in the inner ear tissues, and Sestrin-2 immunolocalized in sensory hair cells and spiral ganglion (SG). The expression of Sestrin-2 was unchanged, and later downregulated, in gentamicin-treated explants from wild-type mice in vitro. Compared with wild-type mice, Sestrin-2 knockout mice exhibited significantly greater hair cell loss in gentamicin-treated cochlear explants. Significant downregulation of phosphorylation of AMP-activated protein kinase alpha (AMPKα) and upregulation of the 70-kDa ribosomal protein S6 kinase (p70S6K) were measured in wild-type cochlear explants exposed to gentamicin compared with their untreated controls. Such regulatory effect was not observed between explants from untreated and gentamicin-treated knockout mice. The gentamicin effect on mTOR signaling was rapamycin-sensitive. Thus, our data provide evidence that Sestrin-2 plays an important role in the protection of hair cells against gentamicin, and the mTOR signaling pathway appears to be modulated by gentamicin during hair cell death.

Activating transcription factor 6-dependent sestrin 2 induction ameliorates ER stress-mediated liver injury

Endoplasmic reticulum (ER) stress is characterized by an accumulation of misfolded proteins, and ER stress reduction is essential for maintaining tissue homeostasis. However, the molecular mechanisms that protect cells from ER stress are not completely understood. The present study investigated the role of sestrin 2 (SESN2) on ER stress and sought to elucidate the mechanism responsible for the hepatoprotective effect of SESN2 in vitro and in vivo. Treatment with tunicamycin (Tm) increased SESN2 protein and mRNA levels and reporter gene activity. Activating transcription factor 6 (ATF6) bound to unfolded protein response elements of SESN2 promoter, transactivated SESN2, and increased SESN2 protein expression. In addition, dominant negative mutant of ATF6α and siRNA against ATF6α blocked the ER stress-mediated SESN2 induction, whereas chemical inhibition of PERK or IRE1 did not affect SESN2 induction by Tm. Ectopic expression of SESN2 in HepG2 cells inhibited CHOP and GRP78 expressions by Tm. Moreover, SESN2 decreased the phosphorylations of JNK and p38 and PARP cleavage, and blocked the cytotoxic effect of excessive ER stress. In a Tm-induced liver injury model, adenoviral delivery of SESN2 in mice decreased serum ALT, AST and LDH activities and the mRNA levels of CHOP and GRP78 in hepatic tissues. Moreover, SESN2 reduced numbers of degenerating hepatocytes, and inhibited caspase 3 and PARP cleavages. These results suggest ATF6 is essential for ER stress-mediated SESN2 induction, and that SESN2 acts as a feedback regulator to protect liver from excess ER stress.

Role of sestrin2 in H2O2-induced PC12 apoptosis

Sestrin2 is involved in different kind of cellular response to stress conditions. However, the function of Sestrin2 in oxidative stress related neurological diseases remains unknown. In this study, we tested whether Sestrin2 has a beneficial effect on PC12 cell apoptosis induced by H₂O₂. We found that H₂O₂ induces expression of Sestrin2 in PC12 cells in a time-dependent and dose-dependent manner. We also found that Knockdown of Sestrin2 using small RNA interference promotes cell apoptosis induced by H₂O₂. In addition, our results show that the c-Jun NH(2)-terminal kinase (JNK)/c-Jun pathway is activated by H₂O₂. Inhibiting the activity of the JNK pathway and JNK siRNA transfection abolishes the increase of Sestrin2 induced by H₂O₂. These findings suggest that the inductive effect of Sestrin2 is mediated by the JNK/c-Jun pathway. In this study, we investigated the role of Sestrin2 in oxidative stress-induced cell apoptosis using PC12 cells as the model, implying that stimulating expression of Sestrin2 might be considered as a neuroprotective target against H₂O₂-induced oxidative stress.

More Insight into BDNF against Neurodegeneration: Anti-Apoptosis, Anti-Oxidation, and Suppression of Autophagy

In addition to its well-established neurotrophic action, brain-derived neurotrophic factor (BDNF) also possesses other neuroprotective effects including anti-apoptosis, anti-oxidation, and suppression of autophagy. We have shown before that BDNF triggers multiple mechanisms to confer neuronal resistance against 3-nitropropionic acid (3-NP)-induced mitochondrial dysfunction in primary rat cortical cultures. The beneficial effects of BDNF involve the induction of anti-oxidative thioredoxin with the resultant expression of anti-apoptotic B-cell lymphoma 2 (Bcl-2) as well as erythropoietin (EPO)-dependent stimulation of sonic hedgehog (SHH). We further revealed that BDNF may bring the expression of sulfiredoxin, an ATP-dependent antioxidant enzyme, to offset mitochondrial inhibition in cortical neurons. Recently, we provided insights into another novel anti-oxidative mechanism of BDNF, which involves the augmentation of sestrin2 expression to endow neuronal resistance against oxidative stress induced by 3-NP; BDNF induction of sestrin2 entails the activation of a pathway involving nitric oxide (NO), cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG), and nuclear factor-κB (NF-κB). Apart from anti-apoptosis and anti-oxidation, we demonstrated in our most recent study that BDNF may activate the mammalian target of rapamycin (mTOR) with resultant activation of transcription factor c-Jun, thereby stimulating the expression of p62/sequestosome-1 to suppress heightened autophagy as a result of 3-NP exposure. Together, our results provide in-depth insight into multi-faceted protective mechanisms of BDNF against mitochondrial dysfunction commonly associated with the pathogenesis of many chronic neurodegenerative disorders. Delineation of the protective signaling pathways elicited by BDNF would endow a rationale to develop novel therapeutic regimens to halt or prevent the progression of neurodegeneration.

Compound C Increases Sestrin2 Expression via Mitochondria-Dependent ROS Production

Compound C is a widely used chemical inhibitor that down-regulates AMP-activated protein kinase (AMPK) activity. However, it has been suggested that compound C exerts AMPK-independent effects in various cells. Here, we investigated whether compound C induces Sestrin2 (SESN2), an antioxidant enzyme induced by diverse stress. In addition, the mechanism responsible for SESN2 induction by compound C was determined. Our results showed that compound C increased SESN2 protein expression in HepG2 cells in a concentration- and time-dependent manner. The induction of SESN2 mRNA was also observed in cells treated with compound C. Increase of SESN2 luciferase activity confirmed transcriptional regulation by compound C and this substance also increased nuclear factor erythroid 2 (NF-E2)-related factor-2 (Nrf2) phosphorylation, which implies that Nrf2 was involved in SESN2 induction. Next, we sought to demonstrate whether production of reactive oxygen species (ROS) accompanied SESN2 expression. Compound C increased ROS production, but this effect was prevented by pretreatment with antioxidants or the mitochondrial complex I inhibitor. Moreover, cyclosporin A, an inhibitor of pore formation in the mitochondrial membrane, attenuated compound C-induced SESN2 induction. However, overexpression of a constitutively active form of AMPK was not able to abolish SESN2 induction by compound C, which implies that its action is independent of AMPK inhibition. In conclusion, this is the first study demonstrating that compound C alters mitochondrial function and induces ROS production, which ultimately leads to phosphorylation of Nrf2 and induction of SESN2.

SESN2 correlates with advantageous prognosis in hepatocellular carcinoma

Background

SESN2 plays important roles in the regulation of cell survival, cell protection, and tumor suppression. However, the relationship between SESN2 expression and the clinicopathological attributes of hepatocellular carcinoma (HCC) is barely investigated.

Methods

One-step quantitative reverse transcription PCR, Western blotting analysis in 15 fresh HCC tissues, and immunohistochemistry (IHC) analysis in a tissue microarray (TMA) containing 100 HCC cases were performed to examine SESN2 expression. Survival analyses by Cox regression method and Kaplan-Meier curve were performed to describe the overall survival of 100 HCC patients.

Results

The SESN2 expression in HCC tissues declined dramatically compared with the corresponding noncancerous tissues, and SESN2 expression was remarkably associated with HBV infection (p = 0.019), HCV infection (p = 0.001), and lymph node metastasis (p = 0.033). Survival analysis further demonstrated that SESN2 expression could serve as an independent prognostic biomarker for overall survival in univariate (p = 0.001) and multivariate analyses (p = 0.003).

Conclusion

The data are the first to indicate that SESN2 might be a novel prognostic marker for HCC and that elevated SESN2 expression predicts advantageous outcomes in HCC patients.

5-Fluorouracil inhibits cell migration by induction of Sestrin2 in colon cancer cells

5-Fluorouracil (5-FU) is a chemotherapeutic agent used in the treatment of colorectal cancer. In this study, we investigated whether 5-FU induces Sestrin2 (SESN2), an antioxidant enzyme, and the role of SESN2 in 5-FU action in colon cancer cells. We found that 5-FU upregulated SESN2 protein expression in both HCT116 and HT29 cells. It also increased transcripts of SESN1 and SESN2, but not of SESN3. Furthermore, we investigated whether production of reactive oxygen species (ROS) was involved in 5-FU-induced SESN2 expression. 5-FU did not increase ROS production nor affect Nrf2 phosphorylation and expression levels. Moreover, SESN2 upregulation by 5-FU was not prevented by pretreatment with antioxidants. Next, we investigated p53 levels after 5-FU treatment to elucidate the regulation of SESN2 by 5-FU. An increase in p53 levels was detected following 5-FU treatment; pifithrin-α, an inhibitor of p53 activation, reversed 5-FU-induced SESN2 expression. 5-FU prevented serum-induced in vitro cell migration, but knockdown of SESN2 or treatment with pifithrin-α reversed a 5-FU-mediated decrease in cell migration. Taken together, our results suggest that 5-FU increases SESN2 levels via a p53-dependent pathway, which contributes to inhibition of cancer cell migration in vitro.

Eupatilin induces Sestrin2-dependent autophagy to prevent oxidative stress

Eupatilin (5,7-dihydroxy-3,4,6-trimethoxyflavone) has many pharmacological activities including anti-inflammation, anti-oxidant and anti-cancer effects. Autophagy is the basic cellular machinery involving the digestion of damaged cellular components. In the present study, we investigated the protection effects of eupatilin against arachidonic acid (AA) and iron-induced oxidative stress in HepG2 cells and tried to elucidate the molecular mechanisms responsible. Eupatilin increased cell viability against AA + iron in a concentration-dependent manner and prevented mitochondrial dysfunction and reactive oxygen species (ROS) production. In addition, AA + iron increased the levels of pro-apoptotic proteins and these changes were prevented by eupatilin. Eupatilin also induced autophagy, as evidenced by the accumulation of microtubule-associated protein 1 light chain3-II and the detection of autophagic vacuoles. Furthermore, the protective effects of eupatilin on mitochondrial dysfunction and ROS production were significantly abolished by autophagy inhibitors. Eupatilin also increased the mRNA level of sestrin-2 and its promoter-driven reporter gene activity, which resulted in the up-regulation of sestrin-2 protein. Finally, gene silencing using sestrin-2 siRNA and the ectopic expression of recombinant adenoviral sestrin-2 indicated that sestrin-2 induction by eupatilin was required for autophagy-mediated cytoprotection against AA + iron. Our results suggest that eupatilin activates sestrin-2-dependent autophagy, thereby preventing oxidative stress induced by AA + iron.

The Expression of the Endogenous mTORC1 Inhibitor Sestrin 2 Is Induced by UVB and Balanced with the Expression Level of Sestrin 1

Sestrin 2 (SESN2) is an evolutionarily conserved regulator of mechanistic target of rapamycin complex 1 (mTORC1) which controls central cellular processes such as protein translation and autophagy. Previous studies have suggested that SESN2 itself is subjected to regulation at multiple levels. Here, we investigated the expression of SESN2 in the skin and in isolated skin cells. SESN2 was detected by immunofluorescence analysis in fibroblasts and keratinocytes of human skin. Differentiation of epidermal keratinocytes was not associated with altered SESN2 expression and siRNA-mediated knockdown of SESN2 did not impair stratum corneum formation in vitro. However, SESN2 was increased in both cell types when the expression of its paralog SESN1 was blocked by siRNA-mediated knock down, indicating a compensatory mechanism for the control of expression. Irradiation with UVB but not with UVA significantly increased SESN2 expression in both keratinocytes and fibroblasts. Upregulation of SESN2 expression could be completely blocked by suppression of p53. These results suggest that SESN2 is dispensable for normal epidermal keratinization but involved in the UVB stress response of skin cells.

Mitochondrial dysfunction induces SESN2 gene expression through Activating Transcription Factor 4

We found that inhibitors of mitochondrial respiratory chain complexes III (myxothiazol) and I (piericidin A) in some epithelial carcinoma cell lines induce transcription of the p53-responsive SESN2 gene that plays an important role in stress response and homeostatic regulation. However, the effect did not depend on p53 because i) there was no induction of p53 after the treatment with piericidin A; ii) after the treatment with myxothiazol the peak of SESN2 gene upregulation occurred as early as 5h, before the onset of p53 activation (13h); iii) a supplementation with uridine that abolishes the p53 activation in response to myxothiazol did not abrogate the induction of SESN2 transcripts; iv) in the p53 negative HCT116 p53 -/- cells SESN2 transcription could be also induced by myxothiazol. In response to the respiratory chain inhibitors we observed an induction of ATF4, the key transcription factor of the integrated stress response (ISR). We found that the induction of SESN2 transcripts could be prevented by the ISR inhibitory small molecule ISRIB. Also, by inhibiting or overexpressing ATF4 with specific shRNA or ATF4-expressing constructs, respectively, we have confirmed the role of ATF4 in the SESN2 gene upregulation induced by mitochondrial dysfunction. At a distance of 228 bp upstream from the SESN2 transcription start site we found a candidate sequence for the ATF4 binding site and confirmed its requirement for the induction of SESN2 in luciferase reporter experiments. We suggest that the upregulation of SESN2 by mitochondrial dysfunction provides a homeostatic feedback that attenuates biosynthetic processes during temporal losses of energy supply from mitochondria thereby assisting better adaptation and viability of cells in hostile environments.

Oleanolic acid attenuates liver ischemia reperfusion injury by HO-1/Sesn2 signaling pathway

BACKGROUND

Ischemia reperfusion injury (IRI) is unavoidable in liver transplantation and hepatectomy. The present study aimed to explore the possible mechanism and the effect of oleanolic acid (OA) in hepatic IRI.

METHODS

Mice were randomly divided into 6 groups based on different treatment. IRI model: The hepatic artery, portal vein, and bile duct to the left and median liver lobes (70% of the liver) were occluded with an atraumatic bulldog clamp for 90 minutes and then the clamp was removed for reperfusion. The mice were sacrificed 6 hours after reperfusion, and blood and liver tissues were collected. Liver injury was evaluated by biochemical and histopathologic examinations. The expressions of Sesn2, PI3K, Akt and heme oxygenase-1 (HO-1) were measured with quantitative real-time RT-PCR and Western blotting.

RESULTS

The serum aminotransferases level and scores of hepatic histology were increased after reperfusion. The increase was attenuated by pretreatment with OA (P<0.01). Compared with the IR group, OA pretreatment significantly up-regulated the expression of Sesn2, PI3K, Akt and HO-1 in IR livers (P<0.05). Administration of zinc protoporphyrin (ZnPP), an inhibitor of HO-1, diminished the OA effect on HO-1 and Sesn2 expressions (P<0.05) and the protective effect of OA on IRI.

CONCLUSIONS

Our results demonstrate that OA can attenuate hepatic IRI. The protective mechanism may be related to the OA-induced HO-1/Sesn2 signaling pathway.

Sensing the Environment Through Sestrins: Implications for Cellular Metabolism

Sestrins are a family of stress-responsive genes that have evolved to attenuate damage induced by stress caused to the cell. By virtue of their antioxidant activity, protein products of Sestrin genes prevent the accumulation of reactive oxygen species within the cell, thereby attenuating the detrimental effects of oxidative stress. In parallel, Sestrins participate in several signaling pathways that control the activity of the target of rapamycin protein kinase (TOR). TOR is a crucial sensor of intracellular and extracellular conditions that promotes cell growth and anabolism when nutrients and growth factors are abundant. In addition to reacting to stress-inducing insults, Sestrins also monitor the changes in the availability of nutrients, which allows them to serve as a key checkpoint for the TOR-regulated signaling pathways. In this review, we will discuss how Sestrins integrate signals from numerous stress- and nutrient-responsive signaling pathways to orchestrate cellular metabolism and support cell viability.

Biochemical Basis of Sestrin Physiological Activities

Excessive accumulation of reactive oxygen species (ROS) and chronic activation of mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) are well-characterized promoters of aging and age-associated degenerative pathologies. Sestrins, a family of highly conserved stress-inducible proteins, are important negative regulators of both ROS and mTORC1 signaling pathways; however, the mechanistic basis of how Sestrins suppress these pathways remains elusive. In the past couple of years, breakthrough discoveries about Sestrin signaling and its molecular nature have markedly increased our biochemical understanding of Sestrin function. These discoveries have also uncovered new potential therapeutic strategies that may eventually enable us to attenuate aging and age-associated diseases.

Sestrin2 protects the myocardium against radiation-induced damage

The purpose of this study was to investigate the role of Sestrin2 in response to radiation-induced injury to the heart and on the cardiomyopathy development in the mouse. Mice with genetic deletion of the Sestrin2 (Sestrin2 knockout mice [Sestrin2 KO]) and treatment with irradiation (22 or 15 Gy) were used as independent approaches to determine the role of Sestrin2. Echocardiography (before and after isoproterenol challenge) and left ventricular (LV) catheterization were performed to evaluate changes in LV dimensions and function. Masson's trichrome was used to assess myocardial fibrosis. Immunohistochemistry and Western blot were used to detect the capillary density. After 22 or 15 Gy irradiation, the LV ejection fraction (EF) was impaired in wt mice at 1 week and 4 months after irradiation when compared with sham irradiation. Compared to wt mice, Sestrin2 KO mice had significant reduction in reduced LVEF at 1 week and 4 months after irradiation. A significant increase in LV end-diastolic pressure and myocardial fibrosis and a significant decrease in capillary density were observed in irradiation-wt mice, as well as in irradiation-Sestrin2 KO mice. Sestrin2 involved in the regulation of cardiomyopathy (such as myocardial fibrosis) after irradiation. Overexpression of Sestrin2 might be useful in limiting radiation-induced myocardial injury.

Sestrin2: A Promising Therapeutic Target for Liver Diseases

Sestrin2 (Sesn2), a highly conserved antioxidant protein, is induced by various stresses, including oxidative and energetic stress, and protects cells against those stresses. In normal physiological conditions, redox-homeostasis plays an essential role in cell survival and performs the cellular functions to protect the cells against oxidative damage. The liver is susceptible to oxidative stress, since it is responsible for xenobiotic detoxification and energy metabolism. For this reason, oxidative stress is associated with the pathogenesis of liver diseases. Recently, the role of Sesn2 has been investigated in liver injury and related diseases. In this paper, we review the role of Sesn2 in the pathophysiology of liver diseases and the potential clinical applications of Sesn2 as a therapeutic target to prevent/treat liver diseases. This article promotes our understanding of liver disease progression and advances the development of strategies for pharmacological intervention.

Chebulic acid prevents hepatic fibrosis induced by advanced glycation end-products in LX-2 cell by modulating Nrf2 translocation via ERK pathway

Advanced glycation end-products (AGEs) are formed during normal aging, and at an accelerated rate in metabolic syndrome patients. Nonalcoholic steatohepatitis (NASH) can be caused by the AGEs in plasma, while glyceraldehyde-derived AGEs (glycer-AGEs) are significantly higher in the serum of NASH patients. In this study, we investigated the molecular mechanisms of chebulic acid, isolated from Terminalia chebula Retz., in the inhibition of glycer-AGEs induced production of reactive oxygen species (ROS) and collagen accumulation using the LX-2 cell line. Chebulic acid significantly inhibited the induction of ROS and accumulation of collagen proteins by glycer-AGEs. ERK phosphorylation and total nuclear factor E2-related factor 2 (Nrf2) protein expression were induced by chebulic acid in a dose-dependent manner. Chebulic acid was also found to induce translocation of Nrf2 into the nucleus, which was attenuated by inhibition of ERK phosphorylation through treatment with PD98059. Following translocation of Nrf2, chebulic acid induced the protein expressions of catalytic subunit of γ-glutamylcysteine synthetase and glutathione synthesis. Collagen accumulation was also significantly reduced by chebulic acid treatment. The observed effects of chebulic acid were all inhibited by PD98059 treatment. Taken together, these results suggest that chebulic acid prevents the glycer-AGEs-induced ROS formation of LX-2 cells and collagen accumulation by ERK-phosphorylation-mediated Nrf2 nuclear translocation, which causes upregulation of antioxidant protein production.

Sestrin2 is induced by glucose starvation via the unfolded protein response and protects cells from non-canonical necroptotic cell death

Sestrin2 is a member of a family of stress responsive proteins, which controls cell viability via antioxidant activity and regulation of the mammalian target of rapamycin protein kinase (mTOR). Sestrin2 is induced by different stress insults, which diminish ATP production and induce energetic stress in the cells. Glucose is a critical substrate for ATP production utilized via glycolysis and mitochondrial respiration as well as for glycosylation of newly synthesized proteins in the endoplasmic reticulum (ER) and Golgi. Thus, glucose starvation causes both energy deficiency and activation of ER stress followed by the unfolding protein response (UPR). Here, we show that UPR induces Sestrin2 via ATF4 and NRF2 transcription factors and demonstrate that Sestrin2 protects cells from glucose starvation-induced cell death. Sestrin2 inactivation sensitizes cells to necroptotic cell death that is associated with a decline in ATP levels and can be suppressed by Necrostatin 7. We propose that Sestrin2 protects cells from glucose starvation-induced cell death via regulation of mitochondrial homeostasis.

Resveratrol and the mitochondria: From triggering the intrinsic apoptotic pathway to inducing mitochondrial biogenesis, a mechanistic view

BACKGROUND

Mitochondria, the power plants of the cell, are known as a cross-road of different cellular signaling pathways. These cytoplasmic double-membraned organelles play a pivotal role in energy metabolism and regulate calcium flux in the cells. It is well known that mitochondrial dysfunction is associated with different diseases such as neurodegeneration and cancer. A growing body of literature has shown that polyphenolic compounds exert direct effects on mitochondrial ultra-structure and function. Resveratrol is known as one of the most common bioactive constituents of red wine, which improves mitochondrial functions under in vitro and in vivo conditions.

SCOPE OF REVIEW

This paper aims to review the molecular pathways underlying the beneficial effects of resveratrol on mitochondrial structure and functions. In addition, we discuss the chemistry and main sources of resveratrol.

MAJOR CONCLUSIONS

Resveratrol represents the promising effects on mitochondria in different experimental models. However, there are several reports on the detrimental effects elicited by resveratrol on mitochondria.

GENERAL SIGNIFICANCE

An understanding of the chemistry and source of resveratrol, its bioavailability and the promising effects on mitochondria brings a new hope to therapy of mitochondrial dysfunction-related diseases.

Are Polyphenols Strong Dietary Agents Against Neurotoxicity and Neurodegeneration?

Life expectancy of most human populations has greatly increased as a result of factors including better hygiene, medical practice, and nutrition. Unfortunately, as humans age, they become more prone to suffer from neurodegenerative diseases and neurotoxicity. Polyphenols can be cheaply and easily obtained as part of a healthy diet. They present a wide range of biological activities, many of which have relevance for human health. Compelling evidence has shown that dietary phytochemicals, particularly polyphenols, have properties that may suppress neuroinflammation and prevent toxic and degenerative effects in the brain. The mechanisms by which polyphenols exert their action are not fully understood, but it is clear that they have a direct effect through their antioxidant activities. They have also been shown to modulate intracellular signaling cascades, including the PI3K-Akt, MAPK, Nrf2, and MEK pathways. Polyphenols also interact with a range of neurotransmitters, illustrating that these compounds can promote their health benefits in the brain through a direct, indirect, or complex action. We discuss whether polyphenols obtained from diet or food supplements are an effective strategy to prevent or treat neurodegeneration. We also discuss the safety, mechanisms of action, and the current and future relevance of polyphenols in clinical treatment of neurodegenerative diseases. As populations age, it is important to discuss the dietary strategies to avoid or counteract the effects of incurable neurodegenerative disorders, which already represent an enormous financial and emotional burden for health care systems, patients, and their families.

Roles of Sestrin2 and Ribosomal Protein S6 in Transient Global Ischemia-Induced Hippocampal Neuronal Injury

Recent studies suggested that sestrin2 is a crucial modulator for the production of reactive oxygen species (ROS). In addition, sestrin2 may also regulate ribosomal protein S6 (RpS6), a molecule important for protein synthesis, through the effect of mammalian target of rapamycin (mTOR) complex that is pivotal for longevity. However, the roles of sestrin2 in cerebral ischemia, in which oxidative stress is one of the major pathogenic mechanisms, are still less understood. In this study, we hypothesized that sestrin2 may protect hippocampal CA1 neurons against transient global ischemia (TGI)-induced apoptosis by regulating RpS6 phosphorylation in rats. We found that sestrin2 expression was progressively increased in the hippocampal CA1 subfield 1–48 h after TGI, reaching the maximal level at 24 h, and declined thereafter. Further, an increased extent of RpS6 phosphorylation, but not total RpS6 protein level, was observed in the hippocampal CA1 subfield after TGI. The sestrin2 siRNA, which substantially blocked the expression of TGI-induced sestrin2, also abolished RpS6 phosphorylation. TGI with reperfusion may induce oxidative stress with the resultant formation of 8-hydroxy-deoxyguanosine (8-OHdG). We found that sestrin2 siRNA further augmented the formation of 8-OHdG induced by TGI with reperfusion for 4 h. Consistently, sestrin2 siRNA also enhanced apoptosis induced by TGI with reperfusion for 48 h based on the analysis of DNA fragmentation by agarose gel electrophoresis, DNA fragmentation sandwich ELISA, and the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. Together these findings indicated that TGI-induced sestrin2 expression contributed to RpS6 phosphorylation and neuroprotection against ischemic injury in the hippocampal CA1 subfield.

The antioxidant function of sestrins is mediated by promotion of autophagic degradation of Keap1 and Nrf2 activation and by inhibition of mTORC1

Sestrins 1 to 3 constitute a family of proteins that are induced in mammalian cells in response to environmental stressors. Despite their apparent lack of intrinsic catalytic antioxidant activity, Sestrins protect cells from oxidative stress by lowering intracellular levels of H2O2. Here we review the mechanisms by which various types of cellular stress induce Sestrin gene transcription as well as those underlying the antioxidant function of these proteins. Several transcriptional factors, including p53, HIF-1, FoxO, C/EBP-β, ATF4, Nrf2, and PGC-1α, contribute directly to the transcriptional activation of Sestrin genes in response to various types of stress. The antioxidant function of Sestrins is mediated by two main pathways. In one pathway, Sestrins promote the p62-dependent autophagic degradation of Keap1 and thereby upregulate Nrf2 signaling and the consequent expression of genes for antioxidant enzymes. In the second pathway, Sestrins block mTORC1 activation and thereby attenuate reactive oxygen species accumulation. This inhibition of mTORC1 activity is achieved either via the AMPK-dependent phosphorylation and activation of TSC2 and consequent inhibition of the GTPase Rheb or via inhibition of the GTPase Rag and consequent prevention of the lysosomal localization of mTORC1 triggered by amino acids. Elucidation of how these pathways operate individually or cooperatively under different stress conditions awaits further study.

Circadian control of β-cell function and stress responses

Circadian disruption is the bane of modern existence and its deleterious effects on health; in particular, diabetes and metabolic syndrome have been well recognized in shift workers. Recent human studies strongly implicate a 'dose-dependent' relationship between circadian disruption and diabetes. Genetic and environmental disruption of the circadian clock in rodents leads to diabetes secondary to β-cell failure. Deletion of Bmal1, a non-redundant core clock gene, leads to defects in β-cell stimulus-secretion coupling, decreased glucose-stimulated ATP production, uncoupling of OXPHOS and impaired glucose-stimulated insulin secretion. Both genetic and environmental circadian disruptions are sufficient to induce oxidative stress and this is mediated by a disruption of the direct transcriptional control of the core molecular clock and Bmal1 on Nrf2, the master antioxidant transcription factor in the β-cell. In addition, circadian disruption also leads to a dysregulation of the unfolded protein response and leads to endoplasmic reticulum stress in β-cells. Both the oxidative and endoplasmic reticulum (ER) stress contribute to an impairment of mitochondrial function and β-cell failure. Understanding the basis of the circadian control of these adaptive stress responses offers hope to target them for pharmacological modulation to prevent and mitigate the deleterious metabolic consequences of circadian disruption.

Nuclear Factor-kappaB-Dependent Sestrin2 Induction Mediates the Antioxidant Effects of BDNF Against Mitochondrial Inhibition in Rat Cortical Neurons

Brain-derived neurotrophic factor (BDNF), in addition to its neurotrophic action, also possesses antioxidant activities. However, the underlying mechanisms remain to be fully defined. Sestrin2 is a stress-responsive gene implicated in the cellular defense against oxidative stress. Currently, the potential functions of sestrin2 in nervous system, in particular its correlation with neurotrophic factors, have not been well established. In this study, we hypothesized that BDNF may enhance sestrin2 expression to confer neuronal resistance against oxidative stress induced by 3-nitropropionic acid (3-NP), an irreversible mitochondrial complex II inhibitor, and characterized the molecular mechanisms underlying BDNF induction of sestrin2 in primary rat cortical cultures. We found that BDNF-mediated sestrin2 expression in cortical neurons required formation of nitric oxide (NO) with subsequent production of 3',5'-cyclic guanosine monophosphate (cGMP) and activation of cGMP-dependent protein kinase (PKG). BDNF induced localization of nuclear factor-kappaB (NF-κB) subunits p65 and p50 into neuronal nuclei that required PKG activities. Interestingly, BDNF exposure led to formation of a protein complex containing at least PKG-1 and p65/p50, which bound to sestrin2 promoter with resultant upregulation of its protein products. Finally, BDNF preconditioning mitigated production of reactive oxygen species (ROS) as a result of 3-NP exposure; this antioxidative effect of BDNF was dependent upon PKG activity, NF-κB, and sestrin2. Taken together, our results indicated that BDNF enhances sestrin2 expression to confer neuronal resistance against oxidative stress induced by 3-NP through attenuation of ROS formation; furthermore, BDNF induction of sestrin2 requires activation of a pathway involving NO/PKG/NF-κB.

The chalcone compound isosalipurposide (ISPP) exerts a cytoprotective effect against oxidative injury via Nrf2 activation

The chalcone compound isosalipurposide (ISPP) has been successfully isolated from the native Korean plant species Corylopsis coreana Uyeki (Korean winter hazel). However, the therapeutic efficacy of ISPP remains poorly understood. This study investigated whether ISPP has the capacity to activate NF-E2-related factor (Nrf2)-antioxidant response element (ARE) signaling and induce its target gene expression, and to determined the protective role of ISPP against oxidative injury of hepatocytes. In HepG2 cells, nuclear translocation of Nrf2 is augmented by ISPP treatment. Consistently, ISPP increased ARE reporter gene activity and the protein levels of glutamate cysteine ligase (GCL) and hemeoxygenase (HO-1), resulting in increased intracellular glutathione levels. Cells pretreated with ISPP were rescued from tert-butylhydroperoxide-induced reactive oxygen species (ROS) production and glutathione depletion and consequently, apoptotic cell death. Moreover, ISPP ameliorated the mitochondrial dysfunction and apoptosis induced by rotenone which is an inhibitor of complex 1 of the mitochondrial respiratory chain. The specific role of Nrf2 activation by ISPP was demonstrated using an ARE-deletion mutant plasmid and Nrf2-knockout cells. Finally, we observed that extracellular signal-regulated kinase (ERK) and AMP-activated protein kinase (AMPK), but not protein kinase C (PKC)-δ or other mitogen-activated protein kinases (MAPKs), are involved in the activation of Nrf2 by ISPP. Taken together, our results demonstrate that ISPP has a cytoprotective effect against oxidative damage mediated through Nrf2 activation and induction of its target gene expression in hepatocytes.

Discovery of oxime-bearing naphthalene derivatives as a novel structural type of Nrf2 activators

Recent studies have demonstrated that oxidative stress insult is one of major causes of tumor formation. Therefore, identify the effective anti-oxidative agents as a preventive approach to stop cancer progression has widely explored. Although, many potent anti-oxidative ingredients in the natural products have been identified but the amount from the nature source hindrances the clinical application. Compound which can activate Nrf2 signaling pathway result unregulated the cellular antioxidant-responses has been demonstrated as an effective chemopreventive approach for cancer treatment. In the present study, certain oxime-bearing naphthalene derivatives were synthesized and evaluated for their Nrf2 activation and anti-proliferative activities. Results indicated (E)-1-(naphthalen-2-yloxy)propan-2-one oxime (11) which increased 2.04-fold Nrf2/ARE-driven luciferase activity was more active than its 1-substituted isomer 10 (1.17-fold) and t-BHQ (1.77-fold), the known Nrf2 activator. The activities were further increased by the replacement of the peripheral methyl group with the phenyl ring in which (Z)-2-(naphthalen-2-yloxy)-1-phenylethanone oxime (13a) exhibited 3.49-fold potency of the positive control. It is worth to mention that compounds 11, 13a, and 13b which showed significant Nrf2 activation are non-cytotoxic to the tested cells with IC50>50μM. This observation strongly suggested that these compounds can be used for chemoprevention. Mechanism studies indicated that these compounds were capable of inducing the phosphorylation of Nrf2 protein at serine 40 which led to the activation of the Nrf2 transcriptional activity.