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

Tanshinone IIA positively regulates the Keap1-Nrf2 system to alleviate pulmonary fibrosis via the sestrin2-sqstm1 signaling axis-mediated autophagy

BACKGROUND

Activation of myofibroblasts, linked to oxidative stress, emerges as a pivotal role in the progression of pulmonary fibrosis (PF). Our prior research has underscored the therapeutic promise of tanshinone IIA (Tan-IIA) in mitigating PF by enhancing nuclear factor-erythroid 2-related factor 2 (Nrf2) activity. Nevertheless, the molecular basis through which Tan-IIA influences Nrf2 activity has yet to be fully elucidated.

METHODS

The influence of Tan-IIA on PF was assessed in vivo and in vitro models. Inhibitors, overexpression plasmids, and small interfering RNA (siRNA) were utilized to probe its underlying mechanism of action in vitro.

RESULTS

We demonstrate that Tan-IIA effectively activates the kelch-like ECH-associated protein 1 (Keap1)-Nrf2 antioxidant pathway, which in turn inhibits myofibroblast activation and ameliorates PF. Notably, the stability and nucleo-cytoplasmic shuttling of Nrf2 is shown to be dependent on augmented autophagic flux, which is in alignment with the observation that Tan-IIA induces autophagy. Inhibition of autophagy, conversely, fosters the activation of extracellular matrix (ECM)-producing myofibroblasts. Further, Tan-IIA initiates an autophagy program through the sestrin 2 (Sesn2)-sequestosome 1 (Sqstm1) signaling axis, crucial for protecting Nrf2 from Keap1-mediated degradation. Meanwhile, these findings were corroborated in a murine model of PF.

CONCLUSION

Collectively, we observed for the first time that the Sqstm1-Sesn2 axis-mediated autophagic degradation of Keap1 effectively prevents myofibroblast activation and reduces the synthesis of ECM. This autophagy-dependent degradation of Keap1 can be initiated by the Tan-IIA treatment, which solidifies its potential as an Nrf2-modulating agent for PF treatment.

Role of sestrins in metabolic and aging-related diseases

Sestrins are a type of highly conserved stress-inducing protein that has antioxidant and mTORC1 inhibitory functions. Metabolic dysfunction and aging are the main risk factors for development of human diseases, such as diabetes, neurodegenerative diseases, and cancer. Sestrins have important roles in regulating glucose and lipid metabolism, anti-tumor functions, and aging by inhibiting the reactive oxygen species and mechanistic target of rapamycin complex 1 pathways. In this review, the structure and biological functions of sestrins are summarized, and how sestrins are activated and contribute to regulation of the downstream signal pathways of metabolic and aging-related diseases are discussed in detail with the goal of providing new ideas and therapeutic targets for the treatment of related diseases.

Sestrin2 Regulates Endoplasmic Reticulum Stress-Dependent Ferroptosis to Engage Pulmonary Fibrosis by Nuclear Factor Erythroid 2-Related Factor 2/Activating Transcription Factor 4 (NRF2/ATF4)

Pulmonary fibrosis (PF) can lead to chronic inflammation, the destruction of alveoli and irreversible lung damage. Sestrin2 is a highly protective stress-inducible protein that is involved in the cell response to various stress factors and the regulation of homeostasis and has a certain protective effect against PF. In this study, TGF-β1 was used to establish a PF cell model. Bleomycin was used to induce PF in mice, and the expression levels of related proteins were detected by western blotting. The levels of the inflammatory cytokine, TNF-α, IL-6, and IL-1β were detected by enzyme-linked immunosorbent assays. Immunoprecipitation was used to verify the interaction between ATF4 and NRF2 and between Sestrin2 and NRF2 to explore the specific mechanism by which Sestrin2 affects PF. The results showed that Sestrin2 inhibited fibroblast-to-myofibroblast transition (FMT), improved inflammation, promoted cell proliferation, and alleviated PF. Activating transcription factor 4/nuclear factor erythroid 2-related factor 2 (NRF2/ATF4) signaling pathway activation could alleviate endoplasmic reticulum stress, inhibit ferroptosis and FMT, and reduce reactive oxygen species levels, thereby alleviating PF. Overexpression of ATF4 and the addition of a ferroptosis inducer reversed Sestrin2-mediated alleviation of PF. In conclusion, Sestrin2 alleviates PF and endoplasmic reticulum stress-dependent ferroptosis through the NRF2/ATF4 pathway.

Resistance exercise alleviates dexamethasone-induced muscle atrophy via Sestrin2/MSTN pathway in C57BL/6J mice

AIM

It has long been recognized that resistance exercise can substantially increase skeletal muscle mass and strength, but whether it can protect against glucocorticoid-induced muscle atrophy and its potential mechanism is yet to be determined. This study aimed to investigate the protective effects of resistance exercise in dexamethasone-induced muscle atrophy and elucidate the possible function of exercise-induced protein Sestrin2 in this process.

METHODS

Eight-week-old male C57BL/6J mice carried out the incremental mouse ladder exercise for 11 weeks. Two weeks before the end of the intervention, mice were daily intraperitoneally injected with dexamethasone. Body composition, muscle mass, and exercise performance were examined to evaluate muscle atrophy. In vitro, C2C12 cells were used for RT-qPCR, Western Blot, and immunofluorescence experiments to elucidate the potential mechanism.

RESULTS

Our results showed that long-term resistance exercise is an effective intervention for dexamethasone-induced muscle atrophy. We also found that Sestrin2 plays a vital role in dexamethasone-induced muscle atrophy. In both animal (P = .0006) and cell models (P = .0266), dexamethasone intervention significantly reduced the protein expression of Sestrin2, which was increased (P = .0112) by resistance exercise. Inversely, overexpression of Sestrin2 improved (P < .0001) dexamethasone-induced myotube cell atrophy by reducing the activation of the ubiquitin-proteasome pathway via inhibiting Forkhead box O3 (FoxO3a) and myostatin (MSTN)/small mother against decapentaplegic (Smad) signaling pathways.

CONCLUSION

Taken together, our results indicated that Sestrin2 may serve as an effective molecule that mimics the protective effect of resistance exercise on dexamethasone-induced muscle atrophy.

Parkin-Mediated Mitophagy by TGF-β Is Connected with Hepatic Stellate Cell Activation

Hepatic stellate cells (HSCs) are the main contributors to the development and progression of liver fibrosis. Parkin is an E3 ligase involved in mitophagy mediated by lysosomes that maintains mitochondrial homeostasis. Unfortunately, there is little information regarding the regulation of parkin by transforming growth factor-β (TGF-β) and its association with HSC trans-differentiation. This study showed that parkin is upregulated in fibrotic conditions and elucidated the underlying mechanism. Parkin was observed in the cirrhotic region of the patient liver tissues and visualized using immunostaining and immunoblotting of mouse fibrotic liver samples and primary HSCs. The role of parkin-mediated mitophagy in hepatic fibrogenesis was examined using TGF-β-treated LX-2 cells with mitophagy inhibitor, mitochondrial division inhibitor 1. Parkin overexpression and its colocalization with desmin in human tissues were found. Increased parkin in fibrotic liver homogenates of mice was observed. Parkin was expressed more abundantly in HSCs than in hepatocytes and was upregulated under TGF-β. TGF-β-induced parkin was due to Smad3. TGF-β facilitated mitochondrial translocation, leading to mitophagy activation, reversed by mitophagy inhibitor. However, TGF-β did not change mitochondrial function. Mitophagy inhibitor suppressed profibrotic genes and HSC migration mediated by TGF-β. Collectively, parkin-involved mitophagy by TGF-β facilitates HSC activation, suggesting mitophagy may utilize targets for liver fibrosis.

Empagliflozin Ameliorates Bleomycin-Induced Pulmonary Fibrosis in Rats by Modulating Sesn2/AMPK/Nrf2 Signaling and Targeting Ferroptosis and Autophagy

Pulmonary fibrosis (PF) is a life-threatening disorder that severely disrupts normal lung architecture and function, resulting in severe respiratory failure and death. It has no definite treatment. Empagliflozin (EMPA), a sodium-glucose cotransporter 2 (SGLT2) inhibitor, has protective potential in PF. However, the mechanisms underlying these effects require further elucidation. Therefore, this study aimed to evaluate the ameliorative effect of EMPA against bleomycin (BLM)-induced PF and the potential mechanisms. Twenty-four male Wister rats were randomly divided into four groups: control, BLM treated, EMPA treated, and EMPA+BLM treated. EMPA significantly improved the histopathological injuries illustrated by both hematoxylin and eosin and Masson's trichrome-stained lung tissue sections, as confirmed by electron microscopic examination. It significantly reduced the lung index, hydroxyproline content, and transforming growth factor β1 levels in the BLM rat model. It had an anti-inflammatory effect, as evidenced by a decrease in the inflammatory cytokines' tumor necrosis factor alpha and high mobility group box 1, inflammatory cell infiltration into the bronchoalveolar lavage fluid, and the CD68 immunoreaction. Furthermore, EMPA mitigated oxidative stress, DNA fragmentation, ferroptosis, and endoplasmic reticulum stress, as evidenced by the up-regulation of nuclear factor erythroid 2-related factor expression, heme oxygenase-1 activity, glutathione peroxidase 4 levels, and a decrease in C/EBP homologous protein levels. This protective potential could be explained on the basis of autophagy induction via up-regulating lung sestrin2 expression and the LC3 II immunoreaction observed in this study. Our findings indicated that EMPA protected against BLM-induced PF-associated cellular stress by enhancing autophagy and modulating sestrin2/adenosine monophosphate-activated protein kinase/nuclear factor erythroid 2-related factor 2/heme oxygenase 1 signaling.

Naringenin is a Potential Immunomodulator for Inhibiting Liver Fibrosis by Inhibiting the cGAS-STING Pathway

BACKGROUND AND AIMS

Naringenin is an anti-inflammatory flavonoid that has been studied in chronic liver disease. The mechanism specific to its antifibrosis activity needs further investigation This study was to focused on the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) pathway in hepatic stellate cells and clarified the antifibrosis mechanism of naringenin.

METHODS

The relationship between the cGAS-stimulator of interferon genes (STING) pathway and liver fibrosis was analyzed using the Gene Expression Omnibus database. Histopathology, immunohistochemistry, fluorescence staining, Western blotting and polymerase chain reaction were performed to assess gene and protein expression levels associated with the cGAS pathway in clinical liver tissue samples and mouse livers. Molecular docking was performed to evaluate the relationship between naringenin and cGAS, and western blotting was performed to study the expression of inflammatory factors downstream of cGAS in vitro.

RESULTS

Clinical database analyses showed that the cGAS-STING pathway is involved in the occurrence of chronic liver disease. Naringenin ameliorated liver injury and liver fibrosis, decreased collagen deposition and cGAS expression, and inhibited inflammation in carbon tetrachloride (CCl₄)-treated mice. Molecular docking found that cGAS may be a direct target of naringenin. Consistent with the in vivo results, we verified the inhibitory effect of naringenin on activated hepatic stellate cells (HSCs). By using the cGAS-specific agonist double-stranded (ds)DNA, we showed that naringenin attenuated the activation of cGAS and its inflammatory factors affected by dsDNA. We verified that naringenin inhibited the cGAS-STING pathway, thereby reducing the secretion of inflammatory factors by HSCs to ameliorate liver fibrosis.

CONCLUSIONS

Interrupting the cGAS-STING pathway helped reverse the fibrosis process. Naringenin has potential as an antihepatic fibrosis drug.

Sestrin2: multifaceted functions, molecular basis, and its implications in liver diseases

Sestrin2 (SESN2), a highly conserved stress-responsive protein, can be triggered by various noxious stimuli, such as hypoxia, DNA damage, oxidative stress, endoplasmic reticulum (ER) stress, and inflammation. Multiple transcription factors regulate SESN2 expression, including hypoxia-inducible factor 1 (HIF-1), p53, nuclear factor E2-related factor 2 (Nrf2), activating transcription factor 4 (ATF4), ATF6, etc. Upon induction, SESN2 generally leads to activation of adenosine monophosphate-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin complex 1 (mTORC1). To maintain cellular homeostasis, SESN2 and its downstream molecules directly scavenge reactive oxygen species or indirectly influence the expression patterns of key genes associated with redox, macroautophagy, mitophagy, ER stress, apoptosis, protein synthesis, and inflammation. In liver diseases including acute liver injury, fatty liver diseases, hepatic fibrosis, and hepatocellular carcinoma (HCC), SESN2 is abnormally expressed and correlated with disease progression. In NAFLD, SESN2 helps with postponing disease progression through balancing glycolipid metabolism and macroautophagy (lipophagy), and rectifying oxidative damage and ER stress. During hepatic fibrosis, SESN2 represses HSCs activation and intrahepatic inflammation, hindering the occurrence and progress of fibrogenesis. However, the role of SESN2 in HCC is controversial due to its paradoxical pro-autophagic and anti-apoptotic effects. In conclusion, this review summarizes the biological functions of SESN2 in hypoxia, genotoxic stress, oxidative stress, ER stress, and inflammation, and specifically emphasizes the pathophysiological significance of SESN2 in liver diseases, aiming to providing a comprehensive understanding for SESN2 as a potential therapeutic target in liver diseases.

Quantitative phosphoproteomic analysis of mice with liver fibrosis by DIA mass spectrometry analysis with PRM verification

Liver fibrosis (LF), commonly associated with chronic liver diseases, is a major public health problem worldwide. Protein phosphorylation is not only an important form of protein modification in organisms but also the most important mechanism to regulate and control the activity and function of proteins, affecting the occurrence and development of many diseases. However, comprehensive phosphoproteomic profiling in LF has not been fully elucidated. In this study, data-independent acquisition (DIA) was used to analyse the phosphoproteomics of mice with LF. A total of 553 phosphopeptides (representing 440 phosphoproteins) had significant phosphorylation levels. Among these phosphoproteins, 49 were upregulated and 401 were downregulated, and 5 phosphoserine (P-Ser) motifs and 2 phosphothreonine (P-Thr) motifs were conserved in LF. GO and KEGG pathway enrichment analyses identified 769 significant GO terms and 49 significant KEGG pathways. Four phosphorylated proteins were selected for parallel reaction monitoring (PRM) verification, and the results were consistent with DIA data. Together, there were significantly different phosphoproteomic profiles in LF, suggesting that protein phosphorylation was related to the occurrence and progression of LF, which could pave the way for further investigation into the related regulatory mechanisms. SIGNIFICANCE: LF is a necessary stage in the development of chronic liver disease to liver cirrhosis and has attracted wide attention. To the best of our knowledge, there are few reports on the phosphorylated proteomics of LF. In this study, DIA and PRM techniques were used to study the liver tissue of mice induced by CCl₄. The results showed that phosphorylation had a significant effect on the activity and function of proteins, and the PRM results were consistent with the trend observed in DIA analysis. This study will help to better reveal the relationship of phosphorylated proteins in LF and lay a foundation for further study of related regulatory mechanisms.

Ferroptosis contribute to hepatic stellate cell activation and liver fibrogenesis

Ferroptosis is a widely known regulator of cell death in connection with the redox state as a consequence of the depletion of glutathione or accumulation of lipid peroxidation. Hepatic stellate cells (HSCs) play a pivotal role in the progression of hepatic fibrosis by increasing the production and secretion of the extracellular matrix. However, the role of ferroptosis in HSC activation and liver fibrogenesis has not been clearly elucidated. The ferroptosis inducer RAS-selective lethal 3 (RSL3) or erastin treatment in HSCs caused cell death. This effect was suppressed only after exposure to ferroptosis inhibitors. We observed induction of ferroptosis by RSL3 treatment in HSCs supported by decreased glutathione peroxidase 4, glutathione deficiency, reactive oxygen species generation, or lipid peroxidation. Interestingly, RSL3 treatment upregulated the expression of plasminogen activator inhibitor-1, a representative fibrogenic marker of HSCs. In addition, treatment with ferroptosis-inducing compounds increased c-JUN phosphorylation and activator protein 1 luciferase activity but did not alter Smad phosphorylation and Smad-binding element luciferase activity. Chronic administration of iron dextran to mice causes ferroptosis of liver in vivo. The expression of fibrosis markers, such as alpha-smooth muscle actin and plasminogen activator inhibitor-1, was increased in the livers of mice with iron accumulation. Hepatic injury accompanying liver fibrosis was observed based on the levels of alanine aminotransferase, aspartate aminotransferase, and hematoxylin and eosin staining. Furthermore, we found that both isolated primary hepatocyte and HSCs undergo ferroptosis. Consistently, cirrhotic liver tissue of patients indicated glutathione peroxidase 4 downregulation in fibrotic region. In conclusion, our results suggest that ferroptosis contribute to HSC activation and the progression of hepatic fibrosis.

Acupuncture Inhibits Morphine Induced-Immune Suppress via Antioxidant System

Objectives

A powerful analgesic called Morphine causes addiction behaviors and immune suppression as a potential oxidative stressor. Acupuncture showed to inhibit oxidative stress-induced hepatic damage, regulate reactive oxygen species, and attenuate morphine addiction behaviors. Therefore, we investigated the potential effects of acupuncture on morphine-induced immune suppression.

Materials and Methods

Rats received morphine intravenously through implanted catheters for 3, 7, or 21 days to determine the optimal condition for morphine-induced immune suppression. Second, we examined whether intravenous (iv.) or intraperitoneal (ip.) administration produced different results. Third, the effects of acupuncture in rats who received morphine for 21 days were investigated. Spleen and submandibular lymph node (S-LN) weights and natural killer (NK) cell activity were measured, and the white pulp diameter, total and cortical spleen thicknesses, and the number of lymphoid follicles in S-LNs were examined. The number of immunoreactive cells was also measured.

Results

Decreased organ weights and increased atrophic changes were observed as morphine-induced immune suppression. However, dose-dependent increased immune suppression was not observed between 5.0 mg/kg and 10.0 mg/kg of morphine. And, 3-day withdrawal did not affect. Similar histopathological findings were observed in 5.0 and 10.0 ip. rats when compared to equal dosages of iv., respectively. The morphine induced-immune suppression evidenced by spleen and left S-LN weights, splenic NK cell activities, histopathological findings, and the immunoreactive cell number were normalized by acupuncture.

Conclusion

These results indicate that acupuncture inhibits morphine-induced immune suppression, maybe via antioxidative action.

Empagliflozin activates Sestrin2-mediated AMPK/mTOR pathway and ameliorates lipid accumulation in obesity-related nonalcoholic fatty liver disease

Empagliflozin (EMPA) therapy has led to improvements in patients with non-alcoholic fatty liver disease (NAFLD). Sestrin2 is a stress-inducible protein that controls the AMPK-mTOR pathway and inhibits oxidative damage in cells. This study investigated the functional implications of EMPA on the multifactorial pathogenesis of NAFLD and potential underlying molecular mechanisms of pathogenesis. An in vitro model of NAFLD was established by treating HepG2 cells with palmitic acid (PA); an in vivo model of NAFLD was generated by feeding C57BL/6 mice a high-fat diet. Investigations of morphology and lipid deposition in liver tissue were performed. Expression patterns of Sestrin2 and genes related to lipogenesis and inflammation were assessed by reverse transcription polymerase chain reaction. Protein levels of Sestrin2 and AMPK/mTOR pathway components were detected by Western blotting. NAFLD liver tissues and PA-stimulated HepG2 cells exhibited excessive lipid production and triglyceride secretion, along with upregulation of Sestrin2 and increased expression of lipogenesis-related genes. EMPA treatment reversed liver damage by upregulating Sestrin2 and activating the AMPK-mTOR pathway. Knockdown of Sestrin2 effectively increased lipogenesis and enhanced the mRNA expression levels of lipogenic and pro-inflammatory genes in PA-stimulated HepG2 cells; EMPA treatment did not affect these changes. Furthermore, Sestrin2 knockdown inhibited AMPK-mTOR signaling pathway activity. The upregulation of Sestrin2 after treatment with EMPA protects against lipid deposition-related metabolic disorders; it also inhibits lipogenesis and inflammation through activation of the AMPK-mTOR signaling pathway. These results suggest that Sestrin2 can be targeted by EMPA therapy to alleviate lipogenesis and inflammation in obesity-related NAFLD.

Sestrin2 protects against cholestatic liver injury by inhibiting endoplasmic reticulum stress and NLRP3 inflammasome-mediated pyroptosis

Chronic exposure to bile acid in the liver due to impaired bile flow induces cholestatic liver disease, resulting in hepatotoxicity and liver fibrosis. Sestrin2, a highly conserved, stress-inducible protein, has been implicated in cellular responses to multiple stress conditions and the maintenance of cellular homeostasis. However, its role in cholestatic liver injury is not fully understood. In this study, we investigated the role of hepatic Sestrin2 in cholestatic liver injury and its underlying mechanisms using in vivo and in vitro approaches. Hepatic Sestrin2 expression was upregulated by activating transcription factor 4 (ATF4) and CCAAT/enhancer-binding protein-β (C/EBP-β) after treatment with bile acids and correlated with endoplasmic reticulum (ER) stress responses. Bile-duct ligation (BDL)-induced hepatocellular apoptosis and liver fibrosis were exacerbated in Sestrin2-knockout (Sesn2^−/−) mice. Moreover, Sestrin2 deficiency enhanced cholestasis-induced hepatic ER stress, whereas Sestrin2 overexpression ameliorated bile acid-induced ER stress. Notably, the mammalian target of rapamycin (mTOR) inhibitor rapamycin and the AMP-activated protein kinase (AMPK) activator AICAR reversed bile acid-induced ER stress in Sestrin2-deficient cells. Furthermore, Sestrin2 deficiency promoted cholestasis-induced hepatic pyroptosis by activating NLRP3 inflammasomes. Thus, our study provides evidence for the biological significance of Sestrin2 and its relationship with cholestatic liver injury, suggesting the potential role of Sestrin2 in regulating ER stress and inflammasome activation during cholestatic liver injury.

A protein that manages the response to cellular stress can help prevent disruptions in bile flow from progressing to liver fibrosis or failure. Disrupted flow leads to the accumulation of bile acids, which triggers a state known as endoplasmic reticulum (ER) stress, fueling inflammation and eventual cell death. Researchers led by Hwan-Woo Park and Jongdae Shin at Konyang University, Daejon, South Korea, have demonstrated that the Sestrin2 protein plays a prominent role in managing this ER stress response to cytotoxic bile acids in cultured liver cells. They subsequently used a Sestrin2-deficient mouse model to demonstrate that the absence of this protein contributes to heightened ER stress and greatly increased liver damage following impaired bile flow. These results suggest that Sestrin2 modulators could offer effective treatments for liver disorders associated with bile flow obstruction.

REDD1 attenuates hepatic stellate cell activation and liver fibrosis via inhibiting of TGF-β/Smad signaling pathway

Liver fibrosis is caused by repetitive hepatic injury. Regulated in development and DNA damage response 1 (REDD1) gene is induced by various stresses and has been studied in cell proliferation and survival. However, the role of REDD1 in hepatic stellate cell activation and hepatic fibrogenesis has not yet been investigated. In the current study, we examined the effect of REDD1 on hepatic fibrogenesis and the underlying molecular mechanism. REDD1 protein was upregulated in the activated primary hepatic stellate cells and transforming growth factor-β (TGF-β)-treated LX-2 cells. REDD1 mRNA levels were also elevated by TGF-β treatment. TGF-β signaling is primarily transduced via the activation of the Smad transcription factor. However, TGF-β-mediated REDD1 induction was not Smad-dependent. Thus, we investigated the transcription factors that influence the REDD1 expression by TGF-β. We found that c-JUN, a component of AP-1, upregulated the REDD1 expression that was specifically suppressed by p38 inhibitor. In silico analysis of the REDD1 promoter region showed putative AP-1-binding sites; additionally, its deletion mutants demonstrated that the AP-1-binding site between -716 and -587 bp within the REDD1 promoter is critical for TGF-β-mediated REDD1 induction. Moreover, REDD1 overexpression markedly inhibited TGF-β-induced plasminogen activator inhibitor-1 (PAI-1) expression and Smad phosphorylation. REDD1 adenovirus infection inhibited CCl₄-induced hepatic injury in mice, which was demonstrated by reduced ALT/AST levels and collagen accumulation. In addition, we observed that REDD1 inhibited CCl₄-induced fibrogenic gene induction and restored GSH and malondialdehyde levels. Our findings implied that REDD1 has the potential to inhibit HSC activation and protect against liver fibrosis.

Target Sestrin2 to Rescue the Damaged Organ: Mechanistic Insight into Its Function

Sestrin2 is a stress-inducible metabolic regulator and a conserved antioxidant protein which has been implicated in the pathogenesis of several diseases. Sestrin2 can protect against atherosclerosis, heart failure, hypertension, myocardial infarction, stroke, spinal cord injury neurodegeneration, nonalcoholic fatty liver disease (NAFLD), liver fibrosis, acute kidney injury (AKI), chronic kidney disease (CKD), and pulmonary inflammation. Oxidative stress and cellular damage signals can alter the expression of Sestrin2 to compensate for organ damage. Different stress signals such as those mediated by P53, Nrf2/ARE, HIF-1α, NF-κB, JNK/c-Jun, and TGF-β/Smad signaling pathways can induce Sestrin2 expression. Subsequently, Sestrin2 activates Nrf2 and AMPK. Furthermore, Sestrin2 is a major negative regulator of mTORC1. Sestrin2 indirectly regulates the expression of several genes and reprograms intracellular signaling pathways to attenuate oxidative stress and modulate a large number of cellular events such as protein synthesis, cell energy homeostasis, mitochondrial biogenesis, autophagy, mitophagy, endoplasmic reticulum (ER) stress, apoptosis, fibrogenesis, and lipogenesis. Sestrin2 vigorously enhances M2 macrophage polarization, attenuates inflammation, and prevents cell death. These alterations in molecular and cellular levels improve the clinical presentation of several diseases. This review will shed light on the beneficial effects of Sestrin2 on several diseases with an emphasis on underlying pathophysiological effects.

Sestrin Proteins Protect Against Lipotoxicity-Induced Oxidative Stress in the Liver via Suppression of C-Jun N-Terminal Kinases

BACKGROUND & AIMS

Sestrin 1/2/3 (Sesn1/2/3) belong to a small family of proteins that have been implicated in the regulation of metabolic homeostasis and oxidative stress. However, the underlying mechanisms remain incompletely understood. The aim of this work was to illustrate the collective function of Sesn1/2/3 in the protection against hepatic lipotoxicity.

METHODS

We used Sesn1/2/3 triple knockout (TKO) mouse and cell models to characterize oxidative stress and signal transduction under lipotoxic conditions. Biochemical, histologic, and physiological approaches were applied to illustrate the related processes.

RESULTS

After feeding with a Western diet for 8 weeks, TKO mice developed remarkable metabolic associated fatty liver disease that was manifested by exacerbated hepatic steatosis, inflammation, and fibrosis compared with wild-type counterparts. Moreover, TKO mice exhibited higher levels of hepatic lipotoxicity and oxidative stress. Our biochemical data revealed a critical signaling node from sestrins to c-Jun N-terminal kinases (JNKs) in that sestrins interact with JNKs and mitogen-activated protein kinase kinase 7 and suppress the JNK phosphorylation and activity. In doing so, sestrins markedly reduced palmitate-induced lipotoxicity and oxidative stress in both mouse and human hepatocytes.

CONCLUSIONS

The data from this study suggest that Sesn1/2/3 play an important role in the protection against lipotoxicity-associated oxidative stress and related pathology in the liver.

Hepatic Stellate Cell Activation and Inactivation in NASH-Fibrosis-Roles as Putative Treatment Targets?

Hepatic fibrosis is the primary predictor of mortality in patients with non-alcoholic steatohepatitis (NASH). In this process, the activated hepatic stellate cells (HSCs) constitute the principal cells responsible for the deposition of a fibrous extracellular matrix, thereby driving the hepatic scarring. HSC activation, migration, and proliferation are controlled by a complex signaling network involving growth factors, lipotoxicity, inflammation, and cellular stress. Conversely, the clearance of activated HSCs is a prerequisite for the resolution of the extracellular fibrosis. Hence, pathways regulating the fate of the HSCs may represent attractive therapeutic targets for the treatment and prevention of NASH-associated hepatic fibrosis. However, the development of anti-fibrotic drugs for NASH patients has not yet resulted in clinically approved therapeutics, underscoring the complex biology and challenges involved when targeting the intricate cellular signaling mechanisms. This narrative review investigated the mechanisms of activation and inactivation of HSCs with a focus on NASH-associated hepatic fibrosis. Presenting an updated overview, this review highlights key cellular pathways with potential value for the development of future treatment modalities.

Neoagarooligosaccharide Protects against Hepatic Fibrosis via Inhibition of TGF-β/Smad Signaling Pathway

Hepatic fibrosis occurs when liver tissue becomes scarred from repetitive liver injury and inflammatory responses; it can progress to cirrhosis and eventually to hepatocellular carcinoma. Previously, we reported that neoagarooligosaccharides (NAOs), produced by the hydrolysis of agar by β-agarases, have hepatoprotective effects against acetaminophen overdose-induced acute liver injury. However, the effect of NAOs on chronic liver injury, including hepatic fibrosis, has not yet been elucidated. Therefore, we examined whether NAOs protect against fibrogenesis in vitro and in vivo. NAOs ameliorated PAI-1, α-SMA, CTGF and fibronectin protein expression and decreased mRNA levels of fibrogenic genes in TGF-β-treated LX-2 cells. Furthermore, downstream of TGF-β, the Smad signaling pathway was inhibited by NAOs in LX-2 cells. Treatment with NAOs diminished the severity of hepatic injury, as evidenced by reduction in serum alanine aminotransferase and aspartate aminotransferase levels, in carbon tetrachloride (CCl4)-induced liver fibrosis mouse models. Moreover, NAOs markedly blocked histopathological changes and collagen accumulation, as shown by H&E and Sirius red staining, respectively. Finally, NAOs antagonized the CCl4-induced upregulation of the protein and mRNA levels of fibrogenic genes in the liver. In conclusion, our findings suggest that NAOs may be a promising candidate for the prevention and treatment of chronic liver injury via inhibition of the TGF-β/Smad signaling pathway.

The potential role of sestrin 2 in liver regeneration

Liver regeneration is a remarkably complex phenomenon conserved across all vertebrates, enabling the restoration of lost liver mass in a matter of days. Unfortunately, extensive damage to the liver may compromise this process, often leading to the death of affected individuals. Ischemia/reperfusion injury (IRI) is a common source of damage preceding regeneration, often present during liver transplantation, resection, trauma, or hemorrhagic shock. Increased oxidative stress and mitochondrial dysfunction are key hallmarks of IRI, which can jeopardize the liver's ability to regenerate. Therefore, a better understanding of both liver regeneration and IRI is of important clinical significance. In the current review, we discuss the potential role of sestrin 2 (SESN2), a novel anti-aging protein, in liver regeneration and ischemia/reperfusion preceding regeneration. We highlight its beneficial role in protecting cells from mitochondrial dysfunction and oxidative stress as key aspects of its involvement in liver regeneration. Additionally, we describe how its ability to promote the expression of Nrf2 bears significant importance in this context. Finally, we focus on a potential novel link between SESN2, mitohormesis and ischemic preconditioning, which could explain some of the protective effects of preconditioning.

Sestrin 2, a potential star of antioxidant stress in cardiovascular diseases

Physiological reactive oxygen species (ROS) play an important role in cellular signal transduction. However, excessive ROS is an important pathological mechanism in most cardiovascular diseases (CVDs), such as myocardial aging, cardiomyopathy, ischemia/reperfusion injury (e.g., myocardial infarction) and heart failure. Programmed cell death, hypertrophy and fibrosis may be due to oxidative stress. Sestrin 2 (Sesn2), a stress-inducible protein associated with various stress conditions, is a potential antioxidant. Sesn2 can suppress the process of heart damage caused by oxidative stress, promote cell survival and play a key role in a variety of CVDs. This review discusses the effect of Sesn2 on the redox signal, mainly via participation in the signaling pathway of nuclear factor erythroid 2-related factor 2, activation of adenosine monophosphate-activated protein kinase and inhibition of mammalian target of rapamycin complex 1. It also discusses the effect of Sesn2's antioxidant activity on different CVDs. We speculate that Sesn2 plays an important role in CVDs by stimulating the process of antioxidation and promoting the adaptation of cells to stress conditions and/or the environment, opening a new avenue for related therapeutic strategies.

Transforming Growth Factor Beta-Induced Foxo3a Acts as a Profibrotic Mediator in Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are major contributors to hepatic fibrogenesis facilitating liver fibrosis. Forkhead box O 3a (FoxO3a) is a member of the forkhead transcription factor family, which mediates cell proliferation and differentiation. However, the expression and function of FoxO3a during HSC activation remain largely unknown. FoxO3a overexpression was related to fibrosis in patients, and its expression was colocalized with desmin or α-smooth muscle actin, representative HSC markers. We also observed upregulated FoxO3a levels in two animal hepatic fibrosis models, a carbon tetrachloride-injected model and a bile duct ligation model. In addition, transforming growth factor beta (TGF-β) treatment in mouse primary HSCs or LX-2 cells elevated FoxO3a expression. When FoxO3a was upregulated by TGF-β in LX-2 cells, both the cytosolic and nuclear levels of FoxO3a increased. In addition, we found that the induction of FoxO3a by TGF-β was due to both transcriptional and proteasome-dependent mechanisms. Moreover, FoxO3a overexpression promoted TGF-β-mediated Smad activation. Furthermore, FoxO3a increased fibrogenic gene expression, which was reversed by FoxO3a knockdown. TGF-β-mediated FoxO3a overexpression in HSCs facilitated hepatic fibrogenesis, suggesting that FoxO3a may be a novel target for liver fibrosis prevention and treatment.

5-Caffeoylquinic acid ameliorates oxidative stress-mediated cell death via Nrf2 activation in hepatocytes

CONTEXT

5-Caffeoylquinic acid (5-CQA) is one of the most abundant compounds found in natural foods including coffee.

OBJECTIVE

We investigated whether 5-CQA had a cytoprotective effect through the NF-E2-related factor 2 (Nrf2)-antioxidant response element (ARE) signalling pathway.

MATERIALS AND METHODS

Nrf2 activation in response to 5-CQA treatment at the concentration of 10-100 μM is evaluated by Western blotting of Nrf2 and ARE reporter gene assay as well as its target gene expression in HepG2 cells. Intracellular reactive oxygen species (ROS) and glutathione (GSH) levels were measured in the tert-butyl hydroperoxide-induced hepatocytes to examined cytoprotective effect of 5-CQA (10-100 μM). The specific role of 5-CQA on Nrf2 activation was examined using Nrf2 knockout cells or Nrf2 specific inhibitor, ML-385.

RESULTS

Nuclear translocation of Nrf2 is increased by 5-CQA in HepG2 cells which peaked at 6 h. Consequently, 5-CQA significantly increases the ARE reporter gene activity and downstream antioxidant proteins, including glutamate cysteine ligase (GCL), hemeoxygenase-1 (HO-1), NAD(P)H quinone oxidoreductase 1, and Sestrin2. Nrf2 deficiency or inhibition completely antagonized ability of 5-CQA to induce HO-1 and GCL expression. Cells pre-treated with 5-CQA were rescued from tert-butyl hydroperoxide-induced ROS production and GSH depletion. Nrf2 activation by 5-CQA was due to increased phosphorylation of MAPKs, AMPK and PKCδ.

DISCUSSION AND CONCLUSIONS

Taken together, our results demonstrate that as a novel Nrf2 activator, 5-CQA, may be a promising candidate against oxidative stress-mediated liver injury. Additional efforts are needed to assess 5-CQA, as a potential therapeutic in liver diseases in vivo and in humans.

Correlation between sestrin2 expression and airway remodeling in COPD

BACKGROUND

Airway remodeling is a major pathological characteristic of chronic obstructive pulmonary disease (COPD), and has been shown to be associated with oxidative stress. Sestrin2 has recently drawn attention as an important antioxidant protein. However, the underlying correlation between sestrin2 and airway remodeling in COPD has yet to be clarified.

METHODS

A total of 124 subjects were enrolled in this study, including 62 control subjects and 62 COPD patients. The pathological changes in airway tissues were assessed by different staining methods. The expression of sestrin2 and matrix metalloproteinase 9 (MMP9) in airway tissues was monitored by immunohistochemistry. Enzyme-linked immunosorbent assays (ELISAs) were used to detect the serum concentrations of sestrin2 and MMP9. The airway parameters on computed tomography (CT) from all participants were measured for evaluating airway remodeling. The relationship between serum sestrin2 and MMP9 concentration and airway parameters in chest CT was also analyzed.

RESULTS

In patients with COPD, staining of airway structures showed distinct pathological changes of remodeling, including cilia cluttered, subepithelial fibrosis, and reticular basement membrane (Rbm) fragmentation. Compared with control subjects, the expression of sestrin2 and MMP9 was significantly increased in both human airway tissues and serum. Typical imaging characteristics of airway remodeling and increased airway parameters were also found by chest CT. Additionally, serum sestrin2 concentration was positively correlated with serum MMP9 concentration and airway parameters in chest CT.

CONCLUSION

Increased expression of sestrin2 is related to airway remodeling in COPD. We demonstrated for the first time that sestrin2 may be a novel biomarker for airway remodeling in patients with COPD.

Sestrins in Physiological Stress Responses

Sestrins are a family of proteins that respond to a variety of environmental stresses, including genotoxic, oxidative, and nutritional stresses. Sestrins affect multiple signaling pathways: AMP-activated protein kinase, mammalian target of rapamycin complexes, insulin-AKT, and redox signaling pathways. By regulating these pathways, Sestrins are thought to help adapt to stressful environments and subsequently restore cell and tissue homeostasis. In this review, we describe how Sestrins mediate physiological stress responses in the context of nutritional and chemical stresses (liver), physical movement and exercise (skeletal muscle), and chemical, physical, and inflammatory injuries (heart). These findings also support the idea that Sestrins are a molecular mediator of hormesis, a paradoxical beneficial effect of low- or moderate-level stresses in living organisms.

Sestrin family - the stem controlling healthy ageing

Sestrins are a family of stress-responsive antioxidant proteins responsible for regulation of cell viability and metabolism. The best known Sestrin targets are mTORC1 and mTORC2 kinases that control different cellular processes including growth, viability, autophagy, and mitochondrial metabolism. Inactivation of the single Sestrin gene in invertebrates has an adverse impact on their healthspan and longevity, whereas each of the three Sestrin genes in mammals and other vertebrate organisms has a different impact on maintenance of a particular tissue, affecting its stress tolerance, function and regenerative capability. As a result, Sestrins attenuate ageing and suppress development of many age-related diseases including myocardial infarction, muscle atrophy, diabetes, and immune dysfunction, but exacerbate development of chronic obstructive pulmonary disease. Moreover, Sestrins play opposite roles in carcinogenesis in different tissues. Stem cells support tissue remodelling that influences ageing, and Sestrins might suppress ageing and age-related pathologies through control of stem cell biology. In this review, we will discuss the potential link between Sestrins, stem cells, and ageing.

Hemistepsin A alleviates liver fibrosis by inducing apoptosis of activated hepatic stellate cells via inhibition of nuclear factor-κB and Akt

Hemistepsin A (HsA), isolated from Hemistepta lyrata (Bunge) Bunge, has the ability to ameliorate hepatitis in mice. However, the effects of H. lyrata and HsA on other types of liver disease have not been explored. In this report, we investigated the effects of H. lyrata and HsA on liver fibrosis and the underlying molecular mechanisms in activated hepatic stellate cells (HSCs). Based on cell viability-guided isolation, we found HsA was the major natural product responsible for H. lyrata-mediated cytotoxicity in LX-2 cells. HsA significantly decreased the viability of LX-2 cells and primary activated HSCs, increased the binding of Annexin V, and altered the expression of apoptosis-related proteins, suggesting that HsA induces apoptosis in activated HSCs. HsA reduced the phosphorylation of IKKε and the transactivation of nuclear factor-κB (NF-κB). Moreover, HsA decreased the phosphorylation of Akt and its downstream signaling molecules. Transfection experiments suggested that inhibition of NF-κB or Akt is essential for HsA-induced apoptosis of HSCs. In a CCl₄-induced liver fibrosis model, HsA administration significantly decreased ALT and AST activities. Furthermore, HsA attenuated CCl₄-mediated collagen deposits and profibrogenic genes expression in hepatic tissue. Thus, HsA may serve as a natural product for managing liver fibrosis through inhibition of NF-κB/Akt-dependent signaling.