Translational regulation of GPx-1 and GPx-4 by the mTOR pathway

Everolimus alleviates CD4+ T cell inflammation by regulating autophagy and cellular redox homeostasis

Aging is associated with the onset and progression of multiple diseases, which limit health span. Chronic low-grade inflammation in the absence of overt infection is considered the simmering source that triggers age-associated diseases. Failure of many cellular processes during aging is mechanistically linked to inflammation; however, the overall decline in the cellular homeostasis mechanism of autophagy has emerged as one of the top and significant inducers of inflammation during aging, frequently known as inflammaging. Thus, physiological or pharmacological interventions aimed at improving autophagy are considered geroprotective. Rapamycin analogs (rapalogs) are known for their ability to inhibit mTOR and thus regulate autophagy. This study assessed the efficacy of everolimus, a rapalog, in regulating inflammatory cytokine production in T cells from older adults. CD4+ T cells from older adults were treated with a physiological dose of everolimus (0.01 µM), and indices of autophagy and inflammation were assessed to gain a mechanistic understanding of the effect of everolimus on inflammation. Everolimus (Ever) upregulated autophagy and broadly alleviated inflammatory cytokines produced by multiple T cell subsets. Everolimus's ability to alleviate the cytokines produced by Th17 subsets of T cells, such as IL-17A and IL-17F, was dependent on autophagy and antioxidant signaling pathways. Repurposing the antineoplastic drug everolimus for curbing inflammaging is promising, given the drug's ability to restore multiple cellular homeostasis mechanisms.

Mechanisms of ferroptosis and targeted therapeutic approaches in lymphoma

Lymphoma is the sixth most common type of cancer worldwide. Under the current treatment standards, patients with lymphoma often fail to respond to treatment or relapse early and require further therapy. Hence, novel therapeutic strategies need to be explored and our understanding of the molecular underpinnings of lymphomas should be expanded. Ferroptosis, a non-apoptotic regulated cell death, is characterized by increased reactive oxygen species and lipid peroxidation due to metabolic dysfunction. Excessive or lack of ferroptosis has been implicated in tumor development. Current preclinical evidences suggest that ferroptosis participates in tumorigenesis, progression, and drug resistance of lymphoma, identifying a potential biomarker and an attractive molecular target. Our review summarizes the core mechanisms and regulatory networks of ferroptosis and discusses existing evidences of ferroptosis induction for the treatment of lymphoma, with intent to provide a framework for understanding the role of ferroptosis in lymphomagenesis and a new perspective of lymphoma treatment.

Butyrate dictates ferroptosis sensitivity through FFAR2-mTOR signaling

Evidence shows that short-chain fatty acids (SCFAs) play an important role in health maintenance and disease development. In particular, butyrate is known to induce apoptosis and autophagy. However, it remains largely unclear whether butyrate can regulate cell ferroptosis, and the mechanism by which has not been studied. In this study, we found that RAS-selective lethal compound 3 (RSL3)- and erastin-induced cell ferroptosis were enhanced by sodium butyrate (NaB). With regard to the underlying mechanism, our results showed that NaB promoted ferroptosis by inducing lipid ROS production via downregulating the expression of solute carrier family 7 member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4). Moreover, the FFAR2-AKT-NRF2 axis and FFAR2-mTORC1 axis accounts for the NaB-mediated downregulation of SLC7A11 and GPX4, respectively, in a cAMP-PKA-dependent manner. Functionally, we found that NaB can inhibit tumor growth and the inhibitory effect could be eliminated by administrating MHY1485 (mTORC1 activator) and Ferr-1 (ferroptosis inhibitor). Altogether, in vivo results suggest that NaB treatment is correlated to the mTOR-dependent ferroptosis and consequent tumor growth through xenografts and colitis-associated colorectal tumorigenesis, implicating the potential clinical applications of NaB for future colorectal cancer treatments. Based on all these findings, we have proposed a regulatory mechanism via which butyrate inhibits the mTOR pathway to control ferroptosis and consequent tumorigenesis.

Ferroptosis in sepsis: The mechanism, the role and the therapeutic potential

Sepsis is a common critical illness in the Intensive care unit(ICU) and its management and treatment has always been a major challenge in critical care medicine. The dysregulated host response to infection, causing systemic multi-organ and multi-system damage is the main pathogenesis. Notably, intense stress during sepsis can lead to metabolic disturbances of ions, lipids and energy in the organism. Ferroptosis is an iron-dependent, non-apoptotic cell death distinguished by a disruption of iron metabolism and iron-dependent accumulation of lipid peroxides. Mounting researches have established that ferroptosis has an essential part in anti-inflammatory and sepsis, and drugs targeting ferroptosis-related molecules, such as ferroptosis inhibitors, are gradually proving their effectiveness in sepsis. This paper summarizes and reviews the pathogenesis of ferroptosis, its regulatory network, and its vital involvement in the initiation of sepsis and related organ damage, and finally discusses the possible target drugs provided by the above mechanisms, describes the dilemmas as well as the outlook, in the hope of finding more links between ferroptosis and sepsis and providing new perspectives for the future treatment of sepsis.

A Genotype-Phenotype Analysis of Glutathione Peroxidase 4 in Human Atrial Myocardium and Its Association with Postoperative Atrial Fibrillation

Heterogeneity in the incidence of postoperative atrial fibrillation (POAF) following heart surgery implies that underlying genetic and/or physiological factors impart a higher risk of this complication to certain patients. Glutathione peroxidase-4 (GPx4) is a vital selenoenzyme responsible for neutralizing lipid peroxides, mediators of oxidative stress known to contribute to postoperative arrhythmogenesis. Here, we sought to determine whether GPX4 single nucleotide variants are associated with POAF, and whether any of these variants are linked with altered GPX4 enzyme content or activity in myocardial tissue. Sequencing analysis was performed across the GPX4 coding region within chromosome 19 from a cohort of patients (N = 189) undergoing elective coronary artery bypass graft (−/+ valve) surgery. GPx4 enzyme content and activity were also analyzed in matching samples of atrial myocardium from these patients. Incidence of POAF was 25% in this cohort. Five GPX4 variants were associated with POAF risk (permutated p ≤ 0.05), and eight variants associated with altered myocardial GPx4 content and activity (p < 0.05). One of these variants (rs713041) is a well-known modifier of cardiovascular disease risk. Collectively, these findings suggest GPX4 variants are potential risk modifiers and/or predictors of POAF. Moreover, they illustrate a genotype−phenotype link with this selenoenzyme, which will inform future mechanistic studies.

HIV-1 hypermethylated guanosine cap licenses specialized translation unaffected by mTOR

The proliferation of viral pathogens is restricted by hosts, but resilient pathogens antagonize the restriction by hosts. Findings explain that HIV-1 blocked mono-methylated guanosine cap by hypermethylation and engaged novel cap-binding complex for virion protein translation unaffected by global translation inhibition. The hypermethylated cap activity required RNA-structure-dependent binding of RNA helicase A/DHX9. eIF4E interaction proceeded on completely spliced HIV messenger RNA templates encoding viral regulatory proteins, thus eIF4E inactivation by catalytic site mTOR inhibitor suppressed regulatory protein translation, while structural/accessory protein translation was maintained. Two mutually exclusive translation pathways antagonize hosts and facilitate HIV-1 proliferation in primary CD4⁺ T cells to the detriment of hosts. eIF4E inactivation imposed an operational rheostat that suppressed regulatory proteins, while maintaining virion production in immune cells. 

Appended to the 5′ end of nascent RNA polymerase II transcripts is 7-methyl guanosine (m⁷G-cap) that engages nuclear cap-binding complex (CBC) to facilitate messenger RNA (mRNA) maturation. Mature mRNAs exchange CBC for eIF4E, the rate-limiting translation factor that is controlled through mTOR. Experiments in immune cells have now documented HIV-1 incompletely processed transcripts exhibited hypermethylated m⁷G-cap and that the down-regulation of the trimethylguanosine synthetase-1–reduced HIV-1 infectivity and virion protein synthesis by several orders of magnitude. HIV-1 cap hypermethylation required nuclear RNA helicase A (RHA)/DHX9 interaction with the shape of the 5′ untranslated region (UTR) primer binding site (PBS) segment. Down-regulation of RHA or the anomalous shape of the PBS segment abrogated hypermethylated caps and derepressed eIF4E binding for virion protein translation during global down-regulation of host translation. mTOR inhibition was detrimental to HIV-1 proliferation and attenuated Tat, Rev, and Nef synthesis. This study identified mutually exclusive translation pathways and the calibration of virion structural/accessory protein synthesis with de novo synthesis of the viral regulatory proteins. The hypermethylation of select, viral mRNA resulted in CBC exchange to heterodimeric CBP80/NCBP3 that expanded the functional capacity of HIV-1 in immune cells.

Inhibition of GPX4 or mTOR overcomes resistance to Lapatinib via promoting ferroptosis in NSCLC cells

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase and mutations in EGFR is a major driver force of lung cancer. EGFR tyrosine kinase inhibitors (TKIs) are group of promising agents to treat cancer patients with EGFR mutations. However, the application of TKIs is often hampered by the development of drug-resistance. In the present study, we studied the role of Glutathione peroxidase 4 (GPX4) and mammalian target of rapamycin (mTOR) in regulation of lung cancer cells response to Lapatinib (Lap). Lap resistant NSCLC cells A549/Lap and H1944/Lap were created and GPX4 was knockdown by lentivirus shGPX4. Change of cell viabilities and cell death were measured by MTT and flow cytometry, respectively. ROS, MDA, GSH and Fe2+ were detected by commercial kits. Xenograft mice was used to assay the in vivo effects of GPX4 on the sensitivity of Lap. We found that GPX4 and mTORC1 signalling was upregulated in Lap resistant NSCLC cells when compared to Lap sensitive NSCLC cells. Mechanistically, upregulation of GPX4 was due to enhanced activation of mTORC1 in Lap resistant NSCLC cells. Inhibition of mTORC1 led to the downregulation of GPX4 which promoted Lap induced ferroptosis as evidenced by increase of ROS, MDA, Fe 2+ and decrease of GSH. Rescue experiments confirmed the role of GPX4 in regulation of Lap induced ferroptosis. In vivo experiments also indicated that silencing of GPX4 enhanced the anticancer effect of Lap via promoting ferroptosis. Overall, targeting GPX4 might be a potential strategy to enhance antitumor effects of Lap.

mTORC1 couples cyst(e)ine availability with GPX4 protein synthesis and ferroptosis regulation

Glutathione peroxidase 4 (GPX4) utilizes glutathione (GSH) to detoxify lipid peroxidation and plays an essential role in inhibiting ferroptosis. As a selenoprotein, GPX4 protein synthesis is highly inefficient and energetically costly. How cells coordinate GPX4 synthesis with nutrient availability remains unclear. In this study, we perform integrated proteomic and functional analyses to reveal that SLC7A11-mediated cystine uptake promotes not only GSH synthesis, but also GPX4 protein synthesis. Mechanistically, we find that cyst(e)ine activates mechanistic/mammalian target of rapamycin complex 1 (mTORC1) and promotes GPX4 protein synthesis at least partly through the Rag-mTORC1-4EBP signaling axis. We show that pharmacologic inhibition of mTORC1 decreases GPX4 protein levels, sensitizes cancer cells to ferroptosis, and synergizes with ferroptosis inducers to suppress patient-derived xenograft tumor growth in vivo. Together, our results reveal a regulatory mechanism to coordinate GPX4 protein synthesis with cyst(e)ine availability and suggest using combinatorial therapy of mTORC1 inhibitors and ferroptosis inducers in cancer treatment.

Investigating the Thioredoxin and Glutathione Systems' Response in Lymphoma Cells after Treatment with [Au(d2pype)2]CL

Lymphoma is a blood cancer comprising various subtypes. Although effective therapies are available, some patients fail to respond to treatment and can suffer from side effects. Antioxidant systems, especially the thioredoxin (Trx) and glutathione (GSH) systems, are known to enhance cancer cell survival, with thioredoxin reductase (TrxR) recently reported as a potential anticancer target. Since the GSH system can compensate for some Trx system functions, we investigated its response in three lymphoma cell lines after inhibiting TrxR activity with [Au(d2pype)2]Cl, a known TrxR inhibitor. [Au(d2pype)2]Cl increased intracellular reactive oxygen species (ROS) levels and induced caspase-3 activity leading to cell apoptosis through inhibiting both TrxR and glutathione peroxidase (Gpx) activity. Expression of the tumour suppresser gene TXNIP increased, while GPX1 and GPX4 expression, which are related to poor prognosis of lymphoma patients, decreased. Unlike SUDHL2 and SUDHL4 cells, which exhibited a decreased GSH/GSSG ratio after treatment, in KMH2 cells the ratio remained unchanged, while glutathione reductase and glutaredoxin expression increased. Since KMH2 cells were less sensitive to treatment with [Au(d2pype)2]Cl, the GSH system may play a role in protecting cells from apoptosis after TrxR inhibition. Overall, our study demonstrates that inhibition of TrxR represents a valid therapeutic approach for lymphoma.

Partial involvement of Nrf2 in skeletal muscle mitohormesis as an adaptive response to mitochondrial uncoupling

Mitochondrial dysfunction is usually associated with various metabolic disorders and ageing. However, salutary effects in response to mild mitochondrial perturbations have been reported in multiple organisms, whereas molecular regulators of cell-autonomous stress responses remain elusive. We addressed this question by asking whether the nuclear factor erythroid-derived-like 2 (Nrf2), a transcription factor and master regulator of cellular redox status is involved in adaptive physiological responses including muscle mitohormesis. Using a transgenic mouse model with skeletal muscle-specific mitochondrial uncoupling and oxidative phosphorylation (OXPHOS) inefficiency (UCP1-transgenic, TG) we show that additional genetic ablation of Nrf2 abolishes an adaptive muscle NAD(P)H quinone dehydrogenase 1 (NQO1) and catalase induction. Deficiency of Nrf2 also leads to decreased mitochondrial respiratory performance although muscle functional integrity, fiber-type profile and mitochondrial biogenesis were not significantly altered. Importantly, Nrf2 ablation did not abolish the induction of key genes and proteins of muscle integrated stress response including the serine, one-carbon cycle, and glycine synthesis (SOG) pathway in TG mice while further increasing glutathione peroxidase (GPX) activity linked to increased GPX1 protein levels. Conclusively, our results tune down the functions controlled by Nrf2 in muscle mitohormesis and oxidative stress defense during mitochondrial OXPHOS inefficiency.

Comparison of glutathione peroxidase-3 protein expression and enzyme bioactivity in normal subjects and patients with sepsis

BACKGROUND

Serum glutathione peroxidase-3 (GPx-3) is known as a key selenoprotein with antioxidant properties. GPx-3 deficiency has been associated with sepsis. The objectives of this study are (1) to compare the GPx-3 protein concentrations and GPx-3 bioactivity in normal healthy subjects and septic patients, and (2) to evaluate the relationship between GPx-3 bioactivity and its protein concentration.

METHODS

Serum samples were collected from 50 normal healthy subjects and 70 septic patients. The reliable bioanalytical methods for GPx-3 protein concentration and bioactivity in human serum were developed and validated. Analyses of GPx-3 bioactivity and GPx-3 protein concentration were then performed.

RESULTS

Geometric mean GPx-3 bioactivity was 78.13U/l for patients with sepsis, significantly lower than normal subjects with 108.21U/l (p<0.0001). Similarly, the GPx-3 protein concentration was significantly lower in patients with sepsis than in normal subjects, with the mean GPx-3 value of 0.78 vs 3.10μg/ml, respectively (p<0.0001). A positive correlation was observed between the GPx-3 bioactivity and its corresponding protein concentration in septic serum samples (R=0.74, p<0.0001), regardless of gender or age difference.

CONCLUSION

These findings suggest that the decrease in GPx-3 bioactivity observed in the septic patients was resulted from the significant sepsis-related decline of GPx-3 protein concentrations.

Glutathione Peroxidase-1 Suppresses the Unfolded Protein Response upon Cigarette Smoke Exposure

Oxidative stress provokes endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) in the lungs of chronic obstructive pulmonary (COPD) subjects. The antioxidant, glutathione peroxidase-1 (GPx-1), counters oxidative stress induced by cigarette smoke exposure. Here, we investigate whether GPx-1 expression deters the UPR following exposure to cigarette smoke. Expression of ER stress markers was investigated in fully differentiated normal human bronchial epithelial (NHBE) cells isolated from nonsmoking, smoking, and COPD donors and redifferentiated at the air liquid interface. NHBE cells from COPD donors expressed heightened ATF4, XBP1, GRP78, GRP94, EDEM1, and CHOP compared to cells from nonsmoking donors. These changes coincided with reduced GPx-1 expression. Reintroduction of GPx-1 into NHBE cells isolated from COPD donors reduced the UPR. To determine whether the loss of GPx-1 expression has a direct impact on these ER stress markers during smoke exposure, Gpx-1-/- mice were exposed to cigarette smoke for 1 year. Loss of Gpx-1 expression enhanced cigarette smoke-induced ER stress and apoptosis. Equally, induction of ER stress with tunicamycin enhanced antioxidant expression in mouse precision-cut lung slices. Smoke inhalation also exacerbated the UPR response during respiratory syncytial virus infection. Therefore, ER stress may be an antioxidant-related pathophysiological event in COPD.

Heart selenoproteins status of metabolic syndrome-exposed pups: A potential target for attenuating cardiac damage

SCOPE

Cardiac hypertrophy is the greatest complication in metabolic syndrome (MS), in dams and in offspring. The most effective therapies to avoid the evolution of MS are anti-oxidants, anti-inflammatories, and insulin sensitizers. Among anti-oxidant elements, Selenium (Se) exerts its functions through selenoproteins, which are essential for the correct functioning of the cardiovascular system. The aim of the study is analyze selenoproteins' implication in the transmission of future cardiovascular problems to MS progeny.

METHODS AND RESULTS

Heart Se deposits, antioxidant enzymes' activities, biomolecular oxidation, and the expression of selenoproteins, AMPK, and NF-kB were measured in the offspring of dams exposed to a fructose-rich diet (65%) during gestation and lactation, with a normal Se content (0.1 ppm). Thyroid hormones and MCP-1 serum levels, as well as blood pressure and heart rate were also measured. Fructose-exposed pups have cardiomegaly, oxidation, and depletion in Se heart deposits, a decrease in selenoproteins' expression and in the p-AMPK/AMPKt energy ratio; an increase in NF-kB p65 expression, and a decrease of thyroid hormones and MCP-1. Heart rate and blood pressure were altered.

CONCLUSION

These data indicate that dietary Se supplementation could be an inexpensive therapy for avoiding future cardiovascular complication in the progeny of MS dams.

Selenoproteins and cardiovascular stress

Dietary selenium (Se) is an essential micronutrient that exerts its biological effects through its incorporation into selenoproteins. This family of proteins contains several antioxidant enzymes such as the glutathione peroxidases, redox-regulating enzymes such as thioredoxin reductases, a methionine sulfoxide reductase, and others. In this review, we summarise the current understanding of the roles these selenoproteins play in protecting the cardiovascular system from different types of stress including ischaemia-reperfusion, homocysteine dysregulation, myocardial hypertrophy, doxirubicin toxicity, Keshan disease, and others.

Exposure of chronic myelogenous leukemia cells to imatinib results in the post-transcriptional induction of manganese superoxide dismutase

The treatment of chronic myelogenous leukemia (CML) with specific tyrosine kinase inhibitors typically results in clinical success, although therapeutic failure frequently occurs. In order to investigate the biological consequences of treating CML cells with such drugs, we previously reported that the antioxidant selenoprotein glutathione peroxidase-1 (GPx-1) was induced by imatinib in both patient samples and cultured cells. Here, we extend these findings to demonstrate that the treatment of CML cell lines, but not non-CML cells, results in an approximately four-fold increase in the levels of another important antioxidant protein, manganese superoxide dismutase (MnSOD), without altering the steady state levels of the corresponding transcript.