Protein disulfide isomerase mediates glutathione depletion-induced cytotoxicity

Role of protein disulfide isomerase in mediating sulfasalazine-induced ferroptosis in HT22 cells: The PDI-NOS-NO-ROS/lipid-ROS cascade

Ferroptosis is a form of regulated cell death resulting from excessive lipid peroxidation. Sulfasalazine (SAS), an anti-inflammatory drug, can induce ferroptosis through inhibiting the system Xc- and triggering glutathione depletion. SAS has attracted considerable interest in recent years because of its potential for repurposing as an anticancer agent. Our recent studies have shown that protein disulfide isomerase (PDI) is an upstream mediator of chemically-induced ferroptosis through catalyzing the dimerization of nitric oxide synthase (NOS) and NO accumulation in cultured HT22 hippocampal neuronal cells. The present study aims to investigate SAS-induced ferroptotic cell death in HT22 cells with a focus on determining the role of PDI in mediating SAS-induced ferroptosis. We find that SAS induces ferroptotic cell death in HT22 cells, which is accompanied by a time-dependent sequential increase in the accumulation of cellular NO, ROS and lipid-ROS. We find that treatment of HT22 cells with SAS activates PDI-mediated iNOS activation (dimerization) and NO accumulation. In addition, SAS also strongly upregulates iNOS protein levels in HT22 cells. PDI knockdown or pharmacological inhibition of PDI's activity each suppresses SAS-induced iNOS dimerization, which is associated with abrogation of SAS-induced accumulation of NO, ROS and lipid-ROS, and a strong protection against ferroptotic cell death. On the other hand, PDI activation through the use of a TrxR1 inhibitor can strongly sensitize cells to SAS-induced ferroptosis. Together, these experimental observations demonstrate a crucial role of PDI in SAS-induced ferroptosis in a cell culture model through the activation of the PDI → NOS → NO → ROS/lipid-ROS pathway. Insights gained from this study also provide effective strategies to selectively sensitizing human cancer cells to SAS-induced ferroptosis, such as through the use of NO-releasing agents or TrxR1 inhibitors.

Strong protection by bazedoxifene against chemically-induced ferroptotic neuronal death in vitro and in vivo

Ferroptosis, a form of regulated cell death associated with glutathione depletion and excess lipid peroxidation, can be induced in cultured cells by chemicals (e.g., erastin and RSL3). It has been shown that protein disulfide isomerase (PDI) is a mediator of chemically-induced ferroptosis and also a crucial target for ferroptosis protection. The present study reports that bazedoxifene (BAZ), a selective estrogen receptor modulator, is an inhibitor of PDI and can strongly rescue neuronal cells from chemically-induced oxidative ferroptosis. We find that BAZ can directly bind to PDI and inhibit its catalytic activity. Computational modeling analysis reveals that BAZ forms a hydrogen bond with PDI's His256 residue. Inhibition of PDI by BAZ markedly reduces iNOS and nNOS dimerization (i.e., catalytic activation) and NO accumulation, and these effects of BAZ are associated with reductions in cellular ROS and lipid-ROS and protection against chemically-induced ferroptosis. In addition, the direct antioxidant activity of BAZ may also partially contribute to its protection against chemically-induced ferroptosis. In vivo animal experiments show that mice treated with BAZ are strongly protected against kainic acid-induced oxidative hippocampal neuronal injury and memory deficits. Together, these results reveal that BAZ is a potent inhibitor of PDI and can strongly protect against chemically-induced ferroptosis in hippocampal neurons both in vitro and in vivo. This work provides evidence for an estrogen receptor-independent, PDI-mediated novel mechanism of neuroprotection by BAZ.

4-Hydroxyestrogen metabolites strongly prevent chemically-induced ferroptotic hepatocyte injury in vitro and in vivo

Ferroptosis is a regulated cell death characterized by excessive accumulation of toxic lipid reactive oxygen species (ROS). Ferroptosis is an underlying cause in some human diseases, including the drug-induced liver injury. The present study aims to determine whether 4-hydroxyestrone (4-OH-E1) and 4-hydroxyestradiol (4-OH-E2), two endogenous catechol estrogens, can prevent chemically-induced ferroptotic hepatocyte injury in vitro and in vivo. The induction of ferroptotic cell death by erastin and RSL3 in rat H-4-II-E and human HuH-7 hepatoma cells is used as in vitro models. 4-OH-E1 and 4-OH-E2 each exhibit a strong protection against erastin/RSL3-induced ferroptosis in H-4-II-E hepatoma cells, and they also strongly abrogate erastin/RSL3-induced accumulation of cellular NO, ROS and lipid-ROS. A similar protective effect is observed with 4-OH-E1 and 4-OH-E2 in RSL3-induced ferroptosis in HuH-7 cells. Mechanistically, these two catechol estrogens protect hepatoma cells against chemically-induced ferroptosis mainly through binding to cellular PDI protein with a high affinity, which leads to inhibition of PDI-catalyzed NOS dimerization (activation), thereby preventing the accumulation of cellular NO, ROS and lipid-ROS. In addition, the direct antioxidant activity of these two estrogens may also partially contribute to their cytoprotective effect. In vivo animal studies show that 4-OH-E1 and 4-OH-E2 also have a strong protective effect against acetaminophen-induced liver injury in a mouse model. Together, the results of this study demonstrate that 4-OH-E1 and 4-OH-E2 are endogenous factors with a strong protective activity against chemically-induced hepatocyte injury both in vitro and in vivo.

An antireductant approach ameliorates misfolded proinsulin-induced hyperglycemia and glucose intolerance in male Akita mice

Protein folding in the endoplasmic reticulum (ER) requires a high ratio of oxidized to reduced glutathione (GSSG/rGSH). Since the GSSG/rGSH depends on total glutathione (tGSH = GSSG + rGSH) levels, we hypothesized that limiting GSH biosynthesis will ameliorate protein misfolding by enhancing the ER oxidative milieu. As a proof-of-concept, we used DL-buthionine-(S,R)-sulfoximine (BSO) to inhibit GSH biosynthesis in Akita mice, which are prone to proinsulin misfolding. We conducted a 2-week intervention to investigate if BSO was safe and a 6-week intervention to find its effect on glucose intolerance. In both cohorts, male heterozygous Akita (AK) and wild-type (WT) mice were continuously administered 15 mM BSO. No adverse effects were observed on body weight, food intake, and water intake in either cohort. Unaltered levels of plasma aspartate and alanine aminotransferases, and cystatin-C, indicate that BSO was safe. BSO-induced decreases in tGSH were tissue-dependent with maximal effects in the kidneys, where it altered the expression of genes associated with GSH biosynthesis, redox status, and proteostasis. BSO treatment decreased random blood glucose levels to 80% and 67% of levels in untreated mice in short-term and long-term cohorts, respectively, and 6-h fasting blood glucose to 82% and 74% of levels in untreated mice, respectively. BSO also improved glucose tolerance by 37% in AK mice in the long-term cohort, without affecting insulin tolerance. Neither glucose tolerance nor insulin tolerance were affected in WT. Data indicate that BSO might treat misfolded proinsulin-induced glucose intolerance. Future studies should investigate the effect of BSO on proinsulin misfolding and if it improves glucose intolerance in individuals with Mutant Insulin Diabetes of Youth.

Raloxifene Prevents Chemically-Induced Ferroptotic Neuronal Death In Vitro and In Vivo

Ferroptosis, a regulated form of cell death characterized by excessive iron-dependent lipid peroxidation, can be readily induced in cultured cells by chemicals such as erastin and RSL3. Protein disulfide isomerase (PDI) has been identified as an upstream mediator of chemically induced ferroptosis and also a target for ferroptosis protection. In this study, we discovered that raloxifene (RAL), a selective estrogen receptor modulator known for its neuroprotective actions in humans, can effectively inhibit PDI function and provide robust protection against chemically induced ferroptosis in cultured HT22 neuronal cells. Specifically, RAL can bind directly to PDI both in vitro and in intact neuronal cells and inhibit its catalytic activity. Computational modeling analysis reveals that RAL can tightly bind to PDI through forming a hydrogen bond with its His256 residue, and biochemical analysis further shows that when PDI's His256 is mutated to Ala256, RAL loses its inhibition of PDI's catalytic activity. This inhibition of PDI by RAL significantly reduces the dimerization of both the inducible and neuronal nitric oxide synthases and the accumulation of nitric oxide, both of which have recently been shown to play a crucial role in mediating chemically induced ferroptosis through subsequent induction of ROS and lipid-ROS accumulation. In vivo behavioral analysis shows that mice treated with RAL are strongly protected against kainic acid-induced memory deficits and hippocampal neuronal damage. In conclusion, this study demonstrates that RAL is a potent inhibitor of PDI and can effectively prevent chemically induced ferroptosis in hippocampal neurons both in vitro and in vivo. These findings offer a novel estrogen receptor-independent mechanism for RAL's neuroprotective actions in animal models and humans.

Protective effect of 2-hydroxyestrone and 2-hydroxyestradiol against chemically induced hepatotoxicity in vitro and in vivo

Ferroptosis is a form of regulated cell death closely associated with glutathione depletion and accumulation of reactive lipid peroxides. In this study, we seek to determine whether 2-hydroxyestrone (2-OH-E1) and 2-hydroxyestradiol (2-OH-E2), 2 major metabolites of endogenous estrone (E1) and 17β-estradiol (E2) formed by cytochrome P450 in the liver, can protect against erastin- and RSL3-induced ferroptosis in hepatoma cells (H-4-II-E and HuH-7) in vitro and acetaminophen-induced mouse liver injury in vivo. We find that 2-OH-E1 and 2-OH-E2 can protect, in a dose-dependent manner, H-4-II-E hepatoma cells against erastin/RSL3-induced ferroptosis. A similar protective effect of 2-OH-E1 and 2-OH-E2 against erastin- and RSL3-induced ferroptosis is also observed in HuH-7 hepatoma cells. These 2 estrogen metabolites can strongly abrogate erastin- and RSL3-induced accumulation of cellular NO, reactive oxygen species (ROS), and lipid-ROS. Mechanistically, 2-OH-E1 and 2-OH-E2 protect cells against chemically induced ferroptosis by binding to cellular protein disulfide isomerase and then inhibiting its catalytic activity and reducing protein disulfide isomerase-mediated activation (dimerization) of inducible nitric oxide synthase, abrogating cellular NO, ROS, and lipid-ROS accumulation. Animal studies show that 2-OH-E1 and 2-OH-E2 also exhibit strong protection against acetaminophen-induced liver injury in mice. Interestingly, although E1 and E2 have a very weak protective effect in cultured hepatoma cells, they exhibit a similarly strong protective effect as 2-OH-E1 and 2-OH-E2 in vivo, suggesting that the metabolic conversion of E1 and E2 to 2-OH-E1 and 2-OH-E2 contributes importantly to their hepatoprotective effect. This study reveals that 2-OH-E1 and 2-OH-E2 are important endogenous factors for protection against chemically induced liver injury in vivo. SIGNIFICANCE STATEMENT: Ferroptosis is an iron-dependent and lipid reactive oxygen species-dependent form of regulated cell death. Recent evidence has shown that protein disulfide isomerase (PDI) is an important mediator of chemically induced ferroptosis and also a new target for ferroptosis protection. This study shows that 2-hydroxyestrone and 2-hydroxyestradiol are 2 inhibitors of PDI that can strongly protect against chemically induced ferroptotic hepatocyte death in vitro and in vivo. This work supports a PDI-mediated, estrogen receptor-independent mechanism of hepatocyte protection by 2-hydroxyestrone and 2-hydroxyestradiol.

Mechanism of RSL3-induced ferroptotic cell death in HT22 cells: crucial role of protein disulfide isomerase

Protein disulfide isomerase (PDI) was recently shown to be an upstream mediator of erastin-induced, glutathione depletion-associated ferroptosis through its catalysis of nitric oxide synthase (NOS) dimerization and nitric oxide (NO) accumulation. A recent study reported that RSL3, a known ferroptosis inducer and glutathione peroxidase 4 (GPX4) inhibitor, can inhibit thioredoxin reductase 1 (TrxR1). The present study seeks to test the hypothesis that RSL3 may, through its inhibition of TrxR1, facilitate PDI activation ( i. e., in a catalytically active, oxidized state), thereby enhancing RSL3-induced ferroptosis through NOS dimerization and NO accumulation. Using HT22 mouse neuronal cells as an in vitro model, we show that treatment of these cells with RSL3 strongly increases NOS protein levels and that PDI-mediated NOS dimerization is activated by RSL3, resulting in NO accumulation. Mechanistically, we find that PDI is activated in cells treated with RSL3 because of its inhibition of TrxR1, and the activated PDI then catalyzes NOS dimerization, which is followed by the accumulation of cellular NO, ROS and lipid-ROS and ultimately ferroptotic cell death. Genetic or pharmacological inhibition of PDI or TrxR1 partially abrogates RSL3-induced NOS activation and the subsequent accumulation of cellular NO, ROS/lipid-ROS, and ultimately ferroptosis in HT22 cells. The results of this study clearly show that PDI activation resulted from RSL3 inhibition of TrxR1 activity contributes crucially to RSL3-induced ferroptosis in a cell culture model through the PDI→NOS→NO→ROS/lipid-ROS pathway, in addition to its known inhibition of GPX4 activity.

Protection of HT22 neuronal cells against chemically-induced ferroptosis by catechol estrogens: protein disulfide isomerase as a mechanistic target

Ferroptosis is a form of regulated cell death, characterized by excessive iron-dependent lipid peroxidation. Biochemically, ferroptosis can be selectively induced by erastin through glutathione depletion or through inhibition of glutathione peroxidase 4 by RSL3, which leads to accumulation of cytotoxic lipid reactive oxygen species (ROS). Protein disulfide isomerase (PDI) was recently shown to mediate erastin/RSL3-induced ferroptosis and thus also become a new target for protection against chemically-induced ferroptosis. The present study aims to identify endogenous compounds that can protect against erastin/RSL3-induced ferroptotic cell death. We find that 2-hydroxyestrone, 2-hydroxyestradiol, 4-hydroxyestrone and 4-hydroxyestradiol, four major endogenous catechol estrogens, are effective inhibitors of PDI, and can strongly protect against chemically-induced ferroptotic cell death in cultured HT22 mouse hippocampal neuronal cells. The CETSA assay showed that these catechol estrogens can bind to PDI in live cells. PDI knockdown attenuates the protective effect of these catechol estrogens against chemically-induced ferroptosis. Mechanistically, inhibition of PDI's catalytic activity by catechol estrogens abrogates erastin/RSL3-induced dimerization of nitric oxide synthase, thereby preventing the subsequent accumulation of cellular nitric oxide, ROS and lipid-ROS, and ultimately ferroptotic cell death. In addition, joint treatment of cells with catechol estrogens also abrogates erastin/RSL3-induced upregulation of nitric oxide synthase protein levels, which also contributes to the cytoprotective effect of the catechol estrogens. In conclusion, the present study demonstrates that the catechol estrogens are protectors of HT22 neuronal cells against chemically-induced ferroptosis, and inhibition of PDI's catalytic activity by these estrogens contributes to a novel, estrogen receptor-independent mechanism of cytoprotection.

Protein disulfide isomerase plays a crucial role in mediating chemically-induced, glutathione depletion-associated hepatocyte injury in vitro and in vivo

Recently we have shown that protein disulfide isomerase (PDI or PDIA1) is involved in mediating chemically-induced, glutathione (GSH) depletion-associated ferroptotic cell death through NOS activation (dimerization) and NO accumulation. The present study aims to determine the role of PDI in mediating chemically-induced hepatocyte injury in vitro and in vivo and whether PDI inhibitors can effectively protect against chemically-induced hepatocyte injury. We show that during the development of erastin-induced ferroptotic cell death, accumulation of cellular NO, ROS and lipid-ROS follows a sequential order, i.e., cellular NO accumulation first, followed by accumulation of cellular ROS, and lastly cellular lipid-ROS. Cellular NO, ROS and lipid-ROS each play a crucial role in mediating erastin-induced ferroptosis in cultured hepatocytes. In addition, it is shown that PDI is an important upstream mediator of erastin-induced ferroptosis through PDI-mediated conversion of NOS monomer to its dimer, which then leads to accumulation of cellular NO, ROS and lipid-ROS, and ultimately ferroptotic cell death. Genetic manipulation of PDI expression or pharmacological inhibition of PDI function each can effectively abrogate erastin-induced ferroptosis. Lastly, evidence is presented to show that PDI is also involved in mediating acetaminophen-induced liver injury in vivo using both wild-type C57BL/6J mice and hepatocyte-specific PDI conditional knockout (PDIfl/fl Alb-cre) mice. Together, our work demonstrates that PDI is an important upstream mediator of chemically-induced, GSH depletion-associated hepatocyte ferroptosis, and inhibition of PDI can effectively prevent this injury.

Strong Protection by 4-Hydroxyestrone against Erastin-Induced Ferroptotic Cell Death in Estrogen Receptor-Negative Human Breast Cancer Cells: Evidence for Protein Disulfide Isomerase as a Mechanistic Target for Protection

Ferroptosis is a recently identified form of regulated cell death, characterized by excessive iron-dependent lipid peroxidation. Recent studies have demonstrated that protein disulfide isomerase (PDI) is an important mediator of chemically induced ferroptosis and also a new target for protection against ferroptosis-associated cell death. In the present study, we identified that 4-hydroxyestrone (4-OH-E1), a metabolic derivative of endogenous estrogen, is a potent small-molecule inhibitor of PDI, and can strongly protect against chemically induced ferroptotic cell death in the estrogen receptor-negative MDA-MB-231 human breast cancer cells. Pull-down and CETSA assays demonstrated that 4-OH-E1 can directly bind to PDI both in vitro and in intact cells. Computational modeling analysis revealed that 4-OH-E1 forms two hydrogen bonds with PDI His256, which is essential for its binding interaction and thus inhibition of PDI's catalytic activity. Additionally, PDI knockdown attenuates the protective effect of 4-OH-E1 as well as cystamine (a known PDI inhibitor) against chemically induced ferroptosis in human breast cancer cells. Importantly, inhibition of PDI by 4-OH-E1 and cystamine or PDI knockdown by siRNAs each markedly reduces iNOS activity and NO accumulation, which has recently been demonstrated to play an important role in erastin-induced ferroptosis. In conclusion, this study demonstrates that 4-OH-E1 is a novel inhibitor of PDI and can strongly inhibit ferroptosis in human breast cancer cells in an estrogen receptor-independent manner. The mechanistic understanding gained from the present study may also aid in understanding the estrogen receptor-independent cytoprotective actions of endogenous estrogen metabolites in many noncancer cell types.

Type 2 Diabetes in Obesity: A Systems Biology Study on Serum and Adipose Tissue Proteomic Profiles

Obesity is associated with metabolic disorders such as insulin resistance and type 2 diabetes mellitus (T2DM), further increasing an already heightened cardiovascular risk. Here, amongst obese class III bariatric surgery patients, we have investigated the effect of T2DM in serum and in two, same patient, adipose tissue (AT) depots through proteomic profile expression analyses. Serum and AT samples from subcutaneous (SAT) and visceral (VAT) fat were collected during bariatric surgery. Bead-based targeted multiplex assay systems were used to simultaneously detect and quantify multiple targets in serum samples (targeted proteomics) and analyze changes in adipokine serum composition. AT samples were assessed through an untargeted proteomics approach. Through a systems biology analysis of the proteomic data, information on the affected biological pathways was acquired. In obese class III individuals, the presence of T2DM induced a significantly higher systemic release of ghrelin, GLP-1, glucagon, MMP3, BAFF, chitinase 3-like 1, TNF-R1 and TNF-R2, and a lower systemic release of IL-8. SAT and VAT proteomes belonging to the same patient showed significant differences in local protein content. While the proteins upregulated in VAT were indicative of metabolic dysregulation, SAT protein upregulation suggested adequate endocrine regulation. The presence of T2DM significantly affected VAT protein composition through the upregulation of dysregulating metabolic pathways, but SAT protein composition was not significantly modified. Our results show that T2DM induces metabolic dysregulation in obese individuals with changes in systemic marker levels and impairment of proteostasis in VAT but not in SAT.

Protection against glutathione depletion-associated oxidative neuronal death by neurotransmitters norepinephrine and dopamine: Protein disulfide isomerase as a mechanistic target for neuroprotection

Oxidative stress is extensively involved in neurodegeneration. Clinical evidence shows that keeping the mind active through mentally-stimulating physical activities can effectively slow down the progression of neurodegeneration. With increased physical activities, more neurotransmitters would be released in the brain. In the present study, we investigated whether some of the released neurotransmitters might have a beneficial effect against oxidative neurodegeneration in vitro. Glutamate-induced, glutathione depletion-associated oxidative cytotoxicity in HT22 mouse hippocampal neuronal cells was used as an experimental model. We showed that norepinephrine (NE, 50 µM) or dopamine (DA, 50 µM) exerted potent protective effect against glutamate-induced cytotoxicity, but this effect was not observed when other neurotransmitters such as histamine, γ-aminobutyric acid, serotonin, glycine and acetylcholine were tested. In glutamate-treated HT22 cells, both NE and DA significantly suppressed glutathione depletion-associated mitochondrial dysfunction including mitochondrial superoxide accumulation, ATP depletion and mitochondrial AIF release. Moreover, both NE and DA inhibited glutathione depletion-associated MAPKs activation, p53 phosphorylation and GADD45α activation. Molecular docking analysis revealed that NE and DA could bind to protein disulfide isomerase (PDI). In biochemical enzymatic assay in vitro, NE and DA dose-dependently inhibited the reductive activity of PDI. We further revealed that the protective effect of NE and DA against glutamate-induced oxidative cytotoxicity was mediated through inhibition of PDI-catalyzed dimerization of the neuronal nitric oxide synthase. Collectively, the results of this study suggest that NE and DA may have a protective effect against oxidative neurodegeneration through inhibition of protein disulfide isomerase and the subsequent activation of the MAPKs‒p53‒GADD45α oxidative cascade.

Mechanism of Erastin-Induced Ferroptosis in MDA-MB-231 Human Breast Cancer Cells: Evidence for a Critical Role of Protein Disulfide Isomerase

Ferroptosis is a form of regulated cell death resulting predominantly from catastrophic accumulation of lipid reactive oxygen species (ROS). While the antioxidant systems that counter ferroptosis have been well characterized, the mechanism underlying ferroptosis-associated accumulation of lipid ROS remains unclear. In this study, we demonstrated that protein disulfide isomerase (PDI) is a novel mediator of ferroptosis, which is responsible for the accumulation of lipid ROS and ultimately ferroptosis in MDA-MB-231 human breast cancer cells. Treatment with erastin led to a significant increase in inducible nitric oxide synthase (iNOS)-mediated nitric oxide production, which contributes to the accumulation of the death-inducing cellular lipid ROS. Small interfering RNA (siRNA)-mediated PDI knockdown or pharmacological inhibition of PDI’s isomerase activity with cystamine strongly suppressed iNOS dimerization and its catalytic activation, subsequently prevented lipid ROS accumulation, and conferred strong protection against erastin-induced ferroptosis. Remarkably, PDI knockdown in MDA-MB-231 cells also largely abrogated the protective effect of cystamine against erastin-induced ferroptotic cell death. Together, these experimental observations demonstrate a noncanonical role of PDI in ferroptosis, which may serve as a potential therapeutic target for ferroptosis-related diseases.

High-quality reference genome of Fasciola gigantica: Insights into the genomic signatures of transposon-mediated evolution and specific parasitic adaption in tropical regions

Fasciola gigantica and Fasciola hepatica are causative pathogens of fascioliasis, with the widest latitudinal, longitudinal, and altitudinal distribution; however, among parasites, they have the largest sequenced genomes, hindering genomic research. In the present study, we used various sequencing and assembly technologies to generate a new high-quality Fasciola gigantica reference genome. We improved the integration of gene structure prediction, and identified two independent transposable element expansion events contributing to (1) the speciation between Fasciola and Fasciolopsis during the Cretaceous-Paleogene boundary mass extinction, and (2) the habitat switch to the liver during the Paleocene-Eocene Thermal Maximum, accompanied by gene length increment. Long interspersed element (LINE) duplication contributed to the second transposon-mediated alteration, showing an obvious trend of insertion into gene regions, regardless of strong purifying effect. Gene ontology analysis of genes with long LINE insertions identified membrane-associated and vesicle secretion process proteins, further implicating the functional alteration of the gene network. We identified 852 predicted excretory/secretory proteins and 3300 protein-protein interactions between Fasciola gigantica and its host. Among them, copper/zinc superoxide dismutase genes, with specific gene copy number variations, might play a central role in the phase I detoxification process. Analysis of 559 single-copy orthologs suggested that Fasciola gigantica and Fasciola hepatica diverged at 11.8 Ma near the Middle and Late Miocene Epoch boundary. We identified 98 rapidly evolving gene families, including actin and aquaporin, which might explain the large body size and the parasitic adaptive character resulting in these liver flukes becoming epidemic in tropical and subtropical regions.

SARS-CoV-2 and Other Respiratory Viruses: What Does Oxidative Stress Have to Do with It?

The phenomenon of oxidative stress, characterized as an imbalance in the production of reactive oxygen species and antioxidant responses, is a well-known inflammatory mechanism and constitutes an important cellular process. The relationship of viral infections, reactive species production, oxidative stress, and the antiviral response is relevant. Therefore, the aim of this review is to report studies showing how reactive oxygen species may positively or negatively affect the pathophysiology of viral infection. We focus on known respiratory viral infections, especially severe acute respiratory syndrome coronaviruses (SARS-CoVs), in an attempt to provide important information on the challenges posed by the current COVID-19 pandemic. Because antiviral therapies for severe acute respiratory syndrome coronaviruses (e.g., SARS-CoV-2) are rare, knowledge about relevant antioxidant compounds and oxidative pathways may be important for understanding viral pathogenesis and identifying possible therapeutic targets.

Protein disulfide isomerase A1 regulates breast cancer cell immunorecognition in a manner dependent on redox state

Oxidoreductase protein disulphide isomerases (PDI) are involved in the regulation of a variety of biological processes including the modulation of endoplasmic reticulum (ER) stress, unfolded protein response (UPR), ER-mitochondria communication and the balance between pro-survival and pro-death pathways. In the current study the role of the PDIA1 family member in breast carcinogenesis was investigated by measuring ROS generation, mitochondrial membrane disruption, ATP production and HLA-G protein levels on the surface of the cellular membrane in the presence or absence of PDIA1. The results showed that this enzyme exerted pro-apoptotic effects in estrogen receptor (ERα)-positive breast cancer MCF-7 and pro-survival in triple negative breast cancer (TNBC) MDA-MB-231 cells. ATP generation was upregulated in PDIA1-silenced MCF-7 cells and downregulated in PDIA1-silenced MDA-MB-231 cells in a manner dependent on the cellular redox status. Furthermore, MCF-7 and MDA-MB-231 cells in the presence of PDIA1 expressed higher surface levels of the non-classical human leukocyte antigen (HLA-G) under oxidative stress conditions. Evaluation of the METABRIC datasets showed that low PDIA1 and high HLA-G mRNA expression levels correlated with longer survival in both ERα-positive and ERα-negative stage 2 breast cancer patients. In addition, analysis of the PDIA1 vs. the HLA-G mRNA ratio in the subgroup of the living stage 2 breast cancer patients exhibiting low PDIA1 and high HLA-G mRNA levels revealed that the longer the survival time of the ratio was high PDIA1 and low HLA-G mRNA and occurred predominantly in ERα-positive breast cancer patients whereas in the same subgroup of the ERα-negative breast cancer mainly this ratio was low PDIA1 and high HLA-G mRNA. Taken together these results provide evidence supporting the view that PDIA1 is linked to several hallmarks of breast cancer pathways including the process of antigen processing and presentation and tumor immunorecognition.

(+)-Aeroplysinin-1 Modulates the Redox Balance of Endothelial Cells

The bioactive natural compound from marine origin, (+)-aeroplysinin-1, has been shown to exhibit potent anti-inflammatory and anti-angiogenic effects. The aim of the present study was to identify new targets for (+)-aeroplysinin-1 in endothelial cells. The sequential use of 2D-electrophoresis and MALDI-TOF-TOF/MS allowed us to identify several differentially expressed proteins. Four of these proteins were involved in redox processes and were validated by Western blot. The effects of (+)-aeroplysinin-1 were further studied by testing the effects of the treatment with this compound on the activity of several anti- and pro-oxidant enzymes, as well as on transcription factors involved in redox homeostasis. Finally, changes in the levels of total reactive oxygen species and mitochondrial membrane potential induced by endothelial cell treatments with (+)-aeroplysinin-1 were also determined. Taken altogether, these findings show that (+)-aeroplysinin-1 has multiple targets involved in endothelial cell redox regulation.

S-nitrosylation of the IGF-1 receptor disrupts the cell proliferative action of IGF-1

The insulin-like growth factor 1 receptor (IGF-1R) is a disulfide-linked heterotetramer containing two α-subunits and two β-subunits. Earlier studies demonstrate that nitric oxide (NO) can adversely affect IGF-1 action in the central nervous system. It is known that NO can induce S-nitrosylation of the cysteine residues in proteins, thereby partly contributing to the regulation of protein function. In the present study, we sought to determine whether S-nitrosylation of the cysteine residues in IGF-1R is an important post-translational modification that regulates its response to IGF-1. Using cultured SH-SY5Y human neuroblastoma cells as an in vitro model, we found that treatment of cells with S-nitroso-cysteine (SNOC), a NO donor that can nitrosylate the cysteine residues in proteins, induces S-nitrosylation of the β subunit of IGF-1R but not its α-subunit. IGF-1Rβ S-nitrosylation by SNOC is coupled with increased dissociation of the IGF-1R protein complex. In addition, disruption of the IGF-1R function resulting from S-nitrosylation of the IGF-1Rβ subunit is associated with disruption of the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling pathways. Further, we observed that SNOC-induced IGF-1Rβ S-nitrosylation results in a dose-dependent inhibition of cell proliferation and survival. Together, these results suggest that elevated nitrosative stress may result in dysfunction of cellular IGF-1R signaling through S-nitrosylation of the cysteine residues in the IGF-1Rβ subunit, thereby disrupting the downstream PI3K and MAPK signaling functions and ultimately resulting in inhibition of cell proliferation and survival.

Proteomics analysis of human placenta reveals glutathione metabolism dysfunction as the underlying pathogenesis for preeclampsia

Hypertensive disorder in pregnancy (HDP) refers to a series of diseases that cause the hypertension during pregnancy, including HDP, preeclampsia (PE) and eclampsia. This study screens differentially expressed proteins of placenta tissues in PE cases using 2D LC-MS/MS quantitative proteomics strategy. A total of 2281 proteins are quantified, of these, 145 altering expression proteins are successfully screened between PE and control cases (p<0.05). Bioinformatics analysis suggests that these proteins are mainly involved in many biological processes, such as oxidation reduction, mitochondrion organization, and acute inflammatory response. Especially, the glutamine metabolic process related molecules, GPX1, GPX3, SMS, GGCT, GSTK1, NFκB, GSTT2, SOD1 and GCLM, are involved in the switching process from oxidized glutathione (GSSG) conversion to the reduced glutathione (GSH) by glutathione, mercapturic acid and arginine metabolism process. Results of this study revealed that glutathione metabolism disorder of placenta tissues may contribute to the occurrence of PE disease.

Protein disulfide isomerase regulates renal AT1 receptor function and blood pressure in rats

The role and mechanism of renal protein disulfide isomerase (PDI) in blood pressure regulation has not been tested before. Here, we test this possibility in Sprague-Dawley rats. Rats were treated with PDI inhibitor bacitracin (100 mg·kg^-1 ip·day^-1 for 14 days), and then blood pressure and renal angiotensin II type 1 (AT₁) receptor function were determined in anesthetized rats. Renal AT₁ receptor function was determined as the ability of candesartan (an AT₁ receptor blocker) to increase diuresis and natriuresis. A second set of vehicle- and bacitracin-treated rats was used to determine biochemical parameters. Systolic blood pressure as well as diastolic blood pressure increased in bacitracin-treated compared with vehicle-treated rats. Compared with vehicle, bacitracin-treated rats showed increased diuresis and natriuresis in response to candesartan (10-µg iv bolus dose) suggesting higher AT₁ receptor function in these rats. These were associated with higher renin activities in the plasma and renal tissues. Furthermore, urinary 8-isoprostane and kidney injury molecule-1 levels were higher and urinary antioxidant capacity was lower in bacitracin-treated rats. Renal protein carbonyl and nitrotyrosine levels also were higher in bacitracin- compared with vehicle-treated rats, suggesting oxidative stress burden in bacitracin-treated rats. Moreover, PDI activity decreased and its protein levels increased in renal tissues of bacitracin-treated rats. Also, nuclear levels of Nrf2 transcription factor, which regulates redox homeostasis, were decreased in bacitracin-treated rats. Furthermore, tissue levels of Keap1, an Nrf2 inhibitory molecule, and tyrosine 216-phosphorylated GSK3β protein, an Nrf2 nuclear export protein, were increased in bacitracin-treated rats. These results suggest that renal PDI by regulating Keap1-Nrf2 pathway acts as an antioxidant, maintaining redox balance, renal AT₁ receptor function, and blood pressure in rats.

[Effect of methamphetamine exposure on S-nitrosylation of protein disulphide isomerase in PC12 cells]

OBJECTIVE

To study the effect of methamphetamine (METH) exposure on S-nitrosylation of protein disulphide isomerase and the neurotoxicity of METH in PC12 cells.

METHODS

PC12 cells were exposed to different concentrations of METH, and the cell viability was assessed using the cell-counting kit-8. PC12 cells exposed to METH in the presence of the NOS inhibitor N-nitro-L-arginine (L-NNA) were examined for cell viability and S-nitrosylation of protein disulphide isomerase using the biotin-switch method, and the changes in cell morphology were examined with HE staining.

RESULTS

METH exposure obviously decreased the cell viability and increased S-nitrosylation of protein disulphide isomerase, and the effect of METH was obviously inhibited by L-NNA treatment.

CONCLUSION

METH can cause obvious neurotoxicity and promote S-nitrosylation of protein disulphide isomerase in PC12 cells.

Protein disulfide isomerases: Redox connections in and out of the endoplasmic reticulum

Protein disulfide isomerases are thiol oxidoreductase chaperones from thioredoxin superfamily. As redox folding catalysts from the endoplasmic reticulum (ER), their roles in ER-related redox homeostasis and signaling are well-studied. PDIA1 exerts thiol oxidation/reduction and isomerization, plus chaperone effects. Also, substantial evidence indicates that PDIs regulate thiol-disulfide switches in other cell locations such as cell surface and possibly cytosol. Subcellular PDI translocation routes remain unclear and seem Golgi-independent. The list of signaling and structural proteins reportedly regulated by PDIs keeps growing, via thiol switches involving oxidation, reduction and isomerization, S-(de)nytrosylation, (de)glutathyonylation and protein oligomerization. PDIA1 is required for agonist-triggered Nox NADPH oxidase activation and cell migration in vascular cells and macrophages, while PDIA1-dependent cytoskeletal regulation appears a converging pathway. Extracellularly, PDIs crucially regulate thiol redox signaling of thrombosis/platelet activation, e.g., integrins, and PDIA1 supports expansive caliber remodeling during injury repair via matrix/cytoskeletal organization. Some proteins display regulatory PDI-like motifs. PDI effects are orchestrated by expression levels or post-translational modifications. PDI is redox-sensitive, although probably not a mass-effect redox sensor due to kinetic constraints. Rather, the "all-in-one" organization of its peculiar redox/chaperone properties likely provide PDIs with precision and versatility in redox signaling, making them promising therapeutic targets.