Protein disulfide isomerase as a novel target for cyclopentenone prostaglandins: implications for hypoxic ischemic injury

The endoplasmic reticulum participated in drug metabolic toxicity

Covalent binding of reactive metabolites formed by drug metabolic activation with biological macromolecules is considered to be an important mechanism of drug metabolic toxicity. Recent studies indicate that the endoplasmic reticulum (ER) could play an important role in drug toxicity by participating in the metabolic activation of drugs and could be a primarily attacked target by reactive metabolites. In this article, we summarize the generation and mechanism of reactive metabolites in ER stress and their associated cell death and inflammatory cascade, as well as the systematic modulation of unfolded protein response (UPR)-mediated adaptive pathways.

Critical roles of protein disulfide isomerases in balancing proteostasis in the nervous system

Protein disulfide isomerases (PDIs) constitute a family of oxidoreductases promoting redox protein folding and quality control in the endoplasmic reticulum. PDIs catalyze disulfide bond formation, isomerization, and reduction, operating in concert with molecular chaperones to fold secretory cargoes in addition to directing misfolded proteins to be refolded or degraded. Importantly, PDIs are emerging as key components of the proteostasis network, integrating protein folding status with central surveillance mechanisms to balance proteome stability according to cellular needs. Recent advances in the field driven by the generation of new mouse models, human genetic studies, and omics methodologies, in addition to interventions using small molecules and gene therapy, have revealed the significance of PDIs to the physiology of the nervous system. PDIs are also implicated in diverse pathologies, ranging from neurodevelopmental conditions to neurodegenerative diseases and traumatic injuries. Here, we review the principles of redox protein folding in the ER with a focus on current evidence linking genetic mutations and biochemical alterations to PDIs in the etiology of neurological conditions.

TorsinA folding and N-linked glycosylation are sensitive to redox homeostasis

The Endoplasmic Reticulum (ER) is responsible for the folding and post-translational modification of secretory proteins, as well as for triaging misfolded proteins. During folding, there is a complex yet only partially understood interplay between disulfide bond formation, which is an enzyme catalyzed event in the oxidizing environment of the ER, along with other post-translational modifications (PTMs) and chaperone-supported protein folding. Here, we used the glycoprotein torsinA as a model substrate to explore the impact of ER redox homeostasis on PTMs and protein biogenesis. TorsinA is a AAA+ ATPase with unusual oligomeric properties and controversial functions. The deletion of a C-terminal glutamic acid residue (∆E) is associated with the development of Early-Onset Torsion Dystonia, a severe movement disorder. TorsinA differs from other AAA+ ATPases since it is an ER resident, and as a result of its entry into the ER torsinA contains two N-linked glycans and at least one disulfide bond. The role of these PTMs on torsinA biogenesis and function and the identity of the enzymes that catalyze them are poorly defined. Using a yeast torsinA expression system, we demonstrate that a specific protein disulfide isomerase, Pdi1, affects the folding and N-linked glycosylation of torsinA and torsinA∆E in a redox-dependent manner, suggesting that the acquisition of early torsinA folding intermediates is sensitive to perturbed interactions between Cys residues and the quality control machinery. We also highlight the role of specific Cys residues during torsinA biogenesis and demonstrate that torsinA∆E is more sensitive than torsinA when these Cys residues are mutated.

Differential roles of exogenous protein disulfide isomerase A3 on proliferating cell and neuroblast numbers in the normal and ischemic gerbils

INTRODUCTION

We examined the effects of exogenous protein disulfide isomerase A3 (PDIA3) on hippocampal neurogenesis in gerbils under control and ischemic damage.

METHODS

To facilitate the delivery of PDIA3 to the brain, we constructed Tat-PDIA3 protein and administered vehicle (10% glycerol) or Tat-PDIA3 protein once a day for 28 days. On day 24 of vehicle or Tat-PDIA3 treatment, ischemia was transiently induced by occlusion of both common carotid arteries for 5 min.

RESULTS

Administration of Tat-PDIA3 significantly reduced ischemia-induced spontaneous motor activity, and the number of NeuN-positive nuclei in the Tat-PDIA3-treated ischemic group was significantly increased in the CA1 region compared to that in the vehicle-treated ischemic group. Ki67- and DCX-immunoreactive cells were significantly higher in the Tat-PDIA3-treated group compared to the vehicle-treated control group. In vehicle- and Tat-PDIA3-treated ischemic groups, the number of Ki67- and DCX-immunoreactive cells was significantly higher as compared to those in the vehicle- and Tat-PDIA3-treated control groups, respectively. In the dentate gyrus, the numbers of Ki67-immunoreactive cells were comparable between vehicle- and Tat-PDIA3-treated ischemic groups, while more DCX-immunoreactive cells were observed in the Tat-PDIA3-treated group. Transient forebrain ischemia increased the expression of phosphorylated cAMP-response element-binding protein (pCREB) in the dentate gyrus, but the administration of Tat-PDIA3 robustly increased pCREB-positive nuclei in the normal gerbils, but not in the ischemic gerbils. Brain-derived neurotrophic factor (BDNF) mRNA expression was significantly increased in the Tat-PDIA3-treated group compared to that in the vehicle-treated group. Transient forebrain ischemic increased BDNF mRNA levels in both vehicle- and Tat-PDIA3-treated groups, and there were no significant differences between groups.

CONCLUSIONS

These results suggest that Tat-PDIA3 enhances cell proliferation and neuroblast numbers in the dentate gyrus in normal, but not in ischemic gerbils, by increasing BDNF mRNA and phosphorylation of pCREB.

The chemistry, biology and pharmacology of the cyclopentenone prostaglandins

The cyclopentenone prostaglandins (CyPGs) are a small group compounds that are a subset of the eicosanoid superfamily, which are metabolites of arachidonic acid as well as other polyunsaturated fatty acids. The CyPGs are defined by a structural feature, namely, a five-membered carbocyclic ring containing an alfa-beta unsaturated keto group. The two most studied members are PGA₂ and 15d-PGJ₂ (15-deoxy-Δ12,14-prostaglandin J₂); other less studied members are PGA₁, Δ¹²-PGJ₂, and PGJ₂. They are involved in a number of biological activities including the ability to resolve chronic inflammation and the growth and survival of cells, particularly those of cancerous or neurological origin. Also, they can activate the prostaglandin DP2 receptor as well as the ligand-dependent transcription factor PPAR-gamma. Their ability to promote the resolution of chronic inflammation makes it of particular interest to have a good understanding of their actions. Since their discovery, the literature on the CyPGs has greatly expanded both in size and in scope; these reports are covered in the current review.

Simple fluorescent reagents for monitoring disulfide reductase and S-nitroso reductase activities in vitro and in live cells in culture

This study describes the theoretical basis and the methods for the facile synthesis and characterization of four fluorogenic probes, N-amido-O-aminobenzoyl-S-nitrosoglutathione (AOASNOG), N-thioamido-fluoresceinyl-S-nitroso-glutathione (TFSNOG), N,N-di(thioamido-fluoresceinyl)-cystine (DTFCys₂) and N,N-di(thioamido-fluoresceinyl)-homocystine (DTFHCys₂). In addition, the study describes the methodology for the application of these reagents for measuring and imaging of free thiols on cell surfaces as well as their use as pseudo substrates for the thiol reductase and S-nitrosothioldenitrosylase activities of protein disulfide isomerase (PDI) and S-nitrosothiol reductase activity of S-nitrosoglutathione reductase (GSNOR) in vitro and on live cells in culture.

Protein disulfide-isomerase A3 significantly reduces ischemia-induced damage by reducing oxidative and endoplasmic reticulum stress

Ischemia causes oxidative stress in the endoplasmic reticulum (ER), accelerates the accumulation of unfolded and misfolded proteins, and may ultimately lead to neuronal cell apoptosis. In the present study, we investigated the effects of protein disulfide-isomerase A3 (PDIA3), an ER-resident chaperone that catalyzes disulfide-bond formation in a subset of glycoproteins, against oxidative damage in the hypoxic HT22 cell line and against ischemic damage in the gerbil hippocampus. We also confirmed the neuroprotective effects of PDIA3 by using PDIA3-knockout HAP1 cells. The HT22 and HAP1 cell lines showed effective (dose-dependent and time-dependent) penetration and stable expression of the Tat-PDIA3 fusion protein 24 h after Tat-PDIA3 treatment compared to that in the control-PDIA3-treated group. We observed that the fluorescence for both 2',7'-dichlorofluorescein diacetate (DCF-DA) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL), which are markers for the formation of hydrogen peroxide (H₂O₂)-induced reactive oxygen species and apoptosis, respectively, was higher in HAP1 cells than in HT22 cells. The administration of Tat-PDIA3 significantly reduced the (1) DCF-DA and TUNEL fluorescence in HT22 and HAP1 cells, (2) ischemia-induced hyperactivity that was observed 1 day after ischemia/reperfusion, (3) ischemia-induced neuronal damage and glial (astrocytes and microglia) activation that was observed in the hippocampal CA1 region 4 days after ischemia/reperfusion, and (4) lipid peroxidation and nitric oxide generation in the hippocampal homogenates 3-12 h after ischemia/reperfusion. Transient forebrain ischemia significantly elevated the immunoglobulin-binding protein (BiP) and C/EBP-homologous protein (CHOP) mRNA levels in the hippocampus at 12 h and 4 days after ischemia, relative to those in the time-matched sham-operated group. Administration of Tat-PDIA3 ameliorated the ischemia-induced upregulation of BiP mRNA levels versus the Tat peptide- or control-PDIA3-treated groups, and significantly reduced the induction of CHOP mRNA levels, at 12 h or 4 days after ischemia. Collectively, these results suggest that Tat-PDIA3 acts as a neuroprotective agent against ischemia by attenuating oxidative damage and blocking the apoptotic pathway that is related to the unfolded protein response in the ER.

Tat-protein disulfide-isomerase A3: a possible candidate for preventing ischemic damage in the spinal cord

In the present study, we searched for possible candidates that can prevent ischemic damage in the rabbit spinal cord. For this study, we used two-dimensional gel electrophoresis followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, in sham- and ischemia-operated animals. As the level of protein disulfide-isomerase A3 (PDIA3) significantly decreased 3 h after ischemia/reperfusion, we further investigated its possible role against ischemic damage using an in vitro spinal cord cell line and in vivo spinal cord ischemic model. The administration of Tat-PDIA3 significantly reduced the hydrogen peroxide-induced formation of reactive oxygen species and cell death, based on terminal deoxynucleotidyl transferase-mediated biotinylated dUTP nick end labeling and a colorimetric WST-1 assay. Further, Tat-PDIA3 significantly ameliorated the ischemia-induced deficits in motor function, based on Tarlov's criteria, 24-72 h after ischemia/reperfusion, as well as the degeneration of motor neurons in the ventral horn 72 h after ischemia/reperfusion. Tat-PDIA3 administration also reduced the ischemia-induced activation of microglia and lipid peroxidation in the motor neurons 72 h after ischemia/reperfusion. PDIA3 also potentially ameliorated the ischemia-induced increase in oxidative markers in serum and decreased the activity of Cu,Zn-superoxide dismutase, Mn-superoxide dismutase, and glutathione peroxidase in spinal cord homogenates, 24 h and 72 h after ischemia/reperfusion. These results suggest that Tat-PDIA3 could be used to protect spinal cord neurons from ischemic damage, due to its modulatory action on the oxidative/anti-oxidative balance. Tat-PDIA3 could be applicable to protects neurons from the ischemic damage induced by thoracoabdominal aorta obstruction.

Prevention of oxytosis-induced c-Raf down-regulation by (arylthio)cyclopentenone prostaglandins is neuroprotective

Prolonged exposure to high concentrations of glutamate leads to cell type specific glutathione depletion and resulting oxidative stress, known as oxytosis. As a result of glutathione depletion, accumulation of reactive oxygen species and Ca²⁺ influx are increased; however, the specific target of oxytosis has yet to be identified. In the present study, we focused on the effect of glutamate-induced oxidative stress on the extracellular-regulated protein kinase (ERK) pathway using the murine hippocampal HT22 cell line. Although the contribution of the ERK pathway to glutamate-induced oxytosis in HT22 cells is controversial, Western blot analysis revealed that glutamate caused down-regulation of mitogen-activated protein kinase kinase kinase (c-Raf) and a resulting decrease in the phosphorylation of c-Raf, as well as of mitogen-activated protein kinase kinase1/2 (MEK1/2) and ERK1/2, downstream components of the c-Raf/MEK/ERK pathway. Furthermore, neuroprotective (arylthio)cyclopentenone prostaglandins prevented glutamate-induced c-Raf down-regulation and consequently maintained the basal activity of c-Raf and its downstream signaling components. A pull-down assay using biotin-labeled cyclopentenone prostaglandins revealed that they preferentially bound to c-Raf relative to other signaling molecules of the ERK pathway, including Ras, MEK1/2, and ERK. These results suggest that neuroprotective (arylthio)cyclopentenone prostaglandins directly bind to c-Raf protein and protect cells from down-regulation of the c-Raf protein itself, resulting in neuroprotection against oxidative stress.

Early-onset torsion dystonia: a novel high-throughput yeast genetic screen for factors modifying protein levels of torsinAΔE

Dystonia is the third most common movement disorder, but its diagnosis and treatment remain challenging. One of the most severe types of dystonia is early-onset torsion dystonia (EOTD). The best studied and validated EOTD-associated mutation, torsinAΔE, is a deletion of a C-terminal glutamate residue in the AAA+ ATPase torsinA. TorsinA appears to be an endoplasmic reticulum (ER)/nuclear envelope chaperone with multiple roles in the secretory pathway and in determining subcellular architecture. Many functions are disabled in the torsinAΔE variant, and torsinAΔE is also less stable than wild-type torsinA and is a substrate for ER-associated degradation. Nevertheless, the molecular factors involved in the biogenesis and degradation of torsinA and torsinAΔE have not been fully explored. To identify conserved cellular factors that can alter torsinAΔE protein levels, we designed a new high-throughput, automated, genome-wide screen utilizing our validated Saccharomyces cerevisiae torsinA expression system. By analyzing the yeast non-essential gene deletion collection, we identified 365 deletion strains with altered torsinAΔE steady-state levels. One notable hit was EUG1, which encodes a member of the protein disulfide isomerase family (PDIs). PDIs reside in the ER and catalyze the formation of disulfide bonds, mediate protein quality control and aid in nascent protein folding. We validated the role of select human PDIs in torsinA biogenesis in mammalian cells and found that overexpression of PDIs reduced the levels of torsinA and torsinAΔE. Together, our data report the first genome-wide screen to identify cellular factors that alter expression levels of the EOTD-associated protein torsinAΔE. More generally, the identified hits help in dissecting the cellular machinery involved in folding and degrading a torsinA variant, and constitute potential therapeutic factors for EOTD. This screen can also be readily adapted to identify factors impacting the levels of any protein of interest, considerably expanding the applicability of yeast in both basic and applied research.

Life and death in the trash heap: The ubiquitin proteasome pathway and UCHL1 in brain aging, neurodegenerative disease and cerebral Ischemia

The ubiquitin proteasome pathway (UPP) is essential for removing abnormal proteins and preventing accumulation of potentially toxic proteins within the neuron. UPP dysfunction occurs with normal aging and is associated with abnormal accumulation of protein aggregates within neurons in neurodegenerative diseases. Ischemia disrupts UPP function and thus may contribute to UPP dysfunction seen in the aging brain and in neurodegenerative diseases. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1), an important component of the UPP in the neuron, is covalently modified and its activity inhibited by reactive lipids produced after ischemia. As a result, degradation of toxic proteins is impaired which may exacerbate neuronal function and cell death in stroke and neurodegenerative diseases. Preserving or restoring UCHL1 activity may be an effective therapeutic strategy in stroke and neurodegenerative diseases.

A Proteomic Study of Memory After Imprinting in the Domestic Chick

The intermediate and medial mesopallium (IMM) of the domestic chick forebrain has previously been shown to be a memory system for visual imprinting. Learning-related changes occur in certain plasma membrane and mitochondrial proteins in the IMM. Two-dimensional gel electrophoresis/mass spectrometry has been employed to identify more comprehensively learning-related expression of proteins in the membrane-mitochondrial fraction of the IMM 24 h after training. We inquired whether amounts of these proteins in the IMM and a control region (posterior pole of the nidopallium, PPN) are correlated with a behavioral estimate of memory for the imprinting stimulus. Learning-related increases in amounts of the following proteins were found in the left IMM, but not the right IMM or the left or right PPN: (i) membrane cognin; (ii) a protein resembling the P32 subunit of splicing factor SF2; (iii) voltage-dependent anionic channel-1; (iv) dynamin-1; (v) heterogeneous nuclear ribonucleoprotein A2/B1. Learning-related increases in some transcription factors involved in mitochondrial biogenesis were also found, without significant change in mitochondrial DNA copy number. The results indicate that the molecular processes involved in learning and memory underlying imprinting include protein stabilization, increased mRNA trafficking, synaptic vesicle recycling, and specific changes in the mitochondrial proteome.

The point mutation UCH-L1 C152A protects primary neurons against cyclopentenone prostaglandin-induced cytotoxicity: implications for post-ischemic neuronal injury

Cyclopentenone prostaglandins (CyPGs), such as 15-deoxy-Δ(12,14)-prostaglandin J2 (15dPGJ2), are reactive prostaglandin metabolites exerting a variety of biological effects. CyPGs are produced in ischemic brain and disrupt the ubiquitin-proteasome system (UPS). Ubiquitin-C-terminal hydrolase L1 (UCH-L1) is a brain-specific deubiquitinating enzyme that has been linked to neurodegenerative diseases. Using tandem mass spectrometry (MS) analyses, we found that the C152 site of UCH-L1 is adducted by CyPGs. Mutation of C152 to alanine (C152A) inhibited CyPG modification and conserved recombinant UCH-L1 protein hydrolase activity after 15dPGJ2 treatment. A knock-in (KI) mouse expressing the UCH-L1 C152A mutation was constructed with the bacterial artificial chromosome (BAC) technique. Brain expression and distribution of UCH-L1 in the KI mouse was similar to that of wild type (WT) as determined by western blotting. Primary cortical neurons derived from KI mice were resistant to 15dPGJ2 cytotoxicity compared with neurons from WT mice as detected by the WST-1 cell viability assay and caspase-3 and poly ADP ribose polymerase (PARP) cleavage. This protective effect was accompanied with significantly less ubiquitinated protein accumulation and aggregation as well as less UCH-L1 aggregation in C152A KI primary neurons after 15dPGJ2 treatment. Additionally, 15dPGJ2-induced axonal injury was also significantly attenuated in KI neurons as compared with WT. Taken together, these studies indicate that UCH-L1 function is important in hypoxic neuronal death, and the C152 site of UCH-L1 has a significant role in neuronal survival after hypoxic/ischemic injury.