Oxidative stress enhances AP-1 and NF-κB-mediated regulation of β2-Glycoprotein I gene expression in hepatoma cells

Redox Balance in Type 2 Diabetes: Therapeutic Potential and the Challenge of Antioxidant-Based Therapy

Oxidative stress is an important factor in the development of type 2 diabetes (T2D) and associated complications. Unfortunately, most clinical studies have failed to provide sufficient evidence regarding the benefits of antioxidants (AOXs) in treating this disease. Based on the known complexity of reactive oxygen species (ROS) functions in both the physiology and pathophysiology of glucose homeostasis, it is suggested that inappropriate dosing leads to the failure of AOXs in T2D treatment. To support this hypothesis, the role of oxidative stress in the pathophysiology of T2D is described, together with a summary of the evidence for the failure of AOXs in the management of diabetes. A comparison of preclinical and clinical studies indicates that suboptimal dosing of AOXs might explain the lack of benefits of AOXs. Conversely, the possibility that glycemic control might be adversely affected by excess AOXs is also considered, based on the role of ROS in insulin signaling. We suggest that AOX therapy should be given in a personalized manner according to the need, which is the presence and severity of oxidative stress. With the development of gold-standard biomarkers for oxidative stress, optimization of AOX therapy may be achieved to maximize the therapeutic potential of these agents.

Binding of AP endonuclease-1 to G-quadruplex DNA depends on the N-terminal domain, Mg2+ and ionic strength

The base excision repair enzyme apurinic/apyrimidinic endonuclease-1 (APE1) is also engaged in transcriptional regulation. APE1 can function in both pathways when the protein binds to a promoter G-quadruplex (G4) bearing an abasic site (modeled with tetrahydrofuran, F) that leads to enzymatic stalling on the non-canonical fold to recruit activating transcription factors. Biochemical and biophysical studies to address APE1's binding and catalytic activity with the vascular endothelial growth factor (VEGF) promoter G4 are lacking, and the present work provides insight on this topic. Herein, the native APE1 was used for cleavage assays, and the catalytically inactive mutant D210A was used for binding assays with double-stranded DNA (dsDNA) versus the native G4 or the G4 with F at various positions, revealing dependencies of the interaction on the cation concentrations K⁺ and Mg²⁺ and the N-terminal domain of the protein. Assays in 0, 1, or 10 mM Mg²⁺ found that dsDNA and G4 substrates required the cation for both binding and catalysis, in which G4 binding increased with [Mg²⁺]. Studies with 50 versus physiological 140 mM K⁺ ions showed that F-containing dsDNA was bound and cleaved by APE1; whereas, the G4s with F were poorly cleaved in low salt and not cleaved at all at higher salt while the binding remained robust. Using Δ33 or Δ61 N-terminal truncated APE1 proteins, the binding and cleavage of dsDNA with F was minimally impacted; in contrast, the G4s required the N-terminus for binding and catalysis is nearly abolished without the N-terminus. With this knowledge, we found APE1 could remodel the F-containing VEGF promoter dsDNA→G4 folds in solution. Lastly, the addition of the G4 ligand pyridostatin inhibited APE1 binding and cleavage of F-containing G4s but not dsDNA. The biological and medicinal chemistry implications of the results are discussed.

Oxidative stress-mediated epigenetic regulation by G-quadruplexes

Many cancer-associated genes are regulated by guanine (G)-rich sequences that are capable of refolding from the canonical duplex structure to an intrastrand G-quadruplex. These same sequences are sensitive to oxidative damage that is repaired by the base excision repair glycosylases OGG1 and NEIL1–3. We describe studies indicating that oxidation of a guanosine base in a gene promoter G-quadruplex can lead to up- and downregulation of gene expression that is location dependent and involves the base excision repair pathway in which the first intermediate, an apurinic (AP) site, plays a key role mediated by AP endonuclease 1 (APE1/REF1). The nuclease activity of APE1 is paused at a G-quadruplex, while the REF1 capacity of this protein engages activating transcription factors such as HIF-1α, AP-1 and p53. The mechanism has been probed by in vitro biophysical studies, whole-genome approaches and reporter plasmids in cellulo. Replacement of promoter elements by a G-quadruplex sequence usually led to upregulation, but depending on the strand and precise location, examples of downregulation were also found. The impact of oxidative stress-mediated lesions in the G-rich sequence enhanced the effect, whether it was positive or negative.

[Ischemia-reperfusion injury after kidney transplantation]

Ischemia-reperfusion injury is an inescapable phenomenon in kidney transplantation. It combines lesional processes of biochemical origin associated with oxydative stress and of immunological origin in connection with the recruitment and activation of innate immunity cells. Histological lesions associate acute tubular necrosis and interstitial œdema, which can progress to interstitial fibrosis. The extent of these lesions depends on donor characteristics (age, expanded criteria donor, etc.) and cold ischemia time. In the short term, ischemia-reperfusion results in delayed recovery of graft function. Cold ischemia time also impacts long-term graft survival. Preclinical models, such as murine and porcine models, have furthered understanding of the pathophysiological mechanisms of ischemia-reperfusion injury. Due to its renal anatomical proximity to humans, the porcine model is relevant to assessment of the molecules administered to a donor or recipient, and also of additives to preservation solutions. Different donor resuscitation and graft perfusion strategies can be studied. In humans, prevention of ischemia-reperfusion injury is a research subject as concerns donor conditioning, additive molecules in preservation solutions, graft reperfusion modalities and choice of the molecules administered to the recipient. Pending significant advances in research, the goal is to achieve the shortest possible cold ischemia time.

New insights into transcriptional reprogramming during cellular stress

Cellular stress triggers reprogramming of transcription, which is required for the maintenance of homeostasis under adverse growth conditions. Stress-induced changes in transcription include induction of cyto-protective genes and repression of genes related to the regulation of the cell cycle, transcription and metabolism. Induction of transcription is mediated through the activation of stress-responsive transcription factors that facilitate the release of stalled RNA polymerase II and so allow for transcriptional elongation. Repression of transcription, in turn, involves components that retain RNA polymerase II in a paused state on gene promoters. Moreover, transcription during stress is regulated by a massive activation of enhancers and complex changes in chromatin organization. In this Review, we highlight the latest research regarding the molecular mechanisms of transcriptional reprogramming upon stress in the context of specific proteotoxic stress responses, including the heat-shock response, unfolded protein response, oxidative stress response and hypoxia response.

Antiphospholipid antibodies in patients with lupus nephritis: clinical correlations and associations with long-term outcomes

Whether the presence or absence of antiphospholipid antibodies (aPL) in patients with lupus nephritis (LN) is associated with differences in clinical outcomes remains unclear. We reviewed LN patients at a single centre during 2000-2017, and compared the clinical features and long-term outcomes between patients who were seropositive or seronegative for aPL. aPL was detected in 53/149 (35.6%) patients with biopsy-proven LN, and anticardiolipin IgM, anticardiolipin IgG, anti-β2 glycoprotein I and lupus anticoagulant was detected in 18.8%, 18.1%, 10.7% and 8.1%, respectively. Follow-up was 155.8 ± 61.0 months, and was similar between aPL-seropositive and -seronegative patients. aPL seropositivity persisted in 94.3% of patients during remission. aPL-seropositive patients showed inferior patient survival (91% and 85% at 10 and 15 years, respectively, compared to 99% and 95% in aPL-seronegative patients; p = 0.043). Nine (6.0%) patients died during follow-up, including six aPL-seropositive (four thrombotic events and two bleeding complications related to anticoagulation) and three aPL-seronegative patients. aPL seropositivity was associated with more rapid decline in estimated glomerular filtration rate (-1.44 mL/min/year compared to -0.38 mL/min/year in aPL-seronegative patients; p = 0.027) and inferior long-term renal survival (82% and 74% at 10 and 15 years, respectively, compared to 91% and 87% in aPL-seronegative patients; p = 0.034). aPL-seropositive patients also had a higher incidence of thrombotic events and miscarriage (32.1% and 13.2%, respectively, compared to 16.7% and 2.1% in the aPL-seronegative group; p = 0.030 and 0.006). We concluded that aPL seropositivity was associated with inferior long-term patient and renal survival and more frequent thrombotic events and miscarriage in LN patients.

Oxidative post-translational modification of βeta 2-glycoprotein I in the pathophysiology of the anti-phospholipid syndrome

The anti-phospholipid syndrome (APS) is a prothrombotic autoimmune disorder characterized by either thrombosis or pregnancy complications in the setting of persistent anti-phospholipid antibodies (aPL). βeta 2-glycoprotein I (β2-GPI) is the major autoantigen in APS that binds anionic phospholipids as well as specific receptors on platelets and endothelial cells resulting in activation of prothrombotic pathways. β2-GPI consists of 5 Domains that exist in a circular or linear form, with the latter occurring after binding to anionic phospholipids. β2-GPI also undergoes dynamic posttranslational modification between oxidized and free thiol forms. The relationship between posttranslational modification and structural conformation is yet to be definitively clarified. Compared with controls, patients with the APS have higher levels of total β2-GPI and lower levels of free thiol β2-GPI. This raises the possibility of using quantification of β2-GPI posttranslational modification as a redox biomarker in the management and diagnosis of the APS.

Preventive and therapeutic effects of MG132 by activating Nrf2-ARE signaling pathway on oxidative stress-induced cardiovascular and renal injury

So far, cardiovascular and renal diseases have brought us not only huge economic burden but also serious society problems. Since effective therapeutic strategies are still limited, to find new methods for the prevention or therapy of these diseases is important. Oxidative stress has been found to play a critical role in the initiation and progression of cardiovascular and renal diseases. In addition, activation of nuclear-factor-E2-related-factor-2- (Nrf2-) antioxidant-responsive element (ARE) signaling pathway protects cells and tissues from oxidative damage. As a proteasomal inhibitor, MG132 was reported to activate Nrf2 expression and function, which was accompanied with significant preventive and/or therapeutic effect on cardiovascular and renal diseases under most conditions; therefore, MG132 seems to be a potentially effective drug to be used in the prevention of oxidative damage. In this paper, we will summarize the information available regarding the effect of MG132 on oxidative stress-induced cardiovascular and renal damage, especially through Nrf2-ARE signaling pathway.

β2-Glycoprotein I inhibits endothelial cell migration through the nuclear factor κB signalling pathway and endothelial nitric oxide synthase activation

β2-GPI (β2-glycoprotein I) is a plasma glycoprotein ascribed with an anti-angiogenic function; however, the biological role and molecular basis of its action in cell migration remain unknown. The aim of the present study was to assess the contribution of β2-GPI to HAEC (human aortic endothelial cell) migration and the details of its underlying mechanism. Using wound healing and Boyden chamber assays, we found that β2-GPI inhibited endothelial cell migration, which was restored by its neutralizing antibody. NF-κB (nuclear factor κB) inhibitors and lentiviral siRNA (small interfering RNA) silencing of NF-κB significantly attenuated the inhibitory effect of β2-GPI on cell migration. Moreover, β2-GPI was found to induce IκBα (inhibitor of NF-κB) phosphorylation and translocation of p65 and p50. We further demonstrated that mRNA and protein levels of eNOS [endothelial NO (nitric oxide) synthase] and NO production were all increased by β2-GPI and these effects were remarkably inhibited by NF-κB inhibitors and siRNAs of p65 and p50. Furthermore, β2-GPI-mediated inhibition of cell migration was reversed by eNOS inhibitors and eNOS siRNAs. The findings of the present study provide novel insight into the ability of β2-GPI to inhibit endothelial cell migration predominantly through the NF-κB/eNOS/NO signalling pathway, which indicates a potential direction for clinical therapy in vascular diseases.

Novel assays of thrombogenic pathogenicity in the antiphospholipid syndrome based on the detection of molecular oxidative modification of the major autoantigen β2-glycoprotein I

Objective

Beta-2-glycoprotein I (β₂GPI) constitutes the major autoantigen in the antiphospholipid syndrome (APS), a common acquired cause of arterial and venous thrombosis. We recently described the novel observation that β₂GPI may exist in healthy individuals in a free thiol (biochemically reduced) form. The present study was undertaken to quantify the levels of total, reduced, and posttranslationally modified oxidized β₂GPI in APS patients compared to various control groups.

Methods

In a retrospective multicenter analysis, the proportion of β₂GPI with free thiols in serum from healthy volunteers was quantified. Assays for measurement of reduced as well as total circulating β₂GPI were developed and tested in the following groups: APS (with thrombosis) (n = 139), autoimmune disease with or without persistent antiphospholipid antibodies (aPL) but without APS (n = 188), vascular thrombosis without APS or aPL (n = 38), and healthy volunteers (n = 91).

Results

Total β₂GPI was significantly elevated in patients with APS (median 216.2 μg/ml [interquartile range 173.3–263.8]) as compared to healthy subjects (median 178.4 μg/ml [interquartile range 149.4–227.5] [P < 0.0002]) or control patients with autoimmune disease or vascular thrombosis (both P < 0.0001). The proportion of total β₂GPI in an oxidized form (i.e., lacking free thiols) was significantly greater in the APS group than in each of the 3 control groups (all P < 0.0001).

Conclusion

This large retrospective multicenter study shows that posttranslational modification of β₂GPI via thiol-exchange reactions is a highly specific phenomenon in the setting of APS thrombosis. Quantification of posttranslational modifications of β₂GPI in conjunction with standard laboratory tests for APS may offer the potential to more accurately predict the risk of occurrence of a thrombotic event in the setting of APS.

Molecular pathophysiology of the antiphospholipid syndrome: the role of oxidative post-translational modification of beta 2 glycoprotein I

It has been well established that antiphospholipid antibodies and specifically those directed against beta 2 glycoprotein I (β2GPI) are pathogenic for the development of thrombosis in the antiphospholipid syndrome (APS). Several groups have shown that anti-β2GPI antibodies, in complex with β2GPI, elicit effects on blood cells and coagulation-fibrinolysis proteins, which prime the arterial and venous vasculature for the development of thrombosis. However, much less is known about the mechanism initiating the production of autoantibodies against β2GPI, a physiological abundant protein of blood. In the current review, novel findings are presented regarding the structure and oxidative post-translational modifications of β2GPI, which trigger the immune response. The majority of circulating β2GPI exists in a form containing unpaired cysteines (free thiols), which constitutes the reduced form of β2GPI. The free thiols exposed on β2GPI are involved in the interaction with platelets and endothelial cells. We propose that this abundant pool of free thiols may serve as an antioxidant reservoir protecting cells or critical molecules from oxidative stress. Oxidation of β2GPI confers an increase in its immunogenicity through a Th1 immunological mechanism. The clinical significance of these observations is that serum from patients with APS, assessed by a novel ELISA assay, have a significant increase in oxidised β2GPI. These findings hold promise, not only for the delineation of the role of β2GPI as an immunological target, but also for the development of improved diagnostic and prognostic assays for APS.