Glutaredoxin 1 mediates the protective effect of steady laminar flow on endothelial cells against oxidative stress-induced apoptosis via inhibiting Bim

Identification and characterization of multidomain monothiol glutaredoxin 3 from diploblastic Hydra

Intracellular antioxidant glutaredoxin controls cell proliferation and survival. Based on the active site, structure, and conserved domain motifs, it is classified into two classes. Class I contains dithiol Grxs with two cysteines in the consensus active site sequence CXXC, while class II has monothiol Grxs with one cysteine residue in the active site. Monothiol Grxs can also have an additional N-terminal thioredoxin (Trx)-like domain. Previously, we reported the characterization of Grx1 from Hydra vulgaris (HvGrx1), which is a dithiol isoform. Here, we report the molecular cloning, expression, analysis, and characterization of another isoform of Grx, which is the multidomain monothiol glutaredoxin-3 from Hydra vulgaris (HvGrx3). It encodes a protein with 303 amino acids and is significantly larger and more divergent than HvGrx1. In-silico analysis revealed that Grx1 and Grx3 have 22.5% and 9.9% identical nucleotide and amino acid sequences, respectively. HvGrx3 has two glutaredoxin domains and a thioredoxin-like domain at its amino terminus, unlike HvGrx1, which has a single glutaredoxin domain. Like other monothiol glutaredoxins, HvGrx3 failed to reduce glutathione-hydroxyethyl disulfide. In the whole Hydra, HvGrx3 was found to be expressed all over the body column, and treatment with H2O2 led to a significant upregulation of HvGrx3. When transfected in HCT116 (human colon cancer cells) cells, HvGrx3 enhanced cell proliferation and migration, indicating that this isoform could be involved in these cellular functions. These transfected cells also tolerate oxidative stress better.

Glutaredoxin-1 promotes lymphangioleiomyomatosis progression through inhibiting Bim-mediated apoptosis via COX2/PGE2/ERK pathway

BACKGROUND

Lymphangioleiomyomatosis (LAM) is a female-predominant interstitial lung disease, characterized by progressive cyst formation and respiratory failure. Clinical treatment with the mTORC1 inhibitor rapamycin could relieve partially the respiratory symptoms, but not curative. It is urgent to illustrate the fundamental mechanisms of TSC2 deficiency to the development of LAM, especially mTORC1-independent mechanisms. Glutaredoxin-1 (Glrx), an essential glutathione (GSH)-dependent thiol-oxidoreductase, maintains redox homeostasis and participates in various processes via controlling protein GSH adducts. Redox signalling through protein GSH adducts in LAM remains largely elusive. Here, we demonstrate the underlying mechanism of Glrx in the pathogenesis of LAM.

METHODS

1. Abnormal Glrx expression in various kinds of human malignancies was identified by the GEPIA tumour database, and the expression of Glrx in LAM-derived cells was detected by real-time quantitative reverse transcription (RT-qPCR) and immunoblot. 2. Stable Glrx knockdown cell line was established to evaluate cellular impact. 3. Cell viability was determined by CCK8 assay. 4. Apoptotic cell number and intracellular reactive oxygen species (ROS) level were quantified by flow cytometry. 5. Cox2 expression and PGE2 production were detected to clarify the mechanism of Bim expression modulated by Glrx. 6. S-glutathionylated p65 was enriched and detected by immunoprecipitation and the direct regulation of Glrx on p65 was determined. 7. The xenograft animal model was established and photon flux was analyzed using IVIS Spectrum.

RESULTS

In LAM, TSC2 negatively regulated abnormal Glrx expression and activation in a mTORC1-independent manner. Knockdown of Glrx increased the expression of Bim and the accumulation of ROS, together with elevated S-glutathionylated proteins, contributing to the induction of apoptotic cell death and inhibited cell proliferation. Knockdown of Glrx in TSC2-deficient LAM cells increased GSH adducts on nuclear factor-kappa B p65, which contributed to a decrease in the expression of Cox2 and the biosynthesis of PGE2. Inhibition of PGE2 metabolism attenuated phosphorylation of ERK, which led to the accumulation of Bim, due to the imbalance of its phosphorylation and proteasome degradation. In xenograft tumour models, knockdown of Glrx in TSC2-deficient LAM cells inhibited tumour growth and increased tumour cell apoptosis.

CONCLUSIONS

Collectively, we provide a novel redox-dependent mechanism in the pathogenesis of LAM and propose that Glrx may be a beneficial strategy for the treatment of LAM or other TSC-related diseases.

Effects of shear stress on vascular endothelial functions in atherosclerosis and potential therapeutic approaches

Different blood flow patterns in the arteries can alter the adaptive phenotype of vascular endothelial cells (ECs), thereby affecting the functions of ECs and are directly associated with the occurrence of lesions in the early stages of atherosclerosis (AS). Atherosclerotic plaques are commonly found at curved or bifurcated arteries, where the blood flow pattern is dominated by oscillating shear stress (OSS). OSS can induce ECs to transform into pro-inflammatory phenotypes, increase cellular inflammation, oxidative stress response, mitochondrial dysfunction, metabolic abnormalities and endothelial permeability, thereby promoting the progression of AS. On the other hand, the straight artery has a stable laminar shear stress (LSS), which promotes the transformation of ECs into an anti-inflammatory phenotype, improves endothelial cell function, thereby inhibits atherosclerotic progression. ECs have the ability to actively sense, integrate, and convert mechanical stimuli by shear stress into biochemical signals that further induces intracellular changes (such as the opening and closing of ion channels, activation and transcription of signaling pathways). Here we not only outline the relationship between functions of vascular ECs and different forms of fluid shear stress in AS, but also aim to provide new solutions for potential atherosclerotic therapies targeting intracellular mechanical transductions.

miRNA in Ischemic Heart Disease and Its Potential as Biomarkers: A Comprehensive Review

Ischemic heart disease (IHD) constitutes the leading global cause of mortality and morbidity. Although significant progress has been achieved in the diagnosis, treatment, and prognosis of IHD, more robust diagnostic biomarkers and therapeutic interventions are still needed to circumvent the increasing incidence of IHD. MicroRNAs (miRNAs) are critical regulators of cardiovascular function and are involved in various facets of cardiovascular biology. While the knowledge of the role of miRNAs in IHD as diagnostic biomarkers has improved, research emphasis on how miRNAs can be effectively used for diagnosis and prognosis of IHD is crucial. This review provides an overview of the biology, therapeutic and diagnostic potential, as well as the caveats of using miRNAs in IHD based on existing research.

Endothelial shear stress signal transduction and atherogenesis: From mechanisms to therapeutics

Atherosclerotic vascular disease and its complications are among the top causes of mortality worldwide. In the vascular lumen, atherosclerotic plaques are not randomly distributed. Instead, they are preferentially localized at the curvature and bifurcations along the arterial tree, where shear stress is low or disturbed. Numerous studies demonstrate that endothelial cell phenotypic change (e.g., inflammation, oxidative stress, endoplasmic reticulum stress, apoptosis, autophagy, endothelial-mesenchymal transition, endothelial permeability, epigenetic regulation, and endothelial metabolic adaptation) induced by oscillatory shear force play a fundamental role in the initiation and progression of atherosclerosis. Mechano-sensors, adaptor proteins, kinases, and transcriptional factors work closely at different layers to transduce the shear stress force from the plasma membrane to the nucleus in endothelial cells, thereby controlling the expression of genes that determine cell fate and phenotype. An in-depth understanding of these mechano-sensitive signaling cascades shall provide new translational strategies for therapeutic intervention of atherosclerotic vascular disease. This review updates the recent advances in endothelial mechano-transduction and its role in the pathogenesis of atherosclerosis, and highlights the perspective of new anti-atherosclerosis therapies through targeting these mechano-regulated signaling molecules.

Protective effect of Glutaredoxin 1 against oxidative stress in lens epithelial cells of age-related nuclear cataracts

Purpose

Glutaredoxin 1 (Grx1) is a key antioxidant protein that catalyzes disulfide redox reactions. In this study, we investigated the expression and protective effect of Grx1 against oxidative stress in nuclear cataracts.

Methods

Human anterior capsule membrane samples were obtained from the eyes of cataract patients (experimental group) and non-cataractous (control group) donors. The levels of Grx1 protein and mRNA expression were investigated. The human lens epithelial (HLE) cell line SRA 01/04 was transfected with Grx1-containing plasmid or Grx1 small interfering RNA, and cultured under H₂O₂ treatment, mimicking oxidative stress conditions. Cell counts, clone formation, cell apoptosis, cell cycle, and levels of oxidized glutathione disulfide and cellular reactive oxygen species (ROS) were evaluated and quantified.

Results

Protein and mRNA transcript levels of Grx1 were significantly lower in the human anterior capsule membrane of the age-related nuclear (ARN) cataract group than in the control group. Grx1 overexpression protected HLE cells from H₂O₂-induced oxidative damage, including alleviating G1 phase arrest, promoting cell proliferation, reducing cell apoptosis, and decreasing intracellular ROS generation. Furthermore, extracellular-signal-regulated kinase (ERK) phosphorylation in the human anterior capsule membrane of ARN patients was higher in the experimental group than in the control group. Grx1 overexpression reduced the levels of oxidized glutathione disulfide and the phosphorylation of ERK. The administration of an ERK phosphorylation inhibitor, PD98059, induced antioxidant effects in Grx1-silenced cells.

Conclusions

Grx1 expression is downregulated in the human anterior capsule membrane of ARN patients, accompanied by an increase in ERK phosphorylation. Thus, Grx1 can protect HLE cells against oxidative stress.

Thiol-based redox-active proteins as cardioprotective therapeutic agents in cardiovascular diseases

Thiol-based redox compounds, namely thioredoxins (Trxs), glutaredoxins (Grxs) and peroxiredoxins (Prxs), stand as a pivotal group of proteins involved in antioxidant processes and redox signaling. Glutaredoxins (Grxs) are considered as one of the major families of proteins involved in redox regulation by removal of S-glutathionylation and thereby reactivation of other enzymes with thiol-dependent activity. Grxs are also coupled to Trxs and Prxs recycling and thereby indirectly contribute to reactive oxygen species (ROS) detoxification. Peroxiredoxins (Prxs) are a ubiquitous family of peroxidases, which play an essential role in the detoxification of hydrogen peroxide, aliphatic and aromatic hydroperoxides, and peroxynitrite. The Trxs, Grxs and Prxs systems, which reversibly induce thiol modifications, regulate redox signaling involved in various biological events in the cardiovascular system. This review focuses on the current knowledge of the role of Trxs, Grxs and Prxs on cardiovascular pathologies and especially in cardiac hypertrophy, ischemia/reperfusion (I/R) injury and heart failure as well as in the presence of cardiovascular risk factors, such as hypertension, hyperlipidemia, hyperglycemia and metabolic syndrome. Further studies on the roles of thiol-dependent redox systems in the cardiovascular system will support the development of novel protective and therapeutic strategies against cardiovascular diseases.

Glutaredoxin 1 protects neurons from oxygen-glucose deprivation/reoxygenation (OGD/R)-induced apoptosis and oxidative stress via the modulation of GSK-3β/Nrf2 signaling

Increasing evidence has indicated that glutaredoxin 1 (GRX1) is a potent antioxidant protein that promotes cell survival under conditions of oxidative stress. Oxidative stress-induced neuronal injury contributes to cerebral ischemia/reperfusion injury. However, the role of GRX1-mediated antioxidant defense against neuronal damage during cerebral ischemia/reperfusion injury has not been thoroughly investigated. Thus, the objective of this study was to evaluate whether GRX1 protects neurons against oxygen-glucose deprivation/reoxygenation (OGD/R)-evoked oxidative stress injury in an in vitro model of cerebral ischemia/reperfusion injury. Our data revealed that GRX1 was induced by OGD/R treatment in neurons. Functional assays indicated that loss of GRX1 exacerbated OGD/R-induced apoptosis and the generation of reactive oxygen species (ROS), while GRX1 up-regulation protected against OGD/R-evoked neuronal injury. Further investigation revealed that GRX1 promoted the nuclear expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and enhanced transcription of the Nrf2/antioxidant response element (ARE) in GOD/R-exposed neurons. Furthermore, GRX1 promoted the activation of Nrf2/ARE associated with the modulation of glycogen synthase kinase-3β (GSK-3β). GSK-3β inhibition blocked GRX1 knockdown-mediated suppression of Nrf2 activation. Notably, the suppression of Nrf2 partially reversed GRX1-mediated anti-oxidative stress injury in OGD/R-exposed neurons. In summary, these findings indicate that GRX1 protects neurons against OGD/R-induced oxidative stress injury by enhancing Nrf2 activation via the modulation of GSK-3β. Our study suggests that GRX1 is a potential neuroprotective protein that protects against cerebral ischemia/reperfusion injury.

miR-30c-5p acts as a therapeutic target for ameliorating myocardial ischemia-reperfusion injury

Coronary heart disease (CHD) is one of the most vital reasons for death and disability all over the world. miRNA, as a plasma index, is quite valuable for disease screening and prognosis prediction in CHD. Mining the molecular mechanism behind miRNA is also helpful for us to find molecular therapeutic strategies. In this research, we found that the expression of plasma miR-30c-5p in CHD patients was obviously lower than that in the control group (CG), which had a high differential value for CHD. We also discovered that miR-30c-5p was obviously correlated with clinical characteristics of CHD patients such as age, NYHA grade, smoking history, hypertension, hyperlipidemia, etc. In prognosis analysis, the miR-30c-5p expression in patients with poor prognosis was dramatically lower than that in those with good one, and the AUC for predicting poor prognosis of CHD was not lower than 0.850. In addition, we also induced myocardial ischemia/reperfusion (I/R) injury model of H9C2 cells through hypoxia/reoxygenation, and found that H9C2 cells also had abnormally down-regulated miR-30c-5p and up-regulated BCL2-like 11 (BCL2L11). Up-regulating miR-30c-5p or down-regulating BCL2L11 were helpful to improve proliferation and apoptosis of I/R injury model. Mechanically, BCL2L11 was also negatively regulated by miR-30c-5p, and up-regulating the former could cancel the in vitro protective effect of up-regulating the latter on H9C2 cell I/R injury model. In vivo research, up-regulating miR-30c-5p or down-regulating BCL2L11 can improve myocardial injury, histopathological changes and apoptosis in rat I/R model.

Analysis of genes and underlying mechanisms involved in foam cells formation and atherosclerosis development

Background

Foam cells (FCs) play crucial roles in the process of all stages of atherosclerosis. Smooth muscle cells (SMCs) and macrophages are the major sources of FCs. This study aimed to identify the common molecular mechanism in these two types of FCs.

Methods

GSE28829, GSE43292, GSE68021, and GSE54666 were included to identify the differentially expressed genes (DEGs) associated with FCs derived from SMCs and macrophages. Gene Ontology biological process (GO-BP) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed by using the DAVID database. The co-regulated genes associated with the two origins of FCs were validated (GSE9874), and their expression in vulnerable atherosclerosis plaques (GSE120521 and GSE41571) was assessed.

Results

A total of 432 genes associated with FCs derived from SMCs (SMC-FCs) and 81 genes associated with FCs derived from macrophages (M-FCs) were identified, and they were mainly involved in lipid metabolism, inflammation, cell cycle/apoptosis. Furthermore, three co-regulated genes associated with FCs were identified: GLRX, RNF13, and ABCA1. These three common genes showed an increased tendency in unstable or ruptured plaques, although in some cases, no statistically significant difference was found.

Conclusions

DEGs related to FCs derived from SMCs and macrophages have contributed to the understanding of the molecular mechanism underlying the formation of FCs and atherosclerosis. GLRX, RNF13, and ABCA1 might be potential targets for atherosclerosis treatment.

Role of Glutaredoxin-1 and Glutathionylation in Cardiovascular Diseases

Cardiovascular diseases are the leading cause of death worldwide, and as rates continue to increase, discovering mechanisms and therapeutic targets become increasingly important. An underlying cause of most cardiovascular diseases is believed to be excess reactive oxygen or nitrogen species. Glutathione, the most abundant cellular antioxidant, plays an important role in the body’s reaction to oxidative stress by forming reversible disulfide bridges with a variety of proteins, termed glutathionylation (GSylation). GSylation can alter the activity, function, and structure of proteins, making it a major regulator of cellular processes. Glutathione-protein mixed disulfide bonds are regulated by glutaredoxins (Glrxs), thioltransferase members of the thioredoxin family. Glrxs reduce GSylated proteins and make them available for another redox signaling cycle. Glrxs and GSylation play an important role in cardiovascular diseases, such as myocardial ischemia and reperfusion, cardiac hypertrophy, peripheral arterial disease, and atherosclerosis. This review primarily concerns the role of GSylation and Glrxs, particularly glutaredoxin-1 (Glrx), in cardiovascular diseases and the potential of Glrx as therapeutic agents.

Insulin‑receptor substrate 1 protects against injury in endothelial cell models of ox‑LDL‑induced atherosclerosis by inhibiting ER stress/oxidative stress‑mediated apoptosis and activating the Akt/FoxO1 signaling pathway

Oxidized low‑density lipoprotein (ox‑LDL)‑induced endothelial cell (EC) injury is a risk factor for atherosclerosis. Therefore, the present study aimed to investigate the effects of insulin‑receptor substrate 1 (IRS‑1) on injury to ox‑LDL‑exposed ECs. For this purpose, thoracic aorta tissues were isolated from rats and cultured to obtain ECs, which were then identified using immunohistochemical staining. IRS‑1 overexpression plasmid (pcDNA3.1‑IRS‑1) and IRS‑1‑small interfering RNA were synthesized and transfected into ECs pre‑exposed to ox‑LDL. MTT and TUNEL assays were performed to evaluate the cell proliferative activity and apoptosis. Intracellular reactive oxygen species (ROS) production was determined by a flow cytometry assay. Reverse transcription‑quantitative PCR was conducted to measure the peroxisome proliferator‑activated receptor gamma co‑activator 1 alpha (Ppargcla), phosphoenolpyruvate carboxykinase 1 (Pck1) and glucose‑6‑phosphatase catalytic subunit (G6pc) gene transcription levels. Western blot analysis was then performed to determine the IRS‑1, forkhead box O1 (FoxO1), phosphorylated (p‑)FoxO1, 78‑kDa glucose‑regulated protein (GRP78), p‑eukaryotic translation initiation factor 2A (eIF2α), CHOP, Akt and p‑Akt expression levels. Immunofluorescence staining was used to evaluate p‑FoxO1 nuclear localization. The results indicated that IRS‑1 significantly enhanced the proliferative activity, whereas it inhibited the apoptosis of ECs in a model of ox‑LDL‑induced atherosclerosis compared with ECs without IRS‑1 treatment (P<0.05). IRS‑1 significantly decreased the p‑FoxO1/FoxO1 ratio compared with ECs without ox‑LDL treatment (P<0.05). IRS‑1 significantly downregulated the expression of ER stress biomarkers, including GRP78, CHOP and the p‑eIF2α/eIF2α ratio in ox‑LDL‑exposed ECs compared with ECs without ISR‑1 treatment (P<0.05). IRS‑1 significantly reduced the intracellular ROS levels in the EC models of ox‑LDL‑induced atherosclerosis compared with ECs without IRS‑1 treatment (P<0.05). Moreover, IRS‑1 promoted the phosphorylation of Akt in the EC models of ox‑LDL‑induced atherosclerosis. IRS‑1 also significantly suppressed the transcription of atherosclerosis‑associated genes in ox‑LDL‑exposed ECs compared with ECs without IRS‑1 treatment (P<0.05). Furthermore, IRS‑1 significantly increased the cytoplasmic localization of p‑FoxO1 in EC models of ox‑LDL‑induced atherosclerosis. On the whole, the findings of the present study demonstrate that IRS‑1 exerts protective effects in an EC model of ox‑LDL‑induced atherosclerosis by inhibiting ER stress/oxidative stress‑mediated apoptosis and activating the Akt/FoxO1 signaling pathway.

Role of rockfish (Sebastes schlegelii) glutaredoxin 1 in innate immunity, and alleviation of cellular oxidative stress: Insights into localization, molecular characteristics, transcription, and function

Glutaredoxins are a group of heat stable oxidoreductases ubiquitously found in prokaryotes and eukaryotes. They are widely known for GSH (glutathione)-dependent protein disulfide reduction and cellular redox homeostasis. This study was performed to identify and characterize rockfish (Sebastes schlegelii) glutaredoxin 1 (SsGrx1) at molecular, transcriptional, and functional levels. The coding sequence of SsGrx1 was 318 bp in length and encoded a protein containing 106 amino acids. The molecular weight and theoretical isoelectric point of the putative SsGrx1 protein were 11.6 kDa and 6.71 kDa, respectively. The amino acid sequence of SsGrx1 comprised a CPYC redox active motif surrounded by several conserved GSH binding sites. The modeled protein structure was found to consist of five α-helices and four β-sheets, similar to human Grx1. SsGrx1 showed a tissue specific expression in all the tissues tested, with the highest expression in the kidney. Immune stimulation by lipopolysaccharides (LPS), polyinosinic:polycytidylic acid (polyI:C), and Streptococcus iniae (S. iniae) could significantly modulate the SsGrx1 expression pattern in the blood and gills. Analysis of its subcellular localization disclosed that SsGrx1 was prominently localized in the cytosol. Recombinant SsGrx1 (rSsGrx1) exhibited significant activity in insulin disulfide reduction assay and HED (β-Hydroxyethyl Disulfide) assay. Furthermore, transient overexpression of SsGrx1 in FHM (fathead minnow) cells significantly enhanced cell survival upon H₂O₂-induced apoptosis. Collectively, our findings strongly suggest that SsGrx1 plays a crucial role in providing rockfish immune protection against pathogens and oxidative stress.

Effect of microRNA-370 on coronary atherosclerosis and its underlying mechanism

As a global health problem, cardiovascular disease threatens the lives of human beings. It has been reported that microRNAs (miRs) are important in regulating coronary atherosclerosis. In the present study, the expression levels of miR-370 in peripheral blood mononuclear cells of patients with coronary atherosclerosis were significantly increased compared with healthy patients, as demonstrated by reverse transcription-quantitative polymerase chain reaction analysis. Additionally, the target of miR-370 was predicted as Forkhead Box 1 (FOXO1) with bioinformatics, and was confirmed by a dual luciferase assay. The mRNA and protein expression levels of FOXO1 were inhibited by miR-370. Furthermore, the invasion and proliferation of human umbilical vein endothelial cells were promoted by miR-370 via inhibiting the expression of FOXO1. The results obtained in the present study demonstrated that miR-370 served an important role in regulating coronary atherosclerosis via targeting FOXO1. The present data also indicated that miR-370 may be a promising molecular target for treating coronary atherosclerosis.

miR-183-96-182 clusters alleviated ox-LDL-induced vascular endothelial cell apoptosis in vitro by targeting FOXO1

OBJECTIVE

To investigate the role of FOXO1 and miR-183-96-182 clusters in ox-LDL induced endothelial cell apoptosis.

METHODS

FOXO1 overexpression (OE) and knockdown (KD) as well as AKT1 OE in human umbilical vein endothelial cells (HUVECs) and human aortic endothelial cells (HAECs) were achieved by lentiviral transduction. Upregulation of miR-183-5p, miR-182-5p or miR-96-5p was mimicked by agomir treatment. FOXO1 gene transcription was monitored by FOXO1 promotor reporter assay. Cell apoptosis in culture was monitored by TiterTACS in situ detection. Regulation of FOXO1 gene expression by an miRNA targeting mechanism was monitored by AGO2-RNA immunoprecipitation assay.

RESULTS

FOXO1 mRNA and protein expression levels in ox-LDL treated HUVECs or HAECs were significantly upregulated due to transcriptional and miRNA targeting mechanisms. MiR-183-5p, miR-182-5p and miR-96-5p expression levels in HUVECs or HAECs were significantly reduced by ox-LDL treatment, the overexpression of which by agomir treatment partially reduced the FOXO1 mRNA/protein expression levels and cell apoptosis which was upregulated by ox-LDL treatment. FOXO1 overexpression antagonized the effect of the agomir treatment indicated above. MiR-183-5p, miR-182-5p and miR-96-5p agomir treatment partially rescued the FOXO1 pSer256/total FOXO1 protein ratio and the AKT1 pSer473 level that were reduced by ox-LDL treatment in the HUVECs or HAECs. AKT1 overexpression significantly reduced FOXO1 protein expression, increased miR-182-5p and miR-183-5p expression, and partially alleviated ox-LDL induced HUVEC or HAEC apoptosis in an miR-183-5p and miR-182-5p-dependent manner.

CONCLUSION

miR-183-96-182 clusters could partially alleviate ox-LDL-induced apoptosis in HUVECs or HAECs by targeting FOXO1.