Mechanistic Role of the Calcium-Dependent Protease Calpain in the Endothelial Dysfunction Induced by MPO (Myeloperoxidase)

Myeloperoxidase as a Promising Therapeutic Target after Myocardial Infarction

Coronary artery disease (CAD) and myocardial infarction (MI) remain leading causes of death and disability worldwide. CAD begins with the formation of atherosclerotic plaques within the intimal layer of the coronary arteries, a process driven by persistent arterial inflammation and oxidation. Myeloperoxidase (MPO), a mammalian haem peroxidase enzyme primarily expressed within neutrophils and monocytes, has been increasingly recognised as a key pro-inflammatory and oxidative enzyme promoting the development of vulnerable coronary atherosclerotic plaques that are prone to rupture, and can precipitate a MI. Mounting evidence also implicates a pathogenic role for MPO in the inflammatory process that follows a MI, which is characterised by the rapid infiltration of activated neutrophils into the damaged myocardium and the release of MPO. Excessive and persistent cardiac inflammation impairs normal cardiac healing post-MI, resulting in adverse cardiac outcomes and poorer long-term cardiac function, and eventually heart failure. This review summarises the evidence for MPO as a significant oxidative enzyme contributing to the inappropriate inflammatory responses driving the progression of CAD and poor cardiac healing after a MI. It also details the proposed mechanisms underlying MPO's pathogenic actions and explores MPO as a novel therapeutic target for the treatment of unstable CAD and cardiac damage post-MI.

Role of neutrophil myeloperoxidase in the development and progression of high-altitude pulmonary edema

BACKGROUND

Neutrophil infiltration and hypoxic pulmonary vasoconstriction induced by hypobaric hypoxic stress are vital in high-altitude pulmonary edema (HAPE). Myeloperoxidase (MPO), an important enzyme in neutrophils, is associated with inflammation and oxidative stress and is also involved in the regulation of nitric oxide synthase (NOS), an enzyme that catalyzes the production of the vasodilatory factor nitric oxide (NO). However, the role of neutrophil MPO in HAPE's progression is still uncertain. Therefore, we hypothesize that MPO is involved in the development of HAPE via NOS.

METHODS

In Xining, China (altitude: 2260 m), C57BL/6 N wild-type and mpo-/- mice served as normoxic controls, while a hypobaric chamber simulated 7000 m altitude for hypoxia. L-NAME, a nitric oxide synthase (NOS) inhibitor to inhibit NO production, was the experimental drug, and D-NAME, without NOS inhibitory effects, was the control. After measuring pulmonary artery pressure (PAP), samples were collected and analyzed for blood neutrophils, oxidative stress, inflammation, vasoactive substances, pulmonary alveolar-capillary barrier permeability, and lung tissue morphology.

RESULTS

Wild-type mice's lung injury scores, permeability, and neutrophil counts rose at 24 and 48 h of hypoxia exposure. Under hypoxia, PAP increased from 12.89 ± 1.51 mmHg under normoxia to 20.62 ± 3.33 mmHg significantly in wild-type mice and from 13.24 ± 0.79 mmHg to 16.50 ± 2.07 mmHg in mpo-/- mice. Consistent with PAP, inducible NOS activity, lung permeability, lung injury scores, oxidative stress response, and inflammation showed more significant increases in wild-type mice than in mpo-/- mice. Additionally, endothelial NOS activity and NO levels decreased more pronouncedly in wild-type mice than in mpo-/- mice. NOS inhibition during hypoxia led to more significant increases in PAP, permeability, and lung injury scores compared to the drug control group, especially in wild-type mice.

CONCLUSION

MPO knockout reduces oxidative stress and inflammation to preserve alveolar-capillary barrier permeability and limits the decline in endothelial NOS activity to reduce PAP elevation during hypoxia. MPO inhibition emerges as a prospective therapeutic strategy for HAPE, offering avenues for precise interventions.

The Roles of Neutrophil-Derived Myeloperoxidase (MPO) in Diseases: The New Progress

Myeloperoxidase (MPO) is a heme-containing peroxidase, mainly expressed in neutrophils and, to a lesser extent, in monocytes. MPO is known to have a broad bactericidal ability via catalyzing the reaction of Cl- with H2O2 to produce a strong oxidant, hypochlorous acid (HOCl). However, the overproduction of MPO-derived oxidants has drawn attention to its detrimental role, especially in diseases characterized by acute or chronic inflammation. Broadly speaking, MPO and its derived oxidants are involved in the pathological processes of diseases mainly through the oxidation of biomolecules, which promotes inflammation and oxidative stress. Meanwhile, some researchers found that MPO deficiency or using MPO inhibitors could attenuate inflammation and tissue injuries. Taken together, MPO might be a promising target for both prognostic and therapeutic interventions. Therefore, understanding the role of MPO in the progress of various diseases is of great value. This review provides a comprehensive analysis of the diverse roles of MPO in the progression of several diseases, including cardiovascular diseases (CVDs), neurodegenerative diseases, cancers, renal diseases, and lung diseases (including COVID-19). This information serves as a valuable reference for subsequent mechanistic research and drug development.

The role and mechanism of myeloperoxidase in dermatomyositis

OBJECTIVE

Dermatomyositis (DM) is the best known subtype of idiopathic inflammatory myopathies. The hallmarks of DM muscle pathology including microangiopathy, inflammatory infiltration, and perifascicular atrophy. Recent findings have revealed pathogenetic effects of myeloperoxidase (MPO) by causing oxidative damage and regulating abnormal immunity in multiple disease conditions. In this study, we aimed to explore the role of MPO in the pathogenesis of DM.

METHODS

The peripheral blood mononuclear cell (PBMC) mRNA expression and DNA methylation of MPO were verified using real-time qPCR and bisulfite pyrosequencing, respectively. Plasma MPO levels were measured with enzyme-linked immunosorbent assay, and their relationships with clinical characteristics were analyzed. The expression and distribution of MPO in muscle were tested by immunofluorescence. Purified human native MPO protein was used to stimulate human dermal microvascular endothelial cells (HDMECs) and skeletal muscle myotubes. The cell viability, tube forming capacity, permeability, adhesion molecule expressions in HDMECs, and atrophy and programmed cell death pathways in myotubes were then observed.

RESULTS

MPO gene methylation was decreased, while mRNA expression and plasma levels were increased in DM. Plasma MPO of DM patients was positively correlated with serum creatine kinase (CK). MPO mainly distributed around endomysia capillaries and perifascicular atrophy in DM muscle biopsies, and was co-localized with CD4+, CD8+ T cells and CD19+ B cells. MPO not only could influence the cell viability, tube forming capacity, permeability and expression of adhesion molecules (including ICAM 1, VCAM 1 and E-selectin) of HDMECs, but also could cause atrophy of myotubes.

CONCLUSIONS

Our study disclosed, for the first time, that MPO plays an important role in promoting inflammatory infiltration and inducing muscle damage in DM patients. MPO may be a potential biomarker for DM muscle involvement and MPO targeted drugs may be promising in DM treatment.

Mechanisms of neutrophil extracellular trap in chronic inflammation of endothelium in atherosclerosis

Cardiovascular diseases are a primary cause of morbidity and mortality around the world. In addition, atherosclerosis (AS)-caused cardiovascular disease is the primary cause of death in human diseases, and almost two billion people suffer from carotid AS worldwide. AS is caused by chronic inflammation of the arterial vessel and is initiated by dysfunction of vascular endothelial cells. Neutrophils protect against pathogen invasion because they function as a component of the innate immune system. However, the contribution of neutrophils to cardiovascular disease has not yet been clarified. Neutrophil extracellular traps (NETs) represent an immune defense mechanism that is different from direct pathogen phagocytosis. NETs are extracellular web-like structures activated by neutrophils, and they play important roles in promoting endothelial inflammation via direct or indirect pathways. NETs consist of DNA, histones, myeloperoxidase, matrix metalloproteinases, proteinase 3, etc. Most of the components of NETs have no direct toxic effect on endothelial cells, such as DNA, but they can damage endothelial cells indirectly. In addition, NETs play a critical role in the process of AS; therefore, it is important to clarify the mechanisms of NETs in AS because NETs are a new potential therapeutic target AS. This review summarizes the possible mechanisms of NETs in AS.

Ginsenoside Rg1 ameliorates chronic intermittent hypoxia-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway

Background

As the major pathophysiological feature of obstructive sleep apnea (OSA), chronic intermittent hypoxia (CIH) is vital for the occurrence of cardiovascular complications. The activation of calpain-1 mediates the production of endothelial reactive oxygen species (ROS) and impairs nitric oxide (NO) bioavailability, resulting in vascular endothelial dysfunction (VED). Ginsenoside Rg1 is thought to against endothelial cell dysfunction, but the potential mechanism of CIH-induced VED remains unclear.

Methods

C57BL/6 mice and human coronary artery endothelial cells (HCAECs) were exposed to CIH following knockout or overexpression of calpain-1. The effect of ginsenoside Rg1 on VED, oxidative stress, mitochondrial dysfunction, and the expression levels of calpain-1, PP2A and p-eNOS were detected both in vivo and in vitro.

Results

CIH promoted VED, oxidative stress and mitochondrial dysfunction accompanied by enhanced levels of calpain-1 and PP2A and reduced levels of p-eNOS in mice and cellular levels. Ginsenoside Rg1, calpain-1 knockout, OKA, NAC and TEMPOL treatment protected against CIH-induced VED, oxidative stress and mitochondrial dysfunction, which is likely concomitant with the downregulated protein expression of calpain-1 and PP2A and the upregulation of p-eNOS in mice and cellular levels. Calpain-1 overexpression increased the expression of PP2A, reduced the level of p-eNOS, and accelerated the occurrence and development of VED, oxidative stress and mitochondrial dysfunction in HCAECs exposed to CIH. Moreover, scavengers of O₂ ^{• -}, H₂O₂, complex Ⅰ or mitoK_ATP abolished CIH-induced impairment in endothelial-dependent relaxation.

Conclusion

Ginsenoside Rg1 may alleviate CIH-induced vascular endothelial dysfunction by suppressing the formation of mitochondrial reactive oxygen species through the calpain-1 pathway.

SARS-CoV-2 Spike triggers barrier dysfunction and vascular leak via integrins and TGF-β signaling

Severe COVID-19 is associated with epithelial and endothelial barrier dysfunction within the lung as well as in distal organs. While it is appreciated that an exaggerated inflammatory response is associated with barrier dysfunction, the triggers of vascular leak are unclear. Here, we report that cell-intrinsic interactions between the Spike (S) glycoprotein of SARS-CoV-2 and epithelial/endothelial cells are sufficient to induce barrier dysfunction in vitro and vascular leak in vivo, independently of viral replication and the ACE2 receptor. We identify an S-triggered transcriptional response associated with extracellular matrix reorganization and TGF-β signaling. Using genetic knockouts and specific inhibitors, we demonstrate that glycosaminoglycans, integrins, and the TGF-β signaling axis are required for S-mediated barrier dysfunction. Notably, we show that SARS-CoV-2 infection caused leak in vivo, which was reduced by inhibiting integrins. Our findings offer mechanistic insight into SARS-CoV-2-triggered vascular leak, providing a starting point for development of therapies targeting COVID-19.

Protective effect of Astragaloside IV on chronic intermittent hypoxia-induced vascular endothelial dysfunction through the calpain-1/SIRT1/AMPK signaling pathway

Vascular endothelial dysfunction (VED) is linked with the pathogenesis of obstructive sleep apnea (OSA) comorbidities, such as cardiovascular disease. Astragaloside IV (As-IV) has exhibited significant improvement for endothelial dysfunction. Nonetheless, the protective mechanism is not clear. Therefore, the present study investigated the potential mechanism of As-IV on VED. Calpain-1 knockout and wild-type C57BL/6 mice exposed to chronic intermittent hypoxia (CIH) were established and treated with As-IV (40, 80 mg/kg) for 4 weeks. Human coronary artery endothelial cells (HCAECs) subjected to CIH exposure were pretreated with As-IV, MDL-28170 (calpain-1 inhibitor) and SRT1720 (SIRT1 activator) for 48 h in vitro. The endothelial function, inflammation, oxidative stress and mitochondrial function were measured to evaluate VED. Our data revealed that As-IV treatment ameliorated CIH-induced endothelial-dependent vasomotion and augmented nitric oxide (NO) production. As-IV administration suppressed the secretion of inflammation, oxidative stress and mitochondrial dysfunction. As-IV treatment reduced the expression of calpain-1 and restored the downregulated expression of SIRT1 and Thr¹⁷² AMPK and Ser¹¹⁷⁷ eNOS phosphorylation. The effects of calpain-1 knockout and SRT1720 were similar to the effect of As-IV on VED. These findings demonstrated that As-IV ameliorated VED induced by chronic intermittent hypoxia via the calpain-1/SIRT1/AMPK signaling pathway.

Efficacy of leupeptin in treating ischemia in a rat hind limb model

Prolonged tourniquet use can lead to tissue ischemia and can cause progressive muscle and nerve injuries. Such injuries are accompanied by calpain activation and subsequent Wallerian-like degeneration. Several known inhibitors, including leupeptin, are known to impede the activity of calpain and associated tissue damage. We hypothesize that employment of leupeptin in a rat model of prolonged hind limb ischemia can mitigate muscle and nerve injuries. Sprague-Dawley rats (n = 10) weighing between 300-400 g were employed in this study. Their left hind limbs were subjected to blood flow occlusion for a period of 2-h using a neonatal blood pressure cuff. Five rats were given twice weekly intramuscular leupeptin injections, while the other five received saline. After 2 weeks, the animals were euthanized, their sciatic nerves and gastrocnemius muscles were harvested, fixed, stained, and analyzed using NIH Image J software. The administration of leupeptin resulted in larger gastrocnemius muscle fiber cross-sectional areas for the right (non-tourniquet applied) hindlimb as compared to that treated with the saline (p = 0.0110). However, no statistically significant differences were found between these two groups for the injured left hindlimb (p = 0.1440). With regards to the sciatic nerve cross-sectional areas and sciatic functional index, no differences were detected between the leupeptin and control treated groups for both the healthy and injured hindlimbs. This research provides new insights on how to employ leupeptin to inhibit the degenerative effects of calpain and preserve tissues following ischemia resulting from orthopedic or plastic surgery procedures.

Elevation of Myeloperoxidase Correlates with Disease Severity in Patients with Hantaan Virus Infection

Hantaan orthohantavirus (HTNV) can cause hemorrhagic fever with renal syndrome (HFRS) characterized by acute kidney injury and hemorrhage. Neutrophils are the most abundant innate immune cell and the body's first line of defense against pathogens. Currently, an increasing number of studies have shown that neutrophils may be a mixed blessing in terms of viral infections. However, the role of neutrophils in HFRS patients with HTNV infection has not been fully declared. In this study, we analyzed plasma levels of both myeloperoxidase (MPO) and MPO-DNA in HFRS patients, together with the clinical parameters. Neutrophil-platelet aggregates (NPAs) during the acute and convalescent phases of HFRS were also assessed. The results showed that plasma MPO-DNA levels had no change in different disease phases or severities of HFRS patients. Whereas plasma MPO significantly increased in the acute phase and critical/severe groups of HFRS patients. Furthermore, plasma MPO was positively correlated with inflammatory clinical parameters, such as white blood cell counts, neutrophil counts, and renal injury-related parameters, such as blood urea nitrogen, blood uric acid, and serum creatinine, as well as negatively correlated with and platelet counts. In addition, NPAs increased both in acute and convalescent phase in HFRS patients compared with normal controls. These results suggested that elevated plasma MPO in HFRS patients correlated with disease severity, together with the increases of NPAs in HFRS patients, which may provide new insights into potential role of neutrophils in the pathogenesis of HFRS.

Unexpected Role of MPO-Oxidized LDLs in Atherosclerosis: In between Inflammation and Its Resolution

Inflammation and its resolution are the result of the balance between pro-inflammatory and pro-resolving factors, such as specialized pro-resolving mediators (SPMs). This balance is crucial for plaque evolution in atherosclerosis, a chronic inflammatory disease. Myeloperoxidase (MPO) has been related to oxidative stress and atherosclerosis, and MPO-oxidized low-density lipoproteins (Mox-LDLs) have specific characteristics and effects. They participate in foam cell formation and cause specific reactions when interacting with macrophages and endothelial cells. They also increase the production of intracellular reactive oxygen species (ROS) in macrophages and the resulting antioxidant response. Mox-LDLs also drive macrophage polarization. Mox-LDLs are known to be pro-inflammatory particles. However, in the presence of Mox-LDLs, endothelial cells produce resolvin D1 (RvD1), a SPM. SPMs are involved in the resolution of inflammation by stimulating efferocytosis and by reducing the adhesion and recruitment of neutrophils and monocytes. RvD1 also induces the synthesis of other SPMs. In vitro, Mox-LDLs have a dual effect by promoting RvD1 release and inducing a more anti-inflammatory phenotype macrophage, thereby having a mixed effect on inflammation. In this review, we discuss the interrelationship between MPO, Mox-LDLs, and resolvins, highlighting a new perception of the role of Mox-LDLs in atherosclerosis.

Protein Phosphatase 2A Deficiency in Macrophages Increases Foam Cell Formation and Accelerates Atherosclerotic Lesion Development

Protein phosphatase 2A (PP2A), a crucial serine/threonine phosphatase, has recently been reported to play an important role in cardiovascular disease. Previous studies have hinted that PP2A is involved in atherosclerosis formation, but the associated mechanisms remain poorly understood. In this study, we investigate the role of PP2A in the pathogenesis of atherosclerosis. In human atherosclerotic coronary arteries, we found that the expression and activity of PP2A decreased significantly when compared to non-atherosclerotic arteries. Additional experiments demonstrated that pharmacological inhibition of PP2A aggravated atherosclerosis of ApoE^−/− mice. Considering the central role of macrophages in atherosclerosis, mice with conditional knockout of the PP2A-Cα subunit in myeloid cells were produced to investigate the function of PP2A in macrophages. Results showed that PP2A deficiency in myeloid cells aggravated atherosclerotic lesions in mice. in vitro experiments indicated that PP2A-deficient macrophages had an enhanced ability of lipid uptake and foam cell formation. Mechanistically, the deficiency of the PP2A in macrophages led to an increase in the phosphorylation level of p38, which contributed to the elevated expression of scavenger receptor CD36, a key factor involved in lipoprotein uptake. Our data suggest that PP2A participates in the pathophysiological process of atherosclerosis. The decrease of PP2A expression and activity in macrophages is a crucial determinant for foam cell formation and the initiation of atherosclerosis. Our study may provide a potential novel approach for the treatment of atherosclerosis.

SARS-CoV-2 Spike triggers barrier dysfunction and vascular leak via integrins and TGF-β signaling

Severe COVID-19 is associated with epithelial and endothelial barrier dysfunction within the lung as well as in distal organs. While it is appreciated that an exaggerated inflammatory response is associated with barrier dysfunction, the triggers of this pathology are unclear. Here, we report that cell-intrinsic interactions between the Spike (S) glycoprotein of SARS-CoV-2 and epithelial/endothelial cells are sufficient to trigger barrier dysfunction in vitro and vascular leak in vivo , independently of viral replication and the ACE2 receptor. We identify an S-triggered transcriptional response associated with extracellular matrix reorganization and TGF-β signaling. Using genetic knockouts and specific inhibitors, we demonstrate that glycosaminoglycans, integrins, and the TGF-β signaling axis are required for S-mediated barrier dysfunction. Our findings suggest that S interactions with barrier cells are a contributing factor to COVID-19 disease severity and offer mechanistic insight into SARS-CoV-2 triggered vascular leak, providing a starting point for development of therapies targeting COVID-19 pathogenesis.

Photoreceptor Cell Calcium Dysregulation and Calpain Activation Promote Pathogenic Photoreceptor Oxidative Stress and Inflammation in Prodromal Diabetic Retinopathy

This study tested the hypothesis that diabetes promotes a greater than normal cytosolic calcium level in rod cells that activates a Ca2+-sensitive protease, calpain, resulting in oxidative stress and inflammation, two pathogenic factors of early diabetic retinopathy. Nondiabetic and 2-month diabetic C57Bl/6J and calpain1 knockout (Capn1-/-) mice were studied; subgroups were treated with a calpain inhibitor (CI). Ca2+ content was measured in photoreceptors using Fura-2. Retinal calpain expression was studied by quantitative RT-PCR and immunohistochemistry. Superoxide and expression of inflammatory proteins were measured using published methods. Proteomic analysis was conducted on photoreceptors isolated from untreated diabetic mice or treated daily with CI for 2 months. Cytosolic Ca2+ content was increased twofold in photoreceptors of diabetic mice as compared with nondiabetic mice. Capn1 expression increased fivefold in photoreceptor outer segments of diabetic mice. Pharmacologic inhibition or genetic deletion of Capn1 significantly suppressed diabetes-induced oxidative stress and expression of proinflammatory proteins in retina. Proteomics identified a protein (WW domain-containing oxidoreductase [WWOX]) whose expression was significantly increased in photoreceptors from mice diabetic for 2 months and was inhibited with CI. Knockdown of Wwox using specific siRNA in vitro inhibited increase in superoxide caused by the high glucose. These results suggest that reducing Ca2+ accumulation, suppressing calpain activation, and/or reducing Wwox up-regulation are novel targets for treating early diabetic retinopathy.

microRNA-193-3p attenuates myocardial injury of mice with sepsis via STAT3/HMGB1 axis

Objective

Little is known regarding the functional role of microRNA-193-3p (miR-193-3p) in sepsis. Hence, the aim of the present study was to investigate the effect of miR-193-3p on myocardial injury in mice with sepsis and its mechanism through the regulation of signal transducers and activators of transcription 3 (STAT3).

Methods

The mice model of sepsis was established by cecal ligation and puncture (CLP), septic mice were injected with miR-193-3p agomir, miR-193-3p antagomir or siRNA-STAT3. The expression of miR-193-3p, STAT3 and HMGB1 in the myocardial tissue of septic mice were detected. Cardiac ultrasound, hemodynamics, myocardial injury markers, inflammatory factors and cardiomyocyte apoptosis in septic mice were measured.

Results

MiR-193-3p expression was reduced while STAT3 expression was increased in septic mice. Down-regulated STAT3 or up-regulated miR-193-3p improved cardiac function, attenuated myocardial injury, inflammation and cardiomyocyte apoptosis in septic mice. Knockdown STAT3 reversed the role of inhibited miR-193-3p for mice with sepsis. miR-193-3p targeted STAT3, thereby inhibiting HMGB1 expression.

Conclusion

This study provides evidence that miR-193-3p targets STAT3 expression to reduce HMGB1 expression, thereby reducing septic myocardial damage. MiR-193-3p might be a potential candidate marker and therapeutic target for sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03022-x.

Trained Immunity and Reactivity of Macrophages and Endothelial Cells

Innate immune cells can develop exacerbated immunologic response and long-term inflammatory phenotype following brief exposure to endogenous or exogenous insults, which leads to an altered response towards a second challenge after the return to a nonactivated state. This phenomenon is known as trained immunity (TI). TI is not only important for host defense and vaccine response but also for chronic inflammations such as cardiovascular and metabolic diseases such as atherosclerosis. TI can occur in innate immune cells such as monocytes/macrophages, natural killer cells, endothelial cells (ECs), and nonimmune cells, such as fibroblast. In this brief review, we analyze the significance of TI in ECs, which are also considered as innate immune cells in addition to macrophages. TI can be induced by a variety of stimuli, including lipopolysaccharides, BCG (bacillus Calmette-Guerin), and oxLDL (oxidized low-density lipoprotein), which are defined as risk factors for cardiovascular and metabolic diseases. Furthermore, TI in ECs is functional for inflammation effectiveness and transition to chronic inflammation. Rewiring of cellular metabolism of the trained cells takes place during induction of TI, including increased glycolysis, glutaminolysis, increased accumulation of tricarboxylic acid cycle metabolites and acetyl-coenzyme A production, as well as increased mevalonate synthesis. Subsequently, this leads to epigenetic remodeling, resulting in important changes in chromatin architecture that enables increased gene transcription and enhanced proinflammatory immune response. However, TI pathways and inflammatory pathways are separated to ensure memory stays when inflammation undergoes resolution. Additionally, reactive oxygen species play context-dependent roles in TI. Therefore, TI plays significant roles in EC and macrophage pathology and chronic inflammation. However, further characterization of TI in ECs and macrophages would provide novel insights into cardiovascular disease pathogenesis and new therapeutic targets. Graphic Abstract: A graphic abstract is available for this article.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Circular RNAs are a novel type of non-coding RNAs in ROS regulation, cardiovascular metabolic inflammations and cancers

Circular RNAs (circRNAs) are a novel class of endogenous non-coding RNAs characterized by a covalently closed-loop structure generated through a special type of alternative splicing termed back-splicing. Currently, an increasing body of evidence has demonstrated that 1) majority of circRNAs are evolutionarily conserved across species, stable, and resistant to RNase R degradation, and often exhibit cell-specific, and tissue-specific/developmental-stage-specific expression and can be largely independent of the expression levels of the linear host gene-encoded linear RNAs; 2) the biogenesis of circRNAs via back-splicing is different from the canonical splicing of linear RNAs; 3) circRNA biogenesis is regulated by specific cis-acting elements and trans-acting factors; 4) circRNAs regulate biological and pathological processes by sponging miRNAs, binding to RNA-binding protein (RBP), regulators of splicing and transcription, modifiers of parental gene expression, and regulators of protein translation or being translated into peptides in various diseases; 5) circRNAs have been identified for their enrichment and stability in exosomes and detected in body fluids such as human blood, saliva, and cerebrospinal fluids, suggesting that these exo-circRNAs have potential applications as disease biomarkers and novel therapeutic targets; 6) several circRNAs are regulated by oxidative stress and mediate reactive oxygen species (ROS) production as well as promote ROS-induced cellular death, cell apoptosis, and inflammation; 7) circRNAs have also emerged as important regulators in atherosclerotic cardiovascular disease, metabolic disease, and cancers; 8) the potential mechanisms of several circRNAs have been described in diseases, hinting at their potential applications as novel therapeutic targets. In this highlight, we summarized the current understandings of the biogenesis and functions of circRNAs and their roles in ROS regulation and vascular inflammation-associated with cardiovascular and metabolic disease. (Word count: 272).

Angiotensin II Decreases Endothelial Nitric Oxide Synthase Phosphorylation via AT1R Nox/ROS/PP2A Pathway

Increasing evidences suggest that angiotensin (Ang) II participates in the pathogenesis of endothelial dysfunction (ED) through multiple signaling pathways, including angiotensin type 1 receptor (AT₁R) mediated NADPH oxidase (Nox)/reactive oxygen species (ROS) signal transduction. However, the detailed mechanism is not completely understood. In this study, we reported that AngII/AT₁R-mediated activated protein phosphatase 2A (PP2A) downregulated endothelial nitric oxide synthase (eNOS) phosphorylation via Nox/ROS pathway. AngII treatment reduced the levels of phosphorylation of eNOS Ser1177 and nitric oxide (NO) content along with phosphorylation of PP2Ac (PP2A catalytic subunit) Tyr307, meanwhile increased the PP2A activity and ROS production in human umbilical vein endothelial cells (HUVECs). These changes could be impeded by AT₁R antagonist candesartan (CAN). The pretreatment of 10⁻⁸ M PP2A inhibitor okadaic acid (OA) reversed the levels of eNOS Ser1177 and NO content. Similar effects of AngII on PP2A and eNOS were also observed in the mesenteric arteries of Sprague-Dawley rats subjected to AngII infusion via osmotic minipumps for 2 weeks. We found that the PP2A activity was increased, but the levels of PP2Ac Tyr307 and eNOS Ser1177 as well as NO content were decreased in the mesenteric arteries. The pretreatments of antioxidant N-acetylcysteine (NAC) and apocynin (APO) abolished the drop of the levels of PP2Ac Tyr307 and eNOS Ser1177 induced by AngII in HUVECs. The knockdown of p22phox by small interfering RNA (siRNA) gave rise to decrement of ROS production and increment of the levels of PP2Ac Tyr307 and eNOS Ser1177. These results indicated that AngII/AT₁R pathway activated PP2A by downregulating its catalytic subunit Tyr307 phosphorylation, which relies on the Nox activation and ROS production. In summary, our findings indicate that AngII downregulates PP2A catalytic subunit Tyr307 phosphorylation to activate PP2A via AT₁R-mediated Nox/ROS signaling pathway. The activated PP2A further decreases levels of eNOS Ser1177 phosphorylation and NO content leading to endothelial dysfunction.

Immune landscape of human prostate cancer: immune evasion mechanisms and biomarkers for personalized immunotherapy

BACKGROUND

Despite recent advances in cancer immunotherapy, the efficacy of these therapies for the treatment of human prostate cancer patients is low due to the complex immune evasion mechanisms (IEMs) of prostate cancer and the lack of predictive biomarkers for patient responses.

METHODS

To understand the IEMs in prostate cancer and apply such understanding to the design of personalized immunotherapies, we analyzed the RNA-seq data for prostate adenocarcinoma from The Cancer Genome Atlas (TCGA) using a combination of biclustering, differential expression analysis, immune cell typing, and machine learning methods.

RESULTS

The integrative analysis identified eight clusters with different IEM combinations and predictive biomarkers for each immune evasion cluster. Prostate tumors employ different combinations of IEMs. The majority of prostate cancer patients were identified with immunological ignorance (89.8%), upregulated cytotoxic T lymphocyte-associated protein 4 (CTLA4) (58.8%), and upregulated decoy receptor 3 (DcR3) (51.6%). Among patients with immunologic ignorance, 41.4% displayed upregulated DcR3 expression, 43.26% had upregulated CTLA4, and 11.4% had a combination of all three mechanisms. Since upregulated programmed cell death 1 (PD-1) and/or CTLA4 often co-occur with other IEMs, these results provide a plausible explanation for the failure of immune checkpoint inhibitor monotherapy for prostate cancer.

CONCLUSION

These findings indicate that human prostate cancer specimens are mostly immunologically cold tumors that do not respond well to mono-immunotherapy. With such identified biomarkers, more precise treatment strategies can be developed to improve therapeutic efficacy through a greater understanding of a patient's immune evasion mechanisms.

The Role of Myeloperoxidase in Biomolecule Modification, Chronic Inflammation, and Disease

Significance: The release of myeloperoxidase (MPO) by activated leukocytes is critical in innate immune responses. MPO produces hypochlorous acid (HOCl) and other strong oxidants, which kill bacteria and other invading pathogens. However, MPO also drives the development of numerous chronic inflammatory pathologies, including atherosclerosis, neurodegenerative disease, lung disease, arthritis, cancer, and kidney disease, which are globally responsible for significant patient mortality and morbidity. Recent Advances: The development of imaging approaches to precisely identify the localization of MPO and the molecular targets of HOCl in vivo is an important advance, as typically the involvement of MPO in inflammatory disease has been inferred by its presence, together with the detection of biomarkers of HOCl, in biological fluids or diseased tissues. This will provide valuable information in regard to the cell types responsible for releasing MPO in vivo, together with new insight into potential therapeutic opportunities. Critical Issues: Although there is little doubt as to the value of MPO inhibition as a protective strategy to mitigate tissue damage during chronic inflammation in experimental models, the impact of long-term inhibition of MPO as a therapeutic strategy for human disease remains uncertain, in light of the potential effects on innate immunity. Future Directions: The development of more targeted MPO inhibitors or a treatment regimen designed to reduce MPO-associated host tissue damage without compromising pathogen killing by the innate immune system is therefore an important future direction. Similarly, a partial MPO inhibition strategy may be sufficient to maintain adequate bacterial activity while decreasing the propagation of inflammatory pathologies.

Dietary salt promotes cognitive impairment through tau phosphorylation

Dietary habits and vascular risk factors promote both Alzheimer's disease and cognitive impairment caused by vascular factors^1-3. Furthermore, accumulation of hyperphosphorylated tau, a microtubule-associated protein and a hallmark of Alzheimer's pathology⁴, is also linked to vascular cognitive impairment^5,6. In mice, a salt-rich diet leads to cognitive dysfunction associated with a nitric oxide deficit in cerebral endothelial cells and cerebral hypoperfusion⁷. Here we report that dietary salt induces hyperphosphorylation of tau followed by cognitive dysfunction in mice, and that these effects are prevented by restoring endothelial nitric oxide production. The nitric oxide deficiency reduces neuronal calpain nitrosylation and results in enzyme activation, which, in turn, leads to tau phosphorylation by activating cyclin-dependent kinase 5. Salt-induced cognitive impairment is not observed in tau-null mice or in mice treated with anti-tau antibodies, despite persistent cerebral hypoperfusion and neurovascular dysfunction. These findings identify a causal link between dietary salt, endothelial dysfunction and tau pathology, independent of haemodynamic insufficiency. Avoidance of excessive salt intake and maintenance of vascular health may help to stave off the vascular and neurodegenerative pathologies that underlie dementia in the elderly.

Inhibition of MPO (Myeloperoxidase) Attenuates Endothelial Dysfunction in Mouse Models of Vascular Inflammation and Atherosclerosis

Objective—

Inflammation-driven endothelial dysfunction initiates and contributes to the progression of atherosclerosis, and MPO (myeloperoxidase) has been implicated as a potential culprit. On release by circulating phagocytes, MPO is thought to contribute to endothelial dysfunction by limiting NO bioavailability via formation of reactive oxidants including hypochlorous acid. However, it remains largely untested whether specific pharmacological inhibition of MPO attenuates endothelial dysfunction. We, therefore, tested the ability of a mechanism-based MPO inhibitor, AZM198, to inhibit endothelial dysfunction in models of vascular inflammation.

Approach and Results—

Three models of inflammation were used: femoral cuff, the tandem stenosis model of plaque rupture in Apoe −/− mice, and C57BL/6J mice fed a high-fat, high-carbohydrate diet as a model of insulin resistance. Endothelial dysfunction was observed in all 3 models, and oral administration of AZM198 significantly improved endothelial function in the femoral cuff and tandem stenosis models only. Improvement in endothelial function was associated with decreased arterial MPO activity, determined by the in vivo conversion of hydroethidine to 2-chloroethidium, without affecting circulating inflammatory cytokines or arterial MPO content. Mechanistic studies in Mpo −/− mice confirmed the contribution of MPO to endothelial dysfunction and revealed oxidation of sGC (soluble guanylyl cyclase) as the underlying cause of the observed limited NO bioavailability.

Conclusions—

Pharmacological inhibition of MPO is a potential strategy to limit endothelial dysfunction in vascular inflammation.

Visual Overview—

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Roles of I2PP2A in the downregulation of eNOS Ser1177 phosphorylation by angiotensin II-activated PP2A

The chronic elevation of angiotensin II (Ang II) is an important cause of endothelial dysfunction (ED). The Ang II/type 1 receptor (AT₁R) signaling pathway can cause endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) dysfunction through various mechanisms leading to ED. The modulation of eNOS phosphorylated at Ser1177 is an important mechanism upregulating eNOS activity. Protein phosphatase 2 A (PP2A) has been reported to dephosphorylate eNOS at Ser1177. The PP2A inhibitor 2 protein (I₂^PP2A) is a specific endogenous inhibitor that binds the catalytic subunit of PP2A and directly inhibits PP2A activity. Therefore, we hypothesized that Ang II might attenuate I₂^PP2A expression to activate PP2A, which downregulates eNOS Ser 1177 phosphorylation, leading to eNOS dysfunction. In our study, we used Ang II-treated human umbilical vein endothelial cells (HUVECs) and, found that the eNOS Ser1177 phosphorylation levels were downregulated, the activity of PP2A was increased, and I₂^PP2A expression was decreased. Furthermore, these effects were blocked by candesartan (CAN). The phosphorylation levels of eNOS Ser1177 were decreased after I₂^PP2A was knocked down by specific siRNA but increased after I₂^PP2A overexpression. We also found that the Ang II treatment decreased the association of I₂^PP2A with PP2A but increased the association between PP2A and eNOS. Taken together, our results suggest that Ang II activates PP2A by downregulating the I₂^PP2A expression through the AT₁R signaling pathway leading to the loss of eNOS Ser1177 phosphorylation and ED.

Redox Regulation of Calpains: Consequences on Vascular Function

SIGNIFICANCE

Calpains (CAPNs) are a family of calcium-activated cysteine proteases. The ubiquitous isoforms CAPN1 and CAPN2 have been involved in the maintenance of vascular integrity, but uncontrolled CAPN activation plays a role in the pathogenesis of vascular diseases. Recent Advances: It is well accepted that chronic and acute overproduction of reactive oxygen species (ROS) is associated with the development of vascular diseases. There is increasing evidence that ROS can also affect the CAPN activity, suggesting CAPN as a potential link between oxidative stress and vascular disease.

CRITICAL ISSUES

The physiopathological relevance of ROS in regulating the CAPN activity is not fully understood but seems to involve direct effects on CAPNs, redox modifications of CAPN substrates, as well as indirect effect on CAPNs via changes in Ca²⁺ levels. Finally, CAPNs can also stimulate ROS production; however, data showing in which context ROS are the causes or the consequences of CAPN activation are missing.

FUTURE DIRECTIONS

Detailed characterization of the molecular mechanisms underlying the regulation of the different members of the CAPN system by specific ROS would help understanding the pathophysiological role of CAPN in the modulation of the vascular function. Moreover, given that CAPNs have been found in different cellular compartments such as mitochondria and nucleus as well as in the extracellular space, identification of new CAPN targets as well as their functional consequences would add new insights in the function of these enigmatic proteases.