Endothelial Cell Redox Regulation of Ischemic Angiogenesis

The significance of glutaredoxins for diabetes mellitus and its complications

Diabetes mellitus is a non-communicable metabolic disease hallmarked by chronic hyperglycemia caused by beta-cell failure. Diabetic complications affect the vasculature and result in macro- and microangiopathies, which account for a significantly increased morbidity and mortality. The rising incidence and prevalence of diabetes is a major global health burden. There are no feasible strategies for beta-cell preservation available in daily clinical practice. Therefore, patients rely on antidiabetic drugs or the application of exogenous insulin. Glutaredoxins (Grxs) are ubiquitously expressed and highly conserved members of the thioredoxin family of proteins. They have specific functions in redox-mediated signal transduction, iron homeostasis and biosynthesis of iron-sulfur (FeS) proteins, and the regulation of cell proliferation, survival, and function. The involvement of Grxs in chronic diseases has been a topic of research for several decades, suggesting them as therapeutic targets. Little is known about their role in diabetes and its complications. Therefore, this review summarizes the available literature on the significance of Grxs in diabetes and its complications. In conclusion, Grxs are differentially expressed in the endocrine pancreas and in tissues affected by diabetic complications, such as the heart, the kidneys, the eye, and the vasculature. They are involved in several pathways essential for insulin signaling, metabolic inflammation, glucose and fatty acid uptake and processing, cell survival, and iron and mitochondrial metabolism. Most studies describe significant changes in glutaredoxin expression and/or activity in response to the diabetic metabolism. In general, mitigated levels of Grxs are associated with oxidative distress, cell damage, and even cell death. The induced overexpression is considered a potential part of the cellular stress-response, counteracting oxidative distress and exerting beneficial impact on cell function such as insulin secretion, cytokine expression, and enzyme activity.

Pretreatment with platelet-rich plasma protects against ischemia-reperfusion induced flap injury by deactivating the JAK/STAT pathway in mice

BACKGROUND

Ischemia-reperfusion (I/R) injury is a major cause of surgical skin flap compromise and organ dysfunction. Platelet-rich plasma (PRP) is an autologous product rich in growth factors, with tissue regenerative potential. PRP has shown promise in multiple I/R-induced tissue injuries, but its effects on skin flap injury remain unexplored.

METHODS

We evaluated the effects of PRP on I/R-injured skin flaps, optimal timing of PRP administration, and the involved mechanisms.

RESULTS

PRP protected against I/R-induced skin flap injury by improving flap survival, promoting blood perfusion and angiogenesis, suppressing oxidative stress and inflammatory response, and reducing apoptosis, at least partly via deactivating Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signalling pathway. PRP given before ischemia displayed overall advantages over that given before reperfusion or during reperfusion. In addition, PRP pretreatment had a stronger ability to reverse I/R-induced JAK/STAT activation and apoptosis than AG490, a specific inhibitor of JAK/STAT signalling.

CONCLUSIONS

This study firstly demonstrates the protective role of PRP against I/R-injured skin flaps through negative regulation of JAK/STAT activation, with PRP pretreatment showing optimal therapeutic effects.

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.

Short-chain acyl-CoA dehydrogenase is a potential target for the treatment of vascular remodelling

OBJECTIVES

Short-chain acyl-CoA dehydrogenase (SCAD), a key enzyme in the fatty acid oxidation process, is not only involved in ATP synthesis but also regulates the production of mitochondrial reactive oxygen species (ROS) and nitric oxide synthesis. The purpose of this study was to investigate the possible role of SCAD in hypertension-associated vascular remodelling.

METHODS

In-vivo experiments were performed on spontaneously hypertensive rats (SHRs, ages of 4 weeks to 20 months) and SCAD knockout mice. The aorta sections of hypertensive patients were used for measurement of SCAD expression. In-vitro experiments with t-butylhydroperoxide (tBHP), SCAD siRNA, adenovirus-SCAD (MOI 90) or shear stress (4, 15 dynes/cm 2 ) were performed using human umbilical vein endothelial cells (HUVECs).

RESULTS

Compared with age-matched Wistar rats, aortic SCAD expression decreased gradually in SHRs with age. In addition, aerobic exercise training for 8 weeks could significantly increase SCAD expression and enzyme activity in the aortas of SHRs while decreasing vascular remodelling in SHRs. SCAD knockout mice also exhibited aggravated vascular remodelling and cardiovascular dysfunction. Likewise, SCAD expression was also decreased in tBHP-induced endothelial cell apoptosis models and the aortas of hypertensive patients. SCAD siRNA caused HUVEC apoptosis in vitro , whereas adenovirus-mediated SCAD overexpression (Ad-SCAD) protected against HUVEC apoptosis. Furthermore, SCAD expression was decreased in HUVECs exposed to low shear stress (4 dynes/cm 2 ) and increased in HUVECs exposed to 15 dynes/cm 2 compared with those under static conditions.

CONCLUSION

SCAD is a negative regulator of vascular remodelling and may represent a novel therapeutic target for vascular remodelling.

A versatile multiplexed assay to quantify intracellular ROS and cell viability in 3D on-a-chip models

Reactive oxygen species (ROS) have different properties and biological functions. They contribute to cell signaling and, in excessive amounts, to oxidative stress (OS). Although ROS is pivotal in a wide number of physiological systems and pathophysiological processes, direct quantification in vivo is quite challenging and mainly limited to in vitro studies. Even though advanced in vitro cell culture techniques, like on-a-chip culture, have overcome the lack of crucial in vivo-like physiological aspects in 2D culture, the majority of in vitro ROS quantification studies are generally performed in 2D. Here we report the development, application, and validation of a multiplexed assay to quantify ROS and cell viability in organ-on-a-chip models. The assay utilizes three dyes to stain live cells for ROS, dead cells, and DNA. Confocal images were analyzed to quantify ROS probes and determine the number of nuclei and dead cells. We found that, in contrast to what has been reported with 2D cell culture, on-a-chip models are more prone to scavenge ROS rather than accumulate them. The assay is sensitive enough to distinguish between different phenotypes of endothelial cells (ECs) based on the level of OS to detect higher level in tumor than normal cells. Our results indicate that the use of physiologically relevant models and this assay could help unravelling the mechanisms behind OS and ROS accumulation. A further step could be taken in data analysis by implementing AI in the pipeline to also analyze images for morphological changes to have an even broader view of OS mechanism.

Loss of Id3 (Inhibitor of Differentiation 3) Increases the Number of IgM-Producing B-1b Cells in Ischemic Skeletal Muscle Impairing Blood Flow Recovery During Hindlimb Ischemia

OBJECTIVE

Neovascularization can maintain and even improve tissue perfusion in the setting of limb ischemia during peripheral artery disease. The molecular and cellular mechanisms mediating this process are incompletely understood. We investigate the potential role(s) for Id3 (inhibitor of differentiation 3) in regulating blood flow in a murine model of hindlimb ischemia (HLI). Approach and Results: HLI was modeled through femoral artery ligation and resection and blood flow recovery was quantified by laser Doppler perfusion imaging. Mice with global Id3 deletion had significantly impaired perfusion recovery at 14 and 21 days of HLI. Endothelial- or myeloid cell-specific deletion of Id3 revealed no effect on perfusion recovery while B-cell-specific knockout of Id3 (Id3BKO) revealed a significant attenuation of perfusion recovery. Flow cytometry revealed no differences in ischemia-induced T cells or myeloid cell numbers at 7 days of HLI, yet there was a significant increase in B-1b cells in Id3BKO. Consistent with these findings, ELISA (enzyme-linked immunoassay) demonstrated increases in skeletal muscle and plasma IgM. In vitro experiments demonstrated reduced proliferation and increased cell death when endothelial cells were treated with conditioned media from IgM-producing B-1b cells and tibialis anterior muscles in Id3BKO mice showed reduced density of total CD31+ and αSMA+CD31+ vessels.

CONCLUSIONS

This study is the first to demonstrate a role for B-cell-specific Id3 in maintaining blood flow recovery during HLI. Results suggest a role for Id3 in promoting blood flow during HLI and limiting IgM-expressing B-1b cell expansion. These findings present new mechanisms to investigate in peripheral artery disease pathogenesis.

The Role of Sirtuin-1 in the Vasculature: Focus on Aortic Aneurysm

Sirtuin-1 (SirT1) is a nicotinamide adenine dinucleotide-dependent deacetylase and the best characterized member of the sirtuins family in mammalians. Sirtuin-1 shuttles between the cytoplasm and the nucleus, where it deacetylates histones and non-histone proteins involved in a plethora of cellular processes, including survival, growth, metabolism, senescence, and stress resistance. In this brief review, we summarize the current knowledge on the anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-senescence effects of SirT1 with an emphasis on vascular diseases. Specifically, we describe recent research advances on SirT1-mediated molecular mechanisms in aortic aneurysm (AA), and how these processes relate to oxidant stress and the heme-oxygenase (HO) system. HO-1 and HO-2 catalyze the rate-limiting step of cellular heme degradation and, similar to SirT1, HO-1 exerts beneficial effects in the vasculature through the activation of anti-oxidant, anti-inflammatory, anti-apoptotic, and anti-proliferative signaling pathways. SirT1 and HO-1 are part of an integrated system for cellular stress tolerance, and may positively interact to regulate vascular function. We further discuss sex differences in HO-1 and SirT1 activity or expression, and the potential interactions between the two proteins, in relation to the progression and severity of AA, as well as the ongoing efforts for translational applications of SirT1 activation and HO-1 induction in the treatment of cardiovascular diseases including AA.

New insights into the role of mitochondria in cardiac microvascular ischemia/reperfusion injury

As reperfusion therapies have become more widely used in acute myocardial infarction patients, ischemia-induced myocardial damage has been markedly reduced, but reperfusion-induced cardiac injury has become increasingly evident. The features of cardiac ischemia-reperfusion (I/R) injury include microvascular perfusion defects, platelet activation and sequential cardiomyocyte death due to additional ischemic events at the reperfusion stage. Microvascular obstruction, defined as a no-reflow phenomenon, determines the infarct zone, myocardial function and peri-operative mortality. Cardiac microvascular endothelial cell injury may occur much earlier and with much greater severity than cardiomyocyte injury. Endothelial cells contain fewer mitochondria than other cardiac cells, and several of the pathological alterations during cardiac microvascular I/R injury involve mitochondria, such as increased mitochondrial reactive oxygen species (mROS) levels and disturbed mitochondrial dynamics. Although mROS are necessary physiological second messengers, high mROS levels induce oxidative stress, endothelial senescence and apoptosis. Mitochondrial dynamics, including fission, fusion and mitophagy, determine the shape, distribution, size and function of mitochondria. These adaptive responses modify extracellular signals and orchestrate intracellular processes such as cell proliferation, migration, metabolism, angiogenesis, permeability transition, adhesive molecule expression, endothelial barrier function and anticoagulation. In this review, we discuss the involvement of mROS and mitochondrial morphofunction in cardiac microvascular I/R injury.

Reactive species-induced microvascular dysfunction in ischemia/reperfusion

Vascular endothelial cells line the inner surface of the entire cardiovascular system as a single layer and are involved in an impressive array of functions, ranging from the regulation of vascular tone in resistance arteries and arterioles, modulation of microvascular barrier function in capillaries and postcapillary venules, and control of proinflammatory and prothrombotic processes, which occur in all segments of the vascular tree but can be especially prominent in postcapillary venules. When tissues are subjected to ischemia/reperfusion (I/R), the endothelium of resistance arteries and arterioles, capillaries, and postcapillary venules become dysfunctional, resulting in impaired endothelium-dependent vasodilator and enhanced endothelium-dependent vasoconstrictor responses along with increased vulnerability to thrombus formation, enhanced fluid filtration and protein extravasation, and increased blood-to-interstitium trafficking of leukocytes in these functionally distinct segments of the microcirculation. The number of capillaries open to flow upon reperfusion also declines as a result of I/R, which impairs nutritive perfusion. All of these pathologic microvascular events involve the formation of reactive species (RS) derived from molecular oxygen and/or nitric oxide. In addition to these effects, I/R-induced RS activate NLRP3 inflammasomes, alter connexin/pannexin signaling, provoke mitochondrial fission, and cause release of microvesicles in endothelial cells, resulting in deranged function in arterioles, capillaries, and venules. It is now apparent that this microvascular dysfunction is an important determinant of the severity of injury sustained by parenchymal cells in ischemic tissues, as well as being predictive of clinical outcome after reperfusion therapy. On the other hand, RS production at signaling levels promotes ischemic angiogenesis, mediates flow-induced dilation in patients with coronary artery disease, and instigates the activation of cell survival programs by conditioning stimuli that render tissues resistant to the deleterious effects of prolonged I/R. These topics will be reviewed in this article.

Important roles of endothelial caveolin-1 in endothelium-dependent hyperpolarization and ischemic angiogenesis in mice

Although increased levels of reactive oxygen species (ROS) are involved in the pathogenesis of cardiovascular diseases, the importance of physiological ROS has also been emerging. We have previously demonstrated that endothelium-derived H₂O₂ is an endothelium-dependent hyperpolarization (EDH) factor and that loss of endothelial caveolin-1 reduces EDH/H₂O₂ in the microcirculation. Caveolin-1 (Cav-1) is a scaffolding/regulatory protein that interacts with diverse signaling pathways, including angiogenesis. However, it remains unclear whether endothelial Cav-1 plays a role in ischemic angiogenesis by modulating EDH/H₂O₂. In the present study, we thus addressed this issue in a mouse model of hindlimb ischemia using male endothelium-specific Cav-1 (eCav-1) knockout (KO) mice. In isometric tension experiments with femoral arteries from eCav-1-KO mice, reduced EDH-mediated relaxations to acetylcholine and desensitization of sodium nitroprusside-mediated endothelium-independent relaxations were noted ( n = 4~6). An ex vivo aortic ring assay also showed that the extent of microvessel sprouting was significantly reduced in eCav-1-KO mice compared with wild-type (WT) littermates ( n = 12 each). Blood flow recovery at 4 wk assessed with a laser speckle flowmeter after femoral artery ligation was significantly impaired in eCav-1-KO mice compared with WT littermates ( n = 10 each) and was associated with reduced capillary density and muscle fibrosis in the legs ( n = 6 each). Importantly, posttranslational protein modifications by reactive nitrogen species and ROS, as evaluated by thiol glutathione adducts and nitrotyrosine, respectively, were both increased in eCav-1-KO mice ( n = 6~7 each). These results indicate that endothelial Cav-1 plays an important role in EDH-mediated vasodilatation and ischemic angiogenesis through posttranslational protein modifications by nitrooxidative stress in mice in vivo. NEW & NOTEWORTHY Although increased levels of reactive oxygen species (ROS) are involved in the pathogenesis of cardiovascular diseases, the importance of physiological ROS has also been emerging. The present study provides a line of novel evidence that endothelial caveolin-1 plays important roles in endothelium-dependent hyperpolarization and ischemic angiogenesis in hindlimb ischemia in mice through posttranslational protein modifications by reactive nitrogen species and ROS in mice in vivo.

Endogenous reduction of miR-185 accelerates cardiac function recovery in mice following myocardial infarction via targeting of cathepsin K

Angiogenesis is critical for re‐establishing the blood supply to the surviving myocardium after myocardial infarction (MI) in patients with acute coronary syndrome (ACS). MicroRNAs are recognised as important epigenetic regulators of endothelial function. The aim of this study was to determine the roles of microRNAs in angiogenesis. Eighteen circulating microRNAs including miR‐185‐5p were differently expressed in plasma from patients with ACS by high‐throughput RNA sequencing. The expressional levels of miR‐185‐5p were dramatically reduced in hearts isolated from mice following MI and cultured human umbilical vein endothelial cells (HUVECs) under hypoxia, as determined by fluorescence in situ hybridisation and quantitative RT‐PCR. Evidence from computational prediction and luciferase reporter gene activity indicated that cathepsin K (CatK) mRNA is a target of miR‐185‐5p. In HUVECs, miR‐185‐5p mimics inhibited cell proliferations, migrations and tube formations under hypoxia, while miR‐185‐5p inhibitors performed the opposites. Further, the inhibitory effects of miR‐185‐5p up‐regulation on cellular functions of HUVECs were abolished by CatK gene overexpression, and adenovirus‐mediated CatK gene silencing ablated these enhancive effects in HUVECs under hypoxia. In vivo studies indicated that gain‐function of miR‐185‐5p by agomir infusion down‐regulated CatK gene expression, impaired angiogenesis and delayed the recovery of cardiac functions in mice following MI. These actions of miR‐185‐5p agonists were mirrored by in vivo knockdown of CatK in mice with MI. Endogenous reductions of miR‐185‐5p in endothelial cells induced by hypoxia increase CatK gene expression to promote angiogenesis and to accelerate the recovery of cardiac function in mice following MI.

Protein disulfide isomerase regulation by nitric oxide maintains vascular quiescence and controls thrombus formation

Essentials Nitric oxide synthesis controls protein disulfide isomerase (PDI) function. Nitric oxide (NO) modulation of PDI controls endothelial thrombogenicity. S-nitrosylated PDI inhibits platelet function and thrombosis. Nitric oxide maintains vascular quiescence in part through inhibition of PDI. SUMMARY: Background Protein disulfide isomerase (PDI) plays an essential role in thrombus formation, and PDI inhibition is being evaluated clinically as a novel anticoagulant strategy. However, little is known about the regulation of PDI in the vasculature. Thiols within the catalytic motif of PDI are essential for its role in thrombosis. These same thiols bind nitric oxide (NO), which is a potent regulator of vessel function. To determine whether regulation of PDI represents a mechanism by which NO controls vascular quiescence, we evaluated the effect of NO on PDI function in endothelial cells and platelets, and thrombus formation in vivo. Aim To assess the effect of S-nitrosylation on the regulation of PDI and other thiol isomerases in the vasculature. Methods and results The role of endogenous NO in PDI activity was evaluated by incubating endothelium with an NO scavenger, which resulted in exposure of free thiols, increased thiol isomerase activity, and enhanced thrombin generation on the cell membrane. Conversely, exposure of endothelium to NO+ carriers or elevation of endogenous NO levels by induction of NO synthesis resulted in S-nitrosylation of PDI and decreased surface thiol reductase activity. S-nitrosylation of platelet PDI inhibited its reductase activity, and S-nitrosylated PDI interfered with platelet aggregation, α-granule release, and thrombin generation on platelets. S-nitrosylated PDI also blocked laser-induced thrombus formation when infused into mice. S-nitrosylated ERp5 and ERp57 were found to have similar inhibitory activity. Conclusions These studies identify NO as a critical regulator of vascular PDI, and show that regulation of PDI function is an important mechanism by which NO maintains vascular quiescence.

Redox regulation of ischemic limb neovascularization - What we have learned from animal studies

Mouse hindlimb ischemia has been widely used as a model to study peripheral artery disease. Genetic modulation of the enzymatic source of oxidants or components of the antioxidant system reveal that physiological levels of oxidants are essential to promote the process of arteriogenesis and angiogenesis after femoral artery occlusion, although mice with diabetes or atherosclerosis may have higher deleterious levels of oxidants. Therefore, fine control of oxidants is required to stimulate vascularization in the limb muscle. Oxidants transduce cellular signaling through oxidative modifications of redox sensitive cysteine thiols. Of particular importance, the reversible modification with abundant glutathione, called S-glutathionylation (or GSH adducts), is relatively stable and alters protein function including signaling, transcription, and cytoskeletal arrangement. Glutaredoxin-1 (Glrx) is an enzyme which catalyzes reversal of GSH adducts, and does not scavenge oxidants itself. Glrx may control redox signaling under fluctuation of oxidants levels. In ischemic muscle increased GSH adducts through Glrx deletion improves in vivo limb revascularization, indicating endogenous Glrx has anti-angiogenic roles. In accordance, Glrx overexpression attenuates VEGF signaling in vitro and ischemic vascularization in vivo. There are several Glrx targets including HIF-1α which may contribute to inhibition of vascularization by reducing GSH adducts. These animal studies provide a caution that excess antioxidants may be counter-productive for treatment of ischemic limbs, and highlights Glrx as a potential therapeutic target to improve ischemic limb vascularization.