Involvement of SSAO/VAP-1 in oxygen-glucose deprivation-mediated damage using the endothelial hSSAO/VAP-1-expressing cells as experimental model of cerebral ischemia

Acute high-altitude hypoxia exposure causes neurological deficits via formaldehyde accumulation

INTRODUCTION

Acute high-altitude hypoxia exposure causes multiple adverse neurological consequences. However, the exact mechanisms are still unclear, and there is no targeted treatment with few side effects. Excessive cerebral formaldehyde (FA) impairs numerous functions, and can be eliminated by nano-packed coenzyme Q10 (CoQ10).

AIMS

In this study, we aimed to investigate whether cerebral FA was accumulated after hypobaric hypoxia exposure, and further explored the preventative effect of CoQ10 through FA elimination.

RESULTS

Accumulated cerebral FA was found in C57BL/6 mice after acute high-altitude hypoxia exposure, which resulted in FA metabolic disturbance with the elevation of semicarbazide-sensitive amine oxidase, and declination of aldehyde dehydrogenase-2. Excessive FA was also found to induce neuronal ferroptosis in vivo. Excitingly, administration with CoQ10 for 3 days before acute hypobaric hypoxia reduced cerebral FA accumulation, alleviated subsequent neuronal ferroptosis, and preserved neurological functions.

CONCLUSION

Cerebral FA accumulation mediates neurological deficits under acute hypobaric hypoxia, and CoQ10 supplementation may be a promising preventative strategy for visitors and sojourners at plateau.

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

Endothelium-Targeted Deletion of microRNA-15a/16-1 Promotes Poststroke Angiogenesis and Improves Long-Term Neurological Recovery

RATIONALE

Angiogenesis promotes neurological recovery after stroke and is associated with longer survival of stroke patients. Cerebral angiogenesis is tightly controlled by certain microRNAs (miRs), such as the miR-15a/16-1 cluster, among others. However, the function of the miR-15a/16-1 cluster in endothelium on postischemic cerebral angiogenesis is not known.

OBJECTIVE

To investigate the functional significance and molecular mechanism of endothelial miR-15a/16-1 cluster on angiogenesis in the ischemic brain.

METHODS AND RESULTS

Endothelial cell-selective miR-15a/16-1 conditional knockout (EC-miR-15a/16-1 cKO) mice and wild-type littermate controls were subjected to 1 hour middle cerebral artery occlusion followed by 28-day reperfusion. Deletion of miR-15a/16-1 cluster in endothelium attenuates post-stroke brain infarction and atrophy and improves the long-term sensorimotor and cognitive recovery against ischemic stroke. Endothelium-targeted deletion of the miR-15a/16-1 cluster also enhances post-stroke angiogenesis by promoting vascular remodeling and stimulating the generation of newly formed functional vessels, and increases the ipsilateral cerebral blood flow. Endothelial cell-selective deletion of the miR-15a/16-1 cluster up-regulated the protein expression of pro-angiogenic factors VEGFA (vascular endothelial growth factor), FGF2 (fibroblast growth factor 2), and their receptors VEGFR2 (vascular endothelial growth factor receptor 2) and FGFR1 (fibroblast growth factor receptor 1) after ischemic stroke. Consistently, lentiviral knockdown of the miR-15a/16-1 cluster in primary mouse or human brain microvascular endothelial cell cultures enhanced in vitro angiogenesis and up-regulated pro-angiogenic proteins expression after oxygen-glucose deprivation, whereas lentiviral overexpression of the miR-15a/16-1 cluster suppressed in vitro angiogenesis and down-regulated pro-angiogenic proteins expression. Mechanistically, miR-15a/16-1 translationally represses pro-angiogenic factors VEGFA, FGF2, and their receptors VEGFR2 and FGFR1, respectively, by directly binding to the complementary sequences within 3'-untranslated regions of those messenger RNAs.

CONCLUSIONS

Endothelial miR-15a/16-1 cluster is a negative regulator for postischemic cerebral angiogenesis and long-term neurological recovery. Inhibition of miR-15a/16-1 function in cerebrovascular endothelium may be a legitimate therapeutic approach for stroke recovery.

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.

Blood-brain barrier dysfunction underlying Alzheimer's disease is induced by an SSAO/VAP-1-dependent cerebrovascular activation with enhanced Aβ deposition

Dysfunctions of the vascular system directly contribute to the onset and progression of Alzheimer's disease (AD). The blood-brain barrier (BBB) shows signs of malfunction at early stages of the disease. When Abeta peptide (Aβ) is deposited on brain vessels, it induces vascular degeneration by producing reactive oxygen species and promoting inflammation. These molecular processes are also related to an excessive SSAO/VAP-1 (semicarbazide-sensitive amine oxidase) enzymatic activity, observed in plasma and in cerebrovascular tissue of AD patients. We studied the contribution of vascular SSAO/VAP-1 to the BBB dysfunction in AD using in vitro BBB models. Our results show that SSAO/VAP-1 expression is associated to endothelial activation by altering the release of pro-inflammatory and pro-angiogenic angioneurins, most highly IL-6, IL-8 and VEGF. It is also related to a BBB structure alteration, with a decrease in tight-junction proteins such as zona occludens or claudin-5. Moreover, the BBB function reveals increased permeability and leukocyte adhesion in cells expressing SSAO/VAP-1, as well as an enhancement of the vascular Aβ deposition induced by mechanisms both dependent and independent of the enzymatic activity of SSAO/VAP-1. These results reveal an interesting role of vascular SSAO/VAP-1 in BBB dysfunction related to AD progression, opening a new window in the search of alternative therapeutic targets for fighting AD.

Inhibition of calcium/calmodulin-dependent protein kinase kinase (CaMKK) exacerbates impairment of endothelial cell and blood-brain barrier after stroke

Brain microvascular endothelial cells play an essential role in maintaining blood-brain barrier (BBB) integrity, and disruption of the BBB aggravates the ischemic injury. CaMKK (α and β) is a major kinase activated by elevated intracellular calcium. Previously, we demonstrated that inhibition of CaMKK exacerbated outcomes, conversely, overexpression reduced brain injury after stroke in mice. Interestingly, CaMKK has been shown to activate a key endothelial protector, sirtuin 1 (SIRT1). We hypothesized that CaMKK protects brain endothelial cells via SIRT1 activation after stroke. In this study, Oxygen-Glucose Deprivation (OGD) was performed in human brain microvascular endothelial cells. Stroke was induced by middle cerebral artery occlusion (MCAO) in male mice. Knockdown of CaMKK β using siRNA increased cell death following OGD. Inhibition of CaMKK β by STO-609 significantly and selectively down-regulated levels of phosphorylated SIRT1 after OGD. Changes in the downstream targets of SIRT1 were observed following STO-609 treatment. The effect of STO-609 on cell viability after OGD was absent, when SIRT1 was concurrently inhibited. We also demonstrated that STO-609 increased endothelial expression of the pro-inflammatory proteins ICAM-1 and VCAM-1 and inhibition of CaMKK exacerbated OGD-induced leukocyte-endothelial adhesion. Finally, intracerebroventricular injection of STO-609 exacerbated endothelial apoptosis and reduced BBB integrity after 24-hr reperfusion following MCAO in vivo. Collectively, these results demonstrated that CaMKK inhibition reduced endothelial cell viability, exacerbated inflammatory responses and aggravated BBB impairment after ischemia. CaMKK activation may attenuate ischemic brain injury via protection of the microvascular system and a reduction in the infiltration of pro-inflammatory factors.

Genome-wide scan for circulating vascular adhesion protein-1 levels: MACROD2 as a potential transcriptional regulator of adipogenesis

AIMS/INTRODUCTION

Vascular adhesion protein-1 (VAP-1) is a membrane-bound amine oxidase highly expressed in mature adipocytes and released into the circulation. VAP-1 has been strongly implicated in several pathological processes, including diabetes, inflammation, hypertension, hepatic steatosis and renal diseases, and is an important disease marker and therapeutic target. Here, we aimed to identify the genetic loci for circulating VAP-1 levels.

MATERIALS AND METHODS

We carried out a genomic-wide linkage scan for the quantitative trait locus of circulating VAP-1 levels in 1,100 Han Chinese individuals from 398 families in the Stanford Asian Pacific Program for Hypertension and Insulin Resistance study. Regional association fine mapping was carried out using additional single-nucleotide polymorphisms.

RESULTS

The estimated heritability of circulating VAP-1 levels is high (h2 = 69%). The most significant quantitative trait locus for circulating VAP-1 was located at 38 cM on chromosome 20, with a maximum empirical logarithm of odds score of 4.11 (P = 6.86 × 10-6 ) in females. Regional single-nucleotide polymorphism fine mapping within a 1-unit support region showed the strongest association signals in the MACRO domain containing 2 (MACROD2) gene in females (P = 5.38 × 10-6 ). Knockdown of MACROD2 significantly suppressed VAP-1 expression in human adipocytes, as well as the expression of key adipogenic genes. Furthermore, MACROD2 expression was found to be positively associated with VAP-1 in human visceral adipose tissue.

CONCLUSION

MACROD2 is a potential genetic determinant of serum VAP-1 levels, probably through transcriptional regulation of adipogenesis.

Inhibition of semicarbazide-sensitive amine oxidase reduces atherosclerosis in apolipoprotein E-deficient mice

Inflammation, oxidative stress, and formation of advanced glycated end products (AGEs) and advanced lipoxidation end products (ALEs) are important for atherosclerosis. Vascular adhesion protein-1 (VAP-1) participates in inflammation and has semicarbazide-sensitive amine oxidase (SSAO) activity, which catalyzes oxidative deamination to produce hydrogen peroxide and aldehydes, leading to generation of AGEs and ALEs. However, the effect of VAP-1/SSAO inhibition on atherosclerosis remains controversial, and no studies used coronary angiography to evaluate if plasma VAP-1/SSAO is a biomarker for coronary artery disease (CAD). Here, we examined if plasma VAP-1/SSAO is a biomarker for CAD diagnosed by coronary angiography in humans and investigated the effect of VAP-1/SSAO inhibition by a specific inhibitor PXS-4728A on atherosclerosis in cell and animal models. In the study, VAP-1/SSAO expression was increased in plaques in humans and in apolipoprotein E (ApoE)-deficient mice, and colocalized with vascular endothelial cells and smooth muscle cells (SMCs). Patients with CAD had higher plasma VAP-1/SSAO than those without CAD. Plasma VAP-1/SSAO was positively associated with the extent of CAD. In ApoE-deficient mice, VAP-1/SSAO inhibition reduced atheroma and decreased oxidative stress. VAP-1/SSAO inhibition attenuated the expression of adhesion molecules, chemoattractant proteins, and proinflammatory cytokines in the aorta, and suppressed monocyte adhesion and transmigration across human umbilical vein endothelial cells. Consequently, the expression of markers for macrophage recruitment and activation in plaques was decreased by VAP-1/SSAO inhibition. Besides, VAP-1/SSAO inhibition suppressed proliferation and migration of A7r5 SMC. Our data suggest that plasma VAP-1/SSAO is a novel biomarker for the presence and the extent of CAD in humans. VAP-1/SSAO inhibition by PXS-4728A is a potential treatment for atherosclerosis.

Stroke, Vascular Dementia, and Alzheimer's Disease: Molecular Links

Stroke is a brain disease that occurs when blood flow stops, resulting in reduced oxygen supply to neurons. Stroke occurs at any time and at any age, but increases after the age of 55. It is the second leading cause of death and the third leading cause of disability-adjusted, life-years. The pathophysiology of ischemic stroke is complex and recent molecular, cellular, and animal models and postmortem brain studies have revealed that multiple cellular changes have been implicated, including oxidative stress/mitochondrial dysfunction, inflammatory responses, micro RNA alterations, and marked changes in brain proteins. These cellular changes provide new information for developing therapeutic strategies for ischemic stroke treatment. Research also revealed that stroke increases with a number of modifiable factors and most strokes can be prevented and/or controlled through pharmacological or surgical interventions and lifestyle changes. Ischemic stroke is the major risk factor for vascular dementia and Alzheimer's disease. This review summarizes the latest research findings on stroke, including causal factors and molecular links between stroke and vascular disease/Alzheimer's disease.

Simvastatin blocks soluble SSAO/VAP-1 release in experimental models of cerebral ischemia: Possible benefits for stroke-induced inflammation control

Beyond cholesterol reduction, statins mediate their beneficial effects on stroke patients through pleiotropic actions. They have shown anti-inflammatory properties by a number of different mechanisms, including the inhibition of NF-κB transcriptional activity and the consequent increase and release of adhesion molecules. We have studied simvastatin's effects on the vascular enzyme semicarbazide-sensitive amine oxidase/vascular adhesion protein 1 (SSAO/VAP-1), which is involved in stroke-mediated brain injury. SSAO/VAP-1 has leukocyte-binding capacity and mediates the expression of other adhesion proteins through signaling molecules generated by its catalytic activity. Our results indicate that soluble SSAO/VAP-1 is released into the bloodstream after an ischemic stimulus, in parallel with an increase in E-selectin and VCAM-1 and correlating with infarct volume. Simvastatin blocks soluble SSAO/VAP-1 release and prevents E-selectin and VCAM-1 overexpression as well. Simvastatin also effectively blocks SSAO/VAP-1-mediated leukocyte adhesion, although it is not an enzymatic inhibitor of SSAO in vitro. In addition, simvastatin-induced changes in adhesion molecules are greater in human brain endothelial cell cultures expressing SSAO/VAP-1, compared to those not expressing it, indicating some synergic effect with SSAO/VAP-1. We think that part of the beneficial effect of simvastatin in stroke is mediated by the attenuation of the SSAO/VAP-1-dependent inflammatory response.

Hypoxia serves a key function in the upregulated expression of vascular adhesion protein‑1 in vitro and in a rat model of hemorrhagic shock

Hemorrhagic shock following major trauma results in mortality, but the function of vascular adhesion protein-1 (VAP-1), implicated in intracranial hemorrhage, remains unknown. This study aimed to determine whether expression of the AOC3 gene and its encoded protein, VAP-1, is altered by hypoxia. Rat hepatic sinusoidal endothelial cells (RHSECs) and rat intestinal microvascular endothelial cells (RIMECs) were transduced with a viral vector carrying AOC3, and AOC3 mRNA expression levels were measured by reverse transcription-quantitative polymerase chain reaction. VAP-1 protein expression levels were measured by western blot analysis and compared between normoxic and hypoxic conditions. Following this, AOC3 mRNA and VAP-1 protein expression levels in hepatic and intestinal tissues were assessed in a rat model of hemorrhagic shock with or without fluid resuscitation; and serum semicarbazide-sensitive amine oxidase (SSAO) activity was measured by fluorometric assays. The effects of 2-bromoethylamine (2-BEA) on AOC3/VAP-1 levels and 24 h survival were investigated. AOC3 mRNA and VAP-1 protein levels were increased in RHSECs and RIMECs by hypoxia, and in hepatic and intestinal tissues from rats following hemorrhagic shock. Hypoxia increased serum SSAO activity in these animals. 2-BEA reduced AOC3 mRNA and VAP-1 protein levels in hepatic and intestinal tissues from rats following hemorrhagic shock, and appeared to improve survival in animals not receiving resuscitation following hemorrhagic shock. In conclusion, hemorrhagic shock upregulates AOC3/VAP-1 expressions, and this potentially occurs via hypoxia. Therefore, inhibition of VAP-1 may be beneficial in the setting of hemorrhagic shock. Further studies are required to confirm these findings and to establish whether VAP-1 may be a valid target for the development of novel therapies for hemorrhagic shock.

Protective effect of the multitarget compound DPH-4 on human SSAO/VAP-1-expressing hCMEC/D3 cells under oxygen-glucose deprivation conditions: an in vitro experimental model of cerebral ischaemia

BACKGROUND AND PURPOSE

Stroke and Alzheimer's disease (AD) are related pathologies in which the cerebrovascular system is involved. Plasma levels of semicarbazide-sensitive amine oxidase/vascular adhesion protein 1 (SSAO/VAP-1, also known as Primary Amine Oxidase -PrAO) are increased in both stroke and AD patients and contribute to the vascular damage. During inflammation, its enzymatic activity mediates leukocyte recruitment to the injured tissue, inducing damage in the blood-brain barrier (BBB) and neuronal tissue. We hypothesized that by altering cerebrovascular function, SSAO/VAP-1 might play a role in the stroke-AD transition. Therefore, we evaluated the protective effect of the novel multitarget-directed ligand DPH-4, initially designed for AD therapy, on the BBB.

EXPERIMENTAL APPROACH

A human microvascular brain endothelial cell line expressing human SSAO/VAP-1 was generated, as the expression of SSAO/VAP-1 is lost in cultured cells. To simulate ischaemic damage, these cells were subjected to oxygen and glucose deprivation (OGD) and re-oxygenation conditions. The protective role of DPH-4 was then evaluated in the presence of methylamine, an SSAO substrate, and/or β-amyloid (Aβ).

KEY RESULTS

Under our conditions, DPH-4 protected brain endothelial cells from OGD and re-oxygenation-induced damage, and also decreased SSAO-dependent leukocyte adhesion. DPH-4 was also effective at preventing the damage induced by OGD and re-oxygenation in the presence of Aβ as a model of AD pathology.

CONCLUSIONS AND IMPLICATIONS

From these results, we concluded that the multitarget compound DPH-4 might be of therapeutic benefit to delay the onset and/or progression of the neurological pathologies associated with stroke and AD, which appear to be linked.

Vascular adhesion protein-1: Role in human pathology and application as a biomarker

Vascular adhesion protein-1 (VAP-1) is a member of the copper-containing amine oxidase/semicarbazide-sensitive amine oxidase (AOC/SSAO) enzyme family. SSAO enzymes catalyze oxidative deamination of primary amines, which results in the production of the corresponding aldehyde, hydrogen peroxide and ammonium. VAP-1 is continuously expressed as a transmembrane glycoprotein in the vascular wall during development and facilitates the accumulation of inflammatory cells into the inflamed environment in concert with other leukocyte adhesion molecules. The soluble form of VAP-1 is released into the circulation mainly from vascular endothelial cells. Over- and under-expression of sVAP-1 result in alterations of the reported reaction product levels, which are involved in the pathogenesis of multiple human diseases. The combination of enzymatic and adhesion capacities as well as its strong association with inflammatory pathologies makes VAP-1 an interesting therapeutic target for drug discovery. In this article, we will review the general characteristics and biological functions of VAP-1, focusing on its important role as a prognostic biomarker in human pathologies. In addition, the potential therapeutic application of VAP-1 inhibitors will be discussed.