Components Of Neurovascular Unit Research Articles

Pericytes in Neurometabolic Diseases

Since brain pericytes guarantee appropriate development and maintenance of the cerebrovascular system, we reviewed their role in neurometabolic diseases (NMDs), a subclass of inborn errors of metabolism that selectively cause neurological sequels and widespread cerebrovascular alterations. Main findings about pericyte involvement in NMDs arise from glutaric acidemia type I (GA-I) models. In this regard, we found that (i) a single intracisternal injection of the main accumulated metabolite (glutaric acid, GA) in rat neonates disturbed the neurovascular unit (NVU) as evidenced by blood-brain barrier hyperpermeability, and altered immunoreactivity of pericyte and astrocyte markers surrounding brain microvessels; (ii) GA-elicited capillary constriction near pericyte somata likely inducing reduced brain blood flow as reported in GA-I patients; (iii) GA-elicited pericyte contraction probably results from a defective interplay among NVU components and could be relevant in case of metabolic decompensation or energetic deficiency. Although pericyte pathological features have been studied in few NMDs, their involvement in NMD pathophysiology is largely unknown. Thus, further studies are needed to identify their roles and therapeutic potentiality.

AT1 -R is involved in the development of long-lasting, region-dependent and oxidative stress-independent astrocyte morphological alterations induced by Ketamine.

Astrocytes play an essential role in the genesis, maturation and regulation of the neurovascular unit. Multiple evidence support that astrocyte reactivity has a close relationship to neurovascular unit dysfunction, oxidative stress and inflammation, providing a suitable scenario for the development of mental disorders. Ketamine has been proposed as a single-use antidepressant treatment in major depression, and its antidepressant effects have been associated with anti-inflammatory properties. However, Ketamine long-lasting effects over the neurovascular unit components remain unclear. Angiotensin II AT1 receptor (AT1 -R) blockers have anti-inflammatory, antioxidant and neuroprotective effects. The present work aims to distinguish the acute and long-term Ketamine effects over astrocytes response extended to other neurovascular unit components, and the involvement of AT1 -R, in prefrontal cortex and ventral tegmental area. Male Wistar rats were administered with AT1 -R antagonist Candesartan/Vehicle (days 1-10) and Ketamine/Saline (days 6-10). After 14days drug-free, at basal conditions or after Ketamine Challenge, the brains were processed for oxidative stress analysis, cresyl violet staining and immunohistochemistry for glial, neuronal activation and vascular markers. Repeated Ketamine administration induced long-lasting region-dependent astrocyte reactivity and morphological alterations, and neuroadaptative changes observed as exacerbated oxidative stress and neuronal activation, prevented by the AT1 -R blockade. Ketamine Challenge decreased microglial and astrocyte reactivity and augmented cellular apoptosis, independently of previous treatment. Overall, AT1 -R is involved in the development of neuroadaptative changes induced by repeated Ketamine administration but does not interfere with the acute effects supporting the potential use of AT1 -R blockers as a Ketamine complementary therapy in mental disorders.

Toll-Like Receptor 4 Signaling in Focal Cerebral Ischemia: a Focus on the Neurovascular Unit

A robust innate immune activation leads to downstream expression of inflammatory mediators that amplify tissue damage and consequently increase the morbidity after stroke. The Toll-like receptor 4 (TLR4) pathway is a major innate immune pathway activated acutely and chronically after stroke. Hence, understanding the intricacies of the temporal profile, specific control points, and cellular specificity of TLR4 activation is crucial for the development of any novel therapeutics targeting the endogenous innate immune response after focal cerebral ischemia. The goal of this review is to summarize the current findings related to TLR4 signaling after stroke with a specific focus on the components of the neurovascular unit such as astrocytes, neurons, endothelial cells, and pericytes. In addition, this review will examine the effects of focal cerebral ischemia on interaction of these neurovascular unit components.

Abstract TP345: Humanin, a Mitochondria-Derived Peptide Improves Outcome After Intracerebral Hemorrhage: Implication of Mitochondria Transfer and Microglia Phenotype Change

Background and Purpose: Astrocytes are the integral components of neurovascular unit where they act as homeostatic regulator, including after brain injury such as stroke. One mechanism by which astrocytes could improve homeostasis is through release of the functional mitochondria (Mt) that subsequently enter the recipient brain cell, adopt to the environment, and provide homeostatic effect. However, the mechanisms underlying beneficial effect of Mt transfer is unclear. Methods and Results: Using cell culture system, we found that the astrocytes release not only intact mitochondria, but also a small bioactive peptide, humanin (HN), a transcriptional product of Mt genome. We further discovered that secreted astrocytic Mt can incorporate into microglia, where they lead to: (1) increased HN level, (2) upregulation of transcription factor PPARγ, and its gene targets including manganese-superoxide dismutase, (3) enhanced phagocytic activities toward red blood cells ( in vitro model of hematoma clearance), and (4) reduced pro-inflammatory responses. This properties of HN suggest its potential beneficial role in intracerebral hemorrhage (ICH). First we found that ICH causes a profound loss of HN in the ICH-affected hemisphere. Next we established that intravenously administered recombinant HN (rHN) reaches the peri-hematoma brain tissue, and when we used it as treatment rHN reduced neurological deficits and improved hematoma clearance, function that normally implicates microglia/macrophages. Conclusions: This study suggests that Mt-derived HN could act as a beneficial secretory factor, including when transferred through Mt to microglia, where it promotes an adaptation to a phagocytic/reparative phenotype. Overall, these studies suggests that the restoration of HN in injured brain may represent a translational target for ICH.

The Neurovascular Unit: Effects of Brain Insults During the Perinatal Period.

The neurovascular unit (NVU) is a relatively recent concept in neuroscience that broadly describes the relationship between brain cells and their blood vessels. The NVU incorporates cellular and extracellular components involved in regulating cerebral blood flow and blood–brain barrier function. The NVU within the adult brain has attracted strong research interest and its structure and function is well described, however, the NVU in the developing brain over the fetal and neonatal period remains much less well known. One area of particular interest in perinatal brain development is the impact of known neuropathological insults on the NVU. The aim of this review is to synthesize existing literature to describe structure and function of the NVU in the developing brain, with a particular emphasis on exploring the effects of perinatal insults. Accordingly, a brief overview of NVU components and function is provided, before discussion of NVU development and how this may be affected by perinatal pathologies. We have focused this discussion around three common perinatal insults: prematurity, acute hypoxia, and chronic hypoxia. A greater understanding of processes affecting the NVU in the perinatal period may enable application of targeted therapies, as well as providing a useful basis for research as it expands further into this area.

Eye-acupuncture intervention reduces cerebro-cortical apoptosis of neurovascular unit in cerebral ischemia-reperfusion injury rats

To observe the effect of eye-acupuncture intervention on cerebro-cortical apoptosis of microvascular endothelial cells, neurons and astrocytes (main components of neurovascular unit) and the expression of Bad (an apoptosis promoter) and B-cell lymphoma-extra large(Bcl-xL) proteins in focal cerebral ischemia-reperfusion injury (CIRI) rats, so as to explore its mechanisms underlying improvement of CIRI. SD rats were randomly divided into control, sham-operation, model 3 h, model 24 h, model 72 h, eye-acupuncture 3 h, eye-acupuncture 24 h and eye-acupuncture 72 h groups(n＝12 in each group). The CIRI model was established by middle cerebral artery occlusion/reperfusion (MCAO/R). Eye-acupuncture was applied to bilateral "Gan" (Liver) regions, "Shen" (Kidney) regions, "Shangjiao" (Upper-energizer) and "Xiajiao" (Lower-energizer) for 20 min, once 3 h and every 12 h after modeling. The expression levels of Bad and Bcl-xL in the ischemic cerebral cortex tissue were detected by Western blot. The apoptotic neurons, microvascular endothelial cells and astrocytes were assayed by immunofluorescence double labeling (Nestin/TUNEL, CD34/TUNEL and glial fibrillary acidic protein [GFAP]/TUNEL) separately. After modeling, the numbers of apoptotic neurons, microvascular endothelial cells and astrocytes in the ischemic cerebral cortex tissue were significantly increased in the model 72 h group than in the sham-operation group (P<0.01). Following the treatment, the numbers of the 3 types of apoptotic cells were markedly lower in the eye-acupuncture 72 h group than in the model 72 h group(P<0.01). The expression levels of Bad and Bcl-xL proteins were notably up-regulated in the model 3 h, model 24 h and model 72 h groups than in the sham operation group(P<0.01). Following eye-acupuncture intervention, modeling induced increase of the Bad expression were obviously reversed in eye-acupuncture 24 h and eye-acupuncture 72 h groups than those in the 2 model groups(P<0.05). And the increase of Bcl-xL expression levels were further increased in the eye-acupuncture groups in comparison with those in the 3 model groups (P<0.01). Eye-acupuncture can down-regulate the expression of Bad protein, and up-regulate the expression of Bcl-xL protein in the ischemic cerebral cortex in CIRI rats, which may contribute to its function in reducing apoptotic neurons, microvascular endothelial cells and astrocytes, suggesting a protective effect of eye-acupuncture intervention on neurovascular unit.

Ultrastructural Features of Neurovascular Units in a Rat Model of Chronic Compressive Spinal Cord Injury.

Chronic spinal cord compression is the most common cause of spinal cord impairment worldwide. Objective of this study is to assess the ultrastructural features of the neurovascular unit (NVU) in a rat model of chronic compressive spinal cord injury, 24 SD rats were divided into two groups: the control group (n = 12), and the compression group (n = 12). A C6 semi-laminectomy was performed in the control group, whereas a water-absorbent polyurethane polymer was implanted into the C6 epidural space in the compression group. The Basso Beattie Bresnahan (BBB) scores and the somatosensory evoked potentials (SEP) were used to evaluate neurological functions. Transmission Electron Microscopy (TEM) was performed to investigate the change of NVU at the 28th day after modeling. Compared with the control group, the compression group shows a significant reduction (P < 0.05) of BBB score and a significant severity (P < 0.05) of abnormal SEP. TEM results of the compression group showed a striking increase in endothelial caveolae and vacuoles; a number of small spaces in tight junctions; a significant increase in pericyte processing area and vessel coverage; an expansion of the basement membrane region; swollen astrocyte endfeet and mitochondria; and the degeneration of neurons and axons. Our study revealed that damage to NVU components occurred followed by chronic compressive spinal cord injury. Several compensatory changes characterized by thicker endothelium, expansive BM, increased pericyte processing area and vessel coverage were also observed.

The High Cost of Stroke and Stroke Cytoprotection Research.

Acute ischemic stroke is inadequately treated in the USA and worldwide due to a lengthy history of neuroprotective drug failures in clinical trials. The majority of victims must endure life-long disabilities that not only affect their livelihood, but also have an enormous societal economic impact. The rapid development of a neuroprotective or cytoprotective compound would allow future stroke victims to receive a treatment to reduce disabilities and further promote recovery of function. This opinion article reviews in detail the enormous costs associated with developing a small molecule to treat stroke, as well as providing a timely overview of the cell-death time-course and relationship to the ischemic cascade. Distinct temporal patterns of cell-death of neurovascular unit components provide opportunities to intervene and optimize new cytoprotective strategies. However, adequate research funding is mandatory to allow stroke researchers to develop and test their novel therapeutic approach to treat stroke victims.

Pericytes in Brain Injury and Repair After Ischemic Stroke.

Pericytes are functional components of the neurovascular unit (NVU). They provide support to other NVU components and maintain normal physiological functions of the blood-brain barrier (BBB). The brain ischemia and reperfusion result in pathological alterations in pericytes. The intimate anatomical and functional interactions between pericytes and other NVU components play pivotal roles in the progression of stroke pathology. In this review, we depict the biology and functions of pericytes in the normal brain and discuss their effects in brain injury and repair after ischemia/reperfusion. Since ischemic stroke occurs mostly in elderly people, we also review age-related changes in pericytes and how these changes predispose aged brains to ischemic/reperfusion injury. Strategies targeting pericyte responses after ischemia and reperfusion may provide new therapies for ischemic stroke.

Neurovascular unit components on a chip as a model to study traumatic brain injury

Neurovascular unit components on a chip as a model to study traumatic brain injury

Neurovascular unit components on a chip as a model to study traumatic brain injury

Neurovascular unit components on a chip as a model to study traumatic brain injury

Protection of Neurovascular Unit Cells with Lithium Chloride and Sodium Valproate Prevents Brain Damage in Neonatal Ischemia/Hypoxia.

Here we studied the cytoprotective effect of lithium chloride and sodium valproate in the in vivo model of neonatal cerebral ischemia/hypoxia and analyzed the influence of these substances on the death of the major neurovascular unit components in experimental ischemia in vitro. Lithium chloride and sodium valproate effectively prevented death of neurons, astrocytes, and endothelial cells in the oxygen-glucose deprivation. This treatment protected the brain of newborn rats from ischemia/hypoxia injury. The results suggest that lithium and sodium valproate can be used for the treatment of neurodegenerative pathologies associated with hypoxia and ischemia in newborns.

Abstract W MP26: Blood Brain Barrier Permeability and Neurovascular Unit Markers of Hemorrhagic Transformation After Rt-pa Administration

Objectives: The administration of rt-PA increases the risk of hemorrhagic transformation (HT) due to an increase in the permeability of the neurovascular unit which allows the extravasation of erythrocytes. In this study we compared the predictive capacity of different neurovascular unit components and their correlation with blood brain barrier (BBB) permeability abnormalities evaluated by advanced neuroimaging. Patients and methods: Eighty-three patients with hemispheric stroke treated with rt-PA who had angio-CT perfusion before fibrinolysis were evaluated. Lesion volumes were calculated on perfusion and permeability maps. HT was assessed in the cranial CT at 24±12h after rt-PA and classified following ECASS II criteria. HT was considered symptomatic (sHT) when it was associated with an increase ≥ 4 points in the NIHSS. The levels of cellular-fibronectin (cFn), total MMP-9, laminin, heparan-sulphate, collagen type IV and protein S100β pre-rtPA and at 2, 24 and 72h post-rtPA were analyzed. Results: Fourteen patients (16.8%) had HT, which was symptomatic in 3 (3.6%). On comparing patients with and without HT independently of the type, only MMP-9 and protein S100β levels at 24h were found to be higher in the HT group. However, baseline cFn levels were higher in patients with PH2 (12.5±5.6 vs. 6.6±3.8μg/mL, p=0.013) and sHT (13.8±6.7 vs. 6.7± 3.9μg/mL, p=0.003) and laminin levels were also lower in patients with PH2 (1.5±0.8 vs. 3.5±2.5ng/mL, p=0.016). In the multivariate analysis, only cFn levels remained as an independent predictor of sHT (OR 1.40;CI 95%, 1.02-1.93; p=0.037). The analysis of the permeability maps yielded cut-off values for the prediction of HT with high specificity and negative predictive values regardless of the threshold used for visualization of the abnormal permeability area. Conclusions: Among different neurovascular unit markers, this study seems to confirm the utility of cFn levels as potential predictors of sHT after rt-PA. Permeability maps would seem to predict the likelihood of not bleeding with high probability.

Protective effect of telmisartan on neurovascular unit and inflammasome in stroke-resistant spontaneously hypertensive rats

Objectives:Hypertension is a crucial risk factor for both stroke and dementia, including Alzheimer’s disease (AD). We inspected the effect of telmisartan on the neurovascular unit (NVU) and related inflammatory responses in spontaneously hypertensive rat stroke resistant (SHR-SR) by observing the components of NVU such as N-acetyl glucosamine oligomer (NAGO), collagen IV, astrocytes, and matrix metalloproteinase-9 (MMP-9), as well as inflammasome NOD-like receptors family protein 3 (NLRP3).Methods:In the present study, we examined the effect of a highly selective angiotensin type 1 (AT-1) antagonist of angiotensin 2 receptor with high lipid solubility, telmisartan, on NVU and related inflammatory responses in SHR-SR with a low dose (0·3 mg/kg/day) only for improving metabolic syndrome, and a high dose (3 mg/kg/day) for improving both metabolic syndrome and SHR-SR hypertension.Results:Compared to normotensive Wistar rats, long-lasting hypertension in SHR-SR disrupted NVU by changing immunohistological components such as NAGO, collagen IV, astrocytes, and MMP-9. SHR-SR also strongly induced AD-related inflammasome NLRP3 in neuronal cells with age. However, such NVU disruption and inflammasome activation were greatly improved with dose-dependent telmisartan treatments.Discussion:These results suggest that telmisartan comprehensively protected the NVU components by reducing inflammatory reactions relative to AD in hypertensive rats, which could also preclude the risk of AD under hypertension.

Abstract W MP84: Erythropoietin Inhibits Oxidation of Tetrahydrobiopterin and Restores Bioavailability of Endothelial Nitric Oxide in Cerebral Microvessels of Hph-1 Mice

Background: While reported neuroprotective effects of erythropoietin (EPO) make it an appealing candidate for its evaluation in protection of neurovascular unit during cerebrovascular or neurodegenerative disorders, effects of EPO on cerebral microvessels, the vascular component of neurovascular unit, have not been studied to date. The present study was designed to determine the effects of EPO in cerebral microvessels derived from wild-type mice and also from hph-1 mice, a genetic mouse model of BH4 deficiency. Methods: Hph-1 mice and wild-type littermates (C57BL/6 background) were administered recombinant human EPO (1000 U/kg/day) intraperitoneally for 3 days. Following treatment, mice were killed by injection of an overdose of pentobarbital, brains were removed and cerebral microvessels were isolated. Results: Treatment of wild-type mice with EPO did not affect BH4 bioavailability, superoxide anion production or basal cGMP levels. We have reported that cerebral microvessels of hph-1 mice demonstrated reduced bioavailability of BH4, increased production of superoxide anions and impaired endothelial NO/cGMP signaling. Treatment of hph-1 mice with EPO attenuated the levels of 7,8-dihydrobiopterin (7,8-BH2; P&lt;0.05, n=5), oxidized product of BH4, and significantly increased the ratio of BH4 to 7,8-BH2 (P&lt;0.05, n=5), indicative of increased bioavailability of BH4 for eNOS activation. Increased superoxide anion production in cerebral microvessels of hph-1 mice were attenuated by EPO treatment (P&lt;0.05, n=5). While eNOS expression remained unchanged, levels of cGMP were significantly increased on EPO treatment in hph-1 mice (P&lt; 0.05, n=6). Furthermore, EPO treatment selectively increased expression of manganese superoxide dismutase. Conclusion: The ability of EPO to attenuate oxidative stress and restore bioavailability of endothelial NO in cerebral microvessels may help to explain mechanisms responsible for cerebrovascular protective effects of EPO.

BLOOD-BRAIN BARRIER DISRUPTION DURING ACUTE ISCHEMIC STROKE - THE ROLE OF MATRIX METALLOPROTEINASES AND TIGHT JUNCTIONS PROTEINS

Ischemic stroke is a major cause of death and disability worldwide. Intravenous administration of recombinant tissue plasminogen activator (rtPA) is the only approved pharmacological therapy for patients with acute ischemic stroke. Treatment with intravenous rtPA is associated with increased rates of intracranial hemorrhage. This review discusses recent findings about the changes of the components of neurovascular unit and the alteration of blood-brain barrier during stroke. The analysis provide information in order to identify factors with predictive value for hemorrhagic transformation of ischemic stroke both within or after the thrombolysis time window.

Soluble epoxide hydrolase inhibitor trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid is neuroprotective in rat model of ischemic stroke

Soluble epoxide hydrolase (sEH) diminishes vasodilatory and neuroprotective effects of epoxyeicosatrienoic acids by hydrolyzing them to inactive dihydroxy metabolites. The primary goals of this study were to investigate the effects of acute sEH inhibition by trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB) on infarct volume, functional outcome, and changes in cerebral blood flow (CBF) in a rat model of ischemic stroke. Focal cerebral ischemia was induced in rats for 90 min followed by reperfusion. At the end of 24 h after reperfusion rats were euthanized for infarct volume assessment by triphenyltetrazolium chloride staining. Brain cortical sEH activity was assessed by ultra performance liquid chromatography-tandem mass spectrometry. Functional outcome at 24 and 48 h after reperfusion was evaluated by arm flexion and sticky-tape tests. Changes in CBF were assessed by arterial spin-labeled-MRI at baseline, during ischemia, and at 180 min after reperfusion. Neuroprotective effects of t-AUCB were evaluated in primary rat neuronal cultures by Cytotox-Flour kit and propidium iodide staining. t-AUCB significantly reduced cortical infarct volume by 35% (14.5 ± 2.7% vs. 41.5 ± 4.5%), elevated cumulative epoxyeicosatrienoic acids-to-dihydroxyeicosatrienoic acids ratio in brain cortex by twofold (4.40 ± 1.89 vs. 1.97 ± 0.85), and improved functional outcome in arm-flexion test (day 1: 3.28 ± 0.5 s vs. 7.50 ± 0.9 s; day 2: 1.71 ± 0.4 s vs. 5.28 ± 0.5 s) when compared with that of the vehicle-treated group. t-AUCB significantly reduced neuronal cell death in a dose-dependent manner (vehicle: 70.9 ± 7.1% vs. t-AUCB0.1μM: 58 ± 5.11% vs. t-AUCB0.5μM: 39.9 ± 5.8%). These findings suggest that t-AUCB may exert its neuroprotective effects by affecting multiple components of neurovascular unit including neurons, astrocytes, and microvascular flow.

Neurovascular Unit in Chronic Pain

Chronic pain is a debilitating condition with major socioeconomic impact, whose neurobiological basis is still not clear. An involvement of the neurovascular unit (NVU) has been recently proposed. In particular, the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB), two NVU key players, may be affected during the development of chronic pain; in particular, transient permeabilization of the barrier is suggested by several inflammatory- and nerve-injury-based pain models, and we argue that the clarification of molecular BBB/BSCB permeabilization events will shed new light in understanding chronic pain mechanisms. Possible biases in experiments supporting this theory and its translational potentials are discussed. Moving beyond an exclusive focus on the role of the endothelium, we propose that our understanding of the mechanisms subserving chronic pain will benefit from the extension of research efforts to the NVU as a whole. In this view, the available evidence on the interaction between analgesic drugs and the NVU is here reviewed. Chronic pain comorbidities, such as neuroinflammatory and neurodegenerative diseases, are also discussed in view of NVU changes, together with innovative pharmacological solutions targeting NVU components in chronic pain treatment.

Mediators of Inflammation as Targets for Chronic Pain Treatment

Mediators of Inflammation as Targets for Chronic Pain Treatment

Protective effects of Chinese herbal medicine Naoshuantong on neurovascular unit in rats with cerebral ischemia/reperfusion injury

To investigate the protective effects of Naoshuantong, a compound traditional Chinese herbal medicine, on the main components of neurovascular unit in rats with cerebral ischemia/reperfusion injury. A total of 30 male Sprague-Dawley rats were randomly divided into sham-operated, ischemia/reperfusion, and ischemia/reperfusion plus Naoshuantong groups. The cerebral ischemia was induced by 1.5 h of middle cerebral artery occlusion, followed by unlocking the thread to induce reperfusion injury. After 24 h of reperfusion, neurological functional deficits were assessed, apoptosis of main components of neurovascular unit was determined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling combined with neuronal nuclei antigen, glial fibrillary acidic protein or CD31 immunofluorescence double staining. Naoshuantong significantly reduced neurological functional deficits, and reduced neuron, astrocyte and vascular endothelium cell apoptosis induced by ischemia/reperfusion injury in the border zone of ischemic cortex. Naoshuantong is effective in protecting the neurovascular unit including neurons, astrocytes and vascular endothelium cells against cerebral ischemia/reperfusion-induced apoptosis.