tPA and proteolysis in the neurovascular unit

From bench to bedside: US-Japan Collaborative Workshop on the NVU

The joint workshop between U.S. and Japanese researchers, supported by The U.S.-Japan Brain Research Cooperative Program, convened in January 2023 at Keio University Mita campus in Tokyo, Japan. The workshop had a threefold objective. Firstly, it aimed to facilitate robust exchanges between U.S. and Japanese researchers engaged in Neurovascular Unit (NVU) research, enhancing the global network of scholars in the field. Secondly, it aimed to encourage the initiation of collaborative research projects, fostering interdisciplinary efforts and synergistic advancements in understanding the brain vascular physiology and central nervous system. Lastly, the workshop emphasized the nurturing of young researchers, recognizing their pivotal role in shaping the future of NVU research. Throughout the workshop, participants discussed fundamental aspects of the NVU, exploring its complex connections and vital functions. By sharing their expertise and insights, the workshop attendees sought to uncover novel approaches to mitigate the burden of neurological diseases for individuals worldwide. This report provides a summary of the presentations and discussions held during the workshop, showcasing the collective efforts and progress made by the participants.

An update on stem cell therapy for stroke patients: Where are we now?

With a foundation built upon initial work from the 1980s demonstrating graft viability in cerebral ischemia, stem cell transplantation has shown immense promise in promoting survival, enhancing neuroprotection and inducing neuroregeneration, while mitigating both histological and behavioral deficits that frequently accompany ischemic stroke. These findings have led to a number of clinical trials that have thoroughly supported a strong safety profile for stem cell therapy in patients but have generated variable efficacy. As preclinical evidence continues to expand through the investigation of new cell lines and optimization of stem cell delivery, it remains critical for translational models to adhere to the protocols established through basic scientific research. With the recent shift in approach towards utilization of stem cells as a conjunctive therapy alongside standard thrombolytic treatments, key issues including timing, route of administration, and stem cell type must each be appropriately translated from the laboratory in order to resolve the question of stem cell efficacy for cerebral ischemia that ultimately will enhance therapeutics for stroke patients towards improving quality of life.

The paradox of tPA in ischemic stroke: tPA knockdown following recanalization improves functional and histological outcomes

Previous studies have demonstrated that endogenous tissue-type plasminogen activator (tPA) is upregulated in the brain after an acute ischemic stroke (AIS). While mixed results were observed in genetic models, the pharmacological inhibition of endogenous tPA showed beneficial effects. Treatment with exogenous recombinant tPA exacerbated brain damage in rodent models of stroke. Despite the detrimental effects of tPA in ischemic stroke, recombinant tPA is administered to AIS patients to recanalize the occluded blood vessels because the benefits of its administration outweigh the risks associated with tPA upregulation and increased activity. We hypothesized that tPA knockdown following recanalization would ameliorate sensorimotor deficits and reduce brain injury. Young male and female rats (2-3 months old) were subjected to transient focal cerebral ischemia by occlusion of the right middle cerebral artery. Shortly after reperfusion, rats from appropriate cohorts were administered a nanoparticle formulation containing tPA shRNA or control shRNA plasmids (1 mg/kg) intravenously via the tail vein. Infarct volume during acute and chronic phases, expression of matrix metalloproteinases (MMPs) 1, 3, and 9, enlargement of cerebral ventricle volume, and white matter damage were all reduced by shRNA-mediated gene silencing of tPA following reperfusion. Additionally, recovery of somatosensory and motor functions was improved. In conclusion, our results provide evidence that reducing endogenous tPA following recanalization improves functional outcomes and reduces post-stroke brain damage.

Modulation of microglial polarization by sequential targeting surface-engineered exosomes improves therapy for ischemic stroke

Microglia are important cells that act on regulating neuroinflammation and neurofunction after the induction of ischemic stroke (IS). Consequently, the efficient accumulation of drugs within ischemic regions, particularly in microglia, serves as a valuable approach for achieving effective therapy by attenuating microglia-mediated cerebral ischemic injury. In this study, we designed mannose (man)-conjugated luteolin (lut)-loaded platelet-derived exosomes (lut/man-pEXO) as surface engineered multifunctional cascade-delivery drug carriers to target ischemic blood vessels and subsequent microglia to enhance drug accumulation and induce neuroprotection of neurovascular unit (NVU) against IS. The results revealed that as platelets naturally gathered in pathological ischemic cerebral vessels, lut/man-pEXO could bind to platelets and efficiently target ischemic injury sites. Moreover, owing to the selective binding affinity of mannose present in lut/man-pEXO towards the mannose receptor expressed on microglia, lut/man-pEXO exhibited superior microglia-targeting properties, inducing the increased uptake of lut by microglia. As a result, lut/man-pEXO regulated microglia by inhibiting the activation of detrimental M1 and promoting the transition towards the anti-inflammatory type (M2), thus attenuating ischemic damage of NVU by reducing the infarct area, rescuing the damage of blood-brain barrier (BBB) and preventing inflammatory transformation of astrocytes.

YangXueQingNaoWan attenuated blood brain barrier disruption after thrombolysis with tissue plasminogen activator in ischemia stroke

ETHNOPHARMACOLOGICAL RELEVANT

YangXueQingNaoWan (YXQNW), a compound Chinese medicine, has been widely used for dizziness, irritability, insomnia, and dreaminess caused by blood deficiency and liver hyperactivity in China. However, whether YXQNW can inhibit cerebral microvascular exudation and cerebral hemorrhage (CH) caused by blood brain barrier (BBB) damage after tissue plasminogen activator (tPA) still unknown.

AIM OF THE RESEARCH

To observe the effect of YXQNW on cerebral microvascular exudation and CH after tPA and investigate its mechanism in protecting BBB.

MATERIALS AND METHODS

Male C57BL/6 N mice suffered from ischemia stroke by mechanical detachment of carotid artery thrombi with the stimulation of ferric chloride. Then mice were treated with tPA (10 mg/kg) and/or YXQNW (0.72 g/kg) at 4.5 h. Cerebral blood flow (CBF), infarct size, survival rate, neurological scores, gait analysis, Evans blue extravasation, cerebral water content, fluorescein isothiocyanate-labeled albumin leakage, hemorrhage, junction and basement membrane proteins expression, leukocyte adhesion and matrix metalloproteinases (MMPs) expression were evaluated 24 h after tPA. Proteomics was used to identify target proteins.

RESULTS

YXQNW inhibited cerebral infarction, neurobehavioral deficits, decreased survival, Evans blue leakage, albumin leakage, cerebral water content and CH after tPA thrombolysis; improved CBF, low-expression and degradation of junction proteins, basement membrane proteins, Arhgap21 and its downstream α-catenin and β-catenin proteins expression; and suppressed the increase of adherent leukocytes and the release of MMP-9 derived from macrophage.

CONCLUSION

YXQNW relieved BBB damage and attenuated cerebral microvascular exudation and CH after tPA thrombolysis. The effect of YXQNW on cerebral microvascular exudation was associated with the inhibition of the low-expression of junction proteins, especially AJs mediated by Rho GTPase-activating protein 21 (Arhgap21), while the effect on CH was associated with the inhibition of leukocyte adhesion, the release of MMP-9 derived from macrophage, and low-expression and degradation of collagen IV and laminin in the vascular basement membrane.

l-borneol promotes neurovascular unit protection in the subacute phase of transient middle cerebral artery occlusion rats: p38-MAPK pathway activation, anti-inflammatory, and anti-apoptotic effect

Our previous study showed l-borneol reduced cerebral infarction in the acute stage after cerebral ischemia, but there is little about the study of subacute phase. We herein investigated the cerebral protective effects of l-borneol on neurovascular units (NVU) in the subacute phase after transient middle cerebral artery occlusion (t-MCAO). The t-MCAO model was prepared by the line embolus method. Zea Longa, mNss, HE, and TTC staining were used to evaluate the effect of l-borneol. We evaluated the mechanisms of l-borneol on inflammation, p38 MAPK pathway, and apoptosis, etc. through various technologies. l-borneol 0.2, 0.1, 0.05 g·kg-1 could significantly reduce cerebral infarction rate, alleviate the pathological injury, and inhibit inflammation reaction. l-borneol could also significantly increase brain blood supply, Nissl bodies, and the expression of GFAP. Additionally, l-borneol activated the p38 MAPK signaling pathway, inhibited cell apoptosis, and maintained BBB integrity. l-borneol had a neuroprotective effect, which was related to activating the p38 MAPK signaling pathway, inhibiting inflammatory response and apoptosis, and improving cerebral blood supply to protect BBB and stabilize and remodel NVU. The study will provide a reference for the use of l-borneol in the treatment of ischemic stroke in the subacute phase.

Secondary neurodegeneration following Stroke: what can blood biomarkers tell us?

Stroke is one of the leading causes of death and the primary source of disability in adults, resulting in neuronal necrosis of ischemic areas, and in possible secondary degeneration of regions surrounding or distant to the initial damaged area. Secondary neurodegeneration (SNDG) following stroke has been shown to have different pathogenetic origins including inflammation, neurovascular response and cytotoxicity, but can be associated also to regenerative processes. Aside from focal neuronal loss, ipsilateral and contralateral effects distal to the lesion site, disruptions of global functional connectivity and a transcallosal diaschisis have been reported in the chronic stages after stroke. Furthermore, SNDG can be observed in different areas not directly connected to the primary lesion, such as thalamus, hippocampus, amygdala, substantia nigra, corpus callosum, bilateral inferior fronto-occipital fasciculus and superior longitudinal fasciculus, which can be highlighted by neuroimaging techniques. Although the clinical relevance of SNDG following stroke has not been well understood, the identification of specific biomarkers that reflect the brain response to the damage, is of paramount importance to investigate in vivo the different phases of stroke. Actually, brain-derived markers, particularly neurofilament light chain, tau protein, S100b, in post-stroke patients have yielded promising results. This review focuses on cerebral morphological modifications occurring after a stroke, on associated cellular and molecular changes and on state-of-the-art of biomarkers in acute and chronic phase. Finally, we discuss new perspectives regarding the implementation of blood-based biomarkers in clinical practice to improve the rehabilitation approaches and post stroke recovery.

Increasing reproducibility in preclinical stroke research: the correlation of immunofluorescence intensity measurements and Western blot analyses strongly depends on antibody clonality and tissue pre-treatment in a mouse model of focal cerebral ischemia

In the setting of stroke, ischemia not only impairs neuronal function, but also detrimentally affects the different components of the neurovascular unit, which are shown to be involved in the transition from reversible to long-lasting tissue damage. In this context, the glial proteins myelin basic protein (MBP) and the 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNP) as well as the vasculature-associated basement membrane proteins laminin and collagen IV have been identified as ischemia-sensitive elements. However, available data from immunofluorescence and Western blot analyses are often found to be contradictory, which renders interpretation of the respective data rather difficult. Therefore, the present study investigates the impact of tissue pre-treatment and antibody clonality on immunofluorescence measurements of the mentioned proteins in a highly reproducible model of permanent middle cerebral artery occlusion. Here, immunofluorescence labeling using polyclonal antibodies revealed an increased immunofluorescence intensity of MBP, CNP, laminin and collagen IV in ischemic areas, although Western blot analyses did not reveal increased protein levels. Importantly, contrary to polyclonal antibodies, monoclonal ones did not provide increased fluorescence intensities in ischemic areas. Further, we were able to demonstrate that different ways of tissue pre-treatment including paraformaldehyde fixation and antigen retrieval may not only impact on fluorescence intensity measurements in general, but rather one-sidedly affect either ischemic or unaffected tissue. Therefore, immunofluorescence intensity measurements do not necessarily correlate with the actual protein levels, especially in ischemia-affected tissue and should always be complemented by different techniques to enhance reproducibility and to hopefully overcome the translational roadblock from bench to bedside.

Rehabilitation in Animal Models of Stroke

OBJECTIVE

The purpose of this review was to evaluate the efficacy of rehabilitation strategies in animal models of stroke and their correlation with human stroke studies.

METHODS

General description of a stroke, functional recovery, and rehabilitation modalities were included from published studies in the field of animal models of cerebral ischemia and ischemia-reperfusion.

RESULTS

In stroke survivors, rehabilitation plays a significant role to improve motor function, cognition, and other subtle behaviors. Targeted pharmacological agents, including neuroprotective drugs, are helpful in animal models of stroke. However, no drug has yet been found that meets the criteria that would make it the Food and Drug Administration-approved treatment for human stroke. Instead, the rehabilitation of stroke in humans is limited to physical and occupational therapy, speech therapy, environmental enrichment, and social activities, as well as spiritual and family support.

CONCLUSION

Studies on stroke injury and the significance of stroke animals' rehabilitation, including physical and pharmacological, approaches are highlighted.

The NG2-glia is a potential target to maintain the integrity of neurovascular unit after acute ischemic stroke

The neurovascular unit (NVU) plays a critical role in health and disease. In the current review, we discuss the critical role of a class of neural/glial antigen 2 (NG2)-expressing glial cells (NG2-glia) in regulating NVU after acute ischemic stroke (AIS). We first introduce the role of NG2-glia in the formation of NVU during development as well as aging-induced damage to NVU and accompanying NG2-glia change. We then discuss the reciprocal interactions between NG2-glia and the other component cells of NVU, emphasizing the factors that could influence NG2-glia. Damage to the NVU integrity is the pathological basis of edema and hemorrhagic transformation, the most dreaded complication after AIS. The role of NG2-glia in AIS-induced NVU damage and the effect of NG2-glia transplantation on AIS-induced NVU damage are summarized. We next discuss the role of NG2-glia and the effect of NG2-glia transplantation in oligodendrogenesis and white matter repair as well as angiogenesis which is associated with the outcome of the patients after AIS. Finally, we review the current strategies to promote NG2-glia proliferation and differentiation and propose to use the dental pulp stem cells (DPSC)-derived exosome as a promising strategy to reduce AIS-induced injury and promote repair through maintaining the integrity of NVU by regulating endogenous NG2-glia proliferation and differentiation.

The interplay between MMP-12 and t-PA in the brain after ischemic stroke

Tissue-type plasminogen activator (t-PA) expression is known to increase following transient focal cerebral ischemia and reperfusion. Previously, we reported downregulation of t-PA upon suppression of matrix metalloproteinase-12 (MMP-12), following transient focal cerebral ischemia and reperfusion. We now present data on the temporal expression of t-PA in the brain after transient ischemia, as well as the interaction between MMP-12 and t-PA, two proteases associated with the breakdown of the blood-brain barrier (BBB) and ischemic brain damage. We hypothesized that there might be reciprocal interactions between MMP-12 and t-PA in the brain after ischemic stroke. This hypothesis was tested using shRNA-mediated gene silencing and computational modeling. Suppression of t-PA following transient ischemia and reperfusion in rats attenuated MMP-12 expression in the brain. The overall effect of t-PA shRNA administration was to attenuate the degradation of BBB tight junction protein claudin-5, diminish BBB disruption, and reduce neuroinflammation by decreasing the expression of the microglia/macrophage pro-inflammatory M1 phenotype (CD68, iNOS, IL-1β, and TNFα). Reduced BBB disruption and subsequent lack of infiltration of macrophages (the main source of MMP-12 in the ischemic brain) could account for the decrease in MMP-12 expression after t-PA suppression. Computational modeling of in silico protein-protein interactions indicated that MMP-12 and t-PA may interact physically. Overall, our findings demonstrate that MMP-12 and t-PA interact directly or indirectly at multiple levels in the brain following an ischemic stroke. The present findings could be useful in the development of new pharmacotherapies for the treatment of stroke.

The neurovascular unit and systemic biology in stroke - implications for translation and treatment

Ischaemic stroke is a leading cause of disability and death for which no acute treatments exist beyond recanalization. The development of novel therapies has been repeatedly hindered by translational failures that have changed the way we think about tissue damage after stroke. What was initially a neuron-centric view has been replaced with the concept of the neurovascular unit (NVU), which encompasses neuronal, glial and vascular compartments, and the biphasic nature of neural-glial-vascular signalling. However, it is now clear that the brain is not the private niche it was traditionally thought to be and that the NVU interacts bidirectionally with systemic biology, such as systemic metabolism, the peripheral immune system and the gut microbiota. Furthermore, these interactions are profoundly modified by internal and external factors, such as ageing, temperature and day-night cycles. In this Review, we propose an extension of the concept of the NVU to include its dynamic interactions with systemic biology. We anticipate that this integrated view will lead to the identification of novel mechanisms of stroke pathophysiology, potentially explain previous translational failures, and improve stroke care by identifying new biomarkers of and treatment targets in stroke.

In vitro analysis of mechanism of pulsed-laser thrombolysis

Thrombolytic therapy in the treatment of cardiogenic acute cerebral embolism caused by coagulated blood carries the risk of hemorrhagic complications, and there is a need to develop safer and more reliable treatment methods. Laser thrombolysis therapy, which utilizes the difference in energy absorption between the thrombus and the arterial wall, has shown promise as a new treatment method because it can selectively act only on the thrombus. It has not been applied clinically, however, and one of the main reasons for this is that its underlying mechanism has not been elucidated. We developed a pulse laser thrombolysis system for treating cerebral blood vessels that consists of a diode-pumped solid-state neodymium-yttrium aluminum garnet laser, which has excellent stability and maintainability and is suitable for clinical applications coupled to a small-diameter optical fiber. Moreover, we analyzed the mechanisms that occur during pulsed laser irradiation of transparent glass tubes and gelatin phantoms. We found that bubbles form as a thermal effect in addition to ablation of the pulsed laser irradiation. Furthermore, we detected no shock waves or water jets associated with the bubbles. We analyzed the bubbles’ dynamics and growth rate, and their effect on a rabbit blood clot phantom. We concluded that the bubbles generated by the laser irradiation physically cut the thrombus and thereby had a thrombectomy effect. We believe that this study will clarify the mechanism of laser thrombolysis therapy and contribute greatly to the realization of its clinical application.

Profiling the neurovascular unit unveils detrimental effects of osteopontin on the blood-brain barrier in acute ischemic stroke

Blood-brain barrier (BBB) dysfunction, characterized by degradation of BBB junctional proteins and increased permeability, is a crucial pathophysiological feature of acute ischemic stroke. Dysregulation of multiple neurovascular unit (NVU) cell types is involved in BBB breakdown in ischemic stroke that may be further aggravated by reperfusion therapy. Therefore, therapeutic co-targeting of dysregulated NVU cell types in acute ischemic stroke constitutes a promising strategy to preserve BBB function and improve clinical outcome. However, methods for simultaneous isolation of multiple NVU cell types from the same diseased central nervous system (CNS) tissue, crucial for the identification of therapeutic targets in dysregulated NVU cells, are lacking. Here, we present the EPAM-ia method, that facilitates simultaneous isolation and analysis of the major NVU cell types (endothelial cells, pericytes, astrocytes and microglia) for the identification of therapeutic targets in dysregulated NVU cells to improve the BBB function. Applying this method, we obtained a high yield of pure NVU cells from murine ischemic brain tissue, and generated a valuable NVU transcriptome database ( https://bioinformatics.mpi-bn.mpg.de/SGD_Stroke ). Dissection of the NVU transcriptome revealed Spp1, encoding for osteopontin, to be highly upregulated in all NVU cells 24 h after ischemic stroke. Upregulation of osteopontin was confirmed in stroke patients by immunostaining, which was comparable with that in mice. Therapeutic targeting by subcutaneous injection of an anti-osteopontin antibody post-ischemic stroke in mice resulted in neutralization of osteopontin expression in the NVU cell types investigated. Apart from attenuated glial activation, osteopontin neutralization was associated with BBB preservation along with decreased brain edema and reduced risk for hemorrhagic transformation, resulting in improved neurological outcome and survival. This was supported by BBB-impairing effects of osteopontin in vitro. The clinical significance of these findings is that anti-osteopontin antibody therapy might augment current approved reperfusion therapies in acute ischemic stroke by minimizing deleterious effects of ischemia-induced BBB disruption.

Four Decades of Ischemic Penumbra and Its Implication for Ischemic Stroke

The ischemic penumbra defined four decades ago has been the main battleground of ischemic stroke. The evolving ischemic penumbra concept has been providing insight for the development of vascular and cellular approaches as well as diagnostic tools for the treatment of ischemic stroke. rt-PA thrombolytic therapy to prevent the transition of ischemic penumbra to core has been approved for acute ischemic stroke within 3 h and was later recommended to extend to 4.5 h after symptom onset. Mechanical thrombectomy was introduced for the treatment of acute ischemic stroke with a therapeutic window of up to 24 h after stroke onset. Multiple modalities brain imaging techniques have been developed that provide guidance to define ischemic penumbra for reperfusion therapy in clinical practice. Cellular and molecular dissection of ischemic penumbra has been providing targets for the development of neuroprotective therapy for ischemic stroke. However, the dynamic nature of ischemic penumbra implicates that infarct core eventually expands into penumbra over time without reperfusion, dictating relative short therapeutic windows and limiting the impact of current reperfusion intervention. Entering the 5^th decade since the introduction, ischemic penumbra remains the main focus of ischemic stroke research and clinical practice. In this review, we summarized the evolving ischemic penumbra concept and its implication in the development of vascular and cellular interventions as well as diagnostic tools for acute ischemic stroke. In addition, we discussed future perspectives on expansion of the campaign beyond ischemic penumbra to develop treatment for ischemic stroke.

Cottonseed Oil Alleviates Ischemic Stroke-Induced Oxidative Stress Injury Via Activating the Nrf2 Signaling Pathway

Oxidative stress is believed to be one of the primary causes in ischemic stroke injury, and the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway is the most important endogenous antioxidative stress damage pathway. Cottonseed oil (CSO), which is used mostly as a solvent for lipid-soluble drugs, has been shown to exert antioxidative effects against peripheral tissue injury. However, the effects and mechanisms of CSO on ischemic stroke-induced oxidative stress injury and the Nrf2 signaling pathway remain largely unknown. In this study, we investigated the potential of CSO in regulating oxidative stress injury induced by middle cerebral artery occlusion and reperfusion (MCAO-R), or oxygen and glucose deprivation and reperfusion (OGD-R). We found that 1.3 mL/kg CSO treatment of male rats with a subcutaneous injection once every other day for 3 weeks significantly improved neurological deficit; reduced infarction volume; alleviated neuronal injuries; reduced the content of ROS and MDA; increased the activity of SOD, GSH, and GSH-PX; and markedly increased the expression of Nrf2. Furthermore, treatment with 10-9 μL/mL CSO to a neuron cell line (HT-22) for 24 h significantly increased cell viability and decreased cell apoptosis after OGD-R injury; significantly reduced the levels of ROS and MDA; increased the activity of SOD, GSH, and GSH-PX; and induced an increase in Nrf2 nuclear translocation. Based on our findings, we conclude that CSO treatment alleviates ischemic stroke injury-induced oxidative stress via activating the Nrf2 signaling pathway, highlighting the potential that CSO has as a therapeutic for ischemic strokes.

Drop-of-blood acoustic tweezing technique for integrative turbidimetric and elastometric measurement of blood coagulation

Many patients develop coagulation abnormalities due to chronic and hereditary disorders, infectious disease, blood loss, extracorporeal circulation, and oral anticoagulant misuse. These abnormalities lead to bleeding or thrombotic complications, the risk of which is assessed by coagulation analysis. Current coagulation tests pose safety concerns for neonates and small children due to large sample volume requirement and may be unreliable for patients with coagulopathy. This study introduces a containerless drop-of-blood method for coagulation analysis, termed "integrated quasi-static acoustic tweezing thromboelastometry" (i-QATT™), that addresses these needs. In i-QATT™, a single drop of blood is forced to levitate and deform by the acoustic radiation force. Coagulation-induced changes in drop turbidity and firmness are measured simultaneously at different instants. The parameters describing early, intermediate, and late stages of the coagulation process are evaluated from the resulting graphical outputs. i-QATT™ rapidly (<10 min) detected hyper- and hypo-coagulable states and identified single deficiency in coagulation factors VII, VIII, IX, X, and XIII. The linear relationship (r² > 0.9) was established between fibrinogen concentration and two i-QATT™ parameters: maximum clot firmness and maximum fibrin level. Factor XIII activity was uniquely measured by the fibrin network formation time (r² = 0.9). Reaction time, fibrin formation rate, and time to firm clot formation were linearly correlated with heparin concentration (r² > 0.7). tPA-induced hyperfibrinolysis was detected in the clot firmness output at 10 min. i-QATT™ provides comprehensive coagulation analysis in point-of-care or laboratory settings, well suited to the needs of neonatal and pediatric patients and adult patients with anemia or blood collection issues.

Extracellular Mitochondria Signals in CNS Disorders

Mitochondria actively participate in the regulation of cell respiratory mechanisms, metabolic processes, and energy homeostasis in the central nervous system (CNS). Because of the requirement of high energy, neuronal functionality and viability are largely dependent on mitochondrial functionality. In the context of CNS disorders, disruptions of metabolic homeostasis caused by mitochondrial dysfunction lead to neuronal cell death and neuroinflammation. Therefore, restoring mitochondrial function becomes a primary therapeutic target. Recently, accumulating evidence suggests that active mitochondria are secreted into the extracellular fluid and potentially act as non-cell-autonomous signals in CNS pathophysiology. In this mini-review, we overview findings that implicate the presence of cell-free extracellular mitochondria and the critical role of intercellular mitochondrial transfer in various rodent models of CNS disorders. We also discuss isolated mitochondrial allograft as a novel therapeutic intervention for CNS disorders.

Retinal Structural and Microvascular Alterations in Different Acute Ischemic Stroke Subtypes

Introduction

Retinal structural and microvascular damages reflect damage to cerebral microvasculature and neurons. We aimed to investigate neovascular unit abnormalities among patients with large-artery atherosclerosis (LAA) or small-vessel occlusion (SAA) and control subjects.

Methods

Twenty-eight LAA patients, forty-one SAA patients, and sixty-five age- and gender-matched controls were recruited. Based on optical coherence tomography angiography (OCTA), retinal capillary vessel density was assessed in the general and local sectors, and the thickness of individual retinal layer was extracted from retinal structural images. The differences between structural and microvascular were analyzed.

Results

The superior peripapillary retinal nerve fiber layer (pRNFL) thickness was significantly different among the three groups, and the LAA group had the thinnest thickness. Compared to the control group, the deep retinal capillary vessel density in other two stroke subgroups were significantly reduced in all regions except in the inferior region (P < 0.05), and the fractal dimension in C2 and C4 regions of deep retina was significantly lower in the LAA group (P < 0.05). Discussion. Compared with superficial microvascular network, deep microvascular network is more sensitive to ischemic stroke. In addition, we have demonstrated quadrant-specific pRNFL abnormalities in LAA and SAA patients. Superior quadrant pRNFL thickness differences between stroke subgroups may suggest that changes in retinal nerve fiber layer are more sensitive to subtype identification than changes in retinal microvascular structure. All in all, the alteration in retinal structural and microvascular may further elucidate the role of the neovascular unit in ischemic stroke, suggesting that the combination of these two indicators could be used for subtype identification to guide prognosis and establish a risk prediction model.

Neurovascular Unit: A critical role in ischemic stroke

Ischemic stroke (IS), a common cerebrovascular disease, results from a sudden blockage of a blood vessel in the brain, thereby restricting blood supply to the area in question, and making a significantly negative impact on human health. Unfortunately, current treatments, that are mainly based on a recanalization of occluded blood vessels, are insufficient or inaccessible to many stroke patients. Recently, the profound influence of the neurovascular unit (NVU) on recanalization and the prognosis of IS have become better understood; in‐depth studies of the NVU have also provided novel approaches for IS treatment. In this article, we review the intimate connections between the changes in the NVU and IS outcomes, and discuss possible new management strategies having practical significance to IS. We discuss the concept of the NVU, as well as its roles in IS blood‐brain barrier regulation, cell preservation, inflammatory immune response, and neurovascular repair. Besides, we also summarize the influence of noncoding RNAs in NVU, and IS therapies targeting the NVU. We conclude that both the pathophysiological and neurovascular repair processes of IS are strongly associated with the homeostatic state of the NVU and that further research into therapies directed at the NVU could expand the range of treatments available for IS.

Disruptions of Circadian Rhythms and Thrombolytic Therapy During Ischemic Stroke Intervention

Several endogenous and exogenous factors interact to influence stroke occurrence, in turn contributing to discernable daily distribution patterns in the frequency and severity of cerebrovascular events. Specifically, strokes that occur during the morning tend to be more severe and are associated with elevated diastolic blood pressure, increased hospital stay, and worse outcomes, including mortality, compared to strokes that occur later in the day. Furthermore, disrupted circadian rhythms are linked to higher risk for stroke and play a role in stroke outcome. In this review, we discuss the interrelation among core clock genes and several factors contributing to ischemic outcomes, sources of disrupted circadian rhythms, the implications of disrupted circadian rhythms in foundational stroke scientific literature, followed by a review of clinical implications. In addition to highlighting the distinct daily pattern of onset, several aspects of physiology including immune response, endothelial/vascular and blood brain barrier function, and fibrinolysis are under circadian clock regulation; disrupted core clock gene expression patterns can adversely affect these physiological processes, leading to a prothrombotic state. Lastly, we discuss how the timing of ischemic onset increases morning resistance to thrombolytic therapy and the risk of hemorrhagic transformation.

Blood-Brain Barrier Damage in Ischemic Stroke and Its Regulation by Endothelial Mechanotransduction

Ischemic stroke, a major cause of mortality in the United States, often contributes to disruption of the blood-brain barrier (BBB). The BBB along with its supportive cells, collectively referred to as the “neurovascular unit,” is the brain’s multicellular microvasculature that bi-directionally regulates the transport of blood, ions, oxygen, and cells from the circulation into the brain. It is thus vital for the maintenance of central nervous system homeostasis. BBB disruption, which is associated with the altered expression of tight junction proteins and BBB transporters, is believed to exacerbate brain injury caused by ischemic stroke and limits the therapeutic potential of current clinical therapies, such as recombinant tissue plasminogen activator. Accumulating evidence suggests that endothelial mechanobiology, the conversion of mechanical forces into biochemical signals, helps regulate function of the peripheral vasculature and may similarly maintain BBB integrity. For example, the endothelial glycocalyx (GCX), a glycoprotein-proteoglycan layer extending into the lumen of bloods vessel, is abundantly expressed on endothelial cells of the BBB and has been shown to regulate BBB permeability. In this review, we will focus on our understanding of the mechanisms underlying BBB damage after ischemic stroke, highlighting current and potential future novel pharmacological strategies for BBB protection and recovery. Finally, we will address the current knowledge of endothelial mechanotransduction in BBB maintenance, specifically focusing on a potential role of the endothelial GCX.

Early Electroacupuncture Extends the rtPA Time Window to 6 h in a Male Rat Model of Embolic Stroke via the ERK1/2-MMP9 Pathway

Background. Recombinant tissue plasminogen activator (rtPA) is the only recommended pharmacological treatment for acute ischemic stroke, but it has a restricted therapeutic time window. When administered at time points greater than 4.5 h after stroke onset, rtPA disrupts the blood-brain barrier (BBB), which leads to serious brain edema and hemorrhagic transformation. Electroacupuncture (EA) exerts a neuroprotective effect on cerebral ischemia; however, researchers have not clearly determined whether EA increases the safety of thrombolysis and extends the therapeutic time window of rtPA administration following ischemic stroke. Objective. The present study was conducted to test the hypothesis that EA extends the therapeutic time window of rtPA for ischemic stroke in a male rat model of embolic stroke. Methods. SD rats were randomly divided into the sham operation group, model group, rtPA group, EA+rtPA group, and rtPA+MEK1/2 inhibitor group. An injection of rtPA was administered 6 h after ischemia. Rats were treated with EA at the Shuigou (GV26) and Neiguan (PC6) acupoints at 2 h after ischemia. Neurological function, infarct volume, BBB permeability, brain edema, and hemorrhagic transformation were assessed at 24 h after ischemia. Western blotting and immunofluorescence staining were performed to detect the levels of proteins involved in the ERK1/2 signaling pathway (MEK1/2 and ERK1/2), tight junction proteins (Claudin5 and ZO-1), and MMP9 in the ischemic penumbra at 24 h after stroke. Results. Delayed rtPA treatment aggravated hemorrhagic transformation and brain edema. However, treatment with EA plus rtPA significantly improved neurological function and reduced the infarct volume, hemorrhagic transformation, brain edema, and EB leakage in rats compared with rtPA alone. EA increased the levels of tight junction proteins, inhibited the activation of the ERK1/2 signaling pathway, and reduced MMP9 overexpression induced by delayed rtPA thrombolysis. Conclusions. EA potentially represents an effective adjunct method to increase the safety of thrombolytic therapy and extend the therapeutic time window of rtPA administration following ischemic stroke. This neuroprotective effect may be mediated by the inhibition of the ERK1/2-MMP9 pathway and alleviation of the destruction of the BBB.

Diabetes Mellitus/Poststroke Hyperglycemia: a Detrimental Factor for tPA Thrombolytic Stroke Therapy

Intravenous administration of tissue-type plasminogen activator (IV tPA) therapy has long been considered a mainstay in ischemic stroke management. However, patients respond to IV tPA therapy unequally with some subsets of patients having worsened outcomes after treatment. In particular, diabetes mellitus (DM) is recognized as a clinically important vascular comorbidity that leads to lower recanalization rates and increased risks of hemorrhagic transformation (HT). In this short-review, we summarize the recent advances in understanding of the underlying mechanisms involved in post-IV tPA worsening of outcome in diabetic stroke. Potential pathologic factors that are related to the suboptimal tPA recanalization in diabetic stroke include higher plasma plasminogen activator inhibitor (PAI)-1 level, diabetic atherogenic vascular damage, glycation of the tPA receptor annexin A2, and alterations in fibrin clot density. While factors contributing to the exacerbation of HT in diabetic stroke include hyperglycemia, vascular oxidative stress, and inflammation, tPA neurovascular toxicity and imbalance in extracellular proteolysis are discussed. Besides, impaired collaterals in DM also compromise the efficacy of IV tPA therapy. Additionally, several tPA combination approaches developed from experimental studies that may help to optimize IV tPA therapy are also briefly summarized. In summary, more research efforts are needed to improve the safety and efficacy of IV tPA therapy in ischemic stroke patients with DM/poststroke hyperglycemia.

CDK5 Targeting as a Therapy for Recovering Neurovascular Unit Integrity in Alzheimer's Disease

The neurovascular unit (NVU) is responsible for synchronizing the energetic demand, vasodynamic changes, and neurochemical and electrical function of the brain through a closed and interdependent interaction of cell components conforming to brain tissue. In this review, we will focus on cyclin-dependent kinase 5 (CDK5) as a molecular pivot, which plays a crucial role in the healthy function of neurons, astrocytes, and the endothelium and is implicated in the cross-talk of cellular adhesion signaling, ion transmission, and cytoskeletal remodeling, thus allowing the individual and interconnected homeostasis of cerebral parenchyma. Then, we discuss how CDK5 overactivation affects the integrity of the NVU in Alzheimer's disease (AD) and cognitive impairment; we emphasize how CDK5 is involved in the excitotoxicity spreading of glutamate and Ca2+ imbalance under acute and chronic injury. Additionally, we present pharmacological and gene therapy strategies for producing partial depletion of CDK5 activity on neurons, astrocytes, or endothelium to recover neuroplasticity and neurotransmission, suggesting that the NVU should be the targeted tissue unit in protective strategies. Finally, we conclude that CDK5 could be effective due to its intervention on astrocytes by its end feet on the endothelium and neurons, acting as an intermediary cell between systemic and central communication in the brain. This review provides integrated guidance regarding the pathogenesis of and potential repair strategies for AD.

Clinical and Neuroimaging Correlation in Patients with COVID-19

BACKGROUND AND PURPOSE

Coronavirus disease 2019 (COVID-19) is increasingly being recognized for its multiorgan involvement, including various neurological manifestations. We examined the frequency of acute intracranial abnormalities seen on CT and/or MR imaging in patients with COVID-19 and investigated possible associations between these findings and clinical parameters, including length of hospital stay, requirement for intubation, and development of acute kidney injury.

MATERIALS AND METHODS

This was a retrospective study performed at a large academic hospital in the United States. A total of 641 patients presented to our institution between March 3, 2020, and May 6, 2020, for treatment of coronavirus disease 2019, of whom, 150 underwent CT and/or MR imaging of the brain. CT and/or MR imaging examinations were evaluated for the presence of hemorrhage, infarction, and leukoencephalopathy. The frequency of these findings was correlated with clinical variables, including body mass index, length of hospital stay, requirement for intubation, and development of acute kidney injury as documented in the electronic medical record.

RESULTS

Of the 150 patients, 26 (17%) had abnormal CT and/or MR imaging findings, with hemorrhage in 11 of the patients (42%), infarction in 13 of the patients (50%), and leukoencephalopathy in 7 of the patients (27%). Significant associations were seen between abnormal CT/MR imaging findings and intensive care unit admission (P = .039), intubation (P = .004), and acute kidney injury (P = .030).

CONCLUSIONS

A spectrum of acute neuroimaging abnormalities was seen in our cohort of patients with coronavirus disease 2019, including hemorrhage, infarction, and leukoencephalopathy. Significant associations between abnormal neuroimaging studies and markers of disease severity (intensive care unit admission, intubation, and acute kidney injury) suggest that patients with severe forms of coronavirus disease 2019 may have higher rates of neuroimaging abnormalities.

Cottonseed oil alleviates ischemic stroke injury by inhibiting the inflammatory activation of microglia and astrocyte

Background

Ischemic stroke is the second leading cause of death globally. The narrow time window for administering effective thrombolytic therapy motivates the search for alternative prevention strategies. Microglia and astrocyte activation-mediated inflammation play a pivotal role in ischemic stroke injury. Cottonseed oil (CSO) has been shown to exert anti-inflammatory effects against peripheral tissue injury, although CSO is mostly used as a solvent for lipid-soluble drugs. However, the role of CSO in neuroprotection against stroke has not been previously reported.

Methods

We treated adult male rats with CSO (1.3 ml/kg, subcutaneous injection, once every other day for 3 weeks) and then constructed a middle cerebral artery occlusion (MCAO) model followed by 24 h of reperfusion. Then, we measured the neurological scores, infarction volume, neuronal injury, and brain edema; we also measured the levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α), degree of microglial and astrocytic activation, protein expression levels of Toll-like receptor 4 (TLR4), nuclear factor kappa B (NF-κB), C3d and S100A10, and the presence of A1 type astrocytes and A2 type astrocytes.

Results

We found that CSO treatment significantly improved the neurological deficit, reduced infarction volume, and alleviated neuronal injuries, blood–brain barrier (BBB) disruption, and brain edema. Additionally, CSO treatment significantly reduced microglial and astrocytic activation, inhibited TLR4 and NF-κB protein expression, and reduced the release of IL-1β, IL-6, and TNF-α. Finally, CSO treatment significantly decreased the number of C3d/glial fibrillary acidic protein (GFAP)-positive cells and C3d protein expression, and increased the number of S100A10/GFAP-positive cells and S100A10 protein expression.

Conclusion

Our results first found that CSO treatment alleviated ischemic stroke injury by reducing microglial and astrocytic activation and inflammation, which was related to the inhibition of TLR4/NF-κB pathway and the reduction of A1 phenotype neurotoxic astrocyte activation, suggesting that CSO could be a new strategy in the prevention of ischemic stroke.

Bone Marrow-Derived NCS-01 Cells Advance a Novel Cell-Based Therapy for Stroke

Human mesenchymal stem cells have been explored for their application in cell-based therapies targeting stroke. Identifying cell lines that stand as safe, accessible, and effective for transplantation, while optimizing dosage, timing, and method of delivery remain critical translational steps towards clinical trials. Preclinical studies using bone marrow-derived NCS-01 cells show the cells' ability to confer functional recovery in ischemic stroke. Coculturing primary rat cortical cells or human neural progenitor cells with NCS-01 cells protects against oxygen-glucose deprivation. In the rodent middle cerebral artery occlusion model, intracarotid artery administration of NCS-01 cells demonstrate greater efficacy than other mesenchymal stem cells (MSCs) at improving motor and neurological function, as well as reducing infarct volume and peri-infarct cell loss. NCS-01 cells secrete therapeutic factors, including basic fibroblast growth factor and interleukin-6, while also demonstrating a potentially novel mechanism of extending filopodia towards the site of injury. In this review, we discuss recent preclinical advancements using in vitro and in vivo ischemia models that support the transplantation of NCS-01 in human stroke trials. These results, coupled with the recommendations put forth by the consortium of Stem cell Therapeutics as an Emerging Paradigm for Stroke (STEPS), highlight a framework for conducting preclinical research with the ultimate goal of initiating clinical trials.

Investigation on beneficial role of l-carnosine in neuroprotective mechanism of ischemic postconditioning in mice: possible role of histidine histamine pathway

OBJECTIVE

The present study was undertaken to investigate the possible role of histidine-histamine pathway in the neuroprotective effects produced by L-carnosine hand in hand with ischemic postconditioning in the animal model of cerebral ischemia.

METHODS

Cerebral ischemia was induced in swiss albino mice by performing BCCAO surgery. Morris water-maze test was utilized to assess the learning ability and memory of the animals. The whole brain acetylcholinesterase (AChE) activity, TBARS, GSH levels and MPO activity were evaluated as the biochemical parameters. For histopathological evaluation of the cerebral infarct size, TTC staining was employed.

RESULTS

Administration of L-carnosine (500   mg/kg, i.p.) successfully attenuated the manifestations of cerebral ischemia. Higher levels of AChE, TBARS, and MPO were observed in BCCAO treated animals, which were successfully attenuated by treatment with L-carnosine and ischemic postconditioning. Whereas administration of L-carnosine and ischemic postconditioning significantly increased the level of GSH in BCCAO treated animals. Moreover, treatment with ranitidine, an H₂ blocker (30 NMol, i.c.v) antagonized the neuroprotective actions of L-carnosine evidenced by decrease in MWM performance, increase in the level of AChE and oxidative stress, while decrease in GSH level in brain. The cerebral infarct size was found to be more in BCCAO inflicted animals, which was improved by the administration of L-carnosine, while the cerebral infarct size worsened by treatment with ranitidine (3   nmol, i.c.v.).

CONCLUSION

It is concluded that L-carnosine exerts neuroprotective effect via involvement of histidine-histamine pathway since the beneficial effects of L-carnosine were abolished by the H₂-blocker.

Recent updates on mechanisms of cell-cell interaction in oligodendrocyte regeneration after white matter injury

In most cases, neurological disorders that involve injuries of the cerebral white matter are accompanied by demyelination and oligodendrocyte damage. Promotion of remyelination process through the maturation of oligodendrocyte precursor cells (OPCs) is therefore proposed to contribute to the development of novel therapeutic approaches that could protect and restore the white matter from central nervous system diseases. However, efficient remyelination in the white matter could not be accomplished if various neighboring cell types are not involved to react with oligodendrocyte lineage cells in this process. Hence, profound understanding of cell-cell interaction between oligodendrocyte lineage cells and other cellular components is an essential step to achieve a breakthrough for the cure of white matter injury. In this mini-review, we provide recent updates on non-cell autonomous mechanisms of oligodendrocyte regeneration by introducing recent studies (e.g. published either in 2018 or 2019) that focus on crosstalk between oligodendrocyte lineage cells and the other constituents of the white matter.

Therapeutic use of extracellular mitochondria in CNS injury and disease

In the central nervous system (CNS), neuronal functionality is highly dependent on mitochondrial integrity and activity. In the context of a damaged or diseased brain, mitochondrial dysfunction leads to reductions in ATP levels, thus impairing ATP-dependent neural firing and neurotransmitter dynamics. Restoring mitochondrial ability to generate ATP may be a basic premise to restore neuronal functionality. Recently, emerging data in rodent and human studies suggest that mitochondria and its components are surprisingly released into extracellular space and potentially transferred between cells. Transferred mitochondria may support oxidative phosphorylation in recipient cells. In this mini-review, we (a) survey recent findings in cell to cell mitochondrial transfer and the presence of cell-free extracellular mitochondria and its components, (b) review experimental details of how to detect extracellular mitochondria and mitochondrial transfer in the CNS, (c) discuss strategies and tissue sources for mitochondria isolation, and (d) explore exogenous mitochondrial transplantation as a novel approach for CNS therapies.

β-Estradiol Protects Against Acidosis-Mediated and Ischemic Neuronal Injury by Promoting ASIC1a (Acid-Sensing Ion Channel 1a) Protein Degradation

Background and Purpose- Sex differences in the incidence and outcome of stroke have been well documented. The severity of stroke in women is, in general, significantly lower than that in men, which is mediated, at least in part, by the protective effects of β-estradiol. However, the detailed mechanisms underlying the neuroprotection by β-estradiol are still elusive. Recent studies have demonstrated that activation of ASIC1a (acid-sensing ion channel 1a) by tissue acidosis, a common feature of brain ischemia, plays an important role in ischemic brain injury. In the present study, we assessed the effects of β-estradiol on acidosis-mediated and ischemic neuronal injury both in vitro and in vivo and explored the involvement of ASIC1a and underlying mechanism. Methods- Cultured neurons and NS20Y cells were subjected to acidosis-mediated injury in vitro. Cell viability and cytotoxicity were measured by methylthiazolyldiphenyl-tetrazolium bromide and lactate dehydrogenase assays, respectively. Transient (60 minutes) focal ischemia in mice was induced by suture occlusion of the middle cerebral artery in vivo. ASIC currents were recorded using whole-cell patch-clamp technique while intracellular Ca2+ concentration was measured with fluorescence imaging using Fura-2. ASIC1a expression was detected by Western blotting and quantitative real-time polymerase chain reaction. Results- Treatment of neuronal cells with β-estradiol decreased acidosis-induced cytotoxicity. ASIC currents and acid-induced elevation of intracellular Ca2+ were all attenuated by β-estradiol treatment. In addition, we showed that β-estradiol treatment reduced ASIC1a protein expression, which was mediated by increased protein degradation, and that estrogen receptor α was involved. Finally, we showed that the level of ASIC1a protein expression in brain tissues and the degree of neuroprotection by ASIC1a blockade were lower in female mice, which could be attenuated by ovariectomy. Conclusions- β-estradiol can protect neurons against acidosis-mediated neurotoxicity and ischemic brain injury by suppressing ASIC1a protein expression and channel function. Visual Overview- An online visual overview is available for this article.

Concise Review: Stem Cell Therapy for Stroke Patients: Are We There Yet?

Four decades of preclinical research demonstrating survival, functional integration, and behavioral effects of transplanted stem cells in experimental stroke models have provided ample scientific basis for initiating limited clinical trials of stem cell therapy in stroke patients. Although safety of the grafted cells has been overwhelmingly documented, efficacy has not been forthcoming. Two recently concluded stroke clinical trials on mesenchymal stem cells (MSCs) highlight the importance of strict adherence to the basic science findings of optimal transplant regimen of cell dose, timing, and route of delivery in enhancing the functional outcomes of cell therapy. Echoing the Stem Cell Therapeutics as an Emerging Paradigm for Stroke and Stroke Treatment Academic Industry Roundtable call for an NIH‐guided collaborative consortium of multiple laboratories in testing the safety and efficacy of stem cells and their derivatives, not just as stand‐alone but preferably in combination with approved thrombolytic or thrombectomy, may further increase the likelihood of successful fruition of translating stem cell therapy for stroke clinical application. The laboratory and clinical experience with MSC therapy for stroke may guide the future translational research on stem cell‐based regenerative medicine in neurological disorders. stem cells translational medicine2019;8:983&988

Hollow Prussian Blue Nanozymes Drive Neuroprotection against Ischemic Stroke via Attenuating Oxidative Stress, Counteracting Inflammation, and Suppressing Cell Apoptosis

Ischemic stroke is a devastating disease and one of the leading causes of mortality worldwide. Overproduction of reactive oxygen and nitrogen species (RONS) following ischemic insult is known as a key factor in exacerbating brain damage. Thus, RONS scavengers that can block excessive production of RONS have great therapeutic potential. Herein, we propose an efficient treatment strategy in which an artificial nanozyme with multienzyme activity drives neuroprotection against ischemic stroke primarily by scavenging RONS. Specifically, through a facile, Bi³⁺-assisted, template-free synthetic strategy, we developed hollow Prussian blue nanozymes (HPBZs) with multienzyme activity to scavenge RONS in a rat model of ischemic stroke. The comprehensive characteristics of HPBZs against RONS were explored. Apart from attenuating oxidative stress, HPBZs also suppressed apoptosis and counteracted inflammation both in vitro and in vivo, thereby contributing to increased brain tolerance of ischemic injury with minimal side effects. This study provides a proof of concept for a novel class of neuroprotective nanoagents that might be beneficial for treatment of ischemic stroke and other RONS-related disorders.

Bexarotene Exerts Protective Effects Through Modulation of the Cerebral Vascular Smooth Muscle Cell Phenotypic Transformation by Regulating PPARγ/FLAP/LTB4 After Subarachnoid Hemorrhage in Rats

Vascular smooth muscle cells (VSMCs) play an important role after a subarachnoid hemorrhage (SAH). The changes in VSMCs following bexarotene treatment after SAH are unknown. In the present study, neurological impairment, decreased cerebral cortical blood flow and transformation of cerebral VSMCs from a contractile to a synthetic phenotype were observed after SAH. Bexarotene reduced neurological impairment, improved cerebral cortical blood flow, inhibited VSMC phenotypic transformation and suppressed the expression of 5-lipoxygenase-activating protein (FLAP) and leukotriene B4 (LTB₄), which was partly reversed by GW9662, an inhibitor of peroxisome proliferator-activated receptor gamma (PPARγ). Mechanistically, sh-PPARγ-mediated phenotypic transformation of VSMCs was partially suppressed by MK886, an antagonist of FLAP. Therefore, we conclude that bexarotene reduced neurological impairment, improved cerebral cortical blood flow and inhibited the VSMC phenotypic transformation after SAH, which was achieved by activating PPARγ-mediated inhibition of FLAP/LTB₄ in VSMCs.

What to Look for on Post-stroke Neuroimaging

The most feared complication after acute ischemic stroke is symptomatic or asymptomatic hemorrhagic conversion. Neuroimaging and clinical criteria are used to predict development of hemorrhage. Seizures after acute ischemic stroke or stroke-like symptoms from seizures are not common but may lead to confusion in the peristroke period, especially if seizures are repetitive or evolve into status epilepticus, which could affect neuroimaging findings. Malignant infarction develops when cytotoxic edema is large enough to lead to herniation and death. Post-stroke neuroimaging prognosticators have been described and should be assessed early so that appropriate treatment is offered before herniation leads to additional tissue injury.

Early Abrogation of Gelatinase Activity Extends the Time Window for tPA Thrombolysis after Embolic Focal Cerebral Ischemia in Mice

Acute ischemic stroke (AIS) is caused by clotting in the cerebral arteries, leading to brain oxygen deprivation and cerebral infarction. Recombinant human tissue plasminogen activator (tPA) is currently the only Food and Drug Administration-approved drug for ischemic stroke. However, tPA has to be administered within 4.5 h from the disease onset and delayed treatment of tPA can increase the risk of neurovascular impairment, including neuronal cell death, blood-brain barrier (BBB) disruption, and hemorrhagic transformation. A key contributing factor for tPA-induced neurovascular impairment is activation of matrix metalloproteinase-9 (MMP-9). We used a clinically-relevant mouse embolic model of focal-cerebral ischemia by insertion of a single embolus of blood clot to block the right middle cerebral artery. We showed that administration of the potent and highly selective gelatinase inhibitor SB-3CT extends the time window for administration of tPA, attenuating infarct volume, mitigating BBB disruption, and antagonizing the increase in cerebral hemorrhage induced by tPA treatment. We demonstrated that SB-3CT attenuates tPA-induced expression of vascular MMP-9, prevents gelatinase-mediated cleavage of extracellular laminin, rescues endothelial cells, and reduces caveolae-mediated transcytosis of endothelial cells. These results suggest that abrogation of MMP-9 activity mitigates the detrimental effects of tPA treatment, thus the combination treatment holds great promise for extending the therapeutic window for tPA thrombolysis, which opens the opportunity for clinical recourse to a greater number of patients.

Refocusing Neuroprotection in Cerebral Reperfusion Era: New Challenges and Strategies

Pathophysiological processes of stroke have revealed that the damaged brain should be considered as an integral structure to be protected. However, promising neuroprotective drugs have failed when translated to clinical trials. In this review, we evaluated previous studies of neuroprotection and found that unsound patient selection and evaluation methods, single-target treatments, etc., without cerebral revascularization may be major reasons of failed neuroprotective strategies. Fortunately, this may be reversed by recent advances that provide increased revascularization with increased availability of endovascular procedures. However, the current improved effects of endovascular therapy are not able to match to the higher rate of revascularization, which may be ascribed to cerebral ischemia/reperfusion injury and lacking of neuroprotection. Accordingly, we suggest various research strategies to improve the lower therapeutic efficacy for ischemic stroke treatment: (1) multitarget neuroprotectant combinative therapy (cocktail therapy) should be investigated and performed based on revascularization; (2) and more efforts should be dedicated to shifting research emphasis to establish recirculation, increasing functional collateral circulation and elucidating brain–blood barrier damage mechanisms to reduce hemorrhagic transformation. Therefore, we propose that a comprehensive neuroprotective strategy before and after the endovascular treatment may speed progress toward improving neuroprotection after stroke to protect against brain injury.

Brain vascular heterogeneity: implications for disease pathogenesis and design of in vitro blood-brain barrier models

The vertebrate blood–brain barrier (BBB) is composed of cerebral microvascular endothelial cells (CEC). The BBB acts as a semi-permeable cellular interface that tightly regulates bidirectional molecular transport between blood and the brain parenchyma in order to maintain cerebral homeostasis. The CEC phenotype is regulated by a variety of factors, including cells in its immediate environment and within functional neurovascular units. The cellular composition of the brain parenchyma surrounding the CEC varies between different brain regions; this difference is clearly visible in grey versus white matter. In this review, we discuss evidence for the existence of brain vascular heterogeneity, focusing on differences between the vessels of the grey and white matter. The region-specific differences in the vasculature of the brain are reflective of specific functions of those particular brain areas. This BBB-endothelial heterogeneity may have implications for the course of pathogenesis of cerebrovascular diseases and neurological disorders involving vascular activation and dysfunction. This heterogeneity should be taken into account when developing BBB-neuro-disease models representative of specific brain areas.

Role of Carbon Monoxide in Neurovascular Repair Processing

Carbon monoxide (CO) is a gaseous molecule produced from heme by heme oxygenase (HO). Endogenous CO production occurring at low concentrations is thought to have several useful biological roles. In mammals, especially humans, a proper neurovascular unit comprising endothelial cells, pericytes, astrocytes, microglia, and neurons is essential for the homeostasis and survival of the central nervous system (CNS). In addition, the regeneration of neurovascular systems from neural stem cells and endothelial precursor cells after CNS diseases is responsible for functional repair. This review focused on the possible role of CO/HO in the neurovascular unit in terms of neurogenesis, angiogenesis, and synaptic plasticity, ultimately leading to behavioral changes in CNS diseases. CO/HO may also enhance cellular networks among endothelial cells, pericytes, astrocytes, and neural stem cells. This review highlights the therapeutic effects of CO/HO on CNS diseases involved in neurogenesis, synaptic plasticity, and angiogenesis. Moreover, the cellular mechanisms and interactions by which CO/HO are exploited for disease prevention and their therapeutic applications in traumatic brain injury, Alzheimer's disease, and stroke are also discussed.

Neurovascular Alterations in Alzheimer's Disease: Transporter Expression Profiles and CNS Drug Access

Despite a century of steady and incremental progress toward understanding the underlying biochemical mechanisms, Alzheimer's disease (AD) remains a complicated and enigmatic disease, and greater insight will be necessary before substantive clinical success is realised. Over the last decade in particular, a large body of work has highlighted the cerebral microvasculature as an anatomical region with an increasingly apparent role in the pathogenesis of AD. The causative interplay and temporal cascade that manifest between the brain vasculature and the wider disease progression of AD are not yet fully understood, and further inquiry is required to properly characterise these relationships. The purpose of this review is to highlight the recent advancements in research implicating neurovascular factors in AD, at both the molecular and anatomical levels. We begin with a brief introduction of the biochemical and genetic aspects of AD, before reviewing the essential concepts of the blood-brain barrier (BBB) and the neurovascular unit (NVU). In detail, we then examine the evidence demonstrating involvement of BBB dysfunction in AD pathogenesis, highlighting the importance of neurovascular components in AD. Lastly, we include within this review research that focuses on how altered properties of the BBB in AD impact upon CNS exposure of therapeutic agents and the potential clinical impact that this may have on people with this disease.

Role of Transporters in Central Nervous System Drug Delivery and Blood-Brain Barrier Protection: Relevance to Treatment of Stroke

Ischemic stroke is a leading cause of morbidity and mortality in the United States. The only approved pharmacologic treatment for ischemic stroke is thrombolysis via recombinant tissue plasminogen activator (r-tPA). A short therapeutic window and serious adverse events (ie, hemorrhage, excitotoxicity) greatly limit r-tPA therapy, which indicates an essential need to develop novel stroke treatment paradigms. Transporters expressed at the blood-brain barrier (BBB) provide a significant opportunity to advance stroke therapy via central nervous system delivery of drugs that have neuroprotective properties. Examples of such transporters include organic anion–transporting polypeptides (Oatps) and organic cation transporters (Octs). In addition, multidrug resistance proteins (Mrps) are transporter targets in brain microvascular endothelial cells that can be exploited to preserve BBB integrity in the setting of stroke. Here, we review current knowledge on stroke pharmacotherapy and demonstrate how endogenous BBB transporters can be targeted for improvement of ischemic stroke treatment.

Astrocyte-specific insulin-like growth factor-1 gene transfer in aging female rats improves stroke outcomes

Middle aged female rats sustain larger stroke infarction and disability than younger female rats. This older group also shows age-related reduction of insulin like growth factor (IGF)-1 in serum and in astrocytes, a cell type necessary for poststroke recovery. To determine the impact of astrocytic IGF-1 for ischemic stroke, these studies tested the hypothesis that gene transfer of IGF-1 to astrocytes will improve stroke outcomes in middle aged female rats. Middle aged (10-12 month old), acyclic female rats were injected with recombinant adeno-associated virus serotype 5 (AAV5) packaged with the coding sequence of the human (h)IGF-1 gene downstream of an astrocyte-specific promoter glial fibrillary acidic protein (GFAP) (AAV5-GFP-hIGF-1) into the striatum and cortex. The AAV5-control consisted of an identical shuttle vector construct without the hIGF-1 gene (AAV5-GFAP-control). Six to eight weeks later, animals underwent transient (90 min) middle cerebral artery occlusion via intraluminal suture. While infarct volume was not altered, AAV5-GFAP-hIGF-1 treatment significantly improved blood pressure and neurological score in the early acute phase of stroke (2 days) and sensory-motor performance at both the early and late (5 days) acute phase of stroke. AAV5-GFAP-hIGF-1 treatment also reduced circulating serum levels of GFAP, a biomarker for blood brain barrier permeability. Flow cytometry analysis of immune cells in the brain at 24 hr poststroke showed that AAV5-GFAP-hIGF-1 altered the type of immune cells trafficked to the ischemic hemisphere, promoting an anti-inflammatory profile. Collectively, these studies show that targeted enhancement of IGF-1 in astrocytes of middle-aged females improves stroke-induced behavioral impairment and neuroinflammation.

How Can We Treat Cancer Disease Not Cancer Cells?

Since molecular biology studies began, researches in biological science have centered on proteins and genes at molecular level of a single cell. Cancer research has also focused on various functions of proteins and genes that distinguish cancer cells from normal cells. Accordingly, most contemporary anticancer drugs have been developed to target abnormal characteristics of cancer cells. Despite the great advances in the development of anticancer drugs, vast majority of patients with advanced cancer have shown grim prognosis and high rate of relapse. To resolve this problem, we must reevaluate our focuses in current cancer research. Cancer should be considered as a systemic disease because cancer cells undergo a complex interaction with various surrounding cells in cancer tissue and spread to whole body through metastasis under the control of the systemic modulation. Human body relies on the cooperative interaction between various tissues and organs, and each organ performs its specialized function through tissue-specific cell networks. Therefore, investigation of the tumor-specific cell networks can provide novel strategy to overcome the limitation of current cancer research. This review presents the limitations of the current cancer research, emphasizing the necessity of studying tissue-specific cell network which could be a new perspective on treating cancer disease, not cancer cells.

Neuroprotective effect of lercanidipine in middle cerebral artery occlusion model of stroke in rats

Oxidative stress, inflammation and apoptotic neuronal cell death are cardinal mechanisms involved in the cascade of acute ischemic stroke. Lercanidipine apart from calcium channel blocking activity possesses anti-oxidant, anti-inflammatory and anti-apoptotic properties. In the present study, we investigated neuroprotective efficacy and therapeutic time window of lercanidipine in a 2h middle cerebral artery occlusion (MCAo) model in male Wistar rats. The study design included: acute (pre-treatment and post-treatment) and sub-acute studies. In acute studies (pre-treatment) lercanidipine (0.25, 0.5 and 1mg/kg, i.p.) was administered 60min prior MCAo. The rats were assessed 24h post-MCAo for neurological deficit score (NDS), motor deficit paradigms (grip test and rota rod) and cerebral infarction via 2,3,5-triphenyltetrazolium chloride (TTC) staining. The most effective dose was found to be at 0.5mg/kg, i.p., which was considered for further studies. Regional cerebral blood flow (rCBF) was monitored till 120min post-reperfusion to assess vasodilatory property of lercanidipine (0.5mg/kg, i.p.) administered at two different time points: 60min post-MCAo and 15min post-reperfusion. In acute studies (post-treatment) lercanidipine (0.5mg/kg, i.p.) was administered 15min, 120min and 240min post-reperfusion. Based on NDS and cerebral infarction via TTC staining assessed 24h post-MCAo, effectiveness was evident upto 120min. For sub-acute studies same dose/vehicle was repeated for next 3days and magnetic resonance imaging (MRI) was performed 96h after the last dose. Biochemical markers estimated in rat brain cortex 24h post-MCAo were oxidative stress (malondialdehyde, reduced glutathione, nitric oxide, superoxide dismutase), blood brain barrier damage (matrix metalloproteinases-2 and -9) and apoptotic (caspase-3 and -9). Lercanidipine significantly reduced NDS, motor deficits and cerebral infarction volume as compared to the control group. Lercanidipine (60min post-MCAo) significantly increased rCBF (86%) as compared to vehicle treated MCAo group (64%) 120min post-reperfusion, but failed to show vasodilatation with 15min post-reperfusion group. Lercanidipine (13.78±2.78%) significantly attenuated percentage infarct volume as evident from diffusion-weighted (DWI) and T2-weighted images as compared to vehicle treated MCAo group (25.90±2.44%) investigated 96h post-MCAo. The apparent diffusion coefficient (ADC) was also significantly improved in lercanidipine group as compared to control group. Biochemical alterations were significantly ameliorated by lercanidipine till 120min post-reperfusion group and MMP-9 inhibition observed even with 240min group. Thus, lercanidipine revealed significant neuroprotective effect mediated through attenuation of oxidative stress, inflammation and apoptosis.

Regulation of Dipeptidyl Peptidase IV in the Post-stroke Rat Brain and In Vitro Ischemia: Implications for Chemokine-Mediated Neural Progenitor Cell Migration and Angiogenesis

Cerebral ischemia evokes abnormal release of proteases in the brain microenvironment that spatiotemporally impact angio-neurogenesis. Dipeptidyl peptidase IV (DPPIV), a cell surface and secreted protease, has been implicated in extracellular matrix remodeling by regulating cell adhesion, migration, and angiogenesis through modifying the functions of the major chemokine stromal-derived factor, SDF1. To elucidate the possible association of DPPIV in ischemic brain, we examined the expression of DPPIV in the post-stroke rat brain and under in vitro ischemia by oxygen glucose deprivation (OGD). We further investigated the effects of DPPIV on SDF1 mediated in vitro chemotactic and angiogenic functions. DPPIV protein and mRNA levels were significantly upregulated during repair phase in the ischemic cortex of the rat brain, specifically in neurons, astrocytes, and endothelial cells. In vitro exposure of Neuro-2a neuronal cells and rat brain endothelial cells to OGD resulted in upregulation of DPPIV. In vitro functional analysis showed that DPPIV decreases the SDF1-mediated angiogenic potential of rat brain endothelial cells and inhibits the migration of Neuro-2a and neural progenitor cells. Western blot analyses revealed decreased levels of phosphorylated ERK1/2 and AKT in the presence of DPPIV. DPPIV inhibitor restored the effects of SDF1. Proteome profile array screening further revealed that DPPIV decreases matrix metalloproteinase-9, a key downstream effector of ERK-AKT signaling pathways. Overall, delayed induction of DPPIV in response to ischemia/reperfusion suggests that DPPIV may play an important role in endogenous brain tissue remodeling and repair processes. This may be mediated through modulation of SDF1-mediated cell migration and angiogenesis.

Effects of Xiaoshuan enteric-coated capsule on neurovascular functions assessed by quantitative multiparametric MRI in a rat model of permanent cerebral ischemia

Background

Buyang Huanwu Decoction (BYHWD) is a Traditional Chinese Medicine (TCM) formula for treating stroke-induced disability. Xiaoshuan enteric-coated capsule (XSECC), derived from the formula BYHWD, is a drug approved by the China Food and Drug Administration (CFDA) for stroke management. To further investigate the potential protective effects of XSECC on neurovascular functions, we endeavour to monitor the neurovascular functions using multimodal magnetic resonance imaging (MRI) and evaluated histopathological changes of neurovascular unit (NVU) after stroke.

Methods

Ischemic stroke was induced by permanent middle cerebral artery occlusion (pMCAO). XSECC (420 mg/kg) was orally administered 2 h after stroke and daily thereafter. T2-weighted imaging (T2WI), T2 relaxometry mapping and diffusion tensor imaging (DTI) were used to measure cerebral infarct volume, edema and white matter fiber integrity, respectively. Neurochemical metabolite levels were monitored by ¹H-magnetic resonance spectroscopy (¹H-MRS). Arterial spin labeling (ASL) – cerebral blood flow (CBF) measurements and structural magnetic resonance angiography (MRA) images provided real-time and dynamic information about vascular hemodynamic dysfunction on the 3rd, 7th and 14th days after pMCAO. At the last imaging time point, immunohistochemistry, immunofluorescence as well as transmission electron microscopy (TEM) were used to test the microscopic and ultrastructural changes of NVU.

Results

T2WI, T2 relaxometry mapping and Fractional anisotropy (FA) in DTI showed that XSECC significantly reduced cerebral infarct volume, relieved edema and alleviated nerve fiber injuries, respectively. ¹H-MRS provided information about improvement of neuronal/glial metabolism after XSECC treatment. Moreover, ASL – CBF measurements combined with MRA showed that XSECC significantly increased CBF and vascular signal strength and alleviated ischemia-induced morphological changes of arteries in ischemic hemisphere within 14 days after stroke. In addition, neuron specific nuclear protein (NeuN), glial fibrillary acidic protein (GFAP), CD34 staining and TEM detection indicated that XSECC not only ameliorated neuronal injury, but also reduced endothelial damage and inhibited astrocyte proliferation.

Conclusions

Our results suggested that XSECC has multi-target neurovascular protective effects on ischemic stroke, which may be closely correlated with the improvement of cerebral blood supply and neuronal/glial metabolism.

Role of serum- and glucocorticoid-inducible kinases in stroke

Increased expression of serum- and glucocorticoid-inducible kinase 1 (SGK1) can be induced by stress and growth factors in mammals, and plays an important role in cancer, diabetes, and hypertension. A recent work suggested that SGK1 activity restores damage in a stroke model. To further investigate the role of SGKs in ischemic brain injury, we examined how SGK inhibitors influence stroke outcome in vivo and neurotoxicity in vitro. Infarct volumes were compared in adult mice with middle cerebral artery occlusion, followed by 24 h reperfusion, in the absence or presence of SGK inhibitors. Neurotoxicity assay, electrophysiological recording, and fluorescence Ca(2+) imaging were carried out using cultured cortical neurons to evaluate the underlying mechanisms. Contrary to our expectation, infarct volume by stroke decreased significantly when SGK inhibitor, gsk650394, or EMD638683, was administrated 30 min before middle cerebral artery occlusion under normal and diabetic conditions. SGK inhibitors reduced neurotoxicity mediated by N-methyl-D-aspartate (NMDA) receptors, a leading factor responsible for cell death in stroke. SGK inhibitors also ameliorated Ca(2+) increase and peak amplitude of NMDA current in cultured neurons. In addition, SGK inhibitor gsk650394 decreased phosphorylation of Nedd4-2 and inhibited voltage-gated sodium currents. These observations suggest that SGK activity exacerbates stroke damage and that SGK inhibitors may be useful candidates for therapeutic intervention. To investigate the role of serum- and glucocorticoid-inducible kinases (SGKs) in ischemic brain injury, we examined how SGK inhibitors influence stroke outcome. Infarct volumes induced by middle cerebral artery occlusion were decreased significantly by SGK inhibitors. The inhibitors also reduced glutamate toxicity, at least partly, by attenuation of NMDA and voltage-gated sodium currents. Thus, SGK inhibition attenuates stroke damage.

Mechanisms of cellular plasticity in cerebral perivascular region

Brain vasculature acts in synergism with neurons to maintain brain function. This neurovascular coupling, or trophic coupling between cerebral endothelium and neuron, is now well accepted as a marker for mapping brain activity. Neurovascular coupling is most active in the perivascular region, in which there are ample opportunities for cell-cell interactions within the neurovascular unit. This trophic coupling between cells maintains neurovascular function and cellular plasticity. Recent studies have revealed that even adult brains contain multiple stem cells of various lineages, which may provide cellular plasticity through the process of differentiation among these stem cell populations. In this chapter, we provide an overview of the process by which neurovascular components contribute to cellular plasticity in the cerebral perivascular regions, focusing on mechanisms of cell-cell interaction in adult brain.