MicroRNA-126-3p/-5p Overexpression Attenuates Blood-Brain Barrier Disruption in a Mouse Model of Middle Cerebral Artery Occlusion

Zebularine protects against blood-brain-barrier (BBB) disruption through increasing the expression of zona occludens-1 (ZO-1) and vascular endothelial (VE)-cadherin

Blood-brain-barrier (BBB) disruption is an important pathological characteristic of ischemic stroke (IS) and mainly results from dysfunction of brain vascular endothelial cells and tight junctions. Zebularine is a novel inhibitor of DNA methyltransferase (DNMT). Here, we assessed its effects on BBB disruption in IS. Firstly, we reported that Zebularine maintained BBB integrity in middle cerebral artery occlusion (MCAO) mice by increasing the expressions of zona occludens-1 (ZO-1) and vascular endothelial (VE)-cadherin. Importantly, we found that Zebularine reduced the production of pro-inflammatory cytokines, attenuated brain edema, and improved neurological deficits. In in vitro experiments, the bEnd.3 brain endothelial cells were exposed to oxygen and glucose deprivation/reoxygenation (OGD/R), and the protective effects of Zebularine were assessed. Our findings demonstrated that Zebularine prevented OGD/R-induced cytotoxicity by reducing the release of lactate dehydrogenase (LDH). Additionally, Zebularine protected bEnd.3 cells against OGD/R-induced hyper-permeability and reduction of trans-endothelial electrical resistance (TEER). Notably, we found that treatment with Zebularine activated the Adenosine 5ʹ-monophosphate (AMP)-activated protein kinase (AMPK) pathway by increasing the phosphorylation of adenosine monophosphate-activated protein kinase α (AMPKα). Blockage of AMPKα using its specific inhibitor compound C abolished the beneficial effects of Zebularine in mitigating endothelial hyper-permeability by reducing the expressions of ZO-1 and VE-cadherin. These findings suggest that the protective effects of Zebularine against OGD/R-induced endothelial hyper-permeability are mediated by the activation of AMPKα. In conclusion, our study sheds light on the potential application of Zebularine in the treatment of IS.

Extracellular vesicles from adipose-derived stem cells promote microglia M2 polarization and neurological recovery in a mouse model of transient middle cerebral artery occlusion

Background

Adipose-derived stem cells (ADSCs) and their extracellular vesicles (EVs) have therapeutic potential in ischemic brain injury, but the underlying mechanism is poorly understood. The current study aimed to explore the contribution of miRNAs in ADSC-EVs to the treatment of cerebral ischemia.

Methods

After the intravenous injection of ADSC-EVs, therapeutic efficacy was evaluated by neurobehavioral tests and brain atrophy volume. The polarization of microglia was assessed by immunostaining and qPCR. We further performed miRNA sequencing of ADSC-EVs and analyzed the relationship between the upregulated miRNAs in ADSC-EVs and microglial polarization-related proteins using Ingenuity Pathway Analysis (IPA).

Results

The results showed that ADSC-EVs reduced brain atrophy volume, improved neuromotor and cognitive functions after mouse ischemic stroke. The loss of oligodendrocytes was attenuated after ADSC-EVs injection. The number of blood vessels, as well as newly proliferated endothelial cells in the peri-ischemia area were higher in the ADSC-EVs treated group than that in the PBS group. In addition, ADSC-EVs regulated the polarization of microglia, resulting in increased repair-promoting M2 phenotype and decreased pro-inflammatory M1 phenotype. Finally, STAT1 and PTEN were highlighted as two downstream targets of up-regulated miRNAs in ADSC-EVs among 85 microglia/macrophage polarization related proteins by IPA. The inhibition of STAT1 and PTEN by ADSC-EVs were confirmed in cultured microglia.

Conclusions

In summary, ADSC-EVs reduced ischemic brain injury, which was associated with the regulation of microglial polarization. miRNAs in ADSC-EVs partly contributed to their function in regulating microglial polarization by targeting PTEN and STAT1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02668-0.

Dexmedetomidine alleviates cognitive impairment by reducing blood-brain barrier interruption and neuroinflammation via regulating Th1/Th2/Th17 polarization in an experimental sepsis model of mice

Clinical studies have shown that dexmedetomidine (DEX) reduces mortality and inflammation in patients with sepsis, and ameliorates cognitive decline in both postoperative and critical care patients. This study aims to explain the neuroprotective effects provided by DEX in mice with cecal ligation and puncture (CLP)-induced polymicrobial sepsis. Mice were treated with DEX intraperitoneally three times every two hours after CLP. The survival rate, body weight, and clinical scores were recorded each day. Morris water maze (MWM) and fear conditioning tests were used to evaluate cognitive function. Blood brain barrier (BBB) permeability, hippocampal inflammation, hippocampal neural apoptosis, and T helper (Th) cell subgroups were assessed. Furthermore, Atipamezole was used to verify that the potential neuroprotective effects in the sepsis-associated encephalopathy (SAE) were mediated by DEX. Compared with the Sham group, CLP mice showed significant cognitive impairment, BBB interruption, excessive neuroinflammation, and neuronal apoptosis. These detrimental effects of CLP were attenuated by DEX. Furthermore, we found that DEX corrects peripheral Th1/Th2/Th17 shift and reduces proinflammatory cytokines in the hippocampus. Additionally, atipamezole prevented DEX's protective effect. Taken together, DEX alleviates cognitive impairments by reducing blood-brain barrier interruption and neuroinflammation by regulating Th1/Th2/Th17 polarization.

Emerging therapeutic targets for cerebral edema

INTRODUCTION

Cerebral edema is a key contributor to death and disability in several forms of brain injury. Current treatment options are limited, reactive, and associated with significant morbidity. Targeted therapies are emerging based on a growing understanding of the molecular underpinnings of cerebral edema.

AREAS COVERED

We review the pathophysiology and relationships between different cerebral edema subtypes to provide a foundation for emerging therapies. Mechanisms for promising molecular targets are discussed, with an emphasis on those advancing in clinical trials, including ion and water channels (AQP4, SUR1-TRPM4) and other proteins/lipids involved in edema signaling pathways (AVP, COX2, VEGF, and S1P). Research on novel treatment modalities for cerebral edema [including recombinant proteins and gene therapies] is presented and finally, insights on reducing secondary injury and improving clinical outcome are offered.

EXPERT OPINION

Targeted molecular strategies to minimize or prevent cerebral edema are promising. Inhibition of SUR1-TRPM4 (glyburide/glibenclamide) and VEGF (bevacizumab) are currently closest to translation based on advances in clinical trials. However, the latter, tested in glioblastoma multiforme, has not demonstrated survival benefit. Research on recombinant proteins and gene therapies for cerebral edema is in its infancy, but early results are encouraging. These newer modalities may facilitate our understanding of the pathobiology underlying cerebral edema.

Epigenetic Regulations of Microglia/Macrophage Polarization in Ischemic Stroke

Ischemic stroke is one of the leading causes of death and disability worldwide. Microglia/macrophages (MMs)-mediated neuroinflammation contributes significantly to the pathological process of ischemic brain injury. Microglia, serving as resident innate immune cells in the central nervous system, undergo pro-inflammatory phenotype or anti-inflammatory phenotype in response to the microenvironmental changes after cerebral ischemia. Emerging evidence suggests that epigenetics modifications, reversible modifications of the phenotype without changing the DNA sequence, could play a pivotal role in regulation of MM polarization. However, the knowledge of the mechanism of epigenetic regulations of MM polarization after cerebral ischemia is still limited. In this review, we present the recent advances in the mechanisms of epigenetics involved in regulating MM polarization, including histone modification, non-coding RNA, and DNA methylation. In addition, we discuss the potential of epigenetic-mediated MM polarization as diagnostic and therapeutic targets for ischemic stroke. It is valuable to identify the underlying mechanisms between epigenetics and MM polarization, which may provide a promising treatment strategy for neuronal damage after cerebral ischemia.

Combined Analysis of Surface Protein Profile and microRNA Expression Profile of Exosomes Derived from Brain Microvascular Endothelial Cells in Early Cerebral Ischemia

Endothelial cell damage is an important pathological basis for the deterioration of acute ischemia stroke. Our previous studies have been exploring the mechanism of blood-brain barrier (BBB) endothelial cell injury in the early stage of cerebral ischemia. Exosomes act as an important intercellular player in neurovascular communication. However, the characteristic of exosomes derived from BBB endothelial cells in early ischemic stroke is poorly understood. We exposed cultured brain microvascular endothelial cells (bEnd.3) to 3 h oxygen glucose deprivation (OGD) to mimic early cerebral ischemia in vitro and compared miRome and surface protein contents of exosomes derived from bEnd.3 cells by miRNA sequencing and the proximity barcoding assay (PBA). A total of 346 differentially miRNA (159 upregulated and 187 downregulated) were identified via miRNA-Seq in bEnd.3 cells after exposure to OGD for 3 h. Moreover, Gene Ontology (GO) and KEGG pathway analyses showed that cell proliferation- and angiogenesis-associated miRNAs were significantly affected. The abnormal changes in top eight miRNAs were further verified by a quantitative polymerase chain reaction (qPCR). PBA experiments showed that the numbers of exosomes carrying the following proteins increased significantly under ischemia, including bFGF, CD146, EPHA2, ABCB5, and ITGB2. These proteins were related to angiogenesis, cell proliferation, and cell inflammation. The network analysis combining PBA data with miRNA-Seq data showed that 79 miRNAs were related to 24 membrane proteins and predicted that there were surface proteins associated with a variety of miRNA molecules, such as ITGA9, XIAP, ADAM1, ITGA2, ITGA3, PDPN, and ITGB1. Meanwhile, there were miRNAs related to various surface proteins including miR-410-3p, miR-378b, and miR-1960. Taken together, our data demonstrated for the first time the changes of exosomal miRNAs and surface protein profiles derived from ischemic microvascular endothelial cells, which may provide new therapeutic targets for BBB protection in ischemic stroke.

Propofol attenuates renal ischemia/reperfusion injury by regulating the MALAT1/miR-126-5p axis

BACKGROUND

Propofol (PPF) plays a protective role in ischemia-reperfusion (I/R) in multiple organs, including renal ischemia-reperfusion injury (RIRI). The present study aimed to investigate the underlying mechanisms by which PPF exerts its protective functions in RIRI.

METHODS

BALB/c mice were employed for the construction of RIRI animal model. PPF pre-treatment was carried out before I/R. An in vitro I/R model was established with HK-2 cells after hypoxia/reoxygenation (H/R) culture, and PPF was utilized to treat the cells before H/R. A quantitative-polymerase chain reaction (qPCR) was conducted to detect long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and miR-126-5p expression levels. Flow cytometry was adopted to detect the apoptosis of HK-2 cells. Bioinformatics analysis, qPCR, a luciferase reporter gene experiment and a RNA immunoprecipitation experiment were used to determine the regulatory relationship between MALAT1 and miR-126-5p. The expression level of vascular endothelial growth factor A (VEGFA) was examined by western blotting.

RESULTS

MALAT1 expression was augmented and miR-126-5p was decreased in RIRI models. PPF pre-treatment remarkably reduced creatinine and urea nitrogen levels in the serum of BALB/c mice with RIRI, and diminished the apoptosis of HK-2 cells treated with H/R. In addition, PPF pre-treatment markedly restrained the expression of MALAT1 in both in vivo and in vitro models and up-regulated miR-126-5p expression. MALAT1 could adsorb miR-126-5p to repress it and up-regulate VEGFA. MALAT1 overexpression reversed the protective effects of PPF on RIRI.

CONCLUSIONS

PPF protects the kidney against RIRI by inhibiting MALAT1 and up-regulating miR-126-5p expression, as well as indirectly inhibiting the expression of VEGFA.

Brain Hypoxia Is Associated With Neuroglial Injury in Humans Post-Cardiac Arrest

Supplemental Digital Content is available in the text.

Secondary brain hypoxia portends significant mortality in ischemic brain diseases; yet, our understanding of hypoxic ischemic brain injury (HIBI) pathophysiology in humans remains rudimentary.

Involvement of noncoding RNA in blood-brain barrier integrity in central nervous system disease

Given the important role of the blood-brain barrier (BBB) in the central nervous system (CNS), increasing studies have been carried out to determine how the structural and functional integrity of the BBB impacts the pathogenesis of CNS diseases such as stroke, traumatic brain injuries (TBIs), and gliomas. Emerging studies have revealed that noncoding RNAs (ncRNAs) help to maintain the integrity and permeability of the BBB, thereby mediating CNS homeostasis. This review summarizes recent studies that focus on the effects of ncRNAs on the BBB in CNS diseases, including regulating the biological processes of inflammation, necrosis, and apoptosis of cells, affecting the translational dysfunction of proteins and regulating tight junctions (TJs). A comprehensive and detailed understanding of the interaction between ncRNAs and the BBB will lay a solid foundation for the development of early diagnostic methods and effective treatments for CNS diseases.

Effective silencing of miR-126 after ischemic stroke by means of intravenous α-tocopherol-conjugated heteroduplex oligonucleotide in mice

Brain endothelial cells (BECs) are involved in the pathogenesis of ischemic stroke. Recently, several microRNAs (miRNAs) in BECs were reported to regulate the endothelial function in ischemic brain. Therefore, modulation of miRNAs in BECs by a therapeutic oligonucleotide to inhibit miRNA (antimiR) could be a useful strategy for treating ischemic stroke. However, few attempts have been made to achieve this strategy via systemic route due to lack of efficient delivery-method toward BECs. Here, we have developed a new technology for delivering an antimiR into BECs and silencing miRNAs in BECs, using a mouse ischemic stroke model. We designed a heteroduplex oligonucleotide, comprising an antimiR against miRNA-126 (miR-126) known as the endothelial-specific miRNA and its complementary RNA, conjugated to α-tocopherol as a delivery ligand (Toc-HDO targeting miR-126). Intravenous administration of Toc-HDO targeting miR-126 remarkably suppressed miR-126 expression in ischemic brain of the model mice. In addition, we showed that Toc-HDO targeting miR-126 was delivered into BECs more efficiently than the parent antimiR in ischemic brain, and that it was delivered more effectively in ischemic brain than non-ischemic brain of this model mice. Our study highlights the potential of this technology as a new clinical therapeutic option for ischemic stroke.

MicroRNA miR-126 attenuates brain injury in septic rats via NF-κB signaling pathway

The purpose of this study was to investigate the impact and mechanism of microRNA miR-126 on brain injury induced by blood-brain barrier (BBB) damage in septic rats. We used cecal ligation and perforation (CLP) to create a rat model of sepsis. The experimental rats were randomly divided into Control group, CLP group, CLP + miR-NC group, CLP + miR-126 group and CLP + miR-126 + NF-κB pathway agonist (PMA) group. MiR-126 expressed in the brain tissue of CLP rats was down-regulated by qRT-PCR. Upregulation of miR-126 in CLP rats could improve brain injury and BBB marker protein level, reduce brain water content, Evans blue extravasation, inflammation, and excessive oxidative stress. This could also result in an inhibition of NF-κB signaling pathway activity. In conclusion, miR-126 overexpression can prevent brain injury caused by BBB damage via the inhibition of NF-κB signaling pathway activity.

TNF-α Receptor Inhibitor Alleviates Metabolic and Inflammatory Changes in a Rat Model of Ischemic Stroke

Hyperglycemia and inflammation, with their augmented interplay, are involved in cases of stroke with poor outcomes. Interrupting this vicious cycle thus has the potential to prevent stroke disease progression. Tumor necrosis factor-α (TNF-α) is an emerging molecule, which has inflammatory and metabolic roles. Studies have shown that TNF-α receptor inhibitor R-7050 possesses neuroprotective, antihyperglycemic, and anti-inflammatory effects. Using a rat model of permanent cerebral ischemia, pretreatment with R-7050 offered protection against poststroke neurological deficits, brain infarction, edema, oxidative stress, and caspase 3 activation. In the injured cortical tissues, R-7050 reversed the activation of TNF receptor-I (TNFRI), NF-κB, and interleukin-6 (IL-6), as well as the reduction of zonula occludens-1 (ZO-1). In the in vitro study on bEnd.3 endothelial cells, R-7050 reduced the decline of ZO-1 levels after TNF-α-exposure. R-7050 also reduced the metabolic alterations occurring after ischemic stroke, such as hyperglycemia and increased plasma corticosterone, free fatty acids, C reactive protein, and fibroblast growth factor-15 concentrations. In the gastrocnemius muscles of rats with stroke, R-7050 improved activated TNFRI/NF-κB, oxidative stress, and IL-6 pathways, as well as impaired insulin signaling. Overall, our findings highlight a feasible way to combat stroke disease based on an anti-TNF therapy that involves anti-inflammatory and metabolic mechanisms.

Circulating miR-155 and JAK2/STAT3 Axis in Acute Ischemic Stroke Patients and Its Relation to Post-Ischemic Inflammation and Associated Ischemic Stroke Risk Factors

Background

“Micro RNAs and their target genes recently have been identified to play a crucial role in the molecular pathogenesis of post-stroke ischemic cellular injury, which elucidates their new role in ischemic stroke diagnosis and therapy”. Thus, we evaluated the relative serum expression of miR-155, an inflammatory micro RNA, and the mRNAs (JAK2/STAT3) in acute ischemic stroke patients and its associations with the inflammatory cytokine TNF-α and different stroke risk factors.

Subjects and Methods

The relative expression of serum miR-155 and mRNAs (JAK2/STAT3) was assessed using RT-PCR, serum TNF-α was measured using ELIZA in 46 acute ischemic stroke patients and 50 control subjects. Receiver operating characteristic (ROC) curve was constructed to assess the specificity and sensitivity of circulating miR-155, JAK2/STAT3 as biomarkers for acute ischemic stroke.

Results

Circulating miR-155, JAK2/STAT3 were significantly up-regulated among stroke patients (8.5, 2.9, 4.2 fold respectively, P<0.001) with significant increase in TNF-α (263.8 ± 10.7 pg/mL, P <0.001). MiR-155, JAK2/STAT3 were positively correlated with TNF-α. MiR-155, JAK2/STAT3 were significantly increased in stroke patients and associated with risk factors such as hypertension, carotid atherosclerosis, and atrial fibrillation. Our study revealed that miR-155 has diagnostic accuracy for acute ischemic stroke where AUC=0.9, (P<0.001).

Conclusion

The elevated expressions of circulating miR-155, JAK2/STAT3, and TNF-α in acute ischemic stroke patients could trigger post-stroke cellular inflammation. MiR-155 could be used as potential inflammatory biomarker for acute ischemic stroke. However, further clinical studies are still needed to determine the exact role of miRNAs and different signal transduction expressions in the stage of acute ischemic stroke.

Epigenetics in blood-brain barrier disruption

The vessels of the central nervous system (CNS) have unique barrier properties. The endothelial cells (ECs) which comprise the CNS vessels contribute to the barrier via strong tight junctions, specific transporters, and limited endocytosis which combine to protect the brain from toxins and maintains brain homeostasis. Blood-brain barrier (BBB) leakage is a serious secondary injury in various CNS disorders like stroke, brain tumors, and neurodegenerative disorders. Currently, there are no drugs or therapeutics available to treat specifically BBB damage after a brain injury. Growing knowledge in the field of epigenetics can enhance the understanding of gene level of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. In this brief review, we summarize the epigenetic mechanisms or regulators that have a protective or disruptive role for components of BBB, along with the promising approaches to regain the integrity of BBB.

Native and Bioengineered Exosomes for Ischemic Stroke Therapy

Exosomes are natural cells-derived vesicles, which are at the forefront toward clinical success for various diseases, including cerebral ischemia. Exosomes mediate cell-to-cell communication in different brain cells during both physiological and pathological conditions. Exosomes are an extensively studied type of extracellular vesicle, which are considered to be the best alternative for stem cell-based therapy. They can be secreted by various cell types and have unique biological properties. Even though native exosomes have potential for ischemic stroke therapy, some undesirable features prevent their success in clinical applications, including a short half-life, poor targeting property, low concentration at the target site, rapid clearance from the lesion region, and inefficient payload. In this review, we highlight exosome trafficking and cellular uptake and survey the latest discoveries in the context of exosome research as the best fit for brain targeting owing to its natural brain-homing abilities. Furthermore, we overview the methods by which researchers have bioengineered exosomes (BioEng-Exo) for stroke therapy. Finally, we summarize studies in which exosomes were bioengineered by a third party for stroke recovery. This review provides up-to-date knowledge about the versatile nature of exosomes with a special focus on BioEng-Exo for ischemic stroke. Standard exosome bioengineering techniques are mandatory for the future and will lead exosomes toward clinical success for stroke therapy.

Long non-coding RNA RMST promotes oxygen-glucose deprivation-induced injury in brain microvascular endothelial cells by regulating miR-204-5p/VCAM1 axis

AIMS

Many long non-coding RNAs (lncRNAs) have been suggested to play critical roles in the pathogenesis of ischemic stroke, including lncRNA rhabdomyosarcoma 2-associated transcript (RMST). We aimed to elucidate the role and molecular mechanism of RMST in ischemic stroke.

MATERIALS AND METHODS

The in vitro ischemic stroke model was established by treating brain microvascular endothelial cells with oxygen-glucose deprivation (OGD). The expression of RMST, miR-204-5p and vascular cell adhesion molecule 1 (VCAM1) were determined by quantitative real-time polymerase chain reaction (qRT-PCR). The interaction between miR-204-5p and RMST or VCAM1 was confirmed using dual-luciferase reporter and RNA immunoprecipitation (RIP) assays. Cell viability, migration and apoptosis were assessed by Cell Counting Kit-8 (CCK-8), wound healing assay and flow cytometry, respectively. Lactic dehydrogenase (LDH) leakage rate was determined by LDH activity assay kit. The protein level of VCAM1 was analyzed by western blot (WB) assay.

KEY FINDINGS

RMST was upregulated in OGD-treated HBMEC and bEnd.3 cells. MiR-204-5p was a direct target of RMST, and miR-204-5p inhibition abated the inhibitory effect of RMST knockdown on OGD-induced injury via inhibiting cell viability and migration and promoting apoptosis in HBMEC and bEnd.3 cells. Moreover, VCAM1 was identified as a direct target of miR-204-5p, and VCAM1 alleviated the effect of miR-204-5p on reduction of OGD-induced injury in HBMEC and bEnd.3 cells. In addition, RMST regulated VCAM1 expression via sponging miR-204-5p.

SIGNIFICANCE

RMST knockdown attenuated OGD-induced injury of HBMEC and bEnd.3 cells via regulating miR-204-5p/VCAM1 axis, indicating a possible therapeutic strategy for future ischemic stroke therapy.

A Selenium Nanocomposite Protects the Mouse Brain from Oxidative Injury Following Intracerebral Hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is a common neurological crisis leading to high mortality and morbidity. Oxidative stress-induced secondary injury plays a critical role in neurological deterioration. Previously, we synthesized a porous Se@SiO2 nanocomposite and identified their therapeutic role in osteonecrosis of the femoral head. Whether this nanocomposite is neuroprotective remains to be elucidated.

METHODS

A porous Se@SiO2 nanocomposite was synthesized, and its biosafety was determined using a CCK-8 assay. The neuroprotective effect was evaluated by TUNEL staining, and intracellular ROS were detected with a DCFH-DA probe in SH-SY5Y cells exposed to hemin. Furthermore, the effect of the nanocomposite on cell apoptosis, brain edema and blood-brain barrier permeability were evaluated in a collagenase-induced ICH mouse model. The potential mechanism was also explored.

RESULTS

The results demonstrated that Se@SiO2 treatment significantly improved neurological function, increased glutathione peroxidase activity and downregulated malonaldehyde levels. The proportion of apoptotic cells, brain edema and blood-brain barrier permeability were reduced significantly in ICH mice treated with Se@SiO2 compared to vehicle-treated mice. In vitro, Se@SiO2 protected SH-SY5Y cells from hemin-induced apoptosis by preventing intracellular reactive oxygen species accumulation.

CONCLUSION

These results suggested that the porous Se@SiO2 nanocomposite exerted neuroprotection by suppressing oxidative stress. Se@SiO2 may be a potential candidate for the clinical treatment of ICH and oxidative stress-related brain injuries.

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.

Pathophysiology of Blood-Brain Barrier Permeability Throughout the Different Stages of Ischemic Stroke and Its Implication on Hemorrhagic Transformation and Recovery

The blood-brain barrier (BBB) is a dynamic interface responsible for maintaining the central nervous system homeostasis. Its unique characteristics allow protecting the brain from unwanted compounds, but its impairment is involved in a vast number of pathological conditions. Disruption of the BBB and increase in its permeability are key in the development of several neurological diseases and have been extensively studied in stroke. Ischemic stroke is the most prevalent type of stroke and is characterized by a myriad of pathological events triggered by an arterial occlusion that can eventually lead to fatal outcomes such as hemorrhagic transformation (HT). BBB permeability seems to follow a multiphasic pattern throughout the different stroke stages that have been associated with distinct biological substrates. In the hyperacute stage, sudden hypoxia damages the BBB, leading to cytotoxic edema and increased permeability; in the acute stage, the neuroinflammatory response aggravates the BBB injury, leading to higher permeability and a consequent risk of HT that can be motivated by reperfusion therapy; in the subacute stage (1-3 weeks), repair mechanisms take place, especially neoangiogenesis. Immature vessels show leaky BBB, but this permeability has been associated with improved clinical recovery. In the chronic stage (>6 weeks), an increase of BBB restoration factors leads the barrier to start decreasing its permeability. Nonetheless, permeability will persist to some degree several weeks after injury. Understanding the mechanisms behind BBB dysregulation and HT pathophysiology could potentially help guide acute stroke care decisions and the development of new therapeutic targets; however, effective translation into clinical practice is still lacking. In this review, we will address the different pathological and physiological repair mechanisms involved in BBB permeability through the different stages of ischemic stroke and their role in the development of HT and stroke recovery.

TFAP2A inhibits microRNA-126 expression at the transcriptional level and aggravates ischemic neuronal injury

Neuronal injury induced by cerebral ischemia poses a serious health risk globally, and there is no effective clinical therapy. This study was performed to investigate the role of transcription factor AP-2 alpha (TFAP2A) in cerebral ischemia, and the underlying mechanisms, using an in-vitro model (PC-12 cells) of oxygen-glucose deprivation (OGD), and an in-vivo model (rat) of transient global cerebral ischemia (tGCI). The results for CCK-8 and Hoechst staining showed that silencing of TFAP2A enhanced the viability and decreased the rate of apoptosis of PC12 cells subjected to OGD. ChIP assays were performed to evaluate the binding of TFAP2A to the promoter region of microRNA (miR)-126, and we found that TFAP2A inhibits the expression of miR-126. Further mechanistic investigation revealed that miR-126 targets polo like kinase 2 (PLK2), and that overexpression of PLK2 activates the IκBα-NF-κB signaling pathway and suppresses the growth of PC12 cells subjected to OGD. For our in-vivo assay, we used TTC staining to analyze the infarction area in the brain tissues of rats, and Nissl staining to evaluate the number of surviving brain neurons. The pathological conditions associated with neuronal injury in rat brain tissues were assessed by staining the tissues with hematoxylin-eosin. Our results indicate that TFAP2A downregulates miR-126, and thereby upregulates PLK2 and activates the IκBα-NF-κB pathway, which increased neuronal injury following cerebral ischemia.

Ischemic Cerebral Endothelial Cell-Derived Exosomes Promote Axonal Growth

BACKGROUND AND PURPOSE

Cerebral endothelial cells (CECs) and axons of neurons interact to maintain vascular and neuronal homeostasis and axonal remodeling in normal and ischemic brain, respectively. However, the role of exosomes in the interaction of CECs and axons in brain under normal conditions and after stroke is unknown.

METHODS

Exosomes were isolated from CECs of nonischemic rats and is chemic rats (nCEC-exos and isCEC-exos), respectively. A multicompartmental cell culture system was used to separate axons from neuronal cell bodies.

RESULTS

Axonal application of nCEC-exos promotes axonal growth of cortical neurons, whereas isCEC-exos further enhance axonal growth than nCEC-exos. Ultrastructural analysis revealed that CEC-exos applied into distal axons were internalized by axons and reached to their parent somata. Bioinformatic analysis revealed that both nCEC-exos and isCEC-exos contain abundant mature miRNAs; however, isCEC-exos exhibit more robust elevation of select miRNAs than nCEC-exos. Mechanistically, axonal application of nCEC-exos and isCEC-exos significantly elevated miRNAs and reduced proteins in distal axons and their parent somata that are involved in inhibiting axonal outgrowth. Blockage of axonal transport suppressed isCEC-exo-altered miRNAs and proteins in somata but not in distal axons.

CONCLUSIONS

nCEC-exos and isCEC-exos facilitate axonal growth by altering miRNAs and their target protein profiles in recipient neurons.

Interplay between C-type lectin receptors and microRNAs in cellular homeostasis and immune response

C-type lectin receptors (CLRs) belong to the family of pattern recognition receptors (PRRs). They have a critical role to play in the regulation of a range of physiological functions including development, respiration, angiogenesis, inflammation, and immunity. CLRs can recognize distinct and conserved exogenous pathogen-associated as well as endogenous damage-associated molecular patterns. These interactions set off downstream signaling cascades, leading to the production of inflammatory mediators, activation of effector immune cells as well as regulation of the developmental and physiological homeostasis. CLR signaling must be tightly controlled to circumvent the excessive inflammatory burden and to maintain the cellular homeostasis. Recently, MicroRNAs (miRNAs) have been shown to be important regulators of expression of CLRs and their downstream signaling. The delicate balance between miRNAs and CLRs seems crucial in almost all aspects of multicellular life. Any dysregulations in the miRNA-CLR axes may lead to tumorigenesis or inflammatory diseases. Here, we present an overview of the current understanding of the central role of miRNAs in the regulation of CLR expression, profoundly impacting upon homeostasis and immunity, and thus, development of therapeutics against immune disorders.

TRPV4-Mediated Regulation of the Blood Brain Barrier Is Abolished During Inflammation

Blood-brain barrier (BBB) dysfunction is critically involved in determining the extent of several central nervous systems (CNS) pathologies and here in particular neuroinflammatory conditions. Inhibiting BBB breakdown could reduce the level of vasogenic edema and the number of immune cells invading the CNS, thereby counteracting neuronal injury. Transient receptor potential (TRP) channels have an important role as environmental sensors and constitute attractive therapeutic targets that are involved in calcium homeostasis during pathologies of the CNS. Transient receptor potential vanilloid 4 (TRPV4) is a calcium permeable, non-selective cation channel highly expressed in endothelial cells. As it is involved in the regulation of the blood brain barrier permeability and consequently cerebral edema formation, we anticipated a regulatory role of TRPV4 in CNS inflammation and subsequent neuronal damage. Here, we detected an increase in transendothelial resistance in mouse brain microvascular endothelial cells (MbMECs) after treatment with a selective TRPV4 inhibitor. However, this effect was abolished after the addition of IFNγ and TNFα indicating that inflammatory conditions override TRPV4-mediated permeability. Accordingly, we did not observe a protection of Trpv4-deficient mice when compared to wildtype controls in a preclinical model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), and no differences in infarct sizes following transient middle cerebral artery occlusion (tMCAO), the experimental stroke model, which leads to an acute postischemic inflammatory response. Furthermore, Evans Blue injections did not show differences in alterations of the blood brain barrier (BBB) permeability between genotypes in both animal models. Together, TRPV4 does not regulate brain microvascular endothelial permeability under inflammation.

HUCBC Treatment Improves Cognitive Outcome in Rats With Vascular Dementia

Background and purpose: Vascular dementia (VaD) is the second common cause of dementia after Alzheimer's disease in older people. Yet, there are no FDA approved drugs specifically for VaD. In this study, we have investigated the therapeutic effects of human umbilical cord blood cells (HUCBC) treatment on the cognitive outcome, white matter (WM) integrity, and glymphatic system function in rats subject to a multiple microinfarction (MMI) model of VaD. Methods: Male, retired breeder rats were subjected to the MMI model (800 ± 100 cholesterol crystals/300 μl injected into the internal carotid artery), and 3 days later were treated with phosphate-buffered saline (PBS) or HUCBC (5 × 10⁶, i.v.). Sham rats were included as naïve control. Following a battery of cognitive tests, rats were sacrificed at 28 days after MMI and brains extracted for immunohistochemical evaluation and Western blot analysis. To evaluate the glymphatic function, fluorescent tracers (Texas Red dextran, MW: 3 kD and FITC-dextran, MW: 500 kD) was injected into the cisterna magna over 30 min at 14 days after MMI. Rats (3-4/group/time point) were sacrificed at 30 min, 3 h, and 6 h, and the tracer movement analyzed using laser scanning confocal microscopy. Results: Compared to control MMI rats, HUCBC treated MMI rats exhibit significantly improved short-term memory and long-term memory exhibited by increased discrimination index in novel object recognition task with retention delay of 4 h and improved novel odor recognition task with retention delay of 24 h, respectively. HUCBC treatment also improves spatial learning and memory as measured using the Morris water maze test compared to control MMI rats. HUCBC treatment significantly increases axon and myelin density increases oligodendrocyte and oligodendrocyte progenitor cell number and increases Synaptophysin expression in the brain compared to control MMI rats. HUCBC treatment of MMI in rats significantly improves glymphatic function by reversing MMI induced delay in the penetration of cerebrospinal fluid (CSF) into the brain parenchyma via glymphatic pathways and reversing delayed clearance from the brain. HUCBC treatment significantly increases miR-126 expression in serum, aquaporin-4 (AQP4) expression around cerebral vessels, and decreases transforming growth factor-β (TGF-β) protein expression in the brain which may contribute to HUCBC induced improved glymphatic function. Conclusions: HUCBC treatment of an MMI rat model of VaD promotes WM remodeling and improves glymphatic function which together may aid in the improvement of cognitive function and memory. Thus, HUCBC treatment warrants further investigation as a potential therapy for VaD.

MicroRNAs in the Blood-Brain Barrier in Hypoxic-Ischemic Brain Injury

Hypoxic-ischemic (HI) brain injury is a leading cause of acute mortality and chronic disability in newborns. Current evidence shows that cerebral microvascular response and compromised blood-brain barrier (BBB) integrity occur rapidly and could primarily be responsible for the brain injury observed in many infants with HI brain injury. MicroRNAs (miRNAs) are a type of highly conserved non-coding RNAs (ncRNAs), which consist of 21-25 nucleotides in length and usually lead to suppression of target gene expression. Growing evidence has revealed that brainenriched miRNAs act as versatile regulators of BBB dysfunctions in various neurological disorders including neonatal HI brain injury. In the present review, we summarize the current findings regarding the role of miRNAs in BBB impairment after hypoxia/ischemia brain injury. Specifically, we focus on the recent progress of miRNAs in the pathologies of neonatal HI brain injury. These findings can not only deepen our understanding of the role of miRNAs in BBB impairment in HI brain injury, but also provide insight into the development of new therapeutic strategies for preservation of BBB integrity under pathological conditions.