Stroke induces gene profile changes associated with neurogenesis and angiogenesis in adult subventricular zone progenitor cells

Sevoflurane Postconditioning Protects From an Early Neurological Deficit After Subarachnoid Hemorrhage: Results of a Randomized Laboratory Study in Rats

BACKGROUND

Subarachnoid hemorrhage (SAH) is associated with neurocognitive impairment. Recent data suggest that sevoflurane attenuates edema formation after SAH in rats. However, so far, no information is available about the long-term repair phase, nor if sevoflurane impacts functionality by increasing vascularity. This study tested whether sevoflurane postconditioning would improve long-term neurologic deficit through increased formation of new vessels close to the hemorrhage area.

METHODS

Fifty-three animals were subjected to SAH or sham surgery with or without a 2-hour sevoflurane postconditioning (versus propofol anesthesia). Animal survival, including dropout animals due to death or reaching termination criteria, as well as neurologic deficit, defined by the Garcia score, were assessed 2 hours after recovery until postoperative day 14. On day 14, blood samples and brain tissue were harvested. Vessel density was determined by the number of cluster of differentiation 31 (CD31)-positive vessels, and activated glial cells by glial fibrillary acidic protein (GFAP)-positive astrocytes per field of view.

RESULTS

The survival rate for sham animals was 100%, 69% in the SAH-propofol and 92% in the SAH-sevoflurane groups. According to the log-rank Mantel-Cox test, survival curves were significantly different ( P = .024). The short-term neurologic deficit was higher in SAH-propofol versus SAH-sevoflurane animals 2 hours after recovery and on postoperative day 1 (propofol versus sevoflurane: 14. 6 ± 3.4 vs 15. 9 ± 2.7 points, P = .034, and 16. 2 ± 3.5 vs 17. 8 ± 0.9 points, P = .015). Overall complete recovery from neurologic deficit was observed on day 7 in both SAH groups (18. 0 ± 0.0 vs 18. 0 ± 0.0 points, P = 1.000). Cortical vascular density increased to 80. 6 ± 15.0 vessels per field of view in SAH-propofol animals (vs 71. 4 ± 10.1 in SAH-sevoflurane, P < .001). Activation of glial cells, an indicator of neuroinflammation, was assessed by GFAP-positive astrocytes GFAP per field of view. Hippocampal GFAP-positive cells were 201 ± 68 vs 179 ± 84 cells per field of view in SAH-propofol versus SAH-sevoflurane animals ( P < .001).

CONCLUSIONS

Sevoflurane postconditioning improves survival by 23% (SAH-sevoflurane versus SAH-propofol). The sevoflurane intervention could attenuate the early neurologic deficit, while the long-term outcome was similar across the groups. A higher vascular density close to the SAH area in the propofol group was not associated with improved outcomes.

The exo-microRNA (miRNA) signaling pathways in pathogenesis and treatment of stroke diseases: Emphasize on mesenchymal stem cells (MSCs)

A major factor in long-term impairment is stroke. Patients with persistent stroke and severe functional disabilities have few therapy choices. Long noncoding RNAs (lncRNAs) may contribute to the regulation of the pathophysiologic processes of ischemic stroke as shown by altered expression of lncRNAs and microRNA (miRNAs) in blood samples of acute ischemic stroke patients. On the other hand, multipotent mesenchymal stem cells (MSCs) increase neurogenesis, and angiogenesis, dampen neuroinflammation, and boost brain plasticity to improve functional recovery in experimental stroke models. MSCs can be procured from various sources such as the bone marrow, adipose tissue, and peripheral blood. Under the proper circumstances, MSCs can differentiate into a variety of mature cells, including neurons, astrocytes, and oligodendrocytes. Accordingly, the capability of MSCs to exert neuroprotection and also neurogenesis has recently attracted more attention. Nowadays, lncRNAs and miRNAs derived from MSCs have opened new avenues to alleviate stroke symptoms. Accordingly, in this review article, we examined various studies concerning the lncRNAs and miRNAs' role in stroke pathogenesis and delivered an overview of the therapeutic role of MSC-derived miRNAs and lncRNAs in stroke conditions.

Mesenchymal stem cells derived from bone marrow and adipose tissue for repairing acute sciatic nerve injury in a rabbit model

Peripheral nerve injury is one of the common disabling clinical conditions and around 50% of the cases end up in permanent impairment. Due to the lack of effective treatment options regenerative medicine employing stem cells is being evaluated. The presented study evaluated and compared regeneration potential of mesenchymal stem cells (MSCs) derived from bone marrow (BM) and adipose tissue (AD) in acute rabbit sciatic nerve injury (axonotmesis) model. A total of n = 54 grey giant rabbits were made subject of the study and divided equally into 3 groups: Control, BM-MSCs in Collagen I and AD-MSCs in Collagen I as per the treatment given. Iliac crest BM and omental AD was harvested from the same donor for isolation and culture of MSCs. The repair of sciatic nerve injury was evaluated on days 60 and 90. The clinical and histopathological scores and SEM morphology was better in cell treated groups as compared to the control. Morphology and histological studies revealed injured nerve in different levels of regenerative process. Gene expression was more than double for N-Cadherin in cell treated groups as compared to the control, especially at day 60. Between cell treated groups, BM-MSCs group showed better response as compared to the AD-MSCs, although statistically non-significant (p > 0.05). Incomplete nerve regeneration observed under various diagnostic parameters was in compliance to the incomplete clinical recovery at day 90. It was concluded that MSCs may improve sciatic nerve healing but fall short of complete regeneration at day 90, although BM-MSCs may have an edge over AD-MSCs.

Allogenic bone marrow-derived mesenchymal stem cells and its conditioned media for repairing acute and sub-acute peripheral nerve injuries in a rabbit model

The present study evaluated healing potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) and BM-MSCs-conditioned medium (BM-MSCs-CM) for acute and subacute injuries in the rabbit peripheral nerve injury model. The regenerative capacity of MSCs was evaluated in 40 rabbits divided into eight groups, four groups each for acute and subacute injury models. BM-MSCs and BM-MSCS-CM were prepared by isolating allogenic bone marrow from the iliac crest. After inducing sciatic nerve crush injury, different treatments consisting of PBS, Laminin, BM-MSCs + laminin, and BM-MSCS-CM + laminin were used on the day of injury in the acute injury model and after ten days of crush injury in the subacute groups. The parameters studied included: pain, total neurological score, gastrocnemius muscle weight and volume ratio, histopathology of the sciatic nerve and gastrocnemius muscle, and scanning electron microscopy (SEM). Findings indicate that BM-MSCs and BM-MSCS-CM have augmented the regenerative capacity in acute and subacute injury groups with a slightly better improvement in the subacute groups than the animals in acute injury groups. Histopathology data revealed different levels of regenerative process undergoing in the nerve. Neurological observations, gastrocnemius muscle evaluation, muscle histopathology, and the SEM results depicted better healing in animals treated with BM-MSCs and BM-MSCS-CM. With this data, it could be concluded that BM-MSCs support the healing of injured peripheral nerves, and the BM-MSCS-CM does accelerate the healing of acute and subacute peripheral nerve injuries in rabbits. However, stem cell therapy may be indicated during the subacute phase for better results.

Epilepsy in Cerebrovascular Diseases: A Narrative Review

BACKGROUND

Epilepsy is a common comorbidity of cerebrovascular disease and an increasing socioeconomic burden.

OBJECTIVE

We aimed to provide an updated comprehensive review on the state of the art about seizures and epilepsy in stroke, cerebral haemorrhage, and leukoaraiosis.

METHODS

We selected English-written articles on epilepsy, stroke, and small vessel disease up until December 2021. We reported the most recent data about epidemiology, pathophysiology, prognosis, and management for each disease.

RESULTS

The main predictors for both ES and PSE are the severity and extent of stroke, the presence of cortical involvement and hemorrhagic transformation, while PSE is also predicted by younger age at stroke onset. Few data exist on physiopathology and seizure semiology, and no randomized controlled trial has been performed to standardize the therapeutic approach to post-stroke epilepsy.

CONCLUSION

Some aspects of ES and PSE have been well explored, particularly epidemiology and risk factors. On the contrary, few data exist on physiopathology, and existing evidence is mainly based on studies on animal models. Little is also known about seizure semiology, which may also be difficult to interpret by non-epileptologists. Moreover, the therapeutic approach needs standardization as regards indications and the choice of specific ASMs. Future research may help to better elucidate these aspects.

Low-Frequency Repetitive Transcranial Magnetic Stimulation in the Early Subacute Phase of Stroke Enhances Angiogenic Mechanisms in Rats

Objective To characterize the repetitive transcranial magnetic stimulation (rTMS) induced changes in angiogenic mechanisms across different brain regions.Methods Seventy-nine adult male Sprague-Dawley rats were subjected to a middle cerebral artery occlusion (day 0) and then treated with 1-Hz, 20-Hz, or sham stimulation of their lesioned hemispheres for 2 weeks. The stimulation intensity was set to 100% of the motor threshold. The neurological function was assessed on days 3, 10, and 17. The infarct volume and angiogenesis were measured by histology, immunohistochemistry, Western blot, and real-time polymerase chain reaction (PCR) assays. Brain tissue was harvested from the ischemic core (IC), ischemic border zone (BZ), and contralateral homologous cortex (CH).Results Optical density of angiopoietin1 and synaptophysin in the IC was significantly greater in the low-frequency group than in the sham group (p=0.03 and p=0.03, respectively). The 1-Hz rTMS significantly increased the level of Akt phosphorylation in the BZ (p<0.05 vs. 20 Hz). Endothelial nitric oxide synthase phosphorylation was increased in the IC (p<0.05 vs. 20 Hz), BZ (p<0.05 vs. 20 Hz), and CH (p<0.05 vs. 20 Hz and p<0.05 vs. sham). Real-time PCR demonstrated that low-frequency stimulation significantly increased the transcriptional activity of the TIE2 gene in the IC (p<0.05).Conclusion Low-frequency rTMS of the ipsilesional hemisphere in the early subacute phase of stroke promotes the expression of angiogenic factors and related genes in the brain, particularly in the injured area.

Molecular mediators of angiogenesis and neurogenesis after ischemic stroke

The mechanisms governing neurological and functional recovery after ischemic stroke are incompletely understood. Recent advances in knowledge of intrinsic repair processes of the CNS have so far translated into minimal improvement in outcomes for stroke victims. Better understanding of the processes underlying neurological recovery after stroke is necessary for development of novel therapeutic approaches. Angiogenesis and neurogenesis have emerged as central mechanisms of post-stroke recovery and potential targets for therapeutics. Frameworks have been developed for conceptualizing cerebral angiogenesis and neurogenesis at the tissue and cellular levels. These models highlight that angiogenesis and neurogenesis are linked to each other and to functional recovery. However, knowledge of the molecular framework linking angiogenesis and neurogenesis after stroke is limited. Studies of potential therapeutics typically focus on one mediator or pathway with minimal discussion of its role within these multifaceted biochemical processes. In this article, we briefly review the current understanding of the coupled processes of angiogenesis and neurogenesis after stroke. We then identify the molecular mediators and signaling pathways found in pre-clinical studies to upregulate both processes after stroke and contextualizes them within the current framework. This report thus contributes to a more-unified understanding of the molecular mediators governing angiogenesis and neurogenesis after stroke, which we hope will help guide the development of novel therapeutic approaches for stroke survivors.

Unraveling the potential of endothelial progenitor cells as a treatment following ischemic stroke

Ischemic stroke is becoming one of the most common causes of death and disability in developed countries. Since current therapeutic options are quite limited, focused on acute reperfusion therapies that are hampered by a very narrow therapeutic time window, it is essential to discover novel treatments that not only stop the progression of the ischemic cascade during the acute phase, but also improve the recovery of stroke patients during the sub-acute or chronic phase. In this regard, several studies have shown that endothelial progenitor cells (EPCs) can repair damaged vessels as well as generate new ones following cerebrovascular damage. EPCs are circulating cells with characteristics of both endothelial cells and adult stem cells presenting the ability to differentiate into mature endothelial cells and self-renew, respectively. Moreover, EPCs have the advantage of being already present in healthy conditions as circulating cells that participate in the maintenance of the endothelium in a direct and paracrine way. In this scenario, EPCs appear as a promising target to tackle stroke by self-promoting re-endothelization, angiogenesis and vasculogenesis. Based on clinical data showing a better neurological and functional outcome in ischemic stroke patients with higher levels of circulating EPCs, novel and promising therapeutic approaches would be pharmacological treatment promoting EPCs-generation as well as EPCs-based therapies. Here, we will review the latest advances in preclinical as well as clinical research on EPCs application following stroke, not only as a single treatment but also in combination with new therapeutic approaches.

Rho/ROCK Pathway and Noncoding RNAs: Implications in Ischemic Stroke and Spinal Cord Injury

Ischemic strokes (IS) and spinal cord injuries (SCI) are major causes of disability. RhoA is a small GTPase protein that activates a downstream effector, ROCK. The up-regulation of the RhoA/ROCK pathway contributes to neuronal apoptosis, neuroinflammation, blood-brain barrier dysfunction, astrogliosis, and axon growth inhibition in IS and SCI. Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), were previously considered to be non-functional. However, they have attracted much attention because they play an essential role in regulating gene expression in physiological and pathological conditions. There is growing evidence that ROCK inhibitors, such as fasudil and VX-210, can reduce injury in IS and SCI in animal models and clinical trials. Recently, it has been reported that miRNAs are decreased in IS and SCI, while lncRNAs are increased. Inhibiting the Rho/ROCK pathway with miRNAs alleviates apoptosis, neuroinflammation, oxidative stress, and axon growth inhibition in IS and SCI. Further studies are required to explore the significance of ncRNAs in IS and SCI and to establish new strategies for preventing and treating these devastating diseases.

Neural Stem Cells for Early Ischemic Stroke

Clinical treatments for ischemic stroke are limited. Neural stem cell (NSC) transplantation can be a promising therapy. Clinically, ischemia and subsequent reperfusion lead to extensive neurovascular injury that involves inflammation, disruption of the blood-brain barrier, and brain cell death. NSCs exhibit multiple potentially therapeutic actions against neurovascular injury. Currently, tissue plasminogen activator (tPA) is the only FDA-approved clot-dissolving agent. While tPA’s thrombolytic role within the vasculature is beneficial, tPA’s non-thrombolytic deleterious effects aggravates neurovascular injury, restricting the treatment time window (time-sensitive) and tPA eligibility. Thus, new strategies are needed to mitigate tPA’s detrimental effects and quickly mediate vascular repair after stroke. Up to date, clinical trials focus on the impact of stem cell therapy on neuro-restoration by delivering cells during the chronic stroke stage. Also, NSCs secrete factors that stimulate endogenous repair mechanisms for early-stage ischemic stroke. This review will present an integrated view of the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury, with an emphasis on early-stage ischemic stroke. Further, this will highlight the impact of early sub-acute NSC delivery on improving short-term and long-term stroke outcomes.

Ninjurin 1 dodecamer peptide containing the N-terminal adhesion motif (N-NAM) exerts proangiogenic effects in HUVECs and in the postischemic brain

Nerve injury-induced protein 1 (Ninjurin 1, Ninj1) is a cell adhesion molecule responsible for cell-to-cell interactions between immune cells and endothelial cells. In our previous paper, we have shown that Ninj1 plays an important role in the infiltration of neutrophils in the postischemic brain and that the dodecamer peptide harboring the Ninj1 N-terminal adhesion motif (N-NAM, Pro²⁶-Asn³⁷) inhibits infiltration of neutrophils in the postischemic brain and confers robust neuroprotective and anti-inflammatory effects. In the present study, we examinedt the pro-angiogenic effect of N-NAM using human umbilical vein endothelial cells (HUVECs) and rat MCAO (middle cerebral artery occlusion) model of stroke. We found that N-NAM promotes proliferation, migration, and tube formation of HUVECs and demonstrate that the suppression of endogenous Ninj1 is responsible for the N-NAM-mediated pro-angiogenic effects. Importantly, a pull-down assay revealed a direct binding between exogenously delivered N-NAM and endogenous Ninj1 and it is N-terminal adhesion motif dependent. In addition, N-NAM activated the Ang1-Tie2 and AKT signaling pathways in HUVECs, and blocking those signaling pathways with specific inhibitors suppressed N-NAM-induced tube formation, indicating critical roles of those signaling pathways in N-NAM-induced angiogenesis. Moreover, in a rat MCAO model, intranasal administration of N-NAM beginning 4 days post-MCAO (1.5 µg daily for 3 days) augmented angiogenesis in the penumbra of the ipsilateral hemisphere of the brain and significantly enhanced total vessel lengths, vessel densities, and pro-angiogenic marker expression. These results demonstrate that the 12-amino acid Ninj1 peptide, which contains the N-terminal adhesion motif of Ninj1, confers pro-angiogenic effects and suggest that those effects might contribute to its neuroprotective effects in the postischemic brain.

Small extracellular vesicles secreted by human iPSC-derived MSC enhance angiogenesis through inhibiting STAT3-dependent autophagy in ischemic stroke

Background

Small extracellular vesicles (sEV) secreted by mesenchymal stem cells (MSC) derived from human induced pluripotent stem cells (iPSC, iMSC-sEV) are considered to have great potential in treating ischemic diseases. Angiogenesis play an important role in post-stroke recovery. However, no studies have yet been conducted to systemically examine the effect and the underlying mechanism of iMSC-sEV on angiogenesis under brain ischemia conditions.

Methods

Ischemic stroke model was performed in rats induced by middle cerebral artery occlusion (MCAO), and the pro-angiogenic capacity of iMSC-sEV was measured. The in vitro effects of iMSC-sEV on the migration and tube formation of endothelial cells were investigated, respectively. Autophagy and autophagy-related signaling pathway were detected in vivo and in vitro.

Results

We found that iMSC-sEV significantly reduced infarct volume, enhanced angiogenesis, and alleviated long-term neurological deficits in rats after stroke. We also demonstrated that iMSC-sEV increased migration and tube formation of endothelial cells in vitro. A further mechanism study revealed that the pro-angiogenic effect of iMSC-sEV was correlated with a reduction in autophagy. Furthermore, iMSC-sEV significantly activated signal transducer and activator of transcription 3 (STAT3), and suppression of STAT3 abolished iMSC-sEV-induced inhibition of autophagy and promotion of angiogenesis in vivo and in vitro.

Conclusions

Taken together, our data indicate that iMSC-sEV promote angiogenesis after ischemic stroke, potentially, by inhibiting autophagy, a process that is partially dependent on STAT3 activation.

Electro-Acupuncture Promotes the Differentiation of Endogenous Neural Stem Cells via Exosomal microRNA 146b After Ischemic Stroke

Background: Evidences indicate that exosomes-mediated delivery of microRNAs (miRNAs or miRs) is involved in the neurogenesis of stroke. This study was to investigate the role of exosomal miRNAs in non-drug therapy of electro-acupuncture (EA) regulating endogenous neural stem cells for stroke recovery.

Methods: The model of focal cerebral ischemia and reperfusion in rats were established by middle cerebral artery occlusion (MCAO) and treated by EA. The exosomes were extracted from peri-ischemic striatum and identified by exosomal biomarkers, and detected differentially expressed miRNAs with microarray chip. Primary stem cells were cultured, and oxygen–glucose deprivation and reperfusion (OGD/R) was used to mimic vitro ischemic injury.

Results: The levels of exosomal biomarkers TSG101 and CD81 were increased in peri-ischemic striatum after EA treatment, and we revealed 25 differentially expressed miRNAs in isolated exosomes, of which miR-146b was selected for further analysis, and demonstrated that EA increased miR-146b expression and its inhibitors could block the effects. Subsequently, we confirmed that EA upregulated miR-146b expression to promote neural stem cells differentiation into neurons in peri-ischemic striatum. In vitro, it was verified that OGD/R hindered neural stem cells differentiation, and miR-146b inhibitors furtherly suppressed its differentiation, simultaneously NeuroD1 was involved in neural stem cells differentiation into neurons. Moreover, in vivo we found EA promoted NeuroD1-mediated neural stem cells differentiation via miR-146b. In addition, EA also could improve neurological deficits through miR-146b after ischemic stroke.

Conclusion: EA promotes the differentiation of endogenous neural stem cells via exosomal miR-146b to improve neurological injury after ischemic stroke.

Neurovascular protection by peroxisome proliferator-activated receptor α in ischemic stroke

Ischemic stroke is a leading cause of death and disability worldwide. Currently, the only pharmacological therapy for ischemic stroke is thrombolysis with tissue plasminogen activator that has a narrow therapeutic window and increases the risk of intracerebral hemorrhage. New pharmacological treatments for ischemic stroke are desperately needed, but no neuroprotective drugs have successfully made it through clinical trials. Beneficial effects of peroxisome proliferator-activated receptor alpha (PPARα) activation on vascular integrity and function have been reported, and PPARα agonists have clinically been used for many years to manage cardiovascular disease. Thus, PPARα has gained interest in recent years as a target for neurovascular disease such as ischemic stroke. Accumulating preclinical evidence suggests that PPARα activation modulates several pathophysiological hallmarks of stroke such as oxidative stress, blood-brain barrier (BBB) dysfunction, and neuroinflammation to improve functional recovery. Therefore, this review summarizes the various actions PPARα exerts in neurovascular health and disease and the potential of employing exogenous PPARα agonists for future pharmacological treatment of ischemic stroke.

Hyaluronic Acid and Regenerative Medicine: New Insights into the Stroke Therapy

Stroke is known as one of the very important public health problems that are related to societal burden and tremendous economic losses. It has been shown that there are few therapeutic approaches for the treatment of this disease. In this regard, the present therapeutic platforms aim to obtain neuroprotection, reperfusion, and neuro recovery. Among these therapies, regenerative medicine-based therapies have appeared as new ways of stroke therapy. Hyaluronic acid (HA) is a new candidate, which could be applied as a regenerative medicine-based therapy in the treatment of stroke. HA is a glycosaminoglycan composed of disaccharide repeating elements (N-acetyl-Dglucosamine and D-glucuronic acid). Multiple lines of evidence demonstrated that HA has critical roles in normal tissues. It can be a key player in different physiological and pathophysiological conditions such as water homeostasis, multiple drug resistance, inflammatory processes, tumorigenesis, angiogenesis, and changed viscoelasticity of the extracellular matrix. HA has very important physicochemical properties i.e., availability of reactive functional groups and its solubility, which make it a biocompatible material for application in regenerative medicine. Given that HAbased bioscaffolds and biomaterials do not induce inflammation or allergies and are hydrophilic, they are used as soft tissue fillers and injectable dermal fillers. Several studies indicated that HA could be employed as a new therapeutic candidate in the treatment of stroke. These studies documented that HA and HA-based therapies exert their pharmacological effects via affecting stroke-related processes. Herein, we summarized the role of the extracellular matrix in stroke pathogenesis. Moreover, we highlighted the HA-based therapies for the treatment of stroke.

Functions of subventricular zone neural precursor cells in stroke recovery

The proliferation and ectopic migration of neural precursor cells (NPCs) in response to ischemic brain injury was first reported two decades ago. Since then, studies of brain injury-induced subventricular zone cytogenesis, primarily in rodent models, have provided insight into the cellular and molecular determinants of this phenomenon and its modulation by various factors. However, despite considerable correlational evidence-and some direct evidence-to support contributions of NPCs to behavioral recovery after stroke, the causal mechanisms have not been identified. Here we discuss the subventricular zone cytogenic response and its possible roles in brain injury and disease, focusing on rodent models of stroke. Emerging evidence suggests that NPCs can modulate harmful responses and enhance reparative responses to neurologic diseases. We speculatively identify four broad functions of NPCs in the context of stroke: cell replacement, cytoprotection, remodeling of residual tissue, and immunomodulation. Thus, NPCs may have pleiotropic functions in supporting behavioral recovery after stroke.

Multipotent mesenchymal stromal cell-derived exosomes improve functional recovery after experimental intracerebral hemorrhage in the rat

OBJECTIVE

Previous studies have demonstrated that transplanted multipotent mesenchymal stromal cells (MSCs) improve functional recovery in rats after experimental intracerebral hemorrhage (ICH). In this study the authors tested the hypothesis that administration of multipotent MSC-derived exosomes promotes functional recovery, neurovascular remodeling, and neurogenesis in a rat model of ICH.

METHODS

Sixteen adult male Wistar rats were subjected to ICH via blood injection into the striatum, followed 24 hours later by tail vein injection of 100 μg protein of MSC-derived exosomes (treatment group, 8 rats) or an equal volume of vehicle (control group, 8 rats); an additional 8 rats that had identical surgery without blood infusion were used as a sham group. The modified Morris water maze (mMWM), modified Neurological Severity Score (mNSS), and social odor-based novelty recognition tests were performed to evaluate cognitive and sensorimotor functional recovery after ICH. All 24 animals were killed 28 days after ICH or sham procedure. Histopathological and immunohistochemical analyses were performed for measurements of lesion volume and neurovascular and white matter remodeling.

RESULTS

Compared with the saline-treated controls, exosome-treated ICH rats showed significant improvement in the neurological function of spatial learning and motor recovery measured at 26-28 days by mMWM and starting at day 14 by mNSS (p < 0.05). Senorimotor functional improvement was measured by a social odor-based novelty recognition test (p < 0.05). Exosome treatment significantly increased newly generated endothelial cells in the hemorrhagic boundary zone, neuroblasts and mature neurons in the subventricular zone, and myelin in the striatum without altering the lesion volume.

CONCLUSIONS

MSC-derived exosomes effectively improve functional recovery after ICH, possibly by promoting endogenous angiogenesis and neurogenesis in rats after ICH. Thus, cell-free, MSC-derived exosomes may be a novel therapy for ICH.

Region-specific and activity-dependent regulation of SVZ neurogenesis and recovery after stroke

Recovery after stroke involves remodeling in brain tissue adjacent to the stroke site. In this remodeling, neurogenesis after stroke involves the formation of new neurons. The role of neurogenesis in stroke recovery and the role of brain and behavioral activity in this process remain undefined. Using orthogonal transgenic mouse tracing and rabies virus approaches, we demonstrate that brain regions unexpectedly compete for new neurons after stroke and that the behavioral or cellular activity establishes this competition. These new neurons synaptically integrate into cortex, and this integration is necessary for poststroke recovery.

Stroke is the leading cause of adult disability. Neurogenesis after stroke is associated with repair; however, the mechanisms regulating poststroke neurogenesis and its functional effect remain unclear. Here, we investigate multiple mechanistic routes of induced neurogenesis in the poststroke brain, using both a forelimb overuse manipulation that models a clinical neurorehabilitation paradigm, as well as local manipulation of cellular activity in the peri-infarct cortex. Increased activity in the forelimb peri-infarct cortex via either modulation drives increased subventricular zone (SVZ) progenitor proliferation, migration, and neuronal maturation in peri-infarct cortex. This effect is sensitive to competition from neighboring brain regions. By using orthogonal tract tracing and rabies virus approaches in transgenic SVZ-lineage-tracing mice, SVZ-derived neurons synaptically integrate into the peri-infarct cortex; these effects are enhanced with forelimb overuse. Synaptic transmission from these newborn SVZ-derived neurons is critical for spontaneous recovery after stroke, as tetanus neurotoxin silencing specifically of the SVZ-derived neurons disrupts the formation of these synaptic connections and hinders functional recovery after stroke. SVZ-derived neurogenesis after stroke is activity-dependent, region-specific, and sensitive to modulation, and the synaptic connections formed by these newborn cells are functionally critical for poststroke recovery.

Modern Concepts in Regenerative Therapy for Ischemic Stroke: From Stem Cells for Promoting Angiogenesis to 3D-Bioprinted Scaffolds Customized via Carotid Shear Stress Analysis

Ischemic stroke is associated with a tremendous economic and societal burden, and only a few therapies are currently available for the treatment of this devastating disease. The main therapeutic approaches used nowadays for the treatment of ischemic brain injury aim to achieve reperfusion, neuroprotection and neurorecovery. Therapeutic angiogenesis also seems to represent a promising tool to improve the prognosis of cerebral ischemia. This review aims to present the modern concepts and the current status of regenerative therapy for ischemic stroke and discuss the main results of major clinical trials addressing the effectiveness of stem cell therapy for achieving neuroregeneration in ischemic stroke. At the same time, as a glimpse into the future, this article describes modern concepts for stroke prevention, such as the implantation of bioprinted scaffolds seeded with stem cells, whose 3D geometry is customized according to carotid shear stress.

Nucleic Acid Therapies for Ischemic Stroke

Stroke remains a leading cause of disability and death worldwide despite significant scientific and therapeutic advances. Therefore, there is a critical need to improve stroke prevention and treatment. In this review, we describe several examples that leverage nucleic acid therapeutics to improve stroke care through prevention, acute treatment, and recovery. Aptamer systems are under development to increase the safety and efficacy of antithrombotic and thrombolytic treatment, which represent the mainstay of medical stroke therapy. Antisense oligonucleotide therapy has shown some promise in treating stroke causes that are genetically determined and resistant to classic prevention approaches such as elevated lipoprotein (a) and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). Targeting microRNAs may be attractive because they regulate factors involved in neuronal cell death and reperfusion-associated injury, as well as neurorestorative pathways. Lastly, microRNAs may aid reliable etiologic classification of stroke subtypes, which is important for effective secondary stroke prevention.

The evolving role of neuro-immune interaction in brain repair after cerebral ischemic stroke

Stroke is the world's leading cause of disability with limited brain repair treatments which effectively improve long-term neurological deficits. The neuroinflammatory responses persist into the late repair phase of stroke and participate in all brain repair elements, including neurogenesis, angiogenesis, synaptogenesis, remyelination and axonal sprouting, shedding new light on post-stroke brain recovery. Resident brain glial cells, such as astrocytes not only contribute to neuroinflammation after stroke, but also secrete a wide range of trophic factors that can promote post-stroke brain repair. Alternatively, activated microglia, monocytes, and neutrophils in the innate immune system, traditionally considered as major damaging factors after stroke, have been suggested to be extensively involved in brain repair after stroke. The adaptive immune system may also have its bright side during the late regenerative phase, affecting the immune suppressive regulatory T cells and B cells. This review summarizes the recent findings in the evolving role of neuroinflammation in multiple post-stroke brain repair mechanisms and poses unanswered questions that may generate new directions for future research and give rise to novel therapeutic targets to improve stroke recovery.

Post-stroke administration of omega-3 polyunsaturated fatty acids promotes neurovascular restoration after ischemic stroke in mice: Efficacy declines with aging

Post-stroke treatment with omega-3 polyunsaturated fatty acids (n-3 PUFAs) may be a promising therapy in young animals but this has not been tested in aged subjects, a population at most risk of ischemic stroke. Herein we examined the therapeutic efficacy of n-3 PUFAs after distal middle cerebral artery occlusion (dMCAO) in young (10-12 weeks old) and aged (18 months old) mice. Post-ischemic mice were randomly assigned to 4 groups that received: 1) regular food with low content of n-3 PUFAs, 2) intraperitoneal docosahexaenoic acid (DHA, a major component of n-3 PUFAs) injections, 3) Fish oil (FO, containing high concentration of n-3 PUFAs) dietary supplement, or 4) combined treatment with DHA and FO dietary supplement. Long-term neurorestoration induced by n-3 PUFA post-stroke administration and its underlying mechanism(s) were analyzed up to 35 days after dMCAO. Aged mice showed more severe neurological deficits than young mice after dMCAO with histological lesions extended to the striatum. Notably, post-stroke treatment with combined DHA injections and FO dietary supplementation was more effective in reducing brain injury and improving sensorimotor function in aged mice than either treatment alone, albeit to a lesser extent than in the young mice. Unlike the improvement in spatial cognitive function observed in young mice, the combined treatment regimen failed to improve cognitive function in aged mice. The reduction in stroke-induced neurological deficits with n-3 PUFA post-treatment was associated with enhanced angiogenesis, oligodendrogenesis, neuron survival and white matter restoration. Together, these results indicate that the neurological benefits of n-3 PUFA administration after stroke extend to older animals and are associated with improved neuronal survival and brain remodeling, therefore suggesting that post-stroke administration of n-3 PUFAs is a viable clinically relevant treatment option against stroke.

Synthetic α5β1 integrin ligand PHSRN is proangiogenic and neuroprotective in cerebral ischemic stroke

Ischemic stroke is the leading cause of disability and death worldwide. An effective therapeutic approach is urgently needed. Stroke-induced angiogenesis and neurogenesis are essential mechanisms in the long-term repair. Extracellular matrix proteins are also involved in tissue self-repair. Recently, a PHSRN (Pro-His-Ser-Arg-Asn) peptide from the fibronectin synergistic motif that can promote wound healing in epithelia and induce endothelial proliferation and cancer cell migration was identified. The therapeutic potential of this peptide in stroke is unknown. Here, we examined the potential of PHSRN in stroke therapy using an ischemic rat model of middle cerebral artery occlusion (MCAO). PHSRN reduced the infarct volume in MCAO rats, improved neurological function, and alleviated motor function impairment. PHSRN targeted the damaged brain region and distributed to endothelial cells after intraperitoneal injection. PHSRN significantly promoted angiogenesis and vascular endothelial growth factor secretion through activation of integrin α5β1 and its downstream intracellular signals, e.g., focal adhesion kinase, Ras, cRaf, and extracellular-signal-regulated kinase. PHSRN treatment also stimulated neurogenesis in MCAO rats, and maintained neuronal survival and neuronal morphologic complexity via induction of VEGF secretion. Together, these results provide insights into the role of integrin α5β1 following ischemia and support the feasibility of using PHSRN peptide in stroke therapy.

RNA-Sequencing Analysis Revealed a Distinct Motor Cortex Transcriptome in Spontaneously Recovered Mice After Stroke

Background and Purpose- Many restorative therapies have been used to study brain repair after stroke. These therapeutic-induced changes have revealed important insights on brain repair and recovery mechanisms; however, the intrinsic changes that occur in spontaneously recovery after stroke is less clear. The goal of this study is to elucidate the intrinsic changes in spontaneous recovery after stroke, by directly investigating the transcriptome of primary motor cortex in mice that naturally recovered after stroke. Methods- Male C57BL/6J mice were subjected to transient middle cerebral artery occlusion. Functional recovery was evaluated using the horizontal rotating beam test. A novel in-depth lesion mapping analysis was used to evaluate infarct size and locations. Ipsilesional and contralesional primary motor cortices (iM1 and cM1) were processed for RNA-sequencing transcriptome analysis. Results- Cluster analysis of the stroke mice behavior performance revealed 2 distinct recovery groups: a spontaneously recovered and a nonrecovered group. Both groups showed similar lesion profile, despite their differential recovery outcome. RNA-sequencing transcriptome analysis revealed distinct biological pathways in the spontaneously recovered stroke mice, in both iM1 and cM1. Correlation analysis revealed that 38 genes in the iM1 were significantly correlated with improved recovery, whereas 74 genes were correlated in the cM1. In particular, ingenuity pathway analysis highlighted the involvement of cAMP signaling in the cM1, with selective reduction of Adora2a (adenosine receptor A2A), Drd2 (dopamine receptor D2), and Pde10a (phosphodiesterase 10A) expression in recovered mice. Interestingly, the expressions of these genes in cM1 were negatively correlated with behavioral recovery. Conclusions- Our RNA-sequencing data revealed a panel of recovery-related genes in the motor cortex of spontaneously recovered stroke mice and highlighted the involvement of contralesional cortex in spontaneous recovery, particularly Adora2a, Drd2, and Pde10a-mediated cAMP signaling pathway. Developing drugs targeting these candidates after stroke may provide beneficial recovery outcome.

Chronic Cerebral Hypoperfusion Induces Alterations of Matrix Metalloproteinase-9 and Angiopoietin-2 Levels in the Rat Hippocampus

Angiogenic factors contribute to cerebral angiogenesis following cerebral hypoperfusion, and understanding these temporal changes is essential to developing effective treatments. The present study examined temporal alterations in angiogenesis-related matrix metalloproteinase-9 (MMP-9) and angiopoietin-2 (ANG-2) expression in the hippocampus following bilateral common carotid artery occlusion (BCCAo). Male Wistar rats (12 weeks of age) were randomly assigned to sham-operated control or experimental groups, and expression levels of MMP-9 and ANG-2 were assessed after BCCAo (1 week, 4 weeks, and 8 weeks), using western blotting. Protein expression increased 1 week after BCCAo and returned to control levels at 4 and 8 weeks. In addition, immunofluorescence staining demonstrated that the MMP-9- and ANG-2-positive signals were primarily observed in the NeuN-positive neurons with very little labeling in non-neuronal cells and no labeling in endothelial cells. In addition, these cellular locations of MMP-9- and ANG-2-positive signals were not altered over time following BCCAo. Other angiogenic factors such as vascular endothelial growth factor and hypoxia-inducible factor did not differ from controls at 1 week; however, expression of both factors increased at 4 and 8 weeks in the BCCAo group compared to the control group. Our findings increase understanding of alterations in angiogenic factors during the progression of cerebral angiogenesis and are relevant to developing effective temporally based therapeutic strategies for chronic cerebral hypoperfusion-associated neurological disorders such as vascular dementia.

Neural stem cell therapy for subacute and chronic ischemic stroke

Neural stem cells (NSCs) play vital roles in brain homeostasis and exhibit a broad repertoire of potentially therapeutic actions following neurovascular injury. One such injury is stroke, a worldwide leading cause of death and disability. Clinically, extensive injury from ischemic stroke results from ischemia-reperfusion (IR), which is accompanied by inflammation, blood-brain barrier (BBB) damage, neural cell death, and extensive tissue loss. Tissue plasminogen activator (tPA) is still the only US Food and Drug Administration-approved clot-lysing agent. Whereas the thrombolytic role of tPA within the vasculature is beneficial, the effects of tPA (in a non-thrombolytic role) within the brain parenchyma have been reported as harmful. Thus, new therapies are needed to reduce the deleterious side effects of tPA and quickly facilitate vascular repair following stroke. The Stroke Treatment Academic Industry Roundtable (STAIR) recommends that stroke therapies "focus on drugs/devices/treatments with multiple mechanisms of action and that target multiple pathways". Thus, based on multifactorial ischemic cascades in various stroke stages, effective stroke therapies need to focus on targeting and ameliorating early IR injury as well as facilitating angiogenesis, neurogenesis, and neurorestorative mechanisms following stroke. This review will discuss the preclinical perspectives of NSC transplantation as a promising treatment for neurovascular injury and will emphasize both the subacute and chronic phase of ischemic stroke.

Diverse Functions and Mechanisms of Pericytes in Ischemic Stroke

Background:

Every year, strokes take millions of lives and leave millions of individuals living with permanent disabilities. Recently more researchers embrace the concept of the neurovascular unit (NVU), which encompasses neurons, endothelial cells (ECs), pericytes, astrocyte, microglia, and the extracellular matrix. It has been well-documented that NVU emerged as a new paradigm for the exploration of mechanisms and therapies in ischemic stroke. To better understand the complex NVU and broaden therapeutic targets, we must probe the roles of multiple cell types in ischemic stroke. The aims of this paper are to introduce the biological characteristics of brain pericytes and the available evidence on the diverse functions and mechanisms involving the pericytes in the context of ischemic stroke.

Methods:

Research and online content related to the biological characteristics and pathophysiological roles of pericytes is review. The new research direction on the Pericytes in ischemic stroke, and the potential therapeutic targets are provided.

Results:

During the different stages of ischemic stroke, pericytes play different roles: 1) On the hyperacute phase of stroke, pericytes constriction and death may be a cause of the no-reflow phenomenon in brain capillaries; 2) During the acute phase, pericytes detach from microvessels and participate in inflammatory-immunological response, resulting in the BBB damage and brain edema. Pericytes also provide benefit for neuroprotection by protecting endothelium, stabilizing BBB and releasing neurotrophins; 3) Similarly, during the later recovery phase of stroke, pericytes also contribute to angiogenesis, neurogenesis, and thereby promote neurological recovery.

Conclusion:

This emphasis on the NVU concept has shifted the focus of ischemic stroke research from neuro-centric views to the complex interactions within NVU. With this new perspective, pericytes that are centrally positioned in the NVU have been widely studied in ischemic stroke. More work is needed to elucidate the beneficial and detrimental roles of brain pericytes in ischemic stroke that may serve as a basis for potential therapeutic targets.

Repulsive guidance molecule a suppresses angiogenesis after ischemia/reperfusion injury of middle cerebral artery occlusion in rats

Repulsive guidance molecule a (RGMa) has now emerged as a molecule with pleiotropic roles, including repulsion, adhesion, migration and differentiation in the nervous system. In this study, adult male Sprague-Dawley (SD) rats received 90-min middle cerebral artery occlusion (MCAO) to observe RGMa/neogenin expression sites after ischemia/reperfusion injury and changes in angiogenesis after treatment with RNA interference using RGMa-specific recombinant adenovirus rAd5-shRNA-RGMa (rAd-shRGMa). To clarify how RGMa mediates angiogenesis, the RGMa function-blocking peptide six fibronectin type III (6FNIII) was also administered, and corresponding changes in vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang2), angiopoietin-1 (Ang1), and brain derived neurotrophic factor (BDNF) were determined by western blotting. Both RGMa and its receptor neogenin were expressed in neurons and vessel endothelial cells after ischemia/reperfusion injury, and angiogenesis, coupled with functional recovery, was enhanced after RNA interference against RGMa compared with the vehicle groups. VEGF, Ang2, Ang1 and BDNF expression levels were significantly increased after intervention with rAd-shRGMa or 6FNIII. Thus, RGMa might suppress angiogenesis via VEGF, Ang2, Ang1 and BDNF after cerebral ischemia/reperfusion injury, which has therapeutic potential by reducing these endogenous detrimental mechanisms.

The roles of endoglin gene in cerebrovascular diseases

Endoglin (ENG, also known as CD105) is a transforming growth factor β (TGFβ) associated receptor and is required for both vasculogenesis and angiogenesis. Angiogenesis is important in the development of cerebral vasculature and in the pathogenesis of cerebral vascular diseases. ENG is an essential component of the endothelial nitric oxide synthase activation complex. Animal studies showed that ENG deficiency impairs stroke recovery. ENG deficiency also impairs the regulation of vascular tone, which contributes to the pathogenesis of brain arteriovenous malformation (bAVM) and vasospasm. In human, functional haploinsufficiency of ENG gene causes type I hereditary hemorrhagic telangiectasia (HHT1), an autosomal dominant disorder. Compared to normal population, HHT1 patients have a higher prevalence of AVM in multiple organs including the brain. Vessels in bAVM are fragile and tend to rupture, causing hemorrhagic stroke. High prevalence of pulmonary AVM in HHT1 patients are associated with a higher incidence of paradoxical embolism in the cerebral circulation causing ischemic brain injury. Therefore, HHT1 patients are at risk for both hemorrhagic and ischemic stroke. This review summarizes the possible mechanism of ENG in the pathogenesis of cerebrovascular diseases in experimental animal models and in patients.

Cell-based and pharmacological neurorestorative therapies for ischemic stroke

Ischemic stroke remains one of most common causes of death and disability worldwide. Stroke triggers a cascade of events leading to rapid neuronal damage and death. Neuroprotective agents that showed promise in preclinical experiments have failed to translate to the clinic. Even after decades of research, tPA remains the only FDA approved drug for stroke treatment. However, tPA is effective when administered 3-4.5 h after stroke onset and the vast majority of stroke patients do not receive tPA therapy. Therefore, there is a pressing need for novel therapies for ischemic stroke. Since stroke induces rapid cell damage and death, neuroprotective strategies that aim to salvage or replace injured brain tissue are challenged by treatment time frames. To overcome the barriers of neuroprotective therapies, there is an increasing focus on neurorestorative therapies for stroke. In this review article, we provide an update on neurorestorative treatments for stroke using cell therapy such as bone marrow derived mesenchymal stromal cells (BMSCs), human umbilical cord blood cells (HUCBCs) and select pharmacological approaches including Minocycline and Candesartan that have been employed in clinical trials. This review article discusses the present understanding of mechanisms of neurorestorative therapies and summarizes ongoing clinical trials. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Epigenetics in Stroke Recovery

Abstract: While the death rate from stroke has continually decreased due to interventions in the hyperacute stage of the disease, long-term disability and institutionalization have become common sequelae in the aftermath of stroke. Therefore, identification of new molecular pathways that could be targeted to improve neurological recovery among survivors of stroke is crucial. Epigenetic mechanisms such as post-translational modifications of histone proteins and microRNAs have recently emerged as key regulators of the enhanced plasticity observed during repair processes after stroke. In this review, we highlight the recent advancements in the evolving field of epigenetics in stroke recovery.

[Influence of vascular endothelial growth factor on angiogenesis and neurogenesis]

Vascular endothelial growth factor (VEGF) is known as a key mediator of angiogenesis, but there is also evidence of its broad significance in neurogenesis and neuroprotection. Cytokines of the VEGF family affect neovascularization and neural development in the brain, particularly during cerebral ischemia, in which there is a coordinated interaction of angiogenesis and neurogenesis that contributes to rapid functional recovery. This review examines the involvement of VEGF family members and their receptors in physiological and pathophysiological processes as well as the relationship between VEGF-A plasma levels and ischemic stroke.

Function of neural stem cells in ischemic brain repair processes

Hypoxic/ischemic injury is the single most important cause of disabilities in infants, while stroke remains a leading cause of morbidity in children and adults around the world. The injured brain has limited repair capacity, and thereby only modest improvement of neurological function is evident post injury. In rodents, embryonic neural stem cells in the ventricular zone generate cortical neurons, and adult neural stem cells in the ventricular-subventricular zone of the lateral ventricle produce new neurons through animal life. In addition to generation of new neurons, neural stem cells contribute to oligodendrogenesis. Neurogenesis and oligodendrogenesis are essential for repair of injured brain. Much progress has been made in preclinical studies on elucidating the cellular and molecular mechanisms that control and coordinate neurogenesis and oligodendrogenesis in perinatal hypoxic/ischemic injury and the adult ischemic brain. This article will review these findings with a focus on the ventricular-subventricular zone neurogenic niche and discuss potential applications to facilitate endogenous neurogenesis and thereby to improve neurological function post perinatal hypoxic/ischemic injury and stroke.

In vivo inhibition of miR-155 significantly alters post-stroke inflammatory response

Background

MicroRNA miR-155 is implicated in modulation of the inflammatory processes in various pathological conditions. In our previous studies, we demonstrated that in vivo inhibition of miR-155 promotes functional recovery after mouse experimental stroke. In the present study, we explored if this beneficial effect is associated with miR-155 inhibition-induced alterations in post-stroke inflammatory response.

Methods

Intravenous injections of a specific miR-155 inhibitor were initiated at 48 h after mouse distal middle cerebral artery occlusion (dMCAO). Temporal changes in the expression of cytokines and key molecules associated with cytokine signaling were assessed at 7, 14, and 21 days after dMCAO, using mouse cytokine gene and protein arrays and Western blot analyses. Electron and immunofluorescence confocal microscopy techniques were used to evaluate the ultrastructural changes, as well as altered expression of specific phenotypic markers, at different time points after dMCAO.

Results

In the inhibitor-injected mice (inhibitor group), there was a significant decrease in CCL12 and CXCL3 cytokine expression at 7 days and significantly increased levels of major cytokines IL-10, IL-4, IL-6, MIP-1α, IL-5, and IL-17 at 14 days after dMCAO. These temporal changes correlated with altered expression of miR-155 target proteins SOCS-1, SHIP-1, and C/EBP-β and phosphorylation levels of cytokine signaling regulator STAT-3. Electron microscopy showed decreased number of phagocytically active peri-vascular microglia/macrophages in the inhibitor samples. Immunofluorescence and Western blot of these samples demonstrated that expression of leukocyte/ macrophage marker CD45 and phagocytosis marker CD68 was reduced at 7 days, and in contrast, significantly increased at 14 days after dMCAO, as compared to controls.

Conclusions

Based on our findings, we propose that in vivo miR-155 inhibition following mouse stroke significantly alters the time course of the expression of major cytokines and inflammation-associated molecules, which could influence inflammation process and tissue repair after experimental cerebral ischemia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0753-x) contains supplementary material, which is available to authorized users.

Identification of miRNomes associated with adult neurogenesis after stroke using Argonaute 2-based RNA sequencing

Neurogenesis is associated with functional recovery after stroke. However, the underlying molecular mechanisms have not been fully investigated. Using an Ago2-based RNA immunoprecipitation to immunoprecipated Ago2-RNA complexes followed by RNA sequencing (Ago2 RIP-seq) approach, we profiled the miRNomes in neural progenitor cells (NPCs) harvested from the subventricular zone (SVZ) of the lateral ventricles of young adult rats. We identified more than 7 and 15 million reads in normal and ischemic NPC libraries, respectively. We found that stroke substantially changed Ago2-associated miRNA profiles in NPCs compared to those in non-ischemic NPCs. We also discovered a new complex repertoire of isomiRs and multiple miRNA-miRNA* pairs and numerous novel miRNAs in the non-ischemic and ischemic NPCs. Among them, pc-3p-17172 significantly regulated NPC proliferation and neuronal differentiation. Collectively, the present study reveals profiles of Ago2-associated miRNomes in non-ischemic and ischemic NPCs, which provide a molecular basis to further investigate the role of miRNAs in mediating adult neurogenesis under physiological and ischemic conditions.

Induction of Neurorestoration From Endogenous Stem Cells

Neural stem cells (NSCs) persist in the subventricular zone lining the ventricles of the adult brain. The resident stem/progenitor cells can be stimulated in vivo by neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and/or physical exercise. In both animals and humans, the differentiation and survival of neurons arising from the subventricular zone may also be regulated by the trophic factors. Since stem/progenitor cells present in the adult brain and the production of new neurons occurs at specific sites, there is a possibility for the treatment of incurable neurological diseases. It might be feasible to induce neurogenesis, which would be particularly efficacious in the treatment of striatal neurodegenerative conditions such as Huntington's disease, as well as cerebrovascular diseases such as ischemic stroke and cerebral palsy, conditions that are widely seen in the clinics. Understanding of the molecular control of endogenous NSC activation and progenitor cell mobilization will likely provide many new opportunities as therapeutic strategies. In this review, we focus on endogenous stem/progenitor cell activation that occurs in response to exogenous factors including neurotrophic factors, hematopoietic growth factors, magnetic stimulation, and an enriched environment. Taken together, these findings suggest the possibility that functional brain repair through induced neurorestoration from endogenous stem cells may soon be a clinical reality.

Promoting recovery from ischemic stroke

Over recent decades, experimental and clinical stroke studies have identified a number of neurorestorative treatments that stimulate neural plasticity and promote functional recovery. In contrast to the acute stroke treatments thrombolysis and endovascular thrombectomy, neurorestorative treatments are still effective when initiated days after stroke onset, which makes them applicable to virtually all stroke patients. In this article, selected physical, pharmacological and cell-based neurorestorative therapies are discussed, with special emphasis on interventions that have already been transferred from the laboratory to the clinical setting. We explain molecular and structural processes that promote neural plasticity, discuss potential limitations of neurorestorative treatments, and offer a speculative viewpoint on how neurorestorative treatments will evolve.

Acute Blockage of Notch Signaling by DAPT Induces Neuroprotection and Neurogenesis in the Neonatal Rat Brain After Stroke

Notch signaling is critically involved in various biological events. Notch undergoes cleavage by the γ-secretase enzyme to release Notch intracellular domain that will translocate into nucleus to result in expression of target gene. γ-Secretase inhibitors have been developed as potential treatments for neurological degenerative diseases, but its effects against ischemic injury remain relatively uncertain. In the present study, we demonstrated that N-[N-(3, 5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a γ-secretase inhibitor not only rescued the cerebral hypoperfusion or ischemia neonatal rats from death, reduced apoptosis in penumbra, but also reduced brain infarct size. Furthermore, DAPT elicited some morphologic hallmarks such as neurogenesis and angiogenesis that related to the brain repair and functional recovery after stroke: increased accumulations of newborn cells in the peri-infarct region with a higher fraction of them adopting immature neuronal and glial markers instead of microglial markers on 5 days, enhanced vascular densities in penumbra at 14 days, and evident regulations of the gene profiles associated with neurogenesis in penumbral tissues. The current results suggest that DAPT is a potential neuroprotectants against ischemic injury in immature brain, and future treatment strategies such as clinical trials using γ-secretase inhibitors would be an attractive therapy for perinatal ischemia.

In Vivo Inhibition of miR-155 Promotes Recovery after Experimental Mouse Stroke

A multifunctional microRNA, miR-155, has been recently recognized as an important modulator of numerous biological processes. In our previous in vitro studies, miR-155 was identified as a potential regulator of the endothelial morphogenesis. The present study demonstrates that in vivo inhibition of miR-155 supports cerebral vasculature after experimental stroke. Intravenous injections of a specific miR-155 inhibitor were initiated at 48 h after mouse distal middle cerebral artery occlusion (dMCAO). Microvasculature in peri-infarct area, infarct size, and animal functional recovery were assessed at 1, 2, and 3 weeks after dMCAO. Using in vivo two-photon microscopy, we detected improved blood flow and microvascular integrity in the peri-infarct area of miR-155 inhibitor-injected mice. Electron microscopy revealed that, in contrast to the control group, these animals demonstrated well preserved capillary tight junctions (TJs). Western blot analysis data indicate that improved TJ integrity in the inhibitor-injected animals could be associated with stabilization of the TJ protein ZO-1 and mediated by the miR-155 target protein Rheb. MRI analysis showed significant (34%) reduction of infarct size in miR-155 inhibitor-injected animals at 21 d after dMCAO. Reduced brain injury was confirmed by electron microscopy demonstrating decreased neuronal damage in the peri-infarct area of stroke. Preservation of brain tissue was reflected in efficient functional recovery of inhibitor-injected animals. Based on our findings, we propose that in vivo miR-155 inhibition after ischemia supports brain microvasculature, reduces brain tissue damage, and improves the animal functional recovery. Significance statement: In the present study, we investigated an effect of the in vivo inhibition of a microRNA, miR-155, on brain recovery after experimental cerebral ischemia. To our knowledge, this is the first report describing the efficiency of intravenous anti-miRNA injections in a mouse model of ischemic stroke. The role of miRNAs in poststroke revascularization has been unexplored and in vivo regulation of miRNAs during the subacute phase of stroke has not yet been proposed. Our investigation introduces a new and unexplored approach to cerebral regeneration: regulation of poststroke angiogenesis and recovery through direct modulation of specific miRNA activity. We expect that our findings will lead to the development of novel strategies for regulating neurorestorative processes in the postischemic brain.

Mechanisms and Functional Significance of Stroke-Induced Neurogenesis

Stroke affects one in every six people worldwide, and is the leading cause of adult disability. After stroke, some limited spontaneous recovery occurs, the mechanisms of which remain largely unknown. Multiple, parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. For years, clinical studies have tried to use exogenous cell therapy as a means of brain repair, with varying success. Since the rediscovery of adult neurogenesis and the identification of adult neural stem cells in the late nineties, one promising field of investigation is focused upon triggering and stimulating this self-repair system to replace the neurons lost following brain injury. For instance, it is has been demonstrated that the adult brain has the capacity to produce large numbers of new neurons in response to stroke. The purpose of this review is to provide an updated overview of stroke-induced adult neurogenesis, from a cellular and molecular perspective, to its impact on brain repair and functional recovery.

Coupling of neurogenesis and angiogenesis after ischemic stroke

Stroke is a leading cause of mortality and severe long-term disability worldwide. Development of effective treatment or new therapeutic strategies for ischemic stroke patients is therefore crucial. Ischemic stroke promotes neurogenesis by several growth factors including FGF-2, IGF-1, BDNF, VEGF and chemokines including SDF-1, MCP-1. Stroke-induced angiogenesis is similarly regulated by many factors most notably, eNOS and CSE, VEGF/VEGFR2, and Ang-1/Tie2. Important findings in the last decade have revealed that neurogenesis is not the stand-alone consideration in the fight for full functional recovery from stroke. Angiogenesis has been also shown to be critical in improving post-stroke neurological functional recovery. More than that, recent evidence has shown a highly possible interplay or dependence between stroke-induced neurogenesis and angiogenesis. Moving forward, elucidating the underlying mechanisms of this coupling between stroke-induced neurogenesis and angiogenesis will be of great importance, which will provide the basis for neurorestorative therapy. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Current knowledge on the neuroprotective and neuroregenerative properties of citicoline in acute ischemic stroke

Ischemic stroke is one of the leading causes of long-lasting disability and death. Two main strategies have been proposed for the treatment of ischemic stroke: restoration of blood flow by thrombolysis or mechanical thrombus extraction during the first few hours of ischemic stroke, which is one of the most effective treatments and leads to a better functional and clinical outcome. The other direction of treatment, which is potentially applicable to most of the patients with ischemic stroke, is neuroprotection. Initially, neuroprotection was mainly targeted at protecting gray matter, but during the past few years there has been a transition from a neuron-oriented approach toward salvaging the whole neurovascular unit using multimodal drugs. Citicoline is a multimodal drug that exhibits neuroprotective and neuroregenerative effects in a variety of experimental and clinical disorders of the central nervous system, including acute and chronic cerebral ischemia, intracerebral hemorrhage, and global cerebral hypoxia. Citicoline has a prolonged therapeutic window and is active at various temporal and biochemical stages of the ischemic cascade. In acute ischemic stroke, citicoline provides neuroprotection by attenuating glutamate exitotoxicity, oxidative stress, apoptosis, and blood–brain barrier dysfunction. In the subacute and chronic phases of ischemic stroke, citicoline exhibits neuroregenerative effects and activates neurogenesis, synaptogenesis, and angiogenesis and enhances neurotransmitter metabolism. Acute and long-term treatment with citicoline is safe and in most clinical studies is effective and improves functional outcome.

Functional genomics indicate that schizophrenia may be an adult vascular-ischemic disorder

In search for the elusive schizophrenia pathway, candidate genes for the disorder from a discovery sample were localized within the energy-delivering and ischemia protection pathway. To test the adult vascular-ischemic (AVIH) and the competing neurodevelopmental hypothesis (NDH), functional genomic analyses of practically all available schizophrenia-associated genes from candidate gene, genome-wide association and postmortem expression studies were performed. Our results indicate a significant overrepresentation of genes involved in vascular function (P < 0.001), vasoregulation (that is, perivascular (P < 0.001) and shear stress (P < 0.01), cerebral ischemia (P < 0.001), neurodevelopment (P < 0.001) and postischemic repair (P < 0.001) among schizophrenia-associated genes from genetic association studies. These findings support both the NDH and the AVIH. The genes from postmortem studies showed an upregulation of vascular-ischemic genes (P = 0.020) combined with downregulated synaptic (P = 0.005) genes, and ND/repair (P = 0.003) genes. Evidence for the AVIH and the NDH is critically discussed. We conclude that schizophrenia is probably a mild adult vascular-ischemic and postischemic repair disorder. Adult postischemic repair involves ND genes for adult neurogenesis, synaptic plasticity, glutamate and increased long-term potentiation of excitatory neurotransmission (i-LTP). Schizophrenia might be caused by the cerebral analog of microvascular angina.

IFN gamma regulates proliferation and neuronal differentiation by STAT1 in adult SVZ niche

The adult subventricular zone (SVZ) is the main neurogenic niche in normal adult brains of mice and rats. Interferon gamma (IFNγ) has somewhat controversially been associated with SVZ progenitor proliferation and neurogenesis. The in vivo involvement of IFNγ in the physiology of the adult SVZ niche is not fully understood and its intracellular mediators are unknown. Here we show that IFNγ, through activation of its canonical signal transducer and activator of transcription 1 (STAT1) pathway, acts specifically on Nestin+ progenitors by decreasing both progenitor proliferation and the number of cycling cells. In addition, IFNγ increases the number of neuroblasts generated without shifting glial fate determination. The final result is deficient recruitment of newborn neurons to the olfactory bulb (OB), indicating that IFNγ-induced stimulation of neuronal differentiation does not compensate for its antiproliferative effect. We conclude that IFNγ signaling via STAT1 in the SVZ acts dually as an antiproliferative and proneurogenic factor, and thereby regulates neurogenesis in normal adult brains.

Hypoxia-controlled matrix metalloproteinase-9 hyperexpression promotes behavioral recovery after ischemia

Matrix metalloproteinase-9 (MMP-9) plays a beneficial role in the sub-acute phase after ischemic stroke. However, unrestrained MMP-9 may disrupt the blood-brain barrier (BBB), which has limited its use for the treatment of brain ischemia. In the present study, we constructed lentivirus mediated hypoxia-controlled MMP-9 expression and explored its role after stroke. Hypoxia response element (HRE) was used to confine MMP-9 expression only to the hypoxic region of mouse brain after 120-min transient middle cerebral artery occlusion. Lentiviruses were injected into the peri-infarct area on day 7 after transient ischemia. We found hyperexpression of exogenous HRE-MMP-9 under the control of hypoxia, and its expression was mainly located in neurons and astrocytes without aggravation of BBB damage compared to the CMV group. Furthermore, mice in the HRE-MMP-9 group showed the best behavioral recovery compared with the normal saline, GFP, and SB-3CT groups. Therefore, hypoxia-controlled MMP-9 hyperexpression during the sub-acute phase of ischemia may provide a novel promising approach of gene therapy for stroke.

Cell replacement therapy: lessons from teleost fish

Many disorders of the CNS are characterized by a massive loss of neurons. A promising therapeutic strategy to cure such conditions is based on the activation of endogenous stem cells. Implementation of this strategy will benefit from a better understanding of stem cell dynamics and the local CNS microenvironment in regeneration-competent vertebrate model systems. Using a spinal cord injury paradigm in zebrafish larvae, Briona and Dorsky (2014) have provided evidence for the existence of two distinct neural stem cell populations. One population has the characteristics of radial glia and expresses the homeobox transcription factor Dbx. The other lacks Dbx but expresses Olig2. These results are placed in the context of other studies that also support the notion of heterogeneity of adult stem cells in the CNS. The implication that differences among stem cell populations, in combination with specific factors from the local cellular microenvironment, might have a decisive impact on the fate choices of the new cells, is discussed. Reviewed evidence suggests that rather few modifications in the signaling pathways involved in the control of stem cell behavior have led, in the course of evolution, to the pronounced differences between mammals and regeneration-competent organisms. As a consequence, rather minor pharmacological manipulations may be sufficient to reactivate the hidden neurogenic potential of the mammalian CNS, and thus make it available for therapeutic applications.