Endothelial progenitor cell research in stroke: a potential shift in pathophysiological and therapeutical concepts

Biomarkers and the outcomes of ischemic stroke

Biomarkers are measurable substances that could be used as objective indicators for disease diagnosis, responses to treatments, and outcomes predictions. In this review, we summarized the data on a number of important biomarkers including glutamate, S100B, glial fibrillary acidic protein, receptor for advanced glycation end-products, intercellular adhesion molecule-1, von willebrand factor, matrix metalloproteinase-9, interleukin-6, tumor necrosis factor-a, activated protein C, copeptin, neuron-specific enolase, tau protein, gamma aminobutyric acid, blood glucose, endothelial progenitor cells, and circulating CD34-positive cells that could be potentially used to indicate the disease burden and/or predict clinical outcome of ischemic stroke. We examined the relationship between specific biomarkers and disease burden and outcomes and discussed the potential mechanisms underlying the relationship. The clinical significance and implications of these biomarkers were also discussed.

Endothelial Progenitor Cells in Neurovascular Disorders—A Comprehensive Overview of the Current State of Knowledge

Endothelial progenitor cells (EPCs) are a population of cells that circulate in the blood looking for areas of endothelial or vascular injury in order to repair them. Endothelial dysfunction is an important component of disorders with neurovascular involvement. Thus, the subject of involvement of EPCs in such conditions has been gaining increasing scientific interest in recent years. Overall, decreased levels of EPCs are associated with worse disease outcome. Moreover, their functionalities appear to decline with severity of disease. These findings inspired the application of EPCs as therapeutic targets and agents. So far, EPCs appear safe and promising based on the results of pre-clinical studies conducted on their use in the treatment of Alzheimer’s disease and ischemic stroke. In the case of the latter, human clinical trials have recently started to be performed in this subject and provided optimistic results thus far. Whereas in the case of migraine, existing findings pave the way for testing EPCs in in vitro studies. This review aims to thoroughly summarize current knowledge on the role EPCs in four disorders with neurovascular involvement, which are Alzheimer’s disease, cerebral small vessel disease, ischemic stroke and migraine, with a particular focus on the potential practical use of these cells as a treatment remedy.

OUP accepted manuscript

Fetal growth restriction (FGR) occurs when a fetus is unable to grow normally due to inadequate nutrient and oxygen supply from the placenta. Children born with FGR are at high risk of lifelong adverse neurodevelopmental outcomes, such as cerebral palsy, behavioral issues, and learning and attention difficulties. Unfortunately, there is no treatment to protect the FGR newborn from these adverse neurological outcomes. Chronic inflammation and vascular disruption are prevalent in the brains of FGR neonates and therefore targeted treatments may be key to neuroprotection. Tissue repair and regeneration via stem cell therapies have emerged as a potential clinical intervention for FGR babies at risk for neurological impairment and long-term disability. This review discusses the advancement of research into stem cell therapy for treating neurological diseases and how this may be extended for use in the FGR newborn. Leading preclinical studies using stem cell therapies in FGR animal models will be highlighted and the near-term steps that need to be taken for the development of future clinical trials.

Endothelial Progenitor Cells Count after Acute Ischemic Stroke Predicts Functional Outcome in Patients with Carotid Atherosclerosis

OBJECTIVES

Circulating Endothelial Progenitor Cells (EPCs) predict cardiovascular outcomes in patients with coronary disease. However, the predictive value of EPCs after ischemic stroke is not well established. We aimed to study the prognostic role of EPCs in patients with acute ischemic stroke and carotid atherosclerosis, focusing on post-stroke functional outcome and stroke recurrences.

MATERIALS AND METHODS

We studied consecutive adult patients with an acute (<7 days) anterior circulation ischemic stroke and carotid atherosclerosis. Cardioembolic strokes were excluded. We measured circulating EPCs by flow cytometry (CD34+/CD133+/KDR+) at inclusion (7±1 days after stroke) and at one year of follow-up. At three months and at one year we registered the modified Rankin Scale score, stroke recurrences and coronary syndromes during the follow-up.

RESULTS

We studied 80 patients with a mean age of 74.3±10.4 years. We divided the population in tertiles according to the EPCs count. At three months we observed a favorable outcome in 25/36 (69.4%) patients in the lowest, 19/22 (86.4%) in the medium and 21/22 (95.5%) in the highest tercile (p=0.037). In the multivariable analysis a higher EPCs count was associated with favorable functional outcome after adjusting for age and baseline NIHSS score (OR=3.61, 95%CI 1.34-9.76; p=0.011). This association persisted at one year of follow-up. We did not find association between counts of EPCs and stroke recurrence.

CONCLUSIONS

In patients with acute ischemic stroke and carotid atherosclerosis, a higher count of EPCs was associated with favorable functional outcome in the mid and long-term follow-up. Counts of EPCs did not predict stroke recurrences.

Role of Stromal Cell-Derived Factor-1 in Endothelial Progenitor Cell-Mediated Vascular Repair and Regeneration

Endothelial progenitor cells (EPCs) are immature endothelial cells that participate in vascular repair and postnatal neovascularization and provide a novel and promising therapy for the treatment of vascular disease. Studies in different animal models have shown that EPC mobilization through pharmacological agents and autologous EPC transplantation contribute to restoring blood supply and tissue regeneration after ischemic injury. However, these effects of the progenitor cells in clinical studies exhibit mixed results. The therapeutic efficacy of EPCs is closely associated with the number of the progenitor cells recruited into ischemic regions and their functional abilities and survival in injury tissues. In this review, we discussed the regulating role of stromal cell-derived factor-1 (also known CXCL12, SDF-1) in EPC mobilization, recruitment, homing, vascular repair and neovascularization, and analyzed the underlying machemisms of these functions. Application of SDF-1 to improve the regenerative function of EPCs following vascular injury was also discussed. SDF-1 plays a crucial role in mobilizing EPC from bone marrow into peripheral circulation, recruiting the progenitor cells to target tissue and protecting against cell death under pathological conditions; thus improve EPC regenerative capacity. SDF-1 are crucial for regulating EPC regenerative function, and provide a potential target for improve therapeutic efficacy of the progenitor cells in treatment of vascular disease.

Simvastatin increases circulating endothelial progenitor cells and inhibits the formation of intracranial aneurysms in rats with diet-induced hyperhomocysteinemia

BACKGROUND AND PURPOSE

Endothelial dysfunction triggers early pathological changes in artery, leading to the formation of intracranial aneurysm (ICA). Increase in plasma homocysteine (Hcy) impairs endothelium and endothelial progenitor cells (EPCs) are critical in repairing damaged endothelium. The aim of this study was to assess the impact of simvastatin on ICA formation in rats with hyperhomocysteinemia (HHcy).

METHODS

ICAs were induced in Male Sprague-Dawley rats after surgical induction in the presence of HHcy induced by a high L-methionine diet with or without oral simvastatin treatment. The size and media thickness of ICAs were evaluated 2 months after aneurysm induction. EPCs and serum vascular endothelial grow factor (VEGF) were measured be flow cytometry and ELISA respectively. Plasma Hcy levels and expression of VEGF, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2), and MMP-9 in aneurysmal walls were examined and correlated with ICA formation.

RESULTS

HHcy accelerates ICA formation and rats treated with simvastatin exhibited a significant increase in media thickness and a reduction in aneurysmal size. Simvastatin increased levels of circulating EPCs and decreased iNOS, MMP-2, MMP-9 and VEGF mRNA levels, while increased eNOS mRNA in aneurysmal tissue.

CONCLUSION

In a rat model, HHcy reduces circulating EPCs and accelerates ICA formation. Simvastatin treatment increases circulating EPCs and inhabits the formation of ICA. We have shown a close association among circulating EPCs, biochemical markers related to vascular remodeling and the formation of ICA.

Exosomes and Exosomal MicroRNAs in Age-Associated Stroke

Aging has been considered to be the most important non-modifiable risk factor for stroke and death. Changes in circulation factors in the systemic environment, cellular senescence and artery hypertension during human ageing have been investigated. Exosomes are nanosize membrane vesicles that can regulate target cell functions via delivering their carried bioactive molecules (e.g. protein, mRNA, and microRNAs). In the central nervous system, exosomes and exosomal microRNAs play a critical role in regulating neurovascular function, and are implicated in the initiation and progression of stroke. MicroRNAs are small non-coding RNAs that have been reported to play critical roles in various biological processes. Recently, evidence has shown that microRNAs are packaged into exosomes and can be secreted into the systemic and tissue environment. Circulating microRNAs participate in cellular senescence and contribute to age-associated stroke. Here, we provide an overview of current knowledge on exosomes and their carried microRNAs in the regulation of cellular and organismal ageing processes, demonstrating the potential role of exosomes and their carried microRNAs in age-associated stroke.

CD34+ cells and endothelial progenitor cell subpopulations are associated with cerebral small vessel disease burden

Background: Endothelial dysfunction is considered to be involved in the pathogenesis of cerebral small vessel disease (CSVD). Endothelial progenitor cells are associated with endothelial dysfunction. The present study was designed to investigate the correlation between the populations of circulating CD34-positive cells and endothelial progenitor cells and CSVD burden. Methodology & results: A total of 364 patients with confirmed diagnosis of CSVD were included in this prospective study. Multiple ordinal logistic regression analyses showed that subjects with higher CSVD burden had significantly decreased circulating CD34⁺ cell level (odds ratio [OR], 0.42; p = 0.034) and significantly increased levels of circulating CD34⁺CD133⁺CD309⁺ and CD34⁺CD133⁺ cells (OR 1.07, p = 0.031; OR 1.03, p = 0.001, respectively), compared with patients with lower CSVD burden. Conclusion: The findings suggest that the levels of circulating CD34⁺ cells, CD34⁺CD133⁺CD309⁺ cells and CD34⁺CD133⁺ cells may be used as potential biomarkers to monitor the disease progression of CSVD.

The Relation of the Brain-Derived Neurotrophic Factor with MicroRNAs in Neurodegenerative Diseases and Ischemic Stroke

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family of growth factors that plays a crucial role in the development of the nervous system while supporting the survival of existing neurons and instigating neurogenesis. Altered levels of BDNF, both in the circulation and in the central nervous system (CNS), have been reported to be involved in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), multiple sclerosis (MS), and ischemic stroke. MicroRNAs (miRNAs) are a class of non-coding RNAs found in body fluids such as peripheral blood and cerebrospinal fluid. Several different miRNAs, and their target genes, are recognized to be involved in the pathophysiology of neurodegenerative and neurovascular diseases. Thus, they present as promising biomarkers and a novel treatment approach for CNS disorders. Currently, limited studies provide viable evidence of miRNA-mediated post-transcriptional regulation of BDNF. The aim of this review is to provide a comprehensive assessment of the current knowledge regarding the potential diagnostic and prognostic values of miRNAs affecting BDNF expression and its role as a CNS disorders and neurovascular disease biomarker. Moreover, a novel therapeutic approach in neurodegenerative diseases and ischemic stroke targeting miRNAs associated with BDNF will be discussed.

Endothelial Progenitor Cells Modulate Inflammation-Associated Stroke Vasculome

Stroke remains a major unmet clinical need that warrants novel therapies. Following an ischemic insult, the cerebral vasculature secretes inflammatory molecules, creating the stroke vasculome profile. The present study evaluated the therapeutic effects of endothelial cells on the inflammation-associated stroke vasculome. qRT-PCR analysis revealed that specific inflammation-related vasculome genes BRM, IκB, Foxf1, and ITIH-5 significantly upregulated by oxygen glucose deprivation (OGD. Interestingly, co-culture of human endothelial cells (HEN6) with human endothelial cells (EPCs) during OGD significantly blocked the elevations of BRM, IκB, and Foxf1, but not ITIH-5. Next, employing the knockdown/antisense technology, silencing the inflammation-associated stroke vasculome gene, IκB, as opposed to scrambled knockdown, blocked the EPC-mediated protection of HEN6 against OGD. In vivo, stroke animals transplanted with intracerebral human EPCs (300,000 cells) into the striatum and cortex 4 h post ischemic stroke displayed significant behavioral recovery up to 30 days post-transplantation compared to vehicle-treated stroke animals. At 7 days post-transplantation, quantification of the fluorescent staining intensity in the cortex and striatum revealed significant upregulation of the endothelial marker RECA1 and a downregulation of the stroke-associated vasculome BRM, IKB, Foxf1, ITIH-5 and PMCA2 in the ipsilateral side of cortex and striatum of EPC-transplanted stroke animals relative to vehicle-treated stroke animals. Altogether, these results demonstrate that EPCs exert therapeutic effects in experimental stroke possibly by modulating the inflammation-plagued vasculome.

Therapeutic strategy against ischemic stroke with the concept of neurovascular unit

Stroke is one of the leading causes of death and disability globally. Although thrombolytic therapy by t-PA and mechanical thrombectomy have improved outcomes of ischemic stroke patients, both of these approaches are applicable to limited numbers of patients owing to their time constraints. Therefore, development of other treatment approaches such as developing neuroprotective drugs and nerve regeneration therapy is required to overcome ischemic stroke. The concept of the neurovascular unit (NVU) was formalized by the Stroke Progress Review Group of the National Institute of Neurological Disorders and Stroke in 2001. This concept emphasizes the importance not just of neurons but of the interactions between neurons, endothelial cells, astroglia, microglia and associated tissue matrix proteins to investigate the pathological condition of ischemic stroke. Many reports have been published about these interactions. This review focuses on the roles of cells that surround cerebral vasculature, especially endothelial cells, and reports therapeutic strategies against ischemic stroke from four points of view including angiogenesis, neurotrophic effects, protection of NVU components and regenerative therapy.

Astrocyte Signaling in the Neurovascular Unit After Central Nervous System Injury

Astrocytes comprise the major non-neuronal cell population in the mammalian neurovascular unit. Traditionally, astrocytes are known to play broad roles in central nervous system (CNS) homeostasis, including the management of extracellular ion balance and pH, regulation of neurotransmission, and control of cerebral blood flow and metabolism. After CNS injury, cell–cell signaling between neuronal, glial, and vascular cells contribute to repair and recovery in the neurovascular unit. In this mini-review, we propose the idea that astrocytes play a central role in organizing these signals. During CNS recovery, reactive astrocytes communicate with almost all CNS cells and peripheral progenitors, resulting in the promotion of neurogenesis and angiogenesis, regulation of inflammatory response, and modulation of stem/progenitor response. Reciprocally, changes in neurons and vascular components of the remodeling brain should also influence astrocyte signaling. Therefore, understanding the complex and interdependent signaling pathways of reactive astrocytes after CNS injury may reveal fundamental mechanisms and targets for re-integrating the neurovascular unit and augmenting brain recovery.

A Modified Encephalo-Duro-Synangiosis Technique Induced Neovascularization in Symptomatic Atherosclerotic Carotid Artery Occlusion: A Phase I trial

OBJECTIVE

To the best of our knowledge, the present study is the first to assess the safety and feasibility of a modified encephalo-galeo-duro-synangiosis operation in patients with atherosclerotic carotid artery occlusion.

METHODS

Eight patients who had experienced new ipsilateral cerebrovascular events after the diagnosis of carotid artery occlusion were recruited. To facilitate extracranial-to-intracranial collateralization, 5 or 6 burr holes were made, and the dura mater and arachnoid were opened. The patients were closely monitored for complications and underwent conventional angiography, magnetic resonance imaging, and perfusion-weighted magnetic resonance imaging at baseline and 1 year of follow-up. After 10 years, the patients who were still alive were interviewed and assessed for functional outcomes and neurological status.

RESULTS

No surgery-related adverse events were observed, apart from temporary headache and subcutaneous effusion. Four of six patients had developed an extracranial-to-intracranial collateral blood vessels on angiography, and these patients had no incident ischemic events during the follow-up period. During the long-term follow-up period (10 years), 3 patients had died. Of those living, 4 of the 5 patients reported total resolution of the symptoms, with no incident ischemic events. One patient still experienced disability from an ischemic stroke that occurred as a result of the 1-year follow-up angiography.

CONCLUSIONS

Encephalo-duro-galeo-synangiosis for symptomatic carotid occlusion seems to be safe and feasible and might be able to induce extracranial-to-intracranial collaterals in patients with carotid artery occlusion. Further studies are needed to define the optimal therapeutic window and yield of burr hole surgery in the treatment of symptomatic carotid occlusive disease as an adjuvant to extracranial-intracranial bypass.

Protective Effects of Endothelial Progenitor Cell-Derived Extracellular Mitochondria in Brain Endothelium

Endothelial progenitor cells (EPCs) have been pursued as a potential cellular therapy for stroke and central nervous system injury. However, their underlying mechanisms remain to be fully defined. Recent experimental studies suggest that mitochondria may be released and transferred between cells. In this proof-of-concept study, we asked whether beneficial effects of EPCs may partly involve a mitochondrial phenomenon as well. First, EPC-derived conditioned medium was collected and divided into supernatant and particle fractions after centrifugation. Electron microscopy, Western blots, and flow cytometry showed that EPCs were able to release mitochondria. ATP and oxygen consumption assays suggested that these extracellular mitochondria may still be functionally viable. Confocal microscopy confirmed that EPC-derived extracellular mitochondria can be incorporated into normal brain endothelial cells. Adding EPC particles to brain endothelial cells promoted angiogenesis and decreased the permeability of brain endothelial cells. Next, we asked whether EPC-derived mitochondria may be protective. As expected, oxygen-glucose deprivation (OGD) increased brain endothelial permeability. Adding EPC-derived mitochondria particles to the damaged brain endothelium increased levels of mitochondrial protein TOM40, mitochondrial DNA copy number, and intracellular ATP. Along with these indirect markers of mitochondrial transfer, endothelial tightness was also restored after OGD. Taken together, these findings suggest that EPCs may support brain endothelial energetics, barrier integrity, and angiogenic function partly through extracellular mitochondrial transfer. Stem Cells 2018;36:1404-1410.

The anti-microbial peptide SR-0379 stimulates human endothelial progenitor cell-mediated repair of peripheral artery diseases

Ischemia is a serious disease, characterized by an inadequate blood supply to an organ or part of the body. In the present study, we evaluated the effects of the anti-microbial peptide SR-0379 on the stem cell-mediated therapy of ischemic diseases. The migratory and tube-forming abilities of human endothelial progenitor cells (EPCs) were enhanced by treatment with SR-0379 in vitro. Intramuscular administration of SR-0379 into a murine ischemic hindlimb significantly enhanced blood perfusion, decreased tissue necrosis, and increased the number of blood vessels in the ischemic muscle. Moreover, co-administration of SR-0379 with EPCs stimulated blood perfusion in an ischemic hindlimb more than intramuscular injection with either SR-0379 or EPCs alone. This enhanced blood perfusion was accompanied by a significant increase in the number of CD31- and α-SMApositive blood vessels in ischemic hindlimb. These results suggest that SR-0379 is a potential drug candidate for potentiating EPC-mediated therapy of ischemic diseases. [BMB Reports 2017; 50(10): 504-509].

Endothelial progenitor cells: Exploring the pleiotropic effects of statins

Statins have become a cornerstone of risk modification for ischaemic heart disease patients. A number of studies have shown that they are effective and safe. However studies have observed an early benefit in terms of a reduction in recurrent infarct and or death after a myocardial infarction, prior to any significant change in lipid profile. Therefore, pleiotropic mechanisms, other than lowering lipid profile alone, must account for this effect. One such proposed pleiotropic mechanism is the ability of statins to augment both number and function of endothelial progenitor cells. The ability to augment repair and maintenance of a functioning endothelium may have profound beneficial effect on vascular repair and potentially a positive impact on clinical outcomes in patients with cardiovascular disease. The following literature review will discuss issues surrounding endothelial progenitor cell (EPC) identification, role in vascular repair, factors affecting EPC numbers, the role of statins in current medical practice and their effects on EPC number.

Blood-brain barrier breakdown and neovascularization processes after stroke and traumatic brain injury

PURPOSE OF REVIEW

Angiogenesis or vascular reorganization plays a role in recovery after stroke and traumatic brain injury (TBI). In this review, we have focused on two major events that occur during stroke and TBI from a vascular perspective - what is the process and time course of blood-brain barrier (BBB) breakdown? and how does the surrounding vasculature recover and facilitate repair?

RECENT FINDINGS

Despite differences in the primary injury, the BBB changes overlap between stroke and TBI. Disruption of BBB involves a series of events: formation of caveolae, trans and paracellular disruption, tight junction breakdown and vascular disruption. Confounding factors that need careful assessment and standardization are the severity, duration and extent of the stroke and TBI that influences BBB disruption. Vascular repair proceeds through long-term neovascularization processes: angiogenesis, arteriogenesis and vasculogenesis. Enhancing each of these processes may impart beneficial effects in endogenous recovery.

SUMMARY

Our understanding of BBB breakdown acutely after the cerebrovascular injury has come a long way; however, we lack a clear understanding of the course of BBB disruption and BBB recovery and the evolution of individual cellular events associated with BBB change. Neovascularization responses have been widely studied in stroke for their role in functional recovery but the role of vascular reorganization after TBI in recovery is much less defined.

Endothelial progenitor cells are differentially impaired in ANCA-associated vasculitis compared to healthy controls

Background

Endothelial progenitor cells (EPC) are of major importance in vascular repair under healthy circumstances. Vascular injury in need of repair occurs frequently in ANCA-associated vasculitis (AAV). A specialized T cell subset enhancing EPC function and differentiation has recently been described. These angiogenic T cells (T_ang) may have an important impact on the vascular repair process. Therefore, the aim of our study was to investigate EPC and T_ang in AAV.

Methods

Fifty-three patients suffering from AAV and 29 healthy controls (HC) were enrolled in our study. Forty-four patients were in remission, nine patients were in active state of disease. Patients were either untreated or were under monotherapy with low-dose steroids (max. 5 mg/day) at the time of sampling. Circulating EPC and T_ang were determined by flow cytometry (FACS). The functional capacity of EPC was assessed by established cell culture methods.

Results

Circulating EPC were significantly decreased in AAV as compared to HC. The capacity of EPC to differentiate and proliferate was differentially impaired in patients as compared to HC. The outgrowth of endothelial colony-forming cells (ECFC) was severely decreased in patients whereas colony-forming units-endothelial cell (CFU-EC) outgrowth was unaffected. ECFC and CFU-EC differentiation was strictly T cell-dependent. Patients with a relapsing disease course had an impaired ECFC outgrowth and expansion of T_ang as compared to patients with a stable, nonrelapsing disease.

Conclusions

The differentiation process of EPC is impaired in AAV. This may favor insufficient vascular repair promoting a relapsing disease course. Finally, these factors may explain a higher cardiovascular morbidity as has been previously documented in AAV.

Endothelial progenitor cells promote tumor growth and progression by enhancing new vessel formation

Tumor growth and progression require new blood vessel formation to deliver nutrients and oxygen for further cell proliferation and to create a neovascular network exit for tumor cell metastasis. Endothelial progenitor cells (EPCs) are a bone marrow (BM)-derived stem cell population that circulates in the peripheral circulation and homes to the tumor bed to participate in new blood vessel formation. In addition to structural support to nascent vessels, these cells can also regulate the angiogenic process by paracrine secretion of a number of proangiogenic growth factors and cytokines, thus playing a crucial role in tumor neovascularization and development. Inhibition of EPC-mediated new vessel formation may be a promising therapeutic strategy in tumor treatment. EPC-mediated neovascularization is a complex process that includes multiple steps and requires a series of cytokines and modulators, thus understanding the underlying mechanisms may provide anti-neovasculogenesis targets that may be blocked for the prevention of tumor development. The present review stresses the process and contribution of EPCs to the formation of new blood vessels in solid tumors, in an attempt to gain an improved understanding of the underlying cellular and molecular mechanisms involved, and to provide a potential effective therapeutic target for cancer treatment.

Multilayer Membranes of Glycosaminoglycans and Collagen I Biomaterials Modulate the Function and Microvesicle Release of Endothelial Progenitor Cells

Multilayer composite membrane of biomaterials can increase the function of adipose stem cells or osteoprogenitor cells. Recent evidence indicates endothelial progenitor cells (EPCs) and EPCs released microvesicles (MVs) play important roles in angiogenesis and vascular repair. Here, we investigated the effects of biomaterial multilayer membranes of hyaluronic acid (HA) or chondroitin sulfate (CS) and Collagen I (Col I) on the functions and MVs release of EPCs. Layer-by-layer (LBL) technology was applied to construct the multilayer composite membranes. Four types of the membranes constructed by adsorbing either HA or CS and Col I alternatively with different top layers were studied. The results showed that all four types of multilayer composite membranes could promote EPCs proliferation and migration and inhibit cell senility, apoptosis, and the expression of activated caspase-3. Interestingly, these biomaterials increased the release and the miR-126 level of EPCs-MVs. Moreover, the CS-Col I membrane with CS on the top layer showed the most effects on promoting EPCs proliferation, EPCs-MV release, and miR-126 level in EPCs-MVs. In conclusion, HA/CS and Collagen I composed multilayer composite membranes can promote EPCs functions and release of miR-126 riched EPCs-MVs, which provides a novel strategy for tissue repair treatment.

Bioluminescence imaging of transplanted human endothelial colony-forming cells in an ischemic mouse model

Ischemic strokes are devastating events responsible for high mortality and morbidity worldwide each year. Endothelial colony-forming cell (ECFC) therapy holds promise for stroke treatment; however, grafted ECFCs need to be monitored better understand their biological behavior in vivo, so as to evaluate their safety and successful delivery. The objectives of this study are to visualize the fate of infused human cord blood derived ECFCs via bioluminescence imaging (BLI) in an ischemic stroke mouse model and to determine the therapeutic effects of ECFC transplantation. ECFCs derived from human umbilical cord blood were infected with lentivirus carrying enhanced green fluorescent protein (eGFP) and firefly luciferase (Luc2) double fusion reporter gene. Labeled ECFCs were grafted into a photothrombotic ischemic stroke mouse model via intra-arterial injection though the left cardiac ventricle. The homing of infused cells and functional recovery of stroke mice were evaluated using BLI, neurological scoring, and immunohistochemistry. Significantly, BLI signals were highest in the brain on day 1 and decreased steadily until day 14. GFP-positive cells were also found surrounding infarct border zones in brain sections using immunohistochemical staining, suggesting that ECFCs properly homed to the ischemic brain tissue. Using a modified neurological severity score assay and histological analysis of brain slices with CD31 immunostaining in brain tissue, double cortin analysis, and the TdT-mediated dUTP nick end labeling (TUNEL) assay, we demonstrated functional restoration, improved angiogenesis, neurogenesis, and decreased apoptosis in ischemic mice after ECFC infusion. Collectively, our data support that ECFCs may be a promising therapeutic agent for stroke.

Circulating endothelial progenitor cells and the risk of vascular events after ischemic stroke

Background and Purpose

We evaluated the hypothesis that the number of circulating EPC could be associated with the risk of stroke recurrence (SR) or vascular events (VE) after an ischemic stroke.

Methods

We studied prospectively consecutive patients with cerebral infarction within the first 48 hours after the onset. We recorded demographic factors, vascular risk factors, previous Rankin scale (RS) score, and etiology. We analyzed EPC counts by flow cytometry in blood collected at day 7 and defined EPC as CD34+/CD133+/KDR+ cells. Mean follow-up was 29.3 ± 16 months. We evaluated SR as well as VE. Patients were classified as to the presence or absence of EPC in the circulation (either EPC+ or EPC-). Bivariate analyses, Kaplan-Meier survival curves and Cox regression models were used.

Results

We included 121 patients (mean age 70.1±12.6 years; 65% were men). The percentage of EPC+ patients was 47.1%. SR occurred in 12 (9.9%) and VE in 18 (14.9%) patients. SR was associated significantly with a worse prior RS score, previous stroke and etiology, but not with EPC count. VE were associated significantly with EPC-, worse prior RS score, previous stroke, high age, peripheral artery disease and etiology. Cox regression model showed that EPC- (HR 7.07, p=0.003), age (HR 1.08, p=0.004) and a worse prior RS score (HR 5.8, p=0.004) were associated significantly with an increased risk of VE.

Conclusions

The absence of circulating EPC is not associated with the risk of stroke recurrence, but is associated with an increased risk of future vascular events.

COMP-Ang1 Potentiates EPC Treatment of Ischemic Brain Injury by Enhancing Angiogenesis Through Activating AKT-mTOR Pathway and Promoting Vascular Migration Through Activating Tie2-FAK Pathway

Successful recovery from brain ischemia is limited due to poor vascularization surrounding the ischemic zone. Cell therapy with strong angiogenic factors could be an effective strategy to rescue the ischemic brain. We investigated whether cartilage oligomeric matrix protein (COMP)-Ang1, a soluble, stable and potent Ang1 variant, enhances the angiogenesis of human cord blood derived endothelial progenitor cells (hCB-EPCs) for rescuing brain from ischemic injury. COMP-Ang1 markedly improved the tube formation of capillaries by EPCs and incorporation of EPCs into tube formation with human umbilical vein endothelial cells (HUVECs) upon incubation on matrigel in vitro. COMP-Ang1 stimulated the migration of EPCs more than HUVECs in a scratch wound migration assay. The transplanted EPCs and COMP-Ang1 were incorporated into the blood vessels and decreased the infarct volume in the rat ischemic brain. Molecular studies revealed that COMP-Ang1 induced an interaction between Tie2 and FAK, but AKT was separated from the Tie2-FAK-AKT complex in the EPC plasma membrane. Tie2-FAK increased pp38, pSAPK/JNK, and pERK-mediated MAPK activation and interacted with integrins ανβ3, α4, β1, finally leading to migration of EPCs. AKT recruited mTOR, SDF-1, and HIF-1α to induce angiogenesis. Taken together, it is concluded that COMP-Ang1 potentiates the angiogenesis of EPCs and enhances the vascular morphogenesis indicating that combination of EPCs with COMP-Ang1 may be a potentially effective regimen for ischemic brain injury salvage therapy.

High-density lipoproteins in stroke

Besides their well-documented function of reverse transport of cholesterol, high-density lipoproteins (HDLs) display pleiotropic effects due to their antioxidant, antithrombotic, anti-inflammatory and antiapoptotic properties that may play a major protective role in acute stroke, in particular by limiting the deleterious effects of ischaemia on the blood-brain barrier (BBB) and on the parenchymal cerebral compartment. HDLs may also modulate leukocyte and platelet activation, which may also represent an important target that would justify the use of HDL-based therapy in acute stroke. In this review, we will present an update of all the recent findings in HDL biology that could support a potential clinical use of HDL therapy in ischaemic stroke.

Segregation of late outgrowth endothelial cells into functional endothelial CD34- and progenitor-like CD34+ cell populations

Late outgrowth endothelial cells (OECs) that originate from peripheral blood mononuclear cells ex vivo have phenotypic and functional properties of mature endothelial cells. Given the potential therapeutic applications of OECs, understanding their biology is crucial. We have identified two distinct OEC populations based on differential expression of the cell surface marker CD34. OEC colonies lacked CD34 expression (CD34-), expressed CD34 in the majority of cells (CD34+), or showed a mixed expression pattern within a colony (CD34+/-). CD34+ and CD34- OECs were negative for hematopoietic cell marker CD45 and expressed the endothelial cell surface markers CD31, CD146, CD105, and VEGFR-2. Functionally CD34- and CD34+ OECs exhibited strikingly distinct behaviors. CD34- OECs, unlike CD34+ OECs, were capable of sprouting, formed tubes, and responded to angiogenic growth factors in vitro. In vivo, CD34- OECs formed endothelial tubes, while CD34+ OECs, despite being unable to form tubes, promoted infiltration of murine vasculature. Global gene expression profiling in CD34- and CD34+ OECs identified functional importance of the MMP-1/PAR-1 pathway in CD34- OECs. MMP-1 stimulated the expression of VEGFR-2, neuropilin-1, neuropilin-2, and CXCR4 and activated ERK1/2, whereas down-regulation of PAR-1 in CD34- OECs resulted in impaired angiogenic responses in vitro and reduced VEGFR-2 levels. In contrast, the CD34+ OEC colonies expressed high levels of the progenitor cell marker ALDH, which was absent in CD34- OECs. In summary, we show that OECs can be classified into functionally mature endothelial cells (CD34- OECs) that depend on the MMP-1/PAR-1 pathway and progenitor-like angiogenesis-promoting cells (CD34+ OECs).

Gender-linked stem cell alterations in stroke and postpartum depression

Stroke is a significant unmet clinical need. The current stroke treatment of tissue plasminogen activator is limited to the very acute 4.5 h after disease onset which benefits only less than 3% of ischemic stroke patients. Our overarching hypothesis advances the notion that gender, which has been established as a comorbidity factor of stroke, plays a key role in regenerative medicine, in particular stem cell therapy. We hypothesize that gender is a key factor in culture‐induced stemness of adult stem cells. Our goal is to provide new evidence supporting gender effects on stroke and stem cells for the purpose of enhancing our understanding of the pathophysiology of the disease and developing novel stem cell‐based therapeutics targeting gender‐relevant stress hormones as manifested in a stroke‐postpartum depression paradigm.

Intravenous transfusion of endothelial colony-forming cells attenuates vascular degeneration after cerebral aneurysm induction

Cerebral aneurysm (CA) rupture is a major cause of subarachnoid hemorrhage with high morbidity and mortality. Using an animal model, we examined the potential of endothelial colony-forming cells (ECFCs) transfusion on vascular degeneration after CA induction and underlying mechanisms. CA was induced in the right anterior cerebral artery-olfactory artery (ACA/OA) bifurcations in Sprague-Dawley rats with or without ECFCs transfusion. The degeneration of internal elastic lamina (IEL), media thickness and CA size were evaluated. Expression of matrix metalloproteinase-2 and 9 (MMP-2 and 9), tissue inhibitor of metalloproteinase-1 (TIMP-1), macrophage chemoattractant protein-1 (MCP-1), vascular cell adhesion molecule-1 (VCAM-1), nuclear factor κB (NF-κB), endothelial nitric oxide synthase (eNOS), B-cell leukemia/lymphoma-2 (Bcl-2), and inducible nitric oxide synthase (iNOS) were analyzed by quantitative real-time polymerase chain reaction. The macrophages infiltration and apoptosis of smooth muscle cells (SMCs) were examined immunohistologically. Rats in CA+ECFCs transfusion group showed a notable reduction in IEL degeneration, media thinning and CA size compared with those in CA+saline group. ECFCs transfusion inhibited the MMP-driven wall destruction by downregulating MMP-2, MMP-9 expression and upregulating TIMP-1. ECFCs transfusion dramatically decreased VCAM-1 and NF-κB expression, increased eNOS expression and caused no change in MCP-1 expression, which was accompanied by reduced macrophages infiltration. Moreover, ECFCs transfusion reversed downregulation of Bcl-2 expression and upregulation of iNOS expression, and decreased SMCs apoptosis. Collectively, these findings suggest that ECFCs transfusion confers protection against degeneration of aneurysmal wall by inhibiting inflammatory cascades and SMCs apoptosis.

Cerebral microbleeds in patients with Parkinson's disease

Cerebral microbleeds (CMBs) are known to be associated with cognitive impairments in the elderly and in patients with various diseases; however, the nature of this association has not yet been evaluated in Parkinson's disease (PD). In the present study, we analyzed the incidence of CMBs in PD according to cognitive status, and the impact of CMBs on cognitive performance was also evaluated. The CMBs in PD with dementia (n = 36), mild cognitive impairment (MCI, n = 46), or cognitively normal (n = 41) were analyzed using conventional T2*-weighted gradient-recalled echo images. Additionally, the relationship between the presence of CMBs and cognitive performance on individual tests of cognitive subdomains was analyzed using a detailed neuropsychological test. CMBs occurred more frequently in PD patients with dementia (36.1 %) compared to those with MCI (15.2 %), those who are cognitively normal (14.6 %), and normal controls (12.2 %, p = 0.025). However, the significant association of CMBs with PD dementia disappeared after adjusting white matter hyperintensities (WMHs) as a covariate. The frequencies of deep, lobar, and infratentorial CMBs did not differ among the four groups. After adjusting for age, sex, years of education, and WMHs, PD patients with CMBs had poorer performance in attention domain compared with those without CMBs (34.9 vs 42.6, p = 0.018). The present data demonstrate that even though CMBs were inseparably associated with the presence of WMHs, CMBs occur more commonly in PD patients with dementia than in those without dementia. Additionally, the burden of CMBs may contribute to further cognitive impairment in PD.

Simvastatin attenuates TNF‑α‑induced apoptosis in endothelial progenitor cells via the upregulation of SIRT1

Endothelial progenitor cells (EPCs) originate from the bone marrow and can be classified as either early or late EPCs. The focus of this study was on late EPCs, as they play an important role in angiogenesis and vascular proliferation. Evidence suggests that inflammatory and oxidative changes can increase EPC apoptosis. Of note, tumor necrosis factor-α (TNF-α) is a contributing risk factor to the development of atherosclerosis and plays a key role as both an inflammatory mediator and an inducer of apoptosis in endothelial cells. Additionally, a member of the sirtuin family, silent information regulator type-1 (SIRT1), promotes cell survival by repressing p53- and non-p53-dependent apoptosis in response to DNA damage and oxidative stress. Statins have also been shown to play a key role in the prevention of endothelial apoptosis and senescence via their lipid-lowering and anti-inflammatory actions. However, there is little evidence that statins themselves attenuate EPC apoptosis induced by TNF-α. The aim of this study was to demonstrate the effectiveness of one of the most commonly used statins, simvastatin, on decreasing TNF-α-induced apoptosis in EPCs. The results indicated that SIRT1 protein expression was decreased by TNF-α in a time- and dose-dependent manner and that while TNF-α caused a marked increase in the percentage of apoptotic EPCs, application of simvastatin decreased this percentage. A high concentration of simvastatin promoted the expression of SIRT1 and increased the proliferation of EPCs. In conclusion, findings of this study showed that simvastatin is crucial in counteracting the TNF-α-induced apoptosis of EPCs and that this protection may involve the actions of SIRT1.

SDF1-a facilitates Lin-/Sca1+ cell homing following murine experimental cerebral ischemia

BACKGROUND

Hematopoietic stem cells mobilize to the peripheral circulation in response to stroke. However, the mechanism by which the brain initiates this mobilization is uncharacterized.

METHODS

Animals underwent a murine intraluminal filament model of focal cerebral ischemia and the SDF1-A pathway was evaluated in a blinded manner via serum and brain SDF1-A level assessment, Lin-/Sca1+ cell mobilization quantification, and exogenous cell migration confirmation; all with or without SDF1-A blockade.

RESULTS

Bone marrow demonstrated a significant increase in Lin-/Sca1+ cell counts at 24 hrs (272 ± 60%; P<0.05 vs sham). Mobilization of Lin-/Sca1+ cells to blood was significantly elevated at 24 hrs (607 ± 159%; P<0.05). Serum SDF1-A levels were significant at 24 hrs (Sham (103 ± 14), 4 hrs (94 ± 20%, p = NS) and 24 hrs (130 ± 17; p<0.05)). Brain SDF1-A levels were significantly elevated at both 4 hrs and 24 hrs (113 ± 7 pg/ml and 112 ± 10 pg/ml, respectively; p<0.05 versus sham 76 ± 11 pg/ml). Following administration of an SDF1-A antibody, Lin-/Sca1+ cells failed to mobilize to peripheral blood following stroke, despite continued up regulation in bone marrow (stroke bone marrow cell count: 536 ± 65, blood cell count: 127 ± 24; p<0.05 versus placebo). Exogenously administered Lin-/Sca1+ cells resulted in a significant reduction in infarct volume: 42 ± 5% (stroke alone), versus 21 ± 15% (Stroke+Lin-/Sca1+ cells), and administration of an SDF1-A antibody concomitant to exogenous administration of the Lin-/Sca1+ cells prevented this reduction. Following stroke, exogenously administered Lin-/Sca1+ FISH positive cells were significantly reduced when administered concomitant to an SDF1-A antibody as compared to without SDF1-A antibody (10 ± 4 vs 0.7 ± 1, p<0.05).

CONCLUSIONS

SDF1-A appears to play a critical role in modulating Lin-/Sca1+ cell migration to ischemic brain.

Reactive astrocytes promote adhesive interactions between brain endothelium and endothelial progenitor cells via HMGB1 and beta-2 integrin signaling

Endothelial progenitor cells (EPCs) may contribute to neurovascular repair after stroke and neurodegeneration. A key step in this process should involve adhesive interactions between EPCs and the targeted cerebral endothelium. Here, we tested the hypothesis that reactive astrocytes may play a critical role in enhancing adhesive interactions and transmigration of EPCs across cerebral endothelial cells. Transiently seeding EPCs onto a monolayer of RBE.4 rat brain endothelial cells resulted in a time-dependent adherence between the two cell types. Blocking β2 integrins on EPCs or blocking the receptor for advanced glycation endproducts (RAGE) on endothelial cells significantly decreased EPC-endothelial adherence. Next, we tested whether reactive astrocytes can enhance this process by growing EPCs, brain endothelial cells and astrocytes together in a transwell co-culture system. The presence of reactive astrocytes in the lower chamber significantly promoted adherence between EPCs and endothelial cells in the upper chamber. This process involved the release of soluble HMGB1 from reactive astrocytes that then upregulated endothelial expression of RAGE via Egr1 signaling. Directly adding HMGB1 to the transwell system also promoted EPC-endothelial adhesion and accelerated EPC transmigration into the lower chamber. These initial findings provide proof-of-concept that reactive astrocytes promote crosstalk between cerebral endothelium and EPCs. Further investigation of this phenomenon may lead to a better understanding of cell-cell interactions required for neurovascular recovery after stroke.

Intracerebroventricular transplantation of ex vivo expanded endothelial colony-forming cells restores blood-brain barrier integrity and promotes angiogenesis of mice with traumatic brain injury

Endothelial progenitor cells (EPCs) play a key role in tissue repair and regeneration. Previous studies have shown a positive correlation between the number of circulating EPCs and clinical outcomes of patients with traumatic brain injury (TBI). A recent study has further shown that intravenous infusion of human umbilical cord blood-derived endothelial colony-forming cells (ECFCs) improves outcomes of mice subjected to experimental TBI. This follow-up study was designed to determine whether intracerebroventricular (i.c.v.) infusion of ECFCs, which may reduce systemic effects of these cells, could repair the blood-brain barrier (BBB) and promote angiogenesis of mice with TBI. Adult nude mice were exposed to fluid percussion injury and transplanted i.c.v. with ECFCs on day 1 post-TBI. These ECFCs were detected at the TBI zone 3 days after transplantation by SP-DiIC18(3) and fluorescence in situ hybridization. Mice with ECFCs transplant had reduced Evans blue extravasation and brain water content, increased expression of ZO-1 and claudin-5, and showed a higher expression of angiopoietin 1. Consistent with the previous report, mice with ECFCs transplant had also increased microvascular density. Modified neurological severity score and Morris water maze test indicated significant improvements in motor ability, spatial acquisition and reference memory in mice receiving ECFCs, compared to those receiving saline. These data demonstrate the beneficial effects of ECFC transplant on BBB integrity and angiogenesis in mice with TBI.

Endothelial progenitor cells in acute ischemic stroke

OBJECTIVES

The levels of circulating endothelial progenitor cells (EPCs) in ischemic stroke have not been studied extensively and reported results are inconsistent. We aimed to investigate the time course, the prognostic relevance, and the variables associated with EPC counts in patients with ischemic stroke at different time points.

MATERIAL AND METHODS

We studied prospectively 146 consecutive patients with ischemic stroke within the first 48 h from the onset of symptoms (baseline). We evaluated demographic data, classical vascular risk factors, treatment with thrombolysis and statins, stroke etiology, National Institute of Health and Stroke Scale score and outcome (favorable when Rankin scale score 0-2). Blood samples were collected at baseline, at day 7 after stroke (n = 121) and at 3 months (n = 92). The EPC were measured by flow cytometry.

RESULTS

We included 146 patients with a mean age of 70.8 ± 12.2 years. The circulating EPC levels were higher on day 7 than at baseline or at 3 months (P = 0.045). Pretreatment with statins (odds ratio [OR] 3.11, P = 0.008) and stroke etiology (P = 0.032) were predictive of EPC counts in the baseline sample. EPC counts were not associated with stroke severity or functional outcome in all the patients. However, using multivariate analyses, a better functional outcome was found in patients with higher EPC counts in large-artery atherosclerosis and small-vessel disease etiologic subtypes.

CONCLUSIONS

After acute ischemic stroke, circulating EPC counts peaked at day 7. Pretreatment with statins increased the levels of EPC. In patients with large-artery atherosclerosis and small-vessel disease subtypes, higher counts were related to better outcome at 3 months.

Magnetic-based multi-layer microparticles for endothelial progenitor cell isolation, enrichment, and detachment

Although endothelial progenitor cells (EPCs) are useful in many applications including cell-based therapies, their use is still limited due to issues associated with cell culture techniques like a low isolation efficiency, use of harmful proteolytic enzymes in cell cultures, and difficulty in ex vivo expansion. Here, we report a tool to simultaneously isolate, enrich, and detach EPCs without the use of harmful chemicals. In particular, we developed magnetic-based multi-layer microparticles (MLMPs) that (1) magnetically isolate EPCs via anti-CD34 antibodies to avoid the use of Ficoll and harsh shear forces; (2) provide a 3D surface for cell attachment and growth; (3) produce sequential releases of growth factors (GFs) to enrich ex vivo expansion of cells; and (4) detach cells without using trypsin. MLMPs were successful in isolating EPCs from a cell suspension and provided a sequential release of GFs for EPC proliferation and differentiation. The cell enrichment profiles indicated steady cell growth on MLMPs in comparison to commercial Cytodex3 microbeads. Further, the cells were detached from MLMPs by lowering the temperature below 32 °C. Results indicate that the MLMPs have potential to be an effective tool towards efficient cell isolation, fast expansion, and non-chemical detachment.

Therapeutic benefit of a combined strategy using erythropoietin and endothelial progenitor cells after transient focal cerebral ischemia in rats

OBJECTIVE

Many studies have demonstrated beneficial effects of either erythropoietin (EPO) or endothelial progenitor cell (EPC) treatment in cerebral ischemia. To improve post-ischemic tissue repair, we investigated the effect of systemic administration of endothelial colony-forming cells (ECFCs), considered as relevant endothelial progenitors due to their specific vasculogenic activity, in the presence or absence of EPO, on functional recovery, apoptosis, angiogenesis, and neurogenesis in a transient focal cerebral ischemia model in the adult rat.

DESIGN

Experimental study.

INTERVENTION

The rats were divided into four groups 24 hours after ischemia,, namely control, ECFCs, EPO, and ECFCs+EPO, and received a single intravenous injection of ECFCs (5 × 10(6) cells) and/or intraperitoneal administration of EPO (2500 UI/kg per day for 3 days).

MEASUREMENT

Infarct volume, functional recovery, apoptosis, angiogenesis, and neurogenesis were assessed at different time points after ischemia.

MAIN RESULTS

The combination of EPO and ECFCs was the only treatment that completely restored neurological function. The ECFCs+EPO treatment was also the most effective to decrease apoptosis and to increase angiogenesis and neurogenesis in the ischemic hemisphere compared to controls and to groups receiving ECFCs or EPO alone.

CONCLUSION

These results suggest that EPO could act in a synergistic way with ECFCs to potentiate their therapeutic benefits.

Proteomic analysis of endothelial progenitor cells exposed to oxidative stress

Endothelial progenitor cells (EPCs) repair vascular damage and participate in neovascularization. Accumulating evidence has demonstrated that EPCs have therapeutic potential in reactive oxygen species (ROS)-mediated vascular diseases. In this study, to investigate the effects of oxidative stress on EPCs, EPCs were treated with H2O2 at different final concentrations for 3 h. MTT assay, scratch-wound assay and Matrigel invasion assay revealed that cell proliferation, migration and tubule formation and function, respectively, were impaired under H2O2 stress in a concentration-dependent manner. To determine protein response to H2O2 stress, two-dimensional differential in-gel electrophoresis (2D-DIGE) combined with matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF/TOF) mass spectrometry were performed. The results revealed that triosephosphate isomerase and ADP-sugar pyrophosphatase were downregulated, while peroxiredoxin-2, thioredoxin-dependent peroxide reductase, mitochondrial (Prx‑3), peroxiredoxin-6, EGF-containing fibulin-like extracellular matrix protein 1, vimentin and Rab GDP dissociation inhibitor α were upregulated in the H2O2-treated EPCs. To further confirm the results from mass spectrometry, the expression pattern of Prx-3 in response to H2O2 stress was examined by western blot analysis. The data presented in this study provide novel insight into the defensive mechanisms of EPCs and the pathways of oxidative damage in an oxidative environment.

Silica-coated superparamagnetic iron oxide nanoparticles targeting of EPCs in ischemic brain injury

Intravenous transplantation of endothelial progenitor cells (EPCs) reduced ischemic brain injury. However, less cell homing to damaged sites limited its functions. In present study, we labeled EPCs with silica-coated superparamagnetic iron oxide nanoparticles (SiO4@SPIONs) and applied exterior magnetic field to guide SiO4@SPIONs-labeled EPCs (SiO4@SPIONs-EPCs) to the ischemic hemisphere of the brain. We optimized SiO4@SPIONs labeling dose, which did not affect proliferation, migration and tube formation of EPCs in vitro. SiO4@SPIONs-EPCs homing was greatly increased in ischemic hemisphere with magnetic field treatment in mice underwent transient middle cerebral artery occlusion (tMCAO). Injection of SiO4@SPIONs-EPCs and followed by magnetic field treatment showed improved neurobehavioral outcomes, reduced brain atrophic volume, increased microvessel density and VEGF expression in the ischemic perifocal region compared to groups without magnetic field treatment (p < 0.05). Our results demonstrated that exterior magnetic field could guide SiO4@SPIONs-EPCs to ischemic region and enhance therapeutic effect, suggesting that magnetic-guided SiO4@SPIONs-EPCs delivery is a promising approach in cerebral ischemic therapy.

Cell therapy for stroke: emphasis on optimizing safety and efficacy profile of endothelial progenitor cells

Endothelial progenitor cells (EPCs) correspond to a population of cells with novel properties capable of angiogenesis and vasculogenesis, thus they are likely to display unique role in the reconstitution of the blood brain barrier (BBB) after stroke. Laboratory evidence supports safety and efficacy of cell therapy for stroke, with limited clinical trials recently initiated. This lab-to-clinic ascent of cell-based therapeutics has been aided by the establishment of consortium consisting of thought-leaders from academia, industry, National Institutes of Health (NIH) and the United States Food and Drug Administration (FDA). However, there remain unanswered questions prior to realization of large-scale application of cell transplantation in patients. This review article discusses translational challenges associated in cell therapy, emphasizing the need for optimizing both safety and efficacy profiles for advancing the clinical applications of EPC transplantation for stroke patients.

[Cell therapy for stroke: from myth to reality]

INTRODUCTION

Stroke is one of the leading causes of death and disability worldwide. Intravenous recombinant tissue plasminogen activator is the only available therapy for acute ischemic stroke, but its use is limited by a narrow therapeutic window and cannot stimulate endogenous repair and regeneration of damaged brain tissue. Stem cell-based approaches hold much promise as potential novel treatments to restore neurological function after stroke.

STATE OF THE ART

In this review, we summarize data from preclinical and clinical studies to investigate the potential application of stem cell therapies for treatment of stroke. Stem cells have been proposed as a potential source of new cells to replace those lost due to central nervous system injury, as well as a source of trophic molecules to minimize damage and promote recovery. Various stem cells from multiple sources can generate neural cells that survive and form synaptic connections after transplantation in the stroke-injured brain. Stem cells also exhibit neurorevitalizing properties that may ameliorate neurological deficits through stimulation of neurogenesis, angiogenesis and inhibition of inflammation.

PERSPECTIVES/CONCLUSION

Performed in stroke, cell therapy would decrease brain damage and reduce functional deficits. After the damage has been done, it would still improve neurological functions by activating endogenous repair. Nevertheless, many questions raised by experimental studies particularly related to long-term safety and technical details of cell preparation and administration must be resolved before wider clinical use.

Endothelial progenitor cells: therapeutic perspective for ischemic stroke

Endothelial progenitor cells (EPCs), which can be cultured in vitro from mononuclear cells in peripheral blood or bone marrow, express both hematopoietic stem cell and endothelial cell markers on their surface. They are believed to participate in endothelial repair and postnatal angiogenesis due to their abilities of differentiating into endothelial cells and secreting protective cytokines and growth factors. Mounting evidence suggests that circulating EPCs are reduced and dysfunctional in various diseases including hypertension, diabetes, coronary heart disease, and ischemic stroke. Therefore, EPCs have been documented to be a potential biomarker for vascular diseases and a hopeful candidate for regenerative medicine. Ischemic stroke, as the major cause of disability and death, still has limited therapeutics based on the approaches of vascular recanalization or neuronal protection. Emerging evidence indicates that transplantation of EPCs is beneficial for the recovery of ischemic cerebral injury. EPC-based therapy could open a new avenue for ischemic cerebrovascular disease. Currently, clinical trials for evaluating EPC transfusion in treating ischemic stroke are underway. In this review, we summarize the general conceptions and the characteristics of EPCs, and highlight the recent research developments on EPCs. More importantly, the rationale, perspectives, and strategies for using them to treat ischemic stroke will be discussed.

Transplantation of bone marrow-derived endothelial progenitor cells attenuates cerebral ischemia and reperfusion injury by inhibiting neuronal apoptosis, oxidative stress and nuclear factor-κB expression

The aim of the present study was to investigate the neuroprotective effects of bone marrow-derived endothelial progenitor cell (EPC) transplantation against cerebral ischemia/reperfusion (I/R) injury in rats and to delineate the possible underlying mechanisms. Cerebral I/R injury was established by 2 h of middle cerebral artery occlusion (MCAO) followed by reperfusion for 24 h. EPCs were isolated from bone marrow of the donor rats, grown in conditioned medium, and characterized by flow cytometry analysis of several surface markers. Labeled EPCs (106 cells) were infused into rats at the onset of reperfusion and 12 h after reperfusion via the tail vein. Infarct volume was assessed at 24 h after reperfusion by using triphenyltetrazolium chloride (TTC) staining. The expression of cell apoptosis-related proteins including Bcl-2 and Bax was determined by western blot analysis, and the activity of caspase-3 was also measured. We evaluated the activities of some antioxidative enzymes, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), the non-enzymatic scavenger glutathione (GSH) and detected the content of malondialdehyde (MDA) in the ischemic penumbra. Moreover, the expression of nuclear factor-κB (NF-κB) in the ischemic regions of rats was examined by immunohistochemical staining and western blot analysis. The results showed that transplantation of EPCs significantly reduced the cerebral infarct volume, decreased caspase-3 activity, upregulated Bcl-2 expression, and downregulated the expression of Bax and NF-κB. Furthermore, reduced levels of MDA, significantly elevated activities of SOD and GSH as well as GSH-PX were also found in I/R rats transplanted with EPCs. Collectively, our data demonstrated that transplantation of bone marrow-derived EPCs exerts potent neuroprotective functions against cerebral I/R injury in rats, and the protective effects may be associated with its antioxidative and anti-apoptotic properties.

Beneficial effects of statins on endothelial progenitor cells

In recent years, endothelial progenitor cells (EPCs) have been demonstrated to play an important role during tissue vascularization and endothelium homeostasis in adults. In addition, EPCs have been implicated in the pathophysiology of cardiovascular and cerebrovascular disease, such that a decreased number of EPCs may not only be a risk indicator but also a potential therapeutic target. Of the many agents that have been examined to increase EPCs and enhance their function, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors or statins are one of the most intriguing. Accumulated evidence has demonstrated that statins promote EPC mobilization, proliferation, migration, adhesion, differentiation and reduce senescence and apoptosis independent of their serum lipid-lowering effect. This review summarizes the understanding of current mechanisms explaining the myriad of beneficial effects of statins on EPCs and discusses future challenges for studies involving statins and subpopulations of EPCs. However, the pharmacologic mechanisms of action of statins on EPCs remain at the cellular level, whereas the putative molecular mechanisms await further studies.

Astrocytic high-mobility group box 1 promotes endothelial progenitor cell-mediated neurovascular remodeling during stroke recovery

Crosstalk between the brain and systemic responses in blood is increasingly suspected of playing critical roles in stroke. However, how this communication takes place remains to be fully understood. Here, we show that reactive astrocytes can release a damage-associated molecular-pattern molecule called high-mobility-group-box-1 (HMGB1) that promotes endothelial progenitor cell (EPC)-mediated neurovascular remodeling during stroke recovery. Conditioned media from reactive astrocytes increase EPC proliferation in vitro. siRNA suppression of HMGB1 in astrocytes or blockade of the HMGB1 receptor for advanced glycation endproducts in EPCs prevents this effect. In a mouse model of focal cerebral ischemia, reactive astrocytes in the peri-infarct cortex up-regulate HMGB1 at 14 d poststroke, along with an accumulation of endogenous EPCs. In vivo siRNA suppression of HMGB1 blocks this EPC response, reduces peri-infact angiogenesis, and worsens neurological deficits. Taken together, these molecular and in vivo findings support a previously undescribed mechanism of crosstalk between reactive astrocytes and EPCs wherein HMGB1 promotes neurovascular remodeling and functional recovery after stroke and brain injury.

Temporal profile of molecular signatures associated with circulating endothelial progenitor cells in human ischemic stroke

Endothelial progenitor cells (EPC) have been associated with good functional outcome in ischemic stroke. From preclinical studies, it has been reported that EPC proliferation is mediated by several molecular markers, including vascular endothelial growth factor (VEGF), stromal cell-derived factor-1α (SDF-1α), and the activity of matrix metalloproteinase-9 (MMP-9). Therefore, our aim was to study the role of these molecular factors in EPC proliferation in human ischemic stroke. Forty-eight patients with first episode of nonlacunar ischemic stroke were prospectively included in the study within 12 hr of symptom onset. EPC colonies were classified as early-outgrowth colony forming unit-endothelial cell (CFU-EC) and quantified at admission, at 24 and 72 hr, at day 7, and at 3 months. At the same time, serum levels of VEGF, SDF-1α, and active MMP-9 were measured by ELISA. The primary endpoint was EPC increment during the first week, which was defined as the difference in the number of CFU-EC between day 7 and admission. We found that VEGF (r = 0.782), SDF-1α (r = 0.828), and active MMP-9 (r = 0.740) levels at 24 hr from stroke onset showed a strong correlation with EPC increment. Similar results were found for VEGF levels at 72 hr (r = 0.839) and at day 7 (r = 0.602) as well as for active MMP-9 levels at 72 hr (r = 0.442) and at day 7 (r = 0.474). In the multivariate analyses, serum levels of VEGF at 72 hr (B: 0.074, P < 0.0001) and SDF-1α at 24 hr (B: 0.049, P = 0.008) were independent factors for EPC increment during the first week of evolution. These findings suggest that VEGF and SDF-1α may mediate EPC proliferation in human ischemic stroke.

SDF-1α induces angiogenesis after traumatic brain injury

This study aimed to investigate the effects of SDF-1α on brain angiogenesis and neurological functional recovery in rats after traumatic brain injury (TBI) and the potentially involved mechanisms. Youth male Wistar rats were injured via lateral fluid percussion injury and then randomly divided into one of 3 groups: I. vehicle treated group; II. SDF-1α neutralizing antibody treated group and III. rhSDF-1α treated group. rhSDF-1α and its neutralizing antibody or normal saline were administered to the brain penumbra via stereotactic injection 30min after TBI. Modified neurological severity score (mNSS) and Morris water maze (MWM) test were used to assess the neurologic functional recovery (n=6/group). 14days after injury, animals were euthanized and brain tissues were collected for quantitative real time polymerase chain reaction (qRT-PCR) (n=6/group) and immunohistochemistry (n=6/group) analysis. mNSS and MWM test indicated distinct amelioration of neurological disability in rhSDF-1α group(P<0.05). Microvessel density (MVD) of rhSDF-1α treated animals was remarkably increased around the injured area. On the contrary, MVD of the SDF-1α antibody administrated group was significantly decreased compared to that of vehicle treated animals (P<0.05). The mNSS and MVD had significant negative correlation as tested by Spearman rank correlation coefficient. Immunofluorescence staining showed that CD34 and CXCR4 co-expressed on microvessels. The rhSDF-1α treated animals had greater, contrarily, the SDF-1α antibody treated animals had lesser number of double positive microvessels compared to that of vehicle treated animals. The mRNA expression of CD34 and CXCR4 was obviously elevated in the rhSDF-1α administration group, conversely, declined in SDF-1α antibody treated animals around the injured area compared with that of the vehicle treatment group (P<0.05). These data indicated that SDF-1α could induce angiogenesis after TBI, potentially via SDF-1/CXCR4 axis.

A subpopulation of endothelial progenitor cells with low aldehyde dehydrogenase activity attenuates acute ischemic brain injury in rats

Previous studies have examined the therapeutic effect of endothelial progenitor cells (EPCs) during the chronic phase of cerebral infarction in rats; however, few studies have investigated the effects of EPCs during the acute phase of infarction. In this study, we evaluated the therapeutic effect of EPCs with low aldehyde dehydrogenase activity (Alde-Low EPCs) in rats with acute cerebral infarction, and our results provide insight that may help to identify a therapeutic mechanism of EPCs for acute cerebral infarction. The administration of Alde-Low EPCs into rats with acute cerebral infarction results in the accumulation and migration of the Alde-Low EPCs into the infarct area and the subsequent decrease of infarct volume. Moreover, we found that the stromal cell-derived factor-1 (SDF-1) and CXC chemokine receptor 4 (CXCR4) signaling pathway may regulate the accumulation of Alde-Low EPCs. The transplantation of Alde-Low EPCs may represent a potential treatment strategy for acute cerebral infarction.

Stem Cells for Neurovascular Repair in Stroke

Stem cells exert therapeutic effects against ischemic stroke via transplantation of exogenous stem cells or stimulation of endogenous stem cells within the neurogenic niches of subventricular zone and subgranular zone, or recruited from the bone marrow through peripheral circulation. In this paper, we review the different sources of stem cells that have been tested in animal models of stroke. In addition, we discuss specific mechanisms of action, in particular neurovascular repair by endothelial progenitor cells, as key translational research for advancing the clinical applications of stem cells for ischemic stroke.