Endothelial progenitor cell transplantation improves long-term stroke outcome in mice

Stem cell-based cell therapy for neuroprotection in stroke: A review

Neurological disorders, such as stroke, are triggered by a loss of neurons and glial cells. Ischemic stroke remains a substantial problem for industrialized countries. Over the previous few decades our understanding about the pathophysiology of stroke has enhanced, nevertheless, more awareness is required to advance the field of stroke recovery. Existing therapies are incapable to adequately relief the disease outcome and are not appropriate to all patients. Meanwhile, the majority of patients continue to show neurological deficits even subsequent effective thrombolysis, recuperative therapies are immediately required that stimulate brain remodeling and repair once stroke damage has happened. Cell therapy is emergent as a hopeful new modality for increasing neurological recovery in ischemic stroke. Numerous types of stem cells from various sources have been identified and their possibility and efficiency for the treatment of stroke have been investigated. Stem cell therapy in patients with stroke using adult stem cells have been first practiced in clinical trials since 15 years ago. Even though stem cells have revealed a hopeful role in ischemic stroke in investigational studies besides early clinical pilot studies, cellular therapy in human is still at a primary stage. In this review, we summarize the types of stem cells, various delivery routes, and clinical application of stem cell-based therapy for stroke treatment.

Impaired functional recovery of endothelial colony-forming cells from moyamoya disease in a chronic cerebral hypoperfusion rat model

OBJECTIVEEndothelial colony-forming cells (ECFCs) isolated from pediatric patients with moyamoya disease (MMD) have demonstrated decreased numbers and defective functioning in in vitro experiments. However, the function of ECFCs has not been evaluated using in vivo animal models. In this study, the authors compared normal and MMD ECFCs using a chronic cerebral hypoperfusion (CCH) rat model.METHODSA CCH rat model was made via ligation of the bilateral common carotid arteries (2-vessel occlusion [2-VO]). The rats were divided into three experimental groups: vehicle-treated (n = 8), normal ECFC-treated (n = 8), and MMD ECFC-treated (n = 8). ECFCs were injected into the cisterna magna. A laser Doppler flowmeter was used to evaluate cerebral blood flow, and a radial arm maze test was used to examine cognitive function. Neuropathological examinations of the hippocampus and agranular cortex were performed using hematoxylin and eosin and Luxol fast blue staining in addition to immunofluorescence with CD31, von Willebrand factor, NeuN, myelin basic protein, glial fibrillary acidic protein, and cleaved caspase-3 antibodies.RESULTSThe normal ECFC-treated group exhibited improvement in the restoration of cerebral perfusion and in behavior compared with the vehicle-treated and MMD ECFC-treated groups at the 12-week follow-up after the 2-VO surgery. The normal ECFC-treated group showed a greater amount of neovasculogenesis and neurogenesis, with less apoptosis, than the other groups.CONCLUSIONSThese results support the impaired functional recovery of MMD ECFCs compared with normal ECFCs in a CCH rat model. This in vivo study suggests the functional role of ECFCs in the pathogenesis of MMD.

A preventive injection of endothelial progenitor cells prolongs lifespan in stroke-prone spontaneously hypertensive rats

There is a pressing need for new approaches to prevent stroke. Endothelial progenitor cells (EPCs) promote vascular repair and revascularization in the ischemic brain. The present study sought to evaluate whether preventive delivery of EPCs could prevent or protect against stroke. Stroke-prone spontaneously hypertensive rats (SHR-SP) received a single injection of EPCs, and their survival time was monitored. In addition, at 28 and/or 42 days after a single injection of EPCs, SHR-SP and mice were subjected to cerebral ischemia, and cerebral ischemic injury, local angiogenesis and in vivo EPC integration were determined. Other experiments examined the effects of EPC conditioned medium, and the distribution of donor EPCs taken from GFP transgenic mice. It was found that EPC-pretreated SHR-SP showed longer lifespans than untreated controls. A single preventive injection of EPCs could produce persistent protective effects against cerebral ischemic injury (lasting at least 42 days), and promote local angiogenesis in the ischemic brain, in two types of animals (SHR-SP and normotensive mice). EPCs of donor origin could be detected in the recipient peripheral blood, and integrated into the recipient ischemic brains. Furthermore, it was suggested that mouse EPCs might exert paracrine effects on cerebral ischemic injury in addition to their direct angiogenic effects. In conclusion, a single preventive injection of EPCs prolonged the lifespan of SHR-SP, and protected against cerebral ischemic injury for at least 7 weeks. It is implied that EPC injection might be a promising candidate for a preventive role in patients at high risk for stroke.

Revascularization and endothelial progenitor cells in stroke

Stroke is one of the leading causes of death and disability worldwide. Tremendous improvements have been achieved in the acute care of stroke patients with the implementation of stroke units, thrombolytic drugs, and endovascular trombectomies. However, stroke survivors with neurological deficits require long periods of neurorehabilitation, which is the only approved therapy for poststroke recovery. With this scenario, more treatments are urgently needed, and only the understanding of the mechanisms of brain recovery might contribute to identify new therapeutic agents. Fortunately, brain injury after stroke is counteracted by the birth and migration of several populations of progenitor cells towards the injured areas, where angiogenesis and vascular remodeling play a key role providing trophic support and guidance during neurorepair. Endothelial progenitor cells (EPCs) constitute a pool of circulating bone-marrow derived cells that mobilize after an ischemic injury with the potential to incorporate into the damaged endothelium, to form new vessels, or to secrete trophic factors stimulating vessel remodeling. The circulating levels of EPCs are altered after stroke, and several subpopulations have proved to boost brain neurorepair in preclinical models of cerebral ischemia. The goal of this review is to discuss the current state of the neuroreparative actions of EPCs, focusing on their paracrine signaling mechanisms thorough their secretome and released extracellular vesicles.

Pro- and antiangiogenic therapies: current status and clinical implications

Blood vessels nurture every part of the human body. Consequently, abnormalities in the vasculature are closely associated with a variety of diseases, including cerebral stroke, heart disease, retinopathy, and cancer. Pro- or antiangiogenic therapies can influence these diseases by regulating the growth of new blood vessels from a pre-existing vascular network or dampening excessive blood growth. However, clinical translation of these approaches is slow and challenging. In this review, we discuss recent preclinical approaches to regulate angiogenesis and their potential and risks in a clinical setting.-Rust, R., Gantner, C., Schwab, M. E. Pro- and antiangiogenic therapies: current status and clinical implications.

Aging- and vascular-related pathologies

Our aging population is set to grow considerably in the coming decades. In fact, the number of individuals older than 65 years will double by 2050. This projected increase in people living with extended life expectancy represents an inevitable upsurge in the presentation of age-related pathologies. However, our current understanding of the impact of aging on a number of biological processes is unfortunately inadequate. Cardiovascular, cerebrovascular, and neurodegenerative diseases are particularly prevalent in the elderly population. Intriguingly, these pathologies are all associated with vascular dysfunction, suggesting that the process of aging can induce structural and functional impairments in vascular networks. Together with elevated cell senescence, pre-existing comorbidities, and the emerging concept of age-associated inflammatory imbalance, impaired vascular functions can significantly increase one's risk in acquiring age-related diseases. In this short review, we highlight some current clinical and experimental evidence of how biological aging contributes to three vascular-associated pathologies: atherosclerosis, stroke, and Alzheimer's disease.

HIF-prolyl hydroxylase 2 silencing using siRNA delivered by MRI-visible nanoparticles improves therapy efficacy of transplanted EPCs for ischemic stroke

Endothelial progenitor cell (EPC)-based therapy has brought potential benefits to stroke patients as an important restorative therapeutics. However, its efficacy is limited by poor migration and survival ability. Here, we found out that hif-prolyl hydroxylase 2 (PHD2) silencing could enhance the migration and survival ability of EPCs which could improve the therapy efficacy for ischemic stroke. We successfully developed a siRNA delivery system, which could achieve siRNA delivery and EPCs tracking with magnetic resonance imaging (MRI) simultaneously. Besides, combining MRI and bioluminescence imaging (BLI), we successfully observed full temporal profile of EPCs dynamics in vivo. Furthermore, we found out that PHD2 silencing in EPCs elevated the expression of C-X-C chemokine receptor type 4 (CXCR4) and hypoxia-inducible factor 1α (HIF-1α), which enhanced the migration and survival ability of EPCs respectively. Significantly decreased infarct volume, functional deficits and increased fractional anisotrophy (FA) value, fiber counts were observed in the siPHD2-EPCs (EPCs transfected with siRNA targeting PHD2) group. What's more, higher level of BNDF, CD31, DCX, NeuN and MBP were also observed in the siPHD2-EPCs group. Altogether, our study provides an effective method to improve EPC-based therapy efficacy for ischemic stroke.

cxcl12-engineered endothelial progenitor cells enhance neurogenesis and angiogenesis after ischemic brain injury in mice

Background

Ischemic stroke causes a multitude of brain damage. Neurovascular injury and myelin sheath degradation are two manifestations of ischemic brain damage. Therapeutic strategies aiming only at repairing the neural components or the vessels cannot efficiently restore neurological function. Endothelial progenitor cells (EPCs) have the advantages of both promoting angiogenesis and secreting trophic factors that would promote neurogenesis. Chemokine cxcl12 gene therapy has also been shown to promote angiogenesis, neurogenesis, and remyelination, attracting EPCs, neural progenitor cells, and oligodendrocyte progenitor cells (OPCs) to the injured sites of the brain. In this work, we tested whether these two therapeutics can be combined by genetically engineering the EPCs with cxcl12 to harness the synergistic effects of these two interventions.

Methods

We used lentivirus (LV) to deliver cxcl12 gene into human umbilical cord blood EPCs to generate the engineered CXCL12-EPCs, which were then delivered into the perifocal region at 1 week after permanent middle cerebral artery occlusion to investigate the effects of CXCL12-EPCs on the functional recovery and angiogenesis, neurogenesis, and remyelination in ischemic stroke mice. Green fluorescent protein (gfp) gene-modified EPCs and LV-CXCL12 gene therapy were used as controls.

Results

CXCL12-EPC treatment significantly reduced brain atrophy and improved neurobehavioral function at 5 weeks after brain ischemia. The treatment resulted in increased blood vessel density and myelin sheath integrity, and promoted neurogenesis, angiogenesis, and the proliferation and migration of OPCs. In-vitro data showed that CXCL12-EPCs performed better in proliferation and tube formation assays and expressed a higher level of vascular endothelial growth factor compared to GFP-EPCs.

Conclusions

The synergistic treatment of CXCL12-EPCs outperformed the single therapies of GFP-EPCs or LV-CXCL12 gene therapy in various aspects related to post-ischemic brain repair. cxcl12-engineered EPCs hold great potential in the treatment of ischemic stroke.

Cell-Based Therapies in Acute Kidney Injury (AKI)

Acute kidney injury frequently occurs in hospitalized patients all over the world. The prognosis remains poor since specific therapies for promoting kidney regeneration/repair are still missing. In recent years cell-based strategies have improved AKI outcomes under experimental circumstances. Four groups of cells, each of them displaying certain biological and functional characteristics have been evaluated in AKI, induced Pluripotent Stem Cells (iPSCs), Spermatagonial Stem Cells (SSCs), Proangiogenic Cells (PACs) and Endothelial Colony Forming Cells (ECFCs), and Mesenchymal Stem Cells (MSCs). All of these have been documented to stabilize either parameters of kidney excretory dysfunction and/or certain morphological parameters. The mechanisms responsible for AKI protection include direct (cell incorporation) and indirect processes, the latter being mediated by humoral factors and particularly by the production of so-called extracellular vesicles. Cell-derived vesicular organelles have been shown to carry pro-regenerative micro-RNA molecules which stabilize the vascular and tubular function. The first trials in humans have been initiated, the majority of such trials employs MSCs. However, any transfer of cell-based strategies in the clinical practice is potentially associated with significant difficulties. These include cell availability, tolerance and competence. The article intends to summarize essential informations about all of the four populations mentioned above and to discuss implications for the management of human AKI.

MicroRNA-126 Priming Enhances Functions of Endothelial Progenitor Cells under Physiological and Hypoxic Conditions and Their Therapeutic Efficacy in Cerebral Ischemic Damage

Endothelial progenitor cells (EPCs) have shown the potential for treating ischemic stroke (IS), while microRNA-126 (miR-126) is reported to have beneficial effects on endothelial function and angiogenesis. In this study, we investigated the effects of miR-126 overexpression on EPCs and explore the efficacy of miR-126-primed EPCs (EPC^miR-126) in treating IS. The effects of miR-126 overexpression on EPC proliferation, migratory, tube formation capacity, reactive oxygen species (ROS) production, and nitric oxide (NO) generation were determined. In in vivo study, the effects of EPC^miR-126 on the cerebral blood flow (CBF), neurological deficit score (NDS), infarct volume, cerebral microvascular density (cMVD), and angiogenesis were determined. Moreover, the levels of circulating EPCs (cEPCs) and their contained miR-126 were measured. We found (1) miR-126 overexpression promoted the proliferation, migration, and tube formation abilities of EPCs; decreased ROS; and increased NO production of EPCs via activation of PI3K/Akt/eNOS pathway; (2) EPC^miR-126 was more effective than EPCs in attenuating infarct volume and NDS and enhancing cMVD, CBF, and angiogenesis; and (3) infusion of EPC^miR-126 increased the number and the level of miR-126 in cEPCs. Our data indicate that miR-126 overexpression enhanced the function of EPCs in vitro and in vivo.

Endothelial Progenitor Cell Secretome and Oligovascular Repair in a Mouse Model of Prolonged Cerebral Hypoperfusion

BACKGROUND AND PURPOSE

Endothelial progenitor cells (EPCs) have been extensively investigated as a therapeutic approach for repairing the vascular system in cerebrovascular diseases. Beyond vascular regeneration per se, EPCs may also release factors that affect the entire neurovascular unit. Here, we aim to study the effects of the EPC secretome on oligovascular remodeling in a mouse model of white matter injury after prolonged cerebral hypoperfusion.

METHODS

The secretome of mouse EPCs was analyzed with a proteome array. In vitro, the effects of the EPC secretome and its factor angiogenin were assessed on primary oligodendrocyte precursor cells and mature human cerebral microvascular endothelial cells (hCMED/D3). In vivo, mice were subjected to permanent bilateral common carotid artery stenosis, then treated with EPC secretome at 24 hours and at 1 week, and cognitive outcome was evaluated with the Y maze test together with oligodendrocyte precursor cell proliferation/differentiation and vascular density in white matter at 4 weeks.

RESULTS

Multiple growth factors, cytokines, and proteases were identified in the EPC secretome, including angiogenin. In vitro, the EPC secretome significantly enhanced endothelial and oligodendrocyte precursor cell proliferation and potentiated oligodendrocyte precursor cell maturation. Angiogenin was proved to be a key factor since pharmacological blockade of angiogenin signaling negated the positive effects of the EPC secretome. In vivo, treatment with the EPC secretome increased vascular density, myelin, and mature oligodendrocytes in white matter and rescued cognitive function in the mouse hypoperfusion model.

CONCLUSIONS

Factors secreted by EPCs may ameliorate white matter damage in the brain by boosting oligovascular remodeling.

Recovery of Neurovascular Unit Integrity by CDK5-KD Astrocyte Transplantation in a Global Cerebral Ischemia Model

Astrocytes play metabolic and structural support roles and contribute to the integrity of the blood-brain barrier (BBB), linking communication between neurons and the endothelium. Cyclin-dependent kinase 5 (CDK5) likely exerts a dual effect on the endothelium and astrocytes due to its involvement in migration and angiogenesis; the overactivation of CDK5 is associated with dysfunction in glutamate recapture and hypoxia. Recently, we proposed that CDK5-targeted astrocytes facilitate the recovery of neurological and motor function in transplanted ischemic rats. In the current study, we treated cerebral ischemic rats and endothelial cells exposed to glutamate toxicity with CDK5 knock-down (CDK5-KD) astrocytes to determine the role of CDK5 in neurovascular integrity. We found that the effects of CDK5-KD were sustained for 4 months, preventing neuronal and astrocyte loss, facilitating the recovery of the BBB via the production of BDNF by endogenous astrocytes (GFP^-) surrounding vessels in the motor cortex and the corpus callosum of global ischemic rats, and improving neurological performance. These findings were supported by the in vitro findings of increased transendothelial resistance, p120-ctn+ adhesion and reduced intercellular gaps induced by a CDK5 inhibitor (roscovitine) in bEnd.3 cells in a glutamate-toxicity model. Additionally, CDK5-KD astrocytes in co-culture protected the endothelial cell viability, increased BDNF release from astrocytes, increased BDNF immunoreactivity in neighboring astrocytes and endothelial cells and enhanced cell adhesion in a glutamate-toxicity model. Altogether, these findings suggest that a CDK5 reduction in astrocytes protects the endothelium, which promotes BDNF release, endothelial adhesion, and the recovery of neurovascular unit integrity and brain function in ischemic rats.

Highly efficient local delivery of endothelial progenitor cells significantly potentiates angiogenesis and full-thickness wound healing

Wound therapy with a rapid healing performance remains a critical clinical challenge. Cellular delivery is considered to be a promising approach to improve the efficiency of healing, yet problems such as compromised cell viability and functionality arise due to the inefficient delivery. Here, we report the efficient delivery of endothelial progenitor cells (EPCs) with a bioactive nanofibrous scaffold (composed of collagen and polycaprolactone and bioactive glass nanoparticles, CPB) for enhancing wound healing. Under the stimulation of CPB nanofibrous system, the viability and angiogenic ability of EPCs were significantly enhanced through the activation of Hif-1α/VEGF/SDF-1α signaling. In vivo, CPB/EPC constructs significantly enhanced the formation of high-density blood vessels by greatly upregulating the expressions of Hif-1α, VEGF, and SDF-1α. Moreover, owing to the increased local delivery of cells and fast neovascularization within the wound site, cell proliferative activity, granulation tissue formation, and collagen synthesis and deposition were greatly promoted by CPB/EPC constructs resulting in rapid re-epithelialization and regeneration of skin appendages. As a result, the synergistic enhancement of wound healing was observed from CPB/EPC constructs, which suggests the highly efficient delivery of EPCs. CPB/EPC constructs may become highly competitive cell-based therapeutic products for efficient impaired wound healing application. This study may also provide a novel strategy to develop bioactive cell therapy constructs for angiogenesis-related regenerative medicine.

STATEMENT OF SIGNIFICANCE

This paper reported a highly efficient local delivery of EPCs using bioactive glass-based CPB nanofibrous scaffold for enhancing angiogenesis and wound regeneration. In vitro study showed that CPB can promote the proliferation, migration, and tube formation of EPCs through upregulation of the Hif-1α/VEGF/SDF-1α signaling pathway, indicating that the bioactivity and angiogenic ability of EPCs can be highly maintained and promoted by the CPB scaffold. Moreover, CPB/EPC constructs effectively stimulated the regeneration of diabetic wounds with satisfactory vascularization and better healing outcomes in a full-thickness wound model, suggesting that the highly efficient delivery of EPCs to wound site facilitates angiogenesis and further leads to wound healing. The high angiogenic capacity and excellent healing ability make CPB/EPC constructs highly competitive in cell-based therapeutic products for efficient wound repair application.

Temporal Dynamics of Gene Expression During Endothelial Cell Differentiation From Human iPS Cells: A Comparison Study of Signalling Factors and Small Molecules

Endothelial cell (EC) therapy may promote vascular growth or reendothelization in a variety of disease conditions. However, the production of a cell therapy preparation containing differentiated, dividing cells presenting typical EC phenotype, functional properties and chemokine profile is challenging. We focused on comparative analysis of seven small molecule-mediated differentiation protocols of ECs from human induced pluripotent stem cells. Differentiated cells showed a typical surface antigen pattern of ECs as characterized with flow cytometry analysis, functional properties, such as tube formation and ability to uptake acetylated LDL. Gene expression analysis by RNA sequencing revealed an efficient silencing of pluripotency genes and upregulation of genes related to cellular adhesion during differentiation. In addition, distinct patterns of transcription factor expression were identified during cellular reprogramming providing targets for more effective differentiation protocols in the future. Altogether, our results suggest that the most optimal EC differentiation protocol includes early inhibition of Rho-associated coiled-coil kinase and activation of cyclic AMP signaling, and inhibition of transforming growth factor beta signaling after mesodermal stage. These findings provide the first systematic characterization of the most potent signalling factors and small molecules used to generate ECs from human induced pluripotent stem cells and, consequently, this work improves the existing EC differentiation protocols and opens up new avenues for controlling cell fate for regenerative EC therapy.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

Silencing a Multifunctional microRNA Is Beneficial for Stroke Recovery

Stroke-induced endothelial cell injury leads to destruction of cerebral microvasculature and significant damage to the brain tissue. A subacute phase of cerebral ischemia is associated with regeneration involving the activation of vascular remodeling, neuroplasticity, neurogenesis, and neuroinflammation processes. Effective restoration and improvement of blood supply to the damaged brain tissue offers a potential therapy for stroke. microRNAs (miRNAs) are recently identified small RNA molecules that regulate gene expression and significantly influence the essential cellular processes associated with brain repair following stroke. A number of specific miRNAs are implicated in regulating the development and propagation of the ischemic tissue damage as well as in mediating post-stroke regeneration. In this review, I discuss the functions of the miRNA miR-155 and the effect of its in vivo inhibition on brain recovery following experimental cerebral ischemia. The article introduces new and unexplored approach to cerebral regeneration: regulation of brain tissue repair through a direct modulation of specific miRNA activity.

MicroRNA-126/stromal cell-derived factor 1/C-X-C chemokine receptor type 7 signaling pathway promotes post-stroke angiogenesis of endothelial progenitor cell transplantation

Stroke is the most common cause of mortality worldwide. Post-stroke angiogenesis is of great significance to the treatment of strokes. The aim of the present study was to investigate the mechanism underlying the angiogenesis-promoting effect of microRNA‑126 (miR‑126)‑associated signaling pathways using a stroke model in vivo and a cell migration model in vitro. Bone marrow‑derived endothelial progenitor cells (EPCs) were extracted and identified using a density gradient method. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) was performed to examine the expression levels of miR‑126 and C‑X‑C chemokine receptor type 7 (CXCR7). Target genes of miR‑126 were analyzed using TargetScan software version 7.1 (www.targetscan.org/). In addition, a reporter gene assay and RT‑qPCR were performed to determine the target genes of miR‑126. The effect of miR‑126 on cell migration was examined using a cell migration model in vitro and a middle cerebral artery occlusion model of mice was established in vivo. The miR‑126 antagomir‑treated EPCs were infused into stroke mice. Microvessel density, nerve function score and infarction volume were assessed. Flow cytometric analysis indicated that cluster of differentiation (CD)34, CD133 and vascular endothelial growth factor receptor 2 were partly expressed on the cell surface of bone marrow‑derived EPCs. In addition, the expression levels of Di‑acetylated‑low density lipoprotein and Ulex europaeus agglutinin 1 were positive. Stromal cell‑derived factor 1 (SDF-1) was identified as a target gene of miR‑126, which was confirmed by a reporter gene assay and RT‑qPCR. Cell migration examination demonstrated that the neutralizing antibody of CXCR7 blocked miR‑126 angomir‑induced migration of EPCs. Microvessel density increased, while nerve function score and infarction volume decreased following infusion of miR-126 angomir‑treated EPCs. Furthermore, miR‑126 angomir improved the efficacy of EPC treatment. Thus, miR‑126 improved the migration of EPCs via the miR‑126/SDF‑1/CXCR7 signaling pathway.

Adult stem cells in psychiatric disorders - New discoveries in peripheral blood

The new area of research in psychiatric disorders is concerned with abnormal regeneration processes. The role of brain neurogenesis has been studied for decades. New discoveries, concerned with the pluripotency of VSEL cells and the role of factors involved in stem cell trafficking in peripheral blood create hope that it will be possible to develop a better understanding of the processes of neuroregeneration/neurodegeneration. There is an ongoing research investigating concentrations of: sphingosine -1-phosphate, SDF-1, elements of complement cascade, and stem cells in peripheral blood, including their possible connection to psychiatric disorders. Collected data, suggesting an abnormal course of regeneration processes in psychiatric disorders, raises hope of finding new potential markers of psychosis and anxiety disorders.

Circulating Progenitor Cells Correlate with Memory, Posterior Cortical Thickness, and Hippocampal Perfusion

BACKGROUND

Bone marrow-derived progenitor cells survey the vasculature and home to sites of tissue injury where they can promote repair and regeneration. It has been hypothesized that these cells may play a protective role neurodegenerative and vascular cognitive impairment.

OBJECTIVE

To evaluate progenitor cell levels in older adults with and without mild cognitive impairment (MCI), and to relate circulating levels to memory, brain volume, white matter lesion volume, and cerebral perfusion.

METHOD

Thirty-two older adults, free of stroke and cardiovascular disease, were recruited from the community and evaluated for diagnosis of MCI versus cognitively normal (CN). Participants underwent brain MRI and blood samples were taken to quantify progenitor reserve using flow cytometry (CD34+, CD34+CD133+, and CD34+CD133+CD309+ cells).

RESULTS

Participants with MCI (n = 10) exhibited depletion of all CPC markers relative to those who were CN (n = 22), after controlling for age, sex, and education. Post-hoc age, sex, and education matched comparisons (n = 10 MCI, n = 10 CN) also revealed the same pattern of results. Depletion of CD34+ cells correlated with memory performance, left posterior cortical thickness, and bilateral hippocampal perfusion. Participants exhibited low levels of vascular risk and white matter lesion burden that did not correlate with progenitor levels.

CONCLUSIONS

Circulating progenitor cells are associated with cognitive impairment, memory, cortical atrophy, and hippocampal perfusion. We hypothesize that progenitor depletion contributes to, or is triggered by, cognitive decline and cortical atrophy. Further study of progenitor cell depletion in older adults may benefit efforts to prevent or delay dementia.

Monotropein promotes angiogenesis and inhibits oxidative stress-induced autophagy in endothelial progenitor cells to accelerate wound healing

Attenuating oxidative stress‐induced damage and promoting endothelial progenitor cell (EPC) differentiation are critical for ischaemic injuries. We suggested monotropein (Mtp), a bioactive constituent used in traditional Chinese medicine, can inhibit oxidative stress‐induced mitochondrial dysfunction and stimulate bone marrow‐derived EPC (BM‐EPC) differentiation. Results showed Mtp significantly elevated migration and tube formation of BM‐EPCs and prevented tert‐butyl hydroperoxide (TBHP)‐induced programmed cell death through apoptosis and autophagy by reducing intracellular reactive oxygen species release and restoring mitochondrial membrane potential, which may be mediated viamTOR/p70S6K/4EBP1 and AMPK phosphorylation. Moreover, Mtp accelerated wound healing in rats, as indicated by reduced healing times, decreased macrophage infiltration and increased blood vessel formation. In summary, Mtp promoted mobilization and differentiation of BM‐EPCs and protected against apoptosis and autophagy by suppressing the AMPK/mTOR pathway, improving wound healing in vivo. This study revealed that Mtp is a potential therapeutic for endothelial injury‐related wounds.

Brain-immune interactions in perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia remains the primary cause of acute neonatal brain injury, leading to a high mortality rate and long-term neurological deficits, such as behavioral, social, attentional, cognitive and functional motor deficits. An ever-increasing body of evidence shows that the immune response to acute cerebral hypoxia-ischemia is a major contributor to the pathophysiology of neonatal brain injury. Hypoxia-ischemia provokes an intravascular inflammatory cascade that is further augmented by the activation of resident immune cells and the cerebral infiltration of peripheral immune cells response to cellular damages in the brain parenchyma. This prolonged and/or inappropriate neuroinflammation leads to secondary brain tissue injury. Yet, the long-term effects of immune activation, especially the adaptive immune response, on the hypoxic-ischemic brain still remain unclear. The focus of this review is to summarize recent advances in the understanding of post-hypoxic-ischemic neuroinflammation triggered by the innate and adaptive immune responses and to discuss how these mechanisms modulate the brain vulnerability to injury. A greater understanding of the reciprocal interactions between the hypoxic-ischemic brain and the immune system will open new avenues for potential immunomodulatory therapy in the treatment of neonatal brain injury.

Mobilization of endothelial progenitor cell in patients with acute ischemic stroke

Endothelial progenitor cells (EPCs) have important effect in tissue repair in ischemic organs. The present study was conducted to demonstrate the mobilization of EPCs and its possible mechanism after acute ischemic stroke (AIS). A total of 148 individuals were examined, including 106 patients with ischemic stroke and 42 healthy controls. Seventy-one patients with imaging-confirmed AIS were examined at days 1, 7, 14, and 21 after stroke onset. Circulating EPCs were quantified by flow cytometry using CD133 and KDR surface markers. Serum stromal cell-derived factor-1 (SDF-1) concentrations were determined by enzyme-linked immunosorbent assay. Patients with AIS had significantly lower EPC level than that in the controls (0.022 ± 0.013 vs 0.051 ± 0.020; p < 0.01). This difference did not remain significant after adjusting for risk factors at multivariate analysis. Blood pressure, triglyceride, low-density lipoprotein (LDL), and fasting blood sugar were inversely correlated with EPC levels (p < 0.01). Systolic blood pressure and LDL remained independent predictors of baseline EPC levels. The number of circulating EPCs increased on day 7 after AIS, reached a peak on day 14, and decreased on day 21. The concentration of SDF-1 had similar changes. The increment of EPCs was correlated with the infarct volume (r = 0.708; p = 0.006) and SDF-1 concentration on day 14 (r = 0.714; p < 0.001). Baseline EPC level in patients with AIS reflects the cumulative vascular endothelial damage. EPCs could be mobilized into peripheral circulation in response to stroke stress. This mobilization was associated with the increased expression of SDF-1.

Getting Closer to an Effective Intervention of Ischemic Stroke: The Big Promise of Stem Cell

Stem cell therapy for ischemic stroke has widely been explored. Results from both preclinical and clinical studies have immensely supported the judicious use of stem cells as therapy. These provide an attractive means for preserving and replacing the damaged brain tissues following an ischemic attack. Since the past few years, researchers have used various types of stem cells to replenish insulted neuronal and glial cells in neurological disorders. In the present review, we discuss different types of stem cells employed for the treatment of ischemic stroke and mechanisms and challenges these cells face once introduced into the living system. Further, we also present different ways to maneuver and overcome challenges to translate the advances made at the preclinical level to clinics.

Constitutive Expression of Adiponectin in Endothelial Progenitor Cells Protects a Rat Model of Cerebral Ischemia

Endothelial progenitor cells (EPCs), as precursors to endothelial cells, play a significant part in the process of endogenous blood vessel repair and maintenance of endothelial integrity. Adiponectin (APN) is an adipocyte-specific adipocytokine. In this study, we aim to test whether we transplant a combined graft of EPCs transfected with the adiponectin gene into a rat model of cerebral ischemia could improve functional recovery after middle cerebral artery occlusion (MCAO). Sprague-Dawley (SD) rats were randomly divided into a MCAO control group, a MCAO EPC treatment group, and a MCAO LV-APN-EPC treatment group. A focal cerebral ischemia and reperfusion model was induced by the intraluminal suture method. After 2 h of reperfusion, EPCs were transplanted by injection through the tail vein. A rotarod test was conducted to assess behavioral function before MCAO and on days 1, 7, and 14 after MCAO. After 14 d, TTC staining, CD31 immunofluorescence, and TUNEL staining were used to evaluate infarct volume, microvessel density, and cell apoptosis. Results revealed that behavioral function, infarct area percentage, microvessel density, and cell apoptosis rates were more favorable in the LV-APN-EPC treatment group than in the EPC treatment group. These data suggested that gene-modified cell therapy may be a useful approach for the treatment of ischemic stroke.

Effect of ischaemic brain injury on sexual function in adult mice

Objective

Priapism refers to a condition with persistent abnormal erection of the penis, which is usually caused by disease or injury in the brain or spinal cord, or obstruction to the outflow of blood through the dorsal vein at the root of the penis, without sexual desires. The effect of cerebral ischaemia on sexual function is unknown. The aim of this study is to explore whether priapism occurs in adult mice. Furthermore, we examined the relationship between priapism and the region of infarct in the brain.

Design

Adult male CD-1 mice who underwent permanent middle cerebral artery occlusion (pMCAO) were closely examined from 2 hours to 14 days postoperation.

Results

We found that priapism occurs in ∼80% of the mice with pMCAO, which could persist up to 14 days. Further study has demonstrated that the occurrence of priapism is related to the infarct region: priapism is found only in mice with ischaemic injury extending to the hypothalamus and the hippocampus regions.

Conclusion

Our result suggested priapism may be used as a deep brain injury marker for evaluating brain injury in mice after pMCAO.

Chronic Exposure to Subtherapeutic Antibiotics Aggravates Ischemic Stroke Outcome in Mice

Subtherapeutic antibiotics have been widely used in agriculture since the 1950s, which can be accumulated in human body through various approaches and may have long-term consequences. However, there is limited information about the link between chronic subtherapeutic antibiotic exposure and the outcome of ischemic brain injury. Here we showed that long-term treatment with subtherapeutic chlortetracycline, penicillin or vancomycin, which were widely used in agriculture approved by US Food and Drug Administration (FDA), could impair EPC functions, reduce ischemic brain angiogenesis and aggravate cerebral ischemic injury and long-term stroke outcomes in mice. In addition, transplantated EPCs from chronic antibiotic-treated mice showed a lower therapeutic effect on cerebral ischemic injury reduction and local angiogenesis promotion compared to those from control mice, and EPCs from the donor animals could integrate into the recipient ischemic brain in mice. Furthermore, transplanted EPCs might exert paracrine effects on cerebral ischemic injury reduction in mice, which could be impaired by chronic antibiotic exposure. In conclusion, chronic subtherapeutic antibiotic exposure aggravated cerebral ischemic injury in mice, which might be partly attributed to the impairment of both EPC-mediated angiogenesis and EPCs' paracrine effects. These findings reveal a previously unrecognized impact of chronic subtherapeutic antibiotic exposure on ischemic injury.

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Chronic exposure to subtherapeutic antibiotics aggravates long-term stroke outcome in mice.

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Chronic exposure to subtherapeutic antibiotics impairs endothelial progenitor cell functions in mice.

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Chronic exposure to subtherapeutic antibiotics reduces ischemic brain angiogenesis in mice.

Subtherapeutic antibiotics have been widely used in agriculture since the 1950s, which can be accumulated in human body through various approaches and may have long-term consequences. However, there is limited information about the link between chronic subtherapeutic antibiotic exposure and the outcome of ischemic brain injury. Here we showed that chronic treatment with subtherapeutic chlortetracycline, penicillin or vancomycin, which were widely used in agriculture approved by US Food and Drug Administration (FDA), could impair endothelial progenitor cells-mediated angiogenesis and aggravate long-term stroke outcome in mice. These findings reveal a previously unrecognized impact of chronic subtherapeutic antibiotic exposure on ischemic injury.

Endothelial Progenitor Cells for Ischemic Stroke: Update on Basic Research and Application

Ischemic stroke is one of the leading causes of human death and disability worldwide. So far, ultra-early thrombolytic therapy is the most effective treatment. However, most patients still live with varying degrees of neurological dysfunction due to its narrow therapeutic time window. It has been confirmed in many studies that endothelial progenitor cells (EPCs), as a kind of adult stem cells, can protect the neurovascular unit by repairing the vascular endothelium and its secretory function, which contribute to the recovery of neurological function after an ischemic stroke. This paper reviews the basic researches and clinical trials of EPCs especially in the field of ischemic stroke and addresses the combination of EPC application with new technologies, including neurovascular intervention, synthetic particles, cytokines, and EPC modification, with the aim of shedding some light on the application of EPCs in treating ischemic stroke in the future.

Stem cell therapy for abrogating stroke-induced neuroinflammation and relevant secondary cell death mechanisms

Ischemic stroke is a leading cause of death worldwide. A key secondary cell death mechanism mediating neurological damage following the initial episode of ischemic stroke is the upregulation of endogenous neuroinflammatory processes to levels that destroy hypoxic tissue local to the area of insult, induce apoptosis, and initiate a feedback loop of inflammatory cascades that can expand the region of damage. Stem cell therapy has emerged as an experimental treatment for stroke, and accumulating evidence supports the therapeutic efficacy of stem cells to abrogate stroke-induced inflammation. In this review, we investigate clinically relevant stem cell types, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs), very small embryonic-like stem cells (VSELs), neural stem cells (NSCs), extraembryonic stem cells, adipose tissue-derived stem cells, breast milk-derived stem cells, menstrual blood-derived stem cells, dental tissue-derived stem cells, induced pluripotent stem cells (iPSCs), teratocarcinoma-derived Ntera2/D1 neuron-like cells (NT2N), c-mycER(TAM) modified NSCs (CTX0E03), and notch-transfected mesenchymal stromal cells (SB623), comparing their potential efficacy to sequester stroke-induced neuroinflammation and their feasibility as translational clinical cell sources. To this end, we highlight that MSCs, with a proven track record of safety and efficacy as a transplantable cell for hematologic diseases, stand as an attractive cell type that confers superior anti-inflammatory effects in stroke both in vitro and in vivo. That stem cells can mount a robust anti-inflammatory action against stroke complements the regenerative processes of cell replacement and neurotrophic factor secretion conventionally ascribed to cell-based therapy in neurological disorders.

Evaluation of velvet antler total protein effect on bone marrow‑derived endothelial progenitor cells

Lu Rong, velvet antler (VA), is a traditional Chinese medicine, which is used as a food supplement and therapeutic drug in China, Japan, Russia, New Zealand and Southeast Asia. The regenerative characteristics of VA have resulted in great research interest, particularly regarding the fields of organ grafting and stem cell differentiation. Various VA proteomic studies verified that proteins act as the primary bioactive components of VA. The present study aimed to investigate if VA proteins (VA-pro) influence endothelial progenitor cell (EPC) viability. Various methods have previously been used to investigate VA-pro, including freeze-drying technology, ultrasonic wave methods, high performance liquid chromatography-mass spectrometry, EPCs extraction and culture. Results demonstrated that VA-pro promoted EPCs proliferation and migration, particularly at a concentration of 1 mg/ml. Furthermore, VA-pro increased the activation level of Notch1 intracellular domain and Hes1, and the level of phosphorylated-Akt and phosphorylated-mechanistic target of rapamycin. VA-pro may therefore affect EPC viability via regulation of the Notch and Akt signaling pathways. The present study revealed the effects and potential molecular mechanism of VA-pro on EPCs, and suggested an association between VA regeneration characteristics and the optimization of EPC viability. These findings may contribute to EPC transplantation research and aid in providing a novel treatment method for vascular diseases in the future.

Endothelial progenitor cells transplantation attenuated blood-brain barrier damage after ischemia in diabetic mice via HIF-1α

Background

Blood-brain barrier impairment is a major indicator of endothelial dysfunction in diabetes. Studies showed that endothelial progenitor cell (EPC) transplantation promoted angiogenesis and improved function recovery after hind limb ischemia in diabetic mice. The effect of EPC transplantation on blood-brain barrier integrity after cerebral ischemia in diabetic animals is unknown. The aim of this study is to explore the effect of EPC transplantation on the integrity of the blood-brain barrier after cerebral ischemia in diabetic mice.

Methods

EPCs were isolated by density gradient centrifugation and characterized by flow cytometry and immunostaining. Diabetes was induced in adult male C57BL/6 mice by a single injection of streptozotocin at 4 weeks before surgery. Diabetic mice underwent 90-minute transient middle cerebral artery occlusion surgery and received 1 × 10⁶ EPCs transplantation immediately after reperfusion. Brain infarct volume, blood-brain barrier permeability, tight junction protein expression, and hypoxia inducible factor-1α (HIF-1α) mRNA level were examined after treatment.

Results

We demonstrated that neurological deficits were attenuated and brain infarct volume was reduced in EPC-transplanted diabetic mice after transient cerebral ischemia compared to the controls (p < 0.05). Blood-brain barrier leakage and tight junction protein degradation were reduced in EPC-transplanted mice (p <0.05). EPCs upregulated HIF-1α expression while HIF-1α inhibitor PX-478 abolished the beneficial effect of EPCs.

Conclusions

We conclude that EPCs protected blood-brain barrier integrity after focal ischemia in diabetic mice through upregulation of HIF-1α signaling.

Challenging the great vascular wall: Can we envision a simple yet comprehensive therapy for stroke?

Stroke is a leading cause of death in adult life, closely behind ischemic heart disease, and causes a significant and abiding socioeconomic burden. However, current therapies are not able to ensure full neurologic and/or sequelae-free recovery to all stroke survivors. We believe treatment efficacy and patient rehabilitation could be enhanced significantly by targeting blood-brain barrier (BBB) deregulation and inflammation-induced barrier loss that occurs after stroke. In this pathological context, bone marrow-derived endothelial progenitor cells (EPC) enter the bloodstream towards the lesion site, but their insufficient numbers and impaired angiogenic ability compromise neurovascular regeneration. In this context, cell-based therapies have become increasingly appealing since treating patients with large numbers of mesenchymal or hematopoietic stem/progenitor cells alone may boost repair. However, this approach could be met with several challenges in terms of logistics and cost; hence, the development of a drug delivery system suitable for intravenous administration and functionalized for selective uptake by circulating EPC could enhance their restorative potential without perceived complications. The ability to encapsulate proangiogenic and anti-inflammatory agents, such as retinoic acid, and to safely and easily deliver them systemically may open new therapeutic perspectives for the treatment of cerebrovascular disorders. Copyright © 2017 John Wiley & Sons, Ltd.

Vascular precursor cells in tissue injury repair

Vascular precursor cells include stem cells and progenitor cells giving rise to all mature cell types in the wall of blood vessels. When tissue injury occurs, local hypoxia and inflammation result in the generation of vasculogenic mediators which orchestrate migration of vascular precursor cells from their niche environment to the site of tissue injury. The intricate crosstalk among signaling pathways coordinates vascular precursor cell proliferation and differentiation during neovascularization. Establishment of normal blood perfusion plays an essential role in the effective repair of the injured tissue. In recent years, studies on molecular mechanisms underlying the regulation of vascular precursor cell function have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches to treat chronic wounds and ischemic diseases in vital organ systems. Verification of safety and establishment of specific guidelines for the clinical application of vascular precursor cell-based therapy remain major challenges in the field.

Monomeric CXCL12 outperforms its dimeric and wild type variants in the promotion of human endothelial progenitor cells' function

CXCL12 overexpression improves neurobehavioral recovery during post-ischemic stroke through multiple mechanisms including promoting endothelial progenitor cells function in animal models. It has been proposed that the monomer and dimer forms possess differential chemotactic and regulatory function. The aim of present study is to explore whether a monomeric or dimeric CXCL12 plays a different role in the endothelial progenitor cells proliferation, migration, and tube-formation in vitro. In this study, we transferred monomeric, dimeric and wild type CXCL12 gene into endothelial progenitor cells via lentiviral vectors. We investigated endothelial progenitor cells function following the interaction of CXCL12/CXCR4 or CXCL12/CXCR7 and downstream signaling pathways. Our results showed that the monomeric CXCL12 transfected endothelial progenitor cells had enhanced ability in cell proliferation, migration, and tube-formation compared to that in dimeric or wild type controls (p < 0.05). Both CXCR4 and CXCR7 were significantly overexpressed in the monomeric CXCL12 transfected endothelial progenitor cells compared to that in the dimeric or wide type controls (p < 0.05). The function of migration, but not proliferation or tube-formation, was significantly reduced in the monomeric CXCL12 transfected endothelial progenitor cells when the cells were pre-treated with either CXCR4 inhibitor AMD3100 or siCXCR7 (p < 0.05), suggesting this cell function was partially regulated by CXCL12/CXCR4 and CXCL12/CXCR7 signal pathways. Our study demonstrated that monomeric CXCL12 was the fundamental form, which played important roles in endothelial progenitor cells' proliferation, migration, and tube-formation.

The Therapeutic Value of Bone Marrow-Derived Endothelial Progenitor Cell Transplantation after Intracerebral Hemorrhage in Rats

Aims

To study the effect of endothelial progenitor cell (EPC) treatment on intracerebral hemorrhage (ICH) in rats and elucidate possible mechanisms.

Methods

The rats were randomly divided into three groups: (1) EPC group: ICH + EPC, (2) phosphate-buffered saline group: ICH + PBS, and (3) sham group. EPCs were transplanted intravenously 6 h after ICH. Modified neurological severity score was used to evaluate neurological function. Blood–brain barrier (BBB) integrity was evaluated. Dead cells, inflammatory cytokines, and neuroprotective cytokines were assessed to investigate possible mechanisms.

Results

The animals in the EPC group showed significant improvement in neurological function at 48 h, 72 h, and 7 days after ICH, compared with those in the PBS group. EPC transplantation significantly reduced brain edema and the number of dead cells in the hematoma boundary areas. The intensity of Evans Blue was decreased, and expression levels of zonula occluden-1 and claudin-5 were increased in the EPC group. Proinflammatory cytokines, including interferon-γ, IL-6, and TNF-α, were decreased, whereas anti-inflammatory cytokines, including transforming growth factor-β1 and IL-10, were increased in the EPC group. In addition, expression levels of brain-derived neurotrophic factor, vascular endothelial growth factor, and neurotrophic growth factor were increased following transplantation of EPCs.

Conclusion

EPC transplantation could improve neurological function of ICH rats. The protective effect may be mediated by promotion of neuroprotective cytokine secretion, restoration of the BBB, reduction of cell death, and the decrease in inflammation.

Rehabilitation Treatment and Progress of Traumatic Brain Injury Dysfunction

Traumatic brain injury (TBI) is a major cause of chronic disability. Worldwide, it is the leading cause of disability in the under 40s. Behavioral problems, mood, cognition, particularly memory, attention, and executive function are commonly impaired by TBI. Spending to assist, TBI survivors with disabilities are estimated to be costly per year. Such impaired functional outcomes following TBI can be improved via various rehabilitative approaches. The objective of the present paper is to review the current rehabilitation treatment of traumatic brain injury in adults.

Perinatal Brain Injury As a Consequence of Preterm Birth and Intrauterine Inflammation: Designing Targeted Stem Cell Therapies

Chorioamnionitis is a major cause of preterm birth and brain injury. Bacterial invasion of the chorion and amnion, and/or the placenta, can lead to a fetal inflammatory response, which in turn has significant adverse consequences for the developing fetal brain. Accordingly, there is a strong causal link between chorioamnionitis, preterm brain injury and the pathogenesis of severe postnatal neurological deficits and cerebral palsy. Currently there are no treatments to protect or repair against brain injury in preterm infants born after pregnancy compromised by intrauterine infection. This review describes the injurious cascade of events in the preterm brain in response to a severe fetal inflammatory event. We will highlight specific periods of increased vulnerability, and the potential effects of therapeutic intervention with cell-based therapies. Many clinical trials are underway to investigate the efficacy of stem cells to treat patients with cerebral palsy. Stem cells, obtained from umbilical cord tissue and cord blood, normally discarded after birth, are emerging as a safe and potentially effective therapy. It is not yet known, however, which stem cell type(s) are the most efficacious for administration to preterm infants to treat brain injury-mediated inflammation. Individual stem cell populations found in cord blood and tissue, such as mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs), have a number of potential benefits that may specifically target preterm inflammatory-induced brain injury. MSCs have strong immunomodulatory potential, protecting against global and local neuroinflammatory cascades triggered during infection to the fetus. EPCs have angiogenic and vascular reparative qualities that make them ideal for neurovascular repair. A combined therapy using both MSCs and EPCs to target inflammation and promote angiogenesis for re-establishment of vital vessel networks is a treatment concept that warrants further investigation.

Hypoxia Response Element-Regulated MMP-9 Promotes Neurological Recovery via Glial Scar Degradation and Angiogenesis in Delayed Stroke

Matrix metalloproteinase 9 (MMP-9) plays a beneficial role in the delayed phase of middle cerebral artery occlusion (MCAO). However, the mechanism is obscure. Here, we constructed hypoxia response element (HRE)-regulated MMP-9 to explore its effect on glial scars and neurogenesis in delayed ischemic stroke. Adult male Institute of Cancer Research (ICR) mice underwent MCAO and received a stereotactic injection of lentivirus carrying HRE-MMP-9 or normal saline (NS)/lentivirus-GFP 7 days after ischemia. We found that HRE-MMP-9 improved neurological outcomes, reduced ischemia-induced brain atrophy, and degraded glial scars (p < 0.05). Furthermore, HRE-MMP-9 increased the number of microvessels in the peri-infarct area (p < 0.001), which may have been due to the accumulation of endogenous endothelial progenitor cells (EPCs) in the peri-infarct area after glial scar degradation. Finally, HRE-MMP-9 increased the number of bromodeoxyuridine-positive (BrdU⁺)/NeuN⁺ cells and the expression of PSD-95 in the peri-infarct area (p < 0.01). These changes could be blocked by vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor SU5416 and MMP-9 inhibitor 2-[[(4-phenoxyphenyl)sulfonyl]methyl]-thiirane (SB-3CT). Our results provided a novel mechanism by which glial scar degradation and vascular endothelial growth factor (VEGF)/VEGFR2-dependent angiogenesis may be key procedures for neurological recovery in delayed ischemic stroke after HRE-MMP-9 treatment. Therefore, HRE-MMP-9 overexpression in the delayed ischemic brain is a promising approach for neurological recovery.

A Novel CXCR4 antagonist enhances angiogenesis via modifying the ischaemic tissue environment

Endothelial progenitor cells (EPCs) play a capital role in angiogenesis via directly participating in neo-vessel formation and secreting pro-angiogenic factors. Stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4 play a critical role in the retention and quiescence of EPCs within its niche in the bone marrow. Disturbing the interaction between SDF-1 and CXCR4 is an effective strategy for EPC mobilization. We developed a novel CXCR4 antagonist P2G, a mutant protein of SDF-1β with high antagonistic activity against CXCR4 and high potency in enhancing ischaemic angiogenesis and blood perfusion. However, its direct effects on ischaemic tissue remain largely unknown. In this study, P2G was found to possess a robust capability to promote EPC infiltration and incorporation in neo-vessels, enhance the expression and function of pro-angiogenic factors, such as SDF-1, vascular endothelial growth factor and matrix metalloprotein-9, and activate cell signals involved in angiogenesis, such as proliferating cell nuclear antigen, protein kinase B (Akt), extracellular regulated protein kinases and mammalian target of rapamycin, in ischaemic tissue. Moreover, P2G can attenuate fibrotic remodelling to facilitate the recovery of ischaemic tissue. The capability of P2G in direct augmenting ischaemic environment for angiogenesis suggests that it is a potential candidate for the therapy of ischaemia diseases.

Intravenously Transplanted Human Bone Marrow Endothelial Progenitor Cells Engraft Within Brain Capillaries, Preserve Mitochondrial Morphology, and Display Pinocytotic Activity Toward Blood-Brain Barrier Repair in Ischemic Stroke Rats

Stroke is a life-threatening disease with limited therapeutic options. Cell therapy has emerged as an experimental stroke treatment. Blood-brain barrier (BBB) impairment is a key pathological manifestation of ischemic stroke, and barrier repair is an innovative target for neurorestoration in stroke. Here, we evaluated via electron microscopy the ability of transplanted human bone marrow endothelial progenitor cells (hBMEPCs) to repair the BBB in adult Sprague-Dawley rats subjected to transient middle cerebral artery occlusion (tMCAO). β-galactosidase prelabeled hBMEPCs were intravenously transplanted 48 hours post-tMCAO. Ultrastructural analysis of microvessels in nontransplant stroke rats revealed typical BBB pathology. At 5 days post-transplantation with hBMEPCs, stroke rats displayed widespread vascular repair in bilateral striatum and motor cortex, characterized by robust cell engraftment within capillaries. hBMEPC transplanted stroke rats exhibited near normal morphology of endothelial cells (ECs), pericytes, and astrocytes, without detectable perivascular edema. Near normal morphology of mitochondria was also detected in ECs and perivascular astrocytes from transplanted stroke rats. Equally notable, we observed numerous pinocytic vesicles within engrafted cells. Robust engraftment and intricate functionality of transplanted hBMEPCs likely abrogated stroke-altered vasculature. Preserving mitochondria and augmenting pinocytosis in cell-based therapeutics represent a new neurorestorative mechanism in BBB repair for stroke. Stem Cells 2017;35:1246-1258.

Endothelial Colony Forming Cells (ECFCs) in murine AKI - implications for future cell-based therapies

Background

In recent years, early Endothelial Progenitor Cells (eEPCs) have been proven as effective tool in murine ischemic AKI and in diabetic nephropathy. The mechanisms of eEPC-mediated vasoprotection have been elucidated in detail. Besides producing a diverse range of humoral factors, the cells also act by secreting vasomodulatory microvesicles. Only few data in contrast have been published about the role of so-called Endothelial Colony Forming Cells (ECFCs - late EPCs) in ischemic AKI. We thus aimed to investigate ECFC effects on postischemic kidney function over several weeks. Our special interest focused on endothelial-to-mesenchymal transition (EndoMT), peritubular capillary density (PTCD), endothelial alpha-Tubulin (aT - cytoskeletal integrity), and endothelial p62 (marker of autophagocytic flux).

Methods

Eight to twelve weeks old male C57Bl/6 N mice were subjected to bilateral renal pedicle clamping for 35 or 45 min, respectively. Donor-derived syngeneic ECFCs (0.5 × 10⁶) were i.v. injected at the end of ischemia. Animals were analyzed 1, 4 and 6 weeks later.

Results

Cell therapy improved kidney function exclusively at week 1 (35 and 45 min). Ischemia-induced fibrosis was diminished in all experimental groups by ECFCs, while PTCD loss remained unaffected. Significant EndoMT was detected in only two of 6 groups (35 min, week 4 and 45 min, week 6), ECFCs reduced EndoMT only in the latter. Endothelial aT declined under almost all experimental conditions and these effects were further aggravated by ECFCs. p62 was elevated in endothelial cells, more so after 45 than after 35 min of ischemia. Cell therapy did not modulate p62 abundances at any time point.

Conclusion

A single dose of ECFCs administered shortly post-ischemia is capable to reduce interstitial fibrosis in the mid- to long-term whereas excretory dysfunction is improved only in a transient manner. There are certain differences in renal outcome parameters between eEPCs and ECFC. The latter do not prevent animals from peritubular capillary loss and they also do not further elevate endothelial p62. We conclude that differences between eEPCs and ECFCs result from certain mechanisms by which the cells act around and within vessels. Overall, ECFC treatment was not as efficient as eEPC therapy in preventing mice from ischemia-induced mid- to long-term damage.

Cold water swimming pretreatment reduces cognitive deficits in a rat model of traumatic brain injury

A moderate stress such as cold water swimming can raise the tolerance of the body to potentially injurious events. However, little is known about the mechanism of beneficial effects induced by moderate stress. In this study, we used a classic rat model of traumatic brain injury to test the hypothesis that cold water swimming preconditioning improved the recovery of cognitive functions and explored the mechanisms. Results showed that after traumatic brain injury, pre-conditioned rats (cold water swimming for 3 minutes at 4°C) spent a significantly higher percent of times in the goal quadrant of cold water swim, and escape latencies were shorter than for non-pretreated rats. The number of circulating endothelial progenitor cells was significantly higher in pre-conditioned rats than those without pretreatment at 0, 3, 6 and 24 hours after traumatic brain injury. Immunohistochemical staining and Von Willebrand factor staining demonstrated that the number of CD34⁺ stem cells and new blood vessels in the injured hippocampus tissue increased significantly in pre-conditioned rats. These data suggest that pretreatment with cold water swimming could promote the proliferation of endothelial progenitor cells and angiogenesis in the peripheral blood and hippocampus. It also ameliorated cognitive deficits caused by experimental traumatic brain injury.

Modification of Bone Marrow Stem Cells for Homing and Survival During Cerebral Ischemia

Over the last decade, major advances have been made in stem cell-based therapy for ischemic stroke, which is one of the leading causes of death and disability worldwide. Various stem cells from bone marrow, such as mesenchymal stem cells (MSCs), hematopoietic stem cells (HSCs), and endothelial progenitor cells (EPCs), have shown therapeutic potential for stroke. Concomitant with these exciting findings are some fundamental bottlenecks that must be overcome in order to accelerate their clinical translation, including the low survival and engraftment caused by the harsh microenvironment after transplantation. In this chapter, strategies such as gene modification, hypoxia/growth factor preconditioning, and biomaterial-based methods to improve cell survival and homing are summarized, and the potential strategies for their future application are also discussed.

Electroacupuncture modulates stromal cell-derived factor-1α expression and mobilization of bone marrow endothelial progenitor cells in focal cerebral ischemia/reperfusion model rats

Stromal cell-derived factor-1α(SDF-1α) plays a crucial role in regulating the mobilization, migration and homing of endothelial progenitor cells(EPCs). Electroacupuncture(EA), a modern version of Traditional Chinese Medicine, can improve neurological recovery and angiogenesis in cerebral ischemic area. This study aimed to investigate the effects of electroacupuncture(EA) on the mobilization and migration of bone marrow EPCs and neurological functional recovery in rats model after focal cerebral ischemia/reperfusion and the potentially involved mechanisms. Sprague-Dawley rats received filament occlusion of the right middle cerebral artery for 2h followed by reperfusion for 12h, 1d, 2d, 3d, 7d respectively. Rats were randomly divided into sham group, model group and EA group. After 2h of the reperfusion, EA was given at the "Baihui" (GV 20)/Siguan ("Hegu" (LI 4)/"Taichong" (LR 3)) acupoints in the EA group. Modified neurological severity score (mNSS) was used to assess the neurological functional recovery. EPCs number and SDF-1α level in bone marrow(BM) and peripheral blood(PB) were detected by using fluorescence-activated cell sorting (FACS) analysis and quantitative real time polymerase chain reaction (qRT-PCR) respectively. An mNSS test showed that EA treatment significantly improved the neurological functional outcome. EPCs number in PB and BM were obviously increased in the EA group. After cerebral ischemia, the SDF-1α level was decreased in BM while it was increased in PB, which implied a gradient of SDF-1α among BM and PB after ischemia. It suggested that the forming of SDF-1α concentration gradient can induce the mobilization and homing of EPCs. Eletroacupuncture as a treatment can accelerate and increase the forming of SDF-1α concentration gradient to further induce the mobilization of EPCs and angiogenesis in ischemic brain and improve the neurological function recovery.

Erythropoietin Stimulates Endothelial Progenitor Cells to Induce Endothelialization in an Aneurysm Neck After Coil Embolization by Modulating Vascular Endothelial Growth Factor

: This study explored a new approach to enhance aneurysm (AN) neck endothelialization via erythropoietin (EPO)-induced endothelial progenitor cell (EPC) stimulation. Results suggest that EPO enhanced the endothelialization of a coiled embolization AN neck by stimulating EPCs via vascular endothelial growth factor modulation. Thus, the promotion of endothelialization with EPO provides an additional therapeutic option for preventing the recurrence of ANs. Endovascular coil embolization is an attractive therapy for cerebral ANs, but recurrence is a main problem affecting long-term outcomes. In this study, we explored a new approach to enhance AN neck endothelialization via EPO-induced EPC stimulation. Ninety adult male Sprague-Dawley rats were selected for an in vivo assay, and 60 of them underwent microsurgery to create a coiled embolization AN model. The animals were treated with EPO, and endothelial repair was assessed via flow cytometry, immunofluorescence, electronic microscopy, cytokine detection, and routine blood work. EPO improved the viability, migration, cytokine modulation, and gene expression of bone marrow-derived EPCs and the results showed that EPO increased the number of circulating EPCs and improved endothelialization compared with untreated rats (p < .05). EPO had no significant effect on the routine blood work parameters. In addition, the immunofluorescence analysis showed that the number of KDR(+) cells in the AN neck was elevated in the EPO-treated group (p < .05). Further study demonstrated that EPO promoted EPC viability and migration in vitro. The effects of EPO may be attributed to the modulation of vascular endothelial growth factor (VEGF). In particular, EPO enhanced the endothelialization of a coiled embolization AN neck by stimulating EPCs via VEGF modulation. Thus, the promotion of endothelialization with EPO provides an additional therapeutic option for preventing the recurrence of ANs.

SIGNIFICANCE

Erythropoietin (EPO) is involved in erythropoiesis and related conditions and is reported to enhance stem-cell mobilization from bone marrow while elevating stem-cell viability and function. In this study, EPO was also found to stimulate endothelial progenitor cells to induce the endothelialization of a coiled embolic aneurysm neck via vascular endothelial growth factor modulation. Endothelialization induction provides an additional therapeutic opportunity during vascular inner layer repair and remodeling. The results provide important information on the unique role EPO plays during vascular repair and remodeling.

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.

Postischemic microvasculopathy and endothelial progenitor cell-based therapy in ischemic AKI: update and perspectives

Acute kidney injury (AKI) dramatically increases mortality of hospitalized patients. Incidences have been increased in recent years. The most frequent cause is transient renal hypoperfusion or ischemia which induces significant tubular cell dysfunction/damage. In addition, two further events take place: interstitial inflammation and microvasculopathy (MV). The latter evolves within minutes to hours postischemia and may result in permanent deterioration of the peritubular capillary network, ultimately increasing the risk for chronic kidney disease (CKD) in the long term. In recent years, our understanding of the molecular/cellular processes responsible for acute and sustained microvasculopathy has increasingly been expanded. The methodical approaches for visualizing impaired peritubular blood flow and increased vascular permeability have been optimized, even allowing the depiction of tissue abnormalities in a three-dimensional manner. In addition, endothelial dysfunction, a hallmark of MV, has increasingly been recognized as an inductor of both vascular malfunction and interstitial inflammation. In this regard, so-called regulated necrosis of the endothelium could potentially play a role in postischemic inflammation. Endothelial progenitor cells (EPCs), represented by at least two major subpopulations, have been shown to promote vascular repair in experimental AKI, not only in the short but also in the long term. The discussion about the true biology of the cells continues. It has been proposed that early EPCs are most likely myelomonocytic in nature, and thus they may simply be termed proangiogenic cells (PACs). Nevertheless, they reliably protect certain types of tissues/organs from ischemia-induced damage, mostly by modulating the perivascular microenvironment in an indirect manner. The aim of the present review is to summarize the current knowledge on postischemic MV and EPC-mediated renal repair.

Neuroprotective effects of systemic cerebral endothelial cell transplantation in a rat model of cerebral ischemia

Human cerebral microvascular endothelial cell line (hCMEC)/D3 cells, which are from a stable clonal cell line of human immortalized cerebral endothelial cells, were intra-arterially transplanted through the common carotid artery in a rat model of photochemical-induced cerebral ischemia. Their therapeutic effects on infarct size, blood-brain barrier (BBB) breakdown, and outcome were examined. The hCMEC/D3 cells were genetically modified with the firefly luciferase gene for in vivo imaging post-transplantation. Transplanted hCMEC/D3 cells were identified in the infarcted brain by bioluminescence imaging at 1 day after transplantation. Compared with the control group, the hCMEC/D3-transplanted group showed reduced infarct size on day 3, reduced Evans blue dye leakage on day 1 indicating decreased BBB breakdown, and early recovery from Rotarod test neurological deficits. The hCMEC/D3-transplanted group also showed decreased levels of matrix metalloproteinase (MMP)-9, which were inversely correlated with TIMP-1 levels on post-transplantation days 1 and 3. The expression of tumor necrosis factor-α and interleukin-1β were markedly diminished in the hCMEC/D3-transplanted group compared with controls. The systemically transplanted cells selectively migrated and integrated into the ischemically lesioned area, which accelerated neurological recovery. This new cerebral endothelial cell-based therapy may hold promise for clinical trials in patients with ischemic stroke.