Postischemic IGF-1 gene transfer promotes neurovascular regeneration after experimental stroke

The Effect of Leukocyte- and Platelet-Rich Fibrin on Central and Peripheral Nervous System Neurons-Implications for Biomaterial Applicability

Leukocyte- and Platelet-Rich Fibrin (L-PRF) is a second-generation platelet concentrate that is prepared directly from the patient's own blood. It is widely used in the field of regenerative medicine, and to better understand its clinical applicability we aimed to further explore the biological properties and effects of L-PRF on cells from the central and peripheral nervous system. To this end, L-PRF was prepared from healthy human donors, and confocal, transmission, and scanning electron microscopy as well as secretome analysis were performed on these clots. In addition, functional assays were completed to determine the effect of L-PRF on neural stem cells (NSCs), primary cortical neurons (pCNs), and peripheral dorsal root ganglion (DRG) neurons. We observed that L-PRF consists of a dense but porous fibrin network, containing leukocytes and aggregates of activated platelets that are distributed throughout the clot. Antibody array and ELISA confirmed that it is a reservoir for a plethora of growth factors. Key molecules that are known to have an effect on neuronal cell functions such as brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), vascular endothelial growth factor (VEGF), and platelet-derived growth factor (PDGF) were slowly released over time from the clots. Next, we found that the L-PRF secretome had no significant effect on the proliferative and metabolic activity of NSCs, but it did act as a chemoattractant and improved the migration of these CNS-derived stem cells. More importantly, L-PRF growth factors had a detrimental effect on the survival of pCNs, and consequently, also interfered with their neurite outgrowth. In contrast, we found a positive effect on peripheral DRG neurons, and L-PRF growth factors improved their survival and significantly stimulated the outgrowth and branching of their neurites. Taken together, our study demonstrates the positive effects of the L-PRF secretome on peripheral neurons and supports its use in regenerative medicine but care should be taken when using it for CNS applications.

Relationship between insulin-like growth factor-1 and cerebral small vessel disease and its mechanisms: advances in the field

Insulin-like growth factor-1 (IGF-1) is an active polypeptide protein that closely resembles the structural sequence of insulin and is involved in a variety of metabolic processes in the body. Decreased IGF-1 circulation levels are associated with an increased risk of stroke and a poorer prognosis, but the relationship with cerebral small vessel disease (cSVD) is unclear. Some studies found that the level of IGF-1 in patients with cSVD was significantly reduced, but the clinical significance and underlying mechanisms are unknown. This article reviews the correlation between IGF-1 and cerebrovascular disease and explores the potential relationship and mechanism between IGF-1 and cSVD.

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

Analysis and identification of key anti-inflammatory molecules in Eerdun Wurile and exploration of their mechanism of action in microglia

Ethnomedicine Eerdun Wurile (EW) can significantly promote poststroke neuro-recovery through modulation of microglia polarization. Fraction 4-6 (F4-6) isolated from EW via serial fractionation inhibits the expression of pro-inflammatory genes in LPS stimulated microglia. However, the key active molecules of F4-6 have not been identified. Herein, we identified alantolactone (Ala) and dehydrodiisoeugenol (Deh) as the active anti-inflammatory components of F4-6 by UPLC-qTof MS analysis. We confirmed that, F4-6, Ala, Deh and mixture of Ala and Deh (Mix) downregulate the expression of several pro-inflammatory genes including Ccl2, Cox2 and Il6 in LPS-treated microglia in a similar pattern. At the same time upregulate the expression of anti-inflammatory genes including Hmox1, Tgfβ, Igf1 and Creb1. Moreover, the conditioned culture media obtained from F4-6 treated microglia significantly enhanced proliferation of N2a cells, and promoted neurite outgrowth possibly through upregulation of Nefh and Dlg4. Mechanistically, F4-6 strongly downregulated the expression of NF-κB p65, while also inhibiting the nuclear translocation of p65, leading to the suppression of transcription of pro-inflammatory genes initiated by NF-κB. Collectively, our data identified and quantified the key chemicals of EW and provide insights into the optimization of the herbal composition for neuroprotection.

Interactions of Glutamate and Gamma Amino Butyric Acid with the Insulin-like growth factor system in Traumatic Brain Injury (TBI) and/or Cardiovascular Accidents (CVA or stroke): A systematic review

The brain maintains homeostasis of neural excitation in part through the receptor-mediated signaling of Glutamate (Glu) and Gamma Amino Butyric Acid (GABA), but localized injuries cause cellular release of excess Glu leading to neurotoxicity. The literature strongly supports the role of Insulin-like growth factor-1 (IGF-1) in adult brain neuroprotection and repair, and research supporting the existence of molecular interactions between Glu, GABA, and IGF-1 in vitro and in normal animals raises the question of whether and/or how the Glu/GABA system interacts with IGF-1 post-injury. This systematic review was undertaken to explore works addressing this question among adults with a history of traumatic brain injury (TBI) and/or cerebrovascular accident (CVA; stroke). The literature was searched for human and animal studies and only four animal papers met inclusion criteria. The SYRCLE criteria was used to evaluate risk of bias; results varied between categories and papers. All the included studies, one on TBI and three on stroke, supported the molecular relationship between the excitatory and IGF-1 systems; two studies provided direct, detailed molecular evidence. The results point to the importance of research on the role of this protective system in pathological brain injury; a hypothetical proposal for future studies is presented.

Lentivirus- or AAV-mediated gene therapy interventions in ischemic stroke: A systematic review of preclinical in vivo studies

Due to the limited therapeutic options after ischemic stroke, gene therapy has emerged as a promising choice, especially with recent advances in viral vector delivery systems. Therefore, we aimed to provide the current state of the art of lentivirus (LV) and adeno-associated virus (AAV) mediated gene interventions in preclinical ischemic stroke models. A systematic analysis including qualitative and quantitative syntheses of studies published until December 2020 was performed. Most of the 87 selected publications used adult male rodents and the preferred stroke model was transient middle cerebral artery occlusion. LV and AAV vectors were equally used for transgene delivery, however loads of AAVs were higher than LVs. Serotypes having broad cell tropism, the use of constitutive promoters, and virus delivery before the stroke induction via stereotaxic injection in the cortex and striatum were preferred in the analyzed studies. The meta-analysis based on infarct volume as the primary outcome confirmed the efficacy of the preclinical interventions. The quality assessment exposed publication bias and setbacks in regard to risks of bias and study relevance. The translational potential could increase by using specific cell targeting, post-stroke interventions, non-invasive systematic delivery, and use of large animals.

Therapeutic potential of neurotrophic factors in Alzheimer's Disease

INTRODUCTION

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia among the elderly population. AD is accompanied with the dysregulation of specific neurotrophic factors (NTFs) and their receptors, which plays a critical role in neuronal degeneration. NTFs are small proteins with therapeutic potential for human neurodegenerative diseases. These growth factors are categorized into four families: neurotrophins, neurokines, the glial cell line-derived NTF family of ligands, and the newly discovered cerebral dopamine NTF/mesencephalic astrocyte-derived NTF family. NTFs are capable of preventing cell death in degenerative conditions and can increase the neuronal growth and function in these disorders. Nevertheless, the adverse side effects of NTFs delivery and poor diffusion of these factors in the brain restrict the efficacy of NTFs therapy in clinical situations.

MATERIALS AND METHODS

In this review, we focus on the current advances in the use of NTFs to treat AD and summarize previous experimental and clinical studies for supporting the protective and therapeutic effects of these factors.

CONCLUSION

Based on reports, NTFs are considered as new and promising candidates for treating AD and AD-associated cognitive impairment.

Preclinical and clinical evidence of IGF-1 as a prognostic marker and acute intervention with ischemic stroke

Ischemic strokes are highly prevalent in the elderly population and are a leading cause of mortality and morbidity worldwide. The risk of ischemic stroke increases in advanced age, corresponding with a noted decrease in circulating insulin growth factor-1 (IGF-1). IGF-1 is a known neuroprotectant involved in embryonic development, neurogenesis, neurotransmission, cognition, and lifespan. Clinically, several studies have shown that reduced levels of IGF-1 correlate with increased mortality rate, poorer functional outcomes, and increased morbidities following an ischemic stroke. In animal models of ischemia, administering exogenous IGF-1 using various routes of administration (intranasal, intravenous, subcutaneous, or topical) at various time points prior to and following insult attenuates neurological damage and accompanying behavioral changes caused by ischemia. However, there are some contrasting findings in select clinical and preclinical studies. This review discusses the role of IGF-1 as a determinant factor of ischemic stroke outcomes, both within the clinical settings and preclinical animal models. Furthermore, the review provides insight on the role of IGF-1 in mechanisms and cellular processes that contribute to stroke damage.

Hypothesizing Nutrigenomic-Based Precision Anti-Obesity Treatment and Prophylaxis: Should We Be Targeting Sarcopenia Induced Brain Dysfunction?

Background: The United States Centers for Disease Control and Prevention (CDC) estimates a total obesity rate of 30% for 12 states and a 20% obesity rate nationwide. The obesity epidemic continues to increase in spite of preventative measures undertaken worldwide. Pharmacological treatments promise to reduce total fat mass. However, medications may have significant side effects and can be potentially fatal. Data Retrieval: This brief review, based on a PUBMED search of the key terms "Obesity" and" Sarcopenia," will present evidence to corroborate the existence of Reward Deficiency Syndrome (RDS) in obesity and the involvement of catecholaminergic pathways in substance seeking behavior, particularly as it relates to carbohydrates cravings. Expert Opinion: The genetic basis and future genetic testing of children for risk of aberrant generalized craving behavior are considered a prevention method. Here we present evidence supporting the use of precursor amino acid therapy and modulation of enkephalinase, MOA, and COMT inhibition in key brain regions. Such treatments manifest in improved levels of dopamine/norepinephrine, GABA, serotonin, and enkephalins. We also present evidence substantiating insulin sensitivity enhancement via Chromium salts, which affect dopamine neuronal synthesis regulation. We believe our unique combination of natural ingredients will influence many pathways leading to the promotion of well-being and normal healthy metabolic functioning. Sarcopenia has been shown to reduce angiogenesis and possible cerebral blood flow. Exercise seems to provide a significant benefit to overcome this obesity-promoting loss of muscle density. Conclusion: Utilization of proposed nutrigenomic formulae based on coupling genetic obesity risk testing promotes generalized anti-craving of carbohydrates and can inhibit carbohydrate bingeing, inducing significant healthy fat loss and relapse prevention.

Microglia as the Critical Regulators of Neuroprotection and Functional Recovery in Cerebral Ischemia

Microglial activation is considered as the critical pathogenic event in diverse central nervous system disorders including cerebral ischemia. Proinflammatory responses of activated microglia have been well reported in the ischemic brain and neuroinflammatory responses of activated microglia have been believed to be the potential therapeutic strategy. However, despite having proinflammatory roles, microglia can have significant anti-inflammatory roles and they are associated with the production of growth factors which are responsible for neuroprotection and recovery after ischemic injury. Microglia can directly promote neuroprotection by preventing ischemic infarct expansion and promoting functional outcomes. Indirectly, microglia are involved in promoting anti-inflammatory responses, neurogenesis, and angiogenesis in the ischemic brain which are crucial pathophysiological events for ischemic recovery. In fact, anti-inflammatory cytokines and growth factors produced by microglia can promote neuroprotection and attenuate neurobehavioral deficits. In addition, microglia regulate phagocytosis, axonal regeneration, blood-brain barrier protection, white matter integrity, and synaptic remodeling, which are essential for ischemic recovery. Microglia can also regulate crosstalk with neurons and other cell types to promote neuroprotection and ischemic recovery. This review mainly focuses on the roles of microglia in neuroprotection and recovery following ischemic injury. Furthermore, this review also sheds the light on the therapeutic potential of microglia in stroke patients.

Research progress of IGF-1 and cerebral ischemia

Cerebral ischemic disease is a group of diseases that cause insufficient blood supply to the cerebrum, cerebellum or brain stem for different reasons, resulting in corresponding nervous system symptoms. Cardiovascular disease is the leading cause of death in the world. Among them, the death caused by cerebral ischemia accounts for the vast majority, and it is one of the fatal diseases in the middle-aged and elderly at present. Epidemiologic studies have projected increasing mortality due to cardiovascular disease worldwide (about 23.3 million people by 2030) because of the aging population. However, related studies have shown that insulin-like growth factor I (IGF-1) is a multifunctional cell proliferation regulator. It plays an important role in cerebral ischemia. It is effective in promoting cell differentiation, proliferation and individual development. Studies have shown that IGF-1 signaling pathway is a key pathway controlling cell growth and survival. There may be five mechanisms in cerebral ischemia: prevention of intracellular calcium overload, inhibition of the upregulation of nNOS, IGF-1upregulations activating HIF-1α, regulation of Bcl-2 to resist apoptosis, and enhancement of vascular endothelial function. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3)/Ca2+. IGF-1 plays an important role in cerebral ischemia and myocardial ischemia, mainly by activating downstream of IGF-1, controlling cell death and differentiation or transcription work, improving the function of heart muscle cells, reducing the myocardial cell apoptosis induced by myocardial infarction, regulating endogenous protection and restoration of cerebral ischemia injury, thus protecting cerebral and myocardial injury. Related studies have shown that bcl-2 exerts great influence on both cerebral ischemia and myocardial ischemia. Therefore, the relevant pathways and targets of cerebral ischemia and myocardial ischemia and the role of IGF-1 in protecting the heart are reviewed in this paper.

Neurogenesis After Stroke: A Therapeutic Perspective

Stroke is a major cause of death and disability worldwide. Yet therapeutic strategies available to treat stroke are very limited. There is an urgent need to develop novel therapeutics that can effectively facilitate functional recovery. The injury that results from stroke is known to induce neurogenesis in penumbra of the infarct region. There is considerable interest in harnessing this response for therapeutic purposes. This review summarizes what is currently known about stroke-induced neurogenesis and the factors that have been identified to regulate it. Additionally, some key studies in this field have been highlighted and their implications on future of stroke therapy have been discussed. There is a complex interplay between neuroinflammation and neurogenesis that dictates stroke outcome and possibly recovery. This highlights the need for a better understanding of the neuroinflammatory process and how it affects neurogenesis, as well as the need to identify new mechanisms and potential modulators. Neuroinflammatory processes and their impact on post-stroke repair have therefore also been discussed.

Treatment with Atorvastatin During Vascular Remodeling Promotes Pericyte-Mediated Blood-Brain Barrier Maturation Following Ischemic Stroke

We previously showed that newly formed vessels in ischemic rat brain have high blood-brain barrier (BBB) permeability at 3 weeks after stroke due to a lack of major endothelial tight junction proteins (TJPs), which may exacerbate edema in stroke patients. Atorvastatin was suggested a dose-dependent pro-angiogenic effect and ameliorating BBB permeability beyond its cholesterol-lowering effects. This study examined our hypothesis that, during vascular remodeling after stroke, treatment with atorvastatin could facilitate BBB maturation in remodeling vasculature in ischemic brain. Adult spontaneously hypertensive rats underwent middle cerebral artery occlusion with reperfusion (MCAO/RP). Atorvastatin, at dose of 3 mg/kg, was delivered daily starting at 14 days after MCAO/RP onset for 7 days. The rats were studied at multiple time points up to 8 weeks with multimodal-MRI, behavior tests, immunohistochemistry, and biochemistry. The delayed treatment of atorvastatin significantly reduced infarct size and BBB permeability, restored cerebral blood flow, and improved the neurological outcome at 8 weeks after MCAO/RP. Postmortem studies showed that atorvastatin promoted angiogenesis and stabilized the newly formed vessels in peri-infarct areas. Importantly, atorvastatin facilitated maturation of BBB properties in the new vessels by promoting endothelial tight junction (TJ) formation. Further in vivo and in vitro studies demonstrated that proliferating peri-vascular pericytes expressing neural-glial antigen 2 (NG2) mediated the role of atorvastatin on BBB maturation through regulating endothelial TJ strand formations. Our results suggested a therapeutic potential of atorvastatin in facilitating a full BBB integrity and functional stroke recovery, and an essential role for pericyte-mediated endothelial TJ formation in remodeling vasculature.

Inhibition of LPA5 Activity Provides Long-Term Neuroprotection in Mice with Brain Ischemic Stroke

Stroke is a leading cause of long-term disability in ischemic survivors who are suffering from motor, cognitive, and memory impairment. Previously, we have reported suppressing LPA₅ activity with its specific antagonist can attenuate acute brain injuries after ischemic stroke. However, it is unclear whether suppressing LPA₅ activity can also attenuate chronic brain injuries after ischemic stroke. Here, we explored whether effects of LPA₅ antagonist, TCLPA5, could persist a longer time after brain ischemic stroke using a mouse model challenged with tMCAO. TCLPA5 was administered to mice every day for 3 days, starting from the time immediately after reperfusion. TCLPA5 administration improved neurological function up to 21 days after tMCAO challenge. It also reduced brain tissue loss and cell apoptosis in mice at 21 days after tMCAO challenge. Such long-term neuroprotection of TCLPA5 was associated with enhanced neurogenesis and angiogenesis in post-ischemic brain, along with upregulated expression levels of vascular endothelial growth factor. Collectively, results of the current study indicates that suppressing LPA₅ activity can provide long-term neuroprotection to mice with brain ischemic stroke.

Lineage tracing: technology tool for exploring the development, regeneration, and disease of the digestive system

Lineage tracing is the most widely used technique to track the migration, proliferation, and differentiation of specific cells in vivo. The currently available gene-targeting technologies have been developing for decades to study organogenesis, tissue injury repairing, and tumor progression by tracing the fates of individual cells. Recently, lineage tracing has expanded the platforms available for disease model establishment, drug screening, cell plasticity research, and personalized medicine development in a molecular and cellular biology perspective. Lineage tracing provides new views for exploring digestive organ development and regeneration and techniques for digestive disease causes and progression. This review focuses on the lineage tracing technology and its application in digestive diseases.

Potential Immunotherapeutic Targets on Myeloid Cells for Neurovascular Repair After Ischemic Stroke

Neurological deficits and cognitive dysfunctions caused by acute ischemic stroke pose enormous burden to the stroke families and the communities. Restoration of the normal function of the neurovascular unit following ischemic stroke is critical for improving neurological recovery and cognitive functions after stroke. Recent evidence suggests that the myeloid cells including both the resident microglia and infiltrating monocytes/macrophages and neutrophils are highly plastic in response to the environmental cues. They intimately interact with multiple components of the neurovascular unit in response to the alarmins, danger associated pattern molecules (DAMPs) and other signals released from the ischemic brain. The aim of this review is to discuss the reciprocal interactions between the myeloid cells and the ischemic neurovascular unit during the late repair phase of cerebral ischemic stroke. We also summarize potential immunotherapeutic targets on myeloid cells and new therapeutic approaches targeting myeloid cells, such as cell transplantation, mitochondrial dynamic and extracellular vesicles-based therapy et al to enhance neurovascular repair for better stroke recovery.

Ginsenoside F1 promotes angiogenesis by activating the IGF-1/IGF1R pathway

Ischemic stroke is one of the most lethal and highly disabling diseases that seriously affects the human health and quality of life. A therapeutic angiogenic strategy has been proposed to alleviate ischemia-induced injury by promoting angiogenesis and improving cerebrovascular function in the ischemic regions. The insulin-like growth factor 1 (IGF-1)/insulin-like growth factor 1 receptor (IGF1R) axis is crucial for cerebral angiogenesis and neurogenesis. However, effective drugs that prevent cerebral ischemic injury by inducing cerebral angiogenesis via activation of the IGF1R pathway are lacking. Here, we screened a pro-angiogenic agent ginsenoside F1 (GF1), a ginseng saponin isolated from a traditional Chinese medicine that was widely used in ischemic stroke treatment. It promoted the proliferation, mobility and tube formation of human umbilical vein endothelial cells and human brain microvascular endothelial cells, as well as pericytes recruitment to the endothelial tubes. GF1 stimulated vessel sprouting in the rat arterial ring and facilitated neovascularization in chicken embryo chorioallantoic membrane (CAM). In the in vivo experiments, GF1 rescued the axitinib-induced vascular defect in zebrafish. It also increased the microvessel density (MVD) and improved focal cerebral blood perfusion in the rat middle cerebral artery occlusion (MCAO) model. Mechanism studies revealed that GF1-induced angiogenesis depended on IGF1R activation mediated by the autocrine IGF-1 loop in endothelial cells. Based on our findings, GF1-induced activation of the IGF-1/IGF1R pathway to promote angiogenesis is an effective approach to alleviate cerebral ischemia, and GF1 is a potential agent that improves cerebrovascular function and promotes recovery from ischemic stroke.

Inflammation and neural repair after ischemic brain injury

Stroke causes neuronal cell death and destruction of neuronal circuits in the brain and spinal cord. Injury to the brain tissue induces sterile inflammation triggered by the extracellular release of endogenous molecules, but cerebral inflammation after stroke is gradually resolved within several days. In this pro-resolving process, inflammatory cells adopt a pro-resolving or repairing phenotype in the injured brain, activating endogenous repairing programs. Although the mechanisms involved in the transition from inflammation to neural repair after stroke remain largely unknown to date, some of the mechanisms for inflammation and neural repair have been clarified in detail. This review focuses on the molecular or cellular mechanisms involved in sterile inflammation and neural repair after stroke. This accumulation of evidence may be helpful for speculating about the endogenous repairing mechanisms in the brain and identifying therapeutic targets for improving the functional prognoses of stroke patients.

Pivotal role of innate myeloid cells in cerebral post-ischemic sterile inflammation

Inflammatory responses play a multifaceted role in regulating both disability and recovery after ischemic brain injury. In the acute phase of ischemic stroke, resident microglia elicit rapid inflammatory responses by the ischemic milieu. After disruption of the blood-brain barrier, peripheral-derived neutrophils and mononuclear phagocytes infiltrate into the ischemic brain. These infiltrating myeloid cells are activated by the endogenous alarming molecules released from dying brain cells. Inflammation after ischemic stroke thus typically consists of sterile inflammation triggered by innate immunity, which exacerbates the pathologies of ischemic stroke and worsens neurological prognosis. Infiltrating immune cells sustain the post-ischemic inflammation for several days; after this period, however, these cells take on a repairing function, phagocytosing inflammatory mediators and cellular debris. This time-specific polarization of immune cells in the ischemic brain is a potential novel therapeutic target. In this review, we summarize the current understanding of the phase-dependent role of innate myeloid cells in ischemic stroke and discuss the cellular and molecular mechanisms of their inflammatory or repairing polarization from a therapeutic perspective.

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.

PEGylated insulin-like growth factor-I affords protection and facilitates recovery of lost functions post-focal ischemia

Insulin-like growth factor-I (IGF-I) is involved in the maturation and maintenance of neurons, and impaired IGF-I signaling has been shown to play a role in various neurological diseases including stroke. The aim of the present study was to investigate the efficacy of an optimized IGF-I variant by adding a 40 kDa polyethylene glycol (PEG) chain to IGF-I to form PEG-IGF-I. We show that PEG-IGF-I has a slower clearance which allows for twice-weekly dosing to maintain steady-state serum levels in mice. Using a photothrombotic model of focal stroke, dosing from 3 hrs post-stroke dose-dependently (0.3–1 mg/kg) decreases the volume of infarction and improves motor behavioural function in both young 3-month and aged 22–24 month old mice. Further, PEG-IGF-I treatment increases GFAP expression when given early (3 hrs post-stroke), increases Synaptophysin expression and increases neurogenesis in young and aged. Finally, neurons (P5–6) cultured in vitro on reactive astrocytes in the presence of PEG-IGF-I showed an increase in neurite length, indicating that PEG-IGF-I can aid in sprouting of new connections. This data suggests a modulatory role of IGF-I in both protective and regenerative processes, and indicates that therapeutic approaches using PEG-IGF-I should be given early and where the endogenous regenerative potential is still high.

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

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

Hydrogel-delivered brain-derived neurotrophic factor promotes tissue repair and recovery after stroke

Stroke is the leading cause of adult disability. Systemic delivery of candidate neural repair therapies is limited by the blood-brain barrier and off-target effects. We tested a bioengineering approach for local depot release of BDNF from the infarct cavity for neural repair in chronic periods after stroke. The brain release levels of a hyaluronic acid hydrogel + BDNF were tested in several stroke models in mouse (strains C57Bl/6, DBA) and non-human primate ( Macaca fascicularis) and tracked with MRI. The behavioral recovery effects of hydrogel + BDNF and the effects on tissue repair outcomes were determined. Hydrogel-delivered BDNF diffuses from the stroke cavity into peri-infarct tissue over 3 weeks in two mouse stroke models, compared with 1 week for direct BDNF injection. Hydrogel delivery of BDNF promotes recovery of motor function. Mapping of motor system connections indicates that hydrogel-BDNF induces axonal sprouting within existing cortical and cortico-striatal systems. Pharmacogenetic studies show that hydrogel-BDNF induces the initial migration of immature neurons into the peri-infarct cortex and their long-term survival. In chronic stroke in the non-human primate, hydrogel-released BDNF can be detected up to 2 cm from the infarct, a distance relevant to human functional recovery in stroke. The hydrogel can be tracked by MRI in mouse and primate.

Deleting IGF-1 receptor from forebrain neurons confers neuroprotection during stroke and upregulates endocrine somatotropin

Insulin-like growth factors control numerous processes, namely somatic growth, metabolism and stress resistance, connecting this pathway to aging and age-related diseases. Insulin-like growth factor signaling also impacts on neurogenesis, neuronal survival and structural plasticity. Recent reports demonstrated that diminished insulin-like growth factor signaling confers increased stress resistance in brain and other tissues. To better understand the role of neuronal insulin-like growth factor signaling in neuroprotection, we inactivated insulin-like growth factor type-1-receptor in forebrain neurons using conditional Cre-LoxP-mediated gene targeting. We found that brain structure and function, including memory performance, were preserved in insulin-like growth factor receptor mutants, and that certain characteristics improved, notably synaptic transmission in hippocampal neurons. To reveal stress-related roles of insulin-like growth factor signaling, we challenged the brain using a stroke-like insult. Importantly, when charged with hypoxia-ischemia, mutant brains were broadly protected from cell damage, neuroinflammation and cerebral edema. We also found that in mice with insulin-like growth factor receptor knockout specifically in forebrain neurons, a substantial systemic upregulation of growth hormone and insulin-like growth factor-I occurred, which was associated with significant somatic overgrowth. Collectively, we found strong evidence that blocking neuronal insulin-like growth factor signaling increases peripheral somatotropic tone and simultaneously protects the brain against hypoxic-ischemic injury, findings that may contribute to developing new therapeutic concepts preventing the disabling consequences of stroke.

Grafted Subventricular Zone Neural Stem Cells Display Robust Engraftment and Similar Differentiation Properties and Form New Neurogenic Niches in the Young and Aged Hippocampus

The engraftment and differentiation of alkaline phosphatase-positive neural stem cells (NSCs) expanded from the postnatal subventricular zone (SVZ), 3 months after grafting into the intact young or aged rat hippocampus, were examined. Both young and aged hippocampi supported robust engraftment and similar differentiation of SVZ-NSC graft-derived cells.

As clinical application of neural stem cell (NSC) grafting into the brain would also encompass aged people, critical evaluation of engraftment of NSC graft-derived cells in the aged hippocampus has significance. We examined the engraftment and differentiation of alkaline phosphatase-positive NSCs expanded from the postnatal subventricular zone (SVZ), 3 months after grafting into the intact young or aged rat hippocampus. Graft-derived cells engrafted robustly into both young and aged hippocampi. Although most graft-derived cells pervasively migrated into different hippocampal layers, the graft cores endured and contained graft-derived neurons expressing neuron-specific nuclear antigen (NeuN) and γ-amino butyric acid in both groups. A fraction of migrated graft-derived cells in the neurogenic subgranular zone-granule cell layer also expressed NeuN. Neuronal differentiation was, however, occasionally seen amid graft-derived cells that had migrated into non-neurogenic regions, where substantial fractions differentiated into S-100β+ astrocytes, NG2+ oligodendrocyte progenitors, or Olig2+ putative oligodendrocytes. In both age groups, graft cores located in non-neurogenic regions displayed many doublecortin-positive (DCX+) immature neurons at 3 months after grafting. Analyses of cells within graft cores using birth dating and putative NSC markers revealed that DCX+ neurons were newly born neurons derived from engrafted cells and that putative NSCs persisted within the graft cores. Thus, both young and aged hippocampi support robust engraftment and similar differentiation of SVZ-NSC graft-derived cells. Furthermore, some grafted NSCs retain the “stemness” feature and produce new neurons even at 3 months after grafting, implying that grafting of SVZ-NSCs into the young or aged hippocampus leads to establishment of new neurogenic niches in non-neurogenic regions.

Significance

The results demonstrate that advanced age of the host at the time of grafting has no major adverse effects on engraftment, migration, and differentiation of grafted subventricular zone-neural stem cells (SVZ-NSCs) in the intact hippocampus, as both young and aged hippocampi promoted excellent engraftment, migration, and differentiation of SVZ-NSC graft-derived cells in the present study. Furthermore, SVZ-NSC grafts showed ability for establishing neurogenic niches in non-neurogenic regions, generating new neurons for extended periods after grafting. This phenomenon will be beneficial if these niches can continuously generate new neurons and glia in the grafted hippocampus, as newly generated neurons and glia are expected to improve, not only the microenvironment, but also the plasticity and function of the aged hippocampus. Overall, these results have significance because the potential application of NSC grafting for treatment of neurodegenerative disorders at early stages of disease progression and age-related impairments would mostly involve aged persons as recipients.

Functions and mechanisms of microglia/macrophages in neuroinflammation and neurogenesis after stroke

Microglia/macrophages are the major immune cells involved in the defence against brain damage. Their morphology and functional changes are correlated with the release of danger signals induced by stroke. These cells are normally responsible for clearing away dead neural cells and restoring neuronal functions. However, when excessively activated by the damage-associated molecular patterns following stroke, they can produce a large number of proinflammatory cytokines that can disrupt neural cells and the blood-brain barrier and influence neurogenesis. These effects indicate the important roles of microglia/macrophages in the pathophysiological processes of stroke. However, the modifiable and adaptable nature of microglia/macrophages may also be beneficial for brain repair and not just result in damage. These distinct roles may be attributed to the different microglia/macrophage phenotypes because the M1 population is mainly destructive, while the M2 population is neuroprotective. Additionally, different gene expression signature changes in microglia/macrophages have been found in diverse inflammatory milieus. These biofunctional features enable dual roles for microglia/macrophages in brain damage and repair. Currently, it is thought that the proper inflammatory milieu may provide a suitable microenvironment for neurogenesis; however, detailed mechanisms underlying the inflammatory responses that initiate or inhibit neurogenesis remain unknown. This review summarizes recent progress concerning the mechanisms involved in brain damage, repair and regeneration related to microglia/macrophage activation and phenotype transition after stroke. We also argue that future translational studies should be targeting multiple key regulating molecules to improve brain repair, which should be accompanied by the concept of a "therapeutic time window" for sequential therapies.

Clinical tests of neurotrophic factors for human neurodegenerative diseases, part 1: Where have we been and what have we learned?

Over the past 25years, about 3 dozen clinical reports have been published regarding the safety and possible efficacy of neurotrophic factors in patients with various neurodegenerative diseases. This effort involved a half dozen different neurotrophic factors, using at least 5 different general delivery approaches for ALS (amyolateral sclerosis), peripheral neuropathies, PD (Parkinson's disease) and AD (Alzheimer's disease). While none of these efforts have yet produced efficacy data sufficiently robust or reliable to establish neurotrophic factors as treatments for any human disease, the obstacles encountered and novel information reported, when viewed collectively, provide important insight to help future efforts. Three consistent themes emerge from these publications: (1) unexpected and undesirable side effects, at times serious, have plagued many efforts to deliver neurotrophic factors to humans; (2) the magnitude and consistency of clinical benefit has been disappointing; (3) by far that most consistently proposed reason for the side effects and poor efficacy has been inadequate dosing and delivery. This paper reviews and attempts to synthesize the available data derived from clinical tests of neurotrophic factors for neurodegenerative diseases. The obstacles encountered, the solutions attempted, and the lessons learned are discussed. The vast majority of solutions have involved changes in dosing paradigms and dose levels, which has primarily led to improved safety outcomes. However, lack of adequate efficacy remains a significant issue. While current efforts continue to focus exclusively on still-further changes in dosing parameters, a review of available data argues that it may now be the time to ask whether other, non-dose-related variables should be given more serious consideration as being responsible for the great divide that exists between the robust effects seen in animal models and the relatively weak effects seen in human neurodegenerative patients. Foremost among these appears to be the severe degeneration seen in the majority of patients enrolled in past and current trials testing neurotrophic factors in humans. A companion paper (Bartus and Johnson, 2016), reviews the contemporary data and concludes that compelling empirical evidence already exists for enrolling earlier-stage subjects as likely essential to achieving more robust and reliable benefit.

Neurogenesis in Stroke Recovery

Stroke, resulting from limited blood flow to the brain, is one of the most important causes of morbidity and mortality worldwide. Stroke is classified as ischemic, due to lack of blood flow, or hemorrhagic, due to bleeding. Because 87 % of strokes are classified as ischemic, this type will be the predominant focus of this review. Except for thrombolytic therapy, there is no established treatment to reduce the neurological deficits caused by ischemic stroke. Therefore, it is necessary to develop new therapeutic strategies designed to improve neurological functions after ischemic stroke. Recently, therapies to enhance neurogenesis after ischemic stroke have been investigated. However, these approaches have not led to successful clinical outcomes. This review addresses the pathophysiology of stroke, neurogenesis after stroke, and how to stimulate these processes based on the current literature. Finally, ongoing clinical trials to improve neurological functions after stroke by enhancing neurogenesis are discussed in this review.

Coupling of neurogenesis and angiogenesis after ischemic stroke

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

Pre-existing interleukin 10 in cerebral arteries attenuates subsequent brain injury caused by ischemia/reperfusion

Recurrent stroke is difficult to treat and life threatening. Transfer of anti-inflammatory gene is a potential gene therapy strategy for ischemic stroke. Using recombinant adeno-associated viral vector 1 (rAAV1)-mediated interleukin 10 (IL-10), we investigated whether transfer of beneficial gene into the rat cerebral vessels during interventional treatment for initial stroke could attenuate brain injury caused by recurrent stroke. Male Wistar rats were administered rAAV1-IL-10, rAAV1-YFP, or saline into the left cerebral artery. Three weeks after gene transfer, rats were subjected to occlusion of the left middle cerebral artery (MCAO) for 45 min followed by reperfusion for 24 h. IL-10 levels in serum were significantly elevated 3 weeks after rAAV1-IL-10 injection, and virus in the cerebral vessels was confirmed by in situ hybridization. Pre-existing IL-10 but not YFP decreased the neurological dysfunction scores, brain infarction volume, and the number of injured neuronal cells. AAV1-IL-10 transduction increased heme oxygenase (HO-1) mRNA and protein levels in the infarct boundary zone of the brain. Thus, transduction of the IL-10 gene in the cerebral artery prior to ischemia attenuates brain injury caused by ischemia/reperfusion in rats. This preventive approach for recurrent stroke can be achieved during interventional treatment for initial stroke.

Post-ischemic inflammation regulates neural damage and protection

Post-ischemic inflammation is important in ischemic stroke pathology. However, details of the inflammation process, its resolution after stroke and its effect on pathology and neural damage have not been clarified. Brain swelling, which is often fatal in ischemic stroke patients, occurs at an early stage of stroke due to endothelial cell injury and severe inflammation by infiltrated mononuclear cells including macrophages, neutrophils, and lymphocytes. At early stage of inflammation, macrophages are activated by molecules released from necrotic cells [danger-associated molecular patterns (DAMPs)], and inflammatory cytokines and mediators that increase ischemic brain damage by disruption of the blood–brain barrier are released. After post-ischemic inflammation, macrophages function as scavengers of necrotic cell and brain tissue debris. Such macrophages are also involved in tissue repair and neural cell regeneration by producing tropic factors. The mechanisms of inflammation resolution and conversion of inflammation to neuroprotection are largely unknown. In this review, we summarize information accumulated recently about DAMP-induced inflammation and the neuroprotective effects of inflammatory cells, and discuss next generation strategies to treat ischemic stroke.

Stimulation of cerebral angiogenesis by gene delivery

Angiogenesis, an important process for long term neurological recovery, could be induced by ischemic brain injury. In this chapter, we describe a system to deliver adeno-associated viral (AAV) vector-mediated gene therapy for ischemic stroke. This includes the methods to construct, produce, and purify an AAV vector expressing target gene and an approach to quantify the number of microvessels and capillary density with synchrotron radiation angiography (SRA) imaging.

AAV-mediated targeting of gene expression to the peri-infarct region in rat cortical stroke model

BACKGROUND

For stroke patients the recovery of cognitive and behavioral functions is often incomplete. Functional recovery is thought to be mediated largely by connectivity rearrangements in the peri-infarct region. A method for manipulating gene expression in this region would be useful for identifying new recovery-enhancing treatments.

NEW METHOD

We have characterized a way of targeting adeno-associated virus (AAV) vectors to the peri-infarct region of cortical ischemic lesion in rats 2days after middle cerebral artery occlusion (MCAo).

RESULTS

We used magnetic resonance imaging (MRI) to show that the altered properties of post-ischemic brain tissue facilitate the spreading of intrastriatally injected nanoparticles toward the infarct. We show that subcortical injection of green fluorescent protein-encoding dsAAV7-GFP resulted in transduction of cells in and around the white matter tract underlying the lesion, and in the cortex proximal to the lesion. A similar result was achieved with dsAAV7 vector encoding the cerebral dopamine neurotrophic factor (CDNF), a protein with therapeutic potential.

COMPARISON WITH EXISTING METHODS

Viral vector-mediated intracerebral gene delivery has been used before in rodent models of ischemic injury. However, the method of targeting gene expression to the peri-infarct region, after the initial phase of ischemic cell death, has not been described before.

CONCLUSIONS

We demonstrate a straightforward and robust way to target AAV vector-mediated over-expression of genes to the peri-infarct region in a rat stroke model. This method will be useful for studying the action of specific proteins in peri-infarct region during the recovery process.

Endothelin-1-induced focal cerebral ischemia in the growth hormone/IGF-1 deficient Lewis Dwarf rat

Aging is a major risk factor for cerebrovascular disease. Growth hormone (GH) and its anabolic mediator, insulin-like growth factor (IGF)-1, decrease with advancing age and this decline has been shown to promote vascular dysfunction. In addition, lower GH/IGF-1 levels are associated with higher stroke mortality in humans. These results suggest that decreased GH/IGF-1 level is an important factor in increased risk of cerebrovascular diseases. This study was designed to assess whether GH/IGF-1-deficiency influences the outcome of cerebral ischemia. We found that endothelin-1-induced middle cerebral artery occlusion resulted in a modest but nonsignificant decrease in cerebral infarct size in GH/IGF-1 deficient dw/dw rats compared with control heterozygous littermates and dw/dw rats with early-life GH treatment. Expression of endothelin receptors and endothelin-1-induced constriction of the middle cerebral arteries were similar in the three experimental groups. Interestingly, dw/dw rats exhibited reduced brain edema and less astrocytic infiltration compared with their heterozygous littermates and this effect was reversed by GH-treatment. Because reactive astrocytes are critical for the regulation of poststroke inflammatory processes, maintenance of the blood-brain barrier and neural repair, further studies are warranted to determine the long-term functional consequences of decreased astrocytic activation in GH/IGF-1 deficient animals after cerebral ischemia.

Neurovascular recovery via co-transplanted neural and vascular progenitors leads to improved functional restoration after ischemic stroke in rats

The concept of the “neurovascular unit,” emphasizing the interactions between neural and vascular components in the brain, raised the notion that neural progenitor cell (NPC) transplantation therapy aimed at neural repair may be insufficient for the treatment of ischemic stroke. Here, we demonstrate that enhanced neurovascular recovery via cotransplantation of NPCs and embryonic stem cell-derived vascular progenitor cells (VPCs) in a rat stroke model is correlated with improved functional recovery after stroke. We found that cotransplantation promoted the survival, migration, differentiation, and maturation of neuronal and vascular cells derived from the cotransplanted progenitors. Furthermore, it triggered an increased generation of VEGF-, BDNF-, and IGF1-expressing neural cells derived from the grafted NPCs. Consistently, compared with transplantation of NPCs alone, cotransplantation more effectively improved the neurobehavioral deficits and attenuated the infarct volume. Thus, cotransplantation of NPCs and VPCs represents a more effective therapeutic strategy for the treatment of stroke than transplantation of NPCs alone.

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Neural and vascular progenitor cell cotransplantation therapy for ischemic stroke

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Better neurovascular recovery by cotransplanted progenitor cells in the infarct area

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Better infarction reduction and functional restoration by cotransplantation

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Neurovascular recovery likely mediated by neural production of growth/trophic factors

Increase of circulating miR-223 and insulin-like growth factor-1 is associated with the pathogenesis of acute ischemic stroke in patients

Background

The relationship between circulating microRNA-223 and pathogenesis of acute ischemic stroke is unknown. Here we investigated the roles and possible targets of circulating microRNA-223 in human ischemic stroke within the first 72 hours.

Methods

Blood samples were collected from patients within 72 hours after cerebral ischemia (n = 79) and compared with healthy control samples (n = 75). The level of possible downstream factors of microRNA-223 including insulin-like growth factor-1, insulin-like growth factor-1 receptor and interleukin-6 was examined by ELISA assay. The relationship between the microRNA-223 level and NIHSS scores, TOAST subtypes, and infarct volume was analyzed respectively. In addition, twelve adult male CD-1 mice underwent middle cerebral artery occlusion using the suture technique. Circulating blood and brain tissue in the ischemic ipsilateral hemisphere were collected at 24 hours after middle cerebral artery occlusion. microRNA-223 was detected by real-time polymerase chain reactions.

Results

microRNA-223 levels in the circulating blood of acute ischemic stroke patients were greatly increased compared to the control (p < 0.05). microRNA-223, which were negatively correlated with NIHSS scores (r = −0.531, p < 0.01) and infarct volume (r = −0.265, p = 0.039), was significantly up-regulated in large artery and small artery strokes. The plasma level of insulin-like growth factor-1 was positively associated with that of microRNA-223 (r = 0.205, p = 0.022). Moreover, microRNA-223 in blood and brain were positively correlated (r = 0.834, p < 0.05), and they were up-regulated significantly in mice that underwent middle cerebral artery occlusion (p < 0.05).

Conclusions

Our results suggest that microRNA-223 is associated with acute ischemic stroke and possibly plays a role in stroke through up-regulating growth factor such as insulin-like growth factor-1 gene.

MicroRNA-210 overexpression induces angiogenesis and neurogenesis in the normal adult mouse brain

Angiogenesis and neurogenesis are crucial processes for brain tissue repair and remodeling after brain injury. Current study shows that microRNA-210 (miR-210) promotes vascular endothelial cell migration and tube formation under hypoxia in vitro. Whether miR-210 overexpression promotes focal angiogenesis and neurogenesis in the normal adult brain is unknown. Adult male C57BL/6 mice (n=54) underwent stereotactic injection of a lentiviral vector carrying miR-210 (LV-miR-210). Following 28 days of miR-210 gene transfer, endothelial cell and neural precursor cell proliferation, microvessel density and downstream angiogenic factor were genotyped. miR-210 was highly expressed in neurons, astrocytes and endothelial cells of the LV-miR-210-injected brain hemisphere. The endothelial cell proliferation and the number of newly formed microvessels were greatly increased in the LV-miR-210-treated mice compared with the controls (P<0.05). Neural progenitor cells in the subventricular zone were greatly increased compared with the controls (P<0.05). The data indicate that miR-210 is a key factor at the microRNA level in promoting angiogenesis and neurogenesis, which was associated with local increased vascular endothelial growth factor (VEGF) levels, suggesting that miR-210 may be a potential target for ischemic stroke therapy.

Receptor tyrosine kinase (RTK) signalling in the control of neural stem and progenitor cell (NSPC) development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.

Insulin-like growth factor-1 in CNS and cerebrovascular aging

Insulin-like growth factor-1 (IGF-1) is an important anabolic hormone that decreases with age. In the past two decades, extensive research has determined that the reduction in IGF-1 is an important component of the age-related decline in cognitive function in multiple species including humans. Deficiency in circulating IGF-1 results in impairment in processing speed and deficiencies in both spatial and working memory. Replacement of IGF-1 or factors that increase IGF-1 to old animals and humans reverses many of these cognitive deficits. Despite the overwhelming evidence for IGF-1 as an important neurotrophic agent, the specific mechanisms through which IGF-1 acts have remained elusive. Recent evidence indicates that IGF-1 is both produced by and has important actions on the cerebrovasculature as well as neurons and glia. Nevertheless, the specific regulation and actions of brain- and vascular-derived IGF-1 is poorly understood. The diverse effects of IGF-1 discovered thus far reveal a complex endocrine and paracrine system essential for integrating many of the functions necessary for brain health. Identification of the mechanisms of IGF-1 actions will undoubtedly provide critical insight into regulation of brain function in general and the causes of cognitive decline with age.

Early inhibition of MMP activity in ischemic rat brain promotes expression of tight junction proteins and angiogenesis during recovery

In cerebral ischemia, matrix metalloproteinases (MMPs) have a dual role by acutely disrupting tight junction proteins (TJPs) in the blood-brain barrier (BBB) and chronically promoting angiogenesis. Since TJP remodeling of the neurovascular unit (NVU) is important in recovery and early inhibition of MMPs is neuroprotective, we hypothesized that short-term MMP inhibition would reduce infarct size and promote angiogenesis after ischemia. Adult spontaneously hypertensive rats had a transient middle cerebral artery occlusion with reperfusion. At the onset of ischemia, they received a single dose of the MMP inhibitor, GM6001. They were studied at multiple times up to 4 weeks with immunohistochemistry, biochemistry, and magnetic resonance imaging (MRI). We observed newly formed vessels in peri-infarct regions at 3 weeks after reperfusion. Dynamic contrast-enhanced MRI showed BBB opening in new vessels. Along with the new vessels, pericytes expressed zonula occludens-1 (ZO-1) and MMP-3, astrocytes expressed ZO-1, occludin, and MMP-2, while endothelial cells expressed claudin-5. The GM6001, which reduced tissue loss at 3 to 4 weeks, significantly increased new vessel formation with expression of TJPs and MMPs. Our results show that pericytes and astrocytes act spatiotemporally, contributing to extraendothelial TJP formation, and that MMPs are involved in BBB restoration during recovery. Early MMP inhibition benefits neurovascular remodeling after stroke.

Astrocyte-Specific Overexpression of Insulin-Like Growth Factor-1 Protects Hippocampal Neurons and Reduces Behavioral Deficits following Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) survivors often suffer from long-lasting cognitive impairment that stems from hippocampal injury. Systemic administration of insulin-like growth factor-1 (IGF-1), a polypeptide growth factor known to play vital roles in neuronal survival, has been shown to attenuate posttraumatic cognitive and motor dysfunction. However, its neuroprotective effects in TBI have not been examined. To this end, moderate or severe contusion brain injury was induced in mice with conditional (postnatal) overexpression of IGF-1 using the controlled cortical impact (CCI) injury model. CCI brain injury produces robust reactive astrocytosis in regions of neuronal damage such as the hippocampus. We exploited this regional astrocytosis by linking expression of hIGF-1 to the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter, effectively targeting IGF-1 delivery to vulnerable neurons. Following brain injury, IGF-1Tg mice exhibited a progressive increase in hippocampal IGF-1 levels which was coupled with enhanced hippocampal reactive astrocytosis and significantly greater GFAP levels relative to WT mice. IGF-1 overexpression stimulated Akt phosphorylation and reduced acute (1 and 3d) hippocampal neurodegeneration, culminating in greater neuron survival at 10d after CCI injury. Hippocampal neuroprotection achieved by IGF-1 overexpression was accompanied by improved motor and cognitive function in brain-injured mice. These data provide strong support for the therapeutic efficacy of increased brain levels of IGF-1 in the setting of TBI.

Revisiting the timing hypothesis: biomarkers that define the therapeutic window of estrogen for stroke

Significantly extended life expectancy coupled with contemporary sedentary lifestyles and poor nutrition has created a global epidemic of cardiovascular disease and stroke. For women, this issue is complicated by the discrepant outcomes of hormone therapy (HT) for stroke incidence and severity as well as the therapeutic complications for stroke associated with advancing age. Here we propose that the impact of estrogen therapy cannot be considered in isolation, but should include age-related changes in endocrine, immune, and nucleic acid mediators that collaborate with estrogen to produce neuroprotective effects commonly seen in younger, healthier demographics. Due to their role as modulators of ischemic cell death, the post-stroke inflammatory response, and neuronal survival and regeneration, this review proposes that Insulin-like Growth Factor (IGF)-1, Vitamin D, and discrete members of the family of non-coding RNA peptides called microRNAs (miRNAs) may be crucial biochemical markers that help determine the neuroprotective "window" of HT. Specifically, IGF-1 confers neuroprotection in concert with, and independently of, estrogen and failure of the insulin/IGF-1 axis is associated with metabolic disturbances that increase the risk for stroke. Vitamin D and miRNAs regulate and complement IGF-1 mediated function and neuroprotective efficacy via modulation of IGF-1 availability and neural stem cell and immune cell proliferation, differentiation and secretions. Together, age-related decline of these factors differentially affects stroke risk, severity, and outcome, and may provide a novel therapeutic adjunct to traditional HT practices.

Risperidone enhances the vulnerability to stroke in hypertensive rats

BACKGROUND

Stroke is the second most common cause of death and a major cause of disability worldwide. Risperidone is an atypical antipsychotic drug that may increase the risk of stroke. The present work examined whether risperidone enhances the vulnerability to stroke in hypertensive rats and the potential mechanisms underlying such action.

METHODS

Experiment 1: Wistar-Kyoto (WKY) rats, spontaneously hypertensive rats (SHRs) and stroke-prone SHRs (SHR-SPs) were treated with risperidone (0.8 and 2.4 mg/kg/d) or vehicle for 30 consecutive days. Tissue damage in response to middle cerebral artery occlusion (MCAO) was measured microscopically. The activity of superoxide dismutase, glutathione peroxidase, the levels of malondialdehyde were also determined. Experiment 2: Survival data were recorded in SHR-SPs that received daily risperidone perpetually. Experiment 3: Effect of risperidone on interleukin-6 and tumor necrosis factor-α was examined in quiescent or LPS-activated cortical microglias from WKY rats. Experiment 4: Potential damage of risperidone exposure to neurons was examined in primary neuronal culture obtained from WKY rats, SHRs, and SHR-SPs.

RESULTS

Risperidone increased infarct areas upon MCAO in SHR-SPs and SHRs, but not in WKY rats. Survival time in SHR-SPs was shortened by risperidone. Apoptosis was augmented by risperidone through enhanced Bax. Risperidone also increased endothelial injury.

CONCLUSIONS

Risperidone enhances the vulnerability to stroke in hypertensive rats through increasing neuronal apoptosis and endothelial injury.

Gene delivery with viral vectors for cerebrovascular diseases

Recent achievements in the understanding of molecular events involved in the pathogenesis of central nervous system (CNS) injury have made gene transfer a promising approach for various neurological disorders, including cerebrovascular diseases. However, special obstacles, including the post-mitotic nature of neurons and the blood-brain barrier (BBB), constitute key challenges for gene delivery to the CNS. Despite the various limitations in current gene delivery systems, a spectrum of viral vectors has been successfully used to deliver genes to the CNS. Furthermore, recent advancements in vector engineering have improved the safety and delivery of viral vectors. Numerous viral vector-based clinical trials for neurological disorders have been initiated. This review will summarize the current implementation of viral gene delivery in the context of cerebrovascular diseases including ischemic stroke, hemorrhagic stroke and subarachnoid hemorrhage (SAH). In particular, we will discuss the potentially feasible ways in which viral vectors can be manipulated and exploited for use in neural delivery and therapy.

Role of neural precursor cells in promoting repair following stroke

Stem cell-based therapies for the treatment of stroke have received considerable attention. Two broad approaches to stem cell-based therapies have been taken: the transplantation of exogenous stem cells, and the activation of endogenous neural stem and progenitor cells (together termed neural precursors). Studies examining the transplantation of exogenous cells have demonstrated that neural stem and progenitor cells lead to the most clinically promising results. Endogenous activation of neural precursors has also been explored based on the fact that resident precursor cells have the inherent capacity to proliferate, migrate and differentiate into mature neurons in the uninjured adult brain. Studies have revealed that these neural precursor cell behaviours can be activated following stroke, whereby neural precursors will expand in number, migrate to the infarct site and differentiate into neurons. However, this innate response is insufficient to lead to functional recovery, making it necessary to enhance the activation of endogenous precursors to promote tissue repair and functional recovery. Herein we will discuss the current state of the stem cell-based approaches with a focus on endogenous repair to treat the stroke injured brain.