Transcriptional regulation of neurogenesis: potential mechanisms in cerebral ischemia

Novel insight into the therapeutical potential of flavonoids from traditional Chinese medicine against cerebral ischemia/reperfusion injury

Cerebral ischemia/reperfusion injury (CIRI) is a major contributor to poor prognosis of ischemic stroke. Flavonoids are a broad family of plant polyphenols which are abundant in traditional Chinese medicine (TCM) and have beneficial effects on several diseases including ischemic stroke. Accumulating studies have indicated that flavonoids derived from herbal TCM are effective in alleviating CIRI after ischemic stroke in vitro or in vivo, and exhibit favourable therapeutical potential. Herein, we systematically review the classification, metabolic absorption, neuroprotective efficacy, and mechanisms of TCM flavonoids against CIRI. The literature suggest that flavonoids exert potential medicinal functions including suppressing excitotoxicity, Ca2+ overloading, oxidative stress, inflammation, thrombin's cellular toxicity, different types of programmed cell deaths, and protecting the blood-brain barrier, as well as promoting neurogenesis in the recovery stage following ischemic stroke. Furthermore, we identified certain matters that should be taken into account in future research, as well as proposed difficulties and opportunities in transforming TCM-derived flavonoids into medications or functional foods for the treatment or prevention of CIRI. Overall, in this review we aim to provide novel ideas for the identification of new prospective medication candidates for the therapeutic strategy against ischemic stroke.

Oleoylethanolamide ameliorates motor dysfunction through PPARα-mediates oligodendrocyte differentiation and white matter integrity after ischemic stroke

BACKGROUND AND AIM

Our previous study has revealed that OEA promotes motor function recovery in the chronic stage of ischemic stroke. However, the neuroprotective mechanism of OEA on motor function recovery after stroke still is unexplored. Therefore, the aim of this study was to explore the effects of OEA treatment on angiogenesis, neurogenesis, and white matter repair in the peri-infarct region after cerebral ischemia.

EXPERIMENTAL PROCEDURE

The adult male rats were subjected to 2 h of middle cerebral artery occlusion. The rats were treated with 10 and 30 mg/kg OEA or vehicle daily starting from day 2 after ischemia induction until they were sacrificed.

KEY RESULTS AND CONCLUSIONS

The results revealed that OEA increased cortical angiogenesis, neural progenitor cells (NPCs) proliferation, migration, and differentiation. OEA treatment enhanced the survival of newborn neurons and oligodendrogenesis, which eventually repaired the cortical neuronal injury and improved motor function after ischemic stroke. Meanwhile, OEA treatment promoted the differentiation of oligodendrocyte progenitor cells (OPCs) and oligodendrogenesis by activating the PPARα signaling pathway. Our results showed that OEA restores motor function by facilitating cortical angiogenesis, neurogenesis, and white matter repair in rats after ischemic stroke. Therefore, we demonstrate that OEA facilitates functional recovery after ischemic stroke and propose the hypothesis that the long-term application of OEA mitigates the disability after stroke.

Targeted Disruption of the MORG1 Gene in Mice Causes Embryonic Resorption in Early Phase of Development

The mitogen-activated protein kinase organizer 1 (MORG1) is a scaffold molecule for the ERK signaling pathway, but also binds to prolyl-hydroxylase 3 and modulates HIFα expression. To obtain further insight into the role of MORG1, knockout-mice were generated by homologous recombination. While Morg1+/- mice developed normally without any apparent phenotype, there were no live-born Morg1-/- knockout offspring, indicating embryonic lethality. The intrauterine death of Morg1-/- embryos is caused by a severe failure to develop brain and other neuronal structures such as the spinal cord and a failure of chorioallantoic fusion. On E8.5, Morg1-/- embryos showed severe underdevelopment and proliferative arrest as indicated by absence of Ki67 expression, impaired placental vascularization and altered phenotype of trophoblast giant cells. On E9.5, the malformed Morg1-/- embryos showed defective turning into the final fetal position and widespread apoptosis in many structures. In the subsequent days, apoptosis and decomposition of embryonic tissue progressed, accompanied by a massive infiltration of inflammatory cells. Developmental aberrancies were accompanied by altered expression of HIF-1/2α and VEGF-A and caspase-3 activation in embryos and extraembryonic tissues. In conclusion, the results suggest a multifactorial process that causes embryonic death in homozygous Morg1 mutant mice, described here, to the best of our knowledge, for the first time.

Implications of Hypothalamic Neural Stem Cells on Aging and Obesity-Associated Cardiovascular Diseases

The hypothalamus, one of the major regulatory centers in the brain, controls various homeostatic processes, and hypothalamic neural stem cells (htNSCs) have been observed to interfere with hypothalamic mechanisms regulating aging. NSCs play a pivotal role in the repair and regeneration of brain cells during neurodegenerative diseases and rejuvenate the brain tissue microenvironment. The hypothalamus was recently observed to be involved in neuroinflammation mediated by cellular senescence. Cellular senescence, or systemic aging, is characterized by a progressive irreversible state of cell cycle arrest that causes physiological dysregulation in the body and it is evident in many neuroinflammatory conditions, including obesity. Upregulation of neuroinflammation and oxidative stress due to senescence has the potential to alter the functioning of NSCs. Various studies have substantiated the chances of obesity inducing accelerated aging. Therefore, it is essential to explore the potential effects of htNSC dysregulation in obesity and underlying pathways to develop strategies to address obesity-induced comorbidities associated with brain aging. This review will summarize hypothalamic neurogenesis associated with obesity and prospective NSC-based regenerative therapy for the treatment of obesity-induced cardiovascular conditions.

Acute Normobaric Hypoxia Lowers Executive Functions among Young Men despite Increase of BDNF Concentration

BACKGROUND

Decreased SpO₂ during hypoxia can cause cognitive function impairment, and the effects of acute hypoxia on high-order brain functions such as executive processing remain unclear. This study's goal was to examine the impact of an acute normobaric hypoxia breathing session on executive function and biological markers.

METHODS

Thirty-two healthy subjects participated in a blind study performing two sessions of single 30 min breathing bouts under two conditions (normoxia (NOR) and normobaric hypoxia (NH), FIO₂ = 0.135). The Stroop test was applied to assess cognitive function.

RESULTS

No significant difference was observed in the Stroop interference in the "reading" part of the test in either condition; however, there was a significant increase in the "naming" part under NH conditions (p = 0.003), which corresponded to a significant decrease in SpO₂ (p < 0.001). There was a significant increase (p < 0.013) in the brain-derived neurotrophic factor (BDNF) level after NH conditions compared to the baseline, which was not seen in NOR. In addition, a significant drop (p < 0.001) in cortisol levels in the NOR group and a slight elevation in the NH group was noticed.

CONCLUSIONS

According to these findings, acute hypoxia delayed cognitive processing for motor execution and reduced the neural activity in motor executive and inhibitory processing. We also noted that this negative effect was associated with decreased SpO₂ irrespective of a rise in BDNF.

RNA-seq analysis reveals potential molecular mechanisms of ZNF580/ZFP580 promoting neuronal survival and inhibiting apoptosis after Hypoxic-ischemic brain damage

Neonatal hypoxic-ischemic brain damage (HIBD) is one of the main causes of neonatal acute death and chronic nervous system impairment, but still lacks effective treatments. ZNF580/ZFP580, reported in our previous studies, may be a newly identified member of the Krüppel-like factor (KLF) family, and has anti-apoptotic effects during ischemic myocardial injury. In the present study, we showed that the expression levels of both ZFP580/ZNF580 mRNA and protein increased significantly in neonatal HIBD rats and oxygen-glucose deprivation (OGD) SH-SY5Y cell models. ZNF580 overexpression promoted neuron survival and suppressed neuron apoptosis after OGD in neuron-like SH-SY5Y cells, while interference with ZNF580 resulted in the opposite results. RNA-seq analysis identified 248 differentially-expressed genes (DEGs) between ZNF580 overexpression SH-SY5Y cells and interference-expressed SH-SY5Y cells. Gene Ontology functional enrichment analysis showed that these DEGs played significant roles in the growth, development, and regeneration of axons, DNA biosynthetic processes, DNA replication, and apoptosis. Kyoto Encyclopedia of Genes and Genomes enrichment analysis indicated that these DEGs were found in some pathways, including ferroptosis, glutamatergic synapses, protein processing in the endoplasmic reticulum, estrogen signaling pathways, the TGF-beta signaling pathway, and the longevity regulating pathway. The qRT-PCR validation results were consistent with RNA-seq results, which showed that HSPA5, IGFBP3, NTN4, and KLF9 increased in ZNF580-overexpressed SH-SY5Y cells and decreased in interference-expressed SH-SY5Y cells, when compared with normal cells. Together, the results suggested that ZNF580 targeted these genes to inhibit neuronal apoptosis.

Effect of Acute Normobaric Hypoxia Exposure on Executive Functions among Young Physically Active Males

Background: On the one hand, hypoxic exposure may result in progressive brain metabolism disturbance, causing subsequent cognitive impairments. On the other hand, it might also enhance neurogenesis and brain vascularization as well as accelerate cerebral blood flow, leading to cognitive function improvement. The aim of this study was to investigate whether progressive stages of normobaric hypoxia (NH) (FIO₂ = 13%, FIO₂ = 12%, and FIO₂ = 11%) differentially affect post-exposure cognitive performance. Methods: Fifteen physically active men (age = 23.1 ± 2.1) participated in the study. The Stroop test (ST) was applied to assess cognitive function. To generate NH conditions, a hypoxic normobaric air generator was used. Results: We observed an executive function impairment (“naming” interference p < 0.05) after NH exposure (FIO₂ = 13%). After exposure at FIO₂ = 12% and FIO₂ = 11%, no changes were observed in the Stroop test. Also, changes in SpO₂ during subsequent NH exposure were observed. Conclusions: The current investigation shows that executive functions deteriorate after acute NH exposure and this post-exposure deterioration is not proportional to the normobaric hypoxia stages among young physically active males.

Intermittent fasting increases adult hippocampal neurogenesis

INTRODUCTION

Intermittent fasting (IF) has been suggested to have neuroprotective effects through the activation of multiple signaling pathways. Rodents fasted intermittently exhibit enhanced hippocampal neurogenesis and long-term potentiation (LTP) at hippocampal synapses compared with sedentary animals fed an ad libitum (AL) diet. However, the underlying mechanisms have not been studied. In this study, we evaluated the mechanistic gap in understanding IF-induced neurogenesis.

METHODS

We evaluated the impact of 3 months of IF (12, 16, and 24 hr of food deprivation on a daily basis) on hippocampal neurogenesis in C57BL/6NTac mice using immunoblot analysis.

RESULTS

Three-month IF significantly increased activation of the Notch signaling pathway (Notch 1, NICD1, and HES5), neurotrophic factor BDNF, and downstream cellular transcription factor, cAMP response element-binding protein (p-CREB). The expression of postsynaptic marker, PSD95, and neuronal stem cell marker, Nestin, was also increased in the hippocampus in response to 3-month IF.

CONCLUSIONS

These findings suggest that IF may increase hippocampal neurogenesis involving the Notch 1 pathway.

Administration of human umbilical cord blood mononuclear cells restores bladder dysfunction in streptozotocin-induced diabetic rats

OBJECTIVE

This study evaluated the effect of human umbilical cord blood mononuclear cells (HUCB-MNCs) on bladder dysfunction in streptozotocin (STZ; 35 mg/kg, i.v.)-induced diabetic rats.

METHODS

Adult male Sprague-Dawley rats (n = 30) were equally divided into three groups: control group, STZ-diabetic group, and HUCB-MNC-treated group (1 × 10⁶ cells). HUCB-MNCs were isolated by density gradient centrifugation from eight healthy donors and injected into the corpus cavenosum in STZ-diabetic rats 4 weeks after the induction of diabetes. Studies were performed 4 weeks after HUCB-MNC or vehicle injection. In vitro organ bath studies were performed on bladder strips, whereas protein expression of hypoxia-inducible factor (HIF)-1α, vascular endothelial growth factor (VEGF), and α-smooth muscle actin (SMA) in the bladder and the ratio of smooth muscle cells (SMCs) to collagen were determined using western blotting and Masson trichrome staining.

RESULTS

Neurogenic contractions of detrusor smooth muscle strips were 55% smaller in the diabetic group than control group (P < 0.05); these contractions were normalized by HUCB-MNC treatment. In addition, HUCB-MNC treatment restored the impaired maximal carbachol-induced contractile response in detrusor strips in the diabetic group (29%; P < 0.05). HUCB-MNC treatment improved the KCl-induced contractile response in the diabetic bladder (68%; P < 0.05), but had no effect on ATP-induced contractile responses. Increased expression of HIF-1α and VEGF protein and decreased expression of α-SMA protein and the SMC/collagen ratio in diabetic rats were reversed by HUCB-MNC.

CONCLUSION

Administration of HUCB-MNCs facilitates bladder function recovery, which is likely related to downregulation of HIF-1α expression and attenuation of fibrosis in STZ-diabetic rats.

Astragaloside IV Protects Primary Cerebral Cortical Neurons from Oxygen and Glucose Deprivation/Reoxygenation by Activating the PKA/CREB Pathway

Stroke is one of the major leading causes of death and disability worldwide, and post-stroke cognitive impairment is a major contributor to this disability. Astragaloside IV (AST-IV) is a primary bioactive compound of Radix Astragali, which is widely used in traditional Chinese medicine to treat stroke. AST-IV was found to possess cognition-enhancing properties against ischemic stroke; however, the mechanisms underlying this effect remain largely elusive. Mitochondrial health is critical to cell viability after ischemic injury. Cyclic AMP response element-binding protein (CREB) is a transcription factor that can be activated by protein kinase A (PKA) to preserve mitochondria, regulate memory and cognitive functions. We used an in vitro model of ischemic injury via oxygen and glucose deprivation (OGD) of cultured neurons, which led to PKA inactivation and decreased CREB phosphorylation, reduced cell viability, and increased neuronal apoptosis. We hypothesized that AST-IV could protect OGD-exposed cerebral cortical neurons by modulating the PKA/CREB signaling pathway and preserving mitochondrial function. We found that the mitochondrial and cellular injuries induced by OGD were reversed following treatment with AST-IV. The activity of neuronal mitochondria was evaluated by measuring the mitochondrial potential and the levels of reactive oxygen species (ROS) and adenosine triphosphate (ATP). AST-IV significantly enhanced PKA and CREB phosphorylation and prevented OGD-induced mitochondrial dysfunction, thereby protecting neurons exposed to OGD from injury and death. Furthermore, the effects of AST-IV were partially blocked by a PKA inhibitor. Collectively, these data elucidated the molecular mechanisms underlying the protective effects of AST-IV against ischemic injury in cortical neurons.

The role of neurogenesis in neurorepair after ischemic stroke

Stroke consists of an abrupt reduction of cerebral blood flow resulting in hypoxia that triggers an excitotoxicity, oxidative stress, and neuroinflammation. After the ischemic process, neural precursor cells present in the subventricular zone of the lateral ventricle and subgranular zone of the dentate gyrus proliferate and migrate towards the lesion, contributing to the brain repair. The neurogenesis is induced by signal transduction pathways, growth factors, attractive factors for neuroblasts, transcription factors, pro and anti-inflammatory mediators and specific neurotransmissions. However, this endogenous neurogenesis occurs slowly and does not allow a complete restoration of brain function. Despite that, understanding the mechanisms of neurogenesis could improve the therapeutic strategies for brain repair. This review presents the current knowledge about brain repair process after stroke and the perspectives regarding the development of promising therapies that aim to improve neurogenesis and its potential to form new neural networks.

Caveolin-1 and MLRs: A potential target for neuronal growth and neuroplasticity after ischemic stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide. Thrombolytic therapy, the only established treatment to reduce the neurological deficits caused by ischemic stroke, is limited by time window and potential complications. Therefore, it is necessary to develop new therapeutic strategies to improve neuronal growth and neurological function following ischemic stroke. Membrane lipid rafts (MLRs) are crucial structures for neuron survival and growth signaling pathways. Caveolin-1 (Cav-1), the main scaffold protein present in MLRs, targets many neural growth proteins and promotes growth of neurons and dendrites. Targeting Cav-1 may be a promising therapeutic strategy to enhance neuroplasticity after cerebral ischemia. This review addresses the role of Cav-1 and MLRs in neuronal growth after ischemic stroke, with an emphasis on the mechanisms by which Cav-1/MLRs modulate neuroplasticity via related receptors, signaling pathways, and gene expression. We further discuss how Cav-1/MLRs may be exploited as a potential therapeutic target to restore neuroplasticity after ischemic stroke. Finally, several representative pharmacological agents known to enhance neuroplasticity are discussed in this review.

Lymphotoxin β receptor-mediated NFκB signaling promotes glial lineage differentiation and inhibits neuronal lineage differentiation in mouse brain neural stem/progenitor cells

BACKGROUND

Lymphotoxin (LT) is a lymphokine mainly expressed in lymphocytes. LTα binds one or two membrane-associated LTβ to form LTα2β1 or LTα1β2 heterotrimers. The predominant LTα1β2 binds to LTβ receptor (LTβR) primarily expressed in epithelial and stromal cells. Most studies on LTβR signaling have focused on the organization, development, and maintenance of lymphoid tissues. However, the roles of LTβR signaling in the nervous system, particularly in neurogenesis, remain unknown. Here, we investigated the role of LTβR-mediated NFκB signaling in regulating neural lineage differentiation.

METHODS

The C57BL/6J wild-type and GFAP-dnIκBα transgenic mice were used. Serum-free embryoid bodies were cultured from mouse embryonic stem cells and further induced into neural stem/progenitor cells (NSCs/NPCs). Primary neurospheres were cultured from embryonic and adult mouse brains followed by monolayer culture for amplification/passage. NFκB activation was determined by adenovirus-mediated NFκB-firefly-luciferase reporter assay and p65/RelB/p52 nuclear translocation assay. LTβR mRNA expression was evaluated by quantitative RT-PCR and LTβR protein expression was determined by immunohistochemistry and Western blot analysis. Multilabeled immunocytochemistry or immunohistochemistry followed by fluorescent confocal microscopy and quantitative analysis of neural lineage differentiation were performed. Graphing and statistical analysis were performed with GraphPad Prism software.

RESULTS

In cultured NSCs/NPCs, LTα1β2 stimulation induced an activation of classical and non-classical NFκB signaling. The expression of LTβR-like immunoreactivity in GFAP+/Sox2+ NSCs was identified in well-established neurogenic zones of adult mouse brain. Quantitative RT-PCR and Western blot analysis validated the expression of LTβR in cultured NSCs/NPCs and brain neurogenic regions. LTβR expression was significantly increased during neural induction. LTα1β2 stimulation in cultured NSCs/NPCs promoted astroglial and oligodendrocytic lineage differentiation, but inhibited neuronal lineage differentiation. Astroglial NFκB inactivation in GFAP-dnIκBα transgenic mice rescued LTβR-mediated abnormal phenotypes of cultured NSCs/NPCs.

CONCLUSION

This study provides the first evidence for the expression and function of LTβR signaling in NSCs/NPCs. Activation of LTβR signaling promotes glial lineage differentiation. Our results suggest that neurogenesis is regulated by the adaptive immunity and inflammatory responses.

Genetic Deletion of Krüppel-Like Factor 11 Aggravates Ischemic Brain Injury

Krüppel-like factors (KLFs) belong to the zinc finger family of transcription factors, and their function in the CNS is largely unexplored. KLF11 is a member of the KLF family, and we have previously demonstrated that peroxisome proliferator-activated receptor gamma-mediated cerebral protection during ischemic insults needs recruitment of KLF11 as its critical coactivator. Here, we sought to determine the role of KLF11 itself in cerebrovascular function and the pathogenesis of ischemic stroke. Transient middle cerebral artery occlusion (MCAO) was performed in KLF11 knockout and wild-type control mice, and brain infarction was analyzed by TTC staining. BBB integrity was assessed by using Evans Blue and TMR-Dextran extravasation assays. KLF11 KO mice exhibited significantly larger brain infarction and poorer neurological outcomes in response to ischemic insults. Genetic deficiency of KLF11 in mice also significantly aggravated ischemia-induced BBB disruption by increasing cerebrovascular permeability and edema. Mechanistically, KLF11 was found to directly regulate IL-6 in the brains of ischemic mice. These findings suggest that KLF11 acts as a novel protective factor in ischemic stroke. Elucidating the functional importance of KLF11 in ischemia may lead us to discover novel pharmacological targets for the development of effective therapies against ischemic stroke.

Effect of intermittent normobaric hypoxia on aerobic capacity and cognitive function in older people

OBJECTIVES

Physical exercise, especially aerobic training, improves physical performance and cognitive function of older people. Furthermore, it has been speculated that age-associated deteriorations in physical performance and cognitive function could be counteracted through exposures to passive intermittent normobaric hypoxia (IH). Thus, the present investigation aimed at investigating the effect of passive IH combined with subsequent aerobic training on hematological parameters and aerobic physical performance (V˙O_2max) as well as peripheral levels of the neurotrophin brain-derived neurotrophic factor (BDNF) and cognitive function.

DESIGN

Randomized controlled trial in a repeated measure design.

METHODS

34 older participants were randomly assigned to an intervention group (IG) or control group (CG). While IG was supplied with passive IH for 90min, CG breathed ambient air. Subsequently, both groups underwent 30min of aerobic training three times per week for four consecutive weeks. Aerobic physical performance and cognitive function was tested with spiroergometry and the Stroop test. Blood samples were taken to measure hematological parameters and the peripheral serum BDNF-level.

RESULTS

We found increases in the values of hematological parameters, the time to exhaustion in the load test and an augmented and sustainable improvement in cognitive function within the IG of the older people only. However, in both groups, the V˙O_2max and serum BDNF-level did not increase.

CONCLUSIONS

Based on these results, hypoxic training seems to be beneficial to enhance hematological parameters, physical performance and cognitive function in older people. The current hypoxic-dose was not able to enhance the serum BDNF-level or V˙O_2max.

Downregulation of survivin regulates adult hippocampal neurogenesis and apoptosis, and inhibits spatial learning and memory following traumatic brain injury

Survivin, a unique member of the inhibitor of the apoptosis protein (IAP) family, has been suggested to play a crucial role in promoting the cell cycle and mediates mitosis during embryonic development. However, the role of survivin following traumatic brain injury (TBI) in adult neurogenesis and apoptosis in the mouse dentate gyrus (DG) remains only partially understood. We adopted adenovirus-mediated RNA interference (RNAi) as a means of suppressing the expression of survivin and observed its effects on adult regeneration and neurological function in mice after brain injury. The mice were subjected to TBI, and the ipsilateral hippocampus was then examined using reverse transcription polymerase chain reaction (RT-PCR) and Western blotting analyses. Brain slices were stained for 5'-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX). Our data showed that survivin knockdown inhibits the proliferation and differentiation of neural precursor cells (NPCs) in the DG of the hippocampus soon after TBI. Furthermore, downregulation of survivin results in a significant increase in programmed cell death in the DG, as assessed using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and 4',6-diamidino-2-phenylindole (DAPI) double staining. The Morris water maze (MWM) test was adopted to evaluate neurological function, which confirmed that knockdown of survivin worsened the memory capacity that was already compromised following TBI. Survivin in adult mice brains after TBI can be successfully down-regulated by RNAi, which inhibited adult hippocampal neurogenesis, promoted apoptotic cell death, and resulted in a negative role in the recovery of dysfunction following injury.

Systems approach to the study of brain damage in the very preterm newborn

Background: A systems approach to the study of brain damage in very preterm newborns has been lacking.

Methods: In this perspective piece, we offer encephalopathy of prematurity as an example of the complexity and interrelatedness of brain-damaging molecular processes that can be initiated inflammatory phenomena.

Results: Using three transcription factors, nuclear factor-kappa B (NF-κB), Notch-1, and nuclear factor erythroid 2 related factor 2 (NRF2), we show the inter-connectedness of signaling pathways activated by some antecedents of encephalopathy of prematurity.

Conclusions: We hope that as biomarkers of exposures and processes leading to brain damage in the most immature newborns become more readily available, those who apply a systems approach to the study of neuroscience can be persuaded to study the pathogenesis of brain disorders in the very preterm newborn.

Krüpple-like factors in the central nervous system: novel mediators in stroke

Transcription factors play an important role in the pathophysiology of many neurological disorders, including stroke. In the past three decades, an increasing number of transcription factors and their related gene signaling networks have been identified, and have become a research focus in the stroke field. Krüppel-like factors (KLFs) are members of the zinc finger family of transcription factors with diverse regulatory functions in cell growth, differentiation, proliferation, migration, apoptosis, metabolism, and inflammation. KLFs are also abundantly expressed in the brain where they serve as critical regulators of neuronal development and regeneration to maintain normal brain function. Dysregulation of KLFs has been linked to various neurological disorders. Recently, there is emerging evidence that suggests KLFs have an important role in the pathogenesis of stroke and provide endogenous vaso-or neuro-protection in the brain's response to ischemic stimuli. In this review, we summarize the basic knowledge and advancement of these transcriptional mediators in the central nervous system, highlighting the novel roles of KLFs in stroke.

Normobaric oxygen for cerebral ischemic injury

Oxygen inhalation has been shown to increase oxygen supply to tissues after cerebral ischemia/ reperfusion injury, protecting injured neural cells. However, hyperbaric oxygen may aggravate oxidative stress. By contrast, normobaric oxygen has the rapid and non-invasive characteristics and may have therapeutic effects on ischemic/hypoxic disease. Rats inhaled normobaric oxygen (95% O2) for 6 consecutive days, and then a rat model of focal cerebral ischemia was established. Nissl and 2,3,5-triphenyltetrazolium chloride (TTC) staining revealed that normobaric oxygen pretreatment improved neurological deficits and reduced infarct volume. Immunohistochemical staining and western blot assay revealed that the expression of hypoxia-inducible factor-1α, Notch-1, vascular endothelial growth factor and erythropoietin were increased. Behavioral studies also verified that neurological deficit scores increased. The hypoxia-inducible factor inhibitor 2-methoxyestradiol treatment at 1 hour before administration of normobaric oxygen could suppress the protective effect of normobaric oxygen. Given these observations, normobaric oxygen pretreatment may alleviate cerebral ischemic injury via the hypoxia-inducible factor signal pathway.

Transcription factor changes following long term cerebral ischemia/reperfusion injury

The present study established a rat model of cerebral ischemia/reperfusion injury using four-vessel occlusion and found that hippocampal CA1 neuronal morphology was damaged, and that there were reductions in hippocampal neuron number and DNA-binding activity of cAMP response element binding protein and CCAAT/enhancer binding protein, accompanied by decreased learning and memory ability. These findings indicate that decline of hippocampal cAMP response element binding protein and CCAAT/enhancer binding protein DNA-binding activities may contribute to neuronal injury and learning and memory ability reduction induced by cerebral ischemia/reperfusion injury.

Erythromycin pretreatment induces tolerance against focal cerebral ischemia through up-regulation of nNOS but not down-regulation of HIF-1α in rats

The purpose of this study was to determine whether the antibiotic erythromycin induces tolerance against focal cerebral ischemia, and the possible underlying mechanism including the involvement of neuronal nitric oxide synthase (nNOS) and hypoxia-inducible factor-1α (HIF-1α). In rat focal cerebral ischemia models, we found that erythromycin preconditioning could significantly decrease the cerebral infarct volume and brain edema. Meanwhile, the neurological deficits from day 4 through 7 after surgery were also remarkably decreased after erythromycin preconditioning. Moreover, erythromycin preconditioning induced significantly increased nNOS levels and decreased HIF-1α levels in both mRNA and protein expression. This study for the first time indicated that erythromycin preconditioning could induce focal brain ischemic tolerance and attenuate brain injury of subsequent transient focal cerebral ischemia. The potential mechanism may be due to up-regulation of nNOS, but the HIF-1α system was not involved.

Electroacupuncture pretreatment induces tolerance against focal cerebral ischemia through activation of canonical Notch pathway

Background

Electroacupuncture (EA) pretreatment can induce the tolerance against focal cerebral ischemia. However, the underlying mechanisms have not been fully understood. Emerging evidences suggest that canonical Notch signaling may be involved in ischemic brain injury. In the present study, we tested the hypothesis that EA pretreatment-induced tolerance against focal cerebral ischemia is mediated by Notch signaling.

Results

EA pretreatment significantly enhanced Notch1, Notch4 and Jag1 gene transcriptions in the striatum, except Notch1 intracellular domain level, which could be increased evidently by ischemia. After ischemia and reperfusion, Hes1 mRNA and Notch1 intracellular domain level in ischemic striatum in EA pretreatment group were increased and reached the peak at 2 h and 24 h, respectively, which were both earlier than the peak achieved in control group. Intraventricular injection with the γ-secretase inhibitor MW167 attenuated the neuroprotective effect of EA pretreatment.

Conclusions

EA pretreatment induces the tolerance against focal cerebral ischemia through activation of canonical Notch pathway.

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation, survival, migration and lineage differentiation of neural stem/progenitor cells. Such dynamic process is tightly regulated by intrinsic and extrinsic factors and complex signaling pathways. Misregulated neurogenesis contributes much to a large range of neurodevelopmental defects and neurodegenerative diseases. The signaling of NFκB regulates many genes important in inflammation, immunity, cell survival and neural plasticity. During neurogenesis, NFκB signaling mediates the effect of numerous niche factors such as cytokines, chemokines, growth factors, extracellular matrix molecules, but also crosstalks with other signaling pathways such as Notch, Shh, Wnt/β-catenin. This review summarizes current progress on the NFκB signaling in all aspects of neurogenesis, focusing on the novel role of NFκB signaling in initiating early neural differentiation of neural stem cells and embryonic stem cells.

Neurotrophic effect of citrus 5-hydroxy-3,6,7,8,3',4'-hexamethoxyflavone: promotion of neurite outgrowth via cAMP/PKA/CREB pathway in PC12 cells

5-Hydroxy-3,6,7,8,3′,4′-hexamethoxyflavone (5-OH-HxMF), a hydroxylated polymethoxyflavone, is found exclusively in the Citrus genus, particularly in the peels of sweet orange. In this research, we report the first investigation of the neurotrophic effects and mechanism of 5-OH-HxMF in PC12 pheochromocytoma cells. We found that 5-OH-HxMF can effectively induce PC12 neurite outgrowth accompanied with the expression of neuronal differentiation marker protein growth-associated protein-43(GAP-43). 5-OH-HxMF caused the enhancement of cyclic AMP response element binding protein (CREB) phosphorylation, c-fos gene expression and CRE-mediated transcription, which was inhibited by 2-naphthol AS-E phosphate (KG-501), a specific antagonist for the CREB-CBP complex formation. Moreover, 5-OH-HxMF-induced both CRE transcription activity and neurite outgrowth were inhibited by adenylate cyclase and protein kinase A (PKA) inhibitor, but not MEK1/2, protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3K) or calcium/calmodulin-dependent protein kinase (CaMK) inhibitor. Consistently, 5-OH-HxMF treatment increased the intracellular cAMP level and downstream component, PKA activity. We also found that addition of K252a, a TrKA antagonist, significantly inhibited NGF- but not 5-OH-HxMF-induced neurite outgrowth. These results reveal for the first time that 5-OH-HxMF is an effective neurotrophic agent and its effect is mainly through a cAMP/PKA-dependent, but TrKA-independent, signaling pathway coupling with CRE-mediated gene transcription. A PKC-dependent and CREB-independent pathway was also involved in its neurotrophic action.

Notch signaling proteins HES-1 and Hey-1 bind to insulin degrading enzyme (IDE) proximal promoter and repress its transcription and activity: implications for cellular Aβ metabolism

Cerebral amyloid β (Aβ) accumulation is pathogenically associated with sporadic Alzheimer's disease (SAD). BACE-1 is involved in Aβ generation while insulin-degrading enzyme (IDE) partakes in Aβ proteolytic clearance. Vulnerable regions in AD brains show increased BACE-1 protein levels and enzymatic activity while the opposite occurs with IDE. Another common feature in SAD brains is Notch1 overexpression. Here we demonstrate an increase in mRNA levels of Hey-1, a Notch target gene, and a decrease of IDE transcripts in the hippocampus of SAD brains as compared to controls. Transient transfection of Notch intracellular domain (NICD) in N2aSW cells, mouse neuroblastoma cells (N2a) stably expressing human amyloid precursor protein (APP) Swedish mutation, reduce IDE mRNA levels, promoting extracellular Aβ accumulation. Also, NICD, HES-1 and Hey-1 overexpression result in decreased IDE proximal promoter activity. This effect was mediated by 2 functional sites located at -379/-372 and -310-303 from the first translation start site in the -575/-19 (556 bp) fragment of IDE proximal promoter. By site-directed mutagenesis of the IDE promoter region we reverted the inhibitory effect mediated by NICD transfection suggesting that these sites are indeed responsible for the Notch-mediated inhibition of the IDE gene expression. Intracranial injection of the Notch ligand JAG-1 in Tg2576 mice, expressing the Swedish mutation in human APP, induced overexpression of HES-1 and Hey-1 and reduction of IDE mRNA levels, respectively. Our results support our theory that a Notch-dependent IDE transcriptional modulation may impact on Aβ metabolism providing a functional link between Notch signaling and the amyloidogenic pathway in SAD.

Impedance measurement for real time detection of neuronal cell death

Detection of neuronal cell death is a standard requirement in cell culture models of neurodegenerative diseases. Although plenty of viability assays are available for in vitro applications, most of these are endpoint measurements providing only little information on the kinetics of cell death. Here, we validated the xCELLigence system based on impedance measurement for real-time detection of cell death in a neuronal cell line of immortalized hippocampal neurons (HT-22 cells), neuronal progenitor cells (NPC) and differentiated primary cortical neurons. We found a good correlation between impedance measurements and endpoint viability assays in HT-22 cells and NPC, for detecting proliferation, cell death kinetics and also neuroprotective effects of pharmacological inhibitors of apoptosis. In primary neurons we could not detect dendritic outgrowth during differentiation of the cells. Cell death in primary neurons was detectable by the xCELLigence system, however, the changes in the cell index on the basis of impedance measurements depended to a great extent on the severity of the insult. Cell death induced by ionomycin, e.g. shows as a fast paced process involving a strong cellular disintegration, which allows for impedance-based detection. Cell death accompanied by less pronounced morphological changes like glutamate induced cell death, however, is not well accessible by this approach. In conclusion, our data show that impedance measurement is a convenient and reliable method for the detection of proliferation and kinetics of cell death in neuronal cell lines, whereas this method is less suitable for the assessment of neuronal differentiation and viability of primary neurons.

Role of transcription factors in neurogenesis after cerebral ischemia

Studies have revealed that the adult mammalian brain has the capacity to regenerate some neurons after cerebral ischemia. And this perspective on neurogenesis adds to the conceptual framework for strategies for the repair of ischemia-induced brain injury, that is, if the effect of ischemia-induced neurogenesis is enhanced, then the recovery of brain function after stroke can be promoted. Neurogenesis is a multistep process that requires the proliferation of neural stem/progenitor cells, migration and that new cells differentiate, survive and integrate into existing neural networks. For that to occur, the same concerted action of various factors is needed, especially transcription factors which regulate the expression of many moleculars and interact with them to promote neurogenesis. This review article gives a brief overview of some transcription factors (NF-κB, Hes, STAT3, AP-1, CREB, HIF1, Pax6, Tcf/Lef, Gli, Sox2, Olig2, Dlx2, TLX, Bmi-1) in ischemia-induced neurogenesis.

The Wnt /β-catenin signaling pathway in the adult neurogenesis

The Wnt/β-catenin signaling pathway plays an important role in neural development, β-catenin is a central component of the Wnt/β-catenin signaling pathway, which not only performs the function of transmitting information in the cytoplasm, but also translocates to the nucleus-activating target gene transcription. The target genes in neural tissues have not been fully revealed, but the effects of the Wnt/β-catenin signaling pathway in adult neurogenesis have been demonstrated by ongoing research, which are significative to the basic research and treatment of neuronal degeneration diseases. Here, we review key findings to show the characteristics of β-catenin and its pivotal nature in the Wnt/β-catenin signaling pathway in a number of molecular studies. We also review current literature on the role of β-catenin in adult neurogenesis, which consists of an active process encompassing the proliferation, migration, differentiation and final synaptogenesis.

TWEAK regulates proliferation and differentiation of adult neural progenitor cells

The cytokine TWEAK is expressed in the brain and is induced in cerebral ischemia and other brain disorders. TWEAK regulates proliferation and differentiation of progenitor cells but its effect on adult neural progenitor cells is still unknown. Therefore, we investigated the proliferation of neural progenitor cells from the subventricular zone of adult mice in response to TWEAK treatment. TWEAK inhibited proliferation of neural progenitor cells through its membrane receptor Fn14. The reduced proliferation was not due to cell death. By using a reporter assay we found that TWEAK activated the transcription factor NF-κB in adult neural progenitor cells. Blockade of NF-κB signaling reversed the inhibition of cell proliferation by TWEAK. In addition, TWEAK induced neuronal differentiation of neural progenitor cells and lowered the expression of hes1, a transcription factor that prevents neuronal differentiation. In adult mice deficient of the TWEAK receptor Fn14, neurogenesis was reduced in the subventricular zone. In conclusion, our data show that TWEAK regulates adult neurogenesis in the subventricular zone by binding to the membrane receptor Fn14 and activating NF-κB.

Frizzled-10 promotes sensory neuron development in Xenopus embryos

Formation of the vertebrate nervous system requires coordinated cell-cell interactions, intracellular signalling events, gene transcription, and morphogenetic cell movements. Wnt signalling has been involved in regulating a wide variety of biological processes such as embryonic patterning, cell proliferation, cell polarity, motility, and the specification of cell fate. Wnt ligands associate with their receptors, members of the frizzled family (Fz). In Xenopus, five members of the frizzled family are expressed in the early nervous system. We have investigated the role of Xenopus frizzled-10 (Fz10) in neural development. We show that Fz10 is expressed in the dorsal neural ectoderm and neural folds in the region where primary sensory neurons develop. Fz10 mediates canonical Wnt signalling and interacts with Wnt1 and Wnt8 but not Wnt3a as shown in synergy assays. We find that Fz10 is required for the late stages of sensory neuron differentiation. Overexpression of Fz10 in Xenopus leads to an increase in the number of sensory neurons. Loss of Fz10 function using morpholinos inhibits the development of sensory neurons in Xenopus at later stages of neurogenesis and this can be rescued by co-injection of modified Fz10B and beta-catenin. In mouse P19 cells induced by retinoic acid to undergo neural differentiation, overexpression of Xenopus Fz10 leads to an increase in the number of neurons generated while siRNA knockdown of endogenous mouse Fz10 inhibits neurogenesis. Thus we propose Fz10 mediates Wnt1 signalling to determine sensory neural differentiation in Xenopus in vivo and in mouse cell culture.

Quetiapine regulates neurogenesis in ischemic mice by inhibiting NF-kappaB p65/p50 expression

OBJECTIVES

Previously, we showed that quetiapine, an atypical antipsychotic drug, significantly attenuated neurodegeneration induced by global cerebral ischemia (GCI). The present work investigates the effects of quetiapine on neurogenesis.

METHODS

Mice were treated with quetiapine (10 or 20 mg/kg/day; intraperitoneal injection) for 2 weeks and then subjected to GCI on day 15. Seven days after GCI, the mice were killed. Neuronal injury and neurogenesis were analysed using hematoxylin-eosin and 5-bromo-20-deoxyuridine stainings. Levels of nuclear factor kappaB (NF-kappaB) p65/p50 expressions were determined by immunohistochemistry and Western blot analysis.

RESULTS

Global cerebral ischemia resulted in neuronal injury, neurogenesis and NF-kappaB p65/p50 expressions in hippocampus, especially in the dentate gyrus. Pre-administration of quetiapine significantly alleviated neuronal injury, while inhibiting neurogenesis and down-regulating NF-kappaB p65/p50 expression.

DISCUSSION

NF-kappaB plays a key role in regulating neuron damage and neurogenesis. This work suggests that down-regulation of NF-kappaB expression may be one of the mechanisms by which quetiapine inhibits neurogenesis.

Ambivalent aspects of interleukin-6 in cerebral ischemia: inflammatory versus neurotrophic aspects

Interleukin-6 (IL-6) is pleiotropic cytokine involved in many central nervous system disorders including stroke, and elevated serum IL-6 has been found in acute stroke patients. IL-6 is implicated in the inflammation, which contributes to both injury and repair process after cerebral ischemia. However, IL-6 is one of the neurotrophic cytokines sharing a common receptor subunit, gp130, with other neurotrophic cytokines, such as leukemia inhibitory factor (LIF) and ciliary neurotrophic factor. The expression of IL-6 is most prominently identified in neurons in the peri-ischemic regions, and LIF expression shows a similar pattern. The direct injection of these cytokines into the brain after ischemia can reduce ischemic brain injury. The cytokine receptors are localized on the neuron surface, suggesting that neurons are the cytokine target. The major IL-6 downstream signaling pathway is JAK-STAT, and Stat3 activation occurs mainly in neurons during postischemic reperfusion. Further investigation is necessary to clarify the exact role of Stat3 signaling in neuroprotection. Taken together, the information suggests that IL-6 plays a double role in cerebral ischemia, as an inflammatory mediator during the acute phase and as a neurotrophic mediator between the subacute and prolonged phases.

The Notch pathway mediates expansion of a progenitor pool and neuronal differentiation in adult neural progenitor cells after stroke

Molecular mechanisms by which stroke increases neurogenesis have not been fully investigated. Using neural progenitor cells isolated from the subventricular zone (SVZ) of the adult rat subjected to focal cerebral ischemia, we investigated the Notch pathway in regulating proliferation and differentiation of adult neural progenitor cells after stroke. During proliferation of neural progenitor cells, ischemic neural progenitor cells exhibited substantially increased levels of Notch, Notch intracellular domain (NICD), and hairy enhancer of split (Hes) 1, which was associated with a significant increase of proliferating cells. Blockage of the Notch pathway by short interfering ribonucleic acid (siRNA) against Notch or a gamma secretase inhibitor significantly reduced Notch, NICD and Hes1 expression and cell proliferation induced by stroke. During differentiation of neural progenitor cells, Notch and Hes1 expression was downregulated in ischemic neural progenitor cells, which was coincident with a significant increase of neuronal population. Inhibition of the Notch pathway with a gamma secretase inhibitor further substantially increased neurons, but did not alter astrocyte population in ischemic neural progenitor cells. These data suggest that the Notch signaling pathway mediates adult SVZ neural progenitor cell proliferation and differentiation after stroke.

Alpha-synuclein alters Notch-1 expression and neurogenesis in mouse embryonic stem cells and in the hippocampus of transgenic mice

Altered expression and mutations in alpha-synuclein (alpha-syn) have been linked to Parkinson's disease (PD) and related disorders. The neurological alterations in PD patients have been associated with degeneration of dopaminergic cells and other neuronal populations. Moreover, recent studies in murine models have shown that alterations in neurogenesis might also contribute to the neurodegenerative phenotype. However, the mechanisms involved and the effects of alpha-syn expression on neurogenesis are not yet clear. To this end, murine embryonic stem (mES) cells were infected with lentiviral (LV) vectors expressing wild-type (WT) and mutant alpha-syn. Compared with mES cells infected with LV-green fluorescent protein (GFP), cells expressing WT and mutant alpha-syn showed reduced proliferation as indicated by lower 5-bromo-2'-deoxyuridine uptake, increased apoptosis, and reduced expression of neuronal markers such as neuron specific enolase and beta-III tubulin. The alterations in neurogenesis in alpha-syn-expressing mES cells were accompanied by a reduction in Notch-1 and Hairy and enhancer of split-5 (Hes-5) mRNA and protein levels. Moreover, levels of total Notch-1 and Notch intracellular domain (NICD) were lower in mES cells expressing WT and mutant alpha-syn compared with GFP controls. The reduced survival of alpha-syn-expressing mES cells was reverted by overexpressing constitutively active NICD. Similarly, in alpha-syn transgenic mice, the alterations in neurogenesis in the hippocampal subgranular zone were accompanied by decreased Notch-1, NICD, and Hes-5 expression. Together, these results suggest that accumulation of alpha-syn might impair survival of NPCs by interfering with the Notch signaling pathway. Similar mechanisms could be at play in PD and Lewy body disease.

The role of ATP and adenosine in the brain under normoxic and ischemic conditions

By taking advantage of some recently synthesized compounds that are able to block ecto-ATPase activity, we demonstrated that adenosine triphosphate (ATP) in the hippocampus exerts an inhibitory action independent of its degradation to adenosine. In addition, tonic activation of P2 receptors contributes to the normally recorded excitatory neurotransmission. The role of P2 receptors becomes critical during ischemia when extracellular ATP concentrations increase. Under such conditions, P2 antagonism is protective. Although ATP exerts a detrimental role under ischemia, it also exerts a trophic role in terms of cell division and differentiation. We recently reported that ATP is spontaneously released from human mesenchymal stem cells (hMSCs) in culture. Moreover, it decreases hMSC proliferation rate at early stages of culture. Increased hMSC differentiation could account for an ATP-induced decrease in cell proliferation. ATP as a homeostatic regulator might exert a different effect on cell trophism according to the rate of its efflux and receptor expression during the cell life cycle. During ischemia, adenosine formed by intracellular ATP escapes from cells through the equilibrative transporter. The protective role of adenosine A(1) receptors during ischemia is well accepted. However, the use of selective A(1) agonists is hampered by unwanted peripheral effects, thus attention has been focused on A(2A) and A(3) receptors. The protective effects of A(2A) antagonists in brain ischemia may be largely due to reduced glutamate outflow from neurones and glial cells. Reduced activation of p38 mitogen-activated protein kinases that are involved in neuronal death through transcriptional mechanisms may also contribute to protection by A(2A) antagonism. Evidence that A(3) receptor antagonism may be protective after ischemia is also reported.