Attenuation of Notch signaling promotes the differentiation of neural progenitors into neurons in the hippocampal CA1 region after ischemic injury

The Notch pathway regulates autophagy after hypoxic-ischemic injury and affects synaptic plasticity

Following neonatal hypoxic-ischemia (HI) injury, it is crucial factor to reconstruct neural circuit and maintain neural network homeostasis for neurological recovery. A dynamic balance between the synthesis and degradation of synaptic protein is required for maintaining synaptic plasticity. Protein degradation is facilitated by autophagy. This study aimed to investigate the regulation of synaptic structural plasticity by the Notch pathway, by assessing changes in Notch pathway activation and their effects on synaptic proteins and autophagy after HI injury. The study involved 48 male newborn Yorkshire piglets, each weighing 1.0-1.5 kg and 3 days old. They were randomly assigned to two groups: the HI group and the Notch pathway inhibitor + HI group (n = 24 per group). Each group was further divided into six subgroups according to HI duration (n = 4 per group): a control subgroup, and 0-6, 6-12, 12-24, 24-48, and 48-72 h subgroups. The expression of Notch pathway-related proteins, including Notch1, Hes1, and Notch intracellular domains, increased following HI injury. The expression of autophagy proteins increased at 0-6 h and 6-12 h post-HI. The expression of synaptic proteins, such as postsynaptic density protein 95 (PSD95) and synaptophysin, increased 6-12 h and 12-24 h after HI, respectively. Notably, the increased expression of these proteins was reversed by a Notch pathway inhibitor. Transmission electron microscopy revealed the presence of autophagosome structures in synapses. These findings shed light on the underlying mechanisms of neurological recovery after HI injury and may provide insights into potential therapeutic targets for promoting neural circuit reconstruction and maintaining neural network homeostasis.

The Signaling Pathways and Targets of Natural Compounds from Traditional Chinese Medicine in Treating Ischemic Stroke

Ischemic stroke (IS) is a common neurological disorder associated with high disability rates and mortality rates. At present, recombinant tissue plasminogen activator (r-tPA) is the only US(FDA)-approved drug for IS. However, due to the narrow therapeutic window and risk of intracerebral hemorrhage, r-tPA is currently used in less than 5% of stroke patients. Natural compounds have been widely used in the treatment of IS in China and have a wide range of therapeutic effects on IS by regulating multiple targets and signaling pathways. The keywords "ischemia stroke, traditional Chinese Medicine, Chinese herbal medicine, natural compounds" were used to search the relevant literature in PubMed and other databases over the past five years. The results showed that JAK/STAT, NF-κB, MAPK, Notch, Nrf2, and PI3K/Akt are the key pathways, and SIRT1, MMP9, TLR4, HIF-α are the key targets for the natural compounds from traditional Chinese medicine in treating IS. This study aims to update and summarize the signaling pathways and targets of natural compounds in the treatment of IS, and provide a base of information for the future development of effective treatments for IS.

Post-stroke Neurogenesis: Friend or Foe?

The substantial clinical burden and disability after stroke injury urges the need to explore therapeutic solutions. Recent compelling evidence supports that neurogenesis persists in the adult mammalian brain and is amenable to regulation in both physiological and pathological situations. Its ability to generate new neurons implies a potential to contribute to recovery after brain injury. However, post-stroke neurogenic response may have different functional consequences. On the one hand, the capacity of newborn neurons to replenish the damaged tissue may be limited. In addition, aberrant forms of neurogenesis have been identified in several insult settings. All these data suggest that adult neurogenesis is at a crossroads between the physiological and the pathological regulation of the neurological function in the injured central nervous system (CNS). Given the complexity of the CNS together with its interaction with the periphery, we ultimately lack in-depth understanding of the key cell types, cell-cell interactions, and molecular pathways involved in the neurogenic response after brain damage and their positive or otherwise deleterious impact. Here we will review the evidence on the stroke-induced neurogenic response and on its potential repercussions on functional outcome. First, we will briefly describe subventricular zone (SVZ) neurogenesis after stroke beside the main evidence supporting its positive role on functional restoration after stroke. Then, we will focus on hippocampal subgranular zone (SGZ) neurogenesis due to the relevance of hippocampus in cognitive functions; we will outline compelling evidence that supports that, after stroke, SGZ neurogenesis may adopt a maladaptive plasticity response further contributing to the development of post-stroke cognitive impairment and dementia. Finally, we will discuss the therapeutic potential of specific steps in the neurogenic cascade that might ameliorate brain malfunctioning and the development of post-stroke cognitive impairment in the chronic phase.

Rehabilitation training improves nerve injuries by affecting Notch1 and SYN

Objective

The aim of this study was to investigate the effects of rehabilitation training on Notch1 and synaptophysin (SYN) levels in brain tissues of rats with chronic cerebral ischemia.

Methods

Eighty-one male Sprague-Dawley rats were divided into nine groups: three Sham groups, three Model groups, and three training groups. There were nine rats in each group. At different time points, the apoptosis cell rate was analyzed by the TUNEL assay, and the expression levels of Notch1 and SYN in brain tissues were analyzed by immunohistochemical staining and RT-qPCR assay.

Results

The apoptosis cell rate of training groups was significantly higher on day 28 (P < 0.05). The protein and mRNA levels of both Noth1 and SYN in training groups were significantly higher on day 28 (P < 0.05).

Conclusion

Rehabilitation training could improve nerve cell apoptosis by increasing the expression of both Notch1 and SYN.

A novel mouse model for the study of endogenous neural stem and progenitor cells after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in the US. Neural stem/progenitor cells (NSPCs) persist in the adult brain and represent a potential cell source for tissue regeneration and wound healing after injury. The Notch signaling pathway is critical for embryonic development and adult brain injury response. However, the specific role of Notch signaling in the injured brain is not well characterized. Our previous study has established a Notch1CR2-GFP reporter mouse line in which the Notch1CR2 enhancer directs GFP expression in NSPCs and their progeny. In this study, we performed closed head injury (CHI) in the Notch1CR2-GFP mice to study the response of injury-activated NSPCs. We show that CHI induces neuroinflammation, cell death, and the expression of typical TBI markers (e.g., ApoE, Il1b, and Tau), validating the animal model. In addition, CHI induces cell proliferation in GFP+ cells expressing NSPC markers, e.g., Notch1 and Nestin. A significant higher percentage of GFP+ astrocytes and GABAergic neurons was observed in the injured brain, with no significant change in oligodendrocyte lineage between the CHI and sham animal groups. Since injury is known to activate astrogliosis, our results suggest that injury-induced GFP+ NSPCs preferentially differentiate into GABAergic neurons. Our study establishes that Notch1CR2-GFP transgenic mouse is a useful tool for the study of NSPC behavior in vivo after TBI. Unveiling the potential of NSPCs response to TBI (e.g., proliferation and differentiation) will identify new therapeutic strategy for the treatment of brain trauma.

Axonal regeneration and functional recovery driven by endogenous Nogo receptor antagonist LOTUS in a rat model of unilateral pyramidotomy

The adult mammalian central nervous system (CNS) rarely recovers from injury. Myelin fragments contain axonal growth inhibitors that limit axonal regeneration, thus playing a major role in determining neural recovery. Nogo receptor-1 (NgR1) and its ligands are among the inhibitors that limit axonal regeneration. It has been previously shown that the endogenous protein, lateral olfactory tract usher substance (LOTUS), antagonizes NgR1-mediated signaling and accelerates neuronal plasticity after spinal cord injury and cerebral ischemia in mice. However, it remained unclear whether LOTUS-mediated reorganization of descending motor pathways in the adult brain is physiologically functional and contributes to functional recovery. Here, we generated LOTUS-overexpressing transgenic (LOTUS-Tg) rats to investigate the role of LOTUS in neuronal function after damage. After unilateral pyramidotomy, motor function in LOTUS-Tg rats recovered significantly compared to that in wild-type animals. In a retrograde tracing study, labeled axons spanning from the impaired side of the cervical spinal cord to the unlesioned hemisphere of the red nucleus and sensorimotor cortex were increased in LOTUS-Tg rats. Anterograde tracing from the unlesioned cortex also revealed enhanced ipsilateral connectivity to the impaired side of the cervical spinal cord in LOTUS-Tg rats. Moreover, electrophysiological analysis showed that contralesional cortex stimulation significantly increased ipsilateral forelimb movement in LOTUS-Tg rats, which was consistent with the histological findings. According to these data, LOTUS overexpression accelerates ipsilateral projection from the unlesioned cortex and promotes functional recovery after unilateral pyramidotomy. LOTUS could be a future therapeutic option for CNS injury.

The Notch pathway in CNS homeostasis and neurodegeneration

The role of the Notch signaling pathway in neural development has been well established over many years. More recent studies, however, have demonstrated that Notch continues to be expressed and active throughout adulthood in many areas of the central nervous system. Notch signals have been implicated in adult neurogenesis, memory formation, and synaptic plasticity in the adult organism, as well as linked to acute brain trauma and chronic neurodegenerative conditions. NOTCH3 mutations are responsible for the most common form of hereditary stroke, the progressive disorder cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Notch has also been associated with several progressive neurodegenerative diseases, including Alzheimer's disease, multiple sclerosis, and amyotrophic lateral sclerosis. Although numerous studies link Notch activity with CNS homeostasis and neurodegenerative diseases, the data thus far are primarily correlative, rather than functional. Nevertheless, the evidence for Notch pathway activity in specific neural cellular contexts is strong, and certainly intriguing, and points to the possibility that the pathway carries therapeutic promise. This article is categorized under: Nervous System Development > Flies Signaling Pathways > Cell Fate Signaling Nervous System Development > Vertebrates: General Principles.

TGF-β2 Induces Gli1 in a Smad3-Dependent Manner Against Cerebral Ischemia/Reperfusion Injury After Isoflurane Post-conditioning in Rats

Isoflurane (ISO) post-conditioning attenuates cerebral ischemia/reperfusion (I/R) injury, but the underlying mechanism is incompletely elucidated. Transforming growth factor beta (TGF-β) and hedgehog (Hh) signaling pathways govern a wide range of mechanisms in the central nervous system. We aimed to investigate the effect of the TGF-β2/Smad3 and sonic hedgehog (Shh)/Glioblastoma (Gli) signaling pathway and their crosstalk in the hippocampus of rats with ISO post-conditioning after cerebral I/R injury. Adult male Sprague-Dawley rats were subjected to middle cerebral artery occlusion (MCAO), 1.5 h occlusion and 24 h reperfusion (MCAO/R). To assess the effect of ISO after I/R injury, various approaches were used, including neurobehavioral tests, TTC staining, HE staining, Nissl staining, TUNEL staining, immunofluorescence (IF), qRT-PCR (quantitative real-time polymerase chain reaction) and Western blot. The ISO post-conditioning group (ISO group) received 1 h ISO post-conditioning when reperfusion was initiated, leading to lower infarct volumes and neurologic deficit scores, more surviving neurons, and less damaged and apoptotic neurons. IF staining, qRT-PCR and Western blot showed high expression levels of TGF-β2, Shh and Gli1 in the hippocampal CA1 of the ISO group. Phosphorylated Smad3 (p-Smad3), Patched (Ptch), and Smoothed (Smo) were also increased at protein level in the ISO group, whereas total Smad3 expression did not change in all groups. When TGF-β2 inhibitor, pirfenidone, or Smad3 inhibitor, SIS3 HCl, were administered, the expression levels of p-Smad3 and Gli1 were reduced, and surviving pyramidal neurons decreased. By contrast, the expression levels of TGF-β2 and p-Smad3 did not change significantly after pre-injection of Smo inhibitor cyclopamine, but reduced the expression levels of Shh, Ptch, and Gli1. Moreover, Gli showed the lowest expression levels with pirfenidone combined with cyclopamine. These findings indicate that the TGF-β and hedgehog signaling pathways mediate the neuroprotection of ISO post-conditioning after cerebral I/R injury, and crosstalk between two pathways at the Gli1 level.

New Neurons in the Post-ischemic and Injured Brain: Migrating or Resident?

The endogenous potential of adult neurogenesis is of particular interest for the development of new strategies for recovery after stroke and traumatic brain injury. These pathological conditions affect endogenous neurogenesis in two aspects. On the one hand, injury usually initiates the migration of neuronal precursors (NPCs) to the lesion area from the already existing, in physiological conditions, neurogenic niche - the ventricular-subventricular zone (V-SVZ) near the lateral ventricles. On the other hand, recent studies have convincingly demonstrated the local generation of new neurons near lesion areas in different brain locations. The striatum, cortex, and hippocampal CA1 region are considered to be locations of such new neurogenic zones in the damaged brain. This review focuses on the relative contribution of two types of NPCs of different origin, resident population in new neurogenic zones and cells migrating from the lateral ventricles, to post-stroke or post-traumatic enhancement of neurogenesis. The migratory pathways of NPCs have also been considered. In addition, the review highlights the advantages and limitations of different methodological approaches to the definition of NPC location and tracking of new neurons. In general, we suggest that despite the considerable number of studies, we still lack a comprehensive understanding of neurogenesis in the damaged brain. We believe that the advancement of methods for in vivo visualization and longitudinal observation of neurogenesis in the brain could fundamentally change the current situation in this field.

Analysis of long non-coding RNA expression profiles in neonatal rats with hypoxic-ischemic brain damage

Hypoxic-ischemic brain damage (HIBD) which is a common cause of acute mortality and neurological dysfunction in neonates still lacks effective therapeutic methods. Long non-coding RNAs (lncRNAs) were demonstrated to play a crucial role in many diseases. To give a foundation for subsequent functional studies of lncRNAs in HIBD, we investigated the profiling of lncRNAs and messenger RNAs (mRNAs) using neonatal HIBD rat model. Six neonatal rats were divided into sham-operated group (n = 3) and HIBD group (n = 3) randomly. Deep RNA sequencing was implemented to find out the meaningful lncRNAs and mRNAs. Quantitative real-time PCR was used to validate expressions of lncRNAs and mRNAs. The Gene Ontology (GO) and kyoto encyclopedia of genes a genomes (KEGG) database were used to predict functions of lncRNAs. A total of 328 differentially expressed lncRNAs (177 down-regulated vs 151 up-regulated) and 7157 differentially expressed mRNAs (2552 down-regulated vs 4605 up-regulated) were identified. The Quantitative real-time PCR results showed significant differential expressions of five lncRNAs and five mRNAs which were consistent with the RNA-Seq data. Gene ontology and KEGG analysis showed these lncRNAs and their expression-correlated mRNAs were closely related to the Janus tyrosine kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway, NF-kappa B signaling pathway, Toll-like receptor signaling pathway, calcium signaling pathway, Notch signaling pathway, mitogen activated protein kinase signaling pathway, neuroactive ligand-receptor interaction pathway and more. The results of our study identified the characterization and expression profiles of lncRNAs in neonatal HIBD and may be a basis for further therapeutic research. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and *Open Data* because it provided all relevant information to reproduce the study in the manuscript and because it made the data publicly available. The data can be accessed at https://osf.io/yf3da/. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Lipoxin A4 Regulates Lipopolysaccharide-Induced BV2 Microglial Activation and Differentiation via the Notch Signaling Pathway

Inflammatory responses contribute to the pathogenesis of various neurological diseases, and microglia plays an important role in the process. Activated microglia can differentiate into the pro-inflammatory, tissue-damaging M1 phenotype or the anti-inflammatory, tissue-repairing M2 phenotype. Regulating microglia differentiation, hence limiting a harmful response, might help improve the prognosis of inflammation-related nervous system diseases. The present study aimed 1. to observe the anti-inflammatory effect of lipoxin A4 (LXA4) on the inflammatory response associated to lipopolysaccharide (LPS)-induced microglia activation, 2. to clarify that LXA4 modulates the activation and differentiation of microglia induced by LPS stimulation, 3. to determine whether LXA4 regulates the activation and differentiation of microglia through the Notch signaling pathway, 4. to provide a foundation for the use of LXA4 for the treatment of inflammatory related neurological diseases. To construct a model of cellular inflammation, immortalized murine BV2 microglia cells were provided 200 ng/ml LPS. To measure the mRNA and protein levels of inflammatory factors (interleukin [IL]-1β, IL-10, and tumor necrosis factor [TNF]-α) and M1 and M2 microglia markers (inducible nitric oxide synthase [iNOS], cluster of differentiation [CD]32, arginase [Arg]1, and CD206), we performed quantitative reverse transcription polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA), immunofluorescence, or flow cytometry. To determine the mRNA and protein levels of Notch signaling components (Notch1, Hes1, and Hes5), we performed qRT-PCR and western blot. LXA4 inhibits the expression of Notch1 and Hes1 associated with M1 type microglial differentiation and decreases the M1 type microglia marker iNOS and related inflammatory factors IL-1β and TNF-α. Moreover, LXA4 upregulates the expression of the M2-associated Hes5, as well as the expression of the M2 microglia marker Arg1 and the associated inflammatory factor IL-10. These effects are blocked by the administration of the γ-secretase inhibitor DAPT, a specific blocker of the Notch signaling pathway. LXA4 inhibits the microglia activation induced by LPS and the differentiation into M1 type with pro-inflammatory effect, while promoting the differentiation to M2 type with anti-inflammatory effect. LXA4 downregulates the inflammatory mediators IL-1β, TNF-α, and iNOS, while upregulating the anti-inflammatory mediator IL-10, which acts through the Notch signaling pathway.

HIF-1α is Critical for the Activation of Notch Signaling in Neurogenesis During Acute Epilepsy

Emerging evidence suggests that hypoxia-inducible factors (specifically, HIF-1α) and Notch signaling are involved in epileptogenesis and that cross-coupling exists between HIF-1α and Notch signaling in other diseases, including tumors and ischemia. However, the exact molecular mechanisms by which HIF-1α and Notch signaling affect the development of epilepsy, especially regarding neurogenesis, remain unclear. In the present study, we investigated the role of HIF-1α in neurogenesis and whether Notch signaling is involved in this process during epileptogenesis by assessing hippocampal apoptosis, neuronal injury, and the proliferation and differentiation of neural stem cells (NSCs) in four groups, including control, epilepsy, epilepsy+2-methoxyestradiol (2ME2) and epilepsy+GSI-IX (DAPT) groups. Our data demonstrated that HIF-1α mediated neurogenesis during acute epilepsy, which required the participation of Notch signaling. The immunoprecipitation data illustrated that HIF-1α activated Notch signaling by physically interacting with the Notch intracellular domain (NICD) in epilepsy. In conclusion, our results suggested that HIF-1α-Notch signaling enhanced neurogenesis in acute epilepsy and that neurogenesis during epileptogenesis was reduced once this pathway was blocked; thus, members of this pathway might be potential therapeutic targets for epilepsy.

Huwe1 is a novel mediator of protection of neural progenitor L2.3 cells against oxygen‑glucose deprivation injury

Hypoxic‑ischemic encephalopathy is one of the most notable causes of brain injury in newborns. Cerebral ischemia and reperfusion lead to neuronal damage and neurological disability. In vitro and in vivo analyses have indicated that E3 ubiquitin protein ligase (Huwe1) is important for the process of neurogenesis during brain development; however, the exact biological function and the underlying mechanism of Huwe1 remain controversial. In the present study, neural progenitor cells, L2.3, of which we previously generated from rat E14.5 cortex, were used to investigate the role of Huwe1 and its effects on the downstream N‑Myc‑Delta‑like 3‑Notch1 signaling pathway during oxygen‑glucose deprivation (OGD). To evaluate the role of Huwe1 in L2.3 cells, transduction, cell viability, lactate dehydrogenase, 5‑bromo‑2'deoxyurine incorporation, western blotting and immunocytochemical assays were performed. The results of the present study indicated that Huwe1 rescued L2.3 cells from OGD‑induced insults by inhibiting proliferation and inducing neuronal differentiation. In addition, Huwe1 was suggested to mediate the survival of L2.3 cells by inhibiting the activation of the N‑Myc‑Notch1 signaling pathway. Of note, the effects of Huwe1 on Notch1 signaling were completely abolished by knockdown of N‑Myc, indicating that Huwe1 may require N‑Myc to suppress the activation of the Notch1 signaling in L2.3 cells. The determination of the neuroprotective function of the Huwe1‑N‑Myc‑Notch1 axis may provide insight into novel potential therapeutic targets for the treatment of ischemic stroke.

Inhibition of Notch1 Signaling at the Subacute Stage of Stroke Promotes Endogenous Neurogenesis and Motor Recovery After Stroke

Background and Purpose: It is still not clear whether Notch1 signaling inhibition can promote functional outcomes after stroke, given that it plays time-dependent roles in the sequential process of endogenous neurogenesis. The purpose of this study was to identify the appropriate time frame for Notch1 signaling inhibition according to the temporal evolution of Notch1 signaling activation and the responses of neural stem cells (NSCs), in order to target it for therapeutic intervention and stimulate neurorestorative strategies after stroke.

Methods: Sprague-Dawley (SD) rats were subjected to 90-min of middle cerebral artery occlusion (MCAO). Rats were sacrificed before, and at day 1, day 2, day 3, day 4, and day 7 after ischemia for immunohistochemical analysis of the Notch intracellular domain (NICD), Nestin and doublecortin (Dcx). Next, MCAO rats were treated with the γ-secretase inhibitor N-[N-(3,5-di uorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT) or with saline at day 4 after ischemia, and subsequently evaluated with behavioral test analysis and magnetic resonance imaging (MRI). The rat brains were then harvested for immunohistochemical analysis of Dcx, NeuN and myelin basic protein (MBP) at 2, 3, 4, and 8 weeks.

Results: Notch1 signaling was maximally activated at day 3 after ischemia in parallel with the temporal evolution of NSCs. Inhibiting Notch1 signaling at day 4 after reperfusion with DAPT further promoted recovery of MRI parameters of the corticospinal tract (CST) and the functional outcomes, concomitantly with an increase in neuroblasts, their migration to the ischemic boundary, and potential differentiation to mature neurons, as well as the amelioration of axonal bundle integrity.

Conclusion: Inhibition of Notch1 signaling at the subacute stage of stroke could maximally promote endogenous neurogenesis and axonal reorganization.

ASIC1 promotes differentiation of neuroblastoma by negatively regulating Notch signaling pathway

In neurons, up-regulation of Notch activity either inhibits neurite extension or causes retraction of neurites. Conversely, inhibition of Notch1 facilitates neurite extension. Acid-sensing ion channels (ASICs) are a family of proton-gated cation channels, which play critical roles in synaptic plasticity, learning and memory and spine morphogenesis. Our pilot proteomics data from ASIC1a knock out mice implicated that ASIC1a may play a role in regulating Notch signaling, therefore, we explored whether or not ASIC1a regulates neurite growth during neuronal development through Notch signaling. In this study, we determined the effects of ASIC1a on neurite growth in a mouse neuroblastoma cell line, NS20Y cells, by modulating ASIC1a expression. We also determined the relationship between ASIC1a and Notch signaling on neuronal differentiation. Our results showed that down-regulation of ASIC1a in NS20Y cells inhibits CPT-cAMP induced neurite growth, while over expression of ASIC1a promotes its growth. In addition, down-regulation of ASIC1a increased the expression of Notch1 and its target gene Survivin while inhibitor of Notch significantly prevented the neurite extension induced by ASIC1a in NS20Y cells. These data indicate that Notch1 signaling may be required for ASIC1a-mediated neurite growth and neuronal differentiation.

MRI detects protective effects of DAPT treatment with modulation of microglia/macrophages at subacute and chronic stages following cerebral ischemia

Notch homolog 1 (Notch 1) signaling is regarded as a potential therapeutic target for modulating the inflammatory response and exhibiting neuroprotective effects in cerebral injury following stroke. N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butylester (DAPT) efficiently inhibits activation of the Notch 1 signaling pathway in microglia and may protect brain tissue from ischemic damage. However, the temporal proliferation and morphological alterations of microglia/macrophages throughout progression of the disease, as well as the comprehensive alterations of the whole brain following DAPT treatment, remain to be elucidated. The present study evaluated the temporal proliferation and the morphological alterations of microglia/macrophages over the period of the subacute and chronic stages, in addition to dynamic alterations of brain tissue, using the magnetic resonance imaging (MRI) method, following DAPT treatment. Sprague-Dawley rats (n=40) were subjected to 90 min of middle cerebral artery occlusion and were treated with DAPT (n=20) or acted as controls with no treatment (n=20). The two groups of rats underwent MRI scans prior to the induction of stroke symptoms and at 24 h, 7, 14, 21 and 28 days following the stroke. A total of five rats from each group were sacrificed at 7, 14, 21 and 28 days following induction of stroke. Compared with control rats, the MRI data of the ipsilateral striatum in treated rats revealed ameliorated brain edema at the subacute stage and recovered brain tissue at the chronic stage. In addition to this, treatment attenuated the round-shape and promoted a ramified-shape of microglia/macrophages. The present study confirmed the protective effect of DAPT treatment by dynamically monitoring the cerebral alterations and indicated the possibility of DAPT treatment to alter microglial characteristics to induce a protective effect, via inhibition of the Notch signaling pathway.

Pharmacological approaches to intervention in hypomyelinating and demyelinating white matter pathology

White matter disease afflicts both developing and mature central nervous systems. Both cell intrinsic and extrinsic dysregulation result in profound changes in cell survival, axonal metabolism and functional performance. Experimental models of developmental white matter (WM) injury and demyelination have not only delineated mechanisms of signaling and inflammation, but have also paved the way for the discovery of pharmacological approaches to intervention. These reagents have been shown to enhance protection of the mature oligodendrocyte cell, accelerate progenitor cell recruitment and/or differentiation, or attenuate pathological stimuli arising from the inflammatory response to injury. Here we highlight reports of studies in the CNS in which compounds, namely peptides, hormones, and small molecule agonists/antagonists, have been used in experimental animal models of demyelination and neonatal brain injury that affect aspects of excitotoxicity, oligodendrocyte development and survival, and progenitor cell function, and which have been demonstrated to attenuate damage and improve WM protection in experimental models of injury. The molecular targets of these agents include growth factor and neurotransmitter receptors, morphogens and their signaling components, nuclear receptors, as well as the processes of iron transport and actin binding. By surveying the current evidence in non-immune targets of both the immature and mature WM, we aim to better understand pharmacological approaches modulating endogenous oligodendroglia that show potential for success in the contexts of developmental and adult WM pathology. This article is part of the Special Issue entitled 'Oligodendrocytes in Health and Disease'.

Temporal changes in the response of SVZ neural stem cells to intraventricular administration of growth factors

In vivo growth factor (GF) treatment is a promising approach to enhance the regenerative capacity of neural stem cells (NSCs) for brain repair. However, how exogenous GFs affect endogenous NSCs is not well understood. This study investigated the impact of intraventricular administration of fibroblast growth factor 2 and epidermal growth factor on NSCs in the subventricular zone of intact adult mice. GFs were administered for various periods (3, 7, 10, and 14 days), and the proliferation and neuronal production of NSCs were assessed during and after GF treatment. We found that proliferation of NSCs and their progeny is markedly augmented during the first 7 days after the initiation of GF treatment. GF treatment for longer periods, however, did not lead to further increases in the NSC pool, but rather attenuated such proliferation and inhibited neurogenesis. As a result, the production of new olfactory bulb neurons was increased in animals treated with GFs for 7 days but decreased in animals treated for 14 days. These results show time-dependent changes in the response of NSCs to exogenous GFs and demonstrate that precise control of the duration of GF treatment is important for significant enhancement of neuronal production by NSCs in vivo for brain repair.

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.

Methylprednisolone inhibits the proliferation and affects the differentiation of rat spinal cord-derived neural progenitor cells cultured in low oxygen conditions by inhibiting HIF-1α and Hes1 in vitro

Although there is much controversy over the use of methylprednisolone (MP), it is one of the main drugs used in the treatment of acute spinal cord injury (SCI). The induction of the proliferation and differentiation of endogenous neural progenitor cells (NPCs) is considered a promising mode of treatment for SCI. However, the effects of MP on spinal cord-derived endogenous NPCs in a low oxygen enviroment remain to be delineated. Thus, the aim of this study was to investigate the potential effects of MP on NPCs cultured under low oxygen conditions in vitro and to elucidate the molecular mechanisms involved. Fetal rat spinal cord-derived NPCs were harvested and divided into 4 groups: 2 groups of cells cultured under normal oxygen conditions and treated with or without MP, and 2 groups incubated in 3% O2 (low oxygen) treated in a similar manner. We found that MP induced suppressive effects on NPC proliferation even under low oxygen conditions (3% O2). The proportion of nestin-positive NPCs decreased from 51.8±2.46% to 36.17±3.55% following the addition of MP and decreased more significantly to 27.20±2.68% in the cells cultured in 3% O2. In addition, a smaller number of glial fibrillary acidic protein (GFAP)-positive cells and a greater number of microtubule-associated protein 2 (MAP2)-positive cells was observed following the addition of MP under both normal (normoxic) and low oxygen (hypoxic) conditions. In response to MP treatment, hypoxia-inducible factor-1α (HIF-1α) and the Notch signaling pathway downstream protein, Hes1, but not the upstream Notch-1 intracelluar domain (NICD), were inhibited. After blocking NICD with a γ-secretase inhibitor (DAPT) MP still inhibited the expression of Hes1. Our results provide insight into the molecular mechanisms responsible for the MP-induced inhibition of proliferation and its effects on differentiation and suggest that HIF-1α and Hes1 play an important role in this effect.

Timing of the cell cycle exit of differentiating hippocampal neural stem cells

Neural stem cells contribute to mammalian brain tissue turnover in specific locations throughout life. Differentiation of stem cells is associated with terminal mitosis and cell cycle exit, but it is unclear how the timing and signaling of these are interlinked. Here, we have investigated the cell cycle exit characteristics in comparison with morphological changes during hippocampal stem cell differentiation in an adult mammalian cell line. Our results suggest that the cell-specific gene pathway induction is fast and robust and takes place in one day, whereas the cell cycle exit machinery is slower and takes several days to fully execute. The hippocampal differentiation is associated with epigenetic changes, such as Ezh2 down regulation and histone methylation. A small percentage of stem cells is able to resist differentiation-induced terminal mitosis for weeks in culture, and can be reverted to proliferation by re-adding the mitotic growth factors.

The neuroprotective effects of isoflurane preconditioning in a murine transient global cerebral ischemia-reperfusion model: the role of the Notch signaling pathway

Inhalational anesthetic preconditioning can induce neuroprotective effects, and the notch signaling pathway plays an important role in neural progenitor cell differentiation and the inflammatory response after central nervous system injury. This study evaluated whether the neuroprotective effect of isoflurane preconditioning is mediated by the activation of the notch signaling pathway. Mice were divided into two groups consisting of those that did or did not receive preconditioning with isoflurane. The expression levels of notch-1, notch intracellular domain (NICD), and hairy and enhancer of split (HES-1) were measured in mice subjected to transient global cerebral ischemia-reperfusion injury. The notch signaling inhibitor DAPT and conditional notch-RBP-J knockout mice were used to investigate the mechanisms of isoflurane preconditioning-induced neuroprotection. Immunohistochemical staining, real-time polymerase chain reaction assays, and Western blotting were performed. Isoflurane preconditioning induced neuroprotection against global cerebral ischemia. Preconditioning up-regulated the expression of notch-1, HES-1, and NICD after ischemic-reperfusion. However, these molecules were down-regulated at 72 h after ischemic-reperfusion. The inhibition of notch signaling activity by DAPT significantly attenuated the isoflurane preconditioning-induced neuroprotection, and similar results were obtained using notch knockout mice. Our results demonstrate that the neuroprotective effects of isoflurane preconditioning are mediated by the pre-activation of the notch signaling pathway.

Electroacupuncture enhances hippocampal NSCs proliferation in cerebral ischemia-reperfusion injured rats via activation of notch signaling pathway

The purpose of this study was to investigate the mechanisms by which electroacupuncture (EA) enhances hippocampal neural stem cells (NSCs) proliferation in cerebral ischemia-reperfusion (I/R) injured rats. A total of 72 male adult Sprague-Dawley rats were randomly divided into the sham operation control group (SC), the ischemia control group (IC) and the EA group. Middle cerebral artery occlusion (MCAO) was performed to establish the focal cerebral I/R injury model. Proliferation of hippocampal NSCs in cerebral I/R injured rats was determined by the Nestin immunohistochemical staining. Activation of the notch signaling pathway was detected by Western blotting and reverse transcription polymerase chain reaction analysis. The serum level of neurotrophic factors, e.g., the brain-derived neurotrophic factor (BDNF) and the Glial cell line-derived neurotrophic factor (GDNF), was measured using enzyme-linked immunosorbent assay (ELISA). The results showed that EA at Quchi (LI11) and Zusanli (ST36) acupoints significantly alleviated neurological deficits, reduced infarct volumes and promoted the proliferation of hippocampal NSCs in cerebral I/R injured rats. The crucial signaling molecules in the notch signaling pathway were activated and the secretion of BDNF and GDNF was increased upon EA. The protein and mRNA levels of Cyclin D1, Cdk4 and p-Rb were increased, while p21 and p27 transcripts were suppressed by notch signaling. These results suggest that the up-regulatory effect of EA on the notch signaling pathway and neurotrophic factor secretion may result in the promotion of NSCs proliferation and consequently a therapeutic effect on cerebral ischemia.

DAPT protects brain against cerebral ischemia by down-regulating the expression of Notch 1 and nuclear factor κB in rats

Gamma-secretase inhibitor, N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butyl ester (DAPT) suppresses the activation of Notch 1 signaling, which is recognized as the cell fate signaling and may participate in inflammatory processes together with NF-κB pathway that contributes to the brain damage after stroke. DAPT has important pharmacological roles in many diseases. However, little is known about the effect of DAPT on NF-κB during cerebral ischemia. This study investigated the time course expression of Notch 1 and the effects of DAPT on Notch 1 and NF-jB after MCAO. The results showed that Notch 1 signaling was up-regulated at the early stage after MCAO, DAPT down-regulated the expression of Notch 1 and NF-κB and protected brain from damage caused by MCAO. These results may indicate that the downregulation of Notch 1–NF-κB pathway after ischemia by administration of DAPT is a potential mechanism for its protection.

Cortical endogenic neural regeneration of adult rat after traumatic brain injury

Focal and diffuse neuronal loss happened after traumatic brain injury (TBI). With little in the way of effective repair, recent interest has focused on endogenic neural progenitor cells (NPCs) as a potential method for regeneration. Whether endogenic neural regeneration happened in the cortex of adult rat after TBI remains to be determined. In this study, rats were divided into a sham group and a TBI group, and the rat model of medium TBI was induced by controlled cortical impact. Rats were injected with BrdU at 1 to 7 days post-injury (dpi) to allow identification of differentiated cells and sacrificed at 1, 3, 7, 14 and 28 dpi for immunofluorescence. Results showed nestin(+)/sox-2(+) NPCs and GFAP(+)/sox-2(+) radial glial (RG)-like cells emerged in peri-injured cortex at 1, 3, 7, 14 dpi and peaked at 3 dpi. The number of GFAP(+)/sox-2(+) cells was less than that of nestin(+)/sox-2(+) cells. Nestin(+)/sox-2(+) cells from posterior periventricle (pPV) immigrated into peri-injured cortex through corpus callosum (CC) were found. DCX(+)/BrdU(+) newborn immature neurons in peri-injured cortex were found only at 3, 7, 14 dpi. A few MAP-2(+)/BrdU(+) newborn neurons in peri-injured cortex were found only at 7 and 14 dpi. NeuN(+)/BrdU(+) mature neurons were not found in peri-injured cortex at 1, 3, 7, 14 and 28 dpi. While GFAP(+)/BrdU(+) astrocytes emerged in peri-injured cortex at 1, 3, 7, 14, 28 dpi and peaked at 7 dpi then kept in a stable state. In the corresponding time point, the percentage of GFAP(+)/BrdU(+) astrocytes in BrdU(+) cells was more than that of NPCs or newborn neurons. No CNP(+)/BrdU(+) oligodendrocytes were found in peri-injured cortex. These findings suggest that NPCs from pPV and reactive RG-like cells emerge in peri-injured cortex of adult rats after TBI. It can differentiate into immature neurons and astrocytes, but the former fail to grow up to mature neurons.

Notch signaling in the brain: in good and bad times

Notch signaling is an evolutionarily conserved pathway, which is fundamental for neuronal development and specification. In the last decade, increasing evidence has pointed out an important role of this pathway beyond embryonic development, indicating that Notch also displays a critical function in the mature brain of vertebrates and invertebrates. This pathway appears to be involved in neural progenitor regulation, neuronal connectivity, synaptic plasticity and learning/memory. In addition, Notch appears to be aberrantly regulated in neurodegenerative diseases, including Alzheimer's disease and ischemic injury. The molecular mechanisms by which Notch displays these functions in the mature brain are not fully understood, but are currently the subject of intense research. In this review, we will discuss old and novel Notch targets and molecular mediators that contribute to Notch function in the mature brain and will summarize recent findings that explore the two facets of Notch signaling in brain physiology and pathology.

Retinol palmitate prevents ischemia-induced cell changes in hippocampal neurons through the Notch1 signaling pathway in mice

Retinol palmitate, an analog of vitamin A, plays multiple roles in the nervous system, including neural differentiation, axon outgrowth, and neural patterning, and is also an antioxidative agent and thereby potential neuroprotectant for brain ischemia. The present study aimed at investigating the protective effects of retinol palmitate against ischemia-induced brain injury in a bilateral common carotid artery occlusion (BCCAO) model in mice. Ischemia induced by 20-min BCCAO resulted in significant neuronal morphological changes and reactive astrocyte proliferation in the hippocampus, particularly in the CA1 region, and these changes were accompanied by increased Notch1 expression. Intraperitoneal retinol palmitate administration before ischemia reduced ischemic neurons with Notch1 expression; the differences were statistically significant in both the 1.2mg/kg group and 12 mg/kg group. These results show that retinol palmitate prevents brain ischemia-induced neuronal injury with Notch1 expression and that Notch1 signaling could be involved in the neuroprotective mechanism. Retinol palmitate could be a treatment option for human brain infarction.

Hyperbaric oxygenation reduces long-term brain injury and ameliorates behavioral function by suppression of apoptosis in a rat model of neonatal hypoxia-ischemia

Neonatal hypoxia-ischemia (HI) produces neurodegeneration and brain injury, and leads to behavioral and cognitive dysfunction. Hyperbaric oxygen (HBO) treatment may potentially be neuroprotective in HI injury. The aim of this study was to examine any neuroprotection by HBO treatment on long-term neurological function in the rat model of neontatal HI. Seven-day-old rats were subjected to HI or sham surgery. HBO treatment was administered (2.5 ATA for 90 min) 1h after hypoxia exposure. Sensorimotor (grip test and rota-rod) and cognitive tests (inhibitory avoidance and Morris water maze) were performed at postnatal day 28 to day 60. The extent of brain damage was determined by histological evaluation. Apoptosis, caspase-3 and apoptosis inducing factor (AIF) expression were assessed by immunohistochemistry 12, 24, and 48 h after HI. HI-treated animals had significantly worse sensorimotor and cognitive performances than those in the Sham group. HBO treatment led to significant improvements in neurobehavioral functions compared to the HI group, especially for cognitive performances. Morphological evaluation revealed a remarkable recovery of brain injury in the HBO group. Furthermore, the improvements in neurobehavioral impairments were correlated with the reduction in lesion size of the hippocampus and cerebral cortex. The proportion of apoptotic cells significantly increased with time after HI, and HBO significantly inhibited apoptotic cell death. The proportion of caspase-3 positive cells and nuclear AIF translocation increased and peaked at 24h after HI injury. HBO-treated rats showed decreased expression of these proteins compared to HI-treated animals. In conclusion, our results suggested that HBO treatment was effective in promoting long-term functional and histological recovery against neonatal HI brain injury. HBO-induced neuroprotection was associated with suppression of apoptosis by inhibiting caspase-3 and AIF-mediated pathways. Further studies evaluating its associated molecular and cellular mechanism are needed.

Effects of low temperatures on proliferation-related signaling pathways in the hippocampus after traumatic brain injury

To evaluate the influence of low temperatures on the proliferation of neural stem cells (NSCs) and the regulation of their signaling pathways after brain trauma, we examined changes in the expression levels of specific miRNAs and their target genes. We also evaluated NSC proliferation in the hippocampus after brain trauma under low-temperature conditions. We found that the expression profile of miRNAs in the hippocampus after trauma changed at both normal and low temperatures, and the expression of miR-34a decreased significantly lower in rats exposed to low temperatures. There was significant proliferation of endogenous NSCs in the hippocampus after brain trauma at both temperatures, but NSC proliferation was slower at low temperatures. In addition, the expression of Notch1 significantly increased in the hippocampus after brain trauma at both temperatures. However, at low temperatures, the degree of up-regulation of Notch signaling molecules was significantly lower. We conclude that low-temperature environments can inhibit the proliferation of endogenous NSCs in the hippocampus, possibly by alleviating the effects of miR-34a down-regulation and Notch signaling up-regulation induced by traumatic brain injury.

IKKβ/NF-κB disrupts adult hypothalamic neural stem cells to mediate a neurodegenerative mechanism of dietary obesity and pre-diabetes

Adult neural stem cells (NSCs) are known to exist in a few regions of the brain; however, the entity and physiological/disease relevance of adult hypothalamic NSCs (htNSCs) remain unclear. This work shows that adult htNSCs are multipotent and predominantly present in the mediobasal hypothalamus of adult mice. Chronic high-fat-diet feeding led to not only depletion but also neurogenic impairment of htNSCs associated with IKKβ/NF-κB activation. In vitro htNSC models demonstrated that their survival and neurogenesis markedly decreased on IKKβ/NF-κB activation but increased on IKKβ/NF-κB inhibition, mechanistically mediated by IKKβ/NF-κB-controlled apoptosis and Notch signalling. Mouse studies revealed that htNSC-specific IKKβ/NF-κB activation led to depletion and impaired neuronal differentiation of htNSCs, and ultimately the development of obesity and pre-diabetes. In conclusion, adult htNSCs are important for the central regulation of metabolic physiology, and IKKβ/NF-κB-mediated impairment of adult htNSCs is a critical neurodegenerative mechanism for obesity and related diabetes.

Notch signaling pathway regulates proliferation and differentiation of immortalized Müller cells under hypoxic conditions in vitro

Previous studies have indicated that Müller glia in chick and fish retinas can re-enter the cell cycle, express progenitor genes, and regenerate neurons via the Notch signaling pathway in response to retinal damage or growth factors. Here, we investigated the role of Notch signaling and the effect of hypoxia, as a means to induce retinal damage, on the proliferation of an immortalized Müller cell line (rMC-1 cells). Our data showed that rMC-1 cells expressed Müller glia and neural and retinal progenitor markers but did not express neuronal or retinal markers. Hypoxia increased rMC-1 cell proliferation by activating the positive cell-cycle regulators, cyclins A and D1, as well as the neural and retinal progenitor markers, Notch1, Hes1, nestin, Sox2, Msi1, Pax6, and NeuroD1. However, hypoxia did not significantly influence the expression of Müller glial markers GS, CRALBP, and cyclin D3 or the death of the rMC-1 cells. The increase in cell proliferation induced by hypoxia was greatly attenuated by blocking Notch signaling with the inhibitor DAPT, resulting in the reduced expression of positive cell-cycle regulators (cyclins A and D1) and neural and retinal progenitor markers (Notch1, Hes1, Sox2, Pax6, and NeuroD1). Blockade of the Notch signaling pathway by DAPT after hypoxia promoted the differentiation of rMC-1 cells to neurons, as demonstrated by the induction of neural marker (Tuj1), retinal amacrine (Syntaxin1), and retinal ganglion cell (Brn3b) markers, although the expression of the latter marker was low. Taken together, our data indicate that Notch signaling is required for proliferation under hypoxic conditions either by activating the positive cell-cycle regulators or by skewing their de-differentiation towards a neural progenitor lineage. These findings indicate that the Notch signaling pathway regulates hypoxia-induced proliferation and differentiation of Müller glia.

Suppression of astrocyte lineage in adult hippocampal progenitor cells expressing hippocampal cholinergic neurostimulating Peptide precursor in an in vivo ischemic model

Hippocampal cholinergic neurostimulating peptide (HCNP) is known to promote differentiation of septohippocampal cholinergic neurons. The HCNP precursor protein (HCNP-pp) may play several roles, for example, as an ATP-binding protein, a Raf kinase inhibitor protein, and a phosphatidylethanolamine-binding protein, as well as a precursor for HCNP. This study therefore aimed to elucidate the involvement of HCNP-pp in specific neural lineages after stroke using a hypoxic-ischemic (HI) rat model of brain ischemia. The specific neural lineages in the hippocampus were investigated 14 days after ischemia. Some bromodeoxyuridine (BrdU)(+) neural progenitor cells in the hippocampus of hypoxic, HI, or sham-operated rats expressed HCNP-pp. Almost half of the BrdU(+)/HCNP-pp(+) cells also expressed the oligodendrocyte lineage marker 2',3'-cyclic nucleotide 3'-phosphodiesterase, whereas only a few BrdU(+)/HCNP-pp(+) cells in the hippocampus in HI brains expressed the neuronal lineage marker, doublecortin (DCX). Interestingly, no BrdU(+)/HCNP-pp(+) progenitor cells in hypoxic, HI, or sham-operated brains expressed the astrocyte lineage marker, glial fibrillary acidic protein. Together with previous in vitro data, the results of this study suggest that the expression level of HCNP-pp regulates the differentiation of neural progenitor cells into specific neural lineages in the HI hippocampus, indicating that neural stem cell fate can be controlled via the HCNP-pp mediating pathway.

Notch signaling components are upregulated during both endochondral and intramembranous bone regeneration

Previous studies have demonstrated that Notch signaling regulates endochondral and intramembranous bone formation by controlling cell proliferation and differentiation. Notch signaling has also been shown to regulate healing in a variety of tissues. The objective of this study was to characterize and compare activation of the Notch signaling pathway during endochondral and intramembranous bone healing using tibial fracture and calvarial defect injury models, respectively. Bilateral tibial fractures or bilateral 1.5 mm diameter calvarial defects were created in mice, and tissues were harvested at 0, 5, 10, and 20 days post-fracture. Gene expression of Notch signaling components was upregulated during both tibial fracture and calvarial defect healing, with expression generally higher during tibial fracture healing. The most highly expressed ligand and receptor during healing, Jag1 and Notch2 (specifically the activated receptor, known as NICD2), were similarly localized in mesenchymal cells during both modes of healing, with expression decreasing during chondrogenesis, but remaining present in osteoblasts at all stages of maturity. Results suggest that in addition to embryological bone development, Notch signaling regulates both endochondral and intramembranous bone healing.

MicroRNA-146a inhibits glioma development by targeting Notch1

Dysregulated epidermal growth factor receptor (EGFR) signaling through either genomic amplification or dominant-active mutation (EGFR(vIII)), in combination with the dual inactivation of INK4A/ARF and PTEN, is a leading cause of gliomagenesis. Our global expression analysis for microRNAs revealed that EGFR activation induces miR-146a expression, which is further potentiated by inactivation of PTEN. Unexpectedly, overexpression of miR-146a attenuates the proliferation, migration, and tumorigenic potential of Ink4a/Arf(-/-) Pten(-/-) Egfr(vIII) murine astrocytes. Its ectopic expression also inhibits the glioma development of a human glioblastoma cell line in an orthotopic xenograft model. Such an inhibitory function of miR-146a on gliomas is largely through downregulation of Notch1, which plays a key role in neural stem cell maintenance and is a direct target of miR-146a. Accordingly, miR-146a modulates neural stem cell proliferation and differentiation and reduces the formation and migration of glioma stem-like cells. Conversely, knockdown of miR-146a by microRNA sponge upregulates Notch1 and promotes tumorigenesis of malignant astrocytes. These findings indicate that, in response to oncogenic cues, miR-146a is induced as a negative-feedback mechanism to restrict tumor growth by repressing Notch1. Our results provide novel insights into the signaling pathways that link neural stem cells to gliomagenesis and may lead to new strategies for treating brain tumors.

Not(ch) just development: Notch signalling in the adult brain

The Notch pathway is often regarded as a developmental pathway, but components of Notch signalling are expressed and active in the adult brain. With the advent of more sophisticated genetic manipulations, evidence has emerged that suggests both conserved and novel roles for Notch signalling in the adult brain. Not surprisingly, Notch is a key regulator of adult neural stem cells, but it is increasingly clear that Notch signalling also has roles in the regulation of migration, morphology, synaptic plasticity and survival of immature and mature neurons. Understanding the many functions of Notch signalling in the adult brain, and its dysfunction in neurodegenerative disease and malignancy, is crucial to the development of new therapeutics that are centred around this pathway.

Transient activation of Notch signaling in the injured adult brain

Brain injury induces various kinds of cellular responses that lead to tissue regeneration and repair. Recent studies have demonstrated that resident progenitors proliferate and then differentiate into mature neuronal cells. We show here that proliferating cells in the cryo-injured cerebral cortex transiently expressed Notch1 immunoreactivity in their cytoplasm. Since activated Notch signaling regulates cellular fate in the developing nervous system, similar regulation may exist in the injured adult brain. To monitor the Notch signaling pathway, we examined whether components of the signaling pathway were co-expressed in Notch1-positive cells. Presenilin-1, a membrane-spanning protease that is required for the release of the Notch intracellular domain, was detected in the Notch1-positive cells and Hes1, a target of the Notch intracellular domain, also co-localized with Notch1 three days after cryo-injury. These results suggest that transient activity of the Notch signaling pathway is involved in the regulation of proliferation and differentiation of progenitors in the injured brain.