Notch signaling imparts and preserves neural stem characteristics in the adult brain

Zebrafish: A New Promise to Study the Impact of Metabolic Disorders on the Brain

Zebrafish has become a popular model to study many physiological and pathophysiological processes in humans. In recent years, it has rapidly emerged in the study of metabolic disorders, namely, obesity and diabetes, as the regulatory mechanisms and metabolic pathways of glucose and lipid homeostasis are highly conserved between fish and mammals. Zebrafish is also widely used in the field of neurosciences to study brain plasticity and regenerative mechanisms due to the high maintenance and activity of neural stem cells during adulthood. Recently, a large body of evidence has established that metabolic disorders can alter brain homeostasis, leading to neuro-inflammation and oxidative stress and causing decreased neurogenesis. To date, these pathological metabolic conditions are also risk factors for the development of cognitive dysfunctions and neurodegenerative diseases. In this review, we first aim to describe the main metabolic models established in zebrafish to demonstrate their similarities with their respective mammalian/human counterparts. Then, in the second part, we report the impact of metabolic disorders (obesity and diabetes) on brain homeostasis with a particular focus on the blood-brain barrier, neuro-inflammation, oxidative stress, cognitive functions and brain plasticity. Finally, we propose interesting signaling pathways and regulatory mechanisms to be explored in order to better understand how metabolic disorders can negatively impact neural stem cell activity.

Regulating Endogenous Neural Stem Cell Activation to Promote Spinal Cord Injury Repair

Spinal cord injury (SCI) affects millions of individuals worldwide. Currently, there is no cure, and treatment options to promote neural recovery are limited. An innovative approach to improve outcomes following SCI involves the recruitment of endogenous populations of neural stem cells (NSCs). NSCs can be isolated from the neuroaxis of the central nervous system (CNS), with brain and spinal cord populations sharing common characteristics (as well as regionally distinct phenotypes). Within the spinal cord, a number of NSC sub-populations have been identified which display unique protein expression profiles and proliferation kinetics. Collectively, the potential for NSCs to impact regenerative medicine strategies hinges on their cardinal properties, including self-renewal and multipotency (the ability to generate de novo neurons, astrocytes, and oligodendrocytes). Accordingly, endogenous NSCs could be harnessed to replace lost cells and promote structural repair following SCI. While studies exploring the efficacy of this approach continue to suggest its potential, many questions remain including those related to heterogeneity within the NSC pool, the interaction of NSCs with their environment, and the identification of factors that can enhance their response. We discuss the current state of knowledge regarding populations of endogenous spinal cord NSCs, their niche, and the factors that regulate their behavior. In an attempt to move towards the goal of enhancing neural repair, we highlight approaches that promote NSC activation following injury including the modulation of the microenvironment and parenchymal cells, pharmaceuticals, and applied electrical stimulation.

Regenerative neurogenic response from glia requires insulin-driven neuron-glia communication

Understanding how injury to the central nervous system induces de novo neurogenesis in animals would help promote regeneration in humans. Regenerative neurogenesis could originate from glia and glial neuron-glia antigen-2 (NG2) may sense injury-induced neuronal signals, but these are unknown. Here, we used Drosophila to search for genes functionally related to the NG2 homologue kon-tiki (kon), and identified Islet Antigen-2 (Ia-2), required in neurons for insulin secretion. Both loss and over-expression of ia-2 induced neural stem cell gene expression, injury increased ia-2 expression and induced ectopic neural stem cells. Using genetic analysis and lineage tracing, we demonstrate that Ia-2 and Kon regulate Drosophila insulin-like peptide 6 (Dilp-6) to induce glial proliferation and neural stem cells from glia. Ectopic neural stem cells can divide, and limited de novo neurogenesis could be traced back to glial cells. Altogether, Ia-2 and Dilp-6 drive a neuron-glia relay that restores glia and reprogrammes glia into neural stem cells for regeneration.

Lineage tracing reveals the hierarchical relationship between neural stem cell populations in the mouse forebrain

Since the original isolation of neural stem cells (NSCs) in the adult mammalian brain, further work has revealed a heterogeneity in the NSC pool. Our previous work characterized a distinct, Oct4 expressing, NSC population in the periventricular region, through development and into adulthood. We hypothesized that this population is upstream in lineage to the more abundant, well documented, GFAP expressing NSC. Herein, we show that Oct4 expressing NSCs give rise to neurons, astrocytes and oligodendrocytes throughout the developing brain. Further, transgenic inducible mouse models demonstrate that the rare Oct4 expressing NSCs undergo asymmetric divisions to give rise to GFAP expressing NSCs in naïve and injured brains. This lineage relationship between distinct NSC pools contributes significantly to an understanding of neural development, the NSC lineage in vivo and has implications for neural repair.

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

Resetting cancer stem cell regulatory nodes upon MYC inhibition

MYC deregulation is common in human cancer and has a role in sustaining the aggressive cancer stem cell populations. MYC mediates a broad transcriptional response controlling normal biological programmes, but its activity is not clearly understood. We address MYC function in cancer stem cells through the inducible expression of Omomyc-a MYC-derived polypeptide interfering with MYC activity-taking as model the most lethal brain tumour, glioblastoma. Omomyc bridles the key cancer stemlike cell features and affects the tumour microenvironment, inhibiting angiogenesis. This occurs because Omomyc interferes with proper MYC localization and itself associates with the genome, with a preference for sites occupied by MYC This is accompanied by selective repression of master transcription factors for glioblastoma stemlike cell identity such as OLIG2, POU3F2, SOX2, upregulation of effectors of tumour suppression and differentiation such as ID4, MIAT, PTEN, and modulation of the expression of microRNAs that target molecules implicated in glioblastoma growth and invasion such as EGFR and ZEB1. Data support a novel view of MYC as a network stabilizer that strengthens the regulatory nodes of gene expression networks controlling cell phenotype and highlight Omomyc as model molecule for targeting cancer stem cells.

Buyang Huanwu decoction up-regulates Notch1 gene expression in injured spinal cord

Expression of genes in the Notch signaling pathway is altered in the injured spinal cord, which indicates that Notch participates in repair after spinal cord injury. Buyang Huanwu decoction, a traditional Chinese herbal preparation, can promote the growth of nerve cells and nerve fibers; however, it is unclear whether Buyang Huanwu decoction affects the Notch signaling pathway in injured spinal cord. In this study, a rat model was established by injuring the T10 spinal cord. At 2 days after injury, rats were intragastrically administered 2 mL of 0.8 g/mL Buyang Huanwu decoction daily until sacrifice. Real-time reverse transcription polymerase chain reaction analysis demonstrated that at 7, 14 and 28 days after injury, the expression of Notch1 was increased in the Buyang Huanwu decoction group compared with controls. These findings confirm that Buyang Huanwu decoction can promote the expression of Notch1 in rats with incomplete spinal cord injury, and may indicate a mechanism to promote the repair of spinal cord injury.

Electroacupuncture promotes neural stem cell proliferation and neurogenesis in the dentate gyrus of rats following stroke via upregulation of Notch1 expression

Neural stem cells (NSCs) are important in rehabilitation following stroke. Electroacupuncture (EA) treatment has been observed to promote the recovery of neurological functions subsequent to stroke, however, the effects of EA on the proliferation and differentiation of NSCs and its potential mechanisms remain to be elucidated. In the present study, rats, in which a stroke was induced through middle cerebral artery occlusion (MCAO), were treated with EA or control manipulation for 21 days. The modified Neurological Severity score and Morris water maze tests were used to assess the neurological functions of the rats. Bromodeoxyuridine (BrdU)/glial fibrillary acidic protein (GFAP) or BrdU/neuronal marker (NeuN) double immunofluorescence staining were used to examine the proliferation and differentiation of the NSCs. Reverse transcription quantitative polymerase chain reaction (RT‑qPCR) and western blot analyses were performed to detect the expression levels of Notch1 and Hes1 in the dentate gyrus (DG) of the hippocampus of rats following MCAO. The results demonstrated that EA treatment significantly improved the neurological functional recovery of rats following stroke. A significant increase was observed in the number of BrdU+/GAFP+ and BrdU+/NeuN+ cells in the DG area in the EA‑treated rats compared with that of the control group. RT‑qPCR analysis revealed that EA treatment significantly increased the expression levels of Notch1 and Hes1, which may account for the enhanced proliferation and differentiation of NSCs. In conclusion, to the best of our knowledge, the present study was the first to demonstrate that EA treatment promoted NSC proliferation and neurogenesis in the DG area through the upregulation of Notch signaling following a stroke; therefore, EA may be a useful novel therapeutic strategy in future stroke treatment.

SOX2+ cell population from normal human brain white matter is able to generate mature oligodendrocytes

OBJECTIVES

A number of neurodegenerative diseases progress with a loss of myelin, which makes them candidate diseases for the development of cell-replacement therapies based on mobilisation or isolation of the endogenous neural/glial progenitor cells, in vitro expansion, and further implantation. Cells expressing A2B5 or PDGFRA/CNP have been isolated within the pool of glial progenitor cells in the subcortical white matter of the normal adult human brain, all of which demonstrate glial progenitor features. However, the heterogeneity and differentiation potential of this pool of cells is not yet well established.

METHODS

We used diffusion tensor images, histopathology, and immunostaining analysis to demonstrate normal cytoarchitecture and the absence of abnormalities in human temporal lobe samples from patients with mesial temporal sclerosis. These samples were used to isolate and enrich glial progenitor cells in vitro, and later to detect such cells in vivo.

RESULTS

We have identified a subpopulation of SOX2+ cells, most of them co-localising with OLIG2, in the white matter of the normal adult human brain in vivo. These cells can be isolated and enriched in vitro, where they proliferate and generate immature (O4+) and mature (MBP+) oligodendrocytes and, to a lesser extent, astrocytes (GFAP+).

CONCLUSION

Our results demonstrate the existence of a new glial progenitor cell subpopulation that expresses SOX2 in the white matter of the normal adult human brain. These cells might be of use for tissue regeneration procedures.

Lgr5-positive supporting cells generate new hair cells in the postnatal cochlea

The prevalence of hearing loss after damage to the mammalian cochlea has been thought to be due to a lack of spontaneous regeneration of hair cells, the primary receptor cells for sound. Here, we show that supporting cells, which surround hair cells in the normal cochlear epithelium, differentiate into new hair cells in the neonatal mouse following ototoxic damage. Using lineage tracing, we show that new hair cells, predominantly outer hair cells, arise from Lgr5-expressing inner pillar and third Deiters cells and that new hair cell generation is increased by pharmacological inhibition of Notch. These data suggest that the neonatal mammalian cochlea has some capacity for hair cell regeneration following damage alone and that Lgr5-positive cells act as hair cell progenitors in the cochlea.

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Hair cells regenerate after damage to the neonatal mouse cochlea

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Generation of hair cells is increased by inhibition of Notch

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Hair cells regenerate by transdifferentiation with minimal proliferation

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Regenerated hair cells arise from Lgr5-positive supporting cells

Extracellular matrix: a dynamic microenvironment for stem cell niche

Background

Extracellular matrix (ECM) is a dynamic and complex environment characterized by biophysical, mechanical and biochemical properties specific for each tissue and able to regulate cell behavior. Stem cells have a key role in the maintenance and regeneration of tissues and they are located in a specific microenvironment, defined as niche.

Scope of review

We overview the progresses that have been made in elucidating stem cell niches and discuss the mechanisms by which ECM affects stem cell behavior. We also summarize the current tools and experimental models for studying ECM–stem cell interactions.

Major conclusions

ECM represents an essential player in stem cell niche, since it can directly or indirectly modulate the maintenance, proliferation, self-renewal and differentiation of stem cells. Several ECM molecules play regulatory functions for different types of stem cells, and based on its molecular composition the ECM can be deposited and finely tuned for providing the most appropriate niche for stem cells in the various tissues. Engineered biomaterials able to mimic the in vivo characteristics of stem cell niche provide suitable in vitro tools for dissecting the different roles exerted by the ECM and its molecular components on stem cell behavior.

General significance

ECM is a key component of stem cell niches and is involved in various aspects of stem cell behavior, thus having a major impact on tissue homeostasis and regeneration under physiological and pathological conditions. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

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Stem cells have a key role in the maintenance and regeneration of tissues.

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The extracellular matrix is a critical regulator of stem cell function.

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Stem cells reside in a dynamic and specialized microenvironment denoted as niche.

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The extracellular matrix represents an essential component of stem cell niches.

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Bioengineered niches can be used for investigating stem cell–matrix interactions.

Differential expression of Notch1 intracellular domain and p21 proteins, and their clinical significance in gastric cancer

Changes in the expression of the Notch1 intracellular domain (NICD) and p21 proteins have been shown to be closely associated with the development and progression of a number of cancers. The present study aimed to investigate the expression levels of the two proteins in gastric carcinoma and precancerous lesions, and to determine the clinical significance of this. A total of 109 gastric cancer, 57 precancerous gastric lesion, 50 chronic superficial gastritis and 17 normal gastric mucosa patients were recruited for immunohistochemical staining of NICD and p21 protein expression. The protein expression levels in the gastric cancer patient samples were associated with the clinicopathological and survival data. NICD protein levels were upregulated gradually from normal gastric mucosae through chronic superficial gastritis and precancerous gastric lesions to gastric cancer tissues (P<0.01), whereas p21 protein levels were downregulated accordingly (P<0.01). Increased NICD and a loss of p21 expression were closely associated with tumor dedifferentiation, depth of tumor invasion, lymph node metastasis, surface morphology and Lauren classification in gastric cancer. Thus, NICD expression was inversely associated with p21 expression. In addition, the overall survival rate was greater in NICD⁻ and P21⁺ patients than in NICD⁺ and P21⁻ patients, respectively (P<0.05). The COX regression multivariate analysis revealed that NICD⁺, p21⁻, depth of tumor invasion and lymph node metastasis were all independent prognostic factors for patients with gastric cancer. NICD and p21 proteins are differentially expressed in gastric cancer and the aberrant expression of these proteins is associated with an advanced tumor stage, tumor metastasis and overall patient survival. Future studies are required to further evaluate the two proteins as novel prognostic markers for patients with gastric cancer.