Inducible expression of noggin selectively expands neural progenitors in the adult SVZ

Mimicking the neural stem cell niche: An engineer’s view of cell: material interactions

Neural stem cells have attracted attention in recent years to treat neurodegeneration. There are two neurogenic regions in the brain where neural stem cells reside, one of which is called the subventricular zone (SVZ). The SVZ niche is a complicated microenvironment providing cues to regulate self-renewal and differentiation while maintaining the neural stem cell’s pool. Many scientists have spent years understanding the cellular and structural characteristics of the SVZ niche, both in homeostasis and pathological conditions. On the other hand, engineers focus primarily on designing platforms using the knowledge they acquire to understand the effect of individual factors on neural stem cell fate decisions. This review provides a general overview of what we know about the components of the SVZ niche, including the residing cells, extracellular matrix (ECM), growth factors, their interactions, and SVZ niche changes during aging and neurodegenerative diseases. Furthermore, an overview will be given on the biomaterials used to mimic neurogenic niche microenvironments and the design considerations applied to add bioactivity while meeting the structural requirements. Finally, it will discuss the potential gaps in mimicking the microenvironment.

Molecular Mechanisms and Clinical Application of Multipotent Stem Cells for Spinal Cord Injury

Spinal Cord Injury (SCI) is a common neurological disorder with devastating psychical and psychosocial sequelae. The majority of patients after SCI suffer from permanent disability caused by motor dysfunction, impaired sensation, neuropathic pain, spasticity as well as urinary complications, and a small number of patients experience a complete recovery. Current standard treatment modalities of the SCI aim to prevent secondary injury and provide limited recovery of lost neurological functions. Stem Cell Therapy (SCT) represents an emerging treatment approach using the differentiation, paracrine, and self-renewal capabilities of stem cells to regenerate the injured spinal cord. To date, multipotent stem cells including mesenchymal stem cells (MSCs), neural stem cells (NSCs), and hematopoietic stem cells (HSCs) represent the most investigated types of stem cells for the treatment of SCI in preclinical and clinical studies. The microenvironment of SCI has a significant impact on the survival, proliferation, and differentiation of transplanted stem cells. Therefore, a deep understanding of the pathophysiology of SCI and molecular mechanisms through which stem cells act may help improve the treatment efficacy of SCT and find new therapeutic approaches such as stem-cell-derived exosomes, gene-modified stem cells, scaffolds, and nanomaterials. In this literature review, the pathogenesis of SCI and molecular mechanisms of action of multipotent stem cells including MSCs, NSCs, and HSCs are comprehensively described. Moreover, the clinical efficacy of multipotent stem cells in SCI treatment, an optimal protocol of stem cell administration, and recent therapeutic approaches based on or combined with SCT are also discussed.

A TCF7L2-responsive suppression of both homeostatic and compensatory remyelination in Huntington disease mice

Huntington's disease (HD) is characterized by defective oligodendroglial differentiation and white matter disease. Here, we investigate the role of oligodendrocyte progenitor cell (OPC) dysfunction in adult myelin maintenance in HD. We first note a progressive, age-related loss of myelin in both R6/2 and zQ175 HD mice compared with wild-type controls. Adult R6/2 mice then manifest a significant delay in remyelination following cuprizone demyelination. RNA-sequencing and proteomic analysis of callosal white matter and OPCs isolated from both R6/2 and zQ175 mice reveals a systematic downregulation of genes associated with oligodendrocyte differentiation and myelinogenesis. Gene co-expression and network analysis predicts repressed Tcf7l2 signaling as a major driver of this expression pattern. In vivo Tcf7l2 overexpression restores both myelin gene expression and remyelination in demyelinated R6/2 mice. These data causally link impaired TCF7L2-dependent transcription to the poor development and homeostatic retention of myelin in HD and provide a mechanism for its therapeutic restoration.

Astrocyte and Oligodendrocyte Responses From the Subventricular Zone After Injury

Under normal conditions, neural stem cells (NSCs or B cells) in the adult subventricular zone (SVZ) give rise to amplifying neural progenitor cells (NPCs or C cells), which can produce neuroblasts (or A cells) that migrate to the olfactory bulb and differentiate into new neurons. However, following brain injury, these cells migrate toward the injury site where they differentiate into astrocytes and oligodendrocytes. In this review, we will focus on recent findings that chronicle how astrocytes and oligodendrocytes derived from SVZ-NSCs respond to different types of injury. We will also discuss molecular regulators of SVZ-NSC proliferation and their differentiation into astrocytes and oligodendrocytes. Overall, the goal of this review is to highlight how SVZ-NSCs respond to injury and to summarize the regulatory mechanisms that oversee their glial response. These molecular and cellular processes will provide critical insights needed to develop strategies to promote brain repair following injury using SVZ-NSCs.

Acute Response and Neuroprotective Role of Myo/Nog Cells Assessed in a Rat Model of Focal Brain Injury

Focal brain injury in the form of a needlestick (NS) results in cell death and induces a self-protective response flanking the lesion. Myo/Nog cells are identified by their expression of bone morphogenetic protein inhibitor Noggin, brain-specific angiogenesis inhibitor 1 (BAI1) and the skeletal muscle specific transcription factor MyoD. Myo/Nog cells limit cell death in two forms of retinopathy. In this study, we examined the acute response of Myo/Nog cells to a NS lesion that extended from the rat posterior parietal cortex to the hippocampus. Myo/Nog cells were identified with antibodies to Noggin and BAI1. These cells were the primary source of both molecules in the uninjured and injured brain. One day after the NS, the normally small population of Myo/Nog cells expanded approximately eightfold within a 1 mm area surrounding the lesion. Myo/Nog cells were reduced by approximately 50% along the lesion with an injection of the BAI1 monoclonal antibody and complement. The number of dying cells, identified by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), was unchanged at this early time point in response to the decrease in Myo/Nog cells. However, increasing the number of Myo/Nog cells within the lesion by injecting BAI1-positive (+) cells isolated from the brains of other animals, significantly reduced cell death and increased the number of NeuN+ neurons compared to brains injected with phosphate buffered saline or exogenous BAI1-negative cells. These findings demonstrate that Myo/Nog cells rapidly react to injury within the brain and increasing their number within the lesion is neuroprotective.

Adult Neurogenesis: A Story Ranging from Controversial New Neurogenic Areas and Human Adult Neurogenesis to Molecular Regulation

The generation of new neurons in the adult brain is a currently accepted phenomenon. Over the past few decades, the subventricular zone and the hippocampal dentate gyrus have been described as the two main neurogenic niches. Neurogenic niches generate new neurons through an asymmetric division process involving several developmental steps. This process occurs throughout life in several species, including humans. These new neurons possess unique properties that contribute to the local circuitry. Despite several efforts, no other neurogenic zones have been observed in many years; the lack of observation is probably due to technical issues. However, in recent years, more brain niches have been described, once again breaking the current paradigms. Currently, a debate in the scientific community about new neurogenic areas of the brain, namely, human adult neurogenesis, is ongoing. Thus, several open questions regarding new neurogenic niches, as well as this phenomenon in adult humans, their functional relevance, and their mechanisms, remain to be answered. In this review, we discuss the literature and provide a compressive overview of the known neurogenic zones, traditional zones, and newly described zones. Additionally, we will review the regulatory roles of some molecular mechanisms, such as miRNAs, neurotrophic factors, and neurotrophins. We also join the debate on human adult neurogenesis, and we will identify similarities and differences in the literature and summarize the knowledge regarding these interesting topics.

Bone morphogenetic proteins (BMPs) in the central regulation of energy balance and adult neural plasticity

The current worldwide obesity pandemic highlights a need to better understand the regulation of energy balance and metabolism, including the role of the nervous system in controlling energy intake and energy expenditure. Neural plasticity in the hypothalamus of the adult brain has been implicated in full-body metabolic health, however, the mechanisms surrounding hypothalamic plasticity are incompletely understood. Bone morphogenetic proteins (BMPs) control metabolic health through actions in the brain as well as in peripheral tissues such as adipose, together regulating both energy intake and energy expenditure. BMP ligands, receptors, and inhibitors are found throughout plastic adult brain regions and have been demonstrated to modulate neurogenesis and gliogenesis, as well as synaptic and dendritic plasticity. This role for BMPs in adult neural plasticity is distinct from their roles in brain development. Existing evidence suggests that BMPs induce weight loss through hypothalamic pathways, and part of the mechanism of action may be through inducing neural plasticity. In this review, we summarize the data regarding how BMPs affect neural plasticity in the adult mammalian brain, as well as the relationship between central BMP signaling and metabolic health.

The impact of trophic and immunomodulatory factors on oligodendrocyte maturation: Potential treatments for encephalopathy of prematurity

Encephalopathy of prematurity (EoP) is a major cause of morbidity in preterm neonates, causing neurodevelopmental adversities that can lead to lifelong impairments. Preterm birth-related insults, such as cerebral oxygen fluctuations and perinatal inflammation, are believed to negatively impact brain development, leading to a range of brain abnormalities. Diffuse white matter injury is a major hallmark of EoP and characterized by widespread hypomyelination, the result of disturbances in oligodendrocyte lineage development. At present, there are no treatment options available, despite the enormous burden of EoP on patients, their families, and society. Over the years, research in the field of neonatal brain injury and other white matter pathologies has led to the identification of several promising trophic factors and cytokines that contribute to the survival and maturation of oligodendrocytes, and/or dampening neuroinflammation. In this review, we discuss the current literature on selected factors and their therapeutic potential to combat EoP, covering a wide range of in vitro, preclinical and clinical studies. Furthermore, we offer a future perspective on the translatability of these factors into clinical practice.

The differentiation effect of bone morphogenetic protein (BMP) on human amniotic epithelial stem cells to express ectodermal lineage markers

Stem cells are a promising tool for treatment of a variety of degenerative diseases. Human amniotic epithelial stem cells (hAECs) have desirable and unique characteristics that make them a proper candidate for cell therapy. In this study, we have investigated the effects of BMP-4 (bone morphogenetic protein-4) and its inhibition on differentiation of AECs into ectodermal lineages. Analysis of AEC-derived ectodermal lineages (neurons and keratinocytes) was performed by using flow cytometry technique for Map2 and β-tubulin (as neuron markers), Olig2 and MBP (as oligodendrocyte markers), and K14 and K10 (as keratinocyte markers). The results of this study illustrated that noggin (as BMP antagonist), BMP4, and both BMP4 and heparin (together or separately) increased neural and keratinocyte marker expression, respectively. The expression of markers MAP2, olig2, and K14 in hAECs has been significantly decreased 21 days after exposure to differentiation medium (without growth factors) compared with isolation day, which supports the hypothesis that AECs can be dedifferentiated into pluripotent cells. Moreover, activation and inhibition of BMP signaling have no effects on viability of hAECs. The results of this study showed that BMP signaling and its inhibition are the key factors for ectodermal lineage differentiation of amnion-derived stem cells.

Galectin-3 modulates postnatal subventricular zone gliogenesis

Postnatal subventricular zone (SVZ) neural stem cells generate forebrain glia, namely astrocytes and oligodendrocytes. The cues necessary for this process are unclear, despite this phase of brain development being pivotal in forebrain gliogenesis. Galectin‐3 (Gal‐3) is increased in multiple brain pathologies and thereby regulates astrocyte proliferation and inflammation in injury. To study the function of Gal‐3 in inflammation and gliogenesis, we carried out functional studies in mouse. We overexpressed Gal‐3 with electroporation and using immunohistochemistry surprisingly found no inflammation in the healthy postnatal SVZ. This allowed investigation of inflammation‐independent effects of Gal‐3 on gliogenesis. Loss of Gal‐3 function via knockdown or conditional knockout reduced gliogenesis, whereas Gal‐3 overexpression increased it. Gal‐3 overexpression also increased the percentage of striatal astrocytes generated by the SVZ but decreased the percentage of oligodendrocytes. These novel findings were further elaborated with multiple analyses demonstrating that Gal‐3 binds to the bone morphogenetic protein receptor one alpha (BMPR1α) and increases bone morphogenetic protein (BMP) signaling. Conditional knockout of BMPR1α abolished the effect of Gal‐3 overexpression on gliogenesis. Gain‐of‐function of Gal‐3 is relevant in pathological conditions involving the human forebrain, which is particularly vulnerable to hypoxia/ischemia during perinatal gliogenesis. Hypoxic/ischemic injury induces astrogliosis, inflammation and cell death. We show that Gal‐3 immunoreactivity was increased in the perinatal human SVZ and striatum after hypoxia/ischemia. Our findings thus show a novel inflammation‐independent function for Gal‐3; it is necessary for gliogenesis and when increased in expression can induce astrogenesis via BMP signaling.

Antagonizing bone morphogenetic protein 4 attenuates disease progression in a rat model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset, fatal neurodegenerative syndrome characterized by the systemic loss of motor neurons with prominent astrocytosis and microgliosis in the spinal cord and brain. Astrocytes play an essential role in maintaining extracellular microenvironments that surround motor neurons, and are activated by various insults. Growing evidence points to a non-cell autonomous neurotoxicity caused by chronic and sustained astrocytic activation in patients with neurodegenerative diseases, including ALS. However, the mechanisms that underlie the harmful effects of astrocytosis in patients with ALS remain unresolved. We focused on bone morphogenetic proteins as a major soluble factor that promotes astrocytogenesis and its activation in the adult spinal cord. In a transgenic rat model with ALS-linked mutant Cu/Zn superoxide dismutase gene, BMP4 was progressively up-regulated in reactive astrocytes of the spinal ventral horns, whereas the BMP-antagonist noggin was decreased in association with neuronal degeneration. Continuous intrathecal noggin supplementation after disease onset significantly ameliorated motor dysfunction symptoms, neurogenic muscle atrophy, and extended survival of symptomatic ALS model rats, despite lack of deterrence against neuronal death itself. The exogenous noggin inhibited astrocytic hypertrophy, astrocytogenesis, and neuroinflammation by inactivating both Smad1/5/8 and p38 mitogen-activated protein kinase pathways. Moreover, intrathecal infusion of a Bmp4-targeted antisense oligonucleotides and provided selective Bmp4 knockdown in vivo, which suppressed astrocyte and microglia activation, reproducing the aforementioned results by noggin treatment. Collectively, we clarified the involvement of BMP4 in the processes of excessive gliosis that exacerbate the disease progression of the ALS model rats. Our study demonstrated that BMP4, with its downstream signaling, might be a novel therapeutic target for disease-modifying therapies in ALS.

Being a Neural Stem Cell: A Matter of Character But Defined by the Microenvironment

The cells that build the nervous system, either this is a small network of ganglia or a complicated primate brain, are called neural stem and progenitor cells. Even though the very primitive and the very recent neural stem cells (NSCs) share common basic characteristics that are hard-wired within their character, such as the expression of transcription factors of the SoxB family, their capacity to give rise to extremely different neural tissues depends significantly on instructions from the microenvironment. In this chapter we explore the nature of the NSC microenvironment, looking through evolution, embryonic development, maturity and even disease. Experimental work undertaken over the last 20 years has revealed exciting insight into the NSC microcosmos. NSCs are very capable in producing their own extracellular matrix and in regulating their behaviour in an autocrine and paracrine manner. Nevertheless, accumulating evidence indicates an important role for the vasculature, especially within the NSC niches of the postnatal brain; while novel results reveal direct links between the metabolic state of the organism and the function of NSCs.

Temporal Changes in Transcription Factor Expression Associated with the Differentiation State of Cerebellar Neural Stem/Progenitor Cells During Development

During central nervous development, multi-potent neural stem/progenitor cells located in the ventricular/subventricular zones are temporally regulated to mostly produce neurons during early developmental stages and to produce glia during later developmental stages. After birth, the rodent cerebellum undergoes further dramatic development. It is also known that neural stem/progenitor cells are present in the white matter (WM) of the postnatal cerebellum until around P10, although the fate of these cells has yet to be determined. In the present study, it was revealed that primary neurospheres generated from cerebellar neural stem/progenitor cells at postnatal day 3 (P3) mainly differentiated into astrocytes and oligodendrocytes. In contrast, primary neurospheres generated from cerebellar neural stem/progenitor cells at P8 almost exclusively differentiated into astrocytes, but not oligodendrocytes. These results suggest that the differentiation potential of primary neurospheres changes depending on the timing of neural stem/progenitor cell isolation from the cerebellum. To identify the candidate transcription factors involved in regulating this temporal change, we utilized DNA microarray analysis to compare global gene-expression profiles of primary neurospheres generated from neural stem/progenitor cells isolated from either P3 or P8 cerebellum. The expression of zfp711, zfp618, barx1 and hoxb3 was higher in neurospheres generated from P3 cerebellum than from P8 by real-time quantitative PCR. Several precursor cells were found to express zfp618, barx1 or hoxb3 in the WM of the cerebellum at P3, but these transcription factors were absent from the WM of the P8 cerebellum.

Bone Morphogenetic Protein Promotes Lewis X Stage-Specific Embryonic Antigen 1 Expression Thereby Interfering with Neural Precursor and Stem Cell Proliferation

The glycoprotein Prominin-1 and the carbohydrate Lewis X stage-specific embryonic antigen 1 (LeX-SSEA1) both have been extensively used as cell surface markers to purify neural stem cells (NSCs). While Prominin-1 labels a specialized membrane region in NSCs and ependymal cells, the specificity of LeX-SSEA1 expression and its biological significance are still unknown. To address these issues, we have here monitored the expression of the carbohydrate in neonatal and adult NSCs and in their progeny. Our results show that the percentage of immunopositive cells and the levels of LeX-SSEA1 immunoreactivity both increase with postnatal age across all stages of the neural lineage. This is associated with decreased proliferation in precursors including NSCs, which accumulate the carbohydrate at the cell surface while remaining quiescent. Exposure of precursors to bone morphogenetic protein (BMP) increases LEX-SSEA1 expression, which promotes cell cycle withdrawal by a mechanism involving LeX-SSEA1-mediated interaction at the cell surface. Conversely, interference with either BMP signaling or with LeX-SSEA1 promotes proliferation to a similar degree. Thus, in the postnatal germinal niche, the expression of LeX-SSEA1 increases with age and exposure to BMP signaling, thereby downregulating the proliferation of subependymal zone precursors including NSCs. Stem Cells 2017;35:2417-2429.

Methods of reactivation and reprogramming of neural stem cells for neural repair

Research on the biology of adult neural stem cells (NSCs) and induced NSCs (iNSCs), as well as NSC-based therapies for diseases in central nervous system (CNS) has started to generate the expectation that these cells may be used for treatments in CNS injuries or disorders. Recent technological progresses in both NSCs themselves and their derivatives have brought us closer to therapeutic applications. Adult neurogenesis presents in particular regions in mammal brain, known as neurogenic niches such as the dental gyrus (DG) in hippocampus and the subventricular zone (SVZ), within which adult NSCs usually stay for long periods out of the cell cycle, in G0. The reactivation of quiescent adult NSCs needs orchestrated interactions between the extrinsic stimulis from niches and the intrinsic factors involving transcription factors (TFs), signaling pathway, epigenetics, and metabolism to start an intracellular regulatory program, which promotes the quiescent NSCs exit G0 and reenter cell cycle. Extrinsic and intrinsic mechanisms that regulate adult NSCs are interconnected and feedback on one another. Since endogenous neurogenesis only happens in restricted regions and steadily fails with disease advances, interest has evolved to apply the iNSCs converted from somatic cells to treat CNS disorders, as is also promising and preferable. To overcome the limitation of viral-based reprogramming of iNSCs, bioactive small molecules (SM) have been explored to enhance the efficiency of iNSC reprogramming or even replace TFs, making the iNSCs more amenable to clinical application. Despite intense research efforts to translate the studies of adult and induced NSCs from the bench to bedside, vital troubles remain at several steps in these processes. In this review, we examine the present status, advancement, pitfalls, and potential of the two types of NSC technologies, focusing on each aspects of reactivation of quiescent adult NSC and reprogramming of iNSC from somatic cells, as well as on progresses in cell-based regenerative strategies for neural repair and criteria for successful therapeutic applications.

Resveratrol Induces Differentiation of Human Umbilical Cord Mesenchymal Stem Cells into Neuron-Like Cells

Objective. Human umbilical cord mesenchymal stem cells (hUC-MSCs) potentially differentiate to various types of cells including neuron-like cells. The natural polyphenol resveratrol benefits patients with many diseases including ischemic brain injury. We hypothesize that resveratrol induces differentiation of hUC-MSCs into neuron-like cells. Methods. Flow cytometry was used to determine the surface antigens in different stage of hUC-MSCs (P2, P5, and P10). Nestin, neuron-specific enolase (NSE), and glial fibrillary acidic protein (GFAP) were detected by immunocytochemistry, Western blotting, and real time RT-PCT. The cultured hUC-MSCs were treated with resveratrol at different concentrations (0, 7.5, 15.0, and 30.0 mg/L). Nestin, GFAP, and NSE protein and mRNA were measured at posttreatment time points of 2 h, 4 h, 6 h, 12 h, and 24 h. Results. Neuron-like cells were found in hUC-MSCs treated by resveratrol at concentrations of 15.0 and 30.0 mg/L, but not in hUC-MSCs treated with vehicle and 7.5 mg/L resveratrol. Furthermore, immunocytochemical staining revealed that nestin and NSE immunoreactivities were positive in resveratrol-treated hUC-MSCs at concentrations of 15.0 and 30.0 mg/L. Resveratrol treatment significantly increased nestin and NSE protein and mRNA levels 4 h after the treatment. However, resveratrol treatment did not change GFAP immunoreactivities and protein and mRNA expression levels in cultured hUC-MSCs. Conclusions. Taken together, resveratrol treatment induces a differentiation of hUC-MSCs into neuron-like cells at relatively high concentrations.

miR-410 controls adult SVZ neurogenesis by targeting neurogenic genes

Over-expression of the early neural inducer, Noggin, in nestin positive subventricular zone (SVZ), neural stem cells (NSC) promotes proliferation and neuronal differentiation of neural progenitors and inhibits the expression of a CNS-enriched microRNA-410 (miR-410) (Morell et al., 2015). When expressed in neurospheres derived from the adult SVZ, miR-410 inhibits neuronal and oligodendrocyte differentiation, and promotes astrocyte differentiation. miR-410 also reverses the increase in neuronal differentiation and decreased astroglial differentiation caused by Noggin over-expression. Conversely, inhibition of miR-410 activity promotes neuronal and decreases astroglial differentiation of NSC. Using computer prediction algorithms and luciferase reporter assays we identified multiple neurogenic genes including Elavl4 as downstream targets of miR-410 via the canonical miRNA-3'UTR interaction. Over-expression of Elavl4 transcripts without the endogenous 3'UTR rescued the decrease in neuronal differentiation caused by miR-410 overexpression. Interestingly, we also observed that miR-410 affected neurite morphology; over-expression of miR-410 resulted in the formation of short, unbranched neurites. We conclude that miR-410 expression provides a new link between BMP signaling and the crucial lineage choice of adult neural stem cells via its ability to bind and control the expression of neurogenic gene transcripts.

Bone morphogenetic protein dominantly suppresses epidermal growth factor-induced proliferative expansion of adult forebrain neural precursors

A single asymmetric division by an adult neural stem cell (NSC) ultimately generates dozens of differentiated progeny, a feat made possible by the proliferative expansion of transit-amplifying progenitor cells (TAPs). Although NSC activation and TAP expansion is determined by pro- and anti-proliferative signals found within the niche, remarkably little is known about how these cells integrate simultaneous conflicting signals. We investigated this question focusing on the subventricular zone (SVZ) niche of the adult murine forebrain. Using primary cultures of SVZ cells, we demonstrate that Epidermal Growth Factor (EGF) and Bone Morphogenetic Protein (BMP)-2 are particularly powerful pro- and anti-proliferative factors for SVZ-derived neural precursors. Dose-response experiments showed that when simultaneously exposed to both signals, BMP dominantly suppressed EGF-induced proliferation; moreover, this dominance extended to all parameters of neural precursor behavior tested, including inhibition of proliferation, modulation of cell cycle, promotion of differentiation, and increase of cell death. BMP's anti-proliferative effect did not involve inhibition of mTORC1 or ERK signaling, key mediators of EGF-induced proliferation, and had distinct stage-specific consequences, promoting TAP differentiation but NSC quiescence. In line with these in vitro data, in vivo experiments showed that exogenous BMP limits EGF-induced proliferation of TAPs while inhibition of BMP-SMAD signaling promotes activation of quiescent NSCs. These findings clarify the stage-specific effects of BMPs on SVZ neural precursors, and support a hierarchical model in which the anti-proliferative effects of BMP dominate over EGF proliferation signaling to constitutively drive TAP differentiation and NSC quiescence.