Dynamic spatiotemporal coordination of neural stem cell fate decisions occurs through local feedback in the adult vertebrate brain

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Multimodal imaging of neural progenitor cell fate in rodents

For clinical application of stem cell-based therapies, noninvasive detection of applied stem cells is of high importance. We report on the feasibility of detecting implanted neural progenitor cells (NPCs) noninvasively and follow their fate and functional status by sequential multimodal molecular imaging and reporter gene technology. We investigated C17.2 cells stably expressing herpes simplex virus type 1-thymidine kinase (HSV-1-tk) and green fluorescent protein (gfp) (C17.2-tkIRESgfp = C17.2-TIG) or HSV-1-tk, gfp, and firefly luciferase (luc) (C17.2-lucIREStkgfp = C17.2-LITG) and determined the detection sensitivity of positron emission tomography (PET) and bioluminescence imaging (BLI) for these cells in culture and in vivo in subcutaneous and intracranial glioma models. In addition, PET and BLI were used to further investigate and follow the fate of implanted C17.2-LITG cells in an intracranial glioma model. We show that both imaging modalities are sensitive in detecting reporter gene expressing NPCs; however, PET, by the use of 9-[4-[(18)F]fluoro-3-hydroxymethyl)butyl]guanine ([(18)F]FHBG), detects NPCs only at sites of disrupted blood-brain barrier. Furthermore, both imaging modalities can be used to detect stem cell fate and migration and indicate excessive proliferation and aberrant migration. In conclusion, multimodal imaging can be used for longitudinal noninvasive monitoring of grafted NPCs in rodents.     

Regulation of neural progenitor cell fate by anandamide

Exogenous application of neural progenitor cells (NPCs) has successful implications in treating brain disorders, and research is beginning to identify ways to mimic this exogenous application by activating endogenous stem cell compartments. The recent discovery of a functional endocannabinoid system in murine NPCs (mNPCs) represents one potential therapeutic means to influence endogenous stem cell compartments. High levels of the endogenous cannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) persist during CNS inflammation and infection. The goal of this study was to assess the influence of AEA on mNPCs to identify how the endocannabinoid system influences mNPCs in vitro, a potential model to investigate effects of endocannabinoids on endogenous stem cell compartments. Our results show that AEA affects mNPC cell fate determination. Initial glial differentiation was observed, followed by induction of neuronal differentiation with AEA treatment. Cell survival and apoptosis was not affected by AEA. These effects were coupled by an increased phosphorylation of cAMP-responsive element (CRE) binding protein (CREB).     

Abeta40 promotes neuronal cell fate in neural progenitor cells

Sequential cleavage of the amyloid precursor protein (APP) by beta- and then gamma- secretase gives rise to Abeta(1-40) (Abeta40), a major species of Abeta (beta-amyloid) produced by neurons under physiological conditions. Abeta(1-42) (Abeta42), a minor species of Abeta, is also produced by a similar but less understood mechanism of the gamma-secretase. The physiological functions of these Abeta species remain to be defined. In this report, we demonstrate that freshly prepared soluble Abeta40 significantly promotes neurogenesis in primary neural progenitor cells (NPCs). First, Abeta40 increases neuronal markers as determined by NeuN expression and Tuj1 promoter activity, differing from Abeta42, which induces astrocyte markers in NPCs. Second, Abeta40 induces neuronal differentiation at the end of S-phase in the cell cycle. Third, Abeta40 promotes NPC entry into S-phase, playing a role in NPC self-renewal. Interestingly, Abeta40 does not significantly increase apoptotic indexes such as DNA condensation and DNA fragmentation. In addition, Abeta40 does not augment caspase-3 activation in NeuN(+) or nestin(+) cells. Collectively, this report provides strong evidence that Abeta40 is a neurogenic factor and suggests that the debilitated function of Abeta40 in neurogenesis may account for the shortage of neurons in Alzheimer's disease.     

Viral infection and neural stem/progenitor cell's fate: implications in brain development and neurological disorders

Viral infections in the prenatal (during pregnancy) and perinatal period have been a common cause of brain malformation. Besides the immediate neurological dysfunctions, virus infections may critically affect CNS development culminating in long-term cognitive deficits. Most of these neurotropic viruses are most damaging at a critical stage of the host, when the brain is in a dynamic stage of development. The neuropathology can be attributed to the massive neuronal loss induced by the virus as well as lack of CNS repair owing to a deficit in the neural stem/progenitor cell (NSPC) pool or aberrant formation of new neurons from NSPCs. Being one of the mitotically active populations in the post natal brain, the NSPCs have emerged as the potential targets of neurotropic viruses. The NSPCs are self-renewing and multipotent cells residing in the neurogenic niches of the brain, and, therefore, hampering the developmental fate of these cells may adversely affect the overall neurogenesis pattern. A number of neurotropic viruses utilize NSPCs as their cellular reservoirs and often establish latent and persistent infection in them. Both HIV and Herpes virus infect NSPCs over long periods of time and reactivation of the virus may occur later in life. The virus infected NSPCs either undergoes cell cycle arrest or impaired neuronal or glial differentiation, all of which leads to impaired neurogenesis. The disturbances in neurogenesis and CNS development following neurotropic virus infections have direct implications in the viral pathogenesis and long-term neurobehavioral outcome in infected individuals.     

The influence of immunosuppressive drugs on neural stem/progenitor cell fate in vitro

In allogenic and xenogenic transplantation, adequate immunosuppression plays a major role in graft survival, especially over the long term. The effect of immunosuppressive drugs on neural stem/progenitor cell fate has not been sufficiently explored. The focus of this study is to systematically investigate the effects of the following four different immunotherapeutic strategies on human neural progenitor cell survival/death, proliferation, metabolic activity, differentiation and migration in vitro: (1) cyclosporine A (CsA), a calcineurin inhibitor; (2) everolimus (RAD001), an mTOR-inhibitor; (3) mycophenolic acid (MPA, mycophenolate), an inhibitor of inosine monophosphate dehydrogenase and (4) prednisolone, a steroid. At the minimum effective concentration (MEC), we found a prominent decrease in hNPCs' proliferative capacity (BrdU incorporation), especially for CsA and MPA, and an alteration of the NAD(P)H-dependent metabolic activity. Cell death rate, neurogenesis, gliogenesis and cell migration remained mostly unaffected under these conditions for all four immunosuppressants, except for apoptotic cell death, which was significantly increased by MPA treatment.     

Two rounds of whole genome duplication in the ancestral vertebrate

The hypothesis that the relatively large and complex vertebrate genome was created by two ancient, whole genome duplications has been hotly debated, but remains unresolved. We reconstructed the evolutionary relationships of all gene families from the complete gene sets of a tunicate, fish, mouse, and human, and then determined when each gene duplicated relative to the evolutionary tree of the organisms. We confirmed the results of earlier studies that there remains little signal of these events in numbers of duplicated genes, gene tree topology, or the number of genes per multigene family. However, when we plotted the genomic map positions of only the subset of paralogous genes that were duplicated prior to the fish–tetrapod split, their global physical organization provides unmistakable evidence of two distinct genome duplication events early in vertebrate evolution indicated by clear patterns of four-way paralogous regions covering a large part of the human genome. Our results highlight the potential for these large-scale genomic events to have driven the evolutionary success of the vertebrate lineage.     

Patterns of neural stem and progenitor cell division may underlie evolutionary cortical expansion

The dramatic evolutionary expansion of the cerebral cortex of Homo sapiens underlies our unique higher cortical functions, and therefore bears on the ultimate issue of what makes us human. Recent insights into developmental events during early proliferative stages of cortical development indicate how neural stem and progenitor cells might interact to produce cortical expansion during development, and could shed light on evolutionary changes in cortical structure.     

NAD+ controls neural stem cell fate in the aging brain

Loss of the coenzyme NAD⁺, which is required for many energy‐dependent cellular processes, has emerged as a potentially unifying mechanism for age‐related conditions. A study in this issue of The EMBO Journal identifies a novel link between depletion of NAD⁺ and age‐associated loss of proliferating adult neural stem/progenitor cells in the murine brain (Stein & Imai, 2014 ). These data have important implications for how brain function might decline with age.     

Gene therapy of experimental brain tumors using neural progenitor cells

Glioblastomas, the most frequent and malignant of primary brain tumors, have a very poor prognosis. Gene therapy of glioblastomas is limited by the short survival of viral vectors and by their difficulty in reaching glioblastoma cells infiltrating the brain parenchyma. Neural stem/progenitor cells can be engineered to produce therapeutic molecules and have the potential to overcome these limitations because they may travel along the white matter, like neoplastic cells, and engraft stably into the brain. Retrovirus-mediated transfer of the gene for interleukin-4 is an effective treatment for rat brain glioblastomas. Here, we transferred the gene for interleukin-4 into C57BL6J mouse primary neural progenitor cells and injected those cells into established syngeneic brain glioblastomas. This led to the survival of most tumor-bearing mice. We obtained similar results by implanting immortalized neural progenitor cells derived from Sprague-Dawley rats into C6 glioblastomas. We also documented by magnetic resonance imaging the progressive disappearance of large tumors, and detected 5-bromodeoxyuridine-labeled progenitor cells several weeks after the injection. These findings support a new approach for gene therapy of brain tumors, based on the grafting of neural stem cells producing therapeutic molecules.     

Transforming growth factor-beta1 regulates the fate of cultured spinal cord-derived neural progenitor cells

Abstract. Objectives: We have evaluated the physiological roles of transforming growth factor‐β1 (TGF‐β1) on differentiation, migration, proliferation and anti‐apoptosis characteristics of cultured spinal cord‐derived neural progenitor cells. Methods: We have used neural progenitor cells that had been isolated and cultured from mouse spinal cord tissue, and we also assessed the relevant reaction mechanisms using an activin‐like kinase (ALK)‐specific inhibitory system including an inhibitory RNA, and found that it involved potential signalling molecules such as phosphatidylinositol‐3‐OH kinase (PI3K)/Akt and mitogen‐activated protein kinase (MAPK)/extracellular signal‐regulated kinase (ERK1/2). Results and Conclusions: Transforming growth factor‐β1‐mediated cell population growth was activated after treatment and was also effectively blocked by an ALK41517‐synthetic inhibitor (4‐(5‐benzo(1,3) dioxol‐5‐yl‐4‐pyridine‐2‐yl‐1H‐imidazole‐2‐yl) benzamide (SB431542) and ALK siRNA, thereby indicating the involvement of SMAD2 in the TGF‐β1‐mediated growth and migration of these neural progenitors cells (NPC). In the present study, TGF‐β1 actively induced NPC migration in vitro. Furthermore, TGF‐β1 demonstrated extreme anti‐apoptotic behaviour against hydrogen peroxide‐mediated apoptotic cell death. At low dosages, TGF‐β1 enhanced (by approximately 76%) cell survival against hydrogen peroxide treatment via inactivation of caspase‐3 and ‐9. TGF‐β1‐treated NPCs down‐regulated Bax expression and cytochrome c release; in addition, the cells showed up‐regulated Bcl‐2 and thioredoxin reductase 1. They also had increased p38, Akt and ERK1/2 phosphorylation, showing the involvement of both the PI3K/Akt and MAPK/ERK1/2 pathways in the neuroprotective effects of TGF‐β1. Interestingly, these effects operate on specific subtypes of cells, including neurones, neural progenitor cells and astrocytes in cultured spinal cord tissue‐derived cells. Lesion sites of spinal cord‐overexpressing TGF‐β1‐mediated prevention of cell death, cell growth and migration enhancement activity have been introduced as a possible new basis for therapeutic strategy in treatment of neurodegenerative disorders, including spinal cord injuries.     

Morphogen to mitogen: the multiple roles of hedgehog signalling in vertebrate neural development

Sonic hedgehog has received an enormous amount of attention since its role as a morphogen that directs ventral patterning in the spinal cord was discovered a decade ago. Since that time, a bewildering array of information has been generated concerning both the components of the hedgehog signalling pathway and the remarkable number of contexts in which it functions. Nowhere is this more evident than in the nervous system, where hedgehog signalling has been implicated in events as disparate as axonal guidance and stem cell maintenance. Here we review our present knowledge of the hedgehog signalling pathway and speculate about areas in which further insights into this versatile pathway might be forthcoming.     

A chemical screening system for glucocorticoid stress hormone signaling in an intact vertebrate

Glucocorticoids, steroid hormones of the adrenal gland, are an integral part of the stress response and regulate glucose metabolism. Natural and synthetic glucocorticoids are widely used in anti-inflammatory therapy but can have severe side effects. In vivo tests are needed to identify novel glucocorticoids and to screen compounds for unwanted effects on glucocorticoid signaling. We created the Glucocorticoid Responsive In vivo Zebrafish Luciferase activitY assay to monitor glucocorticoid signaling in vivo. The GRIZLY assay detects stress-induced glucocorticoid production in single zebrafish larvae, measures disruption of glucocorticoid signaling by an organotin pollutant metabolite, and specifically identifies a compound stimulating endogenous glucocorticoid production in a chemical screen. Our assay has broad applications in stress research, environmental monitoring, and drug discovery.     

Diversifying neural cells through order of birth and asymmetry of division

A key question in developmental neurobiology is how the diversity of cell types that make up the mature nervous system are generated from a common set of progenitor cells. Drosophila genes governing temporal cell fate determination and asymmetric cell divisions involving numb may represent evolutionarily conserved mechanisms for regulating cell fate diversification in the developing nervous system.