Cell surface N-glycans mediated isolation of mouse neural stem cells

Emerging roles of prominin-1 (CD133) in the dynamics of plasma membrane architecture and cell signaling pathways in health and disease

Prominin-1 (CD133) is a cholesterol-binding membrane glycoprotein selectively associated with highly curved and prominent membrane structures. It is widely recognized as an antigenic marker of stem cells and cancer stem cells and is frequently used to isolate them from biological and clinical samples. Recent progress in understanding various aspects of CD133 biology in different cell types has revealed the involvement of CD133 in the architecture and dynamics of plasma membrane protrusions, such as microvilli and cilia, including the release of extracellular vesicles, as well as in various signaling pathways, which may be regulated in part by posttranslational modifications of CD133 and its interactions with a variety of proteins and lipids. Hence, CD133 appears to be a master regulator of cell signaling as its engagement in PI3K/Akt, Src-FAK, Wnt/β-catenin, TGF-β/Smad and MAPK/ERK pathways may explain its broad action in many cellular processes, including cell proliferation, differentiation, and migration or intercellular communication. Here, we summarize early studies on CD133, as they are essential to grasp its novel features, and describe recent evidence demonstrating that this unique molecule is involved in membrane dynamics and molecular signaling that affects various facets of tissue homeostasis and cancer development. We hope this review will provide an informative resource for future efforts to elucidate the details of CD133's molecular function in health and disease.

Functional roles of glycoconjugates in the maintenance of stemness and differentiation process of neural stem cells

Neural stem cells (NSCs) possess a high proliferative potential and capacity for self-renewal with retention of multipotency to differentiate into brain-forming cells. NSCs have gained a considerable attention because of their potential application in treatment strategies on the basis of transplantation for neurodegenerative disorders and nerve injuries. Although several signaling pathways have been reportedly involved in the fate determination process of NSCs, the molecular mechanisms underlying the maintenance of neural cell stemness and differentiation process remain largely unknown. Glycoconjugates expressed in the NSC niche in the brain offer markers of NSCs; moreover, they serve as cell regulators, which are actively involved in the modulation of signal transduction. The glycans function on NCS surfaces by recruiting growth factor receptors to specific microdomains as components of glycolipids, thereby mediating the ligand-receptor interactions both indirectly and directly as components of proteoglycans and interacting with specific lectin-type receptors as components of ligand glycoproteins. In this review, we outline current knowledge of the possible functional mechanisms of glycoconjugates to determine cell fates, which are associated with their expression pattern and structural characteristic features.

Cell-permeable p38 MAP kinase promotes migration of adult neural stem/progenitor cells

Endogenous neural stem/progenitor cells (NPCs) can migrate toward sites of injury, but the migration activity of NPCs is insufficient to regenerate damaged brain tissue. In this study, we showed that p38 MAP kinase (p38) is expressed in doublecortin-positive adult NPCs. Experiments using the p38 inhibitor SB203580 revealed that endogenous p38 participates in NPC migration. To enhance NPC migration, we generated a cell-permeable wild-type p38 protein (PTD-p38WT) in which the HIV protein transduction domain (PTD) was fused to the N-terminus of p38. Treatment with PTD-p38WT significantly promoted the random migration of adult NPCs without affecting cell survival or differentiation; this effect depended on the cell permeability and kinase activity of the fusion protein. These findings indicate that PTD-p38WT is a novel and useful tool for unraveling the roles of p38, and that this protein provides a reasonable approach for regenerating the injured brain by enhancing NPC migration.

Purification, Visualization, and Molecular Signature of Neural Stem Cells

Neural stem cells (NSCs) are isolated from primary brain tissue and propagated as a heterogeneous mix of cells, including neural progenitors. To date, NSCs have not been purified in vitro to allow study of their biology and utility in regenerative medicine. In this study, we identify C1qR1 as a novel marker for NSCs and show that it can be used along with Lewis-X (LeX) to yield a highly purified population of NSCs. Using time-lapse microscopy, we are able to follow NSCs forming neurospheres, allowing their visualization. Finally, using single-cell polymerase chain reaction (PCR), we determine the molecular signature of NSCs. The single-cell PCR data suggest that along with the Notch and Shh pathways, the Hippo pathway plays an important role in NSC activity.

Microglia enhance neurogenesis and oligodendrogenesis in the early postnatal subventricular zone

Although microglia have long been considered as brain resident immune cells, increasing evidence suggests that they also have physiological roles in the development of the normal CNS. In this study, we found large numbers of activated microglia in the forebrain subventricular zone (SVZ) of the rat from P1 to P10. Pharmacological suppression of the activation, which produces a decrease in levels of a number of proinflammatory cytokines (i.e., IL-1β, IL-6, TNF-α, and IFN-γ) significantly inhibited neurogenesis and oligodendrogenesis in the SVZ. In vitro neurosphere assays reproduced the enhancement of neurogenesis and oligodendrogenesis by activated microglia and showed that the cytokines revealed the effects complementarily. These results suggest that activated microglia accumulate in the early postnatal SVZ and that they enhance neurogenesis and oligodendrogenesis via released cytokines.

Transplantation of CD15-enriched murine neural stem cells increases total engraftment and shifts differentiation toward the oligodendrocyte lineage

Neural stem cell (NSC) transplantation is a promising therapeutic approach for neurological diseases. However, only a limited number of cells can be transplanted into the brain, resulting in relatively low levels of engraftment. This study investigated the potential of using a cell surface marker to enrich a primary NSC population to increase stable engraftment in the recipient brain. NSCs were enriched from the neonatal mouse forebrain using anti-CD15 (Lewis X antigen, or SSEA-1) in a "gentle" fluorescence-activated cell sorting protocol, which yielded >98% CD15-positive cells. The CD15-positive cells differentiated into neurons, astrocytes, and oligodendrocytes in vitro, after withdrawal of growth factors, demonstrating multipotentiality. CD15-positive cells were expanded in vitro and injected bilaterally into the ventricles of neonatal mice. Cells from enriched and unenriched donor populations were found throughout the neuraxis, in both neurogenic and non-neurogenic regions. Total engraftment was similar at 7 days postinjection, but by 28 days postinjection, after brain organogenesis was complete, the survival of donor cells was significantly increased in CD15-enriched grafts over the unenriched cell grafts. The engrafted cells were heterogeneous in morphology and differentiated into all three neural lineages. Furthermore, in the CD15-enriched grafts, there was a significant shift toward differentiation into oligodendrocytes. This strategy may allow better delivery of therapeutic cells to the developing central nervous system and may be particularly useful for treating diseases involving white matter lesions.

Functions of neurotrophins and growth factors in neurogenesis and brain repair

The identification and isolation of multipotent neural stem and progenitor cells in the brain, giving rise to neurons, astrocytes, and oligodendrocytes initiated many studies in order to understand basic mechanisms of endogenous neurogenesis and repair mechanisms of the nervous system and to develop novel therapeutic strategies for cellular regeneration therapies in brain disease. A previous review (Trujillo et al., Cytometry A 2009;75:38-53) focused on the importance of extrinsic factors, especially neurotransmitters, for directing migration and neurogenesis in the developing and adult brain. Here, we extend our review discussing the effects of the principal growth and neurotrophic factors as well as their intracellular signal transduction on neurogenesis, fate determination and neuroprotective mechanisms. Many of these mechanisms have been elucidated by in vitro studies for which neural stem cells were isolated, grown as neurospheres, induced to neural differentiation under desired experimental conditions, and analyzed for embryonic, progenitor, and neural marker expression by flow and imaging cytometry techniques. The better understanding of neural stem cells proliferation and differentiation is crucial for any therapeutic intervention aiming at neural stem cell transplantation and recruitment of endogenous repair mechanisms.

Isolation of cortical mouse oligodendrocyte precursor cells

The reliable isolation of primary oligodendrocyte progenitors cells (OPCs) holds promise as both a research tool and putative therapy for the study and treatment of central nervous system (CNS) disease and trauma. Stringently characterized primary mouse OPCs is of additional importance due to the power of transgenics to address mechanism(s) involving single genes. In this study, we developed and characterized a reproducible method for the primary culture of OPCs from postnatal day 5-7 mouse cerebral cortex. We enriched an O4(+) OPC population using Magnetic Activated Cell Sorting (MACS) technology. This technique resulted in an average yield of 3.68×10(5)OPCs/brain. Following isolation, OPCs were glial fibrillary acidic protein(-) (GFAP(-)) and O4(+). Following passage and with expansion, OPCs were O4(+), A2B5(+), and NG2(+). Demonstrating their bi-potentiality, mouse OPCs differentiated into either more complex, highly arborized O4(+) or O1(+) oligodendrocytes (OLs) or GFAP(+) astrocytes. This bi-potentiality is lost, however, in co-culture with rat embryonic day 15 derived dorsal root ganglia (DRG). Following 7-14 days of OPC/DRG co-culture, OPCs aligned with DRG neurites and differentiated into mature OLs as indicated by the presence of O1 and myelin basic protein (MBP) immunostaining. Addition of ciliary neurotrophic factor (CNTF) to conditioned media from OPC/DRG co-cultures improved OPC differentiation into mature O1(+) and MBP(+) OLs. This method allows for the study of primary mouse cortical OPC survival, maturation, and function without relying on oligosphere formation or the need for extensive passaging.

Eyes wide open: a critical review of sphere-formation as an assay for stem cells

Sphere-forming assays have been widely used to retrospectively identify stem cells based on their reported capacity to evaluate self-renewal and differentiation at the single-cell level in vitro. The discovery of markers that allow the prospective isolation of stem cells and their progeny from their in vivo niche allows the functional properties of purified populations to be defined. We provide a historical perspective of the evolution of the neurosphere assay and highlight limitations in the use of sphere-forming assays in the context of neurospheres. We discuss theoretical and technical considerations of experimental design and interpretation that surround the use of this assay with any tissue.

Schwann cell plasticity after spinal cord injury shown by neural crest lineage tracing

After spinal cord injury (SCI), various cell types are recruited to the lesion site, including Schwann cells, which originate in the neural crest and normally myelinate axons in the peripheral nervous system. Here, we investigated the differentiation states, migration patterns, and roles of neural crest derivatives following SCI, using two transgenic mouse lines carrying neural crest-specific reporters, P0-Cre/Floxed-EGFP and Wnt1-Cre/Floxed-EGFP. In these mice, EGFP is expressed only in the neural crest cell lineage. Immunohistochemical analysis revealed that most of the EGFP(+) cells that infiltrated the lesion site after SCI were Schwann cells. Seven days after SCI, the P0-positive, mature Schwann cells residing at the nerve roots had dedifferentiated into P0(-)/p75(+) immature Schwann cells, which proliferated and began migrating into the lesion site. The dedifferentiation of the Schwann cells was corroborated by their expression of phosphorylated c-Jun, which promotes dedifferentiation and inhibits the expression of myelin-associated genes in the peripheral nerves. Thereafter, the number of EGFP(+)/p75(+) immature Schwann cells decreased and that of EGFP(+)/P0(+) mature cells increased gradually, indicating that the cells redifferentiated into mature Schwann cells within the lesion site. This study draws on the advantages offered by transgenic mouse lines bearing a genetic cell-lineage marker and extends previous work by describing the origins and behavior of the neural crest-derived cells that contribute to endogenous repair after SCI. This process, involving Schwann cell plasticity, is a novel repair mechanism for the lesioned mammalian spinal cord.

Lectins as a tool for detecting neural stem/progenitor cells in the adult mouse brain

Glycoconjugates are biopolymers that are broadly distributed in the central nervous system, including the cell surface of neural stem cells or neural precursor cells (NSCs/NPCs). Glycoconjugates can be recognized by carbohydrate-binding proteins, lectins. Two lectins, Phaseolus vulgaris lectin agglutinin E-form (PHA-E4) and wheat germ agglutinin (WGA) have been reported to be useful in isolating NSCs/NPCs by fluorescence-activated cell sorting (FACS) or immunopanning methods. In this study, we analyzed the lectin-binding properties of NSCs/NPCs in two neurogenic regions of the adult mouse brain to determine whether PHA-E4 and WGA exhibit specific binding patterns on sections and whether there are other lectins presenting the binding pattern similar to those of PHA-E4 and WGA in lectin histochemistry. Among nine types of lectins, peanut agglutinin was localized to the white matter and four lectins bound to cells within the subventricular zone (SVZ) of the lateral ventricle. Lectin histochemistry combined with immunohistochemistry demonstrated that one lectin, Ricinus communis agglutinin, specifically detected type A neuronal precursors and that the remaining three lectins, Agaricus bisporus agglutinin (ABA), PHA-E4, and WGA, recognized type B NSCs and type C transient amplifying cells in the SVZ. These three lectins also recognized type 1 quiescent neural progenitors and type 2a amplifying neural progenitors in the subgranular layer of the dentate gyrus. Lectin histochemistry of the neurosphere culture also yielded similar results. These observations suggest that, in addition to PHA-E4 and WGA, ABA lectin may also be applicable in FACS or immunopanning for the isolation of NSCs/NPCs.

Cell surface N-glycans-mediated isolation of mouse neural stem cells

The isolation of neural stem cells (NSCs) has been hampered by the lack of valid cell-surface antigens on NSCs, and novel valuable markers have been proposed. Glycan (oligosaccharide chain) is a potential candidate as a marker to isolate NSCs, because the species and the combination order of saccharides in glycan generate remarkable structural diversity and specificity. At present, the expression of hundreds of glycoconjugates with glycans have been found in the NSCs; however, just a few glycan-epitopes have been identified as valuable cell-surface markers. This review focused on the isolation of NSC using glycoprotein, especially complex type N-glycans. The cell-surface N-glycan-mediated isolation of NSCs is therefore expected to provide a comprehensive understanding of the biologic characteristics of NSCs in the brain, and thereby help to develop novel strategies in the field of regenerative medicine.

HNK-1 epitope-carrying tenascin-C spliced variant regulates the proliferation of mouse embryonic neural stem cells

Neural stem cells (NSCs) possess high proliferative potential and the capacity for self-renewal with retention of multipotency to differentiate into neuronal and glial cells. NSCs are the source for neurogenesis during central nervous system development from fetal and adult stages. Although the human natural killer-1 (HNK-1) carbohydrate epitope is expressed predominantly in the nervous system and involved in intercellular adhesion, cell migration, and synaptic plasticity, the expression patterns and functional roles of HNK-1-containing glycoconjugates in NSCs have not been fully recognized. We found that HNK-1 was expressed in embryonic mouse NSCs and that this expression was lost during the process of differentiation. Based on proteomics analysis, it was revealed that the HNK-1 epitopes were almost exclusively displayed on an extracellular matrix protein, tenascin-C (TNC), in the mouse embryonic NSCs. Furthermore, the HNK-1 epitope was found to be present only on the largest isoform of the TNC molecules. In addition, the expression of HNK-1 was dependent on expression of the largest TNC variant but not by enzymes involved in the biosynthesis of HNK-1. By knocking down HNK-1 sulfotransferase or TNC by small interfering RNA, we further demonstrated that HNK-1 on TNC was involved in the proliferation of NSCs via modulation of the expression level of the epidermal growth factor receptor. Our finding provides insights into the function of HNK-1 carbohydrate epitopes in NSCs to maintain stemness during neural development.

Lysosome-associated membrane protein 1 is a major SSEA-1-carrier protein in mouse neural stem cells

Stage-specific embryonic antigen-1 (SSEA-1) is a well-known carbohydrate antigenic epitope of undifferentiated cells, including neural stem cells (NSCs). However, the exact nature of the carrier proteins has not been fully characterized. Using proteomics analyses, we herein report that a lysosomal protein, LAMP-1, is a major carrier protein of SSEA-1 in NSCs, despite the common belief that SSEA-1 is mainly expressed on the cell surface and constitutes a component of the extracellular matrix. Furthermore, we found that SSEA-1 on LAMP-1 is completely ablated in differentiated cells derived from NSCs. Our finding raises the possibility that the expression of SSEA-1-positive LAMP-1 is associated with the "stemness" of NSCs.

Characterization of GD3 ganglioside as a novel biomarker of mouse neural stem cells

Neural stem cells (NSCs) are undifferentiated neural cells characterized by their high proliferative potential and the capacity for self-renewal with retention of multipotency. Over the past two decades, there has been a huge effort to identify NSCs morphologically, genetically, and molecular biologically. It is still controversial, however, what bona fide NSCs are. To define and characterize NSCs more systematically, it is crucial to explore novel cell-surface marker molecules of NSCs. In this study, we focused on GD3, a b-series ganglioside that is enriched in the immature brain and the subventricular zone (SVZ) of the postnatal and adult brain, and evaluated the usefulness of GD3 as a cell-surface biomarker for identifying NSCs. We demonstrated that GD3 was expressed in more than 80% of NSCs prepared from embryonic, postnatal, and adult mouse brain tissue by the neurosphere culture method. The percentage of GD3-expressing NSCs in neurospheres was nearly the same as it was in neurospheres derived from embryonic, postnatal, and adult brains but decreased drastically to about 40% after differentiation. GD3(+) cells isolated from embryonic mouse striata, postnatal, and adult mouse SVZs by fluorescence-activated cell sorting with an R24 anti-GD3 monoclonal antibody efficiently generated neurospheres compared with GD3(-) cells. These cells possessed multipotency to differentiate into neurons, astrocytes, and oligodendrocytes. These data indicate that GD3 is a unique and powerful cell-surface biomarker to identify and isolate NSCs.