As stem cell products are increasingly entering early stage clinical trials, we are learning from experience about how cell products may be best assessed for safety and efficacy. In two papers ...published in this issue of Stem Cell Reports, a human neural stem cell product, HuCNS-SC, failed to demonstrate efficacy in central nervous system repair in two different animal models (Anderson et al., 2017; Marsh et al., 2017), although closely related research-grade cell products showed evidence of efficacy. This indicates the need for increased cell characterization to determine comparability of lots proposed for pre-clinical and clinical use. Without such improvements, pre-clinical data supporting a clinical study might not adequately reflect the performance of subsequent batches of cells intended for use in patients.
•Failure of clinical versus research-grade neural stem cell lots in preclinical models•Could improved comparability and potency assays reduce negative clinical results?•Should patients and clinicians be given cell-line specific information for trials?•Potential role for increased peer-review during regulatory approval process
Temple and Studer discuss two recent studies that raise concerns about cell characterization of a neural stem cell product intended for clinical use. The variability observed between clinical versus research-grade cell lots in pre-clinical studies imply that negative clinical results may have been avoidable by more detailed characterization and mechanism-based potency assays in the final cell product.
Neural stem cells (NSCs) have great potential for self-renewal, which must be tightly regulated to generate appropriate cell numbers during development and to prevent tumor formation. The ...Ras-MAPK-ERK pathway affects mitogen-stimulated proliferation, and negative regulators are likely to be important for keeping self-renewal in check. Sprouty-related protein with an EVH1 domain (Spred1) is a recently discovered negative Ras-MAPK-ERK regulator linked to a neurofibromatosis 1 (NF-1)-like human syndrome; however, its role in CNS development has not been explored. We show that Spred1 is highly enriched in CNS germinal zones during neurogenesis. Spred1 knockdown increases NSC self-renewal and progenitor proliferation cell-autonomously, and overexpression causes premature differentiation. Surprisingly, Spred1 knockdown in vivo in the embryonic mouse forebrain frequently resulted in periventricular heterotopia, developmental abnormalities often associated with mutations in genes in the vesicular trafficking pathway that cause disruption of germinal zones and impair cell migration. In cortical progenitor cells, Spred1 localizes within distinct vesicles, indicating a potential role in transport. Spred1 knockdown gradually leads to disruption of the apical ventricular zone and loss of radial glia alignment. This impairs late neuronal migration, resulting in the formation of periventricular masses. Thus, Spred1 is critical for normal cortical development, as it modulates progenitor self-renewal/proliferation and helps maintain the integrity and organization of germinal zones.
Neural stem cells are reported to lie in a vascular niche, but there is no direct evidence for a functional relationship between the stem cells and blood vessel component cells. We show that ...endothelial cells but not vascular smooth muscle cells release soluble factors that stimulate the self-renewal of neural stem cells, inhibit their differentiation, and enhance their neuron production. Both embryonic and adult neural stem cells respond, allowing extensive production of both projection neuron and interneuron types in vitro. Endothelial coculture stimulates neuroepithelial cell contact, activating Notch and Hes1 to promote self-renewal. These findings identify endothelial cells as a critical component of the neural stem cell niche.
Many neurological and psychiatric disorders affect the cerebral cortex, and a clearer understanding of the molecular processes underlying human corticogenesis will provide greater insight into such ...pathologies. To date, knowledge of gene expression changes accompanying corticogenesis is largely based on murine data. Here we present a searchable, comprehensive, temporal gene expression data set encompassing cerebral cortical development from human embryonic stem cells (hESCs). Using a modified differentiation protocol that yields neurons suggestive of prefrontal cortex, we identified sets of genes and long noncoding RNAs that significantly change during corticogenesis and those enriched for disease-associations. Numerous alternatively spliced genes with varying temporal patterns of expression are revealed, including TGIF1, involved in holoprosencephaly, and MARK1, involved in autism. We have created a database (http://cortecon.neuralsci.org/) that provides online, query-based access to changes in RNA expression and alternatively spliced transcripts during human cortical development.
•Temporal RNA-seq resource of human cortical development from hESCs•Protocol resulting in enrichment for prefrontal cortical fates•Identified genes with temporally regulated splicing during corticogenesis•Online, searchable database of temporal profile and associated disease information
Using RNA-seq, van de Leemput and Boles et al. have established a resource profiling the transcriptional changes occurring during human cortical development using an in vitro model.
Age-related macular degeneration (AMD) is associated with dysfunction and death of retinal pigment epithelial (RPE) cells. Cell-based approaches using RPE-like cells derived from human pluripotent ...stem cells (hPSCs) are being developed for AMD treatment. However, most efficient RPE differentiation protocols rely on complex, stepwise treatments and addition of growth factors, whereas small-molecule–only approaches developed to date display reduced yields. To identify new compounds that promote RPE differentiation, we developed and performed a high-throughput quantitative PCR screen complemented by a novel orthogonal human induced pluripotent stem cell (hiPSC)-based RPE reporter assay. Chetomin, an inhibitor of hypoxia-inducible factors, was found to strongly increase RPE differentiation; combination with nicotinamide resulted in conversion of over onehalf of the differentiating cells into RPE. Single passage of the whole culture yielded a highly pure hPSC-RPE cell population that displayed many of the morphological, molecular, and functional characteristics of native RPE.
Asymmetric cell divisions are a fundamental feature of neural development, and misregulation can lead to brain abnormalities or tumor formation. During an asymmetric cell division, molecular ...determinants are segregated preferentially into one daughter cell to specify its fate. An important goal is to identify the asymmetric determinants in neural progenitor cells, which could be tumor suppressors or inducers of specific neural fates. Here, we show that the double-stranded RNA-binding protein Stau2 is distributed asymmetrically during progenitor divisions in the developing mouse cortex, preferentially segregating into the Tbr2+ neuroblast daughter, taking with it a subset of RNAs. Knockdown of Stau2 stimulates differentiation and overexpression produces periventricular neuronal masses, demonstrating its functional importance for normal cortical development. We immunoprecipitated Stau2 to examine its cargo mRNAs, and found enrichment for known asymmetric and basal cell determinants, such as Trim32, and identified candidates, including a subset involved in primary cilium function.
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► The RNA binding protein Stau2 is asymmetrically distributed in neural progenitors ► Perturbation of Stau2 levels causes abnormal CNS progenitor behavior ► Stau2-associated transcripts include known and potentially novel fate determinants ► Asymmetric segregation of RNA networks via Stau2 contributes to cell diversification
Stem cells divide asymmetrically during development to expand progeny while maintaining the stem cell pool. This paper shows that the RNA binding protein Stau2, together with its cargo mRNA, segregates asymmetrically in proliferating neuroblasts to regulate normal cortical development.
Knowledge of the detailed mechanism by which proteins such as human αB- crystallin and human lysozyme inhibit amyloid beta (Aβ) peptide aggregation is crucial for designing treatment for Alzheimer's ...disease. Thus, unconstrained, atomistic molecular dynamics simulations in explicit solvent have been performed to characterize the Aβ17-42 assembly in presence of the αB-crystallin core domain and of lysozyme. Simulations reveal that both inhibitor proteins compete with inter-peptide interaction by binding to the peptides during the early stage of aggregation, which is consistent with their inhibitory action reported in experiments. However, the Aβ binding dynamics appear different for each inhibitor. The binding between crystallin and the peptide monomer, dominated by electrostatics, is relatively weak and transient due to the heterogeneous amino acid distribution of the inhibitor surface. The crystallin-bound Aβ oligomers are relatively long-lived, as they form more extensive contact surface with the inhibitor protein. In contrast, a high local density of arginines from lysozyme allows strong binding with Aβ peptide monomers, resulting in stable complexes. Our findings not only illustrate, in atomic detail, how the amyloid inhibitory mechanism of human αB-crystallin, a natural chaperone, is different from that of human lysozyme, but also may aid de novo design of amyloid inhibitors.
Neural progenitor cells (NPCs) divide and differentiate in a precisely regulated manner over time to achieve the remarkable expansion and assembly of the layered mammalian cerebral cortex. Both ...intrinsic signaling pathways and environmental factors control the behavior of NPCs during cortical development. Heparan sulphate proteoglycans (HSPG) are critical environmental regulators that help modulate and integrate environmental cues and downstream intracellular signals. Syndecan-1 (Sdc1), a major transmembrane HSPG, is highly enriched in the early neural germinal zone, but its function in modulating NPC behavior and cortical development has not been explored. In this study we investigate the expression pattern and function of Sdc1 in the developing mouse cerebral cortex. We found that Sdc1 is highly expressed by cortical NPCs. Knockdown of Sdc1 in vivo by in utero electroporation reduces NPC proliferation and causes their premature differentiation, corroborated in isolated cells in vitro. We found that Sdc1 knockdown leads to reduced levels of β-catenin, indicating reduced canonical Wnt signaling. Consistent with this, GSK3β inhibition helps rescue the Sdc1 knockdown phenotype, partially restoring NPC number and proliferation. Moreover, exogenous Wnt protein promotes cortical NPC proliferation, but this is prevented by Sdc1 knockdown. Thus, Sdc1 in the germinal niche is a key HSPG regulating the maintenance and proliferation of NPCs during cortical neurogenesis, in part by modulating the ability of NPCs to respond to Wnt ligands.
In the developing cerebral cortex, neurons are born on a predictable schedule. Here we show in mice that the essential timing mechanism is programmed within individual progenitor cells, and its ...expression depends solely on cell-intrinsic and environmental factors generated within the clonal lineage. Multipotent progenitor cells undergo repeated asymmetric divisions, sequentially generating neurons in their normal in vivo order: first preplate cells, including Cajal-Retzius neurons, then deep and finally superficial cortical plate neurons. As each cortical layer arises, stem cells and neuroblasts become restricted from generating earlier-born neuron types. Growth as neurospheres or in co-culture with younger cells did not restore their plasticity. Using short-hairpin RNA (shRNA) to reduce Foxg1 expression reset the timing of mid- but not late-gestation progenitors, allowing them to remake preplate neurons and then cortical-plate neurons. Our data demonstrate that neural stem cells change neuropotency during development and have a window of plasticity when restrictions can be reversed.
The vascular compartment of the adult brain ventricular-subventricular zone (V-SVZ) is a critical regulator of neural stem cell and progenitor function. Blood enters the V-SVZ via arteries and ...arterioles to capillaries that then connect with venules and veins to return blood to the heart. We found that stromal cell-derived factor 1 (SDF1) is expressed by a subpopulation of V-SVZ vessels, the capillaries, and that actively proliferating neural stem cells (NSCs) and progenitors are preferentially associated with these SDF1-positive vessels. In contrast, slowly dividing or quiescent NSCs are most prevalent near SDF1-negative vessels. By conditional knockout, we found that loss of SDF1 signaling in NSCs stimulates lineage progression and NSC displacement from the vessel niche. With aging, SDF1/CXCR4 signaling is dysregulated, coincident with reduced proliferation and increased displacement of dividing cells from the vasculature. Our findings demonstrate SDF1-based vascular heterogeneity in the niche and suggest that reduced SDF1 signaling contributes to age-related declines in adult neurogenesis.
•SDF1 is expressed on capillaries but not venule or arterioles in the V-SVZ niche•Proliferating NSCs prefer SDF1-expressing vasculature•Knockdown of SDF1's receptor causes lineage progression•Aging results in reductions in SDF1/CXCR4 signaling
The vascular compartment of the adult neurogenic niche is a major regulatory hub for neural stem cells. Here, Kokovay and colleagues show that the chemokine SDF1 is expressed by a subset of the blood vessels within the niche associated with proliferating progenitors. Knockdown of the SDF1 receptor leads to aberrant lineage progression.
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