Small molecules greatly improve conversion of human-induced pluripotent stem cells to the neuronal lineage. Stem Cells Int. 2012;2012:140427. [PMID: 22567022 PMCID: PMC3339118 DOI: 10.1155/2012/140427]

Human-Induced Pluripotent Stem Cell (iPSC)-Derived GABAergic Neuron Differentiation in Bipolar Disorder

Bipolar disorder (BP) is a recurring psychiatric condition characterized by alternating episodes of low energy (depressions) followed by manias (high energy). Cortical network activity produced by GABAergic interneurons may be critical in maintaining the balance in excitatory/inhibitory activity in the brain during development. Initially, GABAergic signaling is excitatory; with maturation, these cells undergo a functional switch that converts GABAA channels from depolarizing (excitatory) to hyperpolarizing (inhibitory), which is controlled by the intracellular concentration of two chloride transporters. The earliest, NKCC1, promotes chloride entry into the cell and depolarization, while the second (KCC2) stimulates movement of chloride from the neuron, hyperpolarizing it. Perturbations in the timing or expression of NKCC1/KCC2 may affect essential morphogenetic events including cell proliferation, migration, synaptogenesis and plasticity, and thereby the structure and function of the cortex. We derived induced pluripotent stem cells (iPSC) from BP patients and undiagnosed control (C) individuals, then modified a differentiation protocol to form GABAergic interneurons, harvesting cells at sequential stages of differentiation. qRT-PCR and RNA sequencing indicated that after six weeks of differentiation, controls transiently expressed high levels of NKCC1. Using multi-electrode array (MEA) analysis, we observed that BP neurons exhibit increased firing, network bursting and decreased synchrony compared to C. Understanding GABA signaling in differentiation may identify novel approaches and new targets for treatment of neuropsychiatric disorders such as BP.

Enhanced electrophysiological activity and neurotoxicity screening of environmental chemicals using 3D neurons from human neural precursor cells purified with PSA-NCAM

The assessment of neurotoxicity for environmental chemicals is of utmost importance in ensuring public health and environmental safety. Multielectrode array (MEA) technology has emerged as a powerful tool for assessing disturbances in the electrophysiological activity. Although human embryonic stem cell (hESC)-derived neurons have been used in MEA for neurotoxicity screening, obtaining a substantial and sufficiently active population of neurons from hESCs remains challenging. In this study, we successfully differentiated neurons from a large population of human neuronal precursor cells (hNPC) purified using a polysialylated neural cell adhesion molecule (PSA-NCAM), referred to as hNPCPSA-NCAM+. The functional characterization demonstrated that hNPCPSA-NCAM+-derived neurons improve functionality by enhancing electrophysiological activity compared to total hNPC-derived neurons. Furthermore, three-dimensional (3D) neurons derived from hNPCPSA-NCAM+ exhibited reduced maturation time and enhanced electrophysiological activity on MEA. We employed subdivided population analysis of active mean firing rate (MFR) based on electrophysiological intensity to characterize the electrophysiological properties of hNPCPSA-NCAM+-3D neurons. Based on electrophysiological activity including MFR and burst parameters, we evaluated the sensitivity of hNPCPSA-NCAM+-3D neurons on MEA to screen both inhibitory and excitatory neuroactive environmental chemicals. Intriguingly, electrophysiologically active hNPCPSA-NCAM+-3D neurons demonstrated good sensitivity to evaluate neuroactive chemicals, particularly in discriminating excitatory chemicals. Our findings highlight the effectiveness of MEA approaches using hNPCPSA-NCAM+-3D neurons in the assessment of neurotoxicity associated with environmental chemicals. Furthermore, we emphasize the importance of selecting appropriate signal intensity thresholds to enhance neurotoxicity prediction and screening of environmental chemicals.

From 2D to 3D: Development of Monolayer Dopaminergic Neuronal and Midbrain Organoid Cultures for Parkinson's Disease Modeling and Regenerative Therapy

Parkinson's Disease (PD) is a prevalent neurodegenerative disorder that is characterized pathologically by the loss of A9-specific dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) of the midbrain. Despite intensive research, the etiology of PD is currently unresolved, and the disease remains incurable. This, in part, is due to the lack of an experimental disease model that could faithfully recapitulate the features of human PD. However, the recent advent of induced pluripotent stem cell (iPSC) technology has allowed PD models to be created from patient-derived cells. Indeed, DA neurons from PD patients are now routinely established in many laboratories as monolayers as well as 3D organoid cultures that serve as useful toolboxes for understanding the mechanism underlying PD and also for drug discovery. At the same time, the iPSC technology also provides unprecedented opportunity for autologous cell-based therapy for the PD patient to be performed using the patient's own cells as starting materials. In this review, we provide an update on the molecular processes underpinning the development and differentiation of human pluripotent stem cells (PSCs) into midbrain DA neurons in both 2D and 3D cultures, as well as the latest advancements in using these cells for drug discovery and regenerative medicine. For the novice entering the field, the cornucopia of differentiation protocols reported for the generation of midbrain DA neurons may seem daunting. Here, we have distilled the essence of the different approaches and summarized the main factors driving DA neuronal differentiation, with the view to provide a useful guide to newcomers who are interested in developing iPSC-based models of PD.

Suppressor of Fused Regulation of Hedgehog Signaling is Required for Proper Astrocyte Differentiation

Hedgehog signaling is essential for vertebrate development; however, less is known about the negative regulators that influence this pathway. Using the mouse P19 embryonal carcinoma cell model, suppressor of fused (SUFU), a negative regulator of the Hedgehog (Hh) pathway, was investigated during retinoic acid (RA)-induced neural differentiation. We found Hh signaling increased activity in the early phase of differentiation, but was reduced during terminal differentiation of neurons and astrocytes. This early increase in pathway activity was required for neural differentiation; however, it alone was not sufficient to induce neural lineages. SUFU, which regulates signaling at the level of Gli, remained relatively unchanged during differentiation, but its loss through CRISPR-Cas9 gene editing resulted in ectopic expression of Hh target genes. Interestingly, these SUFU-deficient cells were unable to differentiate toward neural lineages without RA, and when directed toward these lineages, they showed delayed and decreased astrocyte differentiation; neuron differentiation was unaffected. Ectopic activation of Hh target genes in SUFU-deficient cells remained throughout RA-induced differentiation and this was accompanied by the loss of Gli3, despite the presence of the Gli3 message. Thus, the study indicates the proper timing and proportion of astrocyte differentiation requires SUFU, likely acting through Gli3, to reduce Hh signaling during late-stage differentiation.

Modelling ciliopathy phenotypes in human tissues derived from pluripotent stem cells with genetically ablated cilia

The functions of cilia-antenna-like organelles associated with a spectrum of disease states-are poorly understood, particularly in human cells. Here we show that human pluripotent stem cells (hPSCs) edited via CRISPR to knock out the kinesin-2 subunits KIF3A or KIF3B can be used to model ciliopathy phenotypes and to reveal ciliary functions at the tissue scale. KIF3A-/- and KIF3B-/- hPSCs lacked cilia, yet remained robustly self-renewing and pluripotent. Tissues and organoids derived from these hPSCs displayed phenotypes that recapitulated defective neurogenesis and nephrogenesis, polycystic kidney disease (PKD) and other features of the ciliopathy spectrum. We also show that human cilia mediate a critical switch in hedgehog signalling during organoid differentiation, and that they constitutively release extracellular vesicles containing signalling molecules associated with ciliopathy phenotypes. The capacity of KIF3A-/- and KIF3B-/- hPSCs to reveal endogenous mechanisms underlying complex ciliary phenotypes may facilitate the discovery of candidate therapeutics.

Human Astrocytes Model Derived from Induced Pluripotent Stem Cells

Induced pluripotent stem cell (iPSC)-based disease modeling has a great potential for uncovering the mechanisms of pathogenesis, especially in the case of neurodegenerative diseases where disease-susceptible cells can usually not be obtained from patients. So far, the iPSC-based modeling of neurodegenerative diseases has mainly focused on neurons because the protocols for generating astrocytes from iPSCs have not been fully established. The growing evidence of astrocytes' contribution to neurodegenerative diseases has underscored the lack of iPSC-derived astrocyte models. In the present study, we established a protocol to efficiently generate iPSC-derived astrocytes (iPasts), which were further characterized by RNA and protein expression profiles as well as functional assays. iPasts exhibited calcium dynamics and glutamate uptake activity comparable to human primary astrocytes. Moreover, when co-cultured with neurons, iPasts enhanced neuronal synaptic maturation. Our protocol can be used for modeling astrocyte-related disease phenotypes in vitro and further exploring the contribution of astrocytes to neurodegenerative diseases.

Exosome/microvesicle content is altered in leucine-rich repeat kinase 2 mutant induced pluripotent stem cell-derived neural cells

Extracellular vesicles, including exosomes/microvesicles (EMVs), have been described as sensitive biomarkers that represent disease states and response to therapies. In light of recent reports of disease-mirroring EMV molecular signatures, the present study profiled two EMVs from different Parkinson's disease (PD) tissue sources: (a) neural progenitor cells derived from an endogenous adult stem/progenitor cell, called adult human neural progenitor (AHNP) cells, that we found to be pathological when isolated from postmortem PD patients' substantia nigra; and (b) leucine-rich repeat kinase 2 (LRRK2) gene identified patient induced pluripotent stem cells (iPSCs), which were used to isolate EMVs and begin to characterize their cargoes. Initial characterization of EMVs derived from idiopathic patients (AHNPs) and mutant LRRK2 patients showed differences between both phenotypes and when compared with a sibling control in EMV size and release based on Nanosight analysis. Furthermore, molecular profiling disclosed that neurodegenerative-related gene pathways altered in PD can be reversed using gene-editing approaches. In fact, the EMV cargo genes exhibited normal expression patterns after gene editing. This study shows that EMVs have the potential to serve as sensitive biomarkers of disease state in both idiopathic and gene-identified PD patients and that following gene-editing, EMVs reflect a corrected state. This is relevant for both prodromal and symptomatic patient populations where potential responses to therapies can be monitored via non-invasive liquid biopsies and EMV characterizations.

A compendious summary of Parkinson's disease patient-derived iPSCs in the first decade

The number of Parkinson's disease (PD) patients increases with aging, which brings heavy burden to families and society. The emergence of patient-derived induced pluripotent stem cells (iPSCs) has brought hope to the current situation of lacking new breakthroughs in diagnosis and treatment of PD. In this article, we reviewed and analyzed the current researches related to PD patient-derived iPSCs, in order to provide solid theoretical basis for future study of PD. In 2008, successful iPSCs derived from PD patients were reported. The current iPSCs research in PD mostly focused on the establishment of specific iPSCs models of PD patients carrying susceptible genes. The main source of PD patient-derived iPSCs is skin fibroblasts and the mainstream reprogramming methodology is the mature "four-factor" method, which introduces four totipotent correlation factors Oct4, Sox2, Klf4 and c-Myc into somatic cells. The main sources of iPSCs are patients with non-pedigrees and there have been no studies involving both PD patients and unaffected carriers within the same family. Most of the existing studies of PD patient-derived iPSCs started with the induction method for obtaining dopaminergic neurons in the first instance, but therapeutic applications are being increased. Although it is not the ultimate panacea, and there are still some unsolved problems (e.g., whether the mutated genes should be corrected or not), a better understanding of iPSCs may be a good gift for both PD patients and doctors due to their advantages in diagnosis and treatment of PD.

G2019S Variation in LRRK2: An Ideal Model for the Study of Parkinson's Disease?

Parkinson's disease (PD) is the second most common neurodegenerative disorder and has plagued humans for more than 200 years. The etiology and detailed pathogenesis of PD is unclear, but is currently believed to be the result of the interaction between genetic and environmental factors. Studies have found that PD patients with the LRRK2:G2019S variation have the typical clinical manifestations of PD, which may be familial or sporadic, and have age-dependent pathogenic characteristics. Therefore, the LRRK2:G2019S variation may be an ideal model to study the interaction of multiple factors such as genetic, environmental and natural aging factors in PD in the future. This article reviewed the progress of LRRK2:G2019S studies in PD research in order to provide new research ideas and directions for the pathogenesis and treatment of PD.

Neuronal Trans-differentiation by Transcription Factors Ascl1 and Nurr1: Induction of a Dopaminergic Neurotransmitter Phenotype in Cortical GABAergic Neurons

Neurons with a desired neurotransmitter phenotype can be differentiated from induced pluripotent stem cells or from somatic cells only through tedious protocols with relatively low yield. Readily available cortical neurons isolated from embryonic rat brain, which have already undergone a complete neuronal differentiation process, might serve as alternative template source. These cultures consist of 85% glutamatergic and 15% GABAergic neurons, and we attempted to trans-differentiate them into dopaminergic neurons. Transcription factors Nurr1, Lmx1A and Pitx3, essential determinants of a dopaminergic cell fate during CNS development, were not sufficient to induce tyrosine hydroxylase expression in a significant number of cells. Combining Nurr1 with the generic neuronal differentiator and re-programming factor Ascl1, however, resulted in generation of neurons which express dopaminergic markers TH, AADC, VMAT2 and DAT. Only neurons of GABAergic phenotype could be trans-differentiated towards a dopaminergic neurotransmitter phenotype, while for glutamatergic neurons, this process proved to be neurotoxic. Intriguingly, GABAergic neurons isolated from embryonal midbrain could not be trans-differentiated into dopaminergic neurons by Ascl1 and Nurr1. Thus, in principle, post-mitotic embryonal neurons can serve as templates for neurons with a desired neurotransmitter phenotype. However, neurotransmitter phenotype plasticity critically depends on the differentiation history of the template neurons, which can result in relatively low yields of dopaminergic neurons.

Neural stem cell differentiation into mature neurons: Mechanisms of regulation and biotechnological applications

The abilities of stem cells to self-renew and form different mature cells expand the possibilities of applications in cell-based therapies such as tissue recomposition in regenerative medicine, drug screening, and treatment of neurodegenerative diseases. In addition to stem cells found in the embryo, various adult organs and tissues have niches of stem cells in an undifferentiated state. In the central nervous system of adult mammals, neurogenesis occurs in two regions: the subventricular zone and the dentate gyrus in the hippocampus. The generation of the different neural lines originates in adult neural stem cells that can self-renew or differentiate into astrocytes, oligodendrocytes, or neurons in response to specific stimuli. The regulation of the fate of neural stem cells is a finely controlled process relying on a complex regulatory network that extends from the epigenetic to the translational level and involves extracellular matrix components. Thus, a better understanding of the mechanisms underlying how the process of neurogenesis is induced, regulated, and maintained will provide elues for development of novel for strategies for neurodegenerative therapies. In this review, we focus on describing the mechanisms underlying the regulation of the neuronal differentiation process by transcription factors, microRNAs, and extracellular matrix components.

The addition of human iPS cell-derived neural progenitors changes the contraction of human iPS cell-derived cardiac spheroids

BACKGROUND

We havebeen attempting to use cardiac spheroids to construct three-dimensional contractilestructures for failed hearts. Recent studies have reported that neuralprogenitors (NPs) play significant roles in heart regeneration. However, theeffect of NPs on the cardiac spheroid has not yet been elucidated.

OBJECTIVE

This studyaims to demonstrate the influence of NPs on the function of cardiac spheroids.

METHODS

Thespheroids were constructed on a low-attachment-well plate by mixing humaninduced pluripotent stem (hiPS) cell-derived cardiomyocytes and hiPScell-derived NPs (hiPS-NPs). The ratio of hiPS-NPs was set at 0%, 10%, 20%,30%, and 40% of the total cell number of spheroids, which was 2500. The motionwas recorded, and the fractional shortening and the contraction velocity weremeasured.

RESULTS

Spheroidswere formed within 48 h after mixing the cells, except for the spheroidscontaining 0% hiPS-NPs. Observation at day 7 revealed significant differencesin the fractional shortening (analysis of variance; p = 0.01). The bestfractional shortening was observed with the spheroids containing 30% hiPS-NPs.Neuronal cells were detected morphologically within the spheroids under aconfocal microscope.

CONCLUSION

Theaddition of hiPS-NPs influenced the contractile function of the cardiacspheroids. Further studies are warranted to elucidate the underlying mechanism.

Highly efficient methods to obtain homogeneous dorsal neural progenitor cells from human and mouse embryonic stem cells and induced pluripotent stem cells

Background

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have been widely used to generate cellular models harboring specific disease-related genotypes. Of particular importance are ESC and iPSC applications capable of producing dorsal telencephalic neural progenitor cells (NPCs) that are representative of the cerebral cortex and overcome the challenges of maintaining a homogeneous population of cortical progenitors over several passages in vitro. While previous studies were able to derive NPCs from pluripotent cell types, the fraction of dorsal NPCs in this population is small and decreases over several passages. Here, we present three protocols that are highly efficient in differentiating mouse and human ESCs, as well as human iPSCs, into a homogeneous and stable population of dorsal NPCs. These protocols will be useful for modeling cerebral cortical neurological and neurodegenerative disorders in both mouse and human as well as for high-throughput drug screening for therapeutic development.

Methods

We optimized three different strategies for generating dorsal telencephalic NPCs from mouse and human pluripotent cell types through single or double inhibition of bone morphogenetic protein (BMP) and/or SMAD pathways. Mouse and human pluripotent cells were aggregated to form embryoid bodies in suspension and were treated with dorsomorphin alone (BMP inhibition) or combined with SB431542 (double BMP/SMAD inhibition) during neural induction. Neural rosettes were then selected from plated embryoid bodies to purify the population of dorsal NPCs. We tested the expression of key dorsal NPC markers as well as nonectodermal markers to confirm the efficiency of our three methods in comparison to published and commercial protocols.

Results

Single and double inhibition of BMP and/or SMAD during neural induction led to the efficient differentiation of dorsal NPCs, based on the high percentage of PAX6-positive cells and the NPC gene expression profile. There were no statistically significant differences in the variation of PAX6 and SOX1-positive NPCs between the two human pluripotent cell-derived methods; therefore, both methods are suitable for producing stable dorsal NPCs. When further differentiated into mature neurons, NPCs gave rise to a population of almost exclusively forebrain cortical neurons, confirming the dorsal fate commitment of the progenitors.

Conclusions

The methods described in this study show improvements over previously published studies and are highly efficient at differentiating human and mouse pluripotent cell types into dorsal PAX6-positive NPCs and eventually into forebrain cortical neurons.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0812-6) contains supplementary material, which is available to authorized users.

Small Molecules for Neural Stem Cell Induction

Generation of induced pluripotent stem cells (iPSCs) from other somatic cells has provided great hopes for transplantation therapies. However, these cells still cannot be used for clinical application due to the low reprogramming and differentiation efficiency beside the risk of mutagenesis and tumor formation. Compared to iPSCs, induced neural stem cells (iNSCs) are easier to terminally differentiate into neural cells and safe; thus, iNSCs hold more opportunities than iPSCs to treat neural diseases. On the other hand, recent studies have showed that small molecules (SMs) can dramatically improve the efficiency of reprogramming and SMs alone can even convert one kind of somatic cells into another, which is much safer and more effective than transcription factor-based methods. In this study, we provide a review of SMs that are generally used in recent neural stem cell induction studies, and discuss the main mechanisms and pathways of each SM.

In Vitro Differentiation of Neural-Like Cells from Human Embryonic Stem Cells by A Combination of Dorsomorphin, XAV939, and A8301

Objective

Motor neuron differentiation from human embryonic stem cells (hESCs) is a goal of regenerative medicine to provide cell therapy as treatments for diseases that damage motor neurons. Most protocols lack adequate efficiency in generating functional motor neurons. However, small molecules present a new approach to overcome this challenge. The aim of this research is to replace morphogen factors with a cocktail of efficient, affordable small molecules for effective, low cost motor neuron differentiation.

Materials and Methods

In this experimental study, hESCs were differentiated into motor neuron by the application of a small molecule cocktail that consisted of dorsomorphin, A8301, and XAV939. During the differentiation protocol, we selected five stages and assessed expressions of neural markers by real-time polymerase chain reaction (PCR), immunofluorescence staining, and flow cytometry. Motor neuron ion currents were determined by whole cell patch clamp recording.

Results

Immunofluorescence staining and flow cytometry analysis of hESC-derived neural ectoderm (NE) indicated that they were positive for NESTIN (92.68%), PAX6 (64.40%), and SOX1 (82.11%) in a chemically defined adherent culture. The replated (hESC)-derived NE differentiated cells were positive for TUJ1, MAP2, HB9 and ISL1. We evaluated the gene expression levels with real-time reverse transcriptase-PCR at different stages of the differentiation protocol. Voltage gated channel currents of differentiated cells were examined by the whole-cell patch clamp technique. The hESC-derived motor neurons showed voltage gated delay rectifier K⁺, Na⁺ and Ca²⁺ inward currents.

Conclusion

Our results indicated that hESC-derived neurons expressed the specific motor neuron markers specially HB9 and ISL1 but voltage clamp recording showed small ionic currents therefore it seems that voltage gated channel population were inadequate for firing action potentials.

Glycation potentiates α-synuclein-associated neurodegeneration in synucleinopathies

α-Synuclein misfolding and aggregation is a hallmark in Parkinson's disease and in several other neurodegenerative diseases known as synucleinopathies. The toxic properties of α-synuclein are conserved from yeast to man, but the precise underpinnings of the cellular pathologies associated are still elusive, complicating the development of effective therapeutic strategies. Combining molecular genetics with target-based approaches, we established that glycation, an unavoidable age-associated post-translational modification, enhanced α-synuclein toxicity in vitro and in vivo, in Drosophila and in mice. Glycation affected primarily the N-terminal region of α-synuclein, reducing membrane binding, impaired the clearance of α-synuclein, and promoted the accumulation of toxic oligomers that impaired neuronal synaptic transmission. Strikingly, using glycation inhibitors, we demonstrated that normal clearance of α-synuclein was re-established, aggregation was reduced, and motor phenotypes in Drosophila were alleviated. Altogether, our study demonstrates glycation constitutes a novel drug target that can be explored in synucleinopathies as well as in other neurodegenerative conditions.

New neurons in adult brain: distribution, molecular mechanisms and therapies

"Are new neurons added in the adult mammalian brain?" "Do neural stem cells activate following CNS diseases?" "How can we modulate their activation to promote recovery?" Recent findings in the field provide novel insights for addressing these questions from a new perspective. In this review, we will summarize the current knowledge about adult neurogenesis and neural stem cell niches in healthy and pathological conditions. We will first overview the milestones that have led to the discovery of the classical ventricular and hippocampal neural stem cell niches. In adult brain, new neurons originate from proliferating neural precursors located in the subventricular zone of the lateral ventricles and in the subgranular zone of the hippocampus. However, recent findings suggest that new neuronal cells can be added to the adult brain by direct differentiation (e.g., without cell proliferation) from either quiescent neural precursors or non-neuronal cells undergoing conversion or reprogramming to neuronal fate. Accordingly, in this review we will also address critical aspects of the newly described mechanisms of quiescence and direct conversion as well as the more canonical activation of the neurogenic niches and neuroblast reservoirs in pathological conditions. Finally, we will outline the critical elements involved in neural progenitor proliferation, neuroblast migration and differentiation and discuss their potential as targets for the development of novel therapeutic drugs for neurodegenerative diseases.

RNA stores tau reversibly in complex coacervates

Nonmembrane-bound organelles that behave like liquid droplets are widespread among eukaryotic cells. Their dysregulation appears to be a critical step in several neurodegenerative conditions. Here, we report that tau protein, the primary constituent of Alzheimer neurofibrillary tangles, can form liquid droplets and therefore has the necessary biophysical properties to undergo liquid-liquid phase separation (LLPS) in cells. Consonant with the factors that induce LLPS, tau is an intrinsically disordered protein that complexes with RNA to form droplets. Uniquely, the pool of RNAs to which tau binds in living cells are tRNAs. This phase state of tau is held in an approximately 1:1 charge balance across the protein and the nucleic acid constituents, and can thus be maximal at different RNA:tau mass ratios, depending on the biopolymer constituents involved. This feature is characteristic of complex coacervation. We furthermore show that the LLPS process is directly and sensitively tuned by salt concentration and temperature, implying it is modulated by both electrostatic interactions between the involved protein and nucleic acid constituents, as well as net changes in entropy. Despite the high protein concentration within the complex coacervate phase, tau is locally freely tumbling and capable of diffusing through the droplet interior. In fact, tau in the condensed phase state does not reveal any immediate changes in local protein packing, local conformations and local protein dynamics from that of tau in the dilute solution state. In contrast, the population of aggregation-prone tau as induced by the complexation with heparin is accompanied by large changes in local tau conformations and irreversible aggregation. However, prolonged residency within the droplet state eventually results in the emergence of detectable β-sheet structures according to thioflavin-T assay. These findings suggest that the droplet state can incubate tau and predispose the protein toward the formation of insoluble fibrils.

Tau is a common neuronal protein that, under circumstances and conditions not well understood to date, self-assembles into intracellular aggregates in several neurodegenerative diseases including Alzheimer disease. These aggregates are formed of fibrous polymers. The mechanism by which this critical transition from a soluble protein to insoluble fibrous material occurs is unknown. We have discovered a novel state in which many tau molecules become compacted into a protein-rich droplet while maintaining their solubility and native-like protein conformations. Chemists refer to this dense liquid droplet state as a complex coacervate phase, and it is held together by the opposite charges of their constituents, ions, and water. In the case of the tau protein, the oppositely charged constituent is RNA. Indeed, we found that in human neuronal cell culture, tau selectively binds to a category of RNA known as tRNA. Interestingly, tau and RNA favorably condense to a complex coacervate phase when the charges between them are matched and at elevated temperatures, such that tau-RNA droplets could be observed at physiologically viable protein concentrations simply by increasing the temperature from room to physiological temperatures. When the tau-RNA–dense droplets are incubated together over time, tau transitions to a conformation similar to that found in pathological fibers. Our experiments therefore demonstrate physicochemical properties of tau that may predispose it to undergo changes associated with neurodegenerative disease.

Generation of iPSC-derived Human Brain Organoids to Model Early Neurodevelopmental Disorders

The restricted availability of suitable in vitro models that can reliably represent complex human brain development is a significant bottleneck that limits the translation of basic brain research into clinical application. While induced pluripotent stem cells (iPSCs) have replaced the ethically questionable human embryonic stem cells, iPSC-based neuronal differentiation studies remain descriptive at the cellular level but fail to adequately provide the details that could be derived from a complex, 3D human brain tissue. This gap is now filled through the application of iPSC-derived, 3D brain organoids, "Brains in a dish," that model many features of complex human brain development. Here, a method for generating iPSC-derived, 3D brain organoids is described. The organoids can help with modeling autosomal recessive primary microcephaly (MCPH), a rare human neurodevelopmental disorder. A widely accepted explanation for the brain malformation in MCPH is a depletion of the neural stem cell pool during the early stages of human brain development, a developmental defect that is difficult to recreate or prove in vitro. To study MCPH, we generated iPSCs from patient-derived fibroblasts carrying a mutation in the centrosomal protein CPAP. By analyzing the ventricular zone of microcephaly 3D brain organoids, we showed the premature differentiation of neural progenitors. These 3D brain organoids are a powerful in vitro system that will be instrumental in modeling congenital brain disorders induced by neurotoxic chemicals, neurotrophic viral infections, or inherited genetic mutations.

Fibrin hydrogels induce mixed dorsal/ventral spinal neuron identities during differentiation of human induced pluripotent stem cells

We hypothesized that generating spinal motor neurons (sMNs) from human induced pluripotent stem cell (hiPSC)-derived neural aggregates (NAs) using a chemically-defined differentiation protocol would be more effective inside of 3D fibrin hydrogels compared to 2D poly-L-ornithine(PLO)/laminin-coated tissue culture plastic surfaces. We performed targeted RNA-Seq using next generation sequencing to determine the substrate-specific differences in gene expression that regulate cell phenotype. Cells cultured on both substrates expressed sMN genes CHAT and MNX1, though persistent WNT signaling contributed to a higher expression of genes associated with interneurons in NAs cultured in 3D fibrin scaffolds. Cells in fibrin also expressed lower levels of astrocyte progenitor genes and higher levels of the neuronal-specific gene TUBB3, suggesting a purer population of neurons compared to 2D cultures.

STATEMENT OF SIGNIFICANCE

Fibrin scaffolds can support the neuronal differentiation of pluripotent stem cells. This study provides insight into how fibrin hydrogels affect neuronal induction by analyzing of the signaling pathways activated during the differentiation process. These insights can then be used to tailor the properties of these hydrogels to optimize the generation of sMNs for regenerative medicine applications.

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.

Sequential Differentiation of Embryonic Stem Cells into Neural Epithelial-Like Stem Cells and Oligodendrocyte Progenitor Cells

BACKGROUND

Recent advances in stem cell technology afford an unlimited source of neural progenitors and glial cells for cell based therapy in central nervous system (CNS) disorders. However, current differentiation strategies still need to be improved due to time-consuming processes, poorly defined culture conditions, and low yield of target cell populations.

METHODOLOGY/PRINCIPLE FINDINGS

This study aimed to provide a precise sequential differentiation to capture two transient stages: neural epithelia-like stem cells (NESCs) and oligodendrocytes progenitor cells (OPCs) derived from mouse embryonic stem cells (ESCs). CHIR99021, a glycogen synthase kinase 3 (GSK-3) inhibitor, in combination with dual SMAD inhibitors, could induce ESCs to rapidly differentiate into neural rosette-like colonies, which facilitated robust generation of NESCs that had a high self-renewal capability and stable neuronal and glial differentiation potentials. Furthermore, SHH combined with FGF-2 and PDGF-AA could induce NESCs to differentiate into highly expandable OPCs. These OPCs not only robustly differentiated into oligodendrocytes, but also displayed an increased migratory activity in vitro.

CONCLUSIONS/SIGNIFICANCE

We developed a precise and reliable strategy for sequential differentiation to capture NESCs and OPCs derived from ESCs, thus providing unlimited cell source for cell transplantation and drug screening towards CNS repair.

Induced pluripotent stem cells and Parkinson's disease: modelling and treatment

Many neurodegenerative disorders, such as Parkinson's disease (PD), are characterized by progressive neuronal loss in different regions of the central nervous system, contributing to brain dysfunction in the relevant patients. Stem cell therapy holds great promise for PD patients, including with foetal ventral mesencephalic cells, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). Moreover, stem cells can be used to model neurodegenerative diseases in order to screen potential medication and explore their mechanisms of disease. However, related ethical issues, immunological rejection and lack of canonical grafting protocols limit common clinical use of stem cells. iPSCs, derived from reprogrammed somatic cells, provide new hope for cell replacement therapy. In this review, recent development in stem cell treatment for PD, using hiPSCs, as well as the potential value of hiPSCs in modelling for PD, have been summarized for application of iPSCs technology to clinical translation for PD treatment.

Pluripotent Human embryonic stem cell derived neural lineages for in vitro modelling of enterovirus 71 infection and therapy

BACKGROUND

The incidence of neurological complications and fatalities associated with Hand, Foot & Mouth disease has increased over recent years, due to emergence of newly-evolved strains of Enterovirus 71 (EV71). In the search for new antiviral therapeutics against EV71, accurate and sensitive in vitro cellular models for preliminary studies of EV71 pathogenesis is an essential prerequisite, before progressing to expensive and time-consuming live animal studies and clinical trials.

METHODS

This study thus investigated whether neural lineages derived from pluripotent human embryonic stem cells (hESC) can fulfil this purpose. EV71 infection of hESC-derived neural stem cells (NSC) and mature neurons (MN) was carried out in vitro, in comparison with RD and SH-SY5Y cell lines.

RESULTS

Upon assessment of post-infection survivability and EV71 production by the various types, it was observed that NSC were significantly more susceptible to EV71 infection compared to MN, RD (rhabdomyosarcoma) and SH-SY5Y cells, which was consistent with previous studies on mice. The SP81 peptide had significantly greater inhibitory effect on EV71 production by NSC and MN compared to the cancer-derived RD and SH-SY5Y cell lines.

CONCLUSIONS

Hence, this study demonstrates that hESC-derived neural lineages can be utilized as in vitro models for studying EV71 pathogenesis and for screening of antiviral therapeutics.

Elevated α-synuclein caused by SNCA gene triplication impairs neuronal differentiation and maturation in Parkinson's patient-derived induced pluripotent stem cells

We have assessed the impact of α-synuclein overexpression on the differentiation potential and phenotypic signatures of two neural-committed induced pluripotent stem cell lines derived from a Parkinson's disease patient with a triplication of the human SNCA genomic locus. In parallel, comparative studies were performed on two control lines derived from healthy individuals and lines generated from the patient iPS-derived neuroprogenitor lines infected with a lentivirus incorporating a small hairpin RNA to knock down the SNCA mRNA. The SNCA triplication lines exhibited a reduced capacity to differentiate into dopaminergic or GABAergic neurons and decreased neurite outgrowth and lower neuronal activity compared with control cultures. This delayed maturation phenotype was confirmed by gene expression profiling, which revealed a significant reduction in mRNA for genes implicated in neuronal differentiation such as delta-like homolog 1 (DLK1), gamma-aminobutyric acid type B receptor subunit 2 (GABABR2), nuclear receptor related 1 protein (NURR1), G-protein-regulated inward-rectifier potassium channel 2 (GIRK-2) and tyrosine hydroxylase (TH). The differentiated patient cells also demonstrated increased autophagic flux when stressed with chloroquine. We conclude that a two-fold overexpression of α-synuclein caused by a triplication of the SNCA gene is sufficient to impair the differentiation of neuronal progenitor cells, a finding with implications for adult neurogenesis and Parkinson's disease progression, particularly in the context of bioenergetic dysfunction.

Human induced pluripotent stem cells in Parkinson's disease: A novel cell source of cell therapy and disease modeling

Human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs) are two novel cell sources for studying neurodegenerative diseases. Dopaminergic neurons derived from hiPSCs/hESCs have been implicated to be very useful in Parkinson's disease (PD) research, including cell replacement therapy, disease modeling and drug screening. Recently, great efforts have been made to improve the application of hiPSCs/hESCs in PD research. Considerable advances have been made in recent years, including advanced reprogramming strategies without the use of viruses or using fewer transcriptional factors, optimized methods for generating highly homogeneous neural progenitors with a larger proportion of mature dopaminergic neurons and better survival and integration after transplantation. Here we outline the progress that has been made in these aspects in recent years, particularly during the last year, and also discuss existing issues that need to be addressed.

Importance of being Nernst: Synaptic activity and functional relevance in stem cell-derived neurons

Functional synaptogenesis and network emergence are signature endpoints of neurogenesis. These behaviors provide higher-order confirmation that biochemical and cellular processes necessary for neurotransmitter release, post-synaptic detection and network propagation of neuronal activity have been properly expressed and coordinated among cells. The development of synaptic neurotransmission can therefore be considered a defining property of neurons. Although dissociated primary neuron cultures readily form functioning synapses and network behaviors in vitro, continuously cultured neurogenic cell lines have historically failed to meet these criteria. Therefore, in vitro-derived neuron models that develop synaptic transmission are critically needed for a wide array of studies, including molecular neuroscience, developmental neurogenesis, disease research and neurotoxicology. Over the last decade, neurons derived from various stem cell lines have shown varying ability to develop into functionally mature neurons. In this review, we will discuss the neurogenic potential of various stem cells populations, addressing strengths and weaknesses of each, with particular attention to the emergence of functional behaviors. We will propose methods to functionally characterize new stem cell-derived neuron (SCN) platforms to improve their reliability as physiological relevant models. Finally, we will review how synaptically active SCNs can be applied to accelerate research in a variety of areas. Ultimately, emphasizing the critical importance of synaptic activity and network responses as a marker of neuronal maturation is anticipated to result in in vitro findings that better translate to efficacious clinical treatments.

Discovery of a Novel Polymer for Human Pluripotent Stem Cell Expansion and Multilineage Differentiation

A scalable and cost-effective synthetic polymer substrate that supports robust expansion and subsequent multilineage differentiation of human pluripotent stem cells (hPSCs) with defined commercial media is presented. This substrate can be applied to common cultureware and used off-the-shelf after long-term storage. Expansion and differentiation of hPSCs are performed entirely on the polymeric surface, enabling the clinical potential of hPSC-derived cells to be realized.

Connectivity and circuitry in a dish versus in a brain

In order to understand and find therapeutic strategies for neurological disorders, disease models that recapitulate the connectivity and circuitry of patients’ brain are needed. Owing to many limitations of animal disease models, in vitro neuronal models using patient-derived stem cells are currently being developed. However, prior to employing neurons as a model in a dish, they need to be evaluated for their electrophysiological properties, including both passive and active membrane properties, dynamics of neurotransmitter release, and capacity to undergo synaptic plasticity. In this review, we survey recent attempts to study these issues in human induced pluripotent stem cell-derived neurons. Although progress has been made, there are still many hurdles to overcome before human induced pluripotent stem cell-derived neurons can fully recapitulate all of the above physiological properties of adult mature neurons. Moreover, proper integration of neurons into pre-existing circuitry still needs to be achieved. Nevertheless, in vitro neuronal stem cell-derived models hold great promise for clinical application in neurological diseases in the future.

Neural Differentiation of Human Pluripotent Stem Cells for Nontherapeutic Applications: Toxicology, Pharmacology, and In Vitro Disease Modeling

Human pluripotent stem cells (hPSCs) derived from either blastocyst stage embryos (hESCs) or reprogrammed somatic cells (iPSCs) can provide an abundant source of human neuronal lineages that were previously sourced from human cadavers, abortuses, and discarded surgical waste. In addition to the well-known potential therapeutic application of these cells in regenerative medicine, these are also various promising nontherapeutic applications in toxicological and pharmacological screening of neuroactive compounds, as well as for in vitro modeling of neurodegenerative and neurodevelopmental disorders. Compared to alternative research models based on laboratory animals and immortalized cancer-derived human neural cell lines, neuronal cells differentiated from hPSCs possess the advantages of species specificity together with genetic and physiological normality, which could more closely recapitulate in vivo conditions within the human central nervous system. This review critically examines the various potential nontherapeutic applications of hPSC-derived neuronal lineages and gives a brief overview of differentiation protocols utilized to generate these cells from hESCs and iPSCs.

Induced pluripotent stem cells and their use in cardiac and neural regenerative medicine

Stem cells are unique pools of cells that are crucial for embryonic development and maintenance of adult tissue homeostasis. The landmark Nobel Prize winning research by Yamanaka and colleagues to induce pluripotency in somatic cells has reshaped the field of stem cell research. The complications related to the usage of pluripotent embryonic stem cells (ESCs) in human medicine, particularly ESC isolation and histoincompatibility were bypassed with induced pluripotent stem cell (iPSC) technology. The human iPSCs can be used for studying embryogenesis, disease modeling, drug testing and regenerative medicine. iPSCs can be diverted to different cell lineages using small molecules and growth factors. In this review we have focused on iPSC differentiation towards cardiac and neuronal lineages. Moreover, we deal with the use of iPSCs in regenerative medicine and modeling diseases like myocardial infarction, Timothy syndrome, dilated cardiomyopathy, Parkinson’s, Alzheimer’s and Huntington’s disease. Despite the promising potential of iPSCs, genome contamination and low efficacy of cell reprogramming remain significant challenges.

Deriving retinal pigment epithelium (RPE) from induced pluripotent stem (iPS) cells by different sizes of embryoid bodies

Pluripotent stem cells possess the ability to proliferate indefinitely and to differentiate into almost any cell type. Additionally, the development of techniques to reprogram somatic cells into induced pluripotent stem (iPS) cells has generated interest and excitement towards the possibility of customized personal regenerative medicine. However, the efficiency of stem cell differentiation towards a desired lineage remains low. The purpose of this study is to describe a protocol to derive retinal pigment epithelium (RPE) from iPS cells (iPS-RPE) by applying a tissue engineering approach to generate homogenous populations of embryoid bodies (EBs), a common intermediate during in vitro differentiation. The protocol applies the formation of specific size of EBs using microwell plate technology. The methods for identifying protein and gene markers of RPE by immunocytochemistry and reverse-transcription polymerase chain reaction (RT-PCR) are also explained. Finally, the efficiency of differentiation in different sizes of EBs monitored by fluorescence-activated cell sorting (FACS) analysis of RPE markers is described. These techniques will facilitate the differentiation of iPS cells into RPE for future applications.

Physical cues of cell culture materials lead the direction of differentiation lineages of pluripotent stem cells

Differentiation methods of hPSCs into specific cell lineages. Differentiation of hPSCsviaEB formation (types AB, A–D) or without EB formation (types E–H).

Striatal Transplantation of Human Dopaminergic Neurons Differentiated From Induced Pluripotent Stem Cells Derived From Umbilical Cord Blood Using Lentiviral Reprogramming

Human induced pluripotent stem cells (hiPSCs) are promising sources for regenerative therapies like the replacement of dopaminergic neurons in Parkinson's disease. They offer an unlimited cell source that can be standardized and optimized to produce applicable cell populations to gain maximal functional recovery. In the present study, human cord blood-derived iPSCs (hCBiPSCs) were differentiated into dopaminergic neurons utilizing two different in vitro protocols for neural induction: (protocol I) by fibroblast growth factor (FGF-2) signaling, (protocol II) by bone morphogenetic protein (BMP)/transforming growth factor (TGF-β) inhibition. After maturation, in vitro increased numbers of tyrosine hydroxylase (TH)-positive neurons (7.4% of total cells) were observed by protocol II compared to 3.5% in protocol I. Furthermore, 3 weeks after transplantation in hemiparkinsonian rats in vivo, a reduced number of undifferentiated proliferating cells was achieved with protocol II. In contrast, proliferation still occurred in protocol I-derived grafts, resulting in tumor-like growth in two out of four animals 3 weeks after transplantation. Protocol II, however, did not increase the number of TH(+) cells in the striatal grafts of hemiparkinsonian rats. In conclusion, BMP/TGF-β inhibition was more effective than FGF-2 signaling with regard to dopaminergic induction of hCBiPSCs in vitro and prevented graft overgrowth in vivo.

Higher vulnerability and stress sensitivity of neuronal precursor cells carrying an alpha-synuclein gene triplication

Parkinson disease (PD) is a multi-factorial neurodegenerative disorder with loss of dopaminergic neurons in the substantia nigra and characteristic intracellular inclusions, called Lewy bodies. Genetic predisposition, such as point mutations and copy number variants of the SNCA gene locus can cause very similar PD-like neurodegeneration. The impact of altered α-synuclein protein expression on integrity and developmental potential of neuronal stem cells is largely unexplored, but may have wide ranging implications for PD manifestation and disease progression. Here, we investigated if induced pluripotent stem cell-derived neuronal precursor cells (NPCs) from a patient with Parkinson's disease carrying a genomic triplication of the SNCA gene (SNCA-Tri). Our goal was to determine if these cells these neuronal precursor cells already display pathological changes and impaired cellular function that would likely predispose them when differentiated to neurodegeneration. To achieve this aim, we assessed viability and cellular physiology in human SNCA-Tri NPCs both under normal and environmentally stressed conditions to model in vitro gene-environment interactions which may play a role in the initiation and progression of PD. Human SNCA-Tri NPCs displayed overall normal cellular and mitochondrial morphology, but showed substantial changes in growth, viability, cellular energy metabolism and stress resistance especially when challenged by starvation or toxicant challenge. Knockdown of α-synuclein in the SNCA-Tri NPCs by stably expressed short hairpin RNA (shRNA) resulted in reversal of the observed phenotypic changes. These data show for the first time that genetic alterations such as the SNCA gene triplication set the stage for decreased developmental fitness, accelerated aging, and increased neuronal cell loss. The observation of this "stem cell pathology" could have a great impact on both quality and quantity of neuronal networks and could provide a powerful new tool for development of neuroprotective strategies for PD.

Combining small molecules for cell reprogramming through an interatomic analysis

The knowledge available about the application and generation of induced pluripotent stem cells (iPSC) has grown since their discovery, and new techniques to enhance the reprogramming process have been described. Among the new approaches to induce iPSC that have gained great attention is the use of small molecules for reprogramming. The application of small molecules, unlike genetic manipulation, provides for control of the reprogramming process through the shifting of concentrations and the combination of different molecules. However, different researchers have reported the use of "reprogramming cocktails" with variable results and drug combinations. Thus, the proper combination of small molecules for successful and enhanced reprogramming is a matter for discussion. However, testing all potential drug combinations in different cell lineages is very costly and time-consuming. Therefore, in this article, we discuss the use of already employed molecules for iPSC generation, followed by the application of systems chemo-biology tools to create different data sets of protein-protein (PPI) and chemical-protein (CPI) interaction networks based on the knowledge of already used and new reprogramming cocktail combinations. We further analyzed the biological processes associated with PPI-CPI networks and provided new potential protein targets to be inhibited or expressed for stem cell reprogramming. In addition, we applied a new interference analysis to prospective targets that could negatively affect the classical pluripotency-associated factors (SOX2, NANOG, KLF4 and OCT4) and thus potentially improve reprogramming protocols.

Functional differentiation of midbrain neurons from human cord blood-derived induced pluripotent stem cells

Introduction

Human induced pluripotent stem cells (hiPSCs) offer great promise for regenerative therapies or in vitro modelling of neurodegenerative disorders like Parkinson’s disease. Currently, widely used cell sources for the generation of hiPSCs are somatic cells obtained from aged individuals. However, a critical issue concerning the potential clinical use of these iPSCs is mutations that accumulate over lifetime and are transferred onto iPSCs during reprogramming which may influence the functionality of cells differentiated from them. The aim of our study was to establish a differentiation strategy to efficiently generate neurons including dopaminergic cells from human cord blood-derived iPSCs (hCBiPSCs) as a juvenescent cell source and prove their functional maturation in vitro.

Methods

The differentiation of hCBiPSCs was initiated by inhibition of transforming growth factor-β and bone morphogenetic protein signaling using the small molecules dorsomorphin and SB 431542 before final maturation was carried out. hCBiPSCs and differentiated neurons were characterized by immunocytochemistry and quantitative real time-polymerase chain reaction. Since functional investigations of hCBiPSC-derived neurons are indispensable prior to clinical applications, we performed detailed analysis of essential ion channel properties using whole-cell patch-clamp recordings and calcium imaging.

Results

A Sox1 and Pax6 positive neuronal progenitor cell population was efficiently induced from hCBiPSCs using a newly established differentiation protocol. Neuronal progenitor cells could be further maturated into dopaminergic neurons expressing tyrosine hydroxylase, the dopamine transporter and engrailed 1. Differentiated hCBiPSCs exhibited voltage-gated ion currents, were able to fire action potentials and displayed synaptic activity indicating synapse formation. Application of the neurotransmitters GABA, glutamate and acetylcholine induced depolarizing calcium signal changes in neuronal cells providing evidence for the excitatory effects of these ligand-gated ion channels during maturation in vitro.

Conclusions

This study demonstrates for the first time that hCBiPSCs can be used as a juvenescent cell source to generate a large number of functional neurons including dopaminergic cells which may serve for the development of novel regenerative treatment strategies.

Effects of erythropoietin in murine-induced pluripotent cell-derived panneural progenitor cells

Induced cell fate changes by reprogramming of somatic cells offers an efficient strategy to generate autologous pluripotent stem (iPS) cells from any adult cell type. The potential of iPS cells to differentiate into various cell types is well established, however the efficiency to produce functional neurons from iPS cells remains modest. Here, we generated panneural progenitor cells (pNPCs) from mouse iPS cells and investigated the effect of the neurotrophic growth factor erythropoietin (EPO) on their survival, proliferation and neurodifferentiation. Under neural differentiation conditions, iPS-derived pNPCs gave rise to microtubule-associated protein-2 positive neuronlike cells (34% to 43%) and platelet-derived growth factor receptor positive oligodendrocytelike cells (21% to 25%) while less than 1% of the cells expressed the astrocytic marker glial fibrillary acidic protein. Neuronlike cells generated action potentials and developed active presynaptic terminals. The pNPCs expressed EPO receptor (EPOR) mRNA and displayed functional EPOR signaling. In proliferating cultures, EPO (0.1-3 U/mL) slightly improved pNPC survival but reduced cell proliferation and neurosphere formation in a concentration-dependent manner. In differentiating cultures EPO facilitated neurodifferentiation as assessed by the increased number of β-III-tubulin positive neurons. Our results show that EPO inhibits iPS pNPC self-renewal and promotes neurogenesis.

DNA-dependent protein kinase is a context dependent regulator of Lmx1a and midbrain specification

The identification of small molecules capable of directing pluripotent cell differentiation towards specific lineages is highly desirable to both reduce cost, and increase efficiency. Within neural progenitors, LIM homeobox transcription factor 1 alpha (Lmx1a) is required for proper development of roof plate and cortical hem structures of the forebrain, as well as the development of floor plate and midbrain dopaminergic neurons. In this study we generated homologous recombinant cell lines expressing either luciferase or β-lactamase under the control of the Lmx1a promoter, and used these cell lines to investigate kinase-mediated regulation of Lmx1a activity during neuronal differentiation. A screen of 143 small molecule tyrosine kinase inhibitors yielded 16 compounds that positively or negatively modulated Lmx1a activity. Inhibition of EGF, VEGF and DNA-dependent protein kinase (DNA-PK) signaling significantly upregulated Lmx1a activity whereas MEK inhibition strongly downregulated its activity. Quantitative FACS analysis revealed that the DNA-PK inhibitor significantly increased the number of Lmx1a+ progenitors while subsequent qPCR showed an upregulation of Notch effectors, the basic helix-loop-helix genes, Hes5 and Hey1. FACS further revealed that DNA-PK-mediated regulation of Lmx1a+ cells is dependent on the rapamycin-sensitive complex, mTORC1. Interestingly, this DNA-PK inhibitor effect was preserved in a co-culture differentiation protocol. Terminal differentiation assays showed that DNA-PK inhibition shifted development of neurons from forebrain toward midbrain character as assessed by Pitx3/TH immunolabeling and corresponding upregulation of midbrain (En1), but not forebrain (FoxG1) transcripts. These studies show that Lmx1a signaling in mouse embryonic stem cells contributes to a molecular cascade establishing neuronal specification. The data presented here identifies a novel regulatory pathway where signaling from DNA-PK appears to suppress midbrain-specific Lmx1a expression.

LRRK2 mutations cause mitochondrial DNA damage in iPSC-derived neural cells from Parkinson's disease patients: reversal by gene correction

Parkinson's disease associated mutations in leucine rich repeat kinase 2 (LRRK2) impair mitochondrial function and increase the vulnerability of induced pluripotent stem cell (iPSC)-derived neural cells from patients to oxidative stress. Since mitochondrial DNA (mtDNA) damage can compromise mitochondrial function, we examined whether LRRK2 mutations can induce damage to the mitochondrial genome. We found greater levels of mtDNA damage in iPSC-derived neural cells from patients carrying homozygous or heterozygous LRRK2 G2019S mutations, or at-risk individuals carrying the heterozygous LRRK2 R1441C mutation, than in cells from unrelated healthy subjects who do not carry LRRK2 mutations. After zinc finger nuclease-mediated repair of the LRRK2 G2019S mutation in iPSCs, mtDNA damage was no longer detected in differentiated neuroprogenitor and neural cells. Our results unambiguously link LRRK2 mutations to mtDNA damage and validate a new cellular phenotype that can be used for examining pathogenic mechanisms and screening therapeutic strategies.

The effects of hedgehog on RNA binding protein Msi1 during the osteogenic differentiation of human cord blood-derived mesenchymal stem cells

Human umbilical cord blood (UCB)-derived mesenchymal stem cells (MSCs) are useful tools for regenerative medicine due to their capacity for self-renewal and multi-lineage differentiation. The appropriate clinical application of MSCs for regenerative medicine requires an integrated understanding of multiple signaling pathways that regulate cell proliferation, stemness and differentiation. However, the potential molecular mechanisms mediating these functions are not completely understood. The effects of hedgehog (Hh) signaling on the osteogenic differentiation of MSCs are still controversial, and the underlying mechanisms are unclear. In the present study, we evaluated the direct effects of Hh signaling on the osteogenic differentiation of hUCB-MSCs and investigated potential downstream regulatory mechanisms responsible for Hh signaling. We observed that Hh signaling acts as a negative regulator of osteogenic differentiation through the suppression of RNA-binding Msi1, which in turn suppresses the expression of Wnt1 and the miR-148 family, especially miR-148b. Moreover, Hh and Msi1 are considered to be potential stemness markers of hUCB-MSCs due to their differentiation-dependent expression profiles. This study provides new insights into mechanisms regulating MSC differentiation and may have implications for a variety of therapeutic applications in the clinic.

BMP and TGF-β pathway mediators are critical upstream regulators of Wnt signaling during midbrain dopamine differentiation in human pluripotent stem cells

Although many laboratories currently use small molecule inhibitors of the BMP (Dorsomorphin/DM) and TGF-β (SB431542/SB) signaling pathways in protocols to generate midbrain dopamine (mDA) neurons from hES and hiPS cells, until now, these substances have not been thought to play a role in the mDA differentiation process. We report here that the transient inhibition of constitutive BMP (pSMADs 1, 5, 8) signaling, either alone or in combination with TGF-β inhibition (pSMADs 2, 3), is critically important in the upstream regulation of Wnt1-Lmx1a signaling in mDA progenitors. We postulate that the mechanism via which DM or DM/SB mediates these effects involves the up-regulation in SMAD-interacting protein 1 (SIP1), which results in greater repression of the Wnt antagonist, secreted frizzled related protein 1 (Sfrp1) in stem cells. Accordingly, knockdown of SIP1 reverses the inductive effects of DM/SB on mDA differentiation while Sfrp1 knockdown/inhibition mimics DM/SB. The rise in Wnt1-Lmx1a levels in SMAD-inhibited cultures is, however, accompanied by a reciprocal down-regulation in SHH-Foxa2 levels leading to the generation of few TH+ neurons that co-express Foxa2. If however, exogenous SHH/FGF8 is added along with SMAD inhibitors, equilibrium in these two important pathways is achieved such that authentic (Lmx1a+Foxa2+TH+) mDA neuron differentiation is promoted while alternate cell fates are suppressed in stem cell cultures. These data indicate that activators/inhibitors of BMP and TGF-β signaling play a critical upstream regulatory role in the mDA differentiation process in human pluripotent stem cells.