Functional integration of embryonic stem cell-derived neurons in vivo

Glutamatergic Neurons Differentiated from Embryonic Stem Cells: An Investigation of Differentiation and Associated Diseases

Neurons that have been derived from various types of stem cells have recently undergone significant study due to their potential for use in various aspects of biomedicine. In particular, glutamatergic neurons differentiated from embryonic stem cells (ESCs) potentially have many applications in both basic research and regenerative medicine. This review summarized the literatures published thus far and focused on two areas related to these applications. Firstly, these neurons can be used to investigate neuronal signal transduction during differentiation and this means that the genes/proteins/markers involved in this process can be identified. In this way, the dynamic spatial and temporal changes associated with neuronal morphology can be investigated relatively easily. Such an in vitro system can also be used to study how neurons during neurogenesis integrate into normal tissue. At the same time, the integration, regulation and functions of extracellular matrix secretion, various molecular interactions, various ion channels, the neuronal microenvironment, etc., can be easily traced. Secondly, the disease-related aspects of ESC-derived glutamatergic neurons can also be studied and then applied therapeutically. In the future, greater efforts are needed to explore how ESC-differentiated glutamatergic neurons can be used as a neuronal model for the study of Alzheimer’s disease (AD) mechanistically, to identify possible therapeutic strategies for treating AD, including tissue replacement, and to screen for drugs that can be used to treat AD patients. With all of the modern technology that is available, translational medicine should begin to benefit patients soon.

The 5-HT6 Receptors in the Ventrolateral Orbital Cortex Attenuate Allodynia in a Rodent Model of Neuropathic Pain

Mechanical allodynia, characterized by a painful sensation induced by innocuous stimuli, is thought to be caused by disruption in pain-related regions. Identification and reversal of this pathologic neuroadaptation are therefore beneficial for clinical treatment. Previous evidence suggests that 5-HT₆ receptors in the ventrolateral orbital cortex (VLO) are involved in neuropathic pain, but their function is poorly understood. The aim of the present study is to unveil the role of 5-HT₆ receptors in the VLO and the underlying mechanisms in pain modulation. Here, by using the spared nerve injury (SNI) pain model, first, we report that 5-HT₆ receptor protein decreased in the contralateral VLO compared with the ipsilateral VLO in rats with allodynia. Second, microinjection of the selective 5-HT₆ receptor agonists EMD-386088 and WAY-208466 into the contralateral VLO consistently and significantly depressed allodynia. Third, microinjection of the selective antagonist SB-258585 blocked the agonist-induced anti-allodynic effect, while the antagonist applied alone to the VLO had no effect. Furthermore, the anti-nociceptive effect of EMD-386088 on neuropathic pain was prevented by the adenylate cyclase (AC) inhibitor SQ-22536, and protein kinase A (PKA) inhibitor H89, suggesting that AC/PKA signaling might underlie the antinociception of agonists. Finally, the 5-HT₆ receptors were found to be colocalized with a glutamate transporter (EAAC1) by immunofluorescent staining, and the glutamate receptor antagonist kynurenic acid was found to completely block antinociception. These findings indicated that the antinociceptive effect of 5-HT₆ receptor agonists might occur via interaction with the glutamatergic system. Altogether, the agonists activated 5-HT₆ receptors present in the glutamatergic neurons in the VLO to facilitate the AC/PKA cascade, which subsequently might evoke glutamate release, thus depressing allodynia. These findings suggest a potential therapeutic role of 5-HT₆ receptor agonists in treating neuropathic pain.

Construction and reconstruction of brain circuits: normal and pathological axon guidance

Perception of our environment entirely depends on the close interaction between the central and peripheral nervous system. In order to communicate each other, both systems must develop in parallel and in coordination. During development, axonal projections from the CNS as well as the PNS must extend over large distances to reach their appropriate target cells. To do so, they read and follow a series of axon guidance molecules. Interestingly, while these molecules play critical roles in guiding developing axons, they have also been shown to be critical in other major neurodevelopmental processes, such as the migration of cortical progenitors. Currently, a major hurdle for brain repair after injury or neurodegeneration is the absence of axonal regeneration in the mammalian CNS. By contrasts, PNS axons can regenerate. Many hypotheses have been put forward to explain this paradox but recent studies suggest that hacking neurodevelopmental mechanisms may be the key to promote CNS regeneration. Here we provide a seminar report written by trainees attending the second Flagship school held in Alpbach, Austria in September 2018 organized by the International Society for Neurochemistry (ISN) together with the Journal of Neurochemistry (JCN). This advanced school has brought together leaders in the fields of neurodevelopment and regeneration in order to discuss major keystones and future challenges in these respective fields.

Human Pluripotent Stem-Cell-Derived Cortical Neurons Integrate Functionally into the Lesioned Adult Murine Visual Cortex in an Area-Specific Way

The transplantation of pluripotent stem-cell-derived neurons constitutes a promising avenue for the treatment of several brain diseases. However, their potential for the repair of the cerebral cortex remains unclear, given its complexity and neuronal diversity. Here, we show that human visual cortical cells differentiated from embryonic stem cells can be transplanted and can integrate successfully into the lesioned mouse adult visual cortex. The transplanted human neurons expressed the appropriate repertoire of markers of six cortical layers, projected axons to specific visual cortical targets, and were synaptically active within the adult brain. Moreover, transplant maturation and integration were much less efficient following transplantation into the lesioned motor cortex, as previously observed for transplanted mouse cortical neurons. These data constitute an important milestone for the potential use of human PSC-derived cortical cells for the reassembly of cortical circuits and emphasize the importance of cortical areal identity for successful transplantation.

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Human PSC-derived cortical neurons efficiently integrate into the adult mouse brain

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PSC-derived human neurons reestablish axonal pathways in the lesioned adult cortex

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Restoration of cortical pathways requires a donor and recipient area-identity match

[Formation of gap junctions between adipose stem cells-derived Schwann cells in a rat model of dyskinesia induced by brain injury]

OBJECTIVE

To investigate the formation of gap junctions between Schwann cells derived from differentiated adipose stem cells implanted in a rat model of dyskinesia induced by brain injury and its positive effect in promoting functional recovery of the rats.

METHODS

In a rat model of hemiplegia induced by motor cortex injury, adipose stem cells or Schwann cells differentiated from adipose stem cells, either with or without RNAi-mediated silencing of Cx43, were transplanted orthotopically in the lesion. The recovery of the motor function of the rats was observed and scored after the transplantation. Rat brain tissues were sampled to detect the expressions of nerve growth factor (NGF) using Western blotting and RT-PCR.

RESULTS

All the 3 cell transplantation therapies obviously improved the motor function scores of the rats as compared with the control rats. The expression of NGF in the brain tissue was significantly lower in the control group than in the cell transplantation groups. NGF expression in the brain tissues of rats receiving transplantation of Schwann cells with Cx43 gene silencing was lower than that in rats receiving Schwann cells without Cx43 silencing, and was similar with that in rats transplanted with adipose stem cells. The results of RT-PCR showed that NGF mRNA level in the control group was significantly lower than that in the other 3 groups. NGF mRNA expression was the highest in Schwann cell group without Cx43 silencing, followed by adipose stem cell group, and then by Schwann cell group with Cx43 silencing.

CONCLUSIONS

In the rat model of dyskinesia induced by brain injury, transplantations of adipose stem cells and adipose stem cells-derived Schwann cells both promote the functional recovery of brain damage, in which gap junction protein Cx43 plays an important role to promote functional gap junction formation possibly by enhancing NGF expression.

The potential and limitations of induced pluripotent stem cells to achieve wound healing

Wound healing is the physiologic response to a disruption in normal skin architecture and requires both spatial and temporal coordination of multiple cell types and cytokines. This complex process is prone to dysregulation secondary to local and systemic factors such as ischemia and diabetes that frequently lead to chronic wounds. Chronic wounds such as diabetic foot ulcers are epidemic with great cost to the healthcare system as they heal poorly and recur frequently, creating an urgent need for new and advanced therapies. Stem cell therapy is emerging as a potential treatment for chronic wounds, and adult-derived stem cells are currently employed in several commercially available products; however, stem cell therapy is limited by the need for invasive harvesting techniques, immunogenicity, and limited cell survival in vivo. Induced pluripotent stem cells (iPSC) are an exciting cell type with enhanced therapeutic and translational potential. iPSC are derived from adult cells by in vitro induction of pluripotency, obviating the ethical dilemmas surrounding the use of embryonic stem cells; they are harvested non-invasively and can be transplanted autologously, reducing immune rejection; and iPSC are the only cell type capable of being differentiated into all of the cell types in healthy skin. This review focuses on the use of iPSC in animal models of wound healing including limb ischemia, as well as their limitations and methods aimed at improving iPSC safety profile in an effort to hasten translation to human studies.

Bioengineering Human Neurological Constructs Using Decellularized Meningeal Scaffolds for Application in Spinal Cord Injury

Spinal cord injury (SCI) is one of the most devastating conditions echoes with inflammation, enhanced fibrosis and larger axonal gaps due to destruction of neurological cells which has caused continuous increasing mortality rate of SCI patients due to absence of suitable treatment modalities. The restoration of structural and functional aspect of damaged neurological tissues at the lesion site in spinal cord has been challenging. Recent developments have showed tremendous potential of neural stem cell-based strategies to form a neuronal relay circuit across the injury gap which facilitates some levels of improvement in SCI condition. However, to provide better therapeutic responses, critical mass of grafted cells must survive for long-term and differentiate into neuronal cells with well-developed axonal networks. Hence, development of tissue specific biological neuronal constructs is highly desirable to provide mechanical and biological support for long-term survival and function of neurological cells within natural biological niche. In this study, we report development of a tissue specific neuronal constructs by culturing human neural precursor cells on decellularized meningeal scaffolds to provide suitable biological neuronal construct which can be used to support mechanical, structural and functional aspect of damaged spinal cord tissues. This particular tissue specific biological construct is immunologically tolerable and provides precisely orchestral three-dimensional platform to choreograph the long-distance axonal guidance and more organized neuronal cell growth. It passes sufficient mechanical and biological properties enriched with several crucial neurotrophins required for long-term survival and function of neurological cells which is required to form proper axonal bridge to regenerate the damaged axonal connectomes at lesion-site in SCI.

7.0 tesla high resolution MRI study on intracerebral migration of magnet-labeled neural stem cells in a mouse model of Alzheimer's disease

OBJECTIVE

To observe the migration characteristics of neural stem cells (NSCs) labeled with the MRI contrast agent superparamagnetic iron oxide (SPIO) in the brain of APP/PS1 transgenic mice with Alzheimer's disease (AD) by 7.0 T high resolution MRI.

METHODS

C57BL/6 mouse NSCs were cultured, amplified, labeled with Feridex and Poly-l-lysine (FE-PLL) and evaluated by transmission electron microscopy (TEM). Using the random number table method, 24 APP/PS1 transgenic AD mice aged 12 months were equally assigned to two groups: animals in group A were transplanted with FE-PLL labeled NSCs and those in group B were transplanted with non-labeled NSCs in the right hippocampus. Twelve wild-type mice of the same age and born from the same litter were used as the control group (group C) and transplanted with FE-PLL labeled NSCs. Using the 7.0 T high resolution MR scanner, the transplanted NSCs were traced in vivo at 1 day, 1 and 2 weeks after cell transplantation. The MRI findings were compared with the histopathological findings.

RESULTS

C57BL/6 mouse NSCs were cultured and amplified successfully. TEM showed large amounts of iron-containing particles in the cytoplasm of transplanted cells. MRI in group A showed the presence of spheroid low signals at the injection point of the hippocampus on T₂*WI one day after transplantation; one weeks later, the low signals were seen diffusing to the surroundings along the injection point, and covering almost the whole hippocampal area but the intensity of the low signals became weaker gradually; two weeks after transplantation, almost all low signals disappeared. In group B, no significant change in low signals was observed in the transplantation area at all designated time points. Although low signals were also observed in the hippocampus after transplantation of FE-PLL labeled NSCs in group C, their size and location remained almost unchanged. Prussian blue staining showed that migration of the FE-PLL labeled NSCs in the hippocampus of the AD mice was consistent with the MRI findings at all designated time points.

CONCLUSION

NSCs underwent diffuse and non-directional migration to the surroundings after they were transplanted to the hippocampus of APP/PS1 transgenic AD mice, and this migration pattern could be traced in vivo by MRI when they were labeled with magnet.

Atorvastatin Inhibits the HIF1α-PPAR Axis, Which Is Essential for Maintaining the Function of Human Induced Pluripotent Stem Cells

We herein report a novel mechanism of action of statin preparations using a new drug discovery method. Milk fat globule-EGF factor 8 protein (MFG-E8) was identified from the secretory component of mouse embryonic fibroblast (MEF) as a cell adhesion-promoting factor effective for screening active cellular agents of human induced pluripotent stem cells (hiPSCs) in vitro using electrochemical impedance. Our analyses showed that atorvastatin did not cause death in myocardial cells differentiated from hiPSCs but reduced the pluripotent cell survival in vitro when using serum- and albumin-free media, and inhibited the ability to form teratomas in mice. This result could have been already the cytopathic effect of atorvastatin, and complete elimination of hiPSCs was confirmed in the xenotransplantation assay. The administration of atorvastatin to hiPSCs caused the expression of hypoxia inducible factor (HIF)1α mRNA to be unchanged at 6 hr and downregulated at 24 hr. In addition, the inhibition of the survival of hiPSCs was confirmed by HIF1α-peroxisome proliferator-activated receptor (PPAR) axis inhibition. These results suggest that the addition of atorvastatin to hiPSC cultures reduces the survival of pluripotent cells by suppressing the HIF1α-PPAR axis. In summary, the HIF1α-PPAR axis has an important role in maintaining the survival of pluripotent hiPSCs.

Neuronal replacement therapy: previous achievements and challenges ahead

Lifelong neurogenesis and incorporation of newborn neurons into mature neuronal circuits operates in specialized niches of the mammalian brain and serves as role model for neuronal replacement strategies. However, to which extent can the remaining brain parenchyma, which never incorporates new neurons during the adulthood, be as plastic and readily accommodate neurons in networks that suffered neuronal loss due to injury or neurological disease? Which microenvironment is permissive for neuronal replacement and synaptic integration and which cells perform best? Can lost function be restored and how adequate is the participation in the pre-existing circuitry? Could aberrant connections cause malfunction especially in networks dominated by excitatory neurons, such as the cerebral cortex? These questions show how important connectivity and circuitry aspects are for regenerative medicine, which is the focus of this review. We will discuss the impressive advances in neuronal replacement strategies and success from exogenous as well as endogenous cell sources. Both have seen key novel technologies, like the groundbreaking discovery of induced pluripotent stem cells and direct neuronal reprogramming, offering alternatives to the transplantation of fetal neurons, and both herald great expectations. For these to become reality, neuronal circuitry analysis is key now. As our understanding of neuronal circuits increases, neuronal replacement therapy should fulfill those prerequisites in network structure and function, in brain-wide input and output. Now is the time to incorporate neural circuitry research into regenerative medicine if we ever want to truly repair brain injury.

Stem cell transplantation therapy for multifaceted therapeutic benefits after stroke

One of the exciting advances in modern medicine and life science is cell-based neurovascular regeneration of damaged brain tissues and repair of neuronal structures. The progress in stem cell biology and creation of adult induced pluripotent stem (iPS) cells has significantly improved basic and pre-clinical research in disease mechanisms and generated enthusiasm for potential applications in the treatment of central nervous system (CNS) diseases including stroke. Endogenous neural stem cells and cultured stem cells are capable of self-renewal and give rise to virtually all types of cells essential for the makeup of neuronal structures. Meanwhile, stem cells and neural progenitor cells are well-known for their potential for trophic support after transplantation into the ischemic brain. Thus, stem cell-based therapies provide an attractive future for protecting and repairing damaged brain tissues after injury and in various disease states. Moreover, basic research on naïve and differentiated stem cells including iPS cells has markedly improved our understanding of cellular and molecular mechanisms of neurological disorders, and provides a platform for the discovery of novel drug targets. The latest advances indicate that combinatorial approaches using cell based therapy with additional treatments such as protective reagents, preconditioning strategies and rehabilitation therapy can significantly improve therapeutic benefits. In this review, we will discuss the characteristics of cell therapy in different ischemic models and the application of stem cells and progenitor cells as regenerative medicine for the treatment of stroke.

Prolonged human neural stem cell maturation supports recovery in injured rodent CNS

Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.

Anatomically Inspired Three-dimensional Micro-tissue Engineered Neural Networks for Nervous System Reconstruction, Modulation, and Modeling

Functional recovery rarely occurs following injury or disease-induced degeneration within the central nervous system (CNS) due to the inhibitory environment and the limited capacity for neurogenesis. We are developing a strategy to simultaneously address neuronal and axonal pathway loss within the damaged CNS. This manuscript presents the fabrication protocol for micro-tissue engineered neural networks (micro-TENNs), implantable constructs consisting of neurons and aligned axonal tracts spanning the extracellular matrix (ECM) lumen of a preformed hydrogel cylinder hundreds of microns in diameter that may extend centimeters in length. Neuronal aggregates are delimited to the extremes of the three-dimensional encasement and are spanned by axonal projections. Micro-TENNs are uniquely poised as a strategy for CNS reconstruction, emulating aspects of brain connectome cytoarchitecture and potentially providing means for network replacement. The neuronal aggregates may synapse with host tissue to form new functional relays to restore and/or modulate missing or damaged circuitry. These constructs may also act as pro-regenerative "living scaffolds" capable of exploiting developmental mechanisms for cell migration and axonal pathfinding, providing synergistic structural and soluble cues based on the state of regeneration. Micro-TENNs are fabricated by pouring liquid hydrogel into a cylindrical mold containing a longitudinally centered needle. Once the hydrogel has gelled, the needle is removed, leaving a hollow micro-column. An ECM solution is added to the lumen to provide an environment suitable for neuronal adhesion and axonal outgrowth. Dissociated neurons are mechanically aggregated for precise seeding within one or both ends of the micro-column. This methodology reliably produces self-contained miniature constructs with long-projecting axonal tracts that may recapitulate features of brain neuroanatomy. Synaptic immunolabeling and genetically encoded calcium indicators suggest that micro-TENNs possess extensive synaptic distribution and intrinsic electrical activity. Consequently, micro-TENNs represent a promising strategy for targeted neurosurgical reconstruction of brain pathways and may also be applied as biofidelic models to study neurobiological phenomena in vitro.

A functional genomics screen in planarians reveals regulators of whole-brain regeneration

Planarians regenerate all body parts after injury, including the central nervous system (CNS). We capitalized on this distinctive trait and completed a gene expression-guided functional screen to identify factors that regulate diverse aspects of neural regeneration in Schmidtea mediterranea. Our screen revealed molecules that influence neural cell fates, support the formation of a major connective hub, and promote reestablishment of chemosensory behavior. We also identified genes that encode signaling molecules with roles in head regeneration, including some that are produced in a previously uncharacterized parenchymal population of cells. Finally, we explored genes downregulated during planarian regeneration and characterized, for the first time, glial cells in the planarian CNS that respond to injury by repressing several transcripts. Collectively, our studies revealed diverse molecules and cell types that underlie an animal’s ability to regenerate its brain.

DOI:http://dx.doi.org/10.7554/eLife.17002.001

Animals differ in the extent to which they can regenerate missing body parts after injury. Humans regenerate poorly after many injuries, especially when the brain becomes damaged after stroke, disease or trauma. On the other hand, planarians – small worms that live in fresh water – regenerate exceptionally well. A whole planarian can regenerate from small pieces of tissue.

The ability of planarians to regenerate their nervous system relies on stem cells called neoblasts, which can migrate through the body and divide to replace lost cells. However, the specific mechanisms responsible for regenerating nervous tissue are largely unknown. Roberts-Galbraith et al. carried out a screen to identify genes that tell planarians whether to regenerate a new brain, what cells to make and how to arrange them.

The study revealed over thirty genes that allow planarians to regenerate their brains after their heads have been amputated. These genes play several different roles in the animal. Some of the genes help neoblasts to make decisions about what kinds of cells they should become. One gene is needed to make an important connection in the planarian brain after injury. Another helps to restore the ability of the planarian to sense its food. The experiments also show that some key genes are switched on in a new cell type that might produce signals to support regeneration.

Lastly, Roberts-Galbraith et al. found that the planarian nervous system contains cells called glia. Previous studies have shown that many of the cells in the human brain are glia and that these cells help nerve cells to survive and work properly. The discovery of glia in planarians means that it will be possible to use these worms to study how glia support brain regeneration and how glia themselves are replaced after injury. In the long term, this work might lead to discoveries that shed light on how tissue regeneration could be improved in humans.

DOI:http://dx.doi.org/10.7554/eLife.17002.002

Neurons Differentiated from Transplanted Stem Cells Respond Functionally to Acoustic Stimuli in the Awake Monkey Brain

Here, we examine whether neurons differentiated from transplanted stem cells can integrate into the host neural network and function in awake animals, a goal of transplanted stem cell therapy in the brain. We have developed a technique in which a small "hole" is created in the inferior colliculus (IC) of rhesus monkeys, then stem cells are transplanted in situ to allow for investigation of their integration into the auditory neural network. We found that some transplanted cells differentiated into mature neurons and formed synaptic input/output connections with the host neurons. In addition, c-Fos expression increased significantly in the cells after acoustic stimulation, and multichannel recordings indicated IC specific tuning activities in response to auditory stimulation. These results suggest that the transplanted cells have the potential to functionally integrate into the host neural network.

Screening of natural compounds with neuronal differentiation promoting effects in a cell-based model

The purpose of this study was to establish a drug screening method for small molecules extracted from traditional Chinese medicines (TCM) that have neuronal differentiation promoting effects, using P19 embryonic carcinoma cell as a cell-based model. First, the constructed plasmid (pTα1-Luc) was transfected into P19 cells to establish a screening model. Second, several TCMs were screened using the established model and all-trans-retinoic acid as a positive control. Finally, the underlying molecular mechanism was explored using immunofluorescence staining, qT-PCR, and Western blot analysis. Our results indicated that the drug screen model was established successfully and that both honokiol and hyperoside induced P19 differentiation into neurons, with the possible molecular mechanism being modulating the Wnt signaling pathway. In conclusion, the drug screening model developed in the present study provides a rapid, cell-based screening platform for identifying natural compounds with neuronal differentiation effects.

Can manipulation of differentiation conditions eliminate proliferative cells from a population of ES cell-derived forebrain cells?

There is preliminary evidence that implantation of primary fetal striatal cells provides functional benefit in patients with Huntington's disease, a neurodegenerative condition resulting in loss of medium-sized spiny neurons (MSN) of the striatum. Scarcity of primary fetal tissue means it is important to identify a renewable source of cells from which to derive donor MSNs. Embryonic stem (ES) cells, which predominantly default to telencephalic-like precursors in chemically defined medium (CDM), offer a potentially inexhaustible supply of cells capable of generating the desired neurons. Using an ES cell line, with the forebrain marker FoxG1 tagged to the LacZ reporter, we assessed effects of known developmental factors on the yield of forebrain-like precursor cells in CDM suspension culture. Addition of FGF2, but not DKK1, increased the proportion of FoxG1-expressing cells at day 8 of neural induction. Oct4 was expressed at day 8, but was undetectable by day 16. Differentiation of day 16 precursors generated GABA-expressing neurons, with few DARPP32 positive MSNs. Transplantation of day 8 precursor cells into quinolinic acid-lesioned striata resulted in generation of teratomas. However, transplantation of day 16 precursors yielded grafts expressing neuronal markers including NeuN, calbindin and parvalbumin, but no DARPP32 6 weeks post-transplantation. Manipulation of fate of ES cells requires optimization of both concentration and timing of addition of factors to culture systems to generate the desired phenotypes. Furthermore, we highlight the value of increasing the precursor phase of ES cell suspension culture when directing differentiation toward forebrain fate, so as to dramatically reduce the risk of teratoma formation.

Functional properties of in vitro excitatory cortical neurons derived from human pluripotent stem cells

The in vitro derivation of regionally defined human neuron types from patient‐derived stem cells is now established as a resource to investigate human development and disease. Characterization of such neurons initially focused on the expression of developmentally regulated transcription factors and neural markers, in conjunction with the development of protocols to direct and chart the fate of differentiated neurons. However, crucial to the understanding and exploitation of this technology is to determine the degree to which neurons recapitulate the key functional features exhibited by their native counterparts, essential for determining their usefulness in modelling human physiology and disease in vitro. Here, we review the emerging data concerning functional properties of human pluripotent stem cell‐derived excitatory cortical neurons, in the context of both maturation and regional specificity.

Optogenetic Stimulation of Neural Grafts Enhances Neurotransmission and Downregulates the Inflammatory Response in Experimental Stroke Model

Compelling evidence suggests that transplantation of neural stem cells (NSCs) from multiple sources ameliorates motor deficits after stroke. However, it is currently unknown to what extent the electrophysiological activity of grafted NSC progeny participates in the improvement of motor deficits and whether excitatory phenotypes of the grafted cells are beneficial or deleterious to sensorimotor performances. To address this question, we used optogenetic tools to drive the excitatory outputs of the grafted NSCs and assess the impact on local circuitry and sensorimotor performance. We genetically engineered NSCs to express the Channelrhodopsin-2 (ChR2), a light-gated cation channel that evokes neuronal depolarization and initiation of action potentials with precise temporal control to light stimulation. To test the function of these cells in a stroke model, rats were subjected to an ischemic stroke and grafted with ChR2-NSCs. The grafted NSCs identified with a human-specific nuclear marker survived in the peri-infarct tissue and coexpressed the ChR2 transgene with the neuronal markers TuJ1 and NeuN. Gene expression analysis in stimulated versus vehicle-treated animals showed a differential upregulation of transcripts involved in neurotransmission, neuronal differentiation, regeneration, axonal guidance, and synaptic plasticity. Interestingly, genes involved in the inflammatory response were significantly downregulated. Behavioral analysis demonstrated that chronic optogenetic stimulation of the ChR2-NSCs enhanced forelimb use on the stroke-affected side and motor activity in an open field test. Together these data suggest that excitatory stimulation of grafted NSCs elicits beneficial effects in experimental stroke model through cell replacement and non-cell replacement, anti-inflammatory/neurotrophic effects.

Restoring nervous system structure and function using tissue engineered living scaffolds

Neural tissue engineering is premised on the integration of engineered living tissue with the host nervous system to directly restore lost function or to augment regenerative capacity following nervous system injury or neurodegenerative disease. Disconnection of axon pathways – the long-distance fibers connecting specialized regions of the central nervous system or relaying peripheral signals – is a common feature of many neurological disorders and injury. However, functional axonal regeneration rarely occurs due to extreme distances to targets, absence of directed guidance, and the presence of inhibitory factors in the central nervous system, resulting in devastating effects on cognitive and sensorimotor function. To address this need, we are pursuing multiple strategies using tissue engineered “living scaffolds”, which are preformed three-dimensional constructs consisting of living neural cells in a defined, often anisotropic architecture. Living scaffolds are designed to restore function by serving as a living labeled pathway for targeted axonal regeneration – mimicking key developmental mechanisms– or by restoring lost neural circuitry via direct replacement of neurons and axonal tracts. We are currently utilizing preformed living scaffolds consisting of neuronal clusters spanned by long axonal tracts as regenerative bridges to facilitate long-distance axonal regeneration and for targeted neurosurgical reconstruction of local circuits in the brain. Although there are formidable challenges in preclinical and clinical advancement, these living tissue engineered constructs represent a promising strategy to facilitate nervous system repair and functional recovery.

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.

Functional integration of human neural precursor cells in mouse cortex

This study investigates the electrophysiological properties and functional integration of different phenotypes of transplanted human neural precursor cells (hNPCs) in immunodeficient NSG mice. Postnatal day 2 mice received unilateral injections of 100,000 GFP+ hNPCs into the right parietal cortex. Eight weeks after transplantation, 1.21% of transplanted hNPCs survived. In these hNPCs, parvalbumin (PV)-, calretinin (CR)-, somatostatin (SS)-positive inhibitory interneurons and excitatory pyramidal neurons were confirmed electrophysiologically and histologically. All GFP+ hNPCs were immunoreactive with anti-human specific nuclear protein. The proportions of PV-, CR-, and SS-positive cells among GFP+ cells were 35.5%, 15.7%, and 17.1%, respectively; around 15% of GFP+ cells were identified as pyramidal neurons. Those electrophysiologically and histological identified GFP+ hNPCs were shown to fire action potentials with the appropriate firing patterns for different classes of neurons and to display spontaneous excitatory and inhibitory postsynaptic currents (sEPSCs and sIPSCs). The amplitude, frequency and kinetic properties of sEPSCs and sIPSCs in different types of hNPCs were comparable to host cells of the same type. In conclusion, GFP+ hNPCs produce neurons that are competent to integrate functionally into host neocortical neuronal networks. This provides promising data on the potential for hNPCs to serve as therapeutic agents in neurological diseases with abnormal neuronal circuitry such as epilepsy.

Effects of context-drug learning on synaptic connectivity in the basolateral nucleus of the amygdala in rats

Context-drug learning produces structural and functional synaptic changes in the circuitry of the basolateral nucleus of the amygdala (BLA). However, how the synaptic changes translated to the neuronal targets was not established. Thus, in the present study, immunohistochemistry with a cell-specific marker and the stereological quantification of synapses was used to determine if context-drug learning increases the number of excitatory and inhibitory/modulatory synapses contacting the gamma-aminobutyric acid (GABA) interneurons and/or the pyramidal neurons in the BLA circuitry. Amphetamine-conditioned place preference increased the number of asymmetric (excitatory) synapses contacting the spines and dendrites of pyramidal neurons and the number of multisynaptic boutons contacting pyramidal neurons and GABA interneurons. Context-drug learning increased asymmetric (excitatory) synapses onto dendrites of GABA interneurons and increased symmetric (inhibitory or modulatory) synapses onto dendrites but not perikarya of these same interneurons. The formation of context-drug associations alters the synaptic connectivity in the BLA circuitry, findings that have important implications for drug-seeking behavior.

Stem cell imaging: from bench to bedside

Although cellular therapies hold great promise for the treatment of human disease, results from several initial clinical trials have not shown a level of efficacy required for their use as a first line therapy. Here we discuss how in vivo molecular imaging has helped identify barriers to clinical translation and potential strategies that may contribute to successful transplantation and improved outcomes, with a focus on cardiovascular and neurological diseases. We conclude with a perspective on the future role of molecular imaging in defining safety and efficacy for clinical implementation of stem cell therapies.

In vivo imaging of transplanted stem cells in the central nervous system

In vivo imaging is increasingly being utilized in studies investigating stem cell-based treatments for neurological disorders. Direct labeling is used in preclinical and clinical studies to track the fate of transplanted cells. To further determine cell viability, experimental studies are able to take advantage of reporter gene technologies. Structural and functional brain imaging can also be used alongside cell imaging as biomarkers of treatment efficacy. Furthermore, it is possible that new imaging techniques could be used to monitor functional integration of stem cell-derived cells with the host nervous system. In this review, we examine recent developments in these areas and identify promising directions for future research at the interface of stem cell therapies and neuroimaging.

Understanding positional cues in salamander limb regeneration: implications for optimizing cell-based regenerative therapies

Regenerative medicine has reached the point where we are performing clinical trials with stem-cell-derived cell populations in an effort to treat numerous human pathologies. However, many of these efforts have been challenged by the inability of the engrafted populations to properly integrate into the host environment to make a functional biological unit. It is apparent that we must understand the basic biology of tissue integration in order to apply these principles to the development of regenerative therapies in humans. Studying tissue integration in model organisms, where the process of integration between the newly regenerated tissues and the ‘old’ existing structures can be observed and manipulated, can provide valuable insights. Embryonic and adult cells have a memory of their original position, and this positional information can modify surrounding tissues and drive the formation of new structures. In this Review, we discuss the positional interactions that control the ability of grafted cells to integrate into existing tissues during the process of salamander limb regeneration, and discuss how these insights could explain the integration defects observed in current cell-based regenerative therapies. Additionally, we describe potential molecular tools that can be used to manipulate the positional information in grafted cell populations, and to promote the communication of positional cues in the host environment to facilitate the integration of engrafted cells. Lastly, we explain how studying positional information in current cell-based therapies and in regenerating limbs could provide key insights to improve the integration of cell-based regenerative therapies in the future.

Slice Culture Method for Studying Migration of Neuronal Progenitor Cells Derived from Human Embryonic Stem Cells (hESC)

In this unit we describe an overlay brain slice culture assay for studying migration of transgenic neurospheres derived from human embryonic stem cells (hESC). Neuronal progenitor cells were generated from hESC by derivation of embryoid bodies and rosettes. Rosettes were transfected using the PiggyBac transposon system with either control plasmids (GFP) or plasmid encoding a gene important for migration of neuronal progenitor cells, Doublecortin (DCX). Transfected cells were subsequently grown in low-adhesion plates to generate transgenic human neurospheres (t-hNS). Organotypic slice cultures were prepared from postnatal rat forebrain and maintained using the interface method, before transfected t-hNS were overlaid below the cortex of each hemisphere. After 1 to 5 days, forebrain slices were fixed and processed for immunofluorescence. The distance at which cells migrated from the center of neurospheres to the host forebrain tissue was measured using Image J software. This protocol provides details for using the slice culture method for studying migration and integration of human neuronal cells into the host brain tissue.

Regenerative medicine in Alzheimer's disease

Identifying novel, effective therapeutics for Alzheimer's disease (AD) is one of the major unmet medical needs for the coming decade. Because the current paradigm for developing and testing disease-modifying AD therapies is protracted and likely to be even longer, with the shift toward earlier intervention in preclinical AD, it is an open issue whether we can develop, test, and widely deploy a novel therapy in time to help the current at-risk generation if we continue to follow the standard paradigms of discovery and drug development. There is an imperative need to find safe and effective preventive measures that can be distributed rapidly to stem the coming wave of AD that will potentially engulf the next generation. We can define regenerative medicine broadly as approaches that use stem cell-based therapies or approaches that seek to modulate inherent neurogenesis. Neurogenesis, although most active during prenatal development, has been shown to continue in several small parts of the brain, including the hippocampus and the subventricular zone, suggesting its potential to reverse cognitive deficits. If AD pathology affects neurogenesis, then it follows that conditions that stimulate endogenous neurogenesis (eg, environmental stimuli, physical activity, trophic factors, cytokines, and drugs) may help to promote the regenerative and recovery process. Herein, we review the complex logistics of potentially implementing neurogenesis-based therapeutic strategies for the treatment of AD.

Novel and robust transplantation reveals the acquisition of polarized processes by cortical cells derived from mouse and human pluripotent stem cells

Current stem cell technologies have enabled the induction of cortical progenitors and neurons from embryonic stem cells (ESCs) and induced pluripotent stem cells in vitro. To understand the mechanisms underlying the acquisition of apico-basal polarity and the formation of processes associated with the stemness of cortical cells generated in monolayer culture, here, we developed a novel in utero transplantation system based on the moderate dissociation of adherens junctions in neuroepithelial tissue. This method enables (1) the incorporation of remarkably higher numbers of grafted cells and (2) quantitative morphological analyses at single-cell resolution, including time-lapse recording analyses. We then grafted cortical progenitors induced from mouse ESCs into the developing brain. Importantly, we revealed that the mode of process extension depends on the extrinsic apico-basal polarity of the host epithelial tissue, as well as on the intrinsic differentiation state of the grafted cells. Further, we successfully transplanted cortical progenitors induced from human ESCs, showing that our strategy enables investigation of the neurogenesis of human neural progenitors within the developing mouse cortex. Specifically, human cortical cells exhibit multiple features of radial migration. The robust transplantation method established here could be utilized both to uncover the missing gap between neurogenesis from ESCs and the tissue environment and as an in vivo model of normal and pathological human corticogenesis.

Analysis of the antiepileptic, ethosuximide impacts on neurogenesis of rat forebrain stem cells

Specific GABAergic interneurons in the hilus are lost in animal models with temporal-lobe epilepsy (TLE). Some preclinical evidence has indicated that GABAergic cells may provide relief from seizures in these models. This study was aimed to examine the ability of ethosuximide, an anticonvulsant drug, to promote neurogenesis in 3-day-old rat forebrain cortex stem cells. Most of the cells were found to be nestin-positive undifferentiated neural stem cells prior to their exposure to ethosuximide. It was noted that the number and percentage of tubulin β-III immunopositive neurons were increased after 6 days treatment with ethosuximide. Upon bFGF withdrawal, exposure to ethosuximide differentiated the stem cells to MAP2 positive neural cells (7.18 ± 0.43, 21.766 ± 0.55 and 41.57 ± 0.5 for control, 0.1 and 1 μM, respectively). GABA immunofluorescence images illustrated that ethosuximide increased GABAergic neurons (7.19 ± 0.32, 23.23 ± 0.55, and 46.30 ± 0.44 for control, 0.1 and 1 μM, respectively). Additionally, BrdU immunofluorescence assay showed that ethosuximide-enhanced nucleus proliferation in the neuronal stem cells. Therefore, the results of this study suggest that ethosuximide may compensate damage caused by seizure attacks and possibly other neuronal loss disorders.

Electrophysiological investigations of synaptic connectivity between host and graft neurons

The functional synaptic integration of grafted stem cell-derived neurons is one of the key aspects of neural cell replacement therapies for neurological disorders such as Parkinson's disease. However, little is currently known about the synaptic connectivity between graft and host cells after transplantation, not only in the settings of clinical trials but also in experimental studies. This knowledge gap is primarily due to the lack of experimental electrophysiological approaches allowing interrogation of synaptic connectivity between prospectively identified host and graft neurons and hampers our understanding of the mechanisms underlying functional integration of stem cell-derived neurons in the host brain, as well as the optimization of protocols for deriving stem cells for neural cell replacement therapy. Recent optogenetic tools allow for direct investigation of connectivity between host and graft neural populations and have already been applied to show bidirectional integration of dopaminergic neurons in a host tissue. These new tools have potential to advance our understanding of functional integration in the near future. Here, we provide an overview of the current literature addressing functional integration of stem cell-derived neurons in the settings of Parkinson's disease models and discuss some experimental paradigms to approach this issue.

Perspectives for computational modeling of cell replacement for neurological disorders

Mathematical modeling of anatomically-constrained neural networks has provided significant insights regarding the response of networks to neurological disorders or injury. A logical extension of these models is to incorporate treatment regimens to investigate network responses to intervention. The addition of nascent neurons from stem cell precursors into damaged or diseased tissue has been used as a successful therapeutic tool in recent decades. Interestingly, models have been developed to examine the incorporation of new neurons into intact adult structures, particularly the dentate granule neurons of the hippocampus. These studies suggest that the unique properties of maturing neurons, can impact circuit behavior in unanticipated ways. In this perspective, we review the current status of models used to examine damaged CNS structures with particular focus on cortical damage due to stroke. Secondly, we suggest that computational modeling of cell replacement therapies can be made feasible by implementing approaches taken by current models of adult neurogenesis. The development of these models is critical for generating hypotheses regarding transplant therapies and improving outcomes by tailoring transplants to desired effects.

Engraftment of nonintegrating neural stem cells differentially perturbs cortical activity in a dose-dependent manner

Neural stem cell (NSC) therapy represents a potentially powerful approach for gene transfer in the diseased central nervous system. However, transplanted primary, embryonic stem cell- and induced pluripotent stem cell-derived NSCs generate largely undifferentiated progeny. Understanding how physiologically immature cells influence host activity is critical to evaluating the therapeutic utility of NSCs. Earlier inquiries were limited to single-cell recordings and did not address the emergent properties of neuronal ensembles. To interrogate cortical networks post-transplant, we used voltage sensitive dye imaging in mouse neocortical brain slices, which permits high temporal resolution analysis of neural activity. Although moderate NSC engraftment largely preserved host physiology, subtle defects in the activation properties of synaptic inputs were induced. High-density engraftment severely dampened cortical excitability, markedly reducing the amplitude, spatial extent, and velocity of propagating synaptic potentials in layers 2-6. These global effects may be mediated by specific disruptions in excitatory network structure in deep layers. We propose that depletion of endogenous cells in engrafted neocortex contributes to circuit alterations. Our data provide the first evidence that nonintegrating cells cause differential host impairment as a function of engrafted load. Moreover, they emphasize the necessity for efficient differentiation methods and proper controls for engraftment effects that interfere with the benefits of NSC therapy.

Region-specific integration of embryonic stem cell-derived neuronal precursors into a pre-existing neuronal circuit

Enduring reorganization is accepted as a fundamental process of adult neural plasticity. The most dramatic example of this reorganization is the birth and continuously occurring incorporation of new neurons into the pre-existing network of the adult mammalian hippocampus. Based on this phenomenon we transplanted murine embryonic stem (ES)-cell derived neuronal precursors (ESNPs) into murine organotypic hippocampal slice cultures (OHC) and examined their integration. Using a precise quantitative morphological analysis combined with a detailed electrophysiology, we show a region-specific morphological integration of transplanted ESNPs into different subfields of the hippocampal tissue, resulting in pyramidal neuron-like embryonic stem cell-derived neurons (ESNs) in the Cornu Ammonis (CA1 and CA3) and granule neuron-like ESNs in the dentate gyrus (DG), respectively. Subregion specific structural maturation was accompanied by the development of dendritic spines and the generation of excitatory postsynaptic currents (EPSCs). This cell type specific development does not depend upon NMDA-receptor-dependent synaptic transmission. The presented integration approach was further used to determine the cell-autonomous function of the pan-neurotrophin receptor p75 (P75(NTR)), as a possible negative regulator of ESN integration. By this means we used p75(NTR)-deficient ESNPs to study their integration into a WT organotypic environment. We show here that p75(NTR) is not necessary for integration per se but plays a suppressing role in dendritic development.

In vivo bioluminescence reporter gene imaging for the activation of neuronal differentiation induced by the neuronal activator neurogenin 1 (Ngn1) in neuronal precursor cells

PURPOSE

Facilitation of the ability of neuronal lineages derived from transplanted stem cells to differentiate is essential to improve the low efficacy of neuronal differentiation in stem cell therapy in vivo. Neurogenin 1 (Ngn1), a basic helix-loop-helix factor, has been used as an activator of neuronal differentiation. In this study, we monitored the in vivo activation of neuronal differentiation by Ngn1 in neuronal precursor cells using neuron-specific promoter-based optical reporters.

METHODS

The NeuroD promoter coupled with the firefly luciferase reporter system (pNeuroD-Fluc) was used to monitor differentiation in F11 neuronal precursor cells. In vitro luciferase activity was measured and normalized by protein content. The in vivo-jetPEI(TM) system was used for in vivo transgene delivery. The IVIS 100 imaging system was used to monitor in vivo luciferase activity.

RESULTS

The Ngn1-induced neuronal differentiation of F11 cells generated neurite outgrowth within 2 days of Ngn1 induction. Immunofluorescence staining demonstrated that early and late neuronal marker expression (βIII-tubulin, NeuroD, MAP2, NF-M, and NeuN) was significantly increased at 3 days after treatment with Ngn1. When Ngn1 and the pNeuroD-Fluc vector were cotransfected into F11 cells, we observed an approximately 11-fold increase in the luciferase signal. An in vivo study showed that bioluminescence signals were gradually increased in Ngn1-treated F11 cells for up to 3 days.

CONCLUSION

In this study, we examined the in vivo tracking of neuronal differentiation induced by Ngn1 using an optical reporter system. This reporter system could be used effectively to monitor the activation efficiency of neuronal differentiation in grafted stem cells treated with Ngn1 for stem cell therapy.

Systematic Review of Induced Pluripotent Stem Cell Technology as a Potential Clinical Therapy for Spinal Cord Injury

Transplantation therapies aimed at repairing neurodegenerative and neuropathological conditions of the central nervous system (CNS) have utilized and tested a variety of cell candidates, each with its own unique set of advantages and disadvantages. The use and popularity of each cell type is guided by a number of factors including the nature of the experimental model, neuroprotection capacity, the ability to promote plasticity and guided axonal growth, and the cells' myelination capability. The promise of stem cells, with their reported ability to give rise to neuronal lineages to replace lost endogenous cells and myelin, integrate into host tissue, restore functional connectivity, and provide trophic support to enhance and direct intrinsic regenerative ability, has been seen as a most encouraging step forward. The advent of the induced pluripotent stem cell (iPSC), which represents the ability to “reprogram” somatic cells into a pluripotent state, hails the arrival of a new cell transplantation candidate for potential clinical application in therapies designed to promote repair and/or regeneration of the CNS. Since the initial development of iPSC technology, these cells have been extensively characterized in vitro and in a number of pathological conditions and were originally reported to be equivalent to embryonic stem cells (ESCs). This review highlights emerging evidence that suggests iPSCs are not necessarily indistinguishable from ESCs and may occupy a different “state” of pluripotency with differences in gene expression, methylation patterns, and genomic aberrations, which may reflect incomplete reprogramming and may therefore impact on the regenerative potential of these donor cells in therapies. It also highlights the limitations of current technologies used to generate these cells. Moreover, we provide a systematic review of the state of play with regard to the use of iPSCs in the treatment of neurodegenerative and neuropathological conditions. The importance of balancing the promise of this transplantation candidate in the light of these emerging properties is crucial as the potential application in the clinical setting approaches. The first of three sections in this review discusses (A) the pathophysiology of spinal cord injury (SCI) and how stem cell therapies can positively alter the pathology in experimental SCI. Part B summarizes (i) the available technologies to deliver transgenes to generate iPSCs and (ii) recent data comparing iPSCs to ESCs in terms of characteristics and molecular composition. Lastly, in (C) we evaluate iPSC-based therapies as a candidate to treat SCI on the basis of their neurite induction capability compared to embryonic stem cells and provide a summary of available in vivo data of iPSCs used in SCI and other disease models.

Increasing doublecortin expression promotes migration of human embryonic stem cell-derived neurons

Human embryonic stem cell-derived neuronal progenitors (hNPs) provide a potential source for cellular replacement following neurodegenerative diseases. One of the greatest challenges for future neuron replacement therapies will be to control extensive cell proliferation and stimulate cell migration of transplanted cells. The doublecortin (DCX) gene encodes the protein DCX, a microtubule-associated protein essential for the migration of neurons in the human brain. In this study, we tested whether increasing the expression of DCX in hNPs would favorably alter their proliferation and migration. Migration and proliferation of hNPs was compared between hNPs expressing a bicistronic DCX/IRES-GFP transgene and those expressing a green fluorescent protein (GFP) transgene introduced by piggyBac-mediated transposition. The DCX-transfected hNPs showed a significant decrease in their proliferation and migrated significantly further on two different substrates, Matrigel and brain slices. Additionally, a dense network of nestin-positive (+) and vimentin+ fibers were found to extend from neurospheres transplanted onto brain slices, and this fiber growth was increased from neurospheres containing DCX-transfected hNPs. In summary, our results show that increased DCX expression inhibits proliferation and promotes migration of hNPs.

High-frequency hippocampal oscillations activated by optogenetic stimulation of transplanted human ESC-derived neurons

After transplantation, individual stem cell-derived neurons can functionally integrate into the host CNS; however, evidence that neurons derived from transplanted human embryonic stem cells (hESCs) can drive endogenous neuronal network activity in CNS tissue is still lacking. Here, using multielectrode array recordings, we report activation of high-frequency oscillations in the β and γ ranges (10-100 Hz) in the host hippocampal network via targeted optogenetic stimulation of transplanted hESC-derived neurons.

Selective elimination of human pluripotent stem cells by an oleate synthesis inhibitor discovered in a high-throughput screen

The use of human pluripotent stem cells (hPSCs) in cell therapy is hindered by the tumorigenic risk from residual undifferentiated cells. Here we performed a high-throughput screen of over 52,000 small molecules and identified 15 pluripotent cell-specific inhibitors (PluriSIns), nine of which share a common structural moiety. The PluriSIns selectively eliminated hPSCs while sparing a large array of progenitor and differentiated cells. Cellular and molecular analyses demonstrated that the most selective compound, PluriSIn #1, induces ER stress, protein synthesis attenuation, and apoptosis in hPSCs. Close examination identified this molecule as an inhibitor of stearoyl-coA desaturase (SCD1), the key enzyme in oleic acid biosynthesis, revealing a unique role for lipid metabolism in hPSCs. PluriSIn #1 was also cytotoxic to mouse blastocysts, indicating that the dependence on oleate is inherent to the pluripotent state. Finally, application of PluriSIn #1 prevented teratoma formation from tumorigenic undifferentiated cells. These findings should increase the safety of hPSC-based treatments.

[Cell therapy for stroke: from myth to reality]

INTRODUCTION

Stroke is one of the leading causes of death and disability worldwide. Intravenous recombinant tissue plasminogen activator is the only available therapy for acute ischemic stroke, but its use is limited by a narrow therapeutic window and cannot stimulate endogenous repair and regeneration of damaged brain tissue. Stem cell-based approaches hold much promise as potential novel treatments to restore neurological function after stroke.

STATE OF THE ART

In this review, we summarize data from preclinical and clinical studies to investigate the potential application of stem cell therapies for treatment of stroke. Stem cells have been proposed as a potential source of new cells to replace those lost due to central nervous system injury, as well as a source of trophic molecules to minimize damage and promote recovery. Various stem cells from multiple sources can generate neural cells that survive and form synaptic connections after transplantation in the stroke-injured brain. Stem cells also exhibit neurorevitalizing properties that may ameliorate neurological deficits through stimulation of neurogenesis, angiogenesis and inhibition of inflammation.

PERSPECTIVES/CONCLUSION

Performed in stroke, cell therapy would decrease brain damage and reduce functional deficits. After the damage has been done, it would still improve neurological functions by activating endogenous repair. Nevertheless, many questions raised by experimental studies particularly related to long-term safety and technical details of cell preparation and administration must be resolved before wider clinical use.

Delivery of epidermal neural crest stem cells (EPI-NCSC) to hippocamp in Alzheimer's disease rat model

BACKGROUND

Alzheimer's disease (AD) is characterized by progressive neuronal loss in hippocamp. Epidermal neural crest stem cells (EPI-NCSC) can differentiate into neurons, astrocytes and oligodendrocytes. The purpose of this study was to evaluate the effects of transplanting EPI-NCSC into AD rat model.

METHODS

Two weeks after induction of AD by injection of Amyloid-β1-40 into CA1 area of rat hippocamp, Y-maze and single-trial passive avoidance tests were used to show deficit of learning and memory abilities. EPI-NCSC were obtained from the vibrissa hair follicle of rat, cultured and labeled with bromodeoxyuridine. When Alzheimer was proved by behavioral tests, EPI-NCSC was transplanted into CA3 area of hippocamp in AD rat model. The staining of EPI-NCSC markers (nestin and SOX10) was done in vitro. Double-labeling immunofluorescence was performed to study survival and differentiation of the grafted cells.

RESULTS

We showed that transplanted EPI-NCSC survive and produce many neurons and a few glial cells, presenting glial fibrillary acidic protein. Total number of granule cells in hippocamp was estimated to be more in the AD rat model with transplanted cells as compared to AD control group. We observed that rats with hippocampal damage made more errors than control rats on the Y-maze, when reward locations were reversed.

CONCLUSION

Transplanted cells were migrated to all areas of hippocamp and the total number of granule cell in treatment group was equal compared to control group. Transplantation of EPI-NCSC into hippocamp might differentiate into cholinergic neurons and could cure impairment of memory in AD rat model.

Teratocarcinoma Formation in Embryonic Stem Cell-Derived Neural Progenitor Hippocampal Transplants

Embryonic stem cells (ESCs) hold great therapeutic potential due to their ability to differentiate into cells of the three primary germ layers, which can be used to repopulate disease-damaged tissues. In fact, two cell therapies using ESC derivatives are currently in phase I clinical trials. A main concern in using ESCs and their derivatives for cell transplantation is the ability of undifferentiated ESCs to generate tumors in the host. Positive selection steps are often included in protocols designed to generate particular cell types from ESCs; however, the transition from ESC to progenitor cell or terminally differentiated cell is not synchronous, and residual undifferentiated cells often remain. In our transplants of ESC-derived neural progenitors (ESNPs) into the adult mouse hippocampus, we have observed the formation of teratocarcinomas. We set out to reduce teratocarcinoma formation by enrichment of ESNPs using fluorescence-activated cell sorting (FACS) and have found that, although enrichment prior to transplant reduces the overall rate of teratocarcinoma formation, the tumorigenicity of cell batches can vary widely, even after FACS enrichment to as much as 95% ESNPs. Our data suggest that this variability may be due to the percentage of residual ESCs remaining in the transplant cell population and to the presence of pluripotent epiblast-like cells, not previously identified in transplant batches. Our data emphasize the need for stringent characterization of transplant cell populations that will be used for cell replacement therapies in order to reduce the risk of tumor formation.

Cooperative binding of KLF4, pELK-1, and HDAC2 to a G/C repressor element in the SM22α promoter mediates transcriptional silencing during SMC phenotypic switching in vivo

RATIONALE

We previously identified conserved G/C Repressor elements in the promoters of most smooth muscle cell (SMC) marker genes and demonstrated that mutation of this element within the SM22α promoter nearly abrogated repression of this transgene after vascular wire injury or within lesions of ApoE-/- mice. However, the mechanisms regulating the activity of the G/C Repressor are unknown, although we have previously shown that phenotypic switching of cultured SMC is dependent on Krupple-like factor (KLF)4.

OBJECTIVE

The goals of the present studies were to ascertain if (1) injury-induced repression of SM22α gene after vascular injury is mediated through KLF4 binding to the G/C Repressor element and (2) the transcriptional repressor activity of KLF4 on SMC marker genes is dependent on cooperative binding with pELK-1 (downstream activator of the mitogen-activated protein kinase pathway) and subsequent recruitment of histone de-acetylase 2 (HDAC2), which mediates epigenetic gene silencing.

METHODS AND RESULTS

Chromatin immunoprecipitation (ChIP) assays were performed on chromatin derived from carotid arteries of mice having either a wild-type or G/C Repressor mutant SM22α promoter-LacZ transgene. KLF4 and pELK-1 binding to the SM22α promoter was markedly increased after vascular injury and was G/C Repressor dependent. Sequential ChIP assays and proximity ligation analyses in cultured SMC treated with platelet-derived growth factor BB or oxidized phospholipids showed formation of a KLF4, pELK-1, and HDAC2 multiprotein complex dependent on the SM22α G/C Repressor element.

CONCLUSIONS

Silencing of SMC marker genes during phenotypic switching is partially mediated by sequential binding of pELK-1 and KLF4 to G/C Repressor elements. The pELK-1-KLF4 complex in turn recruits HDAC2, leading to reduced histone acetylation and epigenetic silencing.

What do we know about the neurogenic potential of different stem cell types?

Cell therapies, based on transplantation of immature cells, are being considered as a promising tool in the treatment of neurological disorders. Many efforts are being concentrated on the development of safe and effective stem cell lines. Nevertheless, the neurogenic potential of some cell lines, i.e., the ability to generate mature neurons either in vitro or in vivo, is largely unknown. Recent evidence indicate that this potential might be distinct among different cell lines, therefore limiting their broad use as replacement cells in the central nervous system. Here, we have reviewed the latest advancements regarding the electrophysiological maturation of stem cells, focusing our attention on fetal-derived-, embryonic-, and induced pluripotent stem cells. In summary, a large body of evidence supports the biological safety, high neurogenic potential, and in some diseases probable clinical efficiency related to fetal-derived cells. By contrast, reliable data regarding embryonic and induced pluripotent stem cells are still missing.

Strategies for enrichment and selection of stem cell-derived tissue precursors

Human embryonic stem cells have the capacity for self-renewal and pluripotency and thus are a primary candidate for tissue engineering and regenerative therapies. These cells also provide an opportunity to study the development of human tissues ex vivo. To date, numerous human embryonic stem cell lines have been derived and characterized. In this review, we will detail the strategies used to direct tissue-specific differentiation of embryonic stem cells. We also will discuss how these strategies have produced new sources of tissue-specific progenitor cells. Finally, we will describe the next generation of methods being developed to identify and select stem cell-derived tissue precursors for experimental study and clinical use.

A comparison between neurally induced bone marrow derived mesenchymal stem cells and olfactory ensheathing glial cells to repair spinal cord injuries in rat

Cell therapy has proven to be a highly promising method in clinical applications, raising so much hope for the treatment of injured tissues with low, if any, self regeneration potential such as central and peripheral nervous system. Neurally induced bone marrow derived mesenchymal stem cells (NIMSCs) as well as olfactory ensheathing cells (OECs) were transplanted in a rat model of sub-acute spinal cord injury and the behavioral and histological analyses were conducted. A balloon-compression technique was used to produce an injury at T8-T9 level of spinal cord. After a week post injury, rats were injected with either NIMSCs or OECs at the center of developing lesion cavity, 3mm cranial and 3mm caudal to the cavity. Weekly behavioral assessment using BBB score was done over five-week period post transplantation and finally histological assessment was performed to locate labeled cells in the tissue in order to evaluate the reduction of cavity formation and axonal regeneration. Evaluation of locomotor performance showed significant behavioral improvement in NIMSC group over OEC and control groups. The histological analyses revealed the presence of transplanted cells in the spinal cord parenchyma. Volume of injured area that was occupied with syrinx cavity in NIMSC group was significantly less than control group. In addition, meanwhile neurofilament-positive axons significantly showed higher expression in rats receiving NIMSC compared to the other two groups. In conclusion NIMSC caused both behavioral and histological improvement that potentially makes them a promising candidate for cell therapy approaches of spinal cord injuries.

Recent therapeutic strategies for spinal cord injury treatment: possible role of stem cells

Spinal cord injury (SCI) often results in significant dysfunction and disability. A series of treatments have been proposed to prevent and overcome the formation of the glial scar and inhibitory factors to axon regrowth. In the last decade, cell therapy has emerged as a new tool for several diseases of the nervous system. Stem cells act as minipumps providing trophic and immunomodulatory factors to enhance axonal growth, to modulate the environment, and to reduce neuroinflammation. This capability can be boosted by genetical manipulation to deliver trophic molecules. Different types of stem cells have been tested, according to their properties and the therapeutic aims. They differ from each other for origin, developmental stage, stage of differentiation, and fate lineage. Related to this, stem cells differentiating into neurons could be used for cell replacement, even though the feasibility that stem cells after transplantation in the adult lesioned spinal cord can differentiate into neurons, integrate within neural circuits, and emit axons reaching the muscle is quite remote. The timing of cell therapy has been variable, and may be summarized in the acute and chronic phases of disease, when stem cells interact with a completely different environment. Even though further experimental studies are needed to elucidate the mechanisms of action, the therapeutic, and the side effects of cell therapy, several clinical protocols have been tested or are under trial. Here, we report the state-of-the-art of cell therapy in SCI, in terms of feasibility, outcome, and side effects.

Producing striatal phenotypes for transplantation in Huntington's disease

Neural transplantation as a therapeutic strategy in neurodegenerative disorders offers to replace cells lost during the disease process, with the potential to reconstruct dysfunctional circuitry, thus alleviating associated disease symptoms. The focal loss of striatal cells, specifically medium-sized spiny neurons (MSN) in Huntington's disease (HD), makes transplantation a therapeutic option. Here, we review the progress made in generating striatal MSN phenotypes for transplantation in HD. We discuss the use of primary fetal tissue as a donor source in both preclinical and clinical studies and assess the options for renewable cell sources. We evaluate progress in directing the differentiation of renewable cells towards a striatal MSN phenotype for HD.

Induced neuronal cells: how to make and define a neuron

Cellular plasticity is a major focus of investigation in developmental biology. The recent discovery that induced neuronal (iN) cells can be generated from mouse and human fibroblasts by expression of defined transcription factors suggested that cell fate plasticity is much wider than previously anticipated. In this review, we summarize the most recent developments in this nascent field and suggest criteria to help define and categorize iN cells that take into account the complexity of neuronal identity.