Directed evolution of motor neurons from genetically engineered neural precursors

The enhanced generation of motor neurons from mESCs by MgAl layered double hydroxide nanoparticles

The committed differentiation of stem cells into neurons is a promising therapeutic strategy for neurological diseases. Predifferentiation of transplanted stem cells into neural precursors could enhance their utilization and control the direction of differentiation. Embryonic stem cells with totipotency can differentiate into specific nerve cells under appropriate external induction conditions. Layered double hydroxide (LDH) nanoparticles have been proven to regulate the pluripotency of mouse ESCs (mESCs), and LDH could be used as carrier in neural stem cells for nerve regeneration. Hence, we sought to study the effects of LDH without loaded factors on mESCs neurogenesis in this work. A series of characteristics analyses indicated the successful construction of LDH nanoparticles. LDH nanoparticles that may adhere to the cell membranes had insignificant effect on cell proliferation and apoptosis. The enhanced differentiation of mESCs into motor neurons by LDH was systematically validated by immunofluorescent staining, quantitative real-time PCR analysis and western blot analysis. In addition, transcriptome sequencing analysis and mechanism verification elucidated the significant regulatory roles of focal adhesion signaling pathway in the enhanced mESCs neurogenesis by LDH. Taken together, the functional validation of inorganic LDH nanoparticles promoting motor neurons differentiation provide a novel strategy and therapeutic prospect for the clinical transition of neural regeneration.

Safe nanoengineering and incorporation of transplant populations in a neurosurgical grade biomaterial, DuraGen PlusTM, for protected cell therapy applications

High transplant cell loss is a major barrier to translation of stem cell therapy for pathologies of the brain and spinal cord. Encapsulated delivery of stem cells in biomaterials for cell therapy is gaining popularity but experimental research has overwhelmingly used laboratory grade materials unsuitable for human clinical use - representing a further barrier to clinical translation. A potential solution is to use neurosurgical grade materials routinely used in clinical protocols which have an established human safety profile. Here, we tested the ability of Duragen Plus™ - a clinical biomaterial used widely in neurosurgical duraplasty procedures, to support the growth and differentiation of neural stem cells- a major transplant population being tested in clinical trials for neurological pathology. Genetic engineering of stem cells yields augmented therapeutic cells, so we further tested the ability of the Duragen Plus™ matrix to support stem cells engineered using magnetofection technology and minicircle DNA vectors- a promising cell engineering approach we previously reported (Journal of Controlled Release, 2016 a &b). The safety of the nano-engineering approach was analysed for the first time using sophisticated data-independent analysis by mass spectrometry-based proteomics. We prove that the Duragen Plus™ matrix is a promising biomaterial for delivery of stem cell transplant populations, with no adverse effects on key regenerative parameters. This advanced cellular construct based on a combinatorial nano-engineering and biomaterial encapsulation approach, could therefore offer key advantages for clinical translation.

Transplantation of hypoxic preconditioned neural stem cells benefits functional recovery via enhancing neurotrophic secretion after spinal cord injury in rats

Spinal cord injury (SCI) is a debilitating, costly, and common pathological condition that affects the function of central nervous system (CNS). To date, there are few promising therapeutic strategies available for SCI. To look for a suitable therapeutic strategy, we have developed a sublethal hypoxic preconditioning procedure using Fluorescence-activated cell sorting (FACS) analysis, LDH releasing, and cell viability assays in vitro. Meanwhile, we have examined the benefits of neural stem cells (NSCs) transplantation prior to hypoxic preconditioning on functional recovery and potential mechanism via MRI screening, H&E, and Nissl staining, immunofluorescence staining and Elisa assays. Our data showed that transplantation of hypoxic prconditioned NSCs could enhance neuronal survival, especially 5-TH⁺ and ChAT⁺ neurons, in the injured spinal cord to reinforce functional benefits. The hypoxia exposure upregulated HIF-1α, neurotrophic and growth factors including neurotrophin-3 (NT-3), glial cell-derived neurotrophic factor (GDNF), and brain-derived neurotrophic factor (BDNF) in vitro and in vivo. Furthermore, functional recovery, including locomotor and hypersensitivities to mechanical and thermal stimulation assessed via behavioral and sensory tests, improved significantly in rats with engraftment of NSCs after hypoxia exposure from day 14 post-SCI, compared with the control and N-NSCs groups. In short, the approach employed in this study could result in functional recovery via upregulating neurotrophic and growth factors, which implies that hypoxic preconditioning strategy could serve as an effective and feasible strategy for cell-based therapy in the treatment of SCI in rats.

Insights into cell-free therapeutic approach: Role of stem cell "soup-ernatant"

Current advances in medicine have revolutionized the field of regenerative medicine dramatically with newly evolved therapies for repair or replacement of degenerating or injured tissues. Stem cells (SCs) can be harvested from different sources for clinical therapeutics, which include fetal tissues, umbilical cord blood, embryos, and adult tissues. SCs can be isolated and differentiated into desired lineages for tissue regeneration and cell replacement therapy. However, several loopholes need to be addressed properly before this can be extended for large-scale therapeutic application. These include a careful approach for patient safety during SC treatments and tolerance of recipients. SC treatments are associated with a number of risk factors and require successful integration and survival of transplanted cells in the desired microenvironment with concurrent tissue regeneration. Recent studies have focused on developing alternatives that can replace the cell-based therapy using paracrine factors. The development of stem "cell free" therapies can be devoted mainly to the use of soluble factors (secretome), extracellular vesicles, and mitochondrial transfer. The present review emphasizes on the paradigms related to the use of SC-based therapeutics and the potential applications of a cell-free approach as an alternative to cell-based therapy in the area of regenerative medicine.

Current Neurogenic and Neuroprotective Strategies to Prevent and Treat Neurodegenerative and Neuropsychiatric Disorders

The adult central nervous system is commonly known to have a very limited regenerative capacity. The presence of functional stem cells in the brain can therefore be seen as a paradox, since in other organs these are known to counterbalance cell loss derived from pathological conditions. This fact has therefore raised the possibility to stimulate neural stem cell differentiation and proliferation or survival by either stem cell replacement therapy or direct administration of neurotrophic factors or other proneurogenic molecules, which in turn has also originated regenerative medicine for the treatment of otherwise incurable neurodegenerative and neuropsychiatric disorders that take a huge toll on society. This may be facilitated by the fact that many of these disorders converge on similar pathophysiological pathways: excitotoxicity, oxidative stress, neuroinflammation, mitochondrial failure, excessive intracellular calcium and apoptosis. This review will therefore focus on the most promising achievements in promoting neuroprotection and neuroregeneration reported to date.

A new method for generating high purity motoneurons from mouse embryonic stem cells

A common problem with using embryonic stem (ES) cells as a source for analysis of gene expression, drug toxicity, or functional characterization studies is the heterogeneity that results from many differentiation protocols. The ability to generate large numbers of high purity differentiated cells from pluripotent stem cells could greatly enhance their utility for in vitro characterization studies and transplantation in pre-clinical injury models. Population heterogeneity is particularly troublesome for post-mitotic neurons, including motoneurons, because they do not proliferate and are quickly diluted in culture by proliferative phenotypes, such as glia. Studies of motoneuron biology and disease, in particular amyotrophic lateral sclerosis, can benefit from high purity motoneuron cultures. In this study, we engineered a transgenic-ES cell line where highly conserved enhancer elements for the motoneuron transcription factor Hb9 were used to drive puromycin N-acetyltransferase expression in ES cell-derived motoneurons. Antibiotic selection with puromycin was then used to obtain high purity motoneuron cultures following differentiation of mouse ES cells. Purity was maintained during maturation allowing the production of consistent, uniform populations of cholinergic ES cell-derived motoneurons. Appropriate functional properties of purified motoneurons were verified by acetylcholinesterase activity and electrophysiology. Antibiotic selection, therefore, can provide an inexpensive alternative to current methods for isolating ES cell-derived motoneurons at high purity that does not require specialized laboratory equipment and provides a unique platform for studies in motoneuron development and degeneration.

Transplantation of mesenchymal stem cells in ALS

Amyotrophic lateral sclerosis (ALS) is a devastating incurable, neurodegenerative disease that targets motor neurons (MNs) in the primary motor cortex, brainstem, and spinal cord, leading to muscle atrophy, paralysis, and death due to respiratory failure within 2-5 years. Currently, there is no cure for ALS. The development of a therapy that can support or restore MN function and attenuate toxicity in the spinal cord provides the most comprehensive approach for treating ALS. Mesenchymal stem cells might be suitable for cell therapy in ALS because of their immunomodulatory and protective properties. In this review, the authors discuss the major challenges to the translation of in vitro and animal studies of MSCs therapy in the clinical setting.

Guiding Differentiation of Stem Cells in Vivo by Tetracycline-Controlled Expression of Key Transcription Factors

Transplantation of stem or progenitor cells is an attractive strategy for cell replacement therapy. However, poor long-term survival and insufficiently reproducible differentiation to functionally appropriate cells in vivo still present major obstacles for translation of this methodology to clinical applications. Numerous experimental studies have revealed that the expression of just a few transcription factors can be sufficient to drive stem cell differentiation toward a specific cell type, to transdifferentiate cells from one fate to another, or to dedifferentiate mature cells to pluripotent stem/progenitor cells (iPSCs). We thus propose here to apply the strategy of expressing the relevant key transcription factors to guide the differentiation of transplanted cells to the desired cell fate in vivo. To achieve this requires tools allowing us to control the expression of these genes in the transplant. Here, we describe drug-inducible systems that allow us to sequentially and timely activate gene expression from the outside, with a particular emphasis on the Tet system, which has been widely and successfully used in stem cells. These regulatory systems offer a tool for strictly limiting gene expression to the respective optimal stage after transplantation. This approach will direct the differentiation of the immature stem/progenitor cells in vivo to the desired cell type.

The influence of piezoelectric scaffolds on neural differentiation of human neural stem/progenitor cells

Human neural stem/progenitor cells (hNSCs/NPCs) are a promising cell source for neural tissue engineering because of their ability to differentiate into various neural lineages. In this study, hNSC/NPC differentiation was evaluated on piezoelectric, fibrous scaffolds. These smart materials have an intrinsic material property where transient electric potential can be generated in the material upon minute mechanical deformation. hNSCs/NPCs cultured on the scaffolds and films differentiated into β-III tubulin-positive cells, a neuronal cell marker, with or without the presence of inductive factors. In contrast, hNSCs/NPCs cultured on laminin-coated plates were predominantly nestin positive, a NSC marker, in the control medium. Gene expression results suggest that the scaffolds may have promoted the formation of mature neural cells exhibiting neuron-like characteristics. hNSCs/NPCs differentiated mostly into β-III tubulin-positive cells and had the greatest average neurite length on micron-sized, annealed (more piezoelectric), aligned scaffolds, demonstrating their potential for neural tissue-engineering applications.

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.

Directed induction of functional motor neuron-like cells from genetically engineered human mesenchymal stem cells

Cell replacement using stem cells is a promising therapeutic approach to treat degenerative motor neuron (MN) disorders, such as amyotrophic lateral sclerosis and spinal cord injury. Human bone marrow-derived mesenchymal stem cells (hMSCs) are a desirable cell source for autologous cell replacement therapy to treat nervous system injury due to their plasticity, low immunogenicity, and a lower risk of tumor formation than embryonic stem cells. However, hMSCs are inefficient with regards to differentiating into MN-like cells. To solve this limitation, we genetically engineered hMSCs to express MN-associated transcription factors, Olig2 and Hb9, and then treat the hMSCs expressing Olig2 and Hb9 with optimal MN induction medium (MNIM). This method of induction led to higher expression (>30% of total cells) of MN markers. Electrophysiological data revealed that the induced hMSCs had the excitable properties of neurons and were able to form functional connections with muscle fibers in vitro. Furthermore, when the induced hMSCs were transplanted into an injured organotypic rat spinal cord slice culture, an ex vivo model of spinal cord injury, they exhibited characteristics of MNs. The data strongly suggest that induced Olig2/Hb9-expressing hMSCs were clearly reprogrammed and directed toward a MN-like lineage. We propose that methods to induce Olig2 and Hb9, followed by further induction with MNIM have therapeutic potential for autologous cell replacement therapy to treat degenerative MN disorders.

Delayed functional maturation of human neuronal progenitor cells in vitro

INTRODUCTION

Differentiation of neuronal progenitor cells (NPCs) in vitro into functional neurons is dependent on a complex cascade of molecular signaling pathways, many of which remain unknown. More specifically, in human NPCs the relationship between the expression of typical neuronal marker proteins and functional properties, such as firing action potential and synaptic transmission, is not well understood. In the present report, the immunocytochemical, morphological and electrophysiological changes that human NPCs undergo during neuronal differentiation in vitro were investigated.

METHODS

Human NPCs were differentiated toward a neuronal phenotype. The time course of the expression of neuronal markers and morphological cell changes was mapped and passive and active electrophysiological membrane properties assessed, throughout the neuronal maturation process.

RESULTS

The acquisition of neuronal markers preceded functional physiological maturation by several weeks. Cell input resistance decreased in the first 2 weeks as cells became less sensitive to input current, while cell capacitance progressively increased with continued neuronal process growth. Functional maturation was observed only by the fifth/sixth week, preceded by a marked increase in Na+ and K+ currents. In contrast, electrophysiological maturation of rodent precursor cells was observed at the end of the first week in vitro. Functionally, human neuronal cells became capable of firing action potentials and forming active synaptic contacts. Many features of the firing pattern however remained immature.

CONCLUSIONS

The results showed that human NPCs develop remarkably slowly and retain immature neuronal features for a prolonged period. The importance of Na-dependent activity for proper neuronal maturation is emphasized.

Cell number and timing of transplantation determine survival of human neural stem cell grafts in stroke-damaged rat brain

Neural stem cells (NSCs) derived from human fetal striatum and transplanted as neurospheres survive in stroke-damaged striatum, migrate from the implantation site, and differentiate into mature neurons. Here, we investigated how various steps of neurogenesis are affected by intrastriatal transplantation of human NSCs at different time points after stroke and with different numbers of cells in each implant. Rats were subjected to middle cerebral artery occlusion and then received intrastriatal transplants of NSCs. Transplantation shortly after stroke (48 hours) resulted in better cell survival than did transplantation 6 weeks after stroke, but the delayed transplantation did not influence the magnitude of migration, neuronal differentiation, and cell proliferation in the grafts. Transplanting greater numbers of grafted NSCs did not result in a greater number of surviving cells or increased neuronal differentiation. A substantial number of activated microglia was observed at 48 hours after the insult in the injured striatum, but reached maximum levels 1 to 6 weeks after stroke. Our findings show that the best survival of grafted human NSCs in stroke-damaged brain requires optimum numbers of cells to be transplanted in the early poststroke phase, before the inflammatory response is established. These findings, therefore, have direct clinical implications.

Combined linkage and linkage disequilibrium analysis of a motor speech phenotype within families ascertained for autism risk loci

Using behavioral and genetic information from the Autism Genetics Resource Exchange (AGRE) data set we developed phenotypes and investigated linkage and association for individuals with and without Autism Spectrum Disorders (ASD) who exhibit expressive language behaviors consistent with a motor speech disorder. Speech and language variables from Autism Diagnostic Interview-Revised (ADI-R) were used to develop a motor speech phenotype associated with non-verbal or unintelligible verbal behaviors (NVMSD:ALL) and a related phenotype restricted to individuals without significant comprehension difficulties (NVMSD:C). Using Affymetrix 5.0 data, the PPL framework was employed to assess the strength of evidence for or against trait-marker linkage and linkage disequilibrium (LD) across the genome. Ingenuity Pathway Analysis (IPA) was then utilized to identify potential genes for further investigation. We identified several linkage peaks based on two related language-speech phenotypes consistent with a potential motor speech disorder: chromosomes 1q24.2, 3q25.31, 4q22.3, 5p12, 5q33.1, 17p12, 17q11.2, and 17q22 for NVMSD:ALL and 4p15.2 and 21q22.2 for NVMSD:C. While no compelling evidence of association was obtained under those peaks, we identified several potential genes of interest using IPA. CONCLUSION: Several linkage peaks were identified based on two motor speech phenotypes. In the absence of evidence of association under these peaks, we suggest genes for further investigation based on their biological functions. Given that autism spectrum disorders are complex with a wide range of behaviors and a large number of underlying genes, these speech phenotypes may belong to a group of several that should be considered when developing narrow, well-defined, phenotypes in the attempt to reduce genetic heterogeneity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11689-010-9063-2) contains supplementary material, which is available to authorized users.

Comparative profiling of microRNA expression between neural stem cells and motor neurons in embryonic spinal cord in rat

Neural stem cells' transplantation has been proposed as a future therapy for spinal cord injury. The challenge is how to make proportionally more neural stem cells differentiate into spinal motor neurons. Recent reports reveal that microRNAs play an important role in regulating stem cell self-renewal and differentiation. The aim of this study was to compare the profiling of microRNA expression between neural stem cells and motor neurons and to find candidate targets that direct differentiation of neural stem cells into motor neurons. We performed a parallel isolation and purification of motor neurons and neural stem cells from the same rat embryonic spinal cord sample. With the high-throughput TaqMan low-density array platform, 44 differentially expressed microRNAs were identified (22 specially expressed microRNAs in motor neurons and neural stem cells, respectively). Using bioinformatic methods, clustering, transcriptional regulation and target genes of differential microRNAs were analyzed. Furthermore, miR-126 specially expressed in cultured motor neurons identified by TaqMan low-density array was significantly elevated in choline acetyltransferase-positive neurons differentiated from the neural stem cells. These findings suggest that specially expressed microRNAs may contribute to the directed differentiation of neural stem cells into motor neurons and are potential targets for therapeutic interventions following spinal cord injury.

Challenges of stem cell therapy for spinal cord injury: human embryonic stem cells, endogenous neural stem cells, or induced pluripotent stem cells?

Spinal cord injury (SCI) causes myelopathy, damage to white matter, and myelinated fiber tracts that carry sensation and motor signals to and from the brain. The gray matter damage causes segmental losses of interneurons and motoneurons and restricts therapeutic options. Recent advances in stem cell biology, neural injury, and repair, and the progress toward development of neuroprotective and regenerative interventions are the basis for increased optimism. This review summarizes the pathophysiological mechanisms following SCI and compares human embryonic, adult neural, and the induced pluripotent stem cell-based therapeutic strategies for SCI.

Stem cells in human neurodegenerative disorders--time for clinical translation?

Stem cell-based approaches have received much hype as potential treatments for neurodegenerative disorders. Indeed, transplantation of stem cells or their derivatives in animal models of neurodegenerative diseases can improve function by replacing the lost neurons and glial cells and by mediating remyelination, trophic actions, and modulation of inflammation. Endogenous neural stem cells are also potential therapeutic targets because they produce neurons and glial cells in response to injury and could be affected by the degenerative process. As we discuss here, however, significant hurdles remain before these findings can be responsibly translated to novel therapies. In particular, we need to better understand the mechanisms of action of stem cells after transplantation and learn how to control stem cell proliferation, survival, migration, and differentiation in the pathological environment.

Stem cell-based therapies for spinal cord injury

Spinal cord injury (SCI) results in loss of nervous tissue and consequently loss of motor and sensory function. There is no treatment available that restores the injury-induced loss of function to a degree that an independent life can be guaranteed. Transplantation of stem cells or progenitors may support spinal cord repair. Stem cells are characterized by self-renewal and their ability to become any cell in an organism. Promising results have been obtained in experimental models of SCI. Stem cells can be directed to differentiate into neurons or glia in vitro, which can be used for replacement of neural cells lost after SCI. Neuroprotective and axon regeneration-promoting effects have also been credited to transplanted stem cells. There are still issues related to stem cell transplantation that need to be resolved, including ethical concerns. This paper reviews the current status of stem cell application for spinal cord repair.

Astrocytic protection of spinal motor neurons but not cortical neurons against loss of Als2/alsin function

Three neurodegenerative diseases affecting upper and/or lower motor neurons have been associated with loss of ALS2/Alsin function: juvenile amyotrophic lateral sclerosis, primary lateral sclerosis and infantile-onset ascending hereditary spastic paralysis. The distinct neuronal vulnerability and the role of glia in these diseases remains, however, unclear. We here demonstrate that alsin-depleted spinal motor neurons can be rescued from defective survival and axon growth by co-cultured astrocytes. The astrocytic rescue is mediated by a soluble protective factor rather than by cellular contact. Cortical neurons are intrinsically as vulnerable to alsin depletion as spinal motor neurons but cannot be rescued by co-cultured astrocytes. To our knowledge, these data provide the first example of non-cell-autonomous glial effects in a recessive form of motor neuron disease and a potential rationale for the higher vulnerability of upper versus lower motor neurons in ALS2/Alsin-linked disorders.

Neural stem cells: mechanisms of fate specification and nuclear reprogramming in regenerative medicine

Recently, intense interest in the potential use of neural stem cells (NSC) in the clinical therapy of brain disease and injury has resulted in rapid progress in research on the properties of NSC, their innate and directed differentiation potential and the induced reprogramming of differentiated somatic cells to revert to a pluripotent NSC-like state. The aim of this review is to give an overview of our current operational definitions of the NSC lineage, the growing understanding of extrinsic and intrinsic mechanisms, including heritable but reversible epigenetic chromatin modifications that regulate the maintenance and differentiation of NSC in vivo, and to emphasize ground-breaking efforts of cellular reprogramming with the view to generating patient-specific stem cells for cell replacement therapy. This is set against a summary of current practical procedures for the isolation, research and application of NSC, and of the state of the art in NSC-based regenerative medicine of the nervous system. Both provide the backdrop for the translation of recent findings into innovative clinical applications, with the hope of increasing the safety, efficiency and ethical acceptability of NSC-based therapies in the near future.