Using stem cells and iPS cells to discover new treatments for Parkinson's disease

Fetal cell transplantation can improve the symptoms of Parkinson's disease (PD) patients for more than a decade. In some patients, alpha-synuclein aggregates and Lewy bodies have been observed in the transplanted neurons without functional significance. Recently stem cells have emerged as an ethically acceptable source of cells for transplantation but, importantly, the type of stem cell matters. While the lineage restriction of adult neural stem cells limits their clinical applicability for patients with PD, human pluripotent stem cells provide an opportunity to replace specific types of degenerating neurons. Now, cellular reprogramming technology can provide patient-specific neurons for neural transplantation and problems with cell fate specification and safety are resolving. Induced pluripotent stem (iPS) cell-derived neurons are also a unique tool for interpreting the genetic basis for an individual's risk of developing PD into clinically meaningful information. For example, clinical trials for neuroprotective molecules need to be tested in presymptomatic individuals when the neurons can still be protected. Patient-specific neural cells can also be used to identify an individual's responsiveness to drugs and to understand the mechanisms of the disease. Along these avenues of investigation, stem cells are enabling research for new treatments in PD.     

Cell replacement therapy for central nervous system diseases

The brain and spinal cord can not replace neurons or supporting glia that are lost through traumatic injury or disease. In pre-clinical studies, however, neural stem and progenitor cell transplants can promote functional recovery. Thus the central nervous system is repair competent but lacks endogenous stem cell resources. To make transplants clinically feasible, this field needs a source of histocompatible, ethically acceptable and non-tumorgenic cells. One strategy to generate patient-specific replacement cells is to reprogram autologous cells such as fibroblasts into pluripotent stem cells which can then be differentiated into the required cell grafts. However, the utility of pluripotent cell derived grafts is limited since they can retain founder cells with intrinsic neoplastic potential. A recent extension of this technology directly reprograms fibroblasts into the final graftable cells without an induced pluripotent stem cell intermediate, avoiding the pluripotent caveat. For both types of reprogramming the conversion efficiency is very low resulting in the need to amplify the cells in culture which can lead to chromosomal instability and neoplasia. Thus to make reprogramming biology clinically feasible, we must improve the efficiency. The ultimate source of replacement cells may reside in directly reprogramming accessible cells within the brain.     

Generation of Human-Induced Pluripotent Stem Cells to Model Spinocerebellar Ataxia Type 2 In vitro

Spinocerebellar ataxia type 2 (SCA2) is caused by triple nucleotide repeat (CAG) expansion in the coding region of the ATAXN2 gene on chromosome 12, which produces an elongated, toxic polyglutamine tract, leading to Purkinje cell loss. There is currently no effective therapy. One of the main obstacles that hampers therapeutic development is lack of an ideal disease model. In this study, we have generated and characterized SCA2-induced pluripotent stem (iPS) cell lines as an in vitro cell model. Dermal fibroblasts (FBs) were harvested from primary cultures of skin explants obtained from a SCA2 subject and a healthy subject. For reprogramming, hOct4, hSox2, hKlf4, and hc-Myc were transduced to passage-3 FBs by retroviral infection. Both SCA2 iPS and control iPS cells were successfully generated and showed typical stem cell growth patterns with normal karyotype. All iPS cell lines expressed stem cell markers and differentiated in vitro into cells from three embryonic germ layers. Upon in vitro neural differentiation, SCA2 iPS cells showed abnormality in neural rosette formation but successfully differentiated into neural stem cells (NSCs) and subsequent neural cells. SCA2 and normal FBs showed a comparable level of ataxin-2 expression; whereas SCA2 NSCs showed less ataxin-2 expression than normal NSCs and SCA2 FBs. Within the neural lineage, neurons had the most abundant expression of ataxin-2. Time-lapsed neural growth assay indicated terminally differentiated SCA2 neural cells were short-lived compared with control neural cells. The expanded CAG repeats of SCA2 were stable throughout reprogramming and neural differentiation. In conclusion, we have established the first disease-specific human SCA2 iPS cell line. These mutant iPS cells have the potential for neural differentiation. These differentiated neural cells harboring mutations are invaluable for the study of SCA2 pathogenesis and therapeutic drug development.     

Induced pluripotent stem cells and promises of neuroregenerative medicine

First created in 2006 from adult somatic cells by a simple molecular genetic trick, induced pluripotent stem cells (iPS) system is the latest platform in stem cell research. Induced pluripotent stem cells are produced by nuclear reprogramming technology and they resemble embryonic stem cells (ES) in key elements; they possess the potentiality to differentiate into any type of cell in the body. More importantly, the iPS platform has distinct advantage over ES system in the sense that iPS-derived cells are autologous and therefore the iPS-derived transplantation does not require immunosuppressive therapy. In addition, iPS research obviates the political and ethical quandary associated with embryo destruction and ES research. This remarkable discovery of cellular plasticity has important medical implications. This brief review summarizes currently available stem cell platforms, with emphasis on cellular reprogramming and iPS technology and its application in disease modeling and cell replacement therapy in neurodegenerative diseases.     

Current advances in the treatment of Parkinson's disease with stem cells

Stem cell replacement has emerged as the novel therapeutic strategy for Parkinson's disease (PD). Control of motor behavior is lost in PD due to the selective degeneration of mesencephalic dopamine neurons (DA) in the substantia nigra. This progressive loss of DA neurons results in devastating symptoms for which there is no cure. Debilitating side effects often result from chronic pharmacological treatment, hence current investigations into cell transplantation therapy as a substitute and/or adjuvant to other therapeutics. Clinical trials with fetal DA tissue have provided evidence that cell transplantation could be a viable alternative. Limited availability of fetal tissue, combined with variable outcome led to emphasis on other sources of cells, such as stem cells. This review focuses on three stem cell sources (embryonic, neural, and adult mesenchymal). Also discussed is the molecular differentiation into mature DA neurons, the various protocols that have been developed to generate DA neurons from various stem cells, and the current state of stem cell therapy for PD.     

Cell Therapeutics in Parkinson’s Disease

The main pathology underlying motor symptoms in Parkinson’s disease (PD) is a rather selective degeneration of nigrostriatal dopamine (DA) neurons. Intrastriatal transplantation of immature DA neurons, which replace those neurons that have died, leads to functional restoration in animal models of PD. Here we describe how far the clinical translation of the DA neuron replacement strategy has advanced. We briefly summarize the lessons learned from the early clinical trials with grafts of human fetal mesencephalic tissue, and discuss recent findings suggesting susceptibility of these grafts to the disease process long-term after implantation. Mechanisms underlying graft-induced dyskinesias, which constitute the only significant adverse event observed after neural transplantation, and how they should be prevented and treated are described. We summarize the attempts to generate DA neurons from stem cells of various sources and patient-specific DA neurons from fully differentiated somatic cells, with particular emphasis on the requirements of these cells to be useful in the clinical setting. The rationale for the new clinical trial with transplantation of fetal mesencephalic tissue is described. Finally, we discuss the scientific and clinical advancements that will be necessary to develop a competitive cell therapy for PD patients.     

Transplantation of Human-Induced Pluripotent Stem Cell-Derived Neural Precursors into Early-Stage Zebrafish Embryos

Induced pluripotent stem cells (iPS cells) generated from somatic cells through reprogramming hold great promises for regenerative medicine. However, how reprogrammed cells survive, behave in vivo, and interact with host cells after transplantation still remains to be addressed. There is a significant need for animal models that allow in vivo tracking of transplanted cells in real time. In this regard, the zebrafish, a tropical freshwater fish, provides significant advantage as it is optically transparent and can be imaged in high resolution using confocal microscopy. The principal goal of this study was to optimize the protocol for successful short-term and immunosuppression-free transplantation of human iPS cell-derived neural progenitor cells into zebrafish and to test their ability to differentiate in this animal model. To address this aim, we isolated human iPS cell-derived neural progenitor cells from human fibroblasts and grafted them into (a) early (blastocyst)-stage wild-type AB zebrafish embryos or (b) 3-day-old Tg(gfap:GFP) zebrafish embryos (intracranial injection). We found that transplanted human neuronal progenitor cells can be effectively grafted and that they differentiate and survive in zebrafish for more than 2 weeks, validating the model as an ideal platform for in vivo screening experiments. We conclude that zebrafish provides an excellent model for studying iPS cell-derived cells in vivo.     

The search for a curative cell therapy in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder, characterised by the progressive loss of dopaminergic neurons in the substantia nigra, and typically treated by dopamine replacement. This treatment, although very effective in the early stages of the disease, is not curative and has side-effects. As such there has been a search for a more definitive treatment for this condition, which has mainly concentrated on replacing the lost neurons with neural grafts. Possible cell sources for replacement range from autologous grafts of dopamine secreting cells to allografts of fetal ventral mesencephalon and neural precursor cells derived from fetal tissue or embryonic stem cells. Some of these cells have been the subject of clinical trials, which to date have produced disparate outcomes. Therefore, whilst cell therapies remain a promising treatment for PD, there is need for further refinement of the techniques involved in this experimental procedure, before any new trials in patients are undertaken.     

Direct reprogramming of somatic cells into neural stem cells or neurons for neurological disorders

Direct reprogramming of somatic cells into neurons or neural stem cells is one of the most important fron-tier ifelds in current neuroscience research. Without undergoing the pluripotency stage, induced neurons or induced neural stem cells are a safer and timelier manner resource in comparison to those derived from induced pluripotent stem cells. In this prospective, we review the recent advances in generation of induced neurons and induced neural stem cellsin vitro andin vivo and their potential treatments of neurological disorders.     

Differentiation of induced pluripotent stem cells into functional oligodendrocytes

The technology to generate autologous pluripotent stem cells (iPS cells) from almost any somatic cell type has brought various cell replacement therapies within clinical research. Besides the challenge to optimize iPS protocols to appropriate safety and GMP levels, procedures need to be developed to differentiate iPS cells into specific fully differentiated and functional cell types for implantation purposes. In this article, we describe a protocol to differentiate mouse iPS cells into oligodendrocytes with the aim to investigate the feasibility of IPS stem cell-based therapy for demyelinating disorders, such as multiple sclerosis. Our protocol results in the generation of oligodendrocyte precursor cells (OPCs) that can develop into mature, myelinating oligodendrocytes in-vitro (co-culture with DRG neurons) as well as in-vivo (after implantation in the demyelinated corpus callosum of cuprizone-treated mice). We report the importance of complete purification of the iPS-derived OPC suspension to prevent the contamination with teratoma-forming iPS cells.     

Direct lineage conversion of astrocytes to induced neural stem cells or neurons

Since the generation of induced pluripotent stem cells in 2006, cellular reprogramming has attracted increasing attention as a revolutionary strategy for cell replacement therapy. Recent advances have revealed that somatic cells can be directly converted into other mature cell types, which eliminates the risk of neoplasia and the generation of undesired cell types. Astrocytes become reactive and undergo proliferation, which hampers axon regeneration following injury, stroke, and neurodegenerative diseases. An emerging technique to directly reprogram astrocytes into induced neural stem cells(i NSCs) and induced neurons(i Ns) by neural fate determinants brings potential hope to cell replacement therapy for the above neurological problems. Here, we discuss the development of direct reprogramming of various cell types into i Ns and i NSCs, then detail astrocyte-derived i NSCs and i Ns in vivo and in vitro. Finally, we highlight the unsolved challenges and opportunities for improvement.     

Induced pluripotent stem (iPS) cells as <Emphasis Type="Italic">in vitro</Emphasis> models of human neurogenetic disorders

The recent discovery of genomic reprogramming of human somatic cells into induced pluripotent stem cells offers an innovative and relevant approach to the study of human genetic and neurogenetic diseases. By reprogramming somatic cells from patient samples, cell lines can be isolated that self-renew indefinitely and have the potential to develop into multiple different tissue lineages. Additionally, the rapid progress of research on human embryonic stem cells has led to the development of sophisticated in vitro differentiation protocols that closely mimic mammalian development. In particular, there have been significant advances in differentiating human pluripotent stem cells into defined neuronal types. Here, we summarize the experimental approaches employed in the rapidly evolving area of somatic cell reprogramming and the methodologies for differentiating human pluripotent cells into neurons. We also discuss how the availability of patient-specific fibroblasts offers a unique opportunity for studying and modeling the effects of specific gene defects on human neuronal development in vitro and for testing small molecules or other potential therapies for the relevant neurogenetic disorders.     

RNA配合Oct4重编程小鼠神经干细胞为诱导多潜能干细胞

目的 研究小RNA在细胞重编程过程中的作用。 方法 运用MiR-294和MiR-302a配合单因子Oct4来重编程小鼠神经干细胞，并对所得的诱导多潜能干（induced pluripotent stem, iPS）细胞进行鉴定。 结果 利用MiR-294和MiR-302a可将单因子诱导体系的诱导效率提高7倍（0.1% vs 0.014%），所得iPS细胞保持未分化状态，碱性磷酸酶，SSEA-1和Oct4检测均为阳性。 结论 本实验证实了小RNA在细胞重编程过程中的重要调节作用，探索出了一套安全高效的重编程诱导体系。     

Induced pluripotent stem cell lines from Huntington's disease mice undergo neuronal differentiation while showing alterations in the lysosomal pathway

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an excessive expansion of a CAG trinucleotide repeat in the gene encoding the protein huntingtin, resulting in an elongated stretch of glutamines near the N-terminus of the protein. Here we report the derivation of a collection of 11 induced pluripotent stem (iPS) cell lines generated through somatic reprogramming of fibroblasts obtained from the R6/2 transgenic HD mouse line. We show that CAG expansion has no effect on reprogramming efficiency, cell proliferation rate, brain-derived neurotrophic factor level, or neurogenic potential. However, genes involved in the cholesterol biosynthesis pathway, which is altered in HD, are also affected in HD-iPS cell lines. Furthermore, we found a lysosomal gene upregulation and an increase in lysosome number in HD-iPS cell lines. These observations suggest that iPS cells from HD mice replicate some but not all of the molecular phenotypes typically observed in the disease; additionally, they do not manifest increased cell death propensity either under self-renewal or differentiated conditions. More studies will be necessary to transform a revolutionary technology into a powerful platform for drug screening approaches.     

Neural stem cell‐based treatment for neurodegenerative diseases

Human neurodegenrative diseases such as Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) are caused by a loss of neurons and glia in the brain or spinal cord. Neurons and glial cells have successfully been generated from stem cells such as embryonic stem cells (ESCs), mesenchymal stem cells (MSCs) and neural stem cells (NSCs), and stem cell‐based cell therapies for neurodegenerative diseases have been developed. A recent advance in generatioin of a new class of pluripotent stem cells, induced pluripotent stem cells (iPSCs), derived from patients' own skin fibroblasts, opens doors for a totally new field of personalized medicine. Transplantation of NSCs, neurons or glia generated from stem cells in animal models of neurodegenrative diseases, including PD, HD, ALS and AD, demonstrates clinical improvement and also life extension of these animals. Additional therapeutic benefits in these animals can be provided by stem cell‐mediated gene transfer of therapeutic genes such as neurotrophic factors and enzymes. Although further research is still needed, cell and gene therapy based on stem cells, particularly using neurons and glia derived from iPSCs, ESCs or NSCs, will become a routine treatment for patients suffering from neurodegenerative diseases and also stroke and spinal cord injury.     

The first reported generation of several induced pluripotent stem cell lines from homozygous and heterozygous Huntington's disease patients demonstrates mutation related enhanced lysosomal activity

Neuronal disorders, like Huntington's disease (HD), are difficult to study, due to limited cell accessibility, late onset manifestations, and low availability of material. The establishment of an in vitro model that recapitulates features of the disease may help understanding the cellular and molecular events that trigger disease manifestations. Here, we describe the generation and characterization of a series of induced pluripotent stem (iPS) cells derived from patients with HD, including two rare homozygous genotypes and one heterozygous genotype. We used lentiviral technology to transfer key genes for inducing reprogramming. To confirm pluripotency and differentiation of iPS cells, we used PCR amplification and immunocytochemistry to measure the expression of marker genes in embryoid bodies and neurons. We also analyzed teratomas that formed in iPS cell-injected mice. We found that the length of the pathological CAG repeat did not increase during reprogramming, after long term growth in vitro, and after differentiation into neurons. In addition, we observed no differences between normal and mutant genotypes in reprogramming, growth rate, caspase activation or neuronal differentiation. However, we observed a significant increase in lysosomal activity in HD-iPS cells compared to control iPS cells, both during self-renewal and in iPS-derived neurons. In conclusion, we have established stable HD-iPS cell lines that can be used for investigating disease mechanisms that underlie HD. The CAG stability and lysosomal activity represent novel observations in HD-iPS cells. In the future, these cells may provide the basis for a powerful platform for drug screening and target identification in HD.     

The science and ethics of cell-based therapies for Parkinson's disease

Parkinson's Disease (PD) is an age-related, disabling neurodegenerative disorder. Although sufferers usually respond to dopamine agonists for extended periods, the disease remains progressive and adverse drug effects can compromise effective long term treatment. Cell-based therapies have been the subject of much hype and optimism with regard to PD. Proof of principle was provided in the 1980s with fetal tissue transplantation trials demonstrating successful graft survival. Embryonic stem cells and reprogrammed or transdifferentiated somatic cells may provide alternative sources of tissue with the potential to overcome the material shortages and technical difficulties that have hindered fetal neural transplants. This article will review the state of the science for cell based therapies and examine the ethical issues that societies must negotiate regarding their clinical use.