Prospects of stem cell therapy for replacing dopamine neurons in Parkinson's disease

Development of a stereotaxic device for low impact implantation of neural constructs or pieces of neural tissues into the mammalian brain

Implanting pieces of tissue or scaffolding material into the mammalian central nervous system (CNS) is wrought with difficulties surrounding the size of tools needed to conduct such implants and the ability to maintain the orientation and integrity of the constructs during and after their transplantation. Here, novel technology has been developed that allows for the implantation of neural constructs or intact pieces of neural tissue into the CNS with low trauma. By “laying out” (instead of forcibly expelling) the implantable material from a thin walled glass capillary, this technology has the potential to enhance neural transplantation procedures by reducing trauma to the host brain during implantation and allowing for the implantation of engineered/dissected tissues or constructs in such a way that their orientation and integrity are maintained in the host. Such technology may be useful for treating various CNS disorders which require the reestablishment of point-to-point contacts (e.g., Parkinson's disease) across the adult CNS, an environment which is not normally permissive to axonal growth.

Towards translational therapies for multiple system atrophy

Multiple system atrophy (MSA) is a fatal adult-onset neurodegenerative disorder of uncertain etiopathogenesis manifesting with autonomic failure, parkinsonism, and ataxia in any combination. The underlying neuropathology affects central autonomic, striatonigral and olivopontocerebellar pathways and it is associated with distinctive glial cytoplasmic inclusions (GCIs, Papp-Lantos bodies) that contain aggregates of α-synuclein. Current treatment options are very limited and mainly focused on symptomatic relief, whereas disease modifying options are lacking. Despite extensive testing, no neuroprotective drug treatment has been identified up to now; however, a neurorestorative approach utilizing autologous mesenchymal stem cells has shown remarkable beneficial effects in the cerebellar variant of MSA. Here, we review the progress made over the last decade in defining pathogenic targets in MSA and summarize insights gained from candidate disease-modifying interventions that have utilized a variety of well-established preclinical MSA models. We also discuss the current limitations that our field faces and suggest solutions for possible approaches in cause-directed therapies of MSA.

The proteome of the differentiating mesencephalic progenitor cell line CSM14.1 in vitro

The treatment of Parkinson's disease by transplantation of dopaminergic (DA) neurons from human embryonic mesencephalic tissue is a promising approach. However, the origin of these cells causes major problems: availability and standardization of the graft. Therefore, the generation of unlimited numbers of DA neurons from various types of stem or progenitor cells has been brought into focus. A source for DA neurons might be conditionally immortalized progenitor cells. The temperature-sensitive immortalized cell line CSM14.1 derived from the mesencephalon of an embryonic rat has been used successfully for transplantation experiments. This cell line was analyzed by unbiased stereology of cell type specific marker proteins and 2D-gel electrophoresis followed by mass spectrometry to characterize the differentially expressed proteome. Undifferentiated CSM14.1 cells only expressed the stem cell marker nestin, whereas differentiated cells expressed GFAP or NeuN and tyrosine hydroxylase. An increase of the latter cells during differentiation could be shown. By using proteomics an explanation on the protein level was found for the observed changes in cell morphology during differentiation, when CSM14.1 cells possessed the morphology of multipolar neurons. The results obtained in this study confirm the suitability of CSM14.1 cells as an in vitro model for the study of neuronal and dopaminergic differentiation in rats.

Autologous mesenchymal stem cell therapy for progressive supranuclear palsy: translation into a phase I controlled, randomized clinical study

Background

Progressive Supranuclear Palsy (PSP) is a sporadic and progressive neurodegenerative disease which belongs to the family of tauopathies and involves both cortical and subcortical structures. No effective therapy is to date available.

Methods/design

Autologous bone marrow (BM) mesenchymal stem cells (MSC) from patients affected by different type of parkinsonisms have shown their ability to improve the dopaminergic function in preclinical and clinical models. It is also possible to isolate and expand MSC from the BM of PSP patients with the same proliferation rate and immuphenotypic profile as MSC from healthy donors. BM MSC can be efficiently delivered to the affected brain regions of PSP patients where they can exert their beneficial effects through different mechanisms including the secretion of neurotrophic factors.

Here we propose a randomized, placebo-controlled, double-blind phase I clinical trial in patients affected by PSP with MSC delivered via intra-arterial injection.

Discussion

To our knowledge, this is the first clinical trial to be applied in a no-option parkinsonism that aims to test the safety and to exploit the properties of autologous mesenchymal stem cells in reducing disease progression. The study has been designed to test the safety of this “first-in-man” approach and to preliminarily explore its efficacy by excluding the placebo effect.

Trial registration

NCT01824121

Enhancement of polysialic acid expression improves function of embryonic stem-derived dopamine neuron grafts in Parkinsonian mice

There has been considerable progress in obtaining engraftable embryonic stem (ES) cell-derived midbrain dopamine neurons for cell replacement therapy in models of Parkinson's disease; however, limited integration and striatal reinnervation of ES-derived grafts remain a major challenge for future clinical translation. In this paper, we show that enhanced expression of polysialic acid results in improved graft efficiency in correcting behavioral deficits in Parkinsonian mice. This result is accompanied by two potentially relevant cellular changes: greater survival of transplanted ES-derived dopamine neurons and robust sprouting of tyrosine hydroxylase-positive processes into host tissue. Because the procedures used to enhance polysialic acid are easily translated to other cell types and species, this approach may represent a general strategy to improve graft integration in cell-based therapies.

Auto-attraction of neural precursors and their neuronal progeny impairs neuronal migration

Limited neuronal migration into host brain tissue is a key challenge in neural transplantation. We found that one important mechanism underlying this phenomenon is an intrinsic chemotactic interaction between the grafted neural precursor cells (NPCs) and their neuronal progeny. NPCs secrete the receptor tyrosine kinase ligands FGF2 and VEGF, which act as chemoattractants for neurons. Interference with these signaling pathways resulted in enhanced migration of human neurons from neural clusters.

Region-specific restoration of striatal synaptic plasticity by dopamine grafts in experimental parkinsonism

Intrastriatal transplantation of dopaminergic neurons can restore striatal dopamine levels and improve parkinsonian deficits, but the mechanisms underlying these effects are poorly understood. Here, we show that transplants of dopamine neurons partially restore activity-dependent synaptic plasticity in the host striatal neurons. We evaluated synaptic plasticity in regions distal or proximal to the transplant (i.e., dorsolateral and ventrolateral striatum) and compared the effects of dopamine- and serotonin-enriched grafts using a rat model of Parkinson disease. Naïve rats showed comparable intrinsic membrane properties in the two subregions but distinct patterns of long-term synaptic plasticity. The ventrolateral striatum showed long-term potentiation using the same protocol that elicited long-term depression in the dorsolateral striatum. The long-term potentiation was linked to higher expression of postsynaptic AMPA and N2B NMDA subunits (GluN2B) and was dependent on the activation of GluN2A and GluN2B subunits and the D1 dopamine receptor. In both regions, the synaptic plasticity was abolished after a severe dopamine depletion and could not be restored by grafted serotonergic neurons. Solely, dopamine-enriched grafts could restore the long-term potentiation and partially restore motor deficits in the rats. The restoration could only be seen close to the graft, in the ventrolateral striatum where the graft-derived reinnervation was denser, compared with the distal dorsolateral region. These data provide proof of concept that dopamine-enriched transplants are able to functionally integrate into the host brain and restore deficits in striatal synaptic plasticity after experimental parkinsonism. The region-specific restoration might impose limitations in symptomatic improvement following neural transplantation.

Engraftment of mouse embryonic stem cells differentiated by default leads to neuroprotection, behaviour revival and astrogliosis in parkinsonian rats

We report here protection against rotenone-induced behavioural dysfunction, striatal dopamine depletion and nigral neuronal loss, following intra-striatal transplantation of neurons differentiated from murine embryonic stem cells (mES). mES maintained in serum free medium exhibited increase in neuronal, and decrease in stem cell markers by 7th and 10th days as revealed by RT-PCR and immunoblot analyses. Tyrosine hydroxylase, NURR1, PITX3, LMX1b and c-RET mRNA showed a significant higher expression in differentiated cells than in mES. Dopamine level was increased by 3-fold on 10th day as compared to 7 days differentiated cells. Severity of rotenone-induced striatal dopamine loss was attenuated, and amphetamine-induced unilateral rotations were significantly reduced in animals transplanted with 7 days differentiated cells, but not in animals that received undifferentiated ES transplant. However, the ratio of contralateral to ipsilateral swings in elevated body swing test was significantly reduced in both the transplanted groups, as compared to control. Striatal grafts exhibited the presence of tyrosine hydroxylase positive cells, and the percentage of dopaminergic neurons in the substantia nigra was also found to be higher in the ipsilateral side of 7 days and mES grafted animals. Increased expression of CD11b and IBA-1, suggested a significant contribution of these microglia-derived factors in controlling the limited survival of the grafted cells. Astrocytosis in the grafted striatum, and significant increase in the levels of glial cell line derived neurotrophic factor may have contributed to the recovery observed in the hemiparkinsonian rats following transplantation.

Dopamine D2 receptor-mediated epidermal growth factor receptor transactivation through a disintegrin and metalloprotease regulates dopaminergic neuron development via extracellular signal-related kinase activation

Dopamine D2 receptor (D2R)-mediated extracellular signal-regulated kinase (ERK) activation plays an important role in the development of dopaminergic mesencephalic neurons. Here, we demonstrate that D2R induces the shedding of heparin-binding epidermal growth factor (EGF) through the activation of a disintegrin and metalloprotease (ADAM) 10 or 17, leading to EGF receptor transactivation, downstream ERK activation, and ultimately an increase in the number of dopaminergic neurons and their neurite length in primary mesencephalic cultures from wild-type mice. These outcomes, however, were not observed in cultures from D2R knock-out mice. Our findings show that D2R-mediated ERK activation regulates mesencephalic dopaminergic neuron development via EGF receptor transactivation through ADAM10/17.

The pharmacology of regenerative medicine

Regenerative medicine is a rapidly evolving multidisciplinary, translational research enterprise whose explicit purpose is to advance technologies for the repair and replacement of damaged cells, tissues, and organs. Scientific progress in the field has been steady and expectations for its robust clinical application continue to rise. The major thesis of this review is that the pharmacological sciences will contribute critically to the accelerated translational progress and clinical utility of regenerative medicine technologies. In 2007, we coined the phrase "regenerative pharmacology" to describe the enormous possibilities that could occur at the interface between pharmacology, regenerative medicine, and tissue engineering. The operational definition of regenerative pharmacology is "the application of pharmacological sciences to accelerate, optimize, and characterize (either in vitro or in vivo) the development, maturation, and function of bioengineered and regenerating tissues." As such, regenerative pharmacology seeks to cure disease through restoration of tissue/organ function. This strategy is distinct from standard pharmacotherapy, which is often limited to the amelioration of symptoms. Our goal here is to get pharmacologists more involved in this field of research by exposing them to the tools, opportunities, challenges, and interdisciplinary expertise that will be required to ensure awareness and galvanize involvement. To this end, we illustrate ways in which the pharmacological sciences can drive future innovations in regenerative medicine and tissue engineering and thus help to revolutionize the discovery of curative therapeutics. Hopefully, the broad foundational knowledge provided herein will spark sustained conversations among experts in diverse fields of scientific research to the benefit of all.

The rise of cell therapy trials for stroke: review of published and registered studies

Stroke is the second leading cause of death and the third leading cause of disability worldwide. Approximately 16 million first-ever strokes occur each year, leading to nearly 6 million deaths. Nevertheless, currently, very few therapeutic options are available. Cell therapies have been applied successfully in different hematological diseases, and are currently being investigated for treating ischemic heart disease, with promising results. Recent preclinical studies have indicated that cell therapies may provide structural and functional benefits after stroke. However, the effects of these treatments are not yet fully understood and are the subject of continuing investigation. Meanwhile, different clinical trials for stroke, the majority of them small, nonrandomized, and uncontrolled, have been reported, and their results indicate that cell therapy seems safe and feasible in these conditions. In the last 2 years, the number of published and registered trials has dramatically increased. Here, we review the main findings available in the field, with emphasis on the clinical results. Moreover, we address some of the questions that have been raised to date, to improve future studies.

Pluripotent stem cells for Parkinson's disease: progress and challenges

Parkinson's disease (PD) is a common debilitating neurodegenerative disease. The motor symptoms of PD are caused mainly by a progressive loss of dopaminergic neurons from the substania nigra, resulting in a loss of dopamine production. Current therapies are palliative and, in the long term, ineffective. In addition, some can result in significant clinical side effects. The relatively localized pathology of PD makes it an ideal candidate for cell replacement therapy. Initial efforts focused on fetal cell transplantation, and significant clinical benefit lasting more than 10 years has been reported in some cases. However, the approach is controversial and results have been inconsistent. Inherent limitations of this approach for widespread use are the limited availability and variability of transplant material. In contrast, the self-renewal and differentiation potential of human pluripotent stem cells (hPSCs) make them a promising alternative cell source for cell replacement therapy for PD. Efforts in the past decade have demonstrated that hPSCs can be induced to differentiate in culture to functional dopaminergic neurons. Studies in delivering these cells into PD animal models have demonstrated survival, engraftment, and behavioral deficit improvements. Several groups are developing these cells with clinical trials in mind. Here, we review the state of the technology and consider the suitability of current manufacturing processes, cell purity, and tumorgenicity for clinical testing.

Biodegradable microparticles for strictly regulating the release of neurotrophic factors

A lot of research has been carried out in the last decade to find a cure for neurodegenerative diseases especially Parkinson's disease but to little avail. In this study we have demonstrated the use of poly(lactic-co-glycolic acid) (PLGA)/collagen biodegradable microparticles formed using water-in-oil-in-water (W/O/W) double emulsion method, as a neurotrophic factor delivery vehicle. The microparticles were encapsulated with glial cell-derived neurotrophic factor (GDNF) fused with collagen binding peptide (CBP) immobilized to the inner collagen phase. The novelty lies in the strict regulation of release of GDNF-CBP from the microparticles as compared to a burst release from standard microparticles. The microparticles were demonstrated to be non-cytotoxic till 300 μg/2 × 10⁵ cells and revealed a maximum release of 250 ng GDNF-CBP/mg microparticles in 0.3% collagenase. Differentiation of neural progenitor cells (NPCs) into mature neurons was demonstrated by co-culturing microparticles with cells in a medium containing collagenase which enabled the release of encapsulated GDNF-CBP, signaling the differentiation of NPCs into microtubule-associated protein 2 (MAP2)-expressing neurons. The successful ability of these microparticles to deliver neurotrophic factors and allow differentiation of NPCs into mature neurons provides some scope in its use for the treatment of Parkinson's disease and other neurodegenerative diseases.

Neurogenic potential of hESC-derived human radial glia is amplified by human fetal cells

The efficient production of human neocortical neurons from human embryonic stem cells (hESC) is the primary requirement for studying early stages of human cortical development. We used hESC to obtain radial glial cells (hESC-RG) and then compared them with RG cells isolated from human fetal forebrain. Fate of hESC-RG cells critically depends on intrinsic and extrinsic factors. The expression of Pax6 (intrinsic factor) has a similar neurogenic effect on hESC-RG differentiation as reported for human fetal RG cells. Factors from the microenvironment also play a significant role in determining hESC-RG cell fate. In contrast to control cultures, wherein hESC-RG generate mainly astroglia and far fewer neurons, in co-cultures with human fetal forebrain cells, the reverse was found to be true. This neurogenic effect was partly due to soluble factors from human fetal brain cultures. The detected shift towards neurogenesis has significance for developing future efficient neuro-differentiation protocols. Importantly, we established that hESC-RG cells are similar in many respects to human fetal RG cells, including their proliferative capacity, neurogenic potential, and ability to generate various cortical neuronal sub-types. Unlike fetal RG cells, the hESC-RG cells are readily available and can be standardized, features that have considerable practical advantages in research and clinics.

Composite Brains: Toward a Systems Theory of Neural Reconstruction

The results of uncontrolled, open-label clinical trials indicate that reconstructive cellular therapies have the capacity to produce meaningful functional improvements in patients with brain disorders. However, the transplantation of fetal cells has not progressed to viable best practice treatment for any brain disorder. A conceptual approach, referred to as the Repair Model, has served as a useful heuristic for initiating research in the field and guiding the development of new practices. Analysis of evidence for the treatment of Parkinson's disease indicates that recovery following neural grafting is a complex process influenced by factors beyond the replacement of neurons. An alternative approach, the Composite Brain Model, is outlined to address limitations of the Repair Model. A hierarchical, open-system model is proposed, which aims to track the interactions between the grafted cells, the host brain, and the environment. The Composite Brain Model emphasizes the importance of the interactions between the patient, their physical and social environment, and the provision of rehabilitation during recovery. It is proposed that the Composite Brain Model is useful in providing an alternative perspective for research, theory building, and practice.

Wnt5a cooperates with canonical Wnts to generate midbrain dopaminergic neurons in vivo and in stem cells

Wnts are a family of secreted proteins that regulate multiple steps of neural development and stem cell differentiation. Two of them, Wnt1 and Wnt5a, activate distinct branches of Wnt signaling and individually regulate different aspects of midbrain dopaminergic (DA) neuron development. However, several of their functions and interactions remain to be elucidated. Here, we report that loss of Wnt1 results in loss of Lmx1a and Ngn2 expression, as well as agenesis of DA neurons in the midbrain floor plate. Remarkably, a few ectopic DA neurons still emerge in the basal plate of Wnt1(-/-) mice, where Lmx1a is ectopically expressed. These results indicate that Wnt1 orchestrates DA specification and neurogenesis in vivo. Analysis of Wnt1(-/-);Wnt5a(-/-) mice revealed a greater loss of Nurr1(+) cells and DA neurons than in single mutants, indicating that Wnt1 and Wnt5a interact genetically and cooperate to promote midbrain DA neuron development in vivo. Our results unravel a functional interaction between Wnt1 and Wnt5a resulting in enhanced DA neurogenesis. Taking advantage of these findings, we have developed an application of Wnts to improve the generation of midbrain DA neurons from neural and embryonic stem cells. We thus show that coordinated Wnt actions promote DA neuron development in vivo and in stem cells and suggest that coordinated Wnt administration can be used to improve DA differentiation of stem cells and the development of stem cell-based therapies for Parkinson's disease.

Stem cells and the treatment of Parkinson's disease

Progress in Parkinson's disease (PD) research has been hampered by the lack of an appropriate model which exhibits the core pathology seen in the human brain. Recent advances in deriving cells with neuronal phenotypes from patients with neurodegenerative disorders through cellular reprogramming offer a unique tool for disease modelling and may help shed light on the molecular pathogenesis that drives the progression of the disease. This technology may also help in establishing platforms for drug screening and open up exciting new prospects for cell grafting. In this review, we will discuss progress made in differentiating stem cells into authentic dopamine neurons and where we stand with respect to clinical trials with these cells in patients with PD. We will also examine the various approaches used in cellular reprogramming and their differentiation into patient-specific midbrain dopamine neurons, with an emphasis particularly on modelling familial cases of PD to recapitulate disease phenotypes. This review will highlight some of the challenges that need to be addressed for this technology to have any potential clinical application in cell therapy and personalised medicine.

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.

Clinical experience with stem cells and other cell therapies in neurological diseases

To overcome the limited capacity of the CNS for regeneration, the theoretical alternative would be to use stem cells for more effective management of chronic degenerative and inflammatory neurological conditions, and also of acute neuronal damage from injuries or cerebrovascular diseases. Although the adult brain contains small numbers of stem cells in restricted areas, this intrinsic stem cell repertoire is small and does not measurably contribute to functional recovery. Embryonic cells carrying pluripotent and self-renewal properties represent the stem cell prototype, but there are additional somatic stem cells that may be harvested and expanded from various tissues during adult life. Stem cell transplantation is based on the assumption that such cells may have the potential to regenerate or support the survival of the existing, partially damaged cells. This review summarizes the state-of-the-art and the clinical worldwide experience with the use of various types of stem cells in neurological diseases.

Stem cell grafting improves both motor and cognitive impairments in a genetic model of Parkinson's disease, the aphakia (ak) mouse

Stem cell-based cell replacement of lost midbrain dopamine (mDA) neurons is a potential therapy for Parkinson's disease (PD). Toward this goal, it is critical to optimize various aspects of cell transplantation and to assess functional recovery through behavioral tests in validated animal model(s) of PD. At present, cell transplantation studies are being done almost exclusively in neurotoxin-based animal models, because few genetic models of PD exhibit robust mDA neuronal loss. Here we used a genetic model of PD, the aphakia mouse, which demonstrates selective degeneration of mDA neurons in the substantia nigra. We systematically investigated the functional effects of transplanting embryonic stem cell-derived cells at different stages of in vitro differentiation: embryoid body (EB), neural progenitor (NP), and neuronal differentiated (ND) stages. We found that transplantation of NP cells yielded the best outcomes for both survival and behavioral improvement, while transplantation of EB and ND cells resulted in high teratoma-like tumor formation and poor survival, respectively. In behavioral paradigms specific to basal ganglia, the NP cells group prominently improved motor behavioral defects 1 and 2 months posttransplantation. Furthermore, we found that NP cell transplantation also improved cognitive impairments of aphakia mice, as examined by the passive avoidance task. Importantly, these graft-induced functional improvements well correlated with survival of tyrosine hydroxylase-positive DA neurons. Taken together, we propose that the aphakia mouse can serve as a novel and useful platform for cell transplantation studies to assess both neurological and cognitive improvements and that NP stage cells represent an optimal stage for transplantation.

Human placental decidua basalis-derived mesenchymal stem cells differentiate into dopamine neuron-like cells with no response to long-term culture in vitro

Human placental decidua basalis-derived mesenchymal stem cells (DBMSCs) have been identified as valuable sources for cell transplantation. In this study, we found that DBMSCs could be induced to form neural stem cells in the form of neurospheres. These neurospheres were further differentiated into dopamine neuron-like cells with a cocktail of cytokines. The differentiated DBMSCs were verified through the presence of a neuron-like morphology, the expression of specific dopamine neuron makers, and the production of dopamine. In addition, this differentiation capacity of DBMSCs was not affected by long-term culture, and the cells maintained a normal karyotype in vitro. The dopamine neuronal differentiation and the relative safety transplantation potential of DBMSCs may facilitate stem cell therapeutic approaches to Parkinson's disease.

Human midbrain precursors activate the expected developmental genetic program and differentiate long-term to functional A9 dopamine neurons in vitro. Enhancement by Bcl-X(L)

Understanding the molecular programs of the generation of human dopaminergic neurons (DAn) from their ventral mesencephalic (VM) precursors is of key importance for basic studies, progress in cell therapy, drug screening and pharmacology in the context of Parkinson's disease. The nature of human DAn precursors in vitro is poorly understood, their properties unstable, and their availability highly limited. Here we present positive evidence that human VM precursors retaining their genuine properties and long-term capacity to generate A9 type Substantia nigra human DAn (hVM1 model cell line) can be propagated in culture. During a one month differentiation, these cells activate all key genes needed to progress from pro-neural and pro-dopaminergic precursors to mature and functional DAn. For the first time, we demonstrate that gene cascades are correctly activated during differentiation, resulting in the generation of mature DAn. These DAn have morphological and functional properties undistinguishable from those generated by VM primary neuronal cultures. In addition, we have found that the forced expression of Bcl-X(L) induces an increase in the expression of key developmental genes (MSX1, NGN2), maintenance of PITX3 expression temporal profile, and also enhances genes involved in DAn long-term function, maintenance and survival (EN1, LMX1B, NURR1 and PITX3). As a result, Bcl-X(L) anticipates and enhances DAn generation.

Modular design of artificial tissue homeostasis: robust control through synthetic cellular heterogeneity

Synthetic biology efforts have largely focused on small engineered gene networks, yet understanding how to integrate multiple synthetic modules and interface them with endogenous pathways remains a challenge. Here we present the design, system integration, and analysis of several large scale synthetic gene circuits for artificial tissue homeostasis. Diabetes therapy represents a possible application for engineered homeostasis, where genetically programmed stem cells maintain a steady population of β-cells despite continuous turnover. We develop a new iterative process that incorporates modular design principles with hierarchical performance optimization targeted for environments with uncertainty and incomplete information. We employ theoretical analysis and computational simulations of multicellular reaction/diffusion models to design and understand system behavior, and find that certain features often associated with robustness (e.g., multicellular synchronization and noise attenuation) are actually detrimental for tissue homeostasis. We overcome these problems by engineering a new class of genetic modules for ‘synthetic cellular heterogeneity’ that function to generate beneficial population diversity. We design two such modules (an asynchronous genetic oscillator and a signaling throttle mechanism), demonstrate their capacity for enhancing robust control, and provide guidance for experimental implementation with various computational techniques. We found that designing modules for synthetic heterogeneity can be complex, and in general requires a framework for non-linear and multifactorial analysis. Consequently, we adapt a ‘phenotypic sensitivity analysis’ method to determine how functional module behaviors combine to achieve optimal system performance. We ultimately combine this analysis with Bayesian network inference to extract critical, causal relationships between a module's biochemical rate-constants, its high level functional behavior in isolation, and its impact on overall system performance once integrated.

Over the last decade several relatively small synthetic gene networks have been successfully implemented and characterized, including oscillators, toggle switches, and intercellular communication systems. However, the ability to engineer large-scale synthetic gene networks for controlling multicellular systems with predictable and robust behavior remains a challenge. Here we present a novel combination of computational methods to aid the iterative design and optimization of such synthetic biological systems. We apply these methods to the design and analysis of an artificial tissue homeostasis system that exhibits coordinated control of cellular proliferation, differentiation, and cell-death. Achieving artificial tissue homeostasis would be therapeutically relevant for diseases such as Type I diabetes, for instance by transplanting genetically engineered stem cells that stably maintain populations of insulin-producing beta-cells despite normal cell death and autoimmune attacks. To manage complexity in the design process, we employ principles of logic abstraction and modularity and investigate their limits in biological networks. In this work, we find factors often associated with robustness (e.g., multicellular synchronization and noise attenuation) to be actually detrimental, and overcome these problems by engineering genetic modules that generate beneficial population heterogeneity. A combination of computational methods elucidates how these modules function to enhance robust control, and provides guidance for experimental implementation.

Clinical translation of stem cells in neurodegenerative disorders

Stem cells and their derivatives show tremendous potential for treating many disorders, including neurodegenerative diseases. We discuss here the challenges and potential for the translation of stem-cell-based approaches into treatments for Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis.

Stem cells as in vitro model of Parkinson's disease

Progress in understanding neurodegenerative cell biology in Parkinson's disease (PD) has been hampered by a lack of predictive and relevant cellular models. In addition, the lack of an adequate in vitro human neuron cell-based model has been an obstacle for the uncover of new drugs for treating PD. The ability to generate induced pluripotent stem cells (iPSCs) from PD patients and a refined capacity to differentiate these iPSCs into DA neurons, the relevant disease cell type, promises a new paradigm in drug development that positions human disease pathophysiology at the core of preclinical drug discovery. Disease models derived from iPSC that manifest cellular disease phenotypes have been established for several monogenic diseases, but iPSC can likewise be used for phenotype-based drug screens in complex diseases for which the underlying genetic mechanism is unknown. Here, we highlight recent advances as well as limitations in the use of iPSC technology for modelling PD "in a dish" and for testing compounds against human disease phenotypes in vitro. We discuss how iPSCs are being exploited to illuminate disease pathophysiology, identify novel drug targets, and enhance the probability of clinical success of new drugs.

Long term behavioral effects of functional dopaminergic neurons generated from human neural stem cells in the rat 6-OH-DA Parkinson's disease model. Effects of the forced expression of BCL-X(L)

Parkinson's disease (PD) motor symptoms are caused by the progressive degeneration of ventral mesencephalic (VM) dopaminergic neurons (DAn) in the Substantia Nigra pars compacta (SNpc). Cell replacement therapy for PD is based on the concept that the implantation of DAn in the striatum can functionally restore the dopamine levels lost in the disease. In the current study we have used an immortalized human VM neural stem cell line (hVM1) that generates DAn with the A9 phenotype. We have previously found that the forced expression of Bcl-X(L) in these cells enhances DAn generation and improves, short-term, d-amphetamine-induced rotation after transplantation in the 6-OH-DA rat model of PD 2-month post-grafting. Since functional maturation of human A9 DAn in vivo requires long survival times, in the present study we investigated the behavioral amelioration induced by the transplantation of these precursors (naïve and Bcl-X(L)-modified) in the striatum of Parkinsonian rats for up to 5 months. The main findings observed are an improvement on drug-induced behaviour and importantly, in spontaneous behavior tests for both cell-transplanted groups. Finally, we have also tested whether the grafts could ameliorate cognitive performance in PD, in addition to motor deficits. Significant difference was observed for T-maze alternation test in the cell-transplanted animals as compared to sham operated ones. To our knowledge, this is the first report showing an amelioration in spontaneous motor behavior and in cognitive performance in Parkinsonian animals after receiving human VM neural stem cell grafts. Histological studies confirmed that the grafts generated mature dopaminergic cells.

[Embryonic stem cells in the treatment of severe cardiac insufficiency]

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which optimizing cardiac specification of the embryonic stem cells, purifying the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis and controlling the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a pre-requisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Chromaffin cells: the peripheral brain

Chromaffin cells probably are the most intensively studied of the neural crest derivates. They are closely related to the nervous system, share with neurons some fundamental mechanisms and thus were the ideal model to study the basic mechanisms of neurobiology for many years. The lessons we have learned from chromaffin cell biology as a peripheral model for the brain and brain diseases pertain more than ever to the cutting edge research in neurobiology. Here, we highlight how studying this cell model can help unravel the basic mechanisms of cell renewal and regeneration both in the central nervous system (CNS) and neuroendocrine tissue and also can help in designing new strategies for regenerative therapies of the CNS.

Embryonic stem cells for severe heart failure: why and how?

The experience accumulated in cardiac cell therapy suggests that regeneration of extensively necrotic myocardial areas is unlikely to be achieved by the sole paracrine effects of the grafted cells but rather requires the conversion of these cells into cardiomyocytes featuring the capacity to substitute for those which have been irreversibly lost. In this setting, the use of human pluripotent embryonic stem cells has a strong rationale. The experimental results obtained in animal models of myocardial infarction are encouraging. However, the switch to clinical applications still requires to address some critical issues, among which the optimization of the cardiac specification of the embryonic stem cells, the purification of the resulting progenitor cells so as to graft a purified population devoid from any contamination by residual pluripotent cells which carry the risk of tumorigenesis, and the control of the expected allogeneic rejection by clinically acceptable methods. If the solution to these problems is a prerequisite, the therapeutic success of this approach will also depend on the capacity to efficiently transfer the cells to the target tissue, to keep them alive once engrafted, and to allow them to spatially organize in such a way that they can contribute to the contractile function of the heart.

Intrathecal application of autologous bone marrow cell preparations in Parkinsonian syndromes

BACKGROUND

A growing number of patients is treated with intrathecal application of autologous bone marrow cells (aBMCs), but clinical data are completely lacking in movement disorders. We provide first clinical data on efficacy and safety of this highly experimental treatment approach in parkinsonian syndromes.

METHODS

Retrospective data collection from patients with parkinsonism who spontaneously sought cell treatment. The application procedure was neither recommended nor performed by the authors.

RESULTS

We report 17 patients with parkinsonian syndromes (Parkinson's disease [PD], n = 7; multiple system atrophy [MSA], n = 7; various, n = 3) who received intrathecal application of aBMCs. We did not observe any changes in motor function, activities of daily living, global clinical impression, or antiparkinsonian medication after a median observation period of 10 months. Two patients reported a worsening of parkinsonian symptoms, but the intervention was otherwise safe and well-tolerated.

CONCLUSIONS

Intrathecal application of aBMCs in uncontrolled conditions produces no clinical benefit in parkinsonian syndromes.

Cell replacement therapy for Parkinson's disease: how close are we to the clinic?

Cell replacement therapy (CRT) offers great promise as the future of regenerative medicine in Parkinson´s disease (PD). Three decades of experiments have accumulated a wealth of knowledge regarding the replacement of dying neurons by new and healthy dopaminergic neurons transplanted into the brains of animal models and affected patients. The first clinical trials provided the proof of principle for CRT in PD. In these experiments, intrastriatal transplantation of human embryonic mesencephalic tissue reinnervated the striatum, restored dopamine levels and showed motor improvements. Sequential controlled studies highlighted several problems that should be addressed prior to the wide application of CRT for PD patients. Moreover, owing to ethical and practical problems, embryonic stem cells require replacement by better-suited stem cells. Several obstacles remain to be surpassed, including identifying the best source of stem cells for A9 dopaminergic neuron generation, eliminating the risk of tumor formation and the development of graft-induced dyskinesias, and standardizing dopaminergic cell production in order to enable clinical application. In this article, we present an update on CRT for PD, reviewing the research milestones, various stem cells used and tailored differentiation methods, and analyze the information gained from the clinical trials.

Aβ-degrading enzymes: potential for treatment of Alzheimer disease

There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), insulin-degrading enzyme, and endothelin-converting enzyme reduce Aβ levels and protect against cognitive impairment in mouse models of AD. The activity of several Aβ-degrading enzymes rises with age and increases still further in AD, perhaps as a physiological response to minimize the buildup of Aβ. The age- and disease-related changes in expression of more recently recognized Aβ-degrading enzymes (e.g. NEP-2 and cathepsin B) remain to be investigated, and there is strong evidence that reduced NEP activity contributes to the development of cerebral amyloid angiopathy. Regardless of the role of Aβ-degrading enzymes in the development of AD, experimental data indicate that increasing the activity of these enzymes (NEP in particular) has therapeutic potential in AD, although targeting their delivery to the brain remains a major challenge. The most promising current approaches include the peripheral administration of agents that enhance the activity of Aβ-degrading enzymes and the direct intracerebral delivery of NEP by convection-enhanced delivery. In the longer term, genetic approaches to increasing the intracerebral expression of NEP or other Aβ-degrading enzymes may offer advantages.

Prospects for translational regenerative medicine

Translational medicine is an evolutional concept that encompasses the rapid translation of basic research for use in clinical disease diagnosis, prevention and treatment. It follows the idea "from bench to bedside and back", and hence relies on cooperation between laboratory research and clinical care. In the past decade, translational medicine has received unprecedented attention from scientists and clinicians and its fundamental principles have penetrated throughout biomedicine, offering a sign post that guides modern medical research toward a patient-centered focus. Translational regenerative medicine is still in its infancy, and significant basic research investment has not yet achieved satisfactory clinical outcomes for patients. In particular, there are many challenges associated with the use of cell- and tissue-based products for clinical therapies. This review summarizes the transformation and global progress in translational medicine over the past decade. The current obstacles and opportunities in translational regenerative medicine are outlined in the context of stem cell therapy and tissue engineering for the safe and effective regeneration of functional tissue. This review highlights the requirement for multi-disciplinary and inter-disciplinary cooperation to ensure the development of the best possible regenerative therapies within the shortest timeframe possible for the greatest patient benefit.

Contamination of mesenchymal stem-cells with fibroblasts accelerates neurodegeneration in an experimental model of Parkinson's disease

Pre-clinical studies have supported the use of mesenchymal stem cells (MSC) to treat highly prevalent neurodegenerative diseases such as Parkinson's disease (PD) but preliminary trials have reported controversial results. In a rat model of PD induced by MPTP neurotoxin, we first observed a significant bilateral preservation of dopaminergic neurons in the substantia nigra and prevention of motor deficits typically observed in PD such as hypokinesia, catalepsy, and bradykinesia, following intracerebral administration of human umbilical cord-derived MSC (UC-MSC) early after MPTP injury. However, surprisingly, administration of fibroblasts, mesenchymal cells without stem cell properties, as a xenotransplantation control was highly detrimental, causing significant neurodegeneration and motor dysfunction independently of MPTP. This observation prompted us to further investigate the consequences of transplanting a MSC preparation contaminated with fibroblasts, a plausible circumstance in cell therapy since both cell types display similar immunophenotype and can be manipulated in vitro under the same conditions. Here we show for the first time, using the same experimental model and protocol, that transplantation of UC-MSC induced potent neuroprotection in the brain resulting in clinical benefit. However, co-transplantation of UC-MSC with fibroblasts reverted therapeutic efficacy and caused opposite damaging effects, significantly exacerbating neurodegeneration and motor deficits in MPTP-exposed rats. Besides providing a rationale for testing UC-MSC transplantation in early phases of PD aiming at delaying disease progression, our pre-clinical study suggests that fibroblasts may be common cell contaminants affecting purity of MSC preparations and clinical outcome in stem cell therapy protocols, which might also explain discrepant clinical results.

Cell-based therapy for neural disorders--anticipating challenges

Neurological syndromes, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, Huntington's disease, amyotrophic lateral sclerosis, and lysosomal storage disorders, such as Battens disease, are devastating because they result in increasing loss of cognitive and physical function. Sadly, no drugs are currently available to halt their progression. The relative paucity of curative approaches for these and other conditions of the nervous system have led to a widespread evaluation of alternative treatment modalities including cell-based interventions. Several cell types have been tested successfully in animal models where safety and efficacy have been demonstrated. Early clinical trials have also been initiated in humans, and some have shown a degree of success albeit on a more limited scale than in animal experiments. Recent demonstrations that pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, can differentiate into a variety of specific neural phenotypes has stimulated worldwide enthusiasm for developing cell-based intervention of neurological disease. Indeed, several groups are preparing investigational new drug applications to treat disorders as diverse as macular degeneration, lysosomal storage diseases, and Parkinson's disease. It is noteworthy that cell replacement therapies for neurological conditions face key challenges, some of which are unique, because of the development and organization of the nervous system, its metabolism, and connectivity. Choice of the cell (or cells), the process of manufacturing them, defining the delivery pathway, developing and testing in an appropriate preclinical model, selecting a patient population, and visualizing and following or monitoring patients all pose specific issues as related to the central and peripheral nervous systems. In this review, we address a myriad of challenges that are solvable, but require careful planning and attention to the special demands of the human nervous system.

Enhancing CNS repair in neurological disease: challenges arising from neurodegeneration and rewiring of the network

Repair of the central nervous system (CNS) constitutes an integral part of treating neurological disease and plays a crucial role in restoring CNS architecture and function. Distinct strategies have been developed to reconstruct the damaged neural tissue, with many tested preclinically in animal models. We review cell replacement-based repair strategies. By taking spinal cord injury, cerebral ischaemia and degenerative CNS disorders as examples for CNS repair, we discuss progress and potential problems in utilizing embryonic stem cells and adult neural/non-neural stem cells to repair cell loss in the CNS. Nevertheless, CNS repair is not simply a matter of cell transplantation. The major challenge is to induce regenerating neural cells to integrate into the neural network and compensate for damaged neural function. The neural cells confront an environment very different from that of the developmental stage in which these cells differentiate to form interwoven networks. During the repair process, one of the challenges is neurodegeneration, which can develop from interrupted innervations to/from the targets, chronic inflammation, ischaemia, aging or idiopathic neural toxicity. Neurodegeneration, which occurs on the basis of a characteristic vascular and neural web, usually presents as a chronically progressive process with unknown aetiology. Currently, there is no effective treatment to stop or slow down neurodegeneration. Pathological changes from patients with Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis indicate a broken homeostasis in the CNS. We discuss how the blood-brain barrier and neural networks are formed to maintain CNS homeostasis and their contribution to neurodegeneration in diseased conditions. Another challenge is that some inhibitors produced by CNS injury do not facilitate the regenerating neural cells to incorporate into a pre-existing network. We review glial responses to CNS injury. Of note, the reactive astrocytes not only encompass the lesions/pathogens but may also form glial scars to impede regenerating axons from traversing the lesions. In addition, myelin debris can prevent axon growth. Myelination enables saltatory transduction of electrical impulses along axonal calibers and actually provides trophic support to stabilize the axons. Therefore, repair strategies should be designed to promote axonal growth, myelination and modulate astrocytic responses. Finally, we discuss recent progress in developing human monoclonal IgMs that regulate CNS homeostasis and promote neural regeneration.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.

Genetic therapy for the nervous system

Genetic therapy is undergoing a renaissance with expansion of viral and synthetic vectors, use of oligonucleotides (RNA and DNA) and sequence-targeted regulatory molecules, as well as genetically modified cells, including induced pluripotent stem cells from the patients themselves. Several clinical trials for neurologic syndromes appear quite promising. This review covers genetic strategies to ameliorate neurologic syndromes of different etiologies, including lysosomal storage diseases, Alzheimer's disease and other amyloidopathies, Parkinson's disease, spinal muscular atrophy, amyotrophic lateral sclerosis and brain tumors. This field has been propelled by genetic technologies, including identifying disease genes and disruptive mutations, design of genomic interacting elements to regulate transcription and splicing of specific precursor mRNAs and use of novel non-coding regulatory RNAs. These versatile new tools for manipulation of genetic elements provide the ability to tailor the mode of genetic intervention to specific aspects of a disease state.

A novel animal model of hippocampal cognitive deficits, slow neurodegeneration, and neuroregeneration

Long-term adrenalectomy (ADX) results in an extensive and specific loss of dentate gyrus granule cells in the hippocampus of adult rats. This loss of granule cells extends over a period of weeks to months and ultimately results in cognitive deficits revealed in a number of tasks that depend on intact hippocampal function. The gradual nature of ADX-induced cell death and the ensuing deficits in cognition resemble in some important respects a variety of pathological conditions in humans. Here, we characterize behavioural and cellular processes, including adult neurogenesis, in the rat ADX model. We also provide experimental evidence for a neurogenic treatment strategy by which the lost hippocampal cells may be replaced, with the goal of functional recovery in mind.

Wnt5a-dopamine D2 receptor interactions regulate dopamine neuron development via extracellular signal-regulated kinase (ERK) activation

The dopamine D2 receptor (D2R) plays an important role in mesencephalic dopaminergic neuronal development, particularly coupled with extracellular signal-regulated kinase (ERK) activation. Wnt5a protein is known to regulate the development of dopaminergic neurons. We analyzed the effect of Wnt5a on dopaminergic neuron development in mesencephalic primary cultures from wild-type (WT) and D2R knock-out (D2R(-/-)) mice. Treatment with Wnt5a increased the number and neuritic length of dopamine neurons in primary mesencephalic neuronal cultures from WT mice, but not from D2R(-/-) mice. The effect of Wnt5a was completely blocked by treatment with D2R antagonist or inhibitors of MAPK or EGFR. Wnt5a-mediated ERK activation in mesencephalic neuronal cultures was inhibited by treatment of D2R antagonist and EGFR inhibitors in WT mice. However, these regulations were not observed for D2R(-/-) mice. Co-immunoprecipitation and displacement of [(3)H]spiperone from D2R by Wnt5a demonstrated that Wnt5a could bind with D2R. This interaction was confirmed by GST pulldown assays demonstrating that the domain including transmembrane domain 4, second extracellular loop, and transmembrane domain 5 of D2R binds to Wnt5a. These results suggest that the interaction between D2R and Wnt5a has an important role in dopamine neuron development in association with EGFR and the ERK pathway.