Midbrain dopaminergic development in vivo and in vitro from embryonic stem cells

Negative Symptoms of Schizophrenia and Dopaminergic Transmission: Translational Models and Perspectives Opened by iPSC Techniques

Negative symptoms (NS) represent a heterogeneous dimension of schizophrenia (SCZ), associated with a poor functional outcome. A dysregulated dopamine (DA) system, including a reduced D1 receptor activation in the prefrontal cortex, DA hypoactivity in the caudate and alterations in D3 receptor activity, seems to contribute to the pathogenesis of NS. However, failure to take into account the NS heterogeneity has slowed down progress in research on their neurobiological correlates and discoveries of new effective treatments. A better neurobiological characterization of NS is needed, and this requires objective quantification of their features that can be applied in translational models, such as animal models and human inducible pluripotent stem cells (iPSC). In this review we summarize the evidence for dopaminergic alterations relevant to NS in translational animal models focusing on dysfunctional motivation, a core aspect of NS. Among others, experiments on mutant rodents with an overexpression of DA D2 or D3 receptors and the dopamine deficient mice are discussed. In the second part we summarize the findings from recent studies using iPSC to model the pathogenesis of SCZ. By retaining the genetic background of risk genetic variants, iPSC offer the possibility to study the effect of de novo mutations or inherited polymorphisms from subgroups of patients and their response to drugs, adding an important tool for personalized psychiatry. Given the key role of DA in NS, we focus on findings of iPSC-derived DA neurons. Since implementation of iPSC-derived neurons to study the neurobiology of SCZ is a relatively recent acquisition, the available data are limited. We highlight some methodological aspects of relevance in the interpretation of in vitro testing results, including limitations and strengths, offering a critical viewpoint for the implementation of future pharmacological studies aimed to the discovery and characterization of novel treatments for NS.

Acrolein-mediated alpha-synuclein pathology involvement in the early post-injury pathogenesis of mild blast-induced Parkinsonian neurodegeneration

Survivors of blast-induced traumatic brain injury (bTBI) have increased susceptibility to Parkinson's disease (PD), characterized by α-synuclein aggregation and the progressive degeneration of nigrostriatal dopaminergic neurons. Using an established bTBI rat model, we evaluated the changes of α-synuclein and tyrosine hydroxylase (TH), known hallmarks of PD, and acrolein, a reactive aldehyde and marker of oxidative stress, with the aim of revealing key pathways leading to PD post-bTBI. Indicated in both animal models of PD and TBI, acrolein is likely a point of pathogenic convergence. Here we show that after a single mild bTBI, acrolein is elevated up to a week, systemically in urine, and in whole brain tissue, specifically the substantia nigra and striatum. Acrolein elevation is accompanied by heightened α-synuclein oligomerization, dopaminergic dysregulation, and acrolein/α-synuclein interaction in the same brain regions. We further show that acrolein can directly modify and oligomerize α-synuclein in vitro. Taken together, our data suggests acrolein likely plays an important role in inducing PD pathology following bTBI by encouraging α-synuclein aggregation. These results are expected to advance our understanding of the long-term post-bTBI pathological changes leading to the development of PD, and suggest intervention targets to curtail such pathology.

Midbrain Dopaminergic Neurons Differentiated from Human-Induced Pluripotent Stem Cells

The work with midbrain dopaminergic neurons (mDAN) differentiation might seem to be hard. There are about 40 different published protocols for mDAN differentiation, which are eventually modified according to the respective laboratory. In many cases, protocols are not fully described, failing to provide essential tips for researchers starting in the field. Considering that commercial kits produce low mDAN percentages (20-50%), we chose to follow a mix of four main protocols based on Kriks and colleagues' protocol, from which the resulting mDAN were engrafted with success in three different animal models of Parkinson's disease. We present a differential step-by-step methodology for generating mDAN directly from human-induced pluripotent stem cells cultured with E8 medium on Geltrex, without culture on primary mouse embryonic fibroblasts prior to mDAN differentiation, and subsequent exposure of neurons to rock inhibitor during passages for improving cell viability. The protocol described here allows obtaining mDAN with phenotypical and functional characteristics suitable for in vitro modeling, cell transplantation, and drug screening.

Using primary organotypic mouse midbrain cultures to examine developmental neurotoxicity of silver nanoparticles across two genetic strains

Micromass culture systems have been developed as three-dimensional organotypic in vitro alternatives to test developmental toxicity. We have optimized a murine-based embryonic midbrain micromass system in two genetic strains to evaluate neurodevelopmental effects of gold-cored silver nanoparticles (AgNPs) of differing sizes and coatings-20 nm AgCitrate, 110 nm AgCitrate, and 110 nm AgPVP. AgNPs are increasingly used in consumer, commercial, and medical products for their antimicrobial properties and observations of Ag in adult and fetal brain following in vivo exposures to AgNPs have led to concerns about the potential for AgNPs to elicit adverse effects on neurodevelopment and neurological function. Cytotoxicity was assessed at three time points of development by both nominal dose and by dosimetric dose. Ag dosimetry was assessed in cultures and the gold core component of the AgNPs was used as a tracer for determination of uptake of intact AgNPs and silver dissolution from particles in the culture system. Results by both nominal and dosimetric dose show cell death increased significantly in a dose-dependent manner at later time points (days 15 and 22 in vitro) that coincide with differentiation stages of development in both strains. When assessed by dosimetric dose, cultures were more sensitive to smaller particles, despite less uptake of Ag in smaller particles in both strains.

Stem cell transplantation therapy for multifaceted therapeutic benefits after stroke

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

Derivation of Functional Dopamine Neurons from Embryonic Stem Cells

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the selective degeneration of dopaminergic (DA) neurons in the substantia nigra of the midbrain. Pharmacological treatment of PD has been a prevailing strategy. However, it has some limitations because its effectiveness gradually decreases and side effects develop. As an alternative, cell transplantation therapy has been tried. Although transplantation of fetal ventral mesencephalic cells looks promising for the treatment of PD in some cases, ethical and technical problems in obtaining large numbers of human fetal brain tissues also lead to difficulty in its clinical application. Our recent studies showed that a high yield of DA neurons could be derived from embryonic stem (ES) cells and they efficiently induced behavioral recovery in a PD animal model. Here we summarize methods for generation of functional DA neurons from ES cells for application to PD models.

Valproic acid enhances neuronal differentiation of sympathoadrenal progenitor cells

The antiepileptic drug valproic acid (VPA) has been shown to influence the neural differentiation and neurite outgrowth of neural stem cells. Sympathoadrenal progenitor cells share properties with neural stem cells and are considered a potential cell source in the treatment of neurodegenerative diseases. The present study therefore aims at modulating the neural differentiation potential of these cells by treatment with the histone deacetylase inhibitor VPA. We studied the epigenetic effects of VPA in two culture conditions: suspension conditions aimed to expand adrenomedullary sympathoadrenal progenitors within free-floating chromospheres and adherent cell cultures optimized to derive neurons. Treatment of chromospheres with VPA may launch neuronal differentiation mechanisms and improve their neurogenic potential upon transplantation. However, also transplantation of differentiated functional neurons could be beneficial. Treating chromospheres for 7 days with clinically relevant concentrations of VPA (2 mm) revealed a decrease of neural progenitor markers Nestin, Notch2 and Sox10. Furthermore, VPA initiated catecholaminergic neuronal differentiation indicated by upregulation of the neuronal marker β-III-tubulin, the dopaminergic transcription factor Pitx3 and the catecholaminergic enzymes TH and GTPCH. In adherent neural differentiation conditions, VPA treatment improved the differentiation of sympathoadrenal progenitor cells into catecholaminergic neurons with significantly elevated levels of nor- and epinephrine. In conclusion, similar to neural stem cells, VPA launches differentiation mechanisms in sympathoadrenal progenitor cells that result in increased generation of functional neurons. Thus, data from this study will be relevant to the potential use of chromaffin progenitors in transplantation therapies of neurodegenerative diseases.

Epigenetic mechanisms in the development and maintenance of dopaminergic neurons

Mesodiencephalic dopaminergic (mdDA) neurons are located in the ventral mesodiencephalon and are involved in psychiatric disorders and severely affected in neurodegenerative diseases such as Parkinson's disease. mdDA neuronal development has received much attention in the last 15 years and many transcription factors involved in mdDA specification have been discovered. More recently however, the impact of epigenetic regulation has come into focus, and it's emerging that the processes of histone modification and DNA methylation form the basis of genetic switches that operate during mdDA development. Here, we review the epigenetic control of mdDA development, maturation and maintenance. As we highlight, epigenetic mechanisms play a pivotal role in all of these processes and the knowledge gathered from studying epigenetics in these contexts may aid our understanding of mdDA-related pathologies.

Immortalization of neuronal progenitors using SV40 large T antigen and differentiation towards dopaminergic neurons

Transplantation is common in clinical practice where there is availability of the tissue and organ. In the case of neurodegenerative disease such as Parkinson's disease (PD), transplantation is not possible as a result of the non-availability of tissue or organ and therefore, cell therapy is an innovation in clinical practice. However, the availability of neuronal cells for transplantation is very limited. Alternatively, immortalized neuronal progenitors could be used in treating PD. The neuronal progenitor cells can be differentiated into dopaminergic phenotype. Here in this article, the current understanding of the molecular mechanisms involved in the differentiation of dopaminergic phenotype from the neuronal progenitors immortalized with SV40 LT antigen is discussed. In addition, the methods of generating dopaminergic neurons from progenitor cells and the factors that govern their differentiation are elaborated. Recent advances in cell-therapy based transplantation in PD patients and future prospects are discussed.

Spatial and temporal lineage analysis of a Pitx3-driven Cre-recombinase knock-in mouse model

Development and function of mesodiencephalic dopaminergic (mdDA) neurons has received a lot of scientific interest since these neurons are critically involved in neurological diseases as Parkinson and psychiatric diseases as schizophrenia, depression and attention deficit hyperactivity disorder (ADHD). The understanding of the molecular processes that lead to normal development and function of mdDA neurons has provided insight in the pathology and provided critical information on new treatment paradigms. In order to be able to study specific genetic ablation in mdDA neurons a new tools was developed that drives Cre-recombinase under the control of the Pitx3 locus. The Pitx3 gene is well known for its specific expression in mdDA neurons and is present at the onset of terminal differentiation. Analysis of newly generated Pitx3-Cre knock-in mice shows that Cre expression, measured through the activation of eYfp by removal of a "Stop" signal (LoxP-Stop-LoxP-eYfp reporter mouse), is present at the onset of terminal differentiation and mimics closely the native Pitx3 expression domain. In conclusion, we present here a new Cre-driver mouse model to be used in the restricted ablation of interesting genes in mdDA neurons in order to improve our understanding of the underlying molecular programming.

Toward a neurobiology of delusions

Delusions are the false and often incorrigible beliefs that can cause severe suffering in mental illness. We cannot yet explain them in terms of underlying neurobiological abnormalities. However, by drawing on recent advances in the biological, computational and psychological processes of reinforcement learning, memory, and perception it may be feasible to account for delusions in terms of cognition and brain function. The account focuses on a particular parameter, prediction error--the mismatch between expectation and experience--that provides a computational mechanism common to cortical hierarchies, fronto-striatal circuits and the amygdala as well as parietal cortices. We suggest that delusions result from aberrations in how brain circuits specify hierarchical predictions, and how they compute and respond to prediction errors. Defects in these fundamental brain mechanisms can vitiate perception, memory, bodily agency and social learning such that individuals with delusions experience an internal and external world that healthy individuals would find difficult to comprehend. The present model attempts to provide a framework through which we can build a mechanistic and translational understanding of these puzzling symptoms.

Human embryonic stem cell differentiation toward regional specific neural precursors

Human embryonic stem cells (hESCs) are self-renewing pluripotent cells that have the capacity to differentiate into a wide variety of cell types. This potentiality represents a promising source to overcome many human diseases by providing an unlimited supply of all cell types, including cells with neural characteristics. Therefore, this review summarizes early neural development and the potential of hESCs to differentiate under in vitro conditions, examining at the same time the potential use of differentiated hESCs for therapeutic applications for neural tissue and cell regeneration.

Molecular and cellular determinants for generating ES-cell derived dopamine neurons for cell therapy

Embryonic stem (ES) cells can generate midbrain dopaminergic (DA) neuronal phenotypes in vitro and have been successfully applied to restore function in animal models of Parkinson's disease (PD). How can we best integrate our growinginsight into the regulatory cascade of transcription factors guiding midbrain specification to further improve the in vitro differentiation of midbrain DA neurons for cell therapy of PD? To characterize the differentiation of authentic DA neurons in vitro, expression patterns of the numerous midbrain-characteristic markers need to be investigated. When using forced gene expression, such factors have to be closely monitored to avoid generation of nonphysiological cell types. Fluorescent markers such as Pitx3-GFP, TH-GFP, Sox1-GFP or surface antigens have proven useful for elimination of unwanted cell types by cell sorting, thereby averting tumors and increasing the DA fraction for transplantation studies. The importance of appropriate timing during application of extrinsic factors and the influence of cell-cell interactions in the dish has to be taken into account. This conceptual synopsis outlines current objectives, progress, but also challenges, in deriving midbrain DA neurons from pluripotent stem cells for clinical and scientific applications.

Estrogen and the development and protection of nigrostriatal dopaminergic neurons: concerted action of a multitude of signals, protective molecules, and growth factors

The nigrostriatal dopamine system comprises the dopaminergic neurons located in the ventral midbrain, their axonal connections to the forebrain, and their direct cellular target cells in the striatal complex, i.e. GABAergic neurons. The major function of the nigrostriatal dopaminergic unit is the coordination and fine tuning of motor functions at the extrapyramidal level. Numerous biologically active factors including different types of growth factors (neurotrophins, members of the TGFbeta family, IGFs) and peptide/steroid hormones have been identified in the past to be implicated in the regulation of developmental aspects of this neural system. Some of these developmentally active determinants have in addition been found to play a crucial role in the mediation of neuroprotection concerning dopaminergic neurons. Estrogen was identified as such a compound interfering with embryonic neuronal differentiation and cell survival. The physiological mechanisms underlying these effects are very complex and include interactions with other developmental signals (growth factors), inflammatory processes as well as apoptotic events, but also require the activation of nonneuronal cells such as astrocytes. It appears that estrogen is assuming control over or at least influences a multitude of developmental and protective cellular mechanisms rather than taking over the part of a singular protagonist.