Quantitative high-throughput gene expression profiling of human striatal development to screen stem cell-derived medium spiny neurons

Transplanted human neural stem cells rescue phenotypes in zQ175 Huntington's disease mice and innervate the striatum

Huntington's disease (HD), a genetic neurodegenerative disorder, primarily affects the striatum and cortex with progressive loss of medium-sized spiny neurons (MSNs) and pyramidal neurons, disrupting cortico-striatal circuitry. A promising regenerative therapeutic strategy of transplanting human neural stem cells (hNSCs) is challenged by the need for long-term functional integration. We previously described that, with short-term hNSC transplantation into the striatum of HD R6/2 mice, human cells differentiated into electrophysiologically active immature neurons, improving behavior and biochemical deficits. Here, we show that long-term (8 months) implantation of hNSCs into the striatum of HD zQ175 mice ameliorates behavioral deficits, increases brain-derived neurotrophic factor (BDNF) levels, and reduces mutant huntingtin (mHTT) accumulation. Patch clamp recordings, immunohistochemistry, single-nucleus RNA sequencing (RNA-seq), and electron microscopy demonstrate that hNSCs differentiate into diverse neuronal populations, including MSN- and interneuron-like cells, and form connections. Single-nucleus RNA-seq analysis also shows restoration of several mHTT-mediated transcriptional changes of endogenous striatal HD mouse cells. Remarkably, engrafted cells receive synaptic inputs, innervate host neurons, and improve membrane and synaptic properties. Overall, the findings support hNSC transplantation for further evaluation and clinical development for HD.

Understanding and modeling regional specification of the human ganglionic eminence

Inhibitory neurons originating from the ventral forebrain are associated with several neurological conditions. Distinct ventral forebrain subpopulations are generated from topographically defined zones; lateral-, medial- and caudal ganglionic eminences (LGE, MGE and CGE), yet key specification factors often span across developing zones contributing to difficulty in defining unique LGE, MGE or CGE profiles. Here we use human pluripotent stem cell (hPSC) reporter lines (NKX2.1-GFP and MEIS2-mCherry) and manipulation of morphogen gradients to gain greater insight into regional specification of these distinct zones. We identified Sonic hedgehog (SHH)-WNT crosstalk in regulating LGE and MGE fate and uncovered a role for retinoic acid signaling in CGE development. Unraveling the influence of these signaling pathways permitted development of fully defined protocols that favored generation of the three GE domains. These findings provide insight into the context-dependent role of morphogens in human GE specification and are of value for in vitro disease modeling and advancement of new therapies.

Amplification of the PLAG-family genes-PLAGL1 and PLAGL2-is a key feature of the novel tumor type CNS embryonal tumor with PLAGL amplification

Pediatric central nervous system (CNS) tumors represent the most common cause of cancer-related death in children aged 0-14 years. They differ from their adult counterparts, showing extensive clinical and molecular heterogeneity as well as a challenging histopathological spectrum that often impairs accurate diagnosis. Here, we use DNA methylation-based CNS tumor classification in combination with copy number, RNA-seq, and ChIP-seq analysis to characterize a newly identified CNS tumor type. In addition, we report histology, patient characteristics, and survival data in this tumor type. We describe a biologically distinct pediatric CNS tumor type (n = 31 cases) that is characterized by focal high-level amplification and resultant overexpression of either PLAGL1 or PLAGL2, and an absence of recurrent genetic alterations characteristic of other pediatric CNS tumor types. Both genes act as transcription factors for a regulatory subset of imprinted genes (IGs), components of the Wnt/β-Catenin pathway, and the potential drug targets RET and CYP2W1, which are also specifically overexpressed in this tumor type. A derived PLAGL-specific gene expression signature indicates dysregulation of imprinting control and differentiation/development. These tumors occurred throughout the neuroaxis including the cerebral hemispheres, cerebellum, and brainstem, and were predominantly composed of primitive embryonal-like cells lacking robust expression of markers of glial or neuronal differentiation (e.g., GFAP, OLIG2, and synaptophysin). Tumors with PLAGL1 amplification were typically diagnosed during adolescence (median age 10.5 years), whereas those with PLAGL2 amplification were diagnosed during early childhood (median age 2 years). The 10-year overall survival was 66% for PLAGL1-amplified tumors, 25% for PLAGL2-amplified tumors, 18% for male patients, and 82% for female patients. In summary, we describe a new type of biologically distinct CNS tumor characterized by PLAGL1/2 amplification that occurs predominantly in infants and toddlers (PLAGL2) or adolescents (PLAGL1) which we consider best classified as a CNS embryonal tumor and which is associated with intermediate survival. The cell of origin and optimal treatment strategies remain to be defined.

Human Pluripotent Stem Cell-Derived Medium Spiny Neuron-like Cells Exhibit Gene Desensitization

Gene desensitization in response to a repeated stimulus is a complex phenotype important across homeostatic and disease processes, including addiction, learning, and memory. These complex phenotypes are being characterized and connected to important physiologically relevant functions in rodent systems but are difficult to capture in human models where even acute responses to important neurotransmitters are understudied. Here through transcriptomic analysis, we map the dynamic responses of human stem cell-derived medium spiny neuron-like cells (hMSN-like cells) to dopamine. Furthermore, we show that these human neurons can reflect and capture cellular desensitization to chronic versus acute administration of dopamine. These human cells are further able to capture complex receptor crosstalk in response to the pharmacological perturbations of distinct dopamine receptor subtypes. This study demonstrates the potential utility and remaining challenges of using human stem cell-derived neurons to capture and study the complex dynamic mechanisms of the brain.

Do foetal transplant studies continue to be justified in Huntington's disease?

Early CNS transplantation studies used foetal derived cell products to provide a foundation of evidence for functional recovery in preclinical studies and early clinical trials. However, it was soon recognised that the practical limitations of foetal tissue make it unsuitable for widespread clinical use. Considerable effort has since been directed towards producing target cell phenotypes from pluripotent stem cells (PSCs) instead, and there now exist several publications detailing the differentiation and characterisation of PSC-derived products relevant for transplantation in Huntington's disease (HD). In light of this progress, we ask if foetal tissue transplantation continues to be justified in HD research. We argue that (i) the extent to which accurately differentiated target cells can presently be produced from PSCs is still unclear, currently making them undesirable for studying wider CNS transplantation issues; (ii) foetal derived cells remain a valuable tool in preclinical research for advancing our understanding of which products produce functional striatal grafts and as a reference to further improve PSC-derived products; and (iii) until PSC-derived products are ready for human trials, it is important to continue using foetal cells to gather clinical evidence that transplantation is a viable option in HD and to use this opportunity to optimise practical parameters (such as trial design, clinical practices, and delivery strategies) to pave the way for future PSC-derived products.

Generation of striatal neurons from human induced pluripotent stem cells by controlling extrinsic signals with small molecules

Human induced pluripotent stem cells (hiPSCs) are powerful tools for modeling human brain development and treating neurodegenerative diseases. Here we established a robust protocol with high scalability for generating striatal medium spiny neurons (MSNs) from hiPSCs using small molecules under two- and three-dimensional culture conditions. Using this protocol, GSH2⁺ lateral ganglionic eminence (LGE) progenitors were generated in two-dimensional culture by Sonic hedgehog signaling activation using purmorphamine, WNT signaling inhibition using XAV939, and dual-SMAD inhibition using LDN193189 and A83-01. Quantitative PCR analysis revealed sequential expression of LGE and striatal genes during differentiation. These LGE progenitors subsequently gave rise to DARPP32⁺ MSNs exhibiting spontaneous and evoked monophasic spiking activity. Applying this protocol in three-dimensional culture, we generated striatal neurospheres with gene expression profiles and cell layer organization resembling that of the developing striatum, including distinct ventricular and subventricular zones and DARPP32⁺ neurons at the surface. This protocol provides a useful experimental model for studying striatal development and yields cells potentially applicable for regenerative medicine to treat striatum-related disorders such as Huntington's disease.

Dynamic and Cell-Specific DACH1 Expression in Human Neocortical and Striatal Development

DACH1 is the human homolog of the Drosophila dachshund gene, which is involved in the development of the eye, nervous system, and limbs in the fly. Here, we systematically investigate DACH1 expression patterns during human neurodevelopment, from 5 to 21 postconceptional weeks. By immunodetection analysis, we found that DACH1 is highly expressed in the proliferating neuroprogenitors of the developing cortical ventricular and subventricular regions, while it is absent in the more differentiated cortical plate. Single-cell global transcriptional analysis revealed that DACH1 is specifically enriched in neuroepithelial and ventricular radial glia cells of the developing human neocortex. Moreover, we describe a previously unreported DACH1 expression in the human striatum, in particular in the striatal medium spiny neurons. This finding qualifies DACH1 as a new striatal projection neuron marker, together with PPP1R1B, BCL11B, and EBF1. We finally compared DACH1 expression profile in human and mouse forebrain, where we observed spatio-temporal similarities in its expression pattern thus providing a precise developmental description of DACH1 in the 2 mammalian species.

Human Pluripotent Stem Cell-Derived Neurons Are Functionally Mature In Vitro and Integrate into the Mouse Striatum Following Transplantation

Human pluripotent stem cells (hPSCs) are a powerful tool for modelling human development. In recent years, hPSCs have become central in cell-based therapies for neurodegenerative diseases given their potential to replace affected neurons. However, directing hPSCs into specific neuronal types is complex and requires an accurate protocol that mimics endogenous neuronal development. Here we describe step-by-step a fast feeder-free neuronal differentiation protocol to direct hPSCs to mature forebrain neurons in 37 days in vitro (DIV). The protocol is based upon a combination of specific morphogens, trophic and growth factors, ions, neurotransmitters and extracellular matrix elements. A human-induced PSC line (Ctr-Q33) and a human embryonic stem cell line (GEN-Q18) were used to reinforce the potential of the protocol. Neuronal activity was analysed by single-cell calcium imaging. At 8 DIV, we obtained a homogeneous population of hPSC-derived neuroectodermal progenitors which self-arranged in bi-dimensional neural tube-like structures. At 16 DIV, we generated hPSC-derived neural progenitor cells (NPCs) with mostly a subpallial identity along with a subpopulation of pallial NPCs. Terminal in vitro neuronal differentiation was confirmed by the expression of microtubule associated protein 2b (Map 2b) by almost 100% of hPSC-derived neurons and the expression of specific-striatal neuronal markers including GABA, CTIP2 and DARPP-32. HPSC-derived neurons showed mature and functional phenotypes as they expressed synaptic markers, voltage-gated ion channels and neurotransmitter receptors. Neurons displayed diverse spontaneous activity patterns that were classified into three major groups, namely “high”, “intermediate” and “low” firing neurons. Finally, transplantation experiments showed that the NPCs survived and differentiated within mouse striatum for at least 3 months. NPCs integrated host environmental cues and differentiated into striatal medium-sized spiny neurons (MSNs), which successfully integrated into the endogenous circuitry without teratoma formation. Altogether, these findings demonstrate the potential of this robust human neuronal differentiation protocol, which will bring new opportunities for the study of human neurodevelopment and neurodegeneration, and will open new avenues in cell-based therapies, pharmacological studies and alternative in vitro toxicology.

Derivation of Neural Stem Cells from the Developing and Adult Human Brain

Neural stem cells isolated from the developing and adult brain are an ideal source of cells for use in clinical applications such as cell replacement therapy. The clear advantage of these cells over the more commonly utilised embryonic and pluripotent stem cells is that they are already neurally committed. Of particular importance is the fact that these cells don't require the same level of in vitro culture that can be cost and labour intensive. Foetal neural stem cells can be readily derived from the foetal brain and expand in culture over time. Similarly, adult stem cells have been explored for their potential in vitro and in vivo animal models. In this chapter we identify the progress made in developing these cells as well as the advantages of taking them forward for clinical use.

Dissection and Preparation of Human Primary Fetal Ganglionic Eminence Tissue for Research and Clinical Applications

Here, we describe detailed dissection and enzymatic dissociation protocols for the ganglionic eminences from the developing human brain to generate viable quasi-single cell suspensions for subsequent use in transplantation or cell culture. These reliable and reproducible protocols can provide tissue for use in the study of the developing human brain, as well as for the preparation of donor cells for transplantation in Huntington's disease (HD). For use in the clinic as a therapy for HD, the translation of these protocols from the research laboratory to the GMP suite is described, including modification to reagents used and appropriate monitoring and tissue release criteria.

Highly Expandable Human iPS Cell-Derived Neural Progenitor Cells (NPC) and Neurons for Central Nervous System Disease Modeling and High-Throughput Screening

Reprogramming of human somatic cells into induced pluripotent stem (iPS) cells has greatly expanded the set of research tools available to investigate the molecular and cellular mechanisms underlying central nervous system (CNS) disorders. Realizing the promise of iPS cell technology for the identification of novel therapeutic targets and for high-throughput drug screening requires implementation of methods for the large-scale production of defined CNS cell types. Here we describe a protocol for generating stable, highly expandable, iPS cell-derived CNS neural progenitor cells (NPC) using multi-dimensional fluorescence activated cell sorting (FACS) to purify NPC defined by cell surface markers. In addition, we describe a rapid, efficient, and reproducible method for generating excitatory cortical-like neurons from these NPC through inducible expression of the pro-neural transcription factor Neurogenin 2 (iNgn2-NPC). Finally, we describe methodology for the use of iNgn2-NPC for probing human neuroplasticity and mechanisms underlying CNS disorders using high-content, single-cell-level automated microscopy assays. © 2017 by John Wiley & Sons, Inc.

Human t-DARPP is induced during striatal development

Human Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32kDa (DARPP-32, also known as PPP1R1B) gene codes for different transcripts that are mainly translated into two DARPP-32 protein isoforms, full length (fl)-DARPP-32 and truncated (t)-DARPP. The t-DARPP lacks the first 36 residues at the N-terminal, which alters its function. In the central nervous system, fl-DARPP-32 is highly expressed in GABAergic striatal medium spiny neurons (MSNs), where it integrates dopaminergic and glutamatergic input signaling. However, no information about human DARPP-32 isoform expression during MSNs maturation is available. In this study, our aim is to determine the expression of the two DARPP-32 isoforms in human fetal and adult striatal samples. We show that DARPP-32 isoform expression is differentially regulated during human striatal development, with the t-DARPP isoform being virtually absent from whole ganglionic eminence (WGE) and highly induced in the adult striatum (in both caudate and putamen). We next compared the four most common anti-DARPP-32 antibodies used in human specimens, to study their recognition of the two isoforms in fetal and adult human striatal samples by western blot and immunohistochemistry. The four antibodies specifically identify the fl-DARPP-32 in both fetal and adult samples, while t-DARPP form was only detected in adult striatal samples. In addition, the lack of t-DARPP recognition in human adult striatum by the antibody generated against the full-length domain produces in turn different efficacy by immunohistochemical analysis. In conclusion, our results show that expression of human DARPP-32 protein isoforms depends on the striatal neurodevelopmental stage with t-DARPP being specific for the human adult striatum.