Notch promotes neural lineage entry by pluripotent embryonic stem cells

A central challenge in embryonic stem (ES) cell biology is to understand how to impose direction on primary lineage commitment. In basal culture conditions, the majority of ES cells convert asynchronously into neural cells. However, many cells resist differentiation and others adopt nonneural fates. Mosaic activation of the neural reporter Sox-green fluorescent protein suggests regulation by cell-cell interactions. We detected expression of Notch receptors and ligands in mouse ES cells and investigated the role of this pathway. Genetic manipulation to activate Notch constitutively does not alter the stem cell phenotype. However, upon withdrawal of self-renewal stimuli, differentiation is directed rapidly and exclusively into the neural lineage. Conversely, pharmacological or genetic interference with Notch signalling suppresses the neural fate choice. Notch promotion of neural commitment requires parallel signalling through the fibroblast growth factor receptor. Stromal cells expressing Notch ligand stimulate neural specification of human ES cells, indicating that this is a conserved pathway in pluripotent stem cells. These findings define an unexpected and decisive role for Notch in ES cell fate determination. Limiting activation of endogenous Notch results in heterogeneous lineage commitment. Manipulation of Notch signalling is therefore likely to be a key factor in taking command of ES cell lineage choice.

Genetic manipulations reveal a novel role of Notch signaling in promoting and directing embryonic stem cells toward neural fates and suppressing differentiation into other lineages.

Involvement of mitochondrial complex II defects in neuronal death produced by N-terminus fragment of mutated huntingtin

Alterations of mitochondrial function may play a central role in neuronal death in Huntington's disease (HD). However, the molecular mechanisms underlying such functional deficits of mitochondria are not elucidated yet. We herein showed that the expression of two important constituents of mitochondrial complex II, the 30-kDa iron-sulfur (Ip) subunit and the 70-kDa FAD (Fp) subunit, was preferentially decreased in the striatum of HD patients compared with controls. We also examined several mitochondrial proteins in striatal neurons that were infected with lentiviral vectors coding for the N-terminus part of huntingtin (Htt) with either a pathological (Htt171-82Q) or physiological (Htt171-19Q) polyglutamine tract. Compared with Htt171-19Q, expression of Htt171-82Q preferentially decreased the levels of Ip and Fp subunits and affected the dehydrogenase activity of the complex. The Htt171-82Q-induced preferential loss of complex II was not associated with a decrease in mRNA levels, suggesting the involvement of a posttranscriptional mechanism. Importantly, the overexpression of either Ip or Fp subunit restored complex II levels and blocked mitochondrial dysfunction and striatal cell death induced by Htt171-82Q in striatal neurons. The present results strongly suggest that complex II defects in HD may be instrumental in striatal cell death.

miR-125 potentiates early neural specification of human embryonic stem cells

The role of microRNAs (miRNAs) as coordinators of stem cell fate has emerged over the last decade. We have used human embryonic stem cells to identify miRNAs involved in neural lineage commitment induced by the inhibition of TGFβ-like molecule-mediated pathways. Among several candidate miRNAs expressed in the fetal brain, the two isoforms of miR-125 alone were detected in a time window compatible with a role in neural commitment in vitro. Functional analysis indicated that miR-125 isoforms were actively involved in the promotion of pluripotent cell conversion into SOX1-positive neural precursors. miR-125 promotes neural conversion by avoiding the persistence of non-differentiated stem cells and repressing alternative fate choices. This was associated with the regulation by miR-125 of SMAD4, a key regulator of pluripotent stem cell lineage commitment. Activation of miR-125 was directly responsive to the levels of TGFβ-like molecules, placing miR-125 at the core of mechanisms that lead to the irreversible neural lineage commitment of pluripotent stem cells in response to external stimuli.

Differentiation from human pluripotent stem cells of cortical neurons of the superficial layers amenable to psychiatric disease modeling and high-throughput drug screening

Cortical neurons of the superficial layers (II-IV) represent a pivotal neuronal population involved in the higher cognitive functions of the human and are particularly affected by psychiatric diseases with developmental manifestations such as schizophrenia and autism. Differentiation protocols of human pluripotent stem cells (PSC) into cortical neurons have been achieved, opening the way to in vitro modeling of neuropsychiatric diseases. However, these protocols commonly result in the asynchronous production of neurons typical for the different layers of the cortex within an extended period of culture, thus precluding the analysis of specific subtypes of neurons in a standardized manner. Addressing this issue, we have successfully captured a stable population of self-renewing late cortical progenitors (LCPs) that synchronously and massively differentiate into glutamatergic cortical neurons of the upper layers. The short time course of differentiation into neurons of these progenitors has made them amenable to high-throughput assays. This has allowed us to analyze the capability of LCPs at differentiating into post mitotic neurons as well as extending and branching neurites in response to a collection of selected bioactive molecules. LCPs and cortical neurons of the upper layers were successfully produced from patient-derived-induced PSC, indicating that this system enables functional studies of individual-specific cortical neurons ex vivo for disease modeling and therapeutic purposes.

High sensitivity of protoplasmic cortical astroglia to focal ischemia

The generally accepted concept that astrocytes are highly resistant to hypoxic/ischemic conditions has been challenged by an increasing amount of data. Considering the differences in functional implications of protoplasmic versus fibrous astrocytes, the authors have investigated the possibility that those discrepancies come from specific behaviors of the two cell types. The reactivity and fate of protoplasmic and fibrous astrocytes were observed after permanent occlusion of the medial cerebral artery in mice. A specific loss of glial fibrillary acidic protein (GFAP) immunolabeling in protoplasmic astrocytes occurred within minutes in the area with total depletion of regional CBF (rCBF) levels, whereas "classical" astrogliosis was observed in areas with remaining rCBF. Severe disturbance of cell function, as suggested by decreased GFAP content and increased permeability of the blood-brain barrier to macromolecules, was rapidly followed by necrotic cell death, as assessed by ultrastructure and by the lack of activation of the apoptotic protease caspase-3. In contrast to the response of protoplasmic astrocytes, fibrous astrocytes located at the brain surface and in deep cortical layers displayed a transient and limited hypertrophy, with no conspicuous cell death. These results point to a differential sensitivity of protoplasmic versus fibrous cortical astrocytes to blood deprivation, with a rapid demise of the former, adding to the suggestion that protoplasmic astrocytes play a crucial role in the pathogenesis of ischemic injury.

Progressive and selective striatal degeneration in primary neuronal cultures using lentiviral vector coding for a mutant huntingtin fragment

A lentiviral vector expressing a mutant huntingtin protein (htt171-82Q) was used to generate a chronic model of Huntington's disease (HD) in rat primary striatal cultures. In this model, the majority of neurons expressed the transgene so that Western blot analysis and flow cytometry measurement could complement immunohistological evaluation. Mutant huntingtin produced a slowly progressing pathology characterized after 1 month by the appearance of neuritic aggregates followed by intranuclear inclusions, morphological anomalies of neurites, loss of neurofilament 160, increased expression in stress response protein Hsp70, and later loss of neuronal markers such as NeuN and MAP-2. At 2 months post-infection, a significant increase in TUNEL-positive cells confirmed actual striatal cell loss. Interestingly, cortical cultures infected with the same vector showed no sign of neuronal dysfunction despite accumulation of numerous inclusions. We finally examined whether the trophic factors CNTF and BDNF that were found neuroprotective in acute HD models could prevent striatal degeneration in a chronic model. Results demonstrated that both agents were neuroprotective without modifying inclusion formation. The present study demonstrates that viral vectors coding for mutant htt provides an advantageous system for histological and biochemical analysis of HD pathogenesis in primary striatal cultures.

Activation of proinflammatory caspases by cathepsin B in focal cerebral ischemia

Cathepsins and caspases are two families of proteases that play pivotal roles in ischemic cell death. This study investigated the existence of a cross-talk between cathepsin B and proinflammatory caspases in stroke-induced cell death, as recently suggested by in vitro data. Cortical ischemic damage was induced in mice by distal and permanent occlusion of the middle cerebral artery. Cytoplasmic activation of cathepsin B was observed from the early stages of infarction, and displayed an activation pattern parallel to the activation pattern of caspase-1 and -11. Immunohistochemistry revealed the colocalization of cathepsin B with each caspase in cells of the infarct core. The apical position of cathepsin B in both caspase-activation cascades was confirmed by pretreatment of the animals with the cathepsin B inhibitor CA-074, which also potently protected cortical structures from ischemic damage, indicating involvement of the proteases in the lesion process. The results show that cathepsin B release is an early event following occlusion of cerebral arteries, which eventually triggers the activation of proinflammatory caspases in the absence of reperfusion. This new pathway may play a critical role in brain infarction by promoting inflammatory responses, and/or by amplifying the apoptotic process.

Dopamine determines the vulnerability of striatal neurons to the N-terminal fragment of mutant huntingtin through the regulation of mitochondrial complex II

In neurodegenerative disorders associated with primary or secondary mitochondrial defects such as Huntington's disease (HD), cells of the striatum are particularly vulnerable to cell death, although the mechanisms by which this cell death is induced are unclear. Dopamine, found in high concentrations in the striatum, may play a role in striatal cell death. We show that in primary striatal cultures, dopamine increases the toxicity of an N-terminal fragment of mutated huntingtin (Htt-171-82Q). Mitochondrial complex II protein (mCII) levels are reduced in HD striatum, indicating that this protein may be important for dopamine-mediated striatal cell death. We found that dopamine enhances the toxicity of the selective mCII inhibitor, 3-nitropropionic acid. We also demonstrated that dopamine doses that are insufficient to produce cell loss regulate mCII expression at the mRNA, protein and catalytic activity level. We also show that dopamine-induced down-regulation of mCII levels can be blocked by several dopamine D2 receptor antagonists. Sustained overexpression of mCII subunits using lentiviral vectors abrogated the effects of dopamine, both by high dopamine concentrations alone and neuronal death induced by low dopamine concentrations together with Htt-171-82Q. This novel pathway links dopamine signaling and regulation of mCII activity and could play a key role in oxidative energy metabolism and explain the vulnerability of the striatum in neurodegenerative diseases.

Active caspase-8 translocates into the nucleus of apoptotic cells to inactivate poly(ADP-ribose) polymerase-2

Caspase-8 is the prototypic initiator of the death domain receptor pathway of apoptosis. Here, we report that caspase-8 not only triggers and amplifies the apoptotic process at cytoplasmic sites but can also act as an executioner at nuclear levels. In a murine model of acute ischemia, caspase-8 is relocated into the nucleus of apoptotic neurons, where it cleaves PARP-2, a member of the poly(ADP-ribose) polymerase family involved in DNA repair. As indicated by site-directed mutagenesis, PARP-2 cleavage occurs preferentially at the LQMD sequence mapped between the DNA binding and the catalytic domains of the protein. This is close to the cleavage sequence found in Bid, the cytoplasmic target of caspase-8. Activity assays confirm that cleavage of PARP-2 results in inactivation of its poly(ADP-ribosylation) property, proportional to the efficiency of the cleavage. Our findings add to the complexity of proteolytic caspase networks by demonstrating that caspase-8 is in turn an initiator, amplifier, and effector caspase.

Altered spinogenesis in iPSC-derived cortical neurons from patients with autism carrying de novo SHANK3 mutations

The synaptic protein SHANK3 encodes a multidomain scaffold protein expressed at the postsynaptic density of neuronal excitatory synapses. We previously identified de novo SHANK3 mutations in patients with autism spectrum disorders (ASD) and showed that SHANK3 represents one of the major genes for ASD. Here, we analyzed the pyramidal cortical neurons derived from induced pluripotent stem cells from four patients with ASD carrying SHANK3 de novo truncating mutations. At 40-45 days after the differentiation of neural stem cells, dendritic spines from pyramidal neurons presented variable morphologies: filopodia, thin, stubby and muschroom, as measured in 3D using GFP labeling and immunofluorescence. As compared to three controls, we observed a significant decrease in SHANK3 mRNA levels (less than 50% of controls) in correlation with a significant reduction in dendritic spine densities and whole spine and spine head volumes. These results, obtained through the analysis of de novo SHANK3 mutations in the patients' genomic background, provide further support for the presence of synaptic abnormalities in a subset of patients with ASD.

mTOR-dependent proliferation defect in human ES-derived neural stem cells affected by myotonic dystrophy type 1

Patients with myotonic dystrophy type 1 exhibit a diversity of symptoms that affect many different organs. Among these are cognitive dysfunctions, the origin of which has remained elusive, partly because of the difficulty in accessing neural cells. Here, we have taken advantage of pluripotent stem cell lines derived from embryos identified during a pre-implantation genetic diagnosis for mutant-gene carriers, to produce early neuronal cells. Functional characterization of these cells revealed reduced proliferative capacity and increased autophagy linked to mTOR signaling pathway alterations. Interestingly, loss of function of MBNL1, an RNA-binding protein whose function is defective in DM1 patients, resulted in alteration of mTOR signaling, whereas gain-of-function experiments rescued the phenotype. Collectively, these results provide a mechanism by which DM1 mutation might affect a major signaling pathway and highlight the pertinence of using pluripotent stem cells to study neuronal defects.

PPARγ Is Activated during Congenital Cytomegalovirus Infection and Inhibits Neuronogenesis from Human Neural Stem Cells

Congenital infection by human cytomegalovirus (HCMV) is a leading cause of permanent sequelae of the central nervous system, including sensorineural deafness, cerebral palsies or devastating neurodevelopmental abnormalities (0.1% of all births). To gain insight on the impact of HCMV on neuronal development, we used both neural stem cells from human embryonic stem cells (NSC) and brain sections from infected fetuses and investigated the outcomes of infection on Peroxisome Proliferator-Activated Receptor gamma (PPARγ), a transcription factor critical in the developing brain. We observed that HCMV infection dramatically impaired the rate of neuronogenesis and strongly increased PPARγ levels and activity. Consistent with these findings, levels of 9-hydroxyoctadecadienoic acid (9-HODE), a known PPARγ agonist, were significantly increased in infected NSCs. Likewise, exposure of uninfected NSCs to 9-HODE recapitulated the effect of infection on PPARγ activity. It also increased the rate of cells expressing the IE antigen in HCMV-infected NSCs. Further, we demonstrated that (1) pharmacological activation of ectopically expressed PPARγ was sufficient to induce impaired neuronogenesis of uninfected NSCs, (2) treatment of uninfected NSCs with 9-HODE impaired NSC differentiation and (3) treatment of HCMV-infected NSCs with the PPARγ inhibitor T0070907 restored a normal rate of differentiation. The role of PPARγ in the disease phenotype was strongly supported by the immunodetection of nuclear PPARγ in brain germinative zones of congenitally infected fetuses (N = 20), but not in control samples. Altogether, our findings reveal a key role for PPARγ in neurogenesis and in the pathophysiology of HCMV congenital infection. They also pave the way to the identification of PPARγ gene targets in the infected brain.

Congenital infection by human cytomegalovirus (HCMV) might result in permanent neurological sequelae, including sensorineural deafness, cerebral palsies or devastating neurodevelopmental abnormalities. Infants with such sequelae represent about 0.1% of all live births (>5500 per year in the USA). Given the considerable health and societal burden, a better insight on disease pathogenesis is urgently needed to design new therapeutic or prognostic tools. Here, we studied the impact of HCMV on neuronal development, using human neural progenitors (NSC) as a disease model. In particular, we investigated the outcome of infection on Peroxisome Proliferator-Activated Receptor gamma (PPARγ, a key protein in the regulation of metabolism, inflammation and cell differentiation. We disclosed that HCMV infection strongly increases levels and activity of PPARγ in NSCs. In vitro experiments showed that PPARγ activity inhibits the differentiation of NSCs into neurons. We also found increased PPARγ expression in brains of in utero infected fetuses, but not in controls, suggesting that PPARγ is a key effector of HCMV infection also in vivo. Our study provides new insights on the pathogenesis of HCMV infection and paves the way to the discovery of PPARγ-related molecules secreted in the infected brain.

Pathological modeling of TBEV infection reveals differential innate immune responses in human neurons and astrocytes that correlate with their susceptibility to infection

BACKGROUND

Tick-borne encephalitis virus (TBEV) is a member of the Flaviviridae family, Flavivirus genus, which includes several important human pathogens. It is responsible for neurological symptoms that may cause permanent disability or death, and, from a medical point of view, is the major arbovirus in Central/Northern Europe and North-Eastern Asia. TBEV tropism is critical for neuropathogenesis, yet little is known about the molecular mechanisms that govern the susceptibility of human brain cells to the virus. In this study, we sought to establish and characterize a new in vitro model of TBEV infection in the human brain and to decipher cell type-specific innate immunity and its relation to TBEV tropism and neuropathogenesis.

METHOD

Human neuronal/glial cells were differentiated from neural progenitor cells and infected with the TBEV-Hypr strain. Kinetics of infection, cellular tropism, and cellular responses, including innate immune responses, were characterized by measuring viral genome and viral titer, performing immunofluorescence, enumerating the different cellular types, and determining their rate of infection and by performing PCR array and qRT-PCR. The specific response of neurons and astrocytes was analyzed using the same approaches after enrichment of the neuronal/glial cultures for each cellular subtype.

RESULTS

We showed that infection of human neuronal/glial cells mimicked three major hallmarks of TBEV infection in the human brain, namely, preferential neuronal tropism, neuronal death, and astrogliosis. We further showed that these cells conserved their capacity to mount an antiviral response against TBEV. TBEV-infected neuronal/glial cells, therefore, represented a highly relevant pathological model. By enriching the cultures for either neurons or astrocytes, we further demonstrated qualitative and quantitative differential innate immune responses in the two cell types that correlated with their particular susceptibility to TBEV.

CONCLUSION

Our results thus reveal that cell type-specific innate immunity is likely to contribute to shaping TBEV tropism for human brain cells. They describe a new in vitro model for in-depth study of TBEV-induced neuropathogenesis and improve our understanding of the mechanisms by which neurotropic viruses target and damage human brain cells.

Molecular pathways in cerebral ischemia: cues to novel therapeutic strategies

Stroke is one of the leading causes of death and severe disability in most industrialized countries. Despite the extensive research efforts of both academic and industrial laboratories during the last few decades, no changes have been brought about by the design of neuroprotective therapies. The progressive decrease of stroke-induced death and disability is entirely attributable to improvements in the identification and reduction of risk factors. Over the past few years, experimental research has led to the emergence of a wealth of information regarding the complex and interrelated processes of neuronal degeneration and death triggered by ischemia. This unprecedented insight has led to new theories on the mechanisms of ischemic damage, and has suggested new targets and strategies for therapeutic intervention designed to reduce the clinical consequences of stroke. Among current developments, three strategies seem particularly appealing namely, the limitation of initial or secondary neuronal death by inhibition of apoptotic mechanisms, the enhancement of the endogenous capacity of nervous structures to restore lost function, and the replacement of lost cells by transplantation therapy.

The mechanisms of cell death in focal cerebral ischemia highlight neuroprotective perspectives by anti-caspase therapy

A number of studies have validated the importance of caspase activation in ischemia-induced brain damage. Caspases participate in both the initiation and execution phases of apoptosis, and play a central role in neuronal death after global cerebral ischemia. In focal ischemia, apoptosis occurs in the penumbra during the secondary phase of expansion of the lesion. However, ultrastructural and biochemical analysis have also shown signs of apoptosis in the initial lesion, or infarct core, which is traditionally considered necrotic. Specific caspase pathways are activated in the core and in the penumbra, and participate in both cytoplasmic and nuclear apoptotic events, notwithstanding their initial classification as activator or initiator caspases. This confirms previous suggestions that caspase inhibition holds tremendous neuroprotective potential in stroke and other apoptosis-related degenerative diseases. Consequently, two new approaches, aimed at treating stroke-induced brain damage by anti-apoptotic molecules, are being developed in academic and industrial laboratories. These are based, respectively, on the use of small peptide sequences corresponding to the preferred cleavage site of a caspase, and on genomic constructions derived from the fusion of endogenous anti-caspase molecules with a protein transduction domain from the human immunodeficiency virus-1. Fusion proteins containing endogenous caspases inhibitors efficiently counteract apoptosis in vitro. In in vivo models of focal cerebral ischemia, fusion proteins successfully cross the blood brain barrier and protect cells from ischemic death. This new approach by protein therapy could prove to be an interesting alternative for the reduction of the dramatic consequences of stroke, provided that the long-term efficiency of this protection in terms of functional recovery is demonstrated.

Borna disease virus phosphoprotein impairs the developmental program controlling neurogenesis and reduces human GABAergic neurogenesis

It is well established that persistent viral infection may impair cellular function of specialized cells without overt damage. This concept, when applied to neurotropic viruses, may help to understand certain neurologic and neuropsychiatric diseases. Borna disease virus (BDV) is an excellent example of a persistent virus that targets the brain, impairs neural functions without cell lysis, and ultimately results in neurobehavioral disturbances. Recently, we have shown that BDV infects human neural progenitor cells (hNPCs) and impairs neurogenesis, revealing a new mechanism by which BDV may interfere with brain function. Here, we sought to identify the viral proteins and molecular pathways that are involved. Using lentiviral vectors for expression of the bdv-p and bdv-x viral genes, we demonstrate that the phosphoprotein P, but not the X protein, diminishes human neurogenesis and, more particularly, GABAergic neurogenesis. We further reveal a decrease in pro-neuronal factors known to be involved in neuronal differentiation (ApoE, Noggin, TH and Scg10/Stathmin2), demonstrating that cellular dysfunction is associated with impairment of specific components of the molecular program that controls neurogenesis. Our findings thus provide the first evidence that a viral protein impairs GABAergic human neurogenesis, a process that is dysregulated in several neuropsychiatric disorders. They improve our understanding of the mechanisms by which a persistent virus may interfere with brain development and function in the adult.

When a virus enters the brain, it most often induces inflammation, fever, and brain injury, all signs that are indicative of acute encephalitis. Under certain conditions, however, some neurotropic viruses may cause disease in a subtler manner. The Borna disease virus (BDV) is an excellent example of this second class of viruses, as it impairs neural function without cell lysis and induces neurobehavioral disturbances. Recently, we have shown that BDV infects human neural progenitor cells (hNPCs) and impairs neurogenesis, revealing a new mechanism by which BDV may interfere with brain function. In the present study, we identify that a singled-out BDV protein called P causes similar impairment of human neurogenesis, and further show that it leads to diminution in the genesis of a particular neuronal subtype, the GABAergic neurons. We have also found that the expression of several genes involved in the generation and the maturation of neurons is dysregulated by this viral protein, which strongly suggests their implication in P-induced impairment of GABAergic neurogenesis. This study is the first to demonstrate that a viral protein interferes with human GABAergic neurogenesis, a process that is frequently impaired in neuropsychiatric disorders. It may thus contribute to elucidating the molecular bases of psychiatric disorders.

Contribution of Human Pluripotent Stem Cell-Based Models to Drug Discovery for Neurological Disorders

One of the major obstacles to the identification of therapeutic interventions for central nervous system disorders has been the difficulty in studying the step-by-step progression of diseases in neuronal networks that are amenable to drug screening. Recent advances in the field of human pluripotent stem cell (PSC) biology offers the capability to create patient-specific human neurons with defined clinical profiles using reprogramming technology, which provides unprecedented opportunities for both the investigation of pathogenic mechanisms of brain disorders and the discovery of novel therapeutic strategies via drug screening. Many examples not only of the creation of human pluripotent stem cells as models of monogenic neurological disorders, but also of more challenging cases of complex multifactorial disorders now exist. Here, we review the state-of-the art brain cell types obtainable from PSCs and amenable to compound-screening formats. We then provide examples illustrating how these models contribute to the definition of new molecular or functional targets for drug discovery and to the design of novel pharmacological approaches for rare genetic disorders, as well as frequent neurodegenerative diseases and psychiatric disorders.

Rescuing compounds for Lesch-Nyhan disease identified using stem cell-based phenotypic screening

Lesch-Nyhan disease (LND) is a rare monogenic disease caused by deficiency of the salvage pathway enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). LND is characterized by severe neuropsychiatric symptoms that currently cannot be treated. Predictive in vivo models are lacking for screening and evaluating candidate drugs because LND-associated neurological symptoms are not recapitulated in HGPRT-deficient animals. Here, we used human neural stem cells and neurons derived from induced pluripotent stem cells (iPSCs) of children affected with LND to identify neural phenotypes of interest associated with HGPRT deficiency to develop a target-agnostic-based drug screening system. We screened more than 3000 molecules and identified 6 pharmacological compounds, all possessing an adenosine moiety, that corrected HGPRT deficiency-associated neuronal phenotypes by promoting metabolism compensations in an HGPRT-independent manner. This included S-adenosylmethionine, a compound that had already been used as a compassionate approach to ease the neuropsychiatric symptoms in LND. Interestingly, these compounds compensate abnormal metabolism in a manner complementary to the gold standard allopurinol and can be provided to patients with LND via simple food supplementation. This experimental paradigm can be easily adapted to other metabolic disorders affecting normal brain development and functioning in the absence of a relevant animal model.

Human cytomegalovirus infection is associated with increased expression of the lissencephaly gene PAFAH1B1 encoding LIS1 in neural stem cells and congenitally infected brains

Congenital infection of the central nervous system by human cytomegalovirus (HCMV) is a leading cause of permanent sequelae, including mental retardation or neurodevelopmental abnormalities. The most severe complications include smooth brain or polymicrogyria, which are both indicative of abnormal migration of neural cells, although the underlying mechanisms remain to be determined. To gain better insight on the pathogenesis of such sequelae, we assessed the expression levels of a set of neurogenesis-related genes, using HCMV-infected human neural stem cells derived from embryonic stem cells (NSCs). Among the 84 genes tested, we found dramatically increased expression of the gene PAFAH1B1, encoding LIS1 (lissencephaly-1), in HCMV-infected versus uninfected NSCs. Consistent with these findings, western blotting and immunofluorescence analyses confirmed the increased levels of LIS1 in HCMV-infected NSCs at the protein level. We next assessed the migratory abilities of HCMV-infected NSCs and observed that infection strongly impaired the migration of NSCs, without detectable effect on their proliferation. Moreover, we observed increased immunostaining for LIS1 in brains of congenitally infected fetuses, but not in control samples, highlighting the clinical relevance of our findings. Of note, PAFAH1B1 mutations (resulting in either haploinsufficiency or gain of function) are primary causes of hereditary neurodevelopmental diseases. Notably, mutations resulting in PAFAH1B1 haploinsufficiency cause classic lissencephaly. Taken together, our findings suggest that PAFAH1B1 is a critical target of HCMV infection. They also shine a new light on the pathophysiological basis of the neurological outcomes of congenital HCMV infection, by suggesting that defective neural cell migration might contribute to the pathogenesis of the neurodevelopmental sequelae of infection. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Intracerebral transplantation for neurological disorders. Lessons from developmental, experimental, and clinical studies

The use of human pluripotent stem cells (PSCs) for cell therapy faces a number of challenges that are progressively answered by results from clinical trials and experimental research. Among these is the control of differentiation before transplantation and the prediction of cell fate after administration into the human brain, two aspects that condition both the safety and efficacy of the approach. For neurological disorders, this includes two steps: firstly, the identification of the optimal maturation stage for transplantation along the continuum that transforms PSCs into fully differentiated neural cell types, together with the derivation of robust protocols for large-scale production of biological products, and, secondly, the understanding of the effects of environmental cues and their possible interference with transplanted cells commitment. This review will firstly summarize our knowledge on developmental processes that have been applied to achieve robust in vitro differentiation of PSCs into neural progenitors. In a second part, we summarize results from experimental and clinical transplantation studies that help understanding the dialogue that establishes between transplanted cells and their host brain.

Pluripotent stem cells as a model to study non-coding RNAs function in human neurogenesis

As fine regulators of gene expression, non-coding RNAs, and more particularly micro-RNAs (miRNAs), have emerged as key players in the development of the nervous system. In vivo experiments manipulating miRNAs expression as neurogenesis proceeds are very challenging in the mammalian embryo and totally impossible in the human. Human pluripotent stem cells (hPSCs), from embryonic origin (hESCs) or induced from adult somatic cells (iPSCs), represent an opportunity to study the role of miRNAs in the earliest steps of human neurogenesis in both physiological and pathological contexts. Robust protocols are now available to convert pluripotent stem cells into several sub-types of fully functional neurons, recapitulating key developmental milestones along differentiation. This provides a convenient cellular system for dissecting the role of miRNAs in phenotypic transitions critical to brain development and plasticity that may be impaired in neurological diseases with onset during development. The aim of this review is to illustrate how hPSCs can be used to recapitulate early steps of human neurogenesis and summarize recent reports of their contribution to the study of the role of miRNA in regulating development of the nervous system.

Protein Kinase-A Inhibition Is Sufficient to Support Human Neural Stem Cells Self-Renewal

Human pluripotent stem cell-derived neural stem cells offer unprecedented opportunities for producing specific types of neurons for several biomedical applications. However, to achieve it, protocols of production and amplification of human neural stem cells need to be standardized, cost effective, and safe. This means that small molecules should progressively replace the use of media containing cocktails of protein-based growth factors. Here we have conducted a phenotypical screening to identify pathways involved in the regulation of hNSC self-renewal. We analyzed 80 small molecules acting as kinase inhibitors and identified compounds of the 5-isoquinolinesulfonamide family, described as protein kinase A (PKA) and protein kinase G inhibitors, as candidates to support hNSC self-renewal. Investigating the mode of action of these compounds, we found that modulation of PKA activity was central in controlling the choice between self-renewal or terminal neuronal differentiation of hNSC. We finally demonstrated that the pharmacological inhibition of PKA using the small molecule HA1004 was sufficient to support the full derivation, propagation, and long-term maintenance of stable hNSC in absence of any other extrinsic signals. Our results indicated that tuning of PKA activity is a core mechanism regulating hNSC self-renewal and differentiation and delineate the minimal culture media requirement to maintain undifferentiated hNSC in vitro.

Three-dimensional Quantification of Dendritic Spines from Pyramidal Neurons Derived from Human Induced Pluripotent Stem Cells

Dendritic spines are small protrusions that correspond to the post-synaptic compartments of excitatory synapses in the central nervous system. They are distributed along the dendrites. Their morphology is largely dependent on neuronal activity, and they are dynamic. Dendritic spines express glutamatergic receptors (AMPA and NMDA receptors) on their surface and at the levels of postsynaptic densities. Each spine allows the neuron to control its state and local activity independently. Spine morphologies have been extensively studied in glutamatergic pyramidal cells of the brain cortex, using both in vivo approaches and neuronal cultures obtained from rodent tissues. Neuropathological conditions can be associated to altered spine induction and maturation, as shown in rodent cultured neurons and one-dimensional quantitative analysis (1). The present study describes a protocol for the 3D quantitative analysis of spine morphologies using human cortical neurons derived from neural stem cells (late cortical progenitors). These cells were initially obtained from induced pluripotent stem cells. This protocol allows the analysis of spine morphologies at different culture periods, and with possible comparison between induced pluripotent stem cells obtained from control individuals with those obtained from patients with psychiatric diseases.

How do gravity alterations affect animal and human systems at a cellular/tissue level?

The present white paper concerns the indications and recommendations of the SciSpacE Science Community to make progress in filling the gaps of knowledge that prevent us from answering the question: "How Do Gravity Alterations Affect Animal and Human Systems at a Cellular/Tissue Level?" This is one of the five major scientific issues of the ESA roadmap "Biology in Space and Analogue Environments". Despite the many studies conducted so far on spaceflight adaptation mechanisms and related pathophysiological alterations observed in astronauts, we are not yet able to elaborate a synthetic integrated model of the many changes occurring at different system and functional levels. Consequently, it is difficult to develop credible models for predicting long-term consequences of human adaptation to the space environment, as well as to implement medical support plans for long-term missions and a strategy for preventing the possible health risks due to prolonged exposure to spaceflight beyond the low Earth orbit (LEO). The research activities suggested by the scientific community have the aim to overcome these problems by striving to connect biological and physiological aspects in a more holistic view of space adaptation effects.

Establishment of heterozygous and homozygous SHANK3 knockout clonal pluripotent stem cells from the parental hESC line SA001 using CRISPR/Cas9

Phelan-McDermid syndrome (PMS) is a rare genetic disease characterized by a global developmental delay with autism spectrum disorder. PMS is caused by loss of function mutations in the SHANK3 gene leading to SHANK3 protein haploinsufficiency. This study describes the generation of isogenic clones produced from one male human embryonic stem cell line with deletions in SHANK3, in a heterozygous or homozygous manner, using CRISPR/Cas9 indel methodology. Differentiation of these clones into different neuronal lineages will help understanding PMS etiology and find treatments for PMD patients. (85/100 words).