Transcription factor induction of human oligodendrocyte progenitor fate and differentiation

Identity and Maturity of iPSC-Derived Oligodendrocytes in 2D and Organoid Systems

Oligodendrocytes originating in the brain and spinal cord as well as in the ventral and dorsal domains of the neural tube are transcriptomically and functionally distinct. These distinctions are also reflected in the ultrastructure of the produced myelin, and the susceptibility to myelin-related disorders, which highlights the significance of the choice of patterning protocols in the differentiation of induced pluripotent stem cells (iPSCs) into oligodendrocytes. Thus, our first goal was to survey the different approaches applied to the generation of iPSC-derived oligodendrocytes in 2D culture and in organoids, as well as reflect on how these approaches pertain to the regional and spatial fate of the generated oligodendrocyte progenitors and myelinating oligodendrocytes. This knowledge is increasingly important to disease modeling and future therapeutic strategies. Our second goal was to recap the recent advances in the development of oligodendrocyte-enriched organoids, as we explore their relevance to a regional specification alongside their duration, complexity, and maturation stages of oligodendrocytes and myelin biology. Finally, we discuss the shortcomings of the existing protocols and potential future explorations.

Stalled oligodendrocyte differentiation in IDH-mutant gliomas

BACKGROUND

Roughly 50% of adult gliomas harbor isocitrate dehydrogenase (IDH) mutations. According to the 2021 WHO classification guideline, these gliomas are diagnosed as astrocytomas, harboring no 1p19q co-deletion, or oligodendrogliomas, harboring 1p19q co-deletion. Recent studies report that IDH-mutant gliomas share a common developmental hierarchy. However, the neural lineages and differentiation stages in IDH-mutant gliomas remain inadequately characterized.

METHODS

Using bulk transcriptomes and single-cell transcriptomes, we identified genes enriched in IDH-mutant gliomas with or without 1p19q co-deletion, we also assessed the expression pattern of stage-specific signatures and key regulators of oligodendrocyte lineage differentiation. We compared the expression of oligodendrocyte lineage stage-specific markers between quiescent and proliferating malignant single cells. The gene expression profiles were validated using RNAscope analysis and myelin staining and were further substantiated using data of DNA methylation and single-cell ATAC-seq. As a control, we assessed the expression pattern of astrocyte lineage markers.

RESULTS

Genes concordantly enriched in both subtypes of IDH-mutant gliomas are upregulated in oligodendrocyte progenitor cells (OPC). Signatures of early stages of oligodendrocyte lineage and key regulators of OPC specification and maintenance are enriched in all IDH-mutant gliomas. In contrast, signature of myelin-forming oligodendrocytes, myelination regulators, and myelin components are significantly down-regulated or absent in IDH-mutant gliomas. Further, single-cell transcriptomes of IDH-mutant gliomas are similar to OPC and differentiation-committed oligodendrocyte progenitors, but not to myelinating oligodendrocyte. Most IDH-mutant glioma cells are quiescent; quiescent cells and proliferating cells resemble the same differentiation stage of oligodendrocyte lineage. Mirroring the gene expression profiles along the oligodendrocyte lineage, analyses of DNA methylation and single-cell ATAC-seq data demonstrate that genes of myelination regulators and myelin components are hypermethylated and show inaccessible chromatin status, whereas regulators of OPC specification and maintenance are hypomethylated and show open chromatin status. Markers of astrocyte precursors are not enriched in IDH-mutant gliomas.

CONCLUSIONS

Our studies show that despite differences in clinical manifestation and genomic alterations, all IDH-mutant gliomas resemble early stages of oligodendrocyte lineage and are stalled in oligodendrocyte differentiation due to blocked myelination program. These findings provide a framework to accommodate biological features and therapy development for IDH-mutant gliomas.

Transcriptional networks of transient cell states during human prefrontal cortex development

The human brain is divided into various anatomical regions that control and coordinate unique functions. The prefrontal cortex (PFC) is a large brain region that comprises a range of neuronal and non-neuronal cell types, sharing extensive interconnections with subcortical areas, and plays a critical role in cognition and memory. A timely appearance of distinct cell types through embryonic development is crucial for an anatomically perfect and functional brain. Direct tracing of cell fate development in the human brain is not possible, but single-cell transcriptome sequencing (scRNA-seq) datasets provide the opportunity to dissect cellular heterogeneity and its molecular regulators. Here, using scRNA-seq data of human PFC from fetal stages, we elucidate distinct transient cell states during PFC development and their underlying gene regulatory circuitry. We further identified that distinct intermediate cell states consist of specific gene regulatory modules essential to reach terminal fate using discrete developmental paths. Moreover, using in silico gene knock-out and over-expression analysis, we validated crucial gene regulatory components during the lineage specification of oligodendrocyte progenitor cells. Our study illustrates unique intermediate states and specific gene interaction networks that warrant further investigation for their functional contribution to typical brain development and discusses how this knowledge can be harvested for therapeutic intervention in challenging neurodevelopmental disorders.

Rapid differentiation of hiPSCs into functional oligodendrocytes using an OLIG2 synthetic modified messenger RNA

Transcription factors (TFs) have been introduced to drive the highly efficient differentiation of human-induced pluripotent stem cells (hiPSCs) into lineage-specific oligodendrocytes (OLs). However, effective strategies currently rely mainly on genome-integrating viruses. Here we show that a synthetic modified messenger RNA (smRNA)-based reprogramming method that leads to the generation of transgene-free OLs has been developed. An smRNA encoding a modified form of OLIG2, in which the serine 147 phosphorylation site is replaced with alanine, OLIG2^S147A, is designed to reprogram hiPSCs into OLs. We demonstrate that repeated administration of the smRNA encoding OLIG2^S147A lead to higher and more stable protein expression. Using the single-mutant OLIG2 smRNA morphogen, we establish a 6-day smRNA transfection protocol, and glial induction lead to rapid NG2⁺ OL progenitor cell (OPC) generation (>70% purity) from hiPSC. The smRNA-induced NG2⁺ OPCs can mature into functional OLs in vitro and promote remyelination in vivo. Taken together, we present a safe and efficient smRNA-driven strategy for hiPSC differentiation into OLs, which may be utilized for therapeutic OPC/OL transplantation in patients with neurodegenerative disease.

The use of synthetic modified messenger RNA (smRNA) allows for the differentiation of human-induced pluripotent stem cells (hiPSCs) into lineage-specific oligodendrocytes.

Comprehensive Bioinformatics Analysis Combined with Wet-Lab Experiments to Find Target Proteins of Chinese Medicine Monomer

How to use bioinformatics methods to quickly and accurately locate the effective targets of traditional Chinese medicine monomer (TCM) is still an urgent problem needing to be solved. Here, we used high-throughput sequencing to identify the genes that were up-regulated after cells were treated with TCM monomers and used bioinformatics methods to analyze which transcription factors activated these genes. Then, the binding proteins of these transcription factors were analyzed and cross-analyzed with the docking proteins predicted by small molecule reverse docking software to quickly and accurately determine the monomer’s targets. Followeding this method, we predicted that the TCM monomer Daphnoretin (DT) directly binds to JAK2 with a binding energy of −5.43 kcal/mol, and activates the JAK2/STAT3 signaling transduction pathway. Subsequent Western blotting and in vitro binding and kinase experiments further validated our bioinformatics predictions. Our method provides a new approach for quickly and accurately locating the effective targets of TCM monomers, and we also have discovered for the first time that TCM monomer DT is an agonist of JAK2.

The regenerative potential of glial progenitor cells and reactive astrocytes in CNS injuries

Cell therapeutic approaches focusing on the regeneration of damaged tissue have been a popular topic among researchers in recent years. In particular, self-repair scarring from the central nervous system (CNS) can significantly complicate the treatment of an injured patient. In CNS regeneration schemes, either glial progenitor cells or reactive glial cells have key roles to play. In this review, the contribution and underlying mechanisms of these progenitor/reactive glial cells during CNS regeneration are discussed, as well as their role in CNS-related diseases.

Direct Conversion to Achieve Glial Cell Fates: Oligodendrocytes and Schwann Cells

Glia have been known for its pivotal roles in physiological and pathological conditions in the nervous system. To study glial biology, multiple approaches have been applied to utilize glial cells for research, including stem cell-based technologies. Human glial cells differentiated from pluripotent stem cells are now available, allowing us to study the structural and functional roles of glia in the nervous system, although the efficiency is still low. Direct conversion is an advanced strategy governing fate conversion of diverse cell types directly into the desired lineage. This novel strategy stands as a promising approach for preliminary research and regenerative medicine. Direct conversion employs genetic and environmental cues to change cell fate to that with the required functional cell properties while retaining maturity-related molecular features. As an alternative method, it is now possible to obtain a variety of mature cell populations that could not be obtained using conventional differentiation methods. This review summarizes current achievements in obtaining glia, particularly oligodendrocytes and Schwann cells.

Human iPSC-Derived Neural Models for Studying Alzheimer's Disease: from Neural Stem Cells to Cerebral Organoids

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study mechanisms of human neural development, disease modeling, and drug discovery in vitro. Especially in the field of Alzheimer’s disease (AD), where this treatment is lacking, tremendous effort has been put into the investigation of molecular mechanisms behind this disease using induced pluripotent stem cell-based models. Numerous of these studies have found either novel regulatory mechanisms that could be exploited to develop relevant drugs for AD treatment or have already tested small molecules on in vitro cultures, directly demonstrating their effect on amelioration of AD-associated pathology. This review thus summarizes currently used differentiation strategies of induced pluripotent stem cells towards neuronal and glial cell types and cerebral organoids and their utilization in modeling AD and potential drug discovery.

OCT4-induced oligodendrocyte progenitor cells promote remyelination and ameliorate disease

The generation of human oligodendrocyte progenitor cells (OPCs) may be therapeutically valuable for human demyelinating diseases such as multiple sclerosis. Here, we report the direct reprogramming of human somatic cells into expandable induced OPCs (iOPCs) using a combination of OCT4 and a small molecule cocktail. This method enables generation of A2B5⁺ (an early marker for OPCs) iOPCs within 2 weeks retaining the ability to differentiate into MBP-positive mature oligodendrocytes. RNA-seq analysis revealed that the transcriptome of O4⁺ iOPCs was similar to that of O4⁺ OPCs and ChIP-seq analysis revealed that putative OCT4-binding regions were detected in the regulatory elements of CNS development-related genes. Notably, engrafted iOPCs remyelinated the brains of adult shiverer mice and experimental autoimmune encephalomyelitis mice with MOG-induced 14 weeks after transplantation. In conclusion, our study may contribute to the development of therapeutic approaches for neurological disorders, as well as facilitate the understanding of the molecular mechanisms underlying glial development.

Transcription Factor-Based Strategies to Generate Neural Cell Types from Human Pluripotent Stem Cells

In the last years, the use of pluripotent stem cells in studies of human biology has grown exponentially. These cells represent an infinite source for differentiation into several human cell types facilitating the investigation on biological processes, functionality of cells, or diseases mechanisms in relevant human models. In the neurobiology field, pluripotent stem cells have been extensively used to generate the main neuronal and glial cells of the brain. Traditionally, protocols following developmental cues have been applied to pluripotent stem cells to drive differentiation toward different cell lineages; however, these protocols give rise to populations with mixed identities. Interestingly, new protocols applying overexpression of lineage-specific transcription factors (TFs) have emerged and facilitated the generation of highly pure populations of specific subtypes of neurons and glial cells in an easy, reproducible, and rapid manner. In this study, we review protocols based on this strategy to generate excitatory, inhibitory, dopaminergic, and motor neurons as well as astrocytes, oligodendrocytes, and microglia. In addition, we will discuss the main applications for cells generated with these protocols, including disease modeling, drug screening, and mechanistic studies. Finally, we will discuss the advantages and disadvantages of TF-based protocols and present our view of the future in this field.

OLIG2 regulates lncRNAs and its own expression during oligodendrocyte lineage formation

BACKGROUND

Oligodendrocytes, responsible for axon ensheathment, are critical for central nervous system (CNS) development, function, and diseases. OLIG2 is an important transcription factor (TF) that acts during oligodendrocyte development and performs distinct functions at different stages. Previous studies have shown that lncRNAs (long non-coding RNAs; > 200 bp) have important functions during oligodendrocyte development, but their roles have not been systematically characterized and their regulation is not yet clear.

RESULTS

We performed an integrated study of genome-wide OLIG2 binding and the epigenetic modification status of both coding and non-coding genes during three stages of oligodendrocyte differentiation in vivo: neural stem cells (NSCs), oligodendrocyte progenitor cells (OPCs), and newly formed oligodendrocytes (NFOs). We found that 613 lncRNAs have OLIG2 binding sites and are expressed in at least one cell type, which can potentially be activated or repressed by OLIG2. Forty-eight of them have increased expression in oligodendrocyte lineage cells. Predicting lncRNA functions by using a "guilt-by-association" approach revealed that the functions of these 48 lncRNAs were enriched in "oligodendrocyte development and differentiation." Additionally, bivalent genes are known to play essential roles during embryonic stem cell differentiation. We identified bivalent genes in NSCs, OPCs, and NFOs and found that some bivalent genes bound by OLIG2 are dynamically regulated during oligodendrocyte development. Importantly, we unveiled a previously unknown mechanism that, in addition to transcriptional regulation via DNA binding, OLIG2 could self-regulate through the 3' UTR of its own mRNA.

CONCLUSIONS

Our studies have revealed the missing links in the mechanisms regulating oligodendrocyte development at the transcriptional level and after transcription. The results of our research have improved the understanding of fundamental cell fate decisions during oligodendrocyte lineage formation, which can enable insights into demyelination diseases and regenerative medicine.

The potential of mechanistic information organised within the AOP framework to increase regulatory uptake of the developmental neurotoxicity (DNT) in vitro battery of assays

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Current in vivo DNT testing for regulatory purposes is not effective.

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In vitro assays anchored to key neurodevelopmental processes are available.

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Development of Adverse Outcome Pathways is required to increase mechanistic understanding of DNT effects.

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DNT Integrated Approaches to Testing and Assessment for various regulatory purposes should be developed.

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The OECD Guidance Document on use of in vitro DNT battery of assays is currently under development.

A major challenge in regulatory developmental neurotoxicity (DNT) assessment is lack of toxicological information for many compounds. Therefore, the Test Guidelines programme of the Organisation for Economic Cooperation and Development (OECD) took the initiative to coordinate an international collaboration between diverse stakeholders to consider integration of alternative approaches towards improving the current chemical DNT testing. During the past few years, a series of workshops was organized during which a consensus was reached that incorporation of a DNT testing battery that relies on in vitro assays anchored to key neurodevelopmental processes should be developed. These key developmental processes include neural progenitor cell proliferation, neuronal and oligodendrocyte differentiation, neural cell migration, neurite outgrowth, synaptogenesis and neuronal network formation, as well key events identified in the existing Adverse Outcome Pathways (AOPs). AOPs deliver mechanistic information on the causal links between molecular initiating event, intermediate key events and an adverse outcome of regulatory concern, providing the biological context to facilitate development of Integrated Approaches to Testing and Assessment (IATA) for various regulatory purposes. Developing IATA case studies, using mechanistic information derived from AOPs, is expected to increase scientific confidence for the use of in vitro methods within an IATA, thereby facilitating regulatory uptake. This manuscript summarizes the current state of international efforts to enhance DNT testing by using an in vitro battery of assays focusing on the role of AOPs in informing the development of IATA for different regulatory purposes, aiming to deliver an OECD guidance document on use of in vitro DNT battery of assays that include in vitro data interpretation.

Single-cell transcriptomic reveals molecular diversity and developmental heterogeneity of human stem cell-derived oligodendrocyte lineage cells

Injury and loss of oligodendrocytes can cause demyelinating diseases such as multiple sclerosis. To improve our understanding of human oligodendrocyte development, which could facilitate development of remyelination-based treatment strategies, here we describe time-course single-cell-transcriptomic analysis of developing human stem cell-derived oligodendrocyte-lineage-cells (hOLLCs). The study includes hOLLCs derived from both genome engineered embryonic stem cell (ESC) reporter cells containing an Identification-and-Purification tag driven by the endogenous PDGFRα promoter and from unmodified induced pluripotent (iPS) cells. Our analysis uncovers substantial transcriptional heterogeneity of PDGFRα-lineage hOLLCs. We discover sub-populations of human oligodendrocyte progenitor cells (hOPCs) including a potential cytokine-responsive hOPC subset, and identify candidate regulatory genes/networks that define the identity of these sub-populations. Pseudotime trajectory analysis defines developmental pathways of oligodendrocytes vs astrocytes from PDGFRα-expressing hOPCs and predicts differentially expressed genes between the two lineages. In addition, pathway enrichment analysis followed by pharmacological intervention of these pathways confirm that mTOR and cholesterol biosynthesis signaling pathways are involved in maturation of oligodendrocytes from hOPCs.

Generation of oligodendrocytes and establishment of an all-human myelinating platform from human pluripotent stem cells

Oligodendrocytes (OLs) are responsible for myelin production and metabolic support of neurons. Defects in OLs are crucial in several neurodegenerative diseases including multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). This protocol describes a method to generate oligodendrocyte precursor cells (OPCs) from human pluripotent stem cells (hPSCs) in only ~20 d, which can subsequently myelinate neurons, both in vitro and in vivo. To date, OPCs have been derived from eight different hPSC lines including those derived from patients with spontaneous and familial forms of MS and ALS, respectively. hPSCs, fated for 8 d toward neural progenitors, are transduced with an inducible lentiviral vector encoding for SOX10. The addition of doxycycline for 10 d results in >60% of cells being O4-expressing OPCs, of which 20% co-express the mature OL marker myelin basic protein (MBP). The protocol also describes an alternative for viral transduction, by incorporating an inducible SOX10 in the safe harbor locus AAVS1, yielding ~100% pure OPCs. O4⁺ OPCs can be purified and either cryopreserved or used for functional studies. As an example of the type of functional study for which the derived cells could be used, O4⁺ cells can be co-cultured with maturing hPSC-derived neurons in 96/384-well-format plates, allowing the screening of pro-myelinating compounds.

Cell Lineage-Based Stratification for Glioblastoma

Glioblastoma, the predominant adult malignant brain tumor, has been computationally classified into molecular subtypes whose functional relevance remains to be comprehensively established. Tumors from genetically engineered glioblastoma mouse models initiated by identical driver mutations in distinct cells of origin portray unique transcriptional profiles reflective of their respective lineage. Here, we identify corresponding transcriptional profiles in human glioblastoma and describe patient-derived xenografts with species-conserved subtype-discriminating functional properties. The oligodendrocyte lineage-associated glioblastoma subtype requires functional ERBB3 and harbors unique therapeutic sensitivities. These results highlight the importance of cell lineage in glioblastoma independent of driver mutations and provide a methodology for functional glioblastoma classification for future clinical investigations.

Small Alphaherpesvirus Latency-Associated Promoters Drive Efficient and Long-Term Transgene Expression in the CNS

Recombinant adeno-associated viruses (rAAVs) are used as gene therapy vectors to treat central nervous system (CNS) diseases. Despite their safety and broad tropism, important issues need to be corrected such as the limited payload capacity and the lack of small gene promoters providing long-term, pan-neuronal transgene expression in the CNS. Commonly used gene promoters are relatively large and can be repressed a few months after CNS transduction, risking the long-term performance of single-dose gene therapy applications. We used a whole-CNS screening approach based on systemic delivery of AAV-PHP.eB, iDisco+ tissue-clearing and light-sheet microscopy to identify three small latency-associated promoters (LAPs) from the herpesvirus pseudorabies virus (PRV). These promoters are LAP1 (404 bp), LAP2 (498 bp), and LAP1_2 (880 bp). They drive chronic transcription of the virus-encoded latency-associated transcript (LAT) during productive and latent phases of PRV infection. We observed stable, pan-neuronal transgene transcription and translation from AAV-LAPs in the CNS for 6 months post AAV transduction. In several CNS areas, the number of cells expressing the transgene was higher for LAP2 than the large conventional EF1α promoter (1,264 bp). Our data suggest that the LAPs are suitable candidates for viral vector-based CNS gene therapies requiring chronic transgene expression after one-time viral-vector administration.

Transcription Factor-Based Fate Specification and Forward Programming for Neural Regeneration

Traditionally, in vitro generation of donor cells for brain repair has been dominated by the application of extrinsic growth factors and morphogens. Recent advances in cell engineering strategies such as reprogramming of somatic cells into induced pluripotent stem cells and direct cell fate conversion have impressively demonstrated the feasibility to manipulate cell identities by the overexpression of cell fate-determining transcription factors. These strategies are now increasingly implemented for transcription factor-guided differentiation of neural precursors and forward programming of pluripotent stem cells toward specific neural subtypes. This review covers major achievements, pros and cons, as well as future prospects of transcription factor-based cell fate specification and the applicability of these approaches for the generation of donor cells for brain repair.

Mechanical regulation of oligodendrocyte biology

Oligodendrocytes (OL) are a subset of glial cells in the central nervous system (CNS) comprising the brain and spinal cord. The CNS environment is defined by complex biochemical and biophysical cues during development and response to injury or disease. In the last decade, significant progress has been made in understanding some of the key biophysical factors in the CNS that modulate OL biology, including their key role in myelination of neurons. Taken together, those studies offer translational implications for remyelination therapies, pharmacological research, identification of novel drug targets, and improvements in methods to generate human oligodendrocyte progenitor cells (OPCs) and OLs from donor stem cells in vitro. This review summarizes current knowledge of how various physical and mechanical cues affect OL biology and its implications for disease, therapeutic approaches, and generation of human OPCs and OLs.

Paired Related Homeobox Protein 1 Regulates Quiescence in Human Oligodendrocyte Progenitors

Human oligodendrocyte progenitor cells (hOPCs) persist into adulthood as an abundant precursor population capable of division and differentiation. The transcriptional mechanisms that regulate hOPC homeostasis remain poorly defined. Herein, we identify paired related homeobox protein 1 (PRRX1) in primary PDGFαR⁺ hOPCs. We show that enforced PRRX1 expression results in reversible G_1/0 arrest. While both PRRX1 splice variants reduce hOPC proliferation, only PRRX1a abrogates migration. hOPC engraftment into hypomyelinated shiverer/rag2 mouse brain is severely impaired by PRRX1a, characterized by reduced cell proliferation and migration. PRRX1 induces a gene expression signature characteristic of stem cell quiescence. Both IFN-γ and BMP signaling upregulate PRRX1 and induce quiescence. PRRX1 knockdown modulates IFN-γ-induced quiescence. In mouse brain, PRRX1 mRNA was detected in non-dividing OPCs and is upregulated in OPCs following demyelination. Together, these data identify PRRX1 as a regulator of quiescence in hOPCs and as a potential regulator of pathological quiescence.

Differentiation of Mesenchymal Stem Cells to Neuroglia: in the Context of Cell Signalling

The promise of engineering specific cell types from stem cells and rebuilding damaged or diseased tissues has fascinated stem cell researchers and clinicians over last few decades. Mesenchymal Stem Cells (MSCs) have the potential to differentiate into non-mesodermal cells, particularly neural-lineage, consisting of neurons and glia. These multipotent adult stem cells can be used for implementing clinical trials in neural repair. Ongoing research identifies several molecular mechanisms involved in the speciation of neuroglia, which are tightly regulated and interconnected by various components of cell signalling machinery. Growing MSCs with multiple inducers in culture media will initiate changes on intricately interlinked cell signalling pathways and processes. Net result of these signal flow on cellular architecture is also dependent on the type of ligands and stem cells investigated in vitro. However, our understanding about this dynamic signalling machinery is limited and confounding, especially with spheroid structures, neurospheres and organoids. Therefore, the results for differentiating neurons and glia in vitro have been inconclusive, so far. Added to this complication, we have no convincing evidence about the electrical conductivity and functionality status generated in differentiating neurons and glia. This review has taken a step forward to tailor the information on differentiating neuroglia with the common methodologies, in practice.

Stem cell derived oligodendrocytes to study myelin diseases

Oligodendroglial pathology is central to de- and dysmyelinating, but also contributes to neurodegenerative and psychiatric diseases as well as brain injury. The understanding of oligodendroglial biology in health and disease has been significantly increased during recent years by experimental in vitro and in vivo preclinical studies as well as histological analyses of human tissue samples. However, for many of these diseases the underlying pathology is still not fully understood and treatment options are frequently lacking. This is at least partly caused by the limited access to human oligodendrocytes from patients to perform functional studies and drug screens. The induced pluripotent stem cell technology (iPSC) represents a possibility to circumvent this obstacle and paves new ways to study human disease and to develop new treatment options for so far incurable central nervous system (CNS) diseases. In this review, we summarize the differences between human and rodent oligodendrocytes, provide an overview of the different techniques to generate oligodendrocytes from human progenitor or stem cells and describe the results from studies using iPSC derived oligodendroglial lineage cells. Furthermore, we discuss future perspectives and challenges of the iPSC technology with respect to disease modeling, drug screen, and cell transplantation approaches.

Interaction network analysis of YBX1 for identification of therapeutic targets in adenocarcinomas

Human Y-box binding protein-1 (YBX1) is a member of highly conserved cold-shock domain protein family, which is involved in transcriptional as well as translational regulation of many genes. Nuclear localization of YBX1 has been observed in various cancer types and it's overexpression has been linked to adverse clinical outcome and poor therapy response, but no diagnostic or therapeutic correlation has been established so far. This study aimed to identify differentially expressed novel genes among the interactors of YBX1 in different cancer types. Analysis of RNA-Seq data for colorectal, lung, prostate and stomach adenocarcinoma identified 39 unique genes, which are differentially expressed in the four adenocarcinoma types. Gene-enrichment analysis for the differentially expressed genes from individual adenocarcinoma with focus on unique genes resulted in a total of 57 gene sets specific to each adenocarcinoma. Gene ontology for commonly expressed genes suggested the pathways and possible mechanisms through which they affect each adenocarcinoma type considered in the study. Gene regulatory network constructed for the common genes and network topology was analyzed for the central nodes. Here 12 genes were found to play important roles in the network formation; among them, two genes FOXM1 and TOP2A were found to be in central network formation, which makes them a common target for therapeutics. Furthermore, five common differentially expressed genes in all adenocarcinomas were also identified.

Human Pluripotent Stem Cells as Tools for Predicting Developmental Neural Toxicity of Chemicals: Strategies, Applications, and Challenges

The human central nervous system (CNS) is very sensitive to perturbations, since it performs sophisticated biological processes and requires cooperation from multiple neural cell types. Subtle interference from exogenous chemicals, such as environmental pollutants, industrial chemicals, drug components, food additives, and cosmetic constituents, may initiate severe developmental neural toxicity (DNT). Human pluripotent stem cell (hPSC)-based neural differentiation assays provide effective and promising tools to help evaluate potential DNT caused by those toxicants. In fact, the specification of neural lineages in vitro recapitulates critical CNS developmental processes, such as patterning, differentiation, neurite outgrowth, synaptogenesis, and myelination. Hence, the established protocols to generate a repertoire of neural derivatives from hPSCs greatly benefit the in vitro evaluation of DNT. In this review, we first dissect the various differentiation protocols inducing neural cells from hPSCs, with an emphasis on the signaling pathways and endpoint markers defining each differentiation stage. We then highlight the studies with hPSC-based protocols predicting developmental neural toxicants, and discuss remaining challenges. We hope this review can provide insights for the further progress of DNT studies.

Peptide-modified, hyaluronic acid-based hydrogels as a 3D culture platform for neural stem/progenitor cell engineering

Neural stem/progenitor cell (NS/PC)-based therapies have shown exciting potential for regeneration of the central nervous system (CNS) and NS/PC cultures represent an important resource for disease modeling and drug screening. However, significant challenges limiting clinical translation remain, such as generating large numbers of cells required for model cultures or transplantation, maintaining physiologically representative phenotypes ex vivo and directing NS/PC differentiation into specific fates. Here, we report that culture of human NS/PCs in 3D, hyaluronic acid (HA)-rich biomaterial microenvironments increased differentiation toward oligodendrocytes and neurons over 2D cultures on laminin-coated glass. Moreover, NS/PCs in 3D culture exhibited a significant reduction in differentiation into reactive astrocytes. Many NS/PC-derived neurons in 3D, HA-based hydrogels expressed synaptophysin, indicating synapse formation, and displayed electrophysiological characteristics of immature neurons. While inclusion of integrin-binding, RGD peptides into hydrogels resulted in a modest increase in numbers of viable NS/PCs, no combination of laminin-derived, adhesive peptides affected differentiation outcomes. Notably, 3D cultures of differentiating NS/PCs were maintained for at least 70 days in medium with minimal growth factor supplementation. In sum, results demonstrate the use of 3D, HA-based biomaterials for long-term expansion and differentiation of NS/PCs toward oligodendroglial and neuronal fates, while inhibiting astroglial fates. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 704-718, 2019.

Low frequency pulsed electromagnetic field promotes differentiation of oligodendrocyte precursor cells through upregulation of miR-219-5p in vitro

AIM

Spinal cord injury (SCI) is a common demyelinating disorder of the central nervous system. The differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes (OLs), which induce myelination, plays a critical role in the functional recovery following SCI. In this study, the effect of low frequency pulsed electromagnetic field (PEMF) on the differentiation of OPCs and the potential underlying mechanisms were investigated.

MAIN METHODS

OPCs were randomly divided into the PEMF and non-PEMF (NPEMF) groups. Immunofluorescence and western blot assays were performed to assess the expression levels of OLs stage-specific markers after 3, 7, 14, and 21 days of PEMF or NPEMF exposure. qRT-PCR was used to further assess the expression levels of miR-219-5p, miR-338, miR-138, and miR-9, which are associated with OPCs differentiation, and the expression levels of genes associated with miR-219-5p. Finally, following PEMF or NPEMF exposure, qRT-PCR and western blot assays were performed to explore the relationship between miR-219-5p and Lingo1 and between miR-219-5p and PEMF in promoting OPCs differentiation.

KEY FINDINGS

PEMF promoted the differentiation of OPCs. PEMF upregulated the expression level of miR-219-5p and downregulated the expression level of Lingo1 during the differentiation of OPCs. Under PEMF exposure, miR-219-5p targeted Lingo1 and reversed the inhibitory effect of miR-219-5p inhibitor on OPCs differentiation. In addition, PEMF synergized with miR-219-5p to promote OPCs differentiation.

SIGNIFICANCE

Our results, for the first time, indicated that PEMF promoted OPCs differentiation by regulating miR-219-5p activity in vitro.

Various strategies to improve efficacy of stem cell transplantation in multiple sclerosis: Focus on mesenchymal stem cells and neuroprotection

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which predominantly affect young adults and undergo heavy socioeconomic burdens. Conventional therapeutic modalities for MS mostly downregulate aggressive immune responses and are almost insufficient for management of progressive course of the disease. Mesenchymal stem cells (MSCs), due to both immunomodulatory and neuroprotective properties have been known as practical cells for treatment of neurodegenerative diseases like MS. However, clinical translation of MSCs is associated with some limitations such as short-life engraftment duration, little in vivo trans-differentiation and restricted accessibility into damaged sites. Therefore, laboratory manipulation of MSCs can improve efficacy of MSCs transplantation in MS patients. In this review, we discuss several novel approaches, which can potentially enhance MSCs capabilities for treating MS.

Activated T cells induce proliferation of oligodendrocyte progenitor cells via release of vascular endothelial cell growth factor-A

Neuroinflammatory diseases such as multiple sclerosis are characterized by infiltration of lymphocytes into the central nervous system followed by demyelination and axonal degeneration. While evidence suggests that activated T lymphocytes induce neurotoxicity and impair function of neural stem cells, the effect of T cells on oligodendrocyte progenitor cells (OPCs) is still uncertain, partly due to the difficulty in obtaining human OPCs. Here we studied the effect of activated T cells on OPCs using OPCs derived from human hematopoietic stem cells or from human fetal brain. OPCs were exposed to supernatants (sups) from activated T cells. Cell proliferation was determined by EdU incorporation and CellQuanti-Blue assays. Surprisingly, we found that sups from activated T cells induced OPC proliferation by regulating cell cycle progression. Vascular endothelial growth factor A (VEGF-A) transcripts were increased in T cells after activation. Immunodepletion of VEGF-A from activated T cell sups significantly attenuated its effect on OPC proliferation. Furthermore, VEGF receptor 2 (VEGFR2) was expressed on OPCs and its inhibition also attenuated activated T cell-induced OPC proliferation. Thus, activated T cells have a trophic role by promoting OPC proliferation via the VEGFR2 pathway.

Child abuse associates with an imbalance of oligodendrocyte-lineage cells in ventromedial prefrontal white matter

Child abuse (CA) is a major risk factor for depression, and strongly associates with suicidal behavior during adulthood. Neuroimaging studies have reported widespread changes in white matter integrity and brain connectivity in subjects with a history of CA. Although such observations could reflect changes in myelin and oligodendrocyte function, their cellular underpinnings have never been addressed. Using postmortem brain samples from depressed suicides with or without history of CA and matched controls (18 per group), we aimed to characterize the effects of CA on oligodendrocyte-lineage (OL) cells in the ventromedial prefrontal white matter. Using immunoblotting, double-labeling immunofluorescence and stereological estimates of stage-specific markers, we found that CA is associated with increased numbers of mature myelinating oligodendrocytes, accompanied by decreased numbers of more immature OL cells. This was paralleled by an increased expression of transcription factor MASH1, which is involved in the terminal differentiation of the OL, suggesting that CA may trigger an increased maturation, or bias the populations of OL cells toward a more mature phenotype. Some of these effects, which were absent in the brain of depressed suicides with no history of CA, were also found to recover with age, suggesting that changes in the balance of the OL may reflect a transient adaptive mechanism triggered by early-life adversity. In conclusion, our results indicate that CA in depressed suicides is associated with an imbalance of the OL in the ventromedial prefrontal white matter, an effect that could lead to myelin remodeling and long-term connectivity changes within the limbic network.

Oligodendrocyte differentiation from human neural stem cells: A novel role for c-Src

Human neural stem cells (hNSCs) can differentiate into an oligodendrocyte lineage to facilitate remyelination in patients. Molecular mechanisms underlying oligodendrocyte fate specification remains unknown, hindering the development of efficient methods to generate oligodendrocytes from hNSCs. We have found that Neurobasal-A medium (NB) is capable of inducing hNSCs to oligodendrocyte progenitor cells (OPCs). We identified several signaling molecules are altered after cultivation in NB medium, including Akt, ERK1/2 and c-Src. While sustained activation of Akt and ERK1/2 during both NB induction and subsequent differentiation was required for OPC differentiation, c-Src phosphorylation was increased temporally during the period of NB induction. Both pharmacological inhibition and RNA interference confirmed that a transient elevation of phospho-c-Src is critical for OPC induction. Furthermore, inactivation of c-Src inhibited phosphorylation of Akt and ERK1/2. In summary, we identified a novel and critical role of c-Src in guiding hNSC differentiation to an oligodendrocyte lineage.

mTORC1 Activation by Loss of Tsc1 in Myelinating Glia Causes Downregulation of Quaking and Neurofascin 155 Leading to Paranodal Domain Disorganization

Mutations in human tuberous sclerosis complex (TSC) genes TSC1 and TSC2 are the leading causes of developmental brain abnormalities and large tumors in other tissues. Murine Tsc1/2 have been shown to negatively regulate the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in most tissues, and this pathway has been shown to be essential for proper oligodendrocytes/Schwann cell differentiation and myelination. Here, we report that ablation of Tsc1 gene specifically in oligodendrocytes/Schwann cells activates mTORC1 signaling resulting in severe motor disabilities, weight loss, and early postnatal death. The mutant mice of either sex showed reduced myelination, disrupted paranodal domains in myelinated axons, and disorganized unmyelinated Remak bundles. mRNA and protein expression analyses revealed strong reduction in the RNA-binding protein Quaking (Qk) and the 155 kDa glial Neurofascin (NfascNF155). Re-introduction of exogenous Qk gene in Tsc1 mutant oligodendrocytes restored NfascNF155 protein levels indicating that Qk is required for the stabilization of NfascNF155 mRNA. Interestingly, injection of Rapamycin, a pharmacological mTORC1 inhibitor, to pregnant mothers increased the lifespan of the mutant offspring, restored myelination as well as the levels of Qk and NfascNF155, and consequently the organization of the paranodal domains. Together our studies show a critical role of mTORC1 signaling in the differentiation of myelinating glial cells and proper organization of axonal domains and provide insights into TSC-associated myelinated axon abnormalities.

Irf6 directs glandular lineage differentiation of epidermal progenitors and promotes limited sweat gland regeneration in a mouse burn model

BACKGROUND

Damaged or malfunctioning sweat glands (SGs) after a burn injury would cause significant hyperthermia and even death, and there is an unmet need for effective treatment. Genetically reprogrammed stem cells show their potential advantages for inducing SG repair and regeneration.

METHODS

The expression of interferon regulatory factor 6 (IRF6) in skin was tested by immunofluorescence, and Irf6 was overexpressed in epidermal progenitors (EPs) to stimulate SG differentiation. For in-vivo studies, second- and third-degree mouse burn wounds were treated with subcutaneous injection of EPs and Irf6-transfected cells, and cell retention and therapeutic effects were assessed.

RESULTS

IRF6 demonstrated differential expression between the footpad and dorsal skin and was upregulated along with embryonic and postnatal SG development. The Irf6-transfected cells converted their cell phenotypes as seen by gene and protein expression analyses and their morphology closely resembled epidermal-derived glandular cells. Inductive SG cell (SGC) transplantation and in-vivo tracing examination demonstrated that they could survive at damaged sites for 14 days. In comparison, the positive effects of inductive SGCs only result in restoring SG function in second-degree burn wounds but not in third-degree burn wounds as assessed by both perspiration tests and morphological analyses.

CONCLUSIONS

These results suggest that IRF6 plays an important role in directing glandular lineage differentiation of Eps, but that the therapeutic efficacy of inductive SGCs may be restricted to the burn environment.

Muscarinic Receptor M3R Signaling Prevents Efficient Remyelination by Human and Mouse Oligodendrocyte Progenitor Cells

Muscarinic receptor antagonists act as potent inducers of oligodendrocyte differentiation and accelerate remyelination. However, the use of muscarinic antagonists in the clinic is limited by poor understanding of the operant receptor subtype, and questions regarding possible species differences between rodents and humans. Based on high selective expression in human oligodendrocyte progenitor cells (OPCs), we hypothesized that M₃R is the functionally relevant receptor. Lentiviral M₃R knockdown in human primary CD140a/PDGFαR⁺ OPCs resulted in enhanced differentiation in vitro and substantially reduced the calcium response following muscarinic agonist treatment. Importantly, following transplantation in hypomyelinating shiverer/rag2 mice, M₃R knockdown improved remyelination by human OPCs. Furthermore, conditional M₃R ablation in adult NG2-expressing OPCs increased oligodendrocyte differentiation and led to improved spontaneous remyelination in mice. Together, we demonstrate that M₃R receptor mediates muscarinic signaling in human OPCs that act to delay differentiation and remyelination, suggesting that M₃ receptors are viable targets for human demyelinating disease.SIGNIFICANCE STATEMENT The identification of drug targets aimed at improving remyelination in patients with demyelination disease is a key step in development of effective regenerative therapies to treat diseases, such as multiple sclerosis. Muscarinic receptor antagonists have been identified as effective potentiators of remyelination, but the receptor subtypes that mediate these receptors are unclear. In this study, we show that genetic M₃R ablation in both mouse and human cells results in improved remyelination and is mediated by acceleration of oligodendrocyte commitment from oligodendrocyte progenitor cells. Therefore, M₃R represents an attractive target for induced remyelination in human disease.

A Novel Role for Oligodendrocyte Precursor Cells (OPCs) and Sox10 in Mediating Cellular and Behavioral Responses to Heroin

Opiate abuse and addiction have become a worldwide epidemic with great societal and financial burdens, highlighting a critical need to understand the neurobiology of opiate addiction. Although several studies have focused on drug-dependent changes in neurons, the role of glia in opiate addiction remains largely unstudied. RNA sequencing pathway analysis from the prefrontal cortex (PFC) of male rats revealed changes in several genes associated with oligodendrocyte differentiation and maturation following heroin self-administration. Among these genes changed was Sox10, which is regulated, in part, by the chromatin remodeler BRG1/SMARCA4. To directly test the functional role of Sox10 in mediating heroin-induced behavioral plasticity, we selectively overexpressed Sox10 and BRG1 in the PFC. Overexpression of either Sox10 or BRG1 decreased the motivation to obtain heroin infusions in a progressive ratio test without altering the acquisition or maintenance of heroin self-administration. These data demonstrate a critical, and perhaps compensatory, role of Sox10 and BRG1 in oligodendrocytes in regulating the motivation for heroin.

Network-Based Genomic Analysis of Human Oligodendrocyte Progenitor Differentiation

Impaired human oligodendrocyte progenitor cell (hOPC) differentiation likely contributes to failed remyelination in multiple sclerosis. The characterization of molecular pathways that regulate hOPC differentiation will provide means to induce remyelination. In this study, we determined the gene expression profile of PDGFαR⁺ hOPCs during initial oligodendrocyte commitment. Weighted gene coexpression network analysis was used to define progenitor and differentiation-specific gene expression modules and functionally important hub genes. These modules were compared with rodent OPC and oligodendrocyte data to determine the extent of species conservation. These analyses identified G-protein β₄ (GNB4), which was associated with hOPC commitment. Lentiviral GNB4 overexpression rapidly induced human oligodendrocyte differentiation. Following xenograft in hypomyelinating shiverer/rag2 mice, GNB4 overexpression augmented myelin synthesis and the ability of hOPCs to ensheath host axons, establishing GNB4 as functionally important in human myelination. As such, network analysis of hOPC gene expression accurately predicts genes that influence human oligodendrocyte differentiation in vivo.

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Transcriptional database of differentiating human oligodendrocyte progenitor cells

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WGCNA reveals coordinated gene networks in oligodendrocyte specification

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Dataset comparison identifies unique and shared cross-species gene networks

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G-protein β₄ (GNB4) expression accelerates human oligodendrocyte differentiation

Overexpression of Truncated Human DISC1 Induces Appearance of Hindbrain Oligodendroglia in the Forebrain During Development

Genetic, neuroimaging, and gene expression studies suggest a role for oligodendrocyte (OLG) dysfunction in schizophrenia (SZ). Disrupted-in-schizophrenia 1 (DISC1) is a risk gene for major psychiatric disorders, including SZ. Overexpression of mutant truncated (hDISC1), but not full-length sequence of human DISC1 in forebrain influenced OLG differentiation and proliferation of glial progenitors in the developing cerebral cortex concurrently with reduction of OLG progenitor markers in the hindbrain. We examined gene and protein expression of the molecular determinants of hindbrain OLG development and their interactions with DISC1 in mutant hDISC1 mice. We found ectopic upregulation of hindbrain glial progenitor markers (early growth response 2 [Egr2] and NK2 homeobox 2 [Nkx2-2]) in the forebrain of hDISC1 (E15) embryos. DISC1 and Nkx2-2 were coexpressed and interacted in progenitor cells. Overexpression of truncated hDISC1 impaired interactions between DISC1 and Nkx2-2, which was associated with increased differentiation of OLG and upregulation of hindbrain mature OLG markers (laminin alpha-1 [LAMA1] and myelin protein zero [MPZ]) suggesting a suppressive function of endogenous DISC1 in OLG specialization of hindbrain glial progenitors during embryogenesis. Consistent with findings in hDISC1 mice, several hindbrain OLG markers (PRX, LAMA1, and MPZ) were significantly upregulated in the superior temporal cortex of persons with SZ. These findings show a significant effect of truncated hDISC1 on glial identity cells along the rostrocaudal axis and their OLG specification. Appearance of hindbrain OLG lineage cells and their premature differentiation may affect cerebrocortical organization and contribute to the pathophysiology of SZ.

Exposure to fine and ultrafine particulate matter during gestation alters postnatal oligodendrocyte maturation, proliferation capacity, and myelination

Accumulating studies indicate that the brain is a direct target of air pollution exposure during the fetal period. We have previously demonstrated that exposure to concentrated ambient particles (CAPs) during gestation produces ventriculomegaly, periventricular hypermyelination, and enlargement of the corpus callosum (CC) during postnatal development in mice. This study aimed to further characterize the cellular basis of the observed hypermyelination and determine if this outcome, among other effects, persisted as the brain matured. Analysis of CC-1+ mature oligodendrocytes in the CC at postnatal days (PNDs) 11-15 suggest a premature maturational shift in number and proportion of total cells in prenatally CAPs-exposed males and females, with no overall change in total CC cellularity. The overall number of Olig2+ lineage cells in the CC was not affected in either sex at the same postnatal timepoint. Assessment of myelin status at early brain maturity (PNDs 57-61) revealed persistent hypermyelination in CAPs-exposed animals of both sexes. In addition, ventriculomegaly was persistent in CAPs-treated females, with possible amelioration of ventriculomegaly in CAPs-exposed males. When oligodendrocyte precursor cell (OPC) pool status was analyzed at PNDs 57-61, there were significant CAPs-induced alterations in cycling Ki67+/Olig2+ cell number and proportion of total cells in the female CC. Total CC cellularity was slightly elevated in CAPs-exposed males at PNDs 57-61. Overall, these data support a growing body of evidence that demonstrate the vulnerability of the developing brain to environmental insults such as ambient particulate matter. The sensitivity of oligodendrocytes and myelin, in particular, to such an insult warrants further investigation into the mechanistic underpinnings of OPC and myelin disruption by constituent air pollutants.

Age-Dependent Decline in Fate Switch from NG2 Cells to Astrocytes After Olig2 Deletion

NG2 cells are a resident glial progenitor cell population that is uniformly distributed throughout the developing and mature mammalian CNS. Those in the postnatal CNS generate exclusively myelinating and non-myelinating oligodendrocytes and are thus equated with oligodendrocyte precursor cells. Prenatally, NG2 cells in the ventral gray matter of the forebrain generate protoplasmic astrocytes as well as oligodendrocytes. The fate conversion from NG2 cells into protoplasmic astrocytes is dependent on downregulation of the key oligodendrocyte transcription factor Olig2. We showed previously that constitutive deletion of Olig2 in NG2 cells converts NG2 cells in the neocortex into protoplasmic astrocytes at the expense of oligodendrocytes. In this study, we show that postnatal deletion of Olig2 caused NG2 cells in the neocortex but not in other gray matter regions to become protoplasmic astrocytes. However, NG2 cells in the neocortex became more resistant to astrocyte fate switch over the first 3 postnatal weeks. Fewer NG2 cells differentiated into astrocytes and did so with longer latency after Olig2 deletion at postnatal day 18 (P18) compared with deletion at P2. The high-mobility group transcription factor Sox10 was not downregulated for at least 1 month after Olig2 deletion at P18 despite an early transient upregulation of the astrocyte transcription factor NFIA. Furthermore, inhibiting cell proliferation in slice culture reduced astrocyte differentiation from Olig2-deleted perinatal NG2 cells, suggesting that cell division might facilitate nuclear reorganization needed for astrocyte transformation.SIGNIFICANCE STATEMENT NG2 cells are glial progenitor cells that retain a certain degree of lineage plasticity. In the normal postnatal neocortex, they generate mostly oligodendrocyte lineage cells. When the oligodendrocyte transcription factor Olig2 is deleted in NG2 cells in the neocortex, they switch their fate to protoplasmic astrocytes. However, the efficiency of the fate switch decreases with age over the first 3 postnatal weeks and is reduced when cell proliferation is inhibited. As the neocortex matures, sustained expression of the oligodendrocyte lineage-specific key transcription factor Sox10 becomes less dependent on Olig2. Together, our findings suggest a gradual stabilization of the oligodendrocyte lineage genes and loss of lineage plasticity during the first 3 weeks after birth, possibly due to nuclear reorganization.

Differences of immune disorders between Alzheimer's disease and breast cancer based on transcriptional regulation

Although chronic inflammation and immune disorders are of great importance to the pathogenesis of both dementia and cancer, the pathophysiological mechanisms are not clearly understood. In recent years, growing epidemiological evidence and meta-analysis data suggest an inverse association between Alzheimer’s disease (AD), which is the most common form of dementia, and cancer. It has been revealed that some common genes and biological processes play opposite roles in AD and cancer; however, the biological immune mechanism for the inverse association is not clearly defined. An unsupervised matrix decomposition two-stage bioinformatics procedure was adopted to investigate the opposite behaviors of the immune response in AD and breast cancer (BC) and to discover the underlying transcriptional regulatory mechanisms. Fast independent component analysis (FastICA) was applied to extract significant genes from AD and BC microarray gene expression data. Based on the extracted data, the shared transcription factors (TFs) from AD and BC were captured. Second, the network component analysis (NCA) algorithm in this study was presented to quantitatively deduce the TF activities and regulatory influences because quantitative dynamic regulatory information for TFs is not available via microarray techniques. Based on the NCA results and reconstructed transcriptional regulatory networks, inverse regulatory processes and some known innate immune responses were described in detail. Many of the shared TFs and their regulatory processes were found to be closely related to the adaptive immune response from dramatically different directions and to play crucial roles in both AD and BC pathogenesis. From the above findings, the opposing cellular behaviors demonstrate an invaluable opportunity to gain insights into the pathogenesis of these two types of diseases and to aid in developing new treatments.

Enhancing oligodendrocyte differentiation by transient transcription activation via DNA nanoparticle-mediated transfection

Current approaches to derive oligodendrocytes from human pluripotent stem cells (hPSCs) need extended exposure of hPSCs to growth factors and small molecules, which limits their clinical application because of the lengthy culture time required and low generation efficiency of myelinating oligodendrocytes. Compared to extrinsic growth factors and molecules, oligodendrocyte differentiation and maturation can be more effectively modulated by regulation of the cell transcription network. In the developing central nervous system (CNS), two basic helix-loop-helix transcription factors, Olig1 and Olig2, are decisive in oligodendrocyte differentiation and maturation. Olig2 plays a critical role in the specification of oligodendrocytes and Olig1 is crucial in promoting oligodendrocyte maturation. Recently viral vectors have been used to overexpress Olig2 and Olig1 in neural stem/progenitor cells (NSCs) to induce the maturation of oligodendrocytes and enhance the remyelination activity in vivo. Because of the safety issues with viral vectors, including the insertional mutagenesis and potential tumor formation, non-viral transfection methods are preferred for clinical translation. Here we report a poly(β-amino ester) (PBAE)-based nanoparticle transfection method to deliver Olig1 and Olig2 into human fetal tissue-derived NSCs and demonstrate efficient oligodendrocyte differentiation following transgene expression of Olig1 and Olig2. This approach is potentially translatable for engineering stem cells to treat injured or diseased CNS tissues.

STATEMENT OF SIGNIFICANCE

Current protocols to derive oligodendrocytes from human pluripotent stem cells (hPSCs) require lengthy culture time with low generation efficiencies of mature oligodendrocytes. We described a new approach to enhance oligodendrocyte differentiation through nanoparticle-mediated transcription modulation. We tested an effective transfection method using cell-compatible poly (β-amino ester) (PBAE)/DNA nanoparticles as gene carrier to deliver transcription factor Olig1 and Olig2 into human fetal tissue-derived neural stem/progenitor cells, and showed efficient oligodendrocyte differentiation following transgene expression of Olig1 and Olig2. We believe that this translatable approach can be applied to many other cell-based regenerative therapies as well.

Inducible and Deterministic Forward Programming of Human Pluripotent Stem Cells into Neurons, Skeletal Myocytes, and Oligodendrocytes

The isolation or in vitro derivation of many human cell types remains challenging and inefficient. Direct conversion of human pluripotent stem cells (hPSCs) by forced expression of transcription factors provides a potential alternative. However, deficient inducible gene expression in hPSCs has compromised efficiencies of forward programming approaches. We have systematically optimized inducible gene expression in hPSCs using a dual genomic safe harbor gene-targeting strategy. This approach provides a powerful platform for the generation of human cell types by forward programming. We report robust and deterministic reprogramming of hPSCs into neurons and functional skeletal myocytes. Finally, we present a forward programming strategy for rapid and highly efficient generation of human oligodendrocytes.

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Dual genomic safe harbor targeting of the Tet-ON system

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Optimized inducible transgene expression in human pluripotent stem cells

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Deterministic forward programming into neurons, myocytes, and oligodendrocytes

Reprogramming Postnatal Human Epidermal Keratinocytes Toward Functional Neural Crest Fates

During development, neural crest (NC) cells are induced by signaling events at the neural plate border of all vertebrate embryos. Initially arising within the central nervous system, NC cells subsequently undergo an epithelial to mesenchymal transition to migrate into the periphery, where they differentiate into diverse cell types. Here we provide evidence that postnatal human epidermal keratinocytes (KC), in response to fibroblast growth factor 2 and insulin like growth factor 1 signals, can be reprogrammed toward a NC fate. Genome-wide transcriptome analyses show that keratinocyte-derived NC cells are similar to those derived from human embryonic stem cells. Moreover, they give rise in vitro and in vivo to NC derivatives such as peripheral neurons, melanocytes, Schwann cells and mesenchymal cells (osteocytes, chondrocytes, adipocytes, and smooth muscle cells). By demonstrating that human keratin-14+ KC can form NC cells, even from clones of single cells, our results have important implications in stem cell biology and regenerative medicine. Stem Cells 2017;35:1402-1415.

Rapid and efficient generation of oligodendrocytes from human induced pluripotent stem cells using transcription factors

Rapid and efficient protocols to generate oligodendrocytes (OL) from human induced pluripotent stem cells (iPSC) are currently lacking, but may be a key technology to understand the biology of myelin diseases and to develop treatments for such disorders. Here, we demonstrate that the induction of three transcription factors (SOX10, OLIG2, NKX6.2) in iPSC-derived neural progenitor cells is sufficient to rapidly generate O4⁺ OL with an efficiency of up to 70% in 28 d and a global gene-expression profile comparable to primary human OL. We further demonstrate that iPSC-derived OL disperse and myelinate the CNS of Mbp^shi/shiRag^-/- mice during development and after demyelination, are suitable for in vitro myelination assays, disease modeling, and screening of pharmacological compounds potentially promoting oligodendroglial differentiation. Thus, the strategy presented here to generate OL from iPSC may facilitate the studying of human myelin diseases and the development of high-throughput screening platforms for drug discovery.

Accelerated generation of oligodendrocyte progenitor cells from human induced pluripotent stem cells by forced expression of Sox10 and Olig2

Oligodendrocyte progenitor cells (OPCs) hold great promise for treatment of dysmyelinating disorders, such as multiple sclerosis and cerebral palsy. Recent studies on generation of human OPCs mainly use human embryonic stem cells (hESCs) or neural stem cells (NSCs) as starter cell sources for the differentiation process. However, NSCs are restricted in availability and the present method for generation of oligodendrocytes (OLs) from ESCs often requires a lengthy period of time. Here, we demonstrated a protocol to efficiently derive OPCs from human induced pluripotent stem cells (hiPSCs) by forced expression of two transcription factors (2TFs), Sox10 and Olig2. With this method, PDGFRα⁺ OPCs can be obtained in 14 days and O4⁺ OPCs in 56 days. Furthermore, OPCs may be able to differentiate to mature OLs that could ensheath axons when co-cultured with rat cortical neurons. The results have implications in the development of autologous cell therapies.

Targeting human oligodendrocyte progenitors for myelin repair

Oligodendrocyte development has been studied for several decades, and has served as a model system for both neurodevelopmental and stem/progenitor cell biology. Until recently, the vast majority of studies have been conducted in lower species, especially those focused on rodent development and remyelination. In humans, the process of myelination requires the generation of vastly more myelinating glia, occurring over a period of years rather than weeks. Furthermore, as evidenced by the presence of chronic demyelination in a variety of human neurologic diseases, it appears likely that the mechanisms that regulate development and become dysfunctional in disease may be, in key ways, divergent across species. Improvements in isolation techniques, applied to primary human neural and oligodendrocyte progenitors from both fetal and adult brain, as well as advancements in the derivation of defined progenitors from human pluripotent stem cells, have begun to reveal the extent of both species-conserved signaling pathways and potential key differences at cellular and molecular levels. In this article, we will review the commonalities and differences in myelin development between rodents and man, describing the approaches used to study human oligodendrocyte differentiation and myelination, as well as heterogeneity within targetable progenitor pools, and discuss the advances made in determining which conserved pathways may be both modeled in rodents and translate into viable therapeutic strategies to promote myelin repair.

The Activators of Cyclin-Dependent Kinase 5 p35 and p39 Are Essential for Oligodendrocyte Maturation, Process Formation, and Myelination

The regulation of oligodendrocyte development and myelin formation in the CNS is poorly defined. Multiple signals influence the rate and extent of CNS myelination, including the noncanonical cyclin-dependent kinase 5 (Cdk5) whose functions are regulated by its activators p35 and p39. Here we show that selective loss of either p35 or p39 perturbed specific aspects of oligodendrocyte development, whereas loss of both p35 and p39 completely inhibited the development of mature oligodendrocytes and myelination. In the absence of p35, oligodendrocyte differentiation was delayed, process outgrowth was truncated in vitro, and the patterning and extent of myelination were perturbed in the CNS of p35(-/-) mice. In the absence of p39, oligodendrocyte maturation was transiently affected both in vitro and in vivo. However, loss of both p35 and p39 in oligodendrocyte lineage cells completely inhibited oligodendrocyte progenitor cell differentiation and myelination both in vitro and after transplantation into shiverer slice cultures. Loss of p35 and p39 had a more profound effect on oligodendrocyte development than simply the loss of Cdk5 and could not be rescued by Cdk5 overexpression. These data suggest p35 and p39 have specific and overlapping roles in oligodendrocyte development, some of which may be independent of Cdk5 activation.

How to make an oligodendrocyte

Oligodendrocytes produce myelin, an insulating sheath required for the saltatory conduction of electrical impulses along axons. Oligodendrocyte loss results in demyelination, which leads to impaired neurological function in a broad array of diseases ranging from pediatric leukodystrophies and cerebral palsy, to multiple sclerosis and white matter stroke. Accordingly, replacing lost oligodendrocytes, whether by transplanting oligodendrocyte progenitor cells (OPCs) or by mobilizing endogenous progenitors, holds great promise as a therapeutic strategy for the diseases of central white matter. In this Primer, we describe the molecular events regulating oligodendrocyte development and how our understanding of this process has led to the establishment of methods for producing OPCs and oligodendrocytes from embryonic stem cells and induced pluripotent stem cells, as well as directly from somatic cells. In addition, we will discuss the safety of engrafted stem cell-derived OPCs, as well as approaches by which to modulate their differentiation and myelinogenesis in vivo following transplantation.