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

Trametinib, an anti-tumor drug, promotes oligodendrocytes generation and myelin formation

Oligodendrocytes (OLs) are differentiated from oligodendrocyte precursor cells (OPCs) in the central nervous system (CNS). Demyelination is a common feature of many neurological diseases such as multiple sclerosis (MS) and leukodystrophies. Although spontaneous remyelination can happen after myelin injury, nevertheless, it is often insufficient and may lead to aggravated neurodegeneration and neurological disabilities. Our previous study has discovered that MEK/ERK pathway negatively regulates OPC-to-OL differentiation and remyelination in mouse models. To facilitate possible clinical evaluation, here we investigate several MEK inhibitors which have been approved by FDA for cancer therapies in both mouse and human OPC-to-OL differentiation systems. Trametinib, the first FDA approved MEK inhibitor, displays the best effect in stimulating OL generation in vitro among the four MEK inhibitors examined. Trametinib also significantly enhances remyelination in both MOG-induced EAE model and LPC-induced focal demyelination model. More exciting, trametinib facilitates the generation of MBP+ OLs from human embryonic stem cells (ESCs)-derived OPCs. Mechanism study indicates that trametinib promotes OL generation by reducing E2F1 nuclear translocation and subsequent transcriptional activity. In summary, our studies indicate a similar inhibitory role of MEK/ERK in human and mouse OL generation. Targeting the MEK/ERK pathway might help to develop new therapies or repurpose existing drugs for demyelinating diseases.

Gliomas: a reflection of temporal gliogenic principles

The hijacking of early developmental programs is a canonical feature of gliomas where neoplastic cells resemble neurodevelopmental lineages and possess mechanisms of stem cell resilience. Given these parallels, uncovering how and when in developmental time gliomagenesis intersects with normal trajectories can greatly inform our understanding of tumor biology. Here, we review how elapsing time impacts the developmental principles of astrocyte (AS) and oligodendrocyte (OL) lineages, and how these same temporal programs are replicated, distorted, or circumvented in pathological settings such as gliomas. Additionally, we discuss how normal gliogenic processes can inform our understanding of the temporal progression of gliomagenesis, including when in developmental time gliomas originate, thrive, and can be pushed towards upon therapeutic coercion.

Oligodendrocyte progenitor cell-specific delivery of lipid nanoparticles loaded with Olig2 synthetically modified messenger RNA for ischemic stroke therapy

The transcription factor Olig2 is highly expressed throughout oligodendroglial development and is needed for the differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes and remyelination. Although Olig2 overexpression in OPCs is a possible therapeutic target for enhancing myelin repair in ischemic stroke, achieving Olig2 overexpression in vivo remains a formidable technological challenge. To address this challenge, we employed lipid nanoparticle (LNP)-mediated delivery of Olig2 synthetically modified messenger RNA (mRNA) as a viable method for in vivo Olih2 protein overexpression. Specifically, we developed CD140a-targeted LNPs loaded with Olig2 mRNA (C-Olig2) to achieve targeted Olig2 protein expression within PDGFRα+ OPCs, with the goal of promoting remyelination for ischemic stroke therapy. We show that C-Olig2 promotes the differentiation of PDGFRα+ OPCs derived from mouse neural stem cells into mature oligodendrocytes in vitro, suggesting that mRNA-mediated Olig2 overexpression is a rational approach to promote oligodendrocyte differentiation and remyelination. Furthermore, when C-Olig2 was administered to a murine model of ischemic stroke, it led to improvements in blood‒brain barrier (BBB) integrity, enhanced remyelination, and rescued learning and cognitive deficits. Our comprehensive analysis, which included bulk RNA sequencing (RNA-seq) and single-nucleus RNA-seq (snRNA-seq), revealed upregulated biological processes related to learning and memory in the brains of mice treated with C-Olig2 compared to those receiving empty LNPs (Mock). Collectively, our findings highlight the therapeutic potential of multifunctional nanomedicine targeting mRNA expression for ischemic stroke and suggest that this approach holds promise for addressing various brain diseases. STATEMENT OF SIGNIFICANCE: While Olig2 overexpression in OPCs represents a promising therapeutic avenue for enhancing remyelination in ischemic stroke, in vivo strategies for achieving Olig2 expression pose considerable technological challenges. The delivery of mRNA via lipid nanoparticles is considered aa viable approach for in vivo protein expression. In this study, we engineered CD140a-targeted LNPs loaded with Olig2 mRNA (C-Olig2) with the aim of achieving specific Olig2 overexpression in mouse OPCs. Our findings demonstrate that C-Olig2 promotes the differentiation of OPCs into oligodendrocytes in vitro, providing evidence that mRNA-mediated Olig2 overexpression is a rational strategy to foster remyelination. Furthermore, the intravenous administration of C-Olig2 into a murine model of ischemic stroke not only improved blood-brain barrier integrity but also enhanced remyelination and mitigated learning and cognitive deficits. These results underscore the promising therapeutic potential of multifunctional nanomedicine targeting mRNA expression in the context of ischemic stroke.

Disruption of MAM integrity in mutant FUS oligodendroglial progenitors from hiPSCs

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive and fatal neurodegenerative disorder, characterized by selective loss of motor neurons (MNs). A number of causative genetic mutations underlie the disease, including mutations in the fused in sarcoma (FUS) gene, which can lead to both juvenile and late-onset ALS. Although ALS results from MN death, there is evidence that dysfunctional glial cells, including oligodendroglia, contribute to neurodegeneration. Here, we used human induced pluripotent stem cells (hiPSCs) with a R521H or a P525L mutation in FUS and their isogenic controls to generate oligodendrocyte progenitor cells (OPCs) by inducing SOX10 expression from a TET-On SOX10 cassette. Mutant and control iPSCs differentiated efficiently into OPCs. RNA sequencing identified a myelin sheath-related phenotype in mutant OPCs. Lipidomic studies demonstrated defects in myelin-related lipids, with a reduction of glycerophospholipids in mutant OPCs. Interestingly, FUSR521H OPCs displayed a decrease in the phosphatidylcholine/phosphatidylethanolamine ratio, known to be associated with maintaining membrane integrity. A proximity ligation assay further indicated that mitochondria-associated endoplasmic reticulum membranes (MAM) were diminished in both mutant FUS OPCs. Moreover, both mutant FUS OPCs displayed increased susceptibility to ER stress when exposed to thapsigargin, and exhibited impaired mitochondrial respiration and reduced Ca2+ signaling from ER Ca2+ stores. Taken together, these results demonstrate a pathological role of mutant FUS in OPCs, causing defects in lipid metabolism associated with MAM disruption manifested by impaired mitochondrial metabolism with increased susceptibility to ER stress and with suppressed physiological Ca2+ signaling. As such, further exploration of the role of oligodendrocyte dysfunction in the demise of MNs is crucial and will provide new insights into the complex cellular mechanisms underlying ALS.

Early Alzheimer's disease pathology in human cortex involves transient cell states

Cellular perturbations underlying Alzheimer's disease (AD) are primarily studied in human postmortem samples and model organisms. Here, we generated a single-nucleus atlas from a rare cohort of cortical biopsies from living individuals with varying degrees of AD pathology. We next performed a systematic cross-disease and cross-species integrative analysis to identify a set of cell states that are specific to early AD pathology. These changes-which we refer to as the early cortical amyloid response-were prominent in neurons, wherein we identified a transitional hyperactive state preceding the loss of excitatory neurons, which we confirmed by acute slice physiology on independent biopsy specimens. Microglia overexpressing neuroinflammatory-related processes also expanded as AD pathology increased. Finally, both oligodendrocytes and pyramidal neurons upregulated genes associated with β-amyloid production and processing during this early hyperactive phase. Our integrative analysis provides an organizing framework for targeting circuit dysfunction, neuroinflammation, and amyloid production early in AD pathogenesis.

From methylation to myelination: epigenomic and transcriptomic profiling of chronic inactive demyelinated multiple sclerosis lesions

In the progressive phase of multiple sclerosis (MS), the hampered differentiation capacity of oligodendrocyte precursor cells (OPCs) eventually results in remyelination failure. We have previously shown that DNA methylation of Id2/Id4 is highly involved in OPC differentiation and remyelination. In this study, we took an unbiased approach by determining genome-wide DNA methylation patterns within chronically demyelinated MS lesions and investigated how certain epigenetic signatures relate to OPC differentiation capacity. We compared genome-wide DNA methylation and transcriptional profiles between chronically demyelinated MS lesions and matched normal-appearing white matter (NAWM), making use of post-mortem brain tissue (n = 9/group). DNA methylation differences that inversely correlated with mRNA expression of their corresponding genes were validated for their cell-type specificity in laser-captured OPCs using pyrosequencing. The CRISPR-dCas9-DNMT3a/TET1 system was used to epigenetically edit human-iPSC-derived oligodendrocytes to assess the effect on cellular differentiation. Our data show hypermethylation of CpGs within genes that cluster in gene ontologies related to myelination and axon ensheathment. Cell type-specific validation indicates a region-dependent hypermethylation of MBP, encoding for myelin basic protein, in OPCs obtained from white matter lesions compared to NAWM-derived OPCs. By altering the DNA methylation state of specific CpGs within the promotor region of MBP, using epigenetic editing, we show that cellular differentiation and myelination can be bidirectionally manipulated using the CRISPR-dCas9-DNMT3a/TET1 system in vitro. Our data indicate that OPCs within chronically demyelinated MS lesions acquire an inhibitory phenotype, which translates into hypermethylation of crucial myelination-related genes. Altering the epigenetic status of MBP can restore the differentiation capacity of OPCs and possibly boost (re)myelination.

Directional induction of neural stem cells, a new therapy for neurodegenerative diseases and ischemic stroke

Due to the limited capacity of the adult mammalian brain to self-repair and regenerate, neurological diseases, especially neurodegenerative disorders and stroke, characterized by irreversible cellular damage are often considered as refractory diseases. Neural stem cells (NSCs) play a unique role in the treatment of neurological diseases for their abilities to self-renew and form different neural lineage cells, such as neurons and glial cells. With the increasing understanding of neurodevelopment and advances in stem cell technology, NSCs can be obtained from different sources and directed to differentiate into a specific neural lineage cell phenotype purposefully, making it possible to replace specific cells lost in some neurological diseases, which provides new approaches to treat neurodegenerative diseases as well as stroke. In this review, we outline the advances in generating several neuronal lineage subtypes from different sources of NSCs. We further summarize the therapeutic effects and possible therapeutic mechanisms of these fated specific NSCs in neurological disease models, with special emphasis on Parkinson's disease and ischemic stroke. Finally, from the perspective of clinical translation, we compare the strengths and weaknesses of different sources of NSCs and different methods of directed differentiation, and propose future research directions for directed differentiation of NSCs in regenerative medicine.

Early Alzheimer's disease pathology in human cortex is associated with a transient phase of distinct cell states

Cellular perturbations underlying Alzheimer's disease are primarily studied in human postmortem samples and model organisms. Here we generated a single-nucleus atlas from a rare cohort of cortical biopsies from living individuals with varying degrees of Alzheimer's disease pathology. We next performed a systematic cross-disease and cross-species integrative analysis to identify a set of cell states that are specific to early AD pathology. These changes-which we refer to as the Early Cortical Amyloid Response-were prominent in neurons, wherein we identified a transient state of hyperactivity preceding loss of excitatory neurons, which correlated with the selective loss of layer 1 inhibitory neurons. Microglia overexpressing neuroinflammatory-related processes also expanded as AD pathological burden increased. Lastly, both oligodendrocytes and pyramidal neurons upregulated genes associated with amyloid beta production and processing during this early hyperactive phase. Our integrative analysis provides an organizing framework for targeting circuit dysfunction, neuroinflammation, and amyloid production early in AD pathogenesis.

Selective PDE4 subtype inhibition provides new opportunities to intervene in neuroinflammatory versus myelin damaging hallmarks of multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) characterized by focal inflammatory lesions and prominent demyelination. Even though the currently available therapies are effective in treating the initial stages of disease, they are unable to halt or reverse disease progression into the chronic progressive stage. Thus far, no repair-inducing treatments are available for progressive MS patients. Hence, there is an urgent need for the development of new therapeutic strategies either targeting the destructive immunological demyelination or boosting endogenous repair mechanisms. Using in vitro, ex vivo, and in vivo models, we demonstrate that selective inhibition of phosphodiesterase 4 (PDE4), a family of enzymes that hydrolyzes and inactivates cyclic adenosine monophosphate (cAMP), reduces inflammation and promotes myelin repair. More specifically, we segregated the myelination-promoting and anti-inflammatory effects into a PDE4D- and PDE4B-dependent process respectively. We show that inhibition of PDE4D boosts oligodendrocyte progenitor cells (OPC) differentiation and enhances (re)myelination of both murine OPCs and human iPSC-derived OPCs. In addition, PDE4D inhibition promotes in vivo remyelination in the cuprizone model, which is accompanied by improved spatial memory and reduced visual evoked potential latency times. We further identified that PDE4B-specific inhibition exerts anti-inflammatory effects since it lowers in vitro monocytic nitric oxide (NO) production and improves in vivo neurological scores during the early phase of experimental autoimmune encephalomyelitis (EAE). In contrast to the pan PDE4 inhibitor roflumilast, the therapeutic dose of both the PDE4B-specific inhibitor A33 and the PDE4D-specific inhibitor Gebr32a did not trigger emesis-like side effects in rodents. Finally, we report distinct PDE4D isoform expression patterns in human area postrema neurons and human oligodendroglia lineage cells. Using the CRISPR-Cas9 system, we confirmed that pde4d1/2 and pde4d6 are the key targets to induce OPC differentiation. Collectively, these data demonstrate that gene specific PDE4 inhibitors have potential as novel therapeutic agents for targeting the distinct disease processes of MS.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

Cell reprogramming for oligodendrocytes: A review of protocols and their applications to disease modeling and cell-based remyelination therapies

Oligodendrocytes are a type of glial cells that produce a lipid-rich membrane called myelin. Myelin assembles into a sheath and lines neuronal axons in the brain and spinal cord to insulate them. This not only increases the speed and efficiency of nerve signal transduction but also protects the axons from damage and degradation, which could trigger neuronal cell death. Demyelination, which is caused by a loss of myelin and oligodendrocytes, is a prominent feature of many neurological conditions, including Multiple sclerosis (MS), spinal cord injuries (SCI), and leukodystrophies. Demyelination is followed by a time of remyelination mediated by the recruitment of endogenous oligodendrocyte precursor cells, their migration to the injury site, and differentiation into myelin-producing oligodendrocytes. Unfortunately, endogenous remyelination is not sufficient to overcome demyelination, which explains why there are to date no regenerative-based treatments for MS, SCI, or leukodystrophies. To better understand the role of oligodendrocytes and develop cell-based remyelination therapies, human oligodendrocytes have been derived from somatic cells using cell reprogramming. This review will detail the different cell reprogramming methods that have been developed to generate human oligodendrocytes and their applications to disease modeling and cell-based remyelination therapies. Recent developments in the field have seen the derivation of brain organoids from pluripotent stem cells, and protocols have been devised to incorporate oligodendrocytes within the organoids, which will also be reviewed.

Understanding neural development and diseases using CRISPR screens in human pluripotent stem cell-derived cultures

The brain is arguably the most complex part of the human body in form and function. Much remains unclear about the molecular mechanisms that regulate its normal and pathological physiology. This lack of knowledge largely stems from the inaccessible nature of the human brain, and the limitation of animal models. As a result, brain disorders are difficult to understand and even more difficult to treat. Recent advances in generating human pluripotent stem cells (hPSCs)-derived 2-dimensional (2D) and 3-dimensional (3D) neural cultures have provided an accessible system to model the human brain. Breakthroughs in gene editing technologies such as CRISPR/Cas9 further elevate the hPSCs into a genetically tractable experimental system. Powerful genetic screens, previously reserved for model organisms and transformed cell lines, can now be performed in human neural cells. Combined with the rapidly expanding single-cell genomics toolkit, these technological advances culminate to create an unprecedented opportunity to study the human brain using functional genomics. This review will summarize the current progress of applying CRISPR-based genetic screens in hPSCs-derived 2D neural cultures and 3D brain organoids. We will also evaluate the key technologies involved and discuss their related experimental considerations and future applications.

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.

Promoting Oligodendrocyte Differentiation from Human Induced Pluripotent Stem Cells by Activating Endocannabinoid Signaling for Treating Spinal Cord Injury

Transplantation of oligodendrocyte progenitor cell (OPC) at the injury site is being developed as a potential therapeutic strategy for promoting remyelination and locomotor function recovery after spinal cord injury (SCI). To this end, the development of expandable and functional human OPCs is crucial for testing their efficacy in SCI. In mice and rats, the endocannabinoid signaling system is crucial for the survival, differentiation, and maturation of OPCs. Similar studies in humans are lacking currently. Endocannabinoids and exogenous cannabinoids exert their effects mainly via cannabinoid receptors (CB1R and CB2R). We demonstrated that these receptors were differentially expressed in iPSC-derived human NSCs and OPCs, and they could be activated by WIN55212-2 (WIN), a potent CB1R/CB2R agonist to upregulate the endocannabinoid signaling during glial induction. WIN primed NSCs generated more OLIG2 + glial progenitors and migratory PDGFRα + OPC in a CB1/CB2 dependent manner compared to unprimed NSCs. Furthermore, WIN-induced OPCs (WIN-OPCs) robustly differentiated into functional oligodendrocytes and myelinate in vitro and in vivo in a mouse spinal cord injury model. RNA-Seq revealed that WIN upregulated the biological process of positive regulation of oligodendrocyte differentiation. Mechanistically, WIN could act as a partial smoothed (SMO) inhibitor or activate CB1/CB2 to form heteromeric complexes with SMO leading to the inhibition of GLI1 in the Sonic hedgehog pathway. The partial and temporal inhibition of GLI1 during glial induction is shown to promote OPCs that differentiate faster than control's. Thus, CB1R/CB2R activation results in more efficient generation of OPCs that can mature and efficiently myelinate.

Neuroprotective effect of liraglutide in an experimental mouse model of multiple sclerosis: role of AMPK/SIRT1 signaling and NLRP3 inflammasome

The heterogeneous nature of multiple sclerosis (MS) and the unavailability of treatments addressing its intricate network and reversing the disease state is yet an area that needs to be elucidated. Liraglutide, a glucagon-like peptide-1 analogue, recently exhibited intriguing potential neuroprotective effects. The currents study investigated its potential effect against mouse model of MS and the possible underlying mechanisms. Demyelination was induced in C57Bl/6 mice by cuprizone (400 mg/kg/day p.o.) for 5 weeks. Animals received either liraglutide (25 nmol/kg/day i.p.) or dorsomorphin, an AMPK inhibitor, (2.5 mg/Kg i.p.) 30 min before the liraglutide dose, for 4 weeks (starting from the second week). Liraglutide improved the behavioral profile in cuprizone-treated mice. Furthermore, it induced the re-myelination process through stimulating oligodendrocyte progenitor cells differentiation via Olig2 transcription activation, reflected by increased myelin basic protein and myelinated nerve fiber percentage. Liraglutide elevated the protein content of p-AMPK and SIRT1, in addition to the autophagy proteins Beclin-1 and LC3B. Liraglutide halted cellular damage as manifested by reduced HMGB1 protein and consequently TLR-4 downregulation, coupled with a decrease in NF-κB. Liraglutide also suppressed NLRP3 transcription. Dorsomorphin pre-administration indicated a possible interplay between AMPK/SIRT1 and NLRP3 inflammasome activation as it partially reversed liraglutide’s effects. Immunohistochemical examination of Iba⁺ microglia emphasized these findings. In conclusion, liraglutide exerts neuroprotection against cuprizone-induced demyelination via anti-inflammatory, autophagic flux activation, NLRP3 inflammasome suppression, and anti-apoptotic mechanisms, possibly mediated, at least in part, via AMPK/SIRT1, autophagy, TLR-4/ NF-κB/NLRP3 signaling.

The Integration of Cell Therapy and Biomaterials as Treatment Strategies for Remyelination

Multiple sclerosis (MS) is a chronic degenerative autoimmune disease of the central nervous system that causes inflammation, demyelinating lesions, and axonal damage and is associated with a high rate of early-onset disability. Disease-modifying therapies are used to mitigate the inflammatory process in MS but do not promote regeneration or remyelination; cell therapy may play an important role in these processes, modulating inflammation and promoting the repopulation of oligodendrocytes, which are responsible for myelin repair. The development of genetic engineering has led to the emergence of stable, biocompatible biomaterials that may promote a favorable environment for exogenous cells. This review summarizes the available evidence about the effects of transplantation of different types of stem cells reported in studies with several animal models of MS and clinical trials in human patients. We also address the advantages of combining cell therapy with biomaterials.

Expression of Lineage Transcription Factors Identifies Differences in Transition States of Induced Human Oligodendrocyte Differentiation

Oligodendrocytes (OLs) are critical for myelination and are implicated in several brain disorders. Directed differentiation of human-induced OLs (iOLs) from pluripotent stem cells can be achieved by forced expression of different combinations of the transcription factors SOX10 (S), OLIG2 (O), and NKX6.2 (N). Here, we applied quantitative image analysis and single-cell transcriptomics to compare different transcription factor (TF) combinations for their efficacy towards robust OL lineage conversion. Compared with S alone, the combination of SON increases the number of iOLs and generates iOLs with a more complex morphology and higher expression levels of myelin-marker genes. RNA velocity analysis of individual cells reveals that S generates a population of oligodendrocyte-precursor cells (OPCs) that appear to be more immature than those generated by SON and to display distinct molecular properties. Our work highlights that TFs for generating iOPCs or iOLs should be chosen depending on the intended application or research question, and that SON might be beneficial to study more mature iOLs while S might be better suited to investigate iOPC biology.

Novel in vitro Experimental Approaches to Study Myelination and Remyelination in the Central Nervous System

Myelin is the lipidic insulating structure enwrapping axons and allowing fast saltatory nerve conduction. In the central nervous system, myelin sheath is the result of the complex packaging of multilamellar extensions of oligodendrocyte (OL) membranes. Before reaching myelinating capabilities, OLs undergo a very precise program of differentiation and maturation that starts from OL precursor cells (OPCs). In the last 20 years, the biology of OPCs and their behavior under pathological conditions have been studied through several experimental models. When co-cultured with neurons, OPCs undergo terminal maturation and produce myelin tracts around axons, allowing to investigate myelination in response to exogenous stimuli in a very simple in vitro system. On the other hand, in vivo models more closely reproducing some of the features of human pathophysiology enabled to assess the consequences of demyelination and the molecular mechanisms of remyelination, and they are often used to validate the effect of pharmacological agents. However, they are very complex, and not suitable for large scale drug discovery screening. Recent advances in cell reprogramming, biophysics and bioengineering have allowed impressive improvements in the methodological approaches to study brain physiology and myelination. Rat and mouse OPCs can be replaced by human OPCs obtained by induced pluripotent stem cells (iPSCs) derived from healthy or diseased individuals, thus offering unprecedented possibilities for personalized disease modeling and treatment. OPCs and neural cells can be also artificially assembled, using 3D-printed culture chambers and biomaterial scaffolds, which allow modeling cell-to-cell interactions in a highly controlled manner. Interestingly, scaffold stiffness can be adopted to reproduce the mechanosensory properties assumed by tissues in physiological or pathological conditions. Moreover, the recent development of iPSC-derived 3D brain cultures, called organoids, has made it possible to study key aspects of embryonic brain development, such as neuronal differentiation, maturation and network formation in temporal dynamics that are inaccessible to traditional in vitro cultures. Despite the huge potential of organoids, their application to myelination studies is still in its infancy. In this review, we shall summarize the novel most relevant experimental approaches and their implications for the identification of remyelinating agents for human diseases such as multiple sclerosis.

Derivation of Oligodendrocyte Precursors from Adult Bone Marrow Stromal Cells for Remyelination Therapy

Transplantation of oligodendrocyte precursors (OPs) is potentially therapeutic for myelin disorders but a safe and accessible cell source remains to be identified. Here we report a two-step protocol for derivation of highly enriched populations of OPs from bone marrow stromal cells of young adult rats (aMSCs). Neural progenitors among the aMSCs were expanded in non-adherent sphere-forming cultures and subsequently directed along the OP lineage with the use of glial-inducing growth factors. Immunocytochemical and flow cytometric analyses of these cells confirmed OP-like expression of Olig2, PDGFRα, NG2, and Sox10. OPs so derived formed compact myelin both in vitro, as in co-culture with purified neurons, and in vivo, following transplantation into the corpus callosum of neonatal shiverer mice. Not only did the density of myelinated axons in the corpus callosum of recipient shiverer mice reach levels comparable to those in age-matched wild-type mice, but the mean lifespan of recipient shiverer mice also far exceeded those of non-recipient shiverer mice. Our results thus promise progress in harnessing the OP-generating potential of aMSCs towards cell therapy for myelin disorders.

SOX9-induced Generation of Functional Astrocytes Supporting Neuronal Maturation in an All-human System

Astrocytes, the main supportive cell type of the brain, show functional impairments upon ageing and in a broad spectrum of neurological disorders. Limited access to human astroglia for pre-clinical studies has been a major bottleneck delaying our understanding of their role in brain health and disease. We demonstrate here that functionally mature human astrocytes can be generated by SOX9 overexpression for 6 days in pluripotent stem cell (PSC)-derived neural progenitor cells. Inducible (i)SOX9-astrocytes display functional properties comparable to primary human astrocytes comprising glutamate uptake, induced calcium responses and cytokine/growth factor secretion. Importantly, electrophysiological properties of iNGN2-neurons co-cultured with iSOX9-astrocytes are indistinguishable from gold-standard murine primary cultures. The high yield, fast timing and the possibility to cryopreserve iSOX9-astrocytes without losing functional properties makes them suitable for scaled-up production for high-throughput analyses. Our findings represent a step forward to an all-human iPSC-derived neural model for drug development in neuroscience and towards the reduction of animal use in biomedical research.

Novel Tools and Investigative Approaches for the Study of Oligodendrocyte Precursor Cells (NG2-Glia) in CNS Development and Disease

Oligodendrocyte progenitor cells (OPCs), also referred to as NG2-glia, are the most proliferative cell type in the adult central nervous system. While the primary role of OPCs is to serve as progenitors for oligodendrocytes, in recent years, it has become increasingly clear that OPCs fulfil a number of other functions. Indeed, independent of their role as stem cells, it is evident that OPCs can regulate the metabolic environment, directly interact with and modulate neuronal function, maintain the blood brain barrier (BBB) and regulate inflammation. In this review article, we discuss the state-of-the-art tools and investigative approaches being used to characterize the biology and function of OPCs. From functional genetic investigation to single cell sequencing and from lineage tracing to functional imaging, we discuss the important discoveries uncovered by these techniques, such as functional and spatial OPC heterogeneity, novel OPC marker genes, the interaction of OPCs with other cells types, and how OPCs integrate and respond to signals from neighboring cells. Finally, we review the use of in vitro assay to assess OPC functions. These methodologies promise to lead to ever greater understanding of this enigmatic cell type, which in turn will shed light on the pathogenesis and potential treatment strategies for a number of diseases, such as multiple sclerosis (MS) and gliomas.

Mini-Review: Induced pluripotent stem cells and the search for new cell-specific ALS therapeutic targets

Amongst the most important discoveries in ALS pathobiology are the works demonstrating that multiple cell types contribute to disease onset and progression. However, a significant limitation in ALS research is the inability to obtain tissues from ALS patient brain and spinal cord during the course of the disease. In vivo modeling has provided insights into the role of these cell subtypes in disease onset and progression. However, in vivo models also have shortcomings, including the reliance on a limited number of models based upon hereditary forms of the disease. Therefore, using human induced pluripotent stem cells (iPSC) reprogrammed from somatic cells of ALS patients, with both hereditary and sporadic forms of the disease, and differentiated into cell subtypes of both the central nervous system (CNS) and peripheral nervous system (PNS), have become powerful complementary tools for investigating basic mechanisms of disease as well as a platform for drug discovery. Motor neuron and other neuron subtypes, as well as non-neuronal cells have been differentiated from human iPSC and studied for their potential contributions to ALS pathobiology. As iPSC technologies have advanced, 3D modeling with multicellular systems organised in microfluidic chambers or organoids are the next step in validating the pathways and therapeutic targets already identified. Precision medicine approaches with iPSC using either traditional strategies of screening drugs that target a known pathogenic mechanism as well as "blind-to-target" drug screenings that allow for patient stratification based on drug response rather than clinical characteristics are now being employed.

NPC2 as a Prognostic Biomarker for Glioblastoma Based on Integrated Bioinformatics Analysis and Cytological Experiments

Glioblastoma (GBM) is one of the most common and fatal malignancies worldwide, while its prognostic biomarkers are still being explored. This study aims to identify potential genes with clinical and prognostic significance by integrating bioinformatics analysis and investigating their function in HNSCC. Based on the Single-cell RNA sequencing (scRNA-seq) results of H3K27M-glioma cells, computational bioinformatics methods were employed for selecting prognostic biomarker for GBM. The protein NPC2 (NPC Intracellular Cholesterol Transporter 2), which has been shown to be related to lipoprotein metabolism and innate immune system, was identified to be upregulated in GBM. NPC2 showed a relatively higher expression in GBM samples, and a negative correlation with tumor purity and tumor infiltrating immune cells. Additionally, NPC2 was knocked down in U87-MG and U251 cells line, and cell proliferation and migration capability were evaluated with CCK-8, scratch and transwell assay, respectively. Cytological experiments has shown that NPC2 overexpression inhibited GBM cells proliferation and migration, indicating its important role in GBM progression. This is the first investigation into the prognostic value of NPC2 interact with GBM. The potential molecular factor NPC2 have been identified as a prognostic biomarker for GBM.

Human stem cell-derived oligodendrocytes: From humanized animal models to cell therapy in myelin diseases

Oligodendrocytes are main targets in demyelinating and dysmyelinating diseases of the central nervous system (CNS), but are also involved in accidental, neurodegenerative and psychiatric disorders. The underlying pathology of these diseases is not fully understood and treatments are still lacking. The recent discovery of the induced pluripotent stem cell (iPSC) technology has open the possibility to address the biology of human oligodendroglial cells both in the dish and in vivo via engraftment in animal models, and paves the way for the development of treatment for myelin disorders. In this review, we make a short overview of the different sources human oligodendroglial cells, and animal models available for pre-clinical cell therapy. We discuss the anatomical and functional benefit of grafted iPSC-progenitors over their brain counterparts, their use in disease modeling and the missing gaps that still prevent to study their biology in the most integrated way, and to translate iPSC-stem cell based therapy to the clinic.