MicroRNA expression profiling of oligodendrocyte differentiation from human embryonic stem cells

Loss of miR-145 promotes remyelination and functional recovery in a model of chronic central demyelination

Strategies for treating progressive multiple sclerosis (MS) remain limited. Here, we found that miR-145-5p is overabundant uniquely in chronic lesion tissues from secondary progressive MS patients. We induced both acute and chronic demyelination in miR-145 knockout mice to determine its contributions to remyelination failure. Following acute demyelination, no advantage to miR-145 loss could be detected. However, after chronic demyelination, animals with miR-145 loss demonstrated increased remyelination and functional recovery, coincident with altered presence of astrocytes and microglia within the corpus callosum relative to wild-type animals. This improved response in miR-145 knockout animals coincided with a pathological upregulation of miR-145-5p in wild-type animals with chronic cuprizone exposure, paralleling human chronic lesions. Furthermore, miR-145 overexpression specifically in oligodendrocytes (OLs) severely stunted differentiation and negatively impacted survival. RNAseq analysis showed altered transcriptome in these cells with downregulated major pathways involved in myelination. Our data suggest that pathological accumulation of miR-145-5p is a distinctive feature of chronic demyelination and is strongly implicated in the failure of remyelination, possibly due to the inhibition of OL differentiation together with alterations in other glial cells. This is mirrored in chronic MS lesions, and thus miR-145-5p serves as a potential relevant therapeutic target in progressive forms of MS.

Regulators of Oligodendrocyte Differentiation

Myelination has evolved as a mechanism to ensure fast and efficient propagation of nerve impulses along axons. Within the central nervous system (CNS), myelination is carried out by highly specialized glial cells, oligodendrocytes. The formation of myelin is a prolonged aspect of CNS development that occurs well into adulthood in humans, continuing throughout life in response to injury or as a component of neuroplasticity. The timing of myelination is tightly tied to the generation of oligodendrocytes through the differentiation of their committed progenitors, oligodendrocyte precursor cells (OPCs), which reside throughout the developing and adult CNS. In this article, we summarize our current understanding of some of the signals and pathways that regulate the differentiation of OPCs, and thus the myelination of CNS axons.

The therapeutic potential of microRNAs to ameliorate spinal cord injury by regulating oligodendrocyte progenitor cells and remyelination

Spinal cord injury (SCI) can cause loss of sensory and motor function below the level of injury, posing a serious threat to human health and quality of life. One significant characteristic feature of pathological changes following injury in the nervous system is demyelination, which partially contributes to the long-term deficits in neural function after injury. The remyelination in the central nervous system (CNS) is mainly mediated by oligodendrocyte progenitor cells (OPCs). Numerous complex intracellular signaling and transcriptional factors regulate the differentiation process from OPCs to mature oligodendrocytes (OLs) and myelination. Studies have shown the importance of microRNA (miRNA) in regulating OPC functions. In this review, we focus on the demyelination and remyelination after SCI, and summarize the progress of miRNAs on OPC functions and remyelination, which might provide a potential therapeutic target for SCI treatments.

Hypothermia effects on neuronal plasticity post spinal cord injury

BACKGROUND

SCI is a time-sensitive debilitating neurological condition without treatment options. Although the central nervous system is not programmed for effective endogenous repairs or regeneration, neuroplasticity partially compensates for the dysfunction consequences of SCI.

OBJECTIVE AND HYPOTHESIS

The purpose of our study is to investigate whether early induction of hypothermia impacts neuronal tissue compensatory mechanisms. Our hypothesis is that although neuroplasticity happens within the neuropathways, both above (forelimbs) and below (hindlimbs) the site of spinal cord injury (SCI), hypothermia further influences the upper limbs' SSEP signals, even when the SCI is mid-thoracic.

STUDY DESIGN

A total of 30 male and female adult rats are randomly assigned to four groups (n = 7): sham group, control group undergoing only laminectomy, injury group with normothermia (37°C), and injury group with hypothermia (32°C +/-0.5°C).

METHODS

The NYU-Impactor is used to induce mid-thoracic (T8) moderate (12.5 mm) midline contusive injury in rats. Somatosensory evoked potential (SSEP) is an objective and non-invasive procedure to assess the functionality of selective neuropathways. SSEP monitoring of baseline, and on days 4 and 7 post-SCI are performed.

RESULTS

Statistical analysis shows that there are significant differences between the SSEP signal amplitudes recorded when stimulating either forelimb in the group of rats with normothermia compared to the rats treated with 2h of hypothermia on day 4 (left forelimb, p = 0.0417 and right forelimb, p = 0.0012) and on day 7 (left forelimb, p = 0.0332 and right forelimb, p = 0.0133) post-SCI.

CONCLUSION

Our results show that the forelimbs SSEP signals from the two groups of injuries with and without hypothermia have statistically significant differences on days 4 and 7. This indicates the neuroprotective effect of early hypothermia and its influences on stimulating further the neuroplasticity within the upper limbs neural network post-SCI. Timely detection of neuroplasticity and identifying the endogenous and exogenous factors have clinical applications in planning a more effective rehabilitation and functional electrical stimulation (FES) interventions in SCI patients.

MicroRNAs dysregulated in multiple sclerosis affect the differentiation of CG-4 cells, an oligodendrocyte progenitor cell line

Introduction

Demyelination is one of the hallmarks of multiple sclerosis (MS). While remyelination occurs during the disease, it is incomplete from the start and strongly decreases with its progression, mainly due to the harm to oligodendrocyte progenitor cells (OPCs), causing irreversible neurological deficits and contributing to neurodegeneration. Therapeutic strategies promoting remyelination are still very preliminary and lacking within the current treatment panel for MS.

Methods

In a previous study, we identified 21 microRNAs dysregulated mostly in the CSF of relapsing and/or remitting MS patients. In this study we transfected the mimics/inhibitors of several of these microRNAs separately in an OPC cell line, called CG-4. We aimed (1) to phenotypically characterize their effect on OPC differentiation and (2) to identify corroborating potential mRNA targets via immunocytochemistry, RT-qPCR analysis, RNA sequencing, and Gene Ontology enrichment analysis.

Results

We observed that the majority of 13 transfected microRNA mimics decreased the differentiation of CG-4 cells. We demonstrate, by RNA sequencing and independent RT-qPCR analyses, that miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage as evidenced by the downregulation of premyelinating oligodendrocyte (OL) [Tcf7l2, Cnp (except for miR-145-5p)] and mature OL (Plp1, Mbp, and Mobp) markers, whereas only miR-214-3p promotes OPC differentiation. We further propose a comprehensive exploration of their change in cell fate through Gene Ontology enrichment analysis. We finally confirm by RT-qPCR analyses the downregulation of several predicted mRNA targets for each microRNA that possibly support their effect on OPC differentiation by very distinctive mechanisms, of which some are still unexplored in OPC/OL physiology.

Conclusion

miR-33-3p, miR-34c-5p, and miR-124-5p arrest OPC differentiation at a late progenitor stage and miR-145-5p at a premyelinating stage, whereas miR-214-3p promotes the differentiation of CG-4 cells. We propose several potential mRNA targets and hypothetical mechanisms by which each microRNA exerts its effect. We hereby open new perspectives in the research on OPC differentiation and the pathophysiology of demyelination/remyelination, and possibly even in the search for new remyelinating therapeutic strategies in the scope of MS.

Disturbed Oligodendroglial Maturation Causes Cognitive Dysfunction in Schizophrenia: A New Hypothesis

BACKGROUND AND HYPOTHESIS

Cognitive impairment is a hallmark of schizophrenia, but no effective treatment is available to date. The underlying pathophysiology includes disconnectivity between hippocampal and prefrontal brain regions. Supporting evidence comes from diffusion-weighted imaging studies that suggest abnormal organization of frontotemporal white matter pathways in schizophrenia.

STUDY DESIGN

Here, we hypothesize that in schizophrenia, deficient maturation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes substantially contributes to abnormal frontotemporal macro- and micro-connectivity and subsequent cognitive deficits.

STUDY RESULTS

Our postmortem studies indicate a reduced oligodendrocyte number in the cornu ammonis 4 (CA4) subregion of the hippocampus, and others have reported the same histopathological finding in the dorsolateral prefrontal cortex. Our series of studies on aerobic exercise training showed a volume increase in the hippocampus, specifically in the CA4 region, and improved cognition in individuals with schizophrenia. The cognitive effects were subsequently confirmed by meta-analyses. Cell-specific schizophrenia polygenic risk scores showed that exercise-induced CA4 volume increase significantly correlates with OPCs. From animal models, it is evident that early life stress and oligodendrocyte-related gene variants lead to schizophrenia-related behavior, cognitive deficits, impaired oligodendrocyte maturation, and reduced myelin thickness.

CONCLUSIONS

Based on these findings, we propose that pro-myelinating drugs (e.g., the histamine blocker clemastine) combined with aerobic exercise training may foster the regeneration of myelin plasticity as a basis for restoring frontotemporal connectivity and cognition in schizophrenia.

The role of microRNAs in neurobiology and pathophysiology of the hippocampus

MicroRNAs (miRNAs) are short non-coding and well-conserved RNAs that are linked to many aspects of development and disorders. MicroRNAs control the expression of genes related to different biological processes and play a prominent role in the harmonious expression of many genes. During neural development of the central nervous system, miRNAs are regulated in time and space. In the mature brain, the dynamic expression of miRNAs continues, highlighting their functional importance in neurons. The hippocampus, as one of the crucial brain structures, is a key component of major functional connections in brain. Gene expression abnormalities in the hippocampus lead to disturbance in neurogenesis, neural maturation and synaptic formation. These disturbances are at the root of several neurological disorders and behavioral deficits, including Alzheimer's disease, epilepsy and schizophrenia. There is strong evidence that abnormalities in miRNAs are contributed in neurodegenerative mechanisms in the hippocampus through imbalanced activity of ion channels, neuronal excitability, synaptic plasticity and neuronal apoptosis. Some miRNAs affect oxidative stress, inflammation, neural differentiation, migration and neurogenesis in the hippocampus. Furthermore, major signaling cascades in neurodegeneration, such as NF-Kβ signaling, PI3/Akt signaling and Notch pathway, are closely modulated by miRNAs. These observations, suggest that microRNAs are significant regulators in the complicated network of gene regulation in the hippocampus. In the current review, we focus on the miRNA functional role in the progression of normal development and neurogenesis of the hippocampus. We also consider how miRNAs in the hippocampus are crucial for gene expression mechanisms in pathophysiological pathways.

Proteomic investigation of neural stem cell to oligodendrocyte precursor cell differentiation reveals phosphorylation-dependent Dclk1 processing

Oligodendrocytes are generated via a two-step mechanism from pluripotent neural stem cells (NSCs): after differentiation of NSCs to oligodendrocyte precursor/NG2 cells (OPCs), they further develop into mature oligodendrocytes. The first step of this differentiation process is only incompletely understood. In this study, we utilized the neurosphere assay to investigate NSC to OPC differentiation in a time course-dependent manner by mass spectrometry-based (phospho-) proteomics. We identify doublecortin-like kinase 1 (Dclk1) as one of the most prominently regulated proteins in both datasets, and show that it undergoes a gradual transition between its short/long isoform during NSC to OPC differentiation. This is regulated by phosphorylation of its SP-rich region, resulting in inhibition of proteolytic Dclk1 long cleavage, and therefore Dclk1 short generation. Through interactome analyses of different Dclk1 isoforms by proximity biotinylation, we characterize their individual putative interaction partners and substrates. All data are available via ProteomeXchange with identifier PXD040652.

Remyelination in multiple sclerosis from the miRNA perspective

Remyelination relies on the repair of damaged myelin sheaths, involving microglia cells, oligodendrocyte precursor cells (OPCs), and mature oligodendrocytes. This process drives the pathophysiology of autoimmune chronic disease of the central nervous system (CNS), multiple sclerosis (MS), leading to nerve cell damage and progressive neurodegeneration. Stimulating the reconstruction of damaged myelin sheaths is one of the goals in terms of delaying the progression of MS symptoms and preventing neuronal damage. Short, noncoding RNA molecules, microRNAs (miRNAs), responsible for regulating gene expression, are believed to play a crucial role in the remyelination process. For example, studies showed that miR-223 promotes efficient activation and phagocytosis of myelin debris by microglia, which is necessary for the initiation of remyelination. Meanwhile, miR-124 promotes the return of activated microglia to the quiescent state, while miR-204 and miR-219 promote the differentiation of mature oligodendrocytes. Furthermore, miR-138, miR-145, and miR-338 have been shown to be involved in the synthesis and assembly of myelin proteins. Various delivery systems, including extracellular vesicles, hold promise as an efficient and non-invasive way for providing miRNAs to stimulate remyelination. This article summarizes the biology of remyelination as well as current challenges and strategies for miRNA molecules in potential diagnostic and therapeutic applications.

The epigenetic landscape of oligodendrocyte lineage cells

The epigenetic landscape of oligodendrocyte lineage cells refers to the cell-specific modifications of DNA, chromatin, and RNA that define a unique gene expression pattern of functionally specialized cells. Here, we focus on the epigenetic changes occurring as progenitors differentiate into myelin-forming cells and respond to the local environment. First, modifications of DNA, RNA, nucleosomal histones, key principles of chromatin organization, topologically associating domains, and local remodeling will be reviewed. Then, the relationship between epigenetic modulators and RNA processing will be explored. Finally, the reciprocal relationship between the epigenome as a determinant of the mechanical properties of cell nuclei and the target of mechanotransduction will be discussed. The overall goal is to provide an interpretative key on how epigenetic changes may account for the heterogeneity of the transcriptional profiles identified in this lineage.

Women in the field of multiple sclerosis: How they contributed to paradigm shifts

History is full of women who made enormous contributions to science. While there is little to no imbalance at the early career stage, a decreasing proportion of women is found as seniority increases. In the multiple sclerosis (MS) field, 44% of first authors and only 35% of senior authors were female. So, in this review, we highlight ground-breaking research done by women in the field of MS, focusing mostly on their work as principal investigators. MS is an autoimmune disorder of the central nervous system (CNS), with evident paradigm shifts in the understating of its pathophysiology. It is known that the immune system becomes overactivated and attacks myelin sheath surrounding axons. The resulting demyelination disrupts the communication signals to and from the CNS, which causes unpredictable symptoms, depending on the neurons that are affected. Classically, MS was reported to cause mostly physical and motor disabilities. However, it is now recognized that cognitive impairment affects more than 50% of the MS patients. Another shifting paradigm was the involvement of gray matter in MS pathology, formerly considered to be a white matter disease. Additionally, the identification of different T cell immune subsets and the mechanisms underlying the involvement of B cells and peripheral macrophages provided a better understanding of the immunopathophysiological processes present in MS. Relevantly, the gut-brain axis, recognized as a bi-directional communication system between the CNS and the gut, was found to be crucial in MS. Indeed, gut microbiota influences not only different susceptibilities to MS pathology, but it can also be modulated in order to positively act in MS course. Also, after the identification of the first microRNA in 1993, the role of microRNAs has been investigated in MS, either as potential biomarkers or therapeutic agents. Finally, concerning MS therapeutical approaches, remyelination-based studies have arisen on the spotlight aiming to repair myelin loss/neuronal connectivity. Altogether, here we emphasize the new insights of remarkable women that have voiced the impact of cognitive impairment, white and gray matter pathology, immune response, and that of the CNS-peripheral interplay on MS diagnosis, progression, and/or therapy efficacy, leading to huge breakthroughs in the MS field.

MicroRNAs in oligodendrocyte development and remyelination

Oligodendrocytes are the glial cells responsible for the formation of myelin around axons of the central nervous system (CNS). Myelin is an insulating layer that allows electrical impulses to transmit quickly and efficiently along neurons. If myelin is damaged, as in chronic demyelinating disorders such as multiple sclerosis (MS), these impulses slow down. Remyelination by oligodendrocytes is often ineffective in MS, in part because of the failure of oligodendrocyte precursor cells (OPCs) to differentiate into mature, myelinating oligodendrocytes. The process of oligodendrocyte differentiation is tightly controlled by several regulatory networks involving transcription factors, intracellular signaling pathways, and extrinsic cues. Understanding the factors that regulate oligodendrocyte development is essential for the discovery of new therapeutic strategies capable of enhancing remyelination. Over the past decade, microRNAs (miRNAs) have emerged as key regulators of oligodendrocyte development, exerting effects on cell specification, proliferation, differentiation, and myelination. This article will review the role of miRNAs on oligodendrocyte biology and discuss their potential as promising therapeutic tools for remyelination.

The Effects of Sesquiterpene Lactones on the Differentiation of Human or Animal Cells Cultured In-Vitro: A Critical Systematic Review

Cellular differentiation is pivotal in health and disease. Interfering with the process of differentiation, such as inhibiting the differentiation of adipocytes and inducing the differentiation of cancer cells, is considered a therapeutic approach. Sesquiterpene lactones, primarily found in plants, have been attracted attention as differentiating/dedifferentiating agents tested on various human or animal cells. However, a consensus on sesquiterpene lactones’ effects and their mechanism of action is required. In this sense, through a systematic review, we have investigated the differentiating/dedifferentiating effects of sesquiterpene lactones on human or animal cells. 13 different cell lines originated from humans, mice, and rats, in addition to the effects of a total of 21 sesquiterpene lactones, were evaluated in the included studies. These components had either inducing, inhibiting, or no effect on the cells, mediating their effects through JAK-STAT, PI3K-Akt, mitogen-activated protein kinases, NFκB, PPARγ pathways. Although nearly all inducing and inhibiting effects were attributed to cancerous and normal cells, respectively, this is likely a result of a biased study design. Few studies reported negative results along with others, and no study was found reporting only negative results. As a result, not only are the effects and mechanism of action of sesquiterpene lactones not vivid but our knowledge and decisions are also misconducted. Moreover, there is a significant knowledge gap regarding the type of evaluated cells, other sesquiterpene lactones, and the involved signaling pathways. In conclusion, sesquiterpene lactones possess significant effects on differentiation status, leading to potentially efficient therapy of obesity, osteoporosis, and cancer. However, reporting negative results and further investigations on other cells, sesquiterpene lactones, and signaling pathways are highly suggested to pave the path of sesquiterpene lactones to the clinic more consciously.

OUP accepted manuscript

In oligodendrocytes of the vertebrate central nervous system a complex network of transcriptional regulators is required to ensure correct and timely myelination of neuronal axons. Here we identify Zfp276, the only mammalian ZAD-domain containing zinc finger protein, as a transcriptional regulator of oligodendrocyte differentiation and central myelination downstream of Sox10. In the central nervous system, Zfp276 is exclusively expressed in mature oligodendrocytes. Oligodendroglial deletion of Zfp276 led to strongly reduced expression of myelin genes in the early postnatal mouse spinal cord. Retroviral overexpression of Zfp276 in cultured oligodendrocyte precursor cells induced precocious expression of maturation markers and myelin genes, further supporting its role in oligodendroglial differentiation. On the molecular level, Zfp276 directly binds to and represses Sox10-dependent gene regulatory regions of immaturity factors and functionally interacts with the transcriptional repressor Zeb2 to enable fast transition of oligodendrocytes to the myelinating stage.

The Potential Role of miRNAs as Predictive Biomarkers in Neurodevelopmental Disorders

Neurodevelopmental disorders are defined as a set of abnormal brain developmental conditions marked by the early childhood onset of cognitive, behavioral, and functional deficits leading to memory and learning problems, emotional instability, and impulsivity. Autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, fragile X syndrome, and Down's syndrome are a few known examples of neurodevelopmental disorders. Although they are relatively common in both developed and developing countries, very little is currently known about their underlying molecular mechanisms. Both genetic and environmental factors are known to increase the risk of neurodevelopmental disorders. Current diagnostic and screening tests for neurodevelopmental disorders are not reliable; hence, individuals with neurodevelopmental disorders are often diagnosed in the later stages. This negatively affects their prognosis and quality of life, prompting the need for a better diagnostic biomarker. Recent studies on microRNAs and their altered regulation in diseases have shed some light on the possible role they could play in the development of the central nervous system. This review attempts to elucidate our current understanding of the role that microRNAs play in neurodevelopmental disorders with the hope of utilizing them as potential biomarkers in the future.

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.

Downregulation of microRNA-199a-5p alleviated lidocaine-induced sensory dysfunction and spinal cord myelin lesions in a rat model

Lidocaine induces neurotoxicity in the spinal cord, but the underlying mechanisms remain unclear. In this study, we evaluated the effects of miR-199a-5p on 10 % lidocaine neurotoxicity. Increased expression of miR-199a-5p in the spinal cord of rats treated with 10 % lidocaine was assessed by qRT-PCR. Furthermore, after miR-199a-5p antagomir administration, the sensory dysfunction and myelin sheath lesions (evaluated by semithin sections stained with toluidine blue, electron microscopy, g-ratios and myelin thickness) induced by 10 % lidocaine were alleviated. Myelin regulatory factor (MYRF), a key molecule of myelin sheath development, was predicted to be a target gene of miR-199a-5p by the TargetScan and miRBase databases. MYRF and its downstream factors myelin basic protein (MBP), proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG) were significantly decreased after intrathecal 10 % lidocaine administration. Moreover, these changes were reversed after miR-199a-5p antagomir administration. FISH-immunofluorescence showed coexpression of miR-199a-5p and MYRF in the spinal cord white matter of rats. A luciferase reporter assay further demonstrated the functional association between miR-199a-5p and MYRF. Overall, miR-199a-5p upregulation is involved in 10 % lidocaine-induced spinal cord toxicity through regulation of MYRF. Therefore, downregulating miR-199a-5p expression may be a potential strategy to ameliorate spinal cord neurotoxicity induced by 10 % lidocaine.

Oligodendrocyte Intrinsic miR-27a Controls Myelination and Remyelination

Remyelination requires the generation of new oligodendrocytes (OLs), which are derived from oligodendrocyte progenitor cells (OPCs). Maturation of OPCs into OLs is a multi-step process. Here, we describe a microRNA expressed by OLs, miR-27a, as a regulator of OL development and survival. Increased levels of miR-27a were found in OPCs associated with multiple sclerosis (MS) lesions and in animal models of demyelination. Increased levels of miR-27a led to inhibition of OPC proliferation by cell-cycle arrest, as well as impaired differentiation of human OPCs (hOPCs) and myelination by dysregulating the Wnt-β-catenin signaling pathway. In vivo administration of miR-27a led to suppression of myelinogenic signals, leading to loss of endogenous myelination and remyelination. Our findings provide evidence supporting a critical role for a steady-state level of OL-specific miR-27a in supporting multiple steps in the complex process of OPC maturation and remyelination.

The Role of MicroRNAs in Repair Processes in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disorder characterised by demyelination of central nervous system neurons with subsequent damage, cell death and disability. While mechanisms exist in the CNS to repair this damage, they are disrupted in MS and currently there are no treatments to address this deficit. In recent years, increasing attention has been paid to the influence of the small, non-coding RNA molecules, microRNAs (miRNAs), in autoimmune disorders, including MS. In this review, we examine the role of miRNAs in remyelination in the different cell types that contribute to MS. We focus on key miRNAs that have a central role in mediating the repair process, along with several more that play either secondary or inhibitory roles in one or more aspects. Finally, we consider the current state of miRNAs as therapeutic targets in MS, acknowledging current challenges and potential strategies to overcome them in developing effective novel therapeutics to enhance repair mechanisms in MS.

MiRNA-145-5p prevents differentiation of oligodendrocyte progenitor cells by regulating expression of myelin gene regulatory factor

The roles of specific microRNAs (miRNA) in oligodendrocyte (OL) differentiation have been studied in depth. However, miRNAs in OL precursors and oligodendrocyte progenitor cells (OPCs) have been less extensively investigated. MiR-145-5p is highly expressed in OPCs relative to differentiating OLs, suggesting this miRNA may serve a function specifically in OPCs. Knockdown of miR-145-5p in primary OPCs led to spontaneous differentiation, as evidenced by an increased proportion of MAG⁺ cells, increased cell ramification, and upregulation of multiple myelin genes including MYRF, TPPP, and MAG, and OL cell cycle exit marker Cdkn1c. Supporting this transition to a differentiating state, proliferation was reduced in miR-145-5p knockdown OPCs. Further, knockdown of miR-145-5p in differentiating OLs showed enhanced differentiation, with increased branching, myelin membrane production, and myelin gene expression. We identified several OL-specific genes targeted by miR-145-5p that exhibited upregulation with miR-145-5p knockdown, including myelin gene regulatory factor (MYRF), that could be regulating the prodifferentiation phenotype in both miR-145 knockdown OPCs and OLs. Indeed, spontaneous differentiation with knockdown of miR-145-5p was fully rescued by concurrent knockdown of MYRF. However, proliferation rate was only partially rescued with MYRF knockdown, and overexpression of miR-145-5p in OPCs increased proliferation rate without affecting expression of already lowly expressed differentiation genes. Taken together, these data suggest that in OPCs miR-145-5p both prevents differentiation at least in part by preventing expression of MYRF and promotes proliferation via as-yet-unidentified mechanisms. These findings clarify the need for differential regulation of miR-145-5p between OPCs and OLs and may have further implications in demyelinating diseases such as multiple sclerosis where miR-145-5p is dysregulated.

Human Pluripotent Stem Cell-Derived Extracellular Vesicles: Characteristics and Applications

Extracellular vesicles (EVs), including exosomes and microvesicles, are found to play an important role in various biological processes and maintaining tissue homeostasis. Because of the protective effects, stem cell-derived EVs can be used to reduce oxidative stress and apoptosis in the recipient cells. In addition, EVs/exosomes have been used as directional communication tools between stem cells and parenchymal cells, giving them the ability to serve as biomarkers. Likewise, altered EVs/exosomes can be utilized for drug delivery by loading with proteins, small interfering RNAs, and viral vectors, in particular, because EVs/exosomes are able to cross the blood-brain barrier. In this review article, the properties of human induced pluripotent stem cell (iPSC)-derived EVs are discussed. The biogenesis, that is, how EVs originate in the endosomal compartment or from the cell layer of microvesicles, EV composition, the available methods of purification, and characterizations of EVs/exosomes are summarized. In particular, EVs/exosomes derived from iPSCs of different lineage specifications and the applications of these stem cell-derived exosomes in neurological diseases are discussed. Impact statement In this review, we summarized the work related to extracellular vesicles (EVs) derived from human pluripotent stem cells (hPSCs). In particular, EVs/exosomes derived from hPSCs of different lineage specifications and the applications of these stem cell-derived exosomes in neurological diseases are discussed. The results highlight the important role of cell-cell interactions in neural cellular phenotype and neurodegeneration. The findings reported in this article are significant for pluripotent stem cell-derived cell-free products toward applications in stem cell-based therapies.

Epigenetic regulation of oligodendrocyte differentiation: From development to demyelinating disorders

The maintenance of progenitor states or the differentiation of progenitors into specific lineages requires epigenetic remodeling of the gene expression program. In the central nervous system, oligodendrocyte progenitors (OPCs) give rise to oligodendrocytes (OLs), whose main function has been thought to be to produce myelin, a lipid-rich structure insulating the axons. However, recent findings suggest diverse OL transcriptional states, which might imply additional functions. The differentiation of OPCs into postmitotic OLs is a highly regulated and sensitive process and requires temporal waves of gene expression through epigenetic remodeling of the genome. In this review, we will discuss recent advances in understanding the events shaping the chromatin landscape through histone modifications and long noncoding RNAs during OPC differentiation, in physiological and pathological conditions. We suggest that epigenetic regulation plays a fundamental role in governing the accessibility of transcriptional machinery to DNA sequences, which ultimately determines functional outcomes in OLs.

Schizophrenia-associated MicroRNA-Gene Interactions in the Dorsolateral Prefrontal Cortex

Schizophrenia-associated anomalies in gene expression in postmortem brain can be attributed to a combination of genetic and environmental influences. Given the small effect size of common variants, it is likely that we may only see the combined impact of some of these at the pathway level in small postmortem studies. At the gene level, however, there may be more impact from common environmental exposures mediated by influential epigenomic modifiers, such as microRNA (miRNA). We hypothesise that dysregulation of miRNAs and their alteration of gene expression have significant implications in the pathophysiology of schizophrenia. In this study, we integrate changes in cortical gene and miRNA expression to identify regulatory interactions and networks associated with the disorder. Gene expression analysis in post-mortem prefrontal dorsolateral cortex (BA 46) (n = 74 matched pairs of schizophrenia, schizoaffective, and control samples) was integrated with miRNA expression in the same cohort to identify gene-miRNA regulatory networks. A significant gene-miRNA interaction network was identified, including miR-92a, miR-495, and miR-134, which converged with differentially expressed genes in pathways involved in neurodevelopment and oligodendrocyte function. The capacity for miRNA to directly regulate gene expression through respective binding sites in BCL11A, PLP1, and SYT11 was also confirmed to support the biological relevance of this integrated network model. The observations in this study support the hypothesis that miRNA dysregulation is an important factor in the complex pathophysiology of schizophrenia.

From OPC to Oligodendrocyte: An Epigenetic Journey

Oligodendrocytes provide metabolic and functional support to neuronal cells, rendering them key players in the functioning of the central nervous system. Oligodendrocytes need to be newly formed from a pool of oligodendrocyte precursor cells (OPCs). The differentiation of OPCs into mature and myelinating cells is a multistep process, tightly controlled by spatiotemporal activation and repression of specific growth and transcription factors. While oligodendrocyte turnover is rather slow under physiological conditions, a disruption in this balanced differentiation process, for example in case of a differentiation block, could have devastating consequences during ageing and in pathological conditions, such as multiple sclerosis. Over the recent years, increasing evidence has shown that epigenetic mechanisms, such as DNA methylation, histone modifications, and microRNAs, are major contributors to OPC differentiation. In this review, we discuss how these epigenetic mechanisms orchestrate and influence oligodendrocyte maturation. These insights are a crucial starting point for studies that aim to identify the contribution of epigenetics in demyelinating diseases and may thus provide new therapeutic targets to induce myelin repair in the long run.

Differential Effects of Extracellular Vesicles of Lineage-Specific Human Pluripotent Stem Cells on the Cellular Behaviors of Isogenic Cortical Spheroids

Extracellular vesicles (EVs) contribute to a variety of signaling processes and the overall physiological and pathological states of stem cells and tissues. Human induced pluripotent stem cells (hiPSCs) have unique characteristics that can mimic embryonic tissue development. There is growing interest in the use of EVs derived from hiPSCs as therapeutics, biomarkers, and drug delivery vehicles. However, little is known about the characteristics of EVs secreted by hiPSCs and paracrine signaling during tissue morphogenesis and lineage specification. Methods: In this study, the physical and biological properties of EVs isolated from hiPSC-derived neural progenitors (ectoderm), hiPSC-derived cardiac cells (mesoderm), and the undifferentiated hiPSCs (healthy iPSK3 and Alzheimer’s-associated SY-UBH lines) were analyzed. Results: Nanoparticle tracking analysis and electron microscopy results indicate that hiPSC-derived EVs have an average size of 100–250 nm. Immunoblot analyses confirmed the enrichment of exosomal markers Alix, CD63, TSG101, and Hsc70 in the purified EV preparations. MicroRNAs including miR-133, miR-155, miR-221, and miR-34a were differently expressed in the EVs isolated from distinct hiPSC lineages. Treatment of cortical spheroids with hiPSC-EVs in vitro resulted in enhanced cell proliferation (indicated by BrdU+ cells) and axonal growth (indicated by β-tubulin III staining). Furthermore, hiPSC-derived EVs exhibited neural protective abilities in Aβ42 oligomer-treated cultures, enhancing cell viability and reducing oxidative stress. Our results demonstrate that the paracrine signaling provided by tissue context-dependent EVs derived from hiPSCs elicit distinct responses to impact the physiological state of cortical spheroids. Overall, this study advances our understanding of cell‒cell communication in the stem cell microenvironment and provides possible therapeutic options for treating neural degeneration.

Inhibitory milieu at the multiple sclerosis lesion site and the challenges for remyelination

Regeneration of myelin, following injury, can occur within the central nervous system to reinstate proper axonal conductance and provide trophic support. Failure to do so renders the axons vulnerable, leading to eventual degeneration, and neuronal loss. Thus, it is essential to understand the mechanisms by which remyelination or failure to remyelinate occur, particularly in the context of demyelinating and neurodegenerative disorders. In multiple sclerosis, oligodendrocyte progenitor cells (OPCs) migrate to lesion sites to repair myelin. However, during disease progression, the ability of OPCs to participate in remyelination diminishes coincident with worsening of the symptoms. Remyelination is affected by a broad range of cues from intrinsic programming of OPCs and extrinsic local factors to the immune system and other systemic elements including diet and exercise. Here we review the literature on these diverse inhibitory factors and the challenges they pose to remyelination. Results spanning several disciplines from fundamental preclinical studies to knowledge gained in the clinic will be discussed.

Expression of DDR1 in the CNS and in myelinating oligodendrocytes

Discoidin domain receptor 1 (DDR1) is a tyrosine kinase receptor that is activated by fibrillar collagens. Here, we review the expression and role of DDR1 in the central nervous system (CNS). In a murine model, DDR1 is expressed in oligodendrocytes in the developing brain and during remyelination. In human adult brain tissue, DDR1 is detected in a similar pattern as other classical myelin proteins such as myelin basic protein (MBP). Up to 50 transcripts of DDR1 have been detected in human tissues, of which 5 isoforms have been identified. In the human brain, all 5 isoforms are detectable, but DDR1b is the most highly expressed, and DDR1c is coexpressed with myelin genes. DDR1 sequence variants have been associated with psychiatric disorders, and upregulation of this gene occurs in gliomas. Moreover, mutations in DDR1 have been found in tumors of Schwann cells, which are the myelinating cells of the peripheral nervous system. All these data suggest that DDR1 plays a role in myelination and is relevant to neuropsychiatric diseases.

miR-381 Attenuates Peripheral Neuropathic Phenotype Caused by Overexpression of PMP22

Charcot-Marie Tooth disease type 1A (CMT1A), the major type of CMT, is caused by duplication of peripheral myelin protein 22 (PMP22) gene whose overexpression causes structural and functional abnormalities in myelination. We investigated whether miRNA-mediated regulation of PMP22 expression could reduce the expression level of PMP22, thereby alleviating the demyelinating neuropathic phenotype of CMT1A. We found that several miRNAs were down-regulated in C22 mouse, a CMT1A mouse model. Among them, miR-381 could target 3′ untranslated region (3′UTR) of PMP22 in vitro based on Western botting and quantitative Real Time-PCR (qRT-PCR) results. In vivo efficacy of miR-381 was assessed by administration of LV-miR-381, an miR-381 expressing lentiviral vector, into the sciatic nerve of C22 mice by a single injection at postnatal day 6 (p6). Administration of LV-miR-381 reduced expression level of PMP22 along with elevated level of miR-381 in the sciatic nerve. Rotarod performance analysis revealed that locomotor coordination of LV-miR-381 administered C22 mice was significantly enhanced from 8 weeks post administration. Electrophysiologically, increased motor nerve conduction velocity was observed in treated mice. Histologically, toluidine blue staining and electron microscopy revealed that structural abnormalities of myelination were improved in sciatic nerves of LV-miR-381 treated mice. Therefore, delivery of miR-381 ameliorated the phenotype of peripheral neuropathy in CMT1A mouse model by down-regulating PMP22 expression. These data suggest that miRNA can be used as a potent therapeutic strategy to control diseases with copy number variations such as CMT1A.

A critical role for miR-184 in the fate determination of oligodendrocytes

Background

New insights on cellular and molecular aspects of both oligodendrocyte (OL) differentiation and myelin synthesis pathways are potential avenues for developing a cell-based therapy for demyelinating disorders comprising multiple sclerosis. MicroRNAs (miRNA) have broad implications in all aspects of cell biology including OL differentiation. MiR-184 has been identified as one of the most highly enriched miRNAs in oligodendrocyte progenitor cells (OPCs). However, the exact molecular mechanism of miR-184 in OL differentiation is yet to be elucidated.

Methods and results

Based on immunochemistry assays, qRT-PCR, and western blotting findings, we hypothesized that overexpression of miR-184 in either neural progenitor cells (NPCs) or embryonic mouse cortex stimulated the differentiation of OL lineage efficiently through regulating crucial developmental genes. Luciferase assays demonstrated that miR-184 directly represses positive regulators of neural and astrocyte differentiation, i.e., SOX1 and BCL2L1, respectively, including the negative regulator of myelination, LINGO1. Moreover, blocking the function of miR-184 reduced the number of committed cells to an OL lineage.

Conclusions

Our data highlighted that miR-184 could promote OL differentiation even in the absence of exogenous growth factors and propose a novel strategy to improve the efficacy of OL differentiation, with potential applications in cell therapy for neurodegenerative diseases.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1208-y) contains supplementary material, which is available to authorized users.

Emerging Roles of miRNAs in Brain Development and Perinatal Brain Injury

In human beings the immature brain is highly plastic and depending on the stage of gestation is particularly vulnerable to a range of insults that if sufficiently severe, can result in long-term motor, cognitive and behavioral impairment. With improved neonatal care, the incidence of major motor deficits such as cerebral palsy has declined with prematurity. Unfortunately, however, milder forms of injury characterized by diffuse non-cystic white matter lesions within the periventricular region and surrounding white matter, involving loss of oligodendrocyte progenitors and subsequent axonal hypomyelination as the brain matures have not. Existing therapeutic options for treatment of preterm infants have proved inadequate, partly owing to an incomplete understanding of underlying post-injury cellular and molecular changes that lead to poor neurodevelopmental outcomes. This has reinforced the need to improve our understanding of brain plasticity, explore novel solutions for the development of protective strategies, and identify biomarkers. Compelling evidence exists supporting the involvement of microRNAs (miRNAs), a class of small non-coding RNAs, as important post-transcriptional regulators of gene expression with functions including cell fate specification and plasticity of synaptic connections. Importantly, miRNAs are differentially expressed following brain injury, and can be packaged within exosomes/extracellular vesicles, which play a pivotal role in assuring their intercellular communication and passage across the blood-brain barrier. Indeed, an increasing number of investigations have examined the roles of specific miRNAs following injury and regeneration and it is apparent that this field of research could potentially identify protective therapeutic strategies to ameliorate perinatal brain injury. In this review, we discuss the most recent findings of some important miRNAs in relation to the development of the brain, their dysregulation, functions and regulatory roles following brain injury, and discuss how these can be targeted either as biomarkers of injury or neuroprotective agents.

Stem Cells as Potential Targets of Polyphenols in Multiple Sclerosis and Alzheimer's Disease

Alzheimer's disease (AD) and multiple sclerosis are major neurodegenerative diseases, which are characterized by the accumulation of abnormal pathogenic proteins due to oxidative stress, mitochondrial dysfunction, impaired autophagy, and pathogens, leading to neurodegeneration and behavioral deficits. Herein, we reviewed the utility of plant polyphenols in regulating proliferation and differentiation of stem cells for inducing brain self-repair in AD and multiple sclerosis. Firstly, we discussed the genetic, physiological, and environmental factors involved in the pathophysiology of both the disorders. Next, we reviewed various stem cell therapies available and how they have proved useful in animal models of AD and multiple sclerosis. Lastly, we discussed how polyphenols utilize the potential of stem cells, either complementing their therapeutic effects or stimulating endogenous and exogenous neurogenesis, against these diseases. We suggest that polyphenols could be a potential candidate for stem cell therapy against neurodegenerative disorders.

Comparison of multi-lineage differentiation of hiPSCs reveals novel miRNAs that regulate lineage specification

MicroRNAs (miRNAs) are known to be crucial players in governing the differentiation of human induced pluripotent stem cells (hiPSCs). Despite their utter importance, identifying key lineage specifiers among the myriads of expressed miRNAs remains challenging. We believe that the current practice in mining miRNA specifiers via delineating dynamic fold-changes only is inadequate. Our study, therefore, provides evidence to pronounce "lineage specificity" as another important attribute to qualify for these lineage specifiers. Adopted hiPSCs were differentiated into representative lineages (hepatic, nephric and neuronal) over all three germ layers whilst the depicted miRNA expression changes compiled into an integrated atlas. We demonstrated inter-lineage analysis shall aid in the identification of key miRNAs with lineage-specificity, while these shortlisted candidates were collectively known as "lineage-specific miRNAs". Subsequently, we followed through the fold-changes along differentiation via computational analysis to identify miR-192 and miR-372-3p, respectively, as representative candidate key miRNAs for the hepatic and nephric lineages. Indeed, functional characterization validated that miR-192 and miR-372-3p regulate lineage differentiation via modulation of the expressions of lineage-specific genes. In summary, our presented miRNA atlas is a resourceful ore for the mining of key miRNAs responsible for lineage specification.

Deep sequencing identification of miRNAs in pigeon ovaries illuminated with monochromatic light

Background

The use of light of different wavelengths has grown popular in the poultry industry. An optimum wavelength is believed to improve pigeon egg production, but little is known about the role of microRNAs (miRNAs) in the effects of monochromatic light on ovarian pigeon function. Herein, we harvested ovaries from pigeons reared under monochromatic light of different wavelength and performed deep sequencing on various tissues using an Illumina Solexa high-throughput instrument.

Results

We obtained 66,148,548, 67,873,805, and 71,661,771 clean reads from ovaries of pigeons reared under red light (RL), blue light (BL), and white light (WL), respectively. We identified 1917 known miRNAs in nine libraries, of which 524 were novel. Three and five differentially expressed miRNAs were identified in BL vs. WL and RL vs. WL groups, respectively. Quantitative reverse transcription PCR was used to validate differentially expressed miRNAs (miR-200, miR-122, and miR-205b). In addition, 5824 target genes were annotated as differentially expressed miRNAs, most of which are involved in reproductive pathways including oestrogen signalling, cell cycle, and oocyte maturation. Notably, ovarian miR-205b expression was significantly negatively correlated with its target 11β-hydroxysteroid dehydrogenase type 1 (HSD11B1).

Conclusions

miRNA–mRNA network analysis suggests that miR-205b targeting of HSD11B1 plays a key role in the effects of monochromatic light on pigeon egg production. These findings indicate that monochromatic light shortens the oviposition interval of pigeons, which may be useful for egg production and pigeon breeding.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4831-6) contains supplementary material, which is available to authorized users.

Decoding cell signalling and regulation of oligodendrocyte differentiation

Oligodendrocytes are fundamental for the functioning of the nervous system; they participate in several cellular processes, including axonal myelination and metabolic maintenance for astrocytes and neurons. In the mammalian nervous system, they are produced through waves of proliferation and differentiation, which occur during embryogenesis. However, oligodendrocytes and their precursors continue to be generated during adulthood from specific niches of stem cells that were not recruited during development. Deficiencies in the formation and maturation of these cells can generate pathologies mainly related to myelination. Understanding the mechanisms involved in oligodendrocyte development, from the precursor to mature cell level, will allow inferring therapies and treatments for associated pathologies and disorders. Such mechanisms include cell signalling pathways that involve many growth factors, small metabolic molecules, non-coding RNAs, and transcription factors, as well as specific elements of the extracellular matrix, which act in a coordinated temporal and spatial manner according to a given stimulus. Deciphering those aspects will allow researchers to replicate them in vitro in a controlled environment and thus mimic oligodendrocyte maturation to understand the role of oligodendrocytes in myelination in pathologies and normal conditions. In this study, we review these aspects, based on the most recent in vivo and in vitro data on oligodendrocyte generation and differentiation.

Epigenetic regulation of astrocyte function in neuroinflammation and neurodegeneration

Epigenetic mechanisms control various functions throughout the body, from cell fate determination in development to immune responses and inflammation. Neuroinflammation is one of the prime contributors to the initiation and progression of neurodegeneration in a variety of diseases, including Alzheimer's and Parkinson's diseases. Because astrocytes are the largest population of glial cells, they represent an important regulator of CNS function, both in health and disease. Only recently have studies begun to identify the epigenetic mechanisms regulating astrocyte responses in neurodegenerative diseases. These epigenetic mechanisms, along with the epigenetic marks involved in astrocyte development, could elucidate novel pathways to potentially modulate astrocyte-mediated neuroinflammation and neurotoxicity. This review examines the known epigenetic mechanisms involved in regulation of astrocyte function, from development to neurodegeneration, and links these mechanisms to potential astrocyte-specific roles in neurodegenerative disease with a focus on potential opportunities for therapeutic intervention.

Functional integration of complex miRNA networks in central and peripheral lesion and axonal regeneration

New players are emerging in the game of peripheral and central nervous system injury since their physiopathological mechanisms remain partially elusive. These mechanisms are characterized by several molecules whose activation and/or modification following a trauma is often controlled at transcriptional level. In this scenario, microRNAs (miRNAs/miRs) have been identified as main actors in coordinating important molecular pathways in nerve or spinal cord injury (SCI). miRNAs are small non-coding RNAs whose functionality at network level is now emerging as a new level of complexity. Indeed they can act as an organized network to provide a precise control of several biological processes. Here we describe the functional synergy of some miRNAs in case of SCI and peripheral damage. In particular we show how several small RNAs can cooperate in influencing simultaneously the molecular pathways orchestrating axon regeneration, inflammation, apoptosis and remyelination. We report about the networks for which miRNA-target bindings have been experimentally demonstrated or inferred based on target prediction data: in both cases, the connection between one miRNA and its downstream pathway is derived from a validated observation or is predicted from the literature. Hence, we discuss the importance of miRNAs in some pathological processes focusing on their functional structure as participating in a cooperative and/or convergence network.

The Role of microRNA Markers in the Diagnosis, Treatment, and Outcome Prediction of Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that affects many people worldwide. Treatment focuses on controlling secondary injury cascade and improving regeneration. It has recently been suggested that both the secondary injury cascade and the regenerative process are heavily regulated by microRNAs (miRNAs). The measurement of specific biomarkers could improve our understanding of the disease processes, and thereby provide clinicians with the opportunity to guide treatment and predict clinical outcomes after SCI. A variety of miRNAs exhibit important roles in processes of inflammation, cell death, and regeneration. These miRNAs can be used as diagnostic tools for predicting outcome after SCI. In addition, miRNAs can be used in the treatment of SCI and its symptoms. Significant laboratory and clinical evidence exist to show that miRNAs could be used as robust diagnostic and therapeutic tools for the treatment of patients with SCI. Further clinical studies are warranted to clarify the importance of each subtype of miRNA in SCI management.

Mature Let-7 miRNAs fine tune expression of LIN28B in pluripotent human embryonic stem cells

MicroRNAs (miRNA) are central regulators of diverse biological processes and are important in the regulation of stem cell self-renewal. One of the widely studied miRNA-protein regulators is the Lin28-Let-7 pair. In this study, we demonstrate that contrary to the well-established models of mouse ES cells (mESC) and transformed human cancer cells, the pluripotent state of human ES cells (hESC) involves expression of mature Let-7 family miRNAs with concurrent expression of all LIN28 proteins. We show that mature Let-7 miRNAs are regulated during hESC differentiation and have opposite expression profile with LIN28B. Moreover, mature Let-7 miRNAs fine tune the expression levels of LIN28B protein in pluripotent hESCs, whereas silencing of LIN28 proteins have no effect on mature Let-7 levels. These results bring novel information to the highly complex network of human pluripotency and suggest that maintenance of hESC pluripotency differs greatly from the mESCs in regard to LIN28-Let-7 regulation.

miRNAs As Emerging Regulators of Oligodendrocyte Development and Differentiation

Chronic demyelination is a hallmark of neurological disorders such as multiple sclerosis (MS) and several leukodystrophies. In the central nervous system (CNS), remyelination is a regenerative process that is often inadequate during these pathological states. In the MS context, in situ evidence suggests that remyelination is mediated by populations of oligodendrocyte progenitor cells (OPCs) that proliferate, migrate, and differentiate into mature, myelin-producing oligodendrocytes at sites of demyelinated lesions. The molecular programming of OPCs into mature oligodendrocytes is governed by a myriad of complex intracellular signaling pathways that modulate this process. Recent research has demonstrated the importance of specific and short non-coding RNAs, known as microRNAs (miRNAs), in regulating OPC differentiation and remyelination. Fortunately, it may be possible to take advantage of numerous developmental studies (both human and rodent) that have previously characterized miRNA expression profiles from the early neural progenitor cell to the late myelin-producing oligodendrocyte. Here we review much of the work to date and discuss the impact of miRNAs on OPC and oligodendrocyte biology. Additionally, we consider the potential for miRNA-mediated therapy in the context of remyelination and brain repair.

A review of induced pluripotent stem cell, direct conversion by trans-differentiation, direct reprogramming and oligodendrocyte differentiation

Rapid progress in the field of stem cell therapy and cellular reprogramming provides convincing evidence of its feasibility in treating a wide range of pathologies through autologous cell replacement therapy. This review article describes in detail on three widely used approaches of somatic cell reprogramming: induced pluripotent stem cells, direct conversion and direct reprogramming, in the context of demyelination in the CNS. The potential limitations of each reprogramming technique are reviewed along with their distinct molecular approach to reprogramming. This is followed by an analysis on the scopes and challenges of its translational applications in deriving oligodendrocyte progenitor cells and oligodendrocytes for cell replacement treatment of demyelinating conditions in the CNS.

Impaired oligodendrocyte maturation in preterm infants: Potential therapeutic targets

Preterm birth is an evolving challenge in neonatal health care. Despite declining mortality rates among extremely premature neonates, morbidity rates remain very high. Currently, perinatal diffuse white matter injury (WMI) is the most commonly observed type of brain injury in preterm infants and has become an important research area. Diffuse WMI is associated with impaired cognitive, sensory and psychological functioning and is increasingly being recognized as a risk factor for autism-spectrum disorders, ADHD, and other psychological disturbances. No treatment options are currently available for diffuse WMI and the underlying pathophysiological mechanisms are far from being completely understood. Preterm birth is associated with maternal inflammation, perinatal infections and disrupted oxygen supply which can affect the cerebral microenvironment by causing activation of microglia, astrogliosis, excitotoxicity, and oxidative stress. This intricate interplay of events negatively influences oligodendrocyte development, causing arrested oligodendrocyte maturation or oligodendrocyte cell death, which ultimately results in myelination failure in the developing white matter. This review discusses the current state in perinatal WMI research, ranging from a clinical perspective to basic molecular pathophysiology. The complex regulation of oligodendrocyte development in healthy and pathological conditions is described, with a specific focus on signaling cascades that may play a role in WMI. Furthermore, emerging concepts in the field of WMI and issues regarding currently available animal models are put forward. Novel insights into the molecular mechanisms underlying impeded oligodendrocyte maturation in diffuse WMI may aid the development of novel treatment options which are desperately needed to improve the quality-of-life of preterm neonates.

Transcriptional and Epigenetic Regulation of Oligodendrocyte Development and Myelination in the Central Nervous System

Central nervous system (CNS) myelination by oligodendrocytes (OLs) is a highly orchestrated process involving well-defined steps from specification of neural stem cells into proliferative OL precursors followed by terminal differentiation and subsequent maturation of these precursors into myelinating OLs. These specification and differentiation processes are mediated by profound global changes in gene expression, which are in turn subject to control by both extracellular signals and regulatory networks intrinsic to the OL lineage. Recently, basic transcriptional mechanisms that control OL differentiation and myelination have begun to be elucidated at the molecular level and on a genome scale. The interplay between transcription factors activated by differentiation-promoting signals and master regulators likely exerts a crucial role in controlling stage-specific progression of the OL lineage. In this review, we describe the current state of knowledge regarding the transcription factors and the epigenetic programs including histone methylation, acetylation, chromatin remodeling, micro-RNAs, and noncoding RNAs that regulate development of OLs and myelination.

MicroRNA: Key regulators of oligodendrocyte development and pathobiology

MicroRNAs (miRNAs or miRs) are a group of small non-coding RNAs that function through binding to messenger RNA (mRNA) targets and downregulating gene expression. miRNAs have been shown to regulate many cellular functions including proliferation, differentiation, development and apoptosis. Recently, evidence has grown which shows the involvement of miRs in oligodendrocyte (OL) specification and development. In particular, miRs-138, -219, -338, and -9 have been classified as key regulators of OL development, acting at various points in the OL lineage and influencing precursor cell transit into mature myelinating OLs. Many studies have emerged which link miRNAs with OL and myelin pathology in various central nervous system (CNS) diseases including multiple sclerosis (MS), ischemic stroke, spinal cord injury, and adult-onset autosomal dominant leukodystrophy (ADLD).

The role of microRNA-30c in the self-renewal and differentiation of C6 glioma cells

BACKGROUND

Sphere formation, one method for identifying self-renewal ability, has been used to report that cancer stem-like cells exist in rat C6 glioma cells. Recent studies suggested that cancer stem-like cells share the stem cell properties of self-renewal and multipotent ability of neural stem cells and might be regulated by microRNAs (miRNAs). However, the mechanism of miRNA involvement in the sphere formation and neural differentiation abilities of cancer stem-like cells is poorly understood.

RESULTS

We found that miRNA-30c could assist in sphere formation of C6 cells under defined conditions in neural stem cell medium DMEM/F12-bFGF-EGF-B27. Moreover, overexpression of miRNA-30c might reduce 3-isobutyl-1-methylxanthine (IBMX)-induced neural differentiation, as the expression of neural markers, especially glial fibrillary acidic protein (GFAP), decreased. Further experiments revealed that miRNA-30c inhibited the IBMX-induced astrocyte differentiation via targeting the upstream genes and inactivating phosphorylation of STAT3 of the JAK-STAT3 pathway. Subsequently, the expression of GFAP was reduced and the number of astrocyte differentiation from C6 cells decreased.

CONCLUSIONS

Our findings suggest that miRNA-30c could play a regulatory role in self-renewal and neural differentiation in C6 glioma cells.

Early intervention for spinal cord injury with human induced pluripotent stem cells oligodendrocyte progenitors

Induced pluripotent stem (iPS) cells are at the forefront of research in regenerative medicine and are envisaged as a source for personalized tissue repair and cell replacement therapy. Here, we demonstrate for the first time that oligodendrocyte progenitors (OPs) can be derived from iPS cells generated using either an episomal, non-integrating plasmid approach or standard integrating retroviruses that survive and differentiate into mature oligodendrocytes after early transplantation into the injured spinal cord. The efficiency of OP differentiation in all 3 lines tested ranged from 40% to 60% of total cells, comparable to those derived from human embryonic stem cells. iPS cell lines derived using episomal vectors or retroviruses generated a similar number of early neural progenitors and glial progenitors while the episomal plasmid-derived iPS line generated more OPs expressing late markers O1 and RIP. Moreover, we discovered that iPS-derived OPs (iPS-OPs) engrafted 24 hours following a moderate contusive spinal cord injury (SCI) in rats survived for approximately two months and that more than 70% of the transplanted cells differentiated into mature oligodendrocytes that expressed myelin associated proteins. Transplanted OPs resulted in a significant increase in the number of myelinated axons in animals that received a transplantation 24 h after injury. In addition, nearly a 5-fold reduction in cavity size and reduced glial scarring was seen in iPS-treated groups compared to the control group, which was injected with heat-killed iPS-OPs. Although further investigation is needed to understand the mechanisms involved, these results provide evidence that patient-specific, iPS-derived OPs can survive for three months and improve behavioral assessment (BBB) after acute transplantation into SCI. This is significant as determining the time in which stem cells are injected after SCI may influence their survival and differentiation capacity.

Prognostic microRNAs in high-grade glioma reveal a link to oligodendrocyte precursor differentiation

MicroRNA expression can be exploited to define tumor prognosis and stratification for precision medicine. It remains unclear whether prognostic microRNA signatures are exclusively tumor grade and/or molecular subtype-specific, or whether common signatures of aggressive clinical behavior can be identified. Here, we defined microRNAs that are associated with good and poor prognosis in grade III and IV gliomas using data from The Cancer Genome Atlas. Pathway analysis of microRNA targets that are differentially expressed in good and poor prognosis glioma identified a link to oligodendrocyte development. Notably, a microRNA expression profile that is characteristic of a specific oligodendrocyte precursor cell type (OP1) correlates with microRNA expression from 597 of these tumors and is consistently associated with poor patient outcome in grade III and IV gliomas. Our study reveals grade-independent and subtype-independent prognostic molecular signatures in high-grade glioma and provides a framework for investigating the mechanisms of brain tumor aggressiveness.