MicroRNA-212 inhibits oligodendrocytes during maturation by down-regulation of differentiation-associated gene expression

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.

Transcriptomic analysis of spinal cord regeneration after injury in Cynops orientalis

Cynops orientalis (C. orientalis) has a pronounced ability to regenerate its spinal cord after injury. Thus, exploring the molecular mechanism of this process could provide new approaches for promoting mammalian spinal cord regeneration. In this study, we established a model of spinal cord thoracic transection injury in C. orientalis, which is an endemic species in China. We performed RNA sequencing of the contused axolotl spinal cord at two early time points after spinal cord injury - during the very acute stage (4 days) and the subacute stage (7 days) - and identified differentially expressed genes; additionally, we performed Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses, at each time point. Transcriptome sequencing showed that 13,059 genes were differentially expressed during C. orientalis spinal cord regeneration compared with uninjured animals, among which 4273 were continuously down-regulated and 1564 were continuously up-regulated. Down-regulated genes were most enriched in the Gene Ontology term "multicellular organismal process" and in the ribosome pathway at 10 days following spinal cord injury. We found that multiple genes associated with energy metabolism were down-regulated and multiple genes associated with the lysosome were up-regulated after spinal cord injury, indicating the importance of low metabolic activity during wound healing. Immune response-associated pathways were activated during the early acute phase (4 days), while the expression of extracellular matrix proteins such as glycosaminoglycan and collagen, as well as tight junction proteins, was lower at 10 days post-spinal cord injury than 4 days post-spinal cord injury. However, compared with 4 days post-injury, at 10 days post-injury neuroactive ligand-receptor interactions were no longer down-regulated, up-regulated differentially expressed genes were enriched in pathways associated with cancer and the cell cycle, and SHH, VIM, and Sox2 were prominently up-regulated. Immunofluorescence staining showed that glial fibrillary acidic protein was up-regulated in axolotl ependymoglial cells after injury, similar to what is observed in mammalian astrocytes after spinal cord injury, even though axolotls do not form a glial scar during regeneration. We suggest that low intracellular energy production could slow the rapid amplification of ependymoglial cells, thereby inhibiting reactive gliosis, at early stages after spinal cord injury. Extracellular matrix degradation slows cellular responses, represses the expression of neurogenic genes, and reactivates a transcriptional program similar to that of embryonic neuroepithelial cells. These ependymoglial cells act as neural stem cells: they migrate and proliferate to repair the lesion and then differentiate to replace lost glial cells and neurons. This provides the regenerative microenvironment that allows axon growth after injury.

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.

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.

Inhibiting miR-466b-5p Attenuates Neonatal White Matter Injury by Targeting Lpar1

miR-466b-5p is aberrantly upregulated in oligodendrocyte precursor cells (OPCs) after white matter injury (WMI). However, its roles in neonatal WMI pathogenesis are unknown. In this study, P3 rats were subjected to hypoxia-ischemia to establish a neonatal WMI model. A bioinformatic analysis was conducted to predict the possible target of miR-466b-5p as Lpar1. RT-PCR was performed to validate the expression of miR-466b-5p and Lpar1 mRNA. The miR-466b-5p antagomir was intracerebroventricularly administrated to inhibit miR-466b-5p; OPC differentiation, apoptosis, proliferation, and myelination were analyzed using immunofluorescence staining, western blotting, and electron microscopy. In addition, the behavioral performance of the rats was measured with the Morris water maze test. Sox10 expression and PLP trafficking were examined to elucidate the mechanism by which miR-466b-5p regulates WMI pathogenesis. We found that after inhibiting miR-466b-5p, the Edg2 protein was increased, OPC differentiation and myelinated axon formation were enhanced, and the rats' behavioral performance was improved, whereas OPC proliferation and apoptosis were not affected. Furthermore, the expression of Sox10 was promoted while PLP trafficking was attenuated after miR-466b-5p inhibition. We conclude that miR-466b-5p is involved in the regulation of WMI pathogenesis, partly through the Lpar1/Edg2/Sox10 and Lpar1/Edg2/PLP signaling pathways.

Identification of miRNAs That Mediate Protective Functions of Anti-Cancer Drugs During White Matter Ischemic Injury

We have previously shown that two anti-cancer drugs, CX-4945 and MS-275, protect and preserve white matter (WM) architecture and improve functional recovery in a model of WM ischemic injury. While both compounds promote recovery, CX-4945 is a selective Casein kinase 2 (CK2) inhibitor and MS-275 is a selective Class I histone deacetylase (HDAC) inhibitor. Alterations in microRNAs (miRNAs) mediate some of the protective actions of these drugs. In this study, we aimed to (1) identify miRNAs expressed in mouse optic nerves (MONs); (2) determine which miRNAs are regulated by oxygen glucose deprivation (OGD); and (3) determine the effects of CX-4945 and MS-275 treatment on miRNA expression. RNA isolated from MONs from control and OGD-treated animals with and without CX-4945 or MS-275 treatment were quantified using NanoString nCounter^® miRNA expression profiling. Comparative analysis of experimental groups revealed that 12 miRNAs were expressed at high levels in MONs. OGD upregulated five miRNAs (miR-1959, miR-501-3p, miR-146b, miR-201, and miR-335-3p) and downregulated two miRNAs (miR-1937a and miR-1937b) compared to controls. OGD with CX-4945 upregulated miR-1937a and miR-1937b, and downregulated miR-501-3p, miR-200a, miR-1959, and miR-654-3p compared to OGD alone. OGD with MS-275 upregulated miR-2134, miR-2141, miR-2133, miR-34b-5p, miR-153, miR-487b, miR-376b, and downregulated miR-717, miR-190, miR-27a, miR-1959, miR-200a, miR-501-3p, and miR-200c compared to OGD alone. Interestingly, miR-501-3p and miR-1959 were the only miRNAs upregulated by OGD, and downregulated by OGD plus CX-4945 and MS-275. Therefore, we suggest that protective functions of CX-4945 or MS-275 against WM injury maybe mediated, in part, through miRNA expression.

Functions of noncoding RNAs in glial development

Glia are widely distributed in the central nervous system and are closely related to cell metabolism, signal transduction, support, cell migration, and other nervous system development processes and functions. Glial development is complex and essential, including the processes of proliferation, differentiation, and migration, and requires precise regulatory networks. Noncoding RNAs (ncRNAs) can be deeply involved in glial development through gene regulation. Here, we review the regulatory roles of ncRNAs in glial development. We briefly describe the classification and functions of noncoding RNAs and focus on microRNAs (miRNAs) and long ncRNAs (lncRNAs), which have been reported to participate extensively during glial formation. The highlight of this summary is that miRNAs and lncRNAs can participate in and regulate the signaling pathways of glial development. The review not only describes how noncoding RNAs participate in nervous system development but also explains the processes of glial development, providing a foundation for subsequent studies on glial development and new insights into the pathogeneses of related neurological diseases.

Multifaceted Regulation of MicroRNA Biogenesis: Essential Roles and Functional Integration in Neuronal and Glial Development

MicroRNAs (miRNAs) are small, non-coding RNAs that function as endogenous gene silencers. Soon after the discovery of miRNAs, a subset of brain-enriched and brain-specific miRNAs were identified and significant advancements were made in delineating miRNA function in brain development. However, understanding the molecular mechanisms that regulate miRNA biogenesis in normal and diseased brains has become a prevailing challenge. Besides transcriptional regulation of miRNA host genes, miRNA processing intermediates are subjected to multifaceted regulation by canonical miRNA processing enzymes, RNA binding proteins (RBPs) and epitranscriptomic modifications. Further still, miRNA activity can be regulated by the sponging activity of other non-coding RNA classes, namely circular RNAs (circRNAs) and long non-coding RNAs (lncRNAs). Differential abundance of these factors in neuronal and glial lineages partly underlies the spatiotemporal expression and function of lineage-specific miRNAs. Here, we review the continuously evolving understanding of the regulation of neuronal and glial miRNA biogenesis at the transcriptional and posttranscriptional levels and the cooperativity of miRNA species in targeting key mRNAs to drive lineage-specific development. In addition, we review dysregulation of neuronal and glial miRNAs and the detrimental impacts which contribute to developmental brain disorders.

The Role of the lncRNA-LRCF in Propofol-Induced Oligodendrocyte Damage in Neonatal Mouse

In this study, LRCF, a long noncoding RNA (lncRNA) related to cognitive function, which was first discovered and named by our group, was shown to be involved in the propofol-induced proliferation and apoptosis of oligodendrocytes (OLGs). Our systematic study showed that LRCF expression differs in OLGs of mice of different ages. We found that neonatal mice with a high level of LRCF typically showed greater propofol-induced injury of OLGs. Mechanistic research has shown that LRCF can block the HIF-1α/miR138-5p/Caspase-3 pathway by binding to miR138-5p to form a microRNA (miRNA) sponge and result in cell damage through HIF-1α/Caspase-3 pathway in propofol induced OLGs. This may be the intrinsic reason why neonatal animals with high levels of LRCF tend to develop learning disability and neuro-degeneration more frequently than adults' after exposure to general anesthesia. When LRCF is highly expressed, HIF-1α directly regulates the transcription of the Caspase-3 gene by binding to the transcription factor binding site (TFBS) in its promoter, which induces OLGs apoptosis. LRCF is crucial for the mutual activation of the HIF-1α/miR138-5p/Caspase-3 OLGs survival pathway and the HIF-1α/Caspase-3 OLGs damage pathway. This study is the first to report that up-regulation of HIF-1α in OLGs treated with Propofol can promote apoptosis through HIF-1α/caspase-3 pathway and resist apoptosis through HIF-1α/miR-138-5p/caspase-3 pathway. The effect of HIF-1α on Caspase-3 expression depends on LRCF expression, which provides important theoretical support for gene therapy targeting LRCF. The further significance of this study is points to an involvement of the genetic background with high LRCF expression may serve as an important marker for identifying patients with a high risk of OLGs injury by Propofol. Thus, caution should be taken when administrating propofol in these patients, especially pediatric patients with high level of LRCF.

Oligodendrocyte lineage cells and depression

Depression is a common mental illness, affecting more than 300 million people worldwide. Decades of investigation have yielded symptomatic therapies for this disabling condition but have not led to a consensus about its pathogenesis. There are data to support several different theories of causation, including the monoamine hypothesis, hypothalamic-pituitary-adrenal axis changes, inflammation and immune system alterations, abnormalities of neurogenesis and a conducive environmental milieu. Research in these areas and others has greatly advanced the current understanding of depression; however, there are other, less widely known theories of pathogenesis. Oligodendrocyte lineage cells, including oligodendrocyte progenitor cells and mature oligodendrocytes, have numerous important functions, which include forming myelin sheaths that enwrap central nervous system axons, supporting axons metabolically, and mediating certain forms of neuroplasticity. These specialized glial cells have been implicated in psychiatric disorders such as depression. In this review, we summarize recent findings that shed light on how oligodendrocyte lineage cells might participate in the pathogenesis of depression, and we discuss new approaches for targeting these cells as a novel strategy to treat depression.

Epigenetic regulation of oligodendrocyte myelination in developmental disorders and neurodegenerative diseases

Oligodendrocytes are the critical cell types giving rise to the myelin nerve sheath enabling efficient nerve transmission in the central nervous system (CNS). Oligodendrocyte precursor cells differentiate into mature oligodendrocytes and are maintained throughout life. Deficits in the generation, proliferation, or differentiation of these cells or their maintenance have been linked to neurological disorders ranging from developmental disorders to neurodegenerative diseases and limit repair after CNS injury. Understanding the regulation of these processes is critical for achieving proper myelination during development, preventing disease, or recovering from injury. Many of the key factors underlying these processes are epigenetic regulators that enable the fine tuning or reprogramming of gene expression during development and regeneration in response to changes in the local microenvironment. These include chromatin remodelers, histone-modifying enzymes, covalent modifiers of DNA methylation, and RNA modification-mediated mechanisms. In this review, we will discuss the key components in each of these classes which are responsible for generating and maintaining oligodendrocyte myelination as well as potential targeted approaches to stimulate the regenerative program in developmental disorders and neurodegenerative diseases.

Potential microRNA-related targets in clearance pathways of amyloid-β: novel therapeutic approach for the treatment of Alzheimer's disease

Imbalance between amyloid-beta (Aβ) peptide synthesis and clearance results in Aβ deregulation. Failure to clear these peptides appears to cause the development of Alzheimer's disease (AD). In recent years, microRNAs have become established key regulators of biological processes that relate among others to the development and progression of neurodegenerative diseases, such as AD. This review article gives an overview on microRNAs that are involved in the Aβ cascade and discusses their inhibitory impact on their target mRNAs whose products participate in Aβ clearance. Understanding of the mechanism of microRNA in the associated signal pathways could identify novel therapeutic targets for the treatment of AD.

miR-212-5p attenuates ferroptotic neuronal death after traumatic brain injury by targeting Ptgs2

Ferroptosis, a newly discovered form of iron-dependent regulated cell death, has been implicated in traumatic brain injury (TBI). MiR-212-5p has previously been reported to be downregulated in extracellular vesicles following TBI. To investigate whether miR-212-5p is involved in the ferroptotic neuronal death in TBI mice, we first examined the accumulation of malondialdehyde (MDA) and ferrous ion, and the expression of ferroptosis-related molecules at 6 h, 12 h, 24 h, 48 h and 72 h following controlled cortical impact (CCI) in mice. There was a significant upregulation in the expression of Gpx4 and Acsl4 at 6 h, Slc7a11 from 12 h to 72 h, and Nox2 and Sat1 from 6 h to 72 h post injury. Similarly, an upregulation in the expression of Gpx4 at 6 h, Nox2 from 6 h to 72 h, xCT from 12 h to 72 h, and Sat1 at 72 h after CCI was observed at the protein level. Interestingly, MDA and ferrous ion were increased whereas miR-212-5p was decreased in the CCI group compared to the sham group. Furthermore, we found that overexpression of miR-212-5p attenuated ferroptosis while downregulation of miR-212-5p promoted ferroptotic cell death partially by targeting prostaglandin-endoperoxide synthase-2 (Ptgs2) in HT-22 and Neuro-2a cell lines. In addition, administration of miR-212-5p in CCI mice significantly improved learning and spatial memory. Collectively, these findings indicate that miR-212-5p may protect against ferroptotic neuronal death in CCI mice partially by targeting Ptgs2.

MicroRNA-26b inhibits oligodendrocyte precursor cell differentiation by targeting adrenomedullin in spinal cord injury

Oligodendrocyte precursor cells (OPCs) serve as a reservoir of newborn oligodendrocytes (OLs) in pathological and homeostatic conditions. After spinal cord injury (SCI), OPCs are activated to generate myelinating OLs, contributing to remyelination and functional recovery; however, the underlying molecular mechanisms remain unclear. Here, microRNA-26b (miR-26b) expression in the spinal cord tissues of SCI rats was examined by real-time polymerase chain reaction analysis. The influences of miR-26b on locomotor recovery following SCI were assessed utilizing Basso, Beattie, and Bresnahan (BBB) scores. The effects of miR-26b on OPC differentiation were explored using immunofluorescence and western blot analyses in vitro and in vivo. The potential targets that are modulated by miR-26b were identified by bioinformatics, luciferase reporter assays, and western blot analyses. The effects of adrenomedullin (ADM) on OPC differentiation were explored in vitro using immunofluorescence and western blot analyses. We demonstrated that miR-26b was significantly downregulated after SCI. BBB scores showed that miR-26b exacerbated the locomotor function deficits induced by SCI. In vitro, miR-26b inhibited the differentiation of primary rat OPCs. In vivo, miR-26b suppressed OPC differentiation in SCI rats. Bioinformatics analyses and experimental detection revealed that miR-26b directly targeted ADM in OPCs. In addition, knockdown of ADM suppressed the differentiation of primary rat OPCs. Our study provides evidence that ADM may mediate miR-26b-inhibited OPC differentiation in SCI.

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.

Down-regulation of interleukin-33 expression in oligodendrocyte precursor cells impairs oligodendrocyte lineage progression

Interleukin-33 (IL-33), a member of the IL1 family, has been found to be expressed in oligodendrocytes (OLGs) and released as an alarmin from injured OLGs to work on other glial cell-types in the central nervous system. However, its functional role in OLGs remains unclear. Herein, we present that IL-33 was mainly expressed in the nucleus of CC1⁺ -oligodendrocytes (OLGs) in mouse and rat corpus callosum, as well as NG2⁺ -oligodendrocyte precursor cells (OPCs). The in vitro study indicated that the amount of IL-33 expressing in OPCs was higher when compared to that detected in OLGs. Results from the experiments using lentivirus-mediated shRNA delivery against IL-33 expression (IL33-KD) in OPCs showed that IL33-KD reduced the differentiation of OLGs into mature OLGs along with the down-regulation of OLG differentiation-related genes and mature OLG marker proteins, myelin basic protein (MBP) and proteolipid protein (PLP). Alternatively, we observed reduced differentiation of OLGs that were prepared from the brains of IL-33 gene knockout (IL33-KO) mice with anxiolytic-like behavior. Observations were correlated with the results showing lower levels of MBP and PLP in IL33-KO cultures than those detected in the control cultures prepared from wildtype (WT) mice. Transmission Electron Microscopy (TEM) analysis revealed that the myelin structures in the corpus callosum of the IL33-KO mice were impaired compared to those observed in the WT mice. Overall, this study provides important evidence that declined expression of IL-33 in OPCs suppresses the maturation of OLGs. Moreover, gene deficiency of IL-33 can disrupt OLG maturation and interfere with myelin compaction. Cover Image for this issue: doi: 10.1111/jnc.14522.

MicroRNA-219 Inhibits Proliferation and Induces Differentiation of Oligodendrocyte Precursor Cells after Contusion Spinal Cord Injury in Rats

MicroRNA-219 (miR-219) regulates the proliferation and differentiation of oligodendrocyte precursor cells (OPCs) during central nervous system (CNS) development. OPCs only differentiate into oligodendrocytes (OLs) in the healthy CNS, but can generate astrocytes (As) after injury. We hypothesized that miR-219 may modulate OPC proliferation and differentiation in a cervical C5 contusion spinal cord injury (SCI) model. After injury, we observed a decrease in the miR-219 level and quantity of OLs and an increase in the number of OPCs and As. Silencing of miR-219 by its antagomir in vivo produced similar results, but of greater magnitude. Overexpression of miR-219 by its agomir in vivo increased the number of OLs and suppressed generation of OPCs and As. Luxol fast blue staining confirmed that SCI caused demyelination and that the extent of demyelination was attenuated by miR-219 overexpression, but aggravated by miR-219 reduction. Monocarboxylate transporter 1 (MCT-1) may be implicated in the regulation of OPC proliferation and differentiation mediated by miR-219 following contusion SCI. Collectively, our data suggest that miR-219 may mediate SCI-induced OPC proliferation and differentiation, and MCT-1 may participate in this process as a target of miR-219.

Bone marrow-derived mesenchymal stem cells-derived exosomes prevent oligodendrocyte apoptosis through exosomal miR-134 by targeting caspase-8

Ischemic stroke causes severe brain damage and remains one of the leading causes of morbidity and mortality worldwide. The microRNA-134 (miR-134) is involved in regulating the process of ischemia injury in neural cells and brain with ischemia stroke. The role of miR-134 in ischemic stroke remains poorly understood. The purpose of the current study was to investigate the effect of bone marrow-derived mesenchymal stem cells (BMSCs)-derived exosomal miR-134 on rat oligodendrocytes (OLs) apoptosis and its underlying mechanism of action. The results demonstrated that levels of miR-134 in BMSCs-exosome decreased but increased incaspase-8 after oxygen-glucose deprivation (OGD) treatment. Exosomal miR-134 significantly inhibited apoptosis by decreasing caspase-8 expression and activity in OGD-treated group cultured with BMSCs-exosome and OLs. In addition, the miR-134 mimics decreased caspase-8 expression in OGD-treated OLs, whereas miR-134 inhibitors exacerbated the changes in the expression of the procaspase-8 and caspase-8 cleaved product proteins caused by OGD. The caspase-8 knockdown using caspase-8 small interfering RNA decreased OLs apoptosis, reversing the improvements that the miR-134 inhibited cells apoptosis by targeting caspase-8. Taken together, these results demonstrated that BMSCs-derived exosomes suppressed OLs apoptosis through exosomal miR-134 by negatively regulating the caspase-8-dependent apoptosis pathway and may, therefore, be a novel potential therapeutic target for ischemic stroke treatment.

MicroRNA-135a-5p promotes neuronal differentiation of pluripotent embryonal carcinoma cells by repressing Sox6/CD44 pathway

MicroRNA-135a-5p has been reported to play a potential role in the generation of new neurons. However, the underlying targets of miR-135a-5p in regulating neuronal differentiation have been poorly understood. Our study recently has uncovered that Sox6 and CD44 genes were significantly downregulated during neuronal differentiation of P19 cells, a multipotent cell type. We then found that Sox6 directly bound to the promoter of CD44. Importantly, we identified Sox6 as a direct target of miR-135a-5p. Additionally, we demonstrated that miR-135a-5p is crucial for the neuronal differentiation of P19 cells. More significantly, we found that Sox6 overexpression could overturn miR-135a-5p-mediated neuronal differentiation and dendrite development. In conclusion, these findings indicated that miR-135a-5p/Sox6/CD44 axis provides an important molecular target mechanism for neurodifferentiation.

Function of B-Cell CLL/Lymphoma 11B in Glial Progenitor Proliferation and Oligodendrocyte Maturation

B-cell CLL/lymphoma 11B (Bcl11b) – a C2H2 zinc finger transcriptional factor – is known to regulate neuronal differentiation and function in the development of the central nervous system (CNS). Although its expression is reduced during oligodendrocyte (OLG) differentiation, its biological role in OLGs remains unknown. In this study, we found that the downregulation of Bcl11b gene expression in glial progenitor cells (GPCs) by lentivirus-mediated gene knockdown (KD) causes a reduction in cell proliferation with inhibited expression of stemness-related genes, while increasing the expression of cell cyclin regulator p21. In contrast, OLG specific transcription factors (Olig1) and OLG cell markers, including myelin proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG), were upregulated in Bcl11b-KD GPCs. Chromatin immunoprecipitation (ChIP) analysis indicated that Bcl11b bound to the promoters of Olig1 and PLP, suggesting that Bcl11b could act as a repressor for Olig1 and PLP, similar to its action on p21. An increase in the number of GC⁺- or PLP⁺- OLGs derived from Bcl11b-KD GPCs or OLG precursor cells was also observed. Moreover, myelin basic protein (MBP) expression in OLGs derived from Bcl11b-KD GPCs was enhanced in hippocampal neuron co-cultures and in cerebellar brain-slice cultures. The in vivo study using a lysolecithin-induced demyelinating animal model also indicated that larger amounts of MBP⁺-OLGs and PLP⁺-OLGs derived from implanted Bcl11b-KD GPCs were present at the lesioned site of the white matter than in the scramble group. Taken together, our results provide insight into the functional role of Bcl11b in the negative regulation of GPC differentiation through the repression of OLG differentiation-associated genes.