Oct4-induced oligodendrocyte progenitor cells enhance functional recovery in spinal cord injury model

The ENCODE mouse postnatal developmental time course identifies regulatory programs of cell types and cell states

Postnatal genomic regulation significantly influences tissue and organ maturation but is under-studied relative to existing genomic catalogs of adult tissues or prenatal development in mouse. The ENCODE4 consortium generated the first comprehensive single-nucleus resource of postnatal regulatory events across a diverse set of mouse tissues. The collection spans seven postnatal time points, mirroring human development from childhood to adulthood, and encompasses five core tissues. We identified 30 cell types, further subdivided into 69 subtypes and cell states across adrenal gland, left cerebral cortex, hippocampus, heart, and gastrocnemius muscle. Our annotations cover both known and novel cell differentiation dynamics ranging from early hippocampal neurogenesis to a new sex-specific adrenal gland population during puberty. We used an ensemble Latent Dirichlet Allocation strategy with a curated vocabulary of 2,701 regulatory genes to identify regulatory "topics," each of which is a gene vector, linked to cell type differentiation, subtype specialization, and transitions between cell states. We find recurrent regulatory topics in tissue-resident macrophages, neural cell types, endothelial cells across multiple tissues, and cycling cells of the adrenal gland and heart. Cell-type-specific topics are enriched in transcription factors and microRNA host genes, while chromatin regulators dominate mitosis topics. Corresponding chromatin accessibility data reveal dynamic and sex-specific regulatory elements, with enriched motifs matching transcription factors in regulatory topics. Together, these analyses identify both tissue-specific and common regulatory programs in postnatal development across multiple tissues through the lens of the factors regulating transcription.

Microarray analysis of lncRNAs and mRNAs in spinal cord contusion rats with iPSC-derived A2B5+ oligodendrocyte precursor cells transplantation

Spinal cord injury (SCI) is a severe complication of spinal trauma with high disability and mortality rates. Effective therapeutic methods to alleviate neurobehavioural deficits in patients with SCI are still lacking. In this study, we established a spinal cord contusion (SCC) model in adult Sprague Dawley rats. Induced pluripotent stem cell-derived A2B5+ oligodendrocyte precursor cells (iP-A2B5+OPCs) were obtained from mouse embryonic fibroblasts and injected into the lesion sites of SCC rats. Serological testing and magnetic resonance imaging were employed to determine the effect of iP-A2B5+OPCs cell therapy. The Basso-Beattie-Bresnahan score and inclined plane test were performed on days 1, 3, 7, and 14 after cell transplantation, respectively. Differentially expressed long non-coding RNAs (lncRNAs) and messenger RNAs (mRNAs) were detected by microarray analysis. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses were performed to analyse the biological functions of these lncRNAs and mRNAs. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to verify variations in the expression of crucial target genes. The results demonstrated that induced pluripotent stem cells exhibited embryonic stem cell-like morphology and could differentiate into diverse neural cells dominated by oligodendrocytes. The neurobehavioural performance of rats treated with iP-A2B5+OPCs transplantation was better than that of rats with SCC without cell transplantation. Notably, we found that 22 lncRNAs and 42 mRNAs were concurrently altered after cell transplantation, and the key lncRNA (NR_037671) and target gene (Cntnap5a) were identified in the iP-A2B5+OPCs group. Moreover, RT-qPCR revealed that iP-A2B5+OPCs transplantation reversed the downregulation of NR_037671 induced by SCC. Our findings indicated that iP-A2B5+OPCs transplantation effectively improves neurological function recovery after SCC, and the mechanism might be related to alterations in the expression of lncRNAs and mRNAs, such as NR_037671 and Cntnap5a.

Hydrogen peroxide in breast milk is crucial for gut microbiota formation and myelin development in neonatal mice

Early life environment influences mammalian brain development, a growing area of research within the Developmental Origins of Health and Disease framework, necessitating a deeper understanding of early life factors on children's brain development. This study introduces a mouse model, LAO1 knockout mice, to investigate the relationship between breast milk, the gut microbiome, and brain development. The results reveal that breast milk's reactive oxygen species (ROS) are vital in shaping the neonatal gut microbiota. Decreased hydrogen peroxide (H2O2) levels in milk disrupt the gut microbiome and lead to abnormal metabolite production, including D-glucaric acid. This metabolite inhibits hippocampal myelin formation during infancy, potentially contributing to behavioral abnormalities observed in adulthood. These findings suggest that H2O2 in breast milk is crucial for normal gut microbiota formation and brain development, with implications for understanding and potentially treating neurodevelopmental disorders in humans.

Direct cellular reprogramming and transdifferentiation of fibroblasts on wound healing-Fantasy or reality?

Induced pluripotent stem cell (iPSC) technology is one of the de novo approaches in regeneration medicine and has led to new research applications for wound healing in recent years. Fibroblasts have attracted wide attention as the first cell line used for differentiation into iPSCs. Researchers have found that fibroblasts can be induced into different types of cells in variable mediums or microenvironments. This indicates the potential "stem" characteristics of fibroblasts in terms of direct cellular reprogramming compared with the iPSC detour. In this review, we described the morphology and biological function of fibroblasts. The stem cell characteristics and activities of fibroblasts, including transdifferentiation into myofibroblasts, osteogenic cells, chondrogenic cells, neurons, and vascular tissue, are discussed. The biological values of fibroblasts are then briefly reviewed. Finally, we discussed the potential applications of fibroblasts in clinical practice.

Differentiation state and culture conditions impact neural stem/progenitor cell-derived extracellular vesicle bioactivity

Extracellular vesicles (EVs) derived from neural progenitor/stem cells (NPSCs) have shown promising efficacy in a variety of preclinical models. However, NPSCs lack critical neuroregenerative functionality such as myelinating capacity. Further, culture conditions used in NPSC EV production lack standardization, limiting reproducibility challenging and potentially potency of the overall approach via lack of optimization. Here, we assessed whether oligodendrocyte precursor cells (OPCs) and immature oligodendrocytes (iOLs), which are further differentiated than NPSCs and which both give rise to mature myelinating oligodendrocytes, could yield EVs with neurotherapeutic properties comparable or superior to those from NPSCs. We additionally examined the effects of extracellular matrix (ECM) coating materials and the presence or absence of growth factors in cell culture on the ultimate properties of EVs. The data show that OPC EVs and iOL EVs performed similarly to NPSC EVs in cell proliferation and anti-inflammatory assays, but NPSC EVs performed better in a neurite outgrowth assay. Additionally, the presence of nerve growth factor (NGF) in culture was found to maximize NPSC EV bioactivity among the conditions tested. NPSC EVs produced under rationally-selected culture conditions (fibronectin + NGF) enhanced axonal regeneration and muscle reinnervation in a rat nerve crush injury model. These results highlight the need for standardization of culture conditions for neurotherapeutic NPSC EV production.

In Vitro Effects of Methylprednisolone over Oligodendroglial Cells: Foresight to Future Cell Therapies

The implantation of oligodendrocyte precursor cells may be a useful therapeutic strategy for targeting remyelination. However, it is yet to be established how these cells behave after implantation and whether they retain the capacity to proliferate or differentiate into myelin-forming oligodendrocytes. One essential issue is the creation of administration protocols and determining which factors need to be well established. There is controversy around whether these cells may be implanted simultaneously with corticosteroid treatment, which is widely used in many clinical situations. This study assesses the influence of corticosteroids on the capacity for proliferation and differentiation and the survival of human oligodendroglioma cells. Our findings show that corticosteroids reduce the capacity of these cells to proliferate and to differentiate into oligodendrocytes and decrease cell survival. Thus, their effect does not favour remyelination; this is consistent with the results of studies with rodent cells. In conclusion, protocols for the administration of oligodendrocyte lineage cells with the aim of repopulating oligodendroglial niches or repairing demyelinated axons should not include corticosteroids, given the evidence that the effects of these drugs may undermine the objectives of cell transplantation.

Metformin Improves Functional Outcomes, Activates Neural Precursor Cells, and Modulates Microglia in a Sex-Dependent Manner After Spinal Cord Injury

Spinal cord injury (SCI) results in devastating patient outcomes with few treatment options. A promising approach to improve outcomes following SCI involves the activation of endogenous precursor populations including neural stem and progenitor cells (NSPCs) which are located in the periventricular zone (PVZ), and oligodendrocyte precursor cells (OPCs) found throughout the parenchyma. In the adult spinal cord, resident NSPCs are primarily mitotically quiescent and aneurogenic, while OPCs contribute to ongoing oligodendrogenesis into adulthood. Each of these populations is responsive to SCI, increasing their proliferation and migration to the site of injury; however, their activation is not sufficient to support functional recovery. Previous work has shown that administration of the FDA-approved drug metformin is effective at promoting endogenous brain repair following injury, and this is correlated with enhanced NSPC activation. Here, we ask whether metformin can promote functional recovery and neural repair following SCI in both males and females. Our results reveal that acute, but not delayed metformin administration improves functional outcomes following SCI in both sexes. The functional improvement is concomitant with OPC activation and oligodendrogenesis. Our data also reveal sex-dependent effects of metformin following SCI with increased activation of NSPCs in females and reduced microglia activation in males. Taken together, these findings support metformin as a viable therapeutic strategy following SCI and highlight its pleiotropic effects in the spinal cord.

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

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

Application and prospects of somatic cell reprogramming technology for spinal cord injury treatment

Spinal cord injury (SCI) is a serious neurological trauma that is challenging to treat. After SCI, many neurons in the injured area die due to necrosis or apoptosis, and astrocytes, oligodendrocytes, microglia and other non-neuronal cells become dysfunctional, hindering the repair of the injured spinal cord. Corrective surgery and biological, physical and pharmacological therapies are commonly used treatment modalities for SCI; however, no current therapeutic strategies can achieve complete recovery. Somatic cell reprogramming is a promising technology that has gradually become a feasible therapeutic approach for repairing the injured spinal cord. This revolutionary technology can reprogram fibroblasts, astrocytes, NG2 cells and neural progenitor cells into neurons or oligodendrocytes for spinal cord repair. In this review, we provide an overview of the transcription factors, genes, microRNAs (miRNAs), small molecules and combinations of these factors that can mediate somatic cell reprogramming to repair the injured spinal cord. Although many challenges and questions related to this technique remain, we believe that the beneficial effect of somatic cell reprogramming provides new ideas for achieving functional recovery after SCI and a direction for the development of treatments for SCI.

Induced Endothelial Cell-Integrated Liver Assembloids Promote Hepatic Maturation and Therapeutic Effect on Cholestatic Liver Fibrosis

The transplantation of pluripotent stem cell (PSC)-derived liver organoids has been studied to solve the current donor shortage. However, the differentiation of unintended cell populations, difficulty in generating multi-lineage organoids, and tumorigenicity of PSC-derived organoids are challenges. However, direct conversion technology has allowed for the generation lineage-restricted induced stem cells from somatic cells bypassing the pluripotent state, thereby eliminating tumorigenic risks. Here, liver assembloids (iHEAs) were generated by integrating induced endothelial cells (iECs) into the liver organoids (iHLOs) generated with induced hepatic stem cells (iHepSCs). Liver assembloids showed enhanced functional maturity compared to iHLOs in vitro and improved therapeutic effects on cholestatic liver fibrosis animals in vivo. Mechanistically, FN1 expressed from iECs led to the upregulation of Itgα5/β1 and Hnf4α in iHEAs and were correlated to the decreased expression of genes related to hepatic stellate cell activation such as Lox and Spp1 in the cholestatic liver fibrosis animals. In conclusion, our study demonstrates the possibility of generating transplantable iHEAs with directly converted cells, and our results evidence that integrating iECs allows iHEAs to have enhanced hepatic maturation compared to iHLOs.

Disease Modeling of Neurodegenerative Disorders Using Direct Neural Reprogramming

Understanding the pathophysiology of CNS-associated neurological diseases has been hampered by the inaccessibility of patient brain tissue to perform live analyses at the molecular level. To this end, neural cells obtained by differentiation of patient-derived induced pluripotent stem cells (iPSCs) are considerably helpful, especially in the context of monogenic-based disorders. More recently, the use of direct reprogramming to convert somatic cells to neural cells has emerged as an alternative to iPSCs to generate neurons, astrocytes, and oligodendrocytes. This review focuses on the different studies that used direct neural reprogramming to study disease-associated phenotypes in the context of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Transgene and Chemical Transdifferentiation of Somatic Cells for Rapid and Efficient Neurological Disease Cell Models

For neurological diseases, molecular and cellular research relies on the use of model systems to investigate disease processes and test potential therapeutics. The last decade has witnessed an increase in the number of studies using induced pluripotent stem cells to generate disease relevant cell types from patients. The reprogramming process permits the generation of a large number of cells but is potentially disadvantaged by introducing variability in clonal lines and the removal of phenotypes of aging, which are critical to understand neurodegenerative diseases. An under-utilized approach to disease modeling involves the transdifferentiation of aged cells from patients, such as fibroblasts or blood cells, into various neural cell types. In this review we discuss techniques used for rapid and efficient direct conversion to neural cell types. We examine the limitations and future perspectives of this rapidly advancing field that could improve neurological disease modeling and drug discovery.

Progression in translational research on spinal cord injury based on microenvironment imbalance

Spinal cord injury (SCI) leads to loss of motor and sensory function below the injury level and imposes a considerable burden on patients, families, and society. Repair of the injured spinal cord has been recognized as a global medical challenge for many years. Significant progress has been made in research on the pathological mechanism of spinal cord injury. In particular, with the development of gene regulation, cell sequencing, and cell tracing technologies, in-depth explorations of the SCI microenvironment have become more feasible. However, translational studies related to repair of the injured spinal cord have not yielded significant results. This review summarizes the latest research progress on two aspects of SCI pathology: intraneuronal microenvironment imbalance and regenerative microenvironment imbalance. We also review repair strategies for the injured spinal cord based on microenvironment imbalance, including medications, cell transplantation, exosomes, tissue engineering, cell reprogramming, and rehabilitation. The current state of translational research on SCI and future directions are also discussed. The development of a combined, precise, and multitemporal strategy for repairing the injured spinal cord is a potential future direction.

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

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

Oligodendroglia Generated From Adult Rat Adipose Tissue by Direct Cell Conversion

Obtaining oligodendroglial cells from dispensable tissues would be of great interest for autologous or immunocompatible cell replacement therapy in demyelinating diseases, as well as for studying myelin-related pathologies or testing therapeutic approaches in culture. We evaluated the feasibility of generating oligodendrocyte precursor cells (OPCs) from adult rat adipose tissue by expressing genes encoding transcription factors involved in oligodendroglial development. Adipose-derived mesenchymal cells were lentivirally transduced with tetracycline-inducible Sox10, Olig2, Zfp536, and/or Nkx6.1 transgenes. Immunostaining with the OPC-specific O4 monoclonal antibody was used to mark oligodendroglial induction. O4- and myelin-associated glycoprotein (MAG)-positive cells emerged after 3 weeks when using the Sox10 + Olig2 + Zfp536 combination, followed in the ensuing weeks by GFAP-, O1 antigen-, p75NTR (low-affinity NGF receptor)-, and myelin proteins-positive cells. The O4⁺ cell population progressively expanded, eventually constituting more than 70% of cells in culture by 5 months. Sox10 transgene expression was essential for generating O4⁺ cells but was insufficient for inducing a full oligodendroglial phenotype. Converted cells required continuous transgene expression to maintain their glial phenotype. Some vestigial characteristics of mesenchymal cells were maintained after conversion. Growth factor withdrawal and triiodothyronine (T₃) supplementation generated mature oligodendroglial phenotypes, while FBS supplementation produced GFAP⁺- and p75NTR⁺-rich cultures. Converted cells also showed functional characteristics of neural-derived OPCs, such as the expression of AMPA, NMDA, kainate, and dopaminergic receptors, as well as similar metabolic responses to differentiation-inducing drugs. When co-cultured with rat dorsal root ganglion neurons, the converted cells differentiated and ensheathed multiple axons. We propose that functional oligodendroglia can be efficiently generated from adult rat mesenchymal cells by direct phenotypic conversion.

OCT4-induced oligodendrocyte progenitor cells promote remyelination and ameliorate disease

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

Microglia Impede Oligodendrocyte Generation in Aged Brain

Purpose

Age-related increase in myelin loss may be responsible for brain atrophy, and the mechanism is not completely understood. We aim to comprehensively delineate oligodendrocyte heterogeneity in young and aged mice and to reveal the underlying mechanism for myelin loss during aging.

Methods

Diffusion tensor imaging and immunofluorescent staining were performed to verify the demyelination in the aged brains of both rodents and human. Further, the single-cell RNA sequencing data of all brain cells from young and aged mice were deeply analyzed to identify the subsets of oligodendrocyte lineage cells. Cell-to-cell interaction analysis was performed to detect the mechanism of observed changes in oligodendrocyte generation.

Results

Oligodendrocytes were observed to up-regulate several senescence associated genes in aged brain. Four clusters of oligodendrocyte precursor cells (OPCs) were identified in both young and aged brains. The number of those OPCs in basal state was significantly increased, while the OPCs in the procedure of differentiation were immensely decreased in aged brain. Furthermore, it was identified that activated microglia in the aged brain released inflammatory factors to suppress OPC differentiation. Stat1 might be a potential target to transform senescent microglia into tissue repair type to promote oligodendrocyte generation.

Conclusion

These results provided a perspective on how age activated microglia could impede remyelination and might give a new therapeutic target for age-related remyelinating diseases.

Intranasal Administration of Undifferentiated Oligodendrocyte Lineage Cells as a Potential Approach to Deliver Oligodendrocyte Precursor Cells into Brain

Oligodendrocyte precursor cell (OPC) migration is a mechanism involved in remyelination; these cells migrate from niches in the adult CNS. However, age and disease reduce the pool of OPCs; as a result, the remyelination capacity of the CNS decreases over time. Several experimental studies have introduced OPCs to the brain via direct injection or intrathecal administration. In this study, we used the nose-to brain pathway to deliver oligodendrocyte lineage cells (human oligodendroglioma (HOG) cells), which behave similarly to OPCs in vitro. To this end, we administered GFP-labelled HOG cells intranasally to experimental animals, which were subsequently euthanised at 30 or 60 days. Our results show that the intranasal route is a viable route to the CNS and that HOG cells administered intranasally migrate preferentially to niches of OPCs (clusters created during embryonic development and adult life). Our study provides evidence, albeit limited, that HOG cells either form clusters or adhere to clusters of OPCs in the brains of experimental animals.

In Vivo Expression of Reprogramming Factor OCT4 Ameliorates Myelination Deficits and Induces Striatal Neuroprotection in Huntington's Disease

White matter atrophy has been shown to precede the massive loss of striatal GABAergic neurons in Huntington’s disease (HD). This study investigated the effects of in vivo expression of reprogramming factor octamer-binding transcription factor 4 (OCT4) on neural stem cell (NSC) niche activation in the subventricular zone (SVZ) and induction of cell fate specific to the microenvironment of HD. R6/2 mice randomly received adeno-associated virus 9 (AAV9)-OCT4, AAV9-Null, or phosphate-buffered saline into both lateral ventricles at 4 weeks of age. The AAV9-OCT4 group displayed significantly improved behavioral performance compared to the control groups. Following AAV9-OCT4 treatment, the number of newly generated NSCs and oligodendrocyte progenitor cells (OPCs) significantly increased in the SVZ, and the expression of OPC-related genes and glial cell-derived neurotrophic factor (GDNF) significantly increased. Further, amelioration of myelination deficits in the corpus callosum was observed through electron microscopy and magnetic resonance imaging, and striatal DARPP32⁺ GABAergic neurons significantly increased in the AAV9-OCT4 group. These results suggest that in situ expression of the reprogramming factor OCT4 in the SVZ induces OPC proliferation, thereby attenuating myelination deficits. Particularly, GDNF released by OPCs seems to induce striatal neuroprotection in HD, which explains the behavioral improvement in R6/2 mice overexpressing OCT4.

Sequentially induced motor neurons from human fibroblasts facilitate locomotor recovery in a rodent spinal cord injury model

Generation of autologous human motor neurons holds great promise for cell replacement therapy to treat spinal cord injury (SCI). Direct conversion allows generation of target cells from somatic cells, however, current protocols are not practicable for therapeutic purposes since converted cells are post-mitotic that are not scalable. Therefore, therapeutic effects of directly converted neurons have not been elucidated yet. Here, we show that human fibroblasts can be converted into induced motor neurons (iMNs) by sequentially inducing POU5F1(OCT4) and LHX3. Our strategy enables scalable production of pure iMNs because of the transient acquisition of proliferative iMN-intermediate cell stage which is distinct from neural progenitors. iMNs exhibited hallmarks of spinal motor neurons including transcriptional profiles, electrophysiological property, synaptic activity, and neuromuscular junction formation. Remarkably, transplantation of iMNs showed therapeutic effects, promoting locomotor functional recovery in rodent SCI model. Together, our advanced strategy will provide tools to acquire sufficient human iMNs that may represent a promising cell source for personalized cell therapy.

Overexpression of the transcription factors OCT4 and KLF4 improves motor function after spinal cord injury

Introduction

Astrogliosis and glial scar formation following spinal cord injury (SCI) are viewed as major obstacles that hinder axonal regeneration and functional recovery. Regulating the glial scar and axonal regeneration in the lesion site is important for treating SCI.

Aims

Considering the important role of astrocyte in glial scar formation and subsequent axonal regeneration, we intended to investigate the effect of the transcription factors OCT4 and KLF4 on astrocyte and the underlying mechanism after spinal cord contusion injury in transgenic mice.

Results

Western blotting, q‐PCR, immunofluorescence, and functional evaluation suggested that glial fibrillary acidic protein (GFAP) expression decreased in the lesion area, the porosity of the scar increased, and remyelination enhanced. Mice overexpressing the transcription factors OCT4 and KLF4 had higher Basso Mouse Scale scores than did the control mice. Moreover, using immunofluorescence and Western blotting, we discovered that some astrocytes expressed nestin and sox2 protein, suggesting that these astrocytes were reprogrammed into neural stem cell‐like cells. Furthermore, a cell scratch assay showed that the migration ability of the astrocytes was significantly inhibited in the presence of the transcription factors OCT4 and KLF4. In addition, we demonstrated that the Hippo/Yap pathway was activated after these two transcription factors overexpressed in astrocytes.

Conclusions

In summary, these results suggest that overexpression of the transcription factors OCT4 and KLF4 could induce astrocyte reprogramming, which subsequently improves remyelination and functional recovery after SCI.

Robust and Reproducible Generation of Induced Neural Stem Cells from Human Somatic Cells by Defined Factors

BACKGROUND AND OBJECTIVES

Recent studies have described direct reprogramming of mouse and human somatic cells into induced neural stem cells (iNSCs) using various combinations of transcription factors. Although iNSC technology holds a great potential for clinical applications, the low conversion efficiency and limited reproducibility of iNSC generation hinder its further translation into the clinic, strongly suggesting the necessity of highly reproducible method for human iNSCs (hiNSCs). Thus, in orderto develop a highly efficient and reproducible protocol for hiNSC generation, we revisited the reprogramming potentials of previously reported hiNSC reprogramming cocktails by comparing the reprogramming efficiency of distinct factor combinations including ours.

METHODS

We introduced distinct factor combinations, OSKM (OCT4+SOX2+KLF4+C-MYC), OCT4 alone, SOX2 alone, SOX2+HMGA2, BRN4+SKM+SV40LT (BSKMLT), SKLT, SMLT, and SKMLT and performed comparative analysis of reprogramming potentials of distinct factor combinations in hiNSC generation.

RESULTS

Here we show that ectopic expression of five reprogramming factors, BSKMLT leads the robust hiNSC generation (>80 folds enhanced efficiency) from human somatic cells compared with previously described factor combinations. With our combination, we were able to observe hiNSC conversion within 7 days of transduction. Throughout further optimization steps, we found that both BRN4 and KLF4 are not essential for hiNSC conversion.

CONCLUSIONS

Our factor combination could robustly and reproducibly generate hiNSCs from human somatic cells with distinct origins. Therefore, our novel reprogramming strategy might serve as a useful tool for hiNSC-based clinical application.

SOX2 protein transduction directly converts human fibroblasts into oligodendrocyte-like cells

Oligodendrocyte precursor cells (OPCs) are ideal therapeutic cells for treatment of spinal cord injuries and diseases that affect myelin. However, it is necessary to generate a cell population with a low risk of teratoma formation and oncogenesis from a patient's somatic cells. In this study, we investigated the direct reprogramming of fibroblasts to oligodendrocyte-like cells in one step with a safe non-genetic delivery method that used protein transduction. Cell morphology and the lineage-specific marker expression profile indicated that human foreskin fibroblasts (HFFs) were converted into oligodendrocyte-like cells by the application of pluripotency factors and the use of a permissible induction medium. Our data demonstrated that SOX2 was sufficient to directly drive OPC fate conversion from HFF by a genetic-free approach. Therefore, this work has provided a strategy to OPC reprogramming by a non-integrating approach for future use in disease modeling and may ultimately provide applications for patient-specific cell-based regenerative medicine.

Direct cell-fate conversion of somatic cells: Toward regenerative medicine and industries

Cells of multicellular organisms have diverse characteristics despite having the same genetic identity. The distinctive phenotype of each cell is determined by molecular mechanisms such as epigenetic changes that occur throughout the lifetime of an individual. Recently, technologies that enable modification of the fate of somatic cells have been developed, and the number of studies using these technologies has increased drastically in the last decade. Various cell types, including neuronal cells, cardiomyocytes, and hepatocytes, have been generated using these technologies. Although most direct reprogramming methods employ forced transduction of a defined sets of transcription factors to reprogram cells in a manner similar to induced pluripotent cell technology, many other strategies, such as methods utilizing chemical compounds and microRNAs to change the fate of somatic cells, have also been developed. In this review, we summarize transcription factor-based reprogramming and various other reprogramming methods. Additionally, we describe the various industrial applications of direct reprogramming technologies.

Brief review: Can modulating DNA methylation state help the clinical application of oligodendrocyte precursor cells as a source of stem cell therapy?

Oligodendrocyte precursor cells (OPCs) are one of the major cell types in cerebral white matter, which are generated from neural progenitor cells (NPCs) and give rise to mature oligodendrocytes. Although past studies have extensively examined how OPCs are generated from NPCs and how OPCs differentiate into mature oligodendrocytes, the underlying mechanisms remain unelucidated. In particular, the roles of DNA methylation and the related enzymes DNA methyltransferases (DNMTs) in oligodendrocyte lineage cells are still mostly unknown, although DNA methylation plays a critical role in cell fate decision in multiple cell types. Recently, OPCs were proposed as a promising source of cell-based therapy for patients with oligodendrocyte/myelin damage. Therefore, understanding the mechanisms underlying the involvement of DNMTs in OPCs would help to develop an approach for the efficient preparation of OPCs for cell-based therapy. As a part of the special issue for "Stem Cell Therapy" in Brain Research, this mini-review article first overviews the potential for clinical application of OPCs for cell-based therapy, and then summarizes the key findings of DNMT roles in OPCs, focusing on OPC generation and differentiation.

Oct4 and Hnf4α-induced hepatic stem cells ameliorate chronic liver injury in liver fibrosis model

Direct conversion from fibroblasts to generate hepatocyte like-cells (iHeps) bypassing the pluripotent state has been described in previous reports as an attractive method acquiring hepatocytes for cell-based therapy. The limited proliferation of iHeps, however, has hampered it uses in cell-based therapy. Since hepatic stem cells (HepSCs) possess self-renewal and bipotency with the capacity to differentiate into both hepatocytes and cholangiocytes, they have therapeutic potential for treating liver disease. Here, we investigated the therapeutic effects of induced HepSCs (iHepSCs) on a carbon tetrachloride (CCl₄)-induced liver fibrosis model. We demonstrate that Oct4 and Hnf4a are sufficient to convert fibroblasts into expandable iHepSCs. Hepatocyte-like cells derived from iHepSCs (iHepSC-HEPs) exhibit the typical morphology of hepatocytes and hepatic functions, including glycogen storage, low-density lipoprotein (LDL) uptake, Indocyanine green (ICG) detoxification, drug metabolism, urea production, and albumin secretion. iHepSCs-derived cholangiocyte-like cells (iHepSC-CLCs) expressed cholangiocyte-specific markers and formed cysts and tubule-like structures with apical-basal polarity and secretory function in three-dimensional culture condition. Furthermore, iHepSCs showed anti-inflammatory and anti-fibrotic effects in CCl₄-induced liver fibrosis. This study demonstrates that Oct4 and Hnf4α-induced HepSCs show typical hepatic and biliary functionality in vitro. It also presents the therapeutic effect of iHepSCs in liver fibrosis. Therefore, directly converting iHepSCs from somatic cells may facilitate the development of patient-specific cell-based therapy for chronic liver damage.

Metastable Reprogramming State of Single Transcription Factor-Derived Induced Hepatocyte-Like Cells

We previously described the generation of induced hepatocyte-like cells (iHeps) using the hepatic transcription factor Hnf1a together with small molecules. These iHeps represent a hepatic state that is more mature compared with iHeps generated with multiple hepatic factors. However, the underlying mechanism of hepatic conversion involving transgene dependence of the established iHeps is largely unknown. Here, we describe the generation of transgene-independent iHeps by inducing the ectopic expression of Hnf1a using both an episomal vector and a doxycycline-inducible lentivirus. In contrast to iHeps with sustained expression of Hnf1a, transgene-independent Hnf1a iHeps lose their typical morphology and in vitro functionality with rapid downregulation of hepatic markers upon withdrawal of small molecules. Taken together, our data indicates that the reprogramming state of single factor Hnf1a-derived iHeps is metastable and that the hepatic identity of these cells could be maintained only by the continuous supply of either small molecules or the master hepatic factor Hnf1a. Our findings emphasize the importance of a factor screening strategy for inducing specific cellular identities with a stable reprogramming state in order to eventually translate direct conversion technology to the clinic.

In vivo conversion of astrocytes to oligodendrocyte lineage cells in adult mice demyelinated brains by Sox2

Sox2 transcription factor has been frequently used for reprograming starting cells to neural progenitor/stem cells. In vivo administration of Sox2 in the adult mouse brain reprogrammed the transduced astrocytes to neurons. In searching for adequate cell source for repairing the myelin insults, here, we studied the possible conversion of astrocytes to oligodendrocyte lineage cells by Sox2, while an extensive demyelination exists in animal brain. Lentiviral particles expressing Sox2-GFP were injected into the corpora callosa of animals fed with cuprizone diet for 12 weeks. Transduced cells were mainly astrocytes that changed their fate to oligodendrocyte lineage cells by time. For further conformation astrocytes received the vector in culture and then transplanted to the animal brains. Tracing the fate of transplanted cells showed their conversion to oligodendrocyte lineage cells. In vitro transduced cell were also maintained in the oligodendrocyte progenitor cell (OPC) induction medium. Produced OPC-like cells were positive for specific markers. This study provides a new strategy for endogenous production of myelinating cells. After optimizing the experimental conditions for safety and feasibility, this approach may contribute into future cell based therapies in patients with white matter insults as like as those with multiple sclerosis.

Trichostatin A Promotes the Conversion of Astrocytes to Oligodendrocyte Progenitors in a Defined Culture Medium

The generation of oligodendrocyte progenitor cells (OPCs) offers tremendous opportunities for cell replacement therapy in demyelinating diseases such as multiple sclerosis (MS) and spinal cord injury. Recently, the prospect of reprogramming terminally differentiated adult cells towards another mature somatic cell or progenitor cells without an intermediate pluripotent state has been of interest. Trichostatin A is a histone deacetylase inhibitor which opens the chromatin and facilitates the transcription of silence genes. In this study, we have treated human astrocytes line U87 and primary culture of mouse astrocytes with TSA for 12 h, prior their transfer to OPC induction medium. Then we evaluated the morphology and the fate of the treated astrocytes at post-treatment days. Both cell lines acquired OPC morphology and expressed OPC specific markers. Following transfer to differentiation medium, U87-derived iOPCs differentiated to oligodendrocyte like cells and expressed PLP as a mature oligodendrocyte marker. Our results introduced TSA as an inducer for production of OPCs from astrocytes and could be considered a potential way for the treatment of demyelinating diseases.

Comparing stemness gene expression between stem cell subpopulations from peripheral blood and adipose tissue

Cell therapy presents a promising alternative for the treatment of degenerative diseases. The main sources of adult stem cells are bone marrow, adipose tissue and peripheral blood. Within those tissues, there are cell subpopulations that share pluripotential characteristics. Nevertheless, there is insufficient data to determine which of these stem cell subtypes would have a better possibility to differentiate to a specific tissue. The objective of this research was to analyze and compare the stemness genes expression from peripheral blood and adipose tissue of plastic adherent cells, and those immune-selected by the CD133⁺ and CD271⁺ membrane markers. On all cell subpopulation groups, self-renew capacity, the membranes markers CD73, CD90 and CD105, as well as the stemness genes NANOG, OCT4, SOX2, REX1, NOTCH1 and, NESTIN expression were analyzed. Results showed that all samples presented the minimal criteria to define them as human stem cells. All cell subpopulation were capable of self-renewal. Nevertheless, the subpopulation cell types showed differences on the time needed to reach confluence. The slowest doubling times were for those cells bearing the CD133 marker from both sources. Surface markers determined by flow cytometry were positive for CD73, CD90 and, CD105, and negative for CD45. The stemness gene expression was positive in all subpopulation. However, there were significant differences in the amount and pattern of expression among them. Those differences could be advantageous in finding the best option for their application on cell therapy. Cells with high expression of OCT4 gene could be a better opportunity for neuron differentiation like CD133⁺ blood cells. On the other hand, lowest expression of NOTCH1 on CD271⁺ cells from the same source could be a better possibility for myoblast differentiation. The observed differences could be used as an advantage to find which cell type and from the different source; this represents the best option for its application on cell therapy. Experiments focused on the best response to specific differentiation, are conducted in order to confirm those possibilities.

Promoting Myelin Repair through In Vivo Neuroblast Reprogramming

Demyelination is frequently observed in a variety of CNS insults and neurodegenerative diseases. In rodents, adult neural stem cells can generate oligodendrocytes and participate to myelin repair. However, these cells mainly produce migratory neuroblasts that differentiate in the olfactory bulb. Here, we show that, in the demyelination context, a small subset of these neuroblasts can spontaneously convert into myelinating oligodendrocytes. Furthermore, we demonstrate that the contribution of neuroblasts to myelin repair can be improved by in vivo forced expression of two transcription factors: OLIG2 and SOX10. These factors promote directed fate conversion of endogenous subventricular zone neuroblasts into mature functional oligodendrocytes, leading to enhanced remyelination in a cuprizone-induced mouse model of demyelination. These findings highlight the unexpected plasticity of committed neuroblasts and provide proof of concept that they could be targeted for the treatment of demyelinated lesions in the adult brain.

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Sox10 and Olig2 convert endogenous neuroblasts into myelinating oligodendrocytes

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Converted cells migrate to the corpus callosum, striatum, and cortex

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Converted cells produce myelin and participate to the formation of node of Ranvier

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Forced neuroblast conversion improves myelin regeneration

AAV-KLF7 Promotes Descending Propriospinal Neuron Axonal Plasticity after Spinal Cord Injury

DPSN axons mediate and maintain a variety of normal spinal functions. Unsurprisingly, DPSN tracts have been shown to mediate functional recovery following SCI. KLF7 could contribute to CST axon plasticity after spinal cord injury. In the present study, we assessed whether KLF7 could effectively promote DPSN axon regeneration and synapse formation following SCI. An AAV-KLF7 construct was used to overexpress KLF7. In vitro, KLF7 and target proteins were successfully elevated and axonal outgrowth was enhanced. In vivo, young adult C57BL/6 mice received a T10 contusion followed by an AAV-KLF7 injection at the T7–9 levels above the lesion. Five weeks later, overexpression of KLF7 was expressed in DPSN. KLF7 and KLF7 target genes (NGF, TrkA, GAP43, and P0) were detectably increased in the injured spinal cord. Myelin sparring at the lesion site, DPSN axonal regeneration and synapse formation, muscle weight, motor endplate morphology, and functional parameters were all additionally improved by KLF7 treatment. Our findings suggest that KLF7 promotes DPSN axonal plasticity and the formation of synapses with motor neurons at the caudal spinal cord, leading to improved functional recovery and further supporting the potential of AAV-KLF7 as a therapeutic agent for spinal cord injury.

A Novel Three-Dimensional Culture System for Oligodendrocyte Precursor Cells

Oligodendrocytes are generated from oligodendrocyte precursor cells (OPCs). Mechanisms of OPC differentiation have been extensively examined with two-dimensional cell culture systems. However, these cellular events may be more accurately represented using a three-dimensional (3D) model. In this study, we report the development of a novel 3D OPC culture system using gels composed of a mixture of collagen and hyaluronan, wherein cultured rat primary OPCs can proliferate and differentiate into oligodendrocytes. Our data show that the gel concentration and cell-seeding density are critical factors for the numbers of OPCs and oligodendrocytes in our 3D culture system. In addition, Notch signaling, which supports cell-to-cell communication, may also be important for OPC function in our system because a Notch inhibitor DAPT suppressed OPC proliferation and differentiation. Taken together, cultured rat OPCs can grow in collagen-/hyaluronan-based gels, and our novel 3D OPC culture system may offer a useful platform for examining the mechanisms of OPC function in vitro.

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

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

GAT-1 mediated GABA uptake in rat oligodendrocytes

Stimulated by the results of a recent paper on the effects of tiagabine, a selective inhibitor of the main GABA transporter GAT-1, on oligodendrogenesis, we verified the possibility that GAT-1 may be expressed in oligodendrocytes using immunocytochemical methods and functional assays. Light microscopic analysis of the subcortical white matter of all animals revealed the presence of numerous GAT-1+ cells of different size (from 3 to 29 µm) and morphology. An electron microscope analysis revealed that, besides fibrous astrocytes and interstitial neurons, GAT-1 immunoreactivity was present in immature and mature oligodendrocytes. Co-localization studies between GAT-1 and markers specific for oligodendrocytes (NG2 and RIP) showed that about 12% of GAT-1 positive cells in the white matter were immature oligodendrocytes, while about 15% were mature oligodendrocytes. In vitro functional assays showed that oligodendrocytes exhibit tiagabine-sensitive Na⁺ -dependent GABA uptake. Although relationships between GABA and oligodendrocytes have been known for many years, this is the first demonstration that GAT-1 is expressed in oligodendrocytes. The present results on the one hand definitely closes the era of "neuronal" and "glial" GABA transporters, on the other they suggest that oligodendrocytes may contribute to pathophysiology of the several diseases in which GAT-1 have been implicated to date. GLIA 2017;65:514-522.

Clinical application of oligodendrocyte precursor cells for cell-based therapy

Oligodendrocyte precursor cells (OPCs), which give rise to mature oligodendrocytes (OLs), play important roles in maintaining white matter function. Even during the adulthood period, OPCs comprise roughly 5% of all cells in the forebrain and retain a capability to become myelinated OLs. Recently, OPCs have been proposed as a novel source for cell-based therapy. For the purpose, OPCs can be obtained from embryonic stem cells, induced pluripotent stem cells, and directly converted cells derived from patients. Here, we will provide a brief review of the potential of using OPCs as a cell-based therapy for treating various neurological diseases.

Mechanisms of Axonal Damage and Repair after Central Nervous System Injury

Central nervous system (CNS) injury initiates spatial and temporal neurodegeneration. Under pathologic conditions, damaged glial cells cannot supply sufficient metabolites to neurons, leading to energy deficiency for neuronal axons. The widespread disruption of cellular membranes causes disturbed intracellular signaling via dysregulated ionic gradients in neurons. Although several deleterious cascades are activated during the acute phase of CNS injury, some compensatory responses may tend to promote axonal repair during the chronic/remodeling phase. Because it may not be easy to block all multifactorial neurodegenerative pathways after CNS injury, supporting or boosting endogenous regenerative mechanisms would be an important therapeutic approach for CNS diseases. In this mini-review, we briefly but broadly introduce basic mechanisms that trigger axonal degeneration and then discuss potential targets for promoting axonal regeneration after CNS injury.

Efficient Generation of Functionally Active Spinal Cord Neurons from Spermatogonial Stem Cells

Neural stem cells (NSCs) are hitherto regarded as perspective candidates for cell transplantation in clinical therapies for multilevel spinal cord injury and function restoration. However, the extreme drawbacks of NSCs available for injury transplantation still represent a significant bottleneck in neural regeneration medicine. Therefore, it is essential to establish a suitable cell reservoir as an issue-free alternative. Here, we demonstrate that spermatogonial stem cells (SSCs) derived from rat testis robustly give rise to terminally differentiated, functionally mature spinal cord neurons by using an optimized differentiation protocol. After performing a 3-week in vitro differentiation procedure, most cells exhibited neural morphological features and were Tuj-1 positive. Of note, approximately 60 % of the obtained cells coexpressed choline acetyltransferase (CHAT), acetylcholinesterase (AchE), and calcitonin gene-related peptide (CGRP). More importantly, apart from acquisition of neural antigenic and biochemical properties, nearly all neurons efficiently exhibited in vitro functionality similar to wild-type neurons, such as synapse formation, increased neuronal calcium influx, and electrophysiology. This is the first report revealing consistent and reproducible generation of large amounts of functional neurons from SSCs. Collectively, this system is suitable for studies of SSC transdifferentiation into neuronal cells and can provide sufficient neurons for the treatment of spinal cord injury as well as for genetic and small molecule screenings.

Oct4 transcription factor in conjunction with valproic acid accelerates myelin repair in demyelinated optic chiasm in mice

Multiple sclerosis is a demyelinating disease with severe neurological symptoms due to blockage of signal conduction in affected axons. Spontaneous remyelination via endogenous progenitors is limited and eventually fails. Recent reports showed that forced expression of some transcription factors within the brain converted somatic cells to neural progenitors and neuroblasts. Here, we report the effect of valproic acid (VPA) along with forced expression of Oct4 transcription factor on lysolecithin (LPC)-induced experimental demyelination. Mice were gavaged with VPA for one week, and then inducible Oct4 expressing lentiviral particles were injected into the lateral ventricle. After one-week induction of Oct4, LPC was injected into the optic chiasm. Functional remyelination was assessed by visual-evoked potential (VEP) recording. Myelination level was studied using FluoroMyelin staining and immunohistofluorescent (IHF) against proteolipid protein (PLP). IHF was also performed to detect Oct4 and SSEA1 as pluripotency markers and Olig2, Sox10, CNPase and PDGFRα as oligodendrocyte lineage markers. One week after injection of Oct4 expressing vector, pluripotency markers SSEA1 and Oct4 were detected in the rims of the 3rd ventricle. LPC injection caused extensive demyelination and significantly delayed the latency of VEP wave. Animals pre-treated with VPA+Oct4 expressing vector, showed faster recovery in the VEP latency and enhanced myelination. Immunostaining against oligodendrocyte lineage markers showed an increased number of Sox10+ and myelinating cells. Moreover, transdifferentiation of some Oct4-transfected cells (GFP+ cells) to Olig2+ and CNPase+ cells was confirmed by immunostaining. One-week administration of VPA followed by one-week forced expression of Oct4 enhanced myelination by converting transduced cells to myelinating oligodendrocytes. This finding seems promising for enhancing myelin repair within the adult brains.

Oct4-induced oligodendrocyte progenitor cells enhance functional recovery in spinal cord injury model

The generation of patient-specific oligodendrocyte progenitor cells (OPCs) holds great potential as an expandable cell source for cell replacement therapy as well as drug screening in spinal cord injury or demyelinating diseases. Here, we demonstrate that induced OPCs (iOPCs) can be directly derived from adult mouse fibroblasts by Oct4-mediated direct reprogramming, using anchorage-independent growth to ensure high purity. Homogeneous iOPCs exhibit typical small-bipolar morphology, maintain their self-renewal capacity and OPC marker expression for more than 31 passages, share high similarity in the global gene expression profile to wild-type OPCs, and give rise to mature oligodendrocytes and astrocytes in vitro and in vivo. Notably, transplanted iOPCs contribute to functional recovery in a spinal cord injury (SCI) model without tumor formation. This study provides a simple strategy to generate functional self-renewing iOPCs and yields insights for the in-depth study of demyelination and regenerative medicine.