Isolation and long-term expansion of functional, myelinating oligodendrocyte progenitor cells from neonatal rat brain

MicroRNA-7188-5p and miR-7235 regulates Multiple sclerosis in an experimental mouse model

The short non-coding microRNAs (miRNAs) have emerged as reliable modulators of various pathological conditions including autoimmune diseases in mammals. The current study, aims to identify new potential differential expressed miRNAs and their downstream mRNA targets of the autoimmune disease, Multiple sclerosis (MS). The study identifies a new set of miRNA(s) that are probably implicated in MS using computational tools. The study further carried-out different in vivo and in vitro experiments to check these identified miRNAs could be role in as therapeutic and prognostic applications. Preliminary insilico screening revealed that miR-659-3p, miR-659-5p, miR-684, miR-3607-3p, miR-3607-5p, miR-3682-3p, miR-3682-5p miR-4647, miR-7188-3p, miR-7188-5p and miR-7235 are specifically elevated in the secondary lymphoid cells of EAE mice. In addition, expression of the downstream target mRNA of these miRNAs such as FXBO33, SGMS-1, ZDHHC-9, GABRA-3, NRXN-2 were reciprocal to miRNA expression in lymphoid cells. These confirmed by applying the mimic and silencing miRNA models, suggesting new inflammatory target genes of these promising miRNA markers. The in vivo adoptive transfer model revealed that the suppression of miRNA-7188-5p and miR-7235 changed the pattern of astrocytes and CNS pathophysiology. The current study opens a new miRNA and their mRNA targets in MS disease. The absence of miRNA-7188-5p and miR-7235 enhanced the disease alleviation, confirms the regulatory effect of these targets. These optimized results highlights new set of miRNA's with therapeutic potential in experimental MS. Further studies are required to confirm these miRNA as therapeutic biomarker.

Generation of Oligodendrocyte Progenitor Cells From Mouse Bone Marrow Cells

Oligodendrocyte progenitor cells (OPCs) are a subtype of glial cells responsible for myelin regeneration. Oligodendrocytes (OLGs) originate from OPCs and are the myelinating cells in the central nervous system (CNS). OLGs play an important role in the context of lesions in which myelin loss occurs. Even though many protocols for isolating OPCs have been published, their cellular yield remains a limit for clinical application. The protocol proposed here is novel and has practical value; in fact, OPCs can be generated from a source of autologous cells without gene manipulation. Our method represents a rapid, and high-efficiency differentiation protocol for generating mouse OLGs from bone marrow-derived cells using growth-factor defined media. With this protocol, it is possible to obtain mature OLGs in 7–8 weeks. Within 2–3 weeks from bone marrow (BM) isolation, after neurospheres formed, the cells differentiate into Nestin⁺ Sox2⁺ neural stem cells (NSCs), around 30 days. OPCs specific markers start to be expressed around day 38, followed by RIP⁺O4⁺ around day 42. CNPase⁺ mature OLGs are finally obtained around 7–8 weeks. Further, bone marrow-derived OPCs exhibited therapeutic effect in shiverer (Shi) mice, promoting myelin regeneration and reducing the tremor. Here, we propose a method by which OLGs can be generated starting from BM cells and have similar abilities to subventricular zone (SVZ)-derived cells. This protocol significantly decreases the timing and costs of the OLGs differentiation within 2 months of culture.

Rapid Serum-Free Isolation of Oligodendrocyte Progenitor Cells from Adult Rat Spinal Cord

Oligodendrocyte progenitor cells (OPCs) play a pivotal role in both health and disease within the central nervous system, with oligodendrocytes, arising from resident OPCs, being the main myelinating cell type. Disruption in OPC numbers can lead to various deleterious health defects. Numerous studies have described techniques for isolating OPCs to obtain a better understanding of this cell type and to open doors for potential treatments of injury and disease. However, the techniques used in the majority of these studies involve several steps and are time consuming, with current culture protocols using serum and embryonic or postnatal cortical tissue as a source of isolation. We present a primary culture method for the direct isolation of functional adult rat OPCs, identified by neuron-glial antigen 2 (NG2) and platelet derived growth factor receptor alpha (PDGFrα) expression, which can be obtained from the adult spinal cord. Our method uses a simple serum-free cocktail of 3 growth factors - FGF₂, PDGF_AA, and IGF-I, to expand adult rat OPCs in vitro to 96% purity. Cultured cells can be expanded for at least 10 passages with very little manipulation and without losing their phenotypic progenitor cell properties, as shown by immunocytochemistry and RT-PCR. Cultured adult rat OPCs also maintain their ability to differentiate into GalC positive cells when incubated with factors known to stimulate their differentiation. This new isolation method provides a new source of easily accessible adult stem cells and a powerful tool for their expansion in vitro for studies aimed at central nervous system repair.

Isolation, Expansion, and Maturation of Oligodendrocyte Lineage Cells Obtained from Rat Neonatal Brain and Optic Nerve

Oligodendrocytes are the myelin-forming cells in the central nervous system (CNS) and their loss or dysfunction is a hallmark of CNS demyelinating diseases, such as multiple sclerosis (MS), hypoxic-ischemic demyelination, or spinal cord injury. In the rodent CNS, oligodendrocyte progenitor cells (OPCs) arise in multiple ventral and dorsal locations of the forebrain during late embryogenesis and early postnatal periods. OPCs migrate out from these germinal zones and disperse throughout the CNS, to populate the developing white and gray matter. There, OPCs can begin to mature through a series of intermediate states characterized by the expression of stage-specific proteins until completely differentiated into postmitotic myelinating oligodendrocytes. Elucidating the cellular and molecular mechanisms that control oligodendrocyte maturation requires isolating OPCs and premyelinating oligodendrocytes by rapid and reliable methods that provide high yield, pure and viable culture, being a powerful tool to characterize their differentiation and potential capacity for myelin repair after injury. This chapter describes in detail two simple and efficient protocols for the preparation of highly enriched rat OPC populations and immature oligodendrocytes derived from mixed glial cultures and optic nerves, respectively. Functional oligodendrocytes obtained with these protocols can be cocultured with primary neurons to study myelination.

High Yield of Adult Oligodendrocyte Lineage Cells Obtained from Meningeal Biopsy

Oligodendrocyte loss can lead to cognitive and motor deficits. Current remyelinating therapeutic strategies imply either modulation of endogenous oligodendrocyte precursors or transplantation of in vitro expanded oligodendrocytes. Cell therapy, however, still lacks identification of an adequate source of oligodendrocyte present in adulthood and able to efficiently produce transplantable cells. Recently, a neural stem cell-like population has been identified in meninges. We developed a protocol to obtain high yield of oligodendrocyte lineage cells from one single biopsy of adult rat meningeal tissue. From 1 cm2 of adult rat spinal cord meninges, we efficiently expanded a homogenous culture of 10 millions of meningeal-derived oligodendrocyte lineage cells in a short period of time (approximately 4 weeks). Meningeal-derived oligodendrocyte lineage cells show typical mature oligodendrocyte morphology and express specific oligodendrocyte markers, such as galactosylceramidase and myelin basic protein. Moreover, when transplanted in a chemically demyelinated spinal cord model, meningeal-derived oligodendrocyte lineage cells display in vivo-remyelinating potential. This oligodendrocyte lineage cell population derives from an accessible and adult source, being therefore a promising candidate for autologous cell therapy of demyelinating diseases. In addition, the described method to differentiate meningeal-derived neural stem cells into oligodendrocyte lineage cells may represent a valid in vitro model to dissect oligodendrocyte differentiation and to screen for drugs capable to promote oligodendrocyte regeneration.

Primary Spinal OPC Culture System from Adult Zebrafish to Study Oligodendrocyte Differentiation In Vitro

Endogenous oligodendrocyte progenitor cells (OPCs) are a promising target to improve functional recovery after spinal cord injury (SCI) by remyelinating denuded, and therefore vulnerable, axons. Demyelination is the result of a primary insult and secondary injury, leading to conduction blocks and long-term degeneration of the axons, which subsequently can lead to the loss of their neurons. In response to SCI, dormant OPCs can be activated and subsequently start to proliferate and differentiate into mature myelinating oligodendrocytes (OLs). Therefore, researchers strive to control OPC responses, and utilize small molecule screening approaches in order to identify mechanisms of OPC activation, proliferation, migration and differentiation. In zebrafish, OPCs remyelinate axons of the optic tract after lysophosphatidylcholine (LPC)-induced demyelination back to full thickness myelin sheaths. In contrast to zebrafish, mammalian OPCs are highly vulnerable to excitotoxic stress, a cause of secondary injury, and remyelination remains insufficient. Generally, injury induced remyelination leads to shorter internodes and thinner myelin sheaths in mammals. In this study, we show that myelin sheaths are lost early after a complete spinal transection injury, but are re-established within 14 days after lesion. We introduce a novel, easy-to-use, inexpensive and highly reproducible OPC culture system based on dormant spinal OPCs from adult zebrafish that enables in vitro analysis. Zebrafish OPCs are robust, can easily be purified with high viability and taken into cell culture. This method enables to examine why zebrafish OPCs remyelinate better than their mammalian counterparts, identify cell intrinsic responses, which could lead to pro-proliferating or pro-differentiating strategies, and to test small molecule approaches. In this methodology paper, we show efficient isolation of OPCs from adult zebrafish spinal cord and describe culture conditions that enable analysis up to 10 days in vitro. Finally, we demonstrate that zebrafish OPCs differentiate into Myelin Basic Protein (MBP)-expressing OLs when co-cultured with human motor neurons differentiated from induced pluripotent stem cells (iPSCs). This shows that the basic mechanisms of oligodendrocyte differentiation are conserved across species and that understanding the regulation of zebrafish OPCs can contribute to the development of new treatments to human diseases.

Electric Signals Regulate the Directional Migration of Oligodendrocyte Progenitor Cells (OPCs) via β1 Integrin

The guided migration of neural cells is essential for repair in the central nervous system (CNS). Oligodendrocyte progenitor cells (OPCs) will normally migrate towards an injury site to re-sheath demyelinated axons; however the mechanisms underlying this process are not well understood. Endogenous electric fields (EFs) are known to influence cell migration in vivo, and have been utilised in this study to direct the migration of OPCs isolated from neonatal Sprague-Dawley rats. The OPCs were exposed to physiological levels of electrical stimulation, and displayed a marked electrotactic response that was dependent on β1 integrin, one of the key subunits of integrin receptors. We also observed that F-actin, an important component of the cytoskeleton, was re-distributed towards the leading edge of the migrating cells, and that this asymmetric rearrangement was associated with β1 integrin function.

In vitro and ex vivo models of multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disorder of the central nervous system (CNS). Current therapies suppress a misdirected myelin-destructive immune response. To combat the progressive, neurodestructive phase of MS, the therapeutic research focus is currently on compounds that might boost the endogenous potential of the brain to remyelinate axons, thereby achieving lesion repair. Here, we describe the testing of fingolimod on cultures of oligodendrocytes (OLs) and organotypic brain slices. We detail the protocols, pros, and cons of these in vitro and ex vivo approaches, along with the potential benefit of exploiting skin-punch biopsies from patients with MS, before concluding with a summary of future developments.

Clonal Heterogeneity in the Neuronal and Glial Differentiation of Dental Pulp Stem/Progenitor Cells

Cellular heterogeneity presents an important challenge to the development of cell-based therapies where there is a fundamental requirement for predictable and reproducible outcomes. Transplanted Dental Pulp Stem/Progenitor Cells (DPSCs) have demonstrated early promise in experimental models of spinal cord injury and stroke, despite limited evidence of neuronal and glial-like differentiation after transplantation. Here, we report, for the first time, on the ability of single cell-derived clonal cultures of murine DPSCs to differentiate in vitro into immature neuronal-like and oligodendrocyte-like cells. Importantly, only DPSC clones with high nestin mRNA expression levels were found to successfully differentiate into Map2 and NF-positive neuronal-like cells. Neuronally differentiated DPSCs possessed a membrane capacitance comparable with primary cultured striatal neurons and small inward voltage-activated K(+) but not outward Na(+) currents were recorded suggesting a functionally immature phenotype. Similarly, only high nestin-expressing clones demonstrated the ability to adopt Olig1, Olig2, and MBP-positive immature oligodendrocyte-like phenotype. Together, these results demonstrate that appropriate markers may be used to provide an early indication of the suitability of a cell population for purposes where differentiation into a specific lineage may be beneficial and highlight that further understanding of heterogeneity within mixed cellular populations is required.

Examining the properties and therapeutic potential of glial restricted precursors in spinal cord injury

In the aftermath of spinal cord injury, glial restricted precursors (GRPs) and immature astrocytes offer the potential to modulate the inflammatory environment of the injured spinal cord and promote host axon regeneration. Nevertheless clinical application of cellular therapy for the repair of spinal cord injury requires strict quality-assured protocols for large-scale production and preservation that necessitates long-term in vitro expansion. Importantly, such processes have the potential to alter the phenotypic and functional properties and thus therapeutic potential of these cells. Furthermore, clinical use of cellular therapies may be limited by the inflammatory microenvironment of the injured spinal cord, altering the phenotypic and functional properties of grafted cells. This report simulates the process of large-scale GRP production and demonstrates the permissive properties of GRP following long-term in vitro culture. Furthermore, we defined the phenotypic and functional properties of GRP in the presence of inflammatory factors, and call attention to the importance of the microenvironment of grafted cells, underscoring the importance of modulating the environment of the injured spinal cord.

Co-culture of oligodendrocytes and neurons can be used to assess drugs for axon regeneration in the central nervous system

We present a novel in vitro model in which to investigate the efficacy of experimental drugs for the promotion of axon regeneration in the central nervous system. We co-cultured rat hippocampal neurons and cerebral cortical oligodendrocytes, and tested the co-culture system using a Nogo-66 receptor antagonist peptide (NEP1–40), which promotes axonal growth. Primary cultured oligodendrocytes suppressed axonal growth in the rat hippocampus, but NEP1–40 stimulated axonal growth in the co-culture system. Our results confirm the validity of the neuron-oligodendrocyte co-culture system as an assay for the evaluation of drugs for axon regeneration in the central nervous system.

Glial restricted precursors maintain their permissive properties after long-term expansion but not following exposure to pro-inflammatory factors

Glial restricted precursors (GRP) are a promising cellular source for transplantation therapy of spinal cord injury (SCI), capable of creating a permissive environment for axonal growth and regeneration. However, there are several issues regarding the nature of their permissive properties that remain unexplored. For example, cellular transplantation strategies for spinal cord repair require the preparation of a large number of cells, but it is unknown whether the permissive properties of GRP are maintained following the process of in vitro expansion. We used rat GRP isolated from the embryonic day 13.5 spinal cord to compare the properties of early (10-20 days) and late (120-140 days) passage GRP. We found that late passage GRP showed comparable effects on neurite outgrowth of adult rat DRG to early passage GRP in both in vitro co-culture and conditioned medium experiments. In addition, to further examine the effects of the inflammatory cascade activated in the aftermath of SCI on the microenvironment, we studied the direct effects of strong inflammatory mediators, Lipopolysaccharide and interferon gamma (LPS and IFNɤ, respectively), on the properties of GRP. We showed that exposure to these pro-inflammatory mediators altered GRP phenotype and attenuated their growth-promoting effects on neurite outgrowth in a dose dependent manner. Taken together, our data suggest that GRP maintain their growth-promoting properties following extensive in vitro passaging and underscore the importance of modulating the inflammatory environment at the injured spinal cord.

Crosstalk between macrophages and astrocytes affects proliferation, reactive phenotype and inflammatory response, suggesting a role during reactive gliosis following spinal cord injury

Background

Large-scale macrophage infiltration and reactive astrogliosis are hallmarks of early spinal cord injury (SCI) pathology. The exact nature of the macrophage response and relationship between these phenomena have not been explored in detail. Here, we have investigated these responses using a combination of in vivo SCI models, organotypic and primary cultures.

Methods

In vivo macrophage response was investigated using a contusive injury mouse model. Interactions between astrocytes and macrophages were studied in primary or organotypic cultures. Proliferation was assessed though MTT assay and nucleotide incorporation and gene expression changes through qPCR.

Results

Seven days following contusive SCI, a mixed M1/M2 macrophage response was seen in the injury site. Conditioned medium from primary M1, but not M2, macrophages are able to induce astrocyte proliferation in both organotypic spinal cord cultures and primary astrocytes. Soluble factors from M1 macrophages induce a reactive astrocyte gene expression pattern, whereas M2 factors inhibit expression of these genes. M2-stimulated astrocytes are also able to decrease both M1 and M2 macrophage proliferation and decrease TNFα production in M1 macrophages.

Conclusions

These results suggest a strong role of M1 macrophages in inducing reactive astrogliosis and the existence of an astrocyte-mediated negative feedback system in order to dampen the immune response. These results, combined with the poor outcomes of the current immunosuppressive steroid treatments in SCI, indicate the need for more targeted therapies, taking into account the significantly different effects of M1 and M2 macrophages, in order to optimise outcome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0327-3) contains supplementary material, which is available to authorized users.