Regenerating CNS myelin - from mechanisms to experimental medicines

Myelin plasticity in adulthood and aging

The central nervous system maintains the potential for molecular and cellular plasticity throughout life. This flexibility underlies fundamental features of neural circuitry including the brain's ability to sense, store, and properly adapt to everchanging external stimuli on time scales from seconds to years. Evidence for most forms of plasticity are centered around changes in neuronal structure and synaptic strength, however recent data suggests that myelinating oligodendrocytes exhibit certain forms of plasticity in the adult. This plasticity ranges from the generation of entirely new myelinating cells to more subtle changes in myelin sheath length, thickness, and distribution along axons. The extent to which these changes dynamically modify axonal function and neural circuitry and whether they are directly related to mechanisms of learning and memory remains an open question. Here we describe different forms of myelin plasticity, highlight some recent evidence for changes in myelination throughout life, and discuss how defects in these forms of plasticity could be associated with cognitive decline in aging.

Astrocytes in myelination and remyelination

Astrocytes are known to play critical roles in central nervous system development, homeostasis, and response to injury. In addition to well-defined functions in synaptic signalling and blood-brain barrier control, astrocytes are now emerging as important contributors to white matter health. Here, we review the roles of astrocytes in myelin formation and regeneration (remyelination), focusing on both direct interactions with oligodendrocyte lineage cells, and indirect influences via crosstalk with central nervous system resident macrophages, microglia.

The microbiota regulates murine inflammatory responses to toxin-induced CNS demyelination but has minimal impact on remyelination

People with multiple sclerosis have a microbiota distinct from healthy controls, and there is growing interest in how these differences might contribute to the onset and progression of CNS autoimmunity. However, the impact that the microbiota may also have on the endogenous regeneration of myelin—remyelination—has not yet been explored. Here we show that inflammatory responses during remyelination depend upon the microbiota, being modulated by antibiotics or probiotics or in germ-free mice. In contrast, these interventions had minimal impact on the activity of oligodendrocyte progenitor cells, with only supratherapeutic doses of antibiotics having an inhibitory effect. Our results suggest that endogenous CNS remyelination is largely resilient to interventions that modify the microbiota.

The microbiota is now recognized as a key influence on the host immune response in the central nervous system (CNS). As such, there has been some progress toward therapies that modulate the microbiota with the aim of limiting immune-mediated demyelination, as occurs in multiple sclerosis. However, remyelination—the regeneration of myelin sheaths—also depends upon an immune response, and the effects that such interventions might have on remyelination have not yet been explored. Here, we show that the inflammatory response during CNS remyelination in mice is modulated by antibiotic or probiotic treatment, as well as in germ-free mice. We also explore the effect of these changes on oligodendrocyte progenitor cell differentiation, which is inhibited by antibiotics but unaffected by our other interventions. These results reveal that high combined doses of oral antibiotics impair oligodendrocyte progenitor cell responses during remyelination and further our understanding of how mammalian regeneration relates to the microbiota.

Oligodendrocytes in Development, Myelin Generation and Beyond

Oligodendrocytes are the myelinating cells of the central nervous system (CNS) that are generated from oligodendrocyte progenitor cells (OPC). OPC are distributed throughout the CNS and represent a pool of migratory and proliferative adult progenitor cells that can differentiate into oligodendrocytes. The central function of oligodendrocytes is to generate myelin, which is an extended membrane from the cell that wraps tightly around axons. Due to this energy consuming process and the associated high metabolic turnover oligodendrocytes are vulnerable to cytotoxic and excitotoxic factors. Oligodendrocyte pathology is therefore evident in a range of disorders including multiple sclerosis, schizophrenia and Alzheimer’s disease. Deceased oligodendrocytes can be replenished from the adult OPC pool and lost myelin can be regenerated during remyelination, which can prevent axonal degeneration and can restore function. Cell population studies have recently identified novel immunomodulatory functions of oligodendrocytes, the implications of which, e.g., for diseases with primary oligodendrocyte pathology, are not yet clear. Here, we review the journey of oligodendrocytes from the embryonic stage to their role in homeostasis and their fate in disease. We will also discuss the most common models used to study oligodendrocytes and describe newly discovered functions of oligodendrocytes.

Stem cell derived oligodendrocytes to study myelin diseases

Oligodendroglial pathology is central to de- and dysmyelinating, but also contributes to neurodegenerative and psychiatric diseases as well as brain injury. The understanding of oligodendroglial biology in health and disease has been significantly increased during recent years by experimental in vitro and in vivo preclinical studies as well as histological analyses of human tissue samples. However, for many of these diseases the underlying pathology is still not fully understood and treatment options are frequently lacking. This is at least partly caused by the limited access to human oligodendrocytes from patients to perform functional studies and drug screens. The induced pluripotent stem cell technology (iPSC) represents a possibility to circumvent this obstacle and paves new ways to study human disease and to develop new treatment options for so far incurable central nervous system (CNS) diseases. In this review, we summarize the differences between human and rodent oligodendrocytes, provide an overview of the different techniques to generate oligodendrocytes from human progenitor or stem cells and describe the results from studies using iPSC derived oligodendroglial lineage cells. Furthermore, we discuss future perspectives and challenges of the iPSC technology with respect to disease modeling, drug screen, and cell transplantation approaches.

Metformin Restores CNS Remyelination Capacity by Rejuvenating Aged Stem Cells

The age-related failure to produce oligodendrocytes from oligodendrocyte progenitor cells (OPCs) is associated with irreversible neurodegeneration in multiple sclerosis (MS). Consequently, regenerative approaches have significant potential for treating chronic demyelinating diseases. Here, we show that the differentiation potential of adult rodent OPCs decreases with age. Aged OPCs become unresponsive to pro-differentiation signals, suggesting intrinsic constraints on therapeutic approaches aimed at enhancing OPC differentiation. This decline in functional capacity is associated with hallmarks of cellular aging, including decreased metabolic function and increased DNA damage. Fasting or treatment with metformin can reverse these changes and restore the regenerative capacity of aged OPCs, improving remyelination in aged animals following focal demyelination. Aged OPCs treated with metformin regain responsiveness to pro-differentiation signals, suggesting synergistic effects of rejuvenation and pro-differentiation therapies. These findings provide insight into aging-associated remyelination failure and suggest therapeutic interventions for reversing such declines in chronic disease.

Cryogel scaffolds for regionally constrained delivery of lysophosphatidylcholine to central nervous system slice cultures: A model of focal demyelination for multiple sclerosis research

The pathology of multiple sclerosis (MS) is typified by focal demyelinated areas of the brain and spinal cord, which results in axonal degeneration and atrophy. Although the field has made much progress in developing immunomodulatory therapies to reduce the occurrence of these focal lesions, there is a conspicuous lack of licensed effective therapies to reduce axonal degeneration or promote repair. Remyelination, carried out by oligodendrocytes, does occur in MS, and is protective against axonal degeneration. Unfortunately, remyelination is not very efficient, and ultimately fails and so there is a research focus to generate new therapeutics to enhance remyelination leading to neuroprotection. To develop these therapies, we need preclinical models that well reflect remyelination in MS. We have previously characterized an ex vivo model that uses lysophosphatidylcholine (LPC) to cause acute and global demyelination of tissue slices, followed by spontaneous remyelination, which has been widely used as a surrogate for in vivo rodent models of demyelination. However, this ex vivo model lacks the focal demyelinated lesions seen in MS, surrounded by normal tissue from which the repairing oligodendrocytes are derived. Therefore, to improve the model, we have developed and characterized small macroporous cryogel scaffolds for controlled/regional delivery of LPC with diameters of either 0.5, 1 or 2 mm. Placement of LPC loaded scaffolds adjacent to ex vivo cultured mouse brain and spinal cord slices induced focal areas of demyelination in proximity to the scaffold. To the best of our knowledge, this is the first such report of spatial mimicry of the in vivo condition in ex vivo tissue culture. This will allow not only the investigation into focal lesions, but also provides a better platform technology with which to test remyelination-promoting therapeutics. STATEMENT OF SIGNIFICANCE: This manuscript is the first report of using macroporous hydrogels (cryogels) as a research tool for lysophosphatidylcholine (LPC) delivery, in order to create an ex vivo model of focal demyelination in the brain and spinal cord, which is of great relevance to multiple sclerosis research. Here, we transform an existing ex vivo model of demyelination by delivering LPC to focal regions of brain and spinal cord slice cultures. We have developed an easy-to-handle cylindrical and macroporous PEG-based sponge-like scaffold material (cryogel) that can deliver LPC only to a small area of the slice. Such cryogels are ideal as a delivery system in this culture model as they exhibit a soft but robust nature, with high mechanical deformability in their dry and swollen state, with no need to stay permanently hydrated. In addition, the synthesis of these cryogels is simple and easy to reproduce via photochemical cryopolymerisation using a PEG-diacrylate monomer and a photoinitiator, which are both commercially available. This more accurate model of demyelination will not only allow researchers to gain a better understanding of the CNS remyelination process in diseases such as MS, but also provides a platform technology, which could be utilized to screen and test pro-remyelination compounds which may help to find new therapeutics for progressive MS.

The Rise of Molecules Able To Regenerate the Central Nervous System

Injury to the adult central nervous system (CNS) usually leads to permanent deficits of cognitive, sensory, and/or motor functions. The failure of axonal regeneration in the damaged CNS limits functional recovery. The lack of information concerning the biological mechanism of axonal regeneration and its complexity has delayed the process of drug discovery for many years compared to other drug classes. Starting in the early 2000s, the ability of many molecules to stimulate axonal regrowth was evaluated through automated screening techniques; many hits and some new mechanisms involved in axonal regeneration were identified. In this Perspective, we discuss the rise of the CNS regenerative drugs, the main biological techniques used to test these drug candidates, some of the most important screens performed so far, and the main challenges following the identification of a drug that is able to induce axonal regeneration in vivo.

Myelin in the Central Nervous System: Structure, Function, and Pathology

Oligodendrocytes generate multiple layers of myelin membrane around axons of the central nervous system to enable fast and efficient nerve conduction. Until recently, saltatory nerve conduction was considered the only purpose of myelin, but it is now clear that myelin has more functions. In fact, myelinating oligodendrocytes are embedded in a vast network of interconnected glial and neuronal cells, and increasing evidence supports an active role of oligodendrocytes within this assembly, for example, by providing metabolic support to neurons, by regulating ion and water homeostasis, and by adapting to activity-dependent neuronal signals. The molecular complexity governing these interactions requires an in-depth molecular understanding of how oligodendrocytes and axons interact and how they generate, maintain, and remodel their myelin sheaths. This review deals with the biology of myelin, the expanded relationship of myelin with its underlying axons and the neighboring cells, and its disturbances in various diseases such as multiple sclerosis, acute disseminated encephalomyelitis, and neuromyelitis optica spectrum disorders. Furthermore, we will highlight how specific interactions between astrocytes, oligodendrocytes, and microglia contribute to demyelination in hereditary white matter pathologies.

Central Nervous System Remyelination: Roles of Glia and Innate Immune Cells

In diseases such as multiple sclerosis (MS), inflammation can injure the myelin sheath that surrounds axons, a process known as demyelination. The spontaneous regeneration of myelin, called remyelination, is associated with restoration of function and prevention of axonal degeneration. Boosting remyelination with therapeutic intervention is a promising new approach that is currently being tested in several clinical trials. The endogenous regulation of remyelination is highly dependent on the immune response. In this review article, we highlight the cell biology of remyelination and its regulation by innate immune cells. For the purpose of this review, we discuss the roles of microglia, and also astrocytes and oligodendrocyte progenitor cells (OPCs) as they are being increasingly recognized to have immune cell functions.

Developmental cell death regulates lineage-related interneuron-oligodendroglia functional clusters and oligodendrocyte homeostasis

The first wave of oligodendrocyte precursor cells (firstOPCs) and most GABAergic interneurons share common embryonic origins. Cortical firstOPCs are thought to be replaced by other OPC populations shortly after birth, maintaining a consistent OPC density and making postnatal interactions between firstOPCs and ontogenetically-related interneurons unlikely. Challenging these ideas, we show that a cortical firstOPC subpopulation survives and forms functional cell clusters with lineage-related interneurons. Favored by a common embryonic origin, these clusters display unexpected preferential synaptic connectivity and are anatomically maintained after firstOPCs differentiate into myelinating oligodendrocytes. While the concomitant rescue of interneurons and firstOPCs committed to die causes an exacerbated neuronal inhibition, it abolishes interneuron-firstOPC high synaptic connectivity. Further, the number of other oligodendroglia populations increases through a non-cell-autonomous mechanism, impacting myelination. These findings demonstrate unprecedented roles of interneuron and firstOPC apoptosis in regulating lineage-related cell interactions and the homeostatic oligodendroglia density.

During cortical development the first wave of oligodendrocyte precursor cells (OPCs) completely disappear by programmed cell death, so that it is presumed that this OPC population does not play a role at postnatal stages. In this study, authors use lineage tracing in different transgenic mice to show that a subpopulation of OPCs from the first wave survives at postnatal stages and display a preferential synaptic connectivity with their ontogenetically-related interneurons compared to other OPCs or interneurons

A modified flavonoid accelerates oligodendrocyte maturation and functional remyelination

Myelination delay and remyelination failure following insults to the central nervous system (CNS) impede axonal conduction and lead to motor, sensory and cognitive impairments. Both myelination and remyelination are often inhibited or delayed due to the failure of oligodendrocyte progenitor cells (OPCs) to mature into myelinating oligodendrocytes (OLs). Digestion products of the glycosaminoglycan hyaluronan (HA) have been implicated in blocking OPC maturation, but how these digestion products are generated is unclear. We tested the possibility that hyaluronidase activity is directly linked to the inhibition of OPC maturation by developing a novel modified flavonoid that functions as a hyaluronidase inhibitor. This compound, called S3, blocks some but not all hyaluronidases and only inhibits matrix metalloproteinase activity at high concentrations. We find that S3 reverses HA-mediated inhibition of OPC maturation in vitro, an effect that can be overcome by excess recombinant hyaluronidase. Furthermore, we find that hyaluronidase inhibition by S3 accelerates OPC maturation in an in vitro model of perinatal white matter injury. Finally, blocking hyaluronidase activity with S3 promotes functional remyelination in mice with lysolecithin-induced demyelinating corpus callosum lesions. All together, these findings support the notion that hyaluronidase activity originating from OPCs in CNS lesions is sufficient to prevent OPC maturation, which delays myelination or blocks remyelination. These data also indicate that modified flavonoids can act as selective inhibitors of hyaluronidase activity and can promote OPC maturation, making them excellent candidates to accelerate myelination or promote remyelination following perinatal and adult CNS insults.

Quetiapine has an additive effect to triiodothyronine in inducing differentiation of oligodendrocyte precursor cells through induction of cholesterol biosynthesis

Multiple sclerosis (MS) is characterized by demyelinated lesions in the central nervous system. Destruction of myelin and secondary damage to axons and neurons leads to significant disability, particularly in people with progressive MS. Accumulating evidence suggests that the potential for myelin repair exists in MS, although for unclear reasons this process fails. The cells responsible for producing myelin, the oligodendrocytes, and their progenitors, oligodendrocyte precursor cells (OPCs), have been identified at the site of lesions, even in adults. Their presence suggests the possibility that endogenous remyelination without transplantation of donor stem cells may be a mechanism for myelin repair in MS. Strategies to develop novel therapies have focused on induction of signaling pathways that stimulate OPCs to mature into myelin-producing oligodendrocytes that could then possibly remyelinate lesions. We have been investigating pharmacological approaches to enhance OPC differentiation, and have identified that the combination of two agents, triiodothyronine (T3) and quetiapine, leads to an additive effect on OPC differentiation and consequent myelin production via both overlapping and distinct signaling pathways. While the ultimate production of myelin requires cholesterol biosynthesis, we identified that quetiapine enhances gene expression in this pathway more potently than T3. Two blockers of cholesterol production, betulin and simvastatin, reduced OPC differentiation into myelin producing oligodendrocytes. Elucidating the nature of agents that lead to complementary and additive effects on oligodendrocyte differentiation and myelin production may pave the way for more efficient induction of remyelination in people with MS.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Myelin status and oligodendrocyte lineage cells over time after spinal cord injury: What do we know and what still needs to be unwrapped?

Spinal cord injury (SCI) affects over 17,000 individuals in the United States per year, resulting in sudden motor, sensory and autonomic impairments below the level of injury. These deficits may be due at least in part to the loss of oligodendrocytes and demyelination of spared axons as it leads to slowed or blocked conduction through the lesion site. It has long been accepted that progenitor cells form new oligodendrocytes after SCI, resulting in the acute formation of new myelin on demyelinated axons. However, the chronicity of demyelination and the functional significance of remyelination remain contentious. Here we review work examining demyelination and remyelination after SCI as well as the current understanding of oligodendrocyte lineage cell responses to spinal trauma, including the surprisingly long-lasting response of NG2+ oligodendrocyte progenitor cells (OPCs) to proliferate and differentiate into new myelinating oligodendrocytes for months after SCI. OPCs are highly sensitive to microenvironmental changes, and therefore respond to the ever-changing post-SCI milieu, including influx of blood, monocytes and neutrophils; activation of microglia and macrophages; changes in cytokines, chemokines and growth factors such as ciliary neurotrophic factor and fibroblast growth factor-2; glutamate excitotoxicity; and axon degeneration and sprouting. We discuss how these changes relate to spontaneous oligodendrogenesis and remyelination, the evidence for and against demyelination being an important clinical problem and if remyelination contributes to motor recovery.

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.

Tanshinone IIA attenuates demyelination and promotes remyelination in A. cantonensis-infected BALB/c mice

BACKGROUND

Angiostrongylus cantonensis infection can cause demyelination in the central nervous system, and there is no effective treatment.

METHODS

We used dexamethasone, Tanshinone IIA (TSIIA) and Cryptotanshinone(Two traditional Chinese medicine monomers) in combination with albendazole (AB, a standard anti-helminthic compound) to observe their therapeutic effect on demyelination in A. cantonensis-infected mice. Luxol fast blue staining and electron microscope of myelin sheath, Oligodendrocyte (OL) number and myelin basic protein (MBP) expression in brain was detected in above groups.

RESULTS

TSIIA+AB facilitated OL proliferation and significantly increased both myelin sheath thickness and the population of small-diameter axons. In addition, TSIIA treatment inhibited the expression of inflammation-related factors (interleukin [IL]-6, IL-1β, tumor necrosis factor [TNF]-α, inducible nitric oxide synthase [iNOS]) rather than inhibiting eosinophil infiltration in brain. TSIIA also decreased microglial activation and shifted their phenotype from M1 to M2.

CONCLUSIONS

Taken together, these results provide evidence that TSIIA combined with AB may be an effective treatment for demyelination caused by A. cantonensis infection and other demyelinating diseases.

D-Aspartate treatment attenuates myelin damage and stimulates myelin repair

Glutamate signaling may orchestrate oligodendrocyte precursor cell (OPC) development and myelin regeneration through the activation of glutamate receptors at OPC‐neuron synapses. D‐Aspartate is a D‐amino acid exerting modulatory actions at glutamatergic synapses. Chronic administration of D‐Aspartate has been proposed as therapeutic treatment in diseases related to myelin dysfunction and NMDA receptors hypofunction, including schizophrenia and cognitive deficits. Here, we show, by using an in vivo remyelination model, that administration of D‐Aspartate during remyelination improved motor coordination, accelerated myelin recovery, and significantly increased the number of small‐diameter myelinated axons. Chronically administered during demyelination, D‐Aspartate also attenuated myelin loss and inflammation. Interestingly, D‐Aspartate exposure stimulated OPC maturation and accelerated developmental myelination in organotypic cerebellar slices. D‐Aspartate promoting effects on OPC maturation involved the activation of glutamate transporters, AMPA and NMDA receptors, and the Na⁺/Ca²⁺ exchanger NCX3. While blocking NMDA or NCX3 significantly prevented D‐Aspartate‐induced [Ca²⁺]_i oscillations, blocking AMPA and glutamate transporters prevented both the initial and oscillatory [Ca²⁺]_i response as well as D‐Aspartate‐induced inward currents in OPC. Our findings reveal that D‐Aspartate treatment may represent a novel strategy for promoting myelin recovery.

The Molecular Basis for Remyelination Failure in Multiple Sclerosis

Myelin sheaths in the central nervous system (CNS) insulate axons and thereby allow saltatory nerve conduction, which is a prerequisite for complex brain function. Multiple sclerosis (MS), the most common inflammatory autoimmune disease of the CNS, leads to the destruction of myelin sheaths and the myelin-producing oligodendrocytes, thus leaving behind demyelinated axons prone to injury and degeneration. Clinically, this process manifests itself in significant neurological symptoms and disability. Resident oligodendroglial precursor cells (OPCs) and neural stem cells (NSCs) are present in the adult brain, and can differentiate into mature oligodendrocytes which then remyelinate the demyelinated axons. However, for multiple reasons, in MS the regenerative capacity of these cell populations diminishes significantly over time, ultimately leading to neurodegeneration, which currently remains untreatable. In addition, microglial cells, the resident innate immune cells of the CNS, can contribute further to inflammatory and degenerative axonal damage. Here, we review the molecular factors contributing to remyelination failure in MS by inhibiting OPC and NSC differentiation or modulating microglial behavior.

Aging restricts the ability of mesenchymal stem cells to promote the generation of oligodendrocytes during remyelination

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) that leads to severe neurological deficits. Due to their immunomodulatory and neuroprotective activities and their ability to promote the generation of oligodendrocytes, mesenchymal stem cells (MSCs) are currently being developed for autologous cell therapy in MS. As aging reduces the regenerative capacity of all tissues, it is of relevance to investigate whether MSCs retain their pro-oligodendrogenic activity with increasing age. We demonstrate that MSCs derived from aged rats have a reduced capacity to induce oligodendrocyte differentiation of adult CNS stem/progenitor cells. Aging also abolished the ability of MSCs to enhance the generation of myelin-like sheaths in demyelinated cerebellar slice cultures. Finally, in a rat model for CNS demyelination, aging suppressed the capability of systemically transplanted MSCs to boost oligodendrocyte progenitor cell (OPC) differentiation during remyelination. Thus, aging restricts the ability of MSCs to support the generation of oligodendrocytes and consequently inhibits their capacity to enhance the generation of myelin-like sheaths. These findings may impact on the design of therapies using autologous MSCs in older MS patients.

Regional differences in white matter integrity in stimulant use disorders: A meta-analysis of diffusion tensor imaging studies

BACKGROUND

Converging lines of evidence from diffusion tensor imaging (DTI) studies reveal significant alterations in white matter (WM) microstructure in the prefrontal cortex of chronic stimulant users compared to controls, suggesting compromised axonal microstructure and/or myelin.

METHODS

A meta-analysis of DTI-based WM integrity was conducted for white matter regions across the corpus callosum and association fibers. Articles were sourced and selected using PRISMA guidelines for systematic review and meta-analysis. Inclusion and exclusion criteria were determined by the authors in order to best capture WM integrity among individuals with primary stimulant use in comparison to healthy control subjects.

RESULTS

Eleven studies that focused on region-of-interest (ROI)-based analysis of WM integrity were extracted from an initial pool of 113 independent studies. Analysis across ROIs indicated significantly lower fractional anisotropy (FA) values in stimulant use groups compared to controls with a small to moderate overall effect (Hedges' g = -0.37, 95% CI [-0.54, -0.20]). Eigenvalues were also analyzed, revealing a significant effect for radial diffusivity (RD; Hedges' g = 0.24, 95% CI [0.01, 0.47]) but not axial diffusivity (AD; Hedges' g = 0.05, 95% CI [-0.20, 0.29]) or mean diffusivity (MD; Hedges' g = 0.20, 95% CI [-0.01, 0.41]). Subgroup analyses based on specific ROIs, primary substance use, poly-substance use, and imaging technology were also explored.

CONCLUSION

Results of the present study suggest a consistent effect of compromised WM integrity for individuals with stimulant use disorders. Furthermore, no significant differences were found between cocaine and methamphetamine-based groups.

Naturally Occurring Nervonic Acid Ester Improves Myelin Synthesis by Human Oligodendrocytes

The dysfunction of oligodendrocytes (OLs) is regarded as one of the major causes of inefficient remyelination in multiple sclerosis, resulting gradually in disease progression. Oligodendrocytes are derived from oligodendrocyte progenitor cells (OPCs), which populate the adult central nervous system, but their physiological capability to myelin synthesis is limited. The low intake of essential lipids for sphingomyelin synthesis in the human diet may account for increased demyelination and the reduced efficiency of the remyelination process. In our study on lipid profiling in an experimental autoimmune encephalomyelitis brain, we revealed that during acute inflammation, nervonic acid synthesis is silenced, which is the effect of shifting the lipid metabolism pathway of common substrates into proinflammatory arachidonic acid production. In the experiments on the human model of maturating oligodendrocyte precursor cells (hOPCs) in vitro, we demonstrated that fish oil mixture (FOM) affected the function of hOPCs, resulting in the improved synthesis of myelin basic protein, myelin oligodendrocyte glycoprotein, and proteolipid protein, as well as sphingomyelin. Additionally, FOM reduces proinflammatory cytokines and chemokines, and enhances fibroblast growth factor 2 (FGF2) and vascular endothelial growth factor (VEGF) synthesis by hOPCs was also demonstrated. Based on these observations, we propose that the intake of FOM rich in the nervonic acid ester may improve OL function, affecting OPC maturation and limiting inflammation.

Oligodendrocyte Differentiation and Myelination Is Potentiated via GABAB Receptor Activation

Differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes (OLs) is a key event for axonal myelination in the central nervous system (CNS). Several growth factors and neurotransmitters like GABA are postulated as important regulators of that process, and different protein kinases may also participate in OL differentiation and myelination. However, the molecular mechanisms underlying the regulation of myelination by neurotransmitters are only partially known. In the present study, we provide evidence showing that GABA receptors (GABARs) play an important role in OL differentiation. First, we observed that OPCs and OLs synthesize GABA and expressed GABAR and transporters, both in vitro and in vivo and, in contrast to GABA_ARs, the subunits GABA_B1R and GABA_B2R are expressed in OLs over time. Then, we found that exogenous GABA increases the number of myelin segments and MBP expression in DRG-OPC cocultures, indicating that GABA regulates myelination when OLs are in contact with axons. Notably, in purified rat OPC cultures, chronic treatment with GABA and baclofen, specific GABA_BR agonist, accelerates OPC differentiation by enhancing the processes branching and myelin protein expression, effects that are reverted in presence of GABA_BR specific antagonist CGP55845. Exposure of OPCs to baclofen promotes the Src-phosphorylation, and the baclofen-induced maturation is attenuated in presence of the Src-family kinases inhibitor PP2. None of these effects are mediated by the GABA_AR agonist muscimol. Together, these results highlight the relevance of the GABAergic system in OL differentiation, and indicate that this functional role is mediated through GABA_BR involving the participation of Src-family kinases. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Transforming growth factor-beta renders ageing microglia inhibitory to oligodendrocyte generation by CNS progenitors

It is now well-established that the macrophage and microglial response to CNS demyelination influences remyelination by removing myelin debris and secreting a variety of signaling molecules that influence the behaviour of oligodendrocyte progenitor cells (OPCs). Previous studies have shown that changes in microglia contribute to the age-related decline in the efficiency of remyelination. In this study, we show that microglia increase their expression of the proteoglycan NG2 with age, and that this is associated with an altered micro-niche generated by aged, but not young, microglia that can divert the differentiation OPCs from oligodendrocytes into astrocytes in vitro. We further show that these changes in ageing microglia are generated by exposure to high levels of TGFβ. Thus, our findings suggest that the rising levels of circulating TGFβ known to occur with ageing contribute to the age-related decline in remyelination by impairing the ability of microglia to promote oligodendrocyte differentiation from OPCs, and therefore could be a potential therapeutic target to promote remyelination.

Central nervous system regeneration is driven by microglia necroptosis and repopulation

Failed regeneration of CNS myelin contributes to clinical decline in neuroinflammatory and neurodegenerative diseases, for which there is an unmet therapeutic need. Here we reveal that efficient remyelination requires death of proinflammatory microglia followed by repopulation to a pro-regenerative state. We propose that impaired microglia death and/or repopulation may underpin dysregulated microglia activation in neurological diseases, and we reveal therapeutic targets to promote white matter regeneration.

The interleukin-4/PPARγ signaling axis promotes oligodendrocyte differentiation and remyelination after brain injury

The repair of white matter damage is of paramount importance for functional recovery after brain injuries. Here, we report that interleukin-4 (IL-4) promotes oligodendrocyte regeneration and remyelination. IL-4 receptor expression was detected in a variety of glial cells after ischemic brain injury, including oligodendrocyte lineage cells. IL-4 deficiency in knockout mice resulted in greater deterioration of white matter over 14 d after stroke. Consistent with these findings, intranasal delivery of IL-4 nanoparticles after stroke improved white matter integrity and attenuated long-term sensorimotor and cognitive deficits in wild-type mice, as revealed by histological immunostaining, electron microscopy, diffusion tensor imaging, and electrophysiology. The selective effect of IL-4 on remyelination was verified in an ex vivo organotypic model of demyelination. By leveraging primary oligodendrocyte progenitor cells (OPCs), microglia-depleted mice, and conditional OPC-specific peroxisome proliferator-activated receptor gamma (PPARγ) knockout mice, we discovered a direct salutary effect of IL-4 on oligodendrocyte differentiation that was mediated by the PPARγ axis. Our findings reveal a new regenerative role of IL-4 in the central nervous system (CNS), which lies beyond its known immunoregulatory functions on microglia/macrophages or peripheral lymphocytes. Therefore, intranasal IL-4 delivery may represent a novel therapeutic strategy to improve white matter integrity in stroke and other brain injuries.

The repair and remyelination of white matter are of paramount importance for functional recovery after brain injuries. This study shows that interleukin-4 plays an essential role in oligodendrocyte differentiation and long-term white matter recovery, beyond its well-known immunoregulatory functions, and is mediated by the PPARγ axis.

Neuronal activity-dependent myelin repair after stroke

Brain tissue undergoes substantial activity-dependent reorganisation after stroke due to neuronal plasticity, leading to partial functional recovery in patients. Concurrent myelin repair is crucial for proper neuronal network function and reorganisation. Myelin repair after stroke might occur as myelin plasticity or as remyelination through the recruitment and differentiation of oligodendrocyte precursor cells (OPCs), which become myelin-forming oligodendrocytes (OLs). These two processes might share a similar guiding mechanism, which is postulated to depend on neuronal activity and glutamate signaling to OPCs. However, with ageing, the ability of OPCs to differentiate into myelinating OLs decreases due to changes in their ion channel and neurotransmitter receptor expression profile, rendering them less sensitive to neuronal activity. Because of their unique ability to replace damaged OLs, OPCs represent a potential therapeutic target for myelin repair in the context of stroke.

Circulating transforming growth factor-β1 facilitates remyelination in the adult central nervous system

Oligodendrocyte maturation is necessary for functional regeneration in the CNS; however, the mechanisms by which the systemic environment regulates oligodendrocyte maturation is unclear. We found that Transforming growth factor (TGF)-β1, which is present in higher levels in the systemic environment, promotes oligodendrocyte maturation. Oligodendrocyte maturation was enhanced by adult mouse serum treatment via TGF-β type I receptor. Decrease in circulating TGF-β1 level prevented remyelination in the spinal cord after toxin-induced demyelination. TGF-β1 administration promoted remyelination and restored neurological function in a multiple sclerosis animal model. Furthermore, TGF-β1 treatment stimulated human oligodendrocyte maturation. These data provide the therapeutic possibility of TGF-β for demyelinating diseases.

CNS myelination and remyelination depend on fatty acid synthesis by oligodendrocytes

Oligodendrocytes (OLs) support neurons and signal transmission in the central nervous system (CNS) by enwrapping axons with myelin, a lipid-rich membrane structure. We addressed the significance of fatty acid (FA) synthesis in OLs by depleting FA synthase (FASN) from OL progenitor cells (OPCs) in transgenic mice. While we detected no effects in proliferation and differentiation along the postnatal OL lineage, we found that FASN is essential for accurate myelination, including myelin growth. Increasing dietary lipid intake could partially compensate for the FASN deficiency. Furthermore, FASN contributes to correct myelin lipid composition and stability of myelinated axons. Moreover, we depleted FASN specifically in adult OPCs to examine its relevance for remyelination. Applying lysolecithin-induced focal demyelinating spinal cord lesions, we found that FA synthesis is essential to sustain adult OPC-derived OLs and efficient remyelination. We conclude that FA synthesis in OLs plays key roles in CNS myelination and remyelination.

The Shh receptor Boc is important for myelin formation and repair

Myelination leads to the formation of myelin sheaths surrounding neuronal axons and is crucial for function, plasticity and repair of the central nervous system (CNS). It relies on the interaction of the axons and the oligodendrocytes: the glial cells producing CNS myelin. Here, we have investigated the role of a crucial component of the Sonic hedgehog (Shh) signalling pathway, the co-receptor Boc, in developmental and repairing myelination. During development, Boc mutant mice display a transient decrease in oligodendroglial cell density together with delayed myelination. Despite recovery of oligodendroglial cells at later stages, adult mutants still exhibit a lower production of myelin basic protein correlated with a significant decrease in the calibre of callosal axons and a reduced amount of the neurofilament NF-M. During myelin repair, the altered OPC differentiation observed in the mutant is reminiscent of the phenotype observed after blockade of Shh signalling. In addition, Boc mutant microglia/macrophages unexpectedly exhibit the apparent inability to transition from a highly to a faintly ramified morphology in vivo Altogether, these results identify Boc as an important component of myelin formation and repair.

Aberrant oligodendroglial-vascular interactions disrupt the blood-brain barrier, triggering CNS inflammation

Disruption of the blood-brain barrier (BBB) is critical to initiation and perpetuation of disease in multiple sclerosis (MS). We report an interaction between oligodendroglia and vasculature in MS that distinguishes human white matter injury from normal rodent demyelinating injury. We find perivascular clustering of oligodendrocyte precursor cells (OPCs) in certain active MS lesions, representing an inability to properly detach from vessels following perivascular migration. Perivascular OPCs can themselves disrupt the BBB, interfering with astrocyte endfeet and endothelial tight junction integrity, resulting in altered vascular permeability and an associated CNS inflammation. Aberrant Wnt tone in OPCs mediates their dysfunctional vascular detachment and also leads to OPC secretion of Wif1, which interferes with Wnt ligand function on endothelial tight junction integrity. Evidence for this defective oligodendroglial-vascular interaction in MS suggests that aberrant OPC perivascular migration not only impairs their lesion recruitment but can also act as a disease perpetuator via disruption of the BBB.

Stage-dependent regulation of oligodendrocyte development and enhancement of myelin repair by dominant negative Master-mind 1 protein

Notch signaling has been implicated in the inhibition of oligodendrocyte differentiation and myelin gene expression during early development. However, inactivation of a particular Notch or Hes gene only produces a mild phenotype in oligodendrocyte development possibly due to the functional redundancies among closely related family members. To uncover the full role of Notch signaling in myelin development and regeneration, we generated the Sox10^rtTA/+ ; TetO-dnMAML1 double transgenic mice in which expression of dominant negative Master-mind 1 (dnMAML1) gene can be selectively induced in oligodendrocyte precursor cells (OPCs) for complete blockade of Notch signaling. It is found that dnMAML1 expression leads to robust precocious OL differentiation and premature axonal myelination in the spinal cord, possibly by upregulating Nkx2.2 and downregulating Pdgfra expression. Unexpectedly, at late embryonic stages, dnMAML1 expression dramatically increased the number of OPCs, indicating a stage-dependent effect of Notch signaling on OPC proliferation. In addition, dnMAML1 also significantly enhances axonal remyelination following chemical-induced demyelination, providing a promising therapeutic target for lesion repair in demyelinating disease.

Uncovering the biology of myelin with optical imaging of the live brain

Myelin has traditionally been considered a static structure that is produced and assembled during early developmental stages. While this characterization is accurate in some contexts, recent studies have revealed that oligodendrocyte generation and patterns of myelination are dynamic and potentially modifiable throughout life. Unique structural and biochemical properties of the myelin sheath provide opportunities for the development and implementation of multimodal label-free and fluorescence optical imaging approaches. When combined with genetically encoded fluorescent tags targeted to distinct cells and subcellular structures, these techniques offer a powerful methodological toolbox for uncovering mechanisms of myelin generation and plasticity in the live brain. Here, we discuss recent advances in these approaches that have allowed the discovery of several forms of myelin plasticity in developing and adult nervous systems. Using these techniques, long-standing questions related to myelin generation, remodeling, and degeneration can now be addressed.

Cyclin-dependent Kinase 18 Promotes Oligodendrocyte Precursor Cell Differentiation through Activating the Extracellular Signal-Regulated Kinase Signaling Pathway

The correct differentiation of oligodendrocyte precursor cells (OPCs) is essential for the myelination and remyelination processes in the central nervous system. Determining the regulatory mechanism is fundamental to the treatment of demyelinating diseases. By analyzing the RNA sequencing data of different neural cells, we found that cyclin-dependent kinase 18 (CDK18) is exclusively expressed in oligodendrocytes. In vivo studies showed that the expression level of CDK18 gradually increased along with myelin formation during development and in the remyelination phase in a lysophosphatidylcholine-induced demyelination model, and was distinctively highly expressed in oligodendrocytes. In vitro overexpression and interference experiments revealed that CDK18 directly promotes the differentiation of OPCs, without affecting their proliferation or apoptosis. Mechanistically, CDK18 activated the RAS/mitogen-activated protein kinase kinase 1/extracellular signal-regulated kinase pathway, thus promoting OPC differentiation. The results of the present study suggest that CDK18 is a promising cell-type specific target to treat demyelinating disease.

Targeting P2X4 and P2X7 receptors in multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system characterized by massive infiltration of immune cells, demyelination, and axonal loss. However, spontaneous myelin repair can occur during the course of the disease. A major component of this regenerative process is a robust innate immune response consisting of infiltrating macrophages and brain microgliosis. Therefore, specifically targeting myeloid cells could be an attractive therapeutic approach. Purinergic receptors control not only immune cell function together with the activation of microglia and astrocytes, but also neuronal and oligodendroglial survival in the pathology. Thus, targeting these receptors can modulate a whole variety of responses. In this review, we will summarize recent findings highlighting the potential of P2X4 and P2X7 as therapeutic targets for MS.

Diversity in the oligodendrocyte lineage: Plasticity or heterogeneity?

Heterogeneity is a widely recognized phenomenon within the majority of cell types in the body including cells of the central nervous system (CNS). The heterogeneity of neurons based on their distinct transmission modes and firing patterns has been recognized for decades, and is necessary to coordinate the immense variety of functions of the CNS. More recently, heterogeneity in glial cells has been identified, including heterogeneity in oligodendrocyte progenitor cells (OPCs) and oligodendrocytes. OPC subpopulations have been described based on their developmental origin, anatomical location in the grey or white matter, and expression of surface receptors. Oligodendrocytes are categorised according to differences in gene expression, myelinogenic potential, and axon specificity. Much of what is described as heterogeneity in oligodendrocyte lineage cells (OLCs) is based on phenotypic differences. However, without evidence for functional differences between putative subgroups of OLCs, distinguishing heterogeneity from plasticity and lineage state is difficult. Identifying functional differences between phenotypically distinct groups are therefore necessary for a deeper understanding of the role of OLCs in health and disease.

Oligodendrocyte precursor cells as a therapeutic target for demyelinating diseases

The mechanisms regulating differentiation of multipotent oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes (OLs) are critical to our understanding of myelination and remyelination. Following acute demyelination in the central nervous system, adult OPCs migrate to the injury site, differentiate into OLs and generate new myelin sheaths. A common feature of regenerative processes is the fact that remyelination efficiency declines with aging and, accounts for the observation that chronic demyelinating diseases like multiple sclerosis (MS) are characterized by an ineffective remyelination. Without doubt, impairment of OPC differentiation is an essential determinant of the aging effects in remyelination. However, spontaneous remyelination is limited in demyelinating diseases such as MS, owing in part to the failure of adult OPCs to differentiate into myelinating OLs. The inability to restore myelin after injury compromises axon integrity and renders them vulnerable to degeneration. Although the genes that regulate the proliferation and differentiation of OPCs during development have been intensively studied, relatively little is known about the molecular signals that regulate the function of adult OPCs after demyelination. Elucidating the mechanisms regulating OPC differentiation are key to identifying pharmacological targets for remyelination-enhancing therapy. This review will discuss OPC biology, myelination, and possible pharmacological targets for promoting the differentiation of OPCs as a strategy to enhance remyelination, including the potential for nanoscale delivery.

Neuronal activity in vivo enhances functional myelin repair

In demyelinating diseases such as Multiple Sclerosis (MS), demyelination of neuronal fibers impairs impulse conduction and causes axon degeneration. While neuronal activity stimulates oligodendrocyte production and myelination in normal conditions, it remains unclear whether the activity of demyelinated axons restores their loss-of-function in a harmful environment. To investigate this question, we established a model to induce a moderate optogenetic stimulation of demyelinated axons in the corpus callosum at the level of the motor cortex in which cortical circuit activation and locomotor effects were reduced in adult freely moving mice. We demonstrate that a moderate activation of demyelinated axons enhances the differentiation of oligodendrocyte precursor cells onto mature oligodendrocytes, but only under a repeated stimulation paradigm. This activity-dependent increase in the oligodendrocyte pool promotes an extensive remyelination and functional restoration of conduction, as revealed by ultrastructural analyses and compound action potential recordings. Our findings reveal the need of preserving an appropriate neuronal activity in the damaged tissue to promote oligodendrocyte differentiation and remyelination, likely by enhancing axon-oligodendroglia interactions. Our results provide new perspectives for translational research using neuromodulation in demyelinating diseases.

Targeted Oligodendrocyte Apoptosis in Optic Nerve Leads to Persistent Demyelination

The optic nerve represents one of the simplest regions of the CNS and has been useful in developing an understanding of glial development and myelination. While the visual system is frequently affected in demyelinating conditions, utilizing the optic nerve to model demyelination/remyelination studies has been difficult due to its accessibility, relatively small size, and dense nature that makes direct injections challenging. Taking advantage of the lack of oligodendrocytes and myelination in the mouse retina, we have developed a model in which the induction of apoptosis in mature oligodendrocytes allows for the selective, non-invasive generation of demyelinating lesions in optic nerve. Delivery of an inducer of oligodendrocyte apoptosis by intravitreous injection minimizes trauma to the optic nerve and allows for the assessment of oligodendrocyte death in the absence of injury related factors. Here we show that following induction of apoptosis, oligodendrocytes are lost within 3 days. The loss of oligodendrocytes is associated with limited microglial and astrocyte response, is patchy along the nerve, and results in localized myelin loss. Unlike in other regions of the murine CNS, where local demyelination stimulates activation of local oligodendrocyte precursors and remyelination, optic nerve demyelination induced by oligodendrocyte apoptosis fails to recover and results in persistent areas of myelin loss. Over time these chronic lesions change cellular composition and ultimately become devoid of GFAP+ astrocytes and OPCs. Why the optic nerve lesions fail to repair may reflect the lack of early immune responsiveness and provide a novel model of chronic demyelination.

Genetic Elimination of Connective Tissue Growth Factor in the Forebrain Affects Subplate Neurons in the Cortex and Oligodendrocytes in the Underlying White Matter

Connective tissue growth factor (CTGF) is a secreted extracellular matrix-associated protein, which play a role in regulating various cellular functions. Although the expression of CTGF has been reported in the cortical subplate, its function is still not clear. Thus, to explore the significance of CTGF in the brain, we created a forebrain-specific Ctgf knockout (FbCtgf KO) mouse model. By crossing Ctgf^fl/fl mice with Emx1-Cre transgenic mice, in which the expression of Cre is prenatally initiated, the full length Ctgf is removed in the forebrain structures. In young adult (2–3 months old) FbCtgf KO mice, subplate markers such as Nurr1 and Cplx3 are still expressed in the cortical layer VIb; however, the density of the subplate neurons is increased. Interestingly, in these mutants, we found a reduced structural complexity in the subplate neurons. The distribution patterns of neurons and glial cells, examined by immunohistochemistry, are comparable between genotypes in the somatosensory cortex. However, increased densities of mature oligodendrocytes, but not immature ones, were noticed in the external capsule underneath the cortical layer VIb in young adult FbCtgf KO mice. The features of myelinated axons in the external capsule were then examined using electron microscopy. Unexpectedly, the thickness of the myelin sheath was reduced in middle-aged (>12 months old), but not young adult FbCtgf KO mice. Our results suggest a secretory function of the subplate neurons, through the release of CTGF, which regulates the density and dendritic branching of subplate neurons as well as the maturation and function of nearby oligodendrocytes in the white matter.

Transferrin Enhances Microglial Phagocytic Capacity

Transferrin (Tf) is a glycoprotein playing a critical role in iron homeostasis and transport and distribution throughout the body and within tissues and cells. This molecule has been shown to accelerate the process of myelination and remyelination in the central nervous system (CNS) in vivo and induce oligodendroglial cell maturation in vitro. While the mechanisms involved in oligodendroglial precursor cell (OPC) differentiation have not been fully elucidated yet, our group has previously described the first molecular events taking place in OPC in response to extracellular Tf. Here, we show the effect of Tf on the different glial cell populations. We demonstrate that, after a CNS demyelinating injury, Tf can be incorporated by all glial cells-i.e., microglia, astrocytes, and OPC-and that, acting on microglial cells in vitro, Tf increases microglial proliferation rates and phagocytic capacity. It may be then speculated that the in vivo correlation of this process could generate a favorable microenvironment for OPC maturation and remyelination.

Molecular Control of Oligodendrocyte Development

Myelin is a multilayer lipid membrane structure that wraps and insulates axons, allowing for the efficient propagation of action potentials. During developmental myelination of the central nervous system (CNS), oligodendrocyte progenitor cells (OPCs) proliferate and migrate to their final destination, where they terminally differentiate into mature oligodendrocytes and myelinate axons. Lineage progression and terminal differentiation of oligodendrocyte lineage cells are under tight transcriptional and post-transcriptional control. The characterization of several recently identified regulatory factors that govern these processes, which are the focus of this review, has greatly increased our understanding of oligodendrocyte development and function. These insights are critical to facilitate efforts to enhance OPC differentiation in neurological disorders that disrupt CNS myelin.

Scaffold-Mediated Sustained, Non-viral Delivery of miR-219/miR-338 Promotes CNS Remyelination

The loss of oligodendrocytes (OLs) and subsequently myelin sheaths following injuries or pathologies in the CNS leads to debilitating functional deficits. Unfortunately, effective methods of remyelination remain limited. Here, we present a scaffolding system that enables sustained non-viral delivery of microRNAs (miRs) to direct OL differentiation, maturation, and myelination. We show that miR-219/miR-338 promoted primary rat OL differentiation and myelination in vitro. Using spinal cord injury as a proof-of-concept, we further demonstrate that miR-219/miR-338 could also be delivered non-virally in vivo using an aligned fiber-hydrogel scaffold to enhance remyelination after a hemi-incision injury at C5 level of Sprague-Dawley rats. Specifically, miR-219/miR-338 mimics were incorporated as complexes with the carrier, TransIT-TKO (TKO), together with neurotrophin-3 (NT-3) within hybrid scaffolds that comprised poly(caprolactone-co-ethyl ethylene phosphate) (PCLEEP)-aligned fibers and collagen hydrogel. After 1, 2, and 4 weeks post-treatment, animals that received NT-3 and miR-219/miR-338 treatment preserved a higher number of Olig2+ oligodendroglial lineage cells as compared with those treated with NT-3 and negative scrambled miRs (Neg miRs; p < 0.001). Additionally, miR-219/miR-338 increased the rate and extent of differentiation of OLs. At the host-implant interface, more compact myelin sheaths were observed when animals received miR-219/miR-338. Similarly within the scaffolds, miR-219/miR-338 samples contained significantly more myelin basic protein (MBP) signals (p < 0.01) and higher myelination index (p < 0.05) than Neg miR samples. These findings highlight the potential of this platform to promote remyelination within the CNS.