Leukemia inhibitory factor regulates the timing of oligodendrocyte development and myelination in the postnatal optic nerve

Understanding the Ultra-Rare Disease Autosomal Dominant Leukodystrophy: an Updated Review on Morpho-Functional Alterations Found in Experimental Models

Autosomal dominant leukodystrophy (ADLD) is an ultra-rare, slowly progressive, and fatal neurodegenerative disorder associated with the loss of white matter in the central nervous system (CNS). Several years after its first clinical description, ADLD was found to be caused by coding and non-coding variants in the LMNB1 gene that cause its overexpression in at least the brain of patients. LMNB1 encodes for Lamin B1, a protein of the nuclear lamina. Lamin B1 regulates many cellular processes such as DNA replication, chromatin organization, and senescence. However, its functions have not been fully characterized yet. Nevertheless, Lamin B1 together with the other lamins that constitute the nuclear lamina has firstly the key role of maintaining the nuclear structure. Being the nucleus a dynamic system subject to both biochemical and mechanical regulation, it is conceivable that changes to its structural homeostasis might translate into functional alterations. Under this light, this review aims at describing the pieces of evidence that to date have been obtained regarding the effects of LMNB1 overexpression on cellular morphology and functionality. Moreover, we suggest that further investigation on ADLD morpho-functional consequences is essential to better understand this complex disease and, possibly, other neurological disorders affecting CNS myelination.

Nimodipine Exerts Beneficial Effects on the Rat Oligodendrocyte Cell Line OLN-93

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS). Therapy is currently limited to drugs that interfere with the immune system; treatment options that primarily mediate neuroprotection and prevent neurodegeneration are not available. Here, we studied the effects of nimodipine on the rat cell line OLN-93, which resembles young mature oligodendrocytes. Nimodipine is a dihydropyridine that blocks the voltage-gated L-type calcium channel family members Cav1.2 and Cav1.3. Our data show that the treatment of OLN-93 cells with nimodipine induced the upregulation of myelin genes, in particular of proteolipid protein 1 (Plp1), which was confirmed by a significantly greater expression of PLP1 in immunofluorescence analysis and the presence of myelin structures in the cytoplasm at the ultrastructural level. Whole-genome RNA sequencing additionally revealed the upregulation of genes that are involved in neuroprotection, remyelination, and antioxidation pathways. Interestingly, the observed effects were independent of Cav1.2 and Cav1.3 because OLN-93 cells do not express these channels, and there was no measurable response pattern in patch-clamp analysis. Taking into consideration previous studies that demonstrated a beneficial effect of nimodipine on microglia, our data support the notion that nimodipine is an interesting drug candidate for the treatment of MS and other demyelinating diseases.

Remyelination in PNS and CNS: current and upcoming cellular and molecular strategies to treat disabling neuropathies

Myelin is a lipid-rich nerve cover that consists of glial cell's plasmalemma layers and accelerates signal conduction. Axon-myelin contact is a source for many developmental and regenerative signals of myelination. Intra- or extracellular factors including both enhancers and inhibitors are other factors affecting the myelination process. Myelin damages are observed in several congenital and hereditary diseases, physicochemical conditions, infections, or traumatic insults, and remyelination is known as an intrinsic response to injuries. Here we discuss some molecular events and conditions involved in de- and remyelination and compare the phenomena of remyelination in CNS and PNS. We have explained applying some of these molecular events in myelin restoration. Finally, the current and upcoming treatment strategies for myelin restoration are explained in three groups of immunotherapy, endogenous regeneration enhancement, and cell therapy to give a better insight for finding the more effective rehabilitation strategies considering the underlying molecular events of a lesion formation and its current condition.

Sensitive timing of undifferentiation in oligodendrocyte progenitor cells and their enhanced maturation in primary visual cortex of binocularly enucleated mice

Sensory experience modulates proliferation, differentiation, and migration of oligodendrocyte progenitor cells (OPCs). In the mouse primary visual cortex (V1), visual deprivation-dependent modulation of OPCs has not been demonstrated. Here, we demonstrate that undifferentiated OPCs developmentally peaked around postnatal day (P) 25, and binocular enucleation (BE) from the time of eye opening (P14-15) elevated symmetrically-divided undifferentiated OPCs in a reversible G0/G1 state even more at the bottom lamina of the cortex by reducing maturing oligodendrocyte (OL) lineage cells. Experiments using the sonic hedgehog (Shh) signaling inhibitor cyclopamine in vivo suggested that Shh signaling pathway was involved in the BE-induced undifferentiation process. The undifferentiated OPCs then differentiated within 5 days, independent of the experience, becoming mostly quiescent cells in control mice, while altering the mode of sister cell symmetry and forming quiescent as well as maturing cells in the enucleated mice. At P50, BE increased mature OLs via symmetric and asymmetric modes of cell segregation, resulting in more populated mature OLs at the bottom layer of the cortex. These data suggest that fourth postnatal week, corresponding to the early critical period of ocular dominance plasticity, is a developmentally sensitive period for OPC state changes. Overall, the visual loss promoted undifferentiation at the early period, but later increased the formation of mature OLs via a change in the mode of cell type symmetry at the bottom layer of mouse V1.

Leukemia inhibitory factor regulates Schwann cell proliferation and migration and affects peripheral nerve regeneration

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that stimulates neuronal development and survival. Our previous study has demonstrated that LIF mRNA is dysregulated in the peripheral nerve segments after nerve injury. Here, we show that LIF protein is abundantly expressed in Schwann cells after rat sciatic nerve injury. Functionally, suppressed or elevated LIF increases or decreases the proliferation rate and migration ability of Schwann cells, respectively. Morphological observations demonstrate that in vivo application of siRNA against LIF after peripheral nerve injury promotes Schwann cell migration and proliferation, axon elongation, and myelin formation. Electrophysiological and behavior assessments disclose that knockdown of LIF benefits the function recovery of injured peripheral nerves. Differentially expressed LIF affects the metabolism of Schwann cells and negatively regulates ERFE (Erythroferrone). Collectively, our observations reveal the essential roles for LIF in regulating the proliferation and migration of Schwann cells and the regeneration of injured peripheral nerves, discover ERFE as a downstream effector of LIF, and extend our understanding of the molecular mechanisms underlying peripheral nerve regeneration.

More attention on glial cells to have better recovery after spinal cord injury

Functional improvement after spinal cord injury remains an unsolved difficulty. Glial scars, a major component of SCI lesions, are very effective in improving the rate of this recovery. Such scars are a result of complex interaction mechanisms involving three major cells, namely, astrocytes, oligodendrocytes, and microglia. In recent years, scientists have identified two subtypes of reactive astrocytes, namely, A1 astrocytes that induce the rapid death of neurons and oligodendrocytes, and A2 astrocytes that promote neuronal survival. Moreover, recent studies have suggested that the macrophage polarization state is more of a continuum between M1 and M2 macrophages. M1 macrophages that encourage the inflammation process kill their surrounding cells and inhibit cellular proliferation. In contrast, M2 macrophages promote cell proliferation, tissue growth, and regeneration. Furthermore, the ability of oligodendrocyte precursor cells to differentiate into adult oligodendrocytes or even neurons has been reviewed. Here, we first scrutinize recent findings on glial cell subtypes and their beneficial or detrimental effects after spinal cord injury. Second, we discuss how we may be able to help the functional recovery process after injury.

The impact of trophic and immunomodulatory factors on oligodendrocyte maturation: Potential treatments for encephalopathy of prematurity

Encephalopathy of prematurity (EoP) is a major cause of morbidity in preterm neonates, causing neurodevelopmental adversities that can lead to lifelong impairments. Preterm birth-related insults, such as cerebral oxygen fluctuations and perinatal inflammation, are believed to negatively impact brain development, leading to a range of brain abnormalities. Diffuse white matter injury is a major hallmark of EoP and characterized by widespread hypomyelination, the result of disturbances in oligodendrocyte lineage development. At present, there are no treatment options available, despite the enormous burden of EoP on patients, their families, and society. Over the years, research in the field of neonatal brain injury and other white matter pathologies has led to the identification of several promising trophic factors and cytokines that contribute to the survival and maturation of oligodendrocytes, and/or dampening neuroinflammation. In this review, we discuss the current literature on selected factors and their therapeutic potential to combat EoP, covering a wide range of in vitro, preclinical and clinical studies. Furthermore, we offer a future perspective on the translatability of these factors into clinical practice.

Neuroregenerative and protective functions of Leukemia Inhibitory Factor in perinatal hypoxic-ischemic brain injury

Neonatal hypoxic-ischemic encephalopathy remains the most important neurological problem of the newborn. Delays in diagnosing perinatal brain injuries are common, preventing access to acute therapies. Therefore, there is a critical need for therapeutic strategies that are beneficial when delivered beyond 24 h after birth. Here we show that Leukemia Inhibitory Factor (LIF) functions as an essential injury-induced neurotrophic cytokine in the CNS and that non-invasively administering LIF as late as 3 days after a hypoxic-ischemic insult improves neurological function. Using a mouse model of late preterm brain injury we show that astroglial and microglial/macrophage reactivity to hypoxia-ischemia was diminished at 3 days of recovery, but then exacerbated at 2 weeks of recovery in LIF haplodeficient mice. There also were significantly more CD68+/Iba-1+ cells in the ipsilateral striatum in LIF-Het mice compared to WT mice at 2 weeks of recovery. This desynchronized glial response was accompanied by increased neuronal cell death in the striatum and neocortex (Fluorojade C), hypomyelination (reduced MBP staining and thinner external capsule), increased extent of brain damage (Nissl) and diminished neurological function on sensorimotor tests. To our surprise, injured LIF-Het mice had ~7-fold higher IGF-1 levels than injured WT mice at 3 days after HI injury. Intranasally administered LIF activated the Jak-Stat-3 pathway both within the subventricular zone and the neocortex at 30 min after administration. When delivered with a delay of 3 days after the insult, intranasal LIF reduced the extent of brain injury by ~60%, attenuated astrogliosis and microgliosis in striatum, improved subcortical white matter thickness, increased numbers of Olig2+ cells in corpus callosum and improved performance on sensorimotor tests at 2 weeks of recovery. These studies provide key pre-clinical data recommending LIF administration as a neuroprotectant and regenerative cytokine and they highlight the feasibility of pursuing new therapeutics targeting the tertiary phase of neurodegeneration for hypoxic-ischemic encephalopathies.

Extrinsic Factors Driving Oligodendrocyte Lineage Cell Progression in CNS Development and Injury

Oligodendrocytes (OLs) generate myelin membranes for the rapid propagation of electrical signals along axons in the central nervous system (CNS) and provide metabolites to support axonal integrity and function. Differentiation of OLs from oligodendrocyte progenitor cells (OPCs) is orchestrated by a multitude of intrinsic and extrinsic factors in the CNS. Disruption of this process, or OL loss in the developing or adult brain, as observed in various neurological conditions including hypoxia/ischemia, stroke, and demyelination, results in axonal dystrophy, neuronal dysfunction, and severe neurological impairments. While much is known regarding the intrinsic regulatory signals required for OL lineage cell progression in development, studies from pathological conditions highlight the importance of the CNS environment and external signals in regulating OL genesis and maturation. Here, we review the recent findings in OL biology in the context of the CNS physiological and pathological conditions, focusing on extrinsic factors that facilitate OL development and regeneration.

Injury type-dependent differentiation of NG2 glia into heterogeneous astrocytes

The glial scar is comprised of a heterogeneous population of reactive astrocytes. NG2 glial cells (also known as oligodendrocyte progenitor cells or polydendrocytes) may contribute to this heterogeneity by differentiating into astrocytes in the injured CNS, but there have been conflicting reports about whether astrocytes comprise a significant portion of the NG2 cell lineage. By using genetic fate mapping after spinal cord injury (SCI) and experimental autoimmune encephalomyelitis (EAE) in mice, the goal of this study was to confirm and extend upon previous findings, which have shown that NG2 cell plasticity varies across CNS injuries. We generated mice that express tdTomato in NG2 lineage cells and express GFP under the Aldh1l1 or Glt1 promoter so that NG2 glia-derived astrocytes can be detected by their expression of GFAP and/or GFP. We found that astrocytes comprise approximately 25% of the total NG2 cell lineage in the glial scar by 4 weeks after mid-thoracic contusive SCI, but only 9% by the peak of functional deficit after EAE. Interestingly, a subpopulation of astrocytes expressed only GFP without co-expression of GFAP, uncovering their heterogeneity and the possibility of an underestimation of NG2 glia-derived astrocytes in previous studies. Additionally, we used high performance liquid chromatography to measure the level of tamoxifen and its metabolites in the spinal cord and show that genetic labeling of NG2 glia-derived astrocytes is not an artifact of residual tamoxifen. Overall, our data demonstrate that a heterogeneous population of astrocytes are derived from NG2 glia in an injury type-dependent manner.

Effect of glial cells on remyelination after spinal cord injury

Remyelination plays a key role in functional recovery of axons after spinal cord injury. Glial cells are the most abundant cells in the central nervous system. When spinal cord injury occurs, many glial cells at the lesion site are immediately activated, and different cells differentially affect inflammatory reactions after injury. In this review, we aim to discuss the core role of oligodendrocyte precursor cells and crosstalk with the rest of glia and their subcategories in the remyelination process. Activated astrocytes influence proliferation, differentiation, and maturation of oligodendrocyte precursor cells, while activated microglia alter remyelination by regulating the inflammatory reaction after spinal cord injury. Understanding the interaction between oligodendrocyte precursor cells and the rest of glia is necessary when designing a therapeutic plan of remyelination after spinal cord injury.

The role of the leukemia inhibitory factor receptor in neuroprotective signaling

Several neurotropic cytokines relay their signaling through the leukemia inhibitory factor receptor. This 190kDa subunit couples with the 130kDa gp130 subunit to transduce intracellular signaling in neurons and oligodendrocytes that leads to expression of genes associated with neurosurvival. Moreover, activation of this receptor alters the phenotype of immune cells to an anti-inflammatory one. Although cytokines that activate the leukemia inhibitory factor receptor have been studied in the context of neurodegenerative disease, therapeutic targeting of the specific receptor subunit has been understudied in by comparison. This review examines the role of this receptor in the CNS and immune system, and its application in the treatment in stroke and other brain pathologies.

Severe Convulsions and Dysmyelination in Both Jimpy and Cx32/47 -/- Mice may Associate Astrocytic L-Channel Function with Myelination and Oligodendrocytic Connexins with Internodal Kv Channels

The Jimpy mouse illustrates the importance of interactions between astrocytes and oligodendrocytes. It has a mutation in Plp coding for proteolipid protein and DM20. Its behavior is normal at birth but from the age of ~2 weeks it shows severe convulsions associated with oligodendrocyte/myelination deficits and early death. A normally occurring increase in oxygen consumption by highly elevated K+ concentrations is absent in Jimpy brain slices and cultured astrocytes, reflecting that Plp at early embryonic stages affects common precursors as also shown by the ability of conditioned medium from normal astrocytes to counteract histological abnormalities. This metabolic response is now known to reflect opening of L-channels for Ca2+. The resulting deficiency in Ca2+ entry has many consequences, including lack of K+-stimulated glycogenolysis and release of gliotransmitter ATP. Lack of purinergic stimulation compromises oligodendrocyte survival and myelination and affects connexins and K+ channels. Mice lacking the oligodendrocytic connexins Cx32 and 47 show similar neurological dysfunction as Jimpy. This possibly reflects that K+ released by intermodal axonal Kv channels is transported underneath a loosened myelin sheath instead of reaching the extracellular space via connexin-mediated transport to oligodendrocytes, followed by release and astrocytic Na+,K+-ATPase-driven uptake with subsequent Kir4.1-facilitated release and neuronal uptake.

Understanding the NG2 Glial Scar after Spinal Cord Injury

NG2 cells, also known as oligodendrocyte progenitor cells, are located throughout the central nervous system and serve as a pool of progenitors to differentiate into oligodendrocytes. In response to spinal cord injury (SCI), NG2 cells increase their proliferation and differentiation into remyelinating oligodendrocytes. While astrocytes are typically associated with being the major cell type in the glial scar, many NG2 cells also accumulate within the glial scar but their function remains poorly understood. Similar to astrocytes, these cells hypertrophy, upregulate expression of chondroitin sulfate proteoglycans, inhibit axon regeneration, contribute to the glial-fibrotic scar border, and some even differentiate into astrocytes. Whether NG2 cells also have a role in other astrocyte functions, such as preventing the spread of infiltrating leukocytes and expression of inflammatory cytokines, is not yet known. Thus, NG2 cells are not only important for remyelination after SCI but are also a major component of the glial scar with functions that overlap with astrocytes in this region. In this review, we describe the signaling pathways important for the proliferation and differentiation of NG2 cells, as well as the role of NG2 cells in scar formation and tissue repair.

A silver lining of neuroinflammation: Beneficial effects on myelination

Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.

STAT3 and SOCS3 regulate NG2 cell proliferation and differentiation after contusive spinal cord injury

NG2 cells, also known as oligodendrocyte progenitors or polydendrocytes, are a major component of the glial scar that forms after spinal cord injury. NG2 cells react to injury by proliferating around the lesion site and differentiating into oligodendrocytes and astrocytes, but the molecular mechanism is poorly understood. In this study, we tested the role of the transcription factor STAT3, and its suppressor SOCS3, in NG2 cell proliferation and differentiation after spinal cord injury. Using knockout mice in which STAT3 or SOCS3 are genetically deleted specifically in NG2 cells, we found that deletion of STAT3 led to a reduction in oligodendrogenesis, while deletion of SOCS3 led to enhanced proliferation of NG2 cells within the glial scar after spinal cord injury. Additionally, STAT3 and SOCS3 were not required for astrogliogenesis from NG2 cells after spinal cord injury. Interestingly, genetic deletion of STAT3 and SOCS3 did not have opposing effects, suggesting that SOCS3 may have targets other than the STAT3 pathway in NG2 cells after spinal cord injury. Altogether, our data show that both STAT3 and SOCS3 play important, yet unexpected, roles in NG2 cell proliferation and differentiation after spinal cord injury.

Activation of oligodendroglial Stat3 is required for efficient remyelination

Multiple sclerosis is the most prevalent demyelinating disease of the central nervous system (CNS) and is histologically characterized by perivascular demyelination as well as neurodegeneration. While the degree of axonal damage is correlated with clinical disability, it is believed that remyelination can protect axons from degeneration and slow disease progression. Therefore, understanding the intricacies associated with myelination and remyelination may lead to therapeutics that can enhance the remyelination process and slow axon degeneration and loss of function. Ciliary neurotrophic factor (CNTF) family cytokines such as leukemia inhibitory factor (LIF) and interleukin 11 (IL-11) are known to promote oligodendrocyte maturation and remyelination in experimental models of demyelination. Because CNTF family member binding to the gp130 receptor results in activation of the JAK2/Stat3 pathway we investigated the necessity of oligodendroglial Stat3 in transducing the signal required for myelination and remyelination. We found that Stat3 activation in the CNS coincides with myelination during development. Stimulation of oligodendrocyte precursor cells (OPCs) with CNTF or LIF promoted OPC survival and final differentiation, which was completely abolished by pharmacologic blockade of Stat3 activation with JAK2 inhibitor. Similarly, genetic ablation of Stat3 in oligodendrocyte lineage cells prevented CNTF-induced OPC differentiation in culture. In vivo, while oligodendroglial Stat3 signaling appears to be dispensable for developmental CNS myelination, it is required for oligodendrocyte regeneration and efficient remyelination after toxin-induced focal demyelination in the adult brain. Our data suggest a critical function for oligodendroglial Stat3 signaling in myelin repair.

Unwrapping Neurotrophic Cytokines and Histone Modification

The conventional view that neuroinflammatory lesions contain strictly pro- and anti-inflammatory cytokines is being challenged. Some proinflammatory products e.g. TNF-α are crucial intermediates in axon regeneration, oligodendroglial renewal and remyelination. A more functional system of nomenclature classifies cytokines by their neuro 'protective' or 'suppressive' properties. Beyond the balance of these 'environmental' or 'extrinsic' signals, specific 'intrinsic' determinants of cytokine signalling appear to influence the outcome of axoglial regeneration. In this commentary, we examine the potential importance of cytokine-induced histone modification on oligodendrocyte differentiation. Neuroinflammation mediates the release of astrocytic leukaemia inhibitory factor (LIF) and erythropoietin (EPO) which potentiates oligodendrocyte differentiation and myelin production. Meanwhile, histone deacetylation strongly suppresses important inhibitors of oligodendrocyte differentiation. Given that LIF and EPO induce histone deacetylases in other systems, future studies should examine whether this mechanism significantly influences the outcome of cytokine-induced remyelination, and whether epigenetic drug targets could potentiate the effects of exogenous cytokine therapy.

Leukemia Inhibitory Factor Haplodeficiency Desynchronizes Glial Reactivity and Exacerbates Damage and Functional Deficits after a Concussive Brain Injury

Reactions of both astrocytes and microglia to central nervous system injury can be beneficial or detrimental to recovery. To gain insights into the functional importance of gliosis, we developed a new model of adolescent closed-head injury (CHI) and interrogated the behavioral, physiological, and cellular outcomes after a concussive CHI in leukemia inhibitory factor (LIF) haplodeficient mice. These mice were chosen because LIF is important for astrocyte and microglial activation. Behaviorally, the LIF haplodeficient animals were equally impaired 4 h after the injury, but in the subsequent 2 weeks, the LIF haplodeficient mice acquired more severe motor and sensory deficits, compared with wild type mice. The prolonged accumulation of neurological impairment was accompanied by desynchronization of the gliotic response, increased cell death, axonal degeneration, diminished callosal compound action potential, and hypomyelination. Our results clearly show that LIF is an essential injury-induced cytokine that is required to prevent the propagation of secondary neurodegeneration.

Infection as an Environmental Trigger of Multiple Sclerosis Disease Exacerbation

Over the past several decades, significant advances have been made in identifying factors that contribute to the pathogenesis of multiple sclerosis (MS) and have culminated in the approval of some effective therapeutic strategies for disease intervention. However, the mechanisms by which environmental factors, such as infection, contribute to the pathogenesis and/or symptom exacerbation remain to be fully elucidated. Relapse frequency in MS patients contributes to neurological impairment and, in the initial phases of disease, serves as a predictor of poor disease prognosis. The purpose of this review is to examine the evidence that supports a role for peripheral infection in modulating the natural history of this disease. Evidence supporting a role for infection in promoting exacerbation in animal models of MS is also reviewed. Finally, a few mechanisms by which infection may exacerbate symptoms of MS and other neurological diseases are discussed. Those who comprise the majority of MS patients acquire approximately two upper-respiratory infections per year; furthermore, this type of infection doubles the risk for MS relapse, underscoring the contribution of this relationship as being potentially important and particularly detrimental.

Leukemia inhibitory factor (LIF)

Leukemia inhibitory factor (LIF) is the most pleiotropic member of the interleukin-6 family of cytokines. It utilises a receptor that consists of the LIF receptor β and gp130 and this receptor complex is also used by ciliary neurotrophic growth factor (CNTF), oncostatin M, cardiotrophin1 (CT1) and cardiotrophin-like cytokine (CLC). Despite common signal transduction mechanisms (JAK/STAT, MAPK and PI3K) LIF can have paradoxically opposite effects in different cell types including stimulating or inhibiting each of cell proliferation, differentiation and survival. While LIF can act on a wide range of cell types, LIF knockout mice have revealed that many of these actions are not apparent during ordinary development and that they may be the result of induced LIF expression during tissue damage or injury. Nevertheless LIF does appear to have non-redundant actions in maternal receptivity to blastocyst implantation, placental formation and in the development of the nervous system. LIF has also found practical use in the maintenance of self-renewal and totipotency of embryonic stem cells and induced pluripotent stem cells.

Oligodendrocyte Precursor Cells in Spinal Cord Injury: A Review and Update

Spinal cord injury (SCI) is a devastating condition to individuals, families, and society. Oligodendrocyte loss and demyelination contribute as major pathological processes of secondary damages after injury. Oligodendrocyte precursor cells (OPCs), a subpopulation that accounts for 5 to 8% of cells within the central nervous system, are potential sources of oligodendrocyte replacement after SCI. OPCs react rapidly to injuries, proliferate at a high rate, and can differentiate into myelinating oligodendrocytes. However, posttraumatic endogenous remyelination is rarely complete, and a better understanding of OPCs' characteristics and their manipulations is critical to the development of novel therapies. In this review, we summarize known characteristics of OPCs and relevant regulative factors in both health and demyelinating disorders including SCI. More importantly, we highlight current evidence on post-SCI OPCs transplantation as a potential treatment option as well as the impediments against regeneration. Our aim is to shed lights on important knowledge gaps and to provoke thoughts for further researches and the development of therapeutic strategies.

Myelin repair in vivo is increased by targeting oligodendrocyte precursor cells with nanoparticles encapsulating leukaemia inhibitory factor (LIF)

Multiple sclerosis (MS) is a progressive demyelinating disease of the central nervous system (CNS). Many nerve axons are insulated by a myelin sheath and their demyelination not only prevents saltatory electrical signal conduction along the axons but also removes their metabolic support leading to irreversible neurodegeneration, which currently is untreatable. There is much interest in potential therapeutics that promote remyelination and here we explore use of leukaemia inhibitory factor (LIF), a cytokine known to play a key regulatory role in self-tolerant immunity and recently identified as a pro-myelination factor. In this study, we tested a nanoparticle-based strategy for targeted delivery of LIF to oligodendrocyte precursor cells (OPC) to promote their differentiation into mature oligodendrocytes able to repair myelin. Poly(lactic-co-glycolic acid)-based nanoparticles of ∼120 nm diameter were constructed with LIF as cargo (LIF-NP) with surface antibodies against NG-2 chondroitin sulfate proteoglycan, expressed on OPC. In vitro, NG2-targeted LIF-NP bound to OPCs, activated pSTAT-3 signalling and induced OPC differentiation into mature oligodendrocytes. In vivo, using a model of focal CNS demyelination, we show that NG2-targeted LIF-NP increased myelin repair, both at the level of increased number of myelinated axons, and increased thickness of myelin per axon. Potency was high: a single NP dose delivering picomolar quantities of LIF is sufficient to increase remyelination. Impact statement Nanotherapy-based delivery of leukaemia inhibitory factor (LIF) directly to OPCs proved to be highly potent in promoting myelin repair in vivo: this delivery strategy introduces a novel approach to delivering drugs or biologics targeted to myelin repair in diseases such as MS.

Systematic identification of 3'-UTR regulatory elements in activity-dependent mRNA stability in hippocampal neurons

Ongoing neuronal activity during development and plasticity acts to refine synaptic connections and contributes to the induction of plasticity and ultimately long-term memory storage. Activity-dependent, post-transcriptional control of mRNAs occurs through transport to axonal and dendritic compartments, local translation and mRNA stability. We have identified a mechanism that contributes to activity-dependent regulation of mRNA stability during synaptic plasticity in rat hippocampal neurons. In this study, we demonstrate rapid, post-transcriptional control over process-enriched mRNAs by neuronal activity. Systematic analysis of the 3'-UTRs of destabilized transcripts, identifies enrichment in sequence motifs corresponding to microRNA (miRNA)-binding sites. The miRNAs that were identified, miR-326-3p/miR-330-5p, miR-485-5p, miR-666-3p and miR-761 are predicted to regulate networks of genes important in plasticity and development. We find that these miRNAs are developmentally regulated in the hippocampus, many increasing by postnatal day 14. We further find that miR-485-5p controls NGF-induced neurite outgrowth in PC12 cells, tau expression and axonal development in hippocampal neurons. miRNAs can function at the synapse to rapidly control and affect short- and long-term changes at the synapse. These processes likely occur during refinement of synaptic connections and contribute to the induction of plasticity and learning and memory.

Multiple Sclerosis and the LIF/IL-6 Axis: Use of Nanotechnology to Harness the Tolerogenic and Reparative Properties of LIF

Leukaemia inhibitory factor (LIF) plays a critical role in “stemness” versus “differentiation”, a property that underpins the core value of LIF as a therapeutic for both the treatment of autoimmune disease and for promoting tissue repair. This value can be realized using nano-engineering technology, where a new generation of tools can, with unprecedented ability, manipulate biological functions. One striking example is the treatment of multiple sclerosis (MS). The underpinning biology is the newly identified LIF/IL-6 axis in T lymphocytes, which can tilt the behaviour between immune tolerance versus immune attack. This LIF/IL-6 axis is ideally suited to nanotherapeutic manipulation, given its inherent mechanistic simplicity of two mutually opposing feed-forward loops that determine either tolerogenic (LIF) or inflammatory (IL-6) immunity. Using LIF that is formulated in biodegradable nanoparticles (LIF-NP) and targeted to CD4+ T cells, the axis is harnessed towards immune tolerance. This has implications for the treatment of autoimmune diseases, where the clinical burden is immense. It encompasses more than 100 diseases and, in the USA alone, costs more than $100 billion in direct health care costs annually. Other properties of LIF include the promotion of healthy neuro-glial interactions within the central nervous system (CNS), where, in addition to MS, LIF-NP therapy is relevant to inflammatory neurodegenerative diseases that represent a large and increasing need within aging populations. Thirdly, LIF is a reparative growth factor that can maintain genomic plasticity. LIF-NP supports the use of stem cell-based therapies in regenerative medicine plus augment therapeutic benefits within the patient. These core properties of LIF are greatly amplified in value by the advantage of being formulated as nanoparticles, namely (i) targeted delivery, (ii) exploitation of endogenous regulatory pathways and (iii) creation of surrogate micro-stromal niches. We discuss LIF-NP as a means to harness endogenous pathways for the treatment of MS, both to reset immune self-tolerance and to promote repair of myelin that is required to support health within the nervous system.

Stem cell therapy for glaucoma: science or snake oil?

In recent years there has been substantial progress in developing stem cell treatments for glaucoma. As a downstream approach that targets the underlying susceptibility of retinal ganglion and trabecular meshwork cells, stem cell therapy has the potential to both replace lost, and protect damaged, cells by secreting neurotrophic factors. A variety of sources, including embryonic cells, adult cells derived from the central nervous system, and induced pluripotent stem cells show promise as therapeutic approaches. Even though safety concerns and ethical controversies have limited clinical implementation, some institutions have already commercialized stem cell therapy and are using direct-to-consumer advertising to attract patients with glaucoma. We review the progress of stem cell therapy and its current commercial availability.

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Oligodendroglia and neurotrophic factors in neurodegeneration

Myelination by oligodendroglial cells (OLs) enables the propagation of action potentials along neuronal axons, which is essential for rapid information flow in the central nervous system. Besides saltatory conduction, the myelin sheath also protects axons against inflammatory and oxidative insults. Loss of myelin results in axonal damage and ultimately neuronal loss in demyelinating disorders. However, accumulating evidence indicates that OLs also provide support to neurons via mechanisms beyond the insulating function of myelin. More importantly, an increasing volume of reports indicates defects of OLs in numerous neurodegenerative diseases, sometimes even preceding neuronal loss in pre-symptomatic episodes, suggesting that OL pathology may be an important mechanism contributing to the initiation and/or progression of neurodegeneration. This review focuses on the emerging picture of neuronal support by OLs in the pathogenesis of neurodegenerative disorders through diverse molecular and cellular mechanisms, including direct neuron-myelin interaction, metabolic support by OLs, and neurotrophic factors produced by and/or acting on OLs.

Human mesenchymal stem cells isolated from olfactory biopsies but not bone enhance CNS myelination in vitro

Spinal cord injury (SCI) is a devastating condition with limited capacity for repair. Cell transplantation is a potential strategy to promote SCI repair with cells from the olfactory system being promising candidates. Although transplants of human olfactory mucosa (OM) are already ongoing in clinical trials, the repair potential of this tissue remains unclear. Previously, we identified mesenchymal-like stem cells that reside in the lamina propria (LP-MSCs) of rat and human OM. Little is known about these cells or their interactions with glia such as olfactory ensheathing cells (OECs), which would be co-transplanted with MSCs from the OM, or endogenous CNS glia such as oligodendrocytes. We have characterized, purified, and assessed the repair potential of human LP-MSCs by investigating their effect on glial cell biology with specific emphasis on CNS myelination in vitro. Purified LP-MSCs expressed typical bone marrow MSC (BM-MSC) markers, formed spheres, were clonogenic and differentiated into bone and fat. LP-MSC conditioned medium (CM) promoted oligodendrocyte precursor cell (OPC) and OEC proliferation and induced a highly branched morphology. LP-MSC-CM treatment caused OEC process extension. Both LP and BM-MSCs promoted OPC proliferation and differentiation, but only myelinating cultures treated with CM from LP and not BM-MSCs had a significant increase in myelination. Comparison with fibroblasts and contaminating OM fibroblast like-cells showed the promyelination effect was LP-MSC specific. Thus LP-MSCs harvested from human OM biopsies may be an important candidate for cell transplantation by contributing to the repair of SCI.

Leukemia inhibitory factor is essential for subventricular zone neural stem cell and progenitor homeostasis as revealed by a novel flow cytometric analysis

Stem cells rely on extracellular signals produced by the niche, which dictate their ability to self-renew, expand and differentiate. It is essential to have sensitive and reproducible methods of either quantifying or isolating these stem cells and progenitors to understand their intrinsic properties and how extrinsic signals regulate their development. However, stem cells are difficult to distinguish from multipotential progenitors, which may look and act like them. Here we define a 4-color flow cytometry panel using CD133, LeX, CD140a, NG2 to define a neural stem cell (NSC) as well as 4 classes of multipotential progenitors and 3 classes of bipotential progenitors, several of which have not been described previously. We performed gain and loss of function studies for leukemia inhibitory factor (LIF) and showed a depletion of NSCs, a subset of multipotential neural precursors and immature oligodendrocytes in LIF null mice. Gain of function studies showed that LIF increased the abundance of these precursors. Our studies also show that these NPs have differential requirements for LIF and ciliary neurotrophic factor (CNTF) and for epidermal growth factor (EGF), fibroblast growth factor (FGF-2) and platelet-derived growth factor (PDGF) for their propagation in vitro. Surprisingly, the related cytokine, CNTF, was less potent than LIF in increasing the NSCs and more potent than LIF in increasing the PDGF responsive multipotential precursors. Finally, we show that LIF increases the expression of the core transcription factors: Klf4, Fbx15, Nanog, Sox2 and c-Myc. Altogether our FACS (fluorescence-activated cell sorter) analyses reveal that the neonatal subventricular zone is far more heterogeneous than previously suspected and our studies provide new insights into the signals and mechanisms that regulate their self-renewal and proliferation.

LIF-dependent signaling: new pieces in the Lego

LIF, a member of the IL6 family of cytokine, displays pleiotropic effects on various cell types and organs. Its critical role in stem cell models (e.g.: murine ES, human mesenchymal cells) and its essential non redundant function during the implantation process of embryos, in eutherian mammals, put this cytokine at the core of many studies aiming to understand its mechanisms of action, which could benefit to medical applications. In addition, its conservation upon evolution raised the challenging question concerning the function of LIF in species in which there is no implantation. We present the recent knowledge about the established and potential functions of LIF in different stem cell models, (embryonic, hematopoietic, mesenchymal, muscle, neural stem cells and iPSC). We will also discuss EVO-DEVO aspects of this multifaceted cytokine.

Exogenous leukemia inhibitory factor stimulates oligodendrocyte progenitor cell proliferation and enhances hippocampal remyelination

New CNS neurons and glia are generated throughout adulthood from endogenous neural stem and progenitor cells. These progenitors can respond to injury, but their ability to proliferate, migrate, differentiate, and survive is usually insufficient to replace lost cells and restore normal function. Potentiating the progenitor response with exogenous factors is an attractive strategy for the treatment of nervous system injuries and neurodegenerative and demyelinating disorders. Previously, we reported that delivery of leukemia inhibitory factor (LIF) to the CNS stimulates the self-renewal of neural stem cells and the proliferation of parenchymal glial progenitors. Here we identify these parenchymal glia as oligodendrocyte (OL) progenitor cells (OPCs) and show that LIF delivery stimulates their proliferation through the activation of gp130 receptor signaling within these cells. Importantly, this effect of LIF on OPC proliferation can be harnessed to enhance the generation of OLs that express myelin proteins and reform nodes of Ranvier in the context of chronic demyelination in the adult mouse hippocampus. Our findings, considered together with the known beneficial effects of LIF on OL and neuron survival, suggest that LIF has both reparative and protective activities that make it a promising potential therapy for CNS demyelinating disorders and injuries.

Oligodendrocyte progenitor cells proliferate and survive in an immature state following treatment with an axolemma-enriched fraction

The ability of an AEF (axolemma-enriched fraction) to influence the proliferation, survival and differentiation of OPC (oligodendrocyte progenitor cells) was evaluated. Following addition of AEF to cultured OPC, the AEF associated with the outer surface of OPC so that subsequent metabolic events were likely mediated by direct AEF-OPC contact. Addition of AEF to the cultured OPC resulted in a dose- and time-dependent increase in proliferation that was partially dependent on Akt (protein kinase B) and MAPK (mitogen-activated protein kinase) activation. The major mitogen in an AEF-SE (soluble 2.0 M NaCl extract of the AEF) was identified as aFGF (acidic fibroblast growth factor) and accounted for 50% of the mitogenicity. The remaining 50% of the mitogenicity had properties consistent with bFGF (basic fibroblast growth factor) but was not unequivocally identified. Under conditions that limit the survival of OPC in culture, AEF treatment prolonged the survival of the OPC. Antigenic and morphological examination of the AEF-treated OPC indicated that the AEF treatment helped the OPC survive in a more immature state. The potential downstream metabolic pathways potentially activated in OPC by AEF and the consequences of these activated pathways are discussed. The results of these studies are consistent with the view that direct contact of axons with OPC stimulates their proliferation and survival while preventing their differentiation.

Astrocyte proximity modulates the myelination gene fabric of oligodendrocytes

Extensive literature documented that astrocytes release neurotransmitters, cytokines and other signaling molecules to modulate migration, maturation and myelin synthesis of oligodendrocytes through mechanisms primarily converging on cytosolic [Ca2+] transients. Considering the long-term effects, it is expected that astrocyte-conditioned medium is a major regulator of gene expression in oligodendrocytes even in the absence of cytosol-to-cytosol communication via astrocyte-oligodendrocyte gap junction channels. Indeed, by comparing the transcriptomes of immortalized precursor oligodendrocyte (Oli-neu) cells when cultured alone and co-cultured with non-touching astrocytes we found profound changes in the gene expression level, control and networking. Remarkably, the astrocyte proximity was more effective in remodeling the myelination (MYE) gene fabric and its control by cytokine receptor (CYR)-modulated intercellular Ca2+-signaling (ICS) transcriptomic network than the dibutyryl-cAMP (db-cAMP) treatment-induced transformation into myelin-associated glycoprotein-positive oligodendrocyte-like cells. Moreover, astrocyte proximity up-regulated 37 MYE genes and switched on another 14 MYE, 23 ICS and 4 CYR genes, enhancing the roles of the leukemia inhibitory factor receptor and connexins Cx29 and Cx47. The novel prominent gene analysis identified the enhancer of zeste homolog 2 as the most relevant MYE gene in the astrocyte proximity, notch gene homolog 1 in control and B-cell leukemia/lymphoma 2 in differentiated Oli-neu cells.

Therapeutic potential of LIF in multiple sclerosis

Therapies for multiple sclerosis (MS) reduce the relapse rate but are unable to stop neurological decline. Here, we evaluate the potential of leukemia inhibitory factor (LIF) as a novel therapeutic in diseases with a neurodegenerative and inflammatory component, such as MS. LIF, which can be a proinflammatory cytokine, can also modulate the immune response in a beneficial way. Recent evidence demonstrates a crucial role of LIF in neuroprotection and axonal regeneration as well as the prevention of demyelination. Finally, LIF is an important survival factor for stem cells and neuronal precursors. Therefore, we propose that LIF is a potential therapeutic candidate for MS.