Proliferation Of Oligodendrocyte Precursor Cells Research Articles

Integrin-Linked Kinase (ILK) Deletion Disrupts Oligodendrocyte Development by Altering Cell Cycle

During development, oligodendrocytes are initially specified, after which oligodendrocyte precursor cells (OPCs) migrate and proliferate before differentiating into myelinating cells. Lineage-specific programming of oligodendrocytes results from sensing environmental cues through membrane-bound receptors and related intracellular signaling molecules. Integrin-linked kinase (ILK) is an important protein that is expressed at the inner margins of the plasma membrane and can mediate some of these signals. The current studies demonstrate that ILK deletion reduces the proliferation and differentiation of OPCs in the developing CNS. There was a significant decrease in the number of OPCs and mature oligodendrocytes throughout postnatal development in Olig1Cre^+/− × ILK^fl/fl mice. These changes were accompanied by reduced numbers of myelinated axons. Key proteins involved in cell cycle regulation were dysregulated. Cyclin D1/D3 and cyclin-dependent kinase 2/4 (cdc2/cdc4) were downregulated and the cell cycle inhibitor protein p27 Kip1 was upregulated. Therefore, ILK deletion impaired the developmental profile, proliferation, and differentiation of OPCs by altering the expression of regulatory cytoplasmic and nuclear factors. <b>SIGNIFICANCE STATEMENT</b> Integrin-linked kinase (ILK) is a scaffolding protein involved in integrating signals from the extracellular environment and communicating those signals to downstream effectors within cells. It has been proposed to regulate aspects of oligodendrocyte process extension and thereby myelination. However, the current studies demonstrate that it has an earlier impact on cells in this lineage. Knocking down ILK in Olig1-Cre-expressing cells reduces the pool of oligodendrocyte progenitor cells (OPCs). This smaller pool of OPCs results from altered cell cycle and reduced cell proliferation. These cells myelinate fewer axons than in wild-type mice and, in corpus callosum, the myelin is thinner than in controls. Interestingly, the smaller pool of spinal cord oligodendrocytes generates myelin that is of normal thickness.

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.

Cardiomyocyte-released factors stimulate oligodendrocyte precursor cells proliferation

The heart produces multiple diffusible factors that are involved in a number of physiological processes, but the action of these factors on the central nervous system is not well understood. In this study, we found that one or more factors released by cardiomyocytes promote oligodendrocyte precursor cell (OPC) proliferation in vitro. Mouse OPCs co-cultured with mouse cardiomyocytes showed higher proliferative ability than OPCs cultured alone. In addition, cardiomyocyte-conditioned media was sufficient to promote OPC proliferation. The phosphorylation of phosphatidylinositol (PI) 3-kinase and extracellular signal-regulated kinase (ERK) in OPCs is necessary for the enhancement of OPC proliferation by cardiomyocyte-conditioned media. These data indicate that heart-derived factors have the ability to directly regulate the function of central nervous system (CNS) cells.

Integrin-Linked Kinase (ILK) Deletion Disrupts Oligodendrocyte Development by Altering Cell Cycle

Integrin-linked kinase (ILK) is a scaffolding protein involved in integrating signals from the extracellular environment and communicating those signals to downstream effectors within cells. It has been proposed to regulate aspects of oligodendrocyte process extension and thereby myelination. However, the current studies demonstrate that it has an earlier impact on cells in this lineage. Knocking down ILK in Olig1-Cre-expressing cells reduces the pool of oligodendrocyte progenitor cells (OPCs). This smaller pool of OPCs results from altered cell cycle and reduced cell proliferation. These cells myelinate fewer axons than in wild-type mice and, in corpus callosum, the myelin is thinner than in controls. Interestingly, the smaller pool of spinal cord oligodendrocytes generates myelin that is of normal thickness.

Epidermal growth factor preserves myelin and promotes astrogliosis after intraventricular hemorrhage.

Intraventricular hemorrhage (IVH) leads to reduced myelination and astrogliosis of the white matter in premature infants. No therapeutic strategy exists to minimize white matter injury in survivors with IVH. Epidermal growth factor (EGF) enhances myelination, astrogliosis, and neurologic recovery in animal models of white matter injury. Here, we hypothesized that recombinant human (rh) EGF treatment would enhance oligodendrocyte precursor cell (OPC) maturation, myelination, and neurological recovery in preterm rabbits with IVH. In addition, rhEGF would promote astrogliosis by inducing astroglial progenitor proliferation and GFAP transcription. We tested these hypotheses in a preterm rabbit model of IVH and evaluated autopsy samples from human preterm infants. We found that EGF and EGFR expression were more abundant in the ganglionic eminence relative to the cortical plate and white matter of human infants and that the development of IVH reduced EGF levels, but not EGFR expression. Accordingly, rhEGF treatment promoted proliferation and maturation of OPCs, preserved myelin in the white matter, and enhanced neurological recovery in rabbits with IVH. rhEGF treatment inhibited Notch signaling, which conceivably contributed to OPC maturation. rhEGF treatment contributed to astrogliosis by increasing astroglial proliferation and upregulating GFAP as well as Sox9 expression. Hence, IVH results in a decline in EGF expression; and rhEGF treatment preserves myelin, restores neurological recovery, and exacerbates astrogliosis by inducing proliferation of astrocytes and enhancing transcription of GFAP and Sox9 in pups with IVH. rhEGF treatment might improve the neurological outcome of premature infants with IVH. GLIA 2016;64:1987-2004.

Regenerative Capacity of Macrophages for Remyelination.

White matter injury, consisting of loss of axons, myelin, and oligodendrocytes, is common in many neurological disorders and is believed to underlie several motor and sensory deficits. Remyelination is the process in which the insulative myelin sheath is restored to axons, thereby facilitating recovery from functional loss. Remyelination proceeds with oligodendrocyte precursor cells (OPCs) that differentiate into oligodendrocytes to synthesize the new myelin sheath after demyelination. This process is influenced by several factors, including trophic factors, inhibitory molecules in the lesion microenvironment, age of the subject, as well as the inflammatory response. Currently studied strategies that enhance remyelination consist of pharmacological approaches that directly induce OPC differentiation or using agents to neutralize the inhibitory microenvironment. Another strategy is to harness a reparative inflammatory response. This response, coordinated by central nervous system resident microglia and peripherally-derived infiltrating macrophages, has been shown to be important in the remyelination process. These innate immune cells perform important functions in remyelination, including the proteolysis and phagocytosis of inhibitory molecules present in the lesion microenvironment, the provision of trophic and metabolic factors to OPCs, in addition to iron handling capacity. Additionally, an initial pro-inflammatory phase followed by a regulatory/anti-inflammatory phase has been shown to be important for OPC proliferation and differentiation, respectively. This review will discuss the beneficial roles of macrophages/microglia in remyelination and discuss therapeutic strategies to obtain the optimal regenerative macrophage phenotype for enhanced remyelination.

A Novel Brainstem Hemorrhage Model by Autologous Blood Infusion in Rat: White Matter Injury, Magnetic Resonance Imaging, and Neurobehavioral Features

Primary brainstem hemorrhage (BSH) has the highest mortality and morbidity as a subtype of intracerebral hemorrhage. A major limitation of BSH research is the lack of a corresponding animal model. The purpose of this study was to establish a novel rat model of BSH and to characterize the resulting brain injury, especially focusing on white matter injury. BSH was produced by stereotactically injecting autologous whole blood into the pons. Time course of hematoma resolution was observed by 7-T magnetic resonance imaging. White matter injury was evaluated in detail by multiple parameters including diffuse tensor imaging (DTI), demyelination, axonal injury, oligodendrocyte degeneration, and oligodendrocyte precursor cell proliferation. Brain water content and neurobehavior were also evaluated. Blood infusion (30 µL) led to a stable, reproducible hematoma in the right basotegmental pons. The hematoma absorption started, became obvious, and was nearly completed at 7, 14, and 30 days, respectively. Hematoma caused obvious brain edema at 3 days. White mater injury was observed pathologically, which was in line with decreased fractional anisotropy (FA) in DTI in the pons. FA reduction was also noticed in the cerebral peduncle and medulla. Behavioral abnormality persisted for at least 14 days and neurofunction was recovered within 1 month. This novel model can produce a stable hematoma resulting in brain edema, white matter injury, and neurofunctional deficits, which could be useful for future investigation of pathophysiological mechanisms and new treatment evaluation after BSH.

After Intracerebral Hemorrhage, Oligodendrocyte Precursors Proliferate and Differentiate Inside White-Matter Tracts in the Rat Striatum.

Damage to myelinated axons contributes to neurological deficits after acute CNS injury, including ischemic and hemorrhagic stroke. Potential treatments to promote re-myelination will require fully differentiated oligodendrocytes, but almost nothing is known about their fate following intracerebral hemorrhage (ICH). Using a rat model of ICH in the striatum, we quantified survival, proliferation, and differentiation of oligodendrocyte precursor cells (OPCs) (at 1, 3, 7, 14, and 28 days) in the peri-hematoma region, surrounding striatum, and contralateral striatum. In the peri-hematoma, the density of Olig2+ cells increased dramatically over the first 7 days, and this coincided with disorganization and fragmentation of myelinated axon bundles. Very little proliferation (Ki67+) of Olig2+ cells was seen in the anterior subventricular zone from 1 to 28 days. However, by 3 days, many were proliferating in the peri-hematoma region, suggesting that local proliferation expands their population. By 14 days, the density of Olig2+ cells declined in the peri-hematoma region, and, by 28 days, it reached the low level seen in the contralateral striatum. At these later times, many surviving axons were aligned into white-matter bundles, which appeared less swollen or fragmented. Oligodendrocyte cell maturation was prevalent over the 28-day period. Densities of immature OPCs (NG2+Olig2+) and mature (CC-1+Olig2+) oligodendrocytes in the peri-hematoma increased dramatically over the first week. Regardless of the maturation state, they increased preferentially inside the white-matter bundles. These results provide evidence that endogenous oligodendrocyte precursors proliferate and differentiate in the peri-hematoma region and have the potential to re-myelinate axon tracts after hemorrhagic stroke.

Connexin-based channels contribute to metabolic pathways in the oligodendroglial lineage.

Oligodendrocyte precursor cells (OPCs) undergo a series of energy-consuming developmental events; however, the uptake and trafficking pathways for their energy metabolites remain unknown. In the present study, we found that 2-NBDG, a fluorescent glucose analog, can be delivered between astrocytes and oligodendrocytes through connexin-based gap junction channels but cannot be transferred between astrocytes and OPCs. Instead, connexin hemichannel-mediated glucose uptake supports OPC proliferation, and ethidium bromide uptake or increase of 2-NBDG uptake rate is correlated with intracellular Ca(2+) elevation in OPCs, indicating a Ca(2+)-dependent activation of connexin hemichannels. Interestingly, deletion of connexin 43 (Cx43, also known as GJA1) in astrocytes inhibits OPC proliferation by decreasing matrix glucose levels without impacting on OPC hemichannel properties, a process that also occurs in corpus callosum from acute brain slices. Thus, dual functions of connexin-based channels contribute to glucose supply in oligodendroglial lineage, which might pave a new way for energy-metabolism-directed oligodendroglial-targeted therapies.

Oligodendrocyte survival, proliferation, and maturation is dependent on 3D hydrogel mechanics

Event Abstract Back to Event Oligodendrocyte survival, proliferation, and maturation is dependent on 3D hydrogel mechanics Lauren N. Russell1 and Kyle Lampe1 1 University of Virginia, Chemical Engineering, United States Introduction: Millions of people suffer from damage or disease to the central nervous system (CNS), such as through a spinal cord injury or multiple sclerosis, resulting in a loss of myelin. In the CNS, oligodendrocytes extend processes which wrap around neuronal axons to generate myelin, an electrically insulating layer conducive to rapid, controlled neuronal signaling. Diminished myelin distorts and slows neuronal communication and causes neuronal degeneration and death. Cell loaded biomaterials are a potential method of repair, but have rarely been investigated for oligodendroglial specification[1]. Here, we investigate how mechanical properties of a polyethylene glycol based hydrogel affect proliferation and differentiation of two oligodendrocyte precursor cell (OPC) lines. Materials and Methods: Hydrogels with controllable storage moduli were formed by photoinitiation of methacrylated polyethylene glycol (PEG) with molecular weights and concentrations ranging from 4600 to 8000 g/mol and 7.5% to 20% (wt/v), respectively. Gelation was accomplished by photoinitiation of LAP at 365 nm and 4 mW/cm2 with OPCs[2],[3] encapsulated at 1x107 cells/ml. Both GFP+ MADM and N20.1 OPC cell lines were studied. ATP and DNA were quantitatively analyzed at discrete time points using high throughput luminescence and fluorescence assays to determine the viability and proliferation. LIVE/DEAD confocal microscopy verified ATP and DNA results. Results and Discussion: PEG molecular weights of 4600, 6000, and 8000 g/mol at 7.5% (wt/v) yielded hydrogels with storage moduli of 1,420 Pa, 795 Pa, and 418 Pa, respectively, similar to different regions of native brain tissue. LIVE/DEAD staining at 1 through 7 days indicated highest viability in the 4600 g/mol condition with high viability for all conditions at 7 days (Figure 1). DNA, cell number, and presence of colonies revealed that proliferation occurred in all conditions with the largest colonies present in less stiff hydrogels. When laminin was incorporated at 25 μg/ml, OPCs spread and extended processes, indicating maturation. Viability and proliferation was also impacted by hydrogel mechanics as the most compliant materials (lowest % wt/v) led to greatest ATP and DNA values with a significant increase over time (Figure 2). Conclusions: The material properties of PEG hydrogels influence oligodendrocyte-like cell proliferation, indicating their potential use in controlled growth of oligodendrocytes for CNS regeneration. In particular, these cell lines favor the more compliant matrices found with either the higher molecular weight conditions (Figure 1) or the lower weight percents of macromer during polymerization (Figure 2). Cellular morphology and process extension is also impacted by these features (Figure 1) and is being investigated toward maturation and oligodendrocyte regeneration. This is the first research to date showing a specific effect of hydrogel modulus on OPC proliferation and maturation. Current research is focused on incorporating topographical cues and degradable subunits into the hydrogel to promote a favorable intracellular redox state. UVA Biotechnology Training Program for fellowship to LNR; Zong and Gaultier labs at UVA for OPC cell lines

Abstract B16: Deciphering individual roles of p53 and NF1 in the cell of origin for malignant glioma and the implications of targeted therapy

Abstract Glioma is currently an incurable disease. Identifying the cell of origin for glioma could provide critical insights for developing effective therapies. We previously used a mouse genetic system termed Mosaic Analysis using Double Markers (MADM) to introduce p53 and NF1 mutations into neural stem cells to determine which cell type is responsible for gliomagenesis. The unequivocal GFP-labeling of sparse mutant cells generated by MADM enabled us to study the entire course of tumor development, from pre-transforming stages to full malignancy. Based on thorough histological, transcriptomic, and genetic analyses we identified oligodendrocyte precursor cells (OPCs) as the cell of origin in this glioma model. Here, we sought to understand the distinct role of p53 and NF1 in the transformation of OPCs since understanding these roles can give us a more thorough insight into how future therapies may be designed. The MADM system generates sparse GFP+ null and RFP+ sibling WT OPCs in an otherwise colorless, heterozygous mouse, allowing us to assess the impact of TSG loss on the capacity of cells to proliferate, survive, and differentiate. The loss of NF1 alone significantly increased mutant OPC proliferation with a proportional decrease in differentiation. However, massively over-expanded NF1-null OPCs did not transform into malignant gliomas, implicating the critical role of p53 in tumor suppression. Surprisingly, the loss of p53 alone had no effect on mutant OPC number, proliferation, or differentiation, suggesting that p53 function as a braking system that won't manifest its activity in the absence of driver mutation, such as NF1 loss. Next, we set out to test whether restoring either TSG function in tumor OPC cell lines would have any therapeutic efficacy. The restoration of wild type p53 led to a significant increase in both cell-cycle arrest and cell death. Since p53 function is commonly altered from mutations in patients, rather than complete loss of the protein, we tested whether restoring mutant p53 function with PRIMA-1 would have the same biological response as WT p53. We found that the restoration of mutant p53 function resulted in similar levels of cell cycle arrest and cell death as WT p53. This finding suggests that rescuing p53 function using small molecules may be of high value for future therapies. It also suggests that the loss of p53 activity is not a permanent fixture of tumor cells but that p53 can still exert it's tumor suppressor activity after transformation. Next we tested the therapeutic effects of the restoration of the GAP domain of NF1, which should reduce Ras activity in tumor OPCs. We found that the expression of WT but not the “GAP-dead” NF1-GAP led to a decrease in proliferation and an increase in differentiation of glioma cells. To test pharmacological compounds, we explore the possibility of targeting downstream effectors of Ras signaling, specifically mTOR inhibition because phospho-Akt level is elevated in tumor OPCs compared to WT OPCs. When we inhibited mTOR activity in MADM tumor mice at an age that is critical for mutant OPC expansion prior to transformation, we found that it blocked the ability of mutant OPCs to over-expand, suggesting that mTOR inhibition could potentially prevent gliomagenesis. In summary our data demonstrates that while NF1 loss increases OPC proliferation and decreases differentiation, p53 loss is critical for transformation and that restoring the function of either of these pathways has profound effects on tumor OPC biology that could be translated into future therapeutic strategies. Citation Format: Phillippe P. Gonzalez, Hui Zong. Deciphering individual roles of p53 and NF1 in the cell of origin for malignant glioma and the implications of targeted therapy. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B16.

Alterations in hippocampal myelin and oligodendrocyte precursor cells during epileptogenesis

Recent reports have described damage to myelinated fibers in the central nervous system (CNS) in patients with temporal lobe epilepsy (TLE) and animal models. However, only limited data are available on the dynamic changes that occur in myelinated fibers, oligodendrocytes (which are myelin-forming cells), and oligodendrocyte precursor cells (OPCs), which are a reservoir of new oligodendrocytes, in the hippocampus throughout epileptogenesis. The current study was designed to examine this issue using a rat model of lithium-pilocarpine-induced epilepsy. Electroencephalography (EEG), immunofluorescence, and Western blot analysis showed that the loss of myelin and oligodendrocytes in the rat hippocampus began during the acute stage of epileptogenesis, and the severity of this loss increased throughout epileptogenesis. Accompanying this loss of myelin and oligodendrocytes, OPCs in the rat hippocampus became activated and their populations increased during several phases of epileptogenesis (the acute, latent and chronic phases). The transcription factors olig1 and olig2, which play crucial roles in regulating OPC proliferation, differentiation and remyelination, were up-regulated during the early phases (the acute and latent phases) followed by a sharp decline in their expression during the chronic and late chronic phases.This study is the first to confirm the loss of myelin and oligodendrocytes during lithium-pilocarpine-induced epileptogenesis accompanied by a transient increase in the number of OPCs. Prevention of the loss of myelin and oligodendrocytes may provide a novel treatment strategy for epilepsy.

18β-glycyrrhetinic acid suppresses experimental autoimmune encephalomyelitis through inhibition of microglia activation and promotion of remyelination.

Microglia are intrinsic immune cells in the central nervous system (CNS). The under controlled microglia activation plays important roles in inflammatory demyelination diseases, such as multiple sclerosis (MS). However, the means to modulate microglia activation as a therapeutic modality and the underlying mechanisms remain elusive. Here we show that administration of 18β-glycyrrhetinic acid (GRA), by using both preventive and therapeutic treatment protocols, significantly suppresses disease severity of experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice. The treatment effect of GRA on EAE is attributed to its regulatory effect on microglia. GRA-modulated microglia significantly decreased pro-inflammatory profile in the CNS through suppression of MAPK signal pathway. The ameliorated CNS pro-inflammatory profile prevented the recruitment of encephalitogenic T cells into the CNS, which alleviated inflammation-induced demyelination. In addition, GRA treatment promoted remyelination in the CNS of EAE mice. The induced remyelination can be mediated by the overcome of inflammation-induced blockade of brain-derived neurotrophic factor expression in microglia, as well as enhancing oligodendrocyte precursor cell proliferation. Collectively, our results demonstrate that GRA-modulated microglia suppresses EAE through inhibiting microglia activation-mediated CNS inflammation, and promoting neuroprotective effect of microglia, which represents a potential therapeutic strategy for MS and maybe other neuroinflammatory diseases associated with microglia activation.

Rosiglitazone Promotes White Matter Integrity and Long-Term Functional Recovery After Focal Cerebral Ischemia.

Oligodendrogenesis is essential for white matter repair after stroke. Although agonists of peroxisome proliferator-activated receptors γ confer neuroprotection in models of cerebral ischemia, it is not known whether this effect extends to white matter protection. This study tested the hypothesis that the peroxisome proliferator-activated receptors γ agonist rosiglitazone enhances oligodendrogenesis and improves long-term white matter integrity after ischemia/reperfusion. Male adult C57/BL6 mice (25-30 g) were subjected to 60-minute middle cerebral artery occlusion and reperfusion. Rosiglitazone (3 mg/kg) was injected intraperitoneally once daily for 14 days beginning 2 hours after reperfusion. Sensorimotor and cognitive functions were evaluated ≤21 days after middle cerebral artery occlusion. Immunostaining was used to assess infarct volume, myelin loss, and microglial activation. Bromodeoxyuridine (BrdU) was injected for measurements of proliferating NG2(+) oligodendrocyte precursor cells (OPCs) and newly generated adenomatous polyposis coli(+) oligodendrocytes. Mixed glial cultures were used to confirm the effect of rosiglitazone on oligodendrocyte differentiation and microglial polarization. Rosiglitazone significantly reduced brain tissue loss, ameliorated white matter injury, and improved sensorimotor and cognitive functions for at least 21 days after middle cerebral artery occlusion. Rosiglitazone enhanced OPC proliferation and increased the numbers of newly generated mature oligodendrocytes after middle cerebral artery occlusion. Rosiglitazone treatment also reduced the numbers of Iba1(+)/CD16(+) M1 microglia and increased the numbers of Iba1(+)/CD206(+) M2 microglia after stroke. Glial culture experiments confirmed that rosiglitazone promoted oligodendrocyte differentiation, perhaps by promoting microglial M2 polarization. Rosiglitazone treatment improves long-term white matter integrity after cerebral ischemia, at least, in part, by promoting oligodendrogenesis and facilitating microglial polarization toward the beneficial M2 phenotype.

Remyelination After Cuprizone-Induced Demyelination Is Accelerated in Juvenile Mice

Remyelination capacity decreases with age in adult mice, but data comparing remyelination capacity after toxic demyelination in developing mice versus adult mice are not available. We treated 3-week-old and adult C57BL/6 mice with cuprizone for 1 to 5 weeks and studied demyelination/remyelination and cellular reactions in the corpus callosum and motor cortex by histology, immunohistochemistry, and electron microscopy. We compared results between the 2 treated groups and age-matched controls. In juvenile mice, significant demyelination was detectable in the corpus callosum on Week 2 and in the motor cortex on Week 5. Oligodendrocyte loss, microglial activation, and acute axonal damage peaked on Week 2. Increased numbers of oligodendrocyte precursor cells were evident on Week 1, and remyelination was detectable on Week 3. Juvenile mice showed more rapid demyelination than adult mice, which may be related to greater vulnerability of oligodendrocytes, lower myelin content, or dose-dependent cuprizone effects. Earlier activation of microglia and proliferation of oligodendrocyte precursor cells probably contributed to accelerated remyelination and less pronounced axonal damage. Our data indicate that oligodendroglial regeneration and remyelination are enhanced in the maturing rodent brain compared with the young-adult rodent brain.

Shh Signaling through the Primary Cilium Modulates Rat Oligodendrocyte Differentiation

Primary Cilia (PC) are a very likely place for signal integration where multiple signaling pathways converge. Two major signaling pathways clearly shown to signal through the PC, Sonic Hedgehog (Shh) and PDGF-Rα, are particularly important for the proliferation and differentiation of oligodendrocytes, suggesting that their interaction occurs in or around this organelle. We identified PC in rat oligodendrocyte precursor cells (OPCs) and found that, while easily detectable in early OPCs, PC are lost as these cells progress to terminal differentiation. We confirmed the interaction between these pathways, as cyclopamine inhibition of Hedgehog function impairs both PDGF-mediated OPC proliferation and Shh-dependent cell branching. However, we failed to detect PDGF-Rα localization into the PC. Remarkably, ciliobrevin-mediated disruption of PC and reduction of OPC process extension was counteracted by recombinant Shh treatment, while PDGF had no effect. Therefore, while PDGF-Rα-dependent OPC proliferation and survival most probably does not initiate at the PC, still the integrity of this organelle and cilium-centered pathway is necessary for OPC survival and differentiation.

Aspirin Promotes Oligodendroglial Differentiation Through Inhibition of Wnt Signaling Pathway.

Aspirin, one of the most commonly used anti-inflammatory drugs, has been recently reported to display multiple effects in the central nervous system (CNS), including neuroprotection and upregulation of ciliary neurotrophic factor (CNTF) expression in astrocytes. Although it was most recently reported that aspirin could promote the proliferation and differentiation of oligodendrocyte precursor cells (OPCs) after white matter lesion, the underlying mechanisms remain unclear. To dissect the effects of aspirin on oligodendroglial development and explore possible mechanisms, we here demonstrated the following: (i) in vitro treatment of aspirin on OPC cultures significantly increased the number of differentiated oligodendrocytes (OLs) but had no effect on the number of proliferative OPCs, indicating that aspirin can promote OPC differentiation but not proliferation; (ii) in vivo treatment of aspirin on neonatal (P3) rats for 4days led to a nearly twofold increase in the expression of myelin basic protein (MBP), devoid of change in OPC proliferaion, in the corpus callosum (CC); (iii) finally, aspirin treatment increased the phosphorylation level of β-catenin and counteracted Wnt signaling pathway synergist QS11-induced suppression on OPC differentiation. Together, our data show that aspirin can directly target oligodendroglial lineage cells and promote their differentiation through inhibition of Wnt/β-catenin signaling pathway. These findings suggest that aspirin may be a novel candidate for the treatment of demyelinating diseases.

Schwann cells induce Proliferation and Migration of Oligodendrocyte Precursor Cells Through Secretion of PDGF-AA and FGF-2.

Our previous study has showed that co-grafted Schwann cells (SCs) promote proliferation and migration of the grafted oligodendrocyte precursor cells (OPCs). However, how the co-grafted SCs affect OPCs has not been clarified. In the present study, we confirmed that SC-induced proliferation and migration of OPCs were mediated by SC-secreted factors using SC-conditioned medium (SCM). Then, we detected several candidate factors, PDGF-AA, FGF-2, and IGF-1, in SCs and SCM, and their receptors in OPCs. Finally, by using the selective inhibitors, the effects of these candidate factors on proliferation and migration of OPCs were examined. Our results showed that SCM-stimulated proliferation and migration of OPCs could be markedly decreased by both AG1295 (the inhibitor of PDGFR) and PD173074 (the inhibitor of FGFR). Together, our study suggests that SCs affect proliferation and migration of OPCs through secreting PDGF-AA and FGF-2. Identity of these molecules not only contributes to understand the mechanism of SC-induced proliferation and migration of OPCs but also provides possible target for treatment of CNS diseases.

Protective effects of recombinant human erythropoietin on oligodendrocyte after cerebral infarction

To study biological effect of recombinant human erythropoietin (RhEPO) on the expression of oligodendrocyte in the neuron glia antigen 2(NG2), Nogo receptor-interacting protein 1(LINGO-1), myelin basic protein (MBP) and myelin associated glycoprotein (MAG), and to explore the protective mechanism of RhEPO for oligodendrocyte after cerebral infarction. Experimental rats were randomly divided into the treatment group (RhEPO at a dose of 3 000 U/kg) or saline control group. Both groups received intraperitoneal injection of RhEPO after cerebral ischemia in 30 min, 3 h, 6 h, 12 h and 24 h, which was administered daily for 7 days. The modified neurological severity score (mNSS) and histology were analyzed, and immunohistochemistry was used to detect the protein expression of NG2, MAG, MBP and LINGO-1. The overall mNSS of RhEPO treatment group significantly decreased compared with the saline control group on the seventh day after cerebral infarction (P<0.05). Such treatment effect was more obvious in the treatment group at 30 min and 3 h (P<0.01). Compared with the saline control group, the numbers of NG2 positive cells increased in RhEPO treatment group. In contrast, the expression of LINGO-1 protein significantly decreased (P<0.05), with a dramatic decrease observed at 30 min and 3 h (P<0.01). However, the expression of MBP protein decreased more significantly in saline control group, while the level of the MAG protein expression increased. The differences were statistically significant (P<0.05), especially at 30 min (P<0.01). After cerebral ischemia, RhEPO promotes the proliferation of NG2 positive cells, and inhibits the expression of LINGO-1 and MAG proteins. RhEPO improves the proliferation and differentiation of oligodendrocyte precursor cells, which in turn protects neuronal function, particularly at the early phase of ischemia.

Experimental Demyelination and Remyelination of Murine Spinal Cord by Focal Injection of Lysolecithin

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system characterized by plaque formation containing lost oligodendrocytes, myelin, axons, and neurons. Remyelination is an endogenous repair mechanism whereby new myelin is produced subsequent to proliferation, recruitment, and differentiation of oligodendrocyte precursor cells into myelin-forming oligodendrocytes, and is necessary to protect axons from further damage. Currently, all therapeutics for the treatment of multiple sclerosis target the aberrant immune component of the disease, which reduce inflammatory relapses but do not prevent progression to irreversible neurological decline. It is therefore imperative that remyelination-promoting strategies be developed which may delay disease progression and perhaps reverse neurological symptoms. Several animal models of demyelination exist, including experimental autoimmune encephalomyelitis and curprizone; however, there are limitations in their use for studying remyelination. A more robust approach is the focal injection of toxins into the central nervous system, including the detergent lysolecithin into the spinal cord white matter of rodents. In this protocol, we demonstrate that the surgical procedure involved in injecting lysolecithin into the ventral white matter of mice is fast, cost-effective, and requires no additional materials than those commercially available. This procedure is important not only for studying the normal events involved in the remyelination process, but also as a pre-clinical tool for screening candidate remyelination-promoting therapeutics.