Cell death in the oligodendrocyte lineage: a molecular perspective of life/death decisions in development and disease

The Role of Hyperbaric Oxygen Therapy in Neuroregeneration and Neuroprotection: A Review

Neurogenesis is a high energy-demanding process, which is why blood vessels are an active part of the neurogenic niche since they allow the much-needed oxygenation of progenitor cells. In this regard, although neglected for a long time, the "oxygen niche" should be considered an important intervenient in adult neurogenesis. One possible hypothesis for the failure of numerous neuroprotective trials is that they relied on compounds that target a highly specific neuroprotective pathway. This approach may be too limited, given the complexity of the processes that lead to cell death. Therefore, research should adopt a more multifactorial approach. Among the limited range of agents with multimodal neuromodulatory capabilities, hyperbaric oxygen therapy has demonstrated effectiveness in reducing secondary brain damage in various brain injury models. This therapy functions not only as a neuroprotective mechanism but also as a powerful neuroregenerative mechanism.

An early glycolysis burst in microglia regulates mitochondrial dysfunction in oligodendrocytes under neuroinflammation

Metabolism and energy processes governing oligodendrocyte function during neuroinflammatory disease are of great interest. However, how varied cellular environments affect oligodendrocyte activity during neuroinflammation is unknown. We demonstrate that activated microglial energy metabolism controls oligodendrocyte mitochondrial respiration and activity. Lipopolysaccharide/interferon gamma promote glycolysis and decrease mitochondrial respiration and myelin protein synthesis in rat brain glial cells. Enriched microglia showed an early burst in glycolysis. In microglia-conditioned medium, oligodendrocytes did not respire and expressed less myelin. SCENITH revealed metabolic derangement in microglia and O4-positive oligodendrocytes in endotoxemia and experimental autoimmune encephalitogenic models. The early burst of glycolysis in microglia was mediated by PDPK1 and protein kinase B/AKT signaling. We found that microglia-produced NO and itaconate, a tricarboxylic acid bifurcated metabolite, reduced mitochondrial respiration in oligodendrocytes. During inflammation, we discovered a signaling pathway in microglia that could be used as a therapeutic target to restore mitochondrial function in oligodendrocytes and induce remyelination.

Hydrogel oxygen reservoirs increase functional integration of neural stem cell grafts by meeting metabolic demands

Injectable biomimetic hydrogels have great potential for use in regenerative medicine as cellular delivery vectors. However, they can suffer from issues relating to hypoxia, including poor cell survival, differentiation, and functional integration owing to the lack of an established vascular network. Here we engineer a hybrid myoglobin:peptide hydrogel that can concomitantly deliver stem cells and oxygen to the brain to support engraftment until vascularisation can occur naturally. We show that this hybrid hydrogel can modulate cell fate specification within progenitor cell grafts, resulting in a significant increase in neuronal differentiation. We find that the addition of myoglobin to the hydrogel results in more extensive innervation within the host tissue from the grafted cells, which is essential for neuronal replacement strategies to ensure functional synaptic connectivity. This approach could result in greater functional integration of stem cell-derived grafts for the treatment of neural injuries and diseases affecting the central and peripheral nervous systems.

Conditional depletion of GSK3b protects oligodendrocytes from apoptosis and lessens demyelination in the acute cuprizone model

Apoptosis is recognized as the main mechanism of oligodendrocyte loss in Multiple Sclerosis caused either by immune mediated injury (Barnett & Prineas, ) or a direct degenerative process (oligodendrogliapathy; Lucchinetti et al., ). Cuprizone induced demyelination is the result of non-immune mediated apoptosis of oligodendrocytes (OL) and represents a model of oligodendrogliapathy (Simmons, Pierson, Lee, & Goverman, ). Glycogen Synthase Kinase (GSK) 3b has been shown to be pro-apoptotic for cells other than OL. Here, we sought to investigate whether GSK3b plays a role in cuprizone-induced apoptosis of OL by using a novel inducible conditional knockout (cKO) of GSK3b in mature OL. While depletion of GSK3b has no effect on survival of uninjured OL, it increases survival of mature OL exposed to cuprizone. We show that GSK3b-deficient OLs are protected against caspase-dependent, but not against caspase-independent apoptosis. Active GSK3b is present in the nuclei of OL at peak of caspase-dependent apoptosis. Significant preservation of myelinated axons is associated with GSK3b depletion and glial cell activation is markedly reduced. Collectively, the data show that GSK3b is pro-apoptotic for caspase-dependent cell death, likely through activation of nuclear GSK3b and its depletion promotes survival of oligodendrocytes and attenuates myelin loss.

Creatine Enhances Mitochondrial-Mediated Oligodendrocyte Survival After Demyelinating Injury

Chronic oligodendrocyte loss, which occurs in the demyelinating disorder multiple sclerosis (MS), contributes to axonal dysfunction and neurodegeneration. Current therapies are able to reduce MS severity, but do not prevent transition into the progressive phase of the disease, which is characterized by chronic neurodegeneration. Therefore, pharmacological compounds that promote oligodendrocyte survival could be beneficial for neuroprotection in MS. Here, we investigated the role of creatine, an organic acid involved in adenosine triphosphate (ATP) buffering, in oligodendrocyte function. We found that creatine increased mitochondrial ATP production directly in oligodendrocyte lineage cell cultures and exerted robust protection on oligodendrocytes by preventing cell death in both naive and lipopolysaccharide-treated mixed glia. Moreover, lysolecithin-mediated demyelination in mice deficient in the creatine-synthesizing enzyme guanidinoacetate-methyltransferase (Gamt) did not affect oligodendrocyte precursor cell recruitment, but resulted in exacerbated apoptosis of regenerated oligodendrocytes in central nervous system (CNS) lesions. Remarkably, creatine administration into Gamt-deficient and wild-type mice with demyelinating injury reduced oligodendrocyte apoptosis, thereby increasing oligodendrocyte density and myelin basic protein staining in CNS lesions. We found that creatine did not affect the recruitment of macrophages/microglia into lesions, suggesting that creatine affects oligodendrocyte survival independently of inflammation. Together, our results demonstrate a novel function for creatine in promoting oligodendrocyte viability during CNS remyelination.SIGNIFICANCE STATEMENT We report that creatine enhances oligodendrocyte mitochondrial function and protects against caspase-dependent oligodendrocyte apoptosis during CNS remyelination. This work has important implications for the development of therapeutic targets for diseases characterized by oligodendrocyte death, including multiple sclerosis.

Early Postnatal Lipopolysaccharide Exposure Leads to Enhanced Neurogenesis and Impaired Communicative Functions in Rats

Perinatal infection is a well-identified risk factor for a number of neurodevelopmental disorders, including brain white matter injury (WMI) and Autism Spectrum Disorders (ASD). The underlying mechanisms by which early life inflammatory events cause aberrant neural, cytoarchitectural, and network organization, remain elusive. This study is aimed to investigate how systemic lipopolysaccharide (LPS)-induced neuroinflammation affects microglia phenotypes and early neural developmental events in rats. We show here that LPS exposure at early postnatal day 3 leads to a robust microglia activation which is characterized with mixed microglial proinflammatory (M1) and anti-inflammatory (M2) phenotypes. More specifically, we found that microglial M1 markers iNOS and MHC-II were induced at relatively low levels in a regionally restricted manner, whereas M2 markers CD206 and TGFβ were strongly upregulated in a sub-set of activated microglia in multiple white and gray matter structures. This unique microglial response was associated with a marked decrease in naturally occurring apoptosis, but an increase in cell proliferation in the subventricular zone (SVZ) and the dentate gyrus (DG) of hippocampus. LPS exposure also leads to a significant increase in oligodendrocyte lineage population without causing discernible hypermyelination. Moreover, LPS-exposed rats exhibited significant impairments in communicative and cognitive functions. These findings suggest a possible role of M2-like microglial activation in abnormal neural development that may underlie ASD-like behavioral impairments.

Galanin is an autocrine myelin and oligodendrocyte trophic signal induced by leukemia inhibitory factor

In order to further investigate the molecular mechanisms that regulate oligodendrocyte (OC) survival, we utilized microarrays to characterize changes in OC gene expression after exposure to the cytokines neurotrophin3, insulin, or leukemia inhibitory factor (LIF) in vitro. We identified and validated the induction and secretion of the neuropeptide galanin in OCs, specifically in response to LIF. We next established that galanin is an OC survival factor and showed that autocrine or paracrine galanin secretion mediates LIF-induced OC survival in vitro. We also revealed that galanin is up-regulated in OCs in the cuprizone model of central demyelination, and that oligodendroglial galanin expression is significantly regulated by endogenous LIF in this context. We also showed that knock-out of galanin reduces OC survival and exacerbates callosal demyelination in the cuprizone model. These findings suggest a potential role for the use of galanin agonists in the treatment of human demyelinating diseases.

Glial development: the crossroads of regeneration and repair in the CNS

Given the complexities of the mammalian CNS, its regeneration is viewed as the holy grail of regenerative medicine. Extraordinary efforts have been made to understand developmental neurogenesis, with the hopes of clinically applying this knowledge. CNS regeneration also involves glia, which comprises at least 50% of the cellular constituency of the brain and is involved in all forms of injury and disease response, recovery, and regeneration. Recent developmental studies have given us unprecedented insight into the processes that regulate the generation of CNS glia. Because restorative processes often parallel those found in development, we will peer through the lens of developmental gliogenesis to gain a clearer understanding of the processes that underlie glial regeneration under pathological conditions. Specifically, this review will focus on key signaling pathways that regulate astrocyte and oligodendrocyte development and describe how these mechanisms are reutilized in these populations during regeneration and repair after CNS injury.

High yields of oligodendrocyte lineage cells from human embryonic stem cells at physiological oxygen tensions for evaluation of translational biology

We have established and efficient system to specify NG2/PDGF-Rα/OLIG2+ oligodendrocyte precursor cells (OPCs) from human embryonic stem cells (hESCs) at low, physiological (3%) oxygen levels. This was achieved via both forebrain and spinal cord origins, with up to 98% of cells expressing NG2. Developmental insights reveal a critical role for fibroblast growth factor 2 (FGF-2) in OLIG2 induction via ventral forebrain pathways. The OPCs mature in vitro to express O4 (46%) and subsequently become galactocerebroside (GALC), O1, and myelin basic protein-positive (MBP+) multibranching oligodendrocytes. These were cultured alongside hESC-derived neurons. The electrophysiological properties of human OPCs are similar to those of rat OPCs, with large voltage-gated sodium currents and the ability to fire action potentials. Exposure to a selective retinoid X receptor agonist increased the proportion of O4+ oligodendrocytes that express MBP from 5% to 30%. Thus, we have established a developmentally engineered system to investigate the biological properties of human OPCs and test the effects of putative remyelinating agents prior to clinical application.

Thymoquinone-induced reactive oxygen species causes apoptosis of chondrocytes via PI3K/Akt and p38kinase pathway

Thymoquinone (TQ), a bioactive ingredient of the volatile oil of black seed (Nigella sativa), has been shown to possess anti-neoplastic and anti-inflammatory effects on a variety of tumours. However, the precise mechanism of action is not clear in normal cells such as primary chondrocytes. So, we have investigated the effects of TQ on the apoptosis of chondrocytes with a focus on reactive oxygen species (ROS) production. In in vitro experiments, chondrocytes were cultured with increasing concentrations of TQ for 24 h or with 20 µmol/L TQ for the indicated time periods, and various experiments were performed to detect the apoptotic effects caused by TQ. The results showed that TQ significantly increases apoptosis. Apoptosis was dose- and time-dependently expressed, and the generation of ROS also dramatically increased in a dose-dependent manner. Pretreatment of N-acetyl-L-cysteine (NAC), an inhibitor of ROS, inhibited both TQ-induced apoptosis and ROS generation. Also, TQ up-regulated phosphorylation of phosphatidylinositol 3-kinase/Akt (PI3K/Akt) and mitogen-activated protein kinases ([MAPKs] p38kinase, ERK-1/-2, and JNKinase), and these effects were prevented by pretreatment of NAC. However, pretreatment with inhibitors of PI3K/Akt and MAPKs did not inhibit TQ-caused ROS generation. Among the inhibitors of PI3K/Akt, p38kinase, ERK-1/-2, and JNKinase, pretreatment with LY294002 and SB203580 abolished TQ-induced apoptosis, but PD98059 and SP600125 did not have any effect on TQ-caused apoptosis. These findings suggest that TQ-induced ROS generation regulates apoptosis by modulating PI3K/Akt and p38kinase pathways.

Inhibition of Cell Growth and Induction of Apoptosis by Antrodia camphorata in HER-2/neu-Overexpressing Breast Cancer Cells through the Induction of ROS, Depletion of HER-2/neu, and Disruption of the PI3K/Akt Signaling Pathway

Previously, we demonstrated that a submerged fermentation culture of Antrodia camphorata (AC) promotes cell-cycle arrest and apoptosis in human estrogen receptor-positive/negative breast cancer cells. However, whether AC is effective against HER-2/neu-overexpressing breast cancers has not been thoroughly elucidated. In the present study, we showed that AC exhibited a significant cytotoxic effect against HER-2/neu-overexpressing MDA-MB-453 and BT-474 cells. Immunoblot analysis demonstrated that HER-2/neu and their tyrosine phosphorylation were inhibited by AC in a dose-dependent manner. An increase in intracellular reactive oxygen species (ROS) was observed in AC-treated cells, whereas antioxidant N-acetylcysteine (NAC) significantly prevented AC induced HER-2/neu depletion and cell death, which directly indicates that AC-induced HER-2/neu depletion and cell death was mediated by ROS generation. Also, AC significantly downregulated the expression of cyclin D1, cyclin E, and CDK4 followed by the suppression of PI3K/Akt, and their downstream effectors GSK-3β and β-catenin. Notably, AC-treatment induced apoptotic cell death, which was associated with sub-G1 accumulation, DNA fragmentation, mitochondrial dysfunction, cytochrome c release, caspase-3/-9 activation, PARP degradation, and Bcl-2/Bax dysregulation. Assays for colony formation also confirmed the growth-inhibitory effects of AC. This is the first report confirming the anticancer activity of this potentially beneficial mushroom against human HER-2/neu-overexpressing breast cancers.

Synergistic activity of interleukin-17 and tumor necrosis factor-α enhances oxidative stress-mediated oligodendrocyte apoptosis

Th1 cytokine-induced loss of oligodendrocytes (OLs) is associated with axonal loss in CNS demyelinating diseases such as multiple sclerosis (MS)that contributes to neurological disabilities in affected individuals. Recent studies indicated that, in addition to Th1-phenotype cytokines including tumor necrosis factor (TNF)-α, Th17 phenotype cytokine, interleukin (IL)-17 also involved in the development of MS. In this study, we investigated the direct effect of IL-17 on the survival of OLs in the presence of TNF-α and individually in vitro settings. Our findings suggest that IL-17 alone, however, was not able to affect the survival of OLs, but it exacerbates the TNF-α-induced OL apoptosis as compared with individual TNF-α treatment. This effect of cytokines was ascribed to an inhibition of cell-survival mechanisms, co-localization of Bid/Bax proteins in the mitochondrial membrane and caspase 8 activation mediated release of apoptosis inducing factor from mitochondria in treated OLs. In addition, cytokine treatment disturbed the mitochondrial membrane potential in OLs with corresponding increase in the generation of reactive oxygen species, which were attenuated by N-acetyl cysteine treatment. In addition, combining of these cytokines induced cell-cycle arrest at G1/S phases in OL-like cells and inhibited the maturation of OL progenitor cells that was attenuated by peroxisome proliferator-activated receptor-γ/-β agonists. Collectively, these data provide initial evidence that IL-17 exacerbates TNF-α-induced OL loss and inhibits the differentiation of OL progenitor cells suggesting that antioxidant- or peroxisome proliferator-activated receptor agonist-based therapies have potential to limit CNS demyelination in MS or other related demyelinating disorders.

Proteomics identification and annotation of proteins of a cell line of Bombyx mori, BmN cells

A cell line is an important experimental platform for biological sciences as it can basically reflect the biology of its original organism. In this study, we firstly characterized the proteome of cultured BmN cells, derived from Bombyx mori. Total 1478 proteins were identified with two or more peptides by using 1D (one-dimensional) SDS/PAGE and LTQ-Orbitrap. According to the gene ontology annotation, these proteins presented diverse pI values and molecular masses, involved in various molecular functions, including catalytic activity, binding, molecular transducer activity, motor activity, transcription regulator activity, enzyme regulator activity and antioxidant activity. Some proteins related to virus infection were also identified. These results provided us with useful information to understand the molecular mechanism of B. mori as well as antiviral immunity.

Involvement of Fractin in TGF-beta-induced apoptosis in oligodendroglial progenitor cells

Transforming growth factor-beta (TGF-beta) induces apoptotic cell death during the development of the nervous system. We recently identified that TGF-beta induced apoptosis in oligodendroglial progenitor cells (primary cells as well as oligodendroglial cell line OLI-neu) is characterized by down-regulation of Bcl-xl. In this report, we now focused on mechanisms that mediate TGF-beta dependent Bcl-xl down-regulation in oligodendroglial cells. We showed that the caspase-specific cleavage product Fractin is produced in oligodendroglial cells during TGF-beta-mediated apoptosis, which represents an early event of the cascade. Cleavage of actin into Fractin was dependent on functional actin and caspases, and occurred simultaneously with a Fractin-Bcl-xl-interaction. This Fractin-Bcl-xl interaction indicated a connection between Bcl-xl down-regulation and Fractin appearance, since Bcl-xl regulation was also dependent on caspases and functional actin, and an overexpression of Fractin induced a Bcl-xl protein down-regulation. Further analysis of Fractin-Bcl-xl interaction in other culture systems confirmed these data. In conclusion, we show that Fractin is not only an apoptotic marker, but has indeed a functional role in apoptotic signaling in oligodendrocytes.

Molecular mechanisms involved in injury to the preterm brain

Injury to the premature brain is a major contributor to infant mortality and morbidity, often leading to mental retardation and sensory-motor impairment. The disease process is believed to be caused, sustained, and aggravated by multiple perinatal factors that team up in a multi-hit fashion. Clinical, epidemiological, and experimental studies have revealed that key factors such as inflammation, excitotoxicity, and oxidative stress contribute considerably to white- and gray-matter injury in premature infants, whose brains are particularly susceptible to damage. Depending on the timing, lesions of the immature brain may influence developmental events in their natural sequence and redirect subsequent development. We review current concepts on molecular mechanisms underlying injury to the premature brain.

The role of oxygen in regulating neural stem cells in development and disease

Oxygen (O2) is a substrate for energy production in the cell and is a rapid regulator of cellular metabolism. Recent studies have also implicated O2 and its signal transduction pathways in controlling cell proliferation, fate, and morphogenesis during the development of many tissues, including the nervous system. O2 tensions in the intact brain are much lower than in room air, and there is evidence that dynamic control of O2 availability may be a component of the in vivo neural stem cell (NSC) niche. At lower O2 tensions, hypoxia-inducible factor 1alpha (HIF1alpha) facilitates signal transduction pathways that promote self-renewal (e.g., Notch) and inhibits pathways that promote NSC differentiation or apoptosis (e.g., bone morphogenetic proteins). Increasing O2 tension degrades HIF1alpha, thus promoting differentiation or apoptosis of NSCs and progenitors. These dynamic changes in O2 tension can be mimicked to optimize ex vivo production methods for cell replacement therapies. Conversely, disrupted O2 availability may play a critical role in disease states such as stroke or brain tumor progression. Hypoxia during stroke activates precursor proliferation in vivo, while glioblastoma stem cells proliferate maximally in a more hypoxic environment than normal stem cells, which may make them resistant to certain anti-neoplastic therapies. These findings suggest that O2 response is central to the normal architecture and dynamics of NSC regulation and in the etiology and treatment of brain diseases.

In vitro and in vivo pharmacological models to assess demyelination and remyelination

In making a selection of cellular tools and animal models for generating screening assays in the search for new drugs, one needs to take into consideration the practicality of their use in the drug discovery process. Conducting high-throughput primary screens using libraries of small molecules, close to 1 million members in size, requires the generation of large numbers of cells which are easily acquired, reliably enriched, and reproducibly responsive to standard positive controls. These cells need to be similar in form and function to their counterparts in human disease. In vitro assays that can be mechanized by using robots can therefore save time and costs. In selecting in vivo models, consideration must be given to the species and strain of animal chosen, the appropriateness of the model to human disease, the extent of animal husbandry required during the in-life pharmacological assessment, the technical aspects of generating the model and harvesting the tissues for analyses, the cost of research tools in terms of time and money (demyelinating and remyelinating agents, amount of compound to be generated), and the length of time required for drug testing in the model. A consideration of the translational aspects of the in vivo model compared to those used in the clinic is also important. These themes will be developed with examples for drug discovery in the field of CNS demyelination and repair, specifically as it pertains to multiple sclerosis.

Involvement of the Bcl-2 family members in Pinus massoniana bark extract induced apoptosis in HeLa cells

Pinus massoniana bark extract (PMBE) contains a variety of flavonoids whose antioxidant properties have been confirmed in vitro. This study was undertaken to evaluate the cytotoxic effects and the mechanism of cell death on the PMBE-treated human cervical cancer cell line, HeLa. PMBE treatment led to cell growth inhibition in a dose- and time-dependent manner, and PMBE-induced apoptosis was confirmed by DAPI staining, TUNEL assays and sub-G1 phase accumulation. Cell cycle was also arrested in G2/M phase. Immunoblotting analysis showed that cytochrome c was released, the protein expression of Bax was increased, the protein expression of Bcl-2 was down-regulated and caspase-9 and -3 were activated in PMBE-treated HeLa cells. Taken together, PMBE inhibited proliferation, induces apoptosis and causes cell cycle arrest in HeLa cells, indicating that PMBE may be a potential therapeutic agent for cancer.

The life, death, and replacement of oligodendrocytes in the adult CNS

Oligodendrocytes (OLs) are mature glial cells that myelinate axons in the brain and spinal cord. As such, they are integral to functional and efficient neuronal signaling. The embryonic lineage and postnatal development of OLs have been well-studied and many features of the process have been described, including the origin, migration, proliferation, and differentiation of precursor cells. Less clear is the extent to which OLs and damaged/dysfunctional myelin are replaced following injury to the adult CNS. OLs and their precursors are very vulnerable to conditions common to CNS injury and disease sites, such as inflammation, oxidative stress, and elevated glutamate levels leading to excitotoxicity. Thus, these cells become dysfunctional or die in multiple pathologies, including Alzheimer's disease, spinal cord injury, Parkinson's disease, ischemia, and hypoxia. However, studies of certain conditions to date have detected spontaneous OL replacement. This review will summarize current information on adult OL progenitors, mechanisms that contribute to OL death, the consequences of their loss and the pathological conditions in which spontaneous oligodendrogenesis from endogenous precursors has been observed in the adult CNS.

Increasing in situ nick end labeling of oligodendrocytes in white matter of patients with Binswanger's disease

Increasing evidence suggests the presence of apoptotic cell death in many neurodegenerative diseases. However, in Binswanger's disease (BD), no information is available concerning the apoptosis-related pathologic changes that may occur in the white matter. To investigate whether apoptotic cell death is included in the pathophysiology of the white matter changes in BD, autopsied brains from patients with BD (n = 5) were compared with those of non-neurologic controls (n = 5). Terminal deoxynucleotidyl transferase-mediated dUTP in situ nick end labeling (TUNEL) was used as a marker for cell damage with DNA fragmentation. A proteolipid protein (PLP) messenger RNA (mRNA) hybridization signal was also used as a sensitive and specific marker of oligodendrocytes as well as glial fibrillary acidic protein (GFAP) immunoreactivity as a marker of astrocytes. There were frequent TUNEL-positive cells in the rarefied white matter of patients with BD. TUNEL-positive cells were found 15-fold more numerously in BD than in controls (P < .01). TUNEL-positive cells were presumably oligodendrocytes because of their coexpression with PLP mRNA. The numbers of GFAP-positive astrocytes were significantly decreased in BD compared with those in control subjects. The reduction in numbers of PLP mRNA-positive oligodendrocytes were also seen in BD, but these changes did not reach the level of significance. The pathologic alterations in BD brains include increased TUNEL-positive oligodendrocytes, associated with degradation of myelin. Although TUNEL-positive glial cells did not show typical apoptotic morphologic features, these findings suggest that increase in in situ nick end labeling of oligodendrocytes in white matter may play an important role in the pathophysiology of BD.

Oxygen tension regulates survival and fate of mouse central nervous system precursors at multiple levels

Despite evidence that oxygen regulates neural precursor fate, the effects of changing oxygen tensions on distinct stages in precursor differentiation are poorly understood. We found that 5% oxygen permitted clonal and long-term expansion of mouse fetal cortical precursors. In contrast, 20% oxygen caused a rapid decrease in hypoxia-inducible factor 1alpha and nucleophosmin, followed by the induction of p53 and apoptosis of cells. This led to a decrease in overall cell number and particularly a loss of astrocytes and oligodendrocytes. Clonal analysis revealed that apoptosis in 20% oxygen was due to a complete loss of CD133(lo)CD24(lo) multipotent precursors, a substantial loss of CD133(hi)CD24(lo) multipotent precursors, and a failure of remaining CD133(hi)CD24(lo) cells to generate glia. In contrast, committed neuronal progenitors were not significantly affected. Switching clones from 5% to 20% oxygen only after mitogen withdrawal led to a decrease in total clone numbers but an even greater decrease in oligodendrocyte-containing clones. During this late exposure to 20% oxygen, bipotent glial (A2B5+) and early (platelet-derived growth factor receptor alpha) oligodendrocyte progenitors appeared and disappeared more quickly, relative to 5% oxygen, and late stage O4+ oligodendrocyte progenitors never appeared. These results indicate that multipotent cells and oligodendrocyte progenitors are more susceptible to apoptosis at 20% oxygen than committed neuronal progenitors. This has important implications for optimizing ex vivo production methods for cell replacement therapies.

Hypoxic-ischemic injury in the immature brain--key vascular and cellular players

Over the past decade, much has been learned about the cellular and molecular mechanisms underlying hypoxic-ischemic (H-I) injury in the preterm human brain. The pathogenesis of H-I brain injury is now understood to be multifactorial and quite complex, depending on (i) the severity, intensity and timing of asphyxia, (ii) selective ischemic vulnerability, (iii) the degree of maturity of the brain, and (iv) the characteristics of the ensuing reoxygenation/reperfusion phase. Each of these factors has differential effects on the distinct cell populations in the brain, with certain specific cell types being particularly vulnerable in the developing brain. In this review, we discuss the role of the blood vessels and the distinct cell populations, which are the mayor constitutive elements of the immature brain, in the pathophysiology of H-I lesion. The presence of fragile and poorly anastomosed blood vessels and the existence of disturbances in the blood-brain barrier alter blood flow, vascular tone and nutrient delivery. Brain cells are sensitive to the overstimulation of neurotransmitter receptors, particularly glutamate receptors, which can provoke excitotoxicity leading to the death of neurons and other cells such as astrocytes and oligodendrocyte progenitors. Microglial activation by means of excitatory amino acids and by leukocyte migration initiates the inflammatory response giving rise to an increase in regional cerebral blood flow and promoting astrocyte and oligodendrocyte injuries. A better understanding of these aspects of H-I injury will contribute to more efficient strategies for the management of the associated damage.

The Yin and Yang of cell cycle progression and differentiation in the oligodendroglial lineage

In white matter disorders such as leukodystrophies (LD), periventricular leucomalacia (PVL), or multiple sclerosis (MS), the hypomyelination or the remyelination failure by oligodendrocyte progenitor cells involves errors in the sequence of events that normally occur during development when progenitors proliferate, migrate through the white matter, contact the axon, and differentiate into myelin-forming oligodendrocytes. Multiple mechanisms underlie the eventual progressive deterioration that typifies the natural history of developmental demyelination in LD and PVL and of adult-onset demyelination in MS. Over the past few years, pathophysiological studies have mostly focused on seeking abnormalities that impede oligodendroglial maturation at the level of migration, myelination, and survival. In contrast, there has been a strikingly lower interest for early proliferative and differentiation events that are likely to be equally critical for white matter development and myelin repair. This review highlights the Yin and Yang principles of interactions between intrinsic factors that coordinately regulate progenitor cell division and the onset of differentiation, i.e. the initial steps of oligodendrocyte lineage progression that are obviously crucial in health and diseases.

Transplantation of human embryonic stem cell-derived oligodendrocyte progenitors into rat spinal cord injuries does not cause harm

Demyelination contributes to loss of function following spinal cord injury. We have shown previously that transplantation of human embryonic stem cell-derived oligodendrocyte progenitors into adult rat 200 kD contusive spinal cord injury sites enhances remyelination and promotes recovery of motor function. Previous studies using oligodendrocyte lineage cells have noted a correlation between the presence of demyelinating pathology and the survival and migration rate of the transplanted cells. The present study compared the survival and migration of human embryonic stem cell-derived oligodendrocyte progenitors injected 7 days after a 200 or 50 kD contusive spinal cord injury, as well as the locomotor outcome of transplantation. Our findings indicate that a 200 kD spinal cord injury induces extensive demyelination, whereas a 50 kD spinal cord injury induces no detectable demyelination. Cells transplanted into the 200 kD injury group survived, migrated, and resulted in robust remyelination, replicating our previous studies. In contrast, cells transplanted into the 50 kD injury group survived, exhibited limited migration, and failed to induce remyelination as demyelination in this injury group was absent. Animals that received a 50 kD injury displayed only a transient decline in locomotor function as a result of the injury. Importantly, human embryonic stem cell-derived oligodendrocyte progenitor transplants into the 50 kD injury group did not cause a further decline in locomotion. Our studies highlight the importance of a demyelinating pathology as a prerequisite for the function of transplanted myelinogenic cells. In addition, our results indicate that transplantation of human embryonic stem cell-derived oligodendrocyte progenitor cells into the injured spinal cord is not associated with a decline in locomotor function.

Proteasome inhibition by MG-132 induces apoptotic cell death and mitochondrial dysfunction in cultured rat brain oligodendrocytes but not in astrocytes

Proteasomal dysfunction has been implicated in neurodegenerative disorders and during aging processes. In frontotemporal dementias, corticobasal degeneration, and progressive supranuclear palsy, oligodendrocytes are specifically damaged. Application of proteasomal inhibitors to cultured oligodendrocytes is associated with apoptotic cell death. The present study was undertaken to investigate the death pathway activated in oligodendrocytes by proteasomal inhibition. Our data show that the proteasomal inhibitor MG-132 causes oxidative stress, as indicated by the upregulation of the small heat shock protein heme oxygenase-1 (HO-1) and the appearance of oxidized proteins. Activation of the mitochondrial pathway was involved in the apoptotic process. Mitochondrial membrane potential was disturbed, and cytochrome c was released from the mitochondria. Concomitantly, death-related caspases 3 and 9 were activated and poly(ADP-ribose)-polymerase cleavage occurred. MG-132-induced cell death, DNA-fragmentation, and caspase activation could be prevented by the broad caspase inhibitor zVAD-fmk. In contrast to oligodendrocytes, cultured astrocytes showed resistance to the treatment with proteasomal inhibitors and did not reveal cytotoxic responses. This was also observed in astrocytes differentiated in the presence of dibutyryl cyclic AMP. Hence, individual cells respond differently to proteasomal inhibition and the therapeutic use of proteasomal inhibitors, e.g. for the treatment of cancer or inflammatory diseases, needs to be carefully evaluated.

Studies on cleavage of DNA by N-phosphoryl branched peptides

It was found that Nalpha,Nepsilon-di[N-(O,O-diisopropyl)phosphoryl-L-leucy]-L-lysyl-methyl ester (1) and Nalpha,Nepsilon-di[N-(O,O-diisopropyl)phosphoryl-L-phenylalanyl]-L-lysyl-methyl ester (2) could cleave supercoiled DNA such as PUC19 efficiently in 40 mM Britton-Robinson buffer. The cleavage activities for both were investigated by agarose gel electrophoresis. The T4 ligase experiments implied that the cleavage of DNA occurs via a hydrolytic path. The results showed that the cleavage reaction of DNA is dependent on the value of pH and ionic strength in the solution. DNA cleavage is more efficient by N-phosphoryl branched peptide 2 than by N-phosphoryl branched peptide 1. The experiments also show that hydrolysis of DNA by N-phosphoryl branched peptide 1 was accelerated in the presence of Mg2+ or Zn2+ ions. The interactions of DNA with N-phosphoryl branched peptides were also characterized by melting temperature measurements and circular dichroism (CD) techniques. On the basis of experimental data, the possible mechanism of interactions between DNA with N-phosphoryl branched peptides was discussed.

Lung disease and brain development

With the technical progress made in fetal and neonatal intensive care, perinatal mortality has decreased by 25% over the last decade and has expanded the surviving premature population. Prematurity drastically changes the environment of the developing organism. Striking evidence from a number of disciplines has focused attention on the interplay between the developing organism and the circumstances in which it finds itself. The environmental event during a sensitive period in development, induces injury and/or biological adaptations that lead to altered differentiation of tissues. The organism can express specific adaptive responses to its environment which include short-term changes in physiology as well as long-term adjustments. This review addresses these short-term as well as longer-term changes occurring in lung and brain tissue and illustrates how these changes can be studied using advanced imaging techniques such as magnetic resonance imaging

Tumor necrosis factor-alpha and alphaB-crystallin up-regulation during antibody-mediated demyelination in vitro: a putative protective mechanism in oligodendrocytes

By using an in vitro model of antibody-mediated demyelination, we investigated the relationship between tumor necrosis factor-alpha (TNF-alpha) and heat shock protein (HSP) induction with respect to oligodendrocyte survival. Differentiated aggregate cultures of rat telencephalon were subjected to demyelination by exposure to antibodies against myelin oligodendrocyte glycoprotein (MOG) and complement. Cultures were analyzed 48 hr after exposure. Myelin basic protein (MBP) expression was greatly decreased, but no evidence was found for either necrosis or apoptosis. TNF-alpha was significantly up-regulated. It was localized predominantly in neurons and to a lesser extent in astrocytes and oligodendrocytes, and it was not detectable in microglial cells. Among the different HSPs examined, HSP32 and alphaB-crystallin were up-regulated; they may confer protection from oxidative stress and from apoptotic death, respectively. These results suggest that TNF-alpha, often regarded as a promoter of oligodendroglial death, could alternatively mediate a protective pathway through alphaB-crystallin up-regulation.

Mitochondrial pathway is involved in hydrogen-peroxide-induced apoptotic cell death of oligodendrocytes

Oligodendrocytes, the myelin-forming cells of the CNS, are specifically sensitive to oxidative stress and respond by the onset of programmed cell death (PCD). To further unravel the molecular events underlying their enhanced susceptibility, we have investigated whether mitochondrial damage occurs during oxidative stress-induced PCD in cultured rat brain oligodendrocytes. Mitochondria are considered as a central control point of apoptosis, and mitochondrial dysfunction has been linked to neurodegenerative disease. Upon a number of stimuli through the release of cytochrome c, they coordinate caspase activation, causing morphological and biochemical changes associated with PCD. Oxidative stress was exerted by the application of hydrogen peroxide. The data show that hydrogen peroxide-induced apoptosis in oligodendrocytes involves mitochondrial damage and cytochrome c release and is accompanied by the activation of the death-related caspases 3 and 9. Concomitantly, the activation and nuclear translocation of extracellular signal regulated kinases ERK1,2 are observed, which have been implicated to participate in the regulation of cell death and survival. DNA fragmentation could not be attenuated by the ERK1,2 inhibitor PD 98059, indicating that the ERK1,2- pathway in oligodendrocytes may be involved in the initial survival response after exposure to stressful stimuli.

The life and death of oligodendrocytes in vanishing white matter disease

Vanishing white matter disease (VWM) is a progressive cavitating disease of central white matter due to a deficiency of the translation initiation factor eIF2B. Oligodendrocytes appear to be numerically increased in some white matter areas, while decreased in others. We compared oligodendrocytes of cerebral, cerebellar, and pontine white matter from 5 VWM patients with those of age-matched controls by light microscopy and immunohistochemistry using antibodies to activated caspase-3, bak, bax, bcl-2, survivin, and Ki-67, as well as by the TUNEL technique. Oligodendrocytes were identified morphologically and quantified using an ocular grid. We observed statistically significant increases in their densities at all sites; Ki-67-labeled oligodendrocytes were identified in 2 of 5 patients. Apoptotic oligodendrocytes were documented in 3 of 5 patients, while bcl-2 and survivin labeling was observed in 2 of 5 and 2 of 2 patients, respectively. There was a trend toward an increase in apoptotic labeling of oligodendrocytes that was strongest in the cerebrum, the major locus of VWM, in the youngest and most severely affected patients. These data conclusively demonstrate increased oligodendrocytic densities in VWM; the increase is not an artifact of white matter contraction. Our data also document that oligodendrocytes undergo apoptosis, perhaps in conjunction with major neurologic crises, and that a subset of oligodendrocytes are able to persist and proliferate. Conflicting proliferative, cell-death, and survival signals impact the oligodendrocytes of VWM.

Degenerative and regenerative mechanisms governing spinal cord injury

Spinal cord injury (SCI) is a major cause of disability, and at present, there is no universally accepted treatment. The functional decline following SCI is contributed to both direct mechanical injury and secondary pathophysiological mechanisms that are induced by the initial trauma. These mechanisms initially involve widespread haemorrhage at the site of injury and necrosis of central nervous system (CNS) cellular components. At later stages of injury, the cord is observed to display reactive gliosis. The actions of astrocytes as well as numerous other cells in this response create an environment that is highly nonpermissive to axonal regrowth. Also manifesting important effects is the immune system. The early recruitment of neutrophils and at later stages, macrophages to the site of insult cause exacerbation of injury. However, at more chronic stages, macrophages and recruited T helper cells may potentially be helpful by providing trophic support for neuronal and non-neuronal components of the injured CNS. Within this sea of injurious mechanisms, the oligodendrocytes appear to be highly vulnerable. At chronic stages of SCI, a large number of oligodendrocytes undergo apoptosis at sites that are distant to the vicinity of primary injury. This leads to denudement of axons and deterioration of their conductive abilities, which adds significantly to functional decline. By indulging into the molecular mechanisms that cause oligodendrocyte apoptosis and identifying potential targets for therapeutic intervention, the prevention of this apoptotic wave will be of tremendous value to individuals living with SCI.

Relapsing and remitting multiple sclerosis: pathology of the newly forming lesion

The study describes the clinical and pathological findings in 12 patients with relapsing and remitting multiple sclerosis, who died during or shortly after the onset of a relapse. Pathological changes not previously associated with the formation of new symptomatic lesions were observed in seven cases, namely, extensive oligodendrocyte apoptosis and microglial activation in myelinated tissue containing few or no lymphocytes or myelin phagocytes. No current laboratory model of multiple sclerosis, in particular, experimental allergic encephalomyelitis, is known with these features, which raises the possibility of some novel process underlying new lesion formation in multiple sclerosis.

Radiation-induced apoptosis of oligodendrocytes and its association with increased ceramide and down-regulated protein kinase B/Akt activity

PURPOSE

Oligodendrocytes are cells responsible for myelination in the central nervous system and have been shown to undergo radiation-induced apoptosis. The roles of ceramide and protein kinase B/Akt (PKB/Akt) were assessed in radiation-induced apoptosis of oligodendrocytes in vitro.

MATERIALS AND METHODS

Primary cultures of oligodendrocytes were established from neonatal rat brains and cell identity was assessed by immunohistochemistry. Apoptosis was assessed histologically according to its specific morphologic features using 4',6-diaminido-2-phenylindole, and by transferase-mediated deoxynucleotidyl transferase nick end-labelling staining. The ceramide level was measured using a diacyglycerol kinase assay, and PKB/Akt activity was determined using immunoblotting and a protein kinase assay.

RESULTS

Ionizing radiation, C2-ceramide or wortmannin induced apoptosis in oligodendrocytes but not astrocytes. A rapid increase in ceramide was observed in oligodendrocytes after ionizing radiation. Monensin, an inhibitor of acid sphingomyelinase, reduced the apoptotic response in oligodendrocytes after ionizing radiation. Fumonisin B1, an inhibitor of ceramide synthase, showed no such effect in the cells. Radiation-induced apoptosis of oligodendrocytes was associated with a decrease in PKB activity, similar to that observed after treatment with C2-ceramide or wortmannin, but not after dihydro-C2-ceramide. Confocal microscopy revealed a loss of phosphorylated PKB immunostaining in the nucleus of apoptotic oligodendrocytes after ionizing radiation or C2-ceramide treatment. The level of phosphorylated FKHRL1, a transcription factor phosphorylated by PKB, decreased in irradiated oligodendrocytes.

CONCLUSIONS

A ceramide-PKB-mediated signalling pathway might play a role in radiation-induced apoptosis of oligodendrocytes.

Chemical inhibitors of cyclin-dependent kinases control proliferation, apoptosis and differentiation of oligodendroglial cells

Since cyclin-dependent kinases (Cdks) and their endogenous inhibitors (Cdkis) play an essential role as regulators of cell cycle withdrawal and onset of differentiation within oligodendroglial cells, we assessed here the effects of exogenous chemical Cdk inhibitors (CKIs) on cultured rat cortical oligodendrocyte progenitor cells (OPCs). We showed that purine derivatives and especially roscovitine strongly inhibited OPCs proliferation. In the presence of mitogenic signals, roscovitine synergized with thyroid hormone to stimulate oligodendrocyte differentiation. Roscovitine also prevented oligodendroglial apoptosis induced by growth factor deprivation. We thus demonstrated that small molecular weight chemical CKIs have important effects on crucial events of oligodendroglial development in vitro. This might open prospects for using these apparently well tolerated agents in remyelination strategies.

Transforming growth factor-beta and tumor necrosis factor-alpha cooperate to induce apoptosis in the oligodendroglial cell line OLI-neu

As shown previously, transforming growth factor-beta (TGF-beta) plays an important role during the period of developmental cell death in the nervous system. As with neurons, oligodendrocytes are generated in excess and eliminated by apoptosis. The present study was aimed at investigating the possible interaction of TGF-beta with tumor necrosis factor-alpha (TNF-alpha) in the regulation of cell death in oligodendroglial precursor cells and analyzing the underlying signaling mechanisms. We show that both factors induce apoptosis independently, but cooperate when applied together. The investigation of the signaling events revealed an important role of the JNK pathway during induction of apoptosis. TGF-beta seemed to be more efficient at inducing a release in cytochrome c from mitochondria than TNF-alpha. This might be the consequence of decreased Bcl-xL levels observed in cells treated with TGF-beta but not with TNF-alpha. Both factors stimulated caspase-3 activity, which could be inhibited by caspase-8 or caspase-9 inhibitors. Therefore, we conclude that TNF-alpha and TGF-beta affect partially common pathways but also regulate different steps in the apoptotic cascade.

Nitrosative and oxidative injury to premyelinating oligodendrocytes in periventricular leukomalacia

Periventricular leukomalacia (PVL), the major substrate of cerebral palsy in survivors of prematurity, is defined as focal periventricular necrosis and diffuse gliosis in immature cerebral white matter. We propose that nitrosative and/or oxidative stress to premyelinating oligodendrocytes complicating cerebral ischemia in the sick premature infant is a key mechanism of injury interfering with maturation of these cells to myelin-producing oligodendrocytes and subsequent myelination. Using immunocytochemical markers in autopsy brain tissue from 17 PVL cases and 28 non-PVL controls, we found in the PVL cases: 1) selective regionalization of white matter injury, including preferential involvement of the deep compared to intragyral white matter; 2) prominent activation of microglia diffusely throughout the white matter; 3) protein nitration and lipid peroxidation in premyelinating oligodendrocytes in the diffuse component; 4) preferential death of premyelinating oligodendrocytes diffusely; and 5) virtual sparing of the overlying cerebral cortex, as demonstrated by markers of activated astrocytes and microglia. These data establish that PVL is primarily a white matter disease that involves injury to premyelinating oligodendrocytes, potentially through activation of microglia and release of reactive oxygen and nitrogen species. Agents that prevent nitrosative and oxidative stress may play a key role in ameliorating PVL in premature infants in the intensive care nursery.

Interleukin-1beta promotes oligodendrocyte death through glutamate excitotoxicity

Glutamate excitotoxicity is implicated in the progressive loss of oligodendrocytes in multiple sclerosis, but how glutamate metabolism is dysregulated in the disease remains unclear. Because there is microglia activation in all stages of multiple sclerosis, we determined whether a microglia product, interleukin-1beta, could provide the mechanism for glutamate excitotoxicity. We found that whereas interleukin-1beta did not kill oligodendrocytes in pure culture, it produced apoptosis of oligodendrocytes in coculture with astrocytes and microglia. This requirement for a mixed glia environment suggests that interleukin-1beta impairs the well-described glutamate-buffering capacity of astrocytes. In support, antagonists at AMPA/kainate glutamate receptors, NBQX and CNQX, blocked the interleukin-1beta toxicity to oligodendrocytes. Another microglia/macrophage cytokine, tumor necrosis factor-alpha, also evoked apoptosis of oligodendrocytes in a mixed glia environment in an NBQX-blockable manner. These results provide a mechanistic link between the persistent and insidious microglia activation that is evident in all stages of multiple sclerosis, with the recent appreciation that glutamate excitotoxicity leads to the destruction of oligodendrocytes in the disease.

Differential lipid peroxidation, Mn superoxide, and bcl-2 expression contribute to the maturation-dependent vulnerability of oligodendrocytes to oxidative stress

To understand the basis of oligodendrocyte (OL) susceptibility to oxidative injury, purified rat OL cultures at different stages of maturation were exposed to nitric oxide (NO) donors with fast or slow kinetics of release and to tert-butyl-hydroperoxide, a membrane-permeant organic hydroperoxide. OL precursors (pre-OL) displayed the highest vulnerability to both oxygen or nitrogen reactive species, whereas mature OLs were uniquely vulnerable to long-lasting levels of NO. Cell death occurred by necrosis as well as apoptosis associated with increased caspase-3 activity and, only in the case of pre-OLs, with a decreased expression of the anti-apoptotic protein bcl-2. Pre-OLs were also more susceptible than mature OLs to lipid peroxidation, as measured by F2-isoprostane content in culture media. Finally, pre-OLs, but not mature OLs, expressed high levels of the mitochondrial scavenging enzyme Mn superoxide dismutase, suggesting that pre-OLs may efficiently convert anion superoxide into hydrogen peroxide and, paradoxically, be more predisposed than mature OLs to a toxic imbalance between hydrogen peroxide production and detoxification processes. These data suggest that susceptibility to lipid peroxidation, expression of the scavenging enzyme Mn superoxide dismutase and of the anti-apoptotic protein bcl-2, may contribute to the maturation-dependent vulnerability of OLs to oxidant injury.

Genetic background determines phenotypic severity of the Plp rumpshaker mutation

The rumpshaker mutation of the proteolipid protein (Plp) gene causes dysmyelination in man and mouse. We show that the phenotype in the mouse depends critically on the genetic background in which the mutation is expressed. On the C3H background there is normal longevity whereas changing to a C57BL/6 strain results in seizures and death at around postnatal day 30. The more severe phenotype is associated with less myelin and reduced levels of major myelin proteins. There are also more apoptotic cells, including oligodendrocytes, increased numbers of proliferating cells, increased numbers of NG2+ oligodendrocyte progenitors and increased microglia compared to the milder phenotype. The number of mature oligodendrocytes is similar to wild-type in both strains of mutant, however, suggesting that increased oligodendrocyte death is matched by increased generation from progenitors. The dichotomy of phenotype probably reflects the influence of modifying loci. The localization of these putative modifying genes and their mode of action remain to be determined.

Oligodendrocytes and ischemic brain injury

Oligodendrocytes, myelin-forming glial cells of the central nervous system, are vulnerable to damage in a variety of neurologic diseases. Much is known of primary myelin injury, which occurs in settings of genetic dysmyelination or demyelinating disease. There is growing awareness that oligodendrocytes are also targets of injury in acute ischemia. Recognition of oligodendrocyte damage in animal models of ischemia requires attention to their distinct histologic features or use of specific immunocytochemical markers. Like neurons, oligodendrocytes are highly sensitive to injury by oxidative stress, excitatory amino acids, trophic factor deprivation, and activation of apoptotic pathways. Understanding mechanisms of oligodendrocyte death may suggest new therapeutic strategies to preserve or restore white matter function and structure after ischemic insults.

Trafficking of PLP/DM20 and cAMP signaling in immortalized jimpy oligodendrocytes

The synthesis, transport, and insertion of jimpy proteolipid protein and DM20 were studied in normal (158N) and jimpy (158JP) immortalized oligodendrocyte lines. Four different expression vectors encoding fusion proteins composed of native PLP and DM20 or jimpy PLP or DM20 were linked to enhanced green fluorescent protein (EGFP). All four transfected fusion proteins had similar distributions in the cell bodies and processes of the two cell types. Both normal and jimpy PLP-EGFP and DM20-EGFP were detected in both cell lines as far as 200 microM from the cell body, indicating synthesis and transport of mutated PLP and DM20 toward the plasma membrane. Immunocytochemistry of fixed normal and jimpy cells with the O10 antibody, which recognizes a conformationally sensitive PLP/DM20 epitope, confirmed that normal and jimpy PLP and DM20 were transported to the plasma membrane. Live staining of normal and jimpy cells transiently transfected with the native PLP showed positive staining, indicating PLP was correctly inserted into the membrane of both normal and jimpy oligodendrocytes. However, live staining of normal and jimpy cells transiently transfected with jimpy PLP showed no positive staining, indicating the mutated protein is abnormally inserted into the plasma membrane. Electrophysiological recordings of the resting membrane potential measured in the whole cell mode of the patch-clamp technique showed the absence of a developmentally regulated negative shift in the membrane potential in jimpy cells compared to normal native or immortalized oligodendrocytes. Treatment of 158N cells and native oligodendrocytes with dibutyryl cAMP (dbcAMP) caused morphological and biochemical differentiation, but failed to do so in 158JP cells, suggesting an abnormal signaling pathway in jimpy. The defect in cAMP signaling in jimpy oligodendrocytes was associated with the suppression of increase in mRNA level of the inducible cAMP early repressor (ICER). When the jimpy oligodendrocyte line was transfected with normal PLP or DM20 and exposed to dbcAMP, the cells failed to differentiate. This finding suggests that improper insertion of jimpy protein into the plasma membrane alters the membrane in such a way that certain signaling pathways are permanently altered. The abnormal insertion of jimpy PLP/DM20 into the plasma membrane may be the basis for the lack of cell signaling and abnormal resting potential in jimpy oligodendrocytes.

Apoptosis in Schwann cell cultures is closely interrelated with the activity of the ubiquitin-proteasome proteolytic pathway

Although the participation of the ubiquitin-dependent pathway and of the proteasome in apoptosis has been proposed, its role in this process is not yet clearly defined. In previous studies, we have shown that in the central nervous system of the rat, programmed cell death and the ubiquitin-dependent proteolytic pathway are closely related to each other and that different types of neurons and of glial cells, shown different types of correlation between the two phenomena. In this work, we have used lactacystin, a highly specific inhibitor of the proteasome, to explore in Schwann cell cultures the relationship between the activity of the Ub-dependent pathway and apoptosis. Apoptosis was explored analyzing changes in nuclear morphology, using the Annexin V assay and by flow cytometry. Activity of caspase-3 was also measured. Changes in the levels of ubiquitin-protein conjugates and of the ubiquitin activating enzymes, E1, as well as expression of proteins that instruct the cells to apoptosis (p53, NFkappaB-IkappaB, Bcl2), or that participate in the control and regulation of the cell cycle, were also examined. Our results indicate that the decrease in the activity of the proteasome induced by lactacystin in Schwann cells, induces apoptotic cell death through changes in the concentration of certain key proteins that are involved in the apoptosis-signaling pathways.

TGF-beta induces cell death in the oligodendroglial cell line OLI-neu

We have shown that TGF-beta plays an important role during the period of developmental cell death in the nervous system. Immunoneutralization of TGF-beta prevents ontogenetic neuron death in vivo. Like neurons, oligodendrocytes are generated in excess and eliminated by apoptosis. It has been shown that oligodendrocyte progenitors and newly formed oligodendrocytes are especially susceptible to apoptosis. We choose the oligodendrocyte precursor cell line OLI-neu to address the question if TGF-beta could play a role for the control of oligodendrocyte proliferation and cell death. Flow cytometric analysis revealed that OLI-neu cells arrested in the G1 phase of the cell cycle underwent apoptosis in response to TGF-beta. TUNEL assays, apoptosis ELISA, and caspase assays substantiated the finding that OLI-neu cells died after TGF-beta treatment. Cell death could be inhibited by application of pan-caspase or caspase 8 and 9 inhibitors, whereas the inhibition of calpain was unaffected. Furthermore, we found a reduction of bcl-X(L) at the protein as well as at the mRNA level, while p27 was upregulated. The Smad cascade was activated while TGF-beta reduced the activity of the p42/p44 MAP kinase pathway. Together, these data show that TGF-beta induced apoptotic cell death in cells of oligodendroglial origin, whereby the signaling cascade involved the downregulation of antiapoptotic signaling such as bcl-X(L) leading to the activation of caspases.