Alterations In Oligodendrocytes Research Articles

Cerebral White Matter Alterations Associated With Oligodendrocyte Vulnerability in Organic Acidurias: Insights in Glutaric Aciduria Type I.

The white matter is an important constituent of the central nervous system, containing axons, oligodendrocytes, and its progenitor cells, astrocytes, and microglial cells. Oligodendrocytes are central for myelin synthesis, the insulating envelope that protects axons and allows normal neural conduction. Both, oligodendrocytes and myelin, are highly vulnerable to toxic factors in many neurodevelopmental and neurodegenerative disorders associated with disturbances of myelination. Here we review the main alterations in oligodendrocytes and myelin observed in some organic acidurias/acidemias, which correspond to inherited neurometabolic disorders biochemically characterized by accumulation of potentially neurotoxic organic acids and their derivatives. The yet incompletely understood mechanisms underlying the high vulnerability of OLs and/or myelin in glutaric acidemia type I, the most prototypical cerebral organic aciduria, are particularly discussed.

Spatial and temporal alterations of developing oligodendrocytes induced by repeated sevoflurane exposure in neonatal mice

The general anesthesia associated with long-term cognitive impairment has been causing the concern of the whole society. In particular, repeated anesthetic exposures may affect executive function, processing speed, and fine motor skills, which all directly depended on the functions of oligodendrocytes, myelin, and axons. However, the underlying mechanisms are still largely unknown. To investigate the spatial and temporal alterations in oligodendrocytes in the corpus callosum (CC) and hippocampus following repeated sevoflurane exposures (3%, for 2 h) from postnatal day 6 (P6) to P8, we used immunofluorescence, Western blot, and a battery of behavioral tests. As previously stated, we confirmed that early anesthetic exposures hampered both cognitive and motor performance during puberty in the rotarod and banes tests. Intriguingly, we discovered that the proliferation of oligodendrocyte progenitor cells (OPCs) was immediately enhanced after general anesthesia in the CC and hippocampus from P8 to P32. From P8 through P15, the overall oligodendrocyte population remained constant. However, along with the structural myelin abnormalities, the matured oligodendrocytes statistically reduced in the CC (from P15) and hippocampus (from P32). Administration of clemastine, which could induce OPC differentiation and myelin formation, significantly increased matured oligodendrocytes and promoted myelination and cognition. Collectively, we first demonstrated the bi-directional influence of early sevoflurane exposures on oligodendrocyte maturation and proliferation, which contributes to the cognitive impairment induced by general anesthesia. These findings illustrated the dynamic changes in oligodendrocytes in the developing brain following anesthetic exposures, as well as possible therapeutic strategies for multiple general anesthesia associated cognitive impairment.

An electron microscopic study of neocortex of Syrian hamsters (<i>Mesocricetus auratus</i>) infected with SARS-CoV-2 (Coronaviridae: <i>Coronavirinae: Betacoronavirus: Sarbecovirus</i>)

Convalescent COVID-19 patients have various signs of central nervous system damage, including those directly associated with SARS-CoV-2. Hence, studies of SARS-COV-2 related morphological changes in neocortex are particularly relevant for understanding the mechanisms of their formation and development of approaches to preclinical evaluation of the effectiveness of antiviral drugs. The purpose of the research is a longitudinal study of the ultrastructural alterations in Syrian hamsters neocortex after experimental SARS-CoV-2 infection. Male Syrian hamsters weighing 80100 g, aged 4 to 6 weeks, were infected with 26 l SARS-CoV-2 intranasally with 4104 TCD50/ml of viral particles. The animals were euthanized on days 3, 7 or 28 post-infection, the brain was extracted with the cortex excision. The material analysis was performed using transmission electron microscopy. On day 3 post-infection, the number of moderately hyperchromic neurons in neocortex increased, while by the day 7 the number of apoptotic cells significantly increased. Simultaneously, an increased signs of neuronophagy and representation of atypical glia were observed. Increased number of altered oligodendrocytes was observed on day 28 post-infection. Viral invasion was accompanied by changes in neocortical cells since day 3 post-infection, such as transformation of their nucleus, the rough endoplasmic reticulum and the Golgi vesicles as well as microvascular spasm with perivascular edema. As a result of electron microscopic study, the ultrastructural alterations in neocortex were described in an experimental model of SARS-CoV-2 infection. The findings can be used to identify the mechanisms of infection pathogenesis and to search for the new directions in development of medicines.

TMET-26. PRIMARY OLIGODENDROGLIOMA CELL CULTURE VIABILITY: AN IN VITRO STUDY WITH METABOLIC MODULATORS

Abstract Oligodendrogliomas are tumors that develop from oligodendrocytes, the myelinating cells of the central nervous system. Oligodendrocytes are highly metabolically active cells that synthesize and transfer metabolites to neighboring cells. Given its intimate metabolic relation with neurons, we aim to investigate oligodendrocyte metabolism as an antitumoral target. A recurred oligodendroglioma WHO grade III was surgically removed from a 50-year patient after 10 years of progression-free disease. The tumor sample was mechanically digested and cultured at 37oC, 5% CO2, in DMEM: F12, 10 % FBS and antibiotics. Primary oligodendroglioma cells were trypsinized and seeded in a 96-well plate. After 24 hs, cells were treated with metabolic modulators: metformin (MET, mitochondrial complex II inhibitor, 5 mM), 2 deoxyglucose (2DG, hexokinase inhibitor, 1 mM), 6-aminonicotinamide (6AN, pentose phosphate pathway inhibitor, 50 µM) and/or 1400W and S-methylisothiourea (both iNOS inhibitors, 5 µM, and 50 µM respectively). Standard treatment with temozolomide (TMZ, 200 µM) was also performed. After 5 days of treatment, cells were stained with violet crystal. Two weeks after tumor sample digestion, a primary oligodendroglioma culture was successfully established. In vitro, proliferating cells appeared mostly undifferentiated with reduced branching complexity. Hexokinase inhibition by 2DG notoriously affected the viability of oligodendroglioma cells. Similar results were obtained with standard TMZ treatment. On the other hand, the inhibition of the pentose phosphate pathway by 6AN did not affect the cell monolayer. However, 6AN was able to increase the effect of MET as monotherapy. Both, MET and 2DG altered oligodendrocyte morphology inducing a more fusiform shape. Finally, iNOS inhibition modestly disrupted cell's monolayers and this effect did not seem to be improved by combinatory therapies. Glycolytic inhibitor 2DG resulted effective against oligodendroglioma cells. Whereas further studies are needed to validate these results, a better understanding of metabolic susceptibility could allow the development of better-targeted and more-effective therapeutic approaches.

Parkinson’s disease and multiple system atrophy patient iPSC-derived oligodendrocytes exhibit alpha-synuclein–induced changes in maturation and immune reactive properties

SignificanceOur results demonstrate the existence of early cellular pathways and network alterations in oligodendrocytes in the alpha-synucleinopathies Parkinson's disease and multiple system atrophy. They further reveal the involvement of an immune component triggered by alpha-synuclein protein, as well as a connection between (epi)genetic changes and immune reactivity in multiple system atrophy. The knowledge generated in this study could be used to devise novel therapeutic approaches to treat synucleinopathies.

Insights into myelin dysfunction in schizophrenia and bipolar disorder.

Schizophrenia and bipolar disorder are disabling psychiatric disorders with a worldwide prevalence of approximately 1%. Both disorders present chronic and deteriorating prognoses that impose a large burden, not only on patients but also on society and health systems. These mental illnesses share several clinical and neurobiological traits; of these traits, oligodendroglial dysfunction and alterations to white matter (WM) tracts could underlie the disconnection between brain regions related to their symptomatic domains. WM is mainly composed of heavily myelinated axons and glial cells. Myelin internodes are discrete axon-wrapping membrane sheaths formed by oligodendrocyte processes. Myelin ensheathment allows fast and efficient conduction of nerve impulses through the nodes of Ranvier, improving the overall function of neuronal circuits. Rapid and precisely synchronized nerve impulse conduction through fibers that connect distant brain structures is crucial for higher-level functions, such as cognition, memory, mood, and language. Several cellular and subcellular anomalies related to myelin and oligodendrocytes have been found in postmortem samples from patients with schizophrenia or bipolar disorder, and neuroimaging techniques have revealed consistent alterations at the macroscale connectomic level in both disorders. In this work, evidence regarding these multilevel alterations in oligodendrocytes and myelinated tracts is discussed, and the involvement of proteins in key functions of the oligodendroglial lineage, such as oligodendrogenesis and myelination, is highlighted. The molecular components of the axo-myelin unit could be important targets for novel therapeutic approaches to schizophrenia and bipolar disorder.

A gut-derived metabolite alters brain activity and anxiety behaviour in mice.

Integration of sensory and molecular inputs from the environment shapes animal behaviour. A major site of exposure to environmental molecules is the gastrointestinal tract, in which dietary components are chemically transformed by the microbiota1 and gut-derived metabolites are disseminated to all organs, including the brain2. In mice, the gut microbiota impacts behaviour3, modulates neurotransmitter production in the gut and brain4,5, and influences brain development and myelination patterns6,7. The mechanisms that mediate the gut-brain interactions remain poorly defined, although they broadly involve humoral or neuronal connections. We previously reported that the levels of the microbial metabolite 4-ethylphenyl sulfate (4EPS) were increased in a mouse model of atypical neurodevelopment8. Here we identified biosynthetic genes from the gut microbiome that mediate the conversion of dietary tyrosine to 4-ethylphenol (4EP), and bioengineered gut bacteria to selectively produce 4EPS in mice. 4EPS entered the brain and was associated with changes in region-specific activity and functional connectivity. Gene expression signatures revealed altered oligodendrocyte function in the brain, and 4EPS impaired oligodendrocyte maturation in mice and decreased oligodendrocyte-neuron interactions in ex vivo brain cultures. Mice colonized with 4EP-producing bacteria exhibited reduced myelination of neuronal axons. Altered myelination dynamics in the brain have been associated with behavioural outcomes7,9-14. Accordingly, we observed that mice exposed to 4EPS displayed anxiety-like behaviours, and pharmacological treatments that promote oligodendrocyte differentiation prevented the behavioural effects of 4EPS. These findings reveal that a gut-derived molecule influences complex behaviours in mice through effects on oligodendrocyte function and myelin patterning in the brain.

Prolonged Environmental Enrichment Promotes Developmental Myelination.

Postnatal neurodevelopment is profoundly influenced by environmental experiences. Environmental enrichment is a commonly used experimental paradigm that has uncovered numerous examples of experience-dependent plasticity in health and disease. However, the role of environmental enrichment in normal development, especially glial development, is largely unexplored. Oligodendrocytes, the myelin-forming glia in the central nervous system, provide metabolic support to axons and establish efficient saltatory conduction by producing myelin. Indeed, alterations in myelin are strongly correlated with sensory, cognitive, and motor function. The timing of developmental myelination is uniquely positioned to be influenced by environmental stimuli, as peak myelination occurs postnatally and continues into adulthood. To determine if developmental myelination is impacted by environmental experience, mice were housed in an enriched environment during peak myelination through early adulthood. Using translating ribosome affinity purification, oligodendrocyte-specific RNAs were isolated from subcortical white matter at various postnatal ages. RNA-sequencing revealed that differences in the oligodendrocyte translatome were predominantly evident after prolonged and continuous environmental enrichment. These translational changes corresponded with altered oligodendrocyte lineage cell dynamics and enhanced myelination. Furthermore, consistent with increased developmental myelination, enriched mice displayed enhanced motor coordination on a beam walking task. These findings indicate that protracted environmental stimulation is sufficient to modulate developmental myelination and to promote behavioral function.

White matter alterations in Alzheimer's disease without concomitant pathologies.

AimsMost individuals with AD neuropathological changes have co‐morbidities which have an impact on the integrity of the WM. This study analyses oligodendrocyte and myelin markers in the frontal WM in a series of AD cases without clinical or pathological co‐morbidities.MethodsFrom a consecutive autopsy series, 206 cases had neuropathological changes of AD; among them, only 33 were AD without co‐morbidities. WM alterations were first evaluated in coronal sections of the frontal lobe in every case. Then, RT‐qPCR and immunohistochemistry were carried out in the frontal WM of AD cases without co‐morbidities to analyse the expression of selected oligodendrocyte and myelin markers.ResultsWM demyelination was more marked in AD with co‐morbidities when compared with AD cases without co‐morbidities. Regarding the later, mRNA expression levels of MBP, PLP1, CNP, MAG, MAL, MOG and MOBP were preserved at stages I–II/0–A when compared with middle‐aged (MA) individuals, but significantly decreased at stages III–IV/0–C. This was accompanied by reduced expression of NG2 and PDGFRA mRNA, reduced numbers of NG2‐, Olig2‐ and HDAC2‐immunoreactive cells and reduced glucose transporter immunoreactivity. Partial recovery of some of these markers occurred at stages V–VI/B–C.ConclusionsThe present observations demonstrate that co‐morbidities have an impact on WM integrity in the elderly and in AD, and that early alterations in oligodendrocytes and transcription of genes linked to myelin proteins in WM occur in AD cases without co‐morbidities. These are followed by partial recovery attempts at advanced stages. These observations suggest that oligodendrocytopathy is part of AD.

Progress in iPSC-Based Modeling of Psychiatric Disorders.

Progress in iPSC-based cellular systems provides new insights into human brain development and early neurodevelopmental deviations in psychiatric disorders. Among these, studies on schizophrenia (SCZ) take a prominent role owing to its high heritability and multifarious evidence that it evolves from a genetically induced vulnerability in brain development. Recent iPSC studies on patients with SCZ indicate that functional impairments of neural progenitor cells (NPCs) in monolayer culture extend to brain organoids by disrupting neocorticogenesis in an in vitro model. In addition, the formation of hippocampal circuit-like structures in vitro is impaired in patients with SCZ as is the case for glia development. Intriguingly, chimeric-mice experiments show altered oligodendrocyte and astrocyte development in vivo that highlights the importance of cell–cell interactions in the pathogenesis of early-onset SCZ. Likewise, cortical imbalances in excitatory–inhibitory signaling may result from a cell-autonomous defect in cortical interneuron (cIN) development. Overall, these findings indicate that genetic risk in SCZ impacts neocorticogenesis, hippocampal circuit formation, and the development of distinct glial and neuronal subtypes. In light of this remarkable progress, we discuss current limitations and further steps necessary to harvest the full potential of iPSC-based investigations on psychiatric disorders.

Simultaneous alterations of oligodendrocyte-specific CNP, astrocyte-specific AQP4 and neuronal NF-L demarcate ischemic tissue after experimental stroke in mice

Ischemic stroke not only affects neurons, but also glial and vascular elements. The development of novel neuroprotective strategies thus requires an improved pathophysiological understanding of ischemia-affected cell types that comprise the ‘neurovascular unit’ (NVU). To explore spatiotemporal alterations of oligodendrocytes, astrocytes and neurons after experimental ischemic stroke, we applied a permanent middle cerebral artery occlusion model in mice for 4 and 24 h. Using fluorescence microscopy, the oligodendrocyte marker 2′,3′-cyclic nucleotide phosphodiesterase (CNP), the neuronal neurofilament light chain (NF-L) and the astroglial aquaporin-4 (AQP4) were analyzed in regional relation to one another.Immunofluorescence intensities of CNP and NF-L were simultaneously increased in the ischemic neocortex and striatum. AQP4 immunoreactivity was decreased in the ischemic striatum, which represents the initial and potentially strongest affected site of infarction. The more distant ischemic neocortex and infarct border zones exhibited areas with alternately increased or decreased AQP4 immunoreactivity, leading to an increase of fluorescence intensity in total.Further, deformed CNP-immunopositive processes were found around axonal spheroids, indicating a combined affection of oligodendrocytes and neurons due to ischemia. Importantly, altered AQP4 immunosignals were not limited to the ischemic core, but were also detectable in penumbral areas. This applies for CNP and NF-L also, since altered immunosignals of all three markers coincided regionally at both time points.In conclusion, the present study provides evidence for a simultaneous affection of oligodendrocytes, astrocytes and neurons after experimental focal cerebral ischemia. Consequently, CNP, AQP4 and NF-L immunofluorescence alterations can be utilized to identify ischemia-affected tissue. The simultaneity of the described alterations further strengthens the concept of interdependent NVU components and distinguishes NF-L, CNP and AQP4 as highly ischemia-sensitive elements. Consequently, future therapeutic approaches might influence stroke evolution via strategies simultaneously addressing both neuronal and glial functions.

Ultrastructural pathology of oligodendrocytes adjacent to microglia in prefrontal white matter in schizophrenia

Microglial activation has been proposed to be involved in the pathophysiology of schizophrenia (SCZ). We hypothesized that dystrophic alterations of oligodendrocytes previously reported in the prefrontal white matter in SCZ might be associated with microglial activation in the acute state of SCZ. White matter of the prefrontal cortex (BA10) was studied in post-mortem brain tissue from 21 SCZ cases and 20 normal controls. The SCZ group included 12 subjects with predominantly positive symptoms and 9 subjects with predominantly negative symptoms. Electron microscopy was applied to estimate cell density, size, volume fraction (Vv) and the number (N) of organelles in oligodendrocytes adjacent to microglia and in oligodendrocytes adjacent to myelin, neurons and capillaries and not adjacent to microglia. Cell density of oligodendrocytes was not changed in the SCZ group as compared to controls. Vv and N of mitochondria were significantly decreased, while Vv of vacuoles of endoplasmic reticulum and lipofuscin granules were significantly increased in oligodendrocytes adjacent to either microglia or myelin in the SCZ group and in patients displaying predominantly positive symptoms as compared to the control group. There were no significant differences between oligodendrocytes adjacent to microglia and to myelin. Vv and N of lipofuscin were also increased in peri-capillary oligodendrocytes. There was no effect of clinical subgroups on the parameters of peri-capillary and peri-neuronal oligodendrocytes. Though many ameboid and dystrophic microglia adjacent to oligodendrocytes were found in the SCZ samples, we provide no quantitative evidence that oligodendrocyte dystrophy is associated with microglial activation in white matter in SCZ.

Mechanical Stretch of High Magnitude Provokes Axonal Injury, Elongation of Paranodal Junctions, and Signaling Alterations in Oligodendrocytes

Increasing findings suggest that demyelination may play an important role in the pathophysiology of brain injury, but the exact mechanisms underlying such damage are not well known. Mechanical tensile strain of brain tissue occurs during traumatic brain injury. Several studies have investigated the cellular and molecular events following a static tensile strain of physiological magnitude on individual cells such as oligodendrocytes. However, the pathobiological impact of high-magnitude mechanical strain on oligodendrocytes and myelinated fibers remains under investigated. In this study, we reported that an applied mechanical tensile strain of 30% on mouse organotypic culture of cerebellar slices induced axonal injury and elongation of paranodal junctions, two hallmarks of brain trauma. It was also able to activate MAPK-ERK1/2 signaling, a stretch-induced responsive pathway. The same tensile strain applied to mouse oligodendrocytes in primary culture induced a profound damage to cell morphology, partial cell loss, and a decrease of myelin protein expression. The lower tensile strain of 20% also caused cell loss and the remaining oligodendrocytes appeared retracted with decreased myelin protein expression. Finally, high-magnitude tensile strain applied to 158N oligodendroglial cells altered myelin protein expression, dampened MAPK-ERK1/2 and MAPK-p38 signaling, and enhanced the production of reactive oxygen species. The latter was accompanied by increased protein oxidation and an alteration of anti-oxidant defense that was strain magnitude-dependent. In conclusion, mechanical stretch of high magnitude provokes axonal injury with significant alterations in oligodendrocyte biology that could initiate demyelination.

25. OLIGODENDROCYTE-BASED IMPAIRMENT OF BRAIN CONNECTIVITY AS TARGET FOR NEW TREATMENT STRATEGIES IN SCHIZOPHRENIA

Overall : This symposium has a translational approach. First, we present human post-mortem and in-vivo imaging studies on the pivotal role of oligedondrocyte loss and dysfunction with consecutive impairments of brain connectivity in schizophrenia. Natalya Uranova will show morphometric data on ultrastructural alterations of oligodendrocytes, myelin damage and degeneration and disturbed oligodendrocyte-axon interactions in post-mortem prefrontal white matter in schizophrenia. Adrienne Lahti will report diffusion tensor imaging data suggesting impaired axonal and myelin integrity. Because, MR Spectroscopy permits the non-invasive measurement of neurometabolites, such as N-acetylaspartate, a marker of neuronal integrity, and glutamate, which can be neurotoxic when overproduced, this technique provides further understanding of the relationship between white matter microstructure and neuronal function.Second, we present data from cell culture and animal models suggesting that restoration of oligodendrocyte function (in terms of energy metabolism, maturation and myelin production) is a promising target for the development of novel treatment strategies in schizophrenia. Proteomic studies in postmortem brain by Daniel Martins-de-Souza have suggested a schizophrenia-related energy metabolism dysfunction in oligodendrocytes. These findings have been followed up using oligodendroglia cell lines and induced pluripotent stem cell-derived cerebral organoids, supporting the notion that alterations in glycolysis in oligodendrocytes are pivotal to the overall energy dysfunction in schizophrenia brains. Lan Xiao′s lab has shown that oligodendrocyte dysfunction and impaired myelination in the prefrontal cortex is correlated with schizophrenia-like behavior in mice undergoing prolonged social isolation. Enhancing oligodendrocyte generation and myelin repair by FDA-approved compounds, like quetiapine (an APD) or clemastine (a histamine antagonist) successfully reversed the above phenotype.

Reduced oligodendrocyte density in layer 5 of the prefrontal cortex in schizophrenia.

Neuroimaging and post-mortem studies have implicated altered myelin integrity and oligodendrocyte abnormalities in the dysfunction of neuronal network in schizophrenia, including the prefrontal cortex, Brodmann area (BA) 10. Pyramidal neurons in layer 5 of BA10 are the important link of reciprocal frontal cortical-basal ganglia-thalamic circuits altered in schizophrenia. Previously, we found ultrastructural dystrophic and degenerative alterations of oligodendrocytes in layer 5 of BA10 in schizophrenia. The aim of the study was to estimate the numerical density (Nv) of oligodendrocytes in layer 5 of BA10 in schizophrenia as compared to normal controls. 17 chronic schizophrenia subjects and 22 healthy matched controls were studied in Nissl-stained sections using optical disector method. Group differences were analyzed using ANCOVA followed by post hoc Duncan's test. The Nv of oligodendrocytes was significantly lower (- 32%, p < 0.001) in the schizophrenia group as compared to the control group. Young controls (age < 50years old) showed significantly higher Nv of oligodendrocytes as compared to elderly controls (age > 50years old). Young and elderly schizophrenia subgroups did not differ significantly. Both control subgroups have significantly higher Nv of oligodendrocytes as compared to the schizophrenia subgroups. Decreased Nv of oligodendrocytes found in layer 5 of BA10 may be the result of dystrophic and destructive alterations and/or disrupted development of oligodendrocytes in schizophrenia.

Ultrastructural pathology of oligodendrocytes in white matter in continuous attack-like schizophrenia and a role for microglia

Previously the authors have reported the ultrastructural pathology and deficits of oligodendrocytes in gray and white matter of the prefrontal cortex in continuous paranoid schizophrenia. The aim of the present work was to study the effects of microglia on the ultrastructure of oligodendrocytes in white matter underlying the prefrontal cortex (BA10) in attack-like schizophrenia. Postmortem morphometric electron microscopic study of oligodendrocytes in close apposition to microglia was performed in white matter underlying the prefrontal cortex (BA10). Nine cases of chronic attack-like schizophrenia and 20 normal controls were studied. Areas of oligodendrocytes, volume density (Vv) and the number of mitochondria, vacuoles of endoplasmic reticulum and lipofuscin granules were estimated. Group comparison was performed using ANCOVA. The schizophrenia group differed from the control group by paucity of ribosomes in cytoplasm of oligodendrocytes, cytoplasm swelling, a significant increase in Vv and number of vacuoles and lipofuscin granules. Significant correlations between the parameters of vacuoles and lipofuscin granules and mitochondria were found only in the schizophrenia group. Dystrophic alterations of oligodendrocytes apposed microglial cells were found in the white matter of the prefrontal cortex in chronic schizophrenia as compared to controls. Microglia might contribute to abnormalities of lipid and protein metabolism of oligodendrocytes.

TUBB4A mutations result in specific neuronal and oligodendrocytic defects that closely match clinically distinct phenotypes

Hypomyelinating leukodystrophies are heritable disorders defined by lack of development of brain myelin, but the cellular mechanisms of hypomyelination are often poorly understood. Mutations in TUBB4A, encoding the tubulin isoform tubulin beta class IVA (Tubb4a), result in the symptom complex of hypomyelination with atrophy of basal ganglia and cerebellum (H-ABC). Additionally, TUBB4A mutations are known to result in a broad phenotypic spectrum, ranging from primary dystonia (DYT4), isolated hypomyelination with spastic quadriplegia, and an infantile onset encephalopathy, suggesting multiple cell types may be involved. We present a study of the cellular effects of TUBB4A mutations responsible for H-ABC (p.Asp249Asn), DYT4 (p.Arg2Gly), a severe combined phenotype with hypomyelination and encephalopathy (p.Asn414Lys), as well as milder phenotypes causing isolated hypomyelination (p.Val255Ile and p.Arg282Pro). We used a combination of histopathological, biochemical and cellular approaches to determine how these different mutations may have variable cellular effects in neurons and/or oligodendrocytes. Our results demonstrate that specific mutations lead to either purely neuronal, combined neuronal and oligodendrocytic or purely oligodendrocytic defects that closely match their respective clinical phenotypes. Thus, the DYT4 mutation that leads to phenotypes attributable to neuronal dysfunction results in altered neuronal morphology, but with unchanged tubulin quantity and polymerization, with normal oligodendrocyte morphology and myelin gene expression. Conversely, mutations associated with isolated hypomyelination (p.Val255Ile and p.Arg282Pro) and the severe combined phenotype (p.Asn414Lys) resulted in normal neuronal morphology but were associated with altered oligodendrocyte morphology, myelin gene expression, and microtubule dysfunction. The H-ABC mutation (p.Asp249Asn) that exhibits a combined neuronal and myelin phenotype had overlapping cellular defects involving both neuronal and oligodendrocyte cell types in vitro. Only mutations causing hypomyelination phenotypes showed altered microtubule dynamics and acted through a dominant toxic gain of function mechanism. The DYT4 mutation had no impact on microtubule dynamics suggesting a distinct mechanism of action. In summary, the different clinical phenotypes associated with TUBB4A reflect the selective and specific cellular effects of the causative mutations. Cellular specificity of disease pathogenesis is relevant to developing targeted treatments for this disabling condition.

Ultrastructural pathology of oligodendrocytes in the white matter in continuous paranoid schizophrenia: a role for microglia

Previously the authors have reported the ultrastructural pathology and deficit of oligodendrocytes in gray and white matter of the prefrontal cortex in schizophrenia. The aim of the study was to determine of the effects of microglia on the ultrastructure of oligodendrocytes in the white matter underlying the prefrontal cortex in continuous schizophrenia. Postmortem morphometric electron microscopic study of oligodendrocytes in close apposition to microglia was performed in white matter underlying the prefrontal cortex (BA10). Eleven cases of chronic continuous schizophrenia and 11 normal controls were studied. Areas of oligodendrocytes, of their nuclei and cytoplasm, volume density (Vv) and the number of mitochondria, vacuoles of endoplasmic reticulum and lipofuscin granules were estimated. Group comparison was performed using ANCOVA. The schizophrenia group differed from the control group by paucity of ribosomes in the cytoplasm of oligodendrocytes, a significant decrease in Vv and the number of mitochondria and increase in the number of lipofuscin granules. Significant correlations between the parameters of lipofuscin granules, mitochondria and vacuoles were found only in the schizophrenia group. The number of lipofuscin granules were correlated positively with the illness duration. Dystrophic alterations of oligodendrocytes attached to microglial cells were found in the white matter of the prefrontal cortex in chronic paranoid schizophrenia as compared to controls. The data obtained suggest that microglia might contribute to abnormalities of energy, lipid and protein metabolism of oligodendrocytes in schizophrenia.

Loss of Hippocampal Oligodendrocytes Contributes to the Deficit of Contextual Fear Learning in Adult Rats Experiencing Early Bisphenol A Exposure.

During early development, continuous exposure to environmental contaminants such as bisphenol A (BPA) is known to alter neuronal development, resulting in aberrant brain structure and predisposing individuals to developing neuropsychiatric disorders later in life. While the altered oligodendrocyte (OL) structure and function have been casually linked to the occurrence of numerous psychiatric diseases, it remains open whether early BPA exposure (EBE) also recruits OLs to mediate its toxicity in the brain. Here, we observed that EBE from birth to postnatal day 21 caused a substantial loss of hippocampal OLs in rat pups. The OL loss was enduring and manifested even when the affected pups spanned into their adulthood. In parallel, the expression of two key proteins in mature OLs, myelin basic protein (MBP), and monocarboxylate transporter 1 (MCT1) was markedly downregulated in adult hippocampus with a considerable reduction in the number of myelinated axons. By contrast, the myelination of individual axons remained intact. The altered hippocampal OLs were related to EBE-mediated disruption of estrogen receptor (ER) signaling in developing OLs and could be readily prevented by treatment with low level of ICI 182780, an ER antagonist. Importantly, the adult rats subject to EBE exhibited clear deficit in contextual fear memory, which highly correlated with OL loss and decreased MBP and MCT1 expression in hippocampus. The OL loss may thus represent an alternative route through which EBE has its adversity on the brain and contributes to the development of neuropsychiatric illness.

The cuprizone-induced changes in 1H-MRS metabolites and oxidative parameters in C57BL/6 mouse brain: Effects of quetiapine

Cuprizone is a copper-chelating agent and able to induce oligodendrocyte loss and demyelination in C57BL/6 mouse brain. Recent studies have used the cuprizone-fed mouse as an animal model of schizophrenia to examine putative roles of altered oligodendrocytes in this mental disorder. The present study reported the effects of cuprizone on the brain metabolites and oxidative parameters with the aim of providing neurochemical evidence for the application of the cuprizone mouse as an animal model of schizophrenia. In addition, we examined effects of quetiapine on the cuprizone-induced changes in brain metabolites and oxidative parameters; this atypical antipsychotic was shown to ameliorate the cuprizone-induced demyelination and behavioral changes in previous studies. C57BL/6 mice were fed a standard rodent chow without or with cuprizone (0.2% w/w) for four weeks during which period they were given sterilized saline or quetiapine in saline. The results of the proton magnetic resonance spectroscopy (1H-MRS) showed that cuprizone-feeding decreased 1H-MRS signals of N-acetyl-l-aspartate (NAA), total NAA (NAA + NAAG), and choline-containing compounds (phosphorylcholine and glycerophosphorylcholine), suggestive of mitochondrial dysfunction in brain neurons. Biochemical analyses showed lower activities of catalase and glutathione peroxidase, but higher levels of malondialdehyde and H2O2 in the brain tissue of cuprizone-fed mice, indicative of an oxidative stress. These cuprizone-induced changes were effectively relieved in the mice co-administered with cuprizone and quetiapine, although the antipsychotic alone showed no effect. These findings suggest the toxic effects of cuprizone on mitochondria and an antioxidant capacity of quetiapine, by which this antipsychotic relieves the cuprizone-induced mitochondrial dysfunction in brain cells.