Oligodendrocyte Cultures Research Articles

Role for CXCR2 and CXCL1 on glia in multiple sclerosis

As part of a need to understand myelin repair mechanisms, molecular pathways underlying oligodendrocyte behavior and central nervous system (CNS) remyelination are currently key topics in multiple sclerosis (MS). In the present study, we report expression of a chemoattractant receptor of the immune system, the chemokine receptor, CXCR2, on normal and proliferating oligodendrocytes in active MS lesions. Proliferating oligodendrocytes were occasionally associated with reactive astrocytes positive for CXCL1 (GRO-alpha), the ligand for CXCR2. CXCL1 expression was not seen on astrocytes in control and normal CNS tissue, while CXCR2 expression was constitutive on oligodendrocytes. At the functional level, following stimulation with the proinflammatory cytokine, interleukin-1beta (IL-1beta), we found high-level synthesis of CXCL1 by human fetal astrocytes in vitro. In contrast, human oligodendrocytes in culture expressed the receptor, CXCR2, constitutively. We propose that the concurrence of CXCR2 on oligodendrocytes and induced CXCL1 on hypertrophic astrocytes in MS provides a novel mechanism for recruitment of oligodendrocytes to areas of damage, an essential prerequisite for lesion repair in this devastating human condition.

Cytokine toxicity to oligodendrocyte precursors is mediated by iron

Inflammatory processes play a key role in the pathogenesis of a number of common neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Abnormal iron accumulation is frequently noted in these diseases and compelling evidence exists that iron is involved in inflammatory reactions. Histochemical stains for iron repeatedly demonstrate that oligodendrocytes, under normal conditions, stain more prominently than any other cell type in the brain. Therefore, we examined the hypothesis that cytokine toxicity to oligodendrocytes is iron mediated. Oligodendrocytes in culture were exposed to interferon-gamma (IFN-gamma), interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha). Toxicity was observed in a dose-dependent manner for IFN-gamma and TNF-alpha. IL-1beta was not toxic in the concentrations used in this study. The toxic concentration of IFN-gamma, and TNF-alpha was lower if the cells were iron loaded, but iron loading had no effect on the toxicity of IL-1beta. These data provide insight into the controversy regarding the toxicity of cytokines to oligodendrocytes by revealing that iron status of these cells will significantly impact the outcome of cytokine treatment. The exposure of oligodendrocytes to cytokines plus iron decreased mitochondrial membrane potential but activation of caspase 3 is limited. The antioxidant, TPPB, which targets mitochondria, protected the oligodendrocytes from the iron-mediated cytotoxicity, providing further support that mitochondrial dysfunction may underlie the iron-mediated cytokine toxicity. Therapeutic strategies involving anti-inflammatory agents have met with limited success in the treatment of demyelinating disorders. A better understanding of these agents and the contribution of cellular iron status to cytokine toxicity may help develop a more consistent intervention strategy.

Cytokines Induce Nitric Oxide-mediated mtDNA Damage and Apoptosis in Oligodendrocytes: PROTECTIVE ROLE OF TARGETING 8-OXOGUANINE GLYCOSYLASE TO MITOCHONDRIA

Nitric oxide (NO) that is produced by inducible NO synthase (iNOS) in glial cells is thought to contribute significantly to the pathogenesis of multiple sclerosis. Oligodendrocytes can be stimulated to express iNOS by inflammatory cytokines, which are known to accumulate in the multiple sclerotic brain. The potentially pathological levels of NO produced under these circumstances can target a wide spectrum of intracellular components. We hypothesized that one of the critical targets for damage that leads to disease is mtDNA. In this study, we found that cytokines, in particular a combination of tumor necrosis factor-alpha (50 ng/ml) and IFNgamma (25 ng/ml), cause elevated NO production in primary cultures of rat oligodendrocytes. Western blot analysis revealed a strong enhancement of iNOS expression 48 h after cytokine treatment. Within the same time period, NO-mediated mtDNA damage was shown by Southern blot analysis and by ligation-mediated PCR. Targeting the DNA repair enzyme human 8-oxoguanine DNA glycosylase (hOGG1) to the mitochondria of oligodendrocytes had a protective effect against this cytokine-mediated mtDNA damage. Moreover, it was shown that mitochondrial transport sequence hOGG1-transfected oligodendrocytes had fewer apoptotic cells compared with cells containing vector only following treatment with the cytokines. Subsequent experiments revealed that targeting hOGG1 to mitochondria reduces the activation of caspase-9, showing that this recombinant protein works to reduce apoptosis that is occurring through a mitochondria-based pathway.

Palmitoylation is a sorting determinant for transport to the myelin membrane

Myelin is a specialized membrane enriched in glycosphingolipids and cholesterol that contains a restricted set of proteins. The mechanisms by which oligodendrocytes target myelin components to myelin are not known. To identify the sorting determinants for protein transport to myelin, we used a primary oligodendrocyte culture system in which terminal differentiation is synchronized and there is excessive deposition of myelin-like membranes (MLMs). Because several myelin proteins are palmitoylated, we explored the role of acylation in protein transport to MLMs. We found that palmitoylation-deficient mutants of a major myelin protein, proteolipid protein (PLP/DM20), were less efficiently targeted to MLMs. The N-terminal 13 amino acids of PLP/DM20, which are palmitoylated at three sites, were sufficient to direct a fluorescent fusion protein to MLMs. Mutagenesis of the N-terminal palmitoylation motif abolished the transport of the fusion protein to MLMs, indicating that palmitoylation is required for sorting to myelin. Similar results were obtained in myelinating co-cultures of oligodendrocytes and neurons. Furthermore, the combined farnesylation/palmitoylation signals from c-Ha-Ras and the N-terminal consensus sequence for dual palmitoylation from neuromodulin were sufficient for the transport of fluorescent fusion proteins to MLMs. Thus, we conclude that palmitoylation is a sorting determinant for transport to the myelin membrane.

Excitotoxic oligodendrocyte death and axonal damage induced by glutamate transporter inhibition

Glutamate uptake is crucial to terminate glutamate signaling and to prevent excitotoxicity. The present study describes the expression of functional glutamate transporters GLAST and GLT-1 in oligodendrocytes by means of electrophysiology, uptake assays, and immunocytochemistry. Inhibition of glutamate uptake, both in oligodendrocyte cultures and in isolated optic nerves, increases glutamate levels and causes oligodendrocyte excitotoxicity, which is prevented by alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate receptor antagonists. Furthermore, glutamate transporter inhibitors or antisense oligonucleotides applied onto the optic nerve in vivo lead to oligodendroglial loss, massive demyelination, and severe axonal damage. Overall, these results demonstrate that the integrity of oligodendrocytes and white matter depends on proper glutamate transporter function. Deregulated transporter activity may contribute to acute and chronic white matter damage.

Identification of oligodendrocytes in experimental disease models

The ability to identify oligodendrocytes in culture, in fixed tissue, and in vivo using unique markers is a requisite step to understanding their responses in any damage, recovery, or developmental process. Their nuclei are readily seen in histological preparations of healthy white and gray matter, and their cell bodies can be reliably identified with a variety of immunocytochemical markers. However, there is little consensus regarding optimal methods to assess oligodendrocyte survival or morphology under experimental injury conditions. We review common approaches for histological and immunocytochemical identification of these cells. Transgenic and viral methods for cell type-selective transfer of genes encoding fluorescent proteins offer promising new approaches for manipulating and visualizing oligodendrocytes in models of health and disease.

Polychlorinated Biphenyls Disturb Differentiation of Normal Human Neural Progenitor Cells: Clue for Involvement of Thyroid Hormone Receptors

Polychlorinated biphenyls (PCBs) are ubiquitous environmental chemicals that accumulate in adipose tissues over the food chain. Epidemiologic studies have indicated that PCBs influence brain development. Children who are exposed to PCBs during development suffer from neuropsychologic deficits such as a lower full-scale IQ (intelligence quotient), reduced visual recognition memory, and attention and motor deficits. The mechanisms leading to these effects are not fully understood. It has been speculated that PCBs may affect brain development by interfering with thyroid hormone (TH) signaling. Because most of the data are from animal studies, we established a model using primary normal human neural progenitor (NHNP) cells to determine if PCBs interfere with TH-dependent neural differentiation. NHNP cells differentiate into neurons, astrocytes, and oligodendrocytes in culture, and they express a variety of drug metabolism enzymes and nuclear receptors. Like triiodothyronine (T3), treatment with the mono-ortho-substituted PCB-118 (2,3′,4,4′,5-pentachlorobiphenyl; 0.01–1 μM) leads to a dose-dependent increase of oligodendrocyte formation. This effect was congener specific, because the coplanar PCB-126 (3,3′,4,4′,5-pentachlorobiphenyl) had no effect. Similar to the T3 response, the PCB-mediated effect on oligodendrocyte formation was blocked by retinoic acid and the thyroid hormone receptor antagonist NH-3. These results suggest that PCB-118 mimics T3 action via the TH pathway.

Wnt signaling controls the timing of oligodendrocyte development in the spinal cord

During spinal cord development, oligodendrocytes are generated from a restricted region of the ventral ventricular zone and then spread out into the entire spinal cord. These events are controlled by graded inductive and repressive signals derived from a local organizing center. Sonic hedgehog was identified as an essential ventral factor for oligodendrocyte lineage specification, whereas the dorsal cue was less clear. In this study, Wnt proteins were identified as the dorsal factors that directly inhibit oligodendrocyte development. Wnt signaling through a canonical β-catenin pathway prevents its differentiation from progenitor to an immature state. Addition of rmFz-8/Fc, a Wnt antagonist, increased the number of immature oligodendrocytes in the spinal cord explant culture, demonstrating that endogenous Wnt signaling controls oligodendrocyte development.

Inhibition of Src-like Kinases Reveals Akt-dependent and -independent Pathways in Insulin-like Growth Factor I-mediated Oligodendrocyte Progenitor Survival

Insulin-like growth factor I (IGF-I) has been previously shown to promote survival of oligodendrocyte progenitors; however, the underlying mechanisms are not fully understood. Our aim was to investigate the involvement of phosphatidylinositol 3-kinase (PI3K), MEK1, and Src family tyrosine kinases in IGF-I-mediated oligodendrocyte progenitor survival. In agreement with previous studies, IGF-I promoted cell survival. We show that IGF-I prevented apoptosis induced by growth factor deprivation in a PI3K-dependent and MEK/ERK-independent manner. In addition, IGF-I activated Akt while inhibiting caspase-3 activation, and these effects were reversed by the PI3K inhibitors LY 294002 and wortmannin, but not by the MEK1 inhibitor PD 98059. Interestingly, PP2, a specific Src-like kinase inhibitor, blocked the tyrosine phosphorylation of Src, Fyn, and Lyn and IGF-I-stimulated Akt activation, yet had no significant effects on caspase-3 activation or progenitor survival. To further determine whether Akt is required for IGF-I-mediated survival, oligodendrocyte progenitors were transduced with defective Akt mutants or treated with an Akt inhibitor. Although the Akt mutants and inhibitor decreased Akt activity and reduced basal cell survival, IGF-I could partially rescue oligodendrocyte progenitors by decreasing caspase-3 activation. These results suggest that 1) PI3K is essential for IGF-I-promoted cell survival, 2) downstream activation of Akt-dependent and -independent pathways is involved, and 3) Src-like tyrosine kinases participate in IGF-I-induced Akt activation. Therefore, an unidentified effector(s) of PI3K appears to be involved in conferring complete IGF-I-mediated protection of oligodendrocyte progenitors.

Estimating the life-span of oligodendrocytes from clonal data on their development in cell culture

This paper presents a new method to analyze clonal data on oligodendrocyte development in cell culture. The process of oligodendrocyte generation from precursor cells is modelled as a multi-type Bellman–Harris branching process as suggested in an earlier paper [K. Boucher, A. Zorin, A.Y. Yakovlev, M. Mayer-Pröschel, M. Noble, An alternative stochastic model of generation of oligodendrocytes in cell culture, J. Math. Biol. 43 (2001) 22]. This model has been extended to allow for death of oligodendrocytes as well as a dissimilar distribution of the first mitotic cycle duration as compared to the subsequent cycles of precursor cells, which lengths are assumed to be independent and identically distributed random variables. Since the time-span of oligodendrocytes is not directly observable in clonal data, plausible parametric assumptions are invoked to make estimation problems tractable. In particular, the time to cell death follows a two-parameter gamma distribution, while the lapse of time between the event of cell death and the event of cell disintegration is assumed to be exponentially distributed. A simulated pseudo maximum likelihood method for estimation of model parameters has been developed using simulation-based approximations of the expected numbers and variance-covariance matrices for different types of cells. Finite sample properties of the estimation procedure are studied by computer simulations. The proposed method is illustrated with an analysis of the clonal development of O-2A progenitor cells isolated from the rat optic nerve and the corpus callosum.

The Microtubule-associated Protein Tumor Overexpressed Gene Binds to the RNA Trafficking Protein Heterogeneous Nuclear Ribonucleoprotein A2

In neural cells, such as oligodendrocytes and neurons, transport of certain RNAs along microtubules is mediated by the cis-acting heterogeneous nuclear ribonucleoprotein A2 response element (A2RE) trafficking element and the cognate trans-acting heterogeneous nuclear ribonucleoprotein (hnRNP) A2 trafficking factor. Using a yeast two-hybrid screen, we have identified a microtubule-associated protein, tumor overexpressed gene (TOG)2, as an hnRNP A2 binding partner. The C-terminal third of TOG2 is sufficient for hnRNP A2 binding. TOG2, the large protein isoform of TOG, is the only isoform detected in oligodendrocytes in culture. TOG coimmunoprecipitates with hnRNP A2 present in the cytoskeleton (CSK) fraction of neural cells, and both coprecipitate with microtubule stabilized pellets. Staining with anti-TOG reveals puncta that are localized in proximity to microtubules, often at the plus ends. TOG is colocalized with hnRNP A2 and A2RE-mRNA in trafficking granules that remain associated with CSK-insoluble tissue. These data suggest that TOG mediates the association of hnRNP A2-positive granules with microtubules during transport and/or localization.

Effect of tumor necrosis factor-? on developing optic nerve oligodendrocytes in culture

There is increasing evidence that proinflammatory cytokines are involved in the development of periventricular leukomalacia (PVL), a condition in which developing oliodendrocytes (OLs) are preferentially injured. In the present study, we utilized an in vitro assay to demonstrate that the A2B5+ OL progenitors as well as the O4+ prooligodendrocytes (pro-OLs) were more susceptible to tumor necrosis factor-alpha (TNF-alpha) cytotoxicity than the O4+/O1+ immature OLs. OL progenitors were isolated from optic nerves of 7-day-old rat pups and cultured in chemically defined medium supplemented with platelet-derived growth factor and basic fibroblast growth factor. OL progenitors were allowed to differentiate into pro-OLs and immature OLs under special cultural conditions. Cells at three different developmental stages were subjected to TNF-alpha treatment. Cell death, presumably by apoptosis as evidenced by TUNEL staining and caspase-3 activation, was observed following TNF-alpha treatment. Corresponding to TNF-alpha-induced apoptosis, cell survival rate decreased in a time- and dose-dependent manner. The sensitivity of different OL developmental stages to TNF-alpha decreased with the progression of cell maturation. However, this differential response was not related to differentially expressed TNF-alpha receptors. Consistent with reports that progenitor cells are preferentially injured in PVL, our results may further support the role of TNF-alpha as a potential mediator of PVL.

Repeated injuries dramatically affect cells of the oligodendrocyte lineage: Effects of PDGF and NT‐3 in vitro

In multiple sclerosis, relapses occur and remyelination is incomplete, whereas one demyelinating lesion induced by lysophosphatidyl choline (LPC) in rats is completely remyelinated; this process is accelerated by platelet-derived growth factor (PDGF) (Allamargot et al.: Brain Res 918:28-39,2001) and neurotrophin-3 (NT-3) (Jean et al.: Brain Res 972:110-118,2003). Similarly, oligodendrocyte (OL) progenitors might not be depleted by two to three episodes of toxic demyelination (Penderis et al.: Brain 126:1382-1391,2003); nevertheless this does not allow conclusions about the fate of resident cells (mature OL). As myelinated fibers per OL are constantly decreased in chronic MS plaques (Fressinaud and Jean: J Neurochem 85(suppl):100, 2003), this suggests that OL decreased capability to synthesize new myelin membranes could result from successive relapses, impairing thereby remyelination. Thus, we have determined the consequences of multiple versus unique (Fressinaud and Vallat: J Neurosci Res 38:202-213, 1994) LPC treatments on newborn rat brain pure OL cultures, as well as the putative pro-remyelinating effects of PDGF and of NT-3 in these conditions. Split (0.5. 0(-5) M, 6 h x 4) and multiple (2.10(-5) M, 24 h x 2) LPC doses induced more cell loss than a unique treatment (2 x 10(-5) M, 24 h) and there was no recovery. OL progenitors (A2B5+ cells) and differentiated (CNP+) OL were drastically decreased. Moreover, mature (MBP+) OL disappeared from these cultures, indicating that mature OL are also vulnerable to multiple insults. PDGF, as well as NT-3, induced at least partial recovery, and enhanced OL progenitor proliferation. In cultures treated with either of these growth factors, mature OL represented one-fourth of cells and extended numerous ramified processes and putative myelin balls.

Quantitative analysis of human herpesvirus 6 cell tropism

Although HHV-6A and -6B are known to replicate preferably in human T-lymphocytes, in vitro infection of several other cell types has been described. Also, the finding that both variants use the ubiquitous molecule CD46 as a membrane receptor fully supports the possibility of a broad cellular tropism. However, productive infection, which requires complete progression through the viral replication cycle, depends on multiple cellular processes. Our studies were aimed at determining the differences in replication efficiency according to the cell type infected and at relating these differences to the sequential transcriptional events preceding DNA replication. A strong expression of immediate-early, early, and late genes was only seen in the T-lymphoblastoma lines. In the other cell lines, there was no clear correlation between the level of transcription and the final outcome of replication. Finally, we investigated the cytopathic effects of HHV-6 on different cell types of neural origin (oligodendrocytes, astrocytes, and neurons) in greater detail, and found that although all three sustained HHV-6 replication, HHV-6A was more neurovirulent than HHV-6B. This was confirmed in primary human oligodendrocyte cultures.

Resistance of human adult oligodendrocytes to AMPA/kainate receptor-mediated glutamate injury

Multiple sclerosis is an inflammatory disease of the CNS leading to the destruction of oligodendrocytes (OLs), myelin sheaths and axons. The mediators of tissue injury remain unknown. Glutamate, which can be released by activated immune cells or produced within the CNS, has been implicated as a potential mediator of tissue injury in multiple sclerosis. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) and kainate are highly toxic when added to rodent OL cultures. Using OLs derived from human adult surgical specimens, we investigated AMPA/kainate receptor expression and the effects of receptor stimulation on the viability of human OLs. We find that human adult OLs in vitro express low levels of ionotropic glutamate receptors and are resistant to excitotoxicity mediated by high and sustained doses of AMPA or kainate, even when receptor desensitization is blocked. In contrast, rat OLs show strong AMPA receptor expression and are susceptible to excitotoxicity, as previously demonstrated. Furthermore, we show in human brain sections that OLs do not express AMPA receptors in situ and that glial expression of AMPA receptors is limited to astrocytes. The apparent lack of glutamate receptor expression on human OLs and their resistance to AMPA/kainate toxicity should be considered when postulating mechanisms of tissue injury in multiple sclerosis.

Mash1 specifies neurons and oligodendrocytes in the postnatal brain

Progenitors in the telencephalic subventricular zone (SVZ) remain mitotically active throughout life, and produce different cell types at embryonic, postnatal and adult stages. Here we show that Mash1, an important proneural gene in the embryonic telencephalon, is broadly expressed in the postnatal SVZ, in progenitors for both neuronal and oligodendrocyte lineages. Moreover, Mash1 is required at birth for the generation of a large fraction of neuronal and oligodendrocyte precursors from the olfactory bulb. Clonal analysis in culture and transplantation experiments in postnatal brain demonstrate that this phenotype reflects a cell-autonomous function of Mash1 in specification of these two lineages. The conservation of Mash1 function in the postnatal SVZ suggests that the same transcription mechanisms operate throughout life to specify cell fates in this structure, and that the profound changes in the cell types produced reflect changes in the signalling environment of the SVZ.

Signaling from integrins to Fyn to Rho family GTPases regulates morphologic differentiation of oligodendrocytes.

Differentiation of oligodendrocyte progenitor cells requires activation of the Src family kinase Fyn. The signals that are upstream and downstream of Fyn in oligodendrocytes remain essentially unknown. Here we show that extracellular matrix engagement regulates the morphology of oligodendrocytes and activates Fyn. Infection of primary oligodendrocyte cultures with recombinant adenovirus revealed that expression of Fyn or its downstream target p190RhoGAP induced process extension. This phenotypic change was not observed when kinase-inactive Fyn or GAP-defective p190 mutants were expressed. Because Rho family proteins are regulated by p190, we monitored the effects of introducing dominant-negative (DN) or constitutively activated (CA) versions of Rho, Rac1, or Cdc42 into primary oligodendrocyte cultures. Expression of DN Rho, CA Rac1, or CA Cdc42 induced outgrowth of oligodendrocyte processes, whereas introduction of CA Rho, DN Rac1, or DN cdc42 inhibited oligodendrocyte differentiation, indicating that Rho and Cdc42-Rac1 exert opposing effects on oligodendrocyte differentiation. Direct measurement of Rho family activity revealed that RhoA was downregulated, and Cdc42 and Rac1 were upregulated during differentiation of primary oligodendrocytes. Moreover, inhibition of integrin engagement or of Fyn activation blocked activation of Rac1 and cdc42 as well as myelin basic protein expression. Taken together, these results suggest a linear signal transduction pathway of integrin-Fyn-Rho family GTPases that controls morphologic differentiation of oligodendrocytes.

PH Microdomains in Oligodendrocytes

Oligodendrocytes (OLs) are cells that produce myelin in the central nervous system. Here we use ratiometric pH indicator dye to analyze intracellular pH in OLs in culture. The results reveal alkaline microdomains, which predominate in the perikaryon and proximal dendrites, and acidic microdomains, which predominate in distal dendrites. Spatial nonuniformity of pH is generated by differential subcellular distribution of Na(+)/H(+) exchanger (NHE), which is localized in a punctate distribution in the perikaryon and proximal processes, Na(+)/HCO(3)(-) cotransporter (NBC), which is localized in a punctate distribution in distal dendrites, and carbonic anhydrase isotype II (CAII), which is colocalized with either NHE or NBC. Inhibition of NHE activity by amiloride inhibits regeneration of alkaline microdomains after cytoplasmic acidification, whereas the inhibition of CAII activity with ethoxyzolamide inhibits acidification of dendrites. Fluorescence correlation spectroscopy analysis of CAII microinjected into OLs reveals freely diffusing protein throughout the cell as well as protein associated predominantly with NHE in the perikaryon and predominantly with NBC in the dendrites. Alkaline and acidic microdomains could be generated by transport metabolons consisting of CAII associated with NHE or NBC, respectively. This study provides the first evidence for pH microdomains in cells and describes a mechanism for how they are generated.

Virus persistence in an animal model of multiple sclerosis requires virion attachment to sialic acid coreceptors.

Persistent Theiler's virus infection in the central nervous system (CNS) of mice provides a highly relevant animal model for multiple sclerosis. The low-neurovirulence DA strain uses sialic acid as a coreceptor for cell binding before establishing infection. During adaptation of DA virus to growth in sialic acid-deficient cells, three amino acid substitutions (G1100D, T1081I, and T3182A) in the capsid arose, and the virus no longer used sialic acid as a coreceptor. The adapted virus retained acute CNS virulence, but its persistence in the CNS, white matter inflammation, and demyelination were largely abrogated. Infection of murine macrophage but not oligodendrocyte cultures with the adapted virus was also significantly reduced. Substitution of G1100D in an infectious DA virus cDNA clone demonstrated a major role for this mutation in loss of sialic acid binding and CNS persistence. These data indicate a direct role for sialic acid binding in Theiler's murine encephalomyelitis virus persistence and chronic demyelinating disease.

Proteolytic stress causes heat shock protein induction, tau ubiquitination, and the recruitment of ubiquitin to tau-positive aggregates in oligodendrocytes in culture.

Molecular chaperones and the ubiquitin-proteasome system are participants in the defense against unfolded proteins and provide an effective protein quality control system that is essential for cellular functions and survival. Ubiquitinated tau-positive inclusion bodies containing the small heat shock protein alphaB-crystallin in oligodendrocytes are consistent features of a variety of neurodegenerative diseases, and defects in the proteasome system might contribute to the aggregation process. Oligodendrocytes, the myelin-forming cells of the CNS, are specifically sensitive to stress situations. Here we can show that in cultured rat brain oligodendrocytes proteasomal inhibition by MG-132 or lactacystin caused apoptotic cell death and the induction of heat shock proteins in a time- and concentration-dependent manner. Specifically, alphaB-crystallin was upregulated, and ubiquitinated proteins accumulated. After incubation with MG-132 the tau was dephosphorylated, which enhanced its microtubule-binding capacity. Proteasomal inhibition led to ubiquitination of tau and its association with alphaB-crystallin and to the occurrence of thioflavine S-positive aggregates in the oligodendroglial cytoplasm. These aggregates were positive for tau and also contained ubiquitin and alphaB-crystallin; hence they resembled the glial cytoplasmic inclusions observed in white matter disease and frontotemporal dementias with parkinsonism linked to chromosome 17 (FTDP-17). In summary, the data underscore the specific sensitivity of oligodendrocytes to stress situations and point to a causal relationship of proteasomal impairment and inclusion body formation.