Neuregulin-1 converts reactive astrocytes toward oligodendrocyte lineage cells via upregulating the PI3K-AKT-mTOR pathway to repair spinal cord injury.

Axonal demyelination is a consistent pathological characteristic of Spinal cord injury (SCI). Promoting differentiation of oligodendrocytes is of importance for remyelination. Conversion of reactive astrocytes with stem cell potential to oligodendrocytes is proposed as an innovative strategy for SCI repair. Neuregulin-1 (Nrg1) plays an essential role in the differentiation of oligodendrocytes. Therefore, it's a potential treatment for demyelination in SCI that using Nrg1 to drive reactive astrocytes toward oligodendrocyte lineage cells. In this study, tumor necrosis factor-α (TNF-α) was used to induce dedifferentiation of primary rat spinal cord astrocytes into reactive astrocytes and Nrg1 was used to induce astrocytes in vitro and in vivo. The results showed that astrocytes treated with TNF-α expressed immaturity markers CD44 and Musashi1 at mRNA and protein levels, indicating that TNF-α induced the stem cell state of astrocytes. Nrg1 induced reactive astrocytes to express oligodendrocyte markers PDGFR-α and O4 at mRNA and protein levels, indicating that Nrg1 directly converts reactive astrocytes toward oligodendrocyte lineage cells. Moreover, upregulation of PI3K-AKT-mTOR signaling activation in response to Nrg1 was observed. In rats with SCI, intrathecal treatment with Nrg1 converted reactive astrocytes to oligodendrocyte lineage cells, inhibited astrogliosis, promoted remyelination, protected axons and eventually improved BBB score. All the biological effects of Nrg1 were significantly reversed by the co-administration of Nrg1 and ErbB inhibitor, suggesting that Nrg1 functioned through the receptor ErbB. Our findings indicate that Nrg1 is sufficient to trans-differentiate reactive astrocytes to oligodendrocytes via the PI3K-AKT-mTOR signaling pathway and repair SCI. Delivery of Nrg1 for the remyelination processes could be a promising strategy for spinal cord repair.

Aß oligomers promote oligodendrocyte differentiation and maturation via integrin ß1 and Fyn kinase signaling.

Alzheimer´s disease (AD) is characterized by a progressive cognitive decline that correlates with the levels of amyloid ß-peptide (Aß) oligomers. Strong evidences connect changes of oligodendrocyte function with the onset of neurodegeneration in AD. However, the mechanisms controlling oligodendrocyte responses to Aß are still elusive. Here, we tested the role of Aß in oligodendrocyte differentiation, maturation, and survival in isolated oligodendrocytes and in organotypic cerebellar slices. We found that Aß peptides specifically induced local translation of 18.5-kDa myelin basic protein (MBP) isoform in distal cell processes concomitant with an increase of process complexity of MBP-expressing oligodendrocytes. Aß oligomers required integrin ß1 receptor, Src-family kinase Fyn and Ca2+/CaMKII as effectors to modulate MBP protein expression. The pharmacological inhibition of Fyn kinase also attenuated oligodendrocyte differentiation and survival induced by Aß oligomers. Similarly, using ex vivo organotypic cerebellar slices Aß promoted MBP upregulation through Fyn kinase, and modulated oligodendrocyte population dynamics by inducing cell proliferation and differentiation. Importantly, application of Aß to cerebellar organotypic slices enhanced remyelination and oligodendrocyte lineage recovery in lysolecithin (LPC)-induced demyelination. These data reveal an important role of Aß in oligodendrocyte lineage function and maturation, which may be relevant to AD pathogenesis.

TIMP-1 Promotes Oligodendrocyte Differentiation Through Receptor-Mediated Signaling.

The extracellular protein tissue inhibitor of metalloproteinase (TIMP)-1 is both a matrix metalloproteinase (MMP) inhibitor and a trophic factor. Mice lacking TIMP-1 exhibit delayed central nervous system myelination during postnatal development and impaired remyelination following immune-mediated injury in adulthood. We have previously determined that the trophic action of TIMP-1 on oligodendrocyte progenitor cells (OPCs) to mature into oligodendrocytes is independent of its MMP inhibitory function. However, the mechanism by which TIMP-1 promotes OPC differentiation is not known. To address this gap in our understanding, herein, we report that TIMP-1 signals via a CD63/ß1-integrin receptor complex to activate Akt (protein kinase B) to promote ß-catenin signaling in OPCs. The regulation of ß-catenin by TIMP-1 to promote OPC differentiation was counteracted, but not abrogated, by canonical signaling evoked by Wnt7a. These data provide a previously uncharacterized trophic action of TIMP-1 to regulate oligodendrocyte maturation via a CD63/ß1-integrin/Akt pathway mechanism. These findings contribute to our emerging understanding on the role of TIMP-1 as a growth factor expressed to promote CNS myelination during development and induced in the adult to promote myelin repair.

Increased ceruloplasmin expression caused by infiltrated leukocytes, activated microglia, and astrocytes in injured female rat spinal cords.

Ceruloplasmin (Cp), an enzyme containing six copper atoms, has important roles in iron homeostasis and antioxidant defense. After spinal cord injury (SCI), the cellular components in the local microenvironment are very complex and include functional changes of resident cells and the infiltration of leukocytes. It has been confirmed that Cp is elevated primarily in astrocytes and to a lesser extent in macrophages following SCI in mice. However, its expression in other cell types is still not very clear. In this manuscript, we provide a sensible extension of these findings by examining this system within a female Sprague-Dawley rat model and expanding the scope of inquiry to include additional cell types. Quantitative reverse transcription polymerase chain reaction and Western blot analysis revealed that the Cp mRNA and protein in SCI tissue homogenates were quite consistent with prior publications. However, we observed that Cp was expressed not only in GFAP+ astrocytes (consistent with prior reports) but also in CD11b+ microglia, CNPase+ oligodendrocytes, NeuN+ neurons, CD45+ leukocytes, and CD68+ activated microglia/macrophages. Quantitative analysis proved that infiltrated leukocytes, activated microglia/macrophages, and astrocytes should be the major sources of increased Cp.

Folate Metabolism Regulates Oligodendrocyte Survival and Differentiation by Modulating AMPKα Activity.

Folate, an essential micronutrient, is a critical cofactor in one-carbon metabolism for many cellular pathways including DNA synthesis, metabolism and maintenance. Folate deficiency has been associated with an increased risk of neurological disease, cancer and cognitive dysfunction. Dihydrofolate reductase (DHFR) is a key enzyme to regulate folate metabolism, however folate/DHFR activity in oligodendrocyte development has not been fully understood. Here we show that folate enhances oligodendrocyte maturation both in vitro and in vivo, which is accompanied with upregulation of oligodendrocyte-specific DHFR expression. On the other hand, pharmacological inhibition of DHFR by methotrexate (MTX) causes severe defects in oligodendrocyte survival and differentiation, which could be reversed by folate intake. We further demonstrate that folate activates a metabolic regulator AMPKα to promote oligodendrocyte survival and differentiation. Moreover, activation of AMPKα partially rescues oligodendrocyte defects caused by DHFR-inhibition both in vitro and in vivo. Taken together, these findings identify a previously uncharacterized role of folate/DHFR/AMPKα axis in regulating oligodendrocyte survival and myelination during CNS development.

N-acetylaspartate supports the energetic demands of developmental myelination via oligodendroglial aspartoacylase.

Breakdown of neuro-glial N-acetyl-aspartate (NAA) metabolism results in the failure of developmental myelination, manifest in the congenital pediatric leukodystrophy Canavan disease caused by mutations to the sole NAA catabolizing enzyme aspartoacylase. Canavan disease is a major point of focus for efforts to define NAA function, with available evidence suggesting NAA serves as an acetyl donor for fatty acid synthesis during myelination. Elevated NAA is a diagnostic hallmark of Canavan disease, which contrasts with a broad spectrum of alternative neurodegenerative contexts in which levels of NAA are inversely proportional to pathological progression. Recently generated data in the nur7 mouse model of Canavan disease suggests loss of aspartoacylase function results in compromised energetic integrity prior to oligodendrocyte death, abnormalities in myelin content, spongiform degeneration, and motor deficit. The present study utilized a next-generation "oligotropic" adeno-associated virus vector (AAV-Olig001) to quantitatively assess the impact of aspartoacylase reconstitution on developmental myelination. AAV-Olig001-aspartoacylase promoted normalization of NAA, increased bioavailable acetyl-CoA, and restored energetic balance within a window of postnatal development preceding gross histopathology and deteriorating motor function. Long-term effects included increased oligodendrocyte numbers, a global increase in myelination, reversal of vacuolation, and rescue of motor function. Effects on brain energy observed following AAV-Olig001-aspartoacylase gene therapy are shown to be consistent with a metabolic profile observed in mild cases of Canavan disease, implicating NAA in the maintenance of energetic integrity during myelination via oligodendroglial aspartoacylase.

Krabbe disease: involvement of connexin43 in the apoptotic effects of sphingolipid psychosine on mouse oligodendrocyte precursors.

Krabbe disease is a genetic demyelinating syndrome characterized by deficiency of the enzyme ß-galactosylceramidase, lysosomal psychosine accumulation, and loss of myelin-forming cells. In this study, some apoptotic markers such as apoptotic index (AI), DNA fragmentation, caspase-3, PTEN, Bad, and PI3K were determined in oligodendrocyte precursors from wild type or twitcher mice untreated or treated with psychosine. Twitcher is a natural mouse model of Krabbe disease containing a premature stop codon (W339X) in the ß-galactosylceramidase gene. Moreover, a possible involvement of connexin (Cx)43 in cell death of oligodendrocyte precursors induced by psychosine was investigated with the final aim to provide a contribution to the knowledge of the molecular mechanisms and pathophysiological events that occur in Krabbe disease. Connexins are a multigene family of structurally related trans-membrane proteins able to modulate essential cellular processes such as proliferation, differentiation and migration. Among these, Cx43 is the predominant isoform in many cell types, including neural progenitor cells. Our results showed an increase of AI, DNA fragmentation, caspase-3, PTEN, Bad, and Cx43 associated to a decrease of PI3K, pAKT and pBad. Taken together, these findings suggest an involvement of Cx43 in the psychosine-mediated apoptosis of primary oligodendrocyte progenitors from wild type or twitcher mice, used for the first time as cell models in comparison. It could open unexplored perspective also for other demyelinating diseases.

Activation of CB2 receptor is required for the therapeutic effect of ABHD6 inhibition in experimental autoimmune encephalomyelitis.

Alpha/beta-hydrolase domain 6 (ABHD6) is a novel 2-arachidonoylglycerol (2-AG) hydrolytic enzyme, that can fine-tune the endocannabinoid signaling in the central nervous system. Recently we and others have demonstrated the protective effect of ABHD6 inhibition in the animal models of traumatic brain injury and epileptic seizures. In this study, we investigated the role of targeting ABHD6 in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Post-symptom treatment with an ABHD6 inhibitor WWL70 increased the brain levels of 2-AG and ameliorated the clinical signs of EAE, T cells infiltration, microglia activation and the expression of activated leukocyte cell adhesion molecules. The production of iNOS, COX-2, TNF-α and IL-1ß and the phosphorylation of NF-κB were also significantly reduced by WWL70 treatment. The neuroprotective effect of WWL70 was demonstrated by increased survival of mature oligodendrocytes, reduced demyelination and axonal loss in WWL70 treated EAE mouse spinal cord. The therapeutic effect of WWL70 on EAE was absent by co-administration of CB2 receptor antagonist, but not CB1 receptor antagonist. Consistently, WWL70 did not afford any protection in CB2 receptor knockout mice after EAE induction. Given the increased expression of ABHD6 in microglia/macrophages, but not in T cells, we speculated that inhibition of ABHD6 might enhance 2-AG signaling particularly in microglia/macrophages to exert anti-inflammatory effects via activation of CB2 receptors. These results suggest that inhibition of ABHD6 might be used as an ideal strategy for the treatment of MS and other neurodegenerative diseases.

IL-17A activates ERK1/2 and enhances differentiation of oligodendrocyte progenitor cells.

Inflammatory signals present in demyelinated multiple sclerosis lesions affect the reparative remyelination process conducted by oligodendrocyte progenitor cells (OPCs). Interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and interleukin (IL)-6 have differing effects on the viability and growth of OPCs, however the effects of IL-17A are largely unknown. Primary murine OPCs were stimulated with IL-17A and their viability, proliferation, and maturation were assessed in culture. IL-17A-stimulated OPCs exited the cell cycle and differentiated with no loss in viability. Expression of the myelin-specific protein, proteolipid protein, increased in a cerebellar slice culture assay in the presence of IL-17A. Downstream, IL-17A activated ERK1/2 within 15 min and induced chemokine expression in 2 days. These results demonstrate that IL-17A exposure stimulates OPCs to mature and participate in the inflammatory response.

5-Fluorouracil causes severe CNS demyelination by disruption of TCF7L2/HDAC1/HDAC2 complex in adolescent mice.

Several studies have showed the anti-cancer efficacy of 5-FU (5-fluorouracil) on pediatric tumors. Although the delayed demyelination induced by 5-FU in adult patients has been reported, the effect of 5-FU on oligodendrocyte myelination in adolescence is still unknown. Here, we demonstrate that systemic administration with 5-FU leads to immediate demyelination in the central nervous system (CNS) of adolescent mice, which is mainly attributed to the death of OLs. Gene-chip microarray transcriptome analysis identifies that oligodendrocyte-specific factor TCF7L2 may be a toxic target of 5-FU-impaired myelination. 5-FU-decreased TCF7L2 results in disruption of the interaction between TCF7L2 and HDAC1/2. Inhibition of crucial myelination-promoting factors by 5-FU is more significantly antagonized by co-transfection of TCF7L2, HDAC1 and HDAC2 than TCF7L2 alone. Our findings reveal that 5-FU could acutely induce the severe myelin degeneration in adolescence and disruption of TCF7L2/HDAC1/HDAC2 complex is at least partially involved in 5-FU-induced demyelination.

Ceramide galactosyltransferase expression is regulated positively by Nkx2.2 and negatively by OLIG2.

Myelin, a multilamellar structure extended from oligodendrocytes or Schwann cells, plays a critical role in maintenance of neuronal function, and damage or loss of myelin causes demyelinating diseases such as multiple sclerosis. For precise alignment of the myelin sheath, there is a requirement for expression of galactosylceramide (GalCer), a major glycosphingolipid in myelin. Synthesis of GalCer is strictly limited in oligodendrocytes in a developmental stage-specific manner. Ceramide galactosyltransferase (CGT), a key enzyme for biosynthesis of GalCer, exhibits restricted expression in oligodendrocytes but the mechanism is poorly understood. Based on our assumption that particular oligodendrocyte-lineage-specific transcription factors regulate CGT expression, we co-expressed a series of candidate transcription factors with the human CGT promoter-driving luciferase expression in oligodendroglioma cells to measure the promoter activity. We found that Nkx2.2 strongly activated the CGT promoter. In addition, we identified a novel repressive DNA element in the first intron of CGT and OLIG2, an oligodendrocyte-specific transcription factor, as a binding protein of this element. Moreover, overexpression of OLIG2 completely canceled the activating effect of Nkx2.2 on CGT promoter activity. Expression of CGT mRNA was also upregulated by Nkx2.2, but this upregulation was cancelled by co-expression of OLIG2 with Nkx2.2. Our study suggests that CGT expression is controlled by balanced expression of the negative modulator OLIG2 and positive regulator Nkx2.2, providing new insights into how expression of GalCer is tightly regulated in cell-type- and stage-specific manners.

Histone deacetylase expression in white matter oligodendrocytes after stroke.

Histone deacetylases (HDACs) constitute a super-family of enzymes grouped into four major classes (Class I-IV) that deacetylate histone tails leading to chromatin condensation and gene repression. Whether stroke-induced oligodendrogenesis is related to the expression of individual HDACs in the oligodendrocyte lineage has not been investigated. We found that 2 days after stroke, oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes (OLGs) were substantially reduced in the peri-infarct corpus callosum, whereas at 7 days after stroke, a robust increase in OPCs and OLGs was observed. Ischemic brains isolated from rats sacrificed 7 days after stroke were used to test levels of individual members of Class I (1 and 2) and Class II (4 and 5) HDACs in white matter oligodendrocytes during stroke-induced oligodendrogenesis. Double immunohistochemistry analysis revealed that stroke substantially increased the number of NG2+OPCs with nuclear HDAC1 and HDAC2 immunoreactivity and cytoplasmic HDAC4 which were associated with augmentation of proliferating OPCs, as determined by BrdU and Ki67 double reactive cells after stroke. A decrease in HDAC1 and an increase in HDAC2 immunoreactivity were detected in mature adenomatous polyposis coli (APC) positive OLGs, which paralleled an increase in newly generated BrdU positive OLGs in the peri-infarct corpus callosum. Concurrently, stroke substantially decreased the acetylation levels of histones H3 and H4 in both OPCs and OLGs. Taken together, these findings demonstrate that stroke induces distinct profiles of Class I and Class II HDACs in white matter OPCs and OLGs, suggesting that the individual members of Class I and II HDACs play divergent roles in the regulation of OPC proliferation and differentiation during brain repair after stroke.

Pten loss in Olig2 expressing neural progenitor cells and oligodendrocytes leads to interneuron dysplasia and leukodystrophy.

Therapeutic modulation of phosphatidylinositol 3-kinase (PI3K)/PTEN signaling is currently being explored for multiple neurological indications including brain tumors and seizure disorders associated with cortical malformations. The effects of PI3K/PTEN signaling are highly cell context dependent but the function of this pathway in specific subsets of neural stem/progenitor cells generating oligodendroglial lineage cells has not been fully studied. To address this, we created Olig2-cre:Pten(fl/fl) mice that showed a unique pattern of Pten loss and PI3K activation in Olig2-lineage cells. Olig2-cre:Pten(fl/fl) animals progressively developed central nervous system white matter hypermyelination by 3 weeks of age leading to later onset leukodystrophy, chronic neurodegeneration, and death by 9 months. In contrast, during immediate postnatal development, oligodendroglia were unaffected but abnormal and accelerated differentiation of lateral subventricular zone stem cells produced calretinin-positive interneuron dysplasia. Neural stem cells isolated from Olig2-cre:Pten(fl/fl) mice also exhibited accelerated differentiation and proliferation into calretinin-positive interneurons and oligodendrocytes indicating such effects are cell autonomous. Opposition of the pathway by treatment of human primary neural progenitor cells (NPCs) with the PI3K inhibitor, NVP-BKM120, blocked in vitro differentiation of neurons and oligodendroglia indicating PI3K/PTEN effects on NPCs can be bidirectional. In summary, our results suggest Pten is a developmental rheostat regulating interneuron and oligodendroglial differentiation and support testing of PI3K modulating drugs as treatment for developmental and myelination disorders. However, such agents may need to be administered at ages that minimize potential effects on early stem/progenitor cell development.

Inhibition of NADPH oxidase activation in oligodendrocytes reduces cytotoxicity following trauma.

Spinal cord injury is a debilitating neurological disorder that initiates a cascade of cellular events that result in a period of secondary damage that can last for months after the initial trauma. The ensuing outcome of these prolonged cellular perturbations is the induction of neuronal and glial cell death through excitotoxic mechanisms and subsequent free radical production. We have previously shown that astrocytes can directly induce oligodendrocyte death following trauma, but the mechanisms regulating this process within the oligodendrocyte remain unclear. Here we provide evidence demonstrating that astrocytes directly regulate oligodendrocyte death after trauma by inducing activation of NADPH oxidase within oligodendrocytes. Spinal cord injury resulted in a significant increase in oxidative damage which correlated with elevated expression of the gp91 phox subunit of the NADPH oxidase enzyme. Immunohistochemical analysis confirmed the presence of gp91 phox in oligodendrocytes in vitro and at 1 week following spinal cord injury. Exposure of oligodendrocytes to media from injured astrocytes resulted in an increase in oligodendrocyte NADPH oxidase activity. Inhibition of NADPH oxidase activation was sufficient to attenuate oligodendrocyte death in vitro and at 1 week following spinal cord injury, suggesting that excitotoxicity of oligodendrocytes after trauma is dependent on the intrinsic activation of the NADPH oxidase enzyme. Acute administration of the NADPH oxidase inhibitor apocynin and the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate channel blocker 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione significantly improved locomotor behavior and preserved descending axon fibers following spinal cord injury. These studies lead to a better understanding of oligodendrocyte death after trauma and identify potential therapeutic targets in disorders involving demyelination and oligodendrocyte death.

Nf1 loss and Ras hyperactivation in oligodendrocytes induce NOS-driven defects in myelin and vasculature.

Patients with neurofibromatosis type 1 (NF1) and Costello syndrome Rasopathy have behavioral deficits. In NF1 patients, these may correlate with white matter enlargement and aberrant myelin. To model these features, we induced Nf1 loss or HRas hyperactivation in mouse oligodendrocytes. Enlarged brain white matter tracts correlated with myelin decompaction, downregulation of claudin-11, and mislocalization of connexin-32. Surprisingly, non-cell-autonomous defects in perivascular astrocytes and the blood-brain barrier (BBB) developed, implicating a soluble mediator. Nitric oxide (NO) can disrupt tight junctions and gap junctions, and NO and NO synthases (NOS1-NOS3) were upregulated in mutant white matter. Treating mice with the NOS inhibitor NG-nitro-L-arginine methyl ester or the antioxidant N-acetyl cysteine corrected cellular phenotypes. CNP-HRasG12V mice also displayed locomotor hyperactivity, which could be rescued by antioxidant treatment. We conclude that Nf1/Ras regulates oligodendrocyte NOS and that dysregulated NO signaling in oligodendrocytes can alter the surrounding vasculature. The data suggest that antioxidants may improve some behavioral deficits in Rasopathy patients.

12/15-lipoxygenase expression is increased in oligodendrocytes and microglia of periventricular leukomalacia.

Oxidative stress involving premyelinating oligodendrocytes (OLs) is a major factor in the pathogenesis of preterm white matter injury. In animal and cell culture studies, activation of the lipid-oxidizing enzyme 12/15-lipoxygenase (12/15-LOX) plays a central role as an inflammatory mediator in the pathology of oxidative stress and OL cell death, as well as ischemia and neuronal death. The role of 12/15-LOX, however, is unclear in the developing human brain. The mechanism of 12/15-LOX involves the production of reactive oxygen species through the metabolism of arachidonic acid, as well as direct detrimental effects on organelle membranes. Here we tested the hypothesis that the density of 12/15-LOX-expressing cells is increased in periventricular leukomalacia (PVL). Using immunocytochemistry (ICC) in human paraffin-embedded tissue, 12/15-LOX expression was seen in macrophages of the focally necrotic lesions in the periventricular white matter, as well as in glial cells throughout the surrounding white matter with reactive gliosis. Interestingly, no significant 12/15-LOX expression was detected in neurons in the cerebral cortex overlying the damaged white matter. Using a scoring system from 0 to 3, we assessed the density of 12/15-LOX-expressing cells in diffusely gliotic white matter from 20 to 43 postconceptional (PC) weeks in 19 PVL cases (median = 36 PC weeks) and 10 control (non-PVL) cases (median = 34 PC weeks). The density of 12/15-LOX-positive cells was significantly increased in the diffuse component of PVL (score = 1.17 ± 0.15) compared to controls (score = 0.48 ± 0.21; p = 0.014). Using double-label ICC, 12/15-LOX was observed in PVL in OLs of the O4 and O1 premyelinating stages, as well as in mature OLs as determined with the mature OL marker adenomatous polyposis coli (APC). In addition, 12/15-LOX expression was present in a population of CD68-positive activated microglia. There was no 12/15-LOX expression in reactive astrocytes. Finally we observed terminal deoxynucleotide transferase dUTP nick end-labeling-positive cells within the white matter of PVL that expressed 12/15-LOX and/or within close proximity of 12/15-LOX-positive cells. Our data support a role for 12/15-LOX activation as an inflammatory mediator of injury in PVL, with a contribution of 12/15-LOX to PVL-induced damage to or cell death of OLs, including those at the O1 and O4 stages.

Oligodendrocyte dysfunction in the pathogenesis of amyotrophic lateral sclerosis.

Oligodendrocytes are well known targets for immune-mediated and infectious diseases, and have been suggested to play a role in neurodegeneration. Here, we report the involvement of oligodendrocytes and their progenitor cells in the ventral grey matter of the spinal cord in amyotrophic lateral sclerosis, a neurodegenerative disease of motor neurons. Degenerative changes in oligodendrocytes were abundantly present in human patients with amyotrophic lateral sclerosis and in an amyotrophic lateral sclerosis mouse model. In the mouse model, morphological changes in grey matter oligodendrocytes became apparent before disease onset, increasingly so during disease progression, and oligodendrocytes ultimately died. This loss was compensated by increased proliferation and differentiation of oligodendrocyte precursor cells. However, these newly differentiated oligodendrocytes were dysfunctional as suggested by their reduced myelin basic protein and monocarboxylate transporter 1 expression. Mutant superoxide dismutase 1 was found to directly affect monocarboxylate transporter 1 protein expression. Our data suggest that oligodendroglial dysfunction may be a contributor to motor neuron degeneration in amyotrophic lateral sclerosis.

Is myelin a mitochondrion?

It has been hypothesized that myelin acts like a mitochondrion, generating ATP across the membranes of its sheath. By calculating the proton motive force across the myelin membrane based on known values for the pH and membrane potential of the oligodendrocyte, we find that insufficient energy could be harvested from proton flow across the myelin membrane to synthesize ATP. In fact, if the respiratory chain were present in the myelin membrane, then the ATP synthase would function in reverse, hydrolyzing rather than synthesizing ATP. This calculation places the hypothesis of an energy-producing role for myelin in considerable doubt.

Characterisation and metabolism of astroglia-rich primary cultures from cathepsin K-deficient mice.

Cathepsin K is important for the brain, because its deficiency in mice is associated with a marked decrease in differentiated astrocytes and changes in neuronal patterning in the hippocampus as well as with learning and memory deficits. As cathepsin K activity is most prominent in hippocampal regions of wild type animals, we hypothesised alterations in astrocyte-mediated support of neurons as a potential mechanism underlying the impaired brain functions in cathepsin K-deficient mice. To address this hypothesis, we have generated and characterised astroglia-rich primary cell cultures from cathepsin K-deficient and wild type mice and compared these cultures for possible changes in metabolic support functions and cell composition. Interestingly, cells expressing the oligodendrocytic markers myelin-associated glycoprotein and myelin basic protein were more frequent in astroglia-rich cultures from cathepsin K-deficient mice. However, cell cultures from both genotypes were morphologically comparable and similar with respect to glucose metabolism. In addition, specific glutathione content, glutathione export and γ-glutamyl-transpeptidase activity remained unchanged, whereas the specific activities of glutathione reductase and glutathione-S-transferase were increased by around 50% in cathepsin K-deficient cultures. Thus, lack of cathepsin K in astroglia-rich cultures appears not to affect metabolic supply functions of astrocytes but to facilitate the maturation of oligodendrocytes.

The galactocerebrosidase enzyme contributes to maintain a functional neurogenic niche during early post-natal CNS development.

We report a novel role for the lysosomal galactosylceramidase (GALC), which is defective in globoid cell leukodystrophy (GLD), in maintaining a functional post-natal subventricular zone (SVZ) neurogenic niche. We show that proliferation/self-renewal of neural stem cells (NSCs) and survival of their neuronal and oligodendroglial progeny are impaired in GALC-deficient mice. Using drugs to modulate inflammation and gene transfer to rescue GALC expression and activity, we show that lipid accumulation resulting from GALC deficiency acts as a cell-autonomous pathogenic stimulus in enzyme-deficient NSCs and progeny before upregulation of inflammatory markers, which later sustain a non-cell-autonomous dysfunction. Importantly, we provide evidence that supply of functional GALC provided by neonatal intracerebral transplantation of NSCs ameliorates the functional impairment in endogenous SVZ cells. Insights into the mechanism/s underlying GALC-mediated regulation of early post-natal neurogenic niches improve our understanding of the multi-component pathology of GLD. The occurrence of a restricted period of SVZ neurogenesis in infancy supports the implications of our study for the development of therapeutic strategies to treat this severe pediatric neurodegenerative disorder.