Inhibition of neutral sphingomyelinase 2 reduces extracellular vesicle release from neurons, oligodendrocytes, and activated microglial cells following acute brain injury.

Extracellular Vesicles (EVs) are implicated in the spread of pathogenic proteinsin a growing number of neurological diseases. Given this, there is rising interest in developing inhibitors of Neutral Sphingomyelinase 2 (nSMase2), an enzyme critical in EV biogenesis. Our group recently discovered phenyl(R)-(1-(3-(3,4-dimethoxyphenyl)-2,6-dimethylimidazo[1,2-b]pyridazin-8-yl)pyrrolidin-3-yl)carbamate (PDDC), the first potent, selective, orally-available, and brain-penetrable nSMase2 inhibitor, capable of dose-dependently reducing EVs release in vitro and in vivo. Herein, using multiplexed Surface Plasmon Resonance imaging (SPRi), we evaluated which brain cell-derived EVs were affected by PDDC following acute brain injury. Mice were fed PDDC-containing chow at doses which gave steady PDDC brain exposures exceeding its nSMase2 IC50. Mice were then administered an intra-striatal IL-1ß injection and two hours later plasma and brain were collected. IL-1ß injection significantly increased striatal nSMase2 activity which was completely normalized by PDDC. Using SPRi, we found that IL-1ß-induced injury selectively increased plasma levels of CD171 + and PLP1 + EVs; this EV increase was normalized by PDDC. In contrast, GLAST1 + EVs were unchanged by IL-1ß or PDDC. IL-1ß injection selectively increased EVs released from activated versus non-activated microglia, indicated by the CD11b+/IB4 + ratio. The increase in EVs from CD11b + microglia was dramatically attenuated with PDDC. Taken together, our data demonstrate that following acute injury, brain nSMase2 activity is elevated. EVs released from neurons, oligodendrocytes, and activated microglial are increased in plasma and inhibition of nSMase2 with PDDC reduced these IL-1ß-induced changes implicating nSMase2 inhibition as a therapeutic target for acute brain injury.

c-Jun N-terminal kinase 1 (JNK1) modulates oligodendrocyte progenitor cell architecture, proliferation and myelination.

During Central Nervous System ontogenesis, myelinating oligodendrocytes (OLs) arise from highly ramified and proliferative precursors called oligodendrocyte progenitor cells (OPCs). OPC architecture, proliferation and oligodendro-/myelino-genesis are finely regulated by the interplay of cell-intrinsic and extrinsic factors. A variety of extrinsic cues converge on the extracellular signal-regulated kinase/mitogen activated protein kinase (ERK/MAPK) pathway. Here we found that the germinal ablation of the MAPK c-Jun N-Terminal Kinase isoform 1 (JNK1) results in a significant reduction of myelin in the cerebral cortex and corpus callosum at both postnatal and adult stages. Myelin alterations are accompanied by higher OPC density and proliferation during the first weeks of life, consistent with a transient alteration of mechanisms regulating OPC self-renewal and differentiation. JNK1 KO OPCs also show smaller occupancy territories and a less complex branching architecture in vivo. Notably, these latter phenotypes are recapitulated in pure cultures of JNK1 KO OPCs and of WT OPCs treated with the JNK inhibitor D-JNKI-1. Moreover, JNK1 KO and WT D-JNKI-1 treated OLs, while not showing overt alterations of differentiation in vitro, display a reduced surface compared to controls. Our results unveil a novel player in the complex regulation of OPC biology, on the one hand showing that JNK1 ablation cell-autonomously determines alterations of OPC proliferation and branching architecture and, on the other hand, suggesting that JNK1 signaling in OLs participates in myelination in vivo.

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.

Development of type I/II oligodendrocytes regulated by teneurin-4 in the murine spinal cord.

In the spinal cord, the axonal tracts with various caliber sizes are myelinated by oligodendrocytes and function as high-velocity ways for motor and sensory nerve signals. In some neurological disorders, such as multiple sclerosis, demyelination of small caliber axons is observed in the spinal cord. While type I/II oligodendrocytes among the four types are known to myelinate small diameter axons, their characteristics including identification of regulating molecules have not been understood yet. Here, we first found that in the wild-type mouse spinal cord, type I/II oligodendrocytes, positive for carbonic anhydrase II (CAII), were located in the corticospinal tract, fasciculus gracilis, and the inside part of ventral funiculus, in which small diameter axons existed. The type I/II oligodendrocytes started to appear between postnatal day (P) 7 and 11. We further analyzed the type I/II oligodendrocytes in the mutant mice, whose small diameter axons were hypomyelinated due to the deficiency of teneurin-4. In the teneurin-4 deficient mice, type I/II oligodendrocytes were significantly reduced, and the onset of the defect was at P11. Our results suggest that CAII-positive type I/II oligodendrocytes myelinate small caliber axons in the spinal cord and teneurin-4 is the responsible molecule for the generation of type I/II oligodendrocytes.

The effects of fluoxetine on oligodendrocytes in the hippocampus of chronic unpredictable stress-induced depressed model rats.

Depression is a mental illness which is harmful seriously to the society. This study investigated the effects of fluoxetine on the CNPase+ oligodendrocytes in hippocampus of the depressed rats to explore the new target structure of antidepressants. Male Sprague-Dawley rats were used to build chronic unpredictable stress (CUS) depressed model of rats. Then, the depressed rats were divided into the CUS standard group and the CUS + fluoxetine (CUS/FLX) group. The CUS/FLX group was treated with fluoxetine at dose of 5 mg/(kg·d) from the fifth week to seventh week. After 7 weeks CUS intervention, the sucrose preference of the CUS standard group was significantly lower than that of the control group and the CUS/FLX group. The stereological results showed that the total number of the CNPase+ cells in the CA1, CA3, and DG subfield of the hippocampus in the CUS standard group were significantly decreased, when compared with the CNPase+ cells in the control group. However, the total number of the CNPase+ cells in the CA1 and CA3 subfield of the hippocampus in the CUS standard group was significantly decreased when it compared with CNPase+ cells in the CUS/FLX group. Therefore, fluoxetine might prevent the loss of CNPase+ oligodendrocytes in CA1 and CA3 subfields of hippocampus of the depressed rats. The oligodendrocytes in hippocampus may play an important role in the pathogenesis of depression. The current result might provide structural basis for the future studies that search for new antidepressant strategies.

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.

Inhibition of MAPK/ERK pathway promotes oligodendrocytes generation and recovery of demyelinating diseases.

Oligodendrocytes (OLs) are the myelinating glia of the central nervous system. Injury to OLs causes myelin loss. In demyelinating diseases, such as multiple sclerosis, the remyelination is hindered principally due to a failure of the oligodendrocyte precursor cells (OPCs) to differentiate into mature OLs. To identify inducers of OPC to OL differentiation, a high-throughput screening based on myelin basic protein expression using neural progenitor cells-derived OPCs has been performed and, PD0325901-an MEK (MAPK kinase) inhibitor-is found to significantly enhance OPC to OL differentiation in a dose- and time-dependent manner. Other MEK inhibitors also display similar effect, indicating blockade of MAPK-ERK signaling is sufficient to induce OPC differentiation into OLs. PD0325901 facilitates the formation of myelin sheaths in OPC-neuron co-culture in vitro. And in experimental autoimmune encephalomyelitis model and cuprizone-induced demyelination model, PD0325901 displays significant therapeutic effect by promoting myelin regeneration. Our results suggest that targeting the MAPK-ERK pathway might be an intriguing way to develop new therapies for demyelinating diseases.

Loss of the sphingolipid desaturase DEGS1 causes hypomyelinating leukodystrophy.

Sphingolipid imbalance is the culprit in a variety of neurological diseases, some affecting the myelin sheath. We have used whole-exome sequencing in patients with undetermined leukoencephalopathies to uncover the endoplasmic reticulum lipid desaturase DEGS1 as the causative gene in 19 patients from 13 unrelated families. Shared features among the cases include severe motor arrest, early nystagmus, dystonia, spasticity, and profound failure to thrive. MRI showed hypomyelination, thinning of the corpus callosum, and progressive thalamic and cerebellar atrophy, suggesting a critical role of DEGS1 in myelin development and maintenance. This enzyme converts dihydroceramide (DhCer) into ceramide (Cer) in the final step of the de novo biosynthesis pathway. We detected a marked increase of the substrate DhCer and DhCer/Cer ratios in patients' fibroblasts and muscle. Further, we used a knockdown approach for disease modeling in Danio rerio, followed by a preclinical test with the first-line treatment for multiple sclerosis, fingolimod (FTY720, Gilenya). The enzymatic inhibition of Cer synthase by fingolimod, 1 step prior to DEGS1 in the pathway, reduced the critical DhCer/Cer imbalance and the severe locomotor disability, increasing the number of myelinating oligodendrocytes in a zebrafish model. These proof-of-concept results pave the way to clinical translation.

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.

Caspase-1 inhibition prevents glial inflammasome activation and pyroptosis in models of multiple sclerosis.

Multiple sclerosis (MS) is a progressive inflammatory demyelinating disease of the CNS of unknown cause that remains incurable. Inflammasome-associated caspases mediate the maturation and release of the proinflammatory cytokines IL-1ß and IL-18 and activate the pore-forming protein gasdermin D (GSDMD). Inflammatory programmed cell death, pyroptosis, was recently shown to be mediated by GSDMD. Here, we report molecular evidence for GSDMD-mediated inflammasome activation and pyroptosis in both myeloid cells (macrophages/microglia) and, unexpectedly, in myelin-forming oligodendrocytes (ODCs) in the CNS of patients with MS and in the MS animal model, experimental autoimmune encephalomyelitis (EAE). We observed inflammasome activation and pyroptosis in human microglia and ODCs in vitro after exposure to inflammatory stimuli and demonstrate caspase-1 inhibition by the small-molecule inhibitor VX-765 in both cell types. GSDMD inhibition by siRNA transduction suppressed pyroptosis in human microglia. VX-765 treatment of EAE animals reduced the expression of inflammasome- and pyroptosis-associated proteins in the CNS, prevented axonal injury, and improved neurobehavioral performance. Thus, GSDMD-mediated pyroptosis in select glia cells is a previously unrecognized mechanism of inflammatory demyelination and represents a unique therapeutic opportunity for mitigating the disease process in MS and other CNS inflammatory diseases.

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

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

Oligodendrocytes control potassium accumulation in white matter and seizure susceptibility.

The inwardly rectifying K+ channel Kir4.1 is broadly expressed by CNS glia and deficits in Kir4.1 lead to seizures and myelin vacuolization. However, the role of oligodendrocyte Kir4.1 channels in controlling myelination and K+ clearance in white matter has not been defined. Here, we show that selective deletion of Kir4.1 from oligodendrocyte progenitors (OPCs) or mature oligodendrocytes did not impair their development or disrupt the structure of myelin. However, mice lacking oligodendrocyte Kir4.1 channels exhibited profound functional impairments, including slower clearance of extracellular K+ and delayed recovery of axons from repetitive stimulation in white matter, as well as spontaneous seizures, a lower seizure threshold, and activity-dependent motor deficits. These results indicate that Kir4.1 channels in oligodendrocytes play an important role in extracellular K+ homeostasis in white matter, and that selective loss of this channel from oligodendrocytes is sufficient to impair K+ clearance and promote seizures.

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.

Neural cells generated from human induced pluripotent stem cells as a model of CNS involvement in mucopolysaccharidosis type II.

Mucopolysaccharidosis type II (MPSII) is a rare X-linked lysosomal storage disorder caused by mutations in the iduronate-2-sulfatase (IDS) gene (IDS, Xq28). MPSII is characterized by skeletal deformities, hearing loss, airway obstruction, hepatosplenomegaly, cardiac valvular disease, and progressive neurological impairment. At the cellular level, IDS deficiency leads to lysosomal storage of glycosaminoglycans (GAGs), dominated by accumulation of dermatan and heparan sulfates. Human induced pluripotent stem cells (iPSC) represent an alternative system that complements the available MPSII murine model. Herein we report on the reprogramming of peripheral white blood cells from male and female MPSII patients into iPSC using a non-integrating protocol based on the Sendai virus vector system. We differentiated the iPSC lines into IDS deficient and GAG accumulating ß-Tubulin III+ neurons, GFAP+ astrocytes, and CNPase+ oligodendrocytes. The lysosomal system in these cells displayed structural abnormalities reminiscent of those previously found in patient tissues and murine IDS deficient neuronal stem cells. Furthermore, quantitative determination of GAGs revealed a moderate increase in GAG levels in IDS deficient neurons and glia. We also tested the effects of recombinant IDS and found that the exogenous enzyme was internalized from the culture media and partially decreased the intracellular GAG levels in iPSC-derived neural cells; however, it failed to completely prevent accumulation of GAGs. In summary, we demonstrate that this human iPSC based model expresses the cellular and biochemical features of MPSII, and thus represents a useful experimental tool for further pathogenesis studies as well as therapy development and testing.

The Protein Tyrosine Phosphatase Shp2 Regulates Oligodendrocyte Differentiation and Early Myelination and Contributes to Timely Remyelination.

Shp2 is a nonreceptor protein tyrosine phosphatase that has been shown to influence neurogenesis, oligodendrogenesis, and oligodendrocyte differentiation. Furthermore, Shp2 is a known regulator of the Akt/mammalian target of rapamycin and ERK signaling pathways in multiple cellular contexts, including oligodendrocytes. Its role during later postnatal CNS development or in response to demyelination injury has not been examined. Based on the current studies, we hypothesize that Shp2 is a negative regulator of CNS myelination. Using transgenic mouse technology, we show that Shp2 is involved in oligodendrocyte differentiation and early myelination, but is not necessary for myelin maintenance. We also show that Shp2 regulates the timely differentiation of oligodendrocytes following lysolecithin-induced demyelination, although apparently normal remyelination occurs at a delayed time point. These data suggest that Shp2 is a relevant therapeutic target in demyelinating diseases such as multiple sclerosis.SIGNIFICANCE STATEMENT In the present study, we show that the protein phosphatase Shp2 is an important mediator of oligodendrocyte differentiation and myelination, both during developmental myelination as well as during myelin regeneration. We provide important insight into the signaling mechanisms regulating myelination and propose that Shp2 acts as a transient brake to the developmental myelination process. Furthermore, we show that Shp2 regulates oligodendrocyte differentiation following demyelination and therefore has important therapeutic implications in diseases such as multiple sclerosis.

Decreased levels of PDI and P5 in oligodendrocytes in Alzheimer's disease.

Protein disulfide isomerase (PDI) is a chaperone protein located in the endoplasmic reticulum (ER). Nitric oxide-induced S-nitrosylation of PDI inhibits its enzymatic activity, leading to protein accumulation and activation of the unfolded protein response. Protein disulfide isomerase P5 (P5) is a member of the PDI family that mostly localizes to the ER lumen. Both S-nitrosylated PDI and S-nitrosylated P5 are found in Alzheimer's disease (AD) brain. Previously, we showed that expression of the ER stress marker, growth arrest, and DNA damage protein (GADD34) was significantly increased in neurons and oligodendrocytes in AD brain. In the present study, we showed that PDI and P5 levels were significantly decreased in oligodendrocytes in the brains of AD patients and an AD mouse model. Interestingly, these decreases were evident before the animals displayed typical AD pathology. Because we previously showed that small short interfering RNA knockdown of PDI or P5 could affect the viability of neuronal cells under ER stress, dysfunction of PDI and P5 under ER stress could cause apoptosis of neuronal cells. In summary, we showed that the levels of PDI and P5 were significantly decreased in the oligodendrocytes of AD patients. This phenomenon was also found in an AD mouse model before the animals displayed AD pathology. The overall findings suggest that oligodendrocytes may play important roles in AD pathogenesis.

Acid sphingomyelinase deficiency enhances myelin repair after acute and chronic demyelination.

The cuprizone animal model, also known as the toxic demyelination model, is a well-reproducible model of demyelination- and remyelination in mice, and has been useful in studying important aspect of human demyelinating diseases, including multiple sclerosis. In this study, we investigated the role of acid sphingomyelinase in demyelination and myelin repair by inducing acute and chronic demyelination with 5- or 12-week cuprizone treatment, followed by a 2-week cuprizone withdrawal phase to allow myelin repair. Sphingolipids, in particular ceramide and the enzyme acid sphingomyelinase, which generates ceramide from sphingomyelin, seem to be involved in astrocyte activation and neuronal damage in multiple sclerosis. We used immunohistochemistry to study glial reaction and oligodendrocyte distribution in acid sphingomyelinase deficient mice and wild-type C57BL/6J littermates at various time intervals after demyelination and remyelination. Axonal injury was quantified using amyloid precursor protein and synaptophysin, and gene expression and protein levels were measured using gene analysis and Western blotting, respectively. Our results show that mice lacking acid sphingomyelinase had a significant increase in myelin recovery and a significantly higher oligodendrocyte cell count after 2 weeks remyelination compared to wild-type littermates. Detrimental astroglial distribution was also significantly reduced in acid sphingomyelinase deficient animals. We obtained similar results in experiments using amitriptyline to inhibit acid sphingomyelinase. These findings suggest that acid sphingomyelinase plays a significant role in myelin repair, and its inhibition by amitriptyline may constitute a novel therapeutic approach for multiple sclerosis patients.

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.

In vivocharacterization of the aspartyl-tRNA synthetase DARS: Homing in on the leukodystrophy HBSL.

BACKGROUND: The recently diagnosed leukodystrophy Hypomyelination with Brain stem and Spinal cord involvement and Leg spasticity (HBSL) is caused by mutations of the cytoplasmic aspartyl-tRNA synthetase geneDARS. The physiological role of DARS in translation is to accurately pair aspartate with its cognate tRNA. Clinically, HBSL subjects show a distinct pattern of hypomyelination and develop progressive leg spasticity, variable cognitive impairment and epilepsy. To elucidate the underlying pathomechanism, we comprehensively assessed endogenous DARS expression in mice. Additionally, aiming at creating the first mammalian HBSL model, we genetically engineered and phenotyped mutant mice with a targetedDarslocus. RESULTS: DARS, although expressed in all organs, shows a distinct expression pattern in the adult brain with little immunoreactivity in macroglia but enrichment in neuronal subpopulations of the hippocampus, cerebellum, and cortex. Within neurons, DARS is mainly located in the cell soma where it co-localizes with other components of the translation machinery. Intriguingly, DARS is also present along neurites and at synapses, where it potentially contributes to local protein synthesis.Dars-null mice are not viable and die before embryonic day 11. Heterozygous mice with only one functionalDarsallele display substantially reduced DARS levels in the brain; yet these mutants show no gross abnormalities, including unchanged motor performance. However, we detected reduced pre-pulse inhibition of the acoustic startle response indicating dysfunction of attentional processing inDars+/-mice. CONCLUSIONS: Our results, for the first time, show an in-depth characterization of the DARS tissue distribution in mice, revealing surprisingly little uniformity across brain regions or between the major neural cell types. The complete loss of DARS function is not tolerated in mice suggesting that the identified HBSL mutations in humans retain some residual enzyme activity. The mild phenotype of heterozygousDars-null carriers indicates that even partial restoration of DARS levels would be therapeutically relevant. Despite the fact that they do not resemble the full spectrum of clinical symptoms, the robust pre-pulse inhibition phenotype ofDars+/-mice will be instrumental for future preclinical therapeutic efficacy studies. In summary, our data is an important contribution to a better understanding of DARS function and HBSL pathology.

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.