Disease-associated oligodendrocyte signatures in neurodegenerative disease: the known and unknown.

Nine neurodegenerative diseases, including spinocerebellar ataxia type 7 (SCA7), are caused by the expansion of polyglutamine stretches in the respective disease-causing proteins. A hallmark of these diseases is the aggregation of expanded polyglutamine-containing proteins in nuclear inclusions that also accumulate molecular chaperones and components of the ubiquitin-proteasome system. Manipulation of HSP70 and HSP40 chaperone levels has been shown to suppress aggregates in cellular models, prevent neuronal death in Drosophila, and improve to some extent neurological symptoms in mouse models. An important issue in mammals is the relative expression levels of toxic and putative rescuing proteins. Furthermore, overexpression of both HSP70 and its co-factor HSP40/HDJ2 has never been investigated in mice. We decided to address this question in a SCA7 transgenic mouse model that progressively develops retinopathy, similar to SCA7 patients. To co-express HSP70 and HDJ2 with the polyglutamine protein, in the same cell type, at comparable levels and with the same time course, we generated transgenic mice that express the heat shock proteins specifically in rod photoreceptors. While co-expression of HSP70 with its co-factor HDJ2 efficiently suppressed mutant ataxin-7 aggregation in transfected cells, they did not prevent either neuronal toxicity or aggregate formation in SCA7 mice. Furthermore, nuclear inclusions in SCA7 mice were composed of a cleaved mutant ataxin-7 fragment, whereas they contained the full-length protein in transfected cells. We propose that differences in the aggregation process might account for the different effects of chaperone overexpression in cellular and animal models of polyglutamine diseases.

Oligodendrocyte Progenitor Cell Susceptibility to Injury in Multiple Sclerosis

Remyelination of lesions in the central nervous system contributes to neural repair following clinical relapses in multiple sclerosis. Remyelination is initiated by recruitment and differentiation of oligodendrocyte progenitor cells (OPCs) into myelinating oligodendrocytes. Simvastatin, a blood-brain barrier-permeable statin in multiple sclerosis clinical trials, has been shown to impact the in vitro processes that have been implicated in remyelination. Animals were fed a cuprizone-supplemented diet for 6 weeks to induce localized demyelination in the corpus callosum; subsequent return to normal diet for 3 weeks stimulated remyelination. Simvastatin was injected intraperitoneally during the period of coincident demyelination and OPC maturation (weeks 4 to 6), throughout the entire period of OPC responses (weeks 4 to 9), or during the remyelination-only phase (weeks 7 to 9). Simvastatin treatment (weeks 4 to 6) caused a decrease in myelin load and both Olig2(strong) and Nkx2.2(strong) OPC numbers. Simvastatin treatment (weeks 4 to 9 and 7 to 9) caused a decrease in myelin load, which was correlated with a reduction in Nkx2.2(strong) OPCs and an increase in Olig2(strong) cells, suggesting that OPCs were maintained in an immature state (Olig2(strong)/Nkx2.2(weak)). NogoA+ oligodendrocyte numbers were decreased during all simvastatin treatment regimens. Our findings suggest that simvastatin inhibits central nervous system remyelination by blocking progenitor differentiation, indicating the need to monitor effects of systemic immunotherapies that can access the central nervous system on brain tissue-repair processes.

AGC1-deficiency is a rare genetic neurodegenerative disease caused by defects in the SLC25A12 gene encoding for a mitochondrial aspartate-glutamate carrier, important in the metabolism of brain amino acids and myelin synthesis. AGC1 mutations lead to drastic reduction of carrier activity, which results in hypotonia, developmental delay, intractable epilepsy and cortical atrophy with altered myelin formation in the CNS, most likely due to a dramatic reduction of N-acetyl aspartate levels in the brain. The aim of this thesis was to study the molecular mechanisms underlying AGC1-deficiency in appropriate in vitro (oligodendrocyte precursor cells) and in vivo (SLC25A12 heterozygous knockout mice) disease models in particular by focusing on oligodendrocyte precursor alterations to better define pathogenetic mechanisms that could potentially lead to identify new interesting therapeutic targets. Furthermore, our study focused on the evaluation of Neural Stem Cells proliferation and differentiation in neuronal and glia cells, both astrocytes and oligodendrocytes, in neurospheres derived from the subventricular zone of our mouse model. Lastly, preliminary experiments have been performed on NSCs derived from induced Pluripotent Stem cells from AGC1-deficiency patients and healthy controls, in order to further validate our data in human cells. All results showed a proliferation deficit of OPCs that was not due to mitochondrial biochemical alterations, but rather associated with an alteration of trophic factors essential for maintaining the balance between oligodendrocyte proliferation and differentiation, mainly PDGFα and TGFβ. These results supported that alterations induced by AGC1 reduced activity could impair the physiological cross-talk mediated by growth factors between neurons and OPCs necessary for OPCs proliferation and neuronal survival. The importance of this study lies also on the fact that mitochondrial dysfunction is at the basis not only of AGC1-deficiency, but also of other neurodegenerative and demyelinating diseases, some of which are rare, while others are widely spread, such as multiple sclerosis.

The formation of myelin around axons by oligodendrocytes (OL) poses an enormous synthetic and energy challenge for the glial cell. Local translation of transcripts, including the mRNA for the essential myelin protein Myelin Basic Protein (MBP) at the site of myelin deposition has been recognised as an efficient mechanism to assure proper myelin sheath assembly. Oligodendroglial precursor cells (OPCs) form synapses with neurons and may localise many additional mRNAs in a similar fashion to synapses between neurons. In some diseases in which demyelination occurs, an abundance of OPCs is present but there is a failure to efficiently remyelinate and to synthesise MBP. This compromises axonal survival and function. OPCs are especially sensitive to cellular stress as occurring in neurodegenerative diseases, which can impinge on their ability to translate mRNAs into protein. Stress causes the build up of cytoplasmic stress granules (SG) in which many RNAs are sequestered and translationally stalled until the stress ceases. Chronic stress in particular could convert this initially protective reaction of the cell into damage, as persistence of SG may lead to pathological aggregate formation or long-term translation block of SG-associated RNAs. The recent recognition that many neurodegenerative diseases often exhibit an early white matter pathology with a proliferation of surviving OPCs, renders a study of the stress-associated processes in oligodendrocytes and OPCs especially relevant. Here, we discuss a potential dysfunction of RNA regulation in myelin diseases such as Multiple Sclerosis (MS) and Vanishing white matter disease (VWM) and potential contributions of OL dysfunction to neurodegenerative diseases such as Amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Fragile X syndrome (FXS).

Oligodendrocytes and the “Micro Brake” of Progenitor Cell Proliferation

Preterm cerebral white matter injury (WMI), a major form of prenatal brain injury, may potentially be treated by oligodendrocyte (OL) precursor cell (OPC) transplantation. However, the defective differentiation of OPCs during WMI seriously hampers the clinical application of OPC transplantation. Thus, improving the ability of transplanted OPCs to differentiate is critical to OPC transplantation therapy for WMI. We established a hypoxia-ischemia-induced preterm WMI model in mice and screened the molecules affected by WMI using single-cell RNA sequencing. We revealed that endothelin (ET)-1 and endothelin receptor B (ETB) are a pair of signaling molecules responsible for the interaction between neurons and OPCs and that preterm WMI led to an increase in the number of ETB-positive OPCs and premyelinating OLs. Furthermore, the maturation of OLs was reduced by knocking out ETB but promoted by stimulating ET-1/ETB signaling. Our research reveals a new signaling module for neuron-OPC interaction and provides new insight for therapy targeting preterm WMI.

BackgroundCNS myelination disturbances commonly occur in chronic white matter lesions in neurodevelopmental and adult neurological disorders. Recent studies support that myelination failure can involve a disrupted cellular repair mechanism where oligodendrocyte (OL) progenitor cells (OPCs) proliferate in lesions with diffuse astrogliosis, but fail to fully differentiate to mature myelinating OLs. There are no in vitro models that reproduce these features of myelination failure.ResultsForebrain coronal slices from postnatal day (P) 0.5/1 rat pups were cultured for 1, 5, or 9 days in vitro (DIV). Slices rapidly exhibited diffuse astrogliosis and accumulation of the extracellular matrix glycosaminoglycan hyaluronan (HA), an inhibitor of OPC differentiation and re-myelination. At 1 DIV ~1.5% of Olig2+ OLs displayed caspase-3 activation, which increased to ~11.5% by 9 DIV. At 1 DIV the density of PDGFRα+ and PDGFRα+/Ki67+ OPCs were significantly elevated compared to 0 DIV (P < 0.01). Despite this proliferative response, at 9 DIV ~60% of white matter OLs were late progenitors (preOLs), compared to ~7% in the postnatal day 10 rat (P < 0.0001), consistent with preOL maturation arrest. Addition of HA to slices significantly decreased the density of MBP+ OLs at 9 DIV compared to controls (217 ± 16 vs. 328 ± 17 cells/mm2, respectively; P = 0.0003), supporting an inhibitory role of HA in OL lineage progression in chronic lesions.ConclusionsDiffuse white matter astrogliosis and early OPC proliferation with impaired OL maturation were reproduced in this model of myelination failure. This system may be used to define mechanisms of OPC maturation arrest and myelination failure related to astrogliosis and HA accumulation.

Protein Fate in Neurodegenerative Proteinopathies: Polyglutamine Diseases Join the (Mis)Fold

Objective Cell therapy is a possible effective way to treat myelination disorder diseases.Cell therapy needs to apply a method for culturing oligodendrocyte precursor cells.Therefore, this study was to develop a stable, efficient and economical method for obtaining human oligodendrocyte precursor cells(OPCs) in order to provide cell required for clinical treatment.And this will provide a new option for clinical applications. Methods Human OPCs were obtained through magnetic bead sorting and cultured in OPCs proliferation medium.For a short-time(2, 4, 6, 8 days) and long-time culture, morphology of OPCs was observed.The fourth generation of OPCs was analyzed for expression of OPCs specific markers O4, Sox10 and platelet derived growth factor alpla receptors(PDGFαR) and the capacity to differentiate into oligodendrocytes by immunofluorescence staining.At the same time, the effects of B27 and N1 on OPCs growth state were inspected as well. Results For a short-time culture, OPCs had typical bipolar or tripolar morphology and proliferated in good condition.For a long-time culture, all 4 generations OPCs had typical bipolar or tripolar morphology; the fourth generation OPCs highly(>90%) expressed O4, Sox10 and PDGFαR, after induction, OPCs could be differentiated into oligodendrocytes.After 4 generations of long-time culture, OPCs already maintained the ori-ginal sharp, high purity and had the capacity to differentiate into oligodendrocytes.It was indicated that this culture system was suitable for human OPCs for a long-time culture. Conclusions Overall, using this culture system, isolated human OPCs not only can be stably cultured and proliferated in vitro, but also have the capacity to differentiate into oligodendrocytes.From this reproducible method, a large number of human OPCs can be stably obtained in vitro as conve-nient as possible.And this will provide a new option for clinical applications.This method uses fewer cytokines.Therefore, this method will provide stable, efficient and economical OPCs for cell therapy of myelination disorders or myelin damage diseases. Key words: White matter damage; Oligodendrocyte precursor cells; Proliferation; Oligodendrocyte

Neuroprotective effects of vascular endothelial growth factor A in the experimental autoimmune encephalomyelitis model of multiple sclerosis

White matter disease (WMD) study, which underlies the subsequent progress of cerebral palsy as well as cognitive impairment of premature and/or low birth weight infants, has been focused either on the hypoxia-ischemia damage or cytokine-induced brain damage related with maternal or fetal inflammation. Also, dexamethasone (DEXA) may increase the risk of neuropsychological problem including adverse cognitive and behavioral outcome in preterm infants. Thus, we hypothesized that perinatal DEXA would damage and trigger the death of developing oligodendrocytes (OL) progenitors, and subsequently disturb myelination. In this study, DEXA was administered to neonatal rats for 3 consecutive days subcutaneously between postnatal day 1 (P1) and P3. By using immunofluorescent staining of stage specific OL progenitor markers such as O4 and O1, the morphological changes of OL progenitors were examined and the apoptosis of OL progenitors were visualized by TUNEL staining. Results depicted that relative number of O1 immunoreactive (IR) cells were less to that of O4 IR cells. Multipolar O1 IR cells with short dendritic processes were observed in both control and DEXA group at P3. In the total O1 immunoreactive cells, the relative percentages of apoptosis cells were calculated at P3 as 8.7% in control, 23.0% in DEXA group. The relative percentages of apoptosis in the total O4 immunoreactive cells were measured at P3 as 3.0% in control and 13.5% in DEXA group. OL progenitors' apoptosis may contribute to the overall reduction of immature OLs in cerebral white matter. Therefore, specific stages of OL maturation could clinically be an important factor in determining the susceptibility to DEXA. To elucidate the disease mechanism of the white matter disease, further investigation may be needed whether OL progenitors' decrease by the DEXA administration affects to the myelin formation as developmental stages.

Neuroprotective Effect of Oligodendrocyte Precursor Cell Transplantation in a Long-Term Model of Periventricular Leukomalacia

Increasing neuroimaging studies have revealed gray matter (GM) and white matter (WM) anomalies of several brain regions by voxel-based morphometry (VBM) studies on patients with spinocerebellar ataxia type 3 (SCA3); however, the findings of previous studies on SCA3 patients by VBM studies remain inconsistent. The study aimed to identify consistent findings of gray matter (GM) and white matter (WM) changes in SCA3 patients by voxel-wise meta-analysis of whole-brain VBM studies. VBM studies comparing GM or WM changes in SCA3 patients and healthy controls (HCs) were retrieved from PubMed, Embase, Web of Science, and Medline databases from January 1990 to February 2023. Manual searches were also conducted, and authors of studies were contacted for additional data. The coordinates with significant differences in GM and WM between SCA3 patients and HCs were extracted from each cluster. A meta-analysis was performed using anisotropic effect size-based signed differential mapping (AES-SDM) software. A total of seven studies comprising 160 SCA3 patients and 165 HCs were included in the GM volume meta-analysis. Three studies comprising 57 SCA3 patients and 63 HCs were included for WM volume meta-analysis. Compared with HC subjects, the reduced GM volume in SCA3 patients was found in the bilateral cerebellar hemispheres, cerebellar vermis, pons, right lingual gyrus, and right fusiform gyrus. The decreased WM volume was mainly concentrated in the bilateral cerebellar hemispheres, right corticospinal tract, middle cerebellar peduncles, cerebellar vermis, and left lingual gyrus. No increased density or volume of any brain structures was found. In the jackknife sensitivity analysis, the results remained largely robust. Our meta-analysis clearly found the shrinkage of GM and WM volume in patients with SCA3. These lesions are involved in ataxia symptoms, abnormal eye movements, visual impairment, cognitive impairment, and affective disorders. The findings can explain the clinical manifestations and provide a morphological basis for SCA3.

Certain murine leukemia viruses (MLVs) are capable of inducing fatal progressive spongiform motor neuron disease in mice that is largely mediated by viral Env glycoprotein expression within central nervous system (CNS) glia. While the etiologic mechanisms and the glial subtypes involved remain unresolved, infection of NG2 glia was recently observed to correlate spatially and temporally with altered neuronal physiology and spongiogenesis. Since one role of NG2 cells is to serve as oligodendrocyte (OL) progenitor cells (OPCs), we examined here whether their infection by neurovirulent (FrCasE) or nonneurovirulent (Fr57E) ecotropic MLVs influenced their viability and/or differentiation. Here, we demonstrate that OPCs, but not OLs, are major CNS targets of both FrCasE and Fr57E. We also show that MLV infection of neural progenitor cells (NPCs) in culture did not affect survival, proliferation, or OPC progenitor marker expression but suppressed certain glial differentiation markers. Assessment of glial differentiation in vivo using transplanted transgenic NPCs showed that, while MLVs did not affect cellular engraftment or survival, they did inhibit OL differentiation, irrespective of MLV neurovirulence. In addition, in chimeric brains, where FrCasE-infected NPC transplants caused neurodegeneration, the transplanted NPCs proliferated. These results suggest that MLV infection is not directly cytotoxic to OPCs but rather acts to interfere with OL differentiation. Since both FrCasE and Fr57E viruses restrict OL differentiation but only FrCasE induces overt neurodegeneration, restriction of OL maturation alone cannot account for neuropathogenesis. Instead neurodegeneration may involve a two-hit scenario where interference with OPC differentiation combined with glial Env-induced neuronal hyperexcitability precipitates disease. A variety of human and animal retroviruses are capable of causing central nervous system (CNS) neurodegeneration manifested as motor and cognitive deficits. These retroviruses infect a variety of CNS cell types; however, the specific role each cell type plays in neuropathogenesis remains to be established. The NG2 glia, whose CNS functions are only now emerging, are a newly appreciated viral target in murine leukemia virus (MLV)-induced neurodegeneration. Since one role of NG2 glia is that of oligodendrocyte progenitor cells (OPCs), we investigated here whether their infection by the neurovirulent MLV FrCasE contributed to neurodegeneration by affecting OPC viability and/or development. Our results show that both neurovirulent and nonneurovirulent MLVs interfere with oligodendrocyte differentiation. Thus, NG2 glial infection could contribute to neurodegeneration by preventing myelin formation and/or repair and by suspending OPCs in a state of persistent susceptibility to excitotoxic insult mediated by neurovirulent virus effects on other glial subtypes.