Multiple sclerosis (MS) is a neuroinflammatory disease with a relapsing-remitting disease course at early stages, distinct lesion characteristics in cortical gray versus subcortical white matter, and neurodegeneration at chronic stages. We assessed multilineage cell expression changes using single-nucleus RNA sequencing (snRNA-seq) and validated results using multiplex in situ hybridization in MS lesions. We found selective vulnerability and loss of excitatory CUX2 -expressing projection neurons in upper cortical layers underlying meningeal inflammation; such MS neuron populations showed upregulation of stress pathway genes and long non-coding RNAs. Signatures of stressed oligodendrocytes, reactive astrocytes and activated phagocytosing cells mapped most strongly to the rim of MS plaques. Interestingly, snRNA-seq identified phagocytosing microglia and/or macrophages by their ingestion and perinuclear import of myelin transcripts, confirmed by functional mouse and human culture assays. Our findings indicate lineage- and region-specific transcriptomic changes associated with selective cortical neuron damage and glial activation contributing to MS lesion progression.

The age-associated decrease in the efficiency of CNS remyelination has clear implications for recovery from demyelinating diseases such as multiple sclerosis (MS) that may last for several decades. Developing strategies to reverse the age-associated decline requires the identification of how the regenerative process is impaired. We addressed whether remyelination becomes slower because of an impairment of recruitment of oligodendrocyte progenitors (OPs) or, as is the case in some MS lesions, an impairment of OP differentiation into remyelinating oligodendrocytes. The OP response during remyelination of focal, toxin-induced CNS demyelination in young and old rats was compared by in situ hybridization using probes to two OP-expressed mRNA species: platelet-derived growth factor-alpha receptor and the OP transcription factor myelin transcription factor 1 (MyT1). We found that the expression patterns for the two OP markers are very similar and reveal a delay in the colonization of the demyelinated focus with OPs in the old animals compared with the young animals. By comparing the mRNA expression pattern of MyT1 with that of the myelin proteins myelin basic protein and Gtx, we found that in the old animals there is also a delay in OP differentiation that increases with longer survival times. These results indicate that the age-associated decrease in remyelination efficiency occurs because of an impairment of OP recruitment and the subsequent differentiation of the OPs into remyelinating oligodendrocytes, and that strategies aimed at ameliorating the age-associated decline in remyelination efficiency will therefore need to promote both components of the regenerative process.

Aging causes a decline in tissue regeneration due to a loss of function in adult stem and progenitor cell populations 1. An important example is the deterioration of the regenerative capacity of the widespread and abundant population of central nervous system (CNS) multipotent stem cells known as oligodendrocyte progenitor cells (OPCs) 2. A relatively overlooked potential source for this loss of function is the stem cell niche, a source of cell-extrinsic cues including chemical and mechanical signalling 3,4. In this study, we show that the OPC microenvironment stiffens with age, and that this stiffening is sufficient to cause age-related OPC loss of function. Using biological and novel synthetic scaffolds to mimic the stiffness of young brain we find that isolated aged OPCs (aOPCs) cultured on these scaffolds are molecularly and functionally rejuvenated. When we Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Genome-wide association studies (GWAS) have discovered numerous genomic loci associated with Alzheimer’s disease (AD), yet the causal genes and variants remain incompletely identified. We performed an updated genome-wide AD meta-analysis, which identified 37 risk loci, including novel associations near CCDC6 , TSPAN14 , NCK2 , and SPRED2 . Using three SNP-level fine-mapping methods, we identified 21 SNPs with greater than 50% probability each of being causally involved in AD risk, and others strongly suggested by functional annotation. We followed this with colocalization analyses across 109 gene expression quantitative trait loci (eQTL) datasets, and prioritization of genes using protein interaction networks and tissue-specific expression. Combining this information into a quantitative score, we find that evidence converges on likely causal genes, including the above four genes, and those at previously discovered AD loci, including BIN1 , APH1B , PTK2B , PILRA , and CASS4 .

SummaryThe age-related failure to produce oligodendrocytes from oligodendrocyte progenitor cells (OPCs) is associated with irreversible neurodegeneration in multiple sclerosis (MS). Consequently, regenerative approaches have significant potential for treating chronic demyelinating diseases. Here, we show that the differentiation potential of adult rodent OPCs decreases with age. Aged OPCs become unresponsive to pro-differentiation signals, suggesting intrinsic constraints on therapeutic approaches aimed at enhancing OPC differentiation. This decline in functional capacity is associated with hallmarks of cellular aging, including decreased metabolic function and increased DNA damage. Fasting or treatment with metformin can reverse these changes and restore the regenerative capacity of aged OPCs, improving remyelination in aged animals following focal demyelination. Aged OPCs treated with metformin regain responsiveness to pro-differentiation signals, suggesting synergistic effects of rejuvenation and pro-differentiation therapies. These findings provide insight into aging-associated remyelination failure and suggest therapeutic interventions for reversing such declines in chronic disease.

An association between macrophages and remyelination efficiency has been observed in a variety of different models of CNS demyelination. In order to test whether this association is causal or coincidental, we have examined the effects of macrophage depletion on the rate of remyelination of lysolecithin-induced demyelination in the spinal cord of young adult female rats. Macrophage depletion was achieved by reducing the monocyte contribution to the macrophages within the lesion using the clodronate-liposome technique. This technique not only resulted in a decrease in Ox-42-positive cells in the spleen of treated animals but also in the levels of macrophage scavenger receptor type B mRNA expression within the demyelinating lesion. In animals treated with clodronate-liposomes throughout the remyelination process, there was a significant decrease in the extent of oligodendrocyte remyelination at 3 weeks after lesion induction, but no effect on Schwann cell remyelination. If macrophage depletion was delayed until the second half of the remyelination phase, then there was no effect on the repair outcome, implying that macrophages are required for the early stages of CNS remyelination. The results of this study indicate that the macrophage response is an important component of successful CNS remyelination and that approaches to the treatment of demyelinating disease based on inhibition of the inflammatory response may also impair regenerative events that follow demyelination.

Experimentally induced demyelination due to the direct injection of gliotoxic agents has provided powerful models for studying the biology of remyelination. For the most part, these models have involved injection into white matter tracts of the spinal cord. However, the spinal cord has a number of limitations, such as the size of lesions that it is possible to make and its unsuitability for long‐term direct cannulation for the delivery of putative remyelination‐enhancing agents. In this study, we describe the natural history of three new models of demyelination/remyelination based on the stereotaxic injection of three gliotoxins: lysolecithin, ethidium bromide, and a combination of anti‐galactocerebroside antibody and complement (GalC‐ab/comp) into the caudal cerebellar peduncle of adult rats. All three agents produced large areas of demyelination with minimal axonal damage, which undergo extensive remyelination. Ethidium bromide‐ and GalC‐ab/comp‐induced lesions remyelinated more slowly than those induced by lysolecithin. The contribution to the remyelination of the lesion by Schwann cells reflects the degree of astrocyte damage incurred within the demyelinated area and is greatest for ethidium bromide‐induced demyelination. These new models not only provide further insights into the mechanisms of CNS remyelination but also provide a valuable new resource for addressing a series of key issues relevant to current efforts to promote CNS remyelination either by the enhancement of intrinsic processes or by the transplantation of myelinogenic cells. GLIA 25:216–228, 1999. © 1999 Wiley‐Liss, Inc.

Transplanted olfactory ensheathing cells (OECs) are able to remyelinate demyelinated axons and support regrowth of transected axons after transplantation into the adult CNS. Transplanted Schwann cells (SCs) share these repair properties but have limitations imposed on their behavior by the presence of astrocytes (ACs). Because OECs exist alongside astrocytes in the olfactory bulb, we have hypothesized that they have advantages over SCs in transplant‐mediated CNS repair due to an increased ability to integrate and migrate within an astrocytic environment. In this study, we have tested this hypothesis by comparing the interactions between astrocytes and either SCs or OECs, using a range of in vitro assays. We have shown that (1) astrocytes and SCs segregate into defined non‐overlapping domains in co‐culture, whereas astrocytes and OECs freely intermingle; (2) both SCs and OECs will migrate across astrocyte monolayers, but only OECs will migrate into an area containing astrocytes; (3) SCs spend less time in contact with astrocytes than do OECs; and (4) astrocytes undergo hypertrophy when in contact with SCs, but not with OECs. Expression of N‐cadherin has been implicated as a key mediator of the failure of SCs to integrate with astrocytes. However, we found no differences in the intensity of N‐cadherin immunoreactivity between SCs and OECs, suggesting that it is not the adhesion molecule that accounts for the observed differences. In addition, the number of astrocytes expressing chondroitin sulfate proteoglycans (CSPG) is increased when astrocytes are co‐cultured with Schwann cells compared with the number when astrocytes are grown alone or with OECs. Taken together, these data support the hypothesis that OECs will integrate more extensively than Schwann cells in astrocytic environments and are therefore better candidates for transplant‐mediated repair of the damaged CNS. GLIA 32:214–225, 2000. © 2000 Wiley‐Liss, Inc.