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Ageing causes a decline in tissue regeneration owing to a loss of function of adult stem cell and progenitor cell populations1. One 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 of this loss of function is the stem cell 'niche'—a set of cell-extrinsic cues that include chemical and mechanical signals3,4. Here we show that the OPC microenvironment stiffens with age, and that this mechanical change is sufficient to cause age-related loss of function of OPCs. Using biological and synthetic scaffolds to mimic the stiffness of young brains, we find that isolated aged OPCs cultured on these scaffolds are molecularly and functionally rejuvenated. When we disrupt mechanical signalling, the proliferation and differentiation rates of OPCs are increased. We identify the mechanoresponsive ion channel PIEZO1 as a key mediator of OPC mechanical signalling. Inhibiting PIEZO1 overrides mechanical signals in vivo and allows OPCs to maintain activity in the ageing CNS. We also show that PIEZO1 is important in regulating cell number during CNS development. Thus we show that tissue stiffness is a crucial regulator of ageing in OPCs, and provide insights into how the function of adult stem and progenitor cells changes with age. Our findings could be important not only for the development of regenerative therapies, but also for understanding the ageing process itself. Aged progenitor cells in the rat central nervous system can be made to behave as young cells by reducing the stiffness of the tissue microenvironment, or by inhibiting the mechanosensitive protein PIEZO1. [ABSTRACT FROM AUTHOR]

Purpose: With growing evidence that rare single gene disorders present in the neonatal period, there is a need for rapid, systematic, and comprehensive genomic diagnoses in ICUs to assist acute and long-term clinical decisions. This study aimed to identify genetic conditions in neonatal (NICU) and paediatric (PICU) intensive care populations.Methods: We performed trio whole genome sequence (WGS) analysis on a prospective cohort of families recruited in NICU and PICU at a single site in the UK. We developed a research pipeline in collaboration with the National Health Service to deliver validated pertinent pathogenic findings within 2-3 weeks of recruitment.Results: A total of 195 families had whole genome analysis performed (567 samples) and 21% received a molecular diagnosis for the underlying genetic condition in the child. The phenotypic description of the child was a poor predictor of the gene identified in 90% of cases, arguing for gene agnostic testing in NICU/PICU. The diagnosis affected clinical management in more than 65% of cases (83% in neonates) including modification of treatments and care pathways and/or informing palliative care decisions. A 2-3 week turnaround was sufficient to impact most clinical decision-making.Conclusions: The use of WGS in intensively ill children is acceptable and trio analysis facilitates diagnoses. A gene agnostic approach was effective in identifying an underlying genetic condition, with phenotypes and symptomatology being primarily used for data interpretation rather than gene selection. WGS analysis has the potential to be a first-line diagnostic tool for a subset of intensively ill children. [ABSTRACT FROM AUTHOR]

The cerebellum undergoes rapid growth during the third trimester and is vulnerable to injury and deficient growth in infants born prematurely. Factors associated with preterm cerebellar hypoplasia include chronic lung disease and postnatal glucocorticoid administration. We modeled chronic hypoxemia and glucocorticoid administration in neonatal mice to study whole cerebellar and cell type-specific effects of dual exposure. Chronic neonatal hypoxia resulted in permanent cerebellar hypoplasia. This was compounded by administration of prednisolone as shown by greater volume loss and Purkinje cell death. In the setting of hypoxia and prednisolone, administration of a small molecule Smoothened-Hedgehog agonist (SAG) preserved cerebellar volume and protected against Purkinje cell death. Such protective effects were observed even when SAG was given as a one-time dose after dual insult. To model complex injury and determine cell type-specific roles for the hypoxia inducible factor (HIF) pathway, we performed conditional knockout of von Hippel Lindau (VHL) to hyperactivate HIF1α in cerebellar granule neuron precursors (CGNP) or Purkinje cells. Surprisingly, HIF activation in either cell type resulted in no cerebellar deficit. However, in mice administered prednisolone, HIF overactivation in CGNPs resulted in significant cerebellar hypoplasia, whereas HIF overactivation in Purkinje cells caused cell death. Together, these findings indicate that HIF primes both cell types for injury via glucocorticoids, and that hypoxia/HIF + postnatal glucocorticoid administration act on distinct cellular pathways to cause cerebellar injury. They further suggest that SAG is neuroprotective in the setting of complex neonatal cerebellar injury. [ABSTRACT FROM AUTHOR]

Reactive astrocytes are strongly induced by central nervous system (CNS) injury and disease, but their role is poorly understood. Here we show that a subtype of reactive astrocytes, which we termed A1, is induced by classically activated neuroinflammatory microglia. We show that activated microglia induce A1 astrocytes by secreting Il-1α, TNF and C1q, and that these cytokines together are necessary and sufficient to induce A1 astrocytes. A1 astrocytes lose the ability to promote neuronal survival, outgrowth, synaptogenesis and phagocytosis, and induce the death of neurons and oligodendrocytes. Death of axotomized CNS neurons in vivo is prevented when the formation of A1 astrocytes is blocked. Finally, we show that A1 astrocytes are abundant in various human neurodegenerative diseases including Alzheimer's, Huntington's and Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis. Taken together these findings help to explain why CNS neurons die after axotomy, strongly suggest that A1 astrocytes contribute to the death of neurons and oligodendrocytes in neurodegenerative disorders, and provide opportunities for the development of new treatments for these diseases. [ABSTRACT FROM AUTHOR]

Astrocytes, the most abundant cells in the central nervous system, promote synapse formation and help to refine neural connectivity. Although they are allocated to spatially distinct regional domains during development, it is unknown whether region-restricted astrocytes are functionally heterogeneous. Here we show that postnatal spinal cord astrocytes express several region-specific genes, and that ventral astrocyte-encoded semaphorin 3a (Sema3a) is required for proper motor neuron and sensory neuron circuit organization. Loss of astrocyte-encoded Sema3a leads to dysregulated α-motor neuron axon initial segment orientation, markedly abnormal synaptic inputs, and selective death of α- but not of adjacent γ-motor neurons. In addition, a subset of TrkA+ sensory afferents projects to ectopic ventral positions. These findings demonstrate that stable maintenance of a positional cue by developing astrocytes influences multiple aspects of sensorimotor circuit formation. More generally, they suggest that regional astrocyte heterogeneity may help to coordinate postnatal neural circuit refinement. [ABSTRACT FROM AUTHOR]

In colon cancer, mutation of the Wnt repressor APC (encoding adenomatous polyposis coli) leads to a state of aberrant and unrestricted high-activity signaling. However, the relevance of high Wnt tone in non-genetic human disease is unknown. Here we demonstrate that distinct functional states of Wnt activity determine oligodendrocyte precursor cell (OPC) differentiation and myelination. Mouse OPCs with genetic Wnt dysregulation (high tone) express multiple genes in common with colon cancer, including Lef1, Sp5, Ets2, Rnf43 and Dusp4. Surprisingly, we found that OPCs in lesions of hypoxic human neonatal white matter injury upregulated markers of high Wnt activity and lacked expression of APC. We also found that lack of Wnt repressor tone promoted permanent white matter injury after mild hypoxic insult. These findings suggest a state of pathological high-activity Wnt signaling in human disease tissues that lack predisposing genetic mutation. [ABSTRACT FROM AUTHOR]

The basic helix-loop-helix transcription factors oligodendrocyte transcription factor 1 (OLIG1) and OLIG2 are structurally similar and, to a first approximation, coordinately expressed in the developing CNS and postnatal brain. Despite these similarities, it was apparent from early on after their discovery that OLIG1 and OLIG2 have non-overlapping developmental functions in patterning, neuron subtype specification and the formation of oligodendrocytes. Here, we summarize more recent insights into the separate roles of these transcription factors in the postnatal brain during repair processes and in neurological disease states, including multiple sclerosis and malignant glioma. We discuss how the unique functions of OLIG1 and OLIG2 may reflect their distinct genetic targets, co-regulator proteins and/or post-translational modifications. [ABSTRACT FROM AUTHOR]

The subventricular zone of many adult non-human mammals generates large numbers of new neurons destined for the olfactory bulb. Along the walls of the lateral ventricles, immature neuronal progeny migrate in tangentially oriented chains that coalesce into a rostral migratory stream (RMS) connecting the subventricular zone to the olfactory bulb. The adult human subventricular zone, in contrast, contains a hypocellular gap layer separating the ependymal lining from a periventricular ribbon of astrocytes. Some of these subventricular zone astrocytes can function as neural stem cells in vitro, but their function in vivo remains controversial. An initial report found few subventricular zone proliferating cells and rare migrating immature neurons in the RMS of adult humans. In contrast, a subsequent study indicated robust proliferation and migration in the human subventricular zone and RMS. Here we find that the infant human subventricular zone and RMS contain an extensive corridor of migrating immature neurons before 18 months of age but, contrary to previous reports, this germinal activity subsides in older children and is nearly extinct by adulthood. Surprisingly, during this limited window of neurogenesis, not all new neurons in the human subventricular zone are destined for the olfactory bulb-we describe a major migratory pathway that targets the prefrontal cortex in humans. Together, these findings reveal robust streams of tangentially migrating immature neurons in human early postnatal subventricular zone and cortex. These pathways represent potential targets of neurological injuries affecting neonates. [ABSTRACT FROM AUTHOR]

Permanent damage to white matter tracts, comprising axons and myelinating oligodendrocytes, is an important component of brain injuries of the newborn that cause cerebral palsy and cognitive disabilities, as well as multiple sclerosis in adults. However, regulatory factors relevant in human developmental myelin disorders and in myelin regeneration are unclear. We found that AXIN2 was expressed in immature oligodendrocyte progenitor cells (OLPs) in white matter lesions of human newborns with neonatal hypoxic-ischemic and gliotic brain damage, as well as in active multiple sclerosis lesions in adults. Axin2 is a target of Wnt transcriptional activation that negatively feeds back on the pathway, promoting ?-catenin degradation. We found that Axin2 function was essential for normal kinetics of remyelination. The small molecule inhibitor XAV939, which targets the enzymatic activity of tankyrase, acted to stabilize Axin2 levels in OLPs from brain and spinal cord and accelerated their differentiation and myelination after hypoxic and demyelinating injury. Together, these findings indicate that Axin2 is an essential regulator of remyelination and that it might serve as a pharmacological checkpoint in this process. [ABSTRACT FROM AUTHOR]

Oligodendrocytes and astrocytes are macroglial cells of the vertebrate central nervous system. These cells have diverse roles in the maintenance of neurological function. In the embryo, the genetic mechanisms that underlie the specification of macroglial precursors in vivo appear strikingly similar to those that regulate the development of the diverse neuron types. The switch from producing neuronal to glial subtype-specific precursors can be modelled as an interplay between region-restricted components and temporal regulators that determine neurogenic or gliogenic phases of development, contributing to glial diversity. Gaining insight into the developmental genetics of macroglia has great potential to improve our understanding of a variety of neurological disorders in humans. [ABSTRACT FROM AUTHOR]

Although it is known that the methylation of DNA in 5′ promoters suppresses gene expression, the role of DNA methylation in gene bodies is unclear. In mammals, tissue- and cell type-specific methylation is present in a small percentage of 5′ CpG island (CGI) promoters, whereas a far greater proportion occurs across gene bodies, coinciding with highly conserved sequences. Tissue-specific intragenic methylation might reduce, or, paradoxically, enhance transcription elongation efficiency. Capped analysis of gene expression (CAGE) experiments also indicate that transcription commonly initiates within and between genes. To investigate the role of intragenic methylation, we generated a map of DNA methylation from the human brain encompassing 24.7 million of the 28 million CpG sites. From the dense, high-resolution coverage of CpG islands, the majority of methylated CpG islands were shown to be in intragenic and intergenic regions, whereas less than 3% of CpG islands in 5′ promoters were methylated. The CpG islands in all three locations overlapped with RNA markers of transcription initiation, and unmethylated CpG islands also overlapped significantly with trimethylation of H3K4, a histone modification enriched at promoters. The general and CpG-island-specific patterns of methylation are conserved in mouse tissues. An in-depth investigation of the human SHANK3 locus and its mouse homologue demonstrated that this tissue-specific DNA methylation regulates intragenic promoter activity in vitro and in vivo. These methylation-regulated, alternative transcripts are expressed in a tissue- and cell type-specific manner, and are expressed differentially within a single cell type from distinct brain regions. These results support a major role for intragenic methylation in regulating cell context-specific alternative promoters in gene bodies. [ABSTRACT FROM AUTHOR]

Astrocytes are the most abundant and functionally diverse glial population in the vertebrate central nervous system (CNS). However, the mechanisms underlying astrocyte specification are poorly understood. It is well established that cellular diversification of neurons in the embryo is generated by position-dependent extrinsic signals and combinatorial interactions of transcription factors that direct specific cell fates by suppressing alternative fates. It is unknown whether a comparable process determines embryonic astrocyte identity. Indeed, astrocyte development is generally thought to take place in a position-independent manner. Here we show multiple functions of Stem cell leukaemia (Scl, also known as Tal1), which encodes a basic helix–loop–helix (bHLH) transcription factor, in the regulation of both astrocyte versus oligodendrocyte cell fate acquisition and V2b versus V2a interneuron cell fate acquisition in the p2 domain of the developing vertebrate spinal cord. Our findings demonstrate a regionally restricted transcriptional programme necessary for astrocyte and V2b interneuron development, with striking parallels to the involvement of SCL in haematopoiesis. They further indicate that acquisition of embryonic glial subtype identity might be regulated by genetic interactions between SCL and the transcription factor Olig2 in the ventral neural tube. [ABSTRACT FROM AUTHOR]

Vertebrate macroglial cells have diverse roles in the maintenance of neurological function. This review highlights progress in our understanding of the mechanisms that underlie the specification of precursors for two key macroglial subtypes - oligodendrocytes and astrocytes - in the embryo. These mechanisms are strikingly similar to those that underlie the development of neuronal subtypes, including emergence from localized regions of the neural tube, and involvement of common signalling pathways and downstream transcription factors. The switch from neuronal to glial precursor production can be modelled as a complex interplay between regionally-restricted components and generalized temporal regulators. [ABSTRACT FROM AUTHOR]

An Amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

A correction to the article "Parallel states of pathological Wnt signaling in neonatal brain injury and colon cancer" by Stephen P. J. Fancy, Emily P. Harrington, Sergio E. Baranzini, John C. Silbereis, Lawrence R. Shiow, Tracy J. Yuen, Eric J. Huang, Stavros Lomvardas and David H. Rowitch.