RESUMEN
Myelin is required for the function of neuronal axons in the central nervous system, but the mechanisms that support myelin health are unclear. Although macrophages in the central nervous system have been implicated in myelin health1, it is unknown which macrophage populations are involved and which aspects they influence. Here we show that resident microglia are crucial for the maintenance of myelin health in adulthood in both mice and humans. We demonstrate that microglia are dispensable for developmental myelin ensheathment. However, they are required for subsequent regulation of myelin growth and associated cognitive function, and for preservation of myelin integrity by preventing its degeneration. We show that loss of myelin health due to the absence of microglia is associated with the appearance of a myelinating oligodendrocyte state with altered lipid metabolism. Moreover, this mechanism is regulated through disruption of the TGFß1-TGFßR1 axis. Our findings highlight microglia as promising therapeutic targets for conditions in which myelin growth and integrity are dysregulated, such as in ageing and neurodegenerative disease2,3.
Asunto(s)
Sistema Nervioso Central , Microglía , Vaina de Mielina , Adulto , Animales , Humanos , Ratones , Axones/metabolismo , Sistema Nervioso Central/citología , Sistema Nervioso Central/metabolismo , Sistema Nervioso Central/patología , Microglía/citología , Microglía/metabolismo , Microglía/patología , Vaina de Mielina/metabolismo , Vaina de Mielina/patología , Enfermedades Neurodegenerativas/metabolismo , Enfermedades Neurodegenerativas/patología , Oligodendroglía/metabolismo , Oligodendroglía/patología , Cognición , Factor de Crecimiento Transformador beta1/metabolismo , Receptor Tipo I de Factor de Crecimiento Transformador beta/metabolismo , Metabolismo de los Lípidos , Envejecimiento/metabolismo , Envejecimiento/patologíaRESUMEN
Multiple sclerosis (MS) is a highly prevalent demyelinating autoimmune condition; the mechanisms regulating its severity and progression are unclear. The IL-17-producing Th17 subset of T cells has been widely implicated in MS and in the mouse model, experimental autoimmune encephalomyelitis (EAE). However, the differentiation and regulation of Th17 cells during EAE remain incompletely understood. Although evidence is mounting that the antimicrobial peptide cathelicidin profoundly affects early T cell differentiation, no studies have looked at its role in longer-term T cell responses. Now, we report that cathelicidin drives severe EAE disease. It is released from neutrophils, microglia, and endothelial cells throughout disease; its interaction with T cells potentiates Th17 differentiation in lymph nodes and Th17 to exTh17 plasticity and IFN-γ production in the spinal cord. As a consequence, mice lacking cathelicidin are protected from severe EAE. In addition, we show that cathelicidin is produced by the same cell types in the active brain lesions in human MS disease. We propose that cathelicidin exposure results in highly activated, cytokine-producing T cells, which drive autoimmunity; this is a mechanism through which neutrophils amplify inflammation in the central nervous system.
Asunto(s)
Encefalomielitis Autoinmune Experimental , Esclerosis Múltiple , Animales , Péptidos Catiónicos Antimicrobianos , Péptidos Antimicrobianos , Diferenciación Celular , Encefalomielitis Autoinmune Experimental/patología , Células Endoteliales/metabolismo , Humanos , Ratones , Ratones Endogámicos C57BL , Células TH1/metabolismo , Células TH1/patología , Células Th17/metabolismo , CatelicidinasRESUMEN
Maternal viral infection and immune response are known to increase the risk of altered development of the foetal brain. Given the ongoing global pandemic of coronavirus disease 2019 (COVID-19), investigating the impact of SARS-CoV-2 on foetal brain health is of critical importance. Here, we report the presence of SARS-CoV-2 in first and second trimester foetal brain tissue in association with cortical haemorrhages. SARS-CoV-2 spike protein was sparsely detected within progenitors and neurons of the cortex itself, but was abundant in the choroid plexus of haemorrhagic samples. SARS-CoV-2 was also sparsely detected in placenta, amnion and umbilical cord tissues. Cortical haemorrhages were linked to a reduction in blood vessel integrity and an increase in immune cell infiltration into the foetal brain. Our findings indicate that SARS-CoV-2 infection may affect the foetal brain during early gestation and highlight the need for further study of its impact on subsequent neurological development.
Asunto(s)
COVID-19 , Complicaciones Infecciosas del Embarazo , Embarazo , Femenino , Humanos , SARS-CoV-2/fisiología , Glicoproteína de la Espiga del Coronavirus , HemorragiaRESUMEN
Injury to the developing brain during the perinatal period often causes hypomyelination, leading to clinical deficits for which there is an unmet therapeutic need. Dysregulation of inflammation and microglia have been implicated, yet the molecular mechanisms linking these to hypomyelination are unclear. Using human infant cerebrospinal fluid (CSF) and postmortem tissue, we found that microglial activation of the pro-inflammatory molecular complex the NLRP3 inflammasome is associated with pathology. By developing a novel mouse brain explant model of microglial inflammasome activation, we demonstrate that blocking the inflammasome rescues myelination. In human and mouse, we discovered a link between the inflammasome product IL1ß and increased levels of follistatin, an endogenous inhibitor of activin-A. Follistatin treatment was sufficient to reduce myelination, whereas myelination was rescued in injured explants upon follistatin neutralization or supplementation with exogenous activin-A. Our data reveal that inflammasome activation in microglia drives hypomyelination and identifies novel therapeutic strategies to reinstate myelination following developmental injury.
Asunto(s)
Lesiones Encefálicas , Sustancia Blanca , Activinas , Animales , Modelos Animales de Enfermedad , Folistatina , Inflamasomas/metabolismo , Ratones , Microglía/metabolismo , Proteína con Dominio Pirina 3 de la Familia NLR/metabolismo , Sustancia Blanca/metabolismoRESUMEN
Microglia of the developing brain have unique functional properties but how their activation states are regulated is poorly understood. Inflammatory activation of microglia in the still-developing brain of preterm-born infants is associated with permanent neurological sequelae in 9 million infants every year. Investigating the regulators of microglial activation in the developing brain across models of neuroinflammation-mediated injury (mouse, zebrafish) and primary human and mouse microglia we found using analysis of genes and proteins that a reduction in Wnt/ß-catenin signalling is necessary and sufficient to drive a microglial phenotype causing hypomyelination. We validated in a cohort of preterm-born infants that genomic variation in the Wnt pathway is associated with the levels of connectivity found in their brains. Using a Wnt agonist delivered by a blood-brain barrier penetrant microglia-specific targeting nanocarrier we prevented in our animal model the pro-inflammatory microglial activation, white matter injury and behavioural deficits. Collectively, these data validate that the Wnt pathway regulates microglial activation, is critical in the evolution of an important form of human brain injury and is a viable therapeutic target.
Asunto(s)
Encéfalo/metabolismo , Inflamación/metabolismo , Microglía/metabolismo , Vía de Señalización Wnt/fisiología , Animales , Animales Modificados Genéticamente , Barrera Hematoencefálica/metabolismo , Células Cultivadas , Biología Computacional , Humanos , Ratones , Pez CebraRESUMEN
The most prevalent neurological disorders of myelin include perinatal brain injury leading to cerebral palsy in infants and multiple sclerosis in adults. Although these disorders have distinct etiologies, they share a common neuropathological feature of failed progenitor differentiation into myelin-producing oligodendrocytes and lack of myelin, for which there is an unmet clinical need. Here, we reveal that a molecular pathology common to both disorders is dysregulation of activin receptors and that activin receptor signaling is required for the majority of myelin generation in development and following injury. Using a constitutive conditional knockout of all activin receptor signaling in oligodendrocyte lineage cells, we discovered this signaling to be required for myelination via regulation of oligodendrocyte differentiation and myelin compaction. These processes were found to be dependent on the activin receptor subtype Acvr2a, which is expressed during oligodendrocyte differentiation and axonal ensheathment in development and following myelin injury. During efficient myelin regeneration, Acvr2a upregulation was seen to coincide with downregulation of Acvr2b, a receptor subtype with relatively higher ligand affinity; Acvr2b was shown to be dispensable for activin receptor-driven oligodendrocyte differentiation and its overexpression was sufficient to impair the abovementioned ligand-driven responses. In actively myelinating or remyelinating areas of human perinatal brain injury and multiple sclerosis tissue, respectively, oligodendrocyte lineage cells expressing Acvr2a outnumbered those expressing Acvr2b, whereas in non-repairing lesions Acvr2b+ cells were increased. Thus, we propose that following human white matter injury, this increase in Acvr2b expression would sequester ligand and consequently impair Acvr2a-driven oligodendrocyte differentiation and myelin formation. Our results demonstrate dysregulated activin receptor signaling in common myelin disorders and reveal Acvr2a as a novel therapeutic target for myelin generation following injury across the lifespan.
Asunto(s)
Receptores de Activinas/metabolismo , Diferenciación Celular/fisiología , Linaje de la Célula/fisiología , Oligodendroglía/metabolismo , Receptores de Activinas/genética , Animales , Encéfalo/metabolismo , Encéfalo/patología , Lesiones Encefálicas/metabolismo , Lesiones Encefálicas/patología , Células Cultivadas , Femenino , Humanos , Masculino , Ratones Endogámicos C57BL , Ratones Noqueados , Esclerosis Múltiple/metabolismo , Esclerosis Múltiple/patología , Oligodendroglía/patología , Ratas Sprague-Dawley , Técnicas de Cultivo de Tejidos , Andamios del TejidoRESUMEN
The development and regeneration of myelin by oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), requires profound changes in cell shape that lead to myelin sheath initiation and formation. Here, we demonstrate a requirement for the basal polarity complex protein Scribble in CNS myelination and remyelination. Scribble is expressed throughout oligodendroglial development and is up-regulated in mature oligodendrocytes where it is localised to both developing and mature CNS myelin sheaths. Knockdown of Scribble expression in cultured oligodendroglia results in disrupted morphology and myelination initiation. When Scribble expression is conditionally eliminated in the myelinating glia of transgenic mice, myelin initiation in CNS is disrupted, both during development and following focal demyelination, and longitudinal extension of the myelin sheath is disrupted. At later stages of myelination, Scribble acts to negatively regulate myelin thickness whilst suppressing the extracellular signal-related kinase (ERK)/mitogen-activated protein kinase (MAP) kinase pathway, and localises to non-compact myelin flanking the node of Ranvier where it is required for paranodal axo-glial adhesion. These findings demonstrate an essential role for the evolutionarily-conserved regulators of intracellular polarity in myelination and remyelination.
Asunto(s)
Sistema Nervioso Central/metabolismo , Péptidos y Proteínas de Señalización Intracelular/genética , Oligodendroglía/metabolismo , Animales , Polaridad Celular , Sistema Nervioso Central/ultraestructura , Quinasas MAP Reguladas por Señal Extracelular/genética , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Regulación de la Expresión Génica , Péptidos y Proteínas de Señalización Intracelular/antagonistas & inhibidores , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Ratones , Ratones Transgénicos , Oligodendroglía/ultraestructura , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Transducción de SeñalRESUMEN
Myelination of neuronal axons is a critical aspect of central nervous system development and function. However, the fundamental cellular and molecular mechanisms influencing human developmental myelination and its failure are not fully understood. Here, we used digital spatial transcriptomics of a rare bank of human developing white matter to uncover that a localized dysregulated innate immune response is associated with impeded myelination. We identified that poorly myelinating areas have a distinct signature of Type II interferon signalling in microglia/macrophages, relative to adjacent myelinating areas. This is associated with a surprising increase in mature oligodendrocytes, which fail to form myelin processes appropriately. We functionally link these findings by showing that conditioned media from interferon-stimulated microglia is sufficient to dysregulate myelin process formation by oligodendrocytes in culture. We identify the Type II interferon inducer, Osteopontin (SPP1), as being upregulated in poorly myelinating brains, indicating a potential biomarker. Our results reveal the importance of microglia-mature oligodendrocyte interaction and interferon signaling in regulating myelination of the developing human brain.
Asunto(s)
Microglía , Vaina de Mielina , Humanos , Vaina de Mielina/fisiología , Oligodendroglía/fisiología , Axones/fisiología , EncéfaloRESUMEN
Failed regeneration of myelin around neuronal axons following central nervous system damage contributes to nerve dysfunction and clinical decline in various neurological conditions, for which there is an unmet therapeutic demand. Here, we show that interaction between glial cells - astrocytes and mature myelin-forming oligodendrocytes - is a determinant of remyelination. Using in vivo/ ex vivo/ in vitro rodent models, unbiased RNA sequencing, functional manipulation, and human brain lesion analyses, we discover that astrocytes support the survival of regenerating oligodendrocytes, via downregulation of the Nrf2 pathway associated with increased astrocytic cholesterol biosynthesis pathway activation. Remyelination fails following sustained astrocytic Nrf2 activation in focally-lesioned male mice yet is restored by either cholesterol biosynthesis/efflux stimulation, or Nrf2 inhibition using the existing therapeutic Luteolin. We identify that astrocyte-oligodendrocyte interaction regulates remyelination, and reveal a drug strategy for central nervous system regeneration centred on targeting this interaction.
Asunto(s)
Astrocitos , Factor 2 Relacionado con NF-E2 , Masculino , Ratones , Animales , Humanos , Astrocitos/metabolismo , Factor 2 Relacionado con NF-E2/genética , Factor 2 Relacionado con NF-E2/metabolismo , Sistema Nervioso Central/metabolismo , Oligodendroglía/metabolismo , Vaina de Mielina/metabolismo , Regeneración Nerviosa/fisiología , Colesterol/metabolismoRESUMEN
Synapse loss correlates with cognitive decline in Alzheimer's disease (AD). Data from mouse models suggests microglia are important for synapse degeneration, but direct human evidence for any glial involvement in synapse removal in human AD remains to be established. Here we observe astrocytes and microglia from human brains contain greater amounts of synaptic protein in AD compared with non-disease controls, and that proximity to amyloid-ß plaques and the APOE4 risk gene exacerbate this effect. In culture, mouse and human astrocytes and primary mouse and human microglia phagocytose AD patient-derived synapses more than synapses from controls. Inhibiting interactions of MFG-E8 rescues the elevated engulfment of AD synapses by astrocytes and microglia without affecting control synapse uptake. Thus, AD promotes increased synapse ingestion by human glial cells at least in part via an MFG-E8 opsonophagocytic mechanism with potential for targeted therapeutic manipulation.
Asunto(s)
Enfermedad de Alzheimer , Microglía , Animales , Humanos , Ratones , Astrocitos , Ingestión de Alimentos , SinapsisRESUMEN
Failed regeneration of CNS myelin contributes to clinical decline in neuroinflammatory and neurodegenerative diseases, for which there is an unmet therapeutic need. Here we reveal that efficient remyelination requires death of proinflammatory microglia followed by repopulation to a pro-regenerative state. We propose that impaired microglia death and/or repopulation may underpin dysregulated microglia activation in neurological diseases, and we reveal therapeutic targets to promote white matter regeneration.