RESUMEN
Age is a critical risk factor for many neurologic conditions, including progressive multiple sclerosis. Yet the mechanisms underlying the relationship are unknown. Using lysolecithin-induced demyelinating injury to the mouse spinal cord, we characterized the acute lesion and investigated the mechanisms of increased myelin and axon damage with age. We report exacerbated myelin and axon loss in middle-aged (8-10 months of age) compared with young (6 weeks of age) female C57BL/6 mice by 1-3 d of lesion evolution in the white matter. Transcriptomic analysis linked elevated injury to increased expression of Cybb, the gene encoding the catalytic subunit of NADPH oxidase gp91phox. Immunohistochemistry in male and female Cx3cr1CreER/+:Rosa26tdTom/+ mice for gp91phox revealed that the upregulation in middle-aged animals occurred primarily in microglia and not infiltrated monocyte-derived macrophages. Activated NADPH oxidase generates reactive oxygen species and elevated oxidative damage was corroborated by higher malondialdehyde immunoreactivity in lesions from middle-aged compared with young mice. From a previously conducted screen for generic drugs with antioxidant properties, we selected the antihypertensive CNS-penetrant medication indapamide for investigation. We report that indapamide reduced superoxide derived from microglia cultures and that treatment of middle-aged mice with indapamide was associated with a decrease in age-exacerbated lipid peroxidation, demyelination and axon loss. In summary, age-exacerbated acute injury following lysolecithin administration is mediated in part by microglia NADPH oxidase activation, and this is alleviated by the CNS-penetrant antioxidant, indapamide.SIGNIFICANCE STATEMENT Age is associated with an increased risk for the development of several neurologic conditions including progressive multiple sclerosis, which is represented by substantial microglia activation. We demonstrate that in the lysolecithin demyelination model in young and middle-aged mice, the latter group developed greater acute axonal and myelin loss attributed to elevated oxidative stress through NADPH oxidase in lineage-traced microglia. We thus used a CNS-penetrant generic medication used in hypertension, indapamide, as we found it to have antioxidant properties in a previous drug screen. Following lysolecithin demyelination in middle-aged mice, indapamide treatment was associated with decreased oxidative stress and axon/myelin loss. We propose indapamide as a potential adjunctive therapy in aging-associated neurodegenerative conditions such as Alzheimer's disease and progressive multiple sclerosis.
Asunto(s)
Envejecimiento/fisiología , Antihipertensivos/farmacología , Axones/patología , Indapamida/farmacología , Microglía/metabolismo , Vaina de Mielina/patología , Especies Reactivas de Oxígeno/metabolismo , Animales , Enfermedades Desmielinizantes/genética , Enfermedades Desmielinizantes/patología , Medicamentos Genéricos , Femenino , Peroxidación de Lípido/efectos de los fármacos , Macrófagos/fisiología , Masculino , Malondialdehído/metabolismo , Ratones , Ratones Endogámicos C57BL , NADPH Oxidasa 2/biosíntesis , NADPH Oxidasa 2/genética , NADPH Oxidasas/metabolismo , TranscriptomaRESUMEN
Remyelination following CNS demyelination restores rapid signal propagation and protects axons; however, its efficiency declines with increasing age. Both intrinsic changes in the oligodendrocyte progenitor cell population and extrinsic factors in the lesion microenvironment of older subjects contribute to this decline. Microglia and monocyte-derived macrophages are critical for successful remyelination, releasing growth factors and clearing inhibitory myelin debris. Several studies have implicated delayed recruitment of macrophages/microglia into lesions as a key contributor to the decline in remyelination observed in older subjects. Here we show that the decreased expression of the scavenger receptor CD36 of aging mouse microglia and human microglia in culture underlies their reduced phagocytic activity. Overexpression of CD36 in cultured microglia rescues the deficit in phagocytosis of myelin debris. By screening for clinically approved agents that stimulate macrophages/microglia, we have found that niacin (vitamin B3) upregulates CD36 expression and enhances myelin phagocytosis by microglia in culture. This increase in myelin phagocytosis is mediated through the niacin receptor (hydroxycarboxylic acid receptor 2). Genetic fate mapping and multiphoton live imaging show that systemic treatment of 9-12-month-old demyelinated mice with therapeutically relevant doses of niacin promotes myelin debris clearance in lesions by both peripherally derived macrophages and microglia. This is accompanied by enhancement of oligodendrocyte progenitor cell numbers and by improved remyelination in the treated mice. Niacin represents a safe and translationally amenable regenerative therapy for chronic demyelinating diseases such as multiple sclerosis.
Asunto(s)
Envejecimiento/fisiología , Macrófagos/patología , Microglía/metabolismo , Niacina/metabolismo , Rejuvenecimiento/fisiología , Remielinización/fisiología , Animales , Axones/patología , Enfermedades Desmielinizantes/patología , Humanos , Ratones Transgénicos , Microglía/patología , Esclerosis Múltiple/patología , Fagocitosis/fisiologíaRESUMEN
The article Niacinmediated rejuvenation of macrophage/microglia enhances remyelination of the aging central nervous system, written by Khalil S. Rawji, Adam M.H. Young, Tanay Ghosh, Nathan J. Michaels, Reza Mirzaei, Janson Kappen, Kathleen L. Kolehmainen, Nima Alaeiilkhchi, Brian Lozinski, Manoj K. Mishra, Annie Pu, Weiwen Tang, Salma Zein, Deepak K. Kaushik, Michael B. Keough, Jason R. Plemel, Fiona Calvert, Andrew J. Knights, Daniel J. Gaffney, Wolfram Tetzlaff, Robin J. M. Franklin and V. Wee Yong, was originally published electronically on the publisher's internet.
RESUMEN
For decades lysophosphatidylcholine (LPC, lysolecithin) has been used to induce demyelination, without a clear understanding of its mechanisms. LPC is an endogenous lysophospholipid so it may cause demyelination in certain diseases. We investigated whether known receptor systems, inflammation or nonspecific lipid disruption mediates LPC-demyelination in mice. We found that LPC nonspecifically disrupted myelin lipids. LPC integrated into cellular membranes and rapidly induced cell membrane permeability; in mice, LPC injury was phenocopied by other lipid disrupting agents. Interestingly, following its injection into white matter, LPC was cleared within 24 hr but by five days there was an elevation of endogenous LPC that was not associated with damage. This elevation of LPC in the absence of injury raises the possibility that the brain has mechanisms to buffer LPC. In support, LPC injury in culture was significantly ameliorated by albumin buffering. These results shed light on the mechanisms of LPC injury and homeostasis.
Asunto(s)
Enfermedades Desmielinizantes/metabolismo , Lisofosfatidilcolinas/metabolismo , Lisofosfatidilcolinas/toxicidad , Lípidos de la Membrana/metabolismo , Vaina de Mielina/efectos de los fármacos , Vaina de Mielina/metabolismo , Animales , Células Cultivadas , Enfermedades Desmielinizantes/inducido químicamente , Enfermedades Desmielinizantes/patología , Femenino , Inyecciones Intraventriculares , Lisofosfatidilcolinas/administración & dosificación , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Vaina de Mielina/patología , Espectrometría de Masa por Láser de Matriz Asistida de Ionización Desorción/métodosRESUMEN
Ageing of the central nervous system results in a loss of both grey and white matter, leading to cognitive decline. Additional injury to both the grey and white matter is documented in many neurological disorders with ageing, including Alzheimer's disease, traumatic brain and spinal cord injury, stroke, and multiple sclerosis. Accompanying neuronal and glial damage is an inflammatory response consisting of activated macrophages and microglia, innate immune cells demonstrated to be both beneficial and detrimental in neurological repair. This article will propose the following: (i) infiltrating macrophages age differently from central nervous system-intrinsic microglia; (ii) several mechanisms underlie the differential ageing process of these two distinct cell types; and (iii) therapeutic strategies that selectively target these diverse mechanisms may rejuvenate macrophages and microglia for repair in the ageing central nervous system. Most responses of macrophages are diminished with senescence, but activated microglia increase their expression of pro-inflammatory cytokines while diminishing chemotactic and phagocytic activities. The senescence of macrophages and microglia has a negative impact on several neurological diseases, and the mechanisms underlying their age-dependent phenotypic changes vary from extrinsic microenvironmental changes to intrinsic changes in genomic integrity. We discuss the negative effects of age on neurological diseases, examine the response of senescent macrophages and microglia in these conditions, and propose a theoretical framework of therapeutic strategies that target the different mechanisms contributing to the ageing phenotype in these two distinct cell types. Rejuvenation of ageing macrophage/microglia may preserve neurological integrity and promote regeneration in the ageing central nervous system.
Asunto(s)
Sistema Nervioso Central/inmunología , Inmunosenescencia/inmunología , Macrófagos/inmunología , Microglía/inmunología , Envejecimiento/inmunología , Envejecimiento/patología , Animales , Sistema Nervioso Central/patología , Humanos , Macrófagos/patología , Microglía/patología , Enfermedades del Sistema Nervioso/diagnóstico , Enfermedades del Sistema Nervioso/inmunologíaRESUMEN
Multiple Sclerosis (MS) is a neurodegenerative disease characterized by multiple focal lesions, ongoing demyelination and, for most people, a lack of remyelination. MS lesions are enriched with monocyte-derived macrophages and brain-resident microglia that, together, are likely responsible for much of the immune-mediated neurotoxicity. However, microglia and macrophage also have documented neuroprotective and regenerative roles, suggesting a potential diversity in their functions. Linked with microglial functional diversity, they take on diverse phenotypes developmentally, regionally and across disease conditions. Advances in technologies such as single-cell RNA sequencing and mass cytometry of immune cells has led to dramatic developments in understanding the phenotypic changes of microglia and macrophages. This review highlights the origins of microglia, their heterogeneity throughout normal ageing and their contribution to pathology and repair, with a specific focus on autoimmunity and MS. As phenotype dictates function, the emerging heterogeneity of microglia and macrophage populations in MS offers new insights into the potential immune mechanisms that result in inflammation and regeneration.
Asunto(s)
Microglía/inmunología , Esclerosis Múltiple/inmunología , Animales , Encefalomielitis Autoinmune Experimental/inmunología , Humanos , Macrófagos/inmunología , Monocitos/inmunología , RemielinizaciónRESUMEN
Microglia and infiltrating macrophages are thought to orchestrate the central nervous system (CNS) response to injury; however, the similarities between these cells make it challenging to distinguish their relative contributions. We genetically labeled microglia and CNS-associated macrophages to distinguish them from infiltrating macrophages. Using single-cell RNA sequencing, we describe multiple microglia activation states, one of which was enriched for interferon associated signaling. Although blood-derived macrophages acutely infiltrated the demyelinated lesion, microglia progressively monopolized the lesion environment where they surrounded infiltrating macrophages. In the microglia-devoid sciatic nerve, the infiltrating macrophage response was sustained. In the CNS, the preferential proliferation of microglia and sparse microglia death contributed to microglia dominating the lesion. Microglia ablation reversed the spatial restriction of macrophages with the demyelinated spinal cord, highlighting an unrealized macrophages-microglia interaction. The restriction of peripheral inflammation by microglia may be a previously unidentified mechanism by which the CNS maintains its "immune privileged" status.
Asunto(s)
Enfermedades Desmielinizantes/etiología , Enfermedades Desmielinizantes/metabolismo , Macrófagos/inmunología , Macrófagos/metabolismo , Microglía/inmunología , Microglía/metabolismo , Apoptosis/genética , Biomarcadores , Proliferación Celular , Sistema Nervioso Central/inmunología , Sistema Nervioso Central/metabolismo , Sistema Nervioso Central/patología , Biología Computacional/métodos , Enfermedades Desmielinizantes/patología , Técnica del Anticuerpo Fluorescente , Perfilación de la Expresión Génica , Activación de Macrófagos/genética , Activación de Macrófagos/inmunología , Macrófagos/patología , TranscriptomaRESUMEN
Remyelination is a multistep regenerative process that results in the reformation of myelin sheaths around demyelinated axons and is a critical therapeutic target. Here we show that immediate access to a running wheel following toxin-induced demyelination in mice enhances oligodendrogenesis, the rate of remyelination, and the proportion of remyelinated axons. RNA sequencing suggests broad activation of pro-remyelination pathways including phagocytosis by exercise and highlights peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC1α) activation. By immunohistochemistry and cell type-specific conditional deletion, we confirmed PGC1α within oligodendrocytes as a transiently expressed factor required for the rate of myelin thickening by exercise. We validated the exercise-enhanced clearance of inhibitory lipid debris from lesions. Finally, exercise works in parallel with the remyelinating medication clemastine to produce complete remyelination of lesions. Our study demonstrates physical activity as an integrative means to enhance remyelination and details a multimodal mechanism including the pivotal PGC1α-dependent enhancement of myelin thickness.