26 research outputs found
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Sustained microglial depletion with CSF1R inhibitor impairs parenchymal plaque development in an Alzheimer's disease model.
Many risk genes for the development of Alzheimer's disease (AD) are exclusively or highly expressed in myeloid cells. Microglia are dependent on colony-stimulating factor 1 receptor (CSF1R) signaling for their survival. We designed and synthesized a highly selective brain-penetrant CSF1R inhibitor (PLX5622) allowing for extended and specific microglial elimination, preceding and during pathology development. We find that in the 5xFAD mouse model of AD, plaques fail to form in the parenchymal space following microglial depletion, except in areas containing surviving microglia. Instead, Aβ deposits in cortical blood vessels reminiscent of cerebral amyloid angiopathy. Altered gene expression in the 5xFAD hippocampus is also reversed by the absence of microglia. Transcriptional analyses of the residual plaque-forming microglia show they exhibit a disease-associated microglia profile. Collectively, we describe the structure, formulation, and efficacy of PLX5622, which allows for sustained microglial depletion and identify roles of microglia in initiating plaque pathogenesis
CD200-CD200R1 inhibitory signaling prevents spontaneous bacterial infection and promotes resolution of neuroinflammation and recovery after stroke
Abstract
Background
Ischemic stroke results in a robust inflammatory response within the central nervous system. As the immune-inhibitory CD200-CD200 receptor 1 (CD200R1) signaling axis is a known regulator of immune homeostasis, we hypothesized that it may play a role in post-stroke immune suppression after stroke.
Methods
In this study, we investigated the role of CD200R1-mediated signaling in stroke using CD200 receptor 1-deficient mice. Mice were subjected to a 60-min middle cerebral artery occlusion and evaluated at days 3 and 7, representing the respective peak and early resolution stages of neuroinflammation in this model of ischemic stroke. Infarct size and behavioral deficits were assessed at both time points. Central and peripheral cellular immune responses were measured using flow cytometry. Bacterial colonization was determined in lung tissue homogenates both after acute stroke and in an LPS model of systemic inflammation.
Results
In wild-type (WT) animals, CD200R1 was expressed on infiltrating monocytes and lymphocytes after stroke but was absent on microglia. Early after ischemia (72 h), CD200R1-knockout (KO) mice had significantly poorer survival rates and an enhanced susceptibility to spontaneous bacterial colonization of the respiratory tract compared to wild-type (WT) controls, despite no difference in infarct or neurological deficits. While the CNS inflammation was resolved by day 7 post-stroke in WT mice, brain-resident microglia and monocyte activation persisted in CD200R1-KO mice, accompanied by a delayed, augmented lymphocyte response. At this time point, CD200R1-KO mice displayed greater weight loss, more severe neurological deficits, and impaired motor function compared to WT. Systemically, CD200R1-KO mice exhibited signs of persistent infection including lymphopenia, T cell activation and memory conversion, and narrowing of the TCR repertoire. These findings were confirmed in a second model of acute neuroinflammation induced by systemic endotoxin challenge.
Conclusion
This study defines an essential role of CD200-CD200R1 signaling in stroke. Loss of CD200R1 led to high mortality, increased rates of post-stroke infection, and enhanced entry of peripheral leukocytes into the brain after ischemia, with no increase in infarct size. This suggests that the loss of CD200 receptor leads to enhanced peripheral inflammation that is triggered by brain injury.https://deepblue.lib.umich.edu/bitstream/2027.42/148133/1/12974_2019_Article_1426.pd
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Investigating microglial regulation of the extracellular matrix in health and neurodegenerative disease
Microglia are the primary immune cells of the central nervous system (CNS) parenchyma, and have evolved conceptually from silent sentinels awaiting pathogenic or injurious disturbance to active and central regulators of brain homeostasis and disease (Prinz et al., 2019). Their functional repertoire equips microglia to perform immune as well as non-immune roles, but less is known about the latter. As exacerbated or, on the other hand, deficient microglial function may contribute to brain dyshomeostasis, shedding light on such functions may provide insight into mechanisms underlying disease etiology and pathogenesis. The development of microglial depletion paradigms via inhibition of colony-stimulating factor 1 receptor (CSF1R), expressed in the brain by microglia and required for their survival (Elmore et al., 2014), provides unprecedented capacity for functional investigation by allowing researchers to observe and draw conclusions from the consequences of microglial absence (up to 99% depletion) on CNS processes for virtually any duration of time (Green et al., 2020). Such methods have suggested that microglia dynamically regulate the dendritic spines of neuronal circuits in the adult homeostatic brain (Rice et al., 2017; Rice et al., 2015), for instance, as well as amyloid plaque compaction and deposition in the context of Alzheimer’s disease (AD) (Casali et al., 2020; Huang et al., 2021; Spangenberg et al., 2019).The aim of my thesis is to identify and elucidate the role of microglia in the regulation of the brain extracellular matrix (ECM) – the perisynaptic and synaptic manifestations of which serve as the fourth and most recently addended component of the contemporary model of the quad- or tetra-partite synapse, also consisting of pre- and post-synaptic elements and associated glia (Dityatev and Schachner, 2003; Dityatev et al., 2010). While the ECM is divided into several separate compartments in the brain, one particularly salient instance is the perineuronal net (PNN), a specialized reticular formation that surrounds neuronal subsets and proximal synapses to provide synaptic stability, physical and chemical protection, and other unique physiological properties (Fawcett et al., 2019; Reichelt et al., 2019). Not only are PNNs associated with long-term memory storage (Shi et al., 2019a; Thompson et al., 2018; Tsien, 2013), they protect against oxidative stress and amyloid-β (Cabungcal et al., 2013; Miyata et al., 2007), underscoring their particular relevance to disorders like AD. Among other changes, I found that these ECM structures are reduced in Huntington’s disease (HD) and AD, two brain disorders with disparate etiologies, pathologies, and microglial activation phenotypes. Importantly, I found that early microglial depletion with CSF1R inhibitors prevented PNN loss in both cases. Surprisingly, elimination of microglia also induced dramatic upregulation of PNN density throughout the brains of healthy adult mice. These results define a novel role of microglia in the regulation of PNNs in the homeostatic CNS, which may in turn go awry in neurodegenerative diseases where microglia adopt dyshomeostatic phenotypes
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To Kill a Microglia: A Case for CSF1R Inhibitors
Microglia, the brain's immune sentinels, have garnered much attention in recent years. Researchers have begun to identify the manifold roles that these cells play in the central nervous system (CNS), and this work has been greatly facilitated by microglial depletion paradigms. The varying degrees of spatiotemporal manipulation afforded by such techniques allow microglial ablation before, during, and/or following insult, injury, or disease. We review the major methods of microglial depletion, including toxin-based, genetic, and pharmacological approaches, which differ in key factors including depletion onset, duration, and off-target effects. We conclude that pharmacological CSF1R inhibitors afford the most extensive versatility in manipulating microglia, making them ideal candidates for future studies investigating microglial function in health and disease
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Microglia as hackers of the matrix: sculpting synapses and the extracellular space.
Microglia shape the synaptic environment in health and disease, but synapses do not exist in a vacuum. Instead, pre- and postsynaptic terminals are surrounded by extracellular matrix (ECM), which together with glia comprise the four elements of the contemporary tetrapartite synapse model. While research in this area is still just beginning, accumulating evidence points toward a novel role for microglia in regulating the ECM during normal brain homeostasis, and such processes may, in turn, become dysfunctional in disease. As it relates to synapses, microglia are reported to modify the perisynaptic matrix, which is the diffuse matrix that surrounds dendritic and axonal terminals, as well as perineuronal nets (PNNs), specialized reticular formations of compact ECM that enwrap neuronal subsets and stabilize proximal synapses. The interconnected relationship between synapses and the ECM in which they are embedded suggests that alterations in one structure necessarily affect the dynamics of the other, and microglia may need to sculpt the matrix to modify the synapses within. Here, we provide an overview of the microglial regulation of synapses, perisynaptic matrix, and PNNs, propose candidate mechanisms by which these structures may be modified, and present the implications of such modifications in normal brain homeostasis and in disease
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Microglial depletion prevents extracellular matrix changes and striatal volume reduction in a model of Huntington's disease.
Huntington's disease is associated with a reactive microglial response and consequent inflammation. To address the role of these cells in disease pathogenesis, we depleted microglia from R6/2 mice, a rapidly progressing model of Huntington's disease marked by behavioural impairment, mutant huntingtin (mHTT) accumulation, and early death, through colony-stimulating factor 1 receptor inhibition (CSF1Ri) with pexidartinib (PLX3397) for the duration of disease. Although we observed an interferon gene signature in addition to downregulated neuritogenic and synaptic gene pathways with disease, overt inflammation was not evident by microglial morphology or cytokine transcript levels in R6/2 mice. Nonetheless, CSF1Ri-induced microglial elimination reduced or prevented disease-related grip strength and object recognition deficits, mHTT accumulation, astrogliosis, and striatal volume loss, the latter of which was not associated with reductions in cell number but with the extracellular accumulation of chondroitin sulphate proteoglycans (CSPGs)-a primary component of glial scars. A concurrent loss of proteoglycan-containing perineuronal nets was also evident in R6/2 mice, and microglial elimination not only prevented this but also strikingly increased perineuronal nets in the brains of naïve littermates, suggesting a new role for microglia as homeostatic regulators of perineuronal net formation and integrity