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Neurotoxic reactive astrocytes are induced by activated microglia

Liddelow, Shane A; Guttenplan, Kevin A; Clarke, Laura E; Bennett, Frederick C; Bohlen, Christopher J; Schirmer, Lucas; Bennett, Mariko L; Munch, Alexandra E; Chung, Won-Suk; Peterson, Todd C; Wilton, Daniel K; Frouin, Arnaud; Napier, Brooke A; Panicker, Nikhil; Kumar, Manoj; Buckwalter, Marion S; Rowitch, David H; Dawson, Valina L; Dawson, Ted M; Stevens, Beth; Barres, Ben A
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-1alpha, 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.
PMCID:5404890
PMID: 28099414
ISSN: 1476-4687
CID: 2743332

Normal aging induces A1-like astrocyte reactivity

Clarke, Laura E; Liddelow, Shane A; Chakraborty, Chandrani; Münch, Alexandra E; Heiman, Myriam; Barres, Ben A
The decline of cognitive function occurs with aging, but the mechanisms responsible are unknown. Astrocytes instruct the formation, maturation, and elimination of synapses, and impairment of these functions has been implicated in many diseases. These findings raise the question of whether astrocyte dysfunction could contribute to cognitive decline in aging. We used the Bac-Trap method to perform RNA sequencing of astrocytes from different brain regions across the lifespan of the mouse. We found that astrocytes have region-specific transcriptional identities that change with age in a region-dependent manner. We validated our findings using fluorescence in situ hybridization and quantitative PCR. Detailed analysis of the differentially expressed genes in aging revealed that aged astrocytes take on a reactive phenotype of neuroinflammatory A1-like reactive astrocytes. Hippocampal and striatal astrocytes up-regulated a greater number of reactive astrocyte genes compared with cortical astrocytes. Moreover, aged brains formed many more A1 reactive astrocytes in response to the neuroinflammation inducer lipopolysaccharide. We found that the aging-induced up-regulation of reactive astrocyte genes was significantly reduced in mice lacking the microglial-secreted cytokines (IL-1α, TNF, and C1q) known to induce A1 reactive astrocyte formation, indicating that microglia promote astrocyte activation in aging. Since A1 reactive astrocytes lose the ability to carry out their normal functions, produce complement components, and release a toxic factor which kills neurons and oligodendrocytes, the aging-induced up-regulation of reactive genes by astrocytes could contribute to the cognitive decline in vulnerable brain regions in normal aging and contribute to the greater vulnerability of the aged brain to injury.
PMCID:5828643
PMID: 29437957
ISSN: 1091-6490
CID: 2958252

ApoE4 markedly exacerbates tau-mediated neurodegeneration in a mouse model of tauopathy

Shi, Yang; Yamada, Kaoru; Liddelow, Shane Antony; Smith, Scott T; Zhao, Lingzhi; Luo, Wenjie; Tsai, Richard M; Spina, Salvatore; Grinberg, Lea T; Rojas, Julio C; Gallardo, Gilbert; Wang, Kairuo; Roh, Joseph; Robinson, Grace; Finn, Mary Beth; Jiang, Hong; Sullivan, Patrick M; Baufeld, Caroline; Wood, Michael W; Sutphen, Courtney; McCue, Lena; Xiong, Chengjie; Del-Aguila, Jorge L; Morris, John C; Cruchaga, Carlos; Fagan, Anne M; Miller, Bruce L; Boxer, Adam L; Seeley, William W; Butovsky, Oleg; Barres, Ben A; Paul, Steven M; Holtzman, David M
APOE4 is the strongest genetic risk factor for late-onset Alzheimer disease. ApoE4 increases brain amyloid-beta pathology relative to other ApoE isoforms. However, whether APOE independently influences tau pathology, the other major proteinopathy of Alzheimer disease and other tauopathies, or tau-mediated neurodegeneration, is not clear. By generating P301S tau transgenic mice on either a human ApoE knock-in (KI) or ApoE knockout (KO) background, here we show that P301S/E4 mice have significantly higher tau levels in the brain and a greater extent of somatodendritic tau redistribution by three months of age compared with P301S/E2, P301S/E3, and P301S/EKO mice. By nine months of age, P301S mice with different ApoE genotypes display distinct phosphorylated tau protein (p-tau) staining patterns. P301S/E4 mice develop markedly more brain atrophy and neuroinflammation than P301S/E2 and P301S/E3 mice, whereas P301S/EKO mice are largely protected from these changes. In vitro, E4-expressing microglia exhibit higher innate immune reactivity after lipopolysaccharide treatment. Co-culturing P301S tau-expressing neurons with E4-expressing mixed glia results in a significantly higher level of tumour-necrosis factor-alpha (TNF-alpha) secretion and markedly reduced neuronal viability compared with neuron/E2 and neuron/E3 co-cultures. Neurons co-cultured with EKO glia showed the greatest viability with the lowest level of secreted TNF-alpha. Treatment of P301S neurons with recombinant ApoE (E2, E3, E4) also leads to some neuronal damage and death compared with the absence of ApoE, with ApoE4 exacerbating the effect. In individuals with a sporadic primary tauopathy, the presence of an epsilon4 allele is associated with more severe regional neurodegeneration. In individuals who are positive for amyloid-beta pathology with symptomatic Alzheimer disease who usually have tau pathology, epsilon4-carriers demonstrate greater rates of disease progression. Our results demonstrate that ApoE affects tau pathogenesis, neuroinflammation, and tau-mediated neurodegeneration independently of amyloid-beta pathology. ApoE4 exerts a 'toxic' gain of function whereas the absence of ApoE is protective.
PMCID:5641217
PMID: 28959956
ISSN: 1476-4687
CID: 2743932

Neurotoxic reactive astrocytes induce cell death via saturated lipids

Guttenplan, Kevin A; Weigel, Maya K; Prakash, Priya; Wijewardhane, Prageeth R; Hasel, Philip; Rufen-Blanchette, Uriel; Münch, Alexandra E; Blum, Jacob A; Fine, Jonathan; Neal, Mikaela C; Bruce, Kimberley D; Gitler, Aaron D; Chopra, Gaurav; Liddelow, Shane A; Barres, Ben A
Astrocytes regulate the response of the central nervous system to disease and injury and have been hypothesized to actively kill neurons in neurodegenerative disease1-6. Here we report an approach to isolate one component of the long-sought astrocyte-derived toxic factor5,6. Notably, instead of a protein, saturated lipids contained in APOE and APOJ lipoparticles mediate astrocyte-induced toxicity. Eliminating the formation of long-chain saturated lipids by astrocyte-specific knockout of the saturated lipid synthesis enzyme ELOVL1 mitigates astrocyte-mediated toxicity in vitro as well as in a model of acute axonal injury in vivo. These results suggest a mechanism by which astrocytes kill cells in the central nervous system.
PMID: 34616039
ISSN: 1476-4687
CID: 5045852

Neuroinflammatory astrocyte subtypes in the mouse brain

Hasel, Philip; Rose, Indigo V L; Sadick, Jessica S; Kim, Rachel D; Liddelow, Shane A
Astrocytes undergo an inflammatory transition after infections, acute injuries and chronic neurodegenerative diseases. How this transition is affected by time and sex, its heterogeneity at the single-cell level and how sub-states are spatially distributed in the brain remains unclear. In this study, we investigated transcriptome changes of mouse cortical astrocytes after an acute inflammatory stimulus using the bacterial cell wall endotoxin lipopolysaccharide. We identified fast transcriptomic changes in astrocytes occurring within hours that drastically change over time. By sequencing ~80,000 astrocytes at single-cell resolution, we show that inflammation causes a widespread response with subtypes of astrocytes undergoing distinct inflammatory transitions with defined transcriptomic profiles. We also attribute key sub-states of inflammation-induced reactive astrocytes to specific brain regions using spatial transcriptomics and in situ hybridization. Together, our datasets provide a powerful resource for profiling astrocyte heterogeneity and will be useful for understanding the biological importance of regionally constrained reactive astrocyte sub-states.
PMID: 34413515
ISSN: 1546-1726
CID: 5006402

Monitoring phagocytic uptake of amyloid β into glial cell lysosomes in real time

Prakash, Priya; Jethava, Krupal P; Korte, Nils; Izquierdo, Pablo; Favuzzi, Emilia; Rose, Indigo V L; Guttenplan, Kevin A; Manchanda, Palak; Dutta, Sayan; Rochet, Jean-Christophe; Fishell, Gord; Liddelow, Shane A; Attwell, David; Chopra, Gaurav
Phagocytosis by glial cells is essential to regulate brain function during health and disease. Therapies for Alzheimer's disease (AD) have primarily focused on targeting antibodies to amyloid β (Aβ) or inhibitng enzymes that make it, and while removal of Aβ by phagocytosis is protective early in AD it remains poorly understood. Impaired phagocytic function of glial cells during later stages of AD likely contributes to worsened disease outcome, but the underlying mechanisms of how this occurs remain unknown. We have developed a human Aβ1-42 analogue (AβpH) that exhibits green fluorescence upon internalization into the acidic organelles of cells but is non-fluorescent at physiological pH. This allowed us to image, for the first time, glial uptake of AβpH in real time in live animals. We find that microglia phagocytose more AβpH than astrocytes in culture, in brain slices and in vivo. AβpH can be used to investigate the phagocytic mechanisms responsible for removing Aβ from the extracellular space, and thus could become a useful tool to study Aβ clearance at different stages of AD.
PMCID:8372545
PMID: 34476070
ISSN: 2041-6520
CID: 5011772

Activated microglia drive demyelination via CSF1R signaling

Marzan, Dave E; Brügger-Verdon, Valérie; West, Brian L; Liddelow, Shane; Samanta, Jayshree; Salzer, James L
Microgliosis is a prominent pathological feature in many neurological diseases including multiple sclerosis (MS), a progressive auto-immune demyelinating disorder. The precise role of microglia, parenchymal central nervous system (CNS) macrophages, during demyelination, and the relative contributions of peripheral macrophages are incompletely understood. Classical markers used to identify microglia do not reliably discriminate between microglia and peripheral macrophages, confounding analyses. Here, we use a genetic fate mapping strategy to identify microglia as predominant responders and key effectors of demyelination in the cuprizone (CUP) model. Colony-stimulating factor 1 (CSF1), also known as macrophage colony-stimulating factor (M-CSF) - a secreted cytokine that regulates microglia development and survival-is upregulated in demyelinated white matter lesions. Depletion of microglia with the CSF1R inhibitor PLX3397 greatly abrogates the demyelination, loss of oligodendrocytes, and reactive astrocytosis that results from CUP treatment. Electron microscopy (EM) and serial block face imaging show myelin sheaths remain intact in CUP treated mice depleted of microglia. However, these CUP-damaged myelin sheaths are lost and robustly phagocytosed upon-repopulation of microglia. Direct injection of CSF1 into CNS white matter induces focal microgliosis and demyelination indicating active CSF1 signaling can promote demyelination. Finally, mice defective in adopting a toxic astrocyte phenotype that is driven by microglia nevertheless demyelinate normally upon CUP treatment implicating microglia rather than astrocytes as the primary drivers of CUP-mediated demyelination. Together, these studies indicate activated microglia are required for and can drive demyelination directly and implicate CSF1 signaling in these events.
PMID: 33620118
ISSN: 1098-1136
CID: 4794442

Isoform-dependent APOE secretion modulates neuroinflammation

Hasel, Philip; Liddelow, Shane A
PMID: 33727705
ISSN: 1759-4766
CID: 4819692

Astrocytes have a license to kill inflammatory T cells

Kwon, Alice H K; Liddelow, Shane A
Microbiome-induced interferon signaling through gut-derived natural killer cells is integral to minimize peripheral inflammatory responses in the brain and spinal cord. In a recent issue of Nature, Sanmarco, Wheeler, et al. define how interferon signaling induces LAMP1+TRAIL+ astrocytes, which cause death of inflammatory T cells, mitigating degeneration in a mouse model of demyealination.
PMID: 33852828
ISSN: 1097-4180
CID: 4862532

Astrocytes

Hasel, Philip; Liddelow, Shane A
Philip Hasel and Shane Liddelow introduce astrocytes - glial cells that help to maintain the homeostasis of the central nervous system during development, normal physiology, and aging.
PMID: 33848482
ISSN: 1879-0445
CID: 4862492