A Functionally Defined In Vivo Astrocyte Population Identified by c-Fos Activation in a Mouse Model of Multiple Sclerosis Modulated by S1P Signaling: Immediate-Early Astrocytes (ieAstrocytes)

Abstract

Astrocytes have prominent roles in central nervous system (CNS) function and disease, with subpopulations defined primarily by morphologies and molecular markers often determined in cell culture. Here, we identify an astrocyte subpopulation termed immediate-early astrocytes () that is defined by functional c-Fos activation during CNS disease development. An unbiased screen for CNS cells showing c-Fos activation during experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis (MS), was developed by using inducible, TetTag c-Fos reporter mice that label activated cells with a temporally stable, nuclear green fluorescent protein (GFP). Four-dimensional (3D over time) c-Fos activation maps in the spinal cord were produced by combining tissue clearing (iDISCO) and confocal microscopy that identified onset and expansion of GFP cell populations during EAE. More than 95% of the GFP cells showed glial fibrillary acidic protein (GFAP) immunoreactivity-in contrast to absent or rare labeling of neurons, microglia, and infiltrating immune cells-which constituted that linearly increased in number with progression of EAE. formation was reduced by either astrocyte-specific genetic removal of sphingosine 1-phosphate receptor 1 (S1P) or pharmacological inhibition by fingolimod (FTY720), an FDA-approved MS medicine that can functionally antagonize S1P. s thus represent a functionally defined subset of disease-linked astrocytes that are the first and predominant CNS cell population activated during EAE, and that track with disease severity. Their reduction by a disease-modifying agent supports their therapeutic relevance to MS and potentially other neuroinflammatory and neurodegenerative diseases.

Replicating infant astrocyte behavior in the adult after brain injury improves outcomes

“…1D) [10,19]. Additionally, consistent with our in vivo studies, we detected a large subpopulation GFAP+/ cFOS+ (proliferative [49]/ neuroinflammatory [50]) reactive astrocytes proximal to the injury site in vehicle controls ( Supplementary Fig. 10, 11), but were significantly reduced following rh-ephrin-A1-fc infusion ( Fig.…”

“…Indeed, our results indicate that rh-ephrin-A1-Fc treatment may promote reactive astrocyte-mediated neuroprotection [44] against glutamate excitotoxicity through a GAP43/NFκB-dependent increase in astrocyte-specific EAAT2 [9]. Rh-ephrin-A1-Fc treatment also reduced cFos-associated reactive astrocyte proliferation [55,56], which may have additional implications on neuroinflammation and neurotoxicity [56].…”

“…However, we did observe that ephrin-A5 treatment significantly increased cFOS expression on reactive astrocytes ( Fig. 3E, F) in vitro, associated with increased proliferation [49] and pathological neuroinflammation [50]. In contrast, ephrin-A1 treatment significantly increased GAP43 expression on reactive astrocytes ( Fig.…”

Seasonal decrease in thermogenesis and increase in vasoconstriction explain seasonal response to N6‐cyclohexyladenosine‐induced hibernation in the Arctic ground squirrel (Urocitellus parryii)

“…To detect the neuronal activity associated with the seasonal difference in response to CHA (1 h after injection), we collected the brains at the time when cFos expression was presumed to be at the highest (3 h after injection). cFos can also be expressed in astrocytes associated with differentiation and proliferation (Hisanaga et al, ) or in reactive astrocytes associated with neuroinflammation and pathological conditions (Groves et al, ). We do not expect CHA to promote proliferation or differentiation of astrocytes or to induce neuroinflammation; therefore, we interpret cFos + cells as cFos + neurons, but we cannot rule out involvement of astrocytes.…”

Identification of Socially-activated Neurons

“…The IEG c-Fos encodes for a transcriptional regulator that has become popular for the identification and mapping of recently active neurons due to its rapid transcription and translation following Ca 2+ influx caused by the discharge of Na + -dependent action potentials. In neurons, one of the most influential molecular pathways leading to transcription and translation of c-Fos is the mitogen-activated protein kinase (MAPK) pathway, which is activated by transient increases of intracellular Ca 2+ concentration concentration also lead to c-Fos expression in non-neuronal cells, including astrocytes and microglia (Eun et al, 2004;Groves et al, 2018). Accumulation of c-Fos protein begins approximately 45 min after action potential discharge, reaching peak levels after 1-2 h ( Barros et al, 2015).…”