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Young CSF restores oligodendrogenesis and memory in aged mice via Fgf17

ABSTRACT: Recent understanding of how the systemic environment shapes the brain throughout life has led to numerous intervention strategies to slow brain ageing. Cerebrospinal fluid (CSF) makes up the immediate environment of brain cells, providing them with nourishing compounds. We discovered that infusing young CSF directly into aged brains improves memory function. Unbiased transcriptome analysis of the hippocampus identified oligodendrocytes to be most responsive to this rejuvenated CSF environment. We further showed that young CSF boosts oligodendrocyte progenitor cell (OPC) proliferation and differentiation in the aged hippocampus and in primary OPC cultures. Using SLAMseq to metabolically label nascent mRNA, we identified serum response factor (SRF), a transcription factor that drives actin cytoskeleton rearrangement, as a mediator of OPC proliferation following exposure to young CSF. With age, SRF expression decreases in hippocampal OPCs, and the pathway is induced by acute injection with young CSF. We screened for potential SRF activators in CSF and found that fibroblast growth factor 17 (Fgf17) infusion is sufficient to induce OPC proliferation and long-term memory consolidation in aged mice while Fgf17 blockade impairs cognition in young mice. These findings demonstrate the rejuvenating power of young CSF and identify Fgf17 as a key target to restore oligodendrocyte function in the ageing brain.

ORGANISM(S): Mus musculus Rattus norvegicus

PROVIDER: GSE198008 | GEO | 2022/05/11

REPOSITORIES: GEO

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Project description:BACKGROUND: The gut-brain axis and the intestinal microbiota are emerging as key players in health and disease. Shifts in intestinal microbiota composition affect a variety of systems, however, evidence of their direct impact on cognitive functions is still lacking. We tested whether faecal microbiota transplant (FMT) from aged donor mice into young adult recipients affected the hippocampus, an area of the central nervous system (CNS) known to be affected by the ageing process, and related functions.METHODS AND FINDINGS: Young adult mice were transplanted with the microbiota from either aged or age-matched donor mice. Following transplantation, characterization of the microbiotas and metabolomics profiles along with a battery of cognitive and behavioural tests were performed. Label-free quantitative proteomics was employed to monitor protein expression in the hippocampus of the recipients. Gut permeability, levels of circulating cytokines and expression of markers of microglia cells were also assessed. FMT from aged donors led to impaired spatial learning and memory in young adult recipients, whereas anxiety, explorative behaviour and locomotor activity remained unaffected. This was paralleled by altered expression of proteins involved in synaptic plasticity and neurotransmission in the hippocampus. Also, a strong reduction of bacteria associated with short-chain fatty acids (SCFAs) production (Lachnospiraceae, Faecalibaculum and Ruminococcaceae) and disorders of the CNS (Prevotellaceae and Ruminococcaceae) was observed. Finally, microglia cells of the hippocampus fimbria, acquired an ageing-like phenotype, while gut permeability and levels of circulating cytokines remained unaffected.CONCLUSIONS: These results demonstrate a direct effect of the age-associated shifts of the microbiota on protein expression and key functions of the central nervous system. Furthermore, these results additionally highlight the paramount importance of the gut-brain axis in ageing and provide a strong rationale to devise therapies aiming to restore a young-like microbiota to improve cognitive functions in the elderly.

Project description:Gene-environment interactions mediated at the epigenetic level may provide an initial step in delivering an appropriate response to environmental changes. 5-hydroxymethylcytosine (5hmC), a DNA base derived from 5-methylcytosine (5mC), accounts for ~40% of modified cytosine in brain and has been implicated in DNA methylation-related plasticity. To identify the role of 5hmC in gene-environment interactions, we exposed both young (6-week-old) and aged (18-month-old) mice to both an enriched environment and a standard environment. Exposure to EE significantly improves learning and memory in aged mice and reduces 5hmC abundance in mouse hippocampus. Furthermore, we mapped the genome-wide distribution of 5hmC and found that the alteration of 5hmC modification occurred mainly at gene bodies. In particular, genes involved in axon guidance are enriched among the genes with altered 5hmC modification. These results together suggest that environmental enrichment could modulate the dynamics of 5hmC in hippocampus, which could potentially contribute to improved learning and memory in aged animals. To identify the role of 5hmC in gene-environment interactions, we exposed both young (6-week-old) and aged (18-month-old) C57B/6 mice to both an enriched environment (EE) and a standard environment. Exposure of mice to EE was achieved by keeping a group of mice in the EE chamber, which is larger than the standard cage, includes novel objects, such as toys of varied color and texture, tunnels, an exercise wheel for voluntary exercise, and extra bedding material, along with free access to food and water. Daily exposure to EE was kept at 5 hours during the daylight cycle for 4 consecutive weeks. Control animals were kept in their small cages that are used as standard housing cages (CE) containing bedding, food and access to water. YC, young mice exposing to control environment, YE, young mice exposing to enriched environment, AC, aged mice exposing to control environment, AE, aged mice exposed to enriched environment. Please note that 5hmC-containing DNA enrichment method was inspired by a unique character of beta-glucotransferase that can specifically add glucose to 5hmC modification. With a modified glucose conjugated with biotin, we are able to purify the 5hmC-containing DNA by biotin-streptavidin-based immunoprecipitation.

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Young CSF restores oligodendrogenesis and memory in aged mice via Fgf17

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