Unknown,Transcriptomics,Genomics,Proteomics

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Reduced sialylation triggers complement c3-mediated neuronal loss in aging mice

ABSTRACT: Mice heterozygous for the bifunctional enzyme glucosamine-2-epimerase/N-acetylmannosamine kinase (GNE+/-), which is essential for sialic acid biosynthesis, showed reduced gne transcription and sialylation in different brain regions. We found synapse loss in the hippocampus of GNE+/- mice at 6 months followed by a gradual loss of neurons in the hippocampus and substantia nigra at 12 months. Moreover, GNE+/- mice showed reduced arborization of microglia already at 6 months. A transcriptomic analysis revealed only minor inflammatory changes with slightly increased Interleukin 1β levels, indicating a homeostatic removal of synapses and neurons. Crossbreeding with complement component 3-deficient mice rescued the early onset loss of neurons and synapses in the GNE+/- mice. Thus, an intact sialic acid covered glycocalyx plays an essential role in maintaining brain homeostasis. Even a minor reduction in the sialic acid level leads to reduced microglial arborization and complement-mediated loss of neurons and synapses.

INSTRUMENT(S): NextSeq 500

ORGANISM(S): Mus musculus

SUBMITTER: Aurelien Ginolhac

PROVIDER: E-MTAB-7790 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:GNE Myopathy is a rare, recessively inherited neuromuscular worldwide disorder, caused by a spectrum of bi-allelic mutations in the human GNE gene. GNE encodes a bi-functional enzyme responsible for the rate-limiting step of sialic acid biosynthesis pathway. However, the process in which GNE mutations lead to the development of a muscle pathology is not clear yet. Cellular and mouse models for GNE Myopathy established to date have not been informative. Further, additional GNE functions in muscle have been hypothesized. In these studies, we aimed to investigate gne functions using zebrafish genetic and transgenic models, and characterized them using macroscopic, microscopic, and molecular approaches. We first established transgenic zebrafish lineages expressing the human GNE cDNA carrying the M743T mutation, driven by the zebrafish gne promoter. These fish developed entirely normally. Then, we generated a gne knock-out (KO) fish using the CRISPR/Cas9 methodology. These fish died 8-10 days post-fertilization (dpf), but a phenotype appeared less than 24 hours before death and included progressive body axis curving, deflation of the swim bladder and decreasing movement and heart rate. However, muscle histology uncovered severe defects, already at 5 dpf, with compromised fiber organization. Sialic acid supplementation did not rescue the larvae from this phenotype nor prolonged their lifespan. To have deeper insights into the potential functions of gne in zebrafish, RNA sequencing was performed at 3 time points (3, 5, and 7 dpf). Genotype clustering was progressive, with only 5 genes differentially expressed in gne KO compared to gne WT siblings at 3 dpf. Enrichment analyses of the primary processes affected by the lack of gne also at 5 and 7 dpf point to the involvement of cell cycle and DNA damage/repair processes in the gne KO zebrafish. Thus, we have established a gne KO zebrafish lineage and obtained new insights into gne functions. This is the only model where GNE can be related to clear muscle defects, thus the only animal model relevant to GNE Myopathy to date. Further elucidation of gne precise mechanism-of-action in these processes could be relevant to GNE Myopathy and allow the identification of novel therapeutic targets.

Project description:Brain aging is a chronic process linked to inflammation, microglial activation, and oxidative damage, which can ultimately lead to neuronal loss. Sialic acid-binding immunoglobulin-like lectin-11 (SIGLEC-11) is a human lineage-specific microglial cell surface receptor that recognizes α-2-8-linked oligo-/polysialylated glycomolecules with inhibitory effects on the microglial inflammatory pathways. Recently, the SIGLEC11 gene locus was prioritized as a top tier microglial gene with potential causality to Alzheimer’s disease, although its role in inflammation and neurodegeneration remains poorly understood. In this study, aged Siglec-11 transgenic (tg) mice, which expressed the human SIGLEC-11 receptor on microglia and tissue macrophages, were investigated. The brains of the Siglec-11 tg mice were analyzed in 6-month-old mature mice and 24-month-old aged mice using immunohistochemistry and transcriptomics. Results showed decreased density and fewer clusters of ionized calcium binding adaptor molecule 1 (Iba1)-positive microglial cells in the hippocampus and substantia nigra, as well as less lipid-laden microglia in the Siglec-11 tg in comparison to wildtype (WT) controls. Additionally, Siglec-11 tg mice exhibited less age-related neuronal loss in the substantia nigra pars compacta in comparison to WT mice. Transcriptome analysis revealed suppression of oxidative phosphorylation and inflammatory pathways in Siglec-11 tg brains at 6 months, with further suppression of complement and coagulation cascades at 24 months of age in comparison to WT mice. Gene transcript levels of the pro-inflammatory cytokines tumor necrosis factor alpha (Tnf) and interleukin 1 beta (Il-1b), as well as the oxidative stress markers cytochrome b-245 alpha and beta (Cyba and Cybb) and the nitric oxide synthase 2 (Nos2) were reduced in the brains of 24-month-old Siglec-11 tg mice relative to WT controls. Brains of 24-month-old Siglec-11 tg mice also exhibited lower gene transcription of complement component 4 and integrin alpha M (C4 and Itgam), along with the complement C1q subcomponents a and c (C1qa and C1qc). In summary, aged Siglec-11 tg mice displayed reduced brain inflammation and oxidative stress, as well as protection against age-related neuronal loss in the substantia nigra.

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Reduced sialylation triggers complement c3-mediated neuronal loss in aging mice

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