Project description:CX3CR1, one of the highest expressed genes in microglia in mice and humans, is implicated in numerous microglial functions. However, the molecular mechanisms underlying Cx3cr1 signaling are not well understood. Here, we analyzed transcriptomes of Cx3cr1-deficient microglia under varying conditions by RNA sequencing (RNA-Seq). In 2 mos mice, Cx3cr1 deletion resulted in the downregulation of a subset of immune-related genes, without substantial epigenetic changes in markers of active chromatin. Surprisingly, Cx3cr1-deficient microglia from young mice exhibited a transcriptome consistent with that of aged Cx3cr1-sufficient animals, suggesting a premature aging transcriptomic signature.
Project description:CX3CR1, one of the highest expressed genes in microglia in mice and humans, is implicated in numerous microglial functions. However, the molecular mechanisms underlying Cx3cr1 signaling are not well understood. Here, we analyzed transcriptomes of Cx3cr1-deficient microglia under varying conditions by RNA-Seq. In 2 mos mice, Cx3cr1 deletion resulted in the downregulation of a subset of immune-related genes, without substantial epigenetic changes in markers of active chromatin. Surprisingly, Cx3cr1-deficient microglia from young mice exhibited a transcriptome consistent with that of aged Cx3cr1-sufficient animals, suggesting a premature aging transcriptomic signature. Immunohistochemical analysis of microglia in young and aged mice revealed that loss of Cx3cr1 modulates microglial morphology in a compatible fashion. Our results suggest that CX3CR1 may regulate microglial function in part by modulating the expression levels of a subset of inflammatory genes during chronological aging, making Cx3cr1-deficient mice useful for studying aged microglia.
Project description:We previously discovered a sex-by-genotype defect in microglia function using a germline heterozygous knockout mouse model of Neurofibromatosis type 1 (Nf1+/- mice), in which only microglia from male Nf1+/- mice exhibited defects in purinergic signaling. Herein, we leveraged an unbiased proteomic approach to demonstrate that male, but not female, heterozygous Nf1+/- microglia exhibit differences in protein expression, which largely reflect pathways involved cytoskeletal organization. In keeping with potential defects in cytoskeletal function, only male Nf1+/- microglia had reduced process arborization and surveillance capacity. Next, to determine whether these microglial defects were cell autonomous or reflected adaptive responses to Nf1 heterozygosity in other cells in the brain, we generated conditional microglia Nf1-mutant knockout mice by intercrossing Nf1flox/flox with Cx3cr1-CreER mice (Nf1flox/wt; Cx3cr1-CreER mice, Nf1MG+/- mice). Surprisingly, neither male nor female Nf1MG+/- mouse microglia had impaired process arborization or surveillance capacity. In contrast, when Nf1 heterozygosity was generated in neurons, astrocytes and oligodendrocytes by intercrossing Nf1flox/flox with hGFAP-Cre mice (Nf1flox/wt; hGFAP-Cre mice, Nf1GFAP+/- mice), the microglia defects found in Nf1+/- mice were recapitulated. Collectively, these data reveal that Nf1+/- sexually dimorphic microglia abnormalities are likely not cell-intrinsic properties, but rather reflect a response to Nf1 heterozygosity in other brain cells.
Project description:This project defines the microglial gene expression profile in a transgenic mouse model of Alzheimer's, compared to non-transgenic age-matched controls, at a time when amyloid pathology and microgliosis are rampant. Microglia were sorted live from one hemisphere of cerebral cortex, using GFP expressed from Cx3cr1 locus (mice have one intact copy of Cx3cr1). RNA was isolated from sorted microglia using RNeasy mini. Two groups, PS2APP and non-transgenic, with 9 mice/group, aged 14-15 months. The "SAMPLE_ID" sample characteristic is a sample identifier internal to Genentech. The ID of this project in Genentech's ExpressionPlot database is PRJ0006715
Project description:single cell gene expression profiling of microglia after peripheral nerve injury in Cx3cr1-yfp-creER/+ animals and Cx3cr1-yfp-creER/+; Tnfaip3 fl/fl animals
Project description:Microglia are the resident macrophages of the central nervous system (CNS). Gene profiling identified the transcriptional regulator Sall1 as a microglia signature gene. Given the high expression of Sall1 in microglia, we sought to identify its function in vivo. The Sall1CreER allele has been targeted into the Sall1 locus, therefore Sall1CreER/fl mice (heterozygous for both alleles) allow inducible ablation of Sall1 expression in microglia after tamoxifen treatment. We performed RNA-seq to examine gene expression profiles of microglia sorted from tamoxifen treated adult Sall1CreER/fl mice and Sall1fl/fl control littermates. Microglia were obtained with > 98% purity and the absence of Sall1 was confirmed in Sall1CreER/fl microglia. We could show that deletion of Sall1 in microglia in vivo resulted in the conversion of these cells from resting tissue macrophages into inflammatory phagocytes leading to altered neurogenesis and disturbed tissue homeostasis. Similar changes in gene expression profiles were found in Sall1-deficient microglia isolated from tamoxifen-treated Cx3cr1CreERSall1fl/fl mice. In these mice, deletion of Sall1 is targeted to CX3CR1+ myeloid cells including microglia and CNS-associated macrophages but not to any other CNS-resident cells. This indicated that Sall1 transcriptional regulation maintains microglia identity and physiological properties in the CNS.
Project description:Studies of neuroepigenetic mechanisms in health and disease are hindered by a lack of approaches to analyze both the transcriptome and epigenome of specific cell types isolated from the complex milieu of the CNS. Cell isolation by cell surface markers is complicated by preparation artifacts, changes in markers with experimental conditions, and lack of specific markers. This study validates a Nuclear Tagging and Translating Ribosome Affinity Purification (NuTRAP) approach with tamoxifen (Tam) inducible cell-type specific cre recombination to allow the parallel interrogation of the epigenome and the transcriptome in astrocytes (Aldh1l1-creERT2) or microglia (Cx3cr1-creERT2). The recombined NuTRAP construct labels, in a cell-type specific manner, nuclei (RanGAP1) with biotin and mCherry, and the ribosomes (L10a) with EGFP, enabling INTACT isolation of DNA and TRAP isolation of RNA. Validation experiments by flow cytometry and imaging demonstrate cell-type specific induction of the NuTRAP construct. Transcriptomic studies demonstrate isolation of highly enriched RNA by TRAP and oxidative bisulfite studies of INTACT-isolated DNA demonstrate differential DNA modification patterns in microglia and astrocytes. LPS administration in Cx3cr1 NuTRAP mice demonstrates that microglia-specific transcriptome and epigenome changes are revealed that cannot be detected with tissue-level samples. These experiments demonstrate that the NuTRAP approach can be applied to CNS cell populations and that INTACT approaches can be used to study DNA modifications. These results also provide an approach for generation and validation of NuTRAP neuroscience models crossed to any relevant cell-type specific cre line.
Project description:Diabetic retinopathy, a microvascular disease characterized by irreparable vascular damage, neurodegeneration and neuroinflammation, is a leading complication of diabetes mellitus. Medical interventions slow the progression of disease. However, current therapies do not specifically target microglia, a cell type implicated in mediating disease development. Microglia-mediated inflammation in the diabetic retina is regulated via CX3CR1-FKN signaling, where FKN serves as a dampening signal for microglial activation. Studying this signaling axis is important as polymorphic variants of CX3CR1 are found in 25% of the human population, hCX3CR1I249/M280, resulting in a receptor with lower binding affinity for FKN. Furthermore, disrupted CX3CR1-FKN signaling in CX3CR1-KO and FKN-KO mice leads to exacerbated microglial activation, robust neuronal cell loss and substantial vascular damage in the diabetic retina. Thus, studies to characterize the effects of hCX3CR1I249/M280-expression in microglia-mediated inflammation in the diseased retina are potentially clinically relevant to identify microglia-specific therapies. Our results show that hCX3CR1I249/M280 mice are significantly more susceptible to microgliosis and production of Cxcl10 and TNFα under acute inflammatory conditions. This pathology is exacerbated under diabetic conditions and coincides with robust neuronal loss in comparison to CX3CR1-WT mice. Therefore, to further investigate the role of hCX3CR1I249/M280-expression in microglial responses, we pharmacologically depleted microglia using PLX-5622, a CSF-1R antagonist. PLX-5622 treatment led to a robust (~70%) reduction in Iba1+ microglia in all non-diabetic and diabetic mice. CSF-1R antagonism in diabetic CX3CR1-WT prevented TUJ1+ axonal loss, angiogenesis and fibrinogen deposition. In contrast, PLX-5622 microglia depletion in CX3CR1-KO and hCX3CR1I249/M280 mice did not alleviate TUJ1+ axonal loss or angiogenesis. Interestingly, PLX-5622 treatment reduced fibrinogen deposition in CX3CR1-KO mice but not in hCX3CR1I249/M280 mice, revealing that hCX3CR1I249/M280 receptor variant mice behave differently in terms of vascular pathology compared to CX3CR1-KOs. mRNAseq gene expression analysis in CX3CR1-WT retinal isolates revealed that PLX-5622-induced microglia depletion and repopulation induced a downregulation in genes associated with microglial activation and phagocytosis, B2m, Cx3cr1, and Trem2, and complement-associated synaptic pruning, C1qa, C1qb, and C1qc. Furthermore, mRNAseq analysis of PLX-5622 treated CX3CR1-WT retinas showed lower fold changes in genes encoding proinflammatory mediators (Cxcl10, Ccl2, Il6, Cxcl1, Selp, Il12b, Tnf, Cxcl2, Icam1 and Vcam1) in comparison to diabetic + normal chow mice.