Project description:Alexander disease is a neurodegenerative diseases caused by mutations of GFAP, an astrocyte-specific gene. We used single cell RNA sequencing (scRNA-seq) to analyze the diversity of astrocytes.
Project description:Alexander disease (AxD) is an intractable neurodegenerative disorder caused by GFAP mutations. It is a primary astrocyte disease with a pathological hallmark of Rosenthal fibres within astrocytes. AxD astrocytes show several abnormal phenotypes. Our previous study showed that AxD astrocytes in model mice exhibit aberrant Ca2+ signals that induce AxD aetiology. Here, we show that microglia have unique phenotypes with morphological and functional alterations, which are related to the pathogenesis of AxD. Immunohistochemical studies of 60TM mice (AxD model) showed that AxD microglia exhibited highly ramified morphology. Functional changes in microglia were assessed by Ca2+ imaging using hippocampal brain slices from Iba1-GCaMP6-60TM mice and two-photon microscopy. We found that AxD microglia showed aberrant Ca2+ signals, with high frequency Ca2+ signals in both the processes and cell bodies. These microglial Ca2+ signals were inhibited by pharmacological blockade or genetic knockdown of P2Y12 receptors but not by tetrodotoxin, indicating that these signals are independent of neuronal activity but dependent on extracellular ATP from non-neuronal cells. Our single-cell RNA sequencing data showed that the expression level of Entpd2, an astrocyte-specific gene encoding the ATP-degrading enzyme NTPDase2, was lower in AxD astrocytes than in wild-type astrocytes. In situ ATP imaging using the adeno-associated virus vector GfaABC1D ATP1.0 showed that exogenously applied ATP was present longer in 60TM mice than in wild-type mice. Thus, the increased ATP level caused by the decrease in its metabolizing enzyme in astrocytes could be responsible for the enhancement of microglial Ca2+ signals. To determine whether these P2Y12 receptor-mediated Ca2+ signals in AxD microglia play a significant role in the pathological mechanism, a P2Y12 receptor antagonist, clopidogrel, was administered. Clopidogrel significantly exacerbated pathological markers in AxD model mice and attenuated the morphological features of microglia, suggesting that microglia play a protective role against AxD pathology via P2Y12 receptors. Taken together, we demonstrated that microglia sense AxD astrocyte dysfunction via P2Y12 receptors as an increase in extracellular ATP and alter their morphology and Ca2+ signalling, thereby protecting against AxD pathology. Although AxD is a primary astrocyte disease, our study may facilitate understanding of the role of microglia as a disease modifier, which may contribute to the clinical diversity of AxD.
Project description:Co-cultures of neurons and astrocytes derived from human iPS cells carrying a GFAP (R239C) mutation - an identified cause of Alexander disease (AxD) - were analyzed with single-cell RNA sequencing to assess cell population composition, differential gene expression, and cell-cell interaction differences in AxD co-cultures compared to controls. Oxygen-glucose deprivation (OGD) challenge was applied to identify differences in stress response. Our results suggested differentiation impairment especially in AxD astrocytes, represented by an enriched population of less differentiated cells and downregulation of mature astrocyte genes in AxD astrocytes-containing co-cultures. Furthermore, AxD co-cultures showed increased stress response represented by upregulation of metallothioneins and increased susceptibility to the OGD challenge.
Project description:3D-cultured unguided neural and cortical organoids derived from human iPS cells carrying a GFAP (R239C) mutation - an identified cause of Alexander disease (AxD) - and their isogenic controls were analyzed with scRNA-seq to investigate the effect of the GFAP mutation on brain development, cell type composition, and gene expression. Results of this analysis showed impaired astro- and neurogenesis in both types of organoids (unguided and cortical), including a lack of cells acquiring the astrocyte fate, and an increased abundance of cells differentiating into lineages other than neuroectodermal. The results also suggested dysregulation of extracellular matrix, membrane, and cytoskeleton components, which might have also affected their differentiation trajectories.
Project description:Gene expression analysis was performed in Gfap+/+, Gfap+/R236H, and mGFAPTg170-2 transgenic mice, using the Aldh1l1-eGFP-L10a transgenic line (JD130) to isolate translating ribosomes and purify astrocyte specific transcripts for RNAseq.