Single-nucleus RNA-seq identifies Huntington disease astrocyte states

Abstract

Huntington Disease (HD) is an inherited movement disorder caused by expanded CAG repeats in the Huntingtin gene. We have used single nucleus RNASeq (snRNASeq) to uncover cellular phenotypes that change in the disease, investigating single cell gene expression in cingulate cortex of patients with HD and comparing the gene expression to that of patients with no neurological disease. In this study, we focused on astrocytes, although we found significant gene expression differences in neurons, oligodendrocytes, and microglia as well. In particular, the gene expression profiles of astrocytes in HD showed multiple signatures, varying in phenotype from cells that had markedly upregulated metallothionein and heat shock genes, but had not completely lost the expression of genes associated with normal protoplasmic astrocytes, to astrocytes that had substantially upregulated GFAP and had lost expression of many normal protoplasmic astrocyte genes as well as metallothionein genes. When compared to astrocytes in control samples, astrocyte signatures in HD also showed downregulated expression of a number of genes, including several associated with protoplasmic astrocyte function and lipid synthesis. Thus, HD astrocytes appeared in variable transcriptional phenotypes, and could be divided into several different “states”, defined by patterns of gene expression. Ultimately, this study begins to fill the knowledge gap of single cell gene expression in HD and provide a more detailed understanding of the variation in changes in gene expression during astrocyte “reactions” to the disease.

Cyclic GMP-AMP synthase promotes the inflammatory and autophagy responses in Huntington disease

“…The active TBK1 can also promote Ccl5 and Cxcl10 expression via Tlr signaling; thus, the inflammatory responses in HD may involve cGAS-dependent and cGAS-independent pathways. Previous studies have reported that Ccl5 and Cxcl10 are up-regulated in various HD models ( 74 , 75 ). Interestingly, mHTT has been shown to inhibit the secretion of the Ccl5 protein, as immunocytochemical analysis showed stronger intracellular Ccl5 protein accumulation in HD astrocytes than in WT astrocytes ( 76 ).…”

Crosstalk Between Astrocytes and Microglia: An Overview

“…By constrast, another set of cytokines produced by activated mouse microglia in vitro and composed of IL-1α, TNF-α and complement factor Cq1, induces in mouse astrocytes a putative neurotoxic state astrocytes “A1” ( 83 ). Investigation of astrocytes in Huntington Disease (HD) cingulate gyrus using snRNA-Seq, with extensive confirmatory steps for RNA and protein expression, and comprehensive informatics, disclosed three astrocytic states that mapped to transcriptomic clusters ( 84 ). This study disclosed no evidence in favor of A1 (neurotoxic) or A2 (neuroprotective) astrocytic states in human neurodegenerative disease.…”

Role of astroglial toll-like receptors (TLRs) in central nervous system infections, injury and neurodegenerative diseases

“…Interestingly, the number of A1 astrocytes also increases in healthy brains during normal aging ( Clarke et al, 2018 ). However, single-cell sequencing in the cingulate cortex of HD brains indicated that astrocytes display multiple transcriptional phenotypes and that the expression of genes characteristic of A1, A2 and pan-astrocytes are simultaneously upregulated in the diseased brain ( Al-Dalahmah et al, 2020 ). Based on the expression levels of genes which are considered astrocyte markers, namely GFAP (glial fibrillary acidic protein), SLC1A2 (solute carrier family 1 member 2; excitatory amino acid transporter 2) and MTs (metallothioneins) ( Penkowa, 2006 ), astrocytes have been classified into at least three reactive states.…”