Astrocyte molecular signatures in Huntington’s disease

Abstract

Astrocytes are implicated in neurodegenerative disorders and may contribute to striatal neuron loss or dysfunction in Huntington’s disease (HD). Here, we assessed striatal astrocyte gene and protein signatures in two HD mouse models at three stages and compared our results to human HD data at four clinical grades and to mice exhibiting polyglutamine length–dependent pathology. We found disease-model and stage-specific alterations and discovered a core disease-associated astrocyte molecular signature comprising 62 genes that were conserved between mice and humans. Our results show little evidence of neurotoxic A1 astrocytes that have been proposed to be causal for neuronal death in neurodegenerative disorders such as HD. Furthermore, 61 of the 62-core gene expression changes within astrocytes were reversed in a HD mouse model by lowering astrocyte mutant huntingtin protein (mHTT) expression using zinc finger protein (ZFP) transcriptional repressors. Our findings indicate that HD astrocytes progressively lose essential normal functions, some of which can be remedied by lowering mHTT. The data have implications for neurodegenerative disease rescue and repair strategies as well as specific therapeutic relevance for mHTT reduction and contribute to a better understanding of fundamental astrocyte biology and its contributions to disease.

Single-nucleus RNA-seq identifies Huntington disease astrocyte states

“…3e), are downregulated in reactive astrocytic states in HD. This data is consistent with Diaz-Castro et al [7], where the authors found that there are common genes that are downregulated in both striatal murine astrocytes and post-mortem human striatalderived microarray data, and that these genes were mostly related to calcium ion transport, G-protein coupled receptor signaling, and glutamate receptor signaling. Thus, we contend that viewing astrocytosis in HD in terms of loss of astrocyte function, and gain of potentially neuroprotective phenotypes, is a useful way to view reactive astrocyte states in HD.…”

“…Our data showed that both A1 and A2 genes were increased in bulk RNAseq samples, which is consistent with recent whole tissue RNASeq data from Diaz-Castro et al [7]. However, these A1 versus A2 states did not become more clear on the single cell level.…”

“…Additional evidence from examining HD cases with different grades of severity as well as evidence from experimental models such as astrocyte lineage tracing experiments in conditional HD mice models are needed to query this possibility further. Alternatively, difference in astrocytic reactive states may reflect spatial differences in astrocyte localization in cortical layers with variable susceptibility to neurodegeneration, such as susceptible layers III, V, and VI versus resilient layer II [7,45].…”

“…We then used an unbiased clustering approach using shared nearest neighbor utilizing the scran::buildSNNGraph() function, with dimensionality reduction set to "TSNE". Multiple K values were tested (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) and the number of pre-clusters generated was examined. K = 6 yielded 35 discrete pre-clusters, with the least number of mixed pre-clusters (based on results from the cell classifier-below).…”

“…Thus, we contend that viewing astrocytosis in HD in terms of loss of astrocyte function, and gain of potentially neuroprotective phenotypes, is a useful way to view reactive astrocyte states in HD. Note, however, that the whole tissue RNASeq analysis [7] does not reveal astrocyte transcriptional heterogeneity and would not have defined different astrocyte "states. "…”