Cited by 343Single-cell and spatial transcriptomicsNeuroinflammation and Neurodegeneration MechanismsCell Image Analysis Techniques

The DOI matches its Crossref record; 48 of the 50 references it cites were found in a registry or an index; 21 of the 22 sources its claims cite were checked for support.

Single-Nucleus RNA-Seq Is Not Suitable for Detection of Microglial Activation Genes in Humans

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Abstract

Single-nucleus RNA sequencing (snRNA-seq) is used as an alternative to single-cell RNA-seq, as it allows transcriptomic profiling of frozen tissue. However, it is unclear whether snRNA-seq is able to detect cellular state in human tissue. Indeed, snRNA-seq analyses of human brain samples have failed to detect a consistent microglial activation signature in Alzheimer's disease. Our comparison of microglia from single cells and single nuclei of four human subjects reveals that, although most genes show similar relative abundances in cells and nuclei, a small population of genes (∼1%) is depleted in nuclei compared to whole cells. This population is enriched for genes previously implicated in microglial activation, including APOE, CST3, SPP1, and CD74, comprising 18% of previously identified microglial-disease-associated genes. Given the low sensitivity of snRNA-seq to detect many activation genes, we conclude that snRNA-seq is not suited for detecting cellular activation in microglia in human disease.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

Comparing single-cell and single-nucleus RNA-seq of human microglia from four subjects, most genes had similar abundance, but a small set (~1%) was depleted in nuclei and enriched for microglial activation genes. The authors conclude snRNA-seq is not suited for detecting cellular activation states in human microglia.

Key findings

  • Most genes showed similar normalized abundance in microglial cells and nuclei: 98.6% fell along the diagonal (Pearson’s correlation coefficient = 0.92, p < 2.2e-16). However, 246 genes (1.1%) were less abundant in nuclei (fold change < −2, padj < 0.05), and 67 genes (0.3%) were more abundant in nuclei (fold change > 2, padj < 0.05).
  • Nuclei-depleted genes were enriched for microglial activation signatures: 45 of 257 orthologous DAM genes (NES = −2.16, padj = 3.6e-05), 28 of 200 orthologous ARM genes (NES = −2.01, padj = 3.6e-05), LPS-upregulated genes (NES = −1.86, padj = 3.6e-05), and Mathys et al. Mic1 markers (NES = −2.14, padj = 3.6e-05). Examples included APOE, CST3, SPP1, and CD74; the abstract states this comprises 18% of previously identified microglial-disease-associated genes.
  • In public datasets, cell-abundant genes were depleted in other single-nucleus microglia relative to single-cell microglia (mean microglial Z score 7.95 for cells-to-nuclei, versus 0.01 for cell-to-cell and 0.81 for nuclei-to-nuclei comparisons). Reanalysis of Gerrits et al. data found the same nuclei-depleted pattern when comparing fresh cells to frozen nuclei, but little difference between fresh cells and fresh nuclei.
  • snRNA-seq recovered major cell types from human tissue: 37,060 nuclei yielded 7 major cell types, including microglia (11.3%), but clustering did not convincingly recover differences between other microglial subpopulations.

Methods

  • Paired scRNA-seq of FACS-sorted microglia and snRNA-seq from the same four human temporal cortex samples (epilepsy surgery; ages 7 male, 20, 24, and 50 female) using the 10X Genomics single-cell gene expression v2 kit. After preprocessing, 3,927 microglial nuclei remained; differential abundance analysis used 3,721 nuclei and 14,435 cells after discarding non-microglial clusters.
  • Differential abundance was performed with Seurat using a two-sided Wilcoxon rank sum test with Bonferroni correction; genes with padj < 0.05 and fold change > |2| were considered significant. Functional analysis used GSEA (fgsea) against ranked log fold changes and gene sets from prior studies.
  • Public dataset comparisons used the EWCE package and a MicroglialDepletion package with bootstrapped Z scores across 8 public single-cell or single-nucleus datasets; Gerrits et al. data were downloaded from GEO (GSE135618) and reanalyzed for fresh versus frozen nuclei.

Limitations

  • Stated in the paper: the study used non-diseased tissue, so the authors cannot dismiss the possibility that mRNA localization distributions change in more activated microglia. They also state they cannot attribute cell-versus-nucleus abundance differences to a biological mechanism versus a technical artifact, and the reason for differences between fresh and frozen nuclei is unclear.
  • Stated in the paper: deeper sequencing or increased sample size could possibly compensate for lack of sensitivity, but the sparse nature of snRNA-seq and high human heterogeneity suggest this may remain a problem.
  • Evident from the text: the primary comparison relies on only four non-AD epilepsy surgery subjects, with one patient sample removed due to poor quality, so the findings about disease-associated activation are inferred from gene-set enrichment rather than direct AD patient snRNA-seq in this study.

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Integrity signals

Registry

Crossref · 10.1016/j.celrep.2020.108189

Cites

48 of 48 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Graphical abstract
Graphical abstract CC BY-NC-ND · PubMed Central
Figure 1 Gene Abundance in Single Microglial Cells versus Single Microglial Nuclei of Human Cortical Tissue (A) Mean normalized gene abundance in cells (x axis) and nuclei (y axis). A total of 3,721 nuclei and 14,435 cells were extracted from the cortical tissue of 4 human patients. Red, genes with significantly higher abundance in nuclei (padj < 0.05, fold change > 2); blue, genes that are significantly less abundance in nuclei (padj < 0.05, fold change < −2). Genes were normalized to read depth (per cell), scaled by 10,000, and log-transformed using the natural log. MALAT1 (which had normalized abundance levels of 6.0 and 6.9, respectively, in cells and nuclei) has been removed for visualization purposes. The black dashed line represents no fold change; the gray dotted lines represent 2- and 4-fold differences between cells and nuclei. FC, fold change; R2, correlation coefficient. Full results are available in Table S1. (B) Scatterplot as in (A), per patient (with the same genes highlighted). (C) Each bar represents a comparison between two datasets (X versus Y), with the bootstrapped Z scores representing the extent to which cell-enriched genes (top panel) and nuclear-enriched genes (bottom panel) have lower specificity for microglia in dataset Y relative to that in dataset X. Larger Z scores indicate greater depletion of genes, and red bars indicate a statistically significant depletion (padj < 0.05, by bootstrapping). KI, Karolinska Institutet; AIBS, Allen Institute for Brain Science. See also Figure S1 and S2A and Table S1.
Figure 1 Gene Abundance in Single Microglial Cells versus Single Microglial Nuclei of Human Cortical Tissue (A) Mean normalized gene abundance in cells (x axis) and nuclei (y axis). A total of 3,721 nuclei and 14,435 cells were extracted from the cortical tissue of 4 human patients. Red, genes with significantly higher abundance in nuclei (padj < 0.05, fold change > 2); blue, genes that are significantly less abundance in nuclei (padj < 0.05, fold change < −2). Genes were normalized to read depth (per cell), scaled by 10,000, and log-transformed using the natural log. MALAT1 (which had normalized abundance levels of 6.0 and 6.9, respectively, in cells and nuclei) has been removed for visualization purposes. The black dashed line represents no fold change; the gray dotted lines represent 2- and 4-fold differences between cells and nuclei. FC, fold change; R2, correlation coefficient. Full results are available in Table S1. (B) Scatterplot as in (A), per patient (with the same genes highlighted). (C) Each bar represents a comparison between two datasets (X versus Y), with the bootstrapped Z scores representing the extent to which cell-enriched genes (top panel) and nuclear-enriched genes (bottom panel) have lower specificity for microglia in dataset Y relative to that in dataset X. Larger Z scores indicate greater depletion of genes, and red bars indicate a statistically significant depletion (padj < 0.05, by bootstrapping). KI, Karolinska Institutet; AIBS, Allen Institute for Brain Science. See also Figure S1 and S2A and Table S1.CC BY-NC-ND · PubMed Central
Figure 2 Functional Analysis of Genes That Are Enriched or Depleted in Nuclei (A) Gene set enrichment analysis (GSEA) of gene sets related to cellular location and gene coding sequence (CDS) length. Background genes were ranked according to log fold change of nuclei (3,721 nuclei) versus cells (14,435 cells). Red, higher normalized enrichment score (NES), i.e., more genes associated with nuclear enrichment; blue, negative NES scores (depletion in nuclei). ∗∗∗ represents significance (padj < 0.0005). GC, GC content. (B) GSEA of super-Gene Ontology gene sets against ranked nucleus-cell log fold changes. Only top and bottom categories (according to NES) are shown. Colors as in (A). MHCI, major histocompatibility complex class I. (C) GSEA of selected gene sets from previous studies of microglial activation, against log fold change as in (A). ∗∗∗ represents significance (padj < 0.0005). Mic0, markers of microglial cluster 0 in human brain tissue; Mic1, markers of microglial cluster 1 (activation response to plaques) defined by Mathys et al., 2019 in human brain tissue. ARM, activation response microglia (Sala Frigerio et al., 2019); DAM, disease-associated microglia (Keren-Shaul et al., 2017); LPS, lipopolysaccharide (Gerrits et al., 2019). (D) Scatterplot as in Figure 1A, highlighting in green the DAM genes. A regression line for the highlighted genes is shown in green (slope = 0.60). (E) Scatterplot as in (D), highlighting in green the ARM genes. A regression line for the highlighted genes is shown in green (slope = 0.64). (F) Scatterplot as in (D), highlighting the DAM genes recovered in the study of human activation in AD (Mathys et al., 2019). Purple, DAM genes not recovered in their study; orange, DAM genes recovered in their study. (G) Scatterplot as in (D); green, human activation marker genes defined by Mathys et al. (2019). Gene sets, results of GO clustering, and results of GSEA analysis are available in Table S1. See also Figures S2B–S2G.
Figure 2 Functional Analysis of Genes That Are Enriched or Depleted in Nuclei (A) Gene set enrichment analysis (GSEA) of gene sets related to cellular location and gene coding sequence (CDS) length. Background genes were ranked according to log fold change of nuclei (3,721 nuclei) versus cells (14,435 cells). Red, higher normalized enrichment score (NES), i.e., more genes associated with nuclear enrichment; blue, negative NES scores (depletion in nuclei). ∗∗∗ represents significance (padj < 0.0005). GC, GC content. (B) GSEA of super-Gene Ontology gene sets against ranked nucleus-cell log fold changes. Only top and bottom categories (according to NES) are shown. Colors as in (A). MHCI, major histocompatibility complex class I. (C) GSEA of selected gene sets from previous studies of microglial activation, against log fold change as in (A). ∗∗∗ represents significance (padj < 0.0005). Mic0, markers of microglial cluster 0 in human brain tissue; Mic1, markers of microglial cluster 1 (activation response to plaques) defined by Mathys et al., 2019 in human brain tissue. ARM, activation response microglia (Sala Frigerio et al., 2019); DAM, disease-associated microglia (Keren-Shaul et al., 2017); LPS, lipopolysaccharide (Gerrits et al., 2019). (D) Scatterplot as in Figure 1A, highlighting in green the DAM genes. A regression line for the highlighted genes is shown in green (slope = 0.60). (E) Scatterplot as in (D), highlighting in green the ARM genes. A regression line for the highlighted genes is shown in green (slope = 0.64). (F) Scatterplot as in (D), highlighting the DAM genes recovered in the study of human activation in AD (Mathys et al., 2019). Purple, DAM genes not recovered in their study; orange, DAM genes recovered in their study. (G) Scatterplot as in (D); green, human activation marker genes defined by Mathys et al. (2019). Gene sets, results of GO clustering, and results of GSEA analysis are available in Table S1. See also Figures S2B–S2G.CC BY-NC-ND · PubMed Central

Verification

Claims the paper makes

31 Own result · 11 Supported · 10 Own method · 7 Partly supported · 6 Own interpretation · 1 Mixed support · accuracy not yet measured

Show all 32 claims

  • Probably not a substantial claim. 28
  • It may state two separate claims as one. 12
34 of 34
  • The paper relies on this without support.

    scRNA-seq of whole cells provides an accurate reference for the true cellular transcriptome against which snRNA-seq can be judged.

    “To compare gene abundance in single microglial cells (14,823 cells) and nuclei (3,940 nuclei), we performed a differential abundance analysis between cells and nuclei from the 4 subjects (Figure 1A).”
  • The paper relies on this without support.

    The limitations of snRNA-seq observed with the 10X Genomics v2 kit and frozen tissue generalize to snRNA-seq generally in human disease.

    “we conclude that snRNA-seq is not suited for detecting cellular activation in microglia in human disease.”
  • The paper relies on this without support.

    The four human subjects and non-diseased tissue are representative enough to support conclusions about human microglial activation in disease.

    “One caveat of the present study is that we have used non-diseased tissue, and we cannot dismiss the possibility that mRNA localization distributions change in more activated populations of microglia.”
  • The paper relies on this without support.

    The nuclei-depleted genes are depleted due to technical limitations of snRNA-seq rather than biological differences in nuclear mRNA localization.

    “However, we are unable to attribute the differences in cellular and nuclear abundance to a biological mechanism (for instance, mRNA trafficking) or a technical artifact of the methodology.”
  • The authors state this as an assumption.

    Nuclei with less than 700 counts from the original unfiltered raw count matrix were empty drops rather than nuclei.

    “under the assumption that these were empty drops rather than nuclei”
5 of 5

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Metadata

Authors
Thrupp, N., Sala Frigerio, C., Wolfs, L., Skene, N. G., Fattorelli, N., Poovathingal, S., Fourne, Y., Matthews, P. M., Theys, T., Mancuso, R., de Strooper, B., & Fiers, M.
Affiliations
  • Vlaams Instituut voor Biotechnologie (BE)
  • UK Dementia Research Institute (GB)
  • KU Leuven (BE)
  • University of London (GB)
Corresponding author
Fiers, Mark
Venue
Cell Reports
Publisher
Elsevier BV
Published
2020-09
Volume
32
Issue
13
Pages
108189
ISSN
2211-1247 (ISSN-L)
OpenAlex
W3091491962
Cited by
329
References
50
Citations by year
2026: 40 · 2025: 70 · 2024: 48 · 2023: 57 · 2022: 54 · 2021: 57 · 2020: 2
FWCI
12.36
Type
journal article
Language
en
Open access
Locations
  • Cell Reports (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
  • Lirias (KU Leuven) (submittedVersion, other-oa)
  • PubMed Central (submittedVersion, cc-by-nc-nd)
  • UCL Discovery (University College London) (submittedVersion)
  • Spiral (Imperial College London) (submittedVersion, cc-by-nc-nd)
Funders
  • Fonds Wetenschappelijk Onderzoek
  • Roche
  • KU Leuven
  • Biogen
  • Vlaams Instituut voor Biotechnologie
  • European Resuscitation Council (834682)
  • Alzheimer&apos;s Association
  • Vlaamse regering
  • Alzheimer Society
  • NIHR Imperial Biomedical Research Centre
  • European Commission
  • Novartis
  • UK Dementia Research Institute (FWO 1830717N)
  • GlaxoSmithKline
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Single-cell and spatial transcriptomics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biophysics › Cell Image Analysis Techniques
Keywords
single-nucleus RNA sequencing, microglial activation, human microglia, apolipoprotein E, CST3, osteopontin, CD74, Alzheimer's disease
MeSH terms
Humans, Sequence Analysis, RNA, Microglia, Gene Expression Profiling, Single-Cell Analysis

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