Last updated: 2021-03-29

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Knit directory: liver-disease-atlas/

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Introduction

Here we analysis a patient cohort covering full spectrum of NAFLD (Stage 1-6) generated by Hoang et al..

Libraries and sources

These libraries and sources are used for this analysis.

library(tidyverse)
library(tidylog)
library(here)

library(edgeR)
library(biobroom)

library(AachenColorPalette)
library(cowplot)
library(lemon)

options("tidylog.display" = list(print))
source(here("code/utils-rnaseq.R"))
source(here("code/utils-utils.R"))
source(here("code/utils-plots.R"))

Definition of global variables that are used throughout this analysis.

# i/o
data_path <- "data/human-hoang-nafld"
output_path <- "output/human-hoang-nafld"

# graphical parameters
# fontsize
fz <- 9

Preliminary exploratory analysis

Library size

Barplot of the library size (total counts) for each of the samples.

count_matrix <- readRDS(here(data_path, "count_matrix.rds"))

plot_libsize(count_matrix) +
  my_theme(fsize = fz)

Version Author Date
3340593 christianholland 2021-02-28

Count distribution

Violin plots of the raw read counts for each of the samples.

count_matrix <- readRDS(here(data_path, "count_matrix.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

count_matrix %>%
  tdy("gene", "sample", "count", meta) %>%
  arrange(nafld) %>%
  ggplot(aes(
    x = fct_reorder(sample, as.numeric(nafld)), y = log10(count + 1),
    group = sample, fill = nafld
  )) +
  geom_violin() +
  theme(
    axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1),
    legend.position = "top"
  ) +
  labs(x = NULL) +
  my_theme(grid = "no", fsize = fz)
#> gather: reorganized (440349.1.X_1, 440350.1.X_1, 440351.1.X_4, 440352.1.X_4, 440353.1.X_4, …) into (sample, count) [was 17140x79, now 1336920x3]
#> left_join: added 7 columns (fibrosis, lobular_inflammation, nafld, gender, steatosis, …)
#>            > rows only in x           0
#>            > rows only in y  (        0)
#>            > matched rows     1,336,920
#>            >                 ===========
#>            > rows total       1,336,920

Version Author Date
3340593 christianholland 2021-02-28

PCA of raw data

PCA plot of raw read counts contextualized based on NAFLD stage. Before gene with a constant expression across all samples are removed and count values are transformed to log2 scale. Only the top 1000 most variable genes are used as features.

count_matrix <- readRDS(here(data_path, "count_matrix.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

stopifnot(colnames(count_matrix) == meta$sample)

# remove constant expressed genes and transform to log2 scale
preprocessed_count_matrix <- preprocess_count_matrix(count_matrix)
#> Discarding 239 genes 
#> Keeping 16901 genes


pca_result <- do_pca(preprocessed_count_matrix, meta, top_n_var_genes = 1000)
#> left_join: added 7 columns (fibrosis, lobular_inflammation, nafld, gender, steatosis, …)
#>            > rows only in x    0
#>            > rows only in y  ( 0)
#>            > matched rows     78
#>            >                 ====
#>            > rows total       78

plot_pca(pca_result, feature = "nafld") +
  my_theme(fsize = fz)

Version Author Date
3340593 christianholland 2021-02-28

Data processing

Normalization

Raw read counts are normalized by first filtering out lowly expressed genes, TMM normalization and finally logCPM transformation.

count_matrix <- readRDS(here(data_path, "count_matrix.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

stopifnot(meta$sample == colnames(count_matrix))

dge_obj <- DGEList(count_matrix, group = meta$nafld)

# filter low read counts, TMM normalization and logCPM transformation
norm <- voom_normalization(dge_obj)
#> Discarding 1947 genes 
#> Keeping 15193 genes

saveRDS(norm, here(output_path, "normalized_expression.rds"))

PCA of normalized data

PCA plot of normalized expression data contextualized based on the NAFLD stage. Only the top 1000 most variable genes are used as features.

expr <- readRDS(here(output_path, "normalized_expression.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

pca_result <- do_pca(expr, meta, top_n_var_genes = 1000)
#> left_join: added 7 columns (fibrosis, lobular_inflammation, nafld, gender, steatosis, …)
#>            > rows only in x    0
#>            > rows only in y  ( 0)
#>            > matched rows     78
#>            >                 ====
#>            > rows total       78

saveRDS(pca_result, here(output_path, "pca_result.rds"))

plot_pca(pca_result, feature = "nafld") +
  my_theme(fsize = fz)

Version Author Date
3340593 christianholland 2021-02-28

Differential gene expression analysis

Running limma

Differential gene expression analysis via limma with the aim to identify the transcriptomic signatures of different NAFLD stages.

# load expression and meta data
expr <- readRDS(here(output_path, "normalized_expression.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

stopifnot(colnames(expr) == meta$sample)

# build design matrix
design <- model.matrix(~ 0 + nafld, data = meta)
rownames(design) <- meta$sample
colnames(design) <- levels(meta$nafld)


# define contrasts
contrasts <- makeContrasts(
  stage_1_vs_0 = stage_1 - stage_0,
  stage_2_vs_0 = stage_2 - stage_0,
  stage_3_vs_0 = stage_3 - stage_0,
  stage_4_vs_0 = stage_4 - stage_0,
  stage_5_vs_0 = stage_5 - stage_0,
  stage_6_vs_0 = stage_6 - stage_0,
  levels = design
)

limma_result <- run_limma(expr, design, contrasts) %>%
  assign_deg()
#> Warning: `tbl_df()` is deprecated as of dplyr 1.0.0.
#> Please use `tibble::as_tibble()` instead.
#> This warning is displayed once every 8 hours.
#> Call `lifecycle::last_warnings()` to see where this warning was generated.
#> select: renamed 3 variables (contrast, logFC, pval) and dropped one variable
#> group_by: one grouping variable (contrast)
#> mutate (grouped): new variable 'fdr' (double) with 38,517 unique values and 0% NA
#> ungroup: no grouping variables
#> mutate: new variable 'regulation' (character) with 3 unique values and 0% NA
#> mutate: converted 'regulation' from character to factor (0 new NA)

deg_df <- limma_result %>%
  mutate(contrast_reference = "stage_0")
#> mutate: new variable 'contrast_reference' (character) with one unique value and 0% NA

saveRDS(deg_df, here(output_path, "limma_result.rds"))

Volcano plots

Volcano plots visualizing the transcriptomic signatures of different NAFLD stages.

df <- readRDS(here(output_path, "limma_result.rds"))

df %>%
  filter(contrast_reference == "stage_0") %>%
  plot_volcano() +
  my_theme(grid = "y", fsize = fz)
#> filter: no rows removed
#> rename: renamed one variable (p)

Version Author Date
3340593 christianholland 2021-02-28

z-scores

expr <- readRDS(here(output_path, "normalized_expression.rds"))
meta <- readRDS(here(data_path, "meta_data.rds"))

# extract name of control samples
ctrl_samples <- meta %>%
  filter(nafld == "stage_0") %>%
  pull(sample)
#> filter: removed 74 rows (95%), 4 rows remaining

treated_samples <- meta %>%
  filter(nafld != "stage_0") %>%
  pull(sample)
#> filter: removed 4 rows (5%), 74 rows remaining

# compute mean and standard deviation of gene expression in control sample
ctrl_mean <- expr[, ctrl_samples] %>%
  apply(1, mean)
ctrl_sd <- expr[, ctrl_samples] %>%
  apply(1, sd)

# check whether genes are in correct order
stopifnot(names(ctrl_mean) == colnames(t(expr)))
stopifnot(names(ctrl_mean) == colnames(t(expr)))

# z-score transformation of gene expression w.r.t control samples
z_scores <- expr[, treated_samples] %>%
  t() %>%
  scale(center = ctrl_mean, scale = ctrl_sd) %>%
  t() %>%
  data.frame(check.names = FALSE)

saveRDS(z_scores, here(output_path, "z_scores.rds"))

Time spend to execute this analysis: 00:27 minutes.


sessionInfo()
#> R version 4.0.2 (2020-06-22)
#> Platform: x86_64-apple-darwin17.0 (64-bit)
#> Running under: macOS Mojave 10.14.5
#> 
#> Matrix products: default
#> BLAS:   /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRblas.dylib
#> LAPACK: /Library/Frameworks/R.framework/Versions/4.0/Resources/lib/libRlapack.dylib
#> 
#> locale:
#> [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
#> 
#> attached base packages:
#> [1] stats     graphics  grDevices datasets  utils     methods   base     
#> 
#> other attached packages:
#>  [1] lemon_0.4.5              cowplot_1.1.0            AachenColorPalette_1.1.2
#>  [4] biobroom_1.20.0          broom_0.7.3              edgeR_3.30.3            
#>  [7] limma_3.44.3             here_1.0.1               tidylog_1.0.2           
#> [10] forcats_0.5.0            stringr_1.4.0            dplyr_1.0.2             
#> [13] purrr_0.3.4              readr_1.4.0              tidyr_1.1.2             
#> [16] tibble_3.0.4             ggplot2_3.3.2            tidyverse_1.3.0         
#> [19] workflowr_1.6.2         
#> 
#> loaded via a namespace (and not attached):
#>  [1] Biobase_2.48.0      httr_1.4.2          jsonlite_1.7.2     
#>  [4] modelr_0.1.8        assertthat_0.2.1    renv_0.12.3        
#>  [7] cellranger_1.1.0    yaml_2.2.1          pillar_1.4.7       
#> [10] backports_1.2.1     lattice_0.20-41     glue_1.4.2         
#> [13] digest_0.6.27       promises_1.1.1      rvest_0.3.6        
#> [16] colorspace_2.0-0    htmltools_0.5.0     httpuv_1.5.4       
#> [19] plyr_1.8.6          clisymbols_1.2.0    pkgconfig_2.0.3    
#> [22] haven_2.3.1         scales_1.1.1        whisker_0.4        
#> [25] later_1.1.0.1       git2r_0.27.1        farver_2.0.3       
#> [28] generics_0.1.0      ellipsis_0.3.1      withr_2.3.0        
#> [31] BiocGenerics_0.34.0 cli_2.2.0           magrittr_2.0.1     
#> [34] crayon_1.3.4        readxl_1.3.1        evaluate_0.14      
#> [37] fs_1.5.0            fansi_0.4.1         xml2_1.3.2         
#> [40] tools_4.0.2         hms_0.5.3           lifecycle_0.2.0    
#> [43] munsell_0.5.0       reprex_0.3.0        locfit_1.5-9.4     
#> [46] compiler_4.0.2      rlang_0.4.9         grid_4.0.2         
#> [49] rstudioapi_0.13     labeling_0.4.2      rmarkdown_2.6      
#> [52] codetools_0.2-18    gtable_0.3.0        DBI_1.1.0          
#> [55] R6_2.5.0            gridExtra_2.3       lubridate_1.7.9.2  
#> [58] knitr_1.30          rprojroot_2.0.2     stringi_1.5.3      
#> [61] parallel_4.0.2      Rcpp_1.0.5          vctrs_0.3.6        
#> [64] dbplyr_2.0.0        tidyselect_1.1.0    xfun_0.19