Gene Set Enrichment Analysis with ggpicrust2

Introduction

This vignette demonstrates how to perform Gene Set Enrichment Analysis (GSEA) on PICRUSt2 predicted functional data using the ggpicrust2 package. GSEA is a powerful method for interpreting gene expression data by focusing on gene sets (pathways) rather than individual genes. In the context of microbiome functional prediction, GSEA can help identify pathways that are enriched in different conditions.

Installation

First, make sure you have the necessary packages installed:

# Install ggpicrust2
if (!requireNamespace("ggpicrust2", quietly = TRUE)) {
  devtools::install_github("cafferychen777/ggpicrust2")
}

# Install required Bioconductor packages
if (!requireNamespace("BiocManager", quietly = TRUE)) {
  install.packages("BiocManager")
}

BiocManager::install(c("fgsea", "clusterProfiler", "enrichplot", "DOSE", "pathview"))

# Load the package
library(ggpicrust2)
library(dplyr)
library(ggplot2)

Basic GSEA Analysis

Let’s start with a basic GSEA analysis using the example data provided in the ggpicrust2 package:

# Load example data
data(ko_abundance)
data(metadata)

# Prepare abundance data
abundance_data <- as.data.frame(ko_abundance)
rownames(abundance_data) <- abundance_data[, "#NAME"]
abundance_data <- abundance_data[, -1]

# Run GSEA analysis
gsea_results <- pathway_gsea(
  abundance = abundance_data,
  metadata = metadata,
  group = "Environment",
  pathway_type = "KEGG",
  method = "fgsea",
  rank_method = "signal2noise",
  nperm = 1000,
  min_size = 10,
  max_size = 500,
  p.adjust = "BH",
  seed = 42
)

# View the top results
head(gsea_results)

Annotating GSEA Results

To make the results more interpretable, we can annotate them with pathway names and descriptions:

# Annotate GSEA results
annotated_results <- gsea_pathway_annotation(
  gsea_results = gsea_results,
  pathway_type = "KEGG"
)

# View the annotated results
head(annotated_results)

Visualizing GSEA Results

The ggpicrust2 package provides several visualization options for GSEA results:

Barplot

# Create a barplot of the top enriched pathways
barplot <- visualize_gsea(
  gsea_results = annotated_results,
  plot_type = "barplot",
  n_pathways = 20,
  sort_by = "p.adjust"
)

# Display the plot
barplot

Dotplot

# Create a dotplot of the top enriched pathways
dotplot <- visualize_gsea(
  gsea_results = annotated_results,
  plot_type = "dotplot",
  n_pathways = 20,
  sort_by = "p.adjust"
)

# Display the plot
dotplot

Enrichment Plot

# Create an enrichment plot for a specific pathway
enrichment_plot <- visualize_gsea(
  gsea_results = annotated_results,
  plot_type = "enrichment_plot",
  n_pathways = 10,
  sort_by = "NES"
)

# Display the plot
enrichment_plot

Comparing GSEA and DAA Results

It can be informative to compare the results from GSEA with those from Differential Abundance Analysis (DAA):

# Run DAA analysis
daa_results <- pathway_daa(
  abundance = abundance_data,
  metadata = metadata,
  group = "Environment",
  daa_method = "ALDEx2"
)

# Annotate DAA results
annotated_daa_results <- pathway_annotation(
  pathway = "KO",
  daa_results_df = daa_results,
  ko_to_kegg = TRUE
)

# Compare GSEA and DAA results
comparison <- compare_gsea_daa(
  gsea_results = annotated_results,
  daa_results = annotated_daa_results,
  plot_type = "venn",
  p_threshold = 0.05
)

# Display the comparison plot
comparison$plot

# View the comparison results
comparison$results

Integrated Analysis with ggpicrust2_extended

For a more streamlined workflow, you can use the ggpicrust2_extended function, which integrates both DAA and GSEA analyses:

# Run integrated analysis
integrated_results <- ggpicrust2_extended(
  data = ko_abundance,
  metadata = metadata,
  group = "Environment",
  pathway = "KO",
  daa_method = "LinDA",
  ko_to_kegg = TRUE,
  run_gsea = TRUE,
  gsea_params = list(
    method = "fgsea",
    rank_method = "signal2noise",
    nperm = 1000
  )
)

# Access DAA results
daa_results <- integrated_results$daa_results

# Access GSEA results
gsea_results <- integrated_results$gsea_results

# Access plots
daa_plot <- integrated_results$daa_plot
gsea_plot <- integrated_results$gsea_plot

Conclusion

Gene Set Enrichment Analysis provides a complementary approach to Differential Abundance Analysis for interpreting PICRUSt2 predicted functional data. By focusing on pathways rather than individual features, GSEA can help identify biologically meaningful patterns that might be missed by traditional methods.

The ggpicrust2 package now offers a comprehensive suite of tools for both DAA and GSEA analyses, making it easier to gain insights from microbiome functional prediction data.