Figure 2.

Nicotine-free, but not nicotine-containing, e-cigarettes trigger wide-ranging changes in gene expression in the colon

(A) Principal component analysis (PCA) of the topmost variable genes in the distal colons of the three groups of mice, all exposed to air or e-cig as indicated for 3 months. PCA identified air control and nicotine-containing e-cig group as similar to each other, but distinctly different from the e-cig alone group along the first principal component.

(B) Heatmap visualization of the differentially expressed genes between the three groups of mice. Each row represents one of the genes, whereas columns represent expression averages of replicates for each investigated group. Red color indicates relative over-expression, whereas blue color indicates relative under-expression. Top genes in the Reactome pathway analyses are marked on the left side. Arrowheads on the right side indicate a few genes that remained altered in both e-cig alone and e-cig + nicotine groups (see Figure S2B).

(C–H) Whisker plots display the levels of expression of the genes, as determined by RNA-seq encoding tight junction markers (occludin, C; ZO1, D; and pro-inflammatory cytokines (MCP1), E; IL-8, F; TNF-α, G; Cxcl2, H).

(I and J) KEGG (I) and Reactome (J) pathway analyses of the list of differentially expressed genes (see Table S1) reveal the most up or downregulated pathways. Red color indicates upregulation, whereas blue color indicates the downregulation of gene expression. No significant enrichment of pathways was seen in the list of downregulated genes by KEGG analyses.