Host ALDH2 deficiency aggravates acetaldehyde metabolism disturbance and gut microbiota dysbiosis in chronic alcohol exposure mice

Abstract

Alcohol is inextricably linked with intestinal microbiota as it was absorbed through gut. While mitochondrial aldehyde dehydrogenase 2 (ALDH2), as the major enzyme responsible for metabolizing toxic acetaldehyde to acetate, is important factor influencing alcohol metabolism. However, it is not yet known the relationship between ALDH2 knockout (KO) and gut microbiota profiles in mice under chronic alcohol exposure. Therefore, this study aimed to investigate the effect of 5% v/v alcohol exposure on the gut microbiota of ALDH2 knockout (KO-5%) and wild-type (WT-5%) mice. At the end of 10-week experiment, KO-5% mice exhibited a higher serum acetaldehyde concentration and upregulated expression of pro-inflammatory cytokines in intestine tissue than WT-5% mice. Metagenomic results revealed that the KO-5% mice had a significant decrease in alpha diversities. Moreover, KO-5% mice exhibited gut microbiota dysbiosis with the characteristic of a higher abundance of phylum Proteobacteria, and genera Stenotrophomonas and Ralstonia, whereas the level of genera Lactobacillus, unclassfied Bacilli, and Turicibacter were decreased. Additionally, genera Candidatus Arthromitus and Ralstonia were the most representatives in the KO-5% mice. Further, chronic alcohol exposure resulted in enriched expression of genes associated with bacterial metabolism and cellular processes in gut from WT mice. Taken together, our findings demonstrated a strong interaction between ALDH2 and the gut microbiota to response to alcohol exposure.

Keywords: 16S rRNA gene sequencing; acetaldehyde; chronic alcohol exposure; ileum microbiota; mitochondrial acetaldehyde dehydrogenase 2 (ALDH2).

Figure 1

Establish a chronic alcohol exposure animal model. The level of ALDH2 at mRNA (A) and protein (B) was highly expressed in WT mice when compared with KO mice in both liver and ileum tissues. The daily water intake (C) and body weight (D) during the 10-week alcohol exposure had no significant differences across different experimental groups. Ethanol concentrations (E) and acetaldehyde concentrations (F) were measured at the end of experiment among different groups. Data are presented as “mean ± SD,” *p < 0.05, **p < 0.01.

Figure 2

Effects of chronic alcohol exposure on the mRNA expression of inflammatory biomarkers in ALDH2 knockout mice. (A) Expression of TNF-α. (B) Expression of IL-1β. (C) Expression of IL-6. (D) Expression of IL-10. Data are presented as mean ± SD (n = 3). *p < 0.05, **p < 0.01.

Figure 3

Chronic alcohol exposure resulted in distinct gut microbiota profiles in KO and WT mice. Alpha diversity within samples was measured by Chao1 (A) and Shannon index (B). Scatterplot from Principal Coordinate Analysis (PCoA) of beta diversity was measured by Bray-Curtis index (C) and Unweighted Unifrac distance (D). Results were determined by Kruskal–Wallis test when *p < 0.05, **p < 0.01.

Figure 4

Chronic alcohol exposure resulted in distinct community structure in KO and WT mice. Summary of the relative abundances of bacterial phyla (A) and the top 20 most abundant bacterial genera (B). Each color represents one bacterial species on the stacked bar chart. Relative abundance of special bacteria genera that expressed higher in WT-5% than WT-Control but which has lower abundance in KO-5% than KO-Control mice (C).

Figure 5

Differential represent taxa between KO-5% and WT-5% mice on the basis of Linear discriminant analysis effect size (LEfSe) analysis. Histogram of Linear Discriminant Analysis (LDA) scores indicating statistical different relative levels across all taxa (A). Cladogram revealing the phylogenetic relationships between taxa with the statistically different (B). Circle sizes in the cladogram plot represent the proportion to bacterial abundance, and the yellow circles represent different taxon with no obvious difference.

Figure 6

Differential abundances of bacterial functional pathways between KO-5% and WT-5% mice. All KEGG orthologs shown have an adjusted q value cutoff of 0.05.