A Combined Metabolomic and Proteomic Study Revealed the Difference in Metabolite and Protein Expression Profiles in Ruminal Tissue From Goats Fed Hay or High-Grain Diets

Abstract

Currently, knowledge about the impact of high-grain (HG) feeding on metabolite and protein expression profiles in ruminal tissue is limited. In this study, a combination of proteomic and metabolomic approaches was applied to evaluate metabolic and proteomic changes of the rumen epithelium in goats fed a hay diet (Hay) or HG diet. At the metabolome level, results from principal component analysis (PCA) and PLS-DA revealed clear differences in the biochemical composition of ruminal tissue of the control (Hay) and the grain-fed groups, demonstrating the evident impact of HG feeding on metabolite profile of ruminal epithelial tissues. As compared with the Hay group, HG feeding increased the levels of eight metabolites and decreased the concentrations of seven metabolites in ruminal epithelial tissues. HG feeding mainly altered starch and sucrose metabolism, purine metabolism, glyoxylate and dicarboxylate metabolism, glycerolipid metabolism, pyruvate metabolism, glycolysis or gluconeogenesis, galactose metabolism, glycine, serine and threonine metabolism, and arginine and proline metabolism in ruminal epithelium. At the proteome level, 35 differentially expressed proteins were found in the rumen epithelium between the Hay and HG groups, with 12 upregulated and 23 downregulated proteins. The downregulated proteins were related to fatty acid metabolism, carbohydrate metabolic processes and nucleoside metabolic processes, while most of upregulated proteins were involved in oxidative stress and detoxification. In general, our findings revealed that HG feeding resulted in differential proteomic and metabolomic profiles in the rumen epithelia of goats, which may contribute to better understanding how rumen epithelium adapt to HG feeding.

Keywords: goat; high grain feeding; metabolomics; proteomic; rumen epithelium.

FIGURE 1

(A) Principal component analysis (PCA) of metabolites in rumen epithelium in goats fed hay (Hay) and high grain (HG) diets. PC, the principal component that distinguish the Hay group and the HG group. PC1 is the first principal component; PC2 is the second principal component; PC1 could explained 35.6% of the variation; PC2 explained 19% of the variation. (B) Partial least squares discriminant analysis (PLS-DA) of metabolites in rumen epithelium in goats fed hay (Hay) and high grain (HG) diets. PLS, the principal component that distinguish the Hay group and the HG group. PLS1 is the first principal component; PLS2 is the second principal component. (C) Loading plot of the 91 commonly detected compounds projected into the PLS-DA model, the most important compounds (VIP > 1.2) responsible for the discrimination are labeled and colored in pink, and the other compounds were colored in green. Compounds are labeled by the names used in Table 1. Variables with the same distance from 0 with similar positions are positively correlated. Those in the opposite direction are negatively correlated. (D) Pathway analysis. Plots depicting computed metabolic pathways as a function of –log (p) and pathway impact for the key differential metabolites. The impact is the pathway impact value calculated from pathway topology analysis. The larger size indicates higher pathway enrichment, and the darker color indicates higher pathway impact values.

FIGURE 2

Gene ontology distribution analysis of differentially expressed proteins in the rumen epithelium in goats from the high grain (HG) group and the hay (Hay) group.

FIGURE 3

Protein–protein interaction analysis by the OmicsBean.

FIGURE 4

The p-value of enriched KEGG pathway.