Effects of dietary selenium deficiency and supplementation on liver in grazing sheep: insights from transcriptomic and metabolomic analysis

Abstract

Background: Mineral elements play a crucial role in supporting the life activities and physiological functions of animals. However, numerous studies have revealed that in some geographical areas and certain grazing situations, grazing livestock frequently suffers from mineral element deficiencies due to the loss of mineral elements from grassland forages, such as selenium (Se). To shed fresh light on this issue, this study aims to investigate the impact of dietary Se deficiency and supplementation on the liver of grazing sheep in these challenging conditions.

Method: This study involved 28 grazing Mongolian Wu Ranke sheep with an average body weight of about 32.20 ± 0.37 kg, which were divided into the Se treatment group and the control group. The Se treatment group was fed with the low-Se diet for 60 days and then continued to be fed with the high-Se diet for 41 days. The liver concentration of minerals, transcriptomic analysis, and untargeted metabolomic analysis were conducted to assess the impact of Se deficiency and supplementation on the liver of grazing sheep.

Results: Dietary Se deficiency and supplementation significantly reduced and elevated liver concentration of Se, respectively (p < 0.05). Gene functional enrichment analysis suggested that dietary Se deficiency might impair protein synthesis efficiency, while Se supplementation was found to enhance liver protein synthesis in grazing sheep. AGAP1, ERN1, MAL2, NFIC, and RERG were identified as critical genes through the weighted gene correlation network analysis, the quantitative real-time polymerase chain reaction, and the receiver operating characteristic curve validation that could potentially serve as biomarkers. Metabolomics analysis revealed that dietary Se deficiency significantly reduced the abundance of metabolites such as 5-hydroxytryptamine, while dietary Se supplementation significantly elevated the abundance of metabolites such as 5-hydroxytryptophan (p < 0.05).

Conclusion: Integrative analysis of the transcriptome and metabolome revealed that dietary Se deficiency led to reduced hepatic antioxidant and anti-inflammatory capacity, whereas Se supplementation increased the hepatic antioxidant and anti-inflammatory capacity in grazing Wu Ranke sheep. These findings provide new insights into the effects of dietary Se deficiency and supplementation on the liver of grazing sheep, potentially leading to improved overall health and well-being of grazing livestock.

Keywords: deficiency; metabolomic; selenium; sheep; supplementation; transcriptomics.

Figure 1

Feeding experimental design of the selenium treatment group and control group in 28 grazing Wu Ranke sheep. LSe, the selenium deficient group; LCG, the control group of the selenium deficient treatment period; SSe, the selenium supplement group; SCG, the control group of the selenium supplement treatment period.

Figure 2

Fresh weight of grazing sheep liver. ^NS p > 0.05, * p < 0.05, ** p < 0.01, *** p < 0.001. LSe, the selenium deficient group; LCG, the control group of the selenium deficient treatment period; SSe, the selenium supplement group; SCG, the control group of the selenium supplement treatment period.

Figure 3

The concentration of liver mineral elements in selenium deficient treated and supplement treated compared with the control group. ^NS p > 0.05, * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 4

DEGs identified between different treatment groups. (A) Volcano Plot of DEGs in the selenium deficient group. (B) Volcano Plot of DEGs in the selenium supplement group. The top 10 up-regulated and down-regulated gene names were tagged and sorted by FDR value. DEGs, differentially expressed genes; FDR, false discovery rate.

Figure 5

The Go enrichment of DEGs in the selenium supplement group. Go, gene ontology; DEGs, differentially expressed genes; FDR, false discovery rate.

Figure 6

The Top 5 GSEA enrichment of Go terms. (A) Enriched in the control group of the selenium deficient treatment period. (B) Enriched in the selenium deficient group. (C) Enriched in the control group of the selenium supplement treatment period. (D) Enriched in the selenium supplement group. GSEA, gene set enrichment analysis; Go, gene ontology.

Figure 7

Screening of the candidate critical genes by WGCNA method. (A) Network dendrogram from co-expression topological overlap. Color bars show the correlation of gene expression with liver concentration of selenium. (B) The scatter plot of the association between the turquoise module and gene importance. The genes within the red box are identified as hub genes. (C) The Venn diagram of overlapping genes between DEGs and the hub genes as candidate critical genes. WGCNA, the weighted gene co-expression network analysis; DEGs, differentially expressed genes; LSe, the selenium deficient group; SSe, the selenium supplement group.

Figure 8

The validation of the critical genes. (A) The gene TPM counts of candidate critical genes. (B) The relative mRNA expression levels of NFIC and RERG in the liver by qRT-PCR. (C) The ROC validation for critical genes. ^NS p > 0.05, * p < 0.05, ** p < 0.01, *** p < 0.001. LSe, the selenium deficient group; LCG, the control group of the selenium deficient treatment period; SSe, the selenium supplement group; SCG, the control group of the selenium supplement treatment period; TPM, transcripts per kilobase million reads; qRT-PCR, quantitative real-time polymerase chain reaction; ROC, the receiver operating characteristic curve.

Figure 9

DEMs identified between different treatment groups. (A) Volcano Plot of DEMs in LSe of NEG. (B) Volcano Plot of DEMs in LSe of POS. (C) Volcano Plot of DEMs in SSe of NEG. (D) Volcano Plot of DEMs in SSe of POS. LSe, the selenium deficient group; SSe, the selenium supplement group; NEG, negative ion mode; POS, positive ion mode; DEMs, differential metabolites.

Figure 10

The KEGG pathways enrichment of DEMs in the LSe of NEG (A), LSe of POS (B), SSe of NEG (C), and SSe of POS (D). KEGG, the Kyoto Encyclopedia of Genes and Genomes; DEMs, differential metabolites; LSe, the selenium deficient group; SSe, the selenium supplement group; NEG, negative ion mode; POS, positive ion mode.

Figure 11

The correlation analysis of critical genes and DEMs in the LSe of NEG (A), LSe of POS (B), SSe of NEG (C), and SSe of POS (D). * p < 0.05, ** p < 0.01, *** p < 0.001. DEMs, differential metabolites; LSe, the selenium deficient group; SSe, the selenium supplement group; NEG, negative ion mode; POS, positive ion mode.