Transcriptomic signature of high dietary organic selenium supplementation in sheep: A nutrigenomic insight using a custom microarray platform and gene set enrichment analysis

The objective of this study was to investigate the effect of a high dietary selenium (Se) supplementation on the whole-transcriptome of sheep. A custom-sheep whole-transcriptome microarray, with more than 23,000 unique transcripts, was designed, and then used to profile the global gene expression of sheep after feeding a high dietary supplementation of organic Se. Lactating cross-bred ewes (N = 10, 3 to 4 y of age; 55 to 65 kg BW) at their late lactation [100 ± 31 8 d in milk (DIM)] were acclimated to indoor individual pen feeding of a basal control diet (0.40 mg Se/d, Na-selenite) for 4 wk. Sheep were then kept on a diet with an extra (high) supplementation of organic Se (1.45 mg Se/d as Sel-Plex, Alltech, Australia) for 40 d. Whole blood was collected at 2 time-points [last day of the acclimatization period (T0), and after 40 d of the organic Se supplementation (T40)], then total RNA was isolated and labeled for the subsequent microarray analysis. Significant analysis of microarray (SAM), using t-statistic of the microarray data (T40 versus T0), evidenced the up- and down regulation of 942 and 244 transcripts (false discovery rate; FDR < 0.05), respectively. Seven genes showed the same trend of expression (up- or down-regulation) when tested by qPCR in a cross-validation step. The microarray showed significant upregulation of the following selenoproteins at T40: selenium binding protein 1 (SELENBP1), selenoprotein W1 (SEPW1), glutathione peroxidase 3 (GPX3), and septin 8 (SEPT8), and the expression trends for SEPW1 and SEPT8 were validated using qPCR. Functional annotation of the differentially expressed (DE) genes showed the enrichment of several immune system-related biological processes (lymphocyte activation, cytokine binding, 46 leukocyte activation, T cell differentiation, B cell activation) and pathways (cytokine and interleukin signaling). Moreover, gene set enrichment analysis (GSEA) evidenced the --- enrichment of B and T cell receptors signaling pathways with an enrichment 48 score (ES) of 0.63 and 0.59, respectively. Overall, from a global gene expression (whole-transcriptome) point of view, short-term supplementation of a high dietary organic Se to Se-nondeficient sheep results in a transcriptomic signature that mainly reflects an induced immune-system and a modulation of transcription effect. Also, the present study provides a custom whole transcriptome microarray platform that can be used in further global gene expression studies in the ovine species.