PSXI-27 Effects of managing mature beef bulls on divergent planes of nutrition on sperm transcriptome.

Abstract Though the effect of nutrition on testis development in young bulls has been explored, the molecular processes of the testis and sperm function in response to nutrition in mature bulls are still unknown. Thus, we investigated the effect of divergent planes of nutrition on sperm transcript abundance. Fifteen mature beef bulls were ranked by body weight (BW = 800.4 ± 17.4 kg) and randomly assigned to either a positive (POS, n = 8) or a negative (NEG, n = 7) plane of nutrition in a 112-day experiment. Bulls were fed a common diet, adjusted biweekly to achieve targeted weight gain or loss of 12.5% of original BW. On day 112, electroejaculation was used to collect two ejaculates from each bull. After density gradient centrifugation, sperm total mRNA was isolated and gene expression was measured through RNA-sequencing (n = 6 bulls/group). Differential gene expression analysis was performed using DESeq2, and KEGG pathways were retrieved using the ShinyGo webtool. We identified 365 genes upregulated and 404 downregulated in POS (adj.Pval < 0.1). Interestingly, the DNMT1, DNMT3A, and PRMT8 genes were upregulated in POS. While DNMT1 and DNMT3A encode enzymes responsible for maintenance and de novo methylation, PRMT8 codes a methyltransferase enzyme involved with ordered histone-to-protamine transition. Genes from the caspase and ubiquitin families were downregulated in POS. These families are acting on protein catabolic processes that were previously associated with infertility in men. Also upregulated in POS, the RPTOR gene encodes a protein that modulates mTORC1 in response to nutrient and insulin levels. mTOR is highly involved with spermatogenesis, and its coordinated signaling with AMPK and IGF-1 is essential for Sertoli cell functions. Among the KEGG pathways, we identified the aldosterone synthesis and secretion over-represented by the upregulated genes in POS. In contrast, the downregulated genes were acting on the renin secretion pathway (FDR < 0.05). The aforementioned pathways were previously associated with sperm motility and male fertility. Our findings suggest body condition-sensitive mechanisms between sperm function and transcript abundance. Epigenetic mechanisms through DNA methylation and histone modification seem to be altered in sperm in response to body condition. Taken together, these results provide novel insights into the interplay between nutrition, epigenetics, and potential fertility in mature bulls.