In Vitro Gene Expression Responses of Bovine Rumen Epithelial Cells to Different pH Stresses

SIMPLE SUMMARY: Dietary changes and improper pasture feeding management can lead to subacute rumen acidosis or acute rumen acidosis in cattle. When acidosis occurs, the rumen pH rapidly decreases to an abnormal level and induces lipopolysaccharide (LPS) release by rumen microorganisms. The entry of LPS into the blood through the rumen epithelium induces systemic inflammatory reactions that ultimately result in body damage, reduced performance, and even the death of animals. However, the manner in which genes in the rumen epithelium are regulated in response to pH reduction remains unclear. In this study, transcriptome sequencing and metabolome analysis were performed on rumen epithelial cells at different pH values in vitro to determine the adaptive expressions of genes and metabolites in rumen epithelial cells during the occurrence of rumen acidosis. Our results contribute to a deeper understanding of the response mechanism of the rumen epithelium during the occurrence of rumen acidosis. ABSTRACT: Ruminal acidosis often occurs in production, which greatly affects animal health and production efficiency. Subacute rumen acidosis (SARA) occurs when rumen pH drops rapidly to 5.5–5.8, and acute rumen acidosis (ARA) occurs when rumen pH drops below 5.0, but the molecular regulation mechanism of the rumen epithelium after the rapid decrease in pH is still unclear. Bovine rumen epithelial cells (BRECs) were cultured at pH = 7.4 (control), 5.5 (SARA), and 4.5 (ARA). Transcriptome and metabolomic methods were used to obtain the molecular-based response of BRECs to different pH treatments; pH = 4.5 can significantly induce apoptosis of BRECs. The RNA-seq experiments revealed 1381 differently expressed genes (DEGs) in the control vs. SARA groups (p < 0.05). Fibroblast growth factor (FGF) and tumor necrosis factor (TNF) were upregulated 4.25 and 6.86 fold, respectively, and TLR4 was downregulated 0.58 fold. In addition, 283 DEGs were identified in the control vs. ARA comparison (p < 0.05), and prostaglandin-endoperoxide synthase 2 (PSTG2) was downregulated 0.54 fold. Our research reveals that the MAPK/TNF signaling pathway regulates the inflammatory response of BRECs. Metabolomics identified 35 biochemical compounds that were significantly affected (p < 0.05) in control vs. SARA and 51 in control vs. ARA. Bioinformatics analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database revealed that drug metabolism-cytochrome P450 metabolic and alpha-linolenic acid metabolism changes occurred. These transcriptional and metabolic changes are related to the adaptation of BRECs to low-pH stresses. In conclusion, the combined data analyses presented a worthy strategy to characterize the cellular, transcriptomic, and metabonomic adaptation of BRECs to pH in vitro. We demonstrated transcriptional expression changes in BRECs under pH stress and activation of the molecular mechanisms controlling inflammation.