Concentrate diet modulation of ruminal genes involved in cell proliferation and apoptosis is related to combined effects of short-chain fatty acid and pH in rumen of goats

Short-chain fatty acids (SCFA) regulate cell proliferation and cell apoptosis in gastrointestinal tissue in vitro and in vivo. We have tested the hypothesis that a medium-concentrate intake induces mRNA abundance alterations of genes involved in cell proliferation and cell apoptosis in the rumen epithelium of goats, and that these changes in mRNA abundance are related to ruminal SCFA concentration and ruminal pH. Goats (n = 16) were randomly allocated to 2 groups and fed either a low-concentrate (LC) diet (10% concentrate; n = 8) or a medium-concentrate (MC) diet (35% concentrate; n = 8) in 2 equal portions daily. The individually housed goats were fed separately with their respective diet for 3 wk and were slaughtered 6 h after the morning feed on d 22. In vivo, goats receiving the MC treatment exhibited a greater ruminal SCFA concentration (73.7 mM) compared with those receiving the LC treatment (53.2 mM), and the pH decreased from 6.9 to 6.5. The expression of proliferative genes of cyclin A, cyclin B1, cyclin D1, cyclin E1, CDK1, CDK2, CDK4, and CDK6 mRNA in the MC group was enhanced. The gene expression of apoptosis genes (caspase 3, caspase 8, caspase 9, p53, and Bax) was significantly higher, and the ratio of Bcl-2 to Bax (Bcl-2/Bax) expression was lower in the MC group than in the LC group. The same trend was observed in the population of apoptotic cells analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. The cell density in the stratum germinativum of the MC group was significantly increased compared with that in the LC group. During primary culture of rumen epithelial cells, SCFA or pH treatment alone of the culture medium had significant effects on the expression of most of the genes tested in the present study. Furthermore, SCFA and pH exerted combined effects on the expression of cyclin A, cyclin B1, cyclin E1, CDK6, p53, Bcl-2, and Bcl-2/Bax. Thus, the MC diet induces alteration of gene expression of the genes that regulate both cell proliferation and apoptosis. These genes are regulated by combined effect of ruminal SCFA and ruminal pH.