Morphological adaptation of sheep's rumen epithelium to high-grain diet entails alteration in the expression of genes involved in cell cycle regulation, cell proliferation and apoptosis

Background: The objectives of this study were to characterize changes in the relative m RNA expression of candidate genes and proteins involved in cell cycle regulation, cell proliferation and apoptosis in the ruminal epithelium(RE) of sheep during high-grain(HG) diet adaptation.Results: Twenty sheep were assigned to four groups with five animals each. These animals were assigned to different periods of HG diet(containing 40% forage and 60% concentrate mix) feeding. The HG groups received an HG diet for7(G7, n = 5), 14(G14, n = 5) and 28 d(G28, n = 5), respectively. In contrast, the control group(CON, n = 5) was fed the forage-based diet for 28 d. The results showed that HG feeding linearly decreased(P < 0.001) the ruminal p H, and increased the concentrations of ruminal total volatile fatty acid(linear, P = 0.001), butyrate(linear, P < 0.001), valerate(quadratic P = 0.029) and the level of IGF-1(quadratic, P = 0.043) in plasma. The length(quadratic, P = 0.004), width(cubic, P = 0.015) and surface of the ruminal papillae(linear, P = 0.003) were all enlarged after 14 d of HG diet feeding.HG feeding cubically increased the number of cell layers forming the stratum corneum(SC, P < 0.001) and the thickness of the SC(P < 0.001) and stratum basale(P < 0.001). The proportion of basal layer cells in the RE decreased(linear, P < 0.001) in the G0/G1-phase, but it increased linearly(P = 0.006) in the S-phase and cubically(P = 0.004) in the G2/M-phases. The proportion of apoptosis cells in G7, G14 and G28 was reduced compared to the CON(quadratic, P <0.001). HG diet feeding linearly decreased the m RNA expression of Cyclin E1(P = 0.021) and CDK-2(P = 0.001) and(P = 0.027) the protein expression of Cyclin E1. Feeding an HG diet linearly increased the m RNA expression of genes IGFBP-2(P = 0.034) and IGFBP 5(P < 0.009), while linearly decreasing(P < 0.001) the IGFBP 3 expression. The expression of cell apoptosis gene Caspase 8 decreased(quadratic, P = 0.012), while Bad m RNA expression tended to decrease(cubic, P = 0.053) after HG feeding.Conclusions: These results demonstrated sequential changes in rumen papillae size, cell cycle regulation and the genes involved in proliferation and apoptosis as time elapsed in feeding a high-grain diet to sheep.