Increased maternal consumption of methionine as its hydroxyl analog improves placental angiogenesis and antioxidative capacity in sows

Abstract

Previous evidence suggests that methionine (Met) consumption can promote placental angiogenesis and improve fetal survival. To investigate the mechanisms by which increased levels of Met as hydroxyl-Met (OHMet) improve placental function, forty sows were divided into four groups and fed either a control diet, or diets supplemented with 0.15% OHMet, 0.3% OHMet or 0.3% Met (n = 10). Placentas were collected immediately after expulsion, and extracted proteins were analyzed by tandem mass tag based quantitative proteomic analysis. We found that 0.15% OHMet consumption significantly increased placental vascular density compared with the control. Proteomic analysis identified 5,136 proteins, 87 of these were differentially expressed (P < 0.05, |fold change| > 1.2). Enriched pathways in the Kyoto Encyclopedia of Genes and Genomes for 0.15% OHMet vs. control and 0.15% OHMet vs. 0.3% OHMet were glutathione metabolism; for 0.15% OHMet vs. 0.3% Met, they were NOD-like receptor signaling and apoptosis. Further analysis revealed that 0.15% OHMet supplementation upregulated the protein expression of glutathione-S-transferase (GSTT1) in placentas and trophoblast cells compared with the control and 0.3% OHMet groups, upregulated thioredoxin (TXN) in placentas and trophoblast cells compared with the 0.3% OHMet and 0.3% Met groups, and decreased reactive oxygen species (ROS) levels in trophoblast cells compared with other groups. In contrast, sows fed 0.3% OHMet or 0.3% Met diets increased placental interleukin 1β levels compared with the control, and upregulated the protein expression of complex I-B9 (NDUFA3) compared with the 0.15% OHMet group. Furthermore, homocysteine, an intermediate in the trans-sulphuration pathway of Met, damaged placental function by inhibiting the protein expression of TXN, leading to apoptosis and ROS production. Although dietary 0.15% OHMet supplementation improved placental angiogenesis and increased antioxidative capacity, 0.3% OHMet or 0.3% Met supplementation impaired placental function by aggravating inflammation and oxidative stress, which is associated with cumulative homocysteine levels.