(DL)-methionine and (DL)-methionyl-(DL)-methionine increase intestinal development and activate Wnt/β-catenin signaling activity in domestic pigeons (Columba livia)

This experiment was undertaken to investigate the effects of parental dietary (DL)-methionine ((DL)-Met) and (DL)-methionyl-(DL)-methionine ((DL)-Met-Met) supplementation on the intestinal development of young squabs. A total of 108 pairs of breeding pigeons and 432 one-day-old squabs were randomly divided into 3 groups: the control group (CON) was fed a basal diet (CP = 15%) and the experimental groups were fed a basal diet supplemented with 0.3% (DL)-Met or (DL)-Met-Met. Each pair of breeding pigeons nourished 4 young squabs, and 8 squabs from each treatment were randomly sampled at the end of the experiment. The results indicated that (DL)-Met and (DL)-Met-Met supplementation improved the intestinal morphology and structure in the squabs, as reflected by the increased relative intestinal weight of each small intestinal segment, villus height, and villus to crypt ratio. In addition, (DL)-Met and (DL)-Met-Met supplementation significantly increased the protein expression of cell proliferation markers (Ki67 and PCNA) and tight junction proteins (ZO-1 and Claudin-1) in the jejunum and strengthened the fluorescence signal intensity of Ki67, PCNA and Villin. Moreover, the expression of Wnt/β-catenin signaling pathway-related proteins (Frizzled 7 [FZD7], p-GSK-3β, Active β-catenin, β-catenin, TCF4, c-Myc, and Cyclin D1), and intestinal peptide transporter 1 (PepT1) in the jejunum was considerably higher in the treatment group than in the CON group (P < 0.05), with the (DL)-Met-Met group having the highest expression. Consistently, the molecular docking results predicted the possibility that (DL)-Met or (DL)-Met-Met binds to the membrane receptor FZD7, which mediates Wnt/β-catenin signaling. Collectively, the improvement of the intestinal development in squabs after parental dietary 0.3% (DL)-Met and (DL)-Met-Met supplementation could be through activation of Wnt/β-catenin signaling pathway, and (DL)-Met-Met is superior to (DL)-Met. Our findings may provide basic data for further optimizing the feeding formula of breeding pigeons and improving the growth and development of squabs.