Differential effects of dietary protein contents on jejunal epithelial cells along the villus-crypt axis in nursery piglets.

This study was conducted to determine the effects of different dietary protein contents on jejunal epithelial cells along the crypt-villus axis in nursing piglets. A total of 54 crossbred weaned piglets were randomly assigned to 3 dietary groups (14%, 17%, or 20% CP diets). Six piglets were randomly selected from each treatment and killed for tissue sampling at 10, 25, and 45 d after weaning. Jejunal epithelial cells were sequentially isolated along the crypt-villus axis and yielded 3 "cell fractions" (upper villus, middle villus, and crypt cells), and amino acid contents and the mRNA expression of amino acid transporters and genes related to protein degradation in jejunal epithelial cells were measured. At 10 d after weaning, dietary supplementation with 17% CP significantly increased (P < 0.05) the contents of Tau, Gly, Glu, and Cys in the upper villus compared with 14% or 20% CP. At 25 d after weaning, the 14% CP group had greater (P < 0.05) contents of Glu, Gly, Ala, Thr, Ser, Leu, and Tyr in the upper villus and Thr, Ala, Val, Ile, Tyr, and Lys in the middle villus compared with the 17% or 20% CP group. There was a similar response to feeding 14% low CP content with age, in which there was upregulation in expression, which occurred as early as 10 d postweaning for some genes (L amino acid transporter 1 [LAT1] in the middle villus and excitatory amino acid carrier 1 [EAAC1] in crypt cells) and at 25d postweaning for others (peptide transporter 1 [PEPT1] in the upper villus, B0 neutral amino acid transporter [B^0,+AT1] in middle villus and Y⁺LAT1 in crypt cells). However, the mRNA expression of cationic amino acid transporter 1 (CAT1) in the upper villus and CAT2 in the middle villus was highest (P < 0.05) in the 17% CP group compared with the 14% and 20% CP groups at 10 d after weaning. In addition, the mRNA expression of LAT2 in the middle villus was highest (P < 0.05) in the 17% CP group compared with the 14% and 20% CP groups at 25 d after weaning. The PEPT1 mRNA in the middle villus of the 17% and 20% CP groups was greater (P < 0.05) than that in the 14% CP group at 45 d after weaning. The present study showed that the different CP content levels differentially affected the amino acid content and mRNA expression of the amino acid transporter in enterocytes along the crypt-villus axis and may help identify optimal CP contents in diets for nursery piglets. [ABSTRACT FROM AUTHOR]