Differential proteome analysis along jejunal crypt-villus axis in piglets.

The brush-border membrane (BBM) of enterocytes is responsible for the digestion and absorption of nutrients and ions in the small intestine. To identify the BBM proteins involved in epithelial cell maturation along the crypt-villus axis, enterocytes were sequentially isolated from the villus tip to the crypt of the jejunum from 21-day-old suckling piglets. After preparation of BBM vesicles, we detected 194 proteins in the jejunal epithelial cells by isobaric tags using relative and absolute quantification (iTRAQ) techniques. Of these, 56 BBM proteins were differentially expressed along the crypt-villus axis. During differentiation, the expression of proteins related to digestion and absorption of nutrients was primarily downregulated at the upper, middle villus, or crypt compared to the villus tip, while expression of proteins related to structural and enzyme regulator proteins was largely upregulated. We verified the differences in Na(+)/K(+) -transporting ATPase, galectin-3, and an intestinal-type fatty acid binding protein by western blot or immunochemical analysis. Identification of BBM-associated proteins helps enhance our understanding of digestion and absorption in piglets and other mammals, including humans.