Developmental Expression of PEPT1 and PEPT2 in Rat Small Intestine, Colon, and Kidney

Abstract

Mammalian peptide transporters (PEPT1 and PEPT2) play a pivotal role in the absorption of small peptides from the intestine and kidney, respectively, and in the disposition and targeting of peptide or mimetic drugs. However, there are few reports on the molecular basis of their regulation, especially in the young. The aim of this study was to determine the developmental expression of intestinal and renal oligopeptide transporters in rats from embryonic to adult ages. Intestinal segments were collected (i.e. duodenum, jejunum, ileum, and colon) along with whole kidney, and their mRNA and protein levels were measured. Expression levels of PEPT1 were maximal 3-5 d after birth in the duodenum, jejunum, and ileum, and then declined rapidly. Expression was increased transiently at d 24, most notably in the ileum. Adult protein levels were approximately 70% of that observed on d 3-5. Significant PEPT1 expression was observed in colon during the first week of life, but levels were undetectable shortly thereafter through adulthood. PEPT1 and PEPT2 expression is less regulated in rat kidney and more pronounced in older animals. Peptide transporters were also present as early as d 20 of fetal life for all tissues tested. These results are unique in providing the developmental expression of peptide transporter mRNA and protein in distinct regions of the small intestine, colon, and kidney in rat. Our findings suggest that intestinal expression of PEPT1 is induced postpartum, possibly by suckling, and again at the time of weaning, and that the colon may participate in peptide transport early in life. Expression and molecular cloning studies have resulted in the identification of two distinct proton-coupled oligopeptide transporters in rabbit (1-3), rat (4 -6), and human (7, 8) (i.e. PEPT1 as low-affinity carrier, PEPT2 as high-affinity carrier). The proteins range in size from 707 to 729 amino acids in various species, with high homology between species for a given transporter (approximately 80%) and less homology between transporters for a given species (approximately 50%). The gene products, as predicted by hydropathy analysis, contain 12 membrane-spanning domains and a large extracellular loop between transmembrane domains 9 and 10. The encoded proteins have a number of potential N-glycosylation as well as protein kinase recognition sites, which suggests that the transporters may be regulated by reversible phosphorylation. More recently, a third peptide transporter, PHT1, was cloned from rat brain (9). Encoding a protein of 572 amino acids, hydropathy analysis predicts the presence of 12 transmembrane domains. There are also multiple N-glycosylation sites in the hydrophilic extracellular loop of PHT1, along with potential sites for protein kinase C-dependent phosphorylation. PHT1 is novel in that it transports histidine, as well as small peptides, with high affinity and in a proton gradient-dependent manner. Although expressed in the brain and eye, PHT1 is not found in the intestine or kidney and shows little homology to P...

Ontogenesis of peptide transport and morphological changes in the ovine gastrointestinal tract

“…In the fasted rats, both PepT1 mRNA abundance and protein expression increased three-fold. Due to the parallel changes in mRNA abundance and protein expression, this is suggestive of transcriptional regulation of PepT1, which is in agreement with the data of Shen et al (2001).…”

“…Uptake then remained constant for 6 d postnatal, declined steadily, and reached adult levels by 50 d. More recently, abundance of PepT1 mRNA was reported to be greatest at 4 d of age in the jejunum of rats, and then decreased until reaching adult levels by 28 d of age (Miyamoto et al, 1996). Shen et al (2001) reported PepT1 mRNA abundance was maximal in all segments of the small intestine 3 to 5 d after birth. In the present study, sampling times did not begin until 2 wk of age, but the mRNA transcript that hybridized to our probe was present in all tissues studied by that time.…”

“…Initial appearance of nutrient transporters varies among species (Buddington and Diamond, 1989). In rats, PepT1 mRNA and protein was present in the small intestine beginning at 17 d of embryonic life (Shen et al, 2001). Recently, it was suggested that the colon is a physiologically important tissue in peptide transport early in life (Shen et al, 2001).…”

“…Molecular data on the ontogenesis of PepT1 in laboratory animal species indicate greater mRNA abundance and protein expression during the early postnatal period (Miyamoto, 1996;Shen et al, 2001). Dietary regulation has been implicated as an important factor in the intestinal transport of peptides (Ferraris et al, 1988;Erickson et al, 1995;Shiraga et al, 1999).…”

An update on renal peptide transporters

“…Comparative analysis using Northern and Western blotting techniques has shown an increase in the expression of PEPT1 in the small intestine immediately after birth and expression in the colon, which disappeared in adult stage (59). In the kidney, the expression levels of PEPT1 and PEPT2 increased steadily over time to reach maximal levels 2 wk after birth.…”