Regulatory mechanism governing the diurnal rhythm of intestinal H⁺/peptide cotransporter 1 (PEPT1)

Abstract

The intestinal H(+)/peptide cotransporter 1 (PEPT1) plays important roles as a nutrient and drug transporter. Previously, we reported that rat intestinal PEPT1 showed a diurnal rhythm and that this rhythm is closely related to the feeding schedule. Furthermore, we also demonstrated that transcription factors, Sp1, Cdx2, and peroxisome proliferator-activated receptor-alpha (PPAR-alpha) contribute to the basal, intestine-specific, and fasting-induced expression of PEPT1, respectively. In this study, to clarify the molecular mechanism governing the diurnal rhythm of PEPT1 expression, we compared expression profiles of these transcription factors under two kinds of feeding schedules. The intestinal Sp1 and Cdx2 did not show a circadian accumulation of mRNA or response to the daytime feeding regimen. Plasma free fatty acids, endogenous PPAR-alpha ligands, exhibited a robust circadian fluctuation in phase with that of PEPT1. However, subsequent experiments using PPAR-alpha-null mice revealed the absence of any association between the circadian rhythm of PEPT1 and PPAR-alpha. We then focused on the clock genes (Clock, Bmal1, Per1-2, and Cry1) and clock-controlled gene, albumin D site-binding protein (DBP). A robust and coordinated circadian expression of the clock genes was observed, and daytime feeding entirely inverted the phase except for Clock. The expression of DBP was in phase with that of PEPT1 in both groups. Electrophoretic mobility shift assays and reporter assays revealed that DBP has the ability to bind the DBP binding site located in the distal promoter region of the rat PEPT1 gene and induce the transcriptional activity. These findings indicate that DBP plays pivotal roles in the circadian oscillation of PEPT1.

Bile Acid-regulated Peroxisome Proliferator-activated Receptor-α (PPARα) Activity Underlies Circadian Expression of Intestinal Peptide Absorption Transporter PepT1/Slc15a1

“…Previous studies using PPAR␣-null mice demonstrated that Slc15a1 is typical of PPAR␣ target genes whose expression oscillates in a circadian time-dependent as well as feeding state-dependent manner (28). Although a molecular component of circadian clock has been shown to govern the daily expression of Slc15a1 in laboratory rats (12), the present study demonstrated that the suppressing action of bile acids on PPAR␣ activity is involved in the circadian regulation of the expression of Slc15a1 in mouse intestinal epithelial cells.…”

“…For example, it has been reported that intestinal expression of PepT1 is regulated by insulin, thyroid hormone, epidermal growth factor, and some pharmacological agents (8 -11). In laboratory rodents, the levels of Slc15a1 mRNA and PepT1 protein fluctuate in a time-dependent manner (12), suggesting that the expression of Slc15a1/PepT1 is under the control of a circadian clock.…”

Clock is important for food and circadian regulation of macronutrient absorption in mice

“…For example, apical Na + /glucose cotransporter 1 (SGLT1) and fructose transporter 5 (GLUT5) as well as the basolateral hexose transporter GLUT2 show rhythmic expression (31)(32)(33)(34)(35)(36). In addition, the expression of protoncoupled, oligopeptide transporter 1 (PEPT1), which is also a nutrient and drug transporter, shows diurnal expression ( 32,37 ). We reported that intestinal and hepatic gene expression of microsomal triglyceride transfer protein (MTP), a protein involved in intracellular neutral lipid transfer ( 38,39 ), shows rhythmic expression ( 40 ).…”

Circadian regulation of electrolyte absorption in the rat colon

“…Recent studies indicate that circadian changes in the expression of epithelial transporters might be controlled by the core clock mechanism. This has been demonstrated for the Na ϩ /H ϩ exchanger NHE3, the peptide transporter PEPT1, and monosaccharide transporters SGLT1, GLUT2, and GLUT5 in the intestine (23,28,33) and for NHE3 and the ␣-subunit of the epithelial Na ϩ channel (ENaC) in the renal tubules (7,27). Approximately 3.7% of distal colonic genes are expressed rhythmically (11).…”