RESUMO
Cellular retinol-binding protein type II (CRBPII) is exclusively expressed in the small intestinal absorptive cells. We previously reported that dietary fat induces CRBPII expression within 12 h of fat intake. To examine at which locus of the villus-crypt axis this response to dietary fat occurs, 6-wk-old rats were fed a low-fat diet (7% energy) for 7 d, and then given free access to a high-fat diet (70% energy) for the subsequent 12, 24 or 48 h. Cryostat sectioning of jejunal segments followed by RNA blot hybridization of the transcripts revealed that CRBPII mRNA was expressed maximally in the lower villus, and the immunoreactive protein of CRBPII was expressed maximally in the mid-villus. Feeding the high-fat diet caused a pronounced increase in CRBPII mRNA level from the lower- to middle-villus within 12 h. These results suggest that the CRBPII gene is maximally expressed in the lower villus, and that dietary fat causes an enhancement of CRBPII gene expression in the villus cells.
Assuntos
Gorduras na Dieta/farmacologia , Jejuno/metabolismo , Proteínas Celulares de Ligação ao Retinol/metabolismo , Animais , Northern Blotting/métodos , Dieta/métodos , Gorduras na Dieta/administração & dosagem , Mucosa Intestinal/citologia , Mucosa Intestinal/efeitos dos fármacos , Mucosa Intestinal/metabolismo , Jejuno/citologia , Jejuno/efeitos dos fármacos , Masculino , Microvilosidades/efeitos dos fármacos , Microvilosidades/metabolismo , Ratos , Ratos Sprague-Dawley , Distribuição TecidualRESUMO
Cellular retinol-binding protein type II (CRBPII) is involved in the transport of vitamin A and its metabolism in the small intestine. In the present study, we demonstrated diet-related variations in CRBPII expression in rat jejunum. The CRBPII protein and mRNA levels increased in parallel after the start of feeding period regardless of whether the feeding period was restricted to the hours of darkness or of light. In addition, this variation was observed in the rats fed high-fat diet or low-fat diets, but not in those fed a fat-free diet or in fasted rats. A similar diet-induced variation was seen in the mRNA of liver-type fatty acid-binding protein in rat jejunum. In the transient transfection experiment, unsaturated fatty acid increased rat CRBPII gene promoter activity via the PPARalpha/retinoid X receptor-alpha heterodimer. Taken together, these results suggest that the diet-related variation in CRBPII expression in rat jejunum may be brought about by the transcriptional induction of CRBPII gene expression mainly triggered by dietary fatty acids.