Studies on the physiological function of avian fatty acid binding protein and regulation of gene expression by PPAR-α

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Fatty acid-binding proteins (FABPs) are important factors which regulate the cellular uptake and concentration of fatty acids and lipid metabolism. In avian species, two types of fatty acid binding proteins, L-FABP and Lb-FABP exist in the liver. In the present study, therefore, in order to make it clear the physiological function of avian FAB we tried to detremine 1)cDNA sequences of two FABPs, 2).nutritional and physiological factors affecting their expression, 3)the relevance of PPAR-α for transcription regulation. The cloned cDNA fragments of L-FABP and Lb-FABP coded 125 and 126 amino acids, respectively. The L-FABP mRNA were detected in the liver and intestine while Lb-FABPmRNA was expressed only in the liver. The mRNA abundance of both FABPs were steeply increased during hatching stage. However, the aging, sex-difference and laying performance did not influence the expression of both FABPs, showing that L-FABP and Lb-FABP stably express after the birth. To determine the nutritional regulation of FABPs, chicks were reared under the various nutritional conditions. The fasting decreased mRNA abundance of both FABPs in chicks, but the ingestion of high-fat diet and peroxisome proliferators Wy-14,643 had no influence of the mRNA abundance. There were no remarkable change of hepatic PPAR-α mRNA abundance in any conditions. The 5' -untranslated regions from -566bp to +1 for L-FABP and from -943bp to +1 for Lb-FABP were also cloned and sequenced. It is reported that the rat L-FABP gene contains an peroxisome proliferator response element (PPRE) at -76 to -66 kb. Surprisingly, PPRE were not observed in the chicken L-FABP gene as well as Lb-FABP gene. These results suggest that PPAR-a might not involved in the transcriptional regulation of chicken L-FABP and Lb-FABP gene expression.