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

脂肪酸结合蛋白（Fatty - acid binding protein, FABPs）是调节脂肪酸的细胞摄取、浓度和脂质代谢的重要因子。在鸟类中，肝脏中存在两种脂肪酸结合蛋白，L-FABP和Lb-FABP。因此，在本研究中，为了明确禽FAB的生理功能，我们试图确定1)两个FABPs的cDNA序列，2)营养和生理因素对其表达的影响，3)PPAR-α与转录调控的相关性。克隆的L-FABP和Lb-FABP cDNA片段分别编码125和126个氨基酸。肝脏和肠道中均有L-FABP mRNA表达，而Lb-FABPmRNA仅在肝脏中表达。两种FABPs的mRNA丰度在孵化期均急剧升高。然而，年龄、性别差异和产蛋性能对这两种fabp的表达没有影响，说明L-FABP和Lb-FABP在出生后稳定表达。为了确定FABPs的营养调节作用，在不同营养条件下饲养雏鸡。禁食降低了雏鸡两种FABPs的mRNA丰度，但摄入高脂肪日粮和过氧化物酶体增殖物wy - 14643对mRNA丰度没有影响。在任何条件下肝脏PPAR-α mRNA丰度均无显著变化。L-FABP的-566bp至+1和Lb-FABP的-943bp至+1的5'非翻译区也被克隆和测序。据报道，大鼠L-FABP基因含有一个-76 ~ -66 kb的过氧化物酶体增殖反应元件（PPRE）。令人惊讶的是，在鸡的L-FABP基因和Lb-FABP基因中均未观察到PPRE。这些结果提示PPAR-a可能不参与鸡L-FABP和Lb-FABP基因表达的转录调控。

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.