DIETARY OMEGA-3 FATTY ACIDS, GENE EXPRESSION AND GROWTH

在啮齿动物以及人类婴儿和成人中，饮食中的omega3脂肪酸与较高的能量消耗率、较低的体重增重率和/或较低的脂肪沉积率有关。这些脂肪酸还被证明可以抑制编码脂肪生成限速酶的基因的转录，增强编码线粒体和过氧化体氧化限速酶的转录基因，以及推测的生热解偶联蛋白(UCP)-2的骨骼肌含量。有人建议进行研究，以确定体内代谢和基因组事件是否以一致的方式发生，以增加能量消耗，从而降低脂肪沉积和体重增加的速度，并探索介导omega3脂肪酸影响的特定细胞和核机制。临床研究将在3-6个月大计划接受腹股沟疝修补术的婴儿身上进行，将解决以下假设：omega3脂肪酸调节基因表达从而减少甘油三酯合成的限速酶(即甘油-3-磷酸酰基转移酶)，增加线粒体的限速酶(即肉碱棕榈酰转移酶)和过氧体脂肪酸氧化(即酰基-CoA氧化酶)，以及增加UCP-2和/或-3的丰度，从而导致更大的能量消耗，这是由于过氧化体和/或未偶联的线粒体氧化效率增加所致。婴儿将被随机和盲目地分配到只有不同的α-亚麻酸(占总脂肪酸的1%或4%)的配方奶粉中，大约两周后，在预定的手术期间，将获得肌肉，以测定所引用的转录本的mRNA丰度。能量消耗将同时用间接量热法测定，并与信使核糖核酸丰度相关。将在大鼠身上进行的研究将检验这一假设，即omega3脂肪酸通过减少和/或失活合成丙二酰辅酶A的限速酶的表达和/或使其失活来减少丙二酰辅酶A的产生，丙二酰辅酶A是肉碱棕榈酰转移酶的抑制剂。其他对大鼠的研究将利用DNA酶超敏反应和体内足迹分析来确定UCP-2、UCP-3和乙酰辅酶A氧化酶基因中作为omega3脂肪酸调节目标的DNA区域。总之，拟议的研究将确定omega3脂肪酸控制脂肪代谢关键酶基因表达的分子和细胞机制，以及这些影响对全身能量消耗的影响程度，从而影响脂肪沉积和体重增加的速度。

Dietary omega3 fatty acids have been associated with higher rates of energy expenditure, lower rates of weight gain and/or lower rates of fat deposition in rodents as well as human infants and adults. These fatty acids also have been shown to inhibit transcription of genes encoding rate-limiting enzymes of lipogenesis and to enhance transcription genes encoding rate- limiting enzymes for mitochondrial and peroxisomal oxidation as well as the skeletal muscle content of the putative thermogenic uncoupling protein (UCP)-2. Studies are proposed to determine if the metabolic and genomic events occur in a concerted way in vivo to increase energy expenditure and, hence, decrease rates of fat deposition and weight gain as well as to explore specific cellular and nuclear mechanisms by which the effects of omega3 fatty acids are mediated. Clinical studies, to be conducted in 3-6-month-old infants scheduled for surgical repair of inguinal hernia, will address the hypothesis that omega3 fatty acids regulate gene expression so as to decrease a rate-limiting enzyme of triglyceride synthesis (i.e., glycerol-3-phosphate acyltransferase), increase the rate-limiting enzymes of mitochondrial (i.e., carnitine palmitoyl transferase) and peroxisomal fatty acid oxidation (i.e.,acyl-CoA oxidase) and increase abundance of UCP-2 and/or-3 resulting in greater energy expenditure secondary to the inefficiency of enhanced peroxisomal and/or uncoupled mitochondrial oxidation. Infants will be assigned randomly and blindly to formulas that differ only in alpha-linolenic acid (either 1 percent or 4 percent of total fatty acids) and muscle will be obtained approximately two weeks later, during the scheduled operation, for assay of the mRNA abundance of the cited transcripts. Energy expenditure will be determined at the same time by indirect calorimetry and correlated with mRNA abundances. Studies to be conducted in rats will examine the hypothesis that omega3 fatty acids decrease production of malonyl-CoA, an inhibitor of carnitine palmitoyl transferase, by decreasing expression of and/or inactivating the rate-limiting enzyme for its synthesis, i.e., acetyl-CoA carboxylase. Other studies in rats will utilize DNAse hypersensitivity and in vivo footprinting assays to identify DNA regions in the UCP-2, UCP-3 and acetyl-CoA oxidase genes that are targets for omega3 fatty acid regulation. In toto, the proposed studies will identify molecular and cellular mechanisms by which omega3 fatty acids govern the expression of genes encoding key enzymes of lipid metabolism and the extent to which these effects impact whole body energy expenditure and, hence, rates of fat deposition and weight gain.