Mechanisms for Fetal Hepatic Programming during Intrauterine Growth Restriction

描述(由申请人提供)：越来越多的人类和动物实验证据支持宫内生长受限(IUGR)会导致晚年代谢性疾病的易感性的概念。根据这一概念，胎儿会适应永久性改变组织和器官功能的刺激或侮辱，从而增加对肥胖和糖尿病等成人代谢性疾病的易感性。在许多IUGR动物模型中，关键的糖异生基因如PEPCK的表达是在胎儿发育过程中诱导的。随着肝脏葡萄糖产量(HGP)的增加，PEPCK基因表达增加似乎持续到成年，是糖尿病和胰岛素抵抗的标志。胎儿这种疾病起源的分子机制在很大程度上是未知的。这一建议的长期目标是在分子水平上了解肝脏胰岛素抵抗和未能调节HGP的胎儿起源。我们打算通过在体内和体外对我们的羊IUGR模型进行研究来实现这一目标。我们发表的数据表明，在IUGR胎儿出生前，HGP和PEPCK基因的表达显著上调。我们的初步数据还表明，SIRT1脱乙酰酶及其糖异生靶标PGC1-α在IUGR胎儿肝脏中上调。这些因素提示了一个潜在的新的分子机制，可能是在IUGR过程中慢性诱导PEPCK和HGP的原因。我们将使用体内示踪方法结合胰岛素信号转导试验来研究SIRT1和PGC1-α上调在IUGR胎儿胰岛素和葡萄糖抑制HGP能力下降中起重要调节作用的假说。我们还将使用从IUGR胎儿制备的分离的肝细胞来确定在核水平上对肝脏葡萄糖产生和PEPCK启动子的激素控制。最后，我们将研究PEPCK基因和周围染色质的表观遗传修饰是否解释了IUGR期间基因表达的变化。在我们已建立的IUGR模型中，利用体内和体外技术的结合，我们将更好地了解，特别是在分子水平上，早期调控途径、关键转录因子和表观遗传机制涉及到胎儿晚年胰岛素抵抗和HGP的编程。这些研究的结果将产生重要的、新的概念，关于导致成人代谢性疾病，特别是糖尿病易感性增加的潜在胎儿机制。这项研究还将被用来帮助制定策略，以防止经历过IUGR的人发展为糖尿病和代谢性疾病。

DESCRIPTION (provided by applicant): Increasing human and animal experimental evidence supports the concept that intrauterine growth restriction (IUGR) results in susceptibility to metabolic disease in later life. According to this concept, the fetus adapts to a stimulus or insult that permanently alters tissue and organ function, leading to increased susceptibility to adult metabolic diseases such as obesity and diabetes. In numerous animal models of IUGR the expression of key gluconeogenic genes, such as PEPCK, are induced during fetal development. The increase in PEPCK gene expression along with increased hepatic glucose production (HGP) appears to persist into adulthood and is a hallmark of diabetes and insulin resistance. The molecular mechanisms underlying the origin of this disorder in the fetus are largely unknown. The long-term goal of this proposal is to understand the fetal origins of hepatic insulin resistance and failure to regulate HGP at the molecular level. We intend to achieve this goal with in vivo and in vitro investigations in our sheep model of IUGR. Our published data demonstrate that HGP and PEPCK gene expression are strikingly up-regulated before birth in the IUGR fetus. Our preliminary data also show that the SIRT1 deacetylase and its gluconeogenic target PGC1-alpha are up-regulated in the IUGR fetal liver. These factors suggest a potential novel molecular mechanism that may be responsible for chronic induction of PEPCK and HGP during IUGR. We will investigate the hypothesis that up-regulation of SIRT1 and PGC1-alpha plays an important regulatory role in the reduced ability for insulin and glucose to suppress HGP in the IUGR fetus using in vivo tracer methodology combined with assays of insulin signal transduction. We also will use isolated hepatocytes prepared from the IUGR fetus to determine the hormonal control of hepatic glucose production and the PEPCK promoter at the nuclear level. Lastly, we will investigate whether epigenetic modification of the PEPCK gene and surrounding chromatin explain the changes in gene expression during IUGR. Using this combination of in vivo and in vitro techniques in our well established model of IUGR, we will better understand, particularly at the molecular level, the early regulatory pathways, key transcription factors, and epigenetic mechanisms involved in fetal programming of later life insulin resistance and HGP. The results of these investigations will generate important, novel concepts regarding the underlying fetal mechanisms responsible for increased susceptibility to adult metabolic disease, particularly diabetes. This research also will be used to help develop strategies to prevent the development of diabetes and metabolic disease in individuals that experienced IUGR.