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子宫内生长限制（IUGR）导致晚年易患代谢性疾病的概念。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，从而增加对成人代谢性疾病（如肥胖和糖尿病）的易感性。在许多IUGR动物模型中，关键的糖异生基因，如PEPCK，在胎儿发育期间被诱导表达。PEPCK基因表达的增加伴随着肝糖生成（HGP）的增加似乎持续到成年，是糖尿病和胰岛素抵抗的标志。这种胎儿疾病的分子机制在很大程度上是未知的。该建议的长期目标是了解肝脏胰岛素抵抗的胎儿起源和在分子水平上调节HGP的失败。我们打算在我们的IUGR羊模型中进行体内和体外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基因表达显著上调。我们的初步数据还表明，SIRT1去乙酰化酶及其糖异生靶点pgc1 - α在IUGR胎儿肝脏中上调。这些因素提示了一种潜在的新的分子机制，可能是IUGR期间慢性诱导PEPCK和HGP的原因。我们将利用体内示踪法结合胰岛素信号转导实验，探讨SIRT1和pgc1 - α上调在IUGR胎儿胰岛素和葡萄糖抑制HGP能力降低中发挥重要调节作用的假设。我们还将使用从IUGR胎儿制备的分离肝细胞来确定激素对肝葡萄糖产生和PEPCK启动子在核水平的控制。最后，我们将研究是否表观遗传修饰PEPCK基因和周围染色质解释了IUGR期间基因表达的变化。在我们已经建立的IUGR模型中，使用这种体内和体外技术的结合，我们将更好地理解，特别是在分子水平上，早期调控途径，关键转录因子，以及后期胰岛素抵抗和HGP的胎儿编程的表观遗传机制。这些调查的结果将产生重要的，关于胎儿对成人代谢性疾病，特别是糖尿病易感性增加的潜在机制的新概念。这项研究也将用于帮助制定策略，以防止糖尿病和代谢性疾病的发展在经历过IUGR的个体。

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.