Mechanisms for Fetal Hepatic Programming during Intrauterine Growth Restriction

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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.