The Role of MicroRNAs on Hepatic Growth and Senescence

加速的产后追赶性生长和过早衰老之间的关系是生物学上的重要发现之一。我们实验室和其他机构最近的研究表明，大鼠怀孕期间母体蛋白质限制（MPR，8%蛋白质）以及随后的快速追赶生长会导致肝脏过早衰老、葡萄糖耐受不良和寿命缩短。相反，如果没有追赶性生长（由于一生中维持8%的蛋白质饮食），长寿不会受到阻碍。虽然我们以前已经证明，翻译后组蛋白修饰可能在肝脏的长期胎儿编程中发挥作用，但对microRNA（miRs）在控制肝功能和衰老中的作用知之甚少。使用微阵列分析，我们最近发现miR-193 b，miR-29和miR-140在这些MPR后代的衰老肝脏中发生了改变，并具有追赶性生长。因此，我们研究计划的总体目标是了解肝脏中影响功能，生长和衰老的miRNA靶标的调节和身份。最近，我们证明了（i）在这些MPR后代中，miR-29表达与胰岛素生长因子1（Igf-1）负相关，（ii）这些MPR后代具有增强的肝内质网（ER）应激，（iii）ER应激增加体内神经元miR-29 a。因此，我们的第一个目标是直接评估ER应激对肝脏miR-29 a和其他miR的作用，在体外使用用和不用ER应激活化剂处理的新生大鼠肝细胞的原代培养物，然后测量miR-29，Igf-1表达和其他miR-29靶基因的时间变化。此外，我们还将抑制miR-29的表达，以观察是否可以防止Igf-1的沉默。鉴于细胞周期蛋白D1，细胞周期的一个重要组成部分，已被牵连在过早衰老，并在这些MPR后代的miR-193 b表达呈负相关，我们的第二个目标是表征，如果增加细胞周期蛋白D1与其他组件的细胞周期的损害。为了直接揭示miR-193 b对肝脏中细胞周期蛋白D1和衰老的作用，我们将评估miR-193 b的激活是否改变新生大鼠肝细胞原代培养物中细胞周期蛋白D1的表达、细胞周期和衰老。最后，考虑到miR-140靶向HDAC-4和SIRT 1，这两种组蛋白去乙酰化酶，我们的第三个目标是测试miR-140在体外的改变是否影响总组蛋白H3乙酰化沿着已知受组蛋白乙酰化和MPR影响的肝脏靶基因。总的来说，这些研究将进一步表明miR与肝功能受损、生长和衰老有关。 此外，通过使用这种MPR制度作为一个独特的和高度相关的模型过早衰老，我们可以进一步阐明如何更好地管理低出生体重的后代可以提高哺乳动物的寿命。

The relationship between accelerated postnatal catch-up growth and premature ageing is one of the important discoveries in biology. Recent studies by our laboratory and others has demonstrated that maternal protein restriction (MPR, 8% protein) during pregnancy in rats followed by rapid catch-up growth leads to premature hepatic senescence, glucose intolerance, and decreased longevity. In contrast, if there is no catch-up growth (due to maintenance of an 8% protein diet throughout life), longevity is not hindered. While we have previously demonstrated that posttranslational histone modifications may play a role in the long-term fetal programming of the liver, very little is known about the role of microRNAs (miRs) in governing hepatic function and senescence. Using Microarray analysis, we have recently identified that miR-193b, miR-29, and miR-140 are altered in the senescent livers of these MPR offspring with catch-up growth. Therefore, the overall goal of our research program is to understand the regulation and identity of miRNA targets in the liver which influence function, growth and senescence. Recently we demonstrated that (i) miR-29 expression is inversely related to insulin growth factor 1 (Igf-1) in these MPR offspring, (ii) these MPR offspring have augmented hepatic endoplasmic reticulum (ER) stress, and (iii) ER stress increases neuronal miR-29a in vivo. Therefore, our first objective is to directly assess the role of ER stress on hepatic miR-29a and other miRs in vitro using primary cultures of neonatal rat liver cells treated with and without activators of ER stress followed by measuring temporal changes in miR-29, Igf-1 expression and other miR-29 target genes. In addition, we would also inhibit miR-29 expression to observe if the silencing of Igf-1 could be prevented. Given Cyclin D1, an important component of the cell cycle, has been implicated in premature senescence and is inversely related to miR-193b expression in these MPR offspring, our second objective is to characterize if augmented Cyclin D1 is associated with impairment of other components the cell cycle. To directly implicate the role of miR-193b on Cyclin D1 and senescence in the liver, we will assess if activation of miR-193b alters Cyclin D1 expression, the cell cycle, and senescence in primary cultures of neonatal rat liver cells. Finally, given miR-140 targets HDAC-4 and SIRT1, both histone deacetylases, our third objective is to test if alterations in miR-140 in vitro influences total Histone H3 acetylation along with hepatic target genes known to be affected by histone acetylation and MPR. Collectively, these studies would further implicate miRs with impaired hepatic function, growth and aging. In addition, by using this MPR regime as a unique and highly relevant model of premature senescence, we can further elucidate how better management of low birth weight offspring can improve longevity in mammals.