Tropic Roles for Leptin in the Maturation of Somatotropes

项目总结/摘要 代谢健康严重依赖于脂肪因子瘦素的趋化作用， 下丘脑在围产期发育期间接收正常的代谢信号。垂体前叶 生长激素依赖于瘦素的正常代谢功能，然而， 这种瘦素依赖性和潜在机制代表了我们对瘦素更广泛作用的认识中的一个空白。 本申请的总体目标是确定新生儿瘦素激增对 生长激素成熟我们的第一个假设是正常的生长激素成熟依赖于 以及早期瘦素信号的缺乏改变了成人的生长激素 功能协调发展的我们的第二个假说认为瘦素通过效应子调节生长激素 涉及POU 1F 1/PIT 1转录因子、mRNA翻译控制的途径 蛋白质、Musashi（MSI）和调节性microRNAs（miRNAs）。两个目标将检验这些假设： 目的1研究将确定瘦素信号的丢失如何影响新生儿的成熟， 生长激素及其代谢功能在成人。我们将研究 在动物模型中，瘦素信号是：1）在生长激素后缺失， Lepr外显子1的选择性消融; 2）在瘦素激增期间被瘦素拮抗剂阻断或3）被 产妇营养不良。我们将在营养不良的动物中替换新生的瘦素来验证这一假设 早期瘦素信号对新生儿生长激素的成熟及其在发育过程中的正常功能至关重要。 成年人了目的2研究瘦素对生长激素的调节机制。 这些研究将使用纯化的生长激素细胞群来确定瘦素的作用是否是由 减弱MSI介导的Pou 1f 1、Tsh和Prl mRNA抑制的信号通路。我们还将研究 miRNA介导的Gh和Ghrhr mRNA的抑制，并将采用无偏倚的方法来鉴定 控制生长激素成熟的其他新的瘦素依赖性机制。这种贡献 意义重大，因为它解决了瘦素在预防肥胖中的重要性的全球性问题。 产妇营养不良引起的代谢功能障碍，占全球疾病总数的11% 最终导致35%的儿童死亡。这项研究在概念上是创新的，因为它 扩大了我们对瘦素作用的理解，包括已知的垂体前叶细胞， 重要的代谢传感器，并介绍了新的调节途径瘦素和利用方法 生长激素纯化的进展。预期的工作成果是：（1）调查结果 将充分告知该领域瘦素的营养作用，在生长激素成熟和功能和（2）这项工作 将提供有关瘦素作用机制的信息，这些机制可能是治疗上的靶点， 早期瘦素缺乏导致的严重代谢功能障碍。

PROJECT SUMMARY/ABSTRACT Metabolic health is critically dependent on tropic actions by the adipokine leptin, which programs the hypothalamus during perinatal development to receive normal metabolic signals. Anterior pituitary somatotropes are dependent on leptin for normal metabolic functions, however, the developmental timing of this leptin dependency and underlying mechanisms represent a gap in our knowledge of leptin's broader roles. The overall objective of this application is to ascertain the importance of the neonatal surge of leptin to somatotrope maturation. Our first hypothesis states that normal somatotrope maturation is dependent on perinatal leptin signals and that lack of early leptin signals alters adult somatotrope functions. Our second hypothesis states that leptin regulates somatotropes through effector pathways involving the POU1F1/PIT1 transcription factor, the mRNA translational control protein, Musashi (MSI) and regulatory microRNAs (miRNAs). Two aims will test these hypotheses: Aim 1 studies will determine how the loss of leptin signals impacts neonatal maturation of somatotropes and their metabolic functions in the adult. We will study the neonatal development of somatotropes in animal models in which leptin signals are either: 1) deleted following the somatotrope- selective ablation of Lepr exon 1; 2) blocked by a leptin antagonist during the leptin surge or 3) attenuated by maternal undernutrition. We will replace neonatal leptin in the undernourished animals to test the hypothesis that early leptin signaling is vital for neonatal maturation of somatotropes and their normal function in the adult. Aim 2 studies will identify mechanisms underlying the leptin regulation of somatotropes. These studies will use purified populations of somatotropes to determine if leptin's actions are mediated by signaling pathways that attenuate MSI-mediated repression of Pou1f1, Tsh, and Prl mRNAs. We will also study miRNA-mediated repression of Gh and Ghrhr mRNAs and will employ unbiased approaches to identify additional novel leptin-dependent mechanisms controlling somatotrope maturation. This contribution is significant because it addresses the global problem of the importance of leptin in the prevention of the metabolic dysfunction caused by maternal undernutrition, which contributes to 11% of the total global disease burden, ultimately leading to 35% of child deaths. The proposed research is conceptually innovative because it broadens our understanding of leptin actions to include cells in the anterior pituitary that are known to be important metabolic sensors, and introduces novel regulatory pathways for leptin and utilizes methodological advancements in the purification of somatotropes. The expected outcomes of the work are that (1) the findings will fully inform the field about leptin's tropic role in somatotrope maturation and function and (2) this work will provide information about mechanisms of leptin's action that may be targeted therapeutically to prevent the severe metabolic dysfunction caused by early leptin deficiency.