Systemic Factors that Maintain a Young Liver Phenotype

描述（由申请人提供）：本提案的长期目标是开发能够在衰老期间保持生活质量和独立性的治疗方法。热量限制（CR）在衰老过程中保持健康并延长寿命；然而，分子介质是未知的。在CR和禁食期间，激素ghrelin的产生增加，下丘脑中ghrelin受体（GHS-R1a）的表达上调8倍。对胃饥饿素调节途径的表征提出了衰老表型与内源性胃饥饿素信号通路受损有关的假设，并提出胃饥饿素是CR益处的中介。在CR过程中，动物必须通过改变外周组织的代谢来补偿减少的能量摄入。推测ghrelin对调节能量平衡的下丘脑弓状神经元（hypothalamic arcuate neuron， ARC）上表达的GHS-R1a的调节作用是中枢介导的。通过与ghrelin-/-和Ghsr-/-小鼠比较CR对野生型小鼠ARC神经肽Y （NPY）、针刺相关肽（AGRP）和前opiomelocortin （POMC）神经元的分子效应，可以识别ghrelin介导的信号。通过野生型和ghrelin-/-和Ghsr-/-小鼠的类似比较，可以定义cr诱导的衰老肝脏中ghrelin依赖性代谢变化。这一点很重要，因为肝脏是调节新陈代谢的关键，并受到大脑、胰腺、脂肪和肌肉输入的调节。除了定义ghrelin依赖的代谢作用外，还将比较CR野生型、ghrelin-/-和Ghsr-/-小鼠的寿命。据推测，CR不会延长突变小鼠的寿命。我们每天给野生型小鼠注射稳定的促生长素模拟物，以验证在衰老过程中干预恢复受损的促生长素信号将延长寿命并维持年轻肝脏表型的假设。总之，本研究将确定CR对特定基因、蛋白质和蛋白质修饰所产生的变化，这些基因、蛋白质和蛋白质修饰调节胰岛素敏感性、葡萄糖代谢、肝脏脂肪生成和脂肪积累（脂肪变性），这些都依赖于胃饥饿素。特异性目的1：验证在野生型小鼠中，而在ghrelin-/-和Ghsr-/-小鼠中，CR通过FoxO1介导的途径增加弓状核（ARC）神经元中Npy和Agrp的表达，抑制Pomc的表达，并阐明其分子机制。具体目标2：确定野生型、ghrelin-/-和Ghsr-/-小鼠对与肝脏代谢、葡萄糖耐量、胰岛素敏感性、脂肪变性和寿命有关的长期热量限制的反应差异，并确定分子机制；验证年轻表型可以在AD库中维持的假设。用稳定的促生长素处理野生型衰老小鼠。确定由胃饥饿素介导的CR对衰老的有益作用是至关重要的，因为迄今为止尚未找到临床利基的口服耐受性良好的长效胃饥饿素模拟物的可用性。公共卫生相关性：显著减少实验动物的食物摄入量可预防糖尿病，降低癌症发病率，延长寿命。这些好处与血液中一种叫做胃饥饿素的激素水平的增加有关。胃饥饿素水平随着年龄的增长而下降。我们的研究旨在测试用更稳定的形式替代这种激素是否会在衰老过程中提供健康和生活质量方面的好处。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to develop therapy that will maintain quality of life and independence during aging. Caloric restriction (CR) maintains health during aging and increases longevity; however, the molecular mediator(s) is unknown. During CR and fasting, production of the hormone ghrelin increases and the ghrelin receptor (GHS-R1a) expressed in the hypothalamus is upregulated 8-fold. Characterization of ghrelin regulated pathways led to the hypothesis that the aging phenotype is associated with impaired endogenous ghrelin signaling and that ghrelin is a mediator of the benefits of CR. During CR, the animal must compensate for reduced energy intake by modifying metabolism in peripheral tissues. It is speculated that accommodation is mediated centrally by the action of ghrelin on GHS-R1a expressed on hypothalamic arcuate neurons (ARC) that regulate energy balance. By comparing the molecular effects of CR on ARC neuropeptide Y (NPY), agouti-related peptide (AGRP) and pro-opiomelanocortin (POMC) neurons of wild type mice with ghrelin-/- and Ghsr-/- mice the ghrelin mediated signals can be identified. By similar comparisons in wildtype and ghrelin-/- and Ghsr-/- mice, CR-induced ghrelin dependent metabolic changes in the aging liver can be defined. This is important because the liver is pivotal for regulating metabolism and is modulated by input from the brain, pancreas, fat and muscle. In addition to defining ghrelin dependent metabolic effects, longevity of CR wildtype, ghrelin-/- and Ghsr-/- mice will be compared. It is speculated that CR will not extend the lifespan of the mutant mice. Ad lib fed wildtype mice will be treated daily with a stable ghrelin mimetic to test the hypothesis that intervening to rescue impaired ghrelin signaling during aging will increase longevity and maintain a young liver phenotype. In summary, this research will identify changes resulting from CR on selected genes, proteins and protein modifications that regulate insulin sensitivity, glucose metabolism, lipogenesis and fat accumulation in the liver (steatosis), that are ghrelin dependent. Specific Aim 1: Test the hypothesis that in wildtype, but not in ghrelin-/- and Ghsr-/- mice, that CR increases expression of Npy and Agrp and suppresses expression of Pomc in neurons of the arcuate nucleus (ARC) via FoxO1 mediated pathway and elucidate the molecular mechanisms. Specific Aim 2: Determine the differences in responses of wildtype, ghrelin-/- and Ghsr-/- mice to long-term caloric restriction that pertain to liver metabolism, glucose tolerance, insulin sensitivity, steatosis and longevity and define the molecular mechanisms; test the hypothesis that a young phenotype can be sustained in ad lib. fed wildtype mice during aging by treatment with a stable ghrelin mimetic. Identifying the beneficial effects of CR on aging that are mediated by ghrelin is fundamentally important because of the availability of orally active well tolerated long-acting ghrelin mimetics that have so far not found a clinical niche. Public Health Relevance: Markedly reducing food intake in experimental animals prevents diabetes, lowers the incidence of cancer and prolongs lifespan. These benefits are associated with increases in blood levels of a hormone called ghrelin. Ghrelin levels decline as a function of age. Our research is designed to test whether replacing this hormone with a more stable form will provide health and quality of life benefits during aging.