Role of growth hormone in thiol metabolism, stress resistance and aging

描述（由申请人提供）：本提案的长期目标是描述生长激素缺乏对线粒体功能、抗应激能力和健康寿命的有益影响的机制。我们的研究一直集中在理解这一假设，即在长寿动物中，硫醇代谢的上调导致更大的保护免受细胞应激。申请人的工作已经确定，生长激素（GH）和IGF-I是长寿保证的主要参与者。遗传性侏儒症（艾姆斯）和缺乏功能性GH受体（GHRKO）的小鼠分别表现出GH缺乏或抵抗、延迟衰老和增强的应激抵抗力。有待检验的全球假设是，硫醇代谢在衰老中起着关键作用，GH调节该途径的关键组分，最终导致健康寿命（通过抗应激/保护）和寿命的变化。因此，减少GH信号传递赋予侏儒小鼠生物学优势，导致更好地清除有毒代谢副产物，改变线粒体功能和延长寿命。为了进一步解决和定义这一全球性假设，本提案中将检验两个工作假设，这两个假设都侧重于GH、巯基代谢和衰老之间的关系。第一个是线粒体对分子损伤的易感性由涉及GH和巯基代谢的机制控制，包括蛋白S-巯基化和谷胱甘肽S-转移酶（GST）表达。因此，线粒体GSH/GSSG增加导致呼吸链复合物的谷胱甘肽化增加。这种蛋白质修饰使这些蛋白质对ROS诱导的蛋白水解降解更具抗性，这表明谷胱甘肽化的保护作用，并代表了细胞应激抗性的关键机制。一些GST（解毒的关键）受GH调节，表达水平是疾病易感性的指标，但对GH，GST和衰老之间的关系知之甚少。第二个假设是硫醇代谢和DNA甲基化模式由循环GH水平和饮食蛋氨酸（MET）决定。MET代谢途径在艾姆斯小鼠中高度上调，导致GSH增加和差异DNA甲基化。在该项目中，申请人计划通过以下方式阐明GH、巯基代谢和细胞保护之间的关系：1）将侏儒小鼠中增强的呼吸和抗氧化活性与这些蛋白质的线粒体GSH和谷胱甘肽化增加直接联系起来; 2）提供GH缺乏导致GST系统底物特异性增强的直接证据; 3）定义改变饮食MET后与应激抗性和寿命相关的硫醇代谢的变化;以及4）建立长寿小鼠的第一个表观基因组谱。确定生长激素依赖性途径和机制可能会建议治疗干预，以提高抗应激能力，延缓衰老，治疗衰老相关疾病和延长人类的健康寿命。公共卫生相关性：该建议旨在确定生长激素对与应激抗性和寿命相关的过程的影响，使用两种长寿小鼠品系，艾姆斯侏儒和生长激素受体敲除小鼠。确定生长激素依赖的途径和机制可能表明潜在的治疗干预，以延缓衰老，治疗衰老相关的疾病和延长人类寿命。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to delineate mechanisms of the beneficial effects of growth hormone deficiency on mitochondrial function, stress resistance and health span. Our research has been focused on understanding the hypothesis that in long living animals, an upregulation of thiol metabolism leads to greater protection from cellular stress. The applicant's work has established that growth hormone (GH) and IGF-I are major players in longevity assurance. Mice with hereditary dwarfism (Ames) and those that lack a functional GH receptor (GHRKO) exhibit GH deficiency or resistance (respectively), delayed aging, and enhanced stress resistance. The global hypothesis to be tested is that thiol metabolism plays a key role in aging and that GH modulates key components of this pathway ultimately leading to changes in health span (via stress resistance/protection) and lifespan. Thus, reduced GH signaling confers a biologic advantage to dwarf mice leading to better scavenging of toxic metabolic byproducts, altered mitochondrial function and enhanced longevity. To further address and define this global hypothesis, two working hypotheses will be tested in this proposal, both of which focus on the relationship between GH, thiol metabolism and aging. The first is that the susceptibility of mitochondria to molecular insults is controlled by mechanisms that involve GH and thiol metabolism including protein S-thiolation and gluta- thione S-transferase (GST) expression. As such, increased mitochondrial GSH/GSSG leads to increased glutathionylation of respiratory chain complexes. This protein modification renders these proteins more resistant to ROS-induced proteolytic degradation suggesting a protective role of glutathionylation and represents a key mechanism of cellular stress resistance. Some of the GSTs (key for detoxification) are regulated by GH and expression levels are indicative of disease susceptibility but little is known about the relationship between GH, GST and aging. The second hypothesis is that thiol metabolism and DNA methylation patterns are determined by circulating GH levels and dietary methionine (MET). The MET metabolic pathway is highly upregulated in Ames mice resulting in increased GSH and differential DNA methylation. In this project, the applicant plans to elucidate the relationship between GH, thiol metabolism and cellular protection by: 1) directly linking the enhanced respiratory and antioxidative activities in dwarf mice to increased mitochondrial GSH and glutathionylation of these proteins; 2) providing direct evidence that the lack of GH is responsible for substrate-specific enhancement of the GST system; 3) defining the changes in thiol metabolism linked to stress resistance and longevity following altered dietary MET; and 4) establishing the first epigenomic profile of a long-living mouse. Determining GH-dependent pathways and mechanisms may suggest therapeutic interventions to enhance stress resistance, delay aging, treat aging-related disorders and extend health span in humans. PUBLIC HEALTH RELEVANCE: This proposal is designed to determine the influence of growth hormone on processes related to stress resistance and longevity using two long-living mouse strains, Ames dwarf and growth hormone receptor knockout mice. Determining GH-dependent pathways and mechanisms may suggest potential therapeutic interventions to delay aging treat aging-related disorders and extend life span in humans.