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

描述（由申请人提供）：该提案的长期目标是描述生长激素缺乏对线粒体功能、应激抵抗力和健康寿命的有益影响的机制。我们的研究重点是理解这样一个假设：在长寿的动物中，硫醇代谢的上调可以更好地保护细胞免受压力。申请人的工作已证实生长激素 (GH) 和 IGF-I 在保证长寿方面发挥着重要作用。患有遗传性侏儒症 (Ames) 和缺乏功能性 GH 受体 (GHRKO) 的小鼠分别表现出 GH 缺乏或抵抗、延迟衰老和增强的抗应激能力。待检验的全球假设是，硫醇代谢在衰老中起着关键作用，并且 GH 调节该途径的关键成分，最终导致健康寿命（通过压力抵抗/保护）和寿命的变化。因此，减少 GH 信号传导赋予侏儒小鼠生物学优势，从而更好地清除有毒代谢副产物、改变线粒体功能并延长寿命。为了进一步解决和定义这一全球假设，本提案将测试两个工作假设，这两个假设都侧重于 GH、硫醇代谢和衰老之间的关系。首先，线粒体对分子损伤的敏感性是由涉及 GH 和硫醇代谢的机制控制的，包括蛋白质 S-硫醇化和谷胱甘肽 S-转移酶 (GST) 表达。因此，线粒体 GSH/GSSG 的增加会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具有更强的抵抗力，表明谷胱甘肽化具有保护作用，并且代表了细胞应激抵抗的关键机制。一些 GST（解毒的关键）受 GH 调节，表达水平可指示疾病易感性，但人们对 GH、GST 与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 水平和膳食蛋氨酸 (MET) 决定。 Ames 小鼠中 MET 代谢途径高度上调，导致 GSH 增加和 DNA 甲基化差异增加。在该项目中，申请人计划通过以下方式阐明GH、硫醇代谢和细胞保护之间的关系：1）将侏儒小鼠呼吸和抗氧化活性增强与线粒体GSH和这些蛋白质的谷胱甘肽化增加直接联系起来； 2) 提供直接证据证明 GH 的缺乏导致 GST 系统的底物特异性增强； 3) 确定改变饮食 MET 后与应激抵抗力和寿命相关的硫醇代谢变化； 4) 建立第一个长寿小鼠的表观基因组图谱。确定 GH 依赖性途径和机制可能会建议治疗干预措施，以增强人类的抗应激能力、延缓衰老、治疗与衰老相关的疾病并延长健康寿命。公共健康相关性：该提案旨在使用两种长寿小鼠品系（艾姆斯侏儒小鼠和生长激素受体基因敲除小鼠）确定生长激素对与应激抵抗和长寿相关的过程的影响。确定 GH 依赖性途径和机制可能会提出潜在的治疗干预措施，以延缓衰老、治疗衰老相关疾病并延长人类寿命。

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.