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。我们的研究一直专注于理解这一假设，即在长寿动物中，硫醇代谢上调会导致更好的保护，使其免受细胞压力的影响。申请人的工作已经确定生长激素(GH)和IGF-I是长寿保障的主要参与者。遗传性侏儒症小鼠(Ames)和那些缺乏功能性GH受体(GHRKO)的小鼠分别表现出GH缺乏或抵抗、衰老延迟和抗应激能力增强。有待检验的全球假说是，硫醇代谢在衰老中起关键作用，生长激素调节这一途径的关键成分，最终导致健康寿命(通过应激抵抗/保护)和寿命的变化。因此，生长激素信号的减少为矮小小鼠提供了生物学优势，导致更好地清除有毒代谢副产物，改变线粒体功能，并延长寿命。为了进一步解决和定义这一全球假说，这项提议将测试两个工作假说，这两个假说都集中在生长激素、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受生长激素和硫醇代谢的机制控制，包括蛋白S硫基化和谷胱甘肽S转移酶的表达。因此，线粒体GSH/GSSG的增加导致呼吸链复合体的谷胱甘肽基化增加。这种蛋白质修饰使这些蛋白质对ROS诱导的蛋白质降解更具抵抗力，这表明谷胱甘肽的保护作用，并代表了细胞耐受逆境的关键机制。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与衰老的关系知之甚少。第二个假设是，硫醇代谢和DNA甲基化模式是由循环GH水平和膳食蛋氨酸(MET)决定的。在Ames小鼠中，MET代谢途径高度上调，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生长激素、硫醇代谢和细胞保护之间的关系：1)将矮小鼠增强的呼吸和抗氧化活动与这些蛋白质的线粒体GSH和谷胱甘肽基化增加直接联系起来；2)提供直接证据，证明缺乏GH是底物特异性GST系统增强的原因；3)确定改变饮食后硫醇代谢的变化与抗应激和长寿有关；以及4)建立长寿小鼠的第一个表观基因组图谱。确定生长激素依赖的途径和机制可能会建议进行治疗干预，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，并延长人类的健康寿命。公共卫生相关性：这项建议旨在通过两个长寿小鼠品系Ames侏儒和生长激素受体基因敲除小鼠来确定生长激素对与应激抵抗和长寿相关的过程的影响。确定生长激素依赖的途径和机制可能会为延缓衰老、治疗衰老相关疾病和延长人类寿命提供潜在的治疗干预措施。

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.