Genetic Definition of Mechanisms by which Rapamycin Retards Mammalian Aging

描述（由申请人提供）：雷帕霉素治疗是第一个可靠地使哺乳动物寿命延长10%或更多的药物干预。令人兴奋的是，这种治疗在20个月大的异种小鼠中是有效的，大致类似于人类60岁时的治疗。当前项目的3个独立目标是确定调节雷帕霉素治疗对健康益处的基因，以及控制正常小鼠衰老的关键基因。这个项目是由一种革命性的新小鼠模型，多样性异种杂交（DO），由加里·丘吉尔（共同研究员）开发的。与其他模型相比，DO的遗传多样性高出4倍以上，因为它来自8个高度多样化的近交系，其中包括3个野生来源的M. musculus亚种。由于DO是一种高级杂交，它具有高密度的重组，使得候选基因鉴定比标准的F2或N2杂交精确10倍。我们将在20个月大的DO小鼠中开始治疗，因为老年个体对治疗的反应可能与年轻个体不同，并且为了模拟通常要到60岁左右才开始治疗的人类。将在每只小鼠中测试足够的标记等位基因，以绘制与生理衰老（免疫、肾脏、心脏和代谢）和寿命相关的位点。密集的定位将确定候选基因。目的1验证雷帕霉素通过mTOR通路有益于哺乳动物健康寿命的假设。这一假说预测，雷帕霉素喂养的DO小鼠的衰老将受到mTOR通路基因等位基因的影响。如果这个假设得到证实，我们将确定基因。如果这一假设被拒绝，我们将确定含有基因的替代位点，如药物代谢基因，控制雷帕霉素的益处。目的2检验mTOR通路控制正常衰老的假设。这一假设预测，在雷帕霉素治疗的DO小鼠中，调节衰老的基因（Aim 1）也可以调节同窝对照小鼠的衰老。如果这一假设得到证实，我们将在mTOR通路中发现具有自然变异的基因，这些基因为临床治疗提供了潜在的靶点，并且副作用最小。如果这一假设被拒绝，我们将确定含有调节衰老基因的替代基因座，这将提出新的机制和新的潜在临床治疗方法。如果在Aim 1中，我们没有发现与雷帕霉素益处相关的基因，我们将结合Aim 1和Aim 2的数据来确认和扩展调节正常衰老速率的关键基因的检测。目的3验证了免疫、肾脏、心脏和代谢衰老以及健康寿命受相同基因座调控的假设。如果这一假设得到证实，我们将确定在不同系统中对衰老具有多效性影响的基因。如果这一假设被否定，我们将在每个个体系统中找出调节衰老的基因；炎症标记物遗传调控的这种特异性可以提供将雷帕霉素治疗的益处与其免疫抑制作用分离的手段。无论这一假设是否得到证实，基因鉴定都将为临床治疗提供建议。)

DESCRIPTION (provided by applicant): Rapamycin treatment is the first drug intervention to reliably increase mammalian lifespan by 10% or more. Excitingly, this treatment was effective in heterogeneous mice when initiated at 20 months of age, roughly analogous to human beings at 60 years of age. The 3 independent aims of the current project identify genes regulating health benefits of rapamycin treatment, as well as key genes controlling normal mouse aging. This project is made possible by a revolutionary new mouse model, the diversity outcross (DO), developed by Gary Churchill (Co-Investigator). Compared to other models, the genetic diversity of the DO is more than 4 fold greater, as it was derived from 8 highly diverse inbred strains, including 3 wild-derived M. musculus subspecies. Because the DO is an advanced intercross, it has a high density of recombinations that makes candidate gene identification >10 fold more precise than with a standard F2 or N2 cross. We will initiate treatment in 20-month-old DO mice, because old individuals may respond to treatments differently than young, and to model humans who often would not start treatment until about 60 years of age. Sufficient marker alleles will be tested in each individual mouse to map loci associated with physiological aging (immune, renal, cardiac and metabolic) and lifespan. Dense mapping will identify candidate genes. Aim 1 tests the hypothesis that rapamycin benefits mammalian healthspan (healthy lifespan) via the mTOR pathway. This hypothesis predicts that aging in rapamycin-fed DO mice will be influenced by alleles of mTOR pathway genes. If this hypothesis is verified, we will identify the genes. If this hypothesis is rejected, we will identify alternative loci containing genes, such as drug metabolism genes, that govern rapamycin benefits. Aim 2 tests the hypothesis that the mTOR pathway governs normal aging. This hypothesis predicts that the same genes regulating aging in rapamycin-treated DO mice (Aim 1) also regulate aging in littermate controls. If this hypothesis is verified, we will identify genes with natural variants in the mTOR pathway that provide potential targets for clinical treatments with minimal adverse side effects. If this hypothesis is rejected, we will identify alternative loci containing genes that regulate aging, which would suggest novel mechanisms and novel potential clinical treatments. If, in Aim 1, we do not find genes related to benefits of rapamycin, we will combine Aim 1 and Aim 2 data to confirm and extend detection of key genes regulating normal aging rates. Aim 3 tests the hypothesis that immune, renal, cardiac and metabolic aging, as well as healthspan, are regulated by the same loci. If this hypothesis is verified, we will identify genes that have pleiotropic effects on aging in diverse systems. If this hypothesis is rejected, we will identify genes that regulate aging in each individual system; such specificity in genetic regulation of markers of inflammation could provide the means to decouple benefits of rapamycin treatment from its immune suppressive effects. Whether or not the hypothesis is verified, gene identification will suggest clinical treatments. ) PUBLIC HEALTH RELEVANCE: In the US, two of the most critical medical issues we face are the emotional and financial costs related to ill health in the elderly, which is increasing as the "baby boomer" population ages. In addition to the humanitarian benefits of postponing disease, increases in healthy lifespan will have enormous financial benefits for the US. Dietary rapamycin in mice, started at 20 months of age, increased their healthy lifespan by 15% - equivalent to increasing life expectancy of 60- year-old humans by 10 years. The current study will identify genes whose alleles regulate effects of rapamycin and healthy aging in general. This information will target pathways for interventions to retard aging and extend healthy lifespan in human beings.