Understanding the mechanisms that govern Bst-1 induction upon caloric restriction

描述（由申请人提供）：mTOR通路是一个主要的信号中枢，根据生物体的营养状态协调生长和代谢。它的失调与广泛的常见疾病状态有关，包括癌症、糖尿病和衰老。有趣的是，抑制mTOR信号的两种干预措施——雷帕霉素和热量限制（将热量摄入减少到任意水平的一小部分）——都与小鼠肿瘤生长减少和寿命延长密切相关。然而，对这些生理和病理生理现象的分子机制知之甚少。机体衰老被认为部分是由于干细胞区室功能的逐渐衰退。我们选择关注肠道，特别是了解热量限制（CR）和mTOR抑制对肠道干细胞（ISCs）及其生态位的影响。我们发现，在Paneth细胞中，CR通过抑制mTORC1和上调Bst1的非细胞自主机制，强烈增强了ISCs的自我更新能力。令人惊讶的是，Paneth细胞从CR状态过渡到营养丰富的状态至少维持了3天的CR表型，这表明CR状态本身不仅仅是急性信号事件的结果。该项目的目标是了解CR如何通过mTORC1抑制上调Bst1表达，Bst1表达是CR表型的必要和充分事件。我们考虑的一个假设是mTORC1抑制通过重塑表观基因组稳定地调节Bst1的表达。我们正在使用计算和实验相结合的方法来确定可能介导mTORC1和Bst1基因之间信号级联的候选基因。然后，我们将系统地测试每个候选基因的必要性和充分性，首先在试管类器官共培养中，然后在经过工程改造的小鼠中进行遗传操作，特别是在Paneth细胞群体中。对这一途径的更清晰理解可能会揭示模仿有益CR状态的新方法。为了确定长期CR调控基因表达的机制，我提出了以下具体目标：1：阐明在雷帕霉素抑制CR或mTORC1时调节Bst1 mRNA水平的分子机制。II：确定在specific Aim I中确定的调节因子在CR和雷帕霉素对ISC自我更新的体内效应中的作用。

DESCRIPTION (provided by applicant): The mTOR pathway is a major signaling hub that coordinates growth and metabolism in response to the nutritional state of the organism. Its dysregulation has been implicated in a broad spectrum of common disease states, including cancer, diabetes, and aging. Interestingly, two interventions that suppress mTOR signaling - rapamycin and caloric restriction (a reduction in caloric intake to a fraction of ad libitum levels - have both been robustly linked to diminished tumor growth and augmented lifespan in mice. Little is known, however, about the molecular mechanisms responsible for these physiological and pathophysiological phenomena. Organismal aging is thought to be due, in part, to the progressive functional decline in stem cell compartments. We have chosen to focus on the intestine, and, in particular, on understanding the effects of caloric restriction (CR) and mTOR inhibition on intestinal stem cells (ISCs) and their niche. We find that CR strongly augments the self-renewal capacity of ISCs through a non-cell autonomous mechanism requiring the inhibition of mTORC1 and the upregulation of Bst1 in Paneth cells. Surprisingly, Paneth cells transitioned from CR conditions to nutrient-rich conditions maintained the CR phenotypes for at least 3 days, suggesting that the CR state itself is not simply the consequence of an acute signaling event. The goal of this project is to understand how CR, via mTORC1 inhibition, upregulates Bst1 expression, a necessary and sufficient event for the CR phenotype. One hypothesis we are entertaining is that mTORC1 inhibition stably modulates Bst1 expression by remodeling the epigenome. We are using computational and experimental methods in tandem to identify candidate genes that may mediate the signaling cascade between mTORC1 and the Bst1 gene. We will then systematically test the necessity and sufficiency of each candidate gene, first in test tube-based organoid co-culture and then in mice engineered to afford genetic manipulations specifically in the Paneth cell population. A clearer understanding of this pathway may shed light on new ways of mimicking the beneficial CR state. To determine the mechanisms by which long-term CR regulates gene expression, I propose the following specific aims: I: Elucidate the molecular mechanisms that modulate Bst1 mRNA levels in response to CR or mTORC1 inhibition by rapamycin. II: Determine the role(s) of the regulatory factor(s) identified in Specifc Aim I on the in vivo effects of CR and rapamycin on ISC self-renewal.