Impact of fasting on intestinal stem cells and cancer

项目概要 禁食疗法可以延长包括哺乳动物在内的不同物种的寿命、改善健康或两者兼而有之。禁食 在抑制肿瘤生长方面也具有新兴作用，但人们对其如何影响肿瘤发生或发生知之甚少。 如何利用禁食代谢来治疗已形成的肿瘤。鉴于那个成年人 干细胞协调组织适应并驱动肿瘤发生，了解介导机制 他们对禁食的反应对于增强受伤或衰老后的组织修复具有重要意义 细胞功能下降，可能为癌症提供新的治疗方法。在小鼠肠道中， LGR5 肠道干细胞 (ISC) 驱动肠道内壁的快速更新，我们发现禁食 通过诱导过氧化物酶体增殖物激活受体 δ (PPARd) 驱动的脂肪酸增强 ISC 功能 氧化（FAO）程序，将游离脂肪酸分解成乙酰辅酶A单元。这项工作提出了批评 禁食如何通过FAO途径调节肠道干性的问题。我们假设 β-羟基丁酸（βOHB）是一种酮体，是FAO的生物合成产物，产生乙酰基- CoA，作为介导 ISC 禁食的信号代谢物和能量底物 回应。为了支持这一观点，我们最近发现 LGR5 ISC 强烈表达 产生 βOHB 的生酮途径，包括其限速酶 HMGCS2（3-羟基-3- 甲基戊二酰辅酶 A 合成酶 2)，与非干细胞群相比，禁食会显着升高 ISC 中的 HMGCS2 和 βOHB 水平。小肠中 HMGCS2 的缺失降低了 LGR5 ISC 中的 βOHB 水平 并使它们的分化偏向分泌细胞的命运，我们证明这可以通过外源性来挽救 βOHB 和 I 类组蛋白脱乙酰酶 (HDAC) 抑制剂治疗。从机制上讲，βOHB 充当 信号代谢物通过抑制 HDAC 介导的转录来增强 ISC 中的 NOTCH 程序 镇压。因此，动态控制 ISC 中的 βOHB 水平可以实现快速适应 肠道处于不同的生理状态，如禁食。构成我们目标基础的许多重要问题 仍然关于酮体作为 ISC 中禁食反应的效应器的作用，例如了解 βOHB 在此过程中的体内信号传导（目标 1）和能量（目标 2）作用。另一个关键问题是 破译 ISC 中禁食诱导的 FAO 计划如何影响肿瘤的发生和进展（目标 3）。 ！

PROJECT SUMMARY Fasting regimens can increase lifespan, improve health or both in diverse species including mammals. Fasting also has an emerging role in inhibiting tumor growth, yet little is known about how it impacts tumor initiation or how fasting-imposed metabolism can be therapeutically exploited to treat established tumors. Given that adult stem cells coordinate tissue adaptation and drive tumorigenesis, understanding the mechanism(s) that mediate their response to fasting has important implications for enhancing tissue repair after injury or aging where stem cell function declines, and may provide new therapeutic inroads for cancer. In the mouse intestine, where LGR5+ intestinal stem cells (ISCs) drive the rapid renewal of the intestinal lining, we showed that fasting augments ISC function by inducing a peroxisome proliferator-activated receptor delta (PPARd) driven fatty acid oxidation (FAO) program, which breaks down free fatty acids into acetyl-CoA units. This work raises the critical question of how fasting functions through the FAO pathway to regulate intestinal stemness. We hypothesize that beta-hydroxybutyrate (βOHB), a ketone body and biosynthetic product of FAO generated acetyl- CoA, functions as a signaling metabolite and energetic substrate that mediates the ISC fasting response. In support of this idea, we recently found that the LGR5+ ISCs strongly express enzymes of the ketogenic pathway that produce βOHB, including its rate-limiting enzyme HMGCS2 (3-hydroxy-3- methylglutaryl-CoA synthetase 2), compared to non-stem cell populations and that fasting strongly elevates HMGCS2 and βOHB levels in ISCs. HMGCS2 loss in the small intestine reduces βOHB levels in LGR5+ ISCs and skews their differentiation towards secretory cell fates, which we showed can be rescued by exogenous βOHB and class I histone deacetylases (HDACs) inhibitor treatment. Mechanistically, βOHB acts as a signaling metabolite to reinforce the NOTCH program in ISCs by inhibiting HDAC-mediated transcriptional repression. Dynamic control of βOHB levels in ISCs, therefore, could enable the rapid adaptation of the intestine to diverse physiological states like fasting. Many important questions that form the basis of our aims remain regarding the role ketone bodies as effectors of the fasting response in ISCs such as understanding the in vivo signaling (Aim 1) and energetic (Aim 2) roles of βOHB in this process. Another critical question is to decipher how the fasting-induced FAO program in ISCs influences tumor initiation and progression (Aim 3). !