Impact of fasting on intestinal stem cells and cancer

项目总结 在包括哺乳动物在内的不同物种中，禁食方案可以延长寿命、改善健康或两者兼而有之。禁食 在抑制肿瘤生长方面也有一个新的作用，但人们对它如何影响肿瘤的启动或 如何利用禁食施加的新陈代谢来治疗已建立的肿瘤。考虑到那个成年人 干细胞协调组织适应和驱动肿瘤发生，了解调节机制(S) 它们对禁食的反应对于促进损伤或衰老后的组织修复具有重要意义 细胞功能下降，并可能为癌症提供新的治疗途径。在小鼠的肠道中， LGR5肠道干细胞(ISCs)驱动肠道衬里的快速更新，我们发现禁食 通过诱导过氧化体增殖物激活受体增量(PPARd)驱动的脂肪酸增强ISC功能 氧化(FAO)计划，将游离脂肪酸分解为乙酰辅酶A单位。这项工作提出了关键 禁食如何通过粮农组织途径发挥作用以调节肠干的问题。我们假设 粮农组织的酮体和生物合成产物β-羟基丁酸酯(βOHB)产生乙酰基- CoA，作为信号代谢产物和能量底物，介导ISC禁食 回应。为了支持这一观点，我们最近发现LGR5 ISCs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)，与非干细胞群体相比，禁食显著升高 ISCs中HMGCS2和βoHb水平。小肠HMGCS2缺失降低LGR5ISCs中βOHb水平 并使它们的分化偏向于分泌细胞的命运，我们表明这可以被外源激素拯救 β、OHB和I类组蛋白脱乙酰酶(HDAC)抑制剂治疗。从机制上讲，βohb充当一个 信号代谢产物通过抑制HDAC介导的转录增强ISCs中的Noch程序 压抑。因此，对ISCs中βOHB水平的动态控制可以使ISC快速适应 肠道到不同的生理状态，如禁食。构成我们目标基础的许多重要问题 仍然认为酮小体是ISCs中空腹反应的效应者，例如理解 βOHB的体内信号转导(Aim 1)和能量转导(Aim 2)在这一过程中起着重要作用。另一个关键问题是 解读粮农组织在ISCs中的禁食诱导计划如何影响肿瘤的启动和进展(目标3)。 好了！

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). !