Elucidating the role of fasting in intestinal stemness and tissue regeneration

7.项目总结/摘要 禁食干预改善了小鼠和人类的健康状况。考虑到成体干细胞 组织适应，理解介导禁食反应的机制具有重要意义。 这对增强损伤后的组织修复和干细胞功能下降的衰老具有重要意义。在 在哺乳动物的肠道中，LGR 5+肠干细胞（ISC）驱动肠衬里的快速更新。我们 先前的研究表明，禁食通过诱导过氧化物酶体增殖物激活受体增强ISC功能， δ（PPARδ）驱动的脂肪酸氧化（FAO）程序。然而，在体内的作用，过氧化物酶体增殖物激活受体δ或下游 调节ISC禁食反应的FAO代谢效应物仍然未知。在本提案中，我们 将检验以下假设：1）PPARδ信号传导是体内ISC空腹反应所必需的，2）PPARδ- 激活的FAO通过产生酮体β-羟基丁酸酯刺激肠干性 3）肠道微生物组的变化在介导ISC中是必要的，充分的或两者兼而有之 空腹反应。为了支持这些观点，我们发现PPARδ激动剂治疗模拟了 在ISC上禁食。此外，我们发现，产生酮的生酮途径的酶 代谢产物βOHB，包括其限速步骤HMGCS 2（3-羟基-3-甲基戊二酰辅酶A合成酶2）， 对LGR 5 + ISC高度富集。此外，空腹时HMGCS 2表达和βOHB水平的升高与 ISC功能增强，而HMGCS 2的缺失抑制了ISC传播类器官和偏倚的能力 它们向分泌谱系的分化。重要的是，这些缺陷可以通过βOHB纠正 文化中的待遇。因此，这些观察结果提供了一种可能的途径，通过调节禁食 HMGCS 2介导的生酮作用，以增强ISCs的再生功能。最后，禁食方案是 已知会改变肠道微生物组的组成，但这些变化的程度是ISC禁食的基础。 答复需要澄清。关于过氧化物酶体增殖物激活受体δ在体内的特异性作用， HMGCS 2表达和ISC空腹反应的上游调节因子，HMGCS 2和βOHB的体内作用 作为肠道干性的介质以及禁食肠道微生物群在这些过程中的贡献。

7. Project Summary/Abstract Fasting interventions improve health in mice and in humans. Given that adult stem cells coordinate tissue adaptation, understanding the mechanism(s) that mediate the fasting response has important implications for enhancing tissue repair after injury and in aging where stem cell function declines. In the mammalian intestine, LGR5+ intestinal stem cells (ISCs) drive the rapid renewal of the intestinal lining. We previously showed that fasting augments ISC function by inducing a peroxisome proliferator-activated receptor delta (PPARδ) driven fatty acid oxidation (FAO) program. However, the in vivo role of PPARδ or downstream effector(s) of FAO metabolism that mediate the ISC fasting response remains unknown. In this proposal, we will test the hypotheses that 1) PPARδ signaling is necessary for the in vivo ISC fasting response, 2) PPARδ- activated FAO stimulates intestinal stemness through the production of the ketone body β-hydroxybutyrate (βOHB) in fasting, and 3) changes in the gut microbiome are necessary, sufficient or both in mediating the ISC fasting response. In support of these notions, we find that PPARδ agonist treatment emulates the effects of fasting on ISCs. Furthermore, we find that enzymes of the ketogenic pathway that produce the ketone metabolite βOHB, including its rate-limiting step HMGCS2 (3-hydroxy-3-methylglutaryl-CoA synthetase 2), highly enrich for LGR5+ ISCs. Also, elevation of HMGCS2 expression and βOHB levels upon fasting correlates with enhanced ISC function while loss of HMGCS2 dampens ISC capacity to propagate organoids and biases their differentiation towards the secretory lineage. Importantly, these deficits can be rectified by βOHB treatment in cultures. Thus, these observations provide a possible pathway for fasting through the modulation of HMGCS2-mediated ketogenesis to augment the regenerative function of ISCs. Lastly, fasting regimens are known to alter the gut microbiome composition but the extent to which these changes underlie the ISC fasting response requires elucidation. Remaining questions regarding the specific in vivo role of PPARδ as an upstream regulator of HMGCS2 expression and ISC fasting response, the in vivo role of HMGCS2 and βOHB as mediators of intestinal stemness and the contribution of the fasting gut microbiota in these processes.