To understand the molecular features underlying stem cell aging, we established intestinal epithelial organoids derived from both young and aged mice and investigated alterations in their senescence and epigenetic status. Senescence-related changes including accumulation of senescence-associated β-galactosidase and up-regulation of Cdkn1a (p21) by DNA demethylation were observed in intestinal epithelial organoids derived from aged mice. We also demonstrated that the important stem cell marker Lgr5 was epigenetically silenced by trimethylation of histone H3 lysine 27, inducing suppression of Wnt signaling and a decrease of cell proliferation in organoids from aged mice. We further treated intestinal epithelial organoids from aged mice with nicotinamide mononucleotide (NMN), a key NAD⁺ intermediate. As a result, the organoids showed a higher NAD⁺ level, increased cell proliferative ability, activation of Lgr5 and suppression of senescence-associated genes, indicating that treatment with NMN could ameliorate senescence-related changes in intestinal epithelia. These findings suggest that organoids derived from aged animals could be a powerful research tool for investigating the molecular mechanisms underlying stem cell aging and for development of some form of anti-aging intervention, thus contributing to prolongation of healthy life expectancy.

为了了解干细胞衰老的分子特征，我们建立了来源于年轻和年老小鼠的肠上皮类器官，并研究了它们的衰老和表观遗传状态的变化。在衰老小鼠的肠上皮类器官中观察到了与衰老相关的变化，包括衰老相关的β-半乳糖苷酶的积累和DNA去甲基化对Cdkn1a（p21）的上调作用。我们还证明了重要的干细胞标记物Lgr5通过组蛋白H3赖氨酸27的三甲基化在表观遗传上沉默，诱导Wnt信号的抑制和衰老小鼠类器官中细胞增殖的减少。我们用烟酰胺单核苷酸（NMN）（一种关键的NAD ⁺中间体）进一步治疗了年老小鼠的肠上皮类器官。结果，类器官显示出更高的NAD ⁺水平，增加的细胞增殖能力，Lgr5的激活和抑制衰老相关基因，表明NMN的治疗可以改善肠道上皮细胞衰老相关的变化。这些发现表明，源自老年动物的类器官可能是研究干细胞衰老的分子机制以及开发某种形式的抗衰老干预措施的有力工具，从而有助于延长健康的预期寿命。