Mechanisms of Physiological Organ Shrinkage

项目总结 许多成人器官--例如肠道、乳腺、骨骼肌、皮肤--对减少的 通过缩小其物理尺寸来提高功能需求水平。在这些器官中，细胞死亡的速度比 制造，导致细胞总数减少。肠道是一种广泛保守的需求样本- 被驱动的器官萎缩。在野生动物中，周期性的饥饿会导致肠道缩小60%-75%。 人类也会经历健康的肠道收缩，但过度或失调的细胞丢失可能很快就会变成 病理性的，可见于肠道疾病，如乳糜泻、内毒素血症和贾第鞭毛虫病。然而-不同于 在日常周转过程中平衡细胞分裂/损失的机制--调整细胞的机制 生理性收缩的不平衡几乎是未知的。 阻碍肠道收缩的机械性研究的障碍是缺乏一种易于处理的 实验室模型，该模型必须允许跨时间监控细胞(及其动态行为)，并且必须 拥有细胞特异性标记物和其他工具，以促进机制研究。从历史上看，研究使用了 啮齿动物，但现代研究方案不能复制自然饥荒/盛宴周期。 我的实验室已经开发出一种新的无脊椎动物肠道收缩模型，它既易于处理，又 基因可操控：果蝇的成体中肠，类似于脊椎动物的小肠。我们展示了 这种肠道收缩在果蝇中是保守的，我们证明其潜在的基础是巨大的 通过主动挤压将现在多余的肠细胞挤出。 在这里，我们从净细胞平衡方程式的两个方面来研究肠道收缩：成熟 细胞丧失(目标1)和干细胞能力(目标2)。我们的研究利用了中肠最高级的细胞工具箱- 特定的遗传记者和我们自己的开创性创新，用于实时和纵向成像 活体动物体内功能正常的中肠。在目标1中，我们询问肠道如何感知摄入的食物的损失- 机械压迫，缺乏营养，或两者兼而有之。我们测试了两个已知的挤压调节器， 转录共激活因子YAP/York kie和细胞间钙波在收缩过程中的作用 拉伸。第三，我们探索收缩的肠道是否在器官层面或水平上调节细胞排泄。 单个细胞的数量。在目标2中，我们寻找导致干细胞库75%被淘汰的机制 收缩--即使干细胞有丝分裂矛盾地增加。我们将测试干细胞是否会启动非自我 更新分裂，直接采用末端命运，和/或激活细胞凋亡。 苍蝇肠道的消化生理、干细胞谱系和分子调控与人类相似。 因此，通过阐明在组织生物学这一前沿领域运作的细胞到器官的比例机制，这 该项目可能会为治疗人类疾病的细胞失衡提供线索。

PROJECT SUMMARY Many adult organs--for instance, intestine, mammary gland, skeletal muscle, skin—respond to reduced levels of functional demand by shrinking their physical size. In these organs, cells are lost faster than they are made, leading to a reduction in total cell number. The intestine is a broadly conserved exemplar of demand- driven organ shrinkage. In wild animals, cyclic periods of starvation cause intestinal size to shrink by 60-75%. Humans also undergo healthy intestinal shrinkage, but excessive or dysregulated cell loss can quickly become pathological, as seen in enteropathies like celiac sprue, endotoxemia, and giardiasis. Yet—unlike the mechanisms that balance cell division/loss during everyday turnover—the mechanisms that tune cell imbalance for physiological shrinkage are virtually unknown. The roadblock to mechanistic investigation of intestinal shrinkage has been the lack of a tractable laboratory model, which must allow cells (and their dynamic behaviors) to be monitored across time and must possess cell-specific markers and other tools to facilitate mechanistic studies. Historically, studies used rodents, but modern research protocols cannot replicate natural famine/feast cycles. My lab has developed a new invertebrate model of intestinal shrinkage that is both tractable and genetically manipulable: the Drosophila adult midgut, akin to the vertebrate small intestine. We demonstrate that intestinal shrinkage is conserved in Drosophila, and we document that its underlying basis is the massive squeezing-out of now-superfluous enterocytes through active extrusion. Here, we investigate intestinal shrinkage from both sides of the equation for net cellular balance: mature cell loss (Aim 1) and stem cell capacity (Aim 2). Our studies leverage the midgut’s superlative toolkit of cell- specific genetic reporters and our own pioneering innovations for real-time and longitudinal imaging of functioning midguts inside live animals. In Aim 1, we ask how the gut senses loss of ingested food— mechanical compression, lack of nutrients, or both. We test if two known regulators of extrusion, the transcriptional co-activator YAP/Yorkie and intercellular Ca2+ waves, function during shrinking to increase extrusions. Third, we probe whether a shrinking gut regulates cell extrusions at the organ scale or at the level of individual cells. In Aim 2, we seek the mechanisms that cause a 75% culling of the stem cell pool during shrinkage—even as stem cell mitoses paradoxically increase. We will test if stem cells initiate non-self- renewing divisions, adopt terminal fates directly, and/or activate apoptosis. The fly gut’s digestive physiology, stem cell lineages, and molecular regulation are similar to humans. Hence by elucidating the cell-to-organ scale mechanisms that operate at this frontier of tissue biology, this project may yield leads for therapies to treat cellular imbalances in human disease.