Mechanisms of Physiological Organ Shrinkage

项目摘要 许多成人器官--例如，肠、乳腺、骨骼肌、皮肤--对减少的 通过缩小其物理尺寸来满足功能需求。在这些器官中，细胞的流失速度比它们 导致细胞总数减少。肠道是一个广泛保存的需求范例- 导致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损失会很快成为 病理性的，如在肠病如乳糜泻、内毒素血症和贾第虫病中所见。然而， 在日常周转中平衡细胞分裂/损失的机制-调节细胞分裂/损失的机制 生理收缩不平衡实际上是未知的。 肠道萎缩机制研究的障碍是缺乏一种易于处理的 实验室模型，它必须允许细胞（及其动态行为）跨时间进行监测，必须 拥有细胞特异性标记和其他工具，以促进机制研究。历史上，研究使用 啮齿动物，但现代研究方案无法复制自然饥荒/盛宴周期。 我的实验室开发了一种新的无脊椎动物肠道收缩模型， 基因可操纵的：果蝇成虫的中肠，类似于脊椎动物的小肠。我们证明 肠道收缩在果蝇中是保守的，我们记录了它的潜在基础是大量的 通过主动挤压挤出现在多余的肠细胞。 在这里，我们从净细胞平衡方程的两侧研究肠道收缩： 细胞损失（目标1）和干细胞能力（目标2）。我们的研究利用了中肠最好的细胞工具包- 特定的基因报告和我们自己的开创性创新，用于实时和纵向成像， 在活体动物体内发挥功能的中肠在目标1中，我们问肠道如何感知摄入食物的损失- 机械压迫、缺乏营养或两者兼而有之。我们测试，如果两个已知的监管机构的挤压， 转录辅激活因子雅普/Yorkie和细胞间Ca 2+波，在收缩到增加期间起作用 挤出。第三，我们探索收缩的肠道是否在器官尺度或水平上调节细胞挤出。 单个细胞。在目标2中，我们寻求在体外培养过程中导致75%的干细胞库被淘汰的机制。 萎缩--甚至干细胞有丝分裂矛盾地增加。我们将测试干细胞是否启动非自我- 更新分裂，直接采用末端命运，和/或激活凋亡。 苍蝇肠道的消化生理学、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前沿运作的细胞到器官规模的机制， 该项目可能为治疗人类疾病中细胞失衡的疗法提供线索。

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.