The role of extrusion in controlling epithelial homeostasis

描述（由申请人提供）：挤出在控制上皮稳态中的作用项目概述/摘要上皮为它们包裹的器官提供保护屏障;然而构成该屏障的细胞通过细胞死亡（凋亡）和分裂不断更新。令人惊讶的是，关于是什么触发细胞自然分裂或死亡，或者在体内平衡期间死亡和分裂的细胞数量如何平衡，人们知之甚少。然而，维持这种平衡对于维持屏障功能和预防疾病至关重要：如果死亡率较高，可能会导致哮喘等屏障功能疾病，如果分裂率较高，则会导致实体瘤。通过我们对细胞死亡时如何维持屏障的研究， 我们相信我们已经发现了上皮细胞如何维持稳态细胞数量的一种新机制，我们将在本提案中对此进行进一步研究。我们先前发现，当上皮内的细胞死亡时，它会向邻近的细胞发出信号，形成收缩性肌动球蛋白rng将其挤出。为了做到这一点，垂死的细胞释放出脂质鞘氨醇1-磷酸（S1 P），通过向邻近细胞中的S1 P受体2（S1 P2）发出信号来激活挤出。最近，我们发现在成年结肠组织和发育中的斑马鱼表皮中，上皮细胞在细胞高度拥挤的部位死亡之前似乎会挤出。使用我们设计的一个腔室，活细胞也会在实验过度拥挤时挤出。虽然稳态和过度拥挤诱导的挤出都使用我们定义的凋亡细胞挤出相同的S1 P-S1 P2途径，但活细胞挤出途径由拉伸激活通道Piezo 1激活。重要的是，我们发现破坏牵张激活信号传导或S1 P-S1 P2途径会导致细胞培养物和发育中的斑马鱼中出现细胞团。因此，我们提出了一个模型，其中底层组织提供了对上皮细胞的空间限制，使得任何细胞分裂和/或迁移引起过度拥挤的应变，这诱导活细胞挤出。挤出的细胞由于缺乏生存信号而死亡，同时促进周围的生存和增殖。我们将通过以下方式在目的1和2中测试该假设：1）研究挤压是否促进细胞培养模型中的细胞死亡，和2）测试S1 P2斑马鱼突变体中的细胞团是否由于缺乏细胞因子而导致。 细胞挤出、增殖增加或两者兼有。为了定义什么激活挤出，我们将3）确定压电1拉伸激活通道和钙电流如何介导S1 P以触发挤出，以及4）鉴定对于确定哪些细胞响应于均匀上皮拥挤力而挤出至关重要的细胞-细胞或细胞-基质蛋白。拟议的研究是创新的，因为它研究了上皮细胞如何维持稳态细胞数量的新机制，并使用多学科方法，其中包括我们开发的用于研究上皮细胞的斑马鱼表皮模型和我们与生物工程师开发的细胞过度拥挤装置。该提议具有医学意义，因为上皮稳态的失调可能是大多数实体瘤形成和屏障功能疾病的核心。

DESCRIPTION (provided by applicant): The role of extrusion in controlling epithelial homeostasis Project Summary/Abstract Epithelia provide a protective barrier for the organs they encase; yet cells comprising this barrier are constantly renewed via cell death (apoptosis) and division. Surprisingly little is known about what triggers cells to naturally divide or die or how he number of cells dying and dividing are balanced during homeostasis. However, maintaining this balance is critical for maintaining barrier function and preventing diseases: if the death rate is higher, barrier function diseases such as asthma may result and if the division rate is higher, solid tumors will result. Through our investigations of how cells maintain a barrier when they die, we believe we have discovered a novel mechanism for how epithelia maintain homeostatic cell numbers, which we further investigate in this proposal. We previously discovered that when a cell dies within an epithelium, it signals its neighboring cells to form a contractile actomyosin rng to extrude it out. To do so, the dying cell emits the lipid Sphingosine 1-Phosphate (S1P), which activates extrusion by signaling the S1P receptor 2 (S1P2) in neighboring cells. More recently, we have found that in adult colon tissue and in developing zebrafish epidermis, epithelial cells appear to extrude prior to dying at sites of high cell crowding. Live cells also extrude in respons to experimental overcrowding using a chamber we devised. While both homeostatic and overcrowding-induced extrusion use the same S1P-S1P2 pathway we defined for apoptotic cell extrusion, the live cell extrusion pathway is activated by the stretch-activated channel Piezo 1. Importantly, we found that disrupting either stretch-activated signaling or the S1P-S1P2 pathway leads to cellular masses in both cell culture and developing zebrafish. Thus, we propose a model where the underlying tissue provides a space limit on epithelia so that any cell divisions and/or migrations cause overcrowding strain, which induces live cells to extrude. Extruding cells then die due to lack of survival signaling while promoting surrounding to survive and proliferate. We will test this hypothesis in Aims 1 and 2 by 1) investigating if extrusion promotes cell death in a cell culture model and 2) testing if cell masses in S1P2 zebrafish mutants result from lack of cell extrusion, increased proliferation, or both. To define what activates extrusion, we will 3) determine how Piezo 1 stretch-activated channels and calcium currents mediate S1P to trigger extrusion and 4) identify cell- cell or cell-matrix proteins critical for determining which cells extrude in response to uniform epithelial crowding forces. The proposed research is innovative because it investigates a novel mechanism for how epithelial cells maintain homeostatic cell numbers and uses multidisciplinary approaches, which include a zebrafish epidermal model we have developed to study epithelia and a cell overcrowding device we have developed with a bioengineer. The proposal is medically significant because misregulation of epithelial homeostasis is likely at the heart of most solid tumor formation and barrier function diseases.