Establishing Apoptotic Thresholds: Insights from Neurons and Stem Cells to Cancer

 描述(申请人提供)：尽管已鉴定出哺乳动物细胞凋亡途径的主要组成部分，但令人惊讶的是，不同原代细胞中的凋亡调控差异仍未被探索。我们在细胞凋亡领域的唯一持续贡献是定义了不同类型的细胞如何设置凋亡阈值，以最佳地匹配它们的生理功能并适应不断变化的环境。事实上，我们认为，在生理上不同的细胞类型中，仍有新的细胞凋亡调控模式有待发现。我们的实验室发现，与成纤维细胞等有丝分裂细胞相比，在有丝分裂后的细胞，如神经元、心肌细胞和肌管中，凋亡途径受到高度限制。尽管对凋亡的严格调控对有丝分裂后细胞的长期生存至关重要， 有丝分裂细胞需要保持其快速激活细胞凋亡的能力，因为它们可能处于持续的癌变风险中。因此，细胞必须有效地平衡启动凋亡途径的需要和与细胞死亡相关的风险。事实上，我们已经看到这一点在胚胎干细胞中得到了最好的例证，它的机制既为应对DNA损伤而迅速死亡的凋亡途径提供了条件，也为应对线粒体损伤而启动了细胞生存机制。因此，ES细胞似乎具有对特定损伤刺激做出反应的微妙能力，其机制确保了基因组的完整性和最佳的生存。在这个MIRA提案中，我们希望使用有针对性的和广泛的综合方法来研究细胞凋亡调控的不同机制，并确定它们在健康和疾病中的生理重要性。我们的重点是我们确定的两种极端的细胞凋亡控制：1)在线粒体损伤后抵抗细胞凋亡和促进存活的机制(例如，我们的发现E3连接酶ParC介导了胞浆细胞色素c的降解)，以及2)为细胞快速凋亡做准备的机制(例如，我们的发现，Bax在干细胞中保持在活跃状态)。我们将使用原代神经元和人类胚胎干细胞(HES)，进行创新的筛查，并检查癌症和神经退化模型中的疾病含义。我们尤其感到兴奋的是，MIRA的机会将使我们能够利用HES细胞的强大能力来定义细胞凋亡机制如何随着细胞分化经历动态变化。

 DESCRIPTION (provided by applicant): Despite the identification of the main components of the mammalian apoptotic pathway, the differences in the regulation of apoptosis in various primary cells remain surprisingly unexplored. Our unique ongoing contribution to the apoptosis field has been to define how different cell types set the apoptosis threshold to optimally matche their physiological functions and adapt to changing environments. Indeed, we believe that new paradigms of apoptosis regulation remain to be discovered in physiologically distinct cell types. Our lab has discovered that the apoptotic pathway is highly restricted in postmitotic cells such as neurons, cardiomyocytes, and myotubes, as compared to mitotic cells such as fibroblasts. While a strict regulation of apoptosis is critical for the long-term survival of postmitotic cells, mitotic cells need to maintain their ability to activate apoptosis rapidly as they can be at continual risk of becoming cancerous. Therefore, cells must efficiently balance the need for having a primed apoptotic pathway versus the risks associated with cell death. In fact, we have seen this best exemplified in embryonic stem (ES) cells which engage mechanisms that both prime the apoptotic pathway for rapid death in response to DNA damage, while also engaging cell survival mechanisms in response to mitochondrial damage. Thus, ES cells appear to have an exquisite capability to respond to the specific damage stimuli with mechanisms that ensure both genomic integrity and optimal survival. In this MIRA proposal, we wish to use both targeted and broad integrative approaches to examine the distinct mechanisms of apoptosis regulation and define their physiological importance in health and disease. Our focus is on the two extremes of the apoptosis control we identified: 1) Mechanisms that resistant apoptosis and promote survival after mitochondrial damage (e.g. our findings that the E3 ligase PARC mediates the degradation of cytosolic cytochrome c), and 2) Mechanisms that prime cells for rapid apoptosis (e.g. our discovery that Bax is maintained in an active state in stem cells). We will use primary neurons and human embryonic stem (hES) cells, conduct innovative screens and examine disease implications in models of cancer and neurodegeneration. In particular, we are excited that the MIRA opportunity would enable our ambitious plans to use the powerful capability of hES cells to define how the apoptotic machinery undergoes dynamic changes with cellular differentiation.