Genetic Approaches to Understanding Granulin Function

描述（由申请人提供）：尽管最近取得了进展，但尚不清楚颗粒蛋白前体缺乏如何导致神经退行性疾病额颞叶变性（FTLD）的发展。颗粒蛋白前体被切割成具有生物活性并且可以在功能上对抗颗粒蛋白前体全蛋白的单个颗粒蛋白肽。许多人认为，颗粒蛋白前体缺乏同样地消耗颗粒蛋白前体和颗粒蛋白水平，然而，颗粒蛋白前体缺乏可能导致颗粒蛋白相对于颗粒蛋白前体过量。对颗粒蛋白的功能知之甚少，也没有发现颗粒蛋白受体。我的研究小组的主要重点是利用模式生物来了解颗粒蛋白前体的功能。在这个建议中，我们的目标是确定颗粒蛋白受体，并确定颗粒蛋白的正常功能，因为它们涉及到生物体的应激反应。我们的中心假设是，相对过量的颗粒蛋白是有害的，因为颗粒蛋白损害应激抵抗力。这一假设是基于我们的观察，在C。1）热应激刺激颗粒蛋白前体裂解，和2）单个颗粒蛋白的表达损害应激抗性。这些明确的和可重复的胁迫表型使我们能够利用C. elegans筛选颗粒蛋白受体和了解相关的颗粒蛋白和颗粒蛋白前体功能。我们工作的基本原理是，更好地了解颗粒蛋白功能将导致 更好地了解FTLD的发病机制，并为药物治疗带来新的靶点。我们的第一个目标是确定颗粒蛋白受体和颗粒蛋白功能的下游介质。我们有一个颗粒蛋白生物活性的检测方法，我们可以用它来筛选颗粒蛋白受体。我们的第二个目标是测试颗粒蛋白前体和颗粒蛋白调节应激反应的模型。我们将通过在C. elegans并测量它们对应激抗性的影响。这些研究是重要的，因为为了真正了解颗粒蛋白前体的功能和颗粒蛋白前体替代疗法的后果，还必须了解颗粒蛋白前体和颗粒蛋白的正常生物学特性。在我们看来，这项研究是创新的，因为它试图直接暗示颗粒蛋白过量，而不是颗粒蛋白前体缺乏，作为与颗粒蛋白前体突变相关的神经变性的驱动力。当这些研究成功完成后，预期的结果是颗粒蛋白受体的鉴定，了解颗粒蛋白的正常功能，以及明确颗粒蛋白前体和颗粒蛋白在调节应激抗性中的相对作用。更好地了解颗粒蛋白前体和颗粒蛋白功能将产生一些积极的影响，包括确定药物治疗的新靶点和了解颗粒蛋白前体替代策略的潜在负面后果。这些研究的结果可以迅速转化为脊椎动物模型，以开发神经退行性疾病的新疗法。

DESCRIPTION (provided by applicant): Despite recent progress, it is unclear how progranulin deficiency leads to development of the neurodegenerative disease frontotemporal lobar degeneration (FTLD). Progranulin is cleaved into individual granulin peptides that are bioactive and may functionally oppose the progranulin holoprotein. Many believe that progranulin deficiency equally depletes progranulin and granulin levels yet it may be that progranulin deficiency results in a relative excess of granulins compared to progranulin. Little is known about granulin function and no granulin receptor has been identified. The major focus of my research group is to utilize model organisms to understand progranulin function. In this proposal, our objective is to identify the granulin receptor and to determine the normal function of granulins as they relate to organismal stress response. Our central hypothesis is that relative excess of granulins is harmful because granulins impair stress resistance. This hypothesis is based on our observations that in C. elegans 1) heat stress stimulates progranulin cleavage, and 2) expression of individual granulins impairs stress resistance. These clear and reproducible stress phenotypes allow us to take advantage of the genetic tractability of C. elegans to screen for the granulin receptor and understand relative granulin and progranulin function. The rationale for our work is that better understanding of granulin function will lead to better understanding of FTLD disease mechanism and lead to new targets for drug therapy. Our first aim is to identify the granulin receptor(s) and downstream mediators of granulin function. We have an assay of granulin biological activity that we can use to screen for the granulin receptor. Our second aim is to test the model that progranulin and granulins reciprocally modulate stress response. We will do so by expressing different levels of progranulin and granulin in C. elegans and measuring their effect on stress resistance. These studies are significant because in order to truly understand progranulin function and the consequences of progranulin replacement therapy, one must also understand the normal biological properties of both progranulin and granulins. The proposed research is innovative, in our opinion, because it seeks to directly implicate granulin excess, instead of progranulin deficiency, as the driving forc in neurodegeneration-related to progranulin mutations. When these studies are successfully completed, expected outcomes are identification of the granulin receptor, insight into the normal function of granulins, and clarity regarding the relative roles of progranulin and granulin in modulating stress resistance. Better understanding of progranulin and granulin function will have several positive impacts, including identification of novel targets for drug therapy and understanding of potential negative consequence of progranulin replacement strategies. Findings from these studies can be rapidly translated to vertebrate models in order to develop new therapies for neurodegenerative diseases.