Genetic Approaches to Understanding Granulin Function

描述（由申请人提供）：尽管最近取得了进展，但尚不清楚前颗粒蛋白缺乏如何导致神经退行性疾病额颞叶变性（FTLD）的发展。颗粒蛋白前被切割成个体颗粒蛋白肽，这些肽具有生物活性，可能在功能上与颗粒蛋白前全蛋白相对立。许多人认为，颗粒蛋白前缺乏同样会减少颗粒蛋白前和颗粒蛋白水平，但可能是颗粒蛋白前缺乏导致颗粒蛋白相对于颗粒蛋白前过量。人们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前颗粒蛋白的功能。在这个提议中，我们的目标是鉴定颗粒蛋白受体，并确定颗粒蛋白的正常功能，因为它们与机体应激反应有关。我们的中心假设是，颗粒蛋白的相对过量是有害的，因为颗粒蛋白会损害抗逆性。这一假设是基于我们对秀丽隐杆线虫的观察：1)热应激刺激颗粒蛋白前分裂，2)单个颗粒蛋白的表达削弱了抗逆性。这些清晰和可复制的应激表型使我们能够利用秀丽隐杆线虫的遗传易感性来筛选颗粒蛋白受体，并了解颗粒蛋白和前颗粒蛋白的相对功能。我们工作的基本原理是更好地理解颗粒蛋白的功能将导致

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.