Lysosomal Function of Progranulin and Neurodegeneration

项目总结/摘要 颗粒蛋白原（PGRN）基因的突变与两种不同的神经退行性疾病有关， 额颞叶变性（FTLD）和神经元蜡样质脂褐质沉积症（NCL）。越来越多的证据 提示PGRN在溶酶体中的关键作用。然而，PGRN如何调节溶酶体功能， 防止神经变性仍然是难以捉摸的。我们已经确定了前鞘脂激活素（PSAP）， 鞘脂激活蛋白肽是溶酶体鞘糖脂降解所必需的，作为PGRN结合配偶体。我们 进一步表明PGRN促进PSAP溶酶体从细胞外空间经由神经元转运， 运输受体分拣蛋白。我们发现在PGRN缺陷小鼠中PSAP和saposins的神经元水平降低 以及由于PGRN突变而导致的FTLD患者。此外，我们发现PGRN与PSAP形成复合物 以及溶酶体蛋白酶组织蛋白酶B和D。据报道，组织蛋白酶D缺乏可导致FTLD 我们的初步研究表明，受损的PSAP功能也会导致FTLD相关 小鼠的表型。因此，我们假设PGRN对于适当的PSAP和组织蛋白酶B和D是至关重要的 PSAP和组织蛋白酶功能受损是FTLD-PGRN的一个关键疾病机制。测试 根据这一假设，我们提出了三个具体目标。在Aim 1中，我们将研究PGRN在调节 PSAP功能。将在WT中测定PSAP运输、加工和鞘糖脂代谢， PGRN-/-细胞和组织以及对照和FTLD-PGRN患者样品。在目标2中，我们将确定 通过检查WT和PGRN-/-细胞和组织，PGRN在组织蛋白酶B和D运输和活化中的作用 以及对照和FTLD-PGRN患者样品。在Aim 3中，我们将在小鼠中测定FTLD样表型 用不同水平的PSAP或组织蛋白酶B或D测定PSAP或组织蛋白酶B或D的部分损失， 功能可能导致FTLD疾病进展。此外，PSAP或组织蛋白酶B或D将被 通过腺相关病毒（AAV）过表达，以确定PSAP或组织蛋白酶过表达 可以挽救小鼠中与PGRN丢失相关的表型。总之，这些拟议的研究将摆脱 阐明PGRN如何调节溶酶体功能，并为疾病机制提供新的见解。 FTLD。我们希望我们的研究结果也能促进FTLD-PGRN的治疗开发 其他具有PGRN作用的神经退行性疾病，如阿尔茨海默病。

PROJECT SUMMARY/ABSTRACT Mutations in the Progranulin (PGRN) gene have been linked to two distinct neurodegenerative diseases, frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). Accumulating evidence suggests a critical role of PGRN in the lysosome. However how PGRN regulates lysosomal function and protects against neurodegeneration remains elusive. We have identified prosaposin (PSAP), the precursor of saposin peptides essential for lysosomal glycosphingolipid degradation, as a PGRN binding partner. We further showed that PGRN facilitates PSAP lysosomal trafficking from the extracellular space via the neuronal trafficking receptor sortilin. We found reduced neuronal levels of PSAP and saposins in PGRN deficient mice and in FTLD patients due to PGRN mutations. Moreover, we showed that PGRN forms a complex with PSAP and lysosomal proteases cathepsin B and D. Cathepsin D deficiency has been reported to cause FTLD related pathology and our preliminary studies showed that impaired PSAP function also leads to FTLD related phenotypes in mice. Thus we hypothesize that PGRN is critical for proper PSAP and cathepsin B and D functions and impaired PSAP and cathepsin functions is one key disease mechanism of FTLD-PGRN. To test this hypothesis, we propose three specific aims. In Aim1, we will examine the role of PGRN in regulating PSAP function. PSAP trafficking, processing and glycosphingolipid metabolism will be assayed in WT and PGRN-/- cells and tissues as well as control and FTLD-PGRN patient samples. In Aim2, we will determine the role of PGRN in cathepsin B and D trafficking and activation by examining WT and PGRN-/- cells and tissues as well as control and FTLD-PGRN patient samples. In Aim3, we will assay FTLD like phenotypes in mice with different levels of PSAP or cathepsin B or D to determine whether partial loss of PSAP or cathepsin function could contribute to FTLD disease progression. Furthermore, PSAP or cathepsin B or D will be overexpressed via adeno associated viruses (AAV) to determine whether PSAP or cathepsin overexpression can rescue phenotypes associated with PGRN loss in mice. In summary, these proposed studies will shed light on how PGRN regulates lysosomal function and provide novel insights into the disease mechanism of FTLD. We expect the results from our studies to facilitate therapeutic development for FTLD-PGRN as well other neurodegenerative diseases with a reported role of PGRN, such as Alzheimer’s disease.