Phenotypic effects of brain-directed enzyme therapy for Sanfilippo B syndrome

 描述(申请人提供)：Sanfilippo B综合征是一种由于α-N-乙酰氨基葡萄糖苷酶(NAGLU)缺乏而导致的破坏性溶酶体储存障碍。大多数已经使用或提议的治疗方法包括以某种方式将该酶替换到缺乏酶的宿主中-要么使用野生型供体干细胞(提供缺失的酶)，要么通过基因疗法来传递编码该酶的基因，或者通过重组酶注射。所有这些都依赖于溶酶体酶的特殊性质，这是由甘露糖6-磷酸受体系统实现的：溶酶体酶可以由一个细胞分泌，由另一个细胞通过甘露糖6-磷酸受体摄取，然后穿梭到溶酶体，在那里它们可以作用于减少储存的底物。不幸的是，对于患有Sanfilippo B综合征的人来说，NAGLU在重组表达时不包含足够的甘露糖6-磷酸，因此细胞摄取和溶酶体靶向永远不会发生。我们已经构建了NAGLU和部分胰岛素样生长因子2(IGF2)的融合构建体。IGF2的天然清道夫受体是甘露糖6-磷酸受体(尽管它与甘露糖6-磷酸结合的位置不同)。我们的体外和体内初步数据表明，重组人NAGLU-IGF2具有活性，可以进入细胞，并能高效地减少溶酶体的储存。下一步，这项建议试图解决，是确定重组人NAGLU-IGF2是否会改善Sanfilippo B表型，这是一种进行性认知恶化。在这个项目中，我们建议在体内研究这种潜在的新疗法，以确定它是否可以改善神经行为、躯体疾病和存活率。这些结果将告诉我们，重组NAGLU-IGF2能否作为这种毁灭性疾病的有效酶疗法。这些结果也可能对Sanfilippo B的基因和细胞治疗方法产生影响，使用IGF2介导的溶酶体靶向可能会使其更加有效。

 DESCRIPTION (provided by applicant): Sanfilippo B syndrome is a devastating lysosomal storage disorder due to deficiency of the enzyme alpha-N- acetylglucosaminidase (NAGLU). Most therapeutic approaches that have been used or proposed for the lysosomal storage diseases that are due to missing enzymes involve replacing that enzyme into the deficient host in some way- either using wild-type donor stem cells (which provide the missing enzyme), gene therapy to deliver the gene that encodes the enzyme, or by recombinant enzyme administration. All of these depend on the special property of lysosomal enzymes that is made possible by the mannose 6-phosphate receptor system: lysosomal enzymes can be secreted by a cell, taken up by another cell via mannose 6-phosphate receptors, and shuttled to lysosomes where they can act to reduce stored substrate. Unfortunately for people affected with Sanfilippo B syndrome, NAGLU does not contain sufficient mannose 6-phosphate when expressed recombinantly, so that cellular uptake and lysosomal targeting never take place. We have generated a fusion construct of NAGLU and a portion of insulin-like growth factor 2 (IGF2). The natural scavenger receptor for IGF2 is the mannose 6-phosphate receptor (though it binds at a different site than does mannose 6- phosphate). Our preliminary in vitro and in vivo data show that recombinant human NAGLU-IGF2 is active, enters cells, and can reduce lysosomal storage with high efficiency. The next step, which this proposal seeks to address, is to determine whether recombinant human NAGLU-IGF2 will improve the Sanfilippo B phenotype, which is one of progressive cognitive deterioration. In this project, we propose to study this potential new therapy in vivo, to determine whether it improves neurobehavior, physical disease, and survival. The results will tell us whether recombinant NAGLU-IGF2 can serve as effective enzyme therapy for this devastating disease. Results may also have implications for gene and cell therapy approaches for Sanfilippo B, which might be made more effective with the use of IGF2-mediated lysosomal targeting.