Hedgehog Treatment of Down Syndrome: Establishing Mechanisms

 描述（由申请人提供）：唐氏综合征（DS），由人类21号染色体三体（Hsa 21）引起，是智力残疾最常见的遗传原因。被认为是导致学习问题的结构异常出现在患有这种疾病的人的小脑和海马体中。纠正这些大脑部位的治疗将切实改善患有DS的儿童和年轻人的生活，并使他们更好地融入社会。我们最近发现，出生当天单次注射Sonic Hedgehog（Shh）激动剂SAG 1.1，永久正常化小脑的大小和大体解剖结构，导致更好的成人空间问题解决，并恢复DS Ts 65 Dn小鼠模型CA 1-海马子区学习的电生理相关性。在这一发现转化为治疗方法之前，还有许多问题有待解决。海马行为和生理学的改善是否通过Shh诱导的小脑结构正常化或通过Shh直接刺激发生尚不清楚。将Shh治疗推进到临床的另一个限制是这种强效生长因子的影响范围非常广泛，这使得人们的系统应用成为问题。一种更严格的药物输送方法可能会限制副作用。另一种方法是了解哪些Hsa 21基因在小脑中下调Shh通路反应，这可能表明更多的“药物”靶点。本文提出的实验将首先用169个cDNA的Hsa 21基因表达克隆集筛选Shh应答，其中149个在人和小鼠之间高度保守，20个是人类特异性的。在LIGHT 2试验中显著降低Shh通路活化的基因将在额外的Shh敏感试验中进行评价，以确保它们在不同的生物系统中具有普遍性（特定目的1）。接下来，我们将确定Ts 65 Dn脑中Shh的区域特异性表达如何影响海马功能。使用有条件的“时空”遗传学方法，这将使我们能够在出生时选择性地增加Shh表达24小时， 小脑的浦肯野细胞或海马内的浦肯野细胞，我们将确定小脑Shh表达是否是必要的和/或足以在海马测试中校正成年Ts 65 Dn小鼠的行为和生理学，或者是否需要在大脑的其他部分中的Shh作用（具体目标2）。

 DESCRIPTION (provided by applicant): Down syndrome (DS), caused by trisomy for human chromosome 21 (Hsa21), is the most common genetically defined cause of intellectual disability. Structural abnormalities that are thought to contribute to learning problems are seen in the cerebellum and hippocampus of people with the condition. Treatments to correct these parts of the brain would tangibly improve the lives of children and young adults with DS and would allow them to better integrate into society. We recently showed that a single injection on the day of birth with the Sonic Hedgehog (Shh) agonist, SAG 1.1, permanently normalizes the size and gross anatomy of the cerebellum, leads to better adult spatial problem solving, and restores electrophysiological correlates of learning in the CA1-hippocampal subfield of the Ts65Dn mouse model of DS. A number of questions remain before this finding can be translated to therapy for people. Whether improvements in hippocampal behavior & physiology occur through Shh-induced normalization of cerebellar structure or via direct stimulation with Shh is not known. Another restraint on advancing Shh treatments to the clinic is the very wide range of effects of this potent growth factor, making systemic application in people problematic. A more confined method of drug delivery might limit side effects. Another approach would be to understand which Hsa21 genes act to downregulate the Shh pathway response in cerebellum, which might suggest more "druggable" targets. The experiments proposed here will first screen Shh responses with an Hsa21 Gene Expression clone-set of 169 cDNAs, 149 of which are highly conserved between human and mouse and twenty that are human specific. Genes that significantly decrease Shh pathway activation in the LIGHT2 assay will be evaluated in additional Shh-sensitive assays to assure that they generalize across different biological systems (Specific Aim 1). Next, we will determine how region-specific expression of Shh in the Ts65Dn brain affects hippocampal function. Using a conditional "temporal-spatial" genetics approach that will allow us to increase Shh expression at birth for a 24h period selectively within the Purkinje cells of the cerebellum, or within the hippocampus, we will determine whether cerebellar Shh expression is necessary and/or sufficient to correct the behavior & physiology of adult Ts65Dn mice in hippocampal tests or whether Shh actions in additional parts of the brain are required (Specific Aim 2).