Hedgehog Treatment of Down Syndrome: Establishing Mechanisms

 描述(申请人提供)：唐氏综合症(DS)，由人类21号染色体三体(Hsa21)引起，是最常见的遗传定义的智力残疾原因。结构异常被认为是导致学习问题的原因，在患有这种疾病的人的小脑和海马体中可以看到。矫正大脑这些部分的治疗将明显改善患有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，可以永久性地正常化小脑的大小和大体解剖，导致更好的成人空间问题解决，并恢复Ts65Dn小鼠模型Ts65Dn小鼠模型CA1-海马区学习的电生理关联。在将这一发现转化为对人的治疗之前，还有许多问题需要解决。海马区行为和生理的改善是通过Shh诱导的小脑结构正常化，还是通过Shh的直接刺激，目前尚不清楚。另一个限制Shh治疗进入临床的因素是这种强有力的生长因子的非常广泛的影响，使得全身应用在人身上成为问题。一种更严格的给药方法可能会限制副作用。另一种方法是了解哪些Hsa21基因下调了小脑Shh通路的反应，这可能表明有更多的“可用药”靶点。这里提出的实验将首先用Hsa21基因表达克隆集筛选Shh反应，克隆集由169个cDNA组成，其中149个在人和鼠之间高度保守，20个是人类特有的。在Light2实验中显著降低Shh途径激活的基因将在额外的Shh敏感分析中进行评估，以确保它们在不同的生物系统中具有普遍性(特定目标1)。接下来，我们将确定Shh在Ts65Dn脑中的区域特异性表达如何影响海马区功能。使用一种有条件的“时间-空间”遗传学方法，它将允许我们在出生后的24小时内选择性地增加Shh的表达 对于小脑或海马区的浦肯野细胞，我们将确定在海马区测试中，小脑Shh的表达是否对于纠正成年Ts65Dn小鼠的行为和生理是必要的和/或足够的，或者是否需要大脑其他部位的Shh作用(特定目标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).