孤独症相关的SALM/LAR-RPTP信号复合体的靶标确证

Autism spectrum disorder (ASD) is a pervasive developmental disorder with three core symptoms: deficits in social behavior and language development, repetitive behaviors and restrictive interests. No drug has been approved for ASD core symptoms. Autism’s cause may reside in abnormalities at the synapse that is like the soul of brain. Missense mutations in SALM1, a member of the SALM family of synaptic adhesion molecules, have been observed in autistic patients, while expression of SALM5, another member of this family, significantly decreased. Knockout of SALM1-coding gene in mice may lead to ASD-like behaviors. As revealed by our structural biology study, a SALM5 dimer may interact with two copies of LAR-RPTP, a subfamily of receptor-type protein tyrosine phosphatases, in a trans-manner, thus forming a 2:2 signaling complex for mediating presynaptic differentiation. In this project, we try to validate the SALM/LAR-RPTP signaling complex as a target for anti-ASD drug development. On one hand, we are going to further investigate function-structure relationship of the signaling complex, obtain structural basis of LAR-RPTP recognition by SALM1 and its ASD-associated mutants, and confirm whether knockout of SALM5-coding gene in mouse will result in ASD-like phenotype. On the other hand, we will screen small-molecule compounds that may modulate functions of the SALM/LAR-RPTP signaling complex, and evaluate pharmacological effects of these tool modulators on SALM1- or SAM5-knockout mice. Also, we will investigate action mechanism of these small-molecule tool modulators and decipher how they interact with their targets at the structural level. Hopefully, this project will provide a target for industry to develop anti-ASD drugs.

孤独症谱系障碍，简称孤独症，是一种广泛性发育障碍疾病；临床上尚无针对其核心症状的药物。孤独症发生的可能源于被喻为“大脑灵魂”的突触的功能失调。在孤独症患者中可见突触粘连样分子家族成员SALM1的错义突变或者SALM5的表达水平大大下降；SALM1基因敲除小鼠表现出孤独症核心症状。我们发现SALM5通过与受体酪氨酸酶LAR-RPTP反式互作，形成独特的2：2的信号复合体结构而引起突触分化。本项目试图基于SALM5/LAR-RPTP信号复合体的结构和功能关系，确证其为孤独症药物靶标。一方面，我们将考察SALM1和其孤独症相关的突变体与LAR-RPTP识别的结构基础，并探究SALM5基因敲除小鼠的行为特征。另一方面，我们将筛选可调节SALM/LAR-RPTP信号复合体功能的小分子化合物，评价这些分子工具的药效和作用机制，并获得它们与靶标识别的结构基础。本项目有望为工业界开发孤独症药物提供依据。

目前尚无针对孤独症谱系障碍（简称孤独症，又称为自闭症）核心症状的药物，孤独症发生的分子机制也不明确。孤独症药物靶标的发现和确证充满挑战性。我们基于SALM/LAR-RPTP复合体信号转导机制的独特性，指出该信号复合体作为孤独症药物靶标的可能性。在本项目中，我们解析了SALM1 LRR结构域的晶体结构，发现SALM1可识别LAR-RPTP受体家族，且偏好于与PTPD的互作。我们发现SALM1或SALM5可以抑制LAR-RPTP受体的酪氨酸磷酸酶活性。通过酪氨酸磷酸化蛋白质组学实验，我们发现SALM1或SALM5可以促进海马神经元中蛋白的酪氨酸磷酸化水平升高，而这些蛋白有可能参与SALM/LAR-RPTP信号转导而调节神经突生长或突触分化。我们解析了SALM5和携带有迷你外显子A和B的PTPD的复合物的晶体结构，说明迷你外显子A对受体和配体的识别并非如文献强调的那样重要。我们尝试挖掘PTPD酪氨酸磷酸酶的抑制剂，但失败了。为了更好地评价受体PTPδ磷酸酶抑制剂的药理作用，我们建立了孕期丙戊酸暴露的小鼠自闭症模型，并发现某化合物可干预其部分自闭症样行为。上述工作进展让我们坚信，借助结构生物学等技术，我们终会完成SALM/LAR-RPTP复合体作为自闭症药物靶标的确证。

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