Pérez-Núñez Ramón, Barraza Natalia, Gonzalez-Jamett Arlek, Cárdenas Ana Maria, Barnier Jean-Vianney, Caviedes Pablo
Program of Molecular & Clinical Pharmacology, ICBM, Faculty of Medicine, University of Chile, Independencia, 1027, Santiago, Chile.
CINV, University of Valparaíso, Valparaíso, Chile.
Neurotox Res. 2016 Jul;30(1):76-87. doi: 10.1007/s12640-016-9613-9. Epub 2016 Mar 10.
In humans, Down syndrome (DS) is caused by the presence of an extra copy of autosome 21. The most striking finding in DS patients is intellectual disability and the onset of Alzheimer's disease (AD)-like neuropathology in adulthood. Gene overdose is most likely to underlie both developmental impairments, as well as altered neuronal function in DS. Lately, the disruption of cellular signaling and regulatory pathways has been implicated in DS pathophysiology, and many of such pathways may represent common targets for diverse DS-related genes, which could in turn represent attractive therapeutical targets. In this regard, one DS-related gene Down Syndrome Cell Adhesion Molecule (DSCAM), has important functions in neuronal proliferation, maturation, and synaptogenesis. p21-associated kinases (PAKs) appear as a most interesting possibility for study, as DSCAM is known to regulate the PAKs pathway. Hence, in DS, overexpressed DSCAM could deregulate PAKs activity and affect signaling pathways that regulate synaptic plasticity such as dendritic spine dynamics and axon guidance and growth. In the present work, we used an immortalized cell line derived from the cerebral cortex of an animal model of DS such as the trisomy 16 (Ts16) fetal mouse (named CTb), and a similar cell line established from a normal littermate (named CNh), to study the effect of DSCAM in the PAKs pathway. The present study shows that DSCAM is overexpressed in CTb cells by approximately twofold, compared to CNh cells. Congruently, PAK1, as well as its downstream effectors LIMK and cofilin, stay phosphorylated for longer periods after DSCAM activation in the CTb cells, leading to an altered actin dynamics, expressed as an increased basal F/G ratio and reduced neurite growth, in the trisomic condition. The present work presents the correlation between DSCAM gene overexpression and a dysregulation of the PAK pathway, resulting in altered morphological parameters of neuronal plasticity in the trisomic cell line, namely decreased number and length of processes.
在人类中，唐氏综合征（DS）是由21号常染色体额外拷贝的存在引起的。DS患者最显著的发现是智力残疾以及成年后出现类似阿尔茨海默病（AD）的神经病理学症状。基因剂量过量很可能是发育障碍以及DS中神经元功能改变的基础。最近，细胞信号传导和调节通路的破坏与DS病理生理学有关，许多这样的通路可能代表多种DS相关基因的共同靶点，而这些基因反过来可能是有吸引力的治疗靶点。在这方面，一个与DS相关的基因唐氏综合征细胞粘附分子（DSCAM）在神经元增殖、成熟和突触形成中具有重要功能。p21相关激酶（PAKs）似乎是一个非常有趣的研究对象，因为已知DSCAM调节PAKs通路。因此，在DS中，过度表达的DSCAM可能会使PAKs活性失调，并影响调节突触可塑性的信号通路，如树突棘动态变化以及轴突导向和生长。在本研究中，我们使用了一种源自DS动物模型（如16三体胎儿小鼠）大脑皮层的永生化细胞系（命名为CTb），以及从正常同窝小鼠建立的类似细胞系（命名为CNh），来研究DSCAM在PAKs通路中的作用。本研究表明，与CNh细胞相比，CTb细胞中DSCAM的表达量大约高出两倍。相应地，在CTb细胞中，DSCAM激活后，PAK1及其下游效应分子LIMK和丝切蛋白会在更长时间内保持磷酸化状态，导致肌动蛋白动力学改变，表现为三体条件下基础F/G比值增加和神经突生长减少。本研究揭示了DSCAM基因过度表达与PAK通路失调之间的相关性，导致三体细胞系中神经元可塑性的形态学参数发生改变，即突起的数量和长度减少。
