背景:信号素(Sema)属于在发育过程中引导轴突的驱避性引导线索大家族。特别是,3类Sema(Sema3)是特征最明确的Sema家族成员之一,也是哺乳动物中唯一以分泌蛋白形式产生的。从而发挥自分泌和旁分泌功能。有趣的是,越来越多的研究支持Sema3A在海马和皮质神经发育中的关键作用.这意味着Sema3A信号的改变可能会损害海马和皮质回路,并容易患上自闭症和精神分裂症等疾病。始终如一,已在精神分裂症患者的大脑中检测到Sema3A水平升高,并且Sema3A或Sema3A受体中存在许多多态性,神经菌毛蛋白(Npn1和2)和神经丛蛋白As(PlxnAs),与自闭症有关。
结果:这里我们提供的数据表明,当过度表达时,Sema3A导致人类神经祖细胞(NP)轴突回缩和异常的树突状树干化。同样,Sema3A,当在人类小胶质细胞中过表达时,触发对自身和NP非常有害的促炎过程。的确,在过表达Sema3A培养基的小胶质细胞中孵育的NP在一小时内缩回轴突,然后开始受苦并最终死亡。Sema3A介导的回缩似乎与其与Npn1和PlxnA2受体的结合有关,从而激活下游Fyn酪氨酸激酶途径,促进苏氨酸-丝氨酸激酶细胞周期蛋白依赖性激酶5,CDK5,Tyr15残基的磷酸化和CDK5加工以产生活性片段p35。
结论:本研究将Sema3A确定为人类NP分化的关键调节因子。这可能意味着在神经元发育的早期阶段由于Sema3A过表达而引起的损害可能会损害神经元的组织和连通性,并使神经元在其整个生命周期中可能更容易受到其他损害。
BACKGROUND: Semaphorins (Sema) belong to a large family of repellent guidance cues instrumental in guiding axons during development. In particular, Class 3 Sema (Sema 3) is among the best characterized Sema family members and the only produced as secreted proteins in mammals, thereby exerting both autocrine and paracrine functions. Intriguingly, an increasing number of studies supports the crucial role of the Sema 3A in hippocampal and cortical neurodevelopment. This means that alterations in Sema 3A signaling might compromise hippocampal and cortical circuits and predispose to disorders such as autism and schizophrenia. Consistently, increased Sema 3A levels have been detected in brain of patients with schizophrenia and many polymorphisms in Sema 3A or in the Sema 3A receptors, Neuropilins (Npn 1 and 2) and Plexin As (Plxn As), have been associated to autism.
RESULTS: Here we present data indicating that when overexpressed, Sema 3A causes human neural progenitors (NP) axonal retraction and an aberrant dendritic arborization. Similarly, Sema 3A, when overexpressed in human microglia, triggers proinflammatory processes that are highly detrimental to themselves as well as NP. Indeed, NP incubated in microglia overexpressing Sema 3A media retract axons within an hour and then start suffering and finally die. Sema 3A mediated retraction appears to be related to its binding to Npn 1 and Plxn A2 receptors, thus activating the downstream Fyn tyrosine kinase pathway that promotes the threonine-serine kinase cyclin-dependent kinase 5, CDK5, phosphorylation at the Tyr15 residue and the CDK5 processing to generate the active fragment p35.
CONCLUSIONS: All together this study identifies Sema 3A as a critical regulator of human NP differentiation. This may imply that an insult due to Sema 3A overexpression during the early phases of neuronal development might compromise neuronal organization and connectivity and make neurons perhaps more vulnerable to other insults across their lifespan.