Sempou Emily, Biasini Emiliano, Pinzón-Olejua Alejandro, Harris David A, Málaga-Trillo Edward
Department of Biology, University of Konstanz, Constance, 78457, Germany.
Present address: Department of Pediatrics, Yale University School of Medicine, New Haven, CT, 06520, USA.
Mol Neurodegener. 2016 Feb 9;11:18. doi: 10.1186/s13024-016-0076-5.
Prions and amyloid-β (Aβ) oligomers trigger neurodegeneration by hijacking a poorly understood cellular signal mediated by the prion protein (PrP) at the plasma membrane. In early zebrafish embryos, PrP-1-dependent signals control cell-cell adhesion via a tyrosine phosphorylation-dependent mechanism.
Here we report that the Src family kinases (SFKs) Fyn and Yes act downstream of PrP-1 to prevent the endocytosis and degradation of E-cadherin/β-catenin adhesion complexes in vivo. Accordingly, knockdown of PrP-1 or Fyn/Yes cause similar zebrafish gastrulation phenotypes, whereas Fyn/Yes expression rescues the PrP-1 knockdown phenotype. We also show that zebrafish and mouse PrPs positively regulate the activity of Src kinases and that these have an unexpected positive effect on E-cadherin-mediated cell adhesion. Interestingly, while PrP knockdown impairs β-catenin adhesive function, PrP overexpression enhances it, thereby antagonizing its nuclear, wnt-related signaling activity and disturbing embryonic dorsoventral specification. The ability of mouse PrP to influence these events in zebrafish embryos requires its neuroprotective, polybasic N-terminus but not its neurotoxicity-associated central region. Remarkably, human Aβ oligomers up-regulate the PrP-1/SFK/E-cadherin/β-catenin pathway in zebrafish embryonic cells, mimicking a PrP gain-of-function scenario.
Our gain- and loss-of-function experiments in zebrafish suggest that PrP and SFKs enhance the cell surface stability of embryonic adherens junctions via the same complex mechanism through which they over-activate neuroreceptors that trigger synaptic damage. The profound impact of this pathway on early zebrafish development makes these embryos an ideal model to study the cellular and molecular events affected by neurotoxic PrP mutations and ligands in vivo. In particular, our finding that human Aβ oligomers activate the zebrafish PrP/SFK/E-cadherin pathway opens the possibility of using fish embryos to rapidly screen for novel therapeutic targets and compounds against prion- and Alzheimer's-related neurodegeneration. Altogether, our data illustrate PrP-dependent signals relevant to embryonic development, neuronal physiology and neurological disease.
朊病毒和淀粉样β（Aβ）寡聚体通过劫持由朊病毒蛋白（PrP）在质膜介导的一种了解甚少的细胞信号来引发神经退行性变。在斑马鱼早期胚胎中，PrP - 1依赖的信号通过酪氨酸磷酸化依赖的机制控制细胞间黏附。
我们在此报告，Src家族激酶（SFK）Fyn和Yes在PrP - 1下游发挥作用，以防止体内E - 钙黏蛋白/β - 连环蛋白黏附复合物的内吞作用和降解。相应地，敲低PrP - 1或Fyn/Yes会导致相似的斑马鱼原肠胚形成表型，而Fyn/Yes的表达可挽救PrP - 1敲低的表型。我们还表明，斑马鱼和小鼠的PrP正向调节Src激酶的活性，并且这些激酶对E - 钙黏蛋白介导的细胞黏附有意外的正向作用。有趣的是，虽然敲低PrP会损害β - 连环蛋白的黏附功能，但PrP的过表达会增强它，从而拮抗其核内、与Wnt相关的信号活性并扰乱胚胎的背腹轴特化。小鼠PrP影响斑马鱼胚胎中这些事件的能力需要其具有神经保护作用的多碱性N端，而不是与其神经毒性相关的中央区域。值得注意的是，人Aβ寡聚体上调斑马鱼胚胎细胞中的PrP - 1/SFK/E - 钙黏蛋白/β - 连环蛋白途径，模拟了PrP功能获得的情况。
我们在斑马鱼中的功能获得和功能丧失实验表明，PrP和SFK通过相同的复杂机制增强胚胎黏着连接的细胞表面稳定性，它们通过该机制过度激活触发突触损伤的神经受体。该途径对斑马鱼早期发育的深远影响使这些胚胎成为研究体内受神经毒性PrP突变和配体影响的细胞和分子事件的理想模型。特别是，我们发现人Aβ寡聚体激活斑马鱼PrP/SFK/E - 钙黏蛋白途径，为利用鱼胚胎快速筛选针对朊病毒和阿尔茨海默病相关神经退行性变的新型治疗靶点和化合物开辟了可能性。总之，我们的数据阐明了与胚胎发育、神经元生理学和神经疾病相关的PrP依赖信号。
