3Department of Pediatrics, University of Colorado, Mailbox 8313, 12800 E. 19th Ave, Aurora, CO 80045, USA.
FASEB J. 2014 Jan;28(1):195-205. doi: 10.1096/fj.13-232686. Epub 2013 Sep 13.
Amyloid precursor protein (APP), encoded on Hsa21, functions as a cell adhesion molecule (CAM) in axonal growth cones (GCs) of the developing brain. We show here that axonal GCs of human fetal Down syndrome (DS) neurons (and of a DS mouse model) overexpress APP protein relative to euploid controls. We investigated whether DS neurons generate an abnormal, APP-dependent GC phenotype in vitro. On laminin, which binds APP and β1 integrins (Itgb1), DS neurons formed enlarged and faster-advancing GCs compared to controls. On peptide matrices that bind APP only, but not on those binding exclusively Itgb1 or L1CAM, DS GCs were significantly enlarged (2.0-fold), formed increased close adhesions (1.8-fold), and advanced faster (1.4-fold). In assays involving alternating stripes of monospecific matrices, human control GCs exhibited no preference for any of the substrates, whereas DS GCs preferred the APP-binding matrix (cross-over decreased significantly from 48.2 to 27.2%). Reducing APP expression in DS GCs with siRNA normalized most measures of the phenotype, including substrate choice. These experiments show that human DS neurons exhibit an APP-dependent, abnormal GC phenotype characterized by increased adhesion and altered contact guidance. The results suggest that APP overexpression may perturb axonal pathfinding and circuit formation in developing DS brain.
淀粉样前体蛋白（APP），位于 Hsa21 上，在发育中大脑的轴突生长锥（GC）中作为细胞粘附分子（CAM）发挥作用。我们在这里表明，人胎龄唐氏综合征（DS）神经元的轴突 GC（和 DS 小鼠模型）相对于整倍体对照过度表达 APP 蛋白。我们研究了 DS 神经元是否在体外产生异常的、依赖 APP 的 GC 表型。在层粘连蛋白上，它结合 APP 和 β1 整合素（Itgb1），DS 神经元形成的 GC 比对照物更大且生长更快。在仅结合 APP 而不结合β1 整合素或 L1CAM 的肽基质上，DS GC 明显增大（2.0 倍），形成更多的紧密粘附（1.8 倍），并且生长更快（1.4 倍）。在涉及单特异性基质交替条纹的测定中，人对照 GC 对任何基质都没有偏好，而 DS GC 则偏好结合 APP 的基质（交叉减少了显著，从 48.2 降至 27.2%）。用 siRNA 降低 DS GC 中的 APP 表达可使表型的大多数指标正常化，包括底物选择。这些实验表明，人 DS 神经元表现出依赖 APP 的异常 GC 表型，其特征是增加粘附和改变接触引导。结果表明，APP 过度表达可能会破坏发育中 DS 大脑中的轴突寻路和回路形成。
